A Colorimetric and Fluorescent pH Probe for Extremely Acidic Conditions and its Application in pH Test Paper

Here, we report a highly water‐soluble colorimetric and fluorescent pH probe that works in the pH range 0.2–3.0. The probe showed a rapid response, high stability, and excellent reversibility to acidity. Moreover, the fluorescence of probe was not influenced by the existence of high concentration of cations. The p K a of probe was calculated to be 2.25 ± 0.06. Furthermore, the pH test papers coated with the probe exhibited a distinct color change in acidic conditions.