Photogalvanic Cells Composed of Polymers

When a photochemical process in solution gives a photoresponse at the electrode, the system can form a photogalvanic cell. The photoinduced redox reaction is typical for photogalvanic cells. The most well known photoredox system is thionine (TH+ 23) and ferrous ion88). The excited TH+ is reduced by Fe2+ to give TH and Fe3+ (Eq. (25)). 

Since illumination shifts the equilibrium to the right, the aqueous violet solution is decolorized. When the light is cut off, the color turns again to violet due to the equilibrium shift to the left. The reversible photoredox mixture gave a photopotential when irradiated in a photochemical cell composed of light and dark 

Aliphatic amines act as reducing agents for the photoreduction of phenazine or phenothiazine dyes. It was found that polyamine induces a much higher photopotential than monoamine 91). The value of the photopotential was strongly dependent upon the number of amino or imino groups in one molecule when an oligoamine was used (Fig. 25). The electron transfer from the amine to the excited dye was proposed to be facile due to a bifunctional interaction between the dye and the adjacent free and protonated N-groups of the polyamine (24). 

Photoredox polymers containing both dye and reducing groups were prepared by the reaction of poly(acrylic acid) (PAA) with dye and amine (en) in dry EtOH 92) to get (25). 

The aqueous solution of the photoredox polymer induced photopotential without any other reagent. The photopotential induced by the polymer was much higher than that by the corresponding monomer system, and the value did not depend on the amine/dye ratio contrary to the monomeric system whose photopotential strongly depended on that ratio (Fig. 26). The presence of reductant near the dye and the isolated pendant dye structure were considered to be the cause for the high efficiency of the photoredox polymer. 

---