Studies of calamitic liquid crystalline compounds involving ester-azo central linkages with a biphenyl moiety

Article abstract of DOI:10.1080/15421406.2011.591677

Two mesogenic homologous series involving ester-azo central linkages with a biphenyl moiety have been synthesized, such as 4'-[(4-n-alkoxyphenyl)diazenyl] biphenyl-4-ol (series I) and 4'-[(4-n-alkoxyphenyl) diazenyl]-4-butoxy phenyl biphenyl-4-carboxylate (series II). Azobiphenyl of series I having a free hydroxyl group with strong hydrogen bonding exhibits a high-temperature enantiotropic smectic phase. Whereas in series II, compounds containing C ₁-C₈ carbon atoms exhibit only a monotropic smectic phase and compounds with C₁₀, C₁₂, C₁₄, and C ₁₆ atoms show an enantiotropic smectic phase. These compounds were characterized by elemental analysis, FT-IR, 1H-NMR, and mass spectral studies. The phase transition and mesogenicity of these substances were studied by polarizing optical microscopic and differential scanning calorimetric techniques. Their thermal stabilities and other characteristics are discussed. Copyright Taylor &Francis Group, LLC.

Full text of DOI:10.1080/15421406.2011.591677

Mol. Cryst. Liq. Cryst., Vol. 548: pp. 172–191, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.591677
Studies of Calamitic Liquid Crystalline
Compounds Involving Ester-Azo Central Linkages
with a Biphenyl Moiety
∗
B. T. THAKER, Y. T. DHIMMAR, B. S. PATEL,
D. B. SOLANKI, N. B. PATEL, N. J. CHOTHANI,
AND J. B. KANOJIYA
Department of Chemistry, Veer Narmad South Gujarat University, Surat,
Gujarat, India
Two mesogenic homologous series involving ester-azo central linkages with a biphenyl
ꢀ
moiety have been synthesized, such as 4 -[(4-n-alkoxyphenyl)diazenyl]biphenyl-4-ol
(
ꢀ
series I) and 4 -[(4-n-alkoxyphenyl) diazenyl]-4-butoxy phenyl biphenyl-4-carboxylate
(series II). Azobiphenyl of series I having a free hydroxyl group with strong hydrogen
bonding exhibits a high-temperature enantiotropic smectic phase. Whereas in series II,
compounds containing C –C carbon atoms exhibit only a monotropic smectic phase
1
8
and compounds with C10, C12, C14, and C16 atoms show an enantiotropic smectic
1
phase. These compounds were characterized by elemental analysis, FT-IR, H-NMR,
and mass spectral studies. The phase transition and mesogenicity of these substances
were studied by polarizing optical microscopic and differential scanning calorimetric
techniques. Their thermal stabilities and other characteristics are discussed.
Keywords Biphenyl; ester-azo; nematic and mesophase; smectic
Introduction
While designing new liquid crystal molecules with definite properties, it is necessary to
keep in mind that their mesogenic behavior is strongly influenced by the structure of the
rigid molecular core and by the lateral substitution on the aromatic rings, with the position
of the substituted ring in the molecular core being important [1]. Liquid crystal oligomers
consist of molecules containing two or more mesogenic units interconnected via flexible
spacers, most commonly alkyl chains [2–5]. There is substantial literature on the studies of
biphenyl and its derivatives. 2,3,4-monosubstituted biphenyls have been studied extensively
by various workers [6–13] for their molecular geometry, crystallization behavior, crystal
packing, and thermal motion, while the literature on growth and structural aspects of linearly
chained biphenyls (liquid crystals) is quite insufficient.
Biphenyl esters are typical mesogens with various mesophases having different de-
grees of order according to substituents [14]. There are many examples of rigid, ex-
tended chemical subunits in mesogens. The most common subunit used in synthesizing
∗
Address correspondence to B. T. Thaker, Department of Chemistry, Veer Narmad South Gujarat
University, Surat, Gujarat, India+91-261-226-7957. E-mail: btthaker1@yahoo.co.in
172

Liquid Crystals with Ester-Azo Linking Groups
173
Scheme 1. Series I: synthesis of 4-n-alkoxy anilines.
calamitic liquid crystals is the linearly para-substituted phenyl ring [15]. Functionalized
azobenzenes were among the first successful nematic liquid crystals used in the dis-
play industry [16–20], which constitute an important class of materials for information
processing and storage and are being explored as molecular photoswitches. Recently,
Michael Hird et al. studied the mesomorphic properties of ortho difluoroterphenyls with
a bulky terminal chain [21]. Johnson et al. [22] have synthesized a homologous series of

174
B. T. Thaker et al.
Scheme 2. Series II: synthesis of 4-n-alkoxy benzoyl chlorides.
4-(4-alkylphenylazo)phenols. An attempt has been made to synthesize two series of com-
pounds by using 4-hydroxy biphenyl instead of phenol.
Experimental Methods
Reagents and Techniques
4-hydroxy benzoic acid, alkyl bromide (Lancaster, England), and 4-hydroxy biphenyl were
used without further purification. Acetone, ethanol, methanol, hydrochloric acid (HCl),

Liquid Crystals with Ester-Azo Linking Groups
175
Figure 1. FT-IR spectra of compound A10 (series I).
KOH, NaNO2, NaOH, and thionyl chloride were supplied by Polypharm Mumbai, India;
certain solvents and reagents were used after distillation and purification by using the stan-
dard methods described in the literature [23]. Other auxiliary chemicals were of laboratory
grade. Elemental analyses (C, H, N) were performed at the Central Drug Research Institute
(
CDRI), Lucknow, India. Infrared spectra were recorded by a Perkin-Elmer 2000 FT-IR
−1
spectrophotometer in the frequency range 4000–400 cm with samples embedded in KBr
Figure 2. FT-IR spectra of compound A14 (series I).

176
B. T. Thaker et al.
Figure 3. FT-IR spectra of compound B10 (series II).
1
discs. H-NMR spectra of the compounds were recorded by a Jeol-GSX-400 instrument
using CDCl3 as a solvent and tetramethylsilane as an internal reference at SAIF, Panjab
University, Chandigarh, India. Also, mass spectra of the compounds were recorded at SAIF.
Thin layer chromatography (TLC) analyses were performed using aluminum-backed silica-
gel plates (Merck60 F524) and examined under shortwave UV light. The phase transition
◦
temperatures were measured using Shimadzu DSC-50 at heating and cooling rates of 10 C
−1
min , respectively. The textures of the mesophase were studied using a Leitz Labourlux
polarizing microscope provided with a Kofter heating stage at the Applied Chemistry
Department, M. S. University of Baroda, Vadodara, Gujarat, India.
Figure 4. FT-IR spectra of compound B14 (series II).

Liquid Crystals with Ester-Azo Linking Groups
177
Figure 5. 1H-NMR spectra of compound A10 (series I).
RO
N
N
OH
H21 series 1)
4
ꢀ-[(4-n-alkoxyphenyl)diazenyl] biphenyl-4-ol (where R = C10
Synthesis
Series I compounds synthesized as per Scheme 1
Synthesis of 4-n-Alkoxy Anilines. 4-n-Alkoxy Acetanilides. Paracetamol (0.1 mol), anhy-
drous potassium carbonate (0.15 mol), respectively, n-alkyl bromide (0.15 mol), and dry
acetone (60 ml) were taken in a round-bottom flask (RBF) provided with a condenser and
a guard tube. The reaction mixture was refluxed in a water bath for 8–10 hr. The whole
mass was then added to water and extracted with ether. The ether was evaporated and the
residual solids were obtained as alkoxy acetanilides.

178
B. T. Thaker et al.
Figure 6. 1H-NMR spectra of compound A14 (series I).
RO
N
N
OH
H29 series I)
4
ꢀ-[(4-n-alkoxyphenyl)diazenyl] biphenyl-4-ol (where R = C14
4
-n-Alkoxy Anilines. A mixture of 4-n-alkoxy acetanilide (0.146 mol), water (70 ml),
◦
◦
and concentrated HCl (45 ml) was stirred for 10–12 hr at 90 C–95 C and then cooled
to room temperature. The mixture was made alkaline with 50% NaOH at 20 C. The oily
◦
product (for the lower members C1–C8) was extracted with ether. The ether extract was
dried and concentrated at reduced pressure to give oil, which was purified by distillation.
The higher members (C10–C16) were separated as solid and filtered directly without ether
extraction. The boiling points and melting points of all the alkoxy anilines agree well with
the values reported in the literature [24–26].
Diazotization of Alkoxy Aniline [27]. Alkoxy aniline (0.005 mol, 1.15 g) was taken in
◦ ◦
0 ml of water in a beaker. It was then cooled to 0 C–5 C with ice in an ice bath. Later on,
5
concentrated HCl (0.03 mol, 3.6 ml) was added and the reaction mixture was stirred for 1
◦
hr. A solution of NaNO2 (0.005 mol, 0.35 g) in water (5 ml) previously cooled to 0 C was
then added over a period of 5 min with stirring. The solution was further stirred for another
1
hr. At this stage, Congo red paper turns blue and starch iodide paper also turns blue. It
showed the positive test (i.e., the presence of nitrous acid). Then, sulfamic acid was added
to remove excess of nitrous acid. At this stage, Congo red paper turns blue (positive test)
and starch iodide paper had no effect (negative test). The diazonium salt was obtained as a
clear solution, which was used for subsequent coupling reaction.
ꢀ
Synthesis of 4 -[(4-n-Alkoxyphenyl)Diazenyl]Biphenyl-4-ol. To a well-stirred solution of
4-hydroxy biphenyl (0.005 mol, 0.85 g) in water (50 ml) was added a diazonium chloride

Liquid Crystals with Ester-Azo Linking Groups
179
Figure 7. 1H-NMR spectra of compound B10 (series II).
O
RO
N
N
C
O
OC H
4
9
ꢀ
4
-[(4-n-alkoxyphenyl)diazenyl]4-butoxy phenyl biphenyl-4-carboxylate (where R = C10
H21 series
II).
◦
◦
of alkoxy aniline gradually for 1 hr at 0 C–5 C. The pH (7.0) was maintained by the
addition of NaOH solution (10% w/v). The mixture was stirred for another 3–4 hr for
complete separation and the dye was isolated by filtration, washed with water, dried, and
crystallized from ethyl acetate to get orange-colored crystals. The yield was about 75%. All
the compounds had been purified by column chromatography on silica gel (80–120 mesh)
using a mixture of ethyl acetate/petroleum ether (7/3) as an eluent.
◦
Data. Compound A10 (Series I). Yield: 73%, MP 119 C; elemental analysis for calculated
C 78.10%, H 7.96%, N 6.51%; found C 78.44%, H 8.20%, N 6.02% for C28H34N2O2; FT-IR
− −1
1
(
KBr pallete) 3061 cm (–C–H aromatic stretching), 2850–2920 cm (–CH3 aliphatic
−
1
−1
stretching), 1598 cm (–N N–), 1418–1481 cm (–CH bending of CH2), 1367–1372
−1
−1
−1
cm (–C–H bending of CH3), 817–758 cm (–CH bending out of plane), 723 cm (–CH2
1
rocking); H-NMR (CDCl3): 0.90 ppm (t, 3H, CH3 of aliphatic chain), 1.28–1.85 ppm (m,
16H, –CH2 of alkyl chain), 3.86–3.89 ppm (d, 2H, –OCH2 of alkoxy chain), 6.09 ppm (s,
phenolic –OH free), 6.81–7.29 ppm (m, 12H, Ar–H); mass (GC-MS): molecular weight of
+
compound 486 g/mol and molecular ion peak as (M) at 485.4 (m/z).
Series II compounds synthesized as per Scheme II.
Synthesis of 4-n-Alkoxy Anilines. 4-n-Alkoxy anilines were prepared as described in
Series I.

180
B. T. Thaker et al.
Figure 8. 1H-NMR spectra of compound B14 (series II).
O
RO
N
N
C
O
OC H
4 9
ꢀ
4
-[(4-n-alkoxyphenyl)diazenyl]4-butoxy phenyl biphenyl-4-carboxylate (where R = C14
H
29
series II).
Diazotization of Alkoxy Aniline. Diazotization of alkoxy aniline was carried out as de-
scribed in Series I.
ꢀ
ꢀ
Synthesis of 4 -[(4-n-Alkoxyphenyl)Diazenyl]Biphenyl-4-ol. Synthesis of 4 -[(4-n-
alkoxyphenyl)diazenyl]biphenyl-4-ol was carried out as per the procedure described in
Series I.
Preparation of 4-n-Alkoxy Benzoic Acid [28,29]. 4-hydroxy benzoic acid (0.1 mol, 13.8 g),
corresponding n-alkyl bromide (0.12 mol, 23.20 ml), and KOH (0.25 mol, 14.0 g) were
dissolved in methanol (lower member)/ethanol (higher member) (100 ml) in an RBF fitted
with a reflux condenser and refluxed the mixture in a water bath for 8 hr. Then 10% aqueous
KOH solution (25.0 ml) was added to the flask and reflux continued for 2–3 hr to hydrolyze
any ester if formed. The solution was cooled to room temperature, and the reaction mixture
was acidified by pouring 1:1 ice-cooled dilute HCl and water; the precipitated mass was
filtered and washed by water. Then, the isolated mass was dried in a vacuum oven. The
alkoxy acids were crystallized in methanol until a constant transition temperature was
obtained. The transition temperature thus obtained is in good agreement with the values
reported in the literature.
Preparation of 4-n-Alkoxy Benzoyl Chlorides [30]. 4-n-alkoxy benzoic acid (0.01 mol, 2.5
g) and freshly distilled thionyl chloride (0.03 mol, 2.19 ml) were taken in an RBF attached

Liquid Crystals with Ester-Azo Linking Groups
181
Figure 9. Mass spectra of compound A14 (series I).
to a reflux condenser fitted with a calcium chloride guard tube. The mixture was refluxed
in a water bath till the evolution of HCl gas ceased. Excess of thionyl chloride was distilled
off under pressure using a vacuum pump and the 4-n-alkoxy benzoyl chloride left behind
was directly treated for the next reaction without further purification.
ꢀ
ꢀ
Synthesis of 4 -[(4-n-alkoxyphenyl)Diazenyl]4-Butoxy Phenyl Biphenyl Carboxylate. 4 -
(4-n-alkoxyphenyl)diazenyl]biphenyl-4-ol (0.002 mol, 0.86 g) was dissolved in dry pyri-
[
dine (10 ml) and was added dropwise with occasionally stirring in to ice-cold 4-butoxy
benzoyl chloride (0.002 mol, 0.39 g) in an RFB. Then the mixture was refluxed in a hot
water bath for 2 hr and was allowed to stand for overnight. The mixture was acidified using
cold 1:1 diluted HCl to precipitate the product. The solid obtained was filtered, washed
successively with saturated NaHCO3 solution, dilute NaOH solution, and two to three
times with water; the crude solid thus obtained was purified a number of times using hot
water until a constant melting temperature was obtained. The purity of all of these com-
pounds was checked by TLC, yield in general 65%–75%. All the compounds have been
purified by column chromatography on silica gel (80–120 mesh) using a mixture of ethyl
acetate/petroleum ether (7/3).
◦
Data. Compound B10 (Series II). Yield: 66%, MP 85 C; elemental analysis for calculated
C 77.20%, H 7.64%, N 4.62%; found C 77.57%, H 7.95%, N 4.91% for C39H46N2O4;
−
1
1
−1
FT-IR (KBr pallete) 3037 cm (–C–H aromatic stretching), 2852–2918 cm (–CH3
−
−1
−1
aliphatic stretching), 1687 cm (C O stretching), 1606 cm (–N N–), 1409–1469 cm

182
B. T. Thaker et al.
Figure 10. Mass spectra of compound B10 (series II).
(
–CH bending of CH2), 1370 cm 1 (–C–H bending of CH3), 1255–1064 cm (–C–O–C–
− −1
−1
−1
stretching of alkoxy chain), 819–758 cm (–CH bending out of plane), 717 cm (–CH2
rocking); H-NMR (CDCl3): 0.90 ppm (m, 6H, CH3 of aliphatic chain), 1.29–1.83 ppm (m,
1
28H, –CH2), 3.88–3.95 ppm (m, 4H, –OCH2 of alkoxy chain), 6.87–6.95 ppm (m, 16H,
Ar–H); FAB mass spectra: molecular weight of compound 606 g/mol and molecular ion
+
peak as (M+1) at 607.2 (m/z).
Results and Discussion
The compounds of both series are subjected to elemental analysis. The elemental analysis
data agreed with theoretical values as per the expected structure. The FT-IR spectra of
1
representative compounds are shown in Figs. 1–4. The H-NMR spectra of representative
compounds are shown in Figs. 5–8. The mass spectra of these compounds are shown in
Figs. 9 and 10. The m/z ratios obtained from the spectra of representative samples are
matched with their molecular ion peak. The purity of the compounds is checked by TLC. It
shows one spot, indicating single compound. All the compounds were purified by column
chromatography using silica gel (100–200 mesh) and ethyl acetate/petroleum ether (7:3)
solvent system.
In earlier report [22], the alkoxy was prepared from azophenols using a Pd-catalyzed
coupling reaction of a suitable azobenzene precursor with alkyl zinc chlorides.
In the present case, we have used alkoxy aniline containing C1–C8, C10, C12, C14, and
C16 carbon atoms in the alkoxy chain followed by diazotization with 4-hydroxy biphenyl
using a classical method [31] and the mesogenic properties were investigated for these
compounds.

Liquid Crystals with Ester-Azo Linking Groups
183
Table 1. Transition temperature data of series I
◦
Transition temperature ( C)
Code no.
R = n-alkyl
Sm
I
A1
A2
A3
A4
A5
A6
A7
A8
A10
A12
A14
A16
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
156
150
144
148
130
129
130
104
72
182
177
173
160
158
155
140
136
119
113
102
104
89
87
86
RO
N
N
OH
Series I
In another case, the –OH group of a biphenyl moiety is esterified by the (C4) alkoxy
acid. On the one end, the number of carbon atoms in the alkoxy chain was fixed (C4H9)
and on the other end it was varied (C1–C8, C10, C12, C14, and C16); for these compounds,
the mesogenic properties were also investigated.
Mesomorphic properties and thermal stability for the two new homologous series I and
II were determined by a hot-stage polarizing microscope. Transition temperatures of both
series are given in Tables 1 and 2.
In series I, all compounds exhibit enantiotropic smectic-A mesophase. The plot of
transition temperatures versus the number of carbon atoms in the alkoxy chain (Fig. 11)
exhibits no usual odd–even effect but as the series is ascended the curve shows a falling
tendency.
In series II, compounds containing C1–C8 carbon atoms in the alkoxy chain are
monotropic smectic-A liquid crystalline compounds, whereas C10, C12, C14, and C16 are
enantiotropic smectic-A compounds. The plot showing transition temperatures versus the
number of carbon atoms in the alkoxy chain (Fig. 12) exhibits odd–even effect up to C5
carbon atom.
The transition temperatures data obtained from a polarizing microscope are compared
with differential scanning calorimetry (DSC) data and the data of some representative
compounds are given in Table 3. Both the data are almost comparable. The DSC curves of
compounds of series I and II are shown in Figs. 13–16.
The above two series made it possible to observe the effects of structural changes on
mesomorphic behavior in a system that was studied previously.
The texture of the liquid crystalline compounds is given as microphotographs in
Fig. 17.

184
B. T. Thaker et al.
200
180
160
140
120
100
Sm
I
80
60
40
20
0
0
2
4
6
8
10
12
14
16
Number of carbon atoms
Figure 11. Transition temperature graph of series I.
It has been observed that series I compounds have high transition temperature than
that of series II compounds, in spite of high molecularity of compounds. This is because
of the presence of hydrogen bonding in compounds of series I as reported earlier [32]. The
Table 2. Transition temperature data of series II
Transition temperature
◦
(
in C)
Code no.
R = n-alkyl
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
Sm
II
a
B1
B2
B3
B4
B5
B6
B7
B8
B10
B12
B14
B16
142
120
136
96
110
118
85
84
74
80
162
155
149
142
136
130
128
116
94
a
a
a
a
a
a
a
Decyl
Dodecyl
Tetradecyl
Hexadecyl
92
114
95
100
82
aMonotropic phase.
O
C
RO
N
N
O
OC H
4
9
Series II

Liquid Crystals with Ester-Azo Linking Groups
185
180
160
140
120
100
Sm
I
80
60
40
20
0
0
2
4
6
8
10
12
14
16
Number of carbon atoms
Figure 12. Transition temperature graph of series II.
hydrogen bonding in compounds of series I is confirmed by IR spectra. The IR spectra of
−1
−1
compounds show that the broad band centered between 3430 cm and 3414 cm . This
band disappeared after esterification in series II. Both the series compounds show smectic-
A mesophase because of the presence of a biphenyl ring due to which the lateral cohesion
force is more compared with the terminal cohesion force. That is why the molecules remain
in the form of lamellar bunch.
RO
N
N
OH
Series I
O
RO
N
N
C
O
OC H
4 9
Series II
R
N
N
OH
Series A
C H
N
n
2n+1
N
O
C
C H
5 11
O
Series B
A comparison of the reported 4(4-alkyl phenylazo)phenols shows it is not mesomorphic
ꢀ
(
series A), whereas 4 -[(4-n-alkoxyphenyl)diazenyl]biphenyl-4-ol (series I) is mesomorphic
(
Table 4).
The diazotization reactions are run in aqueous solutions, and there is no difficulty
for higher analogues. The present compound is smectogenic having a higher clearing
temperature than that of phenol analogues.

186
B. T. Thaker et al.
Figure 13. DSC thermogram for compound A10 on heating and cooling (series I).
Compounds with alkyl and alkoxy terminal groups on both sides and phenyl and
biphenyl moieties in the central core and having central linkages are identical in both types
of series compounds.
It has been observed that when an alkyl group is present at the terminal phenyl group,
the clearing temperature is always lower than that of the alkoxy terminal group as indicated
by Gray et al. [33].
Figure 14. DSC thermogram for compound A14 on heating and cooling (series I).

Liquid Crystals with Ester-Azo Linking Groups
187
Figure 15. DSC thermogram for compound B10 on heating and cooling (series II).
Figure 16. DSC thermogram for compound B10 on heating and cooling (series II).

188
B. T. Thaker et al.
Figure 17. Microphotographs of the compounds on heating.
The comparison of the reported 4(4-alkyl phenylazo)phenyl-4-pentylbenzoate
ꢀ
(
series B) with 4 [(4-alkoxy phenyl)diazenyl]4-n-butoxy phenyl biphenyl carboxylate (se-
ries II) reveals that the clearing temperatures of series B compounds are greater than those
of the present series II (Tables 5 and 6). Another interesting observation seen in the above
series is that when the hydrocarbon chains are connected directly to the benzene ring, the
mesophase starts at lower temperatures. In series B, a nematic mesophase starts from very
Table 3. Transition temperature and DSC data of series I and II
Peak temperature
◦
−1
−1 −1
Code no. Transition (Microscopic temperature) (in C) ꢀH (J g ) ꢀS (J g k )
A10
A14
B10
B14
Cr-Sm
Sm-I
Cr-Sm
Sm-I
Cr-Sm
Sm-I
Cr-Sm
Sm-I
71.26 (72)
119.15 (119)
90.46 (87)
99.15 (102)
74.73 (74)
92.50 (94)
100.24 (100)
114.12 (114)
15.5776
27.7671
27.5514
27.7671
25.3786
47.2723
10.1864
33.4346
0.0926
0.0406
0.2070
−0.2367
−0.3153
0.0780
0.1313

Liquid Crystals with Ester-Azo Linking Groups
189
Table 4. Transition temperature data of series A and I
Series A
Series I
n (number of
carbon atoms)
n (number of
carbon atoms)
◦
◦
Isotropic ( C)
Isotropic ( C)
8
76
77
87
91
98
100
104
–
–
–
–
–
1
2
3
4
5
6
7
8
10
12
14
16
182
177
173
160
158
155
140
136
119
113
102
104
1
1
1
1
1
2
2
–
–
–
–
0
2
4
6
8
0
2
first member of the carbon chain, while smectic-C mesophase starts from higher homo-
logues say C14. In the present series II, the clearing temperatures are lower than those of
series B. For the first carbon atom up to C16 carbon atom in the alkyl chain, smectic-A
mesophase was obtained because both ends of the series have alkoxy groups and the middle
core of the series has a biphenyl moiety, which increases the polarizability of the molecule.
As a result of this, the molecule becomes more lamellar, stratified, and highly arranged,
thus showing smectic-A phase.
Conclusion
All the compounds of series I exhibit mesomorphic behavior showing enantiotropic smectic-
A phase. From the comparison of series I and II, it has been observed that the transition
temperature of series I compounds is higher than that of series II, which is due to hydrogen
Table 5. Transition temperature data of series B and series II
n (number of carbon atoms)
Smectic-C
Nematic
Isotropic
2
4
6
8
0
2
4
6
8
0
2
–
–
–
–
–
–
120
84
76
80
86
207.41
200.1
187.7
177.6
169.1
159.1
153.1
146.4
140.7
135.5
130.5
1
1
1
1
1
2
2
79
80.0 (Sm-C)
84.0 (Sm-C)
86.0 (Sm-C)
90.0 (Sm-C)
86.0 (Sm-C)
84.7
89.2
93.3
96.5
100.9

190
B. T. Thaker et al.
Table 6. Transition temperature data of series II
n (number of carbon atoms)
Smectic A
Isotropic
1
2
3
4
5
6
7
8
0
2
4
6
142
120
136
96
110
118
85
84
74
80
100
82
162
155
149
142
136
130
128
116
94
1
1
1
1
92
114
95
bonding present in series I. In series II, mesomorphic compounds show smectic-A phase
from C1 to C8 and hence are monotropic, whereas C10, C12, C14, and C16 are enantiotropic.
Both series are smectogenic because of the presence of a biphenyl moiety in the central
core.
Acknowledgments
We are grateful to Prof. R. A. Vora, retired Prof. and Head, Department of Applied Chem-
istry, Faculty of Technology and Engineering, Kalabhavan, M. S. University of Baroda,
Vadodara, India, for his valuable suggestions. We are also thankful to CDRI, Lucknow, Atul
Industries Ltd., and SAIF Chandigarh for providing facilities such as elemental analysis,
1
FT-IR, H-NMR, mass spectral, and thermal analyses.
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