Small Polarons in Biological Systems [1, 2]
The understanding of the primary events in bacterial photosynthesis is of central importance for the elucidation of the basic mechanisms of the acquisition, storage and disposal of energy in the photosynthetic process. During the last few years, extensive new information on the dynamics of charge separation in reaction centers has emerged from model experiments of picosecond spectroscopy. The theory of electron transfer in biological systems is advanced in terms of nonadiabatic multiphonon radiationless transitions. The conventional theory bears a close similarity to small polaron theory. Extension of the theoretical treatment to account for competition between vibrational relaxation and electronic processes will be presented to describe some ultrafast reactions. The dynamics of the primary events of charge separation are determined by the interplay between intramolecular reorganization and intermolecular engineering. These effects combine in determining the directionality, selectivity and efficiency of charge separation events. Apart from intrinsic biological interest, these systems provide a beautiful example for a micro-electronic gadget operating on a molecular level.