Development of tilt, biaxiality and polar order in bent-core liquid crystals derived from 4′-hydroxybiphenyl-3-carboxylic acid

Abstract

A homologous series of unsymmetric bent-core compounds derived from 4 0 -hydroxybiphenyl-3carboxylic acid and having strongly distinct chains at both ends has been synthesized and characterized.The liquid crystalline self-assembly of the compounds was investigated by differential scanning calorimetry, optical polarizing microscopy, X-ray scattering and electro-optic methods. With increasing chain length and upon cooling a series of smectic phases was observed, starting from SmA phases having an unusual structure composed of domains with a randomized tilt direction. This is followed by a series of biaxial smectic phases, involving a smectic phase composed of tilt domains with increased size (SmC r ), anticlinic and synclinic tilted smectic phases (SmC s , SmC a ) and finally columnar phases with an oblique (Col obl ) or pseudo-rectangular (Col rec ) lattice. This phase sequence is the result of the competition between an emerging tilt, the dense packing of the bent aromatic cores leading to restricted rotation and contributing to phase biaxiality, and the steric distortion of the dense packing by the bulky 3,7-dimethyloctyloxy chains, inhibiting the formation of long range polar order. In all smectic phases the tilt is relatively small, thus providing only weak layer coupling and this provides the basis for sensitive regulatory networks determining the mode of molecular self-assembly in the resulting LC phases. The columnar phases have a tilted B 1rev -like ribbon structure with a temperature and chain length dependent inversion of the sign of birefringence. Though none of the racemic compounds show polar switching, the (S)-enantiomer of one compound shows ferroelectric-like switching in an anticlinic tilted smectic phase (SmC a P R *).

Quantum-Dots Dispersed Bent-core Nematic Liquid Crystals and Cybotactic Clusters: Experimental and Theoretical Insights

“…(15) We now apply a homogenization result in [45] which effectively states that for dilute colloidal suspensions described by a re-scaled (dimensionless) general energy of the form (16), where the inclusions have effective radius α for some 1 < α < 3 2 , the minimizers of…”

“…Owing to these remarkable properties and unusual phase formation, they have been studied extensively in the last two decades. The nematic (N) phase of BLCs itself is capable of manifesting a few of the aforementioned distinct features, such as ferroelectric response, fast switching and macroscopic biaxiality [11][12][13][14][15][16]. In contrast, the N phase of calamitic mesogens does not possess any of these properties.…”

Effects of molecular chirality on self-assembly and switching in liquid crystals at the cross-over between rod-like and bent shapes

“…† Throughout all steps of the synthesis of the enantiomer (S)-2 the stereogenic center of the (S)-3,7-dimethyloctyloxy group was not touched and hence it can be assumed that the final product has approximately equal optical purity as (S)-(À)-b-citronellol (Z99%), used as a starting material. 29,31,51 rac-2 represents an optically inactive racemic mixture of the (R,R), (S,S), (R,S) and (S,R) stereoisomers. Despite being a complex mixture, the LC phase transition temperatures and the sharpness of the phase transitions are the same as for the enantiomeric pure single component compound (S)-2 (see Fig.…”

Synthesis and Characterization of Bent‐Core Liquid Crystal / Modified γ‐Al2O3 Nanocomposites

“…A large number of the bent‐core liquid crystals have been designed and synthesized to understand the relationship between structure and property in bent‐core liquid crystals. Subtle variations in the molecular structure of bent‐core compounds such as lateral substitution, length of terminal alkyl chains, the introducing a chiral moiety in terminals and orientation of the linking group results in significant changes in the type of mesophase observed.…”