Iridium(III) Carbene Phosphors with Fast Radiative Transitions for Blue Organic Light Emitting Diodes and Hyperphosphorescence

Abstract

It is envisioned that the efficient and stable blue OLED phosphors can be synthesized using Ir(III) complexes with electron‐deficient carbene cyclometalates. Therefore, three facially coordinated Ir(III) phosphors f‐ct7a‐ c bearing isomeric purinylidene chelates are obtained. They possess three, two, and one 4‐t‐butylphenyl cyclometalate together with the same number of N‐phenyl appendage on carbene fragments, and exhibit photoluminescence centered (λmax) at 452‒461 nm, fast radiative rate constants (kr) of 7.5–11.3 × 105 s‒1, and high quantum yield (PLQY) up to 80% in degassed toluene at RT. Representative OLED based on f‐ct7c gives maximum external quantum efficiency (EQEmax) of 26.6%, CIE(x,y) of 0.16, 0.15, and low roll‐off with EQE of 22.3% at 1000 cd m‒2. Furthermore, they can be utilized to sensitize a deep blue multiple resonance thermally activated delay fluorescence emitter (MR‐TADF), i.e., t‐DABNA. The corresponding hyper‐OLED device based on alternative f‐ct7b realizes an EQEmax of 36.1%, CIE(x,y) of 0.14, 0.09, and full width at half maximum (FWHM) of 26.5 nm. To the understanding, this is the first report on concurrent achieving both the high EQE and small CIEy value for Ir(III)‐based phosphors.

Selective syntheses of homoleptic Ir(iii) complexes bearing di-CF3-functionalized benzoimidazol-2-ylidenes for generation of blue phosphorescence

“…Hence, tedious separation of isomers was no longer required, which is particularly important for the scale-up operation and marking an essential milestone in syntheses. Moreover, this site-selectivity is of uttermost importance to the widespread employment of di-aryl substituted benzoimidazol-2-ylidene and its analogues, 32–34 as they are deemed superior to their mono- N -aryl counterparts in serving as blue OLED emitters. However, the introduction of either 2,6- or 3,5-dialkylaryl substituents gave only decomposition, while using a 4-substituted aryl group afforded a mixture of up to four isomers, 35–37 confirming the success of the current strategy.…”