The excited states quenching of safranine T by p-benzoquinones in polar solvents

Safranine T is a well known photochemical oxidant. The photoreduction reaction of this dye by various types of electron donors has been studied quite often, and in many cases mechanism accounting for the observed results were proposed and explained in terms of electron transfer theories. Only a few studies seem to exist on reactions of this dye with electrons acceptor. In this work we present results of fluorescence quenching and laser flash photolysis which demonstrate that safranine T may function also as a photochemical reductant with p-benzoquinones as electron accepters in methanol and acetonitrile. Singlet quenching rate constants are nearly diffusion controlled in both solvents. Triplet quenching rates constants were obtained from the decay of the triplet at 830 nm as a function of quinone concentration. They follow a Rehm and Weller type correlation for electron transfer in acetonitrile, while in methanol the rate constants for triplet quenching are substantially larger. (C) 1997 Elsevier Science S.A.