Hydrogen bonding directed supramolecular polymerisation of oligo(phenylene-ethynylene)s: Cooperative mechanism, core symmetry effect and chiral amplification

Article abstract of DOI:10.1002/chem.201200883

The design of supramolecular motifs with tuneable stability and adjustable supramolecular polymerisation mechanisms is of crucial importance to precisely control the properties of supramolecular assemblies. This report focuses on constructing π-conjugated oligo(phenylene ethynylene) (OPE)-based one-dimensional helical supramolecular polymers that show a cooperative growth mechanism. Thus, a novel set of discotic molecules comprising a rigid OPE core, three amide groups, and peripheral solubilising wedge groups featuring C ₃ and C₂ core symmetry was designed and synthesised. All of the discotic molecules are crystalline compounds and lack a columnar mesophase in the solid state. In dilute methylcyclohexane solution, one-dimensional supramolecular polymers are formed stabilised by threefold intermolecular hydrogen bonding and π-π interactions, as evidenced by ¹H NMR measurements. Small-angle X-ray and light scattering measurements reveal significant size differences between the columnar aggregates of C₃- and C₂-symmetrical discotics, that is, the core symmetry strongly influences the nature of the supramolecular polymerisation process. Temperature-dependent CD measurements show a highly cooperative polymerisation process for the C₃-symmetrical discotics. In contrast, the self-assembly of C₂-symmetrical discotics shows a smaller enthalpy release upon aggregation and decreased cooperativity. In all cases, the peripheral stereogenic centres induce a preferred handedness in the columnar helical aggregates. Moreover, one stereogenic centre suffices to fully bias the helicity in the C₂-symmetrical discotics. Finally, chiral amplification studies with the C₃-symmetrical discotics were performed by mixing chiral and achiral discotics (sergeants-and-soldiers experiment) and discotics of opposite chirality (majority-rules experiment). The results demonstrate a very strong sergeants-and-soldiers effect and a rather weak majority-rules effect. Copyright

Full text of DOI:10.1002/chem.201200883

FULL PAPER
DOI: 10.1002/chem.201200883
Hydrogen Bonding Directed Supramolecular Polymerisation of
Oligo(Phenylene-Ethynylene)s: Cooperative Mechanism, Core Symmetry
Effect and Chiral Amplification
Feng Wang, Martijn A. J. Gillissen, Patrick J. M. Stals, Anja R. A. Palmans,* and
E. W. Meijer*[a]
Abstract: The design of supramolecular
motifs with tuneable stability and ad-
justable supramolecular polymerisation
mechanisms is of crucial importance to
precisely control the properties of su-
pramolecular assemblies. This report
focuses on constructing p-conjugated
oligo(phenylene ethynylene) (OPE)-
based one-dimensional helical supra-
molecular polymers that show a coop-
one-dimensional supramolecular poly-
mers are formed stabilised by threefold
intermolecular hydrogen bonding and
p–p interactions, as evidenced by
1H NMR measurements. Small-angle
X-ray and light scattering measure-
ments reveal significant size differences
between the columnar aggregates of
C3- and C2-symmetrical discotics, that
is, the core symmetry strongly influen-
ces the nature of the supramolecular
polymerisation process. Temperature-
dependent CD measurements show a
process for the C3-symmetrical discot-
ics. In contrast, the self-assembly of C2-
symmetrical discotics shows a smaller
enthalpy release upon aggregation and
decreased cooperativity. In all cases,
the peripheral stereogenic centres
induce a preferred handedness in the
columnar helical aggregates. Moreover,
one stereogenic centre suffices to fully
bias the helicity in the C2-symmetrical
discotics. Finally, chiral amplification
studies with the C3-symmetrical discot-
ics were performed by mixing chiral
and achiral discotics (sergeants-and-sol-
diers experiment) and discotics of op-
posite chirality (majority-rules experi-
ment). The results demonstrate a very
strong sergeants-and-soldiers effect and
a rather weak majority-rules effect.
erative growth mechanism. Thus,
a
novel set of discotic molecules compris-
ing a rigid OPE core, three amide
groups, and peripheral solubilising
wedge groups featuring C3 and C2 core
symmetry was designed and synthe-
highly
cooperative
polymerisation
Keywords: cooperative effects
·
ACHTUNGTRENNUNGsised. All of the discotic molecules are
helical structures · polymerization ·
crystalline compounds and lack a col-
umnar mesophase in the solid state. In
dilute methylcyclohexane solution,
self-assembly
chemistry
·
supramolecular
Introduction
bonding in p-conjugated systems is an especially promising
strategy, since the highly selective and directional hydrogen
bonding could increase the binding strength of p-conjugated
molecules, provide enhanced stability to the assemblies, and
position the p-conjugated molecules in a desired arrange-
ment.[2] Up to now, various types of p-conjugated systems,
such as triphenylene, tetrathiafulvalene, porphyrin, phthalo-
cyanine, oligophenylenevinylene and oligofluorene have
been incorporated successfully with hydrogen bonding
motifs,[3] which led to intriguing properties for the resulting
p-functional materials.
Over the past decades, extensive research has been devoted
to the bottom-up self-assembly of p-conjugated systems into
one-dimensional helical objects, for the development of con-
ducting materials with future applications in the fields of
sensing, imaging, and optoelectronic devices.[1] Although p-
conjugated molecules exhibit an intrinsic ability to self-as-
semble into extended structures, more precise control of the
dimensionality and helicity towards well-defined nanoarchi-
tectures is still keenly pursued. Introduction of hydrogen
Oligo(phenylene-ethynylene)s, OPEs, are another type of
rigid p-conjugated systems and have some superior proper-
ties. First, OPEs could serve as molecular wires due to their
planar conformation resulting in lower energy for the elec-
tronic transitions between the chromophores, which is
highly important for improving the performance of optoe-
lectronic devices.[4] Second, the rotational conformational
heterogeneity of the OPEs induces a unidirectional switch-
ing process, which is promising for the development of stim-
uli-responsive materials.[5] Third, the OPEs could act as pre-
cursors for a variety of metal alkynyl compounds, which
[a] Dr. F. Wang, M. A. J. Gillissen, P. J. M. Stals, Dr. A. R. A. Palmans,
Prof. Dr. E. W. Meijer
Institute for Complex Molecular Systems
Laboratory of Macromolecular and Organic Chemistry
Eindhoven University of Technology, PO Box 513
5600 MB Eindhoven (The Netherlands)
Fax : (+31)402-451-036
E-mail: A.Palmans@tue.nl
E.W.Meijer@tue.nl
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200883.
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
1
&
ÞÞ
These are not the final page numbers!

demonstrate outstanding applications in the areas of electri-
cal conductivity, gas storage and nonlinear optics.[6] In addi-
tion, OPEs have found a number of applications in the field
of chemical actuators and sensors.[7] However, comparatively
little effort has been devoted to utilizing hydrogen bonding
as a tool to program the self-assembly of OPEs into ordered
superstructures.[8] Recently, Sanchez and co-workers pre-
pared a series of OPE-based discotic compounds containing
three amide groups, the cooperative self-assembly and pro-
nounced chirality amplification of which highlight the
impact of hydrogen bonding in p-conjugated systems. It is of
paramount importance to establish p-conjugated assemblies
with a cooperative mechanism,[9] since the cooperative poly-
merisation process avoids the formation of many small
oligomers as compared to its isodesmic counterpart.
We have extensively studied the cooperative supramolec-
ular polymerisation of C3-symmetrical benzene-1,3,5-tricar-
boxamides (BTAs) into one-dimensional helical aggregates
in the past years.[10] Here we integrate the internal p-conju-
gated OPE core with the BTA structure to afford novel N-
centred C3-symmetrical discotic tris-amides 1–3 (Figure 1).
The marriage of the conjugated OPEs with amide groups re-
balances the interplay between the noncovalent p–p stack-
ing and hydrogen-bonding interactions. Hence, it raises the
question whether the introduction of different noncovalent
interactions can significantly affect the supramolecular poly-
merisation mechanism. Furthermore, we evaluate the
impact of desymmetrisation of the discotic structure on the
properties of the supramolecular polymers. Desymmetrisa-
tion, which is important for enabling future functionalisa-
tion,[11] is mainly performed in most discotics by altering the
peripheral substituents while leaving the core intact.[11a–c] We
are interested in altering the core structure of C3-symmetri-
cal discotics 1–3, since such modification would lead to a dif-
ferent molecular arrangement within the aggregates. Hence,
to evaluate the effect of reduced core symmetry on the self-
assembly properties, we designed C2-symmetrical discotic
tris-amide (S)-4 (Figure 1). Comparison with C3-symmetrical
discotics reveals the correlations among core-symmetry
effect, supramolecular mechanism and properties of the re-
sulting aggregates, which would be advantageous for estab-
lishment of structure–property relationships of such discotic
compounds. Ultimately, by combination of experimental
techniques with theoretical analysis, we aim to quantitatively
probe the contributions of the different noncovalent interac-
tions and get deeper insight into the molecular parameters
that govern supramolecular polymerisation.
Results and Discussion
Design and synthesis: The C3-symmetrical OPE-based
AHCTUNGTREGdNNUN iscotics 1–3 comprise star-shaped OPEs as the core and
three N-centred amide groups, affording p–p stacking and
hydrogen-bonding interactions, respectively. Three wedge
groups at the periphery are introduced to enhance the solu-
bility in apolar solvents. The
chiral 3,7-dimethyloctyl sub-
stituents in (S)-2 and (R)-3 are
anticipated to induce a helical
bias in the resulting supramo-
lecular assemblies, which allows
investigation of chiral amplifi-
cation by mixing achiral and
chiral discotics. On the other
hand, only one stereogenic
centre is attached at the periph-
ery of C2-symmetrical discotic
tris-amide (S)-4 in order to
avoid diastereomeric mixtures.
The synthetic route to the de-
sired discotic tris-amides 1–4 is
straightforward (Scheme 1). Re-
action of 4-iodoaniline with the
appropriate
trialkoxybenzoic
acid in the presence of N-(3-di-
methylaminopropyl)-N’-ethyl-
carbodiimide
hydrochloride
(EDC) and 4-dimethylamino-
pyridine (DMAP) yielded the
corresponding amides 5a–c,
which were further coupled
with 1,3,5-triethynylbenzene or
(S)-2,7-dimethyloctyl-3,5-di-
Figure 1. Structures of discotic tris-amides 1–4 and schematic representation of the cooperative supramolecular
polymerisation process into helical stacks.
ACHUTNGTRENNUGethyACHTUNGTRNEnNUGN ylbenzamide by utilizing a
&
2
&
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Supramolecular Polymerisation of Oligo(Phenylene-Ethynylene)s
FULL PAPER
Scheme 1. Synthesis of discotic tris-amides 1–4.
Sonogashira cross-coupling reaction to afford the four de-
sired compounds 1–4. PtBu3 was used as the ligand in the
Sonogashira reaction to overcome the steric repulsion prob-
lems exerted by the wedge group, which would significantly
decrease the yield of the reaction.[12] The proposed struc-
tures of the target compounds were confirmed by the NMR
and MALDI-TOF mass spectra (see Supporting Informa-
tion, Figures S1–S6).
symmetry on the melting behaviour of OPE-based discotics.
The morphology of the samples upon cooling from the iso-
tropic phase was further investigated by POM measure-
ments under crossed polarisers (Supporting Information,
Figure S8). All samples display birefringent, immobile tex-
tures characteristic of a crystalline state. Interestingly, linear
compound 1 exhibits a liquid-crystalline phase from 1908C
to 1968C in the first heating run in POM and DSC (Sup-
porting Information, Figure S2a). However, the transition at
1908C does not reappear in the cooling or second heating
run.
Fourier transform IR spectroscopy is a sensitive technique
to investigate the hydrogen-bonding interactions between
the neighbouring amide groups, since the formation of later-
al hydrogen bonds lowers the vibrational energy of the
amide group. In the C=O-centred OPE-based discotics stud-
ied by Sanchez and co-workers, columnar structures stabi-
lised by threefold intermolecular hydrogen bonding were as-
signed and characterised by well-defined bands at 3280 (NH
stretch), 1635 (amide I) and 1545 cmꢀ1 (amide II).[8d] The
FTIR data of discotic tris-amides 1–4 at room temperature
are summarised in Table 1 (see Supporting Informa-
tion, Figure S9 for full spectra). For C3-symmetrical
compounds 1–3, the NH stretching peak is broad-
Solid-state properties of discotic tris-amides 1–4: The ther-
mal behaviour of discotic tris-amides 1–4 was studied by dif-
ferential scanning calorimetry (DSC) and polarised optical
microscopy (POM). The thermal transitions obtained from
the second DSC heating run (Supporting Information, Fig-
ure S7) are summarised in Table 1. All discotic compounds
1–4 show a crystal-to-isotropic transition and lack a colum-
nar mesophase, quite different from previously reported
BTAs.[10c,d] When comparing compounds 1 and 4, in which
one OPE group is replaced by a branched alkylamide chain,
a significant reduction in the melting temperature from 196
to 48.18C is observed, indicative of the impact of reduced
Table 1. DSC and IR data of discotic tris-amides 1–4 in the solid state.
T [8C][a]
(DH
[kJmolꢀ1])
n(N
n(C
~
~
~
n(amide II)
Compound
ened and located at about 3280 cmꢀ1, while a split
C=O stretching band is observed at approximately
1646 and 1578 cmꢀ1 and the amide II band at about
1510 cmꢀ1. The C2-symmetrical compound (S)-4 ex-
hibits similar IR bands to 1–3, except that the NH
stretching vibration is located at a higher wavenum-
ber of 3301 cmꢀ1, suggesting weaker intermolecular
ꢀ
=
O)
[cmꢀ1
H)
[cmꢀ1
[b]
[b]
[b]
G
R
G
]
G
]
G
]
1
K 196.2 (43.4) I
K 178.6 (40.3) I
K 178.7 (41.1) I
K 48.1 (4.7) I
3279
3288
3288
3301
1646, 1578
1647, 1578
1646, 1578
1644, 1580
(S)-2
(R)-3
(S)-4
1510/1495
1509/1495
1545/1495
[a] DSC data were derived from the second heating run. [b] The IR data were ob-
tained at room temperature from the solid materials.
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
3
&
ÞÞ
These are not the final page numbers!

A. R. A. Palmans, E. W. Meijer et al.
hydrogen bonding than the C3-symmetrical analogues.
We recorded variable-temperature IR spectra of (S)-2 and
(S)-4, to investigate the effect of temperature on the hydro-
gen-bonding strength. Based on the above DSC measure-
ment, (S)-2 is a crystalline solid that melts at 1788C. The IR
spectra remain identical up to the melting point. At 2008C
the NH stretch is shifted to a higher wavenumber of
3329 cmꢀ1, and the C=O stretch at 1647 cmꢀ1 is split into
two peaks, one of which corresponds to the unbound C=O
vibration (Figure 2). Observation of similar phenomena for
Figure 3. SAXS profiles for discotic 1 (empty circles; the fitted line is for
a cylindrical form factor with R=1.82 nm and L>52 nm) and (S)-4 (grey
squares; the fitted line is for a spherical form factor with R=1.52 nm).
All measurements were performed in MCH with c=10ꢀ3 m and T=208C.
obtained at a higher concentration of 10ꢀ3 m in MCH clearly
show the difference in the scattering curves between 1 and
(S)-4 (Figure 3). The qꢀ1 slope in the scattered intensity for
1 is typical for elongated structures, whereas the q0 slope
found for (S)-4 is indicative of spherical aggregates. Figure 3
shows an excellent agreement between the data of 1 and a
fit using a cylindrical form factor with R=1.82 nm and L>
52 nm, while the data of (S)-4 fit well to a spherical form
factor with R=1.52 nm. At 10ꢀ4 m, SAXS and static light
scattering (SLS) reveal a qꢀ1 slope in the scattered light in-
tensity, confirming the presence of elongated structures for
1 also at these lower concentrations. The combined SLS and
SAXS data of the aggregates formed by 1 (Supporting Infor-
mation, Figure S12) were fitted to a cylindrical form factor
with a length on the order of hundreds of nanometres. Thus,
although both monomers form aggregates, their sizes differ
considerably.
Figure 2. Variable-temperature IR spectra of (S)-2 at 308C (grey line)
and 2008C (black line). The shaded rectangles indicate the NH (left) and
C=O (right) stretching regions, respectively.
(S)-4 (Supporting Information, Figure S10) suggests that the
hydrogen bonding is significantly weakened and disordered
for the discotic tris-amides at high temperature. Despite the
clear indications of hydrogen bonding between the amide
groups of discotic tris-amides 1–4 in the solid state, we have
no evidence for the formation of columnar structures stabi-
lised by threefold hydrogen bonding. For a similar example
in the literature, formation of 2D sheetlike assemblies from
a large p-conjugated monomer to maximize the p–p interac-
tions in the solid state was reported.[13] Unfortunately, crys-
tal structures of the OPE-based discotic tris-amides could
not be obtained to validate this hypothesis.
Self-assembly mechanism of C3-symmetrical discotic tris-
amides in solution: To get more insight into the self-assem-
bly mechanisms, we investigated the concentration-depend-
1
ent H NMR spectra of C3-symmetrical discotic 1 in CDCl3
Structural characterisation of the discotic tris-amides in solu-
tion: Since solvent molecules provide energetically favour-
ACHTUNGTRENNUNGable contact with the discotic molecules, we investigated the
solution (Figure 4). Chloroform is a solvent of medium po-
larity that limits aggregation in systems that are primarily
governed by hydrogen bonding due to its competitive hydro-
gen-bonding character. Hence, the NMR spectra were mea-
self-assembly of 1–4 in solution. The presence of hydrogen-
bonding and p–p stacking interactions in combination with
solvophobic effects could induce the discotic tris-amides 1–4
to self-assemble in elongated, columnar aggregates in solu-
tion. Therefore, laser light scattering (LLS) and small-angle
X-ray scattering (SAXS) were carried out to investigate the
morphology of the resulting supramolecular polymers.
Dynamic light scattering measurements (DLS) were per-
formed on C3-symmetrical discotic tris-amide 1 and C2-sym-
metrical discotic tris-amide (S)-4 at a concentration of
10ꢀ4 m in methylcyclohexane (MCH). While the DLS results
for 1 are indicative of elongated structures in solution (see
Supporting Information, Figure S11), the scattered light in-
tensity of (S)-4 was too low to gain size information, proba-
bly due to the small size of the aggregates. SAXS profiles
AHCTUNGTREGsNNNU ured at high concentration to strengthen the noncovalent
interactions. In the concentration regime of 0.43–43.4 mm,
the NMR spectra exhibit fast exchange between the mono-
meric and aggregated species. Upon increasing the concen-
tration, significant downfield shifts are observed for the
peaks corresponding to the amide proton, that is, hydrogen
bonding is a crucial driving force for the self-assembly proc-
ess. Moreover, slight upfield shifts of most of the peaks of
the aromatic protons suggest involvement of p–p stacking
interactions even in the polar chloroform environment.
The self-assembly behaviour was then investigated by
means of UV/Vis and CD spectroscopy at room tempera-
ture. The spectral data were measured in MCH and chloro-
form to compare the aggregation behaviour in the two dif-
&
4
&
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Supramolecular Polymerisation of Oligo(Phenylene-Ethynylene)s
FULL PAPER
(S)-3,7-dimethyloctyl group. As expected, a mirror-image
CD spectrum is observed for enantiomer (R)-3 in MCH
(Figure 5a, grey line). Interestingly, the CD spectra of our
N-centred OPE-based discotics are similar in size and shape
to those reported for the C=O-centred OPE-based
AHCTUNGTRENNUNG
discotics,[8d] but opposite in sign when keeping the configura-
tion of the stereogenic centre identical. This suggests that
the helical preference of OPE-based discotics is governed
by both the nature of the amide connectivity, which influen-
ces the conformation of the amides with respect to the p-
conjugated core, and the configuration of the stereogenic
centre. In fact, the importance of amide connectivity to heli-
cal bias was also found in simple alkyl-substituted BTAs, in
which p–p stacking interactions are close to absent.[10d]
In addition, UV/Vis spectroscopy shows that the aggregat-
ed state of (S)-2 exhibits a hypsochromic shift compared to
the molecularly dissolved state (lmax =310 nm in MCH
versus 321 nm in chloroform; Figure 5b). Such blue shift is
consistent with the formation of lateral hydrogen bonds
upon aggregation, which decreases the conjugation between
OPE and amide groups, and indicates formation of H-type
aggregates.[10a–c] Similar UV/Vis behaviour is also observed
for 1, and suggests that the achiral compound is also present
in helical stacks in MCH, but now both helicities are present
in equal amounts.
Temperature-dependent CD measurements were per-
formed on chiral compound (S)-2 in MCH. The temperature
was slowly decreased from 70 to ꢀ108C at a rate of
1 Kminꢀ1 to ensure that the cooling was under thermody-
namic control. At temperatures higher than 408C, the UV/
Vis spectra in MCH are similar to those taken in chloroform
at room temperature (Supporting Information, Figure S13),
while complete disappearence of the CD intensity (Support-
ing Information, Figure S13) reveals a molecularly dissolved
state above 408C. Upon further decreasing the temperature,
the CD effect suddenly appears and gradually increases.
Monitoring the CD intensity at l=322 nm versus the tem-
perature affords a non-sigmoidal melting curve, typical of a
cooperative self-assembly process (Figure 6). The curve
shows two regimes: one in which all molecules are molecu-
larly dissolved (indicated by the absence of a CD effect)
and an elongation regime in which the aggregate rapidly
grows. Upon cooling, at a certain (concentration-dependent)
temperature a large enough nucleus is formed to allow for-
mation of an aggregate. The effect of monomer concentra-
tion on the supramolecular polymerisation process was also
investigated. The temperature Te at which the polymerisa-
tion starts gradually increases (Figure 6) with increasing con-
centration, suggestive of earlier formation of columnar ag-
gregates at a higher monomer concentration.
1
Figure 4. Partial concentration-dependent H NMR spectra of 1 in CDCl3
at different concentrations. a) 0.43, b) 0.87, c) 1.73, d) 5.20, e) 10.4,
f) 16.3, g) 23.7, h) 32.6, and i) 43.4 mm. All measurements: T=258C.
ferent solvents. For the chiral compound (S)-2 at a concen-
tration of 8ꢁ10ꢀ6 m, no CD effect is detected in chloroform,
and this suggests that (S)-2 is molecularly dissolved at this
concentration (Figure 5a, black line). In contrast, in MCH a
bisignate Cotton effect is seen in the wavelength region be-
tween 265 and 370 nm, with a maximum at 294 nm (De=
122 Lmolꢀ1 cmꢀ1, g=1.55ꢁ10ꢀ3) and a minimum at 322 nm
(De=ꢀ184 Lmolꢀ1 cmꢀ1, g=ꢀ1.95ꢁ10ꢀ3; Figure 5a, dark
grey line). This indicates a preferred helicity in the columnar
aggregates formed by (S)-2, induced by the optically active
To obtain the thermodynamic parameters for supramolec-
ular polymerisation of (S)-2, the CD cooling curve was ana-
lysed by applying a recently developed mathematical model
for supramolecular polymerisation[10j] based on equilibria be-
tween monomers, oligomers and polymers, in which the ag-
gregation process is divided into a nucleation regime and an
elongation regime. In the nucleation regime, formation of a
Figure 5. a) CD spectra of (S)-2 (dark grey line) and (R)-3 (grey line) in
MCH at 208C. The spectrum of the molecularly dissolved state of (S)-2
in chloroform is shown as well (black line). b) UV/Vis spectra for (S)-2
in chloroform (black line) and MCH (grey line). All measurements: c=
8ꢁ10ꢀ6 m.
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
5
&
ÞÞ
These are not the final page numbers!

A. R. A. Palmans, E. W. Meijer et al.
Self-assembly mechanism of C2-symmetrical discotic tris-
amide in solution: Self-assembly of C2-symmetrical discotic
tris-amide (S)-4 was investigated with UV and CD spectro-
scopy (Supporting Information, Figure S15A,B). At room
temperature in dilute MCH solution, the bisignate Cotton
effect of (S)-4 appears in the wavelength region between
295 and 365 nm with
a minimum at 316 nm (De=
ꢀ59.0 Lmolꢀ1 cmꢀ1, g=0.73ꢁ10ꢀ3) and
a
maximum at
pro-
342 nm (De=75.5 Lmolꢀ1 cmꢀ1, g=1.95ꢁ10ꢀ3).
A
nounced red shift of around 20 nm is observed compared to
(S)-2. Interestingly, we observe opposite handedness for the
helical aggregates of (S)-4 and (S)-2, in spite of the identical
configurations of the stereogenic centres. Apparently, an
amide group positioned at the centre of the molecule has a
different directing effect than amide groups located at the
periphery.
Figure 6. Net helicity F as a function of temperature for (S)-2 in MCH
probed at l=322 nm at four different concentrations: 1.56ꢁ10ꢀ5 (black
closed squares), 1.03ꢁ10ꢀ5 (grey open squares), 8ꢁ10ꢀ6 (grey closed tri-
angles) and 5.30ꢁ10ꢀ6 m (grey open triangles). The net helicity F is de-
fined as the difference between the fraction of M- and P-type helical ag-
gregates (net helicity=([P]ꢀ[M])/([P]+[M])) and obtained by dividing
the CD effect by the maximal attainable CD effect.
Temperature-dependent CD measurements at l=342 nm
(Figure 7) display a non-sigmoidal melting curve, indicative
of a cooperative supramolecular polymerisation mechanism
for the C2-symmetrical discotics. However, in the elongation
stage, the slope of the curve is less steep than that of (S)-2.
dimer, described by the equilibrium constant K2 for dimeri-
sation, is assumed to result in a stable nucleus. In the elon-
gation regime, where additional monomers add to the grow-
ing polymer chain, all equilibrium constants K (K2 ¼K) are
assumed to be equal. As the nucleation step is highly unfav-
ourable, K2 !K. From non-linear least-squares analysis of
the experimental melting curves, the enthalpy of elongation
DHe and cooperativity factor s, defined as K2/K and a direct
measure for the cooperativity of the system, can be derived.
If s=1, polymerisation is isodesmic (all K are equal) and in-
creasingly small values of s indicate an increasingly cooper-
ative system. To improve the quality of the fit, the cooling
curves measured at different concentrations were fitted si-
multaneously. The enthalpy release DHe is around
ꢀ144 kJmolꢀ1, and s is 3.4ꢁ10ꢀ3. Interestingly, the value of
DHe is significantly more negative than that of the previous-
ly studied C=O-centred BTAs(ꢀ72 kJmolꢀ1), and demon-
strates the impact of enhanced p–p interactions on the ther-
modynamic properties of the supramolecular polymerisation
process.[10j] In addition, the s value of (S)-2 is higher than
that of C=O-centred BTA (s=4.4ꢁ10ꢀ6), and suggests
lower cooperativity in the former case.
Figure 7. Net helicity F as a function of temperature for (S)-4 in MCH
probed at l=342 nm at three different concentrations: 1.60ꢁ10ꢀ5
(black closed squares), 8ꢁ10ꢀ6 m (grey open triangles) and 4.00ꢁ10ꢀ6
m
m
(grey closed triangles). The net helicity F is defined as the difference be-
tween the fraction of M- and P-type helical aggregates ([P]ꢀ[M])/([P]+
[M])) and obtained by dividing the CD effect by the maximal attainable
CD effect.
Additionally, fitting the natural logarithm of the dimen-
sionless concentration (expressed as mole fraction of (S)-2
in MCH) versus the reciprocal of Te results in a modified
van ’t Hoff plot (Supporting Information, Figure S14) that
provides an alternative method to determine the enthalpy
associated with the aggregation process.[10b] The enthalpy
(ꢀ182 kJmolꢀ1, Table 2) obtained from the van ’t Hoff plot
further supports a considerable contribution of p–p stacking
interactions to the self-assembly process.
Since the steepness of the slope is proportional to the en-
thalpy release during aggregation, this is a direct reflection
of weaker noncovalent interactions for the C2-symmetrical
discotics. This assumption is supported by the quantitative
fitting of the normalised cooling curves (DHe =
ꢀ72 kJmolꢀ1, Figure 7) as well as the modified van ’t Hoff
plot (DHe =ꢀ86 kJmolꢀ1
; Supporting Information, Fig-
ure S14). The DHe value is similar to those of previously re-
ported BTAs[10j] and much lower than those of the
above-discussed C3-symmetrical discotics. On the
Table 2. Self-assembly thermodynamic parameters and cooperativity factor s of (S)-2
and (S)-4. The values of DG and K are given at 293 K.
other hand, the cooperativity factor s is determined
to be 3.4ꢁ10ꢀ2, which is an order of magnitude
higher than that of C3-symmetrical analogues and
implies a lower degree of cooperativity for the su-
Compound
DH
[kJmolꢀ1
DS
DG
[kJmolꢀ1
K
s[b]
[a]
[a]
[a]
[a]
G
]
[Jmolꢀ1 Kꢀ1
]
N
]
[Lmolꢀ1
ACHTUNGTERNNUNG ]
(S)-2
(S)-4
ꢀ182
ꢀ86
ꢀ437
ꢀ165
ꢀ40.1
ꢀ38.5
11.0ꢁ106
5.8ꢁ106
3.4ꢁ10ꢀ3
3.4ꢁ10ꢀ2
pramolecular polyACTHNUTRGENUGNmerisation process.
The differences in stability and cooperativity in
[a] Calculated from modified van ’t Hoff plot. [b] Derived from the equilibrium
model.
the self-assembly of C2-and C3-symmetrical discotics
&
6
&
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Supramolecular Polymerisation of Oligo(Phenylene-Ethynylene)s
FULL PAPER
is directly connected to the differences in intermolecular hy-
drogen bonds and p–p stacking interactions. While the
number of amide bonds is the same in both systems, the
strength of the hydrogen-bonding interactions presumably is
not. Previous DFT calculations on C=O-centred OPE-based
discotics showed that the molecules aggregate in helical col-
umnar stacks with adjacent molecules separated by 3.725 ꢂ
and rotated by 108.[8d] The amide groups are twisted out of
plane by around 358 to maximise the intermolecular interac-
tions. However, the requirement for optimal intermolecular
hydrogen bonding in C=O-centred BTAs are a rotation of
608 between adjacent molecules and a dihedral angle of 458
between the amide and the central benzene ring.[10d,g] Clear-
ly, reconciling the preferred orientations of both types of in-
termolecular hydrogen bond in (S)-4 results in a compro-
mise, which most likely decreases the strength of the inter-
action. In addition, the lower number of p–p stacking inter-
actions in the C2-symmetrical discotics compared to the C3-
symmetrical discotics further decreases the stability of the
formed aggregates. In fact, the association constant K calcu-
lated from the van ’t Hoff plots (Table 2) shows a twofold
reduction when the symmetry of the OPE-based discotics is
decreased. This, in combination with a lower s in (S)-4 ex-
plains the differences in aggregate size between 1 and (S)-4
observed in scattering studies.
tion of soldier 1 at a total concentration of 8.0ꢁ10ꢀ6 m, the
shape of the CD spectra remained unchanged while the in-
tensity exhibited a non-linear increase (Supporting Informa-
tion, Figure S16A,B). The net helicity versus sergeant frac-
tion shows mirror-image behaviour for 1/(S)-2 and 1/(R)-3
(Figure 8). In both cases, 5% of sergeant is enough to
AHCTUNGTREGaNNNU chieve the same CD effect as found for the pure chiral ser-
geant. This means that all helical aggregates adopt one
handedness in the presence of only 5% of sergeant. This
strong directing effect indicates that the randomly incorpo-
rated sergeant strongly biases the helical sense of the soldier
aggregates, a direct result of the high cooperativity of this
system.
Next, majority-rules experiments were performed by
mixing enantiomers (S)-2 and (R)-3 in different ratios at a
total concentration of 8.0ꢁ10ꢀ6 m (see Supporting Informa-
tion, Figure S16C for full spectra). The net helicity versus
enantiomeric excess (ee) exhibits only a small deviation
from linearity (Figure 9a). Such a weak majority-rules effect
is not surprising when one considers the chemical structures
Chiral amplification studies on C3-symmetrical discotic tris-
amides in solution: Strategies commonly used to probe
whether chiral information embedded in the molecular
structure can be transferred to achieve amplification of the
perceived supramolecular chirality in supramolecular assem-
blies are the sergeants-and-soldiers experiment and the ma-
jority-rules experiment.[14] In the sergeants-and-soldiers ex-
periment, a small amount of chiral molecules is able to dic-
tate the helical preference of aggregates predominantly
composed of achiral compounds, which lack any preference.
The majority-rules experiment refers to the ability of a
small enantiomeric imbalance to dictate the handedness of
helical aggregates.
The results of mixing of achiral 1 with (S)-2 or (R)-3 are
shown in Figure 8 (the full spectra are given in Supporting
Information, Figure S16A,B). Upon gradual addition of
small fractions of sergeant (S)-2 or (R)-3 to an MCH solu-
Figure 9. a) Net helicity F as a function of ee for scalemic mixtures of
(S)-2 and (R)-3. b) CD cooling curves of mixtures (S)-2 and (R)-3 with
ee=100, 45 and ꢀ100%.
of the monomers. The strong lateral amide hydrogen bond-
ing and OPE p–p interactions in the core, in combination
with the nine stereocentres containing methyl groups at the
periphery of the monomers, significantly reduce the likeli-
hood of mixing opposite enantiomers within one stack. In
fact, similar effects have been observed previously in BTAs
containing sterically demanding side chains[10i] and in por-
phyrin-based discotics containing 12 stereogenic centres.[3g]
Additional evidence for the lack of significant mixing be-
tween (S)-2 and (R)-3 was gathered from measuring the
cooling curves on MCH solutions of (S)-2 and (R)-3 at ee=
Figure 8. Net helicity F as a function of the sergeant fraction (S)-2 and
(R)-3 added to 1.
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
7
&
ÞÞ
These are not the final page numbers!

A. R. A. Palmans, E. W. Meijer et al.
100, 45, and ꢀ100% (Figure 9b). For the pure (S)-2 and
(R)-3, the elongation temperature Te is 36.78C. When the ee
value is reduced to 45%, the Te reduces to 29.78C. A pro-
nounced dependence of the Te on the ee was recently theo-
retically predicted for helical aggregates in which the two
enantiomers show high mismatch penalties, that is, there is a
high energy penalty for an enantiomer to reside in a helical
aggregate of its unpreferred helical sense.[10j] Thus, the 78C
difference in Te for ee=100% and ee=45% confirms poor
mixing of opposite enantiomers in one helical stack type.
to understand the subtleties involved in supramolecular
polyACTHUNRTGNEUNGmerisation processes, and benefit the future construc-
tion of more complex supramolecular aggregates. Hence,
understanding the relationship between molecular structure,
supramolecular polymerisation mechanism and microscopic
properties of supramolecular assemblies is of crucial impor-
tance for the precise control and function of supramolecular
assemblies.
Experimental Section
Conclusion
Materials: (R)-(+)-b-Citronellol and (S)-(ꢀ)-b-citronellol were purchased
from Aldrich. 3,4,5-Trialkoxybenzoic acid was prepared according to a
previously published procedure.[15] All solvents were obtained from Bio-
solve, except for spectrophotometric-grade methylcyclohexane and
chloroform (Aldrich). All other chemicals were obtained from Acros or
Aldrich. Dry dichloromethane was tapped off a distillation setup which
contained molsieves. All other chemicals were used as received.
Novel OPE-based discotic molecules featuring C3 and C2
core symhttp://unabridged.merriam-webster.com/cgi-bin/un-
abridged?va=discotic&x=0&y=0metry were designed and
synthesised to construct one-dimensional, helical, supramo-
lecular polymers. DSC and POM measurements revealed
that, in the solid state, all of the discotic compounds are
crystalline and lack a columnar mesophase. We attribute
this to the presence of the open p-conjugated OPE core,
which for reasons of space filling and maximisation of the
crystal density, does not allow formation of a columnar mes-
ophase. IR spectroscopy shows the presence of intermolecu-
lar hydrogen bonding between neighbouring molecules, but
there is no evidence for the formation of columnar struc-
tures stabilised by threefold hydrogen bonding in the solid
state.
UV-Vis and CD spectroscopy on dilute MCH solutions
demonstrate self-assembly into one-dimensional helical su-
pramolecular polymers with a preferred handedness when
peripheral chiral information is embedded in the side
chains. One stereogenic centre suffices to fully bias the hel-
icity in the C2-symmetrical discotics. Self-assembly is driven
by intermolecular hydrogen bonding and p–p interactions
between neighbouring OPEs. From the temperature-de-
pendent CD and UV/Vis measurements, the thermodynamic
parameters characterising the self-assembly of C3- and C2-
symmetric OPEs were derived. The core symmetry has a
huge impact on the polymerisation mechanism and the sta-
bility of the formed aggregates. The C2-symmetrical OPEs
show a lower enthalpy release, a smaller association con-
stant and a tenfold lower cooperativity compared to the C3-
symmetrical OPEs. The differing thermodynamic parame-
ters of the C3- and C2-symmetrical OPEs affect the sizes of
the resulting assemblies. LLS and SAXS reveal that C3-sym-
metrical OPEs form long columnar structures, while C2-sym-
metrical discotics form spherical aggregates at the same con-
centration. Chiral amplification studies on the C3-symmetri-
cal OPEs reveal a very strong sergeants-and-soldiers effect
and a rather weak majority-rules effect.
Methods: UV/Vis and CD measurements were performed on a Jasco J-
815 spectropolarimeter, for which the sensitivity, time constants and scan
rates were chosen appropriately. Corresponding temperature-dependent
measurements were performed with a PFD-425S/15 Peltier-type tempera-
ture controller with a temperature range of 263–343 K and adjustable
temperature slope; in all cases a temperature slope of 1 Kminꢀ1 was
used. In all other measurements the temperature was set at 208C. In all
experiments the linear dichroism was also measured, and in all cases no
linear dichroism was observed. Separate UV/Vis spectra were obtained
from a PerkinElmer UV/Vis spectrometer Lambda 40 at 208C. Cells with
an optical path length of 1 cm and spectroscopic-grade solvents were em-
ployed. Solutions were prepared by weighing in the necessary amount of
compound for a given concentration and transferring it to a volumetric
flask. Then the flask was three-quarters filled with the spectroscopic-
grade solvent and put in an oscillation bath at 408C for 1 h, after which
the flask was allowed to cool down and filled up to its meniscus. De=CD
effect/(32980ꢁcꢁl), in which c is the concentration in molLꢀ1 and l is the
optical path length in cm. 1H NMR and 13C NMR measurements were
conducted on a Varian Gemini 400 MHz. Proton chemical shifts are re-
ported in ppm downfield from tetramethylsilane (TMS). Carbon chemi-
cal shifts are reported relative to the resonance of CDCl3 as internal
standard. MALDI-TOF-MS were acquired on a Perserptive Bio-system
Voyager-DE PRO spectrometer. In all cases, a-cyano-4-hydroxycinnamic
acid was employed as matrix material. IR spectra were recorded on a
PerkinElmer spectrometer with universal ATR unit. Variable-tempera-
ture IR spectra were recorded on an Excalibur FTS 3000 MXFT-IR from
Biorad. Polarisation optical microscopy was performed with a Jenaval po-
larisation microscope equipped with a Linkam THMS 600 heating device
and crossed polarisers. The thermal transitions were determined by DSC
with a PerkinElmer Pyris DSC under a nitrogen atmosphere with heating
and cooling rates of 10 Kminꢀ1. LLS measurements were conducted with
an ALV/CGS-3 MD-4 compact goniometer system equipped with a mul-
tiple tau digital real time correlator (ALV-7004; solid-state laser: l=
532 nm, 40 mW). The observed
q
range was 5.5ꢁ10ꢀ3 ꢁqꢁ3.2ꢁ
10ꢀ2 nmꢀ1, where q is the magnitude of the scattering vector q=(4pnD/
l)sinACTHNUGTRENUNG(q/2), l the laser wavelength, nD is the solvent refractive index and q
the scattering angle. The liquid samples were held in 5 mm borosilicate
cells. The SAXS measurements were performed at the cSAXS-X12SA
beamline at the Paul Scherrer Institut (PSI) in Villigen (Switzerland).
SAXS images were recorded with a 2D Pilatus 2M detector with 172ꢁ
172 mm pixel size. A sample-to-detector distance of 2.17 m was used to-
gether with an X-ray photon wavelength of 1.0 ꢂ. The observed q range
was 1.8ꢁ10ꢀ1 ꢁqꢁ7.6 nmꢀ1, where q is the magnitude of the scattering
Most importantly, the self-assembly behaviour of the C3-
symmetrical OPEs discussed here differs significantly from
the OPE system recently reported by Sanchez and co-work-
ers[8d,e] and the N- and CO-centred BTAs previously report-
ed by us.[10b–d] We anticipate that the current results will help
vector q=(4p/l)sinACTHNUTRGNE(NUG q/2), l the X-ray wavelength and q the scattering
angle The 2D images were radially averaged to obtain the intensity I(q)
versus q profiles. The liquid samples were held in 2 and 1 mm quartz ca-
pillaries for 10ꢀ4 m and 10ꢀ3 m samples, respectively. Standard data reduc-
&
8
&
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Supramolecular Polymerisation of Oligo(Phenylene-Ethynylene)s
FULL PAPER
tion procedures, that is, subtraction of the contributions of the empty ca-
pillary and solvent, were applied.
90.3 (acetylene C), 87.6 (acetylene C), 71.7 (OCH2), 67.7 (OCH2), 39.4,
39.3, 37.5, 37.4, 36.4, 29.9, 29.7, 28.0, 24.7, 22.7, 22.6, 19.6; MALDI-TOF
MS: m/z 2141.60 [M+H+].
General procedure for the synthesis of amides 5: A solution of the ap-
propriate trialkoxybenzoic acid (0.70 mmol), EDC (0.16 g, 0.76 mmol)
and DMAP (0.055 g, 0.45 mmol) in dichloromethane (25 mL) was stirred
for 1 h at room temperature, and then 4-iodoaniline (0.19 g, 0.85 mmol)
was added. The reaction mixture was stirred for 24 h at room tempera-
ture, filtered, and concentrated to afford pale a yellow oil, which was
washed with water and brine and then dried on MgSO4. The solvent was
removed in vacuo and the crude product was purified by flash column
chromatography (heptane/ethyl acetate 6:1) to provide pure amides 5.
5a: White solid (0.50 g, 82%); 1H NMR (400 MHz, CDCl3, RT): d=7.68
(s, 1H; NH), 7.66 (d, 2H; ArH), 7.41 (d, 2H; ArH), 7.01 (s, 2H; ArH),
4.02 (m, 6H; OCH2), 1.82 (m, 6H; CH2), 1.47 (m, 6H; CH2), 1.20–1.38
(m, 54H; CH2), 0.88 (t, 9H; CH3); 13C NMR (400 MHz, CDCl3, RT): d=
165.8 (C=O), 153.2 (CArO), 141.5 (CArO), 137.9 (CAr), 137.8 (CArNH),
129.4 (CAr), 122.0 (CAr), 105.8 (CAr), 87.6 (CArI), 73.6 (OCH2), 69.4
(OCH2), 31.9, 30.3, 29.7, 29.4, 26.1, 22.7, 14.1; MALDI-TOF MS: m/z
875.64 [M+].
Synthesis of C2-symmetrical discotic tris-amide (S)-4: In a flame-dried
flask under an Ar atmosphere was placed CuI (4.2 mg, 22 mmol), [Pd2-
(tBu)3 (60 mL, 1 mollꢀ1 in toluene, 60 mmol),
ACHUTNRGENUN(G dba)3] (13.8 mg, 15 mmol), PHCATUNGTRENNUGN
diisopropylamine (100 mL, 0.70 mmol), 5a (250 mg, 0.28 mmol), (S)-2,7-
dimethyloctyl-3,5-diethynylbenzamide (30.0 mg, 0.1 mmol) and toluene
(7 mL). The solution was stirred overnight at room temperature and then
concentrated to afford a black oil, which was redissolved in chloroform.
The organic layer was washed with water, 2n aqueous HCl and brine and
dried on MgSO4. The solvent was removed in vacuo, and the crude prod-
uct was purified by flash column chromatography (heptane/chloroform/
acetonitrile 5:3:1) and preparative-scale recycling GPC (chloroform as
eluent) to yield (S)-4 as a pale yellow solid (68.5 mg, 38%). 1H NMR
(400 MHz, CDCl3, RT): d=7.84 (d, 2H; ArH), 7.79 (d, 1H; ArH), 7.78
(s, 2H; NH), 7.66 (d, 4H; ArH), 7.54 (d, 4H; ArH), 7.05 (s, 4H; ArH),
6.07 (t, 1H; NH), 4.04 (m, 12H; OCH2), 3.51 (m, 2H; OCH2), 1.83 (m,
12H; CH2), 1.75 (m, 2H; CH), 1.49 (m, 14H; CH2), 1.15–1.40 (m, 102H),
0.96 (d, 3H; CH3), 0.88 (t, 24H; CH3); 13C NMR (400 MHz, CDCl3, RT):
d=166.1 (C=O), 165.6 (C=O), 153.3 (CArO), 141.8 (CArO), 138.4
(CArNH), 135.5 (CAr), 132.6 (CAr), 129.6 (CAr), 129.3 (CAr), 124.3 (CAr),
119.8 (CAr), 118.4 (CAr), 110.0 (CAr), 105.9 (CAr), 90.7 (acetylene C), 87.6
(acetylene C), 73.6 (OCH2), 69.5 (OCH2), 39.2, 38.4, 37.1, 36.7, 31.9, 30.8,
30.3, 29.8, 29.7, 29.6, 29.4, 28.0, 26.1, 24.7, 22.7, 22.6, 19.6, 14.1; MALDI-
TOF MS: m/z 1805.35 [M+H+].
5b: White solid (0.42 g, 76%); 1H NMR (400 MHz, CDCl3, RT): d=7.65
(d, 2H; ArH), 7.62 (s, 1H; NH), 7.39 (d, 2H; ArH), 7.01 (s, 2H; ArH),
4.04 (m, 6H; OCH2), 1.85 (m, 3H; CH), 1.67 (m, 6H; CH2), 1.60 (m,
3H; CH), 1.07–1.35 (m, 18H; CH2), 0.90 (d, 9H; CH3), 0.84 (t, 18H;
CH3); 13C NMR (400 MHz, CDCl3, RT): d=165.6 (C=O), 153.4 (CArO),
141.6 (CArO), 138.0 (CAr), 137.9 (CArNH), 129.5 (CAr), 122.0 (CAr), 105.9
(CAr), 87.6 (CArI), 71.8 (OCH2), 67.8 (OCH2), 39.4, 39.3, 37.5, 37.3, 36.4,
29.8, 29.7, 28.0, 24.7, 22.7, 22.6, 19.6; MALDI-TOF MS: m/z 791.55
[M+].
ACHTUNGTRENNUNG
5c: White solid (0.38 g, 69%). All data are identical to those of 5b.
General procedure for the synthesis of C3-symmetrical discotic tris-
amides 1–3: CuI (4.2 mg, 22 mmol), [Pd2A(dba)3] (dba=trans,trans-dibenz-
ACHTUNGTRENNUNGylACHTUNGTRENNUNG
ideneacetone; 13.8 mg, 15 mmol), PtBu3 (60 mL, 1 mol lꢀ1 in toluene,
Acknowledgements
CTHUNGTRENNUNG
We acknowledge financial support from the European Commission
under the Seventh Framework Program by means of the grant agreement
for the Integrated Infrastructure Initiative N. 262348 European Soft
Matter Infrastructure (ESMI). We thank ESMI and the SLS for provid-
ing the beam time and we gratefully acknowledge technical assistance of
Dr. Andreas Menzel. The authors thank Dr. Tom F. A. de Greef and
Peter A. Korevaar for their valuable discussions, Rob van der Weegen for
providing starting materials and Dr. Yulan Chen for the artwork. This
work was supported by the European Research Council (ERC Advanced
Grant No. 246829), the Dutch National Research School Combination
Catalysis Controlled by Chemical Design (NRSC-Catalysis) and the
Netherlands Organisation for Scientific Research (NWO - TOP Grant:
10007851).
60 mmol), diisopropylamine (100 mL, 0.70 mmol), 5 (0.40 mmol), 1,3,5-
triethynylbenzene (15.0 mg, 0.10 mmol) and toluene (7 mL) were placed
in flame-dried flask under Ar atmosphere. The solution was stirred over-
night at room temperature and then concentrated to afford black oil,
which was redissolved in chloroform. The organic layer was washed with
water, 2n aqueous HCl and brine and dried on MgSO4. The solvent was
removed in vacuo and the crude product was purified by flash column
chromatography (heptane/chloroform/acetonitrile 5:3:1) and preparative-
scale recycling GPC (chloroform as eluent) to yield C3-symmetrical
ACHTUNGTRENNUNGdiscotic tris-amides.
1: pale yellow solid (96.0 mg, 41%); 1H NMR (400 MHz, CDCl3, RT):
d=7.78 (s, 3H; NH), 7.67 (s, 3H; ArH), 7.65 (d, 6H; ArH), 7.54 (d, 6H;
ArH), 7.04 (s, 6H; ArH), 4.04 (m, 18H; OCH2), 1.82 (m, 12H; CH2),
1.75 (m, 6H; CH2), 1.48 (m, 18H; CH2), 1.12–1.41 (m, 162H; CH2), 0.88
(t, 27H; CH3); 13C NMR (400 MHz, CDCl3, RT): d=165.6 (C=O), 153.3
(CArO), 141.6 (CArO), 138.4 (CArNH), 133.8 (CAr), 132.6 (CAr), 129.6
(CAr), 124.2 (CAr), 119.9 (CAr), 118.4 (CAr), 105.7 (CAr), 90.5 (acetylene
C), 87.7 (acetylene C), 73.6 (OCH2), 69.5 (OCH2), 31.9, 30.3, 29.7, 29.4,
26.1, 22.7, 14.1; MALDI-TOF MS: m/z 2393.82 [M+].
(S)-2: Pale yellow solid (81.5 mg, 38%); 1H NMR (400 MHz, CDCl3,
RT): d=7.77 (s, 3H; NH), 7.66 (d, 6H; ArH), 7.65 (s, 3H; ArH), 7.55 (d,
6H; ArH), 7.06 (s, 6H; ArH), 4.07 (m, 18H; OCH2), 1.88 (m, 9H; CH),
1.71 (m, 18H; CH2), 1.53 (m, 9H; CH), 1.12–1.39 (m, 54H; CH2), 0.95
(d, 27H; CH3), 0.88 (t, 54H; CH3); 13C NMR (400 MHz, CDCl3, RT): d=
165.6 (C=O), 153.5 (CArO), 141.7 (CArO), 138.3 (CArNH), 133.7 (CAr),
132.7 (CAr), 129.6 (CAr), 124.1 (CAr), 119.7 (CAr), 118.6 (CAr), 105.7 (CAr),
90.2 (acetylene C), 87.8 (acetylene C), 71.8 (OCH2), 67.8 (OCH2), 39.4,
39.3, 37.5, 37.3, 36.4, 29.9, 29.7, 28.0, 24.7, 22.7, 22.6, 19.6; MALDI-TOF
MS: m/z 2141.61 [M+H+].
[1] a) F. J. M. Hoeben, P. Jonkheijm, E. W. Meijer, A. P. H. J. Schenning,
Chem. Rev. 2005, 105, 1491–1546; b) X. Feng, V. Marcon, W. Pisula,
M. R. Hansen, J. Kirkpatrick, F. Grozema, D. Andrienko, K.
Kremer, K. Mꢃllen, Nat. Mater. 2009, 8, 421–426; c) A. Ciesielski,
C. A. Palma, M. Bonini, P. Samori, Adv. Mater. 2010, 22, 3506–3520;
d) M. Hasegawa, M. Iyoda, Chem. Soc. Rev. 2010, 39, 2420–2427.
[2] a) M. L. Bushey, T. Q. Nguyen, W. Zhang, D. Horoszewski, C. Nuck-
olls, Angew. Chem. 2004, 116, 5562–5570; Angew. Chem. Int. Ed.
2004, 43, 5446–5453; b) D. Gonzꢄlez-Rodrꢅguez, A. P. H. J. Schen-
ning, Chem. Mater. 2011, 23, 310–325.
[3] a) T. Kitahara, M. Shirakawa, S. Kawano, U. Beginn, N. Fujita, S.
Shinkai, J. Am. Chem. Soc. 2005, 127, 14980–14981; b) J. Puigmartꢅ-
Luis, A. Perez del Pino, E. Laukhina, J. Esquena, V. Laukhin, C.
Rovira, J. Vidal-Gancedo, A. G. Kanaras, R. J. Nichols, M. Brust,
D. B. Amabilino, Angew. Chem. 2008, 120, 1887–1891; Angew.
Chem. Int. Ed. 2008, 47, 1861–1865; c) S. Yagai, S. Kubota, T. Iwa-
shima, K. Kishikawa, T. Nakanishi, T. Karatsu, A. Kitamura, Chem.
Eur. J. 2008, 14, 5246–5257; d) R. Abbel, R. van der Weegen, W.
Pisula, M. Surin, Ph. Leclꢆre, E. W. Meijer, A. P. H. J. Schenning,
Chem. Eur. J. 2009, 15, 9737–9746; e) N. Kumaran, P. A. Veneman,
B. A. Minch, A. Mudalige, J. E. Pemberton, D. F. OꢇBrien, N. R.
Armstrong, Chem. Mater. 2010, 22, 2491–2501; f) F. Helmich, C. C.
(R)-3: Pale yellow solid (75.0 mg, 35%); 1H NMR (400 MHz, CDCl3,
RT): d=7.75 (s, 3H; NH), 7.68 (d, 6H; ArH), 7.65 (s, 3H; ArH), 7.55 (d,
6H; ArH), 7.06 (s, 6H; ArH), 4.08 (m, 18H; OCH2), 1.87 (m, 9H; CH),
1.72 (m, 18H; CH2), 1.53 (m, 9H; CH), 1.13–1.37 (m, 54H; CH2), 0.95
(d, 27H; CH3), 0.87 (t, 54H; CH3); 13C NMR (400 MHz, CDCl3, RT): d=
165.5 (C=O), 153.6 (CArO), 141.6 (CArO), 138.0 (CArNH), 133.7 (CAr),
132.7 (CAr), 129.5 (CAr), 124.1 (CAr), 119.7 (CAr), 118.7 (CAr), 106.2 (CAr),
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
9
&
ÞÞ
These are not the final page numbers!

A. R. A. Palmans, E. W. Meijer et al.
Lee, M. M. L. Nieuwenhuizen, J. C. Gielen, P. C. M. Christianen, A.
Larsen, G. Fytas, Ph. Leclꢆre, A. P. H. J. Schenning, E. W. Meijer,
Angew. Chem. 2010, 122, 4031–4034; Angew. Chem. Int. Ed. 2010,
49, 3939–3942; g) F. Helmich, M. M. J. Smulders, C. C. Lee,
A. P. H. J. Schenning, E. W. Meijer, J. Am. Chem. Soc. 2011, 133,
12238–12246.
[10] a) L. Brunsveld, A. P. H. J. Schenning, M. A. C. Broeren, H. M. Jans-
sen, J. A. J. M. Vekemans, E. W. Meijer, Chem. Lett. 2000, 292–293;
b) M. M. J. Smulders, A. P. H. J. Schenning, E. W. Meijer, J. Am.
Chem. Soc. 2008, 130, 606–611; c) P. J. M. Stals, M. M. J. Smulders,
R. Martin-Rapun, A. R. A. Palmans, E. W. Meijer, Chem. Eur. J.
2009, 15, 2071–2080; d) P. J. M. Stals, J. C. Everts, R. de Bruijn,
I. A. W. Filot, M. M. J. Smulders, R. Martin-Rapun, E. A. Pidko,
T. F. A. de Greef, A. R. A. Palmans, E. W. Meijer, Chem. Eur. J.
2010, 16, 810–821; e) M. M. J. Smulders, I. A. W. Filot, J. M. A.
Leenders, P. van der Schoot, A. R. A. Palmans, A. P. H. J. Schenning,
E. W. Meijer, J. Am. Chem. Soc. 2010, 132, 611–619; f) M. M. J.
Smulders, P. J. M. Stals, T. Mes, T. F. E. Paffen, A. P. H. J. Schenning,
A. R. A. Palmans, E. W. Meijer, J. Am. Chem. Soc. 2010, 132, 620–
626; g) I. A. W. Filot, E. A. Pidko, A. R. A. Palmans, E. W. Meijer,
R. A. van Santen, T. F. A. de Greef, J. Phys. Chem. A J. Phys. Chem.
B. 2010, 114, 13667–13674; h) S. Cantekin, D. W. R. Balkenende,
M. M. J. Smulders, A. R. A. Palmans, E. W. Meijer, Nat. Chem.
2011, 3, 42–46; i) M. A. J. Veld, D. Haveman, A. R. A. Palmans,
E. W. Meijer, Soft Matter 2011, 7, 524–531; j) A. J. Markvoort,
H. M. M. ten Eikelder, P. A. J. Hilbers, T. F. A. de Greef, E. W.
Meijer, Nat. Commun. 2011, 2, 509.
[11] a) J. A. Rego, S. Kumar, I. J. Dmochowski, H. Ringsdorf, Chem.
Commun. 1996, 1031–1032; b) E. J. Foster, J. Babuin, N. Nguyen,
V. E. Williams, Chem. Commun. 2004, 2052–2053; c) X. Feng, W.
Pisula, T. Kudernac, D. Wu, L. Zhi, S. De Feyter, K. Mullen, J. Am.
Chem. Soc. 2009, 131, 4439–4448; d) M. A. J. Gillissen, T. T.
Hoeben, A. J. H. Spiering, J. A. J. M. Vekemans, A. R. A. Palmans,
E. W. Meijer, Isr. J. Chem. 2011, 51, 1118–1127.
[12] A. Soheili, J. Albaneze-Walker, J. A. Murry, P. G. Dormer, D. L.
Hughes, Org. Lett. 2003, 5, 4191–4194.
[13] L. Chen, J. Kim, T. Ishizuka, Y. Honsho, A. Saeki, S. Seki, H. Ihee,
D. Jiang, J. Am. Chem. Soc. 2009, 131, 7287–7292.
[4] a) Y. Yamaguchi, S. Kobayashi, T. Wakamiya, Y. Matsubara, Z.
Yoshida, Angew. Chem. 2005, 117, 7202–7206; Angew. Chem. Int.
Ed. 2005, 44, 7040–7044; b) Y. Yamaguchi, T. Ochi, S. Miyamura, T.
Tanaka, S. Kobayashi, T. Wakamiya, Y. Matsubara, Z. Yoshida, J.
Am. Chem. Soc. 2006, 128, 4504–4505; c) Y. Yamaguchi, Y. Matsu-
bara, T. Ochi, T. Wakamiya, Z. Yoshida, J. Am. Chem. Soc. 2008,
130, 13867–13869; d) R. M. Adhikari, L. Duan, L. Hou, Y. Qiu,
D. C. Neckers, B. K. Shah, Chem. Mater. 2009, 21, 4638–4644.
[5] S. Hçger, D. L. Morrison, V. Enkelmann, J. Am. Chem. Soc. 2002,
124, 6734–6736.
[6] a) T. L. Schull, J. G. Kushmerick, C. H. Patterson, C. George, M. H.
Moore, S. K. Pollack, R. Shashidhar, J. Am. Chem. Soc. 2003, 125,
3202–3203; b) M. P. Cifuentes, C. E. Powell, J. P. Morrall, A. M.
McDonagh, N. T. Lucas, M. G. Humphrey, M. Samoc, S. Houbrechts,
I. Asselberghs, K. Clays, A. Persoons, T. Isoshima, J. Am. Chem.
Soc. 2006, 128, 10819–10832; c) G. J. Zhou, W. Y. Wong, Chem. Soc.
Rev. 2011, 40, 2541–2566; d) K. A. Green, M. P. Cifuentes, M.
Samoc, M. G. Humphrey, Coord. Chem. Rev. 2011, 255, 2025–2038.
[7] U. H. F. Bunz, Macromol. Rapid Commun. 2009, 30, 772–805.
[8] a) A. Ajayaghosh, R. Varghese, S. Mahesh, V. K. Praveen, Angew.
Chem. 2006, 118, 7893–7896; Angew. Chem. Int. Ed. 2006, 45, 7729–
7732; b) K. Sakajiri, T. Sugisaki, K. Moriya, Chem. Commun. 2008,
3447–3449; c) S. Diring, F. Camerel, B. Donnio, T. Dintzer, S. Toffa-
nin, R. Capelli, M. Muccini, R. Ziessel, J. Am. Chem. Soc. 2009, 131,
18177–18185; d) F. Garcia, P. M. Viruela, E. Matesanz, E. Orti, L.
Sanchez, Chem. Eur. J. 2011, 17, 7755–7759; e) F. Garcia, L. San-
chez, J. Am. Chem. Soc. 2012, 134, 734–742.
[14] A. R. A. Palmans, E. W. Meijer, Angew. Chem. 2007, 119, 9106–
9126; Angew. Chem. Int. Ed. 2007, 46, 8948–8968.
[15] S. Ghosh, X. Q. Li, V. Stepanenko, F. Wurthner, Chem. Eur. J. 2008,
14, 11343–11357.
[9] a) D. Zhao, J. S. Moore, Org. Biomol. Chem. 2003, 1, 3471–3491;
b) R. F. Service, Science 2005, 309, 95; c) A. P. H. J. Schenning, E. W.
Meijer, Chem. Commun. 2005, 3245–3258; d) Z. Chen, A. Lohr,
C. R. Saha-MÅller, F. Wurthner, Chem. Soc. Rev. 2009, 38, 564–584;
e) T. F. A. de Greef, M. J. M. Smulders, M. Wolffs, A. P. H. J. Schen-
ning, R. P. Sijbesma, E. W. Meijer, Chem. Rev. 2009, 109, 5687–
5754.
Received: March 15, 2012
Revised: May 11, 2012
Published online: && &&, 0000
&
10
&
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Supramolecular Polymerisation of Oligo(Phenylene-Ethynylene)s
FULL PAPER
Helical supramolecular polymers: Dis-
cotic compounds with C3 or C2 core
symmetry were designed and synthes-
ised to construct oligo(phenylene-ethy-
nylene)-based one-dimensional helical
supramolecular polymers. A remarka-
ble influence of core symmetry on the
thermodynamic parameters of the
Supramolecular Chemistry
F. Wang, M. A. J. Gillissen,
P. J. M. Stals, A. R. A. Palmans,*
E. W. Meijer* ................. &&&& — &&&&
Hydrogen Bonding Directed Supramo-
lecular Polymerisation of Oligo(Phen-
ylene-Ethynylene)s: Cooperative
Mechanism, Core Symmetry Effect
and Chiral Amplification
supramolecular polymerisation process
is demonstrated, which affects the size
of the resulting aggregates (see figure).
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
11
&
ÞÞ
These are not the final page numbers!