Fluorescent probe for sequential recognition of Ga3+ and pyrophosphate anions

Three novel fluorescent probes, 2-(2′-hydroxyphenyl)-4-chloromethylthiazole (1), 2-(2′-hydroxyphenyl)-4-hydroxymethylthiazole (3), and 2-(2′-hydroxyphenyl)-4-iodomethylthiazole (4) were designed for the sequential recognition of Ga3+ and pyrophosphate ions in acetonitrile. Probe 1 selectively detected Ga3+ through a “switch on” response, showing a good association constant (Ka = 6.24 × 104 M−1) and binding with Ga3+ ions in a 1:1 stoichiometry. An in situ generated 1-Ga3+ (1:1) ensemble detected H2P2O73–ions sequentially through a “switch off” response. The “switch on” response occurred with selective complexation of Ga3+ ions due to combined excited state intramolecular proton transfer (ESIPT) and chelation induced enhanced fluorescence (CHEF) effects. An ensemble of 1 and gallium(III) was more selective for pyrophosphate ions than any other anion.