Three armed star mesogens based on 1,3,5-benzenetricarboxylic acid: Synthesis and mesophase characterization

• Star mesogens containing 1,3,5-benzenetricarboxylic acid central unit, two phenyl ring side arm core, ester and azomethine linking groups and terminal alkoxy groups were synthesised.
• The structural changes made in the mesogens such as increasing the terminal chain length causes significant effect in the mesophase sequence.
• The increase of arm length stabilizes the smectic phases.
• Smectic polymorphism was observed on cooling.

A series of star mesogens based on 1,3,5-benzenetricarboxylic acid central core, side arms containing two phenyl rings, linked through azomethine groups and hexamethylene spacers, which connect the central core and side arms were synthesised via divergent approach. The mesogens synthesised and their intermediates were structurally well characterized, using FT-IR, 1H NMR, 13C NMR spectroscopy and elemental analysis techniques. The mesophase characterization was carried out using a hot stage-polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques. Enantiotropic mesophases were observed for all the mesogens synthesised. An increase in the terminal chain length stabilized the smectic phase. Nematic phase was observed for the mesogens with short terminal chain length, whereas smectic polymorphism was observed on increasing the terminal chain length. XRD results suggested a tripod-like assembly of molecules in the mesophase.