Star mesogens-Synthesis and structural characterization using 1D and 2D solution NMR techniques and mesophase characterization

Article abstract of DOI:10.1139/cjc-2012-0165

Novel star mesogens based on trimesic acid and symmetrical side arm cores with terminal alkoxy groups were synthesized via a divergent approach. The central core and side arms were connected through alkyl spacers. All the synthesized mesogens and their intermediates were characterized thoroughly using Fourier transform infrared (FT-IR), ¹H nuclear magnetic resonance (NMR), ¹³C NMR, and mass spectrometers. One representative mesogen was subjected to the two-dimensional (2D) NMR experiments to ascertain the structure of the mesogens. The mesophase characterization was carried out using hot-stage optical polarizing microscopy (HOPM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) techniques. Many of the molecules with an ethyloxy spacer were found to be nonmesogenic, whereas all the molecules with a butyloxy spacer showed liquid crystalline phases. The increase of terminal chain length decreased the transition temperatures. The nematic phase was observed for the mesogens with short terminal chain length, whereas smectic polymorphism was observed on increasing the terminal chain length. The results of a variable temperature powder X-ray diffraction of the representative sample support the smectic layer ordering.

Full text of DOI:10.1139/cjc-2012-0165

196
ARTICLE
Star mesogens — Synthesis and structural characterization
using 1D and 2D solution NMR techniques and mesophase
characterization
A. Shanavas, T. Narasimhaswamy, B.V.N. Phani Kumar, and A. Sultan Nasar
Abstract: Novel star mesogens based on trimesic acid and symmetrical side arm cores with terminal alkoxy groups were
synthesized via a divergent approach. The central core and side arms were connected through alkyl spacers. All the
synthesized mesogens and their intermediates were characterized thoroughly using Fourier transform infrared (FT-IR), 1H
nuclear magnetic resonance (NMR), 13C NMR, and mass spectrometers. One representative mesogen was subjected to the
two-dimensional (2D) NMR experiments to ascertain the structure of the mesogens. The mesophase characterization was
carried out using hot-stage optical polarizing microscopy (HOPM), differential scanning calorimetry (DSC), and X-ray
diffraction (XRD) techniques. Many of the molecules with an ethyloxy spacer were found to be nonmesogenic, whereas all
the molecules with a butyloxy spacer showed liquid crystalline phases. The increase of terminal chain length decreased the
transition temperatures. The nematic phase was observed for the mesogens with short terminal chain length, whereas
smectic polymorphism was observed on increasing the terminal chain length. The results of a variable temperature powder
X-ray diffraction of the representative sample support the smectic layer ordering.
Key words: star mesogens, trimesic acid, azomethine group, nematic, smectic polymorphism.
Résumé : Utilisant des approches divergentes, on a réalisé des synthèses de nouveaux mésogènes en forme étoilée a` base
d'acide trimésique et des portions centrales portant des chaînes latérales symétriques se terminant par des groupes alcoxy.
Les portions centrales et les chaînes latérales sont liées par des alkyles comme groupes intercalaires. On a caractérisé les
mésogènes et leurs intermédiaires par spectroscopies infrarouge a` transformée de Fourier (IR-TF), RMN du 1H, RMN du 13
C
et spectrométrie de masse. Dans le but de confirmer la structure des mésogènes, on a soumis un mésogène représentatif a`
des expériences de RMN 2D. La caractérisation de la mésophase a été effectuée en utilisant les techniques de microscopie
a` polarisation optique avec table chauffante (MPOTC), calorimétrie a` balayage différentiel (CBD) et de diffraction des rayons
X. (DRX). On a trouvé que plusieurs molécules avec des groupes intercalaires éthyloxy ne sont pas mésogènes alors que les
molécules avec des groupes intercalaires butyloxy présentent des phases cristallines liquides. Une augmentation de la
longueur de la chaîne terminale diminue les températures de transition. On a observé une phase nématique pour les
mésogènes avec des longueurs très courtes de la chaîne terminale alors qu'on a observé du polymorphisme smectique par
augmentation de la longueur de la chaîne terminale. Les résultats de la diffraction des rayons X, a` températures variables,
de poudres de l'échantillon représentatif est en accord avec un arrangement smectique de la couche. [Traduit par la
Rédaction]
Mots-clés : mésogènes étoilés, acide trimésique, groupe azométhine, nématique, smectique, polymorphisme.
temperature as well as the physical state of the material.13–16 Dif-
ferent types of star molecules have been synthesized to under-
Introduction
Thermotropic liquid crystals are quintessential materials.1 Con-
ventional thermotropic liquid crystals (rodlike2 (calamitic) or dis-
clike3 (discotic) shaped molecules) are well understood in terms of
structure–property relationships, thermal behaviour, and poly-
morphic sequences, and they have been recognized as excellent
materials for many practical applications, especially in display
devices.4 Apart from conventional molecular shapes, topologi-
cally different molecular shapes like bent-core,5 multiarm or
stars,6 cones,7 shuttlecocks,8 rings,9 and dendrimers10 are gaining
importance in recent years. Among them, multiarm or star-
shaped mesogens are becoming more popular because of the po-
tential applications in plastic electronics11 and nonlinear optical
(NLO)12 devices. These mesogens are fascinating molecules be-
cause of their numerous conformations, which are vulnerable to
stand their packing pattern as well as mesophase formation.17,18
Recently, Lehmann18 classified symmetrical three arm star me-
sogens as ‘Hekates’. A literature search indicates that a greater
number of studies on phloroglucinol-based star mesogens con-
taining no alkyl spacer have been reported.13–18 The studies on
star mesogens with a spacer containing arms, on the other hand,
are fewer. In particular, reports on trimesic acid-based mesogens
are meager.6,19,20 Depending upon the end phenyl ring substitu-
ents, lamellar versus columnar mesophases have been realized in
such mesogens. The insertion of a flexible spacer between the
central phenyl ring and side arms would make a molecule adopt
different conformations, thereby paving the way for the appear-
ance of many mesophase sequences. In this context, we report
here a detailed investigation pertaining to the design, synthesis,
Received 19 May 2012. Accepted 6 October 2012.
A. Shanavas and A. Sultan Nasar. Department of Polymer Science, University of Madras, Guindy Campus, Chennai-600025, India.
T. Narasimhaswamy. Polymer Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai-600020, India.
B.V.N. Phani Kumar. Chemical Physics Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai-600020, India.
Corresponding author: A. Sultan Nasar (e-mail: drasultannasar@yahoo.com).
Can. J. Chem. 91: 196–205 (2013) dx.doi.org/10.1139/cjc-2012-0165
Published at www.nrcresearchpress.com/cjc on 17 October 2012.

Shanavas et al.
197
Scheme 1. Synthesis of a star mesogen (three arm mesogen).
1
and characterization of these important classes of mesogens based
on trimesic acid with an objective to establish the structure–
mesophase formation relationship.
All the H, 13C chemical shifts, and HMBC correlation carbons
are listed in Table 1, whereas HETCOR data are given in the Sup-
plementary data. The 1H NMR spectrum of star mesogen showed
twelve signals with different chemical shift values. Among them,
the higher chemical shift signals resonating at 8.84 ppm and
8.35 ppm as singlets were assigned to H-12 (central ring –CH pro-
tons) and H-5 (N=CH) protons, respectively. Furthermore, DQF
COSY spectrum did not show the coupling partner indicating that
these two signals correspond to isolated protons. On the other
hand, the HETCOR showed H-12 proton correlation to carbon at
134.50 ppm, whereas the azomethine proton correlates with car-
bon at 158.05 ppm. The HMBC spectrum showed H-12 correlation
with two carbons: one at 134.50 ppm, which is direct (one) bond
coupling, and a second one at 165.00 ppm (carbonyl carbon C-10),
which is three bond coupling. The 1H NMR showed four doublets
at 7.79, 7.16, 6.92, and 6.88 ppm corresponding to the methine
protons of ring B and C. It was clearly evident from the DQF COSY
that 7.79 and 6.92 ppm belong to ring C, whereas 7.16 and
6.88 ppm belong to ring B. The HETCOR correlation for 7.79 ppm
is 130.35 ppm and for 6.92 ppm is 114.70 ppm. The HMBC correla-
tion for 7.79 ppm is 158.05 ppm (azomethine carbon, C-5) and
161.48 ppm (quaternary carbon, C-1), whereas for 6.92 ppm, the
correlation is found to be 130.35 ppm. These data clearly sug-
gested that the assignment of these two protons and the carbons
attached to them are H-3, H-2 and C-3, C-2, respectively. Therefore,
the other two protons at 7.16 and 6.88 ppm should be H-7 and H-8,
respectively, and the carbons attached to these protons are subse-
quently identified using HETCOR data.
Results and discussion
Synthesis of star mesogens
In general, multiarm molecules like star molecules or dendrim-
ers are synthesized via a convergent or divergent approach. In a
convergent approach, the central core and the side arms are syn-
thesized separately and connected at the final step, whereas in the
divergent approach, the arms are built-up around the central
core. In the present work, the target mesogens were synthesized
by the divergent approach as shown in Scheme 1. Accordingly,
4-hydroxyalkoxy (ethoxy and butoxy) nitrobenzenes were pre-
pared and linked to trimesic acid to get a trisubstituted nitro
intermediate. Then, it was reduced to an amine, which was fur-
ther reacted with 4-alkoxy benzaldehydes (C2–C16 even carbons)
to get the target mesogens. The spacer length between the side
arm and central phenyl ring has been varied from 2 to 4 (even
carbons), while the terminal chain of each arm was tailored to
have C2–C16 (even carbons). All the synthesized intermediates
and target mesogens were characterized by Fourier transform
1
infrared (FT-IR), H nuclear magnetic resonance (NMR), 13C NMR,
and electron impact mass spectrometry (EI-MS) spectral tech-
niques. One of the mesogens was subjected to two-dimensional
(2D) solution NMR experiments to establish the molecular struc-
ture in detail.
1D and 2D NMR investigations
For the aliphatic spacer and chain, the terminal CH3 and
O-CH2 protons are easily identified by 1H NMR through the
chemical shift and multiplicity and are noticed at 1.42 and
4.06 ppm as a triplet and quartet, respectively. The correspond-
ing carbons are tracked through HETCOR and the values are
14.80 and 67.50 ppm. The two spacer O-CH2 protons resonated
at 4.46 and 4.02 ppm as triplets and showed long range HMBC
with the carbonyl carbon (C-10) and quaternary carbon (C-9),
respectively, and these two protons are identified as H-18 and
H-15, respectively. The other two –CH2 protons resonated at
1.94 and 2.02 ppm as multiplets and are assigned as H-16 and
H-17, respectively, based on the chemical shift value and HMBC
For the complete assignment of chemical shifts of the star me-
sogen, 2D NMR experiments were carried out. The molecular
structure of the mesogen along with the carbon number is shown
in Fig. 1. The assignment of 1H chemical shifts was achieved by the
multiplicity of 1H resonances, as well as the intensity pattern and
the homonuclear double quantum filtered (DQF) correlation spec-
troscopy (COSY) experiment. The corresponding chemical shifts
of carbons connected directly to the protons were identified with
the help of a heteronuclear correlation (HETCOR) experiment,
whereas the heteronuclear multiple bond correlation (HMBC) ex-
periment was used to assign the quaternary carbons.
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Can. J. Chem. Vol. 91, 2013
Fig. 1. The numbering of star mesogens (tris-(((4-ethoxyphenyl)methylidene)amino phenoxybutyl)benzene-1,3,5-tricarboxylate (6a)).
1
Table 1. H NMR and 13C NMR chemical shifts and heteronuclear multiple bond correlations (HMBC)
of the star mesogen.
Carbon
number
13C NMR chemical
shifts (␦, ppm)
Proton
number
1H NMR chemical
shifts (␦, ppm; J, Hz)a
HMBC
C-1
C-2
C-3
C-4
C-5
C-6
C-7
C-8
161.48
114.70
130.35
129.30
158.05
145.30
122.18
114.99
157.30
165.00
131.44
134.50
14.80
—
—
—
H-2
H-3
—
H-5
—
H-7
H-8
—
6.92 (d); (8.4)
7.79 (d); (90.2)
—
8.35 (s)
—
7.16 (d); (9.1)
6.88 (d); (90.1)
—
—
—
C-1, C-2, C-3, C-4
C-1, C-3, C-5
—
C-3, C-6
—
C-6, C-7, C-9
C-6, C-8, C-9
—
C-9
C-10
C-11
C-12
C-13
C-14
C-15
C-16
C-17
C-18
—
—
—
—
H-12
H-13
H-14
H-15
H-16
H-17
H-18
8.84 (s)
C-10, C-12
—
1.42 (t); (60.8)
4.06 (q); (6.9)
4.02 (t); (5.3)
1.94 (m)
2.02 (m)
4.46 (t); (5.3)
67.50
63.70
25.60
26.09
65.50
C-1, C-13
C-9, C-16
C-15, C-16, C-18
C-17, C-18
C-10, C-17
as, singlet; d, doublet; t, triplet; q, quartet; m, multiplet. The values given in parentheses are coupling
constants (J).
data. Thus, the data obtained from the combined utilization of
1D and 2D experiments unequivocally confirm the structure of
the star mesogen.
bination of HOPM and DSC will confirm the appearance of
mesophases and its sequence. According to the synthetic strategy
described in Scheme 1, 16 compounds were synthesized with vari-
ations in the length of the central spacer and terminal chain. The
target mesogens were subjected to HOPM and DSC experiments
for identifying mesophases and their sequence. The mesophases,
transition temperatures, and transition enthalpy, as determined
by HOPM and DSC, are listed in Table 2. For clarity, the series are
named S2 and S4 to imply the length of the central spacers. The
results are presented by series.
HOPM and DSC studies
In general, hot-stage optical polarizing microscopy (HOPM)
would provide the information about mesophase textures, which
is essentially used to identify the mesophases, whereas differen-
tial scanning calorimetry (DSC) is used to measure the mesophase
temperatures like melting, phase transitions, and clearing tem-
peratures, along with transition enthalpy values. Thus, the com-
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Shanavas et al.
199
Table 2. DSC and HOPM data of S4 series mesogens in cooling.
Transitions
observed by DSC
Transition
temperature (°C)
⌬H
(kJ/mol)
Phases observed
by HOPM
Compound
6a
I–N
[N–Cr]
[I–N]
[N–S]
[S–Cr]
[I–N]
[N–S]
[S–CE]
[I–S]
[S–CE]
[I–S]
[S–SC]
[SC–CE]
[E–Cr]
[I–Colr]
[Colr–Colrd
[Colrd–Colx]
I–S
153.4
74.08
144.5
127.1
101.0
139.0
135.0
100.7
139.6
100.2
145.1
108.8
101.8
95.01
136.0
89.2
1.0
16.5
1.5
8.3
18.3
0.9
10.1
4.2
16.4
21.1
24.4
0.9
1.9
7.3
13.9
2.1
4.8
8.0
0.9
1.5
Nematic
Crystallization
Nematic
Smectic
Crystallization
Nenatic
Smectic
Crystal E
Smectic
Crystal E
Smectic
Smectic C
Crystal E
Crystallization
Columnar rectangular
Disordered columnar rectangular
Columnar X
Smectic
6b
6c
6d
6e
6f
]
76.6
6g
148.8
141.0
98.6
95.0
145.7
99.4
[S–SC]
Smectic C
Smectic F
Smectic X
Smectic C
Smectic F
Smectic X
[SC–SF]
[SF–SX]
I–SC
[SC–SF]
[SF–SX]
29.7
16.0
1.5
6h
95.0
53.0
S2 series
observed in HOPM upon cooling the sample. On further cooling,
crystallization occurs for the sample of 6b, whereas the fan tex-
ture of 6c transformed into concentric arc fans. This texture re-
tained its feature until the sample attained room temperature and
was assigned as the crystal E phase. The DSC of 6b and 6c also
confirms these observations; the heating cycle showed a single
transition associated with the crystal to isotropic (Cr–I) phase.
However, the cooling cycle showed three peaks with varying tran-
sition enthalpy values (Fig. 2). Thus, the higher temperature peak
is assigned to the isotropic to nematic (I–N) transition, while the
middle one associated with the high enthalpy value (see Table 2) is
attributed to the SA phase. The low temperature peak of 6b and 6c
were assigned to crystallization and the crystal E phase, respec-
tively, in view of the high enthalpy values.
Similar to S4-C4 (6b) and S4-C6 (6c), S4-C8 (6d) also showed a
single transition when heating the sample on HOPM, as evidenced
by DSC. In HOPM, on cooling the isotropic liquid, however, the fan
texture typical of the SA phase was noticed, which on further
cooling changed to the crystal E phase where the fans underwent
a transition to a texture consisting of arcs.22 In the DSC cooling
scan, two peaks were noticed (Fig. 2) and these peaks support the
HOPM features. In contrast to S4-C2 (6a) to S4-C6 (6c) homologues,
the disappearance of the nematic phase in the S4-C8 (6d) homo-
logue suggests that the tendency to form a smectic phase in-
creases when increasing the terminal chain length. This trend is
commonly noticed in calamitic mesogens.23
On heating, the HOPM and DSC measurements of S4-C10 (6e)
showed a crystal to isotropic liquid transition. On cooling the
isotropic liquid, the HOPM showed a SA (fan texture) phase. On
further cooling, transformation to the SC phase with a broken
fan texture was noticed. This changed to the crystal E phase
with a characteristic texture of concentric arcs upon extended
cooling. These changes were consistent with DSC data wherein
four transitions were observed with different enthalpy values
(Table 2). The appearance of the SC phase in this isomer was
confirmed by noticing a peak at 108 °C with a change in the
baseline and this pattern is typical of a weak first-order transi-
tion usually observed for SA–SC phases.24 The low temperature
Following the strategy shown in Scheme 1, eight compounds
were synthesized by keeping the C2 spacer constant and varying
the terminal chains. The HOPM observations revealed that many
of them are nonmesogenic. For example, the compounds with
terminal chains of C2–C12 failed to show mesophases. However,
the C14 homologue (5g) showed nematic and smectic C phases
monotropically and the C16 homologue (5h) showed an enantio-
tropic phase with similar sequences. These observations were fur-
ther confirmed by DSC studies. The melting temperature of the
homologous series followed an irregular trend even though the
lowest homologue (C2) showed a high melting point compared to
the highest homologue (C16). This trend is normally observed in
calamitic mesogens.21 Even though an enantiotropic mesophase
was observed for the C16 homologue (5h), the mesophase stability
(9.5 °C) was low. This could be attributed to the molecular shape,
it deviates from the rodlike shape, and is also due to the shorter
spacer length.
S4 series
Eight mesogens were prepared in this series by keeping the
spacer length at C4 constant and varying the terminal chain
length from C2 to C16 (even carbons only). In contrast to S2-C2
(5a), the S4-C2 (6a) homologue showed an enantiotropic nematic
phase (TCN = 147.0 °C – TNI = 150.2 °C). The HOPM of the mesogen
upon cooling from isotropic liquid showed spherical droplets
with birefringence. On further cooling, the birefringent droplets
coalesced to a threaded texture. These features are characteristic
of a nematic phase. The DSC scan of the mesogen on heating
showed two peaks corresponding to crystal to nematic (Cr–N) and
nematic to isotropic (N–I) transitions. The cooling scan also
showed two peaks associated with isotropic to nematic (I–N) and
nematic to crystallization (N–Cr) transitions. Thus, the HOPM and
DSC unambiguously support the enantiotropic nematic phase for
the S4-C2 (6a) mesogen.
The C4 (6b) to C12 (6f) homologues, on the other hand, exhib-
ited monotropic polymesomorphism. In the case of S4-C4 (6b) and
S4-C6 (6c), the nematic phase with homeotropy and the focal
conic fan texture characteristic of the smectic A (SA) phase were
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200
Can. J. Chem. Vol. 91, 2013
Fig. 2. DSC cooling curves of the S4 series mesogens.
further cooling, it was first changed to the smectic F phase and
then changed to an unidentified smectic phase. The heating
cycle of the DSC scan showed two peaks for crystal to smectic C
and smectic C to isotropic transitions. The cooling cycle of the
DSC (Fig. 2) also supports the HOPM observations of S4-C16 (6h).
Many homologues of the S4 series exhibited monotropic phases
and hence in DSC heating curves, only the melting temperature
with characteristic transition enthalpy values were noticed. The
cooling cycle, on the other hand, showed multiple transitions
with varying enthalpy values (Table 2). To summarize, the follow-
ing are notable features of the series: enantiotropic nematic phase
of C2 (6a), monotropic mesomorphism of C4–C10 (6b–6e), mono-
tropic columnar phase of C12 (6f), and enantiotropic mesomor-
phism of C14 (6g) and C16 (6h). In ascending the series, a tendency
for smectic phases increased, while the nematic phase vanished at
the C8 homologue (6d). Similarly, the smectic A phase was first
noticed for the C4 homologue (6b) and continued until C14 (6g)
with the exception of C12 (6e). Thus, the HOPM and DSC studies
unambiguously support that the mesogens under investigation
exhibit conventional calamitic mesophases (except the C12 homo-
logue) even though the molecules are C3 symmetric and the over-
25
all shape is nonlinear. Attard et al.
also reported calamitic
mesophases for the star mesogens with a spacer.
Variable temperature powder X-ray diffraction
In addition to HOPM and DSC, the powder X-ray diffraction
technique was used to confirm the mesophase exhibited by the
synthesized mesogen. The X-ray profile for a representative meso-
gen is given in Fig. 4. The powder X-ray diffraction spectra of the
S4-C16 (6h) smectogen recorded at 30 °C (figure not given) showed
a large number of peaks with varying intensity in the 2␪ region of
0°–20°. The X-ray profile recorded at 100 °C showed sharp peaks at
a small angle and wide angle region indicating the crystalline
nature of the sample at 100 °C. The diffractogram recorded at
150 °C (Fig. 4) showed a very sharp reflection at 2␪ = 1.03° and a
broad hump at 2␪ = 13.3°. The disappearance of a large number of
peaks at 150 °C and the presence of a very sharp intense reflection
at 1.03° at the same temperature indicated that the mesogen pos-
sessed a smectic phase. The broad hump at a wide angle region
suggests that the terminal chains are undergoing dynamics typi-
cal of a liquidlike nature. On the other hand, the sharp reflection
at a small angle region suggests lamellar ordering.26 Thus, the
variable temperature powder X-ray diffraction results support
smectic layer ordering and confirm a smectic C phase as evi-
denced in HOPM and DSC. Upon increasing the temperature up to
158 °C, the disappearance of small angle reflection and the pres-
ence of broad hump at a wide angle suggested the isotropic phase
of the sample.
Among the possible conformations of this molecule, ␭ and ␧
conformations (Fig. 5) are considered for proposing a packing
pattern (structure) of the smectic C phase. In the ␭ conforma-
tion, the length of the molecule is contributed to by two arms,
whereas in the ␧ conformation, it is contributed to by one arm.
The d value calculated by the Bragg equation from the small
angle reflection was 86 Å and the length of one arm of S4-C16
was determined using the geometry optimized space-filling
model and the value was approximately 42 Å. Thus, the ␭ con-
formation can support d spacing. However, the volume occu-
pied by the ␭ conformation is more than the volume occupied
by ␧. Therefore, on the other hand, the more possible confor-
mation should be ␧, which requires the bilayer ordering (layer
spacing (d) was contributed to by two molecules) to satisfy the
X-ray data. Indeed, the d/l ratio calculated from the X-ray dif-
fraction pattern was ϳ2,27 which suggested the bilayer order-
ing. Furthermore, to have a ␧ conformation, the central phenyl
ring has to possess linking units in such a way to facilitate the
bending of a third arm. In other words, the third arm of the ␭
conformation should bend back to get a conformation in which
peak observed in the DSC scan is attributed to crystallization
from the crystal E phase texture.
The most surprising feature of this series was the optical tex-
tures of the C12 homologue (6f). Like its predecessor, this meso-
gen showed a single transition for the crystal to isotropic liquid
phase on heating in both the HOPM and DSC. But on cooling, it
showed textures that are quite different from other homologues
of the series. Hence, the sample was cooled from isotropic liquid
at a cooling rate of 0.1 °C/min. The textures (Fig. 3E and 3F) ob-
served on slow cooling include birefringent fanlike batonnets,
spherulite with Maltese crosses, and shapes typical of half-disc
and tapered dendrons. The sample upon further cooling retains
the features with a sufficient growth of their size. These features
suggest that the mesogen shows columnar (Col) phase. In DSC, the
peak corresponding to these textures indicate an enthalpy value
of 13.9 kJ/mol. On further cooling, the sample showed broken fans
protruding spherulites and regions of birefringent domains with
lines. Upon further cooling, concentric lines usually observed for
the crystal E phase were noticed. The DSC cooling curve (Fig. 2)
showed three peaks associated with I–Colr, Colr–Colrd, and Colrd
–
Colx. Based on HOPM features, it was believed that the phase was
columnar rectangular (Colr), which on cooling changed to a disor-
dered columnar rectangular phase (Colrd) and an unidentified co-
lumnar phase (Colx).
The higher homologues, i.e., C14 (6g) and C16 (6h), however,
showed enantiotropic smectic phases. For the S4-C14 (6g) iso-
mer, on heating, HOPM showed an enantiotropic smectic A
phase and the corresponding DSC scan also showed two peaks.
The enthalpy value of the low temperature transition was
57.2 kJ/mol and that of the high temperature transition was
7.9 kJ/mol. The mesogen on cooling from isotropic liquid under
HOPM showed birefringent batonnets. On further cooling, they
coalesced to a broken fan texture of the SC phase. These obser-
vations were also supported by a DSC scan wherein two peaks
with shoulder splittings were observed. The SC phase, on fur-
ther cooling, changed to the SF phase followed by an unidenti-
fied phase (SX). These features are well supported by a DSC scan
wherein two closely spaced transitions were observed from a
low temperature region. The S4-C16 (6h) isomer also showed an
enantiotropic smectic phase when heating the sample. On cool-
ing the mesogen from isotropic liquid,
a characteristic
schlieren texture (HOPM) of the SC phase was observed. On
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Shanavas et al.
201
Fig. 3. HOPM photograph of (A) nematic droplets of 6a at 149 °C, (B) the focal conic fan texture of the smectic A phase of 6b at 126 °C, (C) the
fan texture of the smectic A phase of 6e at 145 °C, (D) the smectic C phase of 6e at 108 °C, (E) the columnar phase of 6f at 132.7 °C, and (F) the
columnar phase of 6f at 109 °C.
all three arms lie parallel to each other. This is, in principle,
feasible for these mesogens as the center phenyl ring is linked
by a flexible ester linking unit rather than an azomethine or
2-Bromoethanol, 4-chlorobutylacetate, 6-chlorohexanol, 4-nitro-
stilbene, which are more rigid.
Experimental
Materials
phenol, 1,3,5-benzenetricarbonyltrichloride, 4-ethoxybenzaldehyde
(4a), 4-butoxybenzaldehyde (4b), 4-hexyloxybenzaldehyde (4c),
n-bromooctane, n-bromodecane, n-bromododecane, n-bromo-
tetradecane, n-bromohexadecane, 4-hydroxybenzaldehyde, and
palladium on charcoal (Pd/C, 10%) were purchased from Sigma-
Conclusions
Two series of star mesogens based on trimesic acid were
synthesized by varying the length of the spacer and terminal
chains through a divergent approach. The structural integrity
Aldrich and used without further purification. N,N=-Dimethyl-
of the synthesized mesogens was verified by spectral tools like
formamide, tetrahydrofuran, ethanol, and methanol (all obtained
FT-IR, 1H NMR, 13C NMR, and EI-MS spectroscopy. The HOPM
from SD Fine chemicals) were purified by standard procedures. Ethyl
investigation of target mesogens showed mesophase character-
acetate, diethyl ether, n-hexane, 2-butanone, acetone, potassium
istics and these were confirmed by DSC. The detailed investiga-
hydroxide (pellets), Celite-540, anhydrous potassium carbonate,
tion by HOPM and DSC of S2 series mesogens confirms only
anhydrous sodium sulphate, and silica gel (100–200 mesh) were ob-
S2-C14 and S2-C16 homologues were mesogenic. In the case of
tained from Merck (India) and used as obtained. Triethylamine (SD
the S4 series, the rich polymorphism was preferentially noticed
Fine chemicals) was distilled and then used.
as monotropes. One of the isomers, i.e., S4-C12, showed a co-
lumnar mesophase. The variable temperature powder X-ray of
representative samples unambiguously confirmed the layer or-
dering of the smectic phase.
Measurements
The FT-IR spectra of samples were recorded by the KBr pellet
method on a Thermo-Mattson FT-IR spectrometer. 1H NMR and 13
C
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202
Can. J. Chem. Vol. 91, 2013
Fig. 4. Variable temperature powder X-ray diffraction spectrum of
6h at 150 °C.
Fig. 5. Pictorial representation of (A) lamda (␭) and (B) epsilon (␧)
conformations of the star mesogen.
NMR spectra of the compounds were recorded using a JEOL GSX
500 NMR spectrometer; the samples were dissolved in CDCl3 and
tetramethylsilane (TMS) was used as an internal standard. The
1
experimental parameters chosen for 1D H and 13C NMR were as
follows: spectral width, 15 and 250 ppm; number of data points,
16384 and 32768; number of scans, 8 and 200; acquisition time,
2.18 and 1.04 s; relaxation delay, 5 and 2 s; and 90° pulse width,
12.62 and 12.25 ␮s; respectively. The EI mass spectra were recorded
using a JEOL DX-303 spectrometer.
Two-dimensional correlation spectra were recorded to track
1H–1H and 1H–13C correlations. A relaxation delay of 1.5 s was used
1
in all the 2D experiments. H–1H COSY: COSY spectra were ob-
tained using the gradient version of the DQF COSY pulse se-
quence. The spectra resulted from a 1024 (F2) × 256 (F1) data matrix
size with one scan per t1 increment. A spectral width of 10 ppm
was used in both F1 and F2 dimensions. 1H–13C HETCOR: HETCOR
spectra were recorded using the standard HETCOR pulse program.
The acquisition parameters were as follows: spectra resulted from
a 1024 × 128 data matrix size with eight scans per t1 increment. A
spectrum width of 180 ppm in F2 and 10 ppm in F1 was recorded.
1H–13C HMBC: The gradient version of HMBC experiments28 was
1
recorded to sketch the long-range (two and three bonds) H–13C
correlations. The long-range coupling constant (nJCH) optimized
was at 8 Hz. The spectra resulted from a 2048 × 256 data matrix
size with eight scans per t1 increment. A spectral width of 10 ppm
in F2 and 180 ppm in F1 was recorded.
Optical polarizing microphotographs were taken using an Olym-
pus BX50 polarizing microscope equipped with a Linkam THMS heat-
ing stage, and a TMS 94 temperature programmer with a C7070
digital camera. The samples were placed between two 12 mm cover
slips and were heated with a programmed heating rate.
Differential scanning calorimetry calibrated for enthalpy and
temperature was performed using TA Instruments Q-10 series.
The experiments were carried out in nitrogen atmosphere at a
heating rate of 10 °C/min. Each sample was subjected to two heat-
ing and cooling cycles and data obtained from the second heating
and cooling was considered for discussion. All the samples were
crimpled in aluminum pans to ensure good thermal contact be-
tween the sample and the pan. Small-angle X-ray scattering spec-
tra were measured with an evacuated high performance SAXS
instrument “SAXSess” (Anton Paar KG, Graz, Austria). The SAX-
Sess was attached to a conventional X-ray generator (Philips, Hol-
land) equipped with a sealed X-ray tube (Cu anode target type
producing Cu K␣ X-rays with a wavelength of 0.154 nm) operating
at 40 kV and 50 mA. The samples were measured using the past
cell method. The scattered X-ray intensities were detected with a
2D-imaging plate detection system Cyclone (Packard, A Packard
Bioscience Company) with the spatial resolution of 50 ␮m × 50 ␮m
per pixel at a sample to detector distance of 265 mm. The measur-
ing times of 30 s yielded sufficient measuring statistics. Scattering
data that were read off from the imaging plate were first corrected
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Shanavas et al.
203
for the absorption of the X-rays in the sample and transformed to
the q scale (q = 4␲/␭·sin ␪/2; program SAXS Quant; Anton Paar KG,
Graz, Austria). The SAXS measurements were further corrected
for the empty cell.
Tris((4-nitrophenoxy)butyl)benzene-1,3,5-tricarboxylate (2b)
Yield: 55%; mp 89–90 °C. IR (KBr, cm−1): 3084 (CHstr aromatic),
2952 and 2878 (–CH2str), 1724 (C=Ostr ester), 1595 and 1504 (C=Cstr
aromatic), 1448 (–CHben), 1339 (–NO2str), 1255 and 1110 (C-O-Cstr of
1
ester). H NMR (CDCl3, 500 MHz, ppm) ␦: 8.78 (s, 3H), 8.15 (d, J =
Synthesis of 2-(4-nitrophenoxy)ethan-1-ol (1a)
9.15, 6H), 6.93 (d, J = 9.2, 6H), 4.47 (t, J = 6.1, 6H), 4.14 (t, J = 5.35, 6H),
2.01 (m, 12H). 13C NMR (CDCl3, 100 MHz, ppm) ␦: 164.96, 163.94,
141.53, 134.53, 131.36, 126.01, 114.47, 68.18, 65.43, 25.83, 25.45.
EI-MS m/z: 789.7 (M+).
In a 500 mL single-necked flask, 12.5 g (90 mmol) of K2CO3, 11.8 g
(85 mmol) of 4-nitrophenol, and 11.2 g (90 mmol) of 2-bromoetha-
nol were taken and were dissolved in 300 mL of 2-butanone. The
solution was refluxed for 8 h. The yellow coloured solid obtained
after removal of the solvent was recrystallized in a 1:3 ratio of the
ethyl acetate–hexane mixed solvent. The product was a pale yel-
low coloured solid. Yield: 61%; mp 79–80 °C. IR (KBr, cm−1): 3268
(–OHstr), 2954 and 2878 (–CH2str), 1600 and 1505 (C=Cstr aromatic),
1457 (–CHben), 1338 (–NO2str), 1268 and 1110 (C-O-Cstr). 1H NMR
(CDCl3, 500 MHz, ppm) ␦: 8.16 (d, J = 9.2, 2H), 6.96 (d, J = 9.15, 2H),
4.16 (t, J = 4.7, 2H), 4.0 (t, J = 4.6, 2H), 2.33 (bs, –OH). 13C NMR (CDCl3,
100 MHz, ppm) ␦: 163.8, 141.7, 126.0, 114.6, 70.0, 61.1. EI-MS m/z:
183.1 (M+)
Synthesis of tris((4-aminophenoxy)ethyl)benzene-1,3,5-
tricarboxylate (3a and 3b)
Compound 2a or 2b (9.92 mmol) was reduced under hydrogen
atmosphere in the presence of a 10% Pd–charcoal catalyst in 100
mL of a 1:1 mixture of ethanol and tetrahydrofuran at room tem-
perature for 48 h. The Pd–C catalyst was removed by filtering the
reaction mixture through the Celite-540 filtering aid and the evap-
oration of the solvents yielded the product. The product was re-
crystallized in a 1:3 mixture of ethyl acetate and hexane. The
product was a reddish brown coloured solid.
Synthesis of 4-(4-nitrophenoxy)butan-1-ol (1b)
Tris((4-aminophenoxy)ethyl)benzene-1,3,5-tricarboxylate (3a)
Yield: 92%; mp 119–121 °C. IR (KBr, cm−1): 3430 and 3366 (–NH2str
free amine), 2961 and 2875 (–CH2str), 1728 (C=Ostr ester), 1631
(–NHben), 1512 (C=Cstr aromatic), 1468 (–CHben), 1259 (C-O-Cstr of
ester). 1H NMR (CDCl3, 500 MHz, ppm) ␦: 8.82 (s, 3H), 6.71 (d, J = 9.2,
6H), 6.60 (d, J = 9.0, 6H), 4.44 (t, J = 6.2, 6H), 3.94 (t, J = 6.2, 6H), 3.00
(bs, –NH2). 13C NMR (CDCl3, 100 MHz, ppm) ␦: 165.01, 151.60, 140.69,
135.06, 131.12, 116.49, 116.22, 66.80, 64.35. EI-MS m/z: 615.6 (M+).
In a 500 mL two-necked flask, 12.5 g (90 mmol) of K2CO3 and
11.8 g (85 mmol) of 4-nitrophenol were taken and were dissolved in
200 mL of dimethylformamide (DMF). The mixture was stirred and
heated to 90 °C followed by the dropwise addition of 100 mL of a
DMF solution containing 13.5 g (90 mmol) of 4-chlorobutylacetate.
The temperature of the mixture was maintained at 90 °C for 5 h.
Then, the reaction mixture was poured into 1 L of distilled water
and extracted with 300 mL (3 × 100 mL) of diethyl ether. The
organic layer was washed with 5% KOH and was put in a flask. To
this, 9.5 g (170 mmol) of KOH, 100 mL of ethanol, and 100 mL of
distilled water were added and the mixture was refluxed for 1 h.
Then, the solution was allowed to cool and poured into 1 L of
distilled water and neutralized with 1 N HCL to get a precipitate.
The precipitate was filtered, washed with distilled water, and
dried under vacuum. The product was recrystallized in a 1:3 ratio
of the ethyl acetate–hexane mixed solvent. The product was a pale
yellow coloured solid. Yield: 72%; mp 69–70 °C. IR (KBr, cm−1): 3514
(–OHstr), 2932 and 2860 (–CH2str), 1591 and 1501 (C=Cstr aromatic),
1457 (–CHben), 1340 (–NO2str), 1259 and 1113 (C-O-Cstr). 1H NMR
(CDCl3, 500 MHz, ppm) ␦: 8.16 (d, J = 9.2, 2H), 6.92 (d, J = 9.2, 2H),
Tris((4-aminophenoxy)butyl)benzene-1,3,5-tricarboxylate (3b)
Yield: 92%; mp 97–98 °C. IR (KBr, cm−1): 3468 and 3385 (–NH2str
free amine), 2934 and 2860 (–CH2str), 1724 (C=Ostr ester), 1636
(–NHben), 1512 (C=Cstr aromatic), 1472 (–CHben), 1237 (C-O-Cstr of
ester). 1H NMR (CDCl3, 500 MHz, ppm) ␦: 8.82 (s, 3H), 6.71 (d, J = 9.2,
6H), 6.61 (d, J = 8.4, 6H), 4.44 (t, J = 6.1, 6H), 3.94 (t, J = 6.1, 6H), 3.09
(bs, –NH2), 1.98 (m, 6H), 1.91 (m, 6H). 13C NMR (CDCl3, 100 MHz,
ppm) ␦: 165.13, 152.09, 140.02, 134.57, 131.44, 116.51, 115.69, 67.94,
65.59, 26.33, 25.64. EI-MS m/z: 699.7 (M+).
Synthesis of 4-alkoxybenzaldehydes (4d–4h)
The synthetic procedure and analytical data of 4-alkoxy-
benzaldehydes (4d–4h) are given in the Supplementary data.
4.08 (t, J = 6.1, 2H), 3.71 (t, J = 6.15, 2H), 1.90 (m, 2H), 1.73 (m, 2H). 13
C
NMR (CDCl3, 100 MHz, ppm) ␦: 164.16, 141.41, 126.01, 114.49, 68.68,
Synthesis of tris-(((4-alkoxyphenyl)methylidene)
aminophenoxyalkyl)benzene-1,3,5-tricarboxylate 5a–5h
and 6a–6h
62.39, 29.13, 25.61. EI-MS m/z: 211.2 (M+).
Synthesis of tris((4-nitrophenoxy)alkyl)benzene-1,3,5-
tricarboxylate (2a and 2b)
In a typical experiment, 1.0 mmol of amine (3a or 3b) and
3.0 mmol of 4-alkoxybenzaldehydes (4a–4h) were taken in a
100 mL conical flask. Ethanol (3 mL) was added to the conical flask,
mixed the reactants thoroughly, and kept the flask inside the
microwave oven (power 80W) for 10 min. Every 1.5 min, the flask
was taken out and the contents were mixed thoroughly and the
process was repeated. The flask was allowed to cool to room tem-
perature and the solid obtained was washed with methanol and
recrystallized in 2-butanone. All the products obtained were pale
brown coloured solids.
Compound 1a or 1b (55 mmol) and 5.5 g (55 mmol) of trieth-
ylamine were dissolved in 200 mL of 2-butanone. To this solution,
a 100 mL of a 2-butanone solution containing 4.8 g (18.3 mmol) of
1,3,5-benzenetricarbonyltrichloride was added dropwise at 0 °C
and the reaction mixture was stirred for 3 h at room temperature.
Then, the triethylamine salt was filtered off and then the solvent
was evaporated. The solid obtained was recrystallized in a 1:3 ratio
of the acetone–methanol mixed solvent. The product obtained
was a pale yellow coloured solid.
Tris-(((4-ethoxyphenyl)methylidene)aminophenoxyethyl)
benzene-1,3,5-tricarboxylate (5a)
Tris((4-nitrophenoxy)ethyl)benzene-1,3,5-tricarboxylate (2a)
Yield: 55%; mp 120–121 °C. IR (KBr, cm−1): 3084 (CHstr aromatic),
2962 and 2878 (–CH2str), 1729 (C=Ostr ester), 1597 and 1510 (C=Cstr
aromatic), 1448 (–CHben), 1344 (–NO2str), 1247 and 1109 (C-O-Cstr of
ester). 1H NMR (deuterated dimethyl sulfoxide (DMSO-d6),
500 MHz, ppm) ␦: 8.55 (s, 3H), 8.13 (d, J = 9.2, 6H), 7.14 (d, J = 9.2, 6H),
4.66 (t, J = 6.2, 6H), 4.48 (t, J = 6.1, 6H). 13C NMR (DMSO-d6, 100 MHz,
ppm) ␦: 164.46, 164.02, 141.53, 134.26, 131.33, 126.39, 115.67, 67.17,
64.43. EI-MS m/z: 705.5 (M+).
Yield: 60%; mp 163–165 °C. IR (KBr, cm−1): 2928 and 2865
(–CH2str), 1729 (C=Ostr ester), 1607 and 1508 (C=C str aromatic), 1243
and 1111 (C-O-Cstr of ester), 1164 (C-O-Cstr). 1H NMR (CDCl3, 500 MHz,
ppm) ␦: 8.88 (s, 3H), 8.35 (s, –CH=N), 7.78 (d, 6H), 7.13 (d, 6H), 6.95
(d, 6H), 6.93 (d, 6H), 4.72 (t, 6H), 4.33 (t, 6H), 4.00 (q, 6H), 1.43 (t, 9H).
13C NMR (CDCl3, 100 MHz, ppm) ␦: 164.92, 161.54, 158.32, 156.82,
145.98, 135.10, 131.15, 130.37, 129.33, 122.23, 115.35, 114.71, 66.21,
64.17, 63.71, 14.84. EI-MS m/z: 1012 (M+).
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Can. J. Chem. Vol. 91, 2013
Tris-(((4-butoxyphenyl)methylidene)aminophenoxyethyl)
benzene-1,3,5-tricarboxylate (5b)
6H), 6.95 (d, 6H), 6.93 (d, 6H), 4.72 (t, 6H), 4.33 (t, 6H), 4.00 (t, 6H),
1.79 (m, 6H), 1.45 (m, 6H), 1.35 (m, 60H), 0.87 (t, 9H). 13C NMR
(CDCl3, 100 MHz, ppm) ␦: 164.92, 161.76, 158.33, 156.82, 145.98,
135.10, 131.15, 130.37, 129.33, 122.23, 115.35, 114.71, 68.26, 66.18,
64.18, 32.02, 29.85, 29.66, 29.40, 29.29, 26.12, 22.80, 14.24. EI-MS
m/z: 1518 (M+ + 1).
Yield: 60%; mp 172–174 °C. IR (KBr, cm−1): 2943 and 2871
(–CH2str), 1724 (C=Ostr ester), 1605 and 1508 (C=Cstr aromatic), 1473
1
(–CHben), 1242 and 1109 (C-O-Cstr of ester), 1162 (C-O-Cstr). H NMR
(CDCl3, 500 MHz, ppm) ␦: 8.88 (s, 3H), 8.35 (s, –CH=N), 7.78 (d, 6H),
7.13 (d, 6H), 6.95 (d, 6H), 6.93 (d, 6H), 4.72 (t, 6H), 4.33 (t, 6H), 4.00
(t, 6H), 1.78 (m, 6H), 1.50 (m, 6H), 0.98 (t, 9H). 13C NMR (CDCl3,
100 MHz, ppm) ␦: 164.92, 161.54, 158.32, 156.82, 145.98, 135.10,
131.15, 130.37, 129.33, 122.23, 115.35, 114.71, 67.94, 66.18, 64.18,
31.32, 19.32, 13.96. EI-MS m/z: 1097 (M+ + 1).
Tris-(((4-hexadecyloxyphenyl)methylidene)aminophenoxyethyl)
benzene-1,3,5-tricarboxylate (5h)
Yield: 60%; mp 148 °C. IR (KBr, cm−1): 2919 and 2851 (–CH2str),
1732 (C=Ostr ester), 1611 and 1572 and 1509 (C=C str aromatic), 1463
1
(–CHben), 1246 (C-O-Cstr of ester), 1163 (C-O-Cstr). H NMR (CDCl3,
Tris-(((4-hexyloxyphenyl)methylidene)aminophenoxyethyl)
benzene-1,3,5-tricarboxylate (5c)
500 MHz, ppm) ␦: 8.88 (s, 3H), 8.35 (s, –CH=N), 7.78 (d, 6H), 7.13
(d, 6H), 6.95 (d, 6H), 6.93 (d, 6H), 4.72 (t, 6H), 4.33 (t, 6H),3.99 (t, 6H),
1.79 (m, 6H), 1.45 (m, 6H), 1.25 (m, 72H), 0.87 (t, 9H).13C NMR (CDCl3,
100 MHz, ppm) ␦: 164.92, 161.76, 158.33, 156.82, 145.98, 135.10,
131.15, 130.37, 129.33, 122.23, 115.35, 114.71, 68.26, 66.18, 64.18,
32.00, 29.80, 29.68, 29.47, 29.29, 26.12, 22.80, 14.24. EI-MS m/z: 1602
(M+ + 1).
Yield: 60%; mp 164–166 °C. IR (KBr, cm−1): 2929 and 2863
(–CH2str), 1734 (C=Ostr ester), 1612 and 1508 (C=Cstr aromatic), 1461
(–CHben), 1226 and 1108 (C-O-Cstr of ester). 1H NMR (CDCl3,
500 MHz, ppm) ␦: 8.88 (s, 3H), 8.35 (s, –CH=N), 7.78 (d, 6H), 7.13 (d,
6H), 6.95 (d, 6H), 6.93 (d, 6H), 4.72 (t, 6H), 4.33 (t, 6H), 4.00 (t, 6H),
1.79 (m, 6H), 1.46 (m, 6H), 1.34 (m, 12H), 0.91 (t, 9H). 13C NMR (CDCl3,
100 MHz, ppm) ␦: 164.92, 161.76, 158.33, 156.82, 145.98, 135.10,
131.15, 130.37, 129.33, 122.23, 115.35, 114.71, 68.26, 66.18, 64.18,
31.68, 29.25, 25.80, 22.71, 14.16. EI-MS m/z: 1181.5 (M+ + 1).
Tris-(((4-ethoxyphenyl)methylidene)aminophenoxybutyl)
benzene-1,3,5-tricarboxylate (6a)
Yield: 60%; mp 146 °C. IR (KBr, cm−1): 2954 and 2871 (–CH2str),
1729 (C=Ostr ester), 1623 (–C=Nstr– imine), 1605 and 1510 (C=Cstr
aromatic), 1472 (–CHben), 1238 (C-O-Cstr of ester), 1165 (C-O-Cstr). 1H
NMR (CDCl3, 500 MHz, ppm) ␦: 8.88 (s, 3H), 8.35 (s, –CH=N), 7.78 (d,
6H), 7.13 (d, 6H), 6.94 (d, 6H), 6.89 (d, 6H), 4.46 (t, 6H), 4.07 (q, 6H),
4.02 (t, 6H), 1.98 (m, 12H), 1.43 (t, 9H). 13C NMR (CDCl3, 100 MHz,
ppm) ␦: 165.08, 161.48, 158.05, 157.30, 145.33, 134.59, 131.44, 130.35,
129.34, 122.18, 114.99, 114.69, 67.54, 65.55, 63.70, 26.10, 25.64, 14.86.
EI-MS m/z: 1096 (M+).
Tris-(((4-octyloxyphenyl)methylidene)aminophenoxyethyl)
benzene-1,3,5-tricarboxylate (5d)
Yield: 60%; mp 161–163 °C. IR (KBr, cm−1): 2930 and 2864
(–CH2str), 1730 (C=Ostr ester), 1610 and 1572 and 1508 (C=Cstr aro-
1
matic), 1469 (–CHben), 1242 (C-O-Cstr of ester), 1164 (C-O-Cstr). H
NMR (CDCl3, 500 MHz, ppm) ␦: 8.88 (s, 3H), 8.35 (s, –CH=N), 7.78 (d,
6H), 7.13 (d, 6H), 6.95 (d, 6H), 6.93 (d, 6H), 4.72 (t, 6H), 4.33 (t, 6H),
4.00 (t, 6H), 1.79 (m, 6H), 1.46 (m, 6H), 1.30 (m, 24H), 0.89 (t, 9H). 13
C
Tris-(((4-butoxyphenyl)methylidene)aminophenoxybutyl)
benzene-1,3,5-tricarboxylate (6b)
NMR (CDCl3, 100 MHz, ppm) ␦: 164.92, 161.76, 158.33, 156.82,
145.98, 135.10, 131.15, 130.37, 129.33, 122.23, 115.35, 114.71, 68.26,
66.18, 64.18, 31.91, 29.46, 29.34, 29.29, 26.12, 22.76, 14.22. EI-MS m/z:
1264.4 (M+).
Yield: 60%; mp 154 °C. IR (KBr, cm−1): 2956 and 2871 (–CH2str),
1731 (C=Ostr ester), 1625 (–C=Nstr– imine), 1606 and 1510 (C=Cstr
aromatic), 1471 (–CHben), 1243 (C-O-Cstr of ester), 1166 (C-O-Cstr). 1H
NMR (CDCl3, 500 MHz, ppm) ␦: 8.88 (s, 3H), 8.35 (s, –CH=N), 7.78 (d,
6H), 7.13 (d, 6H), 6.94 (d, 6H), 6.89 (d, 6H), 4.46 (t, 6H), 4.03 (t, 6H),
Tris-(((4-decyloxyphenyl)methylidene)aminophenoxyethyl)
benzene-1,3,5-tricarboxylate (5e)
Yield: 60%; mp 155–157 °C. IR (KBr, cm−1): 2925 and 2855
(–CH2str), 1731 (C=Ostr ester), 1608 and 1572 and 1508 (C=Cstr aro-
4.00 (t, 6H), 1.97 (m, 12H), 1.78 (m, 6H), 1.50 (m, 6H), 0.98 (t, 9H). 13
C
NMR (CDCl3, 100 MHz, ppm) ␦: 165.08, 161.71, 158.05, 157.30, 145.33,
134.59, 131.44, 130.35, 129.29, 122.18, 114.99, 114.69, 67.93, 67.54,
65.55, 31.32, 26.10, 25.64, 19.32, 13.97. EI-MS m/z: 1181.6 (M+ + 1).
1
matic), 1469 (–CHben), 1253 (C-O-Cstr of ester), 1162 (C-O-Cstr). H
NMR (CDCl3, 500 MHz, ppm) ␦: 8.88 (s, 3H), 8.35 (s, –CH=N), 7.78 (d,
6H), 7.13 (d, 6H), 6.95 (d, 6H), 6.93 (d, 6H), 4.72 (t, 6H), 4.33 (t, 6H),
4.00 (t, 6H), 1.79 (m, 6H), 1.45 (m, 6H), 1.31 (m, 36H), 0.88 (t, 9H). 13
C
Tris-(((4-hexyloxyphenyl)methylidene)aminophenoxybutyl)
benzene-1,3,5-tricarboxylate (6c)
NMR (CDCl3, 100 MHz, ppm) ␦: 164.92, 161.76, 158.33, 156.82,
145.98, 135.10, 131.15, 130.37, 129.33, 122.23, 115.35, 114.71, 68.26,
66.18, 64.18, 32.00, 29.66, 29.50, 29.42, 29.29, 26.12, 22.76, 14.22.
EI-MS m/z: 1349.6 (M+ + 1).
Yield: 60%; mp 151 °C. IR (KBr, cm−1): 2933 and 2868 (–CH2str),
1731 (C=Ostr ester), 1625 (–C=Nstr– imine), 1607 and 1510 (C=Cstr
aromatic), 1472 (–CHben), 1245 (C-O-Cstr of ester), 1166 (C-O-Cstr). 1H
NMR (CDCl3, 500 MHz, ppm) ␦: 8.84 (s, 3H), 8.35 (s, –CH=N), 7.78 (d,
6H), 7.13 (d, 6H), 6.94 (d, 6H), 6.89 (d, 6H), 4.46 (t, 6H), 4.03 (t, 6H),
4.00 (t, 6H), 1.97 (m, 12H), 1.79 (m, 6H), 1.46 (m, 6H), 1.34 (m, 12H),
0.90 (t, 9H). 13C NMR (CDCl3, 100 MHz, ppm) ␦: 165.08, 161.71,
158.05, 157.30, 145.33, 134.59, 131.44, 130.35, 122.18, 114.99, 114.69,
68.25, 67.54, 65.55, 31.67, 29.25, 26.10, 25.79, 25.64, 22.70, 14.15.
EI-MS m/z: 1264.5 (M+).
Tris-(((4-dodecyloxyphenyl)methylidene)aminophenoxyethyl)
benzene-1,3,5-tricarboxylate (5f)
Yield: 60%; mp 150–152 °C. IR (KBr, cm−1): 2924 and 2855
(–CH2str), 1730 (C=Ostr ester), 1611 and 1572 and 1508 (C=Cstr aro-
1
matic), 1473 (–CHben), 1245 (C-O-Cstr of ester), 1164 (C-O-Cstr). H
NMR (CDCl3, 500 MHz, ppm) ␦: 8.88 (s, 3H), 8.35 (s, –CH=N), 7.78 (d,
6H), 7.13 (d, 6H), 6.95 (d, 6H), 6.93 (d, 6H), 4.72 (t, 6H), 4.33 (t, 6H),
4.00 (t, 6H), 1.79 (m, 6H), 1.46 (m, 6H), 1.33 (m, 48H), 0.88 (t, 9H). 13
C
Tris-(((4-octyloxyphenyl)methylidene)aminophenoxybutyl)
benzene-1,3,5-tricarboxylate (6d)
NMR (CDCl3, 100 MHz, ppm) ␦: 164.92, 161.76, 158.33, 156.82,
145.98, 135.10, 131.15, 130.37, 129.33, 122.23, 115.35, 114.71, 68.26,
66.18, 64.18, 32.00, 29.75, 29.71, 29.66, 29.50, 29.42, 29.29, 26.12,
22.76, 14.22. EI-MS m/z: 1434 (M+ + 1).
Yield: 60%; mp 147 °C. IR (KBr, cm−1): 2926 and 2859 (–CH2str),
1729 (C=Ostr ester), 1611 and 1509 (C=Cstr aromatic), 1468 (–CHben),
1243 (C-O-Cstr of ester), 1163 (C-O-Cstr). 1H NMR (CDCl3, 500 MHz,
ppm) ␦: 8.84 (s, 3H), 8.35 (s, –CH=N), 7.78 (d, 6H), 7.13 (d, 6H), 6.94
(d, 6H), 6.89 (d, 6H), 4.46 (t, 6H), 4.03 (t, 6H), 4.00 (t, 6H), 1.97 (m,
12H), 1.79 (m, 6H), 1.46 (m, 6H), 1.31 (m, 24H), 0.88 (t, 9H). 13C NMR
(CDCl3, 100 MHz, ppm) ␦: 165.08, 161.71, 158.05, 157.30, 145.33,
134.59, 131.44, 130.35, 129.29, 122.18, 114.99, 114.69, 68.25, 67.54,
65.55, 31.91, 29.44, 29.34, 29.28, 26.11, 25.64, 22.70, 14.15. EI-MS m/z:
1348.5 (M+).
Tris-(((4-tetradecyloxyphenyl)methylidene)aminophenoxyethyl)
benzene-1,3,5- tricarboxylate (5g)
Yield: 60%; mp 152–154 °C. IR (KBr, cm−1): 2920 and 2852
(–CH2str), 1732 (C=Ostr ester), 1611 and 1509 (C=Cstr aromatic), 1463
1
(–CHben), 1245 (C-O-Cstr of ester), 1163 (C-O-Cstr). H NMR (CDCl3,
500 MHz, ppm) ␦: 8.88 (s, 3H), 8.35 (s, –CH=N), 7.78 (d, 6H), 7.13 (d,
Published by NRC Research Press

Shanavas et al.
205
Tris-(((4-decyloxyphenyl)methylidene)aminophenoxybutyl)
benzene-1,3,5-tricarboxylate (6e)
Acknowledgments
A.S. thanks the Director of the Council of Scientific and In-
dustrial Research, Central Leather Research Institute (CSIR-
CLRI) for giving us permission to carry out the work in the
polymer lab, CLRI. The financial support of the University of
Madras and the CSIR, New Delhi in the form of fellowship is
gratefully acknowledged.
Yield: 60%; mp 147 °C. IR (KBr, cm−1): 2922 and 2853 (–CH2str),
1731 (C=Ostr ester), 1609 and 1508 (C=Cstr aromatic), 1469 (–CHben),
1247 (C-O-Cstr of ester), 1162 (C-O-Cstr). 1H NMR (CDCl3, 500 MHz,
ppm) ␦: 8.84 (s, 3H), 8.35 (s, –CH=N), 7.78 (d, 6H), 7.13 (d, 6H), 6.94
(d, 6H), 6.89 (d, 6H), 4.46 (t, 6H), 4.03 (t, 6H), 4.00 (t, 6H), 1.97 (m,
12H), 1.79 (m, 6H), 1.45 (m, 6H), 1.31 (m, 36H), 0.88 (t, 9H). 13C NMR
(CDCl3, 100 MHz, ppm) ␦: 165.08, 161.71, 158.05, 157.30, 145.33,
134.59, 131.44, 130.35, 129.29, 122.18, 115.01, 114.69, 68.25, 67.54,
65.55, 31.91, 29.66, 29.49, 29.34, 29.29, 26.11, 25.64, 22.77, 14.21.
EI-MS m/z: 1434 (M+ + 1).
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Yield: 60%; mp 139 °C. IR (KBr, cm−1): 2922 and 2851 (–CH2str),
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Tris-(((4-tetradecyloxyphenyl)methylidene)aminophenoxybutyl)
benzene-1,3,5-tricarboxylate (6g)
Yield: 60%; mp 146 °C. IR (KBr, cm−1): 2919 and 2850 (–CH2str),
1731 (C=Ostr ester), 1610 and 1508 (C=Cstr aromatic), 1469 (–CHben),
1248 (C-O-Cstr of ester), 1162 (C-O-Cstr). 1H NMR (CDCl3, 500 MHz,
ppm) ␦: 8.84 (s, 3H), 8.35 (s, –CH=N), 7.78 (d, 6H), 7.13 (d, 6H), 6.94
(d, 6H), 6.89 (d, 6H), 4.46 (t, 6H), 4.03 (t, 6H), 4.00 (t, 6H), 1.97 (m,
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22.77, 14.21. EI-MS m/z: 1602 (M+ + 1).
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Tris-(((4-hexadecyloxyphenyl)methylidene)aminophenoxybutyl)
benzene-1,3,5-tricarboxylate (6h)
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1732 (C=Ostr ester), 1625 (–C=Nstr– imine), 1608 and 1510 (C=Cstr
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158.05, 157.30, 145.33, 134.59, 131.44, 130.35, 129.29, 122.18, 115.01,
114.69, 68.25, 67.54, 65.55, 32.00, 29.78, 29.76, 29.69, 29.66, 29.49,
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Supplementary data
Supplementary data are available with the article through the
journal Web site at http://nrcresearchpress.com/doi/suppl/10.1139/
cjc-2012-0165.
Published by NRC Research Press