The effect of alkyl substitution on the chemical and biological properties of Cu(II) diamine compounds was studied by carefully synthesizing two asymmetrical diamine/copper(II) nitrate salt complexes. The unsubstituted complex A and ethyl substituted complex B were synthesized from hydrated copper nitrate salt and the appropriate diamine ligands and identified by elemental analysis, FTIR and UV-Vis spectroscopy. The chemical properties and solvatochromatic behavior of both complexes were studied by UV-Vis. The antibacterial activity of the two complexes was testes against six bacterial isolates which are common pathogens for humans. The results were interpreted under the light of quantum chemical calculations. Time dependent density functional theory was used to interoperate the UV-Vis spectra of both compounds.