Synthesis of Y-Shaped liquid crystals and the influence of their structure on the phase behavior

Article abstract of DOI:10.1080/15421400902841247

A series of the Y-shaped liquid crystalline (LC) materials based on central 1,2,4-benzenetricarboxylic core was synthesized with variation of the arm length (two or three para-linked phenyl rings) in the Y-shaped mesogen and their dipole architecture (ether or ester terminal and linked groups). Our results indicate that main relationships between molecular structure and mesomorphic behavior well known for the calamitic LC are valid for the Y-shaped compounds too. Smectic mesophases might be obtained by lengthening the mesogen with an additional aromatic core in the arm or with an alkyl chain at the tail. The substitution of the alkoxy terminal groups on to alkanoyl also leads to the enhanced smectic behavior of the Y-shaped molecules. Taylor & Francis Group, LLC.

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Synthesis of Y-Shaped Liquid
Crystals and the Influence of
Their Structure on the Phase
Behavior
Vjacheslav V. Zuev a
a Institute of Macromolecular Compounds of the
Russian Academy of Sciences , Sankt Petersburg,
Russian Federation
Published online: 03 Aug 2009.
To cite this article: Vjacheslav V. Zuev (2009) Synthesis of Y-Shaped Liquid Crystals
and the Influence of Their Structure on the Phase Behavior, Molecular Crystals and
Liquid Crystals, 506:1, 3-12, DOI: 10.1080/15421400902841247
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Mol. Cryst. Liq. Cryst., Vol. 506, pp. 3–12, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400902841247
Synthesis of Y-Shaped Liquid Crystals and the
Influence of Their Structure on the Phase Behavior
Vjacheslav V. Zuev
Institute of Macromolecular Compounds of the Russian Academy of
Sciences, Sankt Petersburg, Russian Federation
A series of the Y-shaped liquid crystalline (LC) materials based on central
1,2,4-benzenetricarboxylic core was synthesized with variation of the arm length
(two or three para-linked phenyl rings) in the Y-shaped mesogen and their dipole
architecture (ether or ester terminal and linked groups). Our results indicate
that main relationships between molecular structure and mesomorphic behavior
well known for the calamitic LC are valid for the Y-shaped compounds too.
Smectic mesophases might be obtained by lengthening the mesogen with an
additional aromatic core in the arm or with an alkyl chain at the tail. The substi-
tution of the alkoxy terminal groups on to alkanoyl also leads to the enhanced
smectic behavior of the Y-shaped molecules.
Keywords: mesomorphic behavior; synthesis; Y-shaped compounds
1. INTRODUCTION
Although liquid crystalline (LC) materials have been known for over a
century, an amazing richness and complexity of new behavior has
been continually discovered, fueling innovation and the development
of novel applications. In many instances, new and non-conventional
LC systems have molecular architectures that do not fall into the
traditional categories of rod-like or disc-like but are characterized by
systems of intermediate shape, which in turn contain several elements
capable of being independently manipulated. This has led to the
discovery of new types of mesophases with fascinating structures,
which have been summarized in several papers [1,2]. From these
studies it is clear that architecture and functionalization are essential
Address correspondence to Vjacheslav V. Zuev, Institute of Macromolecular
Compounds of the Russian Academy of Sciences, Bolshoi pr.31, Sankt Petersburg
199004, Russian Federation. E-mail: zuev@hq.macro.ru
3

4
V. V. Zuev
aspects in the molecular engineering of liquid crystals for controlling
the physical properties that ultimately define the self-organizing
process that leads to mesophase formation; molecular shape, dipole
architecture, space filling effects, deformation ability, chirality, mini-
mal interfacial curvature, microphase segregation, and self-assembly
are all aspects that contribute to and determine the mesophase
structure.
In this context, our article is concerned with Y-shaped LC
compounds. Their basic building blocks are linear rod-like groups
connected via suitable bridging in such a way that they span a
two-dimensional space. Wendorff et al. [3,4] published the first article
concerning such mesogenic molecules. Molecular modeling and synth-
esis indicated that such molecules should have a tendency to display a
nematic phase at least for short tails (methyl through butyl). The aim
of the present article was investigating the influence of length of
terminal alkyl tail, length of arms, and type of bridging groups in
the arms of the Y-shaped mesogens on mesomorphic behavior of
two-dimensional LC compounds.
The number of synthesized LC compounds with the rigid Y-shaped
mesogens is still very limited. The polyesters with the azomethine
based Y-shaped mesogens were synthesized [5,6] but, as mentioned
by the authors themselves, due to the conformational flexibility of
the azomethine group this type of polymer cannot be strictly con-
sidered as Y-shaped segmented LC polymers. The numerous T-shaped
LC compounds synthesized by Tshierske et al. [7] are different because
in all cases one arm of these mesogens is flexible. Similarly the most
other synthesized Y-shaped LC compounds contained the flexible
spacers between the rigid blocks [2,8].
2. RESULTS AND DISCUSSION
The synthesis of such range of materials with functional groups in
specific positions in order to produce the required physical properties
needed careful consideration. 1,2,4-benzenetricarboxylic acid was
selected as central core for building of Y-shaped mesogen. It allows
us to compare our results with results of Wendorff et al. [3,4]. To
exclude laborious synthesis of intermediate 4-alkoxyphenyl- and
4-alkylcarboxy-4-hydroxybenzoates, we prepared 1,2,4-(4-carboxyphen
yloxycarbonyl)benzene acid 1 using interphase condensation of the
acid chloride of 1,2,4-benzenetricarboxylic acid with p-4-hydroxyben
zoic acid (Scheme 1). It was converted in one step to chloride 2, which
was used for synthesis of Y-shaped compounds 3–5 by condensation
with available para-alkoxy or -alkylcarboxyphenols. This method

Synthesis of Y-Shaped LCs
5
SCHEME 1 A synthetic pathway to the Y-shaped compounds 3–5.
was chosen for the preparation of compounds 3–5 because the scale of
reaction may be large and a good yield was essential. The properties of
compounds 3–5 are given in the table. Compounds 3 have high melting
points (about 170ꢀC). The clearing temperatures are unachievable
because the compounds degrade in the temperature range of interest
(about 300ꢀC).
By optical microscopy, each homologue 3 from n ¼ 4 to n ¼ 7 showed
a single smectic A phase. The texture of the phase was either focal-
conic or homeotropic. The comparison with results of Wendorff et al.
(compounds 4 n ¼ 0–3 [3,4]) shows that extension of the length of the

6
V. V. Zuev
arm Y-shaped mesogen from two to three para-connected benzene
rings leads to a dramatic increase of clearing temperatures. Surpris-
ingly, the type of mesophase was changed from nematic to smectic
A. Lattice calculations performed by Wendorff et al. [3,4] for these
molecules using an extended version of the Flory lattice treatment of
rod-like molecules predicted that they should be able to form only
nematic phases. This was supported by synthesis of compounds 4
n ¼ 0–3 [3,4].
However, the extension of the arm in the Y-shaped mesogen
from two to three para-connected benzene rings leads to smectic
phases in compounds 3. This result stimulated us to synthesize com-
pounds 4 with longer terminal alkoxy substituents. These homologues
of 4 have melting points close to value of the butoxy derivative (132C)
synthesized by Wendorff et al. [3] (Table 1). The increase of length of
alkoxy substituents had very little effect on the clearing point. How-
ever, mesomorphic behavior was changed dramatically. Microscopy
TABLE 1 Phase Transition Temperatures, Transitions Enthalpies of
Compounds 3–6
D1Hmb=J gꢁ1
TSN =ꢀC
Tid=ꢀC
D Hie=J gꢁ1
a
c
Compound
n
Tm =ꢀC
3
4
5
6
7
4
5
6
7
3
4
5
6
7
8
9
4
5
6
7
173.9
175.2
174.1
172.0
127.0
125.0
121.3
118.0
91.2
86.3
74.2
17.0
68.0
13.0
16.0
142.0
140.0
135.5
144.5
5.0
6.7
5.6
—
—
—
—
—
—
—
—
—
—
—
5.8
—
4
5
27.5
28.6
26.4
26.2
29.4
28.1
20.1
15.6
18.3
5.2
189.6
186.8
—
190.76
188.0B
187.0
188.9
124.0
138.0
144.0
72.5
2.6
2.8
2.1
3.0
1.8
1.7
1.2
1.0
2.6
—
—
—
—
—
—
—
152.0
—
—
—
4.3
92.0
0.5
1.7
2.1
2.4
1.9
6
25.6
24.6
26.3
22.8
—
146.7
164.0
158.5
148.0
161.5
152.0
—
aMelting point.
bEnthalpy at Tm.
cSmectic A–nematic transition temperature.
dClearing temperature.
eEnthalpy at Ti.

Synthesis of Y-Shaped LCs
7
investigations revealed that these compounds have a tendency to
display smectic A phases, as is apparent from the focal-conic texture
(Fig. 1b). For the compounds 4 n ¼ 4 and 5, a nematic state appeared
upon cooling from isotropic state with a typical schlieren textures
(Fig. 1a) in a very narrow temperature interval (about 1ꢀC). Therefore,
with extension of the alkoxy chain length the smectic behavior of
FIGURE 1 Optical textures of compound 5 (n ¼ 5) obtained on cooling from
the isotropic liquid at 190ꢀC (a); (b) at 180ꢀC.

8
V. V. Zuev
Y-shaped molecules increases as is typical for usual calamitic LC
compounds [1]. To verify this assumption a set of compounds 5 was
synthesized. For calamitic LC compounds it is well known that substi-
tution of a terminal ether group in mesogenic fragments for an ester
leads to enhanced smectic behavior [1]. Indeed, this is so in our case
because all compounds 5 display only a smectic A phase according to
their textures (focal-conic). The replacement of the terminal ether
group with an alkanoyl moiety decreases the melting point, thereby
the compounds 5 n ¼ 6 and 9 display LC state at room temperature.
To extend our comparison with calamitic LC compounds, we synthe-
sized compounds 6 which did not contain an ester group into the
arm in the Y-shaped mesogen that should leads to enhanced nematic
behavior in compare with compounds 4.
The higher melting point values when compared to the 4 analogues
are due to increased polarizability of biphenyl fragment. Also com-
pounds 6 are more compact and may pack efficiently. This is responsi-
ble for the high melting point. However, the result of this structural
change is a significant decrease in a clearing point. For the compounds
6 with n ¼ 4, 5, 6, upon cooling, a nematic phase appeared with a
schlieren texture: this schlieren texture changed on further cooling
for compounds 6 with n ¼ 5 and 6 to focal-conic which were identified
as SA phase. On cooling, the compounds with n ¼ 7 only exhibited SA
phase. Hence, compounds 6 have a tendency to enhanced namatic
behavior in compare to compounds 4. It allows us to come to conclusion
that main relationships between molecular structure and meso-
morphic behavior well known for the calamitic LC are valid for the
Y-shaped compounds too. Our investigation supports the prediction
of Wendorff et al. [3,4] that for appearance of LC behavior at the
Y-shaped molecules each arm of the Y-shaped mesogen should be
quasi mesogen in calamitic LC compounds. Indeed, the results of
Takenaka et al. [9] as well as our investigation [10] were shown
that if the Y-shaped molecules of 1,2,4-trisubstituted benzenes have

Synthesis of Y-Shaped LCs
9
at least in one arm of the Y-shaped mesogen only one substituted
phenyl rings these compounds may displayed only monotropic meso-
phase (nematic or smectic A in dependence from alkyl tail). Calamitic
analogues of compounds 5 n ¼ 4–9 (bisalkyl 4,40-(terephtaloyldioxy)
dibenzoates) displayed at similar alkyl tails only smectic A mesophase
with increased isotropization temperatures on 20–50ꢀC [11,12].
3. CONCLUSION
A series of the Y-shaped LC materials was synthesized with variation
of the arm length in the Y-shaped mesogen and their dipole architec-
ture. Our results indicate that main relationships between molecular
structure and mesomorphic behavior well known for the calamitic LC
are valid for the Y-shaped compounds too. Smectic mesophases might
be obtained by lengthening the mesogen with an additional aromatic
core in the arm or with an alkyl chain at the tail. The substitution
of the alkoxy terminal groups on to alkanoyl leads also to enhanced
smectic behavior of the Y-shaped molecules.
4. EXPERIMENTAL
4.1. Characterization of Materials
The chemical structures for the target materials were identified by
1H NMR spectroscopy using a Bruker MSL 400 spectrometer and IR
spectroscopy using a Bruker Vertex instrument. The purity of the
final compounds was assessed by thin layer chromatography, and
further confirmed by elemental analysis. The analytical data showed
that the percentage errors for the carbon, hydrogen, and chlorine
contents for the target materials were less than 1% as compared with
the calculated results. The transition temperatures and enthalpies
for all materials were determined by differential scanning calorimetry
using a Shimadzu 60 calorimeter at a rate of 5ꢀC minꢁ1. Mesophases
were identified by microscopic textures using a Boetius optical
microscope with hot stage (Germany).
4.2. Preparation of Materials
4-n-Alkoxyphenols and 4-n-alkoxy-40-hydroxybiphenyls was synthe-
sized as described by Williamson reaction from bromoalkanes and
hydroquinone or 4,40-biphenol in the presence of anhydrous potassium
carbonate [13]. 4-Alkylesters of p-hydroxybenzoic acid were obtained
by azeotrope esterification with benzene as solvent and sulfuric acid

10
V. V. Zuev
as catalyst. Chloride of 1,2,4-benzenetricarboxylic acid was obtained
by method [14].
4.2.1. 1,2,4-Tris(4-carboxyphenyloxycarbonyl)benzene (1)
A solution of 5 g (20 mmol) chloride of 1,2,4-benzenetricarboxylic
acid in 30 ml carbon tetrachloride was ultrasonically dispersed with
solution of 12 g of p-oxybenzoic acid in 150 ml of 1 N solution of
NaOH for 5 min. After that the pH of solution was reduced to 8 by
addition of 0.1 N hydrochloric acid. The residue was filtered off,
and washed well with water, 0.1 N hydrochloric acid, again water,
and dried in vacuo. Yield 7.5 g (66%) as white unfusible (before
300ꢀC) powder. 1H NMR (DMSO-d6), d, (J, Hz): fragment of
1,2,4-benzene: 8.79 s (1 H); 8.56 d, (1 H, J 7.85); 8. 31 d, (1 H, J
7.85); fragment of oxybenzoate 7.41–7.45 m (4 H, meta); 7.50 d (2 H,
meta); 8.02–8.07 m (6 H, ortho); 10.29 s(OH). IR (KBr, n, cmꢁ1):
3400–3100, 2869, 2860, 1740(C¼O), 1608, 1496, 1455, 1398, 1286,
1049, 1001, 937, 806, 742. Elemental analysis: found, %: C 63.45;
H 3.50; calc for C30H18O12, %: C 63.16; H 3.18.
4.2.2. Chloride of 1,2,4-Tris(4-carboxyphenyloxycarbonyl)
benzene (2)
Five gram (8 mmol) of 1 was heated with 10 g (50 mmol) of PCl5 for
5 h at 140ꢀC;. The phosphorus oxychloride was removed in vacuo, and
residue was recrystallized from chloroform to yield pale yellow crys-
1
tals. Yield 4.85 g (88%); m.p. 126 C. H NMR (CDCl3), d, (J, Hz): frag-
ment of 1,2,4-benzene 8.86 s (1 H); 8.56 d, (1 H, J 8.14); 8.15 d, (1 H, J
8.14); fragment of oxybenzoate 8.28–8.35 m (4 H, ortho, J 8.7);
8.11–8.17 m (2 H, ortho, J 8.7); 7.43 d (4 H, meta, J 8.8); 7.46 d (2 H,
meta, J 8.8). IR (KBr, n, cmꢁ1): 2869, 2860, 2782, 1750 (C¼O), 1608,
1496, 1455, 1398, 1286, 1251, 1226, 1201, 1049, 1001, 937, 806, 742.
Elemental analysis: found, %: C 57.40; H 2.70; Cl 17.23; calc for
C30H15O9Cl3, %: C 57.58; H 2.42; Cl 17.00.
4.2.3. 1,2,4-Tris(40-n-amyloxybiphenyl-4-oxycarbonylphenyl-
oxycarbonyl)benzene (3, n ¼ 4)
A solution of 210 mg (0.3 mmol) of acid chloride 2, 50 mg
(1.5 mmol) 4-hydroxy-40-amyloxybiphenyl, and 0.2 ml of triethyla-
mine in 10 ml of anhydrous dichloroethane was stirred for 5 h at
room temperature. The resulting solution was poured in 50 ml of
ethanol, the residue was filtered off, dried, and twice recrystallized
from a chloroform-ethanol mixture to yield white crystals. Yield
1
350 mg (90%). H NMR (CDCl3), d, (J,Hz): fragment of 1,2,4-benzene
8.88 s (1 H); 8.56 d, (1 H, J 8.08); 8.31 d, (1 H, J 8.08); fragment of

Synthesis of Y-Shaped LCs
11
oxybenzoate 8.28–8.36 m (4 H, ortho); 8.11–8.17 m (2 H, ortho); 7.38
d (6 H, meta, J 8.08); fragment of biphenyl 6.86–7.01 m (12 H, ortho);
7.30–7.35 m (6 H, ortho); 7.40–7.65 m (6 H, meta); 4.0 t (6 H, OCH2);
1.79–1.80 m (6 H); 1.60–1.67 m (6 H); 1.39–1.47 m (6 H); 0.95 t (9 H).
IR (KBr, n, cmꢁ1): 3039, 2927, 2854, 1740 (C¼O), 1604, 1498,
1441, 1269, 1251, 1197, 1160, 1072, 1001, 917, 802, 756. Elemental
analysis: found, %: C 75.40; H 5.70; calc for C81H72O15, %: C 75.68;
H 5.65.
Other compounds 3 were synthesized in a similar way with yields
of 85–90%.
4.2.4. 1,2,4-Tris(40-n-amyloxyphenyl-
4-oxycarbonylphenyloxycarbonyl)benzene (4, n ¼ 4)
It was synthesized in a similar way with compounds 3 with yield of
87%.
1H NMR (CDCl3), d, (J, Hz): fragment of 1,2,4-benzene 8.89 d (1 H, J
1.64); 8.58 dd, (1 H, J 8.08, J 1.64); 8.16 dd, (1 H, J 8.08, J 1.64); frag-
ment of oxybenzoate 8.28 d (4 H, ortho, J 8.08); 8.33 d (2 H, ortho, J
8.08); 6.98 d (4 H, meta, J 8.08); 6.93 d (2 H, meta, J 8.08); fragment
of phenol 7.11 d (6 H, ortho, J 8.08); 7.44 d (6 H, meta, J 8.08); 3.98 t
(6 H, OCH2); 1.79–1.80 m (6 H); 1.60–1.67 m (6 H); 1.39–1.47 m (6 H);
0.95 t (9 H). IR (KBr, n, cmꢁ1): 3039, 2927, 2854, 1740 (C O), 1604,
=
1498, 1441, 1269, 1251, 1197, 1160, 1072,1001, 917, 802, 756. Elemen-
tal analysis: found, %: C 71.87; H 5.90 calc for C63H60O15, %: C 71.58;
H 5.72.
Other compounds 4 were synthesized in a similar way with yields of
85–90%.
4.2.5. 1,2,4-Tris(40-n-amyloxcarbonylyphenyl-
4-oxycarbonylphenyloxycarbonyl)benzene (5, n ¼ 4)
It was synthesized in a similar way with compounds 3 with yield of
88%. 1NMR (CDCl3), d, (J, Hz): fragment of 1,2,4-benzene 8.90 d (1 H, J
1.64); 8.50 dd, (1 H, J 8.08, J 1.64); 8.17 dd, (1 H, J 8.08, J 1.64); frag-
ment of oxybenzoate 8.30 d (4 H, ortho, J 8.08); 8.35 d (2 H, ortho, J
8.08) 7.45 d (4 H, meta, J 8.08); 7.47 d (2 H, meta, J 8.08); terminal
fragment of oxybenzoate 7.32 d (6 H, ortho, J 8.08); 8.13 d (6 H, meta,
J 8.08); 4.33 t (6 H, OCH2); 1.73–1.80 m (6 H); 1.60–1.67 m (6 H);
1.39–1.47 m (6 H); 0.95 t (9 H). IR (KBr, n, cmꢁ1): 3076, 2960, 2933,
2873, 1742, 1717(C¼O), 1602, 1506, 1466, 1414, 1385, 1260, 1227,
1197, 1160, 1072, 1001, 917, 802, 756. Elemental analysis: found, %:
C 69.80; H 5.10; calc for C66H60O18, %: C 69.46; H 5.30.
Other compounds 5 were synthesized in a similar way with yields of
85–90%.

12
V. V. Zuev
4.2.6. 1,2,4-Tris(40-n-amyloxybiphenylloxycarbonyl)benzene
(6, n ¼ 4)
It was synthesized in a similar way with compounds 3 with use
instead of acid chloride 2 of chloride of 1,2,4-benzenetricarboxylic acid
with yield of 88%. 1H NMR (CDCl3), d, (J, Hz): fragment of 1,2,4-
benzene 8.88 s (1 H); 8.54 d, (1 H, J 8.08); 8.13 d, (1 H, J 8.08); fragment
of biphenyl 6.95–7.01 m (6 H, ortho); 7.30–7.32 m (6 M, meta);
7.47–7.65 m (12 H); 4.0 t (6 H, OCH2); 1.79–1.80 m (6 H); 1.60–1.67 m
(6 H); 1.39–1.47 m (6 H); 0.95 t (9 H). IR (KBr, n, cmꢁ1): 3040, 2960,
2933, 2869, 2860, 2782, 1743 (C¼O), 1608, 1496, 1455, 1398, 1286,
1251, 1226, 1201, 1166, 1100, 1049, 1001, 937, 806, 742. Elemental
analysis: found, %: C 77.45; H 6.50; calc for C60H60O9,%: C 77.90;
H 6.54.
Other compounds 6 were synthesized in a similar way with yields of
85–90%.
ACNOWLEDGMENT
This work was financially supported by the Russian Foundation for
Basic Research (grant 06-08-00195).
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