The O2/H2O redox couple as the origin of the structural/electronic defects in polyanilines

The protonation of N,N'-diphenyl-1,4-phenylenediimine (BQB oligomer, representative of the polyaniline (PANI) unit) by H2SO4 and non-oxidative acids like H3PO4. HCl and CH3COOH is studied by UV-Vis-NIR and resonance Raman spectroscopies. Emphasis is put on the water content effect. The acid-solubilised BQB is reduced to the amine oxidation state: in diluted acids, protonated (BBB)(2+) species are formed while a mixture of radical cations and protonated (BQB)(2+) species is observed for higher concentrations. The results show that redox reactions involving the O-2/H2O couple are present as side-reactions. In concentrated HCl acid, the presence of protonated (BBB) species chlorinated on the ring indicates that the Cl-2/Cl- redox couple participates to the redox phenomena. Side-reactions randomly affect the quinoid or the benzenoid segments of the polyaniline, changing the backbone chain linkage during EB and ES synthesis. This prevents ideal linking for the final ES material and the resulting materials failed to achieve the intrinsic conductivity expected for ideal ES products. (C) 2003 Elsevier Science B.V. All rights reserved.