Electron transfer in aromatic solvents: The importance of quadrupolar interactions

Molecular solvation calculations are performed on a donor-bridge-acceptor ( DBA) molecule in polar and nonpolar environments. A strictly dipolar treatm ent of solvation reproduces experimental values of the reaction free energy , Delta (r)G, determined in nondipolar and weakly dipolar aromatic solvents but does not simultaneously predict accurate values of Delta (r)G in highl y dipolar solvents. By contrast, a solvation model that includes contributi ons from solvent dipole and quadrupole moments (J. Chem. Phys. 1999, ill, 3 630(1)) reproduces Delta (r)G values over a large polarity range. The relia bility of the predicted Delta (r)G and solvent reorganization energies, lam bda (o), are assessed through fitting experimental rate data. The fits disp lay good agreement with the experimental data and the donor-acceptor electr onic couplings derived via these analyses agree with prior determinations. The availability of a model that generates reasonable predictions of Delta (r)G and lambda (o) allows a first exploration of the temperature dependenc e of solvent mediated electronic coupling.