Diving into the optoelectronic properties of Cu(II) and Zn(II) curcumin complexes: a DFT and wavefunction benchmark

Area of Science:

• Computational Chemistry
• Photophysics
• Materials Science

Background:

• Curcumin, a natural food additive, possesses known medicinal properties and potential light-harvesting applications due to its color.
• Existing literature highlights curcumin's biological activities but lacks detailed photophysical descriptions of its metallic complexes.

Purpose of the Study:

• To computationally investigate the photophysical properties of curcumin and its copper(II) and zinc(II) complexes.
• To identify the most accurate computational methods for describing their UV-Vis absorption spectra.

Main Methods:

• Benchmark calculations comparing various Density Functional Theory (DFT) functionals (B3LYP, M06-L, etc.) against NEVPT reference data.
• Assessment of basis sets, solvation effects, and redox states on excited-state properties.
• Analysis of intra-ligand, ligand-to-metal charge transfer (LMCT), and metal-to-ligand charge transfer (MLCT) transitions.

Main Results:

• DFT functional accuracy varies with excitation type; B3LYP is best for general description, M06-L for LMCT.
• Intra-ligand transitions dominate the absorption spectra of curcumin-metal complexes.
• Solvation and chelation have minor effects unless combined with redox processes, which significantly alter spectra due to copper's geometric changes.

Conclusions:

• No single DFT functional accurately describes all transitions, particularly MLCT.
• Computational methods are crucial for understanding curcumin's photophysics in light-harvesting and biological contexts.
• Further refinement of computational approaches is needed for complex charge transfer phenomena.