Photo-oxidation of water to oxygen sensitised by tris(2,2′-bipyridyl)ruthenium( II )

Irradiation of tris(2,2′-bipyridyl)ruthenium(II) in aqueous solution containing a sacrificial electron acceptor results in formation of bipy3Ru3+, a powerful oxidant which is able, in the presence of a redox catalyst, to oxidise water to O2. Both colloidal RuO2 and simple cobalt(II) ions are effective catalysts for O2 production and, with [Co(NH3)5Cl]2+ as sacrificial electron acceptor, the quantum efficiency for formation of O2 was ca. 12 %. However, when the sacrificial electron acceptor was replaced with Fe3+, which is a reversible redox couple, no O2 was observed upon prolonged irradiation. The absence of O2 in this latter system can be explained by kinetic considerations.