Stable Blue Phosphorescence Iridium(III) Cyclometalated Complexes Prompted by Intramolecular Hydrogen Bond in Ancillary Ligand.
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) (tem 3.19 ms) in dichloromethane solution was found to be significantly longer than that of Ir(dfppy)2(pic OMe) (1b) (tem 0.94 ms) because of a substantial difference in the nonradiative decay rate (knr 0.28 x 10(5) s( 1) for (1a) vs 2.99 x 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.
Inorganic chemistry