Synthesis and Mesomorphism of New Calamitic Schiff Bases-Ester Possessing Dialkylamino Terminal Substituent

Abstract

: New calamitic liquid crystals, 4-[{[4-(diethylamino)phenyl]methylidene}amino]phenyl 4- alkyloxybenzoate (nEABAA) containing mesogenic core system which made of three phenyl rings were reported. The ester and imine linkages connected the phenyl rings. At one end of the molecule, the core system was attached to an alkyloxy chain with a variable length -(CH2)n- (where n = 2-10, 12, 14, 16 and 18). At the other end of the molecule, the para position of the phenyl ring is bonded to the diethylamino group. The molecular structure of the current compounds was confirmed by using spectroscopic methods. The mesomorphic characteristics of the title compounds were studied by using a differential scanning calorimeter and a polarizing optical microscope attached to a heating stage. Through observation under microscopy, it was found that all synthesized compounds exhibited only a single (nematic) phase. The exhibition of the monophase variance (nematic) in the current compounds is caused by the presence of the diethylamino group that is attached to the terminal position of the benzylideneaniline core system. The diethylamino group has caused the molecular breadth to increase and this results in a weaker overall lateral intermolecular attraction. Subsequently, it depressed the mesophase thermal stability of the compounds. Thermal properties of the current compounds were compared with the earlier reported analogous and the structure-property relationships of the current compounds have been inferred through this comparison.