The kinetic parameters of porphyrin-photosensitized formation and deactivation of singlet molecular oxygen (O-1(2)) and their dependence on the concentration of the O-1(2) quencher sodium azide were investigated in air-saturated water, ethanol, and aqueous micellar solutions of detergents using time-resolved measurements of oxygen phosphorescence under pulsed laser excitation. The lifetimes of O-1(2) formation and deactivation and the rate constants of O-1(2) quenching by sodium azide were determined. It was shown that, with no azide in the solutions, the rise in phosphorescence intensity after the laser flash corresponded to the kinetics of energy transfer from the porphyrin triplet molecules to oxygen, while the decay kinetics corresponded to the kinetics of O-1(2) deactivation. In the presence of detergent, a considerable increase in the O-1(2) lifetime was observed, which is likely due to the localization of O-1(2) molecules mostly in lipophilic micelles and not in the water phase. If relatively high azide concentrations were used, the lifetime of the porphyrin triplet state did not change but the O-1(2) lifetime decreased to values similar to those in living cells. In this case, the inversion of the phosphorescence kinetic phases was observed. The rise corresponded to O-1(2) deactivation, and the decay, to the energy transfer from triplet porphyrin to oxygen. The data suggest that, in living cells, O-1(2) molecules are also located mainly in lipophilic structures and the O-1(2) lifetime determines the kinetics of the phosphorescence rise after the laser pulse.
