A selective chromone‐based colorimetric chemosensor for detecting Cu²⁺ in near‐perfect aqueous solution and test kit

A colorimetric chemosensor CMF (N′‐[(E)‐(4‐oxo‐4H‐chromen‐3‐yl)methylidene]furan‐2‐carbohydrazide) was applied for detecting Cu 2+ . CMF showed colorimetric selectivity to Cu 2+ through a color variation from colorless to yellow. Binding ratio between CMF and Cu 2+ was analyzed by Job plot to be a 2:1. Limit of detection was found to be 0.38 μM. The practicality of CMF was illustrated by the quantification of Cu 2+ in real samples. In particular, the CMF ‐coated test kit was able to detect the copper ions at a concentration lower than the recommended concentration (31.5 μM) of the World Health Organization (WHO) for copper ion. The binding mode of CMF and copper ions was studied through UV–visible spectroscopy, 1 H NMR titration, ESI‐mass analysis, and DFT calculations. Sensing mechanism of CMF to Cu 2+ was proposed to be the ligand‐to‐metal charge transfer (LMCT) through DFT calculations.