Hierarchical Nanostructures and Topologies of Supramolecular Polymers

Hierarchical self-assembly offers a promising bottom-up paradigm for constructing sophisticated functional materials. However, precise control over the morphology, dimensional uniformity, and polydispersity of hierarchical constructs, along with their higher-order arrangements, remains challenging. Overcoming this barrier requires a fundamental comprehension of molecular organization principles at multiple hierarchical levels. This chapter provides a detailed framework for understanding the formation of hierarchical architectures from diverse molecular assemblies. We begin with the hierarchical self-assembly of barbiturate-functionalized π-conjugated scaffolds and fused complementary nucleobases. These systems exhibit coupled hierarchical processes, wherein heterocyclic units featuring self-complementary hydrogen-bonding motifs undergo supramolecular polymerization via hydrogen-bonded supermacrocycles. Particularly, the curvature induced during the elongation process of barbiturates enables controlled creation of topologically intriguing supramolecular polymers, including toroids and helicoids. We also highlight groundbreaking advances using secondary nucleation, such as the formation of nano-polycatenanes and concentric toroids. We further discuss the hierarchical self-assembly behaviors exhibited by complementary nucleobases linked by π-unit, and scissor-shaped dyads, which exhibit decoupled cyclization and subsequent polymerization processes. Lastly, we address stimuli-responsive modulation of hierarchical self-assembly, emphasizing dynamic functionalities exemplified by reversible folding and unfolding. Collectively, this chapter underscores the profound potential of hierarchical self-assembly in creating novel functional materials with precisely controlled and dynamically adaptive architectures.