Nanostructured liquid crystals combining ionic and electronic functions

Article abstract of DOI:10.1021/ja101366x

New molecular materials combining ionic and electronic functions have been prepared by using liquid crystals consisting of terthiophene-based mesogens and terminal imidazolium groups. These liquid crystals show thermotropic smectic A phases. Nanosegregation of the π-conjugated mesogens and the ionic imidazolium moieties leads to the formation of layered liquid-crystalline (LC) structures consisting of 2D alternating pathways for electronic charges and ionic species. These nanostructured materials act as efficient electrochromic redox systems that exhibit coupled electrochemical reduction and oxidation in the ordered bulk states. For example, compound 1 having the terthienylphenylcyanoethylene mesogen and the imidazolium triflate moiety forms the smectic LC nanostructure. Distinct reversible electrochromic responses are observed for compound 1 without additional electrolyte solution on the application of double-potential steps between 0 and 2.5 V in the smectic A phase at 160 °C. In contrast, compound 2 having a tetrafluorophenylterthiophene moiety and compound 3 having a phenylterthiophene moiety exhibit irreversible cathodic reduction and reversible anodic oxidation in the smectic A phases. The use of poly(3,4-ethylenedioxythiophene)-poly(4-styrene sulfonate) (PEDOT-PSS) as an electron-accepting layer on the cathode leads to the distinct electrochromic responses for 2 and 3. These results show that new self-organized molecular redox systems can be built by nanosegregated π-conjugated liquid crystals containing imidazolium moieties with and without electroactive thin layers on the electrodes.

Full text of DOI:10.1021/ja101366x

Published on Web 05/13/2010
Nanostructured Liquid Crystals Combining Ionic and
Electronic Functions
Sanami Yazaki,† Masahiro Funahashi,*,† Junko Kagimoto,‡ 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 February 16, 2010; E-mail: funahashi@chembio.t.u-tokyo.ac.jp; kato@chiral.t.u-tokyo.ac.jp
Abstract: New molecular materials combining ionic and electronic functions have been prepared by using
liquid crystals consisting of terthiophene-based mesogens and terminal imidazolium groups. These liquid
crystals show thermotropic smectic A phases. Nanosegregation of the π-conjugated mesogens and the
ionic imidazolium moieties leads to the formation of layered liquid-crystalline (LC) structures consisting of
2D alternating pathways for electronic charges and ionic species. These nanostructured materials act as
efficient electrochromic redox systems that exhibit coupled electrochemical reduction and oxidation in the
ordered bulk states. For example, compound 1 having the terthienylphenylcyanoethylene mesogen and
the imidazolium triflate moiety forms the smectic LC nanostructure. Distinct reversible electrochromic
responses are observed for compound 1 without additional electrolyte solution on the application of double-
potential steps between 0 and 2.5 V in the smectic A phase at 160 °C. In contrast, compound 2 having a
tetrafluorophenylterthiophene moiety and compound 3 having a phenylterthiophene moiety exhibit irreversible
cathodic reduction and reversible anodic oxidation in the smectic A phases. The use of poly(3,4-
ethylenedioxythiophene)-poly(4-styrene sulfonate) (PEDOT-PSS) as an electron-accepting layer on the
cathode leads to the distinct electrochromic responses for 2 and 3. These results show that new self-
organized molecular redox systems can be built by nanosegregated π-conjugated liquid crystals containing
imidazolium moieties with and without electroactive thin layers on the electrodes.
Introduction
Efficient and anisotropic ionic conductions have been observed
in these nanostructured LC phases.3 Liquid crystals bearing
The integration of molecular functions in supramolecular
assemblies is a promising approach to the development of new
materials exhibiting enhanced and dynamic functions.1 Self-
organized nanomaterials that exhibit electronic and ionic func-
tions can be obtained by using liquid-crystalline (LC) molecular
assemblies of π-conjugated and ionic molecular components.2-4
Liquid crystals consisting of the ionic and nonionic moieties
self-assemble into the nanosegregated structures such as co-
lumnar (cylinder),3a-c,g,i smectic (layer),3d,e and bicontinuous
cubic3f phases to form anisotropic ion-conductive pathways.
π-conjugated moieties exhibit electronic charge transport4 in
the columnar4f-i,n,o and smectic phases.4j-m The enhanced
transport properties of the electronic charge carriers for these
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† The University of Tokyo.
‡ Tokyo University of Agriculture and Technology.
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10.1021/ja101366x  2010 American Chemical Society

Ion-Active and Electroactive Liquid Crystals
A R T I C L E S
Figure 1. Schematic illustration of a nanostructured smectic LC phase for
the coupling of the ionic and electronic functions.
Figure 2. Molecular structures of liquid crystals 1-3.
liquid crystals have been applied to field-effect transistors5a-h
and electroluminescence devices.5i-k
the efficient redox materials based on liquid crystals 1-3
(Figure 2). These molecules consist of π-conjugated me-
sogens and ionic moieties. They have been designed to induce
smectic A (SmA) phases where the ion and hole transport
layers are alternately formed through the nanosegregation.
A new redox system is also designed by combining poly(3,4-
ethylenedioxythiophene)-poly(4-styrene sulfonate) (PEDOT-
PSS)7 films with the liquid crystals.
Our intention is to develop new redox-active materials by
the combination of ionic and electronic functions in the
nanostructured LC phases (Figure 1). We expect that the
enhanced transportations of ions and electronic charge carriers
couple in the nanosesegregated LC structures to produce new
functional materials.2b,6 In the present paper, we report on
Conventional organic redox-active materials applied to
electrochromic devices,8 actuators,9 and light-emitting elec-
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electrolyte solutions or combined with solid electrolytes.
Recently, we reported the preliminary results of the redox
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Scheme 1. Synthetic Routes of Liquid Crystals 1 and 2
behavior for compound 3 in the LC phase without electrolytes
(Figure 2).2b The ion and hole transportations in the nano-
structured SmA phase induced electrochromism without
electrolytes.
crystals where the structure of ion- and hole-transporting layers
is well-defined on the scale of nanometer.
Results and Discussion
Synthesis of Materials. Compounds 1 and 2 were synthesized
as shown in Scheme 1. The Knoevenagel condensation between
4-(12-bromododecyloxyphenyl)acetonitrile (5) and 5-hexyl-2,2′:
5′,2′′-terthiophene-5′′-carbaldehyde (6) yielded cyanoethylene
derivative 7. The quaternization reaction of N-methylimidazole
with compound 7 followed by anion exchange using silver
triflate afforded liquid crystal 1. The aromatic core of compound
2 was synthesized by the Pd(0)-catalyzed coupling reaction5c,12
between tetrafluorobenzene derivative 9 and 5-bromo-2′-hexyl-
2,2′:5′,2′′-terthiophene derivative 10. The transformation from
the intermediate 11 to compound 2 was carried out by a
procedure similar to that for compound 3.2b
In the redox activity of the liquid crystals combining ionic
and electronic functions, the mobile ions in the nanostructure
play a crucial role. The enhancement of electronic functions
by the combination with ions has been studied in conjugated
polyelectrolytes.11 The conjugated polyelectrolytes consisting
of π-conjugated polymer backbones bearing ionic moieties have
been applied to light-emitting diodes,11a,b light-emitting elec-
trochemical cells,11c-g and solar cells.11h,i However, the elec-
tronic charge carrier mobilities are low, of the order of
10-7-10-6 cm2 V-1 s-1, because of the disordered structures
of the polymers.11c Their ionic conductivities are also low
because of the large viscosity. In contrast, the efficient ion and
hole transports are possible in the nanosegregated smectic liquid
Mesomorphic Behavior. The LC properties of 1-3 are
summarized in Table 1. Compounds 1-3 exhibit the enantio-
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Table 1. Thermal Properties of Liquid Crystals 1-3
compd
thermal propertiesa
1
2
3
Cr
Cr
Cr
79 (18)
75 (16)
90 (48)
SmA
SmA
SmA
185 (7.7)
149 (2.7)
152 (4.3)
Iso
Iso
Iso
a Transition temperatures (°C) are given as the onset of the peaks
detected by the differential scanning calorimetry (DSC) measurements
on the second heating at a scanning rate of 10 °C min-1. The transition
enthalpies (kJ mol-1) are in parentheses. Cr: crystalline. SmA: smectic
A. Iso: isotropic liquid. For liquid crystals 2, the transition peaks
corresponding to the crystallization and melting are observed below the
Cr-SmA transition temperature on the heating cycle in the DSC
thermogram (see Supporting Information).
Figure 4. X-ray diffraction pattern for 1 in the SmA phase at 160 °C.
tropic smectic A (SmA) phases. The focal-conic fan textures
are observed by the polarizing microscope observation for 1
and 2 on polyimide films in the mesomorphic temperature ranges
(Figure 3). On glass substrates, the homeotropic textures for 1
and 2 are observed as dark fields.
The LC structures of 1-3 have been studied by small-angle
X-ray scattering (see Supporting Information, Figure S5) and
wide-angle X-ray diffraction. The wide-angle X-ray diffraction
patterns for compounds 1 and 2 in the SmA phases show two
diffraction peaks indexed as (002) and (003) in the low angle
regions, indicating a layer spacing of 51 Å for compound 1 at
160 °C (Figure 4) and a layer spacing of 51 Å for 2 at 120 °C
(see Supporting Information). In small-angle X-ray scattering
patterns for compounds 1 and 2, weak peaks corresponding to
(001) diffractions are observed (see Supporting Information).
No peaks are observed in the wide-angle regions for 1 and 2
other than the diffusive halo. The molecular lengths of 1 and 2
are estimated to be approximately 47 and 45 Å, respectively,
by molecular mechanics (MM2) calculations. The results
indicate that the LC molecules are arranged in the smectic layers
in the antiparallel manner as shown in Figure 5.13 The
nanosegregation leads to the formation of the LC nanostructures
in which two-dimensional layers of the π-conjugated mesogens
and ionic moieties are separatedly self-organized by the insulat-
ing alkyl chains. The formation of such a layered nanostructure
was also observed for compound 3 in the SmA phase as reported
in our previous communication.2b
Redox Properties in Solution States. The redox properties of
compounds 1-3 in the CH2Cl2 solution states have been
examined by the cyclic voltammetry measurement (Figure 6).
For compound 1, quasi-reversible one-electron oxidation and
one-electron reduction are observed at the half-wave potentials
of 0.86 and -1.62 V versus Ag+/Ag, respectively (Figure 6a).
The cyclic voltammograms of compounds 2 and 3 (Figure 6b,c)
exhibit only quasi-reversible one-electron oxidations without any
reversible reduction peaks within the electrochemical window
of the electrolyte solution. The oxidation peaks of 2 and 3 are
observed at the half-wave potentials of 0.98 and 0.69 V versus
Figure 5. Schematic illustration of a possible structure in the SmA phases
for liquid crystals 1-3. Green cylinders, red ellipsoids, and orange spheres
represent π-conjugated moieties, triflate anions, and imidazolium cations,
respectively. The ionic and π-conjugated moieties are organized into
segregated layers.
Ag+/Ag, respectively. For compound 1, the electron-withdraw-
ing cyano group effectively stabilizes the reduced anionic state,14
leading to the quasi-reversible electrochemical reduction besides
the quasi-reversible oxidation. The tetrafluorophenyl group of
2 also withdraws electrons, leading to an increase in the
oxidation potential. However, the radical anion state of the
π-conjugated system of 2 is not sufficiently stabilized, resulting
in the irreversible reduction. These results show that compound
1 has a suitable mesogen that could be used in the electro-
chromism in the LC state.
Redox Activities in the Bulk States. The redox responses of
liquid crystals 1-3 in the bulk states have been achieved. The
response behavior was measured by monitoring the transmitted
light intensity of a He-Ne laser (λ ) 632.8 nm) through the
Figure 3. Polarizing optical photomicrographs of liquid crystals: 1 (a) and 2 (b) at 120 °C.
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Yazaki et al.
between 0 and 2.5 V. The responses of the transmittance
observed for compound 1 (Figure 7a) are more distinct than
those for 3 (Figure 7b). The value of the driving voltage of 2.5
V for 1 is close to its HOMO-LUMO energy gap of 2.4 V
(see Supporting Information, Figure S2). This observation
suggests that the electrochemical oxidation at the anode couples
with the reduction at the cathode in the SmA phase of compound
1, as shown in Figure 8a. In contrast, the change of the transmit-
tance for compound 3 is almost negligible on the application of
the same potential steps between 0 and 2.5 V (Figure 7b). The
increased applied voltage of 5 V is required to give a clear color
change for liquid crystal 3 as was observed in our preliminary
experiment.2b The value of the HOMO-LUMO energy gap for 3
is 2.8 eV (see Supporting Information, Figure S2). The driving
voltage for 3, which is 2.2 V higher than its HOMO-LUMO
energy gap, can be ascribed to the irreversible cathodic reduction
of compound 3, although the oxidation process of 3 at the anode
is reversible (Figure 8b). After repeated redox cycles, decomposed
red products are observed on the cathode of the cell for liquid
crystal 3. For liquid crystal 2 containing the tetrafluorophenyl
moiety, no color change is observed on the application of the
double-potential steps between 0 and 2.5 V in the SmA phase.
When the applied voltage is increased to 5 V, the color slightly
changes. The irreversible cathodic reduction and the high oxidation
potential for liquid crystal 2 (Figure 6b) result in the unstable
electrochromic behavior.
Figure 6. Cyclic voltammograms of the CH2Cl2 solutions of compounds 1
(a), 2 (b), and 3 (c) (2.0 mM) with a Pt working electrode. The supporting
electrolyte is Bu4NClO4 (0.10 M). The sweep rate is 100 mV s-1 except for
the negative potential region of compound 2, where the rate is 50 mV s-1
.
samples of 1-3 in the cells consisting of two ITO-coated glass
plates. The ITO electrodes were coated with polyimide thin films
to deactivate the surface defects on the ITO.15 The polyimide
thin films preserve the conductivities of the ITO surface.5k The
cells were filled with the compounds in the isotropic states by
capillary action. When the samples were cooled to the SmA
phases, focal-conic fan textures were observed by using a
polarizing optical microscope, indicating that the LC molecules
were aligned parallel to the electrode surfaces. In those
alignments, the smectic layers were vertical to the electrode
surfaces and the electric fields were applied in the direction of
the ion transport layers. Figure 7 shows the responses of the
transmittance for compounds 1 and 3 in the liquid crystal cells
as a function of time on the application of double-potential steps
Liquid crystal 3 was expected to exhibit efficient electro-
chromic responses if the anodic oxidation is coupled with the
Figure 7. Responses of transmittance of the cell with compound 1 in the SmA phase at 160 °C (a) and with compound 3 in the SmA phase at 120 °C (b)
on the application of double-potential steps between 0 V (2.5 s) and 2.5 V (2.5 s). The sample thickness is 4 µm.
Figure 8. Schematic illustration of the redox molecular systems combining ionic and electronic functions. (a) The redox system of liquid crystal 1 exhibiting
reversible reduction besides the reversible oxidation. (b) The redox system of liquid crystal 3 whose anion radical state is not stabilized. The cathodic
reduction is irreversible, while the anodic oxidation is reversible. (c) The redox system of liquid crystal 3 using the PEDOT-PSS thin film as an electron
acceptor coated on the cathode combined with the reversible oxidation of liquid crystal 3. The light-green cylinders represent neutral π-conjugated moieties.
The dark-green cylinders are the oxidized or reduced ones. The red ellipsoids and orange spheres represent triflate anions and imidazolium cations, respectively.
The brown cylinders in (b) represent decomposed products of liquid crystal 3 by the irreversible reduction.
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Ion-Active and Electroactive Liquid Crystals
A R T I C L E S
Figure 9. Responses of the transmittance of the cell with compound 3 in the SmA phase at 120 °C. (a) The double-potential steps between 0 V (2.5 s) and
2 V (2.5 s) are applied to the cell. The cathode and the anode of the cell are coated with PEDOT-PSS and polyimide, respectively. The sample thickness
is 7 µm. (b) The double-potential steps between -1 V (25 s) and 5 V (25 s) are applied to the cell. The cathode and anode of the cell are bare ITO electrodes.
The sample thickness is 4 µm.
Figure 10. Photographs of the cell for compound 3 in the SmA phase at 120 °C at the applied potential of 2 V (a) and 0 V (b). In the cell, the cathode and
the anode are coated with PEDOT-PSS and polyimide films, respectively. The sample thickness is 7 µm.
cathodic reduction as schematically illustrated in Figure 8c. The
PEDOT-PSS layer has been chosen as an electron acceptor
on the cathode for the combination with liquid crystal 3. On
the anode, the electrons released from the π-conjugated systems
of liquid crystal 3 should be compensated rapidly by the electron
acceptance on the cathodic PEDOT-PSS layer (Figure 8c).
Figure 9a shows the responses of the transmittance under the
double-potential application between 0 and 2 V for compound
3 in the ITO cell whose cathode is spin-coated with the
PEDOT-PSS thin film. The distinct responses are observed
under the application of a potential of only 2 V. The fast
switching of the order of several hundred milliseconds is
Figure 11. Ionic conductivities of 1-3 as a function of temperature.
observed in Figure 9a. Figure 9b shows the responses for 3
sandwiched between bare ITO electrodes under the double-
potential application between -1 and 5 V, where the response
time is about several seconds.2b The driving voltage (Figure
9a) is reduced as a consequence of the lower reduction voltage
for PEDOT-PSS compared with that for compound 3. These
fast responses can be attributed to the fast cathodic reduction
of the PEDOT-PSS film coupled with the fast anodic oxidation
of 3. The deactivation of the defects on the ITO anode surface
by the polyimide coating may also contribute to the improve-
ment in the electrochromic behavior. Figures 10 presents the
photographs of the liquid crystal cell whose cathode is coated
with the PEDOT-PSS film for compound 3 in the SmA phase
at 120 °C. The clear change of color between pale yellow and
dark blue is observed under the double-potential application
between 0 and 2 V. For compound 2, coating the cathode with
the PEDOT-PSS thin film is also effective to improve the
electrochromic response (data not shown).
The ionic conductivities of compounds 1-3 parallel to the
smectic layers have been measured by the alternating current
impedance method16 using comb-shaped gold electrodes de-
posited on a glass substrate.3 The samples were embedded
between the electrodes on the substrate covered with another
glass plate. The samples exhibit the homeotropic alignment on
the glass substrates. The ionic conductivities of compounds 1-3
as a function of temperature are shown in Figure 11. The ionic
-4
conductivities are 4.7 × 10 S cm-1 for compound 1 at 160
-4
-4
°C, 1.2 × 10
S cm-1 for 2 at 130 °C, and 3.9 × 10
S
cm-1 for 3 at 120 °C. These values are lower than those for
electrolytes such as a mixture of poly(ethylene oxide) and
lithium salts above 100 °C. However, they are comparable with
those of nanosegregated ionic liquid crystals.3 In the SmA
phases of compounds 1-3, effective ionic transport occurs along
the smectic layers formed by the nanosegregation. Such self-
organization behavior is not observed for conventional poly-
electrolytes.17 The ionic conductivities in the SmA phases of
the liquid crystals 1-3 increase with the temperature because
of the thermal activation process of the ionic transport. For
compounds 2 and 3, which exhibit isotropic-smectic transitions
at around 150 °C, discontinuous increases in the conductivities
are observed at the phase transitions. This behavior was observed
for the columnar and smectic ionic liquid crystals.3 After
Ionic Conductivities. The mobile ions should play a critical
role in the electrochromic responses in the bulk nanosegregated
states of compounds 1-3. In fact, such electrochromism is not
observed in the conventional LC semiconductors based on
π-conjugated systems without ionic moieties or based on ionic
liquid crystals without the π-conjugated chromophores.
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J. AM. CHEM. SOC. VOL. 132, NO. 22, 2010 7707

A R T I C L E S
Yazaki et al.
Measurement of Ionic Conductivities. Temperature dependence
of the ionic conductivities was measured in the cooling process by
the alternating current impedance method using a Schlumberger
Solartron 1260 impedance analyzer (frequency range of 10 Hz to
10 MHz, applied voltage of 0.3 V) equipped with a temperature
controller. The cooling rate was fixed to 2 K min-1. Ionic
conductivities were practically calculated to be the product of 1/Rb
(Ω-1) times cell constants (cm-1) of the 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.
Electrochemical Measurement for the Solutions. Cyclic vol-
tammetry (CV) was performed using an ALS CHI 600B electrochemi-
cal analyzer and a three-electrode cell equipped with a Pt working
electrode, a Pt counter electrode, and an Ag+/Ag reference electrode.
A solution of Bu4NClO4 in CH2Cl2 (0.10 M) was used as the
supporting electrolyte. All the potentials were calibrated with an Fc+/
Fc couple using ferrocene as an internal reference. Spectroelectro-
chemical measurements were conducted on a JASCO V-670 spec-
trometer together with a potentiostat and a three-electrode cell using
the same supporting electrolyte as that used for CV.
Electrochemical Measurement for the Bulk Liquid Crystals.
A He-Ne laser (Melles Griot 05 LPL 479, wavelength 632.8 nm)
was used as a light source to measure the transmittance through
the liquid crystal cell on a hot stage. A photodiode, a serial resistor,
a bipolar amplifier (HAS 4011), a function generator (WF 1943A),
and a digital oscilloscope (Tektronics TDS 3044B) were used for
the light detecting system. The measurements were carried out under
atmospheric conditions. The liquid crystal cells comprised two glass
plates coated with indium tin oxide (ITO) (the area of the electrode
was 4 mm × 4 mm. The ITO electrodes were covered with a thin
film of PEDOT-PSS or polyimide (JSR AL1254). The deposition
of the PEDOT-PSS thin films on the ITO-coated glass plates was
performed by spin-coating them with its dispersion (Aldrich,
1.3-1.7% in H2O) at a rotation speed of 2000 rpm for 300 s,
followed by drying them at 100 °C for 20 min. The thickness of
the cell was calculated from the interference fringes in its absorption
spectrum. The liquid crystals were capillary-filled into the cells in
the isotropic states. The air dissolved in the liquid crystals was
purged with argon in the isotropic state using a vacuum pump before
the measurements. The intensity of the transmitted light through
the liquid crystal cells on the application of potential steps was
detected by the photodiode and recorded using the digital oscil-
loscope. The transmittance was determined as the ratio of the
intensity of the transmitted light through the liquid crystal cell
during the measurement to the intensity before the potential
application. The potential steps were applied by the function
generator and the amplifier.
crystallization, the ion conductivities decrease for 1-3. For
example, the ionic conductivities of 3 suddenly drop because
of the crystallization at 57 °C. These results show that
nanosegeregated layered smectic LC structures can be used for
new electrolytes in functional materials.
Conclusion
The LC nanostructures consisting of the ion-conductive and
electronic charge transport layers have been built by the
association of π-conjugated molecules having ionic moieties.
These liquid crystals 1-3 exhibit nanostructured SmA phases
where high ionic conductivities are observed. The combination
of the enhanced ion and electronic charge transports in the
nanostructured LC phases has resulted in efficient electro-
chromism in the LC bulk states. The low driving voltage and
the reversible electrochemical oxidation and reduction have been
achieved for liquid crystal 1, which forms stabilized cation and
anion radicals. The electrochromic properties of the liquid
crystals have been enhanced by using a PEDOT-PSS layer on
the cathode as an electron-accepting layer. The combination of
the ionic and electronic functions in the nanostructured LC
phases should be effective in applications to various electronic
devices such as light-emitting electrochemical cells and elec-
trochromic devices. The present results show new strategy for
the design of electroactive and ion-active materials.
Experimental Section
1
General Procedures. H and 13C NMR spectra were obtained
using a JEOL JNM-LA400 at 400 and 100 MHz for CDCl3
solutions, respectively. Chemical shifts of 1H and 13C NMR signals
are quoted to Me4Si (δ ) 0.00) and CDCl3 (δ ) 77.00) as internal
standards, respectively. IR measurements were conducted on a
JASCO FT/IR-660 Plus spectrometer. Matrix-assisted laser desorp-
tion ionization time-of-flight (MALDI-TOF) mass spectra were
recorded on an Applied Biosystems Voyager-DE STR spectrometer.
Elemental analyses were carried out with a Yanaco MT-6 CHN
autocorder. A polarizing microscope Olympus BX51 equipped with
a Mettler FP82HT hot stage was used for visual observation of the
optical textures. Differential scanning calorimetry (DSC) measure-
ments were conducted with a NETZSCH DSC 204 Phoenix. X-ray
diffraction (XRD) measurements were carried out on a Rigaku
RINT 2500 diffractometer with a heating stage and with the use of
Ni-filtered Cu KR radiation.
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Acknowledgment. This study was partially supported by Grant-
in-Aid for Scientific Research (A) (Grant No. 19205017) from the
Japan Society for the Promotion of Science (JSPS) and the Global
COE Program for Chemistry Innovation through Cooperation of
Science and Engineering from the Ministry of Education, Culture,
Sports, Science and Technology. S.Y. is thankful for financial
support from JSPS Research Fellowships for Young Scientists. The
authors are grateful to JSR Corporation for supplying the material
forming the polyimide layers.
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Soc. 2006, 128, 8754–8756.
Supporting Information Available: Synthesis of 1 and 2, DSC
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of 2, and small-angle X-ray diffraction patterns of 1 and 2. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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7708 J. AM. CHEM. SOC. VOL. 132, NO. 22, 2010