Electrochemical oxidative polymerization of sodium 4-amino-3-hydroxynaphthalene-1-sulfonate and structural characterization of polymeric products

The new semiconducting, electroactive, water-soluble polymeric material has been synthesized by the electrochemical polymerization of sodium 4-amino-3-hydroxynaphthalene-1-sulfonate (AHNSA-Na salt), from its aqueous solution. The polymeric products were characterized by gel permeation chromatography (GPC), conductivity measurements, cyclic voltammetry, and UV-visible, FTIR, Raman, NMR (1H and 13C) and electron spin resonance (ESR) spectroscopic techniques. GPC profile evidenced chains of molecular weights up to ∼6300, and revealed oligomers (8-mer to 12-mer) as predominant species. FTIR spectroscopy findings of newly formed substitution patterns on naphthalene rings in the poly(AHNSA-Na salt) are well correlated with main coupling modes theoretically predicted by MNDO-PM3 semi-empirical quantum mechanical calculations. Based on these studies, it has been found that the poly(AHNSA-Na salt) consists mainly of dimer units formed via N-C6 and N-C8 coupling reactions. The paramagnetic nature of the poly(AHNSA-Na salt) has been proved by ESR spectroscopy, and its redox activity was confirmed by cyclic voltammetry. Intensity ratio of two new bands in the UV-visible spectrum assigned to the poly(AHNSA-Na salt) polaronic and bipolaronic forms, and the presence of naphthoiminoquinonoid and benzenoid segments detected by FTIR and Raman spectroscopy, indicate prevalence of partly and fully oxidized bipolaronic forms of the poly(AHNSA-Na salt).