Anion Sensing through Redox‐Modulated Fluorescent Halogen Bonding and Hydrogen Bonding Hosts**

Abstract

AbstractAnion sensing via either optical or electrochemical readouts has separately received enormous attention, however, a judicious combination of the advantages of both modalities remains unexplored. Toward this goal, we herein disclose a series of novel, redox‐active, fluorescent, halogen bonding (XB) and hydrogen bonding (HB) BODIPY‐based anion sensors, wherein the introduction of a ferrocene motif induces remarkable changes in the fluorescence response. Extensive fluorescence anion titration, lifetime and electrochemical studies reveal anion binding‐induced emission modulation through intramolecular photoinduced electron transfer (PET), the magnitude of which is dependent on the nature of both the XB/HB donor and anion. Impressively, the XB sensor outperformed its HB congener in terms of anion binding strength and fluorescence switching magnitude, displaying significant fluorescence turn‐OFF upon anion binding. In contrast, redox‐inactive control receptors display a turn‐ON response, highlighting the pronounced impact of the introduction of the redox‐active ferrocene on the optical sensing performance. Additionally, the redox‐active ferrocene motif also serves as an electrochemical reporter group, enabling voltammetric anion sensing in competitive solvents. The combined advantages of both sensing modalities were further exploited in a novel, proof‐of‐principle, fluorescence spectroelectrochemical anion sensing approach, enabling simultaneous and sensitive read out of optical and electrochemical responses in multiple oxidation states and at very low receptor concentration.