Synthesis, Characterization, and DFT Calculations of New Fluorescent Cu(II) Complexes of Heterocyclic Ligands

The synthesis, spectral studies, and quantum chemical investigation of two new copper(II) complexes of fluorescent heterocyclic ligands derived from benzimidazole are reported. The fluorescent heterocyclic ligands are synthesized by the reduction of imidazo[4,5:3,4]benzo[1,2-c]isoxazole derivatives and characterized by elemental analysis, IR, mass, and NMR spectra. Coordination of the bidentate ligands with the Cu(II) cation produce orange complexes. The structures of the complexes are established by spectral, analytical data and Job's method. To gain insight into the geometry and spectral properties of the Cu(II) complexes, DFT calculations are performed at the B3LYP/6-311++G(d,p) level. The DFT-calculated spectral properties are in good agreement with the experimental values, confirming the suitability of the optimized geometries for the copper complexes. The photophysical properties of the ligands and the Cu(II) complexes are characterized by UV-Vis and fluorescence spectroscopy. An efficient charge transfer from the ligand p orbital to the Cu(II) d orbital may be proposed as the main reason for the color of the complexes.