Heteroleptic diimine copper(i) complexes with large extinction coefficients: synthesis, quantum chemistry calculations and physico-chemical properties

Abstract

Using the HETPHEN approach, five new heteroleptic copper(I) complexes composed of a push–pull 4,4′-styryl-6,6′-dimethyl-2,2′-bipyridine ligand and a bulky bis[(2-diphenylphosphino)phenyl]-ether (DPEphos) or a bis2,9-mesityl phenanthroline (Mes₂Phen) were prepared and characterized by electronic absorption spectroscopy, electrochemistry, and TD-DFT calculations. These complexes exhibit very intense absorption bands in the visible region with extinction coefficient in the range of 5–7 × 10⁴ M⁻¹ cm⁻¹. The analysis of the position, intensity and band shape indicates a strong contribution from an intra-ligand charge-transfer transition centered on the styrylbipyridine ligand along with MLCT transitions. These new complexes experimentally demonstrate that good light harvesting properties with bis-diimine copper(I) complexes are a reality if one chooses suitable ligands in the coordination sphere. This constitutes a milestone towards using bis-diimine copper(I) complexes for solar energy conversion (artificial photosynthesis and solar cells).