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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Time-Resolved Photoelectron Studies of Thiophene and 2,5-Dimethylthiophene
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Time-Resolved Photoelectron Studies of Thiophene and 2,5-Dimethylthiophene

机译：噻吩和2,5-二甲基噻吩的时间分辨光电子研究

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摘要

The photoinduced dynamics of thiophene and 2,S-dimethylthiophene (2,5-DMT) were investigated upon excitation at 200 and 255 nm (2,5-DMT only) using time-resolved photoelectron spectroscopy and compared with results from ab initio coupled cluster calculations. For thiophene, depopulation of the initially excited B 2 (pi(3)pi(4)*) state to the lower-lying A(1) (pi(3)pi(4)*) state occurs within 25 +/- 20 fs, with a subsequent bifurcation into a ring-puckering channel and a ring-opening channel with lifetimes of 80 +/- 20 and 450 +/- 50 fs, respectively. For 2,5-DMT, the dynamics following excitation at 200 nm is described by a monoexponential decay with a time constant of 120 +/- 20 fs, while that following excitation at 255 nm is best fit by a biexponential decay with time constants of 115 +/- 20 fs and 15 +/- 3 ps, respectively. The fast signal observed after excitation of 2,5-DMT is assigned to the ring-opening channel, which is favored with respect to thiophene due to a lower excited-state barrier along the ring-opening coordinate and an increased inertia toward the ring-puckering channel. Coupled cluster calculations have been undertaken to compare the relaxation dynamics of thiophene to thiazole and isothiazole. For the latter two molecules, we find a strong gradient along the ring-opening coordinate in the Franck-Condon region of the initially populated pi pi* state and predict that ring-opening is the dominating relaxation channel after photoexcitation. We use the extracted information for a comparison of the thiophene dynamics with the light-induced processes observed in other five-membered heterocyclic molecules.
机译：使用时间分辨的光电子光谱法在200和255nm（仅2,5-DMT）激发时研究了噻吩和2，S-二甲基噻吩（2,5-DMT）的光诱导的动力学，并与AB Initio耦合簇的结果进行比较计算。对于噻吩，最初激发的B 2（Pi（3）Pi（4）*）状态至下位于左侧A（1）（PI（3）PI（4）*）状态发生在25 +/-20之间FS，随后分叉进入环形褶皱通道和开环通道，分别具有80 +/-20和450 +/- 50 fs的寿命。对于2,5-DMT，通过具有120 +/-20fs的时间常数的单凸起衰减描述了200nm之后的动力学，而255nm的激发是最合适的，通过与时间常数的Biexponential衰减最合适115 +/- 20 fs和15 +/- 3 ps。在2,5-DMT激励后观察到的快速信号被分配给开环通道，其由于沿着开环坐标较低的激发 - 状态屏障而受到相对于噻吩的青睐，并且朝向环的增加的惯性 - 褶皱通道。已经进行了耦合的聚类计算，以比较噻吩的松弛动态至噻唑和异噻唑。对于后两种分子，我们在最初填充的PI PI *状态的Franck-Condon区域中找到一个强度梯度，并预测光透镜后的开环是主导的松弛通道。我们使用提取的信息进行噻吩动态与在其他五元杂环分子中观察到的光诱导过程的比较。

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