Synthesis and mesomorphic behaviour of achiral four-ring unsymmetrical bent-core liquid crystals: Nematic phases

•Design of achiral four-ring unsymmetrical bent-core liquid crystals resembling true hockey-stick shaped compounds.•Synthesized compounds are characterized and Phase behaviour is discussed.•Wide range nematic phases and stable supercooling of nematic phase are observed.•Molecular interactions viz., end chain length plays an important role thermal stability of nematic phase. Achiral four ring unsymmetrical bent-core liquid crystals derived from 3-amino-2-methylbenzoic acid have been designed and synthesized with an imine, ester and photochromic azo linking moieties. These hockey-stick shape resembling bent molecules possess an alkoxy chain at one end of the molecule and methyl or methoxy group at the other end. The synthesis, phase transition temperatures and characterization of phase behaviour are discussed. The molecular structure characterization is consistent with data from elemental and spectroscopic analysis. The materials thermal behaviour and phase characterization have been investigated by differential scanning calorimetry and polarizing optical microscopy. All these compounds exhibit enantiotropic nematic phase over wide temperature range. Stable supercooling of nematic phase has been observed in methoxy homologues. The density functional theory (DFT) calculations were performed to obtain the stable molecular conformation, polarizability, dipole moment, Highest occupied molecular orbital (HOMO), Lowest unoccupied molecular orbital (LUMO) energies and bending angle of the compound.