A non-planar pentaphenylbenzene functionalized benzo[2,1,3]thiadiazole derivative as a novel red molecular emitter for non-doped organic light-emitting diodes

Article abstract of DOI:10.1039/b719390d

A novel non-planar pentaphenylbenzene functionalized benzo[2,1,3] thiadiazole derivative (BPTBTD) has been designed and synthesized with only three steps, and applied into non-doped organic light-emitting diodes (OLEDs) as a red molecular emitter. The molecule exhibits good solubility in common organic solvents, excellent thermal stability and film-forming properties. The most important feature is that photoluminescence of BPTBTD shows excellent stablity in different solvents, at different concentrations and in different solid states. Red organic light-emitting diodes were fabricated in a facile non-doped configuration with different thicknesses of emission layers. Saturated red-emission was observed with an emission peak at 621 nm, a maximum external quantum efficiency of 1.0% and a maximum brightness of 1572 cd m^-2. Especially, the properties of devices with thick emission layers are two times better than those of the devices with thin emission layers. These results indicate that the non-planar pentaphenylphenyl functional groups substantially suppressed the tendency for molecular aggregation in thin solid films, leading to a very stable photoluminescence and higher efficiency of devices with thicker layers. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b719390d

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
A non-planar pentaphenylbenzene functionalized benzo[2,1,3]thiadiazole
derivative as a novel red molecular emitter for non-doped organic
light-emitting diodes†
Xiaobo Sun,‡ Xinjun Xu, Wenfeng Qiu, Gui Yu, Hengjun Zhang, Xike Gao, Shiyan Chen,
*
Yanlin Song and Yunqi Liu
Received 17th December 2007, Accepted 12th March 2008
First published as an Advance Article on the web 31st March 2008
DOI: 10.1039/b719390d
A novel non-planar pentaphenylbenzene functionalized benzo[2,1,3]thiadiazole derivative (BPTBTD)
has been designed and synthesized with only three steps, and applied into non-doped organic
light-emitting diodes (OLEDs) as a red molecular emitter. The molecule exhibits good solubility in
common organic solvents, excellent thermal stability and film-forming properties. The most important
feature is that photoluminescence of BPTBTD shows excellent stablity in different solvents, at different
concentrations and in different solid states. Red organic light-emitting diodes were fabricated in a facile
non-doped configuration with different thicknesses of emission layers. Saturated red-emission was
observed with an emission peak at 621 nm, a maximum external quantum efficiency of 1.0% and
a maximum brightness of 1572 cd mꢀ2. Especially, the properties of devices with thick emission layers
are two times better than those of the devices with thin emission layers. These results indicate that the
non-planar pentaphenylphenyl functional groups substantially suppressed the tendency for molecular
aggregation in thin solid films, leading to a very stable photoluminescence and higher efficiency of
devices with thicker layers.
with an intramolecular charge transfer (ICT, donor–p-acceptor)
Introduction
group or an extended big p-conjugation structure, which are easy
to aggregate in highly concentrated solutions and solid states
because of either effective p–p stacking or dipole–dipole inter-
actions.9 To weaken the concentration effect, the doping
approach has been invented and used in fluorescence and phos-
phorescence systems to produce high efficiency OLEDs.10 But the
process of doping is difficult to control. Red non-doped emitters
have been a hot point,11–15 because they can be pristine thin films
with vacuum deposition, which will simplify the procedure of
preparing devices. However, most of them are still fabricated
with donor and acceptor groups. Though a red non-doped
OLED with good performance has been reached, the ICT
molecular structure still affects the efficiency of devices. To
improve the color purity, the thickness of the emitting layer
should be increased, while it will lead a decrease in the efficiency
of the device. The color purity and efficiency are usually
compromised. Therefore, the idea to resolve this problem should
be changed to a structural point to design red molecular emitters
without a donor–acceptor structure.16
Organic electroluminescent materials and light-emitting diodes
(OLEDs) have been the universal subject of intense research and
attracted significant attention because of their potential
applications in colorful flat panel displays and solid state white
illuminations. Since the first small molecular OLEDs and
polymeric OLEDs were pioneered by Tang and Van Slyke1 and
Friend and co-workers,2 numerous conjugated organic molecules
have been designed and synthesized to fabricate OLEDs
with high electroluminescent (EL) efficiencies, good thermal
properties and long lifetimes as well as pure color coordinates
ranges.3–6
For full-color displays, not only is the brightness important,
but color saturation is crucial. However, it is difficult to produce
highly efficient devices with pure luminescence actually. Many
organic emitters exhibit high fluorescent quantum yields in
solution, but they show little or no fluorescence in highly
concentrated solution or solid states.7 The phenomenon is named
‘‘concentration quenching’’, which will also cause emission
spectrum broadening and a bathochromic phenomenon.8 The
effect is especially strong in organic red emitters,3 because red
organic conjugated emitting materials are always constructed
From this point, we sought to design a new red-emitting
molecular structure. Using developing modern organic synthetic
methods, we can organize different functional groups to fabric
suitable molecular structures for special aims. Benzo[1,2,5]thia-
diazole is an attractive heterocycle with a high electron affinity.17
The synthesis and modification of the ring system is easy, so
many small molecules and polymers have been obtained. Thio-
phene-benzo[1,2,5]thiadiazole (BTB), which is one of important
benzo[1,2,5]thiadiazole derivatives, has a red-shift luminescence
at 576 nm with a fluorescence quantum yield 95%.18 And the BTB
derivatives have shown good performances in optical electronic
Beijing National Laboratory for Molecular Sciences, Institute of
Chemistry, Chinese Academy of Sciences, Beijing 100080, P. R. China.
E-mail: liuyq@mail.iccas.ac.cn; Fax: 10-62559373; Tel: 10-62613253
† Electronic supplementary information (ESI) available: TGA curve of
the BPTBTD powder. See DOI: 10.1039/b719390d
‡ Present address: Departments of Chemistry, Center for Nanoscale
Science and Engineering, University of California, Riverside, California
92521, USA.
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devices, such as OLEDs,19–24 organic field-effect transistors
(OFETs)25 and solar cells.26,27 In OLEDs, BTB is often used as
a monomer for polymer materials, but seldom for small
molecules.21,22 The reason is that BTB shows weak photo-
luminescence (PL) in films, though it has a high fluorescence
quantum yield in solvent, which is associated with aggregates.
From a structural point, a strong luminescence for BTB films
should be reached if the intermolecular p–p stacking can be
Results and discussion
Design and synthesis
The process used to prepare the desired compound BPTBTD is
shown in Scheme 1. The symmetric product consists of a fluo-
rophore at the center coupled with two identical pentaphenyl-
phenyl moieties at two sides. The classical heteroaromatic
fluorophore 4,7-di(2-thienyl)-benzo[2,1,3]thiadiazole (2) was
chosen as the parent compound, which was prepared by the
traditional nickel-catalyzed Kumada coupling reaction between
compound 1 and freshly prepared 2-thienylmagnesium bromide.
Non-planar pentaphenylphenyl group was used as the most
important functional group for three reasons: the first one is to
bathochromically shift luminescence to the red region by
extending the molecular conjugated structure; the second is to
suppress the formation of molecular aggregates and minimize
intermolecular p–p stacking in the solid state by having a non-
planar three-dimensional structure;30,31,34 the third is to give the
molecule good thermal stability and film-forming properties as
has been proved by other research groups.8,38 Therefore, it is
expected to have a high thermal stability, good film-forming
ability and excellent solid luminescence. Finally, our molecule
can be seen as a simple line-shaped small molecule containing
seven aryl groups as a framework modified with four benzyl
groups as side groups. Red emission should come from the large
conjugated structure instead of a traditional donor–acceptor ICT
structure.
effectively prevented. Pentaphenylphenyl (Mullen-type)28–33
¨
dendrimer is a three-dimensional non-planar functional group,
which is both shape-persistent and chemically stable. So, it
can exclude p-stacking at lower dendritic generations and
inhibit the formation of molecular aggregation. Thomas et al.
firstly reported star-shaped molecules featuring hexaarylbenzene
based triarylamine donors and a dithienyl benzothiadiazole
acceptor.34 The fluorescence quantum yield of these star-shaped
molecules could reach 66%. Recently, as an excellent construc-
tion block, pentaphenylphenyl has been successfully incorpo-
rated into both small molecules35–38 and polymer materials28,30,31
for OLEDs.
In this study, we have utilized pentaphenylphenyl groups to
functionalize thiophene-benzo[1,2,5]thiadiazole to develop a new
red-emitting structure, BPTBTD (shown in Scheme 1). The
thermal and electronic properties of BPTBTD were investigated
by TGA and cyclic voltammetry. The relationships of molecular
structures and photophysical properties were discussed by
ultraviolet-visible (UV-vis) absorption and photoluminescence
spectra. In addition, red non-doping electroluminescent devices
based on BPTBTD were obtained by a facile vacuum vapor
deposition, and discussed using different thicknesses of emitting
layers.
As shown in Scheme 1, BPTBTD could be easily synthesized
with only three steps: first, the key reactive intermediate 3 was
prepared in a yield of 70% by treatment of compound 2 with
Scheme 1 Synthetic route to the compound BPTBTD.
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N-bromosuccinimide (NBS)–CHCl3. Then, the tolane derivative
4 was synthesized by Pd(0)-catalyzed Hagihara–Sonogashira
coupling of compound 3 with phenylacetylene. At low temper-
atures the reaction led selectively to the formation of compound
4 in high yield (89%). Finally, BPTBTD was obtained by an
intermolecular Diels–Alder reaction between compound 4 and
tetraphenylcyclopentadienone at high temperature.28 Pure
BPTBTD was obtained through silica-gel column purification
and by train sublimation. All intermediates and final products
were characterized unambiguously with 1H NMR spectroscopy,
elemental analysis and mass spectroscopy. For the large molec-
ular weigh of BPTBTD, we employed a MALDI-TOF/MS
measurement, which is to characterize the structure and molec-
ular weight of the new compound directly. Functionalized by the
non-planar pentaphenylphenyl group, BPTBTD has good
solubility, and could be dissolved in many normal organic
solvents, such as toluene, chloroform, and THF, etc.
Fig. 1 UV-vis absorption and photoluminescence spectra of BPTBTD
in solvents of different polarities (1 ꢂ 10ꢀ5 M).
Thermal and electrochemical properties
peaks are located at 328 and 475 nm, and the emission peak is at
594 nm. With moderately polar solvents (THF and CH2Cl2),
similar absorption peaks are located at 332 and 483 nm, and the
emission band is near to 609 nm. When measured in a strong
polar solvent (acetonitrile), the absorption peaks are still
centered at 333 and 485 nm, and the emission peak is at 618 nm.
The absorption and emission wavelength of BPTBTD changed
little with the polarity of the solvent increasing. It resulted in only
a 10 nm shift to the absorption and 20 nm to the emission peaks.
For comparison, the emission wavelength of 4,7-di(2-thienyl)-
benzo[2,1,3]thiadiazole derivative Btza has been shifted about
70 nm ranging from hexane to CH2Cl2.21 Obviously, excited-state
solvatochromism of BPTBTD is very weak. This result clearly
shows that BPTBTD possesses weak dipole–dipole interactions
and/or minimal intermolecular p–p stacking. The PL spectra in
solutions with different concentrations and in solid films could
indicate this view further. As shown in Fig. 2, BPTBTD shows
bright red fluorescence both in solutions with different concen-
trations and in solid films. When the concentration of the
solution is changed from 1 ꢂ 10ꢀ6 M to 1 ꢂ 10ꢀ3 M, the emission
peaks are changed by only 5 nm, which are located at 609–614
The thermal stability of BPTBTD was investigated by ther-
mogravimetric analysis (TGA). The decomposition temperature
(Td) was estimated at about 340 ꢁC (ESI†, Fig. S1). The excellent
thermal stability indicates that BPTBTD can form thermally
stable films by vacuum sublimation. The electronic properties of
BPTBTD were investigated by cyclic voltammetry. When
potential cycling was applied, the compound is electrochemically
stable in THF solution. The onset potentials for reduction
red
(E
) of BPTBTD is about ꢀ1.21 eV. The LUMO of BPTBTD
onset
was estimated at about ꢀ3.60 eV, according to the equation
red
ELUMO ¼ ꢀ(4.8 eV ꢀ EFOC + E
). The corresponding HOMO
onset
was calculated by the LUMO value and the energy gap (Eg ¼
2.16 eV) from the edge of the absorption spectrum, and was
found to be about ꢀ5.76 eV. The relatively low LUMO energy
level suggests that BPTBTD would benefit electron injection and
electron-transport, when is used as an active layer in devices.
Photophysical properties
Non-planar pentaphenylphenyl group was used to functionalize
the fluorophore to achieve stable luminescence. UV-vis absorp-
tion and PL spectra are very important data to testify our design.
The UV-vis absorption and PL spectra of BPTBTD in CH2Cl2
shows that BPTBTD exhibits two absorption peaks located at
332 and 483 nm, which may be deduced to be p–p transitions of
the pentaphenylphenyl group and the core 4,7-di(2-thienyl)-
benzo[2,1,3]thiadiazole, respectively. Benzo[2,1,3]thiadiazole
derivates are always used as electron-withdrawing functional
groups, but no ICT band appeared in the absorption spectrum of
BPTBTD. So, BPTBTD is not an ICT material, and the red
luminescence is the result of conjugated structure enlargement.
As shown in Fig. 1, there is only one emission peak in the PL
spectrum of the solution, which is located at 609 nm. Its fluo-
rescent quantum yield was measured to be 32% in a CH2Cl2
solution relative to fluorescein in water, with a quantum yield of
0.92 at pH > 8.39 To testify the molecular structure directly,
spectra of BPTBTD in different polar solvents were measured.
Fig. 1 shows the photophysical properties in solvents of different
polarities. In a solvent of low polarity (toluene), the absorption
Fig. 2 Photoluminescence spectra of BPTBTD in CH2Cl2 solutions with
different concentrations and in the solid films.
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nm. In the film state, there is nearly no difference in the emission
peaks with different thicknesses. The emission peaks are centered
at 609–610 nm with thicknesses changed from 20 nm to 50 nm,
which are similar to those in solution. Based on these
phenomena, we could make a decision that BPTBTD is a very
stable emitter, which shows little change of emission peaks in
different solvents with different polarity and concentration, even
in solid films. Therefore, BPTBTD can be a good red-emitting
candidate for non-doped OLEDs.
Electroluminescent properties
The new emitter can be easily deposited as pristine thin film by
thermal deposition in a vacuum system. To achieve high
performance in organic EL devices, it is necessary to attain
a hole–electron transporting balance and effective recombination
of holes and electrons in the emitting layer. The devices were
fabricated with the following configuration ITO/NPB (30 nm)/
BPTBTD (x nm)/TPBI (30 nm)/LiF (1 nm)/Al by a sequential
thermal deposition. To improve the color purity, the thicknesses
of BPTBTD were increased from 20 nm to 50 nm. Here,
BPTBTD, NPB, TPBI and LiF were used as emitting layer, hole-
transporting, electron-transporting materials and electron
injection layer, respectively. The proposed energy level diagram
provides further insight into the roles of four functional materials
playing in the device (Fig. 3). In this configuration, holes and
electrons are all restricted in the emission layer.
Fig. 4 EL spectra of devices ITO/NPB/BPTBTD (x nm)/TPBI/LiF/Al.
the device structure.16,41,42 Under different applied voltages, the
emission spectra are very stable (shown in Fig. 5).
Fig. 6 and 7 show the electroluminescent properties of two sets
of devices with different thicknesses of emitting layers. In
Fig. 4 shows the electroluminescence spectra of non-doped
devices with different thicknesses of BPTBTD as the emission
layer. For these two kinds of device, only red emission peaks were
observed from BPTBTD, and no emission peak from other
materials, such as NPB. When the thickness of BPTBTD is 20 nm,
the emission peak is located at 609 nm, which is similar to the
photoluminescence spectra in solid films. The electroluminescent
peak was shifted to 621 nm with the thickness of the emission
layer increasing to 50 nm. The color purity was improved obvi-
ously. There is a phenomenon that emission maximum show a 12
nm red-shift with the thickness of emission layer increasing. The
peaks of the PL spectra are nearly identical in solutions and solid
states, so the red-shifted spectra with different thicknesses are not
due to the excimer of BPTBTD, but the optical interference from
Fig. 5 EL spectra of devices ITO/NPB/BPTBTD (50 nm)/TPBI/LiF/Al
under different voltages.
Fig. 3 Proposed energy level diagram of non-doping OLED with
BPTBTD as the emitting layer (the HOMO and LUMO levels of NPB
and TPBI are rooted in ref. 40)
Fig. 6 Current density–voltage (a) and brightness–voltage (b) charac-
teristics of the devices ITO/NPB/BPTBTD (x nm)/TPBI/LiF/Al.
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good solubility in common organic solvents, excellent thermal
stability and film-forming properties. In different solvents,
BPTBTD exhibits very weak excited-state solvatochromism.
Moreover, BPTBTD also shows stable photoluminescence with
different concentrations in solution and in solid state, which
indicates that the non-planar functional pentaphenylphenyl
group substantially suppressed dipole–dipole interactions and
intermolecular p–p stacking. With increasing thickness of
emission layer for the red OLEDs, an obvious improvement was
achieved in both brightness and efficiency. The experimental
results indicate that BPTBTD has great potential for use in red
OLEDs of high performance with facile preparation methods.
Intensive studies on electroluminescent properties by optimizing
the configurations of the devices (modifying the cathode to
enhance the electron injection or adopting suitable thicknesses)
and modifications to the structures of these derivative materials
are in progress.
Fig. 7 External quantum efficiency–current density characteristics of the
devices ITO/NPB/BPTBTD (x nm)/TPBI/LiF/Al.
Experimental
contrast, when the thickness of the BPTBTD layer was 20 nm,
a brightness of 835 cd mꢀ2 at a current density of 200 mA cmꢀ2
and an external quantum efficiency of 0.43% (corresponding to
0.60 cd Aꢀ1) were acquired. When the thickness of BPTBTD was
increased to 50 nm, a obviously improved performance of the
non-doped OLEDs was obtained with a brightness of 1572 cd
mꢀ2 at a current density of 200 mA cmꢀ2 and a maximum external
quantum efficiency of 1.0% (corresponding to 1.37 cd Aꢀ1).
Obviously, the properties of devices with thick emission layers
are two times better than those of the devices based on thin
emission layers. As reported by many groups, the thickness of the
organic emitting layer has much effect on the properties of
devices. The electroluminescence quantum efficiency of the
devices will be a function of the emitter thickness and used to
determine the width of the carrier recombination zone.43 At the
same electric fields, a large emitter thickness will lead to an
increase in electroluminescence quantum efficiency, because the
width of the carrier recombination zone is large when the
thickness is large. However, if the emitter thickness is much
larger, it will normally lead a concentration quenching. This
phenomenon is obviously special to red emitters. But, our results
show that the electroluminescence quantum efficiency of the
devices was also increased two times over the thin one, when the
thickness was increased above double that of the thin one. For
this point, it justly testifies our design that the molecule BPTBTD
has a non-planar molecular structure, and functional pentaphe-
nylphenyl group substantially suppressed dipole–dipole interac-
tions and intermolecular p–p stacking. So, there is nearly no
concentration quenching in our red emitting devices, when the
emitter thickness is increased. The above discussions imply well
that the molecule BPTBTD has excellent solid properties in the
film, and BPTBTD is a good candidate for efficient and non-
doped red OLEDs.
Materials and instrumentation
2-Bromothiophene, phenylacetylene, 2,3,4,5-tetraphenylcyclo-
penta-2,4-dien-1-one,
tetrakis(triphenylphosphine)palladium
[Pd(PPh3)4] and dichloro[1,3-bis(diphenylphosphino)propane]-
nickel(II) [Ni(dppp)Cl2] were purchased from Aldrich. Other
normal chemical reagents and solvents were obtained from the
Beijing Chemical Plant. Solvents for reactions and photophysical
measurements (DMF, CH2Cl2, THF, etc.) were all distilled
after dehydration according to conventional methods. 4,40-
Bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (NPB) and 1,3,5-
tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) were purchased
and purified by sublimation prior to use.
1H NMR spectra were recorded on a Bruker DMX 300 NMR
spectrometer. UV-vis absorption and fluorescence spectra were
obtained with Hitachi U-3010 and Hitachi F-4500 spectrometers,
respectively. Mass spectra were recorded on an AEI-MA50-MS
spectrometer for EI-MS and a Bruker BIFLEX III Mass Spec-
trometer for MALDI-TOF-MS. Elemental analyses were carried
out on a Carlo-Erba 1160 elemental analyzer. Thermogravi-
metric analyses (TGA) were carried out using a Perkin-Elmer
thermogravimeter (Model TGA7) under a dry nitrogen gas flow,
heating from room temperature to 500 ꢁC, with a heating rate 10
ꢁC minꢀ1. Cyclic voltammetric measurements were carried out in
a conventional three electrode cell using a Pt button working
electrode of 2 mm in diameter, a platinum wire counter electrode,
and a Ag/AgCl reference electrode on a computer-controlled
EG&G Potentiostat/Galvanostat model 283 at room tempera-
ture. Reduction CV of BPTBTD was performed in CH2Cl2
containing Bu4NPF6 (0.1 M) as a supporting electrolyte. The
energy levels were calculated using the ferrocene (EFOC) value of
ꢀ4.8 eV as the standard, while EFOC was calibrated to be 0.45 V
vs. Ag/AgCl electrode in CH2Cl2 solution.
Synthesis of compounds. 4,7-Dibromo-benzo[2,1,3]thiadiazole
(1) was synthesized according to the literature procedure.44
Conclusions
In conclusion, we have synthesized and characterized a novel
non-planar pentaphenylphenyl group to functionalize a ben-
zo[2,1,3]thiadiazole derivative (BPTBTD). This material exhibits
4,7-Di(2-thienyl)-benzo[2,1,3]thiadiazole (2). Magnesium (1.46
g, 60 mmol) was transferred to a three-necked round-bottomed
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flask and heated to 100 ꢁC in a N2 atmosphere for 2 h. After the
flask was cooled to room temperature, dry THF (40 mL) and
a catalytic amount of I2 were added; then the mixture was left to
react for 10 min. 2-Bromothiophene (6.0 mL, 60 mmol) was
carefully added in parts to the solution to avoid an excessive
increase in temperature, and the mixture was refluxed for 2 h to
obtain the corresponding Grignard reagent. 4,7-Dibromo-ben-
zo[2,1,3]thiadiazole 1 (5.90 g, 20 mmol) and [Ni(dppp)Cl2] (1.02
g, 1.88 mmol) were transferred to a separate three-necked round-
bottomed flask connected to a sintered glass filter. After purging
with N2, dry THF (60 mL) was added and the Grignard reagent
was carefully transferred through the filter. The reaction mixture
was refluxed for 20 h, left to stand at room temperature for 2 h,
and then quenched with 1 N HCl. It was then filtered and the
THF solvent was removed in a flash evaporator. The residue was
extracted with water–CH2Cl2 and the organic layer was dried
over anhydrous MgSO4. After the solvent was evaporated under
reduced pressure, the residue was purified by flash silica-gel
(100 nm). As functional layers, NPB works as the hole-trans-
porting layer, TPBI as the hole-blocking and electron-trans-
porting layer. Al was used as the cathode. The materials used as
the emission layers and other organic functional layers were
successively deposited onto the ITO/glass substrates. The emit-
ting area of the EL devices was about 5 mm2. Electrolumines-
cence spectra were recorded on the Hitachi F-4500
spectrophotometer. Current–voltage characteristics for the
OLEDs were measured with a HP4140B semiconductor para-
meter analyzer. Brightness was measured with a spectra scan PR
650 photometer. All device tests were carried out under an
ambient atmosphere at room temperature.
Acknowledgements
This work was supported by the Major State Basic Research
Development Program, the National Natural Science Founda-
tions of China (60736004, 50673093, 60671047, 20573115,
20721061), and Chinese Academy of Sciences.
1
column chromatography to afford the product. Yield: 67%. H
NMR (300 MHz, CDCl3): d ¼ 8.12 (dd, 2 H), 7.89 (s, 2 H), 7.46
(dd, 2 H), 7.22 (dd, 2 H) ppm; MS [electron impact (EI)]: m/z: 300
(M+); elemental analysis calcd (%) for C14H8N2S3: C, 55.97; H,
2.68; N, 9.32. Found: C, 55.90; H, 2.62; N, 9.26.
References
1 C. W. Tang and S. A. Van Slyke, Appl. Phys. Lett., 1987, 51, 913.
2 J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks,
K. Mackay, R. H. Friend, P. L. Burn and A. B. Holmes, Nature,
1990, 347, 539.
4,7-Bis(5-bromo-2-thienyl)-benzo[2,1,3]thiadiazole
Prepared according to a method described previously.45
(3).
3 C. T. Chen, Chem. Mater., 2004, 16, 4389.
4 A. P. Kulkarni, C. J. Tonzola, A. Babel and S. A. Jenekhe,
Chem. Mater., 2004, 16, 4556.
5 Y. Shirota, J. Mater. Chem., 2005, 15, 75.
6 P. L. Burn, S. C. Lo and I. D. W. Samuel, Adv. Mater., 2007, 19, 1675.
7 B. M. Krasovitskii and B. M. Bolotin, Organic Luminescent
Materials, transl. V. G. Vopian, VCH, Weinheim, Germany, 1988.
8 C. T. Chen, C. L. Chiang, Y. C. Lin, L. H. Chan, C. H. Huang,
Z. W. Tsai and C. T. Chen, Org. Lett., 2003, 5, 1261.
9 B. Valeur, Molecular Fluorescence, Wiley-VCH, Weinheim, Germany,
2002.
10 C. W. Tang, S. A. Van Slyke and C. H. Chen, Appl. Phys. Lett., 1989,
65, 3610.
11 W. C. Wu, H. C. Yeh, L. H. Chan and C. T. Chen, Adv. Mater., 2002,
14, 1072.
12 T. H. Huang, J. T. Lin, Y. T. Tao and C. H. Chuen, Chem. Mater.,
2003, 15, 4854.
13 H. C. Yeh, S. J. Yeh and C. T. Chen, Chem. Commun., 2003, 2632.
14 C. L. Chiang, M. F. Wu, D. C. Dai, Y. S. Wen, J. K. Wang and
C. T. Chen, Adv. Funct. Mater., 2005, 15, 231.
15 X. B. Sun, Y. Q. Liu, X. J. Xu, C. Yang, G. Yu, S. Chen, Z. Zhao,
W. Qiu, Y. F. Li and D. B. Zhu, J. Phys. Chem. B, 2005, 109,
10786.
16 Y. Qiu, P. Wei, D. Q. Zhang, J. Qiao, L. Duan, Y. K. Li, Y. Gao and
L. D. Wang, Adv. Mater., 2006, 18, 1607.
17 M. Akhtaruzzaman, N. Kamata, J. Nishida, S. Ando, H. Tada,
M. Tomura and Y. Yamashita, Chem. Commun., 2005, 3183.
18 M. Jayakannan, P. A. Van Hal and R. A. J. Janssen, J. Polym. Sci.,
Part A: Polym. Chem., 2002, 40, 251.
19 C. J. Brabec, C. Winder, N. S. Sariciftci, J. C. Hummelen,
A. Dhanabalan, P. A. van Hal and R. A. J. Janssen, Adv. Funct.
Mater., 2002, 12, 709.
4,7-Bis-(5-phenylethynyl-2-thienyl)-benzo[2,1,3]thiadiazole (4).
A mixture of compound 3 (300 mg, 1.0 mmol), phenylacetylene
(0.24 mL, 2.2 mmol), Pd(PPh3)4 (117 mg, 0.1 mmol) and copper
iodide (38 mg, 0.2 mmol) in THF (20.0 mL) and triethylamine
(20.0 mL) was stirred at 50 ꢁC for 18 h under N2. Cooled to room
temperature, the mixture was put into 100 mL THF and stirred
for 30 min. The mixture was filtered to remove salts and
concentrated by evaporating THF. The remaining solution was
poured into 200 mL of methanol with stirring. A deep red solid
residue was precipitated out immediately, which was filtered and
dried to give the product. Yield: 66%. MS [electron impact (EI)]:
m/z: 500 (M+); elemental analysis calcd (%) for C30H16N2S3: C,
71.97; H, 3.22; N, 5.60. Found: C, 71.67; H, 3.32; N, 5.68.
4,7-Bis-[5-(2,3,4,5-tetraphenyl)phenyl-2-thienyl]-benzo[2,1,3]-
thiadiazole (5) BPTBTD27. A mixture of compound 4 (500 mg,
1.0 mmol) and 2,3,4,5-tetraphenylcyclopenta-2,4-dien-1-one
ꢁ
(844 mg, 2.2 mmol) was heated to 250 C in 10 mL of diphenyl
ether for 16 h. The raw product was washed with 40 mL of cold
n-hexane and purified by flash silica-gel column chromatography
1
to afford the red solid product. Yield: 78%. H NMR (CDCl3,
300 MHz): d ¼ 7.63 (d, 2 H), 7.34 (s, 2 H), 6.99 (d, 10 H), 6.91
(t, 10 H), 6.82–6.88 (brs, 32 H). MS (MALDI-TOF): m/z: 1212
(M+), 1235 (Na+); elemental analysis calcd. (%) for C86H56N2S3:
C, 85.11; H, 4.65; N, 2.31. Found: C, 84.73; H, 4.87; N, 2.65.
20 P. Herguth, X. Jiang, M. S. Liu and A. K. Y. Jen, Macromolecules,
2002, 35, 6094.
21 K. R. J. Thomas, J. T. Lin, M. Velusamy, Y. T. Tao and C. H. Chuen,
Adv. Funct. Mater., 2004, 14, 83.
22 Z. H. Li, M. S. Wong, H. Fukutami and Y. Tao, Chem. Mater., 2005,
17, 5032.
23 T. Yasuda, T. Imase and T. Yamamoto, Macromolecules, 2005, 38,
7378.
24 C. J. Shi, Y. Wu, W. J. Zeng, Y. Q. Xie, K. X. Yang and Y. Cao,
Macromol. Chem. Phys., 2005, 206, 1114.
OLED fabrication and measurements
Indium tin oxide (ITO) coated glass was used as the substrate
and the anode, and was washed with deionized water, acetone,
and ethanol in turn. Multilayered devices were fabricated: ITO/
NPB (30 nm)/BPTBTD(x nm)/TPBI (30 nm)/LiF (1 nm)/Al
2714 | J. Mater. Chem., 2008, 18, 2709–2715
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25 T. Kono, D. Kumaki, J. I. Nishida, T. Sakanoue, M. Kakita,
H. Tada, S. Tokito and Y. Yamashita, Chem. Mater., 2007, 19, 1218.
26 F. Zhang, K. G. Jespersen, C. Bjo¨rstro¨m, M. Svensson,
M. R. Andersson, V. Sundstro¨m, K. Magnusson, E. Moons,
A. Yartsev and O. Ingana¨s, Adv. Funct. Mater., 2006, 16, 667.
36 S. Y. Chen, X. J. Xu, Y. Q. Liu, W. F. Qiu, G. Yu, X. B. Sun,
H. J. Zhang, T. Qi, K. Lu, X. Gao, Y. Liu and D. B. Zhu,
J. Mater. Chem., 2007, 17, 3788.
37 X. J. Xu, S. Y. Chen, G. Yu, C. Di, H. You, D. Ma and Y. Q. Liu,
Adv. Mater., 2007, 19, 1281.
27 N. Blouin, A. Michaud and M. Leclerc, Adv. Mater., 2007, 19, 2295.
28 C. Kubel, S. L. Chen and K. Mullen, Macromolecules, 1998, 31, 6014.
38 Q. Tong, S. Lai, M. Chan, K. Lai, J. Tang, H. Kwong, C. Lee and
S. Lee, Chem. Mater., 2007, 19, 5851.
39 W. C. Sun, K. R. Gee, D. H. Klaubert and R. P. Haugland, J. Org.
Chem., 1997, 62, 6469.
40 C. H. Chen, F. Wu, C. F. Shu, C. H. Chien and Y. T. Tao, J. Mater.
Chem., 2004, 14, 1585.
41 V. Cimrova and D. Neher, J. Appl. Phys., 1996, 79, 3299.
42 J. M. Leger, S. A. Carter, B. Ruhstaller, H. G. Nothofer, U. Scherf,
H. Tillman and H. H. Horhold, Phys. Rev. B, 2003, 68, 054209.
43 J. Kalinowski, L. C. Palilis, W. H. Kim and Z. H. Kafafi, J. Appl.
Phys., 2003, 94, 7764.
44 K. Pilgram, M. Zupan and R. Skiles, J. Heterocycl. Chem., 1970, 7,
629.
45 S. Kato, T. Matsumoto, T. Ishi, T. Thiemann, M. Shigeiwa,
H. Gorohmaru, S. Maeda, Y. Yamashita and S. Mataka,
Chem. Commun., 2004, 2342.
¨
29 S. Setayesh, A. C. Grimsdale, T. Weil, V. Enkelmann, K. Mullen,
¨
F. Meghdadi, E. J. W. List and G. Leising, J. Am. Chem. Soc.,
2001, 123, 946.
30 M. D. Watson, A. Fechtenkotter and K. Mu¨llen, Chem. Rev., 2001,
101, 1267.
31 A. Pogantsch, F. P. Wenzl, E. J. W. List, G. Leising, A. C. Grimsdale
and K. Mullen, Adv. Mater., 2002, 14, 1061.
¨
¨
32 A. C. Grimsdale and K. Mullen, Angew. Chem., Int. Ed., 2005, 44,
5592.
33 J. Wu, W. Pisula and K. Mullen, Chem. Rev., 2007, 107, 718.
¨
34 K. R. J. Thomas, M. Velusamy, J. T. Lin, S. S. Sun, Y. T. Tao and
C. H. Chuen, Chem. Commun., 2004, 2328.
35 C. Huang, C. G. Zhen, S. P. Su, K. P. Loh and Z. K. Chen, Org. Lett.,
2005, 7, 391.
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