Constructing near-infrared dyes with D-A-D-type Stokes shifts based on asymmetric electron-donating properties and their applications.

An excessive amount of sulfur dioxide (SO2) poses a threat to the microenvironment of living organisms and, in severe cases, can cause inflammation, cardiovascular diseases, and respiratory damage. As one of the important atmospheric pollutants, SO2 and its derivatives are widely used in the production of additives and chemicals, and are important factors affecting physiological activities. To achieve the goal of detection, we developed a new near-infrared (NIR) fluorescent probe, Cou-Oxo, which can be used to obtain a ratiometric response to SO2 derivatives in cells, zebrafish, and plant rhizomes. This novel NIR dye with a large π-system was created by combining two small π-dyes. Its structural features led to a markedly expanded Stokes shift of 321 nm. The NIR ratiometric fluorescence properties of the probe were achieved through the addition reaction of SO2 derivatives (HSO3-) to the CC double bond on the Cou-Oxo probe, which possesses a detection limit of 0.942 μM, a short response time (within 30 s), satisfactory biocompatibility, excellent anti-interference, and pH stability. The probe was successfully used to detect changes in exogenous and endogenous SO2 levels in cancer cells and living zebrafish. More interestingly, we successfully visualized SO2 in normal and SO2 poisoned tobacco seedlings as a model.