Synthesis and supramolecular nanostructure of amphiphilic rigid aromatic-flexible dendritic block molecules

We synthesized ABC triblock rigid aromatic-flexible dendritic block molecules consisting of a docosyl chain, rigid aromatic segment, and poly(ethylene oxide) dendrimer. These block molecules were observed to exhibit an ordered structure in the solid state. Small-angle X-ray scattering experiments showed that the rigid-dendritic block molecule based on a more rodlike aromatic unit self-assembles into a 2-D hexagonal columnar structure, whereas the block molecule based on a more wedgelike aromatic unit self-assembles into a 3-D micellar cubic structure. Dynamic light scatterings, scanning electron microscopic (SEM) observations, and UV/vis spectroscopic measurements were carried out to investigate the encapsulation behavior of hydrophobic guests with the block molecules in an aqueous environment. The rigid-dendritic block molecules self-assemble into stable capsulelike micellar aggregates in aqueous solutions in the presence of CHCl3. In addition, the resulting micellar aggregates encapsulate hydrophobic dye molecules within their micellar core. The critical micellar concentration (cmc) values appeared to be very low, as compared to those of conventional surfactants. These results demonstrate that the introduction of a hydrophilic dendritic segment into an extended rigid aromatic segment can lead to a unique self-assembling system that shows aggregation behavior in both solid and dilute solution phases.