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).

Efficient Blue Electrophosphorescence and Hyperphosphorescence Generated by Bis-tridentate Iridium(III) Complexes

“…Now, we report a better design of blue-emissive iridium­(III) metal complexes with electron-deficient carbene pincer chelates on the bis-tridentate metal configuration, giving complexes with a relatively narrowed emission bandwidth and a shortened radiative lifetime at the same time. − To achieve this goal, we substituted imidazolylidene coordination fragments of pincer chelate with a very electron-deficient imidazo­[4,5- b ]­pyridin-2-ylidene fragment in an attempt to lower the π*-orbital energy level of iridium­(III) complexes. This strategy is similar to the cyclometalating carbene complexes that have recently been documented. , Concomitantly, the π*-orbital energy of the dianionic tridentate chelate was increased by the addition of an electron-donating dimethylamine (Me 2 N) group at the pyridinyl entity, which is also linked to a carbazole unit and a pyrazole unit, forming the PzpyCz chelate. The basic drawing of this target molecule ( B0 ) is indicated in Scheme for scrutiny.…”

“…This strategy is similar to the cyclometalating carbene complexes that have recently been documented. 23,29 Concomitantly, the π*-orbital energy of the dianionic tridentate chelate was increased by the addition of an electron-donating dimethylamine (Me 2 N) group at the pyridinyl entity, which is also linked to a carbazole unit and a pyrazole unit, forming the PzpyCz chelate. The basic drawing of this target molecule (B0) is indicated in Scheme 2 for scrutiny.…”

Regioselective Syntheses of Imidazo[4,5-b]pyrazin-2-ylidene-Based Chelates and Blue Emissive Iridium(III) Phosphors for Solution-Processed OLEDs

“…Till date, N-heterocyclic carbenes (NHCs), such as functional imidazolylidene and benzoimidazolylidene cyclometalates, were developed for the synthesis of higher energy (i.e., purple and blue) emitters, − due to the strongly destabilized π*-orbitals of carbene (C^C) chelates. , Six Ir–C bonds of the class of Ir­(C^C) 3 complexes could exert the strongest ligand field strength and notably destabilize the corresponding metal-centered (MC) dd excited states. , Hence, this coordination mode is expected to offer a sufficient large energy-gap between the emissive excited state (T 1 state) and upper lying MC dd excited state, giving a suppressed quenching process, even for blue emitters. Based on these molecular design strategies, some studies were executed by replacing benzoimidazolylidene with 7,9-dihydro-8 H -purin-8-ylidene, imidazo­[4,5- b ]­pyridin-2-ylidene and imidazo­[4,5- b ]­pyrazin-2-ylidene entities for reducing the respective LUMO energy level in achievement of the demanded bright blue emission and capability in fabrication of OLEDs. − …”

Facially Coordinated, Tris‐bidentate Purin‐8‐ylidene Ir(III) Complexes for Blue Electrophosphorescence and Hyperluminescence

“…properties of 8H-purin-8-ylidenebased Ir(III) complexes were investigated by using f-CF 3 and f-PhCF 3 as the representative emitters to fabricate OLEDs due to their better photophysical properties in reference to those of f-1tBu. [13] Conventional host 3,3'-di(9H-carbazol-9-yl)-1,1'biphenyl (mCBP) was utilized for these phosphorescent devices due to its relatively high triplet energy level (2.9 eV) and good charge transporting capability. [24] The device structure consists of indium tin oxide (ITO)/1,4,5,8,9,11-hexaazatriphenylene Adv.…”

“…Recently, we reported a class of homoleptic Ir(III) carbene complexes with 7,9-dihydro-8H-purin-8-ylidene-based cyclometalates, i.e., m-1tBu and f-1tBu, and employed the same for fabrication of blue OLED devices. [13] Their structural drawings are depicted in Scheme 2, and their emission peak max. occurred at 483 and 423 nm in toluene at room temperature (RT).…”