Synthesis and properties of blue-light-emitting anthracene derivative with diphenylamino-fluorene

Article abstract of DOI:10.1016/j.dyepig.2009.10.009

9,10-Bis-(9′,9′-diethyl-7′-diphenylamino-fluoren-2-yl) -anthracene was synthesized from 9.10-anthracene diboronic acid and (7-bromo-9,9-diethyl-fluoren-2-yl)-diphenyl-amine in a Suzuki coupling reaction. A?theoretical calculation of the three-dimensional structure suggests that it has a non-coplanar structure and inhibited intermolecular interactions. Upon excitation, the photoluminescence maximum of 9,10-bis-(9′,9′-diethyl-7′-diphenylamino-fluoren-2-yl) -anthracene in solution and film were at 454?nm (solution) and 462?nm (film). The full width at half maximum of 9,10-bis-(9′,9′-diethyl-7′-diphenylamino-fluoren-2-yl) -anthracene is 54?nm regardless of whether it is in a solution or a solid state. A multi-layered device using 9,10-bis-(9′,9′-diethyl-7′-diphenylamino-fluoren-2-yl) -anthracene as emitting material exhibits maximum quantum efficiency of 3.3% (power efficiency of 2.1?lm/W, current efficiency of 4.17?cd/A) and a blue Commission Internationale de l'Eclairage chromaticity coordinates (x?=?0.14, y?=?0.17).

Full text of DOI:10.1016/j.dyepig.2009.10.009

Dyes and Pigments 85 (2010) 93e98
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis and properties of blue-light-emitting anthracene derivative
with diphenylamino-fluorene
Jong-Won Park a, Pengtao Kang a, Hyuntae Park c, Hyoung-Yun Oh b, Jung-Hwan Yang b,
**
,
a,
*
Yun-Hi Kim c , Soon-Ki Kwon
a School of Materials Science and Engineering and Engineering Research Institute(ERI), Gyeongsang National University, Jinju 660-701, Republic of Korea
b LG Elite, Umeon-Dong, Seoul, Republic of Korea
c Department of Chemistry and RINS, Gyeongsang National University, Jinju 660-701, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
9,10-Bis-(90,90-diethyl-70-diphenylamino-fluoren-2-yl)-anthracene was synthesized from 9.10-anthracene
diboronic acid and (7-bromo-9,9-diethyl-fluoren-2-yl)-diphenyl-amine in a Suzuki coupling reaction.
A theoretical calculation of the three-dimensional structure suggests that it has a non-coplanar structure
and inhibited intermolecular interactions. Upon excitation, the photoluminescence maximum of 9,10-bis-
(90,90-diethyl-70-diphenylamino-fluoren-2-yl)-anthracene in solution and film were at 454 nm (solution)
and 462 nm (film). The full width at half maximum of 9,10-bis-(90,90-diethyl-70-diphenylamino-fluoren-2-
yl)-anthracene is 54 nm regardless of whether it is in a solution or a solid state. A multi-layered device using
9,10-bis-(90,90-diethyl-70-diphenylamino-fluoren-2-yl)-anthracene as emitting material exhibits maximum
quantum efficiency of 3.3% (power efficiency of 2.1 lm/W, current efficiency of 4.17 cd/A) and a blue
Commission Internationale de l'Eclairage chromaticity coordinates (x ¼ 0.14, y ¼ 0.17).
Article history:
Received 20 August 2009
Received in revised form
15 October 2009
Accepted 17 October 2009
Available online 28 October 2009
Keywords:
OLED
Anthracene
Diphenylamino-fluorene
Blue-light-emitting material
Efficiency
Ó 2009 Elsevier Ltd. All rights reserved.
Twisted structure
1. Introduction
systems having all the attributes of high EL efficiency, a long
operational lifetime, and deep-blue color, are rare [3e15].
Small organic molecules and polymers have beenwell researched
as materials for organic light-emitting diodes (OLEDs) after the
reports by Tang et al. [1] in 1987 and Friend et al. [2] in 1990.
Following these reports, academic and industrial research has pro-
gressed in the display market. Organic light-emitting diodes for flat-
panel displays are showing great promise, and a related application
for a flexible flat-panel display is progressing. Full-color displays are
required for red, green, and blue-emitting materials. The deep-blue
color is defined arbitrarily as having blue electroluminescent (EL)
emission with a Commission International de l'Eclairage y coordi-
nate value (CIEy) of 0.15. Such emitters can effectively reduce the
power consumption of a full-color OLED and can also be utilized to
generate light of other colors by energy cascade to a suitable emis-
sive dopant.
The advantages of anthracene are easy substitution at the 9 and
10 positions of anthracene, high thermal stability, high electronic-
stability, and a rigid structure. The introduction of bulky substitu-
ents to the 9 and 10 positions' results in a nonplanar configuration
and rigid structure of anthracene moieties [16] and [17]. As result,
bulky substituted anthracene gives a minimized vibronic mode with
high quantum efficiency [18] and [19]. Many groups have researched
anthracene derivatives, but the factors of high color purity and
stability continue to require improvement in blue OLEDs [20e30].
Fluorene also has a number of advantages, including its capability
to emit in the blue part of the visible spectrum, chemical and photo-
chemical stability, easy synthesis with high purity, liquid crystalline
properties and durability under operation in a LED [15,31e34]. Triar-
ylamine derivatives have been employed as a hole-transport material
with increased bulky volumes and thermal stability [35].
Although many blue-emitting materials have been reported,
such as anthracene, di(styryl)arylene, tetra(phenyl)pyrene, ter-
fluorenes, and tetra(phenyl)silyl derivatives, blue-doped emitter
In the present paper, a new blue-light-emitting material of
9,10-bis-(90,90-diethyl-70-diphenylamino-fluorene-20-yl)anthracene
(BDDFA) was synthesized, and its application to a LED was studied.
The introduction of the bulky 9,9-diethyl-7-diphenylamino-fluo-
renyl group in the 9,10-position of anthracene can suppress
aggregation of planar anthracene segments as well as increase the
* Corresponding author. Tel.: þ82 55 751 5296; fax: þ82 55 753 6311.
** Corresponding authors Tel.: þ82 55 751 6016.
E-mail addresses: ykim@gnu.ac.kr (Y.-H. Kim), skwon@gnu.ac.kr (S.-K. Kwon).
0143-7208/$ e see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.10.009

94
J.-W. Park et al. / Dyes and Pigments 85 (2010) 93e98
hole-transporting capability, the chemical stability, and the thermal
stability and solubility, which results in a bright blue EL emission.
a two-compartment cell with a model that utilized platinum
electrodes at a scan rate of 10 mV/s against a Ag/Agþ (0.1 M AgNO3
in acetonitrile) reference electrode in an anhydrous and nitrogen-
saturated solution of 0.1 Bu4NClO4 in acetonitrile.
2. Experiment
2.1. Materials
2.2.1. Preparation of (7-bromo-9,9-diethyl-fluoren-2-yl)-
diphenyl-amine (DFDA)
Anthracene, fluorene, 1-bromoethane, diphenyl-amine, sodium
tert-butoxide, n-butyl lithium, and triethylborate were purchased
from Aldrich. Tetrahydrofuran (THF) and diethyl ether were puri-
fied by distillation from sodium in the presence of benzophenone.
Methylene dichloride was purified by distillation after drying over
calcium hydride (CaH2). Hexane and ethanol were used without
further purification. All reactions were carried out under a N2
atmosphere.
A mixture of 2,7-dibromo-9,9-diethyl-fluorene (DBDF) (24.7 g,
0.065 mol), diphenyl-amine (5.57 g, 0.033 mol), bis(dibenzylide-
neacetone)palladium (Pd2(dba)3) (0.32 g, 0.036 mol%), bis(diphe-
nylphosphino)-ferrocene(dppf) (0.2 g, 3.6 mol%), and sodium
tert-butoxide (3 g, 0.0312 mol) in toluene (150 mL) was stirred at
80 ꢀC for 18 h under a N2 atmosphere. The mixture was then heated
to 100 ꢀC for 5 h under a N2 atmosphere afterward, the mixture was
cooled to room temperature and 200 mL of water was added to it. The
organic layer was separated with ether and dried over magnesium
sulfate. The solvent was evaporated, the crude product was purified
by column chromatography using a mixture of hexane:dichloro-
methane (1:50) as an eluent. Yield ¼ 19 g (60%). Mp ¼ 148e146 ꢀC.1H
2.2. Instrument
Infrared spectra were obtained with a Genesis II FT-IR spec-
trometer. 1H NMR spectra were recorded on a Bruker Avance
300 MHz spectrometer. Differential scanning calorimetery (DSC)
was performed using a TA DSC 2010 device at a heating rate of
10 ꢀC/min. TGA measurements were performed using a TA TGA
2050 thermal analyzer. Cyclic voltammetry was carried out in
NMR (300 MHz, CDCl3)
d
¼ 7.42e7.56 (m, 4H, AreH), 7.24e7.30
(m, 4H, AreH), 7.01e7.15 (m, 8H, AreH), 1.91 (m, 4H, eCH2e), 0.41
(t, 6H, eCH3); FT-IR (KBr) v ¼ 3254 (AreH), 2960 (CeH),1338 (AreN),
1072 (AreBr). Anal, Calcd for C29H26BrN: C, 74.36: H, 5.59: N, 2.99.
Found: C, 74.31: H, 5.60: N, 2.97.
Br2
1) n-BuLi
Br
Br
(HO)2B
B(OH)2
CCl4
2) B(OC2H5)3
ADB A
1-Bromoethane
Br2
Br
Br
Br
Br
DBDF
Pd(dba)3, DPPF, NaOBu-t
Toluene
H
DBDF
N
+
N
Br
DFDA
Pd(0), K2CO3
THF
2 DFDA
ADBA
N
+
N
Fig. 1. Synthetic Scheme of BDDFA.

J.-W. Park et al. / Dyes and Pigments 85 (2010) 93e98
95
Fig. 2. 1H NMR spectrum (300 MHz, CDCl3) of BDDFA. FT-IR spectrum of BDDFA in KBr
pellet.
2.2.2. Preparation of 9,10-bis-(90,90-diethyl-70-diphenylamino-
fluoren-2-yl)-anthracene (BDDFA)
Fig. 4. TGA and DSC curves of BDDFA.
A
mixture of anthracene-9,10-dibronic acid (ADBA) (5 g,
as the anode, CuPc as the hole-injection layer,
a
-NPD as the hole-
0.018 mol), and DFDA (14.6 g, 0.037 mol) was dissolved in dried THF
(100 mL). After 50 mL of 2 M aqueous potassium carbonate was
added through syringes to the mixture, the reaction mixture was
degassed. Finally, 0.47 g of tetrakis(triphenylphosphine)palladium
(0) was added to the mixture. The mixture was vigorously refluxed
under nitrogen for 48 h. Upon cooling to room temperature, it
was poured into 100 mL of a mixture of methanol and deionized
water (9:1). The crude product was purified by flash chromatog-
raphy with dichloromethan:hexane (1:5) as the eluate.
transport layer, MADN (2-methyl-9,10-di[2-naphthyl]anthracene) as
the host at emitting layer, BDDFA as the guest at emitting layer, Alq3
as the electron-transporting layer, LiF as the electron-injection layer,
and aluminum as the cathode. EL device was fabricated using
successive vacuum deposition of CuPc,
2e3%), Alq3, LiF, and Al electrode on top of the ITO glass substrate.
The ITO glass with a sheet resistance of about 10 was etched for the
a-NPD, MADN (BDDFA,
U
anode electrode pattern and cleaned in ultrasonic baths of isopropyl
alcohol and acetone. The overlap area of Al and ITO electrodes is
about 4 mm2. A UV zone cleaner (Jeilight Company) was used for
further cleaning before vacuum deposition of the organic materials.
Vacuum deposition of the organic materials was carried out under
Yield ¼ 10 g (63%). Mp ¼ 350e352 ꢀC. 1H NMR (300 MHz, CDCl3)
d
¼ 7.72e7.84 (m, 8H, AreH), 7.04e7.42 (m, 32H, AreH), 1.94
(m, 8H, eCH2e), 0.53 (t, 12H, eCH3); 13C NMR (300 MHz, CDCl3)
d
¼ 151.66, 150.01, 148.06, 140.70, 137.68, 130.13, 130.04, 129.22,
127.06, 126.04, 125.02, 123.89, 122.54, 120.47, 119.44, 119.05, 56.26,
32.76, 8.72; FT-IR (KBr) v ¼ 3248 (AreH), 2958 (CeH), 1340 (AreN),
1072 (AreBr). Anal, Calcd for C72H60N2: C, 90.72: H, 6.34: N, 2.94.
Found: C, 90.67: H, 6.38: N, 2.89.
1.0
0.8
0.6
2.3. Fabrication of the LED
The EL device had the structure of a ITO/CuPc/a-NPD/MADN
(BDDFA, 2e3%)/Alq3/LiF/Al device as it used indium-tin oxide (ITO)
0.4
54 nm
0.2
0.0
300
400
500
600
Wavelength(nm)
Fig. 3. Stereo structure of the BDDFA.
Fig. 5. UVevis optical absorption and PL spectra of BDDFA.

96
J.-W. Park et al. / Dyes and Pigments 85 (2010) 93e98
5000
4000
3000
2000
1000
0
0.01
0.008
0.006
0.004
0.002
0.000
6.0
Voltage (V)
4.0 4.5
5.0
5.5 6.0 6.5
Voltage (V)
7.0 7.5
8.0
4.0 4.5
5.0 5.5
6.5 7.0 7.5
8.0
Fig. 6. Current densityevoltage (a) and efficiencyebrightness characteristics (b) of ITO/CuPc/a-NPD/MADN(BDDFA, 2e3%)/Alq3/LiF/Al device.
a pressure of 2 ꢁ 10ꢂ7 torr. The deposition rate for organic materials
was about 0.1 nm/s. The evaporation rate and the thickness of the
film were measured with a quartz oscillator. OLED performance was
studied by measuring the currentevoltageeluminescence (IeVeL)
characteristics, EL, and PL spectra at room temperature. IeVeL
characteristics and CIE color coordinates were measured with
a Keithley SMU238 and Spectrascan PR650. EL spectrum of the
device was measured utilizing a diode array rapid analyzer system
(Professional Scientific Instrument Corp.) Fluorescence spectra of the
solutions in chloroform were measured using a spectrofluorimeter
(Shimadzu Corp.).
half maximum values and the small difference between the photo-
luminescence (PL) maximum of the sample showing pure blue
emission in a solution and in a solid film suggest that there is
minimal intermolecular interaction in the thin film. The obtained
BDDFA exhibits high PL quantum yield in solution. Fsol of material
was determined by using standard procedure with blue quinine
sulfate as reference. The determined Fsol (in CHCl3) of BDDFA is
67 ꢃ 10%. The optical energy band gap of the BDDFA is 2.89 eV, as
calculated from the threshold of the optical absorption (430 nm).
BDDFA exhibits an irreversible oxidation peak at potentials
around 0.42 eV relative to the Ag/AgCl electrode. The oxidation
potential is clearly lower than that of the anthracene derivatives
without arylamine substituents, presumably due to the involvement
of the lone-pair electrons with the amino group during the oxidation
process. The HOMO energy level is correlated to the equation of
IP ¼ Eox þ 4.8 eV, and the LUMO energy level was obtained by the
subtraction of the optical band gap from the IP. The electrolyte was
a 0.1 M Bu4NClO4 solution in anhydrous acetonitrile, and the cell was
purged with nitrogen. In a cyclic voltammogram (CV), the energy
value of the highest occupied molecular orbital (HOMO) was calcu-
lated to be 5.22 eV. According to the UV edge of the band gap energy
(2.89 eV) and HOMO (5.22 eV), the energy values of the lowest
unoccupied molecular orbital (LUMO) was determined as 2.33 eV.
To study the electroluminescence properties of BDDFA, multilayer
devices with the configuration of ITO/copper phthalocyanine (CuPc,
All fabrication steps were performed in clean room conditions.
Measurements were done at room temperature in air.
3. Results and discussion
Fig. 1 shows the synthetic route of BDDFA (9,10-bis-(90,90-
diethyl-70-diphenylamino-fluoren-2-yl)-anthracene). BDDFA was
synthesized by Suzuki coupling reaction of anthracene diboronic
acid and DFDA, which was obtained by N-arylation of 2,7-dibromo-
9,9-diethyl-fluorene and diphenyl-amine. The spectroscopic results
of FT-IR, 1H NMR and the elemental analysis were found to be in
good agreement with the proposed structures of the BDDFA (Fig. 2).
In order to optimize the molecular structure fully, a theoretical
calculation using the PM3 parameterization in the Hyper Chem 5.0
program (Hypercube) was carried out for the characterization of the
three-dimensional structure. Fig. 3 shows the stereo structure of the
BDDFA from the calculative analyses. N,N-diphenylamino-fluorenyl in
the 9 and 10 positions are significantly twisted toward the anthracene
backbone into an angle of 57.61ꢀ. The theoretical calculation of
the three-dimensional structure suggests that it has a non-coplanar
structure with inhibited intermolecular interaction that results in high
levels of luminescent efficiency and color purity. The obtained BDDFA
was readily soluble in common solvents such as chloroform, methy-
lene dichloride, and toluene. The thermal property of the BDDFA was
evaluated by means of TGA in a nitrogen atmosphere. This showed
that 5% weight losses of the BDDFA begin at 420 ꢀC. A differential
60 nm)/1,4-bis[(1-naphthylphenyl)-amino]biphenyl (a-NPD, 20 nm)/
2-methyl-9,10-bis(2-naphtylanthracene) (MADN/BDDFA
2e3%,
20 nm)/Alq3(40 nm)/LiF/Al were fabricated. In this structure, ITO and
Al are the anode and cathode, respectively. The stack of the organic
1.0
0.8
0.6
0.4
0.2
0.0
scanning calorimetry (DSC) measurement showed
a melting
temperature at approximately 351 ꢀC. The DSC and TGA curve shows
that the BDDFA exhibits good thermal stability (Fig. 4).
Fig. 5 depicts the absorption and photoluminescence (PL) spectra
of the dilute solution (in toluene) and the thin film. As shown in
the absorption spectrum, the absorption maxima of the BDDFA were
352 nm, 360 nm and 380 nm, which represent the characteristic
vibrational pattern of the isolated anthracene group. Upon the
excitation, the PL maxima of the BDDFA in the solution and film
were at 454 nm (solution) and 462 nm (film). The full width at half
maximum (FWHM) of the BDDFAwas 54 nm regardless of whether it
was in a solution or in a solid state. The similarity of the full width at
300
400
500
600
700
800
Fig. 7. The EL and solid PL spectra of BDDFA.

J.-W. Park et al. / Dyes and Pigments 85 (2010) 93e98
97
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4.2
4.0
3.8
3.6
3.4
3.2
3.0
2.8
2.6
1000
2000
3000
4000
5000
Brightness (Cd/m2)
Fig. 8. Current densityequantum efficiency of ITO/CuPc/a-NPD/MADN (BDDFA, 2e3%)/
Alq3/LiF/Al device.
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transport layer, MADN (BDDFA, 2e3%) as the emitter, Alq3 as the
electron-transport layer, and LiF as the electron-injection layer. In this
study, MADN was used as a host for blue-emitting electrolumines-
cence devices [3]. The currentevoltageeluminescence (IeVeL) char-
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the ITO/CuPc/a-NPD/MADN(BDDFA, 2e3%)/Alq3/LiF/Al device shows
a maximum value at 462 nm (Fig. 7). The EL spectrum of the BDDFA is
in good agreement with the PL spectrum, indicating the both EL and
PL originate from the same radiative decay process of a singlet exciton.
The brightness of the device was 4600 cd/m2 (7.6 V) at 10 mA
with a turn-on voltage of 4.29 V (0.01 mA). The device showed the
maximum current efficiency of 4.17 cd/A, the maximum power effi-
ciency of 2.1 lm/W and maximum quantum efficiency of 3.3% (Fig. 8).
The CIE color chromaticity of device was (x ¼ 0.14, y ¼ 0.17).
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A new blue emitter, BDDFA, in which two bulky diphenyl-amine-
fluorenes are connected at the 9 and 10 positions of anthracene was
developed. This structure leads to non-coplanar and inhibited inter-
molecular interaction. A multilayer organic EL device constructed
using 2% BDDFA-doped MADN as the emitting layer produced a bright
blue emission with a narrow FWHM of 54 nm. The device achieved
maximum brightness of 4600 cd/m2 and maximum quantum effi-
ciency of 3.3% (power efficiency of 2.1 lm/W, current efficiency of
4.17 cd/A) and exhibits a blue CIE (Commission Internationale de
l'Eclairage) chromaticity coordinates (x ¼ 0.14, y ¼ 0.17).
Acknowledgments
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This research was financially supported by Korea Institute for
Advancement in Technology through the Workforce Development
Program in Strategic Technology, by Strategic Technology Under
Ministry of Knowledge Economy of Korea and by Basic Science
ResearchProgramthroughtheNationalResearchFoundationofKorea
(NRF) funded by the Ministry of Education, Science and Technology
(2009-0068352).
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