Dynamical solvent effects on activated electron-transfer reactions: principles, pitfalls, and progress

Recent experimental and conceptual progress in our understanding of dynamical solvent effects in activated electron-transfer processes are critically reviewed. Understanding the various influences exerted by the solvating environment upon the kinetics of electron-transfer (ET) processes, either in homogeneous solution or at metal-solution and related interfaces, has long captured the attention of experimentalists and theoreticians alike. These roles have been perceived primarily in terms of energetic factors, whereby the solvent is considered to affect the reaction rates via its influence on the net activation barrier to electron transfer, delta. Indeed, such considerations form a mainstay of the well-known Marcus and related theoretical treatments. In these approaches, solvent effects upon delta are separated into so-called intrinsic and extrinsic (or thermodynamic) factors. (Author)