A diaminomaleonitrile based selective colorimetric chemosensor for copper(ii) and fluoride ions

A new and simple colorimetric receptor 1, based on 2,3-diaminomaleonitrile and julolidine moieties, has been synthesized and characterized. 1 showed a selective colorimetric sensing ability for copper(ii) ions by changing color from yellow to colorless, and could be utilized to monitor Cu²⁺ over a wide pH range of 4-12. The detection limit of 1 (2.1 μM) for Cu²⁺ ions is much lower than that recommended by WHO in drinking water (30 μM). Moreover, the receptor 1 can also detect fluoride by color change from yellow to orange, distinguishing the fluoride ions effectively from anions such as CH₃COO^- and CN^-. It was also found that the 1-F^- complex was reversibly bound and could be simply reverted back through treatment with a proper reagent such as HCl. The sensing mechanism for F^- was theoretically supported by DFT and TD-DFT calculations.