In this work, how the excited-state dependent hydrogen bond (H-bond) interactions control photophysical processes have been uncovered by accurate electronic structure calculations for the five lowest-lying states (S₀, S₁, S₂, T₁, and T₂) of three aromatic thioketones and their isomers. The difference in the H-bond nature between S₂ and S₁ gives rise to ultrafast S₂ → S₁ internal conversion via the two-state conical intersection. Strong S₂ fluorescence observed usually in thiocarbonyl compounds is absent in aromatic thioketones with intramolecular H-bonds. Meanwhile, the relatively weak H-bond interactions in S₁ and T₁ states make the S₁, T₂, and T₁ states degenerate or quasi-degenerate. As a result, the T₂ state acts as a relay and enables both forward S₁ → T₁ and reverse T₁ → S₁ processes to occur efficiently, which provides new insights into the mechanism of thermally activated delayed fluorescence (TADF), and could be used to improve the design principle of purely organic TADF materials.

中文翻译：

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激发态依赖性氢键的性质及其在确定芳族硫酮光物理性质中的关键作用

在这项工作中，通过对五种最低状态（S ₀、S ₁、S ₂、T ₁和T ₂ ) 的三种芳族硫酮及其异构体。_{S 2}和S ₁之间氢键性质的差异导致通过两态锥形交叉点产生超快的S ₂ → S ₁内部转换。强S ₂通常在硫代羰基化合物中观察到的荧光在具有分子内氢键的芳族硫酮中不存在。_{同时，S 1}和T ₁态中相对较弱的氢键相互作用使S ₁、T ₂和T ₁态退化或准退化。因此，T ₂状态充当继电器，使正向 S ₁ → T ₁和反向 T ₁ → S ₁过程有效地发生，这为热激活延迟荧光 (TADF) 的机制提供了新的见解，并且可用于改进纯有机 TADF 材料的设计原理。