Organic fluorescence sensor for selectively detecting and quantifying toxic heavy metal ions has received significant interest due to their environmental hazards. Herein, we have designed and synthesized a simple tripodal Schiff base ligand (1) based on hydroxy-naphthaldehyde and tris(2-aminoethyl)amine (TREN) and demonstrated highly selective turn-on fluorescence sensing of Cd²⁺ ions. The free ligand did not show any fluorescence in DMF. In contrast, Cd²⁺ (10^− 4 M) addition exhibited a strong enhancement of fluorescence at 450 nm. Interestingly, other metal ions including Zn²⁺, which exhibit similar chemistry, did not show any turn-on fluorescence. The concentration-dependent studies of 1 with Cd²⁺ showed the detection limit of 6.78 × 10^− 8 M. NMR spectra of 1 with Cd²⁺ and computational studies were performed to understand the mechanism of sense.