Modeling and Characterization of Exciplexes in Photoredox CO 2 Reduction: Insights from Quantum Chemistry and Fluorescence Spectroscopy
Modeling and Characterization of Exciplexes in Photoredox CO 2 Reduction: Insights from Quantum Chemistry and Fluorescence Spectroscopy
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光氧化还原 CO 2 还原中激基复合物的建模和表征：来自量子化学和荧光光谱的见解
DOI：
10.1021/acs.jpca.1c10658
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Mallikarjun Sharada, Shaama
中科院分区：
文献类型：
--
作者：
Kron, Kareesa J.;Hunt, Jonathan Ryan;Dawlaty, Jahan M.;Mallikarjun Sharada, Shaama
激发态芳烃和胺之间的相互作用可以导致具有独特发射行为的结构的形成。这些激发态复合物或激基复合物可以降低芳烃参与其他反应（例如 CO2 还原）的能力，或增加通过 Birch 还原降解的可能性。激基复合物几何形状对于理解光物理行为和探测降解途径是必要的，但计算起来具有挑战性。我们建立了详细的计算协议，用于激基复合物的计算、验证和表征。使用荧光光谱，我们首先证明了激发态低聚（对亚苯基）（OPP）与三乙胺之间形成了激基复合物，该激发态寡聚（对亚苯基）（OPP）已被证明可以成功地进行CO2还原。采用瞬态密度泛函理论来优化这些激基复合物的几何形状，并通过比较发射能量及其溶剂化显色性与实验进行验证。激发态能量分解分析证实了电荷转移相互作用相对于孤立激发态 OPP* 在发射红移中发挥的主导作用。我们发现，尽管激基复合物发射频率很大程度上取决于溶剂电介质，但激基复合物中电荷分离的程度却并非如此。我们的结果还表明，完全电子转移时溶剂分离的离子自由基态的形成与高介电溶剂中的激基复合物形成竞争，从而导致荧光实验中的激基复合物发射强度降低。
Interactions between excited-state arenes and amines can lead to the formation of structures with a distinct emission behavior. These excited-state complexes or exciplexes can reduce the ability of the arene to participate in other reactions, such as CO2reduction, or increase the likelihood of degradation via Birch reduction. Exciplex geometries are necessary to understand photophysical behavior and probe degradation pathways but are challenging to calculate. We establish a detailed computational protocol for calculation, verification, and characterization of exciplexes. Using fluorescence spectroscopy, we first demonstrate the formation of exciplexes between excited-state oligo-(p-phenylene) (OPP), shown to successfully carry out CO2reduction, and triethylamine. Time-dependent density functional theory is employed to optimize the geometries of these exciplexes, which are validated by comparing both emission energies and their solvatochromism with the experiment. Excited-state energy decomposition analysis confirms the predominant role played by charge transfer interactions in the red shift of emissions relative to the isolated excited-state OPP*. We find that although the exciplex emission frequency depends strongly on solvent dielectric, the extent of charge separation in an exciplex does not. Our results also suggest that the formation of solvent-separated ionic radical states upon complete electron transfer competes with exciplex formation in higher-dielectric solvents, thereby leading to reduced exciplex emission intensities in fluorescence experiments.