Ionic liquid crystals derived from guanidinium salts: induction of columnar mesophases by bending of the cationic core

Meta-alkyloxyguanidinium salt-based ionic liquid crystals 3-5, 7 and 9 were synthesised and investigated with respect to the influence of meta-substitution of the cation on the mesomorphic properties. As expected, bending of the mesogenic cation in ion pairs with simple counterions (3-5) decreased melting points irrespective of the anion, but clearing points were influenced by the anion radii. SmA mesophases were formed in all cases. The mesophase formation in guanidinium sulphonates 7 and 9, however, depended not only on meta-substitution but also on the anion, the respective difference between alkyl chain lengths in cation and anion and the number of alkyloxy substituents on the sulphonate, for which a change of mesophase type from smectic to columnar phases was observed. For two derivatives, 7e and 9b, room temperature SmA and Col(h) mesophases could be obtained that were stable for a temperature range of 91K and 55K, respectively. A packing model for both smectic and columnar phases based on powder XRD data was proposed.