Journal
CHEMICAL ENGINEERING JOURNAL
Volume 446, Issue -, Pages -Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.cej.2022.136834
Keywords
Palladium(II) complexes; Red emission; Near-infrared emission; Phosphorescence; Organic light-emitting diodes
Categories
Funding
- National Natural Science Foundation of China [51903157, 52130308]
- Shenzhen Science and Technology Program [KQTD20170330110107046, ZDSYS20210623091813040]
- School of Materials Science and Engineering, Jiangsu Engineering Laboratory of Light-Electricity-Heat Energy-Converting Materials and Applications [GDRGCS2021001]
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Two novel tetradentate cyclometalated palladium(II) complexes were synthesized and used as emissive dopants for red and NIR phosphorescent OLEDs. These complexes exhibited NIR photoluminescence and optimized OLED devices showed high external quantum efficiency.
Palladium(II) complexes based organic light-emitting diodes (OLEDs) have made great progress in emission regions from blue to yellow. However, the red emission OLEDs based on palladium(II) complexes have not been reported, and the related near-infrared (NIR) emission OLEDs are extremely rare. Herein, two novel tetradentate cyclometalated palladium(II) complexes of DPA-Cz-bpy-Pd (Pd-1) and 2Cz-bpy-Pd (Pd-2) were designed and synthesized as emissive dopants for red and NIR phosphorescent OLEDs. These complexes exhibited a short-lived (0.5-1 mu s) metal-to-ligand charge transfer (MLCT) excited state in neat and doped films. NIR photoluminescence peaks at 700 nm and 722 nm were observed in their dichloromethane solution for Pd-1 and Pd-2, respectively. Optimized OLED devices using Pd-1 exhibited peak external quantum efficiency (EQE) of 2.6% with emission peak at 643 nm. This work presents the first example of palladium(II) complexes as red electroluminescent emitters, and sheds light on the potential of palladium(II) complexes for long-wavelength molecular emitters and electroluminescence.
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