Synthesis, structure, and biological properties of Cu(II) complexes based on diimine ligands

•Three new Cu(II) complexes of diimine ligand were prepared.•The crystal structures of Cu(II) complexes have been determined.•DNA/BSA binding behaviors of Cu(II) complexes are performed using electronic absorption titrations and fluorescence spectral studies.•The cytotoxicity of complexes in vitro was evaluated.•The apoptosis-inducing activity was assessed by Annexin-V/PI double staining assay.