Department für Chemie, Ludwig-Maximilians-Universität München, Butenandt-Strasse 11, 81377 München, Germany.
J Phys Chem A. 2012 Nov 1;116(43):10518-28. doi: 10.1021/jp307437f. Epub 2012 Oct 19.
A combination of experimental and theoretical techniques is used to study the photoinduced ring-opening/closure of a trifluoromethyl-indolylfulgide. Time-resolved UV/vis pump and IR probe measurements are performed in the subpicosecond to 50 ps time range. Probing in the mid-IR between 1200 and 1900 cm(-1) provides mode-specific dynamics and reveals photochemical reaction dynamics as well as the presence of a noncyclizable conformer. Ring-opening occurs with about 3 ps. Experiments on the open isomer confirm that the ring-closure occurs on the subpicosecond time scale. They also show a 10 ps transient that can be assigned to internal conversion of a noncyclizable conformer. Quantum chemical calculations with multireference methods are used to explore the complex potential energy landscape in the excited electronic state showing paths for ring-opening and closure reactions as well as for competing side-reactions. The calculations reveal that photoexcitation induces a charge transfer from the indole to the anhydride. The same charge transfer drives the system toward a low-energy conical intersection seam spreading from the closed to the open ring side and is responsible for the ultrafast relaxation to the ground state. The ultrafast photoreactivity comes at the expense of selectivity.
采用实验和理论技术相结合的方法研究了三氟甲基吲哚基呫吨的光诱导开环/闭环反应。在亚皮秒到 50 ps 的时间范围内进行了时间分辨的紫外/可见泵浦和红外探针测量。在 1200 到 1900 cm(-1) 的中红外范围内进行探测提供了特定模式的动力学信息，并揭示了光化学反应动力学以及不可环化构象的存在。开环反应发生在大约 3 ps。对开环异构体的实验证实，闭环反应发生在亚皮秒时间尺度上。它们还显示出一个 10 ps 的瞬态，可以归因于不可环化构象的内转换。采用多参考方法的量子化学计算用于探索激发电子态中的复杂势能面，显示了开环和闭环反应以及竞争副反应的途径。计算表明，光激发诱导吲哚向酐的电荷转移。相同的电荷转移促使系统向低能锥形交叉 seam 移动，从闭环向开环侧扩展，这是超快弛豫到基态的原因。超快光反应是以选择性为代价的。
