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 (K_a = 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 H₂P₂O₇^3–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.