Azo-containing asymmetric bent-core liquid crystals with modulated smectic phases

Abstract

We present the synthesis and characterization of ten asymmetric bent-core liquid crystals with enantiotropic modulated smectic (B 7 type) phases. Their relatively low and wide photosensitive mesomorphic temperature range offers promising potential applications.A new series of azo-containing bent-core liquid crystals derived from 3-hydroxybenzoic acid has been synthesized. Their mesomorphic properties have been characterized by polarizing optical microscopy, differential scanning calorimetry, small-angle x-ray diffraction and electro-optic studies. Almost all the compounds form an enantiotropic modulated smectic (B7 type)phase over relatively broad temperature ranges. Structural modifications, such as the type and length of the terminal chains, the rigidity of wings, and the presence of a Cl-substituent in different positions of the bent core, affect the appearance and temperature range, but not the type of the mesophase of the investigated compounds. Light-induced changes in the texture and phase transition of the mesophase, attributed to the decrease of the order parameter due to the trans-cis isomerization, have also been observed.

Light Tunable Gratings Based on Flexoelectric Effect in Photoresponsive Bent‐Core Nematics

“…The bent molecular shape causes differences also in other physical properties of BCLCs, such as anomalous anisotropies of elastic constants or a giant flexoelectric effect . In addition, the introduction of a functional group that allows for the modulation of the properties of BCLCs by means of magnetic field or light is nowadays of eminent interest. UV light stimulus can stabilize blue phases; it may cause isothermal chirality switching which results in reversible phototuning of the wave vector of electroconvection patterns in cholesterics .…”

Photosensitive bent-core liquid crystals based on methyl substituted 3-hydroxybenzoic acid

“…The negative effect of a larger substituent in the vicinity of the carboxylic unit on the 3-hydroxybenzoic acidbased materials in combination with less exible side chains has recently been described. 26 It is reasonable to assume that the introduction of the azo unit further limits the overall exibility of the substance required for efficient molecular packing within a mesophase.…”

“…The majority of the reported materials possessed one azo group in the molecular structure and exhibited columnar B 1 , lamellar B 2 or a modulated smectic B 7 -type mesophases. 14,25,26 Related materials with two azo groups have been found to be non-mesogenic. 15 Despite the fact that BCLCs based on 3hydroxybenzoic acid substituted in position four with all-ester side arms provided thermally more stable mesophases than the corresponding resorcinol-based analogues, 27 no material based on laterally substituted 3-hydroxybenzoic acid has been reported yet.…”

Polar Order, Mirror Symmetry Breaking, and Photoswitching of Chirality and Polarity in Functional Bent‐Core Mesogens

“…Therefore, combining the ferroelectric and spontaneously chiral LC phases formed by BCLCs and the photoswitchable nature of the azobenzene units could lead to potential new multifunctional materials in which the polar response can be modified with light . For this reason, azobenzene‐based BCLCs have attracted the attention of several researchers in recent years …”