Colorimetric sensing of Cu(II): Cu(II) induced deprotonation of an amide responsible for color changes

9,10-Anthraquinone-based chemosensor 1 indicates the presence of Cu(II) ions among other transition metal ions with high selectivity by a color change from yellow to dark red. Chemosensor 2 shows binding toward Cu(II), Ni(II) and Co(II) with color changes from yellow to dark red, red and pale green, respectively. Especially, Co(II) binding with chemosensor 2 causes significantly green fluorescence. On addition of Cu(II), 1 and 2 exhibit 76 and 80 nm red shifts in absorption wavelength (pH 7.0). The effect on pH by the formation of these 1-Cu(II) and 2-Cu(II) complexes was determined by UV-vis spectroscopic pH titration. In the pH range of 6-7.5, a maximum absorption was observed at 473 nm and exhibited the formation of deprotonated 1-Cu(II) and 2-Cu(II) complexes.