New quinoline α-diimine ligands as fluorescent probes for metal ions: Ultrasound-assisted and conventional synthetic methods

Three new emissive 8-aminoquinoline derived probes (1)–(3) and one dinuclear Zn(II) complex (4) were synthesized and fully characterized. Their absorption spectra show maxima at 310–336 nm, and fluorescence emission between 456 and 498 nm. Compound (1) was characterized by single crystal X-ray diffraction. The effect upon Zn(II) and Cu(II) coordination to compounds (1)–(3) was studied by monitoring the changes in absorption and fluorescence spectra, and complemented by calculation of metal–ligand stability constants. The results indicate that compound (3) is the one that presents the most favorable geometry for coordinating two metal cations, fact that is confirmed by the synthesis of the dinuclear complex (4), with similar molecular geometry.