A ratiometric fluorescent probe for rapid, sensitive and selective detection of sulfur dioxide with large Stokes shifts by single wavelength excitation

4-(Benzothiazol-2-yl)-3-hydroxybenzaldehyde, probe 1, has been developed as a ratiometric fluorescent probe for the sensitive and selective detection of sulfur dioxide with a fast response time (within seconds). This probe itself exhibited a yellow emission (λmaxem = 563 nm) with a 186 nm Stokes shift. Upon treatment with sulfite anions, this probe instantaneously displayed a blue emission (λmaxem = 467 nm) with a 133 nm Stokes shift. The large Stokes shifts and absorption spectral overlap of probe 1 both in the absence and in the presence of SO3(2-)/HSO3(-) allow the fluorescence detection under single wavelength excitation. Importantly, this ratiometric probe was successfully demonstrated for the imaging of intracellular sulfite anions in living cells.