Photoelectrochromism and photohydrolysis of sulfonated polyaniline containing Ru(bpy)32+ film for negative and positive image formation

Sulfonated polyaniline (SPAn) was employed to incorporate photocatalytic molecules directly into a polyaniline (PAn) matrix. Photoinduced electron transfer between SPAn and the tris(2,2′-bipyridyl)ruthenium complex (Ru(bpy)32+) was studied for a Ru(bpy)32+-incorporated SPAn film in solutions containing viologens. The change in the spectrum of the film was observed by the illumination to the electrochemically reduced film under open circuit conditions in an aqueous solution at pH 2.5 containing methylviologen (MV2+). This is due to a photoelectrochromism, caused by the photooxidation of SPAn by the photoexcited Ru(bpy)32+. The film was hydrolyzed in the aqueous solution once the potential was swept above +1.2 V. Ru(bpy)32+ molecules were revealed to accelerate the hydrolysis of the SPAn backbone. Although the illumination to the electrochemically reduced film under open circuit did not seem to induce the hydrolysis under the present conditions, the fully oxidized film was photohydrolyzed by the illumination, leading to a decrease in the absorption corresponding to SPAn at the illuminated part. The photoelectrochromism and photohydrolysis of the film were discussed from a viewpoint of negative and positive image formation, respectively.