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Three novel asymmetric Ir(III) complexes have been rationally designed to optimize their emitting dipole orientations (EDO) and enhance light outcoupling in blue phosphorescent organic light‐emitting diodes (OLEDs), thereby boosting their external quantum efficiency (EQE). Bulky electron‐donating groups (EDGs), namely: carbazole (Cz), di‐tert‐butyl carbazole (tBuCz), and phenoxazine (Pxz) are incorporated into the tridentate dicarbene pincer chelate to induce high degree of packing anisotropy, simultaneously enhancing their photophysical properties. Angle‐dependent photoluminescence (ADPL) measurements indicate increased horizontal transition dipole ratios of 0.89 and 0.90 for the Ir(III) complexes Cz‐dfppy‐CN and tBuCz‐dfppy‐CN, respectively. Analysis of the single crystal structure and density functional theory (DFT) calculation results revealed an inherent correlation between molecular aspect ratio and EDO. Utilizing the newly obtained emitters, the blue OLED devices demonstrated exceptional performance, achieving a maximum EQE of 30.7% at a Commission International de l'Eclairage (CIE) coordinate of (0.140, 0.148). Optical transfer matrix‐based simulations confirmed a maximum outcoupling efficiency of 35% due to improved EDO. Finally, the tandem OLED and hyper‐OLED devices exhibited a maximum EQE of 44.2% and 31.6%, respectively, together with good device stability. This rational molecular design provides straightforward guidelines to reach highly efficient and stable saturated blue emission. [ABSTRACT FROM AUTHOR]

The promising cyclometalated iridium (III) complexes have been proved to possess great potential in vacuum-deposited organic light-emitting diodes (OLEDs) applications for full-color displays and white solid-state lighting sources. Herein, based on the unique bidentate ligand of dibenzo[a,c]phenazine (dbpz) group with strong conjugated effect of aromatic rings for red emission, four novel [3+2+1] coordinated iridium (III) emissive materials have been rationally designed and synthesized. The monodentate ligands of -CN and -OCN have been effectively employed to tune the deep-red emission of 628-675 nm with high photoluminescence quantum yields up to 98%. Moreover, all devices displayed deep-red color coordinates ranging from (0.675, 0.325) to (0.716, 0.284), which is close to the standard-red color coordinates of (0.708, 0.292), as recommended by International Telecommunication Union Radiocommunication (ITU-R) BT.2020. The device based on n BuIr(dbpz)CN with an exciplex cohost has exhibited maximum external quantum efficiencies of 20.7% and good stability. With n BuIr(dbpz)CN as an effective sensitizer, the n BuIr(dbpz)OCN based phosphorescent OLED devices have successfully demonstrated cascading energy transfer processes, contributing to pure red emission with maximum luminance as high as 6471 cd m -2 . Therefore, this work has been successfully demonstrated rational molecular design strategy of [3+2+1] iridium complexes to obtain highly efficient deep-red electrophosphorescent emission., (© 2023 Wiley‐VCH GmbH.)