Mesogenic materials incorporating 4H-1,2,4-triazol-3-thiol moiety: Synthesis, characterization and liquid crystals study

Article abstract of DOI:10.1016/j.molstruc.2018.06.031

Three series of monomers, polymers and thioester cyclic compounds containing 4H-1,2,4-triazol-3-thiol moiety were synthesized and examined for their liquid crystalline properties. All monomers, polymers and thioester compounds were characterized by elemen

Full text of DOI:10.1016/j.molstruc.2018.06.031

Accepted Manuscript
Mesogenic materials incorporating 4H-1,2,4-triazol-3-thiol moiety: Synthesis,
characterization and liquid crystals study
Nisreen H. Karam, Maha T. Sultan, Dhefaf H. Badri, Ammar H. Al-Dujaili
PII:
S0022-2860(18)30732-4
10.1016/j.molstruc.2018.06.031
MOLSTR 25318
DOI:
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Accepted Date:
05 April 2018
08 June 2018
Please cite this article as: Nisreen H. Karam, Maha T. Sultan, Dhefaf H. Badri, Ammar H. Al-Dujaili,
Mesogenic materials incorporating 4H-1,2,4-triazol-3-thiol moiety: Synthesis, characterization and
liquid crystals study, Journal of Molecular Structure (2018), doi: 10.1016/j.molstruc.2018.06.031
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ACCEPTED MANUSCRIPT
Mesogenic materials incorporating 4H-1,2,4-triazol-3-
thiol moiety: Synthesis, characterization
and liquid crystals study
Nisreen H. Karam a, Maha T. Sultan a, Dhefaf H. Badri a,
Ammar H. Al-Dujaili b, *
a
Department of Chemistry, College of Education for Pure Science, Ibn Al-
Haitham, University of Baghdad, Baghdad, Iraq
b
Hamdi Mango Center for Scientific Research, The University of
Jordan, Amman, Jordan P.O. Box 11942 Amman. Jordan
ABSTRACT
Three series of monomers, polymers and thioester cyclic compounds
containing 4H-1,2,4-triazol-3-thiol moiety were synthesized and examined
for their liquid crystalline properties. All monomers, polymers and thioester
1
compounds were characterized by elemental analysis and FTIR, H-NMR
and mass spectroscopy. The phase transition and mesomorphic properties
were investigated by polarized optical microscope (POM) and differential
scanning calorimetry (DSC). The monomer with terminal phenyl substituent
display dimorphism nematic and smectic A (SmA) mesophases. The
corresponding polymers derived from acrylic and phenyl acrylic acid
monomers show nematic mesophase. The only thioester cyclic compound
derived from terephtaloyl chloride show nematic mesophase. The liquid
1

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crystalline behavior has been discussed in terms of structural property
relationships.
Key words:
1,2,4-Triazole
Liquid crystals
Heterocyclic
Polymers
* Corresponding author.
E-mail addresse: ah. aldujaili@gmail.com (A. H. Al-Dujaili).
1. Introduction
During the past decades many series of liquid crystalline compounds
containing heterocyclic groups have been synthesized due to their potentially
wide range of applications, such as in the optical, electrical and biological
medical fields [1-8]. The incorporation of heterocyclic moieties into the rigid
core of thermotropic liquid crystals can result in large changes in their
mesophases and physical properties. The rich polymorphism usually
observed of such structures was attributed to their medium to strong lateral
dipole, high polarizability and anisotropy, low symmetry and non-planar
structure caused by heteroatoms, such as nitrogen, oxygen and sulfur atoms
[9-11]. Usually five member heterocycles are involved and they form part of
the core in rod-shaped, bent-shaped, or disc-shaped molecules.[12-14].
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The triazole ring, which has a five-membered ring of two carbon
atoms and three nitrogen atoms, has two isomers, 1,2,3- and 1,2,4-triazole.
The recognized electron-deficient nature and electron acceptors properties in
1,2,4-triazoles have lead them to be excellent candidates used in many
potential applications as organic and bioactive materials.[15,16]. The
mesomorphic properties of 1,2,3-triazole isomer derivatives have
extensively been carried out in last decade [17–27], while the formation of
1,2,4-triazole derivatives mesophases has rarely been reported.
Thaker and Patel [28,29] have reported the synthesis and
mesomorphic properties of two homologous series containing 1,2,4-triazole
ring at the terminus of the molecule viz. 4-[(4H-1,2,4-triazol-4-ylimino)
methyl] phenyl 4-alkoxybenzoate and 3-hydroxy-4-[(4-1,2,4-triazol-4-
ylimino)methyl] phenyl 4-alkoxybenzoate (where alkoxy group CnH2n+1; n=
1-8, 10, 12, 14 and 16). All the derivatives are mesomorphic in nature
showing enantiotropic nematic phase and the higher member of both series
shows smectic C (SmC) phase. A twelve new bent-shaped mesogens
containing 4-amino-1,2,4-triazole as a central rigid core and terminal alkoxy
substituent have recently been reported [30]. The homologues with short
alkoxy terminal groups do not show any mesomorphic properties, whilst the
analogue with the longest alkoxy terminal groups exhibit enantiotropic
smectic A (SmA) and banana B1, B2, B6 and B7 phases with wide
mesomorphic temperature ranges. We have previously reported the
synthesis of two mesogenic homologous series of mesomorphic compounds
containing 1,2,4-triazole and 1,3,4-thiadiazole in the molecule viz. 1,4-
bis{3-[2-(4-alkoxybenzelideneamino)-
1,3,4-thiadiazole-5-ethylenethio]
1,2,4-triazole-5-yl} phenyl and 5-(4-meth-oxyphenyl)-3- [2-(4-n-
xybenzelidenamino)-1,3,4- thiadiazole-5-methylene- thio]-1,2,4-triazole. All
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compounds of the former series exhibited an enantiotropic nematic
mesophase. The compounds of the later series exhibited enantiotropic
nematic and monotropic smectic A (SmA) mesophases [31].
The present work deals with synthesis, characterization and the liquid
crystalline behaviour of monomers, polymers and compounds containing
4H-1,2,4-triazol-3-thiol unit. The liquid crystalline behaviour and the
structural property relationship were also investigated.
2. Experimental
2.1. Materials and characterization
All chemicals were supplied by Sigma-Aldrich Chemicals Co and used
without further purification. The solvents were commercial grade quality and
were dried and distilled before use. Infrared spectroscopy were carried out
with a Shimadzu 600S Fourier transform infrared spectrometer using KBr
pellets.1H-NMR spectra were recorded on a Brucker 500 MHz spectrometer.
Tetramethylsilane was used as an internal standard and used DMSO and
CDCl3 as solvents. Mass spectrum was recorded on IEOL JMS-7 high
resolution instrument using the electron impact (EI) method. Elemental
analysis (C, H, N) were carried out using a Perkin-Elmer model 2400
instrument. Uncorrected melting points were measured by using Gallen Kamp
melting point apparatus. The transition temperatures and phase transition
enthalpies were determined using a DSC, STA PT-1000LINSIS at a heating
rate of 5 /min. Temperature and heat flow calibrated with standard indium
℃
of purity <99.99%. Mesomorphic textures were observed using a Leica
microscope DM 2500M equipped with Mettler 600 heating stage.
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2.2. Synthesis
The synthetic route used for the synthesis of compounds and polymers
are outlined in Schemes 1 and 2. Acryloyl chloride, 3-phenylacryloyl
chloride and methacryloyl chloride were prepared according to the procedure
described in the literature [32].
Scheme 1
Scheme 2
2.2.1. Synthesis of 1,2-phenylene-bis(N-carbothioamide-hydrazide) [I]
To a stirred solution of compound thiosemicarbazide (0.91g, 10 mmol)
in dry pyridine 15 mL at -5oC, was added dropwise a solution of phthaloyl
chloride (1.015 g, 5 mmol) in dry benzene 15 mL at –5 . The stirring was
℃
continued for half an hour at -5oC and then overnight at room temperature.
The solvent was evaporated and added 30 mL water. The precipitate was
filtered and recrystallized from ethanol.
Yield: 76%, m.p. 208-210 ; FTIR (KBr) (cm-1): 3396-3174 (υNH2,
℃
1
υNH), 1683 (υC=O), 1261 (υC=S); H-NMR (500 MHz, DMSO, δ ppm):
7.56-7.92 (m, 4H, Ar-H), 8.65 (s, 2H, NH2), 9.69 (s, 1H, NHC=S), 12.75 (s,
1H, NHC=O). MS (m/z+1) = 313(M+.), 236(M+. C H ), 248(M+. C H ).
‒
‒
6
5
5
5
Anal. Calcd for C10H12N6O2S2: C, 38.46; H, 3.85; N, 26.92; S, 20.51. Found:
C, 37.97; H, 4.12; N, 26.50; S, 20.87.
2.2.2. Synthesis of 1,2-phenylene-bis(4H-1,2,4-triazol-3-thiol-5-yl) [II]
A solution of compound [I] (3.12 g, 10 mmol) and 20 mL 4% aqueous
sodium hydroxide solution was refluxed for 6 h. After that, the mixture was
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filtered, and then the resulting filtrate was acidified with 10% HCl. The
product was filtered and washed with water, then recrystallized from ethanol.
Yield 60%, m.p. 319-320 . FTIR (KBr) (cm-1): 3422 (υ ), 2651
℃
NH
(υSH), 1627 (υC=N of 1,2,4-triazole ring), 1220 (υC=S). 1H-NMR (500 MHz,
DMSO, δ ppm): 7.34-7.67 (m, 4H, Ar-H), 13.50 (s, 1H, for proton of NH
traizole ring and NH group tautomeric forms with SH group); MS (m/z+1) =
277(M+.), 212(M+. C H ), 200(M+. C H ), 173(M+. C H CNH). Anal.
‒
‒
‒
5
5
6
5
6
5
Calcd for C10H8NS2: C, 43.48; H, 2.90; N, 30.43; S, 23.19. Found: C, 42.82;
H, 3.11; N, 29.92; S, 22.87.
2.2.3. Synthesis of S,S'-5,5'-(1,2-phenylene)bis(4H-1,2,4-triazole-5,3-diyl)
diprop-2-enethioate [IV], S,S'-5,5'-(1,2-phenylene)bis(4H-1,2,4-triazole-5,3-
diyl) bis(3-phenylprop-2-enethioate) [V] and S,S'-5,5'-(1,2-phenylene)bis(4H-
1,2,4-triazole-5,3-diyl) bis(2-methylprop-2-enethioate) [VI]
To a stirred solution of compound (II) (10 mmol), triethylamine (2 mL)
in dried of 10 mL THF, was added dropwise acryloyl chloride, 3-
phenylacryloyl chloride or methacryloyl chloride (20 mmol) at 0 . After
℃
addition has been completed the resulting suspension was stirred at the same
temperature for 5 h. The triethylamine hydrochloride salt was precipitated. It
was filtered and filtrate was poured with stirring into ice water (100 mL), then
the mixture was extracted with of chloroform (50 mL). The organic phase was
dried over anhydrous magnesium sulphate. The chloroform solution was
evaporated to give the desired product.
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S,S'-5,5'-(1,2-phenylene)bis(4H-1,2,4-triazole-5,3-diyl) diprop-2-enethioate
[IV]
Yield 62%, m.p. 96-98 ; FTIR (KBr) (cm-1): 3417 (υ ), 3068 cm-1
℃
NH
(υAr-H), 1678 (υSC=O), 1634 (υCH2=CH-), 1624 (υC=N of 1,2,4-triazole ring). MS
(m/z+1) = 385.
S,S'-5,5'-(1,2-phenylene)bis(4H-1,2,4-triazole-5,3-diyl) bis(3-phenylprop-2-
enethioate) [V]
Yield 69%, m.p. 106-108 ; FTIR (KBr) (cm-1): 3410 (υ ), 3050 (υ
℃
NH
Ar-
H), 1682 (υSC=O), 1637 (υCH2=CH-), 1625 (υC=N of 1,2,4-triazole ring). MS
(m/z+1) = 413. Anal. Calcd for C18H16N6O2S2: C, 52.43; H, 3.88; N, 20.39; S,
15.53. Found: C, 51.31; H, 3.42; N, 20.93; S, 14.79.
S,S'-5,5'-(1,2-phenylene)bis(4H-1,2,4-triazole-5,3-diyl) bis(2-methylprop-2-
enethioate) [VI]
Yield 60%, m.p. 112-114 ; FTIR (KBr) (cm-1): 3415 (υ ), 3059
℃
NH
1
(υAr-H), 1695 (υSC=O), 1633 (υCH2=CH-), 1621 (υC=N of 1,2,4-triazole ring); H-
NMR (500 MHz, CDCl3, δ ppm): 1.41 (s, 3H, CH3), 4.99 (d, J = 1.39 Hz, 1H,
CH2=C-), 5.69 (d, J = 1.41 Hz, 1H, CH2=C-), 6.24-7.10 (m, 4H, Ar-H), 13.10
(s, 1H, for proton of NH traizole ring); MS (m/z+1) = 537.
2.2.4. Synthesis of thioester polymers [VII-IX]
Polymers were synthesized by free-radical polymerization technique
from the corresponding monomers using benzoyl peroxide as an initiator in
toluene at 80°C for 48 h: Monomer IV, V or VI (5 mmol) and benzoyl
peroxide (2wt.%) were dissolved in dry toluene and gentle steam of nitrogen
purged into the solution. The solution was kept in an oil bath at 80°C for 8 h.
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Then the solution was cooled and poured into excess of acetone to
precipitate the polymer. The solution was filtered and the precipitate washed
firstly with 15 mL of toluene and secondly with 15 mL of acetone, and was
dried at 60°C under vacuum for 48 h to afford the desired polymer.
Polymer [VII]
Yield 70%, m.p. 159-161 ; FTIR (KBr) (cm-1): 3406 (υ ), 3064 (υ
℃
NH
Ar-
1
H), 1683 (υSC=O), 1621 (υC=N of 1,2,4-triazole ring); H-NMR (500 MHz,
CDCl3, δ ppm): 1.22-1.55 (m, 2H, -CH2-), 3.04-3.90 (m, 1H, -CH-), 7.56-9.33
(m, 4H, Ar-H), 11.63 (s, 1H, for protons of NH traizole ring).
Polymer [VIII]
Yield 65%, m.p. 192 ; FTIR (KBr) (cm-1): 3420 (υ ), 3070 (υAr-H),
℃
NH
1672 (υSC=O), 1627 (υC=N of 1,2,4-triazole ring).
Polymer [IX]
Yield 76%, m.p. > 300 ; FTIR (KBr) (cm-1): 3408 (υ ), 3066 (υAr-H),
℃
NH
1698 (υSC=O), 1624 (υC=N of 1,2,4-triazole ring).
2.2.5. Synthesis of 1,2-phenylene bis [1,2-phenylene bis(4H-1,2,4-triazole-
3-thioester-5yl)] [XI], 1,3-phenylene bis [1,2-phenylene
bis(4H-1,2,4-
triazole-3-thioester-5yl)] [XII] and of 1,4-phenylene bis[1,2-phenylene
bis(4H-1,2,4-triazole-3-thioester-5yl)] [XIII]
These compounds were synthesized by using the same procedure given
for the synthesis of compounds [IV], [V] and [VI], but used 10 mmol of
phthaloyl chloride, isophthaloyl chloride or terephthaloyl chloride instead of
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20 mmol of acryloyl chloride, 3-phenylacryloyl chloride and methacryloyl
chloride.
1,2-phenylene bis [1,2-phenylene bis(4H-1,2,4-triazole-3-thioester-5yl)] [X]
Yield 85%, m.p. 197-198 ; FTIR (KBr) (cm-1): 3412 (υ ), 3086
℃
NH
1
(υAr-H), 1689 (υSC=O), 1620 (υC=N of 1,2,4-triazole ring); H-NMR (500 MHz,
DMSO, δ ppm): 7.55-8.06 (m, 8H, Ar-H), 13.02 (s, H, for proton of NH
traizole ring); MS (m/z+1) = 417.
1,3-phenylene bis [1,2-phenylene bis(4H-1,2,4-triazole-3-thioester-5yl)] [XI]
Yield 60%, m.p. 214-216 . FTIR (KBr) (cm-1): 3409 (υ ), 3100
℃
NH
(υAr-H), 1683 (υSC=O), 1618 (υC=N of 1,2,4-triazole ring). MS (m/z+1) = 417.
1,4-phenylene bis[1,2-phenylene bis(4H-1,2,4-triazole-3-thioester-5yl)] [XII]
Yield 76%, m.p. 296-298 . FTIR (KBr) (cm-1): 3418 (υ ), 3009
℃
NH
(υAr-H), 1681 (υSC=O), 1626 (υC=N of 1,2,4-triazole ring). MS (m/z+1) = 417.
Anal. Calcd for C18H10N6O2S2: C, 53.20; H, 2.46; N, 20.69; S, 15.76. Found:
C, 52.15; H, 3.13; N, 21.80; S, 14.98.
3. Results and discussion
3.1. Synthesis and characterization
All compounds and their corresponding polymers were prepared by
the synthetic route described in Schemes 1 and 2. All of the new synthesized
compounds gave satisfactory analysis for the proposed structures, which
were confirmed on the basis of their elemental analysis; FTIR and 1H-NMR.
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The observed values of the elemental analyses of the synthesized
compounds are in well agreement with theoretical values indicating structure
of respective compounds.
The carbothioamide derivative [I] was prepared by reacting of
phthaloyl chloride with two moles of thiosemicarbazide by neucleophilic
addition reaction. The FTIR spectrum of compound [I] showed absorption
stretching band at 1261 cm-1 that could be assigned to C=S group in addition
to new bands for asymmetric and symmetric stretching vibration of NH2 and
NH groups appears between 3396-3174 cm-1, also showed stretching band of
1
υC=O (amide) group at 1683 cm-1. The H-NMR spectrum for compound [I],
showed multiple signals in the region δ = 7.56-7.92 ppm for four aromatic
protons, singlet signal appeared at δ = 8.65 ppm for two protons of NH2
groups, signals at δ = 9.69 and 12.75 ppm for two protons of NHC=S and
NHC=O groups. The mass spectrum of compound [I] shows the peaks at
m/z = 77 and 65 of characteristic fragmentation for the aromaticity of
compound [I].
The cyclization of carbothioamiede derivative [I] in medium of
aqueous sodium hydroxide then acidification with hydrochloric acid led to
formation of principal key heterocyclic compound, 1,2,4-triazole-3-thiol
derivative [II]. The FTIR spectrum for compound [II] showed disappearance
bands of the υC=O (amide) groups, that observed in the starting materials
and showed new absorption stretching band at 2651 cm-1 that attributed to
the υSH and 1220 cm-1 for υC=S group. Also, showed stretching bands at the
3422 cm–1 and 1627 cm-1 for υN–H and υC=N (endocyclic) of 1,2,4-triazole
1
ring [33], respectively, this is evidence for ring closure. The H-NMR
spectrum for compound [II], showed multiple signals in the region δ = 7.34-
7.67 ppm for four aromatic protons and signal at δ = 13.50 ppm for proton of
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NH traizole ring and NH group tautomeric forms with SH group. The mass
spectrum of compound [II] shows peak attributed to the presence of triazole
ring (m/z = 104, 102, 57 and 40) also showed peaks at m/z = 77 and 65 for
the aromaticity.
The thio ester monomers [IV], [V] and [VI] were produced from the
reaction of compound 4H-1,2,4-triazol-5-thiol [II] with acryloyl chloride, 3-
phenylacryloyl chloride and methacryloyl chloride in presence of
triethylamine as acid acceptor. The FTIR spectra of these compounds showed
disappearance bands of SH and C=S groups for compound [II] with
appearance absorption stretching band of the thioester (υSC=O) group at 1678
1
cm-1 [34]. The H-NMR spectrum for compound [VI] (as a representative
example), showed signal at δ = 1.41 ppm for three protons of CH3 group,
signals appeared at δ = 4.99 and 5.69 ppm for two protons of (CH2=C-)
group and signals in the region δ = 6.24-7.10 ppm for four aromatic protons
also signal at δ = 13.10 ppm for the proton of NH traizole rings.
The resulting prop-2-enethioate monomers ([IV], [V] and [VI]) were
converted to the corresponding polymers by free-radical polymerization
technique using benzoyl peroxide as an initiator in dry toluene as a solvent.
The characteristic absorption bands in the range at (1634-1637 cm−1) in
FTIR spectra [35, 36] corresponding to (-CH=CH-) groups of monomers
were completely disappeared as a result of the opening of the double bond
on these groups, this is confirmed that the polymerization reaction took
1
place. The H-NMR spectrum for polymer [VII] (as a representative
example), showed signals at δ = 1.22-1.55 ppm for protons of (-CH2-)
groups, signals appeared at δ = 3.04-3.90 ppm for proton of (-CH-) groups
and signals in the region δ = 7.56-9.33 ppm for aromatic protons and signal
at δ =11.63 ppm for proton of NH traizole rings.
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Also, synthesized another thio ester compounds [X], [XI] and [XII] by
reaction of compound 4H-1,2,4-triazol-5-thiol [II] with diacid chlorides
(phthaloyl, isophthaloyl or terephthaloyl chloride). The FTIR spectra of
these compounds also showed disappearance bands of SH and C=S for
compound [II] with appearance absorption stretching band of the thio ester
1
(υSC=O) group. The H-NMR spectrum for compound [X], (as a
representative example) show many signals in the region δ = 7.55-8.06 ppm
for the eight aromatic protons and a singlet signal at δ = 13.02 ppm for two
protons of NH traizole rings. The data of elemental analysis, FTIR, and
1HNMR spectrum along with mass spectrum analyses data confirmed the
structural formula of the synthesized monomers, polymers and thioester
compounds.
3.2. Mesomorphic properties
The liquid crystalline properties of all compounds and polymers were
investigated by POM and DSC. Generally, the thermal behavior obtained by
DSC is consistent with the data observed by POM, where it was possible to
identify the mesomorphic character of the mesophases. Phase identification
was based on the optical textures, using the classification systems reported
by Sackmann and Demus [37] and Gray and Goodby [38]. The phase
transitions temperatures and thermodynamic data are summarized in Table
1.
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Table 1
Transition temperatures ( ) and transition enthalpies
(kJ/mol) of
퐻
∆
℃
monomers ([IV], [V] and [VI]), polymers ([VII], [VIII] and [IX]) and thio
ester compounds ([X], [XI] and [XII]) determined by DSC (10 /min) during
℃
first heating.
Transition temperatures (
H, kJ/mol)
℃) (
∆
Compound No.
[IV]
Cr 107 I
[V]
[VI]
Cr 119 (35.25) SmA 184 (15.46) N 223 (1.70) I
Cr 121 I
[VII]
[VIII]
[IX]
Cr 145 (11.28) N > 350 (a) I
Cr 171 (9.17) N 329 (a) I
Cr > 350 I
[X]
Cr 325 I
[XI]
[XII]
Cr 222 (27.15) SmA 250 (2.21) I
Cr 306 I
(a) = Not detected; Cr = Crystal; N = Nematic; SmA = smectic A; I =
Isotropic transition.
In order to study and analysis the mesomorphic behaviour of the
synthesized compounds, the target compounds and polymers were grouped
into three sets, series A, B and C; for monomers containing bifunctional
prop-2-enethioate group ([IV], [V] and [VI]) (series A). The corresponding
polymers of monomers of series A ([VII], [VIII] and [IX]) (series B), and
the last three thio ester compounds ([X], [XI] and [XII]) (series C).
In series A only compound [V] showed liquid crystalline properties
(Table 1), while the compounds [IV] and [VI] did not show any liquid
crystalline behavior but changes from the solid crystalline state to the
isotropic liquid phase. The DSC thermogram of compound [V] (Fig. 1)
shows three transitions on first heating. Under the POM Compound [V]
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exhibit enantiotropic dimorphism liquid crystalline behavior. On slow
cooling from the isotropic liquid, thread-like texture developed which is
characteristic of nematic phase (Fig. 2). On further cooling focal conic fan
texture displayed as showed in Fig. 3 which is characteristic of smectic A
(SmA) texture. The presence of thio cinnamate and phenyl ring in the
compound [V] could be increase rigidity and polarizability of the core and
extends the molecular length [39] leading to the formation of liquid
crystalline mesophese.
Fig. 1
Fig. 2
Fig. 3
The thermal data of the polymers of series B are gathered in Table 1.
Among the three polymers, [VII], [VIII] and [IX], polymers [VII] and [VIII]
display liquid crystalline behavior. The DSC thermogram of polymers [VII]
and [VIII] show two endothermic transitions between 145°C, >350°C and
171°C and 329°C, respectively corresponding to solid crystalline-liquid
crystalline and high temperature one is liquid crystalline-isotropic liquid
transitions, confirming the formation of liquid crystalline phase. This may be
explained based on the formation of macromolecular structure allow the
terminal molecular interaction between the polymer chains [40]. On heating
under POM of these two polymers, they are exhibited a uniform worm-like
texture [41]. The representative POM photograph of polymer [VII] was
shown in Fig. 4. The polar–polar interaction between triazole rings in [IV]
and [V] monomers (consider as a model to polymers [VII] and [VIII]) is
restricted in polymers [VII] and [VIII] systems lead to nematic like-
character than SmA texture of their models [18].
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Fig. 4
The phase transition temperatures of the compounds in series C are
given in Table 1. Compound [XI], is the only compound in this series
showing liquid crystalline behavior. Reference to the geometry of
compounds [X], [XI] and [XII], compound [XI] derive from phthaloyl
chloride forming bent core mesogene due to angle between 1,2-disubstituted
phenylene ring is 60˚ comparing with 1,3- and 1,4-disubstituted phenylene,
120˚ and 180˚, respectively [14] which are the favor of forming cyclic shape.
It seems that the lateral molecular interaction between the phenylene ring
along with the 1,2,4- triazole heterocyclic in bent core structure favored the
formation of smectic layer mesophase, which does not appear in the
compounds of 1,3- and 1,4-disubstituted phenylene ring with cyclic shape.
The texture of compound [XI] under POM showed a series of dark-lines,
when further cooled; the bands expanded, melt and eventually coalesce to
produce a batonnets texture typical character of SmA (Fig. 5) [42].
Fig. 5
4. Conclusions
In this article three series A, B and C containing 4H-1,2,4-triazol-3-
thiol unit were synthesized and their liquid crystalline properties were
analyzed with respect to their chemical structure. Monomer of series A
derived from phenylacryloyl chloride show dimorphism liquid crystalline
behaviour with SmA and nematic mesophases, comparing with other two
15

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monomers derived from acryloyl and methacryloyl which are not showing
liquid crystalline character. The polymers of series B were synthesized by
free radical polymerization of monomers of series A. Polymers of acryloyl
and phenylacryloyl monomers display liquid crystalline properties with
nematogen character. The restricted of lateral molecular interaction between
1,2,4-triazole in monomers comparing with polymeric system lead to
formation of nematic texture rather than smectic layer texture. Compound
derived from terephtaloyl chloride in series C forming bent-core structure
showed SmA mesophase. The other two compounds of this series derived
from isophtaloyl and terephtaloyl chloride do not show liquid crystalline
behavior. This could be attributed to structural geometry of these two
compounds.
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Figure and Scheme Captions
Scheme 1. The synthetic route of monomers [IV], [V] and [VI] and polymers
[VII], [VIII] and [IX].
Scheme 2. The synthetic route of thioester compounds [X], [XI] and [XII].
Fig. 1. The DSC thermogram of monomer [V].
Fig. 2. Mesophase optical texture of the nematic phase obtained on cooling.
A thread-like texture and the typical nematic droplets (200× magnification)
for the monomer [V] at 211 .
℃
Fig. 3. Mesophase optical texture of the SmA phase obtained on cooling.
A typical focal conic fan texture (200× magnification) for the monomer [V]
at 167 .
℃
Fig. 4. Mesophase optical texture of the nematic phase obtained on cooling.
A worm-like texture (200× magnification) for the polymer [VII] at 159 .
℃
Fig. 5. Mesophase optical texture of the SmA phase obtained on cooling. A
batonnets texture (200× magnification) for the compound [XI] at 237 .
℃
22

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S
H
H N N C NH
2
+
2
2
O
O
C
C
Cl
Cl
pyridine
S
O
O
S
H H
H H
N N C
[I]
H2N C N N C
NH2
C
4% NaOH
N
N
N
N
[II]
HS
SH
N
N
H
H
+
x
SOCl2
X
CH=
CCOOH
CH=
CCOCl
Y
y
[III]a-c
[III]a when X=H, Y=H
[III]b when X=H, Y=C6H5
[III]c when X=CH3, Y=H
(C2H5)3N
THF
N
N
N
N
O
O
C
S
N
X
S
N
X
C
H
H
C
=
C
=
C
H
H
C
Y
[IV]-[VI]
Y
[IV] when X=H , Y=H
[V] when X=H, Y=C6H5
Polymerization
[VI] when X= CH3 , Y= H
N
N
N
N
X
O
S
O
C
X
N
S
N
C
C
C
H
H
C
H
CH
[VII]-[IX]
n
Y
Y
n
[VII] when X=H , Y=H
[VIII] when X=H, Y=C6H5
[IX] when X= CH3 , Y= H
Scheme 1

ACCEPTED MANUSCRIPT
N
N
N
N
[II]
O
HS
SH
N
N
H
H
O
O
C
O
O
Cl
Cl
C
C Cl
C
O
C
Cl
C
Cl
Cl
N
N
S
N
N
N
N
N
N
N
NH
HN
N
NH
N
HN
NH HN
N
S
S
S
S
S
C
C
C
C
O
O
O
C
O
C
O
O
[XII]
[X]
[XI]
Scheme 2

ACCEPTED MANUSCRIPT
Fig. 1
Fig. 2

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Fig. 3
Fig. 4

ACCEPTED MANUSCRIPT
Fig. 5

ACCEPTED MANUSCRIPT
h i g h l i g h t s
 Novel 1,2,4-triazole based mesogenic derivatives were synthesized
and characterized.
 The synthesized compounds were examined for their liquid crystalline
behavior.
 The liquid crystalline behavior is related to the structural property
relationships.
 Effect of the phenyl terminus of vinyl group on the mesomorphic
properties was studied.
 Polymers possessed only nematic phase, while monomers have
smectic and nematic phases.