Comment on "Quantum yield and electron-transfer reaction of the lowest excited state of the uranyl ion"

Abstract

When experiments were conducted with aqueous solutions (pH/sub 2/) of uranyl nitrate and tris (1,10-phenanthroline) ruthenium (II) perchlorate using steady-state fluorescence quenching, quenching of *Ru(phen)/sub 3//sup 2 +/ by UO/sub 2//sup 2 +/ followed Stern-Volmer kinetics, with K/sub sv/ = (1.89 +- 0.20) x 10/sup 2/m/sup -1/. Using this and the known lifetime of *Ru(phen)/sub 3//sup 2 +/ under these conditions (after correcting for quenching by dissolved oxygen), a rate constant of 1.2 x 10/sup 9/M/sup -1/s/sup -1/ was obtained for the quenching process. This is close to the rate of quenching of *Ru(phen)/sub 3//sup 2 +/ by Fe/sup 3 +/ /sup 2/ is slightly higher than the rate of quenching of *Ru(bpy)/sub 3//sup 2 +/ by UO/sub 2//sup 22/ /sup 1/ and is consistent with the same mechanism as in these two cases, i.e., electron transfer. As observed with the Ru(bpy)/sub 3//sup 2 +//UO/sub 2//sup 2 +/ system, prolonged photolysis did not result in any permanent change in the absorption spectrum of the system, demonstrating a high overall photostability. Because of the intense absorption of the Ru(phen)/sub 3//sup 2 +/ species, the steady-state experiments do not permit demonstration of the reverse quenching of *UO/sub 2//sup 2 +/ by Ru(phen)/submore » 3//sup 2 +/. However, studies on the fluorescence excitation spectra are consistent with the occurrence of such a process.« less