Solvent Dependence of Cationic-Exciplex Emission: Limitation of Solvent Polarity Functions and the Role of Hydrogen Bonding
Solvent Dependence of Cationic-Exciplex Emission: Limitation of Solvent Polarity Functions and the Role of Hydrogen Bonding
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阳离子激基复合物发射的溶剂依赖性：溶剂极性函数的限制和氢键的作用
DOI：
10.1021/acs.jpca.0c01774
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Farid, Samir
中科院分区：
文献类型：
--
作者：
Dinnocenzo, Joseph P.;Tingson, Joshua;Young, Ralph H.;Farid, Samir
传统的激基复合物是中性反应物之间激发态电荷生成反应的产物（例如，A* + D → A•–D•+），而阳离子激基复合物是阳离子与中性供体之间的电荷转移反应的产物（例如，A+* + D → A•D•+）。本文将阳离子激基复合物的溶剂依赖性荧光与常规激基复合物的现有数据进行比较。尽管在低至中等极性溶剂中传统激基复合物发射最大值与 Lippert-Mataga 溶剂极性函数的线性相关性已得到充分证明，但在极性较大的溶剂中，相关性通常较差。中度至高极性溶剂中的许多此类图显示出很强的曲率。有趣的是，对于这些相同的情况，发射最大值与溶剂介电常数 (ε) 的关系图呈显着线性。有趣的是，1+ 阳离子激基复合物在腈和醇溶剂中的发射最大值也与 ε 线性相关。阳离子激基复合物发射最大值对 ε 的溶剂依赖性约为传统激基复合物的 1/3，这归因于阳离子激基复合物的激发态和基态的溶剂稳定性。 1+ 的腈和醇溶剂之间的激基复合物发射差异归因于氢键，氢键酸性较高的溶剂中差异更大。
Conventional exciplexes are products of excited-state charge generation reactions between neutral reactants (e.g., A* + D → A•–D•+), whereas cationic exciplexes are products of charge shift reactions of cations with neutral donors (e.g., A+* + D → A•D•+). Compared herein is the solvent-dependent fluorescence of a cationic exciplex with extant data for conventional exciplexes. Although linear correlations of conventional exciplex emission maxima with the Lippert–Mataga solvent polarity function are well documented in low to moderate polarity solvents, the correlations are often poor in more polar solvents. A number of such plots in moderate to high polarity solvents show a strong curvature. Intriguingly, for these same cases, plots of emission maxima versus the solvent dielectric constant (ε) are remarkably linear. Interestingly, emission maxima for the cationic exciplex of1+in nitrile and alcohol solvents also correlate linearly with ε. The solvent dependency for cationic exciplex emission maxima on ε is ca 1/3 of that for conventional exciplexes, which is ascribed to solvent stabilization of both the excited stateand the ground statefor cationic exciplexes. Differences in exciplex emissions between nitrile and alcohol solvents for1+are attributed to hydrogen bonding, with larger differences in higher hydrogen-bond acidity solvents.