Photoreaction of a ZnO gel film chemically modified with β-diketones

Abstract

Chelate formation is confirmed by a red shift of the n → π* absorption peak of benzoylacetone (BzAcH) from 309 to 336 nm with its addition to a sol containing Zn²⁺ ions. The chelate bonds between Zn²⁺ and BzAc⁻ are mostly maintained in the gel film prepared from the sol. Irradiation of the gel film by a Xe lamp with a cut filter (λ_ex > 300 nm) in the presence of H₂O leads to decomposition of the chelate ring. As a result of the photolysis, ZnO–H groups, CH₃CHO and other carbonyl compounds are generated with the lost of CH₃ groups of the BzAc⁻ ligand and H₂O involved in the film. INDO/S calculations on a model complex (Zn(BzAc)(OEt)) assign the n → π* absorption to the electronic transition from a non-bonding molecular orbital (MO) distributed mainly at the phenyl group to an anti-bonding MO localized at the CO bonds. On the basis of these results, a photo-induced hydrolysis mechanism was presented to explain the formation of positive-type patterned ZnO films.