A Novel Fluorene‐Triphenylamine Hybrid That is a Highly Efficient Host Material for Blue‐, Green‐, and Red‐Light‐Emitting Electrophosphorescent Devices

TFTPA (tris[4-(9-phenylfluoren-9-yl)phenyl]amine), a novel host material that contains a triphenylamine core and three 9-phenyl-9-fluorenyl peripheries, was effectively synthesized through a Friedel-Crafts-type substitution reaction. Owing to the presence of its sterically bulky 9-phenyl-9-fluorenyl groups, TFTPA exhibits a high glass transition temperature (186 °C) and is morphologically and electrochemically stable. In addition, as demonstrated from atomic force microscopy measurements, the aggregation of the triplet iridium dopant is significantly diminished in the TFTPA host, resulting in a highly efficient full-color phosphorescence. The performance of TFTPA-based devices is far superior to those of the corresponding mCP- or CBP-based devices, particularly in blue- and red-emitting electrophosphorescent device systems. The efficiency of the FIrpic-based blue-emitting device reached 12 % (26 cd A -1 ) and 18 lm W -1 at a practical brightness of 100 cd m -2 ; the Ir(piq) 2 acac-based red-emitting device exhibited an extremely low turn-on voltage (2.6 V) and a threefold enhancement in device efficiency (9.0 lm W -1 ) relative to those of reference devices based on the CBP host material.

[1]  Ralph N. Adams,et al.  Anodic Oxidation Pathways of Aromatic Amines. Electrochemical and Electron Paramagnetic Resonance Studies , 1966 .

[2]  Shizuo Tokito,et al.  Energy-transfer and light-emission mechanism of blue phosphorescent molecules in guest-host systems , 2004 .

[3]  S. Forrest,et al.  Nearly 100% internal phosphorescence efficiency in an organic light emitting device , 2001 .

[4]  P. Luhanga,et al.  The influence of planarity, rigidity and internal heavy atom upon fluorescence parameters and the intersystem crossing rate constant in molecules with the biphenyl basis. , 2006, Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy.

[5]  A. van Dijken,et al.  Carbazole compounds as host materials for triplet emitters in organic light-emitting diodes: tuning the HOMO level without influencing the triplet energy in small molecules. , 2004, Journal of the American Chemical Society.

[6]  Jang‐Joo Kim,et al.  Energy transfer and device performance in phosphorescent dye doped polymer light emitting diodes , 2003 .

[7]  T. F. Palmer,et al.  Effect of temperature on the triplet states of methyl- and phenyl-substituted biphenyl molecules , 1985 .

[8]  C. Shu,et al.  Synthesis and Characterization of New Polyquinolines Containing 9,9‘-Spirobifluorene Units , 2002 .

[9]  Chung-Chih Wu,et al.  3-(9-Carbazolyl)carbazoles and 3,6-Di(9-carbazolyl)carbazoles as Effective Host Materials for Efficient Blue Organic Electrophosphorescence** , 2007 .

[10]  Ken-Tsung Wong,et al.  Highly Efficient Organic Blue Electrophosphorescent Devices Based on 3,6‐Bis(triphenylsilyl)carbazole as the Host Material , 2006 .

[11]  Chihaya Adachi,et al.  100% phosphorescence quantum efficiency of Ir(III) complexes in organic semiconductor films , 2005 .

[12]  Klaus Meerholz,et al.  Highly Efficient Polymeric Electrophosphorescent Diodes , 2006 .

[13]  Akira Tsuboyama,et al.  Homoleptic cyclometalated iridium complexes with highly efficient red phosphorescence and application to organic light-emitting diode. , 2003, Journal of the American Chemical Society.

[14]  Stephen R. Forrest,et al.  Blue organic electrophosphorescence using exothermic host–guest energy transfer , 2003 .

[15]  S. Forrest,et al.  VERY HIGH-EFFICIENCY GREEN ORGANIC LIGHT-EMITTING DEVICES BASED ON ELECTROPHOSPHORESCENCE , 1999 .

[16]  S. Forrest,et al.  Highly efficient phosphorescent emission from organic electroluminescent devices , 1998, Nature.

[17]  Y. Chien,et al.  Synthesis and properties of 9,9-diarylfluorene-based triaryldiamines. , 2001, Organic letters.

[18]  Jian Li,et al.  Efficient, deep-blue organic electrophosphorescence by guest charge trapping , 2003 .

[19]  Shui-Tong Lee,et al.  Photoluminescence and electroluminescence of a new blue-emitting homoleptic iridium complex , 2006 .

[20]  Yun Chi,et al.  New Dopant and Host Materials for Blue‐Light‐Emitting Phosphorescent Organic Electroluminescent Devices , 2005 .

[21]  Cheng-Hsien Yang,et al.  Synthesis of a high-efficiency red phosphorescent emitter for organic light-emitting diodes , 2004 .

[22]  Y. Shirota,et al.  A Novel Class of π‐Electron Dendrimers for Thermally and Morphologically Stable Amorphous Molecular Materials , 1998 .

[23]  Y. Su,et al.  Highly Efficient Red Electrophosphorescent Devices Based on Iridium Isoquinoline Complexes: Remarkable External Quantum Efficiency Over a Wide Range of Current , 2003 .

[24]  D Murphy,et al.  Highly phosphorescent bis-cyclometalated iridium complexes: synthesis, photophysical characterization, and use in organic light emitting diodes. , 2001, Journal of the American Chemical Society.

[25]  Fumio Sato,et al.  Confinement of triplet energy on phosphorescent molecules for highly-efficient organic blue-light-emitting devices , 2003 .

[26]  Yun Chi,et al.  Orange and Red Organic Light‐Emitting Devices Employing Neutral Ru(II) Emitters: Rational Design and Prospects for Color Tuning , 2006 .

[27]  Ching-Kun Chen,et al.  Novel carbazole/fluorene hybrids: host materials for blue phosphorescent OLEDs. , 2006, Organic letters.

[28]  S. T. Lee,et al.  Reduction of Self‐Quenching Effect in Organic Electrophosphorescence Emitting Devices via the Use of Sterically Hindered Spacers in Phosphorescence Molecules , 2001 .

[29]  J. Salbeck,et al.  Organic Materials for Photonic Devices , 2003 .

[30]  N. Turro.  Modern Molecular Photochemistry , 1978 .

[31]  C. Shu,et al.  Novel distyrylcarbazole derivatives as hole-transporting blue emitters for electroluminescent devices , 2005 .

[32]  Yun Chi,et al.  Organic Light‐Emitting Diodes based on Charge‐Neutral RuII Phosphorescent Emitters , 2005 .

[33]  A. Padmaperuma,et al.  A dibenzofuran-based host material for blue electrophosphorescence. , 2006, Organic letters.

[34]  Stephen R. Forrest,et al.  Transient analysis of organic electrophosphorescence. II. Transient analysis of triplet-triplet annihilation , 2000 .