DIRECT EXPERIMENTAL COMPARISON OF THE THEORIES OF THERMAL AND OPTICALELECTRON-TRANSFER - STUDIES OF A MIXED-VALENCE DINUCLEAR IRON POLYPYRIDYL COMPLEX

The spectral parameters for the optically induced intervalence charge transfer and the rates of thermal electron transfer as a function of t emperature have been measured for a rigid, triply linked mixed-valence dinuclear tris(2,2'-bipyridine)iron complex: The total reorganization al energy associated with the intramolecular electron exchange in this complex is almost:exclusively outer-sphere in nature and comes from t hermal fluctuations of the solvent. Thus, the system can be treated ri gorously at the classical level, where in this context classical refer s to treatments of the nuclear modes. The theories developed to descri be the optical electron transfer and the thermal electron transfer are evaluated by analysis of the Spectral and rate data, respectively. Th e quantities common to both theories are the donor-acceptor coupling m atrix element, H-12, and the total reorganizational energy. Applying t he respective theories to the appropriate corresponding sets of data y ields reorganizational energies that are in excellent agreement irresp ective of the manner in which the temperature dependence is treated; h owever, if the reorganizational energy is assumed to be temperature in dependent; H-12(th) (from the rate data) and H-12(op) (from the spectr al data) differ by a statistically significant factor of similar to 2. 5. If the theoretically predicted temperature-dependent reorganization al energy composed of orientational reorganization of permanent dipole s and reorganization of solvent density is used in the calculations, t he agreement between H-12(op) and H-12(th) improves dramatically. To o ur knowledge, this work constitutes the first attempt to experimentall y compare these two classical theories with this level of rigor. Suppl ementing the experimental comparisons, we have conducted self-consiste nt-field (SCF) and configuration interaction (CI) calculations to obta in theoretical values of H-12(op) and the donor-acceptor orbital separ ation, r for comparison with experimentally determined values.