Synthesis and mesomorphic properties of novel [1,2,3]-triazole mesogenic based compounds

Article abstract of DOI:10.1016/j.molstruc.2012.09.020

A series of five-membered heterocyclic 1,2,3-triazole derivatives with different substituents in N1 position was synthesized. The heterocyclic moiety was connected through an ester function to a p-decyloxyphenyl or p-decyloxybiphenyl tails Polarized micro

Full text of DOI:10.1016/j.molstruc.2012.09.020

Journal of Molecular Structure 1034 (2013) 22–28
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis and mesomorphic properties of novel [1,2,3]-triazole mesogenic
based compounds
b
Chahinez Benbayer a, Narimane Kheddam a, Salima Saïdi-Besbes a, , Elisabeth Taffin de Givenchy ,
⇑
Frédéric Guittard b, Eric Grelet c, Abdel Mounaim Safer a, Aïcha Derdour a
a Laboratoire de Synthèse Organique Appliquée, Faculté des Sciences, Département de Chimie, Université d’Oran Es Senia, BP 1524, El Menaouer, Oran, Algeria
b Université de Nice Sophia Antipolis & CNRS, Laboratoire de Physique de la Matière Condensée, UMR 7336, Groupe surface et interface, 28 avenue Valrose, 06108 Nice cedex 2, France
c Centre de Recherche Paul Pascal, CNRS UPR 8641, Université Bordeaux 1115 avenue Albert Schweitzer, F-33600 Pessac, France
h i g h l i g h t s
"
"
"
Novel [1,2,3]-triazole based mesogenic derivatives were synthesized and characterized.
The smectic A phase appeared to be the dominant phase in these structures.
The incorporation of an ester function within the triazole unit could generate enough dipole which promotes the arrangement of molecules in smectic
layer structures.
"
"
The mesomorphic behavior is closely related to the nature of the substituent X present in N1 position of the heterocycle.
The increase of the mesogenic length causes a decrease in the existence range of the smectic A mesophase in favor of a new nematic mesophase.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 May 2012
Received in revised form 5 September 2012
Accepted 5 September 2012
Available online 14 September 2012
A series of five-membered heterocyclic 1,2,3-triazole derivatives with different substituents in N1 posi-
tion was synthesized. The heterocyclic moiety was connected through an ester function to a p-decyloxy-
phenyl or p-decyloxybiphenyl tails Polarized microscopy studies, X-ray scattering and differential
scanning calorimetry (DSC) analysis revealed that the target compounds exhibit enantiotropic liquid
crystalline properties. Their mesomorphic behavior is closely related to the nature of the substituent X
present in N1 position of the heterocycle.
Keywords:
1,2,3-Triazole
Mesogens
Ó 2012 Elsevier B.V. All rights reserved.
1,3-Dipolar cycloaddition
Smectic mesophases
DSC
1. Introduction
affecting the type of mesophases. Otherwise, by influencing the
direction and magnitude of the dipole moment of the molecule,
Numerous heterocyclic liquid crystalline materials were de-
signed and characterized during the past decades [1–5]. The pres-
ence of a heteroatom as nitrogen, oxygen or sulfur incorporated on
such heterocyclic rings may have a strong effect on the polarity and
polarizability of the molecule, the angle of rotation between its
fragments, the planarity and thereby on the stability of mesopha-
ses and the temperatures of the phase transitions [6,7].
Heteroatoms may also participate in intermolecular interac-
tions which are at the origin of mesomorphism (dipole–dipole
interaction, dispersion, H-bonding, coordinative force, etc.) thus
the heteroatom may affect the sign and magnitude of the dielectric
anisotropy of the liquid crystal mesophase.
It was reported that compounds based on six membered aro-
matic rings containing one or two nitrogen atoms such as pyridine,
tetrazine, pyridazine, give rise to interesting physical properties
[8–12]. The lone pairs of electrons on the nitrogen atoms introduce
attractive forces which induce smectic mesophase formation. The
position of nitrogens may be important as layer formation depends
significantly on how easily the molecules can pack together.
For example, the pyrimidine system as 5-alkyl 2-[4-alkoxyphe-
nyl] pyrimidine exhibit Sc phase and was also used in smectic C
ferroelectric mixtures [13].
Heterocyclic five-membered rings are not generally as condu-
cive to liquid crystal phase formation as six-membered rings due
⇑
Corresponding author. Tel.: +213 775028487.
E-mail address: salima_saidi@yahoo.fr (S. Saïdi-Besbes).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.09.020

C. Benbayer et al. / Journal of Molecular Structure 1034 (2013) 22–28
23
to their relative deviation from linearity and planarity. Compounds
2.2.1. 1-(4-Nitrophenyl)-1-H-[1,2,3]-triazole 4-carboxylic acid, 1-(4-
containing pyrrolyl and 5-methylthienyl rings, described by Nash
and Gray, promote nematic and smectic phases relative to phenyl
homologous [14].
bromophenyl)-1H-[1,2,3]-triazole 4-carboxylic acid, 1-(4-methoxy-
phenyl)-1H-[1,2,3]-triazole) 4-carboxylic acid (2a–c)
One equivalent (4 mmol) of the appropriate p-X-arylazide and
1.1 equivalents (0.31 g, 4.4 mmol) of propargyl acid dissolved in
5 mL of acetone were stirred at 60 °C for 24 h. After solvent evap-
oration, the residue was washed with diethyl ether given the (1,4)
regioisomer (2a–c). The filtrate was then evaporated and the solid
obtained was triturated in hexane affording the (1,5)-regioisomer
(20a–c).
[1,2,3]-triazoles are important type of heterocyclic compounds
and are known to exhibit a wide range of biological activities such
as anti-HIV activity [15], antimicrobial activity against Gram posi-
tive bacteria [16], selective b3 adrenergic receptor agonism [17]
and antianxiety activity [18]. They have been used in a variety of
research areas including non-linear optics (NLOs), organic light-
emitting diodes (OLEDs) and polymeric materials [19]. However,
1,2,3-triazole derivatives exhibiting mesophases have been less of-
ten reported. Nematic and/or smectic C – Smectic A mesophases
formed by these rod-like compounds were observed [20–23].
[1,2,3]-triazole ring is placed at the end of the rigid core or in cen-
tral core position and is linked directly to phenyl rings.
In this paper, we report the synthesis, the characterization and
the mesomorphism behavior of new series of 1,4-disubstituted
[1,2,3] triazole derivatives where the central heterocyclic ring is
connected through an ester function to 4-decyloxyphenyl or 4-dec-
yloxybiphenyl unit leading to extended conjugated system which
can potentially act as a electron transporting materials.
X = NO2, yield: 68%, (2a)/(20a) ratio: 66/34; X = Br, yield: 88%,
(2b)/(20b) ratio: 81/19; X = MeO, yield: 70%, (2c)/(20c) ratio: 96/4.
2.2.1.1. 1-p-Nitrophenyl-1-H-[1,2,3]-triazole 4-carboxylic acid
(2a). mp: 220 °C, IR (KBr): 3138–3617, 3089, 1696, 1519.1H NMR
(300 MHz, DMSO): 8.04 (d, 2H, Ar–H ortho triazole, J3 = 9.20),
8.40 (d, 2H, Ar–H ortho NO2, J3 = 9.20), 8.74 (s, 1H, H-triazole),
12.32 (s, 1H, COOH). 13C NMR (300 MHz, DMSO): 167, 148, 143.2,
134.7, 129.7, 128.3, 123.7.
2.2.1.2. 1-p-Nitrophenyl-1-H-[1,2,3]-triazole 5-carboxylic acid (2a0).
mp: 169 °C, 1H NMR (300 MHz, DMSO): 7.72 (d, 2H, Ar–H ortho tri-
azole, J3 = 9.06), 8.28 (s, 1H, H-triazole), 8.33 (d, 2H, Ar–H ortho
NO2, J3 = 9.06), 12.31 (s, 1H, COOH). 13C NMR (300 MHz, DMSO):
167.5, 148, 140, 134.7, 132.7, 130.3, 123.7.
2. Experimental
2.1. Characterization
2.2.1.3. 1-p-Bromophenyl-1-H-[1,2,3]-triazole 4-carboxylic acid
(2b). mp: 206 °C, 1H NMR (300 MHz, DMSO): 7.35 (d, 2H, Ar–H
ortho triazole, J3 = 9.01), 7.74 (d, 2H, Ar–H ortho Br, J3 = 9.01),
8.73 (s, 1H, H-triazole), 12.61 (s, 1H, COOH). 13C NMR (300 MHz,
DMSO): 167, 143, 132.5, 131.9, 128, 127.9, 123.1.
1H and 13C NMR spectra were recorded on a Brucker 300 MHz
spectrometer. Tetramethylsi–lane was used as an internal refer-
ence for chemical shifts. Infrared spectroscopies were carried out
with a Jasco-4200 Fourier transform infrared spectrometer using
KBr pellets. Column chromatographies were carried out using E-
Merck silica gel (Kieselgel 60, 230–400 mesh) as the stationary
phase. Thin-layer chromatography was carried out on aluminum
plates precoated with Merck silica gel 60F254 and visualized by
means of ultraviolet fluorescence quenching or iodine vapor. Ele-
mental analysis were obtained with a Perkin Elmer 2400 system.
The melting points, transition temperatures and phase transi-
tion enthalpies were determined using a differential scanning cal-
orimetry (DSC) at a heating rate of 5 °C minꢀ1. Mesomorphic
textures were observed using an Olympus microscope equipped
with Mettler Toledo heating stage. Structural characterizations
were performed by X-ray scattering using a Rigaku rotating anode
2.2.1.4. 1-p-Bromophenyl-1-H-[1,2,3]-triazole 5-carboxylic acid (2b0).
mp: 170 °C, 1H NMR (300 MHz, DMSO): 7.38 (d, 2H, Ar–H ortho tri-
azole, J3 = 8.83), 7.30 (d, 2H, Ar–H ortho Br, J3 = 8.83), 8.21 (s, 1H, H-
triazole), 12.31 (s, 1H, COOH). 13C NMR (300 MHz, DMSO): 166.9,
139.6, 132.7, 132, 131.5, 127, 122.9.
2.2.1.5. 1-p-Methoxyphenyl-1-H-[1,2,3]-triazole 4-carboxylic acid
(2c). mp: 215 °C, 1H NMR (300 MHz, DMSO): 3.81 (s, 3H, OCH3),
6.99 (d, 2H, Ar–H ortho OCH3, J3 = 9.02), 7.63 (d, 2H, Ar–H ortho tri-
azole, J3 = 9.02), 8.47 (s, 1H, H-triazole), 12.68 (s, 1H, COOH). 13C
NMR (300 MHz, DMSO): 167.9, 160, 143.6, 131.2, 129.2, 121.7,
115, 60.2.
generator working at a wavelength of 1.54 Å (Cu Ka emission). The
spectra were recorded with a bidimensional detector located at
154 mm from the sample, which was introduced as a powder in
glass capillary tubes (Glas, Muller, Germany) exhibiting a diameter
of 1.5 mm. An in-house made heating stage having an accuracy of
0.01 K was used to monitor sample temperature.
2.2.2. 5-Methyl-1-(4-nitrophenyl)-1H-1,2,3-triazole-4-carboxylic acid
(2d)
4.2 mmol of methyl 5-methyl-1-(4-nitrophenyl)-1H-1,2,3-tria-
zole-4-carboxylate and 35 mL of NaOH 2M were heated at 100 °C
during 24 h. The mixture was then acidified with HCl 35% solution
until pH = 1. The obtained precipitate was filtered, washed several
times with water and dried.
2.2. Synthesis
Yield: 66%, mp: 220 °C, IR (KBr): 3381–3473, 3127, 1716, 1H
NMR (300 MHz, DMSO): 2.35 (s, 3H, CH3), 8.02 (d, 2H, Ar–H ortho
triazole, J = 9.1), 8.45 (d, 2H, Ar–H ortho NO2, J = 9.1 Hz), 12.3 (s, 1H,
COOH). 13C NMR (300 MHz, DMSO): 167.8, 148.3, 139.8, 136.6,
134.6, 125.9, 125.2, 10.2.
All the reagents were purchased from Aldrich and used as re-
ceived. The solvents were of commercial grade quality and were
dried and distilled before use. Methylene chloride was distilled
over calcium hydride.
4-azido-1-nitrobenzene (1a), 4-azido-1-bromobenzene (1b)
and 4-azido-1-methoxybenzene (1c) were prepared according to
Nolting and Michel method [24] with a yield of 79%, 92% and
82% respectively.
2.2.3. [1-(4-X-phenyl)-1H-1,2,3-triazoyl chloride (3a–c) and 5-
methyl-1-(4-nitrophenyl)-1H-1,2,3-triazoyl chloride (3d)
To
a solution of compound 2a–d (2 mmol) was added
Methyl
5-methyl-1-(4-nitrophenyl)-1H-1,2,3-triazole-4-car-
(20 mmol) of thionyl chloride. The reaction mixture was stirred
at 85 °C during 5–6 h under inert atmosphere. After evaporation
of the excess of SOCl2, the crude product was used for the next step
without further purification.
boxylate was prepare according to the procedure described in
the literature [25].
4-decyloxyphenol (4) was synthesized according to Ref. [26].

24
C. Benbayer et al. / Journal of Molecular Structure 1034 (2013) 22–28
Scheme 1. Synthesis of compounds.
2.2.4. 4,40-(Decyloxy)biphenyl-4-ol (5)
Yield: 78%, mp: 152 °C, IR (KBr): 3367, 2921, 1250. 1H NMR
(300 MHz, DMSO-d6): 0.86 (t, 3H, CH3, 3J = 6.60 Hz), 1.29 (m, 14H,
CH2), 1.71 (m, 2H, OCH2–CH2), 3.94 (t, 2H, OCH2, J = 6.3 Hz), 6.81
(d, 2H, ArꢀH ortho OH), 6.95 (d, 2H, ArꢀH ortho OCH2), 7.43 (m,
4H, ArꢀH), 9.42 (s, 1H, OH).
(1 g, 5.4 mmol) of 4,40-biphenol dissolved in 6 mL of dim-
ethylsulfoxyde was added to 0.9 g of KOH. 1-bromodecane
(1.32 g, 6 mmol) were then added dropwise so that the initial tem-
perature was maintained. The reaction was stirred for 24 h at room
temperature.
The resulting mixture was transferred into 60 mL of water, then
acidified with HCl 35% until pH = 2–3. The precipitate was col-
lected by filtration the purified by column chromatography (silica
gel, dichloromethane/acetone 1/1) to give a white solid.
2.2.5. 4-(Decyloxy)phenyl 1-(4-Xphenyl)-1H-1,2,3-triazole-4-
carboxylate (6a–c)
In a typical procedure, 2 mmol of triazoyl chloride (3a–c),
(0.57 g, 5.7 mmol) of triethylamine and 6 mL of freshly distilled

C. Benbayer et al. / Journal of Molecular Structure 1034 (2013) 22–28
25
Table 1
Transition temperatures (°C) and transition enthalpies
D
H (kJ moleꢀ1) of compounds
(6a–d) and (7a–c) determined by DSC (10 °C minꢀ1) during second cycle.
Compound
X
Transition temperatures (°C) [transition enthalpies
H/kJ moleꢀ1
D
]
6a
NO2
Br
Cr (119.40 °C) [19.72] Cr0 (127.63 °C) [11.96] SmA
(222.8 °C) [6.30] I
Cr (127.45 °C) [17.99] I
6b
6c
6d
7a
MeO Cr (51.89 °C) [17.6] SmA (125.32 °C) [17.22] I
NO2
NO2
Cr (152.50 °C) [12.72] SmA (162.18 °C) [9.87] I
Cr (105.5 °C) [18.03] Cr0 (169.65 °C) [27.54] SmA
(182.14 °C) [broad] N (244 °C) [1.12] I
Cr (134.10 °C) [25.0] I
7b
7c
Br
MeO Cr (155.02 °C) [47.19] SmA (237.46 °C) [1.48] N (248 °C)
[broad] I
Fig. 1. Comparative thermal behavior of the final compounds.
dichloromethane were transferred in a round bottom three-necked
flask placed in a ice bath. After purging with nitrogen gas, (0.5 g,
2 mmol) of 4-decyloxyphenol dissolved in 6 mL dichloromethane
were added dropwise. The reaction mixture was heated under re-
flux for 48 h. Water was then added and the organic phase was ex-
tracted, washed three times with an aqueous solution of HCl 1M,
then with water until neutrality and finally dried with MgSO4.
The residue obtained after solvent evaporation was purified with
column chromatography (silica gel, dichloromethane/ethyl acetate
5:1).
2.2.5.1. 4-(Decyloxy)phenyl 1-(4-nitrophenyl)-1H-1,2,3-triazole-4-
carboxylate (6a). Yield: 76%, m.p. 127.63 °C, IR (KBr): 3096, 1727,
1245. 1H NMR (300 MHz, CDCl3): 0.90 (t, 3H, CH3, 3J = 6.64 Hz),
1.35 (m, 14H, CH2), 1.81 (tt, 2H, OCH2–CH2, 3J = 6.55 Hz,
3J = 7.25 Hz), 3.98 (t, 2H, OCH2, 3J = 7.25 Hz), 6.96 (d, 2H, Ar–H
ortho OR, 3J = 9.06 Hz), 7.18 (d, 2H, Ar–H ortho OCO, 3J = 9.06 Hz),
8.08 (d, 2H, Ar–H ortho triazole, 3J = 9.09 Hz), 8.50 (d, 2H, Ar–H
ortho NO2, 3J = 9.09 Hz), 8.81 (s, 1H, triazole). 13C NMR (300 MHz,
CDCl3): 13.25, 21.55, 25.01, 28.22, 30.94, 31.18, 68.90, 114.15,
120.04, 121.19, 124.31, 127.84, 129.86, 143.20, 143.10; 148.32,
154.30, 156.29. Anal. Calcd for C25H30N4O5: C, 64.36; H, 6.48; N,
12.02. Found: C, 64.30; H, 6.23; N, 11.99.
Fig. 2. The representative photomicrographs of (a) the focal conic texture of the
SmA phase for compound 6c at 120 °C, (b) the SmA polygonal texture for compound
6d at 160 °C and (c) the nematic schlieren texture for compound 7c at 241 °C
(240 ꢁ 300
l
m2).
triazole). 13C NMR (300 MHz, CDCl3): 12.64, 21.86, 25.97, 29.71,
31.92, 67.56, 114.81, 122.04, 123.0, 127.51, 130.68, 132.93,
134.58, 143.10, 143, 22, 154.32, 156.34. Anal. Calcd for C25H30BrN3-
O5: C, 60.00; H, 6.04; N, 8.40. Found: C, 59.88; H, 6.14; N, 8.32.
2.2.5.2. 4-(Decyloxy)phenyl 1-(4-bromophenyl)-1H-1,2,3-triazole-4-
carboxylate (6b). Yield: 63%, m.p. 127.45 °C, 1H NMR (300 MHz,
CDCl3): 0.90 (t, 3H, CH3, 3J = 6.64 Hz), 1.34 (m, 14H, CH2), 1.81 (tt,
2H, OCH2–CH2, 3J = 6.52 Hz, 3J = 7.35 Hz), 3.97 (t, 2H, OCH2, 3J
= 6.52 Hz), 6.95 (d, 2H, Ar–H ortho OR, 3J = 9.04 Hz), 7.18 (d, 2H,
Ar–H ortho OCO, 3J = 9.04 Hz), 7.71 (d, 2H, Ar–H ortho triazole,
3J = 9.19 Hz), 7.75 (d, 2H, Ar–H ortho Br, 3J = 9.19 Hz), 8.66 (s, 1H,
2.2.5.3. 4-(Decyloxy)phenyl 1-(4-methoxyphenyl)-1H-1,2,3-triazole-
4-carboxylate (6c). Yield: 80%, m.p. 51.89 °C, 1H NMR (300 MHz,
CDCl3): 0.90 (t, 3H, CH3, 3J = 6.62 Hz), 1.32 (m, 14H, CH2), 1.80 (tt,
2H, OCH2–CH2, 3J = 6.54 Hz, 3J = 7.29 Hz), 3.91 (s, 3H, OCH3), 3.97
(t, 2H, OCH2, 3J = 6.54 Hz), 6.95 (d, 2H, Ar–H ortho OCH3,
3J = 9.02 Hz), 7.08 (d, 2H, Ar–H ortho OR, 3J = 8.99 Hz), 7.17 (d,

26
C. Benbayer et al. / Journal of Molecular Structure 1034 (2013) 22–28
121.65, 125.75, 127.83, 127.90, 128.08, 128.10, 133.31, 134.61,
14.31, 148.00, 150.32, 156.31, 158.89. Anal. Calcd for
31H34N4O5: C, 68.62; H, 6.32; N, 10.33. Found: C, 69.78; H, 6.52;
C
N, 10.09.
2.2.7.2. 4-(Decyloxy)biphenyl 1-(4-bromophenyl)-1H-1,2,3-triazole-
4-carboxylate (7b). Yield: 46%, m.p. 134.10 °C, 1H NMR (300 MHz,
3J = 6.67 Hz),
CDCl3): 0.83 (t, 3H, CH3,
1.26 (m, 14H, CH2), 1.67 (tt,
2H, OCH2–CH2, 3J = 7.17 Hz, 3J = 6.84 Hz), 3.92 (t, 2H, OCH2, 3J
= 6.84 Hz), 6.91 (d, 2H, Ar–H ortho O, 3J = 8.72 Hz), 7.24 (d, 2H,
Ar–H ortho OCO, 3J = 8.75 Hz), 7.43 (d, 2H, Ar–H ortho triazole,
3J = 8.65 Hz), 7.58 (d, 2H, Ar–H ortho Br, 3J = 8.65 Hz), 7.65 (s, 4H,
Ar–H), 8.53 (s, 1H, triazole). 13C NMR (300 MHz, CDCl3): 13.10,
21.66, 25.04, 28.30, 30.88, 67.10, 113.82, 120.73, 121.24, 126.79,
127.10, 131.7, 132.22, 133.31, 147.52, 150.37, 157.86. Anal. Calcd
for C31H34BrN3O3: C, 64.58; H, 5.94; N, 7.29. Found: C, 64.24; H,
5.83; N, 7.13.
2.2.7.3. 4-(Decyloxy)biphenyl 1-(4-methoxyphenyl)-1H-1,2,3-tria-
zole-4-carboxylate (7c). Yield: 48%, m.p. 155.02 °C, 1H NMR
(300 MHz, CDCl3): 0.81 (t, 3H, CH3, 3J = 6.67 Hz), 1.35 (m, 14H,
CH2), 1.72 (tt, 2H, OCH2–CH2, 3J = 7.48 Hz, 3J = 6.49 Hz), 3.82 (s,
3H, OCH3), 3.93 (t, 2H, OCH2, 3J = 6.49 Hz), 6.95 (d, 2H, CHbz-O,
3J = 8.70 Hz), 7.00 (d, 2H, Ar–H ortho OCH3, 3J = 9.04 Hz), 7.24 (d,
2H, Ar–H, 3J = 8.70 Hz), 7.45 (d, 2H, Ar–H, 3J = 8.74 Hz), 7.54 (d,
Fig. 3. Energy minimized structures of compound 6a (top) and homologous
structure without ester function connector (bottom).
2H, Ar–H ortho OCO, 3J = 8.99 Hz), 7.70 (d, 2H, Ar–H ortho triazole,
3J = 9.02 Hz), 8.58 (s, 1H, triazole). 13C NMR (300 MHz, CDCl3):
13.09, 21.74, 28.39, 28.53, 30.94, 54.66, 69.81, 113.94, 114.351,
120.08, 121.45, 124.31, 128.20, 143.20, 146.00, 154.32, 156.30,
160.71. Anal. Calcd for C26H33N3O4: C, 69.16; H, 7.37; N, 9.31.
Found: C, 69.13; H, 8.12; N, 9.16.
2H, Ar–H ortho OCO, 3J = 8.70 Hz), 7.63 (d, 2H, CHbz-N
,
3J = 9.04 Hz), 8.53 (s, 1H, triazole). 13C NMR (300 MHz, CDCl3):
13.10, 21.66, 25.04, 28.30, 30.88, 54.68, 67.09, 113.80, 113.99,
120.79, 121.51, 125.38, 127.09, 128.51, 131.54, 130.9, 131.54,
138.07, 138.86, 143.20, 148.08, 157.82, 158.15, 159.47. Anal. Calcd
for C32H37N3O4: C, 72.84; H, 7.07; N, 7.96. Found: C, 71.80; H, 7.28;
N, 7.31.
2.2.6. 4-(Decyloxy)phenyl 5-methyl 1-(4-nitrophenyl)-1H-1,2,3-
triazole-4-carboxylate (6d)
This compound was prepared by a similar procedure to that de-
scribed for compounds (6a–c) from compound 3d and 4-decyloxy-
phenol (4).
3. Results and discussion
3.1. Synthesis
Yield: 50%, m.p. 152.50 °C, IR (KBr): 3094, 1738, 1205. 1H NMR
(300 MHz, CDCl3): 0.90 (t, 3H, CH3, 3J = 6.73 Hz), 1.29 (m, 14H,
CH2), 1.80 (tt, 2H, OCH2–CH2, 3J = 6.55 Hz, 3J = 7.14 Hz), 2.74 (s,
3H, CH3), 3.97 (t, 2H, OCH2, 3J = 6.55 Hz), 6.94 (d, 2H, Ar–H ortho
O, 3J = 8.92 Hz), 7.17 (d, 2H, Ar–H ortho OCO, 3J = 8.92 Hz), 7.78
(d, 2H, Ar–H ortho triazole, 3J = 8.83 Hz), 8.50 (d, 2H, Ar–H ortho
NO2, 3J = 8.83 Hz). 13C NMR (300 MHz, CDCl3): 4.20, 13.10, 21.66,
24.98, 28.24, 28.37, 28.54, 28.69, 29.95, 30.87, 67.70, 114,10,
121.37, 124.26, 124.88, 134.61, 136.50, 139.32, 143.02, 148.00,
154.30, 160.76. Anal. Calcd for C26H32N4O5: C, 64.98; H, 6.71; N,
11.66. Found: C, 64.85; H, 6.82; N, 11.35.
Synthesis of the 1-H-[1,2,3] triazole-based mesogenic deriva-
tives (6a–d) and (7a–c) and the principal key intermediates is out-
lined in Scheme 1. Aromatic azides (1a–c) were prepared according
to Nolting and Michel method from para-substituted anilines (p-
NO2, p-Br, p-MeO) by reacting with sodium nitrite in HCl media
to accede to diazonium salts which were then transformed into
aryl azides by the addition of sodium azide.
1,3-dipolar cycloaddition was conducted by heating the aryl
azides with propargyl acid at 60 °C during 24 h using acetone as
solvent. Two regioisomers corresponding to the anti (1,4-triazole)
and syn (1,5-triazole) were obtained with unequal proportions.
The 1,4-regioisomers (2a–c) were easily separated by washing
the reaction residues with diethyl ether. The filtrates were then
evaporated and the solids obtained were triturated in hexane
affording the 1,5-regioisomers (20a–c).
2.2.7. 4-(Decyloxy)biphenyl 1-(4-Xphenyl)-1H-1,2,3-triazole-4-
carboxylate (7a–c)
These compounds were prepared by a similar procedure to that
described for compounds (6a–c) from compound (2a–c) and 4,40-
(decyloxy)biphenyl-4-ol (5). They were isolated by column chro-
matography (silica gel, dichloromethane/ethyl acetate 10:1).
The structures of the two isomeric derivatives were supported
by 1H and 13C NMR analysis and examination of relevant literature
[27–29].
2.2.7.1. 4-(Decyloxy)biphenyl 1-(4-nitrophenyl)-1H-1,2,3-triazole-4-
carboxylate (7a). Yield: 76%, m.p. 169.65 °C, IR (KBr): 3135, 1725,
1166. 1H NMR (300 MHz, CDCl3): 0.84 (t, 3H, CH3, 3J = 6.43 Hz),
1.21 (m, 14H, CH2), 1.76 (tt, 2H, OCH2–CH2, 3J = 6.66 Hz,
3J = 5.56 Hz), 3.93 (t, 2H, OCH2, 3J = 6.66 Hz), 6.91 (d, 2H, Ar–H
ortho O, 3J = 8.70 Hz), 7.22 (d, 2H, Ar–H ortho OCO, 3J = 8.62 Hz),
7.54 (d, 2H, Ar–H, 3J = 8.62 Hz), 7.46 (d, 2H, Ar–H, 3J = 8.70 Hz),
8.02 (d, 2H, Ar–H ortho triazole, 3J = 9.07 Hz), 8.42 (d, 2H, Ar–H
ortho NO2, 3J = 9.07 Hz), 8.75 (s, 1H, triazole). 13C NMR (300 MHz,
CDCl3): 14.09, 22.66, 26.04, 29.30, 31.88, 68.11, 114.84, 121.07,
Comparison with 1H NMR data described in literature shows
similar single signal of the triazole-H5 (1,4-regioisomer) which var-
ied from 8.47 to 8.74 ppm whereas the H4 proton of 5-substituted
triazole (1,5-regioisomer) is shifted to lower frequency.
The 5-methyl substituted corresponding acid derivative for
x = NO2 (2d) was prepared by another methodology. First, the 4-
nitroazide (1a) was reacted with acetylacetone in the presence of
triethylamine to afford the methyl-1H-[1,2,3]-triazole-4-carboxyl-
ate [25] which is then hydrolyzed in basic media to afford the cor-
responding acid (2d) with a good yield.

C. Benbayer et al. / Journal of Molecular Structure 1034 (2013) 22–28
27
Fig. 4. Thermogram of compound 6a obtained by DSC during the first cycle at 10 °C/mn and during the second cycle at 5 °C/mn.
The resulting 1H-[1,2,3]-triazole-4-carboxylic acids (2a–d) were
converted to the corresponding triazoyl chlorides (3a–d) with thio-
nyl chloride then reacted with 4-decyloxyphenol (4) or 4,40-(decyl-
oxy)biphenyl-4-ol (5) in dichloromethane to give the aimed [1,2,3]
triazole containing mesogens (6a–d) and (7a–c).
Differential scanning calorimetry investigations confirm the
mesomorphic behavior. Two sharp endothermic peaks, corre-
sponding to melting temperature (high enthalpy) and isotropic
temperature (low enthalpy) were observed. A typical thermogram
obtained by DSC analysis of compound (6a) is presented in Fig. 4.
The mesomorphic behavior of the target compounds is closely re-
lated to the nature of the substituent X present in N1 position of the
heterocycle. The introduction of a bromo substitution is detrimental
to the liquid crystalline behavior since any mesophase was observed
for the corresponding products. The large volume of this atom could
be at the origin of such luck of mesomorphic packing since it reduces
the dipolar interactions which lead to smectic phase.
In the same manner, the existence of a methyl group in the po-
sition 5 of the heterocycle (compound 6d) reduced the thermal sta-
bility of the smectic phase. The stability of the SmA phase was
reduced by a factor of 10 and the clearing temperature was low-
ered by about 60 °C. The main factor contributing to this may be
also the steric effect which is less pronounced than previously.
The elongation of the aromatic rigid core by the introduction of
biphenyl group (7a–c), increases the melting points in comparison
with compounds containing a phenyl group (6a–c). The mesomor-
phic behavior is found to be related to the number of aromatic
rings in the mesogenic core. The introduction of an additional aro-
matic ring (benzene ring) in the series (7a–c) along with the 1,2,3-
triazole heterocyclic favored the formation of a new nematic meso-
phase, which does not appear in the series (6a–c), to the detriment
of the smectic A mesophase.
3.2. Mesomorphic properties
The transition temperatures and phase assignments for the syn-
thesized materials were investigated by thermal polarizing optical
microscopy (POM) and differential scanning calorimetry (DSC). The
results are given in Table 1 and in the bar-graph chart (Fig. 1).
Compounds (6a), (6c), (6d) exhibit enantiotropic liquid crystal-
line behavior. The smectic A phase (SmA) appeared to be the dom-
inant phase in these structures. On slow cooling from the isotropic
liquid, tiny batonnets developed at the edge of melted substance
and grow up to the focal conic fan texture as showed in Fig. 2a
and b which is characteristic of SmA texture.
The linearity deviation caused by the triazole core (148.9 °C)
seems to be, in our case, not sufficient to destroy calamitic meso-
morphic behavior even for compound bearing only three aromatic
rings. The presence of ester polar flexible group within triazole po-
lar unit could not assist the recovery of linearity lost by triazole
ring as seen when comparing, for instance the energy minimized
structure obtained using MM2 method of compound 6a and the
homologous structure without ester connector group (Fig. 3).
Though the mesogen was a non-linear, the ester polar group shall
generate enough dipole in addition to triazole ring unit which pro-
motes the formation of smectic A mesophases.
The occurrence of nematic phases in compounds 7a and c was
evidenced by observation of Schlieren texture of nematic phase.
Fig. 5. X-ray diffraction pattern of the smectic (left), nematic (middle), and isotropic liquid (right) of the BiPhMeO, recorded at T = 170, 235 and 245 °C, respectively. The scale
bar indicates 3 nmꢀ1
.

28
C. Benbayer et al. / Journal of Molecular Structure 1034 (2013) 22–28
As a representative case of nematic phase, the texture of (7c) is
illustrated in Fig. 2c. Upon cooling the isotropic liquid, the appear-
ance of colorful birefringence domains was noted. By cooling the
isotropic liquid phase, Schlieren texture showing a network of
black brushed connecting centers of point and line defects, was ob-
served. On further cooling the nematic phase, more ordered SmA
phase was observed at lower temperature. The co-existence of
the homogeneous (fan-shaped texture) and homeotropic (dark
area) textures confirmed the presence of SmA.
X-ray scattering has been done to confirm the mesomorphic
structure of the different compounds. Fig. 5 displays the typical
patterns obtained for biPhMeO by increasing temperature: sharp
Bragg reflection characteristic of long range positional order in
the smectic phase; ‘‘butterflies’’ anisotropic pattern arising from
nematic ordering, where the large radial width reflects a liquid-like
order; isotropic broad ring characteristic of a liquid order at high
temperature. Despite a study of the smectic layer spacing as a func-
tion of temperature (data not shown), the nature of the smectic
phase (smectic A or smectic C) was difficult to assign by X-ray scat-
tering study [30].
existence range of the smectic A mesophase, in favor of a new
nematic mesophase.
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Two series of novel [1,2,3]-triazole based mesogenic derivatives
were synthesized using the reaction of esterification of 4-decyloxy-
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