Photoredox chemistry of polyoxometalates as a photocatalyst

The photocatalytic action of polyoxometalates (PMs), which is initiated by the photoexcitation of the oxygen-to-metal charge-transfer (O --> MLMCT) bands of PM, is based on the electron-hole pair separation followed by reductive and oxidative reactions with surrounding molecules. It is shown that the O --> MLMCT triplet states are involved in the photoredox reactions in which the significance of the highly negative oxidation potential for the photoreduced PMs can be considered in connection with the photocatalytic H-2 formation from a great variety of organic substrates with their dehydrated oxidation. When the reaction of the photoreduced PMs with the electron acceptor hardly occurs kinetically or thermodynamically, they undergo self-assembled organization to nanosized supramolecules (as a result of photoencapsulation of small molecules and ring cluster formation). Some typical examples for the electron-hole pair separation and the photoredox reactions developed in our laboratory are discussed.