Anion-driven mesogenicity: ionic liquid crystals based on the [closo-1-CB9H10]−cluster

Abstract

Two series of structurally analogous esters (1) and diazenes (2) derived from the [closo-1-CB₉H₁₀]⁻ anion and containing two or three rings in the rigid core were prepared and their liquid crystalline properties investigated. Salts containing NMe₄⁺ or NHEt₃⁺ counterion do not exhibit mesophases, whereas the ion pairs with N-butyl-4-heptyloxypyridinium cation [Pyr] exhibit SmA and occasionally soft crystalline phases in the temperature range of 90–180 °C. Three representative ionic liquid crystals, 1d[Pyr], 1f[Pyr] and 2d[Pyr], were investigated by powder XRD. Absorption spectroscopy demonstrated that ester 1e[Pyr] is transparent above 280 nm and the diazene 2e[Pyr] exhibits absorption bands typical for azobenzene derivatives.