The excited-state molecular dynamics of 7-hydroxyquinoline-8-carboxylic acid (HCA) were studied to observe its fluorescent properties and proton transfer process. The two intramolecular hydrogen bonds (O-H⋯O and O-H⋯N) of the Enol form were both strengthened after photoexcitation to the first excited (S₁) state. The experimentally observed fluorescence emission (465 nm) was attributed to the theoretical Keto form (470 nm), which implies the occurrence of an excited-state intramolecular double proton transfer (ESIDPT) process. The nonadiabatic dynamics results demonstrate that a single proton transfer from the carboxylic to the nitrogen atom (process-A) occurs in 55 fs, which excludes the ESIDPT concert pathway. The potential energy surface results indicate that process-A (0.08 kcal/mol) induces the occurrence of a second proton transfer from the phenol to the oxygen atom (process-B). Compared to the stepwise ESIDPT reaction that begins with process-B (1.53 kcal/mol), process-A is energy favorable in the S₁ state. Therefore, we propose a reaction path of the following: Enol in the ground state (S₀) → Enol in the S₁ state → proton transferred Keto in the S₁ state (stepwise pathway begins with process-A) → Keto in the S₀ state (fluorescence emission at 470 nm) → Enol in the S₀ state (reversed proton transfer). This process confirms what was predicted by Chou (J. Phys. Chem. Lett. 2011, 2, 3063).

研究了7-羟基喹啉-8-羧酸（HCA）的激发态分子动力学，观察其荧光性质和质子转移过程。在光激发至第一次激发后，烯醇形式的两个分子内氢键（OH⋯O和OH⋯N）均被增强（S ₁）状态。实验观察到的荧光发射（465 nm）归因于理论上的酮基形式（470 nm），这意味着发生了激发态分子内双质子转移（ESIDPT）过程。非绝热动力学结果表明，从羧基到氮原子的单质子转移在55 fs内发生，这不包括ESIDPT协同途径。势能表面结果表明，过程A（0.08 kcal / mol）引发了第二次质子从酚到氧原子的转移（过程B）。与从过程B开始的逐步ESIDPT反应（1.53 kcal / mol）相比，过程A在S ₁状态下能量有利。因此，我们提出以下反应路径：基态的烯醇（S ₀）→处于S ₁状态的烯醇→质子转移到处于S ₁状态的酮基（逐步途径始于过程A）→处于S ₀状态的酮基（在470 nm处发出荧光）→处于S ₀状态的烯醇（反转质子）转让）。该过程证实了Chou（J. Phys。Chem。Lett。2011，2，3063）的预测。