Nitroxide reduction by electron transfer from the eosin triplet state: electron paramagnetic resonance and flash photolysis studies

The paramagnetism loss of nitroxide, photosensitized by eosin, was analysed in basic aqueous and micellar media using electron paramagnetic resonance (EPR) spectroscopy. In cetyltrimethylammonium bromide micelles and sodium bis(2-ethylhexyl)sulphosuccinate—n-heptane microemulsions, the paramagnetism decay curves are monoexponential. This is not the case in neat water and sodium dodecylsulphate micelles, for which more complex decays were recorded. It is concluded from flash photolysis measurements that the eosin triplet state is physically quenched by nitroxide and that the latter can be reduced by electron transfer either from the triplet state or from the semireduced form of eosin. This sequence of reactions was confirmed by experiments in micellar media and leads to an understanding of the EPR results.