The mechanism of the photoreaction of uranyl 1,3-diketonate complexes as thin films on silicon surfaces

The photolysis of the complexes UO 2 (OH 2 )(RCOCHCOR) 2 (R  Me or t -C 4 H 9 ) on silicon surfaces leads to the production of uranium oxide. The quantum yields for this process are quite different for the two complexes. The methyl and the tert -butyl-substituted complexes decompose with quantum yields of 0.007 (±40%) and 0.015 (±30%) respectively. In spite of the similarity in chemical formula a detailed mechanistic investigation indicates that two distinct reaction pathways exist for these systems. In the case of the methyl derivative the reactivity is initiated by an excited state hydrogen abstraction through a six-member transition state. The tert -butyl-substituted complex cannot undergo hydrogen abstraction and so the excited state decays by a ligand fragmentation reaction.