Department of Chemistry, Pritzker School of Molecular Engineering, The James Franck Institute and Chicago Center for Theoretical Chemistry, The University of Chicago, Chicago, Illinois 60637, United States.
Department of Chemistry, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455, United States.
J Am Chem Soc. 2021 Apr 21;143(15):5878-5889. doi: 10.1021/jacs.1c00989. Epub 2021 Apr 12.
The dynamics of excited heteroaromatic molecules is a key to understanding the photoprotective properties of many biologically relevant chromophores that dissipate their excitation energy nonreactively and thereby prevent the detrimental effects of ultraviolet radiation. Despite their structural variability, most substituted aromatic compounds share a common feature of a repulsive πσ* potential energy surface. This surface can lead to photoproducts, and it can also facilitate the population transfer back to the ground electronic state by means of a πσ*/S conical intersection. Here, we explore a hidden relaxation route involving the triplet electronic state of aniline, which has recently been discovered by means of time-selected photofragment translational spectroscopy [ , , 141101]. By using the recently available analytical gradients for multiconfiguration pair-density functional theory, it is now possible to locate the minimum-energy crossing points between states of different spin and therefore compute the intersystem crossing rates with a multireference method, rather than with the less reliable single-reference methods. Using such calculations, we demonstrate that the population loss of aniline in the T(ππ*) state is dominated by CHNH → CHNH· + H· dissociation, and we explain the long nonradiative lifetimes of the T(ππ*) state at the excitation wavelengths of 294-264 nm.
激发杂芳环分子的动力学是理解许多与生物相关发色团光保护性质的关键，这些发色团以非反应的方式耗散其激发能，从而防止紫外线辐射的有害影响。尽管它们的结构具有变异性，但大多数取代的芳族化合物都具有一个排斥的 πσ势能面的共同特征。这个表面可以导致光产物，也可以通过 πσ/S 锥形交叉促进回到基态电子态的人口转移。在这里，我们通过时间选择光碎片平移光谱[,, 141101]探索了一种涉及苯胺三重态的隐藏弛豫途径，最近已经发现了这种途径。通过使用最近可用于多组态对密度泛函理论的分析梯度，可以定位不同自旋态之间的最低能量交叉点，从而用多参考方法计算系间窜越速率，而不是使用不太可靠的单参考方法。通过这样的计算，我们证明了在 T(ππ*)态中苯胺的人口损失主要是由 CHNH→CHNH·+H·离解引起的，我们解释了在 294-264nm 的激发波长下 T(ππ*)态的长非辐射寿命。
