The optical absorption properties and fluorescence properties of 3-hydroxy-2-(thiophen-2-yl)chromen-4-one (3-HTC) were simulated by the time-dependent density functional theory (TDDFT) method. The experimental absorption spectrum and fluorescence spectrum were reproduced well by the calculated vertical excitation energies of 3-HTC-a, which corresponds to the intramolecular hydrogen bond O2⋯H1–O1. The excited state intramolecular proton transfer (ESIPT) mechanism of 3-HTC has been systematically investigated. The constructed potential energy curves (PECs) of 3-HTC-a in the S₀ and S₁ states indicate that, after photo-excitation, the intramolecular proton transfer reaction with the H1 atom moving from O1 to O2 occurs more readily in both the dynamics and thermodynamics aspects. In sharp contrast, the weak S⋯H1–O1 bond in 3-HTC-b was weakened in the S₁ state compared with that in the S₀ state, suggesting that the ESIPT process is forbidden. For the first time, it is found that the strong hydrogen bond is further strengthened and the weak hydrogen bond is further weakened in the excited state of 3-HTC. Moreover, the vibrational frequencies of the CO and O–H groups involved in the hydrogen bonds were also studied, and a more clear-cut signature of the hydrogen-bonding dynamics of 3-HTC is provided in this work.

中文翻译：

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从头开始研究3-羟基-2-（噻吩-2-基）铬烯-4-一的激发态质子转移机理†

采用时变密度泛函理论（TDDFT）方法模拟了3-羟基-2-（噻吩-2-基）铬-4-（1-HTC）的光吸收性质和荧光性质。通过计算得到的3-HTC-a的垂直激发能很好地再现了实验吸收光谱和荧光光谱，其对应于分子内氢键O2⋯H1-O1。已经对3-HTC的激发态分子内质子转移（ESIPT）机理进行了系统研究。S ₀和S ₁中3-HTC-a的构造势能曲线（PEC）态表明，在光激发之后，在动力学和热力学方面，具有从O1迁移到O2的H1原子的分子内质子转移反应更容易发生。与之形成鲜明对比的是，与S ₀状态相比，S ₁状态下3-HTC-b中弱的S⋯H1-O1键被削弱，这表明ESIPT过程是被禁止的。首次发现，在3-HTC的激发态下，强氢键进一步增强，而弱氢键进一步减弱。此外，还研究了氢键中涉及的C O和O–H基团的振动频率，这项工作为3-HTC的氢键动力学提供了更清晰的特征。