Deep blue emitters are highly desired and intensively investigated for organic light emitting diodes for high quality full color display or solid state lighting applications. Here a new strategy for deep blue phosphorescent emission is demonstrated through the incorporaiton of 6-membered metal chelation rings in the tetradentate metal complex molecular structure. The platinum metal complex PtNON was synthesized and fully characterized. The emission spectra of PtNON shows a deep blue emission peaking at 438 nm at 77 K and a red-shifted, broadened, and structureless emission band centered at 508 nm at room temperature. The photoluminescent quantum yield of PtNON reaches a high value of 83%, and its luminescent lifetime remains as short as 3.76 μs in a 5% doped PMMA thin film. Organic light emitting diodes devices with PtNON as an emissive material were fabricated, achieving a peak device efficiency of 24.4% in a device structure designed for charge confinement. Furthermore, device architectures using known stable components with PtNON demonstrated an operational lifetime to 70% initial luminance estimated at over 30 000 h at 100 cd/m2 while also retaining moderate efficiencies over 10% despite the high triplet energy over 2.8 eV for the emitter.

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A tetradentate cyclometalated Pt(II) complex (PtN3N) is developed as an efficient, stable phosphorescent emitter. One PtN3N device exhibits an estimated LT of 2057 h at an initial luminance of 1000 cd m , while maintaining an external quantum efficiency of 15.3% at such high brightness, demonstrating performance to overcome the last technical barrier to the commercialization of Pt complexes for many applications.

Highly efficient and stable blue phosphorescent organic light‐emitting diodes are achieved by employing a step‐wise graded doping of platinum(II) 9‐(pyridin‐2‐yl)‐2‐(9‐(pyridin‐2‐yl)‐9H‐carbazol‐2‐yloxy)‐9H‐carbazole (PtNON) in a device setting. A device employing PtNON demonstrates a high peak external quantum efficiency (EQE) of 17.4% with an estimated LT70 lifetime of over 1330 h at a brightness of 1000 cd m−2. PtNON is then investigated as a “triplet sensitizer” in an alternating donor–acceptor doped emissive layer to further improve the device emission color purity by carefully managing an efficient Förster resonant energy transfer from PtNON to 2,5,8,11‐tetra‐tert‐butylperylene as a selected acceptor material. Thus, such OLED devices demonstrate an EQE of 16.9% with color coordinates of (0.16, 0.25) and an estimated luminance (LT70) lifetime of 628 h at a high brightness of 1000 cd m−2.

A series of metal‐assisted delayed fluorescence (MADF) palladium(II) complexes, PdN1N, PdN1N‐dm, and PdN6N, are studied. Their 77 K photoluminescence emission spectra show a narrow primary emission peak at 464, 466, and 470 nm, respectively, with small vibronic peaks characteristic of many phosphorescent emitters. At room temperature (300 K), the dominant emission peaks for PdN1N, PdN1N‐dm, and PdN6N are slightly redshifted to 472, 470, and 476 nm, respectively. In the meantime, a broad sideband is also shown between 410 and 450 nm due to the MADF process. A blue device employing PdN1N‐dm demonstrates an electroluminescence emission peak at 476 nm and the maximum external quantum efficiency (EQE) of 25.1%. The high maximum EQE of the blue organic light‐emitting diode (OLED) device indicates that both the phosphorescence and the delayed fluorescence are very efficient. In addition, a stable OLED device of PdN1N‐dm gives a maximum EQE of 9.8% and the estimated operational lifetime LT70 of 350 h at the practical luminance of 100 cd m−2.