Nanostructured thin films of SiO2 and SnO2 cast on an optically transparent electrode were modified with ruthenium(II) polypyridyl complex, Ru(bpy)(2)(bpy-COOH)(2+), Ru(II). Kinetic and mechanistic details of interaction between iodide ions and excited Ru(II), as well as regeneration of the sensitizer by iodide ions, were elucidated using emission spectroscopy and laser flash photolysis. The reaction between excited Ru(II) and I- in SiO2 films which occurred with a rate constant of 1.0 x 10(8) M-1 s(-1) produced low yields of electron-transfer products. In the case of SnO2 films modified with Ru(II), the charge injection was the dominant process with the production of oxidized sensitizer, Ru(II). The reaction between Ru(III) and I- controls the regeneration of sensitizer in a photochemical solar cells. The oxidation of I- by Ru(III) in SnO2 films as confirmed from the production of I-2(.-) occurred with a rate constant of 1.2 x 10(10) M-1 s(-1).