Department of Nanomaterial Science, Graduate School of Advanced Integration Science, Chiba University, 1-33 Yayoi, Inage-ku, Chiba 263-8522, Japan.
J Phys Chem B. 2011 Sep 22;115(37):10860-70. doi: 10.1021/jp206266e. Epub 2011 Aug 30.
The interionic vibrations in imidazolium-based dicationic ionic liquids (ILs) containing the bis(trifluoromethylsulfonyl)amide (NTf(2)) counteranion were investigated using femtosecond optical-heterodyne-detected Raman-induced Kerr effect spectroscopy. The microscopic nature of the dicationic ILs ([C(n)(MIm)(2)]NTf(2), where n = 6, 10, and 12; MIm = N-methylimidazolium) was compared with that of the corresponding monocationic ILs ([C(n)MIm][NTf(2)], where n = 3, 5, and 6) used as reference samples. Low-frequency Kerr spectra within the frequency range 0-200 cm(-1) of the ILs revealed that (i) the spectral profile of the dicationic ILs as well as that of the corresponding monocationic ILs is bimodal; (ii) the difference in the spectral shapes of the dicationic and monocationic ILs is greater for [C(6)(MIm)(2)]NTf(2) and [C(3)MIm][NTf(2)] than for the ILs with longer alkylene linker/alkyl groups, namely [C(10)(MIm)(2)]NTf(2) and [C(5)MIm][NTf(2)], and [C(12)(MIm)(2)]NTf(2) and [C(6)MIm][NTf(2)]; (iii) the small difference between the dicationic and monocationic ILs is confirmed by the relative intensity of the low-frequency component (ca. 17 cm(-1)) to the high-frequency component (ca. 70 cm(-1)); and (iv) the spectral profiles of the three dicationic ILs are not very different, but the line-shape of the low-frequency Kerr spectrum of 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)amide ([C(3)MIm][NTf(2)]) is significantly different from those of the other two monocationic ILs whose cations have a longer alkyl group. The distinguished line-shape of the low-frequency Kerr spectrum of [C(3)MIm][NTf(2)] from the other ILs can be accounted for by the homogeneous nature in the microstructure of the IL, but the other ILs indicate microsegregation structures due to the longer nonpolar alkylene linker or alkyl group in the cations.
使用飞秒光外差探测拉曼诱导克尔效应光谱研究了含双（三氟甲烷磺酰基）酰胺 (NTf(2) ) 抗衡阴离子的咪唑鎓基二阳离子离子液体（ILs）中的离子间振动。将二阳离子 ILs ([C(n)(MIm)(2)]NTf(2)，其中 n = 6,10 和 12；MIm = N-甲基咪唑鎓) 的微观性质与作为参考样品的相应单阳离子 ILs ([C(n)MIm][NTf(2)]，其中 n = 3,5 和 6) 进行了比较。ILs 在 0-200 cm(-1) 频率范围内的低频 Kerr 光谱表明：(i) 二阳离子 ILs 的光谱轮廓以及相应的单阳离子 ILs 的光谱轮廓呈双峰状；(ii) 二阳离子和单阳离子 ILs 的光谱形状差异对于 [C(6)(MIm)(2)]NTf(2) 和 [C(3)MIm][NTf(2)] 比对于具有更长的亚烷基连接/烷基基团的 ILs 更大，即 [C(10)(MIm)(2)]NTf(2) 和 [C(5)MIm][NTf(2)]，以及 [C(12)(MIm)(2)]NTf(2) 和 [C(6)MIm][NTf(2)]；(iii) 通过低频分量（约 17 cm(-1)) 与高频分量（约 70 cm(-1)) 的相对强度证实了二阳离子 ILs 之间的微小差异；(iv) 三种二阳离子 ILs 的光谱轮廓差异不大，但 1-甲基-3-丙基咪唑鎓双（三氟甲烷磺酰基）酰胺 ([C(3)MIm][NTf(2)]) 的低频 Kerr 光谱的线形状与其他两个阳离子具有更长烷基基团的单阳离子 ILs 明显不同。[C(3)MIm][NTf(2)] 与其他 ILs 的低频 Kerr 光谱的独特线形状可以用 IL 微观结构的均匀性来解释，但其他 ILs 由于阳离子中较长的非极性亚烷基连接或烷基基团而表明微分离结构。
