Anisotropic ion-conductive supramolecular columnar liquid crystals composed of a benzonitrile derivative and ionic liquids

Abstract

Self-organized liquid-crystalline (LC) electrolytes, which feature externally controllable ion channels, are at the forefront of advanced materials for developing next generation batteries and actuators. In this study, we present a novel family of supramolecular columnar liquid crystals that exhibit anisotropic ion-conducting properties. These liquid crystals are formed by self-assembly of a taper-shaped benzonitrile derivative with an amide moiety and ionic liquids (1-ethyl-3-methylimidazolium bromide and 1-butyl-3-methylimidazolium bromide). The cooperative interactions between the nitrile dipole-ion interaction and the bromide anion–amide NH hydrogen bond effectively confine ionic liquids to the center of columns, forming one-dimensional channels. By applying a shearing force, we achieved a uniform horizontal orientation of the supramolecular columns between comb-shaped gold electrodes deposited on a glass substrate. The columnar LC complexes that contained larger cations exhibited higher ionic conductivities compared to those with smaller cations. This can be attributed to the effective ion dissociation resulting from weak Coulombic interactions caused by the larger size of the ionic liquid, as well as the attractive cation-dipole interaction. The present study not only contributes to the understanding of the interplay of noncovalent forces but also offers insights for the design of functional supramolecular materials for future ionic devices.