Electrochemical and photophysical properties of a novel polythiophene with pendant fulleropyrrolidine moieties: Toward "double cable" polymers for optoelectronic devices

Article abstract of DOI:10.1021/jp013077y

We have prepared a novel bithiophene carrying a fulleropyrrolidine substituent. Its electrochemical polymerization affords an electron donor-acceptor material that has been studied by means of electrochemical and spectroscopic techniques. The results from

Full text of DOI:10.1021/jp013077y

70
J. Phys. Chem. B 2002, 106, 70-76
Electrochemical and Photophysical Properties of a Novel Polythiophene with Pendant
Fulleropyrrolidine Moieties: Toward “Double Cable” Polymers for Optoelectronic Devices
Antonio Cravino,*,† Gerald Zerza,† Helmut Neugebauer,† Michele Maggini,*,‡ Stefania Bucella,‡
Enzo Menna,‡ Mattias Svensson,§ Mats R. Andersson,*,§ Christoph J. Brabec,† and
N. Serdar Sariciftci†
Linz Institute for Organic Solar Cells (LIOS), Physical Chemistry, Johannes Kepler UniVersity Linz,
A-4040 Linz, Austria, CMRO-CNR, Organic Chemistry Department, UniVersity of PadoVa, I-35131 PadoVa,
Italy, and Polymer Technology, Chalmers UniVersity of Technology, SE-412 96 Goteborg, Sweden
ReceiVed: August 7, 2001
We have prepared a novel bithiophene carrying a fulleropyrrolidine substituent. Its electrochemical
polymerization affords an electron donor-acceptor material that has been studied by means of electrochemical
and spectroscopic techniques. The results from photoinduced absorption (PIA) and light-induced electron
spin resonance (LESR) experiments demonstrate a photoinduced electron transfer from the polythiophene
backbone to the tethered acceptor moieties.
Introduction
macromolecule with two different pathways (“cables”) for
different signs of charges, thus forcing the formation of
continuous, interconnected network for the transport of both
holes and electrons. In addition, the interaction between the
donor conjugated backbone and the acceptor moiety may be
tuned by varying the chemical structure (nature and length) of
their connecting spacer.23 Further functionalities (such as
amphiphilic groups) may also be added to this “double cable”
primary structure by chemical synthesis, resulting in interesting
self-organized secondary and tertiary structures such as in
biological systems. Such self-organization is proposed to be an
interesting possibility to tailor the desired morphologies by
synthesizing the suitable primary structures.
During the last two decades, research has been increasing in
the field of synthesis and characterization of molecules with
extended π-electron delocalization. In the development of new
applications of organic materials such as conjugated polymers1-3
and fullerenes4-9 in optoelectronics, polymeric light emitting
diodes and displays are today entering the market.10-16 Fur-
thermore, the discovery of a photoinduced electron transfer from
nondegenerate ground-state conjugated polymers to fullerenes17
enabled the fabrication of inexpensive and flexible large-area
solar cells and photodetectors.18,19 For many of the above
applications, a balanced transport of holes and electrons is
important. For instance, the most efficient polymeric solar cells
today fabricated are bulk-heterojunctions,20,21 where the active
layer is a blend of a conjugated polymer as electron donor (hole
transporter) and a soluble fullerene derivative as electron
acceptor (electron transporter). Beyond photoinduced charge
separation, positive carriers are transported to electrodes by the
donor polymer phase and electrons by hopping between
contacting fullerene domains. It has been shown that the power
conversion efficiency of bulk heterojunction solar cells can be
improved dramatically by manipulating the morphology of the
blend.20 Improving the blend morphology by shrinking each of
the interpenetrating two phases’ dimensions below 500 nm leads
to (a) a larger donor-acceptor interfacial contact area and (b)
less spatial separation between fullerene domains.20,22
Poly(3-octylthiophene), mixed with C60, or a soluble fullerene
derivative, has been already utilized for the preparation of
prototype bulk-heterojunction solar cells,24-26 suggesting the
investigation of double-cables consisting of a polythiophene
backbone with tethered fullerene units. Benincori and co-
workers27 and Ferraris et al.28 showed that such fullerene-
substituted polythiophenes substantially retain the favorable
ground-state properties of the individual donor backbone and
acceptor moieties. However, the occurrence of photoinduced
electron transfer, which is essential for photovoltaic applications,
was not investigated. In a recent communication, we have
reported the electrochemical polymerization of fulleropyrrolidine
1 (Scheme 1) and the preliminary characterization of the
resulting material.29 Here we detail the synthesis of monomer
1 and its electrochemical polymerization. The electrochemical
and photophysical properties of poly(1), studied by means of
cyclic voltammetry (CV) and spectroscopic techniques (UV-
vis absorption), photoinduced absorption (PIA), in situ Fourier
transform (FTIR) spectroelectrochemistry and light-induced
electron spin resonance (LESR) show evidence of photoinduced
charge separation. These results show the potential of “double-
cable” polymers as noncomposite active materials for electronic
and photovoltaic devices. While this manuscript was in prepara-
tion, Marcos Ramos and co-workers used a soluble “double-
cable” for the fabrication of promising plastic solar cells.30
The covalent linking of tethered electron accepting and
conducting moieties to an electron donating and hole transport-
ing conjugated polymer backbone appears a viable way for the
preparation of ambipolar conducting “double-cable” polymers
(p-n type). Their primary structure should prevent the occur-
rence of phase separation since the material is basically one
* To whom correspondence should be addressed. Fax: +43-732-2468-
8770. Phone: +43-732-2468-8767. E-mail: antonio.cravino@jKu.at.
† Linz Institute for Organic Solar Cells.
‡ CMRO-CNR.
§ Polymer Technology.
10.1021/jp013077y CCC: $22.00 © 2002 American Chemical Society
Published on Web 12/11/2001

A Polythiophene with Fulleropyrrolidine Moieties
J. Phys. Chem. B, Vol. 106, No. 1, 2002 71
SCHEME 1a
Figure 1. CV of 1 (0.1 M Bu4NPF6 in CH2Cl2). Working electrode Z
Pt foil; quasi reference electrode Z Ag/AgCl wire (-0.44 V vs
ferrocene). Scan rate 100 mV/s.
a Reagents and conditions: (a) K2CO3, acetone, reflux, 8 h, 20%;
(b) K2CO3, acetone, reflux, 8h, 50%; (c) N-methylglycine, C60,
chlorobenzene, reflux, 2 h, 49%; (d) tetrakis(triphenylphosphine)-
palladium(0), DME, NaHCO3(aq), 12 h, 76%; (e) NBS, DMF, 12 h,
87% (crude); (f) 2-thiophene-boronic acid, tetrakis(triphenylphosphine)-
palladium(0), DME, NaHCO3(aq), 12 h, 48%.
Results and Discussion
Synthesis. The route to bithiophene-fulleropyrrolidine 1 is
outlined in Scheme 1. The synthesis begun with commercially
available 4-hydroxybenzaldehyde and 1-iodo-2-[2-(2-iodoeth-
oxy)ethoxy]ethane in a Williamson ether synthesis to give 4-{2-
[2-(2-iodo-ethoxy)-ethoxy]-ethoxy}-benzaldehyde 3 in 20%
yield. Another Williamson etherification of 3 with 4-[2,2′]-
bithiophenyl-3-yl-phenol 2 gave functionalized bithiophene 4
in 50% yield. The bithiophene-fulleropyrrolidine 1 was prepared
by the well-extablished azomethine ylide cycloaddition reaction
to C60.31 Thus, condensation of 4 with N-methylglycine in the
presence of C60 provided 1 in 49% isolated yield after column
chromatography. All spectroscopic and analytical data were
consistent with the molecular structure of derivative 1 (see the
Experimental Section). Bithiophene-fulleropyrrolidine 1 is
soluble in aromatic and chlorinated hydrocarbons but insoluble
in polar solvents such as CH3CN or alcohols. Bithiophene-
phenol 2 was prepared in three steps by applying the Suzuki
coupling reaction. 4-Bromophenol and 3-thiophene boronic acid
were treated with tetrakis(triphenylphosphine)palladium(0) and
aqueous NaHCO3 in dimethoxy ethane to afford 4-thiophen-3-
yl-phenol 5 in 76% yield. Bromination of 5 with N-bromosuc-
cinimide gave the highly reactive 4-(2-bromo-thiophen-3-yl)-
phenol 6 that was immediately coupled with 2-thiophene boronic
acid to afford 2 in 42% isolated yield (from 5).
Figure 2. CV of poly(1) on Pt foils (0.1 M Bu4NPF6 in CH3CN).
Reference electrode and scan rate as in Figure 1.
selected the electrochemical approach for synthesizing “double-
cable” polymers and investigating their photophysical behavior.
The cyclic voltammogram of 1, recorded during potential
cycling between 0 and 1.6 V, is illustrated in Figure 1 (Pt as
working electrode, CH2Cl2). The first scan shows one irrevers-
ible wave peaking at ca. +1.3 V, corresponding to the oxidation
of the monomer. Recurrent potential scanning leads to the
growth of a new redox wave around +0.8 V, related to the
oxidation/rereduction (p-doping/dedoping) of a freshly formed
polymeric film. Similar results were obtained using different
solvents (CH3CN/toluene mixtures) and ITO coated electrodes.
Poly(2) was also prepared as a reference polymer following the
same electrochemical procedure.38 Figure 2 displays the cyclic
voltammogram of poly(1) in monomer-free electrolyte solution.
In the positive region, one wave, which corresponds to the
p-doping/dedoping of the polythiophene backbone, is seen at
about +0.75 V. The linear relationship between the current peak
height and the scan rate (varied from 25 to 200 mV/s) can be
seen in Figure 3. This linear relationship is typical of a redox-
active polymer attached to the electrode and also exemplifies
the stability of poly(1) films toward p-doping.32 Scanning the
cathodic region up to -2.0 V shows several redox waves mainly
related to the multiple reduction of the fullerene moiety.39,40
The irreversible peak at -0.74 V, of unknown origin, is seen
only during the first scan. These results indicate that both the
Electrochemical Polymerization. Electropolymerization as
a tool for the preparation of novel conjugated polymers has
advantages, including the growth of polymeric thin films onto
transparent substrates used for most spectroscopic tech-
niques.32,33 It has been observed that in donor-acceptor dyads
(systems in which an acceptor moiety is covalently linked to a
donor unit) energy transfer can take place competing with
intramolecular charge transfer.34-36 For the design of polymer
and supramolecular structure for photovoltaic materials,37 we

72 J. Phys. Chem. B, Vol. 106, No. 1, 2002
Cravino et al.
Figure 5. UV-vis absorption spectra of poly(1) (solid line) and poly-
(2) (dashed line).
Figure 3. CV (p-doping) of poly(1) at a scan rate of 25, 50, 100, and
200 mV/s.
Figure 6. Photoinduced Vis-NIR absorption spectrum of poly(1).
Excitation at 476 nm (40 mW on a 4 mm diameter spot). T ) 100 K.
Figure 4. CV (reduction) of poly(1). Scan rate 100 mV/s. First, third,
and seventh scan.
process), leading to a lower molecular weight for electrochemi-
cally prepared poly(1).27,33,41 As will be discussed in the
following, the latter explanation is corroborated by the IR
measurements. According to the electrochemical characteriza-
tion, no hints for ground-state donor-acceptor interactions are
observed.
polythiophene backbone and the pendant fullerene moieties
basically retain their individual electrochemical properties (“the
cables do not short”). In contrast to the results found for
p-doping, the reduction of the fullerene moieties leads to changes
of the cyclic voltammogram and loss of electroactivity (Figure
4). We have observed a similar behavior for a double-cable
consisting of a polythiophene carrying tetracyanoanthraquinone-
type moieties.38 This loss of electroactivity upon scanning
negative potentials also affects a subsequent p-doping process.
Considering that both polymers are heavily loaded with acceptor
moieties, the dissolution of the highly negatively charged
material by the polar electrolyte medium, associated to mor-
phological changes in the film structure, cannot be excluded.
After dedoping by keeping the potential at 0 V, yellow-brownish
and nonluminescent films were obtained. Their typical UV-
vis absorption spectrum is shown in Figure 5. For comparison,
Figure 5 shows also the absorption spectrum of the reference
poly(2). The buildup of a conjugated system in poly(1) is
confirmed by the broad absorption feature ranging from about
600 nm to the ITO-glass cutoff at around 300 nm, in which the
π-π* transition is seen by the shoulder at about 460 nm. This
value is considerably blue-shifted as compared to reference
polymer poly(2) that shows a well-defined spectrum, with a
maximum at 530 nm, typical of polythiophenes. Such a blue-
shift, observed also in other “double-cables”,27,38 is proposed
to originate from the shortening of the effective conjugation
length in poly(1). This effect may be explained by steric
hindrance due to the bulkyness of the fullerene substituents or
by the lower solubility of monomer 1 (and its oligomer
intermediates involved in the electrochemical polymerization
Photoinduced Vis-NIR-MIR Absorption and in Situ FTIR
Spectroelectrochemistry. We investigated the nature of the
photoexcitation in poly(1) by means of photoinduced absorption
in the vis-NIR. The PIA spectrum, taken with excitation at 476
nm, is shown in Figure 6. Two bands are observed, one with
maxima at 1.48 eV and one peaking below 0.6 eV. Both these
absorption features might be assigned to positively charged
excitations (widely accepted to be polarons) of a thiophene-
based conjugated backbone.42 Similar photoinduced absorption
bands have been assigned to polarons in long oligothiophenes
(Tn, with n ) 9).43 To shed light into the relaxation kinetics of
the photoexcitations, we have performed intensity and modula-
tion frequency dependence measurements (Figure 7).44,45 Both
PIA features, evaluated by the signal at 1.38 and 0.62 eV, show
a square root excitation intensity dependence, thus indicating
bimolecular recombination kinetics as commonly observed for
charge carriers in conjugated polymer/fullerene blends.46 From
the modulation frequency dependence, a broad distribution of
charged state lifetimes is observed. The best fit has been
obtained using three τ values, in the range from 0.8 to 10 ms.
The strong electron-phonon coupling in conjugated polymers
allows the detection of doping- or photoinduced changes in the
electronic structure also by means of vibrational spectros-
copy.47,48 Even rather complicated conjugated polymers show
relatively simple IR spectra with few intense infrared-active
vibration (IRAV) bands, once they are in the doped or
photoexcited states.49 These bands, which show correspondence

A Polythiophene with Fulleropyrrolidine Moieties
J. Phys. Chem. B, Vol. 106, No. 1, 2002 73
Figure 7. (a) Excitation intensity and (b) modulation frequency dependence of the poly(1) PIA signal.
Figure 8. Photoinduced IR absorption of poly(1). Excitation at 476
nm (20 mW/cm2). T ) 100 K.
Figure 10. IR difference spectra of poly(1) during p-doping; IRAV
range. Sequence: bottom to top.
spectrum, detailed in Figure 10, shows three dominant bands
centered at about 1323, 1130, and 1055 cm-1, that correspond
to those observed in the PIA-FTIR spectrum. The weak bands
at 1600 and 1480 cm-1 might be assigned to end-rings
vibrations, thus suggesting, as already mentioned, the possibility
of a relatively low molecular weight (short chain length).52 The
discussed instability of poly(1) films toward reduction of the
fullerene moieties does not allow the observation of clear in
situ FTIR spectra upon scanning negative potentials.
While these results prove the photoinduced generation of
metastable, positively charged states on the polythiophene
backbone, a definitive evidence of a photoinduced electron
transfer from the latter to the pendant fullerene moieties is
obtained only by ESR, as discussed in the next section.
Light-Induced ESR. The ESR spectra of poly(1) films are
displayed in Figure 11. The dark ESR spectra shows only one
line at a g-factor of 2.0022, which we assign to residual radical-
cations remaining from to the oxidative electropolymerization.
The light-induced ESR spectrum, obtained by subtracting the
“dark” signal from the “light-on” signal, shows the photo-
generation of two paramagnetic species. The positive polaron
on the conjugated backbone has a g-factor of 2.0022, while the
signal at lower g-factor, 2.0004, is typical of fullerene radical-
anions.40,46 These results clearly indicate the occurrence of a
photoinduced electron transfer from the polythiophene backbone
to the pendant fullerene moieties. Also, the steady state LESR
studies clearly show the long-living charge separation in this
noncomposite material as observed earlier in conjugated polymers/
fullerenes composites.46
Figure 9. IR difference spectra of poly(1) during p-doping. Se-
quence: bottom to top.
to Raman-active modes of the neutral polymer, become IR-
active due to the breaking of local symmetry associated with
the charged backbone distortion.47,50 As such, the photoinduced
charge generation in poly(1) is corroborated also by the PIA-
FTIR spectrum depicted in Figure 8 (excitation at 476 nm). As
observed in the PIA-vis-NIR spectrum, broad electronic absorp-
tion bands, with maxima at about 4000 cm-1 (0.49 eV) and
above 7000 cm-1 (>0.87 eV), out of the detection range, are
observed. In addition, three bands are seen in the vibrational
range, at 1315, 1128, and 1039 cm-1, respectively. In agreement
with the bithiophene nature of the repeating unit and with a
charged nature of the photoexcitations in poly(1), such a pattern
displays marked similarity to that of p-doped and photoexcited
polythiophenes.49,51
The difference spectra recorded in-situ during electrochemical
oxidation (p-doping) of poly(1) are shown in Figure 9. Above
2000 cm-1 (ca. 0.25 eV), the spectra are dominated by a very
broad electronic absorption band. The vibrational part of the
Conclusions
We have prepared a novel bithiophene with a tethered
fulleropyrrolidine moiety suitable as a monomer for electropo-

74 J. Phys. Chem. B, Vol. 106, No. 1, 2002
Cravino et al.
Figure 12. Spectroelectrochemical cell for in situ ATR-FTIR spec-
troscopy.
Figure 11. Light-induced ESR spectrum of poly(1). Excitation at 476
nm. T ) 100 K.
Rikadenki RY-PIA x-y recorder. All the experiments were done
at room temperature and under Ar.
lymerization. The polymer films were investigated for their
electrochemical and photophysical properties. The donor back-
bone and the acceptor moieties do not interact in the ground-
state while a photoinduced electron transfer occurs in this
“double-cable” polymer in the excited state, as revealed by PIA
and LESR measurements. The results show that, in addition to
the potential as intrinsic p-n transporting materials in organic
devices, the class of “double-cable” polymers is of high interest
for organic photovoltaics and other optoelectronic devices. The
route to self-organization can be opened by further manipulation
of the primary structure of such noncomposite materials to
dictate the secondary morphology in such systems.
Electron-Transfer Studies and in Situ FTIR Spectroelec-
trochemistry. For spectroscopy in the vis-NIR range, the
polymer was electrodeposited onto ITO coated glass and plastic
foils. The UV-vis absorption spectra of the electrochemically
polymerized films were taken at room temperature on a Cary-3
spectrophotometer. The PIA studies in the vis-NIR were done
using the Ar+ lines at 351 and 476 nm as pump source (40
mW on a 4 mm diameter spot). The pump beam was modulated
mechanically at a chopper frequency of 210 Hz. The change in
the probe beam (120 W, tungsten lamp) transmission (-∆T)
were detected, after dispersion with a 0.3 m monochromator,
in the range 0.55-2.15 eV by a Si-InGaAsSb sandwich detector.
The detector signals were recorded phase-sensitively with a dual-
phase lock-in amplifier. The probe light transmission (T) was
recorded separately using the same chopper frequency, then the
PIA spectra were calculated as -∆T/T. Experiments were done
at 100 K. Polymer films deposited on ZnSe (see below) were
used for photoinduced FTIR absorption measurements (PIA-
FTIR). The samples were placed in a liquid N2 cryostat and
illuminated in the 45° geometry (λ ) 476 nm, 30 mW/cm2).
Ten single beam spectra were recorded in dark and then under
illumination, repeating this sequence 300 times. From the
resulting “light-off” and “light-on” spectra, the PIA was
calculated as -∆T/T. All of the FTIR spectra were recorded
with a resolution of 4 cm-1, by means of a Bruker IFS 66/S
equipped with a liquid N2 cooled MCT detector. Attenuated
total reflection (ATR) FTIR measurements during the electro-
chemical oxidation and reduction of the polymer were done in
situ using the cell depicted schematically in Figure 12. Details
and the setup for in situ spectroelectrochemistry have been
published elsewhere.53-55 The working electrode was a Pt grid
evaporated onto a ZnSe reflection element (when not differently
stated, the other electrochemical parameters and conditions were
as those described in the previous section). During potential
scanning at a rate of 5 mV/s, single-beam IR spectra were
recorded consecutively. Each spectrum covers about 90 mV in
the corresponding CV. By selecting a spectrum taken just prior
of the investigated redox process as reference and relating the
subsequent spectra to this chosen reference, specific electro-
chemically induced spectral changes were observed (the dif-
ference spectra were calculated as ∆(-log TATR), where TATR
is the transmittance in the ATR geometry). For LESR spec-
troscopy, the polymer films on ITO coated plastic, cut in stripes
of approximately 2 mm × 10 mm, were sandwiched and placed
into an ESR quartz tube which was evacuated and then sealed
in Ar atmosphere. The sample was placed in the high-Q-cavity
of a X-band ESR spectrometer and cooled to 100 K. For the
Experimental Section
General. NMR spectra were recorded on a Bruker AF 250
spectrometer at frequencies of 250 MHz for the 1H nucleus, on
a Bruker AM 400 or a Varian XL 400 MHz spectrometer at
frequencies of 400 and 100 MHz for 1H and 13C nuclei,
respectively. Tetramethylsilane (TMS) was used as an internal
1
standard for H and 13C NMR. FTIR spectra of compounds 1,
3, and 4 were recorded on a Perkin-Elmer 1720 X spectropho-
tometer. UV-vis absorption spectra were recorded on a Perkin-
Elmer Lambda 5 spectrophotometer. Matrix assisted laser
desorption ionization time-of-flight mass spectrometry (MALDI-
TOF MS) was performed on a mass spectrometer Reflex
(Bruker) in positive linear mode at 15 kV acceleration voltage,
using 2,5-dihydroxybenzoic acid as matrix. Exact mass deter-
mination was performed on an high-resolution fast atom
bombardment (HRFAB) mass spectrometer KRATOS MS-50
operated at 10 000 resolving power, using a 3-nitrobenzyl
alcohol (3-NBA)/LiCl matrix. The purity of fulleropyrrolidine
1 was checked also by HPLC using an analytical Phenomenex
Luna SiO2 column (250 × 4.6 mm), toluene/ethyl acetate 95:5,
1 mL/min. The elution was monitored with a spectrophotometric
detector at 340 nm.
Electrochemical Polymerization and Cyclic Voltammetry.
For electrochemical polymerization and cyclic voltammetry
(CV) a conventional three-electrode cell was used. The working
and the counter electrodes were Pt foils. An Ag/AgCl wire
(-0.44 V vs ferrocene) was used as quasi-reference electrode.
In this paper, all the potential values refer to this electrode. For
electropolymerization, the supporting electrolyte solution was
0.1 M tetrabutylammonium hexafluorophosphate in anhydrous
CH2Cl2 or Tol/CH3CN 7:3 v/v. Experiments in monomer-free
conditions were carried out using the same electrolyte dissolved
in CH3CN. The electrochemical apparatus consisted of a Jaissle
1002T-NC potentiostat, a Prodis 1/14 I sweep generator and a

A Polythiophene with Fulleropyrrolidine Moieties
J. Phys. Chem. B, Vol. 106, No. 1, 2002 75
1
“light-on” spectrum, illumination was made at 476 nm. To take
into account residual spins due to the oxidative polymerization
process as well as persistent light induced changes, “dark
spectra” and “light-off” spectra were recorded just prior and
after illumination, respectively. The LESR spectrum was then
calculated by subtracting the “dark” signal from the “light-on”
signal.
mol-1cm-1); H NMR (400 MHz, CDCl3/CS2 1:2) δ 7.63 (br
s, 2H), 7.16 (m, 3H), 7.09 (dd, 1H), 6.95 (d, 1H), 6.87 (m, 4H),
6.77 (m, 2H), 4.92 (d, 1H), 4.83 (s, 1H), 4.21 (d, 1H), 4.06 (m,
4H), 3.80 (m, 4H), 3.68 (s, 4H), 2.75 (s, 3H). 13C NMR (100
MHz, CDCl3/CS2 1:2) δ 158.57, 157.86, 156.03, 153.71, 153.29,
153.21, 147.01, 146.99, 146.47, 146.21, 146.06, 146.04, 145.98,
145.94, 145.88, 145.85, 145.82, 145.65, 145.49, 145.33, 145.23,
145.16, 145.10, 145.02, 144.98, 144.95, 144.93, 144.87, 144.43,
144.38, 144.12, 142.87, 142.74, 142.41, 142.34, 142.31, 142.29,
142.02, 141.99, 141.90, 141.87, 141.83, 141.82, 141.77, 141.74,
141.68, 141.56, 141.42, 141.29, 139.94, 139.89, 139.70, 139.33,
138.35, 136.53, 136.32, 135.92, 135.53, 135.51, 130.78, 130.30,
130.11, 128.75, 128.42, 125.40, 123.80, 114.21, 82.86, 77.06,
70.80, 69.75, 69.65, 68.61, 67.13, 39.75; MALDI MS (MW )
1241) m/z 1242 [M + H]+. Calcd exact mass (HR-FAB, 3-NBA/
Li as matrix): 1248.1855. Found: 1248.1779.
Materials. C60 (99.5%) was purchased from Bucky-USA. All
other reagents were purchased from Aldrich and used without
further purification. For column chromatography, Mackerey-
Nagel 60 M silica gel (particle size 230-400 mesh) was used.
For electrochemistry, toluene was distilled and stored over
sodium. CH3CN (Selectipur, Merck) was stored over molecular
sieves (4 Å). Bu4NPF6 was dried in vacuum at 180 °C.
Abbreviations. DMF, N,N-dimethylformamide; NBS, N-
bromosuccinimide; DME, dimethoxy ethane, Rf, thin-layer
chromatography retention factor.
4-Thiophen-3-yl-phenol (5). 4-Bromophenol (8.0 g, 0.046
mol), DME (180 mL), and tetrakis(triphenylphosphine)palla-
dium(0) (0.53 g, 0.46 mmol) were mixed and stirred under
nitrogen for 10 min. 3-Thiophene boronic acid (8.2 g, 0.063
mol), dissolved in DME (20 mL) was added, followed by 1 M
aqueous NaHCO3 (150 mL). The mixture was stirred for 12 h
at reflux temperature, concentrated in vacuo and extracted with
diethyl ether. The organic phase, washed with brine and water,
was dried over Na2SO4. The solvent was removed in vacuo and
5 (5.59 g, 69%) was obtained after crystallization from CH2Cl2
of the crude product: 1H NMR (400 MHz, CDCl3) δ 7.48 (d,
2H), 7.35 (m, 3H), 6.86 (d, 2H), 4.73 (s, 1H); 13C NMR (100
MHz, CDCl3) δ 156.69, 141.92, 127.18, 126.72, 126.00, 125.84,
118.02, 115.66. GC-MS (HR-MS) calcd exact mass: m/z
176.030. Found: m/z 176.024 (-6.6 ppm).
4-(2-Bromo-thiophen-3-yl)-phenol (6). NBS (4.9 g, 0.027
mol) and 5 (5.1 g, 0.029 mol) in DMF (130 mL) were strirred
at room temperature in the dark for 20 h. HCl (1 M, 200 mL)
was added, and the mixture was extracted with diethyl ether.
The organic phase, washed with 10% Na2S2O5 and water, was
dried over Na2SO4, and the solvent was evaporated in vacuo.
The residue, dissolved in 5 mL of ethyl acetate, was poured
into cold pentane (100 mL, -30 °C). After filtration, the solvents
were removed in vacuo yielding 4.0 g of 6 that was used,
immediately after its preparation, for the next step without
further purification.
4-[2,2′]Bithiophenyl-3-yl-phenol (2). Derivative 6 (4.0 g),
DME (85 mL) and tetrakis(triphenylphosphine)palladium(0)
(0.20 g, 0.17 mmol) were mixed and stirred under nitrogen for
10 min. 3-Thiophene boronic acid (3.0 g, 0.023 mol), dissolved
in DME (10 mL), was added, followed by 1 M aqueous
NaHCO3 (100 mL). The reaction mixture was stirred under
nitrogen for 12 h at reflux temperature, concentrated in vacuo
and extracted with diethyl ether. The organic phase, washed
with brine and water, was dried over Na2SO4. The diethyl ether
was removed in vacuo, and the residue, dissolved in CH2Cl2,
was filtered though a short pad of silica gel. After evaporation
of CH2Cl2, the residue, treated with the same solvent, was
filtered and concentrated under reduced pressure. Crystallization
from hexane gave pure 2 [1.5 g, 21% (from 5)]: 1H NMR (400
MHz, CDCl3) δ 7.21 (m, 3H), 7.40 (d, 2H), 6.99 (d, 1H), 6.94
(t, 1H), 6.81 (d, 2H), 4.73 (s, 1H); 13CNMR (100 MHz, CDCl3)
δ 156.85, 138.94, 135.95, 130.50, 130.11, 130.07, 127.04,
126.64, 126.19, 125.52, 123.86, 115.36. GC-MS (HR-MS) calcd
exact mass: m/z 258.017. Found: m/z 258.007.
4-{2-[2-(2-Iodo-ethoxy)-ethoxy]-ethoxy}-benzaldehyde (3).
A mixture of p-hydroxy-benzaldehyde (1.0 g, 8.2 mmol), K2-
CO3 (5.6 g), and 1-iodo-2-[2-(2-iodoethoxy)ethoxy]ethane (4.54
g, 12.3 mmol) in acetone (50 mL) was heated to reflux
temperature for 8 h. After cooling, the mixture was filtered and
concentrated to dryness. The oily residue was purified by column
chromatography (SiO2, toluene/ethyl acetate 9:1) giving 3 (590
mg, 20%) as a yellowish oil. Rf (hexanes/ethyl acetate 8:2) )
0.47; IR (KBr) 2887, 2738, 1687, 1602, 1577, 1510, 1259, 1164,
1
1094, 1055, 837; H NMR (250 MHz, CDCl3) δ 9.88 (s, 1H),
7.83 (m, 2H), 7.02 (m, 2H), 4.22 (t, 2H), 3.90 (t, 2H), 3.78-
3.67 (m, 6H), 3.25 (t, 2H); 13C NMR (100 MHz, CDCl3) δ
190.79, 163.78, 131.93, 130.00, 114.86, 71.936, 70.837, 70.221,
69.524, 67.737, 2.974. Anal. calcd for C13H17O4I: C, 42.87;
H, 4.70. Found: C, 42.58; H, 4.75.
4-(2-{2-[2-(4-[2,2′]Bithiophenyl-3-yl-phenoxy)-ethoxy]-
ethoxy}-ethoxy)-benzaldehyde (4). A mixture of aldehyde 3
(253 mg, 0.69 mmol), K2CO3 (400 mg), and bithiophene 2 (150
mg, 0.58 mmol) in acetone (25 mL) was heated to reflux
temperature for 8 h. After cooling, the resulting mixture was
filtered and concentrated to dryness. The oily residue was
purified by column cromatography (SiO2, hexanes/2-propanol
9:1) giving aldehyde 4 (139 mg, 49%) as a yellowish oily
compound. Rf (hexanes/2-propanol 9:1) ) 0.31. IR (KBr) 3097,
2924, 2866, 1681, 1594, 1571, 1508, 1750, 1305, 1247, 1161,
1126, 1051, 924, 952, 825 cm-1; 1H NMR (400 MHz, CDCl3)
δ 9.87 (s, 1H), 7.813 (m, 2H), 7.26 (m, 2H) 7.25 (d, 1H), 7.17
(dd, 1H), 7.04 (d, 1H), 7.01 (m, 2H), 6.98 (dd, 1H), 6.92 (dd,
1H), 6.88 (m, 2H), 4.22-4.20 (m, 2H), 4.16-4.13 (m, 2H),
3.92-3.86 (m, 4H), 3.77 (s, 4H); 13C NMR (100 MHz, CDCl3)
δ 190.79, 163.81, 158.14, 138.60, 131.93, 130.48, 130.37,
130.03, 128.82, 127.48, 127.06, 126.44, 125.58, 123.89, 114.86,
114.44, 70.951, 70.891, 69.827, 69.527, 67.740, 67.352. Anal.
calcd for C27H26O5S2: C, 65.56; H, 5.30; S, 12.96. Found: C,
64.22; H, 5.33; S, 12.35.
Fulleropyrrolidine-bithiophene (1). A mixture of aldehyde
4 (100 mg, 0.2 mmol), C60 (288 mg, 0.4 mmol), and N-
methylglycine (27 mg, 0.3 mmol) in chlorobenzene (150 mL)
was heated to reflux temperature for 2 h. After cooling to room
temperature, the mixture was concentrated under reduced
pressure to about 30 mL and loaded on top of a SiO2
chromatography column. Elution with toluene/ethyl acetate 9:1
gave first unreacted C60 and then fulleropyrrolidine 1 (122 mg,
49%) as a brown solid. Rf (toluene/ethyl acetate 95:5) 0.34. IR
(KBr) 2852, 1609, 1511, 1499, 1453, 1428, 1294, 1247, 1177,
1124, 1109, 1062, 843, 830, 694 cm-1; UV-vis (CH2Cl2) λ
(ꢀ) 230 (112 530), 256 (125 060), 431 (3963) nm (dm3
Acknowledgment. This work has been supported by the
European Community (JOULE III, Contract JOR3CT980206).
All partners of this European Consortium are gratefully ac-

76 J. Phys. Chem. B, Vol. 106, No. 1, 2002
Cravino et al.
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wissenschaftlichen Forschung” of Austria (Project P-12680-
CHE). M.M. wish to thank MURST (Contract MM03198284)
and CNR (legge 95/95). R. Go´mez is gratefully acknowledged
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