Highly Efficient Orange-Red Thermally Activated Delayed Fluorescence Compounds Comprising Dual Dicyano-Substituted Pyrazine/Quinoxaline Acceptors

Article abstract of DOI:10.1002/cplu.202000703

The π-conjugation of molecules has a large influence on their excited state properties, especially for red thermally activated delayed fluorescence (TADF) materials. Two orange-red TADF compounds comprising dual dicyano-substituted pyrazine/quinoxaline ac

Full text of DOI:10.1002/cplu.202000703

A Multidisciplinary Journal Centering on Chemistry
Accepted Article
Title: Highly Efficient Orange-Red Thermally Activated Delayed
Fluorescence Compounds Comprising Dual Dicyano-Substituted
Pyrazine/Quinoxaline Acceptors
Authors: Hejun Li, Tong Yang, Jiaxuan Wang, Ning Xie, Qingyang
Wang, Yuguang Zhao, and Baoyan Liang
This manuscript has been accepted after peer review and appears as an
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To be cited as: ChemPlusChem 10.1002/cplu.202000703
Link to VoR: https://doi.org/10.1002/cplu.202000703
01/2020

10.1002/cplu.202000703
ChemPlusChem
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Highly Efficient Orange-Red Thermally Activated Delayed
Fluorescence Compounds Comprising Dual Dicyano-Substituted
Pyrazine/Quinoxaline Acceptors
Hejun Li,a,b Tong Yang,c Jiaxuan Wang,c Ning Xie,c Qingyang Wang,c Yincai Xu,c Pro. Yuguang Zhaoa
and Dr. Baoyan Liang*b
a College of Materials Science and Engineering, Jilin University, Changchun 130012, China
b Jihua Laboratory, 13 Nanpingxi Road, Foshan, 528200, Guangdong Province, China
c State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun 130012, China
* Corresponding author. E-mail address: liangby@jihualab.com
Abstract: The π-conjugation of the acceptors influences the
properties of the excited state deeply, especially for red thermally
activated delayed fluorescence (TADF) materials. Two orange-red
TADF compounds comprised of dual dicyano-substituted
pyrazine/quinoxaline acceptors have been designed and synthesized.
of the acceptor units also influence the distribution of the highest
occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO), which influences the properties of the
excited state.[7] The HOMO usually distributes on electron donor
(D) units, and the LUMO mainly concentrates on electron
acceptor (A) units in charge transfer type D-A materials.
Rationally expanding the π-conjugated acceptors can enlarge the
distribution of LUMO, and the centroid distance between HOMO
and LUMO can be increased. As a result, the overlap of HOMO
and LUMO will be decreased and smaller ΔEst will be obtained.
Recently, a few efficient red TADF materials have been
reported.[8] Wang and coworkers reported a large π-conjugated
acceptor, i.e. phenanthro[4,5-abc]phenazine-11,12-dicarbonitrile.
Compounds comprised of this acceptor showed around 80~90%
PLQY in doped films, and the maximum external quantum
efficiency (EQE) of the deep red devices were more than 20%.[9]
The large π-conjugated acceptor seems has a positive impact on
the efficient red TADF materials. However, a large π-conjugated
acceptor usually causes π-π stacking, which may induce serious
aggregation induced quenching.[2c, 9b] So rationally modifying the
degree of conjugate of acceptors is crucial.
TPA-2DCNQ
(3,3'-((phenylazanediyl)bis(4,1-phenylene))bis(2-
phenylquinoxaline-6,7-dicarbonitrile) with extended π-conjugated
quinoxaline as the acceptor exhibits higher photoluminescence
quantum yields in doped films of 0.67~0.71. At the same time, a
smaller energy splitting (ΔEst) of the first singlet excited state and
triplet excited state is also achieved, indicating that enlarging the π-
conjugation of the acceptor rationally is an effective approach to
designing highly efficient long-wavelength TADF materials. Devices
with TPA-2DCNQ as the emitter display maximum external quantum
efficiencies (EQEs) of 12.6~14.0%, which are more than two times
higher than those of TPA-2DCNPZ (6,6'-((phenylazanediyl)bis(4,1-
phenylene))bis(5-phenylpyrazine-2,3-dicarbonitrile) based ones.
Introduction
In this contribution, two orange-red TADF compounds with dual
dicyano-substituted pyrazine/quinoxaline as the acceptors and
triphenylamine unit as the donor have been synthesized. TPA-
2DCNQ (Scheme 1) with larger π-conjugated acceptor shows a
deeper LUMO energy level and a less overlap of HOMO and
LUMO. More importantly, a higher PLQY and a smaller ΔEst are
achieved simultaneously compared with TPA-2DCNPZ (Scheme
1). Eventually, OLED devices with TPA-2DCNQ as emitter display
maximum EQEs of 12.6~14.0%, which is more than 2 times
higher than those of TPA-2DCNPZ based ones.
Organic light-emitting diodes (OLEDs) technology has drawn
more and more attention in flat panel displays and solid-state
lighting fields owing to their flimsy and flexile features.[1] Up to now,
a mass of smartphones and televisions are equipped with OLED
screens. However, red materials are always the short slab among
the three-primary colors, due to the anabatic internal conversion
(IC) coefficient managed by the energy gap law.[2] Red phosphor
materials are widely used in the industry at present owing to the
100% exciton utilization efficiency (EUE).[3] The introduction of
precious metals, such as Ir, Pt, etc., increases the costs and it is
not eco-friendly. Thermally activated delayed fluorescence
(TADF) mechanism was proposed by Adachi and coworkers.[4]
Metal-free TADF materials can also achieve 100% EUE by
reverse intersystem crossing (RISC) process of triplet excitons.
High photoluminescence (PL) quantum yield (PLQY) and small
energy splitting (ΔEst) of the first excited singlet state (S1) and
excited triplet state (T1) are crucial factors for high-performance
TADF materials, but they are contradictory.[5] How to balance
them for highly efficient TADF materials is the issue urgently need
to be addressed.
Results and Discussion
Synthesis
All raw materials were commercially purchased without further
purification. The synthetic routes and molecular structures of
TPA-2DCNPZ and TPA-2DCNQ is depicted in Scheme 1.
Intermediates 1 was synthesized by Sonogashira cross coupling
reaction. Then diketone derivative, intermediate 2, was
synthesized by potassium permanganate involved oxidation
reaction in dilute acid solution. Intermediates 1 and 2 were
synthesized referencing the reported literatures.[10] Finally, the
The π-conjugated skeleton of the acceptor units has a deep
influence on the excited state energy level of the compounds.[6]
On the one hand, rigid π-conjugated skeleton can suppress
harmful structural relaxation; on the other hand, the π-conjugation
1
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Scheme 1. Synthetic steps to product TPA-2DCNPZ and TAP-2DCNQ. a) PPh3, CuI, (PPh3)2PdCl2, NEt3, reflux, 8 h, N2 protection; b) KMnO4, HOAc, acetone/H2O,
reflux, 2.5 h; c) HOAc, reflux, 6 h, N2 protection.
target compounds TPA-2DCNPZ and TPA-2DCNQ were
synthesized by cyclization reactions in acetic acid. They were
characterized by the NMR (nuclear magnetic resonance) (Figure
S1~S4), mass spectrometry (Figure S5~S6) and elemental
analysis, which demonstrated the products were the target
materials.
The thermal properties of TPA-2DCNPZ and TPA-2DCNQ were
measured by thermogravimetric analysis (TGA) and differential
scanning calorimetry (DSC) in a nitrogen atmosphere. The
decomposition temperatures (Td, corresponding to 5% weight
loss) of TPA-2DCNPZ and TPA-2DCNQ were 417 and 513 ℃,
respectively, seen from Figure 1a. The glass transition
temperatures (Tg) of TPA-2DCNPZ and TPA-2DCNQ were 133
and 175 ℃, respectively, obtained from Figure 1b. The high Td
and Tg values suggest that TPA-2DCNPZ and TPA-2DCNQ are
stable under heating and they are applicable for OLEDs devices
fabrication via vacuum deposition technique.
Thermal and electrochemical properties
Cyclic voltammetry (CV) measurements were conducted to test
the electrochemical properties of TPA-2DCNPZ and TPA-2DCNQ.
They showed similar and reversible oxidation curves (Figure 2),
because the redox reactions took place on triphenylamine units.
The HOMO energy levels were calculated to be -5.45 and -5.42
eV, and the LUMO energy levels were calculated to be -3.05 and
-3.16 eV, respectively, based on the absorption spectra of TPA-
2DCNPZ and TPA-2DCNQ (Figure 5). The LUMO of TPA-
2DCNQ is deeper than that of TPA-2DCNPZ because of the
extended π-conjugated acceptor.[2c, 7b-c, 11]
Figure 2. CV curves of TPA-2DCNPZ and TPA-2DCNQ.
Figure 1. TGA (a) and DSC (b) curves of TPA-2DCNPZ and TPA-2DCNQ.
2
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Figure 3. The configuration (a), cell structure (b), and intermolecular interactions of TPA-2DCNQ in single crystal.
θ1', while those between acceptor units and single phenyl rings
were named θ2 and θ2'. The values of θ1 and θ1' were around 37°,
and those of θ2 and θ2' were 37° for TPA-2DCNPZ and 41° for
TPA-2DCNQ. The detailed data are shown in Table S1. The
HOMO and LUMO distributions of TPA-2DCNPZ and TPA-
2DCNQ are shown in Figure 4. For TPA-2DCNPZ, the HOMO
was mainly concentrated on triphenylamine unit and slightly
located at pyrazine units, the LUMO was mainly distributed over
the acceptors and phenyl bridges of triphenylamine, resulting in a
larger overlap of HOMO and LUMO. The HOMO of TPA-2DCNQ
was mainly located at triphenylamine unit, while its LUMO was
Crystal structure analysis
The crystal of TPA-2DCNQ was obtained by solvent evaporation
method using dichloromethane/methyl alcohol mixed solvents.
The configuration of TPA-2DCNQ in crystal is shown in Figure 3a.
The dihedral angles between phenyl bridge of triphenylamine and
quinoxaline units are 13.1 and 61.3°, which will induce
inhomogeneous distribution of LUMO on the dual dicyano-
substituted quinoxaline acceptors. The cell structure and
intermolecular interactions diagrams are shown in Figure 3b and
3c. There are abundant hydrogen bond and C-H…π
intermolecular interactions, which is beneficial to suppress
molecular vibration and rotation induced internal conversion effect, mainly distributed over the acceptors, the overlap of HOMO and
resulting in high PLQY of TPA-2DCNQ.
LUMO was less than that of TPA-2DCNPZ. The overlap integrals
of norm of HOMO and LUMO were 0.454 and 0.400, calculated
via Multiwfn software package. The less overlap of HOMO and
Theoretical calculations
LUMO contributes smaller ΔEst, which was calculated to be 0.368
Density functional theory (DFT) and time-dependent DFT (TD-
eV for TPA-2DCNPZ and 0.299 eV for TPA-2DCNQ.
DFT) calculations at the B3LYP/6-31G(d,p) level were applied for
TPA-2DCNPZ and TPA-2DCNQ to get further insight into the
geometrical and electronic structures of them. The optimized
ground state configurations are shown in Figure S7. The two
dicyano-substituted pyrazine units were nearly symmetrical, while
the two dicyano-substituted quinoxaline units were not, which
may be resulted from steric hindrance caused by the expanded
π-conjugated skeleton. The dihedral angles between phenyl
bridge of triphenylamine and acceptor units were named θ1 and
Photophysical properties
The ultraviolet-visible absorption spectra of TPA-2DCNPZ and
TPA-2DCNQ are shown in Figure 5. The intense absorption
bands at 294 and 322 nm of TPA-2DCNPZ should be attributed
to the π-π* transitions of the aromatic amines and the pyrazine
unit.[7c,11] The more intense absorption band of 360~553 nm was
3
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Figure 4. The HOMO and LUMO distributions and energy levels of TPA-2DCNPZ and TPA-2DCNQ by DFT and TDDFT calculations.
Figure 5. The absorption spectra of TPA-2DCNPZ and TPA-2DCNQ in
dichloromethane (10-5 M).
assigned to intermolecular charge transfer (CT) from
triphenylamine electron-donor unit to dicyano-substituted
pyrazine. TPA-2DCNQ showed a similar and slightly red-shifted
absorption spectrum, but a relatively lower CT absorption
intensity. The molar absorption coefficient is positively associated
with the transition dipole moment. The frontier molecular orbitals’
overlap of TPA-2DNCPZ is larger than that of TPA-2DCNQ,
indicating a higher transition dipole moment of TPA-2DCNPZ.
The transition dipole moment and calculated absorption spectra
of them are shown in Figure S8. TPA-2DCNPZ exhibited higher
CT absorption intensity arisen from the higher transition dipole
moment from S0 to S1. The PL spectra of them in dilute toluene
Figure 6. The PL spectra of TPA-2DCNPZ (a) and TPA-2DCNQ (b) in toluene
at 77 K (10-5 M).
are shown in Figure 6. The energy levels of S1 and T1 were
4
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calculated based on the onset of the spectra at 77 K, which were
2.667, 2.270 eV and 2.562, 2.281 eV for TPA-2DCNPZ and TPA-
2DCNQ, respectively, and the corresponding values of ΔEst were
0.397 and 0.281 eV. In order to explore the properties of TPA-
2DCNPZ and TPA-2DCNQ in thin films, the doped films were
prepared by vacuum evaporation with CBP (4,4'-bis(N-
carbazolyl)-1,1'-biphenyl) as the host. The doping concentrations
were 5 wt%, 10 wt%, and 20 wt%. The PL emission peaks were
located at 570, 581, and 600 nm for TPA-2DCNPZ, those for TPA-
DCNQ were slightly red-shifted, which were located at 574, 593,
and 609 nm, indicating the extended π-conjugated acceptors
usually possess stronger ability of electron-withdrawing.
Moreover, the redshift of TPA-2DCNQ based doped films’ PL
spectra was larger than that of TPA-2DCNPZ based ones from 5
wt% to 20 wt%, which could be contributed to the stronger
intermolecular interactions of TPA-2DCNQ in high-concentration
doped films.[2c] The doped films showed PLQYs of 0.35, 0.33, and
0.23 with the doping concentrations of TPA-2DCNPZ were 5 wt%,
10 wt%, and 20 wt%, respectively. TPA-2DCNQ doped films
showed more than double PLQYs compared with those of TPA-
2DCNPZ at the same doping concentrations, as shown in Figure
7. It’s clearly that the extended π-conjugated acceptor contributed
to the boost of the PLQY, the rigid skeleton of the acceptor was
benefit to restrain the nonradiative process, which proved that the
π-conjugated skeleton of the acceptors has an important impact
on the luminescence properties of long-wavelength TADF
materials. The extended π-conjugated skeleton from dicyano-
substituted pyrazine to dicyano-substituted quinoxaline not only
obtained a stronger electron-withdrawing acceptor, but also a
smaller ΔEst and higher PLQYs were achieved simultaneously.
The results provide an approach to designing high-performance
long-wavelength TADF materials.
the TADF properties of them. The temperature-dependent
transient PL decay curves showed that the proportions of delayed
fluorescence were increased with increasing the test
temperatures from 100~350 K, which further confirmed the TADF
To verify the TADF property of TPA-2DCNPZ and TPA-2DCNQ,
the transient PL decay measurements of the doped films were
carried out, and the transient PL decay measurements at different
temperatures of the 10 wt% doped films were also performed. The
results are shown in Figure 8 and Figure S9. From Figure S9, all
the transient PL decay curves exhibited delayed fluorescence
lifetimes in the time range of 1 and 2 milliseconds, which indicated
Figure 7. The PL spectra and PLQYs of TPA-2DCNPZ and TPA-2DCNQ in
doped films (host: CBP) with concentrations of 5wt%, 10 wt%, and 20 wt%.
Table 1. Photo physical constants of the doped films.
τP
[ns][a]
τTADF
[μs][b]
φP
[%][c]
φTADF
[%][d]
kF
kIC
[*108 s-1][f]
kISC
[*108 s-1][g]
kRISC
films
[*108 s-1][e]
[*104 s-1][h]
5 wt% TPA-2DCNPZ
10 wt% TPA-2DCNPZ
20 wt% TPA-2DCNPZ
5 wt% TPA-2DCNQ
10 wt% TPA-2DCNQ
20 wt% TPA-2DCNQ
6.80
6.55
295
249
197
143
134
106
0.294
0.284
0.204
0.655
0.622
0.638
0.056
0.046
0.026
0.054
0.048
0.032
4.32
4.33
3.57
6.90
5.57
6.14
8.02
8.80
11.96
2.82
2.74
3.02
2.36
2.14
2.00
0.81
0.64
0.46
0.42
0.44
0.27
3.52
3.35
4.23
5.70
9.50
11.16
10.39
[a]: The lifetime of prompt fluorescence. [b]: The lifetime of delayed fluorescence. [c]: The prompt component of the PL quantum
efficiency. [d]: The delayed component of the PL quantum efficiency. [e]: The singlet radiative rate constant. [f]: The singlet internal
conversion rate constant. [g]: The singlet intersystem crossing rate constant. [h]: The triplet reverse intersystem crossing rate constant.
5
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Figure 8. Temperature-dependent transient PL decay curves of TPA-2DCNPZ and TPA-2DCNQ in 10 wt% doped films.
properties of them. The photo physical parameters were
calculated by formulas (see Supporting Information) and the
results are listed in Table 1. The internal conversion rate was
suppressed by the rigid extended π-conjugated acceptor of TPA-
2DCNQ, and higher reverse intersystem crossing rate constants
were simultaneously obtained resulted from the smaller ΔEst.
in these OLED devices are shown in Figure 9, and the relevant
results are shown in Figure 10 and Table 2. The emission peaks
of the EL spectra of TPA-2DCNPZ and TPA-2DCNQ were 576
Table 2. EL performance of the devices.
λEL
[nm]
CEmax
[cd A-1][a]
PEmax
[lm W-1][b]
EQEmax
[%][c]
EQE100
[%][d]
EQE1000
[%][e]
emitter
Electroluminescence properties
10 wt% TPA-
2DCNPZ
576
596
10.4
21.5
6.6
4.4
1.8
6.4
1.0
2.6
The electroluminescence (EL) properties of TPA-2DCNPZ and
TPA-2DCNQ were also measured by fabricating OLED devices
with the structure of [ITO/ TAPC (50 nm)/ TCTA (5 nm)/ CBP: 10
wt% emitters (20 nm)/ TmPyPb (45 nm)/ LiF (1 nm)/ Al (100 nm)].
The ITO (indium tin oxide) and LiF/Al were applied as anode and
cathode, respectively. TAPC and TCTA were hole-transport
layers, while TmPyPb was electron-transport layer. The device
structure, chemical formulas and energy levels of used materials
10 wt% TPA-
2DCNQ
30.2
13.6
[a]: maximum current efficiency; [b]: maximum power efficiency; [c]: maximum
EQE; [d]: EQE at 100 cd m-2; [e]: EQE at 1000 cd m-2.
Figure 9. Device structure, chemical formulas and energy levels of used materials in device fabrication.
6
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Figure 10. EL spectra (a) and EQE-Luminance plots (b) of TPA-2DCNPZ and TPA-DCNQ based devices.
was recorded on a Thermo Fisher ITQ1100 GC/MS mass spectrometer.
Elemental analyses were performed on a flash EA 1112 spectrometer.
Differential scanning calorimetric (DSC) measurements were performed
on a NETZSCH DSC204 instrument at a heating rate of 10 K min–1 under
and 596 nm. The maximum external quantum efficiency (EQE) of
TPA-2DCNPZ was 4.4%, which was 13.6% for TPA-2DCNQ.
Both the higher rate of RISC (kRISC) and PLQY of the emitting layer
of TPA-DCNQ contribute to the higher performance of the devices,
proving the expending π-conjugated acceptors rationally is an
effective designing strategy for long-wavelength TADF materials.
Devices with the emitters’ doping concentrations of 5 wt% and 20
wt% were also fabricated. The devices’ performance was
depicted in Figure S10~S11, the detailed data were summarized
in Table S2. Devices based on 5 wt% doped emitters showed
higher EQEs than those based on 10 wt% and 20 wt% doped
emitters, which could be ascribed to the higher PLQYs of the
doped films. It’s worth to note that 20 wt% doped film of TPA-
2DCNQ displayed higher kRISC than that of 10 wt% doped film as
well as identical PLQY, but the device equipped with 20 wt%
doped TPA-2DCNQ demonstrated a slightly lower EQE of 12.6%,
which may be caused by the more unbalanced carrier migration,
and the efficiency maybe improved by further optimization.
a
nitrogen atmosphere. Thermogravimetric analyses (TGA) were
performed on a TA Q500 thermogravimeter by measuring their weight loss
while heating at a rate of 10 K min–1 from 25 to 800 C under nitrogen.
Electrochemical measurements were performed with a BAS 100W
Bioanalytical electrochemical work station, using platinum disk as working
electrode, platinum wire as auxiliary electrode, and a porous glass wick
Ag/Ag+ as pseudo reference electrode with ferrocene/ferrocenium as the
internal standard. The oxidation potentials were measured in CH2Cl2
solution containing 0.1 M of n-Bu4NPF6 as a supporting electrolyte at a
scan rate of 50 mV s-1. The UV-Vis absorption spectra were recorded by a
Shimadzu UV-2550 spectrophotometer. The emission spectra were
recorded by a Shimadzu RF-5301 PC spectrometer. Both fluorescence
and phosphorescent spectra at low temperature (77 K) were recorded by
Ocean Optics QE Pro with a 365 nm Ocean Optics LLS excitation source.
The absolute fluorescence quantum yields of films were measured on
Edinburgh FLS 920 steady state fluorimeter utilizing an integrating sphere.
Transient PL decay was investigated under vacuum using FLS 920
fluorescence lifetime measurement system.
Conclusion
Single Crystal Structure
Diffraction data were collected on a Rigaku RAXIS-PRID diffractometer
using the ω-scan mode with graphite monochromator Mo•Kα radiation. The
structure was solved using SHELXT and refined with SHELXL. Non-
hydrogen atoms were refined anisotropically. The positions of hydrogen
atoms were calculated and refined isotropically. Deposition Number
2033403 (for TPA-2DCNQ) contains the supplementary crystallographic
data for this paper. These data are provided free of charge by the joint
Cambridge Crystallographic Data Centre and Fachinformationszentrum
Karlsruhe Access Structures service www.ccdc.cam.ac.uk/structures.
In conclusion, two orange-red TADF compounds comprised of
dual dicyano-substituted pyrazine/quinoxaline acceptors were
designed. The extended π-conjugated acceptor of TPA-DCNQ
shows stronger electron-withdrawing ability and deeper LUMO
energy level. With the larger π-conjugated skeleton, the overlap
of HOMO and LUMO is decreased, resulting in a smaller ΔEst and
higher rate of RISC. Moreover, the PLQY is also boosted with the
larger rigid π-conjugated acceptor at the same time. Eventually,
the OLED device with TPA-DCNQ showed highest EQEs of
12.6%~14.0%. The work proves that extending the π-conjugated
acceptor rationally is an effective approach to designing highly
efficient long-wavelength TADF materials.
Theoretical calculation
The ground state geometries of gas state were fully optimized by B3LYP
method including Grimme’s dispersion correction with 6-31G(d,p) basis set
using Gaussian 09 software package.[12] HOMO and LUMO were
visualized with Gaussview 6.0. The overlap integral of norm of HOMO and
LUMO was calculated via Multiwfn software package.[13]
Experimental Section
General Information
Device fabrication
1H and 13C NMR spectra were measured on Bruker AVANCE III 500 MHz
spectrometer with tetramethylsilane as the internal standard. Mass spectra
7
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Glass substrates pre-coated with indium tin oxide (ITO) with a sheet
resistance of 15 Ω per square were thoroughly cleaned in ultrasonic bath
of tetrahydrofuran, detergent, deionized water, acetone and isopropyl
alcohol and treated with plasma for 5 min in sequence. Organic layers
were deposited onto the ITO-coated glass substrates by thermal
evaporation under high vacuum (<5×10–4 Pa). Cathode was patterned
using a shadow mask with an array of 2.0 mm × 2.5 mm openings.
Deposition rates are 1 Å s-1 for organic materials, 0.1 Å s-1 for LiF, and 5 Å
s-1 for Al, respectively. EL spectra and luminance intensities were recorded
by Photo Research PR655. The current density and driving voltage
characteristics were measured by Keithley 2400 simultaneously. External
quantum efficiency was calculated from the current density, luminance,
and EL spectrum, assuming a Lambertian distribution.
Renaud, P. B. Coto, R. D. Costa, S. Gaillard, Adv. Opt. Mater. 2020, 8,
2000260.
[2]
[3]
a) Q. Zhang, H. Kuwabara, W. J. Potscavage, Jr., S. Huang, Y. Hatae,
T. Shibata, C. Adachi, J. Am. Chem. Soc. 2014, 136, 18070-18081; b) S.
Wang, X. Yan, Z. Cheng, H. Zhang, Y. Liu, Y. Wang, Angew. Chem. Int.
Ed. Engl. 2015, 54, 13068-13072; c) C. Li, R. Duan, B. Liang, G. Han, S.
Wang, K. Ye, Y. Liu, Y. Yi, Y. Wang, Angew. Chem. Int. Ed. Engl. 2017,
56, 11525-11529.
a) Y. Zhu, T. Fei, Y. Ma, ChemPlusChem 2016, 81, 73-79; b) Y.
Nishikitani, T. Cho, S. Uchida, S. Nishimura, K. Oyaizu, H. Nishide,
ChemPlusChem 2018, 83, 463-469; c) S. Seo, S. Shitagaki, N. Ohsawa,
H. Inoue, K. Suzuki, H. Nowatari, S. Yamazaki, Jpn. J. Appl. Phys. 2014,
53, 042102; d) B. Liang, Z. Yu, X. Zhuang, J. Wang, J. Wei, K. Ye, Z.
Zhang, Y. Liu, Y. Wang, Chem. Eur. J. 2020, 26, 4410-4418.
H. Uoyama, K. Goushi, K. Shizu, H. Nomura, C. Adachi, Nature 2012,
492, 234-238.
[4]
[5]
Synthesis
a) Y. Tao, K. Yuan, T. Chen, P. Xu, H. Li, R. Chen, C. Zheng, L. Zhang,
W. Huang, Adv. Mater. 2014, 26, 7931-7958; b) Y. Im, M. Kim, Y. J. Cho,
J.-A. Seo, K. S. Yook, J. Y. Lee, Chem. Mater. 2017, 29, 1946-1963; c)
M. Y. Wong, E. Zysman-Colman, Adv. Mater. 2017, 29, 165444.
a) E. Matteucci, A. Baschieri, L. Sambri, F. Monti, E. Pavoni, E. Bandini,
N. Armaroli, ChemPlusChem 2019, 84, 1353-1365; b) X. Li, C. Wang, W.
Song, C. Meng, C. Zuo, Y. Xue, W. Y. Lai, W. Huang, ChemPlusChem
2019, 84, 1623-1629; c) M. Caselli, D. Vanossi, M. Buffagni, M. Imperato,
L. Pigani, A. Mucci, F. Parenti, ChemPlusChem 2019, 84, 1314-1323.
a) J. X. Chen, K. Wang, C. J. Zheng, M. Zhang, Y. Z. Shi, S. L. Tao, H.
Lin, W. Liu, W. W. Tao, X. M. Ou, X. H. Zhang, Adv. Sci. 2018, 5,
1800436; b) R. Furue, K. Matsuo, Y. Ashikari, H. Ooka, N. Amanokura,
T. Yasuda, Adv. Opt. Mater. 2018, 6, 1701147; c) S. Wang, Y. Miao, X.
Yan, K. Ye, Y. Wang, J. Mater. Chem. C 2018, 6, 6698-6704; d) J. X.
Chen, W. W. Tao, W. C. Chen, Y. F. Xiao, K. Wang, C. Cao, J. Yu, S. Li,
F. X. Geng, C. Adachi, C. S. Lee, X. H. Zhang, Angew. Chem. Int. Ed.
Engl. 2019, 58, 14660-14665.
Synthesis
of
6,6'-((phenylazanediyl)bis(4,1-phenylene))bis(5-
phenylpyrazine-2,3-dicarbonitrile) (TPA-2DCNPZ)
[6]
[7]
A mixture of intermediates 2 (1.53 g, 3.00 mmol) and diaminomaleonitrile
(0.97 g, 9.00 mmol) were refluxed in 40.0 mL glacial acetic acid for 6 hours.
After the reaction was completed, the reaction mixture was poured into ice
water. After suction filtration, the residue was purified via silica gel column
chromatography using petroleum ether/dichloromethane (1:1; v/v) as an
eluent to give the product TPA-2DCNPZ as a red solid (1.20 g, 61.2%). 1H
NMR (500 MHz, Methylene Chloride-d2) δ 7.64 (dt, J = 7.1, 1.4 Hz, 4H),
7.57 – 7.43 (m, 10H), 7.43 – 7.37 (m, 2H), 7.29 – 7.23 (m, 1H), 7.22 – 7.15
(m, 2H), 7.10 – 7.00 (m, 4H). 13C NMR (126 MHz, Methylene Chloride-d2)
δ 155.00, 154.54, 149.40, 135.81, 131.26, 130.97, 129.90, 129.77, 129.53,
128.98, 128.80, 126.72, 125.75, 122.63, 113.51, 113.44. MS (m/z): 652.76
[M]+ (calcd: 653.21). Anal. Calcd (100%) for C42H23N9: C, 77.17; H, 3.55;
N, 19.28; Found: C, 77.18; H, 3.76; N, 19.12.
[8]
a) J. H. Kim, J. H. Yun, J. Y. Lee, Adv. Opt. Mater. 2018, 6, 1800255; b)
W. Zeng, H. Y. Lai, W. K. Lee, M. Jiao, Y. J. Shiu, C. Zhong, S. Gong, T.
Zhou, G. Xie, M. Sarma, K. T. Wong, C. C. Wu, C. Yang, Adv. Mater.
2018, 30, 1704961; c) J. Xue, Q. Liang, R. Wang, J. Hou, W. Li, Q. Peng,
Z. Shuai, J. Qiao, Adv. Mater. 2019, 31, 1808242; d) Y. L. Zhang, Q. Ran,
Q. Wang, Y. Liu, C. Hanisch, S. Reineke, J. Fan, L. S. Liao, Adv. Mater.
2019, 31, 1902368; e) Y. J. Yu, Y. Hu, S. Y. Yang, W. Luo, Y. Yuan, C.
C. Peng, J. F. Liu, A. Khan, Z. Q. Jiang, L. S. Liao, Angew. Chem. Int.
Ed. Engl. 2020, 59, 21578-21584.
Synthesis
of
3,3'-((phenylazanediyl)bis(4,1-phenylene))bis(2-
phenylquinoxaline-6,7-dicarbonitrile) (TPA-2DCNQ)
The synthetic methods of TPA-2DNCQ were similar with those of TPA-
2DCNPZ using compound 4,5-diaminophthalonitrile (1.42 g, 8.98 mmol)
instead of diaminomaleonitrile. Finally, TPA-2DCNQ was obtained as a red
1
solid (1.74 g, 69.3%). H NMR (500 MHz, Methylene Chloride-d2) δ 8.62
[9]
a) T. Yang, B. Liang, Z. Cheng, C. Li, G. Lu, Y. Wang, J. Phys. Chem. C
2019, 123, 18585-18592; b) T. Yang, Z. Cheng, Z. Li, J. Liang, Y. Xu, C.
Li, Y. Wang, Adv. Funct. Mater. 2020, 30, 2002681.
(d, J = 6.3 Hz, 4H), 7.86 – 7.60 (m, 4H), 7.52 (dd, J = 7.9, 4.4 Hz, 7H), 7.47
(dd, J = 8.3, 6.7 Hz, 4H), 7.40 (t, J = 7.9 Hz, 2H), 7.27 – 7.15 (m, 2H), 7.13
– 7.01 (m, 4H). 13C NMR (126 MHz, Methylene Chloride-d2) δ 157.38,
156.56, 148.89, 141.74, 141.37, 137.87, 136.76, 136.59, 131.33, 130.16,
129.77, 128.44, 126.31, 125.17, 122.64, 115.31, 114.05, 113.59. MS
(m/z): 752.74 [M]+ (calcd: 753.24). Anal. Calcd (100%) for C50H27N9: C,
79.67; H, 3.61; N, 16.72; Found: C, 79.78; H, 3.76; N, 16.88.
[10] a) M. L. Keshtov, M. I. Buzin, P. V. Petrovskii, E. E. Makhaeva, V. S.
Kochurov, D. V. Marochkin, A. R. Khokhlov, Polym.Sci. Ser. B 2011, 53,
257-266; b) X. Liu, M. Li, T. Han, B. Cao, Z. Qiu, Y. Li, Q. Li, Y. Hu, Z.
Liu, J. W. Y. Lam, X. Hu, B. Z. Tang, J. Am. Chem. Soc. 2019, 141,
11259-11268.
[11] S. Wang, Z. Cheng, X. Song, X. Yan, K. Ye, Y. Liu, G. Yang, Y. Wang,
ACS Appl. Mater. Interfaces 2017, 9, 9892-9901.
Acknowledgements
[12] a) R. Krishnan, J. S. Binkley, R. Seeger, J. A. Pople, J. Chem. Phys.
1980, 72, 650-654; b) C. Lee, W. Yang, R. G. Parr, Phys. Rev. B
Condens. Matter. 1988, 37, 785-789; c) A. D. Becke, J. Chem. Phys.
1993, 98, 5648-5652; d) A. D. Becke, J. Chem. Phys. 1997, 107, 8554-
8560; e) S. Grimme, J. Antony, S. Ehrlich, H. Krieg, J. Chem. Phys. 2010,
132, 154104.
This work was partly supported by the Science Foundation of
Jihua Laboratory.
Keywords: luminescence; organic light-emitting diodes; π-
conjugated acceptors; photophysics; thermally activated delayed
fluorescence
[13] a) C. F.-W. LU Tian, 2011, 69, 2393-2406; b) T. Lu, F. Chen, J. Theor.
Comput. Chem. 2012, 11, 163-183; c) T. Lu, F. Chen, J. Comput. Chem.
2012, 33, 580-592.
Reference
[1]
a) Y. Huang, E. L. Hsiang, M. Y. Deng, S. T. Wu, Light-Sci. Appl. 2020,
9, 105; b) H. Shim, K. Sim, F. Ershad, S. Jang, C. Yu, J. Mater. Chem. C
2020, 8, 10719-10731; c) G. U. Mahoro, J. Fernandez-Cestau, J. L.
8
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10.1002/cplu.202000703
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Higher PLQY of ~70% was obtained for TPA-2DCNQ with extended π-conjugated acceptors, which was twice over than that of TPA-
2DCNPZ (~30%). The rates of RISC of TPA-2DCNQ were also around 10 times higher than that of TPA-2DCNPZ simultaneously.
Ultimately, a higher EQE of TPA-2DCNQ of 13.6% was achieved, which was 3 times higher than that of TPA-2DCNPZ based one
(4.4%). The results indicated that extending the π-conjugated skeleton of acceptors is an effective approach to high-performance
long-wavelength TADF materials.
9
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