Bis-azo-linkage Schiff bases-Part(II): Synthesis, characterization, photoluminescence and DPPH radical scavenging properties of their novel luminescent mononuclear Zn(II) complexes

In this paper, two luminescent Zn(II) complexes with the formula (ZnH2L1,2) were newly synthesized by a one-step reaction of the bis-azo-Schiff base ligands and metal salt. Their mononuclear structure was characterized by different analytical and spectroscopic measurements (elemental analysis, IR, NMR, UV-vis, mass, powder XRD, conductance and magnetic susceptibility). TGA and DTA techniques showed that the complexes were stable above 400 degrees C. The host-guest interaction between the ligands and Zn(II) ion was examined by UV-vis titration. It found a low LOD value for Zn(II) ion in the concentration range of 1.30 x 10(-6) M and 4.40 x 10(-7) M. The stoichiometric ratio and formation constant of ligand-Zn(II) complexation were determined using Benesi-Hildebrand and Job's plots. Upon photoexcitation with Xenon lamp, Zn(II) complexes emitted green luminescence in DMSO solution. The antioxidant activity of the ligands and new Zn(II) complexes was studied by using DPPH radical scavenging assay by fixed reaction time and steady state measurements. The results indicated that the ligands exhibited higher scavenging activity than that of ascorbic acid, but Zn(II) complexes did not have any activity.