title: Bimetallic N-heterocyclic carbene-iridium complexes: investigating metal-metal and metal-ligand communication via electrochemistry and phosphorescence spectroscopy.
abstract: Bimetallic [Ir(COD)Cl] and [Ir(ppy)(2)] (COD = 1,5-cyclooctadiene; ppy = 2-phenylpyridyl) complexes bridged by 1,7-dimethyl-3,5-diphenylbenzobis(imidazolylidene) (1), in addition to their monometallic analogues supported by 1-methyl-3-phenylbenzimidazolylidene (2), were synthesized and studied. Electrochemical analyses indicated that 1 facilitated moderate electronic coupling between [Ir(COD)Cl] units (DeltaE = approximately 60 mV), but not [Ir(ppy)(2)]. The metal-based oxidation potentials for the bimetallic complexes were within 20 mV of those for their monometallic analogues. Furthermore, spectroscopic analyses of the [Ir(ppy)(2)] bimetallic and monometallic complexes revealed nearly identical phosphorescence profiles, indicating that carbene coordination does not affect the energy of the emissive states. Collectively, these results suggest that N-heterocyclic carbenes (NHCs) such as 1 could link together two emissive fragments without altering their fundamental phosphorescence profiles. Ultimately, employing multitopic NHCs as non-interfering molecular connectors could facilitate the rational design of new phosphorescent materials as well as second-generation phosphor dopants.
authors.affiliation: Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University Station A5300, Austin, Texas 78712, USA.
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Tennyson
authors.forename: Evelyn L
authors.initials: EL
authors.lastname: Rosen
authors.forename: Mary S
authors.initials: MS
authors.lastname: Collins
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Lynch
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Bielawski