Constitutional bis(N-salicylideneaniline)s as new class of mesogens: synthesis and thermal properties

Twelve new constitutional bis(N-salicylideneaniline)s (BSANs) belonging to three different series have been prepared and characterised by the two-fold reaction of alkoxyanilines with 2,3-dihydroxyterephthalaldehyde, 4,6-dihydroxyisophthalaldehyde and 2,5-dihydroxyterephthalaldehyde. Their thermal behaviour and liquid crystallinity has been established with the help of polarising optical microscope, differential scanning calorimeter (DSC) and powder X-ray diffraction (XRD). Our study reveals this behaviour as determined by the nature of central core and the number of alkoxy tails. For example, the three series of compounds prepared are either non-mesomorphic or stabilised calamitic and discotic mesophases, such as nematic/smectic C and columnar (Col) phases. These materials represent the first examples of mesogenic BSANs exhibiting mesomorphism.