Organic light‐emitting diodes (OLEDs) are one of the most promising technologies for future displays and lighting. Compared with the blue and green OLEDs that have achieved very high efficiencies by using phosphorescent Ir(III) complexes, the red OLEDs still show relatively low efficiencies because of the lack of high‐performance red‐emitting Ir(III) complexes. Here, three highly efficient asymmetric red‐emitting Ir(III) complexes with two different cyclometalating ligands made by incorporating only one electron‐deficient triarylboron group into the nitrogen heterocyclic ring are reported. These complexes show enhanced photoluminescence quantum yields up to 0.96 and improved electron transporting capacity. In addition, the asymmetric structure can help to improve the solubility of Ir(III) complexes, which is crucial for fabricating OLEDs using the solution method. The photoluminescent and oxidation–reduction properties of these Ir(III) complexes are investigated both experimentally and theoretically. Most importantly, a solution‐processed red OLED achieves extremely high external quantum efficiency, current efficiency, and power efficiency with values of 28.5%, 54.4 cd A−1, and 50.1 lm W−1, respectively, with very low efficiency roll‐off. Additionally, the related device has a significantly extended operating lifetime compared with the reference device. These results demonstrate that the asymmetric diarylboron‐based Ir(III) complexes have great potential for fabricating high‐performance red OLEDs.

A cyclometalating ligand containing a 9-phenyl-9-phosphafluorene oxide (PhFlPO) moiety has been synthesized and used to construct asymmetric tris-heteroleptic cyclometalating Ir III complexes in combination with other ppy-type (Hppy = 2phenylpyridine) ligands containing a functional group with a different charge carrier injection/transporting character. Their photophysical properties, electrochemical behaviors, and electroluminescent (EL) performances have been characterized in detail. Timedependent density functional theory (TD-DFT) and natural transition orbital (NTO) calculation were carried out to gain insight into the photophysical properties of these complexes. The NTO results show that the characters of the lowest triplet excited states (T 1 ) can be delicately manipulated through the combination of different cyclometalating ligands. In addition, the strong electron injection/transporting (EI/ET) ability associated with the PhFlPO moiety can confer EI/ET properties to the asymmetric tris-heteroleptic cyclometalating Ir III complexes. Consequently, the solution-processed organic lightemitting diodes/devices (OLEDs) based on these asymmetric tris-heteroleptic Ir III phosphorescent complexes can exhibit outstanding electroluminescent (EL) performances with the maximum external quantum efficiency (η ext ) of 19.3%, current efficiency (η L ) of 82.5 cd A −1 , and power efficiency (η P ) of 57.3 lm W −1 for the yellow-emitting device. These results show the great potential of a PhFlPO moiety in developing phosphorescent emitters and functional materials with excellent EI/ET properties.

Containing two nitrogen atoms, the electron-deficient pyrimidine ring has excellent coordinating capability with transition metal ions. However, compared with the widely used pyridine ring, applications of the pyrimidine ring in phosphorescent Ir(III) complexes are rare. In this research, two highly emissive pyrimidine-based mononuclear Ir(III) complexes and their corresponding dinuclear Ir(III) complexes were prepared with a simple one-pot reaction. The incorporation of the second Ir(III) center can lead to dramatic differences of both photophysical and electrochemical properties between the mono- and dinuclear complexes. Besides, these properties can also be fine-tuned with different substituents. Theoretical calculations have also been performed to understand their photophysical behaviors. The electroluminescent investigations demonstrate that the pyrimidine-based mono- and dinuclear Ir(III) complexes could show impressive device performance. The vacuum-deposited organic light-emitting diode (OLED) based on the mononuclear Ir(III) complex exhibited an external quantum efficiency (EQE) of 16.1% with almost no efficiency roll-off even at 10 000 cd m. More encouragingly, the solution-processed OLED based on the dinuclear Ir(III) complex achieved the outstanding EQE, current efficiency (CE), and power efficiency (PE) of 17.9%, 52.5 cd A, and 51.2 lm W, respectively, representing the highest efficiencies ever achieved by OLEDs based on dinuclear Ir(III) complexes.

Highly efficient deep-red organic light-emitting devices (OLEDs) are indispensable for developing high-performance red-green-blue (RGB) displays and white OLEDs (WOLEDs). However, the shortage of deep-red emitters with high photoluminescence quantum yields (PLQYs) and balanced charge injection/transport abilities has severely restricted the performance of deep-red OLEDs. Herein, we design and synthesize four efficient emitters by combining the isoquinoline group with the thianthrene 5,5,10,10-tetraoxide group. Benefited from the introduction of the thianthrene 5,5,10,10-tetraoxide group, these Ir­(III) complexes show improved electron-injection/-transport abilities. By enhancing the contribution of the triplet metal-to-ligand charge transfer (3MLCT) in emissions, the asymmetric configuration endows the related deep-red Ir­(III) complexes with high PLQYs of 0.45–0.50 in solutions. More importantly, PLQYs of these Ir­(III) complexes in doped host films increase up to 0.91, which is much higher than PLQYs reported for conventional deep-red Ir­(III) complexes with impressive electroluminescent performance. As a result, solution-processed OLEDs based on these Ir­(III) complexes exhibit deep-red emissions with Commission Internationale de L’Eclairage (CIE x, y) coordinates very close to the National Television System Committee (NTSC)-recommended standard red CIE coordinates of (0.67, 0.33). Furthermore, a deep-red OLED using the asymmetric Ir­(III) complex SOIrOPh as the emitter shows outstanding performance with a peak external quantum efficiency (EQE) of 25.8%, which is the highest EQE reported for solution-processed deep-red OLEDs. This work sheds light on the great potential of utilizing the thianthrene 5,5,10,10-tetraoxide group to develop phosphorescent emitters for highly efficient OLEDs.

Aggregation‐induced emission (AIE)‐active phosphorescent emitters have intrinsic advantages in time‐gated imaging/sensing and improving the electroluminescent efficiencies of organic light‐emitting devices (OLEDs). However, compared with the very prosperous and fruitful developments of AIE‐active fluorescent emitters and related working mechanisms, the progresses on AIE‐active phosphorescent emitters and associated AIE mechanisms are still relatively slow. Herein, the AIE properties of a series of phosphorescent Pt(II) complexes with two monodentate ligands are reported. Compared with the conventional rigid Pt(II) complexes bearing two bidentate ligands or one tri‐/tetradentate ligand, the incorporation of two monodentate ligands provides the resulting Pt(II) complexes with more room to deform their coordination skeletons from the square‐planar geometry in the ground state to the quasi‐tetrahedral configuration in the excited state, causing poor solution emissions. In doped films and aggregate states, intense emissions are observed for these Pt(II) complexes. The as‐fabricated solution‐processed OLED exhibits an impressively high external quantum efficiency of 21.7%. This study provides an effective way to develop excellent AIE‐active phosphorescent emitters.