Photosensitization of oxygen-bridged dicobalt(III) cations by the tris(2,2'-bipyridine)ruthenium(II) excited state. Luminescence quenching and product quantum yields

Abstract

Mechanisms of quenching of the excited state of Ru(bpy)/sub 3//sup 2 +/ by superoxo-bridged dinuclear cobalt(III) complexes are investigated by using luminescence quenching studies and by product quantum yield analysis. Bimolecular quenching constants are of the order of 10/sup 9/ M/sup -1/ s/sup -1/, which is somewhat higher than the value expected on formal charge basis. Formation of Ru(bpy)/sub 3//sup 3 +/ and the cobaltous ion as products of photosensitization although in low yields is explained to occur in an energy-transfer pathway. The energy-transfer pathway accounts for about 10% of the quenching events whereas the excited-state electron-transfer process accounts for 90% of the quenching. The dark redox reaction which follows the energy-transfer pathway leads to the products formed in steady photolysis studies.