Effect of polar substituents on the properties of 1,3,4-oxadiazole-based liquid crystalline materials containing asymmetric cores

Abstract

A series of 1,3,4-oxadiazole-based liquid crystals bearing different polar substituents (n-NPO-X, where X=Me, OMe, Cl, F, CN, and NO₂) at the phenyl 4-position have been synthesized and characterized. These angular oxadiazole-based liquid crystals, which are composed of asymmetric cores containing naphthalene units, exhibit stable mesogenic properties including the nematic and smectic A phases. With analogous structural design, the transition temperatures, mesomorphic phases, optical properties, and internal quantum efficiencies show strong dependence on the terminal substitution. In general, by increasing the terminal dipoles, the temperature ranges of the mesophases are enhanced, and both the absorption and photoluminescence spectra are shifted to longer wavelengths.