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

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).