LUMINESCENCE QUENCHING OF STAR-(UO2F4)2- IN AQUEOUS-SOLUTION BY ANIONS

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-mu-s is observed in the presence of 0.5 M NaF. The *[UO2F4]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.