Oxadiazolyl-Pyridinium as Cationic Scaffold for Fluorinated Ionic Liquid Crystals

Melina S Weber,Antonio Palumbo Piccionello,Andrea Pace,Margit Schulze,Giuseppe Lazzara,Ivana Pibiri

doi:10.3390/app112110347

Melina S Weber, Antonio Palumbo Piccionello + Show 4 more

Open Access

https://doi.org/10.3390/app112110347

Copy DOI

Abstract

The synthesis and characterization of a new class of 1,2,4-oxadiazolylpyridinium as a cationic scaffold for fluorinated ionic liquid crystals is herein described. A series of 12 fluorinated heterocyclic salts based on a 1,2,4-oxadiazole moiety, connected through its C(5) or C(3) to an N-alkylpyridinium unit and a perfluoroheptyl chain, differing in the length of the alkyl chain and counterions, has been synthesized. As counterions iodide, bromide and bis(trifluoromethane)sulfonimide have been considered. The synthesis, structure, and liquid crystalline properties of these compounds are discussed on the basis of the tuned structural variables. The thermotropic properties of this series of salts have been investigated by differential scanning calorimetry and polarized optical microscopy. The results showed the existence of an enantiotropic mesomorphic smectic liquid crystalline phase for six bis(trifluoromethane)sulfonimide salts.

Highlights

Liquid crystals (LCs) can be described as the matter between the isotropic liquid and the anisotropic solid crystal
The liquid crystalline phase possesses some of the characteristics of the order found in the solid crystal as well as some of the disorder existing in liquids and is often referred to as mesophase [1]
The thermotropic liquid crystalline phase behavior of the salts has been characterized using a combination of differential scanning calorimetry (DSC) and polarized optical regioisomer (2) with the reciprocal position of the perfluoroheptyl chain and the 4-pyridyl group with respect to the heteroaromatic core has been prepared according to the ANRORC

Summary

Introduction

Liquid crystals (LCs) can be described as the matter between the isotropic liquid and the anisotropic solid crystal. The liquid crystalline phase possesses some of the characteristics of the order found in the solid crystal as well as some of the disorder existing in liquids and is often referred to as mesophase [1]. Ionic liquids (ILs) are salts which consist of organic cations paired with a variety of anions and melt at low temperatures, usually below. When a liquid crystalline material consists of anion and cations, it is called an ionic liquid crystal (ILC) [4]. Due to the ionic character and the ability to form liquid crystalline phases with structural and sometimes even positional order, the combined properties of ionic liquids and liquid crystals makes the ionic liquid crystals highly attractive for a variety of applications such as ion-conductive materials in batteries [5,6] or dye-sensitized solar cells [7]. The physical properties of IL and ILCs can be tailored by judicious selection of the central core, such as heterocycles, the substituents and their position, the introduction of alkyl chains and fluorinated moieties of various length as well as the right choice

Methods

Results

Conclusion