Spectral characterization and in vitro microbiological activity of new bis-1,8-naphthalimides and their Cu(II) complexes

• The synthesis and characterization of two new bis-1,8-naphthalimides is presented.
• The synthesis of a new copper complexes has been described.
• EPR analysis of complexes is presented.
• Copper complexes possessed good antimicrobial activity.

Two novel bis-1,8-naphthalimide derivatives with different substituents at C-4 position, termed L1 and L2, were synthesized and their photophysical properties in organic solvents with different polarity were investigated. Their Cu(II) complexes were also synthesized to be used as antimicrobial agents. The structural properties of [Cu(L1) (NO3)2] and [Cu(L2) (NO3)2] complexes were studied by nuclear magnetic resonance (NMR) and Fourier transform – infrared (FT-IR) spectroscopies. Cu(II) – ligands complexation at different Cu(II)/ligand molar ratios was studied by means of UV–Vis, fluorescence and electron paramagnetic resonance (EPR) spectroscopies. The results indicate the formation of Cu–N4 and Cu–N2O2 coordinations with different structure and stability conditions for the L1 and L2 derivatives. A different solvent at different polarity also affects the structural properties and the range of stability. L1 provided more stable Cu–N4 complexes than L2. [Cu(L1) (NO3)2] also showed stronger antibacterial and antifungal abilities than those of [Cu(L2) (NO3)2]. These results indicate that [Cu(L1) (NO3)2] works as antimicrobial agent to be used in biomedical and agrochemical applications.