A Diaminomaleonitrile based Schiff Base Colorimetric Sensor for Copper detection using smartphone-assisted RGB and Test kit Methods

A high selective and sensitive detection of Cu2+ in the semi-aqueous phase by the naked eye has always been a challenge. In this paper, a simple compound based on diaminomaleonitrile Schiff base probe (L) was synthesized and its structure was confirmed by 1H, 13C NMR, FTIR, and mass analysis. The probe L showed distinct colorimetric upon interaction with Cu2+ in DMSO:H2O (5:5, v/v) media. The probe L exhibited a key absorption peak at 374 nm due to π→π* transitions of the free probe, upon the interaction with Cu2+ it shifted to 462 nm, which is due to the LMCT mechanism. The probe L binds Cu2+ in a 1:1 ratio with an association constant of (Ka) = 5.02×104 M-1 and this is established by using the Job’s and Benasi-Hilderbrand (BH) methods. The detection limit for Cu2+ can reach a concentration of as low as 0.705 μM with high selectivity, even in a solution containing diverse metal ions. Besides, the selective color change of L with Cu2+ was integrated with a smartphone to monitor the change in the RGB tool and test paper kit. The binding mechanism of L with Cu2+ was studied by using ESI mass and DFT analysis.