Ionic liquid crystals with 1,2,3-triazole + tolane core and a pendant imidazolium unit: mesophases from one- to three-dimensional molecular organisation by the variation of alkoxy chains number and spacer length

Ionic liquid crystals (ILCs) are a class of materials that present a large and varied form of applicability and whose properties can change dramatically with small modifications in their molecular structure. It is, therefore, of great importance to improve the knowledge about the property–molecular structure relationship. In this study, we present the synthesis and characterisation of 7 new rod- and wedge-shaped ILCs, whose liquid crystalline behaviour variation is related to the variations in the number of alkoxy chains and/or in the spacer chain length. All compounds have a rigid core constituted by a tolane group and a 1,2,3-triazole heterocycle, which is connected to a pendant 1-methylimidazolium through a alkyl spacer chain. The mesomorphic properties were studied by DSC, thermogravimetric analysis, polarising optical microscopy, wide angle X-ray diffraction and SAXS with synchrotron radiation. The increase in the number of long alkoxy chains changed the molecular self-assembly from bilayered SmA₂ and SmC₂ to hexagonal columnar, passing through oblique columnar, bicontinuous cubic and hexagonal close-packed mesophase. On the other hand, the increase in the alkyl spacer chain length has an especially significant effect for the compounds with two terminal alkoxy chains, where a Col_o/Col_h – Cub_v – HCP phase sequences were observed.