State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2020 May 5;232:118082. doi: 10.1016/j.saa.2020.118082. Epub 2020 Jan 21.
The new 3-hydroxy-4-pyridylisoquinoline compound is attractive and promising lead structure in drug discovery. The pronounced sensitivity of its emission property toward solvent polarity effect was presented in experiment (J. Org. Chem, 2019, 84, 3011). Nevertheless, the experiment was lack of solvent polarity effect on the excited state intramolecular proton transfer (ESIPT) mechanism in detail. In this study, the ESIPT process of this molecule in different polarity solvents were comprehensively expounded by density functional theory (DFT) and time-dependent DFT (TDDFT) methods. In order to ensure the accuracy of the experiment and roundly explore in theoretical level, two ESIPT pathways (1 and 2) based on the N1 and N2 forms of studied molecule were proposed, among which the ESIPT pathway 1 was derived from experiment. The calculated electronic spectrum of both N1 and N2 forms were rather comparable with the experiment. The calculated intramolecular hydrogen bond (IHB) parameters and infrared (IR) vibration spectra determined the enhancement of IHBs at the S state under different solvents for both N1 and N2 forms. The frontier molecular orbitals (FMOs) analysis proved that the intramolecular charge transfer (ICT) taken place during photoexcitation. The potential energy curves (PECs) at the S and S states were constructed to illustrate the solvent polarity effect on ESIPT mechanism. According to potential energy barriers (PEBs) on the PECs at S state, it is concluded that the ESIPT pathway 1 was forbidden with exceedingly high PEBs (24.585-25.322 kcal/mol), while the ESIPT pathway 2 was feasible with enough low PEBs (0.100-0.510 kcal/mol), which suggested the inconsequence of the experiment. Based on the PEBs of ESIPT pathway 2 in different solvent, the effect of solvent polarity on ESIPT mechanism was depicted. The results are as follows: the S state IHB intensity was enhanced with increasing solvent polarity; the extent of ICT was decreased with the increment of solvent polarity; the S state PEB was decreased as the solvent polarity increased. Indeed in short, the ESIPT reaction became more and more likely as the solvent polarity enhanced. We believe that this investigation will be useful to the utilization and development of property for such photochemical substances.
新型 3-羟基-4-吡啶异喹啉化合物是药物发现中具有吸引力和前景的先导结构。实验中呈现了其发射性质对溶剂极性效应的显著敏感性（J. Org. Chem, 2019, 84, 3011）。然而，实验缺乏对激发态分子内质子转移（ESIPT）机制在不同溶剂中溶剂极性效应的详细研究。在这项研究中，通过密度泛函理论（DFT）和含时密度泛函理论（TDDFT）方法综合阐述了该分子在不同极性溶剂中的 ESIPT 过程。为了确保实验的准确性并全面在理论层面进行探索，基于研究分子的 N1 和 N2 形式提出了两条 ESIPT 途径（1 和 2），其中途径 1 来自于实验。两种 N1 和 N2 形式的计算电子光谱与实验相当吻合。计算得到的分子内氢键（IHB）参数和红外（IR）振动光谱确定了两种 N1 和 N2 形式在不同溶剂下 S 态下 IHB 的增强。前线分子轨道（FMOs）分析证明了光激发过程中发生了分子内电荷转移（ICT）。在 S 和 S 态下构建了势能曲线（PECs），以说明溶剂极性对 ESIPT 机制的影响。根据 S 态 PECs 上的势能垒（PEB），可以得出结论，ESIPT 途径 1 由于过高的 PEB（24.585-25.322 kcal/mol）而被禁止，而 ESIPT 途径 2 则由于足够低的 PEB（0.100-0.510 kcal/mol）而可行，这表明实验是不合理的。基于 ESIPT 途径 2 在不同溶剂中的 PEB，描绘了溶剂极性对 ESIPT 机制的影响。结果表明：随着溶剂极性的增加，S 态 IHB 强度增强；随着溶剂极性的增加，ICT 的程度降低；随着溶剂极性的增加，S 态 PEB 减小。实际上，随着溶剂极性的增加，ESIPT 反应变得越来越容易。我们相信，这项研究将有助于此类光化学物质的应用和发展。
