Through-space communication in a TTF-C60-TTF triad

Article abstract of DOI:10.1039/b613466a

A 2-pyrazolino[60]fullerene-based triad, possessing two TTF units connected with flexible long linkages, has been prepared. Fluorescence quenching was observed in polar and non-polar solvents, suggesting the existence of a through-space photoinduced charg

Full text of DOI:10.1039/b613466a

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PAPER
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Through-space communication in a TTF–C60–TTF triadw
a
b
a
c
´
´
´
´
Frederic Oswald, Stephanie Chopin, Pilar de la Cruz, Jesus Orduna,
Javier Garı
´
n,c Atula S. D. Sandanayaka,d Yasuyuki Araki,d Osamu Ito,*d
Juan Luis Delgado,a Jack Cousseau*b and Fernando Langa*a
Received (in Montpellier, France) 18th September 2006, Accepted 27th November 2006
First published as an Advance Article on the web 19th December 2006
DOI: 10.1039/b613466a
A 2-pyrazolino[60]fullerene-based triad, possessing two TTF units connected with flexible long
linkages, has been prepared. Fluorescence quenching was observed in polar and non-polar
solvents, suggesting the existence of a through-space photoinduced charge separation process with
rates faster than 3.8 ꢀ 109 sꢁ1 and with high efficiency (40.85). The charge separated states were
confirmed by transient absorption spectra in the visible and near-IR regions. The longest lifetime
of the charge separated state was found to be 230 ns in CH2Cl2 solvent.
by less negative reduction potentials compared to other full-
Introduction
erene derivatives such as pyrrolidino[60]fullerenes or Diels–
Alder adducts.8 The small HOMO–LUMO energy gaps in the
corresponding donor–acceptor assemblies,9 consequently, lead
to an efficient behaviour as constituents of plastic solar cells.10
However, donor–acceptor systems formed by TTF and a
2-pyrazolino[60]fullerene have not been reported until now,
despite the evident interest in combining these moieties. In this
study, we now wish to report the facile preparation of an
important intermediate, a bis-anilino derivative in the pyrazo-
lino[60]fullerene (PzC60) series, and the electrochemical and
photophysical behaviour of a new TTF–(spacer)–PzC60–
(spacer)–TTF triad, as shown in Chart 1. For the purposes
of comparison, a reference compound, possessing two heptyl
chains instead of both TTF moieties, was also prepared. In
order to confirm the photoinduced charge separation and
subsequent charge recombination processes, we employed
time-resolved fluorescence measurements in a picosecond
timescale and transient absorption measurements in a nano-
second timescale in the visible and near-IR regions.
Covalently-linked ensembles of electron donor and electron
acceptor moieties constitute a topic of great interest. Such
ensemble systems represent good models for the study of
photoinduced charge separation processes characteristic of
photosynthesis,1 and many of them have already been in-
volved in the fabrication of photovoltaic devices.2 In particu-
lar, in the search for the achievement of a quite long lifetime
for the final charge separated state, and for enhancing the
potential of corresponding donor–acceptor covalent assem-
blies towards practical applications under light illumination,
syntheses of triads, tetrads and polyads have been reported.
However, long sequences of reactions are usually necessary to
synthesize such molecular systems.3 Furthermore, from these
previous studies, obtaining sufficiently long-persisting, charge
separated radical ion pairs appears to be difficult for simple
molecular systems.
On the other hand, fullerene derivatives have been incorpo-
rated into many molecular systems that act as artificial reac-
tion photosynthetic models due to their electrochemical and
photophysical properties. Recently, it has been revealed that
tetrathiafulvalene (TTF) derivatives, which are well known as
excellent electron donors in the ground state, act as electron
donors in photoinduced processes when they are coupled with
fullerenes in molecular dyads and triads.4–6
Results and discussion
Synthesis and characterization
Among TTF derivatives, it is well-known that tetrathio-TTF
units are excellent donors.5 The synthesis of such TTF units is
summarized in Scheme 1, in which tetrathio-TTF derivative 3,
bearing a carboxylic acid group, was prepared from 1 in two
steps. After hydrolysis of TTF-methyl ester 2, obtained by
In our previous work, we also showed that 2-pyrazolino[60]-
fullerenes7 are excellent acceptors, since they are characterized
a Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-
La Mancha, 45071 Toledo, Spain. E-mail:
Fernando.Lpuente@uclm.es; Fax: +34 902 204 130
b
´
´
´
Chimie, Ingenierie Moleculaire et Materiaux d’Angers, UMR CNRS
6200, Universite d’Angers, 2 Bd. Lavoisier, 49045 Angers Cedex 01,
´
France. E-mail: cousseau@sciences.univ-angers.fr; Fax: +33 02 41
73 53 75
c Departamento de Quı´mica Orga´nica, ICMA, Universidad de
Zaragoza-CSIC, E-50009 Zaragoza, Spain
d IMRAM, Tohoku University, Katahira, Aoba-ku, 980-8577 Sendai,
Japan. E-mail: ito@tagen.tohoku.ac.jp; Fax: +81 22-217-5608
w Electronic supplementary information (ESI) available: Character-
ization details and data of the computational studies for the new
compounds described in the paper. See DOI: 10.1039/b613466a.
Chart 1 TTF–(spacer)–PzC60–(spacer)–TTF (7).
ꢂc
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2 h in refluxing CH2Cl2) with fullerene 6 in CH2Cl2 at room
temperature for 10 min.
Following the same procedure, the reaction of n-caprylic
acid chloride with pyrazolino[60]fullerene 6 in CH2Cl2 leads to
the formation of model compound 8 in 95% yield (Scheme 2).
Triads 7 and 8 were purified by several centrifugations with
acetone and methanol, and their purities were checked by
HPLC (see the ESIw).
The structures of TTF derivatives 1–3 and fullerene systems
5–8 were confirmed by their analytical and spectroscopic data,
such as 1H and 13C NMR, however the poor solubility of
compound 8 did not allow the corresponding 13C NMR
spectrum to be obtained. The 1H NMR spectrum of 7 in
CD2Cl2 displayed only the expected signals of the bis-anilino-
pyrazolino[60]fullerene core, the two para-substituted phenyl
systems exhibiting signals at 8.2 and 7.8 ppm, and at 7.6 and
7.5 ppm, respectively. The protons of the two amide NH
groups provided signals at 7.3 and 7.2 ppm, while the signals
corresponding to the protons of the TTF unit appeared
between 2.8 and 0.8 ppm. The 13C NMR spectrum of 7 was
in full agreement with the proposed structure, the signals from
the TTF moiety, as well as from the fullerene system for the
most part, appearing between 148.0 and 137.0 ppm.
The 1H NMR spectrum of 8 showed the corresponding
signals of the para-substituted phenyl moiety and the amide
NH group between 8.2 and 7.1 ppm, and the protons of the
alkyl chain between 2.45 and 2.30 ppm.
Scheme 1 Synthesis of TTF derivatives.
following Becher’s strategy,11 via reaction with lithium hydro-
xide in a water–dioxane medium according to known proce-
dures,12 the expected TTF-acid 3 was obtained in 95% yield.
Finally, the TTF-acid chloride 4 was quantitatively prepared
from compound 3 via the usual method using oxalyl chloride
in CH2Cl2 and reacted in situ.
Compound 6 (Scheme 2) was prepared in 72% yield from
bis-nitrophenylpyrazolinofullerene (5),13 by reduction of the
two nitro functions according to a previously reported proce-
dure.14 A large excess of tin powder was added to a solution of
fullerene derivative 5, followed by several portions of concen-
trated aq. HCl (37%) over 25 min. The reaction was stirred for
72 h at room temperature. The mixture was hydrolyzed and
the resulting solid purified by column chromatography on
silica gel using CH2Cl2 as solvent. Thus, bis-anilino-2-pyrazo-
lino[60]fullerene (6), which is a key and accessible building
block for the preparation of C60-based triads, was easily
obtained. Both amino groups offer further possibilities for
functionalization by simple condensation reactions, and thus
give rise to new derivatives useful for applications in medicinal
chemistry and material science.15
The structures of compounds 3 and 6–8 were also confirmed
by MALDI-TOF mass spectra, which show the expected
molecular ions at m/z = 586.4 (3), 944.0 (6), 2081.0 (7) and
1198.7 (8).
Molecular orbital calculations
The flexibility of the spacers in 7 leads to a high number of
conformations displaying similar energy. A conformational
search was conducted by using simulated annealing with the
MM+ force field, as implemented in Hyperchem, leading to a
minimum energy that corresponds to a bent conformation,
with the center of the TTF moieties placed at 7.0 and 7.2 A,
respectively, from the center of the C60 core (a in Fig. 1).
Conformations with the two TTF moieties separated away
from the C60 (c in Fig. 1) are ca. 22–24 kcal molꢁ1 less stable
than this geometry, while those conformations with one TTF
close to the fullerene spheroid and the other one separated
Finally, triad 7 was obtained in 90% yield (Scheme 2) by
condensation of TTF-acid chloride 4 (synthesized in situ by
treatment of TTF-acid 3 with an excess of oxalyl chloride over
Scheme 2 Synthesis of triad 7 and model compound 8.
ꢂc
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Fig. 2 OSWV data for triad 7, parent TTF 3 and C60
groups according to the electrochemical studies undertaken on
analogous systems.14
Fig. 1 Representative conformers of 7.
Steady-state UV-vis spectra
The absorption spectrum of 7 (Fig. 3) was essentially the same
as the added spectra of precursors 3 and 6. However, a weak
absorption at a wavelength between 400–500 nm can be
ascribed to an extra absorption from the components, suggest-
ing that there is a possible electronic interaction between them
in the ground state. As discussed later, triad 7 was repetitively
subject to laser light; the absorption spectrum measured after
laser photolysis with 400 and 532 nm light was almost the
same as before the laser irradiation, indicating that triad 7 was
considerably photostable.
from it (b in Fig. 1) are ca.12 kcal molꢁ1 above the more stable
conformation. However, we cannot trust these differences in
energy since the MM+ force field yields a poor description of
the p–p interactions that are responsible for the preference for
the folded conformer.
Electrochemical studies
The electrochemical properties of triad 7, and the precursors
TTF-acid 3 and C60, were studied by cyclic voltammetry (CV)
and Osteryoung square-wave voltammetry (OSWV) in a mix-
ture of ortho-dichlorobenzene (o-DCB)/acetonitrile (4 : 1) as
the solvent (Table 1 and Fig. 2). Triad 7 gave rise to three
reversible, one-electron reduction waves (see CV in the ESIw),
which were attributed to the fullerene moiety.16 The first
reduction peak of triad 7 was shifted negatively by 50 mV
compared to that of the pristine C60. Such an appreciable shift
of the reduction wave from that of C60 is similar to that
observed for 6.
Steady-state fluorescence spectra
As a preliminary investigation on the photophysical properties
of triad 7, steady-state fluorescence spectra of fullerene deri-
vatives 5–8 were measured in toluene and CH2Cl2 at room
temperature. No significant differences were observed between
these two solvents (Fig. 4).
Under 430 nm excitation, which can generate the excited
state (S1) of [60]fullerene (1C60*), a broad fluorescence derived
from the [60]fullerene moiety was observed around 700 nm,18
exclusively in the cases of bis-nitrophenyl 5 and bis-heptyl-
amide 8. On the contrary, the fluorescence was almost com-
pletely quenched in bis-TTF derivative 7 and bis-anilino-2-
pyrazolino[60]fullerene 6, even in toluene solvent. Due to
In the cyclic voltammograms (see the ESIw), two reversible
oxidation waves were observed for 3 and 7 in the 0.05–0.11
and 0.33–0.39 V regions, which correspond to the formation of
the radical cation and the dication species of the TTF moi-
ety.17 Comparing these values with the observed Eo1x values of
3, a weak electronic interaction with the C60 sphere in the
ground state of 7 may be anticipated, although the E1red may
also be affected by the Pz moiety in addition to this interac-
tion. The two oxidation potentials observed for bis-amino
fullerene derivative 6 are attributed to the two different NH2
a
Table 1 OSWV data for 6, triad 7, parent TTF-acid 3 and C60
Compound
E1ox/V
E2ox/V
E1red/V
E2red/V
E3red/V
C60
6
3
ꢁ0.96
ꢁ0.99
ꢁ1.37
ꢁ1.39
ꢁ1.84
ꢁ1.99
0.12
0.11
0.05
0.36
0.39
0.33
7
ꢁ1.01
ꢁ139
ꢁ1.90
a
n-Bu4NClO4 (0.1 M); glassy carbon electrode as the working elec-
trode, scan rate, 100 mV sꢁ1, in o-DCB/acetonitrile (4 : 1).
Fig. 3 Steady-state absorption of 7 (0.1 mM), 3 (0.1 mM) and 6
(0.1 mM) in CH2Cl2.
ꢂc
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Fig. 5 (a) Fluorescence spectra of 7 in the 50–1000 ps region,
measured with a streak scope detector (intensity is normalized at 700
nm), and (b) fluorescence time profiles of triad 7 in the 700–750 nm
region, comparing reference 5 in toluene and PhCN; lex = 400 nm.
Fig. 4 Fluorescence spectra of compounds 5–8 using toluene solu-
tions with the same absorption intensity at lexc = 430 nm.
fluorescence quenching of C60, only a charge separation
1
process can be considered, since the energy level of C60* is
The fluorescence peak near to 700 nm can be observed,
which may be invisible in the steady-state fluorescence spectra
in Fig. 4. For the charge separation process of triad 7, the
fluorescence lifetimes were measured in toluene and PhCN, as
shown in Fig. 5(b), in which the fluorescence time profiles in
the lowest among the constituents, such as the TTF and Pz
moiety. In order to discard possible charge separation pro-
cesses from the nitrogen lone pair of the pyrazoline to the C60
cage, as was observed previously in some 2-pyrazolino[60]
fullerenes with donor units linked to the C atom of the
pyrazoline ring,19 we measured the fluorescence spectrum of
7 in the presence of an equimolar amount of trifluoroacetic
acid. In this case, no recovery of the fluorescence was ob-
served, showing that the nitrogen lone pair is not responsible
for the fluorescence quenching. The quenching of fluorescence
in triad 7, not observed in the analogous alkyl derivative 8, can
be ascribed to a through-space electron transfer from the TTF
units to the fullerene moiety, in agreement with theoretical
calculations, which show that triad 7 can adopt a folded
conformation (see Fig. 1). On the other hand, an efficient
fluorescence recovery was observed in the spectrum of 6 with
the addition of TFA, indicating that quenching of the fluor-
escence in 6 is due to a photoinduced electron transfer from
the aniline moiety to the C60 cage; the short distance between
the two anilino groups and the C60 spheroid makes the charge
separation via 1C60* easy.
1
the 700–750 nm region of the C60* moiety of triad 7 showed
the rapid decay of the C60 fluorescence compared to the
pristine C60 and PzC60 (time profile of reference compound 5
(tf0) = 1400 ns).
These time profiles were curve-fitted with a dual exponential
function, from which a major short lifetime and a minor
longer lifetime were evaluated. The major short lifetimes (tf)
are summarized in Table 2. From the tf values, the rate
constants (kSCS) and quantum yields (FCS S) of the charge
1
separation via the C60* moiety were calculated, as listed in
Table 2.
The kCS S and FCS S values are in the range 3.8–10 ꢀ 109 sꢁ1
and 0.85–0.94, respectively, which supports the highly effective
1
charge separation of triad 7 via the C60* moiety, probably
because the charge separation process belongs near to the top
region of the Marcus parabola. Since the kSCS and FCS S values
decrease with increasing the solvent polarity, the sliding down
of the charge separation process from the top to the inverted
region was suggested in the highly polar solvents.
In the case of
a previously reported C60 analogue
Time-resolved fluorescence measurements
[C60(TTF)2] (9) (Chart 2), in which two identical tetrathio-
substituted TTF moieties are connected to C60 through the
same flexible linkers, an appreciable shortening of the fluor-
escence lifetimes was not observed in non-polar and less-polar
solvents.5b It was deduced that the charge separation process
The time-resolved fluorescence spectra of 7 in the time region
from 50–1000 ps, measured by a streak camera, which has a
high sensitivity in this wavelength region, are shown in
Fig. 5(a).
Table 2 Fluorescence lifetime (tf, at 700–750 nm), rate constant (kSCS), quantum yield (FSCS) and free energy change (DGCS S) for charge separation
via 1C60*, rate constant (kCR), radical ion pair lifetime (tRIP) and free energy change (DGCR), for the charge recombination of triad 7a
Solvent
e
tf/ps (fraction (%))
kSCS/sꢁ1
FSCS
DGSCS/eV
kCR/sꢁ1
tRIP/ns
DGCR/eV
Toluene
THF
2.38
7.58
8.93
25.20
36.71
90 (90)
120 (92)
110 (89)
150 (75)
220 (60)
1.0 ꢀ 1010
7.8 ꢀ 109
8.7 ꢀ 109
6.0 ꢀ 109
3.8 ꢀ 109
0.94
0.92
0.93
0.90
0.85
ꢁ0.10
ꢁ0.54
ꢁ0.57
ꢁ0.71
ꢁ0.75
1.6 ꢀ 107
7.7 ꢀ 106
4.4 ꢀ 106
1.8 ꢀ 107
7.4 ꢀ 106
60
130
230
60
ꢁ1.60
ꢁ1.16
ꢁ1.13
ꢁ0.69
ꢁ0.65
CH2Cl2
PhCN
DMF
a
140
kSCS = (1/tf) ꢁ (1/tf0); FCS S = [(1/tf) ꢁ (1/tf0)]/(1/tf0); e = solvent dielectric constant; DGCS S and DGCR were calculated by the same method
previously described, assuming center-to-center distance (RCC) = 7 A.5b
ꢂc
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Chart 2 [C60(TTF)2] (9).
3
took place via the C60* moiety in these solvents.5b On the
other hand, TTF–(spacer)–PzC60–(spacer)–TTF (7), in the
present study, showed faster fluorescence quenching rates in
non-polar and less-polar solvents rather than in highly polar
solvents. Therefore, the charge separation process of triad 7
Fig. 7 Schematic energy diagram: TTF–(spacer)–PzC60–(spacer)–
TTF is abbreviated as TTF–Pz(C60)–TTF.
1
takes place predominantly via the C60* moiety, not via the
3C60* moiety.
As shown in the inset of Fig. 6, the time profile at 1020 nm,
which is the same as those in the visible region, decayed with
almost first-order kinetics, giving a charge-recombination rate
constant (kCR) = 4.4 ꢀ 106 sꢁ1 in CH2Cl2 at room tempera-
ture, from which the lifetime of the radical ion pair (RIP)
(tRIP) was found to be 230 ns (Table 2). Moreover, relatively
long tRIP values were found in THF (130 ns) and DMF
(140 ns), whereas shorter tRIP values were determined in toluene
(60 ns) and PhCN (60 ns). Thus, plots of tRIP values vs. solvent
polarity (1/e) show a maximum, except for PhCN. This
behaviour is quite different from that of [C60(TTF)2] triad 9,
in which a monotonous increase of the tRIP value from 30 ns
(in PhCN) to 110 ns (in toluene) was observed.5b Since this
order cannot be explained by the Marcus theory, some specific
factors, such as preferential solvation of (TTF)ꢃ+–(spacer)–
Pz(C60)ꢃꢁ–(spacer)–TTF, may play important roles.
Furthermore, the slow decay component (ca. 1.3 ns) exhib-
ited a low contribution (10–40%) that follows an intersystem
3
crossing (ISC), leading to the C60* moiety, even in polar
solvents.
Transient absorption spectra
In order to confirm the event of a charge separated state,
transient absorption spectra were measured in various sol-
vents. One example in CH2Cl2 is shown in Fig. 6, in which
broad absorption bands are observed in the wide 550–1200 nm
wavelength region.
These absorption spectra are quite similar to the previously
observed transient spectra for the [C60(TTF)2] triad 9, posses-
sing the same tetrathio-substituted TTFs.5b The absorption
around 1000 nm can be attributed to the radical anion of the
fullerene moiety, whereas the broad band in the 600–900 nm
region can be attributed to the cation radical of tetrathio-
substituted TTF, which decayed at almost the same rate.5b
Therefore, the generation of the radical ion pair
Energy diagram
From Table 2, the free energy changes of charge separation
(DGSCS) via the 1C60* moiety and charge recombination (DGCR
)
were evaluated, as listed in Table 2 using the redox potentials
from Table 1 and optimized structure from Fig. 1. From these
data, the energy diagram can be schematically depicted, as
shown in Fig. 7. The most prominent difference from the
[C60(TTF)2] triad 9 is the absence of the 3C60* moiety route for
the charge separation process, and consequently the absence of
triplet spin character in the RIP. Thus, the observed kSCS and
kCR values may depend mainly on the Marcus theory for the
RIP possessing a singlet spin character. Assuming the reorga-
nization energy to be 0.5–0.7 eV,20 a maximal kCS S value would
be anticipated in intermediate polar solvents but a maximal
kCR value in highly polar solvents.
+
(TTF)ꢃ –(spacer)–Pz(C60)ꢃꢁ–(spacer)–TTF is suggested, in
which an electron is located on the C60 moiety and a hole is
located on one of the tetrathio-substituted TTF moieties.
However, these observations for triad 7, with the pyrazoline
group, do not always trace the Marcus parabola. This suggests
that in this particular molecule, the pyrazoline group influ-
ences both topologically and electronically the stabilization of
the charge separated state and through-space electron transfer.
Conclusions
Fig. 6 Transient absorption spectra of triad 7 observed with 532 nm
laser light excitation in Ar-saturated CH2Cl2. Inset: Time profile at
1020 nm.
A new triad, 7, based on a 2-pyrazolino[60]fullerene system
possessing two TTF units connected with flexible long
ꢂc
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linkages, has been synthesized and its properties compared
with a model compound without TTF units, 8.
dissolved in the minimum amount of dry ethanol was added,
under nitrogen, to a solution of compound 1 (870 mg, 1.61
mmol) in 40 mL dry DMF. After 30 min stirring, methyl 5-
bromopentanoate (0.46 mL, 3.22 mmol) was added and the
reaction mixture stirred at room temperature for a further 4 h.
After the evaporation of DMF, the residue was dissolved in
CH2Cl2 and this organic phase washed with water then dried
over magnesium sulfate. After evaporation of the solvent, the
crude solid was purified by column chromatography (silica gel,
CH2Cl2/hexane 2 : 9), leading to pure compound 2 (90%
yield). 1H NMR (500 MHz, CDCl3/ppm) 3.66 (s, 3 H),
2.79–2.83 (m, 6 H), 2.42 (s, 3 H), 2.34 (t, 2 H, J = 7.3 Hz),
1.75–1.77 (m, 2 H), 1.61–1.67 (m, 6 H), 1.31–1.40 (m, 8 H) and
0.90 (t, 6 H, J = 7.2 Hz).
Electrochemical studies and UV-vis spectra suggest the
existence of a weak electronic interaction in the ground state
between the fullerene cage and the TTF units. In the excited
state, triad 7 showed an efficient quenching of the fluorescence
of the C60 moiety with respect to the emission observed for
alkyl derivative 8. This fluorescence quenching can be ascribed
to a through-space electron transfer from the TTF units to the
C60 moiety.
Laser spectroscopy studies have demonstrated that a highly
effective charge separation of triad 7 in polar and non-polar
solvents (with quantum yields between 0.85 and 0.94) takes
1
place via a C60* moiety. The longest lifetime of the charge
separated state was found to be 230 ns in CH2Cl2 solvent,
clearly longer than other [C60(TTF)2] derivatives previously
observed. These results suggest that the pyrazoline ring parti-
cipates in the photoinduced electron transfer process. Further
investigations are now in progress.
2-Carboxybutylsulfanyl-3-methylsulfanyl-6,7-dipentylsulfanyl-
TTF (3). Compound 2 (0.87 g, 1.45 mmol) was dissolved,
under nitrogen, in 110 mL dioxane in a 1 L three-necked
round-bottomed flask. Then, [LiOH, H2O] (0.61 g, 14.5 mmol)
dissolved in 55 mL water was added dropwise at room
temperature. After 24 h stirring, 220 mL CH2Cl2 and 65 mL
aq. 1 M HCl were added and the resulting mixture kept under
stirring for 24 h. The organic phase was separated, washed
with water until neutral and then dried over anhydrous
magnesium sulfate. After evaporation of the solvent, the
residue was purified by column chromatography (silica gel,
CH2Cl2 then ethyl acetate), giving rise to pure compound 3
(95% yield). 1H NMR (500 MHz, CDCl3/ppm) 2.79–2.84 (m,
6 H), 2.41 (s, 3 H), 2.30 (t, 2 H, J = 7.0 Hz), 1.60–1.75 (m,
8 H), 1.30–1.40 (m, 8 H) and 0.9 (t, 6 H, J = 7.2 Hz); 13C
NMR (50 MHz, CD2Cl2 + Et3N/ppm)22 178.8, 129.3, 128.1,
127.8, 126.4, 110.6, 110.3, 36.6, 36.5, 36.4, 30.9, 29.9, 29.7,
25.3, 22.4, 19.3 and 14.1; MALDI-TOF m/z 586.4 (M+).
Experimental section
All cycloaddition reactions were performed under argon. C60
was purchased from MER Corporation (Tucson, AZ). TLC
using Merck silica gel 60-F254 was used to monitor cycloaddi-
1
tion reactions. H NMR and 13C NMR spectra were recorded
on Varian Mercury 200 and Varian Inova 500 spectrometers.
UV-vis absorption spectra were obtained on a Shimadzu spec-
trophotometer. Steady-state fluorescence spectra were measured
on a Varian Cary spectrofluorophotometer. FT-IR spectra were
recorded on a Nicolet Impact 410 spectrophotometer using KBr
disks. MALDI-TOF mass spectra were obtained on a Voyager-
STR spectrometer. Cyclic voltammetry measurements were
carried out on an Autolab PGSTAT 30 potentiostat using a
BAS MF-2062, Ag/0.01 mol Lꢁ1 AgNO3 as a reference elec-
trode, an auxiliary electrode consisting of a Pt wire, a Metrohm
6.1247.000 conventional glassy carbon electrode (GCE, 3 mm
o.d.) as a working electrode directly immersed into the solution
containing 0.1 mol Lꢁ1 TBAP as an electrolyte in o-DCB/
acetonitrile (4 : 1). A 10 mL electrochemical cell from BAS,
model VC-2, was also used. The reference potential was shifted
by 290 mV towards a more negative potential compared to the
Ag/AgCl scale. E1/2 values were taken as the average of the
anodic and cathodic peak potentials. Scan rate 100 mV sꢁ1. The
ps time-resolved fluorescence spectra were measured using an
argon-ion pumped Ti:sapphire laser (Tsunami; pulse width =
2 ps) and a streak scope (Hamamatsu Photonics; response time =
10 ps). Details of the experimental setup are described else-
where.21 Nanosecond transient absorption spectra in the NIR
region were measured by means of laser-flash photolysis; 532
nm light from a Nd:YAG laser (pulse width = 6 ns) was used
as the exciting source and a Ge-avalanche-photodiode module
was used for detecting the monitoring light from a pulsed Xe
lamp, as described in our previous report.21 Molecular Me-
chanics calculations were performed using the HYPERCHEM
7.5 package.
30-(4-Aminophenyl)-10-(4-aminophenyl)pyrazolino [40,50;1,2][60]
fullerene (6). Tin powder (1.5 g) was added to a solution of 5
(50 mg, 0.05 mmol) in chloroform (75 mL). Concentrated HCl
(25 mL) was added in 5 portions over 25 min, then 0.5 g of tin
powder and a further 5 mL portion of hydrochloric acid were
added. The mixture was stirred at room temperature for 72 h
then neutralized with a concentrated sodium hydroxide solu-
tion. The aqueous phase was extracted with CH2Cl2. The
organic layers were then dried over MgSO4 and evaporated.
The crude solid was purified by column chromatography
(silica gel, CH2Cl2) affording 6 in 72% yield (34 mg, 0.04
mmol). FT-IR (KBr) n/cmꢁ1 3441, 3375, 1616, 1507, 1183,
1107, 822 and 520; 1H NMR (400 MHz, CDCl3/ppm) 8.10
(d, 2 H, J = 8.8 Hz), 7.60 (d, 2 H, J = 8.8 Hz), 6.70 (d, 4 H,
J = 8.8 Hz), 3.90 (bs, 2 H) and 3.76 (bs, 2 H); 13C NMR (100
MHz, CDCl3/ppm) 147.2, 147.0, 146.6, 146.5, 146.2, 146.1,
145.9, 145.7, 145.6, 145.5, 145.2, 145.1, 130.6, 130.1, 128.6,
126.7, 122.5, 122.3, 115.5 and 114.7; MALDI-TOF m/z 944.0
(M+ ꢁ H).
10,30-Bis(4-(2-butylsulfanyl-3-methylsulfanyl-6,7-dipentylsul-
fanyltetrathiafulvalenoyl)phenylamide)-2-pyrazoline[40,50:1,2][60]
fullerene (7). TTF-acid 3 (74 mg, 0.13 mmol) was refluxed in
CH2Cl2 (25 mL) in the presence of a large excess of oxalyl
chloride over 2 h. The solvent and excess of reagent were then
removed under vacuum. The resulting oil was dissolved in 5
6,7-Bis(pentylsulfanyl)-2-methoxycarbonylbutylsulfanyl)-3-
methylsulfanylTTF (2). [CsOH, H2O] (0.406 g, 2.42 mmol)
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mL dry CH2Cl2, and added to a CH2Cl2 solution (50 mL) of 6
(20 mg, 0.02 mmol) and pyridine (15 mL). The mixture was
stirred at room temperature under argon for 10 min. The
solvent was evaporated, and the resulting solid purified by
centrifugation with acetone and then methanol to give 7 in
90% yield (39 mg, 0.02 mmol). FT-IR (KBr) n/cmꢁ1 2917,
2843, 1666, 1589, 1503, 1454, 1397, 1307, 1249, 1180, 1102,
841, 714 and 526; 1H NMR (400 MHz, CD2Cl2/ppm) 8.16
(d, 2 H, J = 6.4 Hz), 7.77 (d, 2 H, J = 6.4 Hz), 7.58 (d, 2 H,
J = 7 Hz), 7.54 (d, 2 H, J = 7 Hz), 7.30 (s, 1 H), 7.21 (s, 1 H),
2.78 (t, 4 H), 2.73 (t, 8 H), 2.34 (s, 3 H), 2.33 (s, 3 H), 2.30
(t, 4 H), 1.80–1.15 (m, 32 H) and 0.88–0.80 (m, 12 H); 13C
NMR (100 MHz, CD2Cl2/ppm) 147.9, 147.5, 146.7, 146.6,
146.5, 146.3, 146.3, 146.2, 146.1, 145.7, 145.5, 144.6, 143.2,
142.7, 142.6, 142.5, 141.4, 140.6, 140.1, 136.8, 136.6, 130.7,
129.9, 124.9, 120.6, 119.7, 38.4, 37.3, 36.8, 36.4, 36.4, 32.5,
31.5, 31.3, 30.3, 30.0, 29.7, 29.6, 24.7, 24.6, 22.9, 19.5 and 14.5;
MALDI-TOF m/z 2081.0 (M+ ꢁ H).
3 P. J. Bracher and D. I. Schuster, Electron Transfer in Functiona-
lized Fullerenes, in Fullerenes: From Synthesis to Optoelectronic
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10,30-Bis(4-(heptanoyl)-phenylamide)-2-pyrazoline[40,50:1,2][60]
fullerene (8). n-Caprylic acid (22 mg, 0.16 mmol) was refluxed in
CH2Cl2 (20 mL) in the presence of a large excess of oxalyl
chloride for 2 h. The solvent and excess reagent were then
removed under vacuum. The resulting oil was dissolved in 5 mL
dry CH2Cl2, and then added to a CH2Cl2 solution of 6 (15 mg,
0.02 mmol) and pyridine (15 mL). The mixture was stirred at
room temperature under argon for 10 min. The solvent was then
evaporated, and the resulting solid purified by centrifugation
with acetone and then methanol to give 8 in 95% yield (18 mg,
0.02 mmol). FT-IR (KBr) n/cmꢁ1 2917, 2843, 1666, 1589, 1503,
1454, 1397, 1307, 1249, 1180, 1102, 841, 714 and 526; 1H NMR
(200 MHz, CDCl3/ppm) 8.23 (d, 2 H, J = 8.6 Hz), 7.85 (d, 2 H,
J = 8.6 Hz), 7.66 (d, 2 H, J = 8.4 Hz), 7.61 (d, 2 H, J = 8.6
Hz), 7.20 (s, 1 H), 7.13 (s, 1 H), 2.45–2.30 (m, 4 H), 1.80–1.20
(m, 20 H) and 0.89 (t, 6 H); MALDI-TOF m/z 1198.7 (Mꢁ).
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Acknowledgements
Financial support for this work was provided by the MEC of
Spain and FEDER funds (projects CTQ2004-00364/BQU,
BQU2002-00219), the Junta de Comunidades de Castilla-La
Mancha (project PAI-05-068). F. O. gives thanks for a grant
from the EU (RTN contract ‘‘FAMOUS’’, HPRN-CT-2002-
00171). The CNRS is also gratefully acknowledged for finan-
cial support, as well as Ministere de la Recherche (France) for
a PhD grant to S. C. We also thank to Dr. Z. Gan for his help
with the photophysical measurements.
20 A. S. D. Sandanayaka, Y. Araki, O. Ito, G. R. Deviprasad, P. M.
Smith, L. M. Rogers, M. E. Zandler and F. D’Souza, Chem. Phys.,
2006, 325, 452.
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236 | New J. Chem., 2007, 31, 230–236