Mesomorphic Behavior of Symmetrical and Unsymmetrical Azomethines with Two Imine Groups

摘要

Seven symmetrical azomethines with two imine groups (HC=N) were synthesized by condensation of the benzene-1,4-dicarboxaldehyde with five amines (first group: >A1->A5) and of the 2,5-thiophenedicarboxaldehyde with two amines (second group: >AT1->AT2). Additionally, two unsymmetrical azomethines were obtained by a two step condensation of benzene-1,4-dicarboxaldehyde with pyren-1-amine (1^st step) (abbreviated hereinafter as >AP1) and then >AP1 was reacted with 4-dodecylaniline or 4-hexadecylaniline (2^nd step) (third group: >AP1A->AP1B). Liquid crystalline properties of the azomethines were studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and UV-vis spectroscopy in the function of temperature [UV-vis(T)]. The Wide-Angle X-ray Diffraction (WAXD) technique was used to probe the structural properties of the azomethines. Mesomorphic behavior was observed for symmetrical and unsymmetrical azomethines, obtained from the benzene-1,4-dicarboxaldehyde and symmetrical ones prepared from 2,5-thiophenedicarboxaldehyde and different amines having aliphatic chains. Based on the POM and DSC measurements the following mesophases were detected: nematic, smectic A, smectic C, smectic F (I), smectic G (J).