Synthesis and mesomorphic properties of novel columnar liquid crystals based on polytopic gallic ethers with multiple-hydrogen bonding cyanuric cores

Article abstract of DOI:10.1016/j.tetlet.2015.08.018

The gallic-cyanuric monomer 4, gallic-cyanuric dimer 5, gallic-cyanuric trimer 6 and gallic-cyanuric tetramer 7 containing multiple hydrogen bond were designed and synthesized in yields of 70-80%. Their symmetric structures were characterized by element a

Full text of DOI:10.1016/j.tetlet.2015.08.018

Tetrahedron Letters 56 (2015) 5465–5469
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Tetrahedron Letters
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Synthesis and mesomorphic properties of novel columnar liquid
crystals based on polytopic gallic ethers with multiple-hydrogen
bonding cyanuric cores
a
a
a,b,
⇑
, Yamin Wu a
Hongyu Guo , Xiaoting Fang , Fafu Yang
a
College of Chemistry and Chemical Engineering, Fujian Normal University, Fuzhou 350007, PR China
Fujian Key Laboratory of Polymer Materials, Fuzhou 350007, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 June 2015
Revised 29 July 2015
Accepted 10 August 2015
Available online 12 August 2015
The gallic–cyanuric monomer 4, gallic–cyanuric dimer 5, gallic–cyanuric trimer 6 and gallic–cyanuric tet-
ramer 7 containing multiple hydrogen bond were designed and synthesized in yields of 70–80%. Their
symmetric structures were characterized by element analyses, FT-IR, ESI-MS, and NMR spectra. Their
hexagonal columnar liquid crystalline phases were confirmed by DSC, POM, and XRD analyses. The scope
of mesomorphic temperature of compounds 5, 6, and 7 is as wide as 45.7, 70.1, and 134.4 °C, respectively.
The more gallic ether units are favorable for excellent mesophase.
Keywords:
Gallic
Ó 2015 Elsevier Ltd. All rights reserved.
Cyanuric
Synthesis
Mesophase
Hydrogen bond
Columnar liquid crystals (LC) have attracted increasing research
interest in recent years based on their 1D charge transport and
self-healing properties, which make them unique promising candi-
dates for use in organic photoelectric devices, organic field effect
transistors, thin film transistors, organic light emitting diodes,
showed several liquid crystals based on hydrogen bonding
supramolecular assemblies by combination with -conjugated
anion receptors. Saigo presented columnar liquid crystals of
p
1
5
3,4,5-tris(11-acryloyloxyundecyloxy)benzoic acid with 2-amino-
1
6
1-propanol based on hydrogen bonding. Shin also exhibited
3
C -symmetric hexa-alkylated liquid crystals with interesting trans-
1
–4
etc.
Usually, the columnar LCs were easily obtained by symmet-
17
ric large conjugated aromatic core with several aliphatic side
chains. For instance, the triphenylene, phthalocyanine, and hex-
abenzocoronene derivatives with three to six aliphatic chains were
formation from smectogen to discogen via hydrogen bonding.
Moreover, Laschat synthesized wedge-shaped 1,2-diamidoben-
zenes forming columnar mesophases via hydrogen bonding,18 but
the similar wedge-shaped molecules without hydrogen bonding
were difficult to show the similar columnar liquid crystals.19
Nonetheless, the columnar liquid crystal of symmetric polytopic
gallic derivatives without a large conjugated aromatic core was
not concerned so far. Inspired by these successful cases of colum-
nar liquid crystal based on hydrogen bonding, in this Letter, we
designed and synthesized several symmetric polytopic gallic
ethers with triazine cyanuric cores containing multiple amino
groups, which could produce multiple hydrogen bonding. The
mesomorphic studies showed that although these cyanuric cores
were not large conjugated aromatic ones, the columnar liquid crys-
tals were observed for these compounds unambiguously due to the
intermolecular action of hydrogen bonding of multiple amino
groups.
5
–10
extensively studied as excellent columnar LCs materials.
Lately,
gallic ethers or their analogues with three long aliphatic chains on
their phenolic groups were seen as good structural units to con-
struct novel columnar LCs by connecting with a large conjugated
aromatic core. For examples, Laschat described saddle-shaped
tetraphenylenes with peripheral gallic esters displaying columnar
1
1
mesophases. Detert reported the synthesis and mesomorphic
properties of some tristriazolotriazine derivatives with 1,2-bis-
substituted or 1,2,3-tri-substituted alkoxy side chains on phenyl
1
2,13
groups.
Our groups also presented novel room-temperature
14
liquid crystals of gallic–perylene–gallic trimers. On the other
hand, some research showed that the hydrogen bonding made
great influences on the formation of liquid crystals when no large
conjugated aromatic structure was introduced as core. Maeda
The synthetic routes for gallic–cyanuric monomer 4, gallic–cya-
nuric dimer 5, gallic–cyanuric trimer 6, and gallic–cyanuric tetra-
mer 7 are illustrated in Scheme 1. Firstly, according to the
⇑
Corresponding author. Tel./fax: +86 591 83465225.
E-mail address: yangfafu@fjnu.edu.cn (F. Yang).
http://dx.doi.org/10.1016/j.tetlet.2015.08.018
040-4039/Ó 2015 Elsevier Ltd. All rights reserved.
0

5
466
H. Guo et al. / Tetrahedron Letters 56 (2015) 5465–5469
OC12H25
OC12H25 C12H25
OC12H
25
OH
HO
OH C12H25
BrC12
CN,K
O
O
OC12H25
H
25
H NCH CH NH
2
2
2
2
CH
OCH3
3
2
CO
3
C H
2 5
OH
NH2
O
OCH
3
O
N
H
O
2
3
1
O
Cl
N
Cl
HN
OC12H25
N
N
CH COCH ,Na CO
3
+
N
N
3
3
2
3
Cl
NH
0-5ഒ
OC12H
25
Cl
N
Cl
C12H25
O
4
C12H25
O
O
HN
O
NH
C
12
25
H O
HN
OC12H25
CH COCH , Na CO
N
N
3
3
2
3
3
+ 4
35ഒ
C12H25
O
N
NH
OC12H25
Cl
C12H25
O
5
C12H25
O
O
H
N
C12H25
O
O
THF,NaHCO3
O
NH
3
+ 5
HN
60ഒ
C
12
H
25
OC12H25
N
N
C12H25
C12H25
O
N
N
H
OC12H25
NH N
H
12 25
C H O
O
O
6
C
12
H
25
O
OC12H25
C
12
25
H O
O
O
OC12H25
C
12
H
25
O
NH
HN
HN
OC12H25
C12H25
O
NH
NH
NH
2
N
N
H
N
H
N
THF,NaHCO3
N
N
5
+
N
N
6
0ഒ
NH
HN
HN
2
C12H25
O
OC12H25
OC12H
25
NH
C
12
H
25
O
7
O
O
C12H25
O
OC12H
25
Scheme 1. The synthetic routes of title compounds 4, 5, 6, and 7.
literature methods,20 by reacting methyl gallate 1 with bromode-
cane in K CO /MeCN, gallic derivative 2 with three long alkyl
chromatography. It was worthy of noting that all these polytopic
gallic ethers with multiple-azo cyanuric cores 4, 5, 6, and 7 were
prepared in simple separating procedures of recrystallization or
flash column chromatography in yields of 70–80%.
2
3
chains was conveniently prepared in yield of 80%. Then the
ammonolysis derivatives 3 was obtained by reacting compound 2
with excess ethylenediamine in yield of 86%. On the other hand,
it was well known that the three Cl groups of cyanuric chloride
could be selectively substituted by changing the reaction temper-
atures. Thus, the gallic–cyanuric monomer 4 was easily synthe-
sized by the nucleophilic substitution of gallic amide derivative 3
The structures of all new compounds 4, 5, 6, and 7 were con-
firmed by element analyses, FT-IR, ESI-MS, and NMR spectra. In
their ESI-MS spectra, all of them showed corresponding molecular
+
+
+
ion peaks (M , MH or MK ) at 865.2, 1584.6, 2226.1, and 3127.8
which suggested the condensation of mono-, di-, tri-, and tetra-
substituted gallic–cyanuric derivatives was successfully accom-
2 3
with cyanuric chloride in Na CO /acetone system under the
1
temperature of 0–5 °C in yield of 80%. Subsequently, reacting
compound 3 with gallic–cyanuric monomer 4 afforded gallic–
cyanuric dimer 5 in same reaction system at 35 °C in yield of
plished as expected. In their H NMR spectra, the corresponding
proton signals were well assigned to their structures. Moreover,
1
3
their C NMR spectra also exhibited corresponding peaks, for
examples the peaks for C@O and OCH at approximately 165 and
7
6%. Furthermore, gallic–cyanuric trimer 6 was obtained by con-
densation of compounds 5 with 3 in NaHCO /THF system at 60 °C
in yield of 70%. Also, by refluxing gallic–cyanuric dimer 5 with
p-phenylene diamine in NaHCO /THF system at 60 °C, gallic–
cyanuric tetramer 7 was separated in yield of 72% after column
2
3
74 ppm, respectively. All these characteristic data supported cer-
tainly the structures of compounds 4, 5, 6, and 7 in Scheme 1.
The differential scanning calorimetry (DSC) was preliminarily
used to investigate the mesomorphic behaviors of compounds 4,
3

H. Guo et al. / Tetrahedron Letters 56 (2015) 5465–5469
5467
3
2
1
0
1
2
3
4
heating process. Compound 5 had two endothermic peaks at
59.6 °C and 96.1 °C on second heating, and two exothermic peaks
at 52.8 °C and 98.5 °C on cooling. Gallic–cyanuric trimer 6
displayed a melting transition at 32.8 °C and a clearing transition
at 102.9 °C upon second heating. Upon cooling an isotropic to
mesophase transition at 28.5 °C and a crystallization peak at
100.8 °C were detected. Compound 7 presented two phase transi-
tion temperatures at ꢀ10.1 °C and 123.9 °C for endothermic peaks
on second heating and two exothermic peaks at ꢀ13.9 °C and
cooling
7
6
5
4
4
-
-
-
-
1
20.5 °C on cooling. These two thermic peaks indicated that
5
6
7
compounds 5, 6, and 7 possess the solid state–mesophase and
mesophase–isotropic phase transition on cooling and second
heating, which were further confirmed by polarizing optical micro-
scopy (POM). The hysteresis phenomena observed for compounds
second heating
50
6
and 7 might be attributed to super-cooling, which was common
0
100
o
150
for such highly viscous materials. Moreover, after calculation, the
scope of mesomorphic temperature of compounds 5, 6, and 7
was as wide as 45.7, 70.1, and 134.4 °C, respectively, indicating
that the more gallic ether units resulted in the wider temperature
of mesophase. The 134.4 °C for compound 7 was outstanding
among the scope of mesophase of various gallic liquid crystals.1
Furthermore, based on the DSC results, the mesophase textures
of compounds 4, 5, 6, and 7 were studied by POM. For compound 4,
no obvious texture of mesophase was seen both upon heating and
cooling. However, compounds 5, 6, and 7 exhibited clearly two
phase transitions of solid state–mesophase and mesophase–isotro-
pic phase on cooling. The temperatures of phase transition were
approximately in agreement with the endothermic (or exothermic)
peaks of DSC on heating and cooling. The textures for compounds
Temperature ( C)
Figure 1. The DSC traces of compounds 4, 5, 6, and 7 on second heating and cooling
scan rate 10 °C min ).
ꢀ
1
(
1–14
Table 1
Transition temperatures (°C) and enthalpies (kJꢁmolꢀ1) of compounds 4, 5, 6 and 7
Phase transitiona
Compd
T(D
H) heating scan
T(DH) cooling scan
4
5
Cr-Iso(Iso-Cr)
Cr-Col(Col-Cr)
Col-Iso(Iso-Col)
Cr-Col(Col-Cr)
Col-Iso(Iso-Col)
Cr-Col(Col-Cr)
Col-Iso(Iso-Col)
26.5(13.64)
59.6(6.79)
52.8(8.62)
32.8(7.56)
28.5(7.31)
ꢀ10.1(10.88)
ꢀ13.9(4.93)
25.5(12.48)
96.1(9.83)
98.5(8.33)
102.9(7.72)
100.8(8.28)
123.9(4.86)
120.5(9.94)
6
7
4, 5, 6, and 7 at corresponding temperatures on cooling are shown
in Figure 2. It can be seen that compound 4 showed no liquid crys-
tal texture but the fan-shape textures for compounds 5, 6, and 7
were observed clearly, which were the typical columnar liquid
a
Cr = crystalline, Col = columnar phase, Iso = isotropic.
2
1–28
5
, 6 and 7. The results are shown in Figure 1 and Table 1. One can
crystals.
These columnar liquid crystals were further con-
see that gallic–cyanuric monomer 4 showed only one thermic peak
upon cooling (25.5 °C) and second heating (26.5 °C), which might
indicate it possesses no mesomorphic property. However, gallic–
cyanuric dimer 5, gallic–cyanuric trimer 6, and gallic–cyanuric tet-
ramer 7 exhibited two thermic peaks for their cooling and second
firmed by X-ray diffraction (XRD) data.
The mesophase structures of compounds 5, 6, and 7 were also
established by XRD studies at mesomorphic temperatures of
85 °C. Figure 3 shows the intensity versus 2h plot for compounds
5, 6, and 7. In the small angle region, two peaks were observed
Figure 2. Mesomorphic textures of compounds 4, 5, 6, and 7 obtained under POM on cooling at 85 °C (ꢂ400).

5
468
H. Guo et al. / Tetrahedron Letters 56 (2015) 5465–5469
5
4
3
2
1
000
000
000
000
000
0
that the aliphatic chains on gallic units were not in the shape of
straightforward spread but in curved formation in mesomorphic
phases. Figure 4 exhibits the proposed arrangement for the molec-
ular stacking within the columns of compound 6 as representative
one. Combining all the data of DSC, POM, and XRD analyses, it
could be deduced that compounds 5, 6, and 7 possess the hexago-
nal columnar liquid crystalline phases. Comparing the structures of
compounds 5, 6, and 7 with the previous columnar gallic liquid
7
6
1
1–14
crystals with large conjugated aromatic cores,
it could be seen
that the triazine cyanuric cores of compounds 5, 6, and 7 without
large conjugated aromatic structures but possessing multiple
hydrogen bonding, played crucial roles in liquid crystalline behav-
iors. The multiple hydrogen bonding reduced the flexibilities of tri-
azine cyanuric structures and enhanced the rigidities like a large
conjugated aromatic core. These results were in accordance with
the previous reports that the hydrogen bonding was favorable for
5
0
10
20
30
40
1
8,19
the formation of columnar liquid crystals.
To the best of our
Scattering angle 2θ (degree)
knowledge, compounds 5, 6, and 7 were the first examples of col-
umn liquid crystals based on symmetric polytopic gallic ethers
with multiple-hydrogen bonding cyanuric cores.
Figure 3. XRD traces of compounds 5, 6, and 7 measured at 85 °C.
In conclusion, by using gallate and cyanuric chloride as starting
materials, the gallic–cyanuric monomer 4, gallic–cyanuric dimer 5,
gallic–cyanuric trimer 6, and gallic–cyanuric tetramer 7 containing
multiple hydrogen bonding cyanuric cores were prepared by the
step-by-step synthetic methods in yields of 70–80%. Their struc-
tures were confirmed by element analyses, FT-IR, ESI-MS, and
NMR spectra. Their mesomorphic behaviors were studied by DSC,
POM, and XRD. The results suggested that they had the hexagonal
columnar liquid crystalline phases although no large conjugated
aromatic cores in compounds 5, 6, and 7. The scope of mesomor-
phic temperature of compounds 5, 6, and 7 was as wide as 45.7,
obviously at 2.58° (or 2.61°, 2.13°) and 2.98° (or 3.01°, 2.51°) for
compounds 5, 6, and 7, respectively. The d-spacing derived from
these angles were calculated as 34.2 Å (or 33.8 Å, 41.4 Å) and
2
9.6 Å (or 29.3 Å, 35.5 Å), which were in agreement with the ratios
p
of 2/ 3, suggesting the hexagonal columnar liquid crystal.
Moreover, the broad halos at 2h = 16–24° were assigned to the
average distances of the molten alkyl chains on gallic units. The
reflections at 23.5° approximately indicated the spacing of approx-
imately 3.8 Å, which is the typical characteristic of intracolumnar
order of columnar liquid crystals with
p–p interactions. Thus, all
these XRD data supported that compounds 5, 6, and 7 were hexag-
onal lattice for their mesophases. On the other hand, the CPK
molecular model indicated that the diameters of compounds 5, 6,
and 7 including the gallic units were 35–44 Å approximately,
which was a little bigger than the intercolumn distances of com-
pounds 5, 6, and 7 in XRD analysis. These results might indicate
7
0.1, and 134.4 °C, respectively. The more gallic ether units
resulted in the wider temperatures of mesophase. The studies on
the synthesis and mesomorphic properties of gallic units with
other cores including multiple hydrogen bonding, and the influ-
ences of hydrogen bonding on mesomorphic properties will be
studied further in a following work.
Figure 4. Schematic representations of the columnar molecular arrangements and the intermolecular H-bonding of compound 6.

H. Guo et al. / Tetrahedron Letters 56 (2015) 5465–5469
5469
9
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Acknowledgments
2
Financial support from the National Natural Science Foundation
of China (No. 21406036), Fujian Natural Science Foundation of
China (No. 2014J01034), Fujian Province Science and Technology
Key Project (2014N0025) and the Program for Innovative
Research Team in Science and Technology in Fujian Province
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Supplementary data
Supplementary data associated with this article can be found, in
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