Impact of charge switching stimuli on supramolecular perylene monoimide assemblies

The development of stimuli-responsive amphiphilic supramolecular nanostructures is an attractive target for systems based on light-absorbing chromophores that can function as photosensitizers in water. We report here on a water soluble supramolecular carboxylated perylene monoimide system in which charge can be switched significantly by a change in pH. This was accomplished by substituting the perylene core with an ionizable hydroxyl group. In acidic environments, crystalline supramolecular nanoribbons with dimensions on the order of 500 × 50 × 2 nm form readily, while in basic solution the additional electrostatic repulsion of the ionized hydroxyl reduces assemblies to very small dimensions on the order of only several nanometers. The HOMO/LUMO levels were also found to be sensitive to pH; in acidic media the HOMO/LUMO levels are –5.65 and –3.70 eV respectively versus vacuum, whereas is in basic conditions they are –4.90 and –3.33 eV, respectively. Utilizing the assemblies as photosensitizers in photocatalytic production of hydrogen with [Mo(3)S(13)](2–) as a catalyst at a pH of 4, H(2) was generated with a turnover number of 125 after 18 hours. Charge switching the assemblies at a pH of 9–10 and using an iron porphyrin catalyst, protons could again be reduced to hydrogen and CO(2) was reduced to CO with a turnover number of 30. The system investigated offers an example of dynamic photosensitizing assemblies that can drive reactions in both acidic and basic media.