LIGHT‐INDUCED ELECTRON TRANSFER REACTIONS BETWEEN CHLOROPHYLL and ELECTRICALLY CHARGED ACCEPTORS IN POSITIVELY and NEGATIVELY CHARGED LIPID BILAYER VESICLES*

Abstract

Abstract— The effects of electrostatic interactions on the dynamics of photoinduced electron transfer reactions involving chlorophyll and electrically charged acceptors (either positively charged methyl viologen or negatively charged sulfonated quinones) have been investigated by laser flash photolysis in lipid bilayer vesicles into which varying amounts (0‐30 mole percent) of positively or negatively charged surfactants were incorporated. Chorophyll triplet decay kinetics were modified due both to vesicle expansion caused by charge repulsion effects, and to changes in the local concentration of quenchers resulting from attractive or repulsive interactions with the vesicle surface. Radical yields were either increased or decreased as a result of electrostatic interactions which occurred between the radical products of triplet quenching and the charged surface, and which acted upon the radical ion‐pair separation process. In some cases, these effects were quite large. Radical decay halftimes were also changed by large amounts as a consequence of either attractive or repulsive forces acting upon the acceptor ion‐radical species, which influenced its ability to undergo reverse electron transfer to oxidized chorophyll. In the most favorable case, approximately 100% of the chlorophyll triplets produced by pulsed laser excitation were converted into radicals, which decayed by reverse electron transfer with a halftime of 70 ms.