Optical switching and anion-induced chromogenic application in conjugated polyazomethine derivatives

New azomethine-containing conjugated polymers linked with fluorene and/or quinoxaline units were synthesized via Suzuki-coupling reaction in the presence of palladium(0) catalyst followed by hydrogenation and polymer reaction with cyclohexanone. The polymer exhibited red absorption color of red and intense red emission in chloroform solution. The polymers in solid state showed instantaneous color change when exposed to acid gas and recovered their initial colors rapidly when kept in air. Using pH-control, reversible optical switching was accomplished in the presence of trifluoroacetic acid (TFA) and triethylamine as an acid and a base, respectively. Diverse colors were demonstrated when exposed to a variety of anions, especially iodide and acetate ions, with the TFA-treated polyazomethines mainly because of difference in proton abstraction ability as well as conformational changes of molecular backbone.