Substitution Effects on the Liquid Crystalline Properties of Thermotropic Liquid Crystals Containing Schiff Base Chalcone Linkages

Two homologous series of Schiff base Chalcones, Series-A: 1-{4-[(2,4-dihydroxy benzylidene) amino] phenyl}-3-(4-alkoxy phenyl) prop-2-en-1-one and series-B: 1-(4-{[1-(2,4-dihydroxyphenyl)ethylidene]amino}phenyl)-3-(4-methoxyphenyl)prop-2-en-1-one were synthesized and the physical characterization was carried out along with spectroscopic techniques (FT-IR, 1H NMR,13C NMR, and MS). The thermotropic properties were investigated by optical polarized light microscopy and differential scanning calorimetry and evaluated as a function of chain length and linking group. In series-A compounds C3 to C8 exhibit the nematic mesophase while compounds C10, C12, C14, and C16 exhibit a smectic phase as well as the nematic mesophase. Compounds C1 and C2 do not exhibit any mesophase. In series-B, all the compounds (C1 to C8, C10, C12, C14, and C16) exhibit only the nematic mesophase.