PAPER

www.rsc.org/materials | Journal of Materials Chemistry

Syntheses and characterization of novel asymmetric bent-core mesogens
exhibiting polar smectic phases
Kinga Gomola,ab Lingfeng Guo,a Surajit Dhara,ac Yoshio Shimbo,a Ewa Gorecka,b Damian Pociecha,bJozef Mieczkowskib and Hideo Takezoea
Received 17th November 2008, Accepted 3rd April 2009First published as an Advance Article on the web 11th May 2009
DOI: 10.1039/b820566c
Three series of asymmetric bent-core compounds were synthesized and their mesomorphic properties
were studied. All the compounds possess 2-methylresorcinol as a central unit and a stilbene bridge asa main element in the structure. Molecules of series I and series II possess only saturated terminal
chains while those of series III have one or both unsaturated chain/s. The mesophases werecharacterized by using optical polarizing microscopy, differential scanning calorimetry, X-ray
diffraction, electrooptic and dielectric measurements, and miscibility studies. All the compounds
exhibit the isotropic to SmAPR phase transition and the B1RevTilted phase at lower temperatures. For
compounds with one olefinic terminal chain, the temperature range of the SmAPR phase was found tobe narrower in comparison to compounds with both saturated terminal chains. A detailed dielectricinvestigation was carried out on both the SmAPR and B1RevTilted phases and two different types ofdynamical behaviour were observed.

1. Introduction
Liquid crystalline phases exhibited by compounds composed ofbent-core molecules have been an important subfield of liquid
crystals because of their great interest in academia and theirgrowing potential in display applications.1 The occurrence of
spontaneous polarization resulting from the polar packing of thebent molecules in the smectic layers that is permitted by thesymmetry2 made the subject more interesting from the fundamental point of view. The most frequently observed smectic
phase exhibited by bent-shaped molecules is the B2 or SmCP
phase in which the molecules are tilted with respect to the layer
normal. This phase may be regarded as the polar variant of the
SmC phase, with C2 symmetry. Depending on the stacking of thesmectic layers and the arrangement of the molecules in the layers,
the SmCP phase may exhibit antiferroelectric or ferroelectric
properties. In some rare cases the polarly ordered molecules are,on average, aligned orthogonal with respect to the layer planes
and a polar interdigitated biaxial SmA (SmAdb) phase results.3 It
is designated as SmAP, when polar switching is possible, and
SmAPA when an antiferroelectric order exists in neighboringlayers.4 Recently we found a polar non-tilted smectic phase,
SmAPR, with random polarization.5–7 This phase appears asuniaxial and nonpolar in the absence of an electric field, but thepolar order can be easily induced by the application of a weak
field.8
Very recently we also reported a novel display mode that canbe realised in the SmAPR phase.9 The most important advantages of this mode in the SmAPR phase are the fast response timea

Department of Organic and Polymeric Materials, Tokyo Institute ofTechnology, O-okayama, Meguro-ku, Tokyo, 152-8552, Japanb
Chemistry Department, Warsaw University, Al. Zwirki i Wigury 101, 02089 Warsaw, PolandcSchool of Physics, University of Hyderabad, 500046, India

4240 | J. Mater. Chem., 2009, 19, 4240–4247(100 ms), essentially no threshold voltage followed by continuous transmittance change, the high contrast ratio (3000:1), andthe wide viewing angle.9 To realise practical display applications,however, we have to solve a number of problems related to: wider
temperature range of SmAPR including room temperature,larger biaxiality, lower operating voltages, stable layer structure,etc. So far only one homologous series of compounds exhibiting
SmAPR is known. So the most urgent issue is to synthesize
a variety of compounds which show the SmAPR phase andcharacterize their mesogenic properties and display performance.
In this paper we report the synthesis of three series of novel bentcore asymmetric compounds in which the lack of symmetry isderived from different lateral substituents and differences in theterminal alkoxy chain lengths; and also in some compounds there
are different carbon-carbon double bonds in one or both of theterminal chains. It is expected that the introduction of the above
structural modifications may result in the decrease of the melting
transition temperature and wider range of the SmAPR phase.
Indeed, we observed the expected result in the transition
temperature but not in the temperature range; i.e., in thecompounds with one olefinic terminal chain, the isotropization
temperatures decreased and the SmAPR phase appeared inslightly narrower temperature ranges in comparison tocompounds with both saturated terminal chains. On the other
hand the SmAPR phase was destabilized for most of the purecompounds possessing unsaturated chains at both branches.

2. Results and discussion
Let us first show mesomorphic properties of the synthesizedcompounds of series I, II and III. The transition temperatures
and associated enthalpies of the compounds of series I (12-NClm) and in series II (14-NCl-m) are summarized in Table 1.
Numbers at both sides of the sample names stand for theThis journal is ª The Royal Society of Chemistry 2009

Table 1 Phase transition temperatures ( C) and corresponding enthalpies [J g1] for compounds of series I (n ¼ 12) and series II (n ¼ 14). Numbers at
both sides of the sample names stand for the numbers of carbons in both end chains. N and Cl stand for substituents NO2 and Cl at the left and rightwings, respectively

Sample nameCr

12-NCl-512-NCl-712-NCl-812-NCl-107
12-NCl-11
12-NCl-125–7
12-NCl-137
12-NCl-14
12-NCl-157
12-NCl-16
12-NCl-187
14-NCl-13
14-NCl-145,6,8
14-NCl-157
14-NCl-16

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




B1RevTilted
104.36 [18.06]
92.45 [13.68]
80.85 [8.75]
123.24 [24.70]
100.72 [45.50]
121.00 [15.70]
103.30 [43.90]
107.00 [51.72]
97.76 [50.19]
118.00 [23.12]
113.71 [20.89]
102.77 [38.58]
116.53 [22.06]
117.70 [21.27]
116.40 [22.47]





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113.03 [10.92]
125.93 [12.95]
127.61 [0.21]
128.30 [0.40]
125.02 [0.55]
125.90 [0.61]
123.30 [0.20]
124.92 [0.66]
123.25 [0.40]
125.97 [0.99]
121.39 [0.20]
126.81 [0.85]
127.72 [1.00]
126.70 [0.86]
125.31 [0.85]

numbers of carbon in both end chains. N and Cl stand for
substituents NO2 and Cl at left and right wings, respectively. A
few materials from series I and II have already been studied andcharacterized by Pociecha et al.6,7 and Shimbo et al.8,9 Asymmetry in the molecular structure in both of these series arises
from different lateral substituents and different lengths of saturated terminal chains except for 12-NCl-12 and 14-NCl-14 whereasymmetry is derived only from the different substituents. The
molecules of series I possess one unchanged dodecyloxy groupconnected to one of the arms, while the length of the second
terminal chain was varied. The short-tailed homologues 12-NCl5 and 12-NCl-7 form exclusively B1RevTilted, the columnar phasemade of layer fragments with 2D density modulation in the plane
perpendicular to the polarization direction.10 Compounds withmiddle and long terminal chains show two enantiotropic mesophases: a lower temperature B1RevTilted phase and a higher
temperature SmAPR phase with uniaxial optical properties, asconfirmed by conoscopic measurements.6 Introduction of a tetradecyloxy group as a terminal chain in series II (14-NCl-m)
resulted in only slightly increased isotropization temperature anddid not influence the range of the SmAPR mesophase during thevariations of length of the second tail.
Table 2 summarizes the transition temperatures and associatedenthalpies for final compounds (series III) with olefinic doublebond(s) in one or both the terminal chain(s). Nomenclature of
the sample names follows the same rules as for series I and II,
except for d which indicates the existence of double bond(s). Allasymmetric bent-core compounds exhibit enantiotropic SmAPR
and monotropic B1RevTilted phases except for two compounds:
11-NCl-11d with undecenyloxy and undecyloxy terminal groups
and 11d-NCl-11d with two unsaturated terminal chains, whichshow no liquid crystalline phases. Introduction of a vinyl group
This journal is ª The Royal Society of Chemistry 2009

SmAPR

Iso

DT (SmAPR)

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


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—
—
2.34
16.30
10.43
10.90
13.00
13.04
13.25
14.09
13.33
12.43
13.55
14.23
15.57

129.95 [12.96]
134.60 [9.72]
135.45 [10.59]
136.80 [10.80]
136.30 [6.60]
137.96 [10.53]
136.50 [10.15]
140.06 [9.77]
134.72 [8.40]
139.24 [9.01]
141.27 [9.08]
140.93 [8.70]
140.88 [8.55]

at the end of a terminal chain decreases the temperatures range of
SmAPR, but does not broaden the range of mesophase. Also the
B1RevTilted phase is supercooled and exists even at room
temperature. The presence of vinyl group at the end of theterminal chain, connected to the arm with chlorine 14-NCl-11d,
resulted in similar properties comparing to compounds possessing a terminal double bond connected to the arm with a nitro
group 11d-NCl-14.
We performed X-ray diffraction measurements in the SmAPR
phase as well as in the B1RevTilted phase on unoriented samples.
For the compound 11d-NCl-14 in the SmAPR phase, twocommensurate reflections could be seen in the small angle region
indicating a smectic ordering of the mesophase as shown in
Fig. 1. The layer spacing d gradually increases as the temperature
is lowered in the SmAPR phase. The X-ray pattern for B1RevTilted
is consistent with a 2D oblique lattice: one of the lattice
parameters, c, is close to the d value. The lattice parameter a,that is related to the length of the layer fragment, increases on
cooling, whereas the unit cell inclination angle, b slightly larger
than 90 , is almost temperature independent as also shown in
Fig. 1.
In order to examine the two mesophases observed in thesecompounds, we carried out miscibility studies between
compound 11d-NCl-14 and the well-studied 14-NCl-14.5–9 The
reference compound has the following sequence of transitions:Cr. 116.5  C B1Rev Tilted 127.7  C SmAPR 141.3  C Iso. The
binary phase diagram obtained is shown in Fig. 2. We can clearly
see that the two phases of compound 11d-NCl-14 are completely
miscible with the mesophases of the standard material over theentire composition range. It is noted that the temperature rangeof SmAPR is broadened and lowered in the mixtures comparing
to pure compounds.
J. Mater. Chem., 2009, 19, 4240–4247 | 4241

Table 2 Phase transition temperatures ( C) and corresponding enthalpies [J g1] for compounds of series III. Numbers at both sides of the sample
names stand for the numbers of carbons in both end chains. N and Cl stand for substituents NO2 and Cl at left and right wings, respectively. d stands forthe existence of double bond(s)Sample name

X

Y

Cr

11-NCl-11d
12-NCl-11d
14-NCl-11d
16-NCl-11d
18-NCl-11d
11d-NCl-14
11d-NCl-11d
11d-ClCl-11d
11d-NN-11d

NO2
NO2
NO2
NO2
NO2
NO2
NO2
Cl
NO2

Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
NO2



B1RevTilted
120.76 [10.95]
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

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SmAPR

105.97 [7.78]
106.10 [12.04]
149.77 [50.31]

119.37 [0.61]
118.50 [0.90]
118.50 [0.95]
117.10 [0.99]
115.83 [0.85]

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123.03 [9.36]
125.76 [10.41]
127.97 [9.79]
129.77 [9.16]
125.36 [9.92]

Iso

DT (SmAPR)

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—
3.66
6.39
9.47
12.67
9.53
—
—
—

Fig. 1 Variation of layer spacing d in the SmAPR phase of 11d-NCl-14
compound (solid circles) and parameters of 2D primitive unit cell in the
B1RevTilted phase: a (open squares), c (open circles) and angle b (opentriangles).

Fig. 3 Photomicrographs (200) of textures of 11d-NCl-14 (a) at 123  C(SmAPR phase) and (b) at 101  C (B1RevTilted phase). Cell thickness 5 mm.

Fig. 2 Binary phase diagram obtained for a mixture of compound 14NCl-14 and 11d-NCl-14. In the mixtures, the SmAPR temperature range
becomes broader compared with those of pure compounds. The continuous line is drawn as a guide to the eyes.

To study the electrooptic switching properties of the mesophases in these compounds, we carried out experiments usinga triangular wave electric field. ITO-coated glass plates were4242 | J. Mater. Chem., 2009, 19, 4240–4247

treated with a polyimide (AL1254) and cured at 180  C. Bothplates were rubbed antiparallel to each other for homogeneousalignment of the compound. An 8.4 mm thick cell was filled with
11d-NCl-14 in the isotropic phase by capillary action. Fig. 3(a)and (b) show optical photomicrographs taken in the SmAPR and
B1RevTilted phases, respectively. When this compound was sandwiched in a cell treated for homeotropic alignment and cooled
from the isotropic phase, a dark view indicating the uniaxial
SmA phase was observed (not shown). In a homogeneous cell at
120  C, one broad polarization current peak for each half cycle
was obtained as shown in Fig. 4(a). The single, broad switchingcurrent peak is characteristic of the switching process in
SmAPR.6 The broadness of the peak indicates field-inducedThis journal is ª The Royal Society of Chemistry 2009

Fig. 5 The real part of the dielectric permittivity (30 ) in the SmAPR and
B1RevTilted phases of 11d-NCl-14 as a function of frequency at various
temperatures. Solid symbols correspond to the data in the SmAPR phase(left vertical scale) and the open symbols correspond to the data in the
B1RevTilted phase (right vertical scale). The continuous lines are the fits to
the Cole–Cole formula. The high frequency mode is an artifact due to thelimited conductivity of ITO electrodes; this mode also exists in the
SmAPR phase.

Fig. 4 (a) Polarization reversal current in the SmAPR phase of 11d-NCl14 at 120  C under the application of a 280 Vpp triangular wave voltage of
frequency 36 Hz; (b) Ps value as a function of temperature. The decreaseof the Ps value in the B1RevTilted phase is due to insufficient voltage toswitch the polarization. Cell thickness 8.4 mm.

alignment of dipoles from a random orientation, through theLangevin process.8,9 In the SmAPR phase the electric polarization, calculated from the integral of the switching peak, increases
with lowering temperature (Fig. 4(b)) from 40 nC/cm2 at 124  C
to 160 nC/cm2 at 115  C, which indicates growing polar orderin this phase. The electric polarization decreases sharply in the
B1RevTilted phase, which is an artifact due to an insufficient field
for breaking the antiferroelectric coupling in this phase.
The dielectric measurements were conducted in a planar,aligned cell. Since below 10 Hz there is a strong ion contribution
to the dielectric response and the cut-off frequency for used ITO
cells is 1MHz, the dielectric measurements were limited toa frequency range 10 Hz–1 MHz. Only a single relaxation mode
was observed in the whole temperature range of liquid crystal
phases. At each temperature the relaxation frequency and modestrength were obtained by fitting experimental points to theCole–Cole formula; the parameter a which indicates the distribution of relaxation frequencies for the dielectric mode was close
to 0 except for in temperature range near the phase transition
where it increases to 0.4. The real part of the dielectric permittivity (30 ) as a function of frequency for the compound 11d-NCl14, at various temperatures is shown in Fig. 5. In the SmAPR
phase the dielectric relaxation frequency increases from 70 to 440
Hz (Fig. 6) and the value of dielectric permittivity decreases from60 to 20, with rising temperature. The high dielectric responsewith low relaxation frequency indicates the presence of a strong
This journal is ª The Royal Society of Chemistry 2009

Fig. 6 Variation of relaxation frequency in the SmAPR (left verticalscale) and B1RevTilted phases (right vertical scale) of 11d-NCl-14 asa function of temperature. Cell thickness 8.4 mm. The continuous lines are
drawn as a guide to the eyes.

positive dipolar correlation and dipole cooperative motions in
the SmAPR phase, which can be thought of as ferroelectric shortrange order in this phase. As indicated by dielectric measurement
results this ferroelectric order of dipoles becomes weaker withincreasing temperature.
In the B1RevTilted phase the dielectric permittivity is one orderof magnitude weaker and the dielectric relaxation frequency
much higher than in the SmAPR phase. The relatively small valueof the dielectric constant in the B1RevTilted phase indicates theantiferroelectric nature of this phase (Fig. 5). In the B1RevTilted
phase that is built of layer fragments, in which molecules aretilted from the layer normal and polarly ordered, the relaxation
mode can be ascribed to fluctuation in the azimuthal orientationof the molecules in the layer fragments. Therefore this mode canbe considered as an analogue of the antiphase azimuthal mode in
the antiferroelectric SmCA* phase made of calamitic or bent-coremolecules. Observation of such a mode in a broken-layer
J. Mater. Chem., 2009, 19, 4240–4247 | 4243

Fig. 7 Effect of DC bias voltage on the dielectric relaxation mode in (a)the SmAPR phase (119  C) and (b) the B1RevTilted phase (94  C) of 11dNCl-14. The relaxation frequency becomes higher with DC bias voltage
in the SmAPR phase. The dielectric response is suppressed by the DC bias
voltage in the B1RevTilted phase. Cell thickness 8.4 mm. The continuouslines are drawn as a guide to the eyes. The high frequency mode is an
artifact due to limited conductivity of ITO electrodes.

columnar phase has already been reported by Gorecka et al.11
However since the dielectric response in the B1RevTilted phase ismuch weaker and at higher frequency than in the antiferroelectric lamellar B2 phase,12 we can assume that azimuthal fluctuation of molecules must be strongly suppressed, most probably
due to some anchoring of the director at boundaries of the layer
fragments. The effect of DC bias on the relaxation mode was also
examined (Fig. 7(a)). In the SmAPR phase it is noted that therelaxation frequency begins to rise keeping the dielectric strength
the same in the field beyond 3 Vmm1. This might be expected, as
under DC bias the collective motion of the dipoles is faster due tothe enhanced correlation length and hence the relaxation
frequency is increased. At still higher bias field the relaxation
mode strength should be completely suppressed. However, fullsuppression was not observed due to the insufficient applied bias,
limited by the equipment used in the experiment. Similar fielddependent behaviour in the kHz frequency range was previously
described by Shimbo et al.8 However, in the compound studied
here the relaxation was observed in the lower frequency range,
probably due to the higher viscosity of the material, as the
SmAPR phase is observed at lower temperatures.

3. Experimental
The molecular structures of the synthesized compounds wereconfirmed by the following analytical methods. Infrared (IR)4244 | J. Mater. Chem., 2009, 19, 4240–4247

spectra were obtained using a JASCO FTIR-460 PLUS spectrometer. The carbon nuclear magnetic resonance (13C NMR)
spectra were recorded on Varian Unity Plus spectrometer operating at 75 MHz, whereas 1H NMR spectra were recorded at
300 MHz. Tetramethylsilane was used as an internal standard.
Chemical shifts were reported in ppm. Thin layer chromatography (TLC) analyses were performed on Merck 60 F254 silica gel
aluminium plates. Column chromatography was carried out at
atmospheric pressure using silica gel (100–200 mesh, Merck).
Compositions of the synthesized compounds were determined byelemental analysis. Phase transition temperatures and associatedenthalpies were determined by differential scanning calorimetry(Pyris Diamond Perkin-Elmer 7) at rates of 1–10  C/min undercooling and heating runs. Texture observation and the identification of the mesophases were done using a polarizing optical
microscope (Olympus, BX50) equipped with a hot stage andtemperature controller (Mettler Toledo FP 82). Electroopticalswitching behaviour was observed using a function generator
connected with a high voltage amplifier. The polarization
reversal current was measured by the standard triangular wave
technique.13 The current was measured across a 1 MU resistanceand the spontaneous polarization value was obtained by integrating the area under the curve. The dielectric measurement was
conducted in a planar aligned cell with an indium tin oxide(ITO)-coated electrode. A frequency response analyzer (Solatron
1255B) with a dielectric interface Solatron (1296) and a Mettler
temperature controller were used for this experiment.
The synthesis of novel bent-core compounds was achieved byfollowing the route depicted in Scheme 1.
3-Chloro-4-hydroxybenzaldehyde,
4-hydroxy-3-nitrobenzaldehyde,
11-bromo-1-undecene,
1-bromoundecane,
1-bromododecane, 1-bromotetradecane, 1-bromohexadecane, 1bromooctadecane, 2-methylresorcinol, DMAP and 18-crown-6,
was used as received from TCI (Tokyo Kasei Kogyo Co, Ltd),
Aldrich and Wako. Alkoxy aldehyde 2 was prepared fromhydroxyaldehyde 1 and the appropriate alkyl bromide or alkenyl
bromide using Williamson etherification, and then was applied ina Wittig reaction with methyl 4-(triphenylphosphoniummethyl)benzoate bromide. The obtained stilbene derivative 3 after
transformation into benzoic acid chloride 4, followed by esterification reaction with resorcinol derivatives 5 gave a mixture ofmonosubstituted 6 and disubstituted 7 products, which wereseparated by column chromatography. Disubstituted products 7
were examined for mesomorphic properties, while monoderivatives 6 were treated with the appropriate benzoic acidchloride, which resulted in the formation of asymmetrical bentcore compounds n-NCl-m.
Synthesis of 3-chloro-4-undec-10-enyloxybenzaldehyde 2
A mixture of 3-chloro-4-hydroxybenzaldehyde 1 (10 g, 64 mmol),
K2CO3 (11.5 g, 83 mmol), KI (13.8 g, 83 mmol) and 11-bromo-1undecene (15.4 ml, 70 mmol) in DMF (200 ml) was heated at 80
C for 8–10 h. Then water was added and the product was
extracted with toluene (3  20 ml), and the organic phase wasdried over MgSO4. The solvent was evaporated and the crude
product was crystallized several times from ethanol. Yield 70%.
2: NMR: d H (300 MHz, CDCl3) 9.84 (s, 1H, CHO), 7.91 (s,1H, Ar), 7.75 (dd, J1 ¼ 8.4 Hz, J2 ¼ 2.1 Hz, 1H, Ar), 7.02 (d,1This journal is ª The Royal Society of Chemistry 2009

Scheme 1 Synthetic route for the preparation of symmetric and asymmetric bent-core molecules for series I–III: i) R1(R2)Br, K2CO3, KI, DMF; ii)
methyl 4-(triphenylphosphoniummethyl)-benzoate bromide, CH2Cl2, THF, 18-crown-6; iii) KOH/EtOH; iv) (COCl)2/toluene; v) TEA, THF, DMAP,
room temp., 4–5 h; vi) TEA, THF, DMAP, reflux 8 h.

J ¼ 8.4 Hz, 1H, Ar), 5.86–5.75 (m, 1H, CH]CH2), 5.03–4.91 (m,2H, CH]CH2), 4.12 (t, J ¼ 6.3 Hz, 2H, OCH2CH2), 2.05–2.01(m, 2H, CH2), 1.90–1.83 (m, 2H, CH2), 1.53–1.31 (m, 12H, CH2);
d C (75 MHz, CDCl3) 189.66, 159.43, 139.12, 131.16, 130.40,
129.92, 123.85, 114.10, 112.37, 69.45, 33.74, 29.39, 29.33, 29.19,
29.04, 28.85, 28.79, 25.81. IR (KBr): nmax/cm1, 2918, 2851, 1683,
1596, 1499, 1322, 1287, 1056, 918. Elemental analysis calc. (%)
for C18H25ClO2 (308.15): C, 70.00, H, 8.16, Cl, 11.48; found C,
69.59, H, 8.14, Cl, 11.65.
13This journal is ª The Royal Society of Chemistry 2009

All alkoxy derivatives were synthesized using a similar
procedure.
Synthesis of 4-{(E)-2-[3-chloro-4-(undec-10enyloxy)phenyl]ethenyl}benzoic acid methyl ester 3
To a solution of methyl 4-(triphenylphosphoniummethyl)benzoate bromide (5.89 g, 12 mmol), dissolved in dry methyl
chloride (70 ml) and tetrahydrofuran (100 ml), anhydrous
J. Mater. Chem., 2009, 19, 4240–4247 | 4245

potassium carbonate (8.4 g, 61 mmol) followed by 18-crown-6(20 mg, 0.07 mmol) were added. The reaction mixture was stirred
at room temperature for 1 h. 3-Chloro-4-undec-10-enyloxybenzaldehyde (5.56 g, 18 mmol) was added to the yellow reaction
mixture which was heated under reflux for 20 h. After filtrationof inorganic salts, the reaction mixture was evaporated todryness and ethanol was added to the oily residue, which led tothe crystallization of product 3. According to the spectral data,
only (E)-stilbene was crystallized from the reaction mixture.
Yield 45%.
3: NMR: d H (300 MHz, CDCl3) 8.01 (d, J ¼ 8.4 Hz, 2H, Ar),
7.56 (d, J ¼ 2.4 Hz, 1H, Ar), 7.52 (d, J ¼ 8.1 Hz, 2H, Ar), 7.33
(dd, J1 ¼ 8.7 Hz, J2 ¼ 2.4 Hz, 1H, Ar), 7.03 (q, J ¼ 16.5 Hz, 2H,
CH]CH), 6.89 (d, J ¼ 8.7 Hz, 1H, Ar), 5.86–5.77 (m, 1H,
CH]CH2), 5.02–4.90 (m, 2H, CH]CH2), 4.04 (t, J ¼ 6.6 Hz,
2H, OCH2CH2), 3.92 (s, 3H, OCH3), 2.05–2.00 (m, 2H, CH2),
1.86–1.79 (m, 2H, CH2), 1.51–1.24 (m, 12H, CH2). d C (75 MHz,CDCl3) 166.83, 154.55, 141.71, 139.20, 130.18, 130.02, 129.52,
128.76, 128.10, 126.50, 126.41, 126.12, 123.34, 114.11, 113.18,
69.23, 52.04, 33.78, 29.45, 29.38, 29.28, 29.09, 29.03, 28.90, 25.90.
IR (KBr): nmax/cm1, 2924, 2852, 1713, 1593, 1501, 1469, 1284,
1192, 1108, 970. Elemental analysis calc. (%) for C27H33ClO3(440,21): C, 73.53, H, 7.54, Cl, 8.04; found C, 73.15, H, 7.60, Cl,
7.95
All stilbene derivatives were synthesized using a similar
procedure.
1

13Synthesis of 4-{(E)-2-[3-chloro-4-(undec-10enyloxy)phenyl]ethenyl}benzoic acid chloride 4

gel eluted with 0.5% of methanol in toluene. The disubstituted
product was crystallized from ethyl acetate. Yield of monosubstituted derivative ¼ 40%, disubstituted ¼ 30%. To the
mixture monosubstituted derivative 6 (0.40 g, 0.75 mmol),triethylamine (1 ml, 7.13 mmol), tetrahydrofuran (100 ml),
DMAP (20 mg, 0.16 mmol), {(E)-2-[4-nitro-3-(dodecyloxy)phenyl]ethenyl}benzoic acid 4 (0.42 g, 0.90 mmol) were added
and the mixture was kept under reflux for 8 h. The asymmetric
final product 12-NCl-11d was purified by column chromatography and double recrystallization from ethyl acetate. Yield of
12-NCl-11d ¼ 20% The range of yields of this step varied from
20–40%.
All asymmetrical products were synthesized using the sameprocedure.
6: NMR: d H (300 MHz, DMSO) 9.60 (s, 1H, Ar–OH), 8.10 (d,J ¼ 8.4 Hz, 2H, Ar), 7.77–7.74 (m, 3H, Ar), 7.55 (dd, J1 ¼ 8.7 Hz,
J2 ¼ 1.8 Hz, 1H, Ar), 7.34 (q, J ¼ 16.2 Hz, 2H, CH]CH), 7.14 (d,J ¼ 8.4 Hz, 1H, Ar), 7.05 (t, J ¼ 8.1 Hz, 1H, Ar), 6.75 (d, J ¼ 8.1
Hz, 1H, Ar), 6.38 (d, J ¼ 7.8 Hz, 1H, Ar), 5.83–5.70 (m, 1H,
CH]CH2), 4.99–4.88 (m, 2H, CH]CH2), 4.05 (t, J ¼ 6.3 Hz,
2H, OCH2CH2), 2.07–1.87 (m, 5H, Ar–CH3, CH2), 1.76 (m, 2H,
CH2), 1.42–1.13 (m, 12H, CH2); d C (75 MHz, DMSO) 164.01,
156.49, 153.93, 150.13, 142.66, 138.84, 130.24, 130.15, 130.08,
127.88, 127.24, 127.17, 126.62, 126.33, 126.22, 121.87, 116.78,
114.63, 113.83, 112.67, 68.66, 40.33, 40.05, 39.77, 39.50, 39.22,
38.94, 38.66, 33.20, 28.95, 28.79, 28.66, 28.51, 28.30, 25.39, 9.13.
IR (KBr): nmax/cm1, 3348, 2927, 2851, 1692, 1593, 1497, 1274,
1261, 1098. Elemental analysis calc. (%) for C33H37ClO4 (532.24):
C, 74.35, H, 7.00, Cl, 6.65; found C, 74.61, H, 6.89, Cl, 6.71.
7 (11d-ClCl-11d): NMR: d H (300 MHz, CDCl3) 8.20 (d, J ¼
8.4 Hz, 4H, Ar), 7.63–7.60 (m, 6H, Ar), 7.39–7.35 (dd, J1 ¼ 2.1
Hz, J2 ¼ 8.7 Hz, 2H, Ar), 7.33–6.91 (m, 9H, Ar, CH]CH), 5.89–
5.75 (m, 2H, CH]CH2), 5.03–4.91(m, 4H, CH]CH2), 4.06 (t, J¼ 6.6 Hz, 4H, OCH2CH2), 2.12 (s, 3H, Ar–CH3), 2.08–2.01 (m,4H, CH2), 1.90–1.81 (m, 4H, CH2), 1.50–1.32 (m, 24H, CH2); d C(75 MHz, CDCl3) 164.35, 154.65, 150.29, 142.56, 139.18, 130.68,
130.05, 130.00, 128.15, 127.64, 126.54, 126.33, 126.27, 123.94,
123.33, 119.89, 114.11, 113.12, 69.19, 33.78, 29.45, 29.37, 29.28,
29.08, 29.01, 28.88, 25.89, 10.09 IR (KBr): nmax/cm1, 2924, 2853,
1723, 1593, 1507, 1260, 1103. Elemental analysis calc. (%) for
C59H66Cl2O6 (942.06): C, 75.22, H 7.06, Cl, 7.53; found C, 74.96,
H, 7.05, Cl, 7.78.
12-NCl-11d: NMR: d H (300 MHz, CDCl3) 8.23–8.19 (m, 4H,Ar), 8.02 (d, J ¼ 2.4 Hz, 1H, Ar), 7.69–7.59 (m, 6H, Ar), 7.36 (dd,J1 ¼ 8.7 Hz, J2 ¼ 2.1 Hz, 1H, Ar), 7.33–6.91 (m, 9H, Ar,
CH]CH), 5.86–7.75 (m, 1H, CH]CH2), 5.03–4.92 (m, 2H,
CH]CH2), 4.13 (t, J ¼ 6.3 Hz, 2H, OCH2CH2), 4.06 (t, J ¼ 6.6
Hz, 2H, OCH2CH2), 2.13 (s, 3H, Ar–CH3), 2.06–2.02 (m, 2H,
CH2), 1.88–1.83 (m, 4H, CH2), 1.50–1.27 (m, 30H, CH2), 0.88 (t,J ¼ 6.6 Hz, 3H, CH2CH3); d C (75 MHz, CDCl3) 164.28, 152.25,
150.33, 150.28, 142.61, 141.97, 139.22, 132.07, 130.77, 130.71,
130.11, 130.03, 129.19, 128.86, 128.17, 127.92, 127.66, 126.37,
126.30, 123.96, 123.45, 123.38, 114.67, 114.11, 113.17, 69.88,
69.27, 33.80, 31.90, 29.62, 29.56, 29.49, 29.46, 29.38, 29.34, 29.29,
29.26, 29.09, 29.02, 28.90, 25.91, 25.80, 22.68, 14.12, 10.11. IR(KBr): nmax/cm1, 2923, 2853, 1732, 1723, 1603, 1592, 1535, 1262,
1231, 1104, 1081. Elemental analysis calc. (%) for C60H70ClNO8(954.63): C, 74.40, H 7.28, N, 1.45, Cl, 3.66; found C, 74.30, H,
7.06, N, 1.46, Cl, 3.57.
1

13

1

To the solution of 4-{(E)-2-[3-chloro-4-(undec-10-enyloxy)phenyl]ethenyl}benzoic acid methyl ester (3 g, 6.81 mmol) in
ethanol (200 ml), a solution of potassium hydroxide (1.15 g, 20.4mmol) in ethanol (15 ml) was added and the mixture was heatedunder reflux for 10–12 h. After cooling the solution, crude
product precipitated as a potassium salt. After drying undervacuum over sodium hydroxide, the obtained salt was suspended
in toluene (200 ml) and treated with an excess of oxalyl chloride(5 ml). The reaction mixture was heated under reflux for 8 h.
After filtration of the precipitated potassium chloride, theremaining solution was evaporated to dryness. The productslowly solidified at room temperature with a yield of 98%.
All benzoic acid chlorides were synthesized using a similar
procedure.
Synthesis of 2-methyl-1,3-{[4-{(E)-2-[4-(dodecyloxy)-3nitrophenyl]-1-ethenyl}benzoyloxy]methyl}benzyl-4-{(E)-2-[3chloro-4-(undec-10-enyloxy)phenyl]-1-ethenyl}benzoate 12-NCl11d

13

1

13

To a solution of 2-methylresorcinol (1.2 g, 9.67 mmol), triethylamine (1 ml, 7.13 mmol) and DMAP (20 mg, 0.16 mmol) in
tetrahydrofuran (100 ml), 4-{(E)-2-[3-chloro-4-(undec-10-enyloxy)phenyl]ethenyl}benzoic acid chloride 4 (0.86 g, 1.93 mmol)
in dichloromethane (30 ml) was added dropwise. The reaction
mixture was stirred at room temperature for 4–5 h, then thesolvent was evaporated to dryness under reduced pressure. The
obtained mixture of monosubstituted 6 and disubstituted 7
products was separated by column chromatography using silica
4246 | J. Mater. Chem., 2009, 19, 4240–4247

This journal is ª The Royal Society of Chemistry 2009

14-NCl-13: NMR: d H (200 MHz, CDCl3) 8.17–8.24 (m, 4H,Ar), 8.02 (d, J ¼ 2.2 Hz, 1H, Ar), 7.54–7.72 (m, 6H, Ar), 7.03–
7.40 (m, 9H, Ar, CH]CH), 6.91 (d, J ¼ 8.2 Hz, 1H, Ar), 3.90–
4.00 (m; 4H, OCH2CH2), 2.12 (s, 3H, Ar-CH3), 1.75–1.94 (m,4H, CH2), 1.26–1.70 (m, 42H, CH2), 0.88 (t, J ¼ 6.0 Hz, 6H,
CH2CH3); d C (50 MHz; CDCl3) 164.56, 164.45, 154.88, 152.41,
150.53, 150.47, 142.79, 142.15, 132.24, 130.91, 130.87, 130.28,
130.19, 129.36, 129.02, 128.35, 128.32, 128.04, 127.82, 126.75,
126.54, 126.43, 126.43, 124.12, 123.6, 123.54, 114.84, 113.34,
70.04, 69.41, 32.09, 29.89, 29.85, 29.77, 29.70, 29.55, 29.46, 29.24,
29.10, 26.11, 26.02, 22.87, 14.32, 14.14, 10.18. IR (KBr): nmax/cm1: 2922, 2852, 1735, 1603, 1534, 1467, 1266, 1231, 1104.
Elemental analysis calc. (%) for C64H80ClNO8 (1025.56): C,
74.86, H, 7.85, N, 1.36, Cl, 3.45; found C, 74.50, H, 7.90, N, 1.45,
Cl, 3.30.
1

S. D. are respectively supported by Japan Society for Promotionof Science and the DST, Govt. of India for the project number
SR/FTP/PS-48/2006 under the SERC Fast Track Scheme.

13

4. Conclusions
The mesomorphic behaviour of several asymmetric bent-corecompounds derived from 2-methylresorcinol, containing
a lateral chloro/nitro group and saturated or unsaturated
terminal alkoxy chain/s, has been investigated. The mesophases
exhibited by these compounds have been characterized as thelamellar uniaxial polar SmA phase (SmAPR) and the brokenlayer type columnar B1RevTilted phase. The cross-section of theblock forming the B1RevTilted phase contains 20–30 molecules.
Introduction of a double bond in the terminal end chain lowers
the isotropization temperatures but also slightly destabilizes thesmectic phase. A similar observation was reported by Achten
et al.14 The dielectric relaxation in the SmAPR phase is muchstronger than in the B1RevTilted phase due to the cooperative
dipolar relaxation. In the antiferroelectric B1RevTilted phase thedielectric response arises from weak anti-phase fluctuation of thepolarization vector in neighbouring layer fragments.

Acknowledgements
This work is partly supported by a Grant-in-Aid for Scientific
Research (S) (16105003) from the Ministry of Education,
Culture, Science, Sports and Technology of Japan. K. G. andThis journal is ª The Royal Society of Chemistry 2009

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