Thermotropic liquid-crystalline properties of 4,4′-dialkoxy-3,3′-diaminobiphenyl compounds and their precursors

A series of 4,4'-dialkoxy-3,3'-diaminobiphenyl compounds were synthesised by three-step procedure that involves alkylation, nitration and reduction reactions. Their chemical structures were characterised by FTIR, H-1 and C-13 spectroscopy and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by a number of experimental techniques including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarising optical microscopy (POM) and variable temperature X-ray diffraction (VT-XRD). The 4,4'-dialkoxy-3,3'-dinitrobipheyl compounds, precursors to the diamine compounds, were also examined for their thermotropic LC properties. POM studies of focal conic textures and VT-XRD of the 3,3'-diaminobiphenyl derivatives having flexible alkyl chains (C-6-C-12) exhibited the smectic A (SmA) phase independent of the length of alkyl chains. Similarly, the 3,3'-dinitrobiphenyl derivatives containing alkyl chains C-7, and C-9-C-11 exhibit the SmA phase, those containing C-8 formed the smectic C (SmC) phase and C-12 formed both the SmA and smectic B (SmB) phases, respectively. The 3,3'-diaminobiphenyl derivatives had excellent thermal stability in the temperature range of 237-329 degrees C, while those of 3,3'-dinitrobiphenyl derivatives were in the temperature range of 270-321 degrees C. The 3,3'-diaminobiphenyl derivatives emitted UV light both in chloroform and acetonitrile. [GRAPHICS] .