Linker-Dependent Conformational Switching in Side-Chain-Type Ferrocene-Functionalized Nanohoops.

Abstract

We report the synthesis of two ferrocene-tethered side-chain nanohoops, Fc[8]CPP-L and Fc[8]CPP-M, via a streamlined shotgun macrocyclization protocol. Systematic variation of the tether length uncovers an interesting structure-property relationship: Fc[8]CPP-L exhibits coexisting intra- and intermolecular ferrocene inclusion, whereas Fc[8]CPP-M displays exclusively intermolecular host-guest arrangements. Remarkably, DFT calculations reveal a low rotational barrier (∼23 kcal mol-1) for the tethered phenyl ring, enabling facile 360° inward rotation of the ferrocene moiety under mild conditions. Electrochemical analyses confirm retained reversible redox activity, with frontier orbitals spatially partitioned between the ferrocene (HOMO) and the CPP backbone (LUMO), facilitating efficient photoinduced electron transfer. This work establishes side-chain engineering as a powerful strategy to program cavity conformation, crystalline polymorphism, and dynamic behavior in organometallic nanohoops, laying the foundation for multi-stimuli-responsive supramolecular materials.