Electrogenerated Chemiluminescence. 35. Temperature Dependence of the ECL Efficiency of Ru(bpy),*+ in Acetonitrile and Evidence for Very High Excited State Yields from Electron Transfer Reactions

The temperature dependence of the ECL emission yield, @ECL, of Ru(bpy)?+ in acetonitrile has been determined and was found to correlate closely with the luminescence quantum yield, @ e , of the lowest R~(bpy) ,~+ dn* metal-to-ligand charge transfer (MLCT) excited state. Evidence is presented that at low temperatures (< -30 "C) the ECL emission yield becomes equal to the luminescence quantum yield implying an efficiency for excited state formation in the electron transfer reaction of Ru(bpy)?+ with Ru(bpy),+ of near 100%. High efficiencies for excited state formation are rationalized on the basis of the excited state spectroscopic properties of Ru(bpy)gP+ and the resulting implications to electron transfer theory and the ECL mechanism are discussed.