Dynamical Solvent Effect on Intramolecular Electron Transfer Rate of Mixed-Valence Biferrocene Monocation

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In the project of the last year we developed a method to determine pico-second order rate constant for intramolecular electron transfer rate by NMR spin-lattice relaxation measurements and was applied to investigate dynamical solvent effect on the rate for mixedvalence biferrocenium mono-cation derivatives. Improvement of the method in accuracy and reliability to determine the rate constant was carried out by reexamining condition and analytical procedure in the NMR relaxation measurements. The experiment were carried out in several new solvent systems, which were chosen by taking account of the solvent dependence of the rates determined in the last year. The reaction paramenters, such as outer and inner reorganization energies, were also obtained from the vis. and nir absorption and the vibrational spectra. These results were analyzed by theories taking account of the dynamical solvent effect. The results are summarized as follows.1. About 2 order smaller values were given by the theories, which disregarded contributions of the internal vibrational modes and faster solvent fluctuations compared with the time scale of the reaction.2. An application of Sumi-Marcus model, where faster modes, such as internal vibration or solvent inertial modes, was treated as classical, showed better coincidence between the theoretical and the experimental values than the case 1.Considering above results, the following conclusions were given for the dynamical solvent effect on the present systems :1. Fast local modes of solvents were responsible to control the rates.2. In the present system, the reactant and the product are always equilibrated, which is quite contrast to photo-induced ultra fast reaction systems previously reported. Quasi-equilibrated solvation to both of the reactant and product should be taken into account to understand the solvent dependence of the rates.