Photoeffects in thin-film molecular-level chromophore-quencher assemblies. 2. Photoelectrochemistry

Photocurrents appear upon visible photolysis of thin films of chlorosulfonated polystyrene ([-CH₂CH(p-C₆H₄SO₂Cl)]_x-; PS-SO₂Cl) containing the chemically attached chromophore [(bpy)₂Ru(5-NH₂phen)](PF₆)₂ (bpy is 2,2′-bipyridine, 5-NH₂phen is 5-amino-1,10-phenanthroline). The chemical attachment is by sulfonamide binding. The photocurrents arise following oxidative quenching of the metal-to-ligand charge-transfer excited state(s) of the complex by paraquat (PQ²⁺) in the presence of the reductive scavenger TEOA, triethanolamine. A kinetic model has been derived that accounts for variations in photocurrent with light intensity and [PQ²⁺] or [TEOA] in the external solution. Comparisons with earlier quenching studies obtained by laser flash photolysis show that only a fraction of the chromophores in the film contribute to the photocurrent. The efficiency of photocurrent production depends upon the concentration gradient of the chromophore. It rises initially as the chromophore content increases but falls dramatically in films where the chromophore has reached the electrode-film interface. Under maximal conditions the per photon absorbed quantum yield for photocurrent production reaches 0.14,0.18 with 0.1 M isopropyl alcohol added.