Di(4-methylphenyl)methano-C60 bis-adduct for efficient and stable organic photovoltaics with enhanced open-circuit voltage

Article abstract of DOI:10.1021/cm201784w

A new class of fullerene bis-adducts-di(4-methylphenyl)methano-C ₆₀ bis-adduct (DMPCBA), di(4-fluorophenyl)methano-C₆₀ bis-adduct (DFPCBA), and diphenylmethano-C₆₀ bis-adduct (DPCBA)-were rationally designed and easily syn

Full text of DOI:10.1021/cm201784w

ARTICLE
pubs.acs.org/cm
Di(4-methylphenyl)methano-C Bis-Adduct for Efficient and Stable
6
0
Organic Photovoltaics with Enhanced Open-Circuit Voltage
Yen-Ju Cheng,* Ming-Hung Liao, Chih-Yu Chang, Wei-Shun Kao, Cheng-En Wu, and Chain-Shu Hsu*
Department of Applied Chemistry, National Chiao Tung University 1001 Ta Hsueh Road, Hsin-Chu, 30010 Taiwan, Republic of China
S Supporting Information
b
ABSTRACT: A new class of fullerene bis-adducts—di(4-methyl-
phenyl)methano-C60 bis-adduct (DMPCBA), di(4-fluorophe-
nyl)methano-C60 bis-adduct (DFPCBA), and diphenylmetha-
no-C60 bis-adduct (DPCBA)—were rationally designed and
easily synthesized. Compared to the lowest unoccupied molecular
orbital (LUMO) energylevel of PC BM (ꢀ3.95 eV), the double
61
functionalization effectively raises the LUMO energy levels of
these fullerene materials to ca. ꢀ3.85 eV, regardless of the
substituent groups (CH ꢀ, Fꢀ, and Hꢀ) at the para-position
3
of the phenyl rings. This phenomenon suggests that the plane of
the phenyl groups is preferentially parallel to the fullerene surface,
leadingto poor orbital interactionswith C and negligible electronic effect. Importantly, such geometry sterically protects and shields the
60
core C structure from severe intermolecular aggregation, rendering it intrinsically soluble, morphologically amorphous, and thermally
60
stable. The device based on the P3HT:DMPCBA blend exhibited an open-circuit voltage (V ) of 0.87 V, a short-circuit current density
oc
2
(
J ) of 9.05 mA/cm , and a fill factor (FF) of 65.5%, leading to a high power conversion efficiency (PCE) of 5.2%, which is superior to
sc
that of the P3HT:PC BM-based device. Most significantly, the amorphous nature of DMPCBA effectively suppresses the thermal-
61
driven aggregation and thus stabilizes the morphology of the P3HT:DMPCBA blend. Consequently, the device retained 80% of its
original PCE value against thermal heating at 160 °C over 20 h.
KEYWORDS: C bis-adduct, open-circuit voltage, morphological stability, organic photovoltaics
60
’
INTRODUCTION
acceptor units. Besides, lowering a polymer’s HOMO level
may inevitably increase its optical band gap and thereby sacrifice
its light-harvesting ability. Developing new fullerene-based ma-
terials that possess intrinsically high-lying LUMO energy levels is
a more achievable alternative to optimize the Voc value. Incor-
poration of electron-donating groups (EDGs) on the peripheral
side of monosubstituted fullerenes has been utilized to elevate
Research on polymer solar cells (PSCs) using organic p-type
(donor) and n-type (acceptor) semiconductors has attracted
1
tremendous scientific and industrial interest in recent years. A
regioregular poly(3-hexylthiophene) (P3HT) and a fullerene deri-
vative ([6,6]-phenyl-C -butyric acid methyl ester (PC BM)) are
the most representative p-type/n-type material pair for polymeric
bulk heterojunction (BHJ) solar cells (PSCs). One of the bottle-
6
1
61
5
2
LUMO energy levels. However, because of the lack of direct
conjugation between the EDG and the core C , the through-
60
necks for the P3HT:PC BM-based devices is the low open-circuit
voltage (V ) of ca. 0.6 V, limiting power-conversion efficiencies
6
1
space electronic effect is relatively weak. Therefore, the variations
in the LUMO energy level of fullerene derivatives are too small to
significantly impact the Voc value. Recently, bis-adduct C60
derivatives have emerged as new materials with higher-lying
LUMO energy levels, compared to their corresponding mono-
oc
(PCEs) to ca. 4%. It is anticipated that a PCE of up to 6% can be
reasonably achieved if the Voc can be significantly improved
to ∼0.9 V. It has been demonstrated that the magnitude of V
oc
value is proportional to the energy difference between the
donor’s highest occupied molecular orbital (HOMO) energy
6
adduct C60 analogues. The second functionalization on the
core structure of the monosubstituted C60 further reduces the
level and the acceptor’s lowest unoccupied molecular orbital
π-conjugation and electron delocalization in the C . This
3
60
(LUMO) level. At the molecular level, either lowering the
structural alteration makes bis-adduct C derivatives have larger
60
HOMO level of the polymer or raising the LUMO level of the
fullerene material could reach greater theoretically Voc values.
Although extensive research effort have been directed to the
development of new low-band gap polymers by employing a
electrochemical reduction potentials and, thus, higher-lying
LUMO levels. Further exploration of new class of C60 bis-
adducts for next generation n-type materials is highly desirable.
Another primary area of concern for traditional P3HT:PC BM
61
4
donorꢀacceptor (D-A) approach, manipulating the HOMO
energy level of the D-A polymers remains challenging, because the
HOMO of the polymers are not only governed by electron-rich
donor units but also are associated with electron-deficient
Received: June 22, 2011
Revised: July 8, 2011
Published: August 04, 2011
r 2011 American Chemical Society
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dx.doi.org/10.1021/cm201784w
|Chem. Mater. 2011, 23, 4056–4062

Chemistry of Materials
ARTICLE
Scheme 1. Synthesis and Chemical Structures of
Diphenylmethano-Based C60 Bis-Adducts
Figure 1. Differential scanning calorimetry (DSC) measurement of C60
bis-adducts with a heating rate of 10 °C/min.
system is the morphological instability. Upon heating, spherical
PCBM with high molecular mobility tends to diffuse out of the7
P3HT matrix and aggregate into larger clusters or single crystals.
Such a progressive phase segregation eventually leads to micrometer-
sized D-A domains with concomitant reduction of device efficiency.
Cyclopropanation is an ideal reaction for fullerene modifica-
tion, because of its high stability and small structural perturba-
tion. Di(4-alkylphenyl)methanofullerene monoadduct deriva-
tives have been used as n-type materials to blend with P3HT
for PSCs. The devices have shown superior Voc values, of up to
8
0
.69 V, which is almost 100 mV higher than that of PC BM.
61
However, the short-circuit current density (J ) is relatively lower,
sc
presumably because of the higher content of insulating alkyl chains.
Wudl et al. have demonstrated that the planes of the two phenyl
rings in diphenylmethanofullerene prefer to lie parallel to the full-
9
erene surface. We envisaged that if a C is doubly functionalized
60
with diphenylmethano moieties, the geometry of the two gem-
inal diphenyl groups can sterically protect and shield the core C60
structure from severe intermolecular aggregation, rendering it
intrinsically amorphous and highly soluble. As such, long alkyl
chains on the phenyl rings to ensure solubility are not necessary.
In this paper, we wish to report a new class of n-type materials,
based on the diphenylmethano-C60 bis-adduct (DPCBA) scaf-
folds (see Scheme 1, presented later in this work). To investigate
the electronic effect in this system, the para position of the four
phenyl rings were substituted by weak electron-donating methyl
groups and electron-withdrawing fluoro groups to afford di(4-
methylphenyl)methano-C60 bis-adduct (DMPCBA), and di(4-
fluorophenyl)methano-C bis-adduct (DFPCBA), respectively.
Furthermore, methylphenylmethano-C60 bis-adduct (MPCBA)
are also synthesized as a reference for comparison. A P3HT-
based solar cell using DMPCBA as the acceptor achieved not only a
high open-circuit voltage of Voc = 0.87 V with an exceptional
power conversion efficiency (PCE) of 5.2%, but also excellent
morphological stability against thermal heating.
Figure 2. Thermogravimetric analysis (TGA) measurement of C60 bis-
adducts with a heating rate of 20 °C/min.
corresponding C60 bis-adducts, using NaH as the base and
toluene as the solvent. These C60 bis-adducts were separated
from the corresponding monoadduct by multiple column chro-
matography. All the final products contain a mixture of regio-
isomers.
Thermal Properties. Encouragingly, the DPCBA-based ma-
terials without any alkyl chain as the solublizing group exhibited
excellent solubility in common organic solvents, implying that
two diphenylmethano moieties on the peripheral side indeed
60
sterically prevent spherical C from close packing. Furthermore,
60
unlike PC BM showing a sharp melting point at 280 °C from
61
differential scanning calorimetry (DSC) measurement, no melt-
ing thermal transition was observed for the DPCBA-based
derivatives (see Figure 1). This again indicates that these
materials are amorphous glasses that have no tendency toward
thermal-driven crystallization. In contrast, by replacing a phenyl
ring with a smaller methyl group, MPCBA shows relatively poor
solubility and becomes crystalline with a melting point observed
at 300 °C. In addition, these materials possess extremely high
thermal stability. DPCBA, MPCBA, and DMPCBA showed
’
RESULTS AND DISCUSSION
Synthesis. The synthesis of these new materials is shown in
Scheme 1. The diphenyl ketone derivatives (1) were first converted
to the corresponding tosylhydrazone moieties (2). Two equiva-
lents (2 equiv) of compound 2 were reacted with C to yield the
decomposition temperature (T
) values as high as 625, 582,
d
and 492 °C, respectively, from the thermal gravimetric analysis
60
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Chemistry of Materials
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Figure 5. Current densityꢀvoltage characteristics of ITO/PEDOT:
PSS/P3HT:C bis-adduct/Ca/Al devices under illumination of AM
6
0
2
1
.5 G, 100 mW/cm .
Figure 3. Absorption spectra of C60 bis-adducts in tetrahydrofuran
ꢀ5
(THF) solutions (10 mol/L). Inset: enlarged absorption spectra in
the visible region from 400 nm to 600 nm.
Photovoltaic and Electron-mobility Characteristics. To
evaluate these C60 bis-adducts, bulk heterojunction solar cells
based on the ITO/PEDOT:PSS/P3HT:C60 bis-adduct/Ca/Al
configuration were fabricated and characterized under simulated
ꢀ
2
1
00 mW cm AM 1.5 G illumination. The current densityꢀ
voltage curves of the devices are shown in Figure 5, and the
corresponding device characteristics with the optimal blending
ratio are shown in Table 1.
Indeed, the newly developed C60 bis-adducts effectively im-
prove the Voc of the devices. Compared to the performance of
P3HT:PC BM (1:1, w/w)-based device, the device using
6
1
P3HT:DPCBA blend (1:1, w/w) showed a higher V of 0.75
oc
2
V and comparable J of 9.48 mA/cm , leading to a higher PCE of
sc
4
.0%. When P3HT was blended with DFPCBA functionalized
with fluoro groups (1:0.8, w/w), the device showed a reduced V
oc
2
value of 0.68 V and a J value of 7.25 mA/cm and a decreased
sc
PCE value of 2.8%. In contrast, with introducing methyl groups
on the phenyl rings in DMPCBA, the device using P3HT:
Figure 4. Cyclic voltammetry of the C60 bis-adducts at a scan rate of
DMPCBA blend (1:1.2, w/w) exhibited a much-enhanced V
oc
30 mV/s.
2
value of 0.87 V, a J value of 9.05 mA/cm , and a higher FF value
sc
of 65.5%, yielding an impressively high PCE value of 5.2%. To the
(TGA) measurement, whereas DFPCBA showed the lowest Td
best of our knowledge, the V value of 0.87 V is the highest value
oc
value, at 323 °C (see Figure 2).
ever reported among the P3HT:fullerenoid PSCs. Furthermore,
Optical Properties. The absorption spectra of these materials
in tetrahydrofuran (THF) solutions are shown in Figure 3. The
absorption profile for each material is essentially similar. It should
be mentioned that DMPCBA exhibited the strongest absorption
intensity in the ultraviolet (UV) region, compared to the other
the device based on P3HT:MPCBA (1:1, w/w) showed a J
sc
2
value of 8.32 mA/cm , a V value of 0.73 V, a FF value of 57.4%,
oc
and, thus, a lower PCE of 3.5%. Note that, although the C60 bis-
adducts contain a mixture of isomers, the devices incorporating
DMPCBA synthesized from different batches all showed con-
sistent and reproducible device characteristics.
ꢀ
5
materials under the same concentration of 10 M in THF.
Electrochemical Properties. The electrochemical properties
of these materials are evaluated by cyclic voltammetry and are
shown in Figure 4. In comparison to the LUMO level of PC BM
The surface morphology of the blends was investigated using
atomic force microscopy (AFM) phase images (Figure 6). It is
found that the P3HT:DMPCBA thin film exhibited the most
homogeneous mixing between two photoactive materials,
whereas the P3HT:MPCBA blend showed relatively larger phase
domains. The structural modification with smaller methyl groups
in MPCBA may strengthen the intermolecular interaction
between MPCBA molecules, leading to a more unfavorable
morphology of the active layer. This comparison manifests that
the diphenylmethano moiety is indeed a superior addend for C60
double functionalization.
6
1
monoadduct (ꢀ3.95 eV), all the bis-adduct compounds indeed
showed higher LUMO energy levels. The LUMO levels of
DPCBA and MPCBA were estimated to be ꢀ3.85 eV and
ꢀ
3.84 eV, respectively. By introducing methyl groups and fluoro
groups at the para-positions of the phenyl groups, both the
LUMO levels of DMPCBA and DFPCBA are located at ꢀ3.85 eV.
These results reveal that the electronic effect on the phenyl
groups is negligible and the LUMO energy levels are almost
independent of the functional groups. This phenomenon has
been observed in the diphenylmethaofullerene monoadduct
derivatives, indicating that the phenyl groups are preferentially
parallel to the fullerene surface and, thus, have poor orbital
To evaluate the electron mobility in the BHJ active layer via
the space-charge-limited current (SCLC) method, electron-only
devices (ITO/Al/P3HT:C bis-adduct/Ca/Al) were fabricated.
60
Despite the amorphous nature, the DPCBA derivatives without
insulating aliphatic chain showed good electron-transporting
7
interactions with C .
60
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Chemistry of Materials
ARTICLE
Table 1. Device Characteristics
b
open-circuit
short-circuit current
fill factor,
power conversion
electron mobility
a
2
2
weight ratio
voltage, Voc (V)
density, Jsc (mA/cm )
FF (%)
efficiency, PCE (%)
(cm /(V s))
ꢀ4
ꢀ5
ꢀ5
ꢀ5
ꢀ4
DPCBA
DMPCBA
DFPCBA
MPCBA
PC61BM
1:1
1:1.2
1:0.8
1:1
0.75
0.87
0.68
0.73
9.48
9.05
7.25
8.32
9.65
55.9
65.5
57.3
57.4
67.4
4.0
5.2
2.8
3.5
3.9
1.3 ꢁ 10
9.0 ꢁ 10
9.3 ꢁ 10
7.7 ꢁ 10
1.3 ꢁ 10
1:1
0.60
a
b
Weight ratio of P3HT to the C60 bis-adducts. Based on ITO/Al/P3HT:C60 bis-adduct/Ca/Al devices using SCLC theory.
Figure 6. Atomic force microscopy (AFM) phase images of (a) P3HT:DFPCBA (1:0.8, w/w), (b) P3HT:DPCBA (1:1, w/w), (c) P3HT:MPCBA
(1:1, w/w), and (d) P3HT:DMPCBA (1:1.2, w/w) films thermally annealed at 150 °C for 5 min.
efficiency of the P3HT:PC BM reference device decreased
6
1
dramatically, from 3.9% to 0.7% after 20 h of isothermal heating.
In sharp contrast, the DMPCBA-based device exhibited much
more stable device characteristics and the PCE smoothly de-
graded to 4.7% for 10 h then to 4.2% over 20 h of heating. Note
that the high Voc value of 0.87 V remains intact against 20 h of
heating.
Optical microscopy (OM) was used to investigate the mor-
phological alteration of the blends of micrometer size under the
influence of heating (Figure 9). Thermal annealing of the P3HT:
PC BM blend induced a severe macrographic alteration, form-
6
1
ing needle-shaped PC BM crystals hundreds of micrometers in
6
1
7d
length. In contract, the morphology of the P3HT:DMPCBA
1:1.2, w/w) blend remains almost unchanged before and after
(
the thermal annealing. The high thermal stability is associated
with the amorphous nature of DMPCBA to preserve the device
characteristics.
Figure 7. JꢀV characteristics of PSCs based on the P3HT:PC BM
6
1
(1:1, w/w) and P3HT:DMPCBA (1:1.2, w/w) blend before and after
isothermal heating at 160 °C for 10 and 20 h.
’
CONCLUSIONS
properties. All the composites exhibited the electron mobilities
ꢀ
4
2
approximately at the magnitude of 1 ꢁ 10 cm /(V s), which is
In summary, we have rationally designed and successfully
comparable to that of the P3HT/PC BM blend (1.3 ꢁ
synthesized a new class of diphenylmethano-based C60 bis-
adducts without incorporating aliphatic side chains as a solubiliz-
ing group. The plane of the phenyl groups lying parallel to the
fullerene surface sterically protects and shields the core C60
structure from severe intermolecular aggregation, rendering it
intrinsically soluble, morphologically amorphous, and thermally
stable. The double functionalization raises the LUMO energy
level of DMPCBA by ∼0.1 eV, compared to that of PC BM.
6
1
ꢀ
4
2
1
0
cm /(V s)) under the same fabrication conditions (see
Table 1).
Morphological Stability against Heating. To investigate
morphological stability under the influence of thermal treatment,
we fabricated a series of devices, based on the configuration of
ITO/PEDOT:PSS/P3HT:DMPCBA(1:1.2, w/w)/Al. These
devices were isothermally heated at 160 °C for 10 and 20 h
prior to the deposition of the top electrode. The corresponding
P3HT:PC BM (1:1, w/w)-based reference devices were also
61
The device based on the P3HT:DMPCBA blend exhibited a V
oc
2
value of 0.87 V, a J value of 9.05 mA/cm , and a FF value of
61
sc
fabricated to test the thermal stability. The current density versus
65.5%, leading to a high PCE of 5.2%, which is superior to that of
potential (JꢀV) curves and the corresponding photovoltaic
the P3HT:PC BM-based device. To the best of our knowledge,
6
1
parameters (PCE, V , J , and FF), as a function of heating time
the V value of 0.87 V represents the highest value ever reported
oc sc
oc
at 160 °C, were plotted in Figures 7 and 8, respectively. The
among the devices based on P3HT:fullerenoid materials. Most
4
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Chemistry of Materials
ARTICLE
Figure 8. Photovoltaic parameters of PSCs based on the P3HT:PC BM (1:1, w/w) blend and P3HT:DMPCBA blend (1:1.2, w/w), as a function of
6
1
heating time at 160 °C. (a) PCE, (b) Jsc, (c) Voc, and (d) FF.
Figure 9. Optical microscopy of P3HT:DMPCBA (1:1.2, w/w) films after thermal annealing at 160 °C for (a) 0 h, (b) 10 h, and (c) 20 h. No obvious
change is observed.
significantly, the amorphous nature of DMPCBA beneficially
suppresses the thermal-driven crystallization and thus stabilizes
the morphology of the P3HT:DMPCBA blend. As a result, the
device retained 80% of its original PCE value against thermal
heating at 160 °C over 20 h.
acetonitrile) was used as the reference electrode. In a mixed solution of
o-dichlorobenzene/acetonitrile (4:1) with 0.1 M TBAPF (tetrabuty-
6
on
lammonium hexafluorophosophate) at 100 mV/s. LUMO = ꢀe(Ered
+
on
4.75), where Ered is the onset reduction potential (in volts) versus
+
Ag/Ag . The AFM images under tapping mode were taken on a Veeco
INNOVA Microscope AFM system with a INNOVA Nanodrive controller.
The optical microscopy images were measured by Zeiss Axiophot.
’
EXPERIMENTAL SECTION
Device Fabrication and Characterization. The ITO/glass
substrates were first cleaned in ultrasonic baths of isopropyl alcohol,
acetone, and isopropyl alcohol. After the ITO/glass substrate was dried
in an oven at 80 °C for 10 min, they were treated with UV-ozone for
20 min. Then, the surface of the ITO substrate was modified by spin-
coating PEDOT:PSS solution (Clevios P AI4083), followed by baking at
150 °C for 10 min in air. The mixture solution of P3HT (18 mg) and C60
bis-adducts with different ratios (18 mg for PC61BM, DPCBA, and
MPCBA; 21.6 mg for DMPCBA; 14.4 mg for DFPCBA) in 1 mL of
o-dichlorobenzene (ODCB) was then spin-coated onto the PEDOT:
PSS layer. The P3HT:C60 bis-adduct blend film was then put into glass
petri dishes while still wet, to undergo a solvent annealing process. After
drying, the samples were annealed at 140 °C for 10 min. The thermal
General Measurement and Characterization. All chemicals
1
were purchased from Aldrich and Acros, unless otherwise specified. H
were recorded on a Varian Unity-300 spectrometer. Differential scan-
ning calorimetry (DSC) was measured on TA Q200 Instrument under a
nitrogen atmosphere at a heating rate of 10 °C/min, and thermogravi-
metric analysis (TGA) was recorded on a PerkinꢀElmer Pyris system
under nitrogen atmosphere at a heating rate of 20 °C/min. Absorp-
tion spectra were collected on a Hitachi U-4100 spectrophotometer.
Electrochemical cyclic voltammetry (CV) was conducted on a CH
Instruments electrochemical analyzer as the workstation. A carbon glass
was used as the working electrode, Pt wire was used as the counter
+
electrode, and Ag/Ag electrode (0.01 M AgNO , 0.1 M TBAP in
3
4
060
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Chemistry of Materials
ARTICLE
stability of the P3HT:PC61BM- and P3HT:DMPCBA-based devices
were subjected to sustained heating at 150 °C for various times prior to
the cathode electrode deposition. The cathode, which was made of
calcium (10 nm thick) and aluminum (100 nm thick), was sequentially
Synthesis of Compound MPCBA. In a similar manner described
above, MPCBA was obtained from 2d (60 mg, 15%). MS (FAB)
m/z: 929.
ꢀ6
evaporated through a shadow mask under high vacuum (<10 Torr).
Each sample consists of four independent pixels defined by an active area
’ ASSOCIATED CONTENT
2
1
S
Supporting Information. H NMR spectra and mass
of 0.04 cm . Finally, the devices were encapsulated and characterized in
b
2
air. The devices were characterized under 100 mW/cm AM 1.5
spectrometry of the new compounds. This information is avail-
simulated light measurement (Yamashita Denso solar simulator). Cur-
rent density (JꢀV) characteristics of PSC devices were obtained by a
Keithley Model 2400 SMU system. Solar illumination conforming the
JIS Class AAA was provided by a SAN-EI 300W solar simulator
equipped with an AM 1.5G filter. The light intensity was calibrated
with a Hamamatsu S1336-5BK silicon photodiode. The performances
presented here are the average of the four pixels of each device. In order
to investigate the electron mobilities of the different blend films,
unipolar devices have been prepared following the same procedure
except that the PEDOT:PSS layer is replaced by evaporated aluminum
able free of charge via the Internet at http://pubs.acs.org/.
’ AUTHOR INFORMATION
Corresponding Author
*
E-mail: yjcheng@mail.nctu.edu.tw (Y.-J.C.), cshsu@mail.nctu.
edu.tw (C.-S.H.).
’
ACKNOWLEDGMENT
This work is supported by the National Science Council and
ATP” of the National Chiao Tung University and Ministry of
(100 nm). The electron mobilities were calculated according to space-
“
charge-limited current theory (SCLC). The JꢀV curves were fitted
Education, Taiwan.
according to the following equation:
!
ꢀ
ꢁ
V2
L3
’ REFERENCES
9
8
J ¼
εμ
(1) (a) Arias, A. C.; MacKenzie, J. D.; McCulloch, I.; Rivnay, J.;
Salleo, A. Chem. Rev. 2010, 110, 3. (b) Yu, G.; Gao, J.; Hummelen, J. C.;
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where ε is the permittivity of the blend film, μ the hole mobility, and L
the film thickness.
Synthesis of Compound 2a. Compound 1a (8 g, 43.9 mmol)
and p-toluenesulfonyl hydrazide (9.81 g, 52.7 mmol) were dissolved in a
mixed solvent of methanol (100 mL) and toluene (100 mL). The
resulting mixture was refluxed using a DeanꢀStark apparatus for 12 h.
After cooling to room temperature, the mixture was concentrated and
methanol was added, then cooled to 0 °C. The precipitated compound
was then collected by filtration and washed by cold methanol three
times. The solid compound was dried overnight under vacuum to get
compound 2a (9 g, 59%).
Synthesis of Compound 2b. In a similar manner described
above, 2b was obtained from 1b (6.3 g, 55%).
Synthesis of Compound 2c. In a similar manner described
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Fromherz, T.; Rispens, M. T.; Sanchez, L.; Hummelen, J. C. Adv. Funct.
Mater. 2001, 11, 374. (b) Scharber, M. C.; M €u hlbacher, D.; Koppe, M.;
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10
(4) (a) Zou, Y.; Najari, A.; Berrouard, P.; Beaupr ꢀe , S.; R ꢀe da Aïch, B.;
1
0
Tao, Y.; Leclerc, M. J. Am. Chem. Soc. 2010, 132, 5330. (b) Piliego, C.;
Holcombe, T. W.; Douglas, J. D.; Woo, C. H.; Beaujuge, P. M.; Fr ꢀe chet,
J. M. J. J. Am. Chem. Soc. 2010, 132, 7595. (c) Li, Z.; Ding, J.; Song, N.;
Lu, J.; Tao, Y. J. Am. Chem. Soc. 2010, 132, 13160. (d) Woo, C. H.;
Beaujuge, P. M.; Holcombe, T. W.; Lee, O. P.; Fr ꢀe chet, J. M. J. J. Am.
Chem. Soc. 2010, 132, 15547. (e) Bronstein, H.; Chen, Z.; Ashraf, R. S.;
Zhang, W.; Du, J.; Durrant, J. R.; Tuladhar, P. S.; Song, K.; Watkins, S. E.;
Geerts, Y.; Wienk, M. M.; Janssen, R. A. J.; Anthopoulos, T.; Sirringhaus,
H.; Heeney, M.; McCulloch, I. J. Am. Chem. Soc. 2011, 133, 3272.
1
0
above, 2c was obtained from 1c (5 g, 70%).
Synthesis of Compound 2d. In a similar manner described
above, 2d was obtained from 1d (6.3 g, 62%).
1
1
Synthesis of Compound DPCBA. To a toluene solution (1 L) of
compound 2a (0.97 g, 2.8 mmol) was added sodium hydride (0.2 g, 8.3
mmol) quickly under nitrogen. After the solution was stirred at room
temperature for 20 min, 0.5 equiv of C60 (1 g, 1.39 mmol) was added.
The resultant purple solution was heated to 70ꢀ80 °C and stirred for
(
f) Chu, T.-Y.; Lu, J.; Beaupr ꢀe , S.; Zhang, Y.; Pouliot, J.-R.; Wakim, S.;
Zhou, J.; Leclerc, M.; Li, Z.; Ding, J.; Tao, Y. J. Am. Chem. Soc. 2011,
33, 4250. (g) Price, S. C.; Stuart, A. C.; Yang, L.; Zhou, H.; You, W.
1
2
0 h. Then, the solution was heated to reflux at 120 °C and stirred for
1
4 h. After cooling to room temperature, the solution was extracted with
J. Am. Chem. Soc. 2011, 133, 4625. (h) Chen, H.-Y.; Hou, J.; Zhang, S.;
Liang, Y.; Yang, G.; Yang, Y.; Yu, L.; Wu, Y.; Li, G. Nat. Photon. 2009,
3, 649. (i) Hou, J.; Chen, H.-Y.; Zhang, S.; Li, G.; Yang, Y. J. Am. Chem.
Soc. 2008, 130, 16144. (j) Huang, F.; Chen, K.-S.; Yip, H.-L.; Hau, S. K.;
Acton, O.; Zhang, Y.; Luo, J.; Jen, A. K.-Y. J. Am. Chem. Soc. 2009,
NH Cl . The organic layer was dried over anhydrous MgSO , and the
4
(aq)
4
solvent was removed by concentration. Finally, the mixture was loaded
into a silica gel column, using toluene and hexane (v/v, 1/4) as the
eluent. The solid was reprecipitated from toluene in methanol five times.
The remaining brown was filtered and washed twice with methanol and
dried overnight under vacuum to get the red brown compound DPCBA
146 mg, 10%). MS (FAB) m/z: 1053.
Synthesis of Compound DMPCBA. In a similar manner de-
scribed above, DMPCBA was obtained from 2b (50 mg, 11%). MS
131, 13886. (k) Qin, R.; Li, W.; Li, C.; Du, C.; Veit, C.; Schleiermacher,
H.-F.; Adersson, M.; Bo, Z.; Liu, Z.; Inganas, O.; Wuerfel, U.; Zhang, F.
J. Am. Chem. Soc. 2009, 131, 14612. (l) Cheng, Y.-J.; Wu, J.-S.; Shih, P.-I.;
Chang, C.-Y.; Jwo, P.-C.; Kao, W.-S.; Hsu, C.-S. Chem. Mater. 2011,
(
23, 2361.
(5) (a) Kooistra, F. B.; Knol, J.; Kastenberg, F.; Popescu, L. M.;
(
FAB) m/z: 1110.
Verhees, W. J. H.; Kroon, J. M.; Hummelen, J. C. Org. Lett. 2007, 9, 551.
(b) Zhang, Y.; Yip, H.-L.; Acton, O.; Hau, S. K.; Huang, F.; Jen, A. K. Y.
Chem. Mater. 2009, 21, 2598. (c) Yang, C.; Kim, J. Y.; Cho, S.; Lee, J. K.;
Heeger, A. J.; Wudl, F. J. Am. Chem. Soc. 2008, 130, 6444. (d) Backer,
Synthesis of Compound DFPCBA. In a similar manner de-
scribed above, DFPCBA was obtained from 2c (55 mg, 15%). MS
FAB) m/z: 1124.
(
4
061
dx.doi.org/10.1021/cm201784w |Chem. Mater. 2011, 23, 4056–4062

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