Sulfur and nitrogen served as electron donors to rescue short wave emission or fluorescence quenching caused by nucleophilic addition

SO₂ is not only a new potential gas signaling molecule, but also an antioxidant and antioxidant metabolite, which plays an important role in biophysiological and pathological processes. However, excessive intake of it can lead to serious complications of various diseases. Indole–iodide conjugated double bonds are often used as a sensitive response site for SO₂, but the fluorescence of the system is often quenched after the nucleophilic addition of SO₂. In this work, we introduced sulfur and nitrogen electron donors into a fluorophore, which rescued the trend of fluorescence quenching and enabled the system to develop a ratiometric fluorescence response for more accurate detection of SO₃²⁻. In addition, this probe can target mitochondria. The probe has good selectivity, sensitivity, a fast response (200 s) and a limit of detection (LOD) of 0.17 μM. Furthermore, the probe was successfully applied to visualize both endogenous and exogenous SO₃²⁻ in Hela cells and zebrafish.