Synthesis and mesomorphic properties of 7-alkoxybezopyrano[2,3-c]pyrazol-3-one

Abstract

A new series of fused polyheterocyclic aromatic compounds, 7-alkoxybezopyrano[2,3-c]pyrazol-3-one (C- n BPP), were synthesised and characterised by infrared, ¹H-nuclear magnetic resonance (NMR), ¹³C-NMR and two-dimensional ¹H-¹³C cosy spectra. Their phase transition behaviour was investigated by differential scanning calorimetry and polarising optical microscopy. All of these compounds showed enantiotropic mesophases with temperature domains of 12–60°C and 22–69°C on heating and cooling processes for a carbon number of the alkoxy chain from 2 to 10. The effect of the length of the alkoxy chain on the mesomorphic properties was discussed. Comparison of C- n BPP and several kinds of coumarin derivatives indicated that the intermolecular hydrogen bonding acted as the driving force of the mesophase formation.

Keywords:

• mesomorphic phase
• hydrogen bonding
• bezopyrano[2,3-c]pyrazol-3-one

Acknowledgements

The authors would like to thank the National Science Foundation Committee of China (Project No. 50802058) and the Youth Foundation of the School of Chemistry and Materials Science, Shaanxi Normal University for financial support of this work.