Novel blue fluorescent emitters structured by linking triphenylamine and anthracene derivatives for organic light-emitting devices with EQE exceeding 5%

Article abstract of DOI:10.1039/c9tc02773d

Achieving an external quantum efficiency exceeding 5% for traditional blue fluorescent organic light emitting devices (OLEDs) is still a current challenge due to the 25% limit of the radiative exciton yield. Bipolar organic molecules with a special hybrid

Full text of DOI:10.1039/c9tc02773d

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Materials Chemistry C
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Novel blue fluorescent emitters structured by
linking triphenylamine and anthracene derivatives
for organic light-emitting devices with EQE
exceeding 5%†
Cite this:DOI: 10.1039/c9tc02773d
a
Jing Zhang,a Yaping Zhao,a Huixia Xu, *a Di Zhang,a Yanqin Miao,
*
Ruth Shinar,b Joseph Shinar,c Hua Wang,
Bingshe Xua and Yucheng Wua
a
Achieving an external quantum efficiency exceeding 5% for traditional blue fluorescent organic light
emitting devices (OLEDs) is still a current challenge due to the 25% limit of the radiative exciton yield.
Bipolar organic molecules with a special hybrid local-excited and charge-transfer state have showed
huge potential to address this issue. Herein, we designed and synthesized two novel bipolar compounds,
namely TPA-AN-NA and TPA-AN-TFP, which were structured by simply linking a donor of triphenylamine
(TPA) and both acceptors of anthracene derivatives. Both resulting compounds show good blue emission
with emission peaks at 468 and 471 nm and photoluminescence quantum yields of 30.68 and 23.96% in
thin films for TPA-AN-NA and TPA-AN-TFP, respectively. They also exhibit good solubility and can
dissolve in several organic solvents with different polarities. Further, the fabricated blue OLEDs with
TPA-AN-NA and TPA-AN-TFP as emitters also realize the corresponding blue emission well with
electroluminescence peaks at 464 and 472 nm, respectively. The TPA-AN-NA-based blue device
achieves a high external quantum efficiency of 5.44% and a radiative exciton yield of 56.68%, exceeding
the theoretical limit.
Received 24th May 2019,
Accepted 5th August 2019
DOI: 10.1039/c9tc02773d
rsc.li/materials-c
The external quantum efficiency (EQE) of fluorescent OLEDs is
limited to only 5%, which is not beneficial for developing high
Introduction
Organic light-emitting devices (OLEDs) are widely considered to be efficiency OLEDs.10–12 Therefore, an effective way to boost the
the next generation display and potential lighting technologies due device efficiency of blue OLEDs is to enable the contribution of
to their unique attributes of high colour contrast, efficiency, light non-emissive triplet excitons to light emission, consequently,
weight, and special flexibility.1–3 Emitting materials are the pre- breaking the 25% limitation of the radiative exciton yield (Zr).
requisites for developing high performance OLEDs. Numerous
Donor–acceptor (D–A)-type bipolar organic molecules with
efforts have been made for obtaining high performance emitting special excited states have displayed tremendous potential to
materials with high quantum yield, good colour purity, and long- address the above-mentioned issue.13,14 Generally, the charge-
term stability. However, compared with the long-band emitting transfer (CT) excited state in D–A molecules with the weak
materials (green and red), the blue ones are still very rare due to bonding energy of the exciton facilitates efficient reverse
their intrinsic large energy gap, poor thermal stability, and low intersystem-crossing (RISC) from triplet to singlet to improve
photoluminescence quantum yield (FPL),4–7 which becomes a Zr.15–17 Simultaneously, the locally excited (LE) state with a high
bottleneck for the development of OLEDs. Typically, in traditional oscillator strength can enhance FPL owing to the overlap of the
blue fluorescent OLEDs, only 25% single excitons can emit highest occupied molecular orbital (HOMO) and the lowest
radiatively, while 75% triplet excitons decay non-radiatively.8,9 unoccupied molecular orbital (LUMO).18 This unique hybrid
local and charge transfer (HLCT) excited state in D–A molecules
a Key Laboratory of Interface Science and Engineering in Advanced Materials,
Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, China.
E-mail: xuhuixia@tyut.edu.cn, miaoyanqin@tyut.edu.cn
can simultaneously contribute to high Zr and high FPL, conse-
quently improving the electroluminescence efficiency of blue
fluorescent OLEDs.19–21
In order to construct efficient blue-light emitting materials
with the HLCT state, the donor and acceptor units should be
carefully selected to regulate the LE and CT excited states.
b Microelectronics Research Canter and Electrical & Computer Engineering
Department, Iowa State University, Ames, IA 50011, USA
c Ames Laboratory, USDOE and Physics & Astronomy Department,
Iowa State University, Ames, IA, 50011, USA
† Electronic supplementary information (ESI) available. See DOI: 10.1039/c9tc02773d Additionally, to avoid the long-band emission, neither a strong
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Fig. 2 Optimized structure and spatial distribution of the HOMO and
LUMO orbitals of TPA-AN-NA and TPA-AN-TFP.
Fig. 1 Molecular structures of TPA-AN-NA and TPA-AN-TFP.
donor nor acceptor should be chosen.10 Triphenylamine (TPA)
is a medium electron-donating group with a unique space
propeller structure with large steric hindrance, which can
effectively reduce the exciton binding energy and favour the
formation of the CT state.22–24 Anthracene (An) is a weak
electron-withdrawing group with a planar conjugated structure,
which will promote the overlap between the HOMO and LUMO
and improve the LE state.25–29
Herein, two novel bipolar compounds were synthesized by
simply linking a donor of TPA and both acceptors of anthracene
derivatives, namely TPA-AN-NA and TPA-AN-TFP, respectively.
The molecular structures of the two blue emitters are shown in
Fig. 1. As expected, two resulting compounds show good blue
emission with emission peaks at 468 and 471 nm and photo-
luminescence quantum yields of 30.68 and 23.96% for TPA-AN-NA
and TPA-AN-TFP in thin films, respectively. And the fabricated
OLED with TPA-AN-NA and TPA-AN-TFP as emitters also realize
the corresponding blue emission well with the EL peak at 464
and 472 nm, respectively. Moreover, the TPA-AN-NA-based blue
device shows excellent electroluminescence performance with
a maximum current efficiency (CE), power efficiency (PE),
Fig. 3 TGA and DSC (inset) curves of TPA-AN-NA and TPA-AN-TFP.
85 and 901, respectively. The conjugation effect between anthracene
and trifluorophenyl was completely suppressed. The comparison
showed that both the compounds exhibited similar LUMO
distributions, which are mainly located in the anthracene
moieties (Fig. 2). The HOMO of TPA-AN-NA was mostly populated
on anthracene and extended to the TPA unit, with a little
contribution from naphthalene, while the HOMO of TPA-AN-TFP
was largely contributed to the TPA group and anthracene.
The thermal stabilities were investigated by TGA and DSC
under a nitrogen atmosphere. As presented in Fig. 3 and
Table 1, compounds TPA-AN-NA and TPA-AN-TFP exhibit high
decomposition temperatures (Td, corresponding to 5% weight
loss) of 395 and 337 1C, respectively, and high Tgs of 125 and
195 1C due to the rigid structure of the anthracene unit. These
results suggest that the two compounds exhibit good thermal and
morphological stabilities, which are important for applications in
organic electronic devices.
and external quantum efficiency (EQE) reaching 7.16 cd Aꢀ1
,
6.09 lm Wꢀ1, and 5.44%, respectively, where the EQE is
obviously higher than the reported limit of 5%. These results
demonstrate that the TPA-and An-based emitters have promis-
ing application in blue OLEDs.
Results and discussion
Structure characteristics
The synthetic routes and molecular structures of TPA-AN-NA
and TPA-AN-TFP are depicted in Scheme S1 (ESI†) and Fig. 1.
Photophysical properties
The intermediate compound 1 and the two target products were The UV-vis absorption and emission spectra in CH2Cl2 solution
prepared through the palladium catalysed Suzuki coupling reaction, and the neat film of TPA-AN-NA and TPA-AN-TFP at room
and then purified by column chromatography on silica gel. The temperature are shown in Fig. 4. The relevant data are also
chemical structures of the compounds were confirmed by 1H NMR summarized in Table 1. The absorption peaks below 300 nm
and 13C NMR, as shown in the ESI.† There are large torsion angles are attributed to the p–p* transitions of benzene rings, while
of 681 between TPA and the adjacent phenyl ring and 721 between the longer wavelength band absorptions appear in the range
anthracene and the phenyl ring in compound TPA-AN-NA (Fig. 2). of 300–400 nm, characteristic of the p–p* transitions from
When electron-withdrawing 3,4,5-trifluorophenyl is introduced into anthracene and TPA. The absorption spectra of TPA-AN-NA
compound TPA-AN-TFP, the two torsion angles are increased to and TPA-AN-TFP displayed similar patterns, suggesting that
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Table 1 The photophysical, electrochemical and thermal properties of TPA-AN-NA and TPA-AN-TFP
a
a
b
b
c
d
e
Compound
labs (nm)
lem (nm)
labs (nm)
lem (nm)
Eg (eV)
HOMO/LUMO (eV)
FPL (%)
Td/Tg (1C)
TPA-AN-NA
TPA-AN-TFP
360, 378, 398
355, 375, 395
495
506
362, 383, 402
360, 379, 400
468
471
2.86
2.83
ꢀ5.37/ꢀ2.51
ꢀ5.41/ꢀ2.58
30.68
23.96
395/125
337/195
a
b
c
d
Measured in CH2Cl2 solution. Measured in the neat film. Obtained from the intersection of absorption and emission spectra. Quantum
e
yield (FPL) from the pure film. From TGA and DSC measurements.
Fig. 5 Cyclic voltammograms of TPA-AN-NA and TPA-AN-TFP in CH2Cl2
solution.
Fig. 4 The UV-vis absorption and emission spectra in CH2Cl2 solution
and the neat film at room temperature of TPA-AN-NA and TPA-AN-TFP.
the electron-withdrawing 3,4,5-trifluorophenyl has no effect on
the ground state.
Solvatochromic effect
To understand the nature of the excited states, the absorption
(Fig. S3, ESI†) and emission (Fig. 6) spectra of TPA-AN-NA and
TPA-AN-TFP were examined in different solvents. The absorption
spectra were insensitive to the solvent polarity, suggesting the low
dipole potential in the ground state. Unlike the absorption spectra,
the emission of TPA-AN-NA and TPA-AN-TFP showed an obvious
solvatochromic effect. As the solvent polarity increased from the
low-polarity hexane to the high-polarity dimethyl sulfoxide (DMSO),
the emission peaks of TPA-AN-NA and TPA-AN-TFP exhibited red-
shifts of 92 and 104 nm, respectively, which correspond to the
remarkable CT-state characteristics. The emission of TPA-AN-TFP
demonstrates a relatively large red-shift due to the strong CT-state
character from TPA to trifluorophenyl and anthracene. The Lippert–
Mataga model was applied for the estimation of the excited state
dipole moments with the increase of solvent polarity.30 The two
compounds exhibited two section linear relations (0.0012 r f r
0.1 and 0.2 r f r 0.305), as shown in Fig. S4 (ESI†), corres-
ponding to the LE state with a small slope in low-polarity
solvents (0.0012 r f r 0.1) and the CT state with a large slope
in high-polarity solvents (0.2 r f r 0.305). In moderate-polarity
solvents (0.1 r f r 0.2), such as chloroform and ethyl ether,
they may possess a hybridized local and charge transfer (HLCT)
state. The excited dipole moment (me) values of TPA-AN-NA and
TPA-AN-TFP were estimated to be 3.73 and 7.63 D in low-polarity
The maximum emission peaks of TPA-AN-NA and TPA-AN-TFP
in CH2Cl2 solution were observed at 495 and 506 nm, respectively.
Compared with TPA-AN-NA, the emission of TPA-AN-TFP
displayed a redshift of 11 nm due to the introduction of
the electron-withdrawing F atoms. It is noteworthy that the
emission peaks of TPA-AN-NA and TPA-AN-TFP in films exhibit
large blue-shifts of B27 and B35 nm relative to those in CH2Cl2
solution, located at 468 nm and 471 nm, respectively, which is
attributed to the large dihedral angle between anthracene
and TPA.
The optical band-gaps (Eg) of TPA-AN-NA and TPA-AN-TFP
were calculated to be 2.86 and 2.83 eV, respectively, from the
intersection between the absorption and emission spectra
in films. The cyclic voltammograms (CV) of TPA-AN-NA and
TPA-AN-TFP are presented in Fig. 5. The HOMO level (EHOMO
)
was calculated according to eqn (1)
EHOMO = ꢀ4.8 ꢀ e(Eocx ꢀ Efox)V
(1)
where Eocx is the first oxidation peak measured from the CV
curve and Eof x is the oxidation peak of ferrocene. The LUMO
level (ELUMO) was calculated from eqn (2)
ELUMO = EHOMO + Eg
(2)
Both TPA-AN-NA and TPA-AN-TFP have almost the same HOMO solvents and increased to 21.72 and 24.72 D in high-polarity
levels (ꢀ5.37 and ꢀ5.41 eV) due to the same donor of TPA. solvents, respectively. Therefore, they possess the LE excited
A LUMO level of ꢀ2.58 eV for compound TPA-AN-TFP is lower state (me o 10 D) in low-polarity solvents and the dominant-CT
than that of ꢀ2.51 eV for TPA-AN-NA because of the electron- state (me 4 20 D) in high-polarity solvents according to HLCT
withdrawing ability of 3,4,5-trifluorophenyl.
theory.31
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Fig. 6 The emission spectra of TPA-AN-NA (a) and TPA-AN-TFP (b) in different solvents.
The transient decay curves in different solvents and thin
films were measured (Fig. S5 and S6; Tables S1 and S2, ESI†).
With increasing polarities, the lifetimes increased with single
exponential, indicating that there was a change from the LE to
CT state. The transient PL spectra in moderate-polarity solvents
(ethyl ether and tetradydrofunan) can be well fitted to a single
exponential decay as shown in Tables S1 and S2 (ESI†), revealing
the HLCT feature of the excited state.32
To further verify the HLCT characteristics of both compounds,
the excited states were calculated by TD-DFT. For TPA-AN-NA, the
hole and particle of S1 showed spatial separation and partly
orbital overlap (Fig. S7, ESI†). The separation section facilitated
the CT state, and the certain orbital overlap led to the LE state,
indicating the formation of HLCT components. On the other
Fig. 7 Excited state (singlet and triplet) energy diagrams of TPA-AN-NA
and TPA-AN-TFP.
hand, the S1 of TPA-AN-TFP displayed CT due to the completely
separate hole and particle. The low-lying triplet state T1 of the two
materials was the LE state because their hole and particle were
almost completely overlapped. The high-lying T3 of TPA-AN-NA
and T2 of TPA-AN-TFP possess the obvious HLCT states. The TPA-AN-TFP (20 nm)/TPBi (50 nm)/LiF (1 nm)/Al (100 nm). In
energy gaps of the S1 and T1 of TPA-AN-NA and TPA-AN-TFP these devices, ITO and Al were used as the anode and the
reached 1.22 and 1.10 eV, and therefore, the RISC process from cathode, respectively; MoO3 and LiF acted as the hole and
the T1 to S1 state by TADF was prevented (Fig. 7). For TPA-AN-NA, electron injection layers, respectively; N,N0-di(1-naphthyl)-N,N0-
the singlet–triplet energy splitting between S1 and T3 states of diphenyl-(1,10-biphenyl)-4,40-diamine (NPB) and tris(4-carbazoyl-
0.004 eV enables a more competitive RISC from T3 to S1. A similar 9-ylphenyl)amine (TCTA) served as the hole-transport layer and
process occurred between S1 and T2 of TPA-AN-TFP due to the the electron blocking layer, respectively; and 1,3,5-tris(N-phenyl-
small energy gap of 0.02 eV. Therefore, the RISC of the two benzimidazole-2-yl)benzene (TPBi) was used as the electron-
compounds can be achieved by a ‘‘hot exciton’’ process, due to transport layer. The molecular structure of organic materials
which the triplet exciton originated from the high-lying states T3 involved in OLED fabrication and the device structure and energy
and T2, respectively.
level diagrams are shown in Scheme 1.
Fig. 8 reveals the EL spectra, current density–voltage-luminance
( J–V–L), current efficiency–current density–power efficiency
Electroluminescence performance
The above characterization analysis indicates that TPA-AN-NA (CE–J–PE), and the external quantum efficiency–luminance
and TPA-AN-TFP as blue emitters have the potential for the (EQE–L) characteristic curves of TPA-AN-NA and TPA-AN-TFP-
development of high-performance blue OLEDs. In order to based non-doped devices, where the key performance parameters
evaluate the EL characteristics of TPA-AN-NA and TPA-AN-TFP, are also listed in Table 2. Two non-doped devices all realize blue
firstly, non-doped devices with TPA-AN-NA and TPA-AN-TFP as emission with peaks located at 464 nm and 472 nm and corres-
emitters were fabricated, and the device structure was as follow: ponding to the CIE coordinates of (0.14, 0.16) and (0.15, 0.24)
ITO/MoO3 (3 nm)/NPB (30 nm)/TCTA (10 nm)/TPA-AN-NA or for TPA-AN-NA and TPA-AN-TFP-based devices, respectively.
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Scheme 1 Energy-level diagram and molecular structures of all materials used in devices.
Clearly, their EL spectra are similar to their PL spectra in thin doped device and 11450 cd mꢀ2, 5.17 cd Aꢀ1, 4.16 lm Wꢀ1, and
films, indicating that the EL emissions originate from the two 3.38% for the TPA-AN-TFP-based doped device, respectively. For
emitting materials themselves. The EL spectra for the two higher device performance, it is likely attributed to a reduced
devices show no changes at various voltages from 4 to 9 V, as exciton quenching in doped devices. The radiative exciton
shown in Fig. S8 and S9 (ESI†), exhibiting extremely high utilization (Zr) for all devices can be calculated using eqn (3)
stability. As shown in Fig. 8(b), the TPA-AN-NA-based device
EQE = g ꢁ FPL ꢁ Zr ꢁ Zout
(3)
shows a low turn-on voltage of 3.0 V, which is lower than that
for the TPA-AN-TFP-based devices, which can be ascribed to a where g is the carrier recombination efficiency, which is assumed
smaller energy barrier between TPA-AN-NA and functional to be 100%; FPL is the PL quantum yield of emitters.33 The FPLs
layers. And the two devices achieve a high luminance of of TPA-AN-NA and TPA-AN-TFP in non-doped films were measured
8344 and 9899 cd mꢀ2 for TPA-AN-NA and TPA-AN-TFP-based to be 30.68 and 23.96%, and 48.07 and 34.72% when doped in CBP
devices, respectively. In addition, the two devices also achieve films, respectively; Zr is the radiative exciton yield and Zout is the
an excellent device efficiency with the maximum CE, PE, and light out-coupling efficiency, which is generally considered to be
EQE of 6.37 cd Aꢀ1, 6.68 lm Wꢀ1, and 4.93% for the TPA-AN-NA- 20%. The calculated Zr values of TPA-AN-NA and TPA-AN-TFP-based
based device and 4.91 cd Aꢀ1, 3.33 lm Wꢀ1, and 2.77% for the non-doped devices are 80.35 and 57.80% respectively, while the Zr
TPA-AN-TFP-based device. The higher efficiency of the TPA-AN-NA- values of the doped devices are 56.58 and 48.68%. These values
based device is owing to the higher fluorescence quantum yield of radiative exciton yields have broken the limitation of 25% for
than that of TPA-AN-TFP-based in the film state.
fluorescent OLEDs, indicating that there was an effective
Considering the influence of the aggregation effect on the up-conversion process from some triplet excitons to singlet ones
emitters, both TPA-AN-NA and TPA-AN-TFP are doped in 4,40- in these devices.
bis(N-carbazolyl)-1,10-biphenyl (CBP) to fabricate two doped
Generally, a high Zr and RISC in fluorescent devices can be
devices with the structure of ITO/MoO3 (3 nm)/NPB (30 nm)/ achieved by three mechanisms: thermally activated delayed
TCTA (10 nm)/CBP: 20 wt% TPA-AN-NA or TPA-AN-TFP (20 nm)/ fluorescence (TADF),34 triplet–triplet annihilation (TTA),35 and
TPBi (50 nm)/LiF (1 nm)/Al (100 nm). As seen in Fig. 8(a), the formation of an HLCT excited state. The transient PL spectra
similar to the non-doped devices, the doped devices also realize of TPA-AN-NA in the film and THF solution show only the single
good blue emission with peaks at 460 and 468 nm. But the exponential decay with lifetimes of 3.42 and 2.31 ns, respectively
doped devices achieve higher EL performance, for example, the (Fig. S6 and Table S1, ESI†). For TPA-AN-TFP, the lifetimes in THF
maximum luminance, CE, PE, and EQE are up to 8246 cd mꢀ2
7.16 cd Aꢀ1, 6.09 lm Wꢀ1, and 5.44% for the TPA-AN-NA-based respectively. No delayed lifetimes in the range of ms were observed.
,
solution and the film are 5.20 and 2.12 ns (Table S2, ESI†),
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Fig. 8 (a) EL spectra at a driven voltage of 8 V; (b) the J–V–L curve; (c) the CE–L–PE curve and (d) the EQE–L curve for non-doped and doped blue
devices based on TPA-AN-NA and TPA-AN-TFP.
Table 2 EL performance of devices based TPA-AN-NA and TPA-AN-TFP
Lmax (cd mꢀ2
)
CEmax (cd Aꢀ1
)
PEmax (lm Wꢀ1
)
EQEmax (%)
CIE (x, y)
a
Emitter
lmax (nm)
Von (V)
TPA-AN-NA
CBP:TPA-AN-NA
TPA-AN-TFP
464
460
472
468
3.0
3.3
3.9
3.6
8344
8246
9899
11 450
6.37
7.16
4.91
5.17
6.68
6.09
3.33
4.16
4.93
5.44
2.77
3.38
(0.14, 0.16)
(0.14, 0.16)
(0.15, 0.24)
(0.14, 0.20)
CBP:TPA-AN-TFP
a
Turn-on voltage estimated at a brightness of 1 cd mꢀ2
.
Furthermore, the correlations between the luminance and the with electroluminescence peaks at 464 and 472 nm and with the
current density of all devices were linear36,37 (Fig. S10, ESI†). These CIE coordinates of (0.14, 0.16) and (0.15, 0.24), respectively. In
results indicate that the high Zr values do not result from TADF or addition, the TPA-AN-NA-based blue device achieves high external
TTA processes. Hence, the HLCT excited states are mainly respon- quantum efficiency exceeding the theoretical limit of 5% in
sible for the high radiative utilization from triplets.
fluorescent blue OLEDs, reaching 5.44%. The achievement of high
singlet exciton-utilizing efficiencies of 80.35 and 56.58% is due to
the formation of the HLCT excited states.
Conclusions
In this work, two novel blue fluorescent materials TPA-AN-NA
and TPA-AN-TFP were designed and synthesized by linking a
donor of triphenylamine (TPA) and both acceptors of anthracene
Experimental section
Materials and methods
derivatives. Both synthesized compounds show a hybrid local- All the reagents and solvents used for the syntheses and
excited and charge-transfer state. The resulting OLEDs with measurements were purchased from commercial suppliers and
TPA-AN-NA and TPA-AN-TFP as emitters exhibit blue emission were used without further purification unless otherwise noted.
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1H NMR and 13C NMR spectra were measured with a Switzerland 127.76, 127.56, 126.26, 126.08, 125.24, 124.57, 124.36, 123.20,
Bruker DR ꢁ 600 spectrometer. UV-vis absorption spectra were 122.88, and 121.40.
measured using a Lambda Bio 40 spectrometer. Photolumines-
Synthesis of N,N-diphenyl-4-(10-(3,4,5-trifluorophenyl)anthracen-
cence (PL) spectra were recorded using a HORIBA FluoroMax-4 9-yl)aniline (TPA-AN-TFP). 9-Bromo-10-(3,4,5-trifluorophenyl)-
spectrophotometer. Absolute quantum yields were determined anthracene (1) and N,N-diphenyl-4-(10-(3,4,5-trifluorophenyl)-
through an absolute method employing an integrating sphere. anthracen-9-yl)aniline (TPA-AN-TFP) were prepared with a similar
Thermogravimetric analysis (TGA) curves were measured using a procedure to that of TPA-AN-NA. The desired product was
Netzsch TG 209F3 thermal analyser under a dry nitrogen atmo- obtained as yellow-green powder (0.6 g, yield: 60%). Purity was
sphere heating from room temperature up to 800 1C at a rate 98%. 1H NMR (600 MHz, CDCl3, d): 7.88–7.84 (m, 2H), 7.64–7.59
of 10 1C minꢀ1. Differential scanning calorimetry (DSC) was (m, 2H), 7.42–7.39 (m, 4H), 7.34 (t, J = 7.9 Hz, 4H), 7.30–7.25
performed using a DSC Q2000 calorimeter at a heating rate of (m, 8H), and 7.10 (dt, J = 18.2, 7.1 Hz, 4H). 13C NMR (151 MHz,
10 1C minꢀ1 from 40 to 300 1C, and then cooling down to room CDCl3, d): 150.68, 150.31, 141.23, 136.01, 134.93, 132.94, 132.59,
temperature rapidly, and heating up to 300 1C at a heating rate 132.33, 130.28, 128.78, 128.06, 127.71, 126.14, 125.87, and 118.58.
of 10 1C minꢀ1 again; the melting temperature (Tm) was
obtained from the first heating scan and the glass transition
temperature (Tg) was determined from the second heating scan.
Conflicts of interest
Cyclic voltammetry (CV) was carried out in a solution of tetra-
There are no conflicts to declare.
butylammonium perchlorate (0.1 M) in acetonitrile at a scan
rate of 100 mV sꢀ1 at room temperature using a conventional three
electrode cell, which consisted of a working electrode platinum Acknowledgements
plate, a counter electrode platinum wire, and a reference
Ames Laboratory is operated by Iowa State University for the
calomel electrode.
US Department of Energy (USDOE) under Contract No. DE-AC
02-07CH11358. This work was financially supported by the
DFT calculation
National Natural Science Foundation of China (61705156,
Theoretical calculations were performed using the Gaussian 03
21071108, 60976018, 61605138 and 61775155) and the Shanxi
package. Geometry optimization was performed by density
functional theory (DFT) with B3LYP/6-31G(d) basis sets.
Provincial Key Innovative Research Team in Science and Technology
(201513002-10). JS was partially supported by Basic Energy Sciences,
Materials Science and Engineering Division, USDOE. We also thank
professor Runfeng Chen of Nanjing University of Posts and Tele-
OLED fabrication and characterization
OLEDs with an area of 3 ꢁ 3 mm2 were fabricated by vacuum communications for calculation data.
deposition onto indium tin oxide (ITO) glass substrates. The
substrates were cleaned, in the following order, with deionized
water, acetone, and ethanol. The electroluminescence (EL) spectra
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Synthesis of TPA-AN-NA and TPA-AN-TFP
Synthesis of 4-(10-(naphthalen-2-yl)anthracen-9-yl)-N,N-diphenyl-
aniline (TPA-AN-NA). A mixture of 4-bromo-N,N-diphenylaniline
(0.973 g, 3 mmol), 9,9-diphenyl-9,10-(10-(naphthalen-2-yl)anthracen-
9-yl)boronic acid (1.15 g, 3.3 mmol), Pd(PPh3)4 (0.173 g, 0.15 mmol)
and K2CO3 (2.0 M aqueous solution, 10.0 mL) were dissolved in
30 mL 1,2-dimethoxyethane, and then heated to reflux for 12 h.
After cooling to room temperature, the solution was extracted with
dichloromethane. The organic material was dried using anhydrous
MgSO4 and concentrated. Then the crude product was purified by
silica gel chromatography. The desired product was obtained as
yellow powder (1 g, yield: 63%). Purity can be reached 96%. 1H NMR
(600 MHz, DMSO, d): 8.19 (d, J = 8.7 Hz, 1H), 8.12 (d, J = 7.8 Hz, 1H),
8.05–8.01 (m, 2H), 7.77 (dd, J = 5.4, 4.3 Hz, 2H), 7.67–7.59 (m, 5H),
7.48 (td, J = 8.8, 6.4, 1.3 Hz, 2H), 7.43–7.38 (m, 8H), 7.25–7.22 (m,
6H), and 7.13 (td, J = 7.4, 1.1 Hz, 2H). 13C NMR (151 MHz, CDCl3, d):
146.01, 145.38, 135.32, 134.88, 131.62, 130.89, 130.32, 128.36,
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