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Rotamer-Specific Photoisomerization of Difluorostilbenes from Transient Absorption and Transient Raman Spectroscopy
The Journal of Physical Chemistry B ( IF 3.3 ) Pub Date : 2018-01-05 00:00:00 , DOI: 10.1021/acs.jpcb.7b09283
M. Quick 1 , A. L. Dobryakov 1 , I. N. Ioffe 2 , F. Berndt 1 , R. Mahrwald 1 , N. P. Ernsting 1 , S. A. Kovalenko 1
Affiliation  

Photoisomerization of 2,2′-, 3,3′-, and 4,4′-difluorostilbene (F2, F3, F4, respectively) in n-hexane, perfluoro-n-hexane, and acetonitrile is studied with broadband transient absorption (TA) and femtosecond stimulated Raman (FSR) spectroscopy and by DFT/TDDFT calculations. F2 and F3 possess three rotamers (rotational isomers) each, while F4 has one single conformation only. These differences are reflected in TA and FSR spectra. Thus F4 reveals a monoexponential decay of TA with τ1 = 172 ps in n-hexane, as expected for a single species. For F2 and F3, the decays are biexponential in all solvents, corresponding to two distinctly discerned rotamers or rotamer fractions. Specifically, for F2 in n-hexane, τ1 = 357 ps (83%) and τ2 = 62 ps (17%), and for F3 in the same solvent, τ1 = 222 ps (57%), and τ2 = 81 ps (43%). The weights in brackets agree with theoretically estimated ground-state abundances of the rotamers. Furthermore, a global fit of the TA and FSR data allows us to extract the spectra of the pure rotamers. The Raman spectra of S0 and S1 are in qualitative agreement with calculations.

中文翻译:

瞬态吸收和瞬态拉曼光谱法研究二氟丁苯的旋转异构体特异性光异构化

在2,2' - ,3,3'-和4,4'- difluorostilbene(F2,F3,F4,分别地)光致异构化Ñ己烷,全氟Ñ己烷,乙腈等进行了研究与宽带瞬态吸收( TA和飞秒激发拉曼光谱(FSR)以及DFT / TDDFT计算。F2和F3各自具有三个旋转异构体(旋转异构体),而F4仅具有一个单一构象。这些差异反映在TA和FSR光谱中。因此F4揭示了TA的单指数衰减与τ 1 = 172个ps的在Ñ正己烷,如预期的单一物种。对于F2和F3,在所有溶剂中的衰减都是双指数的,对应于两个截然不同的旋转异构体或旋转异构体馏分。具体而言,在F2 Ñ己烷,τ1 = 357皮秒(83%)和τ 2 = 62皮秒(17%),以及用于F3在相同溶剂中,τ 1 = 222皮秒(57%),和τ 2 = 81皮秒(43%)。括号中的权重与理论上估计的旋转子的基态丰度相符。此外,TA和FSR数据的全局拟合使我们能够提取纯旋转异构体的光谱。S 0S 1的拉曼光谱与计算定性一致。
更新日期:2018-01-05
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