<p>In this study, a naphthalene-based oxa-aza open-chain fluorescent Schiff base chemosensor (L) was synthesized and characterized for the selective detection of Cd²⁺ ions. The structure of ligand L was confirmed using IR spectroscopy, ¹H NMR, ¹³C NMR, DEPT-135 and mass spectrometry analyses. The photophysical properties and metal-ion sensing behavior of L were systematically investigated in an EtOH/H₂O (9:1, v/v) medium at pH 7.4. The fluorescence response of the ligand was examined in the presence of various metal ions, including Mg²⁺, Ca²⁺, Ba²⁺, Al³⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Cr³⁺, As³⁺, As⁵⁺ and Bi³⁺. Ligand L exhibited a remarkable turn-on fluorescence enhancement upon coordination with Cd²⁺, confirming its high selectivity toward this ion. Fluorescence titration, Job’s plot, and Benesi-Hildebrand analyses validated a 1:1 binding stoichiometry for the [CdL]²⁺ complex, with an binding constant of 5 × 10⁵ M⁻¹. The calculated detection limit 1.9 × 10⁻⁷ M highlights the high sensitivity of L and its strong affinity for Cd²⁺ ions. The observed fluorescence enhancement is attributed to the suppression of the photo-induced electron transfer (PET) process upon metal binding, which activates the emission pathway of the fluorophore. Additionally, the presence of Cd²⁺ and Fe³⁺ ions fulfilled the criteria for an INHIBIT molecular logic gate, further demonstrating the chemosensor’s multifunctional sensing potential.</p> Graphical Abstract <p></p>