Synthesis and mesomorphic behaviors of a series of heterocyclic pyridine-imine-ester based liquid crystals

Abstract

A series of new calamitic liquid crystals, 4-{[(5-methylpyridin-2-yl)imino]methyl}phenyl 4-alkoxybenzoates were synthesized. This series consists of nine members wherein they are differed by the length of alkoxy chain. Spectral analysis results were in accordance with the expected structure. Their thermotropic behaviors were analyzed with Differential Scanning Calorimetry (DSC), Polarizing Optical Microscopy (POM) and powder X-ray diffraction techniques. First member with the shortest alkoxy chain (n = 2) is a non-mesogen. As the alkoxy chain increased to n = 4, the monotropic nematic phase appeared. An enantiotropic mesophase (nematic) was observed for the following three members (n = 6, 8, 10). As the alkoxy chain increased to n = 12, enantiotropic nematic phase exhibited together with monotropic smectic A (SmA) phase. As the alkoxy chain continuously increased to n = 14 and 16, enantiotropic phases were observed for both N and SmA. When moving to n = 18, the nematic phase disappeared and this compound only exhibited a single mesophase (SmA).