Highly Selective Turn-on Fluorescence Sensor for Cd 2+ Ions by Tripodal Organic Ligand

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 Cd 2+ ions. The free ligand did not show any fluorescence in DMF. In contrast, Cd 2+ (10 − 4 M) addition exhibited a strong enhancement of fluorescence at 450 nm. Interestingly, other metal ions including Zn 2+ , which exhibit similar chemistry, did not show any turn-on fluorescence. The concentration-dependent studies of 1 with Cd 2+ showed the detection limit of 6.78 × 10 − 8 M. NMR spectra of 1 with Cd 2+ and computational studies were performed to understand the mechanism of sense. Graphical Abstract