Magneto-LC effects in hydrogen-bonded all-organic radical liquid crystal

Article abstract of DOI:10.1021/jp301930k

To identify the origin of the magneto-LC effects, which refer to the enhancement of intermolecular magnetic interactions in the LC phases of all-organic radical compounds, we have designed and synthesized H-bonded all-organic radical compounds showing nem

Full text of DOI:10.1021/jp301930k

Article
pubs.acs.org/JPCB
Magneto-LC Effects in Hydrogen-Bonded All-Organic Radical Liquid
Crystal
,†
‡
‡
Yoshiaki Uchida,* Katsuaki Suzuki, and Rui Tamura
†
Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan
Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-Nihonmatsu-cho, Sakyo-ku, Kyoto 606-8501,
‡
Japan
*
S Supporting Information
ABSTRACT: To identify the origin of the magneto-LC
effects, which refer to the enhancement of intermolecular
magnetic interactions in the LC phases of all-organic radical
compounds, we have designed and synthesized H-bonded all-
organic radical compounds showing nematic and cholesteric
phases for the first time. They show stronger magneto-LC
effects than in the same LC phases of analogous covalent-
bonded all-organic radical LC compounds. Variable-temper-
ature electron paramagnetic resonance spectroscopy of the
hydrogen-bonded compounds reveals that the inhomogeneous
intermolecular contacts give rise to the magneto-LC effects.
1
. INTRODUCTION
compound must give us important information about the
relationship between the magneto-LC effects and the
inhomogeneous intermolecular contacts.
Paramagnetic liquid crystalline (LC) compounds attract a great
deal of attention because of their fascinating properties in
externally applied fields.
reorientation in a uniform magnetic field and the motion
of magnetic LC droplet in a magnetic field gradient have been
reported. Furthermore, their magnetic susceptibility is known
to be sensitive to an applied electric field. One fascinating
property is the magneto-LC effects, which refers to the
enhancement of intermolecular magnetic interactions in LC
1
−3
Here, we report the synthesis of the first example of all-
organic radical LC compounds with a hydrogen bond in the
mesogen core. The magnto-LC effects of the H-bonded
nitroxide radical LC compounds are evaluated by means of
variable-temperature electron paramagnetic resonance (VT-
EPR) spectroscopy. Furthermore, we have developed a novel
method to discuss the influence of the inhomogeneous
intermolecular contacts in detail using EPR spectra.
For example, their molecular
4
,5
6
7
8
,9
phases. The magneto-LC effects were detected for the first
time as an abrupt increase in magnetic susceptibility at the
crystalline (Cr)-to-LC phase transition of a nitroxide radical LC
2
. EXPERIMENTAL SECTION
8
compound. The understanding of the origin of the magneto-
2.1. Syntheses and Characterization. Nitroxide radical
LC effects is important for the design of molecules showing
larger magnetic susceptibility or even all-organic ferromagnetic
LC materials. Thus, the mechanism leading to specific
intermolecular magnetic interactions in LC phases remains to
carboxylic acid (1), a hydrogen-bond donor for H-bonded LC
compounds, is exhibited in Figure 1. We synthesized racemic 1
(rac-1) and (2S,5S)-enriched 1 (ss-1) according to a previously
1
3
reported procedure. As a hydrogen-bond acceptor, we
8
−10
14
be completely elucidated.
We previously proposed that the
selected molecule 2 with a pyridyl group (Figure 1). The
synthetic procedure for compound 2 is described in the
inhomogeneity of intermolecular contacts in LC phases is one
15
8
Experimental Section. Racemic and enantio-enriched com-
plexes of 1 and 2 (rac-3 and ss-3) were obtained from a
chloroform solution containing equimolar amounts of a
carboxyl group and pyridine moiety. In the infrared (IR)
spectra of rac-3, the absorption bands corresponding to the H-
bonded O−H stretching vibration of the carboxyl groups were
of the factors of the effects.
It has been reported that, when a covalent bond in the
mesogen core is replaced with a hydrogen bond, orientational
11,12
order parameter (S) decreases.
The decrease of the
orientational order in LC phases leads to more inhomogeneity
of the intermolecular contacts. Accordingly, a nitroxide radical
LC compound with such a hydrogen bond in the core region
should show lower S in LC phases than covalent-bonded
compounds, and then, the disordering may enhance the
inhomogeneity of the intermolecular contacts. Therefore,
such a hydrogen-bonded (H-bonded) nitroxide radical LC
−1
observed at 2481 and 1907 cm . In the IR spectra of ss-3, the
Received: February 27, 2012
Revised: July 6, 2012
Published: July 19, 2012
©
2012 American Chemical Society
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Article
2
.1.4. Supramolecular Complexes (rac-3, ss-3). The
supramolecular complexes of the carboxylic acids rac-1 and
ss-1 and the phenylazopyridine 2 were synthesized by a
procedure in the main text of ref 5. rac-1 (0.030 mmol) or ss-1
(
0.017 mmol) and 2 (0.030 or 0.017 mmol) were dissolved in
chloroform (200 μL), and each mixture was slowly evaporated
at 60 °C at normal pressures and then the chloroform was
completely removed in vacuo.
2
.2. Measurements. The X-band EPR spectra were
measured under an applied magnetic field of 0.33 T. Five
measurements were performed at each temperature. Sweep
time was 150 s. Sample was sealed in a glass tube with Ar gas.
The variable temperature XRD patterns were recorded at a
Figure 1. Molecular structures of 1, 2, and 4.
−1
continuous scanning rate of 2° 2θ min at heating and cooling
rates of 4 °C min− using Cu Kα radiation (40 kV, 20 mA),
with the intensity of the diffracted X-rays being collected at
intervals of 0.02° 2θ. DSC was performed at a scanning rate of
absorption bands corresponding to the H-bonded O−H
1
stretching vibration of the carboxyl groups were observed at
−1
2
503 and 1893 cm . In contrast, in the single carboxylic acids
rac-1 and ss-1, there was no absorption resulting from the
hydrogen bonding.
−1
5
°C min .
3. RESULTS AND DISCUSSION
.1. Phase Transition Behavior. The phase transition
2
.1.1. Materials. All reagents were used without further
1
purification. H NMR spectra were recorded using a JNM-
3
ECX400 (JEOL). ESI-mass were recorded with microTOF II
behavior is confirmed by differential scanning calorimetry
DSC), polarized optical microscopy (POM; Figure 2), and X-
(
Bruker)
.1.2. Synthesis of 4-(4-Hydroxyphenylazo)pyridine. 4-
(
2
Aminopyridine (3.0 g, 32 mmol) was dissolved in 25 mL of
hydrochloric acid (7 N), and the resulting solution was cooled
to 0 °C. With stirring, a mixture of 2.0 g (29 mmol) of sodium
nitrite, 2.5 g (27 mmol) of phenol, and sodium hydroxide (25
mmol) in water (20 mL) was added dropwise into the solution
to produce diazonium salt. The reaction mixture was stirred at
0
°C for 2 h. After sodium hydroxide was added to the reaction
mixture to give pH 7, the precipitated solid was collected and
extracted with ethyl acetate. The extracts were washed with
water, dried over MgSO , and filtered. After the solvent was
removed, 4-(4-hydroxyphenylazo)pyridine (1.3 g, 9 mmol) was
4
Figure 2. Optical polarized micrographs showing (a) the Schlieren
texture at 105.0 °C of rac-3 and (b) the fingerprint texture at 120.0 °C
of (2S,5S)-3 in the cooling run.
obtained in 28% yield.
1
H NMR (CD OD, 400 MHz): δ = 6.93 (d, J = 9 Hz, 2H),
3
7
.74 (d, J = 6 Hz, 2H), 7.88 (d, J = 9 Hz, 2H), 8.64 (d, J = 6
ray diffraction (XRD) measurements. All of the ingredients, rac-
+
Hz, 2H). MS (ESI) Found: m/z = 200.0818 [M+1] (199.0739
calc. for C H N O)
1
, ss-1, and 2, are nonmesogenic compounds (Table 1). In
9
9
3
2
.1.3. Synthesis of 4-(4-Octyloxyphenylazo)pyridine (2).
Table 1. Phase Transition Behavior of 1, 2, and 3
Determined by DSC Analysis
To a stirred solution of 4-(4-hydroxyphenylazo)pyridine (500
mg, 2.5 mmol) and K CO (524 mg 3.8 mmol) in
2
3
dimethylformamide (15 mL) was added bromooctane (482
mg, 2.5 mmol). The reaction mixture was stirred at 70 °C for 6
h, poured into water, and then extracted by hexane.
phase transition temperarutes (°C) (ΔH (kJ
−
1
mol ))
a
rac-1
ss-1
2
Cr 156.3 (-) Iso
heating
The extracts were washed with sat. NaHCO , NaOH, and
Cr 135.2 (12.2) Iso
heating
3
brine and dried over MgSO . After the solvent was removed,
Cr 57.3(0.7) Iso
heating
4
the crude products were purified by column chromatography
on silica gel (hexane/dichloromethane = 1:1) to give 2 (505
mg, 1.6 mmol) in 65% yield.
rac-3
Cr 121.7 (32.5) Iso
second heating
second cooling
second heating
second cooling
Iso 117.5 (3.3) N 91.3 (27.4) Cr
Cr 113.4 (27.4) N* 135.3 (4.0) Iso
Iso 133.9 (4.2) N* 101.7 (27.0) Cr
ss-3
1
H NMR (CD3Cl, 400 MHz): δ = 0.90 (t, J = 5 Hz, 3H),
a
1
2
6
.24−1.41 (m, 8H), 1.49 (q, J = 8 Hz, 2H), 1.83 (q, J = 7 Hz,
It is impossible to measure the enthalpy because decomposition
occurs in association with melting.
H), 4.06 (t, J = 7 Hz, 2H), 7.02 (d, J = 9 Hz, 2H), 7.67 (d, J =
Hz, 2H) 7.95 (d, J = 9 Hz, 2H), 8.77 (d, J = 6 Hz, 2H). MS
+
(
ESI) found: m/z = 312.2075 [M+1] (311.1991 calc. for
contrast, DSC charts for rac-3 and ss-3 indicate that the
C H N O).
complexes formed from nonmesogenic components show LC
1
7
25
3
Scheme 1. Synthesis of Compound 2
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Article
phases (Figure S1). XRD measurements for the LC phases gave
no peak. rac-3 showed a Schlieren texture typical for a nematic
(
N) phase by POM (Figure 2a), whereas ss-3 (>99% ee)
exhibited a fingerprint texture characteristic of a cholesteric
N*) phase (Figure 2b). Thus, the LC phases of rac-3 and ss-3
(
can be identified as a monotropic N phase (in the cooling run)
and an enantiotropic N* phase, respectively. This mesophase
stabilization can be ascribed to the effect of the highly planar
structure of the phenylazopyridine unit, which is a core unit of
the H-bonded mesogen.
Figure 3. Temperature dependence of χrel obtained from variable
temperature EPR (VT-EPR) spectroscopy (a) for rac-3 and (b) for ss-
3.2. Temperature Dependence of Magnetic Suscept-
3
. Open and filled circles denote the data in the heating and cooling
ibility. To confirm whether the H-bonded LC compounds
show magneto-LC effects, we performed VT-EPR spectroscopy
for rac-3 between 80 and 135 °C and for ss-3 between 90 and
runs, respectively. Vertical solid and dotted lines denote the melting
points obtained by DSC analysis in the heating run and freezing points
expected by the temperature dependence of g value in the cooling run,
respectively.
1
45 °C in a magnetic field of 0.33 T (X-band) by using a quartz
tube (5 mm ϕ). To evaluate paramagnetic susceptibility from
8
the EPR spectra by previously reported method, we fitted the
value is commonly noted at the Iso-to-LC phase transition in
the cooling run.
16
experimental data to the differential Lorentzian function
The abrupt χrel changes at the melting and freezing points
should be attributed to the molecular paramagnetic anisotropy
2
2
⎧
⎪
⎩
⎫
⎪
⎛
⎞
H − H0
H − H0
I′(H) = −16I′m
/⎨3 + ⎜
⎟ ⎬
Δχ and/or the intermolecular magnetic interactions J. The
⎜
⎝
⎟
⎠
mol
ΔH /2 ⎪
ΔH /2
⎪
pp
pp
⎭
(1)
contribution of Δχ can be expressed in terms of the change
mol
in the g value resulting from magnetic-field-induced molecular
2
where I′ is the maximum peak height of the differential curve,
reorientation. It is well-known that χ is proportional to g
m
rel
8
H is the applied magnetic field, H is the resonant magnetic
when J is constant. By using the experimental g values
0
field, and ΔH is the peak-to-peak line width. To discuss the
evaluated by the method described in Figure S3, however, the
pp
weak effects by using accurately measured data, EPR spectra
were measured in the narrow range of magnetic field as shown
in Figure S2. Meanwhile, the line widths are so wide that the
lines protrude outside the range of magnetic field. Thus, even if
the EPR peaks are double-integrated, the paramagnetic
susceptibility cannot be accurately estimated. Without the
double-integration, we can easily evaluate the paramagnetic
susceptibility (χ) from the parameters I′ , H , and ΔH by eq
increases in χ are expected to be below 0.002% at the melting
rel
and freezing points. This indicates that the Δχ does not
mol
contribute to the abrupt change in χ at the melting and
rel
freezing points of rac-3 and ss-3. These results suggest two
possibilities; one is the case that Cr phases show
antiferromagnetic interactions (J < 0), and the other is the
case that the intermolecular magnetic interactions in the LC
and Iso phases are ferromagnetic (J > 0).
To determine whether the magnetic interactions in the
crystalline phases were antiferromagnetic, we measured the
temperature dependence of the paramagnetic susceptibility in
the temperature range 2−300 K in the first heating run (both
rac-3 and ss-3 show crystalline phases in this temperature
range). The data in the temperature range of 100−300 K were
fitted to the Curie−Weiss law (Figure S4):
m
0
pp
8
2.
2
2
μ gI′ ΔH
B
m
pp
χ =
3
hνH1
(2)
where μ is the Bohr magneton, h is Planck’s constant, ν is the
B
frequency of the absorbed electromagnetic wave, g is the g
factor, which is inversely proportional to H , and H is the
0
1
C
T − θ
χ =
amplitude of the oscillating magnetic field (see the Supporting
Information). The temperature dependence of relative para-
(4)
where C is a Curie constant, T is temperature, and θ is Weiss
constant. C and θ were then estimated for rac-3 (C = 0.37, θ =
magnetic susceptibility (χ ), which is defined as
rel
χ
χ0
−
0.36 K) and ss-3 (C = 0.38, θ = 0.62 K). These results suggest
χrel
=
that the crystalline phases do not show strong antiferromag-
netic intermolecular interactions but remain paramagnetic over
the temperature range. Even if the weak magnetic interactions
vanish at the melting points, the change of the paramagnetic
interactions are smaller than 0.25% over 400K. Thus, to explain
the large increase in the paramagnetic susceptibility at the
melting points (26% and 40% for rac-3 and ss-3, respectively),
the generation of ferromagnetic interactions in the LC phases
should be assumed.
(3)
where χ is the standard paramagnetic susceptibility at 90 °C in
0
the heating run, for rac-3 and ss-3 is shown in Figure 3.
In the heating run, χrel abruptly increases at the melting (Cr-
to-isotropic (Iso) and Cr-to-N* phase transitions) points for
rac-3 (26% increase from 110 to 125 °C) and ss-3 (40%
increase from 109 to 119 °C), respectively; it decreases with
increasing temperature in each phase, as expected from the
Curie−Weiss law. In the cooling run, χrel increases with
decreasing temperature in the Iso and N(N*) phases, abruptly
decreases at the N(N*)-to-Cr phase transition by 16% (16%)
from 105 °C (98 °C) to 100 °C (95 °C), and increases with
decreasing temperature in the Cr phase for rac-3 (ss-3). Similar
The χrel increases at the melting (Cr−N and Cr−N* phase
transition) points of racemic and enantio-enriched samples of a
previous reported covalent-bonded compound 4 shown in
Figure 1 were 16% (from 74 to 78 °C) and 23% (from 73 to 78
8
°C), respectively. The χ increases at the melting points of
rel
to the case of previously reported magneto-LC effects of a
rac-3 and ss-3 are apparently larger than those in the melting
points of covalent-bonded compounds 4. According to Curie−
8
covalent-bonded analogue 4, a very small change in the χ
rel
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The Journal of Physical Chemistry B
Article
Weiss low, the χ increases should decrease as phase transition
rel
temperature increases (see the Supporting Information).
Furthermore, the melting points of rac-4 and ss-4 are lower
than the corresponding transition temperatures of rac-3 and ss-
3
3
, respectively. Thus, the difference in the χrel increase between
and 4 should be larger than it looks. The intense magneto-LC
effects probably result from the existence of the inhomoge-
neous intermolecular contacts.
3.3. VT-EPR Spectroscopy. To discuss the influence of the
inhomogeneous intermolecular contacts on the magneto-LC
effects, we focused on the inhomogeneous broadening of the
EPR spectra. It is well-known that EPR spectra are
inhomogeneously broadened by unresolved proton hyperfine
coupling and magnetic-field modulation, and hence the spectra
become Voigt function, which is the convolution of Gaussian
17
with Lorentzian functions. The Gaussian component of peak-
G
to-peak line width (ΔH ) contains the contribution of
pp
G
unresolved proton hyperfine coupling (ΔH ) and magnetic-
Figure 4. The temperature dependence of linewidths obtained from
variable temperature EPR (VT-EPR) spectroscopy for rac-3 and ss-3.
pp0
field modulation (κH ), where H is the modulation amplitude
m
m
16
L
G
Panels a and b show temperature dependence of ΔH and ΔH for
and κ is a constant. In our case, the contribution of
pp
pp
rac-3, respectively, and panels c and d show temperature dependence
inhomogeneous intermolecular contacts (H ) should be
IIC
L
pp
G
pp
G
pp
of ΔH and ΔH for ss-3. Open and filled circles denote the data in
added to the Gaussian component. Therefore, ΔH can be
18
the heating and cooling runs, respectively. Vertical solid and dotted
lines denote the melting points obtained by DSC analysis in the
heating run and freezing points expected by the temperature
dependence of g value in the cooling run, respectively (Figure S3).
expressed as the sum of their squares
2
2
G
G
pp0
+ κ H + HIIC2
2
2
ΔH = ΔH
pp
m
(5)
Among the terms, only HIIC2 depends on temperature. Thus,
we can discuss the influence of inhomogeneous intermolecular
contacts on the magneto-LC effects by analyzing the temper-
intermolecular contacts in the phases. Thus, we estimate the
contribution of the inhomogeneity on the magnetic interactions
G
G
from the temperature dependence of ΔH . In the heating run,
ature dependence of ΔH . Then, we fitted the spectra obtained
pp
pp
G
pp
ΔH is quite small in the initial Cr phases, increases slightly at
the melting points, and then decreases with increasing
from the numerical integration of the raw data (I(H)) to the
Voigt function
G
pp
temperature for both compounds. The increase in ΔH and
2
2
L
pp
exp[−(H′ − H ) /2σ ]
the decrease in ΔH at the melting points in the heating run
0
I(H) = Iv
dH′
∫
2
indicate the appearance of inhomogeneous spin−spin exchange
H ′ − H
/2
G
pp
1
+
interactions. In the cooling run, ΔH increases with decreasing
L
(
ΔH1 / 2
)
(6)
=
G
temperature in all phases for both compounds; further, ΔH
pp
G
pp
L
G
pp
where σ is equal to ΔH /2, I is a constant, and ΔH
reaches a plateau at the freezing point for rac-3, whereas ΔH
V
1/2
1/2
L
pp
(
3) ΔH , which is the Lorentzian peak-to-peak line width
influenced by the magnitude of intermolecular magnetic
abruptly decreases at the freezing point for ss-3. These
behaviors indicate that inhomogeneous intermolecular contacts
in both LC and Iso phases remain in the crystalline phases to
L
pp
G
pp
interactions. The parameters (ΔH , ΔH , and g) were
obtained from fitting the experimental data to eq 6 as shown
in Figures 4 and S3.
some extent in the cooling run. In fact, we observed a difference
L
pp
in the ΔH and g value in the crystalline phases between the
Generally, intermolecular magnetic interactions are divided
into two factors, (a) spin−spin exchange interactions and (b)
heating and cooling runs (Figures 4 and S3). The crystal
structures obtained by cooling the samples from the LC phases
are likely to be different from the initial crystal structures.
spin−spin dipole interactions. To discuss about the contribu-
L
tion of the two factors the temperature dependence of ΔH is
If magneto-LC effects arise from the inhomogeneous
pp
8
G
pp
useful. When the dipole interactions increase or the exchange
intermolecular contacts, the increase of ΔH at the melting
L
pp
interactions decrease, ΔH increases. For both complexes, in
points for the covalent-bonded analogue 4 could be observed.
L
pp
8
the heating run, ΔH decreases with increasing temperature
We fitted the reported EPR spectra for 4 to eq 6 as shown in
L
pp
G
and the rate of decrease of ΔH increases with increasing
Figure S5. In fact, at the melting points the ΔH of 4 changes
pp
L
pp
temperature up to the melting points. Subsequently, the rate
in the same direction as that of 3, though the ΔH of 4
changes in the opposite direction from that of 3. The former
decreases with increasing temperature in the Iso phases. In the
L
pp
cooling run, ΔH increases with decreasing temperature in all
result indicates that the inhomogeneous contacts between
phases and increases abruptly at the freezing points for both
nitroxide radical groups should occur at the melting points for
L
pp
G
compounds. ΔH decreases when χ abruptly increases at the
both 3 and 4. Whereas the ΔH increase at the melting point
pp
G
pp
melting points, whereas it increases when χ decreases at the
freezing points (Figure 3). Accordingly, we concluded that the
spin−spin exchange interactions are likely to contribute to the
abrupt change in χ at the melting and freezing points. However,
other effects might be responsible for the observed line
broadening. This point will be studied in the near future.
The additional spin−spin exchange interactions in LC and
Iso phases are supposed to arise from the inhomogeneous
of rac-4 is much smaller than that of rac-3, the ΔH increase at
the melting points of ss-4 is a little larger than that of ss-3.
Although we cannot simply compare the results because 4 has a
mesogen core with fewer benzene rings than 3, the introduction
of an H-bond may tend to enhance the inhomogeneity.
Meanwhile, the latter result suggests that 4 is likely to show the
enhancement of spin−spin dipole interactions at the melting
8
points as previously reported. Therefore, we can conclude that
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The Journal of Physical Chemistry B
Article
inhomogeneous intermolecular contacts should give rise to
inhomogeneous intermolecular magnetic interactions, but the
type of spin−spin interactions that is enhanced then is likely to
depend on the molecular structure. In the present case, the
introduction of an H-bond probably would result in the
enhancement of the intermolecular spin−spin exchange
interactions.
compound showing a ferroelectric SmC* phase.” Manuscript
submitted for publication.
(
8) Uchida, Y.; Suzuki, K.; Tamura, R.; Ikuma, N.; Shimono, S.;
Noda, Y.; Yamauchi, J. J. Am. Chem. Soc. 2010, 132, 9746−9752.
9) Lee, C. H.; Kwon, Y. W.; Choi, D. H.; Geerts, Y. H.; Koh, E.; Jin,
J. I. Adv. Mater. 2010, 22, 4405−4409.
10) Suzuki, K.; Uchida, Y.; Tamura, R.; Shimono, S.; Yamauchi, J. J.
Mater. Chem. 2012, 22, 6799−6806.
11) Barmatov, E.; Grande, S.; Filippov, A.; Barmatova, M.; Kremer,
(
(
(
4. CONCLUSIONS
F.; Shibaev, V. Macromol. Chem. Phys. 2000, 201, 2603−2609.
(12) Filippov, A. P. J. Opt. Technol. 2001, 68, 700−703.
(13) Uchida, Y.; Uematsu, T.; Nakayama, Y.; Takahashi, H.; Tsue,
We synthesized the first example of racemic and nonracemic H-
bonded chiral all-organic radical compounds showing N and
N* phases, in which they show stronger magneto-LC effects
than covalent-bonded LC compounds show. The results of VT-
EPR spectroscopy imply that the magneto-LC effects arise from
the inhomogeneous intermolecular contacts. Furthermore, we
believe that spin−spin exchange interactions are probably
responsible for the magneto-LC effects. These results indicate
the possibility of a noncovalent bond being one of the key
components in the synthesis of high-performance LC
compounds with the following intermolecular-contact-depend-
H.; Tanaka, K.; Tamura, R. Chirality 2008, 20, 282−287.
14) Mallia, V. A.; Antharjanam, P. K. S.; Das, S. Liq. Cryst. 2003, 30,
35−141.
15) Mamiya, J.; Yoshitake, A.; Kondo, M.; Yu, Y.; Ikeda, T. J. Mater.
(
1
(
Chem. 2008, 18, 63−65.
(16) Noda, Y.; Shimono, S.; Baba, M.; Yamauchi, J.; Uchida, Y.;
Ikuma, N.; Tamura, R. Appl. Magn. Reson. 2008, 33, 85−93.
(17) Bales, B. L. In Biological Magnetic Resonance; Berliner, L. J.,
Reuben, J., Eds.; Plenum Press: New York, 1989; Vol. 8, pp 77−130.
(18) Bales, B. L.; Peric, M.; Lamy-Freund, M. T. J. Magn. Reson.
19
20
21
1998, 132, 279−286.
ent properties: conductivity, color, charge transfer, and
magnetic properties. To constitute such a principle, additional
work needs to be performed.
(
(
19) Funahashi, M.; Hanna, J.-I. Adv. Mater. 2005, 17, 594−598.
20) Sagara, Y.; Yamane, S.; Mutai, T.; Araki, K.; Kato, T. Adv. Funct.
Mater. 2009, 19, 1869−1875.
21) Araya, K.; Matsunaga, Y. Bull. Chem. Soc. Jpn. 1980, 53, 3079−
3084.
(
ASSOCIATED CONTENT
Supporting Information
Additional discussions and Figures S1−S5. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
*
S
AUTHOR INFORMATION
Corresponding Author
E-mail: yuchida@cheng.es.osaka-u.ac.jp. Tel: +81-6-6850-
256;. Fax: +81-6-6850-6256.
■
*
6
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Grants-in-Aid for Scientific
Research (Nos. 23245008 and 23655127) from Japan Society
for the Promotion of Science (JSPS). Y.U. and K.S. are grateful
to the JSPS Research Fellowships for Young Scientists.
REFERENCES
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(
1) Griesar, K.; Haase, W. In Magnetic Properties of Organic Molecules;
Lahti, P. M., Ed.; Marcel Dekker: New York, 1999; Chapter 16, pp
3
(
25−344.
2) Kaszynski, P. In Magnetic Properties of Organic Molecules; Lahti, P.
M., Ed.; Marcel Dekker: New York, 1999; Chapter 15, pp 305−324.
3) Tamura, R.; Uchida, Y.; Ikuma, N. J. Mater. Chem. 2008, 18,
872−2876.
4) Galyametdinov, Y. G.; Haase, W.; Goderis, B.; Moors, D.;
Driesen, K.; Deun, R. V.; Binnemans, K. J. Phys. Chem. B 2007, 111,
3881−13885.
5) Uchida, Y.; Tamura, R.; Ikuma, N.; Shimono, S.; Yamauchi, J.;
Shimbo, Y.; Takezoe, H.; Aoki, Y.; Nohira, H. J. Mater. Chem. 2009,
9, 415−418.
6) Uchida, Y.; Ikuma, N.; Tamura, R.; Shimono, S.; Noda, Y.;
Yamauchi, J.; Aoki, Y.; Nohira, H. J. Mater. Chem. 2008, 18, 2950−
952.
7) Suzuki, K.; Uchida, Y.; Tamura. R.; Shimono, S.; Yamauchi, J.
Observation of electric field dependence of molecular orientation and
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2
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1
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1
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2
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“
anisotropic magnetic interactions by EPR spectroscopy in the surface-
stabilized liquid crystal cell of an all-organic nitroxide radical
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