Ionization Dynamics of a Phenylenediamine Derivative in Solutions as Revealed by Femtosecond Simultaneous and Stepwise Two-Photon Excitation
Ionization Dynamics of a Phenylenediamine Derivative in Solutions as Revealed by Femtosecond Simultaneous and Stepwise Two-Photon Excitation
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飞秒同时和逐步双光子激发揭示溶液中苯二胺衍生物的电离动力学
DOI：
10.1039/c8cp06530f
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
H. Miyasaka
中科院分区：
文献类型：
--
作者：
M. Koga;Y. Yoneda;H. Sotome;H. Miyasaka
采用非共振同步飞秒瞬时吸收光谱和共振分步双光子激发方法，直接观测了苯二胺衍生物在正己烷、乙醇和乙腈溶液中的光致电离动力学。当通过非共振双光子激发将溶质选择性激发到与气相中的电离势几乎相等的能级时，在极性和非极性溶液中观察到迅速出现自由基阳离子(约100-200fs)。另一方面，在基态激发能级比气相电离势低0.8 eV的情况下，自由基阳离子只出现在亚ps到ps时间尺度的极性溶液中，这表明即使在极性溶液中，光电离也不是直接从高电子激发态发生的。乙醇和乙腈溶液的动力学比较有力地表明，在极性溶液中，导致电离的前体物种的溶剂化过程在较低能量的电子喷射过程中起着关键作用。
Femtosecond transient absorption spectroscopy with off-resonant simultaneous and resonant stepwise two-photon excitation methods were applied to the direct observation of photoionization dynamics of a phenylenediamine derivative in n-hexane, ethanol and acetonitrile solutions. Upon the selective excitation of the solute via the off-resonant two-photon excitation to the energy level almost equivalent with the ionization potential in the gas phase, rapid appearance of the radical cation (within ca. 100–200 fs) was observed in polar and nonpolar solutions. On the other hand, in the case where the excited energy level from the ground state is 0.8 eV lower than the ionization potential in the gas phase, the radical cation appears only in polar solutions in sub-ps to ps time scales, indicating that the photoionization does not occur directly from the highly electronically excited state even in the polar solution. Comparison of the dynamics between ethanol and acetonitrile solutions strongly suggested that the solvation process of the precursor species leading to the ionization took a crucial role in the electron ejection process with lower energy in polar solutions.