Synthesis and properties of novel methanofullerenes having ethylthienyl and/or n-pentyl group for photovoltaic cells

Article abstract of DOI:10.1016/j.tet.2010.06.089

Novel methanofullerenes 3 having ethylthienyl and/or n-pentyl groups were designed and synthesized for the purpose of developing new acceptors for an organic photovoltaic cell with higher performance than that of the [6,6]-phenyl-C₆₁-butylic ac

Full text of DOI:10.1016/j.tet.2010.06.089

Tetrahedron 66 (2010) 7316e7321
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Synthesis and properties of novel methanofullerenes having ethylthienyl
and/or n-pentyl group for photovoltaic cells
*
*
Kazuyuki Moriwaki , Fukashi Matsumoto, Yuko Takao, Daichi Shimizu, Toshinobu Ohno
Osaka Municipal Technical Research Institute, 1-6-50 Morinomiya, Joto-ku, Osaka 536-8553, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel methanofullerenes 3 having ethylthienyl and/or n-pentyl groups were designed and synthesized
for the purpose of developing new acceptors for an organic photovoltaic cell with higher performance
than that of the [6,6]-phenyl-C61-butylic acid methyl ester (PCBM) used as the standard acceptor. The
Received 28 January 2010
Received in revised form 29 June 2010
Accepted 29 June 2010
electronic absorption spectra and cyclic voltammetry (CV) of 3, PCBM, and [6,6]-(thiophene-2-yl)-C61
-
Available online 29 July 2010
butylic acid methyl ester (ThCBM) were measured to estimate solubility and reduction potentials as
characteristics of n-type semiconductor for organic photovoltaic devices. The CV measurements revealed
reversible reduction waves for all of the methanofullerenes and the first reduction potentials of the
n-pentyl-substituted 1-(5-ethylthiophene-2-yl)-[6,6]-methanofullerene[60] (3b) and 1-phenyl-[6,6]-
methanofullerene[60] (3c) were negatively shifted compared to those of the corresponding terminal
methyl ester-substituted homologues (3a and PCBM). The performances of photovoltaic devices con-
sisting of 3b and 3c were slightly higher than those of PCBM.
Keywords:
PCBM
Methanofullerene
Photovoltaic device
Bulk heterojunction
Organic solar cell
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
mobility. Subsequently, PCBM and P3HT were frequently used as
standard n-type and p-type organic semiconductors, respectively,
Ever since silicon-based solar cells were first manufactured for
practical use, there has been considerable expectation that photo-
voltaic system would provide a solution to the energy crisis and the
environmental problems related to global warming. Although sili-
con-based solar cells, due to their relatively high efficiency for
energy conversion, have maintained their unrivaled position as
energy converting devices for a long time,1 their poor cost perfor-
mance and the unstable supply of silicon have prevented the
extensive prevalence of these systems. In spite of their lower en-
ergy conversion, organic photovoltaic cells are attractive as
a promising alternative to silicon-based devices because of their
low weight, flexibility, and anticipated low manufacturing costs. In
particular, since Sariciftci et al. reported that a conversion efficiency
of 2.5% could be achieved using a polymer solar cell based on a bulk
heterojunction of [6,6]-phenyl-C61-butyric acid methyl ester
(PCBM) and poly[2-methoxy-5-(30,70-dimethyloctyloxy)-1,4-phe-
nylenevinylene] (MDMO-PPV),2 the polymer/methanofullerene
photovoltaic system has attracted a great deal of attention as one of
the incoming photovoltaic systems after silicon-based solar cells.
Since then, poly(3-hexylthiophene) (P3HT) has been used as p-type
semiconductor instead of PPV derivatives because of its high
for polymer/methanofullerene photovoltaics,3 and the perfor-
mance of these devices has steadily advanced to a conversion
efficiency of greater than 4%,4 owing to the accumulation of device
preparation know-how, mainly with respect to morphological
control of the active layers in the deposition, spin-coating, and
annealing process.
In order to achieve drastic improvements in device perfor-
mance, the exploration of more appropriate materials is also an
important approach, and several types of polymers have been
considered as P3HT and MDMO-PPV alternatives.5 In contrast,
alternatives to PCBM in the polymer/methanofullerene system
have been very limited, except for a few analogues of PCBM, and
there is no information about the optimum molecular structure of
acceptors to maximize the performance.6
* Corresponding authors. Tel.: þ81 6 6963 8057; fax: þ81 6 6963 8049; e-mail
addresses: mori@omtri.or.jp (K. Moriwaki), ohno@omtri.or.jp (T. Ohno).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.06.089

K. Moriwaki et al. / Tetrahedron 66 (2010) 7316e7321
7317
Recently, Hummelen et al. reported a device fabricated with
a thienyl analogue, ThCBM,7 for the purpose of improving the
miscibility with P3HT. However, there was no clear explanation of
the advantages of ThCBM over PCBM. In our previous study, we
prepared novel PCBM analogues having various types of thienyl
groups and investigated their structural effect on the solubilities
and morphologies of their mixtures with P3HT.8 The morphology of
the bulk hetero films of the obtained methanofullerenes was found
to be different from that of PCBM and the aggregation of P3HT was
restricted by the large volume of the substituents of meth-
anofullerenes. An improvement in solubility by adding an ester
group was also shown.
In this study, novel analogues of PCBM with the phenyl group
replaced by a 2-(5-ethylthienyl) group, or the 3-(methoxycarbonyl)
propyl group by a n-pentyl group, were designed and synthesized,
for the purpose of developing new acceptors on P3HT/meth-
anofullerene devices having much higher performance than
a P3HT/PCBM system and acquiring a guideline for designing
optimum molecular structures for them. The 2-(5-ethylthienyl)
group was selected instead of thienyl group because of stabilization
Scheme 2.
of the oxidizable
a-proton of thiophene by alkylation. We
the case of 2c having a phenyl group, a mixture of [6,6]- and [5,6]-
isomers was produced as expected. The production of [5,6]-PCP
was confirmed by 13C NMR and the electronic absorption spectra,10
and the conversion of the [5,6]- to the [6,6]-isomer was accom-
plished by heating at 170 ꢀC for 4.5 h. In contrast, only the [6,6]-
isomers of EThCBM and EThCP were obtained, and seemed to be
thermodynamically more stable than [5,6]-fulleroid, probably
because of the strong electron-donating effect of the thienyl
substituent.11
This reaction gave not only the monoadduct 3 but also bisad-
ducts 4, which contained some regio-isomers, as shown in
Scheme 3. The bisadducts 4 were a mixture of regio-isomers and
could be confirmed by FD-MS. The total yields of 3 and 4
amounted to approximately 60% of consumed C60 as shown in
Table 1. The inconsistency of the total yields probably resulted
from the production of the multi-adducts, which were separated
by preparative GPC.
investigated the basic properties, such as the electronic absorption
spectra, solubility of these novel methanofullerenes, and perfor-
mance of photovoltaic devices that consisted of P3HT and these
methanofullerenes.
2. Results and discussion
Novel methanofullerenes were synthesized as described in
previous papers.9 Scheme 1 shows the preparation of tosylhy-
drasones 2, the precursors of methanofullerenes. Tosylhydrazones
2a and 2b were synthesized by the reaction of p-toluenesulfonyl
hydrazide (TsNHNH2) with ketones 1a and 1b, respectively, which
were obtained by the FriedeleCrafts acylation of commercially
available 2-ethylthiophene. Tosylhydrazone 2c was prepared from
commercial phenyl n-pentyl ketone as
(Scheme 2).
a starting material
Scheme 1.
Scheme 3.
Methanofullerenes were synthesized from C60 in the presence of
slightly excess amount of tosylhydrazones 2 under basic conditions,
while monitoring the reaction by TLC. EThCBM (3a) having a bu-
tyric acid methyl ester group was easily distinguishable from C60 by
TLC, similar to the case of PCBM. In the case of EThCP (3b) and PCP
(3c) having an n-pentyl group instead of a butyric acid methyl ester
group, the Rf values of 3b and 3c were unexpectedly close to that of
C60. From this result, the methyl ester moiety was obviously found
to influence the polarities of methanofullerenes. In particular, the Rf
value of PCP (3c) has too similar to C60 to monitor the reaction by
TLC. Hence, the reaction of 2c was monitored by HPLC with a C-18
column as an eluent (toluene/methanol¼50:50). In the case of 3b
and 3c, preparative gel permeation chromatography (GPC) was
used for the isolation of the products.
Table 1
Reaction conditions and yields for monoadducts 3 and bisadducts 4
Monoadducts
2
Conversion
of C60 (%)
Yields
of 3 (%)
38 (42)a
35 (36)a
30 (31)a
Yields
of 4 (%)
21 (23)a
21 (23)a
19 (20)a
Total yields
of 3 and 4 (%)
59 (66)a
56 (59)a
49 (51)a
(equiv)
EThCBM (3a)
EthCP (3b)
1.6
1.5
1.2
90
95
98
[6,6]PCP (3c)b
a
Based on consumed C60
.
b
Compound 3c was completely converted from [5,6]-isomer by heating at 170 ꢀ
for 4.5 h.
C
Solubility of the methanofullerenes 3 is one of the most im-
portant properties for the fabrication of photovoltaic devices with
good performance.6d Solubility data were obtained by the absorp-
tion spectroscopic technique because of its higher determination
It is well known that the isomers of both [5,6]-fulleroid and
[6,6]-methanofullerene are often produced in this reaction, and in

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K. Moriwaki et al. / Tetrahedron 66 (2010) 7316e7321
accuracy. Figure 1 shows the electronic absorption spectra of 3,
[5,6]-PCP, and PCBM as comparative samples. All methanofuller-
enes exhibited a small sharp band at 432 nm and two broad bands
around 500 nm and 700 nm, which are characteristic of [6,6]-
methanofullerenes. In contrast, the [5,6]-PCP had no characteristic
bands in [6,6]-isomer and only one broad band at lmax¼542 nm
was observed in the visible region. The solubility in dichloro-
methane was estimated from the absorbance results in the satu-
rated solution and the extinction coefficient of 3 and PCBM at a lmax
of 432 nm, as shown in Table 2.
The conversion efficiency of a solar cell is proportional to the
short circuit current (JSC) and open-circuit voltage (VOC), according
to the equation of
h
¼FF$JSC$VOC, where FF is the fill factor. It has
been reported in some studies that VOC is related to the difference
between the highest occupied molecular orbital (HOMO) of P3HT
as the electron donor and the lowest unoccupied molecular
orbital (LUMO) of methanofullerene as the electron acceptor, and
that the LUMO level of methanofullerene is closely correlated
with the electronic properties of the substituents introduced in
the parent fullerene.13 To estimate the LUMO levels of meth-
anofullerenes, their redox behavior was investigated by cyclic
voltammetry. All of the methanofullerenes exhibited three or four
reversible electroreductions. The first reduction potentials and
energy difference between the peak potentials are listed in
Table 3. All of the first reduction potentials E1/2,red were located at
ꢁ1.143 to ꢁ1.162 V vs the ferrocene/ferrocenium couple (Fc/Fcþ).
The E1/2,red values of 3b and 3c, which had n-pentyl groups, were
negatively shifted by 8e19 mV, as compared to the corresponding
methanofullerenes 3a, PCBM, and ThCBM with a methyl ester
group (Table 3, entries 2 and 3). From these results, we found that
the presence of the ester group lowered the LUMO level of the
methanofullerenes to give a smaller VOC. As a result, the VOC
values of EThCP and PCP, which have no ester group were larger
than that of PCBM.
In relation to JSC, the JSC values of EThCP and PCP were a little
higher than that of PCBM. In general, JSC and FF are strongly related
to the morphology of the active layer. Although we observed and
compared the morphologies of spin-coated P3HT/methanofuller-
enes surfaces, we could not find a large difference between them
and a P3HT/PCBM surface (Fig. 2). The relation between the mor-
phologies and the differences in the molecular structures of the
acceptors is still under investigation.
Figure 1. Electronic absorption spectra of 3a, 3b, 3c, PCBM, and [5,6]PCP in a di-
chloromethane solution.
Table 2
Absorption and solubility of 3, PCBM, and C60 in dichloromethane
Entry
Compound
lmax
3
(Mꢁ1 cmꢁ1
)
Absorbancea
at lmax
Solubility
(g/L)
(nm)
1
2
3
4
5
EThCBM (3a)
EThCP (3b)
[6,6]PCP (3c)
PCBM
432.0
432.0
432.0
431.5
d
2326
2313
1897
2136
d
0.428
0.245
0.287
0.750
d
8.69
4.87
6.64
16.0
0.2612
3. Conclusion
In this study, three novel methanofullerenes 3 were designed
and synthesized by the reaction of C60 with correspondent
tosylhydrazones 2 using the method in previous papers. Only in
the case of PCP (3c) was the [5,6]-fulleroid isomer formed in this
reaction at a lower temperature. The solubilities of the novel
methanofullerenes were examined in dichloromethane, and it
was found that they all had adequate solubilities for fabricating
solar cell devices. Bulk-heterojunction solar cells consisting of
P3HT and the novel methanofullerenes were fabricated and their
performances were evaluated in comparison with those of PCBM
and ThCBM devices. As a result, all of the novel methanofullerene
devices were found to exhibit conversion efficiencies of over
2.2%, which were superior to a PCBM device. The JSC and VOC
values of the devices consisting of EThCP and PCP, which had the
n-pentyl group, were found to be higher than those of EThCBM
and PCBM, which had the methyl ester group. It is considered
that the absence of the ester group raised the LUMO level to give
higher VOC values in the case of devices consisting of EThCP
and PCP.
C60
a
Measured after diluting the saturated solutions by 50 times.
As a result, significant solubility improvements were confirmed
for all of the novel methanofullerene 3 in comparison with that of
C60 (Table 2, entries 1e3). In particular, the influence of methyl ester
group introduced in the methanofullerenes on the solubility was
larger than that of the alkyl group. The influences of the 2-ethyl-
thienyl and phenyl substituents were almost similar, but the
influence of the phenyl substituent was a little greater than that of
2-ethylthienyl group.
Photovoltaic cells of ITO/(PEDOT:PSS)/(P3HT:methanofuller-
ene)/LiF/Al (methanofullerene¼EThCBM (3a), EThCP (3b), PCP (3c),
ThCBM, and PCBM) were fabricated, and their performances were
listed in Table 3, although these data were not optimized. The
conversion efficiency (h) exceeded 2.2% for all of the devices. To our
surprise, EThCP and PCP devices showed slightly higher
than that of PCBM (Table 3, entries 2 and 3).
h values
Table 3
The work and cyclic voltammetry data summarizing the performance of the manufactured photovoltaic devices
JSC (mA cmꢁ2
)
VOC (V)
FF
h
(%)
E1/2,red (V)
DE
b (mV)
a
Entry
Methanofullerene
1
2
3
4
5
EThCBM (3a)
EThCP (3b)
PCP (3c)
PCBM
6.10
6.72
6.79
6.12
6.77
0.628
0.676
0.663
0.619
0.619
0.587
0.568
0.571
0.585
0.601
2.25
2.58
2.57
2.22
2.52
ꢁ1.147
ꢁ1.162
ꢁ1.161
ꢁ1.153
ꢁ1.143
73
81
74
78
72
ThCBM
a
V vs Ferrocene/Ferrocenium couple (Fc/Fcþ). (n-Bu)4NClO4 (0.05 mol dmꢁ3) as a supporting electrolyte in ODCB. Scan rate¼20 mV sꢁ1
.
b
An anodic to cathodic peak separation of cyclic voltammogram.

K. Moriwaki et al. / Tetrahedron 66 (2010) 7316e7321
7319
Figure 2. AFM phase images (500ꢂ500 nm2 area) of fabricated P3HT/fullerenes devices containing (A) EThCP and (B) PCP.
4. Experimental
perchlorate using a Pt electrode as a working electrode and a plat-
inum wire as counter electrode with approximately
a
4.1. Reagents and instruments
2.5ꢂ10ꢁ1 mol dmꢁ3 of the samples. The reference electrode was an
Ag/AgNO3 electrode filled with 0.1 mol dmꢁ3 of (n-Bu)4NClO4 in
acetonitrile. All of the potentials were referenced to the ferrocene/
ferrocenium couple (Fc/Fcþ) as an internal standard. CV measure-
ments were performed three times on each samples and the mean
value of them were shown.
All of the reagents were purchased and used without further
purification. C60 was purchased from Honjo Chemical Inc. 1,2-Di-
chlorobenzene (ODCB) wasdried anddistilled fromcalciumhydride.
ꢀ
Acetonitrile was dried over molecular sieves (3 A). Regioregular
poly(3-hexylthiophene-2,5-diyl) (P3HT) was purchased from
SigmaeAldrich Corp. Poly(3,4-ethylenedioxythiophene):poly-
(styrenesulfonate) (PEDOT:PSS) (Baytron P) was provided by H.C.
Starck Ltd. Preparative GPC was carried out by Japan Analytical In-
dustry, Co., Ltd. LC-908 with a JAIGEL-1H and a JAIGEL-2H GPC col-
umn. 1H NMR and 13C NMR spectra were recorded on a JEOL AL300.
FD-mass spectra were obtained on a JEOL JMS-303HF. Electronic
absorption spectra were recorded on a Shimadzu Corp. UV-3100A.
Cyclic voltammetry was carried out using a BAS Electrochemical
Analyzer Model 630A.
4.3. Synthesis
4.3.1. 5-Ethylthiophene-2-yl (3-methoxycarbonyl)propyl ketone (1a).
2-Ethylthiophene (5.0 g, 45 mmol), methyl 5-chloro-5-oxovaler-
ate (8 g, 49 mmol), and aluminum chloride anhydrous (0.6 g,
4.5 mmol) were dissolved in 40 mL of dry acetonitrile, followed
by heating to the reflux temperature and stirring for 8 h. After
the reaction mixture was cooled to room temperature, it was
poured into 1 L of 1 wt % NaOH aqueous solution and extracted
with toluene. The organic layer was dried over MgSO4 and con-
centrated in vacuo to give a crude product. The purified product
was obtained by silicagel column chromatography using toluene
as an eluent. Isolated yield¼49% (5.3 g); brown oil; HRMS (MALDI
TOF): m/z [MþHþ] calcd for C12H17O3S: 241.0898; found:
4.2. Fabrication of the photovoltaic devices and
determination of the device performances
Photovoltaic devices were fabricated from a blend of P3HT as
a donor and the methanofullerene (3ae3c, PCBM, and ThCBM) as
an acceptor. The PEDOT:PSS layer was prepared by spin-coating on
the top of an indium-tin oxide (ITO) coated glass substrate. Under
dry nitrogen, a chlorobenzene solution of the P3HT and meth-
anofullerene in a 1:0.8 w/w ratio was prepared with a 1 wt %
methanofullerene concentration. Then the P3HT:methanofullerene
blend as the active layer was spin-coated on the PEDOT:PSS layer.
After drying the substrates overnight at ambient temperature un-
der nitrogen, a 0.5 nm layer of LiF and a 100 nm layer of Al were
deposited on the active layer as the cathode. The devices were
encapsulated with a glass plate and epoxy resin to avoid exposure
to the air and moisture after all lamination processes. The device
performance was determined by a solar simulator under simulated
solar illumination (AM1.5G, 100 mW cmꢁ2). The reproducibility of
the measurements was confirmed with three devices for each
sample and the highest performance was shown. After the
measurements, AFM images of the active layers were taken
with a Digital Instruments Nanoscope IIIa at a scan rate of 1.0 Hz in
the tapping mode. Cyclic voltammetry measurements were
performed at ambient temperature under an argon atmosphere
241.0896; 1H NMR (acetone-d6):
d 7.58 (d, 1H, 9.0 Hz), 6.80 (d, 1H,
9.3 Hz), 3.49 (s, 3H), 2.88e2.72 (m, 4H), 2.25 (t, 2H, 5.4 Hz), 1.83
(tt, 2H, 2.4 Hz), 1.15 (t, 3H, 6.5 Hz); 13C NMR (acetone-d6):
d
192.47, 173.77, 157.42, 142.69, 133.46, 126.05, 51.53, 38.03, 33.48,
24.38, 20.62, 15.96.
4.3.2. Methyl 5-(5-ethylthiophene-2-yl)-5-(2-tosylhydrazono)-valer-
ate (2a). Compound 1a (4.7 g, 20 mmol) and p-toluenesulfonehy-
drazide (4.5 g, 24 mmol) were dissolved in 50 mL of methanol,
followed by heating to the reflux temperature and stirring for 24 h.
The reaction mixture was cooled to room temperature to give
a precipitate of product, and the precipitate was collected and
recrystallized from methanol. Isolated yield¼74% (5.9 g); light
yellow crystal: mp 117e119 ꢀC; MALDI TOF-MS: m/z 410 (MþH)þ;
1H NMR (CDCl3):
d 9.32 (s, 1H), 7.81 (d, 2H, 8.4 Hz), 7.38 (d, 2H,
8.1 Hz), 7.21 (d, 1H, 3.6 Hz), 6.73 (d, 1H, 3.6 Hz), 3.65 (s, 3H),
2.83e2.69 (m, 6H), 2.37 (t, 3H, 6.9 Hz), 1.78 (tt, 2H, 6.9 Hz), 1.29 (t,
3H, 7.5 Hz); 13C NMR (CDCl3):
d 174.24, 152.55, 151.24, 144.51,
140.58, 137.49, 130.17, 128.81, 128.07, 124.67, 51.85, 33.25, 27.01,
24.11, 22.37, 21.40, 16.05; IR (KBr): 3187, 2960, 2935, 1715, 1592,
1405, 1341, 1306, 1224, 1164, 1021, 985, 914, 870, 815, 801, 704, 676,
in
a
0.1 mol dmꢁ3 ODCB solution of tetra-n-butylammonium

7320
K. Moriwaki et al. / Tetrahedron 66 (2010) 7316e7321
577, 549, 517 cmꢁ1. Anal. Calcd for C19H24N2O4S2: C, 55.86; H, 5.92;
N, 6.86; O, 15.67; S, 15.70. Found: C, 55.95; H, 6.01; N, 6.89.
60 min at ambient temperature under Ar. Into the solution,
1.5 equiv of 2b (79 mg, 0.21 mmol), sodium methoxide (12 mg,
0.22 mmol), and 2 mL of dry pyridine were added. The mixture was
stirred at 70 ꢀC for 1 h and 100 ꢀC for 1 h. After removal of the
solvent by distillation, the residue was purified by preparative gel
permeation chromatography with chloroform to give EThCP. Iso-
lated yield¼35% (44 mg, 36%; based on consumed C60); brown
4.3.3. 1-(5-Ethylthiophene-2-yl)-1-(3-methoxycarbonyl)propyl-
[6,6]-methanofullerene[60] (EThCBM) (3a) and bis-adduct 4a. C60
(300 mg, 0.42 mmol) was dissolved in 9 mL of dry ODCB by ultra-
sonic treatment for 60 min at ambient temperature under Ar. Into
the solution, 1.6 equiv of 2a (272 mg, 0.67 mmol), 1.6 equiv of
sodium methoxide (36 mg, 0.67 mmol), and 6 mL of dry pyridine
were added. The mixture was stirred at 70 ꢀC for 1 h and 100 ꢀC for
1 h. After removal of the solvent by distillation, the residue was
purified by silicagel column chromatography with toluene to give
EThCBM. Isolated yield¼38% (150 mg, 42%; based on consumed
powder; UVevis (CH2Cl2) lmax¼432 nm (
TOF): m/z [Mꢁ] calcd for C72H18S: 914.1129; found: 914.1151; 1H
NMR (CDCl3): 7.24 (d, 1H, 3.6 Hz), 6.78 (d, 1H, 3.6 Hz), 2.99e2.84
(m, 4H), 1.95e1.85 (m, 2H), 1.55e1.48 (m, 4H), 1.41 (t, 3H, 7.5 Hz),
0.94 (t, 3H, 7.2 Hz); 13C NMR (CDCl3):
148.91, 148.18, 145.88,
3
¼2313): HRMS (MALDI
d
d
145.32, 145.28, 145.25, 145.20, 144.90, 144.87, 144.85, 144.73,
144.64, 144.51, 144.19, 143.91, 143.89, 143.19, 143.12, 143.08, 143.00,
142.98, 142.39, 142.32, 142.22, 141.00, 140.77, 138.32, 138.19, 136.74,
131.57, 122.10, 80.73, 47.17, 34.58, 31.70, 26.85, 23.71, 22.67, 15.57,
14.03; IR (KBr): 2952, 2921, 2852, 2359, 1427, 1375, 1186, 805, 740,
C60); brown powder; UVevis (CH2Cl2) lmax¼432 nm (
HRMS (MALDI TOF): m/z [Mꢁ] calcd for C72H16O2S: 944.0871;
found: 944.0866; 1H NMR (CDCl3):
7.27 (d, 1H, 3.60 Hz), 6.78 (d,
1H, 3.60 Hz), 3.69 (s, 3H), 2.99e2.90 (m, 4H), 2.58 (t, 2H, 7.5 Hz),
2.29e2.19 (m, 2H), 1.41 (t, 3H, 7.5 Hz); 13C NMR (CDCl3):
173.50,
3
¼2326);
d
d
574, 555, 526, 451 cmꢁ1
.
148.50, 148.40, 147.65, 145.74, 145.23, 145.20, 145.18, 145.13, 144.81,
144.72, 144.64, 144.57, 144.47, 144.14, 143.82, 143.78, 143.10, 143.04,
143.00, 142.92, 142.90, 142.26, 142.17, 142.13, 142.11, 140.92, 140.70,
138.26, 138.10, 135.97, 131.77, 122.20, 80.08, 51.66, 46.20, 33.86,
33.71, 23.68, 22.52, 15.53; IR (KBr): 2960, 2328, 1737, 1456, 1428,
Bis-adduct 4b, mixture of regioisomer, was successfully sepa-
rated from the residue by preparative GPC with chloroform and
identified by high-resolution mass spectrometry. Yield¼21% (33 mg,
23%; based on consumed C60); brown powder; HRMS (MALDI TOF):
m/z [Mꢁ] calcd for C84H36S2: 1108.2258; found: 1108.2258.
1376, 1263, 1186, 1170, 983, 885, 806, 741, 572, 562, 525, 445 cmꢁ1
.
Bis-adduct 4a, mixture of regioisomer, was successfully sepa-
rated from the residue by preparative GPC and identified by high-
resolution mass spectrometry. Isolated yield¼21% (103 mg, 23%;
based on consumed C60); brown powder; HRMS (MALDI TOF): m/z
[Mꢁ] calcd for C84H32O4S2: 1168.1742; found: 1168.1770.
4.3.7. 1-Phenyl-1-(2-tosylhydrazono)pentane (2c). n-Hexanophenone
(3.5 g, 20 mmol) and p-toluenesulfonehydrazide (4.5 g, 24 mmol)
were dissolved in 50 mL of methanol, followed by heating to the
reflux temperature and stirring for 24 h. The reaction mixture was
cooled to room temperature to give a precipitate of product, and
the precipitate was collected and recrystallized from methanol.
Isolated yield¼67% (4.6 g); colorless crystal: mp 112e114 ꢀC; MALDI
4.3.4. 5-Ethylthiophene-2-yl n-pentyl ketone (1b). 2-Ethylthiophene
(6.7 g, 60 mmol), n-hexanoyl chloride (8.5 g, 63 mmol), and alumi-
num chloride anhydrous (0.8 g, 6 mmol) were dissolved in 60 mL of
dry acetonitrile, followed by heating to the reflux temperature and
stirring for 8 h. After the reaction mixture was cooled to room tem-
perature, it was poured into 1 L of 1 wt % NaOH aqueous solution and
extracted with toluene. The organic layer was dried over MgSO4 and
concentrated in vacuo to give a crude product. The purified product
wasobtained bysilicagel columnchromatography using 30 vol % of n-
hexane in toluene as an eluent. Yield 67% (8.5 g); brown oil; HRMS
(MALDI TOF): m/z [MþHþ] calcd for C12H19OS: 211.1157; found:
TOF-MS: 345 (MþH)þ; 1H NMR (CDCl3):
d 7.93e7.86 (m, 3H),
7.64e7.60 (m, 2H), 7.35e7.25 (m, 5H), 2.55 (t, 2H, 8.0 Hz), 2.41 (s,
3H), 1.45 (tt, 2H, 7.7 Hz), 1.30e1.24 (m, 4H), 0.83 (t, 3H, 7.1 Hz); 13C
NMR (CDCl3): d 158.43, 155.96, 144.11, 136.51, 135.51, 129.62, 129.54,
129.53, 128.56, 128.40, 128.32, 126.72, 126.40, 31.85, 26.79, 25.58,
22.41, 21.60, 13.85; IR (KBr): 3210, 2951, 2868, 1596, 1474, 1446,
1385, 1342, 1168, 1065, 928, 816, 754, 687, 667, 611, 545, 529 cmꢁ1
.
Anal. Calcd for C19H24N2O2S: C, 66.25; H, 7.02; N, 8.13; O, 9.29; S,
9.31. Found: C, 65.96; H, 7.11; N, 8.04.
211.1148; 1H NMR (acetone-d6):
d
7.68 (d, 1H, 3.9 Hz), 6.93 (d, 1H,
3.9 Hz), 2.93e2.85 (m, 4H), 1.68 (tt, 2H, 2.1 Hz), 1.38e1.28 (m, 7H),
0.90 (t, 3H, 6.9 Hz); 13C NMR (acetone-d6):
193.03, 157.16, 142.96,
4.3.8. 1-n-Pentyl-1-phenyl-[5,6]-methanofullerene[60] ([5,6]PCP) and
bis-adduct 4c. C60 (100 mg, 0.14 mmol) was dissolved in 3 mL of dry
ODCB by ultrasonic treatment for 60 min at ambient temperature
under Ar. Into the solution, 1.2 equiv of 2c (58 mg, 0.17 mmol), so-
dium methoxide (9 mg, 0.17 mmol), and 2 mL of dry pyridine were
added. The mixture was stirred at 70 ꢀC for 1 h and 100 ꢀC for 0.5 h.
After removal of the solvent by distillation, the residue was purified
by preparative gel permeation chromatography with chloroform to
give [5,6]PCP. Isolated yield¼31% (38 mg, 32%; based on consumed
d
133.19, 125.95, 39.00, 32.15, 25.15, 24.38, 23.13, 15.96, 14.21.
4.3.5. 1-(5-Ethylthiophene-2-yl)-1-(2-tosylhydrazono)pentane (2b).
Compound 1b (4.2 g, 20 mmol) and p-toluenesulfonehydrazide
(4.5 g, 24 mmol) were dissolved in 50 mL of methanol, followed by
heating to the reflux temperature and stirring for 24 h. The reaction
mixture was cooled to room temperature to give a precipitate of
product, and the precipitate was collected and recrystallized from
methanol. Isolated yield¼83% (6.3 g); colorless crystal: mp
C60); brown powder; UVevis (CH2Cl2) lmax¼542.5 nm (
HRMS (MALDI TOF): m/z [Mꢁ] calcd for C72H16: 880.1252; found:
880.1255; 1H NMR (CDCl3):
7.97e7.94 (m, 2H), 7.55 (t, 2H, 8.1 Hz),
7.43 (tt, 1H, 9.3 Hz), 1.62e1.57 (m, 2H), 1.21e1.08 (m, 6H), 0.79 (t, 3H,
6.9 Hz); 13C NMR (CDCl3):
147.43, 147.00, 145.19, 144.75, 144.49,
3¼1118);
d
132e134 ꢀC; MALDI TOF-MS: 379 (MþH)þ; 1H NMR (CDCl3):
d 7.91
(t, 3H, 8.1 Hz), 7.29 (t, 2H, 8.1 Hz), 6.99 (d, 1H, 3.6 Hz), 6.64 (d, 1H,
3.6 Hz), 2.79 (q, 2H, 7.8 Hz), 2.50 (t, 2H, 8.0 Hz), 2.40 (s, 3H),
1.53e1.32 (m, 2H), 1.29e1.19 (m, 7H), 0.82 (t, 3H, 6.9 Hz); 13C NMR
d
144.23, 143.96, 143.75, 143.69, 143.55, 143.13, 143.08, 143.07, 142.97,
142.69, 142.65, 142.58, 142.13, 142.10, 141.93, 141.83, 141.33, 140.96,
140.44, 139.81, 138.80, 138.62, 138.11, 137.91, 136.65, 135.10, 130.83,
128.48, 127.52, 61.64, 36.10, 31.84, 23.83, 22.35,13.94; IR (KBr): 2950,
2923, 2855, 2331, 1599, 1509, 1444, 1427, 1382, 1189, 1173, 1118, 1077,
(CDCl3):
d 153.01, 150.91, 144.00, 139.62, 135.39, 129.53, 128.21,
126.66, 123.48, 31.76, 27.49, 26.04, 23.74, 22.42, 15.67, 13.83; IR
(KBr): 3215, 2926, 2858,1595,1480, 1381,1343,1168,1026, 918, 816,
802, 665, 570, 547 cmꢁ1. Anal. Calcd for C19H26N2O2S2: C, 60.28; H,
6.92; N, 7.40; O, 8.45; S, 16.94. Found: C, 60.12; H, 6.90; N, 7.39.
1029, 753, 720, 697, 642, 612, 581, 572, 543, 526 cmꢁ1
.
Bis-adduct 4c, mixture of regioisomer, was successfully sepa-
rated from the residue by preparative GPC and identified by
high-resolution mass spectrometry. Isolated yield¼19% (28 mg,
20%; based on consumed C60); brown powder; HRMS (MALDI TOF):
m/z [Mꢁ] calcd for C84H32: 1040.2504; found: 1040.2540.
4.3.6. 1-(5-Ethylthiophene-2-yl)-1-(n-pentyl)-[6,6]-methanofuller-
ene[60] (EThCP) (3b) and bis-adduct 4b. C60 (100 mg, 0.14 mmol)
was dissolved in 3 mL of dry ODCB by ultrasonic treatment for

K. Moriwaki et al. / Tetrahedron 66 (2010) 7316e7321
7321
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(3c). [5,6]-PCP (38 mg, 0.044 mmol) was dissolved in 3 mL of ODCB
followed by heating to 170 ꢀC, and stirring for 4.5 h. After removal of
the solvent by distillation, the residue was purified by preparative gel
permeation chromatography with chloroform to give [6,6]PCP. Isolated
yield¼97% (37 mg); brown powder; UVevis (CH2Cl2) lmax¼432 nm
(3
¼1897); HRMS (MALDI TOF): m/z [Mꢁ] calcd for C72H16: 880.1252;
found: 880.1250; 1H NMR (CDCl3):
d 7.84 (d, 2H, 6.9 Hz), 7.48e7.35
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Bjorstrom, C.; Svensson, M.; Andersson, M. R.; Sundstrom, V.; Magnusson, K.;
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149.17,148.30,146.00,145.25,145.20,
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143.20, 143.09, 143.06, 143.00, 142.37, 142.29, 142.21, 141.04, 140.78,
138.10, 137.59, 137.37, 132.18, 128.28, 128.06, 80.47, 52.77, 34.33, 31.86,
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1260, 1185, 1092, 1019, 866, 799, 694, 585, 573, 548, 526 cmꢁ1
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Acknowledgements
The author would like to express gratitude Dr. S. Uchida, T. Toya,
and T. Nakamura (Nippon Oil Corp.) for device fabrication and
measurements. This research is supported in part by NEDO (the
New Energy and Industrial Technology Development Organization)
and JST, CREST (Japan Science and Technology Agency, Core
Research for Evolutional Science and Technology).
7. Popescu, L. M.; van’t Hof, P.; Sieval, A. B.; Jonkman, H. T.; Hammelen, J. C. Appl.
Phys. Lett. 2006, 89, 213507.
8. Matsumoto, F.; Moriwaki, K.; Takao, Y.; Ohno, T. Beilstein J. Org. Chem. 2008,
4, 33.
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Chem. 1995, 60, 532; (b) Ohno, T.; Moriwaki, K.; Miyata, T. J. Org. Chem. 2001, 66,
3397.
Supplementary data
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2010.06.089.
10. Prato, M.; Lucchini, V.; Maggini, M.; Stimpfl, E.; Scorrano, G.; Eiermann, M.;
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References and notes
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