Mesomorphic properties of chiral three-arm liquid crystals containing 1,2,4-butanetriol as core

Abstract

A series of symmetric and asymmetric three-arm liquid crystals (TALCs) of which the molecular structure with a central core of 1, 2, 4-butanetriol attached by three rod-like mesogenic moieties have successfully been synthesized. The rod-like mesogenic side arms are 4′-(4-(trifluoromethyl) benzoyloxy) biphenyl-4-carboxylic acid (TFBA) and 4′-(4-(allyloxy) benzoyloxy) biphenyl-4-carboxylic acid (AOBA), respectively. BTA0 and BTA3 are symmetric TALCs with three TFBA or three AOBA as LC side arms, respectively. BTA1 is an asymmetric TALC with one AOBA and two TFBA as side arms. BTA2 is an asymmetric TALC with two AOBA and one TFBA as side arms. The chemical structures and LC properties of the LC side arms and TALCs were characterised by FTIR, 1H NMR, elemental analysis, DSC, TG, POM and X-ray diffractometer. TFBA displayed smectic B (SmB) phase, AOBA exhibited nematic (N) phase. The TALCs all displayed chiral mesophase properties. BTA0 displayed chiral smectic C (SmC∗) mesophase. BTA1, BTA2 and BTA3 exhibited cholesteric (ch) mesophase. In addition, a chiral smectic A (SmA∗) mesophase was observed for BTA1. The results indicated that the 1, 2, 4-butanetriol is vital in inducing chiral mesophase of the TALCs. The side arms also played an important role in the mesophase type and mesogenic region. The TALCs displayed cholesteric mesophase when nematic LC side arm AOBA was introduced into the chiral core. The mesogenic region of the TALCs increased with the content of the wide-mesophase-region LC side arm AOBA introduced into the TALCs increasing. The melting temperature and the clear temperature of the TALCs were lower than those of the LC side arms (TFBA and AOBA). The mesophase regions of the TALCs were wider than those of the LC side arms.