Bis-Triazole-Appended Azobenzene Chromophore for Selective Sensing of Copper(II) Ion

A Cu²⁺-specific colorimetric sensor of bis-triazole-appended azobenzene receptors I and II was designed and synthesized. Receptor II shows high selectivity toward Cu²⁺ in acetonitrile/water (80:20, v/v) solution based on the internal charge transfer (ICT) mechanism. The tridentate coordination behavior was proposed with 1:1 stoichiometry between receptor II and Cu²⁺. Herein, the Cu²⁺ gives rise to a large change in the absorption spectra (from red to pale yellow) that is clearly visible to the naked eye.