Jiang Jie, Zhang Teng-shuo, Xue Jia-dan, Zheng Xuming, Cui Ganglong, Fang Wei-hai
Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, People's Republic of China.
Chemistry College, Beijing Normal University, Beijing 100875, People's Republic of China.
J Chem Phys. 2015 Nov 7;143(17):175103. doi: 10.1063/1.4935047.
Ultrahigh quantum yields of intersystem crossing to the lowest triplet state T1 are observed for 2-thiouracils (2TU), which is in contrast to the natural uracils that predominantly exhibit ultrafast internal conversion to the ground state upon excitation to the singlet excited state. The intersystem crossing mechanism of 2TU has recently been investigated using second-order perturbation methods with a high-level complete-active space self-consistent field. Three competitive nonadiabatic pathways to the lowest triplet state T1 from the initially populated singlet excited state S2 were proposed. We investigate the initial decay dynamics of 2TU from the light absorbing excited states using resonance Raman spectroscopy, time-dependent wave-packet theory in the simple model, and complete-active space self-consistent field (CASSCF) and time dependent-Becke's three-parameter exchange and correlation functional with the Lee-Yang-Parr correlation functional (TD-B3LYP) calculations. The obtained short-time structural dynamics in easy-to-visualize internal coordinates were compared with the CASSCF(16,11) predicted key nonadiabatic decay routes. Our results indicate that the predominant decay pathway initiated at the Franck-Condon region is toward the S2/S1 conical intersection point and S2T3 intersystem crossing point, but not toward the S2T2 intersystem crossing point.
对于2-硫尿嘧啶（2TU），观察到其系间窜越到最低三重态T1的量子产率极高，这与天然尿嘧啶形成对比，天然尿嘧啶在激发到单重激发态后主要表现出超快的内转换回到基态。最近，利用具有高级完全活性空间自洽场的二阶微扰方法研究了2TU的系间窜越机制。提出了从初始占据的单重激发态S2到最低三重态T1的三条竞争性非绝热途径。我们使用共振拉曼光谱、简单模型中的含时波包理论以及完全活性空间自洽场（CASSCF）和含时贝克尔三参数交换关联泛函与李-杨-帕尔关联泛函（TD-B3LYP）计算，研究了2TU从光吸收激发态的初始衰减动力学。将在易于可视化的内坐标中获得的短时间结构动力学与CASSCF(16,11)预测的关键非绝热衰减途径进行了比较。我们的结果表明，在弗兰克-康登区域开始的主要衰减途径是朝向S2/S1锥形交叉点和S2T3系间窜越点，而不是朝向S2T2系间窜越点。
