Supramolecular Photocatalyst with a Rh(III)-Complex Catalyst Unit for CO2 Reduction

The development of supramolecular photocatalysts has been an important target in the field of artificial photosynthesis because of their efficient reduction of CO 2 and water oxidation and reduction, especially for solid materials, such as semiconductor particles, photoelectrodes, and mesoporous light-harvesting materials. We successfully developed the first supramolecular photocatalyst with a Rh complex as a catalyst unit for CO 2 reduction. This new photocatalyst consisting of [Rh(BL)(Cp*)Cl] + as the catalyst and [Ru(dmb) 2 (BL)] 2+ as the photosensitizer (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl, BL = 1,2-bis(4′-methyl[2,2′-bipyridin]-4-yl)ethane, dmb = 4,4′-dimethyl-2,2′-bipyridine) mainly produced formic acid, even though a mixed system of the corresponding mononuclear complexes photocatalytically produced H 2 as the main product. The photocatalytic reaction mechanism was investigated based on in situ UV–vis absorption studies and electrochemical measurements.