Synthesis and mesomorphic behavior of liquid crystal chalconyl esters

Article abstract of DOI:10.1080/15421406.2016.1177883

A chalconyl homologous novel series of thermotropic liquid crystals (LC) have been synthesized and studied with a view to understand and establish the effects of molecular structure on LC properties in thermotropic behaviors. Homologous series consists of 13 homologs (C₁–C₁₈), C₁–C₄ homologs are nonliquid crystals and the rest of the homologs are enantiotropically nematogenic without exhibition of smectic property. Transition temperatures and the textures of the nematic phase were determined by an optical polarizing microscopy, equipped with a heating stage (POM). Texture of a nematic phase are threaded or Schlieren. The Spectral and analytical data confirms the molecular structures of homologs. Cr-N/I and N-I transition curves behaved in normal manner except C₇ homolog which shows negligible abnormality for N-I transition temperature or curve with exhibition of odd-even effect.

Full text of DOI:10.1080/15421406.2016.1177883

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis and mesomorphic behavior of liquid
crystal chalconyl esters
B. B. Jain & R. B. Patel
To cite this article: B. B. Jain & R. B. Patel (2016) Synthesis and mesomorphic behavior of
liquid crystal chalconyl esters, Molecular Crystals and Liquid Crystals, 633:1, 63-71, DOI:
10.1080/15421406.2016.1177883
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1177883
Published online: 24 Aug 2016.
Submit your article to this journal
Article views: 7
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gmcl20
Download by: [University of Exeter]
Date: 01 September 2016, At: 08:00

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –

http://dx.doi.org/./..
Synthesis and mesomorphic behavior of liquid crystal chalconyl
esters
B. B. Jain and R. B. Patel
Chemistry Department, K.K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
A chalconyl homologous novel series of thermotropic liquid crystals
Liquid crystal; mesomorphic;
mesogenic; nematic; smectic
(
LC) have been synthesized and studied with a view to understand and
establish the effects of molecular structure on LC properties in ther-
motropic behaviors. Homologous series consists of 13 homologs (C1–
C ), C –C homologs are nonliquid crystals and the rest of the homologs
1
8
1
4
are enantiotropically nematogenic without exhibition of smectic prop-
erty. Transition temperatures and the textures of the nematic phase
were determined by an optical polarizing microscopy, equipped with
a heating stage (POM). Texture of a nematic phase are threaded or
Schlieren. The Spectral and analytical data confirms the molecular struc-
tures of homologs. Cr-N/I and N-I transition curves behaved in nor-
mal manner except C homolog which shows negligible abnormality
7
for N-I transition temperature or curve with exhibition of odd-even
effect.
Introduction
The interest in the study of liquid crystalline (LC) [1] state of matter has attracted scientists
and technologists because of its dual character as to flow-like isotropic liquid and have to
behave as rigid crystals by thermotropic and lyotropic LC. Chalconyl derivatives are well-
known for their biological activity as antibacterial, antifungal, antimalarial, anticancer [2–8],
etc., and its involvement in many other biological processes in solution or lyotropic state.
Present investigation is planned with a view to understand and establish the relation between
thermotropic mesomorphism and the molecular structure of a substance. The object of the
study is also aimed to provide novel LC material of chalconyl derivatives for study to scientists
and technologists working with multidisciplinary LC state in the benefit of mankind or liv-
ing entities including to the biologists and pharmacists. Novel chalconyl derivatives will con-
sists of three phenyl rings bonded through -COO- and -CO-CH=CH- central bridges and
two terminal flexible end groups -OR and -OC H . LC series of compounds of chalconyl
14
29
ester derivatives is selected for synthesis, which may be biologically active and the present
investigation is targeted to study their thermotropic behaviors through an optical polariz-
ing microscopy after their due characterization. Such thermotropic behaviors of novel LC
compounds will be compared with the structurally similar homologous series to derive
CONTACT R. B. Patel
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
roshanpatel@gmail.com
©

6
4
B. B. JAIN AND R. B. PATEL
group efficiency order, etc., and results will be interpreted in terms of molecular rigidity
and flexibility [9–12]. Number of ester homologous series have been reported till the date
[13–21].
Experimental
Synthesis
4
4
- Hydroxy Benzoic acid was alkylated using suitable alkylating agent (R-X) to convert it into
-n-alkoxy benzoic acids by modified method of Dave and Vora [22]. α- 4- hydroxyl ben-
/
zoyl β-4 - heptyloxy phenyl ethylene (B) was prepared by usual established method [23].
Esters were synthesized by a literature method[30]. Thus, the Chalconyl - ester homolog
derivatives were filtered and washed with sodium bicarbonate and sodium hydroxide solu-
tion and dried and purified till constant transition temperatures using an optical polariz-
ing microscope equipped with a heating stage. 4-hydroxy benzoic acid, Alkyl halides, 4-
hydroxy benzaldehyde, 4-hydroxy acetophenone, dicyclohexyl carbodimide, dimethyl amino
pyridine, DCM, MeOH, acetone required for synthesis were used as received except solvents
which was dried and distilled prior to use. The synthetic route to a series is mentioned in
Schemes 1.
Characterization
Selected members of the novel homologous series were characterized by elemental analy-
1
sis (Table 1), infrared spectroscopy, H NMR spectra. IR spectra were recorded by Perkin-
1
Elmer spectrum GX, H NMR spectra were recorded on Bruker using CDCl as solvent.
3
Microanalysis was performed on a Perkin-Elmer PE2400 CHN analyzer. Transition tempera-
ture and LC properties (textures) were determined using an optical polarizing microscopy
equipped with a heating stage. Textures of nematic phase determined by miscibility
method (Table 2).
Table . Elemental analysis for hexyloxy, decyloxy, dodecyloxy, and hexadecyloxy derivatives.
%Elements found
%Elements theoretical
Sr. No.
Molecular formula
C H O
C
H
C
H

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

  



CHO
CH O

C H O
.




Table . Texture of nematic phase of C, C, C, C by miscibility method.
Sr. No.
Homolog
Texture

C
Threaded
Threaded
Schlieren
Schlieren



C
C
C

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
65
Scheme . The preparation of [Et N-SO H]Cl.


Analytical data
IR Spectra in cm− for octyloxy & dodecyloxy derivatives
Octyloxy: 721Polymethylene (–CH –)n of –OC H , 831(–C–H– def. m di-substituted),
2
8
17
7
59 Polymethylene (–CH –) of –OC H , 952 (–C–H– def. hydrocarbon), 1112(–C–O–)
2 7 15
Str, 1165, 1251 and 1379 (–C–O str in –(CH )n chain), 1458 (–C–H– def. in CH ), 1518
2
2
(
–C=C–)str, 1604 (–C=O group) 1710(–COO– ester group), 2848 and 2922 (–C–H str in
CH ).
3
Dodecyloxy: 718Polymethylene (–CH –)n of –OC H , 815(–C–H– def. m di-
2
12 25
substituted), 767 Polymethylene (–CH –) of –OC H , 952 (–C–H– def. hydrocarbon),
2
7
15
1
110(–C–O–) Str, 1377, 1165 and 1254(–C–O str in –(CH )n chain, 1465(–C–H– def. in
2

6
6
B. B. JAIN AND R. B. PATEL
CH ), 1516 (–C=C–)str, 1602 (–C=O group) 1712 (–COO– ester group), 2848 and 2920
2
(
–C–H str in CH ).
3

HNMR spectra in CDCl in δ ppm for Hexyloxy & Decyloxy Derivative

Hexyloxy: 0.86(t, –CH3 of –C H ), 1.1–1.5 (m, n-poly methylene groups of-
6
13
OC H ),1.75(m, n-poly methylene groups of –OC H ), 3.2–3.4 (s,–OCH -CH -
6
13
7
15
2
2
ofOC H ), 4.03 (s,–OCH -CH -of OC H ), 6.8–7.2 (s,–CO–CH=CH), 8.12 (s, p-
7
15
2
2
6
13
disubstituted phenyl ring).
Decyloxy: 0.83 (t,–CH of –C H ), 1.3–1.6(m, n-poly methylene groups of-OC H ),
3
10 25
10 25
1
4
.77 (m, n-poly methylene groups of –OC H ), 3.4–3.6(s,–OCH -CH -ofOC H ),
7 15 2 2 7 15
.12(s,–OCH -CH -of OC H ), 6.9–7.4 (s,–CO–CH=CH),8.2 (s, p-disubstituted phenyl
2
2
10 21
ꢀ
ꢀ
ring).α-;4-(4 -n-alkoxybenzoyloxy)benzoyl-β-4 ’-tetradecyloxyphenyl ethylenes.
Results and discussion
4
–
-n-Alkoxy benzoic acids are dimeric and on Condensation them with nonmesogenic α - 4
Hydroxy benzoyl β-4 -n-heptyloxy phenyl ethylene (m.p.–), which added chalconyl ester
/
derivatives whose LC property as enantiotropic nematic commences from heptyloxy (C5)
homolog derivative and continued upto octadecyloxy (C ) homolog with absence of smec-
18
togenic property. Transition temperatures (Table 3) as determined from an optical polariz-
ing microscopy with heating stage (POM), were plotted versus the number of carbon atoms
present in n-alkyl chain of the left n-alkoxy terminal end group. Transition curves Cr-N/I and
N-I are obtained by linking like or related points as depicted in a phase diagram (Fig. 1) show-
ing the phase behaviors of a novel series. Cr-N/I transition curve adopts a zigzag path of ris-
ing and falling with overall falling tendency and behaves with normal manner. N-I transition
curve is ascended from C homolog, then it descended from C homolog to C homologs.
7
12
18
Odd-even effect diminishes as series is ascended for higher homologs from and beyond merg-
ing of N-I curves for odd and even members nearby about C homolog. The changing trend
9
in mesomorphic behaviors from homolog to homolog observed for present novel series in
usual manner. Thermal stability for nematic is 102°C, and the total mesophase length ranges
from 14.0°C to 32.0°C at the C -C homolog, respectively. Thus, present novel chalconyl
10
16
ester homologous series is middle-ordered melting type whose melting transition tempera-
tures vary between 67°C and 131°C. Thus, thermotropic properties vary from homolog to
Table . Transition temperature of homologous series in °C.
Transition temperatures in °C
Sr.no
R = n-alkyl group
Smectic
Nematic
Isotropic

C
C
C
C
C
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
.
.
.
.
.












—
.
.
.
.
.
.
.
.
.
C
C
.
.
.
.
.
.
.
.
C
C
C
C
C
C





MOLECULAR CRYSTALS AND LIQUID CRYSTALS
67
Figure . Phase behavior of series.
homolog in present series by changing methylene unit or units of left n-alkoxy terminally sit-
uated end group, keeping rest of the molecular part unchanged throughout the series. Thus,
series is partly nematogenic and low melting type and relatively short ranged liquid crys-
tallinity as well as low thermal stability.
The lowering of transition temperatures of present chalconyl novel ester homologous as
compared to corresponding dimeric 4-n-Alkoxy benzoic acids is attributed to breaking of
hydrogen bonding between two aromatic acid molecules by esterification process. Changes in
transition or melting temperatures are due to odd and even number of carbon atoms present
in n-alkyl chain of the left n-alkoxy group. The nonmesomorphic property of C –C homologs
1
4
is attributed to their inability to resist exposed thermal vibrations which, abruptly breaks the
crystal lattices, and sharply transform into isotropic liquid without exhibition of smectic or
nematic phase due to their high crystallization tendency. High crystallization tendency of a
substances (C –C ) rises from unfavorable magnitudes of anisotropic forces of intermolecular
1
4
end to end and lateral attractions as a consequence of resultant rigidity and flexibility due to
low dipole-dipole interactions and the low magnitudes of dispersion forces through interac-
tions between instantaneous dipoles produced by the oscillation of the electron clouds of the
molecules. Thus, C –C homolog molecules are randomly oriented in all possible directions
1
4
without any ordered molecular arrangement under floating condition. Hence, they neither
show mesophase on heating nor they exhibit monotropic mesophase formation on cooling the
same. However, nematogenic mesophase formation commences late from C homolog and
5
continue up to last C homolog in enantiotropic manners. The increasing length of n-alkyl
18
chain by –CH – unit, the corresponding permanent dipole moment across the long molecu-
2
lar axis and dispersion forces as a consequences of favorable molecular rigidity and flexibility,
causes occurrence of suitable magnitudes of anisotropic forces of intermolecular cohesion

6
8
B. B. JAIN AND R. B. PATEL
Figure . Structurally similar series.
and closeness by end to end attractions only, which manages to float the molecules on the
surface through statistically parallel orientational order only from C to C homologs. Thus
5
18
only nematic mesophase formation induced for C -C . The absence of smectogenic character
5
18
throughout the novel series is due to the unsuitable magnitudes of lateral attractions which fail
to induce lamellar packing of molecules in the crystal lattices from any stage of a novel series.
Therefore molecular polarizability being less effective to form lamellar packing of molecules
in their rigid crystals which fails to adopt the sliding layered molecular arrangement in float-
ing condition, to exhibit smectogenic property, under exposed thermal vibrations. The exhi-
bition of odd-even effect of N-I transition curve is attributed to sequentially added methylene
unit or units at the n-alkyl chain bonded to phenyl ring through oxygen atom. Diminishing
of odd-even effect from and beyond C homolog is due to coiling or bending or flexing or
9
coupling with major axes of a core structure of a molecule for longer n-alkyl chains. The neg-
ligible abnormality in N-I transition temperature of C homolog may be due to the bonding of
7
-
OC H end groups on both the terminals, whose vector sum of bond polarities contributed
7 15
by -OC H on both ends of a molecule being equal in magnitudes and opposite in directions,
7
15
which nullifies the effects due to each other towards total molecular polarities and polarizabil-
ity. Thus, intermolecular dispersion forces of cohesion are disturbed and induce abnormality.
Abnormality observed for C homolog may be attributed to the uncertainty in the status of
18
the longest C n-alkyl chain of left n-alkoxy group. The variations in mesogenic behaviors
18
from homolog to homolog in the same series is due to the sequential addition of methylene
unit or units, which varies suitable or unsuitable magnitudes of molecular rigidity or/and
flexibility responsible to induce mesophase formation. Some mesogenic properties of present
novel series 1 are compared with structurally similar series X [25] and Y [26] as shown below
in Fig. 2.
Homologous series 1 of present investigation and the series A and B chosen for comparison
are structurally identical with respect to three phenyl rings, central bridges the left n-alkoxy
terminal end group -OR for the same homolog from series to series. However, they differ
with respect to Central bridges -COO, -CO-CH=CH (series 1 and A) and -CH=CH-COO,
-
CO-CH=CH (series B), and right-sided terminal tail end group viz. -OC H , -OC H ,
7
15
14 29
respectively from series to series. Thus, the changing mesogenic behaviors and the degree
of mesomorphism depend upon the varying features of the combined effects of molecular
rigidity and flexibility, which induces, due to differing molecular polarity and polarizability
for the same homolog from series to series by changing right-sided terminal end groups. Fol-
lowing Table 4 represents some mesogenic properties in comparative manner for series 1, A,
and B.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
69
Table . Relative thermal stability in °C.
Series→

—
A
B
Smectic-isotropic or smectic-nematic
Commencement of Smectic phase
Nematic-Isotropic Commencement of
Nematic phase
—
—
. (C -C ) C
. (C -C )C
. (C -C ) C
 







Total upper and lower mesophase
length range in °C C -C
— C CC
— C C C C
— C C




i
j
From above Table 4 it is clear that
r
Homologous series 1, A, and B under comparative study are nematogenic with absence
of smectogenic property.
r
The mesogenic property commences from C (series1), C (series A), and C (series B)
5
7
6
homolog.
r
Thermal stability for nematic of series B less than a series A and 1.
The total mesophase length ranges from minimum to maximum in increasing order
from series A to series 1 to series B.
r
r
Thermal resistivity is poor for all the series under comparison.
Homologous series 1, A, and B are almost identical except the difference of methylene
units at the tail end groups at right side of the molecules. Therefore, the molecular flexibility
differs to a very less extent affecting commencement of nematic phase and the intermolec-
ular end to end and cohesive or dispersion forces are nearly equivalent, which facilitate and
stabilize the exhibition of nematic property within definite range of temperature. Enthalpy
values (ꢀH) associated differs from homolog to homolog in the same series and for the same
homolog from series to series which plays role in the thermometric behavior of series to series
and the homolog to homolog. On comparing thermometric behaviors of series 1, A, and X,
the nonplanarity for all the series are equivalent but it slightly differs for the difference of -
CH=CH-COO unit in case of series B, commencement from C homolog for series B and C
6
5
for series 1 and C for series A. The observed difference for thermal stabilities is attributed
7
to the unusual and unexpected molecular status of n-alkyl chain of both ended n-alkoxy ter-
minals -OR and -OC H depending upon resultant differing polarity difference of -OR and
7
15
-
OC H which induces thermal resistivity, degree of mesomorphism, and transition temper-
7 15
atures of homologs. Thus, thermal stabilities and upper and lower mesophase lengths ranges
of series1, A, and B are not much differed in magnitudes.
Conclusions
r
Present novel chalconyl ester series is predominantly nematogenic with absence of smec-
tic property and middle-ordered melting type whose isotropic temperature vary between
9
5°C and 131 °C.
r
Group efficiency order derived for Nematic on the basis of
a) Thermal stability,
b) Commencement of mesophase, and
c) Mesophaselength range are as under:
i) Smectic
(
(
(
(
Series-1 = Series-X = Series-Y
Nematic
Series-A > Series-1 > Series-B

7
0
B. B. JAIN AND R. B. PATEL
(
ii) Nematic
Series-1 > Series-B > Series-A
iii) Nematic
Series-A > Series-1 > Series-B
(
r
r
Molecular structure plays an important role in mesogenic behavior with reference to
changing tail end group and central bridges.
Ester group of present novel investigation may be useful for the agricultural production
for the growth of quality and healthy fruits and flowers, potato, and potato-like material
as well as chalconyl group being biologically active and antibacterial and antifungal may
reduce the consumption of pesticides and insecticides.
Mesomorphism is very sensitive and susceptible to molecular structure.
Novel homolog of chalconyl ester derivatives may be useful in the study of their biological
activity lyotropically as antimalarial, anticancer, antibacterial, etc.
Present study supported early views and raised reliability and credibility to the conclu-
sions drawn earlier.
r
r
r
Acknowledgments
Authors acknowledge thanks to Dr. R. R. Shah, principal of K. K. Shah Jarodwala Maninagar Science
College, Ahmedabad. Authors thank to NFDD Centre for the analytical and spectral services.
References
[
[
1] Reinitzer. (1888). Monatsh., 9, 421.
2] Jain, Upendra K., Bhatia, Rich K., Akkinepally, R., Rao, Ranjit Singh, Saxsena, Ajit K., & Seha,
lrun (2014). Trop. J. Pharm. Res., 13(1), 73–80.
[
3] Gaikwad, Prajkata P., & Desai, Maya, T. (2013). Int. J. Pharm. Res. Rev., 2(12), 40–52.
4] Gray, G. W., & Winster, P. A. (Eds) Liquid crystal and plastic crystals, In: The Role of Liquid Crystal
in Life Processes by G.T. Stewart, Chapter 6.2, Vol. 1, Ellis Harwood: Chichester, U.K., pp. 308–326.
5] Tadwee, I., Shahi, S., Ramteke, V. & Syed, I. (2012). IJPRAS, 1(2), 6–11.
6] Rajesh, G., Mansi, K., Srikant, K., Babasaheb, B., Nageshg, D., Kavita, S., & Ajay, C. (2008). Chem.
Pharm. Bull., 56, 897–901.
[
[
[
[
[
[
7] Lee, Y. S., Lim, S. S., Shin, K. H., Kim, Y. S., Ohuchi, K., & Jung, S. H. (2006). Biol. Pharm. Bull,
2
9, 1028–1031.
8] Calliste, C. A., Le Bail, J. C., Trouilas, P., Poug, C., Chulia, A. J., Duroux, L. J. (2001). Anticancer
Res., 21 , 3949–3956.
9] Hird, M., Toyne, K. J., Gray, G. W., Day, S. E., & Donell, D. G. (1993). Liq. Cryst., 15, 123.
[
10] Collings, P. J., & Hird, M. (1997). Introduction of Liquid Crystals Chemistry and Physics, Taylor and
Francis: Abingdon, U.K
[
[
[
[
[
11] Macros, M., Omenat, A., Serrano, J. L., & Ezcurra A. (1992). Adv. Matter., 4, 285.
12] Hird, M., Toyne, K. J., Gray, G. W., & Day, S. E. (1993). Liq. Cryst., 14, 741.
13] Dermus, D. (1998). Mol. Cryst., 165, 45–84.
14] Dermus, D. (1998). Liq. Cryst., 5, 75–100.
15] Imrie, C. T., & Luckhrust, G. R (1998). Liquid dimers and oligomers. In: Handbook of Liquid
Crystal, Law Molecular Liquid Crystals, Vol. 2B, Demus D., Goodby J. W., Graw G. W., Spiess H.,
&
Vill V. (Eds.), pp. 801–833. Wiley-VCH: Weinheim, U.K.
[
16] (i) Suthar, D. M., & Doshi, A. V. Mol. Cryst. Liq. Cryst., 575, 76–83. (ii) Chauhan, H. N., & Doshi,
A.V. (2013). Mol. Cryst. Liq. Cryst., 570, 92–100. (iii) Chaudhari, R. P., Chauhan, M. L., & Doshi,
A. V. (2013). Mol. Cryst. Liq. Cryst., 575, 88–95. (iv) Bhoya, U. C., Vyas, N. N., & Doshi, A. V.
(
2012). Mol. Cryst. Liq. Cryst., 552, 104–110.
[
17] Suthar, D. M., Doshi, A. A., & Doshi, A. V. (2013). Mol. Cryst. Liq. Cryst., 527, 51–58.
18] Suthar, D. M., Doshi, A. A., & Doshi, A. V. (2013). Mol. Cryst. Liq. Cryst., 582, 79–87.
[

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
71
[
[
[
[
19] Patel, B. H., & Doshi, A. V. (2015). Mol. Cryst. Liq. Cryst., 605, 61–69.
20] Patel, B. H., & Doshi, A. V. (2015). Mol. Cryst. Liq. Cryst., 607, 78–86.
21] Patel, B. H., & Doshi, A. V. (2015). Mol. Cryst. Liq. Cryst., 607, 76–86.
22] Dave, J. S., & Vora, R. A. (1970). In: Liquid Crystals and Ordered Fluids, Johnson, J. F., & Porter,
R. S. (Eds.), p. 447, Plenum Press: New York.
23] Vogel, A. I. (1989). Textbook of Practical Organic Chemistry , 5th ed., p. 946, ELBS and Longman:
London.
[
[24] Uhood, J. A. (2011). International Journal of Molecular Science., 12, 3182–3190.
[25] Jain, B. B., & Patel, R. B. (2015). Mol. Cryst. Liq. Cryst., 630, 121.
[26] Jain, B. B., & Patel, R. B. (2015). Int. Lett. Chem. Phys. Astron., 58, 16–25.