New calamitic mesogens derived from a furan ring: Synthesis, characterization and study of their mesomorphic behavior

Article abstract of DOI:10.1016/j.molliq.2020.114562

A new series of mesogens bearing furan moiety, 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-alkoxybenzoate (C_a-k) was synthesized by different organic methodologies. These mesogens possess an alkoxy chain at one arm and a nitro group at the opposite arm in addition to various linkages (imine and ester). Their chemical structures have been identified by various essential characterization techniques: infrared spectroscopy (FTIR), ¹H and ¹³C nuclear magnetic resonance (NMR), and electron ionization-mass spectrometer (EI-MS). The thermal transition and optical behavior properties of the homologous series have been studied by differential scanning calorimetry (DSC) and a polarizing optical microscope (POM), respectively. The compounds of this series (C_a-C_k) displayed liquid crystalline phases, and all mesogens exhibited an enantiotropic nematic phase (N) in heating and cooling cycles except the compounds (C_d, C_e and C_f), which showed a monotropic nematic phase in the cooling cycle only. Additionally, the last member of this series (C_k) showed a smectic A (SmA) phase in addition to the nematic phase. The obtained results showed that the enantiotropic and monotropic mesogenic properties, in addition to the thermal stability of the mesophase for all mesogens, have been influenced thoroughly by increasing the number of carbon atoms in the terminal alkoxy tail and the nitro group on the other side. In addition to these results, these mesogens could be affected by other factors, such as polarity and polarizability of the linkages and other connected groups in the molecules. The liquid crystalline behaviors of the target compounds have been studied and discussed extensively and compared structurally in related literature.

Full text of DOI:10.1016/j.molliq.2020.114562

MOLLIQ-114562; No of Pages 14
Journal of Molecular Liquids xxx (xxxx) xxx
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
New calamitic mesogens derived from a furan ring: Synthesis, characterization and
study of their mesomorphic behavior
a
b
a,
a
Nabih M. Abdulnabi , Mazin M. Abdul Razzaq Al-Obaidy , Ivan Hameed R. Tomi ⁎, Hamed Jasim Jaffer
a
Mustansiriyah University, College of Science, Department of Chemistry, Baghdad, Iraq
Al-Iraqia University, College of Education, Department of Chemistry, Baghdad, Iraq
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 June 2020
Received in revised form 25 September 2020
Accepted 10 October 2020
Available online xxxx
A new series of mesogens bearing furan moiety, 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
alkoxybenzoate (Ca-k) was synthesized by different organic methodologies. These mesogens possess an alkoxy
chain at one arm and a nitro group at the opposite arm in addition to various linkages (imine and ester). Their
chemical structures have been identified by various essential characterization techniques: infrared spectroscopy
1
13
(FTIR), H and C nuclear magnetic resonance (NMR), and electron ionization-mass spectrometer (EI-MS). The
thermal transition and optical behavior properties of the homologous series have been studied by differential
scanning calorimetry (DSC) and a polarizing optical microscope (POM), respectively. The compounds of this se-
ries (C
heating and cooling cycles except the compounds (C
the cooling cycle only. Additionally, the last member of this series (C
a k
-C
) displayed liquid crystalline phases, and all mesogens exhibited an enantiotropic nematic phase (N) in
, C and C ), which showed a monotropic nematic phase in
) showed a smectic A (SmA) phase in addi-
d
e
f
k
tion to the nematic phase. The obtained results showed that the enantiotropic and monotropic mesogenic prop-
erties, in addition to the thermal stability of the mesophase for all mesogens, have been influenced thoroughly by
increasing the number of carbon atoms in the terminal alkoxy tail and the nitro group on the other side. In addi-
tion to these results, these mesogens could be affected by other factors, such as polarity and polarizability of the
linkages and other connected groups in the molecules. The liquid crystalline behaviors of the target compounds
have been studied and discussed extensively and compared structurally in related literature.
Published by Elsevier B.V.
1. Introduction
changes in the mesogenic properties are greatly related to the type
and number of heteroatoms in the ring as well as the effects of the po-
Aromatic moieties, such as phenyl and naphthalene, make up the
larity and the linearity of the molecules [8–13]. Therefore, many studies
in this field were carried out using different five-membered heterocyclic
moieties, such as furan, pyrrole, thiophene, 1,2,4- and 1,3,4-oxadiazoles,
1,3,4-thiadiazole and triazol, in the mesogen structure. [14–19]. More-
over, an important research line was developed to study the role of
these types of rings in the mesogenic structure and the relationships be-
tween the molecule structure and its mesophase property [20]. In
addition, the introduction of polar substituents within the chemical
structure of the heterocyclic derivatives, such as nitro, cyano, and
other polar groups or linkages, might lead to a substantial change in
the polarizability structure of the molecules that form to design a new
mesogenic system, forming new mesophase textures for the target
compounds and having useful thermal and optical applications [21–23].
Based on the above information, furan is a five-member aromatic
ring, which contains in its composition four carbon atoms and one oxy-
gen atom. The 2,5-disubstituted derivatives of this ring may appear as
liquid crystalline properties, despite containing exocyclic bend angle
common core unit in most of the liquid crystal compounds that have
been prepared over a long period. The main role of these moieties is to
connect the polar π-electron groups with each other to develop the
mesogenic character of the synthesized compounds and to make these
compounds possess liquid crystalline properties in the ranges used in
different applications in this field [1–4]. After extensive work in this
field by many researchers, it is found that the compounds containing
heterocyclic rings have good mesomorphic properties when they re-
place the commonly used aromatic groups [5–7]. It is clear that placing
such heterocyclic rings as a core part of the mesogen structure creates
substantial changes in the mesogenic behaviors in addition to creating
new optical and thermal properties. The heteroatoms in these com-
pounds, such as N, O, and S, have the polar character that could expand
their applications by improving their mesomorphic properties. The
⁎
Corresponding author.
E-mail addresses: ivanhrtomy@yahoo.com, ivanhrtomy@uomustansiriyah.edu.iq
(
C-O-C), a deviation from the linearity (approximately 125°) compared
(I.H.R. Tomi).
to the benzene derivatives [24]. This might be the reason for the scarcity
https://doi.org/10.1016/j.molliq.2020.114562
167-7322/Published by Elsevier B.V.
0
Please cite this article as: N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi, et al., New calamitic mesogens derived from a furan ring:
Synthesis, characterization and study of their mes..., Journal of Molecular Liquids, https://doi.org/10.1016/j.molliq.2020.114562

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
of reported articles in the literature that relate to the derivatives of this
ring and are recorded as mesogens. Therefore, the mesogenic com-
pounds derived from this ring are classified as bent or banana-shaped.
Continuing with our interest concerning the design and synthesis of
new mesogenic materials derived from five-membered heterocyclic
moieties [25–28], we thought it would be valuable to design and
synthesize a series of mesogens bearing a furan ring as a core unit that
conjugated different linkages (CH_N, O-C=O) and to study their
mesomorphic properties.
5-(4-nitrophenyl)furan aldehyde (32 g, 0.262 mol), 4- aminophenol
(28.58 g, 0.262 mol), and 7 drops of glacial acetic acid was dissolved
in absolute ethanol (300 mL) and placed in a 500 mL round-bottom
flask. The reaction mixture was refluxed for one day and then left to
cool down to approximately 25 °C. A precipitate of crude product was
formed, filtered, washed with cold ethanol (50 mL), and recrystallized
−
1
from ethanol. Yield (85%), FTIR (ART, cm ), υmax: 2557–3120
(O\\H), 3063 (C-Harom.) 2968, 2866, 1620 (C=N), 1595, 1577 (C=C),
1
1504, 1321 (NO2sym. and asym.); H NMR (300 MHz, DMSO-d6, δ, ppm):
9
.58 (s, 1H, phenolic OH), 8.51 (s, 1H, CH_N), 8.34 (d, 2H, Ar\\H, Ph at-
tached to –NO , J = 8.76), 8.08 (d, 2H, Ar\\H, Ph attached to –NO , J =
.74), 7.52 (d, 1H, furan ring, J = 3.64), 7.26 (d, 2H, Ar\\H, Ph attached
to –OH, J = 8.46), 7.25 (d, 1H, furan ring, J = 3.97), 6.81 (d, 2H, Ar\\H,
2. Experimental
2
2
8
2.1. Materials and analysis
13
Ph attached to –OH, J = 8.59); C NMR (75 MHz, DMSO-d6, δ, ppm):
No further purification was carried out on the chemicals used in this
156.70 (aromatic C, C-OH), 153.54 (C furan ring), 152.81 (C furan
research. Chemicals were procured by Sigma-Aldrich chemicals Pvt. Ltd.
and were utilized as received. Different analyses were used to character-
ize and confirm the chemical structures of the synthesized final esters
and their intermediates. FTIR spectra for all products were recorded
on a Shimadzu 8400 (ATR) spectrophotometer, while H and C NMR
analyses were run using a Bruker product model ultrashield at 300
and 75 MHz, respectively. The results were measured in (ppm),
tetramethylsilane (TMS) was used as the internal standard and deuter-
2
ring), 146.44 (aromatic C, C-NO ), 144.57 (CH=N), 142.11 (aromatic
C, C-N=CH), 135.16 (aromatic C, C-furan), 125.07 (aromatic C\\H),
124.80 (aromatic C\\H), 124.52 (aromatic C\\H), 122.65 (aromatic
C\\H), 115.78 (C\\H furan ring), 112.47 (C\\H furan ring); (EI-MS)
1
13
+
(relative intensity %) m/z = 308 (M , 100%, base peak), 291 (25%),
261 (40%).
2.2.3. General procedure for synthesis of 4-[((5-(4-nitrophenyl)furan-2-yl)
ated (CDCl
3
and DMSO‑d6) as suitable solvents for final compounds and
methylene)amino]phenyl 4-alkoxybenzoate (Ca-k)
intermediates, respectively. A Shimadzu QP1000EX instrument was
used to measure the mass fragments of the synthesized compounds
using (EI-MS) mode. Mesomorphic studies of the target compounds
were established by polarized optical microscopy (OPM) type (PW-BK
The general procedure for the synthesis of the titled esters was
reported in our previous work with slight modifications [33,34]. In
a 100 mL round-bottom flask, furanimine phenol (B) (1.00 g,
n
0.003 mol) and various 4-alkoxycarboxylic acids (X ) (0.003 mol)
5
000 PR), equipped with a hot-stage model (HS- 400). A thin film of
were dissolved in dry dichloromethane (DCM) (100 mL). The esterifica-
tion coupling reagents, N,N-dicyclohexylcarbodiimide (DCC) (0.66 g,
0.003 mol) and 4-(Dimethylamino)pyridine (DMAP) (0.36 g,
0.003 mol), were added to the reactants and then left in the flask at ap-
proximately 25 °C to stir for one week. The precipitate formed (1,3-
Dicyclohexyl urea DCU) was removed by filtration, and the filtrate
was transferred to a separating funnel for the purification process. It
was then washed with a dilute solution of acetic acid (5%, 80 mL) and
then with distilled water (80 mL). The separated organic layer was
dried with anhydrous magnesium sulfate; then the DCM solvent was re-
moved under reduced pressure. The resulted crude products (Ca-k) were
recrystallized using ethanol.
small amounts in each compound between two squares of glass as a
sandwich was prepared to show the mesogenic textures of the mate-
rials using the polarized light in a microscope. Thermal transitions of
the mesogens were measured by differential scanning calorimetry
(
DSC) using the LINSIS instrument (STAPT-1000), indium metal was
used as a standard for calibration, and the heating and cooling rates
were 5 °C/min in a nitrogen atmosphere.
2.2. Synthesis procedures
2.2.1. 5-(4-nitrophenyl)furan-2-carbaldehyde (A)
The nitro derivative of the furfural aldehyde (A) was prepared using
the method described in our previous work [29]. In a mixture solution of
7% HCl (50 mL) and water (33 mL), 4-nitroaniline (28.56 g, 0.207 mol)
2.2.4. 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
3
a
methoxybenzoate (C )
was dissolved, and a solution of sodium nitrite (14.28 g, 0.207 mol) in
water (37.5 mL) was added slowly at a temperature 0–5 °C. The reac-
tants were then left to stir for 20 min at this temperature and then
filtered. The resulting filtrate was treated with two solutions simulta-
neously. The first solution consisted of furan-2-carboxaldehyde
Yield (82%) as a yellowish solid; FTIR (ART, cm−1), υmax: 3080 (C-
H
arom.), 2978, 2895 (C-Haliph.), 1720 (C=O), 1627 (C=N), 1599 (C=
1
C), 1512, 1327 (NO2sym. and asym.); H NMR (300 MHz, CDCl
3
, δ, ppm):
, J =
8.89), 8.17 (d, 2H, Ar\\H, Ph attached to methoxy, J = 8.85), 7.97 (d,
2H, Ar\\H, Ph attached to –NO , J = 8.80), 7.33 (d, 2H, Ar\\H, middle
8.37 (s, 1H, CH_N), 8.30 (d, 2H, Ar\\H, Ph attached to –NO
2
(
57.05 g, 0.247 mol) in H
CuCl .2H O (7.5 g, 0.06 mol) in water (37.5 mL). The mixture solution
was carried out at room temperature with continuous stirring for
0 min. The temperature of the reactants was raised to 40 °C and left
2
O (75 mL). The second solution consisted of
2
2
2
phenyl, J = 8.83), 7.26 (d, 2H, Ar\\H, middle phenyl, J = 8.80), 7.14
(d, 1H, furan ring, J = 3.65), 7.04 (d, 1H, furan ring, J = 3.86), 7.00 (d,
13
2
2H, Ar\\H, Ph attached to methoxy, J = 8.90), 3.90 (3H, s, -OCH
NMR (75 MHz, CDCl , δ, ppm): 164.94 (aromatic C, C-OR), 164. 00
(C=O), 154.27 (C furan ring), 153.27 (C furan ring), 151.43 (aromatic
C, C-NO ), 149.72 (aromatic C, C\\O), 148.79 (aromatic C, C-N=CH),
3
);
C
to stir for an additional 5 h. A dark orange precipitate was formed, fil-
tered by a Buchner funnel and then washed several times with 5% aque-
ous sodium bicarbonate and distilled water. The crude solid product
was dried at room temperature and then purified by recrystallization
from absolute ethanol. Yield (65%), mp = (202–204 °C), (202–205 °C,
3
2
147.38 (CH=N), 135.31 (aromatic C, C-furan), 132.33 (aromatic C, C-
C=O), 125.03 (aromatic C\\H), 124.36 (aromatic C\\H), 122.59
(aromatic C\\H), 121.98 (aromatic C\\H), 121.71 (aromatic C\\H),
118.00 (aromatic, C\\H), 113.89 (C\\H furan ring), 111.05 (C\\H
−
1
lit. [29], (204–206 °C, lit. [30]; FTIR (ART, cm ), υmax: 3117 (C-
H
arom.), 2841 (C-Haldehydic), 1681 (C=Oaldehyde), 1601, 1520 (C=C),
1
1514, 1342 (NO2 asym. and sym.); H NMR (300 MHz, DMSO-d6, δ, ppm):
.58 (d, 1H, furan, J = 3.75), 7.71 (d, 1H, furan, J = 3.75), 8.12 (d, 2H,
3
furan ring), 55.54 (OCH ); (EI-MS) (relative intensity %) m/z = 442
+
+
7
(M , 15%), 135 (CH
3
O-Ph-C ≡ O , 100%, base peak).
arom., J = 8.80), 8.34 (d, 2H, arom., J = 8.80), 9.68 (s, 1H, aldehydic H).
2
.2.5. 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
2
.2.2. 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenol (B)
The titled compound was synthesized using the general Schiff base
b
ethoxybenzoate (C )
Yield (79%) as a yellowish solid; FTIR (ART, cm−1), υmax: 3078 (C-
procedure described in [31,32] with some adjustments. A mixture of
H
arom.), 2949, 2875 (C-Haliph.), 1714 (C=O), 1626 (C=N), 1602 (C=
2

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
1
C), 1516, 1327 (NO2sym. and asym.); H NMR (300 MHz, CDCl
3
, δ, ppm):
, J =
.98), 8.15 (d, 2H, Ar\\H, Ph attached to ethoxy, J = 8.87), 7.97 (d,
H, Ar\\H, Ph attached to –NO , J = 8.95), 7.33 (d, 2H, Ar\\H, middle
2.2.8. 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
8
8
2
.37 (s, 1H, CH_N), 8.30 (d, 2H, Ar\\H, Ph attached to –NO
2
e
(pentyloxy)benzoate (C )
−1
Yield (70%) as a yellowish solid; FTIR (ART, cm ), υmax: 3086 (C-
2
H
arom.), 2945, 2866 (C-Haliph.), 1726 (C=O), 1622 (C=N), 1597 (C=
1
phenyl, J = 8.86), 7.26 (d, 2H, Ar\\H, middle phenyl, J = 8.82), 7.14
d, 1H, furan ring, J = 3.66), 7.04 (d, 1H, furan ring, J = 3.64), 6.98 (d,
H, Ar\\H, Ph attached to ethoxy, J = 8.90), 4.10–4.17 (q. 2H, -OCH
C), 1512, 1327 (NO2sym. and asym.); H NMR (300 MHz, CDCl
3
, δ, ppm):
, J =
8.38), 8.15 (d, 2H, Ar\\H, Ph attached to pentyloxy, J = 8.34), 7.97 (d,
2H, Ar\\H, Ph attached to –NO , J = 8.39), 7.33 (d, 2H, Ar\\H, middle
(
8.37 (s, 1H, CH_N), 8.30 (d, 2H, Ar\\H, Ph attached to –NO
2
2
1
2
),
1
3
.44–1.49 (3H, t, -CH
3
); C NMR (75 MHz, CDCl
3
, δ, ppm): 166.74
2
(
aromatic C, C-OR), 163. 64 (C=O), 153.28 (C furan ring), 152.78 (C
furan ring), 151.07 (aromatic C, C-NO ), 149.76 (aromatic C, C\\O),
48.75 (aromatic C, C-N=CH), 147.37 (CH=N), 135.32 (aromatic C, C-
furan), 132.30 (aromatic C, C-C=O), 125.02 (aromatic C\\H), 124.88
aromatic C\\H), 122.60 (aromatic C\\H), 121.97 (aromatic C\\H),
21.42 (aromatic C\\H), 117.99 (aromatic, C\\H), 114.35 (C\\H furan
ring), 111.04 (C\\H furan ring), 59.52 (OCH ), 10.45 (OCH CH ); (EI-
CH O-Ph-
phenyl, J = 8.66), 7.26 (d, 2H, Ar\\H, middle phenyl, J = 8.35), 7.13
(d, 1H, furan ring, J = 3.41), 7.03 (d, 1H, furan ring, J = 3.48), 6.98 (d,
2H, Ar\\H, Ph attached to pentyloxy, J = 8.46), 4.03–4.07 (t, 2H,
2
1
-OCH
-OCH
δ, ppm): 164.99 (aromatic C, C-OR), 163. 63 (C=O), 154.25 (C furan
ring), 153.29 (C furan ring), 151.41 (aromatic C, C-NO ), 149.74
2
), 1.79–1.88 (m, 2H, -OCH
2 2
CH ), 1.37–1.50 (m, 4H,
); C NMR (75 MHz, CDCl ,
3 3
13
(
1
2
CH CH CH ), 0.93–0.97 (t, 3H, -CH
2
2
2
2
2
3
2
+
MS) (relative intensity %) m/z = 456 (M , 17%), 149 (CH
C ≡ O , 100%, base peak), 121 (HO-Ph-C ≡ O , 33%), 94 (Ph-OH , 7%).
3
2
+
(aromatic C, C\\O), 148.78 (aromatic C, C-N=CH), 147.36 (CH=N),
135.32 (aromatic C, C-furan), 132.30 (aromatic C, C-C=O), 125.02
+
+
(
1
aromatic C\\H), 124.36 (aromatic C\\H), 122.60 (aromatic C\\H),
21.97 (aromatic C\\H), 121.39 (aromatic C\\H), 117.96 (aromatic,
C\\H), 114.34 (C\\H furan ring), 111.06 (C\\H furan ring), 68.34
OCH ), 28.79 (OCH CH (CH CH ), 28.13, (OCH CH CH CH CH ),
2.46 (OCH (CH CH CH ) 14.00 (O(CH CH ); (EI-MS) (relative
intensity %) m/z = 498 (M , 16%), 191 (CH (CH CH O-ph-
2
.2.6. 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
propoxybenzoate (C
c
)
(
2
2
2
2
2
)
2
3
2
2
2
2
3
−1
Yield (74%) as a yellowish solid; FTIR (ART, cm ), υmax: 3075 (C-
2
2
)
2
2
3
2
)
4
3
H
arom.), 2968, 2893 (C-Haliph.), 1717 (C=O), 1626 (C=N), 1599 (C=C),
+
)
3
2
1
3
+
2
1516, 1329 (NO2sym. and asym.); H NMR (300 MHz, CDCl
3
, δ, ppm): 8.37
, J = 8.94), 8.15
d, 2H, Ar\\H, Ph attached to propoxy, J = 8.83), 7.96 (d, 2H, Ar\\H, Ph
attached to –NO , J = 8.89), 7.33 (d, 2H, Ar\\H, middle phenyl, J =
.78), 7.26 (d, 2H, Ar\\H, middle phenyl, J = 8.75), 7.14 (d, 1H, furan
ring, J = 3.60), 7.03 (d, 1H, furan ring, J = 3.59), 6.99 (d, 2H, Ar\\H, Ph at-
tached to propoxy, J = 8.88), 3.99–4.04 (t, 2H, -OCH ), 1.80–1.89 (m, 2H,
); C NMR (75 MHz, CDCl , δ, ppm):
66.78 (aromatic C, C-OR), 163. 84 (C=O), 153.32 (C furan ring), 152.97
C furan ring), 151.13 (aromatic C, C-NO ), 149.88 (aromatic C, C\\O),
48.69 (aromatic C, C-N=CH), 147.68 (CH=N), 135.29 (aromatic C, C-
furan), 132.35 (aromatic C, C-C=O), 125.06 (aromatic C\\H), 124.91
aromatic C\\H), 122.75 (aromatic C\\H), 122.01 (aromatic C\\H),
21.65 (aromatic C\\H), 118.04 (aromatic, C\\H), 114.47 (C\\H furan
ring), 111.08 (C\\H furan ring), 57.52 (OCH ), 22.45 (OCH CH CH ),
0.45 (OCH CH CH ); (EI-MS) (relative intensity %) m/z = 470
, 16%), 163 (CH
+
C ≡ O , 100%, base peak), 121 (HO-Ph-C ≡ O , 34%), 94 (Ph-
OH , 2%).
(s, 1H, CH_N), 8.29 (d, 2H, Ar\\H, Ph attached to –NO
2
+
(
2
2
.2.9. 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
8
(
hexyloxy)benzoate (C
Yield (81%) as a yellowish solid; FTIR (ART, cm ), υmax: 3059 (C-
f
)
−1
2
H
arom.), 2976, 2885 (C-Haliph.), 1716 (C=O), 1629 (C=N), 1595 (C=
13
-OCH
2
CH
2
), 1.04–1.09 (t, 3H, -CH
3
3
1
C), 1514, 1323 (NO2sym. and asym.); H NMR (300 MHz, CDCl
3
, δ, ppm):
, J =
.88), 8.15 (d, 2H, Ar\\H, Ph attached to hexyloxy, J = 8.84), 7.97 (d,
H, Ar\\H, Ph attached to –NO , J = 8.90), 7.33 (d, 2H, Ar\\H, middle
1
(
1
8
8
2
.37 (s, 1H, CH_N), 8.30 (d, 2H, Ar\\H, Ph attached to –NO
2
2
2
phenyl, J = 8.74), 7.26 (d, 2H, Ar\\H, middle phenyl, J = 8.74), 7.14
d, 1H, furan ring, J = 3.66), 7.04 (d, 1H, furan ring, J = 3.60), 6.98 (d,
H, Ar\\H, Ph attached to hexyloxy, J = 8.88), 4.03–4.07 (t, 2H,
OCH ), 1.78–1.87 (m, 2H, -OCH CH ), 1.25–1.36 (m, 6H, -OCH CH
); C NMR (75 MHz, CDCl , δ, ppm):
64.98 (aromatic C, C-OR), 163. 63 (C=O), 154.23 (C furan ring),
51.40 (C furan ring), 149.73 (aromatic C, C-NO ), 148.77 (aromatic C,
(
1
(
2
2
2
2
3
-
(
2
2
1
2
2
2
1
2
2
3
3
CH
2
)
3
), 0.85–0.89 (t, 3H, -CH
3
3
+
+
(
(
M
3
CH
2 2
CH O-ph-C ≡ O , 100%, base peak), 121
1
1
+
+
HO-Ph-C ≡ O , 50%), 94 (Ph-OH , 4%).
2
C\\O), 147.39 (aromatic C, C-N=CH), 147.20 (CH=N), 135.32
(aromatic C, C-furan), 132.31 (aromatic C, C-C=O), 125.03 (aromatic
C\\H), 124.37 (aromatic C\\H), 122.61 (aromatic C\\H), 121.98
(aromatic C\\H), 121.37 (aromatic C\\H), 118.04 (aromatic, C\\H),
2
.2.7. 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
d
butoxybenzoate (C )
Yield (74%) as a yellowish solid; FTIR (ART, cm−1), υmax: 3070 (C-
H
arom.), 2935, 2880 (C-Haliph.), 1728 (C=O), 1622 (C=N), 1599 (C=
114.34 (C\\H furan ring), 111.07 (C\\H furan ring), 68.36 (OCH
2
3
3
),
),
),
1
C), 1516, 1330 (NO2sym. and asym.); H NMR (300 MHz, CDCl
3
, δ, ppm):
, J =
.93), 8.15 (d, 2H, Ar\\H, Ph attached to butoxy, J = 8.83), 7.96 (d,
H, Ar\\H, Ph attached to –NO , J = 8.96), 7.33 (d, 2H, Ar\\H, middle
31.55 (OCH
25.66 (OCH (CH
14.03 (O(CH CH
(M , 20%), 205 (CH
2
CH
2
(CH
2
)
3
CH
3
), 29.06, (OCH
), 22.59 (OCH
2
CH
(CH
2
CH
2
(CH
2
)
2
CH
CH
8
8
2
.37 (s, 1H, CH_N), 8.29 (d, 2H, Ar\\H, Ph attached to –NO
2
2
2
)
2
CH
2
CH CH
2
3
2
2
)
2
CH CH
2
2
2
)
5
3
); (EI-MS) (relative intensity %) m/z = 512
+
+
2
3
(CH
2
)
4
CH
2
O-ph-C ≡ O , 100%, base peak), 121
+
phenyl, J = 8.84), 7.25 (d, 2H, Ar\\H, middle phenyl, J = 8.81), 7.13
d, 1H, furan ring, J = 3.64), 7.03 (d, 1H, furan ring, J = 3.63), 6.98 (d,
(HO-Ph-C ≡ O , 6%).
(
2
1
0
H, Ar\\H, Ph attached to butoxy, J = 8.90), 4.03–4.08 (t, 2H, -OCH
.77–1.86 (m, 2H, -OCH CH ), 1.46–1.58 (m, 2H, -OCH CH CH
); C NMR (75 MHz, CDCl
2
),
),
2.2.10. 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
2
2
2
2
2
g
(heptyloxy)benzoate (C )
1
3
Yield (73%) as a yellowish solid; FTIR (ART, cm−1), υmax: 3068 (C-
.97–1.02 (t, 3H, -CH
3
3
, δ, ppm): 164.99
(
aromatic C, C-OR), 163. 64 (C=O), 154.26 (C furan ring), 153.28 (C
furan ring), 151.41 (aromatic C, C-NO ), 149.74 (aromatic C, C\\O),
48.76 (aromatic C, C-N=CH), 147.36 (CH=N), 135.31 (aromatic C, C-
furan), 132.30 (aromatic C, C-C=O), 125.58 (aromatic C\\H), 124.35
aromatic C\\H), 122.59 (aromatic C\\H), 121.97 (aromatic C\\H),
21.40 (aromatic C\\H), 117.98 (aromatic, C\\H), 114.34 (C\\H
furan ring), 111.06 (C\\H furan ring), 68.03 (OCH ), 31.13,
) 13.31 (O(CH CH );
(CH
O-ph-C ≡ O , 100%, base peak), 121 (HO-Ph-C ≡ O , 62%), 94
H
arom.), 2945, 2848 (C-Haliph.), 1714 (C=O), 1624 (C=N), 1593 (C=
1
2
C), 1510, 1321 (NO2sym. and asym.); H NMR (300 MHz, CDCl
3
, δ, ppm):
, J =
8.91), 8.15 (d, 2H, Ar\\H, Ph attached to heptyloxy, J = 8.81), 7.97 (d,
2H, Ar\\H, Ph attached to –NO , J = 8.92), 7.33 (d, 2H, Ar\\H, middle
1
8.36 (s, 1H, CH_N), 8.30 (d, 2H, Ar\\H, Ph attached to –NO
2
(
1
2
phenyl, J = 8.74), 7.26 (d, 2H, Ar\\H, middle phenyl, J = 8.75), 7.14
(d, 1H, furan ring, J = 3.64), 7.04 (d, 1H, furan ring, J = 3.59), 6.98 (d,
2H, Ar\\H, Ph attached to heptyloxy, J = 8.85), 4.02–4.07 (t, 2H,
-OCH
(CH
165.02 (aromatic C, C-OR), 163. 64 (C=O), 154.26 (C furan ring),
2
(
(
OCH
2
CH
2
CH
2
CH
3
), 19.19 (OCH
2
CH
2
CH
2
CH
3
+
2
)
3
3
EI-MS) (relative intensity %) m/z = 484 (M , 18%), 177 (CH
3
2
)
2
), 1.78–1.85 (m, 2H, -OCH
2
CH
2
), 1.25–1.48 (m, 8H, O(CH
2 2
)
+
+
13
2
CH
Ph-OH , 6%).
2
2
)
4
), 0.86–0.90 (t, 3H, -CH
3
); C NMR (75 MHz, CDCl , δ, ppm):
3
+
(
3

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
1
51.39 (C furan ring), 149.73 (aromatic C, C-NO
C\\O), 147.38 (aromatic C, C-N=CH), 147.19 (CH=N), 135.31
aromatic C, C-furan), 132.31 (aromatic C, C-C=O), 125.03 (aromatic
C\\H), 124.37 (aromatic C\\H), 122.61 (aromatic C\\H), 121.98
aromatic C\\H), 121.35 (aromatic C\\H), 118.03 (aromatic, C\\H),
2
), 148.76 (aromatic C,
2.2.13. 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
j
(decyloxy)benzoate (C )
−1
(
Yield (84%) as a yellowish solid; FTIR (ART, cm ), υmax: 3059 (C-
H
arom.), 2928, 2852 (C-Haliph.), 1732 (C=O), 1622 (C=N), 1599 (C=
1
(
C), 1514, 1325 (NO2sym. and asym.); H NMR (300 MHz, CDCl
3
, δ, ppm):
, J =
8.98), 8.17 (d, 2H, Ar\\H, Ph attached to decyloxy, J = 8.86), 7.99 (d,
2H, Ar\\H, Ph attached to –NO , J = 8.96), 7.35 (d, 2H, Ar\\H, middle
1
3
14.34 (C\\H furan ring), 111.07 (C\\H furan ring), 68.36 (OCH
1.76 (OCH CH (CH CH ), 29.10, (OCH CH CH (CH CH ), 29.03
CH CH CH ), 25.95 (OCH (CH CH CH CH CH ), 22.61
CH CH CH CH ) 14.09 (O(CH CH ); (EI-MS) (relative
(CH
2
),
8.39 (s, 1H, CH_N), 8.32 (d, 2H, Ar\\H, Ph attached to –NO
2
2
2
2
)
4
3
2
2
2
2
)
3
3
(
(
OCH
OCH
2
(CH
(CH
2
)
3
2
2
3
2
2
)
2
2
2
2
3
2
2
2
)
2
2
2
2
3
+
2
)
6
3
phenyl, J = 8.81), 7.28 (d, 2H, Ar\\H, middle phenyl, J = 8.80), 7.16
(d, 1H, furan ring, J = 3.66), 7.04 (d, 1H, furan ring, J = 3.62), 7.00 (d,
2H, Ar\\H, Ph attached to decyloxy, J = 8.89), 4.04–4.09 (t, 2H,
+
intensity %) m/z = 526 (M , 18%), 219 (CH
3
2 5 2
) CH O-ph-C ≡ O ,
100%, base peak).
-
(
OCH
CH
165.02 (aromatic C, C-OR), 163. 63 (C=O), 156.26 (C furan ring),
153.26 (C furan ring), 151.40 (aromatic C, C-NO ), 149.74
2 2 2 2 2
), 1.80–1.87 (m, 2H, -OCH CH ), 1.30–1.49 (m, 14H, -O(CH )
) ), 0.89–0.93 (t, 3H, -CH ); C NMR (75 MHz, CDCl , δ, ppm):
2 7 3 3
1
3
2
.2.11. 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
(
octyloxy)benzoate (C
Yield (84%) as a yellowish solid; FTIR (ART, cm ), υmax: 3070 (C-
h
)
2
−1
(aromatic C, C\\O), 148.77 (aromatic C, C-N=CH), 147.38 (CH=
N), 135.32 (aromatic C, C-furan), 132.30 (aromatic C, C-C=O),
125.03 (aromatic C\\H), 124.37 (aromatic C\\H), 122.61 (aromatic
C\\H), 121.98 (aromatic C\\H), 121.36 (aromatic C\\H), 118.03
(aromatic, C\\H), 114.34 (C\\H furan ring), 111.07 (C\\H furan
H
arom.), 2939, 2843 (C-Haliph.), 1726 (C=O), 1626 (C=N), 1601 (C=
1
C), 1518, 1332 (NO2sym. and asym.); H NMR (300 MHz, CDCl
3
, δ, ppm):
, J =
.94), 8.15 (d, 2H, Ar\\H, Ph attached to octyloxy, J = 8.83), 7.96 (d,
H, Ar\\H, Ph attached to –NO , J = 8.93), 7.33 (d, 2H, Ar\\H, middle
8
8
2
.36 (s, 1H, CH_N), 8.29 (d, 2H, Ar\\H, Ph attached to –NO
2
2
ring), 68.36 (OCH
(OCH CH CH (CH CH
29.32 (OCH (CH CH (CH
), 27.25 (OCH (CH
CH CH ) 22.68 (OCH
2
), 31.90 (OCH
), 29.36 (OCH
CH ), 29.10 (OCH
2
CH
2
(CH
2
)
7
CH
CH (CH
CH
), 25.99 (OCH
) 14.12 (O(CH
3
), 29.55,
phenyl, J = 8.78), 7.25 (d, 2H, Ar\\H, middle phenyl, J = 8.81), 7.13
d, 1H, furan ring, J = 3.65), 7.04 (d, 1H, furan ring, J = 3.62), 6.98 (d,
H, Ar\\H, Ph attached to octyloxy, J = 8.87), 4.02–4.07 (t, 2H,
OCH ), 1.78–1.87 (m, 2H, -OCH CH ), 1.30–1.48 (m, 10H, -O(CH
2
2
2
2
)
6
3
2
(CH
2
)
2
2
2
)
5
CH ),
3
(
2
-
2
2
)
3
2
2
)
4
3
2
(CH
2
)
4
2
(CH
(CH
2
)
)
3
6
CH
CH
3
2
2
2
)
5
CH
(CH
2
(CH
2
)
2
CH
CH
3
2
2
2
2
2
2
)
2
2
3
2
2
)
7
CH
2
3
2
)
9
CH
3
);
1
3
+
(
1
1
CH
2
)
5
), 0.87–0.92 (t, 3H, -CH
65.01 (aromatic C, C-OR), 163. 64 (C=O), 154.25 (C furan ring),
53.26 (C furan ring), 151.39 (aromatic C, C-NO ), 149.73 (aromatic C,
3
); C NMR (75 MHz, CDCl
3
, δ, ppm):
(EI-MS) (relative intensity %) m/z
=
568 (M
,
10%), 43
+
3 2 3
(CH CH CH , 100%, base peak).
2
C\\O), 148.76 (aromatic C, C-N=CH), 147.38 (CH=N), 135.31
aromatic C, C-furan), 132.30 (aromatic C, C-C=O), 125.03 (aromatic
C\\H), 124.37 (aromatic C\\H), 122.61 (aromatic C\\H), 121.99
aromatic C\\H), 121.36 (aromatic C\\H), 118.05 (aromatic, C\\H),
2.2.14. 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
(dodecyloxy)benzoate (C
(
k
)
−1
Yield (85%) as a yellowish solid; FTIR (ART, cm ), υmax: 3074 (C-
(
H
arom.), 2970, 2848 (C-Haliph.), 1726 (C=O), 1601 (C=N), 1579 (C=
1
1
3
14.34 (C\\H furan ring), 111.08 (C\\H furan ring), 68.36 (OCH
1.80 (OCH CH (CH CH ), 29.33, (OCH CH CH (CH CH ), 29.22
(CH CH (CH CH ), 29.10 (OCH (CH CH CH CH CH ),
5.99 (OCH (CH CH CH CH ) 22.66 (OCH (CH CH CH ) 14.11 (O
CH ); (EI-MS) (relative intensity %) m/z = 540 (M , 100%, base
peak), 121 (HO-Ph-C ≡ O , 5%).
2
),
C), 1508, 1334 (NO2sym. and asym.); H NMR (300 MHz, CDCl
3
, δ, ppm):
, J =
8.95), 8.15 (d, 2H, Ar\\H, Ph attached to dodecyloxy, J = 8.84), 7.96
(d, 2H, Ar\\H, Ph attached to –NO , J = 8.94), 7.33 (d, 2H, Ar\\H, middle
2
2
2
)
5
3
2
2
2
2
)
4
3
8.37 (s, 1H, CH_N), 8.29 (d, 2H, Ar\\H, Ph attached to –NO
2
(
OCH
2
2
)
2
2
2
)
3
3
2
2
)
3
2
2
2
3
2
2
)
2 4
2
2
3
2
)
2 5
2
3
2
+
(
CH
)
2 7
3
phenyl, J = 8.81), 7.25 (d, 2H, Ar\\H, middle phenyl, J = 8.80), 7.14 (d,
1H, furan ring, J = 3.66), 7.04 (d, 1H, furan ring, J = 3.61), 6.98 (d, 2H,
+
Ar\\H, Ph attached to dodecyloxy, J = 8.89), 4.02–4.07 (t, 2H, -OCH
.78–1.87 (m, 2H, OCH CH ), 1.27–1.47 (m, 18H, -O(CH (CH
, δ, ppm): 165.02
(aromatic C, C-OR), 163. 63 (C=O), 156.25 (C furan ring), 153.26 (C
furan ring), 151.39 (aromatic C, C-NO ), 149.74 (aromatic C, C\\O),
2
),
),
1
2
2
2
)
2
2 9
)
1
3
2
.2.12. 4-[((5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
3 3
0.86–0.90 (t, 3H, -CH ); C NMR (75 MHz, CDCl
(
nonyloxy)benzoate (C
i
)
−1
Yield (82%) as a yellowish solid; FTIR (ART, cm ), υmax: 3038 (C-
2
H
arom.), 2945, 2864 (C-Haliph.), 1735 (C=O), 1624 (C=N), 1601 (C=
148.76 (aromatic C, C-N=CH), 147.37 (CH=N), 135.31 (aromatic C, C-
furan), 132.30 (aromatic C, C-C=O), 125.03 (aromatic C\\H), 124.37
(aromatic C\\H), 122.61 (aromatic C\\H), 121.98 (aromatic C\\H),
121.36 (aromatic C\\H), 118.04 (aromatic, C\\H), 114.34 (C\\H furan
1
C), 1514, 1327 (NO2sym. and asym.); H NMR (300 MHz, CDCl
3
, δ, ppm):
, J =
.85), 8.15 (d, 2H, Ar\\H, Ph attached to nonyloxy, J = 8.74), 7.97 (d,
H, Ar\\H, Ph attached to –NO , J = 8.87), 7.33 (d, 2H, Ar\\H, middle
8
8
2
.37 (s, 1H, CH_N), 8.30 (d, 2H, Ar\\H, Ph attached to –NO
2
2
ring), 111.07 (C\\H furan ring), 68.36 (OCH
2
), 31.92 (OCH
), 29.64 (OCH (CH
CH ), 29.56 (OCH
(CH CH ), 29.22 (OCH
(CH CH ), 25.99 (OCH
CH ) 14.13 (O(CH 11CH
CH
2
CH
2
2
2
(CH
2
)
)
phenyl, J = 8.76), 7.26 (d, 2H, Ar\\H, middle phenyl, J = 8.70), 7.14
d, 1H, furan ring, J = 3.64), 7.04 (d, 1H, furan ring, J = 3.59), 6.98 (d,
H, Ar\\H, Ph attached to nonyloxy, J = 8.80), 4.02–4.07 (t, 2H,
OCH ), 1.78–1.85 (m, 2H, -OCH CH ), 1.29–1.48 (m, 12H, -O(CH
9
CH
CH
3
), 29.66, (OCH
2
CH
(CH
), 29.36 (OCH
CH ), 29.10 (OCH
CH ) 22.70 (OCH
2
CH
2
(CH
CH
(CH
2
)
8
CH
3
2
2
)
2
CH
(CH
2
(
2
-
7
3
2
2
), 29.59 (OCH
2
2
)
3
2
(CH
2
)
6
3
2
(CH
)
4
CH
2
(CH
CH
(CH
)
5
CH
(CH
CH
3
2
2
)
5
CH
2
2
)
4
3
2
(CH
2
)
2
2
2
2
)
2
6
2
)
3
3
2
(CH
(CH
2
)
7
CH
CH
2
2
)
2
3
2
1
3
(
1
1
CH
2
)
6
), 0.86–0.91 (t, 3H, -CH
65.00 (aromatic C, C-OR), 163. 64 (C=O), 154.27 (C furan ring),
53.26 (C furan ring), 151.40 (aromatic C, C-NO ), 149.74 (aromatic C,
3
); C NMR (75 MHz, CDCl
3
, δ, ppm):
2
)
8
2
CH
2
3
2
2
)
9
2
+
3
2
)
3
);
+
(EI-MS) (relative intensity %) m/z = 597 (M , 9%), 61 (CH
3
2
CH
2
CH
3
,
2
18%).
C\\O), 148.76 (aromatic C, C-N=CH), 147.38 (CH=N), 135.31
aromatic C, C-furan), 132.30 (aromatic C, C-C=O), 125.03 (aromatic
C\\H), 124.37 (aromatic C\\H), 122.61 (aromatic C\\H), 121.98
aromatic C\\H), 121.36 (aromatic C\\H), 118.04 (aromatic, C\\H),
(
3. Results and discussion
3.1. Synthesis
(
1
3
14.34 (C\\H furan ring), 111.07 (C\\H furan ring), 68.36 (OCH
1.87 (OCH CH (CH CH ), 29.52, (OCH CH CH (CH CH ), 29.37
(CH CH (CH CH ), 29.25 (OCH (CH CH (CH CH ),
9.10 (OCH (CH CH (CH CH ), 25.98 (OCH (CH CH CH CH
2.67 (OCH (CH CH CH ) 14.12 (O(CH CH ); (EI-MS) (relative in-
(CH
2
),
2
2
2
)
6
3
2
2
2
2
)
5
3
The target of this project includes a synthesis of eleven esters bear-
ing furan ring at the core section conjugated with imine, ester, and phe-
nyl moieties. The synthetic routs, as well as the reaction reagents of the
titled compounds (A, B and Ca-k) are outlined in Scheme 1.
The synthesis strategy was started with the preparation of 5-(4-
nitrophenyl)furan-2-carbaldehyde (A) by a previously reported
(
OCH
2
2
)
2
2
2
)
4
3
2
2
)
3
2
2
)
3
3
2
2
2
2
)
4
2
2
)
2
3
2
2
)
5
2
2
3
)
2
2
)
6
2
3
+
2
)
8
3
+
tensity %) m/z = 554 (M , 12%), 247 (CH
3
2
)
7
CH
2
O-ph-C ≡ O ,
+
3 2 3
100%, base peak), 43 (CH CH CH , 32%).
4

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
Scheme 1. The synthetic route and reagents used in the synthesis of compounds (A, B and Ca-k), (i) hydrochloric acid (36.5%), distilled water, sodium nitrite, cupric chloride dihydrate; (ii)
glacial acetic acid, absolute ethanol; (iii) N,N-dicyclohexylcarbodiimide (DCC), 4-(dimethylamino)pyridine (DMAP), dry dichloromethane (DCM), stirring at room temperature around
25 °C for (7 days).
1
procedure [29]; the spectral analyses (FTIR, H NMR) and the melting
point of the aldehyde (A) confirmed its chemical structure. The equimo-
lar quantities of the resulted aldehyde (A) and 4-aminophenol reacted
in the presence of glacial acetic acid to produce furan conjugated
imine phenol (B) in a good yield. The chemical structure of the phenolic
precursor (B) was characterized through spectral methods, such as FTIR,
with the chemical structures of these compounds (see experimental
part). These results provided additional evidence concerning the forma-
tion of the target ester compounds. On the other hand, 13C NMR spectra
of the synthesized esters indicated that the esterification reaction had
taken place through clear signals that appeared approximately
165 ppm in spectra assigned to the carbon in the ester linkage. Fig. 1
1
13
1
H NMR, C NMR, and MS techniques. The most important stretching
vibration band of the imine was noticed at (1620 cm ) and a
broad phenolic hydroxyl band between 2520 and 3120 cm . More-
over, the proton NMR analysis showed the imine proton as a singlet
at 8.51 ppm in addition to the proton of hydroxyl in the phenolic
group as a singlet signal at 9.58 ppm. Two doublets were assigned
shows the H NMR spectra of the compounds (B) and (C
h
). The repre-
−
1
13
sentative spectra of mass and C NMR for C
g
and C
e
compounds respec-
−
1
tively are displayed in Fig. 2.
3.2. Mesomorphic properties
to the two protons of furan (H
3
and H
4
), which were observed at
All the synthesized homologue compounds in this series (Ca-k)
1
(
7.25–7.26 ppm) and (7.51–7.52 ppm) in the H NMR spectrum of
displayed liquid crystalline behaviors. The majority of these compounds
(Ca-c and Cg-k) exhibited the mesomorphic properties during the
heating-cooling cycle (enantiotropic mesogens), while some com-
pounds in the middle of the chain (Cd-f) were mesogens in the cooling
cycle only (monotropic mesogens). The textures of these mesogens
have been recorded by a polarizing optical microscope (POM) equipped
with a thermal stage. The mesogenic phases were characterized by
matching the recorded phases with those previously published in the
literature [36,37]. Moreover, the phase transition temperatures and
the enthalpy changes were obtained by using a differential scanning cal-
orimetry (DSC) technique. The mesophase transition temperatures and
the mesogenic ranges resulted from (POM), and some thermodynamic
parameters (enthalpy kJ/mol and entropy J/mol.k changes) resulted
from (DSC) measurements and are compiled in Table 1.
1
3
the imine-phenol (B). The C NMR and MS analysis results were in
accordance with the usual values and corroborated the suggested
chemical structure of the imine-phenol (B). The overall characteriza-
tion results obtained concluded the formation and the chemical
structure of the imine-phenol intermediate (B).
The target esters in this work were obtained by esterification of
eleven 4-alkoxy benzoic acids (X
cient coupling reagent (DCC, DMAP) with stirring at room temperature
for one week. The 4-alkoxybenzoic acids (X ) were formerly prepared
by a known reported method [35]. Different identification methodolo-
n
) with imine phenol (B) using an effi-
n
1
13
gies, such as FTIR, H NMR, C NMR and EI-MS, were used to character-
ize the chemical structure of the synthesized esters (Ca-k). A sharp
stretching vibration band for carbonyl ester groups of these compounds
−1
was observed in the FTIR spectra at 1714 to 1735 cm . This observation
was associated with the disappearance of the phenolic hydroxyl
stretching band in compound (B). In addition, a characteristic aliphatic
stretching vibration of the methylene and methyl alkyl groups in alkoxy
3.2.1. POM observations
Most of the eleven mesogens in this series (Ca-k) displayed a nematic
phase under (POM) in both heating and cooling cycles. The exception is
three members (Cd-f), which exhibited the nematogenic behavior in the
1
fragment appeared at the usual position. The H NMR spectra of the syn-
thesized esters demonstrated a clear singlet signal of the imine proton
cooling cycle only. The last member in this series (C ) showed
k
moiety between 8.36–8.39 ppm and two doublet signals for the two
smectogenic behavior (SmA), in addition to the nematic phase, upon
protons of the furan ring (H
3
and H
4
) at about (7.13–7.14 ppm) and
heating and cooling tests. The characterization of a liquid crystalline tex-
ture type was based on the mesophase type classified by Sackmann [38]
and Gray [39]. Heating the sample from room temperature to the isotro-
pic phase and cooling it to the crystal phase with continuous monitoring
by POM resulted in different textures of the nematic phase in the homo-
logues in this series: nematic droplets, thread-like associated with
nematic phase, marble and Schlieren. These textures are usually
(
7.03–7.04 ppm). The electronic spectra of the new esters showed an
additional two doublets assigned to four aromatic protons of the new
phenyl, which resulted from the reaction of 4-alkoxy benzoic acids
and appeared at the usual aromatic area. The mass spectrometry analy-
sis of the esters showed the formation of the important fragment ions
+
and molecular ion peaks (M ), which were exactly in accordance
5

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
Fig. 1. 1H NMR spectra for compounds B (top) and C
(down).
h
6

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
g e
Fig. 2. Mass spectrum for compound C (down).
(top) and 13C NMR spectrum for compound C
observed in the nematic phase. Additionally, the fan-shaped texture of
the smectic A in the last member of this series (C ) was very clear in
both heating and cooling scans of this compound. The smectogenic ap-
pearance in the last homologue of this series is due to an increase in the
number of carbon atoms in the alkyl chain of this compound (n = 12)
3.2.2. DSC results
k
The transitions that appeared in the DSC curves of all mesogens in
this series were measured during heating and cooling cycles between
room temperatures and 200 °C, 180 °C, and 160 °C for (Ca-c), (Cd-f
)
)
and (Cg-k), respectively. The first three members in this series (Ca-c
[
40]. Fig. 3 presents selective photomicrographs of different types of
showed two endothermic peaks in the heating process assigned to the
crystal (Cr)-to-nematic (N) and (N)-to-isotropic transitions (I), while
only one exothermic transition appeared clearly in the cooling curves
of the mentioned compounds, which corresponded to the (N)-to-(Cr)
transition. Conversely, the DSC thermograms of the second three
mesogens (Cd-f) showed only one transition in the heating cycle,
the nematic phase in the compounds of this series. On the other hand,
Fig. 4 has shown the optical images of the transitions between two me-
somorphic phases (nematic and smectic A) by heating from room tem-
perature to the isotropic point and then cooling to the crystal phase for
k
the mesogen (C ).
7

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
Table 1
Transition temperatures °C, enthalpies ΔH (KJ/mol), entropies ΔS [J/mol.K] and mesomorphic range °C for compounds of the series Ca-k in first heating and cooling cycles.
Entry
R = OC
n)
n
H
2n+1
Phase sequence
Heating
Mesomorphic range [N], (SmA)
(
Cooling
heating
[43.15]
[37.55]
[45.75]
–
cooling
[56.85]
[101.80]
[96.00]
[79.30]
[48.70]
[44.05]
[79.65]
[84.75]
Cr-N 140.45 (2.51) [6.07]
N-Iso 183.60 (27.44) [60.10]
Cr-N 145.75 (5.74) [13.71]
N-Iso 183.30 (33.79) [74.05]
Cr-N 130.00 (1.66) [4.11]
N-Iso 175.75 (43.12) [96.15]
Iso-N 187.00a
N \\ Cr 130.15 (−25.77) [−63.91]
Iso-N 197.00
N \\ Cr 95.20 (−23.26) [−63.17]
Iso-N 185.00
N \\ Cr 89.00 (−28.07) [−77.54]
Iso-N 180.00
N \\ Cr 100.70 (−21.84) [−58.43]
Iso-N 165.00
N \\ Cr 116.30 (−22.97) [−59.01]
Iso-N 156.00
N \\ Cr 111.95 (−33.65) [−87.42]
Iso-N 154.00
N \\ Cr 74.35 (−23.51) [−67.68]
Iso-N 155.00
N \\ Cr 70.25 (−22.45) [−65.41]
C
C
C
C
C
C
C
C
a
b
c
1
2
3
4
5
6
7
8
a
a
a
d
e
f
Cr-Iso 159.45 (25.84) [59.76]
Cr-Iso 151.00 (26.25) [61.92]
a
–
a
Cr-Iso 147.90 (37.53) [89.18]
Cr-N 123.30 (24.90) [62.82]
–
a
g
h
a
[31.70]
[40.40]
N-Iso 155.00
a
Cr-N 116.60 (28.88) [74.14]
a
N-Iso 157.00
Cr-Cr
1
101.75 (1.18) [3.15]
109.60 (10.67) [27.88]
\\ N 117.30 (20.53) [52.61]
Cr
1
-Cr
2
Iso-N 149.00a
N \\ Cr 81.50 (−27.41) [−77.32]
1
C
i
9
[32.70]
[23.55]
[67.50]
[47.05]
Cr
2
a
N-Iso 150.00
Iso-N 148.00a
N \\ Cr 100.95 (−29.22) [−78.13]
\\ Cr 72.85 (−5.79) [−16.74]
Cr-Cr
N-Iso 150.00
1 1
+ Cr -N 126.45 (36.97) [92.55]
C
C
j
10
12
a
1
Cr
1
a
Cr-SmA 111.90 (35.81) [93.03]
SmA-N 135.00
N-Iso 141.00
Iso-N 139.00
a
a
(23.10)
[6.00]
(61.65)
[4.00]
k
N-SmA 135.00
SmA-Cr 73.35 (−21.86) [−63.11]
a
1
Cr and Cr = crystal phases; N = nematic phase; SmA = smectic A phase; Iso = isotropic liquid phase; (a) the transition were observed under POM.
which can be attributed to the direct isotropization transition, (Cr) to
I), where these compounds turned directly to their isotropic points
those in the heating scan. This behavior may be due to the supercooling
phenomenon in the exothermic process, which needs less energy than
the endothermic process [41]. The resulting transition temperatures to
turn the mesogenic materials to their isotropic points (shown in
Table 1) were influenced by the number of carbon atoms in the alkoxy
terminal chain on the transition between crystal-liquid crystalline
phases. This factor plays a very important role in the nature and thermal
stability range of the mesomorphic phase upon heating and cooling cy-
(
without showing any liquid crystalline properties in the heating scan,
as revealed and confirmed by POM results. Upon cooling the melts of
these mesogens by decreasing the temperatures at a rate of 5 degrees
per min., nematic droplets began to form and then converged to form
the Schlieren and thread-like templates, which are clear characteristics
of the nematic mesophase. On further cooling, the nematic phase faded
and transformed to the Cr phase at 100.70 °C, 116.30 °C and 111.95 °C
cles. For example, the compound (C
k
), which has the longest alkoxy
for the compounds C
, C
d e
f
and C , respectively. They appeared as exother-
chain (R = OC12 25, n = 12) starts to exhibit a smectic phase from
H
mic peaks in the DSC traces of the compounds. The appearance of liquid
crystal properties only in the cooling scan characterizes these com-
pounds as monotropic mesogens. The DSC thermographs of the other
mesogens in this series (Cg-j) showed a Cr-to-N endothermic transition
the nematic mesophase; this behavior is attributed to increases in the
Van der Waals interaction forces between the methylene groups [42].
From the literature [43], the Van der Waals forces between the mole-
cules are one of the intermolecular interactions that affect the packing
of the molecules; these forces increases by increasing the number of
methylene groups in the alkyl chain. The gathering of molecules in lay-
ered form is one of the important and required conditions that must be
contained in the molecules in order to exhibit the smectogenic charac-
ter. The physical interactions between the molecules, in addition to
other factors, such as polarity and polarizability, and the effect of the
molecule constitutions contributed to increasing the congregation of
these molecules as layers. Conversely, the dipole-dipole interactions in
the nitro group are greater than the sum of the van der Waals forces
present in the alkyl groups in the molecules. In the case of the com-
upon heating at 123.30 °C, 116.60 °C, 117.30 °C, and 126.45 °C for C
, and C , respectively. Additionally, the N-to-Cr transitions of these
compounds during the cooling process appeared at 74.35 °C, 70.25 °C,
1.50 °C, and 100.95 °C, respectively. Furthermore, the C and C
j
g h
, C ,
C
i
j
8
i
mesogens showed additional endothermic and exothermic peaks,
which can be attributed to the Cr-to-Cr transitions. The last homologue
member in this series (C
scan and one exothermic transition in the cooling scan at 111.9 °C and
3.35 °C, respectively. They have been attributed to the transition
k
) showed one endothermic peak in the heating
7
from the crystal (Cr)-to-Smectic A (SmA) phase in the heating process
and to the opposite transition in the cooling process. This compound
showed other phase transitions in the (POM) observations, (SmA-N in
the heating phase and N-SmA during the cooling phase), but they
could not be detected by the DSC thermogram of this mesogen. This
phenomenon might be due to the narrow temperature range of these
transitions in heating and cooling processes. The DSC thermographs of
selected compounds in this series are shown in Fig. 5.
k
pound C (n = 12), the van der Waals forces in this compound managed
to partially overcome the dipole-dipole interactions in the nitro group in
addition to the effects of imine and furan moieties. For these reasons,
k
only the compound C has shown a smectic A phase among all the com-
pounds in series Ca-k
.
Furthermore, it was found that the transformation temperatures
from the liquid crystal phase or crystal phase to the isotropic points
for the series mesogens began to decrease smoothly, with increases in
the length of the alkyl group in the alkoxy chain and a minor exception
in some homologues (Table 1). The presented phase diagram in Fig. 6
shows an increase in the curve of the transitions (isotropic-to-
mesophase and mesophase-to-crystal), and then it goes down and up
3
.2.3. Chemical structure effect on the liquid crystal properties of the syn-
thesized mesogens (Ca-k
)
The Thermo-optical results in Table 1 (exhibiting the mesophase
ranges calculated by DSC traces in the cooling cycle) are higher than
8

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
d
Fig. 3. Selected liquid crystalline images for compounds in series Ca-k (a) Schlieren texture of nematic phase for compound (C ) at 177 °C in first cooling scan, (b) thread-like texture
associated with the nematic phase for compound (C
second cooling at 131 °C, (d) Schlieren texture of nematic phase for compound (C
compound (C ) at 110 °C in second cooling scan, (f) thread-like texture associated with the nematic phase for compound (C
g
) at 138 °C in first heating scan, (c) transition from marble texture of nematic phase to crystalline phase for compound (C
) at 136 °C in second cooling scan, (e) thread-like texture associated with the nematic phase for
) at 138 °C in first heating scan.
a
) in
j
j
i
again alternately with increasing carbon atom numbers in the alkoxy
chain. The diagram shows that the curve tendency followed the zigzag
form that resulted from an odd-even effect, with the overall decline
being the tendency of the curve line as the terminal alkoxy chain length
increased. It can be seen that both transition curves behaved in a nor-
mally established way.
heating, but it transformed directly from the solid state to the isotropic
point at the temperature of 147.90 °C while it displayed a nematic phase
during cooling only with a thermal range equal to 44.05 °C. Conversely,
the compound (I6c) showed nematogenic properties both in the heating
and cooling cycles, with thermal stability equal to 144.8 °C. The
f
chemical structures of the two compounds (C ) and (I6c) are shown in
In this work, it is very important to discuss the influence of the pres-
ence of a furan ring on the liquid crystalline properties in the com-
pounds of this series (Ca \\ K). To study this effect, the mesogenic
Scheme 2.
This fundamental difference in the mesomorphic properties be-
tween these two mesogens is due to the difference in their chemical
structures, particularly the presence of the furan ring in the compound
f
properties of a selected compound (C ) from this series has been com-
pared with a compound that has a similar chemical structure (I6c), as re-
ported by Hagar et al. [44]. The only difference between their chemical
compositions is the inserted furan ring between the Schiff base linkage
f
(C ), which led to the disappearance of its liquid crystal properties in
the heating cycle. This result may be attributed to deviation from the
linearity that makes the molecule curved to a degree that loses the lin-
earity required in the calamitic mesogens. The introduction of the 2,5-
disubstituted furan ring as a core in the structure of the compounds
(Ca-k) creates a significant difference in their mesogenic behavior
and 4-nitrophenyl group in the compound (C
The results of the comparison showed that the compound (C
pared in this study did not show any mesophase properties upon
f
).
f
) pre-
9

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
Heaꢀng
Cooling
Cooling
Cooling
Cooling
k
Fig. 4. The sequence of transition between the liquid crystalline phases both in heating and cooling scans of the compound (C ) (a) Fan-shaped texture of the smectic A in first heating scan
at 124 °C (b) transition from Schlieren texture of nematic phase to isotropic phase in first heating scan at 139 °C, (c and d) transition from nematic droplets to Schlieren texture of nematic
phase to Fan-shaped texture of the smectic A phase in second cooling scan at 133 °C, (e) Fan-shaped texture of the smectic A phase in second cooling scan at 111 °C (f) transition from Fan-
shaped texture of the smectic A phase to crystal phase in second cooling scan at 67 °C.
compared to the (I6c). This may be mainly due to the presence of the
bend in the shape of the molecules, which resulted from insertion of
furan moiety that curved from the linearity by an angle of approxi-
mately 129.5° compared to the 1,4-disubstituted benzene ring [45,46].
Due to the bent nature property related to the furan ring, it can be
seen from the literature that the compounds based on furan rings,
which were characterized as mesogens, are less than other heterocyclic
compounds, as mentioned in the introduction. [47–50]. Another
significant factor that may be contributing to the influence in the
mesophase nature and stability is the presence of the polar nitro
group substituted to the para position in the terminal phenyl ring in
the compounds of this series. The high polarity nature possessed by
the nitro group, which increases the polarizability of the molecules,
may be the reason for an increase in the phase stability in some com-
pounds in this series upon the cooling cycle [42,51]. Additionally, the
2
large size of the NO group contributes to filling the space between
10

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
a f k
Fig. 5. Selected DSC thermograms of compounds (a) C , (b) C and (c) C .
11

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
Scheme 3. Representation of the synthesized compounds (Ca-k) and those reported by
Ong (nBA4MP) and Foo (nTMAPB).
Fig. 6. Diagram of phase transition temperature versus the number of carbon atoms in the
terminal alkoxy chain.
•
•
A smectic A phase begins from the 8BA4MP member in the
compounds nBA4MP (pyridine series), while it has appeared
in the last mesogen only from the studied compounds (C ), but
k
all mesogens of the nTMAPB series did not show any type of
smectogenic textures.
All mesogens of the three series (Ca-k, nTMAPB, and nBA4MP) were
compatible in terms of the thermal stability of the mesogenic
phase, where the temperature range in the cooling cycle was
higher than that recorded in the heating scan, regardless of the
length of alkoxy chain in most of the members. The thermal stabil-
the molecules and thus promotes the molecular packing [42,52]. How-
ever, in some cases, the increase in polarity is highly regarded as an ob-
stacle to increasing the stability of the liquid crystalline phase [51].
3.2.4. Mesomorphic comparison with related mesogens
The mesomorphic properties of the series prepared in this work
(Ca-k) were compared with two structurally analogous series reported
by Ong et al. [53] (series nBA4MP) and Foo et al. [54] (series nTMAPB),
as shown in Scheme 3.
ity of the mesogenic phases of the compounds in series Ca-k
nTMAPB, and nBA4MP are listed in Tables 1 and 2.
,
These differences represented in the terminal side group that con-
nected to the Schiff base bond, where it was (4-nitrofuran) in our pres-
ent series (Ca-k), while it was replaced by either pyridine in the Ong
series or thiophene in the Foo series. Moreover, in this work, the oppo-
site terminal side-chain contained an alkoxy group with a carbon num-
ber atoms of 1–10 and 12, while only even numbers were used in the
Ong and Foo series, n = 2–18 and n = 6–18, respectively.
According to the mesomorphic results of the mesogens in the three
series (Ca-k, nBA4MP, and nTMAPB) shown in Scheme 3, we conclude
with the following remarks:
•
The overall stability of the mesophases of the synthesized com-
pounds (Ca-k) is between 23.55–45.75 °C and 44.05–101.80 °C for
Table 2
Liquid crystalline phases stability [Nematic] and (Smectic) in °C of the compounds in series
nBA4MP [49] and nTMAPB [50].
•
The homologue series based on a thiophene ring (nTMAPB) displayed
nematogenic behavior with the exception of the last member
Entry
R= OC
n
H
2n+1 (n)
Mesomorphic range [N], (SmA)
(
18TMAPB), which did not show any mesogenic behavior, while the
compounds of series nBA4MP with pyridine core exhibited a nematic
and/or smectic phase, which was similar to the mesogenic behavior of
compounds in the studied series (Ca-k).
Heating
Cooling
2
BA4MP
2
4
6
[53.0]
[20.7]
[32.7]
[39.1]
[78.6]
[79.0]
[14.1]
(65.3)
[2.4]
(74.6)
(93.1)
(71.2)
(55.9)
(33.5)
4BA4MP
6
8
BA4MP
BA4MP
[
(
[
(
13.9]
29.2)
2.4]
43.7)
8
1
0BA4MP
10
1
1
1
1
2BA4MP
4BA4MP
6BA4MP
8BA4MP
12
14
16
18
(51.3)
(77.0)
(40.1)
(32.9)
Entry
R= OC
n
H
2n+1 (n)
Nematogenic range [N]
Heating
[7.4]
Cooling
6
8
1
1
1
1
1
TMAPB
TMAPB
6
8
[60.4]
[53.8]
[47.6]
[50.8]
[43.6]
[35.7]
–
[14.3]
[17.6]
[16.5]
[14.1]
[11.7]
–
0TMAPB
2TMAPB
4TMAPB
6TMAPB
8TMAPB
10
12
14
16
18
f
Scheme 2. Chemical structure and mesomorphic behavior of compounds C and I6c.
12

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
heating and cooling cycles respectively, while the value of the
range in compounds of the compared series was shown between
Acknowledgments
7
.4–17.6 °C (in heating) and 35.7–60.4 °C (in cooling) for the thiophene
The authors sincerely thank all staff members at Mustansiriyah Uni-
versity, College of Science, Chemistry Department, who collaborated to
provide research requirements in the present work. As well, we thank
the Arab Science of Technology and Foundation group (ASTF) for sup-
plied a polarizing optical microscope to study the liquid crystalline be-
havior of the compounds, which opened a new research line in this field.
series and 20.7–77.0 °C (in heating) and 33.5–93.1 °C (in cooling) for
pyridine series.
It is obvious that the liquid crystalline materials are flexible mol-
ecules that could convert their formations to various shapes, de-
pending on which are more stable. This phenomenon is related to
the chemical structure of the mesogens [55]. The variety and differ-
ences between the mesomorphic behavior of the synthesized com-
pounds (Ca-k) and the reported examples (nTMAPB and nBA4MP)
are due to the molecular geometry of the mesogens that usually con-
tribute to the nature and stability of the mesophase. The insertion of
a 4-nitrophenyl furan-2-yl segment at the terminal side of the com-
pounds in (Ca-k) (instead of pyridine and thiophene rings in the
series nBA4MP and nTMAPB, respectively) led to the differences in
the length and width of molecules in addition to the polarity, polar-
izability, and linearity between the synthesized and the reported
mesogens, which were reflected in the difference between their
mesomorphic behaviors.
Appendix A. Supplementary data
The H, 13C NMR and mass spectra as well as DSC thermograms for
synthesized compounds in this article (Ca-k) can be found in the Supple-
mentary data. Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molliq.2020.114562.
1
References
[
1] A. Gowda, M. Kumar, S. Kumar, Discotic liquid crystals derived from polycyclic aro-
matic cores: from the smallest benzene to the utmost graphene cores, Liq. Cryst. 44
(12−13) (2017) 1990–2017.
[2] Y.A. Getmanenko, S.-W. Kang, N. Shakya, C. Pokhrel, S.D. Bunge, S. Kumar, B.D.
Ellman, R.J. Twieg, Bis (5-alkylthiophen-2-yl) arene liquid crystals as molecular
semiconductors, J. Mater. Chem. C 2 (14) (2014) 2600–2611.
4
. Conclusion
[
3] H. Srinivasa, New symmetric azobenzene molecules of varied central cores: synthe-
sis and characterisation for liquid crystalline properties, Liq. Cryst. 44 (9) (2017)
1
384–1393.
In summary, the preparation, characterization and the study of liq-
[
4] B.T. Thaker, J.B. Kanojiya, R.S. Tandel, Effects of different terminal substituents on the
mesomorphic behavior of some Azo-Schiff base and Azo-Ester-based liquid crystals,
Mol. Cryst. Liq. Cryst. 528 (1) (2010) 120–137.
[5] L.D. Rodrigues, D. Sunil, D. Chaithra, P. Bhagavath, 1, 2, 3/1, 2, 4-Triazole containing
liquid crystalline materials: an up-to-date review of their synthetic design and me-
somorphic behavior, J. Mol. Liq. 297 (2020) 111909.
6] G. Karanlık, H. Ocak, B.B. Eran, New pyridine based liquid crystalline esters with dif-
ferent terminal chains, J. Mol. Struct. 1198 (2019) 126930.
7] Z.-Y. Lei, H.-M. Kuo, C.K. Lai, Mesogenic heterocyclic pyrazoles, isoxazoles and 1, 3,
4-oxadiazoles, Tetrahedron 73 (12) (2017) 1650–1660.
[8] T. Ghosh, M. Lehmann, Recent advances in heterocycle-based metal-free calamitics,
uid crystalline behavior of the newly synthesized series of compounds
viz., 4-[((5-(4- nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-
alkoxybenzoate (Ca-k), has led to the following conclusions:
•
•
All eleven members based on furan moiety in the studied series have
been displayed mesomorphic properties.
Only three homologues (C , C , and C ) showed mesogenic behavior in
d e f
cooling scans only, while other members have exhibited these proper-
ties in both heating and cooling cycles.
The first ten mesogens in this series (Ca-j) showed a nematic
[
[
J. Mater. Chem. C 5 (47) (2017) 12308–12337.
•
•
•
•
[
9] V. Petrov, V. Yashkichev, Liquid-crystalline oxygen-containing heterocyclic deriva-
tives. 2 six-membered rings containing oxygen as structural fragments in liquid
crystals, Mol. Cryst. Liq. Cryst. 518 (2010) 12–39.
10] P. Kaszyński, S. Kapuściński, S. Ciastek-Iskrzycka, Liquid crystalline derivatives of
heterocyclic radicals, Adv. Heterocycl. Chem. (2019) 263–331 Elsevier.
11] K.-T. Lin, H.-M. Kuo, H.-S. Sheu, C.K. Lai, Columnar catenar bisoxazoles and
bisthiazoles, Tetrahedron 70 (37) (2014) 6457–6466.
[12] C. Benbayer, N. Kheddam, S. Saïdi-Besbes, E.T. de Givenchy, F. Guittard, E. Grelet,
A.M. Safer, A. Derdour, Synthesis and mesomorphic properties of novel [1,2,3]-tri-
azole mesogenic based compounds, J. Mol. Struct. 1034 (2013) 22–28.
k
mesophase only except for the last derivative (C ), which displayed
both nematic (N) and smectic A (SmA) phases.
[
[
In compounds (Ca-c and Cg-k), the thermal stability of the nematic
phase shown in the cooling cycle was higher than the nematogenic
range through the heating scan.
The increase in the intermolecular forces between the molecules of
the last compound due to an increase in its alkoxy chain length led
to an appearance of a SmA phase in this compound.
The inclusion of the furan ring within the structure of the series com-
pounds led to the bending of the molecules, which resulted in a de-
crease in their thermal stability range when compared to other
linear compounds that have the same structure, except for the furan
ring (see Scheme 2).
The length of the terminal alkoxy group and the presence of furan and
phenyl rings, as well nitro group and various linkages (Schiff and
ester), within the chemical structure of the molecules have great ef-
fect on the mesogenic properties, where they showed significant dif-
ferences in the mesomorphic behavior when compared with other
related compounds (see Scheme 3).
[
[
[
13] Y.-L. Li, G.-H. Lee, C.K. Lai, Mesogenic bis-heterocycles incorporating both pyrazole
and isoxazole, Tetrahedron 71 (33) (2015) 5296–5307.
14] C.H. Wilsens, B.A. Noordover, S. Rastogi, Aromatic thermotropic polyesters based on
2, 5-furandicarboxylic acid and vanillic acid, Polymer 55 (10) (2014) 2432–2439.
15] M.-C. Chen, S.-C. Lee, C.-C. Ho, T.-S. Hu, G.-H. Lee, C.K. Lai, Calamitic
metallomesogens derived from unsymmetric pyrazoles, Tetrahedron 65 (45)
(2009) 9460–9467.
16] Z. Puterová, J. Romiszewski, J. Mieczkowski, E. Gorecka, Synthesis and study of new
rod-like mesogens containing 2-aminothiophene unit, Tetrahedron 68 (39) (2012)
[
•
8172–8180.
[17] S.Y. Kotian, C.D. Mohan, A.A. Merlo, S. Rangappa, S.C. Nayak, K.L. Rai, K.S. Rangappa,
Small molecule based five-membered heterocycles: a view of liquid crystalline
properties beyond the biological applications, J. Mol. Liq. 297 (2020), 111686.
18] Y. Xiao, H. Gao, T. Wang, R. Zhang, X. Cheng, Synthesis, liquid-crystalline,
photophysical and chemosensor properties of oxadiazole/thiadiazole-based amphi-
philes with glycerol groups, J. Mol. Liq. 244 (2017) 360–367.
19] N.H. Karam, M.T. Sultan, D.H. Badri, A.H. Al-Dujaili, Mesogenic materials incorporat-
ing 4H-1, 2, 4-triazol-3-thiol moiety: synthesis, characterization and liquid crystals
study, J. Mol. Struct. 1171 (2018) 404–410.
20] A. Seed, Synthesis of self-organizing mesogenic materials containing a sulfur-based
five-membered heterocyclic core, Chem. Soc. Rev. 36 (12) (2007) 2046–2069.
[
[
[
Declaration of competing interest
The authors whose names are listed immediately below certify
that they have NO affiliations with or involvement in any organization
or entity with any financial interest (such as honoraria; educational
grants; participation in speakers’ bureaus; membership, employment,
consultancies, stock ownership, or other equity interest; and expert
testimony or patent-licensing arrangements), or non-financial
interest (such as personal or professional relationships, affiliations,
knowledge or beliefs) in the subject matter or materials discussed
in this manuscript.
[21] C.-S. Wang, I.-W. Wang, K.-L. Cheng, C.K. Lai, The effect of polar substituents on the
heterocyclic benzoxazoles, Tetrahedron 62 (40) (2006) 9383–9392.
[
22] T.-S. Hu, K.-T. Lin, C.-C. Mu, H.-M. Kuo, M.-C. Chen, C.K. Lai, Polar effect in columnar
unsymmetric 1, 3, 4-oxa (thia) diazoles, Tetrahedron 70 (48) (2014) 9204–9213.
23] I. Felix-Serrano, N. Trejo-Carbajal, R.J. Rodríguez-González, L. Larios-López, I.
Moggio, E. Arias, R. Torres-Lubián, D. Navarro-Rodríguez, Synthesis and liquid-
crystalline properties of methacrylate monomers carrying a p-terphenyl laterally
substituted with one or two cyano groups, J. Mol. Liq. 241 (2017) 347–354.
24] H. Gallardo, I. Favarin, New mesogenic thiophene and furan derivatives, Liq. Cryst.
13 (1) (1993) 115–125.
[
[
13

N.M. Abdulnabi, M.M. Abdul Razzaq Al-Obaidy, I.H.R. Tomi et al.
Journal of Molecular Liquids xxx (xxxx) xxx
[
[
[
[
[
[
25] G.Q. Ali, I.H.R. Tomi, Study the effect of different terminal substituents on the liquid
crystalline properties of the new synthesized 1, 2, 4-oxadiazole derivatives, J.
Dispers. Sci. Technol. 40 (8) (2019) 1093–1100.
26] I.H. Tomi, H.J. Jaffer, Y.A. Aldhaif, Synthesis and characterization of wide range
mesogenic esters based on asymmetrical 2, 5-disubstituted 1, 3, 4-thiadiazole,
Phase Transit. 91 (4) (2018) 434–448.
27] G.Q. Ali, I.H.R. Tomi, Synthesis and characterization of new mesogenic esters derived
from 1, 2, 4-oxadiazole and study the effect of alkoxy chain length in their liquid
crystalline properties, Liq. Cryst. 45 (3) (2018) 421–430.
28] I.H.R. Tomi, D.T. Al-Heetimi, H.J. Jaffer, Asymmetric 1, 3, 4-thiadiazole derivatives:
synthesis, characterization and studying their liquid crystalline properties, J. Mol.
Struct. 1141 (2017) 176–185.
[41] Ł. Kolek, M. Massalska-Arodź, K. Adrjanowicz, T. Rozwadowski, K. Dychtoń, M.
Drajewicz, P. Kula, Molecular dynamics and cold crystallization process in a
liquid-crystalline substance with para-, ferro- and antiferro-electric phases as stud-
ied by dielectric spectroscopy and scanning calorimetry, J. Mol. Liq. 297 (2020)
111913.
[42] K. Hu, P. Chen, Q. Weng, D. Shi, R. Chen, X. Chen, Z. An, Preparation and properties of
lateral monofluoro-substituted benzoxazole-based mesogenic compounds, Liq.
Cryst. 42 (11) (2015) 1571–1579.
[43] M.N. Garaga, M. Nayeri, A. Martinelli, Effect of the alkyl chain length in 1-alkyl-3-
methylimidazolium ionic liquids on inter-molecular interactions and rotational dy-
namics: a combined vibrational and NMR spectroscopic study, J. Mol. Liq. 210
(2015) 169–177.
[
44] M. Hagar, H. Ahmed, G. Saad, Synthesis and mesophase behaviour of Schiff base/
ester 4-(arylideneamino) phenyl-4 ″-alkoxy benzoates and their binary mixtures,
J. Mol. Liq. 273 (2019) 266–273.
29] I.H.R. Tomi, A.H.R. Al-Daraji, A.M. Abdula, M.F. Al-Marjani, Synthesis, antimicrobial
and docking study of three novel 2,4,5-triarylimidazole derivatives, Journal of
Saudi Chemical Society 20 (2016) S509–S516.
[
[
45] A. Seed, Synthesis of self-organizing mesogenic materials containing a sulfur-based
five-membered heterocyclic core, Chem. Soc. Rev. 36 (12) (2007) 2046–2069.
46] J. Han, F.-Y. Zhang, J.-Y. Wang, Y.-M. Wang, M.-L. Pang, J.-B. Meng, Synthesis and
comparative study of the heterocyclic rings on liquid crystalline properties of 2, 5-
aryl-1, 3, 4-oxa (thia) diazole derivatives containing furan and thiophene units,
Liq. Cryst. 36 (8) (2009) 825–833.
30] M. Mohagheghnezhad, Z. Rafiee, Synthesis and characterization of two novel poly
(amide-imide) s containing pendent (5-(4, 5-diphenyl-1H-imidazol-2-yl) furan-2-
yl) phenyl moieties and natural amino acids linkages for adsorption of Cu (II),
Polym. Bull. (2019) 1–19.
[
31] Y. Harinath, D. Harikishore Kumar Reddy, B. Naresh Kumar, C. Apparao, K. Seshaiah,
Synthesis, spectral characterization and antioxidant activity studies of a bidentate
Schiff base, 5-methyl thiophene-2-carboxaldehyde-carbohydrazone and its Cd(II),
Cu(II), Ni(II) and Zn(II) complexes, Spectrochim. Acta A Mol. Biomol. Spectrosc.
[
47] V.F. Petrov, A.I. Pavluchenko, Furan as a structural fragment in liquid crystals, Mol.
Cryst. Liq. Cryst. 393 (1) (2003) 1–13.
[
48] J. Mills, R. Miller, H. Gleeson, A. Seed, M. Hird, P. Styring, The physical properties of a
series of antiferroelectric hetrocyclic esters, Molecular Crystals and Liquid Crystals
Science and Technology. Section A. Molecular Crystals and Liquid Crystals 303 (1)
101 (2013) 264–272.
[
32] A.B. Gündüzalp, İ. Özsen, H. Alyar, S. Alyar, N. Özbek, Biologically active Schiff bases
containing thiophene/furan ring and their copper(II) complexes: synthesis, spectral,
nonlinear optical and density functional studies, J. Mol. Struct. 1120 (2016)
(
1997) 145–152.
49] H. Gallardo, I. Favarin, New mesogenic thiophene and furan derivatives, Liq. Cryst.
3 (1) (1993) 115–125.
[
[
259–266.
1
[
[
[
33] I.H.R. Tomi, M.M.A.R. Al-Obaidy, A.H.R. Al-Daraji, Synthesis, characterisation and
mesomorphic behaviours of non-symmetrically substituted 1,2,4- and 1,3,4-
oxadiazole derivatives, Liq. Cryst. 44 (4) (2017) 603–608.
34] H.J. Jaffer, Y.A. Aldhaif, I.H. Tomi, Synthesis, characterization of new carboxylic acid
derivatives bearing 1, 3, 4-thiadiazole moiety and study their liquid crystalline be-
haviors, Mol. Cryst. Liq. Cryst. 643 (1) (2017) 199–215.
50] L.A. Karamysheva, E. Kovshev, A. Pavluchenko, K. Roitman, V. Titov, S. Torgova, M.
Grebenkin, New heterocyclic liquid crystalline compounds, Mol. Cryst. Liq. Cryst.
67 (1) (1981) 241–251.
[
[
[
51] L. Zhang, X. Chen, F. Zhao, X. Fan, P. Chen, Z. An, Synthesis and mesomorphic prop-
erties of 2-(4′-alkoxybiphenyl-4-yl)-1 H-benzimidazole derivatives, Liq. Cryst. 40
(3) (2013) 396–410.
35] . A.E. Bradfield, B. Jones, J.N. Rây, Notes, Journal of the Chemical Society (Resumed)
52] H.J. Abboud, S.J. Lafta, I.H.R. Tomi, Synthesis and characterisation of asymmetrical
(0) (1929) 2660–2661.
mesogenic materials based on 2, 5-disubstituted-1, 3, 4-oxadiazole, Liq. Cryst. 44
[
[
[
36] D. Demus, L. Richter, Textures of Liquid Crystals, Verlag Chemie, New York, 1978.
37] D. Ingo, Texture of Liquid Crystals, Wiley-VCH, Weinheim, Germany, 2003.
38] H. Sackmann, D. Demus, The polymorphism of liquid crystals, Mol. Cryst. 2 (1–2)
(14–15) (2017) 2230–2246.
53] L.-K. Ong, S.-T. Ha, G.-Y. Yeap, H.-C. Lin, Heterocyclic pyridine-based liquid crystals:
synthesis and mesomorphic properties, Liq. Cryst. 45 (11) (2018) 1574–1584.
(1966) 81–102.
[54] K.-L. Foo, S.-T. Ha, G. Yeap, S. Lee, Mesomorphic behaviors of a series of heterocyclic
thiophene-imine-ester-based liquid crystals, Phase Transit. 91 (5) (2018) 509–520.
[55] K.N. Patel, A.K. Prajapati, B.V. Kamath, A.V. Bedekar, Synthesis and study of meso-
morphic properties of unsymmetrical cyclohexanone-derived bis-chalcones, Liq.
Cryst. 43 (6) (2016) 729–734.
[
[
39] G.W. Gray, J.W. Goodby, Smectic Liquid Crystals: Textures and Structures, vol. 256,
HEYDEN & SON, 247 SOUTH 41 ST ST., PHILADELPHIA, PA 19104, USA, 1984 (1984).
40] M. Tariq, S. Hameed, I.H. Bechtold, A.J. Bortoluzzi, A.A. Merlo, Synthesis and charac-
terization of some novel tetrazole liquid crystals, J. Mater. Chem. C 1 (35) (2013)
5583–5593.
14