High‐Efficiency Selective Fluoride Ion Probes in Aqueous Media Using 3‐Hydroxyflavone Polymers

Amphiphilic diblock copolymers containing 3‐hydroxyflavone (3‐HF) moieties within hydrophobic poly(methyl methacrylate) (PMMA) segments were synthesized using reversible addition‐fragmentation chain transfer (RAFT) polymerization followed by click chemistry. The 3‐HF units were caged through reaction with excess tert‐butyldimethylsilyl chloride (TBSCl), resulting in the formation of amphiphilic PEG‐b‐P(MMA‐co‐3HF‐TBS) copolymers. When self‐assembled into micelles in aqueous solutions, these copolymers exhibited blue fluorescence, attributed to the inhibition of excited state intramolecular proton transfer (ESIPT) due to the caged 3‐HF moieties. Upon introduction of fluoride ions, a specific desilylation reaction occurred, releasing the 3‐HF units and establishing intramolecular hydrogen bonds. This reaction activated the ESIPT process, causing a blue‐to‐green fluorescence emission shift, with a detection limit of approximately 3.8 μM for fluoride ions. Furthermore, similar fluorescence changes were observed in non‐aqueous acetone solutions, with a detection limit of around 0.2 μM. However, high concentrations of fluoride ions could partially quench the fluorescence due to competitive interactions disrupting intramolecular hydrogen bonding, thereby inhibiting the ESIPT process. This study presents a novel class of fluoride‐reactive polymeric ratiometric probes, capable of both colorimetric and fluorometric sensing of fluoride ions in aqueous media.