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 lambda(max) 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 lambda(max) 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.