Molecular Designs and Properties of Highly Efficient Blue Emitters for OLEDs

Advances made in the molecular design of modern optoelectronic materials have made significant contributions toward the development of organic electronics. The organic light-emitting devices (OLEDs) employing monodisperse or polymeric conjugated materials possess the most promising prospects. However, materials suitable for long-term use as blue light emitters are still far from optimization in terms of stability.In the past few years, interesting materials based on 9,9-diaryl-substituted fluorene as a core structure have been developed in our laboratory. We developed a series of efficient and morphologically stable pyrimidine-containing 9,9'-spirobifluorene-cored oligoaryls as pure blue emitters. The steric hindrance inherent with the molecular structure renders the material with a record-high thin-film PL quantum yield of ～95% and a glass transition temperature (Tg) of ～200 ℃.Blue OLEDs employing this thermally stable compound as the emitting host exhibit unusual endurance for high currents. Injection current over 5,000 mA/cm2 and maximal brightness of～80,000 cd/m2 had been demonstrated, representing the highest values reported for blue OLEDs under dc driving. In addition, a series of oligofluorene homologues have been synthesized. These oligofluorenes exhibit interesting reversible bipolar redox properties and excellent morphological and thermal stability. Furthermore, nondispersive ambipolar high hole and electron mobilities over 10-3 cm2/V.s can be achieved with these oligo(9,9-diarylfluorene)s. In particular, the electron mobility observed represents the highest ever reported for amorphous molecular solids. These intriguing properties together with the high quantum yields in thin films make these oligo(9,9-diarylfluorene)s are promising for OLEDs applications as efficient blue emitters. In this meeting, the synthesis and properties of these materials and their highly efficient OLEDs device characteristics will be discussed.     

A New Approach to Prepare Efficient Blue AIE Emitters for Undoped OLEDs

Two aggregation‐induced emission active luminogens (TPE–pTPA and TPE–mTPA) were successfully synthesized. For comparison, another six similar compounds were prepared. Because of the introduced hole‐dominated triphenylamine (TPA), fluorene groups with high luminous efficiency, and unconjugated linkages, the π conjugation length of the obtained luminogens is effectively restricted to ensure their blue emission. The undoped organic light‐emitting diodes based on TPE–pTPA and TPE–mTPA exhibited blue or deep‐blue emissions, low turn‐on voltages (3 V), and high electroluminescence efficiencies with L_max, η_C,max, and η_P,max values of up to 26 697 cd m^?2, 3.37 cd A^?1, and 2.40 Lm W^?1.     

高效蓝光有机电致磷光主体材料的研究进展

磷光有机发光二极管(PHOLEDs)相对于传统的荧光有机电致发光具有更高的量子效率, 在平板显示和固态照明方面有极大的应用前景. 本工作将近几年来外量子效率高于20%的蓝光PHOLEDs中小分子主体材料进行总结, 并按空穴传输型、电子传输型和双极传输型主体材料分类, 重点介绍这些材料的分子结构、三线态能级、HOMO/LUMO能级、热稳定性、形态稳定性以及作为蓝光PHOLEDs主体材料的器件性能, 以期对主体材料的研究及OLED产业化提供参考价值.     

Dicyano-Imidazole: A Facile Generation of Pure Blue TADF Materials for OLEDs

A series of dicyano-imidazole-based molecules with thermally activated delayed fluorescence (TADF) properties were synthesized to obtain pure blue-emitting organic light-emitting diodes (OLEDs). The targeted molecules used dicyano-imidazole with a short-conjugated system as the electron acceptor to strong intermolecular π-π interactions, and provide a relatively shallow energy level of the lowest unoccupied molecular orbital (LUMO). The cyano group was selected to improve imidazole as an electron acceptor due to its prominent electron-transporting characteristics. Four different electron donors, that is, 9,9-dimethyl-9,10-dihydroacridine (DMAC), 10H-spiro(acridine-9,9’-fluoren) (SPAC), and 9,9-diphenyl-9,10-dihydroacridine (DPAC), were used to alternate the highest occupied molecular orbital (HOMO) energy level to tune the emission color further. The crowded molecular structure in space makes the electron donor and acceptor almost orthogonal, reducing the energy gap (ΔE_ST) between the first excited singlet (S₁) and the triplet (T₁) states and introducing significant TADF property. The efficiencies of the blue-emissive devices with imM-SPAC and imM-DMAC obtained in this work are the highest among the reported imidazole-based TADF-OLEDs, which are 13.8 % and 13.4 %, respectively. Both of Commission Internationale de l′Eclairage (CIE) coordinates are close to the saturated blue region at (0.17, 0.18) and (0.16, 0.19), respectively. Combining these tailor-made TADF compounds with specific device architectures, electroluminescent (EL) emission from sky-blue to deep-blue could be achieved, proving their great potential in EL applications.     

Phosphorescent Pt(II) Emitters for OLEDs: From Triarylboron‐Functionalized Bidentate Complexes to Compounds with Macrocyclic Chelating Ligands

The development of organic light‐emitting diodes (OLEDs) has attracted enormous research efforts from both academia and industry in the past decades and tremendous progress has been made. However, the low operation lifetime of the blue phosphorescent OLEDs remains as one of the greatest bottlenecks limiting further applications of OLEDs. To address this problem, design and synthesis of triplet emitters with high phosphorescence quantum yield (Φ_P) and adequate thermal, chemical, electrical and ultraviolet (UV) stabilities are vital. This review summarizes the progress we made on the development of efficient and robust phosphorescent emitters based on cyclometalated Pt(II) compounds, particularly the ones with blue emission, starting from complexes with triarylboron‐functionalized bidentate ligand to molecules incorporating tetradentate and macrocyclic ligands, with emphasis on their structure‐property relationships.     

Photoelectric and Self-Assembly Properties of Tetrasubstituted Pyrene Discotic Derivatives

To investigate the self-assembly behavior of π-conjugated ethynyl-pyrene discotic derivatives, a series of ethynyl-pyrene discotic materials were designed and synthesized by Sonogashira coupling reaction. The π-conjugated structures were characterized by ¹H-NMR, IR spectroscopy, and elemental analysis. The optical properties of the discotic materials were examined by UV/Vis spectra and fluorescence emission spectra. The band gap of each compound was calculated by cyclic voltammetry with UV/Vis spectroscopy. Interestingly, the substituted groups in the four symmetrical positions did affect the self-assembly properties of as-resulted nano/micro structures. Under the same conditions, compounds 4a–4d could be self-assembled into different morphologies such as micro-tubes (for 4a), micro-wires (for 4b and 4c), and micro-grain crystals (for 4d). All of the results indicated that the discotic materials have the potential for optoelectronic applications.     

Novel liquid crystalline organic semiconducting oligomers incorporating N-heterocyclic carbazole moieties for fluorescent OLEDs

A novel class of nematic liquid crystalline organic semiconducting oligomers incorporating N-heterocyclic carbazole moieties has been synthesised using simple and highly efficient reaction pathways. The electroluminescent colour of these novel oligomers can be varied in a controlled manner by molecular design. The values of the ionisation potential and the electron affinity of these electroluminescent oligomers can also be matched by structural design to the Highest Occupied Molecular Orbital (HOMO) energy level of the electron-blocking layer and the Lowest Unoccupied Molecular Orbital (LUMO) energy level of electron-transporting layer in the Organic light emitting diodes to create low charge-injection barriers for electrons and holes, respectively leading to electroluminescence with an efficacy up to 4.1 cd A^?1.     

新型苯并咪唑衍生物的合成及其生物活性

以香草醛为原料,经2步反应制得中间体--2-(4-羟基-3-甲氧基苯基)-1-氢-苯并咪唑(3); 3分别与取代苯甲酰氯,取代苯乙酰氯和取代苯磺酰氯反应,合成了13个新型的苯并咪唑衍生物(7a~7g, 8a, 8d, 8g, 9a, 9d和9g),其结构经¹H NMR, IR和HR-ESI-MS表征。分别用菌丝生长速率法和曹坳程法测试了7~9的抑菌活性和除草活性。结果表明：c=100 mg·L^-1时,7~9对番茄灰霉病菌,油菜菌核病菌和稻瘟病菌的抑制率分别为13.79%~65.38%, 13.88%~63.78%和34.22%~58.79%; c=300 mg·L^-1时,7g对稗草和反枝苋的芽长抑制率分别为40.20%和80.84%。     

新型蒽衍生物蓝光材料的合成及其光电性能

新型蒽衍生物蓝光材料的合成及其光电性能;蒽;芴;电致发光     

Novel oxazole-based emitters for high efficiency fluorescent OLEDs: Synthesis,characterization, and optoelectronic properties

Two novel oxazole derivatives 4-(6-(4,5-diphenyloxazol-2-yl)pyridin-3-yl)-N,N-diphenylaniline (TPA-PPO) and 2-(5-(4-(9H-carbazol-9-yl)phenyl)pyridin-2-yl)-4,5-diphenyloxazole (CzPh-PPO) have been designed and synthesized. The photophysical, electrochemical and thermal characters of the compounds were systematically investigated, which consistent well with the theoretical DFT calculations. TPA-PPO and CzPh-PPO exhibit high photoluminescent quantum yield of 0.63 and 0.59, respectively. The device using TPA-PPO as the dopant showed deep blue emission with a high EQE of 1.77%. A white OLED was obtained using the single emitter of CzPh-PPO with an EQE of 1.24%.     

新型苯并咪唑衍生物的合成

以苯甲醛甘油缩醛和对甲基苯甲醛甘油缩醛为原料,采用次氯酸钠催化氧化法,制得2-芳基-4-羧基-1,3-二氧戊环中间体;中间体分别与邻苯二胺或N-甲基邻苯二胺反应,合成了4种新型苯并咪唑衍生物(3a~3d),收率为78.0%~80.5%,其结构经UV, ¹H NMR, ¹³C NMR, IR和HR-MS(ESI)表征。      

新型苯并咪唑衍生物的合成及其抗凝血活性

以3-［(3-氨基-4-甲基氨基苯甲酰)吡啶-2-基氨基］丙酸乙酯为原料,与4-氰基-3-氟苯取代基乙酸经环化反应制得3-【【2-｛［(4-氰基-3-氟苯取代基）甲基］-1-甲基-1-H-苯并咪唑-5-基｝羰基】吡啶-2-基】氨基丙酸乙酯（3a, 3e）; 3经水解和酰胺化反应制得3-【【【2-｛［(4-氰基-3-氟苯基)取代基］甲基｝-1-甲基-1H-苯并咪唑-5-基】羰基】吡啶-2-基氨基】丙酰取代胺基（6a~6h）;6与乙酰氧肟酸经环合反应合成了8个新型的苯并咪唑衍生物（7a~7h）,其结构经1H NMR和HR-ESI-MS表征。抗凝血活性结果表明： 7a和7c的抗凝血活性最好,其aPTT值分别为(83.1±4.2) s和(80.7±2.9) s,优于阳性对照药达比加群酯(75.3±2.1)s。     

Disilane- and siloxane-bridged biphenyl and bithiophene derivatives as electron-transporting materials in OLEDs

Optical, electrochemical, and electron-transporting properties of disilane- and siloxane-bridged biphenyl and bithiophene derivatives were investigated, in comparison with those of the monosilane-bridged analogues (siloles). The UV spectra and cyclic voltammograms indicated that elongation of the silicon bridge suppresses the π-conjugation, in accordance with the results of DFT calculations. The DFT calculations indicated also that the disilane-bridged biphenyl and siloxane-bridged bithiophene should have the low-lying HOMOs and LUMOs. The electron-transporting properties were evaluated by the performance of triple-layered OLEDs having vapor-deposited films of the Si-bridged compound, Alq₃, and TPD, as the electron-transport, emitter, and hole-transport, respectively. Of these, the device with a disilane-bridged biphenyl exhibited the high performance with the maximum current density of 590 mA/cm² at the applied electric field of 12 × 10⁷ V/m (applied bias voltage = 13 V) and the maximum luminance of 22 000 cd/m² at 13 × 10⁷ V/m.     

A Rapid Access to Novel and Known Benzimidazole Derivatives Using Silica Chloride as a Reusable Catalyst

A new application of silica chloride as an easily available and reusable solid acid catalyst for the synthesis of benzimidazole and its derivatives through the condensation of o‐phenylenediamines and orthoesters under thermal and solvent‐free conditions is described. This novel and eco‐friendly method is very cheap and has many advantages including excellent yields, short reaction time, and simple work‐up procedure.     

新型吡啶类苯并咪唑衍生物的合成

合成了一系列取代吡啶亚甲基硫代苯并咪唑类衍生物 ,并在过氧乙酸的氧化下得到其相应的亚砜类化合物 ,收率较好 (76%～ 93 % ) .代替了用间氯过氧苯甲酸进行氧化 ,反应过程稳定 ,降低了成本 .产品的结构经元素分析、IR和1HNMR表征 .     

Synthesis of t-butylated diphenylanthracene derivatives as blue host materials for OLED applications

This paper describes the cost-effective synthesis and the photoluminescence of diphenylanthracene derivatives, which are found to be potential blue host materials for organic light emitting diode (OLED) technology.     

Versatile Benzimidazole/Triphenylamine Hybrids: Efficient Nondoped Deep‐Blue Electroluminescence and Good Host Materials for Phosphorescent Emitters

Two new bipolar compounds, N,N,N′,N′‐tetraphenyl‐5′‐(1‐phenyl‐1H‐benzimidazol‐2‐yl)‐1,1′:3′,1′′‐terphenyl‐4,4′′‐diamine ( 1 ) and N,N,N′,N′‐tetraphenyl‐5′‐(1‐phenyl‐1H‐benzimidazol‐2‐yl)‐1,1′:3′,1′′‐terphenyl‐3,3′′‐diamine ( 2 ), were synthesized and characterized, and their thermal, photophysical, and electrochemical properties were investigated. Compounds 1 and 2 possess good thermal stability with high glass‐transition temperatures of 109–129 °C and thermal decomposition temperatures of 501–531 °C. The fluorescence quantum yield of 1 (0.52) is higher than that of 2 (0.16), which could be attributed to greater π conjugation between the donor and acceptor moieties. A nondoped deep‐blue fluorescent organic light‐emitting diode (OLED) using 1 as the blue emitter displays high performance, with a maximum current efficiency of 2.2 cd A⁻¹ and a maximum external efficiency of 2.9 % at the CIE coordinates of (0.17, 0.07) that are very close to the National Television System Committee’s blue standard (0.15, 0.07). Electrophosphorescent devices using the two compounds as host materials for green and red phosphor emitters show high efficiencies. The best performance of a green phosphorescent device was achieved using 2 as the host, with a maximum current efficiency of 64.3 cd A⁻¹ and a maximum power efficiency of 68.3 lm W⁻¹; whereas the best performance of a red phosphorescent device was achieved using 1 as the host, with a maximum current efficiency of 11.5 cd A⁻¹, and a maximum power efficiency of 9.8 lm W⁻¹. The relationship between the molecular structures and optoelectronic properties are discussed.     

Novel four-pyridylbenzene-armed biphenyls as electron-transport materials for phosphorescent OLEDs

A series of four-pyridylbenzene-armed biphenyl derivatives were designed and synthesized as an electron-transport and exciton- and hole-block layer for the fac-tris(2-phenylpyridine)iridium (Ir(PPy)3)-based green phosphorescent organic light-emitting devices (OLEDs), giving improved efficiency in comparison to that with both the electron-transport layer of tris(8-hydroxyquinoline)aluminum (Alq3) and the exciton- and hole-block layer of 2,9-dimethyl-4,7-diphenylphenathroline (BCP).