Self-assembly of carbazole-containing gelators: alignment of the chromophore in fibrous aggregates

Article abstract of DOI:10.1016/j.tet.2007.03.121

Carbazole-containing gelators derived from l-isoleucine have been developed. They form elongated self-assembled fibers in common organic solvents and in liquid crystals, leading to the efficient gelation of these solvents. Spectroscopic studies indicate t

Full text of DOI:10.1016/j.tet.2007.03.121

Tetrahedron 63 (2007) 7358–7365
Self-assembly of carbazole-containing gelators: alignment
of the chromophore in fibrous aggregates
a,y
a
Kazuhiro Yabuuchi, Yusuke Tochigi, Norihiro Mizoshita, Kenji Hanabusa
a
b
a,
*
and Takashi Kato
a
Department of Chemistry and Biotechnology, School of Engineering, The University of Tokyo, 7-3-1 Hongo,
Bunkyo-ku, Tokyo 113-8656, Japan
b
Graduate School of Science and Technology, Shinshu University, Ueda, Nagano 386-8567, Japan
Received 4 January 2007; revised 8 March 2007; accepted 16 March 2007
Available online 23 March 2007
Abstract—Carbazole-containing gelators derived from L-isoleucine have been developed. They form elongated self-assembled fibers in com-
mon organic solvents and in liquid crystals, leading to the efficient gelation of these solvents. Spectroscopic studies indicate that the carbazolyl
moieties are one-dimensionally stacked in the fibers. The stacking of the carbazolyl moieties is reversible by the association and dissociation
of the hydrogen bonding. Moreover, anisotropically aligned fibers have been obtained in a homogeneously oriented smectic state of liquid
crystals. This template behavior would serve as a versatile approach to the functionalization of self-assembled fibers.
Ó 2007 Elsevier Ltd. All rights reserved.
1
. Introduction
Our intention is to induce 1D alignment of carbazolyl moi-
eties by fibrous assembly of gelators. Carbazolyl moieties
are known to exhibit photophysical properties such as photo-
Supramolecular self-assembly is a promising tool for the
fabrication of functional molecular materials. Physical
gels based on fibrous self-assembly of low molecular weight
gelators are one of the representative examples.
gels can be functionalized by the introduction of electro-
1
26
conductivity as seen in poly(N-vinylcarbazole)s. Self-
assembled fibers bearing functional moieties might act as
photoconductive molecular wires by 1D stacking of carb-
azolyl moieties in the fibers. Moreover, the stacking and dis-
sociation of carbazolyl moieties because of non-covalent
self-assembly are expected, which has not been discussed
2
–23
Physical
5
–11
1
2,13
and photo-active
Functional solvents such as liquid crystals,
functional moieties to the gelators.
electro-
1
4–20
2
1
22
10
lytes, and ionic liquids have also been used. For the liquid
crystalline gels, faster switching of the nematic liquid
crystals by the application of electric fields was observed.
Gelators containing cationic moieties were used as templates
for inorganic synthesis. Recently, one-dimensional (1D)
stacking of p-conjugated molecules has attracted attention,
because electronic and ionic 1D conducting paths on the
in detail for a previously reported carbazole-based gelator.
Here we report on the preparation and self-assembling be-
havior of new carbazole-based gelators. Stacking behavior
of the carbazolyl moieties on fibrous self-assembly has
been studied by spectroscopic measurements. Moreover,
unidirectionally aligned fibers have been obtained in an
oriented smectic liquid crystal.
2
3
2
4,25
nanometer-scale can be obtained.
Use of fibrous self-
assemblies of gelators is one promising approach for the
development of functional molecular materials. Gelators in-
corporating electroactive moieties such as oligothiophene,
2. Results and discussion
2.1. Molecular design
5
6
7,8
9
porphyrin, tetrathiafulvalene (TTF), diacetylene, and
1
0
carbazole have been developed. We have recently prepared
unidirectionally aligned fibers of TTF-based gelators in ori-
ented liquid crystals, and measured the electrical conductiv-
Carbazole-containing compounds 1a and 1b shown in
Figure 1 were prepared by the coupling reaction of the
corresponding carbazole-containing amines and N-benzyl-
oxycarbonyl-L-isoleucine as shown in Scheme 1. The carb-
azolyl moiety is attached to an isoleucine-based scaffold
via dodecamethylene and hexamethylene chains, respec-
tively. The isoleucine scaffold often exhibits excellent abil-
ity to form hydrogen-bonded fibrous aggregates in a wide
range of solvents, which leads to gelation of the
8
ity of doped fibers.
Keywords: Organogel; Carbazole; Liquid crystal; Self-assembled fiber.
*
Corresponding author. Tel.: +81 3 5841 7440; fax: +81 3 5841 8661;
e-mail: kato@chiral.t.u-tokyo.ac.jp
Present address: Department of Materials Science and Environmental
Engineering, Faculty of Science and Engineering, Tokyo University of
Science, Yamaguchi, Sanyo-Onoda, Yamaguchi 756-0884, Japan.
y
0
040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.03.121

K. Yabuuchi et al. / Tetrahedron 63 (2007) 7358–7365
7359
Table 1. Gelation properties of isoleucine derivatives for common organic
solvents
a
H
N
O
O
(CH2)n N
Solvent
1a
1b
2
N
H
O
Hexane
Ethyl acetate
Ethanol
Methanol
Acetone
Chloroform
Tetrachloromethane
Benzene
Toluene
DMF
P
G
P
P
G
S
G
G
G
S
I
P
P
P
P
P
P
G
G
S
S
G
G
G
G
S
G
G
G
S
1
a (n = 12)
b (n = 6)
1
H
N
O
O
C18H37
N
H
O
a
ꢀ1
Gelation tests were conducted at 40 g L . The following abbreviations
are used: P, precipitate; I, insoluble; S, solution; G, gel.
2
Figure 1. Molecular structures of gelators 1a, 1b, and 2.
4
,21c
solvents. For example, compound 2 is an efficient
gelator for common organic solvents and liquid
of elongated fibers, which have diameters of several tens of
nanometers. The introduction of carbazolyl moieties does
not cause changes in the morphologies of the fibers.
1
6a,19a,20,21c
crystals.
a and 1b was expected because of the presence of the iso-
leucine scaffold.
Therefore, 1D fibrous self-assembly of
1
2.3. Gelation of liquid crystals
2
.2. Gelation of common organic solvents
The gelation properties of 1a and 1b for liquid crystals 6 and
7 shown in Figure 3 are given in Table 2. Our aim here is
to align the gelator in the smectic phases of 6 and 7. In our
previous study, the alignment of gelators was observed in
The gelation properties of these isoleucine-based com-
pounds for common organic solvents at a concentration of
ꢀ
1
8,18,19
4
0 g L are shown in Table 1. The gelation ability of 1a
nematic and smectic liquid crystals.
compound 6 shows a nematic phase between 38 and 32 C
Liquid crystal
ꢁ
and a smectic A phase below 32 C, while nematic (79–
slightly decreases compared to that of 2. Compound 1b
can gelate only tetrachloromethane and benzene of the sol-
vent examined. These results suggest that the interaction
of the bulky group does not greatly affect the gelation ability
as long as a longer alkyl spacer is used.
ꢁ
ꢁ
ꢁ
65 C) and smectic A (below 65 C) phases are also ob-
served for 7 at higher temperature ranges. Gelation tests
were conducted at a concentration of 3 wt % of the gelators.
As shown in Table 2, only 1a can gelate 6 and 7, while
compound 1b does not gelate these liquid crystals. Sol–gel
transition temperatures (Tsol–gel) were determined for the
LC gels. Figure 4 shows a phase diagram of the mixtures
of liquid crystal 6 and gelator 1a. Compound 1a exhibits
Microscopic observation of xerogels reveals that compounds
1a and 1b form elongated fibrous aggregates in organic
solvents. The SEM image of self-assembled fibers of 1a is
shown in Figure 2. Both compounds form random networks
TBAI
Benzene/50% NaOH aq
Br(CH2) Br + H N
Br (CH2)n N
n
3
a (n = 12)
b (n = 6)
3
O
O
NK
O
NH2NH2•H2O
EtOH, reflux
N
(CH2)n
N
H2N (CH2)n N
DMF, 80 °C
O
4
a (n = 12)
b (n = 6)
5a (n = 12)
5b (n = 6)
4
H
N
O
Z-L-Isoleucine, EDC
CH2Cl2
O
(CH2)n N
N
H
O
1
a (n = 12)
b (n = 6)
1
Scheme 1. Syntheses of 1a and 1b.

7360
K. Yabuuchi et al. / Tetrahedron 63 (2007) 7358–7365
A
Figure 4. Phase diagram of the mixtures of 6/1a. N: nematic, S : smectic A.
reported that anisotropically aligned fibers of 2 and other
gelators were obtained in homogeneously oriented LC
1
8,19
states.
We have found that carbazole-containing gelator
Figure 2. SEM images of self-assembled fibers of 1a formed in ethyl
acetate.
1a also forms oriented fibers in the temperature range of the
smectic A phases of 6 and 7.
The SEM and optical micrograph of the aligned fibers of 1a
grown in the mixture forming an oriented smectic A state of
C8H17
CN
7
on the rubbed polyimide surface are shown in Figure 5.
6
The SEM sample was prepared from a xerogel after extract-
ing 7 by immersing the thin film containing aligned 1a fibers
and 7 in hexane. The inset shows an optical micrograph of
the SEM sample. The growth direction of fibers is parallel
C H17O
CN
8
to the direction of the LC molecules. In contrast, in our pre-
vious study,
7
19a
compound 2 formed aligned fibers grown
Figure 3. Molecular structures of smectic liquid crystals 6 and 7.
Table 2. Gelation properties of isoleucine derivatives for liquid crystals
perpendicular to the direction of LC molecules in oriented
smectic states. The content of 1a in the mixture with 7 shown
in Figure 5 is 10 wt%, which is much larger than that used in
our previous study on 2. The larger amount of 1a in the SA
phase might induce less ordered layer structures, which
results in the disturbance of the development of fibers along
the layer direction.
a
Solvent
1a
1b
2
6
7
G
G
P
P
G
G
a
The anisotropic structures of the gelators have been exam-
ined by polarized infrared spectroscopy. Figure 6 shows
the polar plot for the peak areas of the C^N stretching of
Gelation tests were conducted at 3 wt %. The following abbreviations are
used: P, precipitate; G, gel.
ꢀ
1
ꢀ1
7
at 2225 cm and C]O stretching of 1a at 1688 cm ,
1
6a
sol–gel transition temperatures lower than those of 2. For
example, the T
which indicates that these two stretching bands are parallel
to each other. Therefore, hydrogen-bonded 1D chains of
1a align along the growing direction of fibers. This spectro-
scopic result is consistent with the microscopic observations.
of the mixture containing 3 wt% of 1a is
5 C. The isotropic–nematic and nematic–smectic A transi-
sol–gel
ꢁ
tion temperatures of 6 decrease as the concentration of 1a
1
1
4–16
increases. In our previous studies,
the phase transition
temperatures of liquid crystals were not changed greatly
by the addition of gelators. The present result indicates
that the dissolved carbazole-containing molecules disturb
the order of the LC molecules.
2.5. Self-assembled structures of carbazole-containing
gelators
The temperature-variable spectroscopic studies of the gels
reveal the self-assembling behavior of the gelators on sol–
gel transitions. The infrared measurements of the mixture
of 6 and 1a show that the fibrous self-assembly is driven
by hydrogen bonding, similar to compound 2. The peaks at
1726 (C]O stretching of urethane), 1676 (amide I), and
2
.4. Anisotropic fiber growth in liquid crystals
For the mixtures of gelators and liquid crystals, fibrous self-
assembly occurs in the anisotropic environment on cooling,
if sol–gel transition temperatures are lower than isotropic–
ꢀ
1
1517 cm (amide II) in the sol state shift to 1687, 1644,
and 1542 cm in the gel state, respectively. As for the
1
e,16b,18,19
ꢀ1
anisotropic (LC) transition temperatures.
We

K. Yabuuchi et al. / Tetrahedron 63 (2007) 7358–7365
7361
Figure 5. SEM image (a) and schematic illustration (b) of anisotropically aligned fibers of 1a grown in 7 (1a: 10 wt%) on a rubbed polyimide surface. Inset:
optical micrograph of aligned fibers after the extraction of 7.
Figure 7. Comparison of fluorescent spectra of 1a in ethyl acetate; a gel
state (line) and a sol state (dotted line).
bands appear around 415 and 440 nm. These lower energy
emission bands are attributable to the formation of sand-
2
7,28
wich-type excimers.
These spectral changes suggest
that stacking of carbazolyl moieties occurs on sol–gel tran-
sitions, leading to 1D accumulation of carbazolyl moieties
in self-assembled fibers.
Based on the present results, the phase-segregated structures
consisting of aligned fibers of carbazole-containing gelators
and homogeneously oriented smectic A states are schemati-
cally illustrated in Figure 8. The gelator molecules are one-
dimensionally assembled through hydrogen bonding involving
amide and urethane groups in liquid crystals, resulting in
the formation of oriented fibers. In these fibers, carbazolyl
moieties are stacked on one another, which will lead to the
formation of photoconducting paths.
Figure 6. Polar plot of IR bands for the mixture of 7/1a (1a: 10 wt%).
UV–vis absorption spectra of thin films of the mixture of 6
and 1a, the peak attributable to S –S transition of a carb-
1
0
azolyl moiety shifts from 347 nm in the sol state to 350 nm
in the gel state. Figure 7 shows the fluorescence spectra of
1
a in ethyl acetate. In a sol state, structured emission bands
around 353 and 369 nm are observed, which are assigned to
the monomer and partially overlapped excimer emission
bands of carbazoles, respectively. In the gel state, the mono-
mer emission band at 353 nm disappears, and new emission
3. Conclusion
Carbazole-containing gelators with an isoleucine scaffold
form elongated self-assembled fibers and act as efficient

7362
K. Yabuuchi et al. / Tetrahedron 63 (2007) 7358–7365
carbazole (3.51 g, 21 mmol) in benzene (50 mL) were
added. The reaction mixture was stirred for 3 days at room
temperature, and then poured into water. The solution was
extracted by dichloromethane. The organic layer was
washed with water and brine, and dried on anhydrous
MgSO . After filtration, the solvent was removed under re-
4
duced pressure. The residue was purified by column chroma-
tography, first with hexane and then with hexane/
dichloromethane (8:1) as eluent to afford 3a (7.03 g, 81%)
as a white solid (found: C, 69.35; H, 7.99; N, 3.19. Calcd
1
for C H BrN: C, 69.56; H, 7.78; N, 3.38%); H NMR
2
4 32
(
(
2
4
CDCl , 400 MHz): d 8.13–8.10 (m, 2H, ArH), 7.50–7.40
3
m, 4H, ArH), 7.25–7.21 (m, 2H, ArH), 4.31 (t, J¼6.7 Hz,
H, NCH ), 3.41 (t, J¼6.5 Hz, 2H, BrCH ), 1.87–1.81 (m,
2 2 2
2
2
13
H, NCH CH ), 1.40–1.23 (m, 16H, CH ); C NMR
(CDCl , 67.5 MHz): d 140.41, 125.54, 122.79, 120.32,
3
1
2
1
18.67, 108.63, 43.07, 34.07, 32.81, 29.44, 29.40, 29.36,
8.97, 28.72, 28.16, 27.23; IR (KBr): n 3048, 2920, 2852,
ꢀ
1
598, 1484, 749, 723, 645 cm
.
4.1.2. 1-Bromo-6-carbazol-9-ylhexane (3b). This com-
pound was synthesized as described above for 3a, starting
from 1,6-dibromohexane (11.0 g, 45 mmol) and carbazole
(2.51 g, 15 mmol) to afford 3b (3.87 g, 78%) as a white solid
(
6
found: C, 65.49; H, 6.33; N, 4.08. Calcd for C H BrN: C,
1
5.46; H, 6.10; N, 4.24%); H NMR (CDCl , 400 MHz):
3
8 20
1
Figure 8. Schematic illustration of phase-segregated structures based on 7
and 1a.
d 8.13–8.10 (m, 2H, ArH), 7.49–7.39 (m, 4H, ArH), 7.25–
.22 (m, 2H, ArH), 4.32 (t, J¼4.8 Hz, 2H, NCH ), 3.37 (t,
7
2
gelators for common organic solvents and liquid crystals.
The carbazolyl moieties are stacked in the one-dimension-
ally aligned fibers. Aligned fibers have been obtained in
the homogeneously oriented smectic liquid crystals. These
results may lead to the development of new functional
self-assembled 1D fibers, with the direction of their orienta-
tion being controlled on the substrates.
J¼4.4 Hz, 2H, BrCH ), 1.92–1.88 (m, 2H, NCH CH ),
2
2
2
1.83–1.78 (m, 2H, BrCH CH ), 1.53–1.40 (m, 4H, CH );
2 2 2
C NMR (CDCl , 67.5 MHz): d 140.36, 125.59, 122.80,
1
3
3
120.36, 118.76, 108.57, 42.84, 33.71, 32.54, 28.81, 27.91,
26.45; IR (KBr): n 3044, 2926, 2855, 1593, 1484, 755,
726, 638 cm
ꢀ
1
.
4.1.3. N-(12-Carbazol-9-yldodecyl)phthalimide (4a). A
mixture of 3a (4.14 g, 10 mmol) and potassium phthalimide
4. Experimental
(2.78 g, 15 mmol) in DMF (70 mL) was stirred for 9 h at
ꢁ
8
0 C, and then poured into saturated aqueous NH Cl and
4
4
.1. General method
extracted with ethyl acetate. The organic layer was washed
with water and brine followed by drying on anhydrous
MgSO . After filtration, the solvent was removed under re-
Unless otherwise noted, chemical reagents and solvents were
used without further purification. As for N,N-dimethylform-
amide (DMF) and dichloromethane, commercially available
anhydrous solvents were used for reaction. All reactions were
carried out under an argon atmosphere. As for precursors of
gelators, carbazolylbromoalkanes were synthesized accord-
4
duced pressure. The residue was purified by column chroma-
tography with hexane/ethyl acetate (7:1) as eluent to afford
4a (4.79 g, 100%) as a white solid (found: C, 80.06; H, 7.82;
N, 5.62. Calcd for C H N O : C, 79.96; H, 7.55; N,
3
2 36 2 2
1
5.83%); H NMR (CDCl , 400 MHz): d 8.10 (d, J¼7.2 Hz,
3
2
9
ing to the procedure reported by Bu et al. Synthetic proce-
dures of isoleucine derivatives are shown in Scheme 1. H
2H, ArH), 7.84–7.83 (m, 2H, ArH), 7.71–7.69 (m, 2H,
ArH), 7.48–7.42 (m, 4H, ArH), 7.24–7.20 (m, 2H, ArH),
1
1
3
NMR and C NMR spectra were determined with a Jeol
JNM-400EX and a JNM-270EX. Infrared spectra were
recorded on a Jasco FTIR-660Plus spectrometer. Elemental
analyses were performed with a Perkin–Elmer 2400II
CHNS/O elemental analyzer. UV–vis spectra were recorded
on an Agilent 8453 spectrometer equipped with a Mettler
FP-82HT hot stage. Fluorescent spectra were recorded on
a Jasco FP-777W equipped with an ECT-271 temperature
controller.
4.31 (t, J¼7.4 Hz, 2H, NCH ), 3.67 (t, J¼7.4 Hz, 2H,
2
NCH ), 1.88–1.84 (m, 2H, NCH CH ), 1.66–1.64 (m, 2H,
2
2
2
1
3
NCH CH ), 1.30–1.22 (m, 16H, CH ); C NMR (CDCl3,
2
2
2
67.5 MHz): d 168.45, 140.41, 133.80, 132.18, 125.52,
123.11, 122.79, 120.29, 118.65, 108.63, 43.07, 38.06,
29.45, 29.36, 29.11, 28.93, 28.57, 27.28, 26.83; IR (KBr):
ꢀ
1
n 3046, 2926, 2848, 1772, 1718, 1598, 1484, 750, 721 cm
.
4.1.4. N-(6-Carbazol-9-ylhexyl)phthalimide (4b). This
compound was synthesized as described above for 4a, start-
ing from 3b (3.17 g, 9.6 mmol) and potassium phthalimide
(2.13 g, 11.5 mmol) to afford 4b (3.81 g, 100%) as a yellow-
ish liquid (found: C, 78.70; H, 6.32; N, 6.90. Calcd for
4.1.1. 1-Bromo-12-carbazol-9-yldodecane (3a). To a mix-
ture of tetrabutylammonium iodide (TBAI, 0.310 g,
0
1
.8 mmol) and aqueous 50% sodium hydroxide (50 mL),
,12-dibromododecane (3.51 g, 63 mmol) and a solution of
1
C H N O : C, 78.76; H, 6.10; N, 7.07%); H NMR
26 24 2 2

K. Yabuuchi et al. / Tetrahedron 63 (2007) 7358–7365
7363
(
7
CDCl , 400 MHz): d 8.09 (d, J¼8.0 Hz, 2H, ArH), 7.84–
J¼6.8 Hz, 1H, NHCHCO), 3.21 (m, 2H, NHCH ), 1.89–
3
2
.81 (m, 2H, ArH), 7.72–7.69 (m, 2H, ArH), 7.47–7.38
1.85 (m, 4H, NCH CH , NHCH CH ), 1.47–1.23 (m, 21H,
2
2
2
2
1
3
(
2
m, 4H, ArH), 7.23–7.19 (m, 2H, ArH), 4.31 (t, J¼7.0 Hz,
CH ), 0.93–0.88 (m, 6H, CH );
3
C NMR (CDCl3,
2
H, NCH ), 3.66 (t, J¼7.4 Hz, 2H, NCH ), 1.91–1.84 (m,
100 MHz): d 170.93, 156.31, 140.39, 136.18, 128.52,
128.18, 128.00, 125.52, 122.76, 120.30, 118.64, 108.61,
67.00, 59.90, 43.05, 39.50, 37.29, 29.45, 29.39, 29.17,
28.95, 27.29, 26.83, 24.76, 15.51, 11.34; IR (KBr): n 3295,
3053, 2958, 2924, 2852, 1689, 1646, 1598, 1537, 1485,
2
2
2
(
1
1
H, NCH CH ), 1.68–1.61 (m, 2H, NCH CH ), 1.43–1.37
2
2
2
2
1
3
m, 4H, CH2); C NMR (CDCl , 67.5 MHz): d 168.39,
3
40.36, 133.84, 132.13, 125.57, 123.15, 122.80, 120.31,
18.71, 108.57, 42.90, 37.83, 28.83, 28.45, 26.87, 26.62;
ꢀ
1
IR (KBr): n 3050, 2935, 2857, 1771, 1711, 1596, 1484,
7
784, 721, 696 cm
.
ꢀ
1
51, 720 cm .
4.1.8. N-Benzyloxycarbonyl-L-isoleucine 6-carbazol-9-yl-
4
4
.1.5. 12-Carbazol-9-yldodecylamine (5a). To a solution of
a (1.01 g, 2.1 mmol) in ethanol (50 mL), hydrazine mono-
hexylamide (1b). This compound was synthesized as de-
scribed above for 1a, starting from 5b (1.12 g, 4.2 mmol)
and N-benzyloxycarbonyl-L-isoleucine (1.06 g, 4.0 mmol).
The crude product was purified by column chromatography
first with hexane/ethyl acetate/chloroform (2:1:1) and then
with chloroform as eluent to afford 1b (0.91 g, 44%) as
a white solid (found: C, 74.88; H, 8.04; N, 8.48. Calcd for
hydrate (0.15 mL) was added. The reaction mixture was
stirred for 2 h under reflux followed by the removal of the
solvent under reduced pressure. The residue was dissolved
in chloroform and 10% aqueous NaOH. The solution was ex-
tracted with chloroform. The organic layer was dried on an-
hydrous MgSO . After filtration, the solvent was removed
4
under reduced pressure to afford 5a (0.709 g, 96%) as a yel-
lowish solid (found: C, 82.40; H, 9.98; N, 7.92. Calcd for
ꢁ
C H N O : C, 74.82; H, 7.65; N, 8.18%); mp 172 C
32 39 3 3
1
(from ethyl acetate/chloroform);
H NMR (CDCl3,
400 MHz): d 8.12 (d, J¼7.6 Hz, 1H, ArH), 8.11 (d,
1
C H N : C, 82.23; H, 9.78; N, 7.99%); H NMR
2
J¼6.8 Hz, 1H, ArH), 7.50–7.21 (m, 11H, ArH), 5.77–5.76
4 34 2
(
7
CDCl , 400 MHz): d 8.10 (d, J¼8.0 Hz, 2H, ArH), 7.48–
(m, 1H, NH), 5.29–5.27 (m, 1H, NH), 5.09 (s, 2H, PhCH O),
2
3
.38 (m, 4H, ArH), 7.24–7.19 (m, 2H, ArH), 4.28 (t,
4.30 (t, J¼7.6 Hz, 2H, NCH ), 3.93–3.88 (m, 1H, NHCH),
2
J¼7.2 Hz, 1H, NCH ), 2.70–2.61 (m, 2H, NH CH ), 1.90–
3.26–3.16 (m, 2H, NHCH ), 1.87 (m, 3H, NCH CH ,
2
2
2
2
2
2
1
3
1 C
NMR (CDCl , 67.5 MHz): d 140.43, 125.54, 122.80,
.83 (m, 2H, NCH CH ), 1.44–1.23 (m, 18H, CH );
NHCHCH), 1.45–1.39 (m, 8H, CH ), 0.93–0.88 (m, 6H,
2
2
2
2
1
3
CH3); C NMR (DMSO-d , 100 MHz): d 170.85, 155.88,
6
3
1
2
2
20.32, 118.67, 108.63, 43.09, 42.10, 33.44, 29.53, 29.47,
9.44, 28.97, 27.32, 26.85; IR (KBr): n 3337, 3049, 2923,
139.89, 137.04, 128.20, 127.62, 127.50, 125.56, 121.95,
120.17, 118.53, 109.09, 65.22, 59.16, 42.07, 38.23, 36.24,
28.74, 28.35, 26.09, 25.99, 24.34, 15.29, 10.81; IR (KBr):
n 3298, 3054, 2955, 2935, 2856, 1689, 1642, 1598, 1541,
ꢀ
1
851, 1628, 1597, 1484, 749, 721 cm
.
ꢀ1
4
.1.6. 6-Carbazol-9-ylhexylamine (5b). This compound
1486, 750, 723, 697 cm .
was synthesized as described above for 5a, starting from
b (3.77 g, 9.5 mmol) to afford 5b (2.00 g, 79%) as a yellow-
ish liquid (found: C, 80.92; H, 8.37; N, 10.28. Calcd for
4
4.2. Gelation test
1
C H N : C, 81.16; H, 8.32; N, 10.52%); H NMR
8 22 2
Gelation properties for common organic solvents were tested
1
ꢀ
1
(
7
CDCl , 400 MHz): d 8.11 (d, J¼7.2 Hz, 2H, ArH), 7.49–
at 40 g L . In a typical gelation experiment, an organic sol-
vent (0.5 mL) was added to a weighed sample (20 mg) in
a test tube. The tube was sealed and heated until a clear so-
lution was obtained. The resultant solution was allowed to
cool to room temperature. Then gelation was checked visu-
ally. When the tube could be inverted without any flow, it was
considered as ‘gel’. When the mixture remained solution at
room temperature, it was further cooled in a refrigerator to
check whether gelation occurred at lower temperature.
When the gel formed at lower temperature was stable even
at room temperature, it was also considered as gel. As for
the gelation of liquid crystals, gelators and liquid crystals
were mixed in a sealed test tube in various ratios. If needed,
chloroform was added to obtain a homogeneous solution.
The mixtures were heated to isotropic states, and then cooled
to appropriate temperatures after the removal of chloroform.
3
.39 (m, 4H, ArH), 7.25–7.21 (m, 2H, ArH), 4.31 (d,
J¼7.4 Hz, 2H, NCH ), 2.66–2.62 (m, 2H, NH CH ), 1.92–
2
2
2
1
3
1
NMR (CDCl , 67.5 MHz): d 140.43, 125.59, 122.84,
.85 (m, 2H, NCH CH ), 1.44–1.37 (m, 6H, CH );
C
2
2
2
3
1
2
1
20.36, 118.74, 108.62, 43.00, 41.90, 33.19, 28.97, 27.15,
6.67; IR (KBr): n 3431, 3048, 2926, 2856, 1627, 1595,
ꢀ
1
484, 750, 725 cm
.
4.1.7. N-Benzyloxycarbonyl-L-isoleucine 12-carbazol-9-
yldodecylamide (1a). To a solution of 5a (1.40 g,
4.0 mmol) and N-benzyloxycarbonyl-L-isoleucine (1.06 g,
4.0 mmol) in dichloromethane (40 mL), 1-ethyl-3-(3-di-
methylaminopropyl)carbodiimide hydrochloride (0.92 g,
4
3
.8 mmol) was added. The reaction mixture was stirred for
h. Then the solution was extracted by chloroform. The or-
ganic layer was washed with saturated aqueous NaHCO3
and brine followed by drying on anhydrous MgSO . After
4.3. Characterization of anisotropic gels
4
filtration, the solution was removed under reduced pressure.
The residue was purified by column chromatography with
hexane/ethyl acetate (3:1) as eluent to afford 1a (1.56 g,
The phase transition behavior of the samples was determined
by DSC measurements and microscopic observation. DSC
measurements were performed with a Mettler DSC 30. Heat-
ing and cooling rates were 5 C min in all cases. The tran-
sition temperatures of the gels were taken at the maximum of
transition peaks. A polarizing optical microscope, an Olym-
pus BH2 equipped with a Mettler FP82HT hot stage was
used for visual observation.
6
Calcd for C H N O : C, 76.34; H, 8.60; N, 7.03%); mp
5%) as a white solid (found: C, 76.07; H, 8.37; N, 7.41.
ꢁ
ꢀ1
3
8 51 3 3
ꢁ
1
1
4
1
2
06 C (from hexane/ethyl acetate); H NMR (CDCl3,
00 MHz): d 8.11 (d, J¼7.6 Hz, 2H, ArH), 7.48–7.21 (m,
1H, ArH), 5.76 (m, 1H, NH), 5.30 (m, 1H, NH), 5.10 (s,
H, PhCH O), 4.30 (t, J¼7.2 Hz, 2H, NCH ), 3.92 (t,
2
2

7364
K. Yabuuchi et al. / Tetrahedron 63 (2007) 7358–7365
4
.4. Anisotropic fiber growth in aligned LC states
Rev. 2005, 105, 1491–1546; (g) Ikkala, O.; ten Brinke, G.
Chem. Commun. 2004, 2131–2137.
For anisotropic fiber growth, a parallel rubbed cell made of
glass slides covered with rubbed polyimide layers on its
surface was used. The rubbing directions of two glass slides
were parallel to homogeneously align LC molecules. Micro-
scopic observation of self-assembled fibers was performed
on the samples as described above.
2. (a) Abdallah, D. J.; Weiss, R. G. Adv. Mater. 2000, 12, 1237–
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.5. Scanning electron microscopic (SEM) observation
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56, 77–131; (h) Araki, K.; Yoshikawa, I. Top. Curr. Chem.
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tion was placed on a glass slide (5 mmꢂ5 mm) and frozen by
immersion in liquid nitrogen. Then the solvent was removed
in vacuo. The glass was attached to the SEM sample stage.
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crystals, a mixture of liquid crystal and gelator in isotropic
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.6. Polarized infrared spectroscopy
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2
FP82 hot stage. Samples were prepared in a parallel rubbed
cell using KBr plates instead of glass slides.
1
0, 5311–5322.
4
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Acknowledgements
Partial financial support of Grants-in-Aid for Creative
Scientific Research of ‘Invention of Conjugated Electronic
Structures and Novel Functions’ (No. 16GS0209) (T.K.)
from the Japan Society for the Promotion of Science
ˇ
Koji c´ -Prodi c´ , B.; Zini c´ , M. Chem.—Eur. J. 2001, 7, 3328–
3341.
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(
JSPS) and for The 21st Century COE Program of ‘The
Frontiers of Fundamental Chemistry Focusing on Molecular
Dynamism’ (T.K.) from the Ministry of Education, Culture,
Sports, Science and Technology is gratefully acknowledged.
Two of the authors (K.Y. and N.M.) are thankful for financial
support by the Research Fellowships of JSPS for Young Sci-
entists. We thank Dr. Tatsuya Nishimura and Mr. Yuki Hirai
for their helpful discussion and technical assistance. We are
also grateful to JSR Corporation for supplying the polyimide
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