Effect of lateral substitution on mesogenic properties of fluoro aniline derivatives

Article abstract of DOI:10.1080/15421406.2010.526455

Three new homologous series of liquid crystals with terminal fluoro group and central linkages such as ester and azo groups were synthesized and their mesomorphic properties were studied. All three series are similar in molecular structure with the difference in their lateral substitutions: series I has no lateral substitution, series II has a chloro group as lateral substitution, and series III has a methyl group as lateral substitution. All 12 homologues of each of the series are mesogenic in nature. The nematic phase of the series shows a marble texture and the smectic phase shows a Schlieren texture of the smectic C variety. The mesomorphic characteristics of the series are compared with each other. Copyright Taylor & Francis Group, LLC.

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Effect of Lateral Substitution on
Mesogenic Properties of Fluoro Aniline
Derivatives
Jayrang S. Dave a , C. B. Upasani b & Purvang D. Patel b
a Applied Chemistry Department , Faculty of Technology and
Engineering, The M.S. University of Baroda , Gujarat, India
b Jyoti Om Chemical Research Centre Pvt. Ltd. , Gujarat, India
Published online: 14 Dec 2010.
To cite this article: Jayrang S. Dave , C. B. Upasani & Purvang D. Patel (2010) Effect of Lateral
Substitution on Mesogenic Properties of Fluoro Aniline Derivatives, Molecular Crystals and Liquid
Crystals, 533:1, 73-81, DOI: 10.1080/15421406.2010.526455
To link to this article: http://dx.doi.org/10.1080/15421406.2010.526455
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Mol. Cryst. Liq. Cryst., Vol. 533: pp. 73–81, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421406.2010.526455
Effect of Lateral Substitution on Mesogenic
Properties of Fluoro Aniline Derivatives
JAYRANG S. DAVE,1 C. B. UPASANI,2 AND
PURVANG D. PATEL2
1Applied Chemistry Department, Faculty of Technology and
Engineering, The M.S. University of Baroda, Gujarat, India
2Jyoti Om Chemical Research Centre Pvt. Ltd., Gujarat, India
Three new homologous series of liquid crystals with terminal fluoro group and
central linkages such as ester and azo groups were synthesized and their meso-
morphic properties were studied. All three series are similar in molecular structure
with the difference in their lateral substitutions: series I has no lateral substitution,
series II has a chloro group as lateral substitution, and series III has a methyl group
as lateral substitution. All 12 homologues of each of the series are mesogenic in
nature. The nematic phase of the series shows a marble texture and the smectic
phase shows a Schlieren texture of the smectic C variety. The mesomorphic charac-
teristics of the series are compared with each other.
Keywords Azo ester; chloro and methyl groups; homologues; lateral substitu-
ents; mesophase range; smectic C and nematic mesophase
Introduction
Generally, liquid-crystalline compounds are rod-like molecules with stable central
linkages [1–6]. Lateral substitution makes molecules broad; lateral substituents play
an effective role in mesogenic properties of a mesogenic compound. Studies on the
effect of lateral substitution have been carried out by several researchers. A survey
of the literature indicates that generally the mesophase range of mesogens with lat-
eral substituent is less than that for laterally unsubstituted mesogens [7–18]. Thus, in
order to study the corelation between chemical constitution and mesomorphism,
three new homologous series with ester and azo central linkages, a fluoro terminal
group, and chloro and methyl lateral groups were synthesized and their meso-
morphic properties were studied.
Experimental
4-Hydroxy benzoic acid, the appropriate n-alkyl halides, p-fluoro aniline, phenol,
o-chloro phenol, and ocresol were used as received. Solvents were dried and distilled
Address correspondence to Jayrang S. Dave, Applied Chemistry Department, Faculty of
Technology and Engineering, The M.S. University of Baroda, Vadodara 390 001, Gujarat,
India. E-mail: jayrangdave@yahoo.com
73

74
J. S. Dave, C. B. Upasani, and P. D. Patel
prior to use. Microanalyses of some of the representative compounds were
performed on a Perkin Elmer Series II 2400-CHN analyzer; infrared (IR) spectra
were recorded on a Perkin Elmer GX-FTIR, and nuclear magnetic resonance
(NMR) spectra were measured on a Bruker Avance II-500 spectrometer. Liquid-
crystalline properties were investigated on a Leitz Laborlux 12 POL polarizing
microscope provided with a Kofler heating stage. Differential scanning colarimetry
(DSC) was performed on a Mettler Toledo Star SW 7.01.
1. 4-n-Alkoxy benzoic acids and 4-n-alkoxy benzoyl chlorides were synthesized by
the modified method of Dave and Vora [19].
2. 4-Hydroxyphenylazo-40-fluoro benzene, 3-chloro-4-hydroxyphenylazo-40-fluoro
benzene, and 3-methyl-4-hydroxyphenylazo-40-fluoro benzene were prepared by
a known method [20].
3. The series, namely 4-(40-n-alkoxybenzoyloxy)-phenylazo-400-fluorobenzenes,
4-(40-n-alkoxybenzoyloxy)-3-chlorophenylazo-400-fluorobenzenes, and 4-(40-n-
alkoxybenzoyloxy)-3-methylphenylazo-400-fluorobenzenes were synthesized by
adding dropwise a cold solution of 4-hydroxy phenylazo-40-fluorobenzene (for
series I), 3-chloro-4-hydroxyphenylazo-40-fluorobenzene (for series II), and
3-methyl-4-hydroxyphenylazo-40-fluoro benzene (for series III), respectively, in
dry pyridine to a cold solution of 4-n-alkoxy benzoyl chloride. The mixture
was allowed to stand overnight at room temperature. It was acidified with 1:1
cold HCl and the separated solid was filtered and recrystallized from ethanol until
constant transition temperatures were obtained. These are recorded in Table 1.
The elemental analysis of all the compounds was found to be satisfactory
(Table 2). The synthetic route of the series is shown in Scheme 1.
Fourier Transform Infrared (Nujol, KBr Pellets, Cmꢀ1
Series I: 4-(40-n-butyloxybenzoyloxy)phenylazo-400-fluorobenzenes: 2,937, 1,729
)
=
(-COO-), 1,073 (-C-F), 1,597 (-N N-), 1,496, 1,389, 1,258, 1,169, 1,073, 969, 843,
761, 692.
1H NMR: (CDCl3, 200 MHz, d, ppm, Standard Trimethyl Sulfoxane)
Series I: 4-(40-n-butyloxybenzoyloxy)phenylazo-400-fluorobenzenes: d 1.0 (3H, t,
-CH3), 1.4–1.79 (m, alkyl chain), 4.05 (2H, t, -OCH2-CH2), 6.98 (2H, d, H5), 7.02
(2H, d, H4), 7.36 (2H, d, H2), 7.9 (2H, d, H6), 8.0 (2H, d, H1), 8.1 (2H, d, H3).
Fourier Transform, Infrared (Nujol, KBr Pellets, Cmꢀ1
Series II: 4-(40-n-octyloxybenzoyloxy)3-chlorophenylazo-400-fluorobenzenes: 2,944,
)
=
1,731 (-COO-), 1,066 (-C-F), 1,606 (-N N-), 850 (-C-Cl), 1,504, 1,420, 1,319,
1,264, 1,041, 953, 839, 755, 689.
1H NMR: (CDCl3, 200 MHz, d, ppm, Standard Trimethyl Sulfoxane
Series II: 4-(40-n-octyloxybenzoyloxy)3-chlorophenylazo-400-fluorobenzenes : d 0.9
(3H, t, -CH3), 1.4–1.79 (m, alkyl chain), 4.05 (2H, t, -OCH2-CH2), 6.98 (2H, d, H4),
7.0 (2H, d, H5), 7.36 (2H, d, H2), 7.9 (2H, d, H6), 8.0 (2H, d, H1), 8.1 (2H, d, H3).

Mesogenic Properties of Fluoro Aniline Derivatives
75
ꢁ
Table 1. Transition Temperature C of the Present Series I, II, and III
ꢁ
R¼n-alkyl group
Transition temperatures C
Nematic Isotropic
(Series I) 4-(40-n-alkoxybenzoyloxy)-phenylazo-400- fluorobenzenes
Smectic C
Methyl
Ethyl
Propyl
Butyl
Pentyl
—
—
—
—
—
—
130
122
115
110
100
91
83
93
110
—
206
208
205
209
198
194
182
164
142
131
126
124
Hexyl
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
85
89
93
04
—
—
109
(Series II) 4-(40-n-alkoxybenzoyloxy)-3-chlorophenylazo-400-fluorobenzenes
Methyl
Ethyl
Propyl
Butyl
Pentyl
—
—
—
—
—
—
—
—
—
83
92
96
121
113
105
95
89
85
80
77
75
93
159
167
163
156
150
146
139
126
119
113
110
108
Hexyl
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
—
—
(Series III) 4-(40-n-alkoxybenzoyloxy)-3-methylphenylazo-400-fluorobenzenes
Methyl
Ethyl
Propyl
Butyl
Pentyl
—
—
—
—
—
—
—
—
—
—
81
86
113
109
100
90
84
78
73
69
72
78
148
139
133
128
125
116
109
103
98
Hexyl
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
96
93
91
85
—

76
J. S. Dave, C. B. Upasani, and P. D. Patel
Table 2. Elemental Analysis
Calculated
H (%)
Found
H (%)
Series
Homologue
C (%)
N (%)
C (%)
N (%)
I
II
III
C4
C8
C6
70.40
67.15
71.88
5.35
5.80
6.22
7.14
5.80
6.45
70.24
67.02
71.60
5.29
5.66
5.46
7.18
5.72
6.31
Scheme 1. Synthetic route for series I, II and III.
Fourier Transform Infrared (Nujol, KBr Pellets, Cmꢀ1
Series III: 4-(40-n-hexyloxybenzoyloxy)3-methylphenylazo-400-fluorobenzenes: 2,946,
)
=
1,729 (-COO-), 1,065 (-C-F), 1,603 (-N N-), 1,317 (-C-CH3), 1,498, 1,317, 1,260,
1,096, 842, 724, 689, 615.
1H NMR: (CDCl3, 200 MHz, d, ppm, Standard Trimethyl Sulfoxane)
Series III: 4-(40-n-hexyloxybenzoyloxy)3-methylphenylazo-400-fluorobenzenes : d 0.9
(3H, t, -CH3), 1.3–1.8 (m, alkyl chain), 4.0 (2H, t, -OCH2-CH2), 6.98 (2H, d, H4),
7.0 (2H, d, H5), 7.30 (2H, d, H2), 7.9 (2H, d, H6), 8.1 (2H, d, H1), 8.2 (2H, d, H3).
Results and Discussion
In the present study, 12 homologues from each of the three series, 4-(40-n-alkoxy
benzoyloxy)-phenylazo-400-fluorobenzenes (series I), 4-(40-n-alkoxy benzoyloxy)-3-
chlorophenylazo-400-fluorobenzenes (series II), and 4-(40-n-alkoxy benzoyloxy)-3-
methylphenylazo-400-fluorobenzenes (series III), were synthesized and their
mesomorphic properties were studied.
The general molecular structure of the series is shown in Scheme 2.
All 12 homologues of series I are mesogens; the nematic phase commences from
the first derivative and remains up to the decyl derivative, whereas the smectic C

Mesogenic Properties of Fluoro Aniline Derivatives
77
Scheme 2. General molecular structure of series I, II and III.
phase commences from the octyl derivative and remains to be exhibited up to the last
hexadecyl derivative synthesized. Figure 1 shows the plot of transition temperatures
against number of carbon atoms in the alkoxy chain; it indicates that N-I curve
shows overall falling tendency with a slight increase at the fourth derivative and
merges with the falling S-I curve as the series is ascended. No odd–even effect is
observed in the N-I curves or S-I curves. The Cr-M transitions show a falling tend-
ency from the methyl to heptyl derivative and then a rising tendency from the octyl
derivative to hexadecyl derivative. The nematic phase of the series shows a marble
texture and the smectic phase shows a Schlieren texture of the smectic C variety.
All 12 homologues of series II are mesogens; the nematic phase commences from
the first derivative and remains up to the dodecyl derivative, whereas the smectic C
phase commences from the dodecyl derivative and remains to be exhibited up to the
last hexadecyl derivative synthesized. Figure 2, that is, the plot of transition tempera-
tures against number of carbon atoms in the alkoxy chain, indicates that the N-I
curve shows an overall falling tendency with a slight increase at the second derivative
and merges with the falling S-I curve as the series is ascended.
Here no odd–even effect is observed in the N-I curves or S-I curves. The Cr-M
transitions show a falling tendency from the methyl to decyl derivative and a rising
tendency from the dodecyl derivative to hexadecyl derivative. Here, too, the nematic
phase of the series shows a marble texture and the smectic phase shows a Schlieren
texture of the smectic C variety.
Figure 1. 4-(40-n-Alkoxybenzoyloxy) phenylazo-400-fluorobenzenes (series I).

78
J. S. Dave, C. B. Upasani, and P. D. Patel
Figure 2. 4-(40-n-Alkoxybenzoyloxy)-3chloro phenylazo-400-fluorobenzenes (series II).
All 12 homologues of series III are mesogens; the nematic phase commences
from the first derivative and remains up to the tetradecyl derivative, whereas the
smectic C phase commences from the tetradecyl derivative and remains to be exhib-
ited up to the last hexadecyl derivative synthesized. Figure 3, that is, the plot of tran-
sition temperatures against number of carbon atoms in the alkoxy chain, indicates
that the N-I curve shows an overall falling tendency with a slight increase at the fifth
derivative and merges with a falling S-I curve as the series is ascended.
No odd–even effect is observed in the N-I curve or S-I curves. The Cr-M transi-
tions show a falling tendency from the methyl to dodecyl derivative and a rising
Figure 3. 4-(4-n-Alkoxybenzoyloxy)-3methyl phenylazo-400-fluorobenzenes (series III).

Mesogenic Properties of Fluoro Aniline Derivatives
79
ꢁ
Table 3. Average Mesophase Range C
Commencement of
smectic mesophase
Series
Nematic
Smectic
I
II
III
189.7 (C1 to C10)
143.8 (C1 to C12)
117.09 (C1 to C14)
116.8 (C8 to C16)
103.66 (C12 to C16)
88 (C14 to C16)
C8
C12
C14
tendency from the dectyl derivative to hexadecyl derivative. Like the other two ser-
ies, here also the nematic phase of the series shows a marble texture and the smectic
phase shows a schlieren texture of smectic C variety.
The average nematic mesophase range of series I is 189.7ꢁC, series II is 143.8ꢁC,
and series III is 117.09 ꢁC, similarly the average smectic mesophase range of series I
is 116.8ꢁC, that of series II is 103.6ꢁC, and series III is 88ꢁC. Comparison of average
mesophase range of all three series (Table 3) shows that both the nematic and smec-
tic mesophase range of series II and series III are lower than those of series I. Here,
the nature of lateral substituents has important implications on phase transition tem-
peratures and average mesophase range. The effect of the lateral group in the central
benzene ring causes disruption in the molecular packing, which reduces the tran-
sition temperatures and melting points as well as the mesophase range compared
to the laterally unsubstituted analogues. The introduction of a chloro group (series
II) and a methyl group (series III) in the ortho position of the ester linkage of series I
effectively reduced both the clearing and melting points compared to those of the
parent compound (series I). The commencement of the smectic mesophase is late
in series II and series III compared to series I, which is due to the non-coplanarity
caused by the molecules. Series II and series III both are laterally substituted in com-
parison with series I; the breadth of the molecules of series II and III is increased due
to the presence of a lateral group on the central benzene ring, which decreases both
smectic and nematic thermal stabilities [21]. The difference in commencement of
mesophase type is only because of the different nature of the lateral substitution.
The smectic tendency of the molecule is less effected by the chloro group than the
methyl group [21]. The enthalpies of the butyl derivative of series I, octyl derivative
of series II, and hexyl derivative of series III were measured by DSC. The data are
shown in Table 4 and Fig. 4 shows the DSC curves of the C4 homologue of series I,
the C8 homologue of series II, and the C6 homologue of series III.
Table 4. DSC Data
Heating
Series Member rate (ꢁC minꢀ1
Transition
temperature D (H=Jgꢀ1) D (S=Jgꢀ1 Kꢀ1
)
)
I
Butyl
Octyl
Hexyl
5
5
5
Cr-N 110
N-I 211
Cr-N 77
N-I 126
Cr-N 78
N-I 116
61.49
2.73
83.00
1.65
72.77
0.92
0.160
0.0066
0.237
0.0041
0.207
0.0023
II
III

80
J. S. Dave, C. B. Upasani, and P. D. Patel
Figure 4. DSC curves.
Conclusion
The effect of –Cl and –CH3 lateral substitutents on phase behavior, and phase tran-
sition temperatures was studied. These lateral substituents depress both melting
point and clearing points of the liquid crystals. Mesogens with an ortho lateral sub-
stitution have a reduced smectic and nematic mesophase range compared to the cor-
responding unsubstituted homologues.
Acknowledgment
The authors thank the Head of Applied Chemistry Department, Faculty of Tech-
nology and Engineering, the M.S. University of Baroda, Vadodara, for providing
us with the use of a polarizing optical microscope. We also thank Jyoti Om Chemical
Research Centre Pvt. Ltd., Ankleshwar, for providing laboratory facilities.
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Mesogenic Properties of Fluoro Aniline Derivatives
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