Supramolecular liquid crystals in binary and ternary systems

Article abstract of DOI:10.1016/j.tca.2011.01.033

Five, new laterally methyl-substituted, pyridine-based derivatives (I8-I16) having molecular formula 4-C_nH_2n+1O-C₆H ₄COOC₆H₃(2-CH₃)-NN-C ₅H₄N, with n varies

Full text of DOI:10.1016/j.tca.2011.01.033

Thermochimica Acta 517 (2011) 63–73
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Thermochimica Acta
journal homepage: www.elsevier.com/locate/tca
Supramolecular liquid crystals in binary and ternary systems
Magdi M. Naoum∗, Abdelgawad A. Fahmi, Mohamed A. Alaasar, Rim A. Salem
Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Five, new laterally methyl-substituted, pyridine-based derivatives (I8–I16) having molecular formula 4-
CnH2n+1O–C6H4COOC6H3(2-CH3)–N N–C5H4N, with n varies between 8 and 16 carbons, were prepared
and investigated for their mesophase behavior by differential scanning calorimetry (DSC) and polarized
light microscopy (PLM). All prepared homologues were found to be smectogenic, possessing the smectic
C mesophase. Binary mixtures, covering the whole concentration range, were independently prepared
from corresponding isomers, one from series In and the other from series IIn, in which the methyl group
is introduced this time into position-3. All mixtures were similarly characterized and their binary-phase
diagrams constructed, from which the eutectic composition of each pair of isomers was determined. The
increased stability of the SmC phase of mixtures is a consequence of the enhanced lateral molecular forces
between the two components of the mixture.
Received 6 December 2010
Received in revised form 1 January 2011
Accepted 22 January 2011
Available online 26 February 2011
Keywords:
Supramolecular LCs
4-(4ꢀ-Pyridylazo-2-methylphenyl)-4ꢀꢀ-
alkoxy
benzoates
Hydrogen-bonded 1:1 associates, formed between each of the derivatives (I8–I16) and 4-alkoxybenzoic
acids (IIIm), were prepared and similarly characterized to investigate the effect of lateral methyl orien-
tations on the stability of the mesophases induced by intermolecular hydrogen bonding. All complexes
prepared were investigated for their mesophase behavior by DSC and PLM and found to possess SmC
as the only mesophase observed. The formation of the hydrogen-bonded complexes was confirmed by
constructing their binary phase diagrams with the acid that cover the whole range of concentration of
the two complements.
4-Alkoxybenzoic acids
Binary and ternary mixtures
Finally, the formation of the hydrogen-bonded complexes between the eutectic mixtures of two
pyridine-based isomers (I/II) and 4-alkoxybenzoic acids (IIIm) was confirmed by constructing their appar-
ent binary phase diagrams (actually of three components) with the acid (III) that cover the whole range
of concentration of the two components (eutectic I/II and III).
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
(as proton-acceptors) and 4-alkoxybenzoic acids (as the proton
donors).
Interests in liquid crystalline materials have expanded greatly
in recent years because of their optical properties. They can
be found in a wide spectrum of applications: signpost pan-
els, digital watches, calculators, cell phones, laptop displays,
etc. Nearly all the devices used in our daily life nowadays
use a liquid crystal display. Liquid crystal materials for device
applications are mostly mixtures, usually of eutectic com-
position. Generally, lateral substitution decreases the thermal
stability of both solid and mesophases [1–6]. Supramolecu-
lar liquid crystals are frequently induced, through hydrogen
bonding, between aromatic carboxylic acids, as proton donor,
and pyridine-based components, as proton acceptor [7–15]. We
have previously reported [16–18] the preparation and charac-
terization of some supramolecular, hydrogen-bonded, complexes
between derivatives of pyridylazophenyl substituted benzoates
Thus, toreducethe meltingpoints ofthose previously [16] inves-
tigated supramolecular complexes, attempts were made [19,20]
by introducing lateral methyl group into position-3 of the cen-
tral benzene ring of the pyridine-based component of the complex
[16–18]. In another investigation, we have observed [21] that the
mesophase stability is differently affected by the spatial orientation
of the methyl group substituted once in position-2 and another in
position-3 of the central benzene ring in another group of azo-ester
derivatives, namely, 4-(4ꢀ-substituted phenylazo)-2 (or 3-)-methyl
phenyl)-4ꢀꢀ-alkoxy benzoates [21]. It was found that lateral methyl
substitution in position-2, with respect to the ester group, fur-
nishes compounds mesomorphically more stable, compared with
their isomers, methyl-substituted in position-3. These results have
encouraged us to extend our investigation towards preparation and
characterization of another group of isomers In in which the methyl
group is laterally oriented by an angle different from that of the
previously investigated [20] ones, IIn.
Binary mixtures of liquid crystalline materials can often lead
either to a new liquid crystal phases, not observed in the corre-
∗
Corresponding author. Tel.: +20 127132834; fax: +20 235673673.
E-mail address: magdinaoum@yahoo.co.uk (M.M. Naoum).
0040-6031/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2011.01.033

64
M.M. Naoum et al. / Thermochimica Acta 517 (2011) 63–73
sponding pure components, or to the extension of the temperature
range over which their mesophases are stable [22,23]. The enhance-
ment of the liquid crystalline region often occurs because of the
depression of the melting point, which reaches a minimum at the
eutectic composition. However for certain materials, it is possible to
observe, beside the melting point depression, liquid crystal phases
that are formed via tailoring the molecular interaction between
the components of the mixture thus increasing the stability of the
induced mesophase, i.e., increasing the mesophase-isotropic tran-
sition temperature [24–28].
Transition temperatures were checked and type of mesophase
identified for the newly prepared pyridine-based derivatives (In)
and their complexes with the acids (IIIm), using a standard polar-
ized light microscope PLM (Wild, Germany) attached to a home
made hot-stage. The temperature is measured by a thermocouple
placed just beside the sample and attached to temperature con-
troller made by Brookfield, England.
The purity of samples prepared were checked with thin-layer
chromatography using TLC-sheets coated with silica gel (E. Merck),
whereby spots were detected by a UV-lamp. All the new derivatives
(In) were found to be TLC pure.
The goal of the present study is, first, to prepare a new
group of pyridine based derivatives (I8–I16) and investigate their
mesophase behavior via differential scanning calorimetry (DSC)
and polarized-light microscopy (PLM).
2.1. Preparation of materials
O
The pyridine-based azo dyes (In) were prepared according to
the following scheme:
C
H2n+1CnO
N N
O
N
1) HCl/NaNO2
N
N N
OH
CH3
NH2
N
H3C
2) o-cresol/NaOH
(A)
In
I8, n = 8, I10, n = 10, I12, n = 12, I14, n = 14, I16, n = 16
The second aim is to investigate their ability towards
supramolecular hydrogen-bond formation with 4-alkoxybenzoic
acids, in comparison with those of their 3-methyl-substituted
isomers, IIn [20]. A third aim is to investigate, individually, the
binary-phase behavior of each two pair of isomers, one from each
group, I and II, aiming to elucidate their eutectic compositions.
O
O
C OH
DCC/DMAP
CH2Cl2/ stirring
+
H
2n+1CnO
(A)
O
OC
N
NN
OCnH2n+1
C
H2n+1CnO
O
N N
N
CH3
CH3
(In)
IIn
2.1.1. Preparation of 4-(4ꢀ-pyridylazo)-2-methylphenol (A)
II8, n = 8, II10, n = 10, II12, n = 12, II14, n = 14, II16, n = 16
This was prepared according to the method described by Zhang
and coworkers [30] from 4-aminopyridine and o-cresol. The yield
of the crude product was 62%, and melts at 232.6 ◦C.
Finally, it is planned to investigate again the ability of
each eutectic mixture towards the formation of the three-
component supramolecular hydrogen-bonded complexes with
4-alkoxybenzoic acids, IIIm, aiming to obtain complexes with lower
melting point and greater mesophase stability.
2.1.2. Preparation of
4-(4ꢀ-pyridylazo-2-methylphenyl)-4ꢀꢀ-alkoxy-benzoates (In)
This was prepared by the method previously described [16] for
the preparation of the laterally neat analogues. The solids (≈45%
yield) obtained were crystallized from ethanol and found to be
TLC pure and possess sharp melting temperatures as measured by
DSC and are given in Table 1. Elemental analyses were conducted
for these newly prepared compounds and the results (as given in
Table 1) were consistent with structures proposed.
H2m+1Cm
O
COOH
IIIm
III6, m = 6, III8, m = 8, III10, m = 10, III12, m = 12 and III16, m = 16.
2. Experimental
2.1.3. Preparation of supramolecular complexes
For the preparation of the supramolecular complexes (In/IIIm
or In/IIn/IIIm), binary mixtures of any two complimentary compo-
nents, were prepared in a 1:1 molar ratio by melting the appropriate
amounts of each component, stirring to give an intimate blend, and
then cooling with stirring to room temperature.
For the construction of binary phase diagrams, the mixtures
of the two components were prepared to cover the whole range
of composition. Transition temperatures obtained for all pre-
pared blends, were measured by DSC and phases identified by
PLM. In the phase diagrams, constructed by plotting transi-
tion temperatures versus mixture composition, the symbol “ꢁ”
denotes solid-mesophase, “ꢀ” mesophase-isotropic transitions,
“᭹” mesophase- another mesophase, and, “ꢂ” eutectic tempera-
ture.
The molecular formulae of the newly prepared pyridine-based
derivatives (I8–I16) were confirmed via elemental analyses, 1H
NMR, and mass spectroscopy. The results were in agreement,
within the permissible limits, with the structures assigned.
Infrared absorption spectra were measured with a Perkin-Elmer
B25 spectrophotometer, and 1H NMR spectra with a Varian EM
350L.
Calorimetric measurements were carried out using a PL-DSC of
Polymer Laboratories, England. The instrument was calibrated for
temperature, heat and heat flow according to the method recom-
mended by Cammenga et al. [29]. DSC measurements were carried
out for small samples (2–3 mg) placed in sealed aluminum pans.
All of the thermograms have been achieved at a heating rate of
10 ◦C/min in an inert atmosphere of nitrogen gas (10 ml/min).

M.M. Naoum et al. / Thermochimica Acta 517 (2011) 63–73
65
Table 1
Elemental analyses, transition temperatures (◦C), and transition enthalpies (kJ/mol), for the pyridine-based derivatives In.
Comp. no.
n
Analys. (found)
Calc.
Transition
temperatures
C
H
N
TCr–C
ꢀHCr–C
TC–I
(82.5)
(82.4)
83.1
84.2
(79.1)
ꢀHC–I
I8
8
(72.81) 72.78
(73.57) 73.54
(74.25) 74.22
(74.86)747.82
(75.40) 75.36
(6.97)7.01
(7.40)7.45
(7.78)7.83
(8.13)8.18
(8.44)8.49
(9.44)9.43
(8.88)8.37
(8.38)8.37
(7.94)7.93
(7.54)7.53
91.9
85.8
73.5
79.5
83.2
40.66
61.11
41.04
74.82
77.90
0.78
0.45
0.28
0.97
1.00
I10
I12
I14
I16
10
12
14
16
TCr–C: crystal to SmC transition; TC–I: SmC to isotropic transition (monotropic).
3. Results and discussion
can be seen from Table 1, except for the homologues I12
and I14, other members of the series exhibit monotropic SmC
mesophase. The melting temperatures vary irregularly, as usual,
with the increase of the alkoxy-chain length (n). Alternatively,
the monotropic isotropic-to-SmC transition decreases with the
increase of n. The homologues I12 and I14 were found to exhibit
a narrow range of an enantiotropic SmC phase, namely ≈10
and 5 ◦C, respectively. Comparison of the data of the corre-
sponding isomers in group In and the previously investigated
group IIn [20] revealed that, the position and/or orientation of
the lateral methyl group on the central benzene ring has but
a slight effect on both melting points and smectic C stabil-
ity between each pair of isomers. The SmC phase, as identified
by PLM, of the derivatives I6–I16 was confirmed by construct-
ing their binary phase diagrams with the purely smectogenic
(SmC) acid components III14 and III16, as will be discussed
later.
3.1. Confirmation of molecular structure
The molecular formulae of the newly prepared pyridine-based
homologues (In) were confirmed via elemental analyses, IR, 1H
NMR, and mass spectra. Elemental analyses and infrared spec-
tra were in agreement with the proposed formulae. 1H NMR data
showed expected integrated aliphatic–aromatic ratios. Mass spec-
tra indicated exact molecular masses for the whole molecular
structures and expected fragmentation.
3.2. Phase behavior
3.2.1. Pyridine-based molecules
Transition temperatures and transition enthalpies of the pre-
pared pyridine-based derivatives (In) are given in Table 1. As
Fig. 1. Binary phase diagrams of the pyridine-based derivative (I8) with various alkoxybenzoic acids IIIm. (a) m = 6, (b) m = 8, (c) m = 10, (d) m = 12, and (e) m = 16.

66
M.M. Naoum et al. / Thermochimica Acta 517 (2011) 63–73
Fig. 2. Binary phase diagrams of the pyridine-based derivative (I10) with various alkoxybenzoic acids IIIm. (a) m = 6, (b) m = 8, (c) m = 10, (d) m = 12, and (e) m = 16.
Table 2
Transition temperatures (◦C), transition enthalpies (kJ/mol) of the 1:1 supramolecular complexes (In/IIIm).
System
n
m
TCr–C
99.4
ꢀHCr–C
TC–I
ꢀHC–I
I8/III6
8
6
44.1
30.2
57.6
52.8
51.4
36.0
43.5
54.0
64.2
54.7
43.6
56.7
54.3
82.1
74.6
77.4
59.5
82.9
84.7
61.6
64.7
55.7
52.0
55.6
67.0
161.4
158.8
153.8
151.1
144.0
162.4
157.1
153.7
151.8
145.7
151.2
154.9
153.1
151.0
146.7
149.7
148.1
145.8
142.0
140.2
146.1
151.6
146.1
142.1
141.2
4.0
4.6
4.0
3.9
3.4
3.1
3.3
3.0
3.1
7.0
2.4
4.1
4.2
3.4
5.3
2.9
3.4
3.9
10.1
13.1
4.1
5.0
7.9
8.3
12.0
I8/III8
8
10
12
16
6
106.4
104.8
94.7
I8/III10
I8/III12
I8/III16
I10/III6
I10/III8
I10/III10
I10/III12
I10/III16
I12/III6
I12/III8
I12/III10
I12/III12
I12/III16
I14/III6
I14/III8
I14/III10
I14/III12
I14/III16
I16/III6
I16/III8
I16/III10
I16/III12
I16/III16
90.5
10
12
14
16
109.2
105.8
94.4
96.3
99.6
117.0
97.8
100.2
97.3
104.8
96.2
88.3
93.0
98.7
99.0
104.4
100.1
107.8
103.2
109.7
8
10
12
16
6
8
10
12
16
6
8
10
12
16
6
8
10
12
16
Table 3
Eutectic composition, eutectic transition temperatures and enthalpies for the system In/IIn.
System
n
Mol% In
TCr–C
ꢀHCr–C
TC–I
ꢀHC–I
I8/II8
8
53.4%
48.8%
41.3%
72.3%
73.4%
71.1
65.3
68.1
71.3
70.1
27.4
19.6
36.6
28.1
636
85.7
85.2
81.9
80.3
79.4
0.3
0.3
0.6
2.0
1.3
I10/II10
I12/II12
I14/II14
I16/II16
10
12
14
16

M.M. Naoum et al. / Thermochimica Acta 517 (2011) 63–73
67
3.2.2. Supramolecular hydrogen-bonded complexes (In/IIIm)
Let us first investigate the binary phase behavior of this system,
in order to confirm complex formation between the pyridine-based
derivatives (In) and 4-alkoxybenzoic acids (IIm). Figs. 1–5 represent
binary phase diagrams of the pyridine-based components (I8–I16)
with five homologues of 4-alkoxybenzoic acids (IIIm). As can be
seen from these figures, the nematic phase of the nematogenic acid
III6 and the polymorphic acids III8–III12 disappear upon the addi-
Fig. 3. Binary phase diagrams of the pyridine-based derivative (I12) with various alkoxybenzoic acids IIIm. (a) m = 6, (b) m = 8, (c) m = 10, (d) m = 12, and (e) m = 16.
Fig. 4. Binary phase diagrams of the pyridine-based derivative (I14) with various alkoxybenzoic acids IIIm. (a) m = 6, (b) m = 8, (c) m = 10, (d) m = 12, and (e) m = 16.

68
M.M. Naoum et al. / Thermochimica Acta 517 (2011) 63–73
Fig. 5. Binary phase diagrams of the pyridine-based derivative (I16) with various alkoxybenzoic acids IIIm. (a) m = 6, (b) m = 8, (c) m = 10, (d) m = 12, and (e) m = 16.
tion of the base I8 in an amount that decreases (from 40 to 20 mol%
of In) with the increase of the length of the alkoxy-chain of the
acid component (m). Alternatively, the enantiotropic SmC phase of
all acid homologues is retained in their binary mixtures throughout
almost the whole composition range, confirming the SmC nature of
the mesophase exhibited by newly prepared derivatives, I8–I16. In
each case, complex formation either in the solid or the SmC phase
is evidenced by the formation of two eutectic compositions, one
Fig. 6. Binary phase diagrams of the two pyridine based isomers (In/IIn). (a) n = 8, (b) n = 10, (c) n = 12, (d) n = 14, and (e) n = 16.

M.M. Naoum et al. / Thermochimica Acta 517 (2011) 63–73
69
Table 4
Transition temperatures (◦C), transition enthalpies (kJ/mol) of the 1:1 supramolecular complexes (In/IIn/IIIm).
Complex
n
m
TCr–C
86.2
ꢀHCr–C
TC–I
ꢀHC–I
I8/II8/III6
8
6
20.9
84.6
46.2
69.9
59.7
35.7
50.7
62.5
51.5
56.9
39.6
74.9
48.3
55.3
76.7
60.7
86.6
61.3
71.8
84.1
36.2
48.7
61.8
61.1
59.5
159.3
157.7
152.5
149.4
140.2
155.0
152.0
151.0
152.0
142.0
150.0
150.0
142.0
142.0
137.0
148.3
146.3
144.1
136.1
139.5
148.6
140.4
137.0
135.0
132.0
2.4
3.4
3.1
2.9
3.6
1.5
2.8
2.9
3.0
6.6
3.3
3.9
1.8
4.4
9.0
2.5
3.1
3.6
4.2
2.1
4.1
2.7
5.9
8.2
8.2
I8/II8/III8
I8/II8/III10
I8/II8/III12
I8/II8/III16
8
10
12
16
6
97.7
88.2
97.8
84.5
96.0
86.0
92.0
94.0
92.0
98.0
92.0
92.0
94.0
96.0
85.7
81.8
90.1
94.8
92.6
97.2
85.9
92.0
93.0
101.0
I10/II10/III6
I10/II10/III8
I10/II10/III10
I10/II10/III12
I10/II10/III16
I12/II12/III6
I12/II12/III8
I12/II12/III10
I12/II12/III12
I12/II12/III16
I14/II14/III6
I14/II14/III8
I14/II14/III10
I14/II14/III12
I14/II14/III16
I16/II16/III6
I16/II16/III8
I16/II16/III10
I16/II16/III12
I16/II16/III16
10
12
14
16
8
10
12
16
6
8
10
12
16
6
8
10
12
16
6
8
10
12
16
preceding and the other following the 1:1 molar ratio. Complex
formation is continued in the mesophase since the stability of the
mesophase is greatly enhanced again at the 1:1 molar ratio. Simi-
lar behavior is observed (Figs. 2–5) for the binary mixtures of the
other homologues (I10–I16) with the five homologues of the acid
III6–III16, whereby all diagrams exhibit enhanced SmC stability for
the 1:1 complexes in all the systems In/IIIm.
Having been confirmed, all possible 1:1 complexes made from
each of the homologues In with each of the acids IIIm were pre-
pared and characterized for their phase behavior by DSC and the
type of the mesophase identified by PLM. The results are col-
lected in Table 2. Irrespective of the length of the alkoxy chain, on
either side of the complex, SmC mesophase is the only mesophase
observed in all of the complexes investigated, the stability of the
SmC mesophase was found to decrease slightly with the increase
of n or m. The melting point of the complex, on the other hand, was
found to vary irregularly, as usual, but with small variations with
either n or m.
isomers. This type of interaction practically has lead to one eutectic
composition only. Accordingly, we have decided to start first with
elucidating the eutectic composition of each pair of isomers (In/IIn).
The corresponding binary phase diagrams are represented graphi-
cally in Fig. 6. The eutectic compositions and their phase transitions
and enthalpies are given in Table 3. As can be seen from Fig. 6, except
for the binary mixture I14/II14, there is slight enhancement of the
SmC stability for each of the binary systems (In/IIn). This may indi-
cate that the smectic arrangement of the two isomeric molecules
in the mixture is made face to face allowing the two molecules to
be laterally closer leading to such slight SmC enhancement.
Being determined, each of the eutectic mixture (In/IIn) was first
prepared and then mixed, alternatively, with each of the acid com-
ponents, IIIm. The apparent binary phase diagrams (In/IIn as one
component and IIIm as the second) were constructed and rep-
resented graphically in Figs. 7–11, for n = 8, 10, 12, 14, and 16
carbons, respectively. As can be seen from these figures, in all
ternary systems investigated, the eutectic mixture (In/IIn), acting
as one component, is strongly hydrogen-bonded to the acid com-
ponent regardless of the length of the alkoxy group attached to
either side of the complex. These results add more evidence that
the pyridine-based constituents (In and IIn) of each eutectic mix-
ture (In/IIn) do sterically interact in favor of SmC arrangement, as
deduced before from their binary phase diagrams in Fig. 6. Also
deduced from Figs. 7–11, that the formation of the 1 (acid): 1 (mixed
bases) complexes is evident, in the solid phase, by the two eutec-
tic compositions, one preceding and the other following the 1:1
molar ratio; and in the mesophase by the enhanced SmC stability
at the same composition. Furthermore, in all cases, independent
of n or m, all the 1:1 complexes are purely smectogenic exhibiting
SmC as the only mesophase. This again indicates that the SmC is
the mesophase observed in pure pyridine-based components, 4-
alkoxy benzoic acid, and their binary and ternary supramolecular
complexes. On the other hand, the nematic phase of the lower acid
homologues (III6–III12) disappears completely upon addition of
the eutectic mixture in a mol% that is decreased by the increase of
m.
3.2.2.1. Supramolecular complexes of three components. It was
planned to apply the triangle of composition [31,32] to the ternary
systems In/IIn/IIIm in order to elucidate the eutectic composition
of these ternary systems. In this method, the composition triangle
is constructed by locating each of the eutectic compositions of the
three individual binary mixtures (In/IIn, In/IIIm, and IIn/IIIm) on its
corresponding side and connecting each one to the opposing apex
(representing the third pure component IIIm, IIn, and In, respec-
tively). The point of intersection of the three inner connecting lines
gives the eutectic composition of the ternary system concerned.
Practically, it was observed that this method is not applicable to
cases exhibiting strong intermolecular interaction, such as hydro-
gen bonding. In the present case there are strong intermolecular
interactions, via hydrogen bonding, within two of the three binary
mixtures, namely In/IIIm and IIn/IIIm, which constitute two sides
of composition triangle; in each case, instead, not only one but
two eutectic points were observed one precedes and the other fol-
lows the 1:1 composition. The third side of the triangle represents
the binary mixtures of the two pyridine-based isomers (In and IIn)
which exhibits but relatively weak lateral interaction between the
two methyl groups protruded by different angles within the two
Comparison of the mesomorphic data for the complexes
In/IIn/IIIm (Table 4) with those of their corresponding binary com-
plexes In/IIIm (Table 2), indicates that the addition of the second

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Fig. 7. Binary phase diagrams of the eutectic (I8/II8) with various alkoxybenzoic acids IIIm. (a) m = 6, (b) m = 8, (c) m = 10, (d) m = 12, and (e) m = 16.
Fig. 8. Binary phase diagrams of the eutectic (I10/II10) with various alkoxybenzoic acids IIIm. (a) m = 6, (b) m = 8, (c) m = 10, (d) m = 12, and (e) m = 16.

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Fig. 9. Binary phase diagrams of the eutectic (I12/II12) with various alkoxybenzoic acids IIIm. (a) m = 6, (b) m = 8, (c) m = 10, (d) m = 12, and (e) m = 16.
Fig. 10. Binary phase diagrams of the eutectic (I14/II14) with various alkoxybenzoic acids IIIm. (a) m = 6, (b) m = 8, (c) m = 10, (d) m = 12, and (e) m = 16.

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Fig. 11. Binary phase diagrams of the eutectic (I16/II16) with various alkoxybenzoic acids IIIm. (a) m = 6, (b) m = 8, (c) m = 10, (d) m = 12, and (e) m = 16.
isomeric pyridine-based component IIn to the binary complexes
In/IIIm does not greatly influence the SmC stability. The differ-
ence between the SmC stability of the two complexes is small and
decreases further upon increase of m. This again, as pointed out
above, indicates that the addition of one isomer to the other does
not disturb the smectic arrangement of the system.
(IIn) revealed that position and/or orientation of the lateral
methyl group on the central benzene ring of the pyridine-based
compounds do not affect significantly either the melting point
or the mesophase stability of their hydrogen-bonded associates
with 4-alkoxybenzoic acids.
3. Except for the binary phase I14/II14, there are but slight
enhancements of the SmC stability of each of the binary systems
(In/IIn) indicating that the arrangement of molecules within the
mesophase is in favor of SmC formation.
4. Conclusions
4. The binary phase diagrams of the three-component complexes,
In/IIn as one component and IIIm as the second, revealed that the
addition of the isomer IIn to the complex In/IIIm almost does
not affect the stability of the hydrogen-bonded complex. This
again indicates that the position (or orientation) of the lateral
methyl group does not disturb smectic arrangements either in
the pure pyridine-based component or in its hydrogen-bonded
complexes.
The effect of introducing a lateral methyl group, of different ori-
entation, into the pyridine-based azo-dye derivatives of the type
4-(4ꢀ-pyridylazo-2 (or 3-)-methylphenyl)-4ꢀꢀ-alkoxy benzoates, In
and IIn, on the formation, stability, and type of the mesophase
observed in the prepared derivatives was investigated. The ter-
minal alkoxy group in both series of compounds varies between
8, 10, 12, 14, and 16 carbons. Two groups of hydrogen-bonded
supramolecular complexes were investigated for their mesophase
behavior. In both groups of complexes, five homologues of the
4-alkoxybenzoic acids, III6–III16, were used and the 1:1 molar
complex formation was confirmed by constructing their binary
phase diagrams. In the first group of complexes, In/IIIm, the two
components are a pyridine-based homologue (In) and a homo-
logue of the acids (IIIm). In the second group of complexes, the
pyridine-based components, In/IIn, were the eutectic mixture of
two corresponding isomers from series I and II. The study revealed
the following:
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