Tandem Guest–Host Switching for Chemical-to-Electrochemical Signal Transduction

A chemical-to-electrochemical signal transduction is reported based on the tandem switching of a bis-acridinium macrocycle and a proflavine derivative. Molecular recognition triggers a simultaneous guest–host transformation converting the acridinium units into their redox-inactive acridane counterparts. This unusual switching mechanism arises from the multiresponsive nature of the acridinium receptor, complementary acid–base properties of the host and guest, and stabilization of a water-assisted transition state within the macrocyclic cavity. Coined as tandem guest host switching (TANGHOS), this mechanism was elucidated through a combination of 1 H NMR, UV/vis spectroscopic, computational analyses (DFT, molecular dynamics simulations), and a microkinetic model. When grafted onto a gold surface, the bis-acridinium macrocycle enables the selective electrochemical detection of proflavine from a complex mixture with ten polycyclic aromatic hydrocarbons. Finally, a low coverage ratio still led to amplified electrochemical responses by surface confinement and reaction-coupled recognition.