Solvent reorganization in optical and thermal electron-transfer processes: solvatochromism and intramolecular electron-transfer barriers in spheroidal molecules

Abstract

Expressions for the shift of the absorption and emission band maxima of a solute with changes of the solvent's dielectric properties are presented for solute molecules with shapes and polarizabilities that can be approximated by those of spherical dielectric-continuum cavity. The derivations use a nonequilibrium thermodynamic approach developed by Marcus. An series of accurate approximations for the solvent shifts are presented. The new expressions are shown to reduce to equations previously derived by McRae, Ooshika, Mataga, and others when point-dipole approximations are made and particular values of the solute polarizability are assigned. The polarizability of the solute can be related to the internal dielectric constant of the cavity, and general expressions for the band shift in the point-dipole limit containing the dielectric constant of the cavity as a parameter are derived.