Columnar liquid crystalline self-assembly of hydrogen-bonded rod-coil diblock complexes created from pyrazole/benzoic acid derivatives

Article abstract of DOI:10.1002/bkcs.10556

We synthesized hydrogen-bonded rod-coil diblock complexes having both a rigid rod and a flexible coil by combining bithiophene-conjugated pyrazole derivatives and alkoxy-substituted benzoic acid derivatives. Their self-assembled nanostructures were investigated using polarized optical microscopy, molecular modeling, and X-ray scattering in liquid crystalline (LC) state. They form different types of supramolecularLCphases depending on the numbers and lengths of alkoxy substituents in the benzoic acids. Diblock complexes with low volume ratios of aliphatic coils to rod segments (dioctyloxy chains) self-assembled into lamellar phases; systems with higher ratios (didodecyloxy, trioctyloxy, and tridodecyloxy chains) formed columns. In these columnar structures, two pyrazoles and two benzoic acids formed an aromatic tetramer core through N-H···O and O-H···N hydrogen bonds. Two sets of aromatic tetramers surrounded by flexible aliphatic chains were then stacked to give columnar phases. These are novel examples of supramolecular LC structures comprising hydrogen-bonded pyrazole-benzoic acid derivatives with tetrameric rigid aromatic scaffolds.

Full text of DOI:10.1002/bkcs.10556

Article
DOI: 10.1002/bkcs.10556
BULLETIN OF THE
H.-J. Kim et al.
KOREAN CHEMICAL SOCIETY
Columnar Liquid Crystalline Self-Assembly of Hydrogen-Bonded Rod–
Coil Diblock Complexes Created from Pyrazole/Benzoic acid Derivatives
†
‡
§,*
Ho-Joong Kim, Sung Cho, and Jung Su Park
†Department of Chemistry, Chosun University, Gwangju 501-759, Korea
Department of Chemistry, Chonnam National University, Gwangju 500-757, Korea
‡
§
Department of Chemistry, Sookmyung Women’s University, Seoul 140-742, Korea.
E-mail: jspark@sookmyung.ac.kr
*
Received July 14, 2015, Accepted July 30, 2015, Published online October 4, 2015
We synthesized hydrogen-bonded rod–coil diblock complexes having both a rigid rod and a flexible coil by
combining bithiophene-conjugated pyrazole derivatives and alkoxy-substituted benzoic acid derivatives.
Their self-assembled nanostructures were investigated using polarized optical microscopy, molecular model-
ing, andX-rayscatteringinliquidcrystalline(LC)state. Theyformdifferent typesofsupramolecularLCphases
depending on the numbers and lengths of alkoxy substituents in the benzoic acids. Diblock complexes with
low volume ratios of aliphatic coils to rod segments (dioctyloxy chains) self-assembled into lamellar phases;
systems with higher ratios (didodecyloxy, trioctyloxy, and tridodecyloxy chains) formed columns. In these
columnar structures, two pyrazoles and two benzoic acids formed an aromatic tetramer core through N–HꢀꢀꢀO
and O–HꢀꢀꢀN hydrogen bonds. Two sets of aromatic tetramers surrounded by flexible aliphatic chains were
then stacked to give columnar phases. These are novel examples of supramolecular LC structures comprising
hydrogen-bonded pyrazole–benzoic acid derivatives with tetrameric rigid aromatic scaffolds.
Keywords: Self-assembly, Nanostructure, Liquid crystal, Pyrazole
16–18
Introduction
(LC) nanostructures.
The supramolecular LC structures
and their properties can be precisely tuned by manipulation
of the molecular structure and relative volume fractions of
the coil and rod segments (fcoil/rod). Previous studies showed
that rod–coil diblock molecules self-assemble into diverse
nanostructures such as lamellar, cylindrical, bicontinuous,
and discrete nanostructures in the LC state, depending on
The development of novel functional materials based on self-
organizing systems has attracted much attention because of
their potential applications in biotechnology and materials
1
–4
chemistry.
It is known that various types of noncovalent
intermolecular interactions such as electrostatic interactions,
solvophobic effects, π–π interactions, and hydrogen bonds
are responsible for self-assembly of discrete molecular build-
ing blocks, leading to highly ordered supramolecular struc-
16–18
the value of fcoil/rod
.
Furthermore, external stimuli can
have a significant effect on the strengths and configurations
of the noncovalent interactions between individual rod–coil
building blocks, therefore the resulting LC phases can exhibit
dynamic conformational changes, resulting in significant
changes in the optical or mechanical properties of the supra-
5
–10
tures, and for their functionalities.
Hydrogen bonds are
one of the most useful and important secondary interactions
playing a key role in manipulating assembly and controlling
1
1,12
19–21
functions in many biological and artificial systems.
H-Pyrazole derivatives, which act as hydrogen-bonding
functional groups, have a bond donor (N–H) and acceptor
N) in adjacent positions. It has been observed that these com-
molecular structures.
1
Recently, we synthesized a series of 2,2’-bithiophene-
functionalized N-unsubstituted pyrazole derivatives,
and investigated their supramolecular structures and photo-
(
22
poundscan self-assembleand formvarious types ofhydrogen-
bonded networks, depending on the substituents, including
linear chains, cyclic dimers, trimers, tetramers, and hexamers,
via directional inter- and intra-molecular hydrogen-bonding
chemical properties. Among these derivatives, 4-(2,2’-
bithiophen-5-yl)-3,5-dimethyl-1H-pyrazole is involved in
hydrogen-bonding interactions with the nearest-neighbor N
atom in another molecule. As a result, it forms a two-fold hel-
ical chain-like structure, known as a catemer. In addition
to self-assembly of itself, it has been observed that the
4-dimethyl-1H-pyrazole unit can form hydrogen bonds with
1
3–15
interactions in solution and in crystals.
They can there-
fore be regarded as useful building blocks for the construction
of various supramolecular architectures
Recently, rod–coil diblock molecules consisting of a
rigid rod and a flexible coil segment have aroused interest,
because these can serve as self-assembling building
blocks for the creation of well-defined liquid crystalline
23–25
various carboxylic acids.
This shows that the pyrazoles
can adopt cyclic structures or open-chain dimers via
hydrogen-bonded pair complexes. These properties
prompted us to mix flexible coil-substituted benzoic acids
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and NH-pyrazole-containing aromatic segments in equimolar
amounts to obtain novel supramolecular LC nanostructures
through a combination of intermolecular hydrogen bonding
and phase separation behavior.
In this article, we report the synthesis of rod–coil diblock
complexes consisting of 2,2’-bithiophene-conjugated N-
unsubstituted pyrazoles and alkoxy-substituted benzoic acid
derivatives. We studied their self-assembled nanostructures
in the LC states. On the basis of X-ray diffraction (XRD), dif-
ferential scanning calorimetry (DSC), polarized optical
microscopy (POM), and molecular modeling studies, it was
concluded that these complexes formed tetrameric cyclic
structures (Figure 1(a)), leading to either the unique lamellar
transitions. The small-angle X-ray scattering (SAXS) pattern
of the LC state confirmed that complex 1, containing 3,5-dioc-
tyloxy-substitutedbenzoicacid, self-assembled intoalamellar
phase (Figure 4). The inter-layer distance was 2.56 nm, con-
sistent with the molecular length for complete interdigitation
of the octyloxy chain segments (Figure 1(b)). The wide-angle
X-ray scattering (WAXS) patterns showed a diffuse halo at d
= 0.45 nm; this shows lack of any positional long-range order,
and indicates that 1 forms a disordered lamellar LC phase. As
can be seen from Figure 3 and Table 1, complex 2, containing
3,5-didodecyloxy-substituted benzoic acid, melts into a bire-
ꢁ
fringent LC phase at 61.5 C, followed by isotropic liquid for-
ꢁ
mation at 110 C. The SAXS pattern of 2 after melting into the
(
Figure 1(b)) or columnar LC nanostructures (Figure 1(c)).
birefringent mesophase, shown in Figure 4(b), revealed peaks
corresponding to the (100), (010), (2–10), (200), (210), and
(300) planes. These can be indexed to an oblique columnar
phase with lattice parameters a = 3.55 and b = 3.08 nm, with
Results and Discussion
ꢁ
Synthesis. A series of hydrogen-bonded rod–coil diblock
complexes 1–4 were synthesized by simply mixing equimolar
amounts of 5 and 9a, 9b, 9c, or 9d, respectively. The synthetic
procedures for these synthetic precursors were shown in
Figure 2. 4-(2,2’-Bithiophen-5-yl)-3,5-dimethyl-1H-pyrazole
a characteristic angle of 110 , whereas the WAXS pattern
shows a broad halo, which is a clear indication of liquid-like
order of the rod segments within domains. POM shows that
oncoolingfromtheopticallyisotropicphase,complex2shows
LC properties involving a fibrous texture, similar to that pre-
viously reported for the lamellar columnar mesophase
(
5) was synthesized by Stille cross-coupling of a 1-Boc-4-
26
iodopyrazole derivative with [2,2’-bithiophen]-5-yltributyl-
stannan. Alkoxy-substituted benzoic acids were obtained
from ethyl 3,5-dihydroxybenzoate (7a) and ethyl 3,4,5-
trihydroxybenzoate (7b), which underwent Williamson ether
reactions with the appropriate bromoalkanes to form alkoxy-
substituted benzoates 8a–d. The hydrolysis of 8a–d and sub-
sequent complexations with 5 produced rod–coil diblock
complexes consisting of 2,2’-bithiophene-functionalized N-
unsubstituted pyrazole and an alkoxy-substituted benzoic acid
derivative (3,5-dioctyloxy for 1, 3,5-didodecyloxy for 2,
(Figure 5(a)).
It is estimated that the number (Ncell) of complex 2 in a unit
cell of columnar phase defined as the lattice constants and an
aromatic distance, contain four units of the corresponding
building blocks based on the SAXS results and density calcu-
lation (Table 1). Ncell was calculated using the following equa-
tion: Ncell = ρ × Vcell × N /M, where M is the molecular weight
A
of thecomplex, ρ is thedensity, N
is Avogadro’s number, and
cell is the unit cell volume, defined as a × b × sin(γ ) × 0.45
A
ꢁ
V
27,28
nm.
The rationale for this calculation is based on the pre-
3
,4,5-trioctyloxy for 3, and 3,4,5-tridodecyloxy for 4). The
viously reported solid-state analysis of the cocrystal of 2,4,6-
trimethylbenzoic acid and 3,5-dimethylpyrazole. It shows that
the cocrystallization of these two compounds results in forma-
tion of alternating hydrogen-bonded cyclic tetramer units con-
sisting of two pyrazoles and two benzoic acids via directional
1
13
resulting products were characterized using H and
NMR spectroscopies and mass spectrometry.
C
Structural Investigation. The self-assembling behaviors of
complexes 1–4 in the bulk were investigated using DSC,
POM, molecular dynamics (MD) methods, and XRD. All
the diblock complexes had an ordered structure at room tem-
perature, and the transition temperatures were determined
from the DSC scans (Table 1 and Figure 3). The DSC traces
and POM images of complexes 1–4 showed two phase-transi-
tions, corresponding to solid–LC and LC–isotropic phase
23,24
N–HꢀꢀꢀO and O–HꢀꢀꢀN hydrogen bonds.
It can therefore
be concluded that the two sets of cyclic tetramers are intercon-
nected by the directional bonds between two alkoxy benzoic
acids and two bithiophene-conjugated pyrazole units are sur-
rounded by flexible alkyl chains (Figure 1(a)). In the columnar
phases, two cyclic tetramers are obliquely stacked on top of
(a)
(b)
(c)
S
S
O
H
O
H
N
N
N
N H
H
O
O
S
S
Figure 1. Schematic diagrams of (a) tetramer formed when two pyrazole molecules and two benzoic acids are linked through O–HꢀꢀꢀN and N–
HꢀꢀꢀO hydrogen bonds; (b) molecular organization in lamellar LC phase (complex 1); and (c) molecular organization in oblique columnar LC
phase (complexes 2–4). Green bar indicates tetramer.
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Rod–Coil Diblock Complexes
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ꢁ
Figure 2. Synthetic routes to the compounds 5 and 9a–d. Reagents and conditions: (i) Pd(PPh ) (5 mol %), CuI (5 mol %) THF, 80 C;
(
3
4
ꢁ
ii) ethanol, H SO , reflux; (iii) bromoalkane, K CO , DMF, 80 C; and (iv) NaOH, ethanol, reflux.
2 4 2 3
Table 1. Phase transitions and lattice parameters of complexes 1–4.
ꢁ
ꢁ
Complexes
Phase transition ( C) and corresponding phases
a/nm
b/nm
d/nm
γ/
N
cell
1
2
3
4
Cr 50.1 Lam 100.2 i
Cr 61.5 Colob 110.5 i
Cr 52.5 Colob 107.0 i
Cr 55.0 Colob 114.1 i
—
—
2.56
—
—
110
97
—
3.55
3.32
3.88
3.08
2.96
3.15
4
4
4
—
—
87
Colob, oblique columnar LC phase; i, isotropic liquid; Lam, lamellar LC phase.
ꢁ
DSC traces (peak temperatures, 10 C/min) recorded during the first heating scans.
N
cell, number of complexes in unit cell of columnar phase, calculated as Ncell = ρ × Vcell × N
A
/M, where M is the molecular weight of the complex, ρ is the
ꢁ
density, N
A
is Avogadro’s number, and Vcell is the volume of the unit cell defined by a × b × sin(γ ) × 0.45 nm. The height of the unit cell was assumed to
3
be 0.45 nm obtained from WAXS patterns, indicating the aromatic stacking distance. The densities were assumed to be 1.0 g/cm .
each other and aligned vertical to the resulting columns
Figure 1(c)).
(
To further confirm the above results, molecular modeling
was performed from a low (Hartree–Fock Hamiltonian with
(
(
a)
b)
3
-21G basis set) to a high (density functional theory B3LYP
with 6-31G* basis set) level in a stepwise manner
Figure 6). The model shows that a cyclic tetramer arrange-
(
ment between these two building blocks through hydrogen-
bonding interactions is energetically favorable, as shown in
Figure 1(a). A further calculation based on this energetically
optimized structure suggests that two sets of tetramers com-
prising of four complexes of 2 subsequently stack on top of
each other with a stacking distance of 4.5 Å and mutual rota-
tions to avoid steric hindrance between the aliphatic chains,
giving rise to oblique columnar structures. The calculated
dimensions, a = 3.4 and b = 3.0 nm, obtained using theoretical
dimensional analyses, are in good agreement with the exper-
imental results from the SAXS experiments.
(
(
c)
d)
3
0
60
90
120
Temperature (°C)
Figure 3. DSC thermograms of (a) 1, (b) 2, (c) 3, and (d) 4, showing
first heating cycles at heating rate of 10 C/min.
ꢁ
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For complexes 3 and 4, with 3,4,5-trialkoxy chains, the
SAXS reflections in the LC phases can be indexed on the basis
particular system can modulate the type of supramolecular
LC structure. This change in the supramolecular structure
can be rationalized by considering the microphase separation
between dissimilar parts of the molecule and the space-filling
requirements of the flexible alkyl chains. The formation of a
lamellar phase from complex 1, with a low fcoil/rod (0.64), indi-
cates that the alkyl chains are too short to surround the aro-
matic cores; instead, aromatic tetramers are stacked in
parallel, and then the aliphatic chains are interdigitated to yield
infinite layers. For complexes 2–4, with higher fcoil/rod (0.91
for 2, 0.96 for 3, and 1.37 for 4), the columnar phases allow
more space for the bulky chains, reducing the repulsive force
between aliphatic chains, and enabling adoption of less
of oblique columnar structures with the lattice parameters a =
ꢁ
3
3
.32 and b = 2.96 nm, and γ = 97 for 3, and a = 3.88 and b =
ꢁ
.15 nm, and γ = 87 for 4 (Figure 4(c) and (d)). On cooling
from the optically isotropic liquid state of complex 4 and then
annealing at 70 C, a fan-shaped texture was observed using
ꢁ
POM, furthersupportingLCproperties(Figure 5(b)). Theoret-
ical calculations for complexes 3 and 4 also showed that the
lattice constants of an oblique array can only satisfy four com-
plexes per unit cell within the suggested columnar structures,
which are separated by aliphatic chains, similar to those
observed for complex 2.
29,30
These results show that variations in the length and number
of substituted alkyl chains in the benzoic acid unit in this
strained aromatic packing.
Another point to note is that the influence of the alkyl chain
length on the LC properties is the same for the two families of
complexes with di and trialkoxy chains. When the alkyl chain
of the benzoic acid is elongated, the melting temperature
increases, probably because of an increase in van der Waals
interactions between the hydrophobic tails. Similarly, the iso-
tropic points also increase with increasing alkyl chain length,
giving rise to improved mesophase stability.
(
001)
(
002)
(
(
a)
b)
(
010)
(210)
(
100)
010)
(200)
(2-10)
(300)
Conclusion
(
2
4
6
A series of rod–coil diblock hydrogen-bonded complexes
0
consisting of a 2,2 -bithiophene-functionalized pyrazole
derivative and alkoxy-substituted benzoic acid were synthe-
sized and used as the building blocks for the preparation of
supramolecular LC nanostructures. The systems containing
a dioctyloxy chain self-assembles into lamellar LC phases,
whereas those with higher fcoil/rod values (didodecyloxy, trioc-
tyloxy, and tridodecyloxy chains) form oblique columnar LC
phases. These results can be explained by both the formation
of the cyclic hydrogen-bonded tetramers consisting of two
pyrazole and two benzoic acids in the core unit, and their
π–π stacking interaction. We believe that the use of tetrameric
pyrazole/benzoic acid scaffolds with flexible coil segments,
which are a new type of rod–coil diblock material, could be
a useful strategy for the development of unique columnar
LC nanostructures.
(
100)
010)
(
110)
(
c)
(
(200)
(1-20)
(
100)
(
010)
2
(
d)
4
6
-
1
q
(nm )
Figure 4. SAXS patterns of (a) 1, (b) 2, (c) 3, and (d) 4 against q (q =
ꢁ
4
πsin2θ/λ) at 70 C.
(
a)
(b)
ꢁ
ꢁ
Figure 5. Polarized optical microphotographs of (a) 2 at 70 C and (b) 4 at 70 C, on cooling.
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Rod–Coil Diblock Complexes
KOREAN CHEMICAL SOCIETY
Figure 6. Snapshots of supramolecular structures of hydrogen-bonded rod–coil diblock complexes based on MD calculations. (a) Tetramer
formed by two pyrazole molecules and two benzoic acids through hydrogen bonds. (b) Energetically optimized structure suggests that two tetra-
mers from four units of complex 2 form oblique columnar phases (aromatic cores are green).
Experimental
was monitored using a thermocouple placed close to the
sample.
Chemicals. All reactions were carried out in an argon atmos-
phere. Tetrahydrofuran (THF) was distilled from sodium with
benzophenone. Dichloromethane and dimethylformamide
were distilled over CaH . Pd(PPh ) , CuI, bromooctane, bro-
mododecane, 3,5-dihydroxybenzoic acid, gallic acid, and
THF were purchased from Sigma Aldrich (St. Louis, MO,
USA). Unless otherwise indicated, all starting materials were
obtained from commercial suppliers (Sigma-Aldrich; Lancas-
ter, Spartanburg, SC, USA; TCI, Tokyo, Japan, etc.). Flash
chromatography was performed using silica gel
Synthesis of Complexes 1–4
Synthesis of Compound 5. A mixture of 2,2’-bithiophen-5-
yltributylstannane (5.02 g, 11 mmol), tert-butyl 4-iodo-3,5-
dimethyl-1H-pyrazole-1-carboxylate (2.94 g, 10 mmol),
Pd(PPh ) (0.58 g, 0.5 mmol), and CuI (0.19 g, 1 mmol) in
2
3 4
3
4
THF (50 mL) was stirred for 30 h under reflux conditions
and then cooled to room temperature. The solvent was
removed under vacuum and the residue was purified by col-
1
umn chromatography. H NMR (DMSO): δ 2.29 (q, 1H),
6.94 (d, 1H) 7.06 (q, 1H), 7.25 (m, 2H), 7.46 (q, 1H), 12.42
(1H, s)
60 (230–400 mesh; EM Science, Gibbstown, NJ, USA).
UV light and iodine vapor were used for visualization.
Synthesis ofCompounds7aandb. Compounds7aand bwere
synthesized using similar procedures. The procedure for the
synthesis of7a, usedasan example, wasperformed as follows.
3,5-Hydroxybenzoic acid 6a (5.0 g, 32.5 mmol) was dis-
solved in anhydrous ethanol (50 mL). After addition of con-
1
Equipment. H NMR spectra were recorded in CDCl and
DMSO solutions using a Bruker AM 250 spectrometer
3
(
Bruker, Rheinstetten, Germany). The product purities
were checked using thin-layer chromatography (silica gel
0, Merck, Darmstadt, Germany). Matrix assisted laser
6
centrated H
The ethanol was removed, and the mixture was extracted with
dichloromethane and 10% NaHCO aqueous solution. Com-
bined organic extracts were washed with water and brine, sub-
2 4
SO (0.5 mL), the solution was refluxed for 6 h.
desorption/ionization time of flight (MALDI-TOF) mass
spectra were obtained with a Perceptive Biosystems
Voyager-DE STR (Framingham, MA, USA) using
α-cyano-4-hydroxycinnamic acid as the matrix. A Perkin
Elmer Diamond-DSC differential scanning calorimeter
3
sequently dried over anhydrous MgSO
, and concentrated to
4
yield a white solid (yield, 95%).
1
(Perkim Elmer, Norwalk, CT, USA) equipped with a 1020
7a: H NMR (CDCl
3
, 250 MHz): δ 7.0 (s, 2H, Ar), 6.53 (s,
), 1.38 (t, 3H, CH ).
, 250 MHz): δ 7.47 (s, 2H, Ar), 4.35 (t,
), 1.54 (t, 3H, CH ).
thermal analysis controller was used to identify the thermal
transitions; these are reported as the maxima and minima of
the endothermic or exothermic peaks. The compounds were
synthesized using the procedures shown in Figure 2 and then
purified using silica gel column chromatography. X-ray scat-
tering measurements were performed in transmission mode,
using synchrotron radiation, at the 10C1 X-ray beam lines
at the Pohang Accelerator Laboratory, Korea. The structural
changes on heating were determined by placing the sample
in an aluminum sample holder, which was sealed with a win-
dow of 7 μm thick Kapton film on both sides. The sample was
heated with two cartridge heaters and the sample temperature
2H, Ar), 4.23–4.35 (t, 2H, COOCH
2
3
1
7b: H NMR (CDCl
2H, COOCH
3
2
3
Synthesis of Compounds 8a–d. Compounds 8a–d were
synthesized using identical procedures. A representative syn-
thesis is described for compound 8a. Compound 7a (500 mg,
2.75 mmol), K CO (1.52 g, 11.0 mmol), and bromooctane
2
3
(1.22 g, 6.33 mmol) were dissolved in DMF (40 mL) and
refluxed for 12 h in an argon atmosphere. The mixture was
cooled and the DMF was removed by vacuum distillation.
The resulting mixture was extracted with dichloromethane
and distilled water. The dichloromethane solution was
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Columnar Liquid Crystalline Self-Assembly of Hydrogen-Bonded
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Rod–Coil Diblock Complexes
KOREAN CHEMICAL SOCIETY
collected, dried over anhydrous MgSO , and filtered. The
crude product was purified by column chromatography to
3. F. J. M. Hoeben, P. Jonkheijm, E. W. Meijer, A. P.
4
H. J. Schenning, Chem. Rev. 2005, 105, 1491.
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. Y. Yamamoto, T. Fukushima, Y. Suna, N. Ishii, A. Saeki,
yield 1.02 g (91%) of a viscous liquid.
1
S. Seki, S. Tagawa, M. Taniguchi, T. Kawai, T. Aida, Science
8
a: H NMR (CDCl , 250 MHz): δ 7.17 (s, 2H, Ar), 6.63 (s,
3
2
006, 314, 1761.
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1
H, Ar), 4.36 (q, 2H, COOCH ), 4.97 (t, 4H, Ar–OCH ), 1.77
2 2
5
6
(
m, 2H, OCH CH ), 1.42–0.88 (m, 29H, CH , CH ).
2 2 2 3
4
1
8
b: H NMR (CDCl , 250 MHz): δ 7.17 (s, 2H, Ar), 6.63 (s,
3
1
H, Ar), 4.36 (q, 2H, COOCH ), 4.97 (t, 4H, Ar-OCH ), 1.77
2 2
(
m, 2H, OCH CH ), 1.42–0.88 (m, 45H, CH , CH ).
2 2 2 3
1
8
c: HNMR(CDCl , 250 MHz): δ 7.26 (d, 2H, Ar), 4.35 (q,
7. S. S. Babu, V. K. Praveen, A. Ajayaghosh, Chem. Rev. 2014,
114, 1973.
3
2
H, COOCH ), 4.02 (t, 6H, Ar–OCH ), 1.61–1.85 (m, 6H,
2 2
OCH CH ), 1.49–0.88 (m, 42H, CH , CH ).
8. H. Cui, E. T. Pashuck, Y. S. Velichko, S. J. Weigand,
A. G. Cheetham, C. J. Newcomb, S. I. Stupp, Science 2010,
2
1
2
2
3
8
d: HNMR(CDCl , 250 MHz):δ7.26(d, 2H, Ar), 4.35(q,
3
3
27, 555.
2
H, COOCH ), 4.02 (t, 6H, Ar–OCH ), 1.61–1.85 (m, 6H,
2 2
9
. J. J. van Gorp, J. A. J. M. Vekemans, E. W. Meijer, J. Am. Chem.
Soc. 2002, 124, 14759.
OCH CH ), 1.49–0.88 (m, 66H, CH , CH ).
2
2
2
3
Synthesis of Compounds 9a–d. Compounds 9a–d were
synthesized using similar procedures. A representative syn-
thesis is described for compound 9a. An aqueous solution
of NaOH (97.2 mg, 2.46 mmol, 20 mL) was added to a solu-
tion of 8a (500 mg, 1.23 mmol) in ethanol (30 mL). The reac-
tion mixture was refluxed for 6 h. The mixture was cooled and
then the ethanol was removed using a rotary evaporator. The
mixture was poured onto crushed ice and acidified with con-
centrated HCl. The mixture was repeatedly extracted with
1
1
0. F. Garcia, L. Sanchez, Chem. Eur. J. 2010, 16, 3138.
1. G. A. Jerey, W. Saenger, Hydrogen Bonding in Biological
Structures, Springer-Verlag, Berlin, 1991.
1
2. G. A. Jerey, An Introduction to Hydrogen Bonding, Oxford
University Press, New York, NY, 1997.
13. M. C. Etter, Acc. Chem. Res. 1990, 23, 120.
14. M. C. Etter, J. MacDonald, J. Bernstein, Acta Crystallogr. B
1990, B46, 256.
1
5. J. Bernstein, R. E. Davis, L. Shimoni, N.-L. Chang, Angew.
Chem. Int. Ed. 1995, 34, 1555.
ethyl acetate. The organic layer was dried over MgSO and
concentrated. An off-white solid was obtained by recrystalli-
zation from ethanol.
4
1
6. X. Wang, H. Zhang, M. Shi, X. Wang, Q. Zhou, J. Polym. Sci. A
Polym. Chem. 2005, 43, 733.
1
17. F. Liu, B. Chen, B. Glettner, M. Prehm, M. K. Das,
U. Baumeister, X. Zeng, G. Ungar, C. Tschierske, J. Am. Chem.
Soc. 2008, 130, 9666.
9
a: H NMR (CDCl , 250 MHz): δ 7.23 (s, 2H, Ar), 6.69 (s,
3
1
1
3
3
H, Ar), 3.98 (t, 4H, OCH ), 1.79–0.89 (t, 30H, CH , CH ).
2 2 3
1
9
b: H NMR (CDCl , 250 MHz): δ 7.23 (s, 2H, Ar), 6.69 (s,
3
1
8. M. Lee, B.-K. Cho, W.-C. Zin, Chem. Rev. 2001, 101, 3869.
H, Ar), 3.98 (t, 4H, OCH ), 1.79–0.89 (t, 46H, CH , CH ).
2
2
3
19. X. Xiao, Y.-Q. Fu, J.-J. Zhou, Z.-S. Bo, L. Li, C.-M. Chan,
Macromol. Rapid Commun. 2007, 28, 1003.
20. L. Qiang, Z. Ma, Z. Zheng, R. Yin, W. Huang, Macromol. Rapid
Commun. 2006, 27, 1779.
1
9
c: H NMR (CDCl , 250 MHz): δ 7.32 (s, 2H, Ar),
3
.99–4.1 (t, 6H, OCH ), 0.85–1.89 (m, 45H, CH , CH ).
2
2
3
1
9
d: H NMR (CDCl , 250 MHz): δ 7.32 (s, 2H, Ar),
.99–4.1 (t, 6H, OCH ), 0.85–1.89 (m, 69H, CH , CH ).
3
2
1. H.-J. Kim, Y.-B. Lim, M. Lee, J. Polym. Sci. A Polym. Chem.
008, 46, 1925.
2
2
3
2
Complexation of Compounds 8a-d with 4-(2,2’-Bithiophen-
-yl)-3,5-dimethyl-1H-pyrazole. Complexes 1–4 were all
2
2. J. S. Park, Bull. Korean Chem. Soc. 2014, 35, 1221.
5
2
3. C. Foces-Foces, L. Infantes, F. Aguilar-Parrilla, N. S. Golubev,
H.-H. Limbach, J. Elguero, J. Chem. Soc. Perkin Trans. 1 1996,
prepared using the same procedure. A representative synthesis
is described for 1. Compound 9a (50.0 mg, 0.132 mmol) and
2
, 349.
4. R. M. Claramunt, M. A. Garcia, C. Lopez, J. Elguero, ARKIVOC
005, 2005, 91.
5. S. F. Bureiko, N. S. Golubev, G. S. Denisov, S. Y. Kucherov,
P. M. Tolstoi, Russ. J. Gen. Chem. 2005, 75, 1821.
6. C. Cuerva, J. A. Campo, P. Ovejero, M. R. Torresb, M. Cano,
Dalton Trans. 2014, 43, 8849.
7. J.-W. Choi, J.-H. Han, M.-H. Ryu, B.-K. Cho, Bull. Korean
Chem. Soc. 2011, 32, 781.
8. X. Cheng, F. Liu, X. Zeng, G. Ungar, J. Kain,
S. Diele, M. Prehm, C. Tschierske, J. Am. Chem. Soc. 2011,
4
0
-(2,2’-bithiophen-5-yl)-3,5-dimethyl-1H-pyrazole (34.4 mg,
2
2
2
2
2
.132 mmol)weredissolvedinanhydrousTHFandthesolution
2
ꢁ
was stirred for 30 min at 25 C. The solvent was removed using
a rotary evaporator to yield 1 as a pale-yellow solid.
Acknowledgments. This work was carried out with the sup-
port of the Cooperative Research Program for Agriculture Sci-
ence & Technology Development (Project No. PJ010506),
Rural Development Administration, Republic of Korea.
1
33, 7872.
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Bull. Korean Chem. Soc. 2015, Vol. 36, 2740–2745
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de 2745