Aggregation behavior of dihexadecylviologen bistriflimide ionic liquid crystal in different solvents: influence of polarity and concentration.
Aggregation behavior of dihexadecylviologen bistriflimide ionic liquid crystal in different solvents: influence of polarity and concentration.
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DOI：
10.1039/c8cp03055c
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发表时间：
2018-09
期刊：
影响因子：
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通讯作者：
Shen Li;G. Saielli;Yanting Wang
中科院分区：
文献类型：
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作者：
Shen Li;G. Saielli;Yanting Wang
采用核磁共振氢谱、密度泛函理论计算和分子动力学模拟相结合的方法，研究了1，1‘-二十六烷基-4，4’-联吡啶二[双(三氟甲磺酰基)亚胺]盐(又称二十六烷基紫精双环戊二酰亚胺)在溴代乙腈(ACN)、二氯甲烷(DCM)和氯仿(CDCl3)中的聚集行为。我们发现，极性溶剂乙腈(ACN)不利于离子聚集和团簇形成。在所研究的整个浓度范围内，该体系似乎主要是由一个阳离子和两个阴离子组成的中性离子对，可能处于快速平衡(在核磁共振时间尺度上)，聚集体较小或略大。阳离子物种的扩散系数受浓度的影响很小。相反，氯仿(CDCl3)和二氯甲烷(DCM)的低极性溶剂在一定浓度以上更有利于团簇的形成，紫精在CDCl3中的扩散系数比在ACN中的扩散系数小得多，对浓度的依赖性也更强。分子动力学模拟得到的信息表明，聚集体的结构与紫精基离子液体和离子液晶的各向同性液体的结构相似。如此大的星系团的寿命似乎相对较长，超出了几十纳秒的时间尺度。此外，芳香族质子核磁共振的结果为紫精聚集体内部的介电常数提供了一些见解。
Solutions of 1,1'-dihexadecyl-4,4'-bipyridinium di[bis(trifluoromethanesulfonyl)imide] salt, also known as dihexadecylviologen bistriflimide, in deuterated acetonitrile (ACN), dichloromethane (DCM) and chloroform (CDCl3), respectively, were investigated by the combination of 1H and DOSY NMR spectroscopy, DFT calculations and MD simulation to understand the influence of solvent polarity and solute concentration (10-5-10-1 M) on its aggregation behavior. We found that the polar solvent acetonitrile (ACN) does not favor ion aggregation and cluster formation. In the whole range of concentrations investigated, the system appears to be dominated by neutral ion pairs composed of one cation and two anions, possibly in fast equilibrium (on the NMR time scale) with small or slightly larger aggregates. The diffusion coefficient of the cationic species is only weakly affected by concentration. In contrast, the low-polar solvents of chloroform (CDCl3) and dichloromethane (DCM) strongly favor cluster formation above a certain concentration and the viologen diffusion coefficient in CDCl3 is much smaller and more strongly dependent on concentration than that in ACN. The information obtained from the MD simulations suggests that the aggregates have a structure similar to the isotropic liquid phase of the viologen-based ionic liquids and ionic liquid crystals. The lifetimes of such large clusters appear to be relatively long, beyond the time scale of tens of nanoseconds. Moreover, the results from the aromatic proton NMR resonances provide some insights on the dielectric constants inside the viologen aggregates.