Photooxidation of anthracene derivatives in AOT/heptane reversed micelles

Abstract

The reactivity of different anthracene derivatives toward singlet oxygen has been studied in AOT reverse micelles in heptane as a function of the AOT concentration and w(w = water AOT ) ratio. The reactivity of 9,10-dimethylanthracene, a compound that can be assumed to remain in the heptane, is independent of both AOT and water concentration. For solutes totally incorporated to the micelles (anthracene carboxylic acid (AC −) and dimethyl ethyl-3-(9-anthryl)-propylammonium bromide (AN +), the aromatic consumption rate is independent of AOT concentration but increases when w increases. The w dependence is larger for AC − than for AN +, a result that can be explained in terms of a displacement of AC − toward the micellar water pools. For this compound, the computed bimolecular rate constant becomes, at large w, very close to that obtained in bulk water. The reactivity of anthracene methanol (AM) changes both with the AOT concentration and w. The partition of AM between the micelles and the n-heptane pseudophase was obtained from quenching experiments employing Ru(bpy) 3 +2 as fluorescent probe. The 1O 2-AM results can be explained in terms of the partition of AM and an intramicellar bimolecular rate constant of 1.1 × 10 7 M −1 s −1. This value is larger than that obtained when ethanol is employed as solvent.