Effects of Cyclic-Hydrocarbon Substituents and Linker Length on Physicochemical Properties and Reorientational Dynamics of Imidazolium-Based Ionic Liquids

We synthesized a series of alkylimidazolium-based ionic liquids (ILs) incorporating cyclopentyl, cyclohexyl, or phenyl groups as nonionic units substituted on an acyclic alkyl linker and characterized them with respect to physicochemical properties and reorientational dynamics. The effects of the nonionic substituents and linker length on the properties of these ILs were carefully examined. The physicochemical properties of the ILs are found to partially reflect the properties of the nonionic substituents. While the liquid densities showed a similar trend in linker-length dependence of each series of ILs, a distinct trend was observed for the shear viscosities of them. By comparison of correlation times obtained by 13C NMR spectroscopy, it is revealed that elongation of the linkers influences the characteristic effects of the nonionic substituents on the reorientational dynamics of the system.