Synthesis, characterization and mesophase behavior of new liquid crystalline compounds having chalcone as a central linkage

Article abstract of DOI:10.1080/15421406.2011.570123

Mesogens with a chalcone central linkage are rare. It is believed that the chalcone linkage is not conducive to mesomorphism. But when chalcone linkage is present with other central linkages like azomethine, ester or azo it becomes condusive to mesomorphism. In the present study two new homologous series viz. 1-(4'-butyloxybiphenyl-4-yl)-3-(4-alkoxyphenyl) prop-2-en-1-one (Series-I) and 4-[3-(4'-butoxybiphenyl-4-yl)-3-oxoprop-1-en-1-yl] phenyl 4-alkoxybenzoate (Series-II) were synthesized having the chalcone as a central linkage. Series-I having only chalcone central linkage through it exhibit mesomrphism due to the presence of alkoxy biphenyl group at one end which is rich source to provide to increase linearity and rigidity of the molecule. Series-II which contains chalcone as well as ester as a central linkage and it also exhibit mesomorphism. The compounds of the both series have been characterized by standard methods. Their liquid crystalline properties have been investigated by optical polarizing microscopy and DSC studies. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15421406.2011.570123

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Synthesis, Characterization and
Mesophase Behavior of New Liquid
Crystalline Compounds Having Chalcone
as a Central Linkage
B. T. Thaker a & J. B. Kanojiya a
a Department of Chemistry , Veer Narmad South Gujarat University ,
Surat, India
Published online: 14 Jun 2011.
To cite this article: B. T. Thaker & J. B. Kanojiya (2011) Synthesis, Characterization and Mesophase
Behavior of New Liquid Crystalline Compounds Having Chalcone as a Central Linkage, Molecular
Crystals and Liquid Crystals, 542:1, 84/[606]-98/[620], DOI: 10.1080/15421406.2011.570123
To link to this article: http://dx.doi.org/10.1080/15421406.2011.570123
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Mol. Cryst. Liq. Cryst., Vol. 542: pp. 84=[606]–98=[620], 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421406.2011.570123
Synthesis, Characterization and Mesophase
Behavior of New Liquid Crystalline Compounds
Having Chalcone as a Central Linkage
B. T. THAKER AND J. B. KANOJIYA
Department of Chemistry, Veer Narmad South Gujarat University,
Surat, India
Mesogens with a chalcone central linkage are rare. It is believed that the chalcone
linkage is not conducive to mesomorphism. But when chalcone linkage is present
with other central linkages like azomethine, ester or azo it becomes condusive to
mesomorphism. In the present study two new homologous series viz. 1-(40-butylox-
ybiphenyl-4-yl)-3-(4-alkoxyphenyl) prop-2-en-1-one (Series-I) and 4-[3-(40-
butoxybiphenyl-4-yl)-3-oxoprop-1-en-1-yl] phenyl 4-alkoxybenzoate (Series-II)
were synthesized having the chalcone as a central linkage. Series-I having only chal-
cone central linkage through it exhibit mesomrphism due to the presence of alkoxy
biphenyl group at one end which is rich source to provide to increase linearity and
rigidity of the molecule. Series-II which contains chalcone as well as ester as a
central linkage and it also exhibit mesomorphism.
The compounds of the both series have been characterized by standard methods.
Their liquid crystalline properties have been investigated by optical polarizing
microscopy and DSC studies.
Keywords Biphenyl; chalcone; ester; mesomorphism; mesophase; nematic phase;
smectic phase
Introduction
Mesogens with different central linkages are known [1]. However most of these
central linkages have an even number of linking groups. The chalcone linkage has
an odd number of atoms. Chalcones represent one of the most abundant and ubiqui-
tous groups of natural products [2]. In the past few years, they have been shown to
possess interesting biological properties including anti-invasive [3], anticancer [4],
inhibitory activation [5], antimalarial [6], antimicrobial [7], antimutagenic [8], radio-
protective [9], and anti-inflammatory effects [10] and synthetic intermediates in the
presence of other compounds [11]. Recently, it has been noted that, among many
organic compounds reported for their second harmonic generation, chalcone deriva-
tives are known for their excellent blue light transmittance and good crystallizability
[12–15]. It has also been documented that the chalcone possesses a remarkable
Address correspondence to B. T. Thaker, Department of Chemistry, Veer Narmad South
Gujarat University, Surat-395007, India. Tel.: þ91 261 2227141-46; Fax: þ91 261 2227312;
E-mail: btthaker1@yahoo.co.in
84=[606]

Synthesis, Characterization and Mesophase
85=[607]
nonlinear optical (NLO) property, which is an essential element for optical
communications devices. The other importance of this compound is its high photo-
sensitivity and thermal stability, which are used in developing various crystalline
electro-optical devices [16–18] and also having fluorescent properties [19].
The chalconyl group is also known to be a good photosensitive group [20,21].
The photoreaction of chalconyl groups takes place by irradiation with relatively
longer wavelength UV light than that of the cinnamoyl group. Photosensitive
polymers containing chalcone derivatives have been studied for photoalignment film
[22–25].
In view of the outstanding behavior of chalcone, a systematic study focusing
on the synthesis and characterization of these compounds has been carried out
in our present laboratory over the past few years [26–28]. A very recent investiga-
tion of the molecular structures and characteristics of a series of chalcone
derivatives, with Schiff base and a -methyl Schiff base bridging group has been
reported [29].
Biphenyl provides rich source of liquid crystals which are thermally more stable
than those of benzene substituted analogues, which increase linearity and rigidity of
the molecules. It plays an important role in the formation of liquid crystal having
ferroelectric and anti- ferroelectric properties [30–37], which are widely used in dis-
play device and=or electro-optical devices nowadays. It is believed that the chalcone
linkage is not conducive to mesomorphism, but when chalcone linkage is present
with other central linkages like azomethine, ester or azo it becomes condusive to
mesomorphism. In this article, we report another series of some newly analogues
derived from 4-butoxy biphenyl as a terminal group and synthesized two homolo-
gues series viz., 1-(40-butyloxybiphenyl-4-yl)-3-(4-alkoxyphenyl)prop-2-en-1-one
(Series-I) and 4-[3-(40-butoxybiphenyl-4-yl)-3-oxoprop-1-en-1-yl]phenyl 4-alkoxy-
benzoate (Series-II) to study the effect of different structural modifications on meso-
morphism. The synthetic procedure and thermal properties of these two series are
described in detail.
Experimental
Reagents and Technique
For the synthesis of compounds of the homologous series, following materials were
used. 4-Hydroxy benzoic acid, 4-hydroxybenzaldehyde Merck (Germany), alkyl bro-
mide (Lancaster, England). 4-hydroxy biphenyl (National Chemical, India), Acetyl
Chloride, Anhydrous AlCl3 (Rankem, India). The solvents were used after purifi-
cation using the standard methods described in the literature [38].
Elemental analyses (C, H, N) were performed at G.N.F.C.(Gujarat Narmda
Valley Fertilizer Company Ltd., Bharuch). Infrared spectra were recorded with a
THERMO SCIENTIFIC NICOLET ISO-10 spectrophotometer in the frequency
1
range 4000–400 cmꢀ1 with samples embedded in KBr discs. H-NMR spectra of
the compound were recorded with JEOL-GSX-400 using CDCl3 as a solvent and
TMS as an internal reference, 13C NMR spectra of the compound were recorded
with BRUKER AVANCE II 400 NMR Spectrometer and Mass spectra (EI) of
the compounds at SAIF (Sofisticated Analytical Instrument Facilities), Chandigarh.
Thin-layer chromatography analyses were performed by using aluminium-backed
silica-gel plates (Merck 60 F524) and examined under short-wave UV light.

86=[608]
B. T. Thaker and J. B. Kanojiya
The phase-transition temperatures were measured using
a
METTLER
TOLEDO DSC-1 at heating and cooling rates of 5ꢁC minꢀ1, respectively. The
optical microscopy studies were carried out with a ‘‘Leitz Loborlux 12’’ POL
(Wetzler, Germany) polarizing microscope equipped with a Mettler FP52 hot stage.
The textures of the compounds were observed using polarized light with crossed
polarizers with sample in thin film sandwiched between a glass slide and coverslip.
Synthesis
Synthesis of 4-Alkoxy Benzaldehyde. 4-Alkoxy benzaldehydes were prepared by a
reported method [39–42]. The m.p. of these compounds were compared with the
reported one and they are almost similar to reported values.
Synthesis of 4-n-Alkoxy Benzoic Acid. 4-n-Alkoxy benzoic acid were prepared as
reported by Dave and Vora method [43]. The m.p. of these compounds were
compared with the reported one and they are almost similar to reported values.
Synthesis of 4-Butoxy Biphenyl. In a round-bottom flask, 4-hydroxy biphenyl
(1 mmol) was dissolved in a dry acetone solution containing K2CO3 (1.5 mmol).
The solution was heated to 40ꢁC. 1-Bromobutane (1.02 mmol) was then added
dropwise (1–2 hr) and the mixture thus obtained was heated for 10–12 hr before
being cooled down to room temperature. The resulting solution was then poured
into cruised ice and the precipitate thus formed was filtered off and dried. The
precipitate was purified and recrystallized with acetone.
Synthesis of 1-(40-Butoxybiphenyl-4-yl) Ethanone. Crystallised 4-butoxy-biphenyl
(1 mmol.) was dissolved in dry, redistilled carbon disulphide, contained in a
three-necked flask, equipped with stirrer, dropping-funnel, and condenser. The
solution was cooled to 0–2ꢁC and sieved, anhydrous aluminium chloride
(1.12 mmol.) was added quickly, with stirring. Acetyl chloride (1 mmol.) was then
added during 5–10 min, and the temperature raised gradually to 35ꢁC. The mixture
was kept at 35ꢁC until the reaction seemed to be over, whereupon the whole was
refluxed for 45 min. Ice-cold, concentrated hydrochloric acid was then added to
the cooled mixture to decompose the yellow-green complex. The condenser was
removed, and steam passed under the surface of the solution to remove the
solvent and complete the decomposition of the complex. Stirring was continued as
the mixture was cooled quickly, in order to obtain the brownish-pink solid in a
finely divided state. The solid was separated, dried, and triturated twice by stirring
for 15 min. with ether. The insoluble 40-acetyl derivative was thus separated from
the isomeric 3-ketone, which is soluble in ether. However, when the aluminium
chloride was dried for several hours at 100–120ꢁC and the amounts of acetyl
chloride and aluminium chloride were increased to 1.1 and 1.17 mmol, respec-
tively, the yields were 60–77% in three consecutive preparations [44].
Synthesis of 1-(40-Butoxybiphenyl-4-yl)-3-(4-alkoxyphenyl)prop-2-en-1-one (Series-I).
A
mix of 1-(40-butoxybiphenyl-4-yl) ethanone (1 mmol) and n-alkoxy
benzaldehyde (1 mmol) were dissolved in the alcoholic sodium hydroxide solution
(80 ml ethanol and 10% NaOH solution). The reaction mixture was heated at 80
ꢁC for 7 hr. The mixture was left at room temperature overnight. An HCl aqueous
solution was added to the mixture, and then yellow precipitate was obtained. The

Synthesis, Characterization and Mesophase
87=[609]
precipitate was washed with water until a neutral aqueous solution was obtained.
Then, the solid was washed with methanol and dried under vacuum at 60ꢁC. The
obtained yellow solid recrystallized from acetone. The product was purified by
flash column chromatography using a mixture of hexane=ethyl acetate (7=1) as
eluent [45,46].
Data
Compound I-12. Yield 75%. m.p.115ꢁC. Found: C,82.05; H, 8.62; Calc. for
C37H48O3; C, 82.22; H, 8.88; %. EI-MS m=z (rel.int %): 540 (M)þ IR (KBr):
ꢀ1
=
(C O of chalcone),
t
max=cmꢀ1 2855–2956 cmꢀ1 (C-H aliphatic), 1691 cm
ꢀ1
1603 cmꢀ1 (C C of vinyl gr. of chalcone), 1577 cm
(C C of aromatic),
=
=
1254 cmꢀ1 (C-O-C), 1070 cmꢀ1 (C-O), 1H NMR (CDCl3): d 0.86–0.90 ppm (t,
CH3), 1.27–1.82 ppm (m, CH2), 3.98–4.04 ppm (t, OCH2), 6.94–7.55 ppm (m,
Ar-H), 6.88 & 7.80 ppm (2H, d, olefinic proton). 13C NMR (CDCl3): 14.15 ppm
=
(CH3), 22.71–31.92 ppm (CH2), 67.78 ppm (OCH2), 114.78–141.91 ppm (-CH CH-
=
, Chalcone), 126.61–133.55 ppm (Ar-C), 190.87 (-C O, Chalcone).
Synthesis of 3-(4-Hydroxyphenyl)-1-(40-butoxybiphenyl-4-yl)prop-2-en-1-one. A mix
of 1-(40-butoxybiphenyl-4-yl) ethanone (1 mmol) and 4-hydroxy benzaldehyde
(1 mmol) were dissolved in the alcoholic sodium hydroxide solution (80 ml ethanol
and 10% NaOH solution). The reaction mixture was heated at 80ꢁC for 7 hr. The
mixture was left at room temperature overnight. An HCl aqueous solution was
added to the mixture, and then yellow precipitate was obtained. The precipitate
was washed with water until a neutral aqueous solution was obtained. Then, the
solid was washed with methanol and dried under vacuum at 60ꢁC. The obtained
yellow solid was purified by recrystallization from acetone [45,46].
Synthesis of 4-[3-(40-Butoxybiphenyl-4-yl)-3-oxoprop-1-en-1-yl] Phenyl 4-alkoxy-
benzoate (Series-II). To a mixture of 3-(4-hydroxyphenyl)-1-(40-butoxybiphenyl-
4-yl)prop-2-en-1-one (1 mmol) and 4-n-alkoxy benzoic acid (1 mmol) in 150 ml of
distilled dichloromethane, 0.1 mmol of dimethyl aminopyridine (DMAP) was
added under an argon atmosphere. The mixture was cooled in an ice-water bath,
and after 10 min, 1 mmol of dicyclohexylcarbodiimide (DCC) was added under an
argon atmosphere. The mixture was stirred overnight at room temperature, the
salts were filtered off, and the solvent was evaporated. The crude product was
purified by flash column chromatography using a mixture of hexanes=ethyl
acetate (7=1) as eluent [47,48].
Data
Compound II-12. Yield 82%. m.p.70ꢁC. Found: C,79.86; H, 7.80; Calc.for C44H52O5;
C, 80.00; H, 7.88; %. EI-MS m=z (rel.int %): 660 (M þ 2)þ IR (KBr): tmax=cmꢀ1
ꢀ1
2850–2956 cmꢀ1 (C-H aliphatic), 1726 cmꢀ1 (C O of ester)ꢀ, 11690 cm (C O of
=
=
chalcone), 1606cmꢀ1 (C C of vinyl gr. of chalcone), 1585 cm (C C of aromatic),
=
=
1256cmꢀ1(C-O-C), 1070cmꢀ1 (C-O), H NMR (CDCl3): d 0.86–0.90 ppm (t, CH3),
1.27–1.82 ppm (m, CH2), 3.98–4.04 ppm (t, OCH2), 6.94–7.55 ppm (m, Ar-H),
1
8.02 & 8.14ppm (2H, d, olefinic proton). 13C NMR (CDCl3): 14.15 ppm (CH3),
=
22.71–33.75 ppm (CH2), 68.28 ppm (OCH2), 114.77–141.91 ppm (-CH CH-,

88=[610]
B. T. Thaker and J. B. Kanojiya
=
Chalcone), 114.61–133.54 ppm (Ar-C), 163.53 ppm (C O ester), 170 (-C O,
=
Chalcone).
Synthesis (Reaction Scheme)
Series-I
Synthesis of 4-n-Alkoxy Benzaldehyde.
=
Where R CnH2nþ1, n ¼ 1 to 8,10,12,14,16
Synthesis of 4-Butoxy Biphenyl.
Synthesis of 1-(40-Butoxybiphenyl-4-yl) Ethanone.
Synthesis of 1-(40-Butoxybiphenyl-4-yl)-3-(4-alkoxyphenyl)prop-2-en-1-one.
=
Where R CnH2nþ1, n ¼ 1 to 8,10,12,14,16
1-(40-butoxybiphenyl-4-yl)-3-(4-alkoxyphenyl)prop-2-en-1-one

Synthesis, Characterization and Mesophase
89=[611]
Series-II
Synthesis of 4-n-Alkoxy Benzoicacid.
=
Where R CnH2nþ1, n ¼ 1 to 8,10,12,14,16
Synthesis of 4-Butoxy Biphenyl.
Synthesis of 1-(40-Butoxybiphenyl-4-yl) Ethanone.
Synthesis of 3-(4-Hydroxyphenyl)-1-(40-Butoxybiphenyl-4-yl)prop-2-en-1-one.

90=[612]
B. T. Thaker and J. B. Kanojiya
Synthesis of 4-[3-(40-butoxybiphenyl-4-yl)-3-oxoprop-1-en-1-yl] phenyl 4-alkoxy-
benzoate.
=
Where R CnH2nþ1, n ¼ 1 to 8,10,12,14,16.
Results and Discussion
In order to investigate the influence of the terminal group and central linkages
on mesomorphic and thermal stability, 12 homologous from each of the two
series 1-(40-butoxybiphenyl-4-yl)-3-(4-alkoxyphenyl)prop-2-en-1-one (Series-I) and
4-[3-(40-butoxybiphenyl-4-yl)-3-oxoprop-1-en-1-yl]phenyl-4-alkoxybenzoate (Series-
II) have been synthesized. The mesomorphic properties of all the synthesized com-
pounds have been characterized by differential scanning calorimetry (DSC) and
polarizing optical microscope (PMO) attached with Mettler hot stage.
The transition temperatures of both series are given in Tables 1 and 2. In Series-I
compounds I1–I6 gives sharp melting point and directly convert to isotropic liquid
i.e., the compounds are non-mesogenic, while I7 & I8 exhibit enantiotropic nematic
mesophase. Compounds I10 & I12 exhibit smectic as well as nematic mesophase,
while compounds I14 & I16 exhibit only smectic mesophase (SmC). In second hom-
ologous Series-II all the compounds are mesogenic in nature. Compounds II1-II7
exhibit enantiotropic nematic mesophase, compounds II8, II10 & II12 exhibit enantio-
tropic smectic as well as nematic mesophase, while compounds II14 and II16 exhibit
only SmC mesophase. It is consistent with the assignment of each mesophase type,
using the classification systems reported by Sackmann and Demus [49], Gray and
Goodby [50].
DSC is a valuable method for the detection of phase transition. It yields quan-
titative results; therefore we may draw conclusions concerning the nature of the
phases that occur during the transition. In the present study, enthalpies of two deri-
vatives of Series-I and Series-II were measured by DSC. DSC data of Series-I and
Series-II are recorded in Table 3 which helps the further confirms the mesophase
type. Table 3 shows the phase transition temperatures, associated enthalpy (DH)
and molar entropy (DS) for compounds of Series-I (I12 & I16) and Series-II (II12
&

Synthesis, Characterization and Mesophase
Table 1. Transition temperature of Series-I
91=[613]
Transition temperatureꢁC
Compounds
R¼n alkoxy
Cr
SmC
N
I
I1
I2
I3
I4
I5
I6
I7
I8
I10
I12
I14
I16
Methyl
Ethyl
Propyl
Butyl
Pentyl
.
.
.
.
.
.
.
.
.
.
.
.
160
148
153
140
132
137
112
106
51
–
–
–
–
–
–
–
–
.
–
–
–
–
–
–
–
–
89
66
96
73
–
–
–
–
–
–
.
–
–
–
–
–
.
.
.
.
.
.
.
.
.
.
.
.
Hexyl
–
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
134
130
123
115
–
.
.
48
62
57
.
.
.
–
–
.
–
II16). Enthalpy values of the various transitions agree well with the existing related
literature values [51]. The DSC curves of representative compounds are shown in
Figures 1–4. Microscopic transition temperature values are almost similar to DSC
data.
Table 3 shows the comparison of S-N and N-I transition temperature of the
compound I-12 of Series-I and structurally related compound II-12 of the Series-II.
The SmC mesophase range of the compound I-12 is lower by 7ꢁC when compared
with compound II-12 of the Series-II. The N-I transition temperature of the com-
pound I-12 of Series-I is higher by 45ꢁC when compared with compound II-12 of
the Series-II.
Table 2. Transition temperature of Series-II
Transition temperatureꢁC
Compounds
R¼n alkoxy
Cr
SmC
N
I
II1
II2
II3
II4
II5
II6
II7
II8
II10
II12
II14
II16
Methyl
Ethyl
Propyl
Butyl
Pentyl
.
.
.
.
.
.
.
.
.
.
.
.
102
95
98
89
82
79
77
61
46
41
50
58
–
–
–
–
–
–
–
.
–
–
–
–
–
.
.
.
.
.
.
.
.
.
.
–
–
120
114
111
104
98
93
89
85
78
70
–
.
.
.
.
.
.
.
.
.
.
.
.
Hexyl
–
–
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
73
70
66
67
64
.
.
.
.
–

92=[614]
B. T. Thaker and J. B. Kanojiya
Table 3. DSC data for Series-I and II compounds
Peak Temp.
(Microscopic temp.)ꢁC
DH
DS
Series
Compound
Transition
Jgꢀ1
Jgꢀ1 Kꢀ1
I
I12
Cr-Sm
Sm-N
N-I
Cr-Sm
Sm-I
Cr-Sm
Sm-N
N-I
Cr-Sm
Sm-I
47.24 (48)
65.73 (66)
114.29 (115)
56.72 (57)
72.47 (73)
40.80 (41)
66.04 (66)
69.36 (70)
57.56 (58)
63.70 (64)
19.33
13.29
19.57
52.78
6.44
0.4027
0.2013
0.1701
0.9259
0.0882
0.0290
0.8028
0.1997
0.3688
0.6017
I16
II
II12
1.19
52.99
13.98
21.39
38.51
II16
In Series-I first six compounds do not exhibit mesomorphism. They give sharp
melting points. This is because of lower alkoxy chain which does not increase
polarity and polarizability of the molecules. As the carbon chain increase, the lin-
earity and polarizability of the molecules increase which increase end to end cohesive
force and molecule becomes lamellar showing nematic mesophase. In Series-I smec-
tic mesophase (SmC) appears from higher homologues I10, I12, I14 & I16 while in
Series-II smectic (SmC) mesophase appears from II8, II10, II12, II14 & II16. This is
because the long chains become attracted and interwined, which facilitates the lamel-
lar packing required for smectic phase generation. As a result, the smectic tendency
increase and eventually eliminates the nematic phase.
Figure 1. DSC Curve of the compound I12 of Series-I. (Figure appears in color online.)

Synthesis, Characterization and Mesophase
93=[615]
Figure 2. DSC Curve of the compound I16 of Series-I. (Figure appears in color online.)
In these both series S-I transition usually begins at about the tetradecyloxy and
hexadecyloxy derivatives together with the N-I transition temperatures for the lower
homologous constitute one smoothly falling mesorphic – isotropic transition tem-
peratures. From the plot of transition temperatures against the number of carbon
Figure 3. DSC Curve of the compound II12 of Series-II. (Figure appears in color online.)

94=[616]
B. T. Thaker and J. B. Kanojiya
Figure 4. DSC Curve of the compound II16 of Series-II. (Figure appears in color online.)
atoms (Figs. 5 and 6), it can be noticed that a smooth falling tendency for mesophase
to isotropic has been observed throughout both the series. Both the series also exhi-
bit falling tendency of SmC-N transition temperature for higher homologues. This is
in agreement with the observation reported for such homologous series [1].
Series-I consist chalcone as a cetral linkage. Mesogens with different central lin-
kages are known. However most of these central linkages have an even number of
linking groups. The chalcone linkage has an odd number of atoms. Moreover, very
few low molecular mesogens with the chalcone linkage are known. Chalcone-
=
=
(-CH CH-CO-) linkage is less conducive to mesomorphism compared to -CH N-,
-COO- linkages due to the non-linearity and angle strain arising from the keto
group[19]. Nguyen et al. [52] have reported that a ketonic group linking two phenyl
rings (benzophonene derivatives) is non-conducive to mesomorphism due to the
angular shape of such molecules resulting from the angle of keto group.
Series-I having biphenyl as a central core which is highly polar than benzene
analogues. In general, the molecules of a liquid crystalline compounds possessing
middle and terminal polar groups. Molecules which form liquid crystal have dipole
in their structure often a strong dipole towards the centre and weak dipole towards
Table 4. Different transition temperatures and range of mesophases observed in
Series I and II
SmC mesophase Nematic mesophase
range (ꢁC)
Series Compound SmC
N
I
range (ꢁC)
I
II
I12
II12
48
41
66 115
66 70
18
25
49
04

Synthesis, Characterization and Mesophase
95=[617]
Figure 5. Mesomorphic behaviour as a function of the number of carbon atoms (n) in the
terminal alkoxy chain for Series-I. (Figure appears in color online.)
the end of the molecules. When more than two benzene rings are linked through
more than one central group, the liquid crystalline properties enhance the most.
However, linearity and rigidity are increased by linking up the benzene rings directly
and thus biphenyl provides a rich source of liquid crystals which are thermally more
stable than those benzene substituted analogues. It is observed that the biphenyl ring
plays an important role in the formation of liquid crystals which increase the stability
and phase length of the mesophase. This is the fact that through Series-I having only
chalcone as a central linkage it is conducive to mesomophism due to terminal butoxy
biphenyl ring.
In both the series there is a common features are both having biphenyl core and
one of the chalcone linkage. In Series-I only higher homologues from heptyloxy deri-
vatives shows liquid crystalline properties while in Series-II all the compounds are
mesogenic in nature. This is because in Series-II there are additional ester group
and benzene ring, which increase over all polarisability of the molecule, enhance
Figure 6. Mesomorphic behaviour as a function of the number of carbon atoms (n) in the
terminal alkoxy chain for Series-II. (Figure appears in color online.)

96=[618]
B. T. Thaker and J. B. Kanojiya
the liquid crystalline properties are most. There is decreases in thermal stabilities of
liquid crystal phases in Series–II compounds, may be attributed to have it having
additional ester linkage and alkoxy benzene ring as terminal substitution. An
increase in the breadth forces the long axes of the molecules apart, as a result of
which the interactions are decreased and consequently the liquid crystal tempera-
tures are lowered. A change in the degree of conjugation due to chalcone linkage will
alter both polarisability than ester group. The effect of the change in resultant
moments is subtle, however, consequentially; the decrease in the polarisability will
cause a decrease in the thermal stability of liquid crystal phase in Series -II. Variation
of central ester linkage and benzene ring in Series-II made it possible to observe the
effects of structural changes on mesomorphic system which had not studied
previously.
Conclusion
In this article we have presented the synthesis and characterization of mesogenic two
homologous series viz. 1-(40-butoxybiphenyl-4-yl)-3-(4-alkoxyphenyl)prop-2-en-
1-one (Series-I) which containing only chalcone as a central linkage and 4-[3-
(40-butoxybiphenyl-4-yl)-3-oxoprop-1-en-1-yl]phenyl-4-alkoxybenzoate (Series-II)
which containing chalcone as well as ester linkage and additional benzene ring. In
Series-I the lower member up to hexyloxy derivatives do not exhibit mesomorphism
because their polarity and polarizability of the molecules do not increase. Series-I
consist chalcone as a central linkage which is less conducive to mesomorphism
though the higher member of this series exhibit mesomorphism. This is because of
the butoxy biphenyl ring which is increase linearity and polarizability of the molecule
which make it possible to conducive to mesomorphism. In Series-II it consist chal-
cone as well as ester linkage and another benzene ring which make it more conducive
to mesomorphism. Hence, in Series-II all the compounds show mesomrphism. The
study of these both two homologues series have brought out the fact that
=
=
-CH CH-CO- linkage is less conducive to mesomorphism compared to -CH N-,
-COO- linkages due to the non-linearity and angle strain arising from the keto group
through it exhibit mesomorphism when it attached with polar group like butoxy
biphenyl. The study has provided for the first time, mesogenic compounds with only
chalcone linkage. The present study completes our objective of analyzing and estab-
lishing the effect of different structural modifications on mesomorphism.
Acknowledgment
We are thankful to Department of Applied Chemistry, Faculty of Technology and
Engineering, M. S. University of Baroda, Vadodara for providing us Optical
polarizing microscope for mesophase study.
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