N-phenyl-n-(4-(9,10-diphenylanthracen-7-yl) phenyl)benzenamine for undoped blue organic light-emitting diodes

Article abstract of DOI:10.1166/jnn.2016.12487

In this work, we have designed and synthesized blue emitting materials based on 9,10-diphenylanthracene with aryl amino group such as carbazole and triphenylamine by Suzuki cross-coupling reactions. To investigate the electroluminescent properties of them

Full text of DOI:10.1166/jnn.2016.12487

Article
Journal of
Nanoscience and Nanotechnology
Vol. 16, 8465–8469, 2016
Copyright © 2016 American Scientific Publishers
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Printed in the United States of America
N-phenyl-N-(4-(9,10-diphenylanthracen-7-yl)
phenyl)benzenamine for Undoped Blue Organic
Light-Emitting Diodes
Young Seok Kim1, Dong Young Kim1, Song Eun Lee2, Young Kwan Kim2ꢀ∗, and Seung Soo Yoon1ꢀ∗
1Department of Chemistry, Sungkyunkwan University, 2066, Seobu-ro, Jangan-gu, Suwon-si, Gyeonggi-do, 16419, Republic of Korea
2Department of Information Display, Hongik University, 94, Wausan-ro, Mapo-gu, Seoul, 04066, Republic of Korea
In this work, we have designed and synthesized blue emitting materials based on 9,10-
diphenylanthracene with aryl amino group such as carbazole and triphenylamine by Suzuki
cross-coupling reactions. To investigate the electroluminescent properties of them, devices were
fabricated with a following sequence: Indium-tin-oxide (180 nm)/4,4ꢀ-bis[N-(1-naphthyl)-N-phenyl
amino]biphenyl (50 nm)/Blue materials (30 nm)/bathophenanthroline (30 nm)/lithium quinolate
(2 nm)/Al (100 nm). In particular, a device using N-phenyl-N-(4-(9,10-diphenylanthracen-7-
yl)phenyl)benzenamine showed an efficient blue emission with a luminous, power, and external
quantum efficiency of 3.28 cd/A, 2.19 lm/W, and 1.91% at 20 mA/cm2, respectively.
Keywords: Blue OLED, Anthracene, Carbazole, Triphenylamine, Suzuki Cross-Coupling
IP: 188.68.0.75 On: Wed, 27 Mar 2019 08:02:28
Reactions.
Copyright: American Scientific Publishers
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1. INTRODUCTION
their EL performances were required. Among those are
the substitutions of anthracene core with the various func-
tional groups. Particularly, the introduction of the various
aromatics into C-9 and C-10 positions of anthracene has
provided many materials with the efficient EL properties.
However, only a few systematic studies have investigated
the EL properties of blue-emitting materials with the sub-
stituent at C-2 positions of anthracene emitting core.7
Here, as the continuing effort to the development
of the efficient blue emitters, we designed and synthe-
sized the new blue emitters (1 and 2) based on 9,10-
diphenylanthracene substituted with various aryl amino
groups at C-2 positions of anthracene emitting core.
Particularly, aryl amino groups such as carbazole and
triphenylamine in compounds 1 and 2 have the effec-
tive hole-transporting properties.8 This would lead to the
improved EL efficiencies of devices using them as the
emitting materials.
Over the last years, organic light-emitting diodes (OLEDs)
have received many attentions due to their potential appli-
cations in many fields such as full-color, flat-panel, and
flexible display since research by Tang and VanSlyke in
1987.1
To realize the full-color display, relatively similar devel-
opments of red, green, and blue emitters are indispens-
able. In spite of the many reports about blue emitters such
as pyrene,2 fluorene,3 and anthracene derivatives,4ꢀ5 there
were still improvement requirements in terms of stabilities,
color-purities, and efficiencies compared to red and green
emitters with acceptable efficiencies.
Among them, anthracene has been considered as the
attractive building block of the blue emitter in OLEDs due
to their good photoluminescence (PL) and electrolumines-
cence (EL) properties.
Particularly, 9,10-diphenylanthracene (DPA) has a char-
acter; its high quantum yield in dilute solution.6 How-
ever, self-aggregation and crystallization of DPAs in thin
films bring about degradation of device efficiency and
color purity. Therefore, the suitable strategies to improve
2. EXPERIMENTAL DETAILS
2.1. Synthesis and Charcterization
2-Bromo-9,10-diphenylanthracene
was
synthesized
according to literature.9 1H NMR and 13C NMR
were recorded on Bruker Avance III 500 MHz NMR
∗Authors to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2016, Vol. 16, No. 8
1533-4880/2016/16/8465/005
doi:10.1166/jnn.2016.12487
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N-phenyl-N-(4-(9,10-diphenylanthracen-7-yl)phenyl)benzenamine for Undoped Blue Organic Light-Emitting Diodes
Kim et al.
spectrometer. FT-IR spectra were recorded using a Bruker
VERTEX70 FT-IR spectrometer. Low and high-resolution
mass spectra were measured using Jeol JMS-AX505WA
spectrometer in APCI mode.
quantum efficiency (EQE), and EL spectra of the devices
were measured with a Keithley 2400 source measurement
unit and CS 1000A spectrophotometer.
9-(4-(9,10-diphenylanthracen-7-yl)phenyl)-9H-carbazole
3. RESULTS AND DISCUSSION
(1).
Yield:
73%.
9-(4-(4,4,5,5-tetramethyl-1,3,2-
To develop the blue OLED, we have designed and synthe-
sized a series of phenylcarbazole or triphenylamine substi-
tuted DPA derivatives. Scheme 1 shows the main synthetic
routes and molecular structures of the materials.
Compounds 1 and 2 were synthesized by Suzuki cou-
pling reactions between 2-bromo-9,10-diphenylanthracene
dioxaborolan-2-yl)phenyl)-9H-carbazole (2.1 mmol) and
2-bromo-9,10-diphenylanthracene (1.95 mmol), Pd(PPh3ꢁ4
(0.08 mmol), aqueous 2.0 M K2CO3 (0.02 mol), Ali-
quat 336 (0.2 mmol), and toluene were mixed in a flask
and refluxed for 2 h at 120 ꢁC. After being cooled,
the purification was carried out by recrystallization with
CH2Cl2/EtOH.
and
(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)
or N -phenyl-N -(4-(4,4,5,5-
phenyl)-9H-carbazole
1H NMR (CDCl3, 500 MHz, ꢂ); 8.14 (d, J = 8.0 Hz,
2H), 8.01 (s, 1H), 7.84 (d, J = 9.0 Hz, 2H), 7.76–7.71
(m, 4H), 7.68 (d, J = 7.5 Hz, 1H), 7.64 (t, J = 7.5 Hz,
3H), 7.60–7.57 (m, 5H), 7.54 (t, J = 7.5 Hz, 3H), 7.45
(d, J = 8.5 Hz, 2H), 7.40 (t, J = 7.0 Hz, 2H), 7.36–7.34
(m, 2H), 7.28 (t, J = 7.0 Hz, 2H); 13C NMR (CDCl3,
500 MHz, ꢂ); 140.7. 140.0, 138.9, 138.9, 137.6, 137.1,
136.9, 136.3, 131.4, 131.3, 130.4, 130.1, 130.0, 129.1,
128.6, 128.6, 128.5, 127.9, 127.7, 127.6, 127.3, 127.0,
127.0, 125.9, 125.3, 125.2, 124.7, 124.6, 123.4, 120.3,
120.0 109.8; FT-IR [ATR]: ꢃ (cm−1ꢁ 3054, 2334, 1517,
1451, 1228, 948, 820, 748, 723, 700; APCI-MS (m/zꢁ:
571 [M+]
tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)benzenamine,
respectively in moderate yield.
Figure 1 shows the UV-Vis absorption and PL
emission spectra of these compounds in both diluted
dichloromethane and thin films formed on quartz plates,
respectively. Their photophysical data were summarized in
Table I.
In the UV-Vis absorption spectra, the maximum absorp-
tion wavelengths (ꢄmax) of 1 and 2 appeared at 331 and
354 nm, respectively. The UV-Vis spectra were com-
prised of the combination two main bands that are strong
absorption band at 300–360 nm originated from the tran-
sition of aryl amino groups and relatively weak band at
360–430 nm resulted from the characteristic ꢅ–ꢅ∗ transi-
N-phenyl-N-(4-(9,10-diphenylanthracen-7-yl)phenyl)
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benzenamine (2). Yield: 63%. 1H NMR (CDCl3, 500 MHz,
Copyright: American Sctiioennstifoicf aPnuthbrliascheenresunit.11 PL spectra in dichloromethane
ꢂ); 7.86 (s, 1H), 7.76–7.32 (d, J = 9.0 Hz, 2H), 7.70–7.67
Delivered by Ingenta
of 1 and 2 exhibited blue emission with the ꢄmax at 427
(m, 2H), 7.64–7.60 (m, 5H), 7.58–7.55 (m, 2H), 7.53–7.50
(m, 3H), 7.47–7.42 (m, 3H), 7.34–7.31 (m, 2H), 7.15–7.16
(m, 2H), 7.13–7.07 (m, 7H), 7.04–7.01 (m, 2H); 13C NMR
(CDCl3, 125 MHz, ꢂ); 147.71, 147.56, 147.26, 139.04,
139.02, 136.95, 134.60, 131.38, 131.32, 129.28, 129.24,
129.04, 128.44, 128.23, 127.87, 127.53, 127.05, 127.00,
126.92, 125.10, 124.80, 124.57, 124.30, 124.07, 123.58,
123.04; FT-IR [ATR]: ꢃ (cm−1) 3056, 1588, 1489, 1327,
1279, 818, 697, 672; APCI-MS (m/z): 573 [M+]
and 500 nm. In the case of 1, ꢄmax in thin film was red-
shifted by 23 nm in comparison to that in dichloromethane,
due to the increased intermolecular interactions and self-
aggregations in thin film state than in dichloromethane. In
contrast, the solid PL spectrum of 2 exhibited blue-shifted
ꢄmax by 13 nm, compared to the solution PL spectrum.
According to many reports about diphenylamine deriva-
tives, specific blue-shifts of the maximum wavelength in
solid state from that in solution state were observed. It
was due to the differences in solvation between solu-
tion (CH2Cl2) and solid states. The degree of red-shift is
proportional to the solvent polarity. Therefore, the blue-
shifts of PL spectra of 2 in solid state in comparison with
2.2. Fabrication of Devices
The indium-tin-oxide (ITO)-coated glass was cleaned in
an ultrasonic bath by the following sequence: acetone,
methyl alcohol, distilled water, followed by storage in
isopropyl alcohol for 20 min and drying with a N2
gas gun. The substrates were treated with O2 plasma
Ar environment. Organic layers were deposited by ther-
mal evaporation from resistively heated alumina crucibles
onto the substrate at a rate of 1.0 Å/s. All organic
materials and metal were deposited under high vacuum
(5.0 ×10−7 Torr). The devices were fabricated in the fol-
lowing sequence: ITO (180 nm)/4,4ꢀ-bis(N -(1-naphthyl)-
N -phenylamino)biphenyl (NPB) (50 nm)/Blue materials
1 and 2 (30 nm)/4,7-diphenyl-1,10-phenanthroline (Bphen)
(30 nm)/lithium quinolate (Liq) (2 nm)/Al (100 nm).
Luminous efficiency (LE), power efficiency (PE), external
O
B
N
O
Br
(a)
(a)
+
1
N
O
B
N
O
Br
+
2
N
Scheme 1. Synthetic routes and molecular structures of blue fluorescent
materials 1 and 2. (a): Pd(PPh3ꢁ4, 2.0 M K2CO3, Aliquat 336, Toluene.
8466
J. Nanosci. Nanotechnol. 16, 8465–8469, 2016

Kim et al.
N-phenyl-N-(4-(9,10-diphenylanthracen-7-yl)phenyl)benzenamine for Undoped Blue Organic Light-Emitting Diodes
1.0
0.8
0.6
0.4
0.2
0.0
1.0
indicate that they have stable thermal properties for OLED
application.
1
2
1
2
1
2
0.8
0.6
0.4
0.2
0.0
To research the EL performances of these materials,
the devices were fabricated with the following sequence:
ITO (180 nm)/NPB (50 nm)/1 and 2 (30 nm)/Bphen
(30 nm)/Liq : Al (100 nm). ITO and Liq:Al are the anode
and the cathode, respectively.
The NPB is used as the hole transporting layer (HTL),
Bphen as the electron transporting layer (ETL) as well as
the hole blocking layer (HBL), and the synthesized com-
pounds are used as the emitting materials in emitting layer
(EML). Figure 2 shows the HOMO and LUMO energy-
level diagrams of the synthesized materials, along with the
other materials used in the EL devices. The EL properties
of devices A and B using 1 and 2 as the emitters were
summarized in Table II and EL spectra of those devices at
6 V were shown in the Figure 3.
350
400
450
500
550
600
Wavelength [nm]
Figure 1. UV-Vis absorption spectra (no symbol), PL spectra in CH2Cl2
(closed symbol), and in thin films (opened symbol) of blue emitters
1 and 2.
those in solution (CH2Cl2) imply that 2 was in the more
polar environments in the solution states (CH2Cl2) than in
solvent-free solid states.12
Devices A and B exhibited the blue emission with the
ꢄmax of 461 and 468 nm, respectively, and the Commission
The HOMO energy levels of 1 and 2 were −5.70 and
−5.43 eV, respectively, as shown in Table I. Particularly,
2 with triphenylamine group exhibited the shallower
HOMO level than 1 with carbazole units. This differ-
ence between HOMO levels of the compounds could be
explained by the difference of electron-donating ability
between triphenylamine and carbazole. In the case of 1,
the non-bonding electrons of carbazole unit participated in
the aromatization by satisfying the Hückel’s rule. There-
fore, the electron-donating ability of 1, which contained
carbazole unit, was lower than that of 2, which con-
tained triphenylamine whose non-bonding electrons did
not participate in the aromatization.13 This strong electron-
donating ability of triphenylamine moiety of 2 would lead
to increase the HOMO energy level of 2.
´
Internationale de LEclairage (CIE) of devices A and B
were (0.16, 0.15) and (0.16, 0.25) at 6.0 V, respectively.
This trend of EL emission of devices A and B was well-
compatible with that of PL emission of 1 and 2 in devices
A and B. This observation implies that the emission of
devices A and B originate from the singlet excitons of
the emitters 1 and 2 in devices A and B. Interestingly,
the EL spectrum of device A using emitter 1 was red-
IP: 188.68.0.75 On: Wed, 27 Mar 2019 08:02:28
shifted in comparison with the PL spectrum of 1, while
Copyright: American Scientific Publishers
the EL spectrum of device B using emitter 2 exhibited
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blue-shifted maximum emission peak in comparison with
the PL spectrum of 2. Presumably, the different emission
mechanisms between PL and EL processes would con-
tribute to these interesting observations. In the case of light
emitting process under photo-excitation, light-emission is
The glass transition temperature (Tg), crystallization
temperature (Tc), and melting temperature (Tm) values of
the compounds are measured by DSC and decomposition
temperature (Td) values of them are measured by TGA
method. As shown in the Table I, compound 1 and 2 show
fairly high Tg, Tc, Tm, and Td values and thus these results
Anode
HTL
EML
ETL
Cathode
(180 nm) (50 nm)
(30nm)
(30 nm) (100 nm)
–2.40
–2.57
–2.69
–2.70
Table I. Optical properties of compounds 1 and 2.
Compound
1
2
UV ꢄmax [nm]a
PL ꢄmax [nm]a/b
FWHM [nm]a
HOMO [eV]
LUMO [eV]
Eg [eV]
331
427/450
51.8
−5.70
−2.69
3.01
0.46
101/198/239
375
354
500/487
74.6
−5.43
−2.57
2.86
0.38
85/177/244
351
Liq/ Al
–4.10
2
1
ITO
ꢆfc
–4.70
–5.50
Tg/Tc/Tm [ꢁC]d
Td [ꢁC]e
–5.43
–5.70
Notes: a. In CH2Cl2 (10−5 M). b. Solid thin film on quartz plates. c. Using DPA as
a standard; ꢄex = 360 nm (ꢆf = 0.90 in CH2Cl2ꢁ. d. DSC analysis was performed
under a nitrogen atmosphere by DSC Q2000 V24.11 Build 124 using a scan rate
of 10 ꢁC/min. e. TGA was carried out by TGA Q500 V20. 13 Build using a scan
rate of 10 ꢁC/min.
–6.20
Figure 2. Energy-level diagrams of the materials used in devices
A and B.
J. Nanosci. Nanotechnol. 16, 8465–8469, 2016
8467

N-phenyl-N-(4-(9,10-diphenylanthracen-7-yl)phenyl)benzenamine for Undoped Blue Organic Light-Emitting Diodes
Table II. EL properties of devices A and B.
Kim et al.
(a)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
3.5
3.0
2.5
2.0
1.5
1.0
0.5
LE-A
LE-B
PE-A
PE-B
Device
A
B
Lmax [cd/m2]a
LE [cd/A]a/b
PE [lm/W]a/b
EQE [%]a/b
ꢄmax [nm]c
2081
2.39/2.22
2.09/1.22
1.88/1.80
461
969
3.79/3.28
3.51/2.19
2.21/1.91
468
CIE(xꢀy)c
(0.16, 0.15)
(0.16, 0.25)
Notes: a. Maximum values. b. Value at 20 mA/cm2. c. At 6 V.
0
50
100
150
200
Current density [mA/cm2]
controlled by the intrinsic properties of materials with-
out any interference. On the contrary, in the case of light
emitting process at OLED devices, there are many inter-
faces between anode/HTL, HTL/EML, EML/ETL, and
ETL/cathode. These interfaces could influence to the light
emission properties of devices. During these pathways, the
emitting light from emitting materials could be reflected,
refracted, and diffracted by the strong interferences at
the interfaces. Moreover, when emitting light path to the
organic layer, some amount of light could be absorbed by
the other layer. These would provide the differences in PL
spectrum of the emitter and EL spectrum of device using
the emitter.
(b)
A
B
2.0
1.6
1.2
0.8
0.4
0
50
100
150
200
Current density [mA/cm2]
Figure 4. (a) LEs and PEs, and (b) EQEs of the devices A and B.
Device B exhibited the better EL efficiencies than device
A in the low current–density region, as shown in the
Figure 4. This observation could be explained by the eas-
device A would be widely distributed due to the ineffec-
tive hole injection into EML and high hole mobility in
EML as well as the effective electron injection into EML.
ier hole-injection from the HTL to EML and efficient
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Presumably, in high current density, the populated singlet-
hole-blocking ability between EML aCnodpHyrBigLh.t:DAemviceericBan Scientific Publishers
excitons in relatively narrow recombination zone of device
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using 2 as emitting material, would have the easier hole-
B would become to interact with each other. The resulting
self-quenching in the EML of device B would contribute to
the reduced EL efficiency, and thus high efficiency roll-off
of device B in the high current–density region.14
As shown in the Figure 5, CIE coordinates of the
devices were investigated at different applied voltages and
there are little changes of them. As a result, it is certain
that stable fluorescent emissions of the devices A and B
would be obtained even at the different applied voltages.
injection properties from HTL to ETL than device A using
1 due to the shallower HOMO level of 2 than that of 1.
For the same reason, device B exhibited much stronger
hole-blocking ability between EML and HBL than device
A. However, in the high current–density region, device A
exhibited the better EL efficiencies than device B. These
observations suggest that the exciton-recombination zone
of device A is wider than that of device B. In device B,
the effective hole injection into EML and high hole mobil-
ity in EML together with the ineffective electron injection
into EML make the excitons have the narrow distribution
near the EML/ETL interfaces. However, the excitons in
0.4
A
B
0.3
0.2
0.1
1.0
A
B
3.0
3.5
4.0
4.5
5.0
5.5
6.0
0.8
Voltage [V]
0.6
0.4
0.2
0.0
0.3
0.2
0.1
0.0
A
B
3.0
3.5
4.0
4.5
5.0
5.5
6.0
400
450
500
550
600
650
Voltage [V]
Wavelength [nm]
Figure 5. CIE coordinates of devices A and B at different applied
Figure 3. EL spectra of the devices A and B at 6 V.
voltages.
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J. Nanosci. Nanotechnol. 16, 8465–8469, 2016

Kim et al.
N-phenyl-N-(4-(9,10-diphenylanthracen-7-yl)phenyl)benzenamine for Undoped Blue Organic Light-Emitting Diodes
4. CONCLUSION
4. K. H. Lee, J. K. Park, J. H. Seo, S. W. Park, Y. S. Kim, Y. K. Kim,
and S. S. Yoon, J. Mater. Chem. 21, 13640 (2011).
5. I. Cho, S. H. Kim, J. H. Kim, S. Park, and S. Y. Park, J. Mater.
Chem. 22, 123 (2012).
6. J. K. Park, K. H. Lee, S. Kang, J. Y. Lee, J. S. Park, J. H. Seo, Y. K.
Kim, and S. S. Yoon, Org. Electron. 11, 905 (2010).
7. S. B. Lee, S. N. Park, C. Kim, H. W. Lee, H. W. Lee, Y. K Kim,
and S. S. Yoon, Synth. Met. 203, 174 (2015).
8. M. Zhu, Q. Wang, Y. Gu, X. Cao, C. Zhong, D. Ma, J. Qin, and
C. Yang, J. Mater. Chem. 21, 6409 (2011).
In this work, we have successfully synthesized two blue
emitters by Suzuki coupling reactions based on DPA
unit. Especially, the device using N -phenyl-N -(4-(9,10-
diphenylanthracen-7-yl)phenyl)benzenamine as an emitter
exhibited blue emission with LE, PE, and EQE values
of 3.28 cd/A, 2.19 lm/W, and 1.91% at 20 mA/cm2,
respectively.
9. W. J. Jo, K.-H. Kim, H. C. No, D.-Y. Shin, S.-J. Oh, J.-H Son, Y.-H.
Kim, Y.-K. Cho, Q-H. Zhao, K.-H. Lee, H.-Y. Oh, and S.-K. Kwon,
Synth. Met. 159, 1359 (2009).
10. C.-L. Wu, C.-H. Chang, Y.-T. Chang, C.-T. Chen, C.-T. Chen, and
C.-J. Su, J. Mater. Chem. C 2, 7188 (2014).
Acknowledgment: This research was supported by the
Samsung Display and Basic Science Research Program
through the NRF funded by the Ministry of Education,
Science and Technology, South Korea (2013008105).
11. Y.-H. Chen, S.-L. Lin, Y.-C. Chang, Y.-C. Chen, J.-T. Lin, R.-H.
Lee, W.-J. Kuo, and R.-J. Jeng, Org. Electron. 13, 43 (2012).
12. R. Muangpaisal, W. I. Huang, J. T. Lin, S. Y. Ting, and L. Y. Chen,
Tetrahedron. 70, 2992 (2014).
13. D. A. K. Vezzu, J. C. Deaton, M. Shayeghi, Y. Li, and S. Huo, Org.
Lett. 11, 4310 (2009).
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S. L. Tao, and C. S. Lee, Synth. Met. 162, 415 (2012).
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Received: 1 June 2015. Accepted: 12 August 2015.
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8469