Redox-responsive self-assembly of β-cyclodextrin and ferrocene double-headed amphiphilic molecules

We present a redox-responsive self-assembly based on a unimolecular platform. Three double-headed amphiphilic molecules composed of β-cyclodextrin (β-CD) and ferrocene (Fc) each with an alkyl chain as a linker (βCD-C_m-Fc, m = 2, 6, and 10) were synthesized, and their self-assembly behaviors were investigated. The molecules self-assembled into polydisperse micelles that transformed into vesicles upon oxidization of the Fc moieties to Fc⁺. 2D ¹H NMR results suggest that although the three molecules formed aggregates with similar morphologies, their molecular configurations were different because of the different lengths of the alkyl chains. When the linker was a C₂ chain, no host-guest complexes were formed, whereas host-guest recognition was detected for linker lengths of C₆ and C₁₀. For the oxidized state samples, there were no host-guest interactions for linker lengths of C₂ and C₆, whereas the alkyl chain was locked in the cavity of β-CD by host-guest inclusion for the molecule with a C₁₀ linker. Moreover, reversible redox-responsive self-assemblies based on the three β-CD derivatives with a terminal Fc were successfully achieved. Our results enrich the field of β-CD/Fc reversible self-assembly systems, and provide a possible unimolecular host-guest complexation model in host-guest chemistry.