Evaluation of Ultrafast Intramolecular Electron Transfer Rate by Means of NMR Relaxation

用核磁共振自旋-晶格弛豫方法计算了几种体系的分子内电子转移速率。用旋转弛豫时间、电子自旋弛豫时间等参数验证了该方法的局限性，并对三种混价双二茂铁衍生物(Fe(II)、Fe(III))的反应速率进行了微皮二级测定，结果表明反应速率具有特征行为。双二茂铁单正离子的反应速率常数约为其1，1“‘-二碘衍生物的三倍，但这两种混合价化合物的价带能量和强度相似。这一结果可以归因于外球和内球重组能之比的不同。L-M-L伸缩模式的频率差异是二碘衍生物电子转移速率缓慢的另一个原因，另一方面，乙炔桥联双二茂铁的电子转移速率是双二茂铁电子转移速率的三倍。这一结果与IT波段的测量结果不一致。乙炔桥联络合物的速率与温度的依赖关系表明，核隧穿效应对速率有相当大的影响。这可能是由于混合价络合物的刚性桥联结构所致。只要将溶剂视为介电连续介质，所给出的所有速率都超过了包括溶剂动力学效应在内的任何模型所预测的速率。更快的局部溶剂动态可能至少在一定程度上是控制速率的原因。

The intramolecular electron transfer rates in solution were evaluated in several systems by NMR spin-lattice relaxation measurements. A limitation of this method was confirmed referring the rotational relaxation time and the electron spin relaxation time, etc.The reaction rates with pico second order were observed for three mixed-valence biferrocene derivatives (Fe(II), Fe(III)) and the rates showed a characteristic behavior. The biferrocene monocation showed ca. three times larger rate constant than its 1,1 "'- diiodo derivative, nevertheless these two mixed-valence compounds show similar intervalence band energy and strength. This results can be attributed to difference in the ratio of the outersphere and the innersphere reorganization energy. The frequency difference in the L-M-L stretching modes is another reason of the retardation of the ET rate of diiodo derivatives, On the other hand, an acetylene bridged biferrocene monocation gave three times higher rates than those boferrocene monocation. This result is disagreement with the IT band measurements. The temperature dependence of the rate of the acetylene bridged complex suggested considerable nuclear tunneling effect on the rates. This may be arisen by the rigid bridging structure of the mixed-valence complex.All the rates given in the present studies exceed those predicted any model including solvent dynamical effect as long as solvent is regarded as a dielectric continuum. Faster local solvent dynamics may be, at least partially, responsible to control the rates.