Photophysics of the π,π* and n,π* States of Thymine: MS-CASPT2 Minimum-Energy Paths and CASSCF on-the-Fly Dynamics
Photophysics of the π,π* and n,π* States of Thymine: MS-CASPT2 Minimum-Energy Paths and CASSCF on-the-Fly Dynamics
复制标题
DOI：
10.1021/jp905303g
复制
发表时间：
2009-09-24
影响因子：
2.9
通讯作者：
Blancafort, Lluis
中科院分区：
文献类型：
--
作者：
Asturiol, David;Lasorne, Benjamin;Blancafort, Lluis
用MS-CASPT 2计算和半经典CASSCF动力学计算（包括表面跳跃算法）研究了胸腺嘧啶激发到最低π，π * 态后主要衰变路径上的光动力学沿着.静态计算表明，有两个从Franck-Condon结构的衰变路径，导致一个锥形交叉与基态。第一条路径直接到达交叉点，而第二条路径是间接的，并且涉及pi，pi* 状态的最小值，小障碍以及pi，pi* 和n，pi* 状态之间的交叉。根据静态计算，两条路径具有相似的斜率。沿着间接路径的动力学计算表明，在障碍后，部分轨迹被漏斗到与基态的交叉点，在那里它们被有效地淬火到基态。剩余的轨迹填充n，pi* 状态。它们也在小于1 ps的时间内被淬灭到基态，但是静态计算表明，在用于动力学的CASSCF水平下，n，pi* 态的衰变速率在很大程度上被高估。总体而言，这些结果表明，直接和间接路径都有助于实验发现的亚皮秒衰变分量。间接路径还提供了一种快速布居n，pi* 态的方法，这将解释实验皮秒衰变分量，
The photodynamics along the main decay paths of thymine after excitation to the lowest pi,pi* state have been studied with MS-CASPT2 calculations and semiclassical CASSCF dynamics calculations including a surface hopping algorithm. The static calculations show that there are two decay paths from the Franck-Condon structure that lead to a conical intersection with the ground state. The first path goes directly to the intersection, while the second one is indirect and involves a minimum of the pi,pi* state, a small barrier, and a crossing between the pi,pi* and n,pi* states. From the static calculations, both paths have similar slopes. The dynamics calculations along the indirect path show that, after the barrier, part of the trajectories are funneled to the intersection with the ground state, where they are efficiently quenched to the ground state. The remaining trajectories populate the n,pi* state. They are also quenched to the ground state in less than 1 ps, but the static calculations show that the decay rate of the n,pi* state is largely overestimated at the CASSCF level used for the dynamics, Overall, these results suggest that both direct and indirect paths contribute to the subpicosecond decay components found experimentally. The indirect path also provides a way for fast population of the n,pi* state, which will account for the experimental picosecond decay component,