It is known that two metal ions placed closely enough for their electronic coupling show the metal-to-metal charge transfer (MMCT) in visible-light to near-infrared region. Recently, hetero-bimetallic assemblies located on the pore of mesoporous silica, MCM-41, has been developed as a new class of visible light absorbing chromophore¹, and we have reported that Ti(IV)/Ce(III)/SiO₂ have photocatalytic activity for oxidative decomposition of organic compounds and their quantum efficiency was 5-fold higher than that of N-doped TiO₂ under 460 nm irradiation.² In this study, we have extended the synthesis of Ti(IV)/Ce(III) bimetallic photocatalysts² to polynuclear metal-oxide assemblies by replacing the Ti(IV) ions to polyoxometalates (Mo₆O₁₉^2-, W₆O₁₉^2-, PW₁₂O₄₀^3-). Polyoxometalates, which are atomically well defined metal-oxide clusters, have been reported to have the varieties of molecular structures (shape, size, and charge), thus showing the interesting catalytic and electronic properties. Moreover, polyoxometalates have abilities to store and release the multi number of electrons. Therefore, constructing the Ce(III) to polyoxometalate charge-transfer chromophore allows us to fabricate the all-inorganic molecular photosystems which can induce the multi-electron transfer (MET) reactions under visible-light irradiation. In this presentation, we report the synthesis and photochemical properties of Ce(III)/polyoxometalate assemblies. It was confirmed that Ce(III) ions were replaced by organic ligand of (NBu₄)₂W₆O₁₉, which lead to the formation of an intense CT band in visible-light region.

1. W. Lin, H. Frei. J. Phys. Chem. B, 2005, 109, 4929
2. R. Nakamura, K. Hashimoto et al. JACS, 2007, 129, 9596