Novel oxazepinedione-derived symmetric dimers: synthesis and mesophase characterisation of seven-membered heterocyclic compounds

ABSTRACT

The synthesis and characterisation of three sets of symmetric dimeric compounds composed of seven-membered oxazepinedione heterocyclic rings were carried out. All the dimers possess the tetradecyl- (n = 14) alkyl side chain attached to the nitrogen atom of the oxazepinedione core. The oxazepinedione core in turn was connected with varied connecting spacers (n = 4, 6, 8, 10 and 12). The dimers were spectroscopically characterised by FT-IR, ¹H-NMR, ¹³C-NMR and elemental analysis techniques. The compounds were investigated for liquid crystalline properties using differential scanning calorimetry and polarising optical microscopy with heating assembly. The precursor imines 2a–e itself started exhibiting liquid crystalline SmA/tilted hexatic mesophase. Further fusion of 2a–e with maleic anhydride, succinic anhydride and phthalic anhydride gave the novel oxazepinedione-derived symmetric dimers 3a–e, 4a–e and 5a–e respectively. The dimers 3a–e and 4a–e did not exhibit any liquid crystal (LC) properties. However, the phthalic anhydride-fused oxazepinediones 5a–e show monotropic nematic liquid crystalline phase. The results indicate that the formation of mesophase is dependent on the type of fused oxazepinedione ring.

GRAPHICAL ABSTRACT

KEYWORDS:

• Symmetric dimers
• oxazepinediones
• heterocycle
• nematic
• smectic phase

Acknowledgements

AK-TM extends grateful thanks to Prof. John West and Liquid Crystal Institute at the Kent state University, for molecular model calculations and their hospitality. Authors thank the University Sains Malaysia and the Malaysian Government for financing this project through the short term Grant (304/PKIMIA/6312051) and FRGS Grant (203/PKIMIA/671119). Main author thanks the Department of Chemistry, College of Sciences, University of Anbar.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by the University Sains Malaysia and the Malaysian Government through the short-term Grant [304/PKIMIA/6312051] and FRGS Grant [203/PKIMIA/671119].