Polymer effects in photoinduced charge separation

Abstract

Reverse electron transfer between photogenerated redox pair in bulk aqueous solutions can be efficiently suppressed by collecting the photoliberated electron to the positively charged surface of molecular assemblies such as micelles, bilayers and polymers. Zwitterionic viologen molecules serve as efficient electron carriers, which shuttle between the bulk phase and the surface of molecular assemblies. The molecular assemblies with aligned viologen units at the surface are particularly useful as molecular device for the electron enrichment and storage. Quantitative charge separation of the cage-escaped redox pair can be achieved by the use of the amphiphilic viologen molecular assemblies in combination with the zwitterionic viologen. The lifetime of charge-separated state can be extremely extended in these systems : ca 30 ms for the viologen bilayer and above 1 s for the polymer with pendant viologen. Amphiphilic viologen molecular assemblies also help to increase charge-separation of the photoinduced, intramolecular electron transfer in sensitizeracceptor linked system incorporated into the molecular assemblies. All of these phenomena are ascribed to cooperativity effects of aligned viologen units, which induce electron hopping a long the surface via successive electron exchange between viologen molecules.