Fluorene-substituted pyrenes-Novel pyrene derivatives as emitters in nondoped blue OLEDs

Two highly efficient blue light-emitting materials, 9-phenyl-9-pyrenylfluorene substituted pyrenes (P1, P2), were designed and synthesized. The two compounds demonstrated highly thermal stability and bright blue emission both in solution and in the solid state. Even after being annealed at 150 °C under nitrogen for 24 h, the solid emission spectra showed no obvious changes. The high energy levels of the HOMO (about -5.2 eV) exhibit that they have improved hole-injection/transporting ability. A three layer blue OLED of ITO/TCTA (8 nm)/P2 (30 nm)/BCP (40 nm)/Mg:Ag was obtained with high efficiency (3.08 cd/A, 1.17 lm/W), low turn-on voltage (3.5 V) and high brightness (19885 cd/m²) in ambient air, which is competitive with the best of the doped and nondoped blue OLEDs. These results revealed that these materials are promising as blue emitters for high efficiency OLEDs with a much simpler architecture. We thus exemplified that introducing 9-phenyl-9-pyrenylfluorene onto large aromatic rings is a new method to employ fluorescent dyes with large planar aromatic rings as the blue emitters in nondoped OLEDs without a hole-injection layer.