Luminescence quenching of *[UO2F4]2− in aqueous solutions by anions

Abstract The luminescence lifetime of uranyl ions is strongly increased by complex formation with fluoride ions in neutral aqueous solution. A monoexponential luminescence decay with a lifetime of 160 ± 2 μs is observed in the presence of 0.5 M NaF. The * [UO 2 F 4 ] 2− species oxidizes carboxylate anions by an outer-sphere mechanism. For anions with oxidation potentials higher than 2 V, the logarithms of the quenching rate constants (log k q ) are linearly dependent on the oxidation potentials of the anions ( E ox ). This allows for the estimation of such potentials from kinetic data. The oxidation potentials of carboxylates RCOO − are only slightly dependent on R. The difference between these observations and earlier results may be interpreted in terms of two different pathways for the one-electron oxidation of carboxylates, depending on the balance between the driving force of the electron transfer reaction and the reorganization energies of the redox couples involved.