Chloro-benzothiazole Schiff base ester liquid crystals: synthesis and mesomorphic investigation

Nine new rod-like chlorobenzothiazole based liquid crystals (1–9) containing Schiff base and ester linking groups bearing different terminal substituents are described. Although a few similar chloro substituted benzothiazole compounds are known, none have been studied for their liquid crystal properties. All these compounds possess liquid crystal behaviour except compounds 4 and 8. The effect of the nature of the terminal groups on thermal stability and optical properties of the mesomorphic compounds was evaluated. With the exception of compound 1, all the other compounds possess polarity resulting from the polar chloride atom substituted at position-6 of the benzene ring of the benzothiazole moiety which provides a polar group at the one terminal end of the molecules. The presence of the fused-ring system (benzothiazole) adds a molecular width that contributes to increase the molecular breadth, causing a thickening effect which disrupts the liquid crystalline packing. New compounds were prepared via reaction of phenolic Schiff bases with the corresponding carboxylic acids or the carboxyl Schiff bases with the corresponding phenols. The synthesized compounds were characterized using 1H- and 13C-NMR and FT-IR spectroscopy, mass spectrometry and elemental analysis. Polarised optical microscope and thermal properties ‎were measured to study the thermal and mesophase behaviours.