Hierarchical organization of perylene bisimides and polyoxometalates for photo-assisted water oxidation

The oxygen in Earth’s atmosphere is there primarily because of water oxidation performed by photosynthetic organisms using solar light and one specialized protein complex, photosystem II (PSII). High-resolution imaging of the PSII ‘core’ complex shows the ideal co-localization of multi-chromophore light-harvesting antennas with the functional reaction centre. Man-made systems are still far from replicating the complexity of PSII, as the majority of PSII mimetics have been limited to photocatalytic dyads based on a 1:1 ratio of a light absorber, generally a Ru–polypyridine complex, with a water oxidation catalyst. Here we report the self-assembly of multi-perylene-bisimide chromophores (PBI) shaped to function by interaction with a polyoxometalate water-oxidation catalyst (Ru4POM). The resulting [PBI]5Ru4POM complex shows a robust amphiphilic structure and dynamic aggregation into large two-dimensional paracrystalline domains, a redshifted light-harvesting efficiency of >40% and favourable exciton accumulation, with a peak quantum efficiency using ‘green’ photons (λ > 500 nm). The modularity of the building blocks and the simplicity of the non-covalent chemistry offer opportunities for innovation in artificial photosynthesis. In native photosystem II (PSII), multi-chromophore antennas surround the reaction centre, capturing light and triggering the quantized (four-flashes) photo-oxidation of water to oxygen. The PSII ‘quantasome’ is the most efficient photo-electrolyser built so far. An artificial quantasome has now been developed; it is specifically designed for oxygen evolution by self-assembling light-harvesting-perylene bisimides with a ruthenium polyoxometalate water-oxidation catalyst.