Blue Phosphorescent Zwitterionic Iridium(III) Complexes Featuring Weakly Coordinating nido-Carborane-Based Ligands

Abstract

We report the development of a new class of phosphorescent zwitterionic bis(heteroleptic) Ir(III) compounds containing pyridyl ligands with weakly coordinating nido-carboranyl substituents. Treatment of phenylpyridine-based Ir(III) precursors with C-substituted ortho-carboranylpyridines in 2-ethoxyethanol results in a facile carborane deboronation and the formation of robust and highly luminescent metal complexes. The resulting nido-carboranyl fragments associate with the cationic Ir(III) center through primarily electrostatic interactions. These compounds phosphoresce at blue wavelengths (450-470 nm) both in a poly(methyl methacrylate) (PMMA) matrix and in solution at 77 K. These complexes display structural stability at temperatures beyond 300 °C and quantum yields greater than 40%. Importantly, the observed quantum yields correspond to a dramatic 10-fold enhancement over the previously reported Ir(III) congeners featuring carboranyl-containing ligands in which the boron cluster is covalently attached to the metal. Ultimately, this work suggests that the use of a ligand framework containing a weakly coordinating anionic component can provide a new avenue for designing efficient Ir(III)-based phosphorescent emitters.

Ancillary Ligand Effects on Red‐Emitting Cyclometalated Iridium Complexes

“…Therefore, tuning the emission color and excited‐state dynamics by altering the ancillary ligand structure in heteroleptic iridium complexes with known cyclometalating ligands could be an easier, more efficient, and more expeditious approach. There are several well‐known strategies that use ancillary ligands to tune the emission and/or photochemical properties of cyclometalated iridium complexes over a wide range, including ancillary ligands that are chromophoric and completely change the nature of the excited state or those that have subtler effects on the frontier orbitals and excited states . Our group has recently reported the synthesis and characterization of red‐emitting bis‐cyclometalated Ir III complexes with high efficiency, good device performance, and excellent color purity by using β‐ketoiminate (acNac), β‐diketiminate (NacNac), and smaller bite‐angle N′N ‐diisopropylbenzamidinate (dipba) as the ancillary ligands .…”

“…There are several well-known strategies that use ancillary ligandst o tune the emission and/orp hotochemical properties of cyclometalated iridium complexes over aw ide range, including ancillary ligandst hat are chromophoric and completely change the nature of the excited state or those that have subtler effects on the frontier orbitalsa nd excited states. [20,21,[33][34][35][36] Our group has recently reported the synthesis and characterization of red-emittingb is-cyclometalated Ir III complexes with high efficiency,g ood device performance, and excellent color purity by using b-ketoiminate (acNac), b-diketiminate (NacNac), and smaller bite-angle N'N-diisopropylbenzamidinate (dipba) as the ancillary ligands. [37] We were able to show that the different L^X ligands influence the electronic structures of bis-cyclometalated iridium complexes, in some cases inducing significant redshiftso ft he emission maxima, and in other cases enhancing phosphorescence quantum yields relative to the corresponding acetylacetonate (acac) analogues or the homoleptic tris-cyclometalated complexes featuring the same cyclometalating ligands.…”

Boron‐Functionalized Phosphorescent Iridium(III) Complexes

“…[42] These complexes were synthesized by treatment of phenylpyridine-based Ir III precursors with C-substituted o-carboranylpyridines. The resulted nido-carboranyl fragments associated with the cationic Ir III center primarily through electrostatic interactions.…”

A New Facial Homoleptic Tris‐cyclometalated Iridium(III) Complex with Oxygen‐bridged Triarylamine Units

“…In the last few decades, transition metal complexes have been widely used in the field of light‐emitting materials . In particular, phosphorescent iridium(III) complexes as optical functional materials have attracted a lot of attentions owing to their diverse chemical structures and excellent luminous properties . Especially, homoleptic tris‐cyclometalated phosphorescent iridium(III) complexes with facial structure tend to have more stable structures and better optical properties than other complexes, such as the classic facial phosphorescent iridium(III) complex fac ‐Ir(ppy) 3 (ppy=2‐phenylpyridine) (scheme ) is a famous green light emitting material, and its derivatives are very widely used.…”