Design, Synthesis and Characterization of Achiral Unsymmetrical Four-ring based Hockey-stick Shaped Liquid Crystals: Structure-Property relationship

Hockey-stick-shaped liquid crystals are interesting due to their unusual physical properties. Nematic phase observed in these materials have shown promising ferroelectric-like switching, ease of alignment in a planar and homeotropic cell, large flexoelectricity, etc. Polar moieties viz. F, Cl, NO2, etc., in their molecular architecture lead to the development of permanent dipole moment which in turn affects the phase structure and physical properties. Herein, we have designed and synthesised a new series of four-ring-based hockey-stick-shaped molecules having polar Cl group at one end and variable aliphatic chains at another end of the molecular long axis. The four phenyl rings are attached via one ester and two imine linkages. All the compounds exhibited enantiotropic mesomorphism. The lower homologs (1-5 to 1-8) exclusively showed nematic phase whereas other higher homologs either exhibited nematic and/or smectic A phase. Compound 1-5 showed a stable nematic phase with the highest phase range of about 110 degrees C upon cooling. Detailed X-ray diffraction revealed the internal arrangement of molecules in layers. Density functional theory study confirmed the resultant dipole moment of the molecules (approximately 6 Debye) which in turn cancelled out in the bulk phase due to preferable antiparallel arrangement as a dimer.

Automated summary

Hockey-stick-shaped liquid crystals exhibit unique physical properties such as promising ferroelectric-like switching and large flexoelectricity. The addition of polar moieties can lead to the development of permanent dipole moment in molecules, affecting the phase structure and physical properties.