Fluorescent and photooptical properties of H-bonded LC composites based on stilbazole derivative

Abstract

A novel series of H-bonded LC (smectic and nematic) composites and “model” mixtures without hydrogen bonding based on the stilbazole derivative were prepared. As the matrices of the composites following polymers were synthesized: smectic homopolymer containing p-oxybenzoic groups, nematic copolymer containing p-oxybenzoic and methoxyphenylbenzoic side groups, and nematic homopolymer with methoxyphenylbenzoate groups. The spectral properties of composite films were studied in detail. Significant differences in the fluorescence spectra of H-bonded LC composites and “model” mixtures were revealed. Mechanism of the processes occurring in the films of the LC composites under the action of the UV light was proposed. The mechanism includes a reversible proton transfer involved in the H-bonds formation. It was found that in the oriented films of the nematic composite degree of fluorescence polarization is higher than in the films of a similar mixture without H-bonding. The effect of linearly polarized light on the optical properties of the composite films was studied. It was shown that the highest values of the photoinduced dichroism are achieved in nematic liquid crystals composites. It was revealed that for the irradiated LC composites annealing leads to decease of dichroism values (degree of polarized emission drops to zero), whereas for “model” LC mixture without hydrogen bonding a significant increase in these parameters was found.