“…Relatively few fluorescent pH probes can respond to pH changes in a wide range, eg pH 3‒9, 41 pH 1‒8, 42 pH 2.5‒10, 43 pH 1–9, 44 pH 1–10, 45,46 pH 2–12, 47–49 pH 3.5–13.5, 50 pH 1–13, 51 pH 1–14, 52 or sensitive to pH changes in more than one pH interval, eg pH 2.88‒5 and pH 10–13.78, 53 pH 4.5–7.5 and pH 9–12 54 . The sensing of pH by using fluorescent probes are mainly based on the fluorescence mechanisms of photoinduced electron transfer (PET), 9,13,30,31,38,45 intramolecular charge transfer (ICT), 17,21,47 PET and ICT, 11,39 fluorescence resonance energy transfer (FRET), 22,33,36 protonation‐activable resonance charge transfer (PARCT), 40 through‐bond energy transfer (TBET), 53 and excited state intramolecular proton transfer (ESIPT) 48,49,55 . By far, a number of chemosensors bearing a reaction site for fluorometric detection of mercury, 56–60 hypochlorite, 61–66 nitric oxide, 67 and biothiols and peroxynitrite 68,69 were developed based on specific chemical reactions.…”