Abstract In this work, we theoretically study the excited state multiple proton transfer (ESMPT) mechanism of 9H-pyrido[ 3 , 4 -b]indole (NOR) coupling with acetic acid (AcOH) in DCM solvent. We analyze structural changes, infrared (IR) vibrational spectra and charge redistribution, which reveals the tendency of ESMPT process. Exploring potential energy curves, we confirm that the protonation of pyridine nitrogen firstly occurs, which opens ESMPT reaction. In the whole ESMPT process, the powerful acceptance ability of AcO − plays a vital role. Our investigation not only indicates NOR system undergoes a proton relay process in excited state and clarifies the ambiguous mechanism in previous experiment, but also paves the way for further investigating intermolecular multiple proton transfer interactions in biological and chemical science.

中文翻译：

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阐述9H-吡啶并[3,4-b]吲哚的激发态多质子转移机制

摘要 在这项工作中，我们从理论上研究了 9H-吡啶并[ 3 , 4 -b] 吲哚 (NOR) 与乙酸 (AcOH) 在 DCM 溶剂中的激发态多质子转移 (ESMPT) 机制。我们分析了结构变化、红外 (IR) 振动光谱和电荷重新分布，揭示了 ESMPT 过程的趋势。探索势能曲线，我们确认首先发生吡啶氮的质子化，这开启了 ESMPT 反应。在整个ESMPT过程中，AcO - 强大的接受能力起着至关重要的作用。我们的研究不仅表明 NOR 系统在激发态经历质子中继过程，澄清了先前实验中模糊的机制，而且为进一步研究生物和化学科学中的分子间多质子转移相互作用铺平了道路。