Salicylaldimine-based symmetric dimers: synthesis and thermal behaviour

Several symmetrical dimers comprised of salicylaldimine-moieties connected through ester linkages to the termini of odd-parity alkanediols have been synthesized and investigated for their thermal behaviour. In order to understand the structure-property relations, the lengths of the central alkylene spacers (C3 and C5) as well as those of the terminal alkoxy chains (C6 to C22) have been varied. The dimers with a C3-alkylene spacer are non-liquid crystalline, while some of the compounds having a C5-alkylene spacer exhibit liquid crystalline properties. The dimer, with a C5-alkylene spacer and C6-alkoxy tails, shows an intercalated smectic C (SmCc) phase, whereas the C8, C10, C11, and C12 homologues are non-mesomorphic. The higher homologues of this series with C16, C18, C20 and C22 alkoxy tails show a mesophase that has the signatures of a two-dimensional banana (B1) phase. This mesophase is enantiotropic in the C16 and C18 homologues while it is monotropic in the other homologues. In these dimers, the spac...