Tuning electrical properties of phenanthroimidazole derivatives to construct multifunctional deep-blue electroluminescent materials

In this work, we introduce an n-type group, TPPO (triphenyl phosphine), to the N 1-position of violet-blue fluorophore phenanthroimidazole (PI) and successfully develop one deep-blue ( TPAPOPPI ) and two violet-blue emitters ( 3-CzPOPPI and CzBPOPPI ) for OLEDs (organic light-emitting diodes). With a highly twisted linkage, the TPPO group shows negligible influences on their photophysical properties of the new materials and the materials inherit highly efficient deep-blue and violet-blue emission of the PI unit and its C 2-connected arylamine skeletons. Meanwhile, the TPPO group can open a new channel to transport the electron. The electron injection and transport abilities of the developed emitters are enhanced. Non-doped devices using the 3-CzPOPPI and the CzBPOPPI emitters exhibit an EQE max (external quantum efficiency) of 5.08% and 4.42% with CIE (Commission Internationale de l'Èclarage) coordinates of (0.156, 0.061) and (0.157, 0.071), respectively. Similar efficiencies and even deeper blue emissions (CIE y = 0.050 for 3-CzPOPPI and 0.044 for CzBPOPPI ) were observed in OLEDs with these emitters doped with 4,4′-bis( N -carbazolyl)-1,1′-biphenyl. TPAPOPPI is demonstrated to be a multifunctional deep-blue emitter and presents impressive performances when serving as non-doped (EQE max = 6.69%, CIE: (0.152, 0.095)), and doped (EQE max = 6.61%, CIE: (0.154, 0.068)) as well as a high-performance host for yellow phosphorescent OLED. By doping a yellow phosphorescent dye (PO-01) into a TPAPOPPI host, a white OLED with a high EQE of 20.3% and a low driving voltage of 3.2 V (at 1000 cd m −2 ) is achieved. With enhanced electrical properties, TPAPOPPA can deliver decent efficiencies in non-doped, doped, single-layer, yellow and white OLEDs.