State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, 457 Zhongshan Road, Dalian 116023, Liaoning, China.
Phys Chem Chem Phys. 2018 Jun 6;20(22):15015-15021. doi: 10.1039/c8cp00883c.
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.
采用时间分辨光电子成像方法研究了在 265.7-216.7nm 波长范围内激发时，2,5-二甲基吡咯的超快激发态动力学。结果发现，较长波长（265.7-250.2nm）激发导致 S1（1πσ*）态的布居，其在约 90fs 内衰减出光离化窗口。在较短的泵浦波长（242.1-216.7nm）下，分配不太明确。我们初步将初始光激发态（s）分配给 1π3p 里德堡态（s），对于泵浦波长为 242.1nm、238.1nm、232.6nm 和 216.7nm 的情况，其寿命分别为 159±20fs、125±15fs、102±10fs 和 88±10fs。内部转换到 S1（1πσ*）态最多代表一个次要的衰减通道。还讨论了取代基对吡咯激发态衰减动力学的影响。吡咯环上的甲基取代似乎增强了从 1π3p 里德堡态到基态的直接内部转换，而氮原子上的甲基取代影响较小，内部转换到 S1（πσ*）态是主要通道。
