A linear conjugated core for functional columnar liquid crystals

Article abstract of DOI:10.1039/c2nj20950k

Two series of polycatenar molecules consisting of a π-conjugated rigid core derived from 3-hexen-1,5-diyne coupled to different types of benzoic acid derivatives have been prepared and their potential as multifunctional materials has been investigated. The size ratio between the rigid core and the benzoate-derived groups, which vary in bulk, is crucial to address self-organization, thus indicating the delicate balance of forces involved in liquid crystalline (LC) behaviour. LC nematic, crystalline or LC columnar behaviour is observed depending on the structure of the benzoate moiety. Hexagonal two-dimensional columnar organization is attained for mesogens with benzoate-derived groups bearing six and nine alkoxylic tails. The stacking unit of the columnar organizations is different depending on the total number of tails, twelve or eighteen, with two molecules and half a molecule per columnar stratum, respectively. Macroscopic properties related to molecular structure, such as luminescence, chirality and electroactivity, have also been studied. Luminescent behaviour is observed for all mesogenic materials, which show higher Stokes shifts than in solution. In addition, supramolecular chirality in the mesophase has been observed for a chiral mesogen. Finally, the photoconducting behaviour of two of the columnar materials has been evaluated. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012.

Full text of DOI:10.1039/c2nj20950k

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New Journal of Chemistry
A journal for new directions in chemistry
www.rsc.org/njc
Volume 36 | Number 3 | March 2012 | Pages 513–844
ISSN 1144-0546
COVER ARTICLE
Sierra, Ballesteros et al.
A linear conjugated core for functional columnar liquid crystals

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PAPER
A linear conjugated core for functional columnar liquid crystalsw
a
a
b
c
´
Ana Perez, Jose Luis Serrano, Teresa Sierra,* Alfredo Ballesteros,*
Diana de Saa, Roberto Termine, Upendra Kumar Pandey and Attilio Golemme
´
c
d
d
d
´
Received (in Montpellier, France) 10th November 2011, Accepted 6th January 2012
DOI: 10.1039/c2nj20950k
Two series of polycatenar molecules consisting of a p-conjugated rigid core derived from
3-hexen-1,5-diyne coupled to different types of benzoic acid derivatives have been prepared and
their potential as multifunctional materials has been investigated. The size ratio between the rigid
core and the benzoate-derived groups, which vary in bulk, is crucial to address self-organization,
thus indicating the delicate balance of forces involved in liquid crystalline (LC) behaviour.
LC nematic, crystalline or LC columnar behaviour is observed depending on the structure of
the benzoate moiety. Hexagonal two-dimensional columnar organization is attained for mesogens
with benzoate-derived groups bearing six and nine alkoxylic tails. The stacking unit of the
columnar organizations is different depending on the total number of tails, twelve or eighteen,
with two molecules and half a molecule per columnar stratum, respectively. Macroscopic
properties related to molecular structure, such as luminescence, chirality and electroactivity,
have also been studied. Luminescent behaviour is observed for all mesogenic materials, which
show higher Stokes shifts than in solution. In addition, supramolecular chirality in the mesophase
has been observed for a chiral mesogen. Finally, the photoconducting behaviour of two of the
columnar materials has been evaluated.
Introduction
must be considered for the development of high-performance
functional materials.
The design of multifunctional materials is one of the most
interesting targets in materials chemistry. The combination of
different physical properties in the same material may simplify
the processing required to construct the corresponding devices
and this aspect is of great importance in fields such as organic
optoelectronics.1 In an effort to achieve optoelectronic materi-
als, a great deal of research effort has been focused on the
supramolecular organization of the molecules.2–6 The appro-
priate organization of the different functional building blocks
in such a way that one or several properties are magnified, or
the appearance of cooperative effects in the material due to the
influence of the neighboring molecules, are ideal situations that
In this respect, the combination of liquid crystalline order
with other physical properties is particularly interesting to
obtain multifunctional materials in which the control of the
macroscopic molecular arrangement is essential for a certain
property to manifest itself or to be enhanced, especially those
properties that are direction-dependent.7–9 Liquid crystals
allow us to control order at the microscopic level and this can
be extended to the macroscopic regime through appropriate
processing and bulk alignment. Thus, for example, the effects of
p-conjugation and organization on emission and conductive
properties have led to an increasing interest for columnar liquid
crystals as an approach to luminescent and semiconductor
materials for optoelectronic applications.10 Indeed, columnar
phases of tailor-made mesogenic cores have been synthesized
and investigated with regard to their application as semi-
conductors with high charge-carrier mobility values and intense
fluorescence.11
a
´
Instituto de Nanociencia de Aragon, Quımica Organica, Facultad de
Ciencias, Universidad de Zaragoza, 50009-Zaragoza, Spain
´
´
b
c
´
´
´
Instituto de Ciencia de Materiales de Aragon, Quımica Organica,
Facultad de Ciencias, Universidad de Zaragoza-C.S.I.C.,
50009-Zaragoza, Spain. E-mail: tsierra@unizar.es
´
Departamento de Quımica Organica e Inorganica and Instituto
Universitario de Quımica Organometalica ‘‘Enrique Moles’’,
´
´
´
´
The molecular design of columnar liquid crystals does not
rely on disk-like structures only. Phasmidic or polycatenar
liquid crystals are a family of thermotropic mesogens that are
generally composed of a rod-like core and two half-disk-shaped
units (aromatic end groups containing several flexible tails).12
These mesogenic structures combine the structural and meso-
genic properties of conventional calamitic and discotic liquid
crystals. As a result, polycatenar liquid crystals not only display
´
Unidad Asociada al C.S.I.C., Universidad de Oviedo, C/Julian
´
Claverıa, 8, 33006-Oviedo, Spain. E-mail: abg@uniovi.es
d Centro di Eccellenza CEMIF.CAL, LASCAMM CR-INSTM,
CNR-IPCF UOS CS - LiCryL, Dipartimento di Chimica,
`
Universita della Calabria, 87036 Rende, Italy
w Electronic supplementary information (ESI) available: Synthetic
procedures and compounds analytical data. POM DSC, X-ray diffrac-
tion, UV-Vis, fluorescence, CD measurements, cyclic voltammetry.
See DOI: 10.1039/c2nj20950k
c
830 New J. Chem., 2012, 36, 830–842
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conventional nematic and smectic mesophases, but they also
commonly display columnar mesomorphism in which the compo-
sition of the stacking units is strongly dependent on the particular
structure of the molecule. Furthermore, this approach allows
tailoring of the mesogen design toward the achievement of
functional liquid crystals with luminescent13 and photoconducting
properties suitable for optoelectronic purposes.14
which promote liquid crystalline order through nanosegregation.
Accordingly, calamitic behaviour is observed for compounds
derived from 4-dodecyloxybenzoic acid (A1), whereas columnar
mesomorphism appears for derivatives with twelve (CnB6) and
eighteen (CnB9) terminal chains. Moreover, the properties encoded
in the molecule, i.e. chirality or electronic and luminescent features,
are transferred to the resulting mesomorphic organization and
hence manifested in the final material.
In a previous communication, we described a new polycatenar
mesogen (C3B9 in Chart 1) derived from a new core, 1,6-diphenyl-
3,4-dipropyl-3-hexen-1,5-diyne (C3 in Chart 1).15 This core has
a rod-like shape, high electronic conjugation and fluorescence
properties in solution, which make it interesting to implement
functionality into liquid crystalline materials. The mesogenic
compound, C3B9, self-organized into a Colh mesophase,
which showed an unusual supramolecular organization with
half a molecule constituting the stacking unit of the column.
Furthermore, the new mesogen displayed luminescence in
solution as well as in the mesophase.
Results and discussion
Synthesis
The synthesis of the final compounds was carried out as
outlined in Scheme 1. The synthetic and analytical details
for the conjugated core C3, with propyl groups as substituents
in the central double bond, were described elsewhere.15 The
core C10, with decyl groups as substituents in the central
double bond, was prepared by following the same procedure
as described for C3 (see ESIw).16
The benzoic acid derivatives A1, A2 and A3, with one, two
and three dodecyloxy chains, respectively, were prepared by
Williamson etherification of the corresponding methyl hydroxy-
benzoate with the appropriate alkyl bromide followed by ester
cleavage, as described elsewhere.17 Likewise, the acids B3, B6 and
B9 were prepared, as reported previously, by Williamson ether-
ification of methyl 3,4,5-trihydroxybenzoate with the appropriate
benzyl chloride, followed by ester cleavage.18 Acid B6* is
reported here for the first time (see ESIw) and was synthesized
by following the same procedure as for acids B3, B6 and B9.
Coupling of acid derivatives A and B with either C3 or C10
to give the target compounds was carried out by a double
esterification reaction with DCC catalyzed by DMAP in dry
dichloromethane (Scheme 1).
On the basis of these results, we have explored the possibilities
of tuning the mesomorphic behaviour of this p-conjugated core,
and the effect of the resulting mesomorphic organization on the
optic and electronic properties of the materials. In the present
paper we report two conjugated cores, the previously reported,
C3, and the new one, C10, derived from 1,6-diphenyl-3,4-didecyl-
3-hexen-1,5-diyne (Chart 1).16 These cores have been modified in
the two terminal positions with different types of aromatic acid
bearing long aliphatic chains: acids A, derived from benzoic
acid, and acids B, derived from 3,4,5-tribenzyloxybenzoic acid.
These carboxylate moieties contribute to the design of molecules,
CA and CB (Chart 1), with structurally differentiated parts,
Thermal properties
The two conjugated cores, C3 and C10, are crystalline materials.
The length of the lateral chain has a marked influence on the
melting point; compound C3, bearing the shorter propyl group,
has a higher melting temperature (172 1C) than compound C10
(with the longer decyl lateral group), which has a much lower
melting point of 72 1C. As far as the mesogenic nature of the
acids is concerned, all of them show liquid crystalline behavior
apart from A2 and A3. The mesophase characteristics have
already been reported in the literature for acids A1, B3 and B9.
The mesophase of acid B6 was identified as Colh by POM and
X-ray diffraction (see ESIw).18b,19 Likewise, the chiral acid B6*
shows a Colh phase that is stable over a wide temperature range,
including room temperature. To help the comparison between
acids and their corresponding final compounds, the thermal
behavior of all the acids is listed in Tables 1 and 2.
The thermal behaviour of the potential mesogens, CA and
CB, was characterized by polarizing optical microscopy
(POM) and differential scanning calorimetry (DSC). Phase
transition temperatures and associated enthalpy values are
summarized in Tables 1 and 2.
Rod-like compounds C3A1 and C10A1 showed nematic
behaviour and, in a similar way to the respective C3 and
C10 precursors, C3A1 has higher transition temperatures
Chart 1 Chemical structure of the final compounds prepared by
coupling the rigid p-conjugated core, C, with different benzoic acid
derivatives (types A and B).
c
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New J. Chem., 2012, 36, 830–842 831

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Scheme 1 Synthetic scheme followed to prepare the target compounds.
Table 1 Transition temperatures and associated enthalpy values of compounds CA and their acid precursors A, as determined by DSC
Compound
Transition temperaturesa/1C [enthalpies/kJ molꢀ1
]
A117
Cr1
Cr1
Cr
Cr
Cr
Cr
Cr
Cr
Cr1
32.1 [ꢀ10.8]
94.0 [8.7]
Cr2
Cr2
92.3 [39.3]
118.3 [58.4]
SmC
129.4 [1.9]
N
N
N
137.0 [2.4]
156.8 [3.0]
88.6 [1.7]
I
I
I
I
I
I
I
I
I
A217
A317
56.4 [62.6]
95.6 [71.4]
80.0 [87.8]
52.9 [112.0]
77.1 [61.8]
103.1 [122.1]
25.4 [72.8]
C3A1
C3A2
C3A3
C10A1
C10A2
C10A3
Cr2
36.4 [ꢀ18.1]
Cr3
50.2 [34.7]
Cr: crystalline phase, N: nematic mesophase, SmC: smectic C mesophase, I: isotropic liquid. a Reported are the onset values of transitions observed
for the corresponding second scan at 10 1C minꢀ1
.
Table 2 Transition temperatures and the associated enthalpy values of compounds CB and their acid precursors B, as determined by DSC
Compound
Transition temperaturesa/1C [enthalpies/kJ molꢀ1
]
B318b
B6
Cr
Cr
Cr1
5.6 [17.3]
46.0 [3.7]
ꢀ13.1 [19.9]
Colh
Colh
Cub
Colh
136.8b [4.9]
132.6 [2.6]
117.0 [3.8]
89.6 [1.0]
I
I
I
I
I
I
I
I
I
I
I
B918b
B6*
Cr2
18.1 [ꢀ94.6]
76.3 [63.5]
Cr3
82.7 [109.5]
C3B3
C3B6
C3B9
C3B6*
C10B3
C10B6
C10B9
Cr1
M
25.6 [20.8]
8.1b [30.6]
Cr2
Colh
Colh
Colh
107.0 [29.7]
59.6d [13.6]
58.3 [16.8]
Colh
40.3 [ꢀ84.2]
Cr
Cr
84.6 [149.8]
92.1 [170.5]
Cr1
M
Cr
46.1 [31.4]
7.9b [65.3]
71.8 [199.2]
Cr2
Colh
85.9 [126.5]
52.0 [ꢀ171.7]
Colh
(Colh
98.3 [29.9]
61c,d
)
Cr: crystalline phase, M: unidentified mesophase, Cub: cubic mesophase, Colh: hexagonal columnar mesophase, I: isotropic liquid. a Reported are
the onset values of transitions observed in the second heating–cooling cycle at 10 1C minꢀ1, except for (b), for which the maximum of the peak is
given. Transition temperature determined by POM. Monotropic transition.
c
d
than C10A1. Compound C3A1 shows a broad mesophase
range in contrast to compound C10A1, which has a nematic
phase over a short temperature range. This difference is
probably due to the greater steric hindrance of the decyl
c
832 New J. Chem., 2012, 36, 830–842
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lateral chains,20 which hampers intermolecular interactions in
C10A1 and lowers transition temperatures.
Compounds derived from acid B9, C3B9 and C10B9, show
monotropic mesomorphic behavior. The Colh mesophase of
C3B9 was previously characterized,15 although its data are
herein included for the sake of comparison. The appearance of
a Colh mesophase for C10B9 could only be confirmed by POM.
The textures displayed by both compounds are very similar, of
the schlieren-type with low birefringence (see ESIw).
Compounds derived from acids A2 or A3, with a phasmidic-
like molecular shape, are not liquid crystalline. The increase in
the number of terminal aliphatic chains prevents calamitic
behaviour but their presence is not enough to favor a columnar
arrangement in the mesophase.
In order to enhance molecular p-stacking by nanosegregation,
we synthesized new compounds bearing bulky carboxylate
groups, B. These dendritic moieties, firstly described by Percec,
have been reported to show great self-organization potential.21
Compounds derived from the acid B3 do not exhibit liquid
crystalline behaviour.
Structural characterization of the mesophases
All of the mesomorphic compounds were studied by X-ray
diffraction with the aim of confirming the type of mesophase
and determining the lattice parameters. Most of the experi-
ments were performed at room temperature; however, in some
cases high-temperature experiments were also carried out. The
proposed indexing, lattice constants, and the observed and
calculated maximum diffraction distances of the columnar
mesophases are summarized in Tables 3 and 4. Table 3 collects
the data of the acid precursors B6 and B6*. For B6, only a
diffraction maximum is observed at low angles (see ESIw), which
could not be enough to unambiguously confirm the hexagonal
arrangement. However, the same result has been previously
Compounds with terminal groups derived from acids B6,
B6* and B9 self-organize into columnar mesophases. B6 and
B6* derivatives show enantiotropic mesophases whereas B9
derivatives show monotropic mesomorphism.
From data gathered in Table 2, it can be deduced that
an optimum size-ratio between the bis-dendronized rigid
p-conjugated core and the aliphatic regions (p-stacking and
flexibility, respectively) exists, and this ensures stable mesomorphic
properties. This is the case for compounds C3B6, C10B6 and
C3B6*. Compounds derived from acid B6 show Colh behaviour at
room temperature. In addition, both derivatives, C3B6 (see ESIw)
and C10B6, show a mesophase below 8 1C that could not be
identified. Upon investigation by POM, compound C10B6 showed
a mosaic-like texture (Fig. 1) on cooling from the isotropic liquid
and this remained during the cooling and heating processes, with
color changes corresponding to transitions in the DSC thermo-
grams (see Fig. 1 and ESIw). This compound shows a Colh
mesophase that appears twice during the heating cycle. Indeed,
the enantiotropic Colh mesophase, with a small temperature
interval in the heating process, can be supercooled below room
temperature. Nevertheless, the mesophase is thermodynamically
metastable at room temperature since it crystallizes on heating at
40.3 1C (cold crystallization). DSC thermograms between different
temperature limits showed that this behavior repeats at different
scan temperature limits and the cold crystallization is only avoided
when cooling around 70 1C and further heating.
Table 3 X-Ray diffraction data for the columnar mesophases of acids
B6 and B6*
Compound T/1C Phase Lattice constant/A dobs/A dcalc/A hk
B6
90
24
Colh a = 40.3
Colh a = 35.9
34.9
34.9
10
4.5 (br)
30.5
18.1
B6*
31.1
18.0
15.6
10
11
20
16.0
4.6 (br)
br = broad.
Table 4 X-Ray diffraction data for the columnar mesophases of
compounds C3B6, C10B6, C3B9 and C3B6*
Compound T/1C Phase Lattice constant/A
dobs/A dcalc/A hk
C3B6
24
Colh a = 54.1
47.1
26.9
46.9
27.0
10
11
Compound C3B6* shows Colh mesomorphism and this is
stable at room temperature for long periods of time as con-
firmed by the thermograms recorded after several months.
4.4 (br)
45.4
26.0
79
Colh a = 52.9
45.8
26.4
22.9
17.3
10
11
20
21
23.0
17.9
4.5 (br)
45.5
26.2
C10B6
24
Colh a = 52.3
Colh a = 52.0
45.3
26.1
22.6
10
11
20
22.4
4.4 (br)
45.6
26.0
22.0
4.5 (br)
29.3
4.4 (br)
3.9
41.6
24.0
20.3
96a
45.0
26.0
22.5
10
11
20
C3B9
24
24
Colh a = 33.9
Colh a = 47.7
29.3
10
C3B6*
41.3
23.9
20.7
10
11
20
Fig. 1 Microphotographs (ꢁ20) of the textures observed for compound
C10B6 at different temperatures, which correspond to different tempera-
ture ranges in the DSC thermogram (also shown). All of the photographs
correspond to the same area of the sample.
4.6 (br)
a
X-Ray diffractogram taken at 96 1C in the heating process and
before reaching the isotropic liquid state.
c
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Fig. 2 (a) SAXS diagram corresponding to compound C3B6, taken
at 79 1C. (b) WAXS diagram taken at room temperature (24 1C) for
compound C10B6.
reported for other hexagonal columnar mesophases.11g,17c,22
Moreover, the coherence of the lattice constants calculated for
both compounds, given the different size of the alkoxylic tails,
makes it reasonable to propose Colh behavior for B6. Table 4
contains data for the final columnar materials, except C10B9 for
which it was not possible to perform X-ray diffraction experiments
because of its crystallization tendency after long experiment times.
The X-ray patterns for C3B6 and C10B6 are undoubtedly
characteristic of a Colh mesophase, both at RT and at high
temperature. This was revealed by the presence of different sets
of sharp low-angle maxima with a reciprocal spacing ratio
1 : O3 : O4 : O7, which can be assigned to the respective (10),
(11), (20) and (21) reflections of a two-dimensional hexagonal
lattice (Fig. 2 and ESIw). From the corresponding maxima,
respective lattice parameters of 54.1 A and 52.3 A at room
temperature were determined for both compounds. An outer
broad halo was also observed corresponding to distances of
approximately 4.4 A, which was assigned to short-range
correlation distances between aliphatic chains along the
column. The variation of the a parameter with temperature
was as expected, i.e. lower values were determined as the
temperature increased since this change favours conforma-
tional freedom—especially for aliphatic chains. This result
also supports that the Colh mesophase of C10B6 is structurally
the same at room temperature and upon crystallization and
subsequent melting at 92.1 1C (see the ESIw).
Fig. 3 Proposed models for the disposition of (a) two molecules per
slice of the column in the columnar mesomorphic arrangement of
compound C3B6, and (b) half a molecule per slice of the column in the
columnar mesomorphic arrangement of compound C3B9. The size
measured by stereomodels for the molecule is represented in (b). The
length of the aliphatic part has been estimated considering an all-trans
conformation for the chains.
columns interconnected two by two by the central core of some
of the molecules. The lattice parameter is much smaller than the
parameters of the Colh mesophase found for compounds
derived from acid B6, and this finding supports both models,
the one proposed for C3B6 and C10B6 with Z = 2 and the one
proposed for C3B9 with Z = 0.5 (Fig. 3).
Room temperature X-ray studies (Table 4) and density
calculations confirmed that the behaviour of chiral compound
C3B6* is similar to that of its achiral analogues C3B6 and
C10B6 and involves stacking of disk-like units formed by two
molecules. The shorter hexagonal lattice constant a measured
for C3B6* compared to C3B6 is consistent with the smaller
length and mass of the branched chain.
If a density r close to 1 g cmꢀ3 is supposed for these
compounds, and estimating a periodic stacking of the mole-
cular cores within a column of 4.4 A, it is possible to deduce
that there are two molecules per unit cell (Z = 2). In a
hexagonal lattice there is one column per unit cell and this
can be interpreted as two molecules forming each slice of the
column (Fig. 3). The formation of columns consisting of two
or more molecules per slice has already been described for
other phasmidic-like mesogens.14a-b,23
This is in contrast to what we found for compound C3B9.15
The X-ray pattern for this compound contains only a single
low-angle maximum and two wide-angle reflections. This
pattern, together with POM observations, make us conclude
that the compound self-organizes into a Colh mesophase with
a lattice parameter of 33.9 A and a mean stacking distance of
the cores along the column of 3.9 A. These values allowed
determining that there is half a molecule per unit cell (Z = 0.5),
which corresponds to half a molecule per columnar stratum.
Thus, the hexagonal two-dimensional network consists of
In summary, compounds derived from acids A show meso-
morphic behaviour only for A1 derivatives. Thus, C3A1 and
C10A1, which have a rod-like geometry, show a calamitic
nematic mesophase. The lateral chain (propyl for the C3
derivative or decyl for the C10 derivative) affects intermolecular
interactions. Accordingly, decrease of melting temperature and
significant destabilization of the nematic mesophase occur on
increasing the length of the lateral chain.
As for compounds derived from acids B, more than six
terminal chains in the acid are required to promote meso-
morphism. Compounds bearing twelve chains (C3B6, C10B6
and C3B6*) show stable Colh mesomorphic behavior in which
two molecules form the cross section of the column. Compounds
bearing 18 chains (C3B9 and C10B9) also show Colh liquid
crystalline properties, but in this case the cross section of the
column contains only half a molecule. In an effort to explain
these observations, we propose that B6 is more planar than acid
B9 and that p-stacking interactions are favored for the derivatives
of the former system. In contrast, it may not be possible for all
c
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of the chains in B9 derivatives to be located within the same plane
and stacking of molecules is therefore blocked (indeed, acid B9
shows cubic mesomorphism interpreted by a conical shape).18b In
this situation, the bulky moiety derived from acid B9 can be better
accommodated within the bay formed between two columns that
are covalently linked by the conjugated core, thus favoring
efficient filling of the space to stabilize the mesophase.
Table 5 Quantum yields calculated for all compounds in tetrahydro-
furan and cyclohexane
THF
Cy
THF
Cy
a
a
C3
0.57
0.43
0.40
0.16
0.12
0.12
0.11
0.12
C10
0.65
0.46
0.45
0.17
0.13
0.13
0.11
C3A1
C3A2
C3A3
C3B3
C3B6
C3B9
C3B6*
0.60
0.68
0.52
0.35
0.40
0.32
0.33
C10A1
C10A2
C10A3
C10B3
C10B6
C10B9
0.72
0.68
0.61
0.35
0.38
0.32
Chirooptical properties
To test the possibility of inducing supramolecular chirality
into the columnar assembly of this type of compound,24 we
prepared compound C3B6* in which the acid moiety bears six
chiral tails derived from (S)-citronellol. The Colh mesophase
of this compound shows optical activity by circular dichroism
(Fig. 4), which suggests that the chirality of the polycatenar
phasmid-like molecules is transferred to the supramolecular
organization.25,26 The CD spectrum shown in Fig. 4 is the
average of the spectra recorded upon rotation (in-plane) of the
sample around the light beam every 601. All the spectra were
almost identical for all the orientations (see ESIw).27 The CD
spectrum shows a signal at the maximum of absorption of the
chromophore that disappears upon heating the thin film above
the clearing temperature of the mesophase. This situation is in
contrast to the Colh mesophase of the acid moiety, B6*, which
does not show circular dichroism signals despite the presence
of chiral molecules. This finding can be interpreted in terms of
the chiral supramolecular superstructure of C3B6* being deter-
mined not only by the presence of stereogenic centers but also
favoured by the p-stacking capability of the conjugated core C3
assisted by the tapered dendritic group, B6*.
a
Low solubility.
shoulder at around 360 nm. The emission properties of these
two compounds are similar, with two maxima observed—a
more intense one at 379 nm and a slightly weaker one at
397 nm. The corresponding quantum yields are included in
Table 5. Excitation of crystalline thin films of C3 and C10
at 336 nm gave rise to extremely weak and noisy photo-
luminescence signals in the spectrofluorimeter. In fact, neither
of these compounds is fluorescent to the naked eye when excited
at 365 nm. C3 and C10 are indeed weak emitters in the solid state,
probably due to emission quenching by ‘‘face-to-face’’ stacking,
as deduced from the crystal structure of C3.15
All final compounds, CA and CB, exhibit essentially the
same absorption and emission profiles in solution and these
are similar to those of the core C (Fig. 5). Upon excitation at
335 nm, all of the compounds show two maxima—a more
intense one at 375 nm and a slightly weaker one at 397 nm.
The fluorescence quantum yields of all the compounds were
estimated from emission spectra in cyclohexane and in THF
solutions, with 9,10-diphenylanthracene (Fem = 0.90 in
Luminescent properties
The luminescent properties of both series of compounds were
investigated by absorption and emission spectroscopy in
solution and, where applicable, in the mesophase.
Cores C3 and C10 were studied in THF solution (ESIw).
Their absorption spectra show a maximum at 336 nm with a
Fig. 4 Circular dichroism and absorption spectra of a thin film of
C3B6*. Circular dichroism spectra were recorded in the isotropic phase
at 90 1C and in the columnar mesophase at room temperature. The CD
spectrum is the average of the spectra recorded upon rotation of the
sample around the light beam every 601 in order to compensate for
linear dichroism effects.
Fig. 5 Absorption and emission spectra of all the mesogenic com-
pounds. Solution spectra correspond to cyclohexane solutions. For
compound C3B6* absorption and emission spectra corresponding to
cyclohexane and THF solutions are presented to confirm that there is
no difference in spectral profiles depending on the solvent.
c
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cyclohexane) used as a standard.28 The polarity of the solvent
did not influence the absorption/emission spectrum profiles,
but the fluorescence quantum yields were strongly dependent
on the polarity of the solvent and also on the molecular
structure (Table 5). Non-radiative processes, such as confor-
mational changes or energy transfer, are less likely to occur in
the apolar solvent (cyclohexane) than in the polar solvent
(THF) and this results in higher quantum yields.29 With
respect to the influence of molecular structure, it is interesting
to note that quantum yields are higher for compounds derived
from acids A (F = 0.7–0.5) than for compounds derived from
acids B (F = 0.4–0.3). Small acids A gave rise to compounds
with luminescent properties in cyclohexane that are similar to
those of the conjugated cores, C3 and C10. An overall decrease
of quantum yields is observed on increasing the number of
alkyloxy tails in the acid moiety. Electron-rich alkyloxy groups
can act as fluorescence quenchers, probably through photo-
induced electron-transfer processes.11f,30 Bulky acids B gave
rise to derivatives with lower quantum yields with respect to
compounds derived from acids A. The reason may lie in the
size of the carboxylate moiety, which makes the conjugated
core C more predisposed to undergo distortions or conforma-
tional changes.31
than in C3B9. Nevertheless, the most significant red shift within
this series was observed for compound C3B6*, which shows an
emission maximum at 422 nm. The optical activity found in the
mesophase of C3B6* is consistent with a helical arrangement of
the mesogens, which could likely be responsible for a higher level
of organization of the p-conjugated cores and hence for its
largest red-shifted emission.33
Electroactive properties
In view of the potential applications in optoelectronics of
molecules like those described above, it is important to con-
sider the relative facility to inject holes and electrons, respec-
tively, into the material. This can be approximated from the
molecular electrochemical properties, which were investigated
for C3B6 and C3B9 by cyclic voltammetry (CV) in oxygen-free
THF solutions. The voltammograms registered for C3B6 and
C3B9 are presented in Fig. 6. Only one irreversible process can
be observed in the oxidation region and a reduction process
appears at negative potentials for both compounds. This
reduction process was not visible when the scan was carried
out following the sequence 0 V - ꢀ2 V- 2 V- 0 V (see ESIw).
Likely, the oxidized species of such bulky molecules, with many
aliphatic tails surrounding the conjugated core, evolves and this
makes the redox processes difficult. This may be also the reason
for the poor-resolved recorded voltammograms.
All of the mesogenic compounds showed emission to the
naked eye in their mesomorphic state. The emission spectra of
calamitic compounds C3A1 and C10A1 were recorded at high
temperatures of 100 1C and 82 1C, respectively (Fig. 5). The
luminescence of compounds that show a columnar mesophase
at room temperature was studied under ambient conditions
(Fig. 5), except for compound C10B9, which crystallizes
quickly at room temperature and could not be studied in the
mesophase. In all cases, the absorption spectra in the meso-
phase (see Fig. 5 and ESIw) are essentially the same as those in
solution but emission spectra obtained from mesomorphic
thin films and from solution are quite different. Thin film
spectra show only a single broad peak and this is red-shifted
with respect to the solution emission maxima. Accordingly,
Stokes shifts for all of the compounds are around 75 nm in
the mesophase, i.e. higher than those obtained in solution
(by ca. 40 nm). This indicates lower energy of the emissive
aggregates in the liquid crystalline medium compared to the
monomer species in THF diluted solution, likely related to
significant structural relaxation processes of the excited state
in the former.30b,32
The HOMO and LUMO energy levels referred to the
vacuum level have been estimated by combining electro-
chemical and optical data, and values are summarized in
Table 6. The HOMO was determined from the oxidation potential
by the empirical relationship: HOMO = ꢀ(Eox
+ 4.4) eV
onset
where Eoxonset is the onset potential for the oxidation wave relative
to the Ag/AgCl reference electrode.34 HOMO values for C3B6 and
C3B9 were estimated as ꢀ5.7 and ꢀ5.8 eV, respectively. The
LUMO was deduced from the optical band gap using the
expression: LUMO = HOMO + DEg, and was found to be
ꢀ2.4 and ꢀ2.5 eV for C3B6 and C3B9, respectively.
Variations of the emission maximum wavelength among the
different compounds in the mesophase seem to be related
to their different mesomorphic arrangements. The emission
maxima of both nematic mesogens appear around 404 nm. As
far as columnar mesomorphic materials are concerned, it can
be observed that their corresponding emission maximum wave-
lengths are slightly higher than those of calamitic compounds:
i.e. C3B9 (407 nm), C10B6 (412 nm) and C3B6 (413 nm). The
model proposed for C3B9, in which p-conjugated cores are
randomly distributed between columns, could be a tentative
justification of the shorter emission lmax observed for this
compound with respect to mesogens derived from acid B6.
For C3B6 and C10B6, the whole molecule is included within
the same column, and this situation could limit conformational
freedom and favour interactions between fluorophores14a larger
Fig. 6 Voltammograms corresponding to (a) C3B6 and (b) C3B9
recorded at a scan rate of 100 mV sꢀ1
.
Table 6 Oxidation and reduction potentials estimated for the HOMO
and LUMO levels of C3B6 and C3B9 in THF solutions
Compound Eoxonset/V lonseta/nm DEgb/eV HOMOc/eV LUMOd/eV
C3B6
C3B9
1.31
1.39
374
375
3.3
3.3
ꢀ5.7
ꢀ5.8
ꢀ2.4
ꢀ2.5
a
lonset was determined as the wavelength at which the absorbance is
b
0.05. DEg is the optical bandgap determined from the absorption
spectra. HOMO energy was determined by cyclic voltammetry
c
according to the equation HOMO = ꢀ(Eox
+ 4.4) eV, assuming
the energy level of Ag/AgCl to be 4.4 eV below the vacuum level;
onset
d
LUMO energy was calculated as HOMO + DEg.
c
836 New J. Chem., 2012, 36, 830–842
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1
as a yellow solid (764 mg, 96%). H NMR (400 MHz, CDCl3,
25 1C, TMS): d (ppm) = 7.37 (d, J = 8.7 Hz, 4H), 6.84 (d, J =
8.7 Hz, 4H), 2.64–2.53 (m, 4H), 1.77–1.58 (m, 4H), 1.48–1.25
(m, 28H), 1.03 (s, 18H), 0.98–0.87 (m, 6H), 0.25 (s, 12 H).
13C NMR (CDCl3, 100 MHz, 25 1C): d (ppm) = 155.8 (C),
132.7 (CH), 129.0 (C), 120.1 (CH), 116.6 (C), 98.2 (C), 88.3 (C),
34.9 (CH2), 31.9 (CH2), 29.6 (CH2), 29.5 (CH2), 29.3 (CH2),
29.0 (CH2), 28.5 (CH2), 25.6 (CH3), 22.7 (CH2), 18.2 (C), 14.1
(CH3), ꢀ4.5 (CH3). HRMS (EI) for C36H52O2Si2 [M]+: 768.5691;
found: 768.5698.
Synthesis of (E)-1,6-bis(4-hydroxyphenyl)-3,4-didecyl-3-
hexen-1,5-diyne (C10). To a solution of 2 (538.5 mg, 0.7 mmol)
in THF (30 mL)/DMF (10 mL) at 25 1C was added 2 mL
of saturated KF water solution. After 1 hour, 20 mL of water
was added and the product was extracted with diethylether
(3 ꢁ 20 mL). The organic layer was dried over anhydrous
sodium sulfate and concentrated in vacuo. The crude product
was triturated with hexane to yield C10 as a yellow solid
(337 mg, 89%). Mp = 70–72 1C. 1H NMR (400 MHz, CDCl3,
25 1C, TMS): d (ppm) = 7.39 (d, J = 8.0 Hz, 4H), 6.85
(d, J = 8.4 Hz, 4H), 5.75 (br s, 2H), 2.62 (t, J = 7.2 Hz, 4H),
1.72–1.69 (m, 4H), 1.58–1.18 (m, 28H), 1.01–0.82 (m, 6H).
13C NMR (CDCl3, 100 MHz, 25 1C): d (ppm) = 155.3 (C),
132.9 (CH), 129.0 (C), 116.1 (C), 115.5 (CH), 98.1 (C), 88.2 (C),
34.9 (CH2), 31.8 (CH2), 29.6 (CH2), 29.4 (CH2), 29.3 (CH2),
29.0 (CH2), 28.4 (CH2), 22.6 (CH2), 14.0 (CH3). HRMS (EI) for
C24H24O2 [M]+: 540.3962; found: 540.3973.
Fig. 7 Photoconductivity of C3B6 (homeotropically aligned, 4.0 mm thick
sample; a = 80 cmꢀ1) and C3B9 (partially aligned, 7.5 mm thick sample;
a = 75 cmꢀ1) as a function of the applied electric field, at l = 532 nm.
Room temperature photoconductivity measurements for
compounds C3B6 and C3B9 were performed as a function of
wavelength and electric field on samples that were aligned as
homeotropic monodomains or, at least, partially aligned.
Photoconductivity shows the usual electric field dependence
(Fig. 7). As expected, the photoconductivity of both C3B6 and
C3B9 increases with absorption but even at l = 532 nm, where
absorption is quite small, a photoconduction signal can be
measured. It is not as easy as it may seem to benchmark such
values of photoconductivity against those of other columnar
mesophases. In fact, often only charge mobilities are reported
in the literature, even when transporters are photogenerated.
In addition, experimental results are reported only in terms
of photocurrents (often in arbitrary units) instead of photo-
conductivity and the absorption coefficient at the wavelength
used is seldom indicated. All this hinders a comparison among
different substances. However, it is possible to compare our
results with the photoconductivity of other organic sub-
stances. Our materials show a photoconductivity which is of
the same order of magnitude as the photoconductivity of the
amorphous polymers35 often used as photoconductors, but
much lower than in crystalline composite organic solids.36
Synthesis and characterization of the chiral acid, B6*. The
benzoic acid B6* was synthesized according to the general
procedure described for the synthesis of acid B6.18b (S)-3,7-
Dimethyloctyl bromide was prepared from (S)-8-bromo-2,6-
dimethyloct-2-ene by hydrogenation at high pressure using
PtO2 as catalyst.37
Ethyl 3,4-bis[(S)-3,7-dimethyloctyloxy]benzoate. This product
was purified by flash chromatography on silica gel, eluting with a
mixture hexane/dichloromethane (60/40). A colourless oil was
obtained with a yield of 90%. Rf: 0.45 (hexane/dichloromethane,
60/40). 1H-NMR (400 MHz, CDCl3): d (ppm) = 0.8–0.88
(m, 12H, (CH3)2CH), 0.94–0.96 (m, 6H, CH(CH3)CH2),
1.12–1.40 (m, 15H, CH(CH3)CH2CH2CH2CH + COOCH2CH3),
1.58–1.74 (m, 6H, CH2CH2OAr + CH(CH3)CH2 + (CH3)2CH),
1.84–1.92 (m, 2H, CH2CH2OAr), 4.00–4.11 (m, 4H, CH2CH2OAr),
4.35 (c, 2H, J = 7.1 Hz, COOCH2CH3), 6.86 (d, 1H, J = 6.4 Hz,
Ar-H), 7.54 (d, 1H, J = 2.0 Hz Ar-H), 7.64 (dd, 1H, J = 6.4 Hz,
J = 2.0 Hz, Ar-H). 13C-NMR (400 MHz, CDCl3): d (ppm) =
14.4, 19.7, 22.6, 22.7, 24.7, 28.0, 29.9, 36.0, 36.1, 37.3, 39.2, 60.7,
67.4, 67.6, 111.7, 114.0, 122.7, 123.4, 148.4, 153.0, 166.5. IR (nujol,
Experimental section
Synthesis
Synthesis of the core C10
Synthesis of (E)-1,6-bis[4-(tert-butyldimethylsilyloxy)phenyl]-
3,4-didecyl-3-hexen-1,5-diyne (2). To a solution of decylacetylene
(631.9 mg, 0.812 mL, 3.8 mmol) in THF (50 mL) at ꢀ78 1C
was added dropwise 2.26 mL of n-BuLi (1.6 M, 3.6 mmol). After
5 min, the carbene complex 1 (1.1 g, 2.0 mmol) was added and the
resulting mixture was stirred at ꢀ78 1C until disappearance of the
carbene complex (the solution turned from red to light yellow).
Then, TMSOTf (0.68 mL, 3.8 mmol) was added to one portion
and the mixture was stirred at ꢀ78 1C for 5 min. Finally, 56 mg
(0.5 mmol) of potassium tert-butoxide (KOtBu) were added and
the mixture was transferred to a cold bath at ꢀ201 allowing it to
warm up until colour change was observed. Removal of the
solvents under reduced pressure followed by column chromato-
graphy of the residue on silica gel (hexane, Rf = 0.25) yielded 3
NaCl): 1715, 1600, 1514, 1286, 1270, 1212, 1132, 1105 cmꢀ1
.
3,4-Bis[(S)-3,7-dimethyloctyloxy]benzyl alcohol. The colour-
less oil obtained upon reduction of the ethylester group was used
in the next reaction step without further purification. Rf: 0.76
(hexane/ethyl acetate, 70/30). 1H-NMR (400 MHz, CDCl3):
d (ppm) = 0.85–0.88 (m, 12H, (CH3)2CH), 0.93–0.95 (m, 6H,
CH(CH3)CH2), 1.12–1.38 (m, 12H, CH(CH3)CH2CH2CH2CH),
1.47–1.71 (m, 6H, CH2CH2OAr + CH(CH3)CH2 + (CH3)2CH),
1.82–1.91 (m, 2H, CH2CH2OAr), 3.98–4.06 (m, 4H, CH2CH2OAr),
c
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New J. Chem., 2012, 36, 830–842 837

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4.61 (s, 2H, ArCH2OH), 6.85–6.86 (m, 2H, Ar-H), 6.93 (s, 1H,
Ar-H). 13C-NMR (400 MHz, CDCl3): d (ppm) = 19.7, 22.6, 22.7,
24.7, 28.0, 29.9, 36.2, 36.3, 37.3, 39.2, 65.4, 67.5, 67.7, 112.8, 113.7,
119.5, 133.6, 148.7, 149.3. IR (nujol, NaCl): 3600–3300, 1606, 1590,
1169, 1138 cmꢀ1. MS (MALDI+, dithranol) m/z: 1400 [M +
Na]+. Elemental analysis: calculated for C88H144O11 (1378.08):
C, 76.70%; H, 10.53%; found: C, 76.88%; H, 10.48%.
1513, 1263, 1235, 1163, 1137 cmꢀ1
.
Synthesis and chemical information of final compounds CA
and CB. Coupling of acid derivatives A and B with either C3
or C10 to give the target compounds was carried out by
following the same procedure as described previously for
C3B9.15 The protons noted as H0 correspond to protons of
the lateral chain of the central cores C3 and C10, so that they
are distinguished from protons corresponding to the acid
moiety.
3,4-Bis[(S)-3,7-dimethyloctyloxy]benzyl chloride. The product
was used immediately in the next reaction step without further
purification.
1H-NMR (400 MHz, CDCl3): d (ppm) = 0.85–0.88
(m, 12H, (CH3)2CH), 0.93–0.95 (m, 6H, CH(CH3)CH2),
1.10–1.38 (m, 12H, CH(CH3)CH2CH2CH2CH), 1.47–1.72
(m, 6H, CH2CH2OAr
+ CH(CH3)CH2 + (CH3)2CH),
(E)-1,6-Bis[40-(400-n-dodecyloxybenzoyloxy)phenyl]-3,4-
dipropyl-3-hexen-1,5-diyne, C3A1. C3A1 was purified by chromato-
graphy on silica gel, eluting with a dichloromethane/hexane
(50/50) mixture, and a white solid was obtained (73%). Rf: 0.51
1.82–1.91 (m, 2H, CH2CH2OAr), 3.98–4.06 (m, 4H,
CH2CH2OAr), 4.55 (s, 2H, ArCH2Cl), 6.26 (d, 1H, J =
8.0 Hz, Ar-H), 6.88–6.92 (m, 2H, Ar-H). 13C-NMR (400 MHz,
CDCl3): d (ppm) = 19.7, 22.6, 22.7, 24.7, 28.0, 29.9, 36.2, 37.3,
39.3, 65.4, 67.5, 67.7, 112.9, 113.7, 119.5, 133.6, 148.7, 149.4. IR
1
(dichloromethane/hexane, 60/40). H-NMR (400 MHz, CDCl3):
(nujol, NaCl): 1606, 1590, 1515, 1264, 1236, 1169, 1136 cmꢀ1
.
d (ppm) = 0.89 (t, 6H, J = 6.8 Hz, CH3), 1.02 (t, 6H, J = 7.4 Hz,
CH3 ), 1.25–1.40 (m, 32H, (CH2)8), 1.44–1.51 (m, 4H,
0
Methyl 3,4,5-tris[30,40-bis((S)-3,7-dimethyloctyloxy)benzyloxy]-
benzoate. This product was purified by flash chromatography
on silica gel, eluting with a mixture dichloromethane/hexane
(80/20). A colourless oil was obtained with a 37% yield. Rf: 0.66
(hexane/ethyl acetate, 85/15). 1H-NMR (400 MHz, CDCl3)
d (ppm) = 0.84–0.95 (m, 54H, CH3), 1.08–1.38 (m, 36H,
CH(CH3)CH2CH2CH2CH), 1.44–1.74 (m, 18H, CH2CH2OAr +
CH2CH(CH3) + (CH3)2CH), 1.79–1.91 (m, 6H, CH2CH2OAr),
3.78–3.84 (m, 2H, CH2CH2OAr), 3.87 (s, 3H, COOCH3),
3.92–4.04 (m, 10H, CH2CH2OAr), 5.03–5.04 (m, 6H, ArCH2OAr),
6.72 (d, 1H, J = 8.2 Hz, Ar-H), 6.83–6.86 (m, 3H, Ar-H), 6.93
(dd, 2H, J = 8.2 Hz, J = 1.8 Hz, Ar-H), 6.96 (d, 1H, J = 1.8 Hz,
Ar-H), 6.99 (d, 2H, J = 1.8 Hz), 7.36 (s, 2 H, Ar-H). 13C-NMR
(400 MHz, CDCl3) d (ppm) = 19.5–19.7, 22.6–22.7, 24.7, 28.0,
29.7–30.0, 36.3, 37.4, 39.3, 52.2, 67.2, 67.5–67.6, 71.4, 74.9, 109.9,
113.2, 113.3, 113.5, 114.0, 120.2, 121.1, 125.0, 129.2, 130.0, 142.5,
148.9–149.0, 149.2, 152.6, 166.6. IR (nujol, NaCl): 1718, 1590,
1516, 1265, 1230, 1169, 1138 cmꢀ1. MS (MALDI+, dithranol)
m/z: 1414 [M + Na]+. Elemental analysis calculated for
C89H146O11 (1392.10): C, 76.79%; H, 10.57%; found: C,
76.94%; H, 10.42%.
0
0
OCH2CH2CH2), 1.66–1.75 (m, 4H, CH2 CH3 ), 1.79–1.86
0
(m, 4H, OCH2CH2), 2.58 (t, 4H, J = 7.4 Hz, CQCCH2 ), 4.05
(t, 4H, J = 6.6 Hz, OCH2), 6.97 (d, 4H, J = 8.9 Hz, Ar-H), 7.19
(d, 4H, J = 8.7 Hz, Ar-H), 7.50 (d, 4H, J = 8.7 Hz, Ar-H), 8.13
(d, 4H, J = 8.9 Hz, Ar-H). 13C-NMR (400 MHz, CDCl3):
d (ppm) = 13.7, 14.1, 21.9, 22.7, 26.0, 29.1–29.7, 31.9, 37.1,
68.3, 89.3, 97.8, 114.3, 121.1, 121.2, 121.9, 129.6, 132.3, 132.5,
150.8, 163.6, 164.5. IR (KBr): 1730, 1606, 1510, 1504, 1467,
1254, 1203, 1163, 1067 cmꢀ1. MS (MALDI+, dithranol) m/z:
922 [M + H]+. Elemental analysis calculated for C62H80O6
(921.30): C, 80.83%; H, 8.75%; found: C, 80.41%; H, 8.83%.
(E)-1,6-Bis[40-(400-n-dodecyloxybenzoyloxy)phenyl]-3,4-
didecyl-3-hexen-1,5-diyne, C10A1. C10A1 was purified by chromato-
graphy on silica gel, eluting with a dichloromethane/hexane
(40/60) mixture, and a white solid was obtained (65%). Rf: 0.78
1
(dichloromethane/hexane, 60/40). H-NMR (400 MHz, CDCl3):
0
d (ppm) = 0.85–0.90 (m, 12H, CH3 + CH3 ), 1.20–1.51
0
0
0
(m, 64H, (CH2)9 + (CH2 )7), 1.63–1.70 (m, 4H, CQCH2 CH2 ),
1.79–1.86 (m, 4H, OCH2CH2), 2.58 (t, 4H, J = 7.4 Hz,
0
CQCCH2 ), 4.05 (t, 4H, J = 6.6 Hz, OCH2), 6.97 (d, 4H,
J = 8.9 Hz, Ar-H), 7.19 (d, 4H, J = 8.7 Hz, Ar-H), 7.50
(d, 4H, J = 8.7 Hz, Ar-H), 8.13 (d, 4H, J = 8.9 Hz, Ar-H).
13C-NMR (400 MHz, CDCl3): d (ppm) = 14.1, 22.7, 26.0, 28.5,
29.1–29.7, 31.9, 35.0, 68.3, 89.3, 97.8, 114.3, 121.1, 121.2, 121.9,
129.7, 132.3, 132.5, 150.8, 163.6, 164.6. IR (KBr): 1742, 1606,
1509, 1502, 1466, 1257, 1206, 1162, 1074 cmꢀ1. MS (MALDI+,
dithranol) m/z: 1118 [M + H]+. Elemental analysis calculated
for C76H108O6 (1117.67): C, 81.67%; H, 9.74%; found: C,
81.43%; H, 9.59%.
3,4,5-Tris[30,40-bis((S)-3,7-dimethyloctyloxy)benzyloxy]benzoic
acid, B6*. B6* was purified by flash chromatography on silica
gel, eluting with a mixture dichloromethane/hexane/ethyl
acetate (40/60/2). A transparent wax was obtained with a yield
of 50%. Rf: 0.15 (hexane/ethyl acetate, 80/20). 1H-NMR
(400 MHz, CDCl3): d (ppm) = 0.84–0.95 (m, 54H, CH3),
1.08–1.38 (m, 36H, CH(CH3)CH2CH2CH2CH), 1.44–1.74
(m, 18H, CH2CH2OAr + CH(CH3)CH2 + (CH3)2CH), 1.79–1.91
(m, 6H, CH2CH2OAr), 3.78–3.85 (m, 2H, CH2CH2OAr),
3.94–4.05 (m, 10H, CH2CH2OAr), 5.06 (s, 6H, ArCH2OAr),
6.73 (d, 1H, J = 8.2 Hz, Ar-H), 6.84–6.87 (m, 3H, Ar-H),
6.94 (dd, 2H, J = 8.2, J = 1.8 Hz, Ar-H), 6.97 (d, 1H, J = 1.8
Hz, Ar-H), 7.00 (d, 2H, J = 1.8 Hz, Ar-H), 7.43 (s, 2H, Ar-H).
(E)-1,6-Bis[40-(30 0,40 0-di-n-dodecyloxybenzoyloxy)phenyl]-3,4-
dipropyl-3-hexen-1,5-diyne, C3A2. C3A2 was purified by chromato-
graphy on silica gel, eluting with a dichloromethane/hexane
(50/50) mixture, and a white solid was obtained (68%). Rf: 0.69
1
13C-NMR (400 MHz, CDCl3):
d
(ppm)
=
19.5–19.7,
(dichloromethane/hexane, 60/40). H-NMR (400 MHz, CDCl3):
0
22.6–22.7, 24.7, 28.0, 29.8–29.9, 36.3, 37.4, 39.2, 67.2,
67.5–67.6, 71.4, 74.9, 109.9, 113.1, 113.2, 113.4, 113.9, 120.2,
121.1, 123.8, 129.1, 129.9, 143.1, 148.9–149.0, 149.2, 152.6,
170.1. IR (nujol, NaCl): 1716, 1689, 1590, 1516, 1265, 1230,
d (ppm) = 0.86–0.90 (t, 12H, CH3), 1.02 (t, 6H, J = 7.4 Hz, CH3 ),
1.22–1.42 (m, 64H, (CH2)8), 1.44–1.53 (m, 8H, OCH2CH2CH2),
0
0
1.67–1.76 (m, 4H, CH2 CH3 ), 1.81–1.90 (m, 8H, OCH2CH2),
0
2.58 (t, 4H, J = 7.4 Hz, CQCCH2 ), 4.05–4.10 (m, 8H, OCH2),
c
838 New J. Chem., 2012, 36, 830–842
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6.93 (d, 2H, J = 8.5 Hz, Ar-H), 7.19 (d, 4H, J = 8.7 Hz, Ar-H),
7.50 (d, 4H, J = 8.7 Hz, Ar-H), 7.65 (d, 2H, J = 2.0 Hz, Ar-H),
7.81 (dd, 2H, 3J = 8.5 Hz, 4J = 2.0 Hz, Ar-H). 13C-NMR
(400 MHz, CDCl3): d (ppm) = 13.7, 14.1, 21.9, 22.7, 26.0,
29.1–29.7, 31.9, 37.1, 69.1, 69.4, 89.3, 97.8, 112.0, 114.6, 121.2,
121.3, 122.0, 124.4, 129.6, 132.5, 148.7, 150.9, 153.9, 164.8. IR
(KBr): 1730, 1597, 1519, 1505, 1467 , 1294, 1273, 1254, 1198, 1163,
1143 cmꢀ1. MS (MALDI+, dithranol) m/z: 1312 [M + Na]+.
Elemental analysis calculated for C86H128O8 (1289.93): C, 80.08%;
H, 10.00%; found: C, 79.71%; H, 9.96%.
26.0, 26.1, 28.5, 29.1–29.7, 30.3, 31.9, 32.0, 35.0, 69.2, 73.6, 89.4,
97.8, 108.5, 121.3, 121.9, 123.6, 129.70, 132.5, 143.1, 150.8, 153.0,
164.8. IR (KBr): 1735, 1587, 1505, 1468 , 1231, 1198, 1164, 1130,
1121 cmꢀ1. MS (MALDI+, dithranol) m/z: 1855 [M + H]+.
Elemental analysis calculated for C124H204O10 (1854.94): C,
80.29%; H, 11.08%; found: C, 80.12%; H, 10.79%.
(E)-1,6-Bis{40-[30 0,40 0,50 0-tris(400 0-n-dodecyloxybenzyloxy)
benzoyloxy]phenyl}-3,4-dipropyl-3-hexen-1,5-diyne, C3B3. C3B3
was purified by chromatography on silica gel, eluting with a
dichloromethane/hexane/ether (70/30/1) mixture, and a white
solid was obtained (55–60%). Rf: 0.40 (dichloromethane/hexane,
(E)-1,6-Bis[40-(30 0,40 0-di-n-dodecyloxybenzoyloxy)phenyl]-
3,4-didecyl-3-hexen-1,5-diyne, C10A2. C10A2 was purified by
chromatography on silica gel, eluting with a dichloromethane/
hexane (40/60) mixture, and a white solid was obtained (71%).
1
80/20). H-NMR (400 MHz, CDCl3): d (ppm) = 0.88 (t, 18H,
J = 6.8 Hz, CH3), 1.03 (t, 6H, J = 7.4 Hz, CH3 ), 1.25–1.50
0
0
0
(m, 108H, (CH2)9), 1.69–1.83 (m, 16H, OCH2CH2 + CH2 CH3 ),
0
1
Rf: 0.57 (dichloromethane/hexane, 50/50). H-NMR (400 MHz,
0
2.59 (t, 4H, J = 7.4 Hz, CQCCH2 ), 3.91–3.98 (m, 12H, OCH2),
CDCl3): d (ppm) = 0.85–0.90 (t, 18H, CH3 + CH3 ), 1.22–1.52
5.06 (s, 4H, OCH2Ar), 5.08 (s, 8H, OCH2Ar), 6.77 (d, 4H,
J = 8.7 Hz, Ar-H), 6.90 (d, 8H, J = 8.7 Hz, Ar-H), 7.18
(d, 4H, J = 8.7 Hz, Ar-H), 7.27 (d, 4H, J = 8.6 Hz, Ar-H), 7.35
(d, 8H, J = 8.7 Hz, Ar-H), 7.50–7.52 (m, 8H, Ar-H). 13C-NMR
(400 MHz, CDCl3): d (ppm) = 13.7, 14.1, 21.9, 22.7, 26.1,
29.3–29.7, 31.9, 37.1, 68.0, 68.1, 71.2, 74.7, 89.4, 97.8, 109.8,
114.1, 114.5, 121.3, 121.9, 123.9, 128.4, 129.3, 129.7, 130.3, 132.5,
143.2, 150.7, 152.7, 159.0, 159.1, 164.5. IR (KBr): 1739, 1615,
1585, 1515, 1504, 1250, 1189, 1174, 1127 cmꢀ1. MS (MALDI+,
dithranol) m/z: 2317 [M + Na]+. Elemental analysis calculated
for C152H212O16 (2295.30): C, 79.54%; H, 9.31%; found: C,
79.48%; H, 9.49%.
0
0
0
(m, 100H, (CH2)9 + (CH2 )7), 1.63–1.70 (m, 4H, CH2 CH3 ),
1.81–1.90 (m, 8H, OCH2CH2), 2.58 (t, 4H, J = 7.4 Hz,
0
CQCCH2 ), 4.05–4.10 (m, 8H, OCH2), 6.93 (d, 2H, J =
8.5 Hz, Ar-H), 7.19 (d, 4H, J = 8.7 Hz, Ar-H), 7.50 (d, 4H,
J = 8.7 Hz, Ar-H), 7.65 (d, 2H, J = 2.0 Hz, Ar-H), 7.82 (dd, 2H,
3J = 8.5 Hz, 4J = 2.0 Hz, Ar-H). 13C-NMR (400 MHz, CDCl3):
d (ppm) = 14.1, 22.7, 26.0, 28.5, 29.0–29.7, 31.9, 35.0, 69.1, 69.4,
89.3, 97.8, 111.9, 114.6, 121.2, 121.3, 121.9, 124.4, 129.7, 132.5,
148.7, 150.9, 153.9, 164.8. IR (KBr): 1729, 1598, 1517, 1505,
1467, 1292, 1274, 1252, 1200, 1164, 1143 cmꢀ1. MS (MALDI+,
dithranol) m/z: 1508 [M + Na]+. Elemental analysis calculated
for C100H156O8 (1486.30): C, 80.81%; H, 10.58%; found: C,
80.79%; H, 10.63%.
(E)-1,6-Bis{40-[30 0,40 0,500-tris(40 00-n-dodecyloxybenzyloxy)
benzoyloxy]phenyl}-3,4-didecyl-3-hexen-1,5-diyne,
C10B3.
(E)-1,6-Bis[40-(300,400,500-tri-n-dodecyloxybenzoyloxy)phenyl]-
3,4-dipropyl-3-hexen-1,5-diyne, C3A3. C3A3 was purified by
chromatography on silica gel, eluting with a dichloromethane/
hexane (50/50) mixture, and a white solid was obtained (64%). Rf:
0.59 (dichloromethane/hexane, 60/40). 1H-NMR (400 MHz,
CDCl3): d (ppm) = 0.88 (t, 18H, J = 6.6, CH3), 1.02 (t, 6H,
C10B3 was purified by chromatography on silica gel, eluting
with a dichloromethane/hexane/ether (60/40/1) mixture, then
the solid was washed with acetone to yield C10B3 as a white
solid (54%). Rf: 0.39 (dichloromethane/hexane, 70/30). 1H-
NMR (400 MHz, CDCl3): d (ppm) = 0.86–0.90 (m, 24H,
0
0
CH3 + CH3 ), 1.25–1.50 (m, 136H, (CH2)9 + (CH2 )7),
0
0
0
J = 7.4, CH3 ), 1.25–1.52 (m, H, (CH2)9), 1.67–1.88 (m, 16H,
0
1.64–1.72 (m, 4H, CH2 CH3 ), 1.74–1.83 (m, 12H, OCH2CH2),
0
0
OCH2CH2 + CQCH2 CH2 ), 2.59 (t, 4H, J = 7.4 Hz, C =
2.60 (t, 4H, J = 7.4 Hz, CQCCH2 ), 3.91–3.98 (m, 12H,
0
CCH2 ), 4.01–4.08 (m, 12H, OCH2), 7.18 (d, 4H, J = 8.7 Hz,
OCH2), 5.06 (s, 4H, OCH2Ar), 5.08 (s, 8H, OCH2Ar), 6.77
(d, 4H, J = 8.6 Hz, Ar-H), 6.90 (d, 8H, J = 8.6 Hz, Ar-H),
7.18 (d, 4H, J = 8.6 Hz, Ar-H), 7.27 (d, 4H, J = 8.6 Hz,
Ar-H), 7.35 (d, 8H, J = 8.6 Hz, Ar-H), 7.50–7.52 (m, 8H,
Ar-H). 13C-NMR (400 MHz, CDCl3): d (ppm) = 14.1, 22.7,
26.1, 28.5, 29.1–29.7, 31.9, 35.0, 68.0, 68.1, 71.2, 74.7, 89.4, 97.8,
109.8, 114.1, 114.5, 121.4, 121.9, 123.9, 128.4, 129.3, 129.7,
130.3, 132.5, 143.2, 150.7, 152.7, 159.0, 159.1, 164.5. IR (KBr):
1734, 1615, 1587, 1516, 1504, 1248, 1190, 1173, 1120 cmꢀ1. MS
(MALDI+, dithranol) m/z: 2513 [M + Na]+. Elemental
analysis calculated for C166H240O16 (2491.67): C, 80.02%; H,
9.71%; found: C, 79.82%; H, 9.63%.
Ar-H), 7.40 (s, 4H, Ar-H), 7.51 (d, 4H, J = 8.7 Hz, Ar-H).
13C-NMR (400 MHz, CDCl3): d (ppm) = 13.7, 14.1, 21.9, 22.7,
26.1, 29.3–29.7, 30.3, 31.9, 37.1, 69.2, 73.6, 89.3, 97.8, 108.5, 121.3,
121.9, 123.6, 129.6, 132.5, 143.0,150.8, 152.9, 164.8. IR (KBr):
1738, 1588, 1505, 1467, 1230, 1195, 1162, 1133, 1125 cmꢀ1. MS
(MALDI+, dithranol) m/z: 1658 [M + H]+. Elemental analysis
calculated for C110H176O10 (1658.57): C, 79.66%; H, 10.70%;
found: C, 79.59%; H, 10.69%.
(E)-1,6-Bis[40-(300,400,500-tri-n-dodecyloxybenzoyloxy)phenyl]-
3,4-didecyl-3-hexen-1,5-diyne, C10A3. C10A3 was purified by
chromatography on silica gel, eluting with a dichloromethane/
hexane (40/60) mixture, and a white solid was obtained (59%).
(E)-1,6-Bis{40-[30 0,400,50 0-tris(30 00,40 0 0-di-n-dodecyloxybenzyl-
oxy)benzoyloxy]phenyl}-3,4-dipropyl-3-hexen-1,5-diyne, C3B6.
C3B6 was purified by flash chromatography on silica gel, eluting
with a dichloromethane/hexane/ether (60/40/1) mixture. Then the
solid was washed with acetone to yield the product as a white solid
1
Rf: 0.60 (dichloromethane/hexane, 50/50). H-NMR0 (400 MHz,
CDCl3): d (ppm) = 0.85–0.90 (m, 24H, CH3 + CH3 ), 1.23–1.52
0
0
(m, 136H, (CH2)9 + (CH2)7), 1.63–1.70 (m, 4H, CQCH2 CH2 ),
1.73–1.87 (m, 12H, OCH2CH2), 2.59 (t, 4H, J = 7.4 Hz,
1
0
CQCCH2 ), 4.03–4.08 (m, 12H, OCH2), 7.17 (d, 4H, J =
(37–41%). Rf: 0.41 (dichloromethane/hexane, 70/30). H-NMR
8.7 Hz, Ar-H), 7.40 (s, 4H, Ar-H), 7.50 (d, 4H, J = 8.7 Hz,
Ar-H). 13C-NMR (400 MHz, CDCl3): d (ppm) = 14.1, 22.7,
(400 MHz, CDCl3): d (ppm) = 0.86–0.89 (m, 36H, CH3), 1.03
(t, 6H, J = 7.4 Hz, CH3 ), 1.21–1.50 (m, 216H, CH3(CH2)9),
0
c
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0
0
1.70–1.85 (m, 28H, CH2CH2OAr + C = CCH2 CH2 ), 2.59
0
37.0, 37.4–37.5, 39.3, 67.2, 67.5, 67.6, 71.5, 75.0, 89.4, 97.8,
110.0, 113.2, 113.3, 113.5, 114.0, 120.3, 121.2, 121.4, 121.9,
124.0, 129.1, 129.7, 129.9, 132.5, 143.2, 149.0, 149.2, 150.7,
152.8, 164.5. IR (KBr): 1736, 1591, 1516, 1286, 1232, 1187,
1164, 1139 cmꢀ1. MS (MALDI+, dithranol) m/z: 3086 [M +
Na]+. Elemental analysis calculated for C200H308O22
(3064.57): C, 78.49%; H, 10.12%; found: C, 78.38%; H,
10.13%.
(t, 4H, J = 7.4 Hz, CQCCH2 ), 3.77 (t, 4H, J = 6.5 Hz,
CH2OAr), 3.91–4.00 (m, 20H, CH2OAr), 5.07–5.08 (m, 12H,
ArCH2OAr), 6.74 (d, 2H, J = 8.2 Hz, 6.84–6.86 (m, 6H,
3
5
Ar-H), 6.94 (dd, 4H, J = 8.2 Hz, J = 1.8 Hz, Ar-H), 6.97
(d, 2H, J = 1.8 Hz, Ar-H), 7.00 (d, 2H, J = 1.8 Hz, Ar-H), 7.17
(d, 4H, J = 8.7 Hz, Ar-H), 7.50–7.52 (m, 8H, Ar-H). 13C-NMR
(400 MHz, CDCl3) = 13.7, 14.1, 21.9, 22.7, 26.1–29.8, 31.9, 37.1,
69.0, 69.2, 69.3, 71.5, 89.4, 97.8, 110.0, 113.3, 113.4, 113.6, 114.1,
120.3, 121.1, 121.4, 121.9, 124.0, 129.1, 129.7, 130.0, 132.5, 143.2,
149.0, 149.1, 149.3, 150.7, 152.8, 164.5. IR (KBr): 1736 , 1593,
1519, 1505, 1269, 1228, 1193, 1139, 1117 cmꢀ1. MS (MALDI+,
dithranol) m/z: 3422 [M + Na]+. Elemental analysis calculated
for C224H356O22 (3401.21): C, 79.10%; H, 10.55%; found: C,
78.93%; H, 10.56%.
(E)-1,6-Bis{40-[30 0,40 0,50 0-tris(30 00,40 00,50 0 0-tri-n-dodecyloxy-
benzyloxy)benzoyloxy]phenyl}-3,4-didecyl-3-hexen-1,5-diyne,
C10B9. This compound was purified by chromatography on
silica gel, eluting with a dichloromethane/hexane/ether (55/45/1)
mixture, then the solid was washed with acetone to yield C10B9
as a white solid (37%). Rf: 0.52 (dichloromethane/hexane, 70/30).
1H-NMR (400 MHz, CDCl3): d (ppm) = 0.86–0. 90 (m, 60H,
0
0
(E)-1,6-Bis{40-[30 0,40 0,50 0-tris(30 0 0,400 0-di-n-dodecyloxybenzyloxy)-
benzoyloxy]phenyl}-3,4-didecyl-3-hexen-1,5-diyne, C10B6. This
compound was purified by chromatography on silica gel, eluting
with a dichloromethane/hexane/ether (55/45/1) mixture, then
the solid was washed with acetone to yield C10B6 as a white solid
(40%). Rf: 0.55 (dichloromethane/hexane, 70/30). 1H-NMR
CH3 + CH3 ), 1.22–1.51 (m, 352H, CH3(CH2)9 + CH3(CH2 )7),
0
0
1.64–1.77 (m, 40H, CH2CH2OAr + CH2 CH2 CQC), 2.60
(t, 4H, J = 7.3 Hz, CH2 CQC) 3.78 (t, 8H, J = 6.3 Hz,
0
CH2CH2OAr), 3.87–3.95 (m, 28H, CH2CH2OAr), 5.07–5.09
(m, 12H, ArCH2O), 6.62 (s, 4H, Ar-H), 6.65 (s, 8H, Ar-H),
7.16 (d, 4H, J = 8.6 Hz, Ar-H), 7.49–7.52 (m, 8H, Ar-H).
13C-NMR (500 MHz, CDCl3) d (ppm) = 14.1, 22.7, 26.2–30.4,
31.9, 35.0, 68.9, 69.1, 71.7, 73.3, 73.4, 75.2, 89.4, 97.7, 105.7,
106.2, 106.3, 110.1, 121.5, 121.8, 124.2, 129.7, 131.5, 132.2, 132.5,
137.8, 137.9, 143.2, 150.6, 152.7, 153.0, 153.3, 164.3. IR (KBr):
1739, 1592, 1506, 1234, 1192, 1164, 1119 cmꢀ1. MS (MALDI+,
dithranol) m/z: 4723 [M + Na]+. Elemental analysis calculated
for C310H528O28 (4703.49): C, 79.16%; H, 11.31%; found: C,
79.11%; H, 11.01%.
(4000 MHz, CDCl3): d (ppm) = 0.86–0.89 (m, 42H, CH3
+
0
0
CH3 ), 1.25–1.50 (m, 244H, CH3(CH2)9 + CH3 (CH2 )7),
0
0
1.64–1.85 (m, 28H, CH2CH2OAr + C = CCH2 CH2 ), 2.59
0
(t, 4H, J = 7.4 Hz, CQCCH2 ) 3.76 (t, 4H, J = 6.5 Hz,
CH2OAr), 3.91–4.00 (m, 20H, CH2OAr), 5.06–5.07 (m, 12H,
ArCH2OAr), 6.73 (d, 2H, J = 8.2 Hz), 6.84–6.86 (m, 6H, Ar-H),
3
5
6.94 (dd, 4H, J = 8.2 Hz, J = 1.8 Hz, Ar-H), 6.97 (d, 2H,
J = 1.8 Hz, Ar-H), 7.00 (d, 4H, J = 1.8 Hz, Ar-H), 7.17 (d, 4H,
J = 8.7 Hz, Ar-H), 7.49–7.51 (m, 8H, Ar-H). 13C-NMR
(400 MHz, CDCl3): d (ppm) = 14.1, 22.7, 26.1–29.8, 31.9,
35.0, 69.0, 69.2, 69.3, 71.5, 75.0, 89.4, 97.8, 110.0, 113.3, 113.4,
113.6, 114.1, 120.3, 121.1, 121.4, 121.9, 124.0, 129.1, 129.7,
130.0, 132.5, 143.2, 149.0, 149.1, 149.3, 150.7, 152.8, 164.5. IR
(KBr): 1736, 1593, 1521, 1505, 1269, 1228, 1193, 1138, 1116
cmꢀ1. MS (MALDI+, dithranol) m/z: 3618 [M + Na]+.
Elemental analysis calculated for C238H384O22 (3597.58): C,
79.46%; H, 10.76%; found: C, 79.41%; H, 10.79%.
Characterization techniques
1H (300 and 400 MHz) and 13C (100 MHz) were measured in
CDCl3 on a BRUKER ARX-300 and BRUKER AVANCE-
400 instrument. IR spectra on NaCl pellets were recorded
using a Thermo Nicolet Avatar 380 spectrophotometer. Mass
spectra were obtained on a MICROFLEX Bruker (MALDI+)
spectrometer.
Differential scanning calorimetry (DSC) and thermogravi-
metric analysis (TGA) were performed with DSC-MDSC TA
instruments Q-1000 and Q-2000; and TA Q-5000, respectively.
Liquid crystal textures were studied using an Olympus BX-50
polarizing microscope equipped with a Linkam TMS91 hot
stage and a CS196 hot-stage central processor. Microphoto-
graphs were taken with a digital camera Olympus DP12-2.
X-Ray diffraction measurements were carried out at room
temperature using a Pinhole camera (Anton-Paar) operating
with a point focused Ni-filtered Cu Ka beam. The scattering
angle range of the X-ray set-up is between 2y 11 and 401.
The sample was held in Lindemann glass capillaries (1 mm
diameter) perfectly sealed and heated, when necessary, with a
variable-temperature attachment. The diffraction patterns
were collected on a flat photographic film perpendicular to
the X-ray beam.
(E)-1,6-Bis{40-[30 0,400,500-tris(30 0 0,400 0-bis((S)-3,7-dimethyl-
octyloxy)benzyloxy)benzoyloxy]phenyl}-3,4-dipropyl-3-hexen-
1,5-diyne, C3B6*. C3B6* was purified by chromatography on
silica gel, eluting with a dichloromethane/hexane/ether (55/45/1)
mixture, then the crude product obtained was dissolved in
dichloromethane and purified by precipitation with methanol to
yield C3B6* as opaque wax (32–35%). Rf: 0.46 (dichloromethane/
hexane, 70/30). 1H-NMR (500 MHz, CDCl3) d (ppm) =
0
0.84–0.95 (m, 108H, CH3), 1.03 (t, 6H, J = 7.3 Hz, CH3 ),
1.09–1.37 (m, 72H, (CH3)2CHCH2CH2CH2), 1.46–1.74 (m, 40H,
(CH3)2CH0 + CH2(CH3)CHCH2CH2O + (CH3)2CHCH2
+
0
CQCCH2 CH2 ), 1.78–1.90 (m, 12H, CHCH2CH2O), 2.59
0
(t, 4H, J = 7.3 Hz, CQCCH2 ), 3.80–3.88 (m, 4H, CH2OAr),
3.94–4.06 (m, 20H, CH2OAr), 5.08–5.09 (m, 12H, ArCH2OAr),
6.75 (d, 2H, J = 8.2 Hz), 6.85–6.88 (m, 6H, Ar-H), 6.95 (dd, 4H,
J = 8.2 Hz, J = 1.7 Hz, Ar-H), 6.98 (d, 2H, J = 1.7 Hz, Ar-H),
7.00 (d, 4H, J = 1.7 Hz, Ar-H), 7.17 (d, 4H, J = 8.6 Hz, Ar-H),
7.50–7.51 (m, 8H, Ar-H). 13C-NMR (500 MHz, CDCl3) d (ppm) =
19.5–19.7, 21.9, 22.6, 22.7, 24.7, 28.0, 29.8–30.0, 36.3–36.4,
UV/Vis absorption spectra were collected on an ATI-Unicam
UV4-200 instrument using 10ꢀ4 to 10ꢀ5 M solutions in THF.
Mesophase measurements were carried out at room temperature
in a cast film onto a quartz plate prepared by evaporation of the
solvent (THF) and subsequent melting above the clearing point.
c
840 New J. Chem., 2012, 36, 830–842
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Fluorescence spectra were recorded with a Perkin-Elmer
LS50B spectrophotometer within the wavelength range 340–700.
Solution experiments were recorded in THF solutions of ca. 0.01
absorbance (concentrations 10ꢀ6 to 10ꢀ7 M) in 1 cm quartz cells.
The relative quantum yields of fluorescence (FF) were deter-
mined in THF solutions according to the equation:
Conclusions
The self-organization characteristics of rod-like fluorophores C3
and C10 can be controlled by conjugation to different types of
benzoic acid derivatives. This strategy allows functional materials
to be obtained that combine mesomorphic architectures with
luminescence and photoconducting properties.
2
Depending on the type of acid, the nature of the materials
ranges from nematic liquid crystals, for compounds derived
from 4-dodecyloxybenzoic acid, to columnar liquid crystals,
for compounds that incorporate six or nine terminal tails,
through crystalline solids, for compounds with either four or
six terminal tails. Indeed, the size ratio between the rigid core
and the carboxylate groups, which vary in bulk, is crucial to
address self-organization, thus indicating the delicate balance
of forces involved in liquid crystalline behaviour. As for the
mesomorphic behaviour shown by these materials, it is worth
noting the re-entrant feature of the Colh mesophase in the
heating process of compound C10B6 after a cold crystallization
of the same mesophase. Also, the structure of the Colh
mesophase shown by compound C3B9 with half a molecule
as the circular cross section of column is corroborated, versus
the structure of the column in C3B6, C10B6 and C3B6* in
which two columns form the stacking unit. Furthermore, the
addition of stereogenic centers to terminal chains enables the
transfer of molecular chirality to the columnar supramolecular
organization in C3B6*.
Funk = Fstd(Iunk/Aunk)(Astd/Istd)(Zstd/nunk
)
where Fstd is the fluorescence yield of DPA (diphenylanthracene)
standard (Fstd = 0.9 in 1 M cyclohexane at 298 K), Iunk and Istd
are the integrated areas of the emission peaks of the sample and
the standard, respectively, Aunk and Astd are the absorbances of
the sample and standard, respectively, at the excitation wave-
length lexc (335 nm), and Zunk and Zstd are the refractive indices of
the solvents corresponding to the sample and standard solutions.
In all cases, quantum yields have been determined as the average
of three measurements.
Fluorescence measurements of the mesophase were recorded
in thin films sandwiched between two quartz plates.
CD spectra were recorded on a Jasco J-810. Neat samples
were prepared by casting a solution of the compound C3B6* in
dichloromethane onto a quartz plate.
The cyclic voltammetry experiments were performed on an
Eco Chemie mAutolab electrochemical analyzer. All experiments
were carried out in a three electrode compartment cell with a Pt
wire counter electrode, a glassy carbon working electrode and an
Ag/AgCl reference electrode. The supporting electrolyte used was
0.1 M tetrabutylammonium hexafluorophosphate solution in dry
tetrahydrofuran and the cell containing the solution of the sample
(0,24 mM) and the supporting electrolyte was purged with a
nitrogen gas thoroughly before scanning for its oxidation and
reduction properties. The HOMO values were calculated by using
As functional materials, all of the mesogenic compounds
show luminescence in the mesophase and this indicates that the
supramolecular architecture prevents quenching—in contrast to
the situation in the crystal structure of the chromophores. These
columnar materials behave as photoconductors, with values of
the same order of magnitude as the photoconductivity of the
amorphous polymers.
the following general equation: HOMO = ꢀEox
ꢀ 4.4 eV;
onset
Ered cannot be directly obtained from the CV measurements
because a stable anionic state was not experimentally accessible.
Therefore, LUMO values were estimated from the relation
LUMO = DEg ꢀ HOMO, where DEg was calculated according
Acknowledgements
This work was supported by the MICINN projects MAT2009-
14636-C03-01, CSD2006-00012, CTQ-2007-61048, FEDER
founding (EU), Aragon Government, Principado Asturias
(Project IB08-088) and the MiUR project PRIN 2007
to the relationship DEg = 1239.85/lonset
.
Cells for photoconductivity measurements were obtained
by using ITO substrates with 1 mm wide, lithographically
patterned, conducting electrodes. Cells were cleaned by sequential
30 min sonication in solutions of detergent, deionized (DI) water,
acetone, and isopropanol and then dried at 80 1C for 2 hours in
a vacuum oven. Two substrates were glued together, using
either 1.8 mm or 5.0 mm spacers to control the thickness, which
was later measured by interferometry. Cells were then filled by
capillarity, by heating cells and materials above the melting
temperature on a hot plate. In order to align the liquid crystal
director, samples were annealed in a temperature controlled oven
(INSTEC STC200).
(2007WJMF2W). The authors thank Dr J. Barbera for his
´
kind help and useful discussions.
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842 New J. Chem., 2012, 36, 830–842
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012