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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Photodynamics Simulations of Thymine: Relaxation into the First Excited Singlet State
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Photodynamics Simulations of Thymine: Relaxation into the First Excited Singlet State

机译：胸腺嘧啶的光动力学模拟：弛豫成第一个激发的单重态

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摘要

Ab initio nonadiabatic dynamics simulations are reported for thymine with focus on the S2 f S1 deactivation using the state-averaged CASSCF method. Supporting calculations have been performed on vertical excitations, S1 and S2 minima, and minima on the crossing seam using the MS-CASPT2, RI-CC2, MR-CIS, and MRCISD methods. The photodynamical process starts with a fast (<100 fs) planar relaxation from the S2 ππ* state into the πOπ* minimum of the S2 state. The calculations demonstrate that two π-excited states (denoted ππ* and πOπ*) are actually involved in this stage. The time in reaching the S2/S1 intersections, through which thymine can deactivate to S1, is delayed by both the change in character between the states as well as the flatness of the S2 surface. This deactivation occurs in an average time of 2.6 ps at the lowest-energy region of the crossing seam. After that, thymine relaxes to the nπ* minimum of the S1 state, where it remains until the transfer to the ground state takes place. The present dynamics simulations show that not only the πOπ* S2 trapping but also the trapping in the nπ* S1 minimum contribute to the elongation of the excitedstate lifetime of thymine.
机译：报道了胸腺嘧啶从头开始的非绝热动力学模拟，其重点是使用状态平均CASSCF方法进行的S2 f S1失活。已经使用MS-CASPT2，RI-CC2，MR-CIS和MRCISD方法对垂直激励，S1和S2最小值以及交叉煤层的最小值进行了支持计算。光动力学过程始于从S2π**状态到S2状态的πOπ*最小值的快速（<100 fs）平面弛豫。计算表明，此阶段实际上涉及两个π激发态（表示为ππ*和πOπ*）。胸腺嘧啶可以钝化成S1的时间到达S2 / S1交叉点，这既因状态之间的特征变化以及S2表面的平整度而延迟。在交叉煤层的最低能量区域，平均在2.6 ps的时间内发生这种失活。之后，胸腺嘧啶松弛至S1状态的nπ*最小值，一直保持到转移到基态。当前的动力学模拟表明，不仅πOπ* S2俘获，而且nπ* S1最小值中的俘获都有助于延长胸腺嘧啶的激发态寿命。

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