Efficient blue organic light-emitting diodes with 4H-cyclopenta[def]phenanthrene

Abstract

A novel blue emitters, 2-[10-(4,4-dioctyl-4H-cyclopenta[def]phenanthrene-2-yl)-9-anthryl]-4,4-dioctyl-4Hcyclopenta[ def]phenanthrene (OCPA) and 4,4,4',4',4",4"-hexaoctyl-2,6':2',6"-ter cyclopenta[def]-phenanthrene (TerCPP), has been synthesized and characterized. The introduction of CPP units into the structure of OCPA and TerCPP leads to high efficiency and pure blue color property. Thermal analysis of OCPA and TerCPP reveals their high thermal stability. Their decomposition temperatures, which correspond to a 5% weight loss upon heating during TGA, are around 410 °C for OCPA and 425 °C for TerCPP. The high-quality amorphous films of OCPA and TerCPP with good morphological stability can be prepared by vapor deposition. Multilayer organic EL devices constructed using OCPA and TerCPP as an emitting layer produced bright blue emissions. The UV-visible absorption spectra of theses compounds appear at about 290-400 nm, and their maximum PL emission spectra of OCPA and TerCPP in THF solution appeared at about 438 nm and 390 nm, respectively. The EL spectra showed maximum peaks at about 434 nm and 440 nm, respectively. The turn-on voltage of compounds was about 6V, and the luminous efficiency is 1.0-1.2 cd/A. Emission color of OCPA was deep blue and CIE coordinate (0.16, 0.11) is quite close to that of the National Television System committee (NTSC) standard vlue (0.14, 0.88).