Laser pulse photolysis of amphiphilic anthraquinone-2-sulfonic acid (2-AQS) in liposome buffer solution shows transient electron spin polarization consisting of a net emissive polarization attributable to hydrogen abstraction in a lipid bilayer and a net absorptive pattern caused by electron transfer via the triplet exciplex (3)(2-AQS -Cl )* in an aqueous phase. The diffusion rate of the neutral semiquinone radical from the interior of the lipid bilayer to a bulk water region is determined to be 7 x 10(5) s(-1), suggesting that the rate is slower compared with the micellar system. (C) 2008 Published by Elsevier B.V.