Electron Magnetic Resonance Study of the Photoreduction of Alkylviologens in Anionic Sodium Dodecyl Sulfate and Cationic Dodecyltrimethylammonium Bromide Micelles

Abstract

Photoinduced electron transfer from micellar counterions to a viologen moiety through the micellar interface was studied versus the pendant alkyl chain length, the number of alkyl chains on the viologens, and the interface charge of the micelles. The photoreduction yields decrease more rapidly with increasing alkyl chain length for dialkylviologens than for monoalkylviologens due to greater hydrophobic interactions with the surfactant alkyl chains. This also results in higher photoyields of the monoalkylviologens versus the dialkylviologens due to a shorter electron transfer distance for the monoalkylviologens even though the dialkylviologens have better coupling with the micellar counterions due to an orientation of the viologen moiety parallel to the micellar interface. Larger photoyields are obtained in cationic dodecyltrimethylammonium bromide (DTAB) micelles than in anionic sodium dodecyl sulfate (SDS) micelles because of a lower energy barrier for electron transfer through the positively charged micellar interface. Thus, photoinduced electron transfer across micellar interfaces is controlled first by the energy barrier, second by the electron-transfer distance, and third by the relative orientations of the donor and acceptor.