Blue Phosphorescent Materials Research Articles

Synthesis and Photophysical Properties of Substituted Tris(phenylbenzimidazolinato) IrIII Carbene Complexes as a Blue Phosphorescent Material

AbstractSubstitution effects on the photoluminescence and electrochemical properties and the photochemical stability of tris(phenylbenzimidazolinato)IrIII complexes were investigated. Facial and meridional isomers of a series of complexes having the general structure of Ir(C C)3, where (C C) is (4‐R‐phenyl)benzimidazolinato (R = H, CF3, CN, OCH3), were prepared. They are abbreviated to Ir(pmb)3 (1), Ir(CF3pmb)3 (2), Ir(CNpmb)3 (3), and Ir(Opmb)3 (4), respectively. Electron‐donating or ‐withdrawing groups on the phenyl ring lead to both higher emission quantum yields and longer emission lifetimes compared to those of 1 in each mer and fac series. Particularly, the emission quantum yields were high in the cases of 2a, 3a, 3b, and 4a. No photochemical isomerization was observed in both fac‐ (a) and mer (b) isomers of Ir(pmb)3, Ir(CF3pmb)3, and Ir(CNpmb)3 on irradiation with a 313‐nm wavelength light from a 400 W mercury lamp for more than 20 h. All complexes excluding fac‐Ir(pmb)3 (1a) show excellent photochemical stability in degassed anhydrous thf solution. The locations of the HOMO and LUMO and the lowest excitation energy of these complexes were investigated by DFT and TD‐DFT calculations on fac‐ and mer‐Ir(Opmb)3 (4a and 4b). The HOMO is mainly localized over the Ir metal center and the phenyl moiety, and the LUMO mainly localized over the benzimidazole moiety. The calculated lowest excitation energies agree with the experimental values. The X‐ray single crystal structures obtained for fac‐Ir(CF3pmb)3 (2a) and mer‐Ir(Opmb)3 (4b) are also discussed.

A bipolar host containing 1,2,3-triazole for realizing highly efficient phosphorescent organic light-emitting diodes

We have developed a novel host material, 9,9′-(2-((4-phenyl-1,2,3-triazol-1-yl)methyl)biphenyl-4,4′-diyl)biscarbazole (CBP-TA), for realizing highly efficient blue phosphorescent OLEDs. The maximum external quantum efficiency of the OLED device developed using CBP-TA doped with a blue phosphorescent material was 30% greater than that of a CBP-based device. This enhanced external quantum efficiency resulted from the bipolar properties of the new host, owing to which well-balanced hole and electron transport through the emitting layer was achieved. The excellent bipolar carrier transport properties of the new host were experimentally verified using various OLED device data.

A high triplet energy phosphine oxide derivative as a host and exciton blocking material for blue phosphorescent organic light-emitting diodes

We have designed and synthesized a blue phosphorescent host material based on a phosphine oxide moiety. 2-(diphenylphosphine oxide)-9,9′-spirobifluorene ( SPPO1) was compared with N, N′-dicarbazolyl-3,5-benzene (mCP) as a blue host material in blue phosphorescent organic light-emitting diodes (PHOLEDs). The SPPO1 was effective as a host for blue PHOLEDs and the SPPO1 based blue PHOLEDs showed much higher quantum efficiency than common mCP based blue PHOLEDs. A high quantum efficiency of 16.3% and a current efficiency of 31.4 cd/A were obtained in the blue PHOLED with iridium(III) bis(4,6-(di-fluorophenyl)-pyridinato-N,C2′) picolinate (FIrpic) as a blue phosphorescent dopant. In addition, SPPO1 was also effective as an exciton blocking material for the blue PHOLED.

Investigation of FIrpic in PhOLEDs via LC/MS technique

Abstract The commercial breakthrough of phosphorescent organic white light sources is presently hampered due to the unavailability of a stable blue phosphorescent emitter material. Moreover, only few analytical investigations have been made regarding the chemical degradation of the phosphorescent emitter materials during the processing or the operation of the devices. Organic light emitting devices (OLEDs) containing phosphorescent metal complexes with iridium as central ion were investigated. Special attention was paid to the chemical degradation of the material. The devices were analyzed by means of high performance liquid chromatography coupled with mass spectrometry (HPLC/MS). Electron spray ionization (ESI) was employed as ionization source. Isomerization phenomena of the blue-green emitting heteroleptic iridium complex FIrpic could be observed after the device manufacture and after operation. These findings could give hints on the mechanisms that influence the lifetime of PhOLEDs based on FIrpic or similar blue emitters.

A wide band gap polymer derived from 3,6‐carbazole and tetraphenylsilane as host for green and blue phosphorescent complexes

AbstractWe have synthesized a novel wide band gap polymer P36HCTPSi derived from 3,6‐carbazole and tetraphenylsilane by palladium‐catalyzed Suzuki coupling reaction. The resultant polymer shows a high glass transition temperature (217 °C) and good thermal stability. The conjugation length of P36HCTPSi is effectively confined because of the δ‐Si interrupted polymer backbone. The polymer exhibits a violet emission with a peak at 392 nm in solution, and the band gap estimated from the onset of its absorption is 3.26 eV. The high energy emission and wide band gap of P36HCTPSi make it appropriate host for green and blue emission phosphorescent materials. Efficient energy transfers from P36HCTPSi to both fac‐tris[2‐(2‐pyridyl‐kN)‐5‐methylphenyl]iridium(III) (green emission) and bis[(4,6‐difluorophenyl)pyridinato‐N,C2]‐(picolinato)iridium(III) (blue emission) were observed in photoluminescence (PL) spectra. Highly efficient phosphorescent polymer light‐emitting devices were realized by using P36HCTPSi as the host for iridium complexes, the maximum luminous efficiencies for green and blue devices were 27.6 and 3.4 cd/A, respectively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4784–4792, 2009

Nonconjugated Carbazoles: A Series of Novel Host Materials for Highly Efficient Blue Electrophosphorescent OLEDs

A series of carbazole derivatives was synthesized and their electrical and photophysical properties were investigated. It is shown that the triplet energy levels of these hosts are higher than that of the most popular blue phosphorescent material iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C2′] picolinate (FIrpic) and the most extensively used phosphorescent host material 4,4′-N,N′-dicarbazole-biphenyl (CBP). These new host materials also showed good thermal stability and high glass transition temperatures (Tg) ranging from 78 to 115 °C as the linkage group between the carbazoles was altered. Photophysical measurements indicate that the energy transfer between these new hosts and FIrpic is more efficient than that between CBP and FIrpic. Devices incorporating these novel carbazole derivatives as the host material doped with FIrpic were fabricated with the configurations of ITO/NPB (40 nm)/host:FIrpic (30 nm)/BCP (15 nm)/AlQ (30 nm)/LiF (1 nm)/Al (150 nm). High efficiencies (up to 13.4 cd/A) have been obtained when 1,4-bis (4-(9H-carbazol-9-yl)phenyl)cyclohexane (CBPCH) and bis(4-(9H-carbazol-9-yl)phenyl) ether (CBPE) were used as the host, respectively. Efficiencies obtained from these devices are significantly higher than the efficiency obtained with CBP as the host. At a bias voltage of ∼20 V the maximum luminances of 20 342 and 17 766 cd/m2 were achieved for CBPCH- and CBPE-based devices, respectively, which demonstrates that CBPCH and CBPE can be excellent host materials for blue electrophosphorescent OLEDs.

Wide-Energy-Gap Host Materials for Blue Phosphorescent Organic Light-Emitting Diodes

Two novel wide-energy-gap molecules, 1,3-bis(9-phenyl-9H-fluoren-9-yl)benzene (mDPFB) and 1,4-bis(9-phenyl-9H-fluoren-9-yl)benzene (pDPFB), suitable for blue phosphorescent host materials, were designed and prepared. The thermal, photophysical, and electrochemical properties as well as electroluminescence characteristics were fully investigated. Both mDPFB and pDPFB possess high singlet (4.0 eV) and triplet (2.8 eV) energies, well energy-matched with the deep-blue phosphorescent dopant, iridium(III) bis(4′,6′-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6). The single crystals of the newly synthesized compounds mDPFB and pDPFB were grown, and their crystal structures were determined by X-ray diffraction. Both molecules adopt a rigid twisted tetrahedral crystallographic conformation, and no facial to facial π−π stacking exists in the solid state. The substituents at the 1,4-positions of benzene enhance the twisted degree of the fluorenyl rings and have predominant influence on the thermal and m...

Development of a phosphorescent white OLED with extremely high power efficiency and long lifetime

Abstract— A white OLED device with extremely high power efficiency and long lifetime was developed, in which blue, yellow‐green, and red phosphorescent emitters were used. The performances achieved were 64 lm/W and 10,000 hours of lifetime at an initial luminance of 1000 cd/m2 by using a light outcoupling technique. The device also exhibited the good durability important for practical usage. New technologies, such as blue phosphorescent materials and a sophisticated organic layer structure, were applied to the device. Hopefully, these technologies will open the door to the practical use of OLEDs as light sources.

19.1: Invited Paper: Development of Phosphorescent White OLED with Extremely High Power Efficiency and Long Lifetime

AbstractWe developed white OLED device with extremely high power efficiency and long lifetime, in which blue, yellow‐green and red phosphorescent emitters were used. The performance achieved was 64lm/W, and 10000 hours of lifetime at initial luminance of 1000cd/m2 with light out‐coupling technique. New technologies, such as blue phosphorescent materials and sophisticated organic layer structure, were applied to the device. The device also exhibited good durability such as storage stability, which is important performance in practical use. We hope that the development discussed in this paper opens up a course to practical use of OLED in lighting sources for illumination use, backlights and others.

61.3: Blue Dopants and New Host Materials for Phosphorescent Organic Light-Emitting Diodes

In this paper, we describe two new blue phosphorescent dopant materials FIrtaz and FIrN4. Efficient organic light-emitting diodes(OLEDs) incorporating demonstrate higher-purity blue-lightemission than the long-known FIrpic phosphorophore. New host material SimCP with higher glass-transition temperatures were also found to enhance the blue phosphorescence OLED performance.

Theoretical studies of cyclometalated phenylpyrazol Ir(III) complex using density functional theory

The ground state and low-lying excited electronic states in the Ir(III) complex fac -Ir(ppz) 3 are studied using density functional theory where ppz=phenylprazol and fac =facial. We reported before that this complex was pure blue phosphorescent material with about 450 nm of electroluminescent peak. Herein, the electronic properties of the molecule are studied using the B3LYP functional and the structure analysis of the optimized geometries are processed in comparison with structures of ppz ligand and fac -Ir(ppy) 3 . Excited triplet and singlet states are examined using time-dependent density functional theory (TD-DFT). The calculated energies of the lowest triplet and singlet states are 3.14 and 3.56 eV. All of the low-lying transitions calculated in this study are categorized as metal-to-ligand charge-transfer (MLCT) transitions because the metal orbitals involved in the transitions have significant admixture of ligand π orbitals with amount of metal 5d character of three highest occupied molecular orbitals which are 50.2%, 47.8% and 47.8%, respectively. From the analysis of absorption spectrum of this complex, it was found that the singlets and triplets calculated in this study are distributed in the range of 270–350 and 340–410 nm in absorption spectrum.

TD-DFT Studies of Electronic Structures in Cyclometalated Phenylpyrazol Ir(III) Complexes: Fac-Ir(ppz) 3 and Ir(ppz) 2(acac)

The ground state and low-lying excited electronic states of two related Ir(III)complexes fac-Ir(ppz)3(1)and Ir(ppz)2(acac)(2)are studied using density functional theory where ppz = phenylpyrazol, acac = acetylacetonate and fac = facial. The complex 1 is a blue phosphorescent material with about 450 nm of electroluminescent peak. The ground states of these complexes are studied using Becke's three parameter hybrid functional with Perdew 86(B3LYP)and the structure analysis of the optimized geometries are processed. Excited triplet and singlet states are examined using time-dependent density functional theory. Every low-lying transition for the former molecule and 6 lowest singlet and triplet excitations for the latter molecule are categorized as metal-to-ligand charge-transfer transitions, because the metal orbitals involved in the transitions have significant admixture of ligandπcharacter with amount of metal 5d character in the occupied molecular orbitals related to those transitions. Through the comparison of the calculated excitons with experimental absorption spectra, each peak was examined its originality.