Development of a ratiometric fluorescent probe for sulfite based on a coumarin–benzopyrylium platform

• A coumarin–benzopyrylium platform has been developed for the ratiometric fluorescent sensing of sulfite.
• The method employs the nucleophilic addition of sulfite to 4-position of the benzopyrylium unit of the probe.
• The ratiometric sensing is carried out by interrupting the large π-conjugation system of the probe.
• The proposed probe displays high selectivity for sulfite over other anions and biothiols.

A ratiometric fluorescent probe, 2-(7-diethylamino-2-oxo-2H-1-benzopyran-3-yl)-7-hydroxyl-1-benzopyrylium (1), has been developed for sulfite sensing. The method employs the nucleophilic addition of sulfite to the electrically positive benzopyrylium moiety of 1 to block the π-conjugated system of the whole molecule, which in turn results in significant blue shifts in the absorption and emission spectra of the sensing system. The fluorescence intensity ratio at 485 and 640 nm (I485/I640) increases linearly with sulfite concentration in the range of 0.05–10 μM. The proposed probe shows excellent selectivity toward sulfite over other common anions and biothiols. The bioimaging experiment demonstrates the potential of probe 1 for the ratiometric fluorescent imaging of sulfite in living cells.

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