Supramolecular hybrids of [60]fullerene and single-wall carbon nanotubes

Article abstract of DOI:10.1002/chem.200600114

Noncovalent interactions between purified HiPCO single-wall carbon nanotubes (SWNT) and a [60]fullerene-pyrene dyad, synthesized through a regio-selective double-cyclopropanation process, produce stable suspensions in which the tubes are very well dispers

Full text of DOI:10.1002/chem.200600114

FULL PAPER
Chem. Eur. J. 2006, 12, 3975 – 3983
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3975

DOI: 10.1002/chem.200600114
Supramolecular Hybrids of [60]Fullerene and Single-Wall Carbon Nanotubes
Dirk M. Guldi,*[a] Enzo Menna,[b] Michele Maggini,*[b] Massimo Marcaccio,[c]
Demis Paolucci,[c] Francesco Paolucci,*[c] StØphane Campidelli,[d] Maurizio Prato,*[d]
G. M. Aminur Rahman,[a] and Stefano Schergna[b]
Abstract: Noncovalent interactions between purified HiPCO single-wall carbon
nanotubes (SWNT) and a [60]fullerene–pyrene dyad, synthesized through a regio-
selective double-cyclopropanation process, produce stable suspensions in which
the tubes are very well dispersed, as evidenced by microscopy characterization.
Cyclic voltammetry experiments and photophysical characterization of the suspen-
sions in organic solvents are all indicative of sizeable interactions of the pyrene
moiety with the SWNT and, therefore, of the prevalence in solution of [60]fuller-
ene–pyrene·SWNT hybrids.
Keywords: carbooatnunnbes
cyclic voltammetry · fullerenes ·
noncovalent interactions supra-
molecular chemistry
·
·
AHCTREUNG
Introduction
In this context, carbon nanotubes (CNT), and in particu-
lar, single-wall carbon nanotubes (SWNT) have emerged as
particularly attractive candidates, due to their outstanding
physical, chemical, and mechanical properties, and their
prospects for practical applications.[1] These systems consist
of graphitic layers wrapped seamlessly into cylinders that
originate from defined sections of two-dimensional gra-
phene sheets.[2] With diameters of only a few nanometers
and lengths of up to several centimeters, the length-to-width
ratio of these nanotubes is extremely high. SWNT have a
very broad range of electronic, thermal, and structural prop-
erties that vary according to the particular kind of SWNT. A
setback in the use of CNT is that they are heavily entangled
with one another, which leads to the formation of three-di-
mensional networks in the form of tightly bound bundles.[3]
To overcome the rather poor solubility of CNT in
commonsolvents, it is desirable to develop facile, reproduci-
ble, and practical processing methods. Past work has un-
equivocally demonstrated that the preparation of functional
CNT based nanocomposites (i.e., nanoconjugates and nano-
hybrids) requires a method that assists in disentangling and
dispersing CNT.[4] However, it is evident that subsequent
chemical and physical modification of the surface would be
necessary to realize many of the potential applications.
Some SWNT have diameters that are sufficiently large to
encapsulate various atoms and molecules into their one-di-
mensional nanocavity. So far, empty fullerenes,[5] endo-[6]
and exohedral[7] metallofullerenes, exohedral fullerene de-
rivatives,[8] single elements,[9] ionic salts,[10] alkali metal,[11]
and H2O[12] have been successfully incorporated into the
The intriguing properties of carbon nanostructures have
sparked much interest in recent years, and a broad research
effort has been dedicated to understanding the physical and
physicochemical features of these new allotropes of carbon.
Importantly, the wealth of information that has been gath-
ered has significantly enhanced our general understanding
of how to develop nanometer scale materials and devices
that could shape future technologies.
[a] Prof. Dr. D. M. Guldi, Dr. G. M. A. Rahman
Lehrstuhl für Physikalische Chemie I
Universität Erlangen-Nürnberg
Egerlandstr. 3, 91058 Erlangen (Germany)
Fax : (+49)9131-852-8307
E-mail: guldi@chemie.uni-erlangen.de
[b] Dr. E. Menna, Prof. M. Maggini, Dr. S. Schergna
INSTM, Unit of Padova, Dipartimento di Scienze Chimiche
Università di Padova, Via Marzolo 1, 35131 Padova (Italy)
Fax : (+39)049-827-5239
E-mail: michele.maggini@unipd.it
[c] Dr. M. Marcaccio, Dr. D. Paolucci, Prof. F. Paolucci
INSTM, Unit of Bologna, Dipartimento di Chimica
Università di Bologna, Via Selmi 2, 40126 Bologna (Italy)
Fax : (+39)051-209-9456
E-mail: francesco.paolucci@unibo.it
[d] Dr. S. Campidelli, Prof. M. Prato
INSTM, Unit of Trieste, Dipartimento di Scienze Farmaceutiche
Università di Trieste, Piazzale Europa 1, 34127 Trieste (Italy)
Fax : (+39)040-52-572
E-mail: prato@units.it
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FULL PAPER
nanocavities of SWNT. Due to extensive intermolecular full-
erene–fullerene or fullerene–SWNT interactions, it is ex-
pected that the physicochemical characteristics of these new
materials are not simply a sum of those of fullerenes and
nanotubes: this hypothesis was supported by several experi-
mental and theoretical investigations.[13] Experimental re-
sults and theoretical studies demonstrate that the periodic
array of [60]fullerene molecules gives rise to a hybrid elec-
tronic band that derives its character from both the SWNT
states and the [60]fullerene molecular orbitals.[14]
double-cyclopropanation process. To this end, (3-bromopro-
pyl)carbamic acid tert-butyl ester 3 and 3,5-bis(hydroxyme-
thyl)phenol[16] were reacted in refluxing acetone in the pres-
ence of K2CO3 to afford bisdiol 4 in91% yield.
Derivative 3 was, inturn, prepared from 3-bromopropyl
[17]
amine hydrobromide 2, as described inthe literature.
Re-
actionof 4 with ethylmalonyl chloride in CH2Cl2 and tri-
ethylamine (TEA) gave bismalonate 5 in56% yield. Treat-
ment of 5 with [60]fullerene, I2, and 1,8-diazabicyclo-
[5.4.0]undec-7-ene (DBU) in toluene at room temperature
AHCTREUNG
AHCTREUNG
Here we report ona new type of [60]fullerene-hybridized
SWNT material, in which a covalently linked [60]fullerene–
pyrene conjugate was immobilized onto the surface of
SWNT by using a noncovalent method. The use of pyrene
derivatives is crucial for our approach, namely, solubilization
of SWNT through directed p–p interactions. A series of
physicochemical probes (i.e., electrochemical, spectroscopic,
and microscopic) confirm electronic interactions between
the pyrene part of the [60]fullerene–pyrene conjugate and
SWNT.
afforded the cyclizationproduct 6 in46% yield. This was
deprotected with trifluoroacetic acid inCH Cl2 to yield de-
2
rivative 7, which was reacted with 1-pyrenebutyric acid, N-
hydroxybenzotriazole (HOBT), 1-ethyl-3-(3’-dimethylami-
nopropyl)carbodiimide (EDCI), and 4-methylmorpholine to
give the desired bisadduct 1 in96% yield. The structure and
purity of bisadduct 1 was confirmed by NMR spectroscopy
1
and elemental analysis. In particular, the H NMR spectrum
of 1 shows all the characteristic features of the Cs-symmetri-
cal 1,3-phenylenebis(methylene)-tethered fullerene cis-2 bis-
adduct subunit.[18] Infact, anAB quartet is observed for the
À
À
diastereotopic benzylic CH2 groups and two resonances
are revealed for the aromatic protons of the 1,3,5-trisubsti-
tuted bridging phenyl ring. In addition to the signals corre-
sponding to the [60]fullerene-substituted spacer, the reso-
nances arising from the pyrene moiety are clearly observed
between7.5 and 8.5 ppm.
Results and Discussion
Synthesis of [60]fullerene–pyrene conjugate 1: The prepara-
tionof conjugate 1 began with the synthesis of [60]fullerene-
substituted
Boc-amine
6
(Boc=benzyloxycarbonyl,
Scheme 1). This was obtained through the regioselective re-
[15]
actiondeveloped by the group of F. Diederich,
which pro-
Binding of [60]fullerene–pyrene conjugate 1 to SWNT: The
1·SWNT hybrids were prepared analogously to our previous
work by using porphyrins (i.e., ZnP or H2P).[4m] Stable dis-
persions of 1·SWNT inorganic solvents were achieved from
a mixture of 1 mg of purified HiPCO (www.cnanotech.com)
SWNT and 2 mg of 1 that was stirred for 24 h in12 mL of
DMF or THF. Sonication (Bransonic 52, 112 W) was carried
out for 4 h at 208C followed by strong centrifugation
(90 minat 10000 rpm). The excess 1 was removed by wash-
ing the deposit twice. In the final step, 12 mL of fresh sol-
vent was added to the collected deposit and sonicated for
30 minat 20 8C. The solubility of 1·SWNT at room tempera-
ture is 0.05 mgmLÀ1. The homogeneous dispersion was
stored at 48C for characterization. The black dispersion is
stable in DMF for months and in THF for weeks.
vides [60]fullerene bisadducts through a cyclization reaction
at the [60]fullerene sphere by using bis malonates, in a
Figure 1 shows
a pictorial representation of hybrid
1·SWNT, inwhich the optimized geometry of dyad 1 (at the
PM3 semiempirical level) is shownwith a (9,0) SWNT.
Electrochemical characterization: The electrochemical be-
havior of 1·SWNT was investigated in both CH2Cl2 and
THF, with tetrabutylammonium hexafluorophosphate
(TBAH) as supporting electrolyte. Because the presence of
high ionic concentrations may in principle alter the p–p
stacking interactions between the SWNT and the pyrene
moiety, the samples were sonicated only briefly (<1 min) to
facilitate the dispersionof 1·SWNT inthese solvents. Al-
though similar results were observed for both solvents in the
negative-potential region, the narrower positive-potential
Scheme 1. a) (BOC)2O, TEA, CH2Cl2; b) 3,5-bishydroxymethyl phenol,
K2CO3, acetone; c) ethyl malonyl chloride, TEA, CH2Cl2; d) C60, DBU,
I2, toluene; e) CF3COOH, CH2Cl2; f) 1-pyrene butyric acid, HOBT,
EDCI, 4-methylmorpholine (for abbreviations, see text).
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M. Maggini, D. M. Guldi, F. Paolucci, M. Prato et al.
three discrete peaks, at À0.79, À1.58, and +0.98 V that, by
comparisonwith model 1, were associated with redox pro-
cesses involving the fullerene moiety. The CV curve of the
latter species, obtained under similar conditions (Figure 3),
displays in fact two reduction peaks, denoted as I and II, at
À0.74 and À1.12 V, respectively, and an oxidation peak at
1.19 V (peak A).
Figure 1. Semiempirical (PM3) optimized geometry of conjugate 1 inthe
presence of a (9,0) SWNT.
window that was available for THF prevented a thorough
characterizationof the anodic processes inTHF.
The cyclic voltammetric (CV) curve for a saturated solu-
tionof 1·SWNT in0.05 m TBAH/CH2Cl2 (Figure 2, solid
Figure 3. CV curves for a 0.3 mm solutionof conjugate 1 in0.05 m TBAH/
CH2Cl2. Data recorded at 298 K, scanrate 5 Vs À1. Working electrode, Pt
disc (125 mm diameter). Potentials are referenced to SCE.
Noticeably, peak I inthe CV curve of model species is re-
versible and corresponds to a one-electron reduction, where-
as peak II is irreversible most likely because of follow-up re-
actions associated with electrochemically induced opening
of the cyclopropane ring(s), as typically observed in malo-
nate-fullerenes.[21] Importantly, the anodic peak at 1.19 V in
the CV curve of 1 corresponds to a two-electron oxidation
process (by comparisonwith the first reductionof the fuller-
ene moiety) that results from the superimposition of two
one-electron oxidations, occurring at very close potentials,
as evidenced in the CV curve at low temperature shown in
Figure 4. The corresponding E1/2 values, as obtained by the
Figure 2. CV curves for a saturated solutionof 1·SWNT in0.05 m TBAH/
CH2Cl2 (solid line) and the corresponding baseline (dashed line). Data
recorded at 298 K, scanrate 5 Vs À1. Working electrode, Pt disc (125 mm
diameter). Potentials are referenced to the saturated calomel electrode
(SCE).
line) displays the typical continuum of diffusion-controlled
cathodic current, with onset at ~À0.45 V, which corresponds
to the progressive filling of the empty electronic states of
the SWNTs.[4j] Likewise, in the positive-potential region, the
monotonic increase of anodic current is observed, with
onset at ~+0.15 V and a sharp increase of current at E=
1.3 V, also associated with the rise inthe (filled) electronic
density of state of SWNTs.[4j] Such behavior resembles close-
ly that observed for other classes of functionalized SWNT,
such as pyrrolidine-functionalized SWNTs,[4g] polystyrenesul-
Figure 4. CV curves for a 0.3 mm solutionof conjugate 1 in0.05 m TBAH/
CH2Cl2. Data collected at: 1 VsÀ1 and 298 K (dashed line); 10 VsÀ1 and
223 K (solid line). Working electrode. Pt disc (125 mm diameter). Solid
line is referred to the right y axis, the dashed line to the left y axis. Poten-
tials are referenced to SCE.
fonate-[19] and poly(4-vinyl)pyridine-grafted SWNTs.[20] Su-
A
perimposed to such a continuum of faradaic and pseudoca-
pacitive current, the CV curve in Figure 2 also displays
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digital simulationof the CV curves, were 1.15 and 1.22 V, re-
spectively.
tered oxidation, occurring in 1 close to the pyrene-centered
oxidation, would not be affected significantly by such an in-
teraction, and would, therefore, remain at more-positive po-
tentials (i.e., ꢀ1.2 V), at which the CV curve is dominated
by the increase in the anodic current associated with the oxi-
dationof SWNT.
The anodic behavior of fullerenes and fullerene deriva-
tives has received much less attention than the correspond-
ing cathodic behavior.[22] However, potentials ranging be-
tween1.2 and 1.4 V have beenreported for the first oxida-
tionof bisadducts that are structurally closely related to 1.[23]
One of the two one-electron oxidation processes comprising
peak A is, therefore, attributed to the oxidationof the fuller-
ene moiety, the remaining process being located on the
pyrene moiety.[24]
Photophysical characterization: Absorptionspectroscopy
(Figure 6) also confirms the successful immobilization of 1
Comparisonof the CV curves of 1·SWNT and 1 (Figure 5)
highlighted, besides the typical features due to the SWNT
Figure 6. Absorption spectra of 1-pyrenemethanol (dotted line), dyad 1
(dashed line), and 1·SWNT (solid line) in DMF at RT.
Figure 5. CV curves for a 0.05m TBAH/CH2Cl2 solutionof saturated
1·SWNT (solid line) and 0.3 mm 1 (dashed line). Data recorded at 298 K,
scanrate 5 Vs À1. Working electrode, Pt disc (125 mm diameter). Solid line
is referred to the left y axis, the dashed line to the right y axis. Potentials
are referenced to SCE.
onto the SWNT surface. In particular, the spectrum of 1 is
dominated by the UV characteristics of pyrene with a set of
maxima at 265, 277, 300, 313, 328, and 345 nm, whereas the
[60]fullerene transitions appear only as an overall broaden-
ing. The broadening starts essentially in the UV region and
tails out inthe visible region. Relative to a pyrene reference
(i.e., 1-pyrenemethanol) no significant perturbation of the
absorption characteristics are seen. This finding corrobo-
rates the lack of substantial electronic interactions between
the two p-systems in 1. For a suspension of 1·SWNT, apart
from the pyrene features, the characteristic van Hove singu-
larities of SWNT are discernable in the visible/near-IR
region up to 360 nm, and the p–p* transition of pyrene
dominates the spectrum. Collectively, these observations
confirm the presence of both constituents, SWNT and 1, in
the form of a novel p-complex.
moiety as described above, significant changes in the redox
properties of the fullerene derivative. A general broadening
of the voltammetric peaks is observed with respect to the
model. This may be attributed to joint mass-transport and
charge-transfer kinetics effects derived from association of 1
to the SWNT: both a smaller diffusion coefficient and hin-
dering of electronic interaction between the fullerene deriv-
ative and the electrode surface might, in fact, explain the
overall change in the CV morphology of 1 uponassociation
with the SWNT. Importantly, a dramatic change in the
anodic behavior of the fullerene derivative was observed
uponits itneractionwith SWNT: the oxidationpeak at
0.98 V inthe CV curve of 1·SWNT contrasts with peak A of
1 because 1) it involves only one electron (compared to two
electrons for 1) and 2) it is shifted relative to 1 by about
200 mV towards less-positive potentials. Both effects may be
ascribed to the electronic interaction of pyrene with the
SWNT p-system that would, as observed recently in a simi-
lar system,[25] make oxidationof the pyrene moiety easier.
Inparticular, the measured negative shift of 200 mV of the
pyrene+/pyrene redox potential would correspond to an
~20 kJmolÀ1 stabilizationof the pyrene radical cationby its
interaction with the SWNT. By contrast, the fullerene-cen-
Additional proof for 1·SWNT interactions came from
A
be discussed first (Figure 7).
Inline with previous reports, the photoreactivity of such
hybrids is dominated by the intramolecular transduction of
singlet excited-state energy.[26] Relative to 1-pyrenemethanol
(fluorescence quantum yield=0.1), strong pyrene fluores-
cence (375, 385, 395, and 418 nm) quenching (fluorescence
quantum yield=0.03) inthe UV-visible regionis linked to
an activation of [60]fullerene fluorescence (698 nm) in the
visible/near-IR region (i.e., ~3”10À4). In 1, anexcitation
spectrum of [60]fullerene fluorescence tracks the pyrene ab-
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M. Maggini, D. M. Guldi, F. Paolucci, M. Prato et al.
Figure 8. Differential absorption spectrum (visible and near-IR) obtained
upon nanosecond flash photolysis (355 nm) of 1-pyrenemethanol (solid
line), conjugate 1 (dashed line) and 1·SWNT (dotted line) in nitrogen-sa-
turated DMF with a 50 ns time delay at RT.
Figure 7. RT fluorescence spectra of 1-pyrenemethanol, derivative 1, an d
1·SWNT inDMF with matching absorption, similar to that shownin
Figure 6, at the 329 nm excitation wavelength.
sorption spectrum and, hence, validates the energy-transfer
process. The less-than-unity efficiency for the intramolecular
singlet–singlet energy transfer could be rationalized by size-
able donor–acceptor separation ranging from 10 to about
17 Š because of the conformational freedom of the alkyl
spacer between the [60]fullerene and pyrene moieties. The
corresponding 1·SWNT photoexcitation into the pyrene p–
p* transition at 328 nm results in 1) a further ~7-fold
quenching of the pyrene-centered fluorescence (i.e., 4”
10À3) and 2) a nearly complete elimination of the [60]fuller-
ene-centered fluorescence (i.e., <3”10À5). Such behavior
The triplet–triplet absorptions of pyrene, which are seen
for 1-pyrenemethanol at around 420 nm, are entirely lacking
in 1, regardless of the time delay. The [60]fullerene triplet
converts slowly to the ground state with lifetimes that are
typically around 20 ms. Such reactivity is found in nonpolar
toluene, medium-polar THF, and polar DMF. In contrast,
uponprobing 1·SWNT no appreciable features are seen at
all on the nanosecond scale. This again attests to SWNT-in-
duced processes that compete with [60]fullerene in the excit-
ed-state deactivationof pyrene.
indicates
a
competitive deactivation—SWNT versus
[60]fullerene—of the pyrene singlet-excited state. In this
context, it is important to note that pyrene, which is either
surface-immobilized onto SWNT (i.e., noncovalent p–p in-
teractions) or linked to SWNT (i.e., covalent spacers), gives
rise to strong fluorescence quenching. In other words, the
fluorescence of pyrene and [60]fullerene are excellent
probes for detecting electronic interactions between SWNT
and pyrene.
Similarly, in time-resolved fluorescence experiments we
found that the long-lived pyrene p–p* fluorescence lifetime
(~50 ns) is shortened in 1 (17 ns), whereas that of [60]fuller-
ene remains at 1.5Æ0.2 ns, essentially unchanged relative to
appropriate [60]fullerene references. On the other hand, in
1·SWNT, SWNT-induced deactivation of the pyrene fluores-
cence could not be detected within the instrumental time
resolutionof our apparatus (i.e., 100 ps).
For independent confirmation of the electronic interac-
tions we used nanosecond transient spectroscopy with pho-
toexcitation at 337 nm, which corresponds to a wavelength
of predominant pyrene absorption (i.e., >95%). Inlien
with our fluorescence-based conclusion, the only discernable
features inconjugate 1 are those of the long-lived [60]fuller-
ene triplet, that is, a transient maximum at around 700 nm[27]
(Figure 8).
Microscopic characterization: Transmission electron micros-
A
sample. Two representative images, shown in Figure 9,
reveal high aspect-ratio objects that appear throughout the
scanned regions. The mean length of these objects is typical-
ly on the order of several microns, and their diameters
range between a few nanometers and several tens of nano-
meters. Notably, Figure 9b shows very well-dispersed
SWNT. Inthis regard, 1·SWNT is different from pristine
HiPCO SWNT, inwhich aggregationprevents the observa-
tionof individual SWNTs or very thinbundles.
We also investigated 1·SWNT by atomic force microscopy
(AFM). The sample was prepared by spincoating ona sili-
conwafer from a DMF solutionand revealed the coexis-
tence of individual SWNT (diameters of around 1.2 nm) of
several hundred nanometers in length (Figure 10) and well-
dispersed thin bundles of SWNT. However, we failed to con-
firm microscopically the presence of fullerene moieties on
the SWNT sidewalls. Considering that these AFM pictures
are virtually identical to those obtained upon dispersing
SWNT with amphiphilic pyrene derivatives,[28] the current
homogeneous dispersions are consistent with surface-immo-
bilizationof 1.
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Single-Wall Carbon Nanotubes
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transient spectroscopy that showed competition between
SWNT-induced processes and [60]fullerene in the excited-
state deactivation of pyrene. Use of this nanoscale system
for applications in photovoltaics and molecular electronics is
currently underway.
Experimental Section
Materials: [60]Fullerene was purchased from Bucky USA (99.5%),
HiPCO SWNT was from CNI (www.cnanotech.com). 1-Pyrenebutyric
acid and all other reagents were used as purchased from Sigma-Aldrich
and Fluka. CH2Cl2, THF, and DMF employed for UV/Vis and fluores-
cence measurements were spectrophotometric-grade solvents. Solvents
employed for electrochemical measurements (CH2Cl2 purum, Fluka and
THF, LiChrosolv, Merck) were treated according to procedures described
elsewhere.[22,29] 3,5-Bis(hydroxymethyl)phenol[16] and derivative 2[17] were
prepared as previously described. Tetrabutylammonium hexafluorophos-
phate (TBAH, puriss., Fluka) was used as supporting electrolyte as re-
ceived. The original suspension of 1·SWNT inTHF was dried firstly
under an argon flow to give a black powder that was dispersed in CH2Cl2
and used for the electrochemical characterization.
Instrumentation: Columnchromatography was performed by using silica
gel MN 60 (70–230 Mesh) from Macherey-Nagel. 1H (250.1 MHz) and
13C (62.9 MHz) NMR spectra were recorded by using a Bruker AC-F 250
spectrometer. The ESI-MS spectra were recorded by using a Thermo Fin-
nigan AQA LC/MS: spray voltage À4 kV; capillary voltage À10 V; capil-
lary temperature 1808C; nitrogen as nebulizing gas. The samples were
dissolved in methanol containing 1% trifluoroacetic acid. Elemental
analyses were provided by the facility at the Department of Chemical
Sciences at the University of Padova.
Figure 9. TEM images of 1·SWNT from a DMF solution.
Nanosecond laser flash photolysis ex-
periments were performed by using a
Quanta-Ray CDR Nd:YAG system
(6 ns pulse width) in a front-face exci-
tationgeometry. Fluorescecne life-
times were measured by using a laser
strope fluorescence lifetime spec-
trometer (Photon Technology Inter-
national) with 337 nm laser pulses
from a nitrogen laser fiber coupled to
a lens-based T-formal sample com-
partment equipped with
a strobo-
scopic detector. Emissionspectra
were recorded by using a FluoroMax-
3
(Horiba Company). The experi-
Figure 10. AFM images of 1·SWNT on silicon wafer. The images show the small bundles of nanotubes (left)
and an individual tube (middle). The picture on the right indicates the diameter of the single nanotube.
ments were performed at RT. The
cyclic voltammetry experiments were
performed in
a one-compartment
electrochemical cell of airtight
design, with high-vacuum glass stopcocks fitted with either Teflon or
Viton (DuPont) O-rings to prevent contamination by grease. The connec-
tions to the high-vacuum line and to the Schlenk tube containing the sol-
vent were obtained by spherical joints also fitted with Teflon O-rings.
The cell, containing the supporting electrolyte and the electroactive com-
pound, was dried under vacuum at 363 K for at least 48 h. Afterwards,
the solvent was distilled by a trap-to-trap procedure into the electro-
chemical cell just prior to performing the electrochemical experiment.
The pressure measured inthe electrochemical cell prior to performing
the trap-to-trap distillationof the solvetn was typically (1.0–2.0)”
10À5 mbar. The working electrode was a Pt disc ultramicroelectrode (di-
ameter, 125 mm) sealed in glass. The counterelectrode consisted of a plat-
inum spiral, and the quasireference electrode was a silver spiral. The qua-
sireference electrode drift was negligible for the time required by a single
experiment. Both the counter and the reference electrodes were separat-
ed from the working electrode by ~0.5 cm. Potentials were measured
with respect to the decamethylferrocene standard. E1/2 values correspond
Conclusion
We have shown that [60]fullerene–pyrene conjugate 1 ena-
bled the homogeneous dispersion of purified HiPCO SWNT
in organic solvents. Cyclic voltammetry experiments and
photophysical and microscopic characterization of the dis-
persed material supports the view that p–p interactions be-
tween SWNT and the pyrene moiety govern the association
of 1 with the sidewalls of SWNT, although we were unable
to visualize individual fullerene moieties by appropriate
TEM analysis. In particular, the measured 200 mV positive
shift of pyrene+/pyrene redox potential is indicative of a
direct electronic interaction of pyrene with the SWNT p-
system. This conclusion was corroborated by nanosecond
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M. Maggini, D. M. Guldi, F. Paolucci, M. Prato et al.
to (Epc+Epa)/2 from CV. Voltammograms were recorded by using a
home-made fast potentiostat controlled by an AMEL Model 568 func-
tiongenerator. Data acquisitionwas performed by using a Nicolet Model
3091 digital oscilloscope interfaced to a PC. Digital simulations of the
cyclic voltammetric curves were conducted by using the DigiSim 3.0 soft-
ware by Bioanalytical Systems.
[60]Fullerene–pyrene dyad 1: A solutionof HOBT (12.8 mg, 0.09 mmol),
EDCI (18.1 mg, 0.09 mmol), and 1-pyrene butyric acid (25.0 mg,
0.09 mmol) inCH 2Cl2 (50 mL) was stirred for 15 minand thenadded
dropwise to a suspension of 7 (100.0 mg, 0.08 mmol) and 4-methylmor-
pholine (10.4 ml, 0.09 mmol) inCH Cl2 (15 mL) at 08C. After 20 min, the
2
mixture was washed with water (2”20 mL), dried over MgSO4, and con-
centrated under reduced pressure. The crude product was purified by
Bisdiol 4: K2CO3 (1.5 g, 15.3 mmol) was added to a solutionof derivative
flash columnchromatography (SiO
, eluent: toluene/AcOEt/MeOH
2
2
(804.4 mg, 3.4 mmol) and 3,5-bis(hydroxymethyl)phenol (520.0 mg,
5:4:1) affording 108 mg (96%) of 1 as a brown-red solid material.
3.4 mmol) in acetone (100 mL), and the suspension was kept overnight at
reflux temperature. After cooling to RT, the salts were filtered and
washed with cold ethanol. The filtrate was evaporated under reduced
pressure and the residue, dissolved in CHCl3 (50 mL), was washed with
water (2”35 mL). The organic phase, dried over MgSO4, was concentrat-
ed under reduced pressure to give 960 mg (91%) of 4 as a clear, yellow
1H NMR (250 MHz, CDCl3, 258C, TMS): d=8.40–7.80 (m, 9H; Ph), 7.10
(s, 1H; Ph), 6.71 (s, 2H; Ph), 5.72 (brs, 1H; NH), 5.67 (d, 2J
ACHTREUNG
12.8 Hz, 2H; CH2), 5.07 (d, 2J
4H; CH2), 4.01 (t, 3J
ACHTREUNG
AHCTREUNG
ACHTREUNG
7.1 Hz, 6H; CH3); 13C NMR (62.9 MHz, CDCl3, 258C, TMS): d=177.78,
172.92, 162.85, 158.638, 145.99, 145.69, 145.66, 145.59, 145.30, 145.15,
145.00, 144.53, 144.36, 144.24, 144.12, 143.90, 143.69, 143.50, 143.25,
143.00, 142.18, 141.22, 141.00, 139.87, 138.17, 137.49, 136.19, 135.83,
135.73, 135.52, 134.67, 131.36, 130.84, 129.96, 129.92, 128.74, 128.70,
127.45, 127.39, 127.32, 126.73, 126.70, 125.86, 125.82, 125.05, 124.93,
124.89, 124.79, 123.32, 123.23, 115.42, 112.27, 70.60, 67.24, 66.21, 63.27,
49.18, 36.05, 32.66, 30.92, 27.35, 14.16 ppm; IR (KBr): n˜ =3426, 2973,
1747, 1671, 1600, 1509, 1460, 1368, 1328, 1297, 1233, 1207, 1170, 1099,
1057, 1018, 843, 704, 549, 525 cmÀ1; UV/Vis (CH2Cl2): lmax (e)=220.0
(114463), 234.4 (263371), 244.0 (323675), 265.6 (232328), 276.8 (236551),
313.6 (84216), 328.0 (116411), 344.0 (132947 molÀ1 m3 cmÀ1); elemental
analysis calcd (%) for C101H39NO10 (1426): C 85.05, H 2.76, N 0.98;
found: C 82.77, H 2.50, N 0.91.
1
oil. H NMR (250 MHz, CDCl3, 258C, TMS): d=6.90 (s, 1H; Ph), 6.81 (s,
2H; Ph), 4.64 (s, 2H; OH), 4.62 (s, 4H; CH2), 4.00 (t, 3J
(H,H)=5.8 Hz,
U
2H; CH2), 3.27 (m, 2H; CH2), 1.94 (m, 2H; CH2), 1.42 ppm (s, 9H;
CH3); 13C NMR (62.9 MHz, CDCl3, 258C, TMS): d=158.90, 142.78,
118.30, 117.49, 111.77, 64.46, 64.38, 30.80, 29.36, 28.29, 27.57 ppm; IR
(KBr): n˜ =3350, 2976, 2932, 2874, 1756, 1688, 1597, 1523, 1453, 1391,
1366, 1250, 1164, 1055, 911, 850, 779, 731 cmÀ1
; ESI-MS: m/z: 334
[M+Na]+.
Bismalonate 5: Ethyl malonyl chloride (416.0 ml, 3.70 mmol), previously
dissolved inCH 2Cl2 (25 mL), was slowly added at 08C to a solutionof
4
(460.0 mg, 1.48 mmol) and TEA (515.0 mL, 3.70 mmol) inCH 2Cl2
(75 mL). The solutionwas allowed to warm to RT over a period of
30 min, and was then stirred at that temperature for 4 h. The mixture was
washed with a saturated aqueous NaHCO3 solution(2”30 mL), then
with water (2”50 mL), dried over MgSO4, and concentrated under re-
duced pressure. The crude product was purified by flash columnchroma-
tography (SiO2, eluent: CHCl3 and then CHCl3/MeOH 9:1) affording
447 mg (56%) of 5 as a clear oil. 1H NMR (250 MHz, CDCl3, 258C,
TMS): d=6.90 (s, 1H; Ph), 6.84 (s, 2H; Ph), 5.12 (s, 4H; CH2), 4.19 (q,
Acknowledgements
Funding from MIUR (GR/No. PRIN2004035502, RBAU017S8R,
RBNE01P4JF, RBNE019NKS, RBNE033KMA), ITM-CNR, the Euro-
3J
C
ACHTREUNG
AHCTREUNG
A
7.1 Hz, 6H; CH3); 13C NMR (62.9 MHz, CDCl3, 258C, TMS): d=166.31,
159.15, 155.93, 137.15, 119.92, 114.04, 66.60, 61.56, 41.48, 28.35,
13.98 ppm; IR (KBr): n˜ =3403, 2979, 2939, 1733, 1600, 1515, 1458, 1367,
1331, 1299, 1250, 1032, 852, 777, 713, 685 cmÀ1; ESI-MS: m/z: 540 [M]+
and 563 [M+Na]+.
gemeinschaft (SFB 583), FCI, and the Office of Basic Energy Sciences of
the U.S. Department of Energy are gratefully acknowledged.
[1] a) M. J. OꢁConnel, S. M. Bachilo, C. B. Huffmann, V. C. Moore,
M. S. Strano, E. H. Haroz, K. L. Rialon, P. J. Boul, W. H. Noon, C.
Kittrell, J. Ma, R. H. Hauge, R. B. Weisman, R. E. Smalley, Science
2002, 297, 593; b) M. S. Dresselhaus, G. Dresselhaus, P. C. Eklund,
Science of Fullerenes and Carbon Nanotubes, Academic Press, New
York, 1996; c) A. C. Dillon, T. Gennet, K. M. Jones, J. L. Alleman,
P. A. Parilla, M. J. Heben, Adv. Mater. 1999, 11, 1354; d) S. Paulson,
A. Helsen, N. M. Buongiorno, R. M. Taylor, M. Falvo, R. Superfine,
S. Washburn, Science 2000, 290, 1742; e) L. Sun, R. M. Crooks, J.
Am. Chem. Soc. 2000, 122, 12340; f) B. Z. Tang, H. Xu, Macromole-
cules 1999, 32, 2569; g) P. M. Ajayan, O. Zhou in Carbon Nanotubes:
Synthesis, Structure, Properties, and Applications, Vol. 80 (Eds.: M. S.
Dresselhaus, G. Dresselhaus, P. Avouries), Springer-Verlag, Heidel-
berg, 2001; h) A. Hirsch, Angew. Chem. 2002, 114, 1933; Angew.
Chem. Int. Ed. 2002, 41, 1853; i) D. Tasis, N. Tagmatarchis, V. Geor-
gakilas, M. Prato, Chem. Eur. J. 2003, 9, 4000; j) P. M. Ajayan,
Chem. Rev. 1999, 99, 1787.
[2] a) H. J. Dai, Acc. Chem. Res. 2002, 35, 1035; b) J. T. Hu, T. W.
Odom, C. M. Lieber, Acc. Chem. Res. 1999, 32, 435; c) B. Vigolo, A.
Penicaud, C. Coulon, C. Sauder, R. Pailler, C. Journet, P. Bernier, P.
Poulin, Science 2000, 290, 1331; d) M. Ouyang, J.-L. Huang, C. M.
Liber, Acc. Chem. Res. 2002, 35, 1035.
[3] a) P. M. Ajayan, L. S. Schadler, C. Giannaris, A. Rubio, Adv. Mater.
2000, 12, 750; b) R. J. Chen, Y. Zhang, D. Wang, H. Dai, J. Am.
Chem. Soc. 2001, 123, 3838; c) R. Bandyopadhyaya, E. Nativ-Roth,
O. Regev, R. Yerushalmi-Rozen, Nano Lett. 2002, 2, 25; d) P. Avou-
ris, Acc. Chem. Res. 2002, 35, 1026.
[60]Fullerene bisadduct 6: DBU (622.0 ml, 4.17 mmol) was added at RT
to
a
solutionof [60]fullereen (500 mg, 0.69 mmol),
I
(353.0 mg,
2
1.39 mmol), and bismalonate 5 (371 mg, 0.69 mmol) intoluene (500 mL).
The solution was stirred at that temperature for 3 h, then concentrated
under reduced pressure. The crude product was purified by flash column
chromatography (SiO2, eluent: toluene then toluene/AcOEt 7:3) and
crystallized from CHCl3/hexane affording 400 mg (46%) of 6 as a dark-
red solid. 1H NMR (250 MHz, CDCl3, 258C, TMS): d=7.12 (s, 1H; Ph),
6.80 (s, 2H; Ph), 5.80 (d, 2J=12.8 Hz, 2H; CH2), 5.14 (d, 2J=12.8 Hz,
2H; CH2), 4.60–4.20 (m, 4H; CH2), 4.07 (t, 3J
3.33 (m, 2H; CH2), 2.00 (m, 2H; CH2), 1.46 (s, 9H; CH3), 1.36 ppm (t, J-
(H,H)=7.1 Hz, 6H; CH3); 13C NMR (62.9 MHz, CDCl3, 258C, TMS):
A
3
ACHTREUNG
d=162.91, 162.82, 158.87, 148.72, 147.55, 147.50, 147.34, 146.12, 146.09,
145.77, 145.66, 14538, 145.21, 145.06, 144.62, 144.28, 144.19, 143.99,
143.78, 143.61, 143.30, 143.28, 143.06, 142.33, 141.27, 141.06, 139.97,
138.12, 136.27, 135.87, 129.00, 128.53, 128.20, 115.36, 112.35, 70.65, 67.27,
63.34, 31.55, 28.41, 22.63, 14.14, 14.10 ppm; IR (KBr): n˜ =3431, 2973,
1748, 1715, 1600, 1502, 1460, 1365, 1460, 1365, 1328, 1297, 1233, 1206,
1168, 1101, 1057, 1018, 859, 732, 702, 549, 525 cmÀ1; UV/Vis (CH2Cl2):
lmax (e)=210.4 (61331), 218.4 (67553), 231.2 (121487), 256.8 nm
(144807 molÀ1 m3 cmÀ1); elemental analysis calcd (%) for C68H17NO3
(896): C 91.17, H 1.91, N 1.56; found: C 90.43, H 1.97, N 1.60.
[60]Fullerene derivative 7: A solutionof bisadduct 6 (200 mg, 0.16 mmol)
and trifluoroacetic acid (2.5 mL, 0.03 mmol) in dry CH2Cl2 (50 mL) was
stirred at RT for 30 min. The mixture was concentrated under reduced
pressure to afford the unprotected product 7 as a brownish powder in
nearly quantitative yield. The crude product was used for the next step
without further purification.
[4] a) V. Georgakilas, K. Kordatos, M. Prato, D. M. Guldi, M. Holzing-
er, A. Hirsch, J. Am. Chem. Soc. 2002, 124, 760; b) Y.-P. Sun, K. Fu,
3982
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 3975 – 3983

Single-Wall Carbon Nanotubes
FULL PAPER
Y. Lin, W. Huang, Acc. Chem. Res. 2002, 35, 1096; c) D. M. Guldi,
G. M. A. Rahman, F. Zerbetto, M. Prato, Acc. Chem. Res. 2005, 38,
871; d) N. Tagmatarchis, M. Prato, J. Mater. Chem. 2004, 14, 437;
e) C. A. Dyke, J. M. Tour, Chem. Eur. J. 2004, 10, 812; f) V. Georga-
kilas, D. Voulgaris, E. Vꢂzquez, M. Prato, D. M. Guldi, A. Kuko-
vecz, H. Kuzmany, J. Am. Chem. Soc. 2002, 124, 14318; g) D. M.
Guldi, M. Marcaccio, D. Paolucci, F. Paolucci, N. Tagmatarchis, D.
Tasis, E. Vꢂzquez, M. Prato, Angew. Chem. 2003, 115, 4338; Angew.
Chem. Int. Ed. 2003, 42, 4206; h) D. M. Guldi, M. Holzinger, A.
Hirsch, V. Georgakilas, M. Prato, Chem. Commun. 2003, 1130; i) V.
Georgakilas, N. Tagmatarchis, D. Pantarotto, A. Bianco, J.-P. Briand,
M. Prato, Chem. Commun. 2002, 3050; j) M. Melle-Franco, M. Mar-
caccio, D. Paolucci, F. Paolucci, V. Georgakilas, D. M. Guldi, M.
Prato, F. Zerbetto, J. Am. Chem. Soc. 2004, 126, 1646; k) G. M. A.
Rahman, D. M. Guldi, R. Cagnoli, A. Mucci, L. Schenetti, L. Vac-
cari, M. Prato, J. Am. Chem. Soc. 2005, 127, 10051; l) D. M. Guldi,
G. M. A. Rahman, M. Prato, N. Jux, S. Qin, W. Ford, Angew. Chem.
2005, 117, 2051; Angew. Chem. Int. Ed. 2005, 44, 2015; m) D. M.
Guldi, G. M. A. Rahman, N. Jux, N. Tagmatarchis, M. Prato, Angew.
Chem. 2004, 116, 5642; Angew. Chem. Int. Ed. 2004, 43, 5526.
[5] a) B. W. Smith, M. Monthioux, D. E. Luzzi, Nature 1998, 396, 323;
b) B. W. Smith, D. E. Luzzi, Chem. Phys. Lett. 2000, 321, 169; c) N.
Nakashima, Y. Tanaka, Y. Tomonari, H. Murakami, H. Kataura, T.
Sakaue, K. Yoshikawa, J. Phys. Chem. B 2005, 109, 13076.
[6] a) K. Hirahara, K. Suenaga, S. Bandow, H. Kato, T. Okazaki, H. Shi-
nohara, S. Iijima, Phys. Rev. Lett. 2000, 85, 5384; b) T. Shimada, T.
Okazaki, R. Taniguchi, T. Sugai, H. Shinohara, K. Suenaga, H.
Ohno, S. Mizuno, S. Kishimoto, T. Mizutani, Appl. Phys. Lett. 2002,
81, 4067; c) Y. Maeda, S. Kimura, Y. Hirashima, M. Kanda, Y. Lian,
T. Wakahara, T. Akasaka, T. Hasegawa, H. Tokumoto, T. Shimizu,
H. Kataura, Y. Miyauchi, S. Maruyama, K. Kobayashi, S. Nagase, J.
Phys. Chem. B 2004, 108, 18395.
[7] Y.-B. Sun, Y. Sato, K. Suenaga, T. Okazaki, N. Kishi, T. Sugai, S.
Bandow, S. Iijima, S. Shinohara, J. Am. Chem. Soc. 2005, 127, 17972.
[8] a) D. A. Britz, A. N. Khlobystov, J. Wang, A. S. OꢁNeil, M. Poliakoff,
A. Ardavan, G. D. Briggs, Chem. Commun. 2004, 176; b) D. A.
Britz, A. N. Khlobystov, K. Porfyrakis, A. Ardavan, G. D. Briggs,
Chem. Commun. 2005, 37.
[12] G. Hummer, J. C. Rasaiah, J. P. Noworyta, Nature 2001, 414, 188.
[13] S. Okada, S. Saito, A. Oshiyama, Phys. Rev. Lett. 2001, 86, 3835.
[14] D. J. Hornbaker, S.-J. Kahng, S. Misra, B. W. Smith, A. T. Johnson,
E. J. Mele, D. E. Luzzi, A. Yazdani, Science 2002, 295, 828.
[15] J.-F. Nierengarten, V. Gramlich, F. Cardullo, F. Diederich, Angew.
Chem. 1996, 108, 2242; Angew. Chem. Int. Ed. Engl. 1996, 35, 2101,
and references therein.
[16] P. R. Ashton, D. W. Anderson, C. L. Brown, A. N. Shipway, J. F.
Stoddart, M. S. Tolley, Chem. Eur. J. 1998, 4, 781.
[17] B. Y. Lee, M. Miller, J. Org. Chem. 1983, 48, 24.
[18] S. Zhang, Y. Rio, F. Cardinali, C. Bourgogne, J.-L. Gallani, J.-F.
Nierengarten, J. Org. Chem. 2003, 68, 9787, and references therein.
[19] D. M. Guldi, G. N. A. Rahman, J. Ramey, M. Marcaccio, D. Paoluc-
ci, F. Paolucci, S. Qin, W. T. Ford, D. Balbinot, N. Jux, N. Tagma-
tarchis, M. Prato, Chem. Commun. 2004, 18, 2034.
[20] D. M. Guldi, G. M. A. Rahman, S. Qin, M. Tchoul, W. T. Ford, M.
Marcaccio, D. Paolucci, F. Paolucci, S. Campidelli, M. Prato, Chem.
Eur. J. 2006, 12, 2152.
[21] M. A. Herranz, F. Diederich, L. Echegoyen, Eur. J. Org. Chem.
2004, 2299.
[22] C. Bruno, I. Doubitski, M. Marcaccio, F. Paolucci, D. Paolucci, A.
Zaopo, J. Am. Chem. Soc. 2003, 125, 15738.
[23] C. Boudon, J.-P. Gisselbrecht, M. Gross, L. Isaacs, H. L. Anderson,
R. Faust, F. Diederich, Helv. Chim. Acta 1995, 78, 1334.
[24] D. M. Guldi, M. Marcaccio, F. Paolucci, D. Paolucci, J. Ramey, R.
Taylor, J. A. Burley, J. Phys. Chem. A 2005, 109, 9723.
[25] C. Ehli, G. M. A. Rahman, N. Jux, D. Balbinot, D. M. Guldi, F. Pao-
lucci, M. Marcaccio, D. Paolucci, M. Melle-Franco, F. Zerbetto, un-
published results.
[26] a) R. B. Martin, K. F. Fu, Y.-P. Sun, Chem. Phys. Lett. 2003, 375,
619; b) T. Gareis, O. Kothe, J. Daub, Eur. J. Org. Chem. 1998, 1549;
c) I. B. Martini, B. Ma, T. Da Ros, R. Helgeson, F. Wudl, B. J.
Schwartz, Chem. Phys. Lett. 2000, 327, 253; d) K. Kordatos, T.
Da Ros, M. Prato, C. Luo, D. M. Guldi, Monatsh. Chem. 2001, 132,
63; e) F. Hauke, A. Hirsch, S. Atalick, D. M. Guldi, Eur. J. Org.
Chem. 2005, 1741.
[27] D. M. Guldi, M. Prato, Acc. Chem. Res. 2000, 33, 695.
[28] D. M. Guldi, G. M. A. Rahman, N. Jux, D. Balbinot, U. Hartnagel,
N. Tagmatarchis, M. Prato, J. Am. Chem. Soc. 2005, 127, 9830.
[29] M. Carano, P. Ceroni, L. Mottier, F. Paolucci, S. Roffia, J. Electro-
chem. Soc. 1999, 146, 3357.
[9] R. S. Lee, H. J. Kim, J. E. Fischer, A. Thess, R. E. Smalley, Nature
1997, 388, 255.
[10] R. R. Meyer, J. Sloan, R. E. Dunin-Borkowski, A. I. Kirkland, M. C.
Novotny, S. R. Bailey, J. L. Hutchison, M. L. H. Green, Science 2000,
289, 1324.
[11] a) M. Kalbac, L. Kavan, M. Zukalova, L. Dunsch, J. Phys. Chem. B
2004, 108, 6275; b) L. H. Guan, K. Suenaga, Z. J. Shi, Z. N. Gu, S.
Iijima, Phys. Rev. Lett. 2005, 94, 045502.
Received: January 25, 2006
Published online: April 3, 2006
Chem. Eur. J. 2006, 12, 3975 – 3983
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3983