Femtosecond Stimulated Raman Scattering from Triplet Electronic States: Experimental and Theoretical Study of Resonance Enhancements
Femtosecond Stimulated Raman Scattering from Triplet Electronic States: Experimental and Theoretical Study of Resonance Enhancements
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DOI：
10.1021/acs.jpca.9b05955
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发表时间：
2019-09-12
影响因子：
2.9
通讯作者：
Elles, Christopher G.
中科院分区：
文献类型：
--
作者：
Barclay, Matthew S.;Caricato, Marco;Elles, Christopher G.
飞秒受激拉曼散射(FSRs)是一种探测分子结构动力学的光谱技术。这项技术通常依靠电子共振条件来增加信号强度或增强物种选择性，从而提供特定于振动模式的拉曼增强，并取决于共振电子态的特征。对于已经处于激发电子态的分子，以及多个电子态与拉曼激发能共振或接近共振的系统，共振条件是复杂的，这两种情况通常都是FSR的情况。本文研究了2-苯基噻吩基(PT)最低三重态FSRs谱的激发波长依赖性。除了共振条件使信号强度总体增加外，大多数拉曼光谱的相对强度对激发波长相对不敏感，并且光谱与忽略共振条件所得到的非共振光谱非常相似。另一方面，用梯度近似模拟共振条件计算的共振拉曼光谱正确地预测了少数模式的激发波长依赖关系，但高估了其他模式的相对增强。PT的三重态光谱的弱波长依赖性与同一分子的单重态FSRs光谱的情况形成了对比。我们将这种差异归因于同质加宽、重叠的T-N
Femtosecond stimulated Raman scattering (FSRS) is a spectroscopic technique that probes the structural dynamics of molecules. The technique typically relies on an electronic resonance condition to increase signal strength or enhance species selectivity, giving a Raman enhancement that is vibrational-mode-specific and depends on the character of the resonant electronic state. The resonance condition is complicated for molecules already in an excited electronic state and also for systems where multiple electronic states are resonant or nearly resonant with the Raman excitation energy, both of which are often the case for FSRS. This paper examines the excitation wavelength dependence of the FSRS spectrum for the lowest triplet state of 2-phenylthiophene (PT). Except for an overall increase of the signal strength due to the resonance condition, the relative intensities of most Raman bands are relatively insensitive to the excitation wavelength, and the spectrum is remarkably similar to the calculated off-resonance spectrum obtained by neglecting the resonance condition. On the other hand, calculated resonance Raman spectra using a gradient approximation to simulate the resonance condition correctly predict the excitation wavelength dependence for a few modes but overestimate the relative enhancement of others. The weak wavelength dependence of the triplet spectrum of PT contrasts the case of the singlet FSRS spectrum for the same molecule. We attribute this discrepancy to a combination of homogeneous broadening, overlapping T-N