Organic light-emitting diodes (OLEDs) incorporating Ir(III)-based phosphorescent emitters (PHOLEDs) have achieved remarkable efficiencies in recent years, leading to the development of thinner and less energy-intensive television screens and mobile phone displays. Though red and green PHOLEDs are stable for up to hundreds of thousands of hours, blue PHOLEDs have only been optimized to last for hundreds of hours, which is orders of magnitude lower from the necessary device lifetime for implementation in screens and displays. The design of blue phosphorescent emitters with high quantum yields, sufficient kinetic stability, and suitable energy levels remains a grand challenge in the field. The prevailing design principle for Ir(III)-based phosphorescent emitters involves functionalizing covalently-bound cyclometalating ligands to achieve the desired photophysical properties of the luminescent species. Icosahedral carboranes represent a group of organomimetic clusters that provide a variety of tunable ligand frameworks not attainable with standard aromatic ligands. We recently discovered a new class robust and highly luminescent bis(heteroleptic) Ir(III) complexes containing weakly coordinating nido-carboranyl substituents that associate with the cationic Ir(III) center through primarily electrostatic interactions. These compounds exhibit blue phosphorescent emission both in solution and when doped in PMMA matrices with quantum yields exceeding 40%, and they display structural stability at temperatures beyond 300°C. Importantly, the observed quantum yields correspond to a 10-fold increase compared to those of previously reported Ir(III) complexes with carboranyl-based ligands featuring covalent interactions between the cluster and the Ir(III) center. Ultimately, this work suggests that use of ligands with weakly-coordinating components can potentially provide a new avenue for designing efficient Ir(III)-based phosphorescent emitters.

Blue phosphorescent zwitterionic Ir(III) complexes featuring weakly coordinating ligands

253rd National Meeting (2017)

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