Design of fullerene derivatives for stabilizing LUMO energy using donor groups placed in spatial proximity to the C60 cage

Article abstract of DOI:10.1021/jo3015159

A series of arylated dihydrofullerene derivatives were synthesized to elucidate the effective design of fullerene derivatives for enhancing the performance of organic photovoltaics. The LUMO energy of the fullerenes was estimated by the first reduction po

Full text of DOI:10.1021/jo3015159

Article
pubs.acs.org/joc
Design of Fullerene Derivatives for Stabilizing LUMO Energy using
Donor Groups Placed in Spatial Proximity to the C60 Cage
Fukashi Matsumoto,* Toshiyuki Iwai, Kazuyuki Moriwaki, Yuko Takao, Takatoshi Ito, Takumi Mizuno,
and Toshinobu Ohno*
Osaka Municipal Technical Research Institute, 1-6-50 Morinomiya, Joto-ku, Osaka 536-8553, Japan
S
* Supporting Information
ABSTRACT: A series of arylated dihydrofullerene derivatives were synthesized to elucidate the effective design of fullerene
derivatives for enhancing the performance of organic photovoltaics. The LUMO energy of the fullerenes was estimated by the
first reduction potential and theoretical calculations. The results showed that the methoxy groups substituted at spatial proximity
to the fullerene core offered significant stabilization of the LUMO level. The stabilizing effect of the directly arylated fullerenes is
more significant than that of conventional methanofullerenes. The theoretical investigation was performed with regard to the
electronic interaction between the methoxy and fullerene moieties.
where e is the elementary charge, ED(HOMO) is the highest
INTRODUCTION
■
occupied molecular orbital energy of the donor, and
Due to the many potential applications of fullerenes in
EA(LUMO) is the lowest unoccupied level of the acceptor.
materials and nanotechnology, numerous fullerene derivatives
have been synthesized in the past decade.1 The excellent
Therefore, the LUMO energy of the acceptor should lie at a
shallow level to increase the VOC value, unless the difference
electron-accepting capability of fullerenes has made them
promising materials for organic photovoltaics (OPVs).2 OPVs
between the LUMOs of the donor and acceptor becomes lower
than the exciton binding energy.13 The higher level of the
have drawn considerable attention in recent years, owing to
LUMO energy is easily achieved by increasing the number of
their advantages of low cost of fabrication, low weight, and
substituents on a fullerene cage.14 Blom et al. reported an
suitability in developing flexible devices. The most prominently
increase in VOC when [60]PCBM was replaced with its bis-
adduct analogue.15 Indene-C60 bis-adduct (ICBA) reported by
Li et al., which possesses two indene substituents on a fullerene
cage, also exhibited a higher LUMO energy level than PCBM.
The VOC and power-conversion efficiency of the P3HT-based
OPVs reached 0.84 V and 5.44%, respectively.16 However, the
tris-adduct analogue of PCBM showed significantly reduced
power-conversion efficiency due to the deterioration of electron
transport in the fullerene phase.17 These multiadducts
fundamentally consist of various regioisomers. Therefore, the
purification and isolation of these components is practically
impossible and sometimes results in poor reproducibility of the
device performance. This structural impurity introduces
reported material system for bulk-heterojunction OPVs is the
mixture of poly(3-hexylthiophene) and [6,6]-phenyl-C-61-
butyric acid methyl ester (P3HT:PCBM).3 Recently, there
has been remarkable improvement in the device performance
(up to 7−8%) of OPVs, due to the progress and development
of new conjugated polymer donor materials.4−7 However,
research on novel C60-based acceptor materials to replace
PCBM has not been successful until now.8−11 Investigation into
the development of new acceptor materials is essential in order
to realize significant improvement in device properties.
Nevertheless, an efficient strategy for designing the acceptor
materials has not yet been established.
It is empirically known that the open circuit voltage (VOC) of
OPVs is dictated by the relation12
Received: July 25, 2012
Published: October 4, 2012
VOC = 1/e(|ED(HOMO)| − |EA(LUMO)|) − 0.3
(1)
© 2012 American Chemical Society
9038
dx.doi.org/10.1021/jo3015159 | J. Org. Chem. 2012, 77, 9038−9043

The Journal of Organic Chemistry
Article
disorder into the electronic energy levels, which could
unfavorably affect the electronic properties of the device.18
In contrast, controlling the electronic properties of fullerene
has been studied for a decade, focusing on modification of the
substituents on the fullerene cage. Wudl et al. investigated
through-space orbital interactions between the substituent and
fullerene cage.19 Hummelen et al. showed a significant change
in the LUMO level, by substituting the phenyl ring of PCBM
with electron-donating and electron-withdrawing substitu-
ents.20 Although they aimed to verify the direct through-
space effect of the phenyl substituent toward the fullerene core,
they could not obtain experimental proof of it. They therefore
concluded that the number of methoxy substituents, rather than
the position of the substituents, is of importance. This result
implied that the distance between the substituent and the
fullerene cage was too large to realize a significant through-
space effect, and there was still the possibility of increasing the
VOC by using the electron-donating group substituted at the
closest proximity to the fullerene cage.
diverse arylboronic acids with fullerene (Table 1). The position
of the substitution was completely directed by the boronic acid
Table 1. Synthesis of Arylated Fullerenes by Using Boronic
a
Acids
By employing the above assumption, we aimed to verify the
largest direct through-space effect of a methoxy group on the
fullerene cage, by designing a structure where the o-alkoxy
phenyl group is directly substituted on the carbon cage, instead
of the conventional methano-bridged substitution. To double
the effect of the donating group, the 2,6-dialkoxyphenyl (DAP)
moiety was selected as a key structure of the substituent (Figure
1). Preliminary DFT calculations reveal that this structure is
Figure 1. Schematic structures of the conventional and the newly
designed fullerene derivatives.
effective in raising the LUMO energy and is therefore
promising as a candidate for an acceptor material (vide infra).
In this study, we synthesized a series of directly substituted
fullerene derivatives and evaluated the effect of methoxy groups
toward their energy level. Furthermore, their through-space
effect was investigated by utilizing the natural localized
molecular orbital (NLMO) analysis.
a
b
Conditions: 70 °C, 3 h, molar ratio C60/1/Rh cat. = 1/1.2/0.1. Yield
determined from HPLC area ratio. Values in parentheses are isolated
yields.
RESULTS AND DISCUSSION
■
Arylation of fullerenes, such as the Friedel−Crafts-type
hydroarylation reaction, has been well studied by several
groups.21,22 For example, 1-(4-tolyl)-2-hydrofullerene can be
obtained by the reaction of toluene and fullerene using AlCl3 as
a catalyst.23 However, the target structure as described above
could not be synthesized from m-dimethoxybenzene, which
selectively afforded the 1-(2,4-dimethoxyphenyl)-2-hydrofuller-
ene via electrophilic substitution. To synthesize the arylated
fullerenes that possess methoxy groups at various positions of
the phenyl group, we applied the procedure recently developed
by Itami et al.24 According to this report, arylated fullerenes
were prepared by the rhodium-catalyzed coupling reaction of
group. The reaction was performed at 70 °C for 3 h using 1.2
equiv of boronic acid with respect to C60. Recycle preparative
gel permeation chromatography (GPC) provided the purified
products 2a−f, and the structure of the obtained fullerenes was
confirmed using 1H and 13C NMR, IR, and UV−vis
1
spectroscopy and MALDI-TOF mass spectrometry. In the H
NMR spectra, the signal due to the hydrogen atom directly
connected to the fullerene core appeared at approximately 6.7
ppm. The sharp absorption peak around 430 nm in the UV−vis
spectrum of 2 is characteristic of 1,2-monoadducts of C60.25
The yields of the reaction were increased slightly from the
9039
dx.doi.org/10.1021/jo3015159 | J. Org. Chem. 2012, 77, 9038−9043

The Journal of Organic Chemistry
Article
nonsubstituted arylboronic acid (2a) to the trimethoxy-
substituted acid (2f), because of the difference in the electron
density on the aryl moiety. Unfortunately, the isolated yields
were low (20−50%) due to the difficulty in purification, which
arose from low solubility (<1 mg mL−1 in chloroform) of the
products.
As a preliminary investigation on the effect of the methoxy
group, the LUMO energies of the substituted fullerenes were
predicted using DFT calculations and estimated by electro-
chemical measurements. Geometry-optimized structures of the
products 2a−f were performed using a DFT calculation
program with the PBE functional and the DNP basis set as
isolated molecules in vacuo. The LUMO energies obtained with
this calculation level are shown in Figure 2 (right-hand axis).
results of the direct estimation of the LUMO energy from the
first unoccupied Kohn−Sham orbital.26 According to this
report, the LUMO energy was derived by adding the energy of
the first singlet excitation calculated using TD-DFT to the
HOMO energy of the highest occupied Kohn−Sham orbital at
the DFT level calculation.
Previous work showed good correlation between the LUMO
energies obtained by calculation for isolated molecules in vacuo
and the redox potentials,27 despite the fact that the CV
measurements were performed in solution. However, the
solvation effect cannot be neglected because the dipole
moment from the solvent creates an induced dipole on the
molecules, which may influence electron affinity of the
fullerenes. Therefore, the conductor-like screening model
(COSMO) was used to simulate the solvation environment
of the fullerenes during CV measurements, applying the
dielectric constant of oDCB (ε = 10.12).28
As shown in Figure 3, a strong linear correlation of the
calculated LUMO energies with the experimental values was
Figure 2. LUMO energies of C60 and arylated fullerenes (2a−f),
estimated from the first reduction potentials measured by cyclic
voltammetry (left axis, open circles), and theoretical values by DFT
calculation at the PBE/DNP level (right axis, filled squares).
Figure 3. Plots of the experimental LUMO energy levels versus
theoretical values. The LUMO levels are calculated by (a) PBE/DNP,
(b) PBE/DNP with TD-DFT, (c) PBE/DNP with COSMO, and (d)
PBE/DNP with TD-DFT/COSMO methods. R2 = squared
correlation coefficient for the fit.
The electrochemical properties of the directly arylated
fullerenes 2 were studied by cyclic voltammetry (CV) at
room temperature in o-dichlorobenzene (oDCB). The experi-
ments were carried out using 0.1 M tetra-n-butylammonium
perchlorate as the supporting electrolyte with a Ag/Ag+
reference electrode, platinum working electrode, platinum-
wire counter electrode, and ferrocene/ferrocenium internal
reference. All compounds showed three or four reversible
electroreductions in the potential range from 0 to −2.0 V. It is
assumed that the redox potential of the Fc/Fc+ couple has an
absolute energy level of −4.80 eV relative to vacuum. The
LUMO energy was calculated according to the equation
verified. The squared correlation coefficients reported inside
the plots indicate that the calculation from the combined TD-
DFT (Figure 3b) and COSMO methods (Figure 3c) gave
better results than a simple DFT calculation (Figure 3a).
Furthermore, applying time-dependent DFT calculations with
the inclusion of solvation effects provides a strong correlation
(Figure 3d). These results indicate that the DFT calculation
utilizing the simultaneous TD-DFT/COSMO method is
appropriate for reproducing the results of CV measurements
in solvent environments. The disagreement in the experimental
and theoretical LUMO values for the para-substitution of the
phenyl group in Figure 2 could be attributed to the solvation
effect of oDCB. The estimation of LUMO energy using the
reduction potential can be performed; however, this should be
done with a solid-state measurement, such as inverse
photoelectron spectroscopy (IPES),29 for precise determina-
tion. Nevertheless, we concluded that the methoxy groups
substituted in the ortho-position are more effective than the
para-position and that the estimation of LUMO levels using
DFT calculations is useful for designing novel acceptor
materials.
ELUMO = −(4.80 + ϕ ) (eV)
(2)
red
where ϕred is the first half-wave reduction potentials of the
fullerenes 2a−f relative to Fc/Fc+.
As shown in Figure 2, similar trends were observed in the
experimental and calculated LUMO energies, although the
theoretical energies are overestimated in comparison to the
experimental values. From these data, it can be concluded that
the methoxy groups substituted in the ortho position are
effective for raising the LUMO energy (2c,e). As expected from
the calculations and general considerations, the para-substituted
methoxy on the phenyl group provides a significant effect on
the energy level. However, the experimental values of the para-
substituted products (2d,f) did not change considerably from
those for the unsubstituted products (2c,e). Further theoretical
investigations were therefore performed to address this issue.
Musgrave et al. indicated that the results of the calculation
with the time-dependent density functional theory (TD-DFT)
for estimating LUMO energy were more accurate than the
Figure 4 shows the absorption spectra of the obtained
fullerenes in chloroform at room temperature. A sharp
absorption peak was observed around 430 nm, and this is
minimally shifted toward longer wavelengths with an increasing
number of methoxy substituents on the phenyl ring. This result
9040
dx.doi.org/10.1021/jo3015159 | J. Org. Chem. 2012, 77, 9038−9043

The Journal of Organic Chemistry
Article
Figure 4. UV−vis absorption spectra of arylated fullerenes (2a−f) in
chloroform.
indicates that elevated LUMO energy levels of the arylated
fullerenes are accomplished without decreasing the band gap.
Figure 5 displays the calculated surface plots of the HOMO
and LUMO energies for compound 2e. A majority of the
Figure 6. Comparison of first reduction potentials of methanofuller-
enes (bridged type) and arylated fullerenes (direct type). The values of
bridged-type fullerenes were obtained by Hummelen et al.20
Considering the theoretically optimized structure of the
arylated fullerene 2e, the oxygen lone pair points toward the
surface of the fullerene π system; this facilitates good electronic
overlap between them. To analyze the mechanism of the
LUMO stabilization, natural localized molecular orbital
(NLMO) analysis30 was employed for the optimized structures
at the B3LYP/6-31G(d) level. Figure 7 depicts the NLMO of
Figure 5. HOMO (left) and LUMO (right) surface plots for 2e
computed using B3LYP/6-31G(d).
HOMO and LUMO is located on the fullerene cage with a
small amount on the oxygen atom. This suggests there are weak
interactions between the methoxy group and the cage; however,
there is minimal electron transfer from the 2,6-dimethox-
yphenyl group to the fullerene moiety. Therefore, it can be
proposed that the DAP structure plays a key role in adjusting
the level of the LUMO without creating the charge transfer
(CT) trap bands, which would interfere with efficient
photoelectric conversion.
To further verify the effect of the methoxy groups substituted
at the closest proximity to the fullerene cage, we compared a
series of the first reduction potentials of the substituted
methanofullerenes (bridged type) with the arylated fullerenes
(direct type) (Figure 6). The literature values for the
methanofullerenes20 and the observed values of the arylated
fullerenes were normalized by utilizing PCBM as the standard.
Understandably, the stabilization of LUMO energy in arylated
fullerenes is substantially higher than that of methanofullerenes.
It should also be noted that the value for the 2,4,6-methoxy-
arylated fullerene 2f is close to that of the PCBM bis-adduct.15
The reasons for this phenomenon remain unclear; however,
they should be discussed by taking into account the through-
bond/through-space electronic effects. Because of the lack of
direct conjugation between the phenyl group and the C60 core,
the through-bond effect appears to be relatively weak;
therefore, we focused on studying the through-space effect
between them.
Figure 7. Three-dimensional images of the natural localized molecular
orbital (NLMO) for the delocalization of the oxygen lone pair for the
bridged-type (left) and the direct-type (right) models.
the lone pair on oxygen for the model structures of the bridged-
and direct-type fullerenes. Table 2 summarizes the contribution
of the atomic orbitals, which belong to the C60 cage, oxygen,
and other moieties such as phenyl and methyl groups, to the
Table 2. Contributions of Atomic Orbitals of Each Moiety
for the NLMO in Figure 7
a
model
C60 core (%)
oxygen (%)
others (%)
bridged type
direct type
0.07
0.23
98.37
98.20
1.56
1.57
a
Orbitals on phenyl and methyl groups.
9041
dx.doi.org/10.1021/jo3015159 | J. Org. Chem. 2012, 77, 9038−9043

The Journal of Organic Chemistry
Article
1H, J = 8.1 Hz), 7.22 (ddd, 1H, J = 7.5, 7.5, 1.2 Hz), 6.73 (s, 1H), 4.23
(s, 3H); 13C NMR (75 MHz, CS2/CDCl3) δ 157.87, 153.70, 153.40,
147.19, 146.93, 146.78, 146.05, 145.99, 145.85, 145.82, 145.56, 145.27,
145.05, 144.57, 144.34, 143.00, 142.34, 142.29, 141.90, 141.82, 141.44,
141.35, 139.98, 139.70, 136.50, 135.67, 129.91, 128.54, 121.32, 111.84,
66.15, 61.89, 55.12; FT-IR (KBr) 2924, 2827, 1590, 1455, 1421, 1312,
1203, 1158, 1055, 526 cm−1; HRMS (MALDI-TOF, negative) m/z
calcd for C67H8O [M−] 828.0575, found 828.0580.
1-(2,4-Dimethoxyphenyl)-1,9-dihydro[60]fullerene (2d): dark
brown powder; 37 mg, 31% yield; 1H NMR (300 MHz, CS2/
CDCl3) δ 8.04 (d, 1H, J = 8.4 Hz), 6.86 (d, 1H, J = 2.7 Hz), 6.71 (s,
1H), 6.70 (dd, 1H, J = 8.7, 2.7 Hz), 4.27 (s, 3H), 3.95 (s, 3H); 13C
NMR (75 MHz, CS2/CDCl3) δ 161.21, 158.91, 153.88, 147.27,
146.85, 146.10, 145.92, 145.65, 145.27, 145.16, 144.64, 144.13, 143.05,
142.39, 142.01, 141.88, 141.57, 141.40, 139.99, 139.79, 136.57, 136.44,
129.01, 128.63, 104.26, 100.13, 65.71, 62.02, 55.27, 55.08; FT-IR
(KBr) 2926, 2828, 1605, 1500, 1458, 1207, 1031, 818, 526 cm−1;
HRMS (MALDI-TOF, negative) m/z calcd for C68H10O2 [M−]
858.0681, found 858.0685.
1-(2,6-Dimethoxyphenyl)-1,9-dihydro[60]fullerene (2e): dark
brown powder; 64 mg, 54% yield; 1H NMR (300 MHz, CS2/
CDCl3) δ 7.46 (t, 1H, J = 8.4 Hz), 6.92 (d, 2H, J = 8.4 Hz), 6.69 (s,
1H), 4.06 (s, 6H); 13C NMR (75 MHz, CS2/CDCl3) δ 158.73, 155.77,
154.68, 147.09, 146.09, 145.92, 145.85, 145.15, 144.91, 144.72, 144.57,
143.20, 142.39, 142.32, 142.06, 141.78, 141.48, 141.29, 139.10, 137.20,
134.81, 129.66, 128.82, 128.06, 106.48, 63.53, 63.22, 55.93; FT-IR
(KBr) 2924, 1578, 1469, 1427, 1245, 1109, 515 cm−1; HRMS
(MALDI-TOF, negative) m/z calcd for C68H10O2 [M−] 858.0681,
found 858.0689.
1-(2,4,6-Trimethoxyphenyl)-1,9-dihydro[60]fullerene (2f): dark
brown powder; 40 mg, 32% yield; 1H NMR (300 MHz, CS2/
CDCl3) δ 6.67 (s, 1H), 6.43 (s, 2H), 4.04 (s, 6H), 3.95 (s, 3H); 13C
NMR data could not be obtained due to the extremely low solubility;
FT-IR (KBr) 2928, 1603, 1459, 1340, 1205, 1128, 811 cm−1; HRMS
(MALDI-TOF, negative) m/z calcd for C69H12O3 [M−] 888.0786,
found 888.0788.
NLMO. The majority of the electron density from the lone pair
electrons is strongly localized on the oxygen. Nevertheless, the
contribution of the fullerene core is more significant in the
direct-type than in the bridged-type model. This indicates a
stronger interaction between the lone pair and the π electrons
on the fullerene cage. From this prediction, we concluded that
the LUMO energy of the directly arylated fullerenes was
stabilized to some extent by the through-space effect between
the methoxy group and the fullerene core.
CONCLUSION
■
We developed a new design for an effective acceptor material
for OPVs characterized by the 2,6-dimethoxyphenyl group
directly substituted on the fullerene cage. The methoxy groups
placed at closest proximity to the fullerene core offer a distinct
advantage over conventional methanofullerenes in the stabiliza-
tion of LUMO energies, due to the through-space interaction
between the methoxy and fullerene moieties. To further
understand the though-space effect, the derivatives containing
other substituents, such as amino groups, will be investigated in
future work. The newly designed structure is therefore a
promising alternative for enhancing the voltage of OPVs. The
application of this new class of fullerene derivatives on OPVs is
under way, and it will be reported in future publications. In
addition, we observed an enhanced VOC of 0.8 V using P3HT
and a derivative of 2e in primitive devices.
EXPERIMENTAL SECTION
■
General Methods. Reduction potentials were determined by cyclic
voltammetry (CV) using a platinum working electrode, platinum-wire
counter electrode, and Ag/Ag+ reference electrode. Measurements
were performed under Ar gas; an o-dichlorobenzene solution
containing tetrabutylammonium perchlorate (0.1 M) was used as a
supporting electrolyte, and the scan rate was 20 mV/s at room
Computational Details. Full geometry optimizations and TD-
DFT calculations have been carried out at the PBE/DNP level in
DMol3 (Materials Studio, Accelrys).32 The surface plots of HOMO
and LUMO orbitals of 2e were generated with the Gaussian 03
package33 at the B3LYP/6-31G(d) level. NLMO analyses were
performed for the model compounds at their optimized geometries
at the B3LYP/6-31G(d) level, using the NBO 3.1 program.
1
temperature. H NMR and 13C NMR spectra were recorded using a
300 MHz instrument in deuterated solvents with tetramethylsilane as
an internal reference. Mass spectra were obtained using matrix-assisted
laser desorption ionization time-of-flight mass spectrometry (MALDI
TOF-MS). HPLC analyses were performed using toluene/methanol as
an eluent. 2,4,6-Trimethoxyphenylboronic acid31 and 1-phenyl-1,9-
dihydro[60]fullerene (2a)24 were prepared according to the literature.
All the other solvents and materials are commercially available and
were used as received.
ASSOCIATED CONTENT
■
S
* Supporting Information
1
Figures and tables giving H NMR, 13C NMR, and MALDI-
General Procedure for Synthesis of Arylated Fullerenes. 1-
(3,5-Dimethoxyphenyl)-1,9-dihydro[60]fullerene (2b). The com-
pound was prepared by a modified experimental procedure of the
literature.24 In a 50 mL flask were added 3,5-dimethoxyphenylboronic
acid (30.3 mg, 0.167 mmol), [Rh(cod)(MeCN)2]BF4 (5.20 mg, 13.8
μmol), and C60 (100 mg, 0.139 mmol). Then o-dichlorobenzene (17.0
mL) and H2O (4.20 mL) were added under a stream of argon. After
the mixture was stirred at 70 °C for 3 h, it was extracted with toluene.
The organic layer was dried over NaSO4 and concentrated in vacuo.
The residue was purified by recycle preparative gel permeation
chromatography and centrifuged with methanol to afford 2b (22 mg,
19% yield) as a dark brown powder. 1H NMR (300 MHz, CS2/
CDCl3): δ 7.52 (d, 2H, J = 1.8 Hz), 6.73 (s, 1H), 6.62 (t, 1H, J = 2.1
Hz), 4.00 (s, 6H). 13C NMR (75 MHz, CS2/CDCl3): δ 162.04,
153.51, 152.39, 150.15, 147.45, 146.86, 146.29, 146.12, 145.89, 145.73,
145.46, 145.33, 144.57, 144.47, 143.19, 142.53, 142.23, 142.01, 141.87,
141.57, 141.51, 140.10, 135.77, 106.21, 99.32, 67.90, 63.68, 55.47. FT-
IR (KBr): 2919, 1457, 1428, 1375, 1259, 1031, 754, 526 cm−1. HRMS
(MALDI-TOF, negative): m/z calcd for C68H10O2 [M−] 858.0681,
found 858.0691.
TOF HRMS spectra of new compounds 2b−2f, cyclic
voltammograms of fullerene derivatives, and computational
details. This material is available free of charge via the Internet
at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: matumoto@omtri.or.jp (F.M.); ohno@omtri.or.jp
(T.O.).
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was supported in part by Core Research for
Evolutional Science and Technology (CREST) of the Japan
Science and Technology Agency (JST) and JSPS KAKENHI
Grant Number 23750232, 22550176.
1-(2-Methoxyphenyl)-1,9-dihydro[60]fullerene (2c): dark brown
powder; 40 mg, 35% yield; H NMR (300 MHz, CS2/CDCl3) δ 8.15
(dd, 1H, J = 7.5, 1.5 Hz), 7.57 (ddd, 1H, J = 7.8, 7.8, 1.8 Hz), 7.32 (d,
1
REFERENCES
(1) Thilgen, C.; Diederich, F. Chem. Rev. 2006, 106, 5049−5135.
■
9042
dx.doi.org/10.1021/jo3015159 | J. Org. Chem. 2012, 77, 9038−9043

The Journal of Organic Chemistry
Article
(2) Brabec, C. J.; Sariciftci, N. S.; Hummelen, J. C. Adv. Funct. Mater.
2001, 11, 15−26.
(3) Li, G.; Shrotriya, V.; Yao, Y.; Yang, Y. J. Appl. Phys. 2005, 98,
043704.
(4) Chen, H.-Y.; Hou, J.; Zhang, S.; Liang, Y.; Yang, G.; Yang, Y.; Yu,
L.; Wu, Y.; Li, G. Nat. Photonics 2009, 3, 649−653.
(5) Su, M.-S.; Kuo, C.-Y.; Yuan, M.-C.; Jeng, U. S.; Su, C.-J.; Wei, K.-
H. Adv. Mater. 2011, 23, 3315−3319.
(6) Price, S. C.; Stuart, A. C.; Yang, L.; Zhou, H.; You, W. J. Am.
Chem. Soc. 2011, 133, 4625−4631.
(7) Piliego, C.; Holcombe, T. W.; Douglas, J. D.; Woo, C. H.;
Beaujuge, P. M.; Frec
7597.
́
het, J. M. J. J. Am. Chem. Soc. 2010, 132, 7595−
(8) Zhao, G.; He, Y.; Xu, Z.; Hou, J.; Zhang, M.; Min, J.; Chen, H.-Y.;
Ye, M.; Hong, Z.; Yang, Y.; Li, Y. Adv. Funct. Mater. 2010, 20, 1480−
1487.
(9) Kuhlmann, J.-C.; de Bruyn, P.; Bouwer, R. K. M.; Meetsma, A.;
Blom, P. W. M.; Hummelen, J. C. Chem. Commun. 2010, 46, 7232−
7234.
(10) Lee, H. S.; Yoon, S. C.; Lim, J.; Lee, M.; Lee, C. J. Nanosci.
Nanotechnol. 2008, 8, 4533−4537.
(11) Lee, H. S.; Yoon, S. C.; Lim, J.; Lee, M.; Lee, C. Mol. Cryst. Liq.
Cryst. 2008, 492, 657−666.
(12) Dennler, G.; Scharber, M. C.; Ameri, T.; Denk, P.; Forberich,
K.; Waldauf, C.; Brabec, C. J. Adv. Mater. 2008, 20, 579−583.
(13) Thompson, B. C.; Kim, Y.-G.; McCarley, T. D.; Reynolds, J. R. J.
Am. Chem. Soc. 2006, 128, 12714−12725.
(14) Niinomi, T.; Matsuo, Y.; Hashiguchi, M.; Sato, Y.; Nakamura, E.
J. Mater. Chem. 2009, 19, 5804−5811.
(15) Lenes, M.; Wetzelaer, G.-J. A. H.; Kooistra, F. B.; Veenstra, S.
C.; Hummelen, J. C.; Blom, P. W. M. Adv. Mater. 2008, 20, 2116−
2119.
(16) He, Y.; Chen, H.-Y.; Hou, J.; Li, Y. J. Am. Chem. Soc. 2010, 132,
1377−1382.
(17) Lenes, M.; Shelton, S. W.; Sieval, A. B.; Kronholm, D. F.;
Hummelen, J. C.; Blom, P. W. M. Adv. Funct. Mater. 2009, 19, 3002−
3007.
(18) Frost, J. M.; Faist, M. A.; Nelson, J. Adv. Mater. 2010, 22, 4881−
4884.
(19) Eiermann, M.; Haddon, R. C.; Knight, B.; Li, Q. C.; Maggini,
M.; Martín, N.; Ohno, T.; Prato, M.; Suzuki, T.; Wudl, F. Angew.
Chem., Int. Ed. Engl. 1995, 34, 1591−1594.
(20) Kooistra, F. B.; Knol, J.; Kastenberg, F.; Popescu, L. M.;
Verhees, W. J. H.; Kroon, J. M.; Hummelen, J. C. Org. Lett. 2007, 9,
551−554.
(21) Chen, Z.-X.; Wang, G.-W. J. Org. Chem. 2005, 70, 2380−2383.
(22) Iwashita, A.; Matsuo, Y.; Nakamura, E. Angew. Chem., Int. Ed.
Engl. 2007, 46, 3513−3516.
(23) Kokubo, K.; Tochika, S.; Kato, M.; Sol, Y.; Oshima, T. Org. Lett.
2008, 10, 3335−3338.
(24) Nambo, M.; Noyori, R.; Itami, K. J. Am. Chem. Soc. 2007, 129,
8080−8081.
(25) Meier, M.; Bergosh, R.; Gallagher, M.; Spielmann, H.; Wang, Z.
J. Org. Chem. 2002, 67, 5946−5952.
(26) Zhang, G.; Musgrave, C. B. J. Phys. Chem. A 2007, 111, 1554−
1561.
(27) Suzuki, T.; Maruyama, Y.; Akasaka, T.; Ando, W. J. Am. Chem.
Soc. 1994, 116, 1359−1363.
(28) Tan, K.; Lu, X.; Wang, C.-R. J. Phys. Chem. B 2006, 110, 11098−
11102.
(29) Akaike, K.; Kanai, K.; Ouchi, Y.; Seki, K. Appl. Phys. Lett. 2009,
94, 3309.
(30) Reed, A. E.; Weinhold, F. J. Chem. Phys. 1985, 83, 1736−1740.
(31) Chaumeil, H.; Signorella, S.; Le Drian, C. Tetrahedron 2000, 56,
9655−9662.
(32) Delley, B. J. Chem. Phys. 1991, 94, 7245−7251.
(33) Frisch, M. J., et al. Gaussian 03, Revision C.02; Gaussian, Inc.,
Wallingford, CT, 2004.
9043
dx.doi.org/10.1021/jo3015159 | J. Org. Chem. 2012, 77, 9038−9043