| Abstract
| - A new series of iridium(III) mixed ligand complexes TBA[Ir(ppy)2(CN)2] (1), TBA[Ir(ppy)2(NCS)2](2), TBA[Ir(ppy)2(NCO)2] (3), and [Ir(ppy)2(acac)] (4) (ppy = 2-phenylpyridine; acac = acetoylacetonate,TBA = tetrabutylammonium cation) have been developed and fully characterized by UV−vis, emission,IR, NMR, and cyclic voltammetric studies. The lowest energy MLCT transitions are tuned from 463 to 494nm by tuning the energy of the HOMO levels. These complexes show emission maxima in the blue, green,and yellow region of the visible spectrum and exhibit unprecedented phosphorescence quantum yields,97 ± 3% with an excited-state lifetimes of 1−3 μs in dichloromethane solution at 298 K. The near-unityquantum yields of these complexes are related to an increased energy gap between the triplet emittingstate and the deactivating eg level that have been achieved by meticulous selection of ligands having strongligand field strength. Organic light-emitting devices were fabricated using the complex 4 doped into a purified4,4‘-bis(carbazol-9-yl)biphenyl host exhibiting a maximum of the external quantum efficiencies of 13.2%and a power efficiency of 37 lm/W for the 9 mol % doped system.
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