Polar-end 3,5-diarylisoxazole liquid crystals with SmA and highly ordered CrE mesophases

Abstract

Polar-end 3,5-diarylisoxazol liquid crystals (ILCs) with nitro, amine and bromine polar terminal groups were thermally and structurally characterized. The nitro and bromo terminated compounds exhibited the highly ordered CrE mesophase below the conventional SmA. X-ray data obtained for the SmA mesophase showed that the structural organization of this phase evolves from monolayer SmA₁ (Br), to interdigitated SmA_d (NO₂), and to quasi-bilayer SmA₂ (NH₂). The optical band gap and photoluminescence quantum yields are strongly dependent on the terminal groups and complementary DFT calculations supported the experimental observations. Direct current (DC) electrical measurements demonstrated a significant dependence on temperature, exhibiting increased conductivity at elevated temperatures, regardless of the mesophase. Alternating current (AC) electrical measurements suggested the presence of ionic conduction, with a huge increase in capacitance at low frequencies.