Influence of the chloro substituent on the mesomorphism of unsymmetrical achiral four-ring bent-core compounds: 2D polarization modulated banana phases

Abstract

The synthesis and characterization of stable achiral unsymmetrical four-ring banana-shaped molecules consisting of a laterally chloro substituted 3,4′-disubstituted biphenyl unit with an ester linkage between the phenyl rings as the central unit in 4-(N-4′-n-tetradecyloxysalicylidene)aminophenyl [2-chloro-5-(N-4′-n-tetradecyloxysalicylidene) aminobenzoate] and 4-(N-4′-n-alkyloxysalicylidene)aminophenyl [4-chloro-5-(N-4′-n-alkyloxysalicylidene) aminobenzoate] are presented. These compounds are thermally and hydrolytically stable due to intramolecular hydrogen bonding and exhibit polarization splay modulated and layer undulated (PMLU) B7/B1Rev/Tilted (2D-polarization modulated layer undulated smectic phase, B1RevTilt phase) phase variants. The phase transitions have been confirmed by differential scanning calorimetry and the phases are characterized by polarized optical microscopy. Two representative examples have been characterized by X-ray diffraction studies. DFT calculations of the bending angle, dipole moments, molecular polarizabilities and voltage holding ratio are also presented.