Analysis of the structure of polyaniline absorption spectra based on spectroelectrochemical data

Using the results of spectroelectrochemical experiments (absorption spectra measured at different stationary potentials from 0.0 to 0.8 V versus Ag \A gCl) performed in aqueous acidic medium for polyaniline (PAN) films electro chemically deposited onto SnO2-glass substrates, individual absorption band s composing the spectra were analyzed. The key point of the method used for separation of the individual bands (Alentsev-Fock method) is that one need not have a preliminary notion about real shape, number and positions of in dividual components of the spectrum. The necessary conditions are the follo wing: (1) in the most common case, the number of spectra used for separatio n should be equal to or exceed the number of possible components: (2) the s pectra should contain different proportions of the individual bands. Both w ell-known (cation-radicals (near 435 nm), localized polarons (near 755 nm), quinoid structures (near 665 nm)) and some new absorption bands were found . Comparing these results with our earlier data for electrochemically depos ited and vacuum evaporated PAN films in different acidic media, the newly r evealed band near 570 nm may be attributed to donor-acceptor interaction of quinoid fragments of the polymer chain with counter anions. The band in th e NIR region (> 900 nm), which is often referred to as that of 'free carrie rs', apparently characterizes electron exchange between highly conductive a reas of the film. (C) 2000 Elsevier Science S.A. All rights reserved.