<p>A dual-responsive probe 8-<i>N</i>,<i> N</i>-diethylamino-3-(1<i>H</i>-benzoimidazol-2-yl)-2<i>H</i>-pyrano[2,3-b]quinoline-2-imino (PQI), pyrano[2,3-b]quinoline as fluorophore, two nitrogen atoms as receptor sites, was developed for the colorimetric and fluorescence detection of Hg²⁺ and COCl₂ in different solvents. PQI showed good recognition ability for Hg²⁺ via the absorbance decrease, fluorescence quenching by the formation of PQI-Hg²⁺ complex in MeOH/H₂O (4/1, V/V). In addition, PQI could specifically react with COCl₂ via intramolecular cyclization to form a cyclic urea product, which exhibited absorption and fluorescence emission changes, and then realized the detection of COCl₂. Moreover, the optical responses of PQI to Hg²⁺ and COCl₂ featured high selectivity, fast response (within 30&#xa0;s), and low detection limit (73 nM for Hg²⁺ and 25 nM for COCl₂, respectively). Furthermore, PQI could detect Hg²⁺ in real water samples with good recoveries and small relative standard deviations, and could be prepared as a PQI-loaded test strip to monitor gaseous COCl₂ in an in-site, real-time, highly sensitive manner, demonstrating the practicability of PQI in Hg²⁺ and gaseous COCl₂ detection.</p>