Ultrafast excited-state dynamics of 2,5-dimethylpyrrole.
Ultrafast excited-state dynamics of 2,5-dimethylpyrrole.
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DOI：
10.1039/c8cp00883c
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发表时间：
2018-06
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通讯作者：
Dongyuan Yang;Yanjun Min;Zhichao Chen;Zhigang He;Kaijun Yuan;D. Dai;Xueming Yang;Guorong Wu
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作者：
Dongyuan Yang;Yanjun Min;Zhichao Chen;Zhigang He;Kaijun Yuan;D. Dai;Xueming Yang;Guorong Wu
用时间分辨光电子成像法研究了2，5-二甲基吡咯在265.7-216.7 nm波长激发后的超快激发态动力学。结果表明，在较长波长(265.7-250.2 nm)激发下，会产生S_1(1πσ*)态的布居，该布居约在90秒内衰减出光电离窗口。在较短的泵浦波长(242.1-216.7 nm)下，分配不那么清晰。我们初步将初始光激发态(S)归属于1π的3p里德堡态(S)，在泵浦波长分别为242.1、238.1、232.6和216.7 nm时，其寿命分别为159±20、125±15、102±10和88±10fs。内部转换到S1(1πσ*)状态最多表示一个较小的衰减通道。讨论了甲基取代对吡咯激发态衰变动力学的影响。吡咯环上的甲基取代似乎促进了从1π~3P里德堡态到基态的直接内转换，而N原子上的甲基取代影响较小，到S1(πσ*)态的内转换是主要通道。
The ultrafast excited-state dynamics of 2,5-dimethylpyrrole following excitation at wavelengths in the range of 265.7-216.7 nm is studied using the time-resolved photoelectron imaging method. It is found that excitation at longer wavelengths (265.7-250.2 nm) results in the population of the S1(1πσ*) state, which decays out of the photoionization window in about 90 fs. At shorter pump wavelengths (242.1-216.7 nm), the assignments are less clear-cut. We tentatively assign the initially photoexcited state(s) to the 1π3p Rydberg state(s) which has lifetimes of 159 ± 20, 125 ± 15, 102 ± 10 and 88 ± 10 fs for the pump wavelengths of 242.1, 238.1, 232.6 and 216.7 nm, respectively. Internal conversion to the S1(1πσ*) state represents at most a minor decay channel. The methyl substitution effects on the decay dynamics of the excited states of pyrrole are also discussed. Methyl substitution on the pyrrole ring seems to enhance the direct internal conversion from the 1π3p Rydberg state to the ground state, while methyl substitution on the N atom has less influence and the internal conversion to the S1(πσ*) state represents a main channel.