Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia.
J Chem Phys. 2021 Nov 14;155(18):184302. doi: 10.1063/5.0071847.
Certain chemical groups give rise to characteristic excited-state deactivation mechanisms. Here, we target the role of a protonated N-N chemical group in the excited-state deactivation of protonated indazole by comparison to its isomer that lacks this group, protonated benzimidazole. Gas-phase protonated indazole and protonated benzimidazole ions are investigated at room temperature using picosecond laser pump-probe photodissociation experiments in a linear ion-trap. Excited state lifetimes are measured across a range of pump energies (4.0-5.4 eV). The ππ* lifetimes of protonated indazole range from 390 ± 70 ps using 4.0 eV pump energy to ≤18 ps using 4.6 eV pump energy. The ππ* lifetimes of protonated benzimidazole are systematically longer, ranging from 3700 ± 1100 ps at 4.6 eV pump energy to 400 ± 200 ps at 5.4 eV. Based on these experimental results and accompanying quantum chemical calculations and potential energy surfaces, the shorter lifetimes of protonated indazole are attributed to πσ* state mediated elongation of the protonated N-N bond.
某些化学基团会导致特征的激发态失活机制。在这里，我们通过比较其缺少该基团的异构体——质子化苯并咪唑，来研究质子化吲哚中质子化 N-N 化学基团在质子化吲哚激发态失活中的作用。在室温下，使用皮秒激光泵浦探测光解实验，在线性离子阱中研究了气相质子化吲哚和质子化苯并咪唑离子。在一系列泵能量（4.0-5.4 eV）下测量了激发态寿命。使用 4.0 eV 泵能量时，质子化吲哚的 ππ寿命范围为 390 ± 70 ps，使用 4.6 eV 泵能量时，寿命范围为 ≤18 ps。质子化苯并咪唑的 ππ寿命则更长，使用 4.6 eV 泵能量时，寿命范围为 3700 ± 1100 ps，使用 5.4 eV 泵能量时，寿命范围为 400 ± 200 ps。基于这些实验结果和伴随的量子化学计算和势能面，质子化吲哚较短的寿命归因于 πσ* 态介导的质子化 N-N 键的伸长。
