UNIVERSIDAD COMPLUTENSE DE MADRID 

FACULTAD DE CIENCIAS QUÍMICAS 

 

 
 

 

TESIS DOCTORAL 

 

 
Chiral Molecular Nanographenes: Synthesis and Properties Nanografenos  

 
Moleculares Quirales: Síntesis y Propiedades 

 

 
MEMORIA PARA OPTAR AL GRADO DE DOCTORA 

 

PRESENTADA POR 
 

 

 
Patricia Izquierdo García 

 
 
 

DIRECTORES 
 
 
 

Prof. Nazario Martín León 
Dr. Jesús Manuel Fernández García 

 

 

 

 

© Patricia Izquierdo García, 2024 



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



UNIVERSIDAD COMPLUTENSE DE MADRID 

FACULTAD DE CIENCIAS QUÍMICAS 

 

TESIS DOCTORAL 

 

Chiral Molecular Nanographenes: Synthesis and Properties 

Nanografenos Moleculares Quirales: Síntesis y Propiedades 

 

 

MEMORIA PARA OPTAR AL GRADO DE DOCTORA EN 

QUÍMICA ORGÁNICA presentada por 

Patricia Izquierdo García 

 

 

 

DIRECTORES 

Prof. Nazario Martín León  

Dr. Jesús Manuel Fernández García 

 



 





 

 

AGRADECIMIENTOS 

Primero, agradecer a la Universidad Complutense de Madrid, a la Facultad de 

Química y al Departamento de Química Orgánica por la formación que he podido 

adquirir a lo largo de mi carrera en la química, desde los estudios de grado y máster, 

hasta esta última etapa de formación de la tesis doctoral que, además, he podido 

realizar con un Contrato Predoctoral de Personal Investigador en Formación UCM-

Harvard. 

Nazario y Chus, gracias por convertir estos años en un libro de aventuras, 

concretamente en uno de esos que al terminar te dejan una especie de resaca 

emocional. Pensándolo bien, el título de esta tesis tal vez debería ser algo como 

“Unexpected and Exciting Adventures With Molecular Nanographenes”, pero esa 

discusión ya la dejamos para otro día. 

Es difícil resumir en unas pocas palabras la admiración y respeto que siento por los 

dos. Gracias por acompañarme y darme las herramientas para ser capaz de 

enfrentarme a los desafíos que la química tenía preparados. Gracias por impulsarme 

cuando las fuerzas flaqueaban y por confiar en mí. Gracias por ser tan humanos y 

cercanos, por encontrar siempre las palabras amables y también las más sinceras. 

Gracias por las infinitas horas de fructíferas reuniones discutiendo de química y 

quiralidad, con las que pudimos mantener la cordura cuando parecía que el mundo iba 

a la deriva. Espero seguir desafiando a la mente con la ciencia tal y como me habéis 

enseñado, siempre buscando nuevos objetivos, sin perder la curiosidad, la creatividad 

y el entusiasmo. Gracias por todo, sois referentes para mí, como científicos, como 

mentores y como personas. Así, y como no podría ser de otra manera, la Patri que 

termina esta etapa ha aprendido muchas lecciones que la acompañarán siempre… 

Me gustaría agradecer al Dr. Jarad Mason de la Universidad de Harvard el brindarme 

la oportunidad de trabajar en su laboratorio. Durante los tres meses de estancia en el 

grupo de investigación tuve la posibilidad de asistir a conferencias del más alto nivel 

y de conocer a personas totalmente entusiasmadas con la ciencia y siempre dispuestas 

a ayudar, mencionando especialmente a Joy, Faith, Quichen, Vidhya, Yukyung, Dan, 

Rahil y Miranda. 

A todas las personas que han permitido mejorar los trabajos que se describen en esta 

tesis doctoral. A los colaboradores Juan Casado, Samara Medina, Irena Stará, Jeanne 

Crassous, Sergio Ramírez y David Fresnadillo, por sus aportaciones en el estudio de 

los nanografenos moleculares bicapa. Al colaborador Israel Fernández por realizar los 

cálculos teóricos que soportan los resultados de la formación de espironanografenos 

y nanografenos helicoidalmente organizados. Por último, gracias especialmente a 

Josefina Perles, por arrojar luz con la difracción de rayos-X en todos los trabajos 

desarrollados. Por acompañarnos concienzudamente en todas y cada una de las 

historias que hemos contado, incluso en aquellas que más bien han parecido películas 

de Hitchcock, en las que la esperanza podría llegar a perderse, pero siempre lo 

intentábamos una vez más. 



 

 

Muchas gracias a Lola, Ángel y Elena, que desde el CAI de RMN nos hacen el trabajo 

más sencillo. Gracias a Lola, especialmente por hacer de atleta esperando a recibir el 

testigo del tubo de resonancia con el que cada minuto contaba, porque nuestro querido 

nanografeno isomerizaba. Y, por supuesto, gracias a Elena, por sacar adelante con 

determinación y paciencia todos los desafíos que a priori pudieran parecer locas ideas 

mías. 

Sergio, mi querido Sergio, ¿qué habría sido de mí sin ti estos años? Hay preguntas que 

es mejor no hacerse porque, por suerte, te he tenido a mi lado. Gracias una vez más, 

por conocerme, por entenderme, por hacerme reír y apoyarme cuando tocaba llorar o 

rabiar. Eres la definición de amigo, pero todo esto ya lo sabes. Como esto es mi libro 

y puedo poner “lo que quiera” (y por evitar aquello de que las palabras se las lleva el 

viento), quiero aprovechar para decirte que vales muchísimo, que conseguirás todo lo 

que te propongas, como has hecho hasta ahora. Solo espero que seas consciente de 

ello y que creas en ti y, si no lo consigues, me llamas y yo te lo recuerdo, porque lo 

tengo claro. Y como dice La Pelae para darnos fuerza, “¡¡métele castaña!!”, ya sabes 

cómo sigue… 

Manu, ¡la de cosas que han pasado en lo que han parecido dos días!! Empezamos 

justamente en el cambio generacional del laboratorio, nos dejaron siendo dos 

novatillos y, sin querer, nos convertimos en algo parecido a “papá” y “mamá”. Ahora 

nos vamos nosotros, pero creo que los niños ya son mayores y estarán bien. Gracias 

por estos años en el laboratorio, por estar dispuesto a hablar de química, pero también 

a hacer el mono si era lo que tocaba ese día. Sé que te irá bien en lo que está por venir, 

lo único, no pongas música del infierno o de tienda de ropa el primer día por si hay 

gente de tímpano sensible, prueba primero con algo como Florence... 

Mis tres españolas en Boston, Carlota, María y Natalia, gracias por los paseos en bici, 

los atardeceres en la explanada, los días en la playa, las noches de juegos de mesa (un 

poco hipercompetitivos) y las tardes de peli/siesta. Pero, sobre todo, gracias por 

hacerme sentir en casa a 5000 km de la mía. Con vosotras volví a ser yo misma cuando 

estaba un poco perdida en mi cabeza, y os lo agradeceré siempre. 

Por supuesto, a la gente del grupo, las personas con las que se han forjado recuerdos 

inolvidables, como cantar a pleno pulmón desde Bisbal a los Rebujitos los viernes por 

la tarde cuando el agotamiento llevaba a todos a delirar un poco, excepto a Manu, que 

estaría haciendo alguna columna. Gracias por estos años al inesperablemente sensible 

Sergio, a Gema, que coge las riendas cuando hace falta, a Jaime, Juan, Jenni, Arturo, 

Alex, Carlos, Antonio, Carlos, Valeria, Jesús, Marina, Sergio, Diego, Jesús, Justo, 

Javi, Agus… Gracias a Inés, que desde el principio me contó con total sinceridad lo 

que podría suponer hacer una tesis doctoral y que, por suerte, ha estado para 

apoyarme. A Paul por enseñarme a dar mis primeros pasos en el laboratorio. A los 

profesores del grupo, José, Laura, Salvatore, Beti y, especialmente, a Mª Ángeles por 

el continuo apoyo a lo largo de estos años. Gracias también a Ana, la persona que hace 

que el complejo engranaje del grupo funcione sin problemas echando una mano 

siempre que es necesario. 



 

 

A la gente del departamento, Jon, Vero, Anabel, Román, Paola, Cristina, Lucía, 

Adrián, María, Pablo, Mario, Matías… gracias por las tardes de desconectar y pasar 

un buen rato. Gracias, Andrea, por acogerme desde el primerísimo día, eres de esas 

personas a las que se les nota mucho lo de ser buena gente. Ángeles, has sabido 

entenderme como casi nadie, conocerme más de lo que yo pensaba, gracias por las 

charlas motivacionales y los momentos de desconexión. Tamara, solo me queda 

decirte que lo mejor está por llegar y, ya sabes, llama, grita si me necesitas. Marcos, 

mi hermano encubierto, eres todo vida, con tus ideas locas y tu capacidad para la 

investigación no habrá quién te pare.  

Por último… 

Queridos papá y mamá, lo que veis en este libro es lo que he hecho los últimos años 

jugando a los cacharritos y dibujando. Porque la niña salió de ciencias en la casa de 

las artes y las letras… En este tiempo he intentado hacer todo tal y como me habéis 

enseñado siempre, sin rendirme, con creatividad, paciencia, esfuerzo, determinación, 

valentía y, sobre todo tratando de disfrutar cada día. También he intentado ser fuerte 

como la abuela Trini. He seguido los consejos del abuelo Antonio, de estudiar todo lo 

que pudiera, porque el saber no ocupa lugar. Y, por supuesto, he trabajado duro y lo 

seguiré haciendo para ser una persona de provecho, como decía el abuelo Nicolás. Lo 

de ser cabezota me salía sin querer. 

Begoña, mi loquita hermana pequeña, mi QueenB, gracias por entenderme y estar 

cuando las cosas se torcían. Considerando tus esfuerzos por saber lo que es un anillo 

aromático, te presento el libro ideal, porque trata única y exclusivamente de muchos 

aromáticos. 

Lara, gracias por hacerme tan feliz, por entenderme, por estar siempre en mi equipo, 

por ser siempre mi apoyo incondicional. 

Gracias por ser mi familia, por hacerme quien soy, sin dejarme olvidar de dónde vengo 

y apoyarme siempre, aunque en el fondo no tenga del todo claro a dónde voy… 

  



 

 

 

  



 

 

PUBLICATIONS 

o P. Izquierdo-García, J. M. Fernández-García, I. Fernández, J. Perles, N. Martín, 

Helically Arranged Chiral Molecular Nanographenes, J. Am. Chem. Soc. 2021, 

143, 11864. 

 

o P. Izquierdo-García, J. M. Fernández-García, J. Perles, I. Fernández, N. Martín, 

Electronic Control of the Scholl Reaction: Selective Synthesis of Spiro vs Helical 

Nanographenes, Angew. Chem. Int. Ed. 2023, 62, e202215655. 

 

o P. Izquierdo-García, J. M. Fernández-García, S. Medina Rivero, M. Šámal, J. 

Rybáček, L. Bednárová, S. Ramírez-Barroso, F. J. Ramírez, R. Rodríguez, J. 

Perles, D. García-Fresnadillo, J. Crassous, J. Casado, I. G. Stará, N. Martín, Helical 

Bilayer Nanographenes: Impact of the Helicene Length on the Structural, 

Electrochemical, Photophysical, and Chiroptical Properties, J. Am. Chem. Soc. 

2023, 145, 11599. 

 

o J. M. Fernández-García, P. Izquierdo-García, M. Buendía, S. Filippone, N. Martín, 

Synthetic chiral molecular nanographenes: the key figure of the racemization 

barrier, Chem. Commun. 2022, 58, 2634. 

  



 

 

 

 

 

  



 

 

 

 

   

   

   

   

   

   

   

    

    

    

    

    

    

   

    

    

    

    

    

    

    

     

    

    

    

    

   

    

    

   

    

Table of Contents

SUMMARY................................................................................................................v

RESUMEN.............................................................................................................  xiii

INTRODUCTION.....................................................................................................1

The first 2D atomic crystal: a honeycomb patterned carbon layer..........................1

Trends and Recent Developments  ...........................................................................4

Bilayer graphene: twist to superconductivity  ......................................................4

Graphene molecules: Nanographenes  .................................................................6

1  Chapter 1..........................................................................................................  11

1.1  Introduction to the Synthesis of Nanographenes  ................................  11

1.1.1  Key Reactions for the  π-Extension......................................................  11

1.1.2  Graphitization  ......................................................................................18

1.1.3  Scholl Cyclodehydrogenation  .............................................................19

1.2  Objectives  ...............................................................................................31

1.3  Results and Discussion...........................................................................33

1.3.1  Unexpected Synthesis of Spironanographenes ....................................33

1.3.2  Characterization of  Spironanographene  10  .........................................37

1.3.3  Mechanism of the Scholl reaction  .......................................................47

1.3.4  Electronic Effects Controlling the Scholl Reaction.............................48

1.3.5  Electrochemical and Photophysical Properties....................................50

1.4  Conclusions.............................................................................................57

2  Chapter 2..........................................................................................................61

2.1  Introduction to Chirality  in Nanographenes  .......................................61

2.1.1  From Two-Dimensionality to Chirality  ...............................................63

2.1.2  Chiral Nanographenes and Isomerization Barriers..............................64

2.1.3  Alternative Approaches for Chirality in PAHs  ....................................68

2.2  Objectives  ...............................................................................................71

2.3  Results and Discussion...........................................................................73

2.3.1  Synthesis of Helically Arranged Nanographenes  ................................73

2.3.2  Unexpected Chirality...........................................................................75

2.3.3  Molecular Dynamics: Asymmetric Derivatives  17b,c.........................77

2.3.4  No C−H ···  π  Interactions, No Helicity, No Chirality  .........................81



 

 

 

    

    

    

    

    

   

    

    

    

    

    

    

   

    

    

    

    

    

    

    

    

    

    

   

    

    

   

   

   

   

    

   

   

2.3.5  Electrochemical and Photophysical Properties  ...................................  83

2.3.6  Photophysical Properties of Helically Arranged Nanographenes  .......  86

2.4  Conclusions  .............................................................................................  87

3  Chapter 3.  ........................................................................................................  91

3.1  Introduction to Bilayer Nanographenes..............................................  91

3.1.1  Van der Waals Bilayer Molecular Nanographenes..............................  91

3.1.2  Bilayers from Fused Radicals  .............................................................  94

3.1.3  Covalently Linked Bilayers  ................................................................  95

3.2  Objectives.............................................................................................  101

3.3  Results and Discussion........................................................................  103

3.3.1  Synthesis of Helical Bilayer Nanographenes....................................  103

3.3.2  Electrochemical and Spectroelectrochemical Properties  ..................  105

3.3.3  Photophysical Properties...................................................................  107

3.3.4  Chiroptical Properties of HBNGs  ......................................................111

3.4  Conclusions  ...........................................................................................115

4  Chapter 4  ........................................................................................................119

4.1  Introduction to Stereochemical Control in Nanographenes.............119

4.1.1  Enantioselective Synthesis of Nanographenes...................................119

4.1.2  Chirality Transference: from Atropisomerism to Helical Chirality  ..  120

4.2  Objectives.............................................................................................  125

4.3  Results and Discussion: oxa-Helical Bilayer Nanographenes  .........  127

4.3.1  Enantiospecific Synthesis of oxa-Helical Bilayer Nanographenes...  127

4.3.2  Electrochemical properties  ...............................................................  133

4.3.3  Photophysical Properties...................................................................  135

4.3.4  Chiroptical properties  .......................................................................  136

4.4  Conclusions  ..........................................................................................  137

EXPERIMENTAL SECTION  ................................................................................  141

APPENDIX 1. Chapter 1........................................................................................  165

APPENDIX 2. Chapter 2........................................................................................  175

APPENDIX 3. Chapter 3........................................................................................  181

APPENDIX  4. Chapter 4........................................................................................  193

APPENDIX 5. Spectra  ...........................................................................................  201

REFERENCES  .......................................................................................................  257



 

 

 

 

  



 

 

 

 

 



Abbreviations 

i 

 

ABBREVIATIONS 

1D:  
1H-NMR 
13C-NMR 
19F-NMR 

2D 

Abs 

AFM 

BCPL 

BINOL 

Cat 

CD 

COSY 

CPL 

Cu-TMDA 

 

DBPP 

DBU 

DCE 

DCM 

DDQ 

DEPT 

DFT 

DIPA 

DMF 

E0-0 

E1
1/2ox/red 

e.e. 

Emi 

Fc/Fc+ 

FT-IR 

gabs/lum 

HBC 

HBNG 

HMBC 

HMQC 

HOMO 

HPLC 

HRMS 

INT 

IUPAC 

LUMO 

M 

m, MTDM 

MALDI-ToF 

Monodimensional 

Proton Nuclear Magnetic Resonance 

Carbon Nuclear Magnetic Resonance 

Fluorine Nuclear Magnetic Resonance 

Bidimensional 

Absorption 

Atomic Force Microscope 

Circularly Polarized Luminiscence Brightness 

1,1′-Bi-2-naphthol 

Catalyst 

Circular Dichroism 

COrrelated SpectroscopY 

Circularly Polarized Light 

Di-μ-hydroxo-bis[(N,N,N′,N′-tetramethylethylenediamine)copper(II)] 

chloride 

Dibenzo[fg,ij]phenanthro-[9,10,1,2,3-pqrst]pentaphene 

1,8-Diazabicyclo[5.4.0]undec-7-ene 

Dichloroethane 

Dichloromethane 

2,3-Dichloro-5,6-dicyano-1,4-benzoquinone 

Distortionless Enhancement by Polarization Transfer 

Density Functional Theory 

Diisopropylamine 

N,N-Dimetilformamide 

Optical band gap 

First half wave oxidation/reduction potential 

Enantiomeric excess 

Emission 

Ferrocene/Ferrocenium 

Fourier Transform Infrared Spectroscopy 

Absorption and luminescence dissymmetry factor 

Hexa-peri-hexabenzocoronene 

Helical Bilayer Nanographene 

Heteronuclear Multiple Bond Correlation 

Heteronuclear Multiple Quantum Correlation 

Highest Occupied Molecular Orbital 

High Performance Liquid Chromatography 

High Resolution Mass Spectrometry 

Intermediate 

International Union of Pure and Applied Chemistry 

Lowest Unoccupied Molecular Orbital 

Molar 

Magnetic Dipole Transition Moment 

Matrix-Assisted Laser Desorption/Ionization-Time-of-Flight 



Abbreviations 

ii 

 

NBO 

NICS 

NIR 

NOESY 

[Ox] 

PAH 

r.t. 

SOPT 
tBu-HBC 

TD-DFT 

TFA 

TfOH 

THF 

Tol 

UV-vis 

V 

vs. 

ε 

θ 

λabs/emi 

μ, ETDM 

Φem 

Natural bond order 

Nuclear Independent Chemical Shift 

Near Infrared 

Nuclear Overhauser Effect Spectroscopy 

Oxidation 

Polyaromatic hydrocarbons 

Room temperature 

Second order perturbation theory 

Hexa-tert-butyl-hexa-peri-hexabenzocoronene 

Time-Dependent Density Functional Theory 

Trifluoroacetic acid 

Trifluoromethanesulfonic acid or triflic acid 

Tetrahydrofuran  

Toluene 

Ultraviolet-visible 

Volts 

versus 

Molar Absorption Coefficient 

Angle between ETDM and MTDM 

Absorption/Emission wavelength 

Electric Dipole Transition Moment 

Emission Quantum Yield 

 

   



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Summary 

  



 

 

 

 

  

 



Summary 

v 

 

SUMMARY 

Chapter 1 

The Scholl reaction is key in the synthesis of molecular nanographenes, as it leads to 

graphitization of the precursor polyarenes. The conditions for carrying out the reaction 

involve the use of Lewis acids or Brønsted acids in combination with oxidants such 

as DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone), and the mechanism involves 

the formation of arenium-cation or radical-cation intermediates. However, it is 

difficult to predict the operating mechanism and, sometimes, leads to unexpected 

compounds due to the formation of alternative intermediates or rearrangements. 

In this chapter, the unexpected synthesis of spironanographenes and the control over 

the Scholl reaction, by means of electronic effects on the structure, to obtain a helical 

nanographene, are described. The Scholl reaction on an anthracene-based polyarene 

results in the formation of spirocycles connecting the graphitized units to the central 

anthracene. As revealed by theoretical calculations, this occurs due to the formation 

of very stable trityl-cation intermediates, at positions 9 and 10 of the anthracene. 

Depending on the Scholl reaction conditions, it has been possible to control the 

number of graphitization closures, thus describing the first example in which the 

formation of spirocycles does not interrupt the graphitization. 

 

Pursuing the main objective of synthesizing a helically arranged nanographene 

consisting of two graphitized units (dibenzo[fg,ij]phenanthro-[9,10,1,2,3pqrst] 

pentaphene, DBPP) connected through a central anthracene, the Scholl reaction was 

controlled by the introduction of eight fluorine atoms. The electron-withdrawing 

character of the fluorine atoms destabilizes the formation of the trityl cation at the 



Summary 

vi 

 

positions 9 and 10 of the anthracene, causing the reaction to evolve through the 

arenium cation intermediates, thus, giving rise to the expected graphitized structure. 

In addition to the synthesis and structural characterization of the new molecular 

nanographenes, the characterization of the optoelectronic properties has been carried 

out. Cyclic voltammetry measurements of spironanographene showed higher absolute 

oxidation and reduction potentials (E1
1/2ox= 0.85 V, E1

1/2red= −2.56 V) than those 

corresponding to tBu-HBC (E1
1/2ox= 0.67 V and E1

1/2red= −2.27 V), which evidences 

the disruption of conjugation at the sp3 spiranic carbons connecting the graphitized 

units to the anthracene core. This structural feature has also an impact on the optical 

properties of the absorption and emission spectra, whose bands are blue shifted 

compared to those of tBu-HBC.  

The electronic properties of the helically arranged nanographene also revealed the 

lower π-extension of the graphitized units (DBPP), with respect to the tBu-HBC, 

showing a first oxidation potential at E1
1/2ox= 0.87 V. However, the acceptor character 

is stronger than that of tBu-HBC, as the first reduction potential (E1
1/2red= −1.69 V) is 

highly influenced by the localization of the LUMO on the anthracene electron-

withdrawing core. This behavior is also reflected in the emission spectrum, in which 

a red shift of the bands is observed, compared to tBu-HBC. Interestingly, this structure 

appears to exhibit a dual emission in which the two fluorophores (DBPPs and 

octafluoroanthracene) seem to give rise to the corresponding bands independently. 

Chapter 2 

Most strategies for inducing chirality in nanographenes involve deviation from 

planarity by introducing topological defects. Thus, non-hexagonal cycles and helical 

features are the most extensively studied topological defects. However, the possibility 

of inducing atropisomerism-like axial chirality, in which the chirality arises from the 

restriction of rotation of the structural units around a single bond, has been slightly 

studied. Therefore, in this chapter a new strategy to induce atropisomerism in 

nanographenes is described. In addition, the molecular dynamics, directly related to 

the stability of the chiroptical properties of helically arranged nanographenes, is 

studied. 

With the aim of simplifying the system to carry out the chirality study, nanographenes 

based on two graphitized units (DBPP) connected through a 1,4-disubstituted 

tetrafluorobenzene core have been synthesized, resembling the structure obtained in 

the previous chapter based on related octafluoroanthracene. 



Summary 

vii 

 

 

The initial approach consisted on the synthesis of a nanographene in which both, the 

substituents on the DBPP are the same, and the central core is substituted with four 

fluorine atoms. Subsequent modification of the substituents (in the DBPP and the 

central core) would lead to terphenyl-like atropisomerism. However, once the 

structure in which the DBPPs are substituted with five tert-butyl groups and the 

central benzene with four fluorine atoms in the 2,3,5,6 positions was obtained, two 

unexpected enantiomers were observed in the crystal structure. DFT calculations 

revealed the formation of C−H···π interactions between the DBPP units. These 

interactions occur as a result of the hindered coplanarity between the DBPPs and set 

the structure with a helical arrangement of the subunits, giving rise to two non-

superimposable mirror images. The enantiomers were observed by chiral HPLC; 

however, they could not be isolated due to the racemization observed at room 

temperature. 

For the study of the isomerization barrier, two derivatives were prepared, in which 

one tert-butyl group on each DBPP was exchanged for a OMe group or a hydrogen 

atom. This modification involves the formation of two NMR-distinguishable nearly 

degenerate diastereomers. From a sample enriched in one of the diastereomers it was 

possible to monitor the evolution to equilibrium (1:1 ratio), which allowed us to 

calculate the value of the isomerization barrier, Δ𝐺⧧= 24.6 kcal·mol−1 at 40 ºC, and a 

half-time life of τ1/2 = 107 min. Furthermore, with these experiments it was possible 

to confirm that the 90° rotation of the tetrafluorobenzene unit was the reason for the 

isomerization process. 

Additionally, the electrochemical properties were studied by cyclic voltammetry and 

square wave voltammetry. The tetrafluorobenzene-based nanographenes are weaker 

electron-donor and electron-acceptors than tBu-HBC, which is in agreement with the 

lower π-extension of the DBPP units and the weak conjugation along the structure. 

The same trend was confirmed by absorption and emission spectra measurements, 

which showed blue-shifted bands with respect to tBu-HBC. 

 

 



Summary 

viii 

 

Chapter 3 

In this chapter, the synthesis and characterization of two helical bilayer nanographenes 

(HBNGs) with different number of ortho-fused rings giving rise to two helicenes of 

different lengths, [9] and [11]helicene ([9]HBNG and [11]HBNG), is described. 

These structures, together with the one previously published by our research group 

[10]HBNG (ACIE 2018), form a family whose structural features determine the 

variation of properties. 

Commonly, the properties of molecular nanographenes can be modulated by varying 

the π-extension or by introducing defects in the hexagonal lattice (as described in 

Chapter 2). However, in this chapter we describe the impact of a new structural 

feature, the overlapping degree between two facing layers with intramolecular π,π- 

interaction. Therefore, this chapter details the systematic study of the optoelectronic 

and chiroptical properties of these helical bilayer nanographenes. 

 

The length of the helicene determines the overlapping degree between the graphitized 

layers fused at the ends, with [9]HBNG being the most overlapped (26 rings involved 

in π-π interactions) and [11]HBNG (10 rings involved in π-π interactions) being the 

least overlapped. Moreover, in these structures the π-extension varies with the number 

of rings in the helicene, with [9]HBNG having the lowest π-extension and [11]HBNG 

the highest π-extension. 

Taking these structural features into account, it was possible to study and understand 

the impact of the overlapping degree on the properties. The strongest donor character 

is exhibited by the lower π-extended nanographene [9]HBNG. This behavior is 

attributed to a mixed valence effect whereby the cation and the radical cation 

(oxidized species) are stabilized between the graphitized layers (greater overlapping 

degree). In addition, this structure [9]HBNG shows the most red-shifted emission 

bands, evidencing the communication of the layers through space by π-π interactions. 

Interestingly, the alignment of the electric and magnetic vectors makes [9]HBNG the 

nanographene with the best chiroptical properties, with an absorption and emission 

Higher overlapping

Larger π-extension

Stronger donor character

[9]HBNG [10]HBNG [11]HBNG

ACIE 2018



Summary 

ix 

 

factor of circularly polarized light (gabs and glum) of 3.6·10−2, one of the highest 

reported for carbon structures. 

Chapter 4 

The growing interest in helical bilayer nanographenes, mainly due to their unique 

overlapping characteristics and remarkable chiroptical properties (Chapter 3), makes 

it necessary to search for new strategies to improve synthetic accessibility. In this 

chapter we describe an easily scalable synthetic strategy for chiral bilayer 

nanographenes that avoids the costly separation of enantiomers by chiral HPLC.  

The synthesis starts from the commercially available compound 7-bromo-2-naphthol, 

whose reactivity allows the production of 7,7'-disubstituted BINOL derivatives. The 

configurational stability of BINOL (with axial chirality), and the reactivity of the 

naphthol groups allowed the esterification with enantiomerically pure canforsulfonyl 

chloride for the chemical resolution of the enantiomers of the BINOL-based 

polyarene. Subsequently, the Scholl reaction was performed, in which 

cyclodehydrogenation (graphitization) and enantiospecific cyclodehydration of the 

naphthol groups occurs to give oxa[9]HBNG with chirality transference from axial to 

helical. 

 

In addition, the characterization of the optoelectronic and chiroptical properties has 

been carried out. By means of cyclic voltammetry, the structure oxa[9]HBNG (22 

rings involved in the intramolecular π-π interactions) presents a slightly weaker donor 

character, E1
1/2ox= 0.37 V, than the bilayer [9]HBNG (26 rings involved in the 

intramolecular π-π interactions), E1
1/2ox= 0.35 V, evidencing the influence of the 



Summary 

x 

 

overlapping degree (lower overlapping, weaker donor character). Moreover, the most 

prominent redox variation is observed in the acceptor character, the presence of the 

oxygen atom in the helicene causes the LUMO to localize in the graphitized layers, 

increasing the reduction potential, E1
1/2red= −2.27 V, to values similar to those of tBu-

HBC, E1
1/2red= −2.24 V. In addition, the emission spectrum of oxa[9]HBNG shows 

well-structured blue-shifted bands comparable to those of tBu-HBC, which contrasts 

with the broad red-shifted bands of [9]HBNG. This suggests a lower excimer-like 

contribution due to changes in the LUMO of oxa[9]HBNG (delocalized in the 

graphitized layers), as opposed to [9]HBNG whose LUMO is mainly localized in the 

helicene. Finally, the chiroptical properties of M- and P-oxa[9]HBNG have been 

studied by means of electronic circular dichroism, from which absorption 

dissymmetry factor (gabs) of +3.7·10−3 at 487 nm for M-oxa[9]HBNG, and  −1.8·10−3 

at 487 nm for P-oxa[9]HBNG, have been calculated.



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Resumen 

  



 

 

 

 

 

 



Resumen 

xiii 

 

RESUMEN 

Capítulo 1 

La reacción de Scholl es clave en la síntesis de nanografenos moleculares, ya que da 

lugar a la grafitización de los poliarenos precursores. Las condiciones para llevar a 

cabo la reacción conllevan la utilización de ácidos de Lewis o ácidos de Brønsted en 

combinación con oxidantes como DDQ (2,3-dicloro-5,6-diciano-1,4-benzoquinona) 

y el mecanismo implica la formación de intermedios de tipo catión arenio o catión 

radical. Sin embargo, es difícil predecir el mecanismo operando y, en ocasiones, da 

lugar a compuestos inesperados como resultado de la formación de intermedios 

alternativos o reordenamientos. 

En este capítulo, se describe la síntesis inesperada de espironanografenos y como 

influyen los efectos electrónicos en el control sobre la reacción de Scholl. La reacción 

de Scholl sobre un poliareno basado en un núcleo central de antraceno da lugar a la 

formación de espirociclos que conectan las unidades grafitizadas con el antraceno 

central. Según revelaron los cálculos teóricos, esto ocurre debido a la formación de 

intermedios catión tritilo, muy estables, en las posiciones 9 y 10 del antraceno. 

Dependiendo de las condiciones de Scholl utilizadas se ha podido controlar el número 

de cierres de grafitización, describiendo así el primer ejemplo en el que la formación 

de espirociclos no interrumpe la grafitización. 

 

Persiguiendo el objetivo principal de sintetizar nanografenos helicoidalmente 

organizados formados por dos unidades grafitizadas (dibenzo[fg,ij]phenanthro-

[9,10,1,2,3-pqrst]pentaphene, DBPP) conectadas a través de un antraceno central, se 

controló la reacción de Scholl mediante la introducción de ocho átomos de flúor. El 

carácter electroatractor de los átomos de flúor desestabiliza la formación del catión 



Resumen 

xiv 

 

tritilo en las posiciones 9,10 del antraceno, haciendo que la reacción evolucione por 

los intermedios de tipo catión arenio que dan lugar a la estructura grafitizada esperada. 

Además de la síntesis y caracterización estructural de los nuevos nanografenos 

moleculares, se ha llevado a cabo la caracterización de las propiedades 

optoelectrónicas. Las medidas de voltamperometría cíclica del espironanografeno 

mostraron valores de potenciales de oxidación y reducción más altos en valor absoluto 

(E1
1/2ox= 0.85 V, E1

1/2red= –2.56V) que los correspondientes al tBu-HBC E1
1/2ox= 0.67 

V, E1
1/2red= –2.27 V), lo cual evidencia la interrupción de la conjugación en los 

carbonos espiránicos sp3 que conectan las unidades grafitizadas con el fragmento 

central de antraceno. Esta característica estructural también repercute sobre las 

propiedades ópticas de absorción y emisión, cuyas bandas están más desplazadas al 

azul, frente al tBu-HBC.  

Las propiedades electrónicas del nanografeno helicoidalmente organizado revelaron 

también la menor π-extensión de las unidades grafitizadas (DBPP), respecto al tBu-

HBC, mostrando un primer potencial de oxidación E1
1/2ox= 0.87 V. Sin embargo, el 

carácter aceptor es mejor que en el tBu-HBC, ya que el primer potencial de reducción 

E1
1/2red= –1.69 V se ve altamente influenciado por la localización del LUMO en el 

fragmento electroaceptor de antraceno fluorado. Este comportamiento también se ve 

reflejado en el espectro de emisión, en el cual se observa un desplazamiento de las 

bandas al rojo. Curiosamente, esta estructura parece presentar una emisión dual, en la 

cual los dos fluoróforos (DBPPs y octafluoroantraceno) parecen dar lugar a las 

correspondientes bandas de emisión de manera independiente. 

Capítulo 2 

La mayoría de las estrategias para la inducción de quiralidad en nanografenos 

implican la desviación de la planaridad mediante la introducción de defectos 

topológicos. Así, los ciclos no hexagonales y las unidades helicoidales son las 

características estructurales más estudiadas. Sin embargo, hasta la fecha, solo unos 

pocos ejemplos en la literatura representan la posibilidad de inducir quiralidad axial 

de tipo atropisomería, en la que la quiralidad surge de la restricción de giro de las 

unidades estructurales alrededor de un enlace sencillo. En este capítulo se describe 

una nueva estrategia para inducir atropisomería en nanografenos. Además, se estudia 

la dinámica molecular, directamente relacionada con la estabilidad de las propiedades 

quirópticas de los nanografenos dispuestos helicoidalmente. 

Los nanografenos descritos, formados por dos unidades grafitizadas (DBPP) 

conectadas a través de un fragmento central de tetrafluorobenzeno 1,4-disustituido, 

similares a la estructura basada en octafluoroantraceno obtenida en el capítulo 

anterior, se sintetizaron con el objetivo de simplificar el sistema para llevar a cabo un 

estudio de la quiralidad. 



Resumen 

xv 

 

 

La aproximación inicial consistía en la síntesis un nanografeno en el cual los 

sustituyentes en el DBPP son iguales y el fragmento central de benceno está sustituido 

por cuatro átomos de flúor. La posterior modificación de los sustituyentes daría lugar 

a atropisomería de sistemas terfenilo. Sin embargo, una vez obtenida la estructura en 

la que los DBPPs están sustituidos con cinco grupos tert-butilo y el benceno central 

con cuatro átomos de flúor en las posiciones 2,3,5,6, se observó la formación 

inesperada de dos enantiómeros en la estructura cristalina. Mediante cálculos DFT se 

pudo observar la formación de interacciones de tipo C−H···π entre las unidades de 

DBPP. Estas interacciones se dan como resultado de la imposibilidad de coplanaridad 

entre los DBPPs, y fijan la estructura con una organización helicoidal de las 

subunidades, dando lugar a dos imágenes especulares no superponibles. Los 

enantiómeros se observaron por HPLC quiral, sin embargo, no se pudieron aislar 

debido a su racemización a temperatura ambiente.  

Para el estudio de la barrera de isomerización se prepararon dos derivados en los 

cuales un grupo tert-butilo de cada DBPP se intercambió por un grupo OMe o un 

átomo de hidrógeno. Esta modificación implica la formación de dos diasterómeros 

casi degenerados diferenciables por RMN. A partir de una muestra enriquecida en uno 

de los diasterómeros se pudo monitorizar la evolución hasta el equilibrio (relación 

1:1), lo cual permitió conocer el valor de la barrera de isomerización, Δ𝐺⧧= 24.6 

kcal·mol−1 a 40 ºC, y del tiempo de vida media, τ1/2= 107 min. Además, con estos 

experimentos se pudo confirmar que el giro de 90º de la unidad de tetrafluorobenceno, 

es el motivo por el cual ocurre la isomerización. 

Adicionalmente, se estudiaron las propiedades electroquímicas por voltamperometría 

cíclica y por voltamperometría de onda cuadrada. Los nanografenos basados en 

tetrafluorobenceno son electrodadores y electroaceptores más débiles que el tBu-

HBC, lo cual concuerda con la menor π-extensión de las unidades de DBPP y la débil 

conjugación a lo largo de la estructura. La misma tendencia se confirmó con las 

medidas de espectros de absorción y emisión, que muestran las bandas desplazadas 

hacia el azul respecto al tBu-HBC. 

 



Resumen 

xvi 

 

Capítulo 3 

En este capítulo se describe la síntesis y caracterización de dos nanografenos bicapa 

helicoidales (HBNG) con diferente número de anillos orto-fusionados, dando lugar a 

dos helicenos de distinta longitud, [9] y [11]heliceno ([9]HBNG y [11]HBNG). Estas 

estructuras, junto con la publicada anteriormente por nuestro grupo de investigación, 

[10]HBNG (ACIE 2018), forman una familia cuyas características estructurales 

determinan la variación de las propiedades. 

En nanografenos moleculares es común la modulación de las propiedades mediante la 

variación de la extensión π o mediante la introducción de defectos en la red hexagonal 

(como se describe en el Capítulo 2). Sin embargo, en este trabajo se describe el 

impacto de una nueva característica estructural, el grado de solapamiento entre dos 

capas enfrentadas con interacciones π-π. Por tanto, en este capítulo se detalla el 

estudio sistemático de las propiedades optoelectrónicas y quirópticas de estos 

nanografenos. 

 

La longitud del heliceno determina el grado de solapamiento entre las capas 

grafitizadas fusionadas en los extremos, siendo [9]HBNG la más solapada (26 anillos 

intervienen en las interacciones π-π) y [11]HBNG (10 anillos intervienen en las 

interacciones π-π) la menos solapada. Además, en estas estructuras varía la extensión 

π con el número de anillos en el heliceno, siendo [9]HBNG la de menor extensión π 

y [11]HBNG la de mayor extensión π. 

Teniendo en cuenta estas características estructurales, se pudo estudiar y comprender 

el impacto del grado de solapamiento sobre las propiedades. El carácter dador más 

fuerte lo presenta el nanografeno de menor extensión π, [9]HBNG. Este 

comportamiento se atribuye a un efecto de valencia mixta mediante el cual el catión 

y el catión radical (especies oxidadas) se estabilizan entre las capas grafitizadas. 

Además, esta estructura presenta las bandas de emisión más desplazadas al rojo, 

evidenciando la comunicación de las capas a través del espacio por interacciones π-π. 

Curiosamente, la alineación de los vectores eléctrico y magnético hacen que 

[9]HBNG sea el nanografeno con mejores propiedades quirópticas, con un factor de 

Mayor solapamiento

Mayor extensión π

Caracter dador más fuerte

[9]HBNG [10]HBNG [11]HBNG

ACIE 2018



Resumen 

xvii 

 

absorción y emisión de luz circularmente polarizada (gabs y glum) de 3.6·10−2, uno de 

los más altos descritos hasta ahora para estructuras de carbono. 

Capítulo 4 

El creciente interés en nanografenos bicapa helicoidales debido principalmente a las 

características singulares que aporta el solapamiento π-π y a las destacables 

propiedades quirópticas (Capítulo 3), hace necesaria la búsqueda de nuevas 

estrategias para mejorar la accesibilidad sintética. En este capítulo, se describe una 

estrategia sintética de nanografenos bicapa quirales fácilmente escalable evitando la 

costosa separación de enantiómeros por HPLC quiral.  

La síntesis parte del compuesto 7-bromo-2-naftol, comercialmente disponible, cuya 

reactividad permite la obtención de derivados de BINOL 7,7’-disustituido. La 

estabilidad configuracional del BINOL (con quiralidad axial) y la reactividad de los 

grupos naftol, han permitido la esterificación con cloruro de canforsulfonilo 

enantioméricamente puro para la resolución química de los enantiómeros del 

poliareno basado en BINOL. Posteriormente se ha realizado la reacción de Scholl, en 

la cual ocurre la ciclodeshidrogenación (grafitización) y la ciclodeshidratación 

enantioespecífica de los grupos naftol dando lugar al oxa[9]HBNG con transferencia 

de la quiralidad axial a quiralidad helicoidal. 

 

Además, se ha llevado a cabo la caracterización de las propiedades optoelectrónicas 

y quirópticas. Mediante voltamperometría cíclica se observó la influencia del 

solapamiento (22 anillos intervienen en las interacciones π-π intramoleculares), la 

estructura presenta un carácter dador ligeramente inferior, E1
1/2ox= 0.37 V, a la bicapa 



Resumen 

xviii 

 

[9]HBNG (26 anillos intervienen en las interacciones π-π intramoleculares), E1
1/2ox= 

0.35 V. Sin embargo, la variación más destacada se observa en el carácter aceptor, la 

presencia del átomo de oxígeno en el heliceno hace que el LUMO se localice en las 

capas grafitizadas, aumentando el potencial de reducción, E1
1/2red= −2.27 V, a valores 

similares a los de tBu-HBC, E1
1/2red= −2.24 V. Además, el espectro de emisión del 

oxa[9]HBNG muestra bandas bien estructuradas desplazadas al azul y comparables a 

las del tBu-HBC, lo cual contrasta con las bandas anchas desplazadas al rojo del 

[9]HBNG. Esto sugiere una menor contribución de tipo excímero debido a los 

cambios en el LUMO del oxa[9]HBNG (deslocalizado en las capas grafitizadas), 

frente a [9]HBNG cuyo LUMO se localiza principalmente en el heliceno. Finalmente, 

las propiedades quirópticas de los enantiómeros puros M-oxa[9]HBNG y P-

oxa[9]HBNG se han estudiado por dicroísmo circular, de donde se han obtenido unos 

factores de disimetría de  absorción (gabs) de +3.7·10−3 a 487 nm para M-

oxa[9]HBNG, y  −1.8·10−3 a 487 nm para P-oxa[9]HBNG. 



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Introduction 

 

 

  



 

 

 

  



Introduction 

1 

 

INTRODUCTION 

The first 2D atomic crystal: a honeycomb patterned carbon layer 

“Graphene is the name given to a single layer of carbon atoms densely packed into a 

benzene-ring structure”.1 This is the definition provided by Konstantin Novoselov 

and Andre Geim in their seminal work published in Science 2004, in which they 

isolate graphene for the first time. Until that moment, graphene had been broadly 

explored as a theoretical model2,3,4 and was believed to be unstable in the free state 

with respect to the formation of curved structures as fullerenes or nanotubes. Defying 

the predictions against its existence, monolayer graphene was unexpectedly obtained 

in a way that was as simple as it was ingenious. Using adhesive tape, it was possible 

to exfoliate graphene samples from small fragments of highly oriented pyrolytic 

graphite. The first AFM image of single-layer graphene and its chemical structure are 

represented in Figure 1. 

Along with the discovery of graphene, the striking electronic properties positioned 

this material as the best possible “metal” for metallic transistor applications, offering 

also ballistic transport. In 2005, it was confirmed that the charge carriers in graphene, 

that mimic relativistic particles with zero rest mass having an effective speed of light, 

are massless Dirac fermions.5 Thus, from the electronic properties point of view, 

graphene is a zero-gap semiconductor, Figure 1, right. 

  

Figure 1. First AFM image of single-layer graphene (left, from ref 1), chemical structure of 

graphene (middle), and band structure of graphene with Dirac cones located on a hexagonal 

plane (right). 

This first two-dimensional atomic crystal set a milestone in materials and condensed 

matter science. Only three years after the discovery, in 2007, Geim and Novoselov 

reported a compilation of the properties and potential applications already observed, 

 
1 K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, A. 

A. Fisov, Science 2004, 306, 666. 
2 P. R. Wallace, Phys. Rev. 1947, 71, 622. 
3 J. C. Slonczewski, Phys. Rev. 1958, 109, 272. 
4 G. W. Semenoff, Phys. Rev. Lett. 1984, 53, 2449. 
5 K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, M. I. Katsnelson, I. V. Grigorieva, S. V. Dubonos, 

A. A. Firsov, Nature 2005, 438, 197. 



Introduction 

2 

 

The rise of graphene,6 thus providing clear evidence of the rapid interest of the 

scientific community in this two-dimensional material.  

The accessible procedures to obtain high-quality graphene allowed the fast progress 

of the research. Before 2012 the study of the material parameters had already shown 

outstanding properties. For instance, the electron mobility at room-temperature is of 

2.5·10−5 cm2V−1s−1,7 which exceeds the theoretical limit of 2·10−5 cm2V−1s−1.8 The 

Yong’s modulus, which describes the materials stiffness, is of 1 TPa and the tensile 

strength is of 130 GPa.9 The extreme strength is particularly striking in view of the 

light weigh (0.77 mg/m2). Furthermore, it presents high thermal conductivity,10 

complete impermeability to gases,11 transparency, and the ability to support very high 

densities of electric current (a million times higher than copper).12 This combination 

of properties made graphene a promising material for applications in disruptive 

technologies.13 However, these properties and therefore, the potential applications 

depend on the quality and size of the crystals, which are strongly affected by the 

production method.  

Nowadays there are several methods for the mass-production of graphene,14 which 

allows to control the size, quality, and prize, for particular applications.15 The 

methodologies can be classified in two main approaches, top-down and bottom-up. 

Top-down methods consisting of the exfoliation of graphite, is a straightforward and 

widely used method that can be mechanical, chemical16 or electrochemical.17 

Conversely, the bottom-up approach involves the formation of graphene from smaller 

materials at the atomic or nanometer scale. These methods include chemical vapor 

 
6 A. Geim, K. Novoselov, Nat. Mater. 2007, 6, 183. 
7 A. S. Mayorov, Nano Lett. 2011, 11, 2396. 
8 S. V. Morozov, Phys. Rev. Lett. 2008, 100, 016602. 
9 C. Lee, X. D. Wei, J. W. Kysar, J. Hone, Science 2008, 321, 385. 
10 A. A. Balandin, Nat. Mater. 2011, 10, 569. 
11 J. S. Bunch, S. S. Verbridge, J. S. Alden, A. M. van der Zande, J. M. Parpia, H. G. Craighead, P. L. 

McEuen, Nano Lett. 2008, 8, 2458. 
12 J. Moser, A. Barreiro, A. Bachtold, Appl. Phys. Lett. 2007, 91, 163513. 
13 A. K. Worku, D. W. Ayele, Results Chem. 2023, 5, 100971. 
14 A. Gutiérrez-Cruz, A. R. Ruiz-Hernández, J. F. Vega-Clemente, D. G. Luna-Gazcón, J. Campos-

Delgado, J. Mater. Sci. 2022, 57, 14543. 
15 K. S. Novoselov, V. I. Fal’ko, L. Colombo, P. R. Gellert, M. G. Schwab, K. Kim, Nature 2012, 490, 

192. 
16 K. Parvez, S. Yang, X. Feng, K. Müllen, Synth. Met. 2015, 210, 123. 
17 N. Liu, F. Luo, H. Wu, Y. Liu, C. Zhang, J. Chen, Adv. Funct. Mater. 2008, 18, 1518. 



Introduction 

3 

 

deposition,18,19 epitaxial growth,20 laser-induced,21 laser ablation22 and electric 

discharge “flash” synthesis.23 

Functionalization of graphene 

Alternatively, one of the most exploited properties of graphene is its chemical 

reactivity. The functionalization of the honeycomb backbone is a widely extended 

method for the chemical preparation of graphene derivatives.24 The treatment of 

graphite with oxidative reagents, commonly acids, entails the oxygenation of the 

layers in the borders, as well as in the basal planes, providing the commonly known 

graphene oxide after exfoliation. This material exhibits a mixed sp2−sp3 carbon 

system, and due to its non-conductivity and relative hydrophobicity, it has been widely 

applied in medicine.25,26  

However, for further applications, it is required the restoring of the π network to 

recover the electric conductivity. The “reparation” of the carbon network requires the 

removal of the oxygen-containing functional groups in the layers. This reduction 

process to restore the honeycomb lattice has been achieved by different chemical and 

non-chemical methods,14 and the layer obtained is known as reduced graphene oxide. 

Although the number of remaining defects is important, this material has been used 

in composites, thermal dissipation films and conducting additives.27 

To sum up, the possibilities to obtain graphene are currently wide and technically 

diverse. However, it is important to note that the production methodology is directly 

related to the quality of the material and its properties, which determines its potential 

applications. 

Since the early years of graphene's rise as a tangible and manipulable material, its 

discoverers quickly realized its potential applications, especially in electronics. 

Although, they warned: “despite the reigning optimism about graphene-based 

electronics, ‘graphenium’ microprocessors are unlikely to appear for the next 20 

 
18 K. S. Kim, Y. Zhao, H. Jang, S. Y. Lee, J. M. Kim, K. S. Kim, J.-H. Ahn, P. Kim, J.-Y. Choi, B. H. 

Hong, Nature 2009, 457, 706. 
19 X. Li, W. C. J. An, S. K. J. Nah, D. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S. K. Banerjee, 

L. Colombo, R. S. Ruoff, Science 2009, 324, 1312. 
20 C. Berger, Z. Song, T. Li, X. Li, A. Y. Ogbazghi, R. Feng, Z. Dai, A. N. Marchenkov, E. H. Conrad, P. 

N. First, W. A. De Heer, J. Phys. Chem. B 2004, 108, 19912. 
21 J. Lin, Z. Peng, Y. Liu, F. Ruiz-Zepeda, R. Ye, E. L. G. Samuel, M. J. Yacaman, B. I. Yakobson, J. M. 

Tour, Nat. Commun. 2014, 5, 5714. 
22 M. Qian, Y. S. Zhou, Y. Gao, J. B. Park, T. Feng, S. M. Huang, Z. Sun, L. Jiang, Y. F. Lu, Appl. Phys. 

Lett. 2011, 98, 173108. 
23 D. X. Luong, K. V. Bets, W. A. Algozeeb, M. G. Stanford, C. Kittrell, W. Chen, R. V. Salvatierra, M. 

Ren, E. A. McHugh, P. A. Advincula, Z. Wang, M. Bhatt, H. Guo, V. Mancevski, R. Shahsavari, B. I. 

Yakobson, J. M. Tour, Nature 2020, 577, 647. 
24 A. Adetayo, D. Runsewe, Open J. Compos. Mater. 2019, 9, 207. 
25 Y. Zhu, S. Murali, W. Cai, X. Li, J. W. Suk, J.R. Potts, R.S. Ruoff, Adv. Mater. 2010, 22, 3906. 
26 N. Panwar, A. M. Soehartono, K. K. Chan, S. Zeng, G. Xu, J. Qu, P. Coquet, K.-T. Yong, X. Chen, 

Chem. Rev. 2019, 119, 9559. 
27 L. Lin, H. Peng, Z. Liu, Nat. Mater. 2019, 18, 520. 



Introduction 

4 

 

years”.5 Currently, graphene has been applied to a wide range of fields, including 

electronics, photonics and optoelectronics,28,29,30 fuel cells,31 energy storage,32 

artificial intelligence,33 biomedicine,34 and even cultural heritage.35 Thus, in a 

situation in which graphene is produced in a several thousand tons/year36 scale in the 

present times, it is worth to question what else can be done. 

Trends and Recent Developments 

Bilayer graphene: twist to superconductivity 

Paradoxical though it may seem, one of the current challenges and hot topics in 

graphene is the overlapping of a fixed number of graphene layers by controlling the 

relative twist angle between them. Interestingly, this growing interest, especially in 

graphene bilayers, started in the same year in which Andre Geim and Konstantin 

Novoselov were awarded with Nobel Prize in Physics (2010) "for groundbreaking 

experiments regarding the two-dimensional material graphene" (Figure 2). 

 

Figure 2. The same year that Geim and Novoselov received the Nobel Prize in Physics for 

graphene, new possible phases of matter were expected from twisted bilayer graphene. 

In 2010, Eva Y. Andrei and coworkers reported the observation of van Hove 

singularities in overlapping 2D crystals of graphene with a 1.79º relative twist 

between the layers (Figure 3).37 This observation resulted very intriguing considering 

that new phases of matter can arise near the van Hove singularities (saddle point in 

the electronic band structure leading to a divergence in the density of states, (Figure 

3).38 Thus, indicating the possibility of modulating graphene properties without 

changing its chemical structure, just controlling the number of layers and their relative 

 
28 A. N. Grigorenko, M. Polini, K. S. Novoselov, Nat. Photonics 2012, 6, 749. 
29 J. Wu, H. Lin, D. J. Moss, K. P. Loh, B. Jia, Nat. Rev. Chem. 2023, 7, 162. 
30 F. Bonaccorso, Z. Sun, T. Hasan, A. C. Ferrari, Nat. Photonics 2010, 4, 611. 
31 H. Su, Y. H. Hu, Energy Sci. Eng. 2021, 9, 958. 
32 F. Bonaccorso, L. Colombo, G. Yu, M. Stoller, V. Tozzini, A. C. Ferrari, R. S. Ruoff, V. Pellegrini, 

Science 2015, 347, 1246501. 
33 M. Huang, Z. Li, H. Zhu, Adv. Intell. Syst. 2022, 4, 2200077. 
34 J. Li, H. Zeng, Z. Zeng, Y. Zeng, T. Xie, ACS Biomater. Sci. Eng. 2021, 7, 5363. 
35 E. Galvagno, E. Tartaglia, M. Stratigaki, C. Tossi, L. Marasco, F. Menegazzo, C. Zanardi, F. Omenetto, 

C. Coletti, A. Traviglia, M. Moglianetti, Adv. Funct. Mater. 2024, 2313043. 
36 M. T. U. Safian, K. Umar, M. N. Mohamad Ibrahim, J. Clean. Prod. 2021, 318, 128603. 
37 G. Li, A. Luican, J. M. B. Lopes dos Santos, A. H. Castro Neto, A. Reina, J. Kong, E. Y. Andrei, Nat. 

Phys. 2010, 6, 109. 
38 L. Van Hove, Phys. Rev. 1953, 89, 1189. 

Nobel Prize in Physics 2010

Geim and Novoselov

Van Hove singularities, twisted bilayer graphene



Introduction 

5 

 

twist angle. These early observations were the starting point for the development of 

new metamaterials. 

    

Figure 3. Saddle point (sp) between the two Dirac points (from ref 37) in 1.79º twist bilayer. 

The stacking of two or more atomically thin materials with a relative twist angle or a 

lattice mismatch leads to so-called moiré quantum materials. In 2018, Jarillo-Herrero 

and coworkers described the results expected from the previous observations, a new 

phase of matter in twist bilayer graphene, unconventional superconductivity.39 

The interlayer interaction between two stack graphene layers induces the 

hybridization of their bands, entailing modifications in the low-energy band structure 

depending on the stacking order (AA or AB, Figure 4). Additionally, the relative twist 

angle between the layers modulates the hexagonal moiré patterns, consisting of 

alternating AA and AB stacked regions, in the resulting superlattice, Figure 3 left. The 

precise control over the twist angles revealed that at the particular twist angle of 1.1º, 

termed as the first magic angle, the phase diagram of twisted bilayer graphene is 

similar to that of high-temperature superconductors. 

 

Figure 4. Representation of the stacking possibilities between graphene layers, AA (left), AB 

(right). 

In view of these results and the properties reported so far,40 it is expected that twisted 

bilayer and multilayer graphene will follow the successful path of monolayer 

graphene, with new applications where carbon materials were not sufficiently 

 
39 Y. Cao, V. Fatemi, S. Fang, K. Watanabe, T. Taniguchi, E. Kaxiras, P. Jarillo-Herrero, Nature 2018, 

556, 43. 
40 E. Y. Andrei, D. K. Efetov, P. Jarillo- Herrero, A. H. MacDonald, K. Fai Mak, T. Senthil, E. Tutuc, A. 

Yazdani, A. F. Young, Nat. Rev. Mater. 2021, 6, 201. 

A

A

A

B



Introduction 

6 

 

competitive. It is striking that a simple layer with a honeycomb pattern and the 

thickness of a carbon atom, whose existence was so often questioned, has 

revolutionized the science of materials and condensed matter, allowing the 

development of disruptive technologies already introduced in the society 20 years 

after its discovery. 

Graphene molecules: Nanographenes 

Polycyclic aromatic hydrocarbons have attracted the interest of the scientific 

community probably since Michael Faraday discovered benzene in 1825. The 

multidirectional evolution of sp2-hybridised carbon materials ranges from the 

development of simple molecules to fullerenes (discovered in 1985 by Kroto, Curl 

and Smalley), carbon nanotubes (discovered in 1991, by Iijima and Ichihashi) and 

graphene.  

The knowledge gained in organic reactions and new characterization techniques, has 

enabled the continuous evolution of carbon-based materials. It is therefore not so 

surprising that organic stepwise synthesis is one of the most powerful tools for 

producing graphene molecular fragments. However, it results interesting that the 

grater development of these nanometric-sized fragments, with honeycomb pattern, 

took place in parallel to the emergence of single-layered graphene and its derivatives.  

The smallest and most frequently investigated graphene molecule, hexa-peri-

hexabenzocoronene (HBC), was described for the first time by Halleux in 1958.41 This 

flat structure formed by 42 carbon atoms was for a long time the largest fully 

characterized polyaromatic hydrocarbon (Figure 5). However, the development of 

different methodologies based on stepwise organic synthesis has made possible the 

monodisperse preparation of polycyclic aromatic hydrocarbons with different sizes 

and shapes.42,43 For instance, in 2002, Klaus Müllen et al., pioneers in the preparation 

of molecular graphene fragments, reported one of the largest structures described so 

far (the structure is formed by 222 carbon atoms and has a diameter of 3 nm), 

demonstrating the potential of organic chemistry for obtaining large graphene 

molecules (Figure 5).44 

 
41 A. Halleux, R. H. Martin, G. S. D. King, Helv. Chim. Acta 1958, 41, 1177. 
42 L. Chen, Y. Hernandez, X. Feng, K. Müllen, Angew. Chem. Int. Ed. 2012, 51, 7640. 
43 J. Liu, X. Feng, Angew. Chem. Int. Ed. 2020, 59, 23386. 
44 C. D. Simpson, J. D. Brand, A. J. Berresheim, L. Przybilla, H. J. Räder, K. Müllen, Chem. Eur. J. 2002, 

8, 1424. 



Introduction 

7 

 

 

Figure 5. From benzene and small polyaromatic hydrocarbons to nanographenes. 

In 2012 Müllen and coworkers defined as nanographenes those graphene fragments 

ranging from 1 to 100 nm in size.42 The last decade has marked the boom of 

nanographenes, with a large number of structures reported in the literature.45 From the 

first flat molecules to increasingly sophisticated structures that have demonstrated 

surprising optoelectronic properties, as it will be described in the following chapters.  

The main reason for this still growing interest, is that nanographenes have proved to 

be a suitable alternative in those applications where graphene has more limitations. 

The zero-gap semiconducting nature of graphene limits its application on 

optoelectronics. In contrast, the quantum confinement of the electrons in smaller 

molecular structures, opens the gap between the conduction band and the valence 

band, thus broadening the range of applications in sensing, electronics, or 

photovoltaics.46 

Several review publications on the synthesis and modulation of nanographenes 

properties are currently available.45,47,48,49 Therefore, as with graphene, one wonders 

what’s next. Surprisingly enough, it seems that graphene and its molecular derivatives 

are progressing along the same lines. In the same year that Jarillo-Herrero described 

the superconductivity properties of bilayer graphene (2018),39 our research group 

described the first molecular structure with two covalently connected overlapping 

layers. This marked the beginning of helical bilayer nanographenes, whose rise we are 

currently witnessing, mainly due to their remarkable chiroptical properties, as it will 

be described and discussed in the following chapters. 

 
45 Z. Liu, S. Fu, X. Liu, A. Narita, P. Samori, M. Bonn, H. I. Wang, Adv. Sci. 2022, 9, 2106055. 
46 Y. Gu, Z. Qiu, K. Müllen, J. Am. Chem. Soc. 2022, 144, 11499. 
47 A. Narita, X.-Y. Wang, X. Feng, K. Müllen, Chem. Soc. Rev. 2015, 44, 6616. 
48 S. Song, J. Su, M. Telychko, J. Li, G. Li, Y. Li, C. Su, J. Wu, J. Lu, Chem. Soc. Rev. 2021, 50, 3238. 
49 Y. Segawa, H. Ito, K. Itami, Nat. Rev. Mater. 2016, 1, 15002. 



 

 

 

 

  



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 1 

 

  



 

 

 

 

  



Chapter 1 

11 

 

1 Chapter 1 

1.1 Introduction to the Synthesis of Nanographenes 

The bottom-up approach for the synthesis of nanographenes allows the monodisperse 

preparation of graphene molecular fragments with atomic control. Considering hexa-

peri-hexabenzocoronene (HBC) the smallest nanographene, the general synthetic 

methodology, consists in the synthesis of hexaphenylbenzene (1.1) and the subsequent 

formation of multiple carbon-carbon bonds to obtain the graphitized nanographene, 

HBC (1.2), Figure 1.1. 

 

Figure1.1. General synthetic methodology of molecular nanographenes represented with the 

smallest nanographene, HBC. 

1.1.1 Key Reactions for the π-Extension 

In the first half of the 20th century, Roland Scholl and Eric Clar were pioneers to report 

the synthesis and characterization of polyaromatic hydrocarbons.50 Since then, the 

extensive development of organic chemistry reactions has provided powerful tools for 

the design, synthesis, and characterization of advanced novel aromatic carbon-based 

structures. 

Although numerous strategies for the synthesis of nanographenes can be found in the 

literature, a few key reactions can be identified. The previous stages of precursor 

synthesis require the generation of polyarene-like structures, in which the π-extension 

is increased, and the rings are placed in suitable arrangements for subsequent 

graphitization. The most widely and efficiently proven reactions for the π-extension 

are Diels-Alder cycloaddition, metal-mediated cyclotrimerization of alkynes and 

metal-catalyzed cross couplings. 

In 2000, Müllen and coworkers reported the first synthesis of hexaphenylbenzene 

derivatives by a Diels-Alder reaction between tetraphenylcyclopentadienones 1.3 as 

dienes and aromatic alkynes 1.4 as dienophiles, to achieve the synthesis of 

 
50 (a) R. Scholl, C. Seer, R. Weitzenbök, Chem. Ber. 1910, 43, 2202. (b) R. Scholl, C. Seer, Liebigs Ann. 

Chem. 1912, 394, 111. (c) R. Scholl, C. Seer, Chem. Ber. 1922, 55, 330. (d) E. Clar, D. G. Stewart, J. 

Am. Chem. Soc. 1953, 75, 2667. (e) E. Clar, W. Schmidt, Tetrahedron 1979, 35, 2673. 



Chapter 1 

12 

 

hexaarylbenzenes 1.5 with different substitution patterns.51 By following this strategy, 

the substituents can be incorporated, as shown in Scheme 1.1, through the 

functionalization of the cyclopentadienone and the acetylene. 

 

Scheme 1.1. Synthetic strategy for polyarenes by Diels-Alder cycloaddition. (i) Synthesis of 

diarylacetylene, commonly by Sonogashira coupling. (ii) Aldolic condensation yields 

cyclopentadienones (or cyclones). (iii) Diels-Alder cycloaddition to obtain polyarenes. 

The [4+2] cycloaddition entails the formation of a new benzene ring decorated with 

six functionalized aryl substituents. The reaction occurs with carbon monoxide 

extrusion resulting from a chelotropic elimination once the six-member ring is 

formed, leading to the aromatization of the central benzene ring. 

This methodology has been widely used in the synthesis of nanographenes with 

different shapes and sizes. The possibilities to vary the cyclopentadienone as well as 

the alkyne, and their substitution pattern, allows to obtain a great variety of structures. 

For instance, Wang and coworkers reported the twistacene nanographene52 1.6 

synthesized from a two-fold Diels-Alder cycloaddition between the p-phenylene-

linked cyclopentadienone dimer 1.7 and bis(4-tert-butylphenyl)acetylene (1.8) that 

yielded the polyarene 1.9 showed in Scheme 1.2. 

 
51 S. Ito, M. Wehmeier, J. D. Brand, C. Kübel, R. Epsch, J. P. Rabe, K. Müllen, Chem. Eur. J. 2000, 6, 

4327. 
52 S. Ma, J. Gu, C. Lin, Z. Luo, Y. Zhu, J. Wang, J. Am. Chem. Soc. 2020, 142, 16887. 



Chapter 1 

13 

 

 

Scheme 1.2. Desing of cyclopentadienones to perform the Diels-Alder cycloaddition. 

Following the [4+2] approach, Müllen et al. reported the synthesis of large graphene 

nanoribbon 1.10.53 Starting from the π-extended building block with dual 

functionalization 1.11, the cyclopentadienone and the terminal alkyne (Scheme 1.3), 

the Diels-Alder cycloaddition leads to the polyarene polymer 1.12.  

 
53 A. Narita, I. A. Verzhbitskiy, W. Frederickx, K. S. Mali, S. A. Jensen, M. R. Hansen, M. Bonn, S. De 

Feyter, C. Casiraghi, X. Feng, K. Müllen, ACS Nano 2014, 8, 11622. 



Chapter 1 

14 

 

 

Scheme 1.3. Polymerization by Diels-Alder cycloaddition to prepare graphene nanoribbons. 

The possibility of modifying the alkyne precursor has also been explored. For 

example, Martín et al. reported the synthesis of curved nanographene 1.13 starting 

from cyclooctatetraene with four fused thiophenes substituted with four 4-tert-

butylphenylalkynyl groups 1.14 (Scheme 1.4). The polyarene 1.15 is obtained after 

performing a fourfold Diels-Alder reaction with the corresponding 

cyclopentadienone.54  

 
54 J. Urieta-Mora, M. Krug, W. Alex, J. Perles, I. Fernández, A. Molina-Ontoria, D. M. Guldi, N. Martín, 

J. Am. Chem. Soc. 2020, 142, 4162. 



Chapter 1 

15 

 

 

Scheme 1.4. Synthesis of four-thiophene-fused cyclooctatetraene-based polyarene by Diels-

Alder, followed by graphitization to afford a curved nanographene. 

An alternative to the [4+2] cycloaddition approach is the metal-mediated 

cyclotrimerization of aromatic alkynes 1.16. This reaction has proved to be highly 

efficient when the diarylacetylenes involved are symmetrically substituted. As shown 

in Scheme 1.5, a new benzene ring is formed by joining the aryl substituents coming 

from the acetylene derivative resulting in a polyarene 1.17.  

 

Scheme 1.5. Synthesis of polyarenes by metal-mediated cyclotrimerization of alkynes. 



Chapter 1 

16 

 

Although the reaction efficiency is usually higher when the alkyne precursor is 

symmetrically substituted, Campaña and coworkers reported the large triskelion-

shaped nanographene55 1.18 in which the alkyne 1.19 is asymmetrically substituted 

with a tert-butylphenyl group and a hexabenzocoronene derivative at each side. 

However, the reaction led to the preferential formation of the 1,3,5-substituted 

regioisomer, the polyarene 1.20 (Scheme 1.6). 

 

Scheme 1.6. Synthesis of polyarene by cyclotrimerization of asymmetric alkynes followed by 

graphitization to afford a triskelion-shaped nanographene. 

The third most widely used methodology for the design of polyarenes, e.g. 1.21, 

consists in metal-catalyzed cross-couplings. This alternative approach allows 

changing features as the geometry, the substitution pattern, or the π-extension degree, 

as shown in Scheme 1.7. The variety of cross-coupling reactions available, Suzuki, 

Stille, Yamamoto, Heck... provides great versatility for the modification of the 

structures. 

 
55 C. M. Cruz, I. R. Márquez, S. Castro-Fernández, J. M. Cuerva, E. Maçôas, A. G. Campaña, Angew. 

Chem. Int. Ed. 2019, 58, 8068. 



Chapter 1 

17 

 

 

Scheme 1.7. Synthesis of polyarenes by metal-mediated cross-coupling reactions. 

Following this methodology, Itami and coworkers reported the synthesis of the highly 

curved nanographene 1.22 from different polyarene precursors.56 The introduction of 

4-tert-butylphenyl or biphenyl substituents in a corannulene moiety (1.23 and 1.24, 

respectively) by cross-coupling reactions influence the following graphitization step, 

as different bonds remained to be formed (Scheme 1.8). 

 

Scheme 1.8. Synthesis of two polyarenes through metal-mediated cross-couplings leading to 

a curved nanographene after oxidation. 

 

 
56 K. Kawasumi, Q. Zhang, Y. Segawa, L. T. Scott, K. Itami, Nat. Chem. 2013, 5, 739. 



Chapter 1 

18 

 

1.1.2 Graphitization 

The key step in the synthesis of nanographenes is the graphitization of the polyarene 

precursor. To this end, different reactions can be found in the literature. For instance, 

it can be accomplished by intramolecular catalyzed couplings (Scheme 1.9a),57 C−F 

bond activation, methodology developed by Amsharov et al. (Scheme 1.9b),58 

photochemical cyclization (Scheme 1.9c),59 or flash vacuum pyrolysis, as described 

by Scott et al.60 to achieve the formation of a highly curved π-extended corannulene 

(Scheme 1.9d). These reactions require the previous functionalization of the polyarene 

precursors, commonly with halogens. 

 

 

Scheme 1.9. Graphitization reactions starting from functionalized polyarenes. (a) 

Intramolecular metal-catalyzed cross-coupling. (b) C−F bond activation. (c) Photochemical 

cyclization. (d) Flash vacuum pyrolysis. 

Nevertheless, the most widely used reactions in the synthesis of molecular 

nanographenes are those that do not require the introduction of reactive groups for the 

subsequent graphitization. In this context, electrochemical and on-surface reactions 

are rapidly developing methodologies. Kong et al. reported an electrochemical 

cyclodehydrogenation methodology that requires catalytic equivalents of DDQ (2,3-

dichloro-5,6-dicyano-1,4-benzoquinone) (Scheme 1.10a).61 On-surface reactions 

have proven to be suitable for the graphitization of planar structures. The interaction 

 
57 X.-S. Zhang, Y.-Y. Huang, J. Zhang, W. Meng, Q. Peng, R. Kong, Z. Xiao, J. Liu, M. Huang, Y. Yi, L. 

Chen, Q. Fan, G. Lin, Z. Liu, G. Zhang, L. Jiang, D. Zhang, Angew. Chem. Int. Ed. 2020, 59, 3529. 
58 V. Akhmetov, M. Feofanov, O. Papaianina, S. Troyanov, K. Amsharov, Chem. Eur. J. 2019, 25, 11609. 
59 M. Daigle, A. Picard-Lafond, E. Soligo, J.-F. Morin, Angew. Chem. Int. Ed. 2016, 55, 2042. 
60 L. T. Scott, E. Jackson, Q. Zhang, B. D. Steinberg, M. Bancu, B. Li, J. Am. Chem. Soc. 2012, 134, 107. 
61 W.-J. Kong, L. H. Finger, J. C. A. Oliveira, L. Ackermann, Angew. Chem. Int. Ed. 2019, 58, 6342. 



Chapter 1 

19 

 

of the starting molecules with a metal surface after temperature treatment induce 

graphitization (Scheme 1.10b).62 

 

Scheme 1.10. Graphitization reactions starting from unfunctionalized polyarenes. (a) 

Electrochemical cyclodehydrogenation. (b) On-surface Au(111) graphitization. 

However, most molecular nanographenes reported in the last decade have been 

obtained by conventional organic chemistry in solution. For this purpose, the preferred 

graphitization reaction is the well-known Scholl oxidation. 

1.1.3 Scholl Cyclodehydrogenation 

The  most extended graphitization reaction for molecular nanographenes is the Scholl 

oxidation (Roland Scholl, 1910).63,64 This reaction is a cyclodehydrogenation that 

occurs by double aryl C−H activation leading to the formation of multiple C−C 

covalent bonds.65,66 The reagents to perform this oxidation are Lewis acids (commonly 

AlCl3, MoCl5 and FeCl3) or oxidants in presence of Brønsted acids (as 2,3-dichloro-

5,6-dicyano-1,4-benzoquinone, DDQ, or para-chloranil in combination with methane 

sulfonic acid or trifluoromethanesulfonic acid).  

The Scholl cyclodehydrogenation mechanism has been investigated on multiple 

occasions, both experimental and theoretically. However, it remains controversial. 

The most accepted pathways involve the formation of arenium cation or radical-cation 

intermediates, but discerning the operating mechanism is usually unpredictable. One 

of the major difficulties for the in-depth evaluation to understand the mechanism is 

 
62 B. Cirera, A. Sánchez-Grande, B. de la Torre, J. Santos, S. Edalatmanesh, E. Rodríguez-Sánchez, K. 

Lauwaet, B. Mallada-Faes, R. Zbořil, R. Miranda, O. Gröning, P. Jelínek, N. Martín, D. Écija, Nat. 

Nanotechnol. 2020, 15, 437. 
63 (a) R. Scholl, J. Mansfeld, Ber. Dtsch. Chem. Ges. 1910, 43, 1734. (b) R. Scholl, C. Seer, Justus Liebigs, 

Ann. Chem. 1912, 394, 111. 
64 R. S. Jassas, E. U. Mughal, A. Sadiq, R. I. Alsantali, M. M. Al-Rooqi, N. Naeem, Z. Moussa, S. A. 

Ahmed, RSC Adv. 2021, 11, 32158. 
65 M. Grzybowski, K. Skonieczny, H. Butenschçn, D. T. Gryko, Angew. Chem. Int. Ed. 2013, 52, 9900. 
66 M. Grzybowski, B. Sadowski, H. Butenschçn, D. T. Gryko, Angew. Chem. Int. Ed. 2020, 59, 2998. 



Chapter 1 

20 

 

that the Lewis acids commonly used are also oxidizing agents, and the alternative 

requires the combination of oxidants and protic acids. 

The arenium cation intermediates pathway67,68 is proposed to evolve as shown in 

Scheme 1.11. It starts with the protonation of aryl species, e. g. 1.25, forming the 

intermediate Int 1, an electrophilic σ-complex in case of performing the reaction with 

a Lewis acid, or a cation when using a Brønsted acid. The nucleophilic attack from 

the neighboring benzene ring leads to the formation of a new C−C bond, Int 2. The 

first proton elimination leads to the rearomatization of the first benzene ring, Int 3. 

The subsequent protons and electrons elimination regenerates the aromaticity in the 

system, giving the product 1.26. 

 

Scheme 1.11. Scholl reaction mechanism via arenium cation intermediates. 

Alternatively, the reaction may occur through the formation of radical-cation 

intermediates,69,70,71 such as Int 4 resulting from a single-electron oxidation of 1.27 

(Scheme 1.12). The neighboring nucleophilic phenyl group attacks the radical cation 

to form the new bond Int 5, the subsequent oxidation and deprotonation yields the 

corresponding arenium cation intermediate Int 6, which after deprotonation leads to 

the aromatized compound 1.28. 

 

Scheme 1.12. Scholl reaction mechanism via radical-cation intermediates. 

The difficulty in identifying the mechanism operating on a given substrate is still 

challenging and under continuous study, especially in nanographenes chemistry. The 

formation of unexpected products because of ring migrations, rearrangements, 

transpositions or alternative cyclizations remains mostly unpredictable.72,73 It seems 

to be serendipitous and dependent of multiple factors, such as the molecular structure 

of the precursor, the steric hindrance and strain, the aromaticity, the reaction 

 
67 G. Baddeley, J. Kenner, J. Chem. Soc. 1935, 303. 
68 G. Baddeley, J. Chem. Soc. 1950, 994. 
69 J. Kenner, J. Soc. Chem. Ind. 1933, 42, 470. 
70 L. Zhai, R. Shukla, S. H. Wadumethrige, W. Rathore, J. Org. Chem. 2010, 75, 4748. 
71 L. Zhai, R. Shukla, R. Rathore, Org. Lett. 2009, 11, 3474. 
72 N. Ponugoti, V. Parthasarathy, Chem. Eur. J. 2022, 28, e202103530. 
73 Y. Zhang, S. H. Pun, Q. Miao, Chem. Rev. 2022, 122, 14554. 



Chapter 1 

21 

 

conditions, etc. For example, Wu et al. demonstrated that the use of different Scholl 

reaction conditions on the same polyarene 1.29 can proceed through different 

mechanisms and yield different products. As concluded by DFT calculations, radical 

cation intermediates lead to nanographene 1.30 bearing hexagons¸ and cation 

intermediates lead to nanographene 1.31 bearing two octagonal rings (Scheme 1.13).74 

 

Scheme 1.13. Scholl reaction conditions control the mechanism and the consequent 

nanographene structure. 

1.1.3.1 Rearrangements in the Scholl Reaction 

Aryl migrations and isomerization reactions during the Scholl oxidation have been 

widely observed and have proven to be involved in most of the rearrangements 

occurring in presence of the typical oxidants and acids. 

Sigura and coworkers reported an aryl migration from 1.32 that occurs through the 

formation of radical cation intermediates and involves an attack by MeOH as 

nucleophile, evolving to the ketone containing product 1.33, without observing the 

formation of the expected tetrabenzocoronene structure 1.34 or alternative 

graphitization (Scheme 1.14).75 

 
74 Y. Zou, Y. Han, S. Wu, X. Hou, C. H. E. Chow, J. Wu, Angew. Chem., Int. Ed. 2021, 60, 17654. 
75 F. Ko, K. Hirabayashi, T. Shimizu, K.-I. Sugiura, Tetrahedron 2018, 59, 4251. 



Chapter 1 

22 

 

 

Scheme 1.14. Aryl migration under Scholl reaction conditions involving the incorporation of 

a carbonyl group from methanol. 

However, rearrangements can lead to ring cyclizations. The formation of five-

membered rings together with a rearrangement was reported by Müllen and coworkers 

(Scheme 1.15). Performing the Scholl reaction over 1.35 to obtain the six-membered 

π-extended molecule 1.36 yielded the unexpected formation of two five-membered 

rings and the double 1,2-aryl shift of the tert-butylphenyl units to the neighboring 

positions to obtain 1.37.76  

 

Scheme 1.15. Five-member ring cyclization and aryl rearrangement under Scholl reaction 

conditions. 

Taking advantage of the rearrangement, the same authors designed a suitably 

chlorinated analog 1.38, as shown in Scheme 1.16, to obtain the known rearranged 

structure 1.39 and perform a palladium-catalyzed cyclization providing the π-

extended buckybowl structure 1.40.77 

 
76 J. Liu, A. Narita, S. Osella, W. Zhang, D. Schollmeyer, D. Beljonne, X. Feng, K. Müllen, J. Am. Chem. 

Soc. 2016, 138, 2602. 
77 J. Liu, S. Osella, J. Ma, R. Berger, D. Beljonne, D. Schollmeyer, X. Feng, K. Müllen, J. Am. Chem. 

Soc. 2016, 138, 8364. 



Chapter 1 

23 

 

 

Scheme 1.16. Taking advantage of the rearrangement and cyclization to introduce five-

membered rings leading to a buckybowl structure. 

Rearrangements and cyclization can also provide six-membered rings. Müllen et al. 

evaluated two different polyphenylene isomeric precursors 1.41 and 1.42 (Scheme 

1.17) under oxidation conditions. While 1.41 provided the expected planar 

nanographene 1.43, the polyphenylene 1.42 entailed a 1,2-shift of the central meta-

substituted benzene ring to provide also nanographene 1.43 quantitatively.78 

 

Scheme 1.17. Expected graphitization of polyphenylene 1.41, and rearrangement of 1.42 to 

provide the same nanographene 1.43. 

Furthermore, Müllen and coworkers reported the cyclodehydrogenation of cyclo-

para-phenylene 1.44 yielding to the graphitized cyclo-para-phenylene 1.45 involving 

a 1,2-phenyl shift induced by the strain in the macrocycle (Scheme 1.18).79 

 
78 M. Müller, V. S. Iyer, C. Kübel, V. Enkelmann, K. Müllen, Angew. Chem. Int. Ed. 1997, 36, 1607. 
79 F. E. Golling, M. Quernheim, M. Wagner, T. Nishiuchi, K. Müllen, Angew. Chem. Int. Ed. 2014, 53, 

1525. 



Chapter 1 

24 

 

 

Scheme 1.18. Strain-induced 1,2-phenyl shift. 

Moreover, the electronic nature of the substitution of the polyarene precursor has an 

influence on unexpected reactions during the Scholl oxidation. Alkoxy-substituted 

hexaarylbenzene 1.46, reported by Müllen et al., under Scholl reaction conditions 

leads to the formation of two products, as shown in Scheme 1.19. The spirocompound 

1.47 in which the graphitization is interrupted, and the graphitized 

hexabenzocoronene 1.48 whose formation results from a rearrangement. The methoxy 

substituents starting in pseudo-para positions rearrange to pseudo-meta positions in 

the graphitized structure 1.48.80 

 

Scheme 1.19. The rearrangement induced by the electronic nature of the susbtituents in the 

polyarene 1.46 yields the spirocompound 1.47 and the unexpected hexabenzocoronene 

derivative 1.48. 

 
80 X. Dou, X. Yang, G. J. Bodwell, M. Wagner, V. Enkelmann, K. Müllen, Org. Lett. 2007, 9, 2485. 



Chapter 1 

25 

 

In addition, rearrangements can lead to ring contractions. The 

tetrabenzocyclooctatetraene core of polyphenylene 1.49, shown in Scheme 1.20, 

under Lewis acid conditions yielded the planar hexagon-constituted nanographene 

1.50.81  

 

Scheme 1.20. Ring-contraction rearrangement leading to planar six-membered rings 

nanographene. 

Rearrangement followed by seven-membered rings formation was reported by Durola 

and coworkers (Scheme 1.21). The sterically hindered triarylterphenyl precursor 1.51 

in presence of FeCl3 led to the seven-membered containing compound 1.52 resulting 

from a 1,2-aryl shift.82 

 

Scheme 1.21. Cyclization followed by rearrangement and seven-membered ring formation. 

A similar observation was reported by Narita et al. (Scheme 1.22). The treatment of 

the polyarene 1.53 with DDQ/TfOH yielded the unexpected negatively curved 

nanographene 1.54 containing two seven-membered rings due to a 1,2-naphthyl-

phenyl migration. Theoretical calculations supported the evolution through the 

rearrangement pathway over the formation of the helicene containing graphitized 

nanographene 1.55.83 

 
81 M. Müller, V. S. Iyer, C. Kübel, V. Enkelmann, K. Müllen, Angew. Chem. Int. Ed. 1997, 36, 1607. 
82 A. Pradhan, P. Dechambenoit, H. Bock, F. Durola, J. Org. Chem. 2013, 78, 2266. 
83 Z. Qiu, S. Asako, Y. Hu, C.-W. Ju, T. Liu, L. Rondin, D. Schollmeyer, J.-S. Lauret, K. Müllen, A. 

Narita, J. Am. Chem. Soc. 2020, 142, 14814. 



Chapter 1 

26 

 

 

Scheme 1.22. Rearrangement by 1,2-naphtyl-phenyl migration and subsequent seven-

membered rings cyclization. 

A few examples of pentagon-heptagon containing nanographenes resulting from 

rearrangements have been recently reported.84 Feng and coworkers reported the 

formation of two azulene embedded nanographenes, 1.56 and 1.57 (Scheme 1.23). 

The formation of the unexpected nanographenes results from the bond rotation in the 

polyarene precursor 1.58 and a 1,2-aryl migration with subsequent HI elimination.85 

 

Scheme 1.23. 1,2-Aryl migration rearrangement and subsequent HI elimination leading to two 

azulene-containing nanographenes from different rotamers of the polyarene precursor. 

The simultaneous ring expansion and contraction leading to azulene-embedded 

nanographenes has also been reported by Chi et al. Naphthalene-containing polyarene 

1.59 in presence of DDQ/TfOH leads to the formation of the two fused embedded 

azulenes nanographene 1.60 (Scheme 1.24).86 

 
84 J. Ma, Y. Fu, E. Dmitrieva, F. Liu, H. Komber, F. Hennersdorf, A. A. Popov, J. J. Weigand, J. Liu, X. 

Feng, Angew. Chem. Int. Ed. 2020, 59, 5637. 
85 J. Ma, Y. Fu, E. Dmitrieva, F. Liu, H. Komber, F. Hennersdorf, A. A. Popov, J. J. Weigand, J. Liu, X. 

Feng, Angew. Chem. Int. Ed. 2020, 132, 5686. 
86 Y. Han, Z. Xue, G. Li, Y. Gu, Y. Ni, S. Dong, C. Chi, Angew. Chem. Int. Ed. 2020, 59, 9026. 



Chapter 1 

27 

 

 

Scheme 1.24. Two embedded fused azulenes nanographene. 

1.1.3.2 Functionalization During the Scholl Reaction 

In addition to unexpected rearrangements and cyclizations, functionalization of the 

products can occur during the Scholl reaction. As observed in our research group 

(Scheme 1.25), modifying the reaction conditions could entail modifications in the 

resulting compound. In 2018, the selective formation of corannulene-containing 

nanographenes 1.61, 1.62 and 1.63 was described.87 When the graphitization reaction 

is carried out in the presence of FeCl3 under mild conditions (–50 ºC), the [6]helicene 

embedded nanographene 1.61 is obtained. However, if the reaction is performed at 

higher temperature (80 ºC), another ring is formed, giving the chlorinated 

nanographene 1.62 with a seven-membered ring. Additionally, carrying out the 

reaction with DDQ and triflic acid yields nanographene 1.63, which also contains the 

seven-membered ring. 

 
87 J. M. Fernández-García, P. J. Evans, S. Medina Rivero, I. Fernández, D. García-Fresnadillo, J. Perles, 

J. Casado, N. Martín, J. Am. Chem. Soc. 2018, 140, 17188. 



Chapter 1 

28 

 

 

 Scheme 1.25. Selective synthesis of helical, curved chlorinated and curved nanographenes 

under different Scholl reaction conditions. 

The possibility of chlorinating electron-rich aromatic compounds in presence of FeCl3 

was firstly demonstrated by Niementowski in 1919.88 When performing the Scholl 

reaction, this chlorination is usually undesired and often unexpected, as it may occur 

in all-carbon and hydrogen structures. However, different studies have proven the 

efficiency of the reaction when it occurs simultaneously and selectively on the 

substrate.89 For instance, Stuparu and coworkers have recently reported the 

mechanochemical synthesis of corannulene-containing nanographene 1.64 (Scheme 

1.26). In a solvent-free assembly of polyarene 1.65 with FeCl3, the selective 

chlorination and graphitization occurs with very high yield, 90%.90  

 
88 L. T. Bratz and S. von Niementowski, Ber. Dtsch. Chem. Ges. (A and B Ser.), 1919, 52, 189. 
89 D. M. Baier, S. Gratz, B. Farhadi Jahromi, S. Hellmann, K. Bergheim, W. Pickhardt, R. Schmid, L. 

Borchardt, RSC Adv. 2021, 11, 38026. 
90 J. Stanojkovic, R. William, Z. Zhang, I. Fernández, J. Zhou, R. D. Webster, M. C. Stuparu. Nat. 

Commun. 2023, 14, 803. 



Chapter 1 

29 

 

 

Scheme 1.26. Selective chlorination during mechanochemical Scholl reaction with FeCl3. 

Some authors suggest the use of MoCl5 to perform the Scholl reaction avoiding 

chlorination. However, Itami et al. reported the selective tetrachlorination during the 

graphitization of polyarene 1.66 to give nanographene 1.67 in presence of MoCl5 

(Scheme 1.27).91 

 

Scheme 1.27. Selective chlorination during the Scholl reaction with MoCl5. 

Furthermore, Mastalerz and coworkers reported a double regioselective 

triflyoxylation and cyclization of pentacene-based structure 1.68 while performing the 

Scholl reaction with DDQ and triflic acid to obtain structure 1.69 (Scheme 1.28).92 

Performing the reaction in presence of FeCl3 under mild conditions, lead to the non-

functionalized compound 1.70. 

 

Scheme 1.28. Selective triflyoxylation during Scholl reaction with DDQ and triflic acid. 

Chlorination is not observed when the reaction is performed with FeCl3. 

 
91 T. Fujikawa, N. Mitoma, A. Wakamiya, A. Saeki, Y. Segawa, K. Itami, Org. Biomol. Chem. 2017, 15, 

4697. 
92 X. Yang, M. Hoffmann, F. Rominger, T. Kirschbaum, A. Dreuw, M. Mastalerz, Angew. Chem. Int. Ed. 

2019, 58, 10650. 



Chapter 1 

30 

 

However, the modification of the starting pentacene-based compound functionalized 

with naphthyl groups 1.71 shows a significant impact on the products obtained.93 

When the oxidation reaction is assembled with FeCl3 at reflux of 

dichloromethane/nitromethane (Scheme 1.29), the selectively chlorinated derivative 

1.72 is obtained. In addition, if the reaction is performed with more equivalents of 

DDQ (8 or 10 equiv) and triflic acid, three different products are obtained. In all cases 

two seven-membered rings are formed. Nevertheless, the products can be 

symmetrically substituted with two triflates 1.73, asymmetrically substituted with a 

triflate and a dichlorovinylidene group 1.74 or symmetrically substituted with two 

dichlorovinylidene groups 1.75. 

 

Scheme 1.29. Selective chlorination in presence of FeCl3. Functionalization with triflate and 

dichlorovinylene depending on the reaction conditions using DDQ and triflic acid. 

To conclude, predicting the structure of a nanographene after the Scholl oxidation can 

be challenging regarding the possible rearrangements and functionalization that may 

take place during the reaction. The possibilities to modulate the starting structure, the 

reagents and reaction conditions provide several alternatives to control or conduct the 

reaction towards different products. Furthermore, the knowledge acquired during the 

last decade in the synthesis of molecular nanographenes is paving the way for 

understanding the Scholl cyclodehydrogenation.  

 
93 X. Yang, F. Rominger, M. Mastalerz, Angew. Chem. Int. Ed. 2019, 58, 17577. 



Chapter 1 

31 

 

1.2 Objectives 

The initial objective of this chapter was the synthesis of a helically arranged 

nanographene based on two graphitized units covalently connected through a 9,10-

substituted anthracene core. However, the methodology used, based on the Diels-

Alder reaction to obtain the polyarene, and subsequent Scholl reaction for 

graphitization, led to the unexpected formation of spironanographenes. Once the 

formation of the spirocycles was understood and in pursuit of the initial objective, the 

starting polyarene was modified by substituting the anthracene core with eight 

fluorine atoms. The electronic effects of these substituents controlled the reaction and 

the desired helically arranged nanographene was formed. 

 

Once the synthesis and characterization were performed, the determination of the 

optoelectronic properties was carried out by means of absorption, emission, and 

electrochemical measurements. 



 

32 

 



Chapter 1 

33 

 

1.3 Results and Discussion 

1.3.1 Unexpected Synthesis of Spironanographenes 

The initial hypothesis of this work was the synthesis of nanographene 1 consisting of 

three subunits, two dibenzo[fg,ij]phenanthro-[9,10,1,2,3-pqrst]pentaphene (DBPP) 

connected by a 9,10-substituted anthracene. The synthetic approach (Scheme 1.30) 

starts with a double Sonogashira cross-coupling reaction between 9,10-

dibromoanthracene (2) and two equivalents of 4-(tert-butyl)phenylacetylene (3), 

leading to 9,10-bis[(4-(tert-butyl)phenyl)ethynyl]anthracene (4). Subsequently, 

dialkyne 4 undergoes a two-fold Diels-Alder cycloaddition reaction with two 

equivalents of cyclopentadienone 5 as the diene, affording polyarene 6a after a CO 

extrusion. The final step, the graphitization of 6a, was expected to afford the helically 

arranged nanographene 1. However, the Scholl cyclodehydrogenation led to the 

formation of two spirocycles connecting the polyarene units to the central anthracene 

core. The fine control over the Scholl reaction conditions yielded selectively to 

spirocompounds 7 and 8, and spironanographenes 9 and 10. Modifications in the 

oxidant, the temperature, and the reaction time allowed to control the number of bonds 

formed and, therefore, the graphitization degree of the final compound. 



Chapter 1 

34 

 

 

Scheme 1.30. Synthetic scheme for the synthesis of polyphenylene 6a and further Scholl 

reaction leading to spirocompounds 7 and 8 (3 new C−C bonds), and spironanographenes 9 (7 

new C−C bonds, dashed lines in compound indicates that one of these bonds is not formed) 

and 10 (8 new C−C bonds). 

To the best of our knowledge, very few examples of spironanographenes can be found 

in the literature.94,95 Frequently, the formation of spirocycles during the Scholl reaction 

 
94 S. Liu, D. Xia, M. Baumgarten, ChemPlusChem 2021, 86, 36. 
95 X. Zhang, Z. Xu, W. Si, K. Oniwa, M. Bao, Y. Yamamoto, T. Jin, Nat. Commun. 2017, 8, 15073. 



Chapter 1 

35 

 

results from rearrangements or the formation of stable carbocations and entails the 

interruption of the graphitization process.80,96 However, the graphitization process of 

the polyarene 6a is not compromised by the formation of the spirocycles with the 

central anthracene. 

The use of FeCl3 as oxidant at 85 ºC for 4 hours afforded an isomeric mixture of 

spirocompounds syn 7 and anti 7. During the evaluation of the reaction under these 

relatively harsh conditions, complex mixtures of chlorinated compounds were 

observed by mass spectrometry. This undesired reactivity was prevented by adding a 

silver salt (AgPF6) that precipitates the chlorides generated during the reaction as 

silver chloride.  

Spirocompounds 7 were characterized by the common techniques, NMR, FT-IR and 

mass spectrometry. MALDI-ToF experiments showed an exact mass of 1649.0632, 

which indicated the loss of two hydrogen atoms compared to polyarene 6a (HRMS 

found, 1651.0783). The most relevant NMR information was revealed by 13C-NMR, 

an apparently unshielded aliphatic signal at 63.8 ppm corresponding to a quaternary 

carbon (Appendix 5, spectra). Considering the number of signals, the obtained 

structure might be symmetric, as only signals corresponding to the half of the 

molecule were observed. The exact determination of the structure was complex by 

NMR experiments; therefore, it was necessary to resort to single-crystal X-ray 

diffraction (Appendix 1, crystallographic data). The crystals obtained showed different 

crystallization shapes allowing their manual separation and independent diffraction. 

Needle-shaped crystals corresponded to a polyarene-like structure in which two five-

membered rings formed spirocycles with the central 9,10-anthracene symmetrically, 

forcing the orthogonal arrangement of the five-membered rings with the central 

anthracene. As shown in Figure 1.2a, both 4-tert-butylphenyl rings (in blue) forming 

the spirocycles (in orange) are on the same face of the anthracene, syn 7. Moreover, 

ribbon-shaped crystals were resolved and revealed an anti 7 isomer (Figure 1.2b) in 

which the 4-tert-butylphenyl rings forming the spirocycles are on opposite faces of 

the central anthracene. 

 
96 J. L. Ormsby, T. D. Black, C. L. Hilton, Bharat, B. T. King, Tetrahedron 2008, 64, 11370. 



Chapter 1 

36 

 

 

Figure 1.2. Molecular structure of the compounds (a) syn 7 (b) anti 7 determined by single 

crystal X-ray diffraction, hydrogen atoms have been omitted for clarity. 

The use of FeCl3 as oxidant was also evaluated at low temperatures. At –30 ºC for 30 

minutes, the reaction yielded a partially graphitized isomeric mixture of 

spirocompound 8. MALDI-ToF experiments showed only one peak with an exact 

mass of 1643.0344, which corresponds to the loss of eight hydrogen atoms and the 

subsequent formation of five new bonds. The new structures resulted highly 

asymmetric and the characterization by NMR was challenging (see Appendix 5). The 

structure corresponding to syn 8 was resolved by single crystal X-ray diffraction and 

showed the formation of the previously observed spirocycles and three new C−C 

bonds on one side of the polyarene, Figure 1.3. The bonds formed are those that do 

not involve the 4-tert-butylphenyl group forming the spirocycle, the formation of a 

[5]helicene with an embedded five-membered ring opens the distance between the 

graphitizable rings, thus hindering the bonding. 

 

Figure 1.3. Molecular structure of compound syn 8 solved by single crystal X-ray diffraction, 

hydrogen atoms have been omitted for clarity. 

Assembling the reaction with DDQ as oxidant and triflic acid at –60 ºC for 40 minutes, 

yielded a new apparently graphitized compound 9. Mass spectrometry showed an 

exact mass of 1634.9775, corresponding to the loss of sixteen hydrogen atoms and the 

consequent formation of nine bonds, the two expected spirocycles and seven of eight 

(a) (b)



Chapter 1 

37 

 

C−C bonds in the polyarene moieties. By analyzing the 1H-NMR spectrum in depth 

(see Appendix 5), several singlets at lower field indicated the graphitization of the 

isomers.  

Finally, the use of DDQ as oxidant was evaluated at higher temperatures. At 40 ºC for 

2 hours, the reaction was directed towards the formation of the fully graphitized 

spironanographene 10 as a single isomer. MALDI-ToF experiments confirmed the 

formation of ten bonds, (exact mass, 1632.9375) and NMR experiments showed a 

highly symmetric graphitized structure.  

1.3.2 Characterization of Spironanographene 10 

The 1D and 2D NMR experiments used for the complete characterization of the new 

spironanographene are described below. Considering the symmetry of the structure 

only one half of the molecule is shown, hydrogens have been removed for clarity. 

Signals will be associated to a coloured dot located in the structure with the goal of 

assigning the signals to the corresponding hydrogen and carbon atoms to which is 

bonded.   

The 1D 1H-NMR spectrum of spironanographene 10 shows the expected signals 

(Figure 1.4): at low field eight singlets assignable to the aromatic protons on the 

graphitized side (green dots), four multiplets corresponding to the anthracene moiety 

(blue dots), a spin system composed by a doublet (yellow dot), a doublet of doublets 

(red dot), and a long distance doublet with small 4JH–H (orange dot), corresponding to 

the ring opposite to the spirocycle in the graphitized unit, and at high field five singlets 

(purple dots) corresponding to the tert-butyl groups. 

 

5 tBu Aliphatic singlets

8 Aromatic singlets

4 Multiplets

1 Doublet

1 Doublet of doublets

1 Doublet (small 4JH-H)

(a)



Chapter 1 

38 

 

 

     

Figure 1.4. (a) Structure and the expected signals for 1H-NMR indicating the number and 

multiplicity. (b) Low field 1H-NMR signals. (c) High field 1H-NMR signals corresponding to 

nanographene 10. (d) Assignations considering the 1H-NMR spectrum. 

Considering the multiplicity, the coupling constants and the integration, the following 

protons can be assigned in the structure, Figure 1.4d. The proton at 8.23 ppm (doublet, 

orange dot) is coupled to the proton at 5.80 ppm (double doublet, red dot) with a 4JH–

H of 2.0 Hz. In turn, the proton at 5.80 ppm (double doublet, red dot) shows a coupling 

with the proton at 7.99 ppm (doublet, yellow dot) with a 3JH–H
 of 8.6 Hz. 

In Figure 1.5 the 13C and DEPT NMR spectra are shown. The large number of carbons 

present in the structure usually makes the analysis of these experiments complex. 

Thirty-six of the expected forty-two sp2 carbons are observed, as well as the ten 

expected aliphatic carbons corresponding to the tert-butyl groups (five quaternary 

carbons and five assigned to the −CH3). Additionally, the key signal for the assignation 

of spironanographene 10 is observed at 69.9 ppm (circled in light green). This 

unshielded aliphatic signal corresponds to the quaternary sp3 spiranic carbon. 

1H NMR (500 MHz, CDCl3)

J=8.6 Hz

J=2.0 Hz
J=2.0 Hz

J=8.6 Hz

(b)

(c)

5.80

8.23

7.99

(d)



Chapter 1 

39 

 

 

 

Figure 1.5 13C and DEPT NMR spectra corresponding to spironanographene 10. Assignation 

of the spiranic carbon. 

By means of the HMQC (Heteronuclear Multiple Quantum Correlation) experiment, 

shown in Figure 1.6, the carbons interacting by a 1JC–H coupling constant with 

hydrogens could be assigned. At this point only the carbons interacting with the 

previously assigned hydrogens are indicated and the others will be added later as the 

structure is resolved. Therefore, the following carbons are assigned considering the 

crossings: 8.23 ppm /118.3 ppm (orange dot), 7.99 ppm / 131.1 ppm (yellow dot), 5.80 

ppm /122.8 (red dot). 

5.80

8.23

7.99

69.9



Chapter 1 

40 

 

 

 

Figure 1.6 HMQC 13C-1H NMR experiment corresponding to spironanographene 10. 

Assignation of carbons directly bonded to hydrogens.  

The HMBC (Heteronuclear Multiple Bond Correlation) experiment shows some 

relevant crossings 13C–1H at 3JC–H. The crossings between the spiranic carbon at 69.9 

ppm and the following aromatic hydrogens are key to determine the structure, Figure 

1.7. The singlet at 7.78 ppm interacting at 3JC–H with the spiranic carbon corresponds 

to the hydrogen in the phenyl ring involved in the spirocycle (water blue dot, the 

carbon can also be assigned considering the HMQC in Figure 1.6, 7.78-122.1), the 

multiplet at 7.00 ppm (light-blue dot) corresponds to one of the hydrogens at three 

bonds distance from the spiranic carbon in the anthracene, and the multiplet at 6.66 

ppm (light-blue dot) corresponds to the other hydrogen at three-bonds distance in the 

anthracene from the spiranic carbon.  

5.80

122.8

8.23

118.3

7.99

131.1
69.9



Chapter 1 

41 

 

 

 

Figure 1.7 HMBC 13C-1H NMR experiment corresponding to spironanographene 10. 

Assignation of hydrogens interacting at three bonds distance (3JC–H) with the spiranic carbon.  

The crossings observed in HMBC between the quaternary aliphatic carbons, and the 

aromatic hydrogens allow further assignation of the tert-butyl groups on each phenyl 

ring and one more aromatic hydrogen, as well as the confirmation of the ones located 

so far, Figure 1.8. The aromatic hydrogens at 8.23 (orange dot) and 5.80 (red dot) ppm 

show interaction with the quaternary carbon at 34.0 ppm (orange cross). The 

hydrogens at 8.65 (light green dot) and 7.78 (water blue dot) ppm interact with the 

quaternary carbon at 36.3 ppm (blue cross). 

5.80

122.8

8.23

118.3

7.99

131.1
69.9

7.00

6.66

7.78

122.1



Chapter 1 

42 

 

 

 

Figure 1.8 HMBC 13C-1H NMR experiment corresponding to spironanographene 10. 

Assignation of aliphatic carbons interacting at three bonds distance (3JC–H) with hydrogens.  

The assignation is complemented by homonuclear scalar coupling experiment 1H-1H 

COSY (COrrelated SpectroscopY) that shows the interaction between coupled 

protons, given the rigidity of the structure the interaction between protons at 4JH–H are 

clearly observed, Figure 1.9. The spin system formed between the protons at 8.23, 

5.80 and 7.99 ppm is confirmed, as well as the system formed by the protons at 7.78 

and 8.65 ppm (COSY interaction highlighted in blue). Furthermore, it is observed a 

new coupling for further assignation between the anthracene protons at 7.00 and 6.66 

ppm with the multiplet at 6.61 ppm (dark blue dot, carbon assigned considering the 

previously showed HMQC in Figure 1.6). One more interaction between the protons 

at 9.23 and 8.82 ppm is observed but not yet assignable. 

5.80

122.8

8.23

118.3

7.99

131.1
69.9

7.00

6.66

7.78

122.1

34.03

36.3
8.65



Chapter 1 

43 

 

 

 

Figure 1.9 1H−1H COSY NMR experiment corresponding to spironanographene 10. 

Assignation of aromatic hydrogens showing scalar coupling. 

In these rigid systems in which the protons are located at the periphery of the structure, 

dipole (through space) couplings are usually observed. Therefore, NOESY (Nuclear 

Overhauser Effect Spectroscopy) experiments were performed, Figure 1.10. 

Analyzing the interactions between the aromatic protons, those sharing the bay-region 

of the graphitized area are close enough to show interaction (indicated with yellow 

arrows). Thus, the proton at 8.65 ppm can be assigned by the interaction with the 

proton at 9.07 ppm. Same interaction occurred between protons at 8.82 and 8.23 ppm, 

once located the proton at 8.82 ppm, the one at 9.23 ppm is confirmed by the 

previously observed COSY interaction (Figure 1.9). 

5.80

122.8

8.23

118.3

7.99

131.1
69.91

7.00

6.66

7.78

122.1

34.0

36.3
8.65

6.61

128.2

6.61

128.2

9.23

8.82



Chapter 1 

44 

 

 

 

Figure 1.10 NOESY NMR experiment corresponding to spironanographene 10. Assignation 

of aromatic hydrogens showing dipolar coupling in the bay regions of the graphitized area. 

In addition to interactions between aromatic protons, the NOESY experiment also 

shows interactions between protons in the tert-butyl groups (highlighted in pink) and 

the aromatic protons of the same ring, as shown in Figure 1.11. The interactions 

between the protons at 9.23 and 8.82 ppm with the aliphatic singlet at 1.77 ppm locates 

the tert-butyl in the ring. The same interactions are observed between the protons at 

8.65 and 7.78 ppm with the singlet at 1.50 ppm, and between the protons at 8.23 and 

5.80 ppm with the aliphatic signal at 0.72 ppm.  

5.80

122.8

8.23

118.3

7.99

131.1
69.91

7.00

6.66

7.78

122.1

34.0

36.38.65

6.61

128.2

6.61

128.2

9.23

8.82

9.07

NOESY

NOESY



Chapter 1 

45 

 

 

 

Figure 1.11 NOESY NMR experiment corresponding to spironanographene 10. Assignation 

of tert-butyl groups showing dipolar coupling with the aromatic hydrogens in the same ring. 

So far, only interactions between atoms in the same graphitized unit of the structure 

have been described. This allows the confirmation of the structure; however, it 

remains to identify whether the syn-isomer or the anti-isomer has been obtained.  

The key in the identification of the isomer is observed in the dipolar interaction 

between the aromatic proton at 8.82 ppm and the tert-butyl group at 0.72 ppm, as 

reflected by the corresponding crossover in the NOESY spectrum, Figure 1.11. The 

dipolar coupling between the tert-butyl (highlighted in pink) and the aromatic 

hydrogen (highlighter in green) can only result from the interaction between the two 

graphitized units. Considering the disposition of both possible syn/anti isomers and 

the location of the protons (Figure 1.12), the through-space coupling can only occur 

5.80

122.8

8.23

118.3

7.99

131.1
69.91

7.00

6.66

122.1

7.78

34.0

36.38.65

6.61

128.2

6.61

128.2

9.23

8.82

9.07

NOESY0.72
1.77

1.50



Chapter 1 

46 

 

in syn isomer. Thus, the structure obtained from the Scholl reaction is the 

spironanographene syn 10. 

 

Figure 1.12 Location of the through-space coupled protons (highlighted in green and pink) in 

the corresponding syn and anti-isomers of spironanographene 10. 

In addition to the complete characterization of spironanographene syn 10 by NMR, it 

was possible to resolve the structure by single-crystal X-ray diffraction. As shown in 

Figure 1.13, it is confirmed the formation of the syn isomer, in which the graphitized 

units are arranged orthogonally with respect to the central anthracene. Due to steric 

hindrance between the two units a helical organization is formed across the spiranic 

rings. 

 

Figure 1.13 Molecular structure of the compounds syn 10 resolved by single crystal X-ray 

diffraction, hydrogen atoms have been omitted for clarity. 



Chapter 1 

47 

 

1.3.3 Mechanism of the Scholl reaction 

To further understand the unexpected formation of spironanographene syn 10 against 

the formation of compound 1, DFT calculations at the dispersion-corrected 

PCM(CH2Cl2)-B3LYP-D3/def2-SVP level were carried out. 

 

Figure 1.14 Computed reaction profile for the Scholl and spiro-cyclization reactions involving 

anthracene derivative 6aM as computational model. Free energy values (ΔG, 298 K) are given 

in kcal/mol. Negative numbers in blue indicate the computed NICS(1)zz values (in ppm). All 

data have been computed at the PCM(CH2Cl2)-B3LYP-D3/def2-SVP level.  

In Figure 1.14 is represented the computed reaction profile considering the formation 

of cation intermediates, the formation of radical-cation intermediates leads to the same 

conclusions (see Appendix 1, theoretical calculations), according to the computed 

barrier and reaction energies, it can be concluded that the arenium cation pathway is 

favored over the radical cation mechanism. Starting from the model polyarene 6aM, 

two possible carbocations can be formed under Scholl reaction conditions (FeCl3 or 

DDQ/TfOH). The expected protonation at one of the aryl groups in the periphery of 

the polyarene would provide the intermediate INT1’. However, the formation of the 



Chapter 1 

48 

 

intermediate INT1 if the protonation occurs directly at the anthracene core is strongly 

preferred (ΔΔG= 13.0 kcal/mol) over the expected Scholl intermediate INT1’. 

Additionally, the subsequent Scholl-like cyclization from INT1’, via transition state 

TS1’, is severely hampered in comparison to the alternative cyclization of INT1 

toward the spirocycle of INT2 (both kinetically ΔΔG≠= 14.6 kcal/mol and 

thermodynamically ΔΔGR= 19.2 kcal/mol). Therefore, leaving evidence of the 

preferred reaction pathway leading to spirocycles over the expected Scholl reaction. 

Which is consistent with the formation of partially graphitized spirocompounds 7, 8 

and 9 and the totally graphitized spironanographene 10. 

The reasons for the enhanced stability of the initial intermediate INT1 versus the 

graphitization intermediate INT1' is strongly related to the aromaticity of the involved 

species. Nuclear Independent Chemical Shift (NICS) calculations indicate that the 

aromaticity of the peripheral aryl group in the initial model 6aM (NICS(1)zz= –31.3 

ppm) is dramatically reduced in the protonated intermediate INT1’ (NICS(1)zz= –13.4 

ppm). Whereas, the aromaticity of the lateral ring of the anthracene core (NICS(1)zz= 

–22.4 ppm) increases after the formation of a trityl cation (in orange) in the central 

ring (NICS(1)zz= –26.9 ppm). The formation of a new Clar-sextet in the system 

enhances the thermodynamic stability, being the driving force of the transformation. 

Therefore, the highly stable trityl cation in INT1, LUMO mainly located in the carbon 

bearing the positive charge, evolves to INT2 after a SEAr reaction with one of the 

closest peripheral rings in the polyarene. 

Seeking a structure similar to the target nanographene 1, we considered the possibility 

of decorating the central anthracene with electron withdrawing atoms. NICS(1)zz 

calculations indicated a higher aromaticity (–24.9 ppm) for the hypothetical 

octafluorinated anthracene derivative 6bM than for the cationic specie INT1b (–20.7 

ppm). Thus, the evolution from 6bM to INT1b involves an aromaticity loss 

(ΔNICS(1)zz = –4.2 ppm), against the aromaticity gain previously observed for 6aM, 

which may prevent the presence of the spirocyclization pathway. 

1.3.4 Electronic Effects Controlling the Scholl Reaction  

In section 1.3.1 the unexpected obtaining of spironanographenes with different 

degrees of graphitization has been described. The mechanistic theoretical calculation 

showed the formation of very stable trityl cation implying an aromaticity gain, which 

makes polyarene 6a evolve towards the formation of spirocycles. However, it might 

be expected that the formation of the trityl carbocation in the anthracene core could 

be avoided by introducing electron-withdrawing atoms, therefore leading to a 

derivative of the goal nanographene 1.  

Motivated by the theoretical evidence, the synthesis of polyarene 6b, in which the 

pentaarylbenzene units are connected by an octafluorinated anthracene, was designed. 

As shown in Scheme 1.31, the synthesis starts with a double Sonogashira coupling 

between 9,10-dichloro-1,2,3,4,5,6,7,8-octafluoroanthracene (11) and two equivalents 



Chapter 1 

49 

 

of 4-(tert-butyl)phenylacetylene (3), leading to 9,10-bis[(4-(tert-butyl)phenyl) 

ethynyl]-1,2,3,4,5,6,7,8-octafluoroanthracene (12). The obtained dialkyne 12 

undergoes a Diels-Alder cycloaddition followed by CO extrusion with 

cyclopentadienone 5, affording the polyarene 6b. The final Scholl oxidation of the 

fluorinated polyarene 6b using DDQ as oxidant in presence of triflic acid yields the 

expected nanographene 13.  

In agreement with the theoretical calculations, the electron-withdrawing effects of the 

fluorine atoms decorating the anthracene core control the Scholl reaction by 

preventing the formation of spirocycles. Thus, yielding nanographene 13, in which 

the graphitized units and the fluorinated anthracene are helically arranged.  

 

Scheme 1.31. Synthetic scheme for the preparation of polyphenylene 6b and further Scholl 

reaction leading to helically arranged nanographene 13. 

 



Chapter 1 

50 

 

Structure 13 was fully characterized by NMR (1H, 13C and 19F), FT-IR and high-

resolution mass spectrometry. As shown in Figure 1.15, the great symmetry of the 

structure, three C2 axes, is reflected in the NMR spectra. The spectra show one quarter 

of the molecule; particularly the signals in 1H-NMR are one singlet at 9.22 ppm (red 

dot), four doublets with 4JH-H= 1.7 Hz at 9.17, 8.99 and 8.70 ppm (orange dots), a 

doublet at 7.55 ppm with a 3JH-H= 8.9 Hz (blue dot), a doublet of doublets at 6.99 ppm 

(3JH-H= 8.9 Hz and 4JH-H= 1.7 Hz, green dot) and three aliphatic singlets corresponding 

to the tert-butyl groups at 1.83, 1.78 and 1.20 ppm, with relative intensities 1:2:2. 

Additionally, the 19F-NMR spectra also reveal the symmetry, only two doublets (3JF-

F= 14.4 Hz) are observed. The structure was modelled and showed the expected 

helically arrangement of the moieties, as shown in Figure 1.15. 

 

Figure 1.15. Modelization of helically arranged nanographene 13 and its 1H NMR (500 MHz, 

CDCl3) and 19F NMR (471 MHz, CDCl3) spectra. 

1.3.5 Electrochemical and Photophysical Properties 

The electrochemical properties of spironanographene syn 10 and helically arranged 

nanographene 13 were evaluated by cyclic voltammetry (data summarized in Table 

1.1). The measurements were performed in a 1 M solution of tetrabutylammonium 

hexafluorophosphate as supporting electrolyte in toluene/acetonitrile 1:1, using 

Ag/AgNO3 as reference electrode at room temperature.  



Chapter 1 

51 

 

In Figure 1.16 are represented the voltamperograms corresponding to 

spironanographene syn 10 and hexa-tert-butyl-hexa-peri-hexabenzocoronene (tBu-

HBC) vs Fc/Fc+. As observed, spironanographene syn 10 is a poorer electron acceptor 

than tBu-HBC considering the first quasireversible reduction potentials, E1
1/2red= –2.56 

and E1
1/2red= –2.27 V, respectively. Moreover, considering the first oxidation 

potentials, E1
1/2ox= 0.85 V for syn 10 and E1

1/2ox= 0.67 V for tBu-HBC, it can be also 

concluded that the spironanographene is a weaker electron donor than tBu-HBC.  

 

 

Figure 1.16. Cyclic voltammograms corresponding to spironanographene syn 10 (top) and 

hexa-tert-butyl-hexa-peri-hexabenzocoronene (tBu-HBC, bottom) vs Fc/Fc+ in a 1 M solution 

of tetrabutylammonium hexafluorophosphate in toluene/acetonitrile 1:1. 

The higher electronic band gap of the spironanographene (syn 10 EGAP= 3.13 eV vs 
tBu-HBC 10 EGAP= 2.65 eV) can be explained in terms of the π-extension differences. 

The formation of the spiranic rings entails the disruption of the conjugation, whereas 

in HBC the six rings attached to the central benzene are graphitized and therefore 

conjugated, in spironanographene 10 the conjugation occurs only between five of the 

rings attached to the central benzene. Although the spironanographene presents two 

graphitized layers, the electronic communication is hampered by the sp3 carbon atoms 

forming the spirocycles. 



Chapter 1 

52 

 

The electrochemical properties of the fluorinated helically arranged nanographene 13 

were also evaluated by cyclic voltammetry. As shown in Figure 1.17, the electron 

acceptor character is stronger than that of tBu-HBC, the first quasireversible band 

appears at E1
1/2red= –1.69 V. This significant shift to less negative values respect to 

HBC (E1
1/2red= –2.27 V), is due to the important electron-withdrawing character of the 

perfluorinated anthracene connecting the graphitized units. Further reduction waves 

were observed at E2
1/2red= –2.40, E3

1/2red= –2.47 and E4
1/2red= –2.69 V, indicating that 

nanographene 13 can accept more electrons under these conditions. Regarding the 

donor character, nanographene 13 presents one quasireversible oxidation wave at 

E1
1/2ox= 0.87 V, showing a slightly poorer donor character than tBu-HBC (0.67 V). 

This result could be explained by the reduced π-extension of nanographene 13 vs tBu-

HBC, and by the nearby bonding of the fluorinated anthracene core, which results in 

an electronic band gap lower than that of tBu-HBC (13, EGAP= 2.37 eV vs. tBu-HBC, 

EGAP= 2.65 eV). 

 

Figure 1.17. Cyclic voltammograms corresponding to helically arranged nanographene 13 vs 

Fc/Fc+ in a 1 M solution of tetrabutylammonium hexafluorophosphate in toluene/acetonitrile 

1:1. 

Table 1.1.  Redox potentials of tBu-HBC, syn 10 and 13 vs Fc/Fc+. 

Compound E1
red (V) E2

red (V) E3
red (V) E4

red (V) E1
ox (V) 

tBu-HBC  –2.27 –2.50 –2.79 – 0.67 

syn 10 –2.56 – – – 0.85 

13 –1.69 –2.40 –2.47 –2.69 0.87 

The photophysical properties (data summarized in Table 1.2) of the 

spironanographene 10 were evaluated by UV-vis absorption and emission 

experiments. As shown in Figure 1.18 (left), spironanographene syn 10 absorption 

spectrum presents three well-structured, intense sharp bands (324, 336 and 350 nm) 

and two weaker bands (276 and 391 nm) in the UV region. In the visible region two 



Chapter 1 

53 

 

weak bands are observed at 414 and 438 nm. The emission spectrum shows three well-

structured bands at 439, 456 and 464 nm, and two weaker bands at 484 and 496 nm. 

Using tBu-HBC as reference, the absorption spectra show similar shape, with three 

intense sharp bands in the UV region (344, 360 and 390 nm) and three weak bands in 

the visible region (439, 441 and 443 nm). The emission spectrum shows a broad band 

and a shoulder at 493 and 553, respectively.  

The comparison between spironanographene 10 and tBu-HBC show the same 

tendency previously concluded from the voltammetry measurements. The absorption 

and emission spectra of nanographene 10 are blue-shifted vs tBu-HBC, which seems 

reasonable considering the lower π-extension of the spironanographene and the 

hampered conjugation between the graphitized layers. 

The calculations of the frontier molecular orbitals (Figure 1.18, right) reinforce these 

results. Both orbitals HOMO and LUMO are delocalized in both π-extended layers, 

with no coefficients in the central anthracene core. Furthermore, the TD-DFT 

calculations indicate that the weak bands in the visible region of the absorption 

spectrum of 10 (414 and 438 nm) have rather low oscillator strengths (0.06 and 0.09, 

respectively) because of the vertical transitions’ combinations involving the orbitals 

from HOMO–4 and LUMO+3. 

  

Figure 1.18. Absorption and emission spectra of spironanographene syn 10 (left). Computed 

frontier orbitals HOMO (top right) and LUMO (bottom right) of syn 10 considering a model 

with methyl groups instead of tert-butyl groups. 

The photophysical properties of helically arranged nanographene 13 are represented 

in Figure 1.19. The absorption spectrum shows three intense sharp bands in the UV 

region at 310, 337 and 367 nm, and one weaker band at 381 nm. In the visible region 

three broad less intense bands are observed at 413, 454 and 482 nm. The spectrum 

shows red-shifted same-shaped bands compared to tBu-HBC (sharp intense bands, 



Chapter 1 

54 

 

344, 360 and 390 nm, and weak bands, 439, 441 and 443 nm). To understand the 

nature of the bathochromic shift of 13 vs tBu-HBC, TD-DFT calculations were carried 

out. PCM(hexane)-TD-B3LYP-D3/def2-SVP//B3LYP-D3/def2-SVP calculations on 

the model 13M revealed that the absorption at 482 nm is assigned to the vertical 

transition involving a one-electron promotion from HOMO to LUMO. These π-

orbitals are mainly located at the fluorinated anthracene core (Figure 1.19, right). 

However, the band at 454 nm is associated to the transition from the HOMO–1, π-

delocalized in the graphitized layers and nearly degenerated with the HOMO, to 

LUMO. 

 

Figure 1.19. Absorption and emission spectra of helically arranged 13 (left). Computed 

frontier orbitals of fluorinated nanographene 13M considering a model (right). 

Table 1.2. UV-vis absorption and emission maxima of tBu-HBC, syn 10 and 13 

Compound Absorption λabs
max (nm)  Emission λemi

max (nm) 

tBu-HBC  344, 360, 390, 439, 441, 445 493, 519, 553 

Syn 10 324, 336, 350, 376, 391, 414, 438 439, 456, 465, 484, 496 

13 310, 337, 367, 381, 413, 454, 482 437, 454, 464, 499, 531, 575 



Chapter 1 

55 

 

The emission spectra of nanographene 13 shows two weak sharp bands at 437 and 

464 nm, and more intense broad bands at 501, 531, 575 nm. The unexpected 

overlapping between the absorption and emission spectra suggested an apparent dual 

emission in which the fluorophore fragments in the molecule (fluorinated anthracene 

and graphitized layers) provide emission signals independently. By comparison with 

the emission spectra of the precursors, the broad bands at longer wavelengths agree 

in shape with the emission spectra of 6b, 11 and 12, as shown in Figure 1.20 (left).  

  

Figure 1.20. Emission spectra of precursors 11, 12, 6b and nanographene 13 (left). Excitation 

spectra of nanographene 13 at the emission spectrum maxima wavelengths. 

To confirm that the signals in the emission spectra resulted from the same molecule 

and not from impurities, excitation spectra were recorded (Figure 1.20, right). As the 

spectra obtained did not depend on the selected wavelength, at the expense of an in-

depth photophysical study, it could be in principle concluded that the structure shows 

an apparent dual emission. Further evidence is provided in the discussion of the 

following Chapter 2.3.6. 



 

56 

 

  



Chapter 1 

57 

 

1.4 Conclusions 

Controlling the Scholl reaction can be challenging considering the possible 

rearrangements, unexpected cyclizations or functionalization that may occur under 

oxidation conditions. In this chapter, the electronic control over the Scholl reaction by 

modulating the electron-withdrawing character of the central anthracene core 

connecting two graphitized moieties is described.  

Anthracene-based polyphenylene 6a led to the unexpected formation of 

spirocompounds 7, 8, 9 and 10 with different degrees of graphitization depending on 

the oxidant, temperature, and reaction time, being the first example of spirocycles 

formation under Scholl reaction conditions without interruption of the graphitization. 

DFT calculations nicely explained the formation of the spirocycles considering the 

formation of arenium cation or radical-cation intermediates. The cyclization of the 

spirocycles precedes the graphitization and the key is the formation of a trityl cation 

intermediate that involves an aromaticity gain, providing a much favorable pathway 

than the expected graphitization. 

In contrast, if the anthracene core is substituted with eight electron-withdrawing 

fluorine atoms, the Scholl reaction proceeds through graphitization without forming 

the spirocycles 13. The electronic deficiency in the anthracene hinders the formation 

of the trityl cation, then the reaction evolves through the expected aryl-aryl coupling. 

Electrochemical and photophysical properties of the new spironanographene syn 10 

and helically arranged nanographene 13, showed the electron donor and acceptor 

character of the structures. Considering tBu-HBC as reference (E1
1/2ox= 0.67 V and 

E1
1/2red= –2.27 V), the conjugation interruption by the spiranic sp3 carbon atoms 

connecting the graphitized units entails the separation between oxidation (E1
1/2ox= 0.85 

V) and reduction (E1
1/2red= –2.56V) bands, and the blueshift of the electronic bands, 

resulting in a bandgap opening for nanographene syn 10. However, helically arranged 

nanographene 13 presents a lower bandgap considering the first oxidation (E1
1/2ox= 

0.87 V) and reduction (E1
1/2red= –1.69 V) potentials, this behavior is confirmed by the 

red-shifted bands in the absorption and emission spectra. Furthermore, nanographene 

13 shows a dual emission with bands apparently steaming from both fluorophores, the 

octafluoroanthracene and the graphitized moieties. 



 

 

 

  



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 2 

  



 

 

 

 

 



Chapter 2 

61 

 

2 Chapter 2 

2.1 Introduction to Chirality in Nanographenes 

The first experimental evidence of chirality date back to 1808, when Étienne-Louis 

Malus discovered the polarized light;97 just a few years later, in 1811 Dominique F. J. 

Arago discovered optical rotation in sheets of quartz crystals.98 In 1817, Baptiste Biot 

observed optical activity from solutions of different natural products.99 However, the 

finding of dissymétrie and enantiomerism is acknowledged to Louis Pasteur, who in 

1848 manually separated two enantiomorphous crystals of tartaric acid, dissolved 

them separately and registered their optical activity, finding the same values in 

absolute magnitude but opposite in direction.100  

The following milestone for the understanding of chirality was the determination of 

the three-dimensional arrangement of the atoms in a molecule. In 1874, Jacobus H. 

van’t Hoff discovered and defined the asymmetric carbon atom and illustrated two 

specular images of a tetrahedral carbon, as represented in Figure 2.1a.101 The term of 

chirality was later stablished by Sir William Thomson, Lord Kelvin, in 1907 (Figure 

2.1b)102 “I call any geometrical figure, or group of points, chiral, and say that it has 

chirality, if its image in a plane mirror, ideally realized, cannot be brought to coincide 

with itself.” Using the classic example of hands (in Greek χείρ −kheir−, origin of the 

word chiral) it is shown how the left and the right hands are non-superposable mirror 

images, Figure 2.1c.  

 

Figure 2.1. a) J. H. van’t Hoff’s enantiomers illustration of an asymmetric carbon atom. b) Sir 

W. Thomson (Lord Kelvin) definition of chirality. c) Hands, non-superposable mirror images.  

The increasing complexity of the structures, and the difficulties encountered in the 

nomenclature and identification of chiral molecules led the researchers Robert S. 

Cahn, Christopher K. Ingold and Vladimir Prelog to join forces and set the priority 

 
97 S. Mauskopf, Trans. Am. Philos. Soc. 1976, 66, 56. 
98 S. Mauskopf, Trans. Am. Philos. Soc. 1976, 66, 61. 
99 J.-B. Biot, Mém. Acad. R. Sci. Inst. Fr. 1817, 2, 4. 
100 L. Pasteur, C. R. Séances Acad. Sci. 1848, 26, 535. 
101 J. H. van’t Hoff, Arch. Neerl. 1874, 9, 1. 
102 Lord Kelvin, J. Oxford Univ. Junior Sci. Club 1894, 18, 25. 

(a) (b)

(c)



Chapter 2 

62 

 

rules for the identification of chiral systems.103 In addition, they clarified the definition 

of chirality stated by Lord Kelvin, establishing that the necessary and sufficient 

condition for the existence of optical enantiomers is that a mirror plane converts the 

model into a non-identical one which cannot be superposed on the original by 

translations and rotations only. Therefore, a model which has no symmetry elements 

except for rotational axes may be chiral.104  

Thus, chirality can be central, axial, and planar, depending on whether the chiral 

element is an atom, an axis, or a plane, respectively (Figure 2.2). The definitions 

provided by the IUPAC Gold Book105 (International Union of Pure and Applied 

Chemistry) for the chiral elements are: 

• Chirality centre: “An atom holding a set of ligands in a spatial arrangement which 

is not superposable on its mirror image”. 

• Chirality axis: “An axis about which a set of ligands is held so that it results in a 

spatial arrangement which is not superposable on its mirror image”. 

• Chirality plane: “A planar unit connected to an adjacent part of the structure by a 

bond which results in restricted torsion so that the plane cannot lie in a symmetry 

plane”. 

 

Figure 2.2. Non-superposable mirror images containing an asymmetric carbon atom (central 

chirality), a chirality axis (axial chirality, e.g., allenes and atropisomerism of ortho-substituted 

biphenyls) or a chirality plane (planar chirality, e.g. cyclophanes). Chiral elements are 

represented in yellow. 

 

 

 

 
103 (a) R.S. Cahn, C.K. Ingold and V. Prelog. J. Chem. Soc. 1951, 612. (b) R.S. Cahn, C.K. Ingold and V. 

Prelog. Experientia 1956, 12, 81. 
104 (a) R.S. Cahn, C.K. Ingold and V. Prelog. Angew. Chem. Inter. Ed. 1966, 5, 385. (b) V. Prelog, G. 

Helmchen, Angew. Chem. Int. Ed. 1982, 21, 567. 
105 IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. 

McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). 

*Chirality

centre
* Chirality axis

* Chirality

plane



Chapter 2 

63 

 

2.1.1 From Two-Dimensionality to Chirality 

Chirality is related to the geometry of the molecule and its organization in the three 

dimensions of space. However, the nature of the Csp2 atoms that comprise the 

hexagonal graphene-like networks entails the formation of planar structures implying 

the presence of a symmetry plane (Figure 2.3a).  

The required deviation from planarity to generate asymmetry in the search for inherent 

chirality in nanographenes has been achieved by introducing topological defects 

following two main approaches. On the one hand, the introduction of non-hexagonal 

rings surrounded by fused hexagonal rings. Inner rings smaller than six members (e.g. 

[5]circulene or corannulene) provide bowl-shape structures with positive Gaussian 

curvature. Inner rings larger than six members lead to saddle-shape structures with 

negative Gaussian curvature (e.g. [7]circulene, Figure 2.3b).106 On the other hand, the 

generation of sterically congested structures can induce the torsion of the hexagonal 

networks if the energy cost of the torsional strain, or deformation, minimizes the steric 

interactions (e.g. helicenes, twistacenes, and nanobelts, Figure 2.3c).107  

 

Figure 2.3. (a) Csp2 atoms in a hexagonal network provide planar structures with a symmetry 

plane (σh), in light pink, preventing chirality. (b) *Non-hexagonal rings diverting the structures 

from planarity, positive Gaussian curvature (bowls) and negative Gaussian curvature (saddles). 

(c) Strain-induce deviation from planarity. Chiral axes are represented in yellow. *Corannulene 

and [7]circulene should be substituted to fulfill the symmetry conditions for chirality. 

Considering the sp2 nature of the carbon atoms, the main chiral elements in molecular 

nanographenes, to fulfill the symmetry requirements (absence of symmetry planes and 

inversion centers), are chirality axes or chirality planes (represented in yellow in 

Figure 2.3).  

 
106 M. Rickhaus, M. Mayor, M. Juríček, Chem. Soc. Rev. 2017, 46, 1643. 
107 M. Rickhaus, M. Mayor, M. Juríček, Chem. Soc. Rev. 2016, 45, 1542. 



Chapter 2 

64 

 

2.1.2 Chiral Nanographenes and Isomerization Barriers 

The isomerization processes of the structural features that induce chirality in 

nanographenes (Figure 2.3) do not involve the breaking of covalent bonds. High 

flexibility and molecular dynamics can lead to isomerization. Therefore, additionally 

to the symmetry requirements, the structure must be stereochemically rigid to be 

chiral. 

Understanding the resistance preventing the isomerization (isomerization energy 

barrier) is key to determine if the chiroptical properties are stable in time, proving the 

stereochemical rigidity. According to the isomerization energy barriers, molecular 

nanographenes can be classified in the following dynamic subclasses: flexible, 

detectable, isolable, or rigid. 

2.1.2.1 Flexible Nanographenes (<10 kcal·mol−1) 

Isomerization energy barriers lower than 5 kcal·mol−1 involve fast conformational 

equilibrium making enantiomeric species indistinguishable. The presence of seven-

membered rings usually means low isomerization barriers given the high flexibility 

of this structural feature, for example the saddle-to-saddle inversion of [7]circulene is 

only 0.05 kcal·mol−1. However, these values can be increased by different structural 

features. The negative curvature of nanographene 2.1 arises from the two seven-

membered rings, each one surrounded by six fused rings (four hexagonal and two 

pentagonal), Figure 2.4. The calculated enantiomerization barrier of 5.9 kcal·mol−1 

shows how six fused rings, out of seven possible, tend to increase the value of the 

isomerization barrier due to the steric hindrance between the hydrogen atoms in the 

bay region.108 

Another topological defect usually related to low isomerization barriers is [4]helicene. 

The steric hindrance between the hydrogens in the terminal rings is sufficient to divert 

the structure from planarity, but the rapid interconversion makes the isomers 

impossible to be detected. Thus, the enantiomers of nanographene 2.2 (Figure 2.4) 

were only resolved in solid state.109 

 
Figure 2.4. Flexible nanographenes with isomerization barriers lower than 5 kcal·mol−1. 

 
108 K. Oki, M. Takase, S. Mori, A. Shiotari, Y. Sugimoto, K. Ohara, T. Okujima, H. Uno, J. Am. Chem. 

Soc. 2018, 140, 10430. 
109 J. Liu, B.-W. Li, Y.-Z. Tan, A. Giannakopoulos, C. Sánchez-Sánchez, D. Beljonne, P. Ruffieux, R. 

Fasel, X. L. Feng, K. Müllen, J. Am. Chem. Soc. 2015, 137, 6097. 



Chapter 2 

65 

 

2.1.2.2 Spectroscopically Detectable Chirality (10-20 kcal·mol−1) 

An isomerization barrier of 20 kcal·mol−1 corresponds to a half-time life of τ1/2= 1000 

s at 298 K, which, in most cases, allows the detection of enantiomeric species by 

spectroscopic methods. The majority of nanographenes with Gaussian curvature are 

framed in this range. 

As previously mentioned, the isomerization barriers of [n]circulenes with n−1 fused 

rings tend to be higher than those of the equivalent [n]circulenes. As shown in Figure 

2.5, the energy for the saddle-to-saddle inversion of hexa[7]circulene 2.3 (analog to 

[7]circulene with only six benzene fused rings) is 17 kcal·mol−1 whereas, for 

[7]circulene, the saddle-to-saddle barrier is 0.05 kcal·mol−1. Additionally, greater 

bowl depth, for positively curved nanographenes, or greater saddle depth, for 

negatively curved nanographenes, increase the energy of the bowl-to-bowl or saddle-

to-saddle isomerization barriers.  

In Figure 2.5a is represented a curved molecular nanographene 2.4 consisting of five 

hexa[7]circulene units fused to a central corannulene or [5]circulene.110 Thus, the 

structure presents negative curvature in the periphery and positive curvature in the 

core. The isomerization barriers of the different topological defects were calculated. 

The energy value for the saddle-to-saddle inversion of the seven-membered rings 

(13.6 kcal·mol−1 by NMR and 18.9 kcal·mol−1 by DFT) agrees with the previously 

described trend of hexa[7]circulenes. In addition, the bowl-to-bowl inversion of the 

core, with a bowl depth of 0.37 Å, resulted of 1.7 kcal·mol−1, expectedly lower than 

that of corannulene, 10.4 kcal·mol−1, considering the larger bowl depth, 0.87 Å. 

 

Figure 2.5. (a) [n]Circulenes with n-1 fused rings and bowl depth effects over the 

isomerization barriers of a curved nanographene. (b) Saddle depth effect in negatively curved 

nanographenes. 

 
110 K. Kawasumi, Q. Zhang, Y. Segawa, L. T. Scott, K. Itami, Nat. Chem. 2013, 5, 739. 



Chapter 2 

66 

 

The effect of the saddle depth is observed in [7]circulene derivatives 2.5 and 2.6, 

represented in Figure 2.5b. The peripheral π-extension of the negatively curved 

structure 2.5 involves the generation of two fused [4]helicenes leading to a saddle 

depth of 2.5 Å and an isomerization barrier of 12.2 kcal·mol−1.111 However, a larger 

π-extension yielding seven fused [4]helicene in structure 2.6 results in a lower saddle 

depth, 1.7 Å, and therefore, a lower isomerization barrier, 3.8 kcal·mol−1.112 

2.1.2.3 Isolable Chiral Nanographenes (20-35 kcal·mol−1) 

Barriers beyond 20 kcal·mol−1 usually allow the isolation and manipulation of 

enantiopure compounds. However, the racemization process occurs over time and the 

chiroptical properties are not stable enough for most of the applications. 

Although the introduction of non-hexagonal rings usually leads to a high flexibility of 

the structure and therefore a low isomerization barrier, one of the possibilities to 

increase the rigidity is to fuse rings smaller and larger than hexagons. This is the case 

of the monkey-saddle shape nanographene 2.7 containing three five-membered rings 

and three eight-membered rings fused to a central benzene (Figure 2.6). The 

combination of these topological defects leads to an isomerization barrier of 24.8 

kcal·mol−1.113 

Alternatively, negatively curved nanographenes in which the non-hexagonal ring is 

embedded in a helicene-like topological defect exhibit higher stereochemical rigidity. 

As shown in Figure 2.6, nanographene 2.8 has two seven-membered rings, one 

forming a hexa[7]circulene and the other one embedded forming a [5]helicene, which 

results on a racemization barrier of 25.4 kcal·mol−1.114 

 

Figure 2.6. Isolable chiral nanographenes containing non-hexagonal rings and helical 

topological defects. 

Structures containing [5]helicenes are expected to be in this subclass considering the 

isomerization barrier of [5]helicene is 24.6 kcal·mol−1, however, strategies as the 

functionalization of the terminal rings (fjord region) increase the racemization barrier. 

 
111 X. Gu, H. Li, B. Shan, Z. Liu, Q. Miao, Org. Lett. 2017, 19, 2246. 
112 S. H. Pun, Y. Wang, M. Chu, C. K. Chan, Y. Li, Z. Liu, Q. Miao, J. Am. Chem. Soc. 2019, 141, 9680. 
113 T. Kirschbaum, F. Rominger and M. Mastalerz, Angew. Chem., Int. Ed. 2020, 59, 270. 
114 Z. Qiu, S. Asako, Y. Hu, C.-W. Ju, T. Liu, L. Rondin, D. Schollmeyer, J.-S. Lauret, K. Müllen, A. 

Narita, J. Am. Chem. Soc. 2020, 142, 14814. 



Chapter 2 

67 

 

For instance, nanographene 2.9 has a racemization barrier of 33 kcal·mol−1 arising 

from the [5]helicene functionalize with two bulky tert-butyl groups (Figure 2.6).115   

2.1.2.4 Stereochemically Rigid Nanographenes (>35 kcal·mol−1) 

At 423 K, an enantiomerically pure sample racemizes with a half-time life of τ1/2= 24 

h when the isomerization barrier is 35 kcal·mol−1. The chiral properties are stable 

enough for chiroptical applications. The methodologies above described and the 

presence of helicenes larger than [6]helicenes ensure the stereochemical rigidity. 

As describe above, rings larger than six members embedded in a helicene-like 

structure increases the rigidity. Nanographene 2.10 contains an eight-membered ring 

involved in a [5]helicene-like structure (Figure 2.7). The racemization energy increase 

is such that the measurable lower limit of the barrier resulted in 38.3 kcal·mol−1.116 

Moreover, the functionalization of the fjord region of [5]helicenes with bulky groups 

was sufficient to obtain the stereochemically rigid nanographene 2.11. Additionally, 

the helicity of the substituted [5]helicenes induce the twist of the structure increasing 

the barrier to 38.4 kcal·mol−1 (Figure 2.7).117 

  

Figure 2.7. Stereochemically rigid nanographenes containing non-hexagonal rings and helical 

topological defects. 

The stereochemical rigidity of helicene containing nanographenes depends on the 

number of ortho-fused rings. Taking into account that the isomerization barrier of 

[6]helicene is 36.2 kcal·mol−1, it can be expected that the introduction of longer 

helicenes will lead to stereochemically rigid structures. For instance, nanographene 

2.12 consists of two [6]helicene and two [7]helicene substructures, a combination that 

leads to an isomerization barrier of 58.6 kcal·mol−1 (Figure 2.7).118 

 
115 C. M. Cruz, I. R. Márquez, I. F. A. Mariz, V. Blanco, C. Sánchez-Sánchez, J. M. Sobrado, J. A. Martín-

Gago, J. M. Cuerva, E. Maçôas, A. G. Campaña, Chem. Sci. 2018, 9, 3917. 
116 M. A. Medel, R. Tapia, V. Blanco, D. Miguel, S. P. Morcillo, A. G. Campaña, Angew. Chem., Int. Ed. 

2021, 60, 6094. 
117 X. Xu, R. Munoz-Marmol, S. Vasylevskyi, A. Villa, G. Folpini, F. Scotognella, G. M. Paterno, A. 

Narita, Angew. Chem. Int. Ed. 2023, 62, e202218350. 
118 S. H. Pun, K. M. Cheung, D. Yang, H. Chen, Y. Wang, S. V. Kershaw, Q. Miao, Angew. Chem. Int. 

Ed. 2022, 61, e202113203. 



Chapter 2 

68 

 

2.1.3 Alternative Approaches for Chirality in PAHs 

As shown in the previous section, the design of chiral nanographenes is mainly based 

on the introduction of topological defects that give rise to Gaussian curvature or 

helicity. Only a few examples of alternative approaches to chiral polyaromatic 

hydrocarbons can be found in the literature. For instance, Itami and coworkers 

reported a cyclic chiral polyarene, infinitene 2.13, that consists of two fused 

[8]helicene units acquiring the shape of the infinity symbol.119 As shown in Figure 

2.8, the structure, which could be considered a helically twisted analogue of a saddle-

shaped [12]circulene, fulfills the symmetry conditions as well as the stereochemical 

rigidity, so it is chiral. A larger 8-shaped helical cyclic stereochemically rigid nanobelt 

2.14 was described by Wu et al. The isomerization barrier was estimated to be higher 

than 82.5 kcal·mol−1 (Figure 2.8).120 More recently Wu and coworkers reported a large 

twisted Möbius carbon nanobelt 2.15 (Figure 2.8). The Möbius molecules are also 

inherently chiral, in this case the band-like structure is twisted three times, which 

involves three chiral axis leading to two stable enantiomers (P,P,P or M,M,M).121 In 

addition, untwisted chiral nanobelts as 2.16122 can be considered "molecular nanotube 

fragments", whose chirality steams from the bending vectors of the hypothetically 

open planar structure. 

 

Figure 2.8. Chiral cyclic polyaromatic hydrocarbons, nanobelts. 

An almost unexplored approach to chiral nanographenes is the design of atropisomers. 

As shown in Figure 2.9, the hindered rotation around the single bond (in purple) 

connecting the aromatic substituents leads to enantiomers when the ortho-substituents 

are different two by two. Thus, the cyclic structure 2.17 has three chiral axes along 

the simple bonds (highlighted in purple), leading to three possible pairs of enantiomers 

of a stereochemically rigid structure. However, the reported structures are the 

 
119 M. Krzeszewski, H. Ito, K. Itami, J. Am. Chem. Soc. 2022, 144, 862. 
120 W. Fan, T. Matsuno, Y. Han, X. Wang, Q. Zhou, H. Isobe, J. Wu, J. Am. Chem. Soc. 2021, 143, 15924. 
121 W. Fan, T. M. Fukunaga, S. Wu, Y. Han, Q. Zhou, J. Wang, Z. Li, X. Hou, H. Wei, Y. Ni, H. Isobe, J. 

Wu, Nat. Synth. 2023, 2, 880. 
122 K. Yin Cheung, S. Gui, C. Deng, H. Liang, Z. Xia, Z. Liu, L. Chi, Q. Miao, Chem 2019, 5, 838. 



Chapter 2 

69 

 

enantiomers (R,R,R or S,S,S) resulting from enantiopure starting materials (R or S 

BINOL).123  

 

Figure 2.9. Biphenyl chirality of a cyclic polyaromatic hydrocarbon and a molecular 

nanographene. 

To the best of our knowledge, the only nanographene with atropisomerism described 

in the literature was reported in 2023 by An et al. The structure 2.18 consists of two 

graphitized units containing a heptagonal ring forming a cyclic ether. The graphitized 

fragments are connected by a single bond through which the rotation is restricted. 

Thus, the symmetry and stereochemical rigidity requirements are fulfilled, 

considering that the experimentally determined racemization barrier was found to be 

35 kcal·mol−1 at 443 K (Figure 2.9).124 

 
123 Y. Nojima, M. Hasegawa, N. Hara, Y. Imai, Y. Mazaki, Chem. Commun. 2019, 55, 2749. 
124 S. Li, R. Li, Y.-K. Zhang, S. Wang, B. Ma, B. Zhang, P. An, Chem. Sci. 2023, 14, 3286. 



 

70 

 



Chapter 2 

71 

 

2.2 Objectives 

This chapter is focused on the search for new strategies for the synthesis of molecular 

nanographenes with atropisomerism. For this purpose, a family of orthogonally 

connected nanographenes based on two graphitized units (dibenzo[fg,ij]phenanthro-

[9,10,1,2,3-pqrst]pentaphene, DBPP) attached to a central core was designed. 

Although the first attempt was to study anthracene as the central core, structures 1 

(not obtained) and 13 described in the previous Chapter 1, the chirality of these 

systems has been discussed by using simplified structures, replacing the anthracene 

(or octafluoroanthracene) core by a 1,4-substituted tetrafluorobenzene considering its 

easier functionalization and accessibility. 

 

The work plan consisted on the synthesis of the symmetric derivative and subsequent 

modification of the substituents, in the graphitized moieties and the central core, to 

obtain the atropisomers. However, upon synthesizing the symmetric derivative it was 

observed how the steric hindrance entailed the organization of the graphitized units, 

giving rise to the unexpected chirality of the highly symmetrically substituted 

nanographene (1,4-substituted tetrafluorobenzene connecting the DBPP units 

substituted with five tert-butyl groups). 

Furthermore, racemization was observed while attempting to isolate the enantiomers. 

Thus, the stereochemical rigidity was lower than expected. To determine the 

isomerization barrier, two asymmetric derivatives were prepared by exchanging two 

tert-butyl groups for -OMe or -H, and the isomerization process was evaluated by 

NMR experiments. Finally, the study of the optoelectronic properties was carried out 

by cyclic voltammetry, absorption, and emission measurements. 

 



 

72 

 



Chapter 2 

73 

 

2.3 Results and Discussion 

2.3.1 Synthesis of Helically Arranged Nanographenes 

In this section, the synthesis and characterization of a new family of helically arranged 

nanographenes based on two graphitized units (dibenzo[fg,ij]phenanthro-[9,10,1,2,3-

pqrst]pentaphene, DBPP) connected through a 1,4-substituted tetrafluorobenzene ring 

are described. As detailed in Scheme 2.1, the synthetic methodology starts with a 

double palladium-catalyzed Sonogashira coupling between two equivalents of a 

suitably para-substituted (R= tert-butyl, methoxy or hydrogen) arylacetylene 3a-c and 

1,4-dibromo-2,3,5,6-tetrafluorobenzene (14). The resulting bis[aryl(ethynyl)] 

tetrafluorobenzenes 15a-c undergo a double Diels-Alder cycloaddition with 

cyclopentadienone 5 to afford the corresponding polyarene structures 16a-c. The final 

step is the graphitization by the Scholl reaction of the respective polyphenylene in 

presence of DDQ and triflic acid, thereby effectively yielding helically arranged 

nanographenes 17a-c. 

 

Scheme 2.1. Synthesis of tetrafluorobenzene-based helically arranged nanographenes. 



Chapter 2 

74 

 

As described in the previous Chapter 1, the formation of trityl cation intermediates 

during the Scholl reaction leads to the formation of spirocycles between the 

graphitized units and the central core (Figure 1.13). However, the substitution of the 

central anthracene with eight electron withdrawing fluorine atoms conducts the 

reaction to the formation of the expected helically arranged nanographene 13. 

The fluorine atoms in the above described nanographenes 17a-c have a double 

function, destabilizing the hypothetical carbocation and preventing the six-membered 

ring cyclization between the graphitized DBPP units and the central ring. 

Furthermore, the introduction of fluorine atoms into polyarene structures has proven 

to have no negative impact on the Scholl oxidation leading to unexpected 

rearrangements.125  

The characterization by 1H-NMR, 13C-NMR, 19F-NMR, FT-IR, and high-resolution 

mass spectrometry confirmed the structures. The NMR spectra corresponding to 

nanographene 17a reveals its high symmetry. As shown in Figure 2.10, the spin 

systems, integrals, and multiplicity are the same as those for octafluoroanthracene-

based nanographene 13 by 1H-NMR: one doublet of doublets at 7.63 ppm (3JH-H= 8.77 

Hz and 4JH-H= 1.90 Hz), a doublet at 8.26 ppm (3JH-H= 8.77 Hz), one doublet at 8.81 

ppm (4JH-H= 1.90 Hz), two doublets at 9.01 and 9.11 ppm (4JH-H= 1.65 Hz), one singlet 

at 9.16 ppm, and tree singlets at 1.82, 1.76 and 1.39 ppm corresponding to the tert-

butyl groups with relative intensities 1:2:2. The 19F-NMR shows one singlet 

corresponding to the four magnetically equivalent fluorine atoms in the central 

benzene ring. 

 

Figure 2.10. 1H-NMR spectrum (left) showing the relevant regions, assigned structure in the 

middle, and 19F-NMR spectrum (right). 

 
125 S. Mörsel, R. Kellner, A. Hirsch, Eur. J. Org. Chem. 2023, 26, e202300299. 

1H, 17a 19F, 17a



Chapter 2 

75 

 

2.3.2 Unexpected Chirality 

The structure was unequivocally resolved by single-crystal X-ray diffraction, shown 

in Figure 2.11. Nanographene 17a presents a helical arrangement of the moieties. The 

steric hindrance between the DBPPs themselves, and with the central 

tetrafluorobenzene ring, and the possible rotation around the single bonds connecting 

the fragments cause the structure to acquire a helical organization around a C2 axis 

(shown in yellow, Figure 2.11a), as previously observed in the octafluoroanthracene-

based nanographene 13 (Chapter 1). To identify the helicity, numbers have been 

assigned in increasing order to the structural units considering the view along the C2 

axis (Figure 2.11b). Starting from the closest to the observer (1) and passing through 

the central benzene unit (2) to the furthest (3). 

 

Figure 2.11. a) Front view of nanographene 17a. b) Lateral view of nanographene 17a showing 

the helical arrangement. C2 axis represented in yellow. 

Detailed observation of the nanographene in the crystal structure showed that the 

DBPP fragments exhibit an unexpected curvature, Figure 2.12a. Density functional 

theory (DFT) calculations on the model system 17aM, in which the tert-butyl groups 

were replaced by methyl groups, revealed the occurrence of stabilizing non-covalent 

C−H···π interactions (green surfaces, Figure 2.12b). The interactions between the 

closest peripheral rings of the two DBPPs and between the tetrafluorobenzene ring 

with the closest C–H bonds in the graphitized fragments, lock the peripheral rings 

orthogonally (as represented with the planes in orange and purple in Figure 2.12a) 

inducing the curvature of the DBPP moieties. According to the second order 

perturbation theory (SOPT) of the natural bond order (NBO) method, the attractive 

interactions result from the π(C=C)→σ*(C−H) and σ(C−H)→π*(C=C) electronic 

delocalization, whose associated stabilization energies, ΔE(2), amount to −1.04 and 

−0.68 kcal·mol-1, respectively. 

 

(a) (b)

C2

C2

1
2

3



Chapter 2 

76 

 

 

Figure 2.12. a) Orthogonal disposition of the interacting peripheral rings in the DBPP 

fragments. b) Stabilizing C–H···π interactions (surfaces in green) that set the structure 

geometry. 

Therefore, the steric hindrance between the DBPPs prevents their coplanarity. 

Interestingly, this deviation from planarity entails the bending of the DBPPs, and the 

structure is fixed, so that the three fragments are arranged in a helical fashion. Figure 

2.13a shows the planes containing the central rings of each fragment (the flatter area). 

The plane represented in red contains the central part of the DBPP fragment closest to 

the observer, the plane in green contains the tetrafluorobenzene ring (located in the 

center), and finally the orange plane contains the central rings of the fragment farthest 

from the observer. The helical arrangement of the moieties means that the structure 

contains neither symmetry planes nor inversion centers. The symmetry operations in 

nanographene 17a are three orthogonal C2 rotational axis, therefore, the structure is 

framed in the chiral space-group of symmetry D2. 

Evaluating the packing in the crystal structure it was noticed that two non-

superposable specular images of the nanographene coexist in a 1:1 relation. The 

symmetrical substitution of the central ring does not allow the application of the Cahn-

Ingold-Prelog priority rules. As represented in Figure 2.13b, the numbers assignation 

to the fragments, from the closest to the observer to the farthest, results in a clockwise 

(P isomer) or counterclockwise (M isomer) helicity. 

 

Figure 2.13. a) Lateral view of nanographene 17a representing the planes containing each unit. 

In red, DBPP unit closest to the observer, in green, tetrafluorobenzene, and in orange, farthest 

DBPP unit. b) P (clockwise helicity) and M (counterclockwise helicity) enantiomers of 

nanographene 17a coexisting in the crystal structure.  

90º

(a)

17aM17a

(b)

(b)

1
2

3

1
2

3M P

(a)



Chapter 2 

77 

 

Enantiomers of nanographene 17a were resolved by chiral HPLC (Appendix 2, HPLC 

resolution). However, they could not be isolated as enantiopure samples for the 

determination of chiral properties due to racemization at room temperature. For the 

identification of the isomerization barrier responsible for the racemization, it was 

required to understand the molecular dynamics. Therefore, two asymmetric 

derivatives were prepared by changing one tert-butyl group on each DBPP by a 

methoxy group or hydrogen atom, as shown in Scheme 2.1, providing the 

nanographene derivatives 17b and 17c, respectively. 

2.3.3 Molecular Dynamics: Asymmetric Derivatives 17b,c 

Nanographenes 17b and 17c were obtained as 1:1 anti/syn diastereomers mixture 

when the Scholl reaction was performed at 0 ºC. DFT calculations supported this 

result indicating that the diastereomers are nearly degenerate. 1H-NMR spectra of 

nanographenes 17b and 17c show the duplication of all signals, e.g. two singlets are 

observed at (3.95 and 3.93 ppm, Figure 2.14a) corresponding to the methoxy groups 

on each isomer of 17b. Both 19F-NMR spectra showed the presence of two different 

fluorine atoms corresponding to the anti and syn isomers of each compound (Figure 

2.14b). 

 

Figure 2.14. a) 1H-NMR spectra of nanographene 17b. b) 19F-NMR spectra of nanographenes 

17b and 17c. 

The stereoisomers are anti, if the substituents (-OMe or H) are facing different sides 

of the tetrafluorobenzene, or syn if they are facing the same plane of the central core, 

Figure 2.15a. Thus, these derivatives are obtained as a four-isomers mixture, a pair of 

diastereomers with their corresponding pair of enantiomers. 

In Figure 2.15b, the lateral views of each isomer are shown and, to facilitate the 

isomers assignation, simplified models are represented. The dark grey sticks represent 

the DBPP closer to the observer, the tetrafluorobenzene ring is represented as a green 

line with green dots in the ends representing the fluorine atoms, and the light grey 

sticks represent the DBPP farther from the observer. Finally, the OMe (17b) or H (17c) 

substituents are shown as purple dots.  

(a) 1H, anti/syn 17b
Anti/syn 17b Anti/syn 17c

(b) 19F



Chapter 2 

78 

 

 

Figure 2.15. a) Front view of anti/syn 17b (purple dot: OMe) or 17c (purple dot: H). b) Lateral 

view of the anti/syn diastereomers, assignation of the M/P enantiomers. Simplified models are 

used for better visualization. c) Isomerization by rotation of the central ring: anti→syn. d) 

Isomerization by crossing of the DBPP units: M→P. 

(a) Front view

Anti Syn

(b) Lateral view

Anti Syn

Diastereomers

(c) 90º Rotation of the central C6F4 f(t): Anti / Syn isomerization

1

2
3

1

2
3

1

2

3

1

2
3

P

M M

P

Anti

1

2
3

t0 tSyn

1

2
3

P

(d) Rotation of the DBPP moieties f(t): Racemization

M

Anti

1

2
3

t0 Anti

M

1
2

3P

t

E
n
a
n
ti
o
m

e
rs

1

2
3

P

1

2
3

M
1

2
3

M

1

2

P

3

– OMe (17b)

–H (17c)

90º 

90º 

90º 



Chapter 2 

79 

 

As previously explained, the P enantiomer is that in which the fragments are organized 

clockwise around the chiral axis, and M in which the fragments are organized 

counterclockwise. 

To identify the isomerization barrier (previously revealed by the racemization of 

nanographene 17a), two possible scenarios should be considered. On the one hand, a 

90º rotation of the tetrafluorobenzene core, which leads to isomerization between 

diastereomers (e.g. anti M to syn P, Figure 2.15c). On the other hand, the rotation of 

the DBPP moieties with respect to each other (crossing), entailing racemization, 

interconversion between enantiomers (e.g. anti M to anti P, Figure 2.15d). 

The isomerization barrier was determined by 1H-NMR experiments. To avoid possible 

electronic effects resulting from the methoxy groups in derivative 17b, derivative 17c, 

in which two tert-butyl groups have been removed, was used. As previously 

mentioned, compound 17c was isolated as 1:1 anti/syn mixture when the Scholl 

reaction was performed with DDQ and triflic acid at 0 ºC. However, at −65 ºC, the 

Scholl oxidation of polyphenylene 16c yielded a 70:30 anti/syn isomeric mixture (anti 

and syn isomers assignations by NMR in Appendix 5) with noncomplete conversion. 

After workup to remove the DDQ and triflic acid, the mixture was warmed at 40 ºC 

and monitored by 1H-NMR recording a spectrum every 10 minutes.  

After assigning the signals to each isomer by NMR experiments, it was decided to 

monitor four doublets that were sufficiently separated. The doublets at 8.31 and 8.14 

ppm belonging to the anti isomer, and the doublets at 8.27 and 8.22 to the syn isomer. 

As shown in Figure 2.16, at the beginning of the experiment (t0) the anti/syn ratio is 

70:30 and as time progresses the integrations evolved until both isomers are at a 50:50 

ratio after 15 000 seconds. 

 

Figure 2.16. Isomerization process monitored by performing a 1H-NMR spectrum every 10 

minutes at 40 ºC. 

Anti Syn

t0

15 000 s



Chapter 2 

80 

 

The kinetic constants were determined according to the integrals’ variations. Since the 

concentration of both anti/syn diastereomers is the same at the equilibrium, the 

constants kf and kb are the same (Figure 2.17a). The representation of the 

ln[(XH,8.31−Xeq)/(X0−Xeq)] (XH,8.31, molar fraction of the proton at 8.31 ppm depending 

on time; Xeq, molar fraction of the proton at 8.31 ppm once reached the equilibrium, 

X0, molar fraction of the proton at 8.31ppm at the beginning of the experiment) vs 

time provided a slope of −2.15·10-4 s-1 with a good fitting (r2= 0.9849), Figure 2.17b. 

According to the kinetic equation, the slope corresponds to –(kf+kb), then kf  = kb = 

1.08·10−4 s−1. If these kinetic constants value is introduced to Eyring’s equation,  

k=((κ·kB·T)/h)·e^(−ΔG≠/(RT)), the isomerization barrier at 40 ºC is Δ𝐺⧧= 24.6 

kcal·mol-1, which corresponds to a half-time life of τ1/2 = 107 min. 

 

Figure 2.17. a) Isomerization process monitored by 1H-NMR. b) Variation of the molar 

fraction of anti/syn isomers with time (left) and fitting of ln[(XH,8.31−Xeq)/(X0−Xeq)] vs t (right). 

Since NMR was used for the determination of the isomerization barrier from anti 17c 

to syn 17c, only differentiation between diastereomers is possible, and not between 

enantiomers (nuclei present an equivalent chemical and magnetic environment). Then, 

it can be concluded that the isomerization process involves a 90º rotation of the 

tetrafluorobenzene ring. Which results in interconversion between diastereomers as 

previously illustrated in Figure 2.15c. 

 

 

kf

kb

At eq. [anti]=[syn]→kf =kb

Anti Syn

(a)

(b)

0 2500 5000 7500 10000 12500
-3.0
-2.8
-2.6
-2.4
-2.2
-2.0
-1.8
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0

 

 

 Linear fitting

Slope   -2.15·10
-4

 s
-1

       r
2
   0.9849

ln
[(

X
-X

e
q

)/
(X

0
-X

e
q

)]

Time (s)

Equation y = a + b*x

Weight No Weighting

Residual Sum 

of Squares

0.19798

Pearson's r -0.9928

Adj. R-Square 0.9849

Value

F
Intercept 0.12129

Slope -2.14755E-4

0 3000 6000 9000 12000 15000
0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

 

 

 Xanti

 X
syn

M
o

la
r 

fr
a

c
ti
o

n
, 
X

Time (s)



Chapter 2 

81 

 

2.3.4 No C−H ··· π Interactions, No Helicity, No Chirality 

Considering the backbone of the central rings (highlighted in blue, Figure 2.18), this 

nanographene, a priori, may be considered a π-extended para-terphenyl. Depending 

on the substitution pattern of the central ring, para-terphenyls can be classified in four 

types.126 The asymmetric substitution on the central benzene entails the absence of 

mirror planes and inversion elements, thus different number of isomers are formed 

depending on the remaining symmetry elements. However, when all substituents are 

the same in the central ring (Type 4, Figure 2.18), only one isomer is expected, 

reflection symmetry elements, mirror plane containing the lateral benzene rings and 

mirror plane perpendicular to the central ring, annuls the presence of chirality. 

However, the symmetry planes present on Type 4 para-terphenyls are not possible 

symmetry operations for nanographene 17a. The structure presents two enantiomers 

due to the C–H···π interactions that set the structure with a helical arrangement of the 

fragments DBPP-tetrafluorobenzene-DBPP. Thus, inducing atropisomerism-like 

chirality in a highly symmetric molecule.  

 

Figure 2.18. Considering nanographene 17a a π-extended terphenyl and relation with the 

terphenyl types. 

Moreover, the non-graphitized structures of polyarenes 16b and 16c present the 

symmetry of type 4 terphenyls. The lack of the previously described C−H···π 

interactions (Figure 2.12) due to free bonds rotations means the presence of mirror 

planes and, therefore, no chirality. As shown in Figure 2.19, the NMR spectra of the 

polyarene asymmetric derivatives 16b and 16c present signals corresponding to only 

one isomer (e.g. one singlet corresponding to the methoxy group, four singlets 

corresponding to the tert-butyl groups and one singlet in the 19F-NMR spectra). 

 
126 R. Adams, H. C. Yuan, Chem. Rev. 1933, 12, 261 

X



Chapter 2 

82 

 

 

Figure 2.19. a) 1H-NMR spectrum of polyarene derivative 16b. b) 19F-NMR spectra of 

polyphenylenes 16b and 16c. Only one compound is observed, no isomers. 

In addition, performing the Scholl oxidation of polyarene 16c at −78 ºC provided the 

partially graphitized derivative 17c’ (Figure 2.20), for which only one isomer is 

observed by NMR experiments, e.g. four singlets corresponding to the tert-butyl 

groups and one singlet in 19F-NMR, as shown in Figure 2.20 (assignation by NMR in 

Appendix 5), therefore it can be considered a π-extended type 4 terphenyl (Figure 

2.18). The free rotation of the fragments around the simple bonds entails the lack of 

stereogenic elements. The most stable conformation calculated by DFT 17c’M shows 

a non-chiral orthogonal arrangement, which contrasts to the helical arrangement of 

chiral nanographene 17c. 

 

Figure 2.20. a) 1H and 19F-NMR spectra of partially graphitized non-chiral derivative 17c’. b) 

DFT modelized structure 17c’M showing non-chiral orthogonal arrangement of the moieties. 

 

16b 16c

(a) 1H, 16b (b) 19F

17c’M

(a) 1H, 17c’

19F, 17c’

(b)



Chapter 2 

83 

 

2.3.5 Electrochemical and Photophysical Properties 

The electrochemical properties of nanographenes 17a-c were explored by cyclic 

voltammetry in a toluene/acetonitrile 4:1 mixture using tetrabutylammonium 

hexafluorophosphate as supporting electrolyte, glassy carbon as working electrode, a 

platinum wire as counter electrode, and Ag/AgNO3 as reference electrode, at room 

temperature.  

Molecular nanographenes 17a-c present non-reversible oxidation and reduction 

waves with rather extreme potentials for the technique, finding the main limitation in 

the solvent window (oxidation and reduction of the solvent). After testing several 

measurement conditions, the cyclic voltammograms spectra represented in Figure 

2.21 show the oxidation and reduction potentials, except for the oxidation of 

nanographenes 17a and 17c, for which the square wave voltammetry curves are 

illustrated with dashed lines. Given the low reversibility of most of the observed 

waves, the values of the maxima observed by square wave voltammetry are reported. 

 

Figure 2.21. Cyclic voltammograms corresponding to tBu-HBC, and nanographenes 17a-c vs 

Fc/Fc+ in a 1 M solution of tetrabutylammonium hexafluorophosphate in toluene/acetonitrile 

4:1. With dashed lines are represented the square wave measurements.  

The oxidation and reduction potentials vs. Fc/Fc+ of the new nanographenes and tBu-

HBC are summarized in Table 2.1. Compared to tBu-HBC, these nanographenes are 

poorer electron donor and acceptors, with first reduction waves at E1
red= –2.42 V 

(17a), E1
red= –2.39 V (17b), and E1

red= –2.34 V (17c) vs. E1
red= –2.26 V (tBu-HBC), 

and oxidation waves at E1
ox= 0.92 V (17a), E1

ox= 0.94 V (17b), and E1
ox= 0.97 V (17c) 

vs. E1
ox= 0.80 V (tBu-HBC). This behavior suggests that the conjugation between the 

three fragments (DBPPs and tetrafluorobenzene core) is hampered because of the non-

coplanarity. Therefore, the π-conjugation and extension is lower in the helical 

nanographenes than in tBu-HBC. These observations nicely correlate with the DFT-



Chapter 2 

84 

 

computed energy of the corresponding HOMO (orbital from which the electron is 

released): −5.54 eV (17aM) < −5.21 eV (tBu-HBC), thus showing that a more 

stabilized HOMO (i.e., more negative) is translated into a higher oxidation potential. 

Table 2.1.  Redox potentials of tBu-HBC, 17a, 17b and 17c vs Fc/Fc+. 

Compound E1
red (V) E1

ox (V) 

tBu-HBC  –2.26 0.80 

17a –2.42 0.92 

anti/syn 17b –2.39 0.94 

anti/syn 17c –2.34 0.97 

The optical properties of nanographenes 17a-c were evaluated by UV-vis absorption 

and emission measurements (Figure 2.22). The absorption spectra of this family of 

molecular nanographenes show similar shapes and energies (Figure 2.22, solid lines), 

with three sharp intense absorption bands in the UV region (17a: 317, 356, and 378 

nm; 17b: 320, 357, and 380 nm; 17c: 318, 354, and 377 nm) and three weak bands in 

the visible region (17a: 395, 419, and 444 nm; 17b: 397, 419, and 445 nm; 17c: 395, 

419, and 444 nm). Comparing with tBu-HBC, the shape is very similar, presenting 

three sharp bands in the UV region (344, 360, and 390 nm) and three weak bands in 

the visible region (439, 441, and 443 nm). The blue shifting of the bands of 

nanographenes 17 vs. tBu-HBC agrees with the electrochemical properties previously 

described, since the structures are less conjugated, which also involves the increment 

of the optical band gap (calculated in the intersection between the absorption and 

emission spectra, 17a E0-0= 2.79 eV, 17b E0-0= 2.78 eV, 17c E0-0= 2.79 eV, tBu-HBC 

E0-0=  2.65 eV). 

 

Figure 2.22. Absorption (solid line) and emission (dashed line) spectra of nanographenes 17. 



Chapter 2 

85 

 

To determine the nature of the transitions associated to the obtained UV-vis spectra, 

time-dependent (TD)DFT calculations were carried out on the model 17aM. The 

theoretical data nicely reproduce the occurrence of the bands, the more intense band 

at 395 nm (λcalc= 410 nm, f= 0.18) is assigned to a transition from HOMO−2 to LUMO. 

The two bands at 419 and 444 nm (λcalc= 418 and 420 nm, respectively), show a rather 

low oscillator strength (f= 0.028 and 0.020, respectively), which agrees with rather 

low ε experimentally observed. These last transitions result from a one-electron 

transition from the nearly degenerate HOMO and HOMO−1 (π-molecular orbitals 

delocalized in both DBPP moieties with no measurable coefficient in the central 

tetrafluorobenzene ring, Figure 2.23) to the LUMO, respectively. It is worth to 

mention, that the LUMO is delocalized along three fragments due to the presence of 

twisted π-orbitals connecting the central ring with the DBPPs. The HOMO−2 also 

exhibits coefficients in the central ring, which confirms π-communication in the 

nanographene despite the lack of coplanarity between the fragments. 

 

Figure 2.23. Computed molecular orbitals for 17aM involved in the main UV-vis absorptions. 

The emission spectra of these nanographenes are also very similar, showing three 

bands in the visible region (17a: 446, 474, and 505 nm; 17b: 448, 476, and 507 nm; 

17c: 446, 473, and 504 nm). In these spectra de bands are also blue shifted if compared 

to tBu-HBC (absorption and emission maxima are collected in Table 2.2). 

In addition, the optical energy band gaps were calculated by the intersection of the 

absorption and emission spectra resulting of 2.79 eV (17a), 2.78 eV (17b), and 2.79 

eV (17c). These energy gaps are larger than that of tBu-HBC (2.69 eV), because of 

the lower π-extension of helically arranged nanographenes. 



Chapter 2 

86 

 

Table 2.2.  Absorption and emission bands of tBu-HBC, 17a, 17b and 17c. 

Compound Absorption λabs
max (nm) Emission λem

max (nm) 

tBu-HBC  344, 360, 390, 439, 441, 445 493, 519, 553 

17a 317, 356, 378, 395, 419, 444 446, 474, 505 

Anti/syn 17b 320, 357, 380, 397, 419, 445 448, 476, 507 

Anti/syn 17c 318, 354, 377, 395, 419, 444 446, 519, 553 

2.3.6 Photophysical Properties of Helically Arranged Nanographenes 

As previously mentioned in Chapter 1.3.5, the emission spectra of 

octafluoroanthracene-based nanographene 13 shows a dual emission that could stem 

from the apparently individual emission of the chromophores, octafluoroanthracene 

and DBPP moieties. This observation is based on the similarities shown by the 

emission spectra of nanographene 17a and precursor 12 with the emission spectrum 

of nanographene 13, whose shape suggests the combination of both emission spectra. 

As shown in Figure 2.24, the emission bands for nanographene 13 at lower 

wavelengths could be associated to the emission of the DBPP moieties (similar in 

shape to the emission spectrum of 17a), whereas the more intense broad emission 

bands at longer wavelengths may be related to the octafuoroanthracene core (similar 

in shape to the emission spectrum of 12). 

 

Figure 2.24. Emission spectra comparison between compound 12 and helically arranged nanographenes 

13 and 17a. 

  



Chapter 2 

87 

 

2.4 Conclusions 

The synthesis and characterization of a new series of helically arranged 

nanographenes consisting of two DBPP moieties covalently connected to a central 

1,4-substituted tetrafluorobenzene core has been described. Single-crystal X-ray 

diffraction of nanographene 17a showed a deviation from planarity of the DBPP 

moieties. DFT calculations reproduce the crystalline structure and revealed the 

formation of stabilizing C−H···π interactions that set the structure and support the 

unexpected bending of the DBPPs.  

The resulting helical arrangement of the moieties around the chiral axis leads to the 

formation of two enantiomers for the highly symmetrical nanographene 17a. The 

enantiomers were resolved by chiral HPLC; however, the isolation was not successful 

due to racemization at room temperature. The isomerization process was evaluated by 

NMR experiments of the asymmetrically substituted derivative 17c. The replacement 

of two tert-butyl groups leads to a new pair of nearly degenerated diastereomers 

(anti/syn) with a rotational barrier of Δ𝐺⧧= 24.6 kcal·mol−1 at 40 ºC, and a half-time 

life of τ1/2= 107 min. 

The absence of the C−H···π interactions entails the absence of chirality, as proven by 

the achiral polyarene precursors (16b and 16c) and the also achiral partially 

graphitized nanographene 17c’. Structures in which the helical organization does not 

occur and, therefore, can be classified as type 4 π-extended para-terphenyls. 

The electrochemical properties were evaluated by cyclic voltammetry and square 

wave voltammetry. Helically arranged nanographenes 17a-c are poorer electron donor 

and acceptors than tBu-HBC, with first wave reduction values of E1
red < −2.42 V (17a), 

vs. E1
red= −2.26 V (tBu-HBC), and first wave oxidation values of E1

ox > 0.92 V (17a), 

vs. E1
ox= 0.80 V (tBu-HBC). The absorption and emission spectroscopic properties 

confirmed the same trend, the maxima are blue shifted in comparison with those of 
tBu-HBC, which is related to the lower π-extension of nanographenes 17a-c vs. tBu-

HBC. However, DFT calculations interestingly showed that the LUMO orbital is 

delocalized along the entire molecule due to the presence of twisted π-orbitals 

connecting the central ring with the DBPP fragments, thus allowing the electronic 

communication along the entire molecule. 



 

 

 

 

 

  



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 3 

 

  



 

 

 

 

 



Chapter 3 

91 

 

3 Chapter 3.  

3.1 Introduction to Bilayer Nanographenes 

As described in Chapter 1.1, the wide variety of organic chemistry reactions allows 

the stepwise synthesis of molecular nanographenes with atomic control and, therefore, 

perfectly defined properties. The variety of structures reported in the literature gives 

evidence of the numerous possibilities for modifying the size and shape of these 

graphene molecular fragments. The main approaches are the variation of the π-

extension, and the topological modification of the hexagonal networks, allowing the 

induction of inherent chirality, as detailed in Chapter 2.1. However, having the 

synthetic tools, imagination is the limit and, more recently, special interest has been 

focused on the design of bilayer nanographenes. 

Resembling the multilayer structure of graphite, planar nanographenes tend to 

aggregate by π-π intermolecular interactions. Taking advantage of this behavior, in 

1999 Müllen et al. reported the first supramolecular aggregates of HBC derivatives 

forming ordered columnar structures.127 Thus, in the early 2000’s a great development 

of ordered HBC-based liquid crystals128 took place due to its interest in organic 

electronics.129  

However, it has not been until the last few years that discrete persistent bilayer and 

multilayer systems could be prepared in a controlled manner, i. e. with a fixed number 

of overlapping layers stacked by π-π interactions. Depending on the binding forces 

involved in the bilayer formation, three different approaches have been explored, (i) 

purely supramolecular interactions providing van der Waals molecular 

nanographenes, (ii) bilayers from fused radicals, and (iii) covalently connected 

bilayers. 

3.1.1 Van der Waals Bilayer Molecular Nanographenes 

The design of discrete, persistent bilayers by this approach can be challenging due to 

the labile nature of van der Waals interactions. In addition, the monomer must be 

design in a way that the supramolecular polymerization is hindered. To the best of our 

knowledge, the first van der Waals persistent molecular bilayers were reported in 2019 

by Tan and coworkers.130 As shown in Figure 3.1, the structure 3.1 is a dimer of a 

planar nanographene functionalized with 2,6-dimethylphenyl substituents in the 

periphery. The main purpose of the bulky peripheral groups is to provide solubility to 

nanographenes preventing the formation of multiple aggregates by π-π stacking. 

 
127 A. Fechtenkötter, K. Saalwächter, M. A. Harbison, K. Müllen, H. Wolfgang Spiess, Angew. Chem. Int. 

Ed. 1999, 38, 3039. 
128 T. Wöhrle, I. Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum, J. Litterscheidt, J. Christian Haenle, 

P. Staffeld, A. Baro, F. Giesselmann, S. Laschat, Chem. Rev. 2016, 116, 1139. 
129 J. P. Hill, W. Jin, A. Kosaka, T. Fukushima, H. Ichihara, T. Shimomura, K. Ito, T. Hashizume, N. Ishii, 

T. Aida, Science 2004, 304, 1481. 
130 X.-J. Zhao, H. Hou, X.-T. Fan, Y. Wang, Y.-M. Liu, C. Tang, S.-H. Liu, P.-P. Ding, J. Cheng, D.-H. 

Lin, C. Wang, Y. Yang, Y.-Z. Tan, Nat. Commun. 2019, 10, 3057. 



Chapter 3 

92 

 

However, the suitable design of the monomer allows large π-π interactions between 

two layers. The interlocking between the orthogonal peripheral groups prevents the 

formation of larger aggregates providing a persistent bilayer structure that only 

dissociates into the corresponding monomers by laser ablation. The strong van der 

Waals interactions entail the formation of excited states with different energies to 

those of the degenerate states of the monomers −Davydov splitting−. Transient 

absorption and time-resolved photoluminescence spectroscopic measurements 

showed significant differences between the lifetimes of the bright and dark Davydov 

states resulting from the dimerization. 

 

Figure 3.1. Persistent van der Waals bilayer and trilayer nanographenes. 

The successfully proven strategy to prevent the polymerization while enhancing the 

π-π interactions by the design of suitably substituted π-extended structures was 

followed by Würthner et al. 131  In 2022 they described the controlled formation of 

trilayer 3.2 by alternating π-π stacking between different monomers, a trisimide 

nanographene and two functionalized HBC monomers. As illustrated in Figure 3.1, 

the trisimide nanographene can encompass exactly two equivalents of a same 

symmetry hexabenzocoronene (in yellow) to form the persistent trilayer 3.2. 

Interestingly, the formation of the van der Waals structure protects the trisimide 

nanographene π-surface from oxygen quenching, improving the fluorescence under 

ambient conditions (ΦFL= 12.5% for the trisimide nanographene vs. ΦFL= 21.2% for 

the trilayer). 

More recently, Mastalerz and coworkers have described a new family of twisted chiral 

acenes that undergo an enthalpy driven and solvent dependent dimerization process 

leading to van der Waals bilayers.132 The ribbon monomers forming the twisted bilayer 

3.3 (Figure 3.2), consist of 25 linearly annulated benzene rings. The peripheral 

 
131 B. Pigulski, K. Shoyama, M.-J. Sun, F. Würthner, J. Am. Chem. Soc. 2022, 144, 5718. 
132 X. Yang, M. Brückner, F. Rominger, T. Kirschbaum, M. Mastalerz, Chem 2024, 10, 832. 



Chapter 3 

93 

 

substitution with alkyl side chains leads to an overall 282º contortion of the π-

backbone, along the longitudinal axes, inducing chirality (Figure 2.3, twistacenes). 

Single-crystal X-ray diffraction confirmed the formation of the dimers and revealed 

that the discrete self-assembly of the twisted monomers is based on multiple weak 

non-directing interactions involving the side chains, while the π-π interactions are not 

dominating interactions. Furthermore, the formation of the chiral dimer 3.3 follows 

the sergeant and soldier principle for the chiral induction. Although the cove regions 

(in orange) may lead to different helicities along the backbone, the dimer structure is 

formed between all-M monomers or all-P monomers. 

 

Figure 3.2. Solvent dependent van der Waals bilayers leading to chirality induction (3.3) and 

aggregation induced emission (3.4). 

As above describe, the formation of van der Waals bilayers has a great impact over 

the properties. Although the bilayers formation depends mainly on the structure 

design, the peripheral substitution and the solvent have an important role. In this 

context, our research group have recently described a Csp3-centered molecular 

nanographene, tetrahedraphene, that shows aggregation induced emission.133 TD-

DFT calculations showed that adding a solvent in which the monomer is insoluble 

promotes the dimerization leading to bilayer 3.4, which changes the fluorescence 

color from blue (monomer) to yellow (dimer). This variation may be attributed to the 

 
133 A. Oró, F. Romeo-Gella, J. Perles, J. M. Fernández-García, I. Corral, N. Martín, Angew. Chem. Int. 

Ed. 2023, 62, e202312314. 



Chapter 3 

94 

 

restriction of the rotational and vibrational motions in the bilayer structure, thus 

preventing the non-radiative relaxation of the excited state. 

3.1.2 Bilayers from Fused Radicals 

The formation of the so-called pancake bonded nanographenes are currently emerging 

as a feasible approach to bilayer structures. The control over the stability of open-shell 

structures (mainly radical or diradical species) lies on preventing their intrinsic trend 

to undergo σ- or π-dimerization. However, this behavior has proven to be suitable for 

the controlled formation of persistent bilayer structures. Even though the dimerization 

of radicals is a reversible process, the predominance of the bilayers can be improved 

by π-π interactions. 

Following the previously described strategy to obtain van der Waals bilayer 

nanographenes (Figure 3.1), Tan, Wang and coworkers prepared the bilayer structure 

3.5.134 After reduction reaction with potassium, the structure is transformed into a 

triply negatively charge radical bilayer 3.53·−, represented in Figure 3.3. The π-dimer 

radical anion displays a 96-centre-3-electron pancake bond. Interestingly, the open-

shell bilayer shows spin frustration, resulting of great interest in magnetic materials 

physics. It may indicate that upon reduction doping, π-fused nanographenes could 

present quantum spin liquid properties. 

 

Figure 3.3. Bilayers from π- and σ-fused radicals. 

The well-known σ-dimerization of open-shell molecules has also been explored for 

the preparation of bilayer structures. In this regard, Stępień and coworkers reported 

bilayer 3.6 resulting from the formation of a σ-bond between two radicaloid 

monomers consisting of a hexaazacoronene functionalized with six annulated 

 
134 W. Wang, X.-H. Ma, M. Liu, S. Tang, X. Ding, Y. Zhao, Y.-Z. Tan, M. Kertesz, X. Wang, Angew. 

Chem. 2023, 135, e202217788. 



Chapter 3 

95 

 

naphthalenemonoimide units, as shown in Figure 3.3.135 The combination of 

dispersion and covalent forces with the packaging of sterically hindered groups 

contribute to the high thermodynamic stability of the bilayer dimer. The dissociation 

process to the open-shell monomers was achieved by irradiation with UV or visible 

light, providing an opportunity to design magnetically active nanographenes. 

3.1.3 Covalently Linked Bilayers 

The controlled preparation of bilayer and multilayer structures described in the 

previous sections allows the modulation of the optoelectronic and magnetic 

properties. However, the structural requirements to obtain persistent bilayers by these 

approaches −planar π-extended monomers− prevents the induction of structural 

inherent chirality. As described in Chapter 2.1.1 (Figure 2.3), chirality in 

nanographenes involves deviation from planarity by the introduction of topological 

defects. Therefore, an accessible approach is synthesizing bilayer structures, with 

adjustable optoelectronic and chiroptical properties, in which the overlapping layers 

are linked by covalent bonds. 

Our research group was pioneered in describing the first helical bilayer nanographene 

in 2018.136 The structure of the new molecular nanographene 3.7 consisted of two 

hexa-peri-hexabenzocoronene moieties annulated to a helicene backbone resulting in 

a totally conjugated [10]helical bilayer nanographene, Figure 3.4. The formation of 

the helical feature diverts the structure from planarity inducing chirality and disposing 

the layers face-to-face at an interlayer distance of 3.6 Å. In the same year Jux and co-

workers reported helical nanographene 3.8 consisting of an oxa[7]helicene fused to 

two HBC layers.137 The main difference between these structures is the length and 

shape of the helical backbone, which determines the overlapping between the 

graphitized layers, and the optoelectronic and chiroptical properties. 

The number of turns of the helicene −and the overlapping between the layers at the 

ends− depends on the number and geometry of the ortho-fused rings. The presence of 

five-membered rings opens the inner rim of the helicene decreasing the number of 

turns (defined as the cycle number of helix). Thus, [10]helical nanographene 3.7 is a 

partially overlapped structure, with 14 rings involved in the π-π intramolecular 

interactions, while the length and shape of the helicene in oxa[7]helical nanographene 

3.8 prevents the overlapping between the graphitized layers. 

 

 
135 L. Moshniaha, M. Żyła-Karwowska, P. J. Chmielewski, T. Lis, J. Cybińska, E. Gońka, J. Oschwald, 

T. Drewello, S. Medina Rivero, J. Casado, M. Stępień, J. Am. Chem. Soc. 2020, 142, 3626. 
136 P. J. Evans, J. Ouyang, L. Favereau, J. Crassous, I. Fernández, J. Perles, N. Martín, Angew. Chem. Int. 

Ed. 2018, 57, 6774. 
137 D. Reger, P. Haines, F. W. Heinemann, D. M. Guldi, N. Jux, Angew. Chem. Int. Ed. 2018, 57, 5938. 



Chapter 3 

96 

 

 

Figure 3.4. Helical bilayer nanographene and π-extended oxa[7]helicene. 

Moreover, seven-membered rings embedded in the helical feature close the inner rim 

increasing the number of turns. In this regard, Feng and coworkers reported in 2023 

the non-benzenoid [10]helical bilayer nanographene 3.9 (Figure 3.5).138 The presence 

of two seven-membered rings in the helicene backbone entails the closing of the inner 

rim leading to the total overlapping between the layers, and a small interlayer distance 

of 3.24 Å. The in situ registration of UV-vis-NIR spectra upon oxidation, revealed an 

intervalence charge transfer band in the NIR region for the oxidized species. TD-DFT 

calculations supported the through-space electronic communication between the 

layers. In addition, these helical nanographenes are showing highlighting chiroptical 

absorption (circular dichroism, CD) and emission (circularly polarized luminescence, 

CPL) properties, determined by the dissymmetry factors of absorption (gabs) and 

luminescence (glum). For instance, the enantiomers of nanographene 3.9 present a 

luminescence dissymmetry factor glum of 1.3·10−3.  

 

Figure 3.5. π-Extended helical bilayer nanographenes. 

Also in 2023, Gong et al. reported helical bilayer nanographene 3.10 consisting of a 

pentadecabenzo[9]helicene core and four fused hexabenzocoronene units (Figure 

3.5).139 The rigidity of the structure, due to the π-extension of the helicene, and the 

large overlapping of the layers (28 benzene rings involved in the π-π interactions) 

 
138 L. Yang, Y.-Y. Ju, M. A. Medel, Y. Fu, H. Komber, E. Dmitrieva, J.-J. Zhang, S. Obermann, A. G. 

Campaña, J. Ma, X. Feng, Angew. Chem. Int. Ed. 2023, 62, e202216193. 
139 Y.-J. Shen, N.-T. Yao, L.-N. Diao, Y. Yang, X.-L. Chen, H.-Y. Gong, Angew. Chem. Int. Ed. 2023, 62, 

e202300840. 



Chapter 3 

97 

 

affords an interlayer distance of 2.9 Å. The dissymmetry factors for the isolated 

enantiomers of this nanographene 3.10 are among the highest reported for organic 

molecules, glum= 4.5·10−2 for the P isomer, and glum= 4.22·10−2 for the M isomer. 

CPL-active materials140 have attracted considerable interest due to their potential 

applications in different fields, including photoelectronic devices, data storage, 

sensing, organic light-emitting diodes, chiroptical switching, etc.141 As previously 

mentioned, the CPL intensity is described by the dissymmetry factor glum, which 

represents the ratio of the difference in intensity and the average total luminescence 

intensity: glum= (IL−IR)/[(1/2)(IL+IR)], IL intensity of left-circularly polarized light, IR 

intensity of right-circularly polarized light. Theoretically, the dissymmetry factor can 

be calculated as function of the electric (μ) and magnetic (m) dipole transition 

moments, glum= 4Re[(μ·m)/(|m|2+|μ|2)]. For organic molecular CPL emitters, the 

transitions are usually electric dipole allowed and magnetic dipole forbidden. Thus, 

the magnetic dipole term is much smaller than the electric dipole, and the denominator 

is dominated by |μ|2, which results in |glum| values in the order of 10−5 to 10−2.142   

In addition to the independent study of bilayer molecular nanographenes due to their 

highlighting chiroptical properties, the last year has witnessed a boom in 

structure/property relationship studies on bilayer and multilayer nanographenes. 

Hence, Tan and co-workers reported in 2023 the trilayer nanographenes 3.11 and 3.12 

(Figure 3.6), consisting of three HBC moieties connected by [8]helicenes with 

different topologies.143 As mentioned above, the incorporation of five-membered rings 

in the helicene causes the inner rim to open, directly related to the overlapping 

decrease. Therefore, although the number of rings forming the helicenes in both 

structures is the same, [8]helicenes, the five-membered rings in structure 3.12 cause a 

decrease in the overlapping between the layers. The determination of the 

optoelectronic properties showed that three-layer nanographene with higher interlayer 

overlapping 3.11, has a lower first oxidation potential, stronger bound excitons, and 

longer photoluminescence lifetimes, thus demonstrating the relationship between the 

overlapping degree and the optoelectronic properties. 

 
140 Y. Zhang, S. Yu, B. Han, Y. Zhou, X. Zhang, X. Gao, Z. Tang, Matter 2022, 5, 837. 
141 Y. Deng, M. Wang, Y. Zhuang, S. Liu, W. Huang, Q. Zhao, Light Sci. Appl. 2021, 10, 76. 
142 E. M. Sánchez-Carnerero, A. R. Agarrabeitia, F. Moreno, B. L. Maroto, G. Muller, M. J. Ortiz, S. de 

la Moya, Chem. Eur. J. 2015, 21, 13488. 
143 Y.-Y. Ju, L. Chai, K. Li, J.-F. Xing, X.-H. Ma, Z.-L. Qiu, X.-J. Zhao, J. Zhu, Y.-Z. Tan, J. Am. Chem. 

Soc. 2023, 145, 2815. 



Chapter 3 

98 

 

 

Figure 3.6. Helical trilayer nanographenes with overlapping degree depending on the 

helicenes rings-topology. 

Further than the comparative study of the properties depending on the overlapping 

degree, Feng et al. have reported three helical nanographenes, Figure 3.7,144 in which 

the overlapping degree between contiguous layers remains constant, while the number 

of layers and the π-extension increase. In this case, the multilayered structures based 

on covalently connected HBC units forming [7]helicenes, exhibit low overlapping 

degrees between contiguous layers. However, the global π-π intramolecular 

interactions increases with the number of layers, attributable to the accumulated 

interlayer interactions. Higher number of layers enhances the rigidity of the structures, 

which reduces the interlayer spacing. Thus, the distances are 3.78 Å in bilayer 3.13, 

3.26 Å and 3.57 Å in trilayer 3.14, and 3.56 Å, 3.67 Å and 4.20 Å for the contiguous 

layers in tetralayer 3.15 (from left to right in Figure 3.7). The incremented π-extension 

at higher number of layers seems to be the structural reason for the properties’ 

variation. Tetralayer nanographene 3.15 exhibits more red-shifted emission bands, 

preceded by trilayer 3.14 and bilayer 3.13. This behavior is also observed in the band 

gap variation, the lowest value corresponds to the tetralayer 3.15. Furthermore, the 

electrochemical properties show that the lowest oxidation potential corresponds to the 

most π-extended structure 3.15, which exhibits the strongest donor character. 

Interestingly, this family of nanographenes present highlighting fluorescence quantum 

yields, 45% for bilayer 3.13, 74% for trilayer 3.14, and 91% for tetralayer 3.15. This 

trend in the quantum yields may be related to the number of layers and the consequent 

rigidity enhancement. The chiroptical properties revealed gradually declined values 

of the luminescence dissymmetry factors (glum) with the increasing number of layers, 

7.9·10−3 for bilayer 3.13, 2.6·10−3 for trilayer 3.14, and 1.5·10−3 for tetralayer 3.15. 

 
144 W. Niu, Y. Fu, Z.-L. Qiu, C. J. Schürmann, S. Obermann, F. Liu, A. A. Popov, H. Komber, J. Ma, X. 

Feng, J. Am. Chem. Soc. 2023, 145, 26824. 



Chapter 3 

99 

 

 

Figure 3.7. Helical nanographenes with different number of layers. 

Also very recently, Feng and coworkers have described the structure/property 

relationship between three structural isomers of trilayer nanographenes consisting of 

three HBC units connected by two [7]helicenes.145 The modification of the relative 

fusion positions between the helicenes and the central benzene ring, affords three 

different geometries, ortho-fused nanographene 3.14 (Figure 3.7), meta-fused 

nanographene 3.16, and para-fused nanographene 3.17 (Figure 3.8). Interestingly, the 

structural modifications entail the amplification of the chiroptical responses, affording 

high CD and CPL dissymmetric factors; glum values, 8.7·10−3 for M-3.16, and 13.2·10−3 

for P-3.17. A 3.2-fold and 4.8-fold amplification compared to the glum value of o-3.14. 

 

Figure 3.8. Regioisomeric helical trilayer nanographenes. 

These recent results are evidence of the growing interest in bilayer and multilayer 

nanographenes. Just as deviation from planarity by incorporating topological defects 

entails the induction of chirality, it is feasible to think that enhancing through-space 

intramolecular π-π interactions represents a new dimension in the design of 

 
145 W. Niu, Y. Fu, Q. Deng, Z.-L. Qiu, F. Liu, A. A. Popov, H. Komber, J. Ma, X. Feng, Angew. Chem. 

Int. Ed. 2024, 63, e202319874. 



Chapter 3 

100 

 

nanographenes with advanced properties. A leap out of the designing toolbox in which 

most structures have so far been encompassed, which only considered modifications 

in the hexagonal network topology and the π-extension.  

  



Chapter 3 

101 

 

3.2 Objectives 

In 2018, our research group was pioneer reporting the first helical bilayer 

nanographene (HBNG). Starting from dibromo[6]helicene, the synthesis afforded a 

[10]helicene with two HBCs fused at each end.136 The planarity distortion induced by 

the helical feature, in addition to inducing chirality, dispose the graphitized layers 

face-to-face, providing a fully conjugated partially overlapped molecular 

nanographene. 

The first objective of this chapter is the synthesis and characterization of two helical 

bilayer nanographenes with different helicene lengths, [9]helicene and [11]helicene. 

The variation in the number of ortho-fused rings modulates the overlapping degree 

and the extension of the intramolecular π-π interactions between the layers. 

 

The second and main objective of this chapter is the systematic study of the 

structure/property relationship in this family of bilayer nanographenes with different 

helicene lengths. For this purpose, the comparative study of the electrochemical and 

spectroelectrochemical properties, and the photophysical characterization, including 

Raman analysis, have been carried out. Furthermore, given the chirality of the 

structures, the absorption and emission chiroptical properties have been evaluated by 

circular dichroism (CD) and circularly polarized luminescence (CPL). In addition, 

theoretical calculations have been carried out to support the experimental observations 

for the structure/property correlations. 

  



 

102 

 



Chapter 3 

103 

 

3.3 Results and Discussion 

3.3.1 Synthesis of Helical Bilayer Nanographenes 

Two chiral bilayer nanographenes have been synthesized from different length 

helicenes, [5]helicene and [7]helicene. As detailed in Scheme 3.1, the synthesis starts 

with a Sonogashira coupling between dichloro[5]helicene (18a) or 

dichloro[7]helicene (18b), and (triisopropylsilyl)acetylene leading to the protected 

dialkynylhelicenes 19a and 19b, respectively. Subsequently, the one pot deprotection 

of the TIPS and Sonogashira coupling with 4-tert-butyliodobenzene adds a 4-tert-

butylphenyl group to each triple bond affording compounds 20a and 20b. Thereafter, 

a two-fold Diels-Alder cycloaddition, followed by carbon monoxide extrusion, with 

cyclone 5 provides the corresponding helicene endowed with two penta(4-tert-

butylphenyl)phenyl groups, 21a and 21b. Finally, twelve C−C bonds are formed in 

the Scholl cyclodehydrogenation with DDQ/TfOH, increasing the number of ortho-

fused rings in the helicenes by four, and providing the bilayer molecular 

nanographenes [9]HBNG and [11]HBNG. 

 

Scheme 3.1. Synthesis of helical bilayer nanographenes (HBNGs) with different helicene 

lengths [9]HBNG, [10]HBNG and [11]HBNG. 

The structural characterization was carried out by 1H and 13C-NMR, FT-IR and high-

resolution mass spectrometry, which allowed the confirmation of all intermediates and 

final products. The mass spectra of the graphitized structures [9]HBNG (exact mass= 

1726.9267) and [11]HBNG (exact mass= 1826.9566) show a loss of 24 units with 

respect to the molecular weight of the starting compounds 21a (exact mass= 

1751.1151) and 21b (exact mass= 1851.1429), respectively, confirming the 

cyclodehydrogenative formation of 12 bonds. NMR spectra, show the expected 



Chapter 3 

104 

 

signals corresponding to a half of the molecules, revealing the presence of a C2 

rotational axis (Appendix 5, spectra). 

The structures of [9]HBNG and [11]HBNG were solved by single-crystal X-ray 

diffraction. In both cases, centrosymmetric crystals containing M and P isomers were 

obtained from the corresponding racemic mixtures, which contrast with the 

spontaneous independent crystallization of the enantiomers for [10]HBNG. The 

diverse shapes of the three HBNGs afforded significantly different packing, Figure 

3.9a. As expected, the helicene length determines the bilayer character of the 

structures, namely the overlapping degree between the facing HBC units. As 

represented in Figure 3.9b, the number of rings involved in the π-π interactions 

(represented with dashed lines) between the graphitized layers changes drastically 

from [9]HBNG to [11]HBNG. Structure [9]HBNG is a totally overlapped bilayer 

with 26 rings out of 29 involved in the π-π intramolecular interactions, arranging the 

layers at an average distance of 3.63 Å. The increased number of turns induced by the 

longer helicene length in [10]HBNG causes the displacement of the graphitized 

layers, thereby leading to a partially overlapped bilayer in which 14 rings participate 

in π-π interactions. In the case of [11]HBNG, the extension of the helicene prevents 

the face-to-face placement of the HBC layers, resulting in a shifted bilayer in which 

the 10 rings involved in the π-π interactions are part of the helicene backbone. This 

contrasts with [9]HBNG structure in which the π-π interacting rings are mainly 

located in the HBC units. 

 

Figure 3.9.(a) Packing of the structures [9]HBNG, [10]HBNG and [11]HBNG. (b) Lateral 

views of molecular structures of [9]HBNG, [10]HBNG and [11]HBNG, with dashed lines are 

represented the rings involved in the intramolecular π-π interactions showing the overlapping 

degree variations, tert-butyl groups and hydrogens have been removed for clarity. 

Higher overlapping

[9]HBNG [10]HBNG [11]HBNG

(a)

(b)



Chapter 3 

105 

 

3.3.2 Electrochemical and Spectroelectrochemical Properties 

The electrochemical properties of [9]HBNG, [10]HBNG, and [11]HBNG were 

evaluated by cyclic voltammetry in a 0.1 M 4:1 toluene/acetonitrile solution of 

tetrabutylammonium hexafluorophosphate at room temperature, using Ag/AgNO3 as 

reference electrode, glassy carbon as working electrode, and a platinum wire as 

counter electrode. In Table 3.1 are summarized the oxidation and reduction potentials 

vs. Fc/Fc+, including the data corresponding to tBu-HBC for comparison.  As shown 

in Figure 3.10, all three bilayer nanographenes present two quasi-reversible oxidation 

waves and two quasi-reversible reduction waves. The values for the first oxidation 

potentials follow the order [9]HBNG (0.35 V) < [10]HBNG (0.46 V) < [11]HBNG 

(0.52 V), showing a significantly stronger donor character than tBu-HBC (0.75 V) due 

to the larger π-extension of HBNGs. However, the donor character behavior of 

HBNGs is opposite to that expected according to the π-extension of the bilayer 

nanographenes. The strongest electron donor is the least π-extended structure, 

[9]HBNG, and the weaker electron donor is the largest π-extended structure, 

[11]HBNG.  

 

Figure 3.10. Cyclic voltammograms of HBNGs, [9]HBNG, [10]HBNG, and [11]HBNG vs. 

Fc/Fc+ in a 1 M solution of tetrabutylammonium hexafluorophosphate in toluene/acetonitrile 

4:1. 

The oxidation potential variations suggest that the larger the π-π overlapping (Figure 

3.9), the lower the oxidation potential values. This observation could be accounted for 

by the fact that the radical cation and dication species (Eox
1 and Eox

2, respectively) 

might be stabilized through the interaction between the two graphitized layers. This 

observation agrees with the density functional calculation of the HOMO, which is 

mainly located in the HBC units, and their energies vary in line with the measured 

oxidation potentials (Figure 3.11). 



Chapter 3 

106 

 

 

Table 3.1. Half-wave redox potentials of tBu-HBC, [9]HBNG, [10]HBNG and [11]HBNG vs 

Fc/Fc+. 

 Compound E1
1/2ox (V) E2

1/2ox (V) E1
1/2red (V) E2

1/2red (V) 

tBu-HBC  0.75 – –2.24 –2.40 

[9]HBNG 0.35 0.59 –2.18 –2.46 

[10]HBNG 0.46 0.67 –2.23 –2.55 

[11]HBNG 0.52 0.69 –2.22 –2.46 

In terms of the reduction potentials, the variation is less prominent, being [9]HBNG 

(−2.18 V), [10]HBNG (−2.23 V), and [11]HBNG (−2.22 V). According to DFT 

calculations the LUMO of the three structures is mainly located in the helicene moiety 

(Figure 3.11). In this sense, the scarce bond conjugation along the helicenes may 

explain the minor differences observed in the reduction potentials. 

 

Figure 3.11. Density functional theory calculations of the HOMO and LUMO topologies and 

energies. 

To determine whether the radical cation and dication species are indeed stabilized 

between the layers, and its relation to the stronger donor character of [9]HBNG 

(totally overlapped bilayer), UV-vis-NIR spectroelectrochemical measurements were 

carried out. Using platinum as working electrode, a platinum wire as counter 

electrode, and a silver wire as the reference electrode, in a 0.1 M solution of 

tetrabutylammonium hexafluorophosphate in dichloromethane.  

−0.694

−5.762
−5.839

−0.699

−5.851

[9]HBNG [10]HBNG [11]HBNG

B
3
L
Y

P
/6

-3
1
 G

**
 e

n
e
rg

y

LUMO

HOMO

−0.684



Chapter 3 

107 

 

As shown in Figure 3.12b (blue line), the first oxidation of [9]HBNG involves the 

appearance of two absorption bands at 934 and 540 nm, comparable with the bands 

of tBu-HBC at 797 and 550 nm (Figure 3.12a, blue line), upon formation of the radical 

cation. The redshift of the absorption bands from 797 to 934 nm agrees with the lower 

oxidation potential of [9]HBNG relative to tBu-HBC. Thus, the significant decrease 

of the oxidation potential observed for [9]HBNG (vs. tBu-HBC) suggests a double 

effect: (i) the involvement of the helicene moiety in the oxidation and (ii) considering 

the redshift of the absorption bands, an interlayer charge delocalization, which 

eventually contributes to decrease the oxidation potential.  

 

Figure 3.12. UV-Vis-NIR electronic absorption spectra obtained upon electrochemical 

oxidation of a) tBu-HBC, b) [9]HBNG. Black lines correspond to neutral species, blue lines 

to the first oxidized species and red lines to the second oxidized species. 

Additionally, the most intense absorption band at 373 nm of [9]HBNG in the neutral 

state (Figure 3.12b, black line) progressively shifts to the blue with the first, 362 nm 

(blue line), and the second oxidations, 333 nm (red line). Since this intense sharp band 

in the neutral state is composed of transitions emerging from the helicene and the HBC 

moieties, the described shifting upon oxidation supports that, the charge is jointly 

stabilized by the two structural units.  

3.3.3 Photophysical Properties  

The spectroscopic properties of the bilayer nanographenes were evaluated by UV-vis 

absorption (summarized in Table 3.2) and emission measurements (summarized in 

Table 3.3). Bilayer nanographenes [9]HBNG, [10]HBNG and [11]HBNG display 

non-structured and broad bands in the absorption spectra (Figure 3.13, solid lines), 

which contrast to the structured absorption bands corresponding to tBu-HBC. HBNGs 

show slightly bathochromically sifted maxima in the 373-377 nm interval, compared 

to the tBu-HBC maximum at 360 nm. Interestingly, bilayer nanographenes show 

allowed electronic transitions in the visible region above 400 nm (absorption 

coefficients >104 M−1·cm−1). 

 

(a) (b)tBu-HBC [9]HBNG

540
934

362

333



Chapter 3 

108 

 

Table 3.2. Data from absorption spectra of the HBNGs and tBu-HBC. 

Compound λabs
max /nm (ε /M−1·cm−1) 

tBu-HBC  344 (63,750); 360 (141,700); 390 (46,350); 439 (1,600); 441 (1,650); 445 

(1,800) 

[9]HBNG 349 (94,600); 373 (136,000); 392 (86,300); 435 (20,600); 502 (6,200); 542 

(4,700) 

[10]HBNG 360 (98,600); 377 (103,900); 415 (38,800); 446 (18,700); 462 (14,400); 494 

(8,700) 

[11]HBNG 339 (70,800); 377 (125,000); 415 (58,200); 444 (26,100); 491 (7,300) 

The emission spectra of the three bilayer nanographenes show broad red-shifted non-

structured bands with maxima at 575 nm ([9]HBNG), 543 nm ([10]HBNG), and 528 

nm ([11]HBNG), while the rigid and flat monolayer nanographene tBu-HBC shows a 

well-structured spectrum with a maximum at 484 nm. Interestingly, the lower π-

extended and totally overlapped structure (with larger π-π interactions, Figure 3.9) 

[9]HBNG, shows the most bathochromically shifted fluorescence, being in agreement 

with the electrochemical properties previously described ([9]HBNG shows the 

strongest donor character). 

As illustrated in Figure 3.13 (shaded curves), the emission spectra of HBNGs show 

two main features: (i) in shape, they resemble the emission spectra of helicenes with 

one molecular band disclosing vibronic resolution and (ii) the pronounced broadening 

is typical of excimer-type emissions. The most red-shifted excimer-like band of 

[9]HBNG, agrees with larger π-π interactions resulting from the total overlapping of 

this bilayer. 

  

Figure 3.13. Absorption (solid lines) and emission (shaded curves) spectra of tBu-HBC, 

[9]HBNG, [10]HBNG and [11]HBNG. Picture in the right show samples of the three bilayer 

nanographenes in CHCl3 under 365 nm irradiation. 



Chapter 3 

109 

 

The fluorescence quantum yields were determined by comparison with the emission 

spectra of riboflavin in ethanol (Φem= 0.3±0.03). The variations in the obtained 

fluorescence quantum yields, Φem= 0.22 for [9]HBNG > Φem= 0.10 for [10]HBNG ~ 

Φem= 0.11 for [11]HBNG, do not follow the expected order considering the band gaps 

(estimated from the intersection between the normalized excitation and emission 

spectra), E0-0[9]HBNG= 2.35±0.09 eV < E0-0[10]HBNG= 2.49±0.09 eV < and E0-0 

[11]HBNG= 2.58±0.09 eV. However, this can be partially attributed to the different 

contributions of excimer-like emission in HBNGs. Hence, the structure with the lower 

band gap, totally overlapped [9]HBNG, presents the highest fluorescence quantum 

yield due to the more accentuated excimer-like emission. 

Table 3.3. Data from excitation and fluorescence spectra of the HBNGs and tBu-HBC. 

Compound λem
max /nm (shoulder) E0-0 /eV Φem 

tBu-HBC  
445, 454, 464, 475, 484, 493, 

518, 528, (537), 556, 567 
2.65±0.13 0.02±0.01 

[9]HBNG 575 (611) 2.35±0.09 0.22±0.02 

[10]HBNG 543 (567) 2.49±0.09 0.10±0.01 

[11]HBNG 528 (551) 2.58±0.09 0.11±0.01 

The fluorescence decays of HBNGs are shown in Figure 3.14. While [9]HBNG and 

[10]HBNG required multiexponential fittings of the decay function, [11]HBNG 

exhibited a monoexponential behavior. The calculation of the discrete lifetime 

components (see Appendix 3, photophysical details) provided the intensity-weighted 

average lifetimes, 13.4 ns for [9]HBNG, 12.2 ns for [10]HBNG, and 8.7 ns for 

[11]HBNG.  

 

Figure 3.14. Fluorescence decay profiles of [9]HBNG (left), [10]HBNG (middle) and 

[11]HBNG (right) in chloroform, obtained at different emission detection wavelengths with 

excitation at 405 nm. Instrument response functions (IRF) are shown in red. 

From the amplitude-weighted fluorescence average lifetimes, and fluorescence 

quantum yields, the radiative (kr) and non-radiative (knr) deactivation rate constants of 

the respective singlet excited states were calculated. All three structures present 

similar kr (ca 1−2·107 s−1). However, there is a significant difference between non-

0 50 100 150

1E-4

0.001

0.01

0.1

1

N
o
rm

a
liz

e
d
 i
n
te

n
s
it
y

t[ns]

HB-11

 IRF

 530 nm

 560 nm

[11]HBNG

IRF

530 nm

560 nm

0 50 100 150

1E-4

0.001

0.01

0.1

1

N
o
rm

a
liz

e
d
 i
n
te

n
s
it
y

t[ns]

HB-10

 IRF

 507 nm

 540 nm

 570 nm

 630 nm

[10]HBNG

IRF

507 nm

540 nm

570 nm

630 nm

0 50 100 150

1E-4

0.001

0.01

0.1

1

N
o
rm

a
liz

e
d
 i
n
te

n
s
it
y

t[ns]

HB-9

 IRF

 512 nm

 578 nm

 620 nm  

[9]HBNG

IRF

512 nm

578 nm

620 nm



Chapter 3 

110 

 

radiative deactivation constants (knr), being of 7.0·107 s−1 for totally overlapped 

[9]HBNG, 1.5·108 s−1 for partially overlapped [10]HBNG, and 1.0·108 s−1 for the 

shifted structure [11]HBNG, which means that the layer overlapping, and subsequent 

stronger π-π intramolecular stacking, hinders the structural mobility favoring the 

radiative deactivation. The greater the overlap, the higher the emission quantum yields 

and the longer the fluorescence lifetimes. 

The three bilayer nanographenes were characterized by Raman spectroscopy in solid 

state using different excitation laser wavelengths to avoid the adverse effect of 

fluorescence. For [10]HBNG and [11]HBNG, Raman spectra were obtained at 1064 

nm. For [9]HBNG they were obtained by excitation in the UV region with the 325 

nm laser Raman line, since the intense fluorescence and reabsorption in the NIR 

region prevented obtaining quality Raman spectra at 1064 nm.  

As shown in Figure 3.15, all Raman spectra present two main groups of bands at 1600 

and 1350-1300 cm−1, which correspond to the Raman G and D bands typical of 

vibrational Raman spectra of graphene (see Appendix 3, Figure AP3.2, theoretical 

Raman spectra and assignments of the most representative Raman bands in terms of 

vibrational normal modes). In particular, the Raman spectrum of [10]HBNG 

represents the molecular version of the full Raman spectrum of graphene and 

multilayer graphene (Figure 3.15, left). The face-to-face packing of the graphitized 

layers leads to the activation and appearance of bands associated with the double and 

triple wavenumbers of the fundamental phonon Raman vibrations. The appearance of 

these multiphonon bands at 2779 and 2711 cm−1 (i.e., 2D and 2G) is an intrinsic 

feature observed when switching from graphene to multilayer graphene. 

 

Figure 3.15. Left, solid-state Raman spectrum of [10]HBNG. Right, solid-state Raman spectra 

of tBu-HBC (a), [9]HBNG (b), [10]HBNG (c), and [11]HBNG (d). 

The Raman spectrum of [10]HBNG shows the highest similarity to that of tBu-HBC 

in the region of the G Raman band at 1613 cm−1, whereas the G band of [9]HBNG at 

1630 cm−1 shows the highest difference from tBu-HBC. This variation from 1613 (tBu-

HBC) to 1630 cm−1 ([9]HBNG) may be related to the vibrational mixing of the C−C 

bond stretching of the HBC moiety with that of the helicene (Appendix 3, Figure 

AP3.3). 

3000 2700 2400 2100 1800 1500 1200 900 600

1379 1341

1361

N
o

rm
. 
R

a
m

a
n

 I
n

t.

Raman Shift (cm
-1

)

2711
2779

1800 1700 1600 1500 1400 1300 1200 1100 1000

a

d

c

b1370

13261355

1605

13411361
1613

13671630

13231601

N
o

rm
. 
R

a
m

a
n

 I
n

t.

Raman Shift (cm
-1

)

1613



Chapter 3 

111 

 

3.3.4 Chiroptical Properties of HBNGs 

The racemic mixtures of HBNGs were resolved by means of semipreparative chiral 

HPLC (Chiralpak IE column) using heptane and 1% isopropyl alcohol in toluene as 

mobile phase. All enantioenriched samples showed remarkable enantiomeric excess 

(between 98-99 ee), except for (+)-[10]HBNG that was isolated with a 73% ee 

(Appendix 3).  

 

Figure 3.16. CD spectra of the enantioenriched samples of HBNGs, including the gabs values. 

Scaled by a factor of 1.4 for [10]HBNG considering the purity. 



Chapter 3 

112 

 

The circular dichroism of the six enantioenriched samples showed specular image 

signals for each pair of enantiomers. As illustrated in Figure 3.16, the CD spectra of 

[10]HBNG and [11]HBNG present similar Cotton effects in the visible region, with 

distinguishable contributions corresponding to the helicene backbone and the HBC at 

380 and 450 nm, respectively. Yet, the CD spectra of [9]HBNG show three regions 

with prominent cotton effects in the visible range, the one observed for the longer 

helical bilayers, at 380 nm, and two more at 400 nm and 450 nm, evidencing the mixed 

contributions of the helicene and the HBC, and suggesting the involvement of the 

overlapping in the chiroptical properties.  

The circularly polarized luminescence (CPL) was also recorded for the six 

enantioenriched chiral bilayer nanographenes, Figure 3.17. The three structures 

exhibit intense CPL signals with remarkable asymmetry factors (i.e., glum= 

2(IL−IR)/(IL+IR), IL and IR being the left- and right-handed luminescent emissions, 

respectively).  

 

Figure 3.17. Circularly polarized luminescent (CPL) and normalized emission (PL) spectra of 

(+)- and (−)-HBNGs. 

The |glum| values, as shown in Table 3.4, range from 1.0·10−2 to 3.6·10−2, and are of 

the same order as the circular dichroism dissymmetry factors (gabs), reflecting small 

structural and electronic reorganization of the excited state prior to the emission 

process. Interestingly, the much higher values were obtained for [9]HBNG (|glum|= 

3.610−2 at 580 nm), being remarkable for structures formed only by carbon and 

hydrogen. As proposed by Zinna and co-workers,146 CPL brightness should be 

considered as a unified measure of circularly polarized emission properties. This value 

is calculated from the absorption coefficient, the CPL dissymmetry factor, and the 

quantum yield (BCPL= ε·Φem·glum/2). Thus, the molecular nanographenes described 

 
146 L. Arrico, L. Di Bari, F. Zinna, Chem. Eur. J. 2021, 27, 2920 

Wavelength (nm)

Δ
I 

/ 
1

0
−

2

−4

−2

0

2

4

N
o
rm

a
liz

e
d

P
L

1

0

(−)-[9]HBNG

(−)-[10]HBNG

(+)-[9]HBNG

(−)-[11]HBNG

(+)-[10]HBNG

(+)-[11]HBNG

450 500 550 600 650 700 750 800



Chapter 3 

113 

 

have the following values, BCPL[9]HBNG= 81, BCPL[10]HBNG= 21, and 

BCPL[11]HBNG= 28. 

Table 3.4. Experimental dissymmetry factors from circular dichroism (gabs) and circularly 

polarized luminescence (glum). 

Compound gabs /10−2 (λ, nm) glum /10−2 (λ, nm) 

(+)-[9]HBNG +3.6 (540) +3.6 (580) 

(−)-[9]HBNG −2.8 (540) −3.6 (580) 

(+)-[10]HBNG +1.4 (502) +1.1 (540) 

(−)-[10]HBNG −1.6 (502) −1.0 (540) 

(+)-[11]HBNG +1.0 (490) +0.8 (535) 

(−)-[11]HBNG −1.0 (490) −0.9 (535) 

The experimental glum values agree with the theoretically calculated (TD-DFT) from 

the quantum chemical quantities, the electric transition dipole moment (ETDM, μ) 

and the magnetic transition dipole moment (MTDM, m) according to the equations; 

R= |μ||m|cosθ and gabs= (4|m|/|μ|)cosθ. Adopting the accepted approach of discussing 

the experimental glum compared with the computationally available gabs when emission 

and absorption correspond to the same lowest energy electron transition, the equation 

can be also considered as glum= (4|m|/|μ|)cosθ. The TD-DFT calculations nicely predict 

the experimental order of magnitude and variation of the glum for the three compounds, 

as shown in Figure 3.18. 



Chapter 3 

114 

 

 

Figure 3.18. Direction, moduli and values of the ETDM (blue arrow) and MTDM (red arrows), 

angles between the vectors (θ), and calculated glum values for [9]HBNG, [10]HBNG and 

[11]HBNG, calculated at the optimized CAM-B3LYP/3-21G* geometry. 

The moduli of the ETDM and MTDM transition vectors are higher for [9]HBNG, and 

display the smallest angle (θ= 3.4º, smallest angle entails largest cosine); thus, 

resulting in higher dissymmetry factor value for [9]HBNG. The structural design of 

[9]HBNG results optimal for increasing the gabs and glum. The balanced π-extension 

of the chromophore between the planar HBC (promoting large ETDM) and the 

helicene (promoting large MTDM) is an appealing alternative to obtain good emission 

and chiroptical properties. 

 

 

 

 

ETDM |μ|=1.0160·10−18 esu·cm

MTDM |m|=2.6270·10−21 erg/Gauss

θ=3.4º       glum_calc=1.03·10−2

ETDM |μ|=0.9453·10−18 esu·cm

MTDM |m|=1.4014·10−21 erg/Gauss

θ=17.78º       glum_calc=0.56·10−2

ETDM |μ|=0.8385·10−18 esu·cm

MTDM |m|=1.7485 ·10−21 erg/Gauss

θ=63.51º       glum_calc= 0.37·10−2

[9]HBNG

[10]HBNG

[11]HBNG



Chapter 3 

115 

 

3.4 Conclusions 

To conclude, the synthesis and characterization of two new HBNGs, [9]HBNG and 

[11]HBNG, have been carried out following a methodology similar to that described 

for [10]HBNG.136 The structures have been unequivocally characterized by single-

crystal X-ray diffraction, which has allowed the understanding of the unique bilayer 

arrangement of the layers. The great variations in the overlapping are clearly shown 

by the number of rings involved in the π-π interactions, 26 for totally overlapped 

bilayer [9]HBNG, 14 for partially overlapped bilayer [10]HBNG, and 10 for the 

shifted nanographene [11]HBNG. 

The systematic and comparative study of the properties demonstrate the strong 

influence of the overlapping degree on the optoelectronic properties. Cyclic 

voltammetry measurements unexpectedly showed that the strongest electron donor 

character corresponded to the less π-extended structure [9]HBNG. The in situ 

registration of UV-vis-NIR spectra upon oxidation (spectroelectrochemical 

measurements) showed a red shifting of the bands at higher wavelengths, in the 

absorption spectrum corresponding to the radical cation of [9]HBNG. Thereby 

revealing a charge delocalization between the two HBC layers contributing to a lower 

oxidation potential, i. e. mixed valence band effect. Actually, this intramolecular 

through-space communication supports the differences found in the emission spectra 

of the three bilayers, the most red-shifted maximum corresponds to [9]HBNG, 

followed by [10]HBNG and [11]HBNG. Additionally, the total overlapping of the 

layers is related to the greater fluorescence quantum yield of [9]HBNG, the rigidity 

enhanced by the strong π-π interactions favors the relative radiative deactivation. 

Interestingly, the dissymmetry factors gabs and glum determining the intensity of the 

chiral absorption (CD) and emission (CPL) properties, show greater values for the 

totally overlapped structure [9]HBNG, with values as high as g= 3.6·10−2. These 

values are among the highest reported in literature for carbon and hydrogen 

compounds. 

The experimental findings about this family of HBNGs, demonstrate the influences 

of the unique intramolecular π-π interactions between the covalently connected HBC 

layers over the properties. 



 

 

 

 

  



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 4 

 

  



 

 

 

 

 



Chapter 4 

119 

 

4 Chapter 4 

4.1 Introduction to Stereochemical Control in Nanographenes 

Chirality is a geometrical property, whereby a structure is not superimposable with its 

mirror image. As seen in Chapter 3, it gives rise to properties of high interest in 

advanced materials. However, the determination and application of these properties 

may be challenging since, as seen in Chapter 2, the retention of properties with time 

depends on the energy of the isomerization barriers. Moreover, it is necessary to 

isolate the enantiomers to determine these properties associated to enantioenriched or 

enantiopure samples. Most chiral nanographenes syntheses described in the literature 

lead to racemic mixtures, which involves the subsequent separation of the enantiomers 

by chiral HPLC. These separations are usually complex, time consuming and 

expensive, as well as being a limitation to obtain enantiopure samples in quantities of 

more than a few milligrams.  

4.1.1 Enantioselective Synthesis of Nanographenes 

Alternatively, to avoid the separation process, the enantioselective synthesis of 

nanographenes leading to the controlled formation of enantiomers is very appealing 

and challenging. The enantioselective, or asymmetric, synthesis aims at the 

preferential formation of one enantiomer over another during a chemical reaction. For 

this purpose, a chiral auxiliar component of defined configuration interacts with a 

prochiral molecule generating diastereotopic reactive positions. This difference 

between the reactive positions causes the reaction to evolve preferentially through the 

one with the lowest energy. The configuration of the chiral auxiliary determines the 

preferential interaction with the prochiral molecule, and therefore the 

enantioselectivity of the process. 

In this context, our research group has set a milestone reporting the first 

enantioselective synthesis of a molecular nanographene.147 As shown in Scheme 4.1, 

the enantioselective synthesis starts with previously prepared indandione 4.1, 

containing a polyarene (PAB: pentaaryl benzene). The enantioselective reduction of 

the carbonyl groups, performed in the presence of the S-(4-

methoxy)phenyloxazaborilidine 4.2 and borane, affords the trans-diol S,S-4.3 

(enantiomeric excess, e.e.>97%) and meso-4.3 (cis compound) in 70:30 

diastereomeric ratio. Then, the enantioenriched diol S,S-4.3 undergoes a 

stereoselective intramolecular Friedel-Crafts reaction in which the ortho-position at 

five-bonds distance, attacks the asymmetric carbon with inversion of the configuration 

(via SN2), affording S,S,Sa-4.4 with an e.e.> 97%. The last step is the Scholl reaction, 

which eventually leads to the graphitized chiral nanographene S,S,Sa,M,M-4.5 with an 

enantiomeric excess of 97%. The enantiospecific performance of the final Scholl 

reaction to form M-[6]helicenes allows the retention of the chiral information. 

 
147 M. Buendía, J. M. Fernández-García, J. Perles, S. Filippone, N. Martín, Nat. Synth. 2024, 3, 545. 



Chapter 4 

120 

 

Moreover, if the first enantioselective reduction of 4.1 is performed in the presence of 

the R enantiomer of oxazaborilidine 4.2, nanographene R,R,Ra,P,P-4.5 is obtained 

with a 98% enantiomeric excess.   

 

Scheme 4.1. Enantioselective synthesis of a two-fold inherently chiral nanographene. 

Therefore, the success achieved with this synthesis proves a high stereochemical 

control for the enantioselective preparation of sophisticated carbon nanostructures. 

From the first enantioselective reduction step, a chiral asymmetric carbon (point 

chirality) is generated, subsequently this chirality is transferred to enantioselectively 

obtain a spirocycle (axial chirality), whose configuration entails the enantiospecific 

graphitization reaction in which two helicenes are formed (helical chirality). It is 

worth mentioning that this last step represents the first enantioselective Scholl reaction 

reported in the literature since its first report in 1910. 

4.1.2 Chirality Transference: from Atropisomerism to Helical Chirality 

Alternatively, axially chiral atropisomers have been frequently considered a powerful 

chiral auxiliar to control the helical configuration of helicenes and heterohelicenes. 

The first example was reported in 1972 by Both et al. As represented in Scheme 4.2, 



Chapter 4 

121 

 

the optically pure biphosphonium periodate S-binaphthyl 4.6 with lithium ethoxide 

afforded optically pure P-[5]helicene (4.7).148  

 

Scheme 4.2. First synthesis of optically pure P-[5]helicene through chirality transference from 

an optically pure binaphthyl derivative. 

In 1994, Hanus and coworkers demonstrated the effective intramolecular chirality 

transference from axial chirality to point chirality, and eventually to helical chirality, 

Scheme 4.3. The first key step is the chirality transference during the Stevens 

rearrangement. The enantiopure dinaphthyl azepinium salt S-4.8, under basic 

conditions affords a single enantiomer R,3R-4.9. The obtained compound R,3R-4.9 in 

presence of m-chloroperbenzoic acid undergoes a Cope elimination providing the 

enantiomerically pure P-[5]helicene 4.10, which was also obtained from the 

enantiomerically pure derivative S-4.8 in presence of butyl lithium.149 

 

Scheme 4.3. Synthesis of optically pure [5]helicene from intramolecular chirality transference. 

The synthesis of optically pure sulfur-containing heterohelicenes 4.11 was 

successfully achieved by Osuga et al. in 1997. The optically pure dialdehyde 4.12 was 

obtained through chemical resolution of the precursors. Thus, the McMurry coupling 

reaction from compound 4.12 yields the heterohelicene P-4.11 with axial to helical 

chirality transference, Scheme 4.4.150 

 
148 H. Jürgen Bestmann, W. Both, Angew. Chem. Int. Ed. Engl. 1972, 11, 296. 
149 I. G. Stará, I. Starý, M. Tichf, J. Závada, V. Hanus, J. Am. Chem. Soc. 1994, 116, 5084. 
150 K. Tanaka, H. Suzuki, H. Osuga, J. Org. Chem. 1997, 62, 4465. 



Chapter 4 

122 

 

 

Scheme 4.4. Axial to helical chirality transference during McMurry coupling. 

In 2005 Nozaki and coworkers reported the synthesis of the azahelicene P-4.13 from 

the enantiomerically pure bisphenantryl derivative S-4.14, obtained by chemical 

resolution. The stereospecific double N-arylation leads to the aza[7]helicene with 

optical purity retention, Scheme 4.5.151 

 

Scheme 4.5. Stereospecific double N-arylation to afford an optically pure aza[7]helicene. 

Alternatively, Collins and coworkers reported in 2008, the first application of olefin 

metathesis to obtain helicene molecules, Scheme 4.6. They described a kinetic 

resolution by means of asymmetric ring-closing metathesis from the bisphenanthrene 

derivative 4.15 in presence of a chiral ruthenium catalyst to afford [7]helicene (4.16) 

with a maximum 80% e.e.152 Therefore, in this case, the catalyst is the responsible 

species for the induction of chirality. 

 

Scheme 4.6. Kinetic resolution and asymmetric metathesis for the synthesis of carbohelicenes. 

Starting from enantiopure commercially available R-BINOL, Hu and coworkers 

reported the diastereoselective photochemical synthesis of BINOL-fused helicenes, 

 
151 K. Nakano, Y. Hidehira, K. Takahashi, T. Hiyama, K. Nozaki, Angew. Chem. Int. Ed. 2005, 44, 7136. 
152 A. Grandbois, S. K. Collins, Chem. Eur. J. 2008, 14, 9323. 



Chapter 4 

123 

 

Scheme 4.7. The photocyclization of R,R-4.17 provides the [7]helicenes mixture 

M,R,R-4.18 and P,R,R-4.18 in 2.5:1 ratio, respectively.153 

 

Scheme 4.7. Stereoselective photochemical synthesis of helicenes. 

In the following Scheme 4.8, the synthesis of the enantioenriched [5]helicene 4.19 

with chirality transference from the enantioenriched atropisomer 4.20, is represented. 

As already described in previous examples, the optical purity of the starting material 

with axial chirality determines the optical purity of the helical feature. Therefore, the 

kinetic, chemical or HPLC resolution of the atropisomers is usually required. In this 

case, Ackermann and coworkers reported an asymmetric metalla-electrocatalyzed 

C−H activation for the preparation of the enantioenriched biaryl derivative 4.20.154 

 

Scheme 4.8. Asymmetric metalla-electrocatalysis for the preparation of an atropisomers and 

chirality transference to a [5]helicene derivative. 

Yashima et al. have recently reported the simultaneous enantiopure synthesis of the 

[7]helicene 4.21 and the non-benzenoid[6]helicene 4.22, with opposite helicity, 

Scheme 4.9. The enantiomerically pure S,S-5,6-di(1-naphthyl)benzene derivative 4.23 

 
153 S. Chen, Z. Ge, Q. Jia, K.-P. Wang, L.-H. Gan, Z.-Q. Hu, Chem. Asian J. 2019, 14, 1462. 
154 U. Dhawa, C. Tian, T. Wdowik, J. C. A. Oliveira, J. Hao, L. Ackermann, Angew. Chem. Int. Ed. 2020, 

59, 13451. 



Chapter 4 

124 

 

(isolated by chiral HPLC) in presence of trifluoroacetic acid undergoes two stepwise 

intramolecular alkyne annulations. The helical handedness of the resulting helicenes 

is determined by the double axial precursor. 155  

 

Scheme 4.9. Enantiopure synthesis of [7]helicene and non-benzenoid[6]helicene derivatives. 

These examples representatively illustrate the wide variety of reactions that can be 

carried out with axial-to-helical chirality transference. The suitable design of the 

precursor, as well as the methodology to be followed, are key to obtain efficient 

enantiomeric excesses. Typically, the enantiopurity of the axially chiral precursor 

determines the enantiopurity of the resulting helical feature. In the common case 

where the precursor presents two enantiomers, chiral HPLC can be used for its 

isolation. However, an affordable and easy to scale-up methodology is the chemical 

resolution to obtain diastereomers that can be isolated by a common silica gel 

chromatography column.   

 
155 T. Ikai, K. Oki, S. Yamakawa, E. Yashima, Angew. Chem. Int. Ed. 2023, 62, e202301836. 



Chapter 4 

125 

 

4.2 Objectives 

The main objective of this chapter is the enantiospecific synthesis of helical bilayer 

nanographene. The synthetic design for this purpose consists on the chirality 

transference from the axial chirality of BINOL-based polyarene derivatives to the 

helical chirality characteristic of helical bilayer nanographenes (HBNGs, Chapter 3). 

The strategy is based on the chemical resolution of the polyarene enantiomers with 

axial chirality for the subsequent enantiospecific Scholl reaction. This easily scalable 

methodology starts from simple and commercially affordable building blocks, which 

allows the simplification of the synthetic route while avoiding the costly HPLC 

separation of enantiomers. 

 

Once the synthetic objective was fulfilled, the optoelectronic and chiroptical 

properties were determined. The resulting structure consists of an oxa[9]helical 

bilayer nanographene. The detailed analysis of the nanographene by single-crystal X-

ray diffraction showed the great overlapping of the layers, which is strongly related to 

the variation of the optoelectronic properties as described in the previous Chapter 3. 

However, the electron donor character of the oxygen atom embedded in the helicene 

backbone, modulates the optoelectronic properties, specifically those related to the 

electron-acceptor character of the nanographene. 

  



 

126 

 



Chapter 4 

127 

 

4.3 Results and Discussion: oxa-Helical Bilayer Nanographenes 

4.3.1 Enantiospecific Synthesis of oxa-Helical Bilayer Nanographenes 

In this chapter, the synthesis and characterization of oxa[9]helical bilayer 

nanographene, oxa[9]HBNG, is described. In contrast to the synthesis of [9]HBNG 

described in Chapter 3.3.1, the synthetic methodology starts from 7-bromo-2-naphtol 

instead of requiring the previous preparation of dichloro[5]helicene. Thus, as detailed 

in Scheme 4.1, the first step is an oxidative homocoupling of 7-bromo-2-naphtol (22), 

mediated by a Cu-TMDA catalyst, affording 7,7'-dibromo-1,1'-binaphthyl-2,2'-diol 

(23). Then, a two-fold Sonogashira coupling is performed between the 7,7′-

dibromobinol 23 and two equivalents of 4-(tert-butyl)phenylacetylene (3), providing 

7,7'-bis[(4-(tert-butyl)phenyl)ethynyl]-1,1'-binaphthalyl-2,2'-diol (24). The resulting 

alkynyl containing BINOL was assembled with the cyclopentadienone 5 to perform a 

double Diels-Alder cycloaddition, after in situ carbon monoxide extrusion, the BINOL 

core endowed with two penta(4-tert-butylphenyl)benzene groups is obtained with 

remarkably good yield, 93%. Finally, the Scholl cyclodehydrogenation is performed 

with DDQ and triflic acid. During this last step, twelve carbon-carbon bonds are 

formed providing the graphitization. In addition, the cyclodehydration of the phenol 

groups yields a carbon-oxygen bond formation affording a furane-embedded helicene 

backbone, and thus, the helical bilayer nanographene oxa[9]HBNG.  

 

Scheme 4.1. Synthesis of racemic oxa[9]HBNG from 7-bromo-2-naphtol. 

The building block 1,1'-binaphthyl-2,2'-diol, commonly known as BINOL, is a widely 

used core in synthesis.156  The reactive phenol groups and the axial chirality are the 

 
156 J. M. Brunel, Chem. Rev. 2005, 105, 857. 



Chapter 4 

128 

 

perfect combination for a wide variety of applications. Thus, it has been broadly used 

in asymmetric catalysis, for the design of sophisticated chiral ligands for 

catalysts,157,158 but also in materials chemistry, for instance, as a chiral feature linked 

to photoactive BODIPY dyes,159 and [6]cycloparaphenylene,160 giving rise to 

remarkable chiroptical properties. Furthermore, Mateo-Alonso et al. have recently 

reported the use of 1,1′-binaphthyl-2,2′-diamine for the asymmetric chirality induction 

in a twistacene nanoribbon.161 The covalent binding of two configurationally stable 

biphenyls at the ends of the nanoribbon induce the twisting of the structure with 

conformational discrimination. 

The chirality of 1,1′-binaphthyl derivatives arises from the restricted rotation of the 

naphthyl units around the single bond. The steric hindrance between the hydrogens in 

the positions 8,8′ entails a 23 kcal·mol−1 isomerization barrier in 1,1′-binaphthyl. 

Further functionalization in the 2,2′ positions to obtain 1,1′-binaphthyl-2,2′-diol 

(BINOL) increases the isomerization barrier up to 38 kcal·mol−1, providing 

configurational stability at room temperature.162 

The incorporation of a BINOL core in the structure, as shown in Scheme 4.1, provides 

great versatility considering the configurational stability of the isomers. In addition, 

its reactivity to form furan embedded oxa-helicenes163 provides the possibility of 

modulating, and improving, the optoelectronic and chiroptical properties, as 

demonstrated by different studies of heterohelicenes.164,165,166 

The gram scale synthesis of helical bilayer nanographenes (HBNGs) is still limited 

due to several step synthetic routes. As detailed in Chapter 3, these molecular 

nanographenes have proven remarkable chiroptical properties, however, their 

application as CD or CPL active materials requires the expensive separation of 

enantiomers by chiral HPLC.  

Herein, the easily scalable enantiospecific synthesis of oxa[9]HBNG from low cost 

commercially available starting materials, is described. As detailed in Scheme 4.2, the 

enantiopure preparation of oxa[9]HBNG starts with the functionalization of the 

polyarene 25 with 1R-10-camphorsulphonyl chloride, affording two diastereomers, 

R,M-26a and R,P-26b, easily isolable by silica gel column chromatography. 

 
157 J. Aydin, K. S. Kumar, M. J. Sayah, O. A. Wallner, K. J. Szabó, J. Org. Chem. 2007, 72, 4689 
158 R. Kshatriya, ACS Omega 2023, 8, 17381. 
159 J. Jiménez, R. Prieto-Montero, S. Serrano, P. Stachelek, E. Rebollar, B. L. Maroto, F. Moreno, V. 

Martinez-Martinez, R. Pal, I. García-Moreno, S. de la Moya, Chem. Commun., 2022, 58, 6385. 
160 K. Sato, M. Hasegawa, Y. Nojima, N. Hara, T. Nishiuchi, Y. Imai, Y. Mazaki, Chem. Eur. J. 2021, 

27,1323. 
161 R. K. Dubey, M. Melle-Franco, A. Mateo-Alonso, J. Am. Chem. Soc. 2022, 144, 2765. 
162 N. V. Tkachenko, S. Scheiner, ACS Omega 2019, 4, 6044. 
163 J. Areephong, N. Ruangsupapichart, T. Thongpanchang, Tetrahedron Lett. 2004, 45, 3067. 
164 C. A. Guido, F. Zinna, G. Pescitelli, J. Mater. Chem. C, 2023, 11, 10474. 
165 L. Zhang, I. Song, J. Ahn, M. Han, M. Linares, M. Surin, H.-J. Zhang, J. H. Oh, J. Lin, Nat Commun. 

2021, 12, 142. 
166 M. Cei, L. Di Bari, F. Zinna, Chirality 2023, 35, 192. 



Chapter 4 

129 

 

Thereafter, the camphorsulphonyl group is removed by basic hydrolysis, affording 

enantiopure BINOL-based polyarenes M-25 and P-25. Finally, the Scholl reaction 

providing the helical bilayer nanographene oxa[9]HBNG occurs enantiospecifically. 

The configurationally stable atropisomers M-25 and P-25 are transformed into helical 

fully conjugated nanographenes due to chirality transference, to obtain enantiopure 

M-oxa[9]HBNG and P-oxa[9]HBNG, respectively. 

 

Scheme 4.2. Enantiospecific synthesis of M-oxa[9]HBNG and P-oxa[9]HBNG from M-25 

and P-25, respectively, after chemical resolution of the enantiomers. 



Chapter 4 

130 

 

The cyclodehydration of BINOL derivatives for the preparation of oxahelicenes is a 

commonly used approach.167 However, the reported reaction conditions in presence 

of Brønsted acids (p-toluene sulfonic acid and trifluoromethane sulfonic acid) require 

high temperatures, commonly reflux of toluene, chlorobenzene or xylene, and long 

reaction times, resulting in lower enantiomeric excesses (e.e.) due to racemization.168 

Alternatively, Sasai et al. reported a one-pot enantioselective oxidative coupling 

followed by intramolecular cyclization using a complex chiral vanadium catalyst, 

affording oxa[9]helicene with a maximum 78% ee.169 

Therefore, the mild reaction conditions (−30 ºC for 40 min) used to perform the 

simultaneous cyclodehydrogenation and cyclodehydration, in presence of DDQ and 

triflic acid, is a suitable and affordable approach towards the enantiospecific synthesis 

of a new oxa-helical bilayer nanographene. The mechanism for the cyclodehydration 

of BINOL-like structures to afford furane-embedded helicenes under acidic 

conditions is known to occur through the formation of cation intermediates,163 as 

shown in Scheme 4.3. The tautomerization of one naphthol group in M-25′ under 

acidic conditions provides the electrophilic oxonium intermediate INT1. The 

intramolecular nucleophilic addition of the proximal hydroxy group to the Si face of 

the oxonium provides the five-membered cyclic hemiacetal INT2. Eventually, upon 

dehydration, the system is rearomatized and enantiopure M-oxahelicene is obtained. 

The face for the attack in the enantiospecific cyclization from INT1 to INT2 is 

determined by the fixed spatial orientation of the naphthol groups, which depends on 

the enantiomer of polyarene 25. 

 

Scheme 4.3. Cyclodehydration mechanism through cation intermediates. 

The enantiomeric excess of the M and P-oxa[9]HBNG were evaluated by chiral 

HPLC (column Chiralpack IC 5μm, 98% hexane 2% toluene:isopropanol 4:1, 

Appendix 4), showing  an e.e.> 99% for M-oxa[9]HBNG and e.e.= 99% for P-

oxa[9]HBNG. Considering the enantiospecific mechanism of the reaction, the 

enantiomeric excess depends on the enantiopurity of the starting materials. The 

hydrolisis conditions to afford P and M-25 are mild enough to prevent racemization, 

therefore the proper separation of the diastereomers by silica gel column determines 

 
167 K. Nakanishi, D. Fukatsu, K. Takaishi, T. Tsuji, K. Uenaka, K. Kuramochi, T. Kawabata, K. Tsubaki, 

J. Am. Chem. Soc. 2014, 136, 7101. 
168 S, Hossain, M. Akter, M. Karikomi, Tetrahedron Lett. 2021, 69, 152948. 
169 M. Sako, Y. Takeuchi, T. Tsujihara, J. Kodera, T. Kawano, S. Takizawa, H. Sasai, J. Am. Chem. Soc. 

2016, 138, 11481. 



Chapter 4 

131 

 

the e.e. of the final bilayer nanographene. The purity of the diastereomers was 

determined by 500MHz 1H-NMR, revealing an excellent isolation (purity > 95%). 

The final products, as well as the intermediates, were completely characterized by 

NMR, mass spectrometry and FT-IR. Polyarene derivatives R,M-26a and R,P-26b  

show clear differences by NMR, as expected from diastereomers. The substitution 

with only one camphorsulfonyl group entails a great asymmetry in the spectra. As 

represented in Figure 4.1, both diastereomers present ten singlets, between 1.11 and 

1.00 ppm, corresponding to the tert-butyl groups, which shows the symmetry loss 

after the functionalization, polyarene 25 exhibits signals corresponding to one half of 

the molecule (Appendix 5. Spectra). Among the large number of signals corresponding 

to pure diastereomers R,M-26a and R,P-26b, three can be highlighted to emphasize 

the shifting differences, being also useful to evaluate the purity of both diastereomers 

(see also Appendix 5. Spectra for further comparison). On the one hand, the aliphatic 

singlets, at 0.84 and 0.58 ppm for R,M-26a, and at 0.81 and 0.60 ppm for (R,P)-26b, 

which correspond to the diasterotopic methyl groups in the bridge positions of the 

camphorsulphonyl substituents. On the other hand, the aromatic singlet at 7.02 ppm 

(R,M-26a) and 7.07 ppm (R,P-26b), corresponding to the 8 or 8′ position in the 

BINOL core. 

 
Figure 4.1. 1H-NMR spectra corresponding to diastereomers (R,M)-26a (top) and (R,P)-26b 

(bottom). 

The 1H-NMR characterization of oxa[9]HBNG exhibits eleven singlets and two 

doublets at low field corresponding to the aromatic protons, and five singlets at high 

field corresponding to the tert-butyl groups, shown in Figure 4.2. The number of 

1H-NMR

26a

1H-NMR

26b

0
.8

4

0
.5

8

0
.8

1

0
.6

0

7
.0

2
7
.0

7



Chapter 4 

132 

 

signals reveals the symmetry of the structure due to a C2 axis. As can be seen, the 

expected phenol signal between 3.50 and 4.00 ppm does not appear in the spectrum, 

which is evidence of closure to form the furan-like cycle. In addition, mass 

spectrometry experiments show the loss of 42 units from 25 (exact mass, 1759.1040) 

to oxa[9]HBNG (exact mass, 1716.8948), which agrees to the formation of 12 C−C 

bonds (24 units), and the loss of 18 units due to cyclodehydration to form a new C−O 

bond. 

 

Figure 4.2. 1H-NMR spectrum corresponding to oxa[9]HBNG. 

Furthermore, the structure of diastereomer R,P-26b, as well as both enantiomers of 

nanographene oxa[9]HBNG, were unequivocally characterized by single-crystal X-

ray diffraction. As detailed in Chapter 2.1, atropisomers are assigned looking along 

the chirality axis that contains the single bond with hindered rotation. Thus, placing 

the naphthalene unit substituted with the camphorsulphonyl group at the front (Cahn-

Ingold-Prelog rules), the BINOL derivatives are P if the order follows clockwise 

rotation, and M if the rotation is anticlockwise. Thus, diastereomer 26b presents the 

P-BINOL core, as represented in Figure 4.3.  



Chapter 4 

133 

 

 

Figure 4.3. Single-crystal X-ray structure of 26b, P-BINOL. 

The analysis of nanographene oxa[9]HBNG by single-crystal X-ray diffraction 

showed a partially overlapped bilayer. The incorporation of the oxa-five-membered 

ring to the [9]helicene entails the opening of the inner rim of the helicene, decreasing 

the number of turns. Thus, 22 benzene rings are involved in the intramolecular π-π 

interactions vs. 26 rings in the case of the totally overlapped structure [9]HBNG, 

(Figure 3.9, Chapter 3.3.1). Enantiomerically pure samples of nanographene 

oxa[9]HBNG were crystallized, thus confirming the expected configuration of the 

helicenes considering the enantiospecific mechanism for the cyclization (Scheme 4.3). 

Thus, polyarene M-25 provides M-oxa[9]HBNG and polyarene P-25 provides P-

oxa[9]HBNG (Figure 4.4). 

 

Figure 4.4. Crystal structures of M-oxa[9]HBNG and P-oxa[9]HBNG from their respective 

enantiopure samples. 

4.3.2 Electrochemical properties  

The electrochemical properties of oxa[9]HBNG were evaluated by cyclic 

voltammetry in a 0.1 M solution of tetrabutylammonium hexafluorophosphate in 

toluene/acetonitrile 4:1 using glassy carbon as working electrode, a reference 

electrode of Ag/AgNO3, and a platinum wire as counter electrode. The oxidation and 

reduction potentials vs. Fc/Fc+ are summarized in Table 4.1, along with the potentials 

of [9], [10] and [11]HBNG for comparison purpose. As shown in Figure 4.5, 

*

P

* P*M



Chapter 4 

134 

 

oxa[9]HBNG presents two quasi-reversible oxidation waves and two quasi-reversible 

reduction waves. The potential of the first oxidation wave E1
1/2ox= 0.37 V is slightly 

higher than the first oxidation potential of [9]HBNG E1
1/2ox= 0.35 V. Comparing the 

oxidation waves with those of nanographene 3.8 E1
1/2ox= 0.9 V (in CH2Cl2), 

oxa[7]helical nanographene reported by Jux et al. in which the HBC layers do not 

show intramolecular π-π interactions,137 oxa[9]HBNG shows a significantly stronger 

donor character. As described for [9], [10] and [11]HBNG, the variation of the π-

extension of the helicene (oxa[7]helicene Jux et al. vs oxa[9]HBNG) does not 

necessarily modulates the donor character in layer-overlapping structures. Therefore, 

it can be concluded that the contribution of heteroatom in the helicene has a lower 

impact over the oxidation potential. Therefore, the strong donor character of 

oxa[9]HBNG is attributed to the overlapping degree between the layers. 

Oxa[9]HBNG exhibits less layer overlapping (22 rings involved in the π-π 

interactions) than [9]HBNG (26 rings involved in the π-π interactions), which 

decreases the mixed valence band effect of the bilayer to stabilize the cation and 

radical cation species between the layers, eventually increasing the oxidation potential 

to 0.37 V.  

 

Figure 4.5. Cyclic voltammogram of oxa[9]HBNG showing the half-wave redox potentials 

vs. Fc/Fc+ in a 1 M solution of tetrabutylammonium hexafluorophosphate in 

toluene/acetonitrile 4:1. 

However, the oxygen embedded in the helicene seems to be more important regarding 

the electron acceptor character of oxa[9]HBNG. As described in Chapter 3.3.2, the 

LUMO orbitals of [9], [10] and [11]HBNG, are mainly located in the helicene 

backbones, Figure 3.11. In the case of oxa[9]HBNG, the electron-donor character of 

both the helicene (due to the electron-donor character of the oxygen), and the HBC 

layers, entails the destabilization of the LUMO orbital. Thus, the potential of the first 

reduction wave increases (in absolute value) to E1
1/2red= −2.27 V, revealing a weaker 

electron acceptor character vs. [9], [10] and [11]HBNG (Table 4.1), and even tBu-

HBC (E1
1/2red= −2.24 V). 

1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5

x

x

x

x

-2.52

-2.27

0.66

 

 

C
u
rr

e
n
t

Potential [V] vs, Fc/Fc
+

 CV oxa[9]HBNG

0.37



Chapter 4 

135 

 

Table 4.1. Half-wave redox potentials of oxa[9]HBNG, [9]HBNG, [10]HBNG and 

[11]HBNG. 

Compound E1
1/2ox (V) E2

1/2ox (V) E1
1/2red (V) E2

1/2red (V) 

oxa[9]HBNG 0.37 0.66 –2.27 –2.52 

[9]HBNG 0.35 0.59 –2.18 –2.46 

[10]HBNG 0.46 0.67 –2.23 –2.55 

[11]HBNG 0.52 0.69 –2.22 –2.46 

4.3.3 Photophysical Properties 

The photophysical properties of oxa[9]HBNG were evaluated by UV-vis absorption 

and emission measurements in chloroform (summarized in Table 4.2). Resembling 

bilayer nanographenes [9], [10] and [11]HBNG, oxa[9]HBNG displays non-

structured broad bands in the ultraviolet region of the absorption spectrum (344, 371, 

398 nm very similar to those of the previously described HBNGs, and more structure 

weak bands in the visible region (450, 476, 498 nm) (Figure 4.6, yellow line). 

 

Figure 4.6. Absorption (solid lines) and emission (shaded curves) spectra of oxa[9]HBNG, 

[9]HBNG, and [11]HBNG in chloroform.  

The emission spectrum of oxa[9]HBNG shows well-structured bands with maxima at 

500, 537 and 580 nm, which contrasts with the broad bands display by [9], [10] and 

[11]HBNG. As illustrated in Figure 4.6, the emission bands (shaded curves) of 

oxa[9]HBNG are blue-shifted with respect to the previously described carbon-based 

HBNGs, and are more comparable to those of tBu-HBC. These observations agree 

with the cyclic voltammetry data previously described. The fluorescence quantum 

yield of oxa[9]HBNG resulted of Φem= 0.26, determined by comparison with the 

emission spectra of fluoresceine in ethanol (Φem= 0.97) at 432 nm. The incorporation 

of the oxygen atom in the helicene, modifies the structure and entails the modification 

of the LUMO orbital, which is not farther localized in the helicene moiety, as for 

 oxa[9]HBNG 

 [9]HBNG 

 [11]HBNG

 
t
Bu-HBC

300 350 400 450 500 550 600 650 700

N
o

rm
a

liz
e

d
 o

p
ti
c
a

l 
d
e

n
s
it
y

Wavelength (nm)



Chapter 4 

136 

 

carbon-based HBNGs. This modification involves the variation of the photophysical 

properties, the emission bands are no longer excimer-like, and the quantum yield 

follows the expected order, in which a greater band gap (E0-0, Table 4.2) entails greater 

quantum yield. 

Table 4.2. Data of absorption and fluorescence spectra of HBNGs. 

Compound λabs
max /nm (ε/ M−1·cm−1) λem

max /nm Φem E0-0/eV 

oxa[9]HBNG 

344 (66,647); 371 (141,645); 398 

(71,296); 449 (23,690); 476 

(18,545); 498 (8,102) 

500, 537, 580 0.30 2.55 

[9]HBNG 

349 (94,600); 373 (136,000); 392 

(86,300); 435 (20,600); 502 

(6,200); 542 (4,700) 

575, 611 0.22 2.35 

[10]HBNG 360, 377, 415, 446, 462, 494 543, 567 0.10 2.49 

[11]HBNG 339, 377, 415, 444, 491 528, 551 0.11 2.58 

4.3.4 Chiroptical properties 

The electronic circular dichroism (CD) has been recorded in chloroform for both 

enantiomerically pure nanographenes M-oxa[9]HBNG and P-oxa[9]HBNG. As 

illustrated in Figure 4.7, the spectra of the enantiomers (P-oxa[9]HBNG, brown solid 

line, and M-oxa[9]HBNG, orange solid line) show specular image signals and two 

main regions with prominent Cotton effects. One intense broad band from the 

ultraviolet region to the visible region (300 nm to 470 nm), and one of lower intensity 

at lower energy in the visible region (480 nm). The absorption dissymmetry factors 

represented with dashed lines in Figure 4.7, are gabs= +3.7·10−3 at 487 nm for M-

oxa[9]HBNG, and  gabs= −1.8·10−3 at 487 nm for P-oxa[9]HBNG.  

 

Figure 4.7. CD spectra and gabs values of M-oxa[9]HBNG and P-oxa[9]HBNG. 

300 325 350 375 400 425 450 475 500

-30

-20

-10

0

10

20

30

 

 CD, M-oxa[9]HBNG

 CD, P-oxa[9]HBNG

Wavelength (nm)

-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

 C
D

 (
m

d
e
g
)

 g
a
b
s

 gabs, M-oxa[9]HBNG

 gabs, P-oxa[9]HBNG



Chapter 4 

137 

 

4.4 Conclusions 

To conclude, in this chapter a new approach for the enantiospecific synthesis of helical 

bilayer nanographenes by an easily scalable methodology, is described. The synthesis 

starts from commercially available 7-bromo-2-naphtol that, in presence of copper (II), 

yields axially chiral dibromoBINOL. Taking advantage of the stable axial chirality 

and reactivity of the obtained BINOL-based structures, a chemical resolution was 

carried out by functionalizing the BINOL-based polyarene with enantiopure 

camphorsulphonyl chloride. After a hydrolysis step under mild conditions, 

enantiopure BINOL-based polyarenes P- and M-25 were obtained, which under 

Scholl reaction conditions lead to the corresponding enantiopure P- and M-

oxa[9]HBNG. During the Scholl oxidation two different types of reactions take place, 

the expected cyclodehydrogenation (providing the graphene like structure), and the 

enantiospecific cyclodehydration of the phenol groups yielding the furane embedded 

helicene (chirality transference from axial to helical). The separation of the 

diastereomers by silica gel column afforded the diastereomers with an isomeric excess 

> 95% (by NMR), the performance of this separation determines the enantiomeric 

excess of the final nanographene (e.e.≥ 99% by chiral HPLC). All structures were 

characterized by the common techniques, and single-crystal X-ray diffraction 

confirmed the configuration of the BINOL core in diastereomeric polyarene R,P-26b 

(P-BINOL) and the corresponding enantiomer obtained after hydrolisis and Scholl 

reaction, P-oxa[9]HBNG. Furthermore, the crystal structure of nanographene 

oxa[9]HBNG showed the great overlapping between the layers, being 22 rings 

involved in the intramolecular π-π interactions. 

The great overlapping of the structure explains the variation of the donor character. 

The influence of the electron-donor character of oxygen in the helicene backbone has 

a lower impact on the redox properties than the influence of the overlapping degree 

between the layers. Comparing oxa[9]HBNG with oxa[7]helical nanographene, 

reported by Jux et al., in which the HBC layers do not show intramolecular π-π 

interactions (E1
1/2ox= 0.9 V in DCM),137 and with the corresponding all-carbon 

nanographene [9]HBNG (E1
1/2ox= 0.35 V), the observed first oxidation potential of 

oxa[9]HBNG (E1
1/2ox= 0.37 V) is mainly influenced by the overlapping degree. The 

slightly higher potential than that of the corresponding carbon-based structure agrees 

with the lower overlapping degree (22 vs 26 rings involved in the π-π interactions in 

oxa[9]HBNG and [9]HBNG respectively). The influence of the electron donor 

character of the oxygen-containing helicene is more reflected in the acceptor 

character. In all carbon structures [9], [10] and [11]HBNG the LUMO is located in 

the helicene feature. However, the electron donor character of the oxa[9]helicene leads 

to a higher energy LUMO orbital. Thus, the first reduction potential for oxa[9]HBNG 

(E1
1/2red= −2.27 V) is closer to that of tBu-HBC (E1

1/2red= −2.24 V). In addition, the 

emission spectra show well-structured bands suggesting the lower excimer-like 

contribution and the delocalization of the LUMO in the layers of the structure instead 



Chapter 4 

138 

 

of delocalized in the helicene moiety. Finally, the chiroptical properties of M- and P-

oxa[9]HBNG have been studied by means of electronic circular dichroism, from 

which gabs values of +3.7·10−3 at 487 nm for M-oxa[9]HBNG, and  −1.8·10−3 at 487 

nm for P-oxa[9]HBNG, have been calculated. 

 

 

 

 

 



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Experimental section 

  



 

 

 

 

 

 

 

  

 



Experimental section 

141 

 

EXPERIMENTAL SECTION 

Unless otherwise noted, all materials including solvents were obtained from 

commercial suppliers and used without further purification. Unless otherwise noted, 

all reactions were performed with dry solvents (dried by filtration through alumina 

according to the method described) and under an atmosphere of argon in dried 

glassware with standard vacuum-line techniques. 

All work-up and purification procedures were carried out with reagent-grade solvents 

in air. Silica column chromatography was conducted with Scharlau 40-60 μm silica 

gel. Analytical thin-layer chromatography (TLC) was performed using Silica gel 60 

F254-coated aluminum sheets (Merck). Flash chromatography was performed on Silica 

gel 60 (0.040-0.063 mm, Merck). The developed chromatogram was analyzed by 

solution of Ce(SO4)2·4 H2O (1%) and H3P(Mo3O10)4 (2%) in sulfuric acid (10%) and 

UV lamp (254 nm and 365 nm).  

Microwave reactions were performed in an Anton-Parr Monowave 300 microwave or 

in an Anton-Parr Monowave 400 microwave reactor.  

1H NMR spectra were recorded at 700 (Bruker AVIII), 500 (Bruker AV), 400 (Bruker 

AVIII) or 300 (Bruker AVIII) MHz and 13C NMR spectra were recorded at 176, 126 

or 101 (Bruker AV) MHz. Chemical shifts for 1H NMR and 13C NMR are expressed 

in parts per million (ppm). For referencing of NMR spectra, the residual solvent signal 

(CDCl3 δ 7.26 ppm for 1H and δ 77.16 ppm for 13C, C6D6 δ 7.16 ppm for 1H and δ 

128.06 ppm for 13C, Tetrachloroethane-d2 δ 6.00 ppm for 1H and δ 73.78 ppm for 13C, 

or Methylene Chloride-d2 δ 5.32 ppm for 1H and δ 54.00 ppm for 13C) was used. Data 

are reported as follows: chemical shift, multiplicity (s= singlet, d= doublet, dd= 

doublet of doublets, t= triplet, q= quartet, m= multiplet, bs= broad singlet), coupling 

constant (Hz), and integration. 

MALDI-ToF matrices were trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylid 

ene]-malononitrile (DCTB) or 1,8-dihidroxi-9,10-dihydroanthracen-9-ona (dithranol) 

and mass analysis were performed in a Bruker Ultraflex II using an LTB MNL 106 

laser source. The APCI mass spectra were recorded using an LTQ Orbitrap XL 

(Thermo Fisher Scientific) hybrid mass spectrometer equipped with an APCI ion 

source. The APCI vaporizer and heated capillary temperatures were set to 400 °C and 

200 °C, respectively; the corona discharge current was 3.5 μA. Nitrogen served both 

as the sheath and auxiliary gas at flow rate 55 and 5 arbitrary units, respectively. The 

ionization conditions were the same for low‐resolution as well as high‐resolution 

experiment. The HR spectra were acquired at a resolution of 100 000. 

IR spectra were recorded on a FT-IR Nicolet Magna 750 spectrometer and in KBr cell 

in CHCl3 solution on Nicolet 6700 FT-IR spectrometer (Thermo Fisher Scientific, 

USA) equipped with a standard mid-IR source, a KBr beam-splitter, and a DTGS 

detector and with a cell compartment purged by dry nitrogen.  



Experimental section 

142 

 

Electrochemical measurements were performed using a standard one-compartment, 

three-electrode electrochemical cell connected to an electrochemical analyzer 

(Metrohm Autolab). The working electrode was a glassy carbon electrode (3 mm 

diameter) that was freshly polished with a suspension of Al2O3 in distilled water and 

sonically rinsed with acetone before each measurement. Silver (Ag/0.1 M AgNO3 in 

CH3CN) and platinum wires were used as reference and counter electrodes, 

respectively. Electrochemical grade (Aldrich) tetrabutylammonium hexafluro-

phosphate 0.1 M in toluene:acetonitrile was used as supporting electrolyte. All 

measurements were conducted under dry argon. Solutions were saturated with argon 

for deoxygenation and to maintain an argon blanket for at least 10 minutes prior to 

each measurement. All measurements are referenced to Fc/Fc+ added as internal 

reference. 

UV-vis absorption spectra of nanographenes 10, 13, 17 and oxa[9]HBNG were 

recorded using a Cary 50 Conc spectrophotometer and quartz cells of 1.0 cm optical 

path length. Emission spectra of nanographenes 10, 13 and 17 were acquired in a 

Fluorolog TC-SPC HORIBA-JOVIN YVON spectrofluorometer in quartz cells of 1.0 

cm optical path length. Samples were dissolved in chloroform (Carlo Erba, for 

analysis, ≥99%) and the solutions were in the 1–5 μM range. UV-vis absorption 

spectra of [9], [10] and [11]HBNG were recorded on a UV-vis spectrophotometer 

(Varian Cary 50) using 1 cm quartz cuvette (Suprasil). Room-temperature 

fluorescence spectra were acquired on a spectrofluorimeter (Horiba FluoroLog 3) 

equipped with a high-pressure Xenon lamp and a Hamamatsu R928P photomultiplier 

tube. Fluorescence spectra of [9], [10], [11]HBNG and oxa[9]HBNG were corrected 

for the characteristics of the lamp source and of the detection system. Fluorescence 

lifetimes (τ) were measuring via time-correlated single photon counting (TCSPC) 

measurements employing an Acton SP2500 spectrometer equipped with a PMA 06 

photomultiplier (PicoQuant) and a HydraHarp-400 TCSPC event timer with 1 ps time 

resolution. The excitation source was a 405 nm picosecond pulsed diode laser (LDH-

D-C-405, PicoQuant) driven by a PDL828 driver (PicoQuant) with FWHM < 70 ps. 

Fluorescence decays were analyzed using PicoQuant Fluofit v4.6.5 data analysis 

software.  

Spectroelectrochemical Measurements. In situ UV-vis-NIR spectroelectrochemical 

oxidations of [9], [10] and [11]HBNG were conducted on a Varian Cary 5000 UV-

vis-NIR spectrophotometer. A C3 epsilon potentiostat from BASi was used for the 

electrolysis using a thin layer cell from a demountable omni cell from Specac. In this 

cell a three electrodes system was coupled to conduct in situ spectroelectrochemistry. 

A Pt gauze was used as the working electrode, a Pt wire was used as the counter 

electrode, and an Ag wire was used as the pseudo-reference electrode. The spectra 

were collected at constant electrolysis potential and the potentials were changed in 

interval of 10 mV. The electrochemical medium used was 0.1 M tetrabutylammonium 



Experimental section 

143 

 

hexafluorophosphate, Bu4NPF6, in fresh distilled dichloromethane, at room 

temperature with sample concentrations of 10−3 M. 

Vibrational Raman Spectroscopy. The 1064 nm Raman spectra of tBu-HBC, 

[10]HBNG and [11]HBNG in solid state at room temperature were measured using 

the RAMII FT-Raman module of a VERTEX 70 FT-IR spectrometer (Bruker). A 

continuous–wave Nd–YAG laser working at 1064 nm was employed for excitation, at 

a laser power in the sample not exceeding 10 mW. Raman scattering radiation was 

collected in a back–scattering configuration with a standard spectral resolution of 4 

cm−1. 10000 scans were averaged for each spectrum. The 325 nm Raman spectrum of 

[9]HBNG in solid state at room temperature was obtained with a JASCO NRS-5000 

dispersive laser Raman spectrometer with a confocal microscope and equipped with 

a Peltier cooled CCD detector operating at –60 ºC. Raman spectrum was recorded by 

averaging spectra during 16 min with a resolution of 1-2 cm–1. 

HPLC analysis of nanographene 17a was collected on an Agilent Technologies 1260 

Infinity HPLC system using Regis Pirkle-type covalently modified silica column (4.6 

× 250 mm) Whelk-O2 (R,R). Injection volume was 0.7 μL, flow rate was 1 mL/min 

and eluent was 98:1:1 hexane:isopropanol:tetrahydrofuran. Peaks were confirmed by 

comparison of their UV-Vis spectra to originate from the enantiomers. HPLC analyses 

of [9], [10] and [11]HBNG were performed on Knauer Smartline 1000/2500 isocratic 

system with polarimetric detector (Chiralyser MP, IBZ Messtechnik) connected to 

Clarity chromatography station. Semipreparative HPLC resolutions were performed 

on PuriFlash 5.250 (Interchim) quaternary gradient HPFC/HPLC system equipped 

with DAD detector. Optical rotations were measured using an Autopol IV instrument 

(Rudolph Research Analytical). HPLC analyses of oxa[9]HBNG were performed on 

JASCO LC-4000 series, dotted with a JASCO PU-4180 RHPLC pump, a JASCO AS-

4050 autosampler, and a JASCO CO-4061 column oven; all connected to a JASCO 

CD-4095 UV-vis and CD detector. The HPLC analytical column used was Chiralpack 

IC (5 μm, 25 cm x 4.6 mm ID). 

The ECD spectra of [9], [10] and [11]HBNG were measured on a Jasco 1500 

spectropolarimeter (JASCO International Co. Ltd.) equipped with a fluorescence 

emission monochromator (FMO522) and separate fluorescence emission detector 

(FDT-538). The ECD spectra were measured over a spectral range of 210 nm to 550 

nm in tetrahydrofuran (10-4 M solutions). Measurements were made in a quartz cell 

with a 0.1 cm path length using a scanning speed of 20 nm/min, a response time of 4 

seconds and standard instrument sensitivity. After a baseline correction, the CD 

spectra were expressed in terms of differential molar extinction (Δε). The ECD spectra 

of oxa[9]HBNG were measured on a JASCO J-1500 CD Spectrometer, over a spectral 

range of 250 nm to 550 nm in chloroform (ca. 10−5 M solutions). Measurements were 

made in a quartz cell with a 1 cm path length using a scanning speed of 50 nm/min, a 

response time of 4 seconds and standard instrument sensitivity. 



Experimental section 

144 

 

The circularly polarized luminescence (CPL) measurements of [9], [10] and 

[11]HBNG were performed using a home-built CPL spectrofluoropolarimeter 

(constructed with the help of the JASCO Company). The samples were excited using 

a 90° geometry with a Xenon ozone-free lamp 150 W LS. The following parameters 

were used: emission slit width ≈ 10 mm, integration time= 8 sec, scan speed= 50 

nm/min, accumulations= 5. The concentration of all the samples was ca. 10−6 M.  

Quantum Chemistry Calculations. Density Functional Theory (DFT) quantum 

chemical calculations were performed with the Gaussian’16 suite of programs.  The 

Becke’s three parameter (B3) gradient-corrected exchange functional was used, and 

the non-local correlation was provided by the Lee-Yang-Parr (LYP) expressions. -To 

achieve an improved description of long-range interactions we used the Coulomb-

attenuating hybrid method (CAM-B3LYP), which includes the Hartree-Fock and the 

Becke exchanges as a variable ratio depending on the intermolecular distance. 

Structural optimizations and spectroscopic features were calculated using the split-

valence 3-21g(d) basis set. Raman spectra were obtained from the calculated DFT 

intensities, and the vibrational wavenumbers uniformly scaled by 0.96.  Every band 

was represented by a Gaussian function of 10 cm−1 half-height width. Electronic 

excitation energies were obtained by using the time dependent DFT (TDDFT) 

formalism   for which up to the fifty low-lying energy states were considered. 

  



Experimental section 

145 

 

Chapter 1 

9,10-Bis[(4-(tert-butyl)phenyl)ethynyl] anthracene (4). 

To a dry  10 mL microwave reactor vial under argon 

atmosphere and provided with a magnetic stir bar, CuI 

(0.180 mmol, 34 mg, 0.4 equiv.), Pd(dppf)Cl2 (0.089 mmol, 73 mg, 0.2 equiv.), 9,10-

dibromoanthracene 2 (0.446 mmol, 150 mg, 1 equiv.), 4-(tert-butyl)phenylacetylene 

3 (1.120 mmol, 180 mg, 2.5 equiv.), 4.6 mL of THF anhydrous (previously 

deoxygenated by freeze-pump-thaw) and 1.2 mL of freshly distilled DIPA were added. 

The reaction was carried out for 3 hours at 120 ºC and 600 rpm in a microwave reactor. 

The crude was extracted in DCM washing with NH4Cl (20 mL), water (20 mL) and 

brine (20 mL). The resultant crude was filtered through a silica gel plug with 

dichloromethane and solvent was removed. The product was dissolved in the 

minimum amount of CHCl3 and then methanol was added to obtain a precipitate that 

was filtered to reach to a yellow solid (185 mg, 85%). 1H (300 MHz, CDCl3) δ= 8.72 

− 8.67 (m, 4H), 7.72 (d, J= 8.5 Hz, 4H), 7,66 − 7.60 (m, 4H), 7.48 (d, J= 8.5 Hz, 4H), 

1.38 (s, 18H).  FT-IR (cm−1) 3084, 3059, 3032, 2954, 2949, 2901, 2870, 2858, 2319, 

1910, 1742, 1664, 1617, 1513, 1502, 1456, 1434, 1398, 1361, 1260, 1105, 1024, 829, 

765, 639, 559. HRMS found: 490.2671. Calculated for C38H34, 490.2661.170  

9,10-Bis[penta(4-tert-butyl(phenyl))phenyl] 

anthracene 6a. To a 30 mL dry microwave reactor 

vial, provided with a magnetic stir bar were added, 

2,3,4,5-tetrakis[4-(tert-butyl)phenyl]cyclopenta-2,4 

-dien-1-one 5 (0.569 mmol, 346 mg, 3.1 equiv.) and 

dialkyne 4 (0.183 mmol, 90 mg, 1 equiv.). The reaction was carried out in a microwave 

reactor at 280 ºC and 600 rpm for 40 minutes, repeating these conditions for a total of 

three sequential times. The crude was purified through aluminum oxide 

chromatography column using as eluent a gradient from hexane to hexane:DCM 90:10 

affording the product 6a as a yellow solid (170 mg, 57 %). 1H NMR (300 MHz, 

CDCl3) δ= 7.63 − 7.59 (m, 4H), 6.83 (d, J= 8.5 Hz, 4H), 6.77 − 6.73 (m, 12H), 6.70 

(d, J= 8.5 Hz, 4H), 6.61 (d, J= 8.4 Hz, 8H), 6.49 (d, J= 8.6 Hz, 8H), 6.30 (d, J= 8.4 

Hz, 8H), 1.12 (s, 18H), 1.08 (s, 36H), 0.99 (s, J= 3.3 Hz, 36H). 13C NMR (75 MHz, 

CDCl3) δ= 147.4, 147.2, 146.9, 143.0, 141.3, 140.9, 138.6, 138.5, 137.8, 135.7, 134.5, 

131.5, 131.3, 130.9, 129.6, 127.8, 123.3, 123.1, 123.0, 122.3, 34.2, 34.1, 34.1, 31.2. 

FT-IR (cm-1) 3080, 3051, 3027, 2958, 2905, 2865, 1779, 1662, 1602, 1511, 1462, 

1390, 1361, 1268, 1116, 1020, 831, 567. HRMS found: 1651.0783. Calculated for 

C126H138, 1651.0799. 

 

 
170 W. Fudickar, T. Linker, J. Am. Chem. Soc. 2012, 134, 15071. 



Experimental section 

146 

 

Syn/anti spirocompound 7. In a 25 mL dry 

Schlenk, under argon atmosphere and provided with 

a magnetic stir bar, 6a (0.012 mmol, 20 mg, 1 equiv.) 

and AgPF6 (0.606 mmol, 153 mg, 50 equiv.) were 

dissolved in 5 mL of anhydrous DCE. The solution 

was heated to 85 ºC and a solution of FeCl3 (0.606 

mmol, 77 mg, 50 equiv.) in 2 mL of nitromethane was added dropwise under argon 

bubbling. The reaction was carried out at 85 ºC under Argon bubbling and stirring for 

4 hours. After that time methanol was added to the reaction Schlenk and solvent was 

removed under reduced pressure. The crude was purified through neutral aluminum 

oxide preparative plate with CS2, affording 7 as a white solid (12 mg, 61%). 1H NMR 

(700 MHz, Methylene Chloride-d2) δ= 7.42 – 7.27 (m), 6.96 – 6.88 (m), 6.81 (dd, J= 

8.5, 1.8 Hz), 6.74 – 6.65 (m), 6.53 – 6.47 (m), 6.29 – 6.25 (m), 6.11 (d, J= 8.4 Hz), 

6.07 – 6.02 (m), 1.36 (s), 1.35 (s), 1.34 (s), 1.13 (s), 1.01 (s), 1.03 (s), 1.03 (s), 0.91 

(s), 0.91 (s), 0.90 (s). 13C NMR (176 MHz, Methylene Chloride-d2) δ= 159.8, 151.6, 

150.3, 149.8, 148.4, 147.7, 146.5, 142.5, 142.1, 140.3, 139.6, 139.3, 138.3, 138.0, 

137.9, 135.5, 135.4, 133.1 (bs), 132.2 (bs), 131.7 (bs), 130.7 (bs), 124.2, 123.7, 123.5, 

123.2, 122.9, 63.8, 35.0, 35.0, 34.5, 34.4, 34.2, 31.7, 31.5, 31.4, 31.4. FT-IR (cm-1) 

3072, 3027, 2962, 2929, 2901, 2860, 1735, 1604, 1517, 1475, 1362, 1270, 1115, 1022, 

832. HRMS found: 1649.0642. Calculated for C126H136, 1649.0642.  

Spirocompound 8. In a 10 mL dry Schlenk, under 

argon atmosphere and provided with a magnetic stir 

bar, 6a (0.012 mmol, 20 mg, 1 equiv.) was dissolved 

in 2 mL of anhydrous DCM. The solution was 

cooled to –30 ºC and a solution of FeCl3 (0.606 

mmol, 77 mg, 50 equiv.) in 0.6 mL of nitromethane was added dropwise under argon 

bubbling. The reaction was carried out at –30 ºC under Argon bubbling and stirring 

for 1 hour. After that time methanol was added to the reaction Schlenk and solvent 

was removed under reduced pressure. The crude was heated in ethanol, after cooling 

a yellow solid was filtered, providing 8 as a yellow solid (8 mg, 40%) HRMS found: 

1643.0344. Calculated for C126H130, 1643.0173. 

Spironanographene syn 10. To a 100 mL dry 

round-bottom flask, under argon atmosphere and 

provided with a magnetic stir bar, 1a (0.012 mmol, 

20 mg, 1 equiv.) and DDQ (0.363 mmol, 82 mg, 30 

equiv.) were added and dissolved in 30 mL of 

anhydrous DCM. The solution warmed to 40 ºC with 

stirring. Then, TfOH (4.85 mmol, 0.730 g, 400 equiv.) was added dropwise under 

argon bubbling. The reaction was carried out at 40 ºC under Argon bubbling and 

stirring for 2 hours. After that time a HNaCO3 saturated solution was added to the 

reaction flask and the crude was extracted with DCM and washed twice with a 



Experimental section 

147 

 

HNaCO3 saturated solution (50 mL) and twice with brine (50 mL). From this step the 

organic phase was dried with MgSO4 and filtered, the solvent was removed under 

reduced pressure. Then, the crude was filtered through a small silica gel plug with 

DCM. The solvent was removed under reduced pressure and the product was purified 

by a semipreparative silica gel plate in hexane:DCM 90:20, affording syn 10 as a 

yellow solid (4 mg, 21%). Syn 10 1H NMR (500 MHz, CDCl3) δ= 9.34 (s, 1H), 9.28 

(s, 1H), 9.26 (s, 1H), 9.23 (s, 1H), 9.07 (s, 1H), 8.82 (s, 1H), 8.65 (s, 1H), 8.23 (d, J= 

2.0 Hz, 1H), 7.99 (d, J= 8.6 Hz, 1H), 7.78 (s, 1H), 7.03 – 6.99 (m, 1H), 6.68 – 6.65 

(m, 1H), 6.64 – 6.57 (m, 2H), 5.80 (dd, J = 8.6, 2.0 Hz, 1H), 1.86 (s, 9H), 1.85 (s, 9H), 

1.77 (s, 9H), 1.50 (s, 9H), 0.72 (s, 9H). 13C NMR (126 MHz, CDCl3) δ= 158.6, 152.1, 

149.7, 149.5, 148.6, 148.2, 146.1, 139.3, 137.6, 136.4, 133.2, 131.5, 131.1, 130.9, 

130.8, 130.4, 130.3, 130.2, 130.2, 130.1, 128.5, 127.9, 127.7, 127.6, 127.6, 124.8, 

124.4, 124.3, 123.9, 123.0, 122.9, 122.1, 119.3, 119.2, 118.8, 118.8, 118.7, 118.6, 

118.5, 118.1, 117.9, 69.9, 36.3, 36.0, 36.0, 35.7, 34.0, 32.6, 32.3, 32.3, 32.1, 30.9. FT-

IR (cm-1) 3067, 2957, 2921, 2865, 1751, 1689, 1601, 1476, 1363, 1251, 1202, 1096, 

1023, 870, 620. HRMS found 1632.9375. Calculated for C126H120 1632.9390. 

9,10-Bis[(4-(tert-butyl)phenyl)ethynyl]octafluoro 

anthracene (12). To a dry 30 mL microwave reactor vial 

under argon atmosphere and provided with a magnetic 

stir bar, CuI (0.020 mmol, 4 mg, 0.4 equiv.), Pd(PPh3)2Cl2 

(0.010 mmol, 7 mg, 0.2 equiv.), 9,10-dichloro-1,2,3,4,5,6,7,8-octafluoroanthracene 11 

(0.051 mmol, 20 mg, 1 equiv.), 4-(tert-butyl)phenylacetylene 3 (0.153 mmol, 24 mg, 

3 equiv.), 4 mL of deoxygenated (argon bubbling for 30 minutes) freshly distilled 

triethylamine. The reaction was carried out for 3h and 30 minutes at 80 ºC and 300 

rpm in a microwave reactor. Solvent was removed from the crude under reduced 

pressure then dissolved in DCM and filtered through a silica gel plug column using 

dichloromethane as eluent. The solvent was removed under reduced pressure. The 

obtained solid was precipitated in methanol and filtered to reach compound 12 as a 

red solid (30 mg, 94%). 1H NMR (300 MHz, C6D6) δ= 7.79 (d, J= 8.5 Hz, 4H), 7.26 

(d, J= 8.5 Hz, 4H), 1.18 (s, 18H). 19F NMR (282 MHz, C6D6) δ= −137.88 (d, J= 15.2 

Hz), −154.87 (d, J= 15.2 Hz). 13C{1H}{19F} NMR (126 MHz, C6D6) δ= 153.2, 143.9, 

139.6, 131.9, 126.1, 121.4, 120.7, 111.9, 107.3, 87.5, 31.1, 30.2. FT-IR (cm-1) 3086, 

3040, 2955, 2906, 2865, 2191, 1668, 1502, 1444, 1407, 1363, 1267, 1076, 834, 659, 

561. HRMS found: 634.1880. Calculated for C38H26F8, 634.1907. 

9,10-Bis[penta(4-tert-butyl(phenyl))phenyl] 

octafluoroanthracene (6b). To a 30 mL dry 

microwave reactor vial provided with a 

magnetic stir bar, 2,3,4,5-tetrakis[4-(tert-

butyl)phenyl]cyclopenta-2,4-dien-1-one 5  

(0.098 mmol, 59 mg, 3.1 equiv.) and 12  (0.031 mmol, 20 mg, 1 equiv.) were added. 

The reaction was carried out in a microwave reactor at 280 ºC and 600 rpm for 40 



Experimental section 

148 

 

minutes, repeating these conditions for a total of three sequential times. The resulting 

crude was purified through silica gel chromatography column using as eluent a 

gradient from hexane to CS2 affording 6b as a yellow solid (12 mg, 21%). 1H NMR 

(500 MHz, CDCl3) δ= 6.81 (m, 12H), 6.76 (d, J= 8.0 Hz, 4H), 6.70 – 6.61 (m, 20H), 

6.16 (d, J= 8.0 Hz, 4H), 1.11 (s, 18H), 1.09 (s, 36H), 1.08 (s, 36H). 19F NMR (471 

MHz, CDCl3) δ= −137.53 (d, J= 15.9 Hz), −160.43 (d, J= 15.9 Hz). 13C{1H}{19F} 

NMR (126 MHz, CDCl3) δ= 148.1, 147.7, 141.9, 140.3, 140.3, 137.9, 137.7, 136.4, 

131.8, 131.6, 131.3, 130.0, 129.3, 123.5, 123.3, 122.4, 118.6, 34.2, 31.3, 31.3, 31.2, 

29.9.  FT-IR (cm-1) 3088, 3033, 2961, 2904, 2967, 1675, 1493, 1454, 1362, 1270, 

1072, 1015, 832, 570. HRMS found:1795.0137. Calculated for C126H130F8, 1795.0045. 

Helically arranged nanographene 13. In a 

100 mL dry flask, under argon atmosphere 

and provided with a magnetic stir bar, 

polyphenylene 6b (0.006 mmol, 10 mg, 1 

equiv.) was solved in 15 mL of anhydrous 

DCM. The mixture was cooled to 0 ºC and stirred for five minutes after DDQ (0.245 

mmol, 56 mg, 44 equiv.) addition. Then, under Ar bubbling, TfOH was added 

dropwise (2.290 mmol, 344 mg, 412 equiv.) and the reaction was carried out at 0 ºC 

maintaining the Ar bubbling for 40 minutes. After that time a HNaCO3 saturated 

solution was added to the reaction flask and the crude was extracted with DCM and 

washed twice with a HNaCO3 saturated solution (30 mL) and twice with brine (30 

mL). From this step the organic phase was dried with MgSO4, and the solvent was 

removed under reduced pressure. The crude was manipulated and purified in light 

absence through a silica gel column in hexane:toluene 50:1, affording 13 as a yellow 

solid (6 mg, 63%). 1H NMR (500 MHz, CDCl3) δ= 9.22 (s, 4H), 9.18 (d, J= 1.7 Hz, 

4H), 8.99 (d, J= 1.7 Hz, 4H), 8.71 (d, J= 2.0 Hz, 1H), 7.54 (d, J= 8.9 Hz, 4H), 6.98 

(dd, J= 8.9, 2.0 Hz, 4H), 1.83 (s, 18H), 1.78 (s, 36H), 1.20 (s, 36H). 19F NMR (471 

MHz, CDCl3) δ= −137.41 (d, J= 12.85 Hz), -157.37 (d, J= 12.85 Hz). 13C{1H}{19F} 

NMR (126 MHz, CDCl3) δ= 149.6, 149.6, 135.0, 132.3, 131.4, 130.6, 130.3, 130.0, 

129.7, 127.4, 126.0, 123.5, 123.0, 122.9, 122.0, 121.8, 120.5, 119.5, 119.2, 119.0, 

118.5, 35.9, 35.8, 34.8, 32.2, 32.1, 31.0. FT-IR (cm-1) 2958, 2924, 2875, 2859, 1464, 

1375. HRMS found: 1778.8759. Calculated for C126H114F8, 1778.8793. 

Chapter 2 

1,4-Bis[(4-(tert-butyl)phenyl)ethynyl]tetrafluoro 

benzene (15a). To a dry 10 mL microwave reactor vial 

under argon atmosphere and provided with a magnetic stir 

bar, CuI (0.06 mmol, 12 mg, 0.4 equiv.), Pd(dppf)Cl2 (0.03 mmol, 27 mg, 0.2 equiv.), 

1,4-dibromotetrafluorobenzene 14 (0.16 mmol, 50 mg, 1 equiv.), 4-(tert-

butyl)phenylacetylene 3a (0.41 mmol, 64 mg, 2.5 equiv.), 1.7 mL of anhydrous 

previously deoxygenated THF and 0.4 mL of distilled DIPA were added. The reaction 

was carried out for 3 hours at 120 ºC and 600 rpm in a microwave reactor. The 

 



Experimental section 

149 

 

resulting crude was extracted with DCM and washed with NH4Cl (50 mL), water (50 

mL) and brine (50 mL). The organic phase was dried with MgSO4, filtered through a 

silica gel plug column using dichloromethane as eluent and the solvent was removed 

under reduced pressure. The product was dissolved in the minimum amount of CHCl3 

and then methanol was added to obtain a precipitate that was filtered to reach 15a as 

white solid (59 mg, 79%). 1H NMR (300 MHz, Chloroform-d) δ= 7.54 (d, J= 8.5 Hz, 

4H), 7.42 (d, J= 8.5 Hz, 4H), 1.34 (s, 18H). 19F NMR (471 MHz, Chloroform-d) δ= 

−138.00 (s). 13C{1H) NMR (126 MHz, Chloroform-d) δ= 153.3, 146.6 (dm, 1JC-F= 

243.5 Hz), 131.9, 125.7, 118.8, 104.9 (m) 103.4, 74.3, 35.1, 31.2. FT-IR (cm-1) 3030, 

2959, 2904, 2867, 2229, 2210, 1605, 1522, 1512, 1487, 980, 949, 835. HRMS: 

Calculated for C30H26F4: 462.1971, found: 462.1958. 

1,4-bis[(4-methoxyphenyl)ethynyl]tetrafluoro 

benzene (15b). To a dry 10 mL microwave reactor vial 

under argon atmosphere and provided with a magnetic 

stir bar, CuI (0.06 mmol, 12 mg, 0.4 equiv.), Pd(dppf)Cl2 (0.03 mmol, 27 mg, 0.2 

equiv.), 1,4-dibromotetra fluorobenzene 14 (0.16 mmol, 50 mg, 1 equiv.), 4-

(methoxy)phenylacetylene 3b (0.41 mmol, 54 mg, 2.5 equiv.), 1.7 mL of anhydrous 

previously deoxygenated  THF and 0.4 mL of distilled DIPA were added. The reaction 

was carried out for 3 hours at 120 ºC and 600 rpm in a microwave reactor. The 

resulting crude was extracted with DCM and washed twice with NH4Cl (50 mL), twice 

with water (50 mL) and twice with brine (50 mL). The organic phase was dried with 

MgSO4, filtered through a silica gel plug column using dichloromethane as eluent and 

solvent was removed under reduced pressure. The resulting solid was dissolved in the 

minimum amount of CHCl3 and then methanol was added to obtain a precipitate that 

was filtered to reach 15b as a brown solid (42 mg, 64%). 1H NMR (300 MHz, 

Chloroform-d) δ= 7.54 (d, J= 8.8 Hz, 4H), 6.91 (d, J= 8.8 Hz, 4H), 3.85 (s, 6H). 19F 

NMR (282 MHz, Chloroform-d) δ= −138.3 (s). 13C{1H} NMR (126 MHz, 

Chloroform-d) δ= 160.9, 146.6 (dm, 1JC-F= 261.9 Hz), 133.8, 114.3, 113.9, 104.8 (m), 

103.3, 73.9, 55.5. FT-IR (cm-1) 3022, 3002, 2970, 2937, 2909, 2840, 2228, 2210, 1601, 

1518, 1481, 1246, 1172, 1024, 965, 830. HRMS: Calculated for C24H14F4O2: 

410.0930, found: 410.0910. 

1,4-Bis(phenylethynyl)tetrafluorobenzene (15c). To a dry 10 

mL microwave reactor vial under argon atmosphere and 

provided with a magnetic stir bar, CuI (0.13 mmol, 20 mg, 0.4 

equiv.), Pd(dppf)Cl2 (0.06 mmol, 50 mg, 0.2 equiv.), 1,4-dibromotetrafluorobenzene 

14 (0.32 mmol, 100 mg, 1 equiv.), phenylacetylene 3c (0.81 mmol, 80 mg, 2.5 equiv.), 

3.3 mL of anhydrous previously deoxygenated THF and 0.9 mL of distilled DIPA were 

added. The reaction was carried out for 3 hours at 120 ºC and 600 rpm in a microwave 

reactor. The crude was extracted with DCM and washed twice with NH4Cl (40 mL), 

twice with water (40 mL) and twice with brine (40 mL). The organic phase was dried 

with MgSO4, filtered through a silica gel plug column using dichloromethane as eluent 



Experimental section 

150 

 

and solvent was removed under reduced pressure. The product was dissolved in the 

minimum amount of CHCl3 and then methanol was added to obtain a precipitate that 

was filtered to reach to 15c as beige solid (80 mg, 70%). 1H NMR (300 MHz, 

Chloroform-d) δ= 7.64 – 7.57 (m, 4H), 7.46 – 7.36 (m, 6H). 19F NMR (471 MHz, 

Chloroform-d) δ= −137.70 (s). 13C{1H} (126 MHz, Chloroform-d) δ= 146.7 (dm, 1JC-

F= 254.2 Hz), 132.1, 129.9, 128.7, 121.8, 104.9, 103.2, 74.8. FT-IR (cm-1) 3060, 2232, 

2210, 1484, 1443, 975. HRMS: Calculated for C22H10F4: 350.0719, found: 350.0703. 

1,4-Bis[penta(4-tert-butyl(phenyl))phenyl]tetra 

fluorobenzene 16a. To a 10 mL dry microwave 

reactor vial, provided with a magnetic stir bar, 

2,3,4,5-tetrakis[4-(tert-butyl)phenyl]cyclopenta-

2,4-dien-1-one 5 (0.34 mmol, 200 mg, 3.1 equiv.) 

and 15a (0.09 mmol, 45 mg, 1 equiv.) were added. The reaction was carried out in a 

microwave reactor at 300 ºC and 600 rpm for 30 minutes, repeating these conditions 

for a total of four sequential times and removing carbon monoxide under vacuum 

between each repetition. The resulting crude was dissolved in the minimum amount 

of CHCl3, and methanol was added to obtain a precipitate that was filtered, affording 

16a as a white solid (110 mg, 70%). 1H NMR (500 MHz, Chloroform-d) δ= 7.18 (d, 

J = 8.1 Hz, 4H), 6.83 (d, J = 8.3 Hz, 4H), 6.78 (d, J = 8.6 Hz, 12H), 6.68 (d, J = 8.3 

Hz, 4H), 6.61 (d, J = 8.1 Hz, 4H), 6.59 – 6.48 (m, 12H), 1.25 (s, 36H), 1.08 – 1.07 

(m, 54H). 19F NMR (282 MHz, Chloroform-d) δ= −137.48 (s). 13C{1H} NMR (126 

MHz, Chloroform-d) δ= 148.5, 147.7, 147.6, 143.1 (dm, 1JC-F =256.2 Hz), 142.6, 

141.9, 141.3, 137.7, 137.6, 137.0, 132.39, 131.2, 131.0, 128.9, 125.6, 123.6, 123.2, 

122.8, 119.0 (m), 34.5, 34.2, 31.6, 31.3. FT-IR (cm-1) 3089, 3039, 2962, 2903, 2869, 

1899, 1773, 1657, 1609, 1512, 1469, 1391, 1362, 1268, 1020, 978, 831. HRMS: 

Calculated for C118H130F4=1623.0109, found=1623.0033.  

1,4-Bis[(2-[4-methoxyphenyl)-3,4,5,6-tetra(4-

tert-butyl(phenyl))]phenyl]tetrafluorobenzene 

16b. To a 10 mL dry microwave reactor vial, 

provided with a magnetic stir bar, 2,3,4,5-

tetrakis[4-(tert-butyl)phenyl] cyclopenta-2,4-

dien-1-one 5 (0.23 mmol, 140 mg, 3.1 equiv.) and 15b (0.07 mmol, 30 mg, 1 equiv.) 

were added. The reaction was carried out in a microwave reactor at 300 ºC and 600 

rpm for 30 minutes, repeating these conditions for a total of three times and removing 

carbon monoxide under vacuum between each repetition. The resulting crude was 

dissolved in the minimum amount of CHCl3 and methanol was added to obtain a 

precipitate that was filtered, affording 16b as a nude-colored solid (64 mg, 56%). 1H 

NMR (500 MHz, Chloroform-d) δ= 7.00 (d, J= 8.4 Hz, 2H), 6.81 (d, J= 8.5 Hz, 2H), 

6.77 – 6.73 (m, 4H), 6.66 – 6.48 (m, 12H), 3.73 (s, 3H), 1.23 (s, 9H), 1.10 (s, 9H), 

1.07 (s, 9H), 1.06 (s, 9H). 19F NMR (471 MHz, Chloroform-d) δ= −138.32 (s). 
13C{1H} NMR (126 MHz, Chloroform-d) δ= 157.7, 148.5, 147.7, 147.7, 147.6, 143.3 



Experimental section 

151 

 

(dm, 1JC-F = 246.7 Hz), 142.8, 141.9, 141.4, 141.2, 141.1, 137.7, 137.6, 137.5, 137.0, 

132.4, 131.8, 131.1, 131.0, 130.9, 130.5, 125.7, 123.5, 123.4, 123.2, 123.1, 119.3 (m), 

112.4, 55.3, 34.5, 34.2, 34.2, 31.5, 31.3, 31.3. FT-IR (cm-1) 3087, 3032, 2959, 2901, 

2865, 1899, 1779, 1742, 1661, 1611, 1513, 1467, 1245, 977, 832. HRMS: Calculated 

for C112H118F4O2: 1570.9068, found: 1570.9106. 

1,4-Bis[2-phenyl-3,4,5,6-tetra(4-tert-

butyl(phenyl))phenyl]tetrafluorobenzene 16c. 

To a 10 mL dry microwave reactor vial, provided 

with a magnetic stir bar, 2,3,4,5-tetrakis[4-(tert-

butyl)phenyl]cyclopenta-2,4-dien-1-one 5 (0.35 

mmol, 210 mg, 3.1 equiv.) and 15c  (0.11 mmol, 48 mg, 1 equiv.) were added. The 

reaction was carried out in a microwave reactor at 280 ºC and 600 rpm for 30 minutes, 

repeating these conditions for a total of three times and removing carbon monoxide 

under vacuum between each repetition. The resulting crude dissolved in the minimum 

amount of CHCl3, and methanol was added to obtain a precipitate that was filtered, 

affording 16c as a pale brown solid (141 mg, 82%). 1H NMR (500 MHz, Chloroform-

d) δ= 6.96 (d, J= 8.3 Hz, 4H), 6.88 (t, J= 7.2 Hz, 2H), 6.82 – 6.63 (m, 24H), 6.59 – 

6.57 (m, 8H), 6.49 (d, J= 8.3 Hz, 4H), 1.24 (s, 18H), 1.10 – 1.02 (m, 54H). 19F NMR 

(282 MHz, Chloroform-d) δ= −138.89 (s). 13C{1H}{19F} NMR (126 MHz, 

Chloroform-d) δ= 148.25, 147.8, 147.7, 147.4, 143.3, 142.7, 141.9, 141.8, 141.4, 

140.7, 139.7, 137.6, 137.5, 137.3, 137.0, 131.0, 130.9, 130.8, 130.2, 130.1, 126.7, 

125.7, 125.1, 123.8, 123.3, 123.1, 123.0, 119.5, 34.5, 34.2, 34.1, 31.5, 31.3. FT-IR 

(cm-1) 3090, 3051, 3028, 2960, 2905, 2865, 1896, 1779, 1661, 1603, 1513, 1462, 

1391, 1361, 1269, 1022, 976, 832. HRMS: Calculated for C110H114F4: 1510.8857, 

found: 1510.8841. 

Helically arranged nanographene 17a. To a 100 

mL dry flask, under argon atmosphere and provided 

with a magnetic stir bar, 16a (0.01 mmol, 20 mg, 1 

equiv.), 37 mL of DCM and DDQ (0.54 mmol, 123 

mg, 44 equiv.) were added. The reaction mixture 

was cooled to 0 ºC and stirred for 5 minutes. Then, 

under Ar bubbling, TfOH was added dropwise (5.07 mmol, 760 mg, 412 equiv.)  and 

the reaction was carried out at 0 ºC maintaining the Ar bubbling for 25 minutes. After 

that time, a HNaCO3 saturated solution was added to the reaction flask and the crude 

was extracted with DCM and washed twice with a HNaCO3 saturated solution (40 

mL) and twice with brine (40 mL). The organic phase was dried with MgSO4, and the 

solvent was removed under reduced pressure. The crude was purified by aluminum 

oxide column chromatography using pentane as eluent, affording 17a as a yellow solid 

(13 mg, 80%). 1H NMR (300 MHz, Chloroform-d) δ= 9.16 (s, 4H), 9.11 (d, J= 1.6 

Hz, 4H), 9.01 (d, J= 1.6 Hz, 4H), 8.81 (d, J= 1.9 Hz, 4H), 8.26 (d, J= 8.8 Hz, 4H), 

7.64 (dd, J= 8.8, 1.9 Hz, 4H), 1.82 (s, 18H), 1.76 (s, 36H), 1.39 (s, 36H). 19F NMR 



Experimental section 

152 

 

(282 MHz, Chloroform-d) δ= −137.26 (s). 13C{1H} NMR (126 MHz, Chloroform-d) 

δ= 150.5, 149.9, 149.8, 147.0 (d, 1JC-F= 241.1 Hz), 132.3, 130.7, 130.2, 130.0, 128.3, 

127.5, 126.3, 124.2 (m), 124.2, 123.3, 123.2, 122.6, 122.1, 122.0, 120.2, 119.3, 119.2, 

118.8, 118.5, 35.9, 35.8, 35.1, 32.2, 32.1, 31.3, 29.9. FT-IR (cm-1) 3082, 2952, 2921, 

2852, 1608, 1588, 1479, 1463, 1374, 1246, 981, 871. HRMS: Calculated for 

C118H114F4: 1606.8857, found: 1606.8866. 

Helically arranged nanographene 17b. To a 100 

mL dry flask, under argon atmosphere and 

provided with a magnetic stir bar, 16b (0.01 

mmol, 20 mg, 1 equiv.), 38 mL of DCM and DDQ 

(0.56 mmol, 127 mg, 44 equiv.) were added. The 

reaction mixture was cooled to 0 ºC and stirred for 

5 minutes. Then, under Ar bubbling, TfOH was added dropwise (5.24 mmol, 790 mg, 

412 equiv.)  and the reaction was carried out at 0 ºC maintaining the Ar bubbling for 

25 minutes. After that time, a HNaCO3 saturated solution was added to the reaction 

flask and the crude was extracted with DCM and washed twice with a HNaCO3 

saturated solution (40 mL) and twice with brine (40 mL). The organic phase was dried 

with MgSO4, and the solvent was removed under reduced pressure. The crude was 

filtered through silica gel using DCM as eluent and solvent was removed under 

reduced pressure affording 17b as a green-yellow solid (11 mg, 70%, 1:1 anti/syn). 
1H NMR (500 MHz, Chloroform-d) δ= 9.20 – 9.09 (m, 8H), 9.02 (s, 1H), 8.99 (s, 1H), 

8.93 (s, 1H), 8.91 (s, 1H), 8.82 (d, J= 2.0 Hz, 1H), 8.80 (d, J= 2.0 Hz, 1H), 8.30 – 8.23 

(m, 4H), 8.21 (d, J= 9.2 Hz, 1H), 8.15 (d, J= 8.8 Hz, 1H), 7.62 (dd, J= 8.8, 2.0 Hz, 

1H), 7.54 (dd, J= 8.8, 2.0 Hz, 1H), 7.15 (dd, J= 9.2, 2.6 Hz, 1H), 7.11 (dd, J= 9.2, 2.6 

Hz, 1H), 3.95 (s, 3H), 3.93 (s, 3H), 1.81 (s, 18H), 1.77 – 1.74 (m, 36H), 1.39 – 1.38 

(m, 18H). 19F NMR (471 MHz, Chloroform-d) δ= −137.16 (s), −137.17 (s). 
13C{1H}{19F} NMR (126 MHz, Chloroform-d) δ= 159.0, 159.0, 150.5, 150.5, 149.9, 

149.8, 147.0, 134.4, 134.4, 132.3, 132.3, 130.7, 130.6, 130.6, 130.5, 130.2, 130.1, 

130.0, 129.9, 129.8, 129.7, 129.2, 128.3, 128.2, 127.4, 127.4, 126.5, 126.5, 126.4, 

124.6, 124.4, 124.2, 124.1, 123.4, 123.4, 123.2, 123.2, 122.9, 122.9, 122.7, 122.7, 

122.6, 122.1, 122.0, 121.9, 120.1, 120.1, 119.8, 119.7, 119.4, 119.3, 119.2, 118.8, 

118.7, 118.6, 118.5, 118.3, 119.9, 111.6, 108.2, 107.7, 55.6, 55.5, 35.9, 35.8, 35.1, 

32.1, 32.1, 31.4, 31.3. FT-IR (cm-1) 3075, 2960, 2909, 2865, 1785, 1722, 1610, 1589, 

1458, 1372, 1248, 1044, 979, 870. HRMS: Calculated for C112H102F4O2: 1554.7816, 

found: 1554.7840. 

 

 



Experimental section 

153 

 

Helically arranged nanographene 17c. To a 100 

mL dry flask, under argon atmosphere and 

provided with a magnetic stir bar, 16c (0.01 

mmol, 20 mg, 1 equiv.), 40 mL of DCM and DDQ 

(0.58 mmol, 132 mg, 44 equiv.) were added, the 

reaction mixture was cooled to 0 ºC and stirred for 

5 minutes. Then, under Ar bubbling, TfOH was added dropwise (5.45 mmol, 820 mg, 

412 equiv.)  and the reaction was carried out at 0 ºC maintaining the Ar bubbling for 

25 minutes. After that time, a HNaCO3 saturated solution was added to the reaction 

flask and the crude was extracted with DCM and washed twice with a HNaCO3 

saturated solution (40 mL) and twice with brine (40 mL). The organic phase was dried 

with MgSO4, and the solvent was removed under reduced pressure. The crude was 

purified by silica gel chromatography column performed using a gradient from 

hexane:DCM (12:1) to hexane:DCM (6:1), solvent was removed under reduced 

pressure affording 17c as a yellow solid (12 mg, 77%, 1:1 anti/syn). 1H NMR (500 

MHz, Chloroform-d) δ= 9.17 – 9.15 (m, 4H), 9.13 (s, 2H), 9.11 (s, 2H), 9.02 – 8.99 

(m, 4H), 8.87 − 8.84 (m, 2H), 8.81 (d, J= 1.8 Hz, 1H), 8.80 (d, J= 1.8 Hz, 1H), 8.32 

(d, J= 8.4 Hz, 1H), 8.29 (d, J= 8.4 Hz, 1H), 8.24 (d, J= 8.8 Hz, 1H), 8.15 (d, J= 8.8 

Hz, 1H), 7.68 – 7.64 (m, 2H), 7.61 (dd, J= 8.8, 1.8 Hz, 1H), 7.54 – 7.50 (m, 3H), 1.81 

(s, 18H), 1.76 − 1.74 (m, 36H), 1.38 (s, 9H), 1.37 (s, 9H). 19F NMR (471 MHz, 

Chloroform-d) δ= −137.35 (s), −137.37 (s). 13C{1H}{19F} NMR (126 MHz, 

Chloroform-d) δ= 150.6, 150.5, 150.0, 150.0, 150.0, 149.9, 149.9, 146.9, 132.7, 132.6, 

132.3, 132.2, 130.8, 130.7, 130.6, 130.6, 130.6, 130.3, 130.2, 130.1, 130.1, 130.0, 

130.0, 129.9, 128.3, 128.2, 127.8, 127.7, 127.6, 127.5, 126.4, 126.3, 124.4, 124.3, 

124.2, 124.1, 124.0, 123.5, 123.4, 123.3, 123.3, 123.2, 123.1, 123.1, 122.6, 122.1, 

122.0, 121.9, 121.9, 120.2, 120.1, 119.5, 119.5, 119.4, 119.3, 119.3, 119.2, 119.0, 

118.9, 118.7, 118.6, 118.5, 35.9, 35.8, 35.1, 32.2, 32.1, 31.4, 31.3. FT-IR (cm-1) 3081, 

2959, 2905, 2866, 1607, 1588, 1476, 1458, 1372, 1243, 979, 870. HRMS: Calculated 

for C110H98F4: 1494.7605, found: 1494.7620. 

Nanographene 17c’. To a 100 mL dry flask, 

under argon atmosphere and provided with a 

magnetic stir bar, 16c (0.01 mmol, 10 mg, 1 

equiv.), 20 mL of DCM and DDQ (0.29 mmol, 66 

mg, 44 equiv.) were added. The reaction mixture 

was cooled to −78 ºC and stirred for 5 minutes. 

Then, under Ar bubbling, TfOH was added dropwise (2.72 mmol, 410 mg, 412 equiv.) 

and the reaction was carried out at −78 ºC maintaining the Ar bubbling for 3 hours. 

After that time, a HNaCO3 saturated solution was added to the reaction flask and the 

crude was extracted with DCM and washed twice with a HNaCO3 saturated solution 

(20 mL) and twice with brine (20 mL). The organic phase was dried with MgSO4 and 

filtered through silica gel using DCM as eluent. Solvent was removed under reduced 

pressure affording 17c’ as a yellow solid (7 mg, 75%). 1H NMR (700 MHz, 1,1,2,2-



Experimental section 

154 

 

Tetrachloroethane-d2) δ= 9.16 (s, 1H), 9.15 (s, 1H), 9.01 (s, 1H), 8.99 (s, 1H), 8.77 (d, 

J= 2.1 Hz, 1H), 8.69 (d, J= 2.1 Hz, 1H), 7.86 (d, J= 8.6 Hz, 1H), 7.64 (d, J= 8.8 Hz, 

1H), 7.36 (d, J= 7.4 Hz, 2H), 7.33 (dd, J= 8.6, 2.1 Hz, 1H), 7.23 (t, J= 7.4 Hz, 1H), 

7.18 (t, J= 7.4 Hz, 2H), 7.15 (dd, J= 8.8, 2.1 Hz, 1H), 1.77 (s, 9H), 1.76 (s, 9H), 1.60 

(s, 9H), 1.46 (s, 9H). 19F NMR (282 MHz, 1,1,2,2-Tetrachloroethane-d2) δ= −135.52. 
13C{1H} (176 MHz, 1,1,2,2-Tetrachloroethane-d2) δ= 149.6, 149.4, 149.4, 149.2, 

144.1 (dm, 1JC-F = 236.1 Hz), 142.8, 142.3, 140.1, 131.0, 130.9, 130.6, 130.4, 130.3, 

129.7, 129.3, 128.3, 128.1, 128.0, 127.8, 127.6, 127.4, 126.9, 125.4, 125.0, 123.7, 

123.5, 122.7 (m), 122.0, 121.9, 121.3, 120.6, 120.2, 119.0, 118.9, 118.7, 118.4, 35.4, 

34.9, 34.7, 31.8, 31.7, 31.4, 31.2. Calculated for C110H102F4: 1498.7918, found: 

1498.7570. 

 Chapter 3 

(Pentahelicen-2,13-diyldiethyne-2,1-diyl)bis[tris(1-methyl 

ethyl)silane] (19a). A pressure tube was charged with 

dichlorohelicene 18a (300 mg, 0.865 mmol, 1.0 equiv.), Pd2(dba)3 

(16 mg, 0.017 mmol, 2 mol%), XPhos (33 mg, 0.0688 mmol, 8 

mol%), potassium carbonate (713 mg, 5.160 mmol, 6.0 equiv.), flushed with nitrogen, 

and degassed (by three freeze-pump-thaw cycles) DMF (15 mL) was added. Then 

(triisopropylsilyl)acetylene (770 µL, 3.44 mmol, 4.0 equiv.) was added and the 

reaction mixture was stirred at 120 °C for 16 h. The solvent was evaporated under 

reduced pressure and the residue was purified by flash chromatography on silica gel 

(hexane to hexane-ethyl acetate 20:1) to afford diyne 19a (418 mg, 76%) as an 

amorphous solid. 1H NMR (400 MHz, CDCl3) δ= 8.64 (bd, J= 1.3 Hz, 2H), 7.83 – 

7.90 (m, 8H), 7.53 (dd, J= 8.3, 1.5 Hz, 2H), 1.02 – 1.09 (m, 42H). 13C NMR (101 

MHz, CDCl3) δ= 133.2, 132.6, 132.1, 130.4, 128.9, 127.7, 127.5, 127.4, 127.1, 126.6, 

120.0, 107.7, 90.4, 18.9, 18.8, 11.5. IR, CHCl3 (cm−1): 3064, 3049, 2959, 2944, 2923, 

2891, 2865, 2152, 1606, 1502, 1463, 1438, 1383, 1367, 1301, 1189, 1072, 996, 883, 

849, 678, 660, 634. APCI MS: 639 ([M+H]+). HR APCI MS: Calculated for C44H55Si2: 

639.3842, found: 639.3835. 

 (Heptahelicen-2,17-diyldiethyne-2,1-diyl)bis[tris(1-methyl 

ethyl)silane] (19b). A pressure tube was charged with helicene 

18b (450 mg, 1.011 mmol, 1.0 equiv.), Pd2(dba)3 (18 mg, 0.0202 

mmol, 2 mol%), XPhos (38 mg, 0.0807 mmol, 8 mol%), 

potassium carbonate (837 mg, 6.060 mmol, 6.0 equiv.), flushed 

with nitrogen, and degassed (by three freeze-pump-thaw cycles) DMF (20 mL) was 

added. Then (triisopropylsilyl)acetylene (910 µL, 4.041 mmol, 4.0 equiv.) was added 

and the reaction mixture was stirred at 120 °C for 16 h. The solvent was evaporated 

under reduced pressure and the residue was purified by flash chromatography on silica 

gel (hexane to hexane-ethyl acetate 20:1) to afford diyne 19b (530 mg, 71%) as an 

amorphous solid. 1H NMR (400 MHz, CDCl3) δ= 8.04 (s, 2H), 8.00 (d, J= 8.2 Hz, 

2H), 7.87 (d, J= 8.2 Hz, 2H), 7.73 (d, J= 8.5 Hz, 2H), 7.50 (d, J= 8.5 Hz, 2H), 7.30 – 

 



Experimental section 

155 

 

7.33 (m, 2H), 7.27 (d, J= 8.3 Hz, 2H), 6.99 (dd, J= 8.2, 1.6 Hz, 2H), 1.09 – 1.16 (m, 

42H). 13C NMR (101 MHz, CDCl3) δ= 132.2, 131.53, 131.46, 129.1, 128.8, 128.1, 

127.8, 127.7, 127.4, 127.1, 127.0, 126.8, 126.7, 125.0, 118.9, 107.6, 89.0, 18.9, 11.5. 

IR, CHCl3 (cm−1): 3055, 2959, 2944, 2925, 2892, 2865, 2152, 1606, 1518, 1495, 1463, 

1428, 1390, 1383, 1366, 1308, 1191, 1073, 996, 883, 847, 679, 660, 641. APCI MS: 

739 ([M+H]+). HR ESI MS: Calculated for C52H59Si2: 739.4155, found: 739.4148. 

2,13-Bis[(4-(tert-butyl)phenyl)ethynyl]pentahelicene (20a). 

A 25 mL dry round bottom flask provided with a magnetic stir 

bar was charged with helicene 19a (100 mg, 0.156 mmol, 1 

equiv.), Pd(PPh3)2Cl2 (12 mg, 0.018 mmol, 0.1 equiv.) and CuI (125 mg, 0.656 mmol, 

4 equiv.). The flask was evacuated and backfilled with dry Ag three times to exclude 

moisture and air. Dry THF (1 mL), freshly distilled DIPA (1.5 mL) and 4-tert-

butyliodobenzene (86 mg, 0.329 mmol, 2.0 equiv) were added to the flask and stirred 

for 5 minutes before adding tetrabutylammoniumfloride (TBAF 1.0 M in THF, 0.5 

mL, 0.5 mmol, 3.0 equiv) in one portion. The mixture was stirred at 30 °C for 16 

hours. Silica was poured into the flask and solvent was removed under reduced 

pressure to adsorb the mixture which was then purified by silica gel column 

chromatography with hexane:DCM 10:1 affording the product 20a as a white solid 

(83 mg, 86%). 1H NMR (300 MHz, CDCl3) δ= 8.79 (s, 2H), 7.95 – 7.85 (m, 8H), 7.65 

(dd, J= 8.3, 1.4 Hz, 2H), 7.37 (d, J= 8.0 Hz, 4H), 7.30 (d, J= 8.5 Hz, 4H), 1.30 (d, J= 

0.9 Hz, 18H). 13C NMR (75 MHz, CDCl3) δ= 151.4, 132.8, 132.2, 132.1, 131.5, 130.4, 

129.2, 128.1, 127.7, 127.5, 127.2, 126.7, 125.3, 120.6, 120.0, 89.7, 89.4, 34.9, 31.3. 

FT-IR (cm−1): 3044, 2958, 2863, 2149, 1907, 1793, 1698, 1607, 1517, 1463, 1363, 

1266, 846, 727, 674, 561. HR-MS MALDI-ToF: Calculated for C46H38: 590.2974, 

found: 590.2994. 

2,17-Bis[(4-(tert-butyl)phenyl)ethynyl]heptahelicene 

20b. A 25 mL dry Schlenk provided with a magnetic stir bar 

was charged with helicene 19b (100 mg, 0.135 mmol, 1 

equiv.), Pd(PPh3)2Cl2 (10 mg, 0.013 mmol, 0.1 equiv.) and 

CuI (100 mg, 0.541 mmol, 4 equiv.). The Schlenk was 

evacuated and backfilled with dry Ag two times to exclude moisture and air. Dry THF 

(5 mL), freshly distilled DIPA (1.4 mL) and 4-tert-butyliodobenzene (140 mg, 0.541 

mmol, 4.0 equiv) were added to the Schlenk and stirred for 5 minutes before adding 

tetrabutylammoniumfloride (TBAF 1.0 M in THF, 0.41 mL, 0.41 mmol, 3.0 equiv) in 

one portion. The mixture was stirred at 30 °C for 20 hours. The crude was poured into 

a flask and silica was added, solvent was removed under reduced pressure to adsorb 

the mixture which was then purified by silica gel column chromatography with 

hexane:DCM 100:20 affording the product 20b as a white solid (63 mg, 67%). 1H 

NMR (300 MHz, CDCl3) δ= 8.07 (s, 2H), 8.07 (d, J= 8.2 Hz, 2H), 8.00 (d, J= 8.2 Hz, 

2H), 7.79 (d, J= 8.5 Hz, 2H), 7.54 (d, J= 8.5 Hz, 2H), 7.44 – 7.38 (m, 10H), 7.32 (d, 

J= 8.2 Hz, 2H), 7.04 (dd, J= 8.2, 1.6 Hz, 2H), 1.37 (s, 18H). 13C NMR (126 MHz, 

 



Experimental section 

156 

 

CDCl3) δ= 151.3, 132.2, 131.7, 131.5, 131.3, 129.1, 128.8, 127.8, 127.6, 127.5, 127.4, 

127.1, 127.04, 127.01, 126.9, 125.5, 125.1, 120.9, 118.9, 89.7, 88.8, 35.0, 31.4. FT-

IR (cm−1): 3048, 2959, 2923, 2858, 1907, 1732, 1605, 1503, 1462, 1363, 1264, 1102, 

1017, 834, 549. HR-MS MALDI-ToF: Calculated for C54H42: 690.3287, found: 

690.3267. 

2,13-Bis[penta(4-tert-butyl(phenyl))phenyl]pentahelicene  

21a To a 30 mL microwave vial provided with a magnetic stir 

bar was added 20a (40 mg, 0.068 mmol, 1.0 equiv) and tetra-

2,3,4,5-tetrakis[4-(1,1-dimethylethyl)phenyl]2,4-cyclopen 

tadien-1-one 5 (128 mg, 0.210 mmol, 3.1 equiv). The vial was 

placed in the microwave reactor and heated to 280 °C with a hold time of 40 minutes 

and stirring at 300 rpm, same conditions were repeated for 6 times. After cooling, 

methanol was added, and the crude was sonicated to obtain a suspension. The solid 

was filtered to reach to compound 21a as a brown solid (33 mg, 28%). 1H NMR (300 

MHz, CDCl3) δ= 8.42 (s, 2H), 7.55 (d, J= 8.5 Hz, 2H), 7.46 (d, J= 8.5 Hz, 2H), 7.34 

(s, 2H), 7.23 (s, 2H), 7.05 – 6.57 (m, 32H), 6.51 (d, J= 8.7 Hz, 2H), 6.11 (dd, J= 8.1, 

2.0 Hz, 2H), 5.99 (d, J= 9.1 Hz, 2H), 5.92 (d, J= 8.3 Hz, 2H), 5.84 (d, J= 8.3 Hz, 2H), 

1.24 (s, 18H), 1.14 (s, 18H), 1.09 (s, 18H), 1.01 (s, 18H), 0.57 (s, 18H). 13C NMR 

(126 MHz, CDCl3) δ= 148.1, 147.3, 147.2, 147.1, 146.7, 141.3, 141.0, 140.9, 140.2, 

139.7, 138.5, 138.4, 138.2, 138.0, 137.9, 137.9, 135.7, 133.1, 132.0, 131.6, 131.2, 

130.7, 130.4, 130.1, 129.4, 128.9, 127.2, 126.1, 126.0, 125.7, 124.9, 123.8, 123.0, 

122.8, 122.2, 122.1, 34.4, 34.0, 34.0, 33.9, 33.3, 31.5, 31.3, 31.2, 31.1, 30.8. FT-IR 

(cm−1): 3088, 3053, 2962, 2905, 2870, 1910, 1746, 1615, 1514, 1462, 1393, 1361, 

1270, 1120, 1020, 832, 575. HR-MS MALDI-ToF: Calculated for C134H142: 

1751.1111, found: 1751.1151. 

2,17-Bis[penta(4-tert-butyl(phenyl))phenyl]pentahelicene 

21b. To a 10 mL microwave vial provided with a magnetic stir 

bar was added 20b (30 mg, 0.043 mmol, 1.0 equiv) and tetra-

2,3,4,5-tetrakis[4-(1,1-dimethylethyl)phenyl]2,4-cyclopenta 

dien-1-one 5 (87 mg, 0.14 mmol, 3.1 equiv). The vial was 

placed in the microwave reactor and heated to 280 °C with a 

hold time of 45 minutes and stirring at 600 rpm. After cooling, 

methanol was added, and the crude was sonicated to obtain a 

suspension. The solid was filtered to reach to compound 21b as a brown solid (36 mg, 

45%). 1H NMR (500 MHz, CDCl3) δ= 7.89 (s, 2H), 7.81 (d, J= 8.2 Hz, 2H), 7.72 (d, 

J= 8.2 Hz, 2H), 7.59 z(d, J= 8.6 Hz, 2H), 7.55 (d, J= 8.6 Hz, 2H), 7.13 (d, J= 8.2 Hz, 

2H), 6.88 – 6.50 (m, 34H), 6.47 (d, J= 8.1 Hz, 2H), 5.96 (d, J= 8.1 Hz, 2H), 5.85 (d, 

J= 8.0 Hz, 2H), 5.65 (s, 4H), 1.14 (s, 18H), 1.12 (s, 18H), 1.09 (s, 18H), 1.06 (s, 18H), 

0.43 (s, 18H).13C NMR (126 MHz, CDCl3) δ= 147.5, 147.4, 147.3, 147.2, 146.2, 

140.6, 140.3, 140.3, 139.1, 138.7, 138.4, 138.2, 137.6, 137.2, 136.9, 132.6, 132.2, 

132.0, 131.7, 131.3, 131.2, 131.1, 131.0, 130.4, 129.5, 129.2, 129.0, 128.4, 127.9, 

 



Experimental section 

157 

 

127.4, 126.2, 125.7, 125.4, 124.7, 124.6, 123.2, 123.1, 123.0, 122.9, 122.3, 122.1, 

34.2, 34.2, 34.1, 34.1, 33.3, 31.6, 31.4, 31.4, 31.3, 30.7. FT-IR (cm−1): 3051, 2961, 

2904, 2866, 1899, 1695, 1610, 1510, 1461, 1361, 1270, 831, 572. HR-MS MALDI-

ToF: Calculated for C142H146: 1851.1424, found: 1851.1429. 

[9]Helical bilayer nanographene ([9]HBNG). To a 100 mL 

flask with magnetic stir bar was added polyphenylene 21a (20 

mg, 0.011 mmol, 1 equiv.). The flask was purged and 

backfilled with argon and dry dicloromethane (50 mL) was 

added. A glass Pasteur pipette was attached to an argon inlet 

and dipped into the solution. Argon was bubbled continuously through the solution, 

while stirring, for the duration of the reaction. The mixture was cooled to 0 °C in an 

ice water bath and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) (360 mg, 

1.586 mmol, 140 equiv.) was added in one portion. The mixture was stirred for 5 

minutes and trifluoromethanesulfonic acid (1.20 mL, 2.052 g, 13.67 mmol, 1200 

equiv) was added dropwise. The mixture was stirred at 0 °C for 20 minutes. After that 

time a HNaCO3 saturated solution was added to the reaction flask and the crude was 

extracted with DCM and washed twice with a HNaCO3 saturated solution (50 mL) 

and twice with brine (50 mL). From this step the organic phases were dried with 

MgSO4 and filtered, the solvent was removed under reduced pressure. The mixture 

was purified by silica gel column in hexane:DCM 10:1, affording compound 

[9]HBNG as a yellow solid (12 mg, 61%). 1H NMR (500 MHz, CDCl3) δ= 9.18 (s, 

2H), 9.13 (s, 2H), 9.06 (s, 2H), 8.87 (s, 2H), 8.75 (s, 2H), 8.71 (s, 2H), 8.39 (s, 2H), 

8.21 (s, 2H), 8.20 (s, 2H), 8.14 (s, 2H), 8.13 (s, 2H), 7.96 (d, J= 8.1 Hz, 2H), 7.86 (d, 

J= 8.1 Hz, 2H), 7.61 (s, 2H), 1.93 (s, 18H), 1.86 (s, 18H), 1.82 (s, 18H), 1.43 (s, 18H), 

1.21 (s, 18H). 13C NMR (126 MHz, CDCl3) δ= 147.9, 147.7, 147.4, 146.8, 146.5, 

130.4, 130.3, 130.3, 130.2, 129.9, 129.4, 129.3, 129.0, 128.9, 128.8, 128.7, 127.9, 

127.9, 127.4, 126.8, 126.6, 125.7, 123.7, 123.6, 123.5, 123.4, 122.9, 122.6, 122.3, 

119.8, 119.8, 119.6, 119.5, 119.3, 119.2, 119.0, 118.9, 118.7, 118.3, 118.0, 117.3, 

117.2, 117.2, 116.7, 35.9, 35.8, 35.6, 35.2, 34.6, 32.6, 32.3, 32.3, 32.0, 31.6. FT-IR 

(cm−1): 3102, 3046, 2953, 2906, 2868, 1745, 1606, 1575, 1478, 1361, 1261, 1201, 

867. HR-MS MALDI-ToF: Calculated for C134H118: 1726.9233, found: 1726.9267. 

[11]Helical bilayer nanographene ([11]HBNG). To a 250 mL 

flask with magnetic stir bar was added polyphenylene 21b (55 

mg, 0.094 mmol, 1 equiv.). The flask was purged and 

backfilled with argon and dry dicloromethane (90 mL) was 

added. A glass Pasteur pipette was attached to an argon inlet 

and dipped into the solution. Argon was bubbled continuously 

through the solution, while stirring, for the duration of the 

reaction. The mixture was cooled to 0 °C in an ice water bath and DDQ (320 mg, 

1.409 mmol, 44 equiv) was added in one portion. The mixture was stirred for 5 

minutes and trifluoromethanesulfonic acid (1.16 mL, 1.984 g, 13.22 mmol, 141 equiv) 



Experimental section 

158 

 

was added dropwise. The mixture was stirred at 0 °C for 1 hour, after that time a 

HNaCO3 saturated solution was added to the reaction flask and the crude was 

extracted with DCM and washed twice with a HNaCO3 saturated solution (90 mL) 

and twice with brine (90 mL). From this step the organic phases were dried with 

MgSO4 and filtered, the solvent was removed under reduced pressure. The mixture 

was purified by silica gel column in hexane:DCM 80:20, affording compound 

[11]HBNG as a yellow solid (42 mg, 75%). 1H NMR (700 MHz, CDCl3) δ = 9.47 (s, 

4H), 9.46 (d, J= 7.4 Hz, 4H), 9.38 (d, J= 7.4 Hz, 4H), 9.12 (s, 2H), 8.95 (s, 2H), 8.44 

(s, 2H), 8.20 (s, 2H), 7.35 (s, 2H), 6.93 (d, J= 1.6 Hz, 2H), 6.90 (d, J= 7.5 Hz, 2H), 

6.11 – 6.08 (m, 4H), 5.32 (d, J= 7.9 Hz, 2H), 1.96 (s, 18H), 1.95 (s, 18H), 1.94 (s, 

18H), 1.87 (s, 18H), 0.89 (s, 18H). 13C NMR (176 MHz, CDCl3) δ = 149.3, 149.2, 

149.1, 146.4, 131.6, 131.1, 131.0, 130.9, 130.8, 130.7, 130.7, 130.6, 130.4, 130.4, 

129.1, 128.1, 127.5, 126.9, 126.2, 125.9, 125.2, 125.2, 124.9, 124.9, 124.6, 124.5, 

124.2, 123.9, 123.7, 123.0, 121.3, 121.1, 120.6, 120.5, 120.5, 120.2, 119.9, 119.9, 

119.8, 119.2, 119.1, 119.0, 119.0, 118.7, 118.5, 118.3, 118.0, 36.0, 36.0, 36.0, 34.4, 

32.6, 32.3, 31.3. FT-IR (cm−1): 3077, 3045, 2955, 2906, 2870, 1605, 1572, 1479, 1369, 

1257, 870. HR-MS MALDI-ToF: Calculated for C142H122: 1826.9547, found: 

1826.9566. 

Chapter 4 

7,7'-dibromo-1,1'-binaphthyl-2,2'-diol 23. A 10 mL tube provided 

with a magnetic stir bar was charged with 7-bromo-2-naphtol 22 (500 

mg, 2.241 mmol, 1 equiv.), Cu-TMDA(OH)(Cl) (50 mg, 0.108 

mmol, 0.05 equiv.) and dissolved in DCM (2.5 mL). The mixture was 

sonicated for 5 minutes, the stirred at 25 ºC for 16 h under air. The crude was extracted 

in ethyl acetate washing with water (30 mL) and brine (30 mL). The organic phase 

was dried with Na2SO4, and filtered, and the solvent was removed under reduced 

pressure. The resulting solid was dissolved in the minimum amount of DCM, then, 

hexane was added, and the mixture was sonicated until precipitation. The mixture was 

filtered to obtained compound 23 as a white solid (414 mg, 83%). 1H NMR (300 MHz, 

CDCl3) δ= 7.97 (d, J= 9.0 Hz, 1H), 7.78 (d, J= 8.7 Hz, 1H), 7.48 (dd, J= 8.7, 1.9 Hz, 

1H), 7.40 (d, J= 9.0 Hz, 1H), 7.23 (d, J= 1.9 Hz, 1H), 5.01 (s, 1H).171 

7,7'-bis[(4-(tert-butyl)phenyl)ethynyl]-1,1'-binaphthyl-

2,2'-diol 24. To a dry 30 mL microwave reactor vial under 

argon atmosphere and provided with a magnetic stir bar, CuI 

(120 mg, 0.630 mmol, 0.4 equiv.), Pd(PPh3)2Cl2 (360 mg, 

0.315 mmol, 0.2 equiv.), 7,7'-dibromo-1,1'-binaphthyl-2,2'-diol 23 (700 mg, 1.58 

mmol, 1 equiv.), 4-(tert-butyl)phenylacetylene 3 (740 mg, 4.73 mmol, 3 equiv.), 5 mL 

of anhydrous previously deoxygenated DMF and 3 mL of distilled triethylamine were 

added. The reaction was carried out for 3 hours at 85 ºC and 600 rpm in a microwave 

 
171 Y. Nojima, M. Hasegawa, N. Hara, Y. Imai, Y. Mazakia, Chem. Commun. 2019, 55, 2749. 



Experimental section 

159 

 

reactor. The resulting crude was extracted with DCM and washed two times with HCl 

1M (50 mL), water (50 mL) and brine (50 mL). The organic phase was dried with 

MgSO4, and solvent was removed under reduced pressure. The crude was purified by 

silica gel chromatography column in hexane/ethyl acetate 4:1. Solvent was removed, 

and the product was recrystallized by adding the minimum amount of DCM and 

hexane, obtaining compound 24 as white needles (908 mg, 96%). 1H NMR (500 MHz, 

CDCl3) δ= 7.99 (d, J= 8.9 Hz, 1H), 7.88 (d, J= 8.4 Hz, 1H), 7.50 (dd, J= 8.4, 1.6 Hz, 

1H), 7.41 (d, J= 8.9 Hz, 1H), 7.38 (d, J= 9.1 Hz, 2H), 7.31 – 7.29 (m, 3H), 5.03 (s, 

1H), 1.29 (s, 9H). 13C NMR (126 MHz, CDCl3) δ= 153.5, 151.8, 133.4, 131.6, 131.5, 

129.0, 128.7, 127.3, 125.4, 122.9, 120.0, 118.6, 110.5, 90.7, 89.3, 34.9, 31.3. FT-IR 

(cm−1): 3530, 3333, 3068, 2961, 2864, 1899, 1617, 1505, 1442, 1330, 1192, 1153, 

836, 560.  HRMS: Calculated for C44H38O2: 598.2872, found: 598.2851. 

M*-7,7'-Bis[penta(4-tert-butyl(phenyl)) 

phenyl]-1,1'-binaphthyl-2,2'-diol 25. To a 30 

mL microwave vial provided with a magnetic 

stir bar was added 24 (200 mg, 0.334 mmol, 1.0 

equiv.) and tetra-2,3,4,5-tetrakis[4-(1,1-di 

methylethyl)phenyl]2,4-cyclopentadien-1-one 

5 (610 mg, 1.002 mmol, 3 equiv.). The vial was 

placed in the microwave reactor and heated to 280 °C with a hold time of 45 minutes 

and stirring at 600 rpm. After cooling, the crude was dissolved in the minimum 

amount of DCM, and methanol was added to obtain a suspension. The solid was 

filtered washing with methanol affording compound 25 as a white solid (547 mg, 

93%). 1H NMR (500 MHz, CDCl3) δ= 7.64 (d, J= 8.8 Hz, 1H), 7.42 (d, J= 8.4 Hz, 

1H), 7.04 – 6.99 (m, 2H), 6.94 (s, 1H), 6.85 – 6.71 (m, 10H), 6.67 – 6.58 (m, 8H), 

6.50 (d, J= 8.3 Hz, 2H), 3.74 (s, 1H), 1.09 (s, 9H), 1.07 (s, 27H), 1.05 (s, 9H). 13C 

NMR (126 MHz, CDCl3) δ= 152.3, 147.6, 147.53, 147.48, 147.3, 147.3, 141.0, 140.8, 

140.7, 140.64, 140.59, 140.2, 139.4, 138.1, 138.01, 137.98, 137.8, 137.7, 132.4, 

131.5, 131.2, 131.16, 131.1, 131.0, 130.7, 130.4, 130.2, 128.2, 127.4, 126.8, 126.4, 

124.2, 123.5, 123.4, 123.2, 123.1, 123.0, 122.98, 122.94, 122.9, 117.5, 111.8, 34.23, 

34.19, 34.18, 34.15, 34.11, 31.42, 31.34, 31.32, 31.28. FT-IR (cm−1): 3536, 3055, 

2961, 2905, 2864, 1895, 1617, 1508, 1363, 1268, 832, 571.  HRMS: Calculated for 

C132H142O2: 1759.1010, found: 1759.1040. 

 

 

 

 



Experimental section 

160 

 

M*-7,7'-bis(penta(4-tert-butyl(phenyl))phenyl) 

-2'-hydroxy-[1,1'-binaphthalen]-2-yl (1R)-10-

camphorsulfonate 26a-b. A 10 mL tube provided 

with a magnetic stir bar was charged with BINOL-

polyarene 25 (100 mg, 0.057 mmol, 1 equiv.) and 

(1R)-10-camphor sulphonyl chloride (142 mg, 

0.568 mmol, 10 equiv.). The tube was evacuated 

and backfilled with dry Ag two times to exclude 

moisture and air. Dry DCM (2 mL) and anhydrous 

pyridine (0.05 mL) were added at 0 ºC. The mixture was stirred at 0 ºC for 5 h and 

warmed to 20 ºC for 16 h. The crude was extracted in chloroform washing with NH4Cl 

(50 mL) and brine (50 mL). The organic phase was dried with Mg2SO4, and filtered, 

and the solvent was removed under reduced pressure. The crude was purified by silica 

gel chromatography column with toluene, affording diastereomer 26a (30 mg, 27%) 

and diastereomer 26b (28 mg, 25%).  

M-7,7'-bis(penta(4-tert-butyl(phenyl))phenyl)-2'-hydroxy-[1,1'-binaphthalen]-

2-yl (1R)-10-camphorsulfonate 26a 1H NMR (500 MHz, CDCl3) δ= 7.79 (d, J= 9.0 

Hz, 1H), 7.49 (d, J= 9.1 Hz, 1H), 7.47 (d, J= 8.3 Hz, 1H), 7.42 (d, J= 8.9 Hz, 1H), 

7.28 (d, J= 8.6 Hz, 1H), 7.16 (d, J= 8.4 Hz, 1H), 7.15 (s, 1H), 7.02 (s, 1H), 6.96 (s, 

1H), 6.91 – 6.88 (m, 2H), 6.84 – 6.70 (m, 24H), 6.65 – 6.54 (m, 12H), 6.52 (dd, J= 

8.7 Hz, J= 2.4 Hz, 1H), 6.40 (m, 3H), 3.53 (s, 1H), 2.47 (d, J= 15.1 Hz, 1H), 2.22 – 

2.09 (m, 2H), 1.90 – 1.83 (m, 2H), 1.80 (d, J= 15.1 Hz, 1H), 1.72 (d, J= 18.4 Hz, 1H), 

1.11 (s, 9H), 1.10 (s, 9H), 1.09 – 1.07 (m, 54H), 1.06 (s, 9H), 1.01 (s, 9H), 0.84 (s, 

3H), 0.58 (s, 3H). 13C NMR (126 MHz, CDCl3) δ= 213.2, 150.9, 148.0, 147.9, 147.6, 

147.6, 147.5, 147.4, 147.3, 147.2, 146.3, 141.3, 141.1, 141.03, 140.99, 140.8, 140.7, 

140.6, 140.35, 140.28, 140.2, 140.1, 139.9, 138.5, 138.2, 138.2, 138.0, 137.9, 137.9, 

137.8, 137.7, 137.3, 132.6, 132.5, 132.1, 131.7, 131.5, 131.3, 131.2, 131.0, 130.8, 

130.6, 129.9, 128.5, 127.7, 127.5, 126.9, 126.6, 126.3, 124.2, 123.5, 123.5, 123.1, 

122.9, 122.2, 117.4, 114.3, 57.8, 48.0, 47.6, 42.9, 42.3, 34.29, 34.27, 34.17, 34.15, 

34.13, 34.11, 34.07, 31.49, 31.45, 31.35, 31.33, 31.31, 26.8, 25.1, 19.9, 19.5. FT-IR 

(cm−1): 3534, 3060, 2964, 2864, 1911, 1735, 1512, 1363, 1160, 830, 571. HRMS: 

Calculated for C142H156O5S: 1973.1673, found: 1973.1664. 

P-7,7'-bis(penta(4-tert-butyl(phenyl))phenyl) -2'-hydroxy-[1,1'-binaphthalen]-2-

yl (1R)-10-camphorsulfonate 26b 1H NMR (500 MHz, CDCl3) δ= 7.79 (d, J= 9.0 

Hz, 1H), 7.49 (d, J= 8.9 Hz, 1H), 7.50 – 7.44 (m, 2H), 7.24 (s, 1H), 7.15 – 7.13 (m, 

2H), 7.07 (s, 1H), 6.98 (s, 1H), 6.89 – 6.36 (m, 40H), 6.41 (d, J= 8.2 Hz, 2H), 6.37 (d, 

J= 8.3 Hz, 1H), 3.54 (s, 1H), 2.49 (d, J= 14.9 Hz, 1H), 2.21 – 2.12 (m, 1H), 2.08 – 

2.03 (m, 1H), 1.93 – 1.86 (m, 2H), 1.85 – 1.80 (m, 1H), 1.72 (d, J= 18 Hz, 1H), 1.12 

(s, 9H), 1.11 (s, 9H), 1.09 (s, 9H), 1.08 (s, 9H), 1.07 (s, 9H), 1.07 (s, 9H), 1.07 (s, 9H), 

1.06 (s, 9H), 1.05 (s, 9H), 1.00 (s, 9H), 0.81 (s, 3H), 0.60 (s, 3H). 13C NMR (126 MHz, 

CDCl3) δ= 213.2, 151.0, 147.8, 147.8, 147.7, 147.6, 147.5, 147.4, 147.3, 147.2, 146.4, 



Experimental section 

161 

 

141.3, 141.1, 141.0, 140.8, 140.7, 140.5, 140.3, 140.3, 140.2, 140.2, 140.1, 139.9, 

138.6, 138.3, 138.2, 138.0, 138.0, 137.96, 137.94, 137.8, 137.7, 137.3, 132.7, 132.6, 

132.1, 131.8, 131.2, 131.1, 131.0, 130.9, 130.6, 129.8, 129.6, 128.7, 127.7, 127.6, 

126.9, 126.5, 126.1, 124.5, 124.0, 123.7, 123.5, 123.4, 123.2, 123.1, 123.0, 122.8, 

122.2, 117.7, 114.7, 58.0, 47.9, 47.5, 43.3, 42.4, 34.31, 34.26, 34.18, 34.16, 34.14, 

34.12, 34.06, 31.50, 31.45, 31.36, 31.34, 31.32, 31.30, 26.8, 25.5, 19.9, 19.7.  

M-7,7'-Bis[penta(4-tert-butyl(phenyl)) 

phenyl]-1,1'-binaphthyl-2,2'-diol (M-

25). A 10 mL tube provided with a 

magnetic stir bar was charged with 26a (30 

mg, 0.015 mmol, 1 equiv.) and 1 mL of 

THF. Then NaOH (10 mg, 0.243 mmol, 16 

equiv.) and NBu4Br (49 mg, 0.152 mmol, 

10 equiv.) were dissolved in 0.2 mL of 

distilled water and added to the reaction mixture. The mixture was stirred at 50 ºC for 

16 h. The crude was extracted in DCM washing with NH4Cl (30 mL) and brine (30 

mL). The organic phase was dried with Mg2SO4, and filtered, the solvent was removed 

under reduced pressure. The crude was purified by silica gel chromatography column 

with toluene, affording diastereomer M-25 as a white solid (25 mg, 92%). The same 

procedure was followed from 26b to obtain P-25 as a white solid (27 mg 99%).  

M*- oxa[9]Helical bilayer nanographene (oxa[9]HBNG). 

To a 250 mL flask with magnetic stir bar was added 

polyphenylene 25 (60 mg, 0.034 mmol, 1 equiv.). Dry 

dichloromethane (60 mL) was added. A glass Pasteur pipette 

was attached to an argon inlet and dipped into the solution. 

Argon was bubbled continuously through the solution, 

while stirring, for the duration of the reaction. The mixture was cooled to 0 °C in an 

ice water bath and DDQ (464 mg, 2.040 mmol, 60 equiv.) was added in one portion. 

The mixture was stirred for 5 minutes and trifluoromethanesulfonic acid (0.6 mL, 

1.021 g, 6.183 mmol, 200 equiv.) was added dropwise. The mixture was stirred at 0 

°C for 25 minutes, after that time a HNaCO3 saturated solution was added to the 

reaction flask and the crude was extracted with DCM and washed twice with a 

HNaCO3 saturated solution (100 mL) and twice with brine (100 mL). From this step 

the organic phases were dried with MgSO4 and filtered, the solvent was removed 

under reduced pressure. The mixture was purified by silica gel column in 

hexane:DCM 70:30, affording compound oxa[9]HBNG as a yellow solid (36 mg, 

61%). 1H NMR (500 MHz, CDCl3) δ= 9.54 (s, 1H), 9.35 (s, 1H), 9.34 (s, 1H), 9.29 

(s, 1H), 9.24 (s, 1H), 9.00 (s, 1H), 8.83 (d, J= 8.4 Hz, 1H), 8.58 (d, J= 8.4 Hz, 1H), 

8.35 (s, 1H), 7.98 (s, 1H), 7.62 (s, 1H), 7.39 (s, 1H), 7.15 (s, 1H), 1.98 (s, 9H), 1.91 

(s, 9H), 1.70 (s, 9H), 0.97 (s, 9H), 0.62 (s, 9H). 13C NMR (126 MHz, CDCl3) δ= 154.6, 

148.8, 148.4, 147.8, 147.4, 144.9, 130.6, 130.3, 130.1, 130.0, 129.96, 129.3, 129.2, 



Experimental section 

162 

 

128.55, 128.5, 128.3, 128.1, 127.8, 126.6, 124.1, 124.0, 123.9, 123.6, 123.2, 121.8, 

121.3, 121.0, 120.9, 120.7, 120.6, 120.3, 119.8, 119.5, 119.3, 119.1, 118.8, 118.7, 

118.6, 118.4, 118.0, 117.9, 117.3, 115.9, 112.5, 35.9, 35.8, 35.5, 34.7, 34.4, 32.32, 

32.30, 32.2, 31.4, 30.7. FT-IR (cm−1): 3086, 2951, 2903, 2867, 1856, 1741, 1601, 

1577, 1477, 1462, 1360, 1259, 1232, 941, 966. HRMS: Calculated for C132H116O: 

1716.9026, found: 1716.8948. 

M-oxa[9]helical bilayer nanographene (M-oxa[9]HBNG). To a 50 mL flask with 

magnetic stir bar was added polyphenylene M-25 (20 mg, 0.011 mmol, 1 equiv.). Dry 

dichloromethane (20 mL) was added. A glass Pasteur pipette was attached to an argon 

inlet and dipped into the solution. Argon was bubbled continuously through the 

solution, while stirring, for the duration of the reaction. The mixture was cooled to 

−30 °C in an ice water bath and DDQ (62 mg, 0.273 mmol, 24 equiv.) was added in 

one portion. The mixture was stirred for 5 minutes and trifluoromethanesulfonic acid 

(0.1 mL, 1.136 mmol, 100 equiv.) was added dropwise. The mixture was stirred at 

−30 °C for 50 minutes, after that time a HNaCO3 saturated solution was added to the 

reaction flask and the crude was extracted with DCM and washed twice with a 

HNaCO3 saturated solution (100 mL) and twice with brine (100 mL). From this step 

the organic phases were dried with MgSO4 and filtered, the solvent was removed 

under reduced pressure. The mixture was purified by silica gel preparative in CS2, 

affording compound M-oxa[9]HBNG as a yellow solid (10 mg, 51%). 

P-oxa[9]helical bilayer nanographene (P-oxa[9]HBNG). To a 50 mL flask with 

magnetic stir bar was added polyphenylene P-25 (25 mg, 0.014 mmol, 1 equiv.). Dry 

dichloromethane (25 mL) was added. A glass Pasteur pipette was attached to an argon 

inlet and dipped into the solution. Argon was bubbled continuously through the 

solution, while stirring, for the duration of the reaction. The mixture was cooled to 

−30 °C in an ice water bath and DDQ (77 mg, 0.341 mmol, 24 equiv.) was added in 

one portion. The mixture was stirred for 5 minutes and trifluoromethanesulfonic acid 

(0.12 mL, 1.420 mmol, 100 equiv.) was added dropwise. The mixture was stirred at 

−30 °C for 45 minutes, after that time a HNaCO3 saturated solution was added to the 

reaction flask and the crude was extracted with DCM and washed twice with a 

HNaCO3 saturated solution (100 mL) and twice with brine (100 mL). From this step 

the organic phases were dried with MgSO4 and filtered, the solvent was removed 

under reduced pressure. The mixture was purified by silica gel preparative in CS2, 

affording compound P-oxa[9]HBNG as a yellow solid (10 mg, 40%). 



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix 1 

  



 

 

 

 

 



Appendix 1. Chapter 1 

165 

 

APPENDIX 1. Chapter 1 

Crystallographic Data 

Single crystals suitable for X-ray diffraction analysis were obtained for both isomers 

of compound 7, for compound syn 8, and also for compound syn 10. Crystals of both 

isomers of 7 and compound syn 10 are not stable out of the mother liquor and quickly 

lose crystallinity.  

The structure refinements of syn 7, anti 7 and syn 10 present high wR2 values due to 

the high degree of disorder that many of the atoms in the asymmetric unit display. As 

it is usual in the crystal structures of nanographene molecules, solvent molecules in 

the interstices are extremely disordered, as well as some of the peripheral tBu 

substituents. The coordinates of many of the atoms in these tBu fragments had to be 

refined with the aid of geometrical restraints and/or two alternative sets of positions, 

and for some of the terminal methyl groups the positions found in the electron density 

maps could not account for 100% of the expected electron density. 

Structural details of syn 7 (CCDC 2154765)  

 
Figure AP1.1. Labelled asymmetric unit of compound syn 7 (hydrogen atoms and solvent 

molecules have been omitted for clarity). In the disordered tBu groups only one of the 

alternative sets of position is represented. 

Table AP1.1. Sample and crystal data for syn 7. 

Chemical formula (C126H136)·3.75(H2O) 

Formula weight 1717.90 g/mol 

Temperature 250(2) K 

Wavelength 0.71073 Å 

Crystal habit clear colorless needle 

Crystal system triclinic 

Space group P -1 

a = 12.093 (2) Å α = 98.008(5)° 



Appendix 1. Chapter 1 

166 

 

Unit cell 

dimensions 

 

b = 16.919(2) Å β = 90.350(5)° 

c = 30.799(3) Å γ = 108.296(4)° 

Volume 5916.4(12) Å3 

Density 

(calculated) 
0.964 g/cm3 

Z 2 

Table AP1.2. Data collection and structure refinement for syn 7. 

Theta range for data collection 1.28 to 25.24° 

Index ranges -14<=h<=14, -20<=k<=20, -36<=l<=36 

Reflections collected 61800 

Independent reflections 20875 [R(int) = 0.1106] 

Coverage of independent 

reflections 
97.5% 

Absorption correction multi-scan 

Max. and min. transmission 0.9970 and 0.9820 

Refinement method Full-matrix least-squares on F2 

Refinement program SHELXL-2014/7 (Sheldrick, 2014) 

Function minimized Σ w(Fo
2 - Fc

2)2 

Data / restraints / parameters 20875 / 987 / 1134 

Goodness-of-fit on F2 1.117 

Final R indices 7699 data; I>2σ(I) R1 = 0.1887, wR2 = 0.4676 
 all data R1 = 0.3301 wR2 = 0.5390 

Weighting scheme 
w=1/[σ2(Fo

2)+(0.2000P)2+21.700P] 

where P=(Fo
2+2Fc

2)/3 

Structural details of anti 7 (CCDC 2154766) 

 

Figure AP1.2. Labelled asymmetric unit of compound anti 7 (hydrogen atoms and solvent 

molecules have been omitted for clarity). 

 



Appendix 1. Chapter 1 

167 

 

Table AP1.3. Sample and crystal data for anti 7. 

Chemical formula (C126H136)·0.25 (CH3OH)·3.75 (H2O) 

Formula weight 1725.91 g/mol 

Temperature 150(2) K 

Wavelength 0.71073 Å 

Crystal habit colorless prismatic 

Crystal system triclinic 

Space group P -1 

Unit cell dimensions 

 

a = 17.2815(16) Å α = 65.267(4)° 

b = 19.0056(17) Å β = 72.847(4)° 

c = 19.6699(18) Å γ = 88.649(4)° 

Volume 5569.6(9) Å3 

Density (calculated) 1.029 g/cm3 

Z 2 

Table AP1.4. Data collection and structure refinement for anti 7. 

Theta range for data collection 1.19 to 25.03° 

Index ranges -20<=h<=20, -22<=k<=22, -23<=l<=23 

Reflections collected 105318 

Independent reflections 19632 [R(int) = 0.1960] 

Coverage of independent 

reflections 
99.7% 

Absorption correction multi-scan 

Max. and min. transmission 0.9990 and 1.0000 

Refinement method Full-matrix least-squares on F2 

Refinement program SHELXL-2014/7 (Sheldrick, 2014) 

Function minimized Σ w(Fo
2 - Fc

2)2 

Data / restraints / parameters 9632 / 1434 / 1179 

Goodness-of-fit on F2 1.017 

Final R indices 7130 data; I>2σ(I) R1 = 0.2129, wR2 = 0.4765 
 all data R1 = 0.3573, wR2 = 0.5926 

Weighting scheme 
w=1/[σ2(Fo

2)+(0.3200P)2+19.7000P] 

where P=(Fo
2+2Fc

2)/3 

 

 

 

 

 



Appendix 1. Chapter 1 

168 

 

Structural details of syn 8 (CCDC 2209634)  

 

Figure AP1.3. Labelled asymmetric unit of compound syn 8 (hydrogen atoms and solvent 

molecules have been omitted for clarity). In the disordered tBu groups only one of the 

alternative sets of position is represented. 

Table AP1.5. Sample and crystal data for syn 8. 

Chemical formula C126H130 

Formula weight 1644.29 g/mol 

Temperature 100(2) K 

Wavelength 1.54184 Å 

Crystal habit pale yellow plate 

Crystal system triclinic 

Space group P -1 

Unit cell dimensions 

 

a = 16.8928(3) Å α = 71.5968(18)° 

b = 18.4600(4) Å β = 65.0663(18)° 

c = 19.9255(4)Å γ =  62.9236(19)° 

Volume 4957.6(2) Å3 

Density (calculated) 1.102 g/cm3 

Z 2 

Table AP1.6. Data collection and structure refinement for syn 8. 

Theta range for data collection 2.72 to 68.28° 

Index ranges -19<=h<=20, -22<=k<=21, -20<=l<=24 

Reflections collected 63593 

Independent reflections 18134 [R(int) = 0.0350] 

Coverage of independent 

reflections 
99.8% 

Absorption correction multi-scan 

Max. and min. transmission 1.000 and 0.863 

Refinement method Full-matrix least-squares on F2 

Refinement program SHELXL-2019/1 (Sheldrick, 2019) 



Appendix 1. Chapter 1 

169 

 

Function minimized Σ w(Fo
2 - Fc

2)2 

Data / restraints / parameters 18134 / 69 / 1318 

Goodness-of-fit on F2 1.034 

Final R indices 
13621 data; 

I>2σ(I) 
R1 = 0.0510, wR2 = 0.1320 

 all data R1 = 0.0717, wR2 = 0.1442 

Weighting scheme 
w=1/[σ2(Fo

2)+(0.0754P)2+1.3997P] 

where P=(Fo
2+2Fc

2)/3 

Structural details of syn 10 (CCDC 2209635)  

 
Figure AP1.4. Labelled asymmetric unit of compound syn 10 (hydrogen atoms and solvent 

molecules have been omitted for clarity). In the disordered tBu groups only one of the 

alternative sets of position is represented. 

Table AP1.7. Sample and crystal data for syn 10. 

Chemical formula (C126H120)·2.5 (C2H4Cl2)·2 (H2O) 

Formula weight 956.80 g/mol 

Temperature 150(2) K 

Wavelength 0.71073 Å 

Crystal habit clear intense yellow prismatic 

Crystal system triclinic 

Space group P -1 

Unit cell dimensions 

 

a = 14.1128(7) Å α = 70.4452(19)° 

b = 17.4044(8) Å β = 84.838(2)° 

c = 25.6992(10) Å γ = 84.805(2)° 

Volume 5911.9(5) Å3 

Density (calculated) 1.075 g/cm3 

Z 4 

 

 



Appendix 1. Chapter 1 

170 

 

Table AP1.8. Data collection and structure refinement for syn 10. 

Theta range for data collection 1.69 to 25.03° 

Index ranges -16<=h<=16, -20<=k<=20, -30<=l<=30 

Reflections collected 74424 

Independent reflections 20878 [R(int) = 0.0953] 

Coverage of independent 

reflections 
99.9% 

Absorption correction multi-scan 

Max. and min. transmission 0.9860 and 0.9400 

Refinement method Full-matrix least-squares on F2 

Refinement program SHELXL-2019/1 (Sheldrick, 2019) 

Function minimized Σ w(Fo
2 - Fc

2)2 

Data / restraints / parameters 20878 / 1501 / 1469 

Goodness-of-fit on F2 1.040 

Final R indices 
10247 data; 

I>2σ(I) 
R1 = 0.1189, wR2 = 0.3283 

 all data R1 = 0.2137, wR2 = 0.4036 

Weighting scheme 
w=1/[σ2(Fo

2)+(0.200P)2+19.7000P] 

where P=(Fo
2+2Fc

2)/3 

Theoretical Calculations  

All the calculations reported in this work were obtained with the GAUSSIAN 09 suite 

of programs.172 Electron correlation was partially taken into account using the 

B3LYP173 functional in conjuction with the D3 dispersion correction suggested by 

Grimme et al.174 and the double- quality plus polarization functions def2-SVP175 

basis set for all atoms. Reactants and products were characterized by frequency 

calculations,176 and have positive definite Hessian matrices. Transition states (TSs) 

show only one negative eigenvalue in their diagonalized force constant matrices, and 

their associated eigenvectors were confirmed to correspond to the motion along the 

reaction coordinate. Connections between reactants and products were confirmed 

 
172 Gaussian 09, Revision D.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, 

J. R. Cheeseman, G. Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A. Marenich, 

J. Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. 

Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T. 

Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, 

K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, 

K. Throssell, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. 

Kudin, V. N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, 

S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene, C. Adamo, R. Cammi, J. W. Ochterski, R. L. 

Martin, K. Morokuma, O. Farkas, J. B. Foresman, and D. J. Fox, Gaussian, Inc., Wallingford CT, 2016. 
173 (a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648; b) C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1998, 

37, 785; c) S. H. Vosko, L. Wilk, M. Nusair, Can. J. Phys. 1980, 58, 1200. 
174 S. Grimme, J. Antony, S. Ehrlich, H. Krieg, H. J. Chem. Phys. 2010, 132, 154104. 
175 F. Weigend, R. Alhrichs, Phys. Chem. Chem. Phys. 2005, 7, 3297. 
176 J. W. McIver, A. K. Komornicki, J. Am. Chem. Soc. 1972, 94, 2625. 



Appendix 1. Chapter 1 

171 

 

using the Intrinsic Reaction Coordinate (IRC) method.177 Solvent effects were 

considered by using the Polarizable Continuum Model (PCM).178 This level is 

denoted PCM(solvent)-B3LYP-D3/def2-SVP.  

Calculations of the absorption spectrum were accomplished using time-dependent 

density functional theory (TD-DFT)179 at the B3LYP-D3/def2-SVP level using the 

optimized geometries. The assignment of the excitation energies to the experimental 

bands was performed on the basis of the energy values and oscillator strengths. The 

B3LYP Hamiltonian was chosen because it was proven to provide reasonable UV-vis 

spectra for a variety of chromophores.180  

The aromaticity of the considered species has been assessed by the computation of 

the NICS181 values using the gauge invariant atomic orbital (GIAO) method,182 at the 

B3LYP183 level using the def2-SVP basis set, with the optimized PCM(solvent)-

B3LYP-D3/def2-SVP geometries. 

Non-covalent interactions in compound 10M were assessed by means of the NCIPlot 

method.184 

Cartesian coordinates (in Å) and total energies (in a.u., ZPVE included) of all the 

stationary points discussed in the text. All calculations have been performed at the 

PCM(solvent)-B3LYP-D3/def2-SVP level. 

 
177 C. González, H. B. Schlegel, J. Phys. Chem. 1990, 94, 5523. 
178 (a) S. Miertuš, E. Scrocco, J. Tomasi, Chem. Phys. 1981, 55, 117; (b) J. L. Pascual-Ahuir, E. Silla, I. 

Tuñón, J. Comp. Chem. 1994, 15, 1127; (c) V. Barone, M. Cossi, J. Phys. Chem. A, 1998, 102, 1995. 
179 (a) M. E. Casida, Recent Developments and Applications of Modern Density Functional Theory; 

Elsevier: Amsterdam, 1996; Vol. 4; (b) M. E. Casida, D. P. Chong, Recent Advances in Density 

Functional Methods; World Scientific: Singapore, 1995; Vol. 1, p 155. 
180 For a review, see: A. Dreuw, M. Head-Gordon, M. Chem. Rev. 2005, 105, 4009. 
181 Chen, Z.; Wannere, C. S.; Corminboeuf, C.; Puchta, R.; Schleyer, P. v. R. Chem. Rev. 2005, 105, 3842. 
182 Wolinski, K.; Hilton, J. F.; Pulay, P. J. Am. Chem. Soc. 1990, 112, 8251. 
183 (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648; (b) Lee, C.; Yang, W.; Parr, R. G.  Phys. Rev. B: 

Condens. Matter Mater. Phys. 1988, 37, 785; (c) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 

58, 1200. 
184 Johnson, E. R.; Keinan, S.; Mori-Sánchez, P.; Contreras-García, J.; Cohen, A. J.; Yang, W. J. Am. 

Chem. Soc. 2010, 132, 6498. 



Appendix 1. Chapter 1 

172 

 

 

Figure AP1.5. Radical-cation mechanism towards spironanographenes 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix 2 

  



 

 

 

 

 



Appendix 2. Chapter 2 

175 

 

APPENDIX 2. Chapter 2 

Crystallographic Data 

Single crystals suitable for X-ray diffraction analysis were obtained for compound 

17a. The molecule presents chirality, although the crystals obtained from the racemic 

mixture are racemic. These crystals are not stable out of the mother liquor and quickly 

lose crystallinity. The structure refinement presents a high wR2 value due to the high 

degree of disorder that many of the atoms in the asymmetric unit display. The solvent 

molecules (dichloroethane and water) in the interstices are extremely disordered, as 

well as the peripheral tBu substituents. The coordinates of the atoms in the tBu 

fragments had to be refined with the aid of geometrical restraints, and for some of the 

terminal methyl groups (C60-C62, C104-C106, C108-C110, C112-C114, C116-C118) 

these positions only account for 50% of the corresponding electron density. 

 

Figure AP2.1. Labelled asymmetric unit of compound 17a (solvent molecules are omitted). 

Structural details of 17a (CCDC 2070237)  

Table AP2.1. Sample and crystal data for 17a. 

Chemical 

formula 
(C118H114F4)·(C2H2Cl2)0.5(H2O)4.5 

Formula 

weight 
1737.72 

Temperature 200(2) K 

Wavelength 0.71073 Å 

Crystal size 0.105 x 0.221 x 0.261 mm 

Crystal habit clear orange needle 

Crystal 

system 
monoclinic 

Space group C2/c 

Unit cell 

dimensions 

a = 

35.348(2) 

Å 

α = 90° 



Appendix 2. Chapter 2 

176 

 

 
b = 

31.054(1) 

Å 

β = 

114.553(2)° 

 
c = 

22.447(1) 

Å 

γ = 90° 

Volume 22412(2) Å3  

Z 8 

Table AP2.2. Data collection and structure refinement for 17a. 

Theta range for data collection 1.14 to 23.96° 

Index ranges -33<=h<=40, -34<=k<=28, -25<=l<=16 

Reflections collected 43262  

Independent reflections 16808 [R(int) = 0.0678] 

Coverage of independent 

reflections 
96% 

Absorption correction multi-scan 

Max. and min. transmission 0.9910 and 0.9780 

Structure solution technique direct methods 

Structure solution program SHELXS-97 (Sheldrick 2008) 

Refinement method Full-matrix least-squares on F2 

Refinement program SHELXL-2014/7 (Sheldrick, 2014) 

Function minimized Σ w(Fo
2 - Fc

2)2 

Data / restraints / parameters 16808/33/1057 

Goodness-of-fit on F2 1.123 

Final R indices 8046 data; I>2σ(I) R1 = 0.1564, wR2 = 0.4257 
 all data R1 = 0.2562 wR2 = 0.5056 

Weighting scheme 
w=1/[σ2(Fo

2)+(0.3200P)2+19.700P]  

where P=(Fo
2+2Fc

2)/3 

 

 

 

 

 

 

 

 

 

 



Appendix 2. Chapter 2 

177 

 

Chiral HPLC resolution 

Analytical HPLC analysis was collected on an Agilent Technologies 1260 Infinity 

HPLC system using Regis Pirkle-type covalently modified silica column (4.6 × 250 

mm) Whelk-O2 (R,R). Injection volume was 0.7 μL, flow rate was 1 mL/min and 

eluent was 98:1:1 hexane:isopropanol:tetrahydrofuran. Peaks were confirmed by 

comparison of their UV-Vis spectra to originate from the enantiomers. 

 

 

Figure AP2.2. HPLC chromatogram of racemic 17a recorded at 360 nm. 



 

 

 

 

 

  



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix 3 

 

  



 

 

 

 

  



Appendix 3. Chapter 3 

181 

 

APPENDIX 3. Chapter 3 

Crystallographic data 

Single crystals suitable for X ray diffraction analysis were obtained from the 

respective racemic mixtures containing P and M isomers of compounds [9]HBNG 

and [11]HBNG. In both cases, the resulting crystals belonged to the centrosymmetric 

triclinic P-1 space group, and consequently contained both isomers. For both 

nanographenes, the packing displays voids between the HBNGs that contain highly 

disordered solvent molecules; some of them could be modelled as oxygen atoms from 

water molecules in [9]HBNG, and dichloroethane and oxygen atoms from water in 

[11]HBNG. The crystals were found to be extremely unstable out of their mother 

liquors due to the loss of these interstitial solvent molecules. Additionally, many of 

the tBu groups are also heavily disordered and were modelled with two alternative 

sets of positions. 

Table AP3.1. Sample and crystal data for [9]HBNG. 

CCDC code 2233478 

Chemical formula (C134H118)· 4.38 H2O 

Formula weight 1807.30 g/mol 

Temperature 250(2) K 

Wavelength 0.71073 Å 

Crystal size 0.026 x 0.236 x 0.507 mm 

Crystal habit dark brown-orange plate 

Crystal system triclinic 

Space group P -1 

Unit cell dimensions a = 13.382(4) Å α = 98.887(11)° 
 b = 17.848(5) Å β = 92.864(13)° 
 c = 28.398(8) Å γ = 109.273(11)° 

Volume 6288.(3) Å3  

Z 2 

Density (calculated) 0.955 g/cm3 

Absorption coefficient 0.056 mm-1 

F(000) 1914 

 

Table AP3.2. Data collection and structure refinement for [9]HBNG. 

Theta range for data collection 1.54 to 25.36° 

Index ranges -15<=h<=15, -20<=k<=21, -34<=l<=34 

Reflections collected 217729 

Independent reflections 22608 [R(int) = 0.0631] 

Coverage of independent 

reflections 
98.0% 

Absorption correction Multi-Scan 



Appendix 3. Chapter 3 

182 

 

Max. and min. transmission 1.0000 and 0.9300 

Refinement method Full-matrix least-squares on F2 

Refinement program SHELXL-2019/1 (Sheldrick, 2019) 

Function minimized Σ w(Fo
2 - Fc

2)2 

Data / restraints / parameters 22608 / 1461 / 1386 

Goodness-of-fit on F2 1.028 

Final R indices 
13523 data; 

I>2σ(I) 
R1 = 0.1277, wR2 = 0.3571 

 all data R1 = 0.1900, wR2 = 0.4151 

Weighting scheme 
w=1/[σ2(Fo

2)+(0.2000P)2+22.7000P]; where 

P=(Fo
2+2Fc

2)/3 

Largest diff. peak and hole 1.687 and -0.662 eÅ-3 

R.M.S. deviation from mean 0.251 eÅ-3 

 

Table AP3.3. Sample and crystal data for [11]HBNG. 

CCDC code  2233479 

Chemical formula (C142H122)·1.5(C2H4Cl2)·5 H2O 

Formula weight 2091.02 g/mol 

Temperature 150(2) K 

Wavelength 0.71073 Å 

Crystal size 0.189 x 0.223 x 0.235 mm 

Crystal habit dark brown prism 

Crystal system triclinic 

Space group P -1 

Unit cell dimensions a = 18.7384(8) Å α = 111.0735(15)° 
 b = 20.1754(8) Å β = 108.7063(15)° 
 c = 20.9971(8) Å γ = 102.5524(16)° 

Volume 6500.0(5) Å3  

Z 2 

Density (calculated) 1.069 g/cm3 

Absorption coefficient 0.126 mm-1 

F(000) 2182 

 

Table AP3.4. Data collection and structure refinement for [11]HBNG. 

Theta range for data collection 1.68 to 25.35° 

Index ranges -22<=h<=22, -24<=k<=24, -25<=l<=25 

Reflections collected 101650 

Independent reflections 23790 [R(int) = 0.0383] 

Coverage of independent 

reflections 
99.9% 

Absorption correction Multi-Scan 

Max. and min. transmission 0.9760 and 0.9710 



Appendix 3. Chapter 3 

183 

 

Structure solution technique direct methods 

Structure solution program XT, VERSION 2018/2 

Refinement method Full-matrix least-squares on F2 

Refinement program SHELXL-2019/1 (Sheldrick, 2019) 

Function minimized Σ w(Fo
2 - Fc

2)2 

Data / restraints / parameters 23790 / 1542 / 1538 

Goodness-of-fit on F2 1.052 

Final R indices 
15860 data; 

I>2σ(I) 
R1 = 0.1182, wR2 = 0.3678 

 all data R1 = 0.1630, wR2 = 0.4228 

Weighting scheme 
w=1/[σ2(Fo

2)+(0.3000P)2+7.9001P]; where 

P=(Fo
2+2Fc

2)/3 

Largest diff. peak and hole 2.195 and -0.667 eÅ-3 

R.M.S. deviation from mean 0.220 eÅ-3 

 

Figure AP3.1. Centroids in the overlapping rings in molecules [9]HBNG, [10]HBNG and 

[11]HBNG. Top, zenithal view; bottom, lateral view. 

 

 

 

 

 

 

 

 

 



Appendix 3. Chapter 3 

184 

 

Photophysical Details 

Table AP3.5. Data from the (multi)exponential fittings of the fluorescence decays of helical 

bilayer nanographenes [9]HBNG, [10]HBNG and [11]HBNG, obtained at different emission 

detection wavelengths (peaks or shoulders, sh) with excitation at 405 nm. 

Comp. detect 

(nm) 

τ1 

(ns) 

B1 I1 τ2 

(ns) 

B2 I2 τ3 

(ns) 

B3 I3 τInt 

(ns) 

τAmp 

(ns) 

[9]HBNG 

 512 

(sh) 

11.2 0.51 0.79 3.2 0.49 0.21 - - - 9.5 7.3 

em
max = 

575 nm 

578 

(peak) 

14.3 0.71 0.91 3.2 0.29 0.09 - - - 13.4 11.1 

 620 

(sh) 

14.3 0.66 0.90 3.1 0.34 0.10 - - - 13.2 10.5 

[10]HBNG 

 507 

(sh) 

14.6 0.31 0.78 5.1 0.20 0.18 0.52 0.48 0.04 12.3 5.8 

em
max = 

543 nm 

540 

(peak) 

13.2 0.40 0.90 3.4 0.15 0.09 0.11 0.45 0.01 12.2 5.8 

 570 

(sh) 

13.0 0.48 0.86 3.9 0.24 0.13 0.29 0.28 0.01 11.7 7.3 

 630 

(sh) 

12.3 0.25 0.75 3.7 0.28 0.24 0.12 0.47 0.01 10.1 4.2 

[11]HBNG 

em
max = 

528 nm 

530 

(peak) 

8.7 1.0 - - - - - - - - - 

 560 

(sh) 

8.7 1.0 - - - - - - - - - 

Table AP3.6. Estimated radiative (kr) and nonradiative (knr) deactivation rate constants of the 

singlet excited states calculated with data from the (multi)exponential fitting of the 

fluorescence decays of the helical bilayer nanographenes [9]HBNG, [10]HBNG and 

[11]HBNG, and their respective emission quantum yields. 

Compound Amp
 (ns) em kr

S1→S0 (s-1)a knr
S1→S0 (s-1)b 

[9]HBNG 11.1 0.22 2.0  107 7.0  107 

[10]HBNG 5.8 0.10 1.7  107 1.5  108 

[11]HBNG 8.7 0.11 1.3  107 1.0  108 

akr
S1→S0 =  em/em. b knr

S1→S0 = (1/em) – kr
S1→S0 

 

 

 

 

 

 

 



Appendix 3. Chapter 3 

185 

 

Chiral HPLC of HBNGs 

Racemic bilayer helicenes ([9]HBNG, [10]HBNG, [11]HBNG) were resolved by 

semipreparative CSP HPLC using Chiralpak IE column with a mixture of heptane and 

1% isopropyl alcohol in toluene as mobile phase. Unfortunately, a high loss of 

material was observed during the chromatographic separations, which may indicate 

irreversible adhesion on the column. Below, the experimental conditions of the HPLC 

separations and characterization of the obtained enantioenriched samples are 

summarized. 

Analytical separations were performed on Chiralpak IE (250 x 4.6 mm, 5 µm, 

DAICEL) column using isocratic elution with heptane –5% THF in toluene 60:40 at 

1 mL/min, semi-preparative separations were done using a Chiralpak IE (250 x 20 

mm, 5 µm, DAICEL) column and a gradient elution with heptane– 1% isopropyl 

alcohol in toluene [80:20] to [50:50] at 20 mL/min. Injections of cca 10 mg / 1.5 mL 

of the racemic material in a mixture of 1,1,2,2-tetrachloroethane and heptane (1:2) per 

run were performed. 

 

Figure AP3.2. HPLC chromatogram corresponding to the isolated enantiomers of [9]HBNG. 



Appendix 3. Chapter 3 

186 

 

 

Figure AP3.3. HPLC chromatogram corresponding to the isolated enantiomers of [10]HBNG. 

 

 



Appendix 3. Chapter 3 

187 

 

 

Figure AP3.4. HPLC chromatogram corresponding to the isolated enantiomers of [11]HBNG. 

Table AP3.7. Optical rotation values of the enantioenriched samples. 

Compound 
Optical rotation a 

[α]D20 

HPLC enantiomeric 

purity e.e. (%) 
NMR purityb (wt%) 

(+)-[9]HBNG +6706 98 96 

(−)-[9]HBNG −7120 99 97 

(+)-[10]HBNG +2447 73 94 

(−)-[10]HBNG −4480 99 93 

(+)-[11]HBNG +4033 99 92 

(−)-[11]HBNG −4270 99 92 

a Optical rotations were measured in THF solutions (c = 0.078 – 0.095 g/100mL)  

b Despite drying in vacuo, residual solvents (mainly toluene and/or dichloromethane) were 

found to be present in the resolved samples by 1H NMR (in THF-d8). 

 

 

 

 

 

 

 

 

 

 

 



Appendix 3. Chapter 3 

188 

 

Vibrational Raman Spectroscopy 

 

Figure AP3.5. Experimental (black solid line; λexc = 325 nm) and theoretical (grey solid line) 

Raman spectra of [9]HBNG. Theoretical Raman spectrum was calculated at the optimized 

CAM-B3LYP/3-21G* geometry and scaled down uniformly by a factor of 0.96. 

 

G Band 1585 cm-1

D Band 1305 cm-1

G Band 1609 cm-1



Appendix 3. Chapter 3 

189 

 

 

Figure AP3.6. Vibrational normal coordinates corresponding to G and D bands in the 

computed Raman spectrum of [9]HBNG (Figure S19). Bottom graphene layer is showed in 

light grey for clarity.

G Band 1585 cm-1

D Band 1305 cm-1

G Band 1609 cm-1



 

 

   

  



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix 4 

 

  



 

 

 

 



Appendix 4. Chapter 4 

193 

 

APPENDIX 4. Chapter 4 

Crystallographic Data 

Single clear colorless prism-shaped crystals of 26b were obtained from a methanol-

dichloromethane mixture. A suitable crystal was selected and placed on a MiTeGen 

micromount on an XtaLAB Synergy R, HyPix-Arc 100 diffractometer. The structure was 

solved with the ShelXT (Sheldrick, 2015) structure solution program using the Intrinsic 

Phasing solution method and by using Olex2 (Dolomanov et al., 2009) as the graphical 

interface. The model was refined with version 2018/3 of ShelXL 2018/3 (Sheldrick, 2015) 

using Least Squares minimization. 

Table AP4.1. Data collection and structure refinement for 26b. 

Formula C141.44 H151.31Cl4O 5.75S 

Dcalc/ g·cm−3 1.029 

μ/mm−1 1.302 

Formula Weight 2117.08 

Color Clear colorless 

Shape Prism 

Size/mm3 0.26×0.14×0.08 

T/K 200.00(10) 

Crystal System Orthorhombic 

Flack Parameter 0.081(7) 

Hooft Parameter 0.098(5) 

Space Group P212121 

a/Å 18.2270(2) 

b/Å 21.8090(3) 

c/Å 34.3878(5) 

α/° 90 

β/° 90 

γ/° 90 

V/Å3 13669.6(3) 

Z 4 

Z’ 1 

Wavelength/Å 1.54184 

Radiation type Cu Kα 

Θmin/° 2.399 

Θmax/° 68.528 

Measured Refl. 125896 

Independent Refl. 25016 

Reflections with I > 2(I) 20392 

Rint 0.0758 

Parameters 1409 

Restraints 1328 



Appendix 4. Chapter 4 

194 

 

Largest Peak 0.919 

Deepest Hole −0.551 

GooF 1.058 

wR2 (all data) 0.4032 

wR2 0.3855 

R1 (all data) 0.1514 

R1 0.1414 

Single clear intense orange plate-shaped crystals of P-oxa[9]HBNG were obtained 

from methanol. A suitable crystal 0.17×0.14×0.05 mm3 was selected and placed on a 

MiTeGen micromount on an XtaLAB Synergy R, HyPix-Arc 100 diffractometer. The 

structure was solved with the ShelXT 2018/2 (Sheldrick, 2018) structure solution 

program using the Intrinsic Phasing solution method and by using Olex2 (Dolomanov 

et al., 2009) as the graphical interface. The model was refined with version 2018/3 of 

ShelXL 2018/3 (Sheldrick, 2015) using Least Squares minimization. 

Table AP4.2. Data collection and structure refinement for P-oxa[9]HBNG. 

Formula C132 H116O8 

Dcalc/ g·cm−3 0.922 

μ/mm−1 0.436 

Formula Weight 1830.24 

Color Clear intense orange 

Shape Plate 

Size/mm3 0.17×0.14×0.05 

T/K 200.00(10) 

Crystal System Orthorhombic 

Flack Parameter −2.6(2) 

Hooft Parameter −2.97(16) 

Space Group C2221 

a/Å 17.1383(3) 

b/Å 30.5376(4) 

c/Å 25.1957(7) 

α/° 90 

β/° 90 

γ/° 90 

V/Å3 13186.5(5) 

Z 4 

Z’ 0.5 

Wavelength/Å 1.54184 

Radiation type Cu Kα 

Θmin/° 2.894 

Θmax/° 68.610 

Measured Refl. 61631 



Appendix 4. Chapter 4 

195 

 

Independent Refl. 12073 

Reflections with I > 2(I) 8805 

Rint 0.0577 

Parameters 662 

Restraints 37 

Largest Peak 1.170 

Deepest Hole −0.707 

GooF 1.041 

wR2 (all data) 0.4395 

wR2 0.4138 

R1 (all data) 0.1882 

R1 0.1701 

Single intense brown prism-shaped crystals of M-oxa[9]HBNG were obtained from 

methanol. A suitable crystal 0.27×0.14×0.07 mm3 was selected and placed on a 

MiTeGen micromount on an XtaLAB Synergy R, HyPix-Arc 100 diffractometer. The 

structure was solved with the ShelXT 2018/2 (Sheldrick, 2018) structure solution 

program using the Intrinsic Phasing solution method and by using Olex2 (Dolomanov 

et al., 2009) as the graphical interface. The model was refined with version 2018/3 of 

ShelXL 2018/3 (Sheldrick, 2015) using Least Squares minimization. 

Table AP4.3. Data collection and structure refinement for M-oxa[9]HBNG. 

Formula C132H116O2.25 

Dcalc/ g·cm−3 0.849 

μ/mm−1 0.371 

Formula Weight 1738.24 

Color Intense brown 

Shape Prism 

Size/mm3 0.27×0.14×0.07 

T/K 200.00(10) 

Crystal System Orthorhombic 

Flack Parameter −1.31(18) 

Hooft Parameter −1.59(12) 

Space Group C2221 

a/Å 17.1026(2) 

b/Å 30.4016(3) 

c/Å 26.1587(4) 

α/° 90 

β/° 90 

γ/° 90 

V/Å3 13601.1(3) 

Z 4 

Z’ 0.5 



Appendix 4. Chapter 4 

196 

 

Wavelength/Å 1.54184 

Radiation type Cu Kα 

Θmin/° 2.907 

Θmax/° 68.358 

Measured Refl. 63965 

Independent Refl. 12453 

Reflections with I > 2(I) 9674 

Rint 0.0270 

Parameters 690 

Restraints 779 

Largest Peak 1.320 

Deepest Hole −0.546 

GooF 1.029 

wR2 (all data) 0.3144 

wR2 0.2975 

R1 (all data) 0.1335 

R1 0.1208 

Chiral HPLC of oxa[9]HBNG enantiomers 

The enantiomers were resolved by chiral HPLC using a column Chiralpack IC 5μm, 

98% hexane 2% toluene:isopropanol 4:1, recording the absorption by UV-vis and CD 

at 370 nm. The negative cotton effect for M-oxa[9]HBNG reveals an e.e.>99%. The 

cotton effects in the CD chromatogram of P-oxa[9]HBNG shows an e.e.=99%. 

 



Appendix 4. Chapter 4 

197 

 

 

 

Figure AP4.1. HPLC chromatogram of enantiopure (P)- and (M)-oxa[9]HBNG recorded by 

UV-vis and CD at 370 nm. 

0 1 2 3 4 5 6 7 8 9 10 11

 

 

U
V

 O
p
ti
c
a
l 
d
e
n
s
it
y

Time (min)

 (P)-oxa[9]HBNG

 (M)-oxa[9]HBNG



 

 

 

   

  



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix 5 

  



 

 

 

 

 



Appendix 5. Spectra 

201 

 

APPENDIX 5. Spectra 

Chapter 1 

 

 Figure S1. 1H NMR spectra for compound 4.

1H-NMR, 700 MHz, Chloroform-d

4



Appendix 5. Spectra 

202 

 

 

 

1H-NMR, 300 MHz, Chloroform-d

13C-NMR, 75 MHz, Chloroform-d

DEPT, 75 MHz, Chloroform-d

6a



Appendix 5. Spectra 

203 

 

 

1H-NMR, 700 MHz, Methylene Chloride-d2

13C-NMR, 176 MHz , Methylene Chloride-d2

7



Appendix 5. Spectra 

204 

 

 

 

1H-NMR, 300 MHz, Benzene-d6

8



Appendix 5. Spectra 

205 

 

 

 

9

1H-NMR, 500 MHz, Chloroform-d



Appendix 5. Spectra 

206 

 

 

9

1H-NMR, 500 MHz, Chloroform-d



Appendix 5. Spectra 

207 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

DEPT, 126 MHz, Chloroform-d

10



Appendix 5. Spectra 

208 

 

 

 

1H-NMR, 300 MHz, Benzene-d6

13C-NMR{1H}{19F}, 126 MHz, Benzene-d6

19F-NMR, 282 MHz, Benzene-d6

12



Appendix 5. Spectra 

209 

 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR{1H}{19F}, 126 MHz, Chloroform-d

19F-NMR, 471 MHz, Chloroform-d

6b



Appendix 5. Spectra 

210 

 

 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR{1H}{19F}, 126 MHz, Chloroform-d

19F-NMR, 471 MHz, Chloroform-d

13



Appendix 5. Spectra 

211 

 

Chapter 2 

 

1H-NMR, 300 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

13C-NMR{1H}{19F}, 126 MHz, Chloroform-d

 

15a



Appendix 5. Spectra 

212 

 

 

 

 

19F-NMR, 471 MHz, Chloroform-d

 

15a

DEPT, 126 MHz, Chloroform-d



Appendix 5. Spectra 

213 

 

 

1H-NMR, 300 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

13C-NMR{1H}{19F}, 126 MHz, Chloroform-d

15b

19F-NMR, 471 MHz, Chloroform-d



Appendix 5. Spectra 

214 

 

 

1H-NMR, 300 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

13C-NMR{1H}{19F}, 126 MHz, Chloroform-d

15c



Appendix 5. Spectra 

215 

 

 

19F-NMR, 471 MHz, Chloroform-d

15c



Appendix 5. Spectra 

216 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

13C-NMR{1H}{19F}, 126 MHz, Chloroform-d

16a



Appendix 5. Spectra 

217 

 

 

19F-NMR, 471 MHz, Chloroform-d

16a



Appendix 5. Spectra 

218 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

16b



Appendix 5. Spectra 

219 

 

 

13C-NMR{1H}{19F}, 126 MHz, Chloroform-d

19F-NMR, 282 MHz, Chloroform-d

16b



Appendix 5. Spectra 

220 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

16c



Appendix 5. Spectra 

221 

 

 

13C-NMR{1H}{19F}, 126 MHz, Chloroform-d

19F-NMR, 471 MHz, Chloroform-d

16c



Appendix 5. Spectra 

222 

 

 

1H-NMR, 300 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

17a



Appendix 5. Spectra 

223 

 

 

 

13C-NMR{1H}{19F}, 126 MHz, Chloroform-d

19F-NMR, 471 MHz, Chloroform-d

17a



Appendix 5. Spectra 

224 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

17b



Appendix 5. Spectra 

225 

 

 

13C-NMR{1H}{19F}, 126 MHz, Chloroform-d

19F-NMR, 471 MHz, Chloroform-d

17b



Appendix 5. Spectra 

226 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

17c



Appendix 5. Spectra 

227 

 

 

 

 

13C-NMR{1H}{19F}, 126 MHz, Chloroform-d

19F-NMR, 471 MHz, Chloroform-d

17c



Appendix 5. Spectra 

228 

 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

19F-NMR, 471 MHz, Chloroform-d

17c’



Appendix 5. Spectra 

229 

 

 

 

17c’. H,H-COSY

17c’. H,H-COSY



Appendix 5. Spectra 

230 

 

 

 

17c’. H,H-NOESY

17c’. H,H-NOESY



Appendix 5. Spectra 

231 

 

 

 

17c’. H,H-NOESY

17c’. H,H-NOESY



Appendix 5. Spectra 

232 

 

 

 

17c’



Appendix 5. Spectra 

233 

 

 

 

1H NMR of syn/anti isomeric mixture of 17c

COSY between 8.23 (d, J = 8.8 Hz) and 7.61 (dd, J = 8.8, 1.8 Hz) of 

isomer A (blue), the multiplicities of these signals only are posible in the 

aromatic ring that contains a tBu group with unsubstituted meta position

17c



Appendix 5. Spectra 

234 

 

 

 

Furthemore, also exists COSY between 8.15 (d, J = 8.8 Hz) 

and 7.54 (m) of isomer B

17c

17c



Appendix 5. Spectra 

235 

 

 

 

The tBu groups of both isomers also have nOe with protons at 8.81 (d, J = 

1.8 Hz) and 8.80 (d, J = 1.8 Hz), one for each isomer, but it is very difficult to 

determine the crossing-points of these signals

Additionally, four protons, 8.81 (d, J = 1.8 Hz), 8.80 (d, J = 1.8 Hz), 7.61 (dd, 

J = 8.8, 1.8 Hz) and 7. 54 (dd, J = (.8, 1.8 Hz) have HMBC with the same 

cuaternary carbon (35.1) of a tBu group (two carbons, both isomers)

17c

17c



Appendix 5. Spectra 

236 

 

 

 

Two spin systems: tBu substituted 

phenyl group (pink, protons assigned 

for each isomer); unsubtituted phenyl 

group (orange, unassigned)

17c

17c



Appendix 5. Spectra 

237 

 

 

 

 

 

 

nOe between 8.32 in 

the unsubtituted phenyl 

ring and 8.15 in tBu 

substituted phenyl ring. 

This nOe only can be 

possible with proton 12 

of anti isomer

17c



Appendix 5. Spectra 

238 

 

Chapter 3 

 

 

1H-NMR, 400 MHz, Chloroform-d

13C-NMR, 101 MHz, Chloroform-d

19a

 



Appendix 5. Spectra 

239 

 

 

 

1H-NMR, 400 MHz, Chloroform-d

13C-NMR, 101 MHz, Chloroform-d

19b



Appendix 5. Spectra 

240 

 

 

1H-NMR, 300 MHz, Chloroform-d

13C-NMR, 75 MHz, Chloroform-d

DEPT, 75 MHz, Chloroform-d

20a

 



Appendix 5. Spectra 

241 

 

 

 

 

1H-NMR, 300 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

DEPT, 126 MHz, Chloroform-d

20b



Appendix 5. Spectra 

242 

 

 

 

1H-NMR, 300 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

DEPT, 126 MHz, Chloroform-d

21a

 



Appendix 5. Spectra 

243 

 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

DEPT, 126 MHz, Chloroform-d

21b



Appendix 5. Spectra 

244 

 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

DEPT, 126 MHz, Chloroform-d

[9]HBNG



Appendix 5. Spectra 

245 

 

 

 

1H-NMR, 700 MHz, Chloroform-d

13C-NMR, 176 MHz, Chloroform-d

DEPT, 176 MHz, Chloroform-d

[11]HBNG



Appendix 5. Spectra 

246 

 

Chapter 4 

 

 

1H-NMR, 300 MHz, Chloroform-d

23



Appendix 5. Spectra 

247 

 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

DEPT, 126 MHz, Chloroform-d

24



Appendix 5. Spectra 

248 

 

 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

DEPT, 126 MHz, Chloroform-d

25



Appendix 5. Spectra 

249 

 

 

 

26a

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

DEPT, 126 MHz, Chloroform-d



Appendix 5. Spectra 

250 

 

 

26b

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

DEPT, 126 MHz, Chloroform-d



Appendix 5. Spectra 

251 

 

 

0
.8

4

0
.5

8

0
.8

1

0
.6

0

7
.0

2

7
.0

7

1H-NMR, 500 MHz, Chloroform-d

Low field signals of compounds 26a (blue) and 26b (orange)

High field signals of compounds 26a (blue) and 26b (orange)



Appendix 5. Spectra 

252 

 

1H-NMR, 500 MHz, Chloroform-d

13C-NMR, 126 MHz, Chloroform-d

DEPT, 126 MHz, Chloroform-d

Oxa[9]HBNG



 

 

 

 

  

  



 

 

 

 

  



 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

References 

 

  



 

 

 

 

 



References 

257 

 

REFERENCES 

1. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. 

Grigorieva, A. A. Fisov, Electric Field Effect in Atomically Thin Carbon Films, Science 

2004, 306, 666. 

2. P. R. Wallace, The Band Theory of Graphite, Phys. Rev. 1947, 71, 622. 

3. J. C. Slonczewski, Band Structure of Graphite, Phys. Rev. 1958, 109, 272. 

4. G. W. Semenoff, Condensed-Matter Simulation of a Three-Dimensional Anomaly, Phys. 

Rev. Lett. 1984, 53, 2449. 

5. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, M. I. Katsnelson, I. V. Grigorieva, 

S. V. Dubonos, A. A. Firsov, Two-dimensional gas of massless Dirac fermions in 

graphene, Nature 2005, 438, 197.  

6. A. Geim, K. Novoselov, The Rise of graphene, Nat. Mater. 2007, 6, 183. 

7. A. S. Mayorov, Micrometer-Scale Ballistic Transport in Encapsulated Graphene at Room 

Temperature, Nano Lett. 2011, 11, 2396. 

8. S. V. Morozov, Giant Intrinsic Carrier Mobilities in Graphene and Its Bilayer, Phys. Rev. 

Lett. 2008, 100, 016602. 

9. C. Lee, X. D. Wei, J. W. Kysar, J. Hone, Measurement of the Elastic Properties and 

Intrinsic Strength of Monolayer Graphene, Science 2008, 321, 385. 

10. A. A. Balandin, Thermal Properties of Graphene and Nanostructured Carbon Materials, 

Nat. Mater. 2011, 10, 569. 

11. J. S. Bunch, S. S. Verbridge, J. S. Alden, A. M. van der Zande, J. M. Parpia, H. G. 

Craighead, P. L. McEuen, Impermeable Atomic Membranes from Graphene Sheets, Nano 

Lett. 2008, 8, 2458. 

12. J. Moser, A. Barreiro, A. Bachtold, Current-Induced Cleaning of Graphene, Appl. Phys. 

Lett. 2007, 91, 163513. 

13. A. K. Worku, D. W. Ayele, Recent Advances of Graphene-Based Materials for Emerging 

Technologies, Results in Chemistry 2023, 5, 100971. 

14. A. Gutiérrez-Cruz, A. R. Ruiz-Hernández, J. F. Vega-Clemente, D. G. Luna-Gazcón, J. 

Campos-Delgado, A Review of Top-Down and Bottom-Up Synthesis Methods for the 

Production of Graphene, Graphene Oxide and Reduced Graphene Oxide, J. Mater. Sci. 

2022, 57, 14543. 

15. K. S. Novoselov, V. I. Fal’ko, L. Colombo, P. R. Gellert, M. G. Schwab, K. Kim, A 

Roadmap for Graphene, Nature 2012, 490, 192. 

16. K. Parvez, S. Yang, X. Feng, K. Müllen, Exfoliation of Graphene via Wet Chemical 

Routes, Synth. Met. 2015, 210, 123. 



References 

258 

 

17. N. Liu, F. Luo, H. Wu, Y. Liu, C. Zhang, J. Chen, One-Step Ionic-Liquid-Assisted 

Electrochemical Synthesis of Ionic-Liquid-Functionalized Graphene Sheets Directly 

from Graphite, Adv. Funct. Mater. 2008, 18, 1518. 

18. K. S. Kim, Y. Zhao, H. Jang, S. Y. Lee, J. M. Kim, K. S. Kim, J.-H. Ahn, P. Kim, J.-Y. 

Choi, B. H. Hong, Large-Scale Pattern Growth of Graphene Films for Stretchable 

Transparent Electrodes, Nature 2009, 457, 706. 

19. X. Li, W. C. J. An, S. K. J. Nah, D. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S. 

K. Banerjee, L. Colombo, R. S. Ruoff, Large-Area Synthesis of High-Quality and 

Uniform Graphene Films on Copper Foils, Science 2009, 324, 1312. 

20. C. Berger, Z. Song, T. Li, X. Li, A. Y. Ogbazghi, R. Feng, Z. Dai, A. N. Marchenkov, E. 

H. Conrad, P. N. First, W. A. De Heer, Ultrathin Epitaxial Graphite:  2D Electron Gas 

Properties and a Route toward Graphene-based Nanoelectronics, J. Phys. Chem. B 2004, 

108, 19912. 

21. J. Lin, Z. Peng, Y. Liu, F. Ruiz-Zepeda, R. Ye, E. L. G. Samuel, M. J. Yacaman, B. I. 

Yakobson, J. M. Tour, Laser-Induced Porous Graphene Films from Commercial 

Polymers, Nat. Commun. 2014, 5, 5714. 

22. M. Qian, Y. S. Zhou, Y. Gao, J. B. Park, T. Feng, S. M. Huang, Z. Sun, L. Jiang, Y. F. Lu, 

Formation of Graphene Sheets Through Laser Exfoliation of Highly Ordered Pyrolytic 

Graphite, Appl. Phys. Lett. 2011, 98, 173108. 

23. D. X. Luong, K. V. Bets, W. A. Algozeeb, M. G. Stanford, C. Kittrell, W. Chen, R. V. 

Salvatierra, M. Ren, E. A. McHugh, P. A. Advincula, Z. Wang, M. Bhatt, H. Guo, V. 

Mancevski, R. Shahsavari, B. I. Yakobson, J. M. Tour, Gram-Scale Bottom-up Flash 

Graphene Synthesis, Nature 2020, 577, 647. 

24. A. Adetayo, D. Runsewe, Synthesis and Fabrication of Graphene and Graphene Oxide: 

A Review, Open J. Compos. Mater. 2019, 9, 207. 

25. Y. Zhu, S. Murali, W. Cai, X. Li, J. W. Suk, J.R. Potts, R.S. Ruoff, Graphene and 

Graphene Oxide: Synthesis, Properties, and Applications, Adv. Mater. 2010, 22, 3906. 

26. N. Panwar, A. M. Soehartono, K. K. Chan, S. Zeng, G. Xu, J. Qu, P. Coquet, K.-T. Yong, 

X. Chen, Nanocarbons for Biology and Medicine: Sensing, Imaging, and Drug Delivery, 

Chem. Rev. 2019, 119, 9559. 

27. L. Lin, H. Peng, Z. Liu, Synthesis Challenges for Graphene Industry, Nat. Mat. 2019, 18, 

520. 

28. A. N. Grigorenko, M. Polini, K. S. Novoselov, Graphene Plasmonics, Nat. Photonics 

2012, 6, 749. 

29. J. Wu, H. Lin, D. J. Moss, K. P. Loh, B. Jia, Graphene Oxide for Photonics, Electronics 

and Optoelectronics, Nat. Rev. Chem. 2023, 7, 162. 

30. F. Bonaccorso, Z. Sun, T. Hasan, A. C. Ferrari, Graphene Photonics and Optoelectronics, 

Nat. Photonics 2010, 4, 611. 



References 

259 

 

31. H. Su, Y. H. Hu, Recent Advances in Graphene-Based Materials for Fuel Cell 

Applications, Energy Sci. Eng. 2021, 9, 958. 

32. F. Bonaccorso, L. Colombo, G. Yu,M. Stoller, V. Tozzini, A. C. Ferrari, R. S. Ruoff, V. 

Pellegrini, Graphene, Related Two-Dimensional Crystals, and Hybrid Systems for 

Energy Conversion and Storage, Science 2015, 347, 1246501. 

33. M. Huang, Z. Li, H. Zhu, Recent Advances of Graphene and Related Materials in 

Artificial Intelligence, Adv. Intell. Syst. 2022, 4, 2200077. 

34. J. Li, H. Zeng, Z. Zeng, Y. Zeng, T. Xie, Promising Graphene-Based Nanomaterials and 

Their Biomedical Applications and Potential Risks: A Comprehensive Review, ACS 

Biomater. Sci. Eng. 2021, 7, 5363. 

35. E. Galvagno, E. Tartaglia, M. Stratigaki, C. Tossi, L. Marasco, F. Menegazzo, C. Zanardi, 

F. Omenetto, C. Coletti, A. Traviglia, M. Moglianetti, Present Status and Perspectives of 

Graphene and Graphene-related Materials in Cultural Heritage, Adv. Funct. Mater. 2024, 

2313043. 

36. M. T. U. Safian, K. Umar, M. N. Mohamad Ibrahim, Synthesis and Scalability of 

Graphene and its Derivatives: A Journey Towards Sustainable and Commercial Material, 

J. Clean. Prod. 2021, 318, 128603. 

37. G. Li, A. Luican, J. M. B. Lopes dos Santos, A. H. Castro Neto, A. Reina, J. Kong, E. Y. 

Andrei, Observation of Van Hove Singularities in Twisted Graphene Layers, Nat. Phys. 

2010, 6, 109. 

38. L. Van Hove, The Occurrence of Singularities in the Elastic Frequency Distribution of a 

Crystal, Phys. Rev. 1953, 89, 1189. 

39. Y. Cao, V. Fatemi, S. Fang, K. Watanabe, T. Taniguchi, E. Kaxiras, P. Jarillo-Herrero, 

Unconventional Superconductivity in Magic-angle Graphene Superlattices, Nature 2018, 

556, 43. 

40. E. Y. Andrei, D. K. Efetov, P. Jarillo- Herrero, A. H. MacDonald, K. Fai Mak, T. Senthil, 

E. Tutuc, A. Yazdani, A. F. Young, The Marvels of Moiré Materials, Nat. Rev. Mater. 

2021, 6, 201. 

41. A. Halleux, R. H. Martin, G. S. D. King,Helv. Synthèses dans la série des dérivés 

polycycliques aromatiques hautement condensés. L'hexabenzo-1,12; 2,3; 4,5; 6,7; 8,9; 

10,11-coronène, le tétrabenzo-4,5; 6,7; 11,12; 13,14-péropyrène et le tétrabenzo-1,2; 3,4; 

8,9; 10,11-bisanthène, Chim. Acta 1958, 41, 1177. 

42. L. Chen, Y. Hernandez, X. Feng, K. Müllen, From Nanographene and Graphene 

Nanoribbons to Graphene Sheets: Chemical Synthesis, Angew. Chem. Int. Ed. 2012, 51, 

7640. 

43. J. Liu, X. Feng, Synthetic Tailoring of Graphene Nanostructures with Zigzag-Edged 

Topologies: Progress and Perspectives, Angew. Chem. Int. Ed. 2020, 59, 23386. 

44. C. D. Simpson, J. D. Brand, A. J. Berresheim, L. Przybilla, H. J. Räder, K. Müllen, 

Synthesis of a Giant 222 Carbon Graphite Sheet, Chem. Eur. J. 2002, 8, 1424. 



References 

260 

 

45. Z. Liu, S. Fu, X. Liu, A. Narita, P. Samori, M. Bonn, H. I. Wang, Small Size, Big Impact: 

Recent Progress in Bottom-Up Synthesized Nanographenes for Optoelectronic and 

Energy Applications, Adv. Sci. 2022, 9, 2106055. 

46. Y. Gu, Z. Qiu, K. Müllen, Nanographenes and Graphene Nanoribbons as Multitalents of 

Present and Future Materials Science, J. Am. Chem. Soc. 2022, 144, 11499. 

47. A. Narita, X.-Y. Wang, X. Feng, K. Müllen, New Advances in Nanographene Chemistry, 

Chem. Soc. Rev. 2015, 44, 6616. 

48. S. Song, J. Su, M. Telychko, J. Li, G. Li, Y. Li, C. Su, J. Wu, J. Lu, On-surface Synthesis 

of Graphene Nanostructures with π-Magnetism, Chem. Soc. Rev. 2021, 50, 3238. 

49. Y. Segawa, H. Ito, K. Itami, Structurally Uniform and Atomically Precise Carbon 

Nanostructures, Nat. Rev. Mater. 2016, 1, 15002. 

50. (a) R. Scholl, C. Seer, R. Weitzenbök, Perylen, ein hoch kondensierter aromatischer 

Kohlenwasserstoff C20H12, Chem. Ber. 1910, 43, 2202. (b) R. Scholl, C. Seer, Abspaltung 

aromatisch gebundenen Wasserstoffs und Verknüpfung aromatischer Kerne durch 

Aluminiumchlorid, Liebigs Ann. Chem. 1912, 394, 111. (c) R. Scholl, C. Seer, 

Abspaltung aromatisch gebundenen Wasserstoffes unter Verknüpfung aromatischer 

Kerne durch Aluminiumchlorid, 6. Mitteilung: Versuche mit Phenol-äthern und mit 

Diphenyl-methan, Chem. Ber. 1922, 55, 330. (d) E. Clar, D. G. Stewart, Aromatic 

Hydrocarbons. LXV. Triangulene Derivatives, J. Am. Chem. Soc. 1953, 75, 2667. (e) E. 

Clar, W. Schmidt, Localised vs delocalised molecular orbitals in aromatic hydrocarbons, 

Tetrahedron 1979, 35, 2673. 

51. S. Ito, M. Wehmeier, J. D. Brand, C. Kübel, R. Epsch, J. P. Rabe, K. Müllen, Synthesis 

and Self-Assembly of Functionalized Hexa-peri-hexabenzocoronenes, Chem. Eur. J. 

2000, 6, 4327. 

52. S. Ma, J. Gu, C. Lin, Z. Luo, Y. Zhu, J. Wang, Supertwistacene: A Helical Graphene 

Nanoribbon, J. Am. Chem. Soc. 2020, 142, 16887. 

53. A. Narita, I. A. Verzhbitskiy, W. Frederickx, K. S. Mali, S. A. Jensen, M. R. Hansen, M. 

Bonn, S. De Feyter, C. Casiraghi, X. Feng, K. Müllen, Bottom-Up Synthesis of Liquid-

Phase-Processable Graphene Nanoribbons with Near-Infrared Absorption, ACS Nano 

2014, 8, 11622. 

54. J. Urieta-Mora, M. Krug, W. Alex, J. Perles, I. Fernández, A. Molina-Ontoria, D. M. 

Guldi, N. Martín, Homo and Hetero Molecular 3D Nanographenes Employing a 

Cyclooctatetraene Scaffold, J. Am. Chem. Soc. 2020, 142, 4162. 

55. C. M. Cruz, I. R. Márquez, S. Castro-Fernández, J. M. Cuerva, E. Maçôas, A. G. 

Campaña, A Triskelion-Shaped Saddle–Helix Hybrid Nanographene, Angew. Chem. Int. 

Ed. 2019, 58, 8068. 

56. K. Kawasumi, Q. Zhang, Y. Segawa, L. T. Scott, K. Itami, A Grossly Warped 

Nanographene and the Consequences of Multiple Odd-membered-ring Defects, Nat. 

Chem. 2013, 5, 739. 



References 

261 

 

57. X.-S. Zhang, Y.-Y. Huang, J. Zhang, W. Meng, Q. Peng, R. Kong, Z. Xiao, J. Liu, M. 

Huang, Y. Yi, L. Chen, Q. Fan, G. Lin, Z. Liu, G. Zhang, L. Jiang, D. Zhang, 

Dicyclohepta[ijkl,uvwx]rubicene with Two Pentagons and Two Heptagons as a Stable and 

Planar Non-benzenoid Nanographene, Angew. Chem. Int. Ed. 2020, 59, 3529. 

58. V. Akhmetov, M. Feofanov, O. Papaianina, S. Troyanov, K. Amsharov, Towards 

Nonalternant Nanographenes through Self-Promoted Intramolecular Indenoannulation 

Cascade by C−F Bond Activation, Chem. Eur. J. 2019, 25, 11609. 

59. M. Daigle, A. Picard‐Lafond, E. Soligo, J.-F. Morin, Regioselective Synthesis of 

Nanographenes by Photochemical Cyclodehydrochlorination, Angew. Chem. Int. Ed. 

2016, 55, 2042. 

60. L. T. Scott, E. Jackson, Q. Zhang, B. D. Steinberg, M. Bancu, B. Li, A Short, Rigid, 

Structurally Pure Carbon Nanotube by Stepwise Chemical Synthesis, J. Am. Chem. Soc. 

2012, 134, 107. 

61. W.-J. Kong, L. H. Finger, J. C. A. Oliveira, L. Ackermann, Rhodaelectrocatalysis for 

Annulative C−H Activation: Polycyclic Aromatic Hydrocarbons through Versatile 

Double Electrocatalysis, Angew. Chem. Int. Ed. 2019, 58, 6342. 

62. B. Cirera, A. Sánchez-Grande, B. de la Torre, J. Santos, S. Edalatmanesh, E. Rodríguez-

Sánchez, K. Lauwaet, B. Mallada-Faes, R. Zbořil, R. Miranda, O. Gröning, P. Jelínek, N. 

Martín, D. Écija, Tailoring Topological Order and π-Conjugation to Engineer Quasi-

Metallic Polymers, Nat. Nanotech. 2020, 15, 437. 

63. (a) R. Scholl, J. Mansfeld, Ber. Dtsch. Chem. Ges. 1910, 43, 1734. (b) R. Scholl, C. Seer, 

Justus Liebigs, Abspaltung Aromatisch Gebundenen Wasserstoffs und Verknüpfung 

Aromatischer Kerne durch Aluminiumchlorid, Ann. Chem. 1912, 394, 111. 

64. R. S. Jassas, E. U. Mughal, A. Sadiq, R. I. Alsantali, M. M. Al-Rooqi, N. Naeem, Z. 

Moussa, S. A. Ahmed, Scholl Reaction as a Powerful Tool for the Synthesis of 

Nanographenes: a Systematic Review, RSC Adv. 2021, 11, 32158. 

65. M. Grzybowski, K. Skonieczny, H. Butenschçn, D. T. Gryko, Comparison of Oxidative 

Aromatic Coupling and the Scholl Reaction, Angew. Chem. Int. Ed. 2013, 52, 9900. 

66. M. Grzybowski, B. Sadowski, H. Butenschçn, D. T. Gryko, Synthetic Applications of 

Oxidative Aromatic Coupling—From Biphenols to Nanographenes, Angew. Chem. Int. 

Ed. 2020, 59, 2998. 

67. G. Baddeley, J. Kenner, The Constitution of Apocinchene and Syntheses of its Methyl 

and Ethyl Ethers, J. Chem. Soc. 1935, 303. 

68. G. Baddeley, Hydrogen Chloride–Aluminium Chloride as an Agent of Isomerization, J. 

Chem. Soc. 1950, 994. 

69. J. Kenner, Biographical Memoirs of Fellows of the Royal Society, J. Soc. Chem. Ind. 

1933, 42, 470. 



References 

262 

 

70. L. Zhai, R. Shukla, S. H. Wadumethrige, W. Rathore, Probing the Arenium-Ion 

(ProtonTransfer) versus the Cation-Radical (Electron Transfer) Mechanism of Scholl 

Reaction Using DDQ as Oxidant, J. Org. Chem. 2010, 75, 4748. 

71. L. Zhai, R. Shukla, R. Rathore, Oxidative C−C Bond Formation (Scholl Reaction) with 

DDQ as an Efficient and Easily Recyclable Oxidant, Org. Lett. 2009, 11, 3474. 

72. N. Ponugoti, V. Parthasarathy, Rearrangements in Scholl Reaction, Chem. Eur. J. 2022, 

28, e202103530. 

73. Y. Zhang, S. H. Pun, Q. Miao, The Scholl Reaction as a Powerful Tool for Synthesis of 

Curved Polycyclic Aromatics, Chem. Rev. 2022, 122, 14554. 

74. Y. Zou, Y. Han, S. Wu, X. Hou, C. H. E. Chow, J. Wu, Scholl Reaction of Perylene-Based 

Polyphenylene Precursors under Different Conditions: Formation of Hexagon or 

Octagon?, Angew. Chem. Int. Ed. 2021, 60, 17654. 

75. F. Ko, K. Hirabayashi, T. Shimizu, K.-I. Sugiura, Unexpected Phenyl Group 

Rearrangement of Thiele’s Hydrocarbon Derivative Under Polycyclic Aromatic 

Hydrocarbon Synthesis, Tetrahedron 2018, 59, 4251. 

76. J. Liu, A. Narita, S. Osella, W. Zhang, D. Schollmeyer, D. Beljonne, X. Feng, K. Müllen, 

Unexpected Scholl Reaction of 6,7,13,14-Tetraarylbenzo[k]tetraphene: Selective 

Formation of Five-Membered Rings in Polycyclic Aromatic Hydrocarbons, J. Am. Chem. 

Soc. 2016, 138, 2602. 

77. J. Liu, S. Osella, J. Ma, R. Berger, D. Beljonne, D. Schollmeyer, X. Feng, K. Müllen, 

Fused Dibenzo[a,m]rubicene: A New Bowl-Shaped Subunit of C70 Containing Two 

Pentagons, J. Am. Chem. Soc. 2016, 138, 8364. 

78. M. Müller, V. S. Iyer, C. Kübel, V. Enkelmann, K. Müllen, Polycyclic Aromatic 

Hydrocarbons by Cyclodehydrogenation and Skeletal Rearrangement of 

Oligophenylenes, Angew. Chem. Int. Ed. 1997, 36, 1607. 

79. F. E. Golling, M. Quernheim, M. Wagner, T. Nishiuchi, K. Müllen, Concise Synthesis of 

3D π-Extended Polyphenylene Cylinders, Angew. Chem. Int. Ed. 2014, 53, 1525. 

80. X. Dou, X. Yang, G. J. Bodwell, M. Wagner, V. Enkelmann, K. Müllen, Unexpected 

Phenyl Group Rearrangement during an Intramolecular Scholl Reaction Leading to an 

Alkoxy-Substituted Hexa-peri-hexabenzocoronene, Org. Lett. 2007, 9, 2485. 

81. M. Müller, V. S. Iyer, C. Kübel, V. Enkelmann, K. Müllen, Polycyclic Aromatic 

Hydrocarbons by Cyclodehydrogenation and Skeletal Rearrangement of 

Oligophenylenes, Angew. Chem. Int. Ed. 1997, 36, 1607. 

82. A. Pradhan, P. Dechambenoit, H. Bock, F. Durola, Twisted Polycyclic Arenes by 

Intramolecular Scholl Reactions of C3-Symmetric Precursors, J. Org. Chem. 2013, 78, 

2266. 

83. Z. Qiu, S. Asako, Y. Hu, C.-W. Ju, T. Liu, L. Rondin, D. Schollmeyer, J.-S. Lauret, K. 

Müllen, A. Narita, Negatively Curved Nanographene with Heptagonal and [5]Helicene 

Units, J. Am. Chem. Soc. 2020, 142, 14814. 



References 

263 

 

84. J. Ma, Y. Fu, E. Dmitrieva, F. Liu, H. Komber, F. Hennersdorf, A. A. Popov, J. J. Weigand, 

J. Liu, X. Feng, Helical Nanographenes Containing an Azulene Unit: Synthesis, Crystal 

Structures, and Properties, Angew. Chem. Int. Ed. 2020, 59, 5637. 

85. J. Ma, Y. Fu, E. Dmitrieva, F. Liu, H. Komber, F. Hennersdorf, A. A. Popov, J. J. Weigand, 

J. Liu, X. Feng, Helical Nanographenes Containing an Azulene Unit: Synthesis, Crystal 

Structures, and Properties, Angew. Chem. Int. Ed. 2020, 132, 5686. 

86. Y. Han, Z. Xue, G. Li, Y. Gu, Y. Ni, S. Dong, C. Chi, Formation of Azulene-Embedded 

Nanographene: Naphthalene to Azulene Rearrangement During the Scholl Reaction, 

Angew. Chem. Int. Ed. 2020, 59, 9026. 

87. J. M. Fernández-García, P. J. Evans, S. Medina Rivero, I. Fernández, D. García-

Fresnadillo, J. Perles, J. Casado, N. Martín, π-Extended Corannulene-Based 

Nanographenes: Selective Formation of Negative Curvature, J. Am. Chem. Soc. 2018, 

140, 17188. 

88. L. T. Bratz and S. von Niementowski, Synthesen des 8.8′-Dioxy-5.5′-dichinolyls und ein 

Fall der direkten Chlorierung mittels Eisenchlorids, Ber. Dtsch. Chem. Ges. (A and B 

Ser.), 1919, 52, 189. 

89. D. M. Baier, S. Gratz, B. Farhadi Jahromi, S. Hellmann, K. Bergheim, W. Pickhardt, R. 

Schmid, L. Borchardt, Beyond the Scholl Reaction – One-step Planarization and Edge 

Chlorination of Nanographenes by Mechanochemistry, RSC Adv., 2021, 11, 38026. 

90. J. Stanojkovic, R. William, Z. Zhang, I. Fernández, J. Zhou, R. D. Webster, M. C. 

Stuparu. Synthesis of Precisely Functionalizable Curved Nanographenes via 

Graphitization-induced Regioselective Chlorination in a Mechanochemical Scholl 

Reaction, Nat. Commun. 2023, 14, 803. 

91. T. Fujikawa, N. Mitoma, A. Wakamiya, A. Saeki, Y. Segawa, K. Itami, Synthesis, 

Properties, and Crystal Structures of π-Extended Double [6]helicenes: Contorted Multi-

Dimensional Stacking Lattice, Org. Biomol. Chem. 2017, 15, 4697. 

92. X. Yang, M. Hoffmann, F. Rominger, T. Kirschbaum, A. Dreuw, M. Mastalerz, 

Functionalized Contorted Polycyclic Aromatic Hydrocarbons by a One-Step 

Cyclopentannulation and Regioselective Triflyloxylation, Angew. Chem. Int. Ed. 2019, 

58, 10650. 

93. X. Yang, F. Rominger, M. Mastalerz, Contorted Polycyclic Aromatic Hydrocarbons with 

Two Embedded Azulene Units, Angew. Chem. Int. Ed. 2019, 58, 17577. 

94. S. Liu, D. Xia, M. Baumgarten, Rigidly Fused Spiro-Conjugated π-Systems, Chem. Plus 

Chem. 2021, 86, 36.  

95. X. Zhang, Z. Xu, W. Si, K. Oniwa, M. Bao, Y. Yamamoto, T. Jin, Synthesis of Extended 

Polycyclic Aromatic Hydrocarbons by Oxidative Tandem Spirocyclization and 1,2-aryl 

Migration, Nat. Commun. 2017, 8, 15073. 

96. J. L. Ormsby, T. D. Black, C. L. Hilton, Bharat, B. T. King, Rearrangements in the Scholl 

Oxidation: Implications for Molecular Architectures, Tetrahedron 2008, 64, 11370. 



References 

264 

 

97. S. Mauskopf, Crystals and Compounds: Molecular Structure and Composition in 

Nineteenth-Century French Science, Trans. Am. Philos. Soc. 1976, 66, 56. 

98. S. Mauskopf, Crystals and Compounds: Molecular Structure and Composition in 

Nineteenth-Century French Science, Trans. Am. Philos. Soc. 1976, 66, 61. 

99. J.-B. Biot, The Mathematization of Experimental Physics in Napoleonic France, Mém. 

Acad. R. Sci. Inst. Fr. 1817, 2, 4. 

100. L. Pasteur, C. R. Séances Acad. Sci. 1848, 26, 535. 

101. J. H. van’t Hoff, Sur les Formules de Structure dans L'espace, Arch. Neerl. 1874, 9, 1. 

102. Lord Kelvin, The Molecular Tactics of a Crystal. The 2nd Robert Boyle Lecture J. Oxford 

Univ. Junior Sci. Club 1894, 18, 25. 

103. (a) R.S. Cahn, C.K. Ingold and V. Prelog. Specification of Configuration About 

Quadricovalent Asymmetric Atoms J. Chem. Soc. 1951, 612. (b) R.S. Cahn, C.K. Ingold 

and V. Prelog, The Specification of Asymmetric Configuration in Organic Chemistry, 

Experientia 1956, 12, 81. 

104. (a) R.S. Cahn, C.K. Ingold and V. Prelog. Angew. Chem. Int. Ed.1966, 5, 385. (b) V. 

Prelog, G. Helmchen, Basic Principles of the CIP-System and Proposals for a Revision, 

Angew. Chem. Int. Ed. 1982, 21, 567. 

105. IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled 

by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). 

106. M. Rickhaus, M. Mayor, M. Juríček, Chirality in Curved Polyaromatic Systems, Chem. 

Soc. Rev. 2017, 46, 1643. 

107. M. Rickhaus, M. Mayor, M. Juríček, Strain-induced Helical Chirality in Polyaromatic 

Systems, Chem. Soc. Rev. 2016, 45, 1542. 

108. K. Oki, M. Takase, S. Mori, A. Shiotari, Y. Sugimoto, K. Ohara, T. Okujima, H. Uno, 

Synthesis, Structures, and Properties of Core-Expanded Azacoronene Analogue: A 

Twisted π-System with Two N-Doped Heptagons, J. Am. Chem. Soc. 2018, 140, 10430. 

109. J. Liu, B.-W. Li, Y.-Z. Tan, A. Giannakopoulos, C. Sánchez-Sánchez, D. Beljonne, P. 

Ruffieux, R. Fasel, X. L. Feng, K. Müllen, Toward Cove-Edged Low Band Gap Graphene 

Nanoribbons, J. Am. Chem. Soc. 2015, 137, 6097. 

110. K. Kawasumi, Q. Zhang, Y. Segawa, L. T. Scott, K. Itami, A Grossly Warped 

Nanographene and the Consequences of Multiple Odd-membered-ring Defects, Nat. 

Chem. 2013, 5, 739. 

111. X. Gu, H. Li, B. Shan, Z. Liu, Q. Miao, Synthesis, Structure, and Properties of 

Tetrabenzo[7]circulene, Org. Lett. 2017, 19, 2246. 

112. S. H. Pun, Y. Wang, M. Chu, C. K. Chan, Y. Li, Z. Liu, Q. Miao, Synthesis, Structures, 

and Properties of Heptabenzo[7]circulene and Octabenzo[8]circulene, J. Am. Chem. Soc., 

2019, 141, 9680. 



References 

265 

 

113. T. Kirschbaum, F. Rominger and M. Mastalerz, A Chiral Polycyclic Aromatic 

Hydrocarbon Monkey Saddle, Angew. Chem., Int. Ed., 2020, 59, 270. 

114. Z. Qiu, S. Asako, Y. Hu, C.-W. Ju, T. Liu, L. Rondin, D. Schollmeyer, J.-S. Lauret, K. 

Müllen, A. Narita, Negatively Curved Nanographene with Heptagonal and [5]Helicene 

Units, J. Am. Chem. Soc. 2020, 142, 14814. 

115. C. M. Cruz, I. R. Márquez, I. F. A. Mariz, V. Blanco, C. Sánchez-Sánchez, J. M. Sobrado, 

J. A. Martín-Gago, J. M. Cuerva, E. Maçôas, A. G. Campaña, Enantiopure Distorted 

Ribbon-shaped Nanographene Combining Two-photon Absorption-based Upconversion 

and Circularly Polarized Luminescence, Chem. Sci. 2018, 9, 3917. 

116. M. A. Medel, R. Tapia, V. Blanco, D. Miguel, S. P. Morcillo, A. G. Campaña, Octagon-

Embedded Carbohelicene as a Chiral Motif for Circularly Polarized Luminescence 

Emission of Saddle-Helix Nanographenes, Angew. Chem. Int. Ed. 2021, 60, 6094. 

117. X. Xu, R. Munoz-Marmol, S. Vasylevskyi, A. Villa, G. Folpini, F. Scotognella, G. M. 

Paterno, A. Narita, Synthesis of Bioctacene-Incorporated Nanographene with Near-

Infrared Chiroptical Properties, Angew. Chem. Int. Ed. 2023, 62, e202218350. 

118. S. H. Pun, K. M. Cheung, D. Yang, H. Chen, Y. Wang, S. V. Kershaw, Q. Miao, A Near-

Infrared Absorbing and Emissive Quadruple Helicene Enabled by the Scholl Reaction of 

Perylene, Angew. Chem. Int. Ed. 2022, 61, e202113203. 

119. M. Krzeszewski, H. Ito, K. Itami, Infinitene: A Helically Twisted Figure-Eight 

[12]Circulene Topoisomer,  Infinitene: A Helically Twisted Figure-Eight [12]Circulene 

Topoisomer, J. Am. Chem. Soc. 2022, 144, 862. 

120. W. Fan, T. Matsuno, Y. Han, X. Wang, Q. Zhou, H. Isobe, J. Wu, Synthesis and Chiral 

Resolution of Twisted Carbon Nanobelts, J. Am. Chem. Soc. 2021, 143, 15924. 

121. W. Fan, T. M. Fukunaga, S. Wu, Y. Han, Q. Zhou, J. Wang, Z. Li, X. Hou, H. Wei, Y. Ni, 

H. Isobe, J. Wu, Synthesis and Chiral Resolution of a Triply Twisted Möbius Carbon 

Nanobelt, Nat. Synth. 2023, 2, 880. 

122. K. Yin Cheung, S. Gui, C. Deng, H. Liang, Z. Xia, Z. Liu, L. Chi, Q. Miao, Synthesis of 

Armchair and Chiral Carbon Nanobelts, Chem 2019, 5, 838. 

123. Y. Nojima, M. Hasegawa, N. Hara, Y. Imai, Y. Mazaki, Stereogenic Cyclic 

Oligonaphthalenes Displaying Ring Size-dependent Handedness of Circularly Polarized 

Luminescence (CPL), Chem. Commun. 2019, 55, 2749. 

124. S. Li, R. Li, Y.-K. Zhang, S. Wang, B. Ma, B. Zhang, P. An, BINOL-like Atropisomeric 

Chiral Nanographene, Chem. Sci. 2023, 14, 3286. 

125. S. Mörsel, R. Kellner, A. Hirsch, Thioether-Substituted Hexa-peri-hexabenzocoronenes, 

Eur. J. Org. Chem. 2023, 26, e202300299. 

126. R. Adams, H. C. Yuan, The Stereochemistry of Diphenyls and Analogous Compounds, 

Chem. Rev. 1933, 12, 261. 

127. A. Fechtenkötter, K. Saalwächter, M. A. Harbison, K. Müllen, H. Wolfgang Spiess, 

Highly Ordered Columnar Structures from Hexa-peri-hexabenzocoronenes—Synthesis, 



References 

266 

 

X-ray Diffraction, and Solid-State Heteronuclear Multiple-Quantum NMR 

Investigations, Angew. Chem. Int. Ed. 1999, 38, 3039. 

128. T. Wöhrle, I. Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum, J. Litterscheidt, J. 

Christian Haenle, P. Staffeld, A. Baro, F. Giesselmann, S. Laschat, Discotic Liquid 

Crystals, Chem. Rev. 2016, 116, 1139. 

129. J. P. Hill, W. Jin, A. Kosaka, T. Fukushima, H. Ichihara, T. Shimomura, K. Ito, T. 

Hashizume, N. Ishii, T. Aida, Self-Assembled Hexa-peri-hexabenzocoronene Graphitic 

Nanotube, Science 2004, 304, 1481. 

130. X.-J. Zhao, H. Hou, X.-T. Fan, Y. Wang, Y.-M. Liu, C. Tang, S.-H. Liu, P.-P. Ding, J. 

Cheng, D.-H. Lin, C. Wang, Y. Yang, Y.-Z. Tan, Molecular Bilayer Graphene, Nat. 

Commun. 2019, 10, 3057. 

131. B. Pigulski, K. Shoyama, M.-J. Sun, F. Würthner, Fluorescence Enhancement by 

Supramolecular Sequestration of a C54-Nanographene Trisimide by 

Hexabenzocoronene, J. Am. Chem. Soc. 2022, 144, 5718. 

132. X. Yang, M. Brückner, F. Rominger, T. Kirschbaum, M. Mastalerz, Dispersion-driven 

Formation of Chiral Twisted PAH Double Helices, Chem 2024, 10, 832. 

133. A. Oró, F. Romeo-Gella, J. Perles, J. M. Fernández-García, I. Corral, N. Martín, 

Tetrahedraphene: A Csp3-centered 3D Molecular Nanographene Showing Aggregation-

Induced Emission Angew. Chem. Int. Ed. 2023, 62, e202312314. 

134. W. Wang, X.-H. Ma, M. Liu, S. Tang, X. Ding, Y. Zhao, Y.-Z. Tan, M. Kertesz, X. Wang, 

A Triply Negatively Charged Nanographene Bilayer with Spin Frustration, Angew. Chem. 

Int. Ed. 2023, 135, e202217788. 

135. L. Moshniaha, M. Żyła-Karwowska, P. J. Chmielewski, T. Lis, J. Cybińska, E. Gońka, J. 

Oschwald, T. Drewello, S. Medina Rivero, J. Casado, M. Stępień, Aromatic 

Nanosandwich Obtained by σ-Dimerization of a Nanographenoid π-Radical, J. Am. 

Chem. Soc. 2020, 142, 3626. 

136. P. J. Evans, J. Ouyang, L. Favereau, J. Crassous, I. Fernández, J. Perles, N. Martín, 

Synthesis of a Helical Bilayer Nanographene, Angew. Chem. Int. Ed. 2018, 57, 6774. 

137. D. Reger, P. Haines, F. W. Heinemann, D. M. Guldi, N. Jux, Oxa[7]superhelicene: A π-

Extended Helical Chromophore Based on Hexa-peri-hexabenzocoronenes, Angew. 

Chem. Int. Ed. 2018, 57, 5938. 

138. L. Yang, Y.-Y. Ju, M. A. Medel, Y. Fu, H. Komber, E. Dmitrieva, J.-J. Zhang, S. 

Obermann, A. G. Campaña, J. Ma, X. Feng, Helical Bilayer Nonbenzenoid 

Nanographene Bearing a [10]Helicene with Two Embedded Heptagons, Angew. Chem. 

Int. Ed. 2023, 62, e202216193. 

139. Y.-J. Shen, N.-T. Yao, L.-N. Diao, Y. Yang, X.-L. Chen, H.-Y. Gong, A π-Extended 

Pentadecabenzo[9]Helicene, Angew. Chem. Int. Ed. 2023, 62, e202300840. 

140. Y. Zhang, S. Yu, B. Han, Y. Zhou, X. Zhang, X. Gao, Z. Tang, Circularly Polarized 

Luminescence in Chiral Materials, Matter 2022, 5, 837. 



References 

267 

 

141. Y. Deng, M. Wang, Y. Zhuang, S. Liu, W. Huang, Q. Zhao, Circularly Polarized 

Luminescence from Organic Micro-/nano-structures, Light Sci. Appl. 2021, 10, 76. 

142. E. M. Sánchez-Carnerero, A. R. Agarrabeitia, F. Moreno, B. L. Maroto, G. Muller, M. J. 

Ortiz, S. de la Moya, Circularly Polarized Luminescence from Simple Organic 

Molecules, Chem. Eur. J. 2015, 21, 13488. 

143. Y.-Y. Ju, L. Chai, K. Li, J.-F. Xing, X.-H. Ma, Z.-L. Qiu, X.-J. Zhao, J. Zhu, Y.-Z. Tan, 

Helical Trilayer Nanographenes with Tunable Interlayer Overlaps, J. Am. Chem. Soc. 

2023, 145, 2815. 

144. W. Niu, Y. Fu, Z.-L. Qiu, C. J. Schürmann, S. Obermann, F. Liu, A. A. Popov, H. Komber, 

J. Ma, X. Feng, π-Extended Helical Multilayer Nanographenes with Layer-Dependent 

Chiroptical Properties, J. Am. Chem. Soc. 2023, 145, 26824. 

145. W. Niu, Y. Fu, Q. Deng, Z.-L. Qiu, F. Liu, A. A. Popov, H. Komber, J. Ma, X. Feng, 

Enhancing Chiroptical Responses in Helical Nanographenes via Geometric Engineering 

of Double [7]Helicenes, Angew. Chem. Int. Ed. 2024, e202319874. 

146. L. Arrico, L. Di Bari, F. Zinna, Quantifying the Overall Efficiency of Circularly Polarized 

Emitters, Chem. Eur. J. 2021, 27, 2920. 

147. M. Buendía, J. M. Fernández-García, J. Perles, S. Filippone, N. Martín, Enantioselective 

Synthesis of a Two-fold Inherently Chiral Molecular Nanographene, Nat. Synth. 2024, 3, 

545. 

148. H. Jürgen Bestmann, W. Both, Determination of the Absolute Configuration of (+)-

Pentahelicene, Angew. Chem. Int. Ed. 1972, 11, 296. 

149. I. G. Stará, I. Starý, M. Tichf, J. Závada, V. Hanus, Stereochemical Dichotomy in the 

Stevens Rearrangement of Axially Twisted Dihydroazepinium and Dihydrothiepinium 

Salts. A Novel Enantioselective Synthesis of Pentahelicene, J. Am. Chem. Soc. 1994, 116, 

5084. 

150. K. Tanaka, H. Suzuki, H. Osuga, Non-Photochemical Route to Chiral Disubstituted 

[7]Thiaheterohelicenes via Biaryl- and Carbonyl-Coupling Reactions, J. Org. Chem. 

1997, 62, 4465. 

151. K. Nakano, Y. Hidehira, K. Takahashi, T. Hiyama, K. Nozaki, Stereospecific Synthesis 

of Hetero[7]helicenes by Pd-Catalyzed Double N-Arylation and Intramolecular O-

Arylation, Angew. Chem. Int. Ed. 2005, 44, 7136. 

152. A. Grandbois, S. K. Collins, Enantioselective Synthesis of [7]Helicene: Dramatic Effects 

of Olefin Additives and Aromatic Solvents in Asymmetric Olefin Metathesis, Chem. Eur. 

J. 2008, 14, 9323. 

153. S. Chen, Z. Ge, Q. Jia, K.-P. Wang, L.-H. Gan, Z.-Q. Hu, The Preparation of Enantiopure 

[6]- and [7]Helicenes from Binaphthanol, Chem. Asian J. 2019, 14, 1462. 

154. U. Dhawa, C. Tian, T. Wdowik, J. C. A. Oliveira, J. Hao, L. Ackermann, Enantioselective 

Pallada-Electrocatalyzed C−H Activation by Transient Directing Groups: Expedient 

Access to Helicenes, Angew. Chem. Int. Ed. 2020, 59, 13451. 



References 

268 

 

155. T. Ikai, K. Oki, S. Yamakawa, E. Yashima, Stereospecific Synthesis of Enantiopure 

[6]Helicene Containing a Seven-Membered Ring and [7]Helicene by Acid-Promoted 

Stepwise Alkyne Annulations of Doubly Axial-Chiral Precursors, Angew. Chem. Int. Ed. 

2023, 62, e202301836. 

156. J. M. Brunel, BINOL:  A Versatile Chiral Reagentm, Chem. Rev. 2005, 105, 857. 

157. J. Aydin, K. S. Kumar, M. J. Sayah, O. A. Wallner, K. J. Szabó, Synthesis and Catalytic 

Application of Chiral 1,1‘-Bi-2-naphthol- and Biphenanthrol-Based Pincer Complexes:  

Selective Allylation of Sulfonimines with Allyl Stannane and Allyl Trifluoroborate, J. 

Org. Chem. 2007, 72, 4689. 

158. R. Kshatriya, Recent Advancement in H8–BINOL Catalyzed Asymmetric 

Methodologies, ACS Omega 2023, 8, 17381. 

159. J. Jiménez, R. Prieto-Montero, S. Serrano, P. Stachelek, E. Rebollar, B. L. Maroto, F. 

Moreno, V. Martinez-Martinez, R. Pal, I. García-Moreno, S. de la Moya, BINOL Blocks 

as Accessible Triplet State Modulators in BODIPY Dyes, Chem. Commun., 2022, 58, 

6385. 

160. K. Sato, M. Hasegawa, Y. Nojima, N. Hara, T. Nishiuchi, Y. Imai, Y. Mazaki, Circularly 

Polarized Luminescence of a Stereogenic Curved Paraphenylene Anchoring a Chiral 

Binaphthyl in Solution and Solid State, Chem. Eur. J. 2021, 27,1323. 

161. R. K. Dubey, M. Melle-Franco, A. Mateo-Alonso, Inducing Single-Handed Helicity in a 

Twisted Molecular Nanoribbon, J. Am. Chem. Soc. 2022, 144, 2765. 

162. N. V. Tkachenko, S. Scheiner, Optical Stability of 1,1′-Binaphthyl Derivatives, ACS 

Omega 2019, 4, 6044. 

163. J. Areephong, N. Ruangsupapichart, T. Thongpanchang, A Concise Synthesis of 

Functionalized 7-oxa-[5]-helicenes, Tetrahedron Lett. 2004, 45, 3067. 

164. C. A. Guido, F. Zinna, G. Pescitelli, CPL calculations of [7]helicenes with Alleged 

Exceptional Emission Dissymmetry Values, J. Mater. Chem. C, 2023, 11, 10474. 

165. L. Zhang, I. Song, J. Ahn, M. Han, M. Linares, M. Surin, H.-J. Zhang, J. H. Oh, J. Lin, 

π-Extended Perylene Diimide Double-heterohelicenes as Ambipolar Organic 

Semiconductors for Broadband Circularly Polarized Light Detection, Nat. Commun. 

2021, 12, 142. 

166. M. Cei, L. Di Bari, F. Zinna, Circularly Polarized Luminescence of Helicenes: A Data-

Informed Insight, Chirality 2023, 35, 192. 

167. K. Nakanishi, D. Fukatsu, K. Takaishi, T. Tsuji, K. Uenaka, K. Kuramochi, T. Kawabata, 

K. Tsubaki, Oligonaphthofurans: Fan-Shaped and Three-Dimensional π-Compounds, J. 

Am. Chem. Soc. 2014, 136, 7101. 

168. S. Hossain, M. Akter, M. Karikomi, Synthesis of Oxa[9]helicene Derivatives by 

Cyclodehydration of 1,1′-bibenzo[c]phenanthrene-2,2′-diol Using Phosphorus 

Pentoxide, Tetrahedron Lett. 2021, 69, 152948. 



References 

269 

 

169. M. Sako, Y. Takeuchi, T. Tsujihara, J. Kodera, T. Kawano, S. Takizawa, H. Sasai, 

Efficient Enantioselective Synthesis of Oxahelicenes Using Redox/Acid Cooperative 

Catalysts, J. Am. Chem. Soc. 2016, 138, 11481. 

170. W. Fudickar, T. Linker, Why Triple Bonds Protect Acenes from Oxidation and 

Decomposition, J. Am. Chem. Soc. 2012, 134, 15071. 

171. Y. Nojima, M. Hasegawa, N. Hara, Y. Imai, Y. Mazakia, Stereogenic Cyclic 

Oligonaphthalenes Displaying Rring Size-dependent Handedness of Circularly Polarized 

Luminescence (CPL), Chem. Commun. 2019, 55, 2749. 

172. Gaussian 09, Revision D.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, 

M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji, X. 

Li, M. Caricato, A. Marenich, J. Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P. 

Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, D. Williams-Young, F. Ding, F. 

Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V. G. 

Zakrzewski, J. Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. 

Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, 

K. Throssell, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. 

Brothers, K. N. Kudin, V. N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K. 

Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, 

M. Klene, C. Adamo, R. Cammi, J. W. Ochterski, R. L. Martin, K. Morokuma, O. Farkas, 

J. B. Foresman, and D. J. Fox, Gaussian, Inc., Wallingford CT, 2016. 

173. (a) A. D. Becke, Density‐functional Thermochemistry. III. The Role of Exact Exchange, 

J. Chem. Phys. 1993, 98, 5648; b) C. Lee, W. Yang, R. G. Parr, Development of the Colle-

Salvetti Correlation-energy Formula into a Functional of the Electron Density, Phys. Rev. 

B 1998, 37, 785; c) S. H. Vosko, L. Wilk, M. Nusair, Can. Accurate Spin-dependent 

Electron Liquid Correlation Energies for Local Spin Density Calculations: a Critical 

Analysis, J. Phys. 1980, 58, 1200. 

174. S. Grimme, J. Antony, S. Ehrlich, H. Krieg, H. A Consistent and Accurate ab Initio 

Parametrization of Density Functional Dispersion Correction (DFT-D) for the 94 

Elements H-Pu, J. Chem. Phys. 2010, 132, 154104. 

175. F. Weigend, R. Alhrichs, Balanced Basis Sets of Split Valence, Triple Zeta Valence and 

Quadruple Zeta Valence Quality for H to Rn: Design and Assessment of Accuracy, Phys. 

Chem. Chem. Phys. 2005, 7, 3297. 

176. J. W. McIver, A. K. Komornicki, Structure of Transition States in Organic Reactions. 

General Theory and an Application to the Cyclobutene-butadiene Isomerization using a 

Semiempirical Molecular Orbital Method, J. Am. Chem. Soc. 1972, 94, 2625. 

177. González, C.; Schlegel, H. B. Reaction Path Following in Mass-weighted Internal 

Coordinates, J. Phys. Chem. 1990, 94, 5523. 

178. (a) S. Miertuš, E. Scrocco, J. Tomasi, Electrostatic Interaction of a Solute with a 

Continuum. A Direct Utilizaion of AB Initio Molecular Potentials for the Prevision of 

Solvent Effects, Chem. Phys. 1981, 55, 117; (b) J. L. Pascual-Ahuir, E. Silla, I. Tuñón, 

GEPOL: An Improved Description of Molecular Surfaces. III. A New Algorithm for the 



References 

270 

 

Computation of a Solvent-excluding Surface, J. Comp. Chem. 1994, 15, 1127; (c) V. 

Barone, M. Cossi, Quantum Calculation of Molecular Energies and Energy Gradients in 

Solution by a Conductor Solvent Model, J. Phys. Chem. A, 1998, 102, 1995. 

179. (a) M. E. Casida, Recent Developments and Applications of Modern Density Functional 

Theory; Elsevier: Amsterdam, 1996; Vol. 4; (b) M. E. Casida, D. P. Chong, Recent 

Advances in Density Functional Methods; World Scientific: Singapore, 1995; Vol. 1, p 

155. 

180. For a review, see: A. Dreuw, M. Head-Gordon, M. Single-Reference ab Initio Methods 

for the Calculation of Excited States of Large Molecules, Chem. Rev. 2005, 105, 4009. 

181. Z. Chen, C. S. Wannere, C. Corminboeuf, R. Puchta, P. Schleyer, Nucleus-Independent 

Chemical Shifts (NICS) as an Aromaticity Criterion, Chem. Rev. 2005, 105, 3842. 

182. K. Wolinski, J. F. Hilton, P. Pulay, Efficient Implementation of the Gauge-independent 

Atomic Orbital Method for NMR Chemical Shift Calculations, J. Am. Chem. Soc. 1990, 

112, 8251. 

183. (a) Becke, A. D. Density‐functional Thermochemistry. III. The Role of Exact Exchange, 

J. Chem. Phys. 1993, 98, 5648; (b) Lee, C.; Yang, W.; Parr, R. G.  Development of the 

Colle-Salvetti Correlation-energy Formula into a Functional of the Electron Density, 

Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785; (c) Vosko, S. H.; Wilk, L.; 

Nusair, M. Can. Accurate Spin-dependent Electron Liquid Correlation Energies for Local 

Spin Density Calculations: a Critical Analysis, J. Phys. 1980, 58, 1200. 

184. Johnson, E. R.; Keinan, S.; Mori-Sánchez, P.; Contreras-García, J.; Cohen, A. J.; Yang, 

W. Revealing Noncovalent Interactions, J. Am. Chem. Soc. 2010, 132, 6498. 


	Tesis Patricia Izquierdo García
	PORTADA
	TABLE OF CONTENTS
	SUMMARY
	RESUMEN
	INTRODUCTION
	CHAPTER 1
	CHAPTER 2
	CHAPTER 3
	CHAPTER 4
	EXPERIMENTAL SECTION
	APPENDIX 1. Chapter 1
	APPENDIX 2. Chapter 2
	APPENDIX 3. Chapter 3
	APPENDIX 4. Chapter 4
	APPENDIX 5. Spectra
	REFERENCES