Effects of electronic and nuclear interactions on the excited-state properties and structural dynamics of copper(I) diimine complexes

The effects of structural constraints on the metal-to-ligand charge transfer (MLCT) excited state structural dynamics of cuprous bis-2,9-diphenyl-phenanthroline ([Cu(I)(dpp)2]+) in both coordinating acetonitrile and noncoordinating toluene were studied using X-ray transient absorption (XTA) spectroscopy and density functional theory (DFT) calculations. The phenyl groups attached to the phenanthroline ligands not only effectively shield the Cu(I) center from solvent molecules, but also force a flattened tetrahedral coordination geometry of the Cu(I) center. Consequently, the MLCT state lifetime in [Cu(I)(dpp)2]+ is solvent-independent, unlike the previously studied 2,9-methyl substituted bis-phenanthroline Cu(I) complex. The MLCT state of [Cu(I)(dpp)2]+ still undergoes a “pseudo Jahn-Teller distortion,” with the angle between the two phenanthroline ligand planes decreased further by 7°. The XTA results indicate that, in the MLCT excited state of [Cu(I)(dpp)2]+, the phenyls at the 2, 9 positions of the phen...