Synthesis and properties of new calamitic-shaped liquid crystal compounds with disubstituted octadecyloxy (?OC18H37) tail groups

Article abstract of DOI:10.1080/15421406.2017.1412581

In present study, we have synthesized such newly chalcone-ester linking group based homologous series containing disubstituted octadecyloxy tail part. A series of new chalcones with having three aromatic rings is synthesized and characterised by elemental analyses and spectroscopic techniques such as Fourier transform infrared [FT-IR] and proton magnetic resonance magnetic resonance [¹H NMR] spectroscopy. The mesomorphic properties of these compounds were observed by optical polarized light microscopy (POM) and confirmed by differential scanning calorimetry (DSC). It is found that all the prepared materials display enantiotropic LCs phases except first three homologue in present series. Comp. C₁ to C₁₂ exhibits only enantiotropic nematic phase. However, in higher member comp.C₁₄ to C₁₈ shows enantiotropic SmC and nematic phase. Thermal stability of smectic and nematic phase of present series is found to be 51.33°C and 109.0°C.

Full text of DOI:10.1080/15421406.2017.1412581

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis and properties of new calamitic-shaped
liquid crystal compounds with disubstituted
octadecyloxy (‒OC18H37) tail groups
Vinay S. Sharma, Anuj S. Sharma & R. B. Patel
To cite this article: Vinay S. Sharma, Anuj S. Sharma & R. B. Patel (2017) Synthesis
and properties of new calamitic-shaped liquid crystal compounds with disubstituted
octadecyloxy (‒OC18H37) tail groups, Molecular Crystals and Liquid Crystals, 658:1, 45-58, DOI:
10.1080/15421406.2017.1412581
To link to this article: https://doi.org/10.1080/15421406.2017.1412581
Published online: 08 Mar 2018.
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
https://doi.org/./..
Synthesis and properties of new calamitic-shaped liquid crystal
–
compounds with disubstituted octadecyloxy ( OCH) tail
groups
Vinay S. Sharmaa, 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
Chalcone; enantiotropic;
liquid crystal; nematic
In present study, we have synthesized such newly chalcone-ester link-
ing group based homologous series containing disubstituted octadecy-
loxy tail part. A series of new chalcones with having three aromatic rings
is synthesized and characterised by elemental analyses and spectro-
scopic techniques such as Fourier transform infrared [FT-IR] and proton
magnetic resonance magnetic resonance [1H NMR] spectroscopy. The
mesomorphic properties of these compounds were observed by opti-
cal polarized light microscopy (POM) and confirmed by differential scan-
ning calorimetry (DSC). It is found that all the prepared materials display
enantiotropic LCs phases except first three homologue in present series.
Comp. C1 to C12 exhibits only enantiotropic nematic phase. However, in
higher member comp.C14 to C18 shows enantiotropic SmC and nematic
phase. Thermal stability of smectic and nematic phase of present series
is found to be 51.33°C and 109.0°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

46
V. S. SHARMA ET AL.
1. Introduction
Mesogens or liquid crystal (LC) materials have wide technical applications in the device and
display industry. In addition, these materials are frequently applied in various fields such as
organic light-emitting diodes, biosensors, field-effect transistors, anisotropic networks and
different biological applications [1–2]. 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 [3–5].
Chalcone is a naturally occurring molecule in which two aromatic rings are connected by α,
β-unsaturated ketone linkage with having odd number of carbon atoms [6]. A number of chal-
cone having reported to exhibit a broad spectrum of anti-bacterial, antifungal, antiulcer, anti-
malarial, antitumor, anticancer, anti-inflammatory and antitubercular activity [7–10]. 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 con-
ducive to induce mesophase as compared to imine, ester, azo, vinyl ester linkages group mainly
– =
due to the presence of non-linearity and angle strain arising from the presence of keto ( C O)
group [11]. Furthermore, chalcones are used to establish for fluorescence, polymerization
process and also for dielectric properties [12–13]. Recently, it has been noted that, among
many organic compounds reported for their second harmonic generation, chalcone deriva-
tives are well known for their excellent blue light transmittance as well as good crystallisability
[14–15].
In the literature studies, there are several reports of mesogenic compounds having chal-
cone linkage. Vora and co-worker have reported a homologous series of polymers containing
a chalcone linkage [16]. Soon afterword Chudghar and his co-workers reported a homolo-
gous series containing on ester-chalcone linkages [17]. Doshi et al. have reported chalconyl
ester and chalconyl vinyl ester linkage group inbuilt between three phenyl rings and stud-
ied the effect on mesomorphism by substituted groups at terminal and lateral side [18–20].
Previously, Yellamaggad and co-worker have reported the bent-core unsymmetrical dimers
in which cholesteryl ester and chalconyl moiety are present, which enhances the biaxial-
ity and chirality of the system [21]. R.Gopalakrishnan et al. reported chalcone based sin-
gle crystals, growth, and comparison of two new enone shifted chalcones and their NLO
behaviour [22]. Tandel et al. studied the chain chalconyl polymers compounds to exhibit-
ing threaded type nematic phases [23]. Shah et al. studied a nonlinear homologous series
based on ester and chalcone linkage group [24]. Patel et al. reported rod type homolo-
gous series having chalconyl ester central linkage group and hexyloxy tail group [25]. Gal-
lardo and his coworkers reported a polycatenar liquid crystals series based on bent shaped
chalcone and cyanopyridine molecules [26]. Furthermore, S.Kumar et al. reported chal-
cone based LCs compounds possessing short alkyl chain at one end and other end with
variable chain lengths. These derivatives were reported to exhibit SmC, SmA and nematic
phase [27].
Recently, we have reported homologous series based on three phenyl rings bonded through
–
– –
=
–
–
–
–
=
–
COO , CH CH COO and CO CH CH linking groups as well as varying left n-
alkoxy terminal end group and a fixed tail part at right side ended group and various halogen
group [28–35]. In present investigation, we wish to report the effects of disubstituted octade-
–
cyloxy ( OC18H37) tail group with varying left side chain on mesomorphic behaviours in
present synthesized compounds.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
47
2. Experimental
2.1. Materials
For present synthesized homologous series required materials: 4-hydroxy benzoic acid, n-
alkyl bromide (R-Br) were purchased from Lancaster (England) and SRL (Mumbai), 3,4-
dihydroxy acetophenone, 4-hydroxy benzaldehyde were 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 sol-
vents 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
3,4-dioctadecyloxy acetophenone (A) was prepared by usual established method [36]. Chal-
cone (B) was prepared by reported method [37]. 4-n-alkoxy benzoic acid (C) was pre-
pared by reported method [38]. Esters (D) were synthesized by a method reported in lit-
erature [39]. Thus, the final chalconyl-ester homologue derivatives were filtered, washed with
dilute sodium bicarbonate solution, dried and purified till constant transition temperatures is
obtained by using an polarizing optical microscope (POM) equipped with a heating stage and
differential scanning calorimetry (DSC). The synthetic route of presently synthesized newly
series is mentioned in scheme 1.
... Synthesis of , -dioctyloxy acetophenone (A)
3,4-dioctadecyloxy acetophenone was synthesized by refluxing 3,4-dihydroxy acetophenone
(1 equiv.) with corresponding n-octadecyl bromides (C18H37Br) (2 equiv.) in the presence of
Anhy.K2CO3 (1.2 equiv.) in dry acetone as a solvent [36].
... Synthesis of chalcone (B)
(E)-1-(3, 4-bis (octadecyloxy) phenyl) -3-(4-hydroxy phenyl) prop-2-en-1-one (Chalcone)
was prepared by usual established method reported in literature [37]. (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- ether linkage),

48
V. S. SHARMA ET AL.
1
–
=
–
–
962 (trans, ( CH CH ) alkene). HNMR: 0.88–0.90 (q, 6H, CH3 of polymethylene disub-
–
–
–
–
stituted 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 -n-alkoxy benzoic acid derivatives (C)
4-n-alkoxy benzoic acid were synthesized by refluxing the mixture of 4-hydroxy benzoic acid
(1 equiv.) with corresponding n-alkyl bromides (1 equiv.) in the presence of KOH (1.5 equiv.)
and MeOH/ EtOH as a solvent [38].
... Synthesis of ester derivatives (C)
The compound has been prepared by esterification of the appropriate 4-n-alkoxy benzoic acid
(C) (2.02 mmol) and chalcone (B) (0.246 g, 2.02 mmol), dicyclohexyl carbodiimide (DCC)
(0.457 g, 2.22 mmol) and dimethyl amino pyridine (DMAP) in catalytic amount (0.002 g, 0.2
mmol) in dry CH2Cl2 (DCM) (30 mL) was stirred at room temperature for 12 h. The slightly
observed off white yellow precipitate of dicyclohexyl urea is obtained which was isolated by
filtration and removed, while the filtrate was evaporated by using rota evaporator. The resul-
tant crude residue was purified by column chromatography on silica gel eluting with Ethyl
acetate: Hexane (3:2) [39].
Comp.C1: IR (KBr): vmax/cm−1 3030 (C H str. of alkane), 1620 (C O str. of carbonyl car-
–
=
=
–
–
bon of chalconyl group), 1610 (C C str. of alkene in chalcone), 1750 ( COO group), 1510,
– =
–
–
=
–
1540 ( C C str. of aromatic ring), 1171 (C O str. of ether linkage), 971 (trans, CH CH )
1
–
–
–
group. HNMR: 0.88–0.90 (t, 6H, CH3 of disubstituted OC18H37), 3.81 (s, 3H, OCH3),
1.26–1.28 (m, 38H, disubstituted OC18H37), 1.76 (p, 4H, disubstituted OC18H37), 4.06 (t,
–
–
–
–
–
=
–
4H, disubstituted OC18H37), 8.01 (d, 1H, J = 15.1 Hz, CH CH CO ), 7.42 (d, 1H, J =
–
=
–
–
15.1 Hz, CH CH CO ), 7.11 & 8.12 (d, 4H, first phenyl ring), 7.32 & 7.61 (d, 4H, sec-
ond phenyl ring), 7.92 & 7.12 (d, 3H, third phenyl ring). Elemental analysis: calculated for
C61H95O6: C, 81.97; H, 10.63; O, 10.75%; found: C, 81.93; H, 10.57; O, 81.89%.
Comp. C2: IR (KBr): vmax/cm−1 2951 (C H str. of alkane), 1640 (C O str. of carbonyl
–
=
=
–
–
carbon of chalconyl group), 1608 (C C str. of alkene in chalcone), 1760 (ester, COO
group), 1510 (C C str. of aromatic ring), 991 (C H bending of alkene), 1172 (C O str. of
ether linkage), 971 (trans, CH CH ) group. HNMR: 0.88–0.90 (t, 6H, CH3 of disubsti-
tuted OC18H37), 3.81 (s, 3H, OCH3), 1.26–1.28 (m, 38H, disubstituted OC18H37), 1.76
=
–
–
1
–
=
–
–
–
–
–
–
–
–
(p, 4H, disubstituted OC18H37), 4.06 (t, 6H, disubstituted OC18H37 and OCH2CH3), 1.31
–
–
=
–
–
(q, 3H, OC2H5), 8.01 (d, 1H, J = 15.1 Hz, CH CH CO ), 7.42 (d, 1H, J = 15.1 Hz,
–
=
–
–
CH CH CO ), 7.11 & 8.12 (d, 4H, first phenyl ring), 7.32 & 7.61 (d, 4H, second phenyl
ring), 7.92 & 7.12 (d, 3H, 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.C14: IR (KBr): vmax/cm−1 3031 (C H str. of alkane), 1660 (C O str. of carbonyl
–
=
=
–
–
carbon of chalconyl group), 1604 (C C str. of alkene in chalcone), 1740 ( COO group),
=
–
–
1540 (C C str. of aromatic ring), 991 (C H bending of alkene), 1178 (C O str. of ether
1
–
=
–
–
linkage), 971 (trans, CH CH ) group. HNMR: 0.88–0.90 (t, 9H, CH3 of disubstituted
OC18H37 and monosubstituted OC14H29), 1.26–1.28 (m, 54H, disubstituted OC18H37
–
–
–
–
–
and monosubstituted OC10H21), 1.76 (p, 6H, disubstituted OC18H37 and monosubstituted
–
–
–
OC14H29), 4.04 (t, 6H, disubstituted OC18H37 and monosubstituted OC14H29), 8.01 (d,
–
=
–
–
–
=
–
–
1H, J = 15.1 Hz, CH CH CO ), 7.53 (d, 1H, J = 15.1 Hz, CH CH CO ), 7.12 & 8.02 (d,

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
49
4H, first phenyl ring), 7.32 & 7.70 (d, 4H, second phenyl ring), 7.87 & 7.17 (d, 3H, third phenyl
ring). Elemental analysis: calculated for C72H116O6: C, 80.29; H, 10.78; O, 8.92%; found: C,
80.22; H, 10.73; O, 8.89%.
Comp.C16: IR (KBr): vmax/cm−1 2954 (C H str. of alkane), 1610 (C O str. of carbonyl
–
=
=
–
–
carbon of chalconyl group), 1604 (C C str. of alkene in chalcone), 1740 ( COO group),
1510 (C C str. of aromatic ring), 992 (C H bending of alkene), 1171 (C O str. of ether
linkage), 972 (trans, CH CH ) group. HNMR: 0.88–0.90 (t, 9H, CH3 of disubstituted
OC18H37 and monosubstituted OC16H33), 1.26–1.28 (m, 58H, disubstituted OC18H37
and monosubstituted OC16H33), 1.76 (p, 6H, disubstituted OC18H37 and monosubstituted
OC16H33), 4.06 (t, 6H, disubstituted OC18H37 and monosubstituted OC16H33), 8.01 (d,
1H, J = 15.1 Hz, CH CH CO ), 7.41 (d, 1H, -J = 15.1 Hz, CH CH CO ), 7.11 & 8.02 (d,
4H, first phenyl ring), 7.34 & 7.68 (d, 4H, second phenyl ring), 7.87 & 7.12 (d, 3H, third phenyl
ring). Elemental analysis: calculated for C74H120O6: C, 80.43; H, 10.86; O, 8.69%; found: C,
80.38; H, 10.83; O, 8.61%.
=
–
–
1
–
=
–
–
–
–
–
–
–
–
–
–
–
=
–
–
=
–
–
2.4. Reaction scheme
Scheme . Systematic route of target compounds (i) CHBr, anhydrous KCO, dry acetone, reflux; (ii) KOH,
EtOH, RT,  hr; (iii) R-Br, KOH, MeOH, Reflux; (iv) DCC, DMAP, DCM,  hr. stirring at RT.

50
V. S. SHARMA ET AL.
3. Result and discussion
Here, in present study, we have synthesized newly chalconyl-ester based liquid crystalline
–
compounds having changing left alkoxy ( OR) side chain from lower member (C1) to higher
member (C18) with terminally substituted bis octadecyloxy side chain at terminal side of third
phenyl ring. In the present study, we have study the effect of tail group on mesomorphic
behaviour of presently synthesized newly LCs compounds. A newly chalconyl-ester homol-
ogous series of liquid crystalline (thermotropic) property determined from condensation of
dimeric 4-n-alkoxy benzoic acids and (E)-1-(3, 4-bis (octadecyloxy) phenyl) -3-(4-hydroxy
phenyl) prop-2-en-1-one (chalcone) is synthesized and evaluated their LC behaviour with
some thermometric data to compare mesomorphic behaviours and the molecular structure
through molecular rigidity and flexibility with structurally similar previously reported series.
The phase behaviour of all new synthesised compounds has been investigated by polaris-
ing optical microscope (POM) and confirm by using differential scanning calorimetry (DSC)
analysis.
3.1. POM investigation
We have studied comprehensively the effect of linkage group as well as varying aliphatic alkyl
–
chain length in alkoxy ( OR) group to form calamitic rod type shaped mesogens. It has been
–
proven that changing length of alkyl chain in alkoxy part in ( OR) group, as a result effect on
their LC behaviour arises. Here, in present article, we have synthesized calamitic rod-shaped
–
–
–
=
–
–
homologous series contain ester ( COO ) in presence of chalcone ( CH CH CO ) linking
–
group with terminally substituted bis octadecyloxy ( OC18H37) group at one end and chang-
ing alkyl chain lengths in other end. We have prepared total thirteen compounds from small
–
–
member C1 ( OCH3) to higher member C18 ( OC18H37) in presence of three phenyl core
as rigid core part. The transition temperature of present series is listed below in Table 1. As
seen in Table 1, compounds C1 to C12 display an enantiotropic nematic mesophase, which
was further confirmed by DSC analysis; whereas compounds C14 to C18 exhibiting an enan-
tiotropic SmC and nematic mesophase. Compounds C14 to C18 shows LC behaviour at lower
Figure . Phase diagram of present series-.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
51
Figure . Mesomorphic textures of compounds obtained by POM (a) SmC phase of C homologue on
cooling condition; (b) nematic phase of C homologue on heating condition.
temperature. The textures observed by POM, on cooling from the isotropic liquid, are con-
sistent with the presence of smectic or nematic mesomorphism. Microphotographs of the
textures observed for compounds C14 and C12 are depicted in Figure 2. Mesophase formation
was found to be dependent on the number, position and length of the side alkyl chain which
–
increases the flexibility of molecules attached to the alkoxy side group ( OR) with phenyl
ring as rigid core. As shown in Table 1, compound C1 has higher melting type temperature
(89°C) and higher nematic to isotropic transition temperature range (138.0°C) as compared
to higher member compound C18, whose melting temperature of nematic phase (49°C) and
nematic to isotropic melting temperature (54°C). Compound C18 shows LC property at room
temperature and there is no any crystallization occurred upon cooling from isotropic state to
room temperature (rt).
The plot of transition temperature versus the number of carbon atoms present in n-alkyl
chain in alkoxy group showing Cr-SmC/I, SmC-N and N-I phase behaviour curve men-
tion in Figure 1. The phase diagram shows descending tendency form lower alkyl spacer
(C1) to higher alkyl spacer (C18). The transition curve of Cr-SmC/I showing decreasing ten-
dency from comp.C1 to C18. Cr-SmC/N transition curve starts with decreasing tendency from
comp.C1 to comp.C4 and then increased at comp.C5 and again decreased upto comp.C12
then slightly increased at comp.C16 and then continued to decrease upto last homologue
Table . Transition temperature in °C by POM.
Transition temperatures in C
Sr.no
R = n-alkyl group
Cr-I
Cr-SmC
SmC-N
N-I













C
C
C
C
C
C
C
C
C
C
C
C
C
·
·
·
·
·
·
·
·
·
·
·
·
·
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
·
·
·
.
.
.
.
.
.
.
.
.
.
.
.
.
-
·
·
·
·
·
·
·
·
·
·
·
·
.
.
.
.
.
.
.
.
.
.
-
·
·
·
·
·
·
·
·
·
·
·
·
-
.
.
.
.
.
.
(Cr = Solid Crystal, SmC = Smectic C phase, Nm = Nematic phase, Iso = Isotropic phase).

52
V. S. SHARMA ET AL.
Table . Texture of nematic phase of C, C, C, C by miscibility method.
Sr. No.
Homologue
Texture
Threaded
Schlieren
Threaded
Threaded
Threaded

C
C
C
C
C




C18. In Cr-SmC/N transition cure, odd-even effect is seen due to the presence of odd even
parity of carbon present in alkyl chain in comp.C5 to C6 [40]. N-I transition curve exhibits
descending tendency from remaining three C14 to C18 homologous. It has been noted that,
–
–
as the methylene group ( CH2-) increases in side alkoxy tail part ( OR), the linearity and
polarizability and flexibility of the molecules also increases. Thus, the transition tempera-
ture occurred at lower temperature. The varying of alkoxy side chain from lower alkyl chain
(C1) to higher alkyl chain (C18) has effect on the mesomorphic properties of liquid crystalline
compounds.
The exhibition of nematic phase from comp.C1 to C18 attributed to the disalignment of
molecules of an angle less than ninety degree under the externally exposed thermal vibra-
tions of suitable magnitudes which matches with internal energy stored in a molecule (ꢀH)
as related to the suitable magnitudes of anisotropic forces of intermolecular end to end
attractions, as a consequence of molecular rigidity and flexibility, which favorably arranges
molecules to float on the surface in statistically parallel orientational order to maintain molec-
ular two dimensional array [41]. It has shown that the absence of smectic property in comp.C1
to C12 is mainly due to the absence of lamellar packing arrangement in molecules to directly
displays solid to nematic phase on heating and again shows this phase sequence in cooling
condition respectively.
... Nematic mesophase by miscibility method
The nematic mesophase were also confirmed by using miscibility method which was mention
in below Table 2. Comp.C6, C10, C12 shows threaded type pattern of nematic phase whereas
in comp.C8, schlieren type textural pattern was seen. Comp. C16 homologue shows threaded
type textural pattern of nematic phase.
... 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 2. POM observations reveal that comp.C14 exhibited broken
fan type textural pattern of SmC phase at 49°C on cooling condition, the dark region seen
due to presence of some impurity. Comp. C12 display threaded type textural pattern of nematic
phase observed at 61°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
(comp.C14 to C16) or nematic phase (comp.C1 to C12) phase and second peak correspondence
to smectic to nematic or nematic to isotropic phase.
... Comparative study
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 earlier

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
53
Figure . Structurally similar analogous series.
[42] shown in Figure 3. Homologous series-1 and series-A, -B are identical with respect to
three phenyl rings and chalcone group with presence of alkoxy group at left terminal part.
The geometrical shape of series-1, -B are differ at right terminal side. In series-1 having
bis-substituted octadecyloxy side chain which slightly bent the molecule while in series-1
only mono-substituted octadecyloxy side chain is present which maintain the linearity of the
molecule. Therefore they differ with respect to combined effects of molecular rigidity and
flexibility due to octadecyloxy group at terminal part including intermolecular distance and
molecular polarizability which operates lower ordered melting type LC phase in present all
series. Series-1, -A shows LC property at lower temperature as compare to series-B, this is
happens due to the presence of di-substituted octadecyloxy side chain which increases more
flexibility vibration, polarity and polarizability of molecules as compare to monosubstituted
octadecyloxy group in series-B. The molecular length of series-A is higher as compare to
–
=
–
–
series-1, -B due to presence of vinyl ester ( CH CH COO ) linkage group having ethylene
–
=
–
( CH CH ) part with ester group which increases the stability of mesomorphism higher
–
–
as compare to ester ( COO ) group in series-A and series-B. Presence of second octade-
cyloxy side chain in series-1, -A at lateral side induces smectic property at lower tempera-
ture especially in series-1 comp.C18 shows smectic property at room temperature. However
in series-B monosubstituted octadecyloxy chain is present as a result it displays only nemato-
genic mesophase without exhibiting any smectic property in entire series.
The geometrical shape of series-1 and series-B are shown in below Figure 4. It can be seen
that the geometrical shape of both the series are looking different at right terminal side due
–
to the presence of one more octadecyloxy side group ( OC18H37) at lateral side in series-1
as compare to calamitic rod-shaped type series-B. In series-B, chalcone linkage is present in
–
–
=
=
–
order of ( CO CH CH ) between second and third phenyl ring while in series-1, -A, it’s in
–
–
–
order of ( CH CH CO). The varying left alkoxy side chain ( OR) from lower member (C1)
to higher member (C18) is common in both series.
... Thermal stability
Table 3 shows the average thermal stabilities and temperature range of newly synthesized
homologous series-1 compared with series-A and series-B. The SmC–N thermal stability of

54
V. S. SHARMA ET AL.
Figure . Geometrical shape of series-, -B.
series-A is 79.0°C which is higher as compare to series-1. In series-B, smectic phase is not seen.
Thermal stability of N–I phase of series-B is 122.0°C which is higher as compare to series-1,
-A, this is due to the linearity of molecules without any lateral substituent. Both series-1, -
A have similar thermal stability (120.0°C for series-1 and 120.3°C for series-A). Mesophase
commences early from lower homologue in series-1, -A as compare to series-B. It can be noted
that, thermal stability of Sm-N transition of series-A is higher as compared to series-1 this is
–
=
–
because of the presence of cinnamate linking group which having ethylene ( CH CH ) part
–
–
more as compare to ester ( COO ) group in series-1 which increases its molecular length and
stability.
The temperature range of SmC-N, N-I and total stability of phase transition is listed in
Figure 5. It is clearly seen that, total temperature range of mesophase of series-A is higher as
compare to series-1 and series-B. Comp.C14 (series-1) shows good temperature range as com-
pare to other both of series. Mesophase length of N-I transition of series-B is lower as compare
to other series. Figure 6 represents the proposed mechanism to represents the arrangement of
molecules to induce SmC and nematic type mesophase in heating as well as cooling condition.
3.2. DSC study
DSC is a valuable method for the detection of phase transitions. The thermal behaviour of
novel homologues series were confirmed by using DSC measurement shown in Figure 7. The
transition temperatures and associated with enthalpy changes determined by differential scan-
ning calorimetry (DSC) for compounds are listed in Table 4. DSC thermogram is traced in
both heating and cooling condition. In Figure 7, comp.C2 exhibits two endothermic peaks at
22.67°C, 91.08°C in heating cycle, which correspondence to the presence of crystal to crys-
ꢀ
ꢀ
–
tal (Cr Cr ) and crystal to nematic (Cr -N) phase. That was also confirmed by using POM
Table . Average thermal stability in °C.
Series
Series-
Series-A
Series-B
SmC-N
N-I
.(C-C)
.(C- C)
.°C-.°C(C-C)
.(C-C)
.(C – C)
.°C-.°C(C-C)
-
.(C- C)
.°C-.°C(C-C)
Total temperature range of mesophase

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
55
Figure . Temperature range of phase transition in series-, -A, -B.
analysis. While on cooling condition, these exothermic peaks were traced again at 32.41°C
and 91.26°C. Comp.C6 display two endothermic peak at 38.73°C and 70.68°C during heat-
ing cycle, while on cooling cycle, it appears at 21.69°C and 71.09°C which was indicates the
presence of crystal to crystal and crystal to nematic mesophase transition. Comp.C10 exhibits
two endothermic peaks observed at 41.29°C and 62.41°C on heating cycle which reveals with
POM analysis. On cooling cycle, again these two exothermic peaks traced at 29.77°C and
Figure . Proposed mechanism of present series-.

56
V. S. SHARMA ET AL.
Figure . DSC thermograms of compound (a) comp.C; (b) comp.C; (c) comp.C; (d) comp.C on heating
and cooling cycles.
63.76°C. Comp.C8 shows two endothermic peaks observed at 32.31°C and 71.06°C in heat-
ing condition while on cooling condition it appears at 34.65°C and 71.98°C. It reveals with
POM result. In Figure 8, comp.C3 shows two endothermic peaks observed at 44.21°C which
is corresponded to crystal to crystal transition and 84.36°C confirms the presence of crystal
to mesophase transition on heating condition.
Table . Phase transition temperature (ºC) and enthalpy (J g−) and entropy change (J g −k−) by DSC
measurement.
Heating peak
temperature
(ºC)
Cooling peak
temperature
(ºC)
Comp.
C
Transition
ꢀH (-Jg−
)
ꢀH(Jg−
)
ꢀS (-J g−k−
)
ꢀS (J g−k−
)
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
–
Cr Cr
.
.
>.
.
.
>.
.
.
>.
.
.
>.
.
.
.
-
.
.
-
.
.
-
.
.
-
-
-
-
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
-
.
.
-
.
.
-
.
.
-
-
-
-
.
.
.
.
-
.
.
-
.
.
-
.
.
-
-
-
-
Crꢀ-N
N-I
.
.
.
.
.
.
.
.
.
.
.
.
.
–
C
C
C
C
Cr Cr
Crꢀ-N
N-I
–
Cr Cr
Crꢀ-N
N-I
–
Cr Cr
Crꢀ-N
N-I
–
Cr Cr
Crꢀ-N
N-I
.
>.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
57
Figure . DSC thermograms of comp.C on heating cycle.
4. Conclusion
A new calamitic rod type chalcone-derived LCs compounds based on three phenyl rings as
–
rigid core possessing two linkage and disubstituted octadecyloxy ( OC18H37) side chain at
–
one end and other end with variable alkyl chain length in alkoxy group ( OR). Comp. C1 to
C12 shows enantiotropic nematic phase while higher members comp.C14 to C18 shows enan-
tiotropic smectic as well as nematic property. The LC phase of higher homologous especially
in comp.C14 to C18 displayed at lower temperature with lower thermal stability of mesophase
in present synthesized series.
Acknowledgement
Authors thank Dr. R. R. Shah, principal and management of K. K. Shah Jarodwala
Maninagar Science College, Ahmedabad. Authors thank Miss Akshara Shah (Department of Chem-
istry, Mumbai University) for giving fruitful discussion on DSC analysis. Authors are also thankful to
NFDD Centre for providing analytical and spectral services.
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