Fluorescence in complexes based on quinolines-derivatives: a search for better fluorescent probes

•Bathochromic effect was observed for all complexes synthesized with 5-chloro-8-hydroxyquinoline.•Intense luminescence was observed for complexes with the naked eye.•These complexes could find possible applications in ionic and biological probes

Quinoline-derived fluorescent complexes were designed; synthesized by the reaction of 5-nitro-8-hydroxyquinoline and 5-chloro-8-hydroxyquinoline with Al3+, Mg2+, Zn2+, and Cd2+ salts (1–8); and characterized. The 1H NMR spectra of complexes 1 and 5, containing Al3+, were consistent with an octahedral structure having approximate D3 symmetry, and the results supported the favored facial isomer (fac). Data for complexes 2–4 and 6–8 supported the formation of tetrahedral structures. Intense luminescence was detected for complexes 5–8, even with the naked eye, as indicated by quantum yield values of 0.087, 0.094, 0.051, and 0.021, respectively. Furthermore, in contrast to 5-nitro-8-hydroxyquinoline, the 5-chloro-8-hydroxyquinoline ligand exhibited bands at different energies depending on the coordinated metal, which supported its potential application in ionic and biological probes, as well as in cell imaging.

Graphical abstractIntense fluorescence was detected for complexes 5–8, even with the naked eye.Figure optionsDownload full-size imageDownload as PowerPoint slide