Fullerene nanowires: Self-assembled structures of a low-molecular-weight organogelator fabricated by the Langmuir-Blodgett method

Article abstract of DOI:10.1002/chem.200800493

Fullerene derivative C60TT, which is substituted with the low-molecular-weight organogelator tris(dodecyloxy)benzamide, formed nanowire structures on application of the Langmuir-Blodgett (LB) method. The surface morphology of the C60TT LB film was dependent on the holding time before deposition at a surface pressure of 5 mNm^-1; it changed from a homogeneous monolayer to a bilayer fibrous structure via a fibrous monolayer structure, which was estimated to have dimensions of 1.2 nm in height, 8nm in width, and 5-10 μm in length. From the structural and spectroscopic data, it is inferred that close packing of the fullerene moiety occurs along with intermolecular hydrogen bonding within the monolayer fibrous structure. The morphological changes in the LB film are explained kinetically by the Avrami theory, based on the decrease in the surface area of the monolayer at the air/water interface. The growth of the quasi-one-dimensional fibrous monolayer structures at holding times from 0 to 0.2 h is considered to be an interface-controlled process, whereas the growth of the quasi-one-dimensional bilayer fibrous structures from 0.2 to 18 h is thought to be a diffusion-controlled process.

Full text of DOI:10.1002/chem.200800493

FULL PAPER
DOI: 10.1002/chem.200800493
Fullerene Nanowires: Self-Assembled Structures of a Low-Molecular-Weight
Organogelator Fabricated by the Langmuir–Blodgett Method
Ryo Tsunashima,[a] Shin-ichiro Noro,[a] Tomoyuki Akutagawa,[a, b]
Takayoshi Nakamura,*[a, b] Hiroko Kawakami,[c] and Kazunori Toma[c]
Abstract: Fullerene derivative C60TT,
which is substituted with the low-mo-
lecular-weight organogelator tris(dode-
cyloxy)benzamide, formed nanowire
structures on application of the Lang-
muir–Blodgett (LB) method. The sur-
face morphology of the C60TT LB film
was dependent on the holding time
before deposition at a surface pressure
of 5 mNmꢀ1; it changed from a homo-
geneous monolayer to a bilayer fibrous
structure via a fibrous monolayer struc-
ture, which was estimated to have di-
mensions of 1.2 nm in height, 8 nm in
width, and 5–10 mm in length. From the
structural and spectroscopic data, it is
inferred that close packing of the full-
erene moiety occurs along with inter-
molecular hydrogen bonding within the
monolayer fibrous structure. The mor-
phological changes in the LB film are
explained kinetically by the Avrami
theory, based on the decrease in the
surface area of the monolayer at the
air/water interface. The growth of the
quasi-one-dimensional fibrous mono-
layer structures at holding times from 0
to 0.2 h is considered to be an inter-
face-controlled process, whereas the
growth of the quasi-one-dimensional
bilayer fibrous structures from 0.2 to
18 h is thought to be a diffusion-con-
trolled process.
Keywords:
fullerenes
·
gels
·
·
nanostructures
thin films
·
self-assembly
Introduction
tion of fullerenes[5] has ranged from fullerene dyads[7] and a
triad with porphyrin, showing photoinduced electron trans-
fer with long-lived charge separation, to practical materials
such as liquid crystals, in which a shuttlecock-shaped fuller-
ene is stacked one-dimensionally in a head-to-tail manner to
form a thermotropic hexagonal columnar phase.[8] While
naked [60]fullerene exhibits isotropic intermolecular interac-
tion as a result of its spherical shape, the liquid-crystal mate-
rials were constructed through self-assembly of modified
fullerene derivatives that exhibit anisotropic intermolecular
interactions and/or stacking of molecules.
Since the discovery of [60]fullerene[1] and its macroscale syn-
thesis,[2] researchers have identified a variety of exotic prop-
erties for the material, such as the existence of a supercon-
ducting transition at high temperature in alkali metal salts
of [60]fullerene,[3,4] and a large third-order nonlinear optical
response for thin films of [60]fullerene.[4] The remarkable
physical characteristics of these materials has prompted the
synthesis of a variety of fullerene derivatives for potential
application as functional materials.[5–8] Chemical modifica-
These self-assembly processes are attracting considerable
attention as a powerful tool for the construction of active
nanoscale components, which will be required for future ap-
plications such as nanoscale electronic circuits. In particular,
fiberlike assemblies will be important components in wiring
and other active parts. Fullerenes are promising candidates
for construction of such wiring materials, because they have
a high charge mobility and exhibit metallic conducting be-
havior on carrier doping.[9,10] However, [60]fullerene tends
to form two- or three-dimensional arrays in the aggregated
state, and there have been only a few reports on the fabrica-
tion of fullerene-based, quasi-one-dimensional, fiberlike
nanostructures.[11] To realize these nanostructures through
self-assembly processes, it is essential to employ an appro-
[a] Dr. R. Tsunashima, Dr. S.-i. Noro, Prof. Dr. T. Akutagawa,
Prof. Dr. T. Nakamura
Research Institute for Electronic Science
Hokkaido University, Sapporo 060-0812 (Japan)
Fax : (+81)11-706-4972
E-mail: tnaka@es.hokudai.ac.jp
[b] Prof. Dr. T. Akutagawa, Prof. Dr. T. Nakamura
CREST, Japan Science and Technology Agency (JST)
Kawaguchi 332-0012 (Japan)
[c] Dr. H. Kawakami, Dr. K. Toma
The Noguchi Institute
Tokyo 173-00030 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200800493.
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priate molecular design and fabrication technique. In the
present study, organogelators were adopted, and the LB
technique was applied to construct fullerene nanowires.
Self-assembled fibrous structures have been observed in
low-molecular-weight organogelators. In gels, fibrous struc-
tures become entangled to form three-dimensional net-
works,[12] which are constructed by self-assembly of gelators
through intermolecular interactions such as one-dimensional
hydrogen bonding. Several fullerene-based organogels have
been reported.[13] Cholesterol-appended [60]fullerene
showed gelation properties in dichloromethane.[13b] Modifi-
cation of [60]fullerene to obtain strong one-dimensional in-
termolecular interactions, as is observed for gelators, will
enable us to construct a quasi-one-dimensional array of
[60]fullerene.
An excellent technique for immobilization of self-assem-
bled nanostructures on solid substrates is the LB method.[14]
Although the LB method has been used to prepare two-di-
mensional molecularly thin films, quasi-one-dimensional
nanostructures have often been observed in LB monolay-
ers,[15–17] for example, when molecules exhibit strong aniso-
tropic intermolecular interactions. We have reported the for-
mation of nanowires based on an amphiphilic bis(tetrathia-
fulvalene)-substituted macrocycle on a mica substrate using
the LB method. As a result of one-dimensional p–p stacking
and intermolecular S···S interaction between the tetrathia-
fulvalene moieties, nanowire structures were formed in the
LB films.[16] In our investigations on LB films of organogela-
tors, we recently reported the fabrication of nanofiber struc-
tures of a derivative of 3,4,5-tris(dodecyloxy)benzamide
(ADT) on a solid substrate.[17] The molecule has an amphi-
philic property in addition to gelation ability, which allows
application of the LB method. In the LB films, fibrous struc-
tures with a height of 1.2 nm and a width of 50–100 nm were
observed. The LB methods provided molecularly thin films,
and therefore quasi-one-dimensional nanostructures with
molecular-scale thickness could be obtained on a solid sub-
strate.
organogelator framework;[17,18] therefore, fullerene-based fi-
brous structures with molecular thickness were expected in
the LB films. C60TT formed organogels with chloroform
and adopted a stable monolayer structure at the air/water
interface. Formation of nanowire structures was confirmed
by atomic force microscopy (AFM). A molecular model of
quasi-one-dimensional assembled structures was constructed
from structural and spectroscopic data. The Avrami theory
successfully explains the mechanism of nanowire formation
at the air/water interface.
Results and Discussion
Synthesis and cast film of C60TT: C60TT was synthesized
(Scheme 1, 1–7) through amidation of fulleropyrrolidine[19]
and N-{N-[3,4,5-tris(dodecyloxy)benzoyl]-4-aminobutyril}-6-
aminohexanoic acid (6). Treatment of N-triphenylmethylpyr-
rolidine-C60 with trifluoromethanesulfonic acid in pyridine
gave fulleropyrrolidine (7), which was directly treated with
6. C60TT thus obtained was purified by HPLC (chloro-
form). The C60TT is insoluble in common solvents such as
aliphatic alcohols, acetone, and hexane. An organogel was
formed by a chloroform solution of C60TT at 277 K.[20]
However, the cast film of C60TT did not exhibit a xerogel-
like structure. A layered grain structure, each layer of which
has a height of 6.0 nm, was observed in the AFM image of
the cast film fabricated from chloroform solution at room
temperature (see Supporting Information). From the XRD
measurement, a face spacing of 5.96 nm was confirmed (see
Supporting Information). Taking the length of the molecule
into account, the molecules formed multilayer structures in
each of the grain structures. Similar disklike structures have
been reported in a fullerene amphiphile in a film cast from
aqueous solution with a height 4–5 times larger than the
length of the molecule.[21]
Langmuir–Blodgett film of C60TT: Figure 1 shows the sur-
face pressure–area (p–A) isotherm of C60TT. The surface
pressure began to increase at around A=1.45 nm2. On fur-
ther compression, the surface pressure decreased at
8.6 mNmꢀ1, which suggests either collapse of the Langmuir
film or a phase transition. Langmuir films of C60TT were
transferred onto mica substrates by single withdrawal after
waiting for 0, 0.2, 1.5 or 18 h at a surface pressure of
5 mNmꢀ1.
Here we report on the fabrication of nanowire structures
of a newly synthesized fullerene-linked 3,4,5-tris(dodecylox-
y)benzamide derivative (C60TT) by the LB method. The
molecular structures of ADT and C60TT are shown here.
The 3,4,5-tris(dodecyloxy)benzamide moiety is an excellent
The AFM images of the LB films are shown in Figure 2.
The surface morphology is dependent on the holding time at
5 mNmꢀ1 before deposition. The transfer ratio of each film
was almost unity in all cases. At 0 h, a homogeneous mono-
layer with a thickness of 0.9 nm occupied the major part of
the surface. Fibrous structures with a height of 1.2 nm and a
width of 13 nm were also observed. Taking convolution ef-
fects into account (see Supporting Information),[22] the
actual width of the fibrous structures is 8 nm. The surface
coverage of the fibrous structure increased with increasing
holding time and became dominant at 0.2 h. These fibrous
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Fullerene Nanowires
FULL PAPER
brous structure. The fact that
the morphology of the films de-
posited on the solid substrate
did not change after standing
for one day suggests that the
morphological
changes
oc-
curred at the air/water interface
as a result of holding the Lang-
muir films at 5 mNmꢀ1.
The surface coverage of the
homogeneous
monolayer
(xLhomo) and the monolayer fi-
brous structure (xLfib) at the air/
water interface was estimated
from the surface area of the
Langmuir film and the height
of each structure (see Support-
ing Information). The values
were then compared with those
LB
homo
on a mica substrate (x
and
LB
x
for homogeneous monolay-
fib
er and monolayer fibrous struc-
ture, respectively), as estimated
from the AFM images after
0.2 h. The results are summar-
ized in Table 1. The surface
LB
fib
coverage x was estimated to
Scheme 1. Synthesis of C60TT. Z=benzyloxycarbonyl, WSC=water-soluble carbodiimide, HOBt=hydroxy-
benzotriazole.
be 0.4, which is much smaller
Figure 1. p–A isotherm of C60TT.
structures are considered to be of monolayer thickness,
based on the diameter of the fullerene. As such, we refer to
the fibrous structures as monolayer fibrous structures here-
after.
In the AFM image of the film deposited after 1.5 h, a fi-
brous structure with a height of 1.7 nm was observed. The
height was almost twice that of the homogeneous monolay-
er; this suggests a bilayer structure. The coverage of the bi-
layer fibrous structure increased with increased holding
time. From AFM observations, a transition between two
morphologies could be observed with increasing holding
time at the air/water interface. The first morphology was a
monolayer fibrous structure, and the second a bilayer fi-
Figure 2. AFM images (2”2 mm) of LB films on a mica substrate formed
by single withdrawal after 0, 0.2, 1.5, and 18 h waiting time at
5 mNmꢀ1
a
.
than that expected from the corresponding AFM image in
Figure 2 when the convolution effect is taken into account
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T. Nakamura et al.
Table 1. Surface area (SA) and surface coverage x of the homogeneous
monolayer (homo) and monolayer fibrous structure (fib) estimated from
AFM images (LB) and the surface area at the air/water interface (L) at
0.2 h.
ꢀ
relative to the C H stretching band. In the region from
1600–1700 cmꢀ1 for the 1 mm solution, the band observed at
1660 cmꢀ1 was assigned as a free C=O vibrational band
based on previous reports.[24b–i] This free C=O band de-
creased with increasing concentration. At the same time, a
new band at 1640 cmꢀ1 appeared and increased, and this was
assigned as a hydrogen-bonding C=O band.[24b–i] In the
region of 3100–3500 cmꢀ1 in the 1 mm solution, two bands at
3322 and 3450 cmꢀ1 were assigned to free and hydrogen-
LB
homo
LB
fib
Holding
time [h]
SA [nm2]
xLhomo
x
xLfib
x
0.2
1.29
0.7
0.6
0.3
0.4
LB
fib
[24c–i]
and xLfib values
bonding N H vibrational bands, respectively.
With in-
ꢀ
ꢀ
(see Supporting Information). The x
showed good correspondence, that is, the structures of the
Langmuir film at the air/water interface and the LB film on
the solid substrate are similar. In addition, the area per mol-
ecule in the monolayer fibrous structure at the air/water in-
terface was calculated to be 1.0 nm2, which corresponds to
the cross-sectional area of naked [60]fullerene[23] and sug-
gests close packing of fullerene moieties in the monolayer fi-
brous structures.
creasing concentration, the hydrogen-bonding N H band
showed a redshift to 3295 cmꢀ1 with increased intensity. In
addition, a new band appeared at 3377 cmꢀ1 in the 10 mm
ꢀ
solution, which was assigned to the hydrogen-bonding O H
vibrational mode.[24a,k] The series of intensity increases of the
ꢀ
ꢀ
hydrogen-bonding C=O, N H, and O H bands with increas-
ing concentration indicates an increase in the proportion of
hydrogen-bonded species. The bands observed for the gel
state were assigned to hydrogen-bonding C=O (1632 and
1640 cmꢀ1), N H (3277 and 3295 cmꢀ1), and O H
ꢀ
ꢀ
FTIR and UV/Vis spectroscopy of C60TT and ADT: IR
spectroscopy is a powerful technique for the characteriza-
tion of intermolecular interactions.[24] A large number of
studies of intermolecular interactions in molecular assem-
blies, such as thin films, gels, and liquid crystals, have been
reported.[24b,d–i] Intermolecular interactions in the assembled
structures of C60TT were investigated by IR spectroscopy.
C60TT can form a gel at lower temperatures, so it was diffi-
cult to investigate details of physical and structural proper-
ties of the gel by IR spectroscopy. However, as C60TT is
composed of ADT and [60]fullerene, the structural details of
ADT were characterized and compared with those of LB
films of C60TT. ADT forms stable orgnanogels at room
temperature with, for example, CCl4.[17]
(3377 cmꢀ1). Compared with those of the 10 mm solution,
ꢀ
the bands for free C=O and N H almost disappeared, and
the hydrogen-bonding C=O and N H bands split into two
different bands. This indicates the existence of two different
types of hydrogen-bonded C=O and N H species in the gel.
From the relationship between the N···O distance and the
wavenumber of the C=O vibrational band,[24c] they were es-
timated as 2.891 (1640) and 2.865 Š (1632 cmꢀ1). These re-
sults indicate that the main driving force for gel formation is
intermolecular hydrogen bonding between amide moieties
ꢀ
ꢀ
ꢀ
and between terminal O H groups.
Figure 3b shows IR spectra of the LB film deposited after
holding for 0.2 h at 5 mNmꢀ1 and the cast film of C60TT.
ꢀ
Figure 3a shows IR spectra for solutions of ADT in CCl4
(1–10 mm) and the ADT gel. Once the 10 mm solution was
cooled to 277 K, gelation occurred and the gel was stable at
room temperature. The band observed at 2855 cmꢀ1 (see
The C=O and N H bands of the LB film were observed at
1635 and 3255 cmꢀ1, respectively. In the cast film, these
bands appeared at 1641 and 3290 cmꢀ1, respectively. Al-
though these bands were assigned to hydrogen-bonding C=
ꢀ
ꢀ
Supporting Information) was assigned to the C H stretching
O and N H bands, the bands in the LB films were observed
mode of ADT.[24i] All spectra taken in CCl4 were normalized
at slightly lower wavenumbers than those in the cast film.
This results from the difference in the N···O distances be-
tween adjacent molecules in each of the films. The relation-
ship of the N···O distances and the wavenumbers of the C=
O vibration bands[24c] suggests that stronger hydrogen bonds
are formed in the LB film than in the cast film. Since the
shape of the assembled structures is generally governed by
intermolecular interactions, these differences in hydrogen
bonding are responsible for the different surface morpholo-
ꢀ
gies of the LB and cast films. The C=O and N H bands of
the LB film of C60TT were observed at similar or lower
wavenumber than those of the ADT gel, that is, C60TT in
the LB film forms strong hydrogen bonds comparable to
those in the ADT gel.
The fullerene moieties showed typical absorption bands
due to overlap of adjacent p orbitals in the UV/Vis region.[4]
In the UV/Vis region (see Supporting Information), a p–p*
transition of the fullerene moiety was observed at 30”103 to
32”103 cmꢀ1, in addition to a broad shoulder around 22”
Figure 3. FTIR spectra in the ranges 3100–3500 cmꢀ1 and 1600–1700 cmꢀ1
of a) ADT in CCl4 solution (1, 2, 4, 6, 8, 10 mm) and CCl4 gel (10 mm)
and b) cast and 40-layer LB films of C60TT. The CCl4 gel spectra were
reduced by one-half (3100–3500 cmꢀ1) and one-quarter (1600–1700 cmꢀ1
for ease of comparison.
)
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Fullerene Nanowires
FULL PAPER
103 cmꢀ1. The latter band is related to intermolecular inter-
action between adjacent fullerene moieties.[4]
Thus, the IR and UV/Vis spectra indicate the existence of
intermolecular hydrogen-bonding and p–p interactions be-
tween the fullerene moieties. From the AFM images, the
monolayer fibrous structures were estimated to be 1.2 nm
high and 8 nm wide. Close packing of the fullerene moieties
in the monolayer fibrous structures was also suggested by
the p–A isotherm. From these results, we can infer a possi-
ble molecular model for the monolayer fibrous structures
(Figure 4). Close packing of the fullerene moieties through
Figure 5. Time dependence of the area per molecule at a surface pressure
of 5 mNmꢀ1 (A5) for the C60TT Langmuir film (right axis). The red cir-
cles show the observed normalized area A* (see text). The dotted lines
show a linear fit of ln(lnA*) against lnt (left axis).
G
the Avrami index n is obtained from the slope of the ln-
(lnA*) versus lnt plot.
AHCTREUNG
n
*
A
¼ expðꢀkt Þ
ð2Þ
Figure 4. Schematic molecular model of the monolayer fibrous structure
(C gray, N red, O blue).
The Avrami index n is generally expressed by Equa-
tion (3),in which the parameters h, k, and l relate to the pro-
cesses of nucleation, crystal growth, and growth habit, re-
spectively.[25–27]
p–p interactions is expected in the film plane (Figure 4a).
The side chains should be aligned through intermolecular
hydrogen bonding between amide groups of the alkyl amide
moiety adjacent to the pyrrolidine moiety (Figure 4b).
Taking the height (1.2 nm) of the monolayer fibrous struc-
ture into account, it is considered that the long axis of the
molecule is tilted with respect to the axis normal to the sub-
strate.
n ¼ h þ kl
ð3Þ
From t=0–0.2, n was estimated to be 2.0. Formation of
quasi-one-dimensional fibrous structures was observed in
the AFM image, and because the monolayer fibrous struc-
tures did not grow in the width direction, we assumed that
l=1 and hence h=k=1. Thus, the monolayer fibrous struc-
tures are considered to form by homogeneous nucleation
(h=1) and interface-controlled growth (k=1). Similar pro-
cesses governed by one-dimensional growth have been re-
ported in the formation of fibrous structures of gelators.[26]
On holding the Langmuir film at 5 mNmꢀ1, molecules in the
homogeneous monolayer assemble to create a monolayer fi-
brous structure at the growth interface.
After 0.2 h, bilayer fibrous structures were formed and
grew. The index n is estimated to be 0.5, based on the slope
of 0.61. The h, k, and l parameters are therefore assumed to
be 0, 0.5, and 1, respectively. Thus, the quasi-one-dimension-
al bilayer fibrous structures (l=1) are thought to form by
heterogeneous nucleation (h=0) and diffusion-controlled
growth (k=0.5). After 0.2 h, homogeneous monolayer and
monolayer fibrous structures were present at the air/water
interface. If the bilayer fibrous structures are formed
through assembly of molecules from the homogeneous mon-
olayer, as occurs in the formation of monolayer fibrous
structures, then the kinetics would be governed by an inter-
facial process. However, if the bilayer fibrous structures are
formed by the assembly of monolayer fibrous structures,
then nucleation and growth would occur as a result of close
contact of the monolayer fibrous structures by a diffusion
process. The mobility of fibrous structures at the air/water
Formation mechanism of nanowires: To explain the origin
of the structural changes at the air/water interface, the
Avrami theory[25] was applied. The Avrami equation has
been used to explain the crystal growth of polymers,[25c] gela-
tion,[26] and structural changes in Langmuir films at the air/
water interface.[27] The formation and growth mechanisms of
the monolayer and bilayer fibrous structures at the air/water
interface were considered in terms of the change in surface
area over time. The change in area per molecule while hold-
ing at 5 mNmꢀ1 A5(t) was plotted against holding time
(Figure 5). The A5(t) value decreased with time and became
constant at 1.09 nm2 [A5(1)]. The normalized area A* is de-
fined by Equation (1), which corresponds to the fractional
decrease in area at time t.
*
A
¼ fAðtÞꢀAð1Þg=fAð0ÞꢀAð1Þg
ð1Þ
In the ln
ACHTREUNG
slopes were observed: 2.0 from 0 to 0.2 h, and 0.61 from 0.2
to 18 h. The AFM images of the transferred films also
showed two types of surface morphology, with a transition
at 0.2 h. Therefore, the transition observed in Figure 5 is
likely related to structural changes in the Langmuir film at
the air/water interface. The kinetics of the normalized area
A* are described by the Avrami equation [Eq. (2)], in which
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8173

T. Nakamura et al.
interface should be low, and therefore the growth of bilayer
fibrous structures should always be governed by diffusion.
In fact, the growth rate of the bilayer structures was much
slower than that of the monolayer fibrous structures. Similar
diffusion-controlled growth was also reported for crystalliza-
tion of a polymer in a melt with a large amount of noncrys-
tallizable impurities.[28] Figure 6 shows a schematic view of
mensional diffusion-controlled growth. Use of low-molecu-
lar-weight organogelators and the LB method are proposed
for the development of methods of fabrication of self-assem-
bling nanowires. In addition, Avrami theory provided a ki-
netic mechanism for formation of the fibrous structures.
[60]Fullerene and its derivatives have high carrier mobility
and can be utilized in field-effect transistors.[29] These prop-
erties are also expected in the fullerene nanowires obtained
in this study, and further research will seek to determine
whether this is so.
Experimental Section
Film preparation: A conventional Langmuir trough (NIMA 5152D) was
used for Langmuir film formation and LB film deposition. A chloroform
solution of C60TT (0.5 mm) was spread on a pure water surface. The p–A
isotherms were recorded at 291 K and a barrier speed of 100 mmminꢀ1
.
Films for AFM observations were deposited at a surface pressure of
5 mNmꢀ1 by single up-stroke withdrawal of
a
mica substrate at
Figure 6. Mechanism for the formation of a) a monolayer fibrous struc-
ture and b) a bilayer fibrous structure.
5 mmminꢀ1 (vertical dipping method) after a certain holding time. The
40-layer LB films were transferred at 5 mNmꢀ1 after holding for 0.2 h by
a horizontal-lifting method onto solid substrates. Hydrophobized CaF2
and quartz substrates were used for recording IR and UV/Vis spectra, re-
spectively.
the overall change in structure, from the homogeneous mono-
layer to the bilayer fibrous structure via the monolayer fi-
brous structures. The monolayer fibrous structures are
formed by an interface-controlled process, and these struc-
tures then assemble to form bilayer fibrous structures by a
diffusion-controlled process.
Atomic force microscopy: AFM images were taken under ambient condi-
tions with a SPA-400 multifunction unit equipped with an SPI 3800 probe
station (SII NanoTechnology Inc.) or a JEOL JSPM-5200 Environmental
Scanning Microscope operating in dynamic force mode and/or contact
mode by using commercially available silicon nitride cantilevers with a
spring constant of 15 Nmꢀ1
.
Characterization: IR and UV/Vis spectra were measured on a Perkin–
Elmer Lambda-19 spectrophotometer and
2000 spectrometer, respectively.
a Perkin–Elmer Spectrum
Conclusion
Synthesis: C60TT was synthesized according to Scheme 1. ADT, com-
pound 4, and N-triphenylmethylpyrrolidine-C60 were prepared according
to previously reported methods.[17, 19] All reagents and solvents were pur-
chased from commercial suppliers and were used as provided. Com-
pounds were characterized by 1H NMR spectroscopy, mass spectroscopy
and elemental analysis.
Fullerene nanowires were fabricated from a newly synthe-
sized low-molecular-weight organogelator (C60TT). In con-
trast to the formation of grain structure in the cast film,
monolayer fibrous structures of 1.2 nm in height, 5–10 mm in
length, and 8 nm in width were obtained by the LB method.
Infrared spectroscopy indicated that C60TT in the LB film
is involved in hydrogen bonding comparable to that in the
ADT gel. UV/Vis spectroscopy suggested p–p interactions
between the fullerene moieties in the LB film. A molecular
model of the monolayer fibrous structure was constructed
on the basis of the structural and spectroscopic data. The
surface morphology of the LB film depends on the holding
time at the air/water interface before deposition. A change
from a homogeneous monolayer structure to monolayer fi-
brous structures was observed over 0.2 h, and growth of bi-
layer fibrous structures after 0.2 h. The morphological
changes were considered to originate from structural
changes at the air/water interface, and were explained by
Avrami theory. From 0 to 0.2 h, monolayer fibrous struc-
tures formed by homogeneous nucleation and quasi-one-di-
mensional interface-controlled growth from molecules in the
homogeneous monolayer. After 0.2 h, bilayer fibrous struc-
tures formed by assembly of the monolayer fibrous struc-
tures through heterogeneous nucleation and quasi-one-di-
N-Benzyloxycarbonyl-6-aminohexanoic acid (1): 6-Aminohexanoic acid
(1.42 g, 13.8 mmol) and NaHCO3 (1.73 g, 20.6 mmol) were dissolved in
water (20 mL). Benzyloxycarbonyl chloride (2.4mL, 16.8 mmol) was
added dropwise to the mixture at 08C, which was stirred at room temper-
ature for 18 h. The resulting precipitate was collected by filtration and
washed with hexane. The aqueous layer was acidified with 1n HCl and
extracted with CHCl3. The organic layer was washed with saturated aque-
ous NaCl, dried over Na2SO4, and concentrated in vacuo. The resulting
residue and precipitate were combined and purified by silica-gel column
chromatography (hexane/EtOAc 1:1) to afford
1 (2.34g, 8.81 mmol,
95%). 1H NMR (CDCl3, TMS): d=1.37 (quint, J=7.6 Hz, 2H), 1.53
(quint, J=7.6 Hz, 2H), 1.65 (quint, J=7.6 Hz, 2H), 2.35 (t, J=7.6 Hz,
2H), 3.20 (q, J=7.6 Hz, 2H), 4.77 (m, 1H), 5.27 (s, 2H), 7.36 ppm (m,
5H).
Ethyl N-benzyloxycarbonyl-6-aminohexanoate (2): BF3·Et2O (0.5 mL,
2.37 mmol) was added to a solution of 1 (1.08 g, 4.04 mmol) in EtOH
(20 mL) and the mixture was heated to reflux for 2 h. The reaction mix-
ture was quenched with Et3N (2 mL) and concentrated in vacuo. The res-
idue was purified by column chromatography on silica gel (hexane/
EtOAc 8:2) to give 2 (1.12 g, 3.83 mmol, 94%). 1H NMR (CDCl3, TMS):
d=1.25 (t, J=6.9 Hz, 3H), 1.36 (quint, J=7.6 Hz, 2H), 1.52 (quint, J=
7.6 Hz, 2H), 1.64(quint, J=7.6 Hz, 2H), 2.29 (t, J=7.6 Hz, 2H), 3.20 (q,
J=7.6 Hz, 2H), 4.12 (q, J=6.9 Hz, 2H), 4.74 (m, 1H), 5.09 (s, 2H),
7.36 ppm (m, 5H).
8174
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Fullerene Nanowires
FULL PAPER
Ethyl 6-aminohexanoate (3): A solution of 2 (1.10 g, 3.76 mmol) in EtOH
(20 mL) was stirred in the presence of 10% Pd/C (150 mg) at room tem-
perature under an H2 atmosphere. After stirring for 18 h, the Pd/C was
removed by filtration through Celite to provide a solution of 3 in EtOH,
which was directly used for the synthesis of 5.
[2] W. Krautschmer, L. D. Lamb, K. Fostirpoulos, D. R. Huffman,
Nature 1990, 347, 354.
[3] a) R. C. Haddon, A. F. Hebard, M. J. Rosseinski, D. W. Murphy, S. J.
Duclos, K. B. Lyons, B. Miller, J. M. Zahurak, R. Tycko, G. Dab-
bagh, F. A. Thiel, Nature 1991, 350, 320; b) K. Holczer, O. Klein, S.-
M. Huang, R. B. Kaner, K.-J. Fu, R. L. Whetten, F. Diederich, Sci-
ence 1991, 252, 1154.
[4] a) L. W. Tutt, A. Krost, Nature 1992, 356, 225; b) Optical and Elec-
tronic Properties of Fullerenes and Fullerene-Based Materials (Eds.:
J. Shinar, Z. V. Vardeny, Z. H. Kafafi), Marcel Dekker, New York,
2000.
[5] a) M. Prato, M. Maggini, Acc. Chem. Res. 1998, 31, 519; b) K. E.
Geckeler, S. Samal, Polym. Int. 1999, 48, 743; c) F. Diederich, M.
Gomez-Lopez, Chem. Soc. Rev. 1999, 28, 263; d) A. Bianco, T. D.
Ros, M. Prato, C. Toniolo, J. Pept. Sci. 2001, 7, 208; e) J.-F. Nieren-
garten, New J. Chem. 2004, 28, 1177; f) L. Sanchez, N. Martin, D. M.
Guldi, Angew. Chem. 2005, 117, 5508; Angew. Chem. Int. Ed. 2005,
44, 5374; g) F. Diederich, C. Thilgen, Science 1996, 271, 317.
[6] a) S.-Q. Zhou, C. Burger, B. Chu, M. Sawamura, N. Nagahara, M.
Toganoh, U. E. Hackler, H. Isobe, E. Nakamura, Science 2001, 291,
1944; b) E. Nakamura, H. Isobe, Acc. Chem. Res. 2003, 36, 807; c) T.
Michinobu, T. Nakanishi, J. P. Hill, M. Funahashi, K. Ariga, J. Am.
Chem. Soc. 2006, 128, 10384; d) J. Xiao, Y. Liu, Y. Li, J. Ye Y. Li, X.
Xu, X. Li, H. Liu, C. Huang, S. Cui, D. Zhu, Carbon 2006, 44, 2785.
[7] H. Imahori, K. Tamaki, D. M. Guldo, C. Luo, M. Fujitsuka, O. Ito,
Y. Sakata, S. Fukuzumi, J. Am. Chem. Soc. 2001, 123, 2607.
[8] M. Sawamura, K. Kawai, Y. Matsuo, K. Kanie, T. Kato, E. Naka-
mura, Nature 2002, 419, 702.
Ethyl N-{N-[3,4,5-tris(dodecyloxy)benzoyl]-4-aminobutyril}-6-aminohexa-
noate (5): Compound 4 (843 mg, 1.11 mmol), 1-hydroxybenzotriazole hy-
drate (203 mg, 1.33 mmol), and water-soluble carbodiimide·HCl (260 mg,
1.36 mmol) were dissolved in CH2Cl2 (30 mL). The mixture was stirred at
room temperature for 1 h, and then the above-mentioned solution of 3 in
EtOH was added to the solution. After stirring at room temperature for
2 h, the reaction mixture was diluted with CH2Cl2 and washed with satu-
rated aqueous NaHCO3. The organic layer was dried over Na2SO4 and
concentrated in vacuo. The resulting residue was recrystallized from
MeOH to yield 5 (956 mg, 1.06 mmol, 96% from 4). 1H NMR (CDCl3,
TMS): d=0.88 (t, J=7.6 Hz, 9H), 1.24–1.36 (m, 53H), 1.49 (m, 8H), 1.62
(quint, J=7.6 Hz, 2H), 1.73 (quint, J=7.6 Hz, 2H), 1.81 (quint, J=
7.6 Hz, 4H), 1.96 (m, 2H), 2.28 (t, J=7.6 Hz, 2H), 2.32 (t, J=6.2 Hz,
2H), 3.24(q, J=6.2 Hz, 2H), 3.49 (q, J=6.2 Hz, 2H), 3.98 (t, J=6.9 Hz,
2H), 4.03 (t, J=6.9 Hz, 4H), 4.11 (q, J=6.9 Hz, 2H), 6.03 (t, J=6.2 Hz,
1H), 7.04(s, 2H), 7.10 ppm (t, J=6.2 Hz, 1H).
N-{N-[3,4,5-Tris(dodecyloxy)benzoyl]-4-aminobutyril}-6-aminohexanoic
acid (6): A solution of KOH (421 mg, 7.50 mmol) in water (8 mL) was
added to 5 (930 mg, 1.03 mmol) in EtOH (30 mL), and the mixture
stirred at 408C for 30 min. The reaction mixture was neutralized with 1n
HCl and extracted with CHCl3. The organic layer was washed with satu-
rated aqueous NaCl, dried over Na2SO4, and concentrated in vacuo. The
resulting residue was recrystallized from MeOH to give 6 (854mg,
0.978 mmol, 95%). 1H NMR (CDCl3, TMS): d=0.88 (t, J=7.6 Hz, 9H),
1.24–1.34 (m, 50H), 1.46 (m, 8H), 1.63 (quint, J=7.6 Hz, 2H), 1.73
(quint, J=6.8 Hz, 2H), 1.81 (quint, J=7.6 Hz, 4H), 1.97 (quint, J=
6.9 Hz, 2H), 2.30 (t, J=6.9 Hz, 2H), 2.33 (t, J=6.9 Hz, 2H), 3.26 (q, J=
6.2 Hz, 2H), 3.49 (q, J=6.2 Hz, 2H), 3.99 (t, J=6.9 Hz, 2H), 4.03 (t, J=
6.9 Hz, 4H), 6.03 (m, 1H), 6.87 (m, 1H), 7.02 ppm (s, 2H).
[9] E. Frankevich, Y. Maruyama, H. Ogata, Chem. Phys. Lett. 1993, 214,
39.
[10] F. Stepniak, P. J. Benning, D. M. Poirier, J. H. Weaver, Phys. Rev. B
1993, 48, 1899.
[11] a) T. Nakanishi, N. Miyashita, T. Michinobu, Y. Wakayama, T. Tsur-
uoka, K. Ariga, D. G. Kurth, J. Am. Chem. Soc. 2006, 128, 6328;
b) D. M. Guldi, F. Zerbetto, V. Georgakilas, M. Prato, Acc. Chem.
Res. 2005, 38, 38; c) Y.-G. Guo, C.-J. Li, L.-J. Wan, D.-M. Chem, C.-
R. Wang, C.-L. Bai, Adv. Funct. Mater. 2003, 13, 626; d) N. Nakashi-
ma, T. Ishii, M. Shirakusa, T. Nakanishi, H. Murakami, T. Sagara,
Chem. Eur. J. 2001, 7, 1766; e) A. M. Cassell, C. L. Asplund, J. M.
Tour, Angew. Chem. 1999, 111, 2565; Angew. Chem. Int. Ed. 1999,
38, 2403; f) Y. Gao, Q. Chang, W. Jiao, H. Ye, Y. Li, Y. Wang, Y.
Song, D. Zhu, Appl. Phys. B 2007, 88, 89; g) M. Shirakawa, N.
Fujita, S. Shinkai, J. Am. Chem. Soc. 2003, 125, 9902.
[12] a) J. H. van Esch, B. L. Feringa, Angew. Chem. 2000, 112, 2351;
Angew. Chem. Int. Ed. 2000, 39, 2263; b) R. Wang, C. Geiger, L.
Chen, B. Swason. D. G. Whitten, J. Am. Chem. Soc. 2000, 122, 2399;
c) J. H. Jung, Y. Ono, S. Shinkai, Chem. Eur. J. 2000, 6, 4 552; d) D. J.
Abdallah, R. G. Weiss, Adv. Mater. 2000, 12, 1237.
[13] a) K. Oishi, T. Ishi-i; M. Sano, S. Shinkai, Chem. Lett. 1999, 1089;
M. Sano, S. Shinkai, Chem. Lett. 1999, 1089; b) T. Ishi-i, Y. Ono, S.
Shinkai, Chem. Lett. 2000, 809.
[14] a) D. K. Schwartz, Surf. Sci. Rep. 1997, 27, 241; b) Langmuir–Blodg-
ett Films, (Ed.: M. C. Petty), Cambridge University Press, 1996.
[15] a) M. Sano, A. Kamino, S. Shinkai, J. Phys. Chem. B 2000, 104,
10339; b) M. Matsumoto, K. Tanaka, R. Azumi, Y. Kondo, N. Yoshi-
no, Langmuir 2004, 20, 8728; c) M. S. Chandra, T. P. Radhakrishnan,
Chem. Eur. J. 2006, 12, 2982.
Fullerene-linked 3,4,5-tris(dodecyloxy)benzamide derivative C60TT: A
solution of
6 (55 mg, 0.063 mmol), water-soluble carbodiimide·HCl
(14mg, 0.073 mmol), and 1-hydroxybenzotriazole hydrate (9 mg,
0.058 mmol) in CH2Cl2 (7 mL) was stirred in an ice bath for 1 h under an
Ar atmosphere (solution I). CF3SO3H (0.1 mL) was added to a suspen-
sion of N-triphenylmethylpyrrolidine-C60 (42 mg, 0.041 mmol) in CH2Cl2,
and the mixture stirred for 1 h. The resulting precipitate was collected by
centrifugation, washed several times with wet diethyl ether, and then
dried. The obtained solid was suspended in CH2Cl2 (5 mL) together with
4-dimethylaminopyridine (4 mg) and pyridine (0.5 mL) and added to sol-
ution I. After 3 h of stirring under an Ar atmosphere, the brownish solu-
tion was diluted with CH2Cl2. The organic layer was washed with dilute
HCl, water, and saturated aqueous NaCl, and then dried over MgSO4
and concentrated in vacuo. After purification by HPLC (chloroform),
C60TT was obtained (10 mg, 0.0062 mmol, 10% from 6). 1H NMR
(CDCl3, TMS): d=0.88 (t, J=6.8 Hz, 9H), 1.2–1.3 (m, 48H), 1.46 (m,
4H), 1.57 (m, 2H), 1.63 (m, 2H), 1.73 (m, 4H), 1.81 (m, 6H), 1.95 (m,
4H), 2.36 (t, J=5.7 Hz, 2H), 2.80 (t, J=7.3 Hz, 2H), 3.35 (q, J=6.2 Hz,
2H), 3.50 (q, J=6.2 Hz, 2H), 3.97 (t, J=6.2 Hz, 2H), 4.03 (t, J=6.6 Hz,
2H), 5.36 (s, 2H), 5.45 (s, 2H), 6.29 (t, J=5.7 Hz, 1H), 7.06 (s, 2H),
7.17 ppm (t, J=5.3 Hz, 1H); elemental analysis (%) calcd for
C115H99N3O6: C 85.31, H 6.16, N 2.60; found: C 83.51, H 6.06, N 2.58;
FABMS: m/z: calcd for [M+H]+: 1619; found: 1618.8.
[16] T. Akutagawa, T. Ohta, T. Hasegawa, T. Nakamura, C. A. Christen-
sen, J. Becher, Proc. Natl. Acad. Sci. USA 2002, 99, 5028.
[17] R. Tsunashima, S.-i. Noro, T. Akutagawa, T. Nakamura, T. Karasa-
wa, H. Kawakami, K. Toma, J. Phys. Chem. C 2007, 111, 901.
[18] a) D. Kitamoto, K. Toma, M. Hato in Handbook of Nanostructured
Biomaterials and Their Applications in Nanobiotechnology, Vol. 1
(Ed.: H. S. Nalwa), American Scientific, California, 2005, pp. 239–
271; b) T. Kitahara, M. Shirakawa, S.-I. Kawano, U. Beginn, N.
Fujita, S. Shinkai, J. Am. Chem. Soc. 2005, 127, 14980.
Acknowledgement
This work was partly supported by a Grant-in-Aid for Science Research
from the Ministry of Education, Science, Sports and Culture of Japan.
[19] a) M. Prato, M. Maggini, C. Giacometti, G. Scorrano, G. Sandona,
G. Farnia, Tetrahedron 1996, 52, 5221; b) M. Prato, M. Maggini, Acc.
Chem. Res. 1998, 31, 519.
[1] H. W. Kroto, J. R. Heath, S. C. OꢁBrien, R. F. Curl, R. E. Smalley,
Nature 1985, 318, 162.
Chem. Eur. J. 2008, 14, 8169 – 8176
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8175

T. Nakamura et al.
[20] On slow cooling of a 0.25m solution below 277 K, formation of a jel-
lylike solid was observed.
[21] N. Nakashima, T. Ishii, M. Shirakusa, T. Nakanishi, H. Murakami, T.
Sagara, Chem. Eur. J. 2001, 7, 1766.
olls, J. Am. Chem. Soc. 2001, 123, 8157; i) K. Hanabusa, M. Matsu-
moto, M. Kimura, A. Kakehi, H. Shirai, J. Colloid Interface Sci.
2000, 224, 231; j) D. J. Moore, M. E. Rerek, R. Mendelsohn, J. Phys.
Chem. B 1997, 101, 8933; k) P. Sivagurunathan, F. Liakath Ali Khan,
K. Ramachandran, Z. Phys. Chem. (Muenchen Ger.) 2007, 221, 273.
[25] a) M. Avrami, J. Chem. Phys. 1939, 7, 1103; b) M. Avrami, J. Chem.
Phys. 1940, 8, 212; c) Crystallization of Polymers (Ed.: L. Mandel-
kern), McGraw-Hill, New York, 1964; d) Macromolecular Physics,
Vol. 2 (Ed.: W. Wunderlich), Academic Press, New York, 1976.
[26] a) P. Terech, J. Colloid Interface Sci. 1985, 107, 244; b) X. Y. Liu,
P. D. Sawant, Appl. Phys. Lett. 2001, 19, 3518; c) X. Y. Liu, P. D.
Sawant, Adv. Mater. 2002, 14, 421; d) X. Huang, P. Terech, S. R. Ra-
ghavan, R. G. Weiss, J. Am. Chem. Soc. 2005, 127, 4336; e) X.
Huang, S. R. Raghavan, P. Terech, R. G. Weiss, J. Am. Chem. Soc.
2006, 128, 15341.
[27] a) D. Vollhardt, U. Retter, J. Phys. Chem. 1991, 95, 3723; b) D. Voll-
hardt, M. Ziller, U. Retter, Langmuir 1993, 9, 3208; c) D. Vollhardt,
Adv. Colloid Interface Sci. 1993, 47, 1; d) S. Rugonyi, E. C. Smith,
S. B. Hall, Langmuir 2005, 21, 7303; e) E. S. Nikomarov, Langmuir
1990, 6, 410.
[28] J.-T. Xu, J. P. A. Fairclough; S.-M. Mai, A. J. Ryan, C. Chaibundit,
Macromolecules 2002, 35, 6937; S.-M. Mai, A. J. Ryan, C. Chaibun-
dit, Macromolecules 2002, 35, 6937.
[22] a) D. C. Dahn, K. Cake, L. R. Hale, Ultramicroscopy 1992, 43, 1243;
b) D. J. Keller, F. S. Franke, Surf. Sci. 1993, 294, 409; c) J. Vesenka,
M. Guthold, C. L. Tang, D. Keller, E. Delaine, C. Bustamante, Ultra-
microscopy 1992, 42, 1243; d) K. A. Ramirez-Aguilar, K. L. Rowlen,
Langmuir 1998, 14, 2562; e) J. Loosa, A. Alexeev, N. Grossiord,
C. E. Koning, O. Regev, Ultramicroscopy 2005, 104, 160.
[23] a) Y. S. Obeng, A. J. Bard, J. Am. Chem. Soc. 1991, 113, 6279;
b) N. C. Maliszewskyi, P. A. Heiney, D. H. Jones, R. M. Strongin, M.
Cichy, A. A. B. Smith III, Langmuir 1993, 9, 1439; c) P. Wang, B.
Chen, R. M. Metzger, T. D. Ros, M. Prato, J. Mater. Chem. 1997, 7,
2397; d) J. Milliken, D. Dominguez, H. Nelson, W. R. Barger, Chem.
Mater. 1992, 4, 252.
[24] a) T. Steiner, Angew. Chem. 2002, 114, 50; Angew. Chem. Int. Ed.
2002, 41, 48; b) M. Suzuki, T. Sato, H. Shirai, K. Hanabusa, New J.
Chem. 2006, 30, 1184; c) G. Careri, U. Buontempo, F. Galluzzi, A. C.
Scott, E. Gratton, E. Shyamsunder, Phys. Rev. B 1984, 30, 4689;
d) F. Camerel, L. Bonardi, G. Ulrich, L. Charbonniere, B. Donnio,
C. Bourgogne, D. Guillon, P. Retailleau, R. Ziessel, Chem. Mater.
2006, 18, 5009; e) F. Camerel, B. Donnio, C. Bourgogne, M.
Schmutz, D. Guillon, P. Davidson, R. Ziessel, Chem. Eur. J. 2006,
12, 4216; f) B. Escuder, S. Marti, J. F. Miravet, Langmuir 2005, 21,
6766; g) C. Tan, L. Su, P. Xue, C. Bao, X. Liu, Y. Zhao, J. Mol. Liq.
2006, 124, 32; h) M. L. Bushey, A. Hwang, P. W. Stephens, C. Nuck-
[29] M. Chikamatsu, S. Nagamatsu, Y. Yoshida, K. Saito, K. Yase, Appl.
Phys. Lett. 2005, 87, 203504.
Received: March 17, 2008
Published online: July 21, 2008
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