Anthracene effects on organic light emitting diode performance of tetra-substituted ethylene derivatives

Article abstract of DOI:10.1080/15421400701545387

We synthesized new bluish-green and sky-blue emitting materials, 1,1,2,2-tetrakis(4'-tert-butylbiphenyl)ethane[TBBPE] and 1,1,2,2-tetrakis(4- (anthracen-9-yl)phenyl)ethene[TAPE]. TBBPE and TAPE film showed PL maximum value of 511nm and 492nm. TBBPE OLED device showed bluish-green C.I.E. value of (0.236, 0.412) and high luminance efficiency of 5.02cd/A at 10mA/cm2. TAPE device also showed sky-blue C.I.E. value of (0.213, 0.323) and 3.17cd/A at 10mA/cm2. It is found that TBBPE shows better luminance efficiency than TAPE and TAPE device exhibits relatively lower operating voltage and better C.I.E. value than TBBPE device.

Full text of DOI:10.1080/15421400701545387

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Anthracene Effects on
Organic Light Emitting
Diode Performance of
Tetra-Substituted Ethylene
Derivatives
Soo-Kang Kim a , Jong-Wook Park a & Se-Young Oh b
a Department of Chemistry/Display Research
Center , The Catholic University of Korea , Pucheon,
Korea
b Department of Chemical Engineering , Sogang
University , Mapo, Seoul, Korea
Published online: 22 Sep 2010.
To cite this article: Soo-Kang Kim , Jong-Wook Park & Se-Young Oh (2007)
Anthracene Effects on Organic Light Emitting Diode Performance of Tetra-Substituted
Ethylene Derivatives, Molecular Crystals and Liquid Crystals, 471:1, 89-98, DOI:
10.1080/15421400701545387
To link to this article: http://dx.doi.org/10.1080/15421400701545387
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Mol. Cryst. Liq. Cryst., Vol. 471, pp. 89–98, 2007
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400701545387
Anthracene Effects on Organic Light Emitting
Diode Performance of Tetra-Substituted
Ethylene Derivatives
Soo-Kang Kim
Jong-Wook Park
Department of Chemistry=Display Research Center, The Catholic
University of Korea, Pucheon, Korea
Se-Young Oh
Department of Chemical Engineering, Sogang University, Mapo,
Seoul, Korea
We synthesized new bluish-green and sky-blue emitting materials, 1,1,2,2-tetra-
kis(40-tert-butylbiphenyl)ethane[TBBPE] and 1,1,2,2-tetrakis(4-(anthracen-9-
yl)phenyl)ethene[TAPE]. TBBPE and TAPE film showed PL maximum value of
511 nm and 492 nm. TBBPE OLED device showed bluish-green C.I.E. value of
(0.236, 0.412) and high luminance efficiency of 5.02 cd=A at 10 mA=cm2. TAPE
device also showed sky-blue C.I.E. value of (0.213, 0.323) and 3.17 cd=A at
10 mA=cm2. It is found that TBBPE shows better luminance efficiency than TAPE
and TAPE device exhibits relatively lower operating voltage and better C.I.E. value
than TBBPE device.
Keywords: blue organic light-emitting diode; electroluminescent; McMurry reaction;
tetraphenylethylene
INTRODUCTION
Organic light-emitting diodes (OLEDs) based on organic molecules are
currently the subject of an intense research effort due to their promise
as devices for full-color large display applications [1–3], numerous
conjugated organic molecules have been synthesized and reported
This work was supported by grant No. R01-2006-00010196-0 from the Basic Research
Program of the Korea Science & Engineering Foundation.
Address correspondence to Jong-Wook Park, Department of Chemistry=Display
Research Center, The Catholic University of Korea, Pucheon 420-743, Korea. E-mail:
hahapark@catholic.ac.kr
89

90
S.-K. Kim et al.
to exhibit electroluminescence (EL), from red, to green, to blue [4–6].
In order to make full color OLED display, we need high performance
red, green, blue materials with high EL efficiency, pure color coordi-
nate (C.I.E.) value and long life time as well as material thermal pro-
perty. Host and dopant method in fluorescence and phosphorescence
system have been used to get high efficiency of OLED and red and
green emitters have been developed and improved to commercialize
full color OLED. However, a lot of problems to solve still remain, for
example blue emitting material, the device lifetime and the luminous
efficiency, etc.
Many kinds of blue materials including diarylanthracene, di(styryl)
arylene, fluorene and pyrene have been intensively used and studied
on improved EL property [6]. Conventional one of the commercialized
compounds is 4,40-bis(2,2-diphenylvinyl)-1,10-biphenyl(DPVBi) of Ide-
mitsu kosan, but DPVBi has low Tg of 64ꢀC [7,8]. And it causes recrys-
tallization under long operation and relatively short device life time
compared to green and red color.
In our work, we tried to synthesize new blue chemical structure
including tetra substituted ethylene and anthracene moieties. Chemi-
cal structure of tetra substituted ethylene means fully substituted
chromophore in a molecule and it can provide highly thermal property
due to increased molecular weight compared to not fully substituted
compound such as stilbene moiety.
In this study, we synthesized new tetra substituted ethylene deriva-
tives including benzene and anthracene moieties and characterized
their own electrical and optical properties. The resulting material,
1,1,2,2-tetrakis(40-tert-butylbiphenyl)ethene[TBBPE] and 1,1,2,2-tetra-
kis(4-(anthracen-9-yl)phenyl)ethene[TAPE] were synthesized through
Suzuki and McMurry reaction. Electro-optical properties of these mate-
rials were characterized by cyclic voltammetry (CV), UV-visible and
photoluminescence (PL) spectra. Moreover, multilayer EL devices were
fabricated using these materials as non-doped emitting layer.
EXPERIMENTAL
Synthesis
Synthesis of 1,1,2,2-tetrakis(40-tert-butylbiphenyl)
Ethene [TBBPE]
i) 2-(4-tert-butylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane(1).
1-tert-Butyl-4-bromobenzene(5 ml, 28.7 mmol) was dissolved in 200 ml
of dry THF solution and stirred at ꢁ78ꢀC, then 1.6 M n-BuLi 35 ml
wasadded. Andthenisopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane

Anthracene Effects on Organic Light Emitting Diode
91
(11 ml, 57.5 mmol) was added to the reaction after 30 min. After the
reaction finished, the reaction mixture was extracted with diethyl-ether
and water. The organic layer was dried by anhydrous MgSO4 and fil-
tered. The solution was evaporated. The residue was dissolved in acet-
one and added to methanol. The precipitate was filtered and washed
with methanol (7g, 93.8%).
1H NMR (d, ppm): 7.69(d, 2H), 7.43(d, 2H), 1.32(d, 21H); Fabþ -
mass: 260
ii) Bis(40-tert-butylbiphenyl)methanone(2). Bis(4-bromophenyl)-
methanone(2 g, 5.7 mmol), 2-(4-tert-butylphenyl)-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane(1) (3.26 g, 12.5 mmol), Pd(OAc)2 (0.64 g, 2.85 mmol),
(tris-o-tolyl)3P (0.86 g, 2.85 mmol) were added to DME (250 ml) solution,
then the prepared K2CO3 solution, which was dissolved in DME and
H2O (1:1, 100 ml) solvent, was added to reaction mixture. After the reac-
tion finished, the reaction mixture was extracted with diethyl-ether and
water. The organic layer was dried by anhydrous MgSO4 and filtered.
The solution was evaporated. The residue was dissolved in CHCl3
and added to methanol. The precipitate was filtered and washed with
methanol (2 g, 76%).
1H NMR (d, ppm): 7.92(d, 4H), 7.72(d, 4H), 7.62(d, 4H), 7.52(d, 4H),
1.38(s, 18H); Fabþ -mass: 446.
iii) 1,1,2,2-tetrakis(40-tert-butylbiphenyl)ethene [TBBPE]. Bis(40-tert-
butylbiphenyl)methanone(2) (2 g, 4.5 mmol), Zn-powder (1.06g, 17 mmol)
were added to dried THF solvent (150 ml), then TiCl4(1.5 ml, 13.6 mmol)
were added into the reaction mixture. The mixture was heated to 60ꢀC
for 1 hr under nitrogen. Reactant mixture was cooling down after 1 hr
and then the product was extracted by diethyl-ether. The organic layer
wasdried by anhydrous MgSO4 and filtered. The solution was evaporated.
The residue was dissolved in CHCl3 and added to methanol. The precipi-
tate was filtered and washed with methanol. Yellowish powder was puri-
fied by column chromatography with CHCl3: n-hexane (1:1) eluent to
afford beige solid (TBBPE) (1.2 g, 63%).
1H NMR (d, ppm): 7.16(d, 8H), 7.37(d, 8H), 7.42(d, 8H), 7.51(d, 8H),
1.34 (s, 36H); Fabþ -mass: 860.
Synthesis of 1,1,2,2-tetrakis(4-(Anthracen-9-yl)Phenyl)Ethene
[TAPE]
i) Anthracen-9-yl-9-boronic acid(3). 9-bromoanthracene (4 g, 15.3
mmol) was dissolved in 200 ml of dry THF solution and stirred
at ꢁ78ꢀC, then 1.6 M n-BuLi 20 ml was added. And then triethyl
borate (5.3 ml, 3.1 mmol) was added to the reaction after 30 min. After
the reaction finished, it was then acidified with 2 N HCl solution, and

92
S.-K. Kim et al.
extracted with diethyl-ether and water. The organic layer was dried
by anhydrous MgSO4 and filtered. The solution was evaporated. The
residue was dissolved in acetone and added to CCl4. The precipitate
was filtered and washed with CCl4. (2.5 g, 72.1%).
1H NMR (d, ppm): 8.47(s, 1H), 8.12(d, 2H), 8.01(d, 2H), 7.48(m, 4H),
5.07 (s, 2H); Fabþ -mass: 222.
ii) Bis(4-(anthracen-9-yl)phenyl)methanone(4). Bis(4-bromophenyl)
methanone (1.7 g, 5 mmol), Anthracen-9-yl-9-boronic acid(3)(2.5 g,
11.2 mmol), Pd(PPh3)4 (0.23 g, 0.2 mmol) were added to Toluene
(250 ml) solution, then the prepared K2CO3 solution, which was dis-
solved in H2O solvent, was added to reaction mixture. After the reac-
tion finished, the reaction mixture was extracted with diethyl-ether
and water. The organic layer was dried by anhydrous MgSO4 and fil-
tered. The solution was evaporated. The residue was dissolved in
CHCl3 and added to methanol. The precipitate was filtered and
washed with methanol (2 g, 74.9%).
1H NMR (d,ppm): 8.54(s, 2H), 8.20(d, 4H), 8.07(d, 4H), 7.70(d, 4H),
7.65(d, 4H), 7.49(t, 4H), 7.40 (t, 4H); Fabþ -mass: 534.
iii) 1,1,2,2-tetrakis(4-(anthracen-9-yl)phenyl)ethene [TAPE]. Bis(4-
(anthracen-9-yl)phenyl)methanone(4) (2 g, 3.74 mmol), Zn-powder
(0.88 g, 14.1 mmol) were added to dried THF solvent (150 ml), then
TiCl4 (1.25 ml, 11.3 mmol) were added into the reaction mixture. The
mixture was heated to 60ꢀC for 1hr under nitrogen. Reactant mixture
was cooling down after 1hr and then the product was extracted by
diethyl-ether. The organic layer was dried by anhydrous MgSO4 and
filtered. The solution was evaporated. The residue was dissolved in
CHCl3 and added to methanol. The precipitate was filtered and
washed with methanol.
Yellow powder was purified by column chromatography with
CHCl3: n-hexane (1:1) eluent to afford greenish-yellow solid (TAPE)
(1.1 g, 56.7%).
1H NMR (d, ppm): 8.50(s, 4H), 8.03(d, 8H), 7.74(d, 8H), 7.67(d, 8H),
7.43(d, 8H), 7.35(t, 8H), 7.08 (t, 8H); Fabþ -mass: 1037.
Characterization
1H NMR spectra were recorded on a Brucker, Advance DPX-300. Fast
atom bombardment (FAB) mass spectra were recorded on a JEOL,
JMS-AX505WA, HP5890 seris II. The optical absorption spectra were
measured by a HP 8453 UV-VIS-NIR spectrometer. Perkin Elmer
luminescence spectrometer LS50 (Xenon flash tube) was used for
photo- and electro-luminescence spectroscopy. Melting point (Tm),

Anthracene Effects on Organic Light Emitting Diode
93
grass-transition temperatures (Tg), and crystallization temperatures
(Tc) of respective compounds were measured by differential scanning
calorimetry (DSC) under nitrogen atmosphere using a DSC2910(TA
instrument) and thermogravimetric analysis (TGA) using SDP-
TGA2960 (TA instrument). Redox potential of the compounds were
determined by cyclic voltammetry (CV) using an EG&G 362 electro-
chemical workstation with a scanning rate of 30 ꢂ 200 mV=s. The com-
pound of interest was dissolved in N,N-Dimethylformamide (DMF)
with 0.1 M tetrabutylammonium tetrafluoroborate as the electrolyte.
We used a platinum working electrode and a saturated Ag=AgNO3
referenced electrode. Ferrocene was used for potential calibration
(all reported potentials are referenced against ferrocene=ferrocenium,
FOC) and for reversibility criteria.
For EL device, TBBPE and TAPE were vacuum-deposited on top of=
ꢁ6
˚
˚
˚
NPB(150 A)=2-TNATA (600 A)=ITO(1200 A=30 ohm) under 10
torr,
˚
the rate of deposition being 1 A=sec to give an emitting area of
4 mm2 and other organic layer and aluminum layer were continuously
deposited with same vacuum condition. Current-voltage (I-V) charac-
teristics of the fabricated OLEDs were measured using Keithley
2400 electrometer. Light intensity was obtained by Minolta CS-1000.
RESULTS AND DISCUSSION
The synthesized compounds were prepared by >75% yield of Suzuki
reaction and >50% yield of McMurry reaction (Schemes 1 and 2).
These products were finally purified with column method to have
highly pure powder and were identified NMR, Fabþ -mass.
SCHEME 1 Synthetic route of TBBPE.

94
S.-K. Kim et al.
SCHEME 2 Synthetic route of TAPE.
Figure 1 shows UV-visible and PL spectra of TBBPE and TAPE
films deposited on glass. TAPE exhibited typical anthracene UV
absorption peak of 355 nm, 375 nm and 395 nm. Although two com-
pounds show similar onset point values of 413 and 414 nm in UV-
visible spectra, PL maximum values of TBBPE and TAPE are 511
and 492 nm. We suppose that there is twisted angle between anthra-
cene and phenyl ring. Sakata et al. has also reported that 9-phenylan-
thracene gives 90 degree of twisted angle in previous paper [9]. It
means that twisted anthracene group in TAPE compound may cause
FIGURE 1 UV-visible (solid) and PL spectra (open) of TBBPE(&) and
TAPE(ꢀ) film on glass.

Anthracene Effects on Organic Light Emitting Diode
95
to make decreased conjugation length and longer intermolecule
distance.
We had checked Tg and Tm by using DSC and TGA experiment in
N2 atmosphere, but there was no obvious Tg and Tm point. On TGA
data, we could get high Td point with 402ꢀC of TBBPE and 368ꢀC of
TAPE in 5% loss state which means 95% residue.
The bang gap energy of TBBPE and TAPE are estimated to be 3.00,
2.99 eV respectively. Based on onset point of UV-visible spectrum and
CV data, we calculated HOMO and LUMO levels. The energy band
gaps, HOMO, LUMO level, UVonset, UV and PL maximum values were
summarized in Table 1.
As shown in Table 1, TAPE has lower HOMO level of 5.61 eV com-
pared to TBBPE’s. This might be due to anthracene moiety which has
stable electrochemical oxidation characteristics. In conventional
anthracene derivatives, 9,10-di-(2-naphthyl)anthracene(ADN) and
2-methyl-9,10-di-(2-napthyl)anthracene(MADN) show same HOMO
level of 5.5 eV because of anthracene moiety [6].
EL devices were fabricated using 4,40,400-tris{N,-(2-naphthyl)-N-
phenylamino}-triphenylamine (2-TNATA) as a hole injection layer
(HIL), 4,40-bis[N-(1-naphthyl)-N-phenyl-amino] biphenyl (NPB) as a
hole transporting layer (HTL), TBBPE and TAPE as emitting layer
(EML), tris-(8-hydroxyquinolate)-aluminum(Alq3) as electron trans-
porting layer (ETL), ITO as the anode and LiF=Al as the cathode;
ITO=2-TNATA (60 nm)=NPB (15 nm)=TBBPE or TAPE(30 nm)=
Alq3(30 nm)=LiF (1 nm)=Al (200 nm).
When we compared I-V characteristics of TBBPE and TAPE devices
(Fig. 2), TAPE device showed better I-V curve than TBBPE’s. The
reason could be explained by that the LUMO energy level difference
between TBBPE and Alq3 is larger value of 0.86 eV than 0.48 eV of
TAPE case.
Figure 3 showed EL maximum values of 492 nm and 474 nm
in ITO=2-TNATA(60 nm)=NPB(15 nm)=TBBPE or TAPE(30 nm)=
Alq3(30 nm)=LiF(1 nm)=Al(200 nm) device. The shifted EL maximum
value of about 20 nm from PL was observed in devices, but the expla-
nation of shifted EL maximum value is not clear. According to EL
TABLE 1 Optical and Electrical Properties of Synthetic Compounds
UVonset
(nm)
UVmax
(nm)
PLmax
(nm)
HOMO
(eV)
LUMO
(eV)
Eg
(eV)
TBBPE
TAPE
413
414
358
395
511
492
5.24
5.61
2.24
2.62
3.00
2.99

96
S.-K. Kim et al.
FIGURE 2 Current density-voltage characteristics of ITO=2-TNATA(60 nm)=
NPB(15 nm)=TBBPE(&) or TAPE(ꢀ)(30 nm)=Alq3(30 nm)=LiF(1 nm)=Al device
(inset: energy diagram).
FIGURE 3 EL Spectrum of ITO=2-TNATA(60 nm)=NPB(15 nm)=TBBPE(&)
or TAPE(ꢀ)(30 nm)=Alq3(30 nm)=LiF(1 nm)=Al device at 10 mA=cm2.

Anthracene Effects on Organic Light Emitting Diode
97
TABLE 2 Electroluminescent Property of Multi-Layered Device: ITO=
2-TNATA(60 nm)=NPB(15 nm)=TBBPE or TAPE(30 nm)=Alq3(30 nm)=
LiF(1 nm)=Al(200 nm) device at 10 mA=cm2
Luminance
efficiency
(cd=A)
Power
efficiency
(lm=W)
ELmax
(nm)
Voltage
(V)
C. I. E.
(x, y)
TBBPE
TAPE
492
474
8.9
6.8
5.02
3.17
1.78
1.46
0.236, 0.412
0.213, 0.323
device, TAPE also showed blue shifted maximum wavelength of 18 nm
from TBBPE’s and this tendency is similar with PL result.
We summarized EL efficiency and C.I.E. values in Table 2. TBBPE
OLED device showed bluish-green C.I.E. value of (0.236, 0.412) and
high luminance efficiency of 5.02 cd=A at 10 mA=cm2. TAPE device
also showed sky-blue C.I.E. value of (0.213, 0.323) and 3.17 cd=A at
10 mA=cm2. It is found that TBBPE shows better luminance efficiency
than TAPE and TAPE device exhibits relatively lower operating volt-
age and better C.I.E. value than TBBPE device. The reason of blue
shifted EL maximum value in TAPE device may be that anthracene
moiety causes twisted intramolecule angle and decreased conjugation
length. As we discussed earlier, 9-phenylanthracene group includes 90
degree twisted angle [9] and it breaks molecular planarity and
decreases conjugation length. Moreover, we believe that bulkiness of
anthracene group increases intermolecular distance and this prevents
molecular stacking which is related with longer emission wavelength.
Further studies on EL device using these materials and dopant
materials are underway.
CONCLUSIONS
We synthesized new bluish-green and sky-blue emitting materials,
1,1,2,2-tetrakis(40-tert-butylbiphenyl)ethane[TBBPE] and 1,1,2,2-
tetrakis(4-(anthracen-9-yl)phenyl)ethene[TAPE].
TAPE exhibited typical anthracene UV absorption peak of 355 nm,
375 nm and 395 nm. Although two compounds show similar onset
point values of 413 and 414 nm in UV-visible spectra, PL maximum
values of TBBPE and TAPE are 511 and 492 nm. It means that there
is twisted angle between anthracene and phenyl ring. We believe that
twisted anthracene group in TAPE compound may cause to make
decreased conjugation length and longer intermolecule distance.
TBBPE OLED device showed bluish-green C.I.E. value of (0.236,

98
S.-K. Kim et al.
0.412) and high luminance efficiency of 5.02 cd=A at 10 mA=cm2. TAPE
device also showed sky-blue C.I.E. value of (0.213, 0.323) and
3.17 cd=A at 10 mA=cm2. It is found that TBBPE shows better lumi-
nance efficiency than TAPE and TAPE device exhibits relatively lower
operating voltage and better C.I.E. value than TBBPE device. The rea-
son of blue shifted EL maximum value in TAPE device may be that
anthracene moiety causes twisted intramolecule angle and decreased
conjugation length.
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