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

The absorption spectra of polyaniline (PAN) films obtained by electrochemic al polymerization on transparent SnO2-glass electrodes are analyzed. The sp ectra are recorded at steady-state potentials of 0.0 to 0.8V (Ag/AgCl) in a n aqueous HCl solution. Individual absorption bands, isolated by the Alents ev-Fok method, include both earlier known bands and some new absorption ban ds. The former correspond to pi-pi* transitions in the benzenoid rings (300 -320 nm), radical cations (similar to 435 nm), localized polarons (similar to 755 nm), and quinoid structures (similar to 655 nm). By comparing these results with the spectroelectrochemical data obtained earlier for electroch emically synthesized PAN in solutions of various acids and for vacuum-depos ited PAN, the newly found bands are assigned to different intermolecular in teractions, specifically, a donor-acceptor coupling of the quinoid moieties with counter anions (at 570 nm) and an electron exchange between highly co nducting domains of the film (similar to 900 nm).