Novel efficient blue materials with 4H-cyclopenta[def]phenanthrene for OLEDs

Novel blue emitters, 2-[10-(4,4-dioctyl-4H-cyclopenta[def]phenanthrene-2-yl)-9-anthryl]-4,4-dioctyl-4H-cyclopenta[def]phenanthrene (OCPA) and 4,4,4′,4′,4″,4″-hexaoctyl-2,6′:2′,6″-tercyclopenta[def]phenanthrene (TerCPP) have been synthesized and characterized. The introduction of cyclopenta[def]phenanthrene units into the structure of OCPA and TerCPP leads LEDs with high efficiency and pure blue emission. Thermal analysis of OCPA and TerCPP reveals their high thermal stability. Their decomposition temperatures are around 410 °C for OCPA and 425 °C for TerCPP. The high-quality amorphous films of OCPA and TerCPP were prepared by vapor deposition. UV–visible absorption spectra of the thin films of these compounds appear at about 303–400 nm, and their maximum PL emission appeared at about 434 and 401 nm, respectively. The multi-layered OLEDs with the configuration of ITO/with or without PEDOT:PSS/NPD/OCPA or TerCPP/BAlq or BCP/Alq3/LiF/Al were fabricated to investigate the electroluminescent properties and the current–voltage–luminescence characteristics of the compounds. Multi-layer organic EL devices with OCPA and TerCPP as an emitting layer produced bright blue (434 nm) and sky blue emissions (440 nm), respectively. The device of OCPA with the configuration of ITO/NPD/OCPA/BAlq/Alq3/LiF/Al showed the turn-on voltage of about 5.6 V, the maximum brightness of 2500 cd/m2 (at 11 V), the maximum luminescence efficiency of 1.2 cd/A, and CIE coordinates of 0.16 and 0.12 which are quite close to that of the National Television System Committee (NTSC) standard blue (0.14, 0.08).