AbstracL Fourier Transform EPR (FT-EPR) was used to study the formation and decay of free radicals produced by photoionization of phenothiazine (PTH) solubilized in aqueous SDS and Triton X-100 micellar solutions in the absence and presente of electron aeceptors. C1DEP spectra produced by PTH photoionization in micellar solution differ from those found in homogeneous solution. The effect is attributed to changes in relative importante of single-photon, singlet excited state, and biphotonic, triplet exeited state, photoionization. With quinone acceptors present in the bulk aqueous phase, photoionization of PTH in SDS, results in instantaneous formation of quinone anion radicals that carry the spin polarization of the precursor hydrated electrons. Ir the acceptor is anchored in the micelle, electron capture carmot compete with electron escape hato the aqueous phase. Instead, anion radicals are formed primarily by reductive quenching of 3pTH*. This process gives rise to a spectrum that is attributed to long-lived spin-correlated radical pairs, [PTH+...Q-].