New deep-blue emitting materials based on fully substituted ethylene derivatives

Article abstract of DOI:10.1039/b706606f

New blue fluorescent compounds containing tetra-substituted ethylene moieties have been designed and synthesized. These materials, 1,2-di(4′-tert-butylphenyl)-1,2-bis(4′-(anthracene-9-yl)phenyl) ethene [BPBAPE, 1A], 1,2-diphenyl-1,2-bis(4′-(anthracene-9-yl)phenyl) ethene [PBAPE, 1B], 9,10-bis(4-(1,2,2-tris(4-tert-butylphenyl)vinyl)phenyl) anthracene [BTBPPA, 2A], and 9,10-bis(4-(1,2,2-triphenylvinyl)phenyl)anthracene [BTPPA, 2B], were synthesized through Suzuki and McMurry reactions. By fabricating multilayered non-doped OLED devices using these new blue materials, we achieved luminance efficiencies of 4.00 lm W^-1 (10.33 cd A ^-1 at 8.1 V) for BPBAPE [1A] and 1.82 lm W^-1 (3.93 cd A^-1 at 6.8 V) for BTPPA [2B] at 10 mA cm^-2. The maxima in the electroluminescence spectra of ITO/2-TNATA (60 nm)/NPB (15 nm)/BPBAPE [1A] and BTPPA [2B] (30 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (200 nm) devices were found to be 475 and 452 nm respectively. The BPBAPE [1A] and BTPPA [2B] devices exhibited sky blue emission (0.195, 0.303) and deep blue emission (0.159, 0.135) at 10 mA cm^-2 respectively. The Royal Society of Chemistry.

Full text of DOI:10.1039/b706606f

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www.rsc.org/materials | Journal of Materials Chemistry
New deep-blue emitting materials based on fully substituted ethylene
derivatives{
Soo-Kang Kim, Young-Il Park, In-Nam Kang and Jong-Wook Park*
Received 1st May 2007, Accepted 5th September 2007
First published as an Advance Article on the web 17th September 2007
DOI: 10.1039/b706606f
New blue fluorescent compounds containing tetra-substituted ethylene moieties have been
designed and synthesized. These materials, 1,2-di(49-tert-butylphenyl)-1,2-bis(49-(anthracene-9-
yl)phenyl)ethene [BPBAPE, 1A], 1,2-diphenyl-1,2-bis(49-(anthracene-9-yl)phenyl)ethene [PBAPE,
1B], 9,10-bis(4-(1,2,2-tris(4-tert-butylphenyl)vinyl)phenyl)anthracene [BTBPPA, 2A], and 9,10-
bis(4-(1,2,2-triphenylvinyl)phenyl)anthracene [BTPPA, 2B], were synthesized through Suzuki and
McMurry reactions. By fabricating multilayered non-doped OLED devices using these new blue
materials, we achieved luminance efficiencies of 4.00 lm W21 (10.33 cd A21 at 8.1 V) for BPBAPE
[1A] and 1.82 lm W21 (3.93 cd A21 at 6.8 V) for BTPPA [2B] at 10 mA cm22. The maxima in the
electroluminescence spectra of ITO/2-TNATA (60 nm)/NPB (15 nm)/BPBAPE [1A] and BTPPA
[2B] (30 nm)/Alq3 (30 nm)/LiF (1 nm)/Al (200 nm) devices were found to be 475 and 452 nm
respectively. The BPBAPE [1A] and BTPPA [2B] devices exhibited sky blue emission (0.195,
0.303) and deep blue emission (0.159, 0.135) at 10 mA cm22 respectively.
OLED layers, such as the hole transporting layer (HTL) and
Introduction
the electron transporting layer (ETL). These differences
Organic light-emitting diodes (OLEDs) based on organic
between the electronic levels result in a mismatched carrier
molecules are currently the subject of intense research efforts
balance of electrons and holes and a low EL efficiency.
Many kinds of blue materials including diarylanthracene,15
due to their promise as devices for full-color large display
applications.1–5 To date, numerous conjugated organic mole-
di(styryl)arylene,16 fluorene,17 pyrene18 and fluoranthene19
cules have been synthesized and reported to exhibit electro-
have been intensively investigated and attempts made to
luminescence (EL) ranging from red to green and blue. In
improve their EL properties. 4,49-Bis(2,2-diphenylvinyl)-1,19-
biphenyl (DPVBi)16 is a commercialized compound, but has a
order to fabricate full-color OLED displays, we need high
performance red,6–8 green,2,9 and blue10–13 materials with high
low glass transition temperature Tg of 64 uC,20 undergoes
recrystallization after long operation, and has a short device
EL efficiencies, good thermal properties and long lifetimes as
well as pure color coordinates (Commission Internationale de
lifetime compared to those of green and red materials. In
l’Eclairage (CIE)). Both host and dopant methods have been
addition, some blue materials including DPVBi exhibit film
used in fluorescence and phosphorescence systems to produce
high efficiency OLEDs, and red and green emitters have
been developed and improved to the standard required for
commercializing full-color OLEDs.
roughening during EL operation or after storage. This is
another issue that must be solved if longer lifetimes are to be
achieved.
In a previous study, we have synthesized tetraphenylethylene
derivatives, 1,1,2,2-tetrakis(49-tert-butylphenyl)ethene [TBPE],
1,2-di(49-tert-butylphenyl)-1,2-bis(49-tert-butylbiphenyl)ethene
[BPBBPE] and 1,1,2,2-tetrakis(49-tert-butylbiphenyl)ethene
[TBBPE], as new blue emitting materials.21 TBPE has the
basic structure of these tetra-substituted ethylene derivatives,
in which ethylene is connected to the tertiary butyl (tert-butyl)
phenyl moiety. In this series of compounds, tetra-substituted
ethylene is the core to which the chromophores are attached.
TBBPE has a longer conjugation length than TBPE because
of the biphenyl group. The biphenyl moiety has a higher
fluorescence efficiency (Wf) (0.1522) than the phenyl ring
(0.0423). BPBBPE combines the half segment chromophores
of TBPE and TBBPE.
In recent times, red materials with CIE coordinates (0.67,
0.23) and long lifetimes of more than 100 000 h at 11 cd A21
have been produced. Green emitting materials with CIE
coordinates (0.29, 0.64) and lifetimes of 100 000
h at
21 cd A21 have also been developed. However, the best blue
materials have lifetimes of only 12 000 h at 7 cd A21 and CIE
coordinates (0.14, 0.16).14
It is not easy to produce highly efficient blue materials with
long device lifetimes. The electronic levels of blue materials
with a wide band gap are generally mismatched with the
highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) levels of the other
In this study, we sought to synthesize new blue-emitting
chemical structures by making use of tetra-substituted ethylene
and anthracene moieties. The chemical structure charac-
teristics of tetra-substituted ethylene mean that it has more
chromophores per molecule, and greater thermal stability due
Department of Chemistry/Display Research Center, The Catholic
University of Korea, Bucheon, Kyeonggi, 420-743, Korea.
E-mail: hahapark@catholic.ac.kr; Fax: +82-2-2164-4764;
Tel: +82-2164-4821
{ CCDC reference number 655193. For crystallographic data in CIF
or other electronic format see DOI: 10.1039/b706606f
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their electrical and optical properties (Scheme 1). The materials
1,2-di(49-tert-butylphenyl)-1,2-bis(49-(anthracene-9-yl)phenyl)
ethene [BPBAPE, 1A], 1,2-diphenyl-1,2-bis(49-(anthracene-9-yl)
phenyl)ethene [PBAPE, 1B], 9,10-bis(4-(1,2,2-tris(4-tert-butyl-
phenyl)vinyl)phenyl) anthracene [BTBPPA, 2A], and 9,10-bis(4-
(1,2,2-triphenylvinyl)phenyl)anthracene [BTPPA, 2B] were
synthesized by using the Suzuki and McMurry reactions.
In the B series of synthesized molecules, we removed the
tert-butyl group from compounds BPBAPE [1A] and BTBPPA
[2A] to tune the maximum emitting wavelength.
The thermal and electro-optical properties of these materials
were characterized with differential scanning calorimetry
(DSC), thermogravimetric analysis (TGA), atomic force
microscopy (AFM), cyclic voltammetry (CV), and UV-visible
and photoluminescence (PL) spectroscopy. Multilayered EL
devices were fabricated using these materials as non-doped
emitting layers.
Results and discussion
Synthesis and characterization
Scheme 1 Chemical structures of the synthesized materials and
The synthetic routes for the four compounds are shown in
Scheme 2. We used titanium chloride and zinc catalyst mixed
with THF solvent in the McMurry reaction for synthesizing
ethylene moieties, and used boration and the Suzuki reaction
to carry out the carbon–carbon coupling reactions. In the
McMurry reaction, coupling results in two different coordina-
tions, and there are also two competing factors, the steric
hindrance of the phenyl ring derivatives and the electronic
DPVBi.
to its higher molecular weight, than the conventional stilbene
moiety. Anthracene is a very stable and highly efficient
chromophore (Wf = 0.27) and several studies in this area have
focused on it and related chemical structures.24–28
Therefore, we synthesized new tetra-substituted ethylene
derivatives containing anthracene moieties and characterized
Scheme 2 Synthetic routes of BPBAPE [1A], PBAPE [1B], BTBPPA [2A] and BTPPA [2B].
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Fig. 1 1H NMR spectra of (E)- and (Z)-BPBAPE [1A] (a) and (E)-
BPBAPE [1A] (b) in the range of 7.0 to 8.6 ppm; 600 MHz, d8-THF.
repulsion of the two anions. As a result, the asymmetric
carbonyl compounds consist of equal proportions of the
(E)-form and (Z)-form isomers. The mixed isomers of
BPBAPE [1A] and PBAPE [1B] were separated by using
recrystallization. We used (E)-form compounds in the EL
experiments for BPBAPE [1A] and PBAPE [1B].
Fig. 2 ORTEP drawing of BPBAPE [1A], along with selected
dihedral and bond angles, and bond lengths. The ellipsoid probability
is 35%. The #1 symbol in atom labels indicates that these atoms are at
equivalent position (2x, 2y + 2, 2z + 1).
All compounds were purified with the silica column method
and recrystallization, producing very pure powders that we
characterized with NMR, FT-IR, and FAB-MS analysis.
As the McMurry reactions proceeded, the FT-IR carbonyl
stretching peak at 1650 cm21 completely disappeared, and
overall the NMR proton peaks became more shielded with the
loss of carbonyl groups from the compounds.
propeller-like structure. Also, it was confirmed that the angle
between molecules is 30.3u. In particular, the phenyl and
anthracene groups are perpendicularly oriented with an angle
between them of 98.6(7)u. It is possible that this orientation
prevents chromophore stacking between molecules because of
cross dipole stacking, and that it maintains a high performance
emission band and limits excimer formation.29 However,
since the film is generally created in an amorphous state
after vacuum deposition, this explanation might have some
limitations.
1
Fig. 1 shows the H NMR (600 MHz, d8-THF) spectra of
(E)- and (Z)-BPBAPE [1A] (a) and (E)-BPBAPE [1A] (b). As
can be seen in Fig. 1(a), the mixed isomers result in mixed
proton peaks, whereas after recrystallization the (E)-form
compound exhibits clear spin splitting in Fig. 1(b). The
protons that give rise to the peaks marked c, i.e., c protons,
are more shielded than d protons because c protons are closer
to tertiary butyl groups and further from ethylene moieties
than the d protons. In order to verify the chemical structure,
we recrystallized BPBAPE [1A] and then obtained its XRD
pattern, which confirms that only the (E)-form is present
(Fig. 2). It was also confirmed that PBAPE [1B] contains only
the (E)-form by comparing the NMR peak patterns.
Optical and electrochemical properties
After vacuum deposition of the synthesized compounds onto
glass, we determined their UV-visible and PL spectra. The data
are summarized in Table 1.
The UV maximum values of BPBAPE [1A], PBAPE [1B],
BTBPPA [2A], and BTPPA [2B] are 392, 394, 400, and 402 nm
respectively, and their PL maximum values are 489, 486,
463, and 455 nm respectively. All four compounds contain
anthracene moieties, so exhibit UV-visible absorption near
400 nm.
From the data in Fig. 2, we determined the following
structural characteristics of BPBAPE [1A]: bond distances,
planarity, and bond angles. According to the dihedral
and bond angles, [C(27)–C(22)–C(21)–C(21)#1] (112.4(8)u),
[C(5)–C(6)–C(15)–C(16)] (98.6(7)u), [C(23)–C(22)–C(21)–
C(18)] (109.4(6)u), [C(21)#1–C(21)–C(18)–C(19)] (298.8(8)u),
and [C(22)–C(21)–C(18)] (116.5(4)u), BPBAPE [1A] has a
The spectrum of PBAPE [1B] is blue-shifted by 3 nm with
respect to that of BPBAPE [1A], and the spectrum of BTPPA
[2B] is blue-shifted by 8 nm with respect to that of BTBPPA
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Table 1 Optical, electrical and thermal properties of synthesized compounds
Solution (toluene) Film on glass
UVmax/nm PLmax/nm UVonset/nm UVmax/nm PLmax/nm HOMO/eV LUMO/eV Eg/eV Tg/uC Tc/uC Tm/uC Td/uC
Compound
BPBAPE [1A] 388
PBAPE [1B] 388
BTBPPA [2A] 398
BTPPA [2B] 398
495
482
462
451
409
410
420
420
392
394
400
402
489
486
463
455
5.65
5.63
5.59
5.62
2.62
2.61
2.64
2.67
3.03
3.02
2.95
2.95
155.3 232.0 345.0 356.3
135.6 211.3 290.0 381.5
—
—
—
—
398.0 408.4
337.0 401.7
[2A]. This result can be explained in terms of the donating
effect of the tert-butyl group, as is evident in the similar results
of Chen et al.28
respectively. These results can be explained in terms of the
higher molecular weight of BPBAPE [1A] due to the presence
in it of the tert-butyl group. The Tg and Tc of BTBPPA [2A]
and BTPPA [2B] were not measured, but the Tm were found to
be 398.0 uC and 337.0 uC respectively. Thus Tm also increases
as the molecular weight increases, because of the addition of
the tert-butyl group.
In order to measure the HOMO values of the synthesized
compounds, CV analyses were carried out. According to the
CV data, all the compounds have an electrochemical stability
of greater than 50 cycles.
Since BTBPPA [2A] and BTPPA [2B] have higher molecular
weights than BPBAPE [1A] and PBAPE [1B], they have higher
glass transition temperatures than of BPBAPE [1A] and
PBAPE [1B], 135.6 uC and 155.3 uC respectively. These values
are more than twice that of DPVBi, 64 uC.20 Thus increased
thermal stability has been achieved, which affects the lifetime
of OLED devices. We also measured the degradation
temperatures (Td) of BPBAPE [1A], PBAPE [1B], BTBPPA
[2A], and BTPPA [2B], which were determined from the onset
points of weight loss, and found to be 356.3 uC, 381.5 uC,
408.4 uC, and 401.7 uC respectively. For BPBAPE [1A] and
BTBPPA [2A], which have tert-butyl groups, the difference
between Tm and Td is around 10 uC. In contrast, the difference
between Tm and Td for PBAPE [1B] and BTPPA [2B], which
do not contain tert-butyl groups, is 60–90 uC.
The band gaps of BPBAPE [1A] and PBAPE [1B] were
found to be 3.03 and 3.02 eV respectively, and the band gaps of
BTBPPA [2A] and BTPPA [2B] are the same, 2.95 eV.
The band gaps and the HOMO and LUMO levels are
summarized in Table 1. The HOMO levels of BPBAPE [1A],
PBAPE [1B], BTBPPA [2A], and BTPPA [2B], which all
contain anthracene groups, are all near 5.6 eV, which is about
0.4 V lower than those of TBPE, BPBBPE, and TBBPE.21 The
presence of anthracene moieties is thought to be the principal
factor determining the HOMO levels of these materials. It has
been reported that the HOMO levels of 9,10-di(2-naphthyl)
anthracene (ADN) and 2-methyl-9,10-di(2-napthyl)anthracene
(MADN) as well as of many other compounds that have an
anthracene group are also near 5.5–5.6 eV.25–28 Our result is
thus in agreement with the results of previous studies.
To investigate the morphological stabilities of BTBPPA
[2A], BTPPA [2B] and DPVBi, we prepared thin films of these
materials on indium tin oxide (ITO) substrates by vapor
deposition and determined their surface morphologies with
atomic force microscopy (AFM) before and after annealing at
65 uC for 3 days under a nitrogen atmosphere (see Fig. 4, 5,
and 6). Fig. 4(a), 5(a), and 6(a) were obtained immediately
after vacuum deposition, and Fig. 4(b), 5(b), and 6(b) were
obtained after 3 days storage at room temperature under a
nitrogen atmosphere. Fig. 4(c), 5(c), and 6(c) were obtained
after 3 days at 65 uC under a nitrogen atmosphere. The root
mean square (RMS) roughness of BTBPPA [2A] was found to
be 3.407 nm (immediately after deposition), 3.430 nm (3 days),
and 3.718 nm (3 days, 65 uC). Thus this material forms films
that are stable for long periods of heat exposure and storage.
In contrast, BTPPA [2B] undergoes re-crystallization at 65 uC
under a nitrogen atmosphere (RMS = 38.72 nm), but main-
tains its film surface morphology in the absence of heating
(immediately after deposition, 2.844 nm; 3 days, 3.062 nm).
Thus when there is no tert-butyl group in the synthesized
compounds, the packing between molecules is closer, which
results in recrystallization during high temperature storage.
This result agrees with the AFM results for ADN, 2-(tert-butyl)-
9,10-di(2-naphthyl)anthracene (TBADN), and MADN.28
As shown in Fig. 6, the appearance of DPVBi in the AFM
images is better than those of BTBPPA [2A] and BTPPA
[2B] right after deposition, but surface changes occur during
storage, and the surface is also affected by heating (RMS
Thermal properties
We carried out TGA and DSC to examine the thermal
properties of the synthesized molecules (Table 1).
Fig. 3 shows the DSC data for PBAPE [1B], which of the
four compounds containing anthracene has the lowest mole-
cular weight. Tg, Tc, and Tm of PBAPE [1B] are 135.6 uC,
211.3 uC, and 290.0 uC respectively. Tg, Tc, and Tm
for BPBAPE [1A] are 155.3 uC, 232.0 uC, and 345.0 uC
Fig. 3 DSC (solid line) and TGA (dashed line) data of PBAPE[1B];
10 uC min21, N2 conditions.
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Fig. 6 AFM images of DPVBi: (a) no treatment, (b) 3 days under
nitrogen atmosphere, (c) heat treatment (65 uC for 3 days under
nitrogen atmosphere).
Fig. 4 AFM images of BTBPPA [2A]: (a) no treatment, (b) 3 days
under nitrogen atmosphere, (c) heat treatment (65 uC for 3 days under
nitrogen atmosphere).
roughness immediately after deposition, 2.050 nm; 3 days,
51.75 nm; 3 days with heating, 58.63 nm). Thus the synthesized
compounds BTBPPA [2A] and BTPPA [2B] have better film
morphologies than DPVBi. The results for BPBAPE [1A]
and PBAPE [1B] are similar to those for BTBPPA [2A] and
BTPPA [2B].
Electroluminescence properties
We fabricated EL devices with the synthesized compounds
in the following configuration: ITO/2-TNATA (60 nm)/NPB
(15 nm)/synthesized materials (30 nm)/Alq3 (30 nm)/LiF
(1 nm)/Al (200 nm). We compared the EL properties of
these devices with those of a standard device: ITO/2-TNATA
(60 nm)/NPB (15 nm)/DPVBi (30 nm)/Alq3 (30 nm)/LiF
(1 nm)/Al (200 nm).
The EL maximum values of the BPBAPE [1A] and PBAPE
[1B] devices are 475 and 466 nm respectively, i.e., in the sky
blue range, and those for BTBPPA [2A] and BTPPA [2B] are
463 and 452 nm respectively, i.e., in the deep blue range.
It was identified that ELmax values of BPBAPE [1A] and
PBAPE [1B] devices has been blue shifted compared to the
PLmax values. We could not clearly understand the reasons for
this blue shift in the EL spectra. Nonetheless, we assume that
HIL (hole injection layer) and HTL are related to the blue shift
in the EL spectra, and an additional experiment is being
conducted separately.
Fig. 7 shows the EL spectra of BPBAPE [1A], PBAPE [1B],
BTBPPA [2A], BTPPA [2B], and DPVBi. The spectrum of
PBAPE [1B] is about 9 nm blue-shifted with respect to that of
Fig. 5 AFM images of BTPPA [2B]: (a) no treatment, (b) 3 days
under nitrogen atmosphere, (c) heat treatment (65 uC for 3 days under
nitrogen atmosphere).
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the exception of BTBPPA [2A] exhibit the same I–V charac-
teristics as DPVBi or better.
We suggest that because BTBPPA [2A] has a high number of
tert-butyl groups, i.e., 6 tert-butyl moieties per molecule, its
conductivity is lower, which results in a high turn-on voltage.
PBAPE [1B] and BTPPA [2B] have no tert-butyl groups, so
their devices exhibit the best I–V curves of the synthesized
materials.
The device efficiency data of the compounds are shown in
Table 2. In an earlier study, BPBBPE exhibited a greenish blue
color, i.e. (0.218, 0.335) and an EL luminance efficiency of
2.31 cd A21 21c
The EL color of BPBAPE [1A], to which
.
anthracene was added in order to increase its luminescence
efficiency and to twist the molecular structure, is blue-shifted
with sky-blue CIE coordinates (0.195, 0.303) compared to
BPBBPE. In addition, the efficiency of the BPBAPE [1A]
device is 10.33 cd A21, which is very high for an OLED device
structure without doping, and it has the strongest brightness of
the synthesized compounds. Most importantly, its efficiency is
at least twice that of the conventional DPVBi device.
Fig. 7 EL spectra of ITO/2-TNATA/NPB/BPBAPE [1A] (&),
PBAPE [1B] (%), BTBPPA [2A] ($), BTPPA [2B] (#) and DPVBi
(q)/Alq3/LiF/Al devices at 10 mA cm22
.
We conclude that the devices containing PBAPE [1B] and
BTPPA [2B], which do not contain tert-butyl groups, have
better I–V characteristics than the devices with BPBAPE
[1A] and BTBPPA [2A]. However, the comparison of their
luminance efficiencies produces a different result. The lumi-
nance efficiency of PBAPE [1B] is 40% lower than that of
BPBAPE [1A], and that of BTPPA [2B] is 20% lower than that
of BTBPPA [2A]. However, since BTBPPA [2A] has a high
turn-on voltage, 9.5 V, BTPPA [2B] has a power efficiency that
is about 10% higher. Further, in the absence of the electron-
donating effects of tert-butyl groups, PBAPE [1B] and BTPPA
[2B] exhibit CIE values that closely approach the blue color
with respect to BPBAPE [1A] and BTBPPA [2A]. As a result,
we conclude that the EL efficiencies and CIE values of these
synthesized compounds are affected by the presence of tert-
butyl groups and their inductive effect, as was also concluded
in a previous study of ADN and TBADN.28
Fig. 8 Current density–voltage characteristics of ITO/2-TNATA
(60 nm)/NPB (15 nm)/synthesized material or DPVBi (30 nm)/Alq3
(30 nm)/LiF (1 nm)/Al devices.
The materials that combine anthracene and tetraphenyl-
ethylene moieties produce devices with better luminance
efficiencies than DPVBi. In particular, the BPBAPE [1A]
device exhibits a luminance efficiency of above 10 cd A21 even
without using doping. This high luminance efficiency might be
due to the propeller-like chemical structure of the molecule
and its cross dipole stacking.29 The PBAPE [1B] and BTBPPA
BPBPAE [1A], and the spectrum of BTPPA [2B] is about 11 nm
blue-shifted with respect to that of BTBPPA [2A]. Thus there
is the same blue-shift effect in the EL spectra as found in the
PL spectra.
[2A] devices also exhibit a high luminance efficiency, 5 cd A21
,
Fig. 8 shows the I–V curves of the devices. When we
compare the I–V curves for the BPBAPE [1A], PBAPE [1B],
BTBPPA [2A], and BTPPA [2B] devices, which have similar
HOMO and LUMO levels, we find that these compounds with
and so can also be used as blue emitting layers. Further,
BTPPA [2B] has better thermal properties and a better
luminance efficiency, a lower operating voltage, and a higher
power efficiency than DPVBi. The deep blue CIE coordinates
Table 2 EL performance of multi-layered devices with the structure ITO/2-TNATA (60 nm)/NPB (15 nm)/synthesized material or DPVBi
(30 nm)/Alq3 (30 nm)/LiF (1 nm)/Al (200 nm) at 10 mA cm22
Compound
ELmax/nm
Voltage/V
Luminance efficiency/cd A21
Power efficiency/lm W21
CIE (x, y)
BPBAPE [1A]
PBAPE [1B]
BTBPPA [2A]
BTPPA [2B]
DPVBi
475
466
463
452
465
8.1
6.3
9.5
6.8
7.65
10.33
6.09
5.03
3.93
3.92
4.00
3.05
1.67
1.82
1.61
(0.195, 0.303)
(0.194, 0.268)
(0.165, 0.195)
(0.159, 0.135)
(0.150, 0.160)
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(0.159, 0.135) of the BTPPA [2B] device are further evidence of
capillaries under nitrogen, and mounted on the diffractometer.
The structures were characterized by the application of direct
methods using the SHELXS-96 program and least-squares
refinement using SHELXL-97.
its superior properties.
Conclusions
For the EL devices, all organic layers were deposited under
1026 Torr, with a rate of deposition of 1 s s21 to give an
emitting area of 4 mm2. The LiF and aluminium layers were
continuously deposited under the same vacuum conditions.
The current–voltage (I–V) characteristics of the fabricated
EL devices were obtained with a Keithley 2400 electrometer.
Light intensity was obtained with a Minolta CS-100A.
We have successfully designed and synthesized four useful blue
emitting materials, BPBAPE [1A], PBAPE [1B], BTBPPA [2A]
and BTPPA [2B], which are composed of tetra-substituted
ethylene as a new core site and anthracene chromophore.
We fabricated EL devices with the synthesized compounds
in the following configuration: ITO/2-TNATA (60 nm)/NPB
(15 nm)/synthesized materials (30 nm)/Alq3 (30 nm)/LiF
(1 nm)/Al (200 nm). The EL maximum values of BPBAPE
[1A], PBAPE [1B], BTBPPA [2A], and BTPPA [2B] were found
to be 475, 466, 463, and 452 nm, respectively. All the materials
that combine anthracene and tetraphenylethylene moieties
exhibit better luminance efficiencies than DPVBi. BPBAPE
[1A] exhibits a luminance efficiency above 10 cd A21 without
doping. It might be due to the propeller-like chemical structure
of the molecule and its cross dipole stacking. PBAPE [1B]
and BTBPPA [2A] also exhibit a high luminance efficiency,
5 cd A21, which means they too can be used as blue emitting
layers. In particular, the BTPPA [2B] device has better thermal
properties, a better luminance efficiency, a lower operating
voltage, and a higher power efficiency than the conventional
DPVBi device. Its deep blue CIE coordinates (0.159, 0.135) are
further evidence of its superior properties.
Selected crystal data for BPBAPE [1A]
˚
C62H52, Mr = 797.04, a = 20.268(3) A, b = 10.0519(13) A, c =
˚
3
˚
˚
22.389(3) A, a = 90u, b = 90u, c = 90u, V = 4561.5(10) A , Z =
4, rcalc = 1.161 mg m22, F(000) = 1696, crystal size 0.16 mm 6
0.08 mm 6 0.07 mm, l = 0.71073 A, T = 293(2) K, m =
0.065 mm21, final R indices [I . 2s(I)] R1 = 0.1204, vR2 =
0.2709.{
Synthesis
i) 1,2-Bis(4-bromophenyl)-1,2-bis(4-tert-butylphenyl)ethene
(1) and 4,49,40-(2-(4-bromophenyl)ethene-1,1,2-triyl)tris(tert-
butylbenzene) (2). Bis(4-tert-butylphenyl)methanone (5 g,
17 mmol), (4-tert-butylphenyl)(4-bromophenyl)methanone
(16 g, 51 mmol) and Zn powder (10.6 g, 170 mmol) were
added to dried THF solvent (500 mL), then TiCl4 (15 mL,
136 mmol) was added into the reaction mixture. The mixture
was heated to 60 uC for 1 h under nitrogen. The reactant
mixture was cooled after 1 h and then the product was
extracted with diethyl ether. The organic layer was dried with
anhydrous MgSO4 and filtered. The solution was evaporated.
The residue was dissolved in CHCl3 and added to methanol.
The precipitate was filtered off and washed with methanol.
The mixture powder was separated by using column
chromatography with CHCl3–n-hexane (1 : 10) eluent to
afford a white solid 1,2-bis(4-bromophenyl)-1,2-bis(4-tert-
butylphenyl)ethene (1) (5.2 g) and 4,49,40-(2-(4-bromophenyl)
ethene-1,1,2-triyl)tris(tert-butylbenzene) (2) (5.7 g).
Experimental
General information
1H NMR spectra were recorded on Bruker Avance 500 and
Avance 600 spectrometers. Fast atom bombardment (FAB)
mass spectra were recorded on a JEOL, JMS-AX505WA,
HP5890 series II. Atomic force microscopy (AFM) imaging
was performed in air using a PicoScan system (Molecular
Imaging) equipped with a 5 6 5 mm scanner. Magnetic-ac
(Mac) mode (a non-contact mode) was used for all the AFM
images. The optical absorption spectra were obtained with a
HP 8453 UV-VIS-NIR spectrometer. The melting tempera-
tures (Tm), glass-transition temperatures (Tg), crystallization
temperatures (Tc), and degradation temperatures (Td) of the
compounds were measured by carrying out differential
scanning calorimetry (DSC) under a nitrogen atmosphere
using a DSC2910 (TA Instruments) and thermogravimetric
analysis (TGA) using a SDP-TGA2960 (TA Instruments). A
Perkin Elmer luminescence spectrometer LS50 (xenon flash
tube) was used for photo- and electro-luminescence spectro-
scopy. The redox potentials of the compounds were deter-
mined with cyclic voltammetry (CV) using an EG&G
362 electrochemical workstation with a scanning rate of
50–200 mV s21. The synthesized materials were dissolved in
N,N-dimethylformamide (DMF) with 0.1 M tetrabutylammo-
nium tetrafluoroborate as the electrolyte. We used a platinum
working electrode and a saturated Ag/AgNO3 reference
electrode. Ferrocene was used for potential calibration and
for reversibility criteria.
ii) 1,2-Bis(4-tert-butylphenyl)-1,2-bis(4-(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)phenyl)ethene (3). 1,2-Bis(4-bromophe-
nyl)-1,2-bis(4-tert-butylphenyl)ethene (1) (5 g, 8.3 mmol) was
dissolved in 200 mL of dry THF solution and stirred at 278 uC,
then 1.6 M n-BuLi (20 mL) was added. Next, isopropoxy-
4,4,5,5-tetramethyl-1,3,2-dioxaborolane (6.5 mL, 34 mmol)
was added to the reaction mixture after 30 min. After the
reaction had finished, the reaction mixture was extracted with
diethyl ether and water. The organic layer was dried with
anhydrous MgSO4 and filtered. The solution was evaporated.
The residue was dissolved in acetone and added to methanol.
The precipitate was filtered off and washed with methanol. The
mixture powder was separated by using column chromato-
graphy with ethyl acetate–n-hexane (1 : 9) eluent to afford a
white solid 1,2-bis(4-tert-butylphenyl)-1,2-bis(4-(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)phenyl)ethene (3) (3.2 g, 55%).
1H NMR (CDCl3, 500 MHz): d 7.53 (m, 4H), 7.08 (m, 4H),
6.69 (m, 8H), 1.58 (d, 24H), 1.23 (d, 18H); FAB+-MS: 696.
Crystals of BPBAPE [1A] were obtained from CHCl3/
isopropyl alcohol at room temperature, sealed in glass
4676 | J. Mater. Chem., 2007, 17, 4670–4678
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iii) 1,2-Bis(49-tert-butylphenyl)-1,2-bis(49-(anthracene-9-
yl)phenyl)ethene [BPBAPE, 1A]. 1,2-Bis(4-tert-butylphenyl)-
1,2-bis(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)
ethene (3) (3 g, 4.3 mmol), 9-bromoanthracene (2.5 g,
10 mmol), Pd(OAc)2 (0.29 g, 1.29 mmol), and (tris-o-tolyl)3P
(0.39 g, 1.29 mmol) were added to DME (200 mL) solution,
then a prepared K2CO3 solution, which was dissolved in a
DME and H2O (1 : 1, 100 mL) solvent, was added to the
reaction mixture. After the reaction had finished, the reaction
mixture was extracted with diethyl ether and water. The
organic layer was dried with anhydrous MgSO4 and filtered.
The solution was evaporated. The residue was dissolved in
CHCl3 and added to methanol. The precipitate was filtered off
and washed with methanol. The yellowish powder was purified
by using column chromatography with CHCl3–n-hexane (1 : 2)
eluent to afford a beige solid (BPBAPE, 1A) (3 g, 86%).
1H NMR (THF, 600 MHz): d 8.52 (s, 2H), 8.05 (d, 4H), 7.67
(d, 4H), 7.44 (t, 4H), 7.36 (t, 12H), 7.27 (d, 4H), 7.20 (d, 4H),
1.36 (s,18H); 13C NMR (CDCl3, 500 MHz):149.9, 143.5, 141.4,
140.8, 137.4, 136.7, 131.61, 131.56, 131.48, 130.8, 130.4, 128.5,
127.1, 126.6, 125.4, 125.3, 124.7, 34.8, 31.7; FT-IR (KBr,
cm21): 3049, 3026, 2960, 2901, 2865, 1510, 1441, 1409, 1360,
883, 843, 792, 736; FAB+-MS: 796.
(0.38 g, 1.68 mmol), and (tris-o-tolyl)3P (0.51 g, 1.68 mmol)
were added to DME (200 mL) solution, then a prepared
K2CO3 solution, which was dissolved in a DME and H2O (1 : 1,
100 mL) solvent, was added to the reaction mixture. After the
reaction had finished, the reaction mixture was extracted with
diethyl ether and water. The organic layer was dried with
anhydrous MgSO4 and filtered. The solution was evaporated.
The residue was dissolved in CHCl3 and added to methanol.
The precipitate was filtered off and washed with methanol. The
yellowish powder was purified by using column chromato-
graphy with CHCl3–hexane (1 : 1) eluent to afford a beige solid
(BTBPPA, 2A) (1.3 g, 44%).
1H NMR (CDCl3, 500 MHz): d 7.65 (q, 4H), 7.33 (q, 4H),
7.25 (d, 4H), 7.20 (d, 4H), 7.17 (m, 8H), 7.14–7.07 (m, 12H),
7.02 (d, 4H), 1.30 (d, 36H), 1.25 (s, 18H); 13C NMR (THF,
500 MHz):148.8, 148.6, 143.3, 140.8, 140.3, 136.5, 136.4, 130.9,
130.7, 130.5, 130.2, 129.9, 129.4, 128.2, 126.2, 124.3, 123.9,
123.7, 33.7, 33.2, 31.5, 30.4; FT-IR (KBr, cm21): 3061, 3024,
2962, 2902, 2865, 1508, 1460, 1439, 1390, 1361, 1109, 1020,
942, 836, 800, 771, 741, 693; FAB+-MS: 1175.
vii) 9,10-Bis(4-(1,2,2-triphenylvinyl)phenyl)anthracene
[BTPPA, 2B]. BTPPA was synthesized as for the above series
by using the McMurry and Suzuki coupling reactions.
iv) 1,2-Diphenyl-1,2-bis(49-(anthracene-9-yl)phenyl)ethene
[PBAPE, 1B]. PBAPE was synthesized as for the above series
by using the McMurry and Suzuki coupling reactions.
1H NMR (THF, 500 MHz): d 8.50 (s, 2H), 8.00 (d, 4H), 7.65
(d, 4H), 7.42 (t, 4H), 7.35–7.29 (m, 12H), 7.20 (t, 4H), 7.17 (t,
2H), 7.00 (t, 4H); 13C NMR (CDCl3, 500 MHz):143.8, 143.4,
143.1, 137.2, 137.0, 131.8, 131.68, 131.49, 130.9, 130.3, 128.5,
128.1, 127.1, 126.9, 126.7, 125.7, 125.3; FT-IR (KBr, cm21):
3073, 3049, 3024, 1508, 1491, 1441, 1410, 1358, 943, 887, 753,
736, 699; FAB+-MS: 684.
1H NMR (CDCl3, 500 MHz): d 7.63 (q, 4H), 7.34 (q, 4H),
7.25–7.12 (m, 38H); 13C NMR (CDCl3, 500 MHz): 144.1,
143.7, 143.6, 143.3, 141.8, 141.2, 137.2, 137.1, 131.76, 131.6,
131.45, 130.9, 129.9, 128.03, 127.95, 127.95, 127.81, 127.18,
126.82, 126.78, 125.07; FT-IR (KBr, cm21): 3058, 3025, 1491,
1443, 1394, 1074, 1027, 942, 765, 755, 700; FAB+-MS: 838.
Acknowledgements
This work was supported by Science Scholarship of Seoul City
(2006–2007) and the department specialization Fund, 2007 of
Catholic University of Korea. The authors thank Dr Z. Xie,
Professor Y. Ma and Professor S. W. Kang for XRD data
analysis.
v) 4,4,5,5-Tetramethyl-2-(4-(1,2,2-tris(4-tert-butylphenyl)vi-
nyl)phenyl)-1,3,2-dioxaborolane
(4).
4,49,40-(2-(4-Bromo-
phenyl)ethene-1,1,2-triyl)tris(tert-butylbenzene) (2) (5 g,
8.6 mmol) was dissolved in 200 mL of dry THF solution
and stirred at 278 uC, then 1.6 M n-BuLi (21 mL) was
added. Next, isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane (6.7 mL, 35 mmol) was added to the reaction mixture after
30 min. After the reaction had finished, the reaction mixture
was extracted with diethyl ether and water. The organic layer
was dried with anhydrous MgSO4 and filtered. The solution
was evaporated. The residue was dissolved in acetone and
added to methanol. The precipitate was filtered off and washed
with methanol. The mixture powder was separated by using
column chromatography with ethyl alcohol–n-hexane (1 : 9)
eluent to afford a white solid 4,4,5,5-tetramethyl-2-(4-(1,2,2-
tris(4-tert-butylphenyl)vinyl)phenyl)-1,3,2-dioxaborolane (4)
(3.9 g, 72%).
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