Redox behavior of poly (2-methoxyaniline-5-sulfonic acid) and its remarkable thermochromism, solvatochromism, and ionochromism

A detailed investigation has been carried out of the redox behavior of poly(2-methoxyaniline-5-sulfonic acid) (PMAS) in aqueous solution. Oxidation of PMAS emeraldine salt with aqueous 0.10 M ammonium persulfate proceeded in an analogous fashion to that observed with unsubstituted polyaniline, generating a pale purple species with λmax at 330 and 540 nm, consistent with the fully oxidized pernigraniline base form of PMAS. Subsequent protonation with dilute acid yielded the blue PMAS pernigraniline salt (λmax 670 nm). In contrast to the behavior of previously studied polyanilines, the hydrazine reduction of PMAS emeraldine salt produced an equilibrium mixture of two leucoemeraldine base forms with λmax at 335 and 408 nm, respectively. These PMAS leucoemeraldine base species, believed to be conformers with differing degrees of planarity along their polymer chains, exhibit remarkable thermochromism, solvatochromism, and ionochromism that is unprecedented in polyaniline chemistry.