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Electron-proton transfer mechanism of excited-state hydrogen transfer in phenol−(NH3)n (n = 5) studied by delayed ionization detected femtosecond time-resolved NIR spectroscopy
Chemical Physics ( IF 2.3 ) Pub Date : 2018-08-03 , DOI: 10.1016/j.chemphys.2018.08.004
Mitsuhiko Miyazaki , Nozomi Washio , Masaaki Fujii

The reaction mechanism of a hydrogen transfer reaction has a fundamental importance in wide ranges of chemistry, such as redox reactions and enzymatic reactions. The excited-state hydrogen transfer (ESHT) of phenol–(NH3)n clusters is a benchmark system to study solvation effects on the ESHT reaction mechanism. Recently, we reported that the mechanism of the ESHT reaction changes to electron–proton decoupled transfer for phenol–(NH3)5, from a concerted hydrogen atom transfer for clusters with n < 5, based on observations of picosecond time-resolved NIR/IR spectroscopy (Miyazaki et al., 2018). However, the dynamics of the initial electron-transfer process has not been addressed because the rate is faster than the time-resolution of the picosecond time-resolved measurement. In this study, femtosecond time-resolved NIR spectroscopy was applied to the phenol–(NH3)5 to elucidate the initial electron-transfer process. Time evolutions probed in the range of 6000–9000 cm−1 detected two rise components that can be ascribed to electronic absorptions of the Franck-Condon region of the excitation and the transient charge-transfer complex, respectively. A kinetic analysis determined the time-scale of the initial charge-transfer process to be τCT = 370 ± 55 fs. The fast reaction time supports (almost) a barrier-less charge transfer process predicted by a theoretical calculation that shows solvation-induced strong mixing of ππ*-πσ* states.



中文翻译:

 延迟电离飞秒时间分辨NIR光谱研究苯酚-(NH 3nn = 5)中激发态氢转移的电子-质子转移机理

氢转移反应的反应机理在诸如氧化还原反应和酶促反应等广泛的化学领域中具有根本的重要性。苯酚-(NH 3n团簇的激发态氢转移(ESHT)是研究溶剂化对ESHT反应机理的基准系统。最近,我们报道了ESHT反应的机构改变到电子质子为苯酚(NH解耦传输35用于与集群,从协调一致的氢原子转移Ñ <5,基于皮秒时间分辨NIR / IR光谱的观察结果(Miyazaki等人,2018)。但是,由于速率比皮秒时间分辨测量的时间分辨率快,因此尚未解决初始电子传输过程的动力学问题。在这项研究中,飞秒时间分辨NIR光谱应用于苯酚-(NH 35来阐明初始电子转移过程。在6000–9000 cm -1范围内探测到的时间演变检测到两个上升成分,分别可归因于激发和瞬态电荷转移络合物的Franck-Condon区的电子吸收。动力学分析确定了初始电荷转移过程的时间尺度为τCT  = 370±55 fs。快速的反应时间支持(几乎)无障碍电荷转移过程,该过程由理论计算预测,表明溶剂化引起ππ * -πσ *状态的强混合。

更新日期:2018-11-29
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