A laser flash photolysis study of magnetic field effects in photoinduced electron transfer between Ru (bpy)²⁺₃ and N,N'-dimethylviologen in micellar solutions

Abstract

The kinetics of electron transfer between photoexcited Ru(bpy)²⁺₃ and N,N'-dimethylviologen (MV²⁺) have been studied by means of laser flash photolysis in sodium dodecyl sulfate (SDS) and sodium laurate (SL) micelles. The decay of photoexcited Ru(bpy)²⁺₃ follows first-order kinetics with k_obs 10⁶-10⁷ s^-1, and dependences of k_obs versus surfactant and quencher concentrations were obtained. Analysis of the data showed that the quenching is mainly intramicellar. Although SDS solutions shows no escape of the radicals MV⁺ and Ru(bpy)³⁺₃ from the micelles, for solutions of SL micelles an escape value Φ _es 0.08 was determined. The dependences of Φ _es on the concentration of SL and SDS show a drop in the vicinity of the cmc. Radical MV⁺ is not incorporated into the SL micelles. An increase of Φ _es in the SL micelles up to 20-25% was observed under application of an external magnetic field (B = 0.2-0.47 T) during steady-state irradiation and laser flash photolysis studies. The magnetic field effect is mainly described according to a hyperfine coupling mechanism. Geminate recombination kinetics of the pair ³[MV⁺ Ru(bpy)³⁺₃] was observed in both SDS and SL micelles. Pertinent kinetic analyses were made and the requirements for geminate recombination kinetics observations were discussed.