Co-reporter:Fang Wang, Di Liu, Jiuyan Li, and Mengyao Ma
ACS Applied Materials & Interfaces November 1, 2017 Volume 9(Issue 43) pp:37888-37888
Publication Date(Web):October 11, 2017
DOI:10.1021/acsami.7b11667
9′-Pyridinyl-9′H-9,3′:6′,9″-tercarbazole (PyCz) is a bipolar host material in phosphorescent organic light-emitting diodes (PhOLEDs). A second n-type unit, either pyridine or diphenylphosphine dioxide (DPPO), is introduced onto the pyridine ring of PyCz at para- or metasite to design and prepare four novel “dual n-type unit bipolar host” materials m-BPyCz, p-BPyCz, m-POPyCz, and p-POPyCz. The incorporation of the second n-type unit pulls down the lowest unoccupied molecular orbitals and facilitates electron injection and transportation, resulting in better charge-balancing ability. As a result, these dual n-type unit bipolar hosts exhibit higher efficiencies and slower efficiency roll-off in their blue and green PhOLEDs. In particular, m-POPyCz containing a bulky DPPO as the second n-type unit with a metalinking possesses the best charge-balancing state and generates a maximum external quantum efficiency (ηext) of 27.0% (corresponding to a current efficiency of 51.9 cd A–1 and a power efficiency of 46.5 lm W–1) in its sky-blue device and still remained at a high ηext of 23.6% even at the practical brightness of 1000 cd m–2. These results clearly demonstrate that the “dual n-type unit bipolar hosts” with an optimized substitution position and steric effect is a new and effective type of host materials for high-performance OLEDs.Keywords: charge balance; DPPO; dual n-type unit bipolar host; metalinking; PhOLEDs;
Co-reporter:Wei Li, Jiuyan Li, Di Liu, Deli Li, and Fang Wang
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 33) pp:21497
Publication Date(Web):August 1, 2016
DOI:10.1021/acsami.6b04395
Low driving voltage and high power efficiency are basic requirements when practical applications of organic light emitting diodes (OLEDs) in displays and lighting are considered. Two novel host materials m-PyCNmCP and 3-PyCNmCP incorporating cyanopyridine moiety as electron-transporting unit are developed for use in fac-tris(2-phenylpyridine)iridium(III) (Ir(ppy)3) based green phosphorescent OLEDs (PhOLEDs). Extremely low turn-on voltages of 2.01 and 2.27 V are realized, which are even lower than the theoretical limit of the emitted photon energy (hv)/electron charge (e) (2.37 V) of Ir(ppy)3. High power efficiency of 101.4 lm/W (corresponding to a maximum external quantum efficiency of 18.4%) and 119.3 lm/W (24.7%) are achieved for m-PyCNmCP and 3-PyCNmCP based green PhOLEDs. The excellent EL performance benefits from the ideal parameters of host materials by combining cyano and pyridine to enhance the n-type feature. The energetic favorable alignment of HOMO/LUMO levels of hosts with adjacent layers and the dopant for easy charge injections and direct charge trapping by dopant, their bipolar feature to balance charge transportations, sufficiently high triplet energy and small singlet/triplet energy difference (0.38 and 0.43 eV) combine to be responsible for the extremely low driving voltages and high power efficiencies of the green PhOLEDs.Keywords: cyano; host material; low turn-on voltage; phosphorescent organic light-emitting diodes (PhOLEDs); pyridine
Co-reporter:Wei Li, Jiuyan Li, Di Liu, and Qian Jin
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 34) pp:22382
Publication Date(Web):August 12, 2016
DOI:10.1021/acsami.6b05355
3-(1H-Pyrazol-1-yl)pyridine is used as electron-transporting unit to construct bipolar host materials o-CzPyPz, m-CzPyPz, and p-CzPyPz for application in phosphorescent organic light-emitting diodes (PhOLEDs). By varying the ortho-, meta-, or para-linking mode between the n-type 3-(1H-pyrazol-1-yl)pyridine and the p-type carbazole on phenylene bridge, the optoelectronic parameters are tuned to large extent. The highly twisted o-CzPyPz has high triplet energy of 2.95 eV, while the isomer p-CzPyPz with more coplanar conformation has smaller triplet energy of 2.67 eV. The m-CzPyPz-hosted blue PhOLED exhibits a peak current efficiency of 49.1 cd A–1 (corresponding to an external quantum efficiency of 24.5%) and low-efficiency roll-off, while the p-CzPyPz-hosted green PhOLEDs turns on at 2.8 V and exhibits high efficiencies of 91.8 cd A–1 (96.1 lm W–1 and 27.3%). Furthermore, two-emitting-layer white OLEDs are fabricated with m-CzPyPz or p-CzPyPz as common hosts for both blue and orange phosphors, which realize high efficiencies of 57.8 cd A–1 (45.4 lm W–1 and 23.6%) and 60.7 cd A–1 (38.1 lm W–1 and 23.1%). The optimization of host structure for good matching of host and dopant and finally for the ideal performance is discussed.Keywords: 3-(1H-pyrazol-1-yl)pyridine; bipolar host materials; phosphorescent organic light-emitting diodes (PhOLEDs); simple structure; white
Co-reporter:Wei Li, Jiuyan Li, Di Liu, Fang Wang and Shufen Zhang
Journal of Materials Chemistry A 2015 vol. 3(Issue 48) pp:12529-12538
Publication Date(Web):16 Nov 2015
DOI:10.1039/C5TC02997J
A series of small molecular isomers, namely o-CzCN, m-CzCN, and p-CzCN, are developed for use as bipolar hosts in blue phosphorescent and fluorescent organic light-emitting diodes (OLEDs). Cyano (CN) substituted phenyl is selected as the n-type unit and N-phenyl-substituted carbazole as the p-type unit. By adjusting the ortho-, meta-, and para-linking styles of the functional units, the physical parameters are regularly tuned to a large extent. The study of complete spatial separation of frontier molecular orbitals and single-carrier devices confirm the bipolar feature. Blue phosphorescent and thermally activated delayed fluorescence (TADF) OLEDs were fabricated using iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (FIrpic) and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN) as doped emitters. A maximum current efficiency of 46.81 cd A−1 and an external quantum efficiency of 23.14% were achieved for the phosphorescent OLED with the m-CzCN host. Furthermore, high efficiencies of 29.23 cd A−1 and 14.98% were obtained for the 2CzPN based blue TADF device with the o-CzCN host, which are higher than the best literature value of 13.6% for 2CzPN devices. Both m-CzCN and o-CzCN always perform better than p-CzCN. The influence of the chemical structures on their properties and performance is interpreted for these CN-decorated host materials.
Co-reporter:Wei Li, Jiuyan Li, Fang Wang, Zhuo Gao, and Shufen Zhang
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 47) pp:26206
Publication Date(Web):November 6, 2015
DOI:10.1021/acsami.5b08291
A series of bipolar hosts, namely, 5-(2-(9H-carbazol-9-yl)-phenyl)-1,3-dipyrazolbenzene (o-CzDPz), 5-(3-(9H-carbazol-9-yl)-phenyl)-1,3-dipyrazolbenzene (m-CzDPz), 5-(9-phenyl-9H-carbazol-3-yl)-1,3-dipyrazolbenzene (3-CzDPz), and 5-(3,5-di(9H-carbazol-9-yl)-phenyl)-1,3-dipyrazolbenzene (mCPDPz), are developed for phosphorescent and thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). They are designed by selecting pyrazole as n-type unit and carbazole as p-type one. The triplet energy (ET), the frontier molecular orbital level, and charge transporting abilities, are adjusted by varying the molar ratio of pyrazole to carbazole and the linking mode between them. They have high ET values of 2.76–3.02 eV. Their electroluminescence performance is evaluated by fabricating both phosphorescent and TADF devices with blue or green emitters. The m-CzDPz hosted blue phosphorescent OLEDs achieves high efficiency of 48.3 cd A–1 (26.8%), the 3-CzDPz hosted green phosphorescent device exhibits 91.2 cd A–1 (29.0%). The blue and green TADF devices with 3-CzDPz host also reach high efficiencies of 26.2 cd A–1 (15.8%) and 41.1 cd A–1 (13.3%), respectively. The excellent performance of all these OLEDs verifies that these pyrazole-based bipolar compounds are capable of being universal host materials for OLED application. The influence of molar ratio of n-type unit to p-type one and the molecular conformation of these hosts on their device performance is discussed and interpreted.Keywords: bipolar host; phosphorescent organic light-emitting diodes (OLEDs); pyrazole; thermally activated delayed fluorescence (TADF); universal host materials;
Co-reporter:Lijun Deng, Jiuyan Li, Wei Li
Dyes and Pigments 2014 Volume 102() pp:150-158
Publication Date(Web):March 2014
DOI:10.1016/j.dyepig.2013.11.007
•Carbazole-based small-molecular host materials with dimethylbiphenyl core were synthesized.•They have high triplet energies due to twisted molecular configuration.•Pyrazole-containing molecule show bipolar charge transporting feature.•The solution-processed green and orange OLEDs with them as hosts exhibited high electrophosphorescence efficiencies.Two novel carbazole-based molecules were synthesized by attaching 3,6-bis(3,6-di-tert-butyl-carbazol-9-yl)-carbazole and pyrazole to the dimethylbiphenyl core in a symmetric and asymmetric way. Owing to highly twisted configuration, they exhibit high triplet energy of 2.90 eV. They are suitable for spin coating to make thin films. The complete spatial separation of frontier molecular orbitals and the single-carrier devices study confirm the bipolar feature of pyrazole-containing material. They were used as hosts to fabricate phosphorescent organic light-emitting diodes by wet method. The green devices exhibited maximum efficiencies of 33 cd A−1 and 35 cd A−1, which far exceed that (23 cd A−1) of the control device with the polyvinylcarbazole host. The versatility of these hosts also spread to orange devices and peak efficiencies of 35 cd A−1 and 39 cd A−1 were achieved. The pyrazole-containing material always performed better due to its bipolar charge transporting nature.3,6-Bis(3,6-di-tert-butyl-carbazol-9-yl)-carbazole and pyrazole groups are used as building blocks to construct the small-molecular host materials, which exhibit high efficiencies of 35 and 39 cd A−1 in their solution-processed orange and green phosphorescent organic light-emitting diodes.
Co-reporter:Wei Li;Jiuyan Li;Miao Wang
Israel Journal of Chemistry 2014 Volume 54( Issue 7) pp:867-884
Publication Date(Web):
DOI:10.1002/ijch.201400049
Abstract
As a new technology for flat-panel displays and general lighting sources, solution-processed phosphorescent organic light-emitting diodes (PhOLEDs) unfurl a bright future, due to their merits of high quantum efficiency and easy fabrication. In recent years, great progress has been made in the device performance of solution-processed PhOLEDs, by developing both high-efficiency organometallic phosphors and novel solution-processable organic host materials. This review highlights recently developed organic host materials for triplet guest emitters in solution-processed PhOLEDs. The solution-processable host materials are classified into three types – small molecule, dendrimer, and polymer – according to their molecular architecture and molecular weight. The material design concept and the relationships between the molecular structure, material properties and device performance are the focus of this discussion. A future strategy for the development of high-performance solution-processed host materials is proposed.
Co-reporter:Jiuyan Li;Ting Zhang;Yunjing Liang;Ruixia Yang
Advanced Functional Materials 2013 Volume 23( Issue 5) pp:619-628
Publication Date(Web):
DOI:10.1002/adfm.201201326
Abstract
A group of dendrimers with oligo-carbazole dendrons appended at 4,4′- positions of biphenyl core are synthesized for use as host materials for solution-processible phosphorescent organic light-emitting diodes (PHOLEDs). In comparison with the traditional small molecular host 4,4′-N,N′-dicarbazolebiphenyl (CBP), the dendritic conformation affords these materials extra merits including amorphous nature with extremely high glass transition temperatures (ca. 376 °C) and solution-processibility, but inherent the identical triplet energies (2.60–2.62 eV). In comparison with the widely-used polymeric host polyvinylcarbazole (PVK), these dendrimers possess much higher HOMO levels (–5.61 to –5.42 eV) that facilitate efficient hole injection and are favorable for high power efficiency in OLEDs. The agreeable properties and the solution-processibility of these dendrimers makes it possible to fabricate highly efficient PHOLEDs by spin coating with the dendimers as phosphorescent hosts. The green PHOLED containing Ir(ppy)3 (Hppy = 2-phenyl-pyridine) dopant exhibits high peak efficiencies of 38.71 cd A−1 and 15.69 lm W−1, which far exceed those of the control device with the PVK host (27.70 cd A−1 and 9.6 lm W−1) and are among the best results for solution-processed green PHOLEDs ever reported. The versatility of these dendrimer hosts can be spread to orange PHOLEDs and high efficiencies of 32.22 cd A−1 and 20.23 lm W−1 are obtained, among the best ever reported for solution-processed orange PHOLEDs.
Co-reporter:Lijun Deng, Jiuyan Li, Ge-Xia Wang and Li-Zhu Wu
Journal of Materials Chemistry A 2013 vol. 1(Issue 48) pp:8140-8145
Publication Date(Web):15 Oct 2013
DOI:10.1039/C3TC31893A
A group of small-molecular compounds, namely 6-(3-(9H-carbazol-9-yl)phenyl)-9-ethyl-9H-carbazole-3-carbonitrile (m-CzCzCN), 6-(2-(9H-carbazol-9-yl)phenyl)-9-ethyl-9H-carbazole-3-carbonitrile (o-CzCzCN), 6-(3,5-di(9H-carbazol-9-yl)phenyl)-9-ethyl-9H-carbazole-3-carbonitrile (mCPCzCN), 8-(3-(9H-carbazol-9-yl)phenyl)dibenzo[b,d]furan-2-carbonitrile (m-CzOCN), 8-(3-(9H-carbazol-9-yl)phenyl)dibenzo[b,d]thiophene-2-carbonitrile (m-CzSCN), are designed and synthesized for use as host materials in blue phosphorescent organic light-emitting diodes (PhOLEDs). The p-type carbazole and the n-type cyano-decorated carbazole, dibenzofuran or dibenzothiophene unit are incorporated, to either the meta- or ortho-positions of the phenylene bridge. The bipolar feature was confirmed by theoretical calculation and experimental results of the single-carrier devices. These materials exhibit an excellent performance in their hosted blue phosphorescent OLEDs with iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (Firpic) as the doped emitter. The ortho-substituted o-CzCzCN realizes higher device efficiencies than the meta-substituted isomer m-CzCzCN, with a maximum external quantum efficiency of 21.0% and a current efficiency of 43.9 cd A−1. The device hosted by m-CzSCN also exhibits remarkably high efficiencies of 23.3% and 46.1 cd A−1. Furthermore, these blue PhOLEDs are characterized by a slow efficiency roll-off. Even at a high brightness of 10000 cd m−2, the o-CzCzCN hosted device still retain high efficiencies of 13.6% and 28.5 cd A−1. This is a systematic study of incorporating the CN group onto carbazole, dibenzofuran and dibenzothiophene, to develop high-triplet-energy bipolar hosts for OLED applications.
Co-reporter:Jiuyan Li, Renjie Wang, Ruixia Yang, Wei Zhou and Xin Wang
Journal of Materials Chemistry A 2013 vol. 1(Issue 26) pp:4171-4179
Publication Date(Web):02 May 2013
DOI:10.1039/C3TC30586D
Three 2-aryl-benzothiazole chromophores were designed and synthesized for use as major cyclometalating ligands of iridium complexes, in which the aryl groups were N-phenyl-3-carbazolyl, 2-(9,9-dioctyl)fluorenyl and N-phenyl-2-carbazolyl. The homoleptic tris-cyclometalated and heteroleptic bis-cyclometalated iridium complexes, 1–5, were synthesized using these ligands. By adjusting the chemical structures and then the electronic state of these complexes, we were able to continuously tune the phosphorescence from yellow to saturated red with peak wavelengths in the order of 1 < 2 < 3 < 4 < 5. The quantum chemical calculations and the electrochemical data clearly demonstrate the origin of the phosphorescence color tuning. The organic light-emitting diodes (OLEDs) containing these iridium complexes as doped emitters exhibited yellow to red electrophosphorescence with excellent performance. Particularly, the complex 1 based device produced high efficiencies of 75.9 cd A−1, 48.2 lm W−1, and 23.0% with CIE (0.46, 0.53), which represent the highest efficiencies for yellow OLEDs up to now. Furthermore, 1 was used to fabricate two-element white OLEDs in combination with a blue phosphor and high efficiencies of 57.9 cd A−1 and 21.9% were achieved, which are among the best efficiencies for two-emitting-component white OLEDs reported so far.
Co-reporter:Ting Zhang, Yunjing Liang, Jinling Cheng and Jiuyan Li
Journal of Materials Chemistry A 2013 vol. 1(Issue 4) pp:757-764
Publication Date(Web):07 Nov 2012
DOI:10.1039/C2TC00305H
N,N′-Dicarbazolyl-4,4′-biphenyl (CBP) is one of the most successful uni-polar host materials for phosphorescent organic light-emitting diodes (PhOLEDs). We report the synthesis and properties of one novel CBP derivative, CBP-CN, with two cyano groups (CN) at the 3-site of carbazole rings. The strong electron-withdrawing CN group was introduced with the expectation to promote electron-injecting/-transporting abilities and to achieve bipolar features for CBP-CN. In comparison with the parent CBP, CBP-CN possesses lowered HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) levels and dramatically increased Tg (glass transition temperature, 162 °C), but unaltered HOMO–LUMO band gap and triplet energy (2.69 eV). Green and red PhOLEDs were fabricated with CBP-CN as hosts for traditional iridium phosphors. The maximum luminance efficiency (ηL) of 80.61 cd A−1 (23.13%) was achieved for the green PhOLED, and 10.67 cd A−1 (15.54%) for the red one, which represent efficiency increases of 25–33% compared with those of the best devices with CBP host and are even among the best data for phosphorescent OLEDs reported so far. The theoretical calculation and the carrier-only devices investigation confirmed that the electron-injecting/-transporting character and the bipolar nature of CBP-CN should be responsible for the performance enhancements.
Co-reporter:Ting Zhang, Renjie Wang, Liming Wang, Qian Wang, Jiuyan Li
Dyes and Pigments 2013 Volume 97(Issue 1) pp:155-161
Publication Date(Web):April 2013
DOI:10.1016/j.dyepig.2012.11.022
Novel tridurylboranes based molecules with oligofluorene endcaps, namely tris[(9,9-dioctylfluoren-2-yl)duryl]borane (DBF1) and Tris[(9,9,9′,9′-tetraoctyl-2,2′-bifluoren-7-yl)duryl]borane (DBF2), were designed and synthesized for use in solution-processed phosphorescent organic light-emitting diodes (OLEDs). These materials show good solubility and excellent thermal stability. The photophysical study revealed that there is no significant π-conjugation between the tridurylborane core and the oligoflourene endcaps due to the strong steric hindrance of bulky duryl groups. DBF1 has sufficiently high triplet energy so as to act as host material for green phosphors. Green phosphorescent OLEDs were fabricated by partially solution-processing technique with DBF1 as host and traditional green iridium phosphor as doped emitter. An optimized device exhibited high efficiencies of 36.77 cd A−1, 23.09 lm W−1 and 10.81%, which are close to the best data for partially solution-processed green phosphorescent OLEDs containing small molecular hosts reported so far.Graphical abstractSmall molecular tridurylborane/oligofluorene hybrids are developed for use as solution-processible host materials in green phosphorescent organic light-emitting diodes, which exhibit high electrophosphorecence efficiencies of 36.77 cd A−1 and 10.81%.Highlights► Novel small molecules (DBF1 and DBF2) with tridurylboranes core and oligo-fluorene endcaps were synthesized. ► DBF1 has sufficiently high triplet energy so as to act as host material for green phosphors. ► Green phosphorescent OLEDs were fabricated by spin-coating method with DBF1 as host for iridium phosphor. ► The 36.77 cd A−1 is close to the best efficiency for solution-processed green phosphorescent OLEDs with small molecular host.
Co-reporter:Jiuyan Li, Yongheng Duan, Qing Li
Dyes and Pigments 2013 Volume 96(Issue 2) pp:391-396
Publication Date(Web):February 2013
DOI:10.1016/j.dyepig.2012.08.028
Two novel red fluorescent thieno-[3,4-b]-pyrazine-cored molecules containing tetraphenylethylene as peripheral groups, T-TP and T-TP1, are designed and synthesized. Their photophysical, electrochemical and electroluminescent properties are investigated. They are characterized by large Stokes shifts of over 100 nm. The bulky peripheral groups enable these molecules to be well soluble and provide the site-isolation effect on the planar emissive core. These novel materials are used as non-doped emitting layer to fabricate organic light-emitting diodes (OLEDs) by vacuum evaporation technique. Saturated red emission is obtained with a maximum brightness of 1385 cd m−2 and a luminance efficiency of 0.66 cd A−1.Graphical abstractDecorating the planar thieno[3,4-b]pyrazine emissive core with bulky tetraphenylethylene groups generates the three-dimensional non-planar fluorophors, which exhibit the best performance reported for thieno[3,4-b]pyrazine derivatives so far in their non-doped red light-emitting diodes.Highlights► Decorating thieno-[3,4-b]-pyrazine with bulky tetraphenylethylene groups generated efficient solid-state fluorophores. ► Organic light-emitting diodes were fabricated using these derivatives as non-doped emitting layers. ► Saturated red electroluminescence was obtained with best performance for thieno-[3,4-b]-pyrazine derivatives reported so far.
Co-reporter:Ting Zhang, Hao Dai, Jiuyan Li
Displays 2013 Volume 34(Issue 5) pp:447-451
Publication Date(Web):December 2013
DOI:10.1016/j.displa.2013.08.001
•Synthesis and luminescent properties of carbazole/anthracene hybrided molecules were studied.•Organic light-emitting diodes were fabricated by vacuum evaporation using these materials as non-doped emitter.•Deep-blue electroluminescence with good performance was obtained.Two novel carbazole/anthracene hybrided molecules, namely 2-(anthracen-9-yl)-9-ethyl-9H-carbazole (AnCz) and 2,7-di(anthracen-9-yl)-9-ethyl-9H-carbazole (2AnCz), were designed and synthesized via palladium catalyzed coupling reaction. The anthracene was attached either at the 2-site (AnCz) or at both 2,7-sites (2AnCz) of the central carbazole core to tune the conjugation state and the optoelectronic properties of the resultant molecules. Both of them show good solubility in common organic solvents. They also possess relatively high HOMO levels (−5.39 eV, −5.40 eV) that would facilitate efficient hole injection and be favorable for high power efficiencies when used in organic light-emitting devices (OLEDs). AnCz and 2AnCz were used as non-doped emitter to fabricate OLEDs by vacuum evaporation. Good performance was achieved with maximum luminance efficiency of 2.61 cd A−1 and CIE coordinates of (0.15, 0.12) for AnCz, and 9.52 cd A−1 and (0.22, 0.37) for 2AnCz.
Co-reporter:Lijun Deng, Ting Zhang, Renjie Wang and Jiuyan Li
Journal of Materials Chemistry A 2012 vol. 22(Issue 31) pp:15910-15918
Publication Date(Web):11 Jun 2012
DOI:10.1039/C2JM32811A
Four new cyclometalated iridium(III) complexes containing 2-aryl-5-diphenylphosphorylpyridine ligands, in which the aryl was difluorophenyl (Ir-1), phenyl (Ir-2), 4-(diphenylamino)phenyl (Ir-3) and 2-naphthyl (Ir-4), have been synthesized for application in organic light-emitting diodes (OLEDs). The incorporation of diphenylphosphoryl on the pyridine causes a decrease of the lowest unoccupied molecular orbital (LUMO) for the iridium complexes and the universal bathochromic shift by as much as 50 nm in their phosphorescence. In particular, the presence of the diphenylphosphoryl group on the 2-difluorophenylpyridine ligand of iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (FIrpic) redistributed the LUMO from the ancillary ligand entirely to the cyclometalating ligand. These complexes were used as doped emitters to fabricate OLEDs. The bluish-green device based on Ir-1 exhibited a maximum luminance efficiency of 43.6 cd A−1 (22.8 lm W−1, 9.5%). Highly efficient yellow devices were obtained with 51.6 cd A−1 (27 lm W−1, 14.5%) and 29.6 cd A−1 (15.5 lm W−1, 8.8%) for Ir-2 and Ir-3, respectively. The maximum luminance efficiency of 27.2 cd A−1 (15.5 lm W−1, 9.7%) was achieved for the orange-red device containing Ir-4. Furthermore, a two-emitting-component white OLED was fabricated with Ir-4 in combination with the traditional sky-blue FIrpic and a high efficiency of 23.9 cd A−1 (13.9 lm W−1, 5.4%) with CIE (0.29, 0.43) was realized.
Co-reporter:Renjie Wang, Di Liu, Run Zhang, Lijun Deng and Jiuyan Li
Journal of Materials Chemistry A 2012 vol. 22(Issue 4) pp:1411-1417
Publication Date(Web):24 Nov 2011
DOI:10.1039/C1JM13846D
Two homoleptic and heteroleptic cyclometalated iridium complexes containing the 2-phenylbenzothiozole derivative as the main ligand, 1 and 2, have been synthesized and characterized as efficient orange-red phosphors. Triarylamine was introduced as an important substituent into the 6-position of the benzothiazole ring to tune the photonic and electronic properties of these complexes. Different from most of small molecular iridium complexes, 1 and 2 are solution-processable and their neat films can be obtained by a spin-coating method. Furthermore, their homogeneously dispersed films in a small molecular matrix, 4,4′-N,N′-dicarbazolebiphenyl (CBP), were successfully prepared by solution method even with low doping levels. Organic light-emitting diodes (OLEDs) were fabricated by solution processing the emitting layer containing 1 and 2 as doped emitters in the CBP host. Efficient orange-red electroluminescence by using 5 wt% 2 as the dopant was realized with a maximum efficiency of 14.49 cd A−1 (7.38 lm W−1 and 8.73%) and Commission Internationale de l'Eclairage (CIE) coordinates of (0.60, 0.40), which are among the highest luminance efficiency ever reported for partially solution-processed red and orange-red OLEDs so far. In addition, two-element white OLEDs were achieved with these orange-red phosphors and the traditional blue emitter by spin coating the emission layer. A maximum luminance efficiency of 8.97 cd A−1 and CIE of (0.33, 0.35) were realized.
Co-reporter:Lijun Deng, Xinzeng Wang, Zhengchuan Zhang and Jiuyan Li
Journal of Materials Chemistry A 2012 vol. 22(Issue 37) pp:19700-19708
Publication Date(Web):06 Aug 2012
DOI:10.1039/C2JM33636G
Two novel durene-containing molecules, 1,4-bis-[4-(9-carbazolyl)-phenyl]-durene (CPD) and 1,4-bis-{4-[9-(3,6-(di-tert-butyl)carbazoyl)]-phenyl}-durene (t-BuCPD), which are derived from 4,4′-bis(9-carbazolyl)biphenyl (CBP) by inserting durene in its biphenyl core, are designed and synthesized for use as host materials for blue phosphors in organic light-emitting diodes (OLEDs). Inserting durene in biphenyl causes a right-angle torsion between the durene and the adjacent phenyl groups due to the strong steric hindrance effect of the durene group, confining the effective π-conjugation on only one carbazole and one phenyl and increasing the triplet energies of CPD and t-BuCPD to over 3.0 eV. These durene-decorated molecules show higher thermal stabilities than many other CBP derivatives. Blue phosphorescent OLEDs were fabricated using CPD and t-BuCPD as triplet hosts and traditional iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (Firpic) as a dopant and excellent performances were achieved. In particular, peak efficiencies of 26.2 cd A−1 and 14.8 lm W−1 were realized when CPD was used as both a host and exciton-blocking material. This is the first report using durene to tune the triplet energy levels of phosphorescent host materials.
Co-reporter:Renjie Wang, Lijun Deng, Min Fu, Jinling Cheng and Jiuyan Li
Journal of Materials Chemistry A 2012 vol. 22(Issue 44) pp:23454-23460
Publication Date(Web):21 Sep 2012
DOI:10.1039/C2JM34599D
A group of novel zinc complexes containing 2-hydroxyphenylbenzothiazole (BTZ) ligands were designed and synthesized, in which different substituents (OCH3, CH3, F, CF3, COOCH2CH3) were attached at the 6-position of the benzothiazole ring in the BTZ ligands. Both photoluminescence (PL) and electroluminescence (EL) behaviors of these zinc complexes were investigated. The emission colors of these zinc complexes were readily tuned from bluish-green to yellow by simply varying the substituent, with strong electron-withdrawing substituents being favorable for longer-wavelength fluorescence. Efficient EL was obtained when these zinc complexes were used as non-doped emitting layers in organic light-emitting diodes (OLEDs). Furthermore, these zinc complexes were proved to be capable of acting as triplet hosts for iridium phosphor in red phosphorescent OLEDs. A high external quantum efficiency of 17.5% was realized for the red phosphorescent OLED with the present zinc complexes as hosts and tris(2-phenylisoquinoline)iridium as doped emitter, which is greatly enhanced compared to that (12.6%) of the device with the traditional 4,4′-bis(N-carbazoly)biphenyl (CBP) as host. The present study successfully exploited novel zinc complexes as electron-transporting host materials for phosphorescent OLEDs.
Co-reporter:Renjie Wang, Lijun Deng, Ting Zhang and Jiuyan Li
Dalton Transactions 2012 vol. 41(Issue 22) pp:6833-6841
Publication Date(Web):20 Apr 2012
DOI:10.1039/C2DT12206E
A series of bis(2-phenylbenzothiozolato-N,C2′)iridium(acetylacetonate) [(bt)2Ir(acac)] derivatives, 1–4, were synthesized. Different substituents (CF3, F, CH3, OCH3) were introduced in the benzothiazole ring to study the substituent effect on the photophysical, electrochemical properties and electroluminescent performance of the complexes, and finally to select high-performance phosphors for use in organic light-emitting diodes (OLEDs). All complexes 1–4 and (bt)2Ir(acac) are orange-emitting with tiny spectral difference, despite the variation of the substituent. However, the phosphorescent quantum yield increases with the electron-withdrawing ability of the substituent. This is in contrast to the previous observation that the substituent in the phenyl ring bonded to the metal center of (bt)2Ir(acac) not only affected the luminescent quantum efficiency but also greatly tuned the emission color of the complexes. Quantum chemical calculations revealed that the substituents in this position do not make a significant contribution to both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), which probably accounts for the fact that they do no strongly influence the bandgap and emission color of the complexes. Orange OLEDs were fabricated using 1–4 as doped emitters. The electron-withdrawing CF3 and F groups favor improving the electroluminescence efficiency in comparison with that of the parent (bt)2Ir(acac), while electron-donating CH3 and OCH3 are not favorable for light emission. The complex 1 based OLED exhibited a maximum luminance efficiency of 54.1 cd A−1 (a power efficiency of 24 lm W−1 and an external quantum efficiency of 20%), which are among the best results ever reported for vacuum deposited orange OLEDs so far.
Co-reporter:Ting Zhang, Lijun Deng, Renjie Wang, Wei Zhou, Jiuyan Li
Dyes and Pigments 2012 Volume 94(Issue 3) pp:380-385
Publication Date(Web):September 2012
DOI:10.1016/j.dyepig.2012.01.019
A group of novel fluorene-based copolymers were synthesized and characterized. The trifluoromethylphenylene unit was introduced into the copolymer backbone and its content ratio was varied from 10 mol% to 50 mol%. The electronic bandgap of the copolymer increases regularly with increasing trifluoromethylphenylene ratio. In contrast to pure polyfluorene, the deep-blue fluorescence of these copolymers is quite stable and not contaminated by the well-known green emission associated with fluorenone defects. The copolymers were used as an emitting layer to fabricate organic light-emitting diodes with a pure blue electroluminescence with a CIE coordinate y ≤ 0.10 obtained for most copolymers. Whilst the presence of the trifluoromethylphenylene units in the copolymers seemed unfavorable for charge injection and device current, improved spectral purity and stability in both the photoluminescence and electroluminescence were noted and ascribed to the electron-withdrawing nature of the trifluoromethylphenylene units and the enhanced anti-autoxidation ability of the fluorene rings in these copolymers.In contrast to polyfluorene, the novel fluorene/trifluoromethylphenylene copolymers exhibit pure and stable deep-blue photoluminescence and electroluminescence, which never exhibit the undesired green emission band from keto defects.Highlights► Synthesis and properties of new fluorene/trifluoromethylphenylene copolymers are described. ► Bandgap increases regularly with the content ratio of trifluoromethylphenylene unit. ► The trifluoromethylphenylene unit improves the spectral purity and stability. ► Organic light-emitting diodes are fabricated using these copolymers as emitters. ► Deep-blue electroluminescence with acceptable efficiency was obtained.
Co-reporter:Ting Zhang, Renjie Wang, Huicai Ren, Zhiguang Chen, Jiuyan Li
Polymer 2012 Volume 53(Issue 7) pp:1529-1534
Publication Date(Web):22 March 2012
DOI:10.1016/j.polymer.2012.02.010
Two fluorene-based copolymers (PF-33F and PF-50F) with p-difluorophenylene units in the backbone were synthesized. In comparison with the reference poly(9,9-dioctylfluorene) (PFO), the introduction of p-difluorophenylene units not only increased the fluorescent quantum yields, but also improved the spectra purity and stability of these deep blue emitting copolymers. The famous green emission band at 520 nm from fluorenone defects was never detected for these copolymers even after they were thermal annealed in air at 150 °C. Organic light-emitting diodes were fabricated using them as emitting layer and pure blue electroluminescence was obtained. It was observed that PF-33F based device exhibited much higher current density and brightness than PF-50F and PFO devices. A maximum external quantum efficiency of 1.14% (1.14 cd A−1) and the CIE (0.16, 0.13) were achieved for PF-33F device, which are among the best performance for polyfluorenes reported so far.
Co-reporter:Renjie Wang;Di Liu;Huicai Ren;Ting Zhang;Hongming Yin;Guangye Liu;Jiuyan Li
Advanced Materials 2011 Volume 23( Issue 25) pp:2823-2827
Publication Date(Web):
DOI:10.1002/adma.201100302
Co-reporter:Renjie Wang, Di Liu, Huicai Ren, Ting Zhang, Xinzeng Wang and Jiuyan Li
Journal of Materials Chemistry A 2011 vol. 21(Issue 39) pp:15494-15500
Publication Date(Web):24 Aug 2011
DOI:10.1039/C1JM10757G
Homoleptic tris-cyclometalated iridium(III) complexes containing 2-phenylbenzothiazole derivatives as ligands have been successfully synthesized and characterized for the first time. Electron-donating (CH3, OCH3) and -withdrawing groups (F) were introduced into the 6-position of the benzothiazole moiety in the ligands to verify their influence on the optical and electronic properties of the complexes. Organic light-emitting diodes using these iridium complexes as doped emitters exhibited orange electrophosphorescence with excellent performances. An extremely high brightness of 95800 cd m−2 and a maximum luminance efficiency of 87.9 cd A−1 (46.0 lm W−1) were achieved for the pristine complex without any substituent in the ligand. These performances represent a significant improvement for vacuum-deposited orange OLEDs and the new record of the efficiencies for orange OLEDs reported so far. The substituents in the ligand were observed to be rather unimportant to influence the performance of this series of iridium complexes.
Co-reporter:Ting Zhang, Di Liu, Qian Wang, Renjie Wang, Huicai Ren and Jiuyan Li
Journal of Materials Chemistry A 2011 vol. 21(Issue 34) pp:12969-12976
Publication Date(Web):28 Jul 2011
DOI:10.1039/C1JM11438G
Novel fluorene based deep-blue-emitting molecules with naphthylanthracene endcaps, namely 2,7-di(10-naphthylanthracene-9-yl)-9,9-dioctylfluorene (NAF1) and 7,7′-di(10-naphthylanthracene-9-yl)-9,9,9′,9′-tetraoctyl-2,2′-bifluorene (NAF2), are synthesized by a Suzuki cross-coupling reaction. These materials exhibit excellent thermal and amorphous stabilities, and high fluorescence quantum yield of over 70%. Organic light-emitting devices (OLEDs) using NAF1 or NAF2 as non-doped emitter exhibit bright deep blue electroluminescence with CIE coordinates of (0.15, 0.13) for NAF1, (0.16, 0.13) for NAF2. A maximum power efficiency of 2.2 lm W−1 (4.04 cd A−1, 4.04%) is achieved for NAF1, which is among the highest values ever reported for deep-blue fluorescent OLEDs. A further improved coordinates of (0.15, 0.09) with efficiencies of 3.56 cd A−1 and 2.10 lm W−1 are achieved for NAF1 upon tuning device thickness, which are also among the best data for non-doped deep blue fluorescent OLEDs with a CIE coordinate of y < 0.1. NAF1 serves as excellent host emitter when doped with an orange fluorophore (4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran, DCJTB). Upon careful tuning the doping level, the two-emitting-component (NAF1:DCJTB) OLED realizes efficient white light emission with a power efficiency of 3.01 lm W−1 (7.66 cd A−1), a brightness of 12090 cd m−2, and a standard white light coordinates of (0.33, 0.33). This performance is among the best results ever reported for two-emitting-component white OLEDs based on fluorescent materials.
Co-reporter:Jiuyan Li, Qing Li, and Di Liu
ACS Applied Materials & Interfaces 2011 Volume 3(Issue 6) pp:2099
Publication Date(Web):May 17, 2011
DOI:10.1021/am200317k
A series of novel red-emitting thieno-[3,4-b]-pyrazine-cored molecules containing oligo-carbazole dendrons (called C1-TP, C2-TP) are synthesized. Their photophysical, electrochemical, and electroluminescent properties are investigated. The peripheral carbazolyl units facilitate the hole transporting ability and inhibit the intermolecular interactions, but quench the fluorescence of the thieno-[3,4-b]-pyrazine core through Intramolecular Charge Transfer (ICT). Introduction of a polyphenyl spacer between the core and the first generation carbazole dendrons, i.e., C-DTP, decreases the ICT efficiency. In addition to providing the site-isolation effect on the planar emissive core, these bulky dendrons enable these molecules to be solution processable. As a result, efficient OLEDs with saturated red emission are fabricated by spin coating technique using these dendritic materials as nondoped emitting layer. C-DTP exhibits much better device performance than C1-TP and C2-TP, while the small molecular reference compound containing neither the spacer nor the carbazole dendrons (TP) fails to transmit pure red emission under identical conditions. A brightness of 925 cd m–2 and a luminous efficiency of 0.53 cd A–1 are obtained for C-DTP, which are comparable with OLEDs fabricated from thieno-[3,4-b]-pyrazine-based counterparts by the vacuum deposition method or those assembled with other red fluorescent dendrimers via the solution processing method.Keywords: 4-b]-pyrazine; carbazole dendron; dendrimer; organic light-emitting diodes; red; solution processable; thieno-[3
Co-reporter:Jia You, Guiyang Li, Renjie Wang, Qiuping Nie, Zhonggang Wang and Jiuyan Li
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 39) pp:17825-17830
Publication Date(Web):06 Sep 2011
DOI:10.1039/C1CP21848D
A new dendrimer using pyrene as core and carbazole derivative as dendron has been successfully prepared via Suzuki coupling reaction. Its chemical structure was confirmed through 1H NMR, elemental analysis and MALDI-TOF MS methods. The dendrimer synthesized possessed excellent thermal stability with initial decomposition temperature over 470 °C and high fluorescence quantum yield of 86%. The luminescence spectra showed that, relative to the solution sample, the emission peaks of the solid dendrimer film were apparently broadened and red-shifted, indicating the strong π–π stacking effect between the pyrene moieties. By doping 1.5% of the dendrimer in 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB), a light-emitting diode device was fabricated in the ITO/NPB/NPB:dendrimer (1.5%)/TPBI/Mg:Ag configuration, which emitted a white color with Commission Internationale de L'Eclairage (CIEx,y) coordinates of (0.29, 0.34) and a maximum brightness of 1300 cd m−2, exhibiting promising potential in white light-emitting diode application.
Co-reporter:Xin Wang;Di Liu;Jiuyan Li
Frontiers of Chemistry in China 2010 Volume 5( Issue 1) pp:45-60
Publication Date(Web):2010 March
DOI:10.1007/s11458-009-0208-3
Organic photovoltaic materials are of interest for their future applications in solar cells. Compared to inorganic or dye-sensitized solar cells, organic photovoltaic (OPV) cells offer a huge potential for low-cost large-area solar cells because of their low material consumption per area and easy processing. In the last few years, there have seen an unprecedented growth of interest in OPVs with power conversion efficiency of over 5% attainable. However, OPV’s performance is limited by the narrow light absorption, poor charge carries mobility, and low stability of organic materials, all of which confine its large-scale commercial applications. This review will develop a discussion on the OPV device configuration and operational mechanism after an introduction of the general features of OPV materials. Subsequently, the typical progresses in materials development and performance evolution in recent years will be summarized. The future challenges and prospects faced by organic photovoltaics will be discussed. Finally, the innovative strategy on research of molecular design and device optimization will be suggested with the aim for practical application.
Co-reporter:Jiuyan Li and Di Liu
Journal of Materials Chemistry A 2009 vol. 19(Issue 41) pp:7584-7591
Publication Date(Web):29 Jun 2009
DOI:10.1039/B901618J
Dendrimers are now an important class of materials for use in organic light-emitting diodes (OLEDs). In this Highlight, we make a brief summary of the recent advances on OLEDs by using dendrimers as active materials. In particular, we will focus on several issues related to both the intrinsic structural features and properties, including dendrimer generation and charge mobility, the site isolation effect and prevention of energy transfer, and the host-free character. The potential applications for white electroluminescence via simple dendrimer blending, and host-free blue phosphorescent dendrimers are discussed. Finally, the strategy for dendrimer synthesis will be also discussed.
Co-reporter:Jiu Yan Li, Frédéric Laquai, Gerhard Wegner
Chemical Physics Letters 2009 Volume 478(1–3) pp:37-41
Publication Date(Web):17 August 2009
DOI:10.1016/j.cplett.2009.07.028
Abstract
We report the emissive properties of a fluorene-based polymer, PF-1SOR, in planar asymmetric waveguides under optical pumping. A laser beam homogenizer setup was applied to achieve the flat-top intensity profile of the excitation light. Amplification of deep blue light via stimulated emission (SE) occurred at an energy threshold of 11 μJ cm−2 and the amplified spontaneous emission (ASE) peak could be tuned from 411 to 423 nm. A net gain coefficient of 19.8 cm−1 was obtained by means of the modified variable stripe length (VSL) method. The PF-1SOR thin films delivered a remarkably low loss coefficient of 1.5 cm−1, among the lowest ever reported for a single component polymer waveguide.
Co-reporter:Renjie Wang, Di Liu, Kai Xu, Jiuyan Li
Journal of Photochemistry and Photobiology A: Chemistry 2009 Volume 205(Issue 1) pp:61-69
Publication Date(Web):10 June 2009
DOI:10.1016/j.jphotochem.2009.03.025
A group of novel 2-(2′-hydroxyphenyl)benzothiazole derivatives 1–5 were synthesized with electron-donating or -withdrawing substituent introduced in para position of N atom in benzothiazolyl ring. The excited state intramolecular proton transfer (ESIPT) in 1–5 along with non-substituted 2-(2′-hydroxyphenyl)benzothiazole 6 was studied by means of UV–vis absorption and steady-state fluorescence in solutions. Compounds 1–6 exhibit dual fluorescences including purple normal emission and green tautomer emission. Systematical comparison of the fluorescence of any analogue in a series of solvents ranging from protic ethanol to non-polar hexane demonstrated that polar solvents favor the normal emission while non-polar solvents facilitate ESIPT process and tautomer formation and emission. In either protic or non-polar solvent the tautomer emission intensity of 1–6 decreases consecutively in the order of decreasing electron-donating ability or increasing electron-withdrawing ability of the substituents, on the premise of identical normal emission intensity. This indicates that electron-donating substituents in these derivatives favor ESIPT process and tautomer emission. Competition of intra- and intermolecular hydrogen bonding was studied in dioxane-water binary solvent. It is demonstrated that intermolecular hydrogen bonding with protic solvent impedes ESIPT and tautomer emission. The fluorescent behaviors of 1–6 were interpreted in terms of the population of ground-state rotamers responsible for normal and tautomer emission respectively.
Co-reporter:Jia You, Guiyang Li, Renjie Wang, Qiuping Nie, Zhonggang Wang and Jiuyan Li
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 39) pp:NaN17830-17830
Publication Date(Web):2011/09/06
DOI:10.1039/C1CP21848D
A new dendrimer using pyrene as core and carbazole derivative as dendron has been successfully prepared via Suzuki coupling reaction. Its chemical structure was confirmed through 1H NMR, elemental analysis and MALDI-TOF MS methods. The dendrimer synthesized possessed excellent thermal stability with initial decomposition temperature over 470 °C and high fluorescence quantum yield of 86%. The luminescence spectra showed that, relative to the solution sample, the emission peaks of the solid dendrimer film were apparently broadened and red-shifted, indicating the strong π–π stacking effect between the pyrene moieties. By doping 1.5% of the dendrimer in 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB), a light-emitting diode device was fabricated in the ITO/NPB/NPB:dendrimer (1.5%)/TPBI/Mg:Ag configuration, which emitted a white color with Commission Internationale de L'Eclairage (CIEx,y) coordinates of (0.29, 0.34) and a maximum brightness of 1300 cd m−2, exhibiting promising potential in white light-emitting diode application.
Co-reporter:Renjie Wang, Di Liu, Huicai Ren, Ting Zhang, Xinzeng Wang and Jiuyan Li
Journal of Materials Chemistry A 2011 - vol. 21(Issue 39) pp:NaN15500-15500
Publication Date(Web):2011/08/24
DOI:10.1039/C1JM10757G
Homoleptic tris-cyclometalated iridium(III) complexes containing 2-phenylbenzothiazole derivatives as ligands have been successfully synthesized and characterized for the first time. Electron-donating (CH3, OCH3) and -withdrawing groups (F) were introduced into the 6-position of the benzothiazole moiety in the ligands to verify their influence on the optical and electronic properties of the complexes. Organic light-emitting diodes using these iridium complexes as doped emitters exhibited orange electrophosphorescence with excellent performances. An extremely high brightness of 95800 cd m−2 and a maximum luminance efficiency of 87.9 cd A−1 (46.0 lm W−1) were achieved for the pristine complex without any substituent in the ligand. These performances represent a significant improvement for vacuum-deposited orange OLEDs and the new record of the efficiencies for orange OLEDs reported so far. The substituents in the ligand were observed to be rather unimportant to influence the performance of this series of iridium complexes.
Co-reporter:Renjie Wang, Di Liu, Run Zhang, Lijun Deng and Jiuyan Li
Journal of Materials Chemistry A 2012 - vol. 22(Issue 4) pp:NaN1417-1417
Publication Date(Web):2011/11/24
DOI:10.1039/C1JM13846D
Two homoleptic and heteroleptic cyclometalated iridium complexes containing the 2-phenylbenzothiozole derivative as the main ligand, 1 and 2, have been synthesized and characterized as efficient orange-red phosphors. Triarylamine was introduced as an important substituent into the 6-position of the benzothiazole ring to tune the photonic and electronic properties of these complexes. Different from most of small molecular iridium complexes, 1 and 2 are solution-processable and their neat films can be obtained by a spin-coating method. Furthermore, their homogeneously dispersed films in a small molecular matrix, 4,4′-N,N′-dicarbazolebiphenyl (CBP), were successfully prepared by solution method even with low doping levels. Organic light-emitting diodes (OLEDs) were fabricated by solution processing the emitting layer containing 1 and 2 as doped emitters in the CBP host. Efficient orange-red electroluminescence by using 5 wt% 2 as the dopant was realized with a maximum efficiency of 14.49 cd A−1 (7.38 lm W−1 and 8.73%) and Commission Internationale de l'Eclairage (CIE) coordinates of (0.60, 0.40), which are among the highest luminance efficiency ever reported for partially solution-processed red and orange-red OLEDs so far. In addition, two-element white OLEDs were achieved with these orange-red phosphors and the traditional blue emitter by spin coating the emission layer. A maximum luminance efficiency of 8.97 cd A−1 and CIE of (0.33, 0.35) were realized.
Co-reporter:Lijun Deng, Jiuyan Li, Ge-Xia Wang and Li-Zhu Wu
Journal of Materials Chemistry A 2013 - vol. 1(Issue 48) pp:NaN8145-8145
Publication Date(Web):2013/10/15
DOI:10.1039/C3TC31893A
A group of small-molecular compounds, namely 6-(3-(9H-carbazol-9-yl)phenyl)-9-ethyl-9H-carbazole-3-carbonitrile (m-CzCzCN), 6-(2-(9H-carbazol-9-yl)phenyl)-9-ethyl-9H-carbazole-3-carbonitrile (o-CzCzCN), 6-(3,5-di(9H-carbazol-9-yl)phenyl)-9-ethyl-9H-carbazole-3-carbonitrile (mCPCzCN), 8-(3-(9H-carbazol-9-yl)phenyl)dibenzo[b,d]furan-2-carbonitrile (m-CzOCN), 8-(3-(9H-carbazol-9-yl)phenyl)dibenzo[b,d]thiophene-2-carbonitrile (m-CzSCN), are designed and synthesized for use as host materials in blue phosphorescent organic light-emitting diodes (PhOLEDs). The p-type carbazole and the n-type cyano-decorated carbazole, dibenzofuran or dibenzothiophene unit are incorporated, to either the meta- or ortho-positions of the phenylene bridge. The bipolar feature was confirmed by theoretical calculation and experimental results of the single-carrier devices. These materials exhibit an excellent performance in their hosted blue phosphorescent OLEDs with iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (Firpic) as the doped emitter. The ortho-substituted o-CzCzCN realizes higher device efficiencies than the meta-substituted isomer m-CzCzCN, with a maximum external quantum efficiency of 21.0% and a current efficiency of 43.9 cd A−1. The device hosted by m-CzSCN also exhibits remarkably high efficiencies of 23.3% and 46.1 cd A−1. Furthermore, these blue PhOLEDs are characterized by a slow efficiency roll-off. Even at a high brightness of 10000 cd m−2, the o-CzCzCN hosted device still retain high efficiencies of 13.6% and 28.5 cd A−1. This is a systematic study of incorporating the CN group onto carbazole, dibenzofuran and dibenzothiophene, to develop high-triplet-energy bipolar hosts for OLED applications.
Co-reporter:Lijun Deng, Xinzeng Wang, Zhengchuan Zhang and Jiuyan Li
Journal of Materials Chemistry A 2012 - vol. 22(Issue 37) pp:NaN19708-19708
Publication Date(Web):2012/08/06
DOI:10.1039/C2JM33636G
Two novel durene-containing molecules, 1,4-bis-[4-(9-carbazolyl)-phenyl]-durene (CPD) and 1,4-bis-{4-[9-(3,6-(di-tert-butyl)carbazoyl)]-phenyl}-durene (t-BuCPD), which are derived from 4,4′-bis(9-carbazolyl)biphenyl (CBP) by inserting durene in its biphenyl core, are designed and synthesized for use as host materials for blue phosphors in organic light-emitting diodes (OLEDs). Inserting durene in biphenyl causes a right-angle torsion between the durene and the adjacent phenyl groups due to the strong steric hindrance effect of the durene group, confining the effective π-conjugation on only one carbazole and one phenyl and increasing the triplet energies of CPD and t-BuCPD to over 3.0 eV. These durene-decorated molecules show higher thermal stabilities than many other CBP derivatives. Blue phosphorescent OLEDs were fabricated using CPD and t-BuCPD as triplet hosts and traditional iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (Firpic) as a dopant and excellent performances were achieved. In particular, peak efficiencies of 26.2 cd A−1 and 14.8 lm W−1 were realized when CPD was used as both a host and exciton-blocking material. This is the first report using durene to tune the triplet energy levels of phosphorescent host materials.
Co-reporter:Jiuyan Li and Di Liu
Journal of Materials Chemistry A 2009 - vol. 19(Issue 41) pp:NaN7591-7591
Publication Date(Web):2009/06/29
DOI:10.1039/B901618J
Dendrimers are now an important class of materials for use in organic light-emitting diodes (OLEDs). In this Highlight, we make a brief summary of the recent advances on OLEDs by using dendrimers as active materials. In particular, we will focus on several issues related to both the intrinsic structural features and properties, including dendrimer generation and charge mobility, the site isolation effect and prevention of energy transfer, and the host-free character. The potential applications for white electroluminescence via simple dendrimer blending, and host-free blue phosphorescent dendrimers are discussed. Finally, the strategy for dendrimer synthesis will be also discussed.
Co-reporter:Ting Zhang, Di Liu, Qian Wang, Renjie Wang, Huicai Ren and Jiuyan Li
Journal of Materials Chemistry A 2011 - vol. 21(Issue 34) pp:NaN12976-12976
Publication Date(Web):2011/07/28
DOI:10.1039/C1JM11438G
Novel fluorene based deep-blue-emitting molecules with naphthylanthracene endcaps, namely 2,7-di(10-naphthylanthracene-9-yl)-9,9-dioctylfluorene (NAF1) and 7,7′-di(10-naphthylanthracene-9-yl)-9,9,9′,9′-tetraoctyl-2,2′-bifluorene (NAF2), are synthesized by a Suzuki cross-coupling reaction. These materials exhibit excellent thermal and amorphous stabilities, and high fluorescence quantum yield of over 70%. Organic light-emitting devices (OLEDs) using NAF1 or NAF2 as non-doped emitter exhibit bright deep blue electroluminescence with CIE coordinates of (0.15, 0.13) for NAF1, (0.16, 0.13) for NAF2. A maximum power efficiency of 2.2 lm W−1 (4.04 cd A−1, 4.04%) is achieved for NAF1, which is among the highest values ever reported for deep-blue fluorescent OLEDs. A further improved coordinates of (0.15, 0.09) with efficiencies of 3.56 cd A−1 and 2.10 lm W−1 are achieved for NAF1 upon tuning device thickness, which are also among the best data for non-doped deep blue fluorescent OLEDs with a CIE coordinate of y < 0.1. NAF1 serves as excellent host emitter when doped with an orange fluorophore (4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran, DCJTB). Upon careful tuning the doping level, the two-emitting-component (NAF1:DCJTB) OLED realizes efficient white light emission with a power efficiency of 3.01 lm W−1 (7.66 cd A−1), a brightness of 12090 cd m−2, and a standard white light coordinates of (0.33, 0.33). This performance is among the best results ever reported for two-emitting-component white OLEDs based on fluorescent materials.
Co-reporter:Renjie Wang, Lijun Deng, Min Fu, Jinling Cheng and Jiuyan Li
Journal of Materials Chemistry A 2012 - vol. 22(Issue 44) pp:NaN23460-23460
Publication Date(Web):2012/09/21
DOI:10.1039/C2JM34599D
A group of novel zinc complexes containing 2-hydroxyphenylbenzothiazole (BTZ) ligands were designed and synthesized, in which different substituents (OCH3, CH3, F, CF3, COOCH2CH3) were attached at the 6-position of the benzothiazole ring in the BTZ ligands. Both photoluminescence (PL) and electroluminescence (EL) behaviors of these zinc complexes were investigated. The emission colors of these zinc complexes were readily tuned from bluish-green to yellow by simply varying the substituent, with strong electron-withdrawing substituents being favorable for longer-wavelength fluorescence. Efficient EL was obtained when these zinc complexes were used as non-doped emitting layers in organic light-emitting diodes (OLEDs). Furthermore, these zinc complexes were proved to be capable of acting as triplet hosts for iridium phosphor in red phosphorescent OLEDs. A high external quantum efficiency of 17.5% was realized for the red phosphorescent OLED with the present zinc complexes as hosts and tris(2-phenylisoquinoline)iridium as doped emitter, which is greatly enhanced compared to that (12.6%) of the device with the traditional 4,4′-bis(N-carbazoly)biphenyl (CBP) as host. The present study successfully exploited novel zinc complexes as electron-transporting host materials for phosphorescent OLEDs.
Co-reporter:Lijun Deng, Ting Zhang, Renjie Wang and Jiuyan Li
Journal of Materials Chemistry A 2012 - vol. 22(Issue 31) pp:NaN15918-15918
Publication Date(Web):2012/06/11
DOI:10.1039/C2JM32811A
Four new cyclometalated iridium(III) complexes containing 2-aryl-5-diphenylphosphorylpyridine ligands, in which the aryl was difluorophenyl (Ir-1), phenyl (Ir-2), 4-(diphenylamino)phenyl (Ir-3) and 2-naphthyl (Ir-4), have been synthesized for application in organic light-emitting diodes (OLEDs). The incorporation of diphenylphosphoryl on the pyridine causes a decrease of the lowest unoccupied molecular orbital (LUMO) for the iridium complexes and the universal bathochromic shift by as much as 50 nm in their phosphorescence. In particular, the presence of the diphenylphosphoryl group on the 2-difluorophenylpyridine ligand of iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (FIrpic) redistributed the LUMO from the ancillary ligand entirely to the cyclometalating ligand. These complexes were used as doped emitters to fabricate OLEDs. The bluish-green device based on Ir-1 exhibited a maximum luminance efficiency of 43.6 cd A−1 (22.8 lm W−1, 9.5%). Highly efficient yellow devices were obtained with 51.6 cd A−1 (27 lm W−1, 14.5%) and 29.6 cd A−1 (15.5 lm W−1, 8.8%) for Ir-2 and Ir-3, respectively. The maximum luminance efficiency of 27.2 cd A−1 (15.5 lm W−1, 9.7%) was achieved for the orange-red device containing Ir-4. Furthermore, a two-emitting-component white OLED was fabricated with Ir-4 in combination with the traditional sky-blue FIrpic and a high efficiency of 23.9 cd A−1 (13.9 lm W−1, 5.4%) with CIE (0.29, 0.43) was realized.
Co-reporter:Jiuyan Li, Renjie Wang, Ruixia Yang, Wei Zhou and Xin Wang
Journal of Materials Chemistry A 2013 - vol. 1(Issue 26) pp:NaN4179-4179
Publication Date(Web):2013/05/02
DOI:10.1039/C3TC30586D
Three 2-aryl-benzothiazole chromophores were designed and synthesized for use as major cyclometalating ligands of iridium complexes, in which the aryl groups were N-phenyl-3-carbazolyl, 2-(9,9-dioctyl)fluorenyl and N-phenyl-2-carbazolyl. The homoleptic tris-cyclometalated and heteroleptic bis-cyclometalated iridium complexes, 1–5, were synthesized using these ligands. By adjusting the chemical structures and then the electronic state of these complexes, we were able to continuously tune the phosphorescence from yellow to saturated red with peak wavelengths in the order of 1 < 2 < 3 < 4 < 5. The quantum chemical calculations and the electrochemical data clearly demonstrate the origin of the phosphorescence color tuning. The organic light-emitting diodes (OLEDs) containing these iridium complexes as doped emitters exhibited yellow to red electrophosphorescence with excellent performance. Particularly, the complex 1 based device produced high efficiencies of 75.9 cd A−1, 48.2 lm W−1, and 23.0% with CIE (0.46, 0.53), which represent the highest efficiencies for yellow OLEDs up to now. Furthermore, 1 was used to fabricate two-element white OLEDs in combination with a blue phosphor and high efficiencies of 57.9 cd A−1 and 21.9% were achieved, which are among the best efficiencies for two-emitting-component white OLEDs reported so far.
Co-reporter:Ting Zhang, Yunjing Liang, Jinling Cheng and Jiuyan Li
Journal of Materials Chemistry A 2013 - vol. 1(Issue 4) pp:NaN764-764
Publication Date(Web):2012/11/07
DOI:10.1039/C2TC00305H
N,N′-Dicarbazolyl-4,4′-biphenyl (CBP) is one of the most successful uni-polar host materials for phosphorescent organic light-emitting diodes (PhOLEDs). We report the synthesis and properties of one novel CBP derivative, CBP-CN, with two cyano groups (CN) at the 3-site of carbazole rings. The strong electron-withdrawing CN group was introduced with the expectation to promote electron-injecting/-transporting abilities and to achieve bipolar features for CBP-CN. In comparison with the parent CBP, CBP-CN possesses lowered HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) levels and dramatically increased Tg (glass transition temperature, 162 °C), but unaltered HOMO–LUMO band gap and triplet energy (2.69 eV). Green and red PhOLEDs were fabricated with CBP-CN as hosts for traditional iridium phosphors. The maximum luminance efficiency (ηL) of 80.61 cd A−1 (23.13%) was achieved for the green PhOLED, and 10.67 cd A−1 (15.54%) for the red one, which represent efficiency increases of 25–33% compared with those of the best devices with CBP host and are even among the best data for phosphorescent OLEDs reported so far. The theoretical calculation and the carrier-only devices investigation confirmed that the electron-injecting/-transporting character and the bipolar nature of CBP-CN should be responsible for the performance enhancements.
Co-reporter:Wei Li, Jiuyan Li, Di Liu, Fang Wang and Shufen Zhang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 48) pp:NaN12538-12538
Publication Date(Web):2015/11/16
DOI:10.1039/C5TC02997J
A series of small molecular isomers, namely o-CzCN, m-CzCN, and p-CzCN, are developed for use as bipolar hosts in blue phosphorescent and fluorescent organic light-emitting diodes (OLEDs). Cyano (CN) substituted phenyl is selected as the n-type unit and N-phenyl-substituted carbazole as the p-type unit. By adjusting the ortho-, meta-, and para-linking styles of the functional units, the physical parameters are regularly tuned to a large extent. The study of complete spatial separation of frontier molecular orbitals and single-carrier devices confirm the bipolar feature. Blue phosphorescent and thermally activated delayed fluorescence (TADF) OLEDs were fabricated using iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (FIrpic) and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN) as doped emitters. A maximum current efficiency of 46.81 cd A−1 and an external quantum efficiency of 23.14% were achieved for the phosphorescent OLED with the m-CzCN host. Furthermore, high efficiencies of 29.23 cd A−1 and 14.98% were obtained for the 2CzPN based blue TADF device with the o-CzCN host, which are higher than the best literature value of 13.6% for 2CzPN devices. Both m-CzCN and o-CzCN always perform better than p-CzCN. The influence of the chemical structures on their properties and performance is interpreted for these CN-decorated host materials.
Co-reporter:Renjie Wang, Lijun Deng, Ting Zhang and Jiuyan Li
Dalton Transactions 2012 - vol. 41(Issue 22) pp:NaN6841-6841
Publication Date(Web):2012/04/20
DOI:10.1039/C2DT12206E
A series of bis(2-phenylbenzothiozolato-N,C2′)iridium(acetylacetonate) [(bt)2Ir(acac)] derivatives, 1–4, were synthesized. Different substituents (CF3, F, CH3, OCH3) were introduced in the benzothiazole ring to study the substituent effect on the photophysical, electrochemical properties and electroluminescent performance of the complexes, and finally to select high-performance phosphors for use in organic light-emitting diodes (OLEDs). All complexes 1–4 and (bt)2Ir(acac) are orange-emitting with tiny spectral difference, despite the variation of the substituent. However, the phosphorescent quantum yield increases with the electron-withdrawing ability of the substituent. This is in contrast to the previous observation that the substituent in the phenyl ring bonded to the metal center of (bt)2Ir(acac) not only affected the luminescent quantum efficiency but also greatly tuned the emission color of the complexes. Quantum chemical calculations revealed that the substituents in this position do not make a significant contribution to both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), which probably accounts for the fact that they do no strongly influence the bandgap and emission color of the complexes. Orange OLEDs were fabricated using 1–4 as doped emitters. The electron-withdrawing CF3 and F groups favor improving the electroluminescence efficiency in comparison with that of the parent (bt)2Ir(acac), while electron-donating CH3 and OCH3 are not favorable for light emission. The complex 1 based OLED exhibited a maximum luminance efficiency of 54.1 cd A−1 (a power efficiency of 24 lm W−1 and an external quantum efficiency of 20%), which are among the best results ever reported for vacuum deposited orange OLEDs so far.
Co-reporter:Wei Li, Jiuyan Li, Di Liu, Deli Li and Dan Zhang
Chemical Science (2010-Present) 2016 - vol. 7(Issue 11) pp:NaN6714-6714
Publication Date(Web):2016/07/08
DOI:10.1039/C6SC01797E
By using pyridine and diphenylphosphine oxide (DPPO) as dual n-type units, two novel bipolar hosts, namely (5-(3,5-di(9H-carbazol-9-yl)phenyl)pyridin-3-yl)diphenylphosphine oxide (m-PyPOmCP), and (6-(3,5-di(9H-carbazol-9-yl)phenyl)pyridin-3-yl)diphenylphosphine oxide (p-PyPOmCP) are developed for blue and green phosphorescent organic light-emitting diodes (PhOLEDs). Direct linking of the dual n-type units not only pulls the LUMOs down, but also keeps the HOMO levels shallow, and leads to high triplet energies (2.78–2.86 eV) and small singlet-triplet energy differences (0.23–0.35 eV). Blue and green PhOLEDs are fabricated using FIrpic and Ir(ppy)3 as dopants in the hosts. A low turn-on voltage of 2.6 V is achieved for the green PhOLEDs. The m-PyPOmCP hosted blue PhOLED achieves a high current efficiency of 55.6 cd A−1 (corresponding to a maximum external quantum efficiency of 25.3% and a power efficiency of 43.6 lm W−1). The p-PyPOmCP hosted green PhOLED exhibits an efficiency of 98.2 cd A−1 (28.2% and 102.8 lm W−1). These data are among the best values for blue and green PhOLEDs reported so far. These “dual n-type units” hosts show much better performance than their DPPO-free analogue, clearly proving that the direct linking of DPPO and pyridine as dual n-type units is an effective molecular design strategy for host materials for use in high-performance PhOLEDs.
![3,3'-(5'-(3-(Pyridin-3-yl)phenyl)-[1,1':3',1''-terphenyl]-3,3''-diyl)dipyridine](http://img.cochemist.com/ccimg/921300/921205-03-0.png)
![3,3'-(5'-(3-(Pyridin-3-yl)phenyl)-[1,1':3',1''-terphenyl]-3,3''-diyl)dipyridine](http://img.cochemist.com/ccimg/921300/921205-03-0_b.png)
