Polar derivatives of [closo-1-CB9H10]− and [closo-1-CB11H12]− anions as high Δε additives to a nematic host: a comparison of the CH2CH2 and COO linking groups

Abstract

A series of liquid crystalline pyridinium and sulfonium derivatives of the [closo-1-CB₉H₁₀]⁻ and [closo-1-CB₁₁H₁₂]⁻ anions containing the CH₂CH₂ linking group was prepared and their molecular and crystal structures were determined by single crystal XRD methods. Thermal and dielectric properties of the series were evaluated in a weakly polar nematic host. The highest extrapolated dielectric anisotropy, Δε, was observed for pyridinium zwitterions (up to 56.0). The dielectric data were analyzed with the Maier–Meier formalism augmented with density functional theory calculations, and the results were compared to those obtained for the analogous ester derivatives (COO linking group). The effect of the linking group on thermal and electrooptical properties is discussed.