Photoelectrochemical and spectroscopic studies of sulfonated polyanilines .1. Copolymers of orthanilic acid and aniline

Conducting films of sulfonated polyaniline were produced by copolymerization of orthanilic acid (o-aminobenzenesulfonic acid) with aniline on a platinum electrode. The degree of sulfonation and the oxidation states of the elements were examined using X-ray photoelectron spectroscopy. The copolymer structure was further investigated by in situ Raman spectroscopy (514 nm excitation). Photocurrent profiles on a millisecond time scale in response to a light-flash perturbation were taken, producing exclusively anodic photocurrents for the copolymer in the conductive state. Partial phase diagrams far the sulfonated copolymer were constructed, mapping the conductive regions as a function of pH and electrode potential. Both conductor-insulator boundaries moved by 60 mV per pH unit, consistent with the internal redox processes of the copolymer, while the sulfonated polyaniline was soluble in neutral pH solutions.