Morphological Transitions in the Self-Assembly of Rigid Sphere-Rod Amphiphiles Achieved by Adjusting the Linker...

The morphological transitions of self-assembled supramolecular structures formed by rigid sphere-rod amphiphiles composed of hydrophilic Keggin clusters and hydrophobic oligodialkylfluorene (OF) rods were investigated by varying the alkyl linker length between the two rigid domains. For T-shaped molecules with short C3 linkers, self-assembly in THF/water mixed solvents always resulted in spherical onion-like structures with a fixed interlayer distance. As the water content increases, the number of concentric layers decreases, leading to smaller onion-like assemblies. However, with longer C15 linkers, the self-assembly becomes more complex: they form spherical, multilayered lamellar (striped) structures in mixed solvents with lower THF content, while increasing THF content induces transitions from striped spherical structures to incomplete onion-like structures and eventually complete onion-like structures. UV-vis spectroscopy and analytical ultracentrifugation (AUC) confirm that C15-linked hybrids can undergo conformational changes between T-shaped and I-shaped conformations in response to solvent conditions. This conformational flexibility enables K-C15-TOF4 molecules to adopt an I-shaped conformation at low THF vol%, forming striped spherical structures, whereas at higher THF vol% they switch to a T-shaped conformation, resulting in complete onion-like structures. This study demonstrates that modifying linker length is a simple and effective strategy for regulating the morphology of self-assembled rigid sphere-rod amphiphiles.