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

在去年的项目中，我们开发了一种通过核磁共振自旋-晶格弛豫测量来确定分子内电子转移速率的皮秒级速率常数的方法，并应用于研究溶剂对混合价双硒单阳离子衍生物速率的动态影响。通过对核磁共振弛豫测量的重新检验条件和分析步骤，提高了该方法测定速率常数的准确性和可靠性。实验是在几种新的溶剂体系中进行的，这些溶剂体系是根据去年确定的速率对溶剂的依赖而选择的。通过可见光、近红外吸收光谱和振动谱，得到了反应的内外重组能等参数。对这些结果进行了理论分析，并考虑了动力学溶剂效应。结果总结如下：1。与反应的时间尺度相比，忽略了内部振动模式和更快的溶剂波动的贡献，理论给出的值小了约2个数量级。在Sumi-Marcus模型的应用中，将更快的模态（如内部振动或溶剂惯性模态）视为经典模态，其理论值与实验值之间的符合性优于情形1。综合以上结果，对溶剂对现有体系的动力学影响给出了以下结论：溶剂的快速局部模式控制了反应速率。在本系统中，反应物和产物总是处于平衡状态，这与以往报道的光诱导超快速反应体系形成了鲜明对比。对反应物和生成物的准平衡溶剂化应考虑在内，以了解速率的溶剂依赖性。

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.