VOLUME CHANGES ASSOCIATED WITH INTRAMOLECULAR ELECTRON-TRANSFER DURING MLCT STATE FORMATION - TIME-RESOLVED OPTOACOUSTIC STUDIES OF RUTHENIUM CYANO COMPLEXES

Volume changes associated with the intramolecular photooxidation of Ru -II in bipyridine cyano complexes in aqueous solutions were determined by temperature-dependent laser-induced optoacoustics. The values obta ined are attributed mainly to photoinduced changes in the specific int eractions between the complexes and the water molecules of the first s olvation shell. In particular, the values determined for the formation of the MLCT state in the homologous series Ru(bpy)(CN)(4)(2-), Ru(bpy )(CN)(3)(CNCH3)(-); and Ru(bpy)(CN)(2)(CNCH3)(2). which are expansions for the two first compounds (i.e., Delta V-R = 15, 10, and ca. 0 ml/m ol, respectively). correlate directly with the number of cyanide ligan ds available for donor-acceptor interactions with water. A parallel co rrelation with the number of cyanide ligands is found for the solvent effect on the MLCT energy of the complexes, as measured from the slope of plots of emission energy vs the solvent acceptor number. This corr elation supports the concept of solvent (water in this case) reorganiz ation around the MLCT state being responsible for the volume changes o bserved.