Optoelectronic properties of new functionalized heteroleptic iridium complex

A new functionalized heteroleptic iridium complex coordinated with 1-phenylisoquinoline(1-piq) and a functionalized β-diketone(G1),Ir(1-piq)2G1,was synthesized and characterized by 1H-NMR,mass spectrometry and elemental analysis.The larger conjugation of the replacement of acetylacetone(acac) by a functionalized β-diketonate ligand led to a significant decrease in the HOMO level toward vacuum level,while Ir(1-piq)2G1 and Ir(1-piq)2(acac) showed red phosphorescent emissions of about 620 nm in dichloromethane...     

Suppressed Triplet Exciton Diffusion Due to Small Orbital Overlap as a Key Design Factor for Ultralong‐Lived Room‐Temperature Phosphorescence in Molecular Crystals

Persistent room‐temperature phosphorescence (RTP) under ambient conditions is attracting attention due to its strong potential for applications in bioimaging, sensing, or optical recording. Molecular packing leading to a rigid crystalline structure that minimizes nonradiative pathways from triplet state is often investigated for efficient RTP. However, for complex conjugated systems a key strategy to suppress the nonradiative deactivation is not found yet. Here, the origin of small rates of a nonradiative decay process from triplet states of conjugated molecular crystals showing RTP is reported. Optical microscopy analysis showed that, despite a favorable molecular stacking, an aromatic crystal with strong RTP is characterized by small diffusion length and small values of the diffusion coefficient of triplet excitons. Quantum chemical calculations reveal a large overlap between the lowest unoccupied molecular orbitals but very small overlap between the highest occupied molecular orbitals (HOMOs). Inefficient electron exchange caused by the small overlap of HOMOs prevents triplet excitons from diffusing over long distances and consequently from quenching at defect sites inside the crystal or at the crystal surface. These results will allow design of comprehensive molecular structures to obtain molecular solids with more efficient RTP.     

Aggregation-induced Phosphorescence Enhancement in IrIII Complexes

Transition metal complexes that efficiently emit from an excited state with formally triplet character are an appealing class of compounds. However, they typically suffer from severe quenching, e. g. triplet-triplet annihilation, in aggregated phase that often hampers their use in the solid-state. Nonetheless, an intriguing effect, namely aggregation-induced phosphorescence enhancement, has been sometimes observed, but clear elucidation of the mechanisms underlying this phenomenon is far from trivial. Nowadays, cyclometalated Ir^III emitters play a leading role due to their outstanding features. Aiming at a rationalization of the AIPE effect, an overview of the different classes of Ir^III emitters displaying enhancement of the emission upon aggregation will be herein provided along with their potential applications. Their photophysical properties will be discussed jointly with their X-ray structural analysis. Ir^III complexes represent the largest family of AIPE-active compounds to date.     

Synergistic Intra‐ and Intermolecular Noncovalent Interactions for Ultralong Organic Phosphorescence

Metal‐free ultralong organic phosphorescence (UOP) materials have attracted significant attention owing to their anomalous photophysical properties and potential applications in various fields. Here, three pyrimidine‐based organic luminogens, 9‐(pyrimidin‐2‐yl)‐9H‐carbazole, 9‐(4,6‐dimethylpyrimidin‐2‐yl)‐9H‐carbazole, and 9‐(5‐bromopyrimidin‐2‐yl)‐9H‐carbazole are designed and synthesized, which show efficient yellow UOP with the longest lifetimes up to 1.37 s and the highest absolute phosphorescence quantum yields up to 23.6% under ambient conditions. Theoretical calculations, crystal structures, and photophysical properties of these compounds reveal that intramolecular hydrogen bonding, intermolecular π–π interactions, and intermolecular electronic coupling are responsible for forming dimers and generating highly efficient UOP. Their efficacy as solid materials for data encryption is demonstrated.     

Efficient Persistent Room Temperature Phosphorescence in Organic Amorphous Materials under Ambient Conditions

Persistent emission with a long lifetime (>1 s) from organic materials can only be observed at a low temperature, because of the significant nonradiative deactivation pathway that occurs at room‐temperature (RT). If organic materials with persistent RT emission in air could be developed, they could potentially be utilized for a variety of applications. Here, organic host‐guest materials with efficient persistent RT phosphorescence (RTP) are developed by minimizing the nonradiative deactivation pathway of triplet excitons. The nonradiative deactivation pathway is dependent on both nonradiative deactivation of the guest and quenching by diffusional motion of the host. The rigidity and oxygen barrier properties of the steroidal compound used as the host suppressed the quenching, and the aromatic hydrocarbon used as the guest is highly deuterated to minimize nonradiative deactivation of the guest. Red‐green‐blue persistent RTP with a lifetime >1 s and a quantum yield >10% in air is realized for a pure organic material.     

发光性能稳定的磷光与荧光复合型白光OLED

使用荧光染料TBPe和Ir(ppy)_2acac 、R-4B两种光染料,采用蓝/红绿双发光层的结构,并结合TPBi对空穴的有效限制作用 ,制备了结构为ITO/MoO₃(X nm)/ADN:(2%)TBPe(30 nm)/CBP:Ir(ppy)_2acac(14%):R-4B(2%)(5nm)/TPBi(10 nm)/Alq₃(30nm)/LiF(1nm )/Al(100nm)的磷光与荧光复合的白光OLED,其中,MoO₃的厚 分别为0、15、20、30和40nm,通过改变MoO₃的厚度调控载流子的注入能力,使用空穴阻挡层提高光效; 通过测量其电压、电流、亮度、色坐标和电致发光(EL)光谱等参数,研究不同厚度的MoO ₃对器件发光性能的影响。结果表明,在MoO₃厚为20nm的情况下,器件的效率滚降 最为平缓。在电压分别 为8、9、10、11、12和13V时,器件的色坐标分别为 (0.31,0.33)、(0.30,0.33)、(0.29,0.33)、(0.29,0.33)、(0.29,0.33)和(0.29, 0.33),具有较高的稳定性,原因为采用 蓝/红绿双发光层结构更有利于蓝光的 出射,且使用ADN主体材料掺杂蓝色荧光染料TBPe作为蓝光发光层降低三重态-三重态 湮灭几率。 研究还发现,在电压为11V、器件的亮度为9744cd/m²和电流密度为11.50mA/cm²时,最大器件的电流效率为 7.0cd/A。     

非硅醇盐无机溶胶凝胶法合成蓝色发光材料Sr_2MgSi_2O_7:Eu~(2+),Dy~(3+)

以水玻璃(Na2SiO3)为硅源,柠檬酸三铵为PH值调节剂,通过离子交换,采用溶胶凝胶法低温合成Sr2MgSi2O7Eu2+,Dy3+蓝色发光材料。采用DTA、XRD、荧光光谱等手段对材料进行分析和表征,结果表明:前驱体干凝胶煅烧到1010℃后开始有Sr2MgSi2O7相形成,到1100℃完全转变成高纯相Sr2MgSi2O7,其产物疏松,颗粒小,不需研磨或稍加研磨便得超细粉。它的激发光谱在250～450nm之间存在一个强度较高的激发带,发射峰位于467nm,余辉时间超8h。此外,对溶胶凝胶的形成机理等进行了讨论。     

Phenylimidazole-based homoleptic iridium(III) compounds for blue phosphorescent organic light-emitting diodes with high efficiency and long lifetime

In order to obtain triplet emitters with high stability and efficiency, three homoleptic iridium(III) compounds — specifically, Ir(tpim)₃ (1), Ir(mtpim)₃ (2), and Ir(itpim)₃ (3), where tpim = 1-([1,1′:3′,1″-terphenyl]-2′-yl)-2-(4-fluorophenyl)-1H-imidazole, mtpim = 2-(4-fluorophenyl)-1-(5′-methyl-[1,1′:3′,1″-terphenyl]-2′-yl)-1H-imidazole, and itpim = 2-(4-fluorophenyl)-1-(5′-isopropyl-[1,1′:3′,1″-terphenyl]-2′-yl)-1H-imidazole — were prepared by one-pot reaction of the corresponding phenylimidazole ligand with an Ir(I) complex as a starting material. Compounds 1–3 emit bright sky-blue phosphorescence with λ_max = 459–463 nm and phosphorescent quantum efficiencies of 0.38–0.50. Multi-layer phosphorescent organic light-emitting diodes using compounds 1–3 as the triplet emitters and mCBP (3,3-di(9H-carbazol-9-yl)biphenyl) as the host have been fabricated. Compound 3 doped in the emissive layer demonstrate external quantum efficiency as high as 20.1% at 1000 cd/m². In addition, the device based on compound 1 as an emitter shows a stable lifetime greater than 300 h at 1000 cd/m², which is one of the best results concerning the device lifetime.     

Multifunctional Triphenylamine/Oxadiazole Hybrid as Host and Exciton‐Blocking Material: High Efficiency Green Phosphorescent OLEDs Using Easily Available and Common Materials

A new triphenylamine/oxadiazole hybrid, namely m‐TPA‐o‐OXD, formed by connecting the meta‐position of a phenyl ring in triphenylamine with the ortho‐position of 2,5‐biphenyl‐1,3,4‐oxadiazole, is designed and synthesized. The new bipolar compound is applicable in the phosphorescent organic light‐emitting diodes (PHOLEDs) as both host and exciton‐blocking material. By using the new material and the optimization of the device structures, very high efficiency green and yellow electrophosphorescence are achieved. For example, by introducing 1,3,5‐tris(N‐phenylbenzimidazol‐2‐yl)benzene (TPBI) to replace 2, 9‐dimethyl‐4,7‐diphenyl‐1, 10‐phenanthroline (BCP)/tris(8‐hydroxyquinoline)aluminium (Alq₃) as hole blocking/electron transporting layer, followed by tuning the thicknesses of hole‐transport 1, 4‐bis[(1‐naphthylphenyl)amino]biphenyl (NPB) layer to manipulate the charge balance, a maximum external quantum efficiency (η_EQE,max) of 23.0% and a maximum power efficiency (η_p,max) of 94.3 lm W⁻¹ are attained for (ppy)₂Ir(acac) based green electrophosphorescence. Subsequently, by inserting a thin layer of m‐TPA‐o‐OXD as self triplet exciton block layer between hole‐transport and emissive layer to confine triplet excitons, a η_EQE,max of 23.7% and η_p,max of 105 lm W⁻¹ are achieved. This is the highest efficiency ever reported for (ppy)₂Ir(acac) based green PHOLEDs. Furthermore, the new host m‐TPA‐o‐OXD is also applicable for other phosphorescent emitters, such as green‐emissive Ir(ppy)₃ and yellow‐emissive (fbi)₂Ir(acac). A yellow electrophosphorescent device with η_EQE,max of 20.6%, η_c,max of 62.1 cd A⁻¹, and η_p,max of 61.7 lm W⁻¹, is fabricated. To the author’s knowledge, this is also the highest efficiency ever reported for yellow PHOLEDs.     

Surface temperature of decomposing construction materials studied by laser‐induced phosphorescence

Measurements of surface temperature and mass loss of decomposing construction materials during rapid pyrolysis are presented. Experiments have been performed with samples of low‐density fiberboard, medium‐density fiberboard, particleboard and poly(methyl methacrylate) in a single particle reactor at temperatures between 300° and 600°C. Ultraviolet laser light was used to excite micrometer‐sized thermographic phosphor particles that were deposited on the investigated materials, and the temperature was obtained from temporally resolved measurements of the laser‐induced emission. The wood‐based materials show a similar behavior, with small differences being attributed to differences in material properties. The surface temperature rapidly increases to about 400°C when a particle is introduced to the hot reactor. The initial phase is followed by rapid decomposition during which the surface temperature is 380°–540°C. The heating rate is slowed down during the rapid pyrolysis, and again increases as the remaining char is heated to the reactor temperature. The poly (methyl methacrylate), however, melts and at high temperatures can be characterized as a liquid with a boiling point of about 400°C. Thermographic phosphors are concluded to be suitable for high precision remote measurements of the surface temperature of decomposing construction materials, and possibilities for further studies and developments of the technique are discussed. Copyright © 2004 John Wiley & Sons, Ltd.