The title reaction turns the photoionization of the metal-to-ligand charge-transfer state MLCT of the ruthenium(II)-tris-bipyridyl ion into a catalytic cycle of photoinduced water splitting. To isolate that key step from the complex reaction scheme, the metastable oxidized form OX, [Ru(bpy)(3)](3+), is prepared by a first laser flash, and then photoreduced by a second. An analysis is presented that yields the efficiency eta of the photoreduction from the intensity dependences of the concentrations of MLCT and OX When water is the donor, eta is only about 0.5; for alcohols (1-butanol, 2-propanol, tert-butanol) it is 1. (C) 2007 Elsevier B.V. All rights reserved.