Synthesis And Property Study Of Unsymmetric Bent-core Liquid Crystals

In this thesis, unsymmetric liquid crystalline molecules with 3-amino-2-methylbenzoic acid as bent core, azo group or schiff's base as linkage, and the molecule with 3-amino-2-fluorobenzoic acid containing azo linkage were synthesized. The chemical structures of these molecules were confirmed by 1H NMR and HRMS spectra. Their liquid crystalline properties and phase transition temperatures were studied by differential scanning calorimetry and polarizing optical microscopy, it was found that the melting and clearing points decreased and the liquid crystalline phases reduced as the number of aromatic ring reducing, the molecules with five aromatic rings had the most abundant liquid crystalline phases, whereas the molecule with three aromatic rings linked by azo group only had N phase by cooling, the three-ring fluorinated molecule had no liquid crystalline phase. Comparing the molecules with Schiff base with those with azo group, it was found that the molecules with azo group had better liquid crystalline properties. The azo molecules have an absorption peak between 330-360 nm due toπ-π* electron transition and a weak absorption peak between 430-450 nm due to n-π* electron transition, these molecules have a long thermal response time in dark.