Abstract

The compound Ru(bpy)2(dppz-R)(PF6)2, where bpy is 2,2′-bipyridine and dppz-R is 11-(diethoxyphosphorylmethyl) dipyrido[3,2-a:2′,3′-c]phenazine, was prepared and anchored to mesoporous nanocrystalline (anatase) TiO2 thin films as a probe of the effects of interfacial water on excited-state charge transfer processes at semiconductor interfaces. In nitrogen-saturated fluid acetonitrile, the Ru(bpy)2(dppz-R)(PF6)2 compound was found to be highly photoluminescent. Water was found to quench the excited state by a mechanism adequately described by the Perrin model, from which the radius of quenching was abstracted, 75 ± 2 Å. The Ru(bpy)2(dppz-R) (PF6)2 compounds were found to bind to the TiO2 thin films in high surface coverages, 5 × 10-8 mol cm -2. When these films were immersed in acetonitrile, long-lived excited states (τ = 825 ns) that were quenched by the addition of water were observed. About 30% of the excited states could not be quenched by water. Efficient electron injection, φinj = 0.8, was observed after light excitation of Ru(bpy)2(dppz-R)/TiO2 in a 0.1 M LiClO4/acetonitrile solution. The addition of large concentrations of water, >0.5 M, was found to decrease the injection yield to φinj = 0.3. © 2006 American Chemical Society.