Hydrogen-bond-assisted supramolecular 1-D tape-like structures of mesogenic bis-pyrazoles

Article abstract of DOI:10.1016/j.tet.2012.05.060

Two new series of isomeric bis-pyrazoles 1a-b are prepared, characterized, and their mesomorphic properties investigated. These pyrazoyl derivatives were obtained from the condensation of α,β-diketones 2a-b with hydrazine monohydrate in refluxing THF. Two single crystallographic structures of compounds mesogenic 1a (n=14) and nonmesogenic 1b (n=8) were determined by X-ray analysis. Both 1a-14 and 1b-8 crystallize in a triclinic space group P-1 and monoclinic C2/c group, respectively. An extended H-bonded structure was formed in both crystal lattices, giving a pseudo 1D-polymeric tape-like structure. Derivatives 1a exhibited smectic A/C mesophases, in contrast, derivatives 1b were all nonmesogenic. The difference in mesomorphic behavior was attributed to the between linear conformation and the coplanarity of the five rings over than in 1a. The correlation between the molecular structures and the mesomorphic properties is discussed.

Full text of DOI:10.1016/j.tet.2012.05.060

Tetrahedron 68 (2012) 6231e6239
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Hydrogen-bond-assisted supramolecular 1-D tape-like structures of mesogenic
bis-pyrazoles
Huei-Yun Lin c, Hsiu-Ming Kuo c, Shao-Gang Wen c, Hwo-Shuenn Sheu a, Gene-Hsiang Lee b,
,
Chung K. Lai c
*
a National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan, ROC
b Instrumentation Center, National Taiwan University, Taipei 10660, Taiwan, ROC
c Department of Chemistry, National Central University, Chung-Li 32001, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 April 2012
Received in revised form 9 May 2012
Accepted 15 May 2012
Available online 24 May 2012
Two new series of isomeric bis-pyrazoles 1aeb are prepared, characterized, and their mesomorphic
properties investigated. These pyrazoyl derivatives were obtained from the condensation of a,b-dike-
tones 2aeb with hydrazine monohydrate in refluxing THF. Two single crystallographic structures of
compounds mesogenic 1a (n¼14) and nonmesogenic 1b (n¼8) were determined by X-ray analysis. Both
1ae14 and 1be8 crystallize in a triclinic space group Pꢀ1 and monoclinic C2/c group, respectively. An
extended H-bonded structure was formed in both crystal lattices, giving a pseudo 1D-polymeric tape-like
structure. Derivatives 1a exhibited smectic A/C mesophases, in contrast, derivatives 1b were all non-
mesogenic. The difference in mesomorphic behavior was attributed to the between linear conformation
and the coplanarity of the five rings over than in 1a. The correlation between the molecular structures
and the mesomorphic properties is discussed.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
packing is generally obscured by the molecular structures in de-
signing liquid crystal.
Using H-bonds have now become an important concept to
construct novel molecular architectures1e5 with liquid crystalline
and/or other optic-electric properties. Many unique mesogenic
structures6e10 induced or stabilized by H-bonded were already
known, in which either intermolecular or/and intramolecular H-
bonds were widely applied. However, H-bonds, compared to co-
valent bonds are relatively weak; they are sensitive to the structural
alternation, and any puny deviation in molecular structures might
have a dramatic impact on the propensity of these H-bond stabi-
lized molecules.11,12 Using H-bonded interaction can be twofold;
complementary shapes and intermolecular force. A better or/and
preferable molecular shape formed by a dimeric, trimeric or poly-
meric structure can be created, leading to an appropriate aspect
ratio required to form potential mesogens. This concept was often
used and observed for organic molecules with unconventionally
shapes. Secondly, intermolecular interactions enhanced by induced
H-bonds usually facilitate the formation of mesophases, particu-
larly for those molecules with no dipole group substituted. Nev-
ertheless, the interplay between intermolecular attraction and
Pyrazoles, usually considered as an important member among
aromatic N-heterocycles have attracted substantial studies during
the past decades, particularly in the field of biological chem-
istries.13e15 Part of which stems from their capability of forming
conjugate bases, pyrazoylates and N-substituted derivatives. Pyr-
azoles are also considered electronically as both
s-donor and p-
acceptor ligands.16 In addition, their capabilities of binding transi-
tion metals in a variety of coordination modes17e19 are truly robust.
Moreover, the pyrazoyl-hydrogen (eNH) can capably act as a hy-
drogen-bond donor, which makes the pyrazoles as an excellent
candidate in supramolecular chemistry.20 Such intermolecular hy-
drogen bondings are relatively strong, and many examples with
a dimeric structure was often obtained in many pyrazoylate sys-
tems.21 Also, a trimeric, tetrameric,22 hexameric and catmeric
structures aggregated in the solid states were found.
However, known examples prepared for material chemistry has
been relatively lesser though they are thermally and hydrolytically
very stable. Only few examples of mesogenic pyrazoles23e26 and
their derived metallomesogens27e30 were prepared since first ex-
ample reported in 1992. Some of such metallomesogens31a exhibi-
ted a unique red-luminescent behavior or organogel.31b A few
examples of symmetrical and unsymmetrical mono-pyrazoles and
their metallomesogens were developed and studied by this group.
* Corresponding author. Tel.: þ886 3 4259207; fax: þ886 3 4277972; e-mail
address: cklai@cc.ncu.edu.tw (C.K. Lai).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.05.060

6232
H.-Y. Lin et al. / Tetrahedron 68 (2012) 6231e6239
The exocyclic bond angles resulted from the incorporation of het-
erocyclic rings as core group played an important role in induction/
formation of mesomorphic behavior. In this work, two homolog
series of bis-pyrazoles 1aeb were prepared, characterized and
mesomorphic properties studied. Both compounds 1aeb are in fact
structural isomers. Compounds 1a were all mesogenic, giving SmA/
SmC phases, whereas all compounds 1b were not mesogenic. Two
single crystals 1ae14 and 1be8 were also resolved and analyzed.
The correlation between crystal data and molecular structures was
performed to aim in understanding the relationship between the
structures and the mesomorphic properties. The example illustrated
a supramolecular assembly by bis-pyrazole-based materials, in
which an extended 1D non-covalent bonding network in the solid/
LC states was observed.
these two peaks were all apparently decreased while the peaks were
only slightly shifted to
addition of a drop D2O for 7 h. The elemental analyses of compounds
d
12.47 and 10.99, for example, 1b (n¼8) after
1aeb were all performed to confirm their purities.
2.2. Phase transitions, mesomorphic behavior and thermal
stabilities
The thermal behavior of compounds 1aeb and 2aeb was in-
vestigated by polarized optical microscopy and differential scan-
ning calorimetry. The transition temperatures and enthalpies of the
compounds 1e2 are listed in Table 1. All bis-diketones 2aeb were
nonmesogenic. A phase transition of crystal-to-isotropic was ob-
served, for example, at Tmp¼156.9 ꢁC and 119.1 ꢁC, respectively, for
compound 2a (n¼12) and 2b (n¼12). Compounds 2a have higher
clearing temperatures than those of 2b (n¼12) due to molecular
linearity symmetry. The lack of mesomorphism in 2aeb might be
attributed to the pronounced non-bending linearity observed in
2. Results and discussion
2.1. Synthesis and characterization
similar symmetric b-diketonate systems. An improved mesophase
The synthetic routes21b,32e37 used to prepare bis(pyrazoles)
1aeb are listed in Scheme 1. The bis-diketones 2aeb were synthe-
sized by double condensation of dimethyl terephthalate or dimethyl
isophthalate, the appropriate acetophenone derivatives and sodium
hydride NaH in refluxing THF or dimethoxethane for 24 h under
nitrogen atmosphere. The yields were modest, ranged from 45e65%.
They exist possibly in a few different ketoeenol tautomeric forms.
All compounds were characterized by 1H and 13C NMR spectroscopy.
was often obtained by an introduction of a polar group in-
corporated, such as eCN group. Polar groups can better prefer an
antiparallel arrangement. In contrast, all derivatives 1a (n¼8, 10, 12,
14, 16) exhibited an enantiotropic mesomorphic behavior, whereas
all other derivatives 1b (n¼8, 10, 12, 14) showed crystal phases.
Under optical microscope, compounds 1a exhibited fan-shaped
textures at higher temperatures and Schlieren textures at lower
temperatures (Fig. 1). These two textures were characteristic of
a layer smectic A and C phase expected for the rod-like molecules.
Under optical microscope, a large area of homeotropic domains was
also observed for SmA phase. The clearing temperatures were all
ranged at Tcl¼374.6 (n¼8)e309.4 ꢁC (n¼16) while the melting
temperatures remained at Tmp¼201.2 (n¼8)e185.7 ꢁC (n¼16). On
the other hand, the temperature range of mesophases decreased
On the 1H NMR spectra, two singlet peaks appeared at
and 16.87e17.08 is characteristically assigned for olefinic-H
d 6.81e6.84
d
(eCOH]CH) and enol-H (]CHeOH) groups of compounds 2aeb.
The bis-pyrazoles 1aeb were obtained by the reactions of bis-
diketones 2aeb with excess hydrazine monohydrate in refluxing
THF. These compounds 1aeb isolated as white solid were obtained
by recrystallization from warm THF. The solubility of all pyrazoles
1aeb were relatively poor in THF at room temperature, therefore,
most of final pyrazoles were only characterized by 1H NMR spec-
troscopy. The formation of final pyrazoles was monitored by the
with longer carbon length of alkoxy chains,
D
Tm¼187.2 (n¼8)>
155.0 (n¼12)>127.1 ꢁC (n¼16) on cooling process. The transition
enthalpies of SmA-to-iso phases also decreased with carbon length.
In contrast, all derivatives 1b were not mesogenic. A transition of
crystal-to-isotropic for 1b was observed. Surprisingly, all melting
temperatures of 1b were much lower than those of homologs of 1a
by ca. T¼170.5 (n¼8)e128.1 ꢁC (n¼14). Compounds 1a and 1b are
structurally isomeric. The larger difference on the clearing tem-
peratures might probably be due to the better linearity and
disappearance of a singlet at
addition, a characteristic peak at
d
16.87e17.08 assigned for eCHCOH. In
10.25e10.91 and 12.37e13.37
d
assigned to the pyrazole-H (eNH) was observed. The exchange ex-
periment of pyrazoles with D2O solvent was also performed to
confirm the assignment of two pyrazole-H peaks. The intensities of
Hn(H2C)O
a
b
O
O
O
O(CH2)nH
Hn(H2C)O
Hn(H2C)O
O(CH2)nH
O
O
O
O
O
O
2a
2b
c
c
N
NH
O(CH2)nH
Hn(H2C)O
Hn(H2C)O
O(CH2)nH
HN
N
N
NH
HN
N
1a
1b
Scheme 1. Reactions and reagents. (a) Dimethyl terephthalate (0.50 equiv) in refluxing THF, 24 h, 52e68%; (b) dimethyl isophthalate (0.50 equiv) in refluxing THF, 24 h, 50e66%;
(c) N2H4 (1.5 equiv), acetic acid (0.5 mL), refluxing in CH2Cl2, 24 h, 70e82%.

H.-Y. Lin et al. / Tetrahedron 68 (2012) 6231e6239
6233
oxadiazole-2-yl)benzene.22c,38 They are structurally similar to
1aeb, as a rod-like five-ring structure. The results indicated that
the 1,3-meta-substituted 1,3,4-oxadiazole derivatives exhibited no
mesogenic behavior, whereas, the 1,4-para-substituted 1,3,4-
oxadiazole derivatives formed smectic-like mesophases. A clear-
ing temperature at Tcl¼142.8 ꢁC and Tcl¼224.7 ꢁC (all n’s¼12) was
observed for 1,3- and 1,4-disubstituted benzenes, respectively. This
was also due to a loss of linearity by the presence of the 1,3,4-
oxadiazoles ring, for it is unable to make co-linear disubstitution
bonding. No intermolecular hydrogen bonding was possible in both
meta- and para-bis(1,3,4-oxadiazole-2-yl) benzenes. The impor-
tance of hydrogen bond in 1a (n¼8) was noted by a wider tem-
Table 1
Phase transition temperature (¢J) and enthalpies (Kcal/mol) of 1e2
156.9 (48.1)
Cr
Cr
I
I
I
2a; n = 12
2b; n = 12
1a; n = 8
150.7 (47.2)
119.1 (50.4)
105.8 (92.0)
374.6 (7.62)
348.8 (0.67)
201.2 (13.2)
Cr
SmC
SmA
186.6 (11.0)
196.3 (13.6)
338.8 (0.42)
345.4 (1.27)
373.8 (7.35)
357.0 (6.47)
10
12
14
Cr
Cr
Cr
Cr
SmC
SmC
SmC
SmC
SmA
SmA
SmA
SmA
I
I
I
I
189.4 (12.1)
190.4 (12.8)
342.4 (0.88)
332.1 (1.31)
354.8 (6.25)
341.1 (5.60)
perature range of mesophases observed by
D
T¼173.4 ꢁC over
184.1 (12.2)
190.2 (15.8)
329.6 (1.25)
318.5 (1.68)
339.1 (5.40)
324.7 (4.13)
D
T¼64.3 ꢁC in para-1,4-bis(5-phenyl-1,3,4-oxadiazole-2-yl) ben-
zene (n¼8). Compounds 1aeb were all thermally stable. Thermal
gravimetric analysis (TGA) revealed good thermal stability for both
series of compounds 1aeb. For example, the decomposition tem-
peratures for a 5% weight loss for 1a (n¼14) and 1b (n¼8) were
obtained at Td¼415.7 ꢁC and Td¼398.5 ꢁC, respectively (Fig. 2).
316.4 (1.66)
302.9 (1.64)
322.7 (3.87)
309.4 (2.93)
185.8 (14.9)
185.7 (13.5)
16
180.5 (12.9)
300.9 (1.56)
307.6 (2.74)
204.1 (36.3)
1b; n = 8
Cr
Cr
Cr
Cr
I
I
I
I
197.2 (34.2)
198.7 (32.9)
10
12
14
2.3. Crystal and molecular structures of 1ae14 and 1be8
190.4 (31.9)
191.9 (31.7)
In order to understand the correlation between the molecular
structures and mesomorphic behavior, two single crystals of the
mesogenic 1ae14 and nonmesogenic 1be8 suitable for crystallo-
graphic analysis were obtained by slow diffusion from THF/MeOH at
room temperature and their structures resolved. Fig. 3 shows the
two molecular structures with the atomic numbering schemes.
Table 2 lists their crystallographic and structural refinement data for
the two molecules. Compound 1ae14 crystallizes in a triclinic space
group Pꢀ1 with a Z¼1, and compound 1be8 crystallizes in
a monoclinic space group C2/c with a Z¼8. The overall molecular
shapes of both crystals were considered as linear-shaped or slightly
bent molecules. It is well known that pyrazole has two resonant
isomers,39e42 and the pyrazoylate hydrogen (eNH) can reside on
either two nitrogen atoms, which is so-called tautomeric prototropy.
185.1 (30.8)
181.3 (30.6)
174.6 (30.4)
a: n = carbon length in the alkoxy chains; Cr = crystal, SmC = smectic C, SmA =
smectic A phases, I = isotropic.
coplanarity of compounds 1a over 1b, as confirmed by single crystal
X-ray crystallography. The lack of mesomorphic properties in
compounds 1b was also attributed to the slightly bent structures
and poorer coplanarity of four rings in compounds 1a. The shape
effect of para- and meta-substitution on the formation of meso-
phases has been demonstrated also in bis(5-phenyl-1,3,4-
Fig. 1. Optical textures observed. Top left and right plates: SmA phase at 360.0 ꢁC and SmC phase at 340.0 ꢁC by 1a (n¼8). Bottom left and right plates: SmA phase at 320 ꢁC and SmC
phase at 312.0 ꢁC by 1a (n¼14).

6234
H.-Y. Lin et al. / Tetrahedron 68 (2012) 6231e6239
Table 2
1b (n= 8)
1a (n = 14)
Crystallographic data for crystals 1ae14 and 1be8
100
80
60
40
20
0
Compds.
1a (n¼14)
C52H74N4O2
787.15
200(2)
Triclinic
1b (n¼8)
C40H50N4O2
618.84
200(2)
Monoclinic
C2/c
35.9910(5)
15.8385(2)
13.0469(1)
90
109.9196(7)
90
6992.34(14)
8
2672
Empirical formula
Formula weight
T/K
Crystal system
Space group
Pꢀ1
ꢀ
a/A
10.1536(7)
10.5977(5)
12.0042(9)
76.231(5)
85.607(4)
64.400(4)
1130.92(13)
1
ꢀ
b/A
ꢀ
c/A
ꢁ
ꢁ
a
/
b
/
ꢁ
/
g
3
ꢀ
U/A
Z
F(000)
430
1.156
Dcalcd/Mg mꢀ3
Crystal size/mm3
Range for data collection/ꢁ
Reflection collected
Data, restraints, parameters
Independent reflection
Final R1, wR2
1.176
200
400
600
0.40ꢂ0.13ꢂ0.11
1.75 to 25.00
11,809
3955/0/263
3955 [R(int)¼0.0700]
0.0665, 0.1862
0.55ꢂ0.50ꢂ0.12
1.42 to 27.50
24,966
7969/45/409
7969 [R(int)¼0.0340]
0.0732, 0.2015
o
( C)
Temp.
Fig. 2. TGA plots of compounds 1ae14 and 1be8 (heating rate of 20 ꢁC minꢀ1; N2
atmosphere).
This process has been found to be fast in solution at room temper-
ature. A pair of isomeric structures was observed in some pyrazoles.
Crystallographic data showed that for both compounds 1ae14 and
1be8, the molecules contain only one independent bis-pyrazole
molecule. The two protons of the pyrazole group only reside at
the nitrogen atom N2 and N4 in 1be8, and N2 in 1ae14, adjacent to
neighboring molecule by a trans-conformation. H-bond was then
alternately formed, leading to an infinite Zigzag chain in one di-
ꢁ
ꢀ
rection. A bond distance of 2.17 A [:140.263(153) ] in 1ae14, and
ꢁ
ꢀ
ꢀ
2.09 A [:140.230(126) & 132.334(136)] and 2.09 A in 1be8 was
obtained (Fig. 4). All H-bonds linked together as a pseudo polymeric
supramolecular structure (Fig. 5) formed in both crystals. The de-
the side phenyl groups. The two NeN bond lengths in crystal 1ae14
ꢀ
were equal, whereas, they are nearly equal (i.e.,
D
¼0.0135 A) in
tails about the H-bonding are presented in Table 3. A weak
pep
ꢀ
crystal 1be8. All the CeN bond lengths [1.3366(46)e1.3506(31) A]
interaction (C7eC12/H3, as offset face to face alignment) with
ꢀ
in both crystals are almost equal, and are shorter than the normal
a perpendicular distance of w3.45 A was also observed in 1ae14.
ꢀ
single bond (CeN; 1.47e1.50 A), but close to that of double bond
However, no
pep interaction was observed in 1be8. The pep in-
ꢀ
(C]N; 1.28e1.33 A), indicating that electron density was consider-
teraction may also play an important role in controlling the for-
mation/induction of mesophases (Fig. 6).
ably delocalized on both pyrazoyl rings.
Interestingly, the conformations of two pyrazoles were appar-
ently distinct; they adopt a trans-conformation in 1ae14 and a cis-
conformation in 1be8. The five rings; two pyrazoyl rings and three
phenyl rings in 1ae14 were in fact coplanar, whereas, all five rings
were not coplanar in 1be8. The measured two dihedral angle be-
tween the two pyrazole rings and central phenylene rings in 1be8
are 18.677(83)ꢁ and ꢀ25.257(71)ꢁ, making a total dihedral angle of
41.395(91)ꢁ for two pyrazole rings, resulting in a non-planar con-
formation in 1be8. Notably, an intermolecular H-bond between
pyrazoyl rings was formed in both crystals. However, a traditional
dimeric structure induced by H-bonds often observed in a style of
mono-pyrazole was not formed. Instead, the first pyrazoyl ring
(eNH) in each molecule separately formed hydrogen bonds with
another pyrazole ring (for example, eN2H2/N1 in 1ae14) of the
2.4. Variable temperature powder X-ray diffractions
Variable-temperature powder XRD diffraction experiments
were conducted to confirm the structures of the mesophases of
compound 1a. Fig. 7 shows diffraction plots for 1a (n¼14) at 25 ꢁC,
ꢁ
ꢁ
ꢀ
250 C and 320 C. A d-spacing of w29.70 A was obtained at room
ꢀ
temperature, which was quite close to w29.52 A calculated from
crystallographic data. It was also close to the half of a molecular
ꢀ
length (w56.82 A) as the repeated distance. Upon cooling from
clearing temperature to T¼320 ꢁC, a typical diffraction pattern with
ꢀ
one very strong diffraction peak at w42.69 A was observed. This
peak corresponded to a layer structure, assigned as Miller indices
ꢀ
100. Furthermore, a very broad weak peak of w4.86 A at wide angle
Fig. 3. Two ORTEP plots for compounds 1ae14 (top plot) and 1be8 with the numbering schemes.

H.-Y. Lin et al. / Tetrahedron 68 (2012) 6231e6239
6235
ꢀ
ꢀ
Fig. 4. The hydrogen bonds formed in 1ae14 (top) and 1be8 (bottom); N1eH4¼2.09 A and N3eH2¼2.29 A.
Fig. 5. Pseudo-polymeric structures in 1ae14 (top) and 1be8 (bottom).
Table 3
Hydrogen-bonding geometry and
pe
p
interaction in 1ae14 and 1be8
DeH/A
Compd
Mesophase
d(DeH)
d(H/A)
d(D/A)
:(DHA)/ꢁ
pep interaction
1ae14
1be8
SmA/SmC
Cr
N(2)eHN2/N(1)
N(2)eHN2/N(3)
N(4)eHN4/N(1)
0.88
0.88
0.88
2.17
2.29
2.09
2.90
2.95
2.83
140.263(153)
132.334(136)
140.230(126)
3.45
None
Distances unit in Ǻ.
ꢀ
region was due to halo diffraction. This diffraction pattern was
typically characteristic of a layer structure observed for a SmA
phase. Within the layers of SmA phase, the long axes of the mole-
cules lie parallel to one another, their direction being normal to the
plane of the layer. The layer d-spacing of w42.69 A is much smaller
ꢀ
than the molecular length of 56.68 A obtained from crystallo-
graphic data, indicating that the terminal alkoxy chains in SmA
phase were probably interdigitated to some extent and leading to

6236
H.-Y. Lin et al. / Tetrahedron 68 (2012) 6231e6239
Fig. 6. Intermolecular organization through an infinite zigzag chain formed by H-bonds along the axis in 1ae14 (top) and 1be8 (bottom).
a smaller d-spacing than that at 25 ꢁC. Upon further cooling to
capillary tubes (80 mm long and 0.01 mm thick) from Charles
Supper Co. with an inner diameter of 1.0 mm.
ꢁ
ꢀ
250 C, a diffraction pattern with one strong of w39.80 A and an-
ꢀ
other much weaker peak of w20.01 A was observed, which were
assigned to 001 and 002 indices for a SmC phase. In the SmC phase,
the molecules are tilted with respect to the planes of the layers.
Therefore, the d-spacing in SmC phase is expected to be slightly
than that in SmA phase. A very broad and weak peak at
w4.78e4.86 A was observed, and this peak was assigned to the
molten alkoxy chains. The molecular arrangement in crystal,
smectic C and smectic A phases was proposed in Fig. 8.
4.2. Single crystal X-ray crystallography and powder XRD
diffractometry
X-ray diffraction data were collected at 200 (2) K on a Nonius
ꢀ
Kappa CCD X-ray diffractometer unit using graphite-mono chro-
ꢀ
mated Mo K
a
radiation (
l
¼0.71073 A) from crystals mounted on
glass fibers and quickly coated in epoxy resin. Cell parameters were
retrieved and refined using DENZO-SMN software on all observed
reflections. Data reduction was performed with the DENZOSMN
software. The program package SHELXTL was used for space group
determination, structure solution, and refinement. Refinement was
performed against F2 by weighted full-matrix least-square, and
empirical absorption correction (SADABS) was applied. H atoms
were placed at calculated positions using suitable riding models
with isotropic displacement parameters derived from their carrier
atoms. The powder diffraction data were collected from the
Wiggler-A beam line of the National Synchrotron Radiation Re-
3. Conclusions
The molecular geometry is an important variable in the above
two series of nonlinear, all aromatic five-rings liquid crystals af-
fecting the thermal temperatures, while the mesophase formation
may be controlled by attractive electrostatic interaction. The study
also demonstrated the use of hydrogen bonding to construct the
extended linear polymeric structures in isomeric bis-pyrazoles
1aeb. X-ray crystallographic data indicated a better molecular co-
ꢀ
search Center with a wavelength of 1.3263 A.
linearity of five-ring structure and pep interaction was formed in
1a over 1b, which apparently faciliated the formation of layer
structures of SmA/SmC phase observed in 1a.
4.3. Synthetic preparation of the compounds 1aeb
4.3.1. (2Z,20Z)-1,10-(1,3-Phenylene)bis(3-(4-(dodecyloxy)phenyl)-3-
4. Experimental
hydroxyprop-2-en-1-one)
2b
(n¼12). The
solution
of
4-dodecyloxyacetophenone (3.00 g, 9.02 mmol) and NaH (0.648 g,
0.027 mol) dissolved in 30 mL of dry THF or DME was stirred for
20 min under nitrogen atmosphere. The solution was gently heated
to refluxing temperature, and stirred for 30 min. The solution was
turned deep red. The solution of dimethyl isophthalate (0.875 g,
4.51 mmol) dissolved in 15 mL of THF was dropwise added, and the
solution was then refluxed for 24 h. The solution was cooled and
quenched carefully with distilled water. The dilute aqueous HCl
(1.0 M) was added to raise the pH of the solution to acidic side. The
solution was extracted twice with 50 mL of CH2Cl2/H2O (1/1). The
organic layers were collected and dried over MgSO4. The products
isolated as pale yellow solid were obtained by recrystallization
from acetone/THF or CH3OH/THF. Yield 58e71%. 1H NMR (CDCl3):
4.1. General materials and methods
All chemicals and solvents were reagent grade from Aldrich
Chemical Co., and all solvents were dried by standard techniques.
1H and 13C NMR spectra were measured on a Bruker DRS-200. DSC
thermographs were carried out on a Mettler DSC822 and calibrated
with a pure indium sample. All phase transitions are determined by
a scan rate of 10.0 ꢁC/min. Optical polarized microscopy was carried
out on Zeiss Axioplan 2 equipped with a hot stage system of Mettler
FP90/FP82HT. Elemental analyses were performed on a Heraeus
CHNeOeRapid elemental analyzer. The powder diffraction data
were collected from the Wiggler-A beam line of the National Syn-
chrotron Radiation Research Center (NSRRC) with the wavelength
d
0.86 (t, J¼6.6 Hz, eCH3, 6H), 1.25e1.45 (m, eCH2, 40H), 1.77e1.82
ꢀ
of 1.3263 A. The powder samples were charged in Lindemann
(m, eCH2, 4H), 4.01 (t, J¼6.5 Hz, eOCH2, 4H), 6.84 (s, eCH, 2H), 6.94

H.-Y. Lin et al. / Tetrahedron 68 (2012) 6231e6239
6237
4.3.2. (2Z,20Z)-1,10-(1,3-Phenylene)bis(3-(4-(decyloxy)phenyl)-3-
hydroxyprop-2-en-1-one) 2b (n¼10). Light yellow solid, yield 55%.
1H NMR (CDCl3):
d
0.88 (t, J¼6.3 Hz, eCH3, 6H), 1.25e1.47
(m, eCH2, 32H), 1.75e1.84 (m, eCH2, 4H), 4.00 (t, J¼6.6 Hz, eOCH2,
4H), 6.81 (s, eCH, 2H), 6.84 (d, J¼7.8 Hz, AreH, 4H), 7.58 (t,
J¼7.8 Hz, AreH, 1H), 7.96 (d, J¼8.7 Hz, AreH, 4H), 8.09 (d, J¼6.6 Hz,
AreH, 2H), 8.51 (s, AreH, 1H), 17.02 (s, eOH, 2H). 13C NMR (CDCl3):
d
14.10, 22.68, 25.98, 29.11, 29.34, 29.56, 29.58, 29.63, 31.90, 68.33,
92.59, 114.51, 125.44, 127.61, 129.00 129.45, 130.32, 136.23, 163.11,
183.09, 186.43.
4.3.3. (2Z,20Z)-1,10-(1,4-Phenylene)bis(3-hydroxy-3-(4-(octyloxy)
phenyl)prop-2-en-1-one) 2a (n¼8). Yellow solid, yield 70%. 1H NMR
(CDCl3):
d
0.87 (t, J¼6.6 Hz, eCH3, 6H), 1.28e1.48 (m, eCH2, 40H),
1.75e1.85 (m, eCH2, 4H), 4.02 (t, J¼6.6 Hz, eOCH2, 4H), 6.83
(s, eCH, 2H), 6.95 (d, J¼8.7 Hz, AreH, 4H), 7.96 (d, J¼9.0 Hz, AreH,
4H), 8.04 (s, AreH, 4H),16.87 (s, eOH, 2H). 13C NMR (CDCl3):
d 14.31,
22.88, 26.22, 29.34, 29.55, 32.03, 68.59, 93.24, 114.77, 127.38, 128.10,
129.74, 130.62, 138.77, 163.41, 187.47.
4.3.4. (2Z,20Z)-1,10-(1,4-Phenylene)bis(3-(4-(dodecyloxy)phenyl)-3-
hydroxyprop-2-en-1-one) 2a (n¼12). Yellow solid, yield 75%. 1H
NMR (CDCl3):
d
0.86 (t, J¼6.5 Hz, eCH3, 6H), 1.31e1.56 (m, eCH2,
36H), 1.75e1.84 (m, eCH2, 4H), 4.02 (t, J¼6.5 Hz, eOCH2, 4H), 6.82
(s, eCH, 2H), 6.94 (d, J¼8.7 Hz, AreH, 4H), 7.95 (d, J¼8.7 Hz, AreH,
4H), 8.04 (s, AreH, 4H), 16.92 (s, eOH, 2H). 13C NMR (CDCl3):
d
14.34, 22.92, 26.21, 29.34, 29.58, 29.80, 29.87, 32.14, 68.58,
93.22, 114.75, 127.36, 128.08, 129.73, 138.75, 163.40, 182.03,
187.46.
4.3.5. (2Z,20Z)-1,10-(1,4-Phenylene)bis(3-hydroxy-3-(4-(tetra decy-
loxy)phenyl)prop-2-en-1-one) 2a (n¼14). Yellow solid, yield 78%. 1H
NMR (CDCl3):
d
0.86 (t, J¼6.8 Hz, eCH3, 6H), 1.18e1.54 (m, eCH2,
44H), 1.78e1.85 (m, eCH2, 4H), 4.02 (t, J¼6.6 Hz, eOCH2, 4H), 6.83
(s, eCH, 2H), 6.95 (d, J¼9.0 Hz, AreH, 4H), 7.96 (d, J¼9.0 Hz, AreH,
4H), 8.04 (s, AreH, 4H), 16.93 (s, eOH, 2H).
4.3.6. (2Z,20Z)-1,10-(1,4-Phenylene)bis(3-(4-(hexadecyloxy)phenyl)-
3-hydroxyprop-2-en-1-one) 2a (n¼16). Yellow solid, yield 72%. 1H
NMR (CDCl3):
d
0.86 (t, J¼6.6 Hz, eCH3, 6H), 1.71e1.62 (m, eCH2,
52H), 1.75e1.82 (m, eCH2, 4H), 4.02 (t, J¼6.5 Hz, eOCH2, 4H), 6.83
(s, eCH, 2H), 6.95 (d, J¼8.7 Hz, AreH, 4H), 7.96 (d, J¼9.0 Hz,
AreH, 4H), 8.04 (s, AreH, 4H), 16.93 (s, eOH, 2H). 13C NMR
(CDCl3):
d 14.35, 22.91, 26.21, 29.33, 29.59, 29.81, 29.91, 32.15,
68.57, 93.22, 114.75, 127.36, 129.73, 138.75, 163.40, 163.40, 182.03,
187.47.
4.3.7. 1,3-Bis(5-(4-(dodecyloxy)phenyl)-1H-pyrazol-3-yl)benzene 1b
(n¼12). The solution of (2Z,20Z)-1,10-(1,3-phenylene)bis(3-(4-
(dodecyloxy)phenyl)-3-hydroxyprop-2-en-1-one) (1.00 g) dis-
solved in 30 mL THF was slowly added 0.5 mL of glacial acetic acid
and the solution was stirred for 5 min. Then the hydrazine (1.0 mL)
was added and refluxed for 24 h. The solution was concentrated to
dryness, and the products isolated as white solid were obtained by
recrystallization from THF/CH3OH (hot). Yield 70%. 1H NMR
(DMSO-d6):
d 0.82 (m, eCH3, 6H), 1.24e1.39 (m, eCH2, 36H),
1.70e1.72 (m, eCH2, 4H), 4.01 (t, J¼6.3 Hz, eOCH2, 4H), 7.00 (m,
AreH, 4H), 7.15 (s, eCH, 2H), 7.50 (m, AreH, 1H), 7.75 (m, AreH,
6H), 8.29 (s, AreH, 1H), 10.25 (s, eNH), 10.71 (s, eNH), 13.23
(m, eNH, 2H). Anal. Calcd for C48H66N4O2: C, 78.86; H, 9.10. Found
C, 78.58; H, 9.18.
Fig. 7. Variable-temperature powder XRD diffraction plots of 1ae14. From top to
bottom: the theoretical pattern calculated from the X-ray crystallographic data, at
room temperature, at 250 ꢁC and 320 ꢁC.
(d, J¼9.0 Hz, AreH, 4H), 7.55 (t, J¼7.8 Hz, AreH, 1H), 7.96 (d,
J¼8.7 Hz, AreH, 4H), 8.08 (d, J¼6.6 Hz, AreH, 2H), 8.51 (s, AreH,
4.3.8. 1, 3-Bis(5-(4-(octyloxy)phenyl)-1H-pyrazol-3-yl)benzene 1b
1H),17.02 (s, eOH, 2H). 13C NMR (CDCl3):
d
13.12, 21.68, 24.99, 28.12,
(n¼8). White solid, yield 58%. 1H NMR (THF-d6):
d 0.91
28.35, 28.58, 28.64, 30.91, 67.33, 91.58, 113.51, 124.44, 126.60,
128.00, 128.45, 129.33, 135.22, 162.11, 182.07, 185.43.
(t, J¼5.4 Hz, eCH3, 6H), 1.32e1.50 (m, eCH2, 20H), 1.73e1.81
(m, eCH2, 4H), 3.99 (t, J¼6.5 Hz, eOCH2, 4H), 6.69 (s, eCH, 2H), 7.41

6238
H.-Y. Lin et al. / Tetrahedron 68 (2012) 6231e6239
42.69 Å
29.80 Å
39.80 Å
Cr
SmC
SmA
Fig. 8. The molecular arrangements proposed in Cr, SmC and SmA phases formed in 1a.
(t, J¼7.7 Hz, AreH, 1H), 7.70 (d, J¼6.9 Hz, AreH, 6H), 8.29 (s, AreH,
1H), 10.91 (s, eNH), 12.37 (s, eOH, 2H). Anal. Calcd for C40H50N4O2:
C, 77.63; H, 8.14. Found C, 77.61; H, 8.19.
to poor solubility. Anal. Calcd for C40H50N4O2: C, 77.63; H, 8.14.
Found C, 77.60; H, 8.21.
Acknowledgements
4.3.9. 1, 3-Bis(5-(4-(tetradecyloxy)phenyl)-1H-pyrazol-3-yl)benzene
1b (n¼14). White crystal, yield 50%. Anal. Calcd for C52H74N4O2: C,
79.34; H, 9.46. Found C, 79.23; H, 9.44. The 1H and 13C NMR data
were not obtained due to poor solubility.
We thank the National Science Council of Taiwan, ROC (NSC 100-
2113-M-008-003-MY2) in generous support of this work.
References and notes
4.3.10. 1, 3-Bis(5-(4-(decyloxy)phenyl)-1H-pyrazol-3-yl)benzene 1b
(n¼10). White solid, yield 52%. 1H NMR (DMSO-d6):
d 0.85 (t,
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J¼6.6 Hz, eCH3, 6H), 1.24e1.42 (m, eCH2, 28H), 1.70e1.74 (m, eCH2,
4H), 4.00 (t, J¼6.2 Hz, eOCH2, 4H), 6.94 (m, AreH, 4H), 7.15 (s, eCH,
2H), 7.41 (t, J¼7. 7 Hz, AreH, 1H), 7.67 (m, AreH, 6H), 8.29 (s, AreH,
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1H), 13.23 (m, eNH, 2H). 13C NMR (THF-d6):
d 14.59, 23.72, 27.22,
ꢁ
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1a (n¼16). White solid, yield 73%. The 1H NMR spectra are not
obtained due to poor solubility. Anal. Calcd for C56H82N4O2: C,
79.76; H, 9.80. Found C, 79.64; H, 9.78.
ꢁ
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79.34; H, 9.48. Found C, 79.35; H, 9.54.
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1a (n¼12). White crystal, yield 75%. 1H NMR (DMSO-d6):
d 0.85 (t,
J¼6.6 Hz, eCH3, 6H), 1.25e1.47 (m, eCH2, 36), 1.70e1.74
(m, eOCH2CH2, 4H), 4.00 (t, J¼6.3 Hz, eOCH2, 4H), 6.99 (d,
J¼8.4 Hz, AreH, 4H), 7.11 (s, eCH, 2H), 7.73 (d, J¼8.4 Hz, AreH, 4H),
7.89 (s, AreH, 4H), 10.25 (s, eNH), 10.71 (s, eNH), 13.27 (s, eNH).
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d 0.86 (t,
J¼6.5 Hz, eCH3, 6H), 1.26e1.42 (m, eCH2, 28H), 1.68e1.77
(m, eCH2, 4H), 3.99 (t, J¼6.3 Hz, eOCH2, 4H), 6.99 (d, J¼8.1 Hz,
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