A new N-fluorenyl carbazole host material: Synthesis, physical properties and applications for highly efficient phosphorescent organic light emitting diodes

A new N-fluorenyl carbazole material, 9,9′-bis-(9,9-dimethyl-9H-fluoren-2-yl)-9H,9′H-[3,3′]bicarbazolyl (BDFC), was synthesized by bromination, Ullmann and Yamamoto coupling reactions and confirmed using various spectroscopic studies. Thermogravimetric analysis and differential scanning calorimetry studies show the thermal stability (ΔT5%) of 494.7 °C with high glass transition temperature (Tg) of 177.8 °C. The photophysical and electrochemical studies of BDFC show the photoluminescence at 408 nm and a band gap of 3.01 eV with higher triplet energy of 2.72 eV. The phosphorescent organic light emitting diode using BDFC as host, ITO/di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC)/host: fac-tris(2-phenylpyridine)-iridium [Ir(ppy)3] (5%)/1,3,5-tris(m-pyrid-3-yl-phenyl)benzene (TmPyPB)/LiF/Al, shows the effective confinement of triplet excitons and efficient energy transfer to the guest emitter in the emissive layer, resulted in the higher device efficiencies of 56.3 cd/A, 18.1% and 21.3 lm/W compared with that (48.1 cd/A, 15.3% and 16.3 lm/W) of device based on (4,4′-N,N′-dicarbazole)biphenyl (CBP) as host. The results show that the new host material BDFC could be useful for the efficient organic light emitting diodes.

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► A new N-fluorenyl carbazole material (BDFC) was synthesized and characterized.
► It has the higher thermal stability of 494.7 °C with high Tg of 177.8 °C.
► BDFC shows a band gap of 3.01 eV with higher triplet energy of 2.72 eV.
► PHOLEDs using BDFC as host was fabricated and compared with CBP host based device.
► It exhibits the higher device efficiencies (56.3 cd/A, 18.1% and 21.3 lm/W).