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

• New Schiff base is a promising selective and sensitive fluorescence probe for Cu 2+ . • Sensor exhibits over 95 % of fluorescence quenching in presence of Cu 2+ . • Sensor works at the μM range of concentrations. • DFT and TD-DFT calculations allowed to elucidate the quenching mechanism. • LMCT transition in the complex contributes to the quenching of the fluorescence. A new Schiff base fluorescence probe for Cu 2+ was designed and synthesized by reaction between 2-[(3-formylphenoxy)2-hydroxypropoxy]benzaldehyde and 4-aminophenol. The probe was characterized by elemental analysis, FTIR, 1 H- and 13 C 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 Cu 2+ binds to the ligand ( L ) in semi-aqueous solution (DMF:H 2 O 1:1) and revealed that the probe has high selectivity for Cu 2+ compared to the other metal ions analyzed (Ag + , Co 2+ , Mg 2+ , Ni 2+ , Pb 2+ , Zn 2+ , Cd 2+ , Cr 3+ , Hg 2+ , Na + , Ba 2+ , Mn 2+ and Fe 3+ ). The stoichiometry of the complex formed between Cu 2+ and L has been determined from a Job’s plot as being 1:1 and a structure for the complex Cu 2+ / L is proposed. The mechanism for the quenching of the fluorescence in the presence of Cu 2+ was evaluated on the basis of time-dependent DFT (TD-DFT) results.