In the present study, the results of comprehensive theoretical exploration on the nonradiative relaxation of three (hydroxyphenyl)imidazole-based organic compounds (abbreviated AHP, HPIP, and HPBI) in the gas phase are presented. Having small structural differences, the selected systems have commonalities in the excited state intramolecular proton transfer (ESIPT) process. The ground and S1 excited state potential energy profiles of titled systems have been determined on the basis of the RI-MP2 and RI-CC2 methods, and the effect of small structural distinctions on their photophysical characters will be extensively addressed. Although, in the presence of solvent, high fluorescence quantum yield is another characteristic of AHP and HPIP, owing to accessible conical intersections between the S1/S0 state potential energy profiles of both systems, nonradiative relaxation can be proposed as the most important feature of these two systems in the gas phase. These conical intersections are responsible for ultrafast deactivation of excited systems via internal conversions to the ground state. The nonradiative deactivation mechanism determined in this work deals with the remarkable photostability of the AHP and HPIP molecules.

中文翻译：

---

2-（4'-氨基-2'-羟基苯基）-1H-咪唑并[4,5-c]吡啶及其类似物的激发态质子转移和失活机理：理论研究。

在本研究中，提出了对三种（羟基苯基）咪唑基有机化合物（缩写为AHP，HPIP和HPBI）在气相中进行非辐射弛豫的综合理论探索的结果。所选系统具有小的结构差异，在激发态分子内质子转移（ESIPT）过程中具有共同点。已在RI-MP2和RI-CC2方法的基础上确定了标题系统的基态和S1激发态势能分布图，将广泛讨论小的结构差异对其光物理特性的影响。尽管在存在溶剂的情况下，由于两个系统的S1 / S0状态势能图之间可访问的圆锥形交点，所以高荧光量子产率是AHP和HPIP的另一个特征，可以将非辐射弛豫作为这两个系统在气相中的最重要特征。这些圆锥形交叉点负责通过内部转换为基态来超快停用受激系统。在这项工作中确定的非辐射失活机理涉及AHP和HPIP分子的显着光稳定性。