Regulation of a chromenylium fluorophore with a built-in recognition site for the detection of sulfite†

A double charged cationic pyridinium-fused chromenylium analogue DMCQ with an acceptor–π–acceptor (A–π–A) electronic structure was designed and prepared for the sensitive and selective detection of SO₃²⁻. Undergoing a Michael addition reaction with SO₃²⁻ at the built-in pyridinium moiety in the chromenylium fluorophore, the π-electron structure of the chromenylium skeleton transferred from an (A–π–A) to (A–π–D) system along with a prominent fluorescence enhancement. Based on this specific addition reaction, the DMCQ probe exhibits high selectivity for the detection of SO₃²⁻ over other biologically related species within a wide pH range (4–10). As the highly electron-deficient nature of the pyridinium-fused chromenylium accelerated the reaction with SO₃²⁻, the probe presented a rapid response time (60 s), together with high sensitivity (33 nM). Besides, DMCQ could not only image SO₃²⁻ in living cells but also monitor SO₃²⁻ in food and water samples with a satisfactory recovery of 81.30–112.89%.