PHOTOCURRENTS IN THIN POLYMERIC FILMS - CHROMOPHORE QUENCHER ASSEMBLIES BASED ON POLYPYRROLE

Thin films of polymers consisting of mixtures of poly(N,N-bis(3-pyrrol-1-ylpropyl)-4,4′-bipyridinium) dication (poly-(pyr)2-PQ2+) and poly(tris[4-(2-pyrrol-l-ylethyl)-4′-methyl-2,2′-bipyridine] ruthenium(II)) dication, poIy-(pyr)3-[Ru]2+ have been prepared by co-oxidative electropolymerization of the corresponding pyrrole-containing monomers. Significant photocurrents are observed when the films are photolyzed in the presence of the irreversible electron-transfer donor, triethanolamine (TEOA). The initial step in the photocurrent mechanism is static, oxidative quenching of the metal to ligand charge transfer (MLCT) excited states of the ruthenium complex by poly-(pyr)2-PQ2+. This gives poly-(pyr)2-PQ+ and poly-(pyr)3-[Ru]3+. The photoproduced -[Ru]3+ is subsequently reduced by TEOA. The photocurrent arises by electron transfer to the electrode at the inside via the poly-(pyr)2PQ2+/+ couple. A kinetic model has been derived which explains variations in the photocurrent with light intensity and [TEOA]. The magnitude of the photocurrent depends upon the composition and microstructural array of the chromophore/quencher assembly. Photocurrent efficiencies rise as the ratio of poly-(pyr)2-PQ2+ to poly-(pyr)3-[Ru]2+ increases in copolymeric films. High efficiencies require close contact and intermingling between the -[Ru]2+ and -PQ2+ sites. The conjugated polypyrrole backbone decreases the efficiency by competitive light absorption and by energy-transfer quenching of the MLCT excited state. Under maximal conditions, per photon absorbed quantum efficiencies for photocurrent production of greater than 10% have been achieved. © 1990 American Chemical Society.