A Theory of Electron Transfer and Steady-State Optical Spectra of Chromophores with Varying Electronic Polarizability

Electron transfer (ET) reactions and optical transitions are considered in chromophores with both the dipole moment and the electronic polarizability varying with the transition. An exact solution for reaction free energy surfaces of ET along a reaction coordinate has been obtained in the Drude model for the solute and solvent polarizabilities. The ET surfaces manifest the following effects of a nonzero polarizability variation: they (i) are asymmetric, (ii) have different curvatures at their minima, and (iii) become infinite for reaction coordinates outside a one-sided fluctuation band. The physical origin of these effects is the renormalization of the solute dipole by the solvent reaction field depending on the nonequilibrium solvent configuration. The reorganization energies of ET are substantially different for forward and backward transitions with higher reorganization energy in the state with hider solute polarizability. The dependence of the ET rate on the equilibrium energy gap is quadratic near the rate maximum and is linear at large energy gaps. The energy gap curves are also flatter from the side of exothermic reactions and broader for the state with a higher polarizability. The bandshape analysis of optical transitions is extended to the case of a nonzero polarizability variation.