During efforts to stabilize metal oxide bound chromophores for photoelectrochemical applications, a novel photochemical reaction has been discovered. In the reaction, the bisphosphonate functional groups -C(PO3H2)(2)(OH) in the metal complex [Ru(bpy)(2)(4,4'-(C(OH)(PO3H2)(2)bpy)(2+) are converted into -COOH and H3PO4. The reaction occurs by sensitized formation of O-1(2) by the lowest metal-to-ligand charge transfer excited state(s) of [Ru(bpy)(2)(4,4'-(C(PO3H2)(2)(OH))(2)(bpy))](2+)* followed by O-1(2) oxidation of the bisphosphonate substituent. A related reaction occurs for the bisphosphonate-based drug, risedronic acid, in the presence of OD light, and a singlet oxygen sensitizer ([Ru(bpy)(3)](2+) or Rose Bengal).