Mesophase behavior of four ring ester/azomethine/ester liquid crystals in pure and mixed states

New four-ring ester/azomethine/ester liquid crystal series, 4-alkoxybenzoyloxy 4'-phenylazomethine phenyloxy 4"-alkoxybenzoate In, were prepared, and their thermal stability and mesomorphic activity were investigated. The two wing carboxylic units were used aiming to achieve new mesomorphic properties for the prepared materials. The two ester linkages and the two terminal alkoxy chains were incorporated to modify the molecular structure. The chemical structures of the synthesised compounds were confirmed via FT-IR, NMR and elemental analysis. Differential scanning calorimetry (DSC) and polarising optical microscopy were applied to determine the mesomorphic features of the designed homologues. All of the studied homologous were shown to exhibit superior thermal stability and enormous mesomorphic temperature ranges. Moreover, enantiotropic smectic A and nematic phases were shown to cover all of the homologues. The influence of inclusion the di-ester moieties on the mesophase behaviour was investigated through a comparison with the previously investigated three-ring series bearing only one ester linkage. Two binary phase diagrams were constructed and addressed in terms of the smectic and nematic temperature ranges.