Dielectric and optical anisotropy enhanced by 1,3-dioxolane terminal substitution on tolane-liquid crystals

Abstract

Four series of 1,3-dioxolane-terminated liquid crystals were prepared via multi-step reactions based on 4-alkylcyclohexanecarboxylic acids. Their structures were confirmed by infrared spectrometry (IR), nuclear magnetic resonance (NMR) and mass spectrometry (MS). Their properties were measured by differential scanning calorimetry (DSC), polarising optical microscopy (POM), X-ray diffraction (XRD), Abbe refractometer and an electrical constants instrument. The results show that the positive dielectric anisotropy and birefringence of the tolane-liquid crystals are increased significantly by an introduction of 1,3-dioxolane as a terminal group. The application of the 1,3-dioxolane-terminated liquid crystals in the mixture was investigated and the results show that lower threshold voltage, wider nematic range and higher birefringence are obtained when compared to the mixture containing liquid crystals with buty-3-enyl as a terminal group. The lateral fluoro substituent, alkyne-bridge and 1,3-dioxolane terminal group enhance the stability of the nematic mesophase and the solubility of the corresponding compounds in the common host liquid crystal mixture. Meanwhile, DFT calculations of dipole moments and molecular polarizabilities were used to correlate the experimental findings.