ABSTRACT
We designed and synthesized two blue fluorescent materials based on spiro[9H-fluorene-9, 5′-[5H] indeno[1, 2-b] pyridine via Buchwald-Hartwig amination and Suzuki coupling reaction. To characterize their electroluminescent properties, multilayered organic light emitting diodes (OLEDs) were fabricated with the following device structures: ITO(180 nm)/2-TNATA(60 nm)/NPB(20 nm)/α,β-ADN: 3, 5, or 10 wt% blue dopants (30 nm)/Bphen(30 nm)/Liq(2 nm)/Al(100 nm). All the devices showed blue emissions with high electroluminescent efficiencies. Particularly, a device using 7′-((4-(N,N-diphenyl)-styryl)-4-phenyl)-spiro[9H-fluorene-9, 5′-[5H] indeno[1, 2-b] pyridine] as a dopant material with 10 wt% doping concentration exhibited highly efficient blue emission with an external quantum efficiency of 4.46% at 20 mA/cm2 and the CIE coordinates of (0.18, 0.30) at 1000 cd/m2. In this device, the twisted structural feature of emitter originated from spiro-type core prevented self-quenching and lead to the improved efficiencies even at high doping concentration in the device.
Funding
This research was supported by Samsung Display and the MSIP (Ministry of Science, ICT and Future Planning), Korea, under the ITRC (Information Technology Research Center) support program (IITP-2016-H8501-16-1009) supervised by the IITP (Institute for Information & communications Technology Promotion).