Organization of single-walled carbon nanotubes wrapped with liquid-crystalline π-conjugated oligomers

Article abstract of DOI:10.1039/b818352j

Two oligo(phenylenevinylene)s with cyanobiphenyl terminates were synthesized as non-covalent modifiers of single walled carbon nanotubes (SWNTs). The wrapping of SWNTs with synthesized oligomers enhanced the dispersibility in CHCl₃ by the disso

Full text of DOI:10.1039/b818352j

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Organization of single-walled carbon nanotubes wrapped
with liquid-crystalline p-conjugated oligomers
ab
Noritoshi Miki,a Naoya Adachi,a Yoko Tatewaki,b Kazuchika Ohtaa
*
Mutsumi Kimura,
and Hirofusa Shiraiab
Received 17th October 2008, Accepted 28th November 2008
First published as an Advance Article on the web 22nd January 2009
DOI: 10.1039/b818352j
Two oligo(phenylenevinylene)s with cyanobiphenyl terminates were synthesized as non-covalent
modifiers of single walled carbon nanotubes (SWNTs). The wrapping of SWNTs with synthesized
oligomers enhanced the dispersibility in CHCl3 by the dissociation of SWNT bundle structures. It was
found that the addition of oligomers caused self-organized precipitation from a homogeneous dispersed
solution of SWNT complexes. The self-organized precipitates exhibited thermotropic liquid-crystalline
properties.
Langmuir–Blodgett, and layer-by-layer assembly, have been
Introduction
developed in recent years.5 The alignment of carbon nanotubes
can also be achieved by using liquid crystalline properties.6 Song
and Windle reported on lyotropic liquid-crystalline behavior of
surface-treated multi-walled carbon nanotubes in acidic aqueous
solution.7 Dierking et al. reported orientation control of carbon
nanotubes by dispersing them within nematic liquid crystals.8 In
the present study, we focus on the dynamic changes of organi-
zations including SWNTs by exploiting the liquid crystalline
properties of organic hosts. It was found that when SWNTs are
dispersed into the thermotropic liquid-crystalline hosts, the
self-organization of the hosts induces alignment of dispersed
SWNTs and the alignment can be controlled by applying an
external electric or magnetic field. This alignment control of
SWNTs can switch the electronic conductivity by dynamically
changing the orientation of SWNTs. In this context, we designed
and synthesized novel liquid crystalline hosts 1 and 2 composed
of oligo(phenylenevinylene) segments and cyanobiphenyl
terminates, and we studied the formation of supramolecular
complexes and the possibility of processing new classes of highly
ordered nanostructured composite materials including SWNTs.
Carbon nanotubes have received special attention owing to their
unique mechanical and electronic properties.1 Single-walled
carbon nanotubes (SWNTs) are one-dimensional nanoscopic
seamless fibers with diameters ranging from 0.7 nm to 5 nm and
lengths of several micrometers; moreover, depending on their
chirality and diameter, they can be metallic, semiconducting, or
insulating.2 The precise manipulation of SWNTs can create
nanoscopic devices and circuitry as a result of their strong
anisotropy of conductivity.3 However, a strong intertube inter-
action among SWNTs results in the formation of insoluble
aggregates. Non-controllable aggregation makes it difficult to
manipulate and process them. Much effort has therefore been
invested in recent years to improve their processability.4 SWNTs
have been modified by three methods: first, covalent function-
alization of carboxylic acids with alcohols or primary amines at
the open ends and side walls of SWNTs after oxidation; second,
chemical modification of sidewalls by means of reactions such as
nucleophilic substitutions and the addition of radicals on the
sidewalls of SWNTs; and third, non-covalent functionalization
of sidewalls with organic polymers and surfactants. The disad-
vantage of covalent modification is that the electronic and
mechanical properties of SWNTs are altered by their partial
destruction. In contrast, the non-covalent functionalization on
the sidewalls of SWNTs with organic molecules through van der
Waals or p–p interactions can modify their chemical and phys-
ical properties and improve their processability while still
preserving their SWNT structure. Furthermore, this approach
can also realize the possibility of being able to organize SWNTs
into hierarchical molecular systems through controlled assembly
processes of adsorbed organic molecules.
Results and discussion
Conjugated polymers such as poly(m-phenylene-co-p-phenyl-
enevinylene)s (PmPV)9 and poly(aryleneethynylene)s10 interact
with the sidewalls of carbon nanotubes (CNTs) and form stable
dispersions of complexes in solvents. The meta-linkage in PmPV
leads to dihedral angles in the chain and the conjugated polymer
chain tends to form helical structures. The helical conformation
of PmPV allows inclusion of CNTs through p–p interactions
between the curved surface of CNTs and PmPV.9 In this study,
we focused on the repeating unit of PmPV and designed
p-conjugated oligo(phenylenevinylene)s (OPVs) 1 and 2 as non-
covalent modifiers of SWNTs (Scheme 1). The p-conjugated
OPV segment was intended to interact non-covalently with
the aromatic sidewall of SWNTs, and cyanobiphenyl terminates
were designed to promote a spontaneous organization of
complexes. OPVs 1 and 2 were synthesized by the coupling
reaction of two precursors. Precursor 3 was synthesized by
Many approaches to obtain large-scaled alignments of
SWNTs, such as gas flow, liquid flow, magnetic/electronic fields,
aDepartment of Functional Polymer Science, Faculty of Textile Science and
Technology, Shinshu University, Ueda, 386-8567, Japan. E-mail:
mkimura@shinshu-u.ac.jp; Fax: +81-268-21-5499; Tel: +81-268-21-5499
bCollaborative Innovation Center of Nanotech Fiber (nanoFIC), Shinshu
University, Ueda, 386-8567, Japan
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Scheme 1
a Wittig–Horner coupling reaction of a phosphonate and 3-vinyl
benzaldehyde.11 The other precursors 7 and 8 were synthesized in
three steps. The phenol group in 4, which was synthesized
through a Wittig–Horner coupling reaction of diethyl (3-bro-
mobenzyl)phosphonate with 4-acetoxy benzaldehyde and
hydrolysis of the acetoxy group, was reacted with 12-bromode-
can-1-ol or 2-[2-(2-chloroethoxy)ethoxy]ethanol in the presence
of K2CO3. The obtained products 5 and 6 were subsequently
converted to 7 and 8 by performing a Mitsunobu reaction with 4-
cyano-40-hydroxybiphenyl using DEAD. In the final step, a Heck
coupling reaction of 3 with 7 and 3 with 8 gave target compounds
1 and 2. Both compounds 1 and 2 were fully characterized by 1H
NMR, 13C NMR, FT-IR, and MALDI-TOF-MS spectroscopy.
The precursors and target compounds exhibit an IR absorption
band around 960nm arising from wagging vibration of the
trans-configured double bonds. UV-Vis spectra of 1 and 2
show two broad absorption bands at lmax ¼ 308 and 392 nm in
CHCl3 solution (Fig. 1). Compounds 1 and 2 exhibited a fluo-
rescence band at 450 nm with a shoulder peak at 475 nm. The
absorption and fluorescence spectra are quite different from
those of linear OPVs,12 suggesting the short p-system due to the
meta-linkage of the OPV segment in 1 and 2.
To prepare the complexes 1-SWNTs and 2-SWNTs,13 SWNTs
were added to a solution of the oligomers 1 or 2 in CHCl3, the
mixture was sonicated for 1 h and the resulting suspension was
centrifuged. The dark supernatant was carefully decanted and
the isolated suspension was filtered through a 200 nm pore
diameter PTFE membrane and washed with CHCl3 to remove
excess oligomers. The removal of oligomers was monitored by
measuring the fluorescence of the filtrate. Washing of the black
residue on the membrane with CHCl3 and drying under vacuum
yielded the 1-SWNTs and 2-SWNTs complexes. The complexes
were peeled away from the PTFE membrane and added to 10 ml
of CHCl3, followed by sonication for 10 min to disperse the
complexes. The complexes can be dispersed again into organic
solvents such as CHCl3, CH2Cl2 and THF by sonication and the
dispersed solutions are stable over a period of several months. It
was found that it is possible to produce a homogeneous and
stable suspension of SWNTs by using 1 and 2 even after removal
of the excess free oligomers (Fig. 1 inset). This finding indicates
that the adsorbed oligomers do not desorb from the surface of
SWNTs and that the non-covalent wrapping of SWNTs with
conjugated oligomers prevents reaggregation of SWNTs into
large bundles.
Fig. 1 also shows the UV-Vis spectra of 1 and 1-SWNTs
complex in CHCl3. The solution of the 1-SWNTs complex
showed a broad absorption band from 250 nm to 800 nm
together with a broad absorption band around 330 nm corre-
sponding to 1 adsorbed onto SWNTs. The broad absorption
around 600 and 800 nm reveals the band-to-band transition of
pure SWNTs14 and the shift and broadening of the absorption
bands for 1 in the 1-SWNTs complex can be ascribed to the p–p
interactions between the SWNTs and the OPV segment in 1.9 The
Fig. 1 UV-Vis spectra for 1 (solid line) and 1-SWNTs complex (dotted
line) in CHCl3. The inset shows a photograph of CHCl3 solutions of 1
and 1-SWNTs complex.
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solubilities of SWNTs in the presence of 1 or 2 were estimated
from the absorbance at 700 nm by using the reported specific
extinction coefficient for SWNTs at 700 nm, 3700 ¼ 2.35 ꢀ 104
ratio between the G-band and the D band in the 1-SWNTs
complex is lower than that for SWNTs only, indicating a lack of
chemical and physical damage to SWNTs and a low level of
impurities. The radial breathing mode (RBM) for the 1-SWNTs
complex, which is related to the diameter of SWNTs or the
formation of bundle structures, can be resolved as shown in
Fig. 2. Although there are no peaks for 1 in the RBM region, the
frequency in the RBM of SWNTs revealed a 6 cmꢁ1 shift
compared to that of SWNTs powder. This frequency shift in the
RBM provides evidence of the dissociation of bundle structures
by the functionalization of SWNTs with 1.19
cm2 gꢁ1 15
. The solubilities of SWNTs wrapped with 1 and 2 are
760 and 720 mg Lꢁ1, respectively. Although the solubility of
SWNTs wrapped with PmPV is reported to be about 100 mg Lꢁ1
,
the short OPV segments in 1 and 2 make the insoluble SWNTs
highly soluble in CHCl3 through the stable adsorption of
numerous discrete modifiers onto the side walls of SWNTs. The
contents of oligomers in the complexes were determined by
thermogravimetric analyses (TGA), which provided the weight
fraction of organic oligomers in the complexes.16 While the TGA
profile of the free 1 showed a weight loss of 59% under a nitrogen
atmosphere at 550 ꢂC, the observed weight loss of the 1-SWNTs
complex was 23%. From the TGA analyses, the amounts of 1 and
2 in the complexes were found to be 39 and 40%, respectively.
The fluorescence of 1 was quenched completely by the
formation of a complex with SWNTs.9 The fluorescence
quenching is likely to be the result of photoinduced energy or
electron transfer between the excited conjugated oligomers and
the SWNTs, as previously reported for other complexes with
p-conjugated molecules and polymers as non-covalent modi-
We have investigated the structure of 1-SWNTs complex by
atomic force microscopy (AFM) and transmission electron
microscopy (TEM). An AFM image of the 1-SWNTs complex
prepared by spin evaporation of one drop of its dispersion on
mica shows small SWNT ropes with an average height of about
3.0nm and a length of several micrometers as shown in the inset
of Fig. 2. A TEM image of 1-SWNTs complexes on a TEM grid
also reveals well-separated SWNT bundles. The average diam-
eter of SWNTs in the TEM image was determined to be about
1.4 nm, which is almost coincident with the diameter of typical
SWNTs. The AFM and TEM images are similar to those
observed in dispersed solutions of SWNTs wrapped with non-
covalent modifiers such as conjugated polymers and amphiphilic
biopolymers.9,20 These images indicate that the individual SWNT
strands are twisted into the observed small ropes and these ropes
are partially covered with organic molecules. From these results,
we conclude that the sonication of SWNTs in CHCl3 in the
presence of 1 or 2 diminishes the aggregations among SWNTs by
the covering of single SWNTs or small SWNT ropes with 1 or 2
in organic solvents.
1
fiers.4,9,10 The H NMR spectrum of the 1-SWNTs complex in
CDCl3 indicates significant broadening in the resonances for
protons of 1, suggesting the presence of conductive SWNTs and
ferromagnetic catalysts.17 Furthermore, the proton resonances
of phenylene and vinyl units in the OPV segment are shifted
up-field compared with those of free 1. Similar changes have been
observed in non-covalent functionalizations of SWNTs with
1
PmPV.9 The florescence quenching and the H NMR spectral
change suggest that the OPV segment in 1 interacts strongly with
SWNTs through the intermolecular p–p interactions. The flex-
ible side chains in 1 and 2 adsorbed onto the surface of SWNTs
result in the stable and homogeneous suspension of nanotubes
in organic solutions. Fig. 2 shows the Raman spectra for the
1-SWNTs complex obtained with a laser excitation wavelength
of 514 nm. Raman spectroscopy of the complexes showed D- and
G- bands at 1338 and 1590 cmꢁ1, respectively.18 The peak posi-
tions of the D- and G-bands for the complexes remained unal-
tered from those for only SWNTs powder. The Raman intensity
Self-organization properties among mesogenic units in 1 and 2
coating the exterior surfaces of SWNTs can be used to control
the alignment of SWNTs within the organizations. Whereas
the dispersions of SWNTs wrapped with 1 or 2 are stable, the
Fig. 2 Raman spectra for 1-SWNTs complex (solid line) and SWNTs
powder (dotted line). The inset shows the AFM image of 1-SWNTs
complex on mica.
Fig. 3 A photograph of precipitate formation caused by the addition of
1 into a homogeneous dispersion of 1-SWNTs complex (a), SEM (b and
c) and TEM (d) images of the isolated precipitate.
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addition of excess oligomers into the dispersed solution induces
the formation of aggregates (Fig. 3a). When 1 (5.0 mg) was
dissolved into the dispersion of 1-SWNTs complex (1.0 mg) in
1.0 ml CHCl3, a black precipitate slowly formed and settled out
of the solution. No solid formed upon the addition of 4-cyano-40-
n-pentylbiphenyl (5CB) and oligo(phenylenevinylene) lacking
the terminate cyanobiphenyl segments into the dispersion. The
content of 1 within the precipitate, analyzed by TGA, was about
70 wt%. Scanning electron microscopy (SEM) images of the
precipitate reveal three-dimensional aggregates composed of
SWNT ropes whose diameters are in the range 10–50 nm
(Fig. 3b). The SEM image of the edge of the precipitate clearly
shows that the precipitate contains numerous nanotubes as
shown in Fig. 3c. The TEM image of the precipitate shows an
extensive network structure of ca. 5 nm diameter SWNT ropes
(Fig. 3d). The SWNT ropes in the network structure show
bundles of individual SWNTs, which are highly aligned with the
rope axis. These observations suggest that the additional liquid-
crystalline oligomers act as a glue among complexes and the
addition of the glue leads to the organization of SWNTs
complexes through the interaction among mesogenic units.
A differential scanning calorimetry (DSC) thermogram of 1
was measured by heating and subsequent cooling over the range
of 0 to 170 ꢂC; it showed that 1 exhibited two endothermic peaks
at 87 and 152 ꢂC, corresponding to the phase transition from
crystalline to liquid crystalline and the isotropic transition,
respectively. When the isotropic liquid of 1 was cooled slowly,
the birefringent optical texture appeared in the range of 80 to
150 ꢂC under the temperature-controlled polarized optical
microscope (TPOM) as shown in Fig. 4a. This focal-conic fan-
shaped texture of 1 in the mesophase corresponds to a smectic
liquid-crystalline phase. The precipitate, which was obtained
from the homogeneous dispersion of 1-SWNTs complex by ꢂthe
addition of 1, also exhibited two DSC peaks at 82 and 153 C.
These transition points are almost the same as those of 1. The
TPOM image for the precipitate sample showed a birefringent
optical texture consisting of numerous fibrous assemblies in the
same temperature range (Fig. 4b), and the texture disappeared
above 153 ꢂC. The film was homogeneous and the aggregates of
SWNTs were not observed during heating to 200 ꢂC under
optical microscopy, indicating the stable dispersion of SWNTs
within the liquid crystalline host 1. The XRD patterns at 120 ꢂC
remained unaltered in 1 and the 1-SWNTs complex (d ¼ 3.61,
1.86, and 0.87 nm), suggesting that the inclusion of SWNTs
within the liquid-crystalline 1 does not affect its self-organized
structure. The other oligomer 2 with triethylene glycol spacers
between the phenylenevinylene segment and cyanobiphenyl
terminates exhibited a glass transition temperature around 45 ꢂC,
a broad exothermic peak around 120 ꢂC, and an endothermic
Fig. 4 Polarized optical micrographs of 1 (a) and the precipitate
composed of 1 and SWNTs (b) at 120 ꢂC after cooling from the isotropic
phase. DSC diagrams for the second heating of 2 and the precipitate
composed of 2 and SWNTs at 10 ꢂC/min (c). Polarized optical micro-
graph (d) and SEM (e) of the precipitate composed of 2 and SWNTs at
120 ꢂC after cooling from the isotropic phase.
a birefringent texture in the range of 96–141 ꢂC (Fig. 4d) and
fibrous assemblies containing SWNTs in a rapidly cooled sample
were observed by SEM (Fig. 4e). Thus, the synthesized phenyl-
enevinylene oligomers with cyanobiophenyl terminates can
organize SWNTs with a high aspect ratio into micrometer-sized
fibrous assemblies.
Experimental
General
1H NMR spectra were measured on a Bruker AVANCE 400
FT-NMR spectrometer. Mass spectral data were obtained using
a PerSeptive Biosystems Voyager DE-Pro spectrometer with
dithranol as a matrix. FT-IR spectra were obtained using a Shi-
mazu FTIR-8400 spectrometer. UV-Vis and fluorescence spectra
were measured on a Shimazu MultiSpec-1500 spectrophotometer
and a JASCO FP-750, respectively. Differential scanning calo-
rimeter (DSC) thermograms were recorded on a SII Exstar6000
DSC 6200. Raman spectra were obtained on a HaloLab 5000
spectrophotometer at an excitation wavelength of 532 nm.
Scanning electron microscope (SEM) images were obtained on
ꢂ
peak at 138 C upon heating (Fig. 4c), and 2 did not show any
optical texture from room temperature to 140 ꢂC under TPOM.
On the other hand, the precipitate composed of SWNTs and 2
ꢂ
shows a sharp exothermic peak at 94 C as well as a glass tran-
sition at 45 ꢂC and a melting point at 141 ꢂC. The sharp
exothermic peak suggests that the mixing with SWNTs enhances
the long-range organization of non-liquid-crystalline molecule 2.
A similar DSC change was observed in the case of composite gels
composed of ionic liquids and SWNTs reported by Fukushima
et al.21 Interestingly, TPOM of this precipitate revealed
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a Keyence VE-8800. Transmission electron microscope (TEM)
images were obtained on a JEOL JEM-2010 electron microscope
at an acceleration voltage of 200 kV without any staining.
The specimens for TEM were prepared by the drop casting of
the solution onto amorphous carbon-coated copper grids
(400 mesh). Temperature-controlled polarizing optical micros-
copy (TPOM) was carried out using an Olympus BX-50 with
a Mettler Toledo FP82HT hot stage.
(4H, m, ArH), 7.19 (1H, t, J ¼ 7.6Hz, ArH), 7.03 (1H, d, J ¼ 16.4
Hz, ArCH]CH), 6.85 (1H, d, J ¼ 16.4 Hz, ArCH]CH),
6.82 (2H, s, ArH), 4.87 (1H, s, –OH).
(E)-1-(3-Bromostyryl)-4-(12-hydroxydodecyloxy)benzene (5)
4 (0.75g, 2.73 mmol) and 12-bromodecan-1-ol (0.88g, 3.3 mmol)
were dissolved in 100 ml acetone and K2CO3 (1.88g, 13.7 mmol)
was added to this solution. The mixed solution was stirred under
reflux over one night. Subsequently, the mixture was cooled to
room temperature and the precipitate was filtered off. The filtrate
was evaporated to dryness and the crude mixture was purified
by column chromatography (silica gel) using CHCl3 (Rf ¼ 0.24)
as an eluent. Recrystallisation from 2-methoxyethanol yielded
5 as a white solid. Yield: 0.40g (32%). 1H NMR (CDCl3,
400.13MHz): d (ppm) ¼ 7.63 (1H, s, ArH), 7.43 (2H, d, J ¼
8.8Hz, ArH), 7.37 (1H, d, J ¼ 7.2 Hz, ArH), 7.34 (1H, d, J ¼
7.2Hz, ArH), 7.17 (1H, t, J ¼ 8.0Hz, ArH), 7.04 (1H, d, J ¼ 16.0
Hz, ArCH]CH), 6.88 (1H, d, J ¼ 16.0 Hz, ArCH]CH), 6.87
(2H, d, J ¼ 8.6Hz, ArH), 3.98 (2H, t, J ¼ 6.4Hz, –OCH2–), 3.66,
(2H, t, J ¼ 6.8Hz, –CH2OH), 1.76–1.80 (2H, m, –CH2CH2O–),
1.54–1.58 (2H, m, –CH2CH2OH), 1.21–1.47 (16H, m, –CH2–).
Materials
All chemicals were purchased from commercial suppliers and
used without purification. All solvents were distilled before each
procedure. Purified HiPco-SWNTs were purchased from Carbon
Nanotechnologies, Inc. The purification of product was carried
out by the combination of adsorption column chromatography
(silica gel, Wakogel C-200) and recycling preparative HPLC
(Japan Analytical Industry, Model LC-908). Analytical thin-
layer chromatography was performed on commercial Merck
plates coated with silica gel 60 F254
.
(E,E)-2,5-Bis(3-vinylstyryl)-1,4-hexyloxybenzene (3)
A solution of 3-vinyl benzaldehyde (0.85 ml, 6.65 mmol) and 1,4-
bis(diethylphosphonate-methyl)-2,5-hexyloxybenzene (1.54 g,
2.66 mmol) in dry THF (10 ml) was added dropwise to a THF
solution of potassium t-butoxide (0.9g, 7.98 mmol) under
a nitrogen atmosphere. The reaction mixture was stirred for 3 h
at room temperature and poured into cooled water. After addi-
tion 2 ml of 2M HCl aqueous solution, the aqueous phase was
extracted with CH2Cl2. The combined organic layer was washed
with three 100 ml potions of water and then dried over MgSO4.
After filtration, the solvent was reduced by rotary evaporation.
The product was purified by column chromatography (silica gel)
using CHCl3/n-hexane (v/v ¼ 1:1, Rf ¼ 0.65) as an eluent to give
a pale yellow solid. Yield: 1.1g (78%). 1H NMR (CDCl3,
400.13MHz): d (ppm) ¼ 7.54 (2H, s, ArH), 7.49 (2H, d, J ¼
16.4Hz, ArCH]CH), 7.42–7.45 (2H, m, ArH), 7.30–7.32 (4H,
m, ArH), 7.14 (2H, d, J ¼ 16.4Hz, ArCH]CH), 7.12 (2H, s,
ArH), 6.75 (2H, dd, J ¼ 6.7Hz, –CH]CH2), 5.80 (2H, d, J ¼
16.8Hz, –CH]CH2), 5.28 (2H, d, J ¼ 11.2Hz, –CH]CH2), 4.05
(4H, t, J ¼ 6.4Hz, –OCH2–), 1.85–1.89 (4H, m, –OCH2CH2–),
(E)-1-(3-Bromostyryl)-4-(2-[2-(2-
hydroxyethoxy)ethoxy]ethoxystyryl)benzene (6)
This was synthesized from 4 (1.65g, 6.0mmol) and 2-[2-(2-
chloroethoxy)ethoxy]ethanol (1.74ml, 12.0mmol) following the
same procedure as for 5. The crude product was purified by
column chromatography (silica gel) using CHCl3 (Rf ¼ 0.10) as
1
an eluent to give a white solid. Yield 55%. H NMR (CDCl3,
400.13MHz): d (ppm) ¼ 7.62 (1H, s, ArH), 7.44 (2H, d, J ¼
8.8Hz, ArH), 7.37 (1H, d, J ¼ 7.2 Hz, ArH), 7.34 (1H, d, J ¼
7.2Hz, ArH), 7.18 (1H, t, J ¼ 8.0Hz, ArH), 7.04 (1H, d, J ¼ 16.0
Hz, ArCH]CH), 6.88 (1H, d, J ¼ 16.0 Hz, ArCH]CH),
6.87 (2H, d, J ¼ 8.6Hz, ArH), 4.14–4.17 (2H, m, ArOCH2–),
3.87–3.88 (2H, m, ArOCH2CH2O–), 3.70–3.75 (6H, m, –OCH2),
3.61–3.63 (2H, m, –CH2OH), 2.48 (1H, br, –OH).
7
To
a
mixture of 4-cyano-40-hydroxybiphenyl (0.125g,
0.64mmol), 5 (0.245g, 0.533mmol) and triphenylphosphine
ꢂ
1.37–1.58 (12H, m, –CH2–), 0.92 (6H, t, J ¼ 6.8 Hz, –CH3); 13
C
(PPh3) (0.183g, 0.695 mmol) in dry THF (50ml) cooled to 0 C
NMR (CDCl3, 100.61MHz): d (ppm) ¼ 151.2, 138.2, 137.9,
136.8, 128.8, 128.6, 126.9, 125.8, 125.2, 124.6, 123.8, 114.0, 110.7,
69.6, 31.6, 29.5, 26.0, 22.6, 14.0.
with an iced bath was added dropwise a solution of diethyl
azodicarboxylate (DEAD) in THF under N2. The reaction was
allowed to warm to room temperature and stirred for 3 h. The
reaction was stopped by the addition of water, and THF was
removed under reduced pressure. The resulting aqueous solution
was extracted with diethyl ether. The organic layers were
combined, washed with a 1.0 M aqueous solution of NaOH,
washed with water, dried over MgSO4 and filtered. The filtrate
was evaporated and the crude product was purified by column
chromatography (silica gel) using CHCl3 (Rf ¼ 0.8) as an eluent.
Recrystallisation from 2-methoxyethanol yielded 7 as a white
solid. Yield: 0.30g (89%). 1H NMR (CDCl3, 400.13MHz):
d (ppm) ¼ 7.75 (2H, d, d ¼ 8.0 Hz, ArH), 7.64 (2H, d, J ¼ 8.0Hz,
ArH), 7.63 (1H, s, ArH), 7.52 (2H, d, J ¼ 8.8Hz, ArH), 7.42 (2H,
d, J ¼ 8.8Hz, ArH), 7.37 (1H, d, J ¼ 7.8Hz, ArH), 7.34 (1H, d,
J ¼ 8.8Hz, ArH), 7.17 (1H, t, J ¼ 7.8Hz, ArH), 7.04 (1H, d,
(E)-4-(3-Bromostyryl)phenol (4)
A solution of diethyl (3-bromobenzyl)phosphonate (1.23g,
4.0 mmol) and 4-acetoxy benzaldehyde (0.79g, 4.8 mmol) was
added dropwise to a THF solution of potassium t-butoxide
(1.34g, 12.0 mmol) under a nitrogen atmosphere. The reaction
mixture was stirred for 3 h at room temperature and poured into
cooled water. After addition 2 ml of 2M HCl aqueous solution,
the precipitate was collected and washed with 100 ml water. The
crude product was purified by column chromatography (silica
gel) using CHCl3 (Rf ¼ 0.12) as an eluent to give a white solid.
1
Yield: 0.75g (68%). FT-IR (ATR): 3230 cmꢁ1 (nOH); H NMR
(CDCl3, 400.13MHz): d (ppm) ¼ 7.63 (1H, s, ArH), 7.33–7.40
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J ¼ 16.0 Hz, ArCH]CH), 6.98 (2H, d, J ¼ 8.8Hz, ArH), 6.88
(2H, d, J ¼ 8.6Hz, ArH), 6.87 (1H, d, J ¼ 16.0 Hz, ArCH]CH),
3.95–4.02 (4H, m, –OCH2–), 1.78–1.82 (2H, m, –CH2CH2O–),
1.30–1.47 (16H, m, –CH2–); 13C NMR (CDCl3, 100.61MHz):
d (ppm) ¼ 159.6, 158.6, 145.2, 139.9, 132.6, 130.1, 129.9, 129.7,
129.5, 128.9, 128.3, 127.9, 127.0, 124.9, 119.0, 115.1, 114.7, 110.1,
68.0, 29.2, 25.9; MALDI-TOF-MS for C39H42BrNO2: m/z calcd,
635.24; found 636 [M + H]+.
chromatography (silica gel) using CHCl3 (Rf ¼ 0.22) as an eluent
and recycling preparative HPLC to obtain 2 as a yellow solid.
1
Yield 0.20g (71%). H NMR (CDCl3, 400.13MHz): d (ppm) ¼
7.62–7.69 (6H, m, ArH and ArCH]CH), 7.59 (4H, d, J ¼ 8.1Hz,
ArH), 7.53 (2H, d, J ¼ 16.0Hz, ArCH]CH), 7.49 (4H, d, J ¼
8.3Hz, ArH), 7.46 (4H, d, J ¼ 8.2Hz, ArH), 7.32–7.44 (10H, m,
ArH), 7.14–7.20 (8H, m, ArH and ArCH]CH), 7.10 (2H, d, J ¼
16.1Hz, ArCH]CH), 6.97–7.00 (6H, m, ArH and ArCH]CH),
6.92 (4H, d, J ¼ 8.7Hz, ArH), 4.14–4.17 (8H, m, –OCH2–), 4.09
(4H, t, J ¼ 6.4Hz, –OCH2–), 3.87–3.90 (8H, m, –OCH2–), 3.77
(8H, s, –OCH2–), 1.90–1.92 (4H, m, –OCH2–), 1.52–1.58 (4H, m,
–OCH2–), 1.39–1.40 (8H, m, –OCH2–), 0.91–0.94 (6H, m, –CH3);
13C NMR (CDCl3, 100.61MHz): d (ppm) ¼ 159.5, 158.6, 151.2,
145.1, 138.0, 137.7, 132.6, 129.0, 128.9, 128.8, 128.7, 128.5, 128.3,
127.7, 127.0, 126.5, 125.4, 124.9, 124.5, 123.9, 119.0, 115.2, 114.9,
110.1, 70.9, 69.8, 69.7, 69.6, 67.6, 67.5, 31.7, 29.5, 26.0, 22.7, 14.0;
MALDI-TOF-Ms for C104H104N2O10: m/z calcd, 1541.95; found
1542 [M + H]+.
8
8 was synthesized from 6 (1.0g, 2.48mmol) and 4-cyano-40-
hydroxybiphenyl (0.73g, 3.72mmol) following the same proce-
dure as for 7. The crude product was purified by column
chromatography (silica gel) using CHCl3 (Rf ¼ 0.15) as an eluent.
Recrystallisation from 2-methoxyethanol yielded 8 as a white
solid. Yield 0.9 g (62%). 1H NMR (CDCl3, 400.13MHz): d (ppm)
¼ 7.67 (2H, d, J ¼ 8.8Hz, ArH), 7.62 (1H, s, ArH), 7.61 (2H, d,
J ¼ 8.4Hz, ArH), 7.49 (2H, d, J ¼ 8.8Hz, ArH), 7.40 (2H, d, J ¼
8.8Hz, ArH), 7.34–7.38 (2H, m, ArH), 7.19 (1H, t, J ¼ 8.0Hz,
ArH), 7.02 (1H, d, J ¼ 16.0 Hz, ArCH]CH), 6.99 (2H, d, J ¼
8.8Hz, ArH), 6.88 (2H, d, J ¼ 8.8Hz, ArH), 6.85 (1H, d, J ¼
16.0Hz, ArCH]CH), 4.15 (4H, t, J ¼ 6.4Hz, –OCH2–), 3.88
(4H, t, J ¼ 4.8Hz, –OCH2–), 3.77 (4H, s, –OCH2); 13C NMR
(CDCl3, 100.61MHz): d (ppm) ¼ 159.5, 158.8, 145.1 139.8, 132.6,
130.1, 130.0, 129.7, 129.6, 128.9, 128.3, 127.9, 127.0, 125.0, 119.0,
115.2, 114.9, 110.2, 70.9, 69.8, 67.6, 67.5; MALDI-TOF-MS for
C33H30BrNO4: m/z calcd, 583.14; found 584 [M + H]+.
Dispersion of SWNTs
1 or 2 (18mg) and SWNTs (10mg) were added into 20 ml CHCl3
and mixed solution was sonicated in a bath-type sonicator for
1 h. After sonication, the samples were centrifuged at 3000 rpm
and the supernatant was then carefully decanted. The suspension
was filtered through a 200 nm pore diameter PTFE membrane
filter (Millipore Co) and washed with CHCl3 several times.
The residue was collected and re-suspended in 5 ml CHCl3 by
sonication for 10 min at room temperature.
1
Conclusion
Tributylamine (0.26ml, 1.0mmol) was added to a solution of 3
(0.11g, 0.20mmol), 7 (0.3g, 0.47mmol), Pd(OAc)2 (2.6mg,
11.6mmol) and tri(o-tolyl phosphine) (13mg, 42.6mmol) in dry
DMF (4ml). The solution was bubbled with N2 for 20min and
then the reaction mixture was heated to 90 ꢂC under N2 for 48h.
After cooling, the mixture was poured into methanol. The
precipitated solid was purified by column chromatography (silica
gel) using CHCl3 (Rf ¼ 0.80) as an eluent and recycling prepar-
ative HPLC to obtain 1 as a yellow solid. Yield 0.22g (67%). 1H
NMR (CDCl3, 400.13MHz): d (ppm) ¼ 7.69 (4H, d, J ¼ 8.6Hz,
ArH), 7.62–7.64 (6H, m, ArH and ArCH ¼ CH), 7.51–7.55 (6H,
m, ArH and ArCH ¼ CH), 7.46 (4H, d, J ¼ 8.6Hz, ArH), 7.33–
7.42 (10H, m, ArH and ArCH]CH), 7.14–7.20 (8H, m, ArH
and ArCH]CH), 7.12 (2H, d, J ¼ 16.1Hz, ArCH]CH), 7.00
(2H, d, J ¼ 16.0Hz, ArCH]CH), 6.98 (4H, d, J ¼ 8.8Hz, ArH),
6.90 (4H, d, J ¼ 8.7Hz, ArH), 4.09 (4H, t, J ¼ 6.4Hz, –OCH2–),
4.02 (8H, m, –OCH2–), 1.85–1.88 (12H, m, –CH2–), 1.56–1.59
(12H, m, –CH2–), 1.40–1.42 (8H, m, –CH2–), 1.30–1.35 (24H, m,
–CH2–), 0.91–0.94 (6H, m, –CH3); 13C NMR (CDCl3,
100.61MHz): d (ppm) ¼ 159.5, 158.6, 151.2, 145.1, 138.0, 137.7,
132.6, 129.0, 128.9, 128.8, 128.7, 128.5, 128.3, 127.7, 127.0, 126.5,
125.4, 124.9, 124.5, 123.9, 119.0, 115.2, 114.9, 110.1, 68.0, 31.9,
29.6, 26.1, 22.7, 14.1; MALDI-TOF-MS for C116H128N2O6: m/z
calcd, 1646.27; found 1647 [M + H]+.
Two novel phenylenevinylenes having cyanobiphenyl terminates
were successfully synthesized and characterized. Synthesized
conjugated oligomers 1 and 2 were found to form stable supra-
molecular complexes with SWNTs through strong p–p interac-
tions between the sidewall of SWNTs and phenylenevinylene
segment and wrapping around the SWNTs, imparting excellent
solubility in organic solvents. The addition of excess 1 or 2 into
the dispersed solution induces the formation of precipitates and
the precipitates exhibited thermotropic liquid crystalline phases
(Fig. 5). Birefringent optical textures consisting of numerous
fibrous assemblies appeared in the mesophase range, indicating
that the dispersion of SWNTs within liquid-crystalline hosts
affects the organized structures in the thermotropic liquid-crys-
talline phase. We believe that the dispersion of SWNTs within
liquid-crystalline hosts provides new opportunities for dynami-
cally changing the orientation of SWNTs. The construction
of liquid-crystalline composites containing SWNTs will be of
importance in the development of nanoscopic smart devices such
as electrical switches and circuits through the orientation control
of SWNTs in response to the external stimulus inputs. Fabrica-
tion of devices using liquid crystalline composite materials
composed of 1 or 2 with SWNTs is in progress.
Acknowledgements
2
This work was supported by projects for ‘‘Innovation Creative
Center for Advanced Interdisciplinary Research Areas’’ in
Special Coordination Funds for Promoting Science and
2 was synthesized from 3 and 8 following the same procedure
as for 1. The crude product was purified by column
This journal is ª The Royal Society of Chemistry 2009
J. Mater. Chem., 2009, 19, 1086–1092 | 1091

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