Design, synthesis, and characterisation of symmetrical bent-core liquid crystalline dimers with diacetylene spacer

Abstract

Two new symmetrical bent-core liquid crystalline dimers (B-DA4 and B-DA12) bearing diacetylenes spacer and different terminal alkyl chains were successfully synthesised via Sonagashira coupling reaction. The molecular structures of these dimers were confirmed by ¹H nuclear magnetic resonance (NMR), Fourier transform-infrared spectroscopy (FT-IR), Raman spectroscopy, mass spectrometry, and elemental analysis. Their thermal stability and liquid crystalline properties were characterised by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), polarised light microscopy (PLM), and small-angle X-ray scattering (SAXS). Results showed that the diacetylene group may be thermal polymerised at about 260°C far from thermal decomposition. The dimers exhibited monotropic phase behaviour and typical layered-structure phase with long-range order on a length scale of about 6.3 nm was observed. The results mentioned above offer a promising opportunity to design polydiacetylene nanowires by thermal, UV irradiation, or scanning tunnelling microscope (STM) tip-induced polymerisation.

Keywords:

• symmetrical liquid crystalline dimers
• bent-core liquid crystal
• diacetylene spacer
• monotropic phase behaviour

Acknowledgement

This work is supported by the National Natural Science Foundation of China (No. 51203003).