title: Phosphorescent cyclometalated iridium(III) complexes that contain substituted 2-acetylbenzo[b]thiophen-3-olate ligand for red organic light-emitting devices.
abstract: We report the synthesis of a new class of thermally stable and strongly luminescent cyclometalated iridium(III) complexes 1-6, which contain the 2-acetylbenzo[b]thiophene-3-olate (bt) ligand, and their application in organic light-emitting diodes (OLEDs). These heteroleptic iridium(III) complexes with bt as the ancillary ligand have a decomposition temperature that is 10-20 % higher and lower emission self-quenching constants than those of their corresponding complexes with acetylacetonate (acac). The luminescent color of these iridium(III) complexes could be fine-tuned from orange (e.g., 2-phenyl-6-(trifluoromethyl)benzo[d]thiazole (cf3 bta) for 4) to pure red (e.g., lpt (Hlpt=4-methyl-2-(thiophen-2-yl)quinolone) for 6) by varying the cyclometalating ligands (C-deprotonated C^N). In particular, highly efficient OLEDs based on 6 as dopant (emitter) and 1,3-bis(carbazol-9-yl)benzene (mCP) as host that exhibit stable red emission over a wide range of brightness with CIE chromaticity coordinates of (0.67, 0.33) well matched to the National Television System Committee (NTSC) standard have been fabricated along with an external quantum efficiency (EQE) and current efficiency of 9 % and 10 cd A(-1) , respectively. A further 50 % increase in EQE (>13 %) by replacing mCP with bis[4-(6H-indolo[2,3-b]quinoxalin-6-yl)phenyl]diphenylsilane (BIQS) as host for 6 in the red OLED is demonstrated. The performance of OLEDs fabricated with 6 (i.e., [(lpt)2Ir(bt)]) was comparable to that of the analogous iridium(III) complex that bore acac (i.e., [(lpt)2 Ir(acac)]; 6a in this work) [Adv. Mater.- 2011, 23, 2981] fabricated under similar conditions. By using ntt (Hnnt=3-hydroxynaphtho[2,3-b]thiophen-2-yl)(thiophen-2-yl)methanone) ligand, a substituted derivative of bt, the [(cf3bta)2Ir(ntt)] was prepared and found to display deep red emission at around 700 nm with a quantum yield of 12 % in mCP thin film.
authors.affiliation: HKU-CAS Joint Laboratory on New Materials and Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, Fax: (+852) 2915-5176; HKU Shenzhen Institute of Research and Innovation, Shenzhen 518053 (China).
authors.forename: Chen
authors.initials: C
authors.lastname: Yang
authors.forename: Shiu-Lun
authors.initials: SL
authors.lastname: Lai
authors.forename: Sharon Lai-Fung
authors.initials: SL
authors.lastname: Chan
authors.forename: Kam-Hung
authors.initials: KH
authors.lastname: Low
authors.forename: Gang
authors.initials: G
authors.lastname: Cheng
authors.forename: Kwan-Ting
authors.initials: KT
authors.lastname: Yeung
authors.forename: Chi-Chung
authors.initials: CC
authors.lastname: Kwok
authors.forename: Chi-Ming
authors.initials: CM
authors.lastname: Che
keywords: iridium; ligand effects; light-emitting diodes; luminescence; metalation