title: Stable Blue Phosphorescence Iridium(III) Cyclometalated Complexes Prompted by Intramolecular Hydrogen Bond in Ancillary Ligand.
abstract: Improvement of the stability of blue phosphorescent dopant material is one of the key factors for real application of organic light-emitting diodes (OLEDs). In this study, we found that the intramolecular hydrogen bonding in an ancillary ligand from a heteroleptic Ir(III) complex can play an important role in the stability of blue phosphorescence. To rationalize the role of intramolecular hydrogen bonding, a series of Ir(III) complexes is designed and prepared: Ir(dfppy)2(pic-OH) (1a), Ir(dfppy)2(pic-OMe) (1b), Ir(ppy)2(pic-OH) (2a), and Ir(ppy)2(pic-OMe) (2b). The emission lifetime of Ir(dfppy)2(pic-OH) (1a) (τem = 3.19 μs) in dichloromethane solution was found to be significantly longer than that of Ir(dfppy)2(pic-OMe) (1b) (τem = 0.94 μs), because of a substantial difference in the nonradiative decay rate (knr = 0.28 × 10(5) s(-1) for (1a) vs 2.99 × 10(5) s(-1) for (1b)). These results were attributed to the intramolecular OH···O═C hydrogen bond of the 3-hydroxy-picolinato ligand. Finally, device lifetime was significantly improved when 1a was used as the dopant compared to FIrpic, a well-known blue dopant. Device III (1a as dopant) achieved an operational lifetime of 34.3 h for an initial luminance of 400 nits compared to that of device IV (FIrpic as dopant), a value of 20.1 h, indicating that the intramolecular hydrogen bond in ancillary ligand is playing an important role in device stability.
authors.affiliation: Department of Advanced Materials Chemistry, Korea University , Sejong 30019, South Korea.
authors.forename: Seungjun
authors.initials: S
authors.lastname: Yi
authors.affiliation: Department of Advanced Materials Chemistry, Korea University , Sejong 30019, South Korea.
authors.forename: Jin-Hyoung
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Advanced Materials Chemistry, Korea University , Sejong 30019, South Korea.
authors.forename: Yang-Jin
authors.initials: YJ
authors.lastname: Cho
authors.affiliation: Department of Chemistry, Seoul Women's University , Seoul 01797, South Korea.
authors.forename: Jiwon
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Advanced Materials Chemistry, Korea University , Sejong 30019, South Korea.
authors.forename: Tae-Sup
authors.initials: TS
authors.lastname: Choi
authors.affiliation: Department of Advanced Materials Chemistry, Korea University , Sejong 30019, South Korea.
authors.forename: Dae Won
authors.initials: DW
authors.lastname: Cho
authors.affiliation: Department of Advanced Materials Chemistry, Korea University , Sejong 30019, South Korea.
authors.forename: Chyongjin
authors.initials: C
authors.lastname: Pac
authors.affiliation: Department of Chemistry, Seoul Women's University , Seoul 01797, South Korea.
authors.forename: Won-Sik
authors.initials: WS
authors.lastname: Han
authors.affiliation: Department of Advanced Materials Chemistry, Korea University , Sejong 30019, South Korea.
authors.forename: Ho-Jin
authors.initials: HJ
authors.lastname: Son
authors.affiliation: Department of Advanced Materials Chemistry, Korea University , Sejong 30019, South Korea.
authors.forename: Sang Ook
authors.initials: SO
authors.lastname: Kang