Counter-Ion-Regulated Fluoride Sensing by a Silyl-Protected, Highly Conjugated Molecular Wire: From On-Field Analysis to Quantification of Nerve Gas Simulants

Abstract

We report the design and synthesis of a π-conjugated donor–acceptor molecular probe bearing terminal tert-butyldimethylsilyl (TBDMS)–protected phenolic units and flexible oxyethylene linkers, engineered for selective fluoride sensing in semi-aqueous environments. The probe operates via a fluoride-triggered desilylation mechanism, wherein Si–O bond cleavage generates a strongly electron-donating phenoxide that markedly enhances intramolecular charge transfer (ICT). This transformation induces a distinct bathochromic shift in absorption and a ratiometric fluorescence response, accompanied by aggregation-assisted stabilization of a low-energy emissive state in the presence of weakly coordinating counter-ions. Detailed spectroscopic, time-resolved fluorescence, NMR, mass spectrometric, and theoretical frontier molecular orbital analyses collectively validate the sensing mechanism. The probe exhibits high selectivity for fluoride over competing anions, with sensitivity strongly governed by solvent composition and pH due to fluoride hydration and HF/F⁻ equilibria. Importantly, the system enables quantitative fluoride detection in real water samples (0.5–1.2 ppm) and functions in a portable paper-strip format. Under basic conditions, it further detects diisopropyl fluorophosphate through in situ fluoride release, highlighting a dual-use platform for environmental monitoring and chemical defense applications.