Asymmetric flavone-based liquid crystals: synthesis and properties

ABSTRACT

A series of flavones (n-F) substituted at the 4′, and 6 positions was prepared, characterised by NMR (¹H,¹³C), HRMS, and studied for liquid crystal properties. The 4′-alkoxy,6-methoxyflavones (4-F–16-F) exhibit varying ranges of nematic and smectic A phases as evidenced by polarised optical microscopy and differential scanning calorimetry (DSC). As the tail length is increased, the smectic phase becomes more prevalent. Smectic phases for (8-F–16-F) were further analysed by powder X-ray diffraction (XRD), and the rate of structural transformations was explored by combined DSC/XRD studies. Flavonol 6-F–OH was also prepared but no mesogenic behaviour was observed. The molecular structures of 6-F and 6-F–OH were determined by single-crystal XRD and help to explain the differences in material properties. Additionally, fluorescence and electrochemical studies were conducted on solutions of n-F.

Graphical Abstract

KEYWORDS:

• Liquid crystal
• thermotropic
• flavone
• heterocycle
• fluorescence
• combined DSC/XRD

Acknowledgements

This work is supported by the Department of Chemistry, Virginia Military Institute (VMI Grants-in-Aid) and the Thomas F. and Kate Jeffress Memorial Trust Award (J-944). We would also like to thank Dr. Ed Samulski for helpful discussions. X-ray scattering work was carried out on the 5ID-D beam line at the Advanced Photon Source (APS), Argonne National Laboratory, which is funded by the DOE, and we thank Dr. Steven Weigand at the APS for enabling us to obtain the X-ray data.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work is supported by the Department of Chemistry, Virginia Military Institute (VMI) (VMI Grants-in-Aid) and the Thomas F. and Kate Jeffress Memorial Trust Award (J-944). X-ray scattering work was carried out on the 5ID-D beam line at the Advanced Photon Source (APS), Argonne National Laboratory, which is funded by the DOE.