Interplay between Charge Separation and Singlet Down-Conversion in a Spiro Perylene Diimide–Nanographene Conjugate

Abstract

The synthesis and characterization of a novel nanographene conjugate, PDI-spiro-NG, featuring perylene diimide (PDI) and hexa-peri-hexabenzocoronene (HBC) connected via a spirobifluorene spacer is reported. The synthetic route involved preparation of functionalized PDI and HBC building blocks, subsequent palladium-catalyzed Suzuki cross-coupling, and a final Scholl cyclodehydrogenation reaction. A folded cofacial conformation was confirmed as the thermodynamically favored geometry in solution by 1D ROE NMR experiments and solvent-model DFT calculations, with HOMO and LUMO energy levels separated and localized on the electron-donating HBC and accepting PDI, respectively. In-depth photophysical investigations demonstrated a solvent-dependent interplay between an efficient charge separation and energy transfer. In apolar solvents, the spiro-architecture enables the admixture between a locally excited and charge transfer state, as supported by TD-DFT calculations. Such mixed states result in a drastic suppression of the fast radiative decay channels, kinetically stabilizing the lowest singlet excited state (S1) and yielding an exceptionally long lifetime of ∼100 ns. This unprecedented stabilization enables efficient diffusional quenching by triplet oxygen, unlocking a singlet oxygen down-conversion mechanism with a quantum yield of 116 ± 4%. Our results underscore the potential of PDI-spiro-NG for the transduction of light into electrical or chemical energy for applications in next-generation optoelectronic and energy-conversion devices.