Energetics of electron-transfer reactions in soft condensed media.

The coupling of electronic transitions within molecules to condensed-phase media involves a complex hierarchy of spatial and dynamical scales. Thermodynamics of activation is related to the length scale of microscopic interactions reflected in the non-Arrhenius reaction kinetics. Solvent dynamics make a particularly strong impact on the activation barrier when the time scale of the reaction is comparable to the relaxation time of the solvent, and the reaction barrier becomes nonergodic. Finally, molecular polarizability is responsible for complex nonparabolic free energy surfaces for electron transfer. We discuss the application of these ideas to soft condensed solvents such as supercooled liquids, liquid crystals, and photosynthetic reaction centers.