Synthesis and structural studies of smectic C mesogens with terminal perfluoroalkyl chains

Abstract

4-(2-Perfluorohexyl)-ethoxy-4′-cyanobiphenyl (F6H2OCB) and 4-(2-perfluorooctyl)-ethoxy-4′-cyanobiphenyl (F8H2OCB) were synthesised by Mitsunobu reaction. Liquid crystalline state of F6H2OCB and F8H2OCB was studied by differential scanning calorimetry (DSC) and microscopic observation. Broken fan-shaped texture, which is the characteristic of smectic C phase, was observed between 89.4°C and 162.0°C for F6H2OCB and between 103.7°C and 182.1°C for F8H2OCB. Such a stable smectic C liquid crystal (LC) is rarely reported. Smectic C LC can be transformed to ferroelectric smectic C* by the addition of a chiral compound. Smectic K phase was observed at room temperature for both F6H2OCB and F8H2OCB, and perfluoroalkyl chains were located up and down alternatively. Smectic K phase was proved by the comparison of d (interlayer distance) and L (calculated dimer molecular length) and the non-monotonic and slow decay of the intensities of 00ℓ reflections in X-ray diffraction (XRD).

Keywords:

• smectic C
• smectic K
• ferroelectric liquid crystal
• microscopic texture
• Mitsunobu reaction

Acknowledgements

This research was supported by Basic Science Research Programme through the National Research Foundation of Korea funded by the Ministry of Education and GNU development fund.