Synthesis and electroluminescent properties of blue-light-emitting arylene derivatives end-capped with thiophene groups

Article abstract of DOI:10.1080/15421406.2012.708249

In this study, four blue fluorescent arylenes end-capped with thiophene derivatives have been synthesized. To explore electroluminescent properties of these molecules, multilayer OLEDs device structure of ITO/NPB/EML/BPhen/Al were fabricated. Two multilayer devices, using 3-4, showed the efficient deep blue emissions with CIE_x,y of (0.159, 0.092) and (0.151,0.082) at 9.0V, and the external quantum efficiencies of 1.60 and 0.80%, respectively. A PFVtPh doped-device exhibited the highly efficient blue emission with a maximum luminance of 3480 cd m² at 9.0V, the external quantum efficiency of 5.23%, and CIE_x,y of (0.151, 0.185) at 9.0V. Copyright

Full text of DOI:10.1080/15421406.2012.708249

This article was downloaded by: [McGill University Library]
On: 14 October 2014, At: 15:54
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Molecular Crystals and Liquid Crystals
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gmcl20
Synthesis and Electroluminescent
Properties of Blue-Light-Emitting
Arylene Derivatives End-Capped with
Thiophene Groups
a
a
a
b
Suhyun Oh , Kum Hee Lee , Seul Ong Kim , Ji Hoon Seo , Young
b
a
Kwan Kim & Seung Soo Yoon
a
Department of Chemistry , Sungkyunkwan University , Suwon ,
40-746 , Korea
4
b
Department of Information Display , Hongik University , Seoul ,
21-791 , Korea
1
Published online: 27 Sep 2012.
To cite this article: Suhyun Oh , Kum Hee Lee , Seul Ong Kim , Ji Hoon Seo , Young Kwan Kim &
Seung Soo Yoon (2012) Synthesis and Electroluminescent Properties of Blue-Light-Emitting Arylene
Derivatives End-Capped with Thiophene Groups, Molecular Crystals and Liquid Crystals, 568:1, 15-24,
DOI: 10.1080/15421406.2012.708249
To link to this article: http://dx.doi.org/10.1080/15421406.2012.708249
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“
Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Mol. Cryst. Liq. Cryst., Vol. 568: pp. 15–24, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.708249
Synthesis and Electroluminescent Properties
of Blue-Light-Emitting Arylene Derivatives
End-Capped with Thiophene Groups
1
1
1
SUHYUN OH, KUM HEE LEE, SEUL ONG KIM, JI HOON
2
2
1,∗
SEO, YOUNG KWAN KIM, AND SEUNG SOO YOON
1
Department of Chemistry, Sungkyunkwan University, Suwon 440-746, Korea
Department of Information Display, Hongik University, Seoul 121-791, Korea
2
In this study, four blue fluorescent arylenes end-capped with thiophene derivatives
have been synthesized. To explore electroluminescent properties of these molecules,
multilayer OLEDs device structure of ITO/NPB/EML/BPhen/Al were fabricated. Two
multilayer devices, using 3–4, showed the efficient deep blue emissions with CIEx,y of
(0.159, 0.092) and (0.151,0.082) at 9.0 V, and the external quantum efficiencies of 1.60
and 0.80%, respectively. A PFVtPh doped-device exhibited the highly efficient blue
−
2
emission with a maximum luminance of 3480 cd m at 9.0 V, the external quantum
efficiency of 5.23%, and CIEx,y of (0.151, 0.185) at 9.0 V.
Keywords blue OLEDs; fluorescence; host; suzuki cross-coupling reaction; thiophene
group
Introduction
A variety of efficient electroluminescence materials have been investigated over the past
two decades because of their promising applications in full-color flat-panel displays [1–3].
Compared to red and green materials, many efforts are still needed to further improve the
performance of blue-light-emitting materials because high-performance blue-light-emitting
materials exhibiting ideal color purity, good stability, and high fluorescence efficiency re-
main relatively rare [4–6]. Some of the blue-emitting materials that have been developed
include: anthracene [7–11], carbazole [12–14], oligoquinoline [15], others [16,17]. How-
ever, EL performances of these blue emitters are still needed to be improved.
Thiophene-based materials have attracted considerable attention because of their po-
tential applications in the area of organic light emitting diodes [18] as they possess
good chemical stability and high carrier mobility [19–21]. Recently, a benzothiophene-
substituted compound was reported to have a better electroluminescence performance
than a well-known MADN host [22]. In this study, the synthesis and electroluminescent
properties of four arylene derivatives, 9,10-bis(benzothiophen-2-yl)anthracene (1), 1,4-
ꢀ
bis(benzothiophen-2-yl)naphthalene (2), 4,4 -bis(benzothiophen-2-yl)binaphthyl (3), and
4
ꢀ
,4 -bis(5-methylthiophen-2-yl)binaphthyl (4) are reported. These new emitters are based
∗
Address correspondence to Prof. Seung Soo Yoon, Department of Chemistry, SungKyunKwan
University, Cheoncheon-dong, Jangan-gu, Suwon, 440-746, Korea (ROK). Tel.: (+82)31-290-5971;
Fax: (+82)31-290-7075. E-mail: ssyoon@skku.edu
[431]/15

16/[432]
S. Oh et al.
on arylene emitting units end-capped with thiophene derivatives. In materials 1–3, arylene
ꢀ
emitting moieties such as anthracene, naphthalene, and 1,1 -binaphthylene are end-capped
with two benzothiophenes to test the effect of the core emitting units on their electrolumi-
ꢀ
nescent properties. Furthermore, in materials 3 and 4, 1,1 -binaphthylene emitting core are
connected with two benzothiophenes and 5-methylthiophenes, respectively, to study the
effect of the end-capping groups on their electroluminescent properties. As will be seen in
below, we evaluate the structural effects of the fluorescent materials on the various thermal
and photophysical properties. Also, we demonstrate highly efficient OLEDs using two of
these materials, 3 and 4.
Experimental
Materials and Measurements
All palladium-mediated cross-coupling reactions were performed under a N2 atmo-
sphere. Solvents were carefully dried and distilled from appropriate drying agents
prior to use. Thianaphthene-2-boronic acid, 5-methyl-2-thiopheneboronic acid, 9,10-
ꢀ
dibromoanthracene, and 1,1 -naphthyl were used as received from Aldrich or TCI. The
4
ꢀ
ꢀ
ꢀ
,4 -dibromo-1,1 -binaphthyl [23], 9,10-bis(benzothiophen-2-yl)anthracene (1) and 4 -[2-
(
2-diphenylamino-9,9-diethyl-9H-fluoren-7-yl)vinyl]-p-terphenyl (PFVtPh) were synthe-
1
sized according to previously reported literature [1,2]. H-NMR spectra were recorded on
a Varian Unity Inova 300Nb spectrometer in CDCl3 as the solvent. The FT-IR spectra
were recorded using a Bruker VERTEX70 FT-IR spectrometer. Elemental analysis (EA)
was measured using an EA 1108 spectrometer. Low- and high-resolution mass spectra
were measured using a Jeol JMS-600 spectrometer in the EI mode and a JMS-T100TD
(
AccuTOF-TLC) in the positive ion mode. The UV-vis absorption spectra were measured
−5
in a dichloromethane solution (10 M) using a Shimadzu UV-1650PC. Photolumines-
cence spectra were obtained on an Aminco-Browman series 2 luminescence spectrometer.
Fluorescent quantum yields were determined in a CH2Cl2 solution at 293 K against the
host (ФDPA = 0.90) as a standard. Thermal properties were measured using thermogravi-
metric analysis (TGA) (DTA-TGA, TA-4000 or DTA-6100) under nitrogen at a heat-
ing rate of 10 C min . The HOMO (highest occupied molecular orbital) energy levels
were determined with cyclic voltammetry (CV) in solutions of 0.1 M supporting elec-
trolyte (tetra-n-butylammonium hexafluorophosphate, TBAPF6) and 1.0 mM substrate in
dry dichloromethane under an argon atmosphere, using ferrocene as an internal standard.
The LUMO (lowest unoccupied molecular orbital) energy levels were calculated by sub-
tracting the corresponding optical band gap energies from the HOMO energy values. The
energy band gaps were determined from the intersection of the absorption and photolumi-
nescence spectra. LUMO (lowest unoccupied molecular orbital) energy levels were calcu-
lated by subtracting the corresponding optical band gap energies from the HOMO energy
values.
◦
−1
Synthesis
General Procedure for the Suzuki Cross-Coupling Reaction. A mixture of thianaphthene-2-
boronic acid (690 mg, 3.88 mmol), corresponding dibromoarylene (0.97 mmol), Pd(PPh3)4
(
112 mg, 0.097 mmol), Na2CO3 (411 mg, 3.88 mmol) in H2O (10 mL), THF (30 mL)
◦
and toluene (30 mL) were heated at 85 C under N2 for 14 h. After the reaction
had finished, the solution was extracted twice with toluene. The combined organic

Blue-Light-Emitting Arylene Derivatives
[433]/17
layers were washed with brine and dried over MgSO4. After filteration and evapora-
tion of the solvent, the crude product was purified by column chromatography (silica gel,
hexane:dichloromethane, 10:1).
1
,4-bis(benzothiophen-2-yl)naphthalene (2): Yield: 78.8%. 1H NMR (CDCl3,
3
00 MHz): δ 8.40–8.37 (m, 2H), 7.93 (d, J = 7.2 Hz, 2H), 7.88 (d, J = 6.7 Hz, 2H),
7
.71 (s, 2H), 7.58–7.54 (m, 2H), 7.52–7.51 (m, 2H), 7.45–7.35 (m, 4H); FT-IR (ATR,
−1
+
cm ): 3006, 1738, 1366, 1229, 1033, 827, 770, 744; EIMS (m/z): 393 [M ]. HRMS-TOF
+
(
7
M +H) Calcd for C26H17S2 393.0772, found: 393.0754; Anal. Calcd for C26H16S2 C
9.55, H 4.11, S 16.34, found: C 79.03, H 4.17 S 18.28.
, 4 -bis(benzothiophen-2-yl)binaphthyl (3): Yield: 82.5%. 1H NMR (CDCl3,
ꢀ
4
3
7
00 MHz): δ 8.42 (d, J = 8.5 Hz, 2H), 7.94 (d, J = 7.6 Hz, 2H), 7.92–7.89 (m, 2H),
13
.79 (d, J = 7.2 Hz, 2H), 7.59–7.55 (m, 6H), 7.52–7.49 (m, 2H), 7.48–7.34 (m, 6H);
C
NMR (CDCl3, 75 MHz): δ 142.4, 140.6, 140.5, 139.3, 133.4, 132.7, 132.1, 128.2, 127.5,
−1
1
1
27.3, 126.8, 126.6, 126.3, 124.8,124.6, 124.6,123.9,122.4. FT-IR (ATR, cm ): 3007,
738, 1376, 1216, 1032, 833, 767, 744. EI-MS (m/z): 519 [M ]. HRMS-TOF (M +H)
+
+
Calcd for C36H23S2 519.1241, found 519.1232; Anal. Calcd for C36H22S2 C 83.36, H 4.28,
S 12.36, found: C 82.77, H 4.30, S 13.34.
ꢀ ꢀ ꢀ
,4 -bis(5-methylthiophen-2-yl)binaphthyl (4): A mixture of 4,4 -dibromo-1,1 -
4
binaphthyl (300 mg, 0.73 mmol), 5-methyl-2-thiophene boronic acid (310 mg, 2.18 mmol),
K3PO4 (309 mg, 1.46 mmol), Pd2dba3 (2 mol%) and SPhos (8 mol%) was heated to
◦
8
0 C in n-butanol with stirring for 12 h. The crude product was purified via flash column
chromatography on silica gel (Hexanes) to provide the title compound in a 36.6% yield
1
(
2
119 mg) as a white solid. Yield: 36.6%. H NMR (CDCl3, 300 MHz): δ 8.59 (d, J = 8.7 Hz,
H), 7.66,7.64 (d, J = 7.2 Hz, 2H), 7.52–7.46 (m, 6H), 7.34–7.30 (m, 2H), 7.13–7.12 (d,
13
J = 3.3 Hz, 2H), 6.89–6.88 (m, 2H), 2.61 (s, 6H); C NMR (CDCl3, 75 MHz): δ 140.4,
1
1
4
39.4, 138.4, 133.2, 132.8, 131.9, 127.5, 127.4, 127.3, 127.0, 126.2, 126.1, 126.0, 125.6,
+
+
5.4. EIMS (m/z): 447[M ]. HRMS-TOF (M +H). Calcd for C30H22S2: 446.6257, found:
46.6251.
Fabrication of OLEDs
To fabricate OLEDs, indium-tin-oxide (ITO) thin films coated on glass substrates were used,
which had 30 ꢀ per square of sheets resistivity with 100 nm of thickness. The ITO-coated
glass was cleaned in an ultrasonic bath by the following sequence: acetone, methyl alcohol,
and distilled water; it was then stored in isopropyl alcohol for 48 h and dried by a N2 gas
−
2
gun. The substrates were treated by O2 plasma under 2.0 × 10 torr at 125 W for 2 min
−7
[
24]. All organic materials and metals were deposited under high vacuum (5 × 10 torr).
Two types of multilayer devices, A and B, were fabricated as follows: (device A) ITO/NPB
50 nm)/blue-emitting material 3-4 (30 nm)/Bphen (30 nm)/Liq (2 nm)/Al; (device B)
(
ITO/NPB (50 nm)/8% PFVtPh: compound 3–4 (30 nm)/Bphen (30 nm)/Liq (2 nm)/Al,
where NPB were used as the hole -transporting layer, Bphen as the electron-transporting
layer, and Liq: Al as the composite cathode. The CIE coordinates of the OLEDs were mea-
sured with a Keithly 2400, Chroma meter CS-1000A. Electroluminescence was measured
using a Roper Scientific Pro 300i. The current-voltage-luminance (J-V-L) characteristics,
luminous efficiency (LE), Power efficiency (PE), and CIE chromaticity coordinates of the
devices were measured using a Keithly 2400 source measurement unit and Chroma meter
CS-1000A. Electroluminescence was measured using a Roper Scientific Pro 300i.

18/[434]
S. Oh et al.
Results and Discussion
Scheme 1 shows the structure and synthetic route of the designed blue fluorescent materials
–4. These blue light emitting materials were synthesized by Suzuki coupling reaction be-
1
tween the boronic acid and dibromoarylene afforded the target compounds with moderate
yields. After the conventional purifications such as column chromatography and recrys-
tallization, these newly synthesized blue-emitting materials (1–4) were purified further by
−
3
1
train sublimation at a reduced pressure, below 10 Torr, and fully characterized with H
13
and C NMR, FT-IR, and low- and high-resolution mass spectrometry.
(a)
(b)
Br
(HO)2B
Br
Br
88.6%
87.8%
A
B
S
Br
Br
Br
Br
S
1
2
S
(a)
S
(
HO) B
S
2
S
S
Br
Br
Br
S
S
3
S
(c)
Br
(HO)2B
4
Scheme 1. Molecular structures and synthetic routes of new host materials (1–4). Condition:
a) Pd(PPh CO (2M), THF/toluene, reflux, 14 h. (b) Br /CH Cl , rt, 2 h. (c) Pd dba , K PO
XPhos, n-Butanol, reflux, 14 h.
(
3
)
4, Na
2
3
2
2
2
2
3
3
4
,
High-temperature resistance is a desired feature of OLED materials because of the
unavoidable joule heating under device operating conditions. The thermal properties of
1
–4 were measured by thermogravimetric analysis (TGA, TA-4000 or DTA-6100) under
◦
−1
nitrogen rate of 10 C min , and are listed in Table 1. The TGA thermogram of the
compounds is shown in Fig. 1. All compounds under a nitrogen atmosphere, with the
exception of 2, showed decomposition temperatures (Td: corresponding to 5% weight loss)

Blue-Light-Emitting Arylene Derivatives
[435]/19
Table 1. Photophysical data of blue host materials 1–4
a
a
b
Abs λmax PL λmax PL λmax HOMO LUMO Band gap
Фc Td [ C]
◦
d
Compound
[nm]
[nm]
[nm]
[eV]
[eV]
[eV]
1
2
3
4
380
329
322
328
377
451, 63
440, 69
439, 68
436, 67
425, 54
462
450
441
438
447
5.70
5.81
5.82
5.74
5.50
2.66
2.33
2.56
2.48
2.50
3.04
3.48
3.26
3.26
3.00
0.05
0.22
0.56
0.34
0.54
358
248
384
340
397
MADN
aCH
Cl
solution (10 M). Thin film. Using 9,10-diphenylanthracene (DPA) as a standard; λex
−5
b
c
=
2
2
d
3
60 nm (Ф = 0.90 in CH
2 2
Cl ). Td: the decomposition temperature (5% loss weight).
◦
higher than 340 C. The data demonstrates that the thermal stability of these materials
improves as the size of the aryl groups at the core unit. The excellent thermal stability of
compound 3 may be attributed to a rigid benzothiophenyl-substituted binaphthyl unit in the
molecular core structure. Presumably, the non-coplanar molecular structure of 3 resulting
ꢀ
from the large distortional angle of the 1,1 -binaphthyl units would enable to form thermally
stable amorphous thin films.
UV-vis absorption and photoluminescent (PL) spectra of 1–4 in dichloromethane are
shown in Fig. 2, and the results are summarized in Table 1. Compound 1 exhibited a UV-vis
absorption peaks at 380 nm with the characteristic vibronic peaks of isolated anthracene,
while compounds 2–4 showed shorter main absorption peaks at 329, 322, and 328 nm,
respectively. Figure 2(b) shows the emission spectra of blue materials 1–4 with a PL
maximum of 439–451 nm. The PL emission spectra of 2–4 are almost identical, whereas
the PL spectrum of 1 is red-shifted with a peak at 451 nm. This is likely due to the increase
in π-conjugation length by the anthracene group. Also, PL studies on film of 1–4 were
also performed to examine the emission in the condensed phase. Particularly, the film of
3
58°C
3
100
84°C
2
48°C
80
60
40
20
0
340°C
1
2
3
4
100
200
300
400
500
600
Temperature (°C)
◦
−1
.
Figure 1. TGA curves of new blue host materials recorded at a heating rate of 10 C min

20/[436]
S. Oh et al.
1
0
0
0
0
0
.0 (a)
1.0 (b)
0.8
1
1
2
3
4
2
3
4
.8
.6
.4
.2
.0
0.6
PFVtPh
0.4
0.2
0.0
300
350
400
450
500
550
350
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
Figure 2. (a) The absorption spectra of new host materials, (b) The emission spectra of new host
materials and absorption spectrum of dopant material (PFVtPh) in CH Cl
2
2
.
compounds 3 and 4 exhibited the PL spectra, which are similar to those in the solution
state. Thus, compounds 3 and 4 do not appear to reveal severe aggregation due to the
nonplanar binaphthyl moieties. In Fig. 2(b), the emission spectra of blue materials 1–4
overlap the absorption spectrum of PFVtPh, indicating that it can more effectively accept
energy from materials 2–4 through a F o¨ rster-type energy transfer. Particularly, emission
spectra of compounds 2–4 showed a favorable overlap with the apsorption of a common
blue dopant (PFVtPh), respectively. Thus, this implies that 2–4 can act as good host
materials in devices using PFVtPh as a dopant. The quantum yields of compounds 1–4 are
given in Table 1. The fluorescence quantum yield of compounds 1–4 in dichloromethane
solution at 298 K was measured using (Ф = 0.90) as a calibration standard. The overall
quantum yields of all compounds, with the exception of 1, was high (Ф = 0.22–0.56),
suggesting that these materials have highly efficient electroluminescent properties in OLED
devices.
The highest occupied molecular orbital (HOMO) energy levels of the compounds were
calculated using cyclic voltammetry, using a three-electrode cell with ferrocene (4.8 eV)
[25] as the internal standard. The respective values of the HOMOs for 1–4 thus calculated
were 5.70, 5.81, 5.82, and 5.74 eV, respectively. The four compounds also possessed wide
optical energy band gaps between 3.04 - 3.48 eV. From the HOMO values and the optical
band gap energies available from the intersection of the absorption and photolumines-
cence spectra, the LUMO energies of 1–4 were calculated as: 2.66 (1); 2.33 (2); 2.56 (3);
2.46 eV(4). These compounds possessed higher energy band gaps than these of PFVtPh
(
2.82 eV), implying that energy transfer from materials 1–4 to PFVtPh through a F o¨ rster
energy transfer was expected, indicating them as good host materials in OLED devices
using PFVtPh as a dopant.
Compounds 3 and 4 were selected for electroluminescence measurement because of
suitable emission wavelengths and higher quantum yields. Two types of multilayer devices,
A and B, were fabricated as follows: (device A) ITO/ NPB (50 nm)/ 3 or 4 (30 nm)/ Bphen
(
(
30 nm)/ Liq (2 nm)/ Al; (device B) ITO/ NPB (50 nm)/ 8% PFVtPh: compound 3 or 4
30 nm)/ Bphen (30 nm)/ Liq (2 nm)/ Al. Particularly, B types of devices were fabricated
to test the usefulness of 3 and 4 as the host materials and improve the EL efficiencies of
A type of devices by doping with the suitable dopant. The schematic device structures
and energy level diagrams are shown in Fig. 3. The performance characteristics of these
devices are summarized in Table 2. The EL spectra of devices are shown in Fig. 4. The

Blue-Light-Emitting Arylene Derivatives
[437]/21
Figure 3. Energy-level diagrams of OLEDs.
current density-voltage (J-V) and luminance-voltage (L-V) characteristics for non-doped
and doped (8% PFVtPh) devices are shown in Fig. 5(a). Variations in the luminous and
power efficiencies of device A, as a function of the current density, are shown in Figs
6(a) and (b). The device 3A using was found to be more efficient than the device 4A.
Presumably, the higher quantum yield of 3 (Ф = 0.56) than that of 4 (Ф = 0.34) would
contribute the better EL efficiencies of device 3A than device 4A. Device 3A showed the
−1
efficient blue emission with a maximum luminous efficiency of 1.19 cd A , a maximum
quantum efficiency of 1.60% and CIE coordinates of (0.159, 0.092). In order to increase
EL efficiencies, these materials were doped with the blue fluorescent dopant PFVtPh at a
Table 2. Electroluminescent characteristics of the devices A (non-doped) and B (doped)
Device efficiency Max. efficiency
−
1
−1
Max. L
[cd A ,
[cd A ,
EL, FWHM
[nm]
CIE
[x,y] at 9V
Device
Vona [cd m ]
−2
lm W ,%]
−1
b
lm W ,%]
−1
3
3
4
4
A
B
A
B
3.3
3.0
5.6
4.0
457
3465
428
2134
954
0.97, 0.48, 1.28 1.19, 0.99, 1.60 444, 60 0.159, 0.092
4.93, 2.79, 3.42 7.58, 7.82, 5.23 459, 60 0.151, 0.185
0.56, 0.23, 0.79 0.58, 0.27, 0.80 448, 62 0.151, 0.082
3.28, 1.28, 2.05 3.61, 2.06,2.27
463, 64 0.149, 0.219
MADN-A 4.0
1.08, 0.48, 0.98 1.35, 1.01, 1.45 442, 55 0.153, 0.080
MADN-B 3.0 13330 9.76, 6.02, 6.40 10.1, 9.86, 6.65 457, 60 0.152, 0.192
a
2
b
−2
Turn-on voltage at 1cd/m . At current density of 20 mAcm .

22/[438]
S. Oh et al.
1.0
0.8
0.6
0.4
0.2
0.0
Device 3A
Device 3B
Device 4A
Device 4B
350
400
450
500
550
600
650
Wavelength (nm)
Figure 4. EL spectra of blue emitting devices 3A–4B.
concentration of 8% in the same device structure shown in Fig. 3. Because materials 3 and
4
have higher energy gaps (3.26 eV) compared to the band gap of PFVtPh (Eg ∼ 2.83 eV),
it is possible that efficient F o¨ rster energy transfer takes place from 3 and 4 to PFVtPh.
Thus, the emission of device 3B and 4B would originate from the PFVtPh dopant by an
efficient energy transfer from host 3–4 (Fig. 2). Also, compared to device A, the higher
EL efficiencies of device B excluded the possible contribution of host 3 to the emission
of device 3B. In addition, the hole-trapping, followed by the direct recombination with
electrons at the dopant sites, could additionally contribute to the enhanced EL efficiency.
Particularly, PFVtPh dopant in device 3B can act as a hole trap because the HOMO level
of PFVtPh is near 5.4 eV, as measured with a AC-2 photoelectron spectrometer, which is
higher than the host material 3 (5.82 eV). As a result, device 3B shows the highly efficient
−1
blue emission with a maximum luminous efficiency of 7.58 cd A , a maximum quantum
efficiency of 5.18% and the CIE coordinates of (0.151, 0.185). Notably, doped-devices
3B and 4B showed higher EL efficiency than non-doped devices 3A and 4A, which may
be due partly to the effective exciton formation on dopant materials. This study clearly
1
1
1
1
1
80
60
40
20
00
(
a)
(
b)
3
2
1
0
10
3
3
4A
4
A
B
3
3B
A
1
1
1
0
0
0
4A
B
4B
8
6
4
2
0
0
0
0
0
-1
10
-2
10
0
2
4
6
8
10
12
0
2
4
6
8
10
12
Voltage (V)
Voltage (V)
Figure 5. J-V characteristics (a) and L-V characteristics (b) of the devices 3A–4B.

Blue-Light-Emitting Arylene Derivatives
[439]/23
8
6
4
2
0
(a)
Device 3A
Device 3B
Device 4A
Device 4B
0
20
40
60
80
100
2
120
Current density
(
mA/cm
)
4
3
2
1
0
1
1
1
1
1
1
0
0
0
0
0
10
(b)
(c)
Device 3A
Device 3B
Device 4A
Device 4B
Device 3A
Device 3B
Device 4A
Device 4B
0
1
0
-1
1
0
0
20
40
60
80
100
120
0
20
40
60
80
100
120
2
2
Current density
(mA/cm
)
Current density
(
mA/cm
)
Figure 6. Power efficiencies (a), luminous efficiencies (b), and external quantum efficiencies (c) as
a function of voltage for the devices 3A–4B.
suggests that efficiencies of blue OLEDs can be improved by doping with the suitable
dopant in a host. Interestingly, compared device MADN B, the CIE coordinates of device
3B the improved from (0.152, 0.192) to (0.151,0.185). Presumably, the different solvation
of dopant PFVtPh in MADN and compound 3 would contribute to the improved the blue
color coordinates of device 3B. This study clearly demonstrates the excellent properties of
host material 3, containing thiophene groups, for application in deep blue emitting materials
in OLEDs.
Conclusions
We demonstrated synthesis and electroluminescent properties of blue fluorescent arylene
derivatives end-capped with benzothiophene and thiophene groups. A facile synthesis of
these arylene derivatives was achieved with palladium-catalyzed Suzuki cross coupling as
a key step. The non-doping OLED device using the compound 3 showed the efficient deep
−1
blue emission with a maximum luminance efficiency of 1.19 cd A , a maximum external
quantum efficiency of 1.60% and CIE coordinate of (0.159, 0.092) at 9.0 V. Moreover, using
the compound 3 as a blue host for the PFVtPh dopant, device 3B furnished a efficient blue
−
−1
1
−1
−2
OLED with a maximum luminous efficiency of 7.58 cd A (4.90 cd A at 20 mA cm ),
−1
−2
maximum power efficiency of 7.82 lm W (2.80 lm W at 20 mA cm ), maximum
−2
external quantum efficiency of 5.23% (3.42% at 20 mA cm ), and CIE coordinate of
0.151, 0.185) at 9.0 V.
(

24/[440]
S. Oh et al.
Acknowledgments
This work was supported by a grant 20110004655 from the Korea Science and Engineering
Foundation.
References
[
[
1] Kotha, S., Ghosh, A. K., & Deodhar, K. D. (2004). Synthesis, 4, 549.
2] Kwon, Y. S., Lee, K. H., Kim, G. Y., Seo, J. H., Kim, Y. K., & Yoon, S. S. (2009). J. Nanosci.
Nanotechnol., 9, 7056.
[
[
[
[
[
[
[
3] Huang, F., Niu, Y. H., Zhang, Y., Ka, J. W., Liu, M. S., & Jen, A. K.-Y. (2007). Adv. Mater., 19,
2
010.
4] Lee, J. Y., Park, J. Y., Min, S.-H., Lee, K.-W., & Baek, Y. G. (2007). Thin Solid Films, 515,
726.
5] Lee, K. H., Kang, L. K., Lee, J. Y., Kang, S., Jeon, S. O., Yook, K. S., Lee, J. Y., & Yoon, S. S.
2010). Adv. Funct. Mater., 20, 1345.
6] Lee, K. H., Son, C. S., Lee, J. Y., Kang, S., Yook, K. S., Jeon, S. O., Lee, J. Y., & Yoon, S. S.
2011). Eur. J. Org. Chem., 25, 4788.
7
(
(
7] Lee, K. H., You, J. N., Kang, S., Lee, J. Y., Kwon, H. J., Kim, Y. K. & Yoon, S. S. (2010). Thin
Solid Films, 518, 6253.
8] Sun, Y., Duan, L., Zhang, D., Qiao, J., Dong, G., Wang, L., & Qiu, Y. (2011). Adv. Funct. Mater.,
21, 1881.
9] Lee, K. H., Park, J. K., Seo, J. H., Park, S. W., Kim, Y. S., Kim, Y. K., & Yoon, S. S. (2011).
J. Mater. Chem., 21, 13640.
[10] Park, J. K., Lee, K. H., Park, J. S., Seo, J. H., Kim, Y. K., & Yoon, S. S. (2011). J. Nanosci.
Nanotechnol., 11, 4357.
[
[
11] Zhang, T., Liu, D., Wang, Qi., Wang, R., Ren, H., & Li, J. (2011). J. Mater. Chem., 21, 12969.
12] Park, J. K., Lee, K. H., Kang, S., Lee, J. Y., Park, J. S., Seo, J. H., Kim, Y. K., & Yoon, S. S.
(2010). Organic Electronics, 11, 905.
[
[
[
[
[
[
13] Shen, J. Y., Yang, X. L., Huang, T. H., Lin, J. T., Ke, T. H., Chen, L.-Y., Wu, C. C., & Yeh, M.
C. (2007). Adv. Funct. Mater., 17, 983.
14] Jou, J. H., Wang, W. B., Chen, S. Z., Shyue, J. J., Hsu, M. F., Lin, C. W., Shen, S. M., Wang, C.
J., Liu, C. P., Chen, C. T., Wud, M. F., & Liud, S. W. (2010). J. Mater. Chem., 20, 8411.
15] Tonzola, C. J., Kulkarni, A. P., Gifford, A. P., Kaminsky, W., & Jenekhe, S. A. (2007). Adv.
Funct. Mater., 17, 863.
16] Kim, J. U., Lee, H. B., Shin, J. S., Kim, Y. H., Joe, Y. K., Oh, H. Y., Park, C. G., & Kwon, S.
K. (2005). Synth. Met., 150, 27.
17] Chao, T.-C., Lin, Y.-T., Yang, C.-Y., Hung, T. S., Chou, H.-C., Wu, C.-C., & Wong, K.-T. (2005).
Adv. Mater., 17, 992.
18] Barbarella, G., Favaretto, L., Sotgiu, G., Zambianchi, M., Bongini, A., Arbizzani, C.,
Mastragostino, M., Anni, M., Gigli, G., & Cingolani, R. (2000). J. Am. Chem. Soc., 122,
11971.
[
[
[
19] Katz, H. E., Laquindanum, J. G., & Lovinger, A. (1998). J. Chem. Mater., 10, 633.
20] Fichou, D. J. (2000). Mater. Chem., 10, 571.
21] Kim, S., Lee, J. W., Kang, S. O., Ko, J., Yum, J.-H., Fantacci, S., Angellis, F. D., Censo, D. D.,
Nazeeruddin, M. K., & Gr a¨ tzel, M. (2006). J. Am. Chem. Soc., 128, 16701.
22] Kim, M. S., Chio, B. K., Lee, T. W., Shin, D., Kang, S. K., Kim, J. M., Tamura, S., & Noh, T.
[
[
(
2007). Appl. Phys. Lett., 91, 251111.
23] Lee, J. Y., Park, J.-Y., Min, S.-H., Lee, K.-W., & Baek, Y. G. (2007). Thin Solid Films, 515,
726.
7
[
[
24] Kauffman, J. M., & Moyna, G. (2003). J. Org. Chem., 68, 839.
25] Pommerehne, A., Vestweber, H., Guss, W., Mahrt, R. F., B a¨ ssler, H., Porsch, M., & Daub, J.
(1995). Adv. Mater., 7, 551.