Iridium(III) Phosphors–Bearing Functional 9‐Phenyl‐7,9‐dihydro‐8H‐purin‐8‐ylidene Chelates and Blue Hyperphosphorescent OLED Devices

Abstract

Herein, a series of blue‐emitting Ir(III) phosphors is reported based on the cyclometalating N‐heterocyclic carbenes (NHCs), in which the typical benzimidazolylidene entity is now replaced by a new 7,9‐dihydro‐8H‐purin‐8‐ylidene unit. The two extra‐nitrogen atoms of benzimidazolylidene entity that are successfully fined turn the emission to the true‐blue region. As the proof of concept, both experimental measurement and theoretical calculation of these emitters are conducted, revealing high photoluminescence quantum yields up to 92%, peak maximum located in the region 420–490 nm, and radiative lifetime lower than 1 μs, depending on their stereochemical configuration (i.e., meridional or facial), together with distinctive phenyl cyclometalating appendage. Their photophysical characteristics are among the best of carbene‐based Ir(III) blue phosphors. Blue phosphorescent organic light‐emitting diode (OLED) using one representative derivative m‐2tBu as sole dopant emitter achieves a high external quantum efficiency (EQE) up to 17.0%, and a small efficiency roll‐off of 16% at 1000 cd m−2. Furthermore, a true‐blue hyperphosphorescent OLED with 25 wt% of m‐2tBu as sensitizer and 2 wt% of N7,N7,N13,N13,5,9,11,15‐octaphenyl‐5,9,11,15‐tetrahydro‐5,9,11,15‐tetraaza‐19b,20b‐diboradinaphtho[3,2,1‐de:1′,2′,3′‐jk]pentacene‐7,13‐diamine (ν‐DABNA) as emitter is also fabricated, giving excellent performance with maximum EQE up to 22.0% and Commission Internationale de l’Éclairage (CIE)xy coordinates of (0.120, 0.155).

Keywords

• blue
• carbine
• cyclometalate
• iridium
• organic light emitting diodes
• thermally activated delayed fluorescence