Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, United States.
Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99354, United States.
J Phys Chem Lett. 2022 Nov 24;13(46):10863-10870. doi: 10.1021/acs.jpclett.2c02523. Epub 2022 Nov 16.
Excited-state dynamics of -4,4'-azopyridine in ethanol is studied using femtosecond transient absorption with 30 fs temporal resolution. Exciting the system at three different wavelengths, 460 and 290 (275) nm, to access the S * and S * electronic states, respectively, reveals a 195 cm vibrational coherence, which suggests that the same mode is active in both * and * relaxation channels. Following S-excitation, relaxation proceeds via a nonrotational pathway, where a fraction of the * population is trapped in a planar minimum (lifetime, 2.1 ps), while the remaining population travels further to a second shallow minimum (lifetime, 300 fs) prior to decay into the ground state. Population of the S state leads to 30 fs nonrotational relaxation with a concurrent buildup of * population and nearly simultaneous formation of hot ground-state species. An increase in the -isomer quantum yield upon * versus * excitation is observed, which is opposite to -azobenzene.
使用具有 30fs 时间分辨率的飞秒瞬态吸收技术研究了 -4,4'-偶氮吡啶在乙醇中的激发态动力学。在三个不同波长（460nm 和 290nm（275nm））处激发系统，分别进入 S和 S电子态，揭示了 195cm 的振动相干性，这表明相同的模式在和弛豫通道中都很活跃。S 激发后，通过非旋转途径进行弛豫，其中一部分种群被捕获在平面最小势阱中（寿命为 2.1ps），而其余种群在衰减到基态之前进一步迁移到第二个浅最小势阱（寿命为 300fs）。S 态的布居导致 30fs 的非旋转弛豫，同时种群的增加和热基态物种的几乎同时形成。与 -偶氮苯相反，观察到*激发时 -异构体量子产率的增加。
