Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
J Phys Chem A. 2011 Apr 28;115(16):3807-19. doi: 10.1021/jp107935f. Epub 2011 Jan 4.
Electron photodetachment from the aromatic anion phenolate excited into the π-π* singlet excited state (S(1)) in aqueous solution is studied with ultrafast transient absorption spectroscopy with a time resolution of better than 50 fs. Broad-band transient absorption spectra from 300 to 690 nm are recorded. The transient bands are assigned to the solvated electron, the phenoxyl radical, and the phenolate S(1) excited state, and confirmation of these assignments is achieved using both KNO(3) as electron quencher and time-resolved fluorescence to measure singlet excited state dynamics. The phenolate fluorescence lifetime is found to be short (∼20 ps) in water, but the fast decay is only in part due to the electron ejection channel from S(1). Using global target analysis, two electron ejection channels are identified, and we propose that both vibrationally hot S(1) state and the relaxed S(1) state are direct precursors for the solvated electron. Therefore, electron ejection is found just to compete with picosecond time scale vibrational relaxation and electronic radiationless decay channels. This contrasts markedly with <100 fs electron detachment processes for inorganic anions.
在水溶液中，通过时间分辨率优于 50 fs 的超快瞬态吸收光谱研究了芳香阴离子酚盐从π-π*单重激发态（S(1)）激发的电子光解。记录了从 300 到 690 nm 的宽带瞬态吸收光谱。瞬态带被分配给溶剂化电子、苯氧自由基和酚盐 S(1)激发态，并且通过使用 KNO(3)作为电子猝灭剂和时间分辨荧光来测量单重激发态动力学来确认这些分配。发现酚盐荧光寿命在水中很短（约 20 ps），但快速衰减不仅归因于 S(1)的电子发射通道。使用全局目标分析，鉴定了两个电子发射通道，我们提出振动热 S(1)态和弛豫 S(1)态都是溶剂化电子的直接前体。因此，电子发射发现仅与皮秒时间尺度的振动弛豫和电子无辐射衰减通道竞争。这与无机阴离子的<100 fs 电子脱附过程形成鲜明对比。
