Abstract

The effects of microheterogeneous media (micelles and microemulsions) on the lifetime and, to our knowledge for the first time, on the emission of singlet molecular oxygen (O 2 (a 1Δ g), denoted as 1O 2) were investigated. Micellar media and various types of microemulsions based on anionic (sodiumdodecyl sulfate), cationic (cetyltrimethylammonium chloride) or nonionic (Triton X-100) surfactants were formulated for this purpose. The nonradiative and radiative deactivation rate constants ( k d and k e, respectively) were determined in selected microheterogeneous media and in the pure solvents used for their formulation, by combining steady-state and time-resolved 1O 2 luminescence detection techniques. We have shown that a simple additive model, as used in homogeneous mixtures of solvents, was inadequate for predicting values of k d and k e in organized media. In contrast, both 1O 2 lifetimes ( τ Δ=1/ k d) and k e in the microheterogeneous systems investigated could be predicted with good precision from the composition of the media and the τ Δ and k e values in the pure solvents, using a two-pseudophase kinetic model for the 1O 2 distribution. Such a model takes into account the average times spent by 1O 2 in the aqueous and lipophilic pseudo-phases of the organized media, the corresponding equilibrium constant ( K eq) depending on the nature of the system.

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