A new Schiff base ligand as a fluorescence probe for Cu(II) detection in semi-aqueous solution: synthesis, characterization, fluorescence and mechanistic insight

Abstract A new Schiff base fluorescence probe for Cu2+ was designed and synthesized by reaction between 2-[(3-formylphenoxy)2-hydroxypropoxy]benzaldehyde and 4-aminophenol. The probe was characterized by elemental analysis, FTIR, 1H- and 13C NMR, and fluorescence spectroscopies. DFT calculations were carried out to further characterize the structure of the compound in solution, by carrying out an in-depth conformational study. The obtained results showed fluorescence quenching of the fluorophore when Cu2+ binds to the ligand (L) in semi-aqueous solution (DMF:H2O 1:1) and revealed that the probe has high selectivity for Cu2+ compared to the other metal ions analyzed (Ag+, Co2+, Mg2+, Ni2+, Pb2+, Zn2+, Cd2+, Cr3+, Hg2+, Na+, Ba2+, Mn2+ and Fe3+). The stoichiometry of the complex formed between Cu2+ and L has been determined from a Job’s plot as being 1:1 and a structure for the complex Cu2+/L is proposed. The mechanism for the quenching of the fluorescence in the presence of Cu2+ was evaluated on the basis of time-dependent DFT (TD-DFT) results.