Tuning the thermotropic and lyotropic properties of liquid-crystalline terpyridine ligands

Article abstract of DOI:10.1002/chem.200501431

A rational synthetic strategy is developed to provide compact and simple terpyridine (terpy) mesogens that show liquid-crystallinity both as pure compounds and in organic solution (amphotropic compound). The use of a central 4-methyl-3,5-diacylamino-pheny

Full text of DOI:10.1002/chem.200501431

FULL PAPER
DOI: 10.1002/chem.200501431
Tuning the Thermotropic and Lyotropic Properties ofLiquid-Crystalline
Terpyridine Ligands
Franck Camerel,[a] Bertrand Donnio,[b] Cyril Bourgogne,[b] Marc Schmutz,[c]
Daniel Guillon,[b] Patrick Davidson,[d] and Raymond Ziessel*[a]
Abstract: A rational synthetic strategy
is developed to provide compact and
simple terpyridine (terpy) mesogens
that show liquid-crystallinity both as
pure compounds and in organic solu-
tion (amphotropic compound). The use
of a central 4-methyl-3,5-diacylamino-
phenyl platform equipped with two lat-
eral aromatic rings, each bearing three
appended aliphatic chains, allows con-
nection of a 2,2’:6’,2’’-terpyridine frag-
ment through a polar group such as an
ester, amide, or flat conjugated alkyne
linker. For the T12ester and T12amide
scaffolds, the mesophase is best descri-
bed as a lamellar phase, in which the
molecules self-assemble into columnar
stacks held together in layers. In the
T12amide case, the additional amide
link results in significant stabilization
of the lamellar phase. The driving
forces for the appearance of columnar
ordering are the hydrogen-bonding in-
teractions of the amide groups, which
induce head-to-tail p-stacking of the
terpy subunits. Replacing the polar
linker by a nonpolarized but linear
alkyne spacer, as in the T12ethynyl
compound, provides a columnar meso-
phase organized in a rectangular lattice
of p2gg symmetry. In this arrangement,
two nondiscotic molecules arranged
into dimers by hydrogen bonding and
p–p stacking pile up in a head-to-tail
manner to form columns. In addition,
the T12amide compound proves to be
an excellent gelator of cyclohexane,
linear alkanes, and DMSO. The result-
ing robust and transparent gels are bi-
refringent and formed by large aggre-
gates that are readily aligned by shear-
flow. TEM and freeze-fracture micro-
scopy reveal that the gels have an orig-
inal layered morphology made of
fibers.
Keywords: amphotropic · gelator ·
hydrogen bonds · liquid crystals ·
mesogenic ligand · terpyridine
Introduction
[a]Dr. F. Camerel, Dr. R. Ziessel
Laboratoire de Chimie MolØculaire
Ecole Chimie, Polym›res, MatØriaux (ECPM)
UniversitØ Louis Pasteur-CNRS (UMR 7509)
25 rue Becquerel, 67008 Strasbourg Cedex (France)
Fax : (+33)390-242-635
In the last three decades or so, materials science has devel-
oped into an interdisciplinary field that makes use of organ-
ic, polymeric, and even biological components in addition to
the classical metals and inorganics. One of the challenges
with this is to endow these materials with desirable or pre-
dictable properties such as luminescence, charge transport,
and macroscopic ordering in mesophases.[1–4] In recent years,
there has been a tremendous growth in these scientific areas
loosely described as materials science and supramolecular
chemistry. A wealth of fascinating molecular structures,
often involving interlocking complementary molecular moi-
eties, have appeared for possible use in the future develop-
ment of innovative miniaturized devices.[5,6] Numerous ex-
amples of supramolecular assemblies based on selective
metal-to-ligand interactions have been engineered with the
goal of forming beautiful and highly symmetrical structures.
Elegant strategies have been elaborated to build such as-
semblies and to provide examples of discrete and infinite
helical frameworks,[7] hydrogen-bonded[8] or p–p interacting
E-mail: ziessel@chimie.u-strasbg.fr
[b]Dr. B. Donnio, Dr. C. Bourgogne, Dr. D. Guillon
Institut de Physique et Chimie des MatØriaux de Strasbourg (IPCMS)
Groupe des MatØriaux Organiques (GMO)
UniversitØ Louis Pasteur-CNRS (UMR 7504)
23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2 (France)
[c]Dr. M. Schmutz
Institut Charles Sadron, CNRS - UPR 22
6 rue Boussingault, 67083 Strasbourg Cedex (France)
[d]Dr. P. Davidson
Laboratoire de Physique des Solides, Bât. 510
UniversitØ Paris-Sud, (UMR 8502 CNRS)
91405 Orsay Cedex (France)
Supporting information (Complete experimental section including
preparation and characterization, DSC traces of T12ester and
T12ethynyl compounds, the XRD pattern of the T12ester compound at
1808C) for this article is available on the WWW under http://
www.chemeurj.org/ or from the author.
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networks,[9] three-dimensional complexes displaying defined
channels,[10] cucurbituril assemblies,[11] highly symmetrical
coordination clusters,[12] and organometallic polymers.[13]
Many of the new inorganic supermolecules generated
over the last few years rely on the coordination of transi-
tion-metal cations to polypyridine fragments incorporated
into oligomeric ribbons or macroscopic loops.[14–16] By virtue
of forming relatively stable and well-defined complexes with
metal cations, such ligands have facilitated the assembly of
molecular double- or triple-stranded helicates,[17,18] cate-
nates,[19] ladders, and related exotic frameworks,[20,21] some
of them exhibiting useful catalytic,[22] electronic,[23] or meso-
morphic[24] properties.
ing complexes have many potential applications in fields
such as macromolecular chemistry, biochemistry, photophy-
sics, and nanoscience. In particular, terpy and its multiple
derivatives have been used advantageously as building
blocks for the engineering of novel supramolecular struc-
tures such as spiral lines,[26] dendrimers,[27] micelles,[28] poly-
mers,[29,30] and liquid-crystalline soft materials.[31] Formation
of ordered architectures on surfaces,[32–34] functional molecu-
lar devices,[35] and biochemical applications[36] are particular-
ly challenging.
Ruthenium–terpy complexes have received much atten-
tion in the field of energy suppliers such as solar cells,[37] and
luminescence devices.[38,39] Immobilization of terpy ligands
and complexes on polymer resins could prove to be of im-
portance in the field of molecular catalysis.[40]
Along these lines 2,2’:6’,2’’-terpyridine (terpy) ligands are
particularly attractive because they can form stable com-
plexes with a variety of transition-metal salts.[25] The result-
Although terpy ligands offer an enormous structural di-
versity and tunability in terms of potential properties, stabil-
ity, and processability, they also typically suffer from a lack
of predictability when mesomorphic matter has to be engi-
neered. Multiple strategies have been devised, some of
which try to combine a sufficient number of aliphatic chains
to control not only the shape and the amphipatic character
of the molecule but also the microsegregation process
during self-assembly into the mesophase. But this approach
remains empirical and lacks rationality. Up to now, only di-
nuclear metallomesogens involving segmented and bulky
terpy ligands appeared to behave as liquid-crystalline mate-
rials,[24] whereas the uncomplexed ligand has remained non-
mesomorphic.
One way to overcome these difficulties and to fill the gap
of mesomorphic terpy ligands is to engineer a system in
which additional intermolecular hydrogen-bonding vectors
would stabilize the mesophase.[41] We chose to synthesize
terpy platforms with 1,3-diacylaminobenzene scaffolds to
favor intermolecular hydrogen bonding. The introduction of
a methyl group bisecting the central phenyl cycle is motivat-
ed by the need to tilt the amide vectors out of the plane to
extend the dimensionality of the network. Recently, this ap-
proach was successfully applied to produce liquid-crystalline
phenanthroline ligands and complexes.[42] From a general
point of view acylamino platforms have previously been
identified as key elements for the production of liquid-crys-
talline materials and of efficient gelators of various organic
solvents.[43,44] Some of these gels seem to have great poten-
tial as functional soft materials.[45,46] The gelation of nematic
liquid-crystal phases through hydrogen bonding has previ-
ously been reported and the gels thus formed have proven
to be interesting as dynamic materials in electro-optic devi-
ces and as systems responsive to fast stimuli.[47,48] Recent
studies have described terpy-containing carboxylic acids that
form hydro-gels, in which hydrogen bonding is provided by
an electrostatic interaction induced by proton transfer from
the acidic to the basic nitrogen atoms of the terpy ligand.[49]
As observed in classical liquid-crystalline systems, the
shape of the rigid units plays a dominant role in the organi-
zation of the molecules during the microsegregation proc-
ess.[4,50–54] In our case, it is surmised that the connecting unit
Abstract in French: Ce travail dØcrit une synth›se rationnelle
des tous premiers ligands mØsog›nes à base d’unitØ terpyridi-
ne et montre que les propriØtØs thermotropes et lyotropes de
ces composØs dØpendent notoirement du choixdu connecteur
reliant l’unitØ terpyridine à l’unitØ structurante. L’utilisation
de l’unitØ structurante 4-mØthyl-3,5-diacylaminophØnyle Øqui-
pØe de deuxcycles aromatiques portant 3 chaînes aliphatiques
permet en effet de connecter des sous-unitØs 2,2’:6’,2’’-terpyri-
dine par l’intermØdiaire de groupes polaires tels qu’un ester
ou une fonction amide ou encore par le biais d’une conne-
xion apolaire linØaire comme la liaison triple. La mØsophase
thermotrope obtenue dans le cas des composØs T12ester et
T12amide est une phase lamellaire dans laquelle les molØcules
sont organisØes par un rØseau de liaisons hydrog›ne en colon-
ne maintenue entre-elles par des interactions secondaires de
type p-p au sein des lamelles. Les forces motrices de cette or-
ganisation ont ØtØ ØtudiØes par spectroscopie infrarouge et
par l’Øtude fine de la structure cristalline d’un composØ parent
mod›le obtenu sur monocristal. L’introduction d’une fonction
amide supplØmentaire, par le connecteur, rØsulte dans la sta-
bilisation notoire de cette organisation. Le remplacement des
connecteurs polaires par une liaison triple apolaire permet
d’obtenir une organisation molØculaire diffØrente aboutissant
à la formation d’une mØsophase colomnaire de symØtrie rec-
tangulaire de type p2gg. Dans cet arrangement, deuxmolØcu-
les, n’impliquant plus les mÞmes rØseauxde liaisons hydrog›-
ne et d’interactions de type p, forment des dim›res qui s’empi-
lent tÞte-bÞche pour former des colonnes. De plus, le composØ
portant trois fonctions amides s’av›re Þtre un excellent gØli-
fiant du cyclohexane, des alcanes linØaires et du dimØthylsul-
foxide. Les gels obtenus, robustes et transparents, sont birØ-
fringents et constituØs d’agrØgats pouvant Þtre alignØs sous
Øcoulement. Des Øtudes par microscopie Ølectronique à trans-
mission effectuØes sur des gels diluØs mais Øgalement des rØ-
pliques mØtalliques des gels obtenus apr›s cryofracture rØv›-
lent que la formation de ces gels provient de l’auto-organisa-
tion en solution de plans formØs par juxtaposition parall›le
de fibres.
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Chem. Eur. J. 2006, 12, 4261 – 4274

Terpyridine Liquid Crystals
FULL PAPER
linking the terpy in the 4’-position of the central ring and
the 1,3-diacylaminobenzene will play a prominent role. The
use of an ester or an amide dipole will introduce a kink (A
and B), whereas a single nonpolarized triple bond will favor
a linear and flat arrangement of the subunits (C).[55] Notice
that in the case of the amide linker in B additional supramo-
lecular hydrogen bonding is expected to favor the stabiliza-
tion of the mesophase. The 4’-substitution position was tar-
geted to provide uncrowned ligands likely to p-stack in the
solid state.[56]
ed by dimethylaminopyridine (DMAP). The trisamide deriv-
ative was prepared under similar conditions from 4’-amino-
methyl-2,2’;6’,2’’-terpyridine itself synthesized from 4’-
methyl-2,2’;6’,2’’-terpyridine[58–60]
With platforms bearing active functional groups such as
iodine,[61] introduction of 4’-ethynyl-2,2’:6’,2’’-terpyridine[62]
was realized in the presence of catalytic amounts of Pd0
(Scheme 2).[63]
Mesomorphic behavior ofthe novel terpyridine compounds :
The thermotropic behavior of the terpy ligands was studied
by combining thermogravimetric analyses (TGA), differen-
tial scanning calorimetry (DSC), polarized optical microsco-
py (POM), and small-angle X-ray scattering on powder sam-
ples (SAXS). These data are summarized in Table 1.
Tnesters: From TGA analyses, the degradation temperature
of the compounds was found to be above 2258C. DSC anal-
yses showed that T8ester and T16ester ligands exhibit one
single reversible thermal transition at 2158C and 2058C, re-
spectively, whereas the T12ester ligand displays two reversi-
ble thermal transitions centered at 1538C and 1918C on the
In this report, novel thermo-
tropic liquid-crystalline terpy
ligands are described and the
role of the linker (ester, amide,
and ethynyl) is emphasized in
light of the data obtained by
microscopy, microcalorimetry,
and X-ray diffraction.
Results and Discussion
Synthesis: The synthesis of the
Tnester ligands (n = 8, 12, 16)
was carried out by a conver-
gent strategy outlined in
Scheme 1. Starting from ethyl-
4-methyl-3,5-diaminobenzoate,
the amidation with 3,4,5-trial-
kyloxybenzoic acid chloride (n
= 8, 12, 16) and saponification
yielded the acid platform bear-
ing two amide functions. Six
long aliphatic chains were in-
troduced on the platform to
favor mesophase formation.
The key esterification step re-
quired cross-coupling between
this acid platform and the
4’-hydroxymethyl-2,2’;6’,2’’-
terpy[57] derivative in the pres-
ence of the chloride salt of 1-
ethyl-3-[3-(dimethylamino)pro-
pyl]carbodiimide (EDC·HCl),
under basic conditions provid-
Scheme 1. Reagents and conditions: i) anhydrous Na2CO3, acetone, reflux, 82% n = 8, 82% n = 12, 57% n
= 16; ii) KOH (50 equiv), THF/H2O (v/v), reflux, 85% n = 8, 82% n = 12, 73% n = 16; iii) EDC·HCl
(2 equiv), DMAP (1 equiv), CH2Cl2/THF, RT, 76% n
=
8, 72% n
=
12, 69% n
=
16; iv) EDC·HCl
(2 equiv), DMAP (2 equiv), CH2Cl2, RT, 56%.
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R. Ziessel et al.
temperature cycles up to
2258C. For the T8ester and
T16ester compounds the single
transit was assigned to direct
melting into the isotropic
liquid at 2158C and 2058C for
the T8ester and T16ester li-
gands, respectively. X-ray dif-
fraction patterns obtained for
the T8ester and T16ester com-
pounds below these transition
temperatures displayed several
sharp peaks over the whole 2q
(18ꢀ2qꢀ308) angular range
and confirmed their cristallini-
ty.
Scheme 2. Reagents and conditions: i) [Pd(PPh3)2Cl2](6% mol.), ( iPr)2NH, CuI (10% mol) THF, RT, 32%.
A
Table 1. Thermal behavior of the compounds and X-ray characterization of the mesophases.[a]
At
temperatures
above
1918C the T12ester ligand is in
the isotropic fluid state. On
cooling from the isotropic
liquid, the material becomes
birefringent and fluid and
monodomains are observed in
the texture under polarized
light (Figure 1).
Compound Transition temperatures [8C]
dmeas
[Š]
I
00l hk
dcalcd
[Š]
Mesophase
parameters
measured at
T
(enthalpy
A
T8ester
T12ester
Cr 220 I
I 215 (À48.6) Cr
L1 162 (4.7) L2 196 (8.5) I
26.5
13.2
8.8
7.6
4.6
3.8
26.4
7.5
4.6
3.8
VS 001
26.4
13.2
8.8
T = 1208C
d = 26.4 Š
AM = 121 Š
M
W
M
br
br
002
003
B
A
C
2
2
2
I 191 (À8.3) L2 153 (À5.6) L1
X-ray diffraction patterns
obtained for this compound
were recorded at various tem-
peratures above and below the
thermal transition at 1538C on
cooling from the isotropic
melt. The X-ray pattern ob-
tained at 1008C displayed a
diffuse and broad scattering
halo A, centered at 4.6 Š in
the wide-angle region, indica-
tive of a liquid-like order of
the aliphatic chains and thus of
the fluid-like nature of the
phase (Figure 2). Two other
diffuse scattering halos associ-
ated with distances of about
7.6 and 3.8 Š (halos B and C),
were also observed (halo C is
more visible after mathemati-
cal deconvolution of the scat-
tered halo A signal). In the
small-angle region, the XRD
pattern displayed three reflec-
tions in a 1:2:3 ratio, which
could be indexed as the 001,
002, and 003 reflections of a la-
mellar phase with a periodicity
VS 001
26.4
T = 1808C
d = 26.4 Š
AM = 127 Š
br
br
br
B
A
C
T16ester
Cr 224 (70.8) I
I 205 (-54.7) I
L3 225 (21.8) I
T12amide
26.3
13.0
8.7
7.5
4.6
VS 001
26.1
13.05
8.7
T = 1208C
d = 26.1 Š
AM = 123 Š
M
W
M
br
002
003
B
A
C
I 225 (21.1) L3
3.8
br
T12ethynyl Cr 187 (20.8) PCr 193 (10.0) Colr 200 (21.0) I 32.0
VS
VS
M
M
20
11
31
12
32.0
22.1
15.8
11.6
T = 1988C
a = 64.1 Š
b = 23.6 Š
22.1
15.7
11.7
I 194.5 (À21.9) Colr 174 (À12.2) PCr 150
(À7.0) Cr
Scol
754.5 Š
=
2
11.1
7.7
7.3
M
M
M
22
42
23/
13
53
A
11.0
7.7
7.4
6.6
4.7
4.2
W
br
br
6.7
B
[a] dmeas and dcalcd are the measured and calculated diffraction spacing; I is the intensity of the sharp reflections
(VS = very strong, M = medium, W = weak); br is used for broad scattering halos; 00l and hk are the index-
ations of the reflections corresponding to lamellar and Colr phases; AM is the molecular area (AM = VM/d);
Scol is the columnar cross section area (Scol = 1/2ab); Cr = crystalline phase; I = Isotropic liquid, Colr = rec-
tangular columnar mesophase; PCr = poorly crystallized material; L = Lamellar phase. Definitions of dcalcd
and Vm are given in the Experimental Section.
d
= 26.4 Š. The scattering
first cooling curve (Figure S1, Supporting Information).
NMR experiments performed after the DSC measurements
revealed that the compounds did not degrade after several
corresponding to C is typical for face-to-face distances be-
tween flat aromatic units (here the terpys), the electron den-
sity modulation (diffuse band) being short-range. Moreover,
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Terpyridine Liquid Crystals
FULL PAPER
they displayed a broad scattering halo (A) centered at
~4.6 Š in the wide-angle region, while showing three reflec-
tions in the small-angle region (Figure 3). The broad halo A
Figure 1. T12ester compound examined by optical microscopy between
crossed polarizers upon cooling (symbolized by the cross in the corner of
the picture) at 1488C.
Figure 3. XRD pattern of the T12amide compound at 1208C.
corresponds to the average distance between the molten
chains bonded to the ligand. Two slightly less diffuse halos
B and C were also observed at 7.5 and 3.8 Š and are attrib-
uted to some liquid-like correlations between neighboring
molecules, that is, head-to-tail, face-to-face stacking, as for
the T12ester described above. Three reflections were ob-
served in the small-angle region and indicate the long-range
positional ordering of large objects. The small-angle reflec-
tions could be indexed as the fundamental 001 for the sharp
and intense reflex and as the 002 and 003 higher-order re-
flections of a lamellar phase (d = 26.1 Š at 1208C). The
low intensity of the higher-order reflections 002 and 003,
close to the experimental detection limit, results in an appa-
rent broadening of the peaks. The texture observed by po-
larized optical microscopy below the transition temperature
is composed of growing monodomains characteristic of col-
umnar mesophases (Figure 4). Above 2258C, this compound
is both fluid and isotropic. The phase transition therefore
corresponds to the isotropization of a lamellar liquid-crystal-
line phase and it appears that this compound is also liquid-
crystalline (single-phase) from room temperature to 2258C.
The liquid-crystalline phase observed for the T12amide
compound from room temperature to 2258C is similar to
that observed for the T12ester compound from room temper-
ature to 1538C. On the basis of the DSC and POM analysis
and the XRD analysis, the liquid-crystalline phases observed
for T12ester and T12amide compounds can thus be identified
as lamellar mesophases constituted of layers containing
small columnar aggregates.[64] It also appears that the substi-
tution of the ester link by an additional binding amide
group helps in stabilizing the lamellar phase, as shown by an
increase of the isotropization temperature.
Figure 2. XRD pattern of the T12ester compound at 1008C.
the presence of the diffuse halo B at 7.6 Š (double perio-
dicity) further suggests a short-range, face-to-face, head-to-
tail stacking of the molecules, with the central amphipathic
4-methyl-3,5-diacylaminophenyl platforms pointing in oppo-
site directions. In other words, these diffuse signals indicate
the existence of short-range ordered columnar piling within
the layers. Considering the molecular shape and the occur-
rence of the diffuse scattering in the wide-angle region, mo-
lecular rotation is supposed to be hindered or greatly re-
stricted and is consistent with columnar piling of a dozen
molecules (this correlation length is extracted from halo B).
At 1808C, the diffraction pattern has the same features
(Figure S3, Supporting Information) as those detected at
lower temperature in the L1 phase; the only difference is in
the small-angle region, where a single reflection was detect-
ed, suggesting a decrease in the molecular order within the
lamella (vide infra).
T12amide: TGA measurements performed on the T12amide
compound proved thermal stability up to 2508C. DSC traces
displayed only one reversible transition at 2258C in heating
and cooling cycles. XRD patterns obtained below 2258C re-
vealed that this compound is also liquid crystalline because
T12ethynyl: TGA measurements performed on this com-
pound proved its good thermal stability up to 2508C. The
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R. Ziessel et al.
Figure 4. T12amide compound viewed by optical microscopy under
crossed polarizers (symbolized by the cross in the corner of the picture)
at 2208C.
DSC traces of the T12ethynyl displayed three reversible tran-
sitions. They are close together in the first heating curve but
become well separated on cooling, with an important super-
cooling effect for the low-temperature transitions (Figure S2,
Supporting Information). Above 2008C, the compound ap-
pears fluid and isotropic between crossed polarizers. Cooling
from the isotropic liquid, the compound becomes birefrin-
gent, and a texture typical of a columnar phase with pseudo-
fan shapes is observed (Figure 5a). Between 1748C and
1508C, striations appear on the large oriented domains (Fig-
ure 5b). Below 1508C, cracks indicative of a crystalline ma-
terial are observed (Figure 5c). The second heating curve is
identical to the first.
XRD measurements were performed on heating at varia-
ble temperatures between 180 and 2008C by steps of 28C.
The crystalline nature of the low-temperature phase was
confirmed by the XRD patterns obtained below 1878C,
which display sharp peaks in the wide- and small-angle re-
gions. In the temperature range between 187 and 1938C,
sharp peaks were observed in the small-angle region togeth-
er with a structured broad scattering halo (A) centered at
4.7 Š in the wide-angle region. The structure of this halo
corresponds to interference due to the long carbon chains,
typical of a poorly crystallized material. XRD patterns, ob-
tained in the 193–2008C temperature range, displayed a
broad scattering halo centered at 4.7 Š (halo A), which
proves the fluid-like nature of this phase. In the small-angle
region, several sharp peaks were observed, confirming the
two-dimensional liquid-crystalline nature of this high-tem-
perature phase (Figure 6). These peaks could be indexed in
the p2gg rectangular lattice as (hk) = (20), (11), (31), (12),
(22), (42), (23), (13), (33), (53) and thus the phase was as-
signed as a rectangular columnar mesophase (Colr) with lat-
tice parameters a = 64.1 and b = 23.6 Š at 1988C. The
halo centered at 4.2 Š (halo B) can be attributed to a mean
distance between tilted molecules stacked on top of each
other along the columns.
Figure 5. The T12ethynyl compound viewed by optical microscopy under
crossed polarizers upon cooling (symbolized by the cross in the corner of
the picture) at a) 1938C, b) 1658C, and c) 1338C.
Introduction of an ethynyl junction between the platform
and the terpy fragment made the polar part of the molecule
Figure 6. XRD pattern of the T12ethynyl compound at 1988C.
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Terpyridine Liquid Crystals
FULL PAPER
flatter. The angle constraint imposed by the ester and the
amide dipole in the Tnester and T12amide molecules is re-
moved and the molecule can orient the terpy and the central
phenyl of the platform in the same plane. However, the
more efficient stacking of the polar part of the molecule
also increases the rigidity of the system, as clearly shown by
the higher transition temperatures, the narrower tempera-
ture range of the mesophase, and the stabilization up to
1878C of the crystalline phase compared to the ester and
amide derivatives.
CHCl3) hydrogen bonding is still evident (at 3320 cmÀ1 for
nNH, at 1660 cmÀ1 for nCO, and at 1517 cmÀ1 for dNH).
Molecular modeling: To rationalize the molecular organiza-
tion of these species, in particular within the lamellar meso-
phases observed for the T12ester and T12amide compounds, a
model inspired by the crystal structure of the homologue
TOMeester compound is proposed. Although the molecular
arrangement in the crystalline phase might be different from
that in the mesophase, there are nevertheless some features
in the mesophase reminiscent of the crystal packing, which
may be exploited. The formation of the benzyl amide frame-
work was understood by comparison with the crystal pack-
ing of a parent compound of the Tnester family in which the
six alkoxy terminal chains were replaced by four methoxy
groups in the 3,5 positions (TOMeester).[70a] This compound
FT-IR spectroscopy: IR spectroscopy is a powerful tool for
the study of hydrogen bonds and ordering of hydrocarbon
chains in various states of matter. In the present cases
(T12ester, T12amide, T12ethynyl), the frequencies of the
bands due to CH2 antisymmetric and symmetric modes (na-
¯
A
G
crystallizes in the triclinic space group P1 with a = 8.809(3),
12.032(5), c 16.928(6) Š, a 79.47(3), b =
and 2852 cmÀ1 for all three compounds in the mesophase
and correspond to some ordering of the hydrocarbon chains
with an all-trans conformation.[65,66] However, in dilute
CHCl3 solution, these frequencies shift to 2933 and
2861 cmÀ1 for all three compounds.
b
=
=
=
86.76(3), g = 82.48(3)8, and Z = 2.[70b] The TOMeester ligand
is nonplanar; the peripheral trisubstituted rings are almost
perpendicular to the central phenyl ring while the terpy sub-
unit is tilted by 648 with respect to the central core (Fig-
ure 7a). It should be noted that the two amide vectors point
in opposite directions, which would favor the formation of a
polymeric network. Two remarkable features are evident
from the packing of this compound. First, intermolecular hy-
drogen bonding[71] is responsible for the formation of a one-
dimensional supramolecular edifice (Figure 7b). The tight
hydrogen bonds connect the amide groups of a given mole-
From room temperature to the isotropic melt, all amide
dipoles are involved in hydrogen bonding, as clearly evi-
denced by the nNH and nCO stretching vibrations and dNH de-
formation vibration, which lie in the 3340–3200, 1678—1651,
and 1560–1515 cmÀ1 ranges, respectively.[67,68] Notice that
corresponding values for the free amides are at 3500–
3400 cmÀ1 for nNH, around 1680 cmÀ1 for nCO, and 1550–
[68]
1510 cmÀ1 for dNH
.
For the T12ester and T12amide com-
cule L to its nearest neighbors on top L’ (NH···O
pounds, the nNH bands located at 3331 and 3320 cmÀ1, re-
spectively, become stronger by cooling the isotropic melt to
room temperature. In the T12amide case, a broad single
stretching vibration at 1666 cmÀ1 was observed at 2208C
whereas a splitting of this band at 1660 and 1641 cmÀ1 occur-
red at 588C. The most intriguing situation was found for the
T12ethynyl compound for which a very weak nNH band and a
large nCO band centered at 1665 cmÀ1 were found at 2058C.
Upon cooling from the isotropic melt in the Colr mesophase
at 1898C, a strong nNH band at 3207 cmÀ1 and a sharp nCO
band at 1637 cmÀ1 were found. The dNH deformation vibra-
tions were weak but observed in the mesophases at 1520,
1515, and 1507 cmÀ1 respectively for T12ester, T12amide, and
T12ethynyl.
These values are consistent with strong hydrogen bonding
involving the amide groups and the absence of free-bonded
amides suggests a well-organized state of matter. The high
stability and robustness of gels obtained in organic solvents
from the T12amide compound (vide infra) also suggest a hy-
drogen-bonded network. By dissolving the T12ester and
T12ethynyl compounds in CHCl3 (ca. 10À3 m) hydrogen bond-
ing is likely to be less effective, as confirmed by the nNH at
3427/8 cmÀ1, nCO at 1673/2 cmÀ1, and dNH at 1533/2 cmÀ1,
characteristic of free amide functions.[69] In marked contrast
with these results and in agreement with the increased sta-
bility of the mesophases provided by the T12amide material
is the fact that even at low concentration (<10À4 m in
2.858(37) Š) and bottom L’’ (NH···O 3.097(47) Š) in a cen-
trosymmetric fashion. This strong stabilizing effect forces
the terpy fragments to swing out of the hydrogen-bonded
stacks. Also present are stabilizing interactions between the
almost parallel tetra-substituted phenyl cores with centroid-
centroid distances of L–L’ = 5.6 and L–L’’ = 3.9 Š.
Second, another interesting feature of the molecular
structure is the p–p stacking of the terpy fragments, which
runs along the [100]direction between two adjacent one-di-
mensional, hydrogen-bonded networks. The standard distan-
ces between the terpy fragments in the one-dimensional p–p
stacks lie in the 3.7 (L–L’’) and 4.4 Š (L–L’) range. This zip-
ping effect leads to the formation of planes strongly stabi-
lized by hydrogen-bonding networks and p–p stacking (Fig-
ure 7c).
As mentioned above, the molecule can form both hydro-
gen bonds through the amide groups and p-stacking through
the terpy units. In the crystal packing, a strong directional
hydrogen network is visible. Parallel pseudo-columns are
formed through the stacking of molecular units in a head-to-
tail fashion in order to optimize the hydrogen-bonding inter-
actions. The average distance between two neighboring moi-
eties is about 4.2–4.6 Š, and that between two alternated
molecules corresponds to the a parameter of the triclinic lat-
tice, a = 8.8 Š; the columnar axis is thus aligned along the
a-direction. These pre-existing pseudo-columns are held to-
gether in layers defined by the b and c parameters, an ar-
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R. Ziessel et al.
Figure 7. a) Molecular structure of the TOMeester ligand showing the atom-labeling scheme; b) central trimeric core, setting up the building block of the
supramolecular edifice. A single molecule L of TOMeester (x,y,z) is surrounded by two others (Àx, 1Ày, 1Àz)]for L ’ and (1Àx, 1Ày, 1Àz) for L’’. The hy-
drogen bonds (dotted lines) centro-symmetrically connect the amide groups of L to L’ (NH···O = 2.858(37) Š, NHO angle 147(1)8) and L“ (NH···O =
3.097(47) Š, NHO angle = 135(1)8); c) Plane formed by a zipping effect, through p–p stacking between the terpy fragments, of columns of TOMeester li-
gands stabilized by hydrogen-bonded networks.
rangement that arises from the interactions between pend-
ant terpy units along the c direction and between the dime-
thoxyphenyl rings along the b direction. Extrapolation of
this packing to describe the molecular organization of the
lamellar phase L1 in the T12ester mesophase thus seems
straightforward. Making the assumption that the pseudocol-
umns are still present, the two distances observed at 3.8 and
7.6 Š at 1208C or 3.8 and 7.5 Š at 1808C suggest an alter-
nated stacking of the terpy fragments reminiscent of the
crystalline structure. The chains are thus confined to the two
opposite quadrants perpendicular to the columnar hard
core, preventing the stacking of the trialkoxyphenyl units,
whereas the terpys occupy the free volume left and are still
available for p-stacking interactions. This particular organi-
zation allows for the lateral interactions of the columns,
which are forced to lie parallel and confined in well-defined
layers (Figure 8). The layers are separated from each other
by a dense aliphatic continuum that is responsible for the
loss of intercolumnar interactions in the third direction (b
direction), precluding a columnar phase with two-dimen-
sional symmetry. This arrangement is compatible with the
spacing periodicity deduced from XRD (26.0 Š versus
32.0 Š in the model) and is also in agreement with the mo-
lecular area (6”21 Š2). In order to compensate the surface
generated by the formation of this rigid plane, the chains
ought to be in a very disordered state, likely with some in-
terdigitation. The formation of the L2 phase at higher tem-
peratures likely corresponds to the partial loss of such a mo-
lecular arrangement, which probably results from a decrease
of the stacking interactions and an increase of the molecular
diffusion owing to the thermal fluctuations and from the
larger volume required by the aliphatic chains.[72] The same
description can be used for the T12amide mesophase, which
exhibits the same structural features. Moreover, in view of
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Terpyridine Liquid Crystals
FULL PAPER
Figure 8. Molecular modeling of the layer observed in the mesophases of
the T12ester and T12amide compounds, based on the TOMeester crystallo-
graphic structure.
this, it is now clear why the triamide derivative exhibits a
single lamellar phase (L3), the hydrogen-bonding interac-
tions being much stronger in this case than for the ester-dia-
mide compound, inhibiting a random stacking. This is clear-
ly confirmed by the FT-IR measurements in the various
states of matter (vide supra).
For the ethynyl derivative the columnar cross-section in
the Colr mesophase is not circular and the particular ar-
rangement of the elliptical columnar cross-sections leads to
a rectangular lattice. Such an elliptical shape can be generat-
ed if two molecules are arranged into head-to-tail dimers,
with the terpy unit now located in the same plane as depict-
ed in Figure 9a. These dimers stack on top of each other to
form columns but unlike the previous situation, the columns
do not possess any particular lateral registry, and these col-
umns are arranged into a rectangular lattice. The same types
of interactions are responsible for the formation of the mes-
ophase as for the ester and amide compounds: hydrogen
bonding and p–p stacking. Molecular dynamic calculations
confirmed that such dimers can be perfectly organized into
a rectangular lattice of p2gg symmetry with a = 64.1 Š and
b = 23.6 Š and an occupancy density of 0.9 (Figure 9b).
The proposed models of these novel, self-organized mate-
rials are in keeping with the attribution of the broad peaks
found in the X-ray diffraction patterns for T12ester and T12
amide (A: 4.6 Š; B: 7.6 Š; C: 3.8 Š), as well as for
T12ethynyl (A: 4.7 Š; B: 4.2 Š). Of particular interest is
peak C, attributed to stacking of the terpyridine subunits as
unambiguously found in the molecular structure determined
by analysis of single crystals. The X-ray crystal structure
clearly shows the head-to-tail stacking of the terpyridine
units with a double distance corresponding to the antiparal-
lel stacking periodicity (expected, since the molecules are
not symmetrical). Therefore, it is reasonable to suppose that
the liquid-crystal mesophase of T12ester and T12amide com-
pounds partly retains some of the structural features of the
crystalline phase of the parent compound TOMeester. Owing
to the dynamics and the fluidity of the phase, the peaks are
broadened, which means that the order is short range. The
Figure 9. a) Dimer constructed from two head-to-tail T12ethynyl mole-
cules; b) two-dimensional rectangular unit cell of p2gg symmetry built
with the head-to-tail dimer of the T12ethynyl compound (a = 64.1 Š; b
= 23.6 Š).
shift of the reflection in the case of the ethynyl compound
(peak B) to longer distances indicates a tilt of the molecular
plane (plateau) with respect to the axis of the columns. This
tilt also implies that the second harmonic is dramatically
weak and consequently not visible. This is a common obser-
vation in columnar liquid crystal phases.
Gelation properties ofthe T 12amide compound: Since am-
phiphilic molecules built on a 1,3,5-benzenetricarboxamide
core are known to be good gelators for organic sol-
vents,[43,44,73] the gelation abilities of the T12amide compound
were evaluated in various polar and nonpolar, protic and
nonprotic solvents. This terpy derivative induced gelation of
cyclohexane, linear alkanes from C6 to C12, and dimethyl
sulfoxide (DMSO). Robust and transparent gels were
formed in cyclohexane and in linear alkanes at 258C after
heating a mixture of the ligand and the solvent to form a ho-
mogeneous fluid solution. Upon cooling below the gelation
temperature, the complete volume of solvent is immobilized
and can support its own weight without flowing as shown in
Figure 10a. The organogels exhibited thermally reversible
sol/gel transitions. The minimum gelation concentrations ob-
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R. Ziessel et al.
Figure 10. a) Gelation test in cyclohexane of the T12amide compound in
cyclohexane (2.6% (w/w)). Gel formation is confirmed if the sample
does not flow in a few hours after the test tube is turned upside-down.
b) Texture of a gel of T12amide in cyclohexane (c = 20.85%
(w/w)) ob-
A
served by optical microscopy between crossed polarizers (the black area
corresponds to an isotropic air bubble). The crossed polarizers are sym-
bolized by the white arrows in the top left corner of the picture.
served (MGC, hexane: 0.55% (w/w); cyclohexane: 0.55%
(w/w); dodecane: 0.44% (w/w); DMSO: 1.32% (w/w))
showed that these mesogenic ligands displayed good gelati-
on abilities, comparable to those already reported for other
low-molecular-weight organogelators.[74] The role of hydro-
gen bonding was confirmed by infrared spectroscopy experi-
ments performed with the cyclohexane gel. Two C=O
stretching bands were observed at 1641 and 1660 cmÀ1 and a
single NH stretching vibration at 3279 cmÀ1. These spectro-
scopic data are an unambiguous signature of hydrogen-
bonded amides inducing a hydrogen-bonded network. It
should be noted that transparent gels can also be formed
with the T12ester compound—but at higher concentration
(MGC, cyclohexane: 1.3% (w/w))—and that only turbid
gels are formed with the T12ethynyl compound.
Observations by optical microscopy between crossed po-
larizers proved that the gels of the T12amide compound are
strongly birefringent, which suggests that they form a lyo-
tropic liquid-crystalline phase (Figure 10b). SAXS experi-
ments were therefore performed with gels of the T12amide
compound in cyclohexane. The SAXS intensity was easily
observed, even at the rather low concentration of 12% (w/
w), and the SAXS pattern (Figure 11a) of a well-aligned
sample has an anisotropic “butterfly” shape. This pattern is
typical of a single domain of nematic phase comprised of
large aggregates aligned by the shear-flow that occurs when
the X-ray capillary is filled with sample. The scattered inten-
sity regularly decreases with increasing scattering angle,
which suggests that the aggregates are randomly located (no
positional order), since no diffraction peak can be detected.
In contrast, the SAXS pattern (Figure 11b) of a 21% (w/w)
mixture showed an anisotropic diffuse peak located at q =
0.134 ŠÀ1. The diffuse peak corresponds to a liquid-like
order of the aggregates with an average distance of 74 Š be-
tween them. Even though this scattering data proves that
the mechanical properties of the gels arise from the exis-
tence of large aggregates, this data does not allow us to
Figure 11. SAXS two-dimensional scattering patterns obtained with gels
of the T12amide compound at various concentrations: a) 12% (w/w);
b) 21% (w/w); and c) 38% (w/w). The black arrows point to the diffrac-
tion lines.
identify their nature. More information can be obtained
from electron microscopy images of these gels (see below).
The SAXS pattern (Figure 11c) of a gel of even higher con-
centration, 38% (w/w), displays three sharp diffraction lines
À1
at scattering vectors of 0.235 ŠÀ1, 0.404 ŠÀ1, and 0.47 Š in
ratios 1, 31/2, and 2. These diffraction lines prove that the
T12amide compound stacks in columns that self-assemble on
a hexagonal lattice with a parameter of a = 49 Š at this
concentration. The gels thus clearly form a lyotropic hexag-
onal columnar mesophase.
TEM experiments were performed to examine the mor-
phology of these gel materials and the nature of the large
objects that induce the gelation. Images obtained from very
dilute solutions of T12amide ligand in cyclohexane (0.04%
(w/w)) dried onto a carbon-coated grid reveal the presence
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Terpyridine Liquid Crystals
FULL PAPER
of very thin fibers (2 nm thick and several mm long) (long
arrow on Figure 12a). An interesting feature is that the di-
ameter of these fibers is monodisperse. The fibers also show
a tendency to associate locally to form sheets in this dried
state (short arrow). To directly examine the morphology of
these fibers in the gel state, freeze-fracture electron micro-
scopy (FFEM) experiments were performed on gels of the
T12amide compound in cyclohexane (C>0.55% (w/w)). In
the gels, a clear lamellar structure was observed, which con-
sists of extended layers (several micrometers) of less than
10 nm in thickness (Figure 12b). The organic layers regular-
ly stack to form large, randomly oriented lamellar domains.
Inside the layers fine striations are seen, which correspond
to the individual fibers observed in dilute solution (arrow)
in a highly compacted state. These fibers are self-assembled
into layers with a regular distance of 4 nm (Figure 12c). The
stars likely correspond to solvent areas trapped in between
the layers. It appears that the compound is not a classical or-
ganogelator for which the formation of a three-dimensional
network of entangled, fiber-like aggregates is responsible for
the immobilization of the solvent.[43,44,73–75] These microscop-
ic observations reveal that the gel formation in this case
arises from the self-assembly of lamella in solution (lyo-
tropic system).
TEM experiments confirm the presence of large objects
in solution. Below the minimum concentration for gelation
(MGC), the formation of fibers, monodispersed in diameter,
prevails. Above the MGC, the aggregation of these fibers
into layers is responsible for gelation. The organization of
the layer observed in the gel is probably close to that of the
thermotropic mesophase of the T12amide compound. From
IR experiments, it was demonstrated that hydrogen-bonded
amides play a role in the gel formation. Comparison with
the thermotropic mesophase suggests that the fibers are de-
veloped through an extended one-dimensional network of
hydrogen bonds and these fibers are associated through p–p
stacking between the terpy fragments in solution to form
layers. TEM pictures obtained at various concentrations also
reveal that the compactness of the layer, that is, the distance
between the fibers, remains constant. Since the distance de-
termined by SAXS decreases when concentration increases,
the peak observed on the diffraction pattern can be associat-
ed to interference between the layers. The anisotropy of the
SAXS patterns corresponds to the alignment of the layers
along the flow, that is, the long axis of the capillary, induced
when the capillary was filled.[76] At high concentration,
when the interlayer distance is close to the distance between
the fibers within the layer (~4 nm), the packing of the layers
leads to the formation of a hexagonal array. These micro-
scopic observations and SAXS experiments reveal that the
formation of these gels is certainly induced by the self-as-
sembly of lamella stabilized by hydrogen bonding and p–p
stacking interactions as observed in the thermotropic liquid-
crystalline state.[77]
Conclusion
Our results show that substitution of terpy frameworks with
a 4-methyl-3,5-diacylaminobenzene core equipped with two
secondary amide functions, each carrying a phenyl ring with
three paraffin chains, induces the occurrence of liquid-crys-
talline properties. The nature of the group linking the terpy
to the platform and the length of the aliphatic chains play
crucial roles in the formation of the thermotropic mesophas-
es. For the Tnester family, the octyloxy and hexadecyloxy de-
rivatives were not mesomorphic, whereas the dodecyloxy
compound exhibited mesomorphism from room temperature
to 1918C. Most significantly, the T12amide compound is mes-
omorphic from room temperature to 2258C, extending the
Figure 12. a) Image obtained by TEM of a very dilute solution of the
T12amide compound in cyclohexane (c = 0.04% (w/w)) showing thin
fibers (2 nm thick and several mm long) (long arrow). The fibers show a
tendency to associate to form sheets (short arrow). The black dots visible
in the figure are the Pt particles seen at high magnification. b) Lamellar
structure as observed by FFEM of a gel of T12amide compound in cyclo-
hexane (c = 2.6% (w/w)). The observed layers display fine striations cor-
responding to the individual fibers observed in diluted solution (arrow)
in a highly compacted state. The stars point to solvent areas trapped be-
tween the layers. c) Image obtained by FFEM clearly showing the regular
aggregation of the fibers into layers (interfiber distance = 4 nm).
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R. Ziessel et al.
mesomorphic domain by 348C. In the cases of the T12ester
and T12amide compounds, a lamellar phase containing col-
umnar aggregates was observed. Replacing the ester or
amide link by a triple bond in the T12ethynyl compound nar-
rowed the mesomorphic domain to 20.58C between 194.5
and 1748C on cooling. X-ray scattering confirmed the exis-
tence of a columnar mesophase with rectangular symmetry.
Based on the crystal structure of a model compound
(bearing methoxy groups in place of the aliphatic chains),
we suggest that the lamellar mesophase of the T12ester and
T12amide derivatives is formed by an alternated organization
of the terpy subunits stabilized by p–p stacking interactions
and hydrogen bonding reminiscent of pseudocolumns, in
which all alkyl chains are pushed to both sides of the layer.
For the more rigid molecule bearing a conjugated ethynyl
spacer, the favorable orientations of the terpy and the cen-
tral phenyl in the same plane induce a spatial arrangement
involving head-to-tail dimers, elliptical in shape. Stacking
these dimers gives rise to the formation of columns. In all
three cases, the amide functions are clearly involved in a su-
pramolecular, hydrogen-bonded network, as deduced from
infrared studies and X-ray diffraction studies on single crys-
tals of a model compound. A remarkable feature of the
T12amide derivative is the gelation of hydrocarbon solvents
and DMSO. TEM measurements and SAXS experiments
reveal that this compound is not a classical organogelator;
instead, the gel is likely formed from one-dimensional swel-
ling of a lamellar phase. Furthermore, it appears that the su-
pramolecular organization in solution is reminiscent of the
lamellar organization of the pure compounds, combining hy-
drogen bonding between the amide functions and p–p stack-
ing interactions between the aromatic moieties of the mole-
cules. FFEM experiments allow us to conclude that the
layers are formed from self-assembled fibers.
ized light optical microscopy (POM) on a Leitz microscope equipped
with a Mettler–Toledo FP80 hot-stage and an FP80 central processor. X-
ray scattering measurements were carried out with two different experi-
mental setups. In both cases, a linear monochromatic CuKa1 beam (l =
1.5405 Š) was obtained using a sealed-tube generator (900 W) equipped
with a bent monochromator. In the first set, the transmission Guinier ge-
ometry was used, whereas a Debye—Scherrer like geometry was used in
the second experimental setup. In all cases, the crude powder was filled
in Lindemann glass capillaries of 1 mm diameter and 10 mm wall thick-
ness. Small-angle X-ray scattering experiments with gel samples were per-
formed with laboratory setups described in detail below. Samples were
held in cylindrical Lindemann glass capillaries of 1 mm diameter and
10 mm wall thickness. UV/Vis spectra were recorded using a UVIKON
940/941 dual-beam grating spectrophotometer (Kontron Instruments)
with a 1 cm quartz cell. FT-IR spectra were recorded using a Perkin–
Elmer “spectrum one” spectrometer on the neat liquids or thin films, pre-
pared with a drop of dichloromethane and evaporated to dryness on KBr
pellets. The molecular-modeling calculations were performed on an SGI
Origin 200 4 CPU computer and on an SGI Octane2 workstation using
the DISCOVER 3 molecular mechanics package from Accelrys (www.ac-
celrys.com) with the pcff force field. Transmission electron microscopy
(TEM) experiments were performed with a CM12 Philips microscope on
dilute solution deposited onto a carbon-coated grid and on metallic repli-
cas of the gels obtained by the freeze-fracture technique.
T12ester: 3,5-Bis(3,4,5-tridodecyloxybenzoylamino)-4-methyl benzoic acid
(0.500 g, 0.338 mmol), dimethylaminopyridine (DMAP) (0.041 g,
0.338 mmol), and distilled CH2Cl2 (20 mL) were introduced in a Schlenk
flask under argon. After complete solubilization of the acid under stir-
ring, 1-[3-(dimethyl-amino)propyl]-3-ethylcarbodiimide hydrochloride
(EDCI, 0.065 g, 0.338 mmol) and 4’-hydroxymethyl-2,2’;6’,2’’-terpyridine
(0.089 g, 0.338 mmol) were added to the clear solution. This mixture was
stirred at room temperature overnight. After removal of the solvent, pu-
rification of the product was performed by flash chromatography on
silica gel with CH2Cl2/MeOH (99:1 to 98:2), followed by crystallization
from CH2Cl2/CH3CN, yielding 0.420 g (72%). 1H NMR (CDCl3,
200 MHz): d = 0.87 (t, 3J = 6.3 Hz, 18H; CH3), 1.27 (m, 108H; CH2),
1.76 (m, 12H; CH2), 2.14 (s, 3H; CH3), 3.93 (m, 12H; OCH2), 5.42 (s,
3
2H; OCH2), 7.09 (s, 4H; H arom.), 7.30 (m, 2H; CH), 7.82 (td, J = 7.8,
4J = 1.8 Hz, 2H; CH), 8.11 (s, 2H; CH), 8.38 (s, 2H; CH), 8.59 ppm (m,
6H; CH+NH); 13C{1H} DEPT NMR (75.47 MHz, CDCl3): d = 14.02
(CH3), 14.10 (CH3), 22.69 (CH2), 26.10 (CH2), 29.38 (CH2), 29.46 (CH2),
29.63 (CH2), 29.67 (CH2), 29.70 (CH2), 29.73 (CH2), 29.77 (CH2), 30.36
(CH2), 31.93 (CH2), 65.25 (OCH2), 69.23 (OCH2), 73.48 (OCH2), 106.01
(CH), 119.21 (CH), 121.43 (CH), 123.90 (CH), 124.37 (CH), 136.82 (CH),
148.95 (CH), 127.81 (Cq), 128.88 (Cq), 133.93 (Cq), 136.86 (Cq), 141.51
(Cq), 146.96 (Cq), 153.11 (Cq), 155.66 (Cq), 155.81 (Cq), 165.20 (C=O),
The original design and synthesis of molecules (new
amino terpyridine) together with an interplay of crystal
structure, temperature-dependent infrared studies in the
bulk samples, X-ray diffraction in the solid and liquid-crys-
talline phases, molecular modeling, organogel formation
(SAXS on gels), lyotropic properties, and electron microsco-
py (freeze-fracture and classical TEM) allow us to present
these unconventional mesomorphic compounds. The multi-
disciplinary aspect of this work will be pursued further by
complexation of the empty coordination site with transition
metals in order to endow the resulting material with inter-
esting electronic or optical properties. Work is currently in
progress along these lines.
166.31 ppm (C=O); IR (KBr): n˜
= 3437 (nNH), 3261 (nNH), 2923
(nCH), 2853 (nCH), 1728 (nCOO), 1638 (nCO), 1617 (nCO), 1584 (nC=
C, nC=N), 1519 (dNH), 1490, 1468, 1426, 1407, 1384, 1337, 1275, 1263,
1235, 1214, 1114, 1072, 1041 cmÀ1; UV/Vis (CH2Cl2, 238C): lmax (e) =
277 (73700), 252 (66800 mÀ1 cmÀ1); MS (FAB+, mNBA): m/z (%):
1725.2 (100) [M++H]; elemental analysis calcd (%) for C110H173N5O10: C
76.56, H 10.11, N 4.06; found: C 76.41, H 10.02, N 3.98.
T12amide: A Schlenk flask equipped with a septum and an argon inlet
was charged with 3,5-bis(3,4,5-tridodecyloxybenzoylamino)-4-methylben-
zoic acid (0.35 g, 1.1 equiv, 0.23 mmol) in distilled CH2Cl2 (50 mL) and di-
methylaminopyridine (DMAP, 0.06 g, 2.2 equiv, 0.47 mmol), and the mix-
ture was stirred until the acid was completely dissolved. 1-[3-(dimethyl-
amino)propyl]-3-ethylcarbodiimide
hydrochloride
(EDCI,
0.09 g,
2.2 equiv, 0.47 mmol) and 4’-aminomethyl-2,2’;6’,2’’-terpyridine (0.06 g,
1 equiv, 0.21 mmol) were added to the clear solution, which was stirred
overnight. After evaporation of the solvent, purification was performed
by flash chromatography on silica gel with CH2Cl2/MeOH (99.9:0.1 to
98:2), followed by crystallization from CH2Cl2/CH3CN to yield 0.20 g
(56%). 1H NMR (CDCl3, 300 MHz): d = 0.89 (t, 3J = 4.5 Hz, 18H;
CH3), 1.26 (m, 108H; CH2), 1.72 (m, 12H; CH2), 2.21 (s, 3H; CH3), 3.95
(m, 12H; OCH2), 4.40 (d, 3J = 3.96 Hz, 2H; CH2), 7.20 (m, 6H; H
arom.), 7.66 (td, 3J = 7.7, 4J = 1.7 Hz, 2H; CH), 7.90 (s, 2H; CH), 8.01
(s, 2H; CH), 8.26 (d, 3J = 7.9 Hz, 2H; CH), 8.49 (d, 3J = 4.3 Hz, 2H;
Experimental Section
General: The 300 and 200 (1H), and 75.47 MHz (13C) NMR spectra were
recorded at room temperature with perdeuterated solvents; residual pro-
tiated solvent signals provided internal references. Differential Scanning
Calorimetry (DSC) was performed on a Perkin–Elmer DSC-7 instrument
at a scanning rate of 10 KminÀ1. ThermoGravimetric Analyses (TGA)
were performed on an SDTQ 600 apparatus at a scanning rate of
10 KminÀ1 under argon. Phase behavior was studied by means of polar-
4272
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Chem. Eur. J. 2006, 12, 4261 – 4274

Terpyridine Liquid Crystals
FULL PAPER
CH), 8.65 ppm (s, 3H; NH); 13C{1H} DEPT NMR (75.47 MHz, CDCl3):
d = 13.69 (CH3), 14.10 (CH3), 22.69 (CH2), 26.10 (CH2), 26.16 (CH2),
29.38 (CH2), 29.47 (CH2), 29.62 (CH2), 29.66 (CH2), 29.72 (CH2), 29.75
(CH2), 30.36 (CH2), 31.93 (CH2), 69.16 (OCH2), 73.43 (OCH2), 105.94
(CH), 119.14 (CH), 121.55 (CH), 123.09 (CH), 123.97 (CH), 136.85 (CH),
148.93 (CH), 128.82 (Cq), 132.00 (Cq), 137.02 (Cq), 141.27 (Cq), 148.66
(Cq), 152.24 (Cq), 153.08 (Cq), 154.98 (Cq), 155.53 (Cq), 165.88 (C=O),
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168.02 ppm (C=O); IR (KBr): n˜
= 3437 (nNH), 3271 (nNH), 2923
(nCH), 2853(nCH), 1640 (nCO), 1584 (nC=C, nC=N), 1521 (dNH), 1494,
ACHTREUNG
1468, 1426, 1406 (nCH2), 1384, 1334, 1263, 1232, 1115 cmÀ1; UV/Vis
(CH2Cl2, 238C): lmax (e) = 277 (107700), 252 (96600 mÀ1 cmÀ1); MS
(FAB+, mNBA): m/z (%): 1724.2 (100) [M++H]; elemental analysis
calcd (%) for C110H174N6O9: C 76.61, H 10.17, N 4.87; : C 76.52, H 10.04,
N 4.75.
T12ethynyl: A Schlenk flask was charged with 2,6-bis(3,4,5-tridodecyloxy-
benzoylamino)-4-iodo-toluene (0.500 g, 0.32 mmol), 4’-ethynyl-2,2’:6’,2’’-
terpyridine (0.082 g, 0.32 mmol), [Pd(PPh3)2Cl2](0.014 g, 0.02 mmol),
N
THF (50 mL), and iPr2NH (5 mL). The mixture was thoroughly degassed
with argon. CuI (0.013 g, 0.06 mmol) was added and the mixture was stir-
red at room temperature for 24 h. The organic phase was filtered over
celite, washed with water (150 mL), and dried over MgSO4. After remov-
al of the solvent, chromatography on silica gel treated with triethylamine
(cyclohexane/CH2Cl2, gradient from 80:20 to 0:100) afforded the pure
compound (0.170 g, 32%). 1H NMR (200.1 MHz, CDCl3): d = 0.87 (m,
18H; CH3), 1.1–1.6 (m, 108H; CH2), 1.7–1.9 (m, 12H; CH2), 2.24 (s, 3H;
3
CH3), 4.02 (t, J = 6.05 Hz, 12H; OCH2), 7.13 (s, 4H), 7.32 (m, 2H), 7.67
(s, 2H), 7.84 (td, 3J = 7.7 Hz, 4J = 1.7 Hz, 2H), 8.04 (s, 2H), 8.48 (s,
2H), 8.56 (d, 3J = 7.8 Hz, 2H), 8.67 ppm (d, 3J = 4.0 Hz, 2H); 13C{1H}
DEPT NMR (75.47 MHz, CDCl3): d
= 13.5 (CH3), 14.1 (CH3), 22.7
(CH2), 26.1 (CH2), 29.4 (CH2), 29.6 (CH2), 29.7 (CH2), 30.4 (CH2), 31.9
(CH2), 69.4 (OCH2), 73.6 (OCH2), 106.0 (CH), 121.2 (CH), 122.9 (CH),
123.9 (CH), 125.6 (CH), 136.8 (CH), 149.2 (CH), 87.8 (Cq), 92.9 (Cq),
120.87 (Cq), 128.0 (Cq), 129.1 (Cq), 133.2 (Cq), 136.7 (Cq), 141.7 (Cq),
153.3 (Cq), 155.5 (Cq), 155.7 (Cq), 165.9 ppm (C=O); IR (KBr): n˜
=
3400 (nNH), 3194 (nNH), 2915, 2852, 1638 (nCO), 1607, 1583, 1517
(dNH), 1493, 1467, 1426, 1391, 1337, 1264, 1233, 1114, 1067, 1041 cmÀ1
;
UV/Vis (CH2Cl2, 238C): lmax (e) = 254 (53910), 284 (77110 mÀ1 cmÀ1);
MS (FAB+, mNBA): m/z (%): 1691.2 (100) [M++H]; elemental analysis
calcd (%) for C110H171N5O8: C 78.10, H 10.19, N 4.14; found: C 77.90, H
9.83, N 3.93.
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This work was supported by the University Louis Pasteur (ULP), the
School of Chemical Engineering (ECPM), and the CNRS. We gratefully
acknowledge Dr. Benoît Heinrich for his skilled assistance and helpful
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www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 4261 – 4274