Metal-Ligand Electron-Transfer Complexes: Experimental Investigations of the Limits of Semiclassical Electron- Transfer Theory

在无机化学、生物无机化学和金属有机化学计划的这个项目中，加州理工学院的Harry B.Gray博士和Jay R.Winkler博士将探索在半经典电子转移理论应该被打破的条件下的金属-配体电子转移(ET)过程。为了确定隧道效应的作用，将研究一系列Ir(I)络合物，其中在高驱动力下的ET速率比理论预测的要慢得多。为了帮助从理论上解释ET率，将确定核再有机化参数、温度和同位素对ET率的影响。对Ir(I)二聚体的双分子电子转移反应的系统研究将揭示电子激发产物是否会降低电子转移反应的有效驱动力。在ET比预期慢的区域，光诱导的ET反应往往比类似驱动力下的复合过程快。基于这一事实，我们将研究与弱耦合电子受体配位的不饱和金属络合物，以确定是否可以通过直接光吸收来制备长寿命电荷转移态。发生在化学和生物系统中的一些最重要的过程涉及电子的转移，而这种转移的速度往往对该过程的运行至关重要。一个半先验的理论模型已经被开发出来来解释这些比率。在这项研究中，将使用专门设计的Ir络合物来探索这一理论用来描述电子转移速度的因素。这类研究对于基本理解电子转移和开发新的方法，例如太阳能转换，都是重要的。

In this project in the Inorganic, Bioinorganic, and Organometallic Chemistry Program, Dr. Harry B. Gray and Dr. Jay R. Winkler of the California Institute of Technology will explore metal-ligand electron-transfer (ET) processes under conditions where semiclassical ET theory should break down. To determine the role of tunneling, a series of Ir(I) complexes in which the ET rates at high driving forces are substantially slower than theoretically predicted will be studied. To aid in the theoretical interpretation of the ET rates, nuclear reoganization parameters, temperature, and isotope effects on ET rates will be determined. A systematic investigations of bimolecular ET reactions of Ir(I) dimers will show whether electronic excited products can reduce the effective ET reaction driving force. Photoinduced ET reactions in the region where ET is slower than predicted tend to be faster than recombination processes at comparable driving forces. Based on this fact, coordinatively unsaturated metal complexes with weakly coupled electron acceptors will be investigated to determine whether long-lived charge-transfer states can be prepared by direct light absorption. Some of the most important processes which occur in chemical and biological systems involve the transfer of electrons and the rate of such transfers is often critical to the operation of the process. A semi-empicical theoretical model has been developed to account for these rates. In this study specially designed iridium complexes will be used to probe the factors which this theory uses to describe the rate of electron transfer. Such studies are important both to the basic understanding of electron transfer and to the development of new methods of, for example, solar energy conversion.