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 (MV 2+) 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 ∼ 10 6–10 7 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.