Polyoxometalates in visible-light photocatalysis and solar energy conversion

Polyoxometalates (POMs) are an important class of anionic molecular metal oxides, boasting an enormous range of structures and properties. They are commonly based on the high oxidation states of V, Mo and W and show strong absorptions in the ultraviolet (UV) due to their O-to-metal charge transfer transitions. This feature, and the ability of many species to act as stable, multi-electron acceptors means that POMs have a well-established UV photochemistry, primarily in the oxidation of organic substrates. The last decade has witnessed increasing efforts to achieve photochemistry with POMs under visible light, through sensitization with molecular or semiconductor chromophores, or by extending the visible absorption of the POMs themselves. Notable achievements have included light driven oxidation of water, and light driven reduction of protons to H2. In this review, we summarize these achievements and provide a perspective on a growing body of work exploiting POMs in light energy conversion.