Liquid Crystals and Display Technology

Abstract

Polyesteramides PNOBDME (C 34 H 38 N 2 O 6) n , Poly[oxy(1,2-dodecane)-oxycarbonyl-1,4-phenylene-amine-carbonyl-1,4-phenylene-carbonyl-amine-1,4phenylene-carbonyl], and PNOBEE (C 26 H 22 N 2 O 6) n , Poly[oxy(1,2-butylene)-oxy-carbonyl-1,4-phenylene-amine-carbonyl-1,4-phenylene-carbonyl-amine-1,4-phenylene-carbonyl], have been designed and synthesized as cholesteric liquid crystals (LCs)-through a condensation reaction between 4-4′-(terephthaloyldiaminedibenzoic chloride) (NOBC) and racemic glycol, DL-1,2-dodecanediol or DL-1,2-butanediol, respectively-as chemical modifications of multifunctional cholesteric LC polyesters, involving new properties but holding the precursor helical macromolecular structures. The new compounds have been characterized by 1 H and 13 C-NMR, COSY and HSQC, exhibiting two 1 H-independent sets of signals observed for each enantiomer, attributed to two diastereomeric conformers, gg and gt, of the torsion containing the asymmetric carbon atom in the spacer. They have also been characterized by x-ray diffraction with synchrotron radiation source. Thermal behaviour of the new compounds is studied by thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis. The substitution of the ester groups in the mesogen by amide groups causes an increase of thermal stability with respect to the precursors. Optical rotatory dispersion (ORD) is evaluated. Morphology of powdered PNOBDME exhibits spherical clusters of about 5 μm in diameter homogeneously dispersed. Molecular models show helical polymeric chains with stereoregular head-tail, isotactic structure, explained as due to the higher reactivity of the primary hydroxyl with respect to the secondary one in the glycol through the polycondensation reaction. Besides being biocompatible, these synthetic polyesteramides have proved to act as non-viral vectors in gene therapy and be able to transfect DNA to the nucleus cell. Similar new cationic cholesteric liquid crystal polyesters have also been synthesized in our laboratory.

Green Thermochromic Materials: A Brief Review

“…A thermotropic transition occurs when the isotropic phase transitions into a nematic phase through a shift in the crystal structure along the helical axis. [51] This shift is a common mechanism for thermochromism in liquid crystals which allows them to reflect incident light rays, therefore, exhibiting selective optical properties. [2,19] The most relevant application for functional thermochromic LCs is in sustainable building industry as passive solar heating and cooling systems.…”

“…Liquid crystals, for example, can experience a shift in the alignment of mesogenic molecules from one phase (nematic, cholesteric, or smectic) to another causing a change in opacity, translucency, or transparency as a result of the thermal stimuli. [51,52] This is considered a thermotropic transition. Vanadium dioxide can exhibit a metal-insulator transition that causes a similar shift in the optical spectra, however it is more commonly accepted to consider this as a thermochromic phenomenon due to its pre-existing brown color.…”