Unraveling ultrafast dynamics in photoexcited aniline.
Unraveling ultrafast dynamics in photoexcited aniline.
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DOI：
10.1021/ja3029729
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发表时间：
2012-07
影响因子：
15
通讯作者：
G. Roberts;Craig Williams;J. D. Young;S. Ullrich;M. Paterson;V. Stavros
中科院分区：
文献类型：
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作者：
G. Roberts;Craig Williams;J. D. Young;S. Ullrich;M. Paterson;V. Stavros
结合超快时间分辨速度图成像 (TR-VMI) 方法和完整的活性空间自洽场 (CASSCF) 从头计算，研究苯胺（氨基苯）中的电子激发态动力学，并展望沿着嘌呤衍生 DNA 碱基中的氨基部分模拟 (1)πσ* 介导的动力学。实验与理论之间的协同作用使得能够在广泛的激发波长范围内建立控制苯胺动力学的光化学路径/圆锥形交叉点（CI）的全面图像。 TR-VMI 研究用宽带飞秒激光脉冲（以大于 250 nm (4.97 eV) 的波长为中心）激发到最低的 (1)ππ* 态 (1(1)ππ*)，但不会为 (1)πσ* 驱动的氨基上的 N-H 键裂变产生任何可测量的特征。在 250 至 >240 nm (<5.17 eV) 的波长之间，以 1(1)ππ*/(1)πσ* CI 从 1(1)ππ* 耦合到 (1)πσ* 态，可在 <1 ps 内通过 (1)πσ*/S(0) CI 促进超快非绝热 N-H 键裂变，这一概念得到了 CASSCF 结果的支持。为了激发更高的 2(1)ππ* 态，计算揭示了 2(1)ππ* 和 1(1)ππ* 态之间 CI 耦合的近乎无障碍的路径，使激发态群体能够通过快速顺序 2(1)ππ* → 1(1)ππ* → (1)πσ* → N-H 裂变机制演化，我们观察到这种裂变发生在 155 年 ± 30 fs（240 nm）。我们还假设，在 3(1)ππ* 表面受到 200 nm (6.21 eV) 激发后，类似的 CI 耦合级联可在 170 ± 20 fs 内促进 N-H 键沿 (1)πσ* 态断裂。特别具有启发性的事实是，CASSCF 计算的苯胺中的 CI 几何形状与之前计算的鸟嘌呤氨基部分的 CI 和势能分布非常相似，这强烈表明这里的结果可能为更好地理解这种普遍存在的遗传构件中 (1)πσ* 驱动的动力学奠定了良好的基础。
A combination of ultrafast time-resolved velocity map imaging (TR-VMI) methods and complete active space self-consistent field (CASSCF) ab initio calculations are implemented to investigate the electronic excited-state dynamics in aniline (aminobenzene), with a perspective for modeling (1)πσ* mediated dynamics along the amino moiety in the purine derived DNA bases. This synergy between experiment and theory has enabled a comprehensive picture of the photochemical pathways/conical intersections (CIs), which govern the dynamics in aniline, to be established over a wide range of excitation wavelengths. TR-VMI studies following excitation to the lowest-lying (1)ππ* state (1(1)ππ*) with a broadband femtosecond laser pulse, centered at wavelengths longer than 250 nm (4.97 eV), do not generate any measurable signature for (1)πσ* driven N-H bond fission on the amino group. Between wavelengths of 250 and >240 nm (<5.17 eV), coupling from 1(1)ππ* onto the (1)πσ* state at a 1(1)ππ*/(1)πσ* CI facilitates ultrafast nonadiabatic N-H bond fission through a (1)πσ*/S(0) CI in <1 ps, a notion supported by CASSCF results. For excitation to the higher lying 2(1)ππ* state, calculations reveal a near barrierless pathway for CI coupling between the 2(1)ππ* and 1(1)ππ* states, enabling the excited-state population to evolve through a rapid sequential 2(1)ππ* → 1(1)ππ* → (1)πσ* → N-H fission mechanism, which we observe to take place in 155 ± 30 fs at 240 nm. We also postulate that an analogous cascade of CI couplings facilitates N-H bond scission along the (1)πσ* state in 170 ± 20 fs, following 200 nm (6.21 eV) excitation to the 3(1)ππ* surface. Particularly illuminating is the fact that a number of the CASSCF calculated CI geometries in aniline bear an exceptional resemblance with previously calculated CIs and potential energy profiles along the amino moiety in guanine, strongly suggesting that the results here may act as an excellent grounding for better understanding (1)πσ* driven dynamics in this ubiquitous genetic building block.