Synthesis and characterization of unsymmetrical five-ring achrial banana-shaped compounds with a B2 phase

Article abstract of DOI:10.1080/15421400902841445

Two series of unsymmetrical banana-shaped materials have been prepared with laterally substituted hydroxy and nitro groups. All the compounds exhibit liquid crystalline properties. The syntheses and liquid crystalline properties of these compounds are dis

Full text of DOI:10.1080/15421400902841445

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Synthesis and Characterization
of Unsymmetrical Five-
Ring Achrial Banana-Shaped
Compounds With a B2 Phase
K. C. Majumdar a , S. Chakravorty a & N. Pal a
a Department of Chemistry , University of Kalyani ,
Kalyani, Nadia, West Bengal
Published online: 03 Jun 2009.
To cite this article: K. C. Majumdar , S. Chakravorty & N. Pal (2009) Synthesis and
Characterization of Unsymmetrical Five-Ring Achrial Banana-Shaped Compounds
With a B2 Phase, Molecular Crystals and Liquid Crystals, 503:1, 112-125, DOI:
10.1080/15421400902841445
To link to this article: http://dx.doi.org/10.1080/15421400902841445
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Mol. Cryst. Liq. Cryst., Vol. 503, 112–125, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400902841445
Synthesis and Characterization of Unsymmetrical
Five-Ring Achrial Banana-Shaped Compounds
With a B2 Phase
K. C. Majumdar, S. Chakravorty, and N. Pal
Department of Chemistry, University of Kalyani, Kalyani,
Nadia, West Bengal
Two series of unsymmetrical banana-shaped materials have been prepared with
laterally substituted hydroxy and nitro groups. All the compounds exhibit liquid
crystalline properties. The syntheses and liquid crystalline properties of these
compounds are discussed.
Keywords: B2 phase; lamellar reflection; lateral substitution; unsymmetrical bent
shaped
INTRODUCTION
Liquid crystalline phases exhibited by compounds composed of bent
core (BC) molecules, which form the basis for a new sub field, are
being investigated with renewed interest. This is not only because
of their unique feature of showing chiral form of layered (smectic)
[1,2] or two-dimensional (columnar) [3,4] liquid crystalline phases
exhibiting spontaneous polarization, but also due to the formation
of super helical structures [5] though the materials themselves are
achiral. In general, the mesophases formed by these compounds
are termed as ‘‘Banana’’ phases designated as B1–B8, which have
been identified, based on their textural appearances and X-ray dif-
fraction pattern. The B3 and B4 phases are crystalline mesophases,
while the others are genuine liquid crystals. The most commonly
encountered phases are B1, B2, B7, which have, therefore, been
investigated extensively. Synthesis of both symmetrical and nonsym-
metrical bent core compounds with different chemical architecture
Address correspondence to K. C. Majumdar, Department of Chemistry, University of
Kalyani, Kalyani 741235, Nadia, West Bengal. E-mail: kcm_ku@yahoo.co.in
112

Five-Ring Achrial Banana-Shaped Compounds
113
is of topical interest for understanding the relationship between
chemical structure and mesophase behavior. Introduction of lateral
substituents on the arms of BC molecules for modifying mesomorphic
properties has been carried out [6–10] on a number of different
systems. The influence of lateral substituents on the mesophase
behavior in banana-shaped molecules is much more pronounced than
that in calamatic molecules. The introduction of substituents on the
central core can cause a change of the conformation, e.g., a change of
the bending angle, which dictates whether conventional phase of rod-
like molecules or ‘‘banana phases’’ are formed. Systematic studies
performed on the parent series of five-ring banana-shaped mesogens
has been made to investigate the sensitivity of such compounds
to lateral substitutents attached to the central ring assuming the
following common structure (Fig. 1).
Groups like cyano, methyl, or methoxy at the top of the bent mole-
cules in position R5 prevent the existence of any mesophases [11]. In
contrast, the introduction of small groups like methyl or nitro into
the obtuse angle of the molecules, i.e., in position R2, results in high
mesophase stability [12,13]. One chlorine atom in R4 position results
into substances having a B2 Phase [14]. The additional introduction
of a second chlorine atom at R6 position causes a change of the type
of mesophase from the B-phase to nematic and smectic phases [15].
This surprising behavior has been explained by considering the confor-
mation of the molecules. Nuclear Magnetic Resonance (NMR) investi-
gation in the liquid crystalline state has revealed that the bending
angle between two halves of the bent molecules is changed by substi-
tutents which are situated near the connecting groups. Thus, the
bending angle of about 120ꢀ, expected for the 1,3-phenyl unit was
found for the parent molecule which are unsubstituted at the central
ring. This bending angle is increased by the 4-chlorine atom to 134ꢀ,
and by two chlorine atoms at 4,6-position is about 165ꢀ. In the latter
case, the molecule exhibits a rather rod-like conformation. Therefore,
FIGURE 1 General structure of a bent-shaped molecule.

114
K. C. Majumdar et al.
the existence of phases which are typical for calamitic mesogens is not
surprising. Generally, the substituents attached to the central aro-
matic unit make it possible to vary the bending angle in a delicate
manner. Thus, the phase sequences SmA-SmC-B2 and N-SmA-SmC-
B2 were found with 4-cyano substituted resorcinol derivatives [16].
On the other hand, lateral substituents on the central core, middle
rings, or terminal rings, of five-ring banana-shaped materials can
change the packing of the molecules if the substituents are bulky, or
influence the polar properties of the molecules. It is also well known
that by increasing the number of aromatic rings along the bent core,
the thermal stabilities as well as thermal ranges of the mesophases
are increased. The phase sequence as a function of carbon atom on
ascending a homologous series is well understood [17,18]. Symmetrical
bent core molecules comprising an angular central core substituted
with two identical linear rod-like mesogenic segments generally exhi-
bit higher transition temperatures. To reduce the temperatures and to
perhaps bridge the gap between bent core and rod-like liquid crystal,
nonsymmetrical bent core molecules have been designed and synthe-
sized. In these materials, either the two halves of the molecules or
the linking functional groups attached to angular central core are dif-
ferent [19–21]. In continuation to our study on the synthesis and char-
acterization of liquid crystalline molecule [22–23] here in we report
the synthesis and evaluation of the mesomorphic behavior of nonsym-
metric five ring achiral banana shaped liquid crystals consisting of two
chemically nonidentical rod-like anisometric segments.
EXPERIMENTAL
All the chemicals were procured from either Sigma Aldrich Chemicals
Pvt. Ltd. or Spectrochem, India. Silica gel [(60–120 mesh) was used for
chromatographic separation. Silica gel G [E-Merck (India)] was used
for TLC. Petroleum ether refers to the fraction boiling between 60ꢀC
and 80ꢀC. IR spectra were recorded on a Perkin-Elmer L 120–000A
spectrometer (kmax in cmꢁ1) on KBr disks. UV absorption spectra were
recorded in CHCl3 on a Shimadzu UV-2401PC spectrophotometer
1
(kmax in nm). H NMR (400 MHz) spectra were recorded on a Bruker
DPX-500 spectrometer in CDCl3 (chemical shift in d) with TMS as
internal standard. The liquid crystalline properties were established
by thermal microscopy (Nikon polarizing microscope LV100POL
attached with Instec hot and cold stage HCS302, with STC200 tem-
perature controller configured for HCS302 and the phase transitions
were confirmed by differential scanning calorimetry (Perkin–Elmer
Diamond DSC Pyris1 system).

Five-Ring Achrial Banana-Shaped Compounds
115
SYNTHESIS
The aforesaid series of unsymmetrical banana-shaped materials were
prepared by acid catalyzed condensation of the key intermediate,
namely, 4-formyl-3-hydroxyphenyl 4(n-alkyloxy)-benzoate (7a–d) or
4-formyl-3-nitrophenyl 4(n-alkyloxy)-benzoate (7e–h) with 4-[(3-ami-
nophenoxy)carbonyl]phenyl 4-(n-alkyloxy)benzoate (5a–c) in ethanol
as depicted in Scheme 1. The intermediates (7a–f) were obtained by
SCHEME 1 Reagents and conditions: (i) SOCl2 reflux, 4 hrs, (ii) p-hydroxy
benzaldehyde, CH2Cl2, DMAP, NEt3. rt 4 hr, (iii) Jone’s Oxidation, (iv)
m-nitrophenol, CH2Cl2, DCC, DMAP, (v) H2 Pd-C, Ethylacetate, (vi) 2,4-
dihydroxy benzaldehyde or 4-hydroxy-3-nitrobenzaldehyde, CH2Cl2, DCC,
DMAP, (vii) dehydrated alcohol, AcOH (cat), reflux, 4 h.

116
K. C. Majumdar et al.
esterification of 4-(n-alkyloxy)benzoicacid with 2,4-dihydroxybenz-
aldehyde or 3-nitro-4-hydroxybenzaldehyde in dry dichloromethane
in the presence of dicyclohexylcarbodiimide (DCC), and a catalytic
amount of DMAP. Amines (5a–c) were prepared in five steps starting
from 4-(n-alkyloxy)benzoic acid (1a–c). The compounds were charac-
1
terized from their IR, and H-NMR spectra.
General Procedure for the Esterfication to Prepare 4-
Formyl-3-hydroxyphenyl 4(N-alkyloxy)-benzoate (7a–d) or
4-Formyl-2-nitrophenyl 4(N-alkyloxy)-benzoate (7e,f)
These were prepared according to the reported procedure [24].
General Procedure for the Preparation of 4-[(3-
Aminophenoxy)carbonyl]phenyl 4-(N-alkyloxy)
benzoate 5a–c
These were prepared according to published procedure [25].
General Procedure for the Schiff’s Base Formation 8a–l
A mixture of 4-[(3-aminophenoxy)carbonyl]phenyl 4-(n-hexadecaloxy)-
benzoate 5a (0.1 g, 0.17 mmol) and 4-formyl-3-hydroxyphenyl 4(n-hex-
yloxy)-benzoate 7a (0.08 g, 0.17 mmol) was refluxed in absolute
ethanol (10 mL) in the presence of a catalytic amount of glacial acetic
acid for 1 h. The schiff’s base 8a was precipitated out from reaction
mixture. It was collected, washed repeatedly with hot ethanol, dried
in vacuum. Similarly the other derivatives 8b–l were prepared.
Compound 8a: IR (KBr): n ¼ 3450, 2915, 1735, 1717, 1608 cmꢁ1
,
1H NMR (CDCl3, 400 MHz): dH ¼ 13.34 (s, 1H, OH), 8.64 (s, 1H,
CH¼N), 8.26 (d, 2H, J ¼ 8.4 Hz, ArH), 8.10–8.14 (m, 4H, ArH),
7.45 (t, 1H, J ¼ 8.0 Hz, ArH), 7.41 (d, 1H, J ¼ 8.0 Hz, ArH), 7.35
(d, 2H, J ¼ 8.4 Hz, ArH), 7.14–7.20 (m, 3H, ArH), 6.94–6.98 (m,
4H, ArH), 6.87 (d, 1H, J ¼ 2.0 Hz, ArH), 6.81 (dd, 1H, J ¼ 2.0 Hz,
8.0 Hz, ArH), 4.01–4.05 (m, 4H, OCH2), 0.81–1.84 (m, 62H, aliphatic
hydrogen are overlapped). Anal. Calcd. for C66H87NO9; C, 76.34; H,
8.44; N, 1.35%. Found: C, 76.54; H, 8.60; N, 1.48%.
1
Compound 8b: IR (KBr): H NMR (CDCl3, 400 MHz): dH ¼ 13.34 (s,
1H, OH), 8.66 (s, 1H, CH¼N), 8.28 (dd, 2H, J ¼ 2 Hz, 6.8 Hz,
ArH), 8.11–8.15 (m, 4H, ArH), 7.47 (t, 1H, J ¼ 8.0 Hz, ArH), 7.43
(d, 1H, J ¼ 8.5 Hz, ArH), 7.37 (dd, 2H, J ¼ 2 Hz, 6.8 Hz, ArH),
7.16–7.22 (m, 3H, ArH), 6.96–7.00 (m, 4H, ArH), 6.89 (d, 1H,

Five-Ring Achrial Banana-Shaped Compounds
117
J ¼ 2.2 Hz, ArH), 6.83 (dd, 1H, J ¼ 2.2 Hz, 8.5 Hz, ArH), 4.03–4.07
(m, 4H, OCH2), 0.81–1.81 (m, 58H, aliphatic hydrogens are over-
lapped). 13C NMR (CDCl3, 125 MHz): 164.7, 164.6, 164.2, 164.1,
163.0, 155.9, 152.1, 150.0, 133.8, 132.8, 132.7, 132.2, 130.6, 127.0,
122.5, 121.6, 121.3, 114.9, 114.8, 114.7, 113.6, 68.8, 32.3, 30.1,
30.0, 30.0, 29.9, 29.7, 29.5, 26.3, 23.1, 14.5.
Anal. Calcd. for C64H83NO9; C, 76.08; H, 8.28; N, 1.39%.
Found: C, 76.36; H, 8.48; N, 1.49%.
Compound 8c: IR (KBr): n ¼ 3454, 2919, 1740, 1714, 1607 cmꢁ1
,
1H NMR (CDCl3, 400 MHz): dH ¼ 13.31 (s, 1H, OH), 8.65 (s, 1H,
CH¼N), 8.26 (dd, 2H, J ¼ 2 Hz, 7.0 Hz, ArH), 8.10–8.14 (m, 4H,
ArH), 7.45 (t, 1H, J ¼ 8.0 Hz, ArH), 7.41 (d, 1H, J ¼ 8.4 Hz, ArH),
7.35 (dd, 2H, J ¼ 2 Hz, 6.8 Hz, ArH), 7.16–7.21 (m, 3H, ArH),
6.96–7.05 (m, 4H, ArH), 6.88 (d, 1H, J ¼ 2.2 Hz, ArH), 6.83 (dd,
J ¼ 2.2 Hz, 8.4 Hz, 1H, ArH), 4.03–4.07 (m, 4H, OCH2), 0.81–1.80
(m, 54H, aliphatic hydrogens are overlapped). Anal. Calcd. for
C62H79NO9; C, 75.81; H, 8.11; N, 1.43%. Found: C, 76.03; H, 8.22;
N, 1.50%.
Compound 8d: IR (KBr): n ¼ 3455, 2918, 1739, 1719, 1609 cmꢁ1
,
1H NMR (CDCl3, 400 MHz): dH ¼ 13.34 (s, 1H, OH), 8.64 (s, 1H,
CH¼N), 8.27 (d, 2H, J ¼ 8.0 Hz, ArH,), 8.11–8.15 (m, 4H, ArH),
7.45 (t, 1H, J ¼ 8.0 Hz, ArH), 7.41 (d, 1H, J ¼ 8.4 Hz, ArH), 7.36
(d, 2H, J ¼ 8.0 Hz, ArH), 7.14–7.21 (m, 3H, ArH), 6.94–6.98
(m, 4H, ArH), 6.87 (d, 1H, J ¼ 2.0 Hz, ArH), 6.81 (dd, 1H, J ¼ 2.0 Hz,
Hz, 8.4 Hz, ArH), 4.01–4.05 (m, 4H, OCH2), 0.85–1.82 (m, 58H,
aliphatic hydrogen’s are overlapped). Anal. Calcd. for C64H83NO9;
C, 76.08; H, 8.28; N, 1.39%. Found: C, 76.31; H, 8.40; N, 1.43%.
1
Compound 8e: IR (KBr): n ¼ 3444, 2917, 1733, 1605 cmꢁ1; H NMR
(CDCl3, 400 MHz): dH ¼ 13.38 (s, 1H, OH), 8.64 (s, 1H, CH¼N),
8.26 (d, 2H, J ¼ 8.8 Hz, ArH), 8.10–8.15 (m, 4H, ArH), 7.45 (t, 1H,
J ¼ 8.0 Hz, ArH), 7.41 (d, 1H, J ¼ 8.4 Hz, ArH), 7.35 (d, 2H,
J ¼ 8.8 Hz, ArH), 7.13–7.20 (m, 3H, ArH), 6.94–6.98 (m, 4H, ArH),
6.87 (d, 1H, J ¼ 2.0 Hz, ArH), 6.80 (dd, 1H, J ¼ 2.0 Hz, 8.4 Hz,
ArH), 4.01–4.05 (m, 4H, OCH2), 0.84–1.82 (m, 54H, aliphatic hydro-
gen’s are overlapped). Anal. Calcd. for C62H79NO9; C, 75.81; H, 8.11;
N, 1.43%. Found: C, 76.00; H, 8.40; N, 1.48%.
Compound 8f: IR (KBr): n ¼ 3450, 2919, 1734, 1719, 1604 cmꢁ1
,
1H NMR (CDCl3, 400 MHz): dH ¼ 13.33 (s, 1H, OH), 8.64 (s, 1H,
CH¼N), 8.26 (d, 2H, J ¼ 8.8 Hz, ArH), 8.10–8.14 (m, 4H, ArH),
7.45 (t, 1H, J ¼ 8.0 Hz, ArH), 7.41 (d, 1H, J ¼ 8.4 Hz, ArH), 7.35
(d, 2H, J ¼ 8.8 Hz, ArH), 7.13–7.20 (m, 3H, ArH), 6.94–6.98
(m, 4H, ArH), 6.87 (d, 1H, J ¼ 2.0 Hz, ArH), 6.80 (dd, 1H, J ¼ 2.0 Hz,
Hz, 8.4 Hz, ArH), 4.01–4.05 (m, 4H, OCH2), 0.80–1.83 (m, 50H,

118
K. C. Majumdar et al.
aliphatic hydrogen’s are overlapped). Anal. Calcd. for C60H75NO9;
C, 75.52; H, 7.92; N, 1.47%. Found: C, 75.62; H, 8.08; N, 1.53%.
Compound 8g: IR (KBr): n ¼ 3448, 2916, 1731, 1717, 1603 cmꢁ1
,
1H NMR (CDCl3, 400 MHz): H NMR (CDCl3, 400 MHz): dH ¼ 13.30
(s, 1H, OH), 8.66 (s, 1H, CH¼N), 8.28 (dd, 2H, J ¼ 2.0 Hz, 6.8 Hz,
ArH), 8.12–8.17 (m, 4H, ArH), 7.47 (t, 1H, J ¼ 8.0 Hz, ArH), 7.43
(d, 1H, J ¼ 8.4 Hz, ArH), 7.37 (dd, 2H, J ¼ 2.0 Hz, 6.8 Hz, ArH),
7.15–7.22 (m, 3H, ArH), 6.96–7.00 (m, 4H, ArH), 6.89 (d, 1H,
J ¼ 2.2 Hz, ArH), 6.83 (dd, 1H, J ¼ 2.2 Hz, 8.4 Hz, ArH), 4.01–4.03
(m, 4H, OCH2), 0.86–1.85 (m, 54H, aliphatic hydrogen’s are over-
lapped). Anal. Calcd. for C62H79NO9; C, 75.81; H, 8.11; N, 1.43%.
Found: C, 76.03; H, 8.37; N, 1.49%.
1
Compound 8h: IR (KBr): n ¼ 3455, 2919, 1739, 1719, 1608 cmꢁ1
;
1H NMR (CDCl3, 400 MHz): dH ¼ 13.34 (s, 1H, OH), 8.64 (s, 1H,
CH¼N), 8.26 (d, 2H, J ¼ 8.8 Hz, ArH), 8.10–8.15 (m, 4H, ArH),
7.45 (t, 1H, J ¼ 8.0 Hz, ArH), 7.41 (d, 1H, J ¼ 8.4 Hz, ArH), 7.35
(d, 2H, J ¼ 8.8 Hz, ArH), 7.13–7.20 (m, 3H, ArH), 6.94–6.98
(m, 4H, ArH), 6.87 (d, 1H, J ¼ 2.4 Hz, ArH), 6.80 (dd, 1H, J ¼ 2.4 Hz,
Hz, 8.4 Hz, ArH), 4.01–4.03 (m, 4H, OCH2) 0.84–1.80 (m, 50H,
aliphatic hydrogen’s overlapped). Anal. Calcd. for C60H75NO9;
C, 75.52; H, 7.92; N, 1.47%. Found: C, 75.70; H, 8.12; N, 1.56%.
Compound 8i: IR (KBr): n ¼ 3463, 2919, 1731,1605 cmꢁ1
;
1H NMR
(CDCl3, 400 MHz): dH ¼ 13.35 (s, 1H, OH), 8.66 (s, 1H, CH¼N), 8.28
(dd, 2H, J ¼ 2.0 Hz, 6.8 Hz, ArH), 8.12–8.16 (m, 4H, ArH), 7.47 (t, 1H,
J ¼ 8.0 Hz, ArH), 7.43 (d, 1H, J ¼ 8.4 Hz, ArH), 7.37 (dd, 2H, J ¼ 2 Hz.,
6.8 Hz, ArH), 7.15–7.18 (m, 3H, ArH), 6.96–7.00 (m, 4H, ArH), 6.89
(d, 1H, J¼ 2.0 Hz, ArH), 6.83 (dd, 1H, J ¼ 2.0 Hz, 8.4 Hz, ArH),
4.02–4.07 (m, 4H, OCH2), 0.86–1.83 (m, 46H, aliphatic hydrogen’s
are overlapped). Anal. Calcd. for C58H71NO9; C, 75.21; H, 7.73;
N, 1.51%. Found: C, 75.50; H, 7.90; N, 1.59%.
Compound 8j: IR (KBr): n ¼ 2918, 1744, 1720, 1608 cmꢁ1, H NMR
1
(CDCl3, 400 MHz): dH ¼ 8.61 (d, 1H, J ¼ 1.9 Hz, ArH), 8.54 (s, 1H,
CH¼N), 8.27 (d, 2H, J ¼ 8.3 Hz, ArH), 8.11–8.14 (m, 4H, ArH),
7.47–7.51 (m, 2H, ArH), 7.35 (d, 2H, J ¼ 8.3 Hz, ArH), 7.14–7.19
(m, 3H, ArH), 6.97–6.97 (m, 5H, ArH), 4.01 (t, 4H, J ¼ 6.3 Hz,
OCH2), 0.86–1.84 (m, 62H, aliphatic hydrogen’s are overlapped).
Anal. Calcd. for C66H86N2O10; C, 74.27; H, 8.12; N, 2.62%. Found:
C, 74.45; H, 8.40; N, 2.80%.
Compound 8k: IR (KBr): n ¼ 2920, 1743, 1724, 1604 cmꢁ1, H NMR
1
(CDCl3, 400 MHz): dH ¼ 8.63 (d, 1H, J ¼ 2 Hz, ArH), 8.54 (s, 1H,
CH¼N), 8.27 (d, 2H, J ¼ 8.4 Hz, ArH), 8.12–8.15 (m, 4H, ArH),
7.47–7.51 (m, 2H, ArH), 7.36 (d, 2H, J ¼ 8.4 Hz, ArH), 7.14–7.18
(m, 3H, ArH), 6.97–6.99 (m, 5H, ArH), 4.02 (t, 4H, J ¼ 6.3 Hz,

Five-Ring Achrial Banana-Shaped Compounds
119
OCH2), 0.87–1.83 (m, 46 H, aliphatic hydrogen’s are overlapped).
Anal. Calcd. for C58H70N2O10; C, 72.93; H, 7.39; N, 2.93%. Found:
C, 73.10; H, 7.49; N, 3.00%.
Compound 8l: IR (KBr): n ¼ 2916, 1743, 1720, 1605 cmꢁ1
,
1H NMR
(CDCl3, 400MHz):dH ¼ 8.63 (d, 1H, J¼ 2 Hz, ArH), 8.55 (s, 1H, CH¼N),
8.28 (d, 2H, J¼ 8.7 Hz, ArH), 8.11–8.15 (m, 4H, ArH), 7.46–7.52 (m, 2H,
ArH), 7.36–7.41 (m, 2H, ArH), 7.15–7.18 (m, 3H, ArH), 6.96–7.00 (m,
5H, ArH), 4.04 (t, 4H, J¼ 6.6 Hz, OCH2), 0.86–1.85 (m, 54 H, aliphatic
hydrogen’s are overlapped). Anal. Calcd. for C62H78N2O10; C, 73.63; H,
7.77; N, 2.77%. Found: C, 73.90; H, 7.90; N, 2.85%.
RESULTS AND DISCUSSION
The mesomorphic properties of all the compounds were investigated
using classical techniques. The transition temperatures and the asso-
ciated enthalpy values obtained for compound of series I and II are
summarized in Table 1.
TABLE 1 Summarized Results of the DSC Data
Phase transition temperature ꢀC
Compound
(enthalpy KJ molꢁ1
)
8a
Cr 107.7 (72.9) B2 136.6 (21.3) I
I 135.0 (21.1) B2 83.9 (60.4) Cr
Cr 101.1 (55.8) B2 135.8 (18.7) I
I 133.7 (19.2) B2 69.5 (32.5) Cr
Cr 99.9 (40.1) B2 134.7 (20.2) I
I 132.8 (20.4) B2 66.1 (37.7) Cr
Cr 104.7 (80.5) B2 136.5 (25.8) I
I 132.8 (23.4) B2 68.3 (30.9) Cr
Cr 105.6 (64.4) B2 136.5 (10.0) I
I 126.0 (10.3) B2 59.8 (20.7) Cr
Cr 101.8 (38.3) B2 133.8 (7.2) I
I 127.9 (10.3) B2 56.7 (6.5) Cr
Cr 102.3 (68.7) B2 134.9 (22.3) I
I 133.1 (21.9) B2 70.5 (33.3) Cr
Cr 102.1 (52.2) B2 134.7 (19.0) I
I 132.6 (19.5) B2 68.9 (31.1) Cr
Cr 103.0 (40.7) B2 134.1 (14.3) I
I 132.1 (14.3) B2 68.9 (32.5) Cr
Cr 76.9 (3.6) B2 90.8 (8.3) I
8b
8c
8d
8e
8f
8g
8h
8i
8j
I 91.5 (13.7) B2 48.3 (19.1) Cr
Cr 107.7 (72.9) B2 136.6 (21.3) I
I 96.73 (10.72) B2 47.75 (2.39) Cr
Cr 73.5 (21.7) B2 97.4 (15.3) I
I 95.4 (13.7) B2 48.1 (3.0) Cr
8k
81

120
K. C. Majumdar et al.
Seemingly, the salicylaldimines (series I) and Schiff base (series II)
analogues display virtually the same transitional behavior with
the obvious exception that the transition (melting and the
clearing) temperatures are higher for the former due to the presence of
intramolecular H-bonding. All the compounds of series I and II showed
two transitions in both heating and cooling cycles (Figs. 2 and 3).
The first one corresponds to crystal to liquid crystalline phase tran-
sition, and the second one corresponds to the liquid crystalline phase
to isotropic phase transition. The clearing enthalpy values for this
mesophase are in the range 10–25 KJmolꢁ1. In the case of compounds
8a, 8b, 8c, the melting and clearing temperatures decrease slightly as
the number of -CH2 (methylene) group in the end alkoxy chain
decreases. This trend was found more or less similar to the other com-
pounds of series I. On the other hand, such a trend was not observed
for the compounds of series II. The enthalpy change occurred during
the phase transition is sufficiently larger for compounds of the
series I than that of the series II. This may be due to the presence of
FIGURE 2 DSC thermogram of compound 1. 8i, 2. 8g, 3. 8d, of series I.

Five-Ring Achrial Banana-Shaped Compounds
121
FIGURE 3 DSC thermogram of 4. 8k, 5. 8j, series II.
intramolecular H-bonding. It is also interesting to note that the
melting points are not very high, and the clearing temperatures
are close to about 140ꢀC for series I and 100ꢀC for series II, unlike
many other five ring banana shaped material. Any sample of both
the series when placed in a thin cell with a cell gap of d ¼ 5 ꢂ 0.2 mm
mm with homogeneous planar boundary conditions a stripe-like
texture appears from the isotropic melt, which on further cooling
grows slowly and fills up the whole field of view with circular
domains (Figs. 4 and 5). This is a typical texture of B2 the phase.
On very slow cooling from the isotropic phase B2 phase is stabilized
to almost 85–65ꢀC for salicylaldimines series I and to 48–45ꢀC
for series II, which was further confirmed by different scanning
calorimetry (DSC) study.
In order to evaluate the molecular arrangement within the layer,
X-ray diffraction (XRD) was performed on compound 8i. XRD was
carried out on a Philips powder diffractometer (PAN analytical model
no. pw 3015) operating on X’pert pro software, equipped with a tem-
perature controller permitting low as well as high temperature opera-
tion as needed (with CuKa radiation of k ¼ 1.5418). The diffraction
pattern of an unoriented sample of the mesophase of compound 8i
˚
showed a diffuse peak in the wide angle region with d ¼ 4.6 A
indicating liquid-like in-plane order.

122
K. C. Majumdar et al.
FIGURE 4 Compound 8i in thin cell at 126.9ꢀC.
In addition, three orders of lamellar reflection (in the ratio 1:12:1=3)
in the small angle region could be clearly seen (Fig. 6). The molecular
˚
length L ꢃ 51.1 A was calculated by molecular modeling, assuming
the molecules have fully stretched conformation. As the first
ꢀ
˚
order reflection is found to be at 2h ¼ 2.5205 (d ¼ 35.05 A) which is
sufficiently smaller than the molecular length L, so the molecules
are assumed to be tilted within the layers. From XRD as well as
textural characterization, this mesophase may be identified as
B2 phase. Sadashiva et al. [26] showed excellent B2 ! N transition
by introducing a fluorine atom into one of the arms of a homologous
FIGURE 5 Compound 8i in thin cell at 130.5ꢀC.

Five-Ring Achrial Banana-Shaped Compounds
123
FIGURE 6 XRD diagram of compound 8i at 120ꢀC.
series of symmetric bent core compounds with 2,7-dihydroxy
naphthalene as central core but corresponding analogous derivative
from 1,3-dihydroxy benzene did not show any mesophase. They also
showed SmAdb ! SmAd phase transition by introducing fluorine into
similar position of a homologous series of unsymmetrical bent core
molecule with 3-hydroxy benzoic acid as a central core [27]. On the
other hand, they observed a B7 phase transition by introducing a
cyano or a nitro group on the central phenyl ring [28]. The occur-
rence of calamitic phases in conjunction with the B phases are very
much common for five-ring banana-shaped materials with a lateral
substitution. This may be due to the deviation of the bend angle
between the two arms of the bent core molecules. In our case, we
observed only the B-phase instead of lateral substitution in one of
the arms of the bent-shape molecule. Thus the occurrence of only a
B2 phase over a wide temperature range for all the compounds of
series I and II is quite significant in our case. There are several
examples of the introduction of hydroxy group in one of the arm of
banana-shape material to stabilize the phases. However, to our
knowledge, there is no report of the introduction of a nitro group into
one of the arms of either symmetrical or unsymmetrical five-
ring banana-shaped materials. In conclusion, we have achieved the
synthesis of two new series of unsymmetrical bent shaped com-
pounds with lateral hydroxy and nitro groups. These compounds
exhibit only a B2 phase over a wide temperature range, as observed
by optical microscopy and DSC.

124
K. C. Majumdar et al.
ACKNOWLEDGMENTS
We thank the DST (New Delhi) for financial assistance. Two of us (SC
and NP) are thankful to the CSIR (New Delhi) for their fellowships.
We also thank the Material Science Department of the IACS, Kolkata
for providing us the HRXRD facilities.
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