Luminescent phosphine copper(i) complexes with various functionalized bipyridine ligands: synthesis, structures, photophysics and computational study

Abstract

A new series of luminescent phosphine copper(I) complexes with cyano- and hydroxyl-substituted 2,2′-bipyridine ligands [Cu^I(bpy(CN)₂)(P(PhX)₃)₂](ClO₄) [X = H (1); Me (2); Cl (3)], [Cu^I(bpy(CN)₂)(POP)](ClO₄) (4), [Cu^I(bpy(OH)₂)(PPh₃)₂](ClO₄) (5) and [Cu^I(bpy(OH)₂)(POP)](ClO₄) (6) have been synthesized and characterized. Three of these complexes have been structurally characterized by using X-ray crystallography. The effect of the attaching –CN and –OH groups at the ortho-positions of bpy ligand was investigated. In CH₂Cl₂ solution, these complexes show yellow to orange phosphorescence, with the emission maxima not only sensitive to the electronic nature of the bipyridine ligands, but also considerably varied with the modification of phosphine ligands. In addition, these complexes show intense tunable green to yellow emissions in their solid state. To elucidate the electronic structures and transitions of these complexes, density functional theory (DFT) calculations on representative examples revealed that the lowest energy electronic transition associated with these complexes predominantly originates from metal-to-ligand charge transfer transitions (MLCT).