Self-Assembly of Ultralong Polyion Nanoladders Facilitated by Ionic Recognition and Molecular Stiffness

It is hard to obtain spatially ordered nanostructures via the polyion complexation process due to the inherent flexibility of polymers and isotropicity of ionic interactions. Here we report the formation of polyion assemblies with well-defined, periodically regular internal structure by imparting the proper stiffness to the molecular tile. A stiff bisligand TPE-C4-L2 was designed which is able to form a negatively charged supramolecular polyelectrolyte with transition metal ions. This supramolecular polyelectrolyte slowly self-assembled into polydispersed flat sheets with cocoon-like patterns. Upon the addition of an oppositely charged ordinary polyelectrolyte, the polydispersed cocoons immediately transformed into ultralong, uniform nanoladders as a result of matched ionic density recognition. The supramolecular polyelectrolytes assembled side-by-side, and the negative charges aligned in an array. This structure forced the positively charged polymers to lie along the negative charges so that the perpendicular arrangement of the oppositely charged chains was achieved. Such precise charge recognition will provide insight into the design of advanced materials with hierarchical self-assembled structures.