Fluorescent chiral fluorinated liquid crystalline polymers containing rare earth complexes

Abstract

Fluorescent chiral fluorinated liquid crystalline polymers containing rare earth complexes (RE-LCPs) possessing wonderful liquid crystalline properties and distinct fluorescence properties were graft copolymerized using poly(methylhydrogeno)siloxane (PMHS), a chiral fluorinated liquid crystalline monomer (M₁), and a fluorinated rare earth complex (RE-M₂). The chemical structures and liquid crystalline behaviors of RE-LCPs were characterized using various experimental techniques. The introduction of a low amount of fluorinated rare earth complexes endowed the polymers with momentous luminescence properties. All the polymers were chiral. The rare earth complexes did not change the liquid crystalline textures of the polymers which were confirmed by X-ray diffraction. Fourier transform infrared imaging exhibited that the rare earth complexes were evenly distributed in polymers. A structural model of RE-LCPs was established to express the interaction and the distribution of the components. The RE-LCPs displayed reversible mesomorphic phase transitions, wide mesophase temperature ranges, and high thermal stabilities. The thermogravimetric analysis (TGA) results showed that the decomposition temperatures (5% weight loss) of RE-LCPs were greater than 300 °C in all RE-LCPs. The RE-LCPs can emit soft red light or green light when being excited. Luminescence intensities of the RE-LCPs gradually increased with an increase of rare earth complexes from 0 to 1.5 mol%. The temperature dependence of fluorescence intensity was studied in a liquid crystalline phase, where the fluorescence intensities of RE-LCPs decreased monotonically with the increase of temperature.