Effect of alkyl chain in the terminal ester group on mesomorphic properties of new rod like homologous series: Synthesis and characterization

Article abstract of DOI:10.1080/15421406.2016.1262690

The mesomorphic properties of linear chalconyl ester homologous series can be tuned in a predictable fashion with tail groups (–OC₅H₁₁) substituents on the terminal side and nitro group substitute at lateral position. Novel series consisted 13 members (C₁ to C₈, C₁₀, C₁₂, C₁₄, C₁₆, C₁₈). C₁ to C₅ homologues are nonliquid crystal, C₆ to C₁₈ homologues display smectic and nematic mesophase enantiotropically manner except C₅ homologue, which show only nematogenic mesophase. The texture of the nematic mesophase is of fan-shaped, Schlieren, and nematic droplets type. All these compounds were characterized by elemental analyses and spectroscopic techniques such as [FTIR] and 1H Nuclear magnetic resonance [NMR] spectroscopy. The mesomorphic properties of these compoundswere observed by optical polarized light microscopy (POM) and differential scanning calorimetry (DSC).

Full text of DOI:10.1080/15421406.2016.1262690

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Effect of alkyl chain in the terminal ester group
on mesomorphic properties of new rod like
homologous series: Synthesis and characterization
Vinay S. Sharma & R. B. Patel
To cite this article: Vinay S. Sharma & R. B. Patel (2017) Effect of alkyl chain in the
terminal ester group on mesomorphic properties of new rod like homologous series:
Synthesis and characterization, Molecular Crystals and Liquid Crystals, 643:1, 62-75, DOI:
10.1080/15421406.2016.1262690
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1262690
Published online: 23 Feb 2017.
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Date: 26 February 2017, At: 23:18

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –

http://dx.doi.org/./..
Effect of alkyl chain in the terminal ester group on mesomorphic
properties of new rod like homologous series: Synthesis
and characterization
Vinay S. Sharma and R. B. Patel
Chemistry Department, K.K. Shah Jarodwala Maninagar Science College, Gujarat University, Ahmedabad,
Gujarat, India
ABSTRACT
KEYWORDS
The mesomorphic properties of linear chalconyl ester homologous
series can be tuned in a predictable fashion with tail groups (–OC H )
Calamatic liquid crystal;
enantiotropic; mesophase;
nematic; smectic
5
11
substituents on the terminal side and nitro group substitute at lat-
eral position. Novel series consisted 13 members (C to C , C , C , C ,
1
8
10
12
14
C , C ). C to C homologues are nonliquid crystal, C to C homo-
1
6
18
1
5
6
18
logues display smectic and nematic mesophase enantiotropically man-
ner except C homologue, which show only nematogenic mesophase.
5
The texture of the nematic mesophase is of fan-shaped, Schlieren, and
nematic droplets type. All these compounds were characterized by ele-
1
mental analyses and spectroscopic techniques such as [FTIR] and H
Nuclear magnetic resonance [NMR] spectroscopy. The mesomorphic
properties of these compounds were observed by optical polarized light
microscopy (POM) and differential scanning calorimetry (DSC).
GRAPHICAL ABSTRACT
CONTACT Vinay S. Sharma
Science College, Gujarat University, Ahmedabad , Gujarat, India.
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
vinaysharma@gmail.com
Chemistry Department, K. K. Shah Jarodwala Maninagar
©

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
63
Introduction
Liquid crystal (LC) is an intermediate state of a matter in between the liquid and the crystal
behaving with some typical properties of a liquid as well as some crystalline properties. There
are many kinds of LC materials with different molecular structures, based on which LC could
be divided into three categories, that is, calamatic liquid crystal, bent-shape liquid crystal, and
discotic liquid crystal. Calamatic LCs materials are widely used in a flat-panel display, smart
windows, laser and other photonics. Liquid crystalline (LC) chalconyl ester derivatives play
dual role useful in LC devices and pharmaceutical preparation and therapeutically treatment
to cure diseases within definite range of concentration in solution state [1–5]. Liquid crys-
tals 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. In the nematic
phase, liquid crystal molecules are oriented on average along a particular direction. By apply-
ing an electric or magnetic field the orientation of the molecules can be derived in a probable
approach [6–14]. This mechanism provides the basis for LCDs.
Chalcone is an important class of chemical compound and is being studied extensively
because of its significant use or application in various sectors. In the fields of biology and
biochemistry, chalcone has been claimed to be one of the compounds that plays a vital role
in anti-tumor [15, 16], anti-inflammatory [17, 18], and anti-malaria [19] activities. It has also
been documented that the chalcone possesses a remarkable nonlinear optical (NLO) property,
which is an essential element for optical communications devices [20]. The other importance
of this compound is its high photosensitivity and thermal stability, which are used in devel-
oping various crystalline electro-optical devices [21–23]. The effects of laterally substituted
group on mesogens are considerable interest because these compounds deviate from the clas-
sical rod-like shape [24–30].
Recently, we have reported homologous series based on three phenyl rings bonded through
–
CH=CH–COO– and –CO–CH=CH– linking groups as well as varying left n-alkoxy ter-
minal end group and a fixed tail part at right side ended group and various halogen group
[
31–35]. In present investigation, we have planned to study the effects of tail group (–OC H )
5 11
and lateral group (–NO ) on LCs properties of present synthesized novel homologous series.
2
M. Hird reported review on ferroelectric liquid crystals and development of the technology
to commercially viable devices, with a specific focus on the development of suitable materials
in terms of design, synthesis and properties of ferroelectric LCs material [36]. Numbers
of homologous series or LC materials have been reported in which ester-chalconyl linkage
group is present till the date [37–40]. Group efficiency order and structure relation with
mesomorphism will be derived.
Experimental
Materials
For present synthesized homologous series required materials: 4-hydroxy benzaldehyde,
4
-hydroxy benzoic acid, (Lancaster, England, SRL Mumbai), 3-nitro, 4-hydroxy acetophenone
was purchased from (Sigma Aldrich), Anhydrous K CO , KOH were purchased from (Finar
2
3
Chemicals, India), N,N-dimethyl amino pyridine (DMAP) and Dicyclohexylcarbodiimide
(
DCC) was purchased from Fluka Chemie (Switzerland). R-Br (alkyl halide) (R=C H
,
n
2n+1
n = 1 to 8, 10, 12, 14, 16, 18) were purchased from S.R.L. Chemicals (Mumbai). The solvents
were dried and purified by standard method prior to use.

6
4
V. S. SHARMA AND R. B. PATEL
Measurements
Melting points were taken on Opti-Melt (Automated melting point system). The FT-IR spec-
−1
tra were recorded as KBr pellet on Shimadzu in the range of 3800–600 cm . Microanalysis
was performed on Perkin-Elmer PE 2400 CHN analyser. The texture images were studied on
a trinocular optical polarizing microscope (POM) equipped with a heating plate and digi-
1
13
tal camera. H NMR spectra and C NMR was recorded on a 400 MHz in Bruker Advance
00 in the range of 0.5 ppm-16 ppm using CDCl solvent. The phase transition temperatures
4
3
−1
were measured using Shimadzu DSC-50 at heating and cooling rates of 10°C min . 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 analysis,
the synthesized compound is sandwiched between to glass slide and cover slip and heating
and cooling rate is (2°C / min).
Synthesis
4
-n-alkoxy benzoic acids (1a) prepared by reported method [41]. 1-(4-hydroxy-3-
nitrophenyl)-3-(4-(pentyloxy) phenyl) prop-2-en-1-one (1c) was prepared by usual estab-
lished method [42]. Esters were synthesized by a method reported in literature [43]. Thus,
the Chalconyl-Ester homologue derivatives were filtered, washed with sodium bicarbonate
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 shown
in Scheme 1.
Synthesis of -n-pentyloxy benzaldehyde (b)
4
-n-Alkoxybenzaldehydes (1b) were synthesized by refluxing 4-hydroxybenzaldehyde
(1 equiv.) with corresponding n-pentyl bromides (1 equiv.) in the presence of K CO (1 equiv.)
2
3
and dry acetone as a solvent [44].
Synthesis of -n-alkoxy benzoic acid (a)
4
-hydroxy benzoic acid alkylated by alkylating agent (R-Br), KOH, MeOH (C to C ) and
1 8
Ethanol (C to C ), increasing reflux time period with increasing chain to yield correspond-
1
0
16
1
ing 4-n-alkoxy benzoic acids (1a), which was confirmed by IR and H NMR study [41].
Synthesis of chalcone (c)
Chalcone (1c) was prepared by usual established method reported in literature [42].
Synthesis of ester derivatives
The compound has been prepared by esterification of the appropriate 4-n-alkoxy cinnamic
acid (A) (2.02 mmol) and chalcone (C) (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 CH Cl (DCM) (30 mL) was stirred at room temperature for 48 h.
2
2
The white precipitate of DCU is obtained which was isolated by filtration and discarded, while
the filtrate was evaporated to dryness. The resultant crude residue was purified by column
chromatography on silica gel eluting with dichloromethane: methanol, recrystallization from
methanol: chloroform (2:3) until constant transition temperatures were observed [43].

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
65
Reaction scheme
Scheme . (i) R-Br, KOH, MeOH, Reflux; (ii) C H Br, Anhydrous K CO , Dry Acetone, Reflux; (iii) EtOH, KOH,




R.T. Stirring  hour; (iv) DCC, DMAP, DCM, R.T.  hours.
Analytical data
−1
Chalcone (1c): FT-IR (KBr) in cm : 3016–3030 (–C–H– str in CH ), 1510–1450 (N–O
3
str bands),1450 (N–O str bands), 1365 and 1219 (–C–O str), 940 (trans, –CO–CH=CH–,
–
CH=CH), 802 disubstituted aromatic ring (para), 758 Polymethylene (–CH –) of
2
1
–
OC H (n), 1640 (–C=O) group. H NMR: δH (CDCl , 400 MHz): 0.88 (t, J =
5
11
3
8
.1 Hz, 3H, –CH of –OC H group), 1.31–1.39 (m, J = 7.21, 4H, –(CH ) , 1.76
3
5
11
2 2
(
p, J = 7.52 Hz, 5H, –CH –CH –CH –O–), 4.06 (t, 2H, –OCH –), 8.02 (d, J =
2
2
2
2
1
6
5.1 Hz, 1H, –CO–CH=CH–), 7.53–7.55 (d, J = 15.1Hz, 1H, –CO–CH=CH–), 6.94–
.94 & 7.62–7.61 (4H, J = 7.5 Hz, second phenyl ring), 8.44, 827 & 7.40, (4H,
13
J = 7.1 Hz, first phenyl ring), 5.30 (1H, –OH group).; C NMR (CDCl ): δ ppm
3
1
1
4.0 (CH of –OC H chain), 22.72–29.36 (CH aliphatic), 68.67 (–OCH ), 114.31,
3 5 11 2 2
29.78, 131.21, 120.22, 137.41, 137.42, 157.84 (Ar-C), 120.32 (α carbon of –CO
CH=CH), 144.98 (β carbon of CO–CH=CH), 185.52 (C=O group of chalcone); Elemental
analysis of C H NO : Calc: C; 67.60%, H; 5.91%, O; 22.53%, N; 3.94%, Found: C; 67.52%,
–
20
21
5
H; 5.43%, O; 21.70%, N; 3.90%.
Butyloxy (C ): FT-IR (KBr): 636 Polymethylene (–CH –)n of –OC H ,
4
2
5
11
8
39(–C–H– def. di-substituted-para), 759 Polymethylene (–CH –) of –OC H , 920
2 4 9
(
–C–H– def. hydrocarbon), 1028 and 1068(–C–O–) str, 1197 and 1250 (–C–O
str) in –(CH2)n chain, 1427 (–C–H– def. in CH ), 1510–1450 (–N–O str bands),
2

6
6
V. S. SHARMA AND R. B. PATEL
1
2
–
514 (–C=C–)str, 1658 (–C=O group), 1740 (–COO– ester group), 2840 and
1
960 (–C–H str in CH ). H NMR (CDCl ): δ ppm 0.88–0.90 (t, 6H, –CH of
3
3
3
OC H & –OC H ), 1.31 & 1.45 (q, 8H, –CH of –OC H & –OC H ), 1.76 (P,
5
11
4
9
2
5
11
4
9
1
7
7
0 H of –OC H & –OC H group), 4.06 (t,6H,–O–CH –CH -of –OC H & –OC H ),
5 11 4 9 2 2 5 11 4 9
.56 (d, 1H, J = 15.1 Hz, –CO–CH=CH–), 8.32 (d, 1H, J = 15.1 Hz, –CO–CH=CH–),
.14–7.15 & 8.11–8.12 (d, 4H, left side phenyl ring), 7.82 & 8.68, 8.51 (3H, central phenyl
ring), 7.62–7.61 & 6.94–6.92 (d, 4H, terminal phenyl ring).Elemental analysis of C H NO :
31
33
7
Calc: C; 70.05%, H; 6.21%, O; 21.09%, N; 2.63%, Found: C; 69.95%, H; 6.17%, O; 20.88%, N;
.59%.
Pentyloxy (C ): FT-IR (KBr): 636 Polymethylene (–CH –)n of –OC H , 839(–C–H– def.
2
5
2
4
9
di-substituted-meta), 781 Polymethylene (–CH –) of –OC H , 952 (–C–H– def. hydrocar-
2
5
11
bon), 1028 and 1068(–C–O–) Str, 1197 and 1228 (–C–O str in –(CH )n chain, 1440 (–N–O
2
str.), 930 (Trans, –CH=CH–)str, 1604 and 1666 (–C=O group), 1726 (–COO– ester group),
1
2
–
850 and 2970 (–C–H str in CH ). H NMR (CDCl ): δ ppm 0.88–0.90 (t, 6H, –CH of
3
3
3
OC H & –OC H ), 1.31 (q, 8H, –CH of –OC H & –OC H ), 1.76 (P, 10 H of –OC H
5
11
5
11
2
5
11
5
11
5
11
&
–OC H group), 4.06 (t, 6H,–O–CH –CH -of –OC H & –OC H ), 7.58 (d, 1H, J =
5
11
2
2
5
11
5
11
1
5.1 Hz, –CO–CH=CH–), 8.04 (d, 1H, J = 15.1 Hz, –CO–CH=CH–), 7.14–7.15 & 8.11–
8.12 (d, 4H, left side phenyl ring), 7.82 & 8.68, 8.51 (3H, central phenyl ring), 7.62–7.62 &
6.94–6.93 (d, 4H, terminal phenyl ring).Elemental analysis of C H NO : Calc: C; 70.05%,
32
35
7
H; 6.21%, O; 21.09%, N; 2.63%, Found: C; 69.31%, H; 6.07%, O; 20.93%, N; 2.61%.
Hexyloxy (C ): FT-IR (KBr): 636 Polymethylene (–CH –)n of –OC H , 839(–C–H– def.
6
2
4
9
di-substituted-meta), 688 Polymethylene (–CH –) of –OC H , 951 (–C–H– def. hydro-
2
6
13
carbon), 1028 and 1068(–C–O–) str, 1197 and 1440 (–N–O– str.), 1514 (–C=C–)str, 1604
and 1666 (–C=O group), 1726 (–COO– ester group), 2850 and 2970 (–C–H str in CH ).
3
1
H NMR (CDCl ): δ ppm 0.88–0.90 (t, 6H, –CH of –OC H & –OC H ), 1.39–1.43 (t,
3
3
5
11
6
13
6
H of –OC H , –OC H ), 1.23–1.28 (t, 6H, –CH of –OC H & –OC H ), 1.76 (P, 10
4 9 6 13 2 5 11 6 13
H of –OC H & –OC H group), 4.06 (t,6H,–O–CH –CH -of –OC H & –OC H ),
5
11
6
13
2
2
5
11
6
13
7
7
.58 (d, 1H, J = 15.1 Hz, –CO–CH=CH–), 8.02 (d, 1H, J = 15.1 Hz, CO–CH=CH–),
.14–7.15 & 8.11–8.12 (d, 4H, left side phenyl ring), 7.81 & 8.68, 8.51 (3H, central phenyl
ring), 7.62–7.61 & 6.94–6.93 (d, 4H, terminal phenyl ring).Elemental analysis of C H NO :
33
37
7
Calc: C; 70.84%, H; 6.61%, O; 20.03%, N; 2.50%, Found: C; 70.62%, H; 6.48%, O; 19.89%,
N; 2.47%.
Heptyloxy (C ): FT-IR (KBr): 636 Polymethylene (–CH –)n of –OC H , 839(–C–H– def.
7
2
4
9
di-substituted-meta), 701 Polymethylene (–CH –) of –OC H , 952 (–C–H– def. hydrocar-
2
7
15
bon), 1028 and 1068(–C–O–) str, 1197 and 1228 (–C–O str) in –(CH )n chain, 1440 (–N–O–
2
str.), 1514 (–C=C–)str, 1604 and 1660 (–C=O group), 1760 (–COO– ester group), 2850 and
1
2
–
970 (–C–H str in CH ). H NMR (CDCl ): δ ppm 0.88–0.90 (t, 6H, –CH of –OC H
&
11
3
3
3
5
11
OC H ), 1.39 & 1.43 (q, 8H, –CH of –OC H & –OC H ), 1.76 (P, 10 H of –OC H
7
15
2
5
11
7
15
5
&
–OC H group), 4.06 (t,6H,–O–CH –CH -of –OC H & –OC H ), 7.58 (d, 1H, J =
7
15
2
2
5
11
7
15
1
(
5.1 Hz, –CO–CH=CH–), 8.06 (d, 1H, J = 15.1Hz, –CO–CH=CH–), 7.14–7.15 & 8.11–8.12
d, 4H, left side phenyl ring), 7.81 & 8.68, 8.51 (3H, central phenyl ring), 7.62–7.62 & 6.94–
6
6
.93 (d, 4H, terminal phenyl ring). Elemental analysis of C H NO : Calc: C; 71.20%, H;
34 39 7
.80%, O; 19.54%, N; 2.44%, Found: C; 71.08%, H; 6.73%, O; 19.46%, N; 2.41%.
Decyloxy (C ): FT-IR (KBr): 637 Polymethylene (–CH –)n of –OC H , 839(–C–H– def.
1
0
2
4
9
di-substituted-meta), 821 Polymethylene (–CH –) of –OC H , 952 (–C–H– def. hydro-
carbon), 1028 and 1068(–C–O–) Str, 1197 and 1228 (–C–O str in –(CH )n chain, 1440
2
10 21
2
(
2
–N–O– str.),1514 (–C=C–)str, 1666 (–C=O group), 1730 (–COO– ester group), 2850 and
1
970 (–C–H str in CH ). H NMR (CDCl ): δ ppm 0.88–0.90 (t, 6H, –CH of –OC H
&
3
3
3
5
11

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
67
Table . Texture of nematic phase of C , C , C , C , C , C , C by miscibility method.


    
Sr. No.
Homologue
Texture
Rod like
Broken rod like
Threaded
Schlieren
Needle

C
C
C
C
C
C
C






Rod like
Rod like
–
OC H ), 1.29 (m, of –OC H ), 1.31 (q, 8H, –CH of –OC H & –OC H ), 1.76 (P, 10
10 21 10 21 2 5 11 10 21
H of –OC H & –OC H group), 4.06 (t,6H,–O–CH –CH -of –OC H & –OC H ),
5
11
10 21
2
2
5
11
10 21
7
7
.58 (d, 1H, J = 15.1 Hz, –CO–CH=CH–), 8.02 (d, 1H, J = 15.1 HZ, –CO–CH=CH–),
.14–7.15 & 8.11–8.12 (d, 4H, left side phenyl ring), 7.82 & 8.68, 8.51 (3H, central phenyl
ring), 7.62–7.61 & 6.94–6.92 (d, 4H, terminal phenyl ring). Elemental analysis of C H NO :
37
45
7
Calc: C; 72.19%, H; 7.31%, O; 18.21%, N; 2.27%, Found: C; 72.10%, H; 7.20%, O; 18.12%,
N; 2.22%.
Dodecyloxy (C ): FT-IR (KBr): 636 Polymethylene (–CH –)n of –OC H , 839(–C–H–
1
2
2
4
9
def. di-substituted-meta), 759 Polymethylene (–CH –) of –OC H , 952 (–C–H– def. hydro-
2
12 25
carbon), 1028 and 1068(–C–O–) Str, 1197 and 1228 (–C–O str.) in (–CH ) chain, 1440
2
n
(
2
–N–O– str.),1514 (–C=C–)str, 1640 (–C=O group), 1726 (–COO– ester group), 2850 and
1
970 (–C–H str in CH ). H NMR (CDCl ): δ ppm 0.88–0.90 (t, 6H, –CH of –OC H
&
3
3
3
5
11
–
OC H ), 1.29 (m, of –OC H ), 1.31 (q, 8H, –CH of –OC H & –OC H ), 1.76 (P,
12
25
12 25
2
5
11
12 25
1
7
7
7
0 H of –OC H & –OC H group), 4.06 (t,6H,–O–CH –CH -of –OC H & –OC H ),
5 11 12 25 2 2 5 11 12 25
.58 (d, 1H, J = 15.1 Hz, –CO–CH=CH–), 8.02 (d, 1H, J = 15.1 HZ, –CO–CH=CH–), 7.14–
.15 & 8.11–8.12 (d, 4H, left side phenyl ring), 7.82 & 8.68, 8.51 (3H, central phenyl ring),
.61–7.62 & 6.93–6.92 (d, 4H, terminal phenyl ring). Elemental analysis of C H NO : Calc:
39
49
7
C; 72.78%, H; 7.62%, O; 17.41%, N; 2.17%, Found: C; 72.70%, H; 7.53%, O; 17.32%, N; 2.11%.
Textures of nematic phase were determined by miscibility method, which were given in
Table 1. C homologue shows rod-like mesophase, C shows broken rod-like mesophase, C ,
7
8
12
C shows Schlieren-type nematic droplets, C homologue shows needle type of droplets for-
18
10
mation which was compared with standard LCs materials. Transition temperature of series-1
is shown in Table 2.
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
·
·
·
·
·
·
·
·
·
·
·
·
·
—
—
—
—
—
—
—
·
—
—
—
—
.
.
.
.
.
.
.
.
.
—
—
—
.
.
.
.
.
.
.
.
.
.
.
.
.
·
·
·
·
·
·
·
·
·
·
·
·
·












—
—
—
·
.
.
.
.
.
.
.
.
·
·
·
·
·
·
·




·
·
·
·
·
·
·
·

6
8
V. S. SHARMA AND R. B. PATEL
Result and discussion
POM analysis
In order to study the influence of the central linkage and lateral nitro group with terminal
substituted pentyloxy side chain (–OC H ) tail group on the mesomorphic behavior of liq-
5
11
uid crystalline substances. In this present investigation, we have prepared calamatic rod-type
homologous series in which 13 compounds (C to C , C , C , C , C , C ) are synthesize.
1
8
10
12
14
16
18
In this study, focus on the effect of lateral nitro group on chalconyl ester based homologous
series and also study the effect of flexibility alter by left side chain with fixed tailed group. In
addition, compounds C -C shows enantiotropic smectic as well as nematic phase, while in
6
18
C homologue only exhibit enantiotropic nematic mesophase„ respectively. While rest of the
5
homologue C to C are nonmesomorphic in nature due to short alkyl spacer in left side chain
1
4
causes more crystallinity and directly converted into isotropic phase without display LC phase
either heating or cooling condition. Sm-N and N-I transition curves exhibited odd–even effect
at C and C homologue.
7
5
The nonmesomorphicity of C , C , C , and C homologue is attributed to the low mag-
1
2
3
4
nitudes of intermolecular dispersion forces and low magnitudes of dipole–dipole interfaces
leading to high crystallizing tendency due to short alkyl chain length as result it causes
hasty breaking of crystal lattices because of unsuitable magnitudes of anisotropic forces of
intermolecular desirability. Thus, improper breaking of crystal lattices and directly melts at
reaching its isotropic temperature and on cooling condition solidification is taking place with-
out displaying of liquid crystalline phase.
Phase transition curve of Cr-M, Sm-N, and N-I is plotted against the transition tempera-
ture versus the number of carbon atoms present in n-alkyl chain at (left alkoxy side chain) as
shown in Fig. 1. Cr-I/M transition curve initially falls up to C and rises at C and falling to
4
5
C and then rises to C homologue and then continued decrease up to last C homologue;
7
8
18
this is due to the increasing of flexibility at left alkyl side chain. Odd–even effect is present
at C and C homologue. Sm-N transition curve decrease at C homologue and increase at
5
7
7
C and continued reaching maxima at C homologue and continue falling tendency at C
8
12
16
homologue, this is due to the presence of abnormality effect. N-I transition curve start rises
Figure . Phase diagram of Series-.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
69
Figure . Texture image of Series-l observed between cross polarizers: (a) SmC of C homologue at °C;

(
b) isotropic of C homologue at °C; (c) nematic phase of C homologue at °C.



at C homologue and then gradually decreasing with added methylene unit (–CH –) in alkyl
6
2
chain and provide more spacer and flexibility. The presence of highly polar –NO group sub-
2
stituted at lateral position on central phenyl ring, increases molecular aromaticity, polarity,
and polarizability of molecules.
The presence of odd–even effect and the variation of transition temperatures of homo-
logues are due to the odd and even number of methylene units present in the n-alkyl side
chain of left n-alkoxy chain group. The exhibition of smectogenic phase in present synthesized
homologues from C to C due to the formation of lamellar packing of molecules in crystal
6
18
lattices which maintains sliding layered molecular arrangement in floating condition under
the influence of exposed thermal vibrations in heating and cooling conditions. The exhibi-
tion of nematic property from C to C homologue is attributed to the suitable magnitudes
5
18
of anisotropic end to end side intermolecular attractions and appropriate permanent dipole
moment across the long molecular axis., dispersion forces, dipole–dipole interactions, shape,
size, magnitudes of polarity and polarizability etc., which maintains floating of the homo-
logue in statically parallel orientational order to adopt nematogenic character, under exposed
thermal vibrations; either directly or via smectic phase in enantiotropic manner [45].
Texture images of compounds are mention in Fig. 2, for C homologue, SmC-type texture
8
image observed at 160°C which on continue to heating, it exhibits nematic mesophase at
1
72°C and at 184°C it becomes isotropic. Schlieren-type texture image of nematic phase
observed for C12 homologue at 164°C on heating conditions, respectively, which was

7
0
V. S. SHARMA AND R. B. PATEL
Figure . DSC thermogram of compound C .

confirmed by DSC analysis. Texture study of nematic mesophase is measured by miscibility
method.
DSC study
DSC is a valuable method for detecting phase transitions. The thermal behavior of novel
homologues series were confirmed by using DSC measurement shown in Figs 3–5, respec-
tively. DSC thermogram is traces in heating and cooling condition. In Fig. 3 for C18
homologue, during heating condition first endothermic peak is traces at 102.5°C, which indi-
cates the presence of SmC mesophase. While second endothermic peak traces at 122.5°C,
which indicates the presence of nematic phase, cooled condition again two endothermic
were traces at 97.78°C and 124.1°C. For C16 homologue, two significant peaks is observed
at 106.7°C and 120.68°C and for N-I it’s observed at >140°C. While on cooling condition
it traced at 107.4°C and 121.3°C respectively. This is nearly to the transition temperature
observed by POM investigation. For C homologue, first endothermic peak trace at 159.2°C
6
and second endothermic peak at 183.8°C on heating condition. One endothermic peak trace
Figure . DSC thermogram of compound C .


MOLECULAR CRYSTALS AND LIQUID CRYSTALS
71
Figure . DSC thermogram of compound C / C / C homologue.



for compound C at 179.8°C which indicate the presence of only nematic phase which was
5
confirmed by POM study. Two endothermic peaks traced for C homologue at 142.4°C and
10
1
65.2°C on heating condition. Transition temperature obtained by DSC analysis at heating
and cooling condition and the value of enthalpy and entropy is mention in Table 3. Molecules
of every homologue randomly oriented in all possible directions with high order of disorder
or entropy (ꢀS = ꢀH/T) beyond isotropic temperature and the enthalpy value (ꢀH). But, at
cooled condition, the same from and below isotropic temperature, the mesophase is persisted
to appear reversibly at the high temperature at observed during heating condition. The liq-
uid crystalline phase obtained enantiotropically manner in present series is smectogenic and
nematogenic, respectively.
Thermal stability of mesophase
Some LC parameters evaluated from thermotropic data of presently synthesized novel Series-
1
compared with structurally similar series X which was reported by our research group pre-
viously [46] is mention in Fig. 6. The linearity of the both series are different with first linking
−
− −
Table . Transition temperature (°C) and enthalpy (J g ) and entropy change (J g k ) by DSC
measurement.
Homologues or
Comp.
Heating
scan(°C)
Cooling
scan(°C)
ꢀH
ꢀS
ꢀS
k
(−Jg )
−
ꢀH (Jg
−
)
(J g
− −
k
)
(J g
− −
)
Transition
C18
C16
C10
Cr-SmC
SmC-N
N-I
Cr-SmC
SmC-N
N-I
Cr-SmC
SmC-N
N-I
Cr-N
N-I
Cr-SmC
SmC-N
N-I
.
.
>
.
.
>
.
.
>
.
>
.
.
>
.
.
—
.
.
—
.
.
—
.
—
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
—
.
.
—
.
.
—
.
—
.
.
—
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
—
.
.
—
.
.
—
.
—
.
.
—
C5
C6
.
.

7
2
V. S. SHARMA AND R. B. PATEL
Figure . Structurally similar series- & series-X.
group so their magnitudes of combined effects of molecular rigidity and flexibility change by
–
CH=CH– (ethylene) group is more in series-X as compared to series-1. Presences of –NO2
group at lateral side in series-X which increases the polarity and polarizability of molecule
as compared to series-X. Therefore magnitudes of molecular rigidity and left side flexibil-
ity undergo variations but at tail group remains fixed pentyloxy chain (–OC H ) group in
5
11
series-1 and series X.
The space filling diagram of both the series-1, -X is shown in below Fig. 7. The trans iso-
mer of chalcone is form by reaction of 4-hydroxy, 3-nitro acetophenone with 4-pentyloxy
benzaldehyde in the presence of base which was confirmed by IR analysis and compared with
previously reported in literature. Chalcone linkage group is present in both series with unal-
tered flexibility at terminal side chain (–OC H ) group. The molecular length of series-X
5
11
is more as compared with series-1 due to the presence of vinyl carboxy (–CH=CH–COO–)
linking group, while in series-1, carboxy (–COO–) group is present. Gray et al. [47] explained
that the addition of the double bond to the system increases the length and polarizability of
rod like molecules.
Comparison of thermal stability of mesophase and mesophase length of series-1 with
series-X are mentioned in Table 4. Thermal stability of Sm-N phase in series-1 is 94.37.
While series-X display only nematic phase. N-I thermal stability of series-1 is higher
than series-X. In series-X, vinyl carboxy (–CH=CH–COO–) linkage group is present.
Figure . Space filling model of (a) series- & (b) series-X.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
73
Table . Thermal stability comparison of Sm-N and N-I in Series-, -X.
Series
Series-
Series-X
__
Sm-I or Sm-N or N-Sm
Commencement of
Smectic phase
N-I or I-N
.
(C – C )


C
.
.
Commencement of
Nematic phase
Total mesophase
length
(C – C )
(C – C )




C
C
.°C to .°C
. to .
C C

C C
Figure . Proposed molecular packing of the Sm C phase in present series.
However, in series-1 carboxy (–COO–) central unit group is present which essen-
tially contribute to molecular length and decreases rigidity because of the absence of
–
CH=CH– unit and increases suitable magnitudes of intermolecular end to end attrac-
tions and closeness of molecules atoms. Thus, transition temperature and hence the
thermal stability for nematic mesophase is higher in series 1 as compared to series-X.
The early or late commencement of mesomorphism depends upon the extent of molecular
noncoplanarity.
The proposed molecular packing of the smectic C phase is shown in below Fig. 8. The
arrangement of molecule is isomeric calamatic rod-type shape. This is due to the molecular
packing of the alkyl chains with linking groups oriented tilted way directions and nitro group
substituted at lateral side in smectic layers structure and effect of flexibility to induce smectic
mesophase.
Conclusions
In summary, we have synthesized successfully a novel homologues series with two different
linkage group containing lateral nitro group and pentyloxy side chain. C to C compound do
1
4

74
V. S. SHARMA AND R. B. PATEL
not exhibit liquid crystalline behavior due to high crystallizing tendency, while rest of homo-
logues shows LCs property. We have found that the following synthesized homologous series
shows nematogenic and smectogenic behavior with good thermal stability which was com-
pared with series-X. We have confirmed the mesogenic property for compounds by DSC and
POM. The group efficiency order derived on the basis of thermal stability, early commence-
ment of mesophase, upper and lower mesophase length.
Acknowledgments
Authors acknowledge thanks to Dr. R. R. Shah, principal of K. K. Shah Jarodwala Maninagar Science
College, Ahmedabad. Authors gratefully thanks from Anuj S. Sharma and Akshara P. Shah for valuable
discussion in DSC study (Chemistry department, Gujarat University). Authors also thank to Centre of
Excellence, Rajkot for the spectral services.
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