Nonradiative and radiative deactivation of singlet molecular oxygen (O-2(a(1)Delta(g))) in micellar media and microemulsions

The effects of microheterogeneous media (micelles and microemulsions) on th e lifetime and, to our knowledge for the first time, on the emission of sin glet molecular oxygen (O-2 (a(1)Delta (g)), denoted as O-1(2)) were investi gated. Micellar media and various types of microemulsions based on anionic (sodiumdodecyl sulfate), cationic (cetyltrimethylammonium chloride) or noni onic (Triton X-100) surfactants were formulated for this purpose. The nonra diative and radiative deactivation rate constants (k(d) and k(o), respectiv ely) were determined in selected microheterogeneous media and in the pure s olvents used for their formulation, by combining steady-state and time-reso lved LO, luminescence detection techniques. We have shown that a simple add itive model, as used in homogeneous mixtures of solvents, was inadequate fo r predicting values of k(d) and k(e) in organized media. In contrast, both O-1(2) lifetimes (tau (Delta) = 1/k(d)) and k(e) in the microheterogeneous systems investigated could be predicted with good precision from the compos ition of the media and the tau (Delta) and k(e) values in the pure solvents , using a two-pseudophase kinetic model for the O-1(2) distribution. Such a model takes into account the average times spent by O-1(2) in the aqueous and lipophilic pseudo-phases of the organized media, the corresponding equi librium constant (K-eq) depending on the nature of the system. (C) 2000 Els evier Science B.V. All rights reserved.