Efficient blue organic light-emitting diode using anthracene-derived emitters based on polycyclic aromatic hydrocarbons

Article abstract of DOI:10.1016/j.orgel.2011.02.011

We have synthesized two light-emitting materials based on polycyclic aromatic hydrocarbons (PAHs) for use in blue organic light-emitting diodes (OLEDs). 9-(Phenanthryl)-10-(3-(9-phenylcarbazole-9-yl)anthracene (PPCA) acts as the host and 9,10-bis-biphenyl-4-yl-2,6-diphenylanthracene (BDA) acts as the dopant. PPCA contains an electron-transporting phenanthrene moiety and a hole-transporting 9-phenyl-9H-carbazole moiety in the anthracene core. BDA contains PAHs without amino substituents in the anthracene core. The optimized device structure, ITO/DNTPD (600 )/α-NPB (300 )/PPCA:BDA 5 wt.% (250 )/N1PP (300 )/LiF (5 )/Al (1000 ), is characterized by blue electroluminescence (EL), with a current efficiency of 6.9 cd/A, power efficiency of 3.23 lm/W, and external quantum efficiency of 5.1% at 10 mA/cm² and CIE coordinates of (0.15, 0.18).

Full text of DOI:10.1016/j.orgel.2011.02.011

Organic Electronics 12 (2011) 802–808
Contents lists available at ScienceDirect
Organic Electronics
journal homepage: www.elsevier.com/locate/orgel
Efficient blue organic light-emitting diode using anthracene-derived
emitters based on polycyclic aromatic hydrocarbons
⇑
Jong-Kwan Bin, Jong-In Hong
Department of Chemistry, College of Natural Sciences, Seoul National University, Seoul 151-747, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
We have synthesized two light-emitting materials based on polycyclic aromatic hydrocar-
bons (PAHs) for use in blue organic light-emitting diodes (OLEDs). 9-(Phenanthryl)-10-
(3-(9-phenylcarbazole-9-yl)anthracene (PPCA) acts as the host and 9,10-bis-biphenyl-4-
yl-2,6-diphenylanthracene (BDA) acts as the dopant. PPCA contains an electron-transporting
phenanthrene moiety and a hole-transporting 9-phenyl-9H-carbazole moiety in the anthra-
cene core. BDA contains PAHs without amino substituents in the anthracene core. The opti-
Received 16 September 2010
Received in revised form 21 December 2010
Accepted 13 February 2011
Available online 26 February 2011
Keywords:
Organic light-emitting diode
Blue emission
Anthracene
Polycyclic aromatic hydrocarbons
mized device structure, ITO/DNTPD (600 Å)/a-NPB (300 Å)/PPCA:BDA 5 wt.% (250 Å)/N1PP
(300 Å)/LiF (5 Å)/Al (1000 Å), is characterized by blue electroluminescence (EL), with a cur-
rent efficiency of 6.9 cd/A, power efficiency of 3.23 lm/W, and external quantum efficiency of
5.1% at 10 mA/cm2 and CIE coordinates of (0.15, 0.18).
Ó 2011 Elsevier B.V. All rights reserved.
Introduction
mono- and distyrylarylenes [2–4] and pyrene derivatives
[5]. However, the use of PAHs without amino substituents
In recent years, considerable attention has been paid to
the development of organic emissive materials for full-
color display applications. A number of red- and green-
light-emitting candidates have already been identified for
organic light-emitting diodes (OLEDs); OLEDs based on
these compounds are characterized by high luminous
efficiency, reasonable color purity, and long lifetime.
However, the development of blue OLEDs with high
electroluminescence (EL) efficiency remains a challenge
because of the requirement of a large band-gap energy. It
is well known that a host-dopant system can significantly
improve the device performance in terms of both EL
efficiency and operational lifetime [1]. In general, there
are two different types of dopants that can be used to real-
ize blue light emission: polycyclic aromatic hydrocarbons
(PAHs) with amino substituents and those without amino
substituents. To date, there have been a number of reports
on blue dopants with amino substituents, such as
as blue dopants has not been studied in detail. The band-
gap energy of PAHs is determined by the conjugation
length of the molecules. The advantages of PAHs include
a high fluorescence quantum yield and dense packing
ability [6]. Furthermore, it is known that electronic devices
manufactured using PAHs are relatively stable. PAHs also
help to increase the half-life of undoped and doped OLEDs
by 30–150 times [7]. There have been several reports on
the use of PAHs without amino substituents as EL emitters
[8–10]. For example, Tseng and Yang used 7,8,10-
triphenylfluoranthene (TPF) as the blue host and dipyre-
nylfluorene (DPF) as the blue dopant and achieved an EL
efficiency of 3.33 cd/A and an external quantum efficiency
of 2.48% at Commission International de L’Eclairage (CIE)
coordinates of (0.164, 0.188) [8].
Among the blue-emitting materials, anthracene deriva-
tives have been intensively studied for use as the blue host
material in OLEDs because of their excellent photolumi-
nescence (PL) and EL properties [11–14]. Additionally, the
fluorescent color of anthracene can be easily changed from
blue to green by introducing symmetric or asymmetric
moieties at the C-9 and C-10 positions [15]. However,
tetraaryl-substituted anthracene derivatives acting as blue
⇑
Corresponding author. Tel.: +82 2 880 6682.
E-mail address: jihong@snu.ac.kr (J.-I. Hong).
1566-1199/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.orgel.2011.02.011

J.-K. Bin, J.-I. Hong / Organic Electronics 12 (2011) 802–808
803
light-emitting materials are rare. For example, a blue light
emitter with four substituents at the 2,6,9,10-positions of
anthracene (2,6-bis(9,9-diethyl-9H-fluoren-2-yl)-9,10-di-
phenylanthracene) has been proven to exhibit an EL
efficiency of 5.8 cd/A and an external quantum efficiency
of 2.11% [16]. Chen et al. synthesized 9,10-diphenylanthra-
cene (DPA)-derived copolymers emitting blue light. The
OLEDs fabricated using these DPA-derived copolymers
exhibited sky-blue EL (at CIE coordinates of (0.19, 0.30))
with a peak luminous efficiency of 1.26 cd/A. Still, the
development of OLEDs using anthracene-derived moieties
remains a challenge [17].
without amino substituents (Schemes 1 and 2). Specifically,
PPCA was synthesized from 9-phenyl-9H-carbazole, which
possesses good hole-transporting properties, and phenan-
threne, which has good electron-transporting properties
[18]. We believe that the introduction of carbazole and
phenanthrene elements in the 9,10-anthracene core of
PPCA is an effective method for avoiding molecular aggre-
gation and enhancing the efficiency of transporting elec-
trons and holes (carriers). We examined the light-
emitting performance in devices fabricated using alumi-
num tris(8-hydroxyquinoline) (Alq3) and 1,6-di(pyridin-
3-yl)-3,8-di(naphthalene-1-yl)pyrene (N1PP) [19] as elec-
tron-transport materials. In particular, with the use of
N1PP, which shows high carrier mobility, the EL efficiency
of the blue OLED devices based on PAHs without amino
substituents was significantly improved.
Herein, we report the use of an anthracene-based blue
host, 9-(phenanthryl)-10-(3-(9-phenylcarbazole-9-yl)an-
thracene (PPCA), and a dopant 9,10-bis-biphenyl-4-yl-
2,6-diphenylanthracene (BDA) which contains PAHs
Scheme 1. Synthesis of PPCA.

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J.-K. Bin, J.-I. Hong / Organic Electronics 12 (2011) 802–808
Scheme 2. Synthesis of BDA.
try. Ultraviolet and visible (UV–vis) absorption spectra
were recorded with the use of Beckman DU 650
spectrophotometer.
2. Experimental
a
2.1. Materials and instrument
9-Bromoanthracene,
9-phenanthreneboronic
acid,
2.1.1. 9-Phenanthren-9-yl-anthracene (1)
solution of 9-bromoanthracene (2 g, 7.78 mmol),
9-phenanthreneboronic acid (1.90 g, 8.56 mmol),
9-phenylcarbazole, and 4-bromobiphenyl were purchased
from Tokyo Chemical Industry Co., Ltd., (TCI, Japan) and Al-
drich Chemical Co., (USA). Compounds 1A, 2A, 3, and 4
(Schemes 1 and 2) were synthesized according to literature
methods as well as modified procedures [16,20]. Analytical
thin-layer chromatography was performed using Kieselgel
60F-254 plates provided from Merck KGaA (Germany).
Column chromatography was carried out on Merck silica
gel 60 (70–230 mesh). All the solvents and reagents are
commercially available and were used without further
purification, unless otherwise noted. 1H and 13C nuclear
magnetic resonance (NMR) spectra were recorded in CDCl3
using a Bruker Advance 300 MHz spectrometer. Proton
(1H) NMR chemical shifts in CDCl3 were referenced to
CHCl3 (7.27 ppm). Mass spectra were obtained by means
of gas chromatography/high-resolution mass spectrome-
A
Pd(PPh3)4 (3 mol%), and aqueous K2CO3 (10.8 g, 78 mmol,
water 50 mL) in a toluene (10 mL)–tetrahydrofuran (THF,
50 mL) mixture was heated at a temperature of 100 °C
for 10 h in a N2 atmosphere. After the solvent was evapo-
rated, the residue was treated with water and extracted
with dichloromethane. The crude product was purified by
silica gel column chromatography (10% dichloromethane
(DCM) in n-hexane used as eluent) and further purified
by recrystallization (yield: 87%). 1H NMR (300 MHz,
CDCl3): d (ppm) 7.18 (d, 1H, J = 8.07 Hz), 7.24–7.35 (m,
3H), 7.49 (t, 2H, J = 7.4 Hz), 7.59 (d, 2H, J = 8.60 Hz), 7.75
(m, 2H), 7.80 (t, 1H, J = 7.14 Hz), 7.86 (s, 1H), 7.94 (d, 1H,
J = 7.73 Hz), 8.14 (d, 2H, 8.49 Hz), 8.78 (s, 1H), 8.90 (d, 2H,
J = 8.28 Hz).

J.-K. Bin, J.-I. Hong / Organic Electronics 12 (2011) 802–808
805
2.1.2. 9-Bromo-10-phenanthren-9-yl-anthracene (2)
A solution of bromine (0.91 g, 5.70 mmol) in chloroform
(20 mL) was slowly added to solution of (2 g,
2.3. OLED fabrication
a
1
OLEDs were fabricated by means of vacuum deposition
onto patterned ITO glasses that had been thoroughly
cleaned and subsequently, treated with oxygen plasma.
Blue OLEDs were sequentially fabricated onto the ITO sub-
strates through thermal evaporation of organic layers
(evaporation rate: 2 Å/s; base pressure: 3 ꢀ 10ꢁ6 Torr).
The EL spectra and CIE color coordinates were obtained
using a Spectrascan PR650 photometer, while the cur-
rent–voltage–luminescence (J–V–L) characteristics were
measured using a Keithley 2400 source unit.
5.64 mmol) in chloroform (50 mL) at room temperature.
After stirring for 5 h, the mixture was poured into EtOH.
The residue obtained after filtration was purified by flash
chromatography using dichloromethane (yield: 89%). 1H
NMR (300 MHz, CDCl3): d (ppm) 7.13 (d, 1H, J = 8.10 Hz),
7.26–7.34 (m, 3H), 7.56–7.73 (m, 6H), 7.68–7.81 (m, 1H),
7.83 (s, 1H), 7.93 (d, 1H, J = 6.38 Hz), 8.70 (d, 2H,
J = 8.82 Hz), 8.89 (d, 2H, J = 8.22 Hz).
2.1.3. 9-(Phenanthryl)-10-(3-(9-phenylcarbazole-9-yl)-
anthracene (PPCA)
3. Results and discussion
2A was allowed to react with 2 under Suzuki reaction
conditions, as described in the synthesis of 1, to afford
PPCA (yield: 82%). 1H NMR (300 MHz, CDCl3): d (ppm)
7.31–7.36 (m, 5H), 7.49–7.77 (m, 16H), 7.88–7.97 (m,
4H), 8.14–8.18 (m, 1H), 8.39–8.32 (m, 1H), 8.91 (d, 2H,
J = 8.2 Hz); 13C NMR (75 MHz, CDCl3) d 109.74, 109.77,
100.06, 120.21, 120.51, 122.78, 122.90, 123.19, 123.30,
12.55, 125.08, 125.30, 126.29, 126.74, 126.93, 127.0,
129.09, 127.23, 127.54, 127.65, 128.83, 129.37, 130.04,
130.45, 130.53, 130.69, 130.80, 131.82, 132.84, 134.65,
135.58, 137.78, 138.41, 140.41, 141.40; HRMS (FT MS)
m/z: calcd. for [C46H29N + H]+ 596.23, found [M + H]+
596.24; Anal. calcd. for C46H29N: C, 92.74; H, 4.91; N,
2.35. Found: C, 92.7033; H, 4.9502; N, 2.3309.
3.1. Synthesis
Scheme 1 shows the synthetic route to PPCA. Specifically,
the Pd-catalyzed Suzuki coupling reaction of 9-bromoan-
thracene with 9-phenanthreneboronic acid afforded 1 in
87% yield. Bromination of 1 with 1.01 equiv. of bromine in
chloroform solution led to the formation of 2 in 89% yield.
2A was synthesized through the reaction of 3-bromo-9-
phenylcarbazole with 1.1 equiv. of n-BuLi at ꢁ78 °C and
subsequent quenching of the lithiated complex with trieth-
ylborate. PPCA was synthesized through a Pd-catalyzed
Suzuki coupling reaction, similarly to the case of 1.
Scheme 2 shows the synthetic route to BDA. Specifically,
4 was synthesized according to a previously described pro-
cedure [16]. A suspension of 2,6-dibromoanthraquinone in
Et2O was slowly added to lithium-substituted biphenyl in
order to obtain 3. The latter was aromatized using NaH2PO2
and KI to obtain 4 in 84% yield. The next step was to obtain
BDA through the Pd-catalyzed Suzuki-coupling reaction of
4 with phenylboronic acid in 2 M aqueous K2CO3 solution.
The molecular structures of PPCA and BDA were character-
izedbymeansof 1HNMR, mass spectrometry, andelemental
analysis (EA).
2.1.4. 9,10-Bis-biphenyl-4-yl-2,6-diphenylanthracene (BDA)
4 (2 g, 3.12 mmol) was allowed to react with phenylbo-
ronic acid (0.84 g, 6.87 mmol) under Suzuki reaction condi-
tions, as described in the synthesis of PPCA, to afford BDA
(yield: 72%); 1H NMR (300 MHz, CDCl3): d (ppm) 7.33–7.42
(m, 8H), 7.53–7.73 (m, 14H), 7.81–7.91 (m, 10H), 8.01 (s,
2H); HRMS (FT MS) m/z: calcd. for [C46H29N + H]+ 635.27,
found [M + H]+ 635.28. Anal. calcd. for C50H34: C, 94.60; H,
5.40. Found: C, 94.6206; H, 5.4299.
3.2. Thermal properties and quantum yields
2.2. Electrochemical characterization
The thermal behavior of BDA and PPCA was evaluated
by means of (a) differential scanning calorimetry (DSC)
and (b) thermogravimetric analysis (TGA) under a nitrogen
atmosphere. A 5% weight loss was observed at 398 and
367 °C. The melting point (Tm) of BDA and PPCA was 396
and 326 °C and the decomposition temperature (Td) was
445 and 440 °C, respectively. These data indicate that both
these materials are stable enough to endure the high tem-
perature at which the vacuum vapor deposition is carried
out (see Supporting Information).
The electrochemical properties of PPCA and BDA were
characterized by means of cyclic voltammetry. The oxida-
tion scans were carried out in a 0.1 M solution of tetraethy-
lammonium tetrafluoroborate in anhydrous CH2Cl2.
A
platinum and Ag/AgCl disk were used as the working and
reference electrodes, respectively. Specifically, the plati-
num disk was used as the counter electrode. Based on
the highest occupied molecular orbital (HOMO) energy of
the ferrocene/ferrocenium redox system (-4.8 eV), we were
able to calculate the HOMO energy values of PPCA and BDA
which were both equal to 5.6 eV. The band-gap energies
were measured from the absorption spectra, and the low-
est unoccupied molecular orbital (LUMO) energies were
estimated to be equal to 2.6 eV for PPCA and 2.8 eV for
BDA. The energy levels of PPCA and BDA indicate that För-
ster resonance energy transfer (FRET) takes place between
the host (PPCA) and the dopant (BDA), because as shown in
Fig. 4 the band-gap energy of PPCA is greater than that of
BDA (see Supporting Information) [21,22].
Additionally, the fluorescence quantum yield (
measured using the standard optically diluted method in
CH2Cl2 solution and 9,10-diphenylanthracene ( = 0.90,
U) was
U
in CH2Cl2) as the reference standard. The fluorescence
quantum yield of BDA and PPCA were 0.74 and 0.83,
respectively [23,24].
3.3. Optical properties of PPCA and BDA
Fig. 1 shows the UV absorption and PL spectra of PPCA
and BDA dissolved in dichloromethane as well as in the

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J.-K. Bin, J.-I. Hong / Organic Electronics 12 (2011) 802–808
photoexcitation, the PL emission of PPCA dissolved in the
dichloromethane peaked at a wavelength of approximately
438 nm and at 452 nm in the case of the solid thin film. The
spectral shift in solid state is due to the different dielectric
constant of the surrounding medium [26].
In Fig. 1b, the absorption peaks of BDA dissolved in
dichloromethane show vibrational patterns at a wave-
length of 373 nm, 396 nm, and 419 nm, which are typical
to aryl-substituted anthracene [16,20]. The maximum PL
of BDA dissolved in dichloromethane was observed at a
wavelength of 448 nm and at 456 nm in the case of the so-
lid thin film. Additionally, in the host-dopant system, the
probability of energy transfer from the excited energy do-
nor to the energy acceptor depends on the overlap of the
emission spectrum of the donor with the absorption spec-
trum of the acceptor. This is evident from the spectral
overlap between the PL of PPCA and the UV absorption of
BDA (see Supporting Information) [27–32].
3.4. EL properties and OLED characteristics
Fig. 2 shows the structures of Alq3 and N1PP acting as
electron-transporting materials and the EL spectra of the
5% doped devices driven at 10 mA/cm2. To elucidate the en-
ergy transfer from PPCA to BDA, we fabricated two kinds of
multilayer structures: ITO/DNTPD (600 Å)/a-NPB (300 Å)/
Fig. 1. UV absorption and PL spectra of PPCA and BDA dissolved in
dichloromethane (CH2Cl2) and in the case of solid thin films deposited on
a quartz substrate. (a) Normalized UV absorption and PL spectrum of
PPCA. (b) Normalized absorption and PL spectrum of BDA.
form of solid thin films. Specifically, two major bands are
observed in the UV absorption spectra of the material dis-
solved in dichloromethane and in the form of solid thin
films (Fig. 1a). The first strong absorption, which is ob-
served at a wavelength of 258 nm with a shoulder peak
at 300 nm, can be attributed to the 9-phenyl-9H-carbazole
moiety. The absorption peaks observed at a wavelength of
358 nm, 378 nm, and 398 nm are associated with the
vibronic features of the anthracenyl core [25]. Upon
Fig. 3. EL performance of Device I and II. (a) The current–efficiency and
density–luminance characteristics of Device and II. (b) The power
I
Fig. 2. EL spectra of Device I and II along with the structures of Alq3 and
N1PP.
efficiency–current density–external quantum efficiency characteristics of
Device I and II.

J.-K. Bin, J.-I. Hong / Organic Electronics 12 (2011) 802–808
807
525 nm. We believe that the two higher energy emissions
are due to BDA, while the lower energy emission is due to
Alq3 [33–35].
The experimental results suggest that energy transfer
takes place between the light-emitting and the electron-
transporting layer. Specifically, a peak in the blue-light
emission of Device II was observed at a wavelength of
456 nm, which is almost identical to that of the PL spec-
trum of BDA in the form of a solid thin film (Fig. 1b). This
coincidence indicates that while the light emission of PPCA
(host) is essentially quenched in the light emitting layer of
the 5% doped device, FRET takes place between the host
(PPCA) and the dopant (BDA) [35,36].
Fig. 3 shows the EL performance of Devices I and II,
while their EL efficiencies are summarized in Table 1. Spe-
cifically, Device I showed a current efficiency of 4.30 cd/A,
power efficiency of 2.00 lm/W, and an external quantum
efficiency of 2.50% at 10 mA/cm2 (at CIE coordinates of
(0.15, 0.28)). Device II, on the other hand, delivered a better
performance with a current efficiency of 6.90 cd/A, power
efficiency of 3.23 lm/W, and external quantum efficiency
of 5.10% at 10 mA/cm2 (at CIE coordinates of (0.15, 0.18)).
To further verify the difference between the EL perfor-
mances of Device I and II, we examined their band-gap
energies. Fig. 4 show the HOMO and LUMO energy levels
of the organic material, along with the work functions of
their metal layers. This energy diagram reveals that the en-
ergy barrier (1.5 eV) between the EIL (4.2 eV) and ETL
(Alq3) (2.7 eV) in Device I is larger than the difference
(1.1 eV) between the electrode and N1PP (3.1 eV) in Device
II [19] Since Alq3 is characterized by a higher LUMO level
than N1PP, electron injection from the LiF/Al cathode into
the 5% doped emission layer is rather difficult to be
achieved in Device I. Furthermore, the difference between
the HOMO values of the emitting layer (EML) and the ETL
will cause leakage of holes from the 5% doped emitting
zone into the ETL (Alq3). In Device I, the HOMO level
(5.5 eV) of Alq3 is higher than that of PPCA (5.6 eV). This
difference can explain why the electron–hole recombina-
tion may be unbalanced in the emitting zone of Device I.
This unbalanced charge recombination also shifts the blue
light-emitting zone to a region close to the ETL (Alq3)
(Fig. 4) and therefore, Device I delivers a poor performance.
On the other hand, the HOMO level of N1PP (6.1 eV) is low-
er than that of PPCA (5.6 eV). Because of the energy barrier
(0.5 eV) between the HOMO level of PPCA (5.6 eV) and that
of N1PP (6.1 eV), N1PP can act as a hole blocker preventing
holes from leaking into the ETL. This behavior suggests that
since N1PP has better carrier-transporting and hole-
blocking characteristics, it facilitates electron–hole recom-
bination in the 5% doped emitting zone. Consequently, the
EL performance of Device II is superior to that of Device I.
Fig. 4. HOMO and LUMO energy levels of the materials used for the
fabrication of Device I and II.
PPCA:BDA 5 wt.% (250 Å)/Alq3 (300 Å)/LiF (5 Å)/Al (1000 Å)
(Device I) and ITO/DNTPD (600 Å)/a-NPB (300 Å)/PPCA:BDA
5 wt.% (250 Å)/N1PP (300 Å)/LiF (5 Å)/Al (1000 Å) (Device
II). We used N,N0-di(4-N,N0-diphenylamino)phenyl)-N,N0-
diphenylbenzidine (DNTPD) as the hole-injection layer
(HIL),
-NPB) as the hole-transport layer (HTL), PPCA as the
4,40-bis[N-(1-napthyl)-N-phenylamino]biphenyl
(a
fluorescent blue host, BDA as the fluorescent blue dopant,
N1PP and Alq3 as the electron-transport layers (ETL) [19],
and LiFastheelectron-injection layer (EIL)attheLiF/Al cath-
ode interface. The EL spectrum of Device I, in which Alq3 was
used as an ETL, was found to be different from that of Device
II, which used N1PP as an ETL. In Device I, three major peaks
were observed at a wavelength of 454 nm, 487 nm, and
Table 1
Summary of the characteristics of Devices I and II with Alq3 and N1PP as an ETL.
Device
EL peak [nm]
Current efficiency
Luminance @10
mA/cm2 [cd/m2]
Power efficiency
External quantum
efficiency [%]
CIE coordinates [x,y]
@10 mA/cm2 [cd/A]
@10 mA/cm2 [lm/W]
Device I
Device II
487
456
4.30
6.90
428/3720a
687/4869a
2.00
3.23
2.50
5.10
0.15, 0.28
0.15, 0.18
a
Measured at 100 mA/cm2.

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J.-K. Bin, J.-I. Hong / Organic Electronics 12 (2011) 802–808
[6] B.M. Krasovitskii, B.M. Bolotin, Organic Luminescent Materials
4. Conclusions
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In summary, we have synthesized new anthracene-
based host (PPCA) and dopant (BDA) materials and used
them to fabricate efficient blue OLEDs. PPCA carries an
electron-transporting 9-phenanthrene moiety as well as a
hole-transporting 9-phenyl-9H-carbazole moiety in the
anthracene core. On the other hand, BDA consists of PAHs
without amino substituents in the anthracene core. Charge
balance could be achieved by using N1PP as the electron-
transporting material. The device with the optimized struc-
ture, ITO/DNTPD (600 Å)/a-NPB (300 Å)/PPCA:BDA 5 wt.%
(250 Å)/N1PP (300 Å)/LiF (5 Å)/Al (1000 Å) (Device II), is
characterized by high blue EL performance with a current
efficiency of 6.9 cd/A, a power efficiency of 3.23 lm/W, and
an external quantum efficiency of 5.1% at 10 mA/cm2 at
CIE coordinates of (0.15, 0.18). This study shows that p-con-
jugated anthracene-functionalized PAHs without amino
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Acknowledgments
This study was supported by the Basic Science Research
Program through a National Research Foundation of Korea
(NRF) grant funded by the Ministry of Education, Science
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