Synthesis and mesomorphic properties of new chalconyl-linkage-based liquid crystal compounds: The effect of flexibility

Article abstract of DOI:10.1080/15421406.2016.1263112

A new series of liquid crystals involving chalconyl-based mesogenic units interlinked between two benzene cores were designed and synthesized. The target chalconyl compounds were obtained by the reaction of 4-n-alkoxy benzaldehyde with 4-n-hexadecyloxy (–OC₁₆H₃₃) acetophenone in presence of base. The liquid crystalline properties of synthesized compounds were observed by polarizing optical microscope study. The molecular structures of the compounds were confirmed by Fourier transform infrared, ¹H, and ¹³C nuclear magnetic resonance spectra. The compounds of the series C₃ to C₈, C₁₀, C₁₂, C₁₄, C₁₆, and C₁₈ exhibited mesophase in enantiotropically manner. The transition temperature reduced as alkyl spacer of left side group increased. The observed texture images are droplets, broken fan, and threaded like. Thermal stability of current homologous series for (N-I/I-N) is 69.8°C and for smectic phase (Sm + N) is 58.0°C.

Full text of DOI:10.1080/15421406.2016.1263112

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis and mesomorphic properties of new
chalconyl-linkage-based liquid crystal compounds:
The effect of flexibility
Vinay S. Sharma & R. B. Patel
To cite this article: Vinay S. Sharma & R. B. Patel (2017) Synthesis and mesomorphic properties
of new chalconyl-linkage-based liquid crystal compounds: The effect of flexibility, Molecular
Crystals and Liquid Crystals, 643:1, 129-140, DOI: 10.1080/15421406.2016.1263112
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1263112
Published online: 23 Feb 2017.
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Date: 23 February 2017, At: 23:19

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –

http://dx.doi.org/./..
Synthesis and mesomorphic properties of new
chalconyl-linkage-based liquid crystal compounds: The effect
of flexibility
Vinay S. Sharma and R. B. Patel
Chemistry Department, K. K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
A new series of liquid crystals involving chalconyl-based mesogenic
units interlinked between two benzene cores were designed and
synthesized. The target chalconyl compounds were obtained by the
reaction of 4-n-alkoxy benzaldehyde with 4-n-hexadecyloxy (–OC H )
Chalconyl LCs; nematic;
odd-even; smectic
1
6
33
acetophenone in presence of base. The liquid crystalline properties
of synthesized compounds were observed by polarizing optical
microscope study. The molecular structures of the compounds were
1
13
confirmed by Fourier transform infrared, H, and C nuclear magnetic
resonance spectra. The compounds of the series C to C , C , C ,
3
8
10
12
C , C , and C exhibited mesophase in enantiotropically manner.
14
16
18
The transition temperature reduced as alkyl spacer of left side group
increased. The observed texture images are droplets, broken fan,
and threaded like. Thermal stability of current homologous series for
(
N-I/I-N) is 69.8°C and for smectic phase (Sm + N) is 58.0°C.
GRAPHICAL ABSTRACT
CONTACT Vinay S. Sharma
vinaysharma@gmail.com
Science College, Gujarat University, Ahmedabad , Gujarat, India.
Chemistry Department, K. K. Shah Jarodwala Maninagar
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

1
30
V. S. SHARMA AND R. B. PATEL
Introduction
Liquid crystals (LCs) are matter in a state that has properties between those of conventional
liquid and solid crystals. For instance, a liquid crystal may flow like a liquid, but its molecules
may orient in a crystal-like way [1, 2]. Liquid crystals can be divided into thermotropic,
lyotropic, and metallotropic phases. Thermotropic and lyotropic liquid crystals consist mostly
of organic molecules although few minerals are also known. Presently, we emphasis on ther-
motropic liquid crystals in which, phase transition into liquid crystal phase as temperature
changed [3–8]. Liquid crystals of nematic type are most commonly used in production of liq-
uid crystal displays due to their unique physical properties and wide temperature range. In the
nematic phase, liquid crystal molecules are oriented on average along a particular direction.
By applying an electric or magnetic field the orientation of the molecules can be derived in a
probable approach [9, 10].
A number of chalcone having reported to exhibit a broad spectrum of antibacterial, anti-
fungal, antiulcer, antimalarial, antitumor, anticancer, anti-inflammatory, and antitubercular
[
11–14]. The presence of α, β-unsaturated functional group in chalcone (–CH=CH-CO–)
is responsible for antimicrobial activity, which can be altered depending upon the type of
substituent present on the aromatic rings [15]. Thus, the purpose of the work to synthesized
and studied the effect of chalconyl linkage group and effect of varying alkyl spacer on meso-
morphism.
Doshi et al. synthesized and studied the molecular structure of LC property of chalconyl
ester-based homologous series [16–18]. In our previous work, we reported the isomeric and
nonisomeric homologues series with chalconyl ester linkage group [19–22]. Recently, we
reported newly homologues series based on two phenyl ring and one central chalcone linkage
group [23–24]. Chalcone (Ar–CH=CH–CO–Ar)-based compounds are important interme-
diates in the synthesis of many pharmaceuticals. Some of the chalcone derivatives take a vital
role in numerous fields such as crystallography and nonlinear optical properties [25–31], liq-
uid crystalline polymers, and dye industries and in solar cells [32–35]. Presence of ꢀ-bond
conjugation in chalconyl group (α, β-unsaturated ketone), which leads to a good charge trans-
fer axis and the aromatic rings, act as a tool for a donor and an acceptor [36].
Experimental
Synthesis and method
Alkylation of 4-hydroxy benzaldehyde to give 4-n-alkoxy benzaldehyde is carried out by
reported method [37]. 4-n-hexadecyloxy acetophenone is obtained by alkylation of 4-hydroxy
acetophenone by reported method [38]. Thus, the (E)-chalconyl homologue derivatives (C)
were prepared by usual established method [39]. Final products were collected and filtered,
washed with ethanol solution dried and purified till constant transition temperatures obtained
using an polarizing optical microscope (POM) equipped with a heating stage. Alkyl halides,
acetone, EtOH, KOH, 4-hydroxy acetophenone, 4-hydroxy benzaldehyde required for syn-
thesis were used as received, except solvents which were dried and distilled prior to use. The
synthetic route of the series is mentioned in Scheme 1.
Characterization
Representative homologues of a series were characterized by elemental analysis, infrared
1
spectroscopy, H NMR spectra. IR spectra were recorded on Perkin-Elmer spectrum GX,
1
13
H, and C NMR spectra were recorded on Bruker using CDCl as solvent. Microanalysis
3

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
131
Scheme . Synthetic route to the series-.
was performed on Perkin-Elmer PE 2400 CHN analyzer. Texture images of nematic phase
were determined by miscibility method (Table 1). Transition temperature (Table 2) and LC
properties (textures) were determined using an optical polarizing microscopy equipped
with heating stage. The compound is sandwiched between glass slide and cover slip and the
heating and cooling rate is 2°C.
Analytical data
C (Heptyloxy): IR (KBr): v /cm 1 2914 (C–H str. of alkane), 2842 (C–H str. of –(CH –)n
−
7
max
2
group of –OC H alkyl chain, 1640 (C=O str. of carbonyl carbon of chalconyl group), 1604
16
33
(
C=C str. of alkene in chalcone), 999 (C–H bending of alkene), 1178 (C-O str. of ether linkage
in side chain), 936 (trans, –CH=CH–) group, 770 polymethylene (–CH –) of –OC H , 675
2
7
15
polymethylene (–CH –)n of –OC H , IR data confirms the molecular structure of com-
2
16 33
1
pound C , HNMR: 0.88–0.90 (t, J = 8.0 Hz, 6H, –CH of polymethylene -C H and -
7
3
7
15
C H ), 1.76 (J = 7.1 Hz, 4H, –OC H , and–OC H ), 1.26–1.31 (m, J = 7.2 Hz, 34H,
16
33
7
15
16 33
–
CH –CH –CH - of –OC H and –OC H ), 1.76 (p, 4H, –OC H and –OC H ), 4.06
2 2 2 7 15 16 33 7 15 16 33
(
t, J = 7.0 Hz, 4H, –OCH –CH - of –OC H and –OC H ), 7.59–8.06 (d, J = 15.1 Hz, 2H,
2
2
7
15
16 33
Table . Texture of nematic phase of C , C , C , C , and C by miscibility method.





Sr. No.
Homologue
Texture

C
C
C
C
C
Threaded
Droplets
Droplets
Threaded
Droplets





1
32
V. S. SHARMA AND R. B. PATEL
Table . Transition temperature by POM in °C.
Transition temperatures in °C
Sr. No.
R = n-alkyl group
Cr
Smectic
Nematic
Isotropic

C
C
C
C
C
C
C
C
C
C
C
C
C
·
·
·
·
·
·
·
·
·
·
·
·
·
—
—
—
—
—
—
—
—
·
—
—
—
—
—
—
.
.
.
.
.
.
.
.
.
.
.
.
.
·
·
·
·
·
·
·
·
·
·
·
·
·












—
.
.
.
.
.
.
.
.
.
.
—
·
.
.
.
.
.
.
.
.
.
·
·
·
·
·
·
·




·
·
·
·
·
·
·
·
–
CH=CH–), 7.24, 8.10–8.14 (4H, J = 8.1 Hz, second para-substituted phenyl ring), 6.94–7.61
13
(
4H, J = 8.0 Hz, first phenyl ring with alkoxy chain). C NMR (CDCl ): 164.3, 130.2, 129.2,
3
1
2
29.6, 158.8, 114.9, (Ar-C), 14.1 (–CH ), 183.3 (-C=O group), (31.9, 66.2, 31.7, 25.9, 29.6,
3
9.3, 22.7 (–CH ), 145.3, 121.2 (–CH of -olefin). Elemental analysis: calculated for C H O :
2
38 58
3
C, 81.11%; H, 10.32%; O, 8.54%; found: C, 80.98%; H, 10.28%; O, 8.47%.
−1
C10 (Decyloxy): IR (KBr): vmax/cm 2920 (C–H str. of alkane), 2848 (C–H str. of
(CH –)n group of –OC H alkyl chain, 1630 (C=O str. of carbonyl carbon of chalconyl
–
2
16 33
group), 1604 (C=C str. of alkene in chalcone), 1510, 1543 (C=C str. of aromatic ring), 996
(
(
C–H bending of alkene), 1178 (C-O str. of ether linkage), 1286, 1240 (C-O str. of carbonyl
>CO) group), 972 (trans, –CH=CH–) group, 761 polymethylene (–CH –) of –OC H , 782
2
10 21
polymethylene (–CH –)n of –OC H , IR data confirms the molecular structure of com-
2
16 33
1
pound C , HNMR: 0.89–0.90 (t, J = 8.0 Hz, 6H, –CH of polymethylene -C H and -
10
3
10 21
C H ), 1.76 (p, 4H, J = 7.1 Hz, CH –CH –CH –CH –CH - of –OC H and –OC H ),
16
33
3
2
2
2
2
10 21
16 33
1
4
8
.28–1.31 (m, J = 7.1 Hz, 38H, –CH –CH of –OC H and –OC H ), 4.06 (t, J = 7.1 Hz,
2
3
10 21
16 33
H, –OCH –CH - of –OC H , –OC H ), 7.58–8.04 (d, J = 15.1, 2H, –CH=CH–), 7.18,
2
2
10 21
16 33
.10–8.15 (4H, J = 8.0 Hz, para-substituted phenyl ring), 6.94–7.61 (4H, J = 7.5 Hz, phenyl
13
ring with alkoxy chain), C NMR (CDCl ): 165.3, 157.2, 129.8, 129.7, 114.9, 114.1, (Ar-C),
3
1
(
4.1 (–CH ), 31.9, 68.7, 29.6, 25.9, 29.6, 29.3, 22.7 (–CH ), 189.4 (-C=O group), 145.1, 121.3
3
2
–CH of Olefine). Elemental analysis: calculated for C H O : C, 81.45%; H, 10.59%; O,
41 64 3
7
.94%; found: C, 80.38%; H, 10.48%; O, 7.88%.
−1
C12 (Dodecyloxy): IR (KBr): vmax/cm 2914 (C–H str. of alkane), 2842 (C–H str. of
(CH –)n group of –OC H alkyl chain, 1620 (C=O str. of carbonyl carbon of chal-
–
2
16 33
conyl group), 1608 (C=C str. of alkene in chalcone), 1543 (C=C str. of aromatic ring),
9
91 (C–H bending of alkene), 1178 (C-O str. of ether linkage), 1288, 1246 (C-O str. of
carbonyl (>CO) group), 936 (trans, –CH=CH–) group, 761 polymethylene (–CH –) of
2
–
OC H , 791 polymethylene (–CH –)n of –OC H , IR data confirms the molecular
12 25 2 16 33
1
structure of compound C , HNMR (CDCl ): 0.89 to 0.90 (t, J = 8.0 Hz, 6H, –CH of
12
3
3
polymethylene -C H and -C H ), 1.80 (J = 7.0 Hz, 4H, CH –CH –CH –CH –CH -
12
25
16 33
3
2
2
2
2
of –OC H and –OC H ), 1.28–1.31 (m, 42H, –CH –CH –CH of –OC H and
12
21
16 33
2
2
3
12 25
–
OC H ), 4.06 (t, J = 7.1 Hz, 4H, -O–CH –CH - of –OC H and –OC H ),
16
33
2
2
12 25
16 33
7
.59–8.06 (d, J = 15.1 Hz, 2H, –CH=CH–), 7.20, 8.10–8.14 (4H, J = 8.1 Hz, para-
substituted second phenyl ring), 6.92–7.63 (4H, J = 8.0 Hz, first phenyl ring with alkoxy
chain), 13C NMR (CDCl ): 165.3, 158.6, 130.4, 129.8, 129.4, 114.9, 114.1, (Ar-C), 14.1
3
(
–CH ), 31.9, 68.7, 68.4, 29.6, 25.9, 29.6, 29.3, 22.7 (–CH ), 189.3 (-C=O), 145.1, 121.3
3
2

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
133
(
–CH of -olefin). Elemental analysis: calculated for C H O : C, 81.64%; H, 10.75%; O, 7.59%;
43 68 3
found: C, 81.56%; H, 10.71%; O, 7.52%.
C14 (Tetradecyloxy): IR (KBr): vmax/cm 1 2991 (C–H str. of alkane), 2870 (C–H str. of
−
–
(CH –)n group of –OC H alkyl chain, 1630 (C=O str. of carbonyl group), 1608 (C=C str.
2
16 33
of alkene in chalcone), 1510 (C=C str. of aromatic ring), 991 (C–H bending of alkene), 1178
(
C-O str. of ether linkage), 936 (trans, –CH=CH–) group, 791 polymethylene (–CH –) of
2
–
OC H , 804 polymethylene (–CH –)n of –OC H , IR data confirms the molecular struc-
14 29 2 16 33
1
ture of compound C , HNMR: 0.88–0.90 (t, 6H, –CH of polymethylene -C H and
14
3
14 29
-
(
C H ), 1.79 (p, 4H, CH –CH –CH –CH –CH - of –OC H and –OC H ), 1.29–1.31
16 33 3 2 2 2 2 14 29 16 33
m, 46H, –CH –CH –CH –CH of –OC H and –OC H ), 4.06 (t, 4H, –OCH –CH - of
2 2 2 3 14 29 16 33 2 2
–OC H and –OC H ), 7.59–8.02 (d, J = 15.1 Hz, 2H, –CH=CH–), 7.16, 8.10–8.14 (4H,
14
29
16 33
J = 8.1 Hz, para-substituted second phenyl ring), 6.94–7.62 (4H, J = 8.1 Hz, first phenyl ring
13
with alkoxy chain), C NMR (CDCl ): 165.6, 158.6, 130.2, 129.3, 126.8, 120.2, 114.6, 114.3,
3
(
1
7
Ar-C), 14.1 (–CH ), 31.9, 68.2, 29.6, 25.9, 29.6, 29.3, 22.7 (–CH ), 189.3 (-C=O group), 145.1,
3
2
21.4 (–CH of -olefin). Elemental analysis: calculated for C H O : C, 81.81%; H, 10.90%; O,
45 72 3
.27%; found: C, 80.72%; H, 10.83%; O, 7.22%.
−1
C16 (Hexadecyloxy): IR (KBr): vmax/cm 2990 (C–H str. of alkane), 2891 (C–H str. of
(CH –)n group of –OC H alkyl chain, 1640 (C=O str. of carbonyl carbon of chalconyl
–
2
16 33
group), 1608 (C=C str. of alkene in chalcone), 1543 (C=C str. of aromatic ring), 981 (C–H
bending of alkene), 1178 (C-O str. of ether linkage), 1242 (C-O str. of carbonyl (>C=O)
group), 932 (trans, –CH=CH–) group, 712–7.20 (polymethylene (–CH –)n of –OC H ), IR
2
16 33
1
data confirms the molecular structure of compound C , HNMR: 0.88–0.90 (t, 6H, –CH of
1
6
3
polymethylene -C H ), 1.79 (p, 4H, CH –CH –CH –CH –CH - of –OC H ), 1.29–1.31
16
33
3
2
2
2
2
16 33
(
m, 48H, –CH –CH –CH –CH of –OC H ), 4.06 (t, 4H, –OCH –CH - of –OC H ),
2 2 2 3 16 33 2 2 16 33
7
.58–8.02 (d, J = 15.1 Hz, 2H, –CH=CH–), 7.16, 8.10–8.14 (4H, J = 8.1 Hz, para-substituted
13
second phenyl ring), 6.94–7.61 (4H, J = 8.1 Hz, first phenyl ring with alkoxy chain),
C
NMR (CDCl ): 164.7, 158.9, 130.2, 129.3, 126.8, 120.2, 114.6, 114.3, (Ar-C), 14.1 (–CH ),
3
3
3
1.9, 68.2, 29.6, 25.9, 29.6, 29.3, 22.7 (–CH ), 189.3 (189.2 -C=O group), 145.1, 121.5 (–CH of
2
-
olefin). Elemental analysis: calculated for C H O : C, 81.97%; H, 11.04%; O, 6.97%; found:
47
76
3
C, 81.11%; H, 10.97%; O, 6.68%.
C18 (Octadecyloxy): IR (KBr): vmax/cm 1 2990 (C–H str. of alkane), 2886 (C–H str. of
−
–
(CH –)n group of –OC H alkyl chain, 1630 (>C=O str. of carbonyl carbon of chal-
2
16 33
conyl group), 1610 (C=C str. of alkene in chalcone), 1516 (C=C str. of aromatic ring), 990
(
7
C–H bending of alkene), 1178 (C-O str. of ether linkage), 936 (trans, –CH=CH–) group,
06–761 polymethylene (–CH –) of –OC H and –OC H , IR data confirms the molec-
2
18 37
16 33
1
ular structure of compound C , HNMR: 0.88 (t, 6H, –CH of polymethylene -C H and
18
3
12 25
-
–
C H ), 1.79 (p, 10H, CH –CH –CH –CH –CH - of –OC H and –OC H ), 1.28 (m, 8H
4 9 3 2 2 2 2 12 25 4 9
CH –CH –CH - of –OC H ), 1.29–1.31 (q, 8H, –CH –CH of –OC H and –OC H ),
2 2 2 12 25 2 3 12 25 4 9
4
.06 (t, 4H, –OCH –CH –), 7.59 (d, J = 15.2 Hz, 2H, –CH=CH–), 7.43, 7.28 and 7.83 (4H,
2
2
J = 8.0 Hz, para-substituted second phenyl ring), 7.62 and 6.94, 6.45 (4H, J = 8.1 Hz, first
phenyl ring with alkoxy chain), 13C NMR (CDCl ): 165.6, 158.7, 130.2, 129.8, 129.2, 130.6,
3
1
14.6, 114.3, (Ar-C), 14.1 (–CH ), 31.9, 68.2, 29.6, 25.9, 29.6, 29.3, 22.7 (–CH ), 189.2 (-C=O
3
2
group), 145.1, 121.3 (–CH of -olefin). Elemental analysis: calculated for C H O : C, 82.12%;
49
80
3
H, 11.17%; O, 6.70%; found: C, 82.08%; H, 10.98%; O, 6.60%.
Result and discussion
Here in present article, we have synthesized newly liquid crystalline homologous series based
on single chalconyl linking group and hexadecyloxy side chain at tail group with varying left

1
34
V. S. SHARMA AND R. B. PATEL
Figure . Phase diagram of series-.
side alkoxy side chain (-OR) group. In the present investigation, we study the effect of chal-
conyl linkage group and varying flexibility at left side part on mesomorphism in thirteen
newly synthesized compounds. The phase behavior of all new synthesized compounds has
been investigated by POM.
n-Alkoxybenzaldehyde condensation with 4-hexadecyloxy acetophenone to give α-4-n-
ꢀ
alkoxy phenyl-β-4 -n-hexadecyloxy benzoyl ethylenes. Entire novel homologous series except
first three members (C to C ) of a series are liquid crystalline (C to C ). C to C com-
1
3
4
18
5
18
pounds displayed enantiotropic nematic as well as smectic phase, while in C homologue,
4
it exhibited only monotropically nematic phase. C to C homologues do not shows liq-
1
3
uid crystalline property and directly passes into isotropic mass from solid crystal phase
without display LCs property; this is due to presence of short alkyl spacer and short chain
length of molecule. The phase diagram of present homologous series were plotted against the
transition temperature versus the number of carbon atoms present in n-alkyl chain “R” of left
-
OR group. The Cr-N/I, N-I or I-N, and Sm-N transition curves are obtained as shown in
Fig. 1, respectively. N-I/I-N transition curve gradually descended up to C then increased at
12
C homologue due to the effect of abnormality and then continued descends almost linearly
16
prolonged up to C18 homologue with overall descending tendency. The Cr-M/I transition
curve initially falling up to C homologue and then rising at C homologue and then con-
12
14
tinued to decrease up to last homologue C . The Sm-N transition curve descends up to C
18
12
homologue and then passing through maxima at C homologue and then decreasing at C
14
18
homologue. Odd-even effect is absent in phase behavior of present series. The variations of
mesogenic properties from homologue to homologue in the same series are observed with
changing the number of carbon atoms presence in left n-alkyl chain “R” in -OR group and
keeping rest of the molecular part unaltered throughout the series.
The condensation of nonmesomorphs n-alkoxybenzaldehydes with 4-n-hexadecyloxy ace-
tophenone molecule to extends its molecular lengths, polarity and polarizability, rigidity and
flexibility, permanent dipole moment across a long molecular axis, intermolecular and lat-
eral attractions, suitable magnitude of dispersion forces, and dipole-dipole interaction. These
induce resistivity and misalignment of molecules at a 90° or/and less than 90° angle with
a plane of floating surface under the influence of exposed thermal vibrations to maintain

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
135
floating with statistically parallel orientational order and/or with sliding layered molecular
arrangement for different range or ranges of temperatures to facilitate only nematic or smec-
tic plus nematic mesophase formation for C to C18 homologues. However, the missing of
4
any sort of mesophase formation in case of C and C homologues is attributed to their high
1
3
crystallizing tendencies, which arise from low magnitudes of dispersion forces and also low
magnitudes of dipole-dipole interaction. Thus, abrupt breaking of crystal lattices on heating
the sample substance takes place and sharply transform into isotropic liquid without passing
through liquid crystalline state. However, on cooling condition the same, none of the non-
mesomorphic homologues C and C exhibited monotropic mesophase in irreversible man-
1
3
ner but the homologues from C to C on similar cooling from isotropic state exhibit and
4
18
reappear to nematic and smectic phases.
Lowering of molecular rigidity by only two benzene cores bonded through single chal-
conyl bridge group which lowers the numbers of inter-atomic bonds and bond energy, which
leads to reflect the magnitudes of (ꢁH) enthalpy change of a molecule, and consequently
lowers the molecular thermal resistivity toward exposed thermal vibrations. Therefore, the
lowering of transition temperatures, thermal stabilities for smectic and nematic as well as
mesophase lengths are observed. The terminal intermolecular interactions alternate as the
series is ascended. However, if longer n-alkyl chains bend and come into line with the molec-
ular long axis, the contribution of each new carbon-carbon bond in alkyl chain to change
the polarizability of the molecule in the direction of the long axis is the same, irrespective
of whether the carbon number is odd or even. Changing of the terminal substitution by
increasing the chain length as result alternation of terminal intermolecular attraction and the
N-I temperature should therefore again diminish.
From the texture study of mesophase under the optical polarizing microscope, a typical
nematic phase was observed upon heating and cooling condition of compound C . Optical
6
texture was observed for compound C at 74°C given in Fig. 2(a). A needle type texture of
6
SmC phase was observed for compounds C . The texture observed at 54°C mentioned in
8
Fig. 2(b). A droplets type image of nematic mesophase was observed for compound C at
12
4
8°C shown in Fig. 2(c). A typical texture image of SmC phase was observed for compound
C16 at 42°C mentioned in Fig. 2(d). No other mesophase transition, except crystallization,
was realized on further cooling of compound up to room temperature. All the transition tem-
peratures displayed LCs property at lower temperature. The newly synthesized compound is
sandwiched between glass slide and cover slip and the heating and cooling rate is (2°C/min),
respectively.
The molecular length of 4-n-alkoxy benzaldehyde increases by linking with 4-n-
hexadecyloxy acetophenone, which upgrades the molecular rigidity and flexibility to suitable
and favorable magnitudes of intermolecular cohesion and closeness to induce nematic and
smectic mesophase in enantiotropically manner. The mesophase appear enenatiotropically
manner in present synthesized compounds. Compound C shows smectic as well as nematic
18
mesophase on heating and cooling condition, respectively. Figure 3 signifies the presence nee-
dle type of SmC mesophase in C homologue at 36°C or room temperature observed in cool-
18
ing condition
The absence of mesogenic character in C to C homologue is due to the low magni-
1
3
tudes of dispersion forces and dipole-dipole interactions. The changing trend in mesogenic
properties from homologue to homologue due to increasing the flexibility of molecule
causes by altering n-alkyl chain “R” of -OR group and unexpected status of n-alkyl chain or
end groups of a molecule. The reverse deviating effect from normal sequence of appearing
enantiotropy phase is attributed to the unexpected status of n-alkyl chains which affected

136
V. S. SHARMA AND R. B. PATEL
Figure . Optical micrographs of (a) rod-type texture image in nematic phase at °C of compound C , (b)

SmC phase at °C of compound C , (c) nematic droplets observed at °C of compound C , and (d) SmC


phase at °C of compound C .

molecular lengths from homologue to homologue in the same series which alters molecular
polarity and polarizability. Some thermometric properties and degree of mesomorphism of
presently investigated homologous series-1 compared with structurally similar homologous
series-A [40] as mentioned in Fig. 4. In series-1 and series-A, chalconyl central linkage group
is common part and disubstituted phenyl ring is present in both series.
Figure . SmC phase at °C in C homologue.


MOLECULAR CRYSTALS AND LIQUID CRYSTALS
137
Figure . Structurally similar series.
Following Table 3 represents the thermometric properties in comparative manner as given
under. Thermal stability of Sm-N phase in series-1 is more as compare to series-X and com-
mencement of smecticphase in series-1 at C homologue while in series-A, it’s started from
5
C homologue. Thermal stability of N-I phase of series-A is higher than series-1. In series-
7
1
, C to C homologous displayed nematic mesophase enantiotropically while in series-A,
4 18
C to C homologous shows nematic property in which C to C shows nematic mesophase
2
18
2
6
enantiotropically manner while C to C homologous exhibited monotropynematic phase.
7
18
The total mesophase length of (Sm + N) phase of series-1 is slightly higher than series-A, this
is due to the higher chain length and linearity of series-1 as compare to nonlinear series-A.
The exhibition of smectogenic and nematogenic properties from the synthesized chalconyl
series-1 is attributed to the optimum magnitudes of dispersion forces and dipole-dipole inter-
actions controlling the suitable magnitudes of anisotropic forces of intermolecular cohesion
and closeness to induce smectic plus nematic phase in either reversible or irreversible manner.
Table . Thermal stability in °C.
Series
Series- (–OC H ) (-para)
Series-A (–OC H ) (-meta)


 
Sm-N or N-Sm or Sm-I
.°C
.°C
Commencement of smectic phase
N-I or I-N
(C –C ) C
(C –C ) C







.
.
Commencement of nematic phase
Mesophase length (Sm + N) in °C
(C –C ) C
(C –C ) C
  


.–.°C
.–.°C
C–C
C–C

1
38
V. S. SHARMA AND R. B. PATEL
Figure . Geometrical shape of series- and series-A.
The early or late commencement of smectic and nematic phase is depended upon the extent
of noncoplanarity of a molecule.
The early or late commencement of mesophase formation is related with the extent of
molecular noncoplanirity with the plane of a floating surface. The para-substituted –OC H
1
6
33
(
n), meta-substituted –OC H (n) tail ended n-alkoxy groups are almost equally noncopla-
16 33
nar. Therefore, smectic and/or nematicmesophase commences by the difference of one to
three homologue. The observed difference can be attributed to the positional difference
of tailed n-alkoxy-ended groups, which causes difference in molecular polarizability. The
observed difference in thermal stabilities for nematic by one or six units is attributed to linear
or nonlinear geometrical shape, which is related with the positional status and induced degree
of polarizability of n-alkoxy tail-ended group for the same homologue whose magnitudes of
energy stored (ꢁH) in a molecule vary from increasing series. Therefore, the resistivity toward
exposed thermal vibrations and their corresponding intensity required different suitable mag-
nitudes of mesophase at different lengths with left increasing side chain (-OR).
Geometrical shape of sereis-1 and series-X are different with respect to right side flexi-
ble part of molecule. Series-X is nonlinear as compared to series-1, because of substitution
of hexadecyloxy side chain (–OC H ) on -meta position in series-A, while in series-1 the
16
33
substitution of hexadecyloxy chain at para position. The geometrical shape of series-1 and
series-A mentioned in Fig. 5.
Conclusions
Newly synthesized homologous series based on single chalconyl (–CH=CH-CO–) central
bridge as linking group with side chain is smectogenic and nematogenic in nature, whose
thermal stabilities and the mesophase lengths are lower. Chalconyl group is generally nemato-
genic and bioactive which is useful for devices to be operated at low temperature or room

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
139
temperature, as well as its bioactivity importance. Here, in present article, we have success-
fully synthesized the homologous series which shows LC properties as lower temperature as
present demand. The group efficiency order derived on the basis of (i) thermal stabilities, (ii)
commencement of mesophase, and (iii) upper and lower mesophase lengths for smectic and
nematic are as under.
Acknowledgments
Authors acknowledge thanks to Dr. R. R. Shah, principal and management of K. K. Shah Jarodwala
Maninagar Science College, Ahmedabad. Authors also thank to NFDD Centre for the analytical and
spectral services.
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