Dynamic duo: the differential impact of resorcinarenes on ferrocene redox couple in electroactive host–guest systems

Alternative to complex labelling of resorcinarene hosts with redox-active probes, noncovalent complex formation offers a unique avenue toward bifunctional hosts, which posses redox centers to transduce an electrochemical signal as well as maintaining a guest recognition site. Herein, N-alkyl ammonium resorcinarene halides (NARXs) hosts were evaluated with a well-known redox probe ferrocene (Fc). Specifically, the NARX hosts were designed based on the tuning of the resorcinarene upper rim to allow for hydrogen bonding, pi–pi stacking, ion and halogen binding interactions in organic environments. The NARX host induced a significant anodic shift of Fc E_1/2; once formed, the Fc–NARX complex undergwent oxidation and reduction without Fc dissociation. Data indicate that hydrophobic interactions stabilize Fc interactions with the resorcinarene upper rim, which is directly related to the structural functionalization of the resorcinarene. Thus, we provide evidence for a controlled and tunable redox host–guest system with well-defined redox properties while maintaining the guest recognition site, suggesting that the host is bifunctional.