Nanoparticle mediated photodefluorination monitored by 19F NMR

The photoreduction of monofluorinated phenols and benzoic acids on polyphosphate capped ZnS nanoparticles is examined. Defluorination is monitored using 19F NMR. Photoreductive defluorination on ZnS nanoparticles produces fluoride while direct photolysis produces ring opening products. Reaction on bulk ZnS produces ≪1% defluorination under the same conditions. The quantum yield and turnover numbers are presented for six compounds with the fluoride substituted at different positions around the aromatic ring. The reaction rates are affected by the presence of electron donating or withdrawing groups attached to the aromatic ring. The rates of product produced are 4-fluorophenol > 2-fluorophenol > 3-fluorophenol when the electron donating hydroxyl group is present and the opposite trend of 3-fluorobenzoic acid > 2-fluorobenzoic acid > 4-fluorobenzoic acid when an electron withdrawing group is attached to the benzene.