Diaminomaleonitrile Schiff Base Probe for the Detection of Copper Ions in a Semi-Aqueous Medium and its Applications

A diaminomaleonitrile-based fluorescent probe (CZ-DAMN) for the selective detection of Cu²⁺was synthesized and characterized by FTIR, ¹H-NMR,¹³C-NMR, and mass spectral analysis. The absorbance and fluorescent spectra and competition experiments investigated the sensing behavior of CZ-DAMN towards different metal ions. The results showed that the probe exhibited an enhanced emission at 436 nm (λ_ex = 320) with cyan fluorescence in the presence of Cu²⁺ions over other metal ions in CH₃CN:H₂O (8:2, v/v). A 1:1 stoichiometric binding of the probeCZ-DAMN to Cu²⁺ was observed according to Job's plot analysis. The binding constant was estimated at 7.38 × 10³ M^-1 with a detection limit of 14.81 nM. Turn-on was attributed to the inhibition of photoinduced electron transfer (PET) and -C = N- isomerization following Cu²⁺binding, whereas redshifted absorbance of the free probewas attributed to intramolecular charge transfer (ICT). Several methods were used to study the binding mechanism, including EPR, FTIR, ESI-mass, and DFT/TD-DFT. The probeCZ-DAMN demonstrated the detection of even trace amounts of Cu²⁺ions in real-time pharmaceutical samples. It was also used for on-site Cu²⁺ detection using probe-coated dipsticks.