Photoinduced Electron Transfer in Organized Assemblies

Article abstract of DOI:10.1021/ja00402a049

Photoexcitation of charge-transfer systems pyrene-dimethylaniline and pyrene-dibutylaniline has been studied in several organized assemblies, micelles, microemulsions, and vesicles.Both steady state measurements and pulse laser photolysis date show that the quenching of excited pyrene on the surface by the anilines is rapid but can be described by diffusional-type processes.Detailed mechanisms of the processes are discussed.The main products of the quenching are pyrene anions and dialkylaniline cations.Increasing the size of the assemblies, i.e., micelle to microemulsion or increasing the rigidity of the reactant's environment, i.e., micelle to vesicle, led to decreased yeilds of ions.The yeilds of ions in these latter systems can be restored if polar derivatives of pyrene are used in place of pyrene, thus locating the pyrene chromophore in the region of the assembly surface.Several reactions of the photoproduced pyrene anion were studied, as the lifetime of the anion is sufficiently long (>1 ms) to promote electron transfer between cationic ions such as Eu³⁺ and methyl viologen, in spite of the fact that these ions are strongly repelled by the cationic surfaces of the assemblies.It is concluded that efficient electron transfer and subsequent ion separation only occur when the rectants are located on strongly charged surfaces, where the reactants may move relatively freely, while still remaining bound to the surface.A photodiode effect is suggested to explain the efficient ion separation observed.