Self-assembly of styryl naphthalene amphiphiles in aqueous dispersions and interfacial films: Aggregate structure, assembly properties, photochemistry, and photophysics

A study of phospholipid and fatty acid amphiphiles containing the isomeric trans-alpha- and beta-styrylnaphthalene chromophores is reported. On the basis of simulations for Langmuir films of fatty acids terminated with the two chromophores, it was anticipated that the beta-styrylnaphthalene fatty acids should be able to Pack into compact layers, having an extended glide or herringbone arrangement similar to those observed for corresponding stilbene, tolan, or azobenzene amphiphiles. In contrast, the simulations suggested that such an arrangement might be precluded on steric grounds for the isomeric alpha-styrylnaphthalene derivatives. The experimental studies carried out indicate that the beta-styrylnaphthalene fatty acids and phospholipids do in fact exhibit assembly properties and photophysical behavior similar to that observed for the stilbene and tolan amphiphiles; thus we find evidence for aggregates having similar "signatures" to those observed previously for both films at the air-water interface and aqueous suspensions. The behavior of the alpha-styrylnaphthalene amphiphiles is much more complex. Whereas aqueous dispersions of the phospholipid and highly compressed films at the air-water interface suggest the presence of weak aggregates (possibly dimers) having a translation or face-to-face structure, studies of the fatty acid derivative at the air-water interface suggest that the alpha fatty acid may form a "pinwheel" or herringbone cluster before compression such that drastically different photochemistry and photophysics is observed as a function of compression.