Hexagonal columnar mesophases of polycatenar para-phenylene connected bis-oxadiazole-based liquid crystals

Abstract

In this article polycatenar liquid crystals containing two 1,3,4-oxadiazoles interconnected by a para-substituted benzene ring as the central linking unit and three alkoxy chains at each terminal have been synthesised, and investigated by polarising microscopy, DSC and XRD scattering. Molecules with medium chain length form exclusively hexagonal columnar liquid crystalline phases.

Keywords:

• Bis-oxadiazole
• polycatenar
• hexagonal columnar phase
• liquid crystal

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 21274119, No. 21074105 and No. 20973133), the Yunnan Science Foundation (2010CD018); M.P. acknowledges the support by the Cluster of Excellence ‘Nanostructured Materials’.

Notes

1. Though all LC phases have lower transitions than in the reference [26] the melting points are higher, usually indicating higher sample purity.

2. That the aromatic cores are oriented perpendicular to the column axis is shown by the colour of the fans in the optical micrographs (inset in Figure 1) taken with a λ-plate. The yellow and blue colours define the orientation of the high-index axis as radial rather than tangential. Since the columns are tangential in the fans, and the high-index axis is known to be parallel to the intramolecular π-conjugation pathway along the aromatic cores, it follows that the rigid cores have a preferred direction perpendicular to the columns; (n‖ < n = optically negative).