Study of mixed mesomorphism in binary systems of azo-ester mesogens with structurally dissimilar nonmesogenic as well as mesogenic ester homologues

Article abstract of DOI:10.1080/15421406.2013.807708

We have studied mixed mesomorphism in four binary systems comprising two azo-ester mesogens, viz. 4-(4′-n-alkoxybenzoyloxy)3-methylphenyl azo-2″ and 4″-dimethylbenzenes (where n-alkoxy is n-butoxy or n-hexyloxy), and two ester nonmesogenic and mesogenic components, viz. 4-nitrophenyl-4′-n-alkoxybenzoates (where n-alkoxy is n-butoxy or n-hexyloxy). All the four binary systems are mesogenic in nature, showing nematic phase with threaded/marble texture. The phase diagrams of the binary systems are plotted and eutectic transition temperatures and maximum mesophase ranges of the nematic mesophase in all the systems are determined.

Full text of DOI:10.1080/15421406.2013.807708

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Study of Mixed Mesomorphism in Binary
Systems of Azo-Ester Mesogens With
Structurally Dissimilar Nonmesogenic As
Well As Mesogenic Ester Homologues
Himanshu S. Bhatt a , Purvang D. Patel a & Jayrang S. Dave a
a Department of Applied Chemistry, Faculty of Technology and
Engineering , The M.S. University of Baroda , Vadodara , India
Published online: 16 Dec 2013.
To cite this article: Himanshu S. Bhatt , Purvang D. Patel & Jayrang S. Dave (2013) Study of Mixed
Mesomorphism in Binary Systems of Azo-Ester Mesogens With Structurally Dissimilar Nonmesogenic
As Well As Mesogenic Ester Homologues, Molecular Crystals and Liquid Crystals, 587:1, 80-91, DOI:
10.1080/15421406.2013.807708
To link to this article: http://dx.doi.org/10.1080/15421406.2013.807708
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Mol. Cryst. Liq. Cryst., Vol. 587: pp. 80–91, 2013
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2013.807708
Study of Mixed Mesomorphism in Binary Systems
of Azo-Ester Mesogens With Structurally
Dissimilar Nonmesogenic As Well As Mesogenic
Ester Homologues
HIMANSHU S. BHATT, PURVANG D. PATEL,
AND JAYRANG S. DAVE∗
Department of Applied Chemistry, Faculty of Technology and Engineering,
The M.S. University of Baroda, Vadodara, India
We have studied mixed mesomorphism in four binary systems comprising two
azo-ester mesogens, viz. 4-(4ꢀ-n-alkoxybenzoyloxy)3-methylphenyl azo-2ꢀꢀ and 4ꢀꢀ-
dimethylbenzenes (where n-alkoxy is n-butoxy or n-hexyloxy), and two ester nonmeso-
genic and mesogenic components, viz. 4-nitrophenyl-4ꢀ-n-alkoxybenzoates (where n-
alkoxy is n-butoxy or n-hexyloxy). All the four binary systems are mesogenic in nature,
showing nematic phase with threaded/marble texture. The phase diagrams of the bi-
nary systems are plotted and eutectic transition temperatures and maximum mesophase
ranges of the nematic mesophase in all the systems are determined.
Keywords Azo-ester mesogens; binary systems; mixed mesomorphism; nematic; non-
mesomorphic and mesomorphic ester homologues; phase diagrams
1. Introduction
Physical properties of individual mesogens may or may not undergo modifications in
their mixtures. Sometimes, the modifications become characteristic thereby making the
study of mixtures important. Earlier studies [1–14] have suggested the formation of mixed
mesomorphism by mixing compounds where none, one, or both of them are mesogens.
Most of the binary mixtures do not undergo any change in their mesomorphic textures,
though a few have been reported giving rise to different textures [15]. Emergence of the
mesophase, increase or decrease of the mixed mesomorphic ranges and thermal stabilities,
and the study of the factors that influence the modification have received more attention
[15–19]. Our group has reported mixtures were a higher-order smectic phase emerges
from mixtures of nematogens and a lower-order nematic phase emerges from mixture of
a smectogen [8] and a nonmesogen; binary systems of structurally similar and dissimilar
mesogens and nonmesogens [9, 20] have also been reported. Keeping this in view, we
report here four binary systems consisting of azo-ester mesogens with nonmesogenic and
mesogenic carboxy esters to examine the properties of mixed mesophases.
∗Address correspondence to Jayrang S. Dave, Department of Applied Chemistry, Faculty of
Technology and Engineering, The M.S. University of Baroda, Vadodara 390 001, India. E-mail:
jayrangdave@yahoo.com
80

Mixed Mesomorphism in Binary System of Azo-Ester Mesogens
81
The binary mixtures are composed of azo mesogens, namely, 4-(4ꢀ-n-butoxybenzoy-
loxy)3-methylphenyl azo-2ꢀꢀ,4ꢀꢀ-dimethylbenzene and 4-(4ꢀ-n-hexyloxybenzoyloxy)3-
methylphenyl azo-2ꢀꢀ,4ꢀꢀ-dimethylbenzene, and nonmesogenic as well as mesogenic esters,
namely, 4-nitrophenyl-4ꢀ-n-butoxybenzoate and 4-nitrophenyl-4ꢀ-n-hexyloxybenzoate, re-
spectively.
O
C
H3C
RO
O
N
N
CH3
H3C
Where,
R = C4H9, [BBMPAD]
A1 = 4-(4ꢀ-n-butoxybenzoyloxy)3-methylphenyl azo-2ꢀꢀ,4ꢀꢀ-dimethylbenzene [Cr 90 N
155 I]
R = C6H13, [HBMPAD]
A2 = 4-(4ꢀ-n-hexyloxybenzoyloxy)3-methylphenyl azo-2ꢀꢀ,4ꢀꢀ-dimethylbenzene [Cr 95 N
145 I]
O
RO
C
O
O
N+
O–
Where,
B1 = R = C4H9, 4-nitrophenyl-4ꢀ-n-butoxybenzoate [Cr 55 I] [NPBB]
B2 = R = C6H13, 4-nitrophenyl-4ꢀ-n-hexyloxybenzoate [Cr (52) N 68 I] [NPHB]
The binary systems studied are (1) BBMPAD + NPBB, (2) HBMPAD + NPBB, (3)
BBMPAD + NPHB, and (4) HBMPAD + NPHB.
2. Experimental
2.1 Synthesis
All the chemicals used were of Loba chemie, and Merck grade. 4-(4ꢀ-n-alkoxybenzoy-
loxy)3-methylphenyl azo-2ꢀꢀ,4ꢀꢀ-dimethylbenzenes and 4-nitrophenyl-4ꢀ-n-alkoxybenzoates
were synthesized by reported methods. 4-n-alkoxy benzoic acids and 4-n-alkoxy benzoyl
chlorides were synthesized by the known method [21] and 3-methyl-4-hydroxyphenylazo-
2ꢀ,4ꢀ-dimethyl benzene was also prepared by known method [22]. The above com-
pounds A1 & A2 were synthesized by adding drop wise a cold solution of 3-methyl-4-
hydroxyphenylazo-2ꢀ-4ꢀ-dimethyl benzene in dry pyridine to a cold solution of 4-n-butoxy
benzoyl chloride and 4-n-hexyloxy benzoyl chloride, respectively. The mixture was allowed

82
H. S. Bhatt et al.
to stand overnight at RT. It was acidified with 1:1 cold HCl and the separated solid was fil-
tered and recrystallized from ethanol until constant transition temperatures were obtained.
TLC shows single spot product. The synthetic route is shown in Scheme 1 and Scheme 2.
H3C
H2N
CH3
CH3
HO
RO
RO
COOH
COOH
COCl
3
1
H3C
Cl N2
4
2
H3C
HO
H3C
N
N
CH3
5
O
RO
H3C
O
N
N
CH3
H3C
Scheme 1. Synthetic route 1.
IR spectra: were recorded on a Shimadzu IR-408. Component HBMPAD: 2954–2857
(C H St, Alkyl CH3, SP3 hybridization), 1734 ( C O St. of ester), 1601 ( N N
St.), 1577–1503 ( C C St. of aromatic ring), 1477 ( C H bending of CH2 ), 1247
(aromatic ether St.), 1061( C O St. of ester), 893 (strong C H bending for 1:2:4 tri
substituted benzene ring), 725 (weak C H bending for polymethylene-(CH2)n-) cm−1
.
HO
RO
RO
COOH
COOH
COCl
1
2
3
O
RO
C
O
N+
O–
O
Scheme 2. Synthetic route 2.

Mixed Mesomorphism in Binary System of Azo-Ester Mesogens
83
1H NMR: for HBMPAD (CDCl3, 300 MHz, δ, ppm, standard TMS)
δ = 0.93 (t, 3H, aliphatic CH3), 1.35–1.82 (m, 10H, 5( CH2-)), 1.85 (Qunt. 2H,
COCH2), 4.04(t, 3H, OCH2), 2.32, 2.37, 2.68 (s, 3H, Ar CH3), 6.95–7.06 (m, 4H,
ArH), 7.13–8.17 (m, 6H, ArH).
For azo-ester mesogens:
R = CnH2n+1 [n = 4 or 6];
(1) alcohol, KOH, n-RBr, (2) SOCl2, (3) HCl, NaNO2, H2O/0–5◦C, (4) 2-methyl phenol,
aq. NaOH, at 0–10◦C, pH 8–12, (5) dry pyridine, 1:1 cold HCl.
For nonmesogenic and mesogenic compounds:
R = CnH2n+1 [n = 4 or 6]; (1) alcohol, KOH, RBr, (2) SOCl2, (3) 4-nitrophenol, dry
pyridine, 1:1 cold HCl.
2.2 Preparation and Study of Binary Mixtures
The components were weighed in known proportions and melted together in fusion tubes.
They were thoroughly mixed in their melt to obtain a homogeneous mixture, after which
they were cooled. This procedure was repeated three to four times. The solid obtained was
finally ground and used for determining transition temperatures, by using a Leitz Laborlux
12 POL polarizing microscope fitted with a Kofler heating stage.
3. Results and Discussion
3.1 Binary System 1: BBMPAD (A1) + NPBB (B1)
In this system (Table 1, Fig. 1), the ester component B1 is nonmesomorphic in nature (K 55
I), whereas the azo-ester mesogen A1 is mesomorphic in nature (K 90 N 155 I) exhibiting
nematic phase with Schlieren texture. The mesogenic characteristic commences in the form
of enantiotropic nematic with the addition of as low as 7.74 mole% of A1 component to
B1 and it continues to be exhibited till the last binary mixture studied. System shows
Table 1. BBMPAD (A1) + NPBB (B1)
Transition temperature
(Nematic, ◦C)
Transition temperature
(Isotropic, ◦C)
Mole% of A1
0.00
7.74
—
49
51
55
52
46
45
52
62
80
90
55
58
70
85
88
15.89
24.49
33.54
43.07
53.19
63.85
75.20
87.21
100.00
94
115
128
134
143
155

84
H. S. Bhatt et al.
O
O
C4H9O
C
H3C
N
N
CH3
BBMPAD (A1)
H3C
K 90 N 155 I
O
C4H9O
C
O
O
N+
O–
NPBB (B1)
K 55 I
Cr - M
N - I
160
140
120
100
80
160
140
120
100
80
60
60
40
40
0
20
40
60
80
100
Comp. A1 - 0.00%
Comp. B1 - 100%
Comp. A1 - 100%
Comp. B1 - 0.00%
Mole %
Figure 1. BBMPAD (A1) + NPBB (B1).
threaded/marble texture of nematic phase. The N-I curve shows deviation from linearity.
The maximum mesophase range of 76◦C is obtained at 63.85 mole% of A1. Eutectic point
is obtained at 53.19 mole% of A1 with eutectic temperature 45◦C and mesophase range of
70◦C at this point.

Mixed Mesomorphism in Binary System of Azo-Ester Mesogens
85
Table 2. HBMPAD (A2) + NPBB (B1)
Transition temperature
(Nematic, ◦C)
Transition temperature
Mole% of A2
(Isotropic, ◦C)
0.00
7.30
—
52
51
55
50
47
38
55
63
84
95
55
65
76
81
88
91
96
131
132
141
145
15.05
23.31
32.09
41.37
51.54
62.30
73.96
86.47
100.00
3.2 Binary System 2: HBMPAD (A2) + NPBB (B1)
In this system (Table 2, Fig. 2), the ester component B1 is nonmesomorphic in nature
(K 55 I), whereas the azo mesogen A2 is mesomorphic in nature (K 95 N 145 I) exhibiting
nematic phase with Schlieren texture. The mesogenic characteristic commences in enan-
tiotropic nematic form with the addition of as low as 7.30 mole% of A2 component and it
continues to be exhibited till the last binary mixture studied. The eutectic point is sharp and
obtained at 38◦C with 51.54 mole% of A2; the N-I curve shows deviation from linearity
and highest mesophase range of 76◦C is obtained at 62.30 mole% of A2.
3.3 Binary System 3: BBMPAD (A1) + NPHB (B2)
In this system (Table 3, Fig. 3), the ester component B2 is monotropic mesomorphic in nature
(K (52) N 68 I), whereas the azo-ester mesogen A1 is enantiotropic mesomorphic in nature
Table 3. BBMPAD (A1) + NPHB (B2)
Transition temperature
(Nematic, ◦C)
Transition temperature
(Isotropic, ◦C)
Mole% of A1
0.00
8.38
(52)
52
53
52
50
47
54
63
76
82
90
68
58
68
74
78
103
111
116
122
125
155
17.10
26.10
35.49
45.18
55.29
65.79
76.74
88.11
100.00

86
H. S. Bhatt et al.
O
O
C
H3C
N
N
C6H13O
CH3
HBMPAD (A2)
H3C
K 95 N 145 I
O
C4H9O
C
O
O
N+
O–
NPBB (B1)
K 55 I
Cr - M
N - I
160
140
120
100
80
160
140
120
100
80
60
60
40
0
40
20
40
60
80
100
Comp. A2 - 100%
Comp. B1 - 0.00%
Comp. A2 - 0.00%
Comp. B1 - 100%
Mole %
Figure 2. HBMPAD (A2) + NPBB (B1).
(K 90 N 155 I) showing nematic mesophase. The mesogenic characteristic commences in
enantiotropic nematic form with the addition of as low as 8.38 mole% of A1 component
and it continues to be exhibited till the last binary mixture studied. Binary system shows
threaded/marble texture of nematic phase. The N-I curve shows deviation from linearity and
highest mesophase range of 57◦C is obtained at 55.29 mole% of A1 component. Eutectic
point is obtained at 45.18 mole% of A1 component with eutectic temperature 47◦C.

Mixed Mesomorphism in Binary System of Azo-Ester Mesogens
87
O
C
H3C
C4H9O
O
N
N
CH3
BBMPAD (A1)
H3C
K 90 N 155 I
O
C6H13O
C
O
O
N+
O–
NPHB (B2)
K (52) N 68 I
Figure 3. BBMPAD (A1) + NPHB (B2).

88
H. S. Bhatt et al.
Table 4. HBMPAD (A2) + NPHB (B2)
Transition temperature
(Nematic, ◦C)
Transition temperature
Mole% of A2
(Isotropic, ◦C)
0.00
7.75
(52)
52
52
54
52
46
43
53
65
84
95
68
63
73
85
88
15.92
24.50
33.55
43.10
53.17
63.87
75.18
87.21
100.00
94
109
114
121
128
145
3.4 Binary System 4: HBMPAD (A2) + NPHB (B2)
In this system (Table 4, Fig. 4), the ester component B2 is monotropic nematogen (K (52)
N 68 I), whereas the azo mesogen A2 is enantiotropic nematogen (K 95 N 145 I). The
mesogenic characteristic commences in enantiotropic nematic form with the addition of as
low as 7.75 mole% of A2 component and it continues to be exhibited till the last binary
mixture studied. Binary system shows threaded/marble texture of nematic phase. Here the
eutectic point is sharp at 53.17 mole% of A2; N-I curve shows deviation from linearity and
maximum mesophase range of 66◦C is obtained at eutectic point.
Study of these binary systems indicates that as the molecular geometry of the two
componentsinthebinarymixturediffers, N-I deviatefromlinearity. This nonlineartendency
could be due to different structural moieties forming the terminal groups and central
linkages. Nonlinear behavior of binary phase diagrams, where one of the components has
a strong polar end group, has been reported by other workers earlier also [23–25]. In these
binary systems, deviation from linearity can be attributed to the high tendency of the nitro
group of favoring the formation of oriented fluids. Most of the textures show super cooling
below 35◦C, i.e., they remain in the liquid crystalline phase below 35◦C and then they
crystallize. In all the binary systems, nematic mesophase emerges with the addition of
about 10 mole% of azo-ester mesogens (A1 or A2) in ester components (B1 or B2). All the
binary systems show sharp eutectic point.
So study of liquid crystalline behavior of above-prepared binary mixtures shows that
mixture of two mesogenic components gives better mesomorphic range than individual
components as well as depress solid to mesomorphic transition temperature in mixture.
3.5 Polarizing Optical Microscopic Images of Synthesized Compounds and Prepared
Binary Systems
The mesophases exhibited by systems 1–4 were examined by polarizing optical microscopy
(POM). Thin films of the samples were obtained by sandwiching them between a glass slide
and cover slip. All the prepared binary systems 1–4 were found to exhibit mesomorphism.

Mixed Mesomorphism in Binary System of Azo-Ester Mesogens
89
O
C
H3C
C6H13O
O
N
N
CH3
HBMPAD (A2)
H3C
K 95 N 145 I
O
C6H13O
C
O
O
N+
O–
NPHB (B2)
K (52) N 68 I
Figure 4. HBMPAD (A2) + NPHB (B2).

90
H. S. Bhatt et al.
On cooling from the isotropic liquid to mesomorphic and then mesomorphic to crystals
exhibited nematic mesophase.
Polarizing optical microscopic images of liquid crystalline state of azo mesogens are
as under:
Polarizing optical microscopic images of Schlieren texture of nematic (U) at 114◦C
and (V) at 121◦C of compound A1 and A2 exhibited while cooling.
Polarizing optical microscopic images of liquid crystalline state of prepared binary
systems are as under:
Polarizing optical microscopic images of threaded texture of nematic (W) at 101◦C,
(X) at 102◦C, (Y) at 78◦C, and (Z) at 97◦C of prepared binary systems 1–4 exhibited while
cooling.

Mixed Mesomorphism in Binary System of Azo-Ester Mesogens
4. Conclusion
91
Four binary systems are reported with structurally dissimilar azo-ester mesogens and
nonmesogenic as well as mesogenic ester components. In all binary systems, nematic
mesophase emerges in enantiotropic nematic form with the addition of less than 10 mole%
of azo-ester mesogenic components. In all the four binary systems, N-I curve deviates from
linearity. Some of the mixtures super cool below 35◦C, which can be potential mixtures for
optical display applications.
Acknowledgment
One of the authors (Himanshu S. Bhatt) is thankful to The M.S. University of Baroda,
Vadodara, for the financial support.
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