Polar Switching and Cybotactic Nematic Ordering in 1,3,4-Thiadiazole-Based Short-Core Hockey Stick-Shaped Fluorescent Liquid Crystals

Abstract

We report here the synthesis and thermotropic properties of novel short-core hockey stick-shaped liquid crystalline molecules based on the 1,3,4-thiadiazole core. Polar switching behavior is observed in the cybotactic nematic and smectic mesophases for the bent-core thiadiazole derivatives. The presence of the lateral methoxy moiety in the outer phenyl ring of the four-ring molecules facilitates the formation of spontaneous ordering in the nematic phase observed via X-ray diffraction measurements. Anomalous temperature dependence of spontaneous polarization on cooling is explained by the possible antiferroelectric packing of the molecules that require higher electric field for switching. The compounds exhibited a strong absorption band at ∼356 nm and a blue emission band at ∼445 nm with a good quantum yield of φ f ∼0.39. The mega Stokes shift is observed and depends on the nature of the solvent.

Quantum-dots-dispersed bent-core nematic liquid crystal and cybotactic clusters: Experimental and theoretical insights

“…The last term on the right-hand side of equation ( 4) describes the motion of free-charge carriers in the sample. The characteristic dielectric parameters such as the relaxation frequency (f R ) and the dielectric strength (δ ) are obtained by fitting the experimental dielectric permittivity ( ) and dielectric loss ( ) data simultaneously to the real and the imaginary parts of equation ( 4) given by [12,40,[54][55][56], . The fitting parameters χ 2 and R 2 are generated by the fitting algorithm, so that χ 2 ∼ 0 and R 2 ∼ 1 describe good fits.…”

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

“…The last term on the right-hand side of equation ( 1) describes the motion of free-charge carriers in the sample. The characteristic dielectric parameters such as the relaxation frequency (f R ) and the dielectric strength (δ ) were obtained by fitting the experimental dielectric loss ( ) data to the imaginary part of the equation (1) given by [13,[60][61][62]…”

Observation of “de Vries-like” properties in bent-core molecules

“…Unsymmetrical bent-core molecules or hockey-stick shaped molecules, renowned for their potential physical properties for device applications, such as nematic ferroelectricity, 21 cybotactic nematic phases, 22–26 formation of a polarization modulated layer undulated phase structure, 27–30 and a long range blue phase with a high Kerr constant, 31 barely exhibit “de Vries-like” behaviour. In the past two decades, miscellaneous hockey-stick shaped mesogens (composed of four or more phenyl rings) have been explored.…”

“…dark conglomerate, 32–34 biaxial nematic, 35–37 twist-bend nematic 38–42 and cluster phases. 25,43,44 In the field of bent-core LCs, there are very few reports, mostly in a scattered way that describe “de Vries-like” characteristics. 45–49 Bent-core or hockey-stick shaped LCs with their exceptional physical characteristics, if showed “de Vries-like” behaviour, could be a tremendous advantage for FLC display technology.…”