Imidazolium camphorsulfonamides: Chiral catanionic liquid crystals with tunable thermal properties

We report the synthesis of novel chiral catanionic liquid crystals bearing camphorsulfonamide substructures. The phase behaviour of these long-chain substituted imidazolium sulphates and sulfonates was investigated using X-ray diffraction (XRD), polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). We observed that the phase behaviour clearly depends on the substitution of both cation and anion. The chiral camphorsulfonamide substructures have an unfavourable influence on the formation of liquid crystalline (LC-) phases. Contrary to N,N′-di-alkyl-imidazolium salts, the formation of LC phases was only observed when both cation and anion are substituted with long alkyl chains (C12 or C16). Furthermore, the phase transition temperatures depend on the chain length of the alkyl groups, as higher phase transition temperatures were observed for compounds bearing longer alkyl chains. However, no macroscopic evidence for the formation of chiral mesophases was obtained.

The combination of long-chain substituted chiral imidazolium camphorsulfonamide cations with anionic sulfate or sulfonate surfactants yielded catanionic ionic liquid crystals with tuneable thermal properties.Figure optionsDownload high-quality image (117 K)Download as PowerPoint slideResearch highlights
► Straightforward synthesis of catanionic ionic liquid crystals bearing chiral camphorsulfonamide groups.
► Formation of lamellar SmA phases.
► Change from separated bilayers in the crystalline state to interdigitated bilayers in the LC state.
► Control of the thermal properties via the alkyl chain lengths on both cation and anion.
► No macroscopic evidence for the formation of chiral mesophases was obtained.