A non-adiabatic dynamics study of octatetraene: the radiationless conversion from S2 to S1.
A non-adiabatic dynamics study of octatetraene: the radiationless conversion from S2 to S1.
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DOI：
10.1063/1.4853715
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发表时间：
2013-12
期刊：
影响因子：
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通讯作者：
Zexing Qu;Chungen Liu
中科院分区：
文献类型：
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作者：
Zexing Qu;Chungen Liu
对全反式 1,3,5,7-辛四烯的激发态动力学进行了模拟，以研究超快无辐射 S2 → S1 内部转换过程。采用单激发方法的多参考构型相互作用来优化激发态的平衡结构以及S2/S1圆锥交点，并研究S2/S1态转变的非绝热分子动力学。在圆锥形交叉处，发现分子从原来的平面反式结构扭曲成围绕C3-C4键的近乎垂直的构象，扭转角约为107°。这种结构变化可以导致状态S2和S1在能量上相互接近，并通过破坏电子波函数中的状态间对称禁止性来极大地增加两个状态之间的非绝热耦合。进行表面跳跃分子动力学模拟来描述非绝热过程。当 Franck-Condon 激发到 S2 态时，分子快速扭曲其 C3-C4 键并接近圆锥形交叉区域，在此区域可以进行有效的内部转化为 S1。通过使用指数阻尼函数拟合轨迹平均分数的占用数，估计 S2 状态的衰减时间常数 (τ) 约为 251 fs。该值与之前大约 300-400 fs 的实验测量值相当一致。
Simulation of the excited state dynamics of all-trans-1,3,5,7-octatetraene has been performed to investigate the ultrafast radiationless S2 → S1 internal conversion process. Multireference configuration interaction with single excitation method has been employed to optimize the equilibrium structure of the excited states, as well as the S2/S1 conical intersection, and to investigate the non-adiabatic molecular dynamics of the S2/S1 state transition. At the conical intersection, the molecule is found to be distorted from the original planar trans structure to a nearly perpendicular conformation around C3-C4 bond, with the torsion angle being about 107°. Such structural change can result in mutual approaching of states S2 and S1 in energy, and drastically increase the nonadiabatic coupling between the two states by destroying the inter-state symmetry prohibition in the electronic wavefunctions. Surface-hopping molecular dynamics simulations are performed to describe the non-adiabatic process. Upon the Franck-Condon excitation to the S2 state, the molecule quickly twists its C3-C4 bond and approaches the conical intersection region, where it can undergo efficient internal conversion to S1. The decay time constant (τ) of S2 state is estimated to be around 251 fs by fitting the occupation number of average fraction of trajectories using an exponential damping function. This value is reasonably consistent with previous experimental measurements of around 300-400 fs.