Detection of Copper(II) in Water by Methylene Blue Derivatives

Two novel phenothiazin-5-ium derivatives bearing cyclam moieties (3 a+ and 3 b+) were synthesized and investigated as Cu2+ sensors. Both ligands show intense spectral changes in the presence of Cu2+ in aqueous solutions. The high molar extinction coefficient of the chromophore allows both naked eye detection and spectrophotometric quantitative determination of the cation at a micromolar-concentration scale. 3 a+ was found to outperform 3 b+, showing negligible spectral changes in the presence of excesses of other metal cations.