Synthesis and nanostructures of several tetrathiafulvalene derivatives having the side chains composed of chiral and hydrogen-bonding groups and their charge-transfer complexes

Article abstract of DOI:10.1039/c3dt51464a

Tetrathiafulvalene (TTF) derivatives TTF-Bor, TTF-2UM and TTF-4UM having chiral urethane groups were prepared. Among them, TTF-2UM, TTF-4UM and their charge-transfer (CT) complexes with F₄TCNQ organized the nanowires. The intermolecular hydrogen bonding of the chiral urethane groups and π-stacking of TTF moieties or the formation of CT complexes resulted in a long one-dimensional nanowires. The chiral moieties were responsible for the molecular orientation of TTF cores to give helical structures. Electronic conductivity of the films of nanowires composed of TTF-2UM and TTF-4UM with F₄TCNQ were determined to be 8.0 × 10^-2 and 3.2 × 10^-2 S cm^-1, respectively.

Full text of DOI:10.1039/c3dt51464a

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Synthesis and nanostructures of several
tetrathiafulvalene derivatives having the side chains
composed of chiral and hydrogen-bonding groups
and their charge-transfer complexes†
Cite this: Dalton Trans., 2013, 42, 16121
Yoko Tatewaki,* Takanori Watanabe, Koji Watanabe, Kohei Kikuchi and Shuji Okada
Tetrathiafulvalene (TTF) derivatives TTF-Bor, TTF-2UM and TTF-4UM having chiral urethane groups were
prepared. Among them, TTF-2UM, TTF-4UM and their charge-transfer (CT) complexes with F4TCNQ orga-
nized the nanowires. The intermolecular hydrogen bonding of the chiral urethane groups and π-stacking
of TTF moieties or the formation of CT complexes resulted in a long one-dimensional nanowires. The
chiral moieties were responsible for the molecular orientation of TTF cores to give helical structures. Elec-
tronic conductivity of the films of nanowires composed of TTF-2UM and TTF-4UM with F4TCNQ were
determined to be 8.0 × 10−2 and 3.2 × 10−2 S cm−1, respectively.
Received 3rd June 2013,
Accepted 19th August 2013
DOI: 10.1039/c3dt51464a
www.rsc.org/dalton
oxidation-active and their CT complexes exhibit high conduc-
tivity by forming one-dimensional columnar structures.7 The
Introduction
The present silicon-based technology is thought to be conductivity could be controlled by tuning the electron
approaching its limit. Therefore there are many challenges in amount, molecular packing, on site coulomb energy and trans-
the design and construction of supramolecular nanoarchitec- fer energy between donor and acceptor molecules.7,8 The CT
tures with specific physical properties by tuning the intermole- complexes also form one-dimensional structures with π-stack-
cular non-covalent interactions including hydrogen bonding, ing easily, and this structural characteristic causes the mole-
π-stacking and charge-transfer (CT). Nanowires are considered cular arrangement of nanowires. The nanowires of π-stacked
to be key materials for conducting nanodevices. Nanowires columnar structures of TTF derivatives have been prepared.9
and nanotubes are promising materials for a variety of appli-
We report here the gel formation and long nanowires of
cations including optical and electronic nanodevices and several TTF derivatives with the side chains having chiral and
chemical and biological sensors.1 Successful application of hydrogen bonding groups. The combination of intermolecular
these nanostructured materials into functional nanodevices hydrogen bonding and π-stacking of the TTF moieties may
requires controlled patterning at the micro- and nanometer promote the formation of the nanowire structures. The chiral
scale. Semiconductor and metal nanowires (NWs) and carbon molecules form the π-stacks with helical supramolecular struc-
nanotubes (CNTs) have been the materials of choice for fabri- tures that exhibit some novel physical and chemical
cating sensor devices. Recently, gelators have been investigated properties.
as a source of molecular nanowires.2,3 These self-assembled
nanowires composed of disk-like molecules,4 bio-materials,3
and conducting4 or magnetic5 molecules can be used for
several physical functions.
Results and discussion
TTF derivatives having chiral centers originated from
(−)-borneol and (R)- or (S)-methylbenzylisocyanate, i.e.,
The CT complexes of several TTF derivatives and tetracyano-
quinodimethane (TCNQ) derivatives show a wide range of con-
ductivities from semiconductor to metal.6 TTF units are
TTF-Bor, (S)- or (R)-TTF-2UM and (S)- or (R)-TTF-4UM, were
prepared by the reaction sequence given in Scheme 1.10 In the
TTF derivatives with the end N-(1-phenyl)ethyl groups, 4,5-bis-
Department of Organic Device Engineering, Graduate School of Science and
(2′-cyanoethylthio)-1,3-dithiole-2-one as a starting material was
reacted with 3-bromopropyl-(S)-[N-(1-phenyl)ethyl]carbamate
Engineering, Yamagata University, Yonezawa 992-8510, Japan.
E-mail: ytatewa@yz.yamagata-u.ac.jp, okadas@yz.yamagata-u.ac.jp;
in the presence of dibutyltin dilaurate to yield compound 1S.
Fax: (+81)-238-26-3088
The conversion of 1S into the target 7S was achieved by the
reaction in triethyl phosphite at 110 °C, to give (S)-TTF-4UM as
†Electronic supplementary information (ESI)
available. See DOI:
10.1039/c3dt51464a
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were fully characterized by 1H, 13C NMR spectra and elemental
analysis.
When TTF-Bor was dissolved in several solvents such as
cyclohexane, hexane, carbon tetrachloride, chloroform,
dichloromethane, tetrahydrofuran, diethyl ether, acetone,
ethyl acetate, ethanol, methanol and acetonitrile and the solu-
tions were cooled, the gel was not formed. After removing
solvent from the solutions using rotary evaporators, TTF-Bor
formed an amorphous solid (TTF-Bor-A), which was confirmed
by no birefringence observed by a polarizing microscope. On
the other hand, after slow evaporation of TTF-Bor toluene solu-
tion, the crystals showing birefringence (TTF-Bor-C) were
obtained. The slow evaporation was better for the crystalliza-
tion than the evaporation using rotary evaporators because the
crystallization needed enough time to form the crystals. The
slow evaporation of toluene solution was the best technique
for crystallization. The DSC thermograms showed that the
glass transition temperature of TTF-Bor-A was 76 °C and the
melting point of TTF-Bor-C was 138 °C. The reason why
TTF-Bor-A can form the stable amorphous solid is that the
bulky end substituents inhibit regular molecular stacks.
When (S)-TTF-2UM and (S)-TTF-4UM were dissolved in hot
toluene and cooled at 0 °C, loose gels were formed, indicating
the fibrous aggregate formation of (S)-TTF-2UM and
(S)-TTF-4UM in solution. Atomic force microscopy (AFM)
images of the gels made of (S)-TTF-2UM and (S)-TTF-4UM
showed the nanowires (Fig. 1a and c). The CT complexes of
(S)-TTF-2UM and (S)-TTF-4UM with 2,3,5,6-tetrafluoro-7,7,8,8-
tetracyanoquinodimethane (F4TCNQ) as an electron acceptor
yielded dark-colored gels. By mixing with F4TCNQ, the solu-
tion color of (S)-TTF-2UM and (S)-TTF-4UM were changed
from yellow and orange to dark green and brown, respectively.
Scheme 1 Synthesis of TTF-2UM, TTF-4UM and TTF-Bor.
an air-stable orange powder. (R)-TTF-4UM was synthesized
by the same procedure as that for (S)-TTF-4UM.(S)-
TTF-2UM was synthesized by the reaction between compound
6 and 1S with CsOH after coupling of compounds 3 and 5. On
the other hand, in the TTF derivatives with the borneol-based
groups, (−)-borneol reacted with 2-chloroethyl isocyanate to
give compound 10. Zinc chelate 2 and compound 10 were
mixed in DMF at 125 °C, and the resulting thioketone 11 was
converted to ketone 12 with Hg(OAc)2. TTF-Bor was syn-
thesized by the reaction of 12 in triethyl phosphite at 110 °C,
Fig. 1 AFM images of (a) TTF-2UM, (b) TTF-2UM/F4TCNQ, (c) TTF-4UM and
and was obtained as an orange powder. All the compounds (d) TTF-4UM/F4TCNQ.
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These color changes indicate oxidation of TTF moieties by the redox potential for the reduction of F4TCNQ (+0.70 V vs.
addition of F4TCNQ and the resulting CT complex formation. SCE) was higher than the first oxidation potentials of
The morphologies of the CT complex nanowires were observed TTF-2UM and TTF-4UM, TTF could be oxidized to the radical
by AFM (Fig. 1b and d). The diameters of these nanowires were cation by the addition of F4TCNQ. The CT complexes of
approximately ∼500 nm and the length of fibers was longer TTF-Bor, TTF-2UM and TTF-4UM with F4TCNQ formed the
than 10 μm.
The details of the molecular information in the nanowires
partial charge transfer state.
The FT-IR spectra of the gels composed of TTF-Bor,
have been analyzed by ultraviolet-visible-near infrared (UV-vis- TTF-2UM and TTF-4UM with F4TCNQ showed peaks at 1689
NIR) spectroscopy, Fourier-transform infrared (FT-IR) spec- and 1508 cm−1, 1689 and 1533 cm−1, and 1685 and 1596 cm−1
troscopy, cyclic voltammetry (CV), circular dichroism (CD) respectively, which were assignable to the amide I and II
spectroscopy, and powder X-ray diffraction (XRD). The hydro- bands related to the urethane groups. These results indicate
gen-bonding network seems to be important for the molecular that the hydrogen-bonding network is formed among the
arrangement of TTF stacks. The CD spectra of the loose gels of
TTF-2UM and TTF-4UM exhibited CD activities for every
absorption band (Fig. 2). The Cotton effect centered at 373 and
539 nm for TTF-2UM and 399 and 512 nm for TTF-4UM can be
attributed to helical dipole coupling between TTF rings
through the hydrogen network formation.11
IR spectra of TTF-Bor, TTF-2UM and TTF-4UM and com-
plexes with F4TCNQ are shown in Fig. 3. These CT complexes
exhibited
a broad absorption band in the IR region
(2500–3500 cm−1), which was attributable to the charge trans-
fer between electron-donating TTF moieties and electron-
accepting F4TCNQ.12 CV was measured on TTF derivatives in
dry and degassed dichloromethane solution. The solution of
TTF-2UM and TTF-4UM displayed the reversible one-electron
oxidation waves at E1/2 = +0.553 and +0.522 V vs. SCE in the
anodic window, indicating the formation of stable radical
cations. These redox potentials almost coincided with those of
alkyl-substituted TTFs lacking chiral amide groups.13 Because
Fig. 3 IR spectra of (a) TTF-Bor, (b) TTF-Bor/F4TCNQ, (c) TTF-2UM, (d)
TTF-2UM/F4TCNQ, (e) TTF-4UM and (f ) TTF-4UM/F4TCNQ.
Fig. 2 UV and CD spectra of TTF-2UM and TTF-4UM.
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hydrogen-bonding groups could form conducting nanowires.
The main driving forces for the formation of long and flexible
nanowires were considered to be the intermolecular hydrogen
bonding of the chiral urethane groups and the formation of
CT complexes with F4TCNQ to give segregated columnar struc-
tures. Organization of the one-dimensional stacks results in
long nanowires with approximately ∼500 nm diameter and
above 10 μm length. Finally, the partial physical cross-linking
of these nanowires yields gels. The network structures of such
conductive nanowires will be useful for molecular electronics
devices.
Experimental section
General
1H- and 13C-NMR spectra in CDCl3 were measured using a
JEOL JNM-EX270 spectrometer or a JEOL JNM-ECX 400
spectrometer (Jeol, Akishima, Japan). Chemical shifts are
reported relative to internal TMS. CT complexes were trans-
ferred onto quartz substrates for UV-vis-NIR and CD measure-
ments. FT-IR measurements carried out in KBr pellets and the
films on calcium fluoride substrates. FT-IR spectra were
obtained by a Horiba FT-210 spectrometer (Horiba, Kyoto,
Japan). UV-vis-NIR spectra were measured using a JASCO
V-570. CD spectra were recorded on a JASCO J-710 spectropho-
tometer. AFM images were obtained by a JEOL 5200 operating
under the dynamic force mode. Redox potentials were
obtained using a JASCO J-715, and the experimental was
carried out in dry degassed dichloromethane solutions of
n-Bu4NBF4 (0.1 M). The XRD patterns were recorded on a RIN-
T-Ultimate III with Cu Kα radiation. Melting points were
Fig. 4 Current density–voltage properties of TTF-2UM/F4TCNQ and TTF-4UM/
F4TCNQ.
chiral side chains.14 Thus, TTF-Bor, TTF-2UM and TTF-4UM
with F4TCNQ can be assembled through two different non-
covalent interactions: CT complex formation and hydrogen
bonding. XRD patterns of the nanowires composed of
TTF-2UM and TTF-4UM were characterized by two reflection
peaks, i.e., 0.49 and 2.01 nm for TTF-2UM and 0.49 and
2.74 nm for TTF-4UM (ESI†). The observed distances of
2.01 nm for TTF-2UM and 2.74 nm for TTF-4UM roughly corre-
sponds to the length of the molecular long axis while the dis-
tance of 0.49 nm is assigned to the repetition along the
stacking direction. From these results, we can conclude that
the nanowires of TTF-2UM and TTF-4UM are bundles of one-
dimensional aggregates based on the hydrogen bonding of the
chiral urethane groups.
measured using
a Yanaco MP-500P micro melting-point
apparatus. The conductivities of the nanowires containing TTF
stacks were measured by the two probe method.
The electrical conductivity of the gels of TTF-2UM and
TTF-4UM with F4TCNQ was measured between evaporated
gold electrodes with a gap distance of 500 μm. The substrate
was fully covered with the organic film prepared by drop-
casting of the diluted solution and drying. The film thickness
of the film on the electrode was measured by a stylus-based
surface profiler. The electrical conductivity at room tempera-
ture of the film of TTF-2UM and TTF-4UM with F4TCNQ were
8.0 × 10−2 and 3.2 × 10−2 S cm−1, respectively (Fig. 4). The elec-
tronic conductivities of molecular nanowires composed of the
CT complexes of several TTF derivatives and F4TCNQ have
already been reported.15 By comparing the measured conduc-
tivities in this study with the reported values, it was suggested
that the nanowires had the three-dimensional network struc-
tures to form the pathways for electron transportation.
Materials
All chemicals were purchased from commercial suppliers and
used without purification. Column chromatography was per-
formed with activated alumina. Analytical thin layer chromato-
graphy was performed with commercial Merck plates coated
with silica gel 60 F254
.
1S: dibutyltin dilaurate was added to a solution of 2-bromo-
ethanol (6.37 g, 51.0 mmol) and (S)-(−)-α-methylbenzyl isocya-
nate (5.00 g, 34.0 mmol) in THF (200 ml). The reaction
mixture was stirred at 50 °C. After solvent evaporation from the
reaction mixture, the residue was purified by column chroma-
tography (silica, CH2Cl3), affording 1S as a white powder.
Yield: 8.48 g (31%).
FT-IR (KBr, cm−1): ν = 3344 (–NH–), 2983 (–CH2–), 1693
(–CvO).
1H-NMR (CDCl3, 400 MHz) δ = 7.24–7.37 (m, 5H, Ar-H), 5.09
(brs, 1H, NH(CH3)CH-Ar), 4.84 (qd, J = 6.8, 6.8 Hz, 1H,
Conclusion
We have demonstrated that the TTF-Bor formed amorphous ArCH(CH3)NH–), 4.30–4.41 (m, 2H, BrCH2CH2–), 3.49 (t, J =
structures while TTF-2UM and TTF-4UM having chiral and 5.5 Hz, 2H, BrCH2CH2–), 1.50 (d, J = 6.8 Hz, 3H, ArCH(CH3)NH–)).
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13C-NMR (CDCl3, 100 MHz) δ = 22.25, 29.47, 50.61, 125.78, and dried over anhydrous NaSO4. Then, the solvent was evap-
127.27, 128.52, 143.10, 154.79. orated and the residue was purified by recrystallization
1R: 1R was synthesized according to the same procedure as (CHCl3–hexane), affording (S)-TTF-4UM as an orange powder.
1S.
Yield: 1.50 g (92%). Melting point: 189.6 °C.
(S)-TTF-2UM:
a
solution of cesium hydroxide (0.5 g,
FT-IR (KBr, cm−1): ν = 3404 (–NH–), 3332 (–NH–), 2974
3.33 mmol) in methanol (7 ml) was dropped slowly to a solu- (–CH2–), 2929 (–CH2–), 1693 (–CvO).
tion of 6 (0.47 g, 1.00 mmol) in DMF (20 ml). After stirring for
1H-NMR (CDCl3, 400 MHz) δ = 7.22–7.33 (m, 20H, Ar-H),
30 min, 1S (2.18 g, 8.01 mmol) was added and stirred over- 5.40 (brs, 4H, NH(CH3)CH-Ar), 4.79 (m, 4H, NH(CH3)CH-Ar),
night. The reaction mixture was concentrated in vacuo and 4.09–4.22 (m, 8H, –SCH2CH2–), 3.01 (m, 8H, –SCH2CH2–), 1.45
extracted with CHCl3. The combined organic layer was washed (d, J = 6.9 Hz, 12H, –ArCH(CH3)NH–).
with water and dried over anhydrous NaSO4. Then, solvent was
evaporated and the residue was purified by column chromato- 110.69, 125.91, 127.27, 128.06, 128.59, 143.49, 155.18.
13C-NMR (CDCl3, 100 MHz) δ = 22.41, 35.00, 50.71, 63.14,
graphy (silica, CHCl3), affording (S)-TTF-2UM as an orange
powder.
Anal. C50H52N4O8S8 (1093.49): calcd, C 54.72, H 5.14,
N 5.10, S 23.37%; found C 54.75, H 5.27, N 5.04, S 23.22%.
(R)-TTF-4UM: (R)-TTF-4UM was synthesized according to the
Yield: 0.42 g (57%). Melting point: 110.5 °C.
FT-IR (KBr, cm−1): ν = 3332 (–NH–), 2971 (–CH2–), 2920 same procedure as (S)-TTF-4UM.
(–CH2–), 1693 (–CvO). 1H-NMR (CDCl3, 400 MHz) δ =
10: dibutyltin dilaurate was added to a solution of L-borneol
7.22–7.34 (m, 10H, Ar-H), 5.36 (brs, 2H, ArCH(CH3)NH–), 4.79 (20.5 g, 133 mmol) and 2-chloroethyl isocyanate (16.8 g,
(m, 2H, ArCH(CH3)NH–), 4.24 (m, 2H, SCH2CH2–), 2.98–3.02 159 mmol) in dry THF (300 ml). The reaction mixture was
(m, 4H, SCH2CH2–), 2.41 (s, 6H, –SCH3), 1.46 (d, J = 7.4 Hz, stirred at 50 °C. After solvent evaporation, the residue was puri-
6H, ArCH(CH3)NH–).
fied by column chromatography (silica, CHCl3–ethyl acetate =
13C-NMR (CDCl3, 100 MHz) δ = 19.32, 22.58, 35.09, 50.85, 9 : 1), affording 10 as a white powder.
63.42, 109.98, 111.72, 126.04, 127.39, 127.43, 127.98, 128.72,
143.64, 155.32.
Yield: 29.07 g (84%).
FT-IR (KBr, cm−1): ν = 3313 (–NH–), 1714 (–CvO), 1552
Anal. C30H32N2O4S8 (741.11): calcd, C 48.49, H 4.61, N 3.77, (–NH–), 1309, 1267 (C–O).
S 34.52%; found C 48.64, H 4.61, N 3.61, S 34.24%.
1H-NMR (CDCl3, 400 MHz) δ = 5.31 (brs, 1H), 4.84 (d, J =
(R)-TTF-2UM: (R)-TTF-2UM was synthesized according to 9.5 Hz, 1H), 3.62 (t, J = 5.4 Hz, 2H), 3.52 (dd, J = 5.5 Hz,
the same procedure as (S)-TTF-2UM.
13.3 Hz, 2H), 2.33 (m, 1H), 1.84–1.91 (m, 1H), 1.66–1.75 (m,
7S: a solution of cesium hydroxide (3.0 g, 20.0 mmol) in 2H), 1.20–1.31 (m, 2H), 1.02 (dd, J = 3.2 Hz, 13.6 Hz, 1H), 0.91
methanol (40 ml) was dropped slowly to a solution of 5 (2.88 g, (s, 3H), 0.87 (s, 3H), 0.84 (s, 3H).
10.0 mmol) in DMF (100 ml). Then the mixture was stirred for
30 min. After addition of 1S, the mixture was stirred overnight. 27.70, 36.37, 42.46, 43.51, 44.44, 47.39, 48.37, 79.99, 156.68.
The reaction mixture was concentrated in vacuo and extracted 11: a solution of 10 (10.00 g, 38.49 mmol) and zinc chelate
13C-NMR (100 MHz, CDCl3,) δ = 13.18, 18.49, 19.37, 26.63,
with CHCl3. The combined organic layer was washed with (5.53 g, 7.70 mmol) in DMF (90 ml) was stirred at 125 °C. Then
water and dried over anhydrous NaSO4. Then, the solvent was the reaction mixture was concentrated in vacuo and extracted
evaporated and the residue was purified by column chromato- with CHCl3 and the combined organic layer was washed with
graphy (silica, CHCl3–ethyl acetate = 8 : 2), affording 7S as an water and dried over anhydrous NaSO4. The solvent was evap-
orange powder.
orated and the residue purified by column chromatography
Yield: 2.01 g (36%).
(silica, CHCl3–ethyl acetate = 47 : 3), affording 11 as a yellow
FT-IR (KBr, cm−1): ν = 3430 (–NH–), 3340 (–NH–), 2974 powder.
(–CH2–), 2929 (–CH2–), 1709 (–CvO), 1689 (–CvO).
Yield: 7.19 g (72.3%).
1H-NMR (CDCl3, 400 MHz) δ = 5.30 (1H, s), 4.83 (1H, d, J =
1H-NMR (CDCl3, 400 MHz) δ = 7.23–7.34 (m, 10H, Ar-H),
5.40 (d, J = 6.4 Hz, 2H, ArCH(CH3)NH–), 4.80 (qd, J = 6.9, 9.6 Hz), 3.45 (2H, q, J = 5.9 Hz), 3.07 (2H, t, J = 6.0 Hz), 2.33
6.4 Hz, 2H, ArCH(CH3)NH–), 4.27 (m, 2H, SCH2CH2–), 4.21 (m, (1H, m), 1.67–1.89 (3H, m), 1.20–1.30 (2H, m), 1.02 (1H, dd, J =
2H, SCH2CH2–), 3.00–3.11 (m, 4H, SCH2CH2–), 1.47 (d, J = 3.2 Hz, 13.75 Hz), 0.90 (3H, s), 0.86 (3H, s), 0.84 (3H, s).
6.9 Hz, 6H, ArCH(CH3)NH–).
13C-NMR (CDCl3, 100 MHz) δ = 22.32, 35.28, 50.67, 63.06, 27.99, 36.53, 36.67, 40.50, 44.71, 47.70, 48.67, 80.55, 135.91,
13C-NMR (CDCl3, 100 MHz) δ = 13.49, 18.77, 19.65, 26.94,
125.86, 127.25, 128.54, 143.32, 155.01, 188.96.
7R: 7R was synthesized according to the same procedure
as 7R.
156.85, 210.10.
TTF-Bor: a mixture of 12 (0.82 g, 1.30 mmol) and phosphor-
ous acid triethyl ester (1.5 ml) was stirred at 120 °C for
(S)-TTF-4UM: a solution of 7S (1.68 g, 2.97 mmol) in 12 hours. Then the solvent was evaporated and the residue
toluene (40 ml) was refluxed for 30 min. After addition of purified by column chromatography (silica, hexane–ethyl
phosphorous acid triethyl ester (5 ml) and DMF (10 ml), the acetate = 3 : 2), affording TTF-Bor as a yellow powder.
mixture was stirred overnight. Water was added to the reaction
mixture, and the resulting aqueous solution was extracted with
Yield: 0.51 g (63%). Melting point: 138 °C.
1H-NMR (CDCl3, 400 MHz) δ = 5.22 (s, 1H), 4.83 (d, J =
CHCl3. The combined organic layer was washed with water 9.2 Hz, 1H), 3.42 (m, 2H), 2.99 (m, 2H), 2.33 (m, 1H), 1.84–1.90
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(m, 1H), 1.65–1.74 (m, 2H), 1.21–1.30 (m, 2H), 1.02 (dd, J =
2.98 Hz, 13.51 Hz, 1H), 0.90 (s, 3H), 0.86 (s, 3H), 0.84 (s, 3H).
13C-NMR (CDCl3, 100 MHz) δ = 13.45, 18.73, 19.61, 26.90,
27.94, 36.07, 36.62, 40.35, 44.67, 47.63, 48.62, 80.28, 110.45,
127.76, 156.80.
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Anal. C58H88N4O8S8 (1225.86): calcd, C 56.83, H 7.24,
N 4.57, S 20.93%; found C 57.06, H 7.45, N 4.52, S 20.29%.
Preparation of nanowires
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The hot toluene solutions of TTF-2UM (3 wt%, 36.4 mM) and
TTF-4UM (0.5 wt%, 7.89 mM) were cooled at 0 °C to obtain the
nanowires. Helical nanowires composed of TTF-2UM and
F4TCNQ were prepared by mixing a hot toluene solution of
TTF-2UM (3 wt%, 36.4 mM) with an acetonitrile solution of
F4TCNQ (3 wt%) in the same molar ratio. In the similar
manner, the mixture of hot toluene solution of TTF-4UM
(0.5 wt%, 7.89 mM) and acetonitrile solution of F4TCNQ
(0.5 wt%) in the same molar ratio gave the helical nanowires.
These nanowires were found in the loose gels created after
cooling the mixed solutions. The color of solutions of
TTF-2UM and TTF-4UM were immediately changed from
yellow and orange to dark green and brown, respectively, by
the CT complex formation.
7 P. Cassoux, D. de Caro, L. Valade, H. Casellas, S. Roques
and J.-P. Legros, Synth. Met., 2003, 659, 133.
8 (a) T. Akutagawa, K. Kakiuchi, T. Hasegawa, S. I. Noro,
T. Nakamura, H. Hasegawa, S. Mashiko and J. Becher,
Angew. Chem., Int. Ed., 2005, 44, 7283; (b) P. Jonkheijm,
P. van der Schoot, A. Schenning and E. W. Meijer, Science,
2006, 313, 80; (c) S. I. Stupp, V. LeBonheur, K. Walker,
L. S. Li, K. E. Huggins, M. Keser and A. Amstutz, Science,
1997, 276, 384; (d) C. Joachim, J. K. Gimzewski and
A. Aviram, Nature, 2000, 408, 541; (e) J. C. Nelson,
J. G. Saven, J. S. Moore and P. G. Wolynes, Science, 1997,
277, 1793.
9 (a) F. J. M. Hoeben, P. Jonkheijm, E. W. Meijer and A. P. H.
J. Schenning, Chem. Rev., 2005, 105, 1491; (b) A. R. Hirstm,
B. Escuder, J. F. Miravet and D. K. Smith, Angew. Chem., Int.
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10 (a) N. Svenstrup and J. Becher, Synthesis, 1995, 215;
(b) K. B. Simonsen and J. Becher, Synlett, 1997, 1211;
(c) N. Svenstrup, K. M. Rasmussen, T. K. Hansen and
J. Becher, Synthesis, 1994, 809.
Electrical conductivity
Electrical conductivities of nanowires composed of TTF-2UM
or TTF-4UM and F4TCNQ were measured using the DC two
probe method. Current–voltage (I–V) characteristics were
measured using a Keithley 6517 electrometer, with a constant
bias voltage ranging from −50 to +50 V. Gold electrodes with a
500 μm gap were formed by vacuum evaporation on glass sub-
strates, and the CT complex solution (5 mol l−1) was drop-
casted to cover the substrate and dried. Electrical contacts
were constructed by using gold paste to attach with 25 μm dia-
meter gold wires.
Acknowledgements
11 (a) J. H. Jung, Y. Ono and S. Shinkai, Chem.–Eur. J., 2000, 6,
4552; (b) J. H. Jung, Y. Ono and S. Shinkai, Angew. Chem.,
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M. Mitsutoshi, T. Shimizu and S. Shinkai, J. Am. Chem.
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(e) M. M. Green, C. Khatri and N. C. Peterson, J. Am. Chem.
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This work was supported by a Grant-in-Aid for Scientific
Research on Innovative Areas “coordination programming”
from the Ministry of Education, Culture, Sports, Science and
Technology, Japan.
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