Photoinduced electron transfer from excited [tris(2,2′-bipyridine)ruthenium(II)]2+ to a series of anthraquinones with small positive or negative Gibbs energy of reaction. Marcus behavior and negative activation enthalpies
Photoinduced electron transfer from excited [tris(2,2′-bipyridine)ruthenium(II)]2+ to a series of anthraquinones with small positive or negative Gibbs energy of reaction. Marcus behavior and negative activation enthalpies
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光诱导电子从激发的[三(2,2-联吡啶)钌(II)]2+转移到一系列具有小正或负吉布斯反应能和负活化焓的蒽醌。
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
H. Rau
中科院分区：
文献类型：
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作者：
R. Frank;G. Greiner;H. Rau
电子激发*Ru(bpy)32+在乙腈中的电子转移（ET）猝灭反应中，以2-甲基-、1-氯-和1-硝基蒽醌为猝灭剂，其速率常数kq增加。如果使用碱盐作为支撑电解质，则发现AQ-自由基阴离子与碱阳离子形成特定的缔合物。在非缔合的四烷基铵盐存在下，该体系遵循马库斯理论的预测。本文提出了确定常规反应方案的速率常数的数值方法。分析表明，自由AQ-自由基阴离子形成的量子产率受正向、反向和反向ET的相互作用支配，激活控制的猝灭反应具有负的激活焓。从速率常数系统的数值分析可以推断，这种现象是由反应序列中的初等ET步骤引起的。我们讨论了负活化焓反应的预平衡和基本反应模型，并提出了据我们所知的第一个成功区分它们的例子。
In the electron transfer (ET) quenching reactions of electronically excited *Ru(bpy)32+ in acetonitrile an increase of the rate constant kq is observed in the series of 2-methyl-, 1-chloro-, and 1-nitro-anthraquinone as quenchers. If alkali salts are used as supporting electrolytes the AQ- radical anions are found to form specific associates with the alkali cations. In the presence of non-associating tetraalkylammonium salts the system follows the predictions of Marcus theory. Numerical methods are developed which allow the determination of the rate constants of the conventional reaction scheme. This analysis shows that the quantum yield of free AQ- radical anion formation is governed by the interplay of forward, reverse and back ET. Negative activation enthalpies are found for the activation controlled quenching reactions. From the numerical analysis of the system of rate constants it is inferred that this phenomenon is due to the elementary ET step in the reaction sequence. We discuss the pre-equilibrium and elementary reaction models for reactions with negative activation enthalpy and present, to our knowledge, the first example of successful discrimination between them.