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

• Published in: Journal of materials science Vol. 38; no. 8; pp. 1703 - 1707
• Main Authors: Kawahara, T, Ishida, T, Tada, H, Noma, N, Tohge, N, Ito, S
• Format: Journal Article
• Language: English
• Published: Heidelberg Kluwer Academic Publishers 15.04.2003; Springer; Springer Nature B.V
• Subjects: Absorption; Carbonyl compounds; Carbonyls; Chelates; Chemical bonds; Chemistry; Diketones; Doppler effect; Exact sciences and technology; gels; General and physical chemistry; hydrolysis; ions; irradiation; Materials science; Molecular orbitals; Organic chemistry; Photochemistry; Photolysis; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Red shift; Sol-gel processes; zinc; Zinc oxide; Ultraviolet irradiation; Photolysis; Reaction mechanism; Zinc oxide; Diketone; Photochemical reaction; Infrared spectrum; Absorption spectrum; Organic compounds; Modified material
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1023/A:1023271509004

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 (λₑₓ > 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.