Novel supramolecular columnar liquid crystals based on thiosemicarbazides

Article abstract of DOI:10.1080/10610278.2011.622390

Novel liquid crystal materials based on 3,4-di-n- alkoxybenzoylthiosemicarbazides (3a-h, n=5-10, 12, 14) were synthesised. The mesomorphic properties of these compounds were characterised and studied by differential scanning calorimetry, polarising optica

Full text of DOI:10.1080/10610278.2011.622390

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Supramolecular Chemistry
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Novel supramolecular columnar liquid crystals based on
thiosemicarbazides
E. Y. Elgueta a , M. L. Parra a , J. Barberá b , J. M. Vergara a & J. A. Ulloa a
a Departamento de Química Orgánica , Facultad de Ciencias Químicas, Universidad de
Concepción , Casilla 160-C, Concepción, Chile
b Departamento de Química Orgánica , Facultad de Ciencias-Instituto de Ciencia de
Materiales de Aragón, Universidad de Zaragoza-C.S.I.C. , 50009, Zaragoza, Spain
Published online: 03 Nov 2011.
To cite this article: E. Y. Elgueta , M. L. Parra , J. Barberá , J. M. Vergara & J. A. Ulloa (2011) Novel supramolecular columnar
liquid crystals based on thiosemicarbazides, Supramolecular Chemistry, 23:11, 721-730, DOI: 10.1080/10610278.2011.622390
To link to this article: http://dx.doi.org/10.1080/10610278.2011.622390
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Supramolecular Chemistry
Vol. 23, No. 11, November 2011, 721–730
Novel supramolecular columnar liquid crystals based on thiosemicarbazides
a
a
E.Y. Elgueta , M.L. Parra *, J. Barbera , J.M. Vergara and J.A. Ulloa
a
b
a
´
a
´ ´ ´ ´ ´
Departamento de Quımica Organica, Facultad de Ciencias Quımicas, Universidad de Concepcion, Casilla 160-C, Concepcion, Chile;
´ ´
b
´
Departamento de Quımica Organica, Facultad de Ciencias-Instituto de Ciencia de Materiales de Aragon, Universidad de Zaragoza-
C.S.I.C., 50009 Zaragoza, Spain
(Received 4 July 2011; final version received 7 September 2011)
Novel liquid crystal materials based on 3,4-di-n-alkoxybenzoylthiosemicarbazides (3a–h, n ¼ 5–10, 12, 14) were
synthesised. The mesomorphic properties of these compounds were characterised and studied by differential scanning
calorimetry, polarising optical microscopy and X-ray diffraction. Compound 3a did not show mesomorphic properties; 3b
shows a monotropic hexagonal columnar (Colh) phase. Compounds 3c–h display an enantiotropic Colh phase. The
mesomorphic properties were found to be dependent on the length of alkoxy side chains. In N,N-dimethylformamide
solution, all the compounds displayed a room temperature emission with lmax at 361–332 nm. A thermogravimetric analysis
also was performed.
Keywords: thiosemicarbazides; columnar liquid crystals; mesomorphism
1. Introduction
them have been found to be useful as herbicides,
insecticides and plant growth regulators (20–23).
However, there are no reports on thiosemicabazide
derivatives showing liquid crystalline properties.
Supramolecular chemistry is the chemistry of the non-
covalent intermolecular interaction, covering the struc-
tures and the functions of the entities formed by the
association of two or more chemical species (1). Non-
covalent interactions include hydrogen bonding, electro-
static (ion–ion, ion–dipole and dipole–dipole) inter-
actions, p–p stacking interactions, the Van der Waals
interactions and hydrophobic–hydrophilic effects along
with others (2). These interactions are essential to organise
highly ordered superstructures. In liquid crystals, these
interactions contribute to create rigid cores in both
calamitic and disk-like molecules (3–10). Among the non-
covalent interactions described above, hydrogen bond is
the most important non-covalent interaction to design
supramolecular architectures (11) due to its directionality,
stability, selectivity and reversibility (12). Special atten-
tion has been given to intermolecular hydrogen bonding,
which has been shown to efficiently promote molecular
ordering and stability in a liquid crystalline phase by
allowing it to assume the shape of a large disk in discotic
liquid crystals (13).
In this work, we report the synthesis, characterisation
and mesomorphic properties of novel liquid crystals based
on thiosemicarbazides, specifically the 3,4-n-dialkoxy-
benzoylthiosemicarbazides (series 3a–h). Previously, we
have reported non-mesomorphic 4-n-alkoxybenzoylthio-
semicarbazides (24, 25) (see Figure 2). In contrast to those
compounds, the thiosemicarbazides reported here display
columnar liquid crystal behaviour, which can be attributed
both to the presence of two lateral alkoxy chains and the
intermolecular hydrogen bonding which in turn stabilise
supramolecular structures in a columnar order. It has been
suggested that the formation of hydrogen bonds promote
molecular ordering and stability in a liquid crystalline
phase, thus explaining the appearance of columnar
mesophases (13). In the present hydrogen-bonded systems,
self-assembled columnar liquid crystalline phases are not
formed via discotic molecules, but rather by supra-
molecular ‘discs’ as building blocks generated through
intermolecular hydrogen bonding (26, 27). To our
knowledge, the prepared compounds are the first
thiosemicarbazide derivatives exhibiting liquid crystalline
behaviour in particular Colh phase. Special attention was
paid to the columnar phase behaviour, the effect of the
length of the terminal alkoxy chains on the phase
behaviour, the mesophase structure and the fluorescence
Intermolecular hydrogen bonding plays an important
role in mesophase formation in the hydrazide derivatives
(14–19), which are the most common precursors in the
synthesis of 1,3,4-oxadiazole- and 1,3,4-thiadiazole-based
liquid crystalline derivatives. Thiosemicabazides and their
related heterocyclic compounds have been found to
possess many important biological activities. Some of
*Corresponding author. Email: mparra@udec.cl
ISSN 1061-0278 print/ISSN 1029-0478 online
q 2011 Taylor & Francis
http://dx.doi.org/10.1080/10610278.2011.622390
http://www.tandfonline.com

722
E.Y. Elgueta et al.
of new compounds. Liquid crystals displaying columnar
mesophases are very important due to their great potential
application in semiconducting and photoconducting
devices, light-emitting diodes and sensors based on their
two essential virtues: their anisotropic charge carrier
transport capability and the ‘large area uniformity’ (28).
Two points must be noted. First, series 3a–h
compounds open an interesting possibility for the design
of 2-amino-1,3,4-thiadiazole and/or 2-amino-1,3,4-oxa-
diazole derivatives, because the thiosemicarbazide deriva-
tives are the precursors in the synthesis of these
heterocycles, which might exhibit interesting meso-
morphic and luminescence behaviour. Second, the 2-
amino-1,3,4-thiadiazole and/or 2-amino-1,3,4-oxadiazole
derivatives can be used as precursors in the preparation of
amides and/or Schiff’s bases leading to polycatenar liquid
crystals (24, 25).
As can be seen from Table 1, except for the case of 3a,
which is non-mesomorphic, all the compounds of series 3
exhibit mesomorphic properties. The homologue 3b
displays a monotropic columnar hexagonal mesophase
(Colh), whereas the other homologues (n ¼ 7–10, 12, 14)
show an enantiotropic columnar hexagonal mesophase
(Colh). The textures observed by polarising optical
microscopy (POM), on cooling from the isotropic liquid,
are consistent with the presence of columnar mesomorph-
ism. Microphotographs of the texture observed for the
compounds 3b–h are shown in Figure 1.
The data collected in Table 1 show the effect of
increasing the length of the side chains. The fact that a
columnar phase is observed for compounds 3b (mono-
tropic) and 3c–h (enantiotropic) is evidence of the direct
dependence of the mesomorphism of thiosemicarbazides
on the length of the alkoxy chains.
The melting temperatures of compounds in series
3a–h are in the range 129–1748C. No liquid crystalline
phase was observed for compound 3a, which has the
higher melting point (1748C). Increasing the chain length
results in a lowering of the melting point and in a favouring
of the mesomorphic properties (monotropic for compound
3b and enantiotropic for compounds 3c–h).
With respect to the clearing temperatures and
mesophase ranges, all of these compounds display
moderate clearing temperatures and it is important to
note their broad mesophase ranges. The clearing
temperatures increase with the length of the alkoxy chains
from 1738C for 3c to 1828C for 3f (n-pentyloxy to
n-decyloxy chain); however, when the alkoxy chains
increase by two carbon atoms in 3g (n-dodecyloxy) and
four carbon atoms in 3h (n-tetradecyloxy), this results in a
lowering of the clearing temperature compared with
compound 3f, being the lowest for compound 3h. The
homologue 3f, containing n-decyloxy chains, has a
broader mesomorphic range (388C) than the homologues
3c (208C), 3d (268C), 3e (318C), 3g (198C) and 3h (178C).
The same tendency as for the clearing temperatures is
2. Results and discussion
2.1 Synthesis
The synthesis of the series 3a–h compounds is outlined in
Scheme 1. The thiosemicarbazide derivatives of 3a–h
were synthesised starting with the alkylation of methyl
3,4-dihydroxybenzoate with 1-bromoalkane (n ¼ 5–10,
12, 14) under basic conditions yielding the corresponding
methyl 3,4-n-dialkoxybenzoate 1a–h and proceeding with
condensation with hydrazine hydrate, yielding 3,4-n-
dialkoxyphenylhydrazides 2a–h; these were reacted with
ammonium thiocyanate in concentrated HCl, leading to
the formation of the 3,4-n-dialkoxybenzoylthiosemicarba-
zides 3a–h (24, 25, 30).
2.2 Mesomorphic properties
The phase transition temperatures and enthalpies of the
thiosemicarbazides 3a–h, differing only in the number of
the carbon atoms in the side chains, are listed in Table 1.
Scheme 1. Synthetic route for thiosemicarbazides of series 3a–h.

Supramolecular Chemistry
723
Table 1. Phase transition temperatures (8C), enthalpies (J g21, in parentheses) as determined by DSC, scanning rate 108C min21, DT (8C,
mesomorphic range), Tid (8C, first step of decomposition), Tsd (8C, second process of decomposition) and Twd (8C, whole decomposition
process) for compounds of series 3a–h.
Compound
Phase transitions
DT
Tid
Tsd
Twd
3a (n ¼ 5)
3b (n ¼ 6)
Cr 174 (88.9) I
Cr 162 (80.7) I
I 151 (3.0) Colh 2
Cr 153 (79.3) Colh 173 (2.3) I
I 165 (2.5) Colh 2
Cr 152 (75.0) Colh 174.7 (2.4) I
I 168 (–) Colh 2
Cr 149 (74.8) Colh 180 (2.8) I
I 172 (–) Colh 2
Cr 144 (60.9) Colh 182 (2.2) I
I 175 (–) Colh 2
Cr 133 (58.3) Colh 152 (–) I
I 150 (–) Colh 2
Cr 129 (50.4) Colh 146 (2.2) I
I 148 (3.0) Colh 2
–
–
191
194
242
247
603
604
3c (n ¼ 7)
3d (n ¼ 8)
3e (n ¼ 9)
3f (n ¼ 10)
3g (n ¼ 12)
3h (n ¼ 14)
20
26
31
38
19
17
187
189
185
190
193
195
239
239
233
240
268
265
604
589
603
594
589
605
Note: Cr, crystal phase; Colh, hexagonal columnar phase; I, isotropic phase; –, enthalpy transition not observed.
Figure 1. Optical textures of the columnar hexagonal mesophase obtained on cooling for compounds 3b at 1298C (a), 3c at 1548C (b), 3d
at 1438C (c), 3e at 1568C (d), 3f at 1458C (e) and 1218C (f), 3g at 1028C (g) and compound 3h at 1138C (h).
observed for the mesomorphic temperature ranges. Thus
the mesomorphic range increases with the length of the
alkoxy chains from 3c to 3f and decreases for compounds
3g and 3h, the homologue 3h, with two n-tetradecyloxy
chains, having the lowest mesomorphic range. All of these
observations may well be indicative of the higher degree of
disorder attributable to the longer flexible alkoxy chains in
homologues 3g and 3h.
order was kept at RT, which is also indicative of a high
degree of disorder due to the flexible alkoxy chains, which
hinders crystallisation.
As mentioned above, we have previously reported the
synthesis of non-mesomorphic 4-n-alkoxybenzoylthiose-
micarbazides (Ia–f, see Figure 2) (24, 25). The only
difference between the thiosemicarbazides 3a–h
described here and the thiosemicarbazides Ia–f is the
number of alkoxy chains attached to the benzene ring. The
thiosemicarbazides 3a–h have two n-alkoxy chains,
whereas the thiosemicarbazides (Ia–f) have only one
Upon cooling to room temperature (RT) no crystal-
lisation occurred for compounds 3b–h; only the isotropic-
to-mesophase transition was observed and the columnar

724
E.Y. Elgueta et al.
X-ray experiments were performed at RT on thermally
treated samples of the seven compounds. The thermal
treatment consisted of heating the pristine crystalline
samples to the isotropic liquid or to the mesophase at a
temperature slightly lower than the clearing point. Under
these conditions all the compounds developed their liquid
crystal phase, including 3b, the mesophase of which is
monotropic and could only be obtained upon cooling from
the isotropic liquid. In spite of the metastable character of
the mesophases at RT, all of them remained during the
time of the X-ray experiments.
Figure 2. Structure of reported 4-n-alkoxybenzoylthiosemi-
carbazides (Ia–f).
n-alkoxy chains. The latter are non-mesomorphic and only
a crystal–isotropic transition was observed at ,2008C. On
the other hand, the thiosemicarbazides of series 3a–h have
lower melting points than thiosemicarbazides Ia–f and,
with the exception of homologue 3a, they are meso-
morphic displaying both monotropic (3b) and enantio-
tropic (3c–h) mesomorphism. These results illustrate the
importance of the influence of the number of the side
chains in the occurrence of columnar hexagonal order.
Probably, the mesomorphic properties of benzoylthiose-
micarbazides described here are the result of the hydrogen
bond interactions of the thiosemicarbazide group, which in
turn reinforce the columnar organisation (30).
After the study at RT, the mesophases were studied at a
temperature comprised between the melting and the
clearing point, except for 3b, the mesophase of which
could not be studied at high temperatures because of its
tendency to crystallise. It was observed that this tendency
is more marked at high temperatures than at RT.
Table 2 gathers the structural parameters deduced from
the X-ray measurements. The measured spacing and the
corresponding indexation are collected in Table S1
(Supporting Information, available online). All the
diffractograms are consistent with a hexagonal columnar
mesophase. At RT this is unambiguously revealed by the
presence in the small-angle region of most patterns of a set
of sharp maxima with reciprocal spacing in the ratio
1:31/2:2. These peaks correspond, respectively, to (1 0),
(1 1) and (2 0) reflections from a 2D hexagonal lattice.
The hexagonal lattice constant a is deduced from these
reflections and its value for each compound is shown in
Table 2, as well as the cross-section area of the hexagonal
unit cell S calculated from a. It can be observed that these
parameters evolve in a logical fashion and increases
steadily upon growing the length of the hydrocarbon
chains.
2.3 Thermogravimetric analysis
The thermogravimetric analysis (TGA) curves of solid
samples of 3a–h are given in Figure S1 (Supporting
Information, available online). All solid samples showed
no apparent weight loss between 20 and ,1908C,
indicative of the absence of occluded solvent of crystal-
lisation. All of them started to lose weight at around 1908C
(,1% of weight loss) to 2508C (,10% of weight loss) in a
two-step process and the whole decomposition process
completed near 6008C. As can be seen in Table 1, the
decomposition of the thiosemicarbazides 3a–h starts at a
temperature a few degrees above the isotropic transition:
about 178C for 3a, 328C for 3b, 148C for 3c, 148C for 3d,
58C for 3e, 88C for 3f, 418C for 3g and 498C for 3h. These
differences reflect the evolution of the isotropic transition
temperatures. For example, compounds 3e and 3f have the
highest clearing temperatures whereas compounds 3g and
3h have the lowest clearing temperatures. Therefore,
decomposition starts closer to the isotropic transition for
the former. This analysis is valid for all homologues in
series 3a–h.
Table 2. Structural parameters of the mesophases of
compounds 3b–h determined by XRD; a is the lattice constant of
the Colh phase; S is the cross-section area of the hexagonal unit
cell.
Temperature
(8C)
Lattice constants
2
(A or A )
˚
˚
Compound
Phase
3b
3c
RTa
RTa
159
RTa
160
RTb
160
RTa
150
RTa
136
RTa
139
Colh
Colh
Colh
Colh
Colh
Colh
Colh
Colh
Colh
Colh
Colh
Colh
Colh
a ¼ 33.6, S ¼ 978
a ¼ 35.6, S ¼ 1096
a ¼ 33.0, S ¼ 944
a ¼ 37.5, S ¼ 1219
a ¼ 34.7, S ¼ 1044
a ¼ 39.1, S ¼ 1325
a ¼ 35.6, S ¼ 1096
a ¼ 41.7, S ¼ 1505
a ¼ 36.7, S ¼ 1167
a ¼ 45.4, S ¼ 1784
a ¼ 40.2, S ¼ 1399
a ¼ 47.9, S ¼ 1988
a ¼ 42.3, S ¼ 1548
3d
3e
3f
2.4 X-ray diffraction studies
3g
3h
The mesophases of compounds 3b–h were studied by
X-ray diffraction (XRD) at RT and at high temperature. In
view of the thermal behaviour of the compounds and, in
particular, the absence of crystallisation on cooling from
the isotropic liquid or from the mesophase, the first set of
a RT after cooling from the isotropic liquid.
b RT after heating up to a temperature slightly below the clearing point.

Supramolecular Chemistry
725
directly measured by X-ray measurements because the
patterns do not contain any maximum corresponding to
this parameter. This is not unexpected considering that the
molecules of compounds 3b–h are not in disc shape and
the aggregates of molecules do not necessarily stack at a
periodic repeating distance. However, we can consider that
a group of Z molecules fills a column slice of thickness
Two phenomena are observed at high temperatures: the
hexagonal lattice constant a decreases compared to RT and
(1 1) and (2 0) reflections are much weaker, to the point that
they are masked by the background, so only the
fundamental reflection could be measured. However, in
spite of the disappearance of the higher order reflections, the
mesophase is undoubtedly hexagonal columnar because no
transitions are observed by optical microscopy or by
differential scanning calorimetry (DSC) on cooling down to
RT apart from the isotropic liquid to mesophase transition.
In the large-angle region of the patterns there is only a
broad, diffuse halo characteristic of the melting of the
hydrocarbon chains. This halo corresponds roughly to
˚
about 4–5 A. Applying these consideration to the
parameters obtained at RT, the above-mentioned equation
predicts that seven molecules are needed to fill the cross-
section of a column (Table S1 of the Supplementary
Information, available online). Under this assumption, it is
estimated that for 3b seven molecules (Z ¼ 7) occupies a
˚
˚
distances in the order of about 4.3–4.6 A, with a tendency
height h of 5.2 A and this value evolves in the series to
˚
4.0 A for 3h. We could also predict that eight molecules
to larger values at high temperatures. In the case of 3h, this
halo is relatively sharp at RT and this suggests that the
hydrocarbon chains of this compound are partially
crystallised in spite of the above-mentioned absence of
transition on cooling. It is noticeable that this compound,
together with 3g, yields a RT X-ray pattern with only one
small-angle peak, suggesting some difficulties to adopt a
well-organised mesomorphic hexagonal structure. How-
ever, the microscope textures and the above-mentioned
evolution of the value of the constant a with the chain
length support the assignation of the mesophase of 3g and
3h as hexagonal columnar.
It is interesting to discuss the organisation of these
non-disc-like molecules in the columnar mesophase.
These thiosemicarbazides have the possibility of inter-
molecular hydrogen bonds that allow for the generation of
dimers or even aggregates containing several molecules
(31). For building the columnar mesophase, groups of
these dimers or aggregates are needed to constitute the
supramolecular entity that stack into the columns. This
phenomenon has been described for polycatenar liquid
crystals (32), and in fact the compounds of the present
series can be considered biforked mesogens (32b, 33).
Columnar mesophases generated by supramolecular
aggregation through intermolecular hydrogen bonding
have been reported (13, 18).
˚
(Z ¼ 8) occupy a height of 6.0 A for 3b and evolve to 4.6
for 3h. Another interpretation is to consider that an
increasing number of molecules are needed to fill the same
column height h upon lengthening the chain in the series.
Both interpretations are complementary and in each case
the decrease in h or the increase in Z is compensated by the
increasing hexagonal lattice constant a.
The same conclusions can be qualitatively drawn from
the high-temperature experiments. The shorter values for
the hexagonal lattice constant a compared to RT are
generally accepted as being related to the higher
conformational disorder of the aliphatic chains. In turn
the disordered chains require more space out of the mean
plane perpendicular to the column axis and this must
increase the height h of the column needed to
accommodate the aggregates (Table S1 of the Supplemen-
tary Information, available online).
2.5 Ultraviolet–visible absorption and
photoluminescence spectroscopy
The absorption and the emission of compounds 3a–h in
N,N-dimethylformamide (DMF) are depicted in Figure S2
(Supporting Information, available online), and the
photophysical data are summarised in Table 3. Similar
absorption patterns were observed for all these com-
pounds, and all of them exhibit an intense absorption band
at 331–332 nm. In solution in DMF all the compounds
displayed one emission band at 361–365 nm on excitation
at RT at the absorption maximum. Photoluminescence is
observed for all the compounds in DMF solutions with
quantum yields (fPL) ranging from 3.5% to 5%. The
emission colours of these compounds are all in the purple
region.
The number Z of molecules that form the proposed
supramolecular entity can be estimated by the equation,
rVNA
Z ¼
;
M
where r is the density, V is the unit cell volume, NA is the
Avogadro number and M is the molecular mass. The
density in typical organic compounds has generally a value
between 0.9 and 1 g cm23. In this case, with an important
contribution of the hydrocarbon chains to the molecular
mass, it is reasonable that the density is close to
0.9 g cm23. The unit cell volume is the area S of the 2D
hexagonal lattice (S ¼ a 231/2/2) multiplied by the mean
stacking distance h. In these compounds h cannot be
The photoluminescence quantum yield, fPL, was
calculated according to the equation:
!
h2sample
h2std
Absstd
Asample
fPL < fstd
£
£
£
;
Abssample
Astd

726
E.Y. Elgueta et al.
Table 3. Absorption and photoluminescence spectra of compounds 3a–h.
labs maxa/nm (1 ¼ 3.928 £ 103)b
lem maxc/nm
% fPL
Stokes shift/nm
d
Compound
3a (n ¼ 5)
3b (n ¼ 6)
3c (n ¼ 7)
3d (n ¼ 8)
3e (n ¼ 9)
3f (n ¼ 10)
3g (n ¼ 12)
3h (n ¼ 14)
332.0
332.0
331.0
330.0
331.0
331.0
331.0
331.0
365.1
362.0
361.1
362.0
364.0
362.0
361.1
363.1
4.7
4.1
3.5
3.6
4.2
5.0
4.2
4.2
33.1
30.0
30.1
32.0
33.0
31.0
30.1
32.1
a Measured in DMF.
b Units ¼ M21 cm21
.
c Excited at absorption maxima.
d Standard 9,10-diphenylantracene.
3150–3233 cm21 and the central NH group at 3409 cm21
,
where fPL is the photoluminescence quantum yield of the
standard 9,10-diphenylantracene (fstd ¼ 0.950, ethanol);
Absstd and Abssample are the absorbance of the standard and
sample, respectively; Asample and Astd are the integrated
area of the emission peak of the sample and standard,
respectively; hsample and hstd are the refractive indices of
the sample and standard solutions (pure solvents were
assumed), respectively. The quantum yields and the Stokes
shifts are summarised in Table 3.
and the carbonyl group at 1657 cm21. On heating, these
bands increase in intensity and shift to higher wavenum-
bers. Thus the carbonyl band appears at 1660 cm21 at
1408C, 1663 cm21 at 1708C (Figure 3(a)). The central NH
band appears at 3410 cm21 at 1408C, and at 3412 cm21 at
1708C. In addition, the NZH stretching bands of the
terminal amino group also show a shift by about 3 cm21
(Figure 3(b)). These observations suggest the formation of
the intermolecular hydrogen bonding between CvO,
CvS, NH and NH2 groups. It is suggested that the amide
NZH groups are associated with CvS group via
NZH···SvC intermolecular hydrogen bond-generating
dimers, which are associated with other dimers through
intermolecular interactions of the NH2 groups with CvO
groups via NZH···OvC hydrogen bonding (31). These
intermolecular hydrogen bonds promote molecular order-
ing and stability of the liquid crystalline phase, explaining
the appearance of columnar mesophases.
2.6 FT-IR measurements
In order to examine the presence of the intermolecular
hydrogen bonding, the temperature-dependent FT-IR
spectra of compound 3f have been recorded on heating
at three different temperatures: at 178C (crystal phase), at
1408C (Cr-mesophase transition) and at 1708C (Colh
mesophase), as is shown in Figure 3.
At RT (178C), 3f exhibits the characteristic bands of
NZH stretching vibrations of the terminal amino group at
17°C
17°C
140°C
170°C
140°C
170°C
1720
1700
1680
1660
1640
1620
1600
3500
3000
3300
3200
3100
3000
Wavenumbers (cm–1
)
Wavenumbers (cm–1
)
Figure 3. FT-IR spectra (NaCl crystal plates) for compound 3f: 1720–1600 cm21 regions (a) and 3500–3000 cm21 regions (b) at 17,
140 and 1708C.

Supramolecular Chemistry
727
3. Experimental section
TLC analysis, the mixture was heated at 808C for 10 h. The
reaction mixture was cooled to RT, water (100 ml) was
added, and the product was extracted with diethyl ether.
The combined organic extracts were washed with water
and dried over MgSO4. After filtration, the solvent was
evaporated under reduced pressure, and the crude product
was passed through a column of silica gel using 2% ethyl
acetate in hexane as eluent to afford 1a–f as white solids.
3.1 General
1H and 13C NMR spectra were recorded using a Bruker
Avance 400 MHz spectrometer with DMSO-d6 as solvent
and tetramethylsilane (TMS) as an internal standard. FT-
IR spectra were recorded with a Nicolet Magna 550
spectrometer. Samples were pressed tablets with KBr. The
samples for hydrogen bond study at various temperatures
were sandwiched between two NaCl crystal plates. The
sandwiched samples were held on a hot stage equipped
with a temperature controller. Electrospray-ionisation ion
trap mass spectra (ESI-MS) were recorded on Bruker ion
trap 3000 spectrometer.
Compound
Melting
1a
Liquid Liquid Liquid 47 55 45 52 64
1b
1c
1d 1e 1f
1g 1h
point (8C)
Yield (%)
Transition temperatures and textures of mesophases
were determined by POM using an Olympus BX51 optical
microscope equipped with an Olympus UAN360P
polariser and an Instec HCS302 heat stage.
85
79
81
83 81 86 80 85
The spectroscopic characterisation of 1f as a
representative example is given:
Transition temperatures and enthalpies were investi-
gated by DSC using a Rheometric DSC-V calorimeter.
Samples were encapsulated in aluminium pans and
observed at scanning rate of 58C min21 on heating and
cooling. The instrument was calibrated using an indium
standard (156.68C, 28.44 J g21) under nitrogen atmos-
phere. The purity of the final products was evaluated by
thin layer chromatography.
1H NMR (CDCl3, TMS, 400 MHz): d ¼ 0.91 (t, 6H,
2CH3) 1.29–1.53 (m, 36H, 18CH2); 1.82–1.90 (m, 4H,
2CH2); 3.91 (s, 3H, CH3); 4.07 (m, 4H, 2 ZOCH2); 6.98
(d, J ¼ 8.4 Hz, 1H, H aromatic); 7.56 (d, J ¼ 1.9 Hz, 1H,
H aromatic); 7.66 (dd, J ¼ 8.4 Hz, 1H, H aromatic).
13C NMR (CDCl3, TMS, 100.6 MHz): d ¼ 14.1, 22.7,
26.0, 26.1, 29.1, 29.2, 29.4, 29.5, 29.7, 31.9, 51.8, 64.9
(aliphatic C); 51.9 (OCH3); 69.0 and 69.3 (2 ZOCH2);
111.9, 114.3, 123.5 (aromatic CH); 122.4, 148.5, 153.2
(quaternary aromatic C); 167.0 (CvO).
The mesophases were investigated by XRD. The XRD
patterns were obtained with a pinhole camera (Anton-Paar,
Graz, Austria) operating with a point-focused Ni-filtered
Cu Ka beam. The samples were held in the Lindemann
glass capillaries (0.9 mm diameter). The patterns were
collected on flat photographic film perpendicular to the
X-ray beam. Spacing was obtained via Bragg’s law.
TGAs of solid samples of 3a–h were performed by TA
Instruments (New Castle, Delaware, USA) Q5000IR
under a stream of flowing N2.
FT-IR (KBr, cm21): 2921, 2850 (C sp3-H); 1714
(CvO); 1215 (CZO).
3.2.2 Synthesis of the 3,4-n-dialkoxyphenylhydrazides
(2a–h)
All derivatives were prepared similarly according to the
procedure described elsewhere (24, 25, 29).
Ultraviolet–visible absorbance measurements were
made with Varian Cary 50 instrument between 350 and
900 nm. Luminescence measurements were obtained using
a Varian Cary Eclipse Fluorescence spectrophotometer.
Spectra of the pure compounds were recorded in
1 £ 1024 mol/l DMF solutions under excitation at the
absorption maximum.
General method. A solution of the corresponding
compound of series 1a–h (11 mmol) and an excess of
hydrazine monohydrate in ethanol (100 ml) was heated to
808C for 32 h. Then water (80 ml) was added and the
resulting precipitate was collected, dried under vacuum
and recrystallised from ethanol to yield pure 2a–h
compounds as white solids.
3.2 Synthesis and characterisation
3.2.1 Synthesis of the methyl 3,4-n-dialkoxybenzoates
(1a–h)
Compound
Melting
point (8C)
Yield (%)
2a 2b 2c 2d 2e
103 99 102 104 107
2f
105
2g
101
2h
100
All derivatives were prepared similarly according to the
procedure described in Ref. (29).
82 78 76 79 74
86
80
83
General method. Anhydrous K2CO3 (59 mmol) and
methyl 3,4-dihydroxybenzoate (19.5 mmol) were added
to a deoxygenated mixture of DMF (80 ml) and of 1-
bromodecane (39 mmol) under nitrogen atmosphere. After
The spectroscopic characterisation of 2f as a
representative example is given:

728
E.Y. Elgueta et al.
1H NMR (DMSO-d6, TMS, 400 MHz): d ¼ 0.87 (t,
13C NMR (DMSO-d6, TMS, 100.6 MHz): d ¼ 14.3,
22.5, 26.0, 26.1, 29.1, 29.2, 29.4, 29.5, 31.8 (aliphatic C);
68.7 and 69.0 (2 ZOCH2); 112.7, 113.5, 121.9 (aromatic
CH); 125.1, 148.2, 152.0 (quaternary aromatic C); 165.8
(CvO); 182.6 (CvS).
3H, CH3); 0.89 (t, 3H, CH3); 1.29–1.44 (m, 8H, 4CH2);
1.66–1.74 (m, 4H, 2CH2); 3.96 (m, 4H, 2 ZOCH2); 4.41
(s, 2H, NH2); 6.97 (d, J ¼ 8.9 Hz, 1H, H aromatic); 7.40–
7.42 (m, 2H, H aromatic); 9.59 (s, 1H, NH).
13C NMR (DMSO-d6, TMS, 100.6 MHz): d ¼ 14.3,
22.3, 26.0, 26.1, 28.2, 29.1, 29.2, 29.4, 29.5, 29.7, 31.9,
51.8, 64.9 (aliphatic C); 68.7 and 68.9 (2 ZOCH2); 112.7,
113.0, 120.8 (aromatic CH); 126.0, 148.4, 151.4
(quaternary aromatic C); 166.0 (CvO).
FT-IR (KBr, cm21): 3417 (ZNH); 3250, 3174
(ZNH2); 2927, 2860 (C sp3-H); 1668 (CvO); 1266
(CvS); 1217 (CZO).
ESI: C20H33N3O3S calculated: 395.22; found: 394.90.
Compound 3c. 1H NMR (DMSO-d6, TMS, 400 MHz):
d ¼ 0.86 (t, 6H, 2CH3); 1.27–1.70 (m, 20H, 10CH2); 3.98
(t, 4H, 2 ZOCH2); 6.99 (d, J ¼ 8.8 Hz, 1H, H aromatic);
7.47 (d, J ¼ 7.1 Hz, 2H, H aromatic); 7.55 and 7.85 (s, 2H,
SvCZNH2); 9.28 (s, 1H, SvCZNH); 10.2 (s, 1H,
OvCZNH).
13C NMR (DMSO-d6, TMS, 100.6 MHz): d ¼ 14.3,
22.5, 25.9, 26.0, 28.9, 29.1, 29.2, 31.7 (aliphatic C); 68.7
and 69.0 (2 ZOC H2); 112.8, 113.6, 121.9 (aromatic CH);
125.1, 148.2, 152.0 (quaternary aromatic C); 165.8
(CvO); 182.5 (CvS).
FT-IR (KBr, cm21): 3311, 3254 (ZNH and ZNH2);
2920, 2852 (C sp3-H); 1617 (CvO).
3.2.3 Synthesis of 3,4-n-
dialkoxybenzoylthiosemicarbazides (3a–h)
All derivatives were prepared similarly according to the
procedure described previously by us (24, 25).
General method. The corresponding 3,4-n-dialkoxy-
phenylhydrazide (series 2a–h; 6.7 mmol) was suspended
in 20 ml of alcoholic hydrogen chloride solution and
evaporated under reduced pressure; the residue was heated
under reflux for 30 h with a solution of dry ammonium
thiocyanate (7.4 mmol) in absolute ethanol. The solid was
filtered off, washed several times with water and
recrystallised from ethanol to yield pure 3a–h compounds
as white solids.
FT-IR (KBr, cm21): 3417 (ZNH); 3250, 3174
(ZNH2); 2927, 2860 (C sp3-H); 1668 (CvO); 1266
(CvS); 1217 (CZO).
ESI: C22H37N3O3S calculated: 423.20; found: 423.14.
Compound 3d. 1H NMR (DMSO-d6, TMS, 400 MHz):
d ¼ 0.84 (t, 6H, 2CH3); 1.24–1.69 (m, 24H, 12CH2); 3.99
(t, 4H, 2 ZOCH2); 6.98 (d, J ¼ 8.2 Hz, 1H, H aromatic);
7.46 (d, J ¼ 7.3 Hz, 2H, H aromatic); 7.56 and 7.86 (s, 2H,
SvCZNH2); 9.29 (s, 1H, SvCZNH); 10.2 (s, 1H,
OvCZNH).
13C NMR (DMSO-d6, TMS, 100.6 MHz): d ¼ 14.3,
22.5, 26.0, 26.1, 29.1, 29.2, 29.4, 29.5, 31.8 (aliphatic C);
68.7 and 69.0 (2 ZOCH2); 112.7, 113.5, 121.9 (aromatic
CH); 125.1, 148.2, 152.0 (quaternary aromatic C); 165.8
(CvO); 182.6 (CvS).
Compound
Yield (%)
3a
80
3b
75
3c
76
3d
88
3e
93
3f
85
3g
90
3h
93
Compound 3a. 1H NMR (DMSO-d6, TMS, 400 MHz):
d ¼ 0.84 (t, 6H, 2CH3); 1.24–1.69 (m, 12H, 6CH2); 3.99
(t, 4H, 2 ZOCH2); 6.98 (d, J ¼ 8.2 Hz, 1H, H aromatic);
7.46 (d, J ¼ 7.3 Hz, 2H, H aromatic); 7.56 and 7.86 (s, 2H,
SvCZNH2); 9.29 (s, 1H, SvCZNH); 10.2 (s, 1H,
OvCZNH).
13C NMR (DMSO-d6, TMS, 100.6 MHz): d ¼ 14.3,
22.5, 26.0, 26.1, 29.1, 29.2, 29.4, 29.5, 31.8 (aliphatic C);
68.7 and 69.0 (2 ZOC H2); 112.7, 113.5, 121.9 (aromatic
CH); 125.1, 148.2, 152.0 (quaternary aromatic C); 165.8
(CvO); 182.6 (CvS).
FT-IR (KBr, cm21):3416 (ZNH); 3252, 3178
(ZNH2); 2920, 2851 (C sp3-H); 1666 (CvO); 1268
(CvS); 1219 (CZO).
ESI: C24H41N3O3S calculated: 451.28; found: 451.28.
Compound 3e. 1H NMR (DMSO-d6, TMS, 400 MHz):
d ¼ 0.85 (t, 6H, 2CH3); 1.25–1.70 (m, 28H, 14CH2); 3.99
(t, 4H, 2 ZOCH2); 6.99 (d, J ¼ 8.9 Hz, 1H, H aromatic);
7.46 (d, J ¼ 7.4 Hz, 2H, H aromatic); 7.55 and 7.84 (s, 2H,
SvCZNH2); 9.27 (s, 1H, SvCZNH); 10.1 (s, 1H,
OvCZNH).
13C NMR (DMSO-d6, TMS, 100.6 MHz): d ¼ 14.3,
22.5, 25.5, 26.0, 26.1, 29.1, 29.2, 29.4, 29.5, 31.7 (aliphatic
C); 68.7 and 69.0 (2 ZOC H2); 112.6, 113.5, 121.8
(aromatic CH); 125.1, 148.2, 152.0 (quaternary aromatic
C); 165.8 (CvO); 182.5 (CvS).
FT-IR (KBr, cm21): 3416 (ZNH); 3251, 3178
(ZNH2); 2947 and 2863 (C sp3-H); 1668 (CvO); 1268
(CvS); 1217 (CZO).
ESI: C18H29N3O3S calculated: 367.19; found: 367.10.
Compound 3b. 1H NMR (DMSO-d6, TMS, 400 MHz):
d ¼ 0.84 (t, 6H, 2CH3); 1.24–1.69 (m, 16H, 8CH2); 3.99
(t, 4H, 2 ZOCH2); 6.98 (d, J ¼ 8.2 Hz, 2H, H aromatic);
7.46 (d, J ¼ 7.3 Hz, 2H, H aromatic); 7.56 and 7.86 (s, 2H,
SvCZNH2); 9.29 (s, 1H, SvCZNH); 10.2 (s, 1H,
OvCZNH).
FT-IR (KBr, cm21): 3416 (ZNH); 3252, 3178
(ZNH2); 2920, 2851 (C sp3-H); 1666 (CvO); 1268
(CvS); 1219 (CZO).
ESI: C26H45N3O3S calculated: 479.31; found: 479.23.

Supramolecular Chemistry
729
Compound 3f. 1H NMR (DMSO-d6, TMS, 400 MHz):
d ¼ 0.84 (t, 6H, 2CH3); 1.24–1.69 (m, 32H, 16CH2); 3.99
(t, 4H, 2 ZOCH2); 6.98 (d, J ¼ 8.2 Hz, 1H, H aromatic);
7.46 (d, J ¼ 7.3 Hz, 2H, H aromatic); 7.56 and 7.86 (s, 2H,
SvCZNH2); 9.29 (s, 1H, SvCZNH); 10.2 (s, 1H,
OvCZNH).
the Department of Chemical and Biomolecular Engineering of
the University of California, Berkeley. J.B. thanks the Spanish
project CTQ2009-09030.
References
13C NMR (DMSO-d6, TMS, 100.6 MHz): d ¼ 14.3,
22.5, 26.0, 26.1, 29.1, 29.2, 29.4, 29.5, 31.8 (aliphatic C);
68.7 and 69.0 (2 ZOC H2); 112.7, 113.5, 121.9 (aromatic
CH); 125.1, 148.2, 152.0 (quaternary aromatic C); 165.8
(CvO); 182.6 (CvS).
FT-IR (KBr, cm21): 3417 (ZNH); 3250, 3178
(ZNH2); 2920, 2852 (C sp3-H); 1667 (CvO); 1267
(CvS); 1218 (CZO).
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(ZNH2); 2920, 2851 (C sp3-H); 1666 (CvO); 1268
(CvS); 1219 (CZO).
ESI: C32H57N3O3S calculated: 563.41; found: 563.37.
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d ¼ 0.84 (t, 6H, 2CH3); 1.24–1.69 (m, 48H, 24CH2); 3.99
(t, 4H, 2 ZOCH2); 6.98 (d, J ¼ 8.2 Hz, 1H, H aromatic);
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´
´
in measuring the mass spectra in the laboratory in the Department
of Molecular and Cell Biology and Department of Chemical and
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