Nanostructure Polymorphism Induced By Rotational Freedom of Self-Assembling Amphiphiles

Amphiphiles with strong intermolecular interactions that self-assemble in water have drawn attention due to their high stability and tunability for a range of applications. These strongly interacting amphiphiles tend to be planar and have a high propensity for hydrogen bonding and π-π stacking, thus the morphological design spaces of the corresponding self-assembled nanostructures are constrained. We hypothesized that a broad range of self-assembled morphologies can be achieved by introducing conformational freedom within each amphiphile. In this study, we incorporate a diacetylene domain into the aramid amphiphile (AA) platform, which yields a rotational axis of aramid amphiphile perpendicular to the planes of hydrogen bonding and π-π stacking. We observe polymorphism in AA assemblies with helical, twisted, short planar, or long planar nanoribbons, by varying the concentration and annealing temperature. We demonstrate that polymorphism in AA assemblies originates from changes in molecular packing induced by rotational constraints. This study of self-assembly in AAs serves as a model study for understanding the relationship between rotational freedom and molecular packing within a nanostructure.