An Efficient Fluorescent Probe for Ratiometric pH Measurements in Aqueous Solutions

Just as litmus paper changes from red to blue with an increase in pH, so the fluorescence emission of the oxazole derivative 1 shifts from green to blue. Ratiometric measurements of the fluorescence emissions of the two species, after one- or two-photon excitation, allow 1 to be employed as a pH sensor over the mid-pH range.