Synthesis and characterization of symmetrical eight aromatic ring containing bent-shaped material derived from benzophenone

Article abstract of DOI:10.1080/15421406.2010.526450

A new family of symmetrical eight aromatic ring-containing bent-shaped mesogens in which the central elbow is a ketone has been synthesized and characterized. The effect of the side chain on the mesomorphism has been studied. All the bent derivatives were found to exhibit mesomorphism. The higher homologues of the series exhibit the B1 phase and the lower homologues of the series show the B6 phase. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15421406.2010.526450

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Synthesis and Characterization of
Symmetrical Eight Aromatic Ring
Containing Bent-Shaped Material Derived
from Benzophenone
K. C. Majumdar a , T. Ghosh a & S. Chakravorty a
a Department of Chemistry , University of Kalyani , Kalyani, West
Bengal, India
Published online: 14 Dec 2010.
To cite this article: K. C. Majumdar , T. Ghosh & S. Chakravorty (2010) Synthesis and Characterization
of Symmetrical Eight Aromatic Ring Containing Bent-Shaped Material Derived from Benzophenone,
Molecular Crystals and Liquid Crystals, 533:1, 63-72, DOI: 10.1080/15421406.2010.526450
To link to this article: http://dx.doi.org/10.1080/15421406.2010.526450
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Mol. Cryst. Liq. Cryst., Vol. 533: pp. 63–72, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421406.2010.526450
Synthesis and Characterization of Symmetrical
Eight Aromatic Ring Containing Bent-Shaped
Material Derived from Benzophenone
K. C. MAJUMDAR, T. GHOSH, AND
S. CHAKRAVORTY
Department of Chemistry, University of Kalyani, Kalyani,
West Bengal, India
A new family of symmetrical eight aromatic ring-containing bent-shaped mesogens
in which the central elbow is a ketone has been synthesized and characterized. The
effect of the side chain on the mesomorphism has been studied. All the bent deriva-
tives were found to exhibit mesomorphism. The higher homologues of the series
exhibit the B1 phase and the lower homologues of the series show the B6 phase.
Keywords B1 phase; B6 phase; bent-shaped; eight aromatic rings; HRXRD;
mesogen
Introduction
Liquid-crystalline compounds have found wide application in scientific and techno-
logical areas, especially as flat panel displays [1], light-emitting diodes (OLED) [2],
anisotropic networks [3], and photoconductor and semiconduction materials [4].
Among numerous liquid-crystalline compounds of different shapes synthesized so
far by different research groups, bent-shaped liquid-crystalline compounds are the
most popular [5]. In 1996, Niori et al. [6] reported on ferroelectricity in a smectic
phase formed by banana-shaped Schiff’s base derivatives, first synthesized by
Matsunaga et al. [7]. The distinct molecular structure, unconventional mesomorphic
properties, occurrence of a spontaneous symmetry breaking in some cases, and
special switching behavior of some of their mesophases immediately attracted great
interest [8,9].
These types of materials form several new liquid-crystalline phases designated by
levels B1–B8 and some exhibit interesting ferro- and antiferroelectric properties,
although the molecules are achiral. With the exception of B3 and B4, all the Bn
mesophases represent a lamellar organization without in-plane order. B2, B6, and
B8 can be considered as the analogues of a ‘‘monolayer-smectic,’’ ‘‘intercalated-
smectic,’’ and ‘‘bilayer-smectic,’’ respectively. B5 represents an antiferroelectric
response. B1 and B7 correspond to more complex two-dimensional structures.
Address correspondence to K. C. Majumdar, Department of Chemistry, University of
Kalyani, Kalyani 741235, West Bengal, India. E-mail: kcm_ku@yahoo.co.in
63

64
K. C. Majumdar, T. Ghosh, and S. Chakravorty
In the bent-core molecule, the bending angle is the most important structural
feature for the formation of a polar-order mesophase. Depending on the chemical
structure of the molecule, the bending angle can be varied in the range 105–140ꢀ
in order to show the typical properties of the bent-shaped molecules [10]. Molecules
with a bending angle outside this limit in most cases show nonpolar mesophases [11].
Another interesting factor that influences the mesophase behavior of the bent-core
molecule is the number of phenyl rings in the bent-shaped molecules. Most of the
bent-core molecules discovered so far contain five aromatic rings with a bending
angle around 120ꢀ [12]. There are examples of modification of the bending angle
using five-member heterocyclic units or introducing substitution at the central core.
There are also limited examples of bent-core molecules with three [13], four [13],
six [14], seven [15], and nine aromatic rings [16]. For the past few years we have
synthesized several bent-shaped materials with unusual shapes [17] and studied their
structure–property relationships. In continuation of our earlier efforts, we have
undertaken a study to synthesize a homologous series of banana-shaped materials
containing eight aromatic rings with a deviation of bending angle from the usual
bending angle of bent-core materials. Liquid crystals with a total of eight rings will
possess high molar masses.
Liquid crystal displays [LCDs] derived from high-molecular-mass liquid crystals
are known to possess a number of advantages; for example simple and minimal
fabrication cost, flexibility, high brightness, small switching time, etc., over low-
molar-mass LCDs. These materials can be used in switchable windows, infrared
shutters, angular discriminating filters, thermo-optic and electro-optic switches etc.
[18–22]. Herein we report our results on the synthesis and characterization of
liquid-crystalline properties of the newly synthesized compounds with polarizing
optical microscopy (POM), differential scanning colorimetry (DSC), and high-
resolution X-ray diffraction (HRXRD) experiments.
Experimental
The methodology used for the synthesis of banana-shaped materials 7a-f is depicted
in Scheme 1. Benzophenone was first converted into its dinitro derivative (2), which
was then reduced to the diamine derivative (3). Compounds 6a-f were prepared by
Jones oxidation of ester aldehydes 5a-f followed by esterification with 4-hydroxy
benzaldehyde. The diamino derivative 3 was then heated under reflux with
4-(4-formylbenzoyloxy)phenyl 4-(alkyloxy)benzoates in absolute ethanol in the pres-
ence of a catalytic amount of glacial acetic acid to afford the homologous series 7a-f.
All the chemicals were procured from either Sigma Aldrich Chemicals Pvt. Ltd. or
Spectrochem, Mumbai, India. Silica gel [(60–120 mesh) was used for chromatographic
separation. Silica gel G (E-Merck, India) was used for thin-layer chromatography
(TLC). Petroleum ether refers to the fraction boiling between 60ꢀC and 80ꢀC. Infrared
(IR) spectra were recorded on a Perkin-Elmer L 120-000A spectrometer (nmax in cmꢁ1
)
on KBr disks. 1H nuclear magnetic resonance(NMR) (300MHz, 400 MHz, 500 MHz)
spectra were recorded on a Bruker DPX-300, DPX-400, DPX-500 spectrometer in
CDCl3 (chemical shift in d) with trimethyl siloxane (TMS) as internal standard.
Carbon, hydrogen, nitrogen (CHN) analyses were recorded on a 2400 series II CHN
analyzer (Perkin Elmer). The liquid-crystalline properties were established by thermal
microscopy (Nikon polarizing microscope LV100POL attached with an Instec hot and

Synthesis Eight Aromatic Ring
65
Scheme 1. Reaction conditions and reagents: (i) Conc. H2SO4, fuming HNO3, heat, 60ꢀC,
2 h; (ii) ethyl acctate, SnCl2, 2H2O, conc. HCl(cat) reflux, 4 h; (iii) SOCl2, reflux, 1 h;
(iv) 4-hydroxybenzaldehyde, DCM, aq K2CO3, Bu4NHSO4, 12 h; (v) Jone’s reagent, acctone,
r.t.; (vi) SOCl2, reflux, 1 h; (vii) 4-hydroxy benzaldehyde, DCM, aq K2CO3, Bu4NHSO4, 4 h;
(viii) Dry alcohol, Cat. AcOH, reflux, 4 h.
cold stage HCS302, with STC200 temperature controller configured for HCS302) and
the phase transitions were confirmed by DSC (Perkin-Elmer Diamond DSC system).
General Procedure for the Preparation of Compounds 2 and 3
3,30-Dinitrobenzophenone 2 and 3,30-diaminobenzophenone 3 were prepared
according to our earlier published procedure [10].
General Procedure for the Formation of Aldehydes 6a-f
A mixture of 4-(4-(hexadecyloxy)benzoyloxy)benzoic acid (500 mg, 0.99 mmol) and
SOCl2 was stirred at 100ꢀC for 3 h. After evaporation of the solvent, the residue
was dissolved in CH2Cl2 (20 mL). A solution of 4-hydroxybenzaldehyde (121 mg,
0.99 mmol) in CH2Cl2 (20 mL) and tetrabutyl ammonium hydrogen sulfate (catalytic
amount) was added to the stirred solution of acid chloride. To this reaction mixture
an aqueous solution of K2CO3 (274 mg, 1.98 mmol) was added slowly. After stirring
for 4 h at room temperature, the solution was washed with 5% HCl (2 ꢂ 20 mL) and
then with 5% aqueous NaOH (2 ꢂ 20 mL). The organic layer was dried (Na2SO4) and
the solvent evaporated under reduced pressure. The residue was purified by column
chromatography over silica gel using petroleum. ether-ethyl acetate (9:1) as an eluent
to give aldehyde 6a. The aldehydes 6b-f were prepared accordingly.
Compound 6a. White solid, yield 93%, IR (KBr, cmꢁ1): nmax: 2,916, 1,743, 1,703,
1
1,604. H NMR (CDCl3, 400 MHz): dH ¼ 10.03 (s, 1H), 8.27 (dd, 2H, J ¼ 2.0 Hz,
6.8 Hz), 8.14 (dd, 2H, J ¼ 2.0 Hz, 7.2 Hz), 7.98 (dd, 2H, J ¼ 1.6 Hz, 6.8 Hz),
7.38–7.44 (m, 4H), 6.98 (dd, 2H, J ¼ 2.0 Hz, 7.2 Hz), 4.04 (t, 2H, J ¼ 6.4 Hz), 1.81
(quint, 2H, J ¼ 7.2 Hz), 1.22–1.58 (m, 26H), 0.86 (t, 3H, J ¼ 6.8 Hz). Anal. Calcd.
for C37H46O6: C, 75.74; H, 7.90%. Found: C, 75.90; H, 7.68%.

66
K. C. Majumdar, T. Ghosh, and S. Chakravorty
Compound 6b. White solid, yield 95%, IR (KBr, cmꢁ1): nmax: 2,917, 1,735, 1,702,
1
1,603. H NMR (CDCl3, 400 MHz): dH ¼ 10.03 (s, 1H), 8.27 (dd, 2H, J ¼ 2.0 Hz,
6.8 Hz), 8.13 (dd, 2H, J ¼ 2.0 Hz, 7.2 Hz), 7.97 (dd, 2H, J ¼ 2.0 Hz, 6.8 Hz),
7.37–7.44 (m, 4H), 6.97 (dd, 2H, J ¼ 2.0 Hz, 7.2 Hz), 4.04 (t, 2H, J ¼ 6.4 Hz), 1.79
(quint, 2H, J ¼ 6.8 Hz), 1.27–1.58 (m, 22H), 0.87 (t, 3H, J ¼ 6.8 Hz). Anal. Calcd.
for C35H42O6: C, 75.24; H, 7.58%. Found: C, 75.48; H, 7.71%.
Compound 6c was prepared according to earlier published procedure [26].
Compound 6d. White solid, yield 90%, IR (KBr, cmꢁ1): nmax: 2,917, 1,741, 1,705,
1
1,605. H NMR (CDCl3, 400 MHz): dH ¼ 9.96 (s, 1H), 8.19 (dd, 2H, J ¼ 2.0 Hz,
7.2 Hz), 8.06 (dd, 2H, J ¼ 2.0 Hz, 7.2 Hz), 7.90 (dd, 2H, J ¼ 2.0 Hz, 6.8 Hz),
7.30–7.37 (m, 4H), 6.90 (d, 2H, J ¼ 9.2 Hz), 3.97 (t, 2H, J ¼ 6.4 Hz), 1.72 (quint,
2H, J ¼ 6.4 Hz), 1.15–1.56 (m, 14H), 0.80 (t, 3H, J ¼ 7.2 Hz). Anal. Calcd. for
C31H34O6: C, 74.08; H, 6.82%. Found: C, 74.24; H, 7.03%.
Compound 6e. White solid, yield 92%, IR (KBr, cmꢁ1): nmax: 2,920, 1,743, 1,706,
1
1,606. H NMR (CDCl3, 400 MHz): dH ¼ 10.04 (s, 1H), 8.27 (d, 2H, J ¼ 8.8 Hz),
8.14 (d, 2H, J ¼ 8.8 Hz), 7.97 (d, 2H, J ¼ 8.4 Hz), 7.41 (d, 2H, J ¼ 8.4 Hz), 7.38 (d,
2H, J ¼ 8.8 Hz), 6.98 (d, 2H, J ¼ 8.8 Hz), 4.04 (t, 2H, J ¼ 6.8 Hz), 1.79 (quint, 2H,
J ¼ 6.4 Hz), 1.25–1.63 (m, 10H), 0.88 (t, 3H, J ¼ 6.8 Hz). Anal. Calcd. for
C29H30O6: C, 73.40; H, 6.37%. Found: C, 73.57; H, 6.53%.
Compound 6f. White solid, yield 95%, IR (KBr, cmꢁ1): nmax: 2,920, 1,734, 1,703,
1
1,605. H NMR (CDCl3, 400 MHz): dH ¼ 10.03 (s, 1H), 8.27 (d, 2H, J ¼ 8.8 Hz),
8.14 (d, 2H, J ¼ 8.4 Hz), 7.97 (d, 2H, J ¼ 8.8 Hz), 7.41 (d, 2H, J ¼ 8.4 Hz), 7.38 (d,
2H, J ¼ 8.4 Hz), 6.98 (d, 2H, J ¼ 8.8 Hz), 4.04 (t, 2H, J ¼ 6.4 Hz), 1.81 (quint, 2H,
J ¼ 6.8 Hz), 1.27–1.57 (m, 6H), 0.87 (t, 3H, J ¼ 6.8 Hz). Anal. Calcd. for
C27H26O6: C, 72.63; H, 5.87%. Found: C, 72.85; H, 5.81%.
General Procedure for the Preparation of Compound 7A-E
0
3,3 -Diaminobenzophenone 3 (0.05 g, 0.02 mmol) was heated under reflux with
4-(4-formylbenzoyloxy)phenyl 4-(hexyloxy)benzoates 6a (0.28 g, 0.047 mmol) in
absolute ethanol in the presence of a catalytic amount of glacial acetic acid to afford
the desired product 7a. All the other compounds were prepared according to a simi-
lar procedure as mentioned above.
Compound 7a. Yellow solid, yield 97%, IR (KBr, cmꢁ1): nmax: 2,919, 1,744, 1,734,
1
1,663, 1,628, 1,603. H NMR (CDCl3, 500 MHz): dH ¼ 8.52 (s, 2H), 8.28 (d, 4H,
J ¼ 8.7 Hz), 8.14 (d, 4H, J ¼ 8.8 Hz), 7.99 (d, 4H, J ¼ 8.6 Hz), 7.70 (d, 2H,
J ¼ 7.5 Hz), 7.67 (s, 2H), 7.52 (t, 2H, J ¼ 7.6 Hz), 7.46 (d, 2H, J ¼ 7.8 Hz),
7.36–7.40 (m, 8H), 6.98 (d, 4H, J ¼ 8.9 Hz), 4.04 (t, 4H, J ¼ 6.5 Hz), 1.80 (quint,
4H, J ¼ 6.6 Hz), 1.26–1.50 (m, 52H), 0.87 (t, 6H, J ¼ 7.0 Hz).13C-NMR (CDCl3,
100 MHz): dC ¼ 196.2, 164.3, 164.1, 163.9, 160.3, 155.6, 153.5, 152.0, 138.6, 133.7,
132.4, 131.9, 131.3, 130.2, 129.2, 127.7, 126.5, 125.5, 122.6, 122.3, 122.2, 121.9,
120.9, 114.4, 68.4, 31.9, 29.7, 29.6, 29.5, 29.4, 29.0, 26.0, 22.7, 14.1. Anal. Calcd.
for C87H100N2O11: C, 77.42; H, 7.47; N, 2.08%. Found: C, 77.59; H, 7.63; N, 2.13%.
Compound 7b. Yellow solid, yield 98% IR (KBr, cmꢁ1): nmax: 2,919, 1,743, 1,664,
1,628, 1,603. 1H NMR (CDCl3, 500 MHz): dH ¼ 8.52 (s, 2H), 8.28 (d, 4H,

Synthesis Eight Aromatic Ring
67
J ¼ 8.6 Hz), 8.14 (d, 4H, J ¼ 8.8 Hz), 7.99 (d, 4H, J ¼ 8.6 Hz), 7.70 (d, 2H,
J ¼ 7.5 Hz), 7.67 (s, 2H), 7.52 (t, 2H, J ¼ 7.8 Hz), 7.46 (d, 2H, J ¼ 8.0 Hz), 7.36 (t,
8H, J ¼ 8.4 Hz), 6.98 (d, 4H, J ¼ 8.9 Hz), 4.04 (t, 4H, J ¼ 6.5 Hz), 1.80 (quint, 4H,
J ¼ 6.6 Hz), 1.27–1.56 (m, 44H), 0.87 (t, 6H, J ¼ 7.1 Hz).13C-NMR (CDCl3,
100 MHz): dC ¼ 191.0, 164.3, 164.1, 163.9, 160.3, 155.6, 153.5, 152.0, 138.6, 133.7,
132.4, 131.9, 131.3, 130.3, 129.2, 127.7, 126.5, 125.5, 122.3, 122.2, 121.9, 120.9,
114.4, 68.4, 31.9, 29.7, 29.6, 29.5, 29.4, 29.0, 25.9, 22.7, 14.1. Anal. Calcd. for
C83H92N2O11: C, 77.06; H, 7.17; N, 2.17%. Found: C, 77.29; H, 7.45; N, 2.11%.
Compound 7c. Yellow solid, yield 95%, IR (KBr, cmꢁ1): nmax: 2920, 1743, 1734,
1664, 1628, 1603. 1H NMR (CDCl3, 500 MHz): dH ¼ 8.52 (s, 2H), 8.28 (d, 4H,
J ¼ 9.2 Hz), 8.14 (d, 4H, J ¼ 8.9 Hz), 7.99 (d, 4H, J ¼ 8.8 Hz), 7.70 (d, 2H,
J ¼ 7.6 Hz), 7.67 (s, 2H), 7.52 (t, 2H, J ¼ 7.8 Hz), 7.46 (d, 2H, J ¼ 7.8 Hz),
7.36–7.40 (m, 8H), 6.98 (d, 4H, J ¼ 8.9 Hz), 4.04 (t, 4H, J ¼ 6.5 Hz), 1.80 (quint,
4H, J ¼ 6.5 Hz), 1.27–1.49 (m, 36H), 0.87 (t, 6H, J ¼ 7.1 Hz). 13C-NMR (CDCl3,
100 MHz): dC ¼ 196.2, 164.3, 164.1, 163.9, 160.3, 155.6, 153.5, 152.0, 138.6, 133.7,
132.5, 131.9, 130.3, 129.2, 127.7, 126.5, 125.5, 122.3, 122.2, 121.9, 120.9, 114.4,
68.4, 31.9, 29.7, 29.6, 29.5, 29.4, 29.1, 26.0, 22.7, 14.1. Anal. Calcd. for
C79H84N2O11: C, 76.67; H, 6.84; N, 2.26%. Found: C, 76.94; H, 7.03; N, 2.35%.
Compound 7d. Yellow solid, yield 92%, IR (KBr, cmꢁ1): nmax: 2,920, 2,850, 1,743,
1,734, 1,628, 1,603.1H NMR (CDCl3, 400 MHz): 8.52 (s, 2H), 8.28 (d, 4H,
J ¼ 8.8 Hz), 8.14 (d, 4H, J ¼ 8.8 Hz), 7.99 (d, 4H, J ¼ 8.4 Hz), 7.70 (d, 2H,
J ¼ 7.6 Hz), 7.68 (s, 2H), 7.52 (t, 2H, J ¼ 7.6 Hz), 7.46 (d, 2H, J ¼ 8.0 Hz),
7.36–7.43 (m, 8H), 6.98 (d, 4H, J ¼ 8.8 Hz), 4.04 (t, 4H, J ¼ 6.4 Hz), 1.79 (quint,
4H, J ¼ 6.4 Hz), 1.28–1.62 (m, 28H), 0.87 (t, 6H, J ¼ 6.8 Hz).13C-NMR (CDCl3,
100 MHz): dC ¼ 196.1, 164.3, 164.1, 163.9, 160.3, 155.6, 155.5, 152.0, 138.6, 133.7,
132.4, 131.9, 130.3, 129.2, 127.7, 126.6, 125.5, 122.3, 122.2, 121.9, 120.9, 114.4,
68.4, 31.9, 29.6, 29.4, 29.3, 29.1, 26.0, 22.7, 14.1. Anal. Calcd. for C75H76N2O11:
C, 76.25; H, 6.48; N, 2.37%. Found: C, 76.49; H, 6.63; N, 2.54%.
Compound 7e. Yellow solid, yield 98%, IR (KBr, cmꢁ1): nmax: 2,923, 1,734, 1,655,
1,627, 1,603. 1H NMR (CDCl3, 500 MHz): dH ¼ 8.52 (s, 2H), 8.28 (d, 4H,
J ¼ 8.6 Hz), 8.14 (d,4H, J ¼ 8.9 Hz), 7.99 (d, 4H, J ¼ 8.6 Hz), 7.70 (d, 2H,
J ¼ 7.6 Hz), 7.68 (s, 2H), 7.52 (t, 2H, J ¼ 7.6 Hz), 7.46 (d, 2H, J ¼ 8.4 Hz), 7.36 (t,
8H, J ¼ 8.4 Hz), 6.98 (d, 4H, J ¼ 8.9 Hz), 4.04 (t, 4H, J ¼ 6.6 Hz), 1.80 (quint, 4H,
J ¼ 6.6 Hz), 1.30–1.48 (m, 20H), 0.88 (t, 6H, J ¼ 7.0 Hz).13C-NMR (CDCl3,
75 MHz): dC ¼ 196.1, 164.3, 164.0, 163.8, 160.2, 155.5, 153.6, 153.5, 152.0, 138.6,
133.7, 132.4, 131.9, 130.3, 129.2, 127.6, 126.5, 125.5, 122.3, 122.2, 121.9, 120.9,
114.4, 68.4, 31.8, 29.3, 29.2, 29.0, 26.0, 22.6, 14.1. Anal. Calcd. for C71H68N2O11:
C, 75.78; H, 6.09; N, 2.49%. Found: C, 75.90; H, 6.26; N, 2.53%.
Compound 7f. Yellow solid, yield 90%, IR (KBr, cmꢁ1): nmax: 2,929, 1,736, 1,659,
1,627, 1,603. 1H NMR (CDCl3, 500 MHz): dH ¼ 8.52 (s, 2H), 8.28 (d, 4H,
J ¼ 8.6 Hz), 8.14 (d, 4H, J ¼ 8.9 Hz), 7.99 (d, 4H, J ¼ 8.6 Hz), 7.70 (d, 2H,
J ¼ 7.6 Hz), 7.67 (s, 2H), 7.52 (t, 2H, J ¼ 7.8 Hz), 7.46 (d, 2H, J ¼ 7.8 Hz),
7.36–7.39 (m, 8H), 6.98 (d, 4H, J ¼ 8.9 Hz), 4.04 (t, 4H, J ¼ 6.5 Hz), 1.81 (quint,
4H, J ¼ 6.6 Hz), 1.34–1.50 (m, 12H), 0.91 (t, 6H, J ¼ 7.0 Hz). 13C-NMR (CDCl3,
100 MHz): dC ¼ 196.2, 164.3, 164.1, 163.9, 160.3, 155.6, 153.5, 152.1, 138.6, 133.7,
132.4, 131.9, 130.3, 129.2, 127.7, 126.5, 125.5, 122.3, 122.2, 121.9, 120.9, 114.4,

68
K. C. Majumdar, T. Ghosh, and S. Chakravorty
68.4, 31.6, 29.1, 25.7, 22.6, 14.0. Anal. Calcd. for C67H60N2O11: C, 75.26; H, 5.66; N,
2.62%. Found: C, 75.40; H, 5.77; N, 2.81%.
Results and Discussion
The mesomorphism of all the compounds was investigated using polarizing
microscopy and differential scanning calorimetry. The DSC scans of each of these
compounds were run by raising their temperatures well above the clearing point.
The thermal behavior was found to be reproducible and all the compounds were
thermally stable. The transition temperatures and associated transition enthalpies
obtained from the DSC thermograms are summarized in Table 1. The peak tempera-
tures were given inꢀC and the numbers in the parentheses indicate the transition
enthalpy (DH) in kJ molÀ1. As can be seen from Table 1, all six compounds synthe-
sized were found to be liquid crystalline. All compounds except 7c were found to be
enantiotropic in nature.
In the DSC scan, compounds 7a, 7d, and 7e exhibited some solid–solid phase
transitions in addition to crystal–liquid-crystalline phase transitions and
liquid-crystalline phase–isotropic phase transitions. These types of transitions were
observed only in the DSC scan of those compounds in heating cycles. All the com-
pounds exhibited only one liquid-crystalline phase transition in both heating and
cooling cycles. The melting points as well the clearing temperatures decreased as
the chain length of R increased (compound 7b does not follow the sequence). On
Table 1. Phase transition temperatures (ꢀC) and associated enthalpies (DH, KJ molÀ1
of compounds 7a–f
)

Synthesis Eight Aromatic Ring
69
cooling from the isotropic liquid state, small batonnets were formed, which rapidly
turned into branched lancets (Fig. 1a) and finally coalesced into a mosaic-like texture
(Fig. 1b) with some spherulitic domains for compound 7b. Compounds 7a, 7c, and
7d exhibited a similar type of POM pictogram on cooling from the isotropic liquid.
On cooling from the isotropic liquid state, compound 7e showed the formation
of batonnets that coalesced to a fan texture (Fig. 1c). This mesophase could never be
aligned homeotropically; thus, the possibility of an SmA phase as typical for calami-
tic molecules can be excluded.
In order to determine the structure of the mesophases by XRD, measurements
were carried out in the mesophase temperature ranges of compounds 7c and 7f.
The XRD pattern of the mesophase obtained from compound 7c at 150ꢀC is shown
in Fig. 2. In the small-angle region two sharp reflection peaks were obtained at
˚
˚
d1 ¼ 35.48 A and d2 ¼ 30.98 A, these reflections can be identified as a B1 phase
according to the literature report [23].
The XRD pattern of the mesophase obtained from compound 7f at 160ꢀC
is shown in Fig. 3. Compound 7f in the mesophase exhibited only one sharp reflec-
˚
tion peak at d ¼ 27.25 A. In addition, both compounds exhibited a diffuse peak in
the wide-angle region, indicating a liquid-like corelation within the molecules. For
this compound, the layer spacing was close to the half length (calculated from mol-
ecular modeling) of the molecules. This d-value suggests an intercalated structure.
Figure 1. (a) branched lancets of 7b at 174ꢀC. (b) mosaic-like texture of 7b at 153ꢀC.
(c) Fanlike-texture of 7e at 193ꢀC.

70
K. C. Majumdar, T. Ghosh, and S. Chakravorty
Figure 2. X-ray diffraction diagram of compound 7c at 150ꢀC.
Microscopic observations as well as the X-ray data are in agreement with the results
obtained for intercalated SmC phases of other banana-shaped compounds, desig-
nated as B6 [23].
Yelamaggad et al. [24] reported ‘‘peelable banana’’-shaped materials containing
seven aromatic rings in which the shape biaxiality of a rod-like mesogen is enhanced
by covalently linking the mesogen to a bent-core molecule through a flexible poly-
methylene spacer. These compounds exhibited biaxial smectic and nematic phases.
Shen et al. [15] synthesized a series of achiral seven aromatic ring-containing bent-
shaped materials devoid of Schiff’s base units and observed three types of meso-
phases: rectangular columnar phase, designated as B1; intercalated fluid smectic
phase, Sintercal, and a nematic phase. Due to the high molar mass, not only the melt-
ing points but also the clearing temperatures were rather high. Recently, Gorecka
et al. [16] reported a hexagonal columnar phase for nine aromatic ring-containing
Figure 3. X-ray diffraction diagram of compound 7f at 160ꢀC.

Synthesis Eight Aromatic Ring
71
polycatenar bent-core molecules. Lasac et al. [25] reported a six aromatic ring-
containing bent-shaped mesogen with a 4,40 -dihydroxybenzophenone core. They
reported that the dicatenar compound displayed only the SmC phase, where as while
tetracatenar and polycatenar molecules displayed hexagonal columnar phases.
Recently we reported six aromatic ring-containing bent-shaped material with a
3,30-benzophenone core[17c]. The higher homologues of the series exhibit B2 phase
whereas lower homologues of the series did not exhibit any mesomorphism.
To conclude, we have mainly focused on eight aromatic ring-containing bent-
shaped materials with a 3,30-benzophenone core. All the compounds exhibited meso-
morphism. Four of the six bent-shaped materials exhibited a B1 phase and rest of the
materials exhibited a B6 phase. To the best of our knowledge, this is the first report
of eight aromatic ring-containing bent-core materials. In general, an increase in the
number of aromatic rings in the bent-core increases melting temperature and leads to
nonmesomorphic behavior, so the observation of mesomorphism in all the synthe-
sized bent-core materials is quite interesting. Moreover, the bending angle clearly
deviates from the usual bending angle of bent-core materials, but we did not observe
any other phase besides the general phases expected from the bent-core materials.
We feel that our synthesized compounds are novel due to variations in the aforesaid
two parameters.
Acknowledgment
We thank the DST (New Delhi) for financial assistance. Two of us (T.G. and S.C.)
are grateful to the CSIR (New Delhi) for their fellowships. We are also thankful to
Dr. Raghunathan of Raman Research Institute, Bangalore, for providing the
HRXRD data.
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