Mesomorphism dependence on heterocyclic tail

Article abstract of DOI:10.1080/15421406.2015.1068975

A novel homologous series of liquid crystal materials containing a heterocyclic ring was synthesized with a view to understanding and establishing the relation between liquid crystal (LC) properties and a molecular structure; and with a view to curing skin-related diseases following biological activity studies. The series consist of 13 (C₁ to C₁₈) members. All the members are liquid crystals. The C₄ to C₁₈ members are smectogenic of which C₄ and C₅ are monotropic and remaining members (C₆ to C₁₈) are enantiotropic in nature; whereas all C₁ to C₁₈ members are enantiotropically nematogenic. Hence the C₁, C₂, C₃ members are only nematogenic and the rest of the homologues are smectogenic in addition to nematogenic. Transition temperatures were determined by an polarizing optical microscope equipped with heating stage. Analytical and spectral data confirmed the molecular structures of homologues. It is a middle ordered melting type series. LC properties of a series are compared with the structurally known series.

Full text of DOI:10.1080/15421406.2015.1068975

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Mesomorphism dependence on heterocyclic tail
G. N. Bhola & U. C. Bhoya
To cite this article: G. N. Bhola & U. C. Bhoya (2016) Mesomorphism dependence
on heterocyclic tail, Molecular Crystals and Liquid Crystals, 625:1, 30-37, DOI:
10.1080/15421406.2015.1068975
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Date: 24 February 2016, At: 03:42

MOL. CRYST. LIQ. CRYST.
, VOL. , –
http://dx.doi.org/./..
Mesomorphism dependence on heterocyclic tail
G. N. Bhola and U. C. Bhoya
Department of Chemistry, Saurashtra University, Rajkot, Gujarat, India
ABSTRACT
KEY WORDS
Liquid crystals; Mesogen;
Mesomorphism; Nematic;
Smectic
A novel homologous series of liquid crystal materials containing a het-
erocyclic ring was synthesized with a view to understanding and estab-
lishing the relation between liquid crystal (LC) properties and a molec-
ular structure; and with a view to curing skin-related diseases following
biological activity studies. The series consist of 13 (C1 to C18) members.
All the members are liquid crystals. The C4 to C18 members are smecto-
genic of which C4 and C5 are monotropic and remaining members (C6
to C18) are enantiotropic in nature; whereas all C1 to C18 members are
enantiotropically nematogenic. Hence the C1, C2, C3 members are only
nematogenic and the rest of the homologues are smectogenic in addi-
tion to nematogenic. Transition temperatures were determined by an
polarizing optical microscope equipped with heating stage. Analytical
and spectral data confirmed the molecular structures of homologues.
It is a middle ordered melting type series. LC properties of a series are
compared with the structurally known series.
Introduction
Thermal and lyotropic liquid crystalline states of matter have proved their ability to benefit
mankind since their discovery in 1888[1]. All scientific and technological researchers have
contributed to the LC state with different aims and objectives [2,3,4,5,6,7,8,9,10,11]. Novel
substances are required by a wide variety of researchers. Therefore present investigation is
aimed to synthesize novel thermotropic LC substances through a homologous series and to
establish the effect of molecular structure on liquid crystal properties and the degree of liquid
crystallinity [12,13,14]. Many homologous series and novel LC substances have been reported
to date [15,16,17,18,19,20,21]. The novel homologous series consists of two phenyl rings and
–
–
–
–
–
–
–
one heterocyclic ring bonded through CH CH COO and CO CH=CH central bridges
with changing n-alkoxy terminal end group. LC properties of series will be evaluated and
comparative study with structurally similar homologous series will be carried out in terms
of molecular rigidity and flexibility [22,23,24,25]. Novel LC compounds may be biologically
active against skin diseases.
Experimental
Synthesis
4-n-Alkoxybenzaldehydes were synthesized by refluxing 4-hydroxybenzaldehyde (1 equiv.)
with corresponding n-alkyl bromides (1 equiv.) in the presence of potassium carbonate
CONTACT U. C. Bhoya
drucbhoya@gmail.com, drucbhoya@sauuni.ernet.in
versity, Rajkot-, Gujarat, India
Department of Chemistry, Saurashtra Uni-
©  Taylor & Francis Group, LLC

MOL. CRYST. LIQ. CRYST.
31
Scheme . Synthetic route to the novel series
(1 equiv.) and acetone as a solvent [26]. The resulting 4-n-alkoxybenzaldehydes were reacted
with malonic acid (1.2 equiv.) in the presence of 1–2 drops piperidine as catalyst and pyri-
dine was used as the solvent to yield corresponding trans 4-n-alkoxy cinnamic acids (A)
[27]. 3-(2-Thiophenyl)-1-(4-hydroxyphenyl) 2-propen-1-one (B) was prepared by an estab-
lished method [28] M.P.170–172oC, Yield- 64.8%. Coupling of compounds A and B is done
by Steglich esterifications to yield α-4(4ꢀ-n-alkoxy cinnamoyloxy) benzoyl-β-(2-thiophenyl)
ethylene [29].
The synthetic route to the novel homologous series of ethylene derivatives is shown in
scheme 1.
Characterization
Some of members of the novel series were characterized by elemental analysis (Table 1),
1
Infrared spectroscopy, H NMR spectra and mass spectroscopy. Microanalysis was per-
formed on Euro EA Elemental Analyzer. IR spectra were recorded on Shimadzu FTIR Model
1
IRAffinity-1S (MIRacle 10), HNMR spectra were recorded on Bruker spectrometer using
CDCl3 as a solvent and mass spectra were recorded on Shimadzu GC-MS Model No.QP-2010.
The liquid crystal behavior and the type of textures were determined by miscibility method
on microscopic observations.
Table . Elemental analysis for () Ethyloxy () Hexyloxy () Tetradecyloxy derivatives.
Elements %Found
H
Elements %Calculated
H
Sr. No.
Molecular formula
C
O
C
O



CHOS
CHOS
HOS
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
C

32
G. N. BHOLA AND U. C. BHOYA
Analytical data
Spectral data
HNMR in ppm for butyloxy derivative
–
–
–
–
0.89–0.93 (t,3H, CH3 of OC4H9 group), 1.38–1.53 (m,2H,CH3 CH2 ), 1.71–1.88
–
–
– – – –
–
–
=
–
–
(p,2H, CH2 CH2 O ), 3.91–3.94 (t,2H, CH2 O ), 7.75–7.79 (d,1H, CH CH COO ),
–
=
–
–
–
–
–
6.39–6.43 (d,1H, CH CH COO ), 7.45–7.47 (d,1H, CO CH=CH ), 7.86–7.90 (d,1H,
–
–
=
–
CO CH CH ), 7.45–7.98 (3H, thiophene ring), 7.45–7.47 & 7.98–8.01 (4H, middle
phenyl ring), 6.84–6.86 & 7.34–7.36 (4H, phenyl ring with alkoxy chain). The NMR data are
consistent with the molecular structure.
HNMR in ppm for octyloxy derivative
–
–
–
–
–
–
0.79–0.83(t,3H, CH3 of –OC8H17 group), 1.21–1.27 (m,8H,CH3 CH2 CH2 CH2 CH2 ),
–
–
–
– – – –
–
–
1.35–1.42 (p,2H, CH2 CH2 CH2 O ), 1.69–1.76 (p,2H, CH2 CH2 O ), 3.90–3.94
–
– –
–
=
–
–
–
–
=
–
–
(t,2H, CH2 O ), 7.36–7.30 (d,1H, CH CH COO ), 6.40–6.44 (d,1H, CH CH COO ),
–
–
=
–
–
=
–
7.01–7.03 (d,1H, CO CH CH ), 7.18–7.25 (d,1H, CO CH CH ), 7.75–8.01 (3H, thio-
phene ring),7.27–7.36&7.99–8.01 (4H, middle phenyl ring), 6.84–6.86 & 7.75–7.79 (4H,
phenyl ring with alkoxy chain). The NMR data are consistent with the molecular structure.
IR in cm− for propyloxy derivative
–
–
–
–
3072(C H str. of alkene disubstituted), 2933 & 2872 (C H str. of ( CH2 )n group of –OC3H7),
=
=
1720 (C O str. of carbonyl carbon of ester group), 1653 (C O str. of α,β unsaturated ketone),
=
=
1653 & 1629 (C C str. of alkene), 1593,1573 & 1512 (C C str. of aromatic ring), 1332& 1286
–
–
–
(C H bending of alkene disubstituted), 1251 (C O str. of ether linkage), 1128 (C O str. of
–
ester group), 995,968 & 875 (C H bending of alkene). The IR data are consistent with the
molecular structure.
IR in cm− for heptyloxy derivative
–
–
–
–
3072 (C H str. of alkene disubstituted), 2956 & 2854 (C H str. of ( CH2 )n group of –
OC7H15), 1720 (C=O str. of carbonyl carbon of ester group), 1654 (C=O str. of α,β unsatu-
rated ketone), 1631 (C=C str. of alkene), 1593,1573 &1506 (C=C str. of aromatic ring), 1332,
–
–
1303 & 1288 (C H bending of alkene disubstituted), 1253 (C O str. of ether linkage), 1130
(C O str. of ester group), 964,873& 817 (C H bending of alkene). The IR data are consistent
with the molecular structure.
–
–
Mass spectra of pentyloxy derivative
m/z (rel.int%): 446 (M)+ ,217,201,171,147,119,91,65
Mass spectra of dodecyloxy derivative
m/z (rel.int%): 544(M)+ ,315,230,201,164,147,119,91,55
Results and discussion
Trans 4-n-alkoxy cinnamic acid, on linking with 4-hydroxy chalconyl derivative with thio-
phene heterocyclic ring yielded mesomorphic homologues. Smectic mesophase commences

MOL. CRYST. LIQ. CRYST.
33
Table . Transition temperatures in oC.
Transition temperatures in oC
N Isotropic
Compound No.
R=n-alkyl chain CnHn+
Sm


























–
–
–
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
(.)
(.)
.
.
.
.
.
.
.
.
Sm, Smectic; N, Nematic; ( ) indicate monotropy
from C4 homologue, whereas nematic mesophase commences from very first member of a
series. Thus, mesomorphism is exhibited by all the members of the present novel series of
ethylene derivatives. Transition temperatures (Table 2) as determined by an optical polar-
izing microscope equipped with a heating stage were plotted versus the number of carbon
atoms present in n-alkyl chain of left flexible unit -OR, and then like or related points were
linked to draw the Cr-M, N-I, Sm-N transition curves showing phase behaviors of novel
series in a phase diagram (Fig. 1). Analytical and spectral data confirmed the structures of
novel molecules. Cr-M transition curve adopted zigzag path of rising and falling tendency
from C1 to C4 homologues and then zigzag path extended in negligible proportion with over-
all descending tendency as series is ascended up to C18 homologue. Sm-N transition curve
for odd and even member rises and then passing through maxima at the C8 homologue and
descends up to last homologue. Odd–even effects is observed for the curve up to C9 homo-
logue and then, descended as a single curve up to C18 member of a series. N-I transition curves
Figure . Phase Behavior of Series.

34
G. N. BHOLA AND U. C. BHOYA
for odd and even homologues of a series merge into each other at the C7 homologue and then,
descended as a single curve up to C18 member of a series. Hence N-I transition curve exhib-
ited odd-even effect. Thus, Cr-M, Sm-N and N-I transition curves behave in normal manner,
with overall descending tendency of transition temperatures. Thermal stability for smectic
and nematic are 132.86oC and 152.78oC, respectively; whose total (Sm+N) mesomorphic
phase length varies from 4.4 oC to 26.0 oC. The present series is partly smectogenic and fully
nematogenic whose transition or melting temperatures vary between 119.7oC and 167.8oC.
LC properties vary from homologue to homologue in the same series with alternation of
transition temperatures. As series is ascended from homologue to homologue in the same
series, by progressive sequential addition of methylene unit, the molecular lengths, length
to breath ratio, molecular flexibility, intermolecular end to end and lateral attractions, per-
manent dipole moment across the long molecular axis, dipole-dipole and electron-electron
interactions, dispersion forces; molecular polarity and polarizibility etc. increases or alters as
a consequence of changing molecular flexibility keeping molecular rigidity unchanged. The
above alterations from homologue to homologue undergo in present novel series in such a
manner that, the magnitudes of anisotropic forces become suitable or fittest to cause either
only nematic mesophase formation or nematic mesophase formation in addition to smec-
tic mesophase formation which become possible and favorable. Thus, entire series from C1
to C18 homologues exhibited mesomorphic property with different degree of mesomorphism
and different magnitudes of same property like transition temperature. The exhibition of odd–
even effect and alternation of transition temperatures are attributed to the addition of methy-
lene unit or units in sequential manner at the n-alkyl chain bonded to phenyl ring through
oxygen atom. The disappearance of odd–even effect after merging of curves for odd and even
homologues is attributed to the coiling or flexing or bending or coupling of longer n-alkyl
chain with the principal axis of the core structure. The molecules of homologues are dis-
aligned at an angle ninety or less than ninety degree on the plane of floating surface and resist
the exposed thermal vibrations accordingly for definite range of temperature, depending upon
the magnitudes of thermal resistivity offered by individual homologue due to their individual
combine effect of molecular rigidity and flexibility i.e. energy stored in a molecule in terms
of enthalpy (ꢀH) to facilitate and stabilize nematic or/and smectic mesophase formation for
definite phase length range. Thus, present series is partly smectogenic and fully nematogenic
with middle ordered melting type.
Some mesomorphic properties of presently investigated novel mesogenic series-1, are com-
pared with the structurally similar other known series-X [30] and Y [30] as mentioned in
Fig. 2.
Homologous series-1 of present investigation and the homologous series-X and Y selected
for comparative study are identical with respect to two phenyl rings, two central bridges
Figure . Structurally similar series.

MOL. CRYST. LIQ. CRYST.
35
Table . Average thermal stabilities in °C.
Series →

X
Y
Smectic-Isotropic or Smectic-Nematic
Commencement of smectic mesophase
Nematic-Isotropic
Commencement of nematic phase
Total Mesophase length range (Sm+N)
. (C-C)
. (C-C)
. (C-C)
C
. (C-C)
C
C
. (C-C)
C
C
. (C-C)
C
.(C) to .(C)
.(C) to . (C)
. (C) to . (C)
–
=
–
–
–
–
=
–
–
=
–
–
viz. CH CH COO and CO CH CH or CH CH CO as well as left n-alkoxy
terminal end group for the same homologue from series to series, but their tail groups
viz.
,
and
are different. Therefore, variations in
mesomorphic properties and the degree of mesomorphism are varied with the changing,
combined effects of molecular rigidity and flexibility as emerged from changing features of
series-1, X and Y respectively. Following Table 3 represents some mesomorphic properties of
series-1, X and Y under comparison.
Table 3 indicates that,
r
Homologous series-1, X and Y are smectogenic in addition to nematogenic in character.
r
Smectic and nematic properties of series-1 commences earlier from C4 and C1 homo-
logues respectively; whereas smectic and nematic properties for both homologues series-
X and Y commences equally from C5 homologue.
o
o
r
Smectic thermal stability of series-1 is (132.86 C) same as series-X (132.25 C) and the
lower than a series-Y (159.7oC).
o
r
Nematic thermal stability of series-1 (152.78 C) is lowest among the series under com-
parison and the same is highest (174.1oC) for series-Y and that of series-X is intermittent
(171.5oC) to series-1 and Y.
r
r
Odd-even effects are observed for Sm-N and N-I transition curves for all the series under
comparison.
Mesophase length ranges are in the decreasing order as series-X > series-Y > series-1.
The suitable magnitudes of anisotropic forces of intermolecular end to end and/or lat-
eral attractions as a consequences of favorable molecular rigidity and flexibility as occurred
from molecular structure which induces smectic or/and nematic mesophase or mesophases.
-NO2 and -OCH3 groups bonded to phenyl ring are highly nematogenic polar and polar-
izable groups and their end to end attractions are relatively more than a thiophene unit of
series-1. Therefore, disallignment of molecules on the plane of floating surface for the same
homologue from series to series and from homologue to homologue in the same series differs
under the influence of exposed thermal vibrations. Thus, resistivity towards exposed thermal
vibrations occurs in different degree of temperatures to maintain either statistically parallel
orientational order of molecules or/and focal conic layered or sliding layered arrangement of
molecules. The combine effect of end group polarity and polarizibility in combination with
–
molecular polarity and polarizibility operates mesomorphic tendency. The OCH3 group is
penta atomic and NO2 group is triatomic generates polarizibility for the same homologue
–
in varying proportions which reflects in intermolecular end to end and lateral attractions.
Therefore, nematic thermal stability of series-X and Y are nearly equivalent (171.5oC and
174.1oC) but exceeds by 15oC to 20oC units to the nematic thermal stability of series-1. How-
ever smectic thermal stability of series-1 and X (132.86oC and 132.25oC) is equivalent, but it
is about 28oC less than a series-Y (159.7oC). The smectic and nematic mesophases of series-
1 commences (C4 and C1) earlier than the series-X and Y (from C5) because, the extent of

36
G. N. BHOLA AND U. C. BHOYA
molecular noncoplanarity vary from series to series for the same homologue due to differing
–
magnitudes of molecular flexibility. Almost equipolar and equipolarizable C6H4.NO2 and
–
C6H4.OCH3 units of series-X and Y undergo almost equal degree of molecular noncopla-
narity. Hence, smectic and nematic mesophases commences equally from same C5 member
–
–
of the both series. None of the functional group like NO2 or OCH3 is attached with thio-
phene ring of a series-1, which reduced the molecular flexibility and the extent of molecular
noncoplanarity to cause early commencement of smectic mesophase formation earlier by one
homologue and the commencement of nematic mesophase formation earlier by four homo-
logues. The energy stored in a molecule (ꢀH) varies from homologue to homologue in the
same series and for the same homologue from series to series whose resistivity against exter-
nally exposed thermal vibrations differs in proportionate magnitudes. Hence, the transition
temperatures, degree of mesomorphism and the extent to which type of mesophase facilitated
or hindered is dependent.
Conclusion
r
A novel ester homologous series of thirteen members (C1 to C18) are synthesized to
understand the effect of heterocyclic tail on mesomorphism. Series is partly smectogenic
and fully nematogenic as derived from transn-alkoxy cinnamic acids. Its degree of meso-
morphism is relatively low and it is middle ordered melting type.
r
The group efficiency order derived for smectic and nematic on the basis of (i) thermal
stability (ii) commencement of mesophase and (iii) the total mesophase length are as
under.
(i) Smectic
Nematic
(ii) Smectic
Nematic
(iii) Smectic+ Nematic
r
Liquid crystal properties and the degree of mesomorphism are very sensitive and sus-
ceptible to molecular structure as a consequence of molecular rigidity and flexibility.
r
Present LC materials may be useful for the study of binary system, for the LC devices
workable between 100oC and 147oC.
r
LC material of present investigation may be useful for Dermatological treatment, if stud-
ied properly by researchers working in medical or pharmaceutical fields.
Acknowledgments
Authors acknowledge thanks to the Department of Chemistry (DST-FIST Funded & UGC-SAP Spon-
sored), Saurashtra University, Rajkot, for research work. Authors are also thankful to Dr. A.V. Doshi,
Ex. Principal M.V.M. Science and Home Science College Rajkot, for his valuable cooperation during

MOL. CRYST. LIQ. CRYST.
37
present investigation as and when needed. Also thanks to the National Facility for Drug Discovery
through New Chemical Entities (NCE.s) for analysis of samples.
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