Electroactive supramolecular self-assembled fibers comprised of doped tetrathiafulvalene-based gelators

Article abstract of DOI:10.1021/ja053496z

New electroactive supramolecular fibers have been formed by self-assembly of the derivatives of tetrathiafulvalene (TTF) in liquid crystals. These derivatives are designed and prepared by introducing the TTF moiety to the scaffold derived from amino acids such as L-isoleucine whose derivatives function as organogelators. These TTF-based gelators form stable fibrous aggregates in liquid crystals. These fibers are the first example of hydrogen-bonded one-dimensional aggregates having electroactive moieties whose electrical conductivities were measured after doping. Their electronic states have also been characterized by spectroscopic methods. Unidirectionally aligned fibers are formed in the oriented liquid crystal solvents on the rubbed polyimide surface for further functionalization of the fibers.

Full text of DOI:10.1021/ja053496z

Published on Web 09/30/2005
Electroactive Supramolecular Self-Assembled Fibers
Comprised of Doped Tetrathiafulvalene-Based Gelators
Tetsu Kitamura,† Suguru Nakaso,† Norihiro Mizoshita,† Yusuke Tochigi,†
Takeshi Shimomura,‡ Masaya Moriyama,† Kohzo Ito,‡ and Takashi Kato*,†
Contribution from the Department of Chemistry and Biotechnology, School of Engineering, The
UniVersity of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan, and Graduate School of
Frontier Sciences, The UniVersity of Tokyo, Kashiwanoha, Kashiwa-shi, Chiba 277-8561, Japan
Received May 28, 2005; Revised Manuscript Received August 23, 2005; E-mail: kato@chiral.t.u-tokyo.ac.jp
Abstract: New electroactive supramolecular fibers have been formed by self-assembly of the derivatives
of tetrathiafulvalene (TTF) in liquid crystals. These derivatives are designed and prepared by introducing
the TTF moiety to the scaffold derived from amino acids such as L-isoleucine whose derivatives function
as organogelators. These TTF-based gelators form stable fibrous aggregates in liquid crystals. These fibers
are the first example of hydrogen-bonded one-dimensional aggregates having electroactive moieties whose
electrical conductivities were measured after doping. Their electronic states have also been characterized
by spectroscopic methods. Unidirectionally aligned fibers are formed in the oriented liquid crystal solvents
on the rubbed polyimide surface for further functionalization of the fibers.
Introduction
having tetrathiafulvalene (TTF) moieties. Intensive studies have
focused on TTF for the preparation of conductive materials in
Supramolecular self-assembly is one of the promising ap-
proaches for the fabrication of molecular materials.1 For
example, molecular self-assembly from solution states often
leads to the formation of one-dimensional (1D) solid fibers.2
This process has attracted attention because 1D fibrous solids,
ranging from the submicrometer to nanometer scale, are easily
obtained by simple self-assembly through noncovalent interac-
tions such as hydrogen bonding, ionic interactions, and π-π
stacking in a variety of solvents.2 The network formation of
the fibers in the solvents leads to the preparation of physical
gels. The molecules that drive physical gelation are called
gelators.2 If functional moieties are introduced into each
component of the gelators, new functional 1D objects would
be obtained. Our new approach is to obtain electroactive 1D
fibers through molecular self-assembly processes of gelators
bulk3 and thin film states.4 High conductivities can be expected
for TTF-based materials through the formation of charge-transfer
(CT) complexes with electron acceptors such as tetracyano-p-
quinodimethane (TCNQ) and iodine.3 Molecular switches
incorporating TTF moieties have also been prepared.5
For self-assembled fibers incorporating the TTF moieties, two
examples of bis-arborol-TTF6 and tetra(TTF-crown-ether) ph-
thalocyanine7 were prepared. However, no conductivities of
these solid fibers were measured. Some examples of self-
assembled electroactive fibers based on other electroactive
moieties were obtained by using oligothiophene,8 aromatic
disks,9 phthalocyanine,10 and oligo(p-phenylenevinylene).11
(3) (a) Bryce, M. R. Chem. Soc. ReV. 1991, 20, 355-390. (b) Nielsen, M. B.;
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J. Chem. Soc., Chem. Commun. 1988, 754-756. (c) Dhindsa, A. S.; Song,
Y.-P.; Badyal, J. P.; Bryce, M. R.; Lvov, Y. M.; Petty, M. C.; Yarwood,
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† School of Engineering.
‡ Graduate School of Frontier Sciences.
(1) (a) Service, R. F. Science 2002, 295, 2398-2399. (b) Lehn, J.-M. Science
2002, 295, 2400-2403. (c) Kato, T. Science 2002, 295, 2414-2418. (d)
Hoeben, F. J. M.; Jonkheijm, P.; Meijer, E. W.; Schenning, A. P. H. J.
Chem. ReV. 2005, 105, 1491-1546. (e) Hartgerink, J. D.; Zubarev, E. R.;
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H.; Kato, T. J. Am. Chem. Soc. 2004, 126, 994-995. (j) Sawamura, M.;
Kawai, K.; Matsuo, Y.; Kanie, K.; Kato, T.; Nakamura, E. Nature 2002,
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J. AM. CHEM. SOC. 2005, 127, 14769-14775
14769

A R T I C L E S
Kitamura et al.
Figure 1. Molecular structures of hydrogen bonding TTF derivatives 1-3 and liquid crystals 4 and 5.
Here, we report on new electroactive self-assembled fibers
consisting of organogelators based on TTF. We have found that
stable fibrous aggregates are formed in aromatic liquid crystals.
Iodine-doping has been successfully carried out for the solid-
state self-assembled fibers, leading to the formation of 1D CT
complexes. The conductivities of these 1D materials have been
measured with platinum electrodes (1 mm in width) on a silicon
wafer. Moreover, we have obtained aligned electroactive fibers
for their further functionalization.
Results and Discussion
Molecular Design and Syntheses of TTF Derivatives as
Self-Assembled Materials. TTF derivatives 1-3 containing
amino acid moieties have been prepared in this study (Figure
1). They are designed to form hydrogen-bonded fibrous ag-
gregates. For compound 1, the L-isoleucine-based scaffold is
connected to the TTF moiety through a -CH2OCH2- linker,
while the TTF moiety is directly attached to the scaffold for
compound 2. Simpler amino acid derivatives such as L-
isoleucine were found to form fibrous aggregates in common
organic solvents12,13 and in liquid crystals.14 For compound 3,
a -CH2OCH2- linker is introduced to both sides of the dimeric
L-valine scaffold, which can also form fibrous aggregates in
common organic solvents.13 Compounds 1-3 were synthesized
by condensation of TTF-based carboxylic acids and L-isole-
ucylaminooctadecane or 1,12-bis(L-valylamino)dodecane.
Fibrous Self-Assembly of 1-3 in Common Organic
Solvents. Compounds 1-3 do not show excellent gelling ability
for common organic solvents, although simpler amino acid
Figure 2. AFM image of fibrous aggregates of 1 formed in 4.
derivatives were reported to act as efficient gelators.12,13 For
example, compound 1 gelates only toluene and ethyl acetate
below 10 °C, while no gelation by 1 is observed for polar
solvents such as acetone, ethanol, methanol, and DMF. No stable
fibrous aggregates of 1-3 are obtained in these common organic
solvents. Such lower gelling abilities have been caused by the
introduction of the bulky π-conjugated moieties.
Fibrous Self-Assembly of 1-3 in Liquid Crystals. We have
found that in aromatic liquid crystals of 4 and 5 (Figure 1),
stable fibrous aggregates of 1 and 3 are formed and these
anisotropic solvents are gelated efficiently by these compounds.
A biphenyl compound (4) shows a nematic phase below 34 °C.
Phenyl benzoate liquid crystal 5, which is the 50:50 (wt %)
mixture of 4-propoxyphenyl 4-undecyloxybenzoate and 4-bu-
toxyphenyl 4-undecyloxybenzoate, exhibits a nematic phase
between 83 and 78 °C and a smectic A phase below 78 °C.
The introduction of π-conjugated moiety to the gelators may
enhance their gelling ability for those aromatic liquid crystals.15
Such behavior was observed for gelators containing cyanobi-
phenyl15a and azobenzene15b moieties.
(8) (a) Schoonbeek, F. S.; van Esch, J. H.; Wegewijs, B.; Rep, D. B. A.; de
Haas, M. P.; Klapwijk, T. M.; Kellogg, R. M.; Feringa, B. L. Angew. Chem.,
Int. Ed. 1999, 38, 1393-1397. (b) Meijer, E. W.; et al. J. Am. Chem. Soc.
2002, 124, 1269-1275. (c) Messmore, B. W.; Hulvat, J. F.; Sone, E. D.;
Stupp, S. I. J. Am. Chem. Soc. 2004, 126, 14452-14458.
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T.; Ito, K.; Hashizume, T.; Ishii, N.; Aida, T. Science 2004, 304, 1481-
1483.
(10) (a) van Nostrum, C. F.; Picken, S. J.; Schouten, A.-J.; Nolte, R. J. M. J.
Am. Chem. Soc. 1995, 117, 9957-9965. (b) Engelkamp, H.; Middelbeek,
S.; Nolte, R. J. M. Science 1999, 284, 785-788.
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5149. (b) Jonkheijm, P.; Hoeben, F. J. M.; Kleppinger, R.; van Her-
rikhuyzen, J.; Schenning, A. P. H. J.; Meijer, E. W. J. Am. Chem. Soc.
2003, 125, 15941-15949.
Compounds 1 and 3 form fibrous aggregates of 20-50 nm
in diameter in liquid crystals 4 and 5 at room temperature
(Figure 2) (see Supporting Information), although no stable
fibers of 1-3 are obtained in common organic solvents.
Compound 2 forms aggregates only below room temperature.
Figure 3a shows the phase transition behavior of the mixtures
of 1 and 4 (1/4). The mixtures of 1/4 containing more than 4
(12) Hanabusa, K.; Hiratsuka, K.; Kimura, M.; Shirai, H. Chem. Mater. 1999,
11, 649-655.
(13) Hanabusa, K.; Tanaka, R.; Suzuki, M.; Kimura, M.; Shirai, H. AdV. Mater.
1997, 9, 1095-1097.
(14) (a) Mizoshita, N.; Kutsuna, T.; Hanabusa, K.; Kato, T. Chem. Commun.
1999, 781-782. (b) Kato, T.; Kutsuna, T.; Yabuuchi, K.; Mizoshita, N.
Langmuir 2002, 18, 7086-7088. (c) Suzuki, Y.; Mizoshita, N.; Hanabusa,
K.; Kato, T. J. Mater. Chem. 2003, 13, 2870-2874. (d) Mizoshita, N.;
Hanabusa, K.; Kato, T. AdV. Funct. Mater. 2003, 13, 313-317. (e)
Mizoshita, N.; Suzuki, Y.; Hanabusa, K.; Kato, T. AdV. Mater. 2005, 17,
692-696.
(15) (a) Kato, T.; Kondo, G.; Hanabusa, K. Chem. Lett. 1998, 193-194. (b)
Moriyama, M.; Mizoshita, N.; Yokota, T.; Kishimoto, K.; Kato, T. AdV.
Mater. 2003, 15, 1335-1338.
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Electroactive Supramolecular Self-Assembled Fibers
A R T I C L E S
Figure 4. (a) Optical photomicrograph and (b) AFM image of fibrous
aggregates of 1 formed in the oriented smectic A phase of 5.
Figure 5. Polar plot of the absorbance of the IR bands for the mixture of
1/5 (2 wt %) at 60 °C in the parallel rubbed cell.
Figure 3. Phase transition behavior of the mixtures of (a) 1/4 and (b) 1/5.
Characterization of Fibrous Aggregates. Thermal properties
of the fibers depend on the chemical structures of 1-3.
Compounds 1 and 3 form thermally more stable fibers than does
2. For example, fibrous aggregations of 1-3 (3 wt %) in 4 occur
at 27 °C for 1, at 8 °C for 2, and at 33 °C for 3, respectively.
These results suggest that the introduction of a -CH2OCH2-
spacer between the TTF and the amino acid moieties is effective
to induce stable 1D molecular assemblies. To understand these
differences, we have examined the hydrogen-bonded states of
the amino acid moieties by IR measurements. In the isotropic
states of the mixtures of 1/4, 2/4, and 3/4 at 120 °C, the N-H
and CdO stretching bands of the amide groups are observed at
3400 (br) and 1678 cm-1, respectively. These bands show that
the amide groups are free from hydrogen bonding. For the
fibrous aggregates of both 1 and 3 formed in 4 at room
temperature, the N-H and CdO stretching bands are observed
at 3280 and 1638 cm-1, respectively. The amide bands of the
fibers of 2 appear at 3299 and 1651 cm-1. These observations
indicate that compounds 1 and 3 form intermolecular hydrogen
bonds in the parallel â-sheet conformation,16 while compound
2 forms in a random conformation. These IR results show that
the hydrogen bonding can be more stable for 1 and 3 due to
the presence of the spacer. Without the spacer, the stacking of
the TTF moiety directly disturbs the formation of the stable
conformation for the hydrogen-bonded amide group.
wt % of 1 show sol-gel transition temperatures higher than
the isotropic-nematic transition temperatures. Compound 1
forms randomly dispersed fibers in the isotropic phase of 4.
For the mixtures of 1/4 containing less than 3 wt % of 1,
fibrous aggregation of 1 occurs at temperatures lower than
isotropic-nematic transition temperatures. So, we expected that
oriented fibers of 1 were formed in the oriented monodomain
of the nematic phases on the rubbed polyimide surface. We
previously reported that simpler amino acid derivatives formed
well-oriented fibers in the homogeneously oriented nematic
phases.14c-e However, in contrast, no alignment of self-
assembled fibers of 1 is observed. Randomly dispersed fibers
of 1 are formed even in the oriented nematic state of 4 on
the rubbed polyimide surface. Such observation shows that
molecular structures of the gelators are important for an ef-
ficient template effect in the liquid crystals and compound 1 is
not suitable for the formation of aligned fibers in the nematic
phase.
In the homogeneously oriented smectic A phase of 5, aligned
fibrous aggregates of 1 grow along the smectic layers (Figure
4). This observation shows that 5 functions as a template for
the alignment of the fibers of 1. Figure 3b shows the phase
transition behavior of the mixtures of 1/5. Fibrous aggregates
of 1 are formed in the smectic A phase on cooling the mixtures
of 1/5 from the isotropic states. The lengths and distances of
aligned fibers depend on the concentration of 1 and the cooling
rate. We have obtained the fibrous aggregates of 1 with a length
of more than 500 µm in 5 by slow cooling. For the mixtures of
3/5, no fibers are formed in the temperature range of the smectic
phase of 5 because of the higher aggregation temperatures of
3.
Polarized IR spectra for the oriented mixtures of 1/5 show
that the N-H stretching band of 1 at 3280 cm-1 is perpendicular
to the ring stretching band of 5 at 1605 cm-1 (Figure 5). This
result indicates that the hydrogen-bonded chains formed by TTF
derivative 1 align along the fiber direction. A schematic
(16) Toniolo, C.; Palumbo, M. Biopolymers 1977, 16, 219-224.
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Kitamura et al.
Figure 6. Schematic illustration of the oriented hierarchical structure of
the mixture of 1/5 in the parallel rubbed cell.
Figure 8. IR spectra for the fibrous aggregates of 1 before and after iodine-
doping for 2 min: (a) before doping, (b) immediately after doping, and (c)
1 week after doping.
sample is kept in air for 5 h after exposure to iodine vapor, the
spectrum of the sample significantly changes as follows. The
CT band at 850 nm becomes weaker in intensity, and a broad
band arises at 2300 nm (Figure 7c). This broad band is ascribed
to a band due to a partial CT (mixed-valence) state (Figure 9b).18
The spectrum reaches the steady state after 1 week. No
significant change is then observed for a few months. These
results are in good agreement with the previous results on iodine-
doped Langmuir-Blodgett films having TTF moieties.4 These
films were first oxidized to a full (1:1) CT state (TTF+I- or
TTF+I3-) by exposure to iodine vapor. The full CT state
changed to a more stable mixed-valence conducting state
((TTF)Ix or (TTF)(I3)x (x < 1)) with gradual release of iodine
over time.
Figure 7. UV-vis-NIR spectra for the fibrous aggregates of 1 before
and after iodine-doping for 2 min: (a) before doping, (b) immediately after
doping, (c) 5 h after doping, (d) 1 day after doping, and (e) 1 week after
doping.
illustration of the anisotropic hierarchical structure consisting
of the TTF derivative and liquid crystal materials is shown in
Figure 6.
The UV-vis-NIR spectra of compound 3 before and after
iodine-doping are similar to those of compound 1 (see Sup-
porting Information). The CT band is observed at 1800 nm,
which suggests the formation of a mixed-valence state, and its
energy gap of the fibers of 3 is larger than that of 1. The TTF
moieties of 1 may be fixed in a more favorable conformation
for electronic conduction in the fibers than those of 3.
The changes in the IR spectra also show the formation of
the CT complex (Figure 8). A broad CT band of the mixed-
valence state extends over the IR region (∼1700 cm-1). In
UV-vis spectra for 1-3 were measured in the solution (in
chloroform: 1 × 10-5 mol L-1) and in the aggregated fibrous
solid states (xerogels obtained from the gels based on 4) (see
Supporting Information). Blue shifts (318 to 300 nm for 1, 318
to 306 nm for 2, and 314 to 296 nm for 3) of the π-π* transition
peak for the TTF ring are observed in the aggregation of 1-3,
which is attributable to exciton coupling of TTF rings due to
the formation of H aggregates.17 Such blue shifts were previ-
ously observed for fibrous aggregates containing oligothiophene
groups.8
addition, upon doping a new sharp band appears at 1342 cm-1
,
which is due to the coupling of a conduction electron with the
vibrational mode of the TTF moiety called electron-molecular
vibration (e-mv) coupling (Figure 8b).19 This band becomes
broader with the formation of a mixed-valence state (Figure
8c). For the aligned fibrous aggregates of 1 formed in the
oriented smectic A phase of 5, an anisotropic feature is observed
in the CT band (Figure 10). This result suggests that electronic
conduction may occur along the aligned fibers of 1. The N-H
and CdO stretching bands of the amide groups do not shift
after iodine-doping, which shows that the doping does not
change the hydrogen-bonded structure. We also measured X-ray
diffraction patterns for the iodine-doped samples. The peak due
to the distance of TTF stacking is 4.1 Å before and after doping,
indicating that molecular assembled structures are not disturbed
by iodine-doping (see Supporting Information).20
Doping of Electroactive Self-Assembled Fibers with Elec-
tron Acceptors. We have succeeded in iodine-doping for the
self-assembled fibers maintaining the assembled solid structures.
Electronic states and assembled structures before and after
iodine-doping were examined by UV-vis-NIR (Figure 7) and
IR (Figure 8) spectroscopic methods. Xerogels obtained from
4 were used for the measurements. Figure 7a presents the UV-
vis-NIR spectrum for the fibrous aggregates of 1 before doping.
Immediately after exposure to iodine vapor for 2 min in a sealed
container, new absorption bands are observed at 380, 500
(shoulder), and 850 nm (Figure 7b). The appearance of the band
at 850 nm suggests the formation of a full CT state as illustrated
in Figure 9a.18 The bands at 380 and 500 nm are attributed to
intramolecular transitions of the TTF cation radical. When the
We have obtained UV-vis-NIR and IR spectra for TCNQ-
doped fibrous aggregates of 1 (see Supporting Information). In
(17) Kasha, M.; Rawls, H. R.; El-Bayoumi, M. A. Pure Appl. Chem. 1965, 11,
371-392.
(18) (a) Sugano, T.; Yakushi, K.; Kuroda, H. Bull. Chem. Soc. Jpn. 1978, 51,
1041-1046. (b) Torrance, J. B.; Scott, B. A.; Welber, B.; Kaufman, F. B.;
Seiden, P. E. Phys. ReV. B 1979, 19, 730-741.
(19) Bozio, R.; Zanon, I.; Girlando, A.; Pecile, C. J. Chem. Phys. 1979, 71,
2282-2293.
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Electroactive Supramolecular Self-Assembled Fibers
A R T I C L E S
Figure 9. Schematic illustration of aggregates of hydrogen bonding TTF derivatives doped with iodine: (a) a full charge-transfer state, and (b) a partial
charge-transfer (mixed-valence) state.
Figure 10. Polarized IR spectra for aligned fibrous aggregates of 1, 1 week
Figure 11. Current-voltage characteristics for fibrous aggregates of 1
after iodine-doping for 2 min: (a) parallel to the fiber direction, and (b)
before and after iodine-doping for 2 min: (a) before doping, (b) immediately
perpendicular to the fiber direction.
after doping, and (c) 1 week after doping.
these spectra, the CT band indicative of the formation of a
small because we see no threshold voltages in the I-V curves
of the samples that correspond to energies required for injecting
hole carriers into the fibers.9 The conductivity of the fibrous
aggregates of 3 also increases until it reaches a value of
10-5-10-6 S cm-1. The fibers of 1 doped with TCNQ show a
conductivity of 1 × 10-5 S cm-1. These results suggest that
the fibers forming the CT states function as conductive materials.
We examined temperature dependence of the conductivities
of the fibrous aggregates of 1. Ten days after being iodine-
doped, the sample was used for the measurements. The
conductivity exhibits an exponential dependence on temperature,
which is expressed as σ ) σ0 exp(-Ea/kBT) (Figure 12). This
behavior is characteristic of a semiconductor. The thermal
activation energy for the conductivity in the range 290-190 K
is estimated to be 0.35 eV. For self-assembled materials relevant
to the fibrous materials reported here, Langmuir-Blodgett (LB)
films containing TTF moieties, the conductivities were between
10-1 and 10-3 S cm-1,4 which were higher than those of the
present system (10-5 S cm-1). The thermal activation energies
for the LB films were 0.10-0.25 eV,4 which are lower than
those of the present fibrous materials (0.35 eV). In the present
materials for the measurements of the fibrous materials, the
single fibers have not yet bridged the electrodes. In this case,
the conduction process between fibers is incorporated into the
conductivities.
mixed-valence state is observed at 3500 cm-1. The band due
to the e-mv coupling between conduction electron and the TTF
moiety is observed at 1300 cm-1. The IR spectrum of the fibrous
aggregates of 1 also shows that its hydrogen-bonded structure
does not change after doping with TCNQ. A stable mixed-
valence state is formed immediately after doping with TCNQ,
while 1 week is needed to form the stable state for the iodine-
doping.
Measurements of the Electrical Conductivities of the
Fibers. The electrical conductivities of randomly dispersed
fibrous aggregates of the TTF derivatives (xerogels obtained
from the gels based on 4) were measured at room temperature
in vacuo using a two-probe technique (Figure 11). The fibers
of 1 in the neutral state before doping behave as insulator (σrt
< 3 × 10-10 S cm-1), whereas the conductivity increases
immediately after iodine-doping for 2 min (σrt ) 2 × 10-7
S
cm-1). The UV-vis-NIR and IR spectra of the doped sample
suggest that iodine-doping leads to the formation of the full
CT state. One week after exposure to iodine vapor, the
conductivity reaches a maximum at 3 × 10-5 S cm-1 (see
Supporting Information). The spectra indicate that the mixed
valence state is formed. The current-voltage characteristics of
fibrous aggregates show an ohmic behavior between -1 and
+1 V (Figure 11). The contact resistance should be sufficiently
(20) We have found that iodine-doping for the TTF derivatives in the fibers
induces thermal stabilization of the aggregates. For example, doping 0.25
equiv of iodine into the mixtures of 1/4 (3 wt %) raises fiber formation
temperatures by 15 °C (see Supporting Information). Partial oxidization
of the TTF moieties of 1 by iodine enhances stacking of the TTF moieties,
which leads to the formation of thermally more stable fibers.
Conclusion
We have succeeded in the fabrication of electroactive self-
assembled fibers. The formation of hydrogen bonding between
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J. AM. CHEM. SOC. VOL. 127, NO. 42, 2005 14773

A R T I C L E S
Kitamura et al.
Synthesis of Ethyl (4-Tetrathiafulvalenylmethoxy)acetate. A
mixture of 2-(hydroxymethyl)tetrathiafulvalene (0.81 g, 3.4 mmol),21
NaH (0.27 g, 11 mmol), and dry THF (100 mL) was stirred for 1 h.
Then ethyl bromoacetate (2.0 g, 12 mmol) was added, and the reaction
mixture was stirred for 12 h at room temperature. The reaction mixture
was dissolved in chloroform and washed with water. The organic phase
was dried with MgSO4, and the solvent was evaporated. The crude
material was purified by column chromatography, using an eluent of
1
hexane/chloroform (1:1). Yield: 0.45 g (41%). H NMR (270 MHz,
CDCl3): δ 6.31 (s, 2H), 6.26 (s, 1H), 4.38 (s, 2H), 4.23 (q, J ) 7.3
Hz, 2H), 4.10 (s, 2H), 1.30 ppm (t, J ) 7.1 Hz, 3H). 13C NMR (100
MHz, CDCl3): δ 169.8, 133.3, 119.1, 118.9, 117.7, 68.0, 66.6, 61.1,
14.2 ppm. IR (KBr): ν 2925, 2854, 1748, 1211, 1125, 1094, 795, 778,
646 cm-1. MS (MALDI-TOF): calcd, 319.97 (M+); found, 320.10
(M+).
Synthesis of (4-Tetrathiafulvalenylmethoxy)acetic Acid. A mixture
of ethyl (2-tetrathiafulvalenylmethoxy)acetate (0.45 g, 1.4 mmol), KOH
(0.85 g, 15 mmol), ethanol (27 mL), and water (10 mL) was refluxed
for 1 h. The reaction mixture was acidified with 5% hydrochloric acid,
dissolved in chloroform, and washed with water. The organic phase
was dried with MgSO4, and the solvent was evaporated. Yield: 0.37 g
Figure 12. Temperature dependence of the conductivities of fibrous
aggregates of 1, 10 days after iodine-doping for 2 min.
1
(90%). H NMR (270 MHz, CDCl3): δ 6.32 (s, 2H), 6.29 (s, 1H),
4.40 (s, 2H), 4.16 ppm (s, 2H). 13C NMR (100 MHz, CDCl3): δ 173.7,
132.7, 119.0, 118.3, 108.9, 68.1, 66.0 ppm. IR (KBr): ν 2923, 2853,
1734, 1203, 1120, 795, 648 cm-1. MS (MALDI-TOF): calcd, 291.94
(M+); found, 292.08 (M+).
amino acid derivatives having TTF moieties in liquid crystals
has led to the formation of the electroactive fibrous aggregates.
The doping of fibers by iodine results in the formation of charge
transfer states exhibiting semiconducting values of about 10-5
S cm-1. This may lead to the fabrication of self-assembled 1D
solid conductive fibers, of which direction of orientation is
controlled on the substrate.
Synthesis of N-[(4-Tetrathiafulvalenylmethoxy)acetyl]-L-isole-
ucylaminooctadecane (1). A mixture of (2-tetrathiafulvalenylmethoxy)-
acetic acid (0.36 g, 1.2 mmol), L-isoleucylaminooctadecane (0.70 g,
1.8 mmol), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochlo-
ride (EDC, 0.47 g, 2.5 mmol), 4-(N,N-dimethylamino)pyridine (DMAP,
0.015 g, 0.12 mmol), and dry THF (50 mL) was stirred at room
temperature for 1 day. The reaction mixture was dissolved in chloroform
and washed with saturated NH4Cl aq, saturated NaHCO3 aq, and
saturated NaCl aq. The organic phase was dried with MgSO4, and the
solvent was evaporated. The crude material was purified by column
chromatography, using an eluent of chloroform. The product was
reprecipitated with hexane from chloroform. Yield: 0.38 g (47%). mp
Experimental Section
1
General. H and 13C NMR spectra were recorded on a JEOL GX-
270 or a JEOL JNM-LA400 spectrometer with use of TMS as the
internal standard. IR measurements were conducted on a Jasco FT/IR-
660 Plus spectrometer. UV-vis-NIR absorption spectra were recorded
on a Agilent 8453 or a Hitachi U-4000 spectrometer. Elemental analyses
were carried out with a Perkin-Elmer 2400II elemental analyzer. Mass
spectra (MALDI-TOF-MS) were recorded on a Biosystems BioSpec-
trometry Workstation model Voyager-DE STR spectrometer using
dithranol as the matrix. Recycling preparative GPC was carried out
with a Japan Analytical Industry LC-908 chromatograph. Phase
transition behavior of the materials was examined by differential
scanning calorimetry (DSC) using a Mettler DSC 30 or a Netzsch DSC
204. The heating and cooling rates were 5 °C min-1. Transition
temperatures were taken at the maximum of the transition peaks on
cooling. A polarizing optical microscope Olympus BX51 equipped with
a Mettler FP82HT hot stage was used for visual observation. Tapping-
mode atomic force microscope (AFM) observation was performed with
a Digital Instruments Nanoscope IIIa equipped with a cantilever (NCH-
10V) at room temperature in air. X-ray diffraction measurements were
carried out on a Rigaku RINT 2500 diffractometer using Ni-filtered
Cu KR radiation.
1
134 °C. H NMR (270 MHz, CDCl3): δ 6.96 (d, J ) 8.9 Hz, 1H),
6.31 (s, 2H), 6.29 (s, 1H), 5.79 (t, J ) 4.2 Hz, 1H), 4.38-4.25 (m,
2H), 4.19 (dd, J ) 8.7, 7.7 Hz, 1H), 4.05-3.95 (m, 2H), 3.34-3.18
(m, 2H), 2.01-1.92 (m, 1H), 1.52-1.09 (m, 34H), 0.98-0.85 ppm
(m, 9H). 13C NMR (100 MHz, CDCl3): δ 170.6, 169.0, 134.9, 119.0,
112.0, 68.8, 57.4, 39.6, 37.0, 32.0, 29.5, 26.9, 25.0, 22.7, 15.6, 14.2,
11.3 ppm. UV (CHCl3): λ 318, 370 (sh), 445 nm (sh). IR (KBr): ν
3280, 3060, 2958, 2919, 2850, 1644, 1550, 796, 778, 645 cm-1. Anal.
Calcd for C33H56N2O3S4 (657.07): C, 60.32; H, 8.59; N, 4.26. Found:
C, 60.34; H, 8.59; N, 4.53. MS (MALDI-TOF): calcd, 656.32 (M+);
found, 656.34 (M+).
Synthesis of N-(4-Tetrathiafulvalenylcarbonyl)-L-isoleucylami-
nooctadecane (2). A mixture of 2-carboxytetrathiafulvalene (0.13 g,
0.54 mmol),21 L-isoleucylaminooctadecane (0.21 g, 0.54 mmol), EDC
(0.15 g, 0.80 mmol), DMAP (0.0070 g, 0.0057 mmol), and dry THF
(15 mL) was stirred at room temperature for 1 day. The reaction mixture
was dissolved in chloroform and washed with saturated NH4Cl aq,
saturated NaHCO3 aq, and saturated NaCl aq. The organic phase was
dried with MgSO4, and the solvent was evaporated. The crude material
was purified by column chromatography, using an eluent of hexane/
ethyl acetate (3:1). The product was recrystallized from methanol.
Yield: 0.12 g (36%). mp 68 °C. 1H NMR (270 MHz, CDCl3): δ 7.11
(s, 1H), 6.48 (d, J ) 8.6 Hz, 1H), 6.32 (s, 2H), 5.94 (t, J ) 4.2 Hz,
1H), 4.23 (dd, J ) 8.3, 7.9 Hz, 1H), 3.35-3.15 (m, 2H), 1.94-1.81
(m, 1H), 1.56-1.07 (m, 34H), 0.94-0.85 ppm (m, 9H). 13C NMR (100
Materials. All chemical reagents and solvents were obtained from
commercial sources and used without further purification. As for
tetrahydrofuran (THF) and N,N-dimethylformamide (DMF), com-
mercially available anhydrous solvents were used. All synthetic
reactions were carried out under an argon atmosphere. Nematic liquid
crystal, 4-cyano-4′-pentylbiphenyl (4), was purchased from Tokyo Kasei
Kogyo. Liquid crystal components of 5, 4-propoxyphenyl 4-undecy-
loxybenzoate and 4-butoxyphenyl 4-undecyloxybenzoate, were syn-
thesized by dehydration condensation of corresponding 4-alkyloxyphe-
nols and 4-alkyloxybenzoic acids. Compound 4 shows an isotropic-
nematic transition at 34 °C. Compound 5 shows isotropic-nematic and
nematic-smectic A transitions at 83 and 78 °C, respectively.
(21) (a) Green, D. C. J. Org. Chem. 1979, 44, 1476-1479. (b) Gar´ın, J.; Orduna,
J.; Uriel, S.; Moore, A. J.; Bryce, M. R.; Wegener, S.; Yufit, D. S.; Howard,
J. A. K. Synthesis 1994, 489-493.
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14774 J. AM. CHEM. SOC. VOL. 127, NO. 42, 2005

Electroactive Supramolecular Self-Assembled Fibers
A R T I C L E S
MHz, CDCl3): δ 163.2, 159.1, 130.7, 126.6, 58.7, 39.8, 32.5, 29.6,
26.8, 25.3, 23.0, 15.4, 14.0, 11.1 ppm. UV (CHCl3): λ 318, 420, 600
nm. IR (KBr): ν 3293, 3068, 2954, 2914, 2847, 1650, 1545, 795, 775,
644, 633 cm-1. Anal. Calcd for C31H52N2O2S4 (613.02): C, 60.74; H,
8.55; N, 4.57. Found: C, 60.15; H, 8.80; N, 4.64. MS (MALDI-TOF):
calcd, 612.29 (M+); found, 612.34 (M+).
conductivity measurements were performed for xerogels obtained from
the mixtures of 4 or 5 and hydrogen-bonding TTF derivatives. The
xerogels were prepared by immersing the liquid crystal mixtures in
hexane for a few hours to remove the liquid crystalline component
and were finally dried at room temperature.
Doping of Self-Assembled Fibers with Electron Acceptor. Iodine-
doping of the fibrous aggregates of hydrogen-bonding TTF derivatives
was carried out by exposure to iodine vapor in a sealed container. To
examine the dependence of fiber formation temperatures of hydrogen-
bonding TTF derivatives on molar ratio of iodine, a given amount of
iodine was added to the liquid crystal mixture. Doping of the fibrous
aggregates with tetracyano-p-quinodimethane (TCNQ) was carried out
by placing one drop of acetonitrile solution of TCNQ (0.5 g L-1) on
the sample. After 1 min, the droplet was blown with air, and then the
fibers were washed with acetonitrile.
Synthesis of 1,12-Bis[N-{(2-tetrathiafulvalenylmethoxy)acetyl}-
L-valylamino]dodecane (3). A mixture of (2-tetrathiafulvalenyl-
methoxy)acetic acid (0.31 g, 1.1 mmol), 1,12-bis(L-valylamino)-
dodecane (0.19 g, 0.47 mmol), EDC (0.40 g, 2.1 mmol), DMAP (0.014
g, 0.11 mmol), and dry THF (30 mL) was stirred at room temperature
for 2 days. The reaction mixture was dissolved in chloroform and
washed with saturated NH4Cl aq and water. The organic phase was
dried with MgSO4, and the solvent was evaporated. The crude material
was purified by column chromatography, using an eluent of chloroform/
methanol (20:1). The product was recrystallized from ethyl acetate/
methanol (10:1), followed by GPC. Yield: 0.24 g (54%). mp 110 °C.
1H NMR (400 MHz, CDCl3): δ 7.05 (d, J ) 9.2 Hz, 2H), 6.32 (s,
4H), 6.29 (s, 2H), 6.25 (t, J ) 5.8 Hz, 2H), 4.38-4.27 (m, 4H), 4.22
(dd, J ) 7.2, 7.2 Hz, 2H), 4.05-3.94 (m, 4H), 3.33-3.15 (m, 4H),
2.20-2.11 (m, 2H), 1.51-1.24 (m, 20H), 0.98-0.95 ppm (m, 12H).
13C NMR (100 MHz, CDCl3): δ 170.5, 169.0, 132.8, 119.1, 119.0,
118.2, 112.1, 68.7, 68.2, 58.3, 39.5, 30.8, 29.4, 29.3, 29.1, 26.8, 19.3,
18.3 ppm. UV (CHCl3): λ 314, 370 (sh), 450 nm (sh). IR (KBr): ν
3291, 3063, 2958, 2924, 2851, 1646, 1523, 795, 776, 638 cm-1. Anal.
Calcd for C40H58N4O6S8 (947.44): C, 50.71; H, 6.17; N, 5.91. Found:
C, 50.63; H, 6.17; N, 5.95. MS (MALDI-TOF): calcd, 946.21 (M+);
found, 946.27 (M+) (see Supporting Information).
Gelation Test. In a typical gelation experiment, an organic solvent
(0.1 mL) was added to a weighed sample (4 mg) in a test tube. The
tube was sealed and heated until a clear solution was obtained. The
resultant solution was allowed to cool to room temperature, and gelation
was checked visually. When the tube could be inverted without any
flow, it was considered to be a gel. If the mixture remained as a solution
at room temperature, it was further cooled in a refrigerator (-20 °C),
and if gelation occurred at lower temperatures, it was also considered
to be a gel.
Electrical Conductivity Measurements. The measurements of
electrical conductivities were carried out using a standard two-probe
method in vacuo (<10-5 Torr) with a source measurement unit
(Keithley 236). The platinum electrodes (1 mm in width) used in the
measurements were situated on a silicon wafer coated with an insulating
SiO2 layer (150 nm), which were placed 100 µm apart. The conductivity
values were calculated for the volume of the fibrous aggregates of
hydrogen-bonding TTF derivatives, which bridge electrodes (see
Supporting Information).
Acknowledgment. Financial support of a Grant-in-Aid for
Creative Scientific Research of “Invention of Conjugated
Electronic Structures and Novel Functions” (No. 16GS0209)
(T.K.) from the Japan Society for the Promotion of Science
(JSPS) and for The 21st Century COE Program of “The Frontier
of Fundamental Chemistry Focusing on Molecular Dynamism”
(T.K.) from the Ministry of Education, Culture, Sports, Science
and Technology is gratefully acknowledged. We thank Mr.
Hideki Ichihara and Ms. Aoi Inomata for their assistance in the
measurements of conductivities. We are also grateful to JSR
Corp. for supplying the polyimide material.
Preparation of Liquid Crystal Composites. The composites were
prepared by mixing liquid crystals and hydrogen bonding TTF
derivatives in test tubes. The mixtures in the sealed test tubes were
heated to isotropic states, and then cooled to the required temperatures.
For homogeneously aligned states, the liquid crystal mixtures in the
isotropic states were filled in glass sandwich cells (thickness: 5 µm)
coated with polyimide layers (JSR AL1254), whereby the rubbing
direction of the two surfaces was parallel. The mixtures in the cells
were cooled from the isotropic states at required rates, which were
controlled with a Mettler FP82HT hot stage. For polarized IR
measurements, sample cells were prepared by sandwiching the mixtures
between two CaF2 plates coated with polyimide (JSR AL1254), whereby
the rubbing direction of the two surfaces was parallel.
Supporting Information Available: Synthetic scheme of 1-3,
phase transition diagrams for 3/4 and 3/5, UV-vis absorption
spectra of 1, UV-vis-NIR and IR spectra for the fibrous
aggregates of 3, plot of the fiber formation temperature of 4/1,
X-ray diffraction patterns, UV-vis-NIR and IR spectra for the
fibrous aggregates of 1 doped with TCNQ, conductivity change
with time after iodine-doping, an illustration of the setup for
conductivity measurements, and complete refs 5b and 8b. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Preparation of Xerogel for Characterization. AFM observations,
UV-vis-NIR and IR spectroscopies, X-ray diffraction, and electrical
JA053496Z
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J. AM. CHEM. SOC. VOL. 127, NO. 42, 2005 14775