Vibrational spectra and structure of polyaniline and related compounds

Vibrational spectra of various forms of polyaniline have been analyzed on the basis of data of isotopically substituted analogs and model compounds. White polyaniline (1A) obtained by electrochemical reduction of as-prepared film (2S) followed by hydrazine treatment has been proved to be a genuine poly(imino-1,4-phenylene). Part of the imino-1,4-phenylene (IP) in 1A are converted into its cation (IP⁺) by acid treatment (1S), radical cation (IP⁺) by electrochemical oxidation in non-aqueous medium (doped 1A, conductive), and a structure consisting of a quinone diimine and a benzene ring (-NC₆H₄NC₆H₄-,NP) by exposure to oxygen [1A(O₂)]. Alkali-treated doped 1A, whose vibrational spectra are similar to those of alkali-treated 2S (2A), is composed of IP and NP. A simple scheme of interconversion of the four unit structures, of which radical cation is related to electrical conduction, is useful to understand the complex interconversion of colors and other physicochemical properties of the polyaniline forms. Analysis of the infrared NH stretching region suggests that the polymers form hydrogen bond networks.