Uncatalyzed synthesis of polyphenylacetylene cross-linked by viologen groups and their chemical properties

Polyphenylacetylenes cross-linked with viologen groups (polymers 1a and 1b) were obtained from the reaction of 4-ethynylaniline with 1,1′-bis(2,4-dinitrophenyl)-4,4′-bipyridinium dichloride (salt 1) and the reaction of 4-(1-trimethylsilylethynyl)aniline with salt 1, followed by the deprotection of the trimethylsilyl group. Model compound (model 1) was synthesized by the reaction of 4-ethynylaniline with 1-(2,4-dinitrophenyl)-4,4′-bipyridinium chloride (salt 2). Ultraviolet–visible spectra revealed that the polymers 1a and 1b had an expanded π-conjugation system along the polymer chain: the polymer showed an onset position of absorption at a wavelength approximately 100 nm longer than the corresponding wavelengths of the model compound. Polymers 1a and 1b received a two-step electrochemical reduction in the viologen group within the polymer and an electrochemical oxidation of the polymer backbone.