Temperature dependence of the rate of deactivation of triplet anthracene by metal ions

Abstract

The deactivation of triplet anthracene by Pr^III, Nd^III and Tb^III has been studied over a range of temperatures in methanol + water (9/1 by volume) by laser flash photolysis. The Arrhenious plots for Nd^III and Tb^III are similar to those obtained for quenching of triplet phenanthrene; they show a low temperature regime where the activation energy is small and an energy transfer mechanism is postulated. At higher temperatures the activation energy increases and it is suggested that ligand displacement occurs facilitating energy transfer. Novel behaviour was found for quenching by Pr^III, which is expected to be a less efficient acceptor of energy. The low temperature mechanism was not observed, but instead the activation energy decreases at higher temperatures, where it is postulated that energy transfer, following ligand displacement, becomes rate determining.