New blue emitting material with asymmetric limb structure

Article abstract of DOI:10.1166/jnn.2015.8820

The new assymmetric limb-structured blue light emitting material, composed of anthracene main core, naphthalene units at 9, 10-position of anthracene and xylene units at 2,3-positon of anthracene, was designed and synthesized. The three-dimensional structure from theoretical calculation was characterized to elucidate non-copolar structure with inhibited intermolecular interaction. The limb-structured blue material was thermally stable up to 373°C with T_g of 143°C. ITO/TAPC/CBP (3% BMPNA)/Bphen/LiF/Al device exhibits the maximum quantum efficiency of 3.42% and maximum current efficiency of 3.07 cd/A with deep blue emission of (0.141, 0.115) CIE coordinates.

Full text of DOI:10.1166/jnn.2015.8820

Article
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Nanoscience and Nanotechnology
Vol. 15, 355–359, 2015
Copyright © 2015 American Scientific Publishers
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New Blue Emitting Material with Asymmetric
Limb Structure
Seung-Hoon Hahn1, Jonghee Lee3, Hye Yong Chu3, Jeong-Ik Lee3, Yun Ji Lee2,
Jaeyoung Hwang2, Sung Chul Shin1ꢀ∗, and Yun-Hi Kim1ꢀ∗
1Department of Chemistry and RINS, Gyeongsang National University, Jinju 660-701, Korea
2School of Materials Science and Engineering and Research Institute for Green Energy Convergence
Technology (RIGET), Gyeongsang National University, Jinju 660-701, Korea
3Electronics and Telecommunications Research Institute, 161, Gajeong-dong, Yuseong-gu,
Daejeon, 305-700, South Korea
The new assymmetric limb-structured blue light emitting material, composed of anthracene main
core, naphthalene units at 9, 10-position of anthracene and xylene units at 2,3-positon of
anthracene, was designed and synthesized. The three-dimensional structure from theoretical cal-
culation was characterized to elucidate non-copolar structure with inhibited intermolecular inter-
action. The limb-structured blue material was thermally stable up to 373 ꢀC with Tg of 143 ꢀC.
ITO/TAPC/CBP (3% BMPNA)/Bphen/LiF/Al device exhibits the maximum quantum efficiency of
3.42% and maximum current efficiency of 3.07 cd/A with deep blue emission of (0.141, 0.115) CIE
Delivered by Publishing Technology to: Chinese University of Hong Kong
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coordinates.
Copyright: American Scientific Publishers
Keywords: Blue Emitting, Astmmetric Limb Structure, Anthracene, OLEDs.
1. INTRODUCTION
characteristics.15–18ꢀ20ꢀ21 By adding bulky substituents at
the 9, 10-positions of anthracene, the molecule comes
to be highly non-planar owing to steric interactions
between the substituents and the anthracene core. The
non-coplanar structure provides preventing intermolecu-
lar interactions and reduces self-quenching effects, lead to
improved electroluminescent (EL) performance and color
purity.
Recently, our group has reported that the whole molecule
comes to be highly twisted by introducing bulky sub-
stituents at the 9- and 10-position of anthracene. Conse-
quently, the fluorescence-quenching interactions caused by
intermolecular interactions can be suppressed to some ex-
tent and non-radiative energy decay can be decreased.15–20
In this study, we designed and developed new
asymmetric limb-structured blue light emitting material,
composed of anthracene main core, naphthalene units
at 9, 10-position of anthracene and m-xylene units at
2,3-positon of anthracene. The introduction of m-xylene
substituents at 2,3-positions can reduce highly twisted
structure due to steric hindrance between xylenes than the
inhibited intermolecular interaction, it is expected to have
high efficiency and high color purity.
Organic light-emitting diodes (OLEDs) have been attract-
ing considerable attention because of the enormous poten-
tial in next-generation flat panel displays and solid state
lighting application.1–9 Device construction and impor-
tant progress in material synthesis have led to the real-
ization of full color as well as white OLEDs with
improved lifetimes and efficiencies. In order to develop
high performance materials with desirable properties and
devices with optimized architecture to develop marketable
OLEDs, great effort has been made. Whereas various
red,10ꢀ11 and green12–14 materials with great properties,
materials emitting in the blue color with high efficiency
are still scarce. Consequently, the development of high-
performance blue light emitting materials has received
attention and numerous blue materials like anthracene, flu-
orene, di(styryl)arylene, tetra(phenyl) pyrene, tetra(phenyl)
silylderivatives have been devised.15–17ꢀ19
Anthracene derivatives have been extensively used as
emitting materials in OLEDs due to their interesting
photoluminescence (PL) and electroluminescence (EL)
∗Authors to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2015, Vol. 15, No. 1
1533-4880/2015/15/355/005
doi:10.1166/jnn.2015.8820
355

New Blue Emitting Material with Asymmetric Limb Structure
Hahn et al.
2. EXPERIMENTAL DETAILS
2.1. Materials
CDCl3, ppm): ꢁ8.07–7.96 (m, 10 H), 7.72–7.67 (m, 8 H),
7.64–7.59 (m, 2 H).
All starting materials were purchased from Aldrich and
TCI. Without further purification, all starting materials
were used.
2.7. Synthesis of 2,3-bis(3,5-dimethylphenyl)-9,10-
di(naphthalene-2-yl)Anthracene
Under a nitrogen atmosphere, a mixture of 2,3-dibromo-
9,10-di(naphthalene-2-yl)-9,10-dihydroanthracene (1 g,
1.7 mmol), 3,5-dimethylphenylboronic acid (1.15 g,
7.65 mmol), Pd(pph3ꢂ4 (0.06 g, 0.05 mmol) and K2CO3
solution (2 M, 30 mL) in THF (5 mL) and toluene (30 mL)
was stirred for 48 h at 90 ꢀC. After being cooled to
room temperature, the mixture was extracted with CHCl3.
The organic layer was washed with water and dried over
magnesium sulfate, filtered, and evaporated under reduced
pressure. After removal of the solvents, the residue was
purified by column chromatography on silica gel using a
solvent of hexane/EA (5:1, v/v). Yield (0.9 g, 83%). mp
306ꢀ. IR (KBr): 3071–3031 cm−1 (sp2 C–H), 2950 cm−1
(sp3 C–H). 1H-NMR (300 MHz, CDCl3, ppm): ꢁ8.13–7.88
(m, 13 H), 8.06–7.64 (m, 11 H), 7.58–7.25 (m, 2 H), 1.58
(S, 12 H). EI-MS: m/z 638.
2.2. Instrument
1H NMR spectra were recorded using a Bruker Avance-
300 MHz FT-NMR spectrometer, and chemical shifts
were reported in ppm units with tetramethylsilane
(TMS) as internal standard. FT-IR spectra were recorded
using a Shimadazu FT-IR spectrometer. Melting points
was determined using an Electrothermal digital melting
point IA 9000 analyzer. UV-visible absorption spectra
were obtained in chloroform on a Shimadazu UV-2201
spectrophotometer. The photoluminescence spectra were
obtained in chloroform on a Perkin-Elmer LS50B fluores-
cence spectrometer. The electrochemical properties of the
material were measured by cyclic voltammetry (CV) using
a BAS 100B electrochemical analyzer with a scanning rate
at 50 mV/s in a 0.1 M solution of tetrabutyl ammonium
perchlorate (TBAP) in methylene chloride. Thermogravi-
metric analysis (TGA) was carried out on a TA instruments
210ꢀ0 TGA analyzer under nitrogen atmosphere at a rate of
10 C/min. Differential scanning calorimeter (DSC) was
3. RESULTS AND DISCUSSION
Scheme 1 outlines the synthetic route for BMPNA.
BMPNA was obtained by oxidation, Diels-Alder reaction
following degradation of SO2, Grignard reaction, reduc-
performed using a TA DSC 2010 device under nitrogen
atmosphere at a rate of 10 C/min.
ꢀ
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tion, and Suzuki coupling reaction.
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The obtained BMPNA was fully characterized with
H-NMR, FT-IR and Mass spectroscopies. Theoretical cal-
culation using Spartan08 software in order to fully opti-
mize the molecular structure, was carried out for the
characterization of 3-dimensional structure and the elec-
tron densities of the HOMO and LUMO state. Figure 1
shows the stereostructures and the energy densities of
the HOMO and LUMO states of materials derived from
the calculations. The xylene groups in the 2 and 3 posi-
tions are significantly twisted due to steric hindrance.
The three-dimensional structure from theoretical calcula-
tion suggests that BMPNA has non-copolar structure with
inhibited intermolecular interaction. The electron densities
of HOMO and LUMO levels of BMPNA were localized
in the anthracene unit. From the result, it is suggested
that energy transfer could be occurred from naphthalene
or xylene units to anthracene, and the color of emission
was controlled by anthracene unit.
Copyright: American Scientific Publishers
2.3. Synthesis of 3,4-Dibromothiophene-1,1-Dioxide
The synthesis was carried out by literature method.23 Yield
(12.4 g, 49%). mp 103–104ꢀ. IR (KBr):1309, 1146 cm−1
(S O), 3015 cm−1 (sp2
CDCl3, ppm): ꢁ6.85 (s, 2 H).
C
H). 1H-NMR (300 MHz,
2.4. Synthesis of 2,3-Dibromoanthraquinone
The synthesis was carried out by literature method.23 Yield
(3.2 g, 40.65%). mp 278–279ꢀ. IR (KBr): 1681 cm−1
(C O), 3075 cm−1 (sp2 C H), 1656 cm−1 (C C). H-
1
NMR (300 MHz, CDCl3, ppm): ꢁ8.49 (s, 2 H), 8.38–8.40
(s, 2 H), 7.86–7.89 (s, 2 H).
2.5. Synthesis of 2,3-Dibromo-9,10-di(naphthalene-2-
yl)-9,10-Dihydroanthracene-9,10-diol
The synthesis was carried out by literature method.23 Yield
(1.99 g, 68%). mp 226ꢀ. IR (KBr): 3521 cm−1 (–OH),
3017–3029 cm−1 (sp2
C
H), 1582 cm−1 (C C). 1H-
The photophysical property for BMPNA was investi-
gated by UV and PL spectroscopy. Figure 2 shows the
UV-visible absorption and photoluminescence (PL) spec-
trum of BMPNA in dilute solution (CHCl3ꢂ and in the
film. The absorption spectrum in the diluted solution
expressed vibronic pattern of an isolated anthracene group
(367, 390 and 409 nm).15 The ꢃmax of the PL spec-
tra of BMPNA in solution and in film were 448 nm
and 468 nm, respectively, which indicates the blue
emission.
NMR (300 MHz, CDCl3, ppm): ꢁ8.52 (2 H), 8.38–8.40
(4 H), 7.86–7.89 (6 H), 7.55–7.58 (4 H), 7.31–7.37 (4 H),
3.65 (2 H).
2.6. Synthesis of 2,3-Dibromo-9,10-di(naphthalene-2-
yl)-Anthracene
The synthesis was carried out by literature method.23 Yield
(2.02 g, 83%). mp 298ꢀ. IR (KBr): 3011–3043 cm−1 (sp2
1
C
H), 1752–1734 cm−1 (C C). H-NMR (300 MHz,
356
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Hahn et al.
New Blue Emitting Material with Asymmetric Limb Structure
O
Br
Br
Br
Br
Br
Br
i
ii
iii
S
S
O
O
O
OH
Br
Br
Br
iv
v
Br
HO
BMPNA
Scheme 1. Reagent: (i) (CF3CO)2O, 30%/H2O2; (ii) 1,4-naphthoquinone, CH3COOH; (iii) bromo(2-naphthyl)magnesium, THF; (iv) NaH2PO4, KI,
CH3COOH; (v) 3,5-Dimethylphenylboronic acid, Pd(pph3ꢂ4, 2M K2CO3, toluene, THF.
The electrochemical behavior of BMPNA was inves-
tigated by cyclic voltammetry (CV) using ferrocene as
the internal standard. The highest occupied molecular
orbital (HOMO) and the lowest occupied molecular orbital
(LUMO) level of BMPNA was obtained 5.63 eV and
2.75 eV, respectively, from the calculation of oxidation
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peak potential and optical band gap from UV-edge.
IP: 117.255.247.238 On: Wed, 21 Oct 2015 12:46:20
The thermal properties of BMPNA was investigated
Copyright: American Scientific Publishers
by thermogravimetric analysis (TGA) and differential
scanning calorimetry (DSC) as shown Figure 3. BMPNA
had the glass transition temperature (Tgꢂ of 143 ꢀC.
The decomposition temperature (Td: corresponding to 5%
weight loss) of BMPNA was 373 ꢀC. As a result, the
BMPNA can be made thermally stable amorphous film
despite being relatively low molecular weight organic
compound.
Figure 4 shows the structure of blue OLED which are
fabricated in this study using non-doped BMPNA with
combinations of a different hole injection layer (HIL)
and hole transporting layer (HTL). The detailed
structures of Device A is as follows; Indium tin
oxide (ITO)/NꢀNꢁ-di(naphthalene-1-yl)-N,Nꢁ-diphenyl-
benzidine (NPB) (30 nm)/tris(4-carbazoyl-9-ylphenyl)
amine (TCTA) (10 nm)/BMPNA (30 nm)/4,7-diphenyl-
1,10-phenanthroline (Bphen) (50 nm)/LiF/Al, where
NPB is hole injection layer; TCTA is hole transporting
Figure 1. Three-dimensional structure and HOMO, LUMO density of
BMPNA.
A slight emission red-shift is observed for the film
states, which may be accounted for by the different dielec-
tric constants of the media.22 The absorption and emission
spectra of BMPNA in solution and in the film are summa-
rized in Table I.
Table I. Photophysical, electrochemical properties of BMPNA.
UV-vis (nm)
PL (nm)
HOMO LUMO Eg
Comp
Solution Film Solution Film
(eV)
(eV)
(eV)
BMPNA
367,
390,
409
375,
394,
418
448
468
5.63
2.75
2.88
Figure 2. The UV-vis absorption and emission spectra of BMPNA in
CHCl3.
J. Nanosci. Nanotechnol. 15, 355–359, 2015
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New Blue Emitting Material with Asymmetric Limb Structure
Hahn et al.
Table II. OLED device characteristics using BMPNA as non-doped and
doped blue emitter.
At 10 mA/cm2
At Peak
C.E
EQE
C.E.
Device EQE (%) (V)
(cd/A) (V)
(%) (cd/A)
CIE (x, y)
A
B
C
D
E23
F23
2.28@4
2.37@4
3.02@3.5
3.42@4
3.62@5.59
4.16@5.60
3.45@4
3.58@4
2.81@3.5 2.47
2.03
2.12
3.07
3.21
2.31
2.43
–
(0.192, 0.226)
(0.190, 0.226)
(0.140, 0.122)
(0.141, 0.115)
(0.15, 0.13)
3.07@4
2.71
–
–
–
(0.15, 0.14)
Notes: Device E: ITO/DNTPD (70 nm)/ꢄ-NPD (30 nm)/2,3-diphenyl-9,10-
dinaphtylanthracene doped 9,10-dinaphthyl anthracene (PNA doped ADN,
3%, 20 nm)/Alq3 (40 nm)/LiF/Al. Device F: ITO/DNTPD (70 nm)/ꢄ-NPD
(30 nm)/2,3,9,10-Tetranaphtylanthracene doped 9,10-dinaphthyl anthracene (NNA
doped ADN, 3%, 20 nm)/Alq3 (40 nm)/LiF/Al.
Device C: NPB (40 nm)/tris(4-carbazoyl-9-ylphenyl)amine
(TCTA) (10 nm). The key device performance param-
eters and EL emission characteristics are summarized
in Table II. The non-doped devices showed maximum
quantum efficiency of 2.28–2.37% and maximum cur-
rent efficiency of 3.45–3.58 cd/A. However, The CIE
coordinates of devices A and B are (0.192, 0.226) and
(0.190, 0.226), respectively. To study the electrolumines-
cence performance of BMPNA as a blue dopant material,
well known CBP was used as host. The voltage-current
Figure 3. TGA thermogram (a) and DSC curve (b) of BMPNA.
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density-luminance characteristic of device is shown in
layer; BDNA is the blue emitting layer; Bphen is elec-
IP: 117.255.247.238 On: Wed, 21 Oct 2015 12:46:20
Figure 5. The device D using TAPC as HTL shows the
tron transporting layer and LiF is the electron injection
layer at the Al cathode interface. For device B, we
have changed HIL and HTL structure instead of using
NPB and TCTA of Device A. Device B: NPB(50 nm),
Copyright: American Scientific Publishers
maximum quantum efficiency of 3.42% and maximum
current efficiency of 3.07 cd/A with deep blue emission
of (0.141, 0.115) CIE coordinates. In the device D, the
hole and electron recombination was occurred in emitting
layer. Thus, efficiency and color purity of device D was
better than other devices (A, B and C). The Figure 6
shows the electroluminescence spectrum of device D. The
EL spectrum is consistent with PL of BMPNA. From
the results, the new designed asymmetric limb-structured
BMPNA is recommended new blue emitter.
Figure 5. Current density–voltage–luminance characteristics of the
Figure 4. Energy level of materials applied to OLED.
device D.
358
J. Nanosci. Nanotechnol. 15, 355–359, 2015

Hahn et al.
New Blue Emitting Material with Asymmetric Limb Structure
3. S. O. Kim, K. Thangaraju, S. O. Jung, W. Lu, S. M. Park, J. H.
Lee, J. I. Lee, H. Y. Chu, Y. H. Kim, and S. K. Kwon, J. Nanosci
Nanotechnol. 12, 4370 (2012).
4. H. R. Park, B. Y. Kim, Y. K. Kim, and Y. K. Ha, J. Nanosci
Nanotechnol. 12, 5613 (2012).
5. H. Wang, J. T. Ryu, and Y. H. Kwon, J. Nanosci Nanotechnol.
12, 4330 (2012).
6. H. T. Park, J. H. Lee, I. Kang, H. Y. Chu, J. I. Lee, S. K. Kwon,
and Y. H. Kim, J. Mater. Chem. 22, 2695 (2012).
7. S. J. Yoo, H. J. Yun, I. Kang, K. Thangaraju, S. K. Kwon, and Y. H.
Kim, J. Mater. Chem. C. 1, 2217 (2013).
8. D. H. Oh, Q. Zhao, S. O. Kim, H. T. Park, Y. H. Kim, Y. S.
Park, J. J. Kim, and S. K. Kwon, Macromol. Res. 19, 629
(2011).
9. H. T. Park, D. C. Shin, S. C. Shin, J. H. Kim, S. K. Kwon, and Y. H.
Kim, Macromol. Res. 19, 965 (2011).
10. Y. H. Kim, H. S. Kim, K. H. Lee, S. K. Kwon, and S. H. Kim, Mol.
Cryst. Liq. Cryst. 444, 257 (2006).
11. J. W. Jang, H. Park, M. K. Shin, S. O. Jung, S. K. Kwon, and Y. H.
Kim, Dyes Pigm. 88, 44 (2011).
12. D. M. Kang, J. W. Kang, Y. H. Kim, S. C. Shin, J. J. Kim, and S. K.
Kwon, Adv. Mater. 20, 2003 (2008).
13. Y. S. Park, J. W. Kang, D. M. Kang, Y. H. Kim, S. K. Kwon, and
J. J. Kim, Adv. Mater. 20, 1957 (2008).
14. S. O. Jung, Y. H. Kim, S. K. Kwon, H. Y. Oh, and J. H. Yang, Org.
Electron. 8, 349 (2007).
15. Y. H. Kim, D. C. Shin, S. H. Kim, H. S. Yu, Y. S. Chae, and S. K.
Kwon, Adv. Mater. 13, 1690 (2001).
16. Y. H. Kim, H. C. Jung, S. H. Kim, K. Y. Yang, and S. K. Kwon,
Adv. Funct. Mater. 15, 1799 (2005).
17. J. W. Park, Y. H. Kim, S. H. Jang, S. K. Lee, S. C. Shin, and S. K.
Figure 6. Normalized PL, EL spectra of the device D.
4. CONCLUSION
We devised new limb structured anthracene, BMPNA,
which is composed of anthracene core and naphthalene
units at 9, 10-position of anthracene and xylene units
at 2, 3-positon of anthracene. The theoretical calcula-
tion shows that the synthesized material has non-coplanar
structure owing to steric hindrance of introduced limbs.
The ITO/TAPC/CBP(BMPNA)/Bphen/ LiF/Al structured
OLED device exhibits the maximum quantum efficiency
of 3.42% and maximum current efficiency of 3.07 cd/A
Kwon, Thin Solid Films 516, 8381 (2008).
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with deep blue emission of (0.141, 0.115) CIE coordinates.
IP: 117.255.247.238 On: We1d8,. 2J1. WO. Pcatrk2,0P1. K5a1ng2, :H4.6P:a2rk0, H. Y. Oh, Y. H. Kim, and S. K. Kwon,
Copyright: American ScienDtyifeiscPPigumb. l8is5,h9e3rs(2010).
Acknowledgment: This research was supported by
19. J. U. Kim, H. B. Lee, J. S. Shin, Y. H. Kim, Y. K. Joe, and S. K.
Kwon, Synth. Met. 150, 27 (2005).
20. W. J. Jo, Y. H. Kim, Q. H. Zhao, K. H. Lee, H. Y. Oh, and S. K.
Kwon, Synth. Met. 159, 1359 (2009).
21. M. K. Shin, S. O. Kim, H. T. Park, S. J. Park, H. S. Yu, Y. H. Kim,
and S. K. Kwon, Dyes Pigm. 92, 1075 (2012).
Industrial strategic technology development program
[10035225, Development of core technology for high per-
formance AMOLED on plastic] funded by MKE/KEIT.
References and Notes
1. C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett. 51, 913 (1987).
2. R Kim, D. H. Oh, M. C. Hwang, J. Y. Baek, S. C. Shin, S. K. Kwon,
and Y. H. Kim, J. Nanosci Nanotechnol. 12, 4370 (2012).
22. Y. H. Kim, S. K. Kwon, D. S. Yoo, M. F. Rubner, and M. S.
Wrighton, Chem. Mater. 9, 2699 (1997).
23. R. Kim, S. J. Yoo, E. K. Kim, H. S. Yu, S. C. Shin, S. K. Lee, S. K.
Kwon, and Y. H. Kim, Dyes Pigm. 95, 384 (2012).
Received: 20 May 2012. Accepted: 27 March 2013.
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