Strategic molecular engineering of blue phosphorescent Pt(II)compounds for the development of high-efficiency single-doped white OLEDs

We synthesized two novel Pt(Ⅱ) β-diketonate compounds, 2′,6′-dimethoxy-4-tert-butyl-2,3′-bipyridinato-N,C4′)platinum(Ⅱ)(acetylactonate-O,O) (1) and 2′,6′-dimethoxy-4-trimethylsilyl-2,3′-bipyridinato-N,C4′)platinum(Ⅱ)(acetylactonate-O,O) (2), to develop blue phosphorescent compounds and systematically investigated their photoluminescent and electroluminescent characteristics. The compounds 1 and 2 exhibited bright sky-blue phosphorescence, with a phosphorescence maximum (λmax) at 465 nm and 475 nm, respectively. The luminescence quantum yields were found to be 0.63 for 1 and 0.93 for 2. At high concentrations, both compounds exhibited bright red emission originating from the formation of excimer. However, compound 2, due to effective intermolecular interactions, exhibited a more red-shifted emission than compound 1 at the same concentration. For fabricating phosphorescent organic light-emitting diodes, the compounds 1 and 2 were used as dopants, and a 50:50 mixture of 3′-di(9H-carbazol-9-yl)-1,1′-biphenyl:9-(3′-carbazol-9-yl-5-cyano-biphenyl-3-yl)-9H-carbazole-3-carbonitrile was used as the mixed host. When doped with 20 wt% of compound 2, the electroluminescent device exhibited the best performance, achieving an external quantum efficiency (EQE) of 13.7% at 100 cd/m2 and current efficiency of 35.5 cd A−1. Remarkably, the single-doped compound 2-based device achieved emission with Commission Internationale de L'Eclairage coordinates (x, y) of (0.40, 0.48). To the best of our knowledge, this is one of the highest performing single-doped white organic light-emitting diodes.