Beryllium-Based,High-Triplet-Energy Material as a Host for Blue Phosphorescent Organic Light-Emitting Diodes

A beryllium-based compound, bis[2-(3,5-dimethylpyrazol-1-yl)pyridin-3-olate] beryllium (DmPPBe), was designed and synthesized as a high-triplet-energy host material for blue phosphorescent organic light-emitting diodes. The DmPPBe host showed a high triplet energy of 2.75 eV due to the high-triplet-energy 2-(3,5-dimethylpyrazol-1-yl)pyridin-3-ol ligand. The DmPPBe host was effective as the host material for blue phosphorescent organic light-emitting diodes and a high quantum efficiency of 17.7 % was achieved.     

Layered mixed-anion compounds: Epitaxial growth,active function exploration,and device application

Optoelectronic properties and device applications of layered mixed-anion compounds such as oxychalcogenide LaCuOCh (Ch = chalcogen) and oxypnictide LaT_MOPn (T_M = 3d transition metal, Pn = pnicogen) are reviewed. Several distinctive functions have been found in these materials based on our original material exploration concept. Fabrication of high-quality epitaxial films of LaCuOCh leads to clarifying the excellent electrical and optical properties such as high hole mobility of 8 cm²/(V s) and heavy hole doping at >10²¹ cm^?3 in LaCuOSe, and sharp and tunable-wavelength photoluminescence in the solid–solution systems in LaCuOCh. In addition, a room temperature operation of a light-emitting diode is demonstrated using LaCuOSe as a light-emitting layer. These results suggest that the layered oxychalcogenides have potential for light-emitting layers as well as transparent hole-injection layers in organic/inorganic light-emitting diodes. Furthermore, by extending the material system from the copper-based oxychalcogenides to isostructural compounds, transition metal-based oxypnictides LaT_MOP (T_M = Fe, Ni), we have found novel superconductors, LaFeOP and LaNiOP.     

Color stability and suppressed efficiency roll-off in white organic light-emitting diodes through management of interlayer and host properties

Color stability and efficiency roll-off of white light-emitting diodes (WOLEDs) with blue fluorescent and red phosphorescent emitting materials were manipulated by controlling the charge transport properties of interlayer and triplet host materials. A pure white emission was observed in WOLEDs with a bipolar interlayer and a hole transport type triplet host material. A white color coordinate of (0.31, 0.35) and a current efficiency of 14.4 cd/A were obtained. In addition, color index of WOLEDs could be kept stable up to a high luminance of 10,000 cd/m² and an efficiency roll-off was also suppressed.     

Novel yellow phosphorescent iridium complexes containing a carbazole–oxadiazole unit used in polymeric light-emitting diodes

Yellow iridium complexes Ir(PPOHC)₃ and (PPOHC)₂Ir(acac) (PPOHC: 3-(5-(4-(pyridin-2-yl)phenyl)-1,3,4-oxadiazol-2-yl)-9-hexyl-9H-carbazole) were synthesized and characterized. The Ir(PPOHC)₃ complex has good thermal stability with 5% weight-reduction occurring at 370 °C and a glass-transition temperature of 201 °C. A polymeric light-emitting diode using the Ir(PPOHC)₃ complex as a phosphorescent dopant showed a luminance efficiency of 16.4 cd/A and the maximum external quantum efficiency of 6.6% with CIE coordinates of (0.50, 0.49). A white polymeric light-emitting diode was fabricated using Ir(PPOHC)₃ which showed a luminance efficiency of 15.3 cd/A, with CIE coordinates of (0.39, 0.44). These results indicate that the iridium complexes containing a linked carbazole–oxadiazole unit are promising candidates in high-efficiency electroluminescent devices.     

Novel yellow phosphorescent iridium complexes containing a carbazole-oxadiazole unit used in polymeric light-emitting diodes

Yellow iridium complexes Ir(PPOHC)₃ and (PPOHC)₂Ir(acac) (PPOHC: 3-(5-(4-(pyridin-2-yl)phenyl)-1,3,4-oxadiazol-2-yl)-9-hexyl-9H-carbazole) were synthesized and characterized. The Ir(PPOHC)₃ complex has good thermal stability with 5% weight-reduction occurring at 370 °C and a glass-transition temperature of 201 °C. A polymeric light-emitting diode using the Ir(PPOHC)₃ complex as a phosphorescent dopant showed a luminance efficiency of 16.4 cd/A and the maximum external quantum efficiency of 6.6% with CIE coordinates of (0.50, 0.49). A white polymeric light-emitting diode was fabricated using Ir(PPOHC)₃ which showed a luminance efficiency of 15.3 cd/A, with CIE coordinates of (0.39, 0.44). These results indicate that the iridium complexes containing a linked carbazole-oxadiazole unit are promising candidates in high-efficiency electroluminescent devices.     

High efficient and high color pure blue light emitting materials: New asymmetrically highly twisted host and guest based on anthracene

New asymmetrically highly twisted anthracene derivatives serve as a matched host and guest material in high efficiency blue OLEDs. 2-(2-Methylnaphtathalene-1-yl)-9,10-di(naphthalene-2-yl)anthracene and N-(4-(10-naphthalene-2-yl)anthracene-9-yl)phenyl-N-phenylnaphthalene-2-amine were prepared as host material and as guest material, respectively. Multilayer organic electroluminecent devices constructed using these foregoing twisted anthracene derivatives as the emitting layer gave quantum efficiencies of 5% and exhibited a pure blue emission with CIE chromaticity coordinates x = 0.15, y = 0.14-0.18.     

Synthesis and device performance of an oxygen‐interrupted bipolar polymer host with carbazole and triphenylphosphine oxide in the main chain

A novel bipolar polymer host PC10CzPO, carrying hole‐transporting carbazole and electron‐transporting triphenylphosphine oxide units in the oxygen‐interrupted main chain, was synthesized and characterized. In addition to its excellent thermal stability and miscibility with phosphors, PC10CzPO is also reported to have a triplet energy (E_T) as high as 2.83 eV due to oxygen‐interrupted π‐conjugation, ensuring that PC10CzPO can be used as a suitable host material. The PC10CzPO‐based phosphorescent devices were investigated and compared, while doping with typical blue phosphor {iridium(III)[bis(4,6‐difluorophenyl)pyridinato‐N, C2]picolinate, FIrpic)}, green phosphor {tris[2‐(p‐tolyl)pyridine]iridium(III), Ir(mppy)₃}, and red phosphor [bis(1‐phenyl‐isoquinoline‐C2,N)(acetylacetonato)iridium(III), Ir(piq)₂acac]. As a result, the FIrpic‐based blue devices showed better device performances than those of red and green devices, which was ascribed to more effective energy transfer. This indicates that the choice of proper host and dopant emitters to fabricate phosphorescent polymer light emitting diodes (PhPLED) is a simple and effective approach to optimize device performances. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44461.     

Supramolecular Phosphorescent Polymer Based on Cationic Iridium Complexes for Polymer Light-Emitting Diodes

Three novel orange emission supramolecular phosphorescent polymers (SPPs) with cationic iridium complex have been developed for polymer light-emitting diodes (PLEDs) through efficient self-assembly. The supramolecular assembly process was monitored by ¹H nuclear magnetic resonance (¹H NMR) and viscosity measurement. These SPPs give orange phosphorescence with a peak at about 595 nm and display good thermal properties with a glass-transition temperature (T_g) about 90 °C. The single-emissive-layer PLEDs with charged SPPs exhibited the highest device efficiency of 2.81 cd A^?1 with the Commission Internationale de L’Eclairage coordinates of (0.58, 0.40). The present work reported the charged SPPs self-assembled by the cationic iridium complex for the first time and provided a new guide to develop orange emitters for solution-processable optoelectronic devices.

     

A New Multifunctional Triazine?Carbazole Compound with High Triplet Energy for High-Performance Blue Fluorescence,Green and Red Phosphorescent Host,and Hybrid White Organic Light-Emitting Diodes

A blue fluorescent compound, 9-[4-(4,6-diphenoxy-1,3,5-triazin-2-yl)phenyl]-9H-carbazole (POTC), the triplet energy level of which reaches 2.76 eV, has been designed and synthesized. POTC is an excellent blue emitter as well as host for green and red phosphors, and therefore, matches the requirements of the host for single-emitting-layer fluorescence and phosphorescence hybrid white organic light-emitting diodes (OLEDs). The blue, green, red, and white devices based on POTC show maximum external quantum efficiencies (EQEs) of 2.4, 22.4, 13.0, and 8.1 %, respectively. Even at a high brightness of 1000 cd m⁻², these values maintain EQEs of 2.3, 22.1, 11.1, and 7.0 %, respectively, indicating less than 15 % roll-offs from the maxima.     

The design,synthesis and nonlinear optical properties of a novel,Y-type polyurethane containing tricyanovinylthiophene of high thermal stability

A novel, Y-type polyurethane containing 1-(2,4-dioxyethoxy)phenyl-2-{5-(2,2-dicyanovinyl)-2-thiophenyl}ethenes as nonlinear optical chromophores present within the polymer backbone, was prepared and characterized. The compound was soluble in common organic solvents and displayed thermal stability up to 260 °C and a glass transition temperature (T_g) of 163 °C. The second harmonic generation coefficient (d₃₃) of poled polymer films at the compound's fundamental wavelength of 1560 nm was ～3.72 × 10^?9 esu. Dipole alignment exhibited high thermal stability up to the T_g, and there was no decay in d₃₃ below 148 °C owing to the partial main-chain character of the polymer structure.     

Single-layer white polymer light-emitting diodes based on an iridium (III) complex containing alkyltrifluorene picolinic acid

To explore the relationship between the electronic properties of a host/dopant system and obtain a high-efficiency single-dopant white polymer light-emitting device two novel blue-emitting cyclometalated iridium (III) complexes of (dfppy)₂Ir(Tfl-pic) and (dfppy)₂Ir(Brfl-pic) have been synthesized and characterized, where dfppy is 2-(2,4-difluorophenyl)pyridine, Tfl-pic and Brfl-pic are picolinic acid derivatives containing trialkylfluorene and dibromoalkylfluorene units bridged with an alkoxy chain, respectively. Both iridium (III) complexes exhibited blue emission in dichloromethane solution and their neat films, and possessed good dispersibility and thermal properties. Two different devices using (dfppy)₂Ir(Tfl-pic) as a single component emitter and a blend of poly(N-vinylcarbazole) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole as the host matrix were fabricated. Improved white emission was obtained by adjusting the electron injection layer leading to efficient exciplex emission.     

Single-layer white polymer light-emitting diodes based on an iridium (III) complex containing alkyltrifluorene picolinic acid

To explore the relationship between the electronic properties of a host/dopant system and obtain a high-efficiency single-dopant white polymer light-emitting device two novel blue-emitting cyclometalated iridium (III) complexes of (dfppy)₂Ir(Tfl-pic) and (dfppy)₂Ir(Brfl-pic) have been synthesized and characterized, where dfppy is 2-(2,4-difluorophenyl)pyridine, Tfl-pic and Brfl-pic are picolinic acid derivatives containing trialkylfluorene and dibromoalkylfluorene units bridged with an alkoxy chain, respectively. Both iridium (III) complexes exhibited blue emission in dichloromethane solution and their neat films, and possessed good dispersibility and thermal properties. Two different devices using (dfppy)₂Ir(Tfl-pic) as a single component emitter and a blend of poly(N-vinylcarbazole) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole as the host matrix were fabricated. Improved white emission was obtained by adjusting the electron injection layer leading to efficient exciplex emission.     

Magnetocaloric properties of Gd2MoO6 prepared by a simple and fast method

The experimental study of the specific heat, magnetic susceptibility, and magnetization of Gd₂MoO₆ powder sample was performed in the temperature range between 0.4 K and 300 K in the magnetic fields up to 9 T. Powder sample was prepared via nonconventional mechanochemical/thermal process from powdered oxide precursors. Magnetic ion Gd³⁺ with spin S = 7/2 is responsible for the magnetic properties. The specific heat study in zero magnetic field revealed two anomalies; a phase transition to the ordered state at T_N1 ≈ 0.98 K and a smaller maximum at T_N2 ≈ 0.6 K. Relatively high magnetic density 6.85 g/cm³ of Gd₂MoO₆ predetermines this compound as potential magnetocaloric material with a high cooling performance at cryogenic temperatures. A large conventional magnetocaloric effect was found around 3 K with magnetic entropy change ?ΔS_max ≈ 44 J/(kg K) (300 mJ/(Kcm³)) for magnetic field change from 9 T down to zero with a refrigerant capacity of 464 J/kg. Maximal temperature change -ΔT_ad ≈ 23.8 K was found for initial temperature T_init ≈ 29.9 K for the mentioned change of magnetic field. Alternating susceptibility measurements revealed the presence of two relaxation channels in Gd₂MoO₆ existing in two different time scales ≈ 10^-3 s and ≈ 1 s.     

Crystal structure and photo- and electroluminescent properties of a “sandglass” terbium cluster

The synthesis, crystal structure and photophysical properties of [Tb{Tb₄(hpmba)₈(μ₃-ΟΗ)₄(μ₄-ΟΗ)}₂OH] (hpmba = 2-hydroxy-N-((pyridin-2-yl)methyl)benzamide) was presented. The crystal structure exhibits a novel sandglass-like nonanuclear structure. The complex is strongly emissive with the lifetime about 1.02 ms at 546 nm in CH₃CN at 298 K. The ITO/PVK/complex/Al OLED with the compound as a light-emitting material has also been fabricated; it has a maximum electroluminescence intensity when the driving voltages were increased to 11 V.     

Metallo-homopolymer and metallo-copolymers containing light-emitting poly(fluorene/ethynylene/(terpyridyl)zinc(II)) backbones and 1,3,4-oxadiazole (OXD) pendants

A series of novel metallo-polymers containing light-emitting poly(fluorene/ethynylene/(terpyridyl)zinc(II)) backbones and electron-transporting 1,3,4-oxadiazole (OXD) pendants (attached to the C-9 position of fluorene by long alkyl spacers) were synthesized by self-assembled reactions. The integrated ratios of ¹H NMR spectra reveal a facile result to distinguish the well-defined main-chain metallo-polymeric structures which were constructed by different monomer ligand systems (i.e. single, double, and triple monomer ligands with various pendants). Furthermore, UV-vis and photoluminescence (PL) spectral titration experiments were carried out to verify the metallo-polymeric structures by varying the molar ratios of zinc(II) ions to monomers. As a result, the enhancement of thermal stability (T_d) and quantum yields were introduced by the metallo-polymerization, and their physical properties were mainly affected by the nature of the pendants. The photophysical properties of these metallo-polymers exhibited blue PL emissions (around 418 nm) with quantum yields of 34-53% (in DMF). In contrast to metallo-polymers containing alkyl pendants, the quantum yields were greatly enhanced by introducing 1,3,4-OXD pendants but reduced by carbazole (CAZ) pendants. Moreover, electroluminescent (EL) devices with these light-emitting metallo-polymers as emitters showed green EL emissions (around 550 nm) with turn-on voltages of 6.0-6.5 V, maximum efficiencies of 1.05-1.35 cd A⁻¹ (at 100 mA/cm⁻²), and maximum luminances of 2313-3550 cd/m² (around 15 V), respectively.     

Synthesis and photoluminescent property of star polymers with carbzole pendent and a zinc porphyrin core by ATRP

Styrene-type monomer 9-(4-vinylbenzyl)-9H-carbazole (VBCz) and methacrylate-type monomer 2-(9H-carbazole-9-yl)-ethyl methacrylate (CzEMA) were polymerized to star polymers respectively via atom transfer radical polymerization (ATRP) using zinc 5,10,15,20-tetrakis(4-(2-methyl-2-bromopropoxy) phenyl) porphyrin as an initiator. The emission spectra of two star polymers (star poly(VBCz) and star poly(CzEMA)) in the solid state displayed red light emission, while those of two monomers showed blue light emission. The result demonstrates that effective energy transfer occurs from the carbazole to the Zn porphyrin core. However, two star polymers in DMF solution emit week red light and strong UV light at 350-400 nm, it points that energy transfer cannot occur from the carbazole to the Zn porphyrin core effectively. They exhibit good thermal stability with T_{d poly(VBCz)} = 374 °C and T_{d poly(CzEMA)} = 297 °C at 5% weight loss. The DSC curves show that the glass transition temperature of styrene-type (T_{g poly(VBCz)} = 177 °C) was better than that of methacrylate-type (T_{g poly(CzEMA)} = 148 °C).     

Recombination zone study of phosphorescent organic light-emitting diodes with triplet mixed host emitting structure

Recombination zone of green phosphorescent organic light-emitting diodes (PHOLEDs) with triplet mixed host was studied using red sensing layer. Recombination zone of triplet mixed host device with 4,4′,4″-tris(N-carbazolyl)triphenylamine and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene as hosts was rather dispersed compared with that of single host device with recombination zone near charge transport layer. The recombination zone was shifted to hole transport side at high driving voltage.     

Synthesis and electroluminescence property of new hexaphenylbenzene derivatives including amine group for blue emitters

Three new blue-emitting compounds of 5P-VA, 5P-VTPA, and 5P-DVTPA for organic light-emitting diode (OLED) based on hexaphenylbenzene moiety were demonstrated. Physical properties by the change of the substitution groups of the synthesized materials were systematically examined. Photoluminescence spectrum of the synthesized materials showed maximum emitting wavelengths of about 400 to 447 nm in solution state and 451 to 461 nm in film state, indicating deep blue emission color. OLED devices were fabricated by the synthesized compounds using vacuum deposit process as an emitting layer. The device structure was ITO/2-TNATA 60 nm/ NPB 15 nm/ EML 35 nm/ TPBi 20 nm/ LiF 1 nm/ Al 200 nm. External quantum efficiencies and CIE values of 5P-VA, 5P-VTPA, and 5P-DVTPA were 1.89%, 3.59%, 3.34%, and (0.154, 0.196), (0.150, 0.076), (0.148, 0.120), respectively. 5P-VTPA and 5P-DVTPA exhibited superior highly blue quality and thermal property such as high T_d of 448°C and 449°C.     

Phosphorescent,green-emitting Ir(III) complexes with carbazolyl-substituted 2-phenylpyridine ligands: Effect of binding mode of the carbazole group on photoluminescence and electrophosphorescence

The ligands, 9-((6-phenylpyridin-3-yl)methyl)-9H-carbazole and 9-(4-(pyridin-2-yl)benzyl)-9H-carbazole were synthesized by attaching a carbazolyl group to the pyridine and phenyl rings of 2-phenylpyridine, respectively. Ir(III) complexes were prepared by a simple procedure and the solubility of the novel complexes was significantly better than that of the conventional, green-emitting conventional fac-tris(2-phenylpyridinato-C²,N)iridium(III). The Ir(III) complexes were used to prepare electrophosphorescent polymer light-emitting devices. The device comprising 10% of fac-tris(2-(4′-((9H-carbazol-9-yl)methyl)phenyl)pyridinato-C²,N)iridium(III) exhibited an external quantum efficiency of 7.88%, luminous efficiency of 23.01 cd/A, and maximum brightness of 32,640 cd/m². The color of the emissions of fac-tris(2-(4′-((9H-carbazol-9-yl)methyl)phenyl)pyridinato-C²,N)iridium(III) was similar to that of conventional fac-tris(2-phenylpyridinato-C²,N)iridium(III). This work shows that integration of a rigid hole-transporting carbazole and phosphorescent complex in one molecule provides a new route to highly efficient, solution-processable complexes for electrophosphorescent applications.     

Strong photoluminescence and piezoelectricity properties in Pr-doped Ba(Zr0.2Ti0.8)O3–(Ba0.7Ca0.3)TiO3 ceramics: Influence of concentration and microstructure

(Ba_0.85Ca_0.15)_1−xPr_x(Zr_0.1Ti_0.9)O₃ (where 0 < x < 0.01, abbreviated as BCZT:xPr) ceramics were fabricated by conventional solid-state reaction method. The influence of dopant concentration and microstructure on photoluminescence, ferroelectric, and piezoelectric properties was systematically investigated. The results showed that the photoluminescence spectra of the samples exhibited strong green (530 nm) and red (602 nm) emissions upon excitation of the 430 nm to 500 nm light, which couples well with to the emission band of the commercial blue light-emitting diodes chips. The emission intensities were strongly dependent on the dopant concentration and crystallite size, which reached the optimal value when the crystallite size and dopant concentration were 8 μm and 0.002 mol, respectively. Meanwhile, a large piezoelectric response with d₃₃ = 325 pC/N was obtained for BCZT:0.002Pr near the morphotropic phase boundary. Therefore, the Pr-doped BCZT materials, simultaneously exhibiting excellent luminescent properties and high piezoelectric properties, may have significant technological promise in novel multifunctional devices.