Noncovalent approach to one-dimensional ion conductors: Enhancement of ionic conductivities in nanostructured columnar liquid crystals

Article abstract of DOI:10.1021/ja0775220

Noncovalent design of new liquid-crystalline (LC) columnar assemblies based on an ionic liquid has shown to be useful to achieve anisotropic high ionic conductivities. An equimolar mixture of an ionic liquid, 1-butyl-3- methylimidazolium bromide, and 3-[3,4,5-tri(octyloxy)benzoyloxy]propane-1,2- diol, which is partially miscible with the ionic liquid, exhibits an LC hexagonal columnar phase from -4 to 63°C. This columnar supramolecular assembly forming the nanostructures shows the one-dimensional (1D) ionic conductivity of 3.9 × 10^-3 S cm^-1 at 50°C along the column, which is more than 700 times higher than that of the corresponding covalent-type columnar ionic liquid, 1-methyl-3-[3,4,5-tri(octyloxy)benzyl]- imidazolium bromide, which is 5.3 × 10^-6 S cm^-1 at 50°C. This significant enhancement of the ionic conductivity is attributed to the increase of the mobility of the ionic part.

Full text of DOI:10.1021/ja0775220

Published on Web 01/15/2008
Noncovalent Approach to One-Dimensional Ion Conductors:
Enhancement of Ionic Conductivities in Nanostructured
Columnar Liquid Crystals
Harutoki Shimura,† Masafumi Yoshio,† Koji Hoshino,† Tomohiro Mukai,‡
Hiroyuki Ohno,‡ and Takashi Kato*,†
Department of Chemistry and Biotechnology, School of Engineering, The UniVersity of Tokyo,
Hongo, Bunkyo-ku, Tokyo 113-8656, Japan, and Department of Biotechnology, Tokyo UniVersity
of Agriculture and Technology, Nakacho, Koganei, Tokyo 184-8588, Japan
Received September 29, 2007; E-mail: kato@chiral.t.u-tokyo.ac.jp
Abstract: Noncovalent design of new liquid-crystalline (LC) columnar assemblies based on an ionic liquid
has shown to be useful to achieve anisotropic high ionic conductivities. An equimolar mixture of an ionic
liquid, 1-butyl-3-methylimidazolium bromide, and 3-[3,4,5-tri(octyloxy)benzoyloxy]propane-1,2-diol, which
is partially miscible with the ionic liquid, exhibits an LC hexagonal columnar phase from -4 to 63 °C. This
columnar supramolecular assembly forming the nanostructures shows the one-dimensional (1D) ionic
conductivity of 3.9 × 10-3 S cm-1 at 50 °C along the column, which is more than 700 times higher than
that of the corresponding covalent-type columnar ionic liquid, 1-methyl-3-[3,4,5-tri(octyloxy)benzyl]-
imidazolium bromide, which is 5.3 × 10-6 S cm-1 at 50 °C. This significant enhancement of the ionic
conductivity is attributed to the increase of the mobility of the ionic part.
temperature range to be liquid.1 The self-organization of LC
imidazolium salts has led to the development of low-dimensional
Introduction
Ionic liquids are liquids composed of organic ions.1 They form
disordered molten states at ambient temperature. As these
materials show high ionic conductivities and nonvolatility, they
have advantages for electrolytes in lithium ion batteries, dye-
sensitized solar cells, and fuel cells.2 For further functionalization
of ionic liquids, the introduction of ordered nanostructures and
supramolecular structures3-11 is an important approach. Imida-
zolium-based compounds are widely used as ionic liquids
because of their chemical and electrochemical stability and wider
ion conductors.5,6a-e,7,8 In this case, LC nanostructures that were
macroscopically oriented were used. For example, one-
dimensional (1D) ion conductors composed of organic molecules
have been prepared using columnar LC imidazolium salts.7 The
molecular design of the materials was chemical modification
of imidazolium salts that are normal ionic liquids (Figure 1
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† The University of Tokyo.
‡ Tokyo University of Agriculture and Technology.
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J. AM. CHEM. SOC. 2008, 130, 1759-1765
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A R T I C L E S
Shimura et al.
Figure 1. Schematic illustration of the design of the columnar LC molecules and their assemblies for 1D ion conduction: molecular assembly formed
through noncovalent bonding between an ionic liquid and a fan-shaped structure-inducing molecule (upper) and a fan-shaped molecule bearing an ionic
moiety (lower).
lower). The tri(alkyloxy)phenyl part that has a fan-shaped
structure was attached to the ionic moiety to induce self-
assembly of the molecule into hexagonal columnar structures
due to ionic interactions and nanosegregation between the ionic
and nonionic parts. In these nanostructures, ions are transported
along the direction of the columnar axis. We have also prepared
1D ion-conductive self-standing films by fixing the aligned
columnar LC nanostructures through an in situ polymerization
technique.8 However, their ionic conductivities were still lower
than those required for the practical use (10-2-10-3 S cm-1 at
room temperature) as electrolytes for batteries.12
Supramolecular and noncovalent materials design has been
used to achieve dynamically functional anisotropic materials.4
Our materials design in the present study is that we introduce
more mobile structures in the LC nanostructures (Figure 1
upper). We have employed noncovalent supramolecular ap-
proaches to the materials design. Columnar self-assembled
structures have been designed by self-assembly of simpler ionic
liquids and fan-shaped (aromatic and aliphatic) molecules that
are partially miscible with the salts. If they form nanosegregated
columnar structures through self-assembly of these two partially
interacting molecular components of ionic liquids and fan-
shaped molecules (Figure 1 upper), highly mobile inner columns
could be achieved.
Here, we report on 1D ion-conductive columnar liquid crystals
formed through self-assembly of ionic liquids and dihydroxy-
functionalized fan-shaped molecules. The significant improve-
ment of the conductive properties for the columnar materials
has been successfully achieved by the materials design using
noncovalent molecular interactions.
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A R T I C L E S
0.5 for 2a in the mixture. The mixing of 1a and 2a leads to the
thermal stabilization of the Colh phase compared with the
behavior of 1a itself. The equimolar mixture of 1a and 2a shows
a Colh phase from -4 to 63 °C. The mixture of 1a and 2a in
the molar ratio of 7:3 (1a/2a ) 7:3) shows the highest
columnar-isotropic (Iso) phase transition temperature at 80 °C
in all of the mixtures. All of the mixtures keep low melting
temperatures around 0 °C. However, further increase of 2a in
the mixture leads to the decrease of Colh-Iso phase transition
temperatures. A macroscopic phase separation into two phases
composed of the isotropic liquid and columnar liquid-crystalline
phases occurs when the mole fraction of 2a exceeds 0.5. As
for the binary mixtures of 1b and 2a (Figure 2b), compound
1b is also miscible with 2a up to the mole fraction of 0.5 for
2a in the mixture. The mixtures having more than the mole
fraction of 0.3 for 2a show a Colh phase, while 1b alone and
the mixtures containing less than the fraction of 0.2 for 2a show
cubic (Cub) phases. These Cub phases are viscous and optically
isotropic under the polarizing optical microscope. The isotro-
pization temperatures increase with the increase of the fraction
of 2a until a fraction of 0.5 is achieved for 2a. For instance, an
equimolar mixture of 1b and 2a shows a Colh phase from 24 to
120 °C on heating. These results suggest that these columnar
assemblies are stabilized by the formation of hydrogen bonds
between the ions and the hydroxy groups. Similar stabilization
of the mesophase by hydrogen bonding and charge transfer
interactions has been reported previously.4,15
It is of interest that the mixtures of 1a,b with 2b having the
BF4 ion exhibit macrophase separation and they do not form
homogeneous LC states although 2a shows miscibility with 1a
and 1b. For the supramolecular columnar formation, the ratio
of the volumes for ionic and nonionic parts is important. In the
case of BF4, the anion cannot stay in the inner ionic part of the
column because of its larger size and weaker interactions. The
ionic radius of BF4 is 0.229 nm, while that of Br is 0.196 nm.
In our previous studies,5 we observed that hydroxy-functional
rod-shaped LC molecules forming smectic LC structures were
miscible with 1-ethyl-3-methylimidazolium tetrafluoroborate.
Their layered LC structures having BF4 anions were stabilized
through intermolecular interactions. It is considered that the
formation of smectic sheetlike networks is easier than that of
the columnar networks. Therefore the nanosegregated smectic
phases were stabilized even though ionic interactions based on
BF4 are weaker than those for Br.
Rogers and co-workers reported16 that imidazolium ionic
liquids containing chloride and bromide anions, which are strong
hydrogen bond acceptors, solvated cellulose through hydrogen
bonding between the hydroxy groups and the anions, whereas
ionic liquids with noncoordinating anions BF4 and PF6 did not
serve as solvents for cellulose. Kimizuka and Nakashima also
reported10a that solubility of sugar derivatives in imidazolium
ionic liquids decreased when the bromide anion was replaced
by hydrophobic anions such as PF6 and bis(trifluoromethane-
sulfonyl)imide (TFSI). Moreover, the formation of hydrogen
bonds between imidazolium cations and hydroxy groups was
Figure 2. Phase transition behavior for (a) the mixtures of 1a and 2a and
(b) the mixtures of 1b and 2a on heating. Iso, isotropic; Colh, hexagonal
columnar; Cub, micellar cubic; Cr, crystalline.
Results and Discussion
Liquid-Crystalline Properties. We have designed and
synthesized fan-shaped molecules 1a,b having dihydroxy groups
at their focal point (Figure 1). They were expected to form self-
assembled columnar structures through nanosegregation between
ionophilic and lipophilic parts. We reported that hydroxy
compounds can form stable hydrogen bonds with imidazolium
ions5 and imidazoles.13 Liquid crystallinity of fan-shaped
molecules with polyhydroxy groups has been systematically
examined by Tschierske and co-workers.14 Ionic liquids 1-butyl-
3-methylimidazolium salts with bromide anion 2a and tetrafluo-
roborate anion 2b were chosen for supramolecular organization.
They are common ionic liquids. LC imidazolium salts 3a,b have
also been synthesized to compare the effects of the noncovalent
supramolecular association based on 2a,b on the ionic conduc-
tion and LC behavior of the materials. Compound 1a exhibits
a hexagonal columnar (Colh) phase from 7 to 27 °C on heating.
Figure 2a shows a phase diagram for the mixture of 1a and 2a
as a function of the mole fraction of 2a in the mixture.
Compound 1a is miscible with 2a up to the mole fraction of
(13) (a) Kato, T.; Kawakami, T. Chem. Lett. 1997, 211-212. (b) Kato, T. Struct.
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(14) (a) Borisch, K.; Diele, S.; Go¨ring, P.; Kresse, H.; Tschierske, C. Angew.
Chem., Int. Ed. Engl. 1997, 36, 2087-2089. (b) Borisch, K.; Diele, S.;
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2000, 16, 6701-6708.
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Figure 4. X-ray diffraction pattern of the equimolar mixture of 1a and 2a
at 30 °C.
Figure 3. 1H NMR spectra of (a) 2a alone and (b) the equimolar mixture
of 1a and 2a in CDCl3 (50 mM) at 20 °C. Asterisks denote the proton of
CHCl3.
Figure 5. Intercolumnar distance for the self-assembled mixtures composed
of 1a and 2a.
clarified by the X-ray crystallographic studies by Rogers et al.17
The racemic 1-(2-hydroxypropyl)-3-methylimidazolium tet-
raphenylborate forms a hydrogen-bonded dimer. In this structure,
strong and almost linear hydrogen bonds are formed between
the acidic hydrogen on C2 of the imidazolium ring and the
oxygen atom of the opposing cation.
The interaction between 2a and 1a has been confirmed by
1H NMR experiments (Figure 3). The spectrum for the CDCl3
solution of 2a (50 mM) was compared with that of the equimolar
mixture of 1a and 2a (50 mM). The peak of the proton on C2
of the imidazolium ring for 2a shows a high-field shift in the
presence of 1a (Figure 3). This change is indicative of the
formation of hydrogen bonds between 2a and 1a.2a The IR
spectra for the mixtures also support the existence of the self-
assembled structures (see Supporting Information).
Covalent-type imidazolium salt 3a (Figure 1) exhibits a Colh
phase from -26 to 180 °C, and 3b also shows a Colh phase
from 73 to 180 °C. These phase properties were confirmed by
microscopic observation and X-ray diffraction studies (see
Supporting Information).
The X-ray diffraction measurements for the single compo-
nents of 1a,b and their mixtures with 2a were carried out to
examine the structural changes by noncovalent interactions
between 2a and the hydroxy groups of 1a,b. The X-ray profile
for 1a exhibits the sharp reflections of 2.96 (100), 1.71 (110),
1.48 nm (200) and the broad halo at 0.437 nm, indicating the
formation of a disordered Colh phase (p6mm) (see Supporting
Information). The intercolumnar distance of 1a is 3.42 nm. The
equimolar complex of 1a and 2a exhibits the sharp reflections
of 3.77 (100), 2.53 (110), 1.89 nm (200) and the broad halo at
0.428 nm, as shown in Figure 4. The intercolumnar distance
for the complex is 4.60 nm. Likewise, all other mixtures of 1a
and 2a show the d-spacings with the ratio of 1:1/x3:1/2 in the
diffraction spectra, which is typical for the Colh phase. The
intercolumnar distance for the mixtures increases linearly from
3.42 to 4.60 nm with the increase of the mole fraction of 2a in
the mixtures (Figure 5). These results suggest that 2a is
organized into the center of the columnar structures.
Orientation. Uniaxial orientation of the self-organized
columnar assemblies has been achieved for these two component
systems, which is essential for anisotropic 1D ion conduction.
These columns normally prefer to form random orientation on
the surface of glassy substrates. To align the columns uniaxially,
a shear stress parallel to the surface of the substrate was applied
to the columnar materials comprised of the polydomain struc-
tures. After shearing the materials, no boundary of the columnar
domains was observed under a polarizing microscope. The
macroscopic orientation of columns has been confirmed by
microscope observation and two-dimensional small-angle X-ray
scattering measurements. A split diffraction pattern is observed
for the sheared samples, indicating a uniaxial orientation of
columns along the direction of shearing (Figure 6).8
Ion-Conductive Properties. The columnar LC assemblies
composed of equimolar mixtures of 1a,b and 2a (1a/2a and
1b/2a) and 3a,b were homogeneously aligned by mechanical
shearing in two directions parallel and perpendicular to the
comb-shaped gold electrodes deposited on a glassy substrate.
For these samples, ionic conductivities for two directions parallel
and perpendicular to the columnar axis have been successfully
measured by the alternating current impedance method.7,8 We
have found that the supramolecular noncovalent ion-conductive
LC column of 1a/2a shows high conductivities that are on the
order of 10-3 S cm-1 at ambient temperature.
Figure 7 shows ionic conductivities of 1a/2a and 3a in the
direction parallel (σ|) and perpendicular (σ ) to the columnar
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2003, 5, 731-736.
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Noncovalent Approach to 1D Ion Conductors
A R T I C L E S
Figure 6. Two-dimensional X-ray scattering images of the equimolar
mixture of 1b and 2a in the Colh phase: (a) nonoriented material; (b)
uniaxially oriented material. The arrow shows the direction of shearing.
Figure 8. Molecular structures of columnar LC imidazolium derivatives
4a-f7and 5.8
Figure 7. Arrhenius plots of ionic conductivities for 1a/2a and 3a, and
ionic liquid 2a alone on heating: (B) parallel and (9) perpendicular to the
columnar axis for 1a/2a; (O) parallel and (0) perpendicular to the columnar
axis for 3a; for isotropic ionic liquid 2a (∆).
axis as a function of temperature. The ionic conductivities of
2a are also given in Figure 7. Although the ionic conductivities
(σ|) of the newly designed complex 1a/2a forming the Colh
phase are lower than those of 2a alone that shows the isotropic
liquid state, the values of 1a/2a are in the highest level among
those of columnar liquid crystals based on imidazolium salts.7,8
For example, complex 1a/2a shows the σ| values of 3.9 × 10-3
S cm-1 at 50 °C and 8.2 × 10-3 S cm-1 at 62 °C. We recently
reported on a series of columnar LC imidazolium salts7,8 shown
in Figure 8. These materials show only the conductivities (σ|)
in the range of 10-5-10-8 S cm-1 at 50 °C. For example,
compound 4a7a shows a value of 9.4 × 10-6 S cm-1 at 50 °C,
while compound 58 exhibits a value of 3.1 × 10-5 S cm-1 at
50 °C. For the conductivities of the materials based on the same
anion (Br-), the σ| value of the complex 1a/2a at 50 °C becomes
730 times higher than that (σ| ) 5.3 × 10-6 S cm-1 at 50 °C)
of fan-shaped imidazolium salt 3a prepared in the present study.
Compound 3a must be heated up to 170 °C to achieve the same
value of the conductivity as that of 1a/2a at 50 °C. For 1b/2a,
the σ| value of 3.0 × 10-4 S cm-1 is obtained in the Colh phase
at 80 °C. This value of 1b/2a is 250 times higher than the value
of σ| ) 1.2 × 10-6 S cm-1 at 80 °C for the fan-shaped
imidazolium salt 3b (see Supporting Information). For the
noncovalent-type materials, the enhanced mobility of the ionic
liquid part in the center of the column should improve the ionic
conductivity as we designed. The σ| values of 1a/2a and 3a are
higher than the σ values because the structure-directing
lipophilic part acts as the ion-insulating part. No anisotropy is
observed when the materials become isotropic liquid states
Figure 9. Arrhenius plots of ionic conductivities for 1a/2a, 1b/2a, and
ionic liquid 2a alone: (B) parallel and (9) perpendicular to the columnar
axis for 1a/2a; (() parallel and (1) perpendicular to the columnar axis for
the mixture based on 1b/2a; for isotropic ionic liquid 2a (∆).
above 63 °C and 180 °C for 1a/2a and 3a, respectively. As for
1a/2a, the anisotropy is observed up to 72 °C because 1a/2a
shows a broader isotropization temperature range. These results
indicate that the 1D conducting path is formed in these self-
assembled columnar materials.
Figure 9 compares the ionic conductivities of noncovalent-
type LC materials 1a/2a and 1b/2a. The σ| value of 3.9 × 10-3
S cm-1 for 1a/2a at 50 °C is 79 times higher than that (4.9 ×
10-5 S cm-1) of 1b/2a as a consequence of the lower viscosity
of 1a/2a compared to 1b/2a. The anisotropy (σ|/σ ) of ionic
conductivities for 1a/2a is 7, and that of 1b/2a is 87 at 50 °C.
The higher anisotropy for 1b/2a is due to the longer dodecyloxy
chains of 1b working as more effective insulating walls to block
the leak of ions than the octyloxy chains of 1a. The values of
anisotropy for the noncovalent-type materials show the same
9
J. AM. CHEM. SOC. VOL. 130, NO. 5, 2008 1763

A R T I C L E S
Shimura et al.
were extracted with ethyl acetate. The solvent was evaporated under
reduced pressure. The residue was dissolved in wet ethanol (50 mL,
containing 5% water). After addition of p-toluenesulfonic acid mono-
hydrate (2.30 g, 12.1 mmol), the solution was refluxed for 3 h. After
removal of the solvent under reduced pressure, the residue was dissolved
in ethyl acetate (50 mL) and washed with water and brine, successively.
The resulting organic phase was dried over sodium sulfonate, filtered,
and evaporated in Vacuo. The residue was purified by flash column
chromatography on silica gel (eluent: CHCl3/MeOH ) 20/1) followed
degree as those of the covalent-type materials, depending on
the length of alkyloxy chains.
Recently, we reported that the anisotropy of ionic conductivi-
ties for the polymer thin films of 5 was about 103, which was
in the highest level in the series of our ionic liquid crystal
systems. It is interesting to compare the anisotropies of ionic
conductivities of columnar ionic liquid crystals with those of
electric conductivities of columnar π-conjugated liquid crystals.
The anisotropies of electric conductivities of triphenylene18a and
tricycloquinazoline18b derivatives were in the range of 102 to
103.
1
by GPC to give 1a (1.80 g, 3.10 mmol, 77%) as a liquid crystal. H
NMR (400 MHz, CDCl3): δ ) 7.25 (s, 2 H), 4.46-4.37 (m, 2 H),
4.12-3.92 (m, 7 H), 3.80-3.72 (m, 1 H), 3.72-3.63 (m, 1 H), 2.84
(d, J ) 4.9 Hz, 1 H), 2.41 (t, J ) 6.4 Hz, 1 H), 1.90-1.66 (m, 6 H),
1.56-1.16 (m, 30 H), 0.89 (t, J ) 6.8 Hz, 9H); 13C NMR (100 MHz,
CDCl3): δ ) 167.0, 152.9, 142.8, 123.9, 108.2, 73.5, 70.4, 69.2, 65.8,
63.3, 31.87, 31.80, 30.3, 29.48, 29.34, 29.32, 29.27, 29.26, 26.05, 26.00,
22.66, 22.65, 14.1. IR (KBr): 3426, 2955, 2926, 2856, 1715, 1587,
1500, 1467, 1430, 1381, 1336, 1254, 1219, 1115, 1058, 1013, 915,
864, 816, 765, 722, 667 cm-1. MS (MALDI) calcd for C34H60O7:
580.43. Found: 580.74. Elemental analysis calcd for C34H60O7: C,
70.31; H, 10.41%. Found: C, 70.31; H, 10.65%.
Conclusion
New columnar LC assemblies are formed by self-organization
of an ionic liquid, 1-butyl-3-methylimidazolium bromide, and
mesogenic molecules with hydroxy groups, 3-[3,4,5-tri(alky-
loxy)benzoyloxy]propane-1,2-diol, through noncovalent inter-
molecular interactions. These assemblies are macroscopically
aligned by mechanical shearing. They show ionic conductivities
on the order of 10-3 S cm-1 at ambient temperature which are
higher than those of the corresponding covalent-type of colum-
nar LC ionic liquids that are obtained by chemical modification
of the ionic liquid. The noncovalent material design shown
herein would provide us with low-dimensional ion conductors
with a variety of LC nanostructures.7,8,19
Synthesis of 3-[3,4,5-Tri(dodecyloxy)benzoyloxy]propane-1,2-diol
(1b). The compound was prepared from 3,4,5-tri(dodecyloxy)benzoic
acid and 2,2-dimethyl-1,3-dioxolan-4-methanol by the method described
1
for 1a (65%, a translucent solid). H NMR (400 MHz, CDCl3): δ )
7.25 (s, 2 H), 4.47-4.36 (m, 2 H), 4.13-3.93 (m, 7 H), 3.80-3.72
(m, 1 H), 3.71-3.63 (m, 1 H), 2.80 (d, J ) 4.9 Hz, 1 H), 2.35 (t, J )
6.3 Hz, 1 H), 1.87-1.70 (m, 6 H), 1.56-1.20 (m, 54 H), 0.88 (t, J )
6.8 Hz, 9H); 13C NMR (100 MHz, CDCl3): δ ) 166.9, 152.8, 142.7,
123.9, 108.1, 73.5, 70.3, 69.2, 65.7, 63.3, 31.89, 31.88, 30.3, 29.71,
29.68, 29.67, 29.65, 29.63, 29.60, 29.5, 29.37, 29.36, 29.33, 29.26,
26.05, 26.00, 22.65, 14.1. IR (KBr): 3394, 2919, 2850, 1712, 1587,
Experimental Section
General Procedures. Recycling preparative GPC was conducted
1
with a Japan Analytical Industry LC-908 chromatograph. H and 13C
1503, 1469, 1431, 1389, 1338, 1254, 1220, 1120, 859, 762, 721 cm-1
.
NMR spectra were obtained using a JEOL JNM-LA400 at 400 and
100 MHz in CDCl3, respectively. Chemical shifts of 1H and 13C NMR
signals were quoted to internal standard Me4Si and expressed by
chemical shifts in ppm (δ), multiplicity, coupling constant (Hz), and
relative intensity. IR measurements were conducted on a JASCO FT/
IR-660 Plus on KBr plates. Matrix-assisted laser desorption ionization
time-of-flight (MALDI-TOF) mass spectra were performed on an
Applied Biosystems Voyager-DE STR spectrometer. Elemental analyses
were carried out with a Perkin-Elmer CHNS/O 2400 apparatus and a
Yanaco MT-6 CHN autocorder. Differential scanning calorimetry (DSC)
measurements (scanning rate of 10 K min-1) were conducted with a
NETZSCH DSC 204 Phoenix differential scanning calorimeter. An
Olympus BH-2 optical polarizing microscope equipped with a Mettler
FP82 HT hot-stage was used to verify thermal transitions and
characterize anisotropic textures. Wide-angle X-ray diffraction (WAXD)
patterns were obtained using a Rigaku RINT-2500 diffractometer with
Cu KR radiation. Two-dimensional small-angle X-ray scattering (2D
SAXS) patterns of the aligned materials were also recorded using an
image plate detector (R-AXIS DS3C).
Materials. All chemical reagents and solvents were obtained from
commercial sources and used without purification. All reactions were
carried out under an argon atmosphere in anhydrous solvents.
Synthesis of 3-[3,4,5-Tri(octyloxy)benzoyloxy]propane-1,2-diol
(1a). A solution of 3,4,5-tri(octyloxy)benzoic acid20 (2.03 g, 4.01 mmol),
2,2-dimethyl-1,3-dioxolan-4-methanol (1.35 g, 10.2 mmol), 1-ethyl-3-
(3-dimethylaminopropyl)carbodiimide hydrochloride (1.96 g, 10.2
mmol), and 4-dimethylaminopyridine (0.45 g, 3.68 mmol) in dry CH2-
Cl2 (10 mL) was stirred for 3 h at room temperature. The reaction
mixture was poured into a sat. NH4Cl aqueous solution, and the products
MS (MALDI) calcd for C46H84O7: 748.62. Found: 748.87. Elemental
analysis calcd for C-46H84O7: C, 73.75; H, 11.30%. Found: C, 74.09;
H, 11.20%.
Preparation of Ionic Liquid Mixtures: Before making mixtures,
the materials were dried under reduced pressure over 80 °C. A CH2Cl2
solution of 1a or 1b was added to a requisite amount of a CH2Cl2
solution of an ionic liquid 2a2a or 2b.21 The solvent was removed by
slow evaporation by using the flow of an argon gas, and the resultant
mixture was dried under reduced pressure at 25 °C for 5 h.
Synthesis of 1-Methyl-3-[3,4,5-tri(octyloxy)benzyl]imidazolium
Bromide (3a). A mixture of 3,4,5-tris(octyloxy)benzyl bromide22 (0.284
g, 0.511 mmol) and 1-methylimidazole (0.420 g, 5.11 mmol) in a
pressure tube (100 mL) equipped with a stirring bar was heated at
80 °C for 10 h with vigorous stirring. The reaction mixture was poured
into water and washed. The solid was filtered and then dissolved in
chloroform, and the organic phase was separated. The organic phase
was washed with a sat. NaCl aqueous solution, dried over anhydrous
MgSO4, filtered through a pad of Celite, and concentrated in Vacuo.
The residue was purified by flash column chromatography on silica
gel (eluent: chloroform/methanol ) 10/1), followed by recycling GPC,
and then recrystallized from acetone to give 3a (158 mg, 0.247 mmol)
in a yield of 48% as a white solid. 1H NMR (400 MHz, CDCl3): δ )
10.78 (s, 1H), 7.18 (t, J ) 1.7 Hz, 1H), 7.16 (t, J ) 1.7 Hz, 1H), 6.67
(s, 2H), 5.42 (s, 2H), 4.08 (s, 3H), 3.98 (t, J ) 6.5 Hz, 4H), 3.94 (t, J
) 6.5 Hz, 2H), 1.85-1.56 (m, 6H), 1.52-1.04 (m, 30H), 0.88 (t, J )
7.0 Hz, 9H); 13C NMR (100 MHz, CDCl3): δ ) 153.70, 138.74, 137.30,
127.51, 123.08, 121.54, 104.48 73.37, 69.36, 53.67, 36.71, 31.81, 31.74,
30.23, 29.45, 29.32, 29.29, 29.21, 26.04, 25.98, 22.59, 14.03. IR: 3457,
3378, 3141, 3068, 2925, 2853, 1591, 1559, 1503, 1442, 1388, 1335,
(18) (a) Boden, N.; Bushby, R. J.; Clements, J. J. Chem. Phys. 1993, 98, 5920-
5931. (b) Boden, N.; Borner, R. C.; Bushby, R. J.; Clements, J. J. Am.
Chem. Soc. 1994, 116, 10807-10808.
(21) Nishida, T.; Tashiro, Y.; Yamamoto, M. J. Fluorine Chem. 2003, 120, 135-
(19) Ichikawa, T.; Yoshio, M.; Hamasaki, A.; Mukai, T.; Ohno, H.; Kato, T. J.
Am. Chem. Soc. 2007, 129, 10662-10663.
141.
(22) Hammond, S. R.; Zhou, W. J.; Gin, D. L.; Avlyanov, J. K. Liq. Cryst.
2002, 29, 1151-1159.
(20) Rowe, K. E.; Bruce, D. W. J. Mater. Chem. 1998, 8, 331-341.
9
1764 J. AM. CHEM. SOC. VOL. 130, NO. 5, 2008

Noncovalent Approach to 1D Ion Conductors
A R T I C L E S
1247, 1168, 1111, 987, 855, 771, 752, 723, 700, 621 cm-1. MS
(MALDI) calcd for C35H61N2O3+: 557.5. Found: 557.5.
Acknowledgment. We would like to thank Dr. T. Nishimura
for helpful discussions. This study was partially supported by
Grant-in-Aid for Scientific Research (A) (No. 19205017) (T.K.)
from the Japan Society for the Promotion of Science (JSPS)
and Grant-in-Aid for the Global COE Program for Chemistry
Innovation through Cooperation of Science and Engineering
(T.K.). H.S. is thankful for financial support from JSPS Research
Fellowships for Young Scientists.
Synthesis of 1-Methyl-3-[3,4,5-tri(dodecyloxy)benzyl]imidazolium
Bromide (3b). Titled compound was prepared using the same procedure
1
described for 3a. H NMR (400 MHz, CDCl3): δ ) 10.89 (s, 1H),
7.21 (t, J ) 1.7 Hz, 1H), 7.15 (t, J ) 1.7 Hz, 1H), 6.65 (s, 2H), 5.42
(s, 2H), 4.08 (s, 3H), 3.96 (t, J ) 6.4 Hz, 4H), 3.93 (t, J ) 6.4 Hz,
4H), 1.85-1.65 (m, 6H), 1.52-1.11 (m, 54H), 0.88 (t, J ) 6.8 Hz,
9H); 13C NMR (100 MHz, CDCl3): δ ) 153.75, 138.83, 138.26,
127.55, 122.85, 121.26, 107.48, 73.40, 69.37, 53.77, 36.61, 31.88, 31.87,
30.27, 29.71, 29.67, 29.64, 29.62, 29.60, 29.55, 29.41, 29.32, 26.08,
26.04, 22.64, 14.08. IR: 3436, 3068, 2919, 2850, 1585, 1560, 1501,
1466, 1389, 1335, 1249, 1170, 1111, 861, 754, 721 cm-1. MS (MALDI)
calcd for C47H85N2O3+: 725.7. Found: 725.2.
Measurements of Ionic Conductivities. Temperature dependence
of ionic conductivities was measured by the complex impedance method
using a Schlumberger Solartron 1260 impedance analyzer (frequency
range: 10 Hz-10 MHz, applied voltage: 0.3 V) equipped with a
temperature controller.6d,7a,23 The heating rate of ionic conductivity
measurements was fixed to 3 K min-1 from 30 to 150 °C. Ionic
Supporting Information Available: X-ray diffraction spectra
of 1a in the Colh phase, 1b in the Cub phase, the equimolar
mixture of 1b and 2a in the Colh phase, 3a in the Colh phase,
and 3b in the Colh phase; 1H NMR spectra of 2a alone and the
equimolar mixture of 1a and 2a in CDCl3; Arrhenius plots of
ionic conductivities for 3b; analytical and spectral characteriza-
tion data of 3a and 3b; an example of the impedance spectrum
for the equimolar mixture of 1a and 2a; IR spectra of 1a and
the equimolar mixture of 1a and 2a; and DSC thermograms
and polarized optical microscopic images of 1a, the equimolar
mixture of 1a and 2a, 1b, and the equimolar mixture of 1b and
2a. This material is available free of charge via the Internet at
http://pubs.acs.org.
conductivities were practically calculated to be the product of 1/Rb (Ω-1
)
times cell constants (cm-1) for comb-shaped gold electrodes, which
were calibrated with KCl aqueous solution (1.00 mmol L-1) as a
standard conductive solution. The impedance data (Z) were modeled
as a connection of two RC circuits in series.
(23) Macdonald, J. R. Impedance Spectroscopy Emphasizing Solid Materials
and Systems; John Wiley & Sons: New York, 1987.
JA0775220
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