Synthesis and properties of novel hole transport materials for electroluminescent devices

We synthesized low molecular weight triphenyldiamines (TPDs), novel 1,3,5-tris(diarylamino)benzenes (TDABs), polymeric triphenyldiamines and insoluble triphenylamine networks based on tris(4-ethynylphenyl)amine as hole transport materials for electroluminescent displays. The HOMO energy values as determined from cyclic voltammetry measurements for TPDs and TDABs are between −4.97 and −5.16 eV. By using a polymeric TPD as hole transport layer and tris(8-quinolinolato) aluminium as emitter, LEDs with an onset voltage of 3V and a luminance up to 900 cd/m² were obtained under ambient conditions.     

Synthesis and characterization of 9,10-substituted anthracene derivatives as blue light-emitting and hole-transporting materials for electroluminescent devices

New 9,10-substituted anthracene derivatives were designed and synthesized for application as blue-emitting and hole-transporting materials in electroluminescent devices. They were characterized by H NMR, C NMR, FTIR, UV–vis, PL spectroscopy, and mass spectrometry. The theoretical calculation of three-dimensional structure and the energy densities of HOMO and LUMO states, as well as optical properties of these new obtained materials, supported the claim that they had non-coplanar structures. Their optical, thermal, and electrochemical properties could be tuned by varying the peripheral substituents. All of them were electrochemically and thermally stable molecules. Materials having electron donating triphenylamine as peripheral substituents showed promising potential as both blue light-emitting materials and hole-transporting materials for electroluminescent devices. Efficient blue and Alq3-based green OLEDs with maximum luminance efficiencies and CIE coordinates of 1.65 cd/A and (0.15, 0.16) and 6.25 cd/A and (0.26, 0.49) were achieved, respectively.     

Dispirofluorene-indenofluorene derivatives as new building blocks for blue organic electroluminescent devices and electroactive polymers

A series of new dispiro[fluorene-9',6,9',12-indeno[1,2b]fluorenes] (DSF-IFs) has been synthesised. These new building blocks for blue-light-emitting devices and electroactive polymers combine indenofluorene (IF) and spirobifluorene (SBF) properties. We report here our synthetic investigations towards these new structures and their thermal, structural, photophysical and electrochemical properties. These properties have been compared to those of IF and SBF. We also report the anodic oxidation of DSF-IFs that leads to the formation of non-soluble transparent three-dimensional polymers. The structural and electrochemical behaviour of these polymers has been studied. The first application of these building blocks as new blue-light-emitting materials in organic light-emitting diodes (OLED) is also reported.     

Efficient blue lighting materials based on truxene-cored anthracene derivatives for electroluminescent devices

A new series of anthracene derivatives containing a truxene moiety as the core have been synthesized and characterized. They emit in the blue region with excellent solution fluorescence quantum yields and possess high thermal decomposition temperature (T_d>458 °C). Typical electroluminescence performance was demonstrated by 2-[10-(4-(1-napthenyl)phenyl)anthracene-9-yl]-5,5′,10,10′,15,15′-hexaethyltruxene (NPAT) as the blue lighting material in the OLED with structure of ITO/CFx/NPAT/TPBI or Alq₃/LiF/Al, where TPBI and Alq₃ are 1,3,5-tri(N-phenylbenzimidazol-2-yl)-benzene and tris(8-hydroxyquinolinato)aluminum, respectively. Additionally, the effects of the different thickness of the different electron transporting layers on the device performance were investigated.     

Carbazole dendronised triphenylamines as solution processed high Tg amorphous hole-transporting materials for organic electroluminescent devices

Carbazole dendrimers up to 4th generation were synthesized. They showed significantly high T(g), amorphous and stable electrochemical properties, and great potential as solution processed hole-transporting materials for OLEDs. Alq3-based green devices exhibited high luminance efficiency and CIE coordinates of 4.45 cd A(-1) and (0.29, 0.53), respectively.     

Bifunctional anthracene derivatives as non-doped blue emitters and hole-transporters for electroluminescent devices

New highly fluorescent bifunctional anthracenes showed high thermal and electrochemical stability, and great potential as both blue emitters and hole-transporters for OLEDs. Deep-blue and Alq3-based green devices with maximum efficiencies and CIE coordinates of 1.65 and 6.25 cd A(-1), and (0.15, 0.16) and (0.26, 0.49) were achieved, respectively.     

Synthesis and properties of stable amorphous hole-transporting molecules for electroluminescent devices

New triphenylamine-carbazole end-capped molecules were synthesized by a divergent approach using bromination and Suzuki cross-coupling reactions. All compounds showed an excellent electrochemical reversibility and a good thermal stability. They were fabricated as hole-transporting layers (HTLs) with the device configuration of ITO/HTL/Alq₃/LiF:Al. A bright green emission from the Alq₃ layer with a maximum luminance of 7500 cd/m² was observed at 9.8 V and a low turn-on voltage of 3.4 V.     

Synthesis, characterization and applications of vinylsilafluorene copolymers: New host materials for electroluminescent devices

Vinylsilafluorene (VSiF) was successfully synthesized and copolymerized with vinylcarbazole and methyl methacrylate via free radical copolymerization for the first time. The synthesis, photophysical properties, computational modeling studies, and organic light-emitting devices of the VSiF copolymers were presented. The good coordinated photoluminescent (PL) spectra with the absorption of blue light-emitting materials and the high energy band-gap of the VSiF copolymers were observed. Higher triplet band gap (³ E _g) to host the blue phosphorescent emitters and better HOMO and LUMO than PVK for electron and hole injection and transportation of the VSiF model compounds were revealed by density functional theory (DFT) calculations. The preliminary device results in applications of these copolymers as host materials for green phosphorescent emitters demonstrate the copolymers of VSiF and vinylcarbazole have comparable device performance of polyvinylcarazole (PVK), suggesting a bright future of VSiF as building blocks for host materials.     

Thermal stability of organic electroluminescent devices fabricated using novel charge transporting materials

Novel hole and electron transporting materials have been synthesized to improve the thermal stability of organic electroluminescent (EL) devices. Molecular structures of such hole and electron transporting materials were designed based on triphenylamine (TPA) and oxadiazole (OXD) moieties, respectively. It has been found that the resulting materials have high glass transition temperatures (Tg) over 100°C and the vacuum-deposited thin films are significantly thermally stable. For the two-layer EL devices using the novel hole transporting materials and the typical emitting material, tris(8-quinolinolato) aluminum, the thermal stability has been clearly seen to depend on the Tg of the hole transporting material; excellent thermal stability was achieved. For the three-layer EL device using the novel electron transporting material, good emission efficiency and good stability were achieved. The electron transporting materials have been also applied to the polymeric system with polyvinylcarbazole matrix.     

Toward new materials for organic electroluminescent devices: synthesis, structures, and properties of a series of 2,5-diaryl-3,4-diphenylsiloles

A series of 2,5-diaryl-3,4-diphenylsiloles, with various mono-substituted phenyl groups, extended pi-conjugated groups, and heteroaryl groups as aryl groups at the 2,5-positions, has been prepared by a one-pot synthesis from bis(phenylethynyl)silanes based on the intramolecular reductive cyclization followed by the palladium-catalyzed cross-coupling with aryl halides. Crystal structures and chemical reactivities toward the alkaline desilylation reactions have been studied on the 2,5-bis(p-mono-substituted phenyl)silole derivatives to elucidate the effects of the p-substituents. The UV-visible absorption and fluorescence spectra, and cyclic voltammetry of the 2,5-diarylsiloles have been systematically evaluated. Their photophysical properties as well as their electronic structures significantly depend on the nature of the 2,5-aryl groups.     

Photonic materials for electroluminescent,laser and photovoltaic devices

This article presents an overview of the work that has been done recently in our laboratory concerning the development and application of new conjugated materials with tunable properties. We have designed polymers containing oligo(phenylenevinylene)-type conjugated segments of well defined size and structure isolated either in their main-chain or in the side-chains. Model oligomers corresponding to the conjugated parts of the polymers have also been studied. We show how these materials perform in light-emission applications (light-emitting diodes, lasers) or photovoltaic cells.     

New benzo[b]furans as electroluminescent materials for emitting blue light

[structure: see text] New functionalized mono- and bis-benzo[b]furan derivatives were synthesized and developed as blue-light emitting materials. They possessed a CN, CHO, CH=CHPh, CH=CPh(2), or CH=CHCOOH group at the C4-position. Two benzo[b]furan nuclei in bis-benzo[b]furan derivatives were connected by a divinylbenzene bridge. With good volatility and thermal stability, bis-benzo[b]furan 7a was fabricated as a device. It emitted blue light with brightness 53430 cd/m(2) (at 15.5 V) and high maximum external quantum efficiency 3.75% (at 11 V).     

Novel fluorene/carbazole hybrids with steric bulk as host materials for blue organic electrophosphorescent devices

The problem of self-quenching in organic electrophosphorescence devices has been extensively studied and partially solved by using sterically hindered spacers in phosphorescent dopants. This paper attempts to address this problem by using sterically hindered host materials. Novel fluorene/carbazole hybrids with tert-butyl substitutions, namely 9,9-bis[4-(3,6-di-tert-butylcarbazol-9-yl)phenyl]fluorene (TBCPF) and 9,9-bis[4-(carbazol-9-yl)phenyl]-2,7-di-tert-butylfluorene (CPTBF), have been synthesized and characterized. The compounds exhibit not only high triplet energy (>2.8 eV), but also high glass transition temperature (>160 °C) and thermal stability. The substitution of inert tert-butyl groups to the carbazole/fluorene rings of these host molecules has a remarkable effect on the corresponding properties of the host materials, i.e. enhancing the thermal and electrochemical stability, weakening the intermolecular packing, and tuning the solid-state emission. Blue electrophosphorescent devices with enhanced performance were prepared by utilizing the sterically hindered host materials. The devices based on the four tert-butyl substituted material TBCPF exhibit unusual tolerance of high dopant concentration up to 20% and marked reduction of efficiency roll-off at higher current, indicating significant suppression of self-quenching effect in organic electrophosphorescent devices by the substitution of steric bulks.     

New platinum(II) complexes as triplet emitters for high-efficiency monochromatic pure orange electroluminescent devices

New multi-component orange phosphorescent platinum complexes [Pt(L)(acac)] (Hacac = acetylacetone, HL = (9,9-diethyl-7-pyridin-2-ylfluoren-2-yl)diphenylamine 1, (9,9-diethyl-7-pyridin-2-ylfluoren-2-yl)di(p-tolyl)amine 2) were prepared and characterized by spectroscopic and X-ray crystallographic methods. We report the redox and photophysical properties of 1 and 2 and compare these results with the unsubstituted analogue [Pt(L)(acac)] (HL = 9,9-diethyl-2-pyridin-2-ylfluorene 3). Efficient pure orange-emitting organic light-emitting devices (OLEDs) based on 1 were fabricated. The device performance with 3,5-dicarbazolylbenzene (mCP) as the host can furnish maximium external quantum, current and power efficiencies of 4.65%, 11.75 cd/A and 5.27 lm/W at 7 V, respectively. The device with 4,4′-N,N′-dicarbazolebiphenyl (CBP) as the host can perform better with peak external quantum and current efficiencies of 6.64% and 15.41 cd/A at 7.5 V and a power efficiency of 7.07 lm/W at 6.5 V. Unlike the OLEDs made from other cyclometalated Pt(β-diketonato) complexes in which the electroluminescence spectra generally displayed both the monomeric and excimeric emissions with different relative intensities upon variation of dopant concentration, our devices emit a strong pure orange light with stable CIE color coordinates. From a steric point of view, no evidence of low-energy aggregate emission is observed for a doping level up to 12 wt.%. The present work confers a good platform for the realization of robust triplet emitters in the fabrication of highly efficient monochromatic OLEDs through the design of multifunctional chelating ligands.     

Synthesis and characterization of green to orange electroluminescent copolymers derived from fluorene and 2,3-dimethylnaphthalopyrazine

Series of high molecular weight, readily soluble copolymers were synthesized by Suzuki palladium catalyzed coupling reaction from 9,9-dioctylfluorene and 2,3-dimethylnaphthopyrazine. The absorption, electrochemical and photoluminescence properties of the copolymers were studied. The external electrolu-minescence efficiencies in the devices of configuration indium-tin oxide/polyethylenedioxythiophene-polystyrene sulfonic acid/poly(fluorene-naphthopyrazine)/barium/aluminium varied with the copolymers composition, and the electroluminescence emission peaks of the copolymers were red-shifted from 530 nm to 584 nm as 2,3-dimethylnaphthopyrazine mole contents increasing from 0.5% to 30%. The best device performance was observed for devices fabricated with the copolymer of 2,3-dimethylnathphpyrazine 5% mole contents, showed maximum external quantum efficiency of 1.38% and electroluminescence peaks at around 537 nm.     

Toward functional pi-conjugated organophosphorus materials: design of phosphole-based oligomers for electroluminescent devices

The photophysical, electrochemical, and optoelectronic properties of conjugated systems incorporating dibenzophosphole or phosphole moieties are described. Dibenzophosphole derivatives are not suitable materials for OLEDs due to their weak photoluminescence (PL) in the solid state and the instability of the devices. Variation of the substitution pattern of phospholes and chemical modification of their P atoms afford thermally stable derivatives, which are photo- and electroluminescent. Comparison of the optical properties of solution and thin film of thioxophospholes shows that these compounds do not form aggregates in the solid state. This property, which is also supported by an X-ray diffraction study of three novel derivatives, results in an enhancement of the fluorescence quantum yields in the solid state. In contrast, (phosphole)gold(I) complexes exhibit a broad emission in thin film, which is due to the formation of aggregates. Single- and multilayer OLEDs using these P derivatives as the emissive layer have been fabricated. The emission color of these devices and their performances vary with the nature of the P material. Interestingly, di(2-thienyl)thiooxophosphole is an efficient host for the red dopant DCJTB, and devices using the gold complexes have broad emission spectra.     

含吡啶基团的双极主体材料的合成、性能与蓝光电致磷光器件研究

吡啶类衍生物具有较好的电子传输性能和较高的三线态能级,在有机电致发光中一般用来构建电子传输材料或主体材料中的电子传输单元.本文通过将吡啶的2,6位与三苯胺或N-苯基-咔唑的邻位连接设计合成了两个基于吡啶的双极主体材料DTPAPPy和DCzPPy.它们的三线态能级分别为2.64和2.70eV.以它们作为主体材料制备的基于Firpic的蓝光磷光器件最大电流效率分别为15.4和25.3cd/A.     

Synthesis and electroluminescent properties of naphthalimide derivatives

Naphthalimide derivatives, N-ethyl-4-acetylamino-l ,8-naphthalimide (EAAN) and polymer with N-propyl-4-acetylamino-l,8-naphthalimide (PAAN) side-chain (P-PAAN) were successfully synthesized. Electroluminescent devices of ITO/PVK(120nm)/EAAN(50nm)/Al(150nm) (Ⅰ) and ITO/PVK P-PAAN( 10:1) (50nm)/Al(150nm) (Ⅱ) constructed with EAAN and P-PAAN as the emitting layer were investigated, whereas the single-layer devices of ITO/EAAN or P-PAAN(50nm)/Al(l50nm) (Ⅲ) were not observed to have any e-mission light. The emission results revealed that the exciton recombination formed by positive and negative charge carriers injected from electrodes of devices Ⅰ and Ⅱ was much more balanced than that of devices Ⅲ, which implied that naphthalimide derivatives are a new type of electron-transporting materials with high performance. The electron-transporting properties of naphthalimide derivatives were also elucidated by investigation of the electroluminescent behaviors from both devices of ITO/PPV (80nm)/Al and ITO/P     

Bis(4-diphenylaminophenyl)carbazole end-capped fluorene as solution-processed deep-blue light-emitting and hole-transporting materials for electroluminescent devices

A new highly fluorescent bis(4-diphenylaminophenyl)carbazole end-capped fluorene (TCF) is synthesized and characterized. TCF is an amorphous molecular glass with a high glass transition temperature of 169 °C, is electrochemically stable, and gives strong blue emission both in solution and solid state. It showed greater ability as a solution processed blue emitter and hole-transporter for OLEDs than commonly used NPB. High-efficiency, deep-blue and Alq3-based green devices with luminance efficiencies and CIE coordinates of 0.93 cd/A and (0.16, 0.09), and 3.78 cd/A and (0.29, 0.45) were achieved, respectively.     

Electronic properties of anthracene derivatives for blue light emitting electroluminescent layers in organic light emitting diodes: a density functional theory study

Molecular level parameters are investigated computationally to understand the factors that are responsible for the higher efficiency in derivatives of 9,10-bis(1-naphthyl)anthracene (alpha-ADN), 9,10-bis(2-naphthyl)anthracene (beta-ADN), their tetramethyl derivatives (alpha,beta-TMADN) and the t-Bu derivative (beta-TBADN) as blue light emitting electroluminescent (EL) layers in organic light emitting diodes (OLEDs). DFT studies at the B3LYP/6-31G(d,p) level have been carried out on the substituted anthracenes. The absorption spectra are simulated using time dependent DFT methods (TD-DFT) whereas the emission spectra are approximated by optimizing the excited state by HF/CI-Singles and then carrying out the vertical CI calculations by the TD-DFT method. The reorganization energy for estimating the hole and electron transport is calculated. The transfer integrals between parallely stacked molecules in the bulk state are estimated by calculating the electronic splitting. The substituted anthracenes are compared with unsubstituted anthracene and yet untested 9,10-dianthrylanthracene (TANTH). A larger and slower buildup of the electrons and holes in the EL layer, due to the higher reorganization energy and smaller electronic coupling between the adjacent molecules could lead to an increase in hole-electron recombination in the layer and thus increase the efficiency.