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.