Detection of copper(II) in water by methylene blue derivatives

Two novel phenothiazin-5-ium derivatives bearing cyclam moieties ( 3a + and 3b + ) were synthesized and investigated as Cu 2+ sensors. Both ligands show intense spectral changes in the presence of Cu 2+ 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. 3a + was found to outperform 3b + , showing negligible spectral changes in the presence of excesses of other metal cations.