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/B1_Rev/Tilted (2D-polarization modulated layer undulated smectic phase, B1_RevTilt 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.