QM/MM Studies on the Photophysical Mechanism of a Truncated Octocrylene Model
QM/MM Studies on the Photophysical Mechanism of a Truncated Octocrylene Model
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截断奥克立林模型光物理机制的 QM/MM 研究
DOI：
10.1021/acs.jpca.9b07280
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发表时间：
2019
影响因子：
2.9
通讯作者：
Cui Ganglong
中科院分区：
文献类型：
--
作者：
Chang Xue-Ping;Fang Ye-Guang;Cui Ganglong
甲基2-氰基-3,3-二苯基丙烯酸酯（MCDPA）与八烯（OCR）具有相同的分子骨架，八烯（OCR）是市售防晒霜中最常用的分子之一。然而，其激发态弛豫机制尚不清楚。本文采用QM(CASPT2//CASSCF)/MM方法研究了MCDPA在甲醇溶液中的光谱性质、几何和电子结构、相关的圆锥形交点和交叉点以及激发态弛豫路径。我们发现，在Franck-Condon （FC）区，V（1ππ*）态的能量仅比V ' （1π *）态低2.8 kcal/mol，并分配给实验观察到的最大吸收带。从这两个初始填充的单重态出发，存在三个非辐射弛豫路径来重新填充s0态。在第一种方法中，当在FC区填充V（1ππ*）态时，系统沿V（1ππ*）态绝热演化至最小值，此时系统发生向s的内部转换。在第二种情况下，系统在FC区填充了V′（1π *）态，系统绝热克服了约3.0 kcal/mol的势垒，接近V（1π *）的最小值，最终发生V（1π *）到so0的内转换。在第三个系统中，V′（1ππ*）态首先通过系统间交叉跃迁到t2态，然后通过内部转换衰减到t1态。T1状态最终通过T1/ s0交叉点转换为s0状态。我们目前的工作有助于理解OCR及其变体的光物理。
Methyl 2-cyano-3,3-diphenylacrylate (MCDPA) shares the same molecular skeleton with octocrylene (OCR) that is one of the most common molecules used in commercially available sunscreens. However, its excited-state relaxation mechanism is unclear. Herein, we have used the QM(CASPT2//CASSCF)/MM method to explore spectroscopic properties, geometric and electronic structures, relevant conical intersections and crossing points, and excited-state relaxation paths of MCDPA in methanol solution. We found that in the Franck–Condon (FC) region, the V(1ππ*) state is energetically lower than the V′(1ππ*) state only by 2.8 kcal/mol and is assigned to experimentally observed maximum absorption band. From these two initially populated singlet states, there exist three nonradiative relaxation paths to repopulate the S0state. In the first one, when the V(1ππ*) state is populated in the FC region, the system diabatically evolves along the V(1ππ*) state into its minimum where the internal conversion to S0occurs. In the second one, the V′(1ππ*) state is populated in the FC region and the system adiabatically overcomes a barrier of ca. 3.0 kcal/mol to approach the V(1ππ*) minimum eventually leading to a V(1ππ*)-to-S0internal conversion. In the third one, the V′(1ππ*) state first hops via the intersystem crossing to the T2state, which then decays through the internal conversion to the T1state. The T1state is finally converted to the S0state via the T1/S0crossing point. Our present work contributes to understanding the photophysics of OCR and its variants.