Thermotropic liquid crystals derived from benzopyranobenzopyran-dione. Preparation and physical characterization

Abstract

Tetra-, penta- and hexasubstituted benzopyranobenzopyran-dione with side chains linked via ether or ester groups yield highly polymorphic compounds. The penta- and hexasubstituted ether and ester series include homologues which exhibit columnar discotic mesophases. Miscibility experiments on the ether series indicate that their mesophases are of the D_h (D_E) class. The tetrasubstituted ethers do not appear to be mesogenic, while the corresponding esters were previously shown to exhibit a highly ordered cubic phase. Differential scanning calorimetry, optical polarizing microscopy and X-ray measurements were used to characterize the mesophases and determine their structural parameters.