Synthesis and characterization of new azomethine derivatives exhibiting liquid crystalline properties

Abstract

Azomethine liquid crystals (LCs), constituted by symmetric and asymmetric bithiophene or fluorene units as chromophores, were designed and synthesised. Their thermotropic behaviour was investigated using optical microscopy, differential scanning calorimetry, and wide angle X‐ray diffraction. A lowering of transition temperatures was obtained by the introduction of the lateral methyl group as compared with unsubstituted compounds. The observed LC phases possess the classical textures of calamitic LCs. The optical properties of the target compounds were evaluated, both in solution and in solid state. A blue fluorescence was observed for fluorene containing compounds and a green fluorescence was observed for analogous bithiophene containing compounds. The introduction of a methyl lateral group onto the aromatic rings led to a remarkable increase in the solution emission properties.

Keywords:

• azomethine
• thiophene
• fluorene
• liquid crystals
• optical properties

Acknowledgements

We would like to thank Dr. G. Zotti for CV measurements.

This work has been partially supported by the European project Research Training Network ‘EUROFET’, contract no. HPRN‐CT‐2002‐00327 and the Italian project MIUR‐FIRB RBNE03S7XZ.