Multicompartment-like aggregates formed by a redox-responsive surfactant encapsulated polyoxometalate in DMF/butanol mixed solvent

The unique and interesting aggregation behaviors of a novel surfactant-encapsulated complex (SEC), composed of a Keggin-type polyoxometalate (POM), phosphotungstic acid and a redox-responsive ferrocene-containing cationic surfactant, dimethyldioctadecylammonium bromide (BFDMA), have been investigated in N, N-dimethylformamide (DMF)/butanol mixed solvent. By carefully tuning the composition of the solvent, hollow spherical aggregates with multilayered shells were initially observed with a diameter of 55 + 9 nm using transmission or scanning electron microscopes. Owing to the solvophobic effect and pi-pi stacking interaction between alkyl chains or ferrocene groups, these spherical aggregates were found to gradually fuse together into aggregates with flower-like and finally compartment-like morphologies with an average size of 120-150 nm. Based on X-ray diffraction measurements and the molecular configuration data of SEC, the multilayers in aggregates were composed of bilayers of SEC with the POM inside and three rearranged BFDMA molecules outside. The morphology of such aggregates was partially reversible under electrochemical modulation. Applying an anodic oxidation potential would induce the disassembling of compartment-like aggregates into irregular spheres with a size of about 200 nm, which could be turned back after applying a cathodic reduction potential. The obtained results here should shed light on the design of novel nanostructures from such inorganic/organic hybrid clusters.