College of Physics and Electronics, North China University of Water Resources and Electric Power, Zhengzhou 450046, PR China; State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, PR China.
Basic Teaching Department, Jiaozuo University, Jiaozuo 454000, PR China.
Spectrochim Acta A Mol Biomol Spectrosc. 2019 Mar 5;210:159-164. doi: 10.1016/j.saa.2018.11.021. Epub 2018 Nov 13.
A novel fluorescence molecule (2‑hydroxy‑4‑methoxyphenyl)(phenyl)‑methanone azine (HMPM) has been explored theoretically in this present work. Based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we investigate the excited state hydrogen bonding behaviors and excite state intramolecular proton transfer (ESIPT) process for HMPM molecule. Via simulating the reduced density gradient (RDG) versus sign(λ)ρ, we firstly verify the double intramolecular hydrogen bonds (O1H2⋯N3 and O4H5⋯N6) for HMPM system. Comparing with the changes about these two hydrogen bonds (i.e., bond distances, bond angles and infrared (IR) vibrational spectra), we find that they should be enhanced in the first excited state upon the photo-excitation. The shortened hydrogen bonding distance of H2⋯N3 and H5⋯N6 provide the possibility for ESIPT reaction. Given the photo-excitation process, we confirm the charge redistribution around the hydrogen bonding moieties plays an important role as a driving force for the ESIPT process. Further, via constructing S-state and S-state potential energy surfaces (PESs), we confirm the excited state double proton transfer (ESDPT) is excludable since the high optimized energy and high potential energy barrier. While the low potential barrier for excited state single proton transfer path results in the ultrafast ESIPT reaction, which explains why the initial HMPM fluorescence peak cannot be detected in previous experimental phenomenon. This work not only clarifies the excited state dynamical behavior for HMPM system, but also explains previous experimental phenomenon and attributions about steady state spectra. We hope this work can facilitate novel applications based on the novel HMPM system in future.
本工作从理论上研究了一种新型荧光分子（2-羟基-4-甲氧基苯基）（苯基）甲酮腙（HMPM）。基于密度泛函理论（DFT）和含时密度泛函理论（TDDFT）方法，我们研究了 HMPM 分子的激发态氢键行为和激发态分子内质子转移（ESIPT）过程。通过模拟约化密度梯度（RDG）与 sign(λ)ρ，我们首先验证了 HMPM 体系中的两个分子内氢键（O1H2⋯N3 和 O4H5⋯N6）。通过比较这两个氢键（即键长、键角和红外（IR）振动光谱）的变化，我们发现它们在光激发后应该在第一激发态增强。H2⋯N3 和 H5⋯N6 氢键的缩短为 ESIPT 反应提供了可能性。考虑到光激发过程，我们确认氢键基团周围的电荷重新分布作为 ESIPT 过程的驱动力起着重要作用。此外，通过构建 S 态和 S 态势能面（PESs），我们确认激发态双质子转移（ESDPT）是不可行的，因为优化后的能量高，势能垒高。而激发态单质子转移路径的低势能垒导致超快 ESIPT 反应，这解释了为什么在先前的实验现象中无法检测到初始 HMPM 荧光峰。这项工作不仅阐明了 HMPM 体系的激发态动力学行为，还解释了先前的实验现象和稳态光谱的归因。我们希望这项工作能够促进基于新型 HMPM 体系的未来新应用。
