Highly efficient blue organic light-emitting diodes based on diarylamine-substituted pyrene derivatives

Article abstract of DOI:10.1166/jnn.2019.15929

In this study, we designed and synthesized three blue fluorescence materials based on diarylaminesubstituted pyrene derivatives. Organic Light Emitting-Diodes devices using these materials were fabricated in the following sequence; ITO/2-TNATA (300 A)/NPB (200 A)/α,β-ADN: 10 wt% blue materials 1-3 (300 A)/DNAB (300 A)/Liq (20 A)/Al (1000 A). All devices showed highly efficient blue emissions. Particularly, a device using materials (3) shown highly efficient blue emission with luminous efficiency of 8.94 cd/A, power efficiency of 4.40 lm/W, external quantum efficiency of 6.62% at 20 mA/cm₂, respectively, and the CIE coordinates of (0.16, 0.23) at 6.0 V.

Full text of DOI:10.1166/jnn.2019.15929

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Nanoscience and Nanotechnology
Vol. 19, 1056–1060, 2019
Copyright © 2019 American Scientific Publishers
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Highly Efficient Blue Organic Light-Emitting Diodes
Based on Diarylamine-Substituted Pyrene Derivatives
Seokwon Cho1, Namhee Hwang1, Song Eun Lee2, Young Kwan Kim2ꢀ∗, and Seung Soo Yoon1ꢀ∗
1Department of Chemistry, Sungkyunkwan University, Suwon, Kyeonggi-do 440-746, Korea
2Department of Information Display, Hongik University, Seoul, 121-791, Korea
In this study, we designed and synthesized three blue fluorescence materials based on diarylamine-
substituted pyrene derivatives. Organic Light Emitting-Diodes devices using these materials were
fabricated in the following sequence; ITO/2-TNATA (300 Å)/NPB (200 Å)/ꢀ,ꢁ-ADN: 10 wt% blue
materials 1–3 (300 Å)/DNAB (300 Å)/Liq (20 Å)/Al (1000 Å). All devices showed highly efficient
blue emissions. Particularly, a device using materials (3) shown highly efficient blue emission with
luminous efficiency of 8.94 cd/A, power efficiency of 4.40 lm/W, external quantum efficiency of
6.62% at 20 mA/cm2, respectively, and the CIE coordinates of (0.16, 0.23) at 6.0 V.
Keywords: Blue OLED, Fluorescence, Pyrene, Arylamine.
IP: 193.56.67.84 On: Wed, 26 Dec 2018 12:42:44
1. INTRODUCTION
Herein, we newly designed and synthesized blue fluo-
Copyright: American Scientific Publishers
rescence materials based on diarylamine-substituted three
In recent display market, organic light-emitting diodes
(OLEDs) are received intensive attention because of their
potential application to next generation display such as
flexible and transparent displays.1ꢀ2 However, there are
still problems, among which is the lifetime of the blue
light emitting material.3 This problem on blue-emitting
materials is caused by intrinsic instability and wide
band-gap energy of molecules.4 Until recently, a lot of
researches have been continuing to overcome these prob-
lems. In particular, pyrene, anthracene, chrysene, and
phenanthrene derivatives have been reported by many
groups because these materials have important properties
for blue emitting materials of OLED such as wide energy
gap, high fluorescence quantum yield and high thermal
stability.5–7 For example, Wang et al. synthesized 1,6-
bis(3,5-diphenylphenyl)pyrene that exhibited a luminous
efficiency (LE) and a CIE coordinate of 3.26 cd/A and
(0.15, 0.11) at 6.0 V.8 Also, Jeong et al. synthesized a
pyrene derivative containing two carbazole moieties at 1,6-
position of pyrene with the maximum emission wavelength
of 488 nm and the LE of 3.67 cd/A.9 Moreover, Chercka
et al. reported a material that introduced phenyl carbazole
at positions 2 and 7 of pyrene with CIE coordinate of
(0.16, 0.24) and a maximum external quantum efficiency
(EQE) of 3.19%.10
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pyrene derivatives (material 1, 2, and 3) for OLEDs.
To suppress the self-aggregation effect that reduces elec-
troluminescence (EL) efficiencies, two bulky diarylamine
groups were introduced at positions of 1 and 6 of pyrene.
This structural property effectively prevent red-shifted
emission caused by intermolecular interaction in solid
state, which lead to high color purity of EL emission.11
Also, for effective blue emission, we introduced electron
withdrawing moiety (nitrile) at para-position of linkage,
which would lead to lower the highest occupied molec-
ular orbital (HOMO) energy level of the molecules and
make it have the appropriate band-gap energy for blue
emission.12 Moreover, diarylamine moiety would improve
their hole transporting abilities and enhance charge balance
in the emitting-layer (EML).13 Therefore, OLED device
using these properties of materials 1–3 would lead to the
highly efficient blue emission.
2. EXPERIMENTAL DETAILS
2.1. Synthesis
2.1.1. 4,4ꢀ-[1,6-Pyrenediylbis(phenylamino)]bis-
Benzonitrile (1)
Material 1 was prepared by the following Buchwald-
Hartwig reaction procedure using 1,6-dibromopyrene
(1.39 mmol), 4-(phenylamino)benzonitrile (3.06 mmol),
∗Authors to whom correspondence should be addressed.
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1533-4880/2019/19/1056/005
doi:10.1166/jnn.2019.15929

Cho et al.
Highly Efficient Blue OLEDs Based on Diarylamine-Substituted Pyrene Derivatives
Tris(dibezylideneacetone)dipalladium(0) (0.069 mmol),
2-Dicyclohexylphosphino-2ꢀ,6ꢀ-dimethoxybiphenyl (0.11 mmol)
the OLEDs were measured with a Keithly 2400, Chroma
meter CS-1000A. Electroluminance was measured using a
Roper Scientific Pro 300i.
,
sodium tert-butoxide (9.72 mmol) (Yield: 40.5%).
1H-NMR (500 MHz, CDCl3ꢁ [ꢂ ppm]; 8.20
(d, J = 8.15 Hz, 2H), 8.10 (d, J = 9.18 Hz, 2H), 8.02
(d, J = 9.25 Hz, 2H), 7.87 (d, J = 8.10 Hz, 2H), 7.42
(d, J = 8.92 Hz, 4H), 7.34 (t, J = 7.38 Hz, 4H), 7.26
(d, J = 8.43 Hz, 4H), 7.16 (t, J = 7.32 Hz, 2H), 6.90
(d, J = 8.91 Hz, 4H); APCI-MS m/z = 586[M+]; Anal.
Calcd for C42H26N4: C, 85.98; H, 4.47; N, 9.55. Found:
C, 85.23; H, 4.15; N, 8.97.
3. RESULTS AND DISCUSSION
Syntheses of three blue fluorescent materials 1–3 are
shown in Scheme 1.
Density functional theory (DFT) calculations for
blue fluorescent materials 1–3 using the Becke’s three
parameterized Lee-Yang-Parr (B3LYP) functional with
6-31G∗ basis sets using a suite of Gaussian programs were
carried out to understand the observed properties of the
materials 1–3 on molecular levels. The electron cloud dis-
tributions of LUMO in materials 1–3 are mainly located
in pyrene moiety which is center of molecules. In mate-
rial 1 and 3, the electron cloud distributions of HOMO are
spread widely throughout the molecules. And the electron
cloud distributions of HOMO in material 2 are located
in throughout the molecule apart from two phenyl rings
introduced into diarylamine.
As shown in Figure 1, three-dimensional structures of
materials 1–3 demonstrated that molecules have twisted
structure because of introducing of diarylamine moieties
at 1,6-positions of pyrene. The dihedral angles between
pyrene and benzonitrile moiety substituted at the 1,6-
position of pyrene were calculated to be 56ꢁ, 57ꢁ, and 67ꢁ
2.1.2. 4,4ꢀ-[1,6-Pyrenediylbis((3,5-
diphenyl)phenylamino)]bis-Benzonitrile (2)
The synthetic procedure for material 2 was simi-
lar to that described for material 1 using 4-((1,3-
diphenyl)phenylamino)benzonitrile (3.06 mmol) instead of
4-(phenylamino)benzonitrile, the desired compound was
obtained as a yellow solid (Yield: 51.3%). 1H-NMR
(500 MHz, CDCl3ꢁ [ꢂ ppm]; 8.22 (d, J = 8.15 Hz, 2H),
8.11 (d, J = 9.18 Hz, 2H), 8.01 (d, J = 9.25 Hz, 2H), 7.86
(d, J = 8.10 Hz, 2H), 7.55 (m, 8H), 7.41 (d, J = 8.92 Hz,
4H), 7.33 (m, 12H), 7.28 (d, J = 8.43 Hz, 4H), 7.10
(s, 2H), 6.95 (s, 2H); APCI-MS m/z = 890[M+]; Anal.
Calcd for C66H42N4: C, 88.96; H, 4.75; N, 6.29. Found:
C, 88.35; H, 4.47; N, 6.11.
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2.1.3. 4,4ꢀ-[1,6-Pyrenediylbis(9,10-dimethylfluoren-2-yl-
for materials 1, 2, and 3, respectively. Also, the dihedral
angles between pyrene and other aromatic ring moieties
Copyright: American Scientific Publishers
amino)]bis-Benzonitrile (3)
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(benzene, diphenylbenzene, fluorene) were calculated to be
67ꢁ, 69ꢁ, and 35ꢁ for materials 1, 2, and 3, respectively.
These twisted structural features of materials would effec-
tively suppress the aggregation-quenching by ꢄ–ꢄ stack-
ing in solid state, which is leading to electroluminescent
(EL) efficiency.14
The synthetic procedure for material 3 was similar
to that described for 1 using 4-(9,10-dimethylfluoren-
2-yl-amino)benzonitrile (3.06 mmol) instead of
4-(phenylamino)benzonitrile, the desired compound was
obtained as a yellow solid (Yield: 37.5%). 1H-NMR
(500 MHz, CDCl3ꢁ [ꢂ ppm]; 8.19 (d, J = 8.15 Hz, 2H),
8.12 (d, J = 9.18 Hz, 2H), 8.03 (d, J = 9.25 Hz, 2H), 7.82
(d, J = 8.10 Hz, 2H), 7.54 (m, 6H), 7.40 (d, J = 8.92 Hz,
4H), 7.33 (m, 4H), 7.28 (d, J = 8.43 Hz, 4H), 7.12
(d, J = 8.53 Hz, 2H), 6.93 (s, 2H), 0.51 (s, 12H); APCI-
MS m/z = 818[M+]; Anal. Calcd for C60H42N4: C,87.99;
H, 5.17; N, 6.84. Found: C, 87.32; H, 4.95; N, 6.51.
The UV-Visible absorption spectra of materials 1–3 and
emission spectrum of ꢅ, ꢆ-ADN in dilute dichloromethane
solution are shown in Figure 2(a). And the photolumi-
nescence (PL) spectra of materials 1–3 in dilute solution
Figure 2(b). Their photophysical properties are summa-
rized in Table I. In Figure 2(a), the maximum absorption
wavelength (ꢇmaxꢁ of materials 1–3 appeared at 243 nm,
247 nm and 270 nm in dilute dichloro methane solution
(1×10−5 M), respectively. Also, all materials (1–3) exhib-
ited strong absorption peaks near 330 nm and 405 nm.
And the maximum emission wavelength of materials 1–3
occurred at 459, 458 and 476 nm in dichloromethane solu-
tion (1 ×10−5 M), respectively, in blue region of the vis-
ible spectrum. The maximum intensity of PL spectra of
material 3 showed more red-shifted than material 1 and 2.
The conjugation length of the aryl group in material 3
is longer than other materials (1 and 2), which is leading
to red-shifted emission.15
2.2. OLED Fabrication and Measurements
For OLED fabrication, indium-tin-oxide (ITO) thin films
coated on glass substrates were used, which were
30 ꢃ/square of the sheet resistively and 1000 Å thick. The
ITO-coated glass was cleaned in an ultrasonic bath through
the following sequence: washes with acetone, methyl alco-
hol, and distilled water, storage in isopropyl alcohol for
48 h, and drying with a N2 gas gun.
The substrates were treated by O2 plasma under 2 ×
10−2 Torr at 125 W for 2 min. All organic materi-
als and metal were deposited under high vacuum (5 ×
10−7 Torr). The current density (J), luminance (L), lumi-
nous efficiency (LE), and CIE chromaticity coordinates of
To investigate the EL properties of materi-
als 1–3, OLED devices A–C were fabricated as
J. Nanosci. Nanotechnol. 19, 1056–1060, 2019
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Highly Efficient Blue OLEDs Based on Diarylamine-Substituted Pyrene Derivatives
Cho et al.
Scheme 1. Synthesis of materials 1–3; (a) Pd2(dba)3, toluene, sphos, NaO-tBu, reflux.
Table I. Physical properties of materials 1–3.
UV ꢇamax
(nm)
PL
ꢇamax (nm)
FWHMa HOMO/LUMOb Egc
Material
(nm)
(eV)
(eV) ꢈfd
1
2
3
243
247
241
452
453
476
44
43
61
−5.34/−2.44
−5.33/−2.41
−5.03/−2.23
2.90 0.64
2.92 0.61
2.80 0.75
Measured in CH2Cl2 (ca. 1 × 10 M). bHOMO energy level was deter-
a
−5
IP: 193.56.67.84 On: Wed,N2o6tes:Dec 2018 12:42:44
Copyright: American ScientibfyicloPwu-ebnelrigsyhers
mined
photoelectron spectrometer and LUMO = HOMO + Eg.
cDetermined from the intersection of the absorption and photoluminescence spec-
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tra. dPL quantum yields were determined in CH2Cl2 solution at 298 K against
9,10-diphenylanthracene (DPA) as a reference; ꢇex = 360 nm (ꢈ = 0ꢉ90 in CH2Cl2
solution).
anthracene (ꢅ, ꢆ-ADN): 10 wt% blue materials 1–3
Figure 1. Density functional theory (DFT) calculations for blue fluo-
rescent materials 1–3.
(300
nm)/2-(4-(9,10-di(naphthalen-2-yl)anthracen-7-yl)
phenyl)-1-phenyl-1H-benzo[d]imidazole (DNAB) (300 nm)/
lithium quinolate (Liq) (20 nm)/Al (1000 nm). 2-TNATA
and NPB were selected as the hole injection layer (HIL)
and hole transporting layer (HTL), respectively. Materials
1–3 were used blue dopants in emitting layer (EML),
ꢅ, ꢆ-ADN was selected host material in EML, and DNAB
following structure: ITO (180 nm)/4,4ꢀ ,4ꢀꢀ -Tris[2-
naphthyl(phenyl)amino]triphenylamine (2-TNATA) (300 nm)/
N ,N ꢀ -diphenyl-N ,N ꢀ-(2-napthyl)-(1,1ꢀ-phenyl)-4,4ꢀ-diamine
(NPB) 200 nm/10-(1-naphthalenyl)-9-(2-naphthalenyl)
A
1
(b)
1.0
(a)
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
B
2
C
3
0.8
α,β-ADN
0.6
0.4
0.2
0.0
300
400
500
600
400
500
600
700
Wavelength [nm]
Wavelength [nm]
Figure 2. (a) UV-visible absorption spectra of materials 1–3 and PL emission spectra of ꢅꢀꢆ-ADN; (b) PL emission spectra of materials 1–3 in
10−5 M CH2Cl2 solution.
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Cho et al.
Highly Efficient Blue OLEDs Based on Diarylamine-Substituted Pyrene Derivatives
100000
A
B
C
A
B
C
1.0
0.8
0.6
0.4
0.2
0.0
(a)
(b)
600
400
200
0
10000
1000
100
10
1
0.1
0.01
400
500
600
700
0
4
8
12
Wavelength [nm]
Voltage [V]
LE - A
6
4
2
0
8
6
4
2
0
A
B
C
(c)
(d)
12
8
LE - B
LE - C
PE - A
PE - B
PE - C
4
0
0
100
200
0
50
100
150
200
Current density [mA/cm2]
Current density [mA/cm2]
Figure 3. (a) EL spectra of devices A–C; (b) current density–voltage–luminance (J–V –L) characteristics of devices A–C; (c) luminous efficiency and
power efficiency of devices A–C; (d) external quantum efficiency of devices A–C.
was chosen as the electron-transporting layer (ETL). ITO
efficiencies of devices A–C. Devices A–C were exhibited
IP: 193.56.67.84 On: Wed, 26 Dec 2018 12:42:44
Copyright: American Scientific Publishers
and Liq on the Al were selected anode and cathode, highly efficient blue emissions with the luminous efficien-
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respectively.
cies of 5.16, 5.35 and 8.94 cd/A, power efficiencies of
2.70, 2.80, and 3.84 lm/W, and external quantum efficien-
cies of 3.72, 3.78, and 6.62% at 20 mA/cm2, respectively.
And maximum values of the external quantum efficien-
cies of devices A–C were 4.47, 4.12, and 6.76%, respec-
tively. Interestingly, device C using material 3 showed the
more efficient EL efficiencies than other devices. Com-
pared to material 1 and 2 (ꢈf = 0ꢉ64, 0.61, respectively),
material 3 (ꢈf = 0ꢉ75) has the better fluorescence quan-
tum yield in dilute solution. Furthermore, as shown in
Figure 2(a), the overlap of the emission spectrum of ꢅ,
ꢆ-AND host with the absorption spectrum of dopant 3 is
larger than those of dopants 1 and 2. These observations
imply that the Föster energy transfer from host to dopant in
device C is more effective than those in devices A and B,
and thus lead to the improved EL efficiencies of device C
in comparison with devices A and B.
Figure 3(a) shows the EL spectra of device A–C, and
their EL properties are summarized in Table II. Maximum
intensity of device A–B occurred 459, 458, and 475 nm
in blue region, respectively. Maximum EL emission peak
of all devices matched PL maximum peaks of materials
1–3 in dichloromethane solution. These results indicate
that EL emissions of all devices were from the singlet
excition of blue dopant materials 1–3. On the other hand,
they demonstrated a large shoulder peak with red-shifted
due to excimer formation in high doping concentration of
solid state.16 The Commission International de L’Eclairage
(CIE) chromaticity coordinates of devices A–C were (0.14,
0.17), (0.15, 0.18), and (0.16, 0.23) at 6.0 V, respectively.
Figures 3(b)–(d) demonstrate the current density-
voltage-luminance (J–V –L) characteristics, luminous
efficiencies, power efficiencies and external quantum
Table II. EL properties of devices A–C.
EL ꢇbmax
(nm)
Lc
(cd/m2)
LEc/d
(cd/A)
PEc/d
(lm/W)
EQEc/d
(%)
CIEb
(xꢀy)
Device
Materiala
A
B
C
1
2
3
459
458
475
13,820
17,110
19,505
5.95/5.16
5.77/5.35
9.13/8.94
2.77/2.70
2.80/2.80
4.40/3.84
4.47/3.72
4.12/3.78
6.76/6.62
(0.14, 0.17)
(0.15, 0.18)
(0.16, 0.23)
Notes: aDoping concentration (10% weight). bAt 6.0 V. cMaximum values. dMeasured at a current density of 20 mA/cm2.
J. Nanosci. Nanotechnol. 19, 1056–1060, 2019
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Highly Efficient Blue OLEDs Based on Diarylamine-Substituted Pyrene Derivatives
Cho et al.
4. CONCLUSION
3. I. Moraes, S. Scholz, M. Hermenau, M. L. Tietze, T. Schwab,
S. Hofmann, and M. C. Gather, K. Leo, Organic Electronics 26, 158
(2005).
We synthesized three pyrene derivatives endcapped with
diarylamine moieties. Blue OLEDs were fabricated
by using materials 1–3 as the dopant in the emit-
ting layers. A device using 4,4ꢀ-[1,6-Pyrenediylbis(9,10-
dimethylfluoren-2-yl-amino)]bis-benzonitrile (3) showed
highly efficient blue emission with the luminous efficiency
of 8.94 cd/A, power efficiency of 4.40 lm/W, external
quantum efficiency of 6.62% at 20 mA/cm2, and the CIE
coordinates of (0.16, 0.23) at 6.0 V, respectively. This
study indicates that OLED devices using diarylamine-
substituted pyrene derivatives as blue dopants exhibit the
outstanding performances.
4. X. Yang, X. Xu, and G. Zhou, J. Mater. Chem.
(2015).
C 3, 913
5. M. Zhu and C. Yang, Chem. Soc. Rev. 42, 4963 (2013).
6. H. Shin, C. Lin, H. Shin, and C. Cheng, Adv. Mater. 19, 1409
(2002).
7. S. Tang, W. Li, F. Shen, D. Liu, B. Yang, and Y. Ma, J. Mater. Chem.
22, 4401 (2012).
8. Z. Wanga, C. Xu, W. Wang, X. Dong, B. Zhao, and B. Ji, Dyes and
Pigments 92, 732 (2012).
9. S. Jeong, S. Park, K. Kim, Y. Kwon, K. Ha, B. Choi, and Y. Han,
J. Nanosci. Nanotechnol. 11, 4351 (2011).
10. D. Chercka, S. Yoo, M. Baumgarten, J. Kim, and K. Müllen,
J. Mater. Chem. C 2, 9083 (2014).
11. H. Fukagawa, T. Shimizu, N. Ohbe, S. Tokito, K. Tokumaru, and
H. Fujikake, Org. Electron. 13, 1197 (2012).
12. W. Jia, T. M. Cormick, Q. Liu, H. Fukutani, M. Motala, R. Wang,
Y. Tao, and S. Wang, J. Mater. Chem. 14, 3344 (2004).
13. S. Ku, L. Chi, W. Hung, S. Yang, T. Tsai, K. Wong, Y. Chenc, and
C. Wu, J. Mater. Chem. 19, 1 (2009).
Acknowledgment: This research was supported by
Samsung Display and the MSIP (Ministry of Science, ICT
and Future Planning), Korea, under the ITRC(Information
Technology Research Center) support program (IITP-
2017-2012-0-00542) supervised by the IITP (Institute for
Information and communications Technology Promotion).
14. Z. Liang, Y. Li, J. Yang, Y. Ren, and X. Tao, Tetrahedron Letters
52, 1329 (2011).
References and Notes
15. J. Huang, N. Sun, Y. Dong, R. Tang, P. Lu, P. Cai, Q. Li, D. Ma,
J. Qin, and Z. Li, Adv. Funct. Mater. 23, 2329 (2013).
16. Z. Zhao, S. Chen, J. Lam, Z. Wang, P. Lu, F. Mahtab, H. Sung,
I. Williams, Y. Ma, H. Kwok, and B. Tang, J. Mater. Chem. 21, 7210
(2011).
1. J. Lewis, S. Grego, B. Chalamala, E. Vick, and D. Temple, Appl.
Phys. Lett. 85, 3450 (2004).
2. S. Kim, H. Kwon, S. Lee, H. Shim, Y. Chun, W. Choi, J. Kwack,
D. Han, M. Song, S. Kim, S. Mohammadi, I. Kee, and S. Y. Lee,
Adv. Mater. 23, 3511 (2011).
IP: 193.56.67.84 On: Wed, 26 Dec 2018 12:42:44
Copyright: American Scientific Publishers
Received: 27 November 2017. Accepted: 22 February 2018.
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J. Nanosci. Nanotechnol. 19, 1056–1060, 2019