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High‐Performance Deep‐Red/Near‐Infrared OLEDs with Tetradentate [Pt(O^N^C^N)] Emitters

The emission properties of two series of tetradentate Pt(II) emitters in aggregation forms are studied by density functional theory (DFT), time‐dependent DFT calculations, and photoluminescence (PL) measurements. PL quantum yields (PLQYs) of the complexes bearing type‐I O^N^C^N ligands (Pt‐X‐1 and Pt‐X‐2) increase with the dopant concentration in thin film until 100% [pristine Pt(II) complexes]. For complexes bearing type‐II O^N^C^N ligands (Pt‐X‐3 to Pt‐X‐5), their PLQYs in thin film increase as the dopant concentration increases up to a certain threshold and then quickly decrease with further increase in dopant concentration. Organic light‐emitting devices (OLEDs) with neat and doped Pt(II) emitters are fabricated and characterized. High‐efficiency near‐infrared OLEDs with λmax exceeding 700 nm and external quantum efficiencies (EQEs) of up to 15.84% are realized by using a neat Pt‐X‐1 thin film as the emitting layer (EML). For this device, a high EQE of 11.19% is retained at high current density of 100 mA cm−2; by doping Pt‐X‐5 (26 wt%) into a co‐host structure EML, a red emission with λmax of 661 nm, Commission Internationale de l'Eclairage (CIE) coordinates of (0.63, 0.37), and EQE of 21.75% at 1000 cd m−2 are achieved.