Synthesis and study of new homologous series of ester-chalcone exhibiting nematic phases

Article abstract of DOI:10.1080/15421406.2016.1217711

A novel homologous series of ester-chalcone have been synthesized and their liquid crystals (LCs) properties are studied. All the homologue shows nematic phase except C₁-C₄ homologue. Classical nematic textures are observed in this homologous series with the help of polarizing optical microscope (POM) equipped with hot stage. The role of flexible methylene group spaces, degree of polymerization and central linkage on the exhibition of all the homologue is discussed. The novel homologous series has been characterized by the standard methods (1HNMR, IR, and elemental analysis).

Full text of DOI:10.1080/15421406.2016.1217711

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis and study of new homologous series of
ester-chalcone exhibiting nematic phases
B. B. Jain & R. B. Patel
To cite this article: B. B. Jain & R. B. Patel (2016) Synthesis and study of new homologous series
of ester-chalcone exhibiting nematic phases, Molecular Crystals and Liquid Crystals, 638:1,
35-43, DOI: 10.1080/15421406.2016.1217711
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Date: 19 November 2016, At: 02:31

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Synthesis and study of new homologous series of
ester-chalcone exhibiting nematic phases
B. B. Jain and R. B. Patel
Chemistry Department, K.K. Shah JarodwalaManinagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
Enantiotropic; liquid crystals;
mesomorphic; nematogenic;
smectogenic
A novel homologous series of ester-chalcone have been synthesized
and their liquid crystals (LCs) properties are studied. All the homologue
–
shows nematic phase except C1 C4 homologue. Classical nematic tex-
tures are observed in this homologous series with the help of polarizing
optical microscope (POM) equipped with hot stage. The role of flexible
methylene group spaces, degree of polymerization and central linkage
on the exhibition of all the homologue is discussed. The novel homol-
ogous series has been characterized by the standard methods (1HNMR,
IR, and elemental analysis).
GRAPHICAL ABSTRACT
Introduction
Chalconyl derivatives are well-known for their antibacterial, antifungal, antimalarial, anti-
cancer, etc. [1–7]. biological properties and many other biological processes in solution or
as lyotropic liquid crystals (LC). The liquid crystalline state of the thermotropic type is [8]
exploited in LC devices [9–11]. The present investigation is planned with a view to under-
standing and establishing the relation between thermotropic mesomorphism and the molec-
ular structure of a substance. Secondly, the study will provide novel chalconyl LC materi-
als to scientists and technologists working with LCs. The rigid core of the structure is made
up of ring structures (aromatic) bridged through two central groups and the flexible portion
is made up of terminal end groups. The novel homologous series consists of three phenyl
–
–
–
–
–
rings linked through two central bridge CH=CH COO and CO CH=CH which act as
a rigid core. The left and right terminal end groups of the homologous series are n-alkoxy
and -OC7H15, respectively and these act as flexible units of the homologous series without
CONTACT R.B. Patel
bijendrajain@gmail.com
lege, Gujarat University, Ahmedabad, Gujarat, India.
Chemistry Department, K.K. Shah JarodwalaManinagar Science Col-
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

36
B. B. JAIN AND R. B. PATEL
any lateral substitution. The novel compounds will be characterized by analytical and spec-
tral data. Thermometric data will be evaluated and interpreted in terms of molecular rigid-
ity and flexibility depending on molecular structure and then mesomorphic properties and
behavior will be compared with structurally similar series. Several ester homologous series
with or without chalconyl group have been studied to date [12–21]. Group efficiency order
and structure relation with mesomorphism will be derived.
Experimental
Synthesis
Trans 4-n-alkoxy cinnamic acids (A) were prepared by a modified method [22, 23]. α−4-
Hydroxy benzoyl β−4/heptyloxy ethylene (B) was prepared by the usual established method
[24]. Esters were synthesized through a literature method [25]. Thus, the chalconyl ester
homologue derivatives were decomposed filtered, washed with a solution of sodium bicarbon-
ate and sodium hydroxide followed by water and dried and purified until constant transition
temperatures were obtained using an optical polarising microscope equipped with a heating
stage. Alkyl halides, 4-hydroxybenzaldehyde, 4-hydroxy acetophenone, dicyclohexylcarbod-
imide, dimethyl amino pyridine, DCM, Ethanol, and acetone required for synthesis were used
as received except solvents which were dried and distilled prior to use. The synthetic route to
a series is shown in Scheme 1.
Characterization
Selected members of the novel homologous series were characterized by Elemental Analysis
(Table 1), infrared spectroscopy, 1H NMR spectra. IR spectra were recorded by Perkin-Elmer
spectrum GX,1H NMR spectra were recorded on Bruker using CDCl3 as solvent. Microanal-
ysis was performed on a Perkin-Elmer PE2400 CHN analyzer. Transition temperature and LC
properties (Textures) were determined using an optical polarizing microscopy equipped with
a heating stage. Textures of nematic phase is determined by miscibility method (Table 2).
Analytical data
IR Spectra in cm− for Heptyloxy and Dodecyloxy Derivatives
–
=
–
–
– – –
Octyloxy: 661(Cis CH CH ), 719 Polymethylene ( CH2-)n of -OC7H15, 833( C H def.
–
– – –
m di-substituted), 757 Polymethylene ( CH2-) of -OC7H15, 949 ( C H def. hydrocarbon),
1107( C-O-) Str, 1165,1254 and 1381 ( C-O str in -(CH2)n chain), 1455 ( C H def. in
–
–
– – –
– = – =
–
–
CH2), 1516 ( C C-)str, 1604 ( C O group) 1708 ( COO ester group), 2848 and 2923
– –
( C H str in CH3).
Dodecyloxy: 658(Cis CH CH ), 720 Polymethylene ( CH2-)n of -OC12H25,
– – – – – –
–
=
–
–
–
817( C H def. m di-substituted), 767 Polymethylene ( CH2-) of -OC7H15, 950 ( C H
–
–
def. hydrocarbon), 1110( C-O-) Str, 1375, 1164, and 1252 ( C-O str in -(CH2)n chain,
– – – – =
– =
–
–
1468( C H def. in CH2),1513 ( C C-)str, 1602( C O group) 1712 ( COO ester group),
– –
2849 and 2920 ( C H str in CH3).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
37
Scheme . Synthetic route to the series.
HNMR spectra in CDCl in δ ppm for Hexyloxy & Octadecyloxy Derivative
–
–
Hexyloxy: 0.83(t, CH3 of C6H13), 1.1–1.4(m, n-poly methylene groups of-OC6H13),1.70
–
(m, n-poly methylene groups of -OC7H15), 3.1–3.4 (s,-OCH2 CH2-ofOC7H15), 3.98
Table . Elemental analysis for hexyloxy, decyloxy, tetradecyloxy, and hexadecyloxy derivatives.
%Elements found
%Elements theoretical
Sr. no.
Molecular formula
C
H
C
H

CHO
CHO
CHO
CHO
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.




38
B. B. JAIN AND R. B. PATEL
Table . Texture of nematic phase of C, C, C, C by miscibility method.
Sr. no.
Homologue
Texture

C
C
C
C
Threaded
Threaded
Schlieren
Schlieren



–
–
=
–
–
–
=
(s,-OCH2 CH2-of OC6H13), 6.48 (d, CH CH ),6.9–7.2 (s, CO CH CH), 8.09(s, p-
disubstituted phenyl ring).
–
–
Octadecyloxy: 0.87 (t, CH3 of C18H37), 1.2–1.6(m, n-poly methylene groups of-
OC18H37), 1.75(m, n-poly methylene groups of -OC7H15), 3.4–3.6(s,-OCH2 CH2-
ofOC7H15),
–
–
–
=
–
4.04
(s,-OCH2 CH2-of
OC10H21),6.41
(d, CH CH ),
6.8–7.3
–
–
=
(s, CO CH CH),8.12 (s, p-disubstituted phenyl ring).
α-3-(4ꢀ-n-alkoxycinnamyloxy)benzoyl-β-4ꢀꢀ-heptyloxyphenyl ethylenes
Result and discussions
α-4-(4ꢀ-n-Alkoxycinnamoyloxy) benzoyl −β-4ꢀ-heptyloxyphenyl ethylenes is a non liquid
crystal (NLC) compound which on condensation with trans n-alkoxycinnamic acids yielded
novel chalconyl derivatives. The C1 to C4 homologues are NLCs. The other derivatives are
–
(C5 C18) are enantiotropic nematogens without exhibition of any smectogenic phases. Tran-
sition temperatures (Table 3) were plotted against the number of carbon atoms present in n-
alkyl chain of left n-alkoxy group. Transition curves (Figure 1) Cr-I/N and N/I were obtained
on linking like or related points, which shows phase behaviors of series. Cr-I/N transition
curve adopted zigzag path of rising and falling with overall descending tendency. N-I tran-
sition curve initially rises and then falls with overall descending tendency except negligible
abnormality at the C7 homologue. Odd-even effect is observed for N-I transition curve. The
N-I transition curve for odd and even numbers merge into each other at the decyloxy C10
homologue and then continue as one trend. The single transition curve passes through the
Table . Transition temperature of homologous series.
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
39
Figure . Phase behavior of series.
C12 and continues with a negligible fall at C18 homologue and negligible abnormality from
descending tendency at C7 homologue. Thus, N-I transition curve behaved almost in normal
manner. N-I transition curve for even members occupies higher position than curve (N-I) for
odd members. The nematogenic mesomorphism commences from the pentyloxy (C5) homo-
logue and continues up to the octadecyloxy homologue (C18).
The LC behaviors from homologue to homologue in the same series undergoes varia-
tions. Thermal stability for nematic is 108.0°C whose LC phase length varies from 27.0°C
to 43.0°C at the C8 and C18 homologue, respectively. Thus, it is a middle ordered melting type
series of medium ranged liquid crystallinity. Lowering if transition temperatures of present
novel homologues as compared to corresponding dimeric trans n-alkoxycinnamic acids is
attributed to the breaking of hydrogen bonding between two molecules of aromatic acid by
esterification process. Alterations of transition points are attributed to odd and even number
–
of carbon atoms in alkyl (R) of -OR group. Thenonmesomorphicity of C1 C4 homologues is
attributed to low magnitudes of intermolecular dispersion forces and low dipole-dipole inter-
actions as a consequence of unfavourable molecular rigidity and flexibility, which induces

40
B. B. JAIN AND R. B. PATEL
unsuitable magnitudes of intermolecular end to end and/or lateral cohesion and closeness as
–
well as high crystallising tendency. As a result of this, the molecules of C1 C4 are unable to
resist exposed thermal vibrations and melted sharply to the isotropic state without passing
through LC state. The absence of smectogenic character throughout a novel series is due to
absence of lamellar packing molecules through inadequate intermolecular lateral cohesion.
However, residual intermolecular anisotropic forces of end to end attractions and closeness
–
are strong enough to disalign the molecules of C5 C18 at an angle less than ninety degree
on floating surface and resists the exposed thermal vibrations for some temperature differ-
ence and maintained the molecular arrangement in statistically parallel orientational order to
show the formation of nematic phase as a consequence of end to end favourable magnitudes
of cohesion and closeness. The molecules of homologue either from rigid crystalline state or
nematogenic mesophase, transform into isotropic state, at an isotropic temperature, at which
the molecules are randomly orient in all possible direction with high order of disorder or
randomness or high entropy. But on cooling the isotropic mass from and below isotropic
temperature, the nematic mesophase reappears in reversible manner exactly at a tempera-
ture at which, it had appeared. Odd-even effect observed for N-I transition curve is due to
the sequentially and progressively added methylene unit or units at the left -OR group. The
odd-even effect disappears from and beyond C12 homologue and N-I transition curve pro-
longed as a single transition curve for the higher homologues of longer n-alkyl chair ‘R’ of left
-OR group, because, longer n-alkyl chain may coil or bend or flex or couple to lye with major
axis of the core structure and hence, the alteration diminishes as series is ascended from and
beyond C12 homologue. The negligible abnormality from normal descending tendency at C7
homologue and rising tendency of deviation of N-I transition curve at the C14 homologues
are attributed to the uncertainty in the status of n-alkyl chain R of -OR and n-alkyl chain of
common longer tail end group -OC7H15(n) (Para) of linear shaped molecules of homologues.
Moreover an unique homologue of -OR equal to -OC7H15 and tail end -OC7H15 i.e. in case of
a homologue in which terminal end groups are identically same, the vector sum of all bonds
of -OC7H15 group will be exactly equal in magnitudes and opposite in directions contribute to
ZERO polarity. Therefore the effectiveness of molecular polarity and polarizability may reflect
to molecular flexibility showing more or less or negligible deviation at an unique homologue
involving identically same n-alkoxy terminal end groups in chalconyl ester derivatives. In case
of the rest of the homologues other than C14the group polarity difference between -OR and
-OC7H15(n) reflects the molecular flexibility, descending tendency of each homologue of a
present novel series. The variations in LC properties from homologue to homologue in the
same novel series is attributed to the sequentially added methylene unit or units to n-alkoxy
group (-OR) which alters molecule lengths, permanent dipole moment across the long molec-
ular axis, length to breadth ratio, ratio of the polarity to polarizability, intermolecular cohesion
and closeness due to varied dispersion forces, dipole-dipole interactions etc. Thus, variation
in LC properties of presently investigated homologous series are altered due to attraction of
molecular flexibility keeping unaltered molecular rigidity throughout the same series. The LC
properties of novel series 1 are compared with the structurally analogous or similar series A
[26] and B [27] as shown in Fig. 2.
Homologous series 1 and A are identical with respect to three phenyl rings, central
bridge linking middle and third phenyl ring, left and right terminal end groups for the
same homologue from series 1 to series A. But they differ with respect to central bridges
–
=
–
–
–
–
CH CH COO and COO linking first and middle phenyl rings for the same homo-
logue fro series 1 to series A. Thus, combine effect of molecular rigidity plus flexibility vary
for the same homologue from series to series and from homologue to homologue in the same

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
41
Figure . Structurally similar series.
series. Homologous series 1 and B are identical with respect to three rings, two central bridges
and left terminal end group except right handed tail end groups, -OC7H15 and -OC14H29 for
the same homologue from series 1 to series B and from homologue to homologue in the same
series as a consequence of combined effect of molecular rigidity plus flexibility whose magni-
tudes decides the possibility of inducing LC property and its thermotropic behaviour.Table 4
represents some thermotropic behavior of presently investigated novel chalconyl homologous
series 1 and the series chosen for comparative study.
Table 4 represent that,
• All the three series 1, A and B under comparative study are nematogenic only without
exhibition of Smectic property.
• Mesomorphism commences from C5 homologue in case of series 1 and A, but it com-
mences from C6homologue of a series B.
• Thermal stability of a series 1 is higher than the series A and B.
• The degree of mesomorphism of all the series are almost nearer or in increasing order
from series B to A to 1.
The suitable magnitudes of anisotropic forces of end to end intermolecular cohesion and
closeness as a consequence of favourable molecular rigidity and flexibility which arranges
molecules of all the homologous series (1, A and B) to float on the surface with statistically par-
allel orientational order for different degree of mesomorphism, depending upon individual
varying magnitudes of molecular polarities and polarizability. Thus, only nematic mesophase
formation occurs with absence of smectic phase, due to absence of inadequate magnitudes
of environmental situation and forces of cohesion as required for exhibition of smectogenic
character. Thus, smectogenic character fails to facilitate in all the series 1, A and B under
comparative study. The extent of molecular noncoplanarity for all the series 1, A and B are
–
=
–
equivalent but it slightly differs for the difference of CH CH unit in case of series A. The
observed difference for thermal stabilities is attributed to the unusual and unexpected molec-
ular status of n-alkyl chain of both ended n-alkoxy terminals -OR and -OC7H15 depending
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
–
–
–
– C C
Total upper and lower mesophase
– C C
– C C/
–
length range in °C Ci Cj

42
B. B. JAIN AND R. B. PATEL
upon resultant differing polarity difference of -OR and -OC7H15 which induces thermal resis-
tivity, degree of mesomorphism and transition temperatures of homologues. Thus, thermal
stabilities and upper and lower mesophase lengths ranges of series 1, A and B are not much
differed in magnitudes.
Conclusions
• Presently investigated chalconyl ester series is partly nematogenic whose degree of meso-
morphism is shorter and of low melting type without exhibition of smectogenic property.
• The group efficiency order derived on the basis of (i) thermal stability (ii) early com-
mencement of mesophase and (iii) higher degree mesomorphism are as under.
(i) Smectic Series 1 = Series A = Series B
(ii) NematicSeries 1 > Series A > Series B
(iii) Nematic Series 1 = Series A > Series B
(iv) Nematic Series 1 > Series A > Series B
• Mesomorphism is very sensitive and susceptible to the molecular structure as a conse-
quence of molecular rigidity or/and molecular flexibility.
• Present novel compounds may be useful for the devices to be operated at room temper-
ature or low temperature and their biological activity as antifungal or antibacterial etc.
may be exploited in agricultural production to control and reduce the consumption of
insecticides and pesticides.
• Homologous series with longer n-alkyl chains bonded to third phenyl ring through oxy-
gen atoms as tail end group are nematogenic only of low degree of mesomorphism.
• Difference of group polarities at the two terminal end groups decides the mesogenic
behavior of individual homologue and the same homologous series as a whole.
• Present study support and raised credibility to the conclusions drawn earlier.
Acknowledgments
Authors acknowledge thanks to Dr. R. R. Shah, principal of K. K. Shah Jarodwala Maninagar Science
College, Ahmedabad. Authors thank NFDD Centre for the analytical and spectral services.
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