Influence of polar substituents on the mesomorphism of non-symmetrical achiral four-ring bent-core compounds: synthesis and characterisation

The synthesis and characterisation of stable achiral asymmetrical four-ring banana-shaped molecules are presented. These consist of a laterally fluoro-substituted 3,4ʹ-disubstituted biphenyl unit with an ester linkage between the phenyl rings as the central unit in 4-(N-4ʹ-n-alkyloxysalicylidene)aminophenyl [2-fluoro-5-(N-4ʹ-n-alkyloxy-salicylidene) amino-benzoate]. These compounds are thermally and hydrolytically stable due to inter- or intramolecular hydrogen bonding and exhibit columnar (B1) phases. The phases have been characterised by thermal microscopy and differential scanning calorimetry. A representative example has also been characterised by X-ray diffraction.