LIGHT-INITIATED REDOX REACTIONS IN FUNCTIONAL MICELLAR ASSEMBLIES .2. DYNAMICS IN EUROPIUM(III) SURFACTANT SOLUTIONS

The light-induced reduction of Eu3+ ions by n-methylphenothiazine (MPTH) and the subsequent back electron transfer from Eu2+ to MPTH+ were examined in anionic surfactant aggregates in which Eu3+ together with Na+ or Zn2+ constituted the micellar counterion atmosphere. In the back reaction two well-separated kinetic components can be distinguished arising from a fast intramicellar and a much slower intermicellar reaction. The rapid process obeys first-order kinetics and is competing with the escape of Eu2+ from its native micelle into the solution bulk. Two escape modes have been detected which can be attributed to simple surface detachment of Eu2+ (rate independent of micellar concentration) and direct transfer (hopping) to an adjacent aggregate (rate dependent on micellar concentration). The slower process obeys second-order kinetics, with the rate constant decreasing with increasing micellar concentration. A phenomenological kinetic model is developed which allows us to evaluate the rate constants for the elementary processes involved in the back reaction and to design ways to prevent the intramicellar as well as to retard the intermicellar process. © 1979, American Chemical Society. All rights reserved.