A colorimetric and turn-on fluorescent chemodosimeter 1 based on diaminomaleonitrile was synthesized for Cu2+ detection. It showed high selectivity and sensitivity towards Cu2+ over the other tested metal ions. Probe 1 in acetonitrile exhibited a strong absorption band at 530 nm and weak fluorescence emission when excited at 480 nm, while the addition of Cu2+ could lead to a 30-nm blue shift of the absorption band and a remarkable fluorescence enhancement. Moreover, the detection limit of probe 1 for Cu2+ was calculated to be 28 nM. Quite different from the reported mechanism based on a metal-complexation induced fluorescence enhancement, the sensing mechanism was proved to be based on the Cu2+-promoted hydrolysis reaction, which was confirmed by 1H NMR, 13C NMR and mass spectrum analysis. Studies on probe 2 were carried out to verify the universality of this sensing mechanism.
Keywords: Cu2+; Diaminomaleonitrile; fluorescence enhancement; oxidation.