Jingui Qin

Bio: Jingui Qin is an academic researcher from Wuhan University. The author has contributed to research in topics: Triphenylamine & Chromophore. The author has an hindex of 68, co-authored 384 publications receiving 15844 citations. Previous affiliations of Jingui Qin include Chinese Academy of Sciences.

Organic host materials for phosphorescent organic light-emitting diodes

Abstract: Phosphorescent organic light-emitting diodes (PhOLEDs) unfurl a bright future for the next generation of flat-panel displays and lighting sources due to their merit of high quantum efficiency compared with fluorescent OLEDs. This critical review focuses on small-molecular organic host materials as triplet guest emitters in PhOLEDs. At first, some typical hole and electron transport materials used in OLEDs are briefly introduced. Then the hole transport-type, electron transport-type, bipolar transport host materials and the pure-hydrocarbon compounds are comprehensively presented. The molecular design concept, molecular structures and physical properties such as triplet energy, HOMO/LUMO energy levels, thermal and morphological stabilities, and the applications of host materials in PhOLEDs are reviewed (152 references).

A Simple Carbazole/Oxadiazole Hybrid Molecule: An Excellent Bipolar Host for Green and Red Phosphorescent OLEDs

Abstract: Phosphorescent organic light-emitting diodes (PHOLEDs) continue to attract intense interest because they can, in theory, approach a 100% internal quantum efficiency by utilizing both singlet and triplet excitons. To achieve highly efficient electrophosphorescence by reducing competitive factors such as concentration quenching and triplet–triplet annihilation, phosphorescent emitters of heavy-metal complexes are usually doped into a suitable host material. Thus the synthesis of host materials and dopants are equally important for the formation of efficient PHOLEDs. It is desirable that the host materials have a large enough bandgap for effective energy transfer to the guest, good carrier transport properties for a balanced recombination of carriers in the emitting layer, and energy-level matching with neighboring layers for effective charge injection. Recently, bipolar hosts have aroused considerable interests in the area of organic light-emitting diodes (OLEDs) because they can provide more balance in electron and hole fluxes and simplify device structure. However, a compromise is required between the bipolar transporting property and band gap of the material, because the electron-donating and electron-withdrawing moieties in bipolar molecules unavoidably lower the band gap of the material by intramolecular charge transfer, while the low triplet energy of the host can cause reverse energy transfer from the guest back to the host, which consequently decreases the efficiency of PHOLEDs. To address this issue, most recent molecular designs focus on the interruption of the p conjugation between electron-donating and electron-withdrawing moieties by the incorporation of steric groups and/or meta linkages between the two moieties. Efficient blue (46 lmW , 24%), green (27.3 cdA ) and orange (22 cdA , 7.8%) electrophosphorescence from such small bipolar host molecules has been reported. Carbazole derivatives can be used as host materials because of their high triplet energy and good hole-transporting ability. For example, 4,4’-N,N’-dicarbazolbiphenyl (CBP) is a popular host for triplet emitters. PHOLEDs that use CBP as a host material for various dopants have been reported to have peak efficiencies as high as 28 cdA 1 for green (fac-tris(2-phenylpyridinato-N,C)iridium, [Ir(ppy)3]), [1a] 52 cdA 1 for green (tris[3,6-bis(phenyl)-pyridazinato-N,C]iridium [Ir(BPPya)3]) [7] and 5.82 cdA 1 for deep red (a dendritic iridium complex). Unfortunately, the CBP host is prone to crystallization, especially when the dopant concentration is too low. Furthermore, red PHOLEDs containing a CBP host usually need high driving voltages because the poor energy match between CBP and adjacent holeand electron-transporting layers can result in insufficient and/or unbalanced injection of holes and electrons. It is a worthwhile target to develop host materials with good thermal stability and matching energy levels to replace CBP. Oxadiazole derivatives have been proven to be very effective in improving the injection and transport of electrons. For example, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) and 1,3-bis[4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD7) are usually incorporated in OLEDs as electron-transport materials. Herein we report a novel carbazole/oxadiazole hybrid molecule o-CzOXD linked through the 9-position of carbazole with the ortho position of 2,5-diphenyl-1,3,4-oxadiazole. The bipolar molecule o-CzOXD was easily prepared by an aromatic nucleophilic substitution reaction between carbazole and the fluoroarene, which was activated by the electron-withdrawing oxadiazole, with good yields of over 80% (Scheme 1). The reaction proceeded in the absence of any catalyst, and the product was easily purified by recrystallization from CHCl3/C2H5OH rather than column chromatography. Thus, this simple method has obvious advantages over common palladium-catalyzed coupling reactions. oCzOXD was characterized by H NMR and C NMR spectroscopy, mass spectrometry, and elemental analysis; its molecular structure was further confirmed by X-ray crystallography (Figure 1). The dihedral angle between the carbazole unit and the phenyl ring is 51.48 ; this twist in the

Similar or Totally Different: The Control of Conjugation Degree through Minor Structural Modifications, and Deep-Blue Aggregation-Induced Emission Luminogens for Non-Doped OLEDs

Abstract: Four 4,4-bis(1,2,2-triphenylvinyl)biphenyl (BTPE) derivatives, 4,4-bis(1,2,2-triphenylvinyl)biphenyl, 2,3-bis(1,2,2-triphenylvinyl)biphenyl, 2,4-bis(1,2,2-triphenylvinyl)biphenyl, 3,3-bis(1,2,2-triphenylvinyl)biphenyl and 3,4-bis(1,2,2-triphenylvinyl)biphenyl (oTPE-mTPE, oTPE-pTPE, mTPE-mTPE, and mTPE-pTPE, respectively), are successfully synthesized and their thermal, optical, and electronic properties fully investigated. By merging two simple tetraphenylethene (TPE) units together through different linking positions, the -conjugation length is effectively controlled to ensure the deep-blue emission. Because of the minor but intelligent structural modification, all the four fluorophores exhibit deep-blue emissions from 435 to 459 nm with Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of, respectively, (0.16, 0.14), (0.15, 0.11), (0.16, 0.14), and (0.16, 0.16), when fabricated as emitters in organic light-emitting diodes (OLEDs). This is completely different from BTPE with sky-blue emission (0.20, 0.36). Thus, these results may provide a novel and versatile approach for the design of deep-blue aggregation-induced emission (AIE) luminogens.

Aggregation-Induced Emission: Together We Shine, United We Soar!

Abstract: Ju Mei,†,‡,∥ Nelson L. C. Leung,†,‡,∥ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,†,‡ and Ben Zhong Tang*,†,‡,§ †HKUST-Shenzhen Research Institute, Hi-Tech Park, Nanshan, Shenzhen 518057, China ‡Department of Chemistry, HKUST Jockey Club Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, State Key Laboratory of Molecular Neuroscience, Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China

Aggregation-induced emission

Abstract: Luminogenic materials with aggregation-induced emission (AIE) attributes have attracted much interest since the debut of the AIE concept in 2001. In this critical review, recent progress in the area of AIE research is summarized. Typical examples of AIE systems are discussed, from which their structure–property relationships are derived. Through mechanistic decipherment of the photophysical processes, structural design strategies for generating new AIE luminogens are developed. Technological, especially optoelectronic and biological, applications of the AIE systems are exemplified to illustrate how the novel AIE effect can be utilized for high-tech innovations (183 references).

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

Abstract: A review was presented to demonstrate a historical description of the synthesis of light-emitting conjugated polymers for applications in electroluminescent devices. Electroluminescence (EL) was first reported in poly(para-phenylene vinylene) (PPV) in 1990 and researchers continued to make significant efforts to develop conjugated materials as the active units in light-emitting devices (LED) to be used in display applications. Conjugated oligomers were used as luminescent materials and as models for conjugated polymers in the review. Oligomers were used to demonstrate a structure and property relationship to determine a key polymer property or to demonstrate a technique that was to be applied to polymers. The review focused on demonstrating the way polymer structures were made and the way their properties were controlled by intelligent and rational and synthetic design.

Aggregation-Induced Emission: The Whole Is More Brilliant than the Parts

Abstract: "United we stand, divided we fall."--Aesop. Aggregation-induced emission (AIE) refers to a photophysical phenomenon shown by a group of luminogenic materials that are non-emissive when they are dissolved in good solvents as molecules but become highly luminescent when they are clustered in poor solvents or solid state as aggregates. In this Review we summarize the recent progresses made in the area of AIE research. We conduct mechanistic analyses of the AIE processes, unify the restriction of intramolecular motions (RIM) as the main cause for the AIE effects, and derive RIM-based molecular engineering strategies for the design of new AIE luminogens (AIEgens). Typical examples of the newly developed AIEgens and their high-tech applications as optoelectronic materials, chemical sensors and biomedical probes are presented and discussed.