Laser flash photolysis of metal oxide supported vanadyl catalysts.: Spectroscopic evidence for the ligand-to-metal charge-transfer state

A series of vanadyl containing samples supported on metal oxides (SiO2, Al2O3, K-doped Al2O3, TiO2, MgO and ZnO) have been studied by laser flash photolysis. Excitation at 266 or 308 nm generated transients (300 nm, lambda(max), 500 nm) with lifetimes on the microsecond time scale. These were assigned to the ligand-to-metal charge-transfer triplet excited state. The absorption maximum varied with the nature of the support. Samples having higher vanadium loading showed additional transients attributed to vanadyl aggregates.