Poly(diketopyrrolopyrrole-benzothiadiazole) with ambipolarity approaching 100% equivalency

Article abstract of DOI:10.1002/adfm.201002651

As a characteristic feature of conventional conjugated polymers, it has been generally agreed that conjugated polymers exhibit either high hole transport property (p-type) or high electron transport property (n-type). Although ambipolar properties have been demonstrated from specially designed conjugated polymers, only a few examples have exhibited ambipolar transport properties under limited conditions. Furthermore, there is, as yet, no example with 'equivalent' hole and electron transport properties. We describe the realization of an equivalent ambipolar organic field-effect transistor (FET) by using a single-component visible-near infrared absorbing diketopyrrolopyrrole (DPP)-benzothiadiazole (BTZ) copolymer, namely poly[3,6-dithiene-2-yl-2,5-di(2- decyltetradecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-5',5''-diyl-alt-benzo-2,1, 3-thiadiazol-4,7-diyl] (PDTDPP-alt-BTZ). PDTDPP-alt-BTZ shows not only ideally balanced charge carrier mobilities for both electrons (_e = 0.09 cm²V^-1s^-1) and holes (_h = 0.1 cm²V^-1s^-1) but also its inverter constructed with the combination of two identical ambipolar FETs exhibits a gain of ～35 that is much higher than usually obtained values for unipolar logic. Copyright

Full text of DOI:10.1002/adfm.201002651

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Poly(diketopyrrolopyrrole-benzothiadiazole) with
Ambipolarity Approaching 100% Equivalency
Shinuk Cho, Junghoon Lee, Minghong Tong, Jung Hwa Seo, and Changduk Yang*
demonstrated by utilizing these tech-
As a characteristic feature of conventional conjugated polymers, it has been
generally agreed that conjugated polymers exhibit either high hole transport
property (p-type) or high electron transport property (n-type). Although ambi-
polar properties have been demonstrated from specially designed conjugated
polymers, only a few examples have exhibited ambipolar transport proper-
ties under limited conditions. Furthermore, there is, as yet, no example with
niques, the achievement of the ambipo-
larity from a single-component material
would be the most ideal strategy due to the
attractiveness of easy-solution processing.
Thiophene-based conjugated polymers
such as poly(3-hexylthiophene) (P3HT)
and
poly(2,5-bis(3-tetradecylthiophene-
‘
equivalent’ hole and electron transport properties. We describe the realiza-
2-yl)thieno[3,2-b] thiophene) (PBTTT) have
been preferred for use as active materials
in polymer FETs because of their relatively
tion of an equivalent ambipolar organic field-effect transistor (FET) by using
a single-component visible–near infrared absorbing diketopyrrolopyrrole
[5,6]
high mobility.
The thiophene-based
(
DPP)-benzothiadiazole (BTZ) copolymer, namely poly[3,6-dithiene-2-yl-2,5-
di(2-decyltetradecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-5’,5’’-diyl-alt-benzo-2,1,
-thiadiazol-4,7-diyl] (PDTDPP-alt- BTZ). PDTDPP-alt- BTZ shows not
only ideally balanced charge carrier mobilities for both electrons (␮ =
aromatic conjugated polymers, however,
generally showed unipolar hole trans-
port because of the electron-rich nature
of the thiophene rings. Recently, with
the increasing attention on low band gap
polymers based on donor (D)–acceptor (A)
architecture, electron deficient units (elec-
tron acceptor) such as benzothiadiazole
3
e
.09 cm V s ) and holes (␮ = 0.1 cm V s−1 ) but also its inverter con-
2
−1 −1
2
−1
0
h
structed with the combination of two identical ambipolar FETs exhibits a gain
of ∼ 35 that is much higher than usually obtained values for unipolar logic.
[
8]
(
BTZ),
benzo[1,2-c;4,5-c′]bis[1,2,5]thia-
[
4]
diazole (BBT), and diketopyrrolopyrrole
1
. Introduction
(DPP)[7,9] have been introduced into the polymer backbones,
and are expected to realize effective ambipolar behavior.
Although Marks and coworkers have demonstrated ambipolar
Ambipolar FETs based on conjugated polymers based on both
p-type and n-type channels in one device with thereby simpli-
fied circuit design and fabrication processes, are particularly
[
10]
FETs based on the indenofluorenebis(dicyanovinylene) core,
−4
2
−1 −1
the measured mobility was only ∼ 10 cm V s ; i.e., lower than
bulk-heterojunction (BHJ) bipolar FETs. Bürgi et al. reported
ambipolar near-infrared light-emitting FETs using poly[3,6-
bis-(4’-dodecyl-[2,2′]bithiophenyl-5-yl)-2,5-bis-(2-hexyl-decyl)-
attractive for use in low-cost, flexible, and portable electronic
applications.[
1–3]
Since the typical conjugated polymers show
either high hole mobility or high electron mobility, scientists
have attempted to realize ambipolar FETs by the use of blending
systems as an active layer in the channel, or of bilayers sepa-
2
,5-dihydro-pyrrolo[3,4-]pyrrole-1,4-dione] (BBTDPP1). Janssen
and coworkers reported the ‘nearly’ balanced ambipolar mate-
rial, PDPP3T, with alternating diketopyrrolopyrrole (DPP) and
rately consisting of hole transporting and electron transporting
materials.[
4–7]
Although ambipolar FETs have been successfully
[
4,7]
terthiophene units.
However, the hole mobility was higher
than the electron mobility. In addition, the threshold voltage
of electron channel is higher than threshold voltage of hole
channel. To improve electron transport, we introduce one
more electron deficient building block, benzothiadiazole (BTZ),
in the D–A alternating copolymer consisting of DPP and two
unsubstituted thiophene rings, namely poly[3,6-dithiene-2-yl-2,5-
di(2-decyltetradecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-5′,5″-diyl-
alt-benzo-2,1,3-thiadiazol-4,7-diyl] (PDTDPP-alt-BTZ). Recently,
the initial results on ambipolar PDTDPP-alt-BTZ FETs were
reported; here, we investigate thoroughly their optoelectronic
features to gain a better understanding and with a view to
optimization for high-end applications. We report on the opto-
electronic features of PDTDPP-alt-BTZ using ultraviolet photo-
electron spectroscopy (UPS) that enables determination of the
HOMO and LUMO energies, ambipolar FET characteristics,
J. Lee, Prof. C. Yang
Interdisciplinary School of Green Energy
Ulsan National Institute of Science and Technology (UNIST)
1
00 Banyeon-ri, Eonyang-eup, Ulju-gun, Ulsan, 689-798, Korea
Fax: (+82) 52-217-2909
E-mail: yang@unist.ac.kr
Dr. M. Tong, Dr. J. H. Seo
Center for Polymers and Organic Solids
University of California at Santa Barbara
Santa Barbara, CA 93106-5090, USA
[
11]
Prof. S. Cho
Department of Physics and EHSRC
University of Ulsan
Ulsan 680-749, South Korea
DOI: 10.1002/adfm.201002651
1
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Scheme 1. Synthetic route to PDTDPP-alt-BTZ. Reagents and conditions:
(
i) 2-Decyltetradecylbromide, K CO , DMF, 120 °C, under Ar, 24 h, 55%;
2 3
(
ii) NBS, CHCl , RT, dark and under Ar, 24 h, 53%; (iii) Pd(pph ) , K CO ,
3
3 4
2
3
toluene/H O, 95 °C for 72 h, 75%.
2
density functional calculations of the electronic structure,
absorption and ultrafast photoinduced absorption. In addi-
tion, we demonstrate a high gain inverter using n-channel and
p-channel FETs fabricated from this ambipolar semiconducting
polymer.
2
. Results and Discussion
The synthesis of PDTDPP-alt-BTZ was carried out as
depicted in Scheme 1. Firstly, 3,6-dithiophen-2-yl-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DTDPP, 1) was syn-
[
12]
thesized according to the procedure in the literature.
To
improve the solubility and the film-forming ability of DTDPP-
[
13]
based copolymers, two extended 2-decyltetradecyl chains
were introduced at the 2,5-positions (N atoms in the lactam
ring) of the DTDPP moiety. Dibromination of 1 in CHCl3
afforded 3,6-di(2-bromothiene-5-yl)-2,5-di(2-decyltetradecyl)-
pyrrolo[3,4-c]pyrrole-1,4-dione (2). The alternating copolymer
poly[3,6-dithiene-2-yl-2,5-di(2-decyltetradecyl)-pyrrolo[3,4-c]
pyrrole-1,4-dione-5′,5″-diyl-alt-benzo-2,1,3-thiadiazol-4,7-diyl]
Figure 1. a) UV–vis–NIR absorption spectra of PDTDPP-alt-BTZ in
dilute CHCl solution and thin film on quartz plate. b) UPS spectrum of
3
(
PDTDPP-alt-BTZ) was synthesized by Suzuki polyconden-
sation in toluene using Pd(PPh3)4 as catalyst, from the
dibromo-monomer and commercially available 4,7-
PDTDPP-alt-BTZ.
2
at room temperature. PDTDPP-alt-BTZ in solution displays
diboronicester-2,1,3-benzothiadiazole further purified by
recrystallization from methanol. Through a combination of the
high purity of two monomers and the compensation for the
expected loss in solubility by using the branched solubilizing
groups, PDTDPP-alt-BTZ can be accessed in high molecular
weight, which is a crucial factor for its electronic perform-
ance. PDTDPP-alt-BTZ has good solubility in common
organic solvents such as chloroform, toluene, and chloroben-
zene. Molecular weight and polydispersity index (PDI) of
PDTDPP-alt-BTZ are determined by gel permeation chroma-
tography (GPC) analysis with a polystyrene standard calibra-
tion. PDTDPP-alt-BTZ has a high number-average molecular
a strong broad absorption band with a maximum 901 nm
covering from 600 to 1000 nm, arising from π–π transi-
∗
tions in the polymer backbone. Despite that, the profile in
shape of absorption spectra of PDTDPP-alt-BTZ is essen-
tially unchanged from the solution state to the solid state, the
absorption maximum of PDTDPP-alt-BTZ in film shows a
red-shift by 40 nm compared with that in solution, which is
related not only to the intermolecular interaction in the solid
state caused by the strong polarity of the lactam groups on
[
14]
DTDPP units
but also to the increased vibronic coupling
associated with molecular rigidity imposed by molecular con-
nectivity in solution measurement.
Figure 1b displays the ultraviolet photoelectron spectroscopy
(UPS) spectrum taken for a PDTDPP-alt-BTZ film. The abscissa
−1
weight (M ) of 135.6 kg mol with a PDI of 4.26.
n
The UV–vis–NIR absorption of PDTDPP-alt-BTZ was inves-
tigated in chloroform solution and in the films, as depicted
in Figure 1a. Transparent and uniform polymer film was pre-
pared on quartz by spin-casting from chloroform solution
is the binding energy relative to the Fermi energy (E ) of Au,
F
which is defined by the energy of the electron before excita-
tion relative to the vacuum level. Ecutoff is the high binding
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energy cutoff of the PDTDPP-alt-BTZ and is
determined by linear extrapolation to zero at
the yield of secondary electrons.[15,16] Inset
of Figure 1b shows the HOMO region. The
EHOMO is the onset relative to the E of Au (at
F
0
eV). From Figure 1b, Ecutoff is 16.97 eV, and
EHOMO is 0.87 eV. The ionization potential (IP,
HOMO) is determined by using the incident
photon energy (hν = 21.2 eV) for He I, Ecutoff,
and EHOMO according to the equation,[
17,18]
IP = h
<
− (Ecutoff − EHOMO
)
The electron affinity (EA, LUMO) is esti-
mated by using the HOMO and the optical
gap from the UV–vis–NIR absorption in
Figure 1a. The uncertainty of the EA is due to
a difference between the true gap and optical
[
15–19]
gap by the exciton binding energy.
From the UPS and absorption spectra, the IP
and EA of the PDTDPP-alt-BTZ are 5.1 eV
and 3.9 eV, respectively. Note that the IP of
the polymer is about 5.1 eV, which is approx-
imately 0.3 eV greater than that of regioreg-
ular P3HT. This suggests that the higher IP
arises mainly from the reduced delocaliza-
tion from the fused DPP aromatic ring. The
Figure 3. a) Schematic device structures of PDTDPP-alt-BTZ FET. b) Output characteristics of
ambipolar PDTDPP-alt-BTZ FET. c) Transfer characteristics of ambipolar PDTDPP-alt-BTZ FET
optical data including the absorption peak under p-type operation (V , V < 0) and n-type operation (V , V > 0). d) Transfer characteris-
ds
gs
ds
gs
wavelength (λmax) in both solution and film, tics of fully optimized ambipolar PDTDPP-alt-BTZ FET fabricated with two different electrodes.
opt
Au was used as a source metal and Al was used as a drain metal for easy injection of hole and
electron, respectively.
and the optical band gap (Eg ) as well as the
IP value are summarized in Table 1.
Figure 2 shows tapping mode atomic force
microscopy (AFM) images of PDTDPP-alt-BTZ on PPcB modi-
fied silicon wafer substrate. These AFM images of PDTDPP-
alt-BTZ show that they have aggregated granular surfaces. The
RMS roughness value is 1.15 nm for a 2 μm × 2 μm scan area.
The molecular packing of the copolymer in thin films cast from
solution (onto a Si wafer as substrate) was studied by X-ray dif-
fraction (XRD) analysis. No scattering patterns are observed,
suggesting a macroscopically disordered, amorphous solid
(Figure 2b).
Figure 3a shows the schematic device structures of PDTDPP-
++
alt-BTZ FET fabricated on SiO2 (200 nm)/n Si substrate
covered by a 60 nm thick layer of spun-cast polypropylene-co-
1-butene (PPcB). PPcB layer was introduced as a passivation
layer to remove hydroxyl group which acts as trap sites of elec-
T a b le 1 . Photophysical properties of the copolymer.
[
20]
λmax [nm]
trons.
Figure 3b shows the output characteristic curves of
IP [eV]a)
Egopt [eV]b)
PDTDPP-alt-BTZ FET. Measured output characteristic curves
show typical ambipolar characteristics; diode-like curves at low
gate bias and saturation curves at high gate bias. Furthermore, it
displays beautiful symmetry between p-type operation (Vds < 0,
Vgs < 0) and n-type operation (Vds > 0, Vgs > 0). Figure 3c dem-
onstrates the ambipolar transport proper-
PDTDPP-alt-BTZ
solution
01
film
927
9
5.1
1.2
a)Determined by ambient ultraviolet photoelectron spectroscopy (UPS) technique;
b)Calculated from the absorption band edge of the copolymer film, Egopt = 1240/λedge
ties. PDTDPP-alt-BTZ FETs exhibit balanced
hole and electron mobilities of 0.061 and
2
−1 −1
0
.054 cm V s , respectively.
We obtained the balanced transport using
Ag source-drain electrodes. When different
workfunction metals were used as the source
and drain electrodes, n-type and p-type per-
[
21]
formances were systematically changed.
For the device with Au electrodes, the hole
mobility was slightly higher than the electron
Figure 2. a) Height (left) and phase (right) AFM images and b) X-ray diffraction (XRD) pattern mobility. For the FET with Al electrodes, the
of PDTDPP-alt-BTZ thin film.
electron mobility was higher than the hole
1
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Figure 5. Charge-density isosurface for the HOMO (top) and LUMO
(bottom) levels of PDTDPP-alt-BTZ. Both HOMO and LUMO isosurface
are well delocalized over the entire conjugated main chain.
between electron-acceptor sites. However, in the case of our
PDTDPP-alt-BTZ, since we build D–A–D–A alternating struc-
ture, the distance between electron-acceptor sites is shortened
with reasonably good overlap of the electron wave-function on
successive acceptor sites.
Figure 4. Inverter characteristics of an inverter based on two identical
ambipolar PDTDPP-alt-BTZ FETs. The steepness of the inverter curve
indicates a gain of ∼ 35.
Although the PDTDPP-alt-BTZ itself has an ideal band gap
as a donor material for BHJ solar cells together with good
transport properties for injected charges, no photovoltaic effects
are detected in BHJ solar cells fabricated using the blends with
PC BM or PC BM.
mobility. Therefore, to obtain maximized hole and electron
mobilities, we have made a FET with “two color” electrodes
as shown in Figure 2d. The mobilities obtained from the opti-
mized FET with two color electrodes (Au for source electrode
61
71
2
−1 −1
and Al for drain electrode) were 0.097 cm V
s
for the hole
We found that for pristine PDTDPP-alt-BTZ film, the
photoresponse is very low and there is no detectable photocurrent
in the NIR region (700–1000 nm) in spite of strong absorption
as shown in Figure 6. This lack of a photoresponse at lower
energy peak was also observed on dithienylcyclopentadieneone-
2
−1 −1
and 0.089 cm V
s
for the electron. These values are among
the highest ambipolar equivalency reported for single-
component polymer ambipolar transistors.
The well balanced ambipolar nature of PDTDPP-alt-BTZ
FETs prompted us to examine CMOS-like inverters using two
identical ambipolar transistors with a common gate as the
[26]
thiophene D–A copolymers from our previous work.
In
the case of some D–A copolymers such as poly(2,7-carbazole-
[27]
input voltage (V ) (see Figure 4, inset). Figure 4 shows the
altdithienylbenzothiadiazole) (PCDTBT), it has been reported
that the high-energy excitation generate more carrier than low
energy pump. More detailed studies are currently underway to
explore the interpretation.
IN
output voltage (VOUT) as a function of the input voltage (V ) at
IN
constant supply bias (VDD). The output characteristic of inverter
with positive VDD and VIN works in the first quadrant, while
the output characteristic of inverter with negative VDD and VIN
works in the third quadrant. The steepness of the inverter curve
indicated the maximum gain of ∼ 35, which is a relatively good
value for single-component-based inverters fabricated from
organic FETs.[
The photoexcitation of PDTDPP-alt-BTZ thin film was inves-
tigated by transient photoinduced absorption spectroscopy in
22–24]
The presence of the ambipolarity is explained by the delo-
calized character of the HOMO and LUMO on both donor
and acceptor regions within the repeat unit of the monomer.
Figure 5 depicts the electron-state-density distribution of the
HOMO and LUMO of geometry optimized structures (DFT,
*
B3LYP/6 –31G ) of PDTDPP-alt-BTZ (two repeating units)
using the Gaussium 03 program. Since the side chains in
PDTDPP-alt-BTZ do not contribute significantly to the variation
of chain conformation and charge-density isosurface, they were
excluded from our calculation. The results indicate that the
electron density of HOMO and LUMO are delocalized over the
entire conjugated monomer (both the acceptor unit and donor
unit). Typically, for conventional D–A conjugated copolymers
(D–D–A–D structure), electron transport is hindered because of
the localized character of the LUMO on the electron-acceptor
site.[ The reason of this localization is that there is no elec-
tron wave-function overlap because of relatively long distance
25]
Figure 6. Photocurrent measurement of PDTDPP-alt-BTZ.
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were 0.1 cm V s−1 for the hole and 0.09 cm V s−1 for the
electron. These values are among the highest reported for
single-component polymer ambipolar transistors. The inverter
constructed with the combination of two identical PDTDPP-
alt-BTZ FETs exhibits a gain of ∼ 35.
2
−1
2
−1
4
. Experimental Section
FETs Fabrication: All FETs were fabricated on heavily n-type doped
silicon (Si) wafers with a 200 nm thick thermally grown SiO2 layer as
shown in Figure S1. FETs were fabricated in the top contact geometry.
The n-type doped Si substrate functioned as the gate electrode and the
SiO layer functioned as the gate dielectric. The semiconducting PDTDPP-
2
alt-BTZ layer was spin-cast from solution at 3000 rpm. PDTDPP-alt-BTZ
−1
solution was prepared at 5 mg mL concentration in chlorobenzene. The
thickness of the PDTDPP-alt-BTZ films was approximately 60 nm. Prior
to deposition of PDTDPP-alt-BTZ, the SiO2 surface was modified with
polypropylene-co-1-butene (PPcB) to remove hydroxyl groups from the
Figure 7. Transient photoinduced absorption spectra of PDTDPP-alt-BTZ.
SiO surface. After PDTDPP-alt-BTZ deposition, the films were dried on hot
2
plate stabilized at 80 °C for 30 min. The PDTDPP-alt-BTZ deposition was
carried out in a controlled atmosphere glove box filled with N . Source and
2
the visible and near infrared spectral ranges using excitation
at 800 nm and 400 nm. The transient absorption spectra (TA)
recorded at 0.5 ps time delay are shown in Figure 7. For 400 nm
excitation, TA spectra show a broad negative photoinduced
absorption band (PA) and a positive signal above 1.25 eV
resulting from photo-bleaching (PB) of the absorption band
of the pristine polymer. The TA spectra at 800 nm excitation
shows a clear red shift compared to that for 400 nm excitation.
The positive signal around 1.23 eV (the spectral range of the PL)
was assigned to stimulated emission (SE) band for 800 nm
pump. The absence of SE band for high energy pump (400 nm)
shows the lower exciton generation efficiency, or possibly
higher charge carrier yield, which has been observed in other
D–A copolymers like PCDTBT. The inset shows the dynamics
of photobleaching (PB) band for both pump wavelengths. The
decay of the PB signal measures the recombination decay
dynamics of all the photo-generated excitations. For PDTDPP-
alt-BTZ thin film, the recombination is very fast with a life-
time of about 7 ps for both excitation wavelengths. The time
decay for photinduced absorption (PA) below 1.1 eV shows
similar decay rate as that of PB. Since the photoconductivity is
proportional to the lifetime of the carrier, the fast recombina-
tion of PDTDPP-alt-BTZ may one of the reasons for the low
photocurrent.
drain electrodes were deposited by thermal evaporation using a shadow
mask. The thickness of source and drain electrodes was 50 nm. Channel
length (L) and channel width (W) were 50 μm and 2.0 mm, respectively.
Electrical characterization was performed under N atmosphere using a
2
Keithley semiconductor parametric analyzer (Keithley 4200).
Fabrication of PPCB Layer: The PPcB solution was prepared at
−1
5
mg mL concentration in Decahydronaphthalene, anhydrous solvent
(Aldrich #294772). To completely dissolve, the PPcB solution was kept
at 200 °C for 1 h. The PPcB layer was spin-cast from warm solution at
5000 rpm in air. After deposition, the samples were dried on hot plate
stabilized at 200 °C for 20 min in air. Subsequently, the samples were
moved to glove box filled with N to deposit PDTDPP-alt-BTZ layer.
2
DFT Calculation: DFT calculations were performed using the Gaussian
0
3 package with the nonlocal hybrid Becke three-parameter Lee–Yang–
∗
Parr (B3LYP) function and the 6 –31G basis set to elucidate the HOMO
and LUMO levels after optimizing the geometry of PDTDPP-alt-BTZ
using the same method.
UPS Measurement: The polymer solution was prepared in
−1
(
chlorobenzene) with 5 mg mL for PDTDPP-alt-BTZ. A gold film
75 nm thick was deposited on a pre-cleaned Si substrate with a thin
native oxide. The PDTDPP-alt-BTZ solution was spin-coated at 2000 rpm
on a gold film. Film fabrication was done in a N -atmosphere globe
2
box. To minimize possible influence by exposure to air, the film was
then transferred from the N -atmosphere dry box to the analysis
2
chamber inside an air-free holder. Subsequently, the sample was kept
inside a high-vacuum chamber overnight. The UPS analysis chamber
was equipped with a hemispherical electron-energy analyzer (Kratos
−9
Ultra Spectrometer), and was maintained at 1.0 × 10 Torr. The
UPS measurements were carried out using the He I (hν = 21.2 eV)
source. The electron energy analyzer was operated at constant pass energy
of 10 eV. During UPS measurements, a sample bias of –9 V was used in
order to separate the sample and the secondary edge for the analyzer.
Transient Photoinduced Absorption Spectra (TA): The TA spectra was
measured using pulsed laser pump/probe spectroscopy; the Ti:sapphire
laser system with a regenerative amplifier that provides 100 fs pulses
at photon energies of 1.55 eV, with 1 mJ per pulse at a repetition rate
of 1 kHz. The pump beam was generated using either the fundamental
emission from the Ti:sapphire laser at 800 nm or the second harmonic
at 400 nm. The probe beam in the visible and near infrared spectral
range was obtained from a white light supercontinuum and signal beam
from optical parametric amplifier.
3
. Conclusion
In conclusion, we have demonstrated n-type, p-type equivalent
ambipolar properties from the D–A conjugated copolymer,
PDTDPP-alt-BTZ containing benzothiadiazole (BTZ), diketo-
pyrrolopyrrole (DPP) and two unsubstituted thiophenes.
DFT calculation results shows that the electron density of
HOMO and LUMO are delocalized over the entire conju-
gated monomer (both the acceptor unit and donor unit).
Ambipolar PDTDPP-alt-BTZ FETs show beautiful symmetry
between p-type operation and n-type operation. The mobili-
ties obtained from fully optimized FET with two color elec-
trodes (Au for source electrode and Al for drain electrode)
Materials and Instruments: All starting materials were purchased either
from Aldrich or Acros and used without further purification. All solvents
are ACS grade unless otherwise noted. Anhydrous THF was obtained
by distillation from sodium/benzophenone prior to use. Anhydrous
1
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toluene was used as received. 3,6-dithiene-2-yl-2,5-dihydropyrrolo[3,4-c]
pyrrole-1,4-dione (DTDPP) and 2-decyltetradecylbromide were prepared
according to established literature procedures. 4,7-Diboronicester-
(br, 2H), 8.08–7.96 (br, 2H), 4.23–4.06 (br, 4H), 2.32–2.29 (t, 2H), 1.34–1.03
(br, 80H), 0.90–0.85 (br, 12H). Anal. Calcd for C H BrN O S : C, 68.82; H,
8.92 N, 4.72 Found: C, 68.61; H, 9.19, N, 5.61.
68
105
4
2 3
2
,1,3-benzothiadiazole (BTZ) was purchased from Sigma-Aldrich
Chemical Co., and subsequently recrystallized from methanol.
1
13
H NMR and C NMR spectra were recorded on a VNMRS 600 (Varian,
USA) spectrophotometer using CDCl as solvent and tetramethylsilane Acknowledgements
3
(
TMS) as the internal standard, and MALDI MS spectra were obtained
S.J. and J.L. contributed equally to this work. This work was supported
by Basic Science Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of Education,
Science and Technology (2010–0002494) and the National Research
Foundation of Korea Grant funded by the Korean Government (MEST)
from Ultraflex III (Bruker, Germany). UV–vis–NIR spectra were taken
on Cary 5000 (Varian USA) spectrophotometer. Number-average (Mn)
and weight average (M ) molecular weights, and polydispersity index
(
chromatography (GPC) with Agilent 1200 HPLC Chemstation using a
series of mono disperse polystyrene as standards in THF (HPLC grade)
at 308 K.
w
PDI) of the polymer products were determined by gel permeation
(2010–0019408), (2010–0026916), and (2010–0026163) and Priority
Research Centers Program through the National Research Foundation
of Korea(NRF) funded by the Minstery of Education, Science and
Technology (2009–0093818). Note: This article has been amended on
May 24, 2011 to correct an error in the Conclusion section of the version
first published online.
Synthesisof3,6-dithiene-2-yl-2,5-di(2-decyltetradecyl)-pyrrolo[3,4-c]pyrrole-
1
,4-dione (1): A solution of 2-decyl-tetradecylbromide (9.1 g, 21.7 mmol)
inanhydrousDMF(20mL)wasaddeddropwisetoamixtureof3,6-dithiene-
-yl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (2.8 g, 9.42 mmol),
2
K2CO3 (3.0 g, 21.6 mmol) in anhydrous DMF (55 mL). The mixture
was maintained at 120 °C overnight. The reaction was cooled to room
temperature and poured into water (100 mL). The compound was
extracted in CHCl , washed with brine, dried over MgSO . The solvent
Received: December 17, 2010
Published online: March 25, 2011
3
4
was evaporated under reduced pressure. The crude product was
purified by chromatography on silica with 0–30% dichloromethane in
hexane as eluent. Isolated yield = 5.1 g (55%) as a thick viscous dark
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1
purplish oil. H NMR (CDCl , 600 MHz): δ ppm 8.88 (d, J = 3.85, 2H),
3
7
1
1
4
2
.62 (d, J = 4.9, 2H), 7.27 (d, J = 8.89, 2H), 4.03 (d, J = 7.71, 4H),
[2] E. J. Meijer, D. M. De Leeuw, S. Setayesh, E. Van Veenendaal,
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521.
1
3
.91 (m, 2H), 1.30–1.21 (m, 80H), 0.89–0.87 (m, 12H). C NMR (CDCl3,
50 MHz): δ ppm 161.75, 140.43, 135.19, 130.44, 129.84, 120.38, 107.95,
6.23, 37.75, 31.93, 29.69, 29.67, 29.65, 29.38, 29.37, 29.36, 26.22,
+
2.70, 22.69, 14.13. MALDI-TOF MS (m/z) 973.59(M ). Anal. Calcd for
C H N O S : C, 76.48; H,10.77, N, 2.88. Found: C, 77.04; H, 10.97,
N, 2.96.
62
104
2
2 2
[
4] L. Bürgi, M. Turbiez, R. Pfeiffer, F. Bienewald, H. J. Kirner,
C. Winnewisser, Adv. Mater. 2008, 20, 2217.
Synthesis of 3,6-Di(2-bromothiene-5-yl)-2,5-di (2-decyltetradecyl)-pyrrolo
[
3,4-c]pyrrole-1,4-dione (2): N-Bromosuccinimide (NBS, 1.26 g, 7.08 mmol)
[
5] I. McCulloch, M. Heeney, C. Bailey, K. Genevicius, I. Macdonald,
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was added slowly to a solution of 1 (3 g, 3.08 mmol) in CHCl (100 mL).
The solution was protected from light and stirred at room temperature
for 48 h. The reaction mixture was poured into water (100 mL)
and extracted in CHCl . The organic layer was dried over MgSO4 and
the solvent was evaporated under reduced pressure. The crude product
was purified by chromatography on silica with 0–50% dichloromethane
in hexane as eluent. Isolated yield = 1.8 g (53%) as a thick viscous dark
purplish oil. H NMR(CDCl , 600 MHz): δ ppm 8.62 (d, J = 4.18, 2H),
7
3
2
006, 5, 328.
3
[
6] H. Sirringhaus, P. J. Brown, R. H. Friend, M. M. Nielsen,
K. Bechgaard, B. M. W. Langeveld-Voss, A. J. H. Spiering,
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3
[
7] J. C. Bijleveld, A. P. Zoombelt, S. G. J. Mathijssen, M. M. Wienk,
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.21 (d, J = 4.17, 2H), 3.91 (d, J = 7.71, 4H), 1.87 (m, 2H), 1.29–1.21
1
3
(m, 80H), 0.89–0.86 (m, 12H). C NMR (CDCl , 150 MHz): δ ppm
3
1
61.38, 139.39, 135.31, 131.42, 131.17, 118.95, 108.01, 46.36, 37.77,
3
1.94, 30.00, 29.70, 29.68, 29.66, 29.57, 29.39, 26.20, 22.70, 14.13.
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+
MALDI–TOF MS(m/z) 1131.45(M ). Anal. Calcd for C H Br N O S :
C, 65.82; H, 9.09 N, 2.48. Found: C, 68.14; H, 9.36, N, 2.43.
6
2
102
2
2
2 2
SynthesisofPoly[3,6-dithiene-2-yl-2,5-di(2-decyltetradecyl)-pyrrolo[3,4-c]pyrrole-
1,4-dione-5′,5′′-diyl-alt-benzo-2,1,3-thiadiazol-4,7-diyl] (PDTDPP-alt-BTZ): 2,1,3-
Benzothiadiazole-4,7-bis(boronic acid pinacol ester) (67 mg, 0.17 mmol),
dibromide 2 (200 mg, 0.17 mmol), Aliquat 336 (8 mg, 13 mol%),
2
in a Schlenk flask and purged with argon for 15 min. To this solution,
tetrakis(triphenylphosphine)palladium (10 mg g, 8.6 μmol) was added and
the reaction mixture was heated at 95 °C under vigorous stirring for 72 h. The
reaction was poured into a mixture of methanol and 2.0 M HCl (1:1, 300 mL)
and filtered. The collected dark solid was redissolved in chlorobenzene
[
[
[
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(
10 mL) and added dropwise to methanol (200 mL). The resulting solid
was filtered off and subjected to sequential Soxhlet extraction with methanol
1 d), acetone (1 d), and hexane (1 d) to remove low molecular weight
[
[
(
fraction of the materials. The residue was extracted with chlorobenzene to
give dark purplish product after precipitating again from methanol and drying
in vacuo. Isolated yield of polymer PDTDPP-alt-BTZ = 150 mg (75%). GPC
analysis M = 135.6 kg mol , M = 595 kg mol , and PDI = 4.26 (against PS
standard). H NMR(CDCl , 600 MHz): δ ppm 9.13–9.09 (br, 2H), 8.24–8.16
[
−
1
−1
n
1
w
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