New supramolecular liquid crystals induced by hydrogen bonding between pyridyl-1,2,4-oxadiazole derivatives and 2,5-thiophene dicarboxylic acid

Supramolecular liquid crystalline complexes were obtained from binary mixtures of 3-(4-pyridyl)- 5-(4-n-alkoxy) phenyl-1,2,4-oxadiazoles and 2,5- thiophene dicarboxylic acid. Although the oxadiazole derivatives and the dicarboxylic acid are non-mesomorphic, the H-bonded complexes exhibit mesomorphism. Their liquid crystalline properties were investigated by differential scanning calorimetry and polarizing optical microscopy. The complexes exhibit enantiotropic nematic phases. A structural study involving AM1 semi-empirical calculations is also described.