The structure of a series of poly(amidoamine) dendrimers Gn(C12) generated from a diaminododecane core have been investigated using the photophysical properties of an external dye, nile red. The modified dendrimers Gn(C12) show the ability to host the hydrophobic dye, nile red, in aqueous solution. The ability of Gn(C12) to host nile red has been compared to corresponding amino-core Gn(NH3) and diaminoethane-core Gn(C2) dendrimers of the same generation size. The emission of nile red in aqueous media is significantly enhanced in the presence of Gn(C12) and not at all for Gn(NH3) and Gn(C2). These results imply a strong tendency for the nile red probe to associate with the long methylene chain of the modified dendrimers in aqueous solutions. Moreover, the interactions of these dendrimers with anionic surfactants generate supramolecular assemblies which greatly enhance their ability to accomodate the nile red. Fluorescence polarization and emission as a function of pH were also studied in an effort to elucidate the interaction of the nile red probe with the dendrimer-surfactant assemblies.