Liquid crystalline bis(iV-salicylideneaniline)s: synthesis and thermal behavior of constitutional isomers

摘要

The first examples of mesogenic bis(N-saIicylideneaniline)s (BSANs), wherein two lipophilic (half-disk shaped) entities are interlinked through the dihydroxydiformylbenzene core, were synthesized and characterized. In particular, three constitutional (positional) isomeric BSANs were prepared by the facile twofold condensation of 3,4,5-tris(alkoxy)anilines with 2,3-dihydroxyterephthalaldehyde, 4,6-dihydroxyisophthalaldehyde, and 2,5-dihydroxyterephthalaldehyde and their structures were established by elemental analyses, FT-IR, ~1H NMR, and ~(13)C NMR. Proton NMR experiments demonstrated their existence in enol-imine (OH) form solely. Polarizing optical microscopic, differential scanning calorimet-ric, and powder X-ray diffraction studies evidenced the occurrence of columnar mesomorphism in two sets of isomers.