Dipartimento di Chimica e Chimica Industriale, Università di Pisa, v. Risorgimento 35, I-56126 Pisa, Italy.
J Am Chem Soc. 2011 Apr 6;133(13):5109-23. doi: 10.1021/ja1113529. Epub 2011 Mar 14.
We have simulated the photodynamics of azobenzene by means of the Surface Hopping method. We have considered both the trans → cis and the cis → trans processes, caused by excitation in the n → π* band (S(1) state). To bring out the solvent effects on the excited state dynamics, we have run simulations in four different environments: in vacuo, in n-hexane, in methanol, and in ethylene glycol. Our simulations reproduce very well the measured quantum yields and the time dependence of the intensity and anisotropy of the transient fluorescence. Both the photoisomerization and the S(1) → S(0) internal conversion require the torsion of the N═N double bond, but the N-C bond rotations and the NNC bending vibrations also play a role. In the trans → cis photoconversion the N═N torsional motion and the excited state decay are delayed by increasing the solvent viscosity, while the cis → trans processes are less affected. The analysis of the simulation results allows the experimental observations to be explained in detail, and in particular the counterintuitive increase of the trans → cis quantum yield with viscosity, as well as the relationship between the excited state dynamics and the solvent effects on the fluorescence lifetimes and depolarization.
我们通过表面跳跃方法模拟了偶氮苯的光动力学。我们考虑了由 n → π* 带（S(1) 态）激发引起的顺式 → 反式和顺式 → 反式过程。为了突出溶剂对激发态动力学的影响，我们在四种不同的环境中进行了模拟：真空、正己烷、甲醇和乙二醇。我们的模拟很好地再现了测量的量子产率以及瞬态荧光强度和各向异性的时间依赖性。光异构化和 S(1) → S(0) 内转换都需要 N═N 双键的扭转，但 N-C 键的旋转和 NNC 弯曲振动也起作用。在顺式 → 反式光转化中，N═N 扭转运动和激发态衰减随着溶剂粘度的增加而延迟，而反式 → 顺式过程受影响较小。对模拟结果的分析允许详细解释实验观察结果，特别是与直觉相反的是，随着粘度的增加，顺式 → 反式量子产率增加，以及激发态动力学与溶剂对荧光寿命和去偏振的影响之间的关系。
