Farfan Camille A, Turner Daniel B
Department of Chemistry, New York University, New York, NY 10003, USA.
Phys Chem Chem Phys. 2020 Sep 23;22(36):20265-20283. doi: 10.1039/d0cp03464a.
Despite their important role in photochemistry and expected presence in most polyatomic molecules, conical intersections have been thoroughly characterized in a comparatively small number of systems. Conical intersections can confer molecular photoreactivity or photostability, often with remarkable efficacy, due to their unique structure: at a conical intersection, the adiabatic potential energy surfaces of two or more electronic states are degenerate, enabling ultrafast decay from an excited state without radiative emission, known as nonadiabatic transfer. Furthermore, the precise conical intersection topography determines fundamental properties of photochemical processes, including excited-state decay rate, efficacy, and molecular products that are formed. However, these relationships have yet to be defined comprehensively. In this article, we use an adaptable computational model to investigate a variety of conical intersection topographies, simulate resulting nonadiabatic dynamics, and calculate key photochemical observables. We varied the vibrational mode frequencies to modify conical intersection topography systematically in four primary classes of conical intersections and quantified the resulting rate, total yield, and product yield of nonadiabatic decay. The results reveal that higher vibrational mode frequencies reduce nonadiabatic transfer, but increase the transfer rate and resulting photoproduct formation. These trends can inform progress toward experimental control of photochemical reactions or tuning of molecules' photochemical properties based on conical intersections and their topography.
尽管锥形交叉点在光化学中发挥着重要作用，并且预计存在于大多数多原子分子中，但在相对较少的系统中对其进行了全面表征。由于其独特的结构，锥形交叉点可以赋予分子光反应性或光稳定性，通常具有显著的效果：在锥形交叉点处，两个或多个电子态的绝热势能面是简并的，使得能够从激发态进行无辐射发射的超快衰变，即非绝热转移。此外，精确的锥形交叉点形貌决定了光化学过程的基本性质，包括激发态衰变率、效率以及形成的分子产物。然而，这些关系尚未得到全面定义。在本文中，我们使用一种适应性强的计算模型来研究各种锥形交叉点形貌，模拟由此产生的非绝热动力学，并计算关键的光化学可观测量。我们改变振动模式频率，在四类主要的锥形交叉点中系统地改变锥形交叉点形貌，并量化非绝热衰变的产生率、总产率和产物产率。结果表明，较高的振动模式频率会降低非绝热转移，但会增加转移速率和由此产生的光产物形成。这些趋势可以为基于锥形交叉点及其形貌的光化学反应的实验控制或分子光化学性质的调节提供参考。
