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

Abstract

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 (Delta T-5%) of 494.7 degrees C with high glass transition temperature (T-g) of 177.8 degrees 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. (C) 2011 Elsevier B.V. All rights reserved.