Magnetokinetic Investigations of Spin-Forbidden Electron Back Transfer in Exciplexes and Radical Pairs

Abstract

In this paper we report on spin-orbit coupling induced mag netokinetic effects on the free radical yield of triplet elec tron transfer reactions. From the magnetic field dependence ob served in a variety of mixed solvents the solvent dependent dy namics of short-lived triplet exciplexes is quantitatively de duced. 1.. IntroductioDOne of the most important aspects of photoinduced electron transfer is its superior potential for achieving fast conver sion of electronic exci tation energy into chemical energy. A separation of the transferred electron from the hole it left behind is a crucial step in natural and artificial light energy conversion systems _ In liquid solution such aseparation 1S usually achieved by ctiffusional motion, whereby a primary pair of redox products separates into free radicals. since the pio neering work of Weller, Mataga and others [1] intermediates of photoelectron transfer reactions in solution, viz. exciplexes and radical (ion) pairs (cf. Scheme 1) and their dynamics have been studi ed intens i vel y [ 2 ]. Time-resol ved f 1 uorescence and laser-flash induced excited state absorption spectroscopy have been the most important experimental techniques in these stu dies. One important kinetic requirement for a direct, time~re solved study of the dynarnics of exciplexes and correlated radiKonstanzer Online-Publikations-System (KOPS)