Synthesis and characterization of novel soluble fulleropyrrolidine derivatives and their photovoltaic performance

Article abstract of DOI:10.1166/jnn.2013.7285

Currently, [60] fullerene derivatives are the focus of considerable research due to their important roles in many fields, especially material science. In this study, we synthesized the following two novel fulleropyrrolidine derivatives: C₆₀-fused N-methyl-(4-hexyloxybenzen- 2-yl) pyrrolidine, (p-HOPF) and C₆₀-fused N-methyl-(2-hexyloxybenzen- 2-yl) pyrrolidine, (o-HOPF). Structural assignments of the two fullerene derivatives were made through ¹H NMR and FAB-MS. We also measured the optical and electrochemical properties of p-HOPF and o-HOPF through UV/Vis spectrophotometry and cyclic voltammetry. We found that the difference in the position of the alkoxyl substituent on the phenyl ring greatly affects the characteristics of the molecules. In particular, from the ¹H NMR spectrum, we found that the hydrogen atoms on the carbons adjacent to the oxygens in p-HOPF and o-HOPF have completely different chemical environments. In order to study the effects of the substituent group positions on photovoltaic performance, photovoltaic devices were fabricated. The highest power conversion efficiency, 0.71%, was achieved when using o-HOPF as the electron acceptor. Copyright

Full text of DOI:10.1166/jnn.2013.7285

Copyright © 2013 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 13, 3474–3479, 2013
Synthesis and Characterization of Novel
Soluble Fulleropyrrolidine Derivatives
and Their Photovoltaic Performance
Dongbo Mi and Do-Hoon Hwang∗
Department of Chemistry, and Chemistry Institute for Functional Materials, Pusan National University,
Busan 609-735, Republic of Korea
Currently, [60] fullerene derivatives are the focus of considerable research due to their important
roles in many fields, especially material science. In this study, we synthesized the following two novel
fulleropyrrolidine derivatives: C60-fused N-methyl-(4-hexyloxybenzen-2-yl) pyrrolidine, (p-HOPF) and
C
60-fused N-methyl-(2-hexyloxybenzen-2-yl) pyrrolidine, (o-HOPF). Structural assignments of the
1
two fullerene derivatives were made through H NMR and FAB-MS. We also measured the optical
and electrochemical properties of p-HOPF and o-HOPF through UV/Vis spectrophotometry and
cyclic voltammetry. We found that the difference in the position of the alkoxyl substituent on the
phenyl ring greatly affects the characteristics of the molecules. In particular, from the 1H NMR
spectrum, we found that the hydrogen atoms on the carbons adjacent to the oxygens in p-HOPF
and o-HOPF have completely different chemical environments. In order to study the effects of the
substituent group positions on photovoltaic performance, photovoltaic devices were fabricated. The
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highest power conversion efficiency, 0.71%, was achieved when using o-HOPF as the electron
IP: 117.253.245.207 On: Thu, 15 Oct 2015 08:21:02
acceptor.
Copyright: American Scientific Publishers
Keywords: Fullerene Derivatives, Fulleropyrrolidine, 1,3-Dipolar Reaction, Photovoltaic Devices.
1. INTRODUCTION
salt, which is formed by the condensation of an ꢂ-amino
acid with an aldehyde. The intermediate is generated
in situ and undergoes cycloaddition with [60] Fullerene,
a process known as the Prato reaction. The fulleropyrro-
lidines that are formed each contain a pyrrolidine ring
fused to a junction between two six-membered rings of a
fullerene sphere.19
The key features of this reaction are as follows: (a) the
reactions lead to individual [6,6]-closed isomers, and
(b) the majority of precursors are commercially avail-
able or easily prepared.19 Furthermore, functionalization
of the fullerene sphere through the Prato reaction is eas-
ily accomplished because two substituents (e.g., from the
ꢂ-amino acid moiety and the aldehyde derivative) can be
simultaneously introduced into the pyrrolidine heterocy-
cle as shown in Scheme 1. These advantages make the
Prato reaction useful for the synthesis of new fullerene
derivatives.
In the two decades since [60] fullerene (C60ꢀ was first iso-
lated and produced in bulk quantities in 1985, fullerene
derivatives have been developed and their organic chem-
istry has been successfully studied.1–10 Chemists have been
attracted by their interesting chemistry as well as by poten-
tial applications.11–13 Many successful methods of func-
tionalization have been explored, such as nucleophilic
additions,14 Diels-Alder reactions,14 1,3-dipolar and other
types of cycloadditions,14 oxidations,14 halogenations,14
carbene and nitrene additions,15 hydrogenations,16ꢁ17
organo-transition-metal reactions,18 and others. The 1,3-
dipolar cycloaddition of azomethine ylide is an efficient,
easily processed, and widely applied method that produces
an important class of fullerene derivatives known as the
fulleropyrrolidines.
Scheme 1 shows the formation of the simplest com-
pound of this class, N-methylfulleropyrrolidine to illus-
trate the general approach. The reactive intermediate is
generated through the decarboxylation of an immonium
In this study, we designed and synthesized two novel
fulleropyrrolidine derivatives: C60-fused N-methyl-(4-
hexyloxybenzen-2-yl) pyrrolidine (p-HOPF) 2, and
C60-fused N-methyl-(2-hexyloxybenzen-2-yl) pyrrolidine
(o-HOPF) 4 (Scheme 2). Since solubility is an important
∗Author to whom correspondence should be addressed.
3474
J. Nanosci. Nanotechnol. 2013, Vol. 13, No. 5
1533-4880/2013/13/3474/006
doi:10.1166/jnn.2013.7285

Mi and Hwang Synthesis and Characterization of Novel Soluble Fulleropyrrolidine Derivatives and Their Photovoltaic Performance
Scheme 1. General synthetic route for N-methylfulleropyrrolidine.
prerequisite for the application of [60] fullerene deriva-
tives in common organic semiconductor devices such
as organic thin-film transistors (OTFTs), organic pho-
tovoltaics (OPVs), and devices based on light-induced
intermolecular charge separation, we introduced alkoxyl
groups onto the benzene ring to improve the solubility.
We also presumed that the electrochemical properties of
[60] fullerene could be tuned; in particular, we expected
that the LUMO energy level would be raised after mod-
ification because addends on the [60] fullerene core can
reduce the ꢃ-conjugation length and raise the LUMO
level. This change in electrochemical properties is benefi-
cial for some applications, especially OPV devices. How-
ever, the addends inevitably change the crystal packing,
typically reducing the fullerene–fullerene contact distance,
and they may also reduce the carrier mobility. In order
2. EXPERIMENTAL DETAILS
2.1. Materials
4-Hydroxybenzaldehyde, salicylaldehyde, sodium carbon-
ate, n-bromohexane, sarcosine, 1,2-dichloroethane, 2-ethyl-
hexylbromide, anhydrous dimethylformamide, phosphorus
chloride, anhydrous o-dichlorobenzene, and fullerene were
purchased from Alfa Aesar or Aldrich. All chemicals and
solvents were analytical grade and were used without fur-
ther purification.
2.2. Measurements and Device Fabrications
1H NMR spectra were recorded using a Varian AM-300
spectrometer, absorption spectra were obtained using a
Scinco S-3100 spectrophotometer, and fast atom bom-
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to minimize the impact on the crystal packing of [60]
bardment mass spectra (FAB-MS) were measured using a
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Copyright: American Scientific Publishers
fullerene, we attached only hexyloxy-substituted aryl rings
JEOL-ZMS-DX-303 mass spectrometer. Cyclic voltamme-
try (BAS 100) was performed with a solution of tetrabuty-
lammonium tetrafluoroborate (TBABF4, 0.10 M) as the
electrolyte and the fulleropyrrolidine material (10−3 M) in
to the basic N-methylfulleropyrrolidine structure. The syn-
thetic routes to the fulleropyrrolidine derivatives and their
chemical structures are shown in Scheme 2.
OR
CH3
N
O
O
H
Prato reaction
OR
Na2CO3/DMF
HO
n-bromohexane
H
1
2
RO
H3C
O
O
N
H
H
Na2CO3/DMF
Prato reaction
n-bromohexane
OR
OH
3
R = hexyl group
4
Scheme 2. Synthetic routes and chemical structures of p-HOPF and o-HOPF.
J. Nanosci. Nanotechnol. 13, 3474–3479, 2013
3475

Synthesis and Characterization of Novel Soluble Fulleropyrrolidine Derivatives and Their Photovoltaic Performance Mi and Hwang
1,2-dichlorobenzene; the voltammograms were collected
at a scan rate of 50 mV/s, at room temperature, and
under an argon atmosphere. A glassy carbon electrode
(0.3 mm diameter) was used as the working electrode.
Pt and Ag/AgCl electrodes were used as the counter
electrode and reference electrode, respectively. Composite
solutions of P3HT and the synthesized fulleropyrrolidine
derivatives were prepared using chlorobenzene as the sol-
vent. Polymer photovoltaic devices were fabricated with
the typical sandwich structure of ITO/PEDOT:PSS/active
layer/LiF/Al. The current voltage (I–V ) characteristics of
all the polymer photovoltaic cells were measured under
simulated solar light (100 mW/cm2; AM 1.5 G) provided
by an Oriel 1000 W solar simulator. The characteriza-
tions were carried out in an ambient environment, and
electrical data were recorded using a Keithley 236 source-
measure unit. The intensity of the simulated solar light
was calibrated using a standard Si photodiode detector
(PV measurements Inc.), which in turn was calibrated at
the National Renewable Energy Laboratory (NREL).
1.33 (m, 4 H), 0.89 (t, 3 H). FAB-MS (M+1, C75H23NO):
calcd, 954; found, 955.
2.3.3. Synthesis of 2-(hexyloxy)Benzaldehyde (3)
Salicylaldehyde (5 g, 0.04 mol) and sodium carbonate
(6.57 g, 0.06 mol) were dissolved in 50 ml of DMF, and
the reaction mixture was stirred for 30 min at room tem-
perature. n-Bromohexane (7.39 ml, 0.053 mol) was added,
and the resulting mixture was stirred for 24 h at room tem-
perature. The reaction mixture was extracted three times
using dichloromethane and brine. The organic layer was
separated and dried with anhydrous magnesium sulfate,
and the solvent was removed by rotary evaporation. The
crude product was purified by column chromatography,
1
affording 3 in 75.3% yield (6.37 g). H NMR (300 MHz,
CDCl3ꢀ: ꢄ (ppm) 10.52 (s, 1 H), 7.82 (dd, 1 H), 7.53
(dt, 1 H), 7.02 (m, 2 H), 4.06 (t, 2 H), 1.86∼1.79 (m, 2 H),
1.50∼1.37 (m, 2 H), 1.32 (m, 2 H), 0.90 (t, 3 H).
2.3.4. Synthesis of C60-Fused N-Methyl-
2.3. Synthesis of p-HOPF and o-HOPF
(2-hexyloxybenzen-2-yl) Pyrrolidine (4)
2.3.1. Synthesis of 4-(hexyloxy)Benzaldehyde (1)
A mixture of 3 (0.06 g, 0.28 mmol), [60] fullerene (0.3 g,
0.42 mmol), and sarcosine (0.124 g, 1.4 mmol) was dis-
solved in 100 ml 1,2-dichlorobenzene. After refluxing for
4-Hydroxybenzaldehyde (5 g, 0.04 mol) and sodium car-
bonate (6.57 g, 0.06 mol) were dissolved in 50 ml of
24 h, the reaction was allowed to reach room tempera-
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DMF, and the reaction mixture was stirred for 30 min at
ture, the solvent was partially vacuum-evaporated and the
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room temperature. n-Bromohexane (7.39 ml, 0.053 mol)
was added to the reaction mixture, and the resulting mix-
ture was stirred for 24 h at room temperature. The reaction
mixture was extracted three times using dichloromethane
and brine. The organic layer was separated and dried with
anhydrous magnesium sulfate, and then the solvent was
removed via rotary evaporation. The crude product was
purified by column chromatography to produce a yield of
Copyright: American Scientific Publishers
residue was loaded onto a silica gel column. The black
solid obtained after chromatography (hexane/toluene elu-
ent) was further purified by repetitive centrifugation using
methanol and hexane to yield 0.18 g p-HOPF 4 as a black
1
solid (67% yield). H NMR (300 MHz, CDCl3ꢀ: ꢄ (ppm)
7.96 (dd, 1 H), 7.07 (t, 2 H), 6.89 (d, 1 H), 5.56 (s, 1 H),
4.97 (d, 1 H, J = 9 Hz), 4.31 (d, 1 H, J = 9 Hz), 4.00
(td, 1 H, J = 6 Hz), 3.72 (td, 1 H, J = 6 Hz), 2.80
(s, 3 H), 1.44∼1.25 (m, 8 H), 0.88 (3 H). FAB-MS (M+1,
C75H23NO): calcd, 954; found, 955.
1
83% (7 g). H NMR (300 MHz, CDCl3ꢀ: ꢄ (ppm) 9.87
(s, 1 H), 7.83 (d, 2 H), 7.00 (d, 2 H), 4.03 (t, 2 H), 1.80
(m, 2 H), 1.42 (m, 2 H), 1.32 (m, 2 H), 0.89 (t, 3 H).
3. RESULTS AND DISCUSSION
2.3.2. Synthesis of C60-Fused N-Methyl-
(4-hexyloxybenzen-2-yl) Pyrrolidine (2)
The novel fulleropyrrolidine derivatives (p-HOPF and
o-HOPF) displayed excellent solubility in common organic
solvents such as dichloromethane, chloroform, toluene,
chlorobenzene, and 1,2-dichlorobenzene. A combination
A mixture of 1 (0.06 g, 0.28 mmol), [60] fullerene (0.3 g,
0.42 mmol), and N-methylglycine (sarcosine, 0.124 g,
1.4 mmol) was dissolved in 100 ml 1,2-dichlorobenzene.
After refluxing for 24 h, the reaction was allowed to
reach room temperature, the solvent was partially vacuum
evaporated, and the residue was poured onto a silica gel
column. The black solid obtained after chromatography
(hexane/toluene eluent) was further purified by repetitive
centrifugation using methanol and hexane to yield 0.15 g
p-HOPF as a black solid (56% yield). 1H NMR (300 MHz,
CDCl3ꢀ: ꢄ (ppm) 7.69 (m, 2 H), 6.95 (d, 2 H), 4.97
(d, 1 H, J = 9 Hz), 4.87 (s, 1 H), 4.25 (d, 1 H, J = 9 Hz),
3.95 (t, 2 H), 2.79 (s, 3 H), 1.77 (m, 2 H), 1.44 (m, 2 H),
1
of H NMR and FAB-MS was used to assign the struc-
tures of the new compounds. The characteristic peaks
of the fulleropyrrolidine core were observed in the 1H
NMR spectra of both p-HOPF and o-HOPF. As shown in
Figure 1(a), the two protons in the pyrrolidine ring (Hcꢀ
were clearly separated.
2
Owing to the JHH coupling interaction, each separated
Hc was split again into a doublet with a coupling constant
as high as 9 Hz, which is consistent with other reports.20
Additionally, the protons Hf were clearly split into a triplet
3476
J. Nanosci. Nanotechnol. 13, 3474–3479, 2013

Mi and Hwang Synthesis and Characterization of Novel Soluble Fulleropyrrolidine Derivatives and Their Photovoltaic Performance
k
3.71
3.74
H2O
(a)
CDCl3
i,j
e
i
j
g
e
N
h
b
a
O
f
3.72
3.73
d
b
c
3.69
k
3.76
f
d
c
b
c
g
h
a
MeOH
3.8
3.7
3.6
8
6
4
2
0
(b)
PPM
m
CDCl3
H2O
k
l
i
j
g
h
O
b
g
c
f
N
e
d
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i-l
f
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Fig. 2. (a) Expansion of 1H NMR spectrum of o-HOPF in the region
from 3.8 to 3.6 ppm. (b) Spin-spin splitting and coupling constants for
protons Ha and Hb in o-HOPF.
e
e
b,c
a
d
h
h
and Ch is somewhat restricted, leaving the protons Ha and
Hb inequivalent.
8
6
4
2
0
We recorded the UV-Vis spectra of o-HOPF and
p-HOPF in 1,2-dichlorobenzene solution (10−5 M) to
determine their optical properties. As shown in Figure 3,
[60] Fullerene exhibited an absorption peak at around
330 nm. Absorption has also been observed in the long-
wavelength region, as high as 900 nm (not shown); this
could be considered characteristic property of fullerene-
containing compounds. The absorptions of p-HOPF and
o-HOPF were distinct from those of [60] Fullerene. There
were no apparent absorption peaks around 330 nm, how-
ever, a broad absorption shoulder was observed around
330 nm, and the absorption intensities of these fulleropy-
rrolidine derivatives were much lower than that of [60]
fullerene. Furthermore, the long-wavelength region con-
tained some absorption, as shown in the inset of Figure 3,
that is similar to that found in the [60] Fullerene spec-
trum. This further indicates the successful connection of
the alkoxyl phenyl moiety to the C60 core. Although struc-
tural modification did not improve the absorption ability
of the fullerenes, it is apparent that the optical properties
were significantly affected.
PPM
Fig. 1. (a) 1H NMR spectrum of p-HOPF (2). (b) 1H NMR spectrum
of o-HOPF (4).
1
by the protons Hg. The H NMR spectrum of o-HOPF
was distinct from that of p-HOPF. In Figure 1(b), the two
protons on the carbon adjacent to the oxygen (Ha and Hbꢀ
are separated, clearly indicating that the two protons reside
in distinct chemical environments.
Focusing on Ha or Hb in o-HOPF, we see intuitively
that each resonance is split into a doublet with a coupling
constant of 9 Hz and is further split into a triplet with
a coupling constant as high as 6 Hz. (3JHaHi = JHbHi
=
3
6 Hz). This process is vividly illustrated in Figure 2(b). We
attributed this phenomenon to steric hindrance between the
alkoxyl chain and the nitrogen methyl group. In o-HOPF,
the methyl group and proton h (Ha or Hbꢀ are close
enough for a repulsive interaction and, because of this
steric hindrance, the free rotation of the bond between O
J. Nanosci. Nanotechnol. 13, 3474–3479, 2013
3477

Synthesis and Characterization of Novel Soluble Fulleropyrrolidine Derivatives and Their Photovoltaic Performance Mi and Hwang
Table I. Summary of electrochemical properties of [60] Fullerene,
p-HOPF, and o-HOPF.
1.0
0.5
0.0
C60
o-HOPF
p-HOPF
Er1ed (V) Er2ed (V) Er3ed (V) Er4ed (V) Eonset (V) LUMO (eV)
0.04
0.03
0.02
0.01
0.00
C60
−0.95 −1.35 −1.82
–
−0.76
−0.90
−0.89
−3.78
−3.65
−3.64
p-HOPE −1.04 −1.31 −1.43 −1.99
o-HOPE −1.06 −1.33 −1.46 −2.02
vacuum level; the vacuum level is defined as zero).21ꢁ22
LUMO = −ꢅꢆERed ꢆonsetꢀ − Efocꢀ + 4ꢇ8ꢈ (eV), where
Efoc is the potential of the external standard, the fer-
rocene/ferrocenium ion (Foc/Foc+) couple. The value of
Efoc determined under the same conditions was about
260 mV versus Ag/AgCl. The values of ERed (onset) for
p-HOPF and o-HOPF were −890 and −904 mV, respec-
tively. Thus, the LUMO energy levels of p-HOPF and o-
HOPF relative to the vacuum level were estimated to be
−3.65 and −3.64 eV, respectively. The LUMO energy lev-
els of these two fulleropyrrolidine derivatives were much
higher than that of [60] Fullerene (−3ꢇ78 eV) measured
under the same conditions. However, there are no signif-
icant differences in the electrochemical properties of o-
HOPF and p-HOPF, indicating that the substituent position
of the alkoxyl phenyl group has very little influence on the
electronic energy levels of the C60.
600
800
400
600
Wavelength (nm)
Fig. 3. UV-visible absorption spectra of [60] Fullerene, p-HOPF, and
o-HOPF in 1,2 dichlorobenzene (10−5 M).
The electrochemical properties of fullerenes are very
important: electronic energy levels (especially the LUMO
level) of fullerene derivatives are crucial to their applica-
tions. Therefore, we collected the cyclic voltammograms
of p-HOPF (2) and o-HOPF (4) in 1,2-dichlorobenzene
solution with TBABF4 as the electrolyte. p-HOPF,
o-HOPF, and [60] Fullerene displayed multiple-quasi-
reversible one-electron reduction waves, as shown in
Figure 4.
Recently, OPVs based on interpenetrating blends of
donors and acceptors sandwiched between two asymmet-
ric contacts (two metals with different work functions)
have become very popular. Therefore, owing to their excel-
lent solubility in common organic solvents and higher
LUMO energy levels, which are beneficial for improving
the open circuit voltage (Vocꢀ of photovoltaic cells, our
novel fulleropyrrolidine derivatives, p-HOPF and o-HOPF,
have potential as electron acceptors for the preparation of
organic solar cells. Thus, photovoltaic cells were prepared
with P3HT as the electron donor. In this study, we varied
the weight ratio of the donor and acceptor, and we fabri-
cated devices using different annealing temperatures and
annealing times. Organic solar cells based on o-HOPF and
p-HOPF as electron acceptors showed similar photovoltaic
performances. Cells with o-HOPF as the acceptor and a
composite ratio of 1:0.5 at the pristine state showed the
best photovoltaic performance: a short circuit current (Jscꢀ
of 0.55 mA/cm2, an open circuit voltage (Vocꢀ of 0.52 V,
a fill factor (FF) of 0.25, and a power conversion effi-
ciency (PCE) of 0.71%. Figure 5 shows the photovoltaic
performance of this device under AM 1.5 G illumina-
tion (intensity: 100 mW cm−2ꢀ; the relative parameters are
summarized in Table II.
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These reduction waves were attributed to the fullerene
core, and the first reduction potentials (E1 ꢀ were found
red
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Copyright: American Scientific Publishers
to correspond to the LUMO energy levels of the fullerene
derivatives. Both of the first reduction potentials of the
novel fulleropyrrolidine derivatives were shifted to neg-
ative values with respect to the parent [60] Fullerene.
This indicates that the LUMO energy levels of p-HOPF
and o-HOPF are raised relative to [60] Fullerene. The
measured electrochemical properties are listed in Table I.
The LUMO energy levels were calculated from the onset
reduction potentials (ERed (onset)) on the basis of the
reference energy level of ferrocene (4.8 eV below the
0.006
0.004
0.002
0.000
–0.002
–0.004
–0.006
–0.008
–0.010
–0.012
–0.014
o–HOPF
p–HOPF
C60
The short-circuit currents and the open-circuit voltages
of the devices were similar to those of devices based on
P3HT/PC61BM. However, the PCE was somewhat lower
at the pristine state than that of the P3HT/PC61BM sys-
tem because of the lower FF. Unfortunately, Voc and Jsc
decreased rapidly after annealing. Furthermore, the PCE
decreased even more severely when we increased the
–2.0
–1.5
–1.0
–0.5
0.0
Voltage (V)
Fig. 4. Cyclic voltammograms of [60] Fullerene, p-HOPF, and
o-HOPF.
3478
J. Nanosci. Nanotechnol. 13, 3474–3479, 2013

Mi and Hwang Synthesis and Characterization of Novel Soluble Fulleropyrrolidine Derivatives and Their Photovoltaic Performance
ideal electrochemical properties, these new fulleropyrroli-
dine derivatives were evaluated to determine their potential
0
as novel electron acceptors for donor/acceptor bulk het-
erojunction photovoltaic cells. Thus, we fabricated OPV
cells with ITO/PEDOT:PSS/active layer /LiF/Al configu-
–2
rations, and the highest PCE, 0.71%, was obtained for a
device based on o-HOPF. We believe that better photo-
voltaic performance can be achieved if we further modify
–4
the molecular structure to achieve higher thermal stability.
Acknowledgment: This research was financially sup-
ported by the Ministry of Knowledge Economy
–6
(MKE) under the New and Renewable Energy Pro-
0.0
0.2
Voltage (V)
0.4
0.6
gram through a KETEP grant (No. 20103020010050
and No. 20113010010030) and by the National Science
Foundation (NRF) grant funded by the Korea govern-
ment (MEST) (No. 2011-0011122) through GCRC-SOP
(No.2011-0030668).
active layer pristine state
annealing at 100 for 5 min
annealing at 100 for 10 min
annealing at 120 for 5 min
annealing at 120 for 10 min
P3HT/PCBM pristine state
Fig. 5. Current voltage (I–V ) curves of the devices with P3HT/o-HOPF
(1:0.5) after different annealing temperatures and annealing times.
References and Notes
Table II. Summary of photovoltaic performance of P3HT/o-HOPF
(1:0.5) devices after different annealing temperatures and annealing
times.
1. H. W. Kroto, J. R. Heath, S. C. O’brien, R. F. Curl, and R. E.
Smalley, Nature 318, 162 (1985).
2. W. Kratschmer, L. D. Lamb, K. Fostiropoulos, and D. R. Huffman,
Nature 347, 354 (1990).
Voc (V) Jsc (mA/cm2ꢀ FF (%) PCE (%)
3. R. Taylor, The Chemistry of Fullerenes, World Scientific, River
Edge, NJ (1995).
PCBM (pristine)a
0.54
0.52
0.46
0.39
0.35
0.33
5.5
5.5
4.0
45.4
24.9
1.4
0.71
o-HOPF (pristine)b
4. K. M. Kadish and R. S. Ruoff, Fullerene Chemistry: Physics, and
o-HOPF(100 ꢀC 5 min)b
oHOPF(100 ꢀC 10 min)b
o-HOPF(120 ꢀC 5 min)b
oHOPF(120 ꢀC 10 min)b
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IP3:.12 17.2532.52.645.2007.3O2 n: Thu5,.1AT5e.cOhHnciortsloc2gh0y, ,1TJ5ohhen0C8Wh:i2elme1yi:s0&tr2ySoonfs,thNeewFuYlolerrken(2e0s,00T).hieme, Stuttgart
3.3 Copyr2ig5.h3t: Am0e.2r9ican Scientific Publishers
(1994).
3.2
24.9
0.26
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Two novel fullerene derivatives p-HOPF and o-HOPF
were synthesized for the first time, and their structures
1
were assigned using H NMR and FAB-MS. Both deriva-
tives showed good solubility in common organic sol-
vents. We report herein the effects that the position of an
alkoxylphenyl group attached to the fulleropyrrolidine core
have on its optical and electrochemical properties. Given
their improved solubility in common organic solvents and
Received: 7 November 2011. Accepted: 27 March 2012.
J. Nanosci. Nanotechnol. 13, 3474–3479, 2013
3479