Perylene bisimides (PBIs) are one example of useful p-conjugated molecules that can be used in optoelectronic devices as n-type materials with strong visible light absorption. PBIs can self-assemble into a range of structures, but it is rare to be able to control the packing such that the same PBI can form either H-type or J-type aggregates. This is important because the conductivity pathways and optoelectronic properties are directly affected by this packing. Here, we show that we can control the packing of a single PBI functionalized with an amino acid by a subtle change in pH. Under one set of conditions, H-type aggregates form a gel when the pH is decreased. At a slightly different set of starting conditions, J-type aggregates are formed, but they cannot form a gel when the pH is lowered. We show that films formed from the self-assembled structures have very different photoconductive properties.

usually strongly absorbing in the visible light region and many possess n-type semiconductor behavior when aggregated. [8,9] PBIs often self-assemble in solution at high concentrations or when given a suitable trigger. They typically self-assemble into 1D structures such as nanofibers or nanotubes, a process driven by non-covalent interactions such as hydrogen bonding, van der Waals interactions, and π-π stacking. [2,3,10-14] The electronic properties of PBIs can be tuned by how they are functionalized and by the type of self-assembled aggregate that is formed. [10,15] Using solar energy to generate H 2 and O 2 from water is highly desirable to form part of a "green economy". [16-18] H 2 can be used as a fuel for combustion, within fuel cells and both H 2 and O 2 are also important chemical feedstocks. [17,18] PBIs and the related perylene monoimides (PMIs) have shown promise in the utilization of solar energy to drive chemical reactions, and have been shown to be able to act as effective photocatalysts for both H 2 evolution and O 2 evolution reactions. [19-23] Some of these systems use perylene mono or bis imides in a self-assembled state, but other self-assembled photocatalysts

Perylene bisimides (PBIs) can be functionalised to enable controlled aggregation into complex supramolecular structures and are promising materials for photovoltaic and solar fuel applications.