Effect of pH on photopolymerization reaction of aniline derivatives with the tris(2,2′-bipyridyl)ruthenium complex and the methylviologen system

Photopolymerization of aniline derivatives was revealed to be induced by photoinduced electron transfer (PIET) between the tris(2,2'-bipyridyl)ruthenium complex [Ru(bpy)(3)(2+)] and electroactive molecules. Since the initial photopolymerization reaction depended on PIET between Ru(bpy)32+ and N-phenyl-p-phenylenediamine (PPD), the effect of pll of the polymerization solution on the PIET was investigated to improve the efficiency of the photopolymerization reaction. At lower pH, the quenching reaction of [Ru(bpy)(3)(2+)]* by PPD proceeded with low efficiency due to electrostatic repulsion between molecules concerning the PIET. This was clarified, by comparison with the results concerning the photochemistry in a higher pH solution. On the other hand, a lower pH should be required to induce the propagation because a lower pH inhibited the deprotonation of both aniline derivative and growing poly(aniline) chain. From the detailed analyses for both initial and propagation reactions, the increase in ionic strength was revealed to be a solution to improve the photopolymerization efficiency even in low pH.