title: Micellar Effects on Photoinduced Electron Transfer in Aqueous Solutions Revisited: Dramatic Enhancement of Cage Escape Yields in Surfactant Ru(II) Diimine Complex/[Ru(NH3)6](2+) Systems.
abstract: The effect of cationic micelle incorporation on light induced electron transfer, charge separation and back electron transfer between an aqueous electron donor, [Ru(NH3)6](2+), and a series of Ru(II) diimine complex chromophores/acceptors, is presented. The chromophores have the general formula [(bpy)2Ru(LL)](2+) (LL = bpy; 4-R-4'-methyl-2,2'-bpy, R = pentyl (MC5), terdecyl (MC13), heptadecyl (MC17); 4,4'-di(heptadecyl)-2,2'-bpy (DC17)). Of the five chromophores, the MC13, MC17, and DC17 complexes associate with the added micelle forming surfactant, cetyltrimethylammonium bromide (CTAB). Quenching of the luminescence of the bpy and MC5 complexes by [Ru(NH3)6](2+) is unaffected by addition of surfactant, while rate constants for quenching of the MC13 and MC17 complexes are decreased. Cage escape yields following photoinduced electron transfer to generate [(bpy)2Ru(LL)](+) and [Ru(NH3)6](3+) are approximately 0.1 for all the water-soluble chromophores (excluding DC17) in the absence of added CTAB. In the presence of surfactant, the cage escape yields dramatically increase for the MC13 (0.4) and MC17 (0.6) complexes, while remaining unchanged for [Ru(bpy)3](2+) and the MC5 complex. Back electron transfer of the solvent separated ions is also strongly influenced by the presence of surfactant. For the MC13 and MC17 complexes, back electron transfer rate constants decrease by factors of 270 and 190, respectively. The MC5 complex exhibits two component back electron transfer, with the fast component having a rate constant close to that in the absence of surfactant and a slow component nearly 200 times smaller. Results are interpreted in terms of the partitioning of the 2+ and 1+ forms of the chromophores between aqueous and micellar phases. The extended lifetimes of the radical ions may prove useful in coupling the strong reductants formed to kinetically facile catalysts for reduction of water to hydrogen.
authors.affiliation: Department of Chemistry Tulane University New Orleans, Louisiana 70118, United States.
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Adams
authors.affiliation: Department of Chemistry Tulane University New Orleans, Louisiana 70118, United States.
authors.forename: Russell H
authors.initials: RH
authors.lastname: Schmehl