Xiang-Yang Liu

Pure Hydrocarbon Hosts for ≈100% Exciton Harvesting in Both Phosphorescent and Fluorescent Light‐Emitting Devices

L.-S. Cui, Y.-M. Xie, Y.-K. Wang, Y.-L. Deng, X.-Y. Liu, Dr. Z.-Q. Jiang, Prof. L.-S. Liao Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM) & Collaborative Innovation Center of Suzhou Nano Science and Technology Soochow University Suzhou 215123 , PR China E-mail: zqjiang@suda.edu.cn; lsliao@suda.edu.cn Dr. C. Zhong Department of Chemistry Wuhan University Wuhan 430072 , PR China

Design and Synthesis of Pyrimidine-Based Iridium(III) Complexes with Horizontal Orientation for Orange and White Phosphorescent OLEDs

Two phosphorescent Ir(III) complexes Ir(ppm)2(acac) and Ir(dmppm)2(acac) were synthesized and characterized with emission ranged at 584/600 nm and high photoluminescence quantum yields (PLQYs) of 0.90/0.92, respectively. The angle-dependent PL spectra analysis reveals that the two orange iridium(III) complexes embodied horizontal orientation property. The high photoluminescence quantum yield and high horizontal dipoles ratio determine their excellent device performance. The devices based on Ir(ppm)2(acac) and Ir(dmppm)2(acac) achieved efficiencies of 26.8% and 28.2%, respectively, which can be comparable to the best orange phosphorescent devices reported in the literature. Furthermore, with the introduction of FIrpic as sky-blue emitter, phosphorescent two-element white organic light-emitting devices (OLEDs) have been realized with external quantum efficiencies (EQEs) as high as 25%, which are the highest values among the reported two-element white OLEDs.

Effective Host Materials for Blue/White Organic Light-Emitting Diodes by Utilizing the Twisted Conjugation Structure in 10-Phenyl-9,10-Dihydroacridine Block

Two new 10-phenyl-9,10-dihydroacridine derivatives attached by dibenzothiophene (DBT) and dibenzofuran (DBF) were synthesized. The influence of the substituents of these materials was studied by theoretical calculations (DFT calculation) and experimental measurements. Owing to the twisted N-phenyl ring, both molecules possess sufficiently high triplet energies and are suitable as hosts for phosphorescent organic light-emitting diodes. To evaluate the electroluminescent (EL) performance of these materials, FIrpic-based blue PHOLEDs and two-color white PHOLEDs (FIrpic and PO-01 as the dopants) were fabricated using the common device structures. High external quantum efficiencies (EQE) of 21.1 % and 20.9 % for FIrpic-based blue PHOLEDs were achieved by FPhAc and TPhAc, respectively. The white device based on the host FPhAc achieved a higher performance, with a maximum EQE of 24.7 % than the device with TPhAc as host material.

The study on two kinds of spiro systems for improving the performance of host materials in blue phosphorescent organic light-emitting diodes

The introduction of spiro-acridine-fluorene (SAF) can affect the electronic structure of the whole molecule, which made SAF-based materials exhibit totally different photophysical properties from conventional spirobifluorene-based materials. With these properties, an external quantum efficiency of nearly 25% was achieved for sky-blue phosphorescent organic light-emitting diodes.

The Control of Conjugation Lengths and Steric Hindrance to Modulate Aggregation-Induced Emission with High Electroluminescence Properties and Interesting Optical Properties

A series of novel AIE-active (aggregation-induced emission) molecules, named SAF-2-TriPE, SAF-3-TriPE, and SAF-4-TriPE, were designed and synthesized through facile reaction procedures. We found that incorporation of the spiro-acridine-fluorene (SAF) group, which is famous for its excellent hole-transporting ability and rigid structure, at different substitution positions on the phenyl ring affected the conjugation lengths of these compounds. Consequently, we have obtained molecules with different emission colors and properties without sacrificing good EL (electroluminescence) characteristics. Accordingly, a device that was based on compound SAF-2-TriPE displayed superior EL characteristics: it emitted green light with ηc, max =10.5 cd A(-1) and ηext, max =4.22 %, whereas a device that was based on compound SAF-3-TriPE emitted blue-green light with ηc, max =3.9 cd A(-1) and ηext, max = 1.71 %. These compounds also displayed different AIE performances: when the fraction of water in the THF solutions of these compounds was increased, we observed a significant improvement in the ΦF of compounds SAF-2-TriPE and SAF-3-TriPE; in contrast, compound SAF-4-TriPE showed an abnormal phenomenon, in that it emitted a strong fluorescence in both pure THF solution and in the aggregated state without a significant change in ΦF . Overall, this systematic study confirmed a relationship between the regioisomerism of the luminophore structure and its AIE activity and the resulting electroluminescent performance in non-doped devices.

Utilizing 9,10-dihydroacridine and pyrazine-containing donor–acceptor host materials for highly efficient red phosphorescent organic light-emitting diodes

Two novel materials, 10-(6-(dibenzo[b,d]furan-1-yl)pyrazin-2-yl)-9,9-diphenyl-9,10-dihydroacridine (PrFPhAc) and 10-(6-(dibenzo[b,d]thiophen-1-yl)pyrazin-2-yl)-9,9-diphenyl-9,10-dihydroacridine (PrTPhAc), were designed and synthesized by introducing heterocyclic pyrazine between 9,10-dihydroacridine and dibenzofuran/dibenzothiophene moieties. The basic properties, such as thermal, photophysical and electrochemical properties, were systematically investigated and compared. Both the materials have suitable triplet energies for red phosphorescent organic light-emitting diodes, and dibenzofuran (DBF) derivative PrFPhAc was finally achieved with superior external quantum efficiency of 22%.

Dispiro and Propellane: Novel Molecular Platforms for Highly Efficient Organic Light-Emitting Diodes

The incorporation of spatially oriented aromatic motifs in rigid molecular platforms is of great interest for the design of organic electronic materials. These structures can create unusual packing patterns and charge transport properties in the solid state which are not possible for simple planar structures. Herein, we showed that the novel dispiro and propellane motifs were successfully used as robust molecular platforms for the construction of host materials (TPA, Cz, SF, and SO). The propellane derivative with three functional groups arranged in the staggered conformation was studied for the first time as the host for organic light-emitting diodes (OLEDs). The green and red phosphorescent OLEDs hosted by these dispiro and propellane derivatives exhibited excellent electroluminescence performance. Particularly, the red OLED hosted by the propellane-type SF achieved maximum efficiencies of 47.3 cd A-1, 40.2 lm W-1, and 26.6% and 97.6 cd A-1, 77.8 lm W-1, and 27.0% for the green OLED without any light out-coupling enhancement. These results suggest that the dispiro and propellane molecular platforms have great potential in the construction of OLED materials.

Highly phosphorescent cyclometalated platinum(II) complexes based on 2-phenylbenzimidazole-containing ligands

A series of tetradentate cyclometalated platinum(II) complexes (Pt 1, Pt 2, and Pt 3) based on 2-phenylbenzimidazole-containing ligands have been prepared. Their photophysical properties were investigated by absorption and emission spectroscopy as well as density functional theory calculations. Due to the robustness of their coordination frameworks, these Pt(II) complexes exhibited excellent thermal stabilities with decomposition temperatures above 400 °C. The 2-phenylbenzimidazole motif was functionalized with a twisted aryl group, which discouraged intimate intermolecular interactions, thus leading to constant CIE coordinates at different doping ratios. The effect of replacing a coordinating pyridine group by thiazole and oxazole on photophysical properties, electrochemical behaviors, and electroluminescence performance was studied. Single crystal X-ray diffraction analyses of Pt 1 revealed a weak intra-molecular interaction, particularly a negligible Pt⋯Pt interaction, in the solid state, which was consistent with its electroluminescence properties at a high doping level. Organic light emitting diodes (OLEDs) based on these Pt(II) complexes were fabricated with a typical multiple layered device configuration. Among the three Pt(II) complexes, the pyridine-based Pt 1 compound showed the highest electroluminescence performance with maximum CE, PE, and EQE of 78.5 cd A−1, 66.4 lm W−1, and 22.3%, respectively.

High-Efficiency White Organic Light-Emitting Diodes Integrating Gradient Exciplex Allocation System and Novel D-Spiro-A Materials

How to maintain high power efficiency (PE) and color stability under operating brightness is critical for the white organic light-emitting diodes (WOLEDs). To this end, two novel spiro-type materials STPy3 and STPy4 were designed. These materials could act as a single host and achieve a remarkable external quantum efficiency of 27.5% at 1000 cd m-2; to further optimize the PEs of OLEDs, STPy3/4 and PO-T2T were used as co-host-induced exciplexes, which enhanced the PE of green OLED to over 148.0 lm W-1. Unfortunately, the lower triplet energy level of exciplexes than blue emitters implied it is commonly unsuitable to fabricate WOLEDs. Herein, a new allocation of gradient exciplex (AGE) strategy was developed in which the formed excitons could be rationally allocated in a consequently doped nonuniform profile. The AGE incorporated the advantages of the exciplex with an ultralow turn-on voltage of 2.3 V and efficiency stability of spiro materials. The PE at 1000 cd m-2 was enhanced to 72.7 lm W-1, representing the first exciplex WOLED with the performance exceeding that of conventional fluorescent tubes.

Novel carbazole derivatives designed by an ortho-linkage strategy for efficient phosphorescent organic light-emitting diodes

Two novel carbazole derivatives 2′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-4-carbonitrile (CNPhCz) and 2′-(9H-carbazol-9-yl)-[1,1′:3′,1′′-terphenyl]-4,4′′-dicarbonitrile (DCNPhCz) were designed and prepared as host materials for phosphorescent organic light-emitting diodes (PHOLEDs). CNPhCz and DCNPhCz were synthesized by an ortho-linkage strategy. In CNPhCz, one cyanophenyl and one carbazole unit were attached to the central benzene ring at the neighboring positions, while in DCNPhCz the carbazole group was surrounded by two cyanophenyl groups. The influence of different numbers of electron-withdrawing groups in these host materials on the charge-transport behavior and OLED device performance was studied systematically. Blue and green PHOLEDs based on these hosts were fabricated using common device structures with bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate iridium(III) (FIrpic) and bis(2-phenylpyridine) (acetylacetonate)iridium(III) (Ir(ppy)2(acac)) as the dopants, respectively. The results indicated that the material with a smaller number of electron-withdrawing cyanobenzene groups (CNPhCz) showed better green PHOLED device performance with maximum efficiencies of 88.0 cd A−1, 86.1 lm W−1 and 24.4%.