Structural, Electronic, Thermodynamic, Optical and Nonlinear Optical Properties of Curcumin Complexes with Transition Metals: DFT and TD-DFT Study

Because of their important photonic applications, the curcumin molecules, which can easily be found in nature, are interesting in the study of nonlinear optical (NLO) properties. Density functional theory (DFT) calculations on ground state molecular geometries of [(bpy-CH3)M(curc)] Cl complexes, where M=Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Tc, Ru, Rh, Pd, Ag, Cd, W, Re, Os, Ir, Pt, Au and Hg, have been performed at B3LYP level. Most complexes have a pyramidal geometry with square base, with a few exceptions well understood from the electronic structure of the metal atom. Although the pyramid geometry with square base of the [(bpy-CH3)Zn(curc)] Cl complex is preserved in solution, our DFT calculations show that the Zn lying above the square plane becomes closer and closer to that plane when the solvent is more and more polar, whereas the dipole moment increases in the mean time. The calculated IR spectra for the Zn complex show an increase in the intensity of the peaks of solvated complexes. The effect of solvent on excitation transition types and electronic spectra of the transition metal complexes simulated using DFT-CPCM model shows intra-ligand charge transfer from HOMO to LUMO in polar solvents, but from HOMO to LUMO+1 in apolar solvents. Among a full set of properties of transition metal series complexes with 21 elements, it appears that the Mn, Ag and Re complexes are the best candidates to NLO materials. Finally, an excellent correlation between the magnetic moments per atom and the number of valence electron of the central metals is obtained.