A Ruthenium Complex-Porphyrin-Fullerene-Linked Molecular Pentad as an Integrative Photosynthetic Model

A ruthenium complex, porphyrin sensitizer, fullerene acceptor molecular pentad has been synthesized and a long-lived hole-electron pair was achieved in aqueous solution by photoinduced multistep electron transfer: Upon irradiation by visible light, the excited-state of a zinc porphyrin (¹ ZnP*) was quenched by fullerene (C₆₀ ) to afford a radical ion pair, ^1,3 (ZnP^.+ -C₆₀^.- ). This was followed by the subsequent electron transfer from a water oxidation catalyst unit (Ru^II ) to ZnP^.+ to give the long-lived charge-separated state, Ru^III -ZnP-C₆₀^.- , with a lifetime of 14 μs. The ZnP worked as a visible-light-harvesting antenna, while the C₆₀ acted as an excellent electron acceptor. As a consequence, visible-light-driven water oxidation by this integrated photosynthetic model compound was achieved in the presence of sacrificial oxidant and redox mediator.