Thermal and optical electron transfer involving transition metal complexes: insights from theory and computation

Current theories of electron transfer (ET) kinetics in conjunction with techniques of computational quantum chemistry are reviewed and applied to the analysis of thermal and optical ET processes involving transition metal complexes (TMCs). The roles of geometrical and electronic structure in controlling the relevant energetics and electronic coupling are discussed, and a number of limiting cases of kinetic behavior are displayed. Particular attention is paid to the formulation of the initial and final states involved in the ET, including the consequences of near-degeneracy and spin-orbit coupling. The roles of metal/ligand mixing and other types of 'mediation' of donor/acceptor coupling by molecular spacers are noted and illustrated with calculated results. An example of a detailed computation of activation parameters is also presented, including entropic effects and nuclear tunnelling. (C) 2002 Elsevier Science B.V. All rights reserved.