Organic Host Materials for Solution-Processed Phosphorescent Organic Light-Emitting Diodes

As a new technology for flat-panel displays and general lighting sources, solution-processed phosphorescent organic light-emitting diodes (PhOLEDs) unfurl a bright future, due to their merits of high quantum efficiency and easy fabrication. In recent years, great progress has been made in the device performance of solution-processed PhOLEDs, by developing both high-efficiency organometallic phosphors and novel solution-processable organic host materials. This review highlights recently developed organic host materials for triplet guest emitters in solution-processed PhOLEDs. The solution-processable host materials are classified into three types – small molecule, dendrimer, and polymer – according to their molecular architecture and molecular weight. The material design concept and the relationships between the molecular structure, material properties and device performance are the focus of this discussion. A future strategy for the development of high-performance solution-processed host materials is proposed.     

带烷氧基的苯基蒎烯吡啶铱配合物在聚合物电致发光器件中的应用研究

采用旋涂法将一组带烷氧基的苯基蒎烯吡啶铱（Ⅲ）配合物（It（ROPPPY）3）磷光材料掺杂到PVK中,制作出了聚合物电致发光器件：ITO／PEDOT：PSS（40nm）／PVK0.7：PBD0．3：（x％．）Ir—complex（80nm）／CsV（1．5nm）／Mg：Ag（200nm）．实验结果表明,带有长烷氧基链配体的铱（Ⅲ）配合物能表现出更好的器件行为,当掺杂浓度为3．2％时,器件的最高发光效率达19．9cd／A（7．8lm／W,9．1V）,CIE为（0．20,0．56）;器件最大亮度为15700cd／m^2（8．4V）．通过对这组铱（Ⅲ）配合物的光物理行为及电化学性能的研究,考察了主体材料与配合物之间的能级配置以及能量转移的机理、     

Recent Progresses of Iridium Complex-Containing Macromolecules for Solution-Processed Organic Light-Emitting Diodes

Recent progresses of iridium complexes-containing macromolecules, including the linear polymers, dendrimers as well as supramolecular polymers, for solution-processable phosphorescent organic light-emitting devices, have been reviewed. The synthesis, structural characterization and optoelectronic properties of iridium-based electrophosphorescent materials are summarized.     

高效溶液法小分子磷光电致发光器件研究

以小分子化合物CDBP[4，4＇-bis（carbazo1．9-yl）-9，9-dimethyl-fluorene]为主体材料，Ir（pppy）3[tris（5-phenyl-10，10-dimethyl-4-aza—tficycloundeca-2，4，6-triene）Iridium（Ⅲ）]为磷光客体材料，采用溶液法和真空蒸镀法相结合的制备工艺，制作了小分子磷光电致发光器件．研究表明，通过器件结构的优化，Ir（pppy）3（重量百分比为2）掺杂的多层绿光电致发光器件效率达22．0cd／A，最大亮度达到26600cd／m^2，这一结果可与当今基于真空蒸镀的小分子或基于溶液法的高分子磷光电致发光器件性能相媲美．本工作为降低有机电致发光器件的成本，扩展溶液法有机电致发光器件制备工艺中材料的选择范围提供了实验依据．     

铱配合物磷光探针的合成及细胞荧光成像

磷光铱配合物具有良好的光热稳定性、发光颜色可调性、较长的激发寿命和较高的发光效率等特点。以2-苯基并噻唑衍生物(含有醛基、乙氧基和叔丁基)为主配体、1,10-邻菲罗啉为辅助配体,合成3个磷光铱配合物。通过核磁共振谱和高分辨质谱对其结构进行表征,利用荧光光谱和紫外-可见吸收光谱对其发光性能进行研究,并测试了磷光铱配合物的细胞荧光成像作用。     

Deep-Blue Phosphorescent Emitters with Phosphoryl Groups for Organic Light-Emitting Diodes by Solution Processes

The new deep-blue iridium complex, Ir(dppfm)₂pic, consisting of a phosphoryl group at the 3′-position of the phenyl ring and a methyl group at the 4-position of pyridine, was synthesized and characterized for applications in organic light-emitting diodes (OLEDs). Ir(dppfm)₂pic exhibited an emission peak of 455 nm and high photoluminescence quantum yields of 73 %. Phosphorescent OLEDs based on Ir(dppfm)₂pic exhibited a maximum external quantum efficiency of 7.8 % and Commission Internationale de l’Eclairage (CIE) coordinates of (0.15, 0.22).     

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.     

Controlling Polymer Solubility: Polyfluorenes with Branched Semiperfluorinated Side Chains for Polymer Light-Emitting Diodes

A series of novel polyfluorenes, soluble exclusively in perfluorinated solvents, were prepared. The new materials were studied with regard to orthogonal processing of organic electronic materials. The desired solubility was achieved by introducing semifluorinated side chains to the fluorene monomers. Since the use of long perfluoroalkyl chains (R^F) is restricted due to public health concerns, a synthetic route for polyfluorenes with short R^F chains branched by aromatic units has been developed. The photophysical behavior of the resulting polymers was investigated in solution and thin films by UV/Vis absorption and photoluminescence spectroscopy. The photoluminescence quantum yields were found to be in the range of those of alkylated polyfluorenes. The electroluminescent properties were studied in single-layer polymer light-emitting diodes, with the new polymers as active materials, which exhibited similar characteristics to previously published single-layer devices with polyfluorenes containing long R^F. The wetting properties of different polyfluorene films containing fluorinated, polar, polyethylene glycol, or nonpolar alkyl groups were investigated by contact angle measurements.     

Triazole and Pyridine Hybrid Molecules as Electron-Transport Materials for Highly Efficient Green Phosphorescent Organic Light-Emitting Diodes

A series of triazole and pyridine hybrid molecules, with a triazole core and pyridine periphery, were designed and synthesized as an electron-transport layer (ETL) and a hole/exciton-block layer for green phosphorescent organic light-emitting diodes. Compared with the widely-used electron-transport material (ETM) of 3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole (TAZ) with a triazole core, lower-lying HOMO and LUMO energy levels were obtained with the introduction of pyridine rings onto the periphery of the molecules, giving improved electron injection and carrier confinement. Significantly reduced driving voltages were achieved in a device structure of ITO/HATCN (5 nm)/TAPC (40 nm)/CBP:8 wt % Ir(PPy)₃ (10 nm)/ETL (40 nm)/LiF (1 nm)/Al (90 nm), giving a maximum power efficiency of 72.2 lm W⁻¹ and an external quantum efficiency of 21.8 %, due to the improved electron injection and transport and thus, more balanced carrier recombination, which are much higher than those of the device based on TAZ.     

Modification of Conductive Polymer for Polymeric Anodes of Flexible Organic Light-Emitting Diodes

A conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), was modified with dimethyl sulfoxide (DMSO) in solution state, together with sub-sequential thermal treatment of its spin-coated film. The electrical conductivity increased by more than three orders of magnitude improvement was achieved. The mechanism for the conductivity improvement was studied at nanoscale by particle size analysis, field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). Smaller particle size was observed, resulting in larger contact area and better electrical conductive connections. Connection of conductive PEDOT increased on the surface of the PEDOT:PSS particles, which promoted high conductivity. Flexible anodes based on the modified PEDOT:PSS were fabricated. Flexible organic light-emitting diodes (FOLED) based the polymeric anodes have a comparable performance to those on indium–tin–oxide (ITO) anodes.     

Role of Solution-Processable Polyethylenimine Electrode Interlayer in Fabricating Air-Stable Polymer Light-Emitting Diodes

This work investigates the mechanisms for the enhanced injection of electrons from a solution-processable polyethyleneimine (PEI) interlayer/aluminum (Al), silver (Ag), or gold (Au) electrodes in phenyl-substituted poly(para-phenylene vinylene) (PPV) copolymer (SY-PPV)-based polymer light-emitting diodes (PLEDs). The bilayer cathode significantly enhances electron injection and device performance, and is comparable to that of PLEDs using low work function metals, such as calcium (Ca) or lithium fluoride (LiF)/Al as the cathode. The functions of the PEI interlayer are characterized by current density light intensity voltage (J L V) and photovoltaic measurements, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy. The thin PEI film forms a dipole layer to shift the vacuum level of the electroluminescent polymer and decrease the barrier height for electron injection. The existing dipoles are correlated with a large numbers of amino groups in the PEI polymer. As a result, the PLEDs with PEI/Al, PEI/Ag, and PEI/Au bilayer cathodes exhibit markedly enhanced performances. The application of air-stable metals as the cathode allows flexibility in the design of device cathode structures for real applications.     

Rational Design of Phosphorescent Iridium(III) Complexes for Selective Glutathione Sensing and Amplified Photodynamic Therapy

It is a huge challenge to avoid irreversible damage to normal tissues during irradiation in photodynamic therapy (PDT) for cancer. An effective strategy is to develop smart photosensitizers, which exhibit amplified generation of reactive oxygen species (ROS) through triggering specific reaction in the tumor microenvironment. In this work, we designed a class of glutathione (GSH)-activatable photosensitizers ( Ir1 and Ir4 ) based on an effective strategy of GSH-induced nucleophilic substitution reaction. The addition of GSH, induced changes in both phosphorescence intensity and lifetime of photosensitizers with high sensitivity. Importantly, the amount of singlet oxygen generated was increased significantly by GSH-induced activation reaction. Hence, the photosensitizers can selectively distinguish cancer cells from normal cells through luminescence and lifetime imaging, and can amplify PDT effects in cancer cells, owing to the evidently higher level of GSH compared to normal cells. This work presents a novel paradigm for GSH-amplified PDT against cancer cells and provides a new avenue for smart-responsive theranostic systems that can avoid nonspecific damage to normal cells.     

Langmuir and Langmuir-Blodgett Films of Polyfluorenes and Their Use in Polymer Light-Emitting Diodes

The Langmuir and Langmuir-Blodgett (LB) film properties of two polyfluorene derivatives, namely poly(2,7-9,9′-dihexylfluorene-dyil) (PDHF) and poly(9,9 dihexylfluorene-dyil-vynilene-alt-1,4-phenylene-vyninele) (PDHF-PV), are reported. Surface pressure (П-A) and surface potential (ΔV-A) isotherms indicated that PDHF-PV forms true monolayers at the air/water interface, but PDHF does not. LB films could be transferred onto various types of substrate for both PDHF and PDHF-PV. Only the LB films from PDHF-PV could withstand deposition of a layer of evaporated metal to form a light-emitting diode (PLED), which had typical rectifying characteristics and emitted blue light. It is inferred that the ability of the polymer to form true monomolecular layers at the air/water interface seems to be associated with the viability of the LB films in PLEDs.     

Novel Structures for Porous Silicon Light-Emitting Diodes

In this paper, two novel structures of porous silicon (PS) light-emitting diodes (LEDs) are proposed aiming at the reduction of series resistance, R_s. The basic idea of the novel structures is to suppress the excessive growth of nanoporous silicon (nano-PS) layer that is electroluminescence- (EL-) active but highly resistive. The initial wafer of the first structure consists of a lightly-doped layer stacked on a highly-doped substrate. As a consequence of anodization, nano-PS layer is formed only in the lightly-doped layer, while meso-PS layer with moderate resistivity is formed in the highly-doped substrate. The second structure consists of alternately stacked nano- and meso-PS layers, since it is expected that multiple thin nano-PS layers connected in series are less resistive than a single thick nano-PS layer. Preliminary experimental results proved the effectiveness of these novel structures on the reduction of R_s.     

Cu(I)配合物磷光材料的研究进展

光功能Cu(I)配合物是近年来新材料领域的一个亮点.介绍Cu(I)配合物发光原理,和常见的几种Cu(I)配体及应用开发等方面的研究进展     

Nanocrystallized Organic Thin Films as Effective Light Outcoupling Layers for Organic Light-Emitting Diodes

Light outcoupling from organic light-emitting diodes (OLEDs) is essential for developing energy-saving displays and efficient lighting sources. Nanocrystallized organic thin films exhibiting scattering features have been considered as effective light extractors for OLEDs. This paper reviews recent advancements in nanocrystallized thin films and their applications in OLEDs. Due to the advantages of easy preparation and OLED compatibility, nanocrystallized organic thin films can integrate with OLEDs as external or internal light extractors easily. Significant light enhancement has been achieved. The fabrication methods and mechanisms of light enhancement are discussed.     

Iridium Complexes as a Roadblock for DNA Polymerase during Amplification

Iridium‐based metal complexes containing polypyridyl‐pyrazine ligands show properties of DNA intercalation. They serve as roadblocks to DNA polymerase activity, thereby inhibiting the polymerization process. Upon the addition of increasing concentrations of these iridium complexes, a rapid polymerase chain reaction (PCR)‐based assay reveals the selective inhibition of the DNA polymerization process. This label‐free approach to study the inhibition of fundamental cellular processes via physical roadblock can offer an alternative route toward cancer therapy.