New diaminomaleonitrile derivatives containing aza-crown ether: Selective, sensitive and colorimetric chemosensors for Cu(II)

Two novel soluble chemosensors based on Schiff-base diaminomaleonitrile derivatives which were modified by an aza-crown ether moiety have been synthesized. These chemosensors were fully characterized by 1H NMR, 13C NMR spectroscopy, mass spectrometry, IR, DSC and single crystal X-ray diffraction. The recognition abilities of the sensors with a range of metal ions were evaluated and their photophysical properties have been systematically investigated. DFT theoretical calculations were employed to understand the behavior of the sensors toward the Cu(II). The sensing mechanism was derived through experimental and theoretical calculations. The results consistently indicated that the monoaza-10-crown-5 species was the ideal sensor, which can be utilized to monitor Cu(II) in solution over a wide pH range.