Co-reporter:Jianlei Han, Yuqian Jiang, Ablikim Obolda, Pengfei Duan, Feng Li, and Minghua Liu
The Journal of Physical Chemistry Letters December 7, 2017 Volume 8(Issue 23) pp:5865-5865
Publication Date(Web):November 16, 2017
DOI:10.1021/acs.jpclett.7b02677
Stable luminescent π-radicals with doublet emission have aroused a growing interest for functional molecular materials. We have demonstrated a neutral π-radical dye (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)-methyl (TTM-1Cz) with remarkable doublet emission, which could be used as triplet sensitizer to initiate the photophysical process of triplet–triplet annihilation photon upconversion (TTA-UC). Dexter-like excited doublet-triplet energy transfer (DTET) was confirmed by theoretical calculation. With the same sensitizer, a mixed solution of TTM-1Cz and aromatic emitters could upconvert red light (λ = 635 nm) to blue or cyan light. An anti-Stokes energy shift as large as 0.92 eV was observed from red to blue light upconversion. This finding of DTET phenomena offers a new kind of triplet sensitizer for TTA-UC.
Co-reporter:Yingchang Gao, Ablikim Obolda, Ming Zhang, Feng Li
Dyes and Pigments 2017 Volume 139(Volume 139) pp:
Publication Date(Web):1 April 2017
DOI:10.1016/j.dyepig.2016.12.063
•A novel luminescent Tris(2,4,6-trichlorotriphenyl)methyl radical with two indole moieties connected outside was synthesized.•A pure red OLED with the emission from doublet excitons was firstly reported.•The maximum EQE of the device was 2.4%, and the formation ratio of doublet exciton is up to 100%.A novel derivative of Tris(2,4,6-trichlorotriphenyl)methyl radical was synthesized and used as the emitter of an organic light-emitting diode. Stable electroluminescent (EL) spectra at the full-range driving voltages and pure red color were obtained through optimizing the device structure. The Commission Internationale de L′ Eclairage (CIE) coordinate of the device at 7 V is (0.667, 0.301), which is very close to the red standard CIE coordinate (0.670, 0.330) of NTSC. The maximum external quantum efficiency of the device is 2.4%, and the formation ratio of doublet exciton is nearly 100%.Download high-res image (268KB)Download full-size image
Co-reporter:Shengzhi Dong;Ablikim Obolda;Qiming Peng;Yadong Zhang;Seth Marder
Materials Chemistry Frontiers 2017 vol. 1(Issue 10) pp:2132-2135
Publication Date(Web):2017/09/27
DOI:10.1039/C7QM00273D
A series of multicarbazolyl substituted tris(2,4,6-trichlorophenyl)-methyl (TTM) radical derivatives were synthesized. Red-shifts of the fluorescence emission of the TTM radicals were achieved along with enhanced luminescence efficiency through incorporating substituent groups with strong electron donating ability as well as restricting the rotation of the outer groups. The photostability of the radicals was also significantly enhanced via the incorporation of substituent groups. This work provides a new approach to realize NIR-emitting radicals with high luminescence efficiency.
Co-reporter:Ablikim Obolda;Qiming Peng;Chuanyou He;Tian Zhang;Jiajun Ren;Hongwei Ma;Zhigang Shuai
Advanced Materials 2016 Volume 28( Issue 23) pp:4740-4746
Publication Date(Web):
DOI:10.1002/adma.201504601
Co-reporter:Xiaojun Yin, Dongcheng Chen, Qiming Peng, Yepeng Xiang, Guohua Xie, Zece Zhu, Cheng Zhong, Feng Li, Shijian Su and Chuluo Yang
Journal of Materials Chemistry A 2016 vol. 4(Issue 7) pp:1482-1489
Publication Date(Web):14 Jan 2016
DOI:10.1039/C5TC04198H
Three new pyrimidine-containing star-shaped compounds, namely, 1,3,5-tri(3-(pyrimidin-5-yl)phenyl)benzene (TPM-TPB), 2,4,6-tris(3-(pyrimidin-5-yl)phenyl)-1,3,5-triazine (TPM-TAZ) and 3,5,6-tris(3-(pyrimidin-5-yl)phenyl)-1,2,4-triazine (TPM-i-TAZ), were synthesized and characterized. These new compounds exhibited favorable electronic affinity (Ea >2.81 eV) and the triplet energy levels (ET) up to ∼2.83 eV. X-ray diffraction analysis of the compounds revealed that the intramolecular and intermolecular C–H⋯N hydrogen bonds of TPM-TAZ resulted in high electron mobility up to 2.0 × 10−3 cm2 V−1 s−1. Using these compounds as the electron transporting materials, the blue phosphorescent organic light-emitting devices showed good performance, with a very low turn-on voltage of 2.4 V, a maximum current efficiency of 26.4 cd A−1, and a maximum power efficiency of 26.9 lm W−1.
Co-reporter:Ablikim Obolda, Ming Zhang, Feng Li
Chinese Chemical Letters 2016 Volume 27(Issue 8) pp:1345-1349
Publication Date(Web):August 2016
DOI:10.1016/j.cclet.2016.06.030
The emission manners of organic light-emitting diodes (OLEDs) have experienced almost three-decade evolution. In this review, we briefly summarized the emission manners of OLEDs including: (i) emission from singlet exciton; (ii) emission from triplet exciton; (iii) emission from singlet exciton converted from triplet exciton. Then we introduced a new type of OLEDs with the emission from doublet exciton, wherein organic neutral radicals are used as emitters. Due to the spin-allowed transition of doublet excitons, using neutral radicals as emitters is believed to be a new way to break the 25% upper limit of internal quantum efficiency of OLEDs. The progress of emissive stable neutral radicals is also shortly reviewed.The emission manners of organic light-emitting diodes (OLEDs) have evolved from emission of singlet exciton, then emission of triplet exciton, then emission of singlet exciton converted from triplet exciton, finally to emission of doublet exciton during the three-decades development.
Co-reporter:Ablikim Obolda, Xin Ai, Ming Zhang, and Feng Li
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 51) pp:
Publication Date(Web):December 9, 2016
DOI:10.1021/acsami.6b12338
In a neutral π-radical-based organic light-emitting diode (OLED), although the emission comes from the doublet excitons and their transition to the ground state is spin-allowed, the upper limit of internal quantum efficiency (IQE) is not clear, 50% or 100%? In this work, the deep-red OLEDs based on a neutral π-radical were fabricated. Up to 100% doublet exciton formation ratio was obtained through rational designing device structure and host–guest doping system. This indicates the IQE of neutral π-radical-based OLEDs will reach 100% if the nonradiative pathways of radicals can be suppressed. The maximum external quantum efficiency of the optimized device is as high as 4.3%, which is among the highest values of deep-red/near-infrared OLEDs with nonphosphorescent materials as emitters. Our results also indicate that using partially reduced radical mixture as emitter may be a way to solve aggregation-caused quenching in radical-based OLEDs.Keywords: deep-red OLEDs; doublet exciton; internal quantum efficiency; neutral π-radical; open-shell molecule;
Co-reporter:Xujun Zheng, Qiming Peng, Jie Lin, Yi Wang, Jie Zhou, Yan Jiao, Yuefeng Bai, Yan Huang, Feng Li, Xingyuan Liu, Xuemei Pu and Zhiyun Lu
Journal of Materials Chemistry A 2015 vol. 3(Issue 27) pp:6970-6978
Publication Date(Web):21 May 2015
DOI:10.1039/C5TC00779H
A red naphthalimide derivative with an intramolecular charge-transfer (ICT) feature, namely (E)-2-(4-(t-butyl)phenyl)-6-(2-(6-(diphenylamino)naphthalen-2-yl)vinyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (NA-TNA), was designed and synthesized. Photophysical and magneto-electroluminescence (MEL) characterization results revealed that NA-TNA could harvest triplet excitons via a triplet–triplet annihilation (TTA) process in organic light-emitting diodes (OLEDs) due to the presence of a lower-lying triplet excited state with 3ππ* character. Consequently, using NA-TNA as a guest compound and CzPhONI, another ICT-featured naphthalimide derivative with triplet fusion delayed fluorescence (TFDF) character as host material, a high-performance orange OLED with 6 wt% NA-TNA doped CzPhONI film as the emitting layer was acquired. The maximum current efficiency (LEmax), brightness (Lmax), and external quantum yield (EQEmax) of this OLED is 7.73 cd A−1, 31940 cd m−2 and 5.83%, respectively, while the theoretical EQEmax of this device should not exceed 3.34%. On the contrary, the reference device with a NA-TNA doping level of 1.4 wt% showed much inferior performance, with a LEmax, a Lmax, and an EQEmax of 3.19 cd A−1, 24900 cd m−2 and 2.49%, respectively. The high performance of the 6 wt% NA-TNA doped device was attributed to the efficient harvesting of triplet excitons by both the guest and host materials.
Co-reporter:Chuanyou He, Haoqing Guo, Qiming Peng, Shengzhi Dong and Feng Li
Journal of Materials Chemistry A 2015 vol. 3(Issue 38) pp:9942-9947
Publication Date(Web):31 Aug 2015
DOI:10.1039/C5TC02055G
Deep-blue emission is particularly important for applications of organic light-emitting diodes (OLEDs) in full colour flat-panel displays and solid-state lighting resources. Two asymmetrically twisted anthracene derivatives, 4,5-diphenyl-1,2-bis(4-(10-phenylanthracen-9-yl)phenyl)-1H-imidazole (DPA-PIM) and 1,2-bis(4-(10-phenylanthracen-9-yl)phenyl)-1H-phen-anthro[9,10-d]imidazole (DPA-PPI), for deep-blue OLEDs have been designed and synthesized. The asymmetrically twisted conformations between anthracene and imidazole units in compounds efficiently interrupt molecular π-conjugation and inhibit π–π intermolecular interactions, resulting in high thermal stability and efficient deep-blue emission. The two anthracene derivatives in non-doped OLEDs exhibited blue emission. In particular, the non-doped device based on DPA-PIM achieved an external quantum efficiency (EQE) of 6.5% with CIE coordinates of (0.15, 0.08). In addition, the two emitters in doped devices achieved high EQEs of over 5.0% and much purer blue emission with CIE coordinates of (0.15, 0.06) for DPA-PPI and (0.15, 0.05) for DPA-PIM, which nearly match the CIE coordinates of the European Broadcasting Union (EBU) blue standard of (0.15, 0.06).
Co-reporter:Ping Chen, Li-Ping Wang, Wan-Yi Tan, Qi-Ming Peng, Shi-Tong Zhang, Xu-Hui Zhu, and Feng Li
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 4) pp:2972
Publication Date(Web):January 13, 2015
DOI:10.1021/am508574m
The discovery of triplet excitons participating in the photoluminescent processes in a growing number of pure organic emitters represents an exciting impetus for a diversity of promising opto, bio, and optoelectronic applications. In this contribution, we have studied a small-molecule dithienylbenzothiadiazole-based red-emitting dye red-1b, which shows clearly delayed fluorescence under optical and electrical excitation. The OLED device that contained red-1b as a nondoped solution-processable emitter exhibited a moderately high utilization of exciton amounting to ≈31% and slow efficiency roll-off. Magnetoelectroluminescence measurements revealed the coexistence of reverse intersystem crossing from the lowest triplet state to singlet state (RISC, E-type triplet to singlet up-conversion) and triplet–triplet annihilation (TTA, P-type triplet to singlet up-conversion). Specifically, in low current-density regime, the moderately high exciton utilization is attributed to RISC (i.e., thermally activated delayed fluorescence, TADF), whereas in high current-density regime, TTA may contribute to suppressing efficiency roll-off. Furthermore, the results showed that red-1b may represent a new kind of organic red emitters that display delayed fluorescence in a way differing from the few red emitters investigated so far.Keywords: electroluminescence; exciton utilization; magnetoelectroluminescence; reverse intersystem crossing; triplet−triplet annihilation
Co-reporter:Yu Liu, Peng Li, Hongwei Ma, Ming Zhang and Feng Li
RSC Advances 2015 vol. 5(Issue 16) pp:11942-11945
Publication Date(Web):09 Jan 2015
DOI:10.1039/C4RA16022C
The fluorescence biomolecules flavin mononucleotide (FMN) and lumiflavin were demonstrated as ATP sensors for the first time. FMN and lumiflavin are totally compatible with the human body and can be easily obtained at low cost. The laser and fluorescence of FMN and lumiflavin in aqueous solution can efficiently discriminate ATP from other common anion such as Cl−, Br−, I−, SO42−, NO3− and PPi.
Co-reporter:Qiming Peng;Ablikim Obolda;Dr. Ming Zhang;Dr. Feng Li
Angewandte Chemie International Edition 2015 Volume 54( Issue 24) pp:7091-7095
Publication Date(Web):
DOI:10.1002/anie.201500242
Abstract
Triplet harvesting is a main challenge in organic light-emitting devices (OLEDs), because the radiative decay of the triplet is spin-forbidden. Here, we propose a new kind of OLED, in which an organic open-shell molecule, (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl (TTM-1Cz) radical, is used as an emitter, to circumvent the transition problem of triplet. For TTM-1Cz, there is only one unpaired electron in the highest singly occupied molecular orbital (SOMO). When this electron is excited to the lowest singly unoccupied molecular orbital (SUMO), the SOMO is empty. Thus, transition back of the excited electron to the SOMO is totally spin-allowed. Spectral analysis showed that electroluminescence of the OLED originated from the electron transition between SUMO and SOMO. The magneto-electroluminescence measurements revealed that the spin configuration of the excited state of TTM-1Cz is a doublet. Our results pave a new way to obtain 100 % internal quantum efficiency of OLEDs.
Co-reporter:Qiming Peng;Ablikim Obolda;Dr. Ming Zhang;Dr. Feng Li
Angewandte Chemie International Edition 2015 Volume 54( Issue 24) pp:
Publication Date(Web):
DOI:10.1002/anie.201504417
Co-reporter:Qiming Peng;Ablikim Obolda;Dr. Ming Zhang;Dr. Feng Li
Angewandte Chemie 2015 Volume 127( Issue 24) pp:7197-7201
Publication Date(Web):
DOI:10.1002/ange.201500242
Abstract
Triplet harvesting is a main challenge in organic light-emitting devices (OLEDs), because the radiative decay of the triplet is spin-forbidden. Here, we propose a new kind of OLED, in which an organic open-shell molecule, (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl (TTM-1Cz) radical, is used as an emitter, to circumvent the transition problem of triplet. For TTM-1Cz, there is only one unpaired electron in the highest singly occupied molecular orbital (SOMO). When this electron is excited to the lowest singly unoccupied molecular orbital (SUMO), the SOMO is empty. Thus, transition back of the excited electron to the SOMO is totally spin-allowed. Spectral analysis showed that electroluminescence of the OLED originated from the electron transition between SUMO and SOMO. The magneto-electroluminescence measurements revealed that the spin configuration of the excited state of TTM-1Cz is a doublet. Our results pave a new way to obtain 100 % internal quantum efficiency of OLEDs.
Co-reporter:Qiming Peng;Ablikim Obolda;Dr. Ming Zhang;Dr. Feng Li
Angewandte Chemie 2015 Volume 127( Issue 24) pp:
Publication Date(Web):
DOI:10.1002/ange.201504417
Co-reporter:Wan-Yi Tan;Rui Wang;Min Li;Gang Liu;Ping Chen;Xin-Chen Li;Shun-Mian Lu;Hugh Lu Zhu;Qi-Ming Peng;Xu-Hui Zhu;Wei Chen;Wallace C. H. Choy;Junbiao Peng;Yong Cao
Advanced Functional Materials 2014 Volume 24( Issue 41) pp:6540-6547
Publication Date(Web):
DOI:10.1002/adfm.201401685
Cathode interfacial material (CIM) is critical to improving the power conversion efficiency (PCE) and long-term stability of an organic photovoltaic cell that utilizes a high work function cathode. In this contribution, a novel CIM is reported through an effective and yet simple combination of triarylphosphine oxide with a 1,10-phenanthrolinyl unit. The resulting CIM possesses easy synthesis and purification, a high T g of 116 °C and attractive electron-transport properties. The characterization of photovoltaic devices involving Ag or Al cathodes shows that this thermally deposited interlayer can considerably improve the PCE, due largely to a simultaneous increase in V oc and FF relative to the reference devices without a CIM. Notably, a PCE of 7.51% is obtained for the CIM/Ag device utilizing the active layer PTB7:PC71BM, which far exceeds that of the reference Ag device and compares well to that of the Ca/Al device. The PCE is further increased to 8.56% for the CIM/Al device (with J sc = 16.81 mA cm−2, V oc = 0.75 V, FF = 0.68). Ultraviolet photoemission spectroscopy studies reveal that this promising CIM can significantly lower the work function of the Ag metal as well as ITO and HOPG, and facilitate electron extraction in OPV devices.
Co-reporter:Qiming Peng, Aiwu Li, Yunxia Fan, Ping Chen and Feng Li
Journal of Materials Chemistry A 2014 vol. 2(Issue 31) pp:6264-6268
Publication Date(Web):04 Jun 2014
DOI:10.1039/C4TC00885E
The forward conversion from singlets to triplets and backward conversion from triplets to singlets are both possible in charge-transfer (CT) fluorescence-based organic light-emitting devices (OLEDs) due to the small energy difference between singlet and triplet CT states. Thus, clarifying factors affecting the direction of the conversion is important to obtain highly efficient OLEDs based on thermally activated delayed fluorescence (TADF). Here, we investigated the inter-conversion between singlets and triplets in a CT fluorescence-based OLED via magneto-electroluminescence (MEL) measurements. The values of MELs turned from negative to positive with the increase in driving voltage and electric stressing time, indicating that the direction of the conversion was changed. Both the increase in driving voltage and stressing time can cause the quenching of triplets through triplet–triplet annihilation and triplet–trap interaction, respectively. Thus, the decreased population ratio of triplet to singlet induces the change of the direction of inter-conversion. Our results demonstrate that the singlet–triplet inter-conversion is a dynamic process, and the deactivation rates of singlet and triplet determine the inter-conversion direction.
Co-reporter:Jie Zhou, Ping Chen, Xu Wang, Yan Wang, Yi Wang, Feng Li, Minghui Yang, Yan Huang, Junsheng Yu and Zhiyun Lu
Chemical Communications 2014 vol. 50(Issue 57) pp:7586-7589
Publication Date(Web):18 Mar 2014
DOI:10.1039/C4CC00576G
A charge-transfer-featured naphthalimide derivative with a small exchange energy but a lower lying 3ππ* state than 3CT state is found to contribute to triplet harvesting through a P-type rather than an E-type delayed fluorescence, and could act as a quite promising host to achieve highly efficient OLEDs.
Co-reporter:Ping Chen;Zuhong Xiong;Qiming Peng;Jiangwen Bai;Shitong Zhang
Advanced Optical Materials 2014 Volume 2( Issue 2) pp:142-148
Publication Date(Web):
DOI:10.1002/adom.201300422
Co-reporter:J.W. Bai, P. Chen, Y.L. Lei, Y. Zhang, Q.M. Zhang, Z.H. Xiong, F. Li
Organic Electronics 2014 Volume 15(Issue 1) pp:169-174
Publication Date(Web):January 2014
DOI:10.1016/j.orgel.2013.11.012
•A large positive MEL (23.5%) was obtained at R.T.•The MELs changed their signs both at low-field and high-field components.•The singlet fission and triplet fusion are coexisted in rubrene.•Relative contribution of singlet fission and triplet fusion on MEL changes with decreasing temperature.Organic light emitting diodes (OLEDs) utilizing a singlet–triplet energy-resonant (ES ≈ 2ET) layer (rubrene) were fabricated to investigate the singlet fission and triplet fusion by the magneto-electroluminescence (MEL) of device from R.T. to 20 K. A large positive MEL (23.5%) was obtained at R.T. due to magnetic-field-suppressed singlet fission. With decreasing temperatures, the MELs changed their signs both at low-field and high-field components because of a gradual decrease in singlet fission simultaneously followed by an increasing triplet fusion, leading to a negative MEL around −7.5% at 20 K. Moreover, transient electroluminescence and MELs from the control devices were used to further confirm the exciton fission and fusion processes in rubrene-based OLEDs. Our findings of MEL may provide a useful pathway to study the microscopic dynamics of excited states in organic optoelectronic devices.
Co-reporter:Qiming Peng;Weijun Li;Shitong Zhang;Ping Chen;Yuguang Ma
Advanced Optical Materials 2013 Volume 1( Issue 5) pp:362-366
Publication Date(Web):
DOI:10.1002/adom.201300028
Co-reporter:Ping Chen, Junhua Huang, Zuhong Xiong, Feng Li
Organic Electronics 2013 Volume 14(Issue 2) pp:621-627
Publication Date(Web):February 2013
DOI:10.1016/j.orgel.2012.12.009
By investigating the turn-on and turn-off photovoltage dynamics as a function of aging time, we reported the roles of traps on the energy loss in organic solar cells composing of copper phthalocyanine (CuPc)/fullerene (C60). Illuminating the device with square pulses of light, a peak of transient photovoltage after turn-on was observed after device degradation. After turn-off, the transient photovoltage first goes to the negative before settling back to zero, which is the result of electron trapping in the C60 layer before being neutralized by re-injected holes. Furthermore, by adding a tris (8-hydroxyquinolinato) aluminum buffer to prevent the traps from propagating into C60 layer, the peak after turn-on is greatly suppressed and the negative peak after turn-off vanishes, supporting the trapped electrons in the C60 layer play the critical role in the appearance of peak of the transient photovoltage.Graphical abstractHighlights► We report roles of traps in energy loss for aged OSCs by transient photovoltage. ► Peaks after turn-on and turn-off were observed for microseconds in aged device. ► Peaks are affected by light intensity, background illumination and pulse width. ► Roles of traps were verified by adding Alq3 buffer.
Co-reporter:Qiming Peng, Ping Chen, Feng Li
Synthetic Metals 2013 Volume 173() pp:31-34
Publication Date(Web):1 June 2013
DOI:10.1016/j.synthmet.2013.01.001
We investigate the underlying mechanisms of the magnetic field effects (MFEs), magneto-conductance (MC) and magneto-electroluminescence (MEL), in organic semiconductors by testing three kinds of devices, the electron-only devices, the hole-only devices and the ambipolar devices. There is no or very small MCs in the unipolar devices and much larger MC in the ambipolar devices. The results suggest that the ambipolar injection or exciton formation is a dominant factor to obtain large MCs, and the MEL is in principle a primary effect. Our results are consistent with the electron–hole pair model.Graphical abstractHighlights► Hole-only devices, electron-only devices, and bipolar devices were fabricated. ► The magneto-conductance (MC) and magneto-electroluminescence (MEL) of the three kinds of devices were tested. ► No or very small MCs in the unipolar devices and much larger MC in the bipolar devices. ► Exciton formation is a dominant factor to obtain large MC. ► The MEL is in principle a primary effects and the MC comes from the MEL.
Co-reporter:Ping Chen, Mingliang Li, Qiming Peng, Feng Li, Yu Liu, Qiaoming Zhang, Yong Zhang, Zuhong Xiong
Organic Electronics 2012 Volume 13(Issue 10) pp:1774-1778
Publication Date(Web):October 2012
DOI:10.1016/j.orgel.2012.05.019
Organic magneto-electroluminescence (MEL) based on the charge-transfer (CT) states was investigated to clarify the electron–hole (e–h) pair mechanism for the organic magnetic field effects. The CT state is an ideal object because its emission is a direct intermolecular recombination process without forming intramolecular exciton. We found that the MEL of the CT states is not only greater than that of the exciton, but also exhibits almost no high-field decrease at low temperatures. Our results directly prove the e–h pair mechanism. Meanwhile, the transient electroluminescence measurements with and without magnetic fields confirm that magnetic field has no effect on the charge mobility but on the charge recombination process, implying the charge mobility-related mechanisms may be less dominant above the turn-on voltage.Graphical abstractHighlights► We report magneto-electroluminescence (MEL) of NPB:d(ppy)BF charge-transfer state. ► The MEL of NPB:d(ppy)BF CT state is larger than that of NPB exciton. ► The MEL of NPB:d(ppy)BF CT state does not change with injection current. ► The MEL of NPB:d(ppy)BF CT state exhibits no high-field decay at low temperature. ► Transient EL measurements revealed charge mobility was not changed by magnetic field.
Co-reporter:Qiming Peng, Ping Chen, Jixiang Sun, Feng Li
Organic Electronics 2012 Volume 13(Issue 12) pp:3040-3044
Publication Date(Web):December 2012
DOI:10.1016/j.orgel.2012.08.006
A simple method by employing white organic light-emitting diode (OLED) to simultaneously study the effects of magnetic fields (MFEs) on the fluorescent and phosphorescent emission was presented. The white OLED consisting of the blue fluorescent and red phosphorescent materials was fabricated. The low-pass filter chopped at 500 nm and the high-pass filter chopped at 550 nm were used to separate the MFEs on the blue fluorescence and red phosphorescence, separately. The magnetoelectroluminescences (MELs) on the fluorescence sharply increased at low magnetic field then tended to saturation at high magnetic field. While the MELs on the phosphorescence sharply increased at low magnetic field then slowly monotonically increased as the magnetic field further increased. Our results indicated that the magnetic-field modulated singlet-to-triplet electron–hole pair conversion combining with the magnetic-field modulated triplet–triplet annihilation process are the origins of the MFEs on the electroluminescence.Graphical abstractHighlights► The white OLED consisting of the blue fluorescent and red phosphorescent materials was fabricated. ► The MELs on the fluorescent and phosphorescent emission was simultaneously studied. ► The MELs on the fluorescence tended to saturation at high magnetic field. ► The MELs on the phosphorescence monotonically increased at high magnetic field. ► Magnetic-field modulated e–h pair conversion and TTA processes were proposed.
Co-reporter:Xianjie Li, Yuanxiang Xu, Feng Li, Yuguang Ma
Organic Electronics 2012 Volume 13(Issue 5) pp:762-766
Publication Date(Web):May 2012
DOI:10.1016/j.orgel.2012.01.028
Slice-like organic single crystals of 1,4-bis(2-cyano-2-phenylethenyl)benzene (BCPEB) are grown by the physical vapor transport (PVT) method, and exhibit a very high photoluminescence quantum efficiency (ΦPL) of 75%. The ambipolar behavior of BCPEB single crystals are confirmed using the time of flight technique. The high efficiency and balanced (μh = 0.059 cm2/Vs and μe = 0.070 cm2/Vs) carriers’ mobility imply that the BCPEB single crystal is a promising light-emitting layer in the diodes structure. Intense green electroluminescence (EL) from a diode has been successfully demonstrated at an applied electric field of 2 × 105 V/cm.Graphical abstractHighlights► Slice-like oligo (p-phenylenevinylene) organic single crystals were grown by the physical vapor transport method. ► The organic single crystal exhibited high ΦPL and balanced (μh = 0.059 cm2/Vs and μe = 0.070 cm2/Vs) carrier mobility. ► Intense green electroluminescence (EL) from a diode has been successfully demonstrated at an applied voltage of 14 V.
Co-reporter:Jixiang Sun, Qiming Peng, Xianjie Li, Mingliang Li, Feng Li
Synthetic Metals 2012 Volume 162(3–4) pp:257-260
Publication Date(Web):March 2012
DOI:10.1016/j.synthmet.2011.11.033
Co-reporter:Huan Wang, Feng Li, Bingrong Gao, Zengqi Xie, Suijun Liu, Chunlei Wang, Dehua Hu, Fangzhong Shen, Yuanxiang Xu, Hui Shang, Qidai Chen, Yuguang Ma and Hongbo Sun
Crystal Growth & Design 2009 Volume 9(Issue 11) pp:4945
Publication Date(Web):October 1, 2009
DOI:10.1021/cg9007125
Doping an organic crystal such as an inorganic semiconductor without having a bad influence on crystalline quality is a very difficult task because weak intermolecular interactions and lattice mismatches exist in organic condensed states. We report here the successful growth of tetracene and pentacene-doped trans-1,4-distyrylbenzene (trans-DSB) crystals with high crystalline quality, large size, and excellent optical properties. The doped concentration up to 10% can be achieved by controlling the temperature of the crystal growth zone. The first key point for the crystals with a high doping ratio is the choice of the host (trans-DSB) and guest (tetracene or pentacene) molecules with comparable crystal lattice structures, which ensure less lattice mismatch. The second key point is crystal growth at relative high temperatures by the physical vapor transport (PVT) method, which gives the guest molecules high kinetic energy to incorporate into the crystal lattice of the host. These doped crystals with slice shape and large size (millimeter scale) maintain ordered layer structures and crystal surface continuities, which are verified by X-ray diffraction (XRD) and atomic force microscopy (AFM) analysis. Efficient energy transfer from the host to the guest and the suppressing of the interaction among the guest molecules lead to color-tunable emission and high luminescent efficiencies (blue for undoped trans-DSB, η = 65 ± 4%; green for tetracene-doped trans-DSB, η = 74 ± 4%; red for pentacene-doped trans-DSB, η = 28 ± 4%). Steady-state and time-resolved fluorescence spectroscopy of undoped and doped crystals, and their amplified spontaneous emissions, have been investigated. These doped crystals are expected to be of interest for light-emitting transistors, diodes, and electrically pumped lasers.
Co-reporter:Yupeng Li, Fangzhong Shen, Huan Wang, Feng He, Zengqi Xie, Houyu Zhang, Zhiming Wang, Linlin Liu, Feng Li, Muddasir Hanif, Ling Ye and Yuguang Ma
Chemistry of Materials 2008 Volume 20(Issue 23) pp:7312
Publication Date(Web):November 14, 2008
DOI:10.1021/cm801427s
The supramolecular interactions are of importance for inducing the molecular orientation and constructing functional materials with high performance. In this manuscript we report uniaxially oriented molecular crystal of a cyano substituted oligo(p-phenylene vinylene) 1,4-bis(α-cyano-4-diphenylaminostyryl)-2,5-diphenylbenzene (CNDPASDB) with high luminescence under the driving force of the three-dimensional supramolecular interaction networks. Amplified spontaneous emission (ASE) with a low threshold value of 30.5 kW/cm2 was observed from a high-quality slab-like CNDPASDB crystal and verified by the variable pump stripe method. The net gain coefficient with 55 cm−1 is also measured. The tip of CNDPASDB crystal exhibits polarized self-waveguided emission due to the propagation of polarized light emitted from the uniaxially oriented CNDPASDB molecules along crystal surface.
Co-reporter:Suijun Liu, Feng He, Huan Wang, Hai Xu, Chunyu Wang, Feng Li and Yuguang Ma
Journal of Materials Chemistry A 2008 vol. 18(Issue 40) pp:4802-4807
Publication Date(Web):10 Sep 2008
DOI:10.1039/B807266C
4,4′-Bis(2,2-diphenylvinyl)-1,1′-biphenyl (DPVBi) is a well-known blue-emitting material for electroluminescent devices, but its vacuum evaporated films exhibit a phase transition trend from amorphous to crystalline state, which impacts morphological stability and device lifetime. We report here a cruciform DPVBi derivate, named 2,5,2′,5′-tetrakis(2,2-diphenylvinyl)biphenyl (TDPVBi), in which two 1,4-bis(2,2-diphenylvinyl)benzene segments are linked through a central biphenyl linkage. TDPVBi exhibits very high photoluminescence efficiency in the solid state (80%), and fully amorphous characteristics with high glass transition temperature (Tg = 110 °C). High performance non-doped blue organic light-emitting device (OLED) with Commission Internationale de I'Eclairage (CIE) coordinates of (0.16, 0.21), maximum luminance efficiency of 6.2 cd A−1 (corresponding external quantum efficiency of 3.8%), and maximum luminance exceeding 31170 cd m−2 is achieved based on TDPVBi. The operation lifetime of TDPVBi-based device exhibits a 1.7-fold enhancement relative to that of a similar device based on DPVBi.
Co-reporter:Zengqi Xie, Weijie Xie, Feng Li, Linlin Liu, Huan Wang and Yuguang Ma
The Journal of Physical Chemistry C 2008 Volume 112(Issue 24) pp:9066-9071
Publication Date(Web):May 21, 2008
DOI:10.1021/jp801033j
trans-Distyrylbenzene (trans-DSB), the most typical model compound for poly(p-phenylenevinylene) (PPV) derivatives, has highly efficient and pure blue emission in dilute solution; while in solid or film state, its photoluminescence efficiency decreases dramatically with red-shifted emission, because of the formation of H-aggregate. Herein, we introduce two phenyl substituent groups to the central phenyl ring of trans-DSB, which restrains the formation of H-aggregate efficiently in the condensed state and then induces highly luminescent molecular aggregate modes (X-aggregate and J-aggregate). Most important, the introduction of the phenyl substituent groups makes the resulting compounds form high quality films easily under vacuum deposition conditions. High performance nondoped deep blue organic light-emitting device with CIE (0.15, 0.10), maximum luminous efficiency of 4.2 cd/A (corresponding external quantum efficiency of 3.9%), is achieved on the basis of this kind of material.
Co-reporter:Zengqi Xie, Huan Wang, Feng Li, Weijie Xie, Linlin Liu, Bing Yang, Ling Ye and Yuguang Ma
Crystal Growth & Design 2007 Volume 7(Issue 12) pp:2512
Publication Date(Web):October 31, 2007
DOI:10.1021/cg070270u
We prepared a large slice crystal of trans-DPDSB with a regular shape by the physical vapor transport method and determined its crystal structure, which is different from the needle-like crystal grown in a mixture of chloroform and methanol. In the slice crystal, all of the molecules are packed in layer-by-layer mode with the same molecular orientation, and in one molecular layer, the molecules are packed in a “brick wall” motif (J-aggregate). The crystal has a very high luminescence efficiency of 48 ± 4%, attributed to the special molecular dipole stacking mode, and stimulated emission is observed under optical pumping.
Co-reporter:Feng Li, Xiao Li, Junhu Zhang, Bai Yang
Organic Electronics 2007 Volume 8(Issue 5) pp:635-639
Publication Date(Web):October 2007
DOI:10.1016/j.orgel.2007.06.001
One simple method to increase the light extraction from organic light-emitting devices by using microcontact printed silica colloidal crystals is demonstrated. A close-packed hexagonal silica microsphere arrays is pressed into poly(vinyl alcohol) layer that is spin-coated on the opposite side of the indium–tin–oxide-coated glass substrate. This structure has the similar characteristics of microlens arrays. By using the silica microspheres with the diameters of 400 and 1000 nm those were half pressed into poly(vinyl alcohol), the luminance efficiencies of the devices in the normal direction are increased by a factor of 1.6 and 1.3 at the current density of 7.0 mA/cm2 compared to that of the device using flat glass substrate, respectively, and the shapes of emission spectra exhibit almost no angle dependence.
Co-reporter:Chuanyou He, Haoqing Guo, Qiming Peng, Shengzhi Dong and Feng Li
Journal of Materials Chemistry A 2015 - vol. 3(Issue 38) pp:NaN9947-9947
Publication Date(Web):2015/08/31
DOI:10.1039/C5TC02055G
Deep-blue emission is particularly important for applications of organic light-emitting diodes (OLEDs) in full colour flat-panel displays and solid-state lighting resources. Two asymmetrically twisted anthracene derivatives, 4,5-diphenyl-1,2-bis(4-(10-phenylanthracen-9-yl)phenyl)-1H-imidazole (DPA-PIM) and 1,2-bis(4-(10-phenylanthracen-9-yl)phenyl)-1H-phen-anthro[9,10-d]imidazole (DPA-PPI), for deep-blue OLEDs have been designed and synthesized. The asymmetrically twisted conformations between anthracene and imidazole units in compounds efficiently interrupt molecular π-conjugation and inhibit π–π intermolecular interactions, resulting in high thermal stability and efficient deep-blue emission. The two anthracene derivatives in non-doped OLEDs exhibited blue emission. In particular, the non-doped device based on DPA-PIM achieved an external quantum efficiency (EQE) of 6.5% with CIE coordinates of (0.15, 0.08). In addition, the two emitters in doped devices achieved high EQEs of over 5.0% and much purer blue emission with CIE coordinates of (0.15, 0.06) for DPA-PPI and (0.15, 0.05) for DPA-PIM, which nearly match the CIE coordinates of the European Broadcasting Union (EBU) blue standard of (0.15, 0.06).
Co-reporter:Qiming Peng, Aiwu Li, Yunxia Fan, Ping Chen and Feng Li
Journal of Materials Chemistry A 2014 - vol. 2(Issue 31) pp:NaN6268-6268
Publication Date(Web):2014/06/04
DOI:10.1039/C4TC00885E
The forward conversion from singlets to triplets and backward conversion from triplets to singlets are both possible in charge-transfer (CT) fluorescence-based organic light-emitting devices (OLEDs) due to the small energy difference between singlet and triplet CT states. Thus, clarifying factors affecting the direction of the conversion is important to obtain highly efficient OLEDs based on thermally activated delayed fluorescence (TADF). Here, we investigated the inter-conversion between singlets and triplets in a CT fluorescence-based OLED via magneto-electroluminescence (MEL) measurements. The values of MELs turned from negative to positive with the increase in driving voltage and electric stressing time, indicating that the direction of the conversion was changed. Both the increase in driving voltage and stressing time can cause the quenching of triplets through triplet–triplet annihilation and triplet–trap interaction, respectively. Thus, the decreased population ratio of triplet to singlet induces the change of the direction of inter-conversion. Our results demonstrate that the singlet–triplet inter-conversion is a dynamic process, and the deactivation rates of singlet and triplet determine the inter-conversion direction.
Co-reporter:Xujun Zheng, Qiming Peng, Jie Lin, Yi Wang, Jie Zhou, Yan Jiao, Yuefeng Bai, Yan Huang, Feng Li, Xingyuan Liu, Xuemei Pu and Zhiyun Lu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 27) pp:NaN6978-6978
Publication Date(Web):2015/05/21
DOI:10.1039/C5TC00779H
A red naphthalimide derivative with an intramolecular charge-transfer (ICT) feature, namely (E)-2-(4-(t-butyl)phenyl)-6-(2-(6-(diphenylamino)naphthalen-2-yl)vinyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (NA-TNA), was designed and synthesized. Photophysical and magneto-electroluminescence (MEL) characterization results revealed that NA-TNA could harvest triplet excitons via a triplet–triplet annihilation (TTA) process in organic light-emitting diodes (OLEDs) due to the presence of a lower-lying triplet excited state with 3ππ* character. Consequently, using NA-TNA as a guest compound and CzPhONI, another ICT-featured naphthalimide derivative with triplet fusion delayed fluorescence (TFDF) character as host material, a high-performance orange OLED with 6 wt% NA-TNA doped CzPhONI film as the emitting layer was acquired. The maximum current efficiency (LEmax), brightness (Lmax), and external quantum yield (EQEmax) of this OLED is 7.73 cd A−1, 31940 cd m−2 and 5.83%, respectively, while the theoretical EQEmax of this device should not exceed 3.34%. On the contrary, the reference device with a NA-TNA doping level of 1.4 wt% showed much inferior performance, with a LEmax, a Lmax, and an EQEmax of 3.19 cd A−1, 24900 cd m−2 and 2.49%, respectively. The high performance of the 6 wt% NA-TNA doped device was attributed to the efficient harvesting of triplet excitons by both the guest and host materials.
Co-reporter:Jie Zhou, Ping Chen, Xu Wang, Yan Wang, Yi Wang, Feng Li, Minghui Yang, Yan Huang, Junsheng Yu and Zhiyun Lu
Chemical Communications 2014 - vol. 50(Issue 57) pp:NaN7589-7589
Publication Date(Web):2014/03/18
DOI:10.1039/C4CC00576G
A charge-transfer-featured naphthalimide derivative with a small exchange energy but a lower lying 3ππ* state than 3CT state is found to contribute to triplet harvesting through a P-type rather than an E-type delayed fluorescence, and could act as a quite promising host to achieve highly efficient OLEDs.
Co-reporter:Xiaojun Yin, Dongcheng Chen, Qiming Peng, Yepeng Xiang, Guohua Xie, Zece Zhu, Cheng Zhong, Feng Li, Shijian Su and Chuluo Yang
Journal of Materials Chemistry A 2016 - vol. 4(Issue 7) pp:NaN1489-1489
Publication Date(Web):2016/01/14
DOI:10.1039/C5TC04198H
Three new pyrimidine-containing star-shaped compounds, namely, 1,3,5-tri(3-(pyrimidin-5-yl)phenyl)benzene (TPM-TPB), 2,4,6-tris(3-(pyrimidin-5-yl)phenyl)-1,3,5-triazine (TPM-TAZ) and 3,5,6-tris(3-(pyrimidin-5-yl)phenyl)-1,2,4-triazine (TPM-i-TAZ), were synthesized and characterized. These new compounds exhibited favorable electronic affinity (Ea >2.81 eV) and the triplet energy levels (ET) up to ∼2.83 eV. X-ray diffraction analysis of the compounds revealed that the intramolecular and intermolecular C–H⋯N hydrogen bonds of TPM-TAZ resulted in high electron mobility up to 2.0 × 10−3 cm2 V−1 s−1. Using these compounds as the electron transporting materials, the blue phosphorescent organic light-emitting devices showed good performance, with a very low turn-on voltage of 2.4 V, a maximum current efficiency of 26.4 cd A−1, and a maximum power efficiency of 26.9 lm W−1.
Co-reporter:Suijun Liu, Feng He, Huan Wang, Hai Xu, Chunyu Wang, Feng Li and Yuguang Ma
Journal of Materials Chemistry A 2008 - vol. 18(Issue 40) pp:NaN4807-4807
Publication Date(Web):2008/09/10
DOI:10.1039/B807266C
4,4′-Bis(2,2-diphenylvinyl)-1,1′-biphenyl (DPVBi) is a well-known blue-emitting material for electroluminescent devices, but its vacuum evaporated films exhibit a phase transition trend from amorphous to crystalline state, which impacts morphological stability and device lifetime. We report here a cruciform DPVBi derivate, named 2,5,2′,5′-tetrakis(2,2-diphenylvinyl)biphenyl (TDPVBi), in which two 1,4-bis(2,2-diphenylvinyl)benzene segments are linked through a central biphenyl linkage. TDPVBi exhibits very high photoluminescence efficiency in the solid state (80%), and fully amorphous characteristics with high glass transition temperature (Tg = 110 °C). High performance non-doped blue organic light-emitting device (OLED) with Commission Internationale de I'Eclairage (CIE) coordinates of (0.16, 0.21), maximum luminance efficiency of 6.2 cd A−1 (corresponding external quantum efficiency of 3.8%), and maximum luminance exceeding 31170 cd m−2 is achieved based on TDPVBi. The operation lifetime of TDPVBi-based device exhibits a 1.7-fold enhancement relative to that of a similar device based on DPVBi.
![2,4-Cyclopentadien-1-one, 2,5-diphenyl-3,4-bis[4-[2-[tris(1-methylethyl)silyl]ethynyl]phenyl]-](/data/chemimg/1774900/189619-39-4.png)
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![Pyrene, 1,3,6,8-tetrakis[4-ethynyl-6'-(4-ethynylphenyl)-5'-phenyl[1,1':2',1''-terphenyl]-3'-yl]- (9CI)](/data/chemimg/3784100/912366-15-5_b.png)
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![[1,1':2',1''-Terphenyl]-4,4''-diamine, 4',4'''',4''''''',4''''''''''-(1,3,6,8-pyrenetetrayl)tetrakis[N4,N4,N4'',N4'',3',6'-hexaphenyl-](/data/chemimg/3784100/1639428-45-7.png)
![[1,1':2',1''-Terphenyl]-4,4''-diamine, 4',4'''',4''''''',4''''''''''-(1,3,6,8-pyrenetetrayl)tetrakis[N4,N4,N4'',N4'',3',6'-hexaphenyl-](/data/chemimg/3784100/1639428-45-7_b.png)
![2,4-Cyclopentadien-1-one, 3,4-bis[4-(diphenylamino)phenyl]-2,5-diphenyl-](/data/chemimg/3784100/675610-03-4.png)
![2,4-Cyclopentadien-1-one, 3,4-bis[4-(diphenylamino)phenyl]-2,5-diphenyl-](/data/chemimg/3784100/675610-03-4_b.png)
![Benzenamine, 4-[3,5-bis(4-bromophenyl)-4H-1,2,4-triazol-4-yl]-N,N-diphenyl-](/data/chemimg/3784100/1151695-71-4.png)
![Benzenamine, 4-[3,5-bis(4-bromophenyl)-4H-1,2,4-triazol-4-yl]-N,N-diphenyl-](/data/chemimg/3784100/1151695-71-4_b.png)
![9H-Carbazole, 9,9',9''-[methylidynetris(3,5-dichloro-4,1-phenylene)]tris-](/data/chemimg/3784100/1018803-45-6.png)
![9H-Carbazole, 9,9',9''-[methylidynetris(3,5-dichloro-4,1-phenylene)]tris-](/data/chemimg/3784100/1018803-45-6_b.png)
![Methanone, (2,6-difluorophenyl)[4-[3-[4-(1,2,2-triphenylethenyl)phenoxy]propyl]phenyl]-](/data/chemimg/3779000/1808176-90-0.png)
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![Benzenamine, 4,4'-[9-[4-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl]-9H-carbazole-3,6-diyl]bis[N,N-diphenyl-](/data/chemimg/3784100/1897442-39-5.png)
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![1H-Phenanthro[9,10-d]imidazole, 1,2-bis[4-(10-phenyl-9-anthracenyl)phenyl]-](/data/chemimg/3784100/1809254-72-5.png)
![1H-Phenanthro[9,10-d]imidazole, 1,2-bis[4-(10-phenyl-9-anthracenyl)phenyl]-](/data/chemimg/3784100/1809254-72-5_b.png)
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![1H-Imidazole, 4,5-diphenyl-1,2-bis[4-(10-phenyl-9-anthracenyl)phenyl]-](/data/chemimg/3784100/1809254-73-6_b.png)
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![(6e)-6-[[4-(dimethylamino)anilino]methylidene]cyclohexa-2,4-dien-1-one](http://img.cochemist.com/ccimg/1000/959-74-0.png)
![(6e)-6-[[4-(dimethylamino)anilino]methylidene]cyclohexa-2,4-dien-1-one](http://img.cochemist.com/ccimg/1000/959-74-0_b.png)
![1H-Phenanthro[9,10-d]imidazole, 2-(4-bromophenyl)-1-phenyl-](/data/chemimg/149000/1147081-43-3.png)
![1H-Phenanthro[9,10-d]imidazole, 2-(4-bromophenyl)-1-phenyl-](/data/chemimg/149000/1147081-43-3_b.png)
