Iridium(III) Blue Phosphors with Heteroleptic Carbene Cyclometalates: Isomerization, Emission Tuning, and OLED Fabrications
Yixin Wu, Manli Huang, Lin Cheng, Junyao Zhang, Yi Pan, Shek‐Man Yiu, Kai‐Chung Lau, Jie Yan, Chuluo Yang, Yün Chi
Abstract
Abstract Ir(III) complexes are particularly noted for their excellent photophysical properties in giving blue OLED phosphors. In this study, two distinctive carbene pro‐chelates LAH 2 + and LBH 2 + (or LCH 2 + ) were employed in preparation of heteroleptic Ir(III) complexes, to which LAH 2 + bears a cyano substituted benzoimidazolium along with N‐mesityl appendage, while LBH 2 + (or LCH 2 + ) carries the symmetrical benzoimidazolium entity. Notably, the reversible equilibration at high temperature was observed for m , f ‐ ct14 and m , f ‐ ct15 with a single LA chelate. In contrast, only the mer ‐substituted m ‐ ct16 was obtained upon employing two LA chelates. All Ir(III) complexes exhibited blue photoluminescence ( Φ PL 78 %) with short radiative lifetimes (τ rad 1.05 μs) in solution. The Ph OLED device with m ‐ ct16 afforded an external quantum efficiency (EQE) of 22.8 % at 5000 cd ⋅ m −2 . Moreover, the hyper‐OLED based on m ‐ ct16 and v‐DABNA exhibited EQE 1000 of 32.1 % (EQE recorded at 1000 cd ⋅ m −2 ) and J 90 of 15.0 mA cm −2 (current density at 90 % of max. EQE). Its suppressed efficiency roll‐off (EQE of 32.1 % and 27.7 % at 1000 cd ⋅ m −2 and 10000 cd ⋅ m −2 ) demonstrated a milestone in fabrication of blue OLED devices.