PHOTOINDUCED ELECTRON-TRANSFER REACTIONS OF TRANS-STILBENE SURFACTANTS IN LANGMUIR-BLODGETT ASSEMBLIES AND PHOSPHOLIPID-BILAYERS

The photochemistry and photophysics of a series of stilbene-functional ized fatty acids (SFA) have been examined in homogeneous solutions, su pported Langmuir-Blodgett assemblies, and as guests in phospholipid bi layers and micellar dispersions. The spectroscopic characteristics of stilbene-functionalized derivatives of phosphatidyl choline (SFA-PC) h ave also been examined in organic solvents, aqueous dispersions and aq ueous solution containing an excess of dipalmitoyl choline (DPPC), as well as in aqueous-methanol solutions containing gamma-cyclodextrin. L angmuir-Blodgett assemblies of individual SFAs, as well as mixtures of various SFAs, exhibit spectroscopic properties (blue-shifted absorban ce and red-shifted fluorescence relative to those observed in organic solvents) consistent with the formation of an ''H'' aggregate. The sam e effect is observed for SFA-PCs in aqueous dispersions and in aqueous -methanol solutions containing gamma-cyclodextrin. The ''H'' aggregate is found to be the preferred geometric orientation of the stilbene ch romophores which may correspond to an energy minimum for the systems i nvestigated. Preliminary studies with SFA-PC in methanol-water solutio ns containing gamma-cyclodextrin suggest that an association of only t wo stilbene chromophores is required to form the ''H'' aggregate.