Preliminary communication - The effect of a substituent in the central ring on the liquid crystalline properties of di(4-alkoxycarbonylphenyl) terephthalates

Abstract

Four series of di(4-alkoxycarbonylphenyl) terephthalates with different lateral substituents in the central ring and lengths of the terminal alkyl groups were synthesized. The influence of the lateral substituent on thermodynamical parameters of the phase transitions and elastic properties of the nematic phases (ratio of bend elastic constant to diamagnetic anisotropy K3/Delta chi) were studied by polarizing optical microscopy, differential scanning calorimetry and observations of the Freedericksz transition. It was found that increasing the alkyl chain length and the substituent size in the sequence H, Cl, Br, NO2 results in reduction in stability of the crystal and (as frequently observed in other cases) the liquid crystal phases. The changes in the bend elastic constant and the melting enthalpy caused by the substituent variation are correlated with each other, a fact that is explained by the dependence of short-range lamellar packing on size and polarity of substituent.