Fluorinated Oligoazomethine with Azo Groups in the Main Chain as Stimuli-Responsive Photoactive Materials

Abstract

AbstractAzobenzene and azomethine (imine) photoactive groups attract much interest as efficient building blocks for the construction stimuli-responsive materials. Significant progress has been made on the synthesis of either polyazobenzenes or polyazomethines. At the same time, polymers or oligomers having both azo and azomethine groups are significantly less developed. In this work, the strategy to the synthesis of the light-responsive aldehyde-terminated oligoazomethine with azo groups and meta-oxyphenylene fragments (Azo-Oam-1) in the backbone was proposed. The oligomer with hydroxy groups at ortho position to the imine linkage was prepared by condensation polymerization of tetrafluorobenzene-based bis-hydroxybenzaldehyde with aromatic meta-linked octafluorobiphenylene-based diamine, where an excess of dialdehyde was used. The structure of the oligomer was characterized by Fourier transform infrared spectroscopy technique. Additionally, a model compound was synthesized to prove the formation of imine bond between bis-hydroxybenzaldehyde used in this study and aromatic amine (2-aminophenol). Interestingly that despite the oligomeric nature, Azo-Oam-1 can be solution-cast into flexible solid films with tensile strength of about 13 MPa and high thermal stability (up to 365 °C). The optical spectra of Azo-Oam-1 depend strongly on the solvent concentration and its pH value. The photoisomerization behavior and light-induced birefringence changes in Azo-Oam-1 film were investigated. Finally, we demonstrate the ability to record optical information using Azo-Oam-1 film in the form of polarization gratings.KeywordsAzo-containing polymersPolyazomethinesPerfluorinated fragmentsPhotoisomerizationLight-induced birefringencePolarization gratings