The emission lifetime of Ir(dfppy)2(pic-OH) (τem = 3.19 μs) was found to be significantly longer than of Ir(dfppy)2(pic-OMe) (τem = 0.94 μs), because of a substantial difference in the nonradiative decay rate (knr = 0.28 × 105 s-1 for Ir(dfppy)2(pic-OH) vs. 2.99 × 105 s-1 for Ir(dfppy)2(pic-OMe)). These results were attributed to the intramolecular OH—O=C hydrogen bond of the 3-hydroxy-picolinato ligand, restricting the vibrational modes associated with non-radiative decay processes, for example, triplet d–d transition. In contrast, the emission lifetime of Ir(ppy)2(pic-OH) was similar to that of Ir(ppy)2(pic-OMe), because the energy levels for the emissive triplet state of either Ir(ppy)2(pic-OH) or Ir(ppy)2(pic-OMe) are significantly lower than the triplet d–d transition. Therefore, introducing intramolecular OH—O=C hydrogen bond in ancillary ligand can be a simple but efficient strategy to developing efficient and stable blue phosphorescent. Finally, blue OLEDs device I (Ir(dfppy)2(pic-OH) as dopant) and II (FIrpic as dopant) with the structure of [ITO (150 nm)/HAT-CN (10 nm)/TAPC (85 nm)/Ir(dfppy)2(pic-OH) or FIrpic 8% doped mCP (30 nm)/TMPyPb (30 nm)/Liq/Al (150 nm)] were fabricated and compared. Both devices showed a similar power efficiency, current efficiency, and an external quantum efficiency of &gt;35 lm/W, &gt;38 Cd/A, and &gt;18%, respectively. In contrast, device lifetime was significantly improved when Ir(dfppy)2(pic-OH) was used as the dopant compared to FIrpic. Devices III and IV were fabricated with stable common layer (HTL and ETL) materials, and device III achieved an operational lifetime of 34.3 h for an initial luminance of 400 units compared to device IV with that of 20.1 h, indicating that the intramolecular hydrogen bond in ancillary ligand is playing an important role in device stability.

Stable blue phosphorescence Iridium(III) cyclometalated complexes prompted by intramolecular hydrogen bond in ancillary ligand

251st National Meeting (2016)

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