Lou Zhangrong, Zhou Xiaoyan, Tang Zhe, Zhou Panwang
Institute of Molecular Sciences and Engineering, Institute of Frontier and Interdisciplinary Science, Shandong University, Qingdao 266235, P. R. China.
Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, P. R. China.
J Phys Chem B. 2020 Jun 4;124(22):4564-4572. doi: 10.1021/acs.jpcb.0c02455. Epub 2020 May 20.
The twisted intramolecular charge transfer has been proposed for a number of years and widely accepted to explain the excited-state dynamics of organic molecules. Recently, a new state termed as "twisted and rehybridized intramolecular charge transfer" has been proposed to explain the excited-state dynamics of an aniline-triazine electron donor-acceptor dyad with an alkyne spacer based on ultrafast time-resolved spectroscopy. However, the change of the geometries along the excited-state decay pathway remains unknown. In this study, by optimization of the excited-state geometry of the donor-acceptor dyad and potential energy surface scan along the twisting angle, we successfully reproduce the experimentally observed band in time-resolved infrared absorption spectroscopy. Our calculation results demonstrated that the rehybridization process is not involved and only the twisted intramolecular charge transfer state is formed. Moreover, we located a minimum energy conical intersection between the ground and first excited-state of the donor-acceptor dyad, which is easily reached and corresponding to the primary nonradiative decay pathway of the donor-acceptor dyad. The energy of minimum energy conical intersection is solvent-dependent and consistent with the experimentally observed solvent-dependent lifetime of excited state.
扭曲的分子内电荷转移已被提出多年，并被广泛接受用于解释有机分子的激发态动力学。最近，基于超快时间分辨光谱，人们提出了一种新的状态，称为“扭曲和重新杂化的分子内电荷转移”，以解释具有炔烃间隔基的苯胺 - 三嗪电子供体 - 受体二元体系的激发态动力学。然而，沿着激发态衰变途径的几何结构变化仍然未知。在本研究中，通过优化供体 - 受体二元体系的激发态几何结构并沿扭曲角进行势能面扫描，我们成功地在时间分辨红外吸收光谱中重现了实验观察到的谱带。我们的计算结果表明，不涉及重新杂化过程，仅形成扭曲的分子内电荷转移态。此外，我们找到了供体 - 受体二元体系基态和第一激发态之间的一个最小能量锥形交叉点，它很容易达到，并且对应于供体 - 受体二元体系的主要非辐射衰变途径。最小能量锥形交叉点的能量与溶剂有关，并且与实验观察到的激发态溶剂依赖寿命一致。
