Synthesis, Characterization, and Mesomorphic Properties of New Liquid-Crystalline Compounds involving Ester–Azomethine Central Linkages, Lateral Substitution, and a Thiazole Ring

In continuation with our work on liquid crystals with unconventional molecular structures, two homologous series that have 1,4-disubstitution and 1,3,4-trisubstitution in the central phenyl ring, such as 2[(4-n-alkoxy-benzyloxy) phenyl azomethine]-5-methyl thiazole and 2-[(4-n-alkoxy-benzyloxy)-2-hydroxy salicyladimine]-5-methyl thiazole, have been synthesized. They have been characterized by elemental analysis, FT-IR, 1HNMR, 13CNMR, and mass spectrometry. The liquid-crystalline behavior of these compounds was observed by differential scanning calorimetry (DSC) and polarizing microscopy. All the compounds of the 1,4-disubstituted series show an enantiotropic nematic phase only, whereas the compounds of the 1,3,4-trisubstituted series show smectic and nematic phases. Some mesogens with a lateral hydroxy group were also synthesized to evaluate the effect of this group on melting point, transition temperatures, and mesophase morphology.