Synthesis and mesomorphic properties of new chalconyl-ester based liquid crystals: The effect of tail group

Article abstract of DOI:10.1080/15421406.2017.1344465

A new homologous series viz. 4-(3-(3, 4-dioctadecyloxy) phenyl)-3- oxoprop-1-en-1-yl) phenyl-3-(4-n-alkoxy phenyl) cinnamate) based on two linking groups have been synthesized and characterized. The mesomorphic properties of these compounds were observed by optical polarized light microscopy (POM) and confirmed by differential scanning calorimetry (DSC). All synthesized compounds exhibited LC behaviour except compound C1. Thermal stability of smectic and nematic phase of present series are 79.0°C and 120.0°C whose temperature range is vary from 14 to 20°C and 24 to 56°C respectively. The mesomorphic properties of present series were compared with other structurally related mesogenic homologous series to evaluate the effects of tail group on mesomorphism.

Full text of DOI:10.1080/15421406.2017.1344465

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-ester based liquid crystals: The effect of
tail group
Vinay S. Sharma, Rajesh H. Vekariya, Anuj S. Sharma & R. B. Patel
To cite this article: Vinay S. Sharma, Rajesh H. Vekariya, Anuj S. Sharma & R. B.
Patel (2017) Synthesis and mesomorphic properties of new chalconyl-ester based liquid
crystals: The effect of tail group, Molecular Crystals and Liquid Crystals, 652:1, 10-22, DOI:
10.1080/15421406.2017.1344465
To link to this article: http://dx.doi.org/10.1080/15421406.2017.1344465
Published online: 16 Oct 2017.
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Date: 16 October 2017, At: 08:10

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
https://doi.org/./..
Synthesis and mesomorphic properties of new chalconyl-ester
based liquid crystals: The effect of tail group
Vinay S. Sharmaa, Rajesh H. Vekariyab, Anuj S. Sharmab, and R. B. Patela
aChemistry Department, K.K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India; bDepartment of Chemistry, School of Science, Gujarat University, Ahmedabad, Gujarat, India
ABSTRACT
KEYWORDS
Liquid crystal; nematogenic;
smectogenic; thermotropic
A new homologous series viz. 4-(3-(3, 4-dioctadecyloxy) phenyl)-3-
oxoprop-1-en-1-yl) phenyl-3-(4-n-alkoxy phenyl) cinnamate) based on
two linking groups have been synthesized and characterized. The
mesomorphic properties of these compounds were observed by opti-
cal polarized light microscopy (POM) and confirmed by differential
scanning calorimetry (DSC). All synthesized compounds exhibited LC
behaviour except compound C1. Thermal stability of smectic and
nematic phase of present series are 79.0°C and 120.0°C whose tempera-
ture range is vary from 14 to 20°C and 24 to 56°C respectively. The meso-
morphic properties of present series were compared with other struc-
turally related mesogenic homologous series to evaluate the effects of
tail group on mesomorphism.
GRAPHICAL ABSTRACT
1. Introduction
Study of liquid crystalline state (LC) is a multidisciplinary subject useful to the mankind and
industrial applications through scientist, technologists and technocrats [1–4] due to its unique
property to flow as liquid and optical properties as crystals. Study on LC state is planned with
a view to understand and establish the effect of molecular structure on LC properties as a
consequence of molecular rigidity and flexibility [5–10].
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

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
11
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 [11–13]. Presently, we have focus on thermotropic liquid crystals
in which, phase transition into liquid crystal phase as temperature changed [14–18]. Liquid
crystals in the nematic group are most commonly used in production of liquid crystal displays
(LCD) due to their unique physical properties and wide temperature range [19–20]. 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 [21–27].
A number of chalcone having reported to exhibit a broad spectrum of anti-bacterial,
antifungal, antiulcer, antimalarial, antitumor, anticancer, anti-inflammatory and antituber-
cular activity [28–30]. It is believe that the presence of α, β-unsaturated functional group in
–
=
–
–
chalcone ( CH CH CO ) is responsible for anti-microbial activity, which can be altered
depending upon the type of substituent present on the aromatic rings [31–32]. To the best of
our knowledge, liquid crystalline materials based on chalconyl central linking group are rarely
–
–
=
–
reported in literature. It has been observed that CO CH CH linkage is less conducive
to mesomorphism as compared to CH N , COO , N N , CH CH COO linkages
group because of the presence of non-linearity and angle strain arising from the presence of
–
= – –
– – = – –
=
–
–
– =
–
–
=
–
keto ( C O) group [33]. Surprisingly, when CO CH CH linkage is linked with another
linking group it becomes conductive to exhibits mesophase. In the literature studies, there are
several reports of mesogenic compounds having chalcone linkage.
Previously, Yellamaggad et al. reported the bent-core unsymmetrical dimers in which
cholesteryl ester and chalconyl moiety are present, which enhances the biaxiality and chi-
rality of the system [34]. R.Gopalakrishnan et al. reported chalcone based single crystals,
growth, and comparison of two new enone shifted chalcones and their NLO behaviour [35].
Tandel et al. studied the chain chalconyl polymers compounds to exhibiting threaded type
nematic phases [36]. Vinyl esters linkage group have been well known for last decades of
years, Vora et al. reported binary mixtures of cinnamate esters exhibit a wide range of smec-
tic and nematic mesophase [37]. Doshi et al. reported various homologous series based on
chalconyl and vinyl ester linkage group and studied the effect on mesomorphism [38–40].
Sadashiva et al. reported the synthesis and mesomorphic properties of some ester of trans-4-
n-alkoxy cinnamic acid and trans-4-n-alkoxy-α-methyl cinnamic acid with branched chain
alkyl tails exhibiting ferroelectric and anti-ferroelectric phases [41]. Prajapati et al. studied
some homologous series consisted cinnamate linkage group and show its effect on mesomor-
phic properties of liquid crystalline compounds [42–43]. Recently, Bhoya et al. reported a
calamatic rod type homologous series containing vinyl ester and azomethine linkage groups
[44–45]. Shah et al. studied a nonlinear homologous series based on ester and chalcone link-
age group [46]. Patel et al. reported rod type homologous series having chalconyl ester cen-
tral linkage group and hexyloxy tail group [47]. Gallardo and his coworkers reported a poly-
catenar liquid crystals series based on bent shaped chalcone and cyanopyridine molecules
[48]. Yahya et al. reported a series of azo-ester mesogens containing liquid crystalline acry-
–
late having different terminal groups. They reported –OCH3, OC2H5 and –OCH3 substi-
– –
–
tuted compounds exhibited greater mesophase stability as compare to halogen ( F, Cl, Br)
[49].
Recently, our research team reported different chalconyl ester based linear and nonlinear
homologues series and observed the effect of increasing alkyl spacer at terminal group on
mesomorphism [50–52]. Present work is planned to investigate a new chalconyl-ester based
homologous series and study the effect of disubstituted octyloxy (-OC18H37) tail group on LC
behaviour.

12
V. S. SHARMA ET AL.
2. Experimental
2.1. Materials
For present synthesized homologous series required materials: 4-hydroxy benzaldehyde,
alkyl bromide (R-Br) were purchased from Lancaster (England) and SRL (Mumbai), 3,4-
dihydroxy acetophenone was purchased from (Sigma Aldrich), Malonic acid was purchased
from (Sigma Aldrich), Anhydrous K2CO3 (Finar Chemicals, India), N,N-dimethyl amino
pyridine (DMAP) and Dicyclohexylcarbodiimide (DCC) were purchased from Fluka Chemie
(Switzerland). The solvents were dried and purified by standard method prior to use.
2.2. Measurements
Melting points were taken on Opti-Melt (Automated melting point system). The FT-IR spec-
tra were recorded as KBr pellet on Shimadzu in the range of 3800–600 cm−1. Microanalysis
was performed on Perkin-Elmer PE 2400 CHN analyser. The texture images were studied on
a trinocular optical polarising microscope (POM) equipped with a heating plate and digital
1
1
camera. H NMR spectra was recorded on a 500 MHz NMR Bruker Advance- 400 in the
range of 0.5 ppm-16 ppm using CDCl3 solvent. The phase transition temperatures were mea-
sured using Shimadzu DSC-50 at heating and cooling rates of 10°C min−1. Texture image of
nematic phase were determined by miscibility method, thermodynamic quantities enthalpy
(ꢀH) and entropy (ꢀS = ꢀH/T) are qualitatively discussed. For the POM study, novel syn-
thesized compound is sandwiched between glass slide and cover slip and heating and cooling
rate is (2°C /min) respectively.
2.3. Synthesis
Trans 4-n-alkoxy cinnamic acids (B) prepared by reported method [53]. 3,4-dioctadecyloxy
acetophenone (C) was prepared by usual established method [54]. Chalcone was prepared by
reported method [55]. Esters (D) were synthesized by a method reported in literature [56].
Thus, the chalconyl-ester homologue derivatives were filtered, washed with sodium bicar-
bonate solution, dried and purified till constant transition temperatures is obtain, using an
optical polarizing microscope equipped with a heating stage. The synthetic route to a series
is mentioned in scheme-1.
... Synthesis of -n-alkoxy benzaldehyde (a)
4-n-Alkoxybenzaldehydes were synthesized by refluxing 4-hydroxybenzaldehyde (1 equiv.)
with corresponding n-alkyl bromides (1 equiv.) in the presence of K2CO3 (1 equiv.) and dry
acetone as a solvent [54].
... Synthesis of trans -n-alkoxy cinnamic acid (b)
The resulting 4-n-alkoxybenzaldehydes (1a) were reacted with Malonic acid (1.2 equiv.) in
the presence of 1–2 drops piperidine as catalyst and pyridine (20 mL) as solvent, refluxing the
reaction mixture 3 to 4 hours to yield corresponding trans 4-n-alkoxy cinnamic acids (1b),
which was confirmed by IR study [53].
... Synthesis of , -dioctyloxy acetophenone (c)
3,4-dioctyloxy acetophenone was synthesized by refluxing 3,4 dihydroxy acetophenone
(1 equiv.) with corresponding n-octadecyloxy bromides (C18H37Br) (2 equiv.) in the presence
of Anhy.K2CO3 (1.2 equiv.) in dry acetone as a solvent [54].

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
13
... Synthesis of chalcone (d)
Chalcone (1d) was prepared by usual established method reported in literature [55]. (light
– –
yellow, Yield: 62%), IR (KBr): vmax/cm−1 3440 ( OH str. bonded), 3079–3020 ( C H str.
–
–
– =
– = –
– –
–
aliphatic alkyl group), 1667 ( C O, group), 1580–1610 ( C C ) aromatic, 1280 ( O CH2
1
–
=
–
–
ether linkage), 962 (trans, ( CH CH ) alkene). HNMR: 0.88–0.90 (q, 6H, CH3 of poly-
–
methylene disubstituted –OC18H37), 1.26–1.43 (m, 58H, disubstituted OC18H37), 4.08 (t,
4H, OCH2 CH2 of di substituted –OC18H37), 5.28 (s, 1H, OH group), 7.12 (d, 1H,
CH CH CO ), 7.56 (d, 1H, CH CH CO ), 6.63–7.52 (4H, first phenyl ring), 7.67–7.16
(2H, second phenyl ring), 7.30 (s, 1H, second phenyl ring). Elemental analysis: calculated for
–
=
–
–
–
–
–
–
–
=
–
–
C51H84O4: C, 80.52; H, 11.05; O, 8.42%; found: C, 80.48; H, 10.98; O, 8.37%.
... Synthesis of ester derivatives (C)
The compound has been prepared by esterification of the appropriate 4-n-alkoxy cinnamic
acid (1b) (2.02 mmol) and chalcone (1d) (0.246 g, 2.02 mmol), dicyclohexylcarbodiimide
(DCC) (0.457 g, 2.22 mmol) and dimethylaminopyridine (DMAP) in catalytic amount
(0.002 g, 0.2 mmol) in dry CH2Cl2 (DCM) (30 mL) was stirred at room temperature for
24 h. The slightly observed white precipitate of DCU is obtained which was isolated by fil-
tration and removed, while the filtrate was evaporated to dryness. The resultant crude residue
was purified by column chromatography on silica gel eluting with Ethyl acetate: Hexane (3:2)
[56].
Comp.C4: IR (KBr): vmax/cm−1 3051 (C H str. of alkane), 612 polymethylene–(CH2)
–
–
=
n
=
group of –OC4H9, 1640 (C O str. of carbonyl carbon of chalconyl group), 1608 (C C
str. of alkene in chalcone), 1730 (ester, COO group), 1510, 1540 ( C C str. of aromatic
ring), 1171 (C O str. of ether linkage), 1244 (C O str. of carbonyl (>CO) group, 971 (trans,
CH CH ) group, 770 polymethylene ( CH2 ) of side alkyl chain. HNMR: 0.88–0.90 (t,
–
–
–
–
– =
–
1
–
=
–
–
–
9H, CH3 of disubstituted –OC18H37 and monosubstituted –OC4H9), 1.26–1.43 (m, 58H, dis-
ubstituted –OC18H37), 1.76 (m, 6H, disubstituted –OC18H37 and monosubstituted –OC4H9),
4.06 (t, 6H, disubstituted –OC18H37 and monosubstituted –OC4H9), 7.62 & 6.30 (d, 2H,
–
=
–
–
–
=
–
–
–
=
–
–
CH CH COO ), 8.01 (d, 1H, CH CH CO ), 7.42 (d, 1H, CH CH CO ), 6.81 & 6.62
(4H, first phenyl ring), 7.21 & 7.70 (4H, second phenyl ring), 7.67 & 7.12 (3H, third phenyl
ring), 7.32 (s, 1H, third phenyl ring). Elemental analysis: calculated for C64H98O6: C, 79.83;
H, 5.94; O, 7.48%; found: C, 79.73; H, 5.92; O, 7.39%.
Comp.C6: IR (KBr): vmax/cm−1 2951 (C H str. of alkane), 632 polymethylene group –
–
–
=
=
(CH2 )n of –OC6H13, 1640 (C O str. of carbonyl carbon of chalconyl group), 1604 (C C
str. of alkene in chalcone), 1740 (ester, COO group), 1510 (C C str. of aromatic ring), 991
(C H bending of alkene), 1172 (C O str. of ether linkage), 1284 (C O str. of carbonyl (>CO)
group, 971 (trans, CH CH ) group, 770 polymethylene ( CH2 ) of –OC12H25. HNMR:
0.88–0.90 (t, 9H, CH3 of disubstituted –OC18H37 and monosubstituted –OC6H13), 1.26–1.43
(m, 60H, disubstituted OC18H37), 1.76 (m, 6H, disubstituted –OC18H37 and monosubsti-
–
–
=
–
–
–
–
1
–
=
–
–
–
–
tuted –OC6H13), 4.06 (t, 6H, disubstituted –OC18H37 and monosubstituted –OC6H13), 7.61 &
–
=
–
–
–
=
–
–
–
=
–
–
6.30 (d, 2H, CH CH COO ), 8.01 (d, 1H, CH CH CO ), 7.42 (d, 1H, CH CH CO ),
6.80 & 6.62 (4H, first phenyl ring), 7.21 & 7.69 (4H, second phenyl ring), 7.64 & 7.12 (3H, third
phenyl ring), 7.32 (s, 1H, third phenyl ring). Elemental analysis: calculated for C66H102O6: C,
80.0; H, 10.30; O, 9.69%; found: C, 79.95; H, 10.21; O, 9.64%.
Comp.C10: IR (KBr): vmax/cm−1 2954 (C H str. of alkane), 643 polymethylene group –
(CH2 )n of –OC10H21 alkyl chain, 1640 (C O str. of carbonyl carbon of chalconyl group),
1604 (C C str. of alkene in chalcone), 1730 ( COO group), 1510, 1543 (C C str. of aro-
matic ring), 996 (C H bending of alkene), 1178 (C O str. of ether linkage), 1288, 1246 (C O
–
=
–
=
–
–
=
–
–
–
–
=
–
–
–
str. of carbonyl (>CO) group, 972 (trans, CH CH ) group, 770 polymethylene ( CH2 ) of

14
V. S. SHARMA ET AL.
1
–
–OC18H37. HNMR: 0.88–0.90 (t, 9H, CH3 of disubstituted –OC18H37 and monosubstituted
–OC10H21), 1.26–1.43 (m, 68H, disubstituted –OC18H37 and monosubstituted –OC10H21),
1.76 (m, 6H, disubstituted –OC18H37 and monosubstituted –OC10H21), 4.06 (t, 6H, disubsti-
–
=
–
–
tuted –OC18H37 and monosubstituted –OC10H21), 7.61 & 6.30 (d, 2H, CH CH COO ),
–
=
–
–
–
=
–
–
8.04 (d, 1H, CH CH CO ), 7.42 (d, 1H, CH CH CO ), 6.81 & 6.62 (4H, first phenyl
ring), 7.20 & 7.70 (4H, second phenyl ring), 7.67 & 7.12 (3H, third phenyl ring), 7.32 (s, 1H,
third phenyl ring). Elemental analysis: calculated for C70H110O6: C, 80.30; H, 10.51; O, 9.17%;
found: C, 80.24; H, 10.48; O, 9.07%.
Comp.C18: IR (KBr): vmax/cm−1 2954 (C H str. of alkane), 770 polymethylene –(CH2 )n
–
–
=
group of –OC18H37 alkyl chain, 1610 (C O str. of carbonyl carbon of chalconyl group),
=
–
–
=
1604 (C C str. of alkene in chalcone), 1760 ( COO group), 1510, 1543 (C C str. of aro-
–
–
–
matic ring), 996 (C H bending of alkene), 1171 (C O str. of ether linkage), 1246 (C O
1
–
=
–
str. of carbonyl (>CO) group, 972 (trans, CH CH ) group. HNMR: 0.88–0.90 (t, 9H,
–
CH3 of disubstituted –OC18H37 and monosubstituted –OC4H9), 1.26–1.43 (m, 78H, disub-
stituted –OC18H37), 1.76 (m, 6H, disubstituted –OC18H37 and monosubstituted –OC18H37),
4.06 (t, 6H, disubstituted –OC18H37 and monosubstituted –OC18H37), 7.62 & 6.30 (d, 2H,
–
=
–
–
–
=
–
–
–
=
–
–
CH CH COO ), 8.01 (d, 1H, CH CH CO ), 7.41 (d, 1H, CH CH CO ), 6.81 & 6.62
(4H, first phenyl ring), 7.21 & 7.70 (4H, second phenyl ring), 7.67 & 7.12 (3H, third phenyl
ring), 7.32 (s, 1H, third phenyl ring). Elemental analysis: calculated for C78H126O6: C, 80.82;
H, 10.88; O, 8.29%; found: C, 80.79; H, 10.82; O, 8.25%.
2.4 Reaction scheme
Scheme . Synthetic route for derivatives of series-.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
15
Scheme . Synthetic route of series-.
3. Result and discussion
Here in, we have synthesized newly chalconyl-ester based homologous series contain di sub-
–
stituted octadecyloxy ( OC18H37) side chain at tail group while left terminal part is varying.
In the present investigation, we study the effect of linkage group and varying flexibility on
mesomorphic behaviour of liquid crystalline compounds. The phase behaviour of all new
synthesised compounds has been investigated by polarising optical microscope (POM) and
confirm by using differential scanning calorimetry (DSC) analysis.
3.1. DSC analysis
DSC is a valuable method for the detection of phase transitions. The thermal behaviour
of newly synthesized compounds was confirmed by using DSC measurement shown in
Figure 1. The transition temperatures associated with enthalpy changes and entropy are
mention below in Table 1. In present study, DSC thermogram is traces in heating condition.
It can be seen that, two endothermic peaks are observed in present series at heating condition.
Figure . DSC thermogram of (a) comp.C; (b) comp.C; (c) comp.C; (d) comp.C on heating condition.

16
V. S. SHARMA ET AL.
Table . Phase transition temperature (ºC) and enthalpy (J g−) and entropy change (J g−k−) by DSC
measurement.
Heating
Peak temperature (ºC)
ꢀH
ꢀS
Comp.
C
Transition
(−Jg−
)
(J g−k−
)
Cr-SmC
SmC-N
N-I
Cr-SmC
SmC-N
N-I
Cr-SmC
SmC-N
N-I
Cr-SmC
SmC-N
N-I
.
.
>
.
.
>
.
.
>
.
.
>
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
.
.
—
C
C
C
Compound C4 shows first endothermic peak at 62.23°C, which indicates the presence of
Cr-SmC mesophase and second endothermic peak observed at 76.83°C, which indicates
the presence of SmC-N mesophase. By applying further heating, it is isotropic at >130°C.
Compound C8 shows two endothermic peaks at 52.8°C and 72.23°C on heating condition,
which is nearly to the transition temperature observed by POM study. Compound C10 shows
two endothermic peaks at 58.32°C and 77.32°C on heating condition to confirm the presence
of SmC and N phase which was further confirmed by POM analysis. For compound C12,
the first endothermic peak trace at 54.73°C which shows the presence of SmC phase and on
continue heating second endothermic peak trace at 74.45°C which specifies the presence of
nematic mesophase in heating condition and transferred into isotropic at >112°C, which
was further study by POM study. Transition temperature obtained by DSC analysis at heating
condition and the value of enthalpy and entropy is shown in Table 1.
We measured the phase sequence of C4 homologue which was confirmed by DSC analy-
sis with presence of two endothermic peaks further confirmed by POM study. The observed
textural image is the type of SmC and nematic phase which is mention in below Figure 2.
3.2. POM investigation
Transition temperatures (Table 2) obtained by optical polarising microscope (POM) equipped
with a heating stage. The phase diagram plotted against transition temperatures versus the
Figure . Phase sequence of comp. C on heating condition.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
17
Table . Transition Temperature in °C by POM.
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
·
·
·
·
·
·
·
·
·
·
·
·
·
—
.
.
.
.
.
.
.
.
.
—
—
—
.
.
.
·
·
·
·
·
·
·
·
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
·
.
.
.
.
.
.
.
.
.
·
·
·
·
·
·
·
·
·
·
·
·
.
·
·
·
·
·
·
·
·
·
.
.
.
—
—
number of carbon atoms present in n-alkyl chain ‘R’ of left alkyl chain (-OR) group shown in
Figure 3. Transition curve of Cr-I starts decreasing from lower homologue (C1) to higher
homologue (C18). In present series, smectic and nematic mesophase commences from C2
homologue. Sm-N transition curve shows decreasing tendency from C2 homologue to C12
homologue respectively. Mesomorphic properties of present homologues series were var-
ied by increasing left alkyl chain and keeping left unchanged terminal and lateral octyloxy
–
( OC18H37) group. The geometrical shape of molecule keeping unchanged throughout the
series except changing of methylene carbon units in left side of alkoxy group (-OR). N-I tran-
sition curve starts decreasing from C2 homologue and continued decreasing upto last C18
homologue. It can be noted that, transition temperature decrease when number of methylene
–
–
( CH2 )n unit increase in alkoxy side chain. The higher homologues (C14 to C18) displays
nematic phase without exhibition of any smectic phase, this is due to the presence of more
flexibility and linearity from both the end side alkoxy groups.
The molecular rigidity due to three phenyl rings and two central linking bridges are con-
stant throughout the series, but the changing molecular length from homologue to homologue
Figure . Phase diagram of series-.

18
V. S. SHARMA ET AL.
Table . Texture of Nematic Phase of C, C, C, C by miscibility method.
Sr. No.
Homologue
Texture

C
C
C
Threaded
Rod like
Threaded
Threaded



C, C
–
–
in the same series due to changing number of ( CH2 )n units in alkoxy side chain induces dif-
ferent magnitudes of flexibility contribution to total flexibility including flexibility of common
disubstituted octadecyloxy group present at the tail end. Thus, effective molecular flexibility
occurred due to difference of polarities between two end groups plays the role for nematic
mesophase formation. On the basis of these observations, we can say that moderate alkoxy
side chain on tails groups may be anticipated as most appropriate to gain good mesophase
stability.
In present article, we have synthesized total thirteen compounds, out of thirteen com-
pounds, compound C1 shows nonliquid crystal (NLC) behaviour and directly transform solid
to isotropic liquid without exhibiting LC property, this is due to the presence of short alkyl
–
spacer methoxy ( OCH3) group at left side part and low magnitudes of dispersion forces and
lower magnitudes of dipole-dipole interaction and electronic vibrations cause high crystalline
tendency to directly transform into isotropic mass by breaking of crystal lattices.
... Nematic mesophase by miscibility method
The nematic mesophase were also confirmed by using miscibility method which was mention
in below Table 3. Comp.C10 shows threaded type nematic phase whereas in comp.C12, rod
type textural pattern was seen. Comp. C14 homologue shows threaded type textural pattern of
nematic phase. Comp.C16 to C18 shows threaded type textural pattern of nematic mesophase.
... Textural study
The crystalline compounds placed on clear glass slide sheltered by coverslip were heated to the
isotropic state and heating and cooling rate (2°C/min) respectively and observing mesophase
texture image shown in Figure 4. POM observations reveal that comp.C4 exhibited typical
textural pattern of nematic phase at 81°C on heating condition. Comp. C10 display broken fan
type textural pattern of SmC phase at 52°C on heating condition. Compound C7 shows marble
type textural pattern of SmC phase at 54°C on cooling condition. Compound C12 display grass
like textural pattern of SmC phase at 51°C on heating condition. In cooling cycle, POM reveals
the same textural pattern observed in between isotropic to solid crystal. From POM analysis,
it is clear that the two peaks observed in DSC heating scan are due to crystal transformation
into smectic phase and second peak correspondence to smectic to nematic phase.
We have measure the phase sequence of C4 homologue on cooling condition as shown
in Figure 5. (a) Isotropic mass at 136°C, (b) nematic mesophase start at 82°C, (c) nematic
mesophase at 81°C, (d) cooling nematic mesophase upto 71°C, (e) nematic phase transform
into SmC phase at 63°C, (f) solid crystals are appeared at room temperature. Observed phase
sequence is repeated again during cooled condition and also confirmed by DSC analysis.
The absence of lamellar packing of molecules in their crystal lattice causes absence of smec-
togenic property in C14 to C18 homologues. The exhibition of nematic property (C2 to C18)
by appropriate magnitudes of anisotropic forces end to end attractive cohesion and closeness
of molecules in stastically parallel in floating conditions that directly associated to its rigidity
as well as flexibility exposed thermal vibrations.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
19
Figure . Mesomorphic textures of compounds obtained by POM (a) Nematic phase of C homologue on
heating. (b) SmC phase of C homologue on heating, (c) Sm C phase of C homologue on cooling, (d) Sm C
phase of C homologue on heating.
... Comparative study and thermal stability
Here, we have compared the mesomorphic property of presently investigated series-1 with
structurally similar series-A and series-B which was reported by our research group [59]
shown in Figure 6.
Homologous series-1 and series-X, -Y are identical with respect to three phenyl rings
and two central linkage group which joining the three phenyl rings. But, they differ with
respect to each other at substitution on third phenyl ring. Therefore they differ with respect
to combined effects of molecular rigidity and flexibility including intermolecular dis-
tance and molecular polarizability which operates LC behaviours of series. In series-1, one
Figure . Phase sequence of C homologue on cooling condition by POM.

20
V. S. SHARMA ET AL.
Figure . Structurally similar analogous series.
–
octadecyloxy ( OC18H37) side chain presence at lateral side as compare to series-A and series-
B, which create more flexibility and vibration. Series-A and Series-B displayed nematogenic
property without exhibition of smectogenic character. However, series-1 exhibited smecto-
genic as well as nematogenic property. In series-1, two octyloxy side chain are present at the
–
tail group while in series-A and series-B, monosubstituted octadecyloxy ( OC18H37) and
hexadecyloxy ( OC16H33) group are present on third phenyl ring.
–
Thus, variations in mesomorphic (LC) properties are ascribed to the magnitudes of dif-
fering features of (shapes and terminal end groups) each series for the same homologue and
from lower homologue to higher homologue in the same series. Table 4 shows that smectic
and nematic mesophase length as well as thermal stabilities of series-1, series-A and series-B.
Thermal stability of smectic phase is 79.0°C for series-1. Thermal stability of nematic phase
of series-A is lower as compare to series-1 and series-B, while nematic mesophase commences
early in series-1 as compare to series-A and series-B. Total degree of mesomorphism of series-
1 is higher than series-A and series-B. The early or late commencement of mesophase depends
upon the extent of molecular noncoplanarity caused by central linkage group and their mag-
nitudes of polarity as well as polarizability.
The space-filling diagram indicate the energy minimize in series-1, series-A and series-B
respectively (Figure 7). The geometrical shape of series-1 is nonlinear as compare to series-
–
A and series-B, while the presence of more octyloxy side chain ( OC18H37) on third phenyl
ring increases its polarity and flexibility. Therefore, it proves that they differ with respect to
combined effects of molecular rigidity and flexibility, including intermolecular distance and
molecular polarizability which operates LC behaviours of series. The addition of double bond
–
=
–
( CH CH ) in the system increases the polarizability and molecular length of the molecule
[60].
Table . Average thermal stability in °C.
Series
Series-
Series-A
—
Series-B
—
Sm-N
.
(C-C)
C
.
(C- C)
Commencement of Smectic phase
N-I
.
(C- C)
C
. to .
C C
.
(C- C)
C
. to .
C C
Commencement of Nematic phase
C
Degree of mesomorphism in °C from minimum to maximum
. to .
C
 C

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
21
Figure . Space filling diagram of series- compared with series-X, -Y.
Conclusions
In summary, we have synthesised successfully a novel chalconyl vinyl ester based homologues
series. We have found that the following synthesized homologous series shows smectic as well
as nematic property. We have confirmed the mesogenic property for compounds by DSC and
POM. For more progressive applications of LC phases, it is necessary to recognize more deeply
the structure property relation as well as molecular origin of mesophases behaviour.
Acknowledgement
Authors acknowledge thanks to Dr. R.R. Shah, principal and management of K. K. Shah Jarodwala Man-
inagar Science College, Ahmedabad. Authors are also thankful to NFDD Centre for providing analytical
and spectral services.
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