Mesomorphism of azo-esters and chalcone-esters

Article abstract of DOI:10.1080/15421406.2016.1146910

AOne chalcone-ester homologous series of mesogens α-4-[4^/-n-alkoxybenzoyloxy phenyl β-4^//methoxy benzoyl ethylenes (A) and one azo-ester homologous series of mesogens p-(p^/-n-alkoxybenzoyloxy) phenyl azo-p^//-methoxy benzene (B) being structurally similar are discussed. Both series (A) and (B) differ in respect of central bridges linking two phenyl rings. Mesomorphic properties start from 6th and 1st member of series (A) and (B) respectively. In series (A), 6th to 12th members show both smectogenic and nematogenic properties, and the 14th and 16th members show only nematogenic property. While in series (B), 1st to 10th members show nematogenic properties, 11th member shows both smectogenic and nematogenic properties, while 12th member shows only smectogenic property. Thermal stability of series (A) is relatively high as compared to series (B). Transition temperatures are observed through hot stage polarizing microscope by the miscibility method. Analytical data support the structure of molecules. Textures of series (A) in nematic are threaded and Schlieren in SmecticSmectic A type, while that of series (B) in nematic are threaded in SmecticSmectic A and smectic C.

Full text of DOI:10.1080/15421406.2016.1146910

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Mesomorphism of azo-esters and chalcone-esters
B. B. Jain, Vinay S. Sharma, H. N. Chauhan & R. B. Patel
To cite this article: B. B. Jain, Vinay S. Sharma, H. N. Chauhan & R. B. Patel (2016)
Mesomorphism of azo-esters and chalcone-esters, Molecular Crystals and Liquid Crystals,
630:1, 102-111, DOI: 10.1080/15421406.2016.1146910
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Date: 05 July 2016, At: 03:56

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Mesomorphism of azo-esters and chalcone-esters
B. B. Jain, Vinay S. Sharma, H. N. Chauhan, and R. B. Patel
Chemistry Department, K. K. Shah JarodwalaManinagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
One chalcone-ester homologous series of mesogens α-4-[4/-n-
alkoxybenzoyloxy phenyl β-4//methoxy benzoyl ethylenes (A) and one
azo-ester homologous series of mesogens p-(p/-n-alkoxybenzoyloxy)
phenyl azo-p//-methoxy benzene (B) being structurally similar are
discussed. Both series (A) and (B) differ in respect of central bridges
linking two phenyl rings. Mesomorphic properties start from 6th and 1st
member of series (A) and (B) respectively. In series (A), 6th to 12th mem-
bers show both smectogenic and nematogenic properties, and the 14th
and 16th members show only nematogenic property. While in series (B),
1st to 10th members show nematogenic properties, 11th member shows
both smectogenic and nematogenic properties, while 12th member
shows only smectogenic property. Thermal stability of series (A) is
relatively high as compared to series (B). Transition temperatures are
observed through hot stage polarizing microscope by the miscibility
method. Analytical data support the structure of molecules. Textures of
series (A) in nematic are threaded and Schlieren in SmecticSmectic A
type, while that of series (B) in nematic are threaded in SmecticSmectic
A and smectic C.
Azo-ester; chalcone-ester;
mesogen; mesophase;
nematic; smectic
GRAPHICAL ABSTRACT
CONTACT B. B. Jain
bijendrajain@gmail.com
Ahmedabad-, Gujarat,India.
K. K. Shah JarodwalaManinagar Science College, Gujarat University,
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©  Taylor & Francis Group, LLC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
103
Introduction
The relation between mesomorphic property and molecular structure has been estab-
lished with reference to varying terminally and or laterally substituted functional groups of
molecules, but less attention has been given to central bridges linking phenyl rings [1–6].
Therefore, present investigation is planned with a view to establish the effect of central bridge
on mesomorphic behavior of molecules [7–14]. The number of liquid crystal compounds
consisted of rigid part as two or three phenyl rings bridged through central bridge and flexi-
ble part as varying left polar terminal, alkyl, or alkoxy end group keeping right terminal end
group intact of fix polarity with or without lateral substitution [15–18].
Experimental
Synthesis: Series A
4-Hydroxy benzoic acid is alkylated by using suitable alkylating agents and resulting n-alkoxy
benzoic acid is converted into n-alkoxy benzoyl chloride (X) by using thionyl chloride by
the Dave and Vora method. α-4-Hydroxy phenyl β-4/methoxy benzoyl ethylene (Z) was pre-
pared by reacting p-hydroxyl benzaldehyde and p-methoxy acetophenone by the established
method. Compounds (X) and (Z) condensed in cold dry pyridine by the known method.
Scheme . Synthesis route of series (A) and (B).

104
B. B. JAIN ET AL.
The final product was decomposed, filtered, washed, dried, and recrystallized until a constant
temperature is not obtained.
Series B
4-Hydroxy benzoic acid is alkylated by using suitable alkylating agents, and the resulting n-
alkoxy benzoic acid is converted into n-alkoxy benzoyl chloride (X) by using thionyl chlo-
ride by the Dave and Vora method. 4-((4-Methoxy phenyl)diazenyl) phenol was prepared by
diazotized 4-metoxyaniline and coupling of diazonium salt with phenol in basic condition.
Compounds (X) and (Y) were condensed in cold dry pyridine by the known method. The
final product was decomposed, filtered, washed, dried, and recrystallized until constant tem-
perature is not obtained.
Characterization
Representative homologues of a series were characterized by infrared (IR) spectroscopy, and
1H NMR spectra. IR spectra were recorded by Perkin–Elmer spectrum GX,1 and H NMR
spectra were recorded on Bruker using CDCl3 as a solvent. Transition temperature and LC
properties (textures) were determined using an optical polarizing microscopy equipped with
heating stage. Textures of nematic phase were determined by the miscibility method.
Spectral data
For series (A)
IR in cm−1
Hexyloxy
–
720 (-(CH2)n of –OC6H13), 815 (phenyl ring), 1175 (C O of –OC6H13), 1215, 1260, and 1640
( COO), 930 ( CH=CH ).
–
–
–
Decyloxy
–
–
760 ( (CH2)nof –OC10H21), 830 (phenyl ring), 1175, 1150 (C O of –OC10H21), 1250, 1610,
–
–
–
–
and 1680 ( COO ), 945 ( CH=CH ).
NMR in ppm
Octyloxy
–
–
–
0.983 ( CH3 of –OC8H17), 1.422 ( (CH2)n of –OC8H17), 3.675 ( OCH2 of –OC8H17), 6.565
–
–
and 6.582 ( CH=CH CO), 7.404, 7.093, and 7.636 (phenyl ring).
Dodecyloxy
–
–
–
0.945 ( CH3 of –OC8H17), 1.465 ( (CH2)n of –OC8H17), 3.689 ( OCH2 of –OC8H17), 6.575
–
–
and 6.669 ( CH=CH CO), 6.691, 7.610, and 7.632 (phenyl ring).
Texture Determination
Tetradecyl–nematic–threaded
Decyl–smectic–smectic-A type
Hexyl–smectic–smectic-A type
Octyl–nematic–Schlieren

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
105
For series (B)
IR in cm−1
Butoxy
2291, 2848 confirm alkyl group
1729 confirm >C=O ester
1495, 1463, 1579, 1605 confirm aromatic phenyl ring
1320 Confirm –N=N-
–
1257, 1169 confirm C O ether linkage
844 confirm P- substituted phenyl ring
Octyloxy
2940, 2856 confirm alkyl group
1735 confirm >C=O ester
1500, 1471, 1582, 1610 confirm aromatic phenyl ring
1322 confirm -N=N-
–
1257, 1069 confirm –C O ether linkage
849 confirm P-substituted phenyl ring
Texture determination
Tetradecyl–smectic–smectic-A type
Hexadecyl–smectic–smectic-C type
Butoxy–nematic–threaded
Octyloxy–nematic–threaded
Result and discussion
n-Alkoxy benzoic acids are dimeric through hydrogen bonding. Dimerization disappears as a
result of breaking of hydrogen bonding on esterification by α-4-hydroxy phenyl β-4/methoxy
benzoyl ethylene and 4-((4-methoxy phenyl)diazenyl) phenol, thus transition temperatures
of homologous series (A) and (B) are relatively lower than the corresponding n-alkoxy acids
from which the final products are obtained. α-4-hydroxy phenyl β-4/methoxy benzoyl ethy-
lene and 4-((4-methoxy phenyl)diazenyl) phenol are non-mesomorphic but on linking with
n-alkoxy phenyl ring through central linkage exihibit mesomorphic characteristics. In series
(A), methyl to pentyl derivatives of the series are non-mesogenic, but all others are meso-
genic. The hexyl to dodecyl derivatives are enantiotropically smectogenic and nemactogenic
in character. The tetradecyl and hexadecyl derivatives of the series are only enantiotropi-
cally nematogenic without exhibition of a smectic phase. In series (B), the nematic phase
of mesophase commences from the very first number of the series, polymesomorphism is
exhibited by tetradecyl homologue, i.e. smectic and nemactic mesophases appear one after
the other. Hexadecyl number is purely smectogenic.
Transition temperatures of homologous series given in Table 1 are plotted against the num-
ber of carbon atoms in the n-alkyl chain of left n-alkoxy terminal. Smooth curves are drawn
through similar or related points, the phase diagrams obtained are shown separately in Figs. 1
and 2. In Fig. 1, the solid isotropic or mesomorphic transition curve rises and falls as the series

106
B. B. JAIN ET AL.
Table . Transition temperature of series (A) and (B).
Transition temperatures (ºC)
Smectic
Series
Nematic
Series
Isotropic
Series
Sr. No.
n-alkyl group
(A)
(B)
(A)
(B)
(A)
(B)
.
.
.
.
.
.
.
.
.
.
.
.
Methyl
Ethyl
Propyl
Butyl
Pentyl
Hexyl
Heptyl
Octyl
Decyl
Dodecyl
Tetradecyl
Hexadecyl
—
—
—
—
—
.
.
.
.
.
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
—
.
.
—
Figure . Phase behavior of series (A).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
107
Figure . Phase behavior of series (B).
is ascended with an overall falling nature. The smectic–nematic transition curve initially rises,
passes through maxima, and falls in a usual manner up to decyloxy homologues, but it rises
by 10n in dodecyl derivative. The nematic–isotropic transition curve rises initially and then
adopts a descending tendency as the series is ascended and behaves in a usual manner with an
odd-even effect. In Fig. 2, the nematic–isotropic transition curve shows a smooth descending
tendency as series is ascended. The solid mesomorphic curve follows a zig-zag path of rising
and falling nature. In the case of first and seventh member of the series, it shows rise and
fall of solid nematic transition temperature from and beyond the seventh homologue of this
series, the solid mesomorphic curves show an overall falling tendency with negligible rise at
the eighth and twelfth homologue. Nematic–isotropic transition curve behaves in a normal
manner.
In series (A), non-mesogenic behavior of the first five homologues is attributed to their high
crystallizing tendency arising from their amount of energy released to stabilize in crystalline
solid state at room temperature. These non-mesogenic molecules are unable to resist thermal
vibration and pass directly into isotropic liquid without passing through any mesogenic state,
and rest of the homologues are capable to resist thermal vibration and consequently exhibit
nematic and smectic phases. In series (B), mesogenic behavior started from the first homo-
logue.

108
B. B. JAIN ET AL.
The structurally similar homologous series (A) and (B) [19,20] are as under:
Scheme . Series A and B.
In Figs. 3 and 4, we represent the 3D diagrams of series A and B having different central
linkage groups and present and exhibit different mesogenic properties. The mesomorphic
properties of a substance depend upon polarity, polarizability, aromaticity, linearity, length-
to-breadth ratio, geometrical shape and size, π electron density, and many other factors of
molecules that contribute to the net intermolecular forces of attraction, and hence to the
mesomorphic properties and the degree of mesomorphism.
In Fig. 4, it is clear that geometrical shape of the molecules is linear rod-like without lateral
substitution. Both molecules consist of left alkoxy terminal, three phenyl rings, and –OCH3
right terminal. They differ only with respect to central bridges for the same homologue from
series to series. Molecule of homologous series (A) links three phenyl rings through –COO
(ester) and –CH=CH-CO (chalcone) central bridge, while that of homologous series (B) links
three phenyl rings through –COO (ester) and N=N (azo) central bridge. Thus, aromaticity
due to three phenyl rings of molecules,
The transition temperature of homologous series (A), which is relatively lower than the
transition temperature of homologous series (B), is compared for the same homologues
from series to series. This difference in transition temperature can be directly linked to
Figure . D diagram of series (A) and (B) (where R = side chain).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
109
Figure . Space filling diagram of series (A) and (B).
the difference in intermolecular forces of attraction caused by the difference in length by
–CH=CH-CO, N=N, and length-to-breadth ratio, resulting into difference in polarity
and polarizability of molecules. It is observed that the overall phase length or degree of
mesomorphism (for smectic) by series (A) is more than series (B), while the overall phase
length or degree of mesomorphism (for nematic) by series (B) is more than series (A).
Thus, two-dimensional array of molecules even in the floating condition maintains more
statistically parallel orientational order, resisting thermal vibrations in series (A) than in
series (B). Average thermal stability for smectic and nematic mesophase for homologous
series (A) is more than that for homologous series (B).
On comparing the type of mesomorphic phase exhibited by homologous series (A) and (B)
with series (Z), i.e. α–4–[4/-n-alkoxycinnamoyloxy] phenyl β-4”-methoxy benzoyl ethylenes,
its structure is given below:
Series C (where R = 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16)
Series C (Figure 5) is entirely nematogenic without exhibition of any smectogenic charac-
teristic. Thus, series (C) is smectogenic, while both series (A) and (B) are smectogenic and
nematogenic. Hence, the same central bridge and terminal groups bearing –CH=CH-COO,
and -CH=CH-CO (series C) are nematogenic, and the same central and terminal groups
bearing -COO-, -CH=CH-CO, and –COO-, -N=N- (series A and B) are both smectogenic
and nematogenic. Thus, -COO- group can induce smectic character favorably more, and -
CH=CH-COO- group can induce nematogenic character favorably more. Hence, -CH=CH-
COO- is strong enough to emerge nematic character from smectic character and vice versa.
Thus, group efficiency orders derived for induction of smectic and/or nematic characters are
as under:
Smectic character group efficiency order:
-COO > -CH=CH-COO
-CH=CH-C0 > N=N
Nematic character group efficiency order:
-CH=CH-COO > -COO
-N=N > -CH=CH-CO

110
B. B. JAIN ET AL.
Figure . D Diagram of series (C) (where R = side chain)
Conclusions
In summary, we have examined that ester homologous series are not necessarily smectogenic
but it may be entirely smectogenic or entirely nematogenic or partly smectogenic and partly
nematogenic. We should compare the effect of ester linkage group in series (A) linked with
the chalcone linkage group and the ester linkage group in series (B) at linked with the azo
linkage group. We were able to compare mesomorphism property of series (A) and (B) with
series (C), which determined the effect of vinyl ester at one end.
Acknowledgment
Authors acknowledge thanks to Dr. R.R. Shah, principal of K.K. Shah JarodwalaManinagar Science
College, Ahmedabad.
References
[1] R. Walter. Ber. Disch. Chem. Ges. 1925 B58. 2302.
[2] Dave, J. S., & Vora, R. A. (1970). In: Liquid Crystals and Ordered Fluids, J. F. Johnson & R. S. Porter
(Eds.), Plenum Press: New York, NY, 447 pp.
[3] Doshi, A. V., & Lohar, J. M. (1973). J. Inst. Chemists (India), 65, 15–17.
[4] Dave, J. S., & Vora, R. A. (1974). Mol. Cryst. Liq. Cryst., 28, 209.
[5] (a) Gray, G. W. (1962). Molecular Structure and the Properties of Liquid Crystal, Academic Press:
London. (b) Gray, G. W., &Windsor, P. A. (1974). Liq. Cryst. Plastic Cryst., Vol. 1.1, Chap. 4, Ellis
Harwood: Chichester, UK.
[6] Dave, J. S., & Kurian, G. (1977). Mol. Cryst. Liq. Cryst., 42, 175.
[7] Vogel, A. I. (1989). Textbook of Practical Organic Chemistry, 5th ed., ELBS and Longmann: Lon-
don, 946 pp.
[8] Hird, M., Toyne, K. J., & Gray, G. W. (1993). Liq. Cryst., 14, 741.
[9] Chauhan, M. L., & Doshi, A. V. (2007). J. Indian Chem. Soc., 84, 774.
[10] Patel, V. R., & Doshi, A. V. (2010). Der Pharma Chemica, 2, 429.
[11] Patel, R. B., & Doshi, A. V. (2011). Der Pharma Chemica, 3, 147.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
111
[12] (a) Chauhan, M. L., Pandya, R. N., & Doshi, A. V. (2011). Mol. Cryst. Liq. Cryst., 548, 228. (b)
Doshi, A. V., & Makwana, N. G. (2011). Mol. Cryst. Liq. Cryst., 548, 220. (c) Patel, R. B., Patel, V.
R., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 552, 3. (d) Doshi, A. V., Odedara, D. A., & Patel,
R. B. (2012). Mol. Cryst. Liq. Cryst., 552, 97. (e) Bhoya, U. C., Vyas, N. N., & Doshi, A. V. (2012).
Mol. Cryst. Liq. Cryst., 552, 104.
[13] Sharma, V. S., Solanki, R. B., Patel, P. K., & Patel, R. B. (2016). Mol. Cryst. Liq. Cryst., 625, 137–145.
[14] Doshi, A. V., & Makwana, N. G. (2008). J. Ind. Chem. Soc., 85, 263–266, 257–261.
[15] Chauhan, H. N. & Doshi, A. V. (2012). Der Pharma Chemica, 4(2), 731–736.
[16] Suthar, D. M., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 569, 64.
[17] Chaudhari, R. P., & Doshi, A. V. (2012). Mol. Cryst. Liq. Cryst., 569, 49.
[18] Chauhan, B. C., Shah, R. R. & Doshi, A. V. (2011). Der Pharma Chemica, 3(2), 110–117.
[19] Bhoya, U. C. & Doshi, A. V. (2011). Der Pharma Chemica, 3(2), 135–141.
[20] Chauhan, H. N., & Doshi, A. V. (2013). Mol. Cryst. Liq. Cryst., 570, 12–19.