Mesomorphism and molecular flexibility in novel chalconyl derivatives with two phenyl rings

Article abstract of DOI:10.1080/15421406.2016.1221972

A novel chalconyl liquid crystalline (LC) homologous series with two phenyl rings and one central bridge RO?C₆H₄?CH=CH–CO?C₆H₄(O?C₁₈H₃₇) (meta) has been synthesized and studied with a view to understanding and establishing the effects of molecular structure on thermotropic LC behaviors or properties. Homologous series of present investigation (C₁–C₁₈) consists of thirteen homologues, and thermotropic mesomorphism for nematic and smectic commences from C₃ and C₆ homologues respectively. The C₃, C₄, and C₅ homologues are enantiotropically nematic, whereas, the homologues from C₆ to C₁₈ are monotropically smectic plus nematic. Melting points and transition temperatures were determined using a polarizing optical microscope (POM) equipped with a heating stage. The textures of the nematic phase are threaded or Schlieren and that of a smectic phase are fan shaped of smectic-A or smectic-C type. The Cr?I/M, N?I/I?N, and N-Sm transition curves behave in the normal manner, and the Cr-I/M exhibits an odd-even effect. Analytical, thermal, and spectral data confirm the molecular structures. Thermal stabilities of smectic and nematic are low. Mesophase lengths are very short, ranging between 1–8°C and 14°C. The novel compounds are compared with a known series.

Full text of DOI:10.1080/15421406.2016.1221972

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://china.tandfonline.com/loi/gmcl20
Mesomorphism and molecular flexibility in novel
chalconyl derivatives with two phenyl rings
Vinay S. Sharma, B. B. Jain & R. B. Patel
To cite this article: Vinay S. Sharma, B. B. Jain & R. B. Patel (2016) Mesomorphism and
molecular flexibility in novel chalconyl derivatives with two phenyl rings, Molecular Crystals
and Liquid Crystals, 638:1, 68-76, DOI: 10.1080/15421406.2016.1221972
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Date: 19 November 2016, At: 02:30

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Mesomorphism and molecular flexibility in novel chalconyl
derivatives with two phenyl rings
Vinay. S. Sharma, B. B. Jain, and R. B. Patel
Chemistry Department, Shri K. K Shah Jarodwala Maninagar Science College, Ahmedabad, Gujarat, India
ABSTRACT
KEYWORDS
Chalcone; Liquid crystals;
Mesomorphic; Nematic;
Smectic
A novel chalconyl liquid crystalline (LC) homologous series with
–
–
=
two phenyl rings and one central bridge RO C6H4 CH CH–
–
–
CO C6H4(O C18H37) (meta) has been synthesized and studied with
a view to understanding and establishing the effects of molecular
structure on thermotropic LC behaviors or properties. Homologous
series of present investigation (C1–C18) consists of thirteen homologues,
and thermotropic mesomorphism for nematic and smectic commences
from C3 and C6 homologues respectively. The C3, C4, and C5 homologues
are enantiotropically nematic, whereas, the homologues from C6 to C18
are monotropically smectic plus nematic. Melting points and transition
temperatures were determined using a polarizing optical microscope
(POM) equipped with a heating stage. The textures of the nematic
phase are threaded or Schlieren and that of a smectic phase are fan
–
– –
shaped of smectic-A or smectic-C type. The Cr I/M, N I/I N, and N-Sm
transition curves behave in the normal manner, and the Cr-I/M exhibits
an odd-even effect. Analytical, thermal, and spectral data confirm the
molecular structures. Thermal stabilities of smectic and nematic are
low. Mesophase lengths are very short, ranging between 1–8°C and
14°C. The novel compounds are compared with a known series.
Introduction
Low temperature liquid crystalline (LC) [1] materials are important for applications in
electronic devices, thermographic articles, and additionally for chalconyl derivatives in
the field of agriculture and pharmaceutical preparations through their bioactive nature
[2–10]. The aim of the presently planned investigation is to correlate mesomorphism and
the molecular structure [11–16]. In view of the proposed investigation, a novel homologous
series of chalcone derivatives are synthesized and characterized through elemental analysis,
IR and 1HNMR spectra and thermal data by POM. The evaluated thermometric data will be
interpreted and discussed in terms of molecular rigidity and flexibility [17–20] and finally
appropriate conclusions will be drawn from present investigation. The group efficiency order
will be derived from comparative study of present investigation with structurally similar
analogous series. Several homologous series have been reported to date [21–26].
CONTACT R. B. Patel
roshanpatel@gmail.com
College, Ahmedabad, Gujarat, India
Chemistry Department, Shri K. K Shah Jarodwala Maninagar Science
©  Taylor & Francis Group, LLC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
69
Scheme . Synthetic route to the series.
Experimental
Synthesis
Alkylation of 4-hydroxy benzaldehyde to give 4-n-alkoxy benzaldehyde was carried out by
a reported method [27] 3-n-Octadecyloxy acetophenone was obtained by alkylation of 3-
hydroxy acetophenone by a reported method [28] Thus, the chalconyl homologue deriva-
tives (C) were prepared by a usual established method [29]. Final products were collected and
filtered, washed with ethanol solution dried and purified until constant transition tempera-
tures obtained using an optical polarizing microscope, equipped with a heating stage. Alkyl
halides, acetone, EtOH, KOH, 3-hydroxy acetophenone, 4-hydroxy benzaldehyde required
for synthesis were used as received, except solvents which were dried and distilled prior to
use. The synthetic route to the series is shown below in Scheme 1.
Characterization
Representative homologues of a series were characterized by elemental analysis (Table 1),
1
Infrared spectroscopy, H NMR spectra. IR spectra were recorded on Perkin-Elmer spec-
trum GX, 1H NMR spectra were recorded on Bruker using CDCl3 as solvent. Microanalysis
was performed on Perkin-Elmer PE 2400 CHN analyzer. Transition temperature (Table 2) and
Table . Elemental analysis for () propyloxy () pentyloxy () decyloxy and () dodecyloxy derivatives.
Elements % found
Elements % calculated
Sr. no.
Molecular formula
CHO
C
H
C
H

.
.
.
.
.
.
.
.
.
.
.
.
.



C 
CHO
HO
H
O
.
.
.
C

70
V. S. SHARMA ET AL.
Table . Transition temperature 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
–
–
–
–
–
–
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
–
.
(.)
(.)
(.)
(.)
(.)
(.)
(.)
(.)
(.)
(.)
(.)
(.)
(.)
(.)
(.)
(.)
() Indicates monotropy.
LC properties (Textures) were determined using an optical polarizing microscopy equipped
with heating stage and digital camera (POM). Texture images of nematic phase were deter-
mined by miscibility method (Table 3).
Analytical data
IR Spectra in cm−1 for octyloxy and hexadecyloxy derivatives:
Octyloxy (C)
–
–
–
2914 (C H str. of alkane), 2842 (C H str. of –(CH2 )n group of –OC8H17 alkyl chain, 1640
=
=
(C O str. of carbonyl carbon of chalconyl group), 1604 (C C str. of alkene in chalcone),
1510, 1543 (C C str. of aromatic ring), 999 (C H bending of alkene), 1178 (C O str. of
ether linkage), 1288, 1246 (C O str. of carbonyl (>CO) group), 770 Polymethylene ( CH2 )
of –OC18H37, 675 Polymethylene ( CH2 )n of –OC8H17, 823( C H def. m di-substituted-
=
–
–
–
–
–
–
–
– – –
Para), IR data confirms the molecular structure of comp.C8.
Hexadecyloxy (C)
–
–
–
2916 (C H str. of alkane), 2850 (C H str. of –(CH2 )n group of –OC16H33 group, 1660
=
=
=
(>C O str. of carbonyl group of chalconyl group), 1604(C C str. of alkene), 1543 (C C
str. of aromatic ring), 1004, (C H bending of alkene), 1199 (C O str. of ether linkage), 1251
(C O str. of carbonyl group), 770 Polymethylene ( CH2 ) of –OC18H37, 823 ( C H def. m
–
–
–
–
–
– – –
di-substituted-Para), IR data confirms the molecular structure of comp.C16.
Table . Texture of nematic phase of C, C, C, C by miscibility method.
Sr. no.
Homologue
Texture

C
C
C
C
Schlieren
Threaded
Threaded
Schlieren




MOLECULAR CRYSTALS AND LIQUID CRYSTALS
71
1HNMR spectra in CDCl3 in δ ppm for butyloxy and pentyloxy derivative:
Butyloxy (C)
–
0.88 (t, 6H,
CH3 of polymethylene –C6H13 and –C14H29), 1.79(p, 10H,
–
–
–
–
–
–
–
–
CH3 CH2 CH2 CH2 CH2 of –OC6H13 and –OC14H29), 1.28 (m, 15H –CH2 CH2 CH2
of –OC7H15 and –OC14H29), 1.31 (q, 8H, CH2 CH3), 4.06(t, 4H, OCH2 CH2 ), 7.59 (d,
2H, CH CH ), 7.43, 7.28, and 7.83 (4H, meta substituted phenyl ring), 7.56 and 7.97 (4H,
phenyl ring with alkoxy chain). NMR data confirms the molecular structure of comp.C4.
–
–
–
–
–
–
=
–
Pentyloxy (C)
–
–
–
–
–
–
0.88 (t, 6H, CH3 of –C10H21 and –C14H29), 1.80(p, 10H, CH3 CH2 CH2 CH2 CH2 CH2
–
–
–
–
of OC10H21 and –OC14H29), 1.28 (m, polymethylene 16H –CH2 CH2 CH2 of –OC10H21
and –OC14H29), 1.34 (q, 8H, CH2 CH3), 4.05(t, 4H, OCH2 CH2 ), 7.59 (d, 2H,
CH CH ),7.43, 7.28, and7.83 (4H, meta substituted phenyl ring), 7.56 and 7.97 (4H, phenyl
ring), 6.95 and 7.62 (4H, phenyl ring with alkoxy chain). NMR data confirms the molecular
–
–
–
–
–
–
=
–
structure of comp.C5.
Result and discussion
4-n-Alkoxy benzaldehydes on condensation with 3-octadecyloxy acetophenone yielded thir-
teen chalconyl derivatives (C1–C18) with C3 to C18 homologues as mesogenic. C3–C5 deriva-
tives are enantiotropically nematogenic with absence of smectic property, C6 to C18 deriva-
tives are monotropically nematogenic plus monotropically smectogenic. C1–C2 homologues
are nonmesogenic. Transition temperatures of homologues as determined by POM on plot-
ting for number of carbon atoms present in n-alkyl chain ‘R’ of –OR terminal group and sub-
sequently on linking like or related points, transition curves Cr-I/N, I-N or N-I, N-Sm are
obtained. Cr-I/N transition curve follows a zigzag path of rising and falling values with an
overall falling tendency and so behaves in a normal manner. The N-I or I-N transition curve
follows descending tendency up to C8 homologue and then negligibly ascended up to last
homologue with exhibition of odd-even effect. Thus, it behaved in normal manner neglect-
ing minor deviating effect from C8 or C9 homologue beyond merging of N-I/I-N curves for
higher homologue of longer n-Alkyl chain ‘R’ of –OR group. N-Sm transition curve gradu-
ally rises up to C16 homologue and then descended to C18 homologue member after passing
through maxima at C16 member. Thus, it behaved in normal manner with exhibition of odd-
even effect up to C8 homologue; and then monotropic N-Sm transition curve prolonged as
a single transition curve. The mesophase length for N-Sm transitions are very short, of the
order of one or a fraction of 1°C. The textures of nematic phase are threaded or Schlieren and
that of the smectic phase are focal conic fan shaped smectic-A or smectic-C as judged directly
from the heating top of the POM. Analytical, thermal and spectral data supported molecu-
lar structures of novel homologues. Thermal stabilities for nematic is 64.3°C and that of the
smectic phase are minimum from fraction of 1°C or maximum 1°C. Thus, mesophase lengths
are very small or shorter. The LC properties of thermotropic novel LC chalcones from homo-
logue to homologue in the same series undergo variation with changing; length of molecules
or permanent dipole moment across the longer molecular axis.
The absence of mesomorphic tendency of C1 and C2 homologue is attributed to low mag-
nitudes of intermolecular dispersion forces and low magnitudes of dipole–dipole interactions
which induces unsuitable magnitudes of anisotropic forces of end to end or lateral cohesions
and closeness as a consequence of unfavorable molecular rigidity and flexibility to induce

72
V. S. SHARMA ET AL.
mesomorphism. Therefore, their molecules are unable to withstand the intensity of exposed
thermal vibrations and sharply transform into isotropic liquid without passing through meso-
morphic state. However, the homologues C6–C18 transform from crystalline solid state to
isotropic state without showing of any sort of LC state, but, on cooling, a monotropic nematic
of considerable temperature range results, and then a monotropic smectic mesophase of very
short temperature range. The molecules of C3,C4,C5 under microscopic (POM) examination
on heating top resists exposed thermal vibrations and disalign at an angle less than ninety
degree due to suitable magnitudes of end to end intermolecular cohesions and closeness, as
a result of favorable or suitable magnitudes of dispersion forces, dipole–dipole interactions,
molecular rigidity, and flexibility. Thus, the molecules from C3 to C5 homologues acquire
comfortable thermodynamic environmental situation to set their respective molecules in
statistically parallel orientational order for some degrees of temperature range in reversible
(heating and cooling both) manner which facilitated enantiotropically nematogenic meso-
morphism only. Odd-even effect exhibited by I-N/N-I and N-Sm transition curves of a phase
diagram (Fig. 1) is attributed to the sequentially added methylene unit at the n-alkyl chain
‘R’ of –OR terminal end group. The minor and negligible deviation from normal behavior
of transition curves of a phase diagram from and beyond merging of transition curves con-
tributing to odd-even effect of higher homologues of longer n-alkyl chain ‘R’ and –C18H37
hydrocarbon chain bonded through oxygen atom as terminal or lateral groups with phenyl
rings; which may coil or bend or flex or couple to lie with major axis of core to modify favorable
or unfavorable molecular rigidity and / or flexibility to cause phase behaviors with LC prop-
erties. The variations in mesogenic or LC properties and the degree of mesomorphism from
homologue to homologue in the same novel series are attributed to the sequentially added
carbon atoms in n-alkyl chain ‘R’ of –OR group which may cause variations in the molecular
length, permanent dipole moment across the long molecular axis, length to breadth ratio, the
ratio of the molecular polarity to polarizability, intermolecular dispersion forces due to end
to end or lateral attractions and the magnitudes of closeness, molecular rigidity and /or flexi-
bility etc. Following Fig. 2 represents some structurally similar analogous series-X [30] and Y
[31] chosen for the comparative purpose with presently investigated novel series-1:
Homologous series 1, X, Y under comparative study consisted of two phenyl rings and one
–
–
central bridge –CH = CH CO which contributes identically to the molecular rigidity from
series to series for the same homologue and from homologue to homologue in the same series.
The terminal group –OR, in which n-alkyl chain ‘R’ varies with number of methylene units
from homologue to homologue in the same series but the number of methylene units of ‘R’
remains unaltered for the same homologue from series to series, contributing partly towards
–
sharing of total molecular flexibility. Laterally substituted –OC18H37(n), OC16H33(n) and –
OC14H29(n) groups whose molecular flexibility, group polarities and polarizability vary from
series to series for the same homologue but remains unaltered from homologue to homologue
in the same series respectively due to their respective lateral groups linked to meta position of
second phenyl ring but vary with changing -R. Thus, variations in LC properties among the
series 1, X and Y can be attributed to the varying features related to mesomorphism due to,
even a minute changing features or the total changing flexibility of terminal and / or lateral
groups; for the same homologue from series to series. Following Table 4 represents some ther-
mometric data evaluated from present investigation of series-1 and series-X and Y chosen for
comparative study.
Above Table 4 indicates that,
• The homologous series 1,X and Y are identical with respect to the exhibition of smecto-
genic and nematogenic property.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
73
Figure . Phase behaviors of series.
Figure . Structurally similar analogous series.

74
V. S. SHARMA ET AL.
Table . Thermal stability in°C.
Series→
Series-
Series-X
Series-Y
Sm-I or Sm-N or N-Sm
commencement of
smectic phase
Fraction of °C or °C
 to .°C
(C–C)
C
 to .°C
(C–C)
C
(C–C)
C
.
N-I or I-N
.
.
Commencement of
nematic phase
Mesophase length (total)
(C–C)
C
.–.°C
C/C/C C
(C–C)
C
.–.°C
C C
(C–C)
C
.–.°C
C C/C/C
• Exhibition of smectogenic mesophase commences from C6 (series 1 and Y) or C7 (series-
X) homologue with the difference of only one homologue.
• Nematogenic mesophase commences from C2 (series X and Y) or C3 (series-1) homo-
logue with the difference of only one homologue.
• Thermal stability for nematic increases from series 1 to Y to X. Whereas, stabilization of
smectogenic character is very poor.
• Total mesophase length in higher category follows increasing order as series-X > series-
1 > series-Y whereas in lower category are equal for series-X and Y but more for present
series 1 by 1°C.
Looking to the geometrical shapes, aromaticity, molecular length or the permanent dipole
moment across the long molecular axis, molecular rigidity for the same homologue from
series to series under comparative study (Fig. 2) are identical except the length of laterally
meta substituted –OC18H37 (n), -OC16H33 (n) and –OC14H29 (n) group of series 1, X and Y,
respectively, which differs by –CH2-CH2- unit from series-1 to series X to series Y affect-
ing molecular flexibility if the status of their n-alkyl chains –C18H37 (n), -C16H33 (n) and
–C14H29 (n) are as identical as expected in equal manner. But, longer n-alkyl meta substi-
tuted chain bonded through oxygen atom of lateral group also may cause difference in polar-
ity and polarizability due to gradually added –CH2-CH2- unit and the same longer n-alkyl
chains may coil or bend or flex or couple to lye with major axis of core structure which
may modify magnitudes of flexibility and the magnitudes of intermolecular cohesions and
closeness for the same homologue from series to series under the influence of exposed ther-
mal vibrations when floated on the surface. But experimentally evaluated thermometric data
suggest that, there is very little difference in thermal stabilities, commencements of smec-
tic and nematic phase, degrees of mesomorphism or facilitations of upper and lower total
mesophase lengths as well as the types of mesophases for the same homologue from series
to series, i.e., lengthening of laterally meta substituted n-Alkyl chain bonded through oxygen
atom with phenyl ring are less effective in raising or depressing thermotropic mesomorphic
properties.
Conclusions
r
Chalconyl derivatives consisted of two phenyl rings with laterally meta substituted n-
alkoxy group are predominantly nematogenic and partly smectogenic with its low melt-
ing type behavior.
Group efficiency order derived for smectic and nematic on the basis of (a) thermal stabil-
ities (b) early commencement of mesophase and (c) upper and lower mesophase lengths
are as under.
r

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
75
(a) Smectic
Series 1 = Series X = Series Y
Nematic
Series X > Series Y > Series 1
(b) Smectic
Series 1 = Series Y > Series X
Nematic
Series X = Series Y > Series 1
(c) Total mesophaselengths
Upper: Series X > Series 1 > Series Y
Lower: Series 1 > Series X = Series Y
r
r
Mesomorphism is very sensitive and susceptible to molecular structure as a consequence
of molecular rigidity or/and flexibility.
Present investigation may be useful for the construction of devices to be operated at
low temperature or room temperature. Biological activity of novel compounds may be
exploited and studied for pharmaceutical and agricultural production.
This supported and raised the credibility to the conclusions drawn earlier.
r
Acknowledgments
Authors acknowledge thanks to Dr. R.R. Shah, principal and management of K. K. Shah Jarodwala
Maninagar Science College, Ahmedabad. Authors are also thankful to Dr. A.V. Doshi, Ex-principal of
M.V.M. Science and Home Sci. College-Rajkot for his constant support, inspirations, help, and valuable
comments and suggestions, as and when needed during the course of present investigation. Authors
also thank NFDD Centre for the spectral and analytical services.
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