Femtosecond Raman-Induced Kerr Effect Study of Temperature-Dependent Intermolecular Dynamics in Pyrrolidinium-Based Ionic Liquids: Effects of Anion Species
Femtosecond Raman-Induced Kerr Effect Study of Temperature-Dependent Intermolecular Dynamics in Pyrrolidinium-Based Ionic Liquids: Effects of Anion Species
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吡咯烷基离子液体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：阴离子种类的影响
DOI：
10.1021/acs.jpcb.8b10269
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发表时间：
2019
期刊：
影响因子：
--
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
利用飞秒拉曼诱导克尔效应光谱研究了吡咯烷离子液体（ILs）与10种不同阴离子的分子间振动动力学随温度的变化.不同阴离子的温度依赖性振动光谱特征不同。对于顶部为球形阴离子的离子液体，如四氟硼酸根、六氟磷酸根和三氟甲磺酸根，在50 cm-1以下的低频区光谱强度随温度升高而增加，而在50 cm-1以上的高频区光谱强度几乎不变.在双（氟磺酰基）酰胺和双（全氟烷基磺酰基）酰胺盐中也发现了类似的温度依赖性特征。然而，在各自的温度相对于293 K的差异光谱表明，光谱的双（氟磺酰基）酰胺和双（全氟烷基磺酰基）酰胺盐是在低于50 cm-1的低频区域的温度敏感性更高的四氟硼酸盐，六氟磷酸盐，和三氟甲磺酸盐相比。1-丁基-1-甲基吡咯烷鎓离子液体的光谱与双氰胺和三氰基甲基阴离子显示出特征的温度依赖性;除了在低于50 cm-1的低频区域的光谱强度的增加，在50 cm-1以上的高频侧的光谱的红移观察到随着温度的升高。这意味着平面双氰胺和三氰甲基阴离子的自由振动对低频光谱有很大贡献。我们还比较了1-丁基-1-甲基吡咯烷鎓离子液体和1-（2-甲氧基乙基）-1-甲基吡咯烷鎓离子液体与一些阴离子的温度依赖性低频光谱。虽然在70-150 cm-1范围内光谱形状略有不同，这可以归因于阳离子的分子内振动模式，但光谱形状的温度依赖性非常相似，表明阳离子侧基中的醚取代对低频光谱的温度依赖性影响不大。的IL的脆弱性也估计从温度依赖性粘度和玻璃化转变温度。脆性参数似乎与主要由离子液体的分子间振动引起的低频光谱带的第一阶矩的温度依赖性相关。
We investigated the temperature dependence of the intermolecular vibrational dynamics of pyrrolidinium-based ionic liquids (ILs) with 10 different anion species using femtosecond Raman-induced Kerr effect spectroscopy. The features of the temperature-dependent vibrational spectra vary with the different anions. In the case of the ILs with spherical top anions, such as tetrafluoroborate and hexafluorophosphate, and trifluoromethanesulfonate, the spectral intensity in the low-frequency region below 50 cm–1increases with rising temperature, while that in the high-frequency region above 50 cm–1remains almost unchanged. Similar temperature-dependent features were also found in the bis(fluorosulfonyl)amide and bis(perfluoroalkylsulfonyl)amide salts. However, the difference spectra at respective temperature relative to 293 K indicate that the spectra of the bis(fluorosulfonyl)amide and bis(perfluoroalkylsulfonyl)amide salts are more temperature-sensitive in the low-frequency region below 50 cm–1compared to those of the tetrafluoroborate, hexafluorophosphate, and trifluoromethanesulfonate salts. The spectra of 1-butyl-1-methylpyrrolidinium-based ILs with dicyanamide and tricyanomethide anions show a characteristic temperature dependence; in addition to an increase of the spectral intensity in the low-frequency region below 50 cm–1, a red shift of the spectra in the high-frequency side above 50 cm–1was observed with increasing temperature. This implies that the librational motions of planar dicyanamide and tricyanomethide anions contribute substantially to the low-frequency spectra. We also compared the temperature-dependent low-frequency spectra of 1-butyl-1-methylpyrrolidinium- and 1-(2-methoxyethyl)-1-methylpyrrolidinium-based ILs with some anions. Although the spectral shapes are slightly different in the range of 70–150 cm–1, which can be attributed to the intramolecular vibrational modes of the cations, the temperature dependence of the spectral shapes is quite similar, indicating that the ether substitution in the cation side groups has little effects on the temperature dependence of the low-frequency spectra. The fragilities of the ILs were also estimated from the temperature-dependent viscosities and the glass-transition temperatures. The fragility parameter seems to be correlated with the temperature dependence of the first moment of the low-frequency spectral bands mainly arising from the intermolecular vibrations of the ILs.