Controlling photocatalytic activity by self-assembly – Tuning perylene bisimide photocatalysts for the hydrogen evolution reaction

Amino acid functionalized perylene bisimides (PBIs) form self-assembled structures in solution, the nature of which depends on the local environment. Using a high-throughput photocatalysis setup, five PBIs are studied for the hydrogen evolution reaction (HER) under a range of conditions (pH and hole scavenger concentration) across 350 experiments to explore the relationship between supramolecular structure and photocatalytic activity. Using small angle X-ray scattering (SAXS), NMR spectroscopy and ultraviolet-visible (UV-vis) absorption spectroscopy, it is shown that photocatalytic activity is determined by the nature of the self-assembled aggregate that is formed, demonstrating the potential of self-assembly to tune activity. There is a clear correlation between the presence of charged flexible cylindrical aggregates and the occurrence of photocatalytic H₂ production, with UV–vis spectroscopy indicating that the most active structure type has a distinctive form of π-aggregation which is proposed to enable efficient charge separation across multiple PBI units.