Antiferroelectric Behaviors of the SmCP Phase in Liquid-Crystalline Compounds with Achiral Bent-Core Liquid-Crystalline Molecules Containing Salicylaldimine-Based

Abstract

A new series of bent-shaped mesogens has been synthesized and their mesomorphic properties studied. All compounds exhibit the B2 (SmCP) phase. Compounds with a 3,4′-biphenyldiol central core containing salicylaldimine-based and two terminal tetradecyloxy tails are reported. In addition, the effects of lateral substituent (R˭F and Cl) at the biphenyl core into 3′-position are examined. These substituents have a strong influence in reducing the clearing temperatures and increasing temperature range of the SmCP phase. The electro-optical switching characteristics have been investigated using both triangular-wave and DC electric fields. For several compounds, chirality switching from racemic to the homochiral state was seen after application of a low-frequency AC field. We studied spontaneous polarization, switching time, tilt angle, switching time, voltage-transmittance effect, and dielectric parameters (namely dielectric strength, relaxation frequency, distribution parameter) of a 7.5-µm-thick planar-oriented sample of a highly tilted anti-ferroelectric liquid-crystal material and investigated the correlation between their electro-optical properties and the chemical structures of these compounds.

Keywords:

• Antiferroelectric properties
• bent-core liquid crystals
• homochiral state
• racemic
• salicylaldimine-based

Acknowledgment

We thank Dr. Jey-Jau Lee for help with the XRD experiments at National Synchrotron Radiation Research Center (NSRRC, for the beamline BL17A), in Taiwan. Financial support from the National Science Council of Taiwan (ROC) through 98–2221-E-011–004 is gratefully acknowledged.

Notes

^a Cr = crystalline phase; SmCP = polar SmC phase (i.e., B₂ phase); I = isotropic phase; (• = phase exists).