Towards artificial photosynthesis:: ruthenium-manganese chemistry for energy production

The synthesis and characterisation of supramolecular model systems mimicking the light reactions on the donor side of Photosystem II (PSII) in green plants have been reviewed. In these systems, manganese complexes and tyrosine are electron donors, modelling the manganese cluster and tyrosine(Z) in PSII. The donors have been covalently linked to a photosensitizer, a ruthenium(ii) tris-bipyridyl complex, that plays the role of the P-680 chlorophylls in PSII. It has been demonstrated that, in the presence of an external electron acceptor in solution, the model systems can undergo an intermolecular electron transfer from the photoexcited state of Ru-II to an acceptor, followed by an intramolecular electron transfer from the coordinated Mn complexes or the tyrosine unit to the photogenerated Ru-III. This leads to regeneration of the Ru-II and oxidation of the Mn complexes or generation of a tyrosine radical. The process closely mimics the primary reaction steps on the donor side of PSII.