Multidirectional Charge Separation in Self-Assembled Aggregates of Perylenebisimide-Porphyrin Bola-Supra-Amphiphiles

We report on the synthesis of a hydrogen-bond mediated bola-type supra-amphiphile and assembly thereof in water. The assembly is based on amphiphilic porphyrins and hydrophobic perylenebisimdes (PBI), which both form the resulting bola-form solely through the H-bonding motif, which is shielded by the assembly of the chromophores itself. The amphiphilic porphyrin was functionalized, on one hand, with a cyanuric acid and, on the other hand, with an oligo carboxylate dendron as polar head group. Two Hamilton receptors were linked to the PBI on each imide position. Assembly was achieved by lyophilizing solutions of both components in water/THF mixtures, followed by redispersion in pure water yielding stable suspensions. Cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS) reveal a spherical morphology with diameters ranging from 15 - 100 nm. Once formed, the assemblies showed broadened absorptions and quenched PBI-centered fluorescence. Using time-resolved absorption spectroscopy, the nature of the fluorescence quenching was confirmed to be either charge separation, by which the porphyrin donates an electron to the PBI, or symmetry breaking charge separation, by which π-π stacked PBIs donate and accept electrons. Denaturation of the supra-amphiphile went hand-in-hand with a reinstation of the PBI fluorescence and suppression of charge separation.