Effects of Different Terminal Substituents on the Mesomorphic Behavior of Some Azo-Schiff Base and Azo-Ester-Based Liquid Crystals

In order to investigate the influence of the terminal substitution on mesomorphism, two new series of azo-Schiff base and azo-ester liquid crystals having the following structures have been synthesized. All the compounds possess mesomorphic properties. In series A compounds A1 and A3 exhibit only a nematic mesophase, whereas compounds A2, A4, A5, A6, A7, A8, A9, and A10 exhibit a smectic as well as a nematic phase. In series B compounds B1 to B9 exhibit only a nematic mesophase, and compounds B10 and B11 exhibit a smectic as well as a nematic phase, but compound B12 exhibits only a smectic phase. All these compounds were characterized by elemental analyses and spectroscopic techniques (Fourier transform infrared [FTIR], 1H nuclear magnetic resonance [NMR], and mass spectroscopy). Their mesomorphic properties were measured by optical polarized light microscopy and differential scanning calorimetry (DSC).