Isolation of individual components in the electronic absorption spectra of polyaniline from the spectroelectrochemical data

The absorption spectra of polyaniline (PAN) films obtained by electrochemical polymerization on transparent SnO₂-glass electrodes are analyzed. The spectra are recorded at steady-state potentials of 0.0 to 0.8 V (Ag/AgCl) in an aqueous HC1 solution. Individual absorption bands, isolated by the Alentsev-Fok method, include both earlier known bands and some new absorption bands. The former correspond to π-π* transitions in the benzenoid rings (300-320 nm), radical cations (∼435 nm), localized polarons (∼755 nm), and quinoid structures (∼655 nm). By comparing these results with the spectroelectrochemical data obtained earlier for electrochemically synthesized PAN in solutions of various acids and for vacuum-deposited PAN, the newly found bands are assigned to different intermolecular interactions, specifically, a donor-acceptor coupling of the quinoid moieties with counter anions (at 570 nm) and an electron exchange between highly conducting domains of the film (∼900 nm)