The synthesis of diethyl-8-quinolinyloxymethylphosphonate 1 and 8-quinolinyloxymethylphosphonic acid hemihydroiodide 2 is reported along with their spectroscopic and analytical characteristics (NMR, infrared, mass spectra, and elemental analysis). The single-crystal X-ray structure of 2 is described. Solutions of the disodium phosphonate 3, from 2 and sodium hydroxide, were prepared and used in situ. The coordination complex between 1 and zinc chloride 4 is described according to its single-crystal X-ray structure. The spectrophotometric features (absorption and emission) of 1, 2, 3, and 4 are reported along with the fluorescence response and affinity of 3 to some metal cations. The origin of the fluorescence from compounds 1 and 4 is investigated using density functional theory and the oscillator strength for each transition is computed. Two deactivation pathways, one of which is only weakly emissive, are identified in 4. In contrast to 4, which is only moderately more emissive than 1 a strong zinc-activated fluorescence response is observed from aqueous solutions of 3.