Co-reporter:Hui Xu, Zhi-Feng Xu, Zheng-Yu Yue, Peng-Fei Yan, Bin Wang, Li-Wei Jia, Guang-Ming Li, Wen-Bin Sun and Ju-Wen Zhang
The Journal of Physical Chemistry C October 2, 2008 Volume 112(Issue 39) pp:15517-15525
Publication Date(Web):September 6, 2008
DOI:10.1021/jp803325g
A novel deep blue-emitting ZnII complex Zn(Lc)2 (Lc− = 2-(1-(6-(9H-carbazol-9-yl)hexyl)-1H-benzo[d]imidazol-2-yl)phenolate) based on a carbazole-functionalized N^O ligand was synthesized by a modified method. Other two ZnII complexes (Zn(La)2, La− = 2-(1H-benzo[d]imidazol-2-yl)phenolate; Zn(Lb)2, Lb− = 2-(1-ethyl-1H-benzo[d]imidazol-2-yl)phenolate) were also prepared for comparison. The remarkable substitution effect on the photoluminescent and thermal properties of the complexes was studied. The investigation indicated an unexpected amplifying hypsochromic effect of the substituents on the emission of the complex in the solid state: the larger substituent corresponded to the larger blue shift of the emission of the complex (Zn(Lc)2 has the shortest emission wavelength of 422 nm as the deep blue emission among these three complexes). The stronger steric effect induced by the bulky substitutions should be one of the most important factors. Among the three ZnII complexes, the temperature of decomposition of Zn(Lc)2 is the highest at 427 °C. Cyclic voltammetry (CV) of the complexes showed that the carbazole moieties remarkably improved the hole injection ability of Zn(Lc)2 with the HOMO energy level 0.6 eV higher than those of Zn(La)2 and Zn(Lb)2. The good hole injection and transporting ability of Zn(Lc)2 was further proved by its three-layer devices, in which the electroluminescent (EL) emission mainly originated from the electron-transporting Alq3 layer. Through the four-layer devices with the hole-blocking layer, the pure blue emission of Zn(Lc)2 at 452 nm was demonstrated. Zn(Lc)2 seems favorable among the blue-emitting ZnII complexes with a brightness more than 2000 cd m−2, a high efficiency stability, and an excellent EL spectra stability.
Co-reporter:Mingchen Xie, Chunmiao Han, Jing Zhang, Guohua Xie, and Hui Xu
Chemistry of Materials August 22, 2017 Volume 29(Issue 16) pp:6606-6606
Publication Date(Web):August 1, 2017
DOI:10.1021/acs.chemmater.7b01443
Co-reporter:Hui Xu, Rui Zhu, Ping Zhao, and Wei Huang
The Journal of Physical Chemistry C August 11, 2011 Volume 115(Issue 31) pp:15627-15638
Publication Date(Web):July 13, 2011
DOI:10.1021/jp2029714
Two metallopolymers P1 and P2 were prepared by using a novel polymerizable Eu3+ complex Eu(TTA)3VBADPO (EuMA) (TTA = 2-thenoyltrifluoroacetonate) and vinylcarbazole as the monomers in the ratios of 1:99 and 3:97, respectively, in which VBADPO is 2-(diphenylphosphoryl)-N-(2-(diphenylphosphoryl)-4-methoxyphenyl)-4-methoxy-N-(4-vinylbenzyl)aniline as a polymerizable aryl phosphine oxide ligand with a bipolar structure. The copolymers exhibit the excellent optical properties with photoluminescence quantum yield more than 60% in film. Both Gaussian simulation and electrochemical analysis indicated that the Eu3+-complexed segments form double-carrier traps (Eu-trap) in the copolymers with depth of 0.1 eV for the hole and 0.7 eV for the electron. The single-layer spin-coated devices of P1 and P2 realized the pure red emissions from Eu3+ ions. The biggest luminance of 149.1 cd m–2 was achieved, which is the highest among those of electroluminescent (EL) Eu3+-containing copolymers reported so far. The unusual efficiency stability proves the limited concentration quenching and T–T annihilation in P1 and P2 due to the uniform dispersion of emissive Eu3+ chelate moieties in the host matrix. With the high brightness and very stable efficiencies, P1 is favorable among the high-performance Eu3+-containing copolymers. It is also proved that the formation of carrier-traps in the copolymers is effective to improve EL performances.
Co-reporter:Jing Li;Dongxue Ding;Youtian Tao;Ying Wei;Runfeng Chen;Linghai Xie;Wei Huang
Advanced Materials 2016 Volume 28( Issue 16) pp:3122-3130
Publication Date(Web):
DOI:10.1002/adma.201506286
Co-reporter:Jing Zhang;Chunbo Duan;Chunmiao Han;He Yang;Ying Wei
Advanced Materials 2016 Volume 28( Issue 28) pp:5975-5979
Publication Date(Web):
DOI:10.1002/adma.201600487
Co-reporter:Jing Zhang;Dongxue Ding;Ying Wei;Fuquan Han;Wei Huang
Advanced Materials 2016 Volume 28( Issue 3) pp:479-485
Publication Date(Web):
DOI:10.1002/adma.201502772
Co-reporter:Ye Tao; Lijia Xu; Zhen Zhang; Runfeng Chen; Huanhuan Li; Hui Xu; Chao Zheng;Wei Huang
Journal of the American Chemical Society 2016 Volume 138(Issue 30) pp:9655-9662
Publication Date(Web):July 12, 2016
DOI:10.1021/jacs.6b05042
Current static-state explorations of organic semiconductors for optimal material properties and device performance are hindered by limited insights into the dynamically changed molecular states and charge transport and energy transfer processes upon device operation. Here, we propose a simple yet successful strategy, resonance variation-based dynamic adaptation (RVDA), to realize optimized self-adaptive properties in donor–resonance–acceptor molecules by engineering the resonance variation for dynamic tuning of organic semiconductors. Organic light-emitting diodes hosted by these RVDA materials exhibit remarkably high performance, with external quantum efficiencies up to 21.7% and favorable device stability. Our approach, which supports simultaneous realization of dynamically adapted and selectively enhanced properties via resonance engineering, illustrates a feasible design map for the preparation of smart organic semiconductors capable of dynamic structure and property modulations, promoting the studies of organic electronics from static to dynamic.
Co-reporter:Chunbo Duan, Jing Li, Chunmiao Han, Dongxue Ding, He Yang, Ying Wei, and Hui Xu
Chemistry of Materials 2016 Volume 28(Issue 16) pp:5667
Publication Date(Web):July 21, 2016
DOI:10.1021/acs.chemmater.6b01691
Blue thermally activated delayed fluorescence (TADF) dyes are basically combinations of strong acceptors and weak donors. In this work, a weak acceptor P═O group was employed to construct a series of weak acceptor–strong donor (WASD)-type emitters with a phenoxazine donor, namely 10-(4-(diphenylphosphoryl)phenyl)-10H-phenoxazine (SPXZPO), 10,10′-(4,4′-(phenylphosphoryl)bis(4,1-phenylene))bis(10H-phenoxazine) (DPXZPO), and 10,10′,10″-(4,4′,4″-phosphoryltris(benzene-4,1-diyl))tris(10H-phenoxazine) (TPXZPO). Owing to the insulating effect of P═O on conjugation extension and intramolecular electronic communications, the photoluminescence spectra of these molecules are almost identical, manifesting the superiority of WASD structure in emission color preservation. Simultaneously, the multi-dipolar characteristics of TPXZPO enhance the intramolecular charge transfer (ICT), facilitating reverse intersystem crossing for higher TADF efficiency and shorter lifetime. As a consequence, TPXZPO realized the desired pure-blue electroluminescence peak at 464 nm, accompanied by a favorable external quantum efficiency (ηext) up to 15.3%, 100% exciton utilization, and reduced efficiency roll-offs. Its complementary full-TADF white organic light-emitting diodes also achieved ηext as high as 16.3%, among the best results reported so far for white TADF devices. The success of TPXZPO, the first example of a P═O-based WASD-type blue TADF dye, is attributed to the comprehensive and harmonized effects of the P═O joint on controlling conjugation and intramolecular electronic communication and the multi-dipolar structure on enhancing ICT.
Co-reporter:Wenjing Kan, Chunbo Duan, Mingzhi Sun, Chunmiao Han, and Hui Xu
Chemistry of Materials 2016 Volume 28(Issue 19) pp:7145
Publication Date(Web):September 23, 2016
DOI:10.1021/acs.chemmater.6b03518
The charge flux balance and interfacial optimization are two core concerns when simplifying blue thermally activated delayed fluorescence (TADF) diodes, which reflects the more stringent demand on carrier transporting materials (CTM) as the embodiment of the contradiction between charge transportation and quenching suppression with the opposite requirement on intermolecular interactions. Herein, phenylbenzimidazole (PBI) was used as the core substituted with two diphenylphosphine oxide (DPPO) groups to form six dual-encapsulated charge–exciton separation (CES)-type electron transporting materials (ETM) with the collective name of xyPBIDPO. Through tuning the substitution positions of DPPO group, its two functions of resonance and steric effects were integrated and optimized to enhance charged moiety encapsulation without cost of reducing electroactivity. As the result, among xyPBIDPO, mmPBIDPO successfully realizes the balance of favorable electrical performance and interfacial interaction suppressions in virtue of its doubled mesa-substitution structure and roughly symmetrical configuration, rendering the good electron affinity of 2.8 eV, the high electron mobility by the level of 10–6 cm2 V–1 s–1 and effective PBI-core encapsulation. Consequently, mmPBIDPO was used to extremely simplify the blue TADF devices with the state-of-the-art performance from trilayer and quadruple-layer configurations, such as the maximum external quantum efficiency (EQE) beyond 20% and improved efficiency stability. This work not only established a solid example of CES-type ETM for high-performance simple structured blue TADF devices but also provided the direction of developing this kind of materials in the future.
Co-reporter:Jing Zhang, Dongxue Ding, Ying Wei and Hui Xu
Chemical Science 2016 vol. 7(Issue 4) pp:2870-2882
Publication Date(Web):14 Jan 2016
DOI:10.1039/C5SC04848F
The similarity of thermally activated delayed fluorescence (TADF) dyes and their hosts as pure organic molecules makes hosts predominant in intermolecular interactions and crucial to exciton harvesting and utilization in TADF diodes. DPEPO is the most popular high-energy-gap blue TADF host with steric ortho-substituted diphenylphosphine oxide (DPPO) groups for intermolecular interaction suppression, but suffers from serious efficiency roll-off due to its weak electroactivity. On the contrary, para-substituted DPPO with small steric hindrance is superior in intramolecular electronic coupling. In this work, four constitutional isomers of DPEPO are constructed as diphenylether (DPE) with two diphenylphosphine oxide (DPPO) groups substituted at either the 2 or 4 position, namely 22′DPEPO (viz.DPEPO), 24DPEPO, 24′DPEPO and 44′DPEPO, respectively. On the basis of separation configuration, the steric effect and electroactivity of ortho- and para-substituted DPPOs are successfully integrated in 24′DPEPO, accompanied by remarkably reduced intermolecular interactions due to its unsymmetrical configuration. Compared to its congeners, 24′DPEPO has a rigid structure and locally excited states similar to 22′DPEPO for interaction suppression and improved charge mobility comparable to 44′DPEPO for charge flux balance. Significantly, by virtue of the predominant orientation effect of ortho-DPPO on the T1 location, its T1 state is extremely condensed onto a single phenyl, protected from intermolecular interactions by its remaining five phenyls at its maximum extent. Consequently, 24′DPEPO endowed its DMAC-DPS-based deep-blue devices with state-of-the-art performance, including high color purity with chromaticity coordinates of (0.16, 0.17), external quantum efficiency (EQE) beyond 20% and EQE roll-off as low as 32% at 1000 cd m−2. It is shown that the device performance of 24′DPEPO was far beyond simple integration of those of 22′DPEPO and 44′DPEPO, verifying the significance of host optimization.
Co-reporter:Fuquan Han, Xiaolin Zhang, Jing Zhang, Ying Wei, Xinwen Zhang, Wei Huang and Hui Xu
Chemical Communications 2016 vol. 52(Issue 29) pp:5183-5186
Publication Date(Web):15 Mar 2016
DOI:10.1039/C6CC01414C
Iridium-complexed nanosize phosphors 3D-encapsulated with nine 3,6-di-tert-butyl-N-propyl-carbazole groups were constructed as host-dopant integrated systems, which achieved a high photoluminescence quantum yield beyond 70% from neat evaporated films, and an electroluminescence external quantum efficiency up to ∼8.5% and near-zero roll-offs at 1000 cd m−2 from its dual-layer host-free light-emitting diodes.
Co-reporter:Chaochao Fan, Chunbo Duan, Chunmiao Han, Bin Han, and Hui Xu
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 40) pp:27383
Publication Date(Web):September 23, 2016
DOI:10.1021/acsami.6b10020
Three asymmetrical electron transporters as dibenzothiophene sulfone (DBSO)-diphenylphosphine oxide (DPPO) hybrids, collectively named mnDBSODPO, were designed and prepared. All of these materials achieve the high triplet energy of ∼3.0 eV to restrain the exciton linkage from emissive layers. The dependence of inductive and steric effects for DPPO groups on the substitution position, the intermolecular interaction suppression, the encapsulations of high-polar DBSO cores, and the favorable electrical performance are successfully integrated on 36DBSODPO, which can simultaneously suppress the exciton quenching by formation of an interfacial dipole and enhancing the charge flux balance. As a result, 36DBSODPO endowed its tetralayer blue thermally activated delayed fluorescence (TADF) devices with impressive performance, including the maximum external quantum efficiency around 19%, and reduced efficiency roll-offs, which verifies the great potential of asymmetrical electron transporting materials for highly efficient TADF devices.Keywords: asymmetrical configuration; electron transporting material; interfacial effect; phosphine oxide; thermally activated delayed fluorescence
Co-reporter:Jing Li;Dongxue Ding;Ying Wei;Jing Zhang
Advanced Optical Materials 2016 Volume 4( Issue 4) pp:522-528
Publication Date(Web):
DOI:10.1002/adom.201500673
Co-reporter:Fu-Quan Han, Chun-Miao Han, Hui Xu
Chinese Chemical Letters 2016 Volume 27(Issue 8) pp:1193-1200
Publication Date(Web):August 2016
DOI:10.1016/j.cclet.2016.07.009
Iridium(III) complexes are one of the most important electrophosphorescent dyes with tunable emissions in the range of visible and near infrared lights, high photoluminescence yields and short lifetimes for high-efficiency organic light-emitting diodes (OLED) with 100% exciton harvesting. This review summarizes the recent development of electroluminescent Ir3+ complexes functionalized with host-featured carrier-transporting groups, with emphasis on correlations between functionalization, optoelectronic properties and device performance. According to the introducing approaches, the complexes were sorted with conjugated and aliphatic linkages, as well as the types of functional groups. The modification effect on physical properties and the state-of-the-art device performances were discussed.Recent progress of functionalized Iridium(III) complexes for high-efficiency phosphorescent organic light-emitting diodes was briefly summarized.
Co-reporter:Qun Ye, Zhen Zhang, Zhuang Mao Png, Wei Teng Neo, Tingting Lin, Huining Zeng, Hui Xu, and Jianwei Xu
The Journal of Organic Chemistry 2016 Volume 81(Issue 19) pp:9219-9226
Publication Date(Web):September 20, 2016
DOI:10.1021/acs.joc.6b01785
2,3,5,6-Tetrakis(5′-dodecylthiophen-2-yl)-benzoquinones and 2,3,5,6-tetrakis(5′-dodecylthiophen-2′-yl)-hydroquinones were prepared via the Stille or Suzuki cross-coupling reactions, followed by oxidation by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in the case that aryl groups are dodecylthiophenyl. 2,3,5,6-Tetrakis(5′-dodecylthiophen-2′-yl)benzoquinone and 2,3,5,6-tetrakis(5′-dodecylthiophen-2′-yl)-1,4-bis(dodecyloxy)benzene underwent the Scholl reaction to give their corresponding predictable cyclization products anthra[2,1-b:3,4-b′:6,5-b″:7,8-b‴]tetrathiophene-7,14-dione (3) and anthra[1,2-b:4,3-b′:5,6-b″:8,7-b‴]tetrathiophene (5), respectively. Cyclization of 2,3,4,5-tetra(p-tert-butyl-phenyl) benzoquinones through the Scholl reaction, however, gave rise to a mixture of two cyclization products including an unusual major product, benzo[4′,5′]furo[3′,2′:3,4]triphenyleno[1,2-b]benzofuran (9), with 84% yield and a minor product, 2,3-diphenyltriphenylene-1,4-diol (10), with 11% yield. In contrast, cyclization of 2,3,4,5-tetrakis(p-dodecyloxyphenyl)benzoquinone only afforded 2,3-diphenyltriphenylene-1,4-diol (8) with 34% yield. The optical and electrochemistry properties of these fused aromatics were studied. Light emitting diode devices using compound 9 as the fluorescent dopant were fabricated. A maximum external quantum efficiency of 3.23% was achieved for a 4,4′-bis(carbazole)biphenyl/9 based device, revealing the potential for such fused aromatics as dopant to be a blue LED component, subject to the functionalization on these novel π-structures as well as further device optimization.
Co-reporter:Hui Xu, Qiang Sun, Zhongfu An, Ying Wei, Xiaogang Liu
Coordination Chemistry Reviews 2015 Volumes 293–294() pp:228-249
Publication Date(Web):15 June 2015
DOI:10.1016/j.ccr.2015.02.018
•Recent development of electroluminescent europium(III) complexes is reviewed.•Design principle of optoelectronic europium(III) complexes is introduced.•Ligand functionalization is highlighted to embody structure–property relationships.Lanthanide complexes are widely used as emitters for applications in the fields of bioimaging, molecular sensing, disease diagnosis, and optoelectronics. Particularly, the high luminescence efficiencies of these complexes make them attractive for electroluminescent display and solid-state lighting. As color purity and saturation are the most stringent criteria for red emission in display technology, europium(III) complexes featuring an emission peak centered at ∼612 nm with a narrow bandwidth hold great potential as red-emitting materials. This review highlights the recent development of electroluminescent europium(III) complexes, with emphasis on correlations between molecular structures and optoelectronic performance. After a fundamental introduction on the optical and electrical properties of europium(III) complexes, efforts will be devoted toward the controlled synthesis and functionalization of molecules for improved charge injection/transportation, good processability, and enhanced emission efficiency.
Co-reporter:Chaochao Fan, Chunbo Duan, Ying Wei, Dongxue Ding, Hui Xu, and Wei Huang
Chemistry of Materials 2015 Volume 27(Issue 14) pp:5131
Publication Date(Web):July 10, 2015
DOI:10.1021/acs.chemmater.5b02012
Thermally activated delayed fluorescence (TADF) organic light-emitting diodes arise from the development of high-performance host materials and carrier transporting materials fitting for TADF dyes with optimized respective properties and interplays, making simultaneous performance improvement and device structure simplification feasible. In this work, a highly efficient blue TADF diode with simplified four-layer structure was successfully achieved by utilizing bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) as blue emitter, 4,6-bis(diphenylphosphoryl)dibenzothiophene (DBTDPO) as host, and 4,6-bis(diphenylphosphoryl)dibenzothiophene sulfone (46DBSODPO) as electron-transporting layer. The compatibilities between DBTDPO and DMAC-DPS and DBTDPO and 46DBSODPO were optimized with respect to configuration, polarity, energy level, and interfacial interaction, resulting in the unchanged roughness of ∼0.25 nm before and after doping, high photoluminescence quantum yield over 85%, and reduced interfacial exciplex emissions. With the similar triplet excited energy (T1) of ∼3.0 eV but inferior electrical properties compared to its analogues 28DBSODPO and 37DBSODPO, besides the homogeneity with DBTDPO, 46DBSODPO suppressed the formation of interfacial exciplex and dipole for efficient exciton confinement and electron injection and transportation, in virtue of the steric effects of its ortho-substituted phosphine oxide groups. Consequently, DBTDPO and 46DBSODPO endowed their DMAC-DPS based four-layer devices with the state-of-the-art performance, for example, the maximum external quantum efficiency over 16%, which was more than two-fold of those of conventional electron-transporting material 1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene (TmPyPB). This design strategy about material compatibility could pave a way for developing high-performance blue TADF diodes with simplified configurations.
Co-reporter:Wenjing Kan, Liping Zhu, Ying Wei, Dongge Ma, Mingzhi Sun, Zhongbin Wu, Wei Huang and Hui Xu
Journal of Materials Chemistry A 2015 vol. 3(Issue 21) pp:5430-5439
Publication Date(Web):21 Apr 2015
DOI:10.1039/C5TC00643K
A series of benzimidazole–PO hybrids, PBIPO, DPBIPO and TPBIPO, with different configurations of phosphine oxide (PO)-bridged 2-phenylbenzimidazole (PBI) groups, demonstrate an effective charge–exciton separation (CES) strategy for electron-transport material (ETM) design aimed at interfacial triplet-polaron quenching (TPQ) suppression in hole-predominant phosphorescent organic light-emitting diodes (PHOLEDs). The electronic states of these materials are well-controlled by virtue of their insulating and electron-withdrawing phosphine oxide joints. Their equivalent frontier molecular orbital energy levels (−2.7 and −6.4 eV) and triplet states (3.0 eV) give them identical good electron-injecting/hole-blocking abilities and effective exciton diffusion suppression, establishing a correspondence between electron mobility and interfacial TPQ effect, and the device performance of these ETMs. Stronger interactions between TPPO groups and blue phosphor iridium(III) bis(2-(4,6-difluorophenyl)-pyridinato-N,C2′) picolinate (FIrpic) give rise to the optimized orientation of unsymmetrical PBIPO on the emissive layer (EML) to separate its charged moiety from the EML interface, effectively suppressing interfacial TPQ. Consequently, PBIPO endows its conventional FIrpic-based blue device with state-of-the-art efficiencies of 47.3 cd A−1, 36.0 lm W−1 and 22.2%, which are two- and three-fold those of the common ETM TPBI and its analogue DPBIPO, with a two orders of magnitude higher electron mobility. At 1000 cd m−2, the efficiencies of PBIPO-based devices still remained at 43.5 cd A−1 and 20.1%, making PBIPO among the most efficient high-energy-gap ETMs to date and manifesting the effectiveness of the molecular CES strategy for interfacial TPQ suppression.
Co-reporter:Mingzhi Sun, Liping Zhu, Wenjing Kan, Ying Wei, Dongge Ma, Xuefeng Fan, Wei Huang and Hui Xu
Journal of Materials Chemistry A 2015 vol. 3(Issue 36) pp:9479-9479
Publication Date(Web):24 Aug 2015
DOI:10.1039/C5TC90156A
Correction for ‘Ternary donor–acceptor phosphine oxide hosts with peculiar high energy gap for efficient blue electroluminescence’ by Mingzhi Sun et al., J. Mater. Chem. C, 2015, DOI: 10.1039/c5tc02029h.
Co-reporter:Mingzhi Sun, Liping Zhu, Wenjing Kan, Ying Wei, Dongge Ma, Xuefeng Fan, Wei Huang and Hui Xu
Journal of Materials Chemistry A 2015 vol. 3(Issue 36) pp:9469-9478
Publication Date(Web):31 Jul 2015
DOI:10.1039/C5TC02029H
Ternary donor (D)–acceptor (A)–acceptor (A) molecules are commonly considered as low triplet (T1) energy systems for specific applications. In this work, exception to this behavior was observed in a triangle-shaped D–A–A molecule PCImbPO with unusually high triplet energy of 3.0 eV. Profiting from the enhanced D–A electronic coupling, electron injecting and transporting ability of PCImbPO was dramatically improved with negligible influences on its highest occupied molecular orbital (HOMO) characteristics. Its particular T1 configuration adjustment further gives rise to the separated frontier MO and T1 locations, beneficial to suppress quenching effects. By utilizing PCImbPO as host in blue phosphorescent organic light-emitting diodes (PHOLEDs) and thermally activated delayed fluorescence devices, impressively high external quantum efficiency of 22% and 12% were achieved, respectively. This work established a new understanding of high-energy-gap complicated D–A systems.
Co-reporter:Jing Li, Zhensong Zhang, Chunmiao Han, Dongxue Ding, Yi Zhao, Wei Huang and Hui Xu
Journal of Materials Chemistry A 2015 vol. 3(Issue 26) pp:6709-6716
Publication Date(Web):01 Jun 2015
DOI:10.1039/C5TC01179E
Fluorene and diphenylphosphine oxide were employed as peripheral groups to construct ternary host materials DBFxPODEFn with benzofuran as a core for yellow phosphorescent organic light-emitting diodes (PhOLEDs). Their peripheral group density and ratio were rationally adjusted to suppress quenching and enhance charge balance. The conjugation of DBFxPODEFn was extended appropriately on the basis of meso- and short-axis linkages to render similar optical properties and a medium first triplet energy (T1) of 2.58 eV for efficient and comparable energy transfer to yellow phosphors, making the yellow PhOLED performance correspond to the charge flux balance and quenching effects, viz. the correlation between device performance and their functional group density and spatial arrangement. DBFSPODEF with the desired electron-dominant characteristics and the suppressed triplet–triplet annihilation (TTA) effect endowed its devices with a low driving voltage of <3.8 V and favorable efficiencies of 32.7 lm W−1 and 12.5% at 1000 cd m−2 for lighting applications. This work indicates that an appropriate functionalization and a rational spatial group arrangement are significant for constructing efficient hosts for low-voltage-driven PhOLEDs.
Co-reporter:Dongxue Ding, Zhen Zhang, Ying Wei, Pengfei Yan and Hui Xu
Journal of Materials Chemistry A 2015 vol. 3(Issue 43) pp:11385-11396
Publication Date(Web):29 Sep 2015
DOI:10.1039/C5TC02726H
Two quaternary ambipolar phosphine oxide host materials, 9-(4-(9-(4′-(2-(diphenylphosphoryl)phenoxy)biphenyl-4-yl)-9H-fluoren-9-yl)phenyl)-9H-carbazole (9CzFDPESPO) and 9-(4-(9-(3′-(diphenylphosphoryl)-4′-(2-(diphenylphosphoryl)phenoxy)biphenyl-4-yl)-9H-fluoren-9-yl)phenyl)-9H-carbazole (9CzFDPEPO), were designed and prepared with mixed indirect and multi-insulating linkages to investigate the spatial effect on the electroluminescence performance of high-energy-gap hosts in blue phosphorescence and thermally activated delayed fluorescence light-emitting diodes (PHOLEDs and TADF OLEDs), in comparison to a ternary analogue 9-(4-(9-(4-(diphenylphosphoryl)phenyl)-9H-fluoren-9-yl)phenyl)-9H-carbazole (9CzFSPO). The donor–acceptor (D–A) distance in 9CzFDPESPO is elongated through the involvement of diphenylene as a π-extender, while the second phosphine oxide acceptor on diphenylene of 9CzFDPEPO is utilized to make its D–A distance comparable to that of 9CzFSPO. The single-molecular optoelectronic properties of these three hosts were uniform, owing to the effectively suppressed intramolecular electronic coupling by indirect and multi-insulating linkages. Their similar high triplet energy of 3.0 eV and the suitable energy levels of the highest occupied and the lowest unoccupied molecular orbitals around −6.1 and −2.5 eV, respectively, provide effective energy transfer and carrier injection. In contrast, 9CzFDPESPO shows the highest hole mobility owing to its longest D–A distance, directly indicating the spatial effect. As expected, with the most effectively suppressed spatial effect, 9CzFDPESPO endowed its blue phosphorescence and TADF devices with a state-of-the-art performance, e.g. external quantum efficiencies of 22.5% and 16.7%, respectively, which were the best results for quaternary host materials reported so far.
Co-reporter:Chunmiao Han;Liping Zhu;Jing Li;Fangchao Zhao;Zhen Zhang;Zhaopeng Deng;Dongge Ma;Pengfei Yan
Advanced Materials 2014 Volume 26( Issue 41) pp:7070-7077
Publication Date(Web):
DOI:10.1002/adma.201400710
Co-reporter:Chunmiao Han, Liping Zhu, Fangchao Zhao, Zhen Zhang, Jianzhe Wang, Zhaopeng Deng, Hui Xu, Jing Li, Dongge Ma and Pengfei Yan
Chemical Communications 2014 vol. 50(Issue 20) pp:2670-2672
Publication Date(Web):17 Jan 2014
DOI:10.1039/C3CC49020C
A series of phosphine oxide hosts were constructed to investigate the influence of the triplet state extension in hosts on electrophosphorescence, in which DPESPOPhCz with the carbazolyl-localized triplet state endowed its blue-emitting PHOLEDs with favourable performance, including an external quantum efficiency more than 13%.
Co-reporter:Zhen Zhang ; Zhensong Zhang ; Dongxue Ding ; Ying Wei ; Hui Xu ; Jilin Jia ; Yi Zhao ; Kai Pan ;Wei Huang
The Journal of Physical Chemistry C 2014 Volume 118(Issue 35) pp:20559-20570
Publication Date(Web):August 19, 2014
DOI:10.1021/jp506513x
Hydrocarbon oligomers X9F, including S9F, D9F, and T9F as monomer, dimer, and trimer, respectively, were designed and prepared on the basis of indirect linkage and 9,9-diphenylfluorene (S9F) as repeat unit to form planar, linear, and V-shaped configurations without polarity variation and function amplification. The identical optical and electrochemical properties of X9F were achieved because of the effectively blocked intramolecualr electronic interactions by indirect linkage, including the same T1 value of 2.98 eV, high enough for hosts in blue phosphorescent organic light-emitting diodes (PHOLEDs), and the approximate FMO energy levels, which established the basis for selective investigation of independent configuration effect on the optoelectronic performance of host materials. Density function theory simulation manifested the frontier molecular orbital (FMO) location extension after oligomerization and the specific T1 locations on peripheral fluorenyls in X9F, giving rise to their different carrier-transporting abilities and host-localized triplet–triplet annihilation (TTA) and triplet–polaron quenching (TPQ) effects. As a result, D9F with the linear and locally unsymmetrical configuration revealed electron-predominant characteristics for charge balance, restrained triplet interaction for TTA suppression, and partially separated FMO and T1 locations for TPQ suppression. Consequently, the low driving voltages and the favorable maximum efficiencies, such as ∼11% for external quantum efficiency (EQE), as well as reduced roll-offs less than 8% for EQE at 1000 cd m–2, were achieved by D9F-based blue PHOLEDs as the highest performance among X9F, in which device efficiencies were improved by 50% compared to that of conventional polarized host mCP. It is conceivable that molecular configuration has significant effects on electrical properties and quenching effects of organic semiconductors with remarkable influence on intermolecular interplay and excited-state locations.
Co-reporter:Jianzhe Wang;Dr. Chunmiao Han;Dr. Guohua Xie;Dr. Ying Wei;Dr. Qin Xue; Pengfei Yan;Dr. Hui Xu
Chemistry - A European Journal 2014 Volume 20( Issue 35) pp:11137-11148
Publication Date(Web):
DOI:10.1002/chem.201403244
Abstract
A series of solution-processible electroluminescent (EL) Eu3+ complexes were constructed with a self-host strategy, in which neutral ligands were employed as functionalized bidentate phosphine oxide (PO) ligands named DPEPOArn (DPEPO=bis(2-(diphenylphosphino)phenyl) ether oxide). The solubility of these complexes was dramatically improved owing to the increased ratios of organic components. This further enhanced the antenna effect of these ligands in both singlet and triplet energy-transfer processes to support high photoluminescent quantum yields (PLQYs) up to 86 % for their Eu3+ complexes, which is outstanding among conjugated Eu3+ complexes. Density function theory (DFT) simulations and electrochemical analysis further verified the contributions of DPEPOArn to the carrier injecting/transporting ability of the complexes. In this sense, these functionalized PO ligands served as hosts in optoelectronic processes, which rendered the self-host feature of their Eu3+ complexes. With the enhanced electrical properties, the spin-coated single-layer organic light-emitting diodes (OLEDs) of these complexes achieved improved low driving voltages, such as onset voltages about 6 V, compared to their Eu3+-contained red-emitting polymeric analogues. [Eu(DBM)3DPEPODPNA2] (DBM=1,3-diphenylpropane-1,3-dione, DPNA=diphenylnaphthylamine) with the most enhanced electrical properties and suitable frontier molecular orbital (FMO) and triplet state locations endowed its devices with the biggest maximum luminance of >90 cd m−2 and the highest EL efficiencies. This work verified the potential of small molecular EL Eu3+ complexes for solution-processed OLEDs through rational function integrations.
Co-reporter:Chunmiao Han;Liping Zhu;Jing Li;Fangchao Zhao;Dr. Hui Xu; Dongge Ma; Pengfei Yan
Chemistry - A European Journal 2014 Volume 20( Issue 49) pp:16350-16359
Publication Date(Web):
DOI:10.1002/chem.201404615
Abstract
The correspondence between triplet location effect and host-localized triplet–triplet annihilation and triplet–polaron quenching effects was performed on the basis of a series of naphthyldiphenylamine (DPNA)-modified phosphine oxide hosts. The number and ratio of DPNA and diphenylphosphine oxide was adjusted to afford symmetrical and unsymmetrical molecular structures and different electronic environments. As designed, the first triplet (T1) states were successfully localized on the specific DPNA chromophores. Owing to the meso- and multi-insulating linkages, identical optical properties and comparable electrical performance was observed, including the same first singlet (S1) and T1 energy levels to support the similar singlet and triplet energy transfer and the close frontier molecular orbital energy levels. This established the basis of rational investigation on T1 location effect without interference from other optoelectronic factors.
Co-reporter:Chunmiao Han, Fangchao Zhao, Zhen Zhang, Liping Zhu, Hui Xu, Jing Li, Dongge Ma, and Pengfei Yan
Chemistry of Materials 2013 Volume 25(Issue 24) pp:4966
Publication Date(Web):November 25, 2013
DOI:10.1021/cm403160p
With the aim to rationally figure out the significance of charge and exciton capture in the electrophosphorescent processes in low-triplet-energy hosts involved doping systems, the frontier molecular orbital (FMO) energy levels of a series low-triplet-energy hosts with diphenylphosphine oxide (DPPO) and triphenylamine (TPA), collectively named DPExPOTPAn, were successfully and gradually tuned on the basis of their constant triplet energy levels (T1) of 2.63 eV to get rid of interference from host-dopant energy transfer. It was showed that device efficiencies were directly proportional to the depths of carrier traps formed on the dopants and inversely proportional to the exciton capture ability of the hosts, which were evidenced by the highest external quantum efficiency of ∼15% from FIrpic-based PHOLED of DPESPOTPA with the deepest hole and electron traps and the weakest exciton capture ability among DPExPOTPAn. This work not only demonstrated the great advantages and potential of this kind of host materials for low-driving-voltage application but also clarified the determinants of highly efficient low-triplet-energy hosts for blue PHOLEDs, which are consequentially referable for purposeful molecular design.Keywords: blue electrophosphorescence; charge capture; exciton capture; low triplet energy host; phosphine oxide;
Co-reporter:Weibo Yang, Zhensong Zhang, Chunmiao Han, Zhen Zhang, Hui Xu, Pengfei Yan, Yi Zhao and Shiyong Liu
Chemical Communications 2013 vol. 49(Issue 27) pp:2822-2824
Publication Date(Web):20 Feb 2013
DOI:10.1039/C3CC00133D
Preserved high first triplet energy levels and improved electrical properties of two donor–acceptor type carbazole–phosphine oxide hosts were achieved through short-axis substitution to realize efficient PHOLEDs with extremely low driving voltages of 2.6 V for onset and <3.2 V at 100 cd m−2.
Co-reporter:Chunmiao Han;Zhensong Zhang;Dr. Hui Xu;Jing Li; Yi Zhao; Pengfei Yan; Shiyong Liu
Chemistry - A European Journal 2013 Volume 19( Issue 4) pp:1385-1396
Publication Date(Web):
DOI:10.1002/chem.201203719
Abstract
A series of donor (D)–π–acceptor (A)-type phosphine-oxide hosts (DBFxPOPhCzn), which were composed of phenylcarbazole, dibenzofuran (DBF), and diphenylphosphine-oxide (DPPO) moieties, were designed and synthesized. Phenyl π-spacer groups were inserted between the carbazolyl and DBF groups, which effectively weakened the charge transfer and triplet-excited-state extension. As the result, the first triplet energy levels (T1) of DBFxPOPhCzn are elevated to about 3.0 eV, 0.1 eV higher than their DA-type analogues. Nevertheless, the electrochemical analysis and DFT calculations demonstrated the ambipolar characteristics of DBFxPOPhCzn. The phenyl π spacers hardly influenced the frontier molecular orbital (FMO) energy levels and the carrier-transporting ability of the materials. Therefore, these DπA systems are endowed with higher T1 states, as well as comparable electrical properties to DA systems. Phosphorescent blue-light-emitting diodes (PHOLEDs) that were based on DBFxPOPhCzn not only inherited the ultralow driving voltages (2.4 V for onset, about 2.8 V at 200 cd m−2, and <3.4 V at 1000 cd m−2) but also had much-improved efficiencies, including about 26 cd A−1 for current efficiency, 30 Lm W−1 for power efficiency, and 13 % for external quantum efficiency, which were more than twice the values of devices that are based on conventional unipolar host materials. This performance makes DBFDPOPhCzn among the best hosts for ultralow-voltage-driven blue PHOLEDs reported so far.
Co-reporter:Chunmiao Han;Zhensong Zhang;Dr. Hui Xu;Dr. Guohua Xie;Jing Li; Yi Zhao;Dr. Zhaopeng Deng; Shiyong Liu; Pengfei Yan
Chemistry - A European Journal 2013 Volume 19( Issue 1) pp:141-154
Publication Date(Web):
DOI:10.1002/chem.201203349
Abstract
The controllable tuning of the excited states in a series of phosphine-oxide hosts (DPExPOCzn) was realized through introducing carbazolyl and diphenylphosphine-oxide (DPPO) moieties to adjust the frontier molecular orbitals, molecular rigidity, and the location of the triplet excited states by suppressing the intramolecular interplay of the combined multi-insulating and meso linkage. On increasing the number of substituents, simultaneous lowering of the first singlet energy levels (S1) and raising of the first triplet energy levels (T1, about 3.0 eV) were achieved. The former change was mainly due to the contribution of the carbazolyl group to the HOMOs and the extended conjugation. The latter change was due to an enhanced molecular rigidity and the shift of the T1 states from the diphenylether group to the carbazolyl moieties. This kind of convergent modulation of excited states not only facilitates the exothermic energy transfer to the dopants in phosphorescent organic light-emitting diodes (PHOLEDs), but also realizes the fine-tuning of electrical properties to achieve the balanced carrier injection and transportation in the emitting layers. As the result, the favorable performance of blue-light-emitting PHOLEDs was demonstrated, including much-lower driving voltages of 2.6 V for onset and 3.0 V at 100 cd m−2, as well as a remarkably improved E.Q.E. of 12.6 %.
Co-reporter:Dr. Zhen Zhang;Zhensong Zhang;Dr. Runfeng Chen;Jilin Jia;Chunmiao Han;Dr. Chao Zheng;Dr. Hui Xu;Donghui Yu; Yi Zhao; Pengfei Yan; Shiyong Liu; Wei Huang
Chemistry - A European Journal 2013 Volume 19( Issue 29) pp:9549-9561
Publication Date(Web):
DOI:10.1002/chem.201300466
Abstract
The purposeful modulation of the optoelectronic properties was realised on the basis of a series of the large, conjugated, phosphine oxide hosts 9,9-bis-{4′-[2-(diphenylphosphinoyl)phenoxy]biphenyl-4-yl}-9H-fluorene (DDPESPOF), 9,9-bis-{3′-(diphenylphosphinoyl)-4′-[2-(diphenylphosphinoyl)phenoxy]biphenyl-4-yl}-9H-fluorene (DDPEPOF), 9-[4′-(9-{4′-[2-(diphenylphosphoryl)phenoxy]biphenyl-4-yl}-9H-fluoren-9-yl)biphenyl-4-yl]-9H-carbazole (DPESPOFPhCz) and 9-[4′-(9-{3′-(diphenylphosphoryl)-4′-[2-(diphenylphosphoryl)phenoxy]biphenyl-4-yl}-9H-fluoren-9-yl)biphenyl-4-yl]-9H-carbazole (DPEPOFPhCz). The last two are quaternary with fluorenyls as linking bridges, diphenylphosphine oxide (DPPO) moieties as electron acceptors and diphenylethers and carbazolyls as two different kinds of electron donors. Owing to the fine-organised molecular structures and the mixed indirect and multi-insulating linkages, all of these hosts achieve the same first triplet energy levels (T1) of 2.86 eV for exothermic energy transfer to phosphorescent dopants. The first singlet energy levels (S1) and the carrier injection/transportation ability of the hosts were accurately modulated, so that DPESPOFPhCz and DPEPOFPhCz revealed extremely similar optoelectronic properties. However, the T1 state of the former is localised on fluorenyl, whereas the carbazolyl mainly contributes to the T1 state of the latter. A lower driving voltages and much higher efficiencies of the devices based on DPESPOFPhCz indicated that the chromophore-localised T1 state can suppress the quenching effects through realising independent contributions from the different functional groups to the optoelectronic properties and the embedding and protecting effect on the T1 states by peripheral carrier transporting groups.
Co-reporter:Ye Tao;Jianjian Xiao;Dr. Chao Zheng;Zhen Zhang;Mingkuan Yan;Dr. Runfeng Chen;Dr. Xinhui Zhou;Huanhuan Li;Dr. Zhongfu An;Zhixiang Wang;Dr. Hui Xu; Wei Huang
Angewandte Chemie International Edition 2013 Volume 52( Issue 40) pp:10491-10495
Publication Date(Web):
DOI:10.1002/anie.201304540
Co-reporter:Chunmiao Han ; Zhensong Zhang ; Hui Xu ; Shouzhen Yue ; Jing Li ; Pingrui Yan ; Zhaopeng Deng ; Yi Zhao ; Pengfei Yan ;Shiyong Liu
Journal of the American Chemical Society 2012 Volume 134(Issue 46) pp:19179-19188
Publication Date(Web):October 29, 2012
DOI:10.1021/ja308273y
Two dibenzothiophene (DBT)-based phosphine oxide hosts, named 4-diphenylphosphoryl dibenzothiophene (DBTSPO) and 4,6-bis(diphenylphosphoryl) dibenzothiophene (DBTDPO), were prepared by short-axis substitution with the aim to selectively adjust electrical properties. The combined effects of short-axis substitution and the involvement of electron-donating S atom in conjugation effectively suppress the influence of electron-withdrawing diphenylphosphine oxide (DPPO) moieties on the frontier molecular orbitals and the optical properties. Therefore, DBTSPO and DBTDPO have the nearly same hole injection ability and the excited energy levels, while more electron-transporting DPPOs and the symmetrical configuration endow DBTDPO with enhanced electron-injecting/transporting ability. As the result, on the basis of this short-axis substitution effect, the selective adjustment of electrical properties was successfully realized. With the high first triplet energy level (T1) of 2.90 eV, the suitable energy levels of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of −6.05 and −2.50 eV and the improved carrier-transporting ability, DBTDPO supported its blue- and white-emitting phosphorescent organic light-emitting diodes as the best low-voltage-driving devices reported so far with the lowest driving voltages of 2.4 V for onset and <3.2 V at 1000 cd m–2 (for indoor lighting) accompanied with the high efficiencies of >30 lm W–1 and excellent efficiency stability.
Co-reporter:Donghui Yu, Fangchao Zhao, Zhen Zhang, Chunmiao Han, Hui Xu, Jing Li, Dongge Ma and Pengfei Yan
Chemical Communications 2012 vol. 48(Issue 49) pp:6157-6159
Publication Date(Web):26 Apr 2012
DOI:10.1039/C2CC31066J
An ambipolar ternary deep-blue emitter with CIE coordinates of (0.15, 0.07) and high electroluminescent performance was constructed on the basis of an insulated donor–π–acceptor system through an indirect linkage.
Co-reporter:Chunmiao Han, Guohua Xie, Hui Xu, Zhensong Zhang, Pengfei Yan, Yi Zhao, Shiyong Liu
Dyes and Pigments 2012 Volume 94(Issue 3) pp:561-569
Publication Date(Web):September 2012
DOI:10.1016/j.dyepig.2012.03.013
A phosphine oxide (PO) host containing planar xanthene (XantPO) was chosen to investigate the influence of the structure of chromophores on the properties of the host. Owing to the multi-insulating linkages, the planar structure of XantPO also realizes high first triplet excited level (T1) of 2.92 eV, and supports excellent morphological and thermal stability with the high temperature of glass transition (Tg, 135 °C) and temperature of decomposition (Td, 369 °C). On the basis of theoretical simulation and electrochemical analysis and bright and efficient green and blue phosphorescent organic light-emitting diodes (PHOLEDs) of XantPO, it indicated that the configuration of chromophores in hosts can remarkably influence the device performance even if their optical properties were very approximate.Graphical abstractHighlights► XantPO with planar xanthene was chosen as a host for electrophosphorescence. ► The influence of chromophores’ structures on the host properties is investigated. ► The optical properties of the hosts studied were very approximate. ► However, the device performance was still remarkably influenced. ► This is attributed to the different electrical properties from changed configuration.
Co-reporter:Hui Xu, Guohua Xie, Chunmiao Han, Zhensong Zhang, Zhaopeng Deng, Yi Zhao, Pengfei Yan, Shiyong Liu
Organic Electronics 2012 Volume 13(Issue 9) pp:1516-1525
Publication Date(Web):September 2012
DOI:10.1016/j.orgel.2012.05.003
Two phosphine oxide hosts, 1,8-bis(diphenylphosphoryl)naphthalene (NAPO) and 2,2′-bis(diphenylphosphoryl)-1,1′-binaphthyl (BiNAPO), were designed and synthesized to investigate the influence of molecular configuration and the density of functional substituents on the excited energy levels. With the much bigger conjugated area, BiNAPO has the T1 of 2.46 eV, which is only 0.17 eV less than that of naphthalene. This should be owing to the orthogonal configuration of BiNAPO. Meanwhile, NAPO with the higher density of functional substituents has the much lower T1 of 2.26 eV. It is showed that shortening the conjugated length by tuning molecular configuration and reducing the density of functional substituents can effectively remain T1 of the chromophore. Simultaneously, Gaussian simulation showed that the larger conjugated area and the rational distribution of functional substituents endow BiNAPO with more balanced carrier injecting/transporting ability, which was further proved by nominal singly-carrier-only devices. The low-voltage driving and efficient green-emitting electrophosphorescent devices based on BiNAPO were demonstrated.Graphical abstractDifferent density of funtional subsitituents.Highlights► Two naphthyl phosphine oxide hosts NAPO and BiNAPO were designed and synthesized. ► Optimized molecular configuration and reduced density of substituents can effectively remain T1. ► The carrier injecting/transporting ability can be improved through bigger but blocked conjugate. ► The low-voltage driving and highly efficient green-emitting PHOLEDs were demonstrated.
Co-reporter:Chunmiao Han;Zhensong Zhang;Dr. Hui Xu;Jing Li;Dr. Guohua Xie;Dr. Runfeng Chen; Yi Zhao; Wei Huang
Angewandte Chemie International Edition 2012 Volume 51( Issue 40) pp:10104-10108
Publication Date(Web):
DOI:10.1002/anie.201202702
Co-reporter:Chunmiao Han;Zhensong Zhang;Dr. Hui Xu;Jing Li;Dr. Guohua Xie;Dr. Runfeng Chen; Yi Zhao; Wei Huang
Angewandte Chemie 2012 Volume 124( Issue 40) pp:10251-10255
Publication Date(Web):
DOI:10.1002/ange.201202702
Co-reporter:Chunmiao Han;Guohua Xie;Zhensong Zhang;Linghai Xie;Yi Zhao;Shiyong Liu;Wei Huang
Advanced Materials 2011 Volume 23( Issue 21) pp:2491-2496
Publication Date(Web):
DOI:10.1002/adma.201100322
Co-reporter:Jie Zhao, Guo-Hua Xie, Cheng-Rong Yin, Ling-Hai Xie, Chun-Miao Han, Run-Feng Chen, Hui Xu, Ming-Dong Yi, Zhao-Peng Deng, Shu-Fen Chen, Yi Zhao, Shi-Yong Liu, and Wei Huang
Chemistry of Materials 2011 Volume 23(Issue 24) pp:5331
Publication Date(Web):November 18, 2011
DOI:10.1021/cm201654c
A series of phosphine oxide (PO) hosts based on diphenylphosphine oxide and spiro[fluorene-9,9′-xanthene] (SFX) moieties, SFX2PO, SFX27PO, SFX2′PO, and SFX2′7′PO, were designed and synthesized. On the basis of the different electrical properties of xanthene and fluorene in SFX, the influence of substitution position on the chemical and optophysical properties of the ambipolar-core based systems were investigated in detail. The effective strategy of introducing electron-withdrawing PO moieties in electron-deficient moieties in the molecules accompanied with suitable linkages insulating the electron-rich and -deficient moieties was convincingly demonstrated, which can endow the hosts with much better carrier injecting and transporting ability and high enough T1 for blue and green phosphors. As the results, the operating voltages of the devices based on SFX2PO and SFX27PO were much lower than those of the devices based on SFX2′PO and SFX2′7′PO. Simultaneously, the efficiencies of the SFX2PO based devices were about twice of those of the devices based on SFX2′PO and SFX2′7′PO. We suppose that it is not necessary to achieve too high T1 and improved electron injection through PO moieties at the cost of sacrificing the hole injecting ability of the chromophores. An ideal strategy is preserving high enough T1 and improving electron injection by utilizing PO moieties without reducing hole injection and transportation in the hosts.Keywords: electrophosphorescence; host; phosphine oxide; spiro-compounds; substitution effect;
Co-reporter:Jun-Xi Cai, Teng-Ling Ye, Xue-Feng Fan, Chun-Miao Han, Hui Xu, Li-Li Wang, Dong-Ge Ma, Yang Lin and Peng-Fei Yan
Journal of Materials Chemistry A 2011 vol. 21(Issue 39) pp:15405-15416
Publication Date(Web):01 Sep 2011
DOI:10.1039/C1JM12114F
A series of electrophosphorescent small molecular Ir3+ complexes IrPBIO22, IrPBICO, IrPBIO44 and IrPBIC22O22 for solution-processable host-free organic light-emitting diodes (OLEDs) were designed and synthesized, in which the electron-transporting 1,3,4-oxadiazole (OXD) and hole-transporting carbazole moieties were introduced through aliphatic chains to achieve balanced carrier injection/transporting. The coordinatable OXD groups were successfully and conveniently introduced through the post-substitution of Ir3+ cores. The photophysical investigation showed that compared with the single-position substituted counterparts, the double-position substitution is superior in restraining the quenching effect in solid states to endow the corresponding complexes with the much higher photoluminescence quantum yield (PLQY) in the film. The influences of peripheral carrier transporting (CT) moieties on the energy levels of frontier molecular orbitals were investigated with UPS analysis and Density Function Theory calculation. The dramatic electroluminescent (EL) performance of IrPBIC22O22 based on its host-free spin-coat phosphorescent organic light-emitting diodes (PHOLEDs), especially the remarkably restrained efficiency roll-off less than 16% at 1000 cd m−2 was realized, which demonstrated that the combined modification of the effective segregation of emitting cores by multi-position encapsulation and the balanced carrier injection/transporting through bipolar substitution is an effective strategy for realizing high-efficiency small molecular electrophosphorescent materials with the features of solution processability and strong restraining effect on quenching for host-free devices.
Co-reporter:Run-Feng Chen, Li-Yuan Liu, Hua Fu, Chao Zheng, Hui Xu, Qu-Li Fan, and Wei Huang
The Journal of Physical Chemistry B 2011 Volume 115(Issue 2) pp:242-248
Publication Date(Web):December 21, 2010
DOI:10.1021/jp108476x
Polysilafluorenes have recently received increasing attention for a wide range of optoelectronic applications due to their improved performance over polyfluorenes and polycarbazoles. To reveal their molecular structures, optoelectronic properties, and structure−property relationships, a systematic study of the influence of the linkage pattern on the optoelectronic properties of polysilafluorenes was performed via quantum chemistry calculations. The optimized geometries, electronic properties, frontier molecular orbitals, singlet and triplet energies, ionization potentials, electron affinities, reorganization energies, and absorption and circular dichroism spectra of the model compounds have been calculated and analyzed. The great impacts of the linkage pattern on the structural, electronic, and optical properties of the silafluorene-based materials have been observed, and the effect mode of the linkage pattern has been discussed. Good coordination between the theoretical and experimental results has been found. The unreported poly(1,8-silafluorene)s are expected to be very interesting optoelectronic materials with high electronic bandgap (Eg) and triplet energy (3Eg), high electron injection property, high hole and electron transport properties, strong circular dichroism signals, and modest effective conjugation length, which can be used as high-performance blue or deep-blue light emitting diodes, ambipolar host materials for blue phosphorescent emitters, and helically chiral conjugated materials.
Co-reporter:Chunmiao Han;Guohua Xie;Dr. Hui Xu;Zhensong Zhang;Donghui Yu; Yi Zhao; Pengfei Yan;Zhaopeng Deng;Dr. Qiang Li; Shiyong Liu
Chemistry - A European Journal 2011 Volume 17( Issue 2) pp:445-449
Publication Date(Web):
DOI:10.1002/chem.201001981
Co-reporter:Chunmiao Han;Yongbiao Zhao;Dr. Hui Xu;Jiangshan Chen;Zhaopeng Deng; Dongge Ma;Dr. Qiang Li; Pengfei Yan
Chemistry - A European Journal 2011 Volume 17( Issue 21) pp:5800-5803
Publication Date(Web):
DOI:10.1002/chem.201100254
Co-reporter:Donghui Yu;Yongbiao Zhao;Dr. Hui Xu;Chunmiao Han; Dongge Ma;Zhaopeng Deng; Shan Gao; Pengfei Yan
Chemistry - A European Journal 2011 Volume 17( Issue 9) pp:2592-2596
Publication Date(Web):
DOI:10.1002/chem.201003434
Co-reporter:Chunmiao Han;Guohua Xie;Jing Li;Zhensong Zhang;Dr. Hui Xu;Zhaopeng Deng; Yi Zhao; Pengfei Yan; Shiyong Liu
Chemistry - A European Journal 2011 Volume 17( Issue 32) pp:8947-8956
Publication Date(Web):
DOI:10.1002/chem.201100695
Abstract
An efficient host for blue and green electrophosphorescence, 4,6-bis(diphenylphosphoryl)dibenzofuran (o-DBFDPO), with the structure of a short-axis-substituted dibenzofuran was designed and synthesised. It appears that the greater density of the diphenylphosphine oxide (DPPO) moieties in the short-axis substitution configuration effectively restrains the intermolecular interactions, because only very weak π–π stacking interactions could be observed, with a centroid-to-centroid distance of 3.960 Å. The improved thermal stability of o-DBFDPO was corroborated by its very high glass transition temperature (Tg) of 191 °C, which is the result of the symmetric disubstitution structure. Photophysical investigation showed o-DBFDPO to be superior to the monosubstituted derivative, with a longer lifetime (1.95 ns) and a higher photoluminescent quantum efficiency (61 %). The lower first singlet state excited level (3.63 eV) of o-DBFDPO demonstrates the stronger polarisation effect attributable to the greater number of DPPO moieties. Simultaneously, an extremely high first triplet state excited level (T1) of 3.16 eV is observed, demonstrating the tiny influence of short-axis substitution on T1. The improved carrier injection ability, which contributed to low driving voltages of blue- and green-emitting phosphorescent organic light-emitting diodes (PHOLEDs), was further confirmed by Gaussian calculation. Furthermore, the better thermal and morphological properties of o-DBFDPO and the matched frontier molecular orbital (FMO) levels in the devices significantly reduced efficiency roll-offs. Efficient blue and green electrophosphorescence based on the o-DBFDPO host was demonstrated.
Co-reporter:Hui Xu, Rui Zhu, Ping Zhao, Ling-Hai Xie, Wei Huang
Polymer 2011 Volume 52(Issue 3) pp:804-813
Publication Date(Web):3 February 2011
DOI:10.1016/j.polymer.2010.12.016
Two novel copolymers P1 and P2 were prepared by using the polymerizable aryl phosphine oxide based Eu(TTA)3VBCzDPO (EuM) (VBCzDPO = 3,6-bis(diphenyl-phosphoryl)-9-(4- vinylbenzyl)-9H-carbazole) and vinylcarbazole as the monomers with the compositions of 1:99 and 1:33, respectively. It is showed that the stronger coordinate ability of bidentate APO ligands facilitates the stability of the complex monomer during polymerization, and their beetling coordinate sites and adjustable structure efficiently reduce the steric effect of bulky EuM. Both of photoluminescent (PL) spectra in solution and solid of the copolymers exhibited improved emission from Eu3+ ion. The high PL quantum yield (PL QY) in solid of 60% is realized. Further investigation indicates that for the intra-chain energy transfer VBCzDPO serves as the intermediate and bridge between PVK and Eu(TTA)3, which ensures the high efficiency of whole intra-chain energy transfer. The pure-red emission from the devices of P1 and P2 was demonstrated.Two novel electroluminescent Eu-chelated copolymers P1 and P2 were prepared by using a polymerizable aryl phosphine oxide (APO) ligand based Eu3+ complex and vinylcarbazole as the monomers. The excellent optical and thermal properties were proved. The detail of intra-chain energy transfer in the Eu-containing copolymers was firstly investigated, which showed the intermediate effect of the APO ligands between PVK and Eu(TTA)3. The pure red emission from PLEDs was demonstrated.
Co-reporter:Hui Xu, Wei Huang
Journal of Photochemistry and Photobiology A: Chemistry 2011 Volume 217(Issue 1) pp:213-218
Publication Date(Web):1 January 2011
DOI:10.1016/j.jphotochem.2010.10.011
The intramolecular energy transfer process in a ternary Europium(III) complex Eu(TTA)3(TAPO)2 (1, TAPO = (4-diphenylamine-phenyl)-diphenylphosphine oxide, TTA = 2-thenoyltrifluoroacetonate) was investigated with both steady-state and time-resolved spectroscopic approaches to figure out the detail of the energy transfer between the neutral and anion ligands. The energy transfer from the first singlet excited energy level (S1) of the anion ligand TTA to the first triplet excited energy level (T1) of TAPO was first proved. This discovery supports that when the neutral ligand has an appropriate T1 level between the S1 and T1 levels of the anion ligand, the energy can be transferred from the S1 energy level of the neutral ligands to 5D0 of Eu3+ through a stepwise process: S1TAPO→S1TTA→T1TAPO→T1TTA→D0Eu3+5. This kind of sequential process makes intramolecular energy transfer more efficient, and is one of the most important factors resulting in the great improved photoluminescent performance of 1. It is shown that in ternary lanthanide complexes the efficient energy transfer between the neutral and anion ligands is crucial to the luminescent performance of the complex. And the intramolecular energy transfer can be facilitated by the ladder-like distribution of the excited energy levels.
Co-reporter:Hui Xu, Kun Yin, Wei Huang
Synthetic Metals 2010 Volume 160(19–20) pp:2197-2202
Publication Date(Web):October 2010
DOI:10.1016/j.synthmet.2010.08.009
A novel bidentate aryl phosphine oxide (APO) ligand with fluorene as the chromophore (9,9-diethyl-9H-fluorene-2,7-diyl)bis(diphenylphosphine)oxide (EFDPO), as well as the corresponding Eu3+ complex 1 were designed and synthesized. The strong absorption antennae effect of the functional APO ligands was proved. The effect of EFDPO in the intramolecular singlet and triplet energy transfer was also investigated. It is showed that the rigid structure and the appropriate energy levels of EFDPO not only reduce the energy loss induced by the structure relaxation, but also restrain the solvent quenching and facilitate the energy transfer from EFDPO to Eu3+. The thermal analysis was also performed to prove the improved thermal stability and phase stability of the complex. The complex exhibited good electroluminescent (EL) performance, such as maximum brightness more than 600 cd m−2, E.Q.E. around 2% and stable monochromic red emission at 616 nm.
Co-reporter:Hui Xu, Kun Yin and Wei Huang
The Journal of Physical Chemistry C 2010 Volume 114(Issue 3) pp:1674-1683
Publication Date(Web):December 30, 2009
DOI:10.1021/jp909548t
Three functional bidentate aryl phosphine oxide (APO) derivatives characterized by two diphenylphosphine oxide moieties [2-(diphenylphosphoryl)-N-(2-(diphenylphosphoryl)-4-methoxyphenyl)-4-methoxy-N-(4-methoxyphenyl)aniline (TMOADPO), 3,6-bis(diphenylphosphoryl)-9-ethyl-9H-carbazole (EtCzDPO), and 3,6-bis(diphenylphosphoryl)-9-phenyl-9H-carbazole (PhCzDPO)] bridged with a hole-transporting arylamine, as well as their tertiary complexes [Eu(TTA)3(TMOADPO)2 1, Eu(TTA)3(EtCzDPO)2 2, and Eu(TTA)3(PhCzDPO)2 3 (TTA = 2-thenoyltrifluoroacetonate)], were designed and synthesized. The strong absorption antennae effect of the functional APO ligands was proved. It is shown that their more rigid structure and chelate coordinate mode impart a decreased degree of freedom and form much more compact complex structures, which not only reduces the energy loss caused by the structure relaxation but also restrains the solvent quenching and facilitates the energy transfer from the APO ligands to Eu3+. Thermal analysis was also performed to demonstrate the improved thermal stability and phase stability of the complexes. CV analysis not only indicated excellent carrier-injection ability but also showed the feasibility to tune it by adjusting the kinds and number of functional groups and by designing alternative complex structures. All of the complexes exhibited excellent electroluminescent (EL) performance, such as maximum brightness around 1000 cd m−2, an external quantum efficiency (EQE) around 3%, and stable monochromic red emission at 614 nm. Our investigations demonstrate the potential application of bidentate APO ligands in high EL performance Eu3+ complexes.
Co-reporter:Hui Xu, Dong-Hui Yu, Le-Le Liu, Peng-Fei Yan, Li-Wei Jia, Guang-Ming Li and Zheng-Yu Yue
The Journal of Physical Chemistry B 2010 Volume 114(Issue 1) pp:141-150
Publication Date(Web):December 2, 2009
DOI:10.1021/jp909297d
Three electrophosphorescent small molecular Ir3+ complexes, Ir(HexPhBI)3 1 (HexPhBI = 1-Hexyl-2-phenyl-1H-benzo[d]imidazole), Ir(CzPhBI)3 2 (CzPhBI = 9-(6-(2-phenyl-1H-benzo[d]imidazol-1-yl)hexyl)-9H-carbazole), and Ir(Cz2PhBI)3 3 (Cz2PhBI = 9-(6-(4-(1-(6-(9H-carbazol-9-yl)hexyl)-1H-benzo[d]imidazol-2-yl)phenoxy)hexyl)-9H-carbazole), were synthesized in which 3 was designed with the structure of multiposition encapsulation. Compared to the hexyl-substituted 1, 2 and 3 end-capped with the conjugated carbazole moieties have improved thermal stability. X-ray diffraction analysis proved the amorphous state of 2 and 3. High-photoluminescent efficiencies of 3 are achieved as 72% in solution and 61% in solid. It indicates that the peripheral carbazoles not only facilitate the separation of triplet-emission cores and reduce the intermolecular aggregation but also supply a routine for the intermolecular energy transfer. Electrochemical analysis showed the more oxidation states of 3, which might be anticipated to make it superior to 1 and 2 in hole injection and transporting. The important role of the peripheral carbazole moieties in carrier injection/transporting and the optical properties of the complexes were further investigated by Gaussian simulation. A dramatic electroluminescent (EL) performance, including external quantum efficiency of nearly 6%, low turn-on voltage of 2.5 V, and high brightness over 6000 cd m−2, from the host-free spin-coated device of 3 was achieved. The superiority of multiencapsulation in EL was proved by comparing the EL performance of 2 and 3. By making comparison between the host-free and phosphor-doping devices, it indicated that the combined modification of the aliphatic chains and functional groups in multipositions is a feasible approach to realize the high-efficiency small molecular phosphorescent materials.
Co-reporter:Hui Xu ; Rui Zhu ; Ping Zhao ;Wei Huang
The Journal of Physical Chemistry C () pp:
Publication Date(Web):July 13, 2011
DOI:10.1021/jp2029714
Two metallopolymers P1 and P2 were prepared by using a novel polymerizable Eu3+ complex Eu(TTA)3VBADPO (EuMA) (TTA = 2-thenoyltrifluoroacetonate) and vinylcarbazole as the monomers in the ratios of 1:99 and 3:97, respectively, in which VBADPO is 2-(diphenylphosphoryl)-N-(2-(diphenylphosphoryl)-4-methoxyphenyl)-4-methoxy-N-(4-vinylbenzyl)aniline as a polymerizable aryl phosphine oxide ligand with a bipolar structure. The copolymers exhibit the excellent optical properties with photoluminescence quantum yield more than 60% in film. Both Gaussian simulation and electrochemical analysis indicated that the Eu3+-complexed segments form double-carrier traps (Eu-trap) in the copolymers with depth of 0.1 eV for the hole and 0.7 eV for the electron. The single-layer spin-coated devices of P1 and P2 realized the pure red emissions from Eu3+ ions. The biggest luminance of 149.1 cd m–2 was achieved, which is the highest among those of electroluminescent (EL) Eu3+-containing copolymers reported so far. The unusual efficiency stability proves the limited concentration quenching and T–T annihilation in P1 and P2 due to the uniform dispersion of emissive Eu3+ chelate moieties in the host matrix. With the high brightness and very stable efficiencies, P1 is favorable among the high-performance Eu3+-containing copolymers. It is also proved that the formation of carrier-traps in the copolymers is effective to improve EL performances.
Co-reporter:Hui Xu ; Zhi-Feng Xu ; Zheng-Yu Yue ; Peng-Fei Yan ; Bin Wang ; Li-Wei Jia ; Guang-Ming Li ; Wen-Bin Sun ;Ju-Wen Zhang
The Journal of Physical Chemistry C () pp:
Publication Date(Web):September 6, 2008
DOI:10.1021/jp803325g
A novel deep blue-emitting ZnII complex Zn(Lc)2 (Lc− = 2-(1-(6-(9H-carbazol-9-yl)hexyl)-1H-benzo[d]imidazol-2-yl)phenolate) based on a carbazole-functionalized N^O ligand was synthesized by a modified method. Other two ZnII complexes (Zn(La)2, La− = 2-(1H-benzo[d]imidazol-2-yl)phenolate; Zn(Lb)2, Lb− = 2-(1-ethyl-1H-benzo[d]imidazol-2-yl)phenolate) were also prepared for comparison. The remarkable substitution effect on the photoluminescent and thermal properties of the complexes was studied. The investigation indicated an unexpected amplifying hypsochromic effect of the substituents on the emission of the complex in the solid state: the larger substituent corresponded to the larger blue shift of the emission of the complex (Zn(Lc)2 has the shortest emission wavelength of 422 nm as the deep blue emission among these three complexes). The stronger steric effect induced by the bulky substitutions should be one of the most important factors. Among the three ZnII complexes, the temperature of decomposition of Zn(Lc)2 is the highest at 427 °C. Cyclic voltammetry (CV) of the complexes showed that the carbazole moieties remarkably improved the hole injection ability of Zn(Lc)2 with the HOMO energy level 0.6 eV higher than those of Zn(La)2 and Zn(Lb)2. The good hole injection and transporting ability of Zn(Lc)2 was further proved by its three-layer devices, in which the electroluminescent (EL) emission mainly originated from the electron-transporting Alq3 layer. Through the four-layer devices with the hole-blocking layer, the pure blue emission of Zn(Lc)2 at 452 nm was demonstrated. Zn(Lc)2 seems favorable among the blue-emitting ZnII complexes with a brightness more than 2000 cd m−2, a high efficiency stability, and an excellent EL spectra stability.
Co-reporter:Dongxue Ding, Zhen Zhang, Ying Wei, Pengfei Yan and Hui Xu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 43) pp:NaN11396-11396
Publication Date(Web):2015/09/29
DOI:10.1039/C5TC02726H
Two quaternary ambipolar phosphine oxide host materials, 9-(4-(9-(4′-(2-(diphenylphosphoryl)phenoxy)biphenyl-4-yl)-9H-fluoren-9-yl)phenyl)-9H-carbazole (9CzFDPESPO) and 9-(4-(9-(3′-(diphenylphosphoryl)-4′-(2-(diphenylphosphoryl)phenoxy)biphenyl-4-yl)-9H-fluoren-9-yl)phenyl)-9H-carbazole (9CzFDPEPO), were designed and prepared with mixed indirect and multi-insulating linkages to investigate the spatial effect on the electroluminescence performance of high-energy-gap hosts in blue phosphorescence and thermally activated delayed fluorescence light-emitting diodes (PHOLEDs and TADF OLEDs), in comparison to a ternary analogue 9-(4-(9-(4-(diphenylphosphoryl)phenyl)-9H-fluoren-9-yl)phenyl)-9H-carbazole (9CzFSPO). The donor–acceptor (D–A) distance in 9CzFDPESPO is elongated through the involvement of diphenylene as a π-extender, while the second phosphine oxide acceptor on diphenylene of 9CzFDPEPO is utilized to make its D–A distance comparable to that of 9CzFSPO. The single-molecular optoelectronic properties of these three hosts were uniform, owing to the effectively suppressed intramolecular electronic coupling by indirect and multi-insulating linkages. Their similar high triplet energy of 3.0 eV and the suitable energy levels of the highest occupied and the lowest unoccupied molecular orbitals around −6.1 and −2.5 eV, respectively, provide effective energy transfer and carrier injection. In contrast, 9CzFDPESPO shows the highest hole mobility owing to its longest D–A distance, directly indicating the spatial effect. As expected, with the most effectively suppressed spatial effect, 9CzFDPESPO endowed its blue phosphorescence and TADF devices with a state-of-the-art performance, e.g. external quantum efficiencies of 22.5% and 16.7%, respectively, which were the best results for quaternary host materials reported so far.
Co-reporter:Weibo Yang, Zhensong Zhang, Chunmiao Han, Zhen Zhang, Hui Xu, Pengfei Yan, Yi Zhao and Shiyong Liu
Chemical Communications 2013 - vol. 49(Issue 27) pp:NaN2824-2824
Publication Date(Web):2013/02/20
DOI:10.1039/C3CC00133D
Preserved high first triplet energy levels and improved electrical properties of two donor–acceptor type carbazole–phosphine oxide hosts were achieved through short-axis substitution to realize efficient PHOLEDs with extremely low driving voltages of 2.6 V for onset and <3.2 V at 100 cd m−2.
Co-reporter:Wenjing Kan, Liping Zhu, Ying Wei, Dongge Ma, Mingzhi Sun, Zhongbin Wu, Wei Huang and Hui Xu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 21) pp:NaN5439-5439
Publication Date(Web):2015/04/21
DOI:10.1039/C5TC00643K
A series of benzimidazole–PO hybrids, PBIPO, DPBIPO and TPBIPO, with different configurations of phosphine oxide (PO)-bridged 2-phenylbenzimidazole (PBI) groups, demonstrate an effective charge–exciton separation (CES) strategy for electron-transport material (ETM) design aimed at interfacial triplet-polaron quenching (TPQ) suppression in hole-predominant phosphorescent organic light-emitting diodes (PHOLEDs). The electronic states of these materials are well-controlled by virtue of their insulating and electron-withdrawing phosphine oxide joints. Their equivalent frontier molecular orbital energy levels (−2.7 and −6.4 eV) and triplet states (3.0 eV) give them identical good electron-injecting/hole-blocking abilities and effective exciton diffusion suppression, establishing a correspondence between electron mobility and interfacial TPQ effect, and the device performance of these ETMs. Stronger interactions between TPPO groups and blue phosphor iridium(III) bis(2-(4,6-difluorophenyl)-pyridinato-N,C2′) picolinate (FIrpic) give rise to the optimized orientation of unsymmetrical PBIPO on the emissive layer (EML) to separate its charged moiety from the EML interface, effectively suppressing interfacial TPQ. Consequently, PBIPO endows its conventional FIrpic-based blue device with state-of-the-art efficiencies of 47.3 cd A−1, 36.0 lm W−1 and 22.2%, which are two- and three-fold those of the common ETM TPBI and its analogue DPBIPO, with a two orders of magnitude higher electron mobility. At 1000 cd m−2, the efficiencies of PBIPO-based devices still remained at 43.5 cd A−1 and 20.1%, making PBIPO among the most efficient high-energy-gap ETMs to date and manifesting the effectiveness of the molecular CES strategy for interfacial TPQ suppression.
Co-reporter:Jun-Xi Cai, Teng-Ling Ye, Xue-Feng Fan, Chun-Miao Han, Hui Xu, Li-Li Wang, Dong-Ge Ma, Yang Lin and Peng-Fei Yan
Journal of Materials Chemistry A 2011 - vol. 21(Issue 39) pp:NaN15416-15416
Publication Date(Web):2011/09/01
DOI:10.1039/C1JM12114F
A series of electrophosphorescent small molecular Ir3+ complexes IrPBIO22, IrPBICO, IrPBIO44 and IrPBIC22O22 for solution-processable host-free organic light-emitting diodes (OLEDs) were designed and synthesized, in which the electron-transporting 1,3,4-oxadiazole (OXD) and hole-transporting carbazole moieties were introduced through aliphatic chains to achieve balanced carrier injection/transporting. The coordinatable OXD groups were successfully and conveniently introduced through the post-substitution of Ir3+ cores. The photophysical investigation showed that compared with the single-position substituted counterparts, the double-position substitution is superior in restraining the quenching effect in solid states to endow the corresponding complexes with the much higher photoluminescence quantum yield (PLQY) in the film. The influences of peripheral carrier transporting (CT) moieties on the energy levels of frontier molecular orbitals were investigated with UPS analysis and Density Function Theory calculation. The dramatic electroluminescent (EL) performance of IrPBIC22O22 based on its host-free spin-coat phosphorescent organic light-emitting diodes (PHOLEDs), especially the remarkably restrained efficiency roll-off less than 16% at 1000 cd m−2 was realized, which demonstrated that the combined modification of the effective segregation of emitting cores by multi-position encapsulation and the balanced carrier injection/transporting through bipolar substitution is an effective strategy for realizing high-efficiency small molecular electrophosphorescent materials with the features of solution processability and strong restraining effect on quenching for host-free devices.
Co-reporter:Mingzhi Sun, Liping Zhu, Wenjing Kan, Ying Wei, Dongge Ma, Xuefeng Fan, Wei Huang and Hui Xu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 36) pp:NaN9479-9479
Publication Date(Web):2015/08/24
DOI:10.1039/C5TC90156A
Correction for ‘Ternary donor–acceptor phosphine oxide hosts with peculiar high energy gap for efficient blue electroluminescence’ by Mingzhi Sun et al., J. Mater. Chem. C, 2015, DOI: 10.1039/c5tc02029h.
Co-reporter:Fuquan Han, Xiaolin Zhang, Jing Zhang, Ying Wei, Xinwen Zhang, Wei Huang and Hui Xu
Chemical Communications 2016 - vol. 52(Issue 29) pp:NaN5186-5186
Publication Date(Web):2016/03/15
DOI:10.1039/C6CC01414C
Iridium-complexed nanosize phosphors 3D-encapsulated with nine 3,6-di-tert-butyl-N-propyl-carbazole groups were constructed as host-dopant integrated systems, which achieved a high photoluminescence quantum yield beyond 70% from neat evaporated films, and an electroluminescence external quantum efficiency up to ∼8.5% and near-zero roll-offs at 1000 cd m−2 from its dual-layer host-free light-emitting diodes.
Co-reporter:Jing Zhang, Dongxue Ding, Ying Wei and Hui Xu
Chemical Science (2010-Present) 2016 - vol. 7(Issue 4) pp:NaN2882-2882
Publication Date(Web):2016/01/14
DOI:10.1039/C5SC04848F
The similarity of thermally activated delayed fluorescence (TADF) dyes and their hosts as pure organic molecules makes hosts predominant in intermolecular interactions and crucial to exciton harvesting and utilization in TADF diodes. DPEPO is the most popular high-energy-gap blue TADF host with steric ortho-substituted diphenylphosphine oxide (DPPO) groups for intermolecular interaction suppression, but suffers from serious efficiency roll-off due to its weak electroactivity. On the contrary, para-substituted DPPO with small steric hindrance is superior in intramolecular electronic coupling. In this work, four constitutional isomers of DPEPO are constructed as diphenylether (DPE) with two diphenylphosphine oxide (DPPO) groups substituted at either the 2 or 4 position, namely 22′DPEPO (viz.DPEPO), 24DPEPO, 24′DPEPO and 44′DPEPO, respectively. On the basis of separation configuration, the steric effect and electroactivity of ortho- and para-substituted DPPOs are successfully integrated in 24′DPEPO, accompanied by remarkably reduced intermolecular interactions due to its unsymmetrical configuration. Compared to its congeners, 24′DPEPO has a rigid structure and locally excited states similar to 22′DPEPO for interaction suppression and improved charge mobility comparable to 44′DPEPO for charge flux balance. Significantly, by virtue of the predominant orientation effect of ortho-DPPO on the T1 location, its T1 state is extremely condensed onto a single phenyl, protected from intermolecular interactions by its remaining five phenyls at its maximum extent. Consequently, 24′DPEPO endowed its DMAC-DPS-based deep-blue devices with state-of-the-art performance, including high color purity with chromaticity coordinates of (0.16, 0.17), external quantum efficiency (EQE) beyond 20% and EQE roll-off as low as 32% at 1000 cd m−2. It is shown that the device performance of 24′DPEPO was far beyond simple integration of those of 22′DPEPO and 44′DPEPO, verifying the significance of host optimization.
Co-reporter:Donghui Yu, Fangchao Zhao, Zhen Zhang, Chunmiao Han, Hui Xu, Jing Li, Dongge Ma and Pengfei Yan
Chemical Communications 2012 - vol. 48(Issue 49) pp:NaN6159-6159
Publication Date(Web):2012/04/26
DOI:10.1039/C2CC31066J
An ambipolar ternary deep-blue emitter with CIE coordinates of (0.15, 0.07) and high electroluminescent performance was constructed on the basis of an insulated donor–π–acceptor system through an indirect linkage.
Co-reporter:Chunmiao Han, Liping Zhu, Fangchao Zhao, Zhen Zhang, Jianzhe Wang, Zhaopeng Deng, Hui Xu, Jing Li, Dongge Ma and Pengfei Yan
Chemical Communications 2014 - vol. 50(Issue 20) pp:NaN2672-2672
Publication Date(Web):2014/01/17
DOI:10.1039/C3CC49020C
A series of phosphine oxide hosts were constructed to investigate the influence of the triplet state extension in hosts on electrophosphorescence, in which DPESPOPhCz with the carbazolyl-localized triplet state endowed its blue-emitting PHOLEDs with favourable performance, including an external quantum efficiency more than 13%.
Co-reporter:Jing Li, Zhensong Zhang, Chunmiao Han, Dongxue Ding, Yi Zhao, Wei Huang and Hui Xu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 26) pp:NaN6716-6716
Publication Date(Web):2015/06/01
DOI:10.1039/C5TC01179E
Fluorene and diphenylphosphine oxide were employed as peripheral groups to construct ternary host materials DBFxPODEFn with benzofuran as a core for yellow phosphorescent organic light-emitting diodes (PhOLEDs). Their peripheral group density and ratio were rationally adjusted to suppress quenching and enhance charge balance. The conjugation of DBFxPODEFn was extended appropriately on the basis of meso- and short-axis linkages to render similar optical properties and a medium first triplet energy (T1) of 2.58 eV for efficient and comparable energy transfer to yellow phosphors, making the yellow PhOLED performance correspond to the charge flux balance and quenching effects, viz. the correlation between device performance and their functional group density and spatial arrangement. DBFSPODEF with the desired electron-dominant characteristics and the suppressed triplet–triplet annihilation (TTA) effect endowed its devices with a low driving voltage of <3.8 V and favorable efficiencies of 32.7 lm W−1 and 12.5% at 1000 cd m−2 for lighting applications. This work indicates that an appropriate functionalization and a rational spatial group arrangement are significant for constructing efficient hosts for low-voltage-driven PhOLEDs.
Co-reporter:Mingzhi Sun, Liping Zhu, Wenjing Kan, Ying Wei, Dongge Ma, Xuefeng Fan, Wei Huang and Hui Xu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 36) pp:NaN9478-9478
Publication Date(Web):2015/07/31
DOI:10.1039/C5TC02029H
Ternary donor (D)–acceptor (A)–acceptor (A) molecules are commonly considered as low triplet (T1) energy systems for specific applications. In this work, exception to this behavior was observed in a triangle-shaped D–A–A molecule PCImbPO with unusually high triplet energy of 3.0 eV. Profiting from the enhanced D–A electronic coupling, electron injecting and transporting ability of PCImbPO was dramatically improved with negligible influences on its highest occupied molecular orbital (HOMO) characteristics. Its particular T1 configuration adjustment further gives rise to the separated frontier MO and T1 locations, beneficial to suppress quenching effects. By utilizing PCImbPO as host in blue phosphorescent organic light-emitting diodes (PHOLEDs) and thermally activated delayed fluorescence devices, impressively high external quantum efficiency of 22% and 12% were achieved, respectively. This work established a new understanding of high-energy-gap complicated D–A systems.
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