Liang Ruibin
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, United States.
J Chem Theory Comput. 2021 May 11;17(5):3019-3030. doi: 10.1021/acs.jctc.1c00105. Epub 2021 Apr 21.
The photoisomerization of azobenzene is a prototypical reaction of various light-activated processes in material and biomedical sciences. However, its reaction mechanism has been under debate for decades, partly due to the challenges in computational simulations to accurately describe the molecule's photodynamics. A recent study (. , 142 (49), 20,680-20,690) addressed the challenges by combining the hole-hole Tamm-Dancoff Approximated (hh-TDA) density functional theory (DFT) method with the ab initio multiple spawning (AIMS) algorithm. The hh-TDA-DFT/AIMS method was applied to first-principles nonadiabatic dynamics simulation of azobenzene's photodynamics in the vacuum. However, it remains necessary to benchmark this new method in realistic molecular environments against experimental data. In the current work, the hh-TDA-DFT/AIMS method was employed in a quantum mechanics/molecular mechanics setting to characterize the azobenzene's photodynamics in explicit methanol and -hexane solvents, following both the S (nπ*) and S (ππ*) excitations. The simulated absorption and fluorescence spectra following the S excitation quantitatively agree with the experiments. However, the hh-TDA-DFT method overestimates the torsional barrier on the S state, leading to an overestimation of the S state lifetime. The excited-state population decays to the ground state through two competing channels. The reactive channel partially yields the azobenzene photoproduct, and the unreactive channel exclusively leads to the reactant. The S excitation increases the decay through the unreactive channel and thus decreases the isomerization quantum yield compared to the S excitation. The solvent slows down the azobenzene's torsional dynamics on the S state, but its polarity minimally affects the reaction kinetics and quantum yields. Interestingly, the dynamics of the central torsion and angles of azobenzene play a critical role in determining the final isomer of the azobenzene. This benchmark study validates the hh-TDA-DFT/AIMS method's accuracy for simulating the azobenzene's photodynamics in realistic molecular environments.
偶氮苯的光异构化是材料科学和生物医学中各种光激活过程的典型反应。然而，其反应机理几十年来一直存在争议，部分原因是在计算模拟中准确描述分子光动力学存在挑战。最近的一项研究（……，142(49)，20,680 - 20,690）通过将空穴 - 空穴塔姆 - 丹科夫近似（hh - TDA）密度泛函理论（DFT）方法与从头算多态生成（AIMS）算法相结合来应对这些挑战。hh - TDA - DFT/AIMS方法被应用于偶氮苯在真空中光动力学的第一性原理非绝热动力学模拟。然而，在实际分子环境中根据实验数据对这种新方法进行基准测试仍然很有必要。在当前工作中，hh - TDA - DFT/AIMS方法被用于量子力学/分子力学环境中，以表征偶氮苯在明确的甲醇和正己烷溶剂中的光动力学，同时考虑S（nπ*）和S（ππ*）激发。S激发后的模拟吸收光谱和荧光光谱与实验定量吻合。然而，hh - TDA - DFT方法高估了S态的扭转势垒，导致对S态寿命的高估。激发态粒子通过两个竞争通道衰减到基态。反应性通道部分产生偶氮苯光产物，非反应性通道仅导致反应物。与S激发相比，S激发增加了通过非反应性通道的衰减，从而降低了异构化量子产率。溶剂减缓了偶氮苯在S态的扭转动力学，但其极性对反应动力学和量子产率的影响最小。有趣的是，偶氮苯中心扭转和角度的动力学在决定偶氮苯的最终异构体方面起着关键作用。这项基准研究验证了hh - TDA - DFT/AIMS方法在模拟实际分子环境中偶氮苯光动力学方面的准确性。
