A colorimetric and ratiometric fluorescent probe for sulfite based on an intramolecular cleavage mechanism.

A colorimetric and ratiometric fluorescent sulfite probe, the levulinate of 4-hydroxynaphthalimide, was successfully synthesized from 4-hydroxy-naphthalimide and levulinic acid. Through sulfite-mediated intramolecular cleavage, the probe was converted into 4-hydroxynaphthalimide, which when excited at 450 nm, displayed a large Stokes shift due to the intramolecular charge transfer process. The probe exhibited high selectivity and sensitivity towards sulfite over other typical anionic species (F(-), Cl(-), Br(-), I(-), HPO(4)(2-), SO(4)(2-), NO(3)(-), AcO(-), ClO(4)(-), HCO(3)(-)) in HEPES-buffered solution (25 mm, pH 7.4, 50% acetonitrile, v/v).