Bisulfite (HSO₃–)/Sulfite (SO₃²–) is widely used as a food additive, but excessive use often leads to serious consequences, so the detection of HSO₃–/SO₃²– is of great importance. In this paper, a novel 1,4-diethylpiperazine-modified coumarin-benzopyran derivative (probe QLP) has been synthesized and characterized. In PBS (10 mM, pH = 7.4), QLP displays good selectivity and is sensitive for HSO₃–/SO₃²– over various analytes with fluorescent “OFF–ON” rapid responding (2 min), long-wavelength emission (600 nm), and a detection limit of 177 nM. With the treatment of HSO₃–/SO₃²–, the color of the QLP solution obviously changes from blue-green to yellow, and the fluorescent color of QLP changes from colorless to amaranth. The fluorescence-enhanced mechanism is qualitatively evaluated by density functional theory calculations using the CAM-B3LYP/6-31G (d) method, which reveals that the photoinduced electron transfer leads to the fluorescence emission of the QLP-SO₃H adduct. Importantly, nontoxic QLP can be used to detect HSO₃–/SO₃²– in sugar, natural water samples, and living cells and localized to the mitochondria and monitor the mitochondrial HSO₃–/SO₃²– level.

Despite their status of being widely used as food additives, bisulfite (HSO₃–)/sulfite (SO₃²–) can pose serious health risks when they are excessively added. Therefore, it is vital to develop a new method for detecting HSO₃–/SO₃²– in foodstuff. In this paper, a benzopyran-benzothiazole derivative (probe DCA–Btl) with near-infrared emission was designed and synthesized by constructing a “push-pull” electronic system. DCA–Btl can selectively recognize HSO₃–/SO₃²– via a colorimetric and fluorescence dual channel in DMF/PBS (1:1, v/v, pH = 8.4), and the emission wavelength of DCA–Btl can reach 710 nm. The fluorescence quenching of DCA–Btl after recognition of HSO₃– is attributed to the photoinduced electron transfer (PET) process of the adduct DCA–Btl-HSO₃– as evaluated by the DFT/TD-DFT method. In addition, DCA–Btl has many advantages, including a large Stokes shift (95 nm), good anti-interference ability, and little cytotoxicity. What’s more, DCA–Btl has been successfully applied for the detection of HSO₃–/SO₃²– in actual water samples and food samples such as sugar, red wine, and biscuits with satisfying results, as well as for fluorescent imaging of HSO₃– in living MCF-7 cells.