Blue organic light-emitting diodes containing anthracene derivatives with end-capping phenyl group

Article abstract of DOI:10.1080/15421406.2012.689157

We have synthesized and characterized new blue host materials for OLEDs; 9,10-di-o-tolylanthracene (1), 2-tert-butyl-9,10-diphenylanthracene (2), 10,10-diphenyl-9,9-bianthracene (3), and 1,4-bis(10-phenylanthracen-9-yl)benzene (4). To explore electroluminescent properties of these materials, multilayered OLEDs with the configuration of ITO/NPB (50nm)/Blue emitters (1-4) (30nm)/Liq (2nm)/Al (100nm) were fabricated. Among those non-doped devices, the device 4a employing 4 as an emitter showed high efficiencies of 4.11 cd/A, 3.31 lm/W, and 2.35%, respectively. The device 2b employing 2 as host material for PFVtPh blue dopant material exhibited excellent efficiencies with 5.64 cd/A, 4.14 lm/W, and 4.54%. Taylor and Francis Group, LLC.

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Blue Organic Light-Emitting Diodes
Containing Anthracene Derivatives With
End-Capping Phenyl Group
a
a
b
Heung Soo Jang , Kum Hee Lee , Seok Jae Lee , Young Kwan Kim
b
a
&
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
Version of record first published: 02 Aug 2012.
To cite this article: Heung Soo Jang , Kum Hee Lee , Seok Jae Lee , Young Kwan Kim & Seung Soo
Yoon (2012): Blue Organic Light-Emitting Diodes Containing Anthracene Derivatives With End-Capping
Phenyl Group, Molecular Crystals and Liquid Crystals, 563:1, 173-184
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Mol. Cryst. Liq. Cryst., Vol. 563: pp. 173–184, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.689157
Blue Organic Light-Emitting Diodes Containing
Anthracene Derivatives With End-Capping
Phenyl Group
1
1
2
HEUNG SOO JANG, KUM HEE LEE, SEOK JAE LEE,
2
1,∗
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
We have synthesized and characterized new blue host materials for OLEDs; 9,10-di-
ꢀ
ꢀ
o-tolylanthracene (1), 2-tert-butyl-9,10-diphenylanthracene (2), 10,10 -diphenyl-9,9 -
bianthracene (3), and 1,4-bis(10-phenylanthracen-9-yl)benzene (4). To explore electro-
luminescent properties of these materials, multilayered OLEDs with the configuration of
ITO/NPB (50 nm)/Blue emitters (1–4) (30 nm)/Liq (2 nm)/Al (100 nm) were fabricated.
Among those non-doped devices, the device 4a employing 4 as an emitter showed high
efficiencies of 4.11 cd/A, 3.31 lm/W, and 2.35%, respectively. The device 2b employing
2
5
as host material for PFVtPh blue dopant material exhibited excellent efficiencies with
.64 cd/A, 4.14 lm/W, and 4.54%.
Keywords Blue fluorescent materials; deep blue emitting materials; diphenylan-
thracene; electroluminescence; OLEDs
Introduction
Since the pioneering report of Tang et al., organic light emitting devices (OLEDs) have
attracted enormous interest because of their high efficiency, pure color reproduction, fast
response, and wide viewing angle [1]. For full-color display application, efficient blue,
green, and red emitters are required. Highly efficient and stable green OLEDs have already
been realized [2]. To date, a number of π-conjugated materials have been reported to
exhibit electroluminescence (EL) ranging from red to green and blue. In particular, it is
difficult to generate high-performance blue emissions because the intrinsically wide band-
gap makes it hard to inject charges into blue emitters. As a result, the electroluminescence
(
EL) performance of blue light-emitting devices is generally inferior to those of green- and
red-EL. Thus, the development of novel blue light-emitting materials is of current concern
3]. Recently, various blue emitting materials, such as anthracene [4], di(styryl)arylene [5],
[
and tetra(phenyl)silyl derivatives [6] have been developed.
Anthracene derivatives commonly possess excellent photoluminescence (PL) and elec-
troluminescence (EL) properties [7–9]. Among those, 9,10-Diphenylanthracene (DPA) is
a good candidate for blue host material for OLEDs because it has the suitable band-gap
∗
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
173

174
H. S. Jang et al.
(
E = 3.2 eV) and excellent luminescent quantum yield (Ф = 0.90) in dilute solution [10]
However, the self-aggregation between DPA reduces greatly the EL performances of solid
state OLEDs. Furthermore, it tends to be crystallized in thin films, thereby limiting its
OLEDs applications. For example, crystal formation deconstructs film homogeneity and
raises the resistance of the sample, ultimately leading to device failure [11–13].
In order to prevent these problems, we have synthesized new host materials; 9,10-
di-o-tolylanthracene (1), 2-tert-butyl-9,10-diphenylanthracene (2), 10,10 -diphenyl-9,9 -
bianthracene (3), and 1,4-bis(10-phenylanthracen-9-yl)benzene (4) (Scheme 1). All com-
pounds (1–4) are designed for reducing the intermolecular interaction and preventing the
self-aggregation in solid state devices to improve EL performances [9]. In addition, we
have investigated their optical and electroluminescent properties. Multilayered OLED are
fabricated by using these host materials as the emitting layer (non-doped) and the host
material for PFVtPh [14] and PCVtPh [15] (doped).
ꢀ
ꢀ
Experimental
Synthesis
o-Bromotoluene, bromobenzene, anthraquinone, 2-tert-butylanthraquinine, phenyl boronic
acid, and 1,4-dibromobenzene were used as received from Aldrich or TCI.
ꢀ ꢀ
-Phenyl-10-anthracene boronic acid [16], 10,10 -dibromobiphenyl [17], 4 -[2-(2-
9
Diphenylamino-9,9-diethyl-9H-fluoren-7-yl)vinyl]-p-terphenyl (PFVtPh) [14], and 3-(N-
phenylcarbazol)vinyl-p-tert-phenyl (PCVtPh) [15] were synthesized as reported previ-
ously. The solvent were dried using standard procedures. All reagents were used as received
from commercial sources, unless otherwise stated. All reactions were performed under N2
atmosphere.
9
,10-Di-o-tolylanthracene (1): To 1-bromotoluene (1.22 g, 7.13 mmol) dissolved in
◦
THF (10 mL)was added 4.6 mL of n-butyllithium (1.6 M in hexane) slowly at −78 C. To
the suspension, anthraquinone (0.5 g, 2.37 mmol) in THF (10 mL) was added dropwise
◦
at −78 C. The mixture was left to reach room temperature. The water was added and the
organic phase separated. The water phase was extracted with diethyl ether. The combined
organic fractions were dried over magnesium sulfate and the volatiles removed in vacuo to
deliver a foamy residue. To this residue were added potassium iodide (2.04 g, 12.29 mmol),
sodium hypophosphite monohydrtate (2.04 g, 23.19 mmol), and acetic acid (25 mL), and
the mixture was heated under reflux for 3 h. After cooling, the crude solid was filtered,
washed with water, and recrystallized from CH2Cl2/EtOH, afforded 1 (1.45 g, 81.0%).
1
H-NMR (300 MHz, CDCl3) [δ ppm]: 7.56 (dd, J = 3.3, 6.6 Hz, 4H), 7.48–7.46 (m, 4H),
13
7
[
2
.43–7.38 (m, 4H), 7.32 (dd, J = 3.6, 6.8 Hz, 6H), 1.93 (s, 6H). C-NMR (75 MHz, CDCl3)
δ ppm]: 138.7, 138.1, 136.5, 131.6, 131.5, 130.3, 129.9, 128.1, 127.0, 126.1, 126.0, 125.4,
−1
+
0.0. FT-IR [ATR]: ν 3708, 3680, 2981, 2972, 1738, 1371, 1055, 771, 752 cm MS(EI )
m/z 358 (M ). Anal. calcd for C28H22: C 93.81, H 6.19; found: C 93.11, H 6.39.
+
2-tert-Butyl-9,10-diphenylanthracene (2): To 1-bromobenzene (0.89 g, 5.67 mmol)
dissolved in THF (10 mL)was added 3.54 mL of n-butyllithium (1.6 M in hexane) slowly
◦
at -78 C. To the suspension, 2-tert-butylanthraquinone (1.38 g, 5.0 mmol) in THF (10 mL)
◦
was added dropwise at −78 C. The mixture was left to reach room temperature. The
distilled water was added and the organic phase separated. The water phase was extracted
with diethyl ether. The combined organic fractions were dried over magnesium sulfate
and the volatiles removed in vacuo to deliver a foamy residue. To this residue were added

Blue OLEDs Containing Anthracene
175
potassium iodide (2.77 g, 16.69 mmol), sodium hypophosphite monohydrtate (2.77 g,
1.53 mmol), and acetic acid (22 mL), and the mixture was heated under reflux for 3 h.
3
After cooling, the precipitate was collected, washed with plenty of distilled water, and dried.
Concentration of the CH2Cl2 solution, followed by column chromatography on silica gel
1
with CH2Cl2/hexane, afforded 2 (1.58g, 89.0%). H-NMR (300 MHz, CDCl3) [δ ppm]:
7
2
1
3
3
.71–7.67 (m, 3H), 7.64–7.54 (m, 7H), 7.50–7.45 (m, 4H), 7.42 (s, 1H), 7.32–7.28 (m,
H), 1.26 (s, 9H). 13C-NMR (75 MHz, CDCl3) [δ ppm]: 147.5, 139.5, 137.1, 136.9, 131.6,
30.3, 129.8, 128.7, 128.6, 128.5, 127.6, 127.2, 126.9, 125.1, 124.9, 124.8, 121.4, 35.2,
−1
+
1.0. FT-IR [ATR]: ν 3709, 3680, 2981, 2971, 1738, 1365, 1055, 700 cm MS(EI ) m/z
+
86 (M ). Anal. calcd for C30H26: C 93.22, H 6.78; found: C 92.67, H 7.03.
ꢀ
ꢀ
ꢀ
ꢀ
1
0,10 -Diphenyl-9,9 -bianthryl (3): 10,10 -dibromo-9,9 -bianthryl (1.2 g, 2.34 mmol)
and phenyl boronic acid (0.85 g, 7.02 mmol), Pd(PPh3)4 (0.41 g, 0.35 mmol), aqueous
.0 M Na2CO3 (2.48 g, 22.8 mmol), and toluene (24 ml) were mixed in a flask. The mixture
2
was refluxed for 4 h. When the reaction was completed, water was added to quench the
reaction. After cooling, the crude solid was collected by filtration, washed with water, and
ethanol. The product was recrystallized from CH2Cl2/EtOH, afforded 3 (0.8 g, 67.8%).
1
H-NMR (300 MHz, CDCl3) [δ ppm]: 7.82 (d, J = 8.7 Hz, 4H), 7.69–7.59 (m, 10H),
13
7
.32 (td, J = 1.2, 7.7 Hz, 4H), 7.25 (d, J = 8.4 Hz, 4H), 7.17–7.12 (m, 4H). C-NMR
(75 MHz, CDCl3) [δ ppm]: 139.3, 138.1, 133.7, 131.7, 131.6, 130.4, 128.7, 127.8, 127.5,
−1
+
1
5
27.4, 125.8, 125.5. FT-IR [ATR]: ν 3062, 1739, 1441, 1363, 768, 706 cm MS(EI ) m/z
+
06 (M ). Anal. calcd for C40H26: C 94.83, H 5.17; found: C 93.40, H 5.30.
1
,4-Bis(10-phenylanthracen-9-yl)benzene (4): 1,4dibromobenzene (1 g, 4.23 mmol)
and 10-phenylanthracen-9-yl boronic acid (2.7 g, 9.32 mmol), Pd(PPh3)4 (0.20 g,
.17 mmol), aqueous 2.0 M Na2CO3 (4.49 g, 42.39 mmol), ethanol (21 ml) and toluene
42 ml) were mixed in a flask. The mixture was refluxed for 3 h. When the reaction was
0
(
completed, water was added to quench the reaction. After cooling, the crude solid was
collected by filtration, washed with water, and ethanol. The product was recrystallized
1
from CH2Cl2/EtOH, afforded 4 (2.1 g, 85.4%). H-NMR (300 MHz, CDCl3) [δ ppm]: 7.99
(
d, J = 8.7 Hz, 4H), 7.76 (t, J = 8.7 Hz, 2H), 7.74 (s, 4H), 7.68–7.59 (m, 8H), 7.55 (dd,
J = 1.5, 8.0 Hz, 4H), 7.50–7.48 (m, 4H), 7.44–7.39 (m, 4H). FT-IR [ATR]: ν 3061, 2360,
−1
+
+
+
2
341, 1736, 1440, 1368, 764, 702 cm MS(EI ) m/z 582 (M ). HRMS-TOF (M +H)
Anal. calcd for C48H32N 583.242576: found: 583.23936. Anal. calcd for C46H30: C 94.81,
H 5.19; found: C 93.58, H 5.29.
Fabrication of OLED
−6
OLEDs using red-light-emitting molecules were fabricated by vacuum (10 torr) thermal
evaporation onto pre-cleaned ITO coated glass substrates. All processes were carefully pro-
duced. The indium tin oxide (ITO) was first cleaned with acetone, methyl alcohol, distilled
water, and kept in isopropyl alcohol for 48 h and dried by N2 gas. The substrates were
−
2
treated by O2 plasma under 2.0 × 10 torr at 125 W for 2 min [18]. All organic materials
−7
and metals were deposited under high vacuum (5 × 10 torr). The OLEDs were fabricated
ꢀ
in the following sequence: ITO/4,4 -Bis(N-(1-naphthyl)-N-phenylamino)biphenyl (NPB)
(
(
50 nm)/Blue emitting materials (1–4) (30 nm)/4,7-Diphenyl-1,10-phenanthroline (Bphen)
30 nm)/Lithium quinolate (Liq) (2 nm)/Al (100 nm), NPB as the hole-transporting layer,
Bphen as the electron-transporting layer, and Liq:Al as the composite cathode. The current
density (J), luminance (L), luminous efficiency (LE), and CIE chromaticity coordinates of

176
H. S. Jang et al.
the OLEDs were measured with a Keithly 2400, Chroma meter CS-1000A. Electrolumi-
nance was measured using a Roper Scientific Pro 300i.
Measurements
1H- and 13C-NMR were recorded on a Varian Unity Inova 300Nb spectrometer. FT-IR
spectra were recorded using a Bruker VERTEX70 FT-IR spectrometer. Elemental analysis
(EA) was measured using a 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.
−5
The UV-Vis absorption spectra were measured in CH2Cl2 solution (10 M) using a
−5
Shimadzu UV-1650PC. The photoluminescence were obtained in CH2Cl2 solution (10
M) and thin film using an Amincobrowman series 2 luminescence spectrometer. The
fluorescent quantum yields were determined in the CH2Cl2 solution at 293 K against the
host (ФDPA = 0.90) as a standard. The energy levels were measured with a low-energy
photo-electron spectrometer (Riken-Keiki, AC-2). Thermal property was measured using
thermogravimetric analysis (TGA) (DTA-TGA, TA-4000) under N2 at a heating rate of
◦
1
0 /min.
Results and Discussion
◦
The thermal property of 1–4 was thermally stable up to 276-402 C, as shown by its
decomposition temperature(Td; corresponding to 5% weight loss) determined from its
Thermogravimetric Analyzer(TGA) measurement. The thermal data of the 1–4 were also
listed in Table 1.
The HOMO energy levels of 1–4 were measured by a low-energy photo-electron
spectrometer (Riken-Keiki AC-2). Their HOMO/LUMO energy levels were −5.85/−2.67,
−
5.76/−2.64, −5.75/−2.68, and −5.71/−2.61, respectively. Also, the optical energy band
gaps (Eg) of 1–4 were 3.18, 3.14, 3.07, and 3.10 eV, respectively, as determined from the
absorption spectra. All compounds have higher energy band gaps (≥ 3.07 eV) than those
of PFVtPh(2.82 eV) and PCVtPh(3.10 eV). Thus, it is possible that the efficient F o¨ rster
energy transfer occur from 1–4 to PFVtPh and PCVtPh.
Figure 1 (a) showed that the emission spectra of the host materials (1–4) overlap
with the absorption spectra of dopant materials (PFVtPh and PCVtPh), respectively.
Table 1. Optical properties of new host materials
UVmaxb PLmaxb PLmaxc FWHMd
HOMO/
Eg
a
◦
LUMO [eV] [eV] Фe
Compound Td [ ]
[nm]
[nm]
[nm]
[nm]
1
2
3
4
276
274
374
402
397
375
375
402
398
403
419
452
417
432
445
464
446
447f
40
53
80
48
60f
−5.85/−2.67 3.18 0.85
−5.76/−2.64 3.14 0.96
−5.75/−2.68 3.07 0.52
−5.71/−2.61 3.10 0.85
f
f
f
−5.50 /−2.50 3.0f 0.54
f
f
MADN
398
436
−
5
[
a] The decomposition temperature (5% loss weight). [b] CH
d] FWHM in thin film. [e] Using 9,10-diphenylanthracene as a standard; λex = 360 nm (Ф = 0.90
in CH Cl ). [f.] Ref. 21.
2 2
Cl solution (10 M). [c] Thin film.
[
2
2

Blue OLEDs Containing Anthracene
177
Figure 1. (a) The emission spectra of the host materials (1–4) and absorption spectra of dopant
materials (PFVtPh and PCVtPh) in CH Cl solution, and (b) the emission spectra of 1–4 in solution
2 2
and thin film.
Presumably, PFVtPh (2.82 eV) can effectively accept energy from the host materials (1–4)
through F o¨ rster-type energy transfer than PCVtPh (3.10 eV). The maximum emission
peaks for 1–4 in CH2Cl2 solution ranged from 403 to 452 nm in the deep-blue region.
In particular, 1 is the shorter emission peak (403 nm) than the others in PL spectra. This
result indicates that the introduction of ortho-methyl groups in 9,10-diphenylanthracene
can prevent π-conjugation between anthracene and phenyl moieties through the steric
hindrance. Interestingly, compared to the PL spectrum of 2 and 4, that of 3 shows a red
shift (ca. 35 nm). Their full width at half maximum (FWHM), and the overall quantum
yields of all compounds with the exception of 3 are narrow bandwidth (ca. 40–53 nm) and
high values (ꢀ = 0.85–0.96). As shown in Fig. 1 (b), the emission spectra in thin films of 1–4
are red-shifted compared with those in CH2Cl2 solution owing to the solid-sate effect [19].
The energy band diagrams of the devices 1a–4a are depicted in Fig. 2. The EL
properties of the devices 1a–4a are summarized in Table 2. As shown in Fig. 3, the devices
2a–4a emit blue region at 441–446 nm. Also, their full-width at half maximum (FWHM)
are narrow (56–68 nm). In the case of the device 1a, neither the light nor current is nearly
occurred. Assumedly, the current leakage or catastrophic device failure in the device 1a is
generated, due to the formation of pin-hole or rough surface in thin film [12–14]. Fig. 4
shows the luminance-voltage-current density (L-V-J), luminous efficiencies (LE), power
efficiencies (PE), and external quantum efficiency (EQE) of the devices 1a–4a, respectively.
Devices 2a–4a reveal low turn-on voltages no greater than 4.0 V. The device 4a displays
the excellent EL performances; its luminous efficiency (LE), power efficiency (PE), and
external quantum efficiency (EQE) reach 4.11 cd/A, 3.31 lm/W, and 2.36% (3.16 cd/A,
2
1
.60 lm/W, and 1.80% at 20 mA/cm ), respectively. According to the energy diagrams in
Fig. 2, we attribute high efficiencies of the device 4a to the smaller barrier (0.31 eV) for
hole injection from HTL (NPB) to the EML (4). In the case of 4a having a little difference
between the HOMO values of HTL and EML, the holes from NPB were easily transferred
to EML. This result could be attributed the more balanced charge-transporting properties
within the emissive layer achieved by better charge injection and confinement provided
by HTL(NPB). Although the EL efficiencies are the highest in the device 4a, it appears
at sky-blue region with the CIE coordinates (0.232, 0.237) at 7.0 V because it seems
that the excimer or exciplex formation is taken place in device 4a as shown in the EL spectra.

178

Blue OLEDs Containing Anthracene
179
Figure 2. Energy diagrams of non-doped devices 1a–4a.
In addition, in order to improve the efficiencies, we doped these host materials (1–4)
with blue dopant materials (PFVtPh and PCVtPh) in the concentration of 8% in the same
architecture, respectively. Figure. 5 shows the EL spectra of the devices b (PFVtPh-doped)
and devices c (PCVtPh-doped) and there are summarized in Table 3. The maximum wave-
length (λmax) of the devices 1b–4c appear at 442-498 nm. Interestingly, the phenomenon
such as excimer and exciplex isn’t observed in the doped-devices using compound 4 as
host material. The luminance-voltage (L-V), luminous efficiencies (LE), and external quan-
tum efficiency (EQE) of doped devices (1b–4c) are shown in Figs 6 and 7, respectively.
Figure 3. EL spectra and the CIE coordinates at 7.0 V of the non-doped devices 1a–4a.

180
H. S. Jang et al.
Figure 4. (a) L-V-J characteristics, (b) the luminous efficiencies, (c) power efficiencies, and (d)
external quantum efficiencies as a function of current density for the devices 1a–4a.
Figure 5. EL spectra and the CIE coordinates at 7.0 V of the doped devices; (a) 1b–4b, and (b)
1
c–4c.
Figure 6. L-V characteristics of the doped devices; (a) 1b–4b, and (b) 1c–4c.

181

182
H. S. Jang et al.
Figure 7. (a) The luminous efficiencies, and (b) external quantum efficiencies as a function of current
density for the doped devices (1b–4c).
Regardless of the lowest efficiencies in non-doped device employing compound 2, the de-
vice 2b (PFVtPh-doped) has the highest efficiencies; its luminous efficiency (LE), power
efficiency (PE), and external quantum efficiency (EQE) reach 5.64 cd/A, 4.14 lm/W, and
2
4
.54% (3.92 cd/A, 1.51 lm/W, and 3.06% at 20 mA/cm ), respectively. We conjecture that
compound 2 is the appropriate host material for PFVtPh blue dopant material. Notably,
◦
Scheme 1. Synthesis of new host materials (1–4). Conditions: (a) n-BuLi, THF, −78 C, 3 h; (b) KI,
3 3 4 2 3
NaHPO , Acetic acid, reflux, 3 h; (c) Pd(PPh ) , 2M Na CO , Toluene/EtOH, reflux, 4 h.

Blue OLEDs Containing Anthracene
183
the device 1c is larger red shift than the others. Furthermore, it significantly reveals high
2
2
luminance and current density (3291 cd/m , and 378 mA/cm ) among the devices 1c–4c.
The PFVtPh-doped devices totally show higher EL efficiencies than those of PCVtPh-
doped devices, because of good overlap between the absorption of dopant material
(
PFVtPh) and the emission of host materials (1–4). Hence, the devices (PFVtPh-doped)
are more effective energy transfer (F o¨ rster-type energy transfer from host to dopant) or
direct charge trapping in dopant [20,21]. The more effective hole trapping in the PFVtPh-
doped devices imply that prevent hole leakage from emitting layer to ETL layer. Thus more
efficient exiton formation at devices could contribute to the improved EL efficiencies. Thus,
PFVtPh is more appropriate dopant material for these host materials.
Conclusion
We successfuuly synthesized A series of new blue emitting materials (1–4) based on
diphenylanthracene via reductive coupling or Suzuki cross-coupling reaction. Their elec-
troluminescent properties were investigated by fabrication of multilayered OLEDs. The
device 4a (non-doped device) shows the high luminous efficiency (LE), power efficiency
(
(
(
(
PE), and external quantum efficiency (EQE) reach 4.11 cd/A, 3.31 lm/W, and 2.36%
3.16 cd/A, 1.60 lm/W, and 1.80% at 20 mA/cm ), respectively. Moreover, the device 2b
2
PFVtPh-doped device) exhibits the high efficiencies with 5.63 cd/A, 4.13 lm/W, and 4.49%
2
3.92 cd/A, 1.50 lm/W, and 3.04% at 20 mA/cm ). Furthermore, this device shows blue
emission color with the CIE coordinates of (0.152, 0.153) at 7.0 V. This study clearly sug-
gests that diphenylanthracene derivatives have sufficient potential for display or lighting
applications.
Acknowledgment
This research was supported by Basic Science Research Program through the NRF funded
by the Ministry of Education, Science and Technology (20110004655).
References
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