Synthesis, characterisation and liquid crystal properties of 2,5-bis[5-alkyl(alkoxy)phenyl-1,3,4-oxadiazole]bromobenzenes

A series of new thermal bilateral liquid crystal compounds with the phenylenebis-1,3,4-oxadiazole structure was synthesised. The molecular structures of the oxadiazole compounds were confirmed by FT-IR and ¹H NMR spectroscopy, elemental analysis and mass spectrometry. Thermogravimetric analysis indicates that the compounds in an atmosphere of nitrogen have good thermal stability. Measurements using differential scanning calorimetry, polarising optical microscopy and temperature-dependent wide-angle X-ray diffraction indicated that the liquid crystalline properties are related to the length of the end groups. When the end group was tert-butyl or alkoxy with four and six carbons, the compounds exhibit no liquid crystal phase. However, compounds with end groups containing more than eight carbons show significant bidirectional thermally-induced liquid crystal properties and the structure of the liquid crystal phase is the lamellar smectic A phase. All the compounds exhibit blue fluorescence.