Synthesis, photophysical properties, and computational studies of four-coordinate copper(I) complexes based on benzimidazolylidene N-heterocyclic carbene (NHC) ligands bearing aryl substituents

Three four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes, [Cu(Ph-Benlm-Py)(POP)]PF6 (1), [Cu(Naph-Benlm-Py)(POP)]PF6 (2), and [Cu(Anthr-Benlm-Py)(POP)]PF6 (3) (Ph-BenIm-Py = 3benzy1-1-(pyridin-2-y1)-1H-benzimidazolylidene, Naph-Benlm-Py = 3-(naphthalen-2-y1-1-(pyridin-2y1)-1H- benzimidazolylidene, Anthr-BenIm-Py = 3-(anthracen-9-y1)-1-(pyridin-2-y1)-1H-benzimidazolylidene, and POP = bis[2-diphenylphosphino]-phenyl)ether) have been synthesized and characterized. The different aryl substituents (phenyl, naphthyl, and anthracyl groups) were introduced into NHC ligands and the corresponding photophysical properties of the complexes were systematically investigated. The absorption spectra of all NHC-Cu(I) complexes show a characteristic feature of metal-toligand charge transfer (MLCT) in the lower-energy region. Complex 1 exhibited good photoluminescence (PL) properties companying with the high quantum yields and long excited-state lifetimes, whereas 2 and 3 with naphthyl and anthracyl groups show the low PL efficiency caused by the strong pi-pi stacking interactions. Density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations were employed to rationalize the photophysical properties of the NHC-Cu(I) complexes. (C) 2017 Elsevier B.V. All rights reserved.