PHOTOREDUCTION OF METHYL VIOLOGEN MEDIATED BY TRIS(BIPYRIDYL)RUTHENIUM(II) IN INERT COLLOIDAL SUSPENSIONS

The photoreduction of methyl viologen, covalently attached to a tris(bipyridyl)ruthenium(II) chromophore, in suspensions of positively charged alumina-coated colloidal silica particles, via N-phenylglycine electron donor, is reported. In the tris(bipyridyl)ruthenium(II) complexes, the central metal atom is coordinated to two 4,4'dicarboxy-2,2'-bipyridine ligands and thus carries a net 2-charge at pH 5.0. Coadsorption of the N-phenylglycine and ruthenium chromophore to the colloidal particles results in rapid production of reduced viologen following visible laser flash excitation of the tris(bipyridyl)ruthenium(II) complex. The yield of the radical was dependent upon the concentration of the electron donor added to the system, but its multiphasic decay was independent of both the N-phenylglycine concentration and the initial concentration of the viologen radical cation. Furthermore, both the yield and decay kinetics of the viologen radical cation were relatively independent of the number of intervening methylene units between the ruthenium complex and viologen electron acceptor. The results represent a significant improvement in charge separation yield over those previously reported for the reductive quenching of the carboxylated tris(bipyridyl)ruthenium(II) complex, absent of the covalently attached viologen, by N-phenylglycine in alumina-coated silica colloidal suspensions.