OXIDATION-KINETICS OF A RU(BPY)3(3+) DERIVATIVE IN LANGMUIR-BLODGETT LAYERS - COMPARISON TO RU(BPY)3(3+) IN HOMOGENEOUS SOLUTIONS

Monomolecular layers of Ru(bpy)2(bpy-R2)2+ (R is C19H39) were prepared by the Langmuir-Blodgett method on SnO2/In2O3 surfaces. The Ru(II) was oxidized electrochemically to Ru(III), and the optical absorbance changes observed in the presence of reactants were followed with the aid of a spectrophotometer. The regeneration of the Ru(II) spectrum was found to obey a first-order rate law, the rate of which increased linearly with reactive solute concentration such as halide ions, hydrogen peroxide, cystein, benzohydroquinone, and Fe2+. Exceptions are the oxalate system and the Cl- at high concentrations, where the reaction rate depends only little (Cl-) or shows no dependency (oxalate) on the solute concentration. The effect of the potential field in the vicinity of the layer, hydrophobic interactions with the alkyl segments, and the high local density of Ru(III) in the layer is discussed. The results are compared to homogeneous oxidations by aqueous Ru(bpy)3(3+) in the same reactant systems.