Perylene bisimides (PBIs) are really useful n-type materials. They are highly absorbent in the visible and are thermally stable. It is easy to modify the conjugated core with different functional groups. These different functional moieties can direct the self-assembly into different types aggregates, and strongly affect the solubility. This can lead to dramatically different properties. PBIs are suitable for such light driven processes as solar cells and H<sub>2</sub> evolution due to the formation of a radical anion upon irradiation with different wavelengths of light. By changing the aggregation type and the HOMO-LUMO level of the self-assembling molecules, one can tune the wavelength of light needed to drive these reactions. It is often difficult to control and predict the aggregation in advance and therefore the function of the material. Here, we will describe a levodopa-functionalised PBI that self-assembles into two different supramolecular aggregates depending on subtle changes in the pH of the solution, which show either H-type absorption properties or J-type absorption. We are able to switch between the two aggregation types by changing the pH. With the use of small angle neutron scattering, UV-vis absorption spectroscopy and imaging techniques, we are able to fully analyse these aggregates and post-rationalise the structures with computational modelling. Each of these aggregates exhibits different behaviour, with one being able to self-assemble into a gel upon lowering the pH and one not (Figure 1.). The aggregates interestingly also have different responses to light and we are therefore able to tune the photoconductivity of the materials by changing the aggregate type. This level of control from one molecule just by altering the pH shows great promise in applications such as OPVs and other optoelectronic materials.

Reversible H- and J-type aggregation of a single perylene bisimide leading to different photoconductivity

253rd National Meeting (2017)

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