Reorganization parameters of electronic transitions in electronically delocalized systems. 2. Optical spectra

This is a modification of the condensed-phase band shape analysis of optica l spectra to treat electronically delocalized systems. It incorporates the dependence of the optical observables on the optical transition dipole. Abs orption and emission band shapes are calculated on the basis of adiabatic f ree energy surfaces defined as the functions of the reorganization paramete rs invariant to electronic delocalization and the parameter of electronic d elocalization. The latter is given through the ratio of the transition and differential chromophore dipoles. The linear response relations commonly us ed to connect optical observables to reorganization parameters of electron transfer reactions break down for electronically delocalized systems. The o ptical Stokes shift depends strongly on the delocalization parameter deviat ing downward from twice the adiabatic reorganization energy with electronic delocalization. The Stokes shift is a rising function of solvent polarity for localized systems. An inverted solvent dependence develops for delocali zed complexes: the Stokes shift decreases with solvent polarity. The spectr um of permissible solvent fluctuations is limited from the low-energy side by the adiabatic splitting of the free energy terms inducing narrowing of t he emission optical bands compared to the absorption bands.