Synthesis and characterisation of asymmetrical mesogenic materials based on 2,5-disubstituted-1,3,4-oxadiazole

Abstract

ABSTRACTNew mesogenic homologous series bearing 1,3,4-oxadiazole ring with a nitro terminal group, 4-(5-(4-nitrophenyl)-1,3,4-oxadiazol-2-yl)phenyl 4-((4-methoxybenzylidene)amino)benzoate (G1–G11), were synthesised. Their chemical structures are identified by fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1H-NMR) and elemental analysis. The liquid crystalline properties of the series Gn and their precursory Fn were screened by differential scanning calorimetry and optical polarising microscopy (OPM). The compounds of the series Gn were screened by thermogravimetric analysis to observe their thermal stability. The target compounds (Gn) in this study, were displayed different liquid crystalline mesophase, the first two homologous (G1 and G2) did not show any liquid crystalline behaviour, the homologous (G3–G10) which have an alkoxy terminal group (n = 3–10) exhibited nematic phase, whilst the last derivative of the series (G11), n = 12, displayed SmA phase. The mesomorphic properties of these derivatives were affected by the presence of the nitro group at the end of the molecules which was classified as a strong polar group. Also, the role of alkoxy terminal chain and the bent heterocyclic ring (1,3,4-oxadiazole) in the liquid crystalline properties of these molecules were debated.