Nanostructural organization and anion effects on the temperature dependence of the optical Kerr effect spectra of ionic liquids.
Nanostructural organization and anion effects on the temperature dependence of the optical Kerr effect spectra of ionic liquids.
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DOI：
10.1021/jp066481b
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发表时间：
2007-01
期刊：
影响因子：
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通讯作者：
D. Xiao;J. Rajian;A. Cady;S. Li;R. Bartsch;E. Quitevis
中科院分区：
文献类型：
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作者：
D. Xiao;J. Rajian;A. Cady;S. Li;R. Bartsch;E. Quitevis
通过使用光学外差检测拉曼诱导克尔效应光谱研究了三种咪唑鎓离子液体的分子间光谱随温度的变化。离子液体包含 1,3-戊基甲基咪唑鎓阳离子 ([C(5)mim]+) 和阴离子、溴离子 (Br-)、六氟磷酸盐 (PF(6)-) 和双(三氟甲磺酰基)亚胺 (NTf(2)-)。 [C(5)mim][NTf(2)] 的光学克尔效应 (OKE) 光谱与温度相关，而 [C(5)mim]Br 和 [C(5)mim][PF6] 的 OKE 光谱与温度无关。鉴于这些室温离子液体（RTIL）的堆积密度与温度相关的事实，这些结果是令人惊讶的。 OKE 光谱的温度依赖性以及 [C(5)mim]Br 和 [C(5)mim][PF(6)] 中堆积密度的温度依赖性表明这些液体的密度存在不均匀性。密度不均匀性的存在与最近的分子动力学模拟一致，分子动力学模拟表明RTIL是纳米结构组织的，具有由烷基链聚集产生的非极性区域和由阴离子和阳离子咪唑鎓环的电荷排序产生的离子网络。 OKE 光谱的温度依赖性差异根据 RTIL 极性区域的电荷有序程度合理化。
The intermolecular spectra of three imidazolium ionic liquids were studied as a function of temperature by the use of optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The ionic liquids comprise the 1,3-pentylmethylimidazolium cation ([C(5)mim]+), and the anions, bromide (Br-), hexafluorophosphate (PF(6)-), and bis(trifluoromethanesulfonyl)imide (NTf(2)-). Whereas the optical Kerr effect (OKE) spectrum of [C(5)mim][NTf(2)] is temperature-dependent, the OKE spectra of [C(5)mim]Br and [C(5)mim][PF6] are temperature-independent. These results are surprising in light of the fact that the bulk densities of these room temperature ionic liquids (RTILs) are temperature-dependent. The temperature independence of the OKE spectra and the temperature dependence of the bulk density in [C(5)mim]Br and [C(5)mim][PF(6)] suggest that there are inhomogeneities in the densities of these liquids. The existence of density inhomogeneities is consistent with recent molecular dynamics simulations that show RTILs to be nanostructurally organized with nonpolar regions arising from clustering of the alkyl chains and ionic networks arising from charge ordering of the anions and imidazolium rings of the cations. Differences in the temperature dependences of the OKE spectra are rationalized on the basis of the degree of charge ordering in the polar regions of the RTILs.