Li Yuanyuan, Wen Keke, Feng Songyan, Yuan Huijuan, An Beibei, Zhu Qiuling, Guo Xugeng, Zhang Jinglai
College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, China; State Key Laboratory for Physical Chemistry of Solid Surfaces and Fujian Provincial Key Lab of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2017 Dec 5;187:9-14. doi: 10.1016/j.saa.2017.06.019. Epub 2017 Jun 15.
Excited-state intramolecular proton transfer (ESIPT) reactions occurring in the S state for five molecules, which possess five/six-membered ring intramolecular NH···N or OH···N hydrogen bonds bearing quinoline or 2-phenylpyridine moiety, have been described in detail by the time-dependent density functional theory (TD-DFT) approach using the B3LYP hybrid functional. For the five molecules, the constrained potential energy profiles along the ESIPT reactions show that proton transfer is barrierless in molecules possessing six-membered ring intramolecular H-bonds, which is smoother than that with certain barriers in five-membered ring H-bonding systems. For the latter, chemical modification by a more strong acid group can lower the ESIPT barrier significantly, which harnesses the ESIPT reaction from a difficult type to a fast one. The energy barrier of the ESIPT reaction depends on the intensity of the intramolecular H-bond, which can be measured with the topological descriptors by topology analysis of the bond critical point (BCP) of the intramolecular H-bond. It is found that when the value of electron density ρ(r) at BCP is bigger than 0.025a.u., the corresponding molecule might go through an ultrafast and barrierless ESIPT process, which opens a new scenario to explore the ESIPT reactions.
利用含时密度泛函理论（TD-DFT）方法，采用B3LYP杂化泛函，详细描述了五个分子在S态发生的激发态分子内质子转移（ESIPT）反应，这些分子具有带有喹啉或2-苯基吡啶部分的五/六元环分子内NH···N或OH···N氢键。对于这五个分子，沿ESIPT反应的受限势能剖面图表明，在具有六元环分子内氢键的分子中质子转移是无势垒的，这比五元环氢键系统中存在一定势垒的情况更为平滑。对于后者，用更强的酸基团进行化学修饰可以显著降低ESIPT势垒，从而将ESIPT反应从困难类型转变为快速类型。ESIPT反应的能垒取决于分子内氢键的强度，这可以通过对分子内氢键的键临界点（BCP）进行拓扑分析，用拓扑描述符来测量。研究发现，当BCP处的电子密度ρ(r)值大于0.025 a.u.时，相应的分子可能会经历超快且无势垒的ESIPT过程，这为探索ESIPT反应开辟了新的局面。
