A novel azo-azomethine based fluorescent dye and its Co(II) and Cu(II) metal chelates

Cobalt(II) and copper(II) complexes of a novel Schiff base ligand containing two -NN- chromophore groups, derived from the condensation of 2-hydroxy-5-[(E)-phenyldiazenyl]benzaldehyde with p-aminoazobenzene were synthesized and characterized by analytical and spectroscopic methods. The X-ray powder diffraction analysis was used to determine the unit cell parameters of the synthesized ligand and its metal complexes. Self-isomerization via intramolecular proton transfer was investigated by UV-Vis and theoretical calculations. The effect of solvent polarity on UV-Vis was examined. The electronic structures of compounds were also predicted with computational chemistry methods. Theoretical vibrational and electronic spectra of the metal complexes were obtained from these structures. Binding energies of the metal complexes were obtained by quantum chemical calculations. Upon irradiation the ligands and their metal complexes gave blue light. The (1a) azo-aldehyde and (2a) azo-azomethine ligands revealed quantum yields of 35 and 41% and their excited-state lifetimes were 3.26 and 3.86 ns, respectively. Decreases in photoluminescence intensity and quantum yield upon complexation with metal ions were noted. The thermal behavior to include activation energy (E), entropy (ΔS*), enthalpy (ΔH*) and Gibbs free energy change (ΔG*), using Coats-Redfern (CR) and Horowitz-Metzger (HM) methods, were examined.