Highly phosphorescence iridium complexes and their application in organic light-emitting devices

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 494 nm 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-unity quantum yields of these complexes are related to an increased energy gap between the triplet emitting state and the deactivating eg level that have been achieved by meticulous selection of ligands having strong ligand field strength. Organic light-emitting devices were fabricated using the complex 4 doped into a purified 4,4′-bis(carbazol-9-yl)biphenyl host exhibiting a maximum of the external quantum efficiencies of 13.2% and a power efficiency of 37 Im/W for the 9 mol % doped system.