Colorimetric detection of Cu(II): Cu(II)-induced deprotonation of NH responsible for color change

Chemosensor 1 detects only the presence of Cu2+ ions among other metal ions through a color change from pale yellow to green. 1 functions as a tridentate ligand that binds Cu2+ ions through three amine nitrogen functional groups. In the presence of Cu2+, 1 provided significant color change, while Ag+, Ca2+, Cd2+, Co2+, Fe2+, Fe3+, Hg2+, Mn2+, Ni2+, Pb2+, and Zn2+ metal ions produced only minor changes in UV–vis absorption. The association constant (Ka) for Cu2+ binding to 1 had a value of 1.307 × 103 M−1. The maximum absorption change induced by Cu2+ binding to the chemosensor was observed over the pH range 6.0–10.0. A new band observed at 600 nm indicated the formation of deprotonated 1–Cu2+ complexes.

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