A Near‐IR Fluorimetric Chemosensing System for the Turn‐On Detection of Hydrogen Sulfate Anion

We report a near‐IR fluorescence turn‐on chemosensing system for the selective detection of HSO 4 − anion in aqueous media. This system utilizes the equilibrium between the fluorescent pyrylium salt and its non‐fluorescent diketone form. The pyrylium compound we synthesized (λ flo =674 nm) rapidly converts to its diketone form in the aqueous medium (ethanol‐water 4 : 1). HSO 4 − anion provides proton to diketone form inducing its conversion to pyrylium. Therefore, the sensor system responds to the presence of HSO 4 − by an increase in fluorescence. The change in the fluorescence increase is linear within the 20–55 μM range with a limit of detection of 12.8 μM. The system demonstrates high selectivity for HSO 4 − over other anions, as validated through fluorimetric titration studies. Additionally, interference studies highlight the minimal impact of common anions on bisulfate detection. Reversibility tests reveal the pronounced reversibility of the sensor system, with over 90 % recovery of fluorescence intensity achieved in subsequent iterations.