Structures in Langmuir-Blodgett films of amphiphilic tetrathiafulvalenes and tetrafluorotetracyanoquinodimethane CT complex

Article abstract of DOI:10.1080/15421401003613584

An asymmetric TTF derivative 1 having two arms substituted by amide and chiral groups was synthesized and its CT complex with 2,3,5,6-tetrafluoro-7,7', 8,8'-tetracyano-p-quinodimethane (1-F4TCNQ) were also prepared. Thin film formation at the air-water interface and the film deposition on substrates of 1 and 1-F4TCNQ were investigated. When we deposited the film of 1-F4TCNQ prepared on pure water onto a mica surface by a single upstroke withdrawal, curved nanowire structures were observed on the thin films. On the contrary, 1 without F4TCNQ showed three-dimensional dome structures on the thin films, and the morphologies of the Langmuir-Blodgett (LB) films depended on the existence of F4TCNQ. An average dimension of nanowire was 6.0 (height)×500 (width)×10000 (length) nm3.

Full text of DOI:10.1080/15421401003613584

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Structures in Langmuir-Blodgett Films
of Amphiphilic Tetrathiafulvalenes and
Tetrafluorotetracyanoquinodimethane
CT Complex
Yoko Tatewaki a , Shuji Okada a , Junko Takizawa b , Tatsuya
Hatanaka c , Mutsumi Kimura b c & Hirofusa Shirai b c
a Department of Polymer Science and Engineering , Graduate School
of Science and Engineering, Yamagata University , Yonezawa, Japan
b Collaborative Innovation Center for Nanotech FIBER, Shinshu
University , Ueda, Japan
c Department of Functional Polymer Science , Faculty of Textile
Science and Technology, Shinshu University , Ueda, Japan
Published online: 19 Apr 2010.
To cite this article: Yoko Tatewaki , Shuji Okada , Junko Takizawa , Tatsuya Hatanaka ,
Mutsumi Kimura & Hirofusa Shirai (2010) Structures in Langmuir-Blodgett Films of Amphiphilic
Tetrathiafulvalenes and Tetrafluorotetracyanoquinodimethane CT Complex, Molecular Crystals and
Liquid Crystals, 519:1, 157-162, DOI: 10.1080/15421401003613584
To link to this article: http://dx.doi.org/10.1080/15421401003613584
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Mol. Cryst. Liq. Cryst., Vol. 519: pp. 157–162, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421401003613584
Structures in Langmuir-Blodgett Films
of Amphiphilic Tetrathiafulvalenes and
Tetrafluorotetracyanoquinodimethane
CT Complex
YOKO TATEWAKI,1 SHUJI OKADA,1
JUNKO TAKIZAWA,2 TATSUYA HATANAKA,3
MUTSUMI KIMURA,2,3 AND HIROFUSA SHIRAI2,3
1Department of Polymer Science and Engineering, Graduate School
of Science and Engineering, Yamagata University, Yonezawa, Japan
2Collaborative Innovation Center for Nanotech FIBER,
Shinshu University, Ueda, Japan
3Department of Functional Polymer Science, Faculty of Textile
Science and Technology, Shinshu University, Ueda, Japan
An asymmetric TTF derivative 1 having two arms substituted by amide and chiral
groups was synthesized and its CT complex with 2,3,5,6-tetrafluoro-7,70,8,80-
tetracyano-p-quinodimethane (1-F4TCNQ) were also prepared. Thin film formation
at the air-water interface and the film deposition on substrates of 1 and 1-F4TCNQ
were investigated. When we deposited the film of 1-F4TCNQ prepared on pure water
onto a mica surface by a single upstroke withdrawal, curved nanowire structures
were observed on the thin films. On the contrary, 1 without F4TCNQ showed three-
dimensional dome structures on the thin films, and the morphologies of the Langmuir-
Blodgett (LB) films depended on the existence of F4TCNQ. An average dimension of
nanowire was 6.0 (height) ꢀ 500 (width) ꢀ 10000 (length) nm3.
Keywords Charge transfer; chirality; helical structures; hydrogen bonds;
nanostructures
1. Introduction
Molecular-assembly nanostructures are interesting for the future technologies
since they can be used as basic parts of electronic devices in a nanometer scale.
Generally, such nanostructures are constructed by the combination of intermolecu-
lar interactions such as electrostatic, charge-transfer (CT), hydrogen-bonding and
van der Waals interactions. For example, supramolecular approaches, which have
a structural flexibility to form nanostructures with a variety of sizes and shapes
[1], are effective methods to obtain novel low-dimensional molecular-assembly
Address correspondence to Yoko Tatewaki, Department of Polymer Science and
Engineering, Graduate School of Science and Engineering, Yamagata University, Yonezawa,
Yamagata 992-8510, Japan. E-mail: ytatewa@yz.yamagata-u.ac.jp
157

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Y. Tatewaki et al.
Scheme 1. TTF derivative 1.
nanostructures such as nanodots and nanowires [2]. The other approach is utilization
of the LB technique. This technique provides a way of arranging the molecules by
the orientational effect at the air-water interface as well as surface pressure applied.
These characteristics of the LB method can give rise to well ordered monolayer pack-
ing in a two-dimensional (2D) layer [3]. In addition, the LB method using amphiphi-
lic conducting molecules is promising for building conduction paths [4–8]. In the
previous study, we have reported gel formation originated from molecular-assembly
nanostructures composed of tetrathiafulvalene (TTF) derivatives, which have four
arms substituted by amide and chiral groups, and 2,3,5,6-tetrafluoro-7,70,8,80-
tetracyano-p-quinodimethane (F4TCNQ) [7]. The intermolecular hydrogen bonding
among chiral amide end-groups and the formation of CT complexes result in a long
one-dimensional supramolecular stacking, and the chirality of the end-groups affects
the molecular orientation of TTF cores within the stacks.
In the present study, we synthesized an asymmetric TTF derivative 1 having two
arms substituted by amide and chiral groups as shown in Scheme 1. Its organization
into supramolecular assemblies were investigated for 1 and its CT complex with
F4TCNQ (1-F4TCNQ) by using the LB technique.
2. Experimental
Compound 1 was prepared by referring the procedure for the similar compounds
described in the literature 7. F4TCNQ was purchased from Tokyo Chemical Indus-
try Co., Ltd. The solution of the CT complex 1-F4TCNQ was prepared by mixing
the same amount of solutions of 1 in CHCl3 (1 mM) and F4TCNQ in CH3CN
(1 mM). A conventional LB trough (USI, USI-3-22) was used for formation of the
films and their depositions. Solution of 1 or 1-F4TCNQ was spread on the pure
water as a subphase. The floating layer at the air-water interface was maintained
for 20 min after spreading the solution. Surface pressure-area per molecule (p-A)
isothermes were recorded at 291 K. Deposition surface pressures of 1 and the CT
complex were 20 mNmꢁ1 and 13 mNmꢁ1, respectively. For atomic force microscopy
(AFM) observation, the films at the air-water interface were transferred onto a
freshly-cleaved mica surface by the LB method with a single up-stroke withdrawal.
AFM images were taken by a JSPM-5400 (JEOL) operating in a tapping mode by
using microcantilevers of spring constant of 0.2 Nmꢁ1. For UV-Vis spectral
measurements, 20 layers of the films were transferred by the horizontal

Structures in Langmuir-Blodgett Films
159
lifting method on to quartz substrates (30 ꢀ 10 ꢀ 1 mm3), which were treated by
hexamethyldisilazane (HMDS) vapour to be hydrophobic. UV-Vis spectra were
recorded on a Hitachi U-4100. Column chromatography was performed with
activated alumina (Wako, 200 mesh) or Wakogel C-200. Recycling preparative gel
permeation chromatography was carried out by a JAI recycling preparative HPLC
using CHCl3. Analytical thin-layer chromatography was performed with commercial
Merck plates coated with silica gel 60 F254 or aluminum oxide 60 F254.
Compound 1: A solution of CsOH ꢂ H2O (700 mg, 4.2 mmol) in methanol
(10 mL) was added to a solution of 4,5-bis(20-cyanoethylthio)-1,3-dithiole-2-thione
(931 mg, 2.0 mmol) in acetonitrile (50 mL) over 10 min with stirring at room tempera-
ture. After stirring for 30 min, hexylbromide having (S)-methylbenzylamide end-
group (3.0 g, 10.1 mmol) was added, and the reaction mixture was stirred for 24 h.
The reaction mixture was concentrated in vacuo, and water (50 mL) was added.
The aqueous solution was extracted with CH2Cl2 and the combined organic layer
was washed with water. After drying with NaSO4, the solvent was evaporated,
and the residue was purified by column chromatography (silica, CHCl3), to afford
1 as an orange powder (0.84 g, 53%). 1H NMR (400.13 MHz, CDCl3): d ¼ 7.28
(m, 10H, Ar-H), 5.90 (q, J ¼ 8.0 Hz, 2H, N-H), 5.10 (m, 2H, ꢁCOCNHCHCH3ꢁ),
2.81 (t, 4H, J ¼ 6.60 Hz, ꢁSCH2ꢁ), 2.42 (t, 4H, J ¼ 7.20 Hz, ꢁCH2CONHꢁ), 2.15
(m, 6H, ꢁCH3ꢁ), 1.62 (m, 10H, ꢁSCH2CH2ꢁ, ꢁCONHCHCH3ꢁ), 1.52 ppm (m,
8H, ꢁSCH2CH2CH2CH2ꢁ).
3. Result and Discussion
Figure 1 shows p-A isotherms of the Langmuir film of neutral donor 1 and the CT
complex 1-F4TCNQ. Formations of stable floating layers were confirmed by sharp
increases of the surface pressure during compression. The surface area extrapolated
at 0 mNmꢁ1 of 1-F4TCNQ monolayer was A0 ¼ 0.8 nm2. A kink of the p-A isotherm
was observed at around 20 mNmꢁ1. Compound 1 showed the same behavior on the
Figure 1. p-A isotherms of 1 and 1-F4TCNQ on pure water at 291 K.

160
Y. Tatewaki et al.
Figure 2. Surface morphologies of transferred films of (a) 1 and (b) 1-F4TCNQ by a single
withdrawal from pure water.
p-A isotherm as 1-F4TCNQ although the film of 1 formed the hard film and the
surface pressure arose over 30 mNmꢁ1. The area per molecule at the deposition
surface pressure of 1 was 0.18 nm2 at 20 mNmꢁ1 (A20) and that of 1-F4TCNQ was
0.22 nm2 at p ¼ 13 mNmꢁ1 (A13). Given that the A13 and A20 values are same as
the areas of one close-packed alkyl chains (0.20 nm2). The area per molecule of
neutral donor 1 should be 0.4 nm2, because this compound has two alkyl chains
(0.20 nm2 ꢀ 2). Our results indicate that the floating layers of 1 and 1-F4TCNQ didn’t
create the monolayers.
Figure 2 shows AFM images of LB film composed of 1 and 1-F4TCNQ trans-
ferred onto mica by a single withdrawal. The AFM image of 1 showed the thin films
Figure 3. UV-Vis spectra of 20-layer multilayer films of 1 and 1-F4TCNQ transferred from
pure water.

Structures in Langmuir-Blodgett Films
161
with thickness of about 4 nm and the three-dimensional (3D) dome-type aggregates
with a typical dimension of ꢃ1.2 ꢀ 1.2 mm2 (Fig. 2a). The formation of nanowires
wasn’t observed for neutral donor 1, the neutral 1 was assembled together and aggre-
gated. On the other hand, 1-F4TCNQ formed the thin films with thickness of about
6 nm and the curved nanowires with an average dimension of 6.0 (height) ꢀ 500
(width) ꢀ 10000 (length) nm3 were observed on the thin films (Fig. 2b). The nano-
wires were distributed randomly on the substrate. From these results, we can
conclude that the molecular organization of synthesized TTF molecules is a combi-
nation of the formation of one-dimensional charge transfer stacks and hydrogen
bonding among chiral amide groups.
UV-vis spectra of multilayer films (20 layers) of 1 and 1-F4TCNQ were mea-
sured from 200 to 600 nm (Fig. 3). The complex 1-F4TCNQ showed larger absor-
bance in the whole range measured than 1. In particular, the shoulder band at
391 nm of 1-F4TCNQ is originated from the intramolecular charge transfer between
TTF and TCNQ [9,10]. The absorption band at 320 nm for the LB film of the com-
plex 1-F4TCNQ are assigned to the neutral TTF of 1 indicating the partial CT state.
4. Conclusion
Thin films of 1 and 1-F4TCNQ were formed on a pure water subphase and deposited
on substrate surfaces by LB technique. The LB techniques were useful for arrange-
ment of molecules. Both films deposited on to the mica surfaces showed 2D thin
films. However, in addition to the thin films, 1 showed the 3D dome-type aggregates
and 1-F4TCNQ showed the molecular-assembly curved nanowires. Large network
structures of conductive nanowires will open new possibilities for the construction
of soft electronic nanocircuits like neuronal networks, and 1-F4TCNQ and its
derivatives may be used for such applications. Finally, large network structures of
conductive nanowires will open new possibilities for the construction of soft elec-
tronic nano-circuits such as neuronal networks.
Acknowledgment
This work was partly supported by a Grant-in-Aid for Science Research from the
Ministry of Education, Culture, Sports, Science and Technology of Japan.
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