Visual Simultaneous Detection and Real-Time Monitoring of Cadmium Ions Based on Conjugated Polydiacetylenes

We prepared the monomer <b>PCDA-HP</b> composed of 5-hydroxy-<i>N</i> ¹,<i>N</i> ³-bis(pyridin-2-ylmethyl)isophthalamide (<b>HP</b>) as a cadmium ion tweezer and then polymerized them to form a polydiacetylene (PDA)-based sensor (<b>PDA-HP</b>), which displayed selective and sensitive colorimetric and fluorometric change upon addition of a cadmium ion (Cd²⁺) at both pH 7.4 and 6.8. The <b>PDA-HP</b> polymer was highly selective for Cd²⁺ over other metal ions with colorimetric change. In addition, the <b>PDA-HP</b> chemosensor also showed a red fluorescence change in the presence of Cd²⁺ at both pH 7.4 and 6.8. Naked-eye detection of Cd²⁺ was accomplished in an aqueous solution through a PDA-based sensor system. Finally, the lowest energy structure of an HP chelator was obtained by the crystal structure and density functional theory (DFT) calculations.