ENERGY AND ELECTRON-TRANSFER PROCESSES THROUGH LANGMUIR-BLODGETT MULTILAYERS FORMED FROM ALPHA,OMEGA-DIPHENYLPOLYENE SURFACTANTS

The spectral properties, as well as photoinduced electron and energy-transfer processes, of fatty acid derivatives of alpha,omega-diphenylpolyenes including stilbene, diphenylbutadiene, diphenylhexatriene, and various heteroatom substituted stilbene derivatives were investigated in multilayer assemblies constructed using the Langmuir-Blodgett (LB) technique. The majority of surfactant alpha,omega-diphenylpolyene derivatives were found to exhibit spectral properties characteristic of ''H'' aggregates when incorporated into multilayer assemblies. The tendency of surfactant stilbenes to form ''H'' aggregates was observed to be greater than that exhibited by other alpha,omega diphenylpolyene surfactants studied. Multilayer assemblies containing equal molar ratios of mixed surfactant stilbene derivatives to cosurfactant show ''H'' aggregate spectra and aggregate intermediates absorbing between monomer and pure ''H'' aggregates, possibly ''H'' dimers. Evidently ''H'' aggregate formation predominates over any other type of aggregate formation in these mixed surfactant stilbene assemblies. The fluorescence from either a single stilbene fatty acid (SFA) or mixed SFA assemblies was quenched by various surfactant electron-transfer acceptors, such as surfactant viologen and cobalt complexes. While small spectral differences were observed in the absorption and emission spectra between single and mixed SFA's, large differences were observed between the excited-state behaviors of single and mixed SFA multilayer assemblies. Little if any energy migration occurred among the single SFA monolayers, whereas enhanced energy migration was observed in mixed SFA multilayer assemblies. Directional energy transfer has been demonstrated ated in LB assemblies containing a series of alpha,omega-diphenylpolyene monolayers sequentially layered in order of decreasing energy.