A highly selective and sensitive fluorescence dual-responsive pH probe in water

A structurally simple fluorescence probe, dansyl acid (DA), was reported in the present study. The probe could selectively and sensitively respond to pH from 7.00 to 2.00 in aqueous solution with fluorescence “turn-off” and “turn-on” dual-responses under two different excitation wavelengths. The mechanism of response was further clarified by NMR, UV–vis spectrometry and single crystal X-ray crystallography, which revealed that the pH-induced changes of fluorescence and UV–vis absorption were due to the protonation of nitrogen atom in the dimethylamino group. The fluorescent imaging of NIH 3T3 cells were also provided, which demonstrated the probe was applicable in monitoring intracellular H+.