Photophysics of the excited uranyl ion in aqueous solutions. Part 5.—Fluorescence quenching by micellar solutions of triton X-100
Abstract
The effect of the micelles of Triton X-100 on the biexponential decay of (UO2+2)* has been investigated. Data are analysed in terms of a reversible crossing mechanism for the decay. Azulene fluorescence quenching and 13C n.m.r. studies strongly suggest that uranyl ions are able to penetrate deep inside the micelle core. Micelle quenching for the reversible decay of (UO2+2)* occurs in the interior (kq= 3 × 1010 dm3 mol–1 s–1) and at the surface (kq= 1.5 × 109 mol–1 dm3 s–1) of the micelles. The latter process has a rate virtually identical to that for the free surfactant molecules. Penetration of (UO2+2)* inside the non-polar regions of the micelle core increases solvent exchange rates by ca. two orders of magnitude. Uranyl-ion excimers are formed in occupied micelles. The quenching processes decrease strongly for these species because excimers do not penetrate the micelles.
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