Halogen-bonded ionic liquid crystals: supramolecular organization and ionic transport

Abstract

Ionic liquid crystals (ILCs) are emerging materials that combine the anisotropic self-assembly of liquid crystals with the ionic conductivity of ionic liquids, making them promising candidates for electrochemical applications such as ion-conducting membranes and next-generation electrolytes. In this work, we report the synthesis and characterization of a series of 1-alkyl-3-halopyridinium halides, where both the cationic and anionic components participate in halogen bonding, leading to enhanced mesophase stability and well-defined ionic nanochannels. Compounds with alkyl chains of 12 carbons or longer exhibit Smectic A liquid crystalline phases, with their stability increasing with chain length and halogen bond strength. X-ray diffraction analysis confirms the role of halogen bonding in driving molecular self-assembly and charge segregation, key factors in mesophase formation. Ionic conductivity measurements demonstrate that these ILCs facilitate ion transport through their nanosegregated ionic domains, with conductivities comparable to other liquid crystalline electrolytes. These findings highlight the potential of halogen-bonded ILCs as functional materials for electrochemical devices, providing a tunable platform for the development of advanced ion-conducting materials.