Synthesis and mesomorphic properties of new heterocyclic liquid crystals with Central Ester-Chalcone linkages

A series of new calamitic liquid crystals, 4-[3-(pyridin-4-yl)prop-2-enoyl]phenyl 4-alkyloxybenzoates, comprising a pyridyl core, ester-chalcone central linkage and terminal alkyloxy chain were synthesized and characterized. This series consists of four members that differ by the length of the alkyloxy chain (CnH2n+1O, where n = 10, 12, 14, 16). The structures of the title compounds were elucidated using spectroscopic and spectrometric techniques, such as FT-IR, NMR (1H and 13C) and EI-MS. The mesomorphic properties were studied using differential scanning calorimetry and optical polarizing microscopy. The decyloxy-containing compound was found to be non-mesogenic, whilst the compounds containing n-dodecyloxy to n-hexadecyloxy chains exhibited an enantiotropic smectic A phase with a fan-shaped texture. From the structure-property relationship study, it was proposed that the number of carbons in the alkyloxy chain must be at least 12 (n ≥ 12) to generate the smectic phase in the corresponding substituted ArCOOArCOCHCHC5H4N compounds.