Cu(β-diketonato)₂ bathochromic shifts from the ultraviolet towards the visible region

The DFT-calculated ultraviolet/visible properties of 11 different Cu(β-diketonato)₂ complexes are presented. The selected β-diketonato ligands on the Cu complex contain none, one or two aromatic rings. The experimentally measured absorbance maxima range of the ultraviolet/visible is observed at 295-390 nm, and the calculated range is 302-425 nm, for the 11 complexes in this study. More aromatic rings on the ligand lead to bathochromic shifts of the experimentally measured absorbance maxima from the ultraviolet towards the visible region. Absorbance maxima of the Cu(β-diketonato)₂ complexes with no aromatic rings on the ligand are found to be predominantly ligand-to-metal charge transfer excitations, whereas introducing one or two aromatic rings shifts the excitations to predominantly ligand-to-ligand charge transfer.

DFT calculations were conducted on the neutral molecules with multiplicity 2, using the PBEh1PBE functional and the aug-cc-pVDZ basis set as implemented in the Gaussian 16 package. The selected solvent was acetonitrile, the solvent in which most of the experimental UV/Vis are reported. The molecules were all optimized in the solvent phase, using the IEFPCM. The initial coordinates for the compounds were generated using Chemcraft.

TDDFT of 11 different Cu(β-diketonato)₂ complexes follow the experimental trend. Aromatic rings on the ligand lead to Bathochromic shifts of UV/Visible spectra. No aromatic rings on the ligand lead to ligand-to-metal charge transfer excitations. Aromatic rings on the ligand lead to ligand-to-ligand charge transfer excitations.