Cyclometalated Pt(II) complexes can show intense phosphorescence at room temperature. Their emission properties are determined by both the organic ligand and the metal center. Whereas most of the related studies focus on tuning the properties by designing different types of organic ligands, only several reports investigate the key role played by the metal center. To address this issue, phosphorescent Pt(II) complexes with one, two, and three Pt(II) centers are designed and synthesized. With more Pt(II) centers, the cyclometalated multinuclear Pt(II) complexes display red-shifted emissions with increased photoluminescence quantum yields. Most importantly, solution-processed organic light-emitting diodes (OLEDs) with the conventional device structure using the multinuclear Pt(II) complexes as emitters show excellent performance. The controlled device based on the conventional mononuclear Pt(II) complex shows a peak external quantum efficiency, current efficiency, and power efficiency of 6.4%, 14.4 cd A-1, and 12.1 lm W-1, respectively. The efficiencies are dramatically improved to 10.5%, 21.4 cd A-1, and 12.9 lm W-1 for the OLED based on the dinuclear Pt(II) complex and to 17.0%, 35.4 cd A-1, and 27.2 lm W-1 for the OLED based on the trinuclear Pt(II) complex, respectively. To the best of our knowledge, these efficiencies are among the highest ever reported for the multinuclear Pt(II) complex-based OLEDs.
Keywords: efficiency; organic light-emitting diodes; phosphorescence; trinuclear Pt(II) complex; triphenylamine.