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

在去年的项目中，我们发展了一种通过NMR自旋-晶格弛豫测量确定分子内电子转移速率的皮秒级速率常数的方法，并应用于研究混合价双二茂铁单阳离子衍生物的动力学溶剂效应。通过对核磁共振弛豫实验条件和分析方法的重新考察，提高了速率常数测定方法的准确性和可靠性。实验在几种新的溶剂系统中进行，这些系统是通过考虑去年确定的速率的溶剂依赖性来选择的。同时还得到了维斯的外重组能和内重组能等反应参数。以及NIR吸收和振动光谱。考虑到动态溶剂效应，对上述结果进行了理论分析。研究结果如下：1.与反应的时间尺度相比，忽略了内振动模式的贡献和更快的溶剂波动，理论给出的值小了约2个数量级.应用Sumi-Marcus模型，将较快的模式，如内振动或溶剂惯性模式作为经典模式处理，结果表明理论值与实验值之间的符合程度比情况1更好。溶剂的快速局部模式是控制反应速率的主要因素.在本体系中，反应物和产物总是处于平衡状态，这与以前报道的光诱导超快反应体系形成了鲜明的对比。反应物和产物的准平衡溶剂化应被考虑以理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.