Columnar mesomorphism of bent-rod mesogens containing 1,2,4-oxadiazole rings

Article abstract of DOI:10.1016/j.tet.2011.10.019

In this study, the synthesis, characterization, and mesomorphic properties of ten new bent-rod compounds containing two units of 1,2,4-oxadiazoles are reported. In order to understand the relationship between the structure and the mesomorphic behavior, molecules containing a variety of polar substituents (i.e., I, NO₂, NH₂, OH) on the central rigid core were prepared. The hexagonal columnar mesomorphism was characterized by DSC and POM and the nature of the mesophases was established through XRD studies. The driving force for self-assembly can be explained by microsegregation between the aliphatic parts and the polar parts, producing a dimer, trimer, and tetramer inside a single disc.

Full text of DOI:10.1016/j.tet.2011.10.019

Tetrahedron 67 (2011) 9491e9499
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Columnar mesomorphism of bent-rod mesogens containing 1,2,4-oxadiazole
rings
,
a
a
a
a
b
Hugo Gallardo a , Marli Ferreira , Andre A. Vieira , Eduard Westphal , Fernando Molin , Juliana Eccher ,
*
ꢀ
Ivan H. Bechtold b
a
ꢀ
Departamento de Química-INCT Catalise, Universidade Federal de Santa CatarinadUFSC, 88040-900 Florianopolis, SC, Brazil
Departamento de Física, Universidade Federal de Santa CatarinadUFSC, 88040-900 Florianopolis, SC, Brazil
b
ꢀ
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 July 2011
Received in revised form 5 October 2011
Accepted 6 October 2011
Available online 14 October 2011
In this study, the synthesis, characterization, and mesomorphic properties of ten new bent-rod com-
pounds containing two units of 1,2,4-oxadiazoles are reported. In order to understand the relationship
between the structure and the mesomorphic behavior, molecules containing a variety of polar sub-
stituents (i.e., I, NO2, NH2, OH) on the central rigid core were prepared. The hexagonal columnar
mesomorphism was characterized by DSC and POM and the nature of the mesophases was established
through XRD studies. The driving force for self-assembly can be explained by microsegregation between
the aliphatic parts and the polar parts, producing a dimer, trimer, and tetramer inside a single disc.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Bent-rod
Liquid crystals
1,2,4-Oxadiazoles
Columnar mesomorphic
Synthesis
1. Introduction
polarization to be modified, and thus strongly influences their
physical properties and mesomorphic behavior.17 Also, the pres-
Discotic liquid crystals (DLCs) are of great interest due to their
unique self-assembled structures and potential applications in or-
ganic devices, such as field-effect transistors,1 photovoltaic solar
cells,2 optical data storage devices,3 sensors,4 and electrolumines-
cent displays.5 The main reason for the wide applicability of DLCs is
their high charge-carrier mobility and their one-dimensional (1D)
ence of heteroatoms, such as oxygen, nitrogen, and sulfur atoms,
arranged in a non-symmetric distribution, favors the formation of
a dipole moment and increases the longitudinal and/or lateral in-
teractions.18 Moreover, the incorporation of five-membered heter-
oaromatic rings into the central core of calamitic molecules results
in a bent-shaped core, which favors the formation of special kinds
of self-assembly. Thus, non linear bent-core liquid crystals based on
the oxadiazole heterocycles appear to be of great potential in the
search for the nematic biaxial phase.19
1,2,4-Oxadiazoles derivatives have already been extensively
studied due to their application in medicinal chemistry (antican-
cer,20 anti-inflammatory,21 and anti-HIV agents22). However, al-
though this heterocycle also has potential for applications in
advanced materials (DLCs or film forming compounds), so far it has
not been extensively studied in terms of the properties of such
materials.23
Thus, this paper presents a new set of bent-rod mesogens
(Schemes 1 and 2), which form columnar phases. Besides the
synthesis of these molecules derived from 1,2,4-oxadiazole, we
report herein a study on the relationship between the chemical
structure and the mesomorphic, thermal and optical properties. As
far as we know, columnar liquid crystals containing the 1,2,4-
oxadiazole unit in their structure have not been previously
reported.
aromatic pep
stacking.6
DLCs are typically described as disc-shaped molecules with
a rigid aromatic core and flexible peripheral chains.7 However,
many non-discoid molecules, such as half-disc shaped,8 butterfly-
shaped,9 star-shaped,10 and bent-core,11 have been studied in an
attempt to develop new types of core architecture for columnar
mesophases. The driving forces for the self-assembly of non-
discotic molecules to form a disc-like structure include hydrogen-
bonding,12
pep
interactions,13 ionic interactions,14 and charge-
transfer.15 Another driving force for self-assembly involves micro-
segregation, which is induced by incompatibility between the ar-
omatic rigid core and the alkyl chains, as observed for discotic and
polycatenar liquid crystals.16
The introduction of heterocyclic moieties into the rigid unit of
thermotropic liquid crystals enables their molecular geometry and
* Corresponding author. E-mail address: hugo@qmc.ufsc.br (H. Gallardo).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.10.019

9492
H. Gallardo et al. / Tetrahedron 67 (2011) 9491e9499
Scheme 1. Synthesis of final products (H-2, H-4, I-2, I-4, NO2-2, and NO2-4) and intermediates (OAc-2 and OAc-4). TBAB used only for reaction with compound 2.
Scheme 2. Synthesis of final products (NH2-2, NH2-4, OH-2, and OH-4).
2. Results and discussion
2.1. Synthesis
The structures of all the compounds were characterized by IR, 1H
and 13C NMR spectra and elemental analysis.
2.2. Thermal and mesomorphic behavior
The synthesis of compounds derived from the 1,2,4-oxadiazole ring
was carried out as shown in Scheme 1. Initially, compounds 1 and 2
were alkylated using 1-bromododecane and potassium carbonate
(and TBAB for compound 2), resulting in the intermediate 4-(dode-
cyloxy)benzonitrile (3), and 3,4-bis(dodecyloxy) benzonitrile (4), re-
spectively. The intermediates 4-(dodecyloxy)-N0-hydroxybenzi
midamide (5) and 3,4-bis(dodecyloxy)-N0-hydroxybenzimidamide (6)
were then obtained from compounds 3 and 4 by the Tiemamn re-
action24 using hydroxylamine hydrochloride and potassium hydroxide
in a methanol/water mixture. Finally, the 1,2,4-oxadiazole ring was
formed by the reaction between the corresponding amidoximes and
the freshly prepared acid dichloride 8aed in dry pyridine and under
reflux, affording the compounds (H-2, H-4, I-2, I-4, NO2-2, and NO2-4)
in 34e49% yield.
Compounds OAc-2 and OAc-4 were not isolated, since the
deprotection was performed in situ with NaOH(aq), resulting in
compounds OH-2 and OH-4 (Scheme 2) in 62 and 59% yields, re-
spectively. Compounds NH2-2 and NH2-4 were prepared from NO2-
2 and NO2-4 via reduction of the nitro group by SnCl2$2H2O, with
93 and 90% yields, respectively.
The mesomorphic properties of the final compounds were in-
vestigated by polarized optical microscopy (POM) and differential
scanning calorimetry (DSC). The thermal stability was verified by
thermogravimetric analysis (TGA). These results are summarized in
Table 1. Four of the ten molecules synthesized showed liquid crystal
properties. Compounds H-4, NH2-4, and OH-2 showed a mono-
tropic columnar hexagonal (Colh) mesophase, while compound
OH-4 exhibited a very stable enantiotropic Colh mesophase, with
a range of 101.8 ꢀC (Fig. 1). This compound did not show crystalli-
zation during cooling (at a rate of 10 ꢀC minꢁ1), remaining in
a supercooled state until room temperature.
Fig. 2 shows the mesophase characteristic pseudo focal-conic
texture, which was observed by POM for compounds NH2-4 and
OH-2 when the samples were slowly cooled from the isotropic
state. This texture, accompanied by large homeotropic domains, is
often characteristic of the Colh mesophase25 with a preferentially
uniaxial character.26
A bar graph illustrating the mesophase ranges is shown in the
Fig. 3. In general, polycatenar compounds show nematic (N),

H. Gallardo et al. / Tetrahedron 67 (2011) 9491e9499
9493
Table 1
Transition temperatures (ꢀC), enthalpy changes (kJ molꢁ1), and decomposition
temperatures (ꢀC) of final compounds
Transitiona
T (
D
H)a Heating
T (ꢁD
H)a Cooling
Tdec
b
Compound
H-2
H-4
Cr-I
Cr-I
117.9 (37.4)
81.3 (87.2)
107.9 (31.2)
322
339
I-Colh
Colh-Cr
Cr-I
Cr-I
Cr-I
Cr-I
Cr-I
Cr-I
78.3 (34.6)
58.7 (47.2)
100.7
89.5 (64.6)
100.28 (27.9)
99.5 (56.6)
139.0
I-2
I-4
NO2-2
NO2-4
NH2-2
NH2-4
114.0
305
319
307
320
298
321
105.7 (61.6)
116.8 (68.4)
115.0 (49.63)
143.0
131.1 (24.2)
I-Colh
Colh-Cr
Cr-I
I-Colh
Colh-Cr
Cr-Colh
Colh-I
130.8 (16.5)
98.7 (13.9)
OH-2
OH-4
121.5 (24.9)
300
309
107.4 (25.0)
61.8 (13.7)
176.9 (5.6)
82.8 (56.3)
184.6 (7.4)
Fig. 3. Bar graph showing the phase behavior of the final compounds.
Colh¼enantiotropic liquid crystal; Colhꢁm¼monotropic liquid crystal.
Cr¼crystal phase; Colh¼hexagonal columnar phase; I¼isotropic liquid.
a
Transition determined by DSC and POM at a scan rate of 10 ꢀC minꢁ1
.
b
Thermogravimetric measurements referring to the beginning of decomposition
comparison with H-4, NH2-4, OH-2, and OH-4 can be explained by
the tendency for hydrogen-bonding, dipole, and steric interactions
to occur.16b In the case of the compounds NH2-4, OH-2, and OH-4,
the formation of hydrogen-bonds prevents the free rotation of the
substituent groups, this being responsible for the unique packing.
The TGA investigation of these new bent-rod mesogens derived
from 1,2,4-oxadiazole indicated that they have good thermal sta-
bility, with decomposition temperatures ranging between 298 and
339 ꢀC. Also, we noted that the compounds containing four ali-
phatic chains (H-4, I-4, NO2-4, NH2-4, and OH-4) are slightly more
stable than the compounds with only two (H-2, I-2, NO2-2, NH2-2,
and OH-2). Furthermore, both products without substituent (H-2
and H-4) are more stable than the other molecules. Compounds
with four aliphatic chains showed lower melting points than
compounds with two aliphatic chains.
under a nitrogen atmosphere with heating rate of 10 ꢀC minꢁ1
.
2.3. X-ray diffraction studies
The mesophase assignments made by POM were ratified by
X-ray diffraction analysis. The diffractogram patterns obtained are
characteristic of a hexagonal columnar arrangement, where the
reflection peaks in the low-angle region were attributed as (10),
Fig. 1. Thermogram obtained by DSC analysis of second heating and cooling at
10 ꢀC minꢁ1 showing the thermal transitions for compound OH-4.
(11), (20), and (21) with
1:O3:O4:O7.8a,28 The observed values (d, obsd) were determined by
applying the Bragg’s Law to the diffracted angles and are sum-
marized in Table 2. The calculated values (d, calcd) where obtained
by assuming the first maximum (10) and then the second order
peaks were calculated assuming a hexagonal structure, in order to
compare with the measured values and to confirm the hexagonal
a
reciprocal spacing ratio of
smectic (Sm), columnar (Col), and/or cubic mesophases, depending
on their molecular structure and also on the number and position
of the terminal alkyl chains, the core length and polar sub-
stituents.27 Some final compounds have the thermal properties of
an ordinary solid. This difference in the mesomorphic behavior in
q
Fig. 2. Polarized optical micrographs of columnar phases formed upon cooling from isotropic phase (200ꢂ): observed for compound NH2-4 at 130.3 ꢀC (left) and compound OH-2 at
107.0 ꢀC (right).

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H. Gallardo et al. / Tetrahedron 67 (2011) 9491e9499
Table 2
Based on the results obtained from the X-ray experiments and
considering the density of these materials as 1 g cmꢁ3, the number
of molecules per average unit cell (Z) can be obtained according to
reports in the literature.31 The Z value for H-4 and NH2-4 is three,
which leads to the formation of discs with a total of twelve alkoxy
chains. The mesomorphism observed for H-4 is the result of
a microsegregation between the aliphatic parts and the polar parts
inside the disc.32 However, for NH2-4 the molecules arranged
within the disc can form hydrogen-bonds between the amine
groups. There are four molecules for the OH-2 unit disc, resulting in
a total of eight alkoxy chains. These molecules are arranged within
the disc probably with hydrogen-bonding between the hydroxyl
groups. In the case of H-4 or compounds NH2-4 and OH-2, the
absence of additional stabilization forces leads to the formation of
monotropic Colh mesophases. On the other hand, for the compound
OH-4, there are two molecules per unit disc resulting in eight
alkoxy chains.
X-ray diffraction data for final compounds in mesophases
d, obsd (A) d, calcd (A) a (A) La (A)
ꢁ
ꢁ
ꢁ
ꢁ
Compound Mesophase
Miller
indices
H-4
Colh at 75 ꢀ
C
10
11
20
21
34.6
20.1
17.2
13.1
34.6
20.0
17.3
13.1
40.0 28.6
7.0 (br)
4.6 (br)
3.5 (br)
36.9
NH2-4
Colh at 130 ꢀ
C
10
20
36.9
18.5
42.6 30.0
18.5
7.0 (br)
4.6 (br)
3.5 (br)
36.9
OH-2
OH-4
Colh at 105 ꢀ
Colh at 180 ꢀ
C
C
10
20
36.9
18.5
42.6 31.0
38.7 28.0
19.3
4.6 (br)
3.5 (br)
33.5
19.5
16.7
This compound showed an enantiotropic Colh phase with a very
stable mesomorphism, which can be attributed to the formation of
a dimer through hydrogen-bonding between the hydroxyl group
and the oxadiazole ring nitrogen33 (see Fig. 5).
10
11
20
33.5
19.3
16.8
7.1 (br)
4.6 (br)
3.5 (br)
a
L estimated by ChemBio3D Ultra Software, version 11.0.1.
phase. The lattice constant (a) was obtained by following reports in
the literature.29 The rigid core length (L) of the proposed structures
(dimer, trimer, and tetramer) inside a single disc was calculated in
order to make comparisons with the lattice constant.
Fig. 4 shows the X-ray diffraction pattern of compound OH-4 in
the columnar phase at 180 ꢀC, where the position of the peaks and
the respective distances are indicated. All the liquid crystalline
compounds exhibited similar diffractograms with a broad re-
ꢁ
flection at around 3.5 A, which is consistent with the
p
ep
stacking
between neighboring mesogens within individual columns. This
may indicate a highly ordered mesophase, i.e., a long-range order
along the columns. In addition, the characteristic diffuse peak at
ꢁ
around 4.6 A corresponds to the liquid-like order between the alkyl
ꢁ
chains. The broad peak at around 7.0 A is consistent with the rep-
etition of the distance of two alternated ordered discs. By com-
paring the rigid core length, L, with the distance between the center
of two columns in the hexagonal structure, given by a, one can see
ꢁ
ꢁ
that the difference varies from 10.7 Aꢁ12.6 A. The maximum value
ꢁ
Fig. 5. Suggested molecular organization inside the hexagonal columnar phase based
on X-ray data obtained for OH-4.
estimated for one side chain is 16.0 A, indicating that all the com-
pounds may present interdigitation of the alkoxy chains or non
linear conformations.30
For comparison purposes, we prepared the same compound
OH-4 but with a chain length of only 6 carbons, OH-4 C6. This new
compound also shows columnar mesomorphism (Cr 144.2 Colh
176.5 I ꢀC). These results corroborates with our evidences of co-
lumnar arrangement promoted by hydrogen-bonding, once that
there is no formation of smectic phases, which would indicate
a polycatenar behavior (for DSC, mesophase texture and XRD
analysis, see Supplementary data).
IR spectroscopy was used to examine the hydrogen-bonding in
this dimer. The IR spectra were run on a Varian 3100 FT-IR spec-
trometer. Fig. 6 shows the infrared spectra in solid state (KBr) at
room temperature and for a sample that was heated to a tempera-
ture of 195 ꢀC and then cooled slowly to room temperature, the two
samples were examined between 4000 and 450 cmꢁ1. The forma-
tion of hydrogen-bonds in the dimer is detected through the
modification of the OeH stretching vibrations. The n-OH band in
the solid state at ca. 3290 cmꢁ1 is shifted by ca. 40 cmꢁ1 in the
liquid crystal phase (new band centered at z3250 cmꢁ1). This is
indicative of the formation of a stronger hydrogen bond in the
dimer.
Fig. 4. X-ray diffraction pattern of the hexagonal columnar mesophase of OH-4 at
180 ꢀC.

H. Gallardo et al. / Tetrahedron 67 (2011) 9491e9499
9495
Fig. 7. Optical absorption spectra of the final compounds H-4, NO2-2, NH2-2, and
OH-4, in chloroform solution.
Fig. 6. The infrared spectra in solid state and liquid crystals (KBr) at room temperature
for OH-4.
emission maxima band.35 These compounds exhibited blue emis-
max
sion in solution (
and 156 nm.
l
¼331e457 nm) with stokes shifts between 38
The microsegregation between the aliphatic parts and the polar
parts inside a single disc may explain the absence of meso-
morphism in the compound analogue containing I and NO2 groups,
as efficient packing of molecules is sterically disfavored by the in-
corporation of volumous I and NO2. The Z number observed in all
mesomorphic cases is consistent with the number of alkoxy chains
usually required for columnar phases to be present. Liquid crystal
behavior was found for systems with eight and twelve alkoxy
chains.34
abs
Compounds NO2-2 and NO2-4 showed weakly fluorescence
emission band, therefore, Stokes shift was not calculated.
The optical absorption and emission of the final compounds in
the solid state were measured in thin films, obtained by spin-
coating from chloroform solution onto a quartz plate. The com-
pounds also showed fluorescence in the solid phase (with the ex-
ception of compounds NO2-2, NO2-4), exhibiting emission maxima
at wavelengths between 388 and 506 nm. Most of the compounds
showed a red-shift in the solid state spectrum compared with their
emission wavelengths in chloroform solution while compounds
H-2, H-4, and I-4 showed blue-shifts.
2.4. Absorption properties
The UVevis spectroscopy data for the 1,2,4-oxadiazole final
compounds in chloroform and in thin film are summarized inTable 3.
All compounds exhibited similar absorptions between 250 and
270 nm, having maxima between 262 and 267 nm. In Fig. 7 four
representative examples are shown. These absorption bands are
3. Conclusions
A new series derived from heterocyclic 1,2,4-oxadiazole was
prepared and characterized. The mesomorphic and photophysical
behavior were studied. Four compounds presented liquid-
ecrystalline phases, characterized by POM and DSC. The nature of
the mesophases was established by XRD studies. These materials
showed a tendency toward hexagonal columnar mesomorphism.
Their ability to form Colh despite their bent-rod shape may be
explained by dipole, steric interactions, and hydrogen-bonding
producing a dimer, trimer, and tetramer inside a single disc,
allowing the formation of a columnar phase, which was observed in
attributed to the pep* transitions in the heteroaromatic portion of
the molecule due to the high molar absorption coefficient
(
3
¼1.8e8.1ꢂ104 L molꢁ1 cmꢁ1). For compounds H-4, I-4, NO2-4,
NH2-4, and OH-4 a shoulder and for NH2-2 and OH-2 a minor en-
ergy band is observed between 292 and 347 nm. This second band
corresponds to an nep* transition. Absorption spectra were also
carried out in different solvents as benzene, methanol, and aceto-
nitrile, and the same pattern were observed. Stokes shift were
calculated considering de minor absorption energy band and
Table 3
Summary of photophysical properties of the final compounds
Compound
lmabasx/nma
(
3
/104)b
lmemax/nma,c
Stokes shift/nma
lmabasx/nmd
lmemax/nmd,c
Stokes shift/nmd
H-2
H-4
I-2
I-4
NO2-2
NO2-4
NH2-2
NH2-4
OH-2
OH-4
262 (2.3)
265 (6.4)/303 (2.1)
264 (6.2)
267 (6.4)/301 (2.3)
268 (1.8)/328 (0.3)
266 (2.1)/293 (1.0)
262 (7.8)/347 (0.5)
263 (7.4)/292 (2.5)/344 (0.7)
263 (8.1)/317 (0.8)
265 (4.8)/307 (1.4)
398
440
331
457
de
136
137
67
156
de
de
48
52
38
141
252
246; 311
259; 367
260
388
407
506
424
de
136
96
139
164
de
de
128
68
263
de
263; 300
300; 369
262; 362
259; 338
263; 325
de
395
396
355
448
497
430
423
446
85
121
a
Measured in CHCl3 (5.0ꢂ10ꢁ6 mol Lꢁ1).
b
c
Units¼L molꢁ1 cmꢁ1
.
Excited at absorption maxima in low energy band.
Data recorded from solid thin films.
NO2-2 and NO2-4 are not fluorescents in chloroform solution and solid state.
d
e

9496
H. Gallardo et al. / Tetrahedron 67 (2011) 9491e9499
the X-ray diffraction studies. The compound OH-4 displays a stable
liquid crystal phase over a broad temperature range including at
room temperature after annealing. All of the compounds had good
thermal stability with decomposition temperatures higher than
298 ꢀC. The photophysical properties of these compounds, in so-
lution and in solid state, were evaluated, showing weak blue
emission in solution and variable Stokes shifts of between 38 and
156 nm.
were recorded on a Hitachi-F-4500. For the measurements in solid
state (thin films) an OceanOptics USB4000 spectrophotometer was
used.
We produced thin films of the compounds on glass plates using
the spin-coating technique for the absorption and fluorescence
measurements in solid state. The glass plates were first carefully
cleaned by washing with neutral detergent followed by a sequence
of 30-min sonications in acetone, alcohol, and water, and finally
dried in an oven. The solutions were prepared with chloroform at
a concentration of 2% (wt) and the films produced after spinning at
2000 rpm for 30 s, at room temperature.
4. Experimental
4.1. Materials and characterizations
4.5. Synthesis
The chemicals used in this study were 1-bromododecane (98%,
Acros Organics), 4-hydroxyacetanilide (98%, SigmaeAldrich), 3,4-
dihydroxybenzonitrile (97%, SigmaeAldrich), isophthalic acid (7a)
(99%, SigmaeAldrich), 5-nitroisophthalic acid (7c) (98%, Acros Or-
ganics), 5-aminoisophthalic acid (98þ%, Acros Organics),
5-hydroxyisophthalic acid (99%, Acros Organics). All other in-
organic and organic reagents and solvents were purchased from
commercial sources (SigmaeAldrich, Merck, Acros, Vetec, and
Synth) and used as received. Pyridine was dried by distillation over
KOH, and used as specified. Purifications by column chromatogra-
4.5.1. 4-(Dodecyloxy)benzonitrile (3). Firstly, 15.00 g (126.0 mmol)
of 4-hydroxybenzonitrile (1), 42.30 mL (176.0 mmol) of
1-bromododecane, 52.20 g (378.0 mmol) of K2CO3, and 350 mL of
butanone were placed into
a 500 mL round-bottomed flask
equipped with a condenser. The mixture was then refluxed and
stirred for 24 h. After this period, the suspension was filtered and
washed with hot butanone. The solvent was removed by rotary
evaporation and the solid obtained was recrystallized on ethanol,
affording 33.60 g of a white crystals (93%), mp 41.5e44.0 ꢀC (lit.
42e43 ꢀC).25 IR (KBr, cmꢁ1): nmax: 2916, 2850, 2218 (C^N), 1608,
ꢁ
phy used on silica gel 60e200 mesh 60 A (Acros), and re-
crystallization from commercial grade solvents. Infrared spectra
were recorded on a PerkineElmer model 283 spectrometer using
KBr discs. 1H and 13C NMR were recorded using a Varian Mercury
Plus spectrometer operating at 400 and 100.6 MHz, respectively,
using TMS as the internal standard. Elemental analysis was carried
out using a Carlo Erba model E-1110 instrument. The compounds 5-
iodoisophthalic acid (7b)36 and 5-acetoxyisophthalic acid (7d)37
were prepared by literature methods.
1509, 1302, 1256, 1172, 833, 547. 1H NMR (CDCl3),
d, ppm: 7.55 (d,
J¼8.9 Hz, 2H, AreH), 6.92 (d, J¼8.9 Hz, 2H, AreH), 3.98 (t, J¼6.6 Hz,
2H, eOCH2e), 1.78 (qt, J¼6.6 Hz, 2H, eOCH2CH2e), 1.44 (m, 2H,
eCH2e), 1.22e1.33 (br, 16H, eCH2e), 0.87 (t, J¼6.7 Hz, 3H, eCH3).
13C NMR (CDCl3),
29.9, 29.9, 14.9.
d, ppm: 162.7, 134.2, 119.5, 115.4, 103.8, 68.6, 32.2,
4.5.2. 3,4-Bis(dodecyloxy)benzonitrile (4). Firstly,12.00 g (88.9 mmol)
of 3,4-dihydroxybenzonitrile (2), 53.40 mL (222.2 mmol) of 1-
bromododecane, 49.07 g (355.6 mmol) of K2CO3, 1.43 g (4.44 mmol)
of TBAB, and 350 mL of butanone were placed into a 500 mL round-
bottomed flask equipped with a condenser. The mixture was then
refluxed and stirred for 24 h. After this period the suspension was
filtered, washed with hot butanone and the solvent was removed by
rotary evaporation. The solid obtained was recrystallized over ace-
tonitrile, yielding 39.80 g of a white solid (95%), mp 82.0e82.5 ꢀC (lit.
81e83 ꢀC).25 IR (KBr, cmꢁ1): nmax: 2954, 2918, 2872, 2849, 2221
(C^N), 1597, 1581, 1519, 1468, 1422, 1280, 1244, 1139, 992, 85, 812,
4.2. Thermal analysis
The melting points, thermal transition and mesomorphic tex-
tures were observed with an Olympus BX50 microscope, equipped
with a Mettler Toledo FP 82 hot stage and a PM-30 exposure control
unit. DSC measurements were carried out using a Shimadzu in-
strument with a DSC-50 module. Thermal transitions were de-
termined at a scan rate of 10 ꢀC minꢁ1 and a nitrogen flow of
50 mL minꢁ1. The thermal stability was analyzed using Shimadzu
equipment with a TGA-50 module at a heating rate of 10 ꢀC minꢁ1
722. 1H NMR (CDCl3),
d
, ppm: 7.23 (dd, J¼8.4 Hz and 1.9 Hz, 1H,
and nitrogen flow of 50 mL minꢁ1
.
AreH); 7.07 (d, J¼1.9 Hz, 1H, AreH); 6.86 (d, J¼8.4 Hz, 1H, AreH);
4.02 (t, J¼6.6 Hz, 2H, eOCH2e); 3.98 (t, J¼6.6 Hz, 2H, eOCH2e); 1.83
(m, 4H, eOCH2CH2e); 1.46 (m, 4H, eCH2e); 1.25e1.36 (br, 32H,
4.3. X-ray diffraction analysis
eCH2e); 0.88 (t, J¼6.7 Hz, 6H, eCH3). 13C NMR (DMSO-d6, ꢁ90 ꢀC),
d,
The X-ray diffraction experiments were carried out with the
ppm: 151.8, 147.7, 125.1, 117.6, 115.8, 112.9, 108.0, 68.1, 67.6, 29.9, 27.6,
27.6, 27.5, 27.3, 27.2, 24.1, 20.6, 12.3.
X’PERT-PRO (PANalytical) diffractometer using Cu K
a
radiation
¼1.5418 A), with an applied power of 1.2 kVA. The scans were
performed in continuous mode from 2ꢀ to 30ꢀ (2
angle) and the
ꢁ
(l
q
4.6. Synthesis of amidoximes (5,6)
diffracted radiation collected with an the X’Celerator detector. The
samples were prepared by prior heating (with a hot stage) of an
amount of powder on a glass plate until the compound melted to
the liquid state, followed by cooling to room temperature. As a re-
sult, we obtain a film approximately 1 mm thick. The films were
then placed in the diffractometer chamber on the TCU2000 tem-
perature control unit (Anton Paar), which allows control of the
sample temperature during the measurement. The films were first
heated until the isotropic phase and the diffraction patterns col-
lected during cooling back through the mesophases.
General procedure. Firstly, 41.8 mmol of the appropriate nitrile 3
or 4 and 200 mL of methanol were placed into a 500 mL round-
bottomed flask equipped with a condenser and 92.0 mmol of
NH2OH$HCl and 92.0 mmol of KOH dissolved in 200 mL of meth-
anol/water 8:2 were then added. The resultant mixture was kept
under reflux for 24 h. After this period the solvent was removed by
rotary evaporation and the solid was washed with plenty of water.
The solid obtained was recrystallized on ethanol.
4.6.1. 4-(Dodecyloxy)-N0-hydroxybenzimidamide (5). Yield: 85% of
4.4. UVevis absorption and fluorescence spectroscopy
a white solid, mp 81e83 ꢀC (lit. 81e82 ꢀC).38 IR (KBr, cmꢁ1): nmax
:
3450, 3350, 2920, 2853, 1654, 1611, 1521, 1394, 1253, 826. 1H NMR
(CDCl3),
, ppm: 7.55 (d, J¼8.9 Hz, 2H, AreH), 6.90 (d, J¼8.9 Hz, 2H,
AreH), 4.82 (br, 2H, eNH2), 3.97 (t, J¼6.6 Hz, 2H, eOCH2e), 1.78 (qt,
An HP UVevis model 8453 spectrophotometer was used to re-
cord absorption spectra in solution, while the fluorescence spectra
d

H. Gallardo et al. / Tetrahedron 67 (2011) 9491e9499
9497
J¼6.6 Hz, 2H, eOCH2CH2e), 1.46 (m, 2H, eCH2e), 1.38e1.22 (m,
J¼1.6 Hz, AreH), 8.75 (d, 2H, J¼1.6 Hz, AreH), 8.11 (d, 4H, J¼8.7 Hz,
AreH), 7.02 (d, 4H, J¼8.7 Hz, AreH), 4.04 (t, 4H, J¼6.6 Hz, eOCH2e),
1.82 (qt, 4H, J¼6.6 Hz, eOCH2CH2e), 1.48 (m, 4H, eCH2e), 1.41e1.25
16H, eCH2e), 0.88 (t, J¼6.6 Hz, 3H, eCH3). 13C NMR (CDCl3),
d, ppm:
160.6, 152.6, 127.1, 124.6, 114.5, 68.1, 31.9, 29.6, 29.6, 29.6, 29.6, 29.4,
29.3, 29.2, 26.0, 22.7, 14.1.
(br, 32H, eCH2e), 0.88 (t, 6H, J¼6.6 Hz, eCH3). 13C NMR (CDCl3),
d,
ppm: 173.0, 169.2, 162.0, 140.4, 129.4, 127.2, 126.8, 118.8, 115.1, 94.8,
68.4, 32.2, 29.8, 29.6, 29.6, 29.4, 26.3, 22.9, 14.4. Elemental analysis
C46H61IN4O4: required C, 64.18; H, 7.14; N, 6.51; Found: C, 64.05; H,
7.40; N, 6.42%.
4.6.2. 3,4-Bis(dodecyloxy)-N0-hydroxybenzimidamide
(6). Yield:
93% of white solid, mp 88.5e88.9 ꢀC. IR (KBr, cmꢁ1): nmax: 3449,
3351, 3182, 2919, 2849, 1640, 1592, 1518, 1469, 1440, 1388, 1332,
1265, 1228, 1143, 1125, 724. 1H NMR (CDCl3),
d, ppm: 7.18 (s, 1H,
AreH), 7.12 (d, J¼8.3 Hz, 1H, AreH), 6.86 (d, J¼8.3 Hz, 1H, AreH),
4.83 (br, 2H, eNH2), 4.01 (m, 4H, eOCH2e), 1.81 (m, 4H,
eOCH2CH2e), 1.46 (m, 4H, eCH2e), 1.30e1.24 (m, 32H, eCH2e),
4.7.4. 5,50-(5-Iodo-1,3-phenylene)bis(3-(3,4-bis(dodecyloxy)phenyl)-
1,2,4-oxadiazole) (I-4). The product was recrystallized twice from
2-propanol, to afford 40% of a light violet solid, mp 105.7 ꢀC. IR (KBr,
cmꢁ1): nmax: 2951, 2851, 1605, 1551, 1497, 1486, 1470, 1448, 1388,
0.88 (t, J¼6.6 Hz, 6H, eCH3). 13C NMR (MHz, CDCl3),
d, ppm: 153.1,
150.9, 149.3, 125.3, 118.6, 113.3, 111.5, 69.5, 68.4, 32.2, 30.0, 29.9,
29.9, 29.9, 29.7, 29.6, 29.5, 29.4, 29.3, 26.2, 22.9, 14.4.
1339, 1221, 1226, 1139, 1122, 756. 1H NMR (CDCl3),
d, ppm: 8.98 (t,
1H, J¼1.5 Hz, AreH); 8.76 (d, 2H, J¼1.5 Hz, AreH); 7.76 (dd, 2H,
J¼8.6 Hz and J¼1.8 Hz, AreH); 7.66 (d, 2H, J¼1.8 Hz, AreH); 6.98 (d,
2H, J¼8.6 Hz, AreH); 4.13 (t, 4H, J¼6.4 Hz, eOCH2e); 4.08 (t, 4H,
J¼6.6 Hz, eOCH2e); 1.88 (qt, 4H, J¼6.6 Hz, eOCH2CH2e); 1.86 (qt,
4H, J¼6.4 Hz, eOCH2CH2e), 1.52 (qt, 4H, J¼6.4 Hz, eCH2e), 1.50 (qt,
4H, J¼6.6 Hz, eCH2e), 1.42e1.22 (br, 64H, eCH2e), 0.88 (dt, 12H,
4.7. Synthesis of 1,2,4-oxadiazoles
General procedure. Firstly, 0.5 g of the corresponding acid 7aed,
3 mL of SOCl2 and 1 drop of DMF were placed inside a round-
bottomed flask equipped with a condenser and a drying tube. The
mixture was then refluxed for 4 h. The excess SOCl2 was removed
by vacuum distillation and 2.4 equiv of the hydroxylamine (5, 6)
and 9 mL of dry pyridine were added to the mixture, which was
refluxed for a further 24 h. After this period the solution was cooled
to room temperature and poured into 200 mL of ice/water. The
precipitate was filtered, washed with plenty of water, and purified.
J¼6.6 Hz, eCH3). 13C NMR (CDCl3),
d, ppm: 172.7, 169.1, 151.9, 149.2,
140.1, 126.9, 126.6, 121.0, 118.6, 112.9, 112.0, 94.6, 69.3, 69.1, 31.9,
29.6, 29.6 29.4, 29.4, 29.2, 29.1, 26.0, 26.0, 22.7, 14.1. Elemental
analysis C70H109IN4O6: required C, 68.38; H, 8.94; N, 4.56; Found: C,
68.05; H, 9.08; N, 4.59%.
4.7.5. 5,50-(5-Nitro-1,3-phenylene)bis(3-(4-(dodecyloxy)phenyl)-
1,2,4-oxadiazole) (NO2-2). The solid obtained was purified by col-
umn chromatography (silica gel, CH2Cl2), followed by re-
crystallization on ethyl acetate. Light yellow solid, yield 49%, mp
116.8 ꢀC. IR (KBr, cmꢁ1): nmax: 2924, 2851, 1611, 1540, 1348, 1254,
4.7.1. 1,3-Bis(3-(4-(dodecyloxy)phenyl)-1,2,4-oxadiazol-5-yl)benzene
(H-2). The crude product was purified by column chromatography
(silica gel, CH2Cl2), to give white solid, yield 35%, mp 117.9 ꢀC. IR
(KBr, cmꢁ1): nmax: 3070, 2923, 2852, 1610, 1548, 1469, 1421, 1362,
1172. 1H NMR (CDCl3),
d
, ppm: 9.31 (t, 1H, J¼1.6 Hz, AreH), 9.24 (d,
1253, 1172, 758. 1H NMR (CDCl3),
d
, ppm: 9.05 (t, 1H, J¼1.8 Hz,
2H, J¼1.6 Hz, AreH), 8.14 (d, 4H, J¼8.8 Hz, AreH), 7.04 (d, 4H,
J¼8.8 Hz, AreH), 4.05 (t, 4H, J¼6.6 Hz, eOCH2e), 1.83 (qt, 4H,
J¼6.6 Hz, eOCH2CH2e), 1.49 (m, 4H, eCH2e), 1.41e1.22 (br, 32H,
AreH), 8.42 (dd, 2H, J¼7.8 Hz and J¼1.8 Hz, AreH), 8.13 (d, 4H,
J¼8.4 Hz, AreH), 7.75 (t, 1H, J¼7.8 Hz, AreH), 7.02 (d, 4H, J¼8.4 Hz,
AreH), 4.04 (t, 4H, J¼6.4 Hz, eOCH2e), 1.82 (qt, 4H, J¼6.4 Hz,
eOCH2CH2e), 1.47 (m, 4H, eCH2e), 1.41e1.22 (m, 32H, eCH2e),
eCH2e), 0.88 (t, 6H, J¼6.6 Hz, eCH3). 13C NMR (CDCl3),
d, ppm:
172.4, 169.5, 162.2, 149.4, 132.5, 129.5, 127.5, 126.2, 118.4, 115.1, 68.5,
32.2, 29.9, 29.9, 29.8, 29.8, 29.6, 29.59, 29.4, 26.2, 22.9, 14.4. Ele-
mental analysis C46H61N5O6: required C, 70.83; H, 7.88; N, 8.98;
Found: C, 70.84; H, 8.00; N, 8.93.
0.88 (t, 6H, J¼6.4 Hz, eCH3). 13C NMR (CDCl3),
d, ppm: 174.2, 168.9,
161.7, 131.7, 130.0, 129.2, 127.7, 125.5, 118.8, 114.8, 68.2, 31.9, 29.7,
29.64, 29.60, 29.6, 29.4, 29.4, 29.2, 29.0, 22.7, 14.1. Elemental anal-
ysis C46H62N4O4: required C, 75.17; H, 8.50; N, 7.62; Found: C,
74.94; H, 8.95; N, 7.83%.
4.7.6. 5,50-(5-Nitro-1,3-phenylene)bis(3-(3,4-bis(dodecyloxy)phe-
nyl)-1,2,4-oxadiazole) (NO2-4). The crude product was purified by
column chromatography (silica gel, CH2Cl2) and recrystallized over
ethyl acetate. The yield was 34% of a light yellow powder, mp
115.0 ꢀC. IR (KBr, cmꢁ1): nmax: 3069, 2919, 2850, 1608, 1537, 1467,
4.7.2. 1,3-Bis(3-(3,4-bis(dodecyloxy)phenyl)-1,2,4-oxadiazol-5-yl)
benzene (H-4). The solid obtained was purified by column chro-
matography (silica gel, CH2Cl2), followed by recrystallization on
ethyl acetate, yielding 34% of a white solid, mp 81.3 ꢀC (monotropic
1349, 1280, 1227, 742. 1H NMR (CDCl3),
d, ppm: 9.31 (s, 1H, AreH),
liquid crystal) I, ꢁ78.3 ꢀCdColh, ꢁ58.7 ꢀCdCr. IR (KBr, cmꢁ1): nmax
:
9.25 (s, 2H, AreH), 7.79 (d, 2H, J¼8.3 Hz, AreH), 7.67 (s, 2H, AreH),
6.99 (d, 2H, J¼8.3 Hz, AreH), 4.13 (t, 4H, J¼6.7 Hz, eOCH2e), 4.08 (t,
4H, J¼6.6 Hz, eOCH2e), 1.89 (qt, 4H, J¼6.6 Hz, eOCH2CH2e), 1.87
(qt, 4H, J¼6.7 Hz, eOCH2CH2e), 1.51 (m, 8H, eCH2e), 1.44e1.21 (br,
3069, 2919, 2850, 1607, 1555, 1501, 1467, 1263, 1223, 751. 1H NMR
(CDCl3),
d
, ppm: 9.06 (s, 1H, AreH), 8.44 (d, 2H, J¼7.8 Hz, AreH),
7.78 (d, 2H, J¼8.2 Hz, AreH), 7.75 (t,1H, J¼7.8 Hz, AreH), 7.69 (s, 2H,
AreH), 6.99 (d, 2H, J¼8.2 Hz, AreH), 4.13 (t, 4H, J¼6.4 Hz, eOCH2e),
4.08 (t, 4H, J¼6.6 Hz, eOCH2e),1.88 (qt, 4H, J¼6.6 Hz, eOCH2CH2e),
1.86 (qt, 4H, J¼6.4 Hz, eOCH2CH2e), 1.52 (qt, 4H, J¼6.4 Hz, eCH2e),
1.50 (qt, 4H, J¼6.6 Hz, eCH2e), 1.42e1.24 (br, 64H, eCH2e), 0.88 (t,
64H, eCH2e), 0.88 (m, 12H, eCH3). 13C NMR (CDCl3),
d, ppm: 172.4,
169.6, 152.4, 149.6, 149.4, 132.5, 127.5, 126.2, 121.4, 118.5, 113.2,
112.3, 69.6, 69.36, 32.2, 29.9, 29.9, 29.9, 29.9, 29.7, 29.7, 29.6, 29.5,
29.4, 26.3, 26.2, 22.9, 14.4. Elemental analysis C70H109N5O8: re-
quired C, 73.19; H, 9.56; N, 6.10; Found: C, 72.78; H, 10.55; N, 6.03.
12H, J¼6.4 Hz, eCH3). 13C NMR (CDCl3),
d, ppm: 174.4, 169.3, 152.1,
149.5, 132.0, 130.2, 128.0, 125.8, 121.3, 119.2, 113.2, 112.4, 69.6, 69.3,
32.2, 29.9, 29.7, 29.6, 29.5, 29.4, 26.3, 26.3, 22.9, 14.4. Elemental
analysis C70H110N4O6: required C, 76.18; H, 10.05; N, 5.08; Found: C,
75.46; H, 10.55; N, 5.00%.
4.7.7. Reduction of the compounds NO2-2 and NO2-4. Firstly,
0.38 mmol of the corresponding nitro (NO2-2, NO2-4), 1.92 mmol of
SnCl2$2H2O, 20 mL of ethyl acetate and 5 mL of ethanol were placed
into a round-bottomed flask equipped with a condenser. The
mixture was refluxed for 4 h and the solution was cooled to room
temperature, poured into 100 mL of ice/water and basified to pH 8
with NaOH aqueous solution (10%) under strong magnetic stirring
for 2 h. The organic phase was extracted with CH2Cl2 (2ꢂ30 mL).
The organic phases were combined and washed with NaOH
4.7.3. 5,50-(5-Iodo-1,3-phenylene)bis(3-(4-(dodecyloxy)phenyl)-
1,2,4-oxadiazole) (I-2). The product was recrystallized once over 2-
propanol and once over acetonitrile, obtaining 42% of a white solid,
mp 114.0 ꢀC. IR (KBr, cmꢁ1): nmax: 2914, 2848,1626,1540,1471,1416,
1350, 1242, 1172, 834, 756. 1H NMR (CDCl3),
d, ppm: 8.98 (t, 1H,

9498
H. Gallardo et al. / Tetrahedron 67 (2011) 9491e9499
aqueous solution (5%, 1ꢂ100 mL) and water (2ꢂ100 mL). The or-
ganic phase was dried with anhydrous Na2SO4, the solvent re-
moved and the crude product obtained was purified.
mp (liquid crystal) 82.8 ꢀC, Colh ꢁ184.6 ꢀC. IR (KBr, cmꢁ1): nmax
:
3407, 2923, 2848, 1607, 1564, 1489, 1466, 1443, 1384, 1349, 1267,
1220, 1148, 923, 799. 1H NMR (Pyridine-d5),
d, ppm: 8.79 (t, 1H,
J¼1.6 Hz, AreH), 8.56 (s, 1H, OHeAr), 8.24 (d, 2H, J¼1.6 Hz, AreH),
8.11 (dd, 2H, J¼8.4 Hz and J¼1.9 Hz, AreH), 8.06 (d, 2H, J¼1.9 Hz,
AreH), 7.24 (d, 2H, J¼8.4 Hz, AreH), 4.11 (t, 8H, J¼6.3 Hz,
eOCH2e), 1.88 (m, 8H, eOCH2CH2e), 1.56 (m, 8H, eCH2e),
1.41e1.21 (br, 64H, eCH2e), 0.90 (t, 12H, J¼6.3 Hz, eCH3). 13C NMR
4.7.8. 3,5-Bis(3-(4-(dodecyloxy)phenyl)-1,2,4-oxadiazol-5-yl)aniline
(NH2-2). The crude product was recrystallized once from butanone
and once from 2-propanol, yielding 93% of white powder, mp
143.0 ꢀC. IR (KBr, cmꢁ1): nmax: 3469, 3372, 2926, 2844, 1638, 1607,
1560, 1482,1427,1365,1251, 1177, 841, 755. 1H NMR (CDCl3),
d
, ppm:
(Pyridine-d5), d, ppm: 175.6, 170.0, 160.8, 153.4, 127.6, 122.3, 120.4,
8.39 (s, 1H, AreH), 8.10 (d, 4H, J¼8.9 Hz, AreH), 7.69 (s, 2H, AreH),
7.01 (d, 4H, J¼8.9 Hz, AreH), 4.15 (br, 2H, AreNH2), 4.03 (t, 4H,
J¼6.4 Hz, eOCH2e), 1.82 (qt, 4H, J¼6.4 Hz, eOCH2CH2e), 1.48 (qt,
4H, J¼6.4 Hz, eCH2e), 1.42e1.22 (br, 32H, eCH2e), 0.88 (t, 6H,
120.2, 119.0, 114.7, 113.9, 70.3, 70.0, 32.6, 30.5, 30.4, 30.4, 30.4, 30.3,
30.2, 30.2, 30.1, 27.0, 26.9, 23.4, 23.4, 14.7, 14.7. Elemental analysis
C70H110N4O7: required C, 75.09; H, 9.90; N, 5.00; found: C, 74.70;
H, 10.10; N, 5.00.
J¼6.6 Hz, eCH3). 13C NMR (CDCl3),
d, ppm: 174.7, 169.0, 161.9, 147.9,
129.3, 126.5, 119.1, 117.7, 117.5, 115.0, 68.4, 32.2, 29.9, 29.9, 29.8, 29.8,
29.6, 29.6, 29.4, 26.3, 22.9, 14.4. Elemental analysis C46H63N5O4:
required C, 73.66; H, 8.47; N, 9.34; Found: C, 73.55; H, 8.95; N, 9.29.
Acknowledgements
We thank the following institutions for financial support:
CAPES, CNPq, FAPESC, INCT/INEO and INCT-Catalise. The X-ray
4.7.9. 3,5-Bis(3-(3,4-bis(dodecyloxy)phenyl)-1,2,4-oxadiazol-5-yl)
aniline (NH2-4). The solid obtained was purified by column chro-
matography (silica gel, CHCl3/EtOH 96:4), followed by re-
crystallization in butanone, yielding 90% of a light yellow solid, mp
131.1 ꢀC (monotropic liquid crystal) I, ꢁ130.8 ꢀCdColh,
ꢁ98.7 ꢀCdCr. IR (KBr, cmꢁ1): nmax: 3465, 3344, 2923, 2848, 1634,
1607, 1560, 1427, 1380, 1325, 1263, 1228, 1142, 755. 1H NMR (CDCl3),
ꢀ
diffraction experiments were performed at the Laboratorio de
~
Difracao de Raios-X (LDRX-DF/UFSC).
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tet.2011.10.019.
d
, ppm: 8.41 (t, 1H, J¼1.4 Hz, AreH), 7.76 (dd, 2H, J¼8.5 Hz and
J¼1.9 Hz, AreH), 7.76 (d, 2H, J¼1.4 Hz, AreH), 7.68 (d, 2H, J¼1.9 Hz,
AreH), 6.98 (d, 2H, J¼8.5 Hz, AreH), 4.16 (br, 2H, AreNH2), 4.12 (t,
4H, J¼6.5 Hz, eOCH2e), 4.08 (t, 4H, J¼6.8 Hz, eOCH2e), 1.89 (qt, 4H,
J¼6.5 Hz, eOCH2CH2e), 1.87 (qt, 4H, J¼6.8 Hz, eOCH2CH2e), 1.52
(qt, 4H, J¼6.5 Hz, eCH2e), 1.50 (qt, 4H, J¼6.8 Hz, eCH2e), 1.43e1.21
(br, 64H, eCH2e), 0.89 (t, 6H, J¼6.6 Hz, eCH3), 0.88 (t, 6H, J¼6.8 Hz,
References and notes
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