Lan Zhenggang, Fabiano Eduardo, Thiel Walter
Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, Germany.
J Phys Chem B. 2009 Mar 19;113(11):3548-55. doi: 10.1021/jp809085h.
The photoinduced relaxation dynamics of pyrimidine nucleobases (uracil, thymine, and cytosine) was studied using the surface-hopping approach at the semiempirical OM2/MRCI level of theory. The relevant potential energy surfaces were characterized by performing geometry optimizations of the energy minima of the lowest electronic states and of the most important conical intersections and by computing excitation energies at each configuration. Surface-hopping molecular dynamics simulations were performed to describe the nonadiabatic dynamics after excitation into the optically active state. In each of the molecules, the two lowest excited singlet states are involved in the dynamics, and there are competing relaxation paths. The dynamics is dominated by a two-step relaxation mechanism in uracil and thymine, while the direct decay to the ground state is most important in cytosine. For all three molecules, the simulations yield ultrafast S(2)-S(1) deexcitation within 50 fs and internal conversion to the ground state in less than 1 ps, consistent with recent experimental results from time-resolved photoelectron spectroscopy.
采用表面跳跃方法，在半经验OM2/MRCI理论水平下研究了嘧啶核碱基（尿嘧啶、胸腺嘧啶和胞嘧啶）的光致弛豫动力学。通过对最低电子态的能量极小值和最重要的锥形交叉点进行几何优化，并计算每种构型的激发能，对相关势能面进行了表征。进行了表面跳跃分子动力学模拟，以描述激发到光学活性态后的非绝热动力学。在每个分子中，两个最低激发单重态参与了动力学过程，并且存在相互竞争的弛豫路径。尿嘧啶和胸腺嘧啶的动力学过程以两步弛豫机制为主，而胞嘧啶中直接衰变到基态最为重要。对于所有三个分子，模拟结果表明在50飞秒内实现超快的S(2)-S(1)去激发，并且在不到1皮秒的时间内发生内转换回到基态，这与时间分辨光电子能谱的最新实验结果一致。
