Gao Aihua, Wang Meishan, Liu Yanli, Zhao Yanliang
School of Physics and Optoelectronic Engineering, Ludong University, Yantai 264025, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2024 Dec 5;322:124865. doi: 10.1016/j.saa.2024.124865. Epub 2024 Jul 21.
The trans-cis photoisomerization processes of 4,4'-azopyridine upon S and S excitations have been investigated by nonadiabatic dynamics simulations based on multi-reference CASSCF calculations. 119 sampling trajectories were simulated starting from the trans form excited to the S (S) state and the cis-isomer quantum yield is evaluated to be (3 ± 2)% ((18 ± 4)%), which is qualitatively in agreement with the recent experimental results in ethanol. We found that rotation around the central N-N bond accompanied by the N-N-C symmetrical bending vibrations is the main mechanism in photoisomerization of the target molecule excited to the S and S states. Upon S excitation, S-S transition occurs earlier along the C-N-N-C torsional coordinate, leading to a low cis-isomer quantum yield. Upon S excitation, half of the simulated trajectories are trapped in a potential well on the S state, from which the twisted conical intersections are more easily reached in the internal conversion, resulting in a higher cis-isomer quantum yield.
基于多参考CASSCF计算的非绝热动力学模拟研究了4,4'-偶氮吡啶在S和S激发下的反式-顺式光异构化过程。从激发到S（S）态的反式构型开始模拟了119条采样轨迹，顺式异构体的量子产率评估为（3±2）%（（18±4）%），这在定性上与最近在乙醇中的实验结果一致。我们发现，围绕中心N-N键的旋转伴随着N-N-C对称弯曲振动是目标分子激发到S和S态时光异构化的主要机制。在S激发时，沿着C-N-N-C扭转坐标S-S跃迁更早发生，导致顺式异构体量子产率较低。在S激发时，一半的模拟轨迹被困在S态的势阱中，在内部转换中更容易从该势阱到达扭曲的锥形交叉点，从而导致更高的顺式异构体量子产率。
