ENERGETICS OF CHARGE-TRANSFER REACTIONS IN SOLVENTS OF DIPOLAR AND HIGHER-ORDER MULTIPOLAR CHARACTER .2. RESULTS

We apply the theories developed in the preceding paper (paper I) to ca lculate various energy quantities of charge transfer (CT) reactions in nine solvents that cover a wide range of polarity, and for which inte raction site models (ISM's) may be found in the Literature. Besides th e two surrogate Hamiltonian theories developed in paper I, the renorma lized site-density theory (RST) and the renormalized dielectric theory (RDT), we also investigate a simple harmonic approximation (HXA) for the diabatic free energy profiles, whose characteristic parameters are calculated taking specific advantage of the expression given by the e xtended reference interaction site method (XRISM) for the free energy of solvation. For each CT process we analyze (a) the solvent reorganiz ation energy lambda, (b) the shift of the absorption transition energy due to the solvatochromic effect, and (c) the solvent contribution to the free energy change Delta A. In addition, for a few selected examp les, we also report the detailed diabatic free energy profiles. The ca lculations reported rely on solute-solvent and solvent-solvent pair co rrelation functions obtained with the XRISM integral equation method a pplied to nonpolarizable (with fixed mean partial charges) ISM represe ntations of the solute and solvent molecules. To rectify the omission of the solvent electronic degrees of freedom, we correct the dielectri c part of the solvent reorganization energy with an additive term desi gned to compensate for the use of fixed charge ISM models. Contact wit h theories in which the solvent is represented as a dielectric continu um medium (with or without spatial dispersion) and the solute as a set of charges inside spherical cavities carved out of the dielectric is made straightforwardly within the RDT theory by considering a particul arly simple form of the solute-solvent RISM site-site direct correlati on functions. Using simple ISM models for several solute species, incl uding Reichardt's betaine-30 dye and a porphyrin-quinone (PQ) ''dyad'' recently studied by Mataga and co-workers, we examine the ability of the molecular theories to explain the dependence of charge-transfer en ergetics on dipolar and nondipolar solvents, We find that the solvatoc hromic effect on the absorption energy of betaine-30, which forms the basis of the E(T)(30) empirical solvent polarity scale, is reproduced reasonably well by the RST, RDT, and HXA theories for solvents ranging from carbon tetrachloride to water. In the case of the PQ dyad, we fi nd that the calculated values of lambda in dipolar and nondipolar solv ents are in good agreement with experimental estimates. Our results in dicate that the molecular theories of solvation discussed in this pape r can explain the observation that a solvent with vanishing molecular dipole moment, like benzene, can show unmistakable ''polarity,'' as re flected by its influence on the energetics of CT reactions. We also pr esent calculations that corroborate the suggestion (Sec, VII of paper I) that, compared with the behavior in dipolar solvents, in nonipolar solvents the dependence of lambda with the donor-acceptor separation d istance is practically negligible. (C) 1996 American Institute of Phys ics.