Synthesis and Characterization of Liquid Crystalline Silsesquioxanes Containing Azobenzene Groups

Abstract

Liquid crystalline silsesquioxanes having calamitic mesogenic and azobenzene moieties were synthesized by the hydrosilylation reaction of an inorganic silsesquioxane cube and terminal alkenes using Karstedt's catalyst. Their chemical structures were confirmed by Fourier transform infrared (FTIR) and ¹H- and ²⁹Si-NMR (nuclear magnetic resonance) spectra. These oligomers have good thermostabilities, with the degradation process starting above 265°C. Their mesomorphic and phase behavior were investigated using differential scanning calorimetry (DSC), polarizing optical microscopy (POM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) measurements. The results show that the silsesquioxanes exhibit a broad range of liquid crystalline phases at moderate temperature. The ultraviolet (UV)-induced cis–trans photoisomerization was also studied for the liquid crystalline silsesquioxanes in chloroform.

Keywords:

• Azobenzene groups
• liquid crystals
• silsesquioxanes

Acknowledgment

The reported research was supported by the Ministry of Science and Higher Education (grant no. N205 03431/1568).

Notes

^aFinal molar ratio calculated by ¹H-NMR.

^aTemperature of the samples at 5% loss weight.

^bInflection temperature of the samples between the two mass changes.