Dendronized Triangular Oligo(phenylene ethynylene) Amphiphiles: Nanofibrillar Self-Assembly and Dye Encapsulation

Abstract

Triangular-shaped oligo(phenylene ethynylene) amphiphiles 1 a and 1 b decorated in their periphery with two- and four-branched hydrophilic triethyleneglycol dendron wedges, have been synthesized and their self-assembling properties in solution and onto surfaces investigated. The steric demand produced by the dendritic substituents induces a face-to-face rotated π stacking of the aromatic moieties. Studies on the concentration and temperature dependence confirm this mechanism and provide binding constants of 1.2×105 and 1.7×105 M−1 in acetonitrile for 1 a and 1 b, respectively. Dynamic and static light scattering measurements complement the study of the self-assembly in solution and demonstrate the formation of rod-like supramolecular structures in aqueous solution. The nanofibers formed in solution can be efficiently transferred onto surfaces. Thus, TEM images reveal the presence of strands of various thickness, with the most common being several micrometers long and with diameters of around 70 nm. Some of these nanofibers present folded edges that are indicative of their ribbon-like nature. Interestingly, compound 1 b can also form thick filaments with a rope-like appearance, which points to a chiral arrangement of the fibers. AFM images under highly diluted conditions also reveal long fibers with height profiles that fit well with the molecular dimensions calculated for both amphiphiles. Finally, we have demonstrated the intercalation of the hydrophobic dye Disperse Orange 3 within the filaments and its subsequent release upon increasing the temperature.