Synthesis, characterization and mesomorphic properties of new unsymmetrical azomethine-type liquid crystals derived from 4-biphenyl carboxaldehyde

Synthesis, characterization and thermal properties of a series of four azomethines (1)-(4) derived from 4-biphenyl carboxaldehyde were described. The structures of the azomethines were characterized by means FTIR, 1H, 13C NMR spectroscopy and elemental analysis; the results show an agreement with the proposed structure. The methods of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) were used to describe the liquid-crystalline properties of the azomethines. The mesomorphic properties of the compounds depend on the amine used in the synthesis of imines. In particular, three of them prepared from 4-hexadecylaniline, 4-decylaniline or 4-((4-aminophenyl)diazenyl)-N,N-dimethylbenzenamine (1)-(3) showed smectic A and smectic X mesophases, while the last one obtained from 4-(heptadecafluoroctyl)aniline (4) exhibited SmX2 and nematic mesophases. Current-voltage measurements were performed on ITO/compound/Alq3/Al device with two different thicknesses of the film. Additionally, we compared the mesomorphic behavior of the azomethines presented in this work with another azomethines.