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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Intersystem Crossing in Charge-Transfer Excited States
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Intersystem Crossing in Charge-Transfer Excited States

机译：电荷转移激发态的系统间穿越

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摘要

Absolute rate constants for intersystem crossing (ISC) in exciplexes formed between cyanoanthracenes as acceptors and alkylbenzenes as donors in solvents with low to moderate polarity have been measured. The extent of charge transfer in these particular exciplexes has been determined previously, and thus the dependence of the ISC rate constant on this parameter is obtained. A smooth transition of exciplexes with high locally excited state character to those with essentially pure charge-transfer character argues in favor of a mechanism of intersystem crossing involving a spin-forbidden return electron transfer process to form the locally excited triplet directly. The proposed mechanism is supported by the observed energy gap dependence of the rate constant, and by deuterium isotope effects. External heavy-atom effects in chlorinated solvents are observed. Analysis of the rate constant for intersystem crossing for the pure charge-transfer exciplexes using electron-transfer theory allows determination of the matrix element of the spin-forbidden electron-transfer reaction. It is found to be roughly 3000 times smaller than the matrix element for corresponding spin-allowed electron transfer in similar systems. General principles for the factors that control the mechanisms of intersystem crossing in excited charge-transfer states are discussed.
机译：在低至中等极性的溶剂中，已测定了氰基蒽作为受体和烷基苯作为供体之间形成的激基复合物的系统间交叉（ISC）的绝对速率常数。先前已经确定了这些特定激基复合物中电荷转移的程度，因此获得了ISC速率常数对该参数的依赖性。具有高局部激发态特征的激基复合物向基本上具有纯电荷转移特征的激基复合物的平滑过渡，主张一种系统间交叉的机制，该机制涉及自旋禁止的返回电子转移过程，以直接形成局部激发的三重态。所观察到的速率常数对能隙的依赖性以及氘同位素效应支持了所提出的机理。在氯化溶剂中观察到外部重原子效应。使用电子转移理论分析纯电荷转移激基复合物的体系间交叉的速率常数，可以确定自旋禁止电子转移反应的基质元素。发现在类似系统中，相应的自旋允许电子转移比基质元素小约3000倍。讨论了在激发的电荷转移状态下控制系统间交叉机制的因素的一般原理。

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