Regulating the Self-Assembly Behaviors of Rigid Sphere–Rod Amphiphiles by Tuning the Side-Chain Length

The self-assembly of rigid sphere–rod amphiphiles composed of solvophilic Keggin clusters and rigid solvophobic oligodialkylfluorene (OF) rods is explored with special attention to side-chain length effect. Such amphiphiles are known to self-assemble into onion-like structures containing concentric multilayers in a binary solvent system via the interdigitation of the OF rigid rods. Here, we demonstrate that flexible alkyl side chains (two per OF unit) are important to control the self-assembly behavior. Based on KTOF4 (Keggin T-shaped oligodialkylfluorene with 4 repeat units), regular amphiphilic vesicles, incomplete onion-like structures, and full onion-like structures are observed when the side chains are C2, C4, and C6, respectively. When the side-chain length reaches C10, the inner layers of assemblies disappear, resulting in hollow, incomplete onion-like structures. With very long C16 side chains, the assemblies become less ordered, forming spherical assemblies with near-parallel layers, i.e., pupa-like structures. These flexible side chains act as fillers in the solvophobic domain to optimize the packing of rods. In other words, tuning flexible side-chain length is a simple, rational approach to regulating the microphase transitions among different self-assembled structures for the self-assembly of rigid amphiphiles, offering a versatile design principle for creating hierarchical nanostructures in functional materials.