Kinetics of the quenching of *RuL 2+3 emission by monochloro and dichloro complexes of copper(II) in aqueous solution

Abstract

The quenching of charge-transfer excited states of RuL²⁺₃ complexes (L = 2,2′-bypyridine, 1,10-phenanthroline or related derivatives) by aqueous Cu²⁺ ions has been shown to proceed via an outer-sphere electron-transfer mechanism. However, the dependence of the rate constant on the free energy of reaction is much weaker than expected from a simple theoretical treatment for this series of reactions. In this paper we examine the effects of chloride ion catalysis on the rates of these reactions and deduce the rate constants for quenching by CuCl^(2-n)+_n, with n= 0–2. We find similar, weak free-energy dependences for the rate constants for all three species, although the efficiency of quenching increases with n. The rate constants obtained are discussed within the framework of Marcus' theory for adiabatic outer-sphere electron-transfer reactions.