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

<p>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- (<i>n</i> = 14) alkyl side chain attached to the nitrogen atom of the oxazepinedione core. The oxazepinedione core in turn was connected with varied connecting spacers (<i>n</i> = 4, 6, 8, 10 and 12). The dimers were spectroscopically characterised by FT-IR, <sup>1</sup>H-NMR, <sup>13</sup>C-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 <b>2a–e</b> itself started exhibiting liquid crystalline SmA/tilted hexatic mesophase. Further fusion of <b>2a–e</b> with maleic anhydride, succinic anhydride and phthalic anhydride gave the novel oxazepinedione-derived symmetric dimers <b>3a–e, 4a–e</b> and <b>5a–e</b> respectively. The dimers <b>3a–e</b> and <b>4a–e</b> did not exhibit any liquid crystal (LC) properties. However, the phthalic anhydride-fused oxazepinediones <b>5a–e</b> show monotropic nematic liquid crystalline phase. The results indicate that the formation of mesophase is dependent on the type of fused oxazepinedione ring.</p>