Femtosecond Raman-Induced Kerr Effect Study of Temperature-Dependent Intermolecular Dynamics in Molten Bis(trifluoromethylsulfonyl)amide Salts: Effects of Cation Species
Femtosecond Raman-Induced Kerr Effect Study of Temperature-Dependent Intermolecular Dynamics in Molten Bis(trifluoromethylsulfonyl)amide Salts: Effects of Cation Species
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熔融双（三氟甲基磺酰基）酰胺盐中温度依赖性分子间动力学的飞秒拉曼诱导克尔效应研究：阳离子种类的影响
DOI：
10.1021/acs.jpcb.8b03302
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
Shirota Hideaki
中科院分区：
文献类型：
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作者：
Kakinuma Shohei;Shirota Hideaki
在本研究中，我们利用飞秒喇曼诱导克尔效应光谱研究了阳离子结构对离子液体分子间振动动力学温度依赖性的影响。本研究中使用的离子液体是阳离子1-丁基-3-甲基咪唑[C4MIm]+、1-丁基-1-甲基吡咯烷[C4Py]+、1-丁基吡啶[C4Py]+、丁基二乙基甲基铵[N1224]+、三乙基甲基铵[N2228]+和三乙基膦[P2228]+的双(三氟甲基磺酰)胺[NTF_2]−盐。所有的离子液体都表现出随温度变化的低频光谱。芳香族和非芳香族阳离子液体的光谱随温度变化的差异尤为显著。在芳香族阳离子液体[C4MIm][NTf2]和[C4Py][NTf2]的情况下，随着温度的升高，在约50 cm-1以下的低频区光谱强度增加，约80 cm-1处的高频分量向低频方向移动。相反，基于非芳香族阳离子的离子液体仅在50 cm-1以下的低频区随温度升高而增加，而在50 cm-1以上的光谱的高频区随温度的变化不大。这些结果表明，芳环的存在或不存在是决定光谱特征随温度变化的主要因素，特别是在高频区域。我们还发现，非芳香族四元阳离子的烷基链长和中心原子对光谱特征的温度依赖性影响不大。芳香族阳离子液体的一阶矩比非芳香族阳离子液体的一阶矩对温度更敏感。还考察了离子液体的粘度和脆性随温度的变化。
In this study, we have investigated the effects of cation structures on the temperature dependence of the intermolecular vibrational dynamics of ionic liquids using femtosecond Raman-induced Kerr effect spectroscopy. The ionic liquids used in this study are bis(trifluoromethylsulfonyl)amide [NTf2]−salts of the cations 1-butyl-3-methylimidazolium [C4MIm]+, 1-butyl-1-methylpyrrolidinium [Pyrr14]+, 1-butylpyridinium [C4Py]+, butyldiethylmethylammonium [N1224]+, triethyloctylammonium [N2228]+, and triethyloctylphosphonium [P2228]+. All of the ionic liquids show temperature-dependent low-frequency spectra. A difference in the temperature dependence between the spectra of the aromatic and nonaromatic cation based ionic liquids is especially significant. In the case of the aromatic cation based ionic liquids [C4MIm][NTf2] and [C4Py][NTf2], the spectral intensities in the low-frequency region below ca. 50 cm–1increase and the high-frequency components at ca. 80 cm–1shift to lower frequencies with rising temperature. In contrast, the ionic liquids based on nonaromatic cations only exhibit an increase in the low-frequency region below ca. 50 cm–1with increasing temperature, while the high-frequency region of the spectra above ca. 50 cm–1shows little change with variation of the temperature. These results suggest that the presence or absence of aromatic rings is the main factor in determining the temperature-dependent spectral features, particularly in the high-frequency region. We also found that the alkyl chain length and central atoms of the nonaromatic quaternary cations do not have much influence on the temperature-dependent spectral features. The first moments of the aromatic cation based ionic liquids are a little more sensitive to temperature than those of the nonaromatic cation based ionic liquids. The temperature-dependent viscosities and fragilities of the ionic liquids have also been examined.