Synthesis of new benzobisthiazole materials and a study of their mesomorphic and luminescence properties

Article abstract of DOI:10.1080/10610278.2013.844809

Novel tetra- and hexacatenar materials based on benzobisthiazole derivatives have been synthesised (4a-c, 5a-c and 6a-c) and their mesomorphic properties have been studied by differential scanning calorimetry, polarised optical microscopy and X-ray diffraction. All compounds in series 4a-c display an enantiotropic hexagonal columnar phase, whereas their analogous compounds in series 5a-c did not show mesomorphic behaviour. Compound 6a displays an unidentified monotropic columnar phase, whereas compounds 6b and 6c show an enantiotropic rectangular columnar mesophase. The mesomorphic properties were found to be dependent on the length, position and number of alkoxy chains attached at the end of the rigid core. These compounds also show photoluminescence properties in the visible region and have good quantum yields. A thermogravimetric analysis was also performed.

Full text of DOI:10.1080/10610278.2013.844809

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Synthesis of new benzobisthiazole materials and
a study of their mesomorphic and luminescence
properties
J. Barberáa, E.W. Díazb, M.R. Dahrouchb, E.Y. Elguetab & M.L. Parrab
a Departamento de Química Orgánica, Facultad de Ciencias-Instituto de Ciencia de
Materiales de Aragón, Universidad de Zaragoza-C.S.I.C, 50009 Zaragoza, Spain
b Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad de
Concepción, Casilla 160-C, Concepción, Chile
Published online: 21 Oct 2013.
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To cite this article: J. Barberá, E.W. Díaz, M.R. Dahrouch, E.Y. Elgueta & M.L. Parra (2014) Synthesis of new benzobisthiazole
materials and a study of their mesomorphic and luminescence properties, Supramolecular Chemistry, 26:5-6, 373-382, DOI:
10.1080/10610278.2013.844809
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Supramolecular Chemistry, 2014
Vol. 26, Nos. 5–6, 373–382, http://dx.doi.org/10.1080/10610278.2013.844809
Synthesis of new benzobisthiazole materials and a study of their mesomorphic and
luminescence properties
a
J. Barbera , E.W. Dıaz *, M.R. Dahrouch , E.Y. Elgueta and M.L. Parra *
b
b
b
b
´
´
a
´
Departamento de Quımica Organica, Facultad de Ciencias-Instituto de Ciencia de Materiales de Aragon, Universidad de Zaragoza-
C.S.I.C, 50009 Zaragoza, Spain; Departamento de Quımica Organica, Facultad de Ciencias Quımicas, Universidad de Concepcion,
´
´
b
´
´
´
´
´
Casilla 160-C, Concepcion, Chile
(Received 19 April 2013; accepted 6 September 2013)
Novel tetra- and hexacatenar materials based on benzobisthiazole derivatives have been synthesised (4a–c, 5a–c and 6a–c)
and their mesomorphic properties have been studied by differential scanning calorimetry, polarised optical microscopy and
X-ray diffraction. All compounds in series 4a–c display an enantiotropic hexagonal columnar phase, whereas their
analogous compounds in series 5a–c did not show mesomorphic behaviour. Compound 6a displays an unidentified
monotropic columnar phase, whereas compounds 6b and 6c show an enantiotropic rectangular columnar mesophase. The
mesomorphic properties were found to be dependent on the length, position and number of alkoxy chains attached at the end
of the rigid core. These compounds also show photoluminescence properties in the visible region and have good quantum
yields. A thermogravimetric analysis was also performed.
Keywords: liquid crystal; polycatenar; photoluminescence
1. Introduction
molecules with two or three paraffinic chains at each end
(5). In columnar mesophases, the molecules are self-
organised into columnar stacks. In these columns, the
cores are formed by an overlapped aromatic p system,
generating molecular pathways in one dimension that
permit the transport of electrons, photons and ions (5, 6)
and providing columnar liquid crystals with various
applications: light-emitting diodes (7), photoconductive
semiconductor devices (8), field-effect transistors, photo-
voltaic cells (9), gas sensors (10), memory devices and
electro-optical and optical fibres (11–14).
The first investigations into benzo[1,2-d:4,5-d0]bisthia-
zole units (trans-BBZT) were based on their uses in
polymer synthesis. These polymers could exhibit a high
degree of molecular order, high thermal stabilities and
excellent mechanical properties as a result of efficient
p-stacking and strong intermolecular interactions (15–
18). Materials based on benzobisthiazole units can also
show other attractive electronic properties, such as high
fluorescence, high electron affinity and nonlinear optical
properties (19–28). As a result of these properties, such
materials have been used as electron transport materials in
OLEDs (19), charge photogeneration materials (29, 30),
field-effect transistors and solar cells (31–33).
In recent years, great interest has been focused on devices
based on liquid crystalline materials and these include
organic light-emitting diodes (OLEDs), photovoltaic cells,
transistors and lasers. This interest arises because liquid
crystals offer certain advantages over traditional crystalline
materials and polymers; for example, they show solution
processability, molecular alignment and prevent the
formation of defects in the deposited material (1). For use
in these devices, liquid crystals must meet certain
requirements such as high carrier mobility, high quantum
efficiency and must be photochemically, thermally and
electrochemically stable (1).
Polycatenar liquid crystals (2, 3) are molecules with a
long rod-like core ending in two half-disc moieties with
two or more aliphatic chains at each end. These types of
liquid crystals can exhibit, either in the same series or in a
pure compound, nematic (N), lamellar or smectic (Sm),
cubic (Cub) and/or columnar (Col) mesophases. This
polymorphism depends on various structural factors such
as the number and position of side chains, the length of the
rigid central unit and the presence of polar substituents (4).
The lamellar phase is generally observed when the flexible
side chains are relatively short. When the side chains have
an intermediate length, these compounds have an
intermediate state called a mesomorphic cubic phase.
The columnar mesophases are favoured in tetra- and
hexacatenar liquid crystals with long side chains, namely
Since the initial research into BBZT, which began in
recent years, very few investigations have concerned
liquid crystals that incorporate BBZT as core units in their
structures (34–36). The harsh conditions required to
*Corresponding authors. Email: endiaz@udec.cl; mparra@udec.cl
q 2013 Taylor & Francis

´
J. Barbera et al.
374
obtain BBZT and its derivatives explain why such systems
were not frequently used, in particular in liquid crystals.
Recently, new methods have been used to prepare BBZT
(36, 37) under mild reaction conditions and this allows
new benzobisthiazole structures to be obtained. One of
these methods enabled the easy preparation of a new series
of liquid crystals based on BBZT and these compounds
show high fluorescence quantum yields (36).
reaction between 1 equiv. of 2,5-diamino-1,4-benzene-
dithiol dihydrochloride 1 (15) and 2 equiv. of 4-
(benzyloxy)benzoyl chloride in the presence of N-
methyl-2-pyrrolidone (NMP) as a solvent to give the
corresponding di-benzylated product 2. A debenzylation
reaction on product 2 with a mixture of fuming
hydrochloric acid and glacial acetic acid (39) gave 4,40-
(benzo[1,2-d:4,5-d0]bis(thiazole)-2,6-diyl)diphenol (3).
The mesogens 4a–c to 6a–c were obtained by an
esterification reaction between 1 equiv. of compound 3 and
2 equiv. of the corresponding 3,4-di-n-, 3,5-di-n- and/or
3,4,5-tri-n-alkoxybenzoyl chloride in NMP and tetrahy-
drofuran (THF) as solvents. In this reaction, triethylamine
(TEA) and 4-(N,N-dimethyl)aminopyridine (DMAP) were
used as base and catalyst, respectively (40).
In this publication, new liquid crystalline molecules
were designed that incorporate a benzobisthiazole unit as a
fluorophore and multiple lateral hydrocarbon chains at the
end of the rigid core. The aim of the design was to obtain
photoluminescent columnar liquid crystals with high
quantum yields. This work concerns the synthesis,
characterisation, mesomorphic properties and photolumi-
nescent properties of novel polycatenar liquid crystalline
materials based on benzo[1,2-d:4,5-d0]bisthiazoles. In order
to understand the effect of the number, positions and lengths
of the side chains on the formation of the mesophases, three
groups of mesogens were synthesised: series 4a–c
(tetracatenar 2mp-2mp), series 5a–c (tetracatenar 2 mm-
2 mm) and series 6a–c (hexacatenar 3mpm-3mpm), where
the numbers 2 and 3 represent the number of chains at each
end of the molecule and the letters m and p represent the
positions (meta and para, respectively) of the side chains in
the terminal aromatic rings (38). The side chains are linear
alkoxy chains with 10, 12 and/or 14 carbon atoms.
The poor solubility of compound 2 in common organic
solvents made structural determination by NMR impossible
and the characterisation was therefore limited to infrared
spectroscopy, with the FT-IR spectra clearly showing the
disappearance of the absorption band at around 1700cm21
,
which is the characteristic of the carbonyl group of the
reagent 4-(benzyloxy)benzoyl chloride.
The formation of the final products 4a–c to 6a–c was
clearly evidenced by the characteristic absorption band at
around 1730 cm21 in the FT-IR spectra due to the ester
groups. The series of esters 5a–c and 6a–c were highly
soluble in solvents such as n-hexane, chloroform and THF
1
and were therefore characterised by H and 13C NMR
spectroscopy, MALDI mass spectrometry and elemental
analysis. In contrast, compounds of series 4a–c have very
low solubility in common organic solvents but were
sparingly soluble in chloroform, so it was possible to
2. Results and discussion
2.1 Synthesis
The synthesis of the precursors 2 and 3 and the final
compounds 4a–c to 6a–c is shown in Scheme 1.
The precursor 4,40-(benzo[1,2-d:4,5-d0]bis(thiazole)-
2,6-diyl)diphenol (3) was synthesised by a condensation
1
characterise this series only by H NMR spectroscopy,
albeit with poor resolution, and by MALDI mass
spectrometry and elemental analysis.
Scheme 1. Synthetic route for benzobisthiazoles 4a–c to 6a–c.

Supramolecular Chemistry
375
2.2 Mesomorphic properties
The melting temperatures of compounds in series 6a–
c decrease on lengthening the alkoxy chains (140.48C for
6a, 113.78C for 6b and 109.98C for 6c). The clearing
temperatures increase with the length of the alkoxy chains
(128.58C for 6b and 143.18C for 6c). Thus, the
mesomorphic range increases with the length of the
alkoxy chains (14.88C for 6b and 33.28C for 6c).
The mesomorphic behaviour of compounds 4a–c to 6a–c
was studied by polarising optical microscopy (POM),
thermal analysis (differential scanning calorimetry, DSC)
and X-ray diffraction (XRD). The phase-transition
temperatures and enthalpies are summarised in Table 1.
As can be seen from the results in Table 1, with the
exception of 6a, which is a monotropic liquid crystal, all
compounds of series 4a–c and 6a–c display enantiotropic
mesomorphism, whereas compounds of series 5a–c do not
show mesomorphic properties, exhibiting only a crystal-
line phase. The textures observed by POM for compounds
4a–c and 6a–c, on cooling from the isotropic liquid, are
consistent with the presence of columnar mesomorphism
(see Figure 1). Mesomorphic behaviour was found to be
dependent on the number, position and length of the
flexible side chains attached at the end of the rigid core.
The melting temperatures of compounds in series 4a–
c decrease slightly as the chain length increases (167.58C
for 4a, 164.48C for 4b and 155.28C for 4c). The clearing
temperatures decrease more markedly upon lengthening
the alkoxy chains, with values of 252.48C for 4a, 233.98C
for 4b and 1988C for 4c. Thus, the mesomorphic range
decreases from 4a to 4c, with ranges of 84.98C for 4a,
69.58C for 4b and 42.88C for 4c. Series 5a–c shows the
same trend as series 4a–c; i.e. melting temperatures
(101.18C for 5a, 97.78C for 5b and 92.58C for 5c) decrease
as the chain length increases.
The series of tetracatenar 2mp-2mp mesogens (4a–c),
in which the alkoxy chains are in the 3,4-positions of the
terminal benzene rings, have much higher melting
temperatures than their non-mesomorphic tetracatenar
2 mm-2 mm isomers 5a–c. Compounds 4a–c also have
much higher melting and clearing temperatures than the
hexacatenar 3mpm-3mpm mesogens (6a–c). Clearly,
compounds of series 4a–c have higher thermal stabilities
and broader mesomorphic ranges than compounds of series
6a–c. These observations indicate that the intermolecular
interactions are more favoured in compounds of series 4a–c
than in the analogous non-mesomorphic compounds of
series 5a–c and mesomorphic compounds of series 6a–c.
The weak mesomorphic stability of compounds 6a–c may
be attributed to the large number (six) of alkoxy chains and
the lateral meta positions for four of them, an arrangement
that leads to a reduced packing efficiency due to significant
steric effects and the space-filling requirements of the
alkoxy groups. It is likely that the presence of the two extra
terminal chains in compounds 6a–c leads to a broadening
of the molecular rotation volume (41), which in turn leads to
much lower transition temperatures compared with those of
the analogous tetracatenar compounds 4a–c. In addition,
the bulky alkoxy chains in compounds 6a–c would be
expected to cause comparatively weak interactions between
cores along the column axis (42).
Table 1. Phase-transition temperatures (8C), enthalpies (KJ
mol21, in parentheses) as determined by DSC, scanning rate
108C min21, DT (8C, mesomorphic range) and Tid (8C,
temperature of initial decomposition) for compounds 4a–c to
6a–c.
All of the results outlined above illustrate the
importance of the influence of the length, position and
number of alkoxy chains attached at the end of the rigid
core. We assumed that columnar phases in these materials
are due to the self-assembly of more than one molecule to
give disc-shaped (or similar) molecular aggregates. These
aggregates are arranged in columns due to p–p
interactions (p-stacking) between the central rigid units
of 2,6-bisphenylbenzo[1,2-d:4,5d0]bisthiazole (36).
Compound
Phase transitions
DT (8C) Tid
4a (n ¼ 10) Cr 167.5 (28.6) Colh 252.4 (5.2) I
I 239.0 (5.1) Colh 146.1 (29.7) Cr
84.9
69.5
42.8
–
352
350
342
368
360
359
340
335
337
4b (n ¼ 12) Cr 164.4 (80.8) Colh 233.9 (8.2) I
I 230.6 (7.0) Colh 152.1 (34.9) Cr
4c (n ¼ 14)
5a (n ¼ 10)
5b (n ¼ 12)
5c (n ¼ 14)
6a (n ¼ 10)
Cr 155.2 (62.7) Colh 198a I
I 187a Colh 140.0 (49.6) Cr
Cr 101.1 (12.2) I
I 99.5 (11.4) Cr
Cr 97.7 (10.8) I
I 95.9 (9.9) Cr
Cr 92.5 (8.9) I
–
2.3 Thermogravimetric analysis
–
In order to determine the temperature range in which the
new materials are sensitive to degradation, their thermal
degradation is usually studied before eventual and possible
applications are considered. The thermogravimetric (TG)
behaviour of 4a–c, 5a–c and 6a–c was investigated by
TG analysis under a nitrogen atmosphere. All solid
samples showed no apparent weight loss between 208C
and ,3308C–3608C and this indicates the absence of
occluded solvent. All compounds showed similar high
thermal stability up to 3308C. Compounds 4a–c, 5a–c and
I 91.8 (8.3) Cr
Cr 140.4 (18.1) I
I 140.4 (14.9) Colx 133.3 (1.6) Cr
–
6b (n ¼ 12) Cr 113.7 (0.5) Colr 128.5 (10.0) I
14.8
33.2
I 124.6 (10.4) Colr 111.2 (1.1) Cr
6c (n ¼ 14) Cr 109.9 (0.6) Colr 143.1 (12.3) I
I 137.8 (14.7) Colr 108.5 (0.9) Cr
aOptical data.
Notes: Cr, crystal phase; Colh, hexagonal columnar phase; Colr,
rectangular columnar phase; Colx, unidentified columnar phase; I,
isotropic phase.

´
J. Barbera et al.
376
Figure 1. (Colour online) Optical textures (magnification 20 £ ) observed under POM upon the cooling cycle. (a) Colh phase at 2008C of
4a, (b) Colh phase at 1908C of 4b, (c) Colh phase at 1738C of 4c, (d) Colx phase at 1388C of 6a, (e) Colr phase at 1328C of 6b, (f) Colr phase
at 1218C of 6c.
6a–c started to lose weight at around 330–3608C (,1%
weight loss) to 490–6008C (,85% weight loss) in a one-
step process and the whole decomposition process was
complete at 6008C (see Table 1 and Figure 2). These new
materials are therefore thermally stable at the temperature
range in which they exhibit mesomorphism.
crystalline. This is confirmed by the presence of one or
more sharp, strong maxima in the small-angle region and a
broad, diffuse halo in the large-angle region (Table 2). On
the other hand, the high-temperature patterns of com-
pounds 5a–c were characteristics of a 3D crystalline
phase, as revealed by the presence in the three cases of an
extra sharp reflection in the large-angle region. The X-ray
patterns of compounds 4a–c and the microscope textures
were consistent with a hexagonal columnar mesophase,
whereas the diffractograms of compounds 6b–c contain a
set of three small-angle reflections that can be assigned,
respectively, to the (1 1), (2 0) and (1 2) reflections of a
two-dimensional rectangular lattice (Figure 3). From the
2.4 XRD studies
High-temperature XRD studies were carried out on
compounds 4a–c, 5a–c and 6b–c. Compound 6a was
not studied due to the monotropic nature of its mesophase
and its tendency to crystallise.
measured lattice constants, the lattice area can be
The X-ray patterns confirm that the high-temperature
phases of 4a–c and 6b–c are unambiguously liquid
p
calculated as S ¼ a 2 3/2 for the hexagonal lattice and
Figure 2. (Colour online) Thermal decomposition profiles of 4a, 5a and 6a.

Supramolecular Chemistry
Table 2. Structural data for the mesophases measured by XRD.
377
2
S (A )
˚
Lattice constants (A)
˚
dexp (A)
˚
dcal (A)
˚
Compound
Temperature (8C)
Phase
Colh
h k
Z
4a
190
a ¼ 38.6
h ¼ 4.7
a ¼ 40.0
h ¼ 4.8
a ¼ 42.5
h ¼ 4.6
a ¼ 61.3
b ¼ 51.5
h ¼ 5.3
33.4
4.7 diffa
34.6
33.4
34.6
36.8
1 0
1290
3
3
3
4b
4c
6b
190
190
121
Colh
Colh
Colr
1 0
1 0
1383
1564
4.6 diffa
36.8
4.6 diffa
39.2
30.6
39.43
30.65
23.74
1 1
2 0
1 2
3157
S/2 ¼ 1578
6
Z/2 ¼ 3
24.0
4.5 diffa
41.2
31.0
6c
110
Colr
a ¼ 62
b ¼ 55
h ¼ 5.4
41.1
31.0
25.1
1 1
2 0
1 2
3410
S/2 ¼ 1705
6
Z/2 ¼ 3
24.9
4.5 diffa
Notes: The columns list, respectively, the compound number, the temperature of the experiment, the mesophase type, the measured parameters (a, b: lattice
constants in the columnar mesophase), the experimentally measured spacing, the calculated spacing, the Miller indices, the lattice cross-section and the
number of molecules per lattice.
a diff signifies diffuse.
S ¼ a £ b for the rectangular lattice (Table 2). Assuming
that there must be one column per hexagonal unit cell and
two columns per rectangular unit cell, the values obtained
for S or S/2, respectively, are too large for the stacking of
single molecules and this is consistent with the existence
of aggregates as the stacked entities. Indeed, it can be
predicted on the basis of density estimations that several
molecules are required to fill the cross section of each
column.
organic compounds. The density r in g cm23 of a
columnar mesophase can be calculated using the equation:
ðMꢀZꢀ1024Þ
r ¼
;
ðVꢀNAÞ
3
˚
where M is the molar mass in g, V the unit cell volume in A
and NA Avogadro’s number. Assuming that the density of
the organic mesophases of compounds must be close to
1 g cm23 (43–47) and taking into account that the volume
of the unit cell is Sꢀh, where h is a value taken as the height
The number of molecules per unit cell (Z) can be
estimated on the basis of the expected density for typical
Figure 3. Small-angle X-ray scattering (SAXS) patterns and indexation of (a) the Colh mesophase of compound 4a, (b) the Colh
mesophase of compound 4b, (c) the Colh mesophase of compound 4c, (d) the Colr mesophase of compound 6b and (e) the Colr mesophase
of compound 6c. The (1 2) reflection for compound 6b is weak but visible in the original pattern.

´
J. Barbera et al.
378
of a column stratum (44), Z can be estimated as
volume remains practically unchanged with temperature in
the mesophase, whereas the aliphatic chain volume
increases slightly with temperature (49). From the
accepted correcting factor for the dependence of the
volume per methylene group with temperature (44, 45,
49), it is estimated that the molecular volume must change
by about 3–4% in the thermal range considered (between
1158C and 1908C). This variation leaves the estimated
increase in the molecular volume of 6b compared with 4b
and of 6c compared with 4c at about 29% instead of 30%,
in fair agreement with the change in the molecular mass.
ðSꢀhꢀNAÞ
Z ¼
:
ðMꢀ1024Þ
In this equation, h is unknown due to the absence of a
scattering maximum as a result of the stacking distance,
which in turn is due to the lack of long-range periodicity
along the column axis. However, a reasonable approximate
value for h can be deduced from the diffuse X-ray halo
found at high scattering angles. The diffuse character of
this halo reflects the liquid-like state of the molten
hydrocarbon chains but, at the same time, it is considered
to be associated with the packing of the mesogenic units
(43, 44, 48). Under these circumstances, Z can be
estimated as a function of h and thus it can be concluded
that three molecules of compounds 4a–c are required to
2.5 Ultraviolet–visible absorption and
photoluminescence spectroscopy
The Ultraviolet–visible (UV–vis) absorption and emis-
sion spectra of compounds 4a, 5a and 6a were measured in
dichloromethane solutions (2.5 £ 1025 M; 2.5 £ 1027 M,
respectively). We assumed that the length of the side
chains does not make a difference to the absorption–
photoluminescence spectra, as reported in the literature
(36). Therefore, compounds 4a, 5a and 6a, as representa-
tive members of each series, were chosen for these studies.
The absorption and emission spectra of compounds 4a,
5a and 6a in dichloromethane solutions are depicted in
Figure 4 and the photophysical data are summarised in
Table 3. Similar absorption patterns were observed for
these compounds and all of them exhibit an intense
absorption band at 353 nm, with shoulders at 339 and
372 nm. The molar extinction coefficients at 353 nm were
found to be 6.57 £ 104 M21 cm21 for 4a, 6.30
£ 104 M21 cm21 for 5a and 6.54 £ 104 M21 cm21 for 6a.
As shown in Figure 4, each compound displayed three
emission bands at 384, 405 and 429 nm for 4a; 383, 404
and 427 nm for 5a and 383, 405 and 428 nm for 6a. The
emission colours of these compounds are all in the violet-
blue region, with a maximum wavelength at ,405 nm
(lem.max). The large molar absorption coefficients (see
Table 3) are indicative of highly p-conjugated systems and
˚
fill a column stratum of thickness h ¼ 4.6–4.8 A and three
molecules of 6b–c are required to fill a column stratum of
˚
thickness h ¼ 5.3–5.4 A. In fact, for 6b–c, the estimated
number of molecules per unit cell (Z) is 6, but this value
corresponds to two columns and therefore the number of
molecules per column stratum is Z/2 (Table 2). The higher
thickness h estimated for 6b–c compared with 4a–c must
be related to the higher spatial requirements due to the
larger number of alkyl chains. Furthermore, molecular
tilting, which is usually found in rectangular columnar
mesophases, may play a role.
It must be pointed out that, in non-disc-like molecules, a
columnar stratum does not have a particularly significant
meaning and, in this case, it does not necessarily imply that
the columns result from stacking of discrete disc-shaped
aggregates containing a definite number of molecules on top
of each other. In addition, the mesophase is not a static
system and diffusion of the molecules can take place
between adjacent strata. However, this approach is accepted
to allow for an estimation of the occupation density of the
column (44) and a prediction of the molecular packing
within the columns.
The symmetry of the columnar packing is driven by
the number of hydrocarbon chains attached to the rigid
aromatic units. As mentioned above, a higher number of
chains increase the intermolecular separation along the
column axis and this can permit the molecular tilting
inherent in rectangular symmetry, thus compensating for
the increased steric requirements of the chains.
their absorption band is attributed to spin-allowed p–p
*
transitions involving the benzobisthiazole framework (36).
The photoluminescence quantum efficiencies of 4a, 5a
and 6aindichloromethane solutionwere 0.53, 0.44and 0.49,
respectively. The photoluminescence quantum yield for each
sample (FPL) was determined by comparison with a well-
known reference compound (9,10-diphenylanthracene in
cyclohexane, Fstd ¼ 0.90). Thegeneral equationusedforthe
determination of the relative quantum yield is as follows:
The variation in the thickness of the column stratum
and in the cross-sectional area upon varying the number of
alkyl chains produces a 30% increase in the molecular
volume of 6b compared with 4b and of 6c compared with
4c. This trend is consistent with the change in the
molecular mass, which increases by 28% from 4b to 6b
and 30% from 4c to 6c. The different temperatures of the
measurements can also have an effect on the molecular
volume. It is accepted that the aromatic component of the
!
h2sample
h2std
Absstd
Asample
FPL < Fstd
£
£
£
;
Abssample
Astd
where fstd is the photoluminescence quantum yield of the
standard 9,10-diphenylanthracene (Fstd ¼ 0.90, cyclohex-

Supramolecular Chemistry
379
Figure 4. (Colour online) Normalised UV absorption and PL spectra of compounds 4a, 5a and 6a in dichloromethane.
ane);Absstd andAbssample are theabsorbancesofthestandard
and sample, respectively; Asample and Astd are the integrated
areas of the emission peak of the sample and standard,
respectively; and 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.
The excellent results of mesomorphism, together with
the good photoluminescence properties, stimulate the
investigation of analogous compounds. This work is
currently in progress.
4. Experimental section
4.1 General
3. Conclusions
All reagents were obtained from commercial sources
Merck Chemicals (Darmstadt, Germany) or Sigma-
Aldrich (St. Louis, MO) and used without further
purification. The organic solvents were of analytical
grade quality. The purity of the compounds was checked
by thin-layer chromatography (Merck Kieselgel 60F254,
Merck Chemicals (Darmstadt, Germany)).
1H NMR and 13C NMR spectra were recorded on a
Bruker Avance 400 MHz spectrometer (Karlsruhe,
Germany), with CDCl3 and DMSO-d6 as solvents and
tetramethylsilane as an internal standard. FT-IR spectra
were recorded with a Nicolet Magna 550 spectropho-
tometer (Nicolet Instruments Corporation, Madison, WI,
USA). MALDI experiments were carried out on a Bruker
Microflex spectrometer (Massachusetts, USA). Elemental
analyses were conducted on a Perkin-Elmer 240C
elemental analyser (Massachusetts, USA).
In summary, a simple and straightforward synthesis of new
tetra- and hexacatenar materials containing the benzobisthia-
zole chromophore as the central core have been achieved.
The POM and DSC analysis and XRD showed the
presence of Colh mesomorphism in series 4a–c (tetra-
catenar) and Colr mesomorphism in compounds 6b,c
(hexacatenar). It is important to underline that the very
interesting mesomorphic properties observed in series 4
and 6 depend on the length, position and number of alkoxy
chains attached at the end of the rigid core. As their
thermal degradations only start from 3308C, they are
thermally stable at the temperature range in which they
exhibit mesomorphism and, therefore, potential appli-
cations could be considered. The study of photolumines-
cence properties in the visible region, found in these
materials, reveals very promising results with good
quantum yields.
Transition temperatures and textures of mesophases
were determined by POM using an Olympus BX51 optical
microscope equipped with an Olympus U-TV0.5XC-3
polariser and a LinkamT95-PE hot stage.
Table 3. Photophysical properties of polycatenar benzobisthia-
zoles (4a, 5a and 6a).
Transition temperatures and enthalpies were obtained
by DSC using a TA Instruments Q1000 calorimeter.
Samples were encapsulated in aluminium pans and
observed at a scanning rate of 108C min21 on heating
and cooling. The instrument was calibrated using an
indium standard (156.68C, 28.44 J g21) under a nitrogen
atmosphere.
lmax lem
.
1
Stokes
shift (nm) FPL
max
c
Compound (nm)a
(nm)b
(M21 cm21
)
4a
5a
6a
353
353
353
405
404
405
6.57 £ 104
6.30 £ 104
6.54 £ 104
52
51
52
0.53
0.44
0.49
a Measured in dichloromethane solution (2.5 £ 1025 M).
b Excited at absorption maxima (2.5 £ 1027 M).
c Quantum yield in dichloromethane solutions relative to 9,10-
The mesophases were investigated by XRD. The XRD
patterns were obtained with a pinhole camera (Anton–
diphenylanthracene (Fstd ¼ 0.9 in cyclohexane solution).

´
J. Barbera et al.
380
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) and heated
with a high-temperature attachment. The patterns were
collected on flat photographic film perpendicular to the X-
ray beam and spacing was obtained with Bragg’s law.
TG measurements were conducted with an STA 625
system in platinum pans at prescribed heating rates of
108C min21 in the range of 258C–6508C under a steady
flow of nitrogen (42 ml min21).
alkoxybenzoyl chloride (1.68 mmol) in dry THF (30 ml).
The mixture was stirred at r.t. for 48 h under a nitrogen
atmosphere and then poured into water/ice and neutralised
with aqueous NaOH (10%). The solid was filtered off,
washed several times with water and purified by column
chromatography on silica gel using chloroform as eluent to
yield pure 4a–c to 6a–c as pale-yellow solids.
Compound 4a 4b 4c 5a 5b 5c 6a 6b 6c
Yield (%)
57 40 53 63 59 56 59 50 54
UV–vis absorbance measurements were carried out on a
UV4-200 ATI-Unicam spectrophotometer with a dual beam
between200and600 nm. Luminescencemeasurementswere
obtained on a Perkin-Elmer LS50B (Richmond Scientific
Ltd., Lancashire, Great Britain) between 340 and 700 nm.
4.2.4 Characterisation of compound 4a (n ¼ 10)
FT-IR (KBr) cm21: 3074 (Csp2ZH), 2921; 2853
(Csp3ZH), 1726 (CvO), 1201 (CZO).
1H NMR (CDCl3): d 0.88 (t, 12H, ZCH3), 1.19–1.41
(m, 48H, ZCH2Z), 1.46 (m, 8H, OCH2CH2CH2), 1.87 (m,
8H, OCH2CH2), 4.09 (m, 8H, OCH2), 6.94 (d, 2H, Ar–H),
7.38 (AA0BB0, 4H, Ar–H), 7.68 (d, 2H, Ar–H), 7.84 (dd,
2H, Ar–H), 8.20 (AA0BB0, 4H, Ar–H), 8.56 (s, 2H, Ar–H).
MALDI-TOF-MS calculated for C74H100N2O8S2
[M þ H]þ1209.7, found 1209.9.
4.2 Synthesis and characterisation
4.2.1 Synthesis of compound 2
To a solution of 4-benzyloxybenzoyl chloride (6.21mmol)
and dry THF (40 ml) was slowly added a solution of 2,5-
diamino-1,4-benzenedithiol dihydrochloride (1) (0.75 g,
3.06 mmol) in NMP (125 ml). The resulting mixture was
heated under reflux for 48 h and then cooled to room
temperature (r.t.), poured into ice–water and neutralised with
aqueous NaOH (20%). The resulting precipitate was filtered
off, washed with water and then washed twice with boiling
ethanoltogive2in 72% yield as a yellow solid, m.p..2508C.
FT-IR (KBr) cm21: 3031 (Csp2ZH); 1120 (CZO).
Elemental analysis data (%) for C74H100N2O8S2,
calculated: C 73.47, H 8.33, N 2.32, S 5.30; found: C
73.38, H 8.39, N 2.26, S 5.25.
4.2.5 Characterisation of compound 4b (n ¼ 12)
FT-IR (KBr) cm21: 3080 (Csp2ZH), 2920; 2851
(Csp3ZH), 1725 (CvO), 1200 (CZO).
1H NMR (CDCl3): d 0.87 (m, 12H, ZCH3), 1.20–1.43
(m, 64H, ZCH2Z), 1.52 (m, 8H, OCH2CH2CH2), 1.86 (m,
8H, OCH2CH2), 4.08 (m, 8H, OCH2), 6.96 (d, 2H, Ar–H),
7.39 (AA0BB0, 4H, Ar–H), 7.69 (d, 2H, Ar–H), 7.86 (dd,
2H, Ar–H), 8.20 (AA0BB0, 4H, Ar–H), 8.56 (s, 2H, Ar–H).
MALDI-TOF-MS calculated for C82H116N2O8S2
[M þ H]þ1321.8, found 1321.9.
4.2.2 Synthesis of compound 3
A mixture of compound 2 (1.00 g, 1.80 mmol), glacial
acetic acid (60 ml) and fuming hydrochloric acid (30 ml)
was heated under reflux for 24 h. The mixture was poured
into water/ice and was neutralised with aqueous NaOH
(40%). The crude product was filtered off, washed with
water and then washed with warm acetone to give
compound 3 in 90% yield as a yellow solid, m.p. .2508C.
FT-IR (KBr) cm21: 3123 (OZH); 3020 (Csp2ZH).
1H NMR (DMSO-d6): d 6.95 (d, 4H, J ¼ 8.8 Hz, Ar–H),
7.96 (d, 4H, J ¼ 8.8 Hz, Ar–H), 8.68 (s, 2H, Ar–H), 10.29
(s, 2H, OH).
Elemental analysis data (%) for C82H116N2O8S2,
calculated: C 74.50, H 8.84, N 2.12, S 4.85; found: C
74.42, H 9.02, N 2.07, S 4.76.
13C NMR (DMSO-d6): d 115.0, 116.1, 124.0, 129.2,
133.5, 151.5, 160.7, 168.0.
4.2.6 Characterisation of compound 4c (n ¼ 14)
FT-IR (KBr) cm21: 3076 (Csp2ZH), 2920; 2853
(Csp3ZH), 1726 (CvO), 1200 (CZO).
1H NMR (CDCl3): d 0.89 (t, 12H, ZCH3), 1.18–1.41
(m, 80H, ZCH2Z), 1.47 (m, 8H, ZOCH2CH2CH2), 1.85
(m, 8H, ZOCH2CH2), 4.05 (m, 8H, ZOCH2), 6.93 (d, 2H,
Ar–H), 7.37(AA0BB0, 4H, Ar–H), 7.68(d,2H, Ar–H), 7.84
(dd, 2H, Ar–H), 8.19 (AA0BB0, 4H, Ar–H), 8.58 (s, 2H,
Ar–H).
4.2.3 Synthesis of esters 4a–c to 6a–c
The esters of series 4a–c to 6a–c were synthesised
according to the procedure described in the general method.
General method: A solution of compound 3 (0.311 g,
8.27 £ 1021 mmol), TEA (1.0 ml) and DMAP (0.032 g) in
dry NMP (40 ml) was added to a solution of the
corresponding 3,4-di-n-, 3,5-di-n-, and/or 3,4,5-tri-n-
MALDI-TOF-MS calculated for C90H132N2O8S2
[M þ H]þ1433.9, found 1434.2.

Supramolecular Chemistry
381
Elemental analysis data (%) for C90H132N2O8S2,
calculated: C 75.37, H 9.28, N 1.95, S 4.47; found: C
75.31, H 9.35, N 1.91, S 4.38.
Elemental analysis data (%) for C90H132N2O8S2,
calculated: C 75.37, H 9.28, N 1.95, S 4.47; found: C
75.29, H 9.37, N 1.97, S 4.40.
4.2.7 Characterisation of compound 5a (n ¼ 10)
4.2.10 Characterisation of compound 6a (n ¼ 10)
FT-IR (KBr) cm21: 3081 (Csp2ZH), 2920; 2854
(Csp3ZH), 1737 (CvO), 1204 (CZO).
FT-IR (KBr) cm21: 3072 (Csp2ZH), 2923; 2854
(Csp3ZH), 1733 (CvO), 1201 (CZO).
1H NMR (CDCl3): d 0.89 (t, 12H, ZCH3), 1.21–1.38
(m, 48H, ZCH2), 1.47 (m, 8H, ZOCH2CH2CH2), 1.81 (m,
8H, ZOCH2CH2), 4.01 (t, 8H, ZOCH2), 6.73 (t, 2H, Ar–
H), 7.33 (d, 4H, Ar–H), 7.38 (AA0BB0, 4H, Ar–H), 8.18
(AA0BB0, 4H, Ar–H), 8.53 (s, 2H, Ar–H).
1H NMR (CDCl3): d 0.88 (m, 18H, ZCH3), 1.20–1.41
(m, 72H, ZCH2), 1.50 (m, 12H,OCH2CH2CH2), 1.81 (m,
12H, OCH2CH2), 4.07 (m, 12H, OCH2), 7.38 (AA0BB0 4H,
Ar–H), 7.43 (s, 4H, Ar–H), 8.20 (AA0BB0, 4H, Ar–H),
8.57 (s, 2H, Ar–H).
13C NMR (CDCl3): d 14.3, 22.8, 22.9, 26.2, 26.3, 29.4,
29.5, 29.6, 29.7, 29.8, 29.9, 30.0, 30.1, 30.2, 32.1, 32.2,
69.4, 73.8, 108.8, 115.6, 122.8, 123.6, 129.1, 131.3, 134.8,
143.4, 152.4, 153.2, 153.6, 164.8, 168.1.
13C NMR (CDCl3): d 14.3, 22.8, 26.2, 29.3, 29.5, 29.6,
29.7, 29.8, 32.0, 68.6, 107.5, 108.4, 115.6, 122.6, 129.0,
130.9, 131.3, 134.7, 152.4, 153.4, 160.5, 164,8, 168.0.
MALDI-TOF-MS calculated for C74H100N2O8S2
[M þ H]þ1209.7, found 1209.8.
MALDI-TOF-MS calculated for C94H140N2O10S2
[M þ H]þ1523.0, found 1523.2.
Elemental analysis data (%) for C74H100N2O8S2,
calculated: C 73.47, H 8.33, N 2.32, S 5.30; found: C
73.42, H 8.43, N 2.26, S 5.21.
Elemental analysis data (%) for C94H140N2O10S2,
calculated: C 74.17, H 9.27, N 1.84, S 4.21; found: C
73.97, H 9.32, N 1.78, S 4.15.
4.2.8 Characterisation of compound 5b (n ¼ 12)
FT-IR (KBr) cm21: 3072 (Csp2ZH), 2919; 2850
(Csp3ZH), 1727 (CvO), 1209 (CZO).
4.2.11 Characterisation of compound 6b (n ¼ 12)
FT-IR (KBr) cm21: 3070 (Csp2ZH), 2921; 2851
(Csp3ZH), 1732 (CvO), 1200 (CZO).
1H NMR (CDCl3): d 0.88 (t, 12H, ZCH3), 1.21–1.38
(m, 64H, ZCH2), 1.47 (m, 8H, OCH2CH2CH2), 1.81 (m,
8H, OCH2CH2), 4.01 (t, 8H, OCH2), 6.73 (t, 2H, Ar–H),
7.33 (d, 4H, Ar–H), 7.39 (AA0BB0, 4H, Ar–H), 8.19
(AA0BB0, 4H, Ar–H), 8.55 (s, 2H, Ar–H).
1H NMR (CDCl3): d 0.89 (m, 18H, ZCH3), 1.18–1.43
(m, 96H, ZCH2), 1.50 (m, 12H, OCH2CH2CH2), 1.81 (m,
12H, OCH2CH2), 4.07 (m, 12H, OCH2), 7.38 (AA0BB0,
4H, Ar–H), 7.43 (s, 4H, Ar–H), 8.19 (AA0BB0, 4H, Ar–
H), 8.54 (s, 2H, Ar–H).
13C NMR (CDCl3): d 14.3, 22.8, 26.2, 29.3, 29.4, 29.5,
29.6, 29.7, 29.8, 29.9, 32.1, 68.6, 107.5, 108.4, 115.6, 122.6,
129.1, 130.9, 131.4, 134.7, 152.4, 153.5, 160.5, 164.8, 168.1.
MALDI-TOF-MS calculated for C82H116N2O8S2
[M þ H]þ1321.8, found 1322.0.
13C NMR (CDCl3): d 14.2, 22.8, 26.2, 26.3, 29.4, 29.5,
29.6, 29.7, 29.8, 29.9, 30.0, 30.1, 30.2, 30.3, 30.50, 32.1,
32.2, 69.4, 73.7, 108.7, 115.6, 122.7, 123.6, 129.0, 131.3,
134.7, 143.4, 152.3, 153.1, 153.5, 164.8, 168.0.
MALDI-TOF-MS calculated for C106H164N2O10S2
[M þ H]þ1691.2, found 1691.4.
Elemental analysis data (%) for C82H116N2O8S2,
calculated: C 74.50, H 8.84, N 2.12, S 4.85; found: C
74.44, H 8.90, N 2.03, S 4.79.
Elemental analysis data (%) for C106H164N2O10S2,
calculated: C 75.31, H 9.78, N 1.66, S 3.79; found: C
75.22, H 9.84, N 1.72, S 3.71.
4.2.9 Characterisation of compound 5c (n ¼ 14)
FT-IR (KBr) cm21: 3074 (Csp2ZH), 2919; 2849
(Csp3ZH), 1727 (CvO), 1209 (CZO).
1H NMR (CDCl3): d 0.88 (t, 12H, ZCH3), 1.21–1.40
(m, 80H, ZCH2), 1.47 (m, 8H, OCH2CH2CH2), 1.81 (m,
8H, OCH2CH2), 4.02 (t, 8H, OCH2), 6.73 (t, 2H, Ar–H),
7.33 (d, 4H, Ar–H), 7.39 (AA0BB0, 4H, Ar–H), 8.20
(AA0BB0, 4H, Ar–H), 8.57 (s, 2H, Ar–H).
13C NMR (CDCl3): d 14.3, 22.9, 26.2, 29.3, 29.4, 29.5,
29.6, 29.7, 29.8, 29.9, 30.0, 32.1, 68.6, 107.5, 108.4, 115.6,
122.6, 129.1, 130.9, 131.4, 134.7, 152.4, 153.5, 160.5,
164.8, 168.1.
4.2.12 Characterisation of compound 6c (n ¼ 14)
FT-IR (KBr) cm21: 3072 (Csp2ZH), 2920; 2852
(Csp3ZH), 1734 (CvO), 1195 (CZO).
1H NMR (CDCl3): d 0.88 (m, 18H, ZCH3), 1.19–1.42
(m, 120H, ZCH2), 1.50 (m, 12H, OCH2CH2CH2), 1.81
(m, 12H, OCH2CH2), 4.07 (m, 12H, OCH2), 7.38
(AA0BB0, 4H, Ar–H), 7.43 (s, 4H, Ar–H), 8.20 (AA0BB0,
4H, Ar–H), 8.57 (s, 2H, Ar–H).
13C NMR (CDCl3): d 14.3, 22.8, 26.2, 26.3, 29.4, 29.5,
29.6, 29.7, 29.8, 29.9, 30.0, 30.1, 30.5, 32.1, 32.2, 69.4,
73.8, 108.8, 115.6, 122.8, 123.6, 129.1, 131.3, 134.8,
143.4, 152.4, 153.2, 153.6, 164.8, 168.1.
MALDI-TOF-MS calculated for C90H132N2O8S2
[M þ H]þ1433.9, found 1434.1.

´
J. Barbera et al.
382
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6129–6132.
MALDI-TOF-MS calculated for C118H188N2O10S2
[M þ H]þ1859.4, found 1859.6.
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Elemental analysis data (%) for C118H188N2O10S2,
calculated: C 76.24, H 10.19, N 1.51, S 3.45; found: C
76.19, H 10.25, N 1.46, S 3.37.
Funding
This research was supported by FONDECYT (1100140), CON-
´
ICYT, ‘Direccion de Investigacion’ of the University of Concepcion,
the Spanish project CTQ2012-35692 and FEDER funds.
´
´
(29) Osaheni, J.A.; Jenekhe, S.A.; Perlstein, J. J. Appl. Phys.
Lett. 1994, 64, 3112–3114.
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