Photoinduced electron transfer from N-alkylphenothiazines (PCn, n = 1, 3, 6, 12, and 16) solubilized in sodium dodecyl sulfate (SDS) micelle interacting with poly(ethylene oxide) (PEG) to interface D2O as an electron acceptor is studied with electron spin resonance (ESR) and electron spin echo modulation. The photoproduced radicals are identified as the N-alkylphenothiazine cation radical and the surfactant alkyl chain radical of SDS. The total photoyield decreased from PC1 to PC3 and then increased to PC16 The photoyields increased monotonically with increasing PEO concentration. The photoyields are correlated with the deuterium modulation depth of PCn+ with D2O at the micelle interface as a function of the alkyl chain length of PCn and the concentration of PEO since the modulation depth measures relative changes in the interaction distance between the phenothiazine moiety and interface D2O. The photoyield and deuterium modulation depth trends show a good correlation which indicates that the electron transfer from phenothiazine moiety to interface water is mainly controlled by the distance between them, which is controllably varied by the alkyl chain length of phenothiazine and the intercalation of PEO into the interface region of the SDS micellar headgroup.