A highly sulfite-selective ratiometric fluorescent probe based on ESIPT

The levulinate ester of 2-(benzothiazol-2-yl)phenol, 1, has been developed as a ratiometric fluorescent probe for identifying and quantitating sulfite anions. The mechanism of action is based on the sulfite-triggered intramolecular cleavage of the levulinate moiety to give 1 which, when excited with 310 nm light, decays to its ground state via an excited state intramolecular proton transfer (ESIPT) mediated pathway. We show that the intensity of the ESIPT fluorescent signal relative to that of 1 is proportional to sulfite concentration. This new probe shows good selectivity and high sensitivity for sulfite over other typically encountered anions (F-, Cl-, Br-, I-, HPO42-, SO4-2, NO3-, AcO-, ClO4-, N-3(-), HCO3-) when measured in CH3CN/H2O (50 : 50, v/v) solution.