Cyclometalated Platinum(II) β‐Diketonate Complexes with Extremely High External Quantum Efficiency for White Organic Light‐Emitting Diodes

Abstract Three cyclometalated Pt(II) β‐diketonate compounds with sky‐blue to green phosphorescence are prepared by modifying the substituents of the 2′,6′‐dimethoxy‐2,3′‐bipyridine (OMe₂pypy, C^N) chelate ligand. These molecules have the general formula Pt(C^N)(O^O), where O^O = acetylacetonate; one is unsubstituted (1), one possesses a trimethylsilyl (TMS) substituent (2), and the other is substituted with dimesitylboron (BMes₂) (3). The intermolecular interactions of 2 are greater than those of 1 and 3, based on color mapping and surface area results from Hirshfeld analyses. Time‐dependent density functional theory calculations reveal that the electronic transitions of monomeric 1 and 3 are predominantly intraligand or ligand‐to‐ligand charge transfer mixed with metal‐to‐ligand charge transfer transitions, while for the dimeric forms, dimeric 2, an additional strong metal–metal‐to‐ligand charge transfer transition is observed. White organic light‐emitting diode (WOLED) devices using an 1,3‐bis(N‐carbazolyl)benzene (mCP) or mCP:TSPO1(diphenyl[4‐(triphenylsilyl)phenyl]phosphine oxide) mixed host and 1–3 as dopants are fabricated. With a dopant concentration of 20 wt% in the emissive layer, compound 2 exhibited bright yellow–green emission with a maximum external quantum efficiency (EQE) of 24.9%. This result corresponds to one of the highest EQEs among the reported C^N chelated Pt(II) β‐diketonate‐based WOLEDs.