Self-assembly of aromatic-functionalized amphiphiles: The role and consequences of aromatic-aromatic noncovalent interactions in building supramolecular aggregates and novel assemblies

This feature article presents an overview of a study of several different a romatic-functionalized amphiphiles-fatty acid and phospholipid derivatives. These amphiphiles form organized assemblies when the fatty acids are sprea d as monolayers at the air-water interface or when the phospholipids are di spersed in aqueous solutions. For a wide range of aromatic chromophores-tra ns-stilbene derivatives and a series of "vinylogues" (1,4-diphenyl-1,3-buta diene and 1,6-diphenyl-1,3,5-hexatriene), diphenylacetylenes, and azobenzen es such as phenyl, biphenyl, and terphenyl derivatives and modified stilben es (styryl thiophenes and styryl naphthalenes)-assembly formation is accomp anied by formation of aggregates of the aromatic groups. Results of experim ental studies and simulations indicate that in many cases the aromatics for m a small, stable "unit aggregate" characterized by strong "noncovalent" ed ge-to-face interactions among adjacent aromatics. Although the unit aggrega tes exhibit characteristic spectral shifts and strong induced circular dich roism indicating a chiral "pinwheel" aggregate structure, they may be packe d together in pure films or dispersions to form an extended glide or herrin gbone structure. Although the "pinwheel" unit aggregate and the extended gl ide structure is favored for the majority of aromatics studied, for certain aromatics (styrenes, styrylthiophenes, and alpha-styrylnaphthalenes) a tra nslation layer, characterized by face-to-face noncovalent interactions, is preferred. The glide or herringbone aggregates are readily distinguished fr om the translation aggregates by different spectral signatures and differen t photochemical and photophysical behavior. Factors controlling the type of aggregate and hence extended structure formed from different aromatic func tionalized aromatics include shape and steric factors and strength of the c ompeting noncovalent edge-face and face-face interactions.