Guiding suprastructure chirality of an oligothiophene by a single amino Acid

Article abstract of DOI:10.1021/cm4020767

Within the present work, synthesis and properties of three stereoisomeric hybrid materials consisting of a π-conjugated oligothiophene backbone and a single amino acid (proline), which is attached by click chemistry, are described. The hybrids were in particular investigated regarding their self-assembling behavior in solution. From optical investigations, including circular dichroism spectroscopy, the formation of chiral suprastructures could be deduced and correlated with the stereochemistry of the proline residue. In addition, an elaborate theoretical model of the compounds' self-assembly into suprastructures was developed on the basis of the experimental findings.

Full text of DOI:10.1021/cm4020767

Article
pubs.acs.org/cm
Guiding Suprastructure Chirality of an Oligothiophene by a Single
Amino Acid
Eva-Kathrin Schillinger,†,§ Michael Kumin,‡,∥ Angela Digennaro,† Elena Mena-Osteritz,† Sylvia Schmid,†
̈
Helma Wennemers,‡ and Peter Bauerle*,†
̈
†Institut fur Organische Chemie II und Neue Materialien, Universitat Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
̈
̈
‡Laboratory of Organic Chemistry, D-CHAB, ETH Zurich, Wolfgang Pauli Strasse 10, CH-8093 Zurich, Switzerland
̈
̈
S
* Supporting Information
ABSTRACT: Within the present work, synthesis and properties of three stereoisomeric hybrid materials consisting of a π-
conjugated oligothiophene backbone and a single amino acid (proline), which is attached by click chemistry, are described. The
hybrids were in particular investigated regarding their self-assembling behavior in solution. From optical investigations, including
circular dichroism spectroscopy, the formation of chiral suprastructures could be deduced and correlated with the
stereochemistry of the proline residue. In addition, an elaborate theoretical model of the compounds’ self-assembly into
suprastructures was developed on the basis of the experimental findings.
KEYWORDS: oligothiophene, proline, self-assembly, circular dichroism spectroscopy, atomic force microscopy
Three “bioinspired” oligothiophene−amino acid hybrids with
(2R,4R)-, (2S,4S)-, or (2S,4R)-configuration of the proline
residue were prepared and the consequences of the stereo-
chemistry on the self-assembling properties investigated.
INTRODUCTION
■
As one of the most promising classes of semiconducting π-
conjugated materials, oligo- and polythiophenes have attracted
considerable interest during the last years.1 Regarding their
application in nanoelectronic devices, the highly ordered
organization of π-conjugated compounds on a surface and in
the bulk has been shown to be of crucial importance.2,3
Numerous reports on well-ordered, self-assembled supra-
structures of oligo- and polythiophenes have appeared over
the past decade,4−8 some of them also concerning inherently
chiral systems,9−18 e.g., polythiophenes with amino acid
functionalized side chains16 or oligothiophenes equipped with
chiral oligo(ethylene oxide) chains.12 An intriguing strategy to
guide self-assembly of π-conjugated compounds is the attach-
ment of biological moieties (e.g., peptides, nucleic acids, or
sugars) known to have distinct modes of supramolecular
interaction at their disposal.19−21 Especially peptides have
proven to be promising candidates for the self-assembly of
structurally well-defined oligothiophenes.22−32 In an extension
of our work on peptide-guided self-assembly,33,34 we here
present the synthesis, characterization, and self-assembling
properties of quaterthiophenes decorated with only a single
triazolylproline as an amino acid containing two stereocenters.
RESULTS AND DISCUSSION
■
Synthesis. As a π-conjugated moiety, symmetrically
dodecyl-substituted quaterthiophene 1 (Scheme 1) was chosen,
which had previously been shown to organize into highly
regular superstructures at the liquid−solid interface4,6,8 and in
the bulk.6 To this segment, 4-azidoproline35,36 was attached via
Cu(I)-catalyzed azide−alkyne cycloaddition (the “click” re-
action).37,38 The choice of the amino acid azidoproline was
made on the basis of the fact that this amino acid is easily
accessible and functionalizable and adopts distinctly different
conformations depending on the relative configuration of the
two stereogenic centers.35 In addition, the higher homologues
of proline, oligo-, and polyprolines are known to adopt two
Received: June 26, 2013
Revised: October 17, 2013
Published: October 18, 2013
© 2013 American Chemical Society
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a
Scheme 1. Synthesis of Stereoisomeric Quaterthiophene−Amino Acid Hybrids 8−10
a
(a) POCl3, DMF, C2H4Cl2, reflux, 3 h; (b) K2CO3, MeOH/THF, rt, overnight; (c) [Cu(I)[CH3CN]4]PF6, Cu0, DCM, rt, overnight; (d)
[Cu(I)[CH3CN]4]PF6, Cu0, DCM, rt, overnight; (e) LiOH·H2O, 40 °C, 2.5 h.
different well-defined solvent-dependent helical conformations,
making them interesting objects for future research in this
field.39−46 The synthesis started from didodecyl-substituted
quaterthiophene 1, which was converted into the correspond-
ing monoaldehyde 2 under Vilsmeier−Haack reaction con-
ditions in 63% yield (Scheme 1).
Table 1. UV−Vis, Fluorescence, and Redox Data for
Compounds 8−10
absorption
λmax2
emission
redox
λmax1
ε2
E°
a
a
a
b
oxc1
OT−proline (nm)
(nm)
(L·mol−1·cm−1
)
λmax (nm)
(V)
Subsequent Ohira−Bestman reaction47,48 of aldehyde 2
yielded monoethynylated quaterthiophene 3 in 90% yield.
Freshly prepared, 3 was further reacted with the Boc-protected
(2S,4R)-azidoproline methyl ester 4 using Cu(I)-catalyzed 1,3-
dipolar cycloaddition (click reaction)37,38 to yield fully
protected quaterthiophene−amino acid hybrid 7 in 86%.
Saponification of 7 gave hybrid 10 with free carboxylic acid
functionality and a Boc-protected amino function in 74% yield.
For hitherto unknown reasons, the same synthetic route was
not viable for enantiomeric pair 8 (S,S) and 9 (R,R).
Saponification of the corresponding fully protected hybrids of
8 and 9 led to a partial epimerization at the stereocenter at C4
of the proline ring. The epimerization could not be hindered by
employing different bases and reaction temperatures either.
Monoethynylated quaterthiophene 3 was therefore reacted with
Boc-protected azidoprolines 5 and 6 under Cu(I)-catalyzed
azide−alkyne cycloaddition conditions. (2S,4S)-Hybrid 8 was
obtained in 82% yield and the enantiomeric (2R,4R)-hybrid 9
in 92% yield.
8
257
258
257
389
35300
33200
33500
468, 499,
541
0.42
0.42
0.42
9
388
390
468, 498,
541
10
468, 499,
541
a
b
Measured in n-propanol, c ≈ 7 × 10−5 mol/L. Measured in n-
c
propanol, c ≈ 2 × 10−6 mol/L, excitation at λ = 410 nm. Measured in
dichloromethane (c = 1.0 × 10−3 mol/L) /TBAHFP (0.1 mol/L at
100 mV/s) vs Fc/Fc+. Quasi-reversible redox process, E° determined
51
at I° = 0.855 Ip.
enantiomeric pair 8 and 9, small waves around E = 0.25 V vs
Fc/Fc+ became visible, indicating the formation of oligomers
due to the freely reactive α-position at the oligothiophene
residues. Remarkably, the reversibility of the oxidation is much
more distinct for (2S,4R)-hybrid 10 than for the enantiomers 8
and 9 (Figure 1). This behavior had previously been observed
for the corresponding fully protected amino acid−quaterthio-
phene hybrids as well. Because the only difference between the
pair 8/9 and diastereomer 10 is the stereochemistry at the
amino acid moiety, there must be influence of the spatial
arrangement of the substituents on the amino acid with respect
to the electrode surface. Furthermore, we cannot exclude a
distinct aggregation behavior, which might influence the
reversibility of the redox processes in the hybrids. Similar
phenomena have been reported by Kraatz and co-workers,49,50
who described the electrochemical behavior of ferrocenes
substituted with different numbers of proline residues. The
authors arrive at the conclusion that the redox properties of the
ferrocenyl moiety are sensitive to structural peculiarities of the
Electrochemical Properties. The proline−oligothiophene
hybrids 8−10 were investigated with respect to their oxidation
behavior with cyclic voltammetry (CV). Measurements were
carried out in dichloromethane with tetrabutylammonium
hexafluorophosphate (TBAHFP, 0.1 mol/L) as electrolyte at
a scan speed of 100 mV/s. Typical first quasi-reversible
oxidation waves were found at E° = 0.42 V vs ferrocene/
ferrocenium (Fc/Fc+) for all three compounds, indicating the
formation of stable radical cations (Table 1). Second quasi-
reversible oxidations indicative of stable radical dications were
observed at E° = 0.66 V. In the second scan, for the
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Figure 1. Cyclic voltammogram of (2S,4R)-hybrid 10 (dotted line)
compared to (2S,4S)-derivative 8 (solid line) in dichloromethane/
TBAHFP (0.1 mol/L at 100 mV/s) vs Fc/Fc+.
Figure 2. Circular dichroism spectra of (2S,4S)-compound 8 (red),
(2R,4R)-compound 9 (green), (2S,4R)-hybrid 10 (blue), and a 1:1
mixture of 8 and 9 (orange). All measurements were at c ≈ 7 × 10−5
mol/L in 5% n-propanol/water, except for the 1:1 mixture of 8 and 9
with c ≈ 3.5 × 10‑5 mol/L each in 5% n-propanol/water.
amino acids/peptides engaged. Theoretical studies on model
systems in their case suggested that a spatial anisotropy of the
electron distribution in the molecule is created by the
directional character of an oxygen p-orbital perpendicular to
the cyclopentadiene/amide plane. This, in turn, might also be
responsible for the observed electronic effect in our case.
Optical Properties. Absorption and emission properties of
hybrids 8−10 were investigated in n-propanol. Absorption
spectra showed a main absorption band at λmax = 388−390 nm
caused by the π−π* transition along the long axis of the
conjugated backbone. An additional absorption maximum is
found at λmax ≈ 257−258 nm, which is attributed to the
excitation of the oligothiophene perpendicular to its conjugated
backbone. Emission maxima are located at λmax = 468 and 499
nm with an additional shoulder at λ = 541 nm (Table 1).
Self-Assembly in SolutionCD, UV−vis, Fluores-
cence, and DLS Investigations. For the investigation of
the self-assembly behavior of proline−quaterthiophene hybrids
8−10 in solution, different solvent mixtures of n-propanol and
water were investigated. Mixtures of these two solvents had
been shown in previous investigations of similar compounds to
be suitable media.52 A 1:1 mixture of n-propanol and water did
not lead to any signal in circular dichroism (CD) spectroscopy
for any of the examined conjugates, indicating the absence of
chiral supramolecular aggregates. Upon increasing the water
content, though, a bisignate Cotton effect for both 8 and 9
appeared in CD spectra, which reached its maximum of
intensity in a mixture of 5% n-propanol in water (Figure 2).
As expected for the enantiomers 8 (Figure 2, red curve) and
9 (Figure 2, green curve), mirror-image CD spectra were
observed. (2S,4S)-Hybrid 8 showed an intense, exciton-coupled
signal with negative first and positive second Cotton effects at
427 and 368 nm, which is indicative of aggregates of π−π
interacting conjugated backbones in a left-handed helical
arrangement.41 The correlation between the zero-crossing of
the bisignated bands (λ =392 nm) and the absorption
maximum of the compound in the solvent mixture (λ = 389
nm) evidences the exciton-coupled character of the transition.
Accordingly, (2R,4R)-enantiomer 9 showed a positive couplet
(426 nm, +14 mdeg; 364 nm, −10 mdeg) corresponding to a
right-handed helical arrangement of the aromatic systems.53
Here, the zero-crossing corresponds exactly to the absorption
maximum of the compound in the solvent mixture, located at λ
= 388 nm. CD spectra for both derivatives showed a second set
of very weak bisignate CD signals in the region of λ = 240−290
nm associated with the perpendicular excitation of the
quaterthiophene part and the triazole absorption. Finally,
mirror-image signals for hybrids 8 and 9 appear at 204 nm
(negative and positive Cotton effect, respectively). Interest-
ingly, the diastereomeric (2S,4R)-compound 10 showed a silent
CD spectrum, which accounts for the lack of chirality in the
formed aggregates. Within a racemic 1:1 mixture of 8 and 9, the
strong bisignated signal vanished almost completely (Figure 2,
orange curve).
In UV−vis and fluorescence spectroscopy, aggregation of all
three compounds 8−10 in 5% n-propanol in water was
observed. In absorption spectroscopy, this becomes evident
when comparing the shapes of the absorption bands of 8 in
pure n-propanol and in the 5% n-propanol/water mixture
(Figure 3, left).
The absorption band is desymmetrized in 5% n-propanol/
water compared to pure n-propanol, showing a broader
absorption at low energies (Figure 3, left). For all compounds
a considerable quenching of the fluorescence occurred in the
aqueous solution, accompanied by a red-shift of about 22 nm of
the weakened emission bands (Figure 3, right). For the
diastereomeric counterpart 10, the quenching was even
stronger than for 8 and 9 and resulted in a complete loss of
the fine structure of the emission band (not shown). Whereas
the bathochromic shifts of the emission maxima in 5% n-
propanol/water compared to pure n-propanol might be
attributable to the increase in solvent polarity,54−56 the strong
quenching of the fluorescence for the enantiomeric pair 8 and 9
and diastereomer 10 are likely caused by the aggregate
formation.
The aggregate formation in 5% n-propanol/water solution (c
≈ 7 × 10−5 M) of all three oligothiophene amino acid hybrids
8−10 was proven to exit by dynamic light scattering (DLS)
with an average hydrodynamic diameter of approximately 80−
90 nm at 20 °C. The different stereochemistry in the amino
acid residue resulted in differences in their supramolecular
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Figure 3. Absorption (left) and emission spectra (right) of (2S,4S)-hybrid 8: solid lines, c ≈ 7 × 10−5 mol/L in n-propanol; dashed lines, c ≈ 7 ×
10−5 mol/L in 5% n-propanol/water. Emission spectra: excitation at λ = 410 nm.
Figure 4. Temperature-dependent absorption spectra of (2S,4S)-compound 8 ranging from 10 to 90 °C, c ≈ 3.5 × 10−5 mol/L in 5% n-propanol/
water (left) and temperature-dependent DLS measurements (right).
Figure 5. Temperature-dependent CD spectra of (2S,4S)-compound 8 ranging from 10 to 90 °C, c ≈ 7 × 10−5 mol/L in 5% n-propanol/water (left).
Temperature dependence of the intensity of the CD maxima (black at 428 nm and red at 365 nm) (right).
organization, i.e., leading to nonordered aggregates in the case
of 10 and chiral ones in case of 8 and 9 (Figure 2).
In order to further investigate the stability and nature of the
observed aggregates, temperature-dependent CD, UV−vis, and
DLS investigations were carried out. Aggregates formed by all
three hybrids were found to be stable even at 90 °C. The
temperature-dependent UV−vis spectra showed a gradual
decrease in absorption intensity accompanied by a continuous
shift of the absorption maximum to shorter wavelengths by
increasing temperature (Δλmax(10−90 °C) = 5−6 nm, Figure 4,
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Figure 6. Cation-dependent CD (left) and absorption spectra (right) of (2S,4S)-compound 8, c ≈ 7 × 10−5 mol/L in 5% n-propanol/different salt
solutions: water (red curve) and 15 mM aqueous solutions of lithium chloride (green), sodium chloride (blue), potassium chloride (cyan), cesium
chloride (pink), and tetrabutylammonium chloride (gray).
Figure 7. AFM micrographs of superstructures of 8 on mica substrates. (a) Topography image (2.3 × 2.3 μm). Inset: Detail of the squared area
showing a helical fiber bundle (0.77 × 0.3 μm). (b) Amplitude image (2.3 × 2.3 μm). Inset: Detail of a single helical fiber (0.4 × 0.27 μm).
left). Upon quickly cooling the sample from 90 °C to the
starting temperature of 10 °C, the initially obtained absorption
spectrum could be recovered. In addition, DLS measurements
showed that the average hydrodynamic diameter of the
aggregates for all three compounds 8−10 decreases roughly
by 35 nm when gradually going from 10 to 90 °C (Figure 4,
right).
Temperature-dependent CD spectroscopic experiments for
the enantiomeric pair 8 and 9 showed a decrease of the
magnitude of the bisignate signal when varying the temperature
in steps of 10 °C between 10 and 90 °C (Figure 5, left for 8).
When cooling down to 10 °C again after measurement at 90
°C, the initial spectrum was re-established. The intensity of the
CD spectra correlates linearly with temperature. However, the
two contributions of the bisignated part of the spectra behave
differently (Figure 5). The lower energy CD signal for (2S,4S)-
compound 8 [negative (−) Davydov-splitted part] decreases
faster with an increase in temperature than the high-energy
band [positive (+) Davydov-splitted part]. Furthermore, the
part of the bisignate CD signal at higher energies seems to
reach a limit at 70 °C, the intensity of the signal remaining
constant upon further temperature increments. Finally, at 90
°C an almost pure ( equilibrated) exciton-coupled signal was
observed for 8. The zero-crossing is slighted red-shifted with
increasing temperature. Keeping in mind the dimensionality of
the aggregates in space, the behavior of the CD spectra at low
energies indicates the existence of two interacting components.
One component is of bisignate character and originates from
exciton coupling of stacks of the π-conjugated backbones,
which results in Davydov-splitted contributions (negative at
lower energies and positive at higher ones in the case of 8). The
other component appeared at higher wavelengths (>440 nm in
Figure 3, left) and is attributable to nonexcitonic interactions of
the oligothiophenes in the aggregate (vide infra, discussion of
model).57 The latter can explain the differences in intensity and
temperature behavior of the lower energy CD band versus the
pure positive Davydov component (Figure 5, right). Upon
increasing the temperature the size of the aggregates diminishes
and the contribution of the CD-effect resulting from the
nonexcitonic interaction decreases more strongly than the
Davydov components. Finally, at high temperatures, a nearly
symmetrical bisignate signal, caused by small aggregates
undergoing almost pure exciton coupling of the oligothiophene
backbones, is obtained.
Upon substitution of the aqueous fraction of the 5% n-
propanol/water solvent mixture by buffer solutions with varying
pH, the samples behaved differently. With respect to the
solution containing buffer pH 7.2, the Cotton effect observed
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Figure 8. Calculated energy minimum conformation of hybrid 8. The colored planes highlight the oligothiophene backbone (purple) and the almost
perpendicular H-bond plane located on the carboxylic acid (red).
was similar to the one obtained in the standard mixture of 5%
n-propanol in water. In contrast, the mixture containing buffer
with pH 2, the solution turned turbid immediately after
preparation and no bisignate signal was observed under the
same conditions (data not shown). With time, a precipitate was
observed in a supernatant clear solution, which can be
explained by the very low solubility in aqueous media of 8−
10 in their protonated state. Thus, at pH 7.2, similar to pure
water, acids 8−10 have to be considered to be predominantly
present in their deprotonated anionic form. If this is the case,
the nature and size of the respective countercations has to play
a role for suprastructure formation and the resulting
observations in CD and UV−vis spectroscopy (Figure 6).
Compared to the pure demineralized water as cosolvent (red
curve), the bisignate CD signals resemble each other with only
subtle differences concerning intensity for all salt solutions,
semiempirical calculations with the INDO Austin Model 1
(from the Hypercube package). First, the energy minimum
conformation of hybrid 8 as representative molecule in the gas
phase was calculated. From up to 11 molecular conformations
calculated, the two most stable ones were selected for further
computation of the suprastructure. In these conformations, the
individual thiophenes of the quaterthiophene backbones
arrange in an all-trans fashion. The alkyl chains are completely
extended and coplanar to the delocalized π-system. The
molecular dimensions were calculated to be 2.6 nm along the
short axis of the molecule, 3.6 nm along the long axis of the
molecule, and 0.5 nm in height (Figure 8 and 9).
On the basis of the energy-minimized conformations
obtained, intermolecular interactions of single molecules of 8
were computed for the construction of a model of the self-
assembled superstructures. The theoretical models for the
aggregates were computed to guarantee that all forces and
dipole moments are in balance. The model shown in Figure 9
corresponds to the most densely packed and highly ordered
arrangement of an aggregate of (2S,4S)-derivative 8. No
stabilization was obtained from a front-to-front geometrical
arrangement of the molecules. In contrast, the antiparallel
arrangement of the molecules leads to suprastructures with a
left-handed helicity along the growth axis of the fiber due to
amino acid chirality. Main contributions to energetic
stabilization stem from up to three intermolecular forces:
most importantly, H-bonding between the carboxylic acid
groups of the amino acid moieties and the triazole rings, π−π
stacking of the oligothiophene backbones, and van der Waals
interactions of the alkyl chains. As can be seen from Figure 9,
π−π stacks are an essential constituent of the proposed model
and play a central role in the stability of the aggregates, which
can explain the temperature stability of the superstructures, as
was observed in CD spectroscopy (vide supra). The main
driving forces for fiber growth in the described aggregates are
phase segregation between the hydrophilic and hydrophobic
segments of the π−π stacks and a high packing density.
Although the width of the fibers shown in the model depends
strongly on the number of molecules included in the calculation
(Figure 9c), their height converges to the experimental value of
∼2.3 nm found for the single fibers in the AFM images (vide
supra).
+
except for when the considerably bigger NBu4 cation is
applied. Here, the bisignate CD signal vanishes almost
completely. This behavior is corroborated by UV−vis spec-
troscopy, where a red-shift of the λmax (from 392 to 410 nm)
was observed only in the case of the NBu4Cl solution,
accompanied by a broadness of the absorption band. This,
however, may be attributable to the turbidity of the solution
and the resulting light scattering. The cation size dependence of
spectroscopic results obtained will be further discussed in
connection with a theoretical model for the suprastructures.
Self-Assembly in the Solid Phase. In order to elucidate
the structure of the chiral aggregates in the solid phase, atomic
force microscopy (AFM) investigations were performed for
enantiomer 8 on muscovite mica. The compound was
deposited by spin-coating a toluene solution onto a freshly
cleaved mica surface (c = 10−4 M). The surface was almost fully
covered by a 0.7 nm thin film of the material, on top of which a
network of fibers could be observed (Figure 7). The height of
the film agrees well with a monolayer of 8, in which a parallel
arrangement of the π-conjugated backbones to the substrate
can be postulated. The basic fibers showed an averaged free
length of ca. 1 μm between two connecting nodes and are
characterized by a left-handed helicity. The width and height of
single fibers were determined to be 22 2 and 2.3 0.2 nm,
respectively. In some cases, the fibers coalesce to bundles, in
which the original chirality is preserved (insets of Figure 7a).
The widths of fiber bundles vary between 30 and 80 nm. The
pitch length of the left-handed helical single fibers is calculated
to be 25 1 nm and about 30 nm for the bundles.
A final aspect of suprastructure formation needs to be
addressed. It was shown, that in aqueous solution most likely
the deprotonated acid, i.e., the carboxylate of hybrids 8−10, is
prevalent. In the theoretical models presented here (Figure 9),
though, the protonated acid and the resulting hydrogen-
bonding ability was taken into account. In aqueous
Theoretical Models of Suprastructures. On the basis of
the experimental findings, models of the self-assembled
suprastructures of (2S,4S)-hybrid 8 were deduced from
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Figure 9. Semiempirical model of a left-handed helical fibrillar suprastructure of (2S,4S)-hybrid 8 (hydrogens are omitted for clarity). (a) Schematic
representation of (2S,4S)-hybrid 8: blue boxes, oligothiophene; green cylinders, proline. (b) A pair of 8 (top) and a hydrogen-bonded tetramer of 8
(bottom). (c) Dark blue arrows indicating the growth axis of the fiber, and light blue arrow indicates left-handed helicity.
surroundings, however, a dependence of the spectroscopic
results on the size of added cations was observed (vide supra),
suggesting a crucial role of these ions.
In previous calculations performed by our group, it was
shown that the geometries considering thiophene-2-carboxylic
acid (Figure 10, left column) or a pair of these acids (Figure 10,
right column) do not change drastically, when the protons are
substituted by an alkali metal cation (here lithium or
potassium).
complexation. Taking these theoretical results into account, the
formation of a self-assembled suprastructure similar to the ones
presented above based on interactions between carboxylates
and alkali metal cations becomes plausible. In the case of
(2S,4S)-hybrid 8, these interactions most likely will occur
between a carboxylate, an alkali metal cation, and a triazol
moiety as the second part responsible for complexation. Also,
the dependence of the CD effect observed on the size of the
cations used can be explained (vide supra). The subtle effect
observed going from pure water to aqueous salt solutions of
LiCl, NaCl, KCl, and CsCl is in accordance with the theoretical
results showing that even larger alkali metal cations such as K+
Furthermore, it was shown that also the interactions of two
carboxylates with alkali metal cations placed between them led
to a minimum in energy, suggesting electrostatic interactions or
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Figure 10. Geometries of thiophene-2-carboxylic acid (a) or thiophene-2-carboxyate with Li+ (b) or K+ (c) as cation. Nonessential hydrogens are
omitted for clarity. Cyan, carbon; yellow, sulfur; red, oxygen; white, hydrogen/lithium; purple, potassium.
or Cs+ do not lead to drastic changes in the geometries of the
desorption ionization time-of-flight mass spectrometry (MALDI-
TOF MS) measurements were carried out on a BrukerDaltonik
Reflex III mass spectrometer with the following matrices: 1,2,3-
trihydroxyanthracene (dithranol) and trans-2-(3-(4-tert-butylphenyl)-
complexation (Figure 10). On the contrary, a large cation such
+
as NBu4 can presumably not be accommodated in the
molecular geometries proposed here, thus preventing the self-
2-methyl-2-propenylidene)malononitrile (DCTB). Elemental analyses
assembly of a suprastructure similar to those proposed above.
were performed on a ElementarVario EL and a Carlo Erba 1104.
Cyclic voltammetry experiments were performed with a computer-
CONCLUSION
controlled Autolab PGStat 30 potentiostat in a three-electrode single-
compartment cell with a platinum working electrode, a platinum wire
counter electrode, and an Ag/AgCl reference electrode. All potentials
were internally referenced to the ferrocene/ferrocenium couple.
Optical rotations were obtained by using a Perkin-Elmer 241
polarimeter. Absorption spectra were recorded on a Perkin-Elmer
Lambda 19 spectrometer and fluorescence emission spectra on a
Perkin-Elmer LS 55 spectrometer in 1 cm cuvettes. Circular dichroism
spectroscopy was conducted using an Applied Biophysics Chirascan
spectropolarimeter and a JASCO J-810 spectropolarimeter using 1 cm
cuvettes. Spectra at different temperatures are not corrected for
volume changes of the solvent. Dynamic light scattering (DLS) was
performed on a Malvern Zetasizer Nano ZS (angle 173°, l = 633 nm).
For the preparation of aggregation samples of 8−10 in 5% n-
propanol/water, corresponding equivalents of a stem solution (c ≈ 7 ×
10−3 M) of the respective compound in n-propanol were added to
previously prepared mixtures of n-propanol/water. After mixing the
sample for 30 s with the help of a pipet, measurements were
conducted. For temperature-dependent measurements, the sample was
equilibrated for 5 min at the respective temperature before
measurement. AFM measurements were conducted using a Nano-
scope V (Bruker) in the intermittent tapping mode.
Materials. Copper powder (Merck), trifluoroacetic acid (Merck),
tetrakis(acetonitrile)copper(I) hexafluorophosphate (Sigma-Aldrich),
phosphoryl chloride (Merck), potassium carbonate (Merck), dimethyl-
(2-oxopropyl)phosphonate (Merck) and sodium hydride (Merck, 60%
suspension in paraffin oil) were used without further purification. 3,3‴-
Didodecyl-2,2′;5′,2″; 5″,2‴-quaterthiophene 1,4 tosyl azide,47 (1-
diazo-2-oxopropyl)phosphonate,41 and amino acids 4−643,58,59 were
synthesized according to literature procedures.
3,3‴-Didodecyl-2,2′;5′,2″;5″,2‴-quaterthiophene-5-carbal-
dehyde (2). For the generation of the Vilsmeier reagent, 70 μL of dry
N,N-dimethylformamide (0.9 mmol, 1.5 equiv) was dissolved in 1.3
mL of dry dichloroethane, and 90 μL (0.9 mmol, 1.5 equiv) of POCl3
was added dropwise. The resulting slightly yellow mixture was stirred
for 2 h at room temperature. In a two-neck flask equipped with a reflux
■
In conclusion, three new stereoisomeric hybrid materials
consisting of a π-conjugated oligothiophene and the amino
acid proline have been synthesized by click chemistry. Their
self-assembling behavior in solution accounts for left- and right-
handed chiral aggregates in the case of the enantiomeric pure
hybrids 8 and 9, respectively, and nonchiral aggregation in the
case of diastereomer 10. The analysis of the circular dichroism
and UV−vis spectra in conjunction with theoretical calculations
performed for (2S,4S)-hybrids 8 resulted in a left-handed chiral
model, where the antiparallel arrangement of the molecules
favor the π−π stacking and accounts for the temperature
stability of the aggregates. A left-handed chirality of aggregates
in the solid phase has been demonstrated by atomic force
microscopy.
EXPERIMENTAL SECTION
■
General Procedures. Nuclear magnetic resonance spectra were
recorded on a Bruker AMX 500 (1H NMR, 500 MHz; 13C NMR, 125
MHz) or an Avance 400 spectrometer (1H NMR, 400 MHz; 13C
NMR, 100 MHz) at room temperature. Chemical shift values (δ) are
given in parts per million using residual solvent protons (1H NMR, δH
= 7.26 for CDCl3; 13C NMR, δC = 77.0 for CDCl3) as internal
standard. All reactions except for saponification were performed in
flame-dried glassware under argon and were monitored by thin layer
chromatography (aluminum plates, precoated with silica gel, Merck
Si60 F254). Compounds were detected by UV and ninhydrin.
Preparative column chromatography was performed on glass columns
packed with silica gel, Merck silica 60 (230−400 mesh, 60 Å). Size
exclusion chromatography (SEC) was performed using Bio-Beads S-X-
1 and dichloromethane as eluent. Reversed-phase high-performance
liquid chromatography (RP-HPLC) was performed on Merck-Knauer
equipment, and recycling gel permeation chromatography (r-GPC)
was carried out on Shimadzu equipment. Matrix-assisted laser
4518
dx.doi.org/10.1021/cm4020767 | Chem. Mater. 2013, 25, 4511−4521

Chemistry of Materials
Article
condenser, 400 mg of 3,3‴-didodecyl-2,2′;5′,2″;5″,2‴-quaterthiophene
1 (0.6 mmol, 1 equiv) was dissolved in 2 mL of dry dichloroethane.
The solution was warmed to reflux and the Vilsmeier reagent was
added dropwise. After 3 h under reflux, the reaction mixture was
quenched with 20 mL of saturated NaHCO3 solution and stirred
overnight. The layers were separated; the aqueous layer was extracted
three times with dichloromethane. The combined organic layers were
washed with water and dried over Na2SO4. The solvent was removed
in vacuo. The crude product was purified by column chromatography
(silica gel, dichloromethane as eluent) and gave 261 mg (0.38 mmol,
63%) of 2 as a bright red solid. Mp: 63−64 °C. 1H NMR (400 MHz,
CDCl3): δ = 9.83 (s, 1H, carbonyl-H), 7.59 (s, 1H, H-4), 7.18 (m, 4H,
aqueous layer was extracted with dichloromethane twice. The
combined organic layers were washed with demineralised water and
then they were dried over Na2SO4, and the solvent was removed in
vacuo. The crude product was repeatedly heated to reflux in
demineralized water; after each heating, the amino acid-containing
hot water was removed. This procedure was repeated until the water
removed was free of amino acid (ninhydrin test). The crude product
was further purified by column chromatography (silica gel, hexane/
ethyl acetate 3:2 as eluent) to give 83 mg (86.3 μmol, 86%) of the
1
desired product 7 as an orange-brown resinlike solid. H NMR (400
MHz, CDCl3): δ = 7.67 (s, 1H, triazole-H), 7.25 (s, 1H, H-4), 7.17 (d,
3
3J(H‑5‴,H‑4‴) = 5.14 Hz, 1H, H-5‴), 7.13 (d, J(H‑3′,H‑4′);(H‑4″,H‑3′) = 3.71
3
3
H-4′,3′,4″,5‴), 7.03 (d, J(H‑3″,H‑4″) = 3.78 Hz, 1H, H-3″), 6.94 (d,
Hz, 2H, H-3′, H-4″), 7.05 (d, J(H‑3′, H‑4′) = 3.87 Hz, 1H, H-4′), 7.02
3J(H‑5‴,H‑4‴) = 5.20 Hz, 1H, H-4‴), 2.80 (m, 4H, Ha), 1.68 (m, 4H, Hb),
3
3
(d, J(H‑3″,H‑4″) = 3.84 Hz, 1H, H-3″), 6.93 (d, J(H‑5‴,H‑4‴) = 5.24, 1H,
H-4‴), 5.29 and 5.22 (m, 1H, Hγ), 4.63 and 4.55 (m, 1H, Hα), 4.11,
3.96, and 3.87 (m, 2H, Hδ), 3.79 (s, 3H, methyl ester), 2.98, 2.85, and
2.56 (m, 2H, Hβ), 2.78 (m, 4H, Ha), 1.65 (m, 4H, Hb), 1.44 (s, 9H,
1.26 (m, 36H, Hc‑k), 0.88 (m, 6H, Hl). 13C NMR (100 MHz, CDCl3):
δ = 182.4, 140.9, 140.4, 140.3, 140.1, 139.1, 138.9, 136.3, 136.0, 133.6,
130.1, 130.1, 128.3, 126.6, 124.5, 124.1, 124.0, 31.9, 30.6, 30.2, 29.7,
29.7, 29.6, 29.6, 29.6, 29.5, 29.4, 29.4, 29.4, 29.3, 29.3, 22.7, 14.1. MS
(MALDI-TOF, dithranol): m/z [M + H]+ = 695.0 (calcd for
C41H58OS4 694.3). FT-IR (KBr), ν (cm−1): 3084, 2923, 2847, 2361,
1648, 1426, 1390, 1252, 1162, 801, 725. Anal. Calcd (%) for
C41H58OS4: C 70.84, H 8.41, S 18.45. Found: C 70.67, H 8.44, S
18.19.
3
Boc), 1.25 (m, 36H, Hc‑k), 0.87 (“t”, J(H‑l,H‑k) = 6.81 Hz, 6H, Hl);
separated signals of the minor conformer, 7.66 (s, 1H, triazole), 3.80
(s, 3H, methylester), 1.47 (s, 9H, Boc); ratio minor/major conformer
1:1.4. 13C NMR (100 MHz, CDCl3): δ = 172.7, 172.5, 153.2, 142.8,
140.2, 139.8, 136.9, 136.5, 135.4, 134.7, 130.3, 130.2, 130.0, 130.0,
129.9, 127.3, 126.5, 126.4, 123.8, 123.9, 117.7, 117.5, 81.1, 81.0, 58.3,
57.8, 57.4, 52.6, 52.3, 51.6, 36.4, 35.5, 31.8, 30.6, 30.4, 29.6, 29.6, 29.5,
29.4, 29.4, 29.4, 29.3, 29.2, 28.2, 28.1, 22.6, 14.1. MS (MALDI-TOF,
dithranol): m/z [M + H]+ = 961.5 (calcd for C53H76N4O4S4 960.4),
m/z [M − tBu]+ = 905.4. Anal. Calcd (%) for C53H76N4O4S4: C 66.21,
H 7.97, N 5.83. Found: C 65.94, H 7.92, N 5.90.
3,3‴-Didodecyl-5-ethynyl-2,2′;5′,2″;5″,2‴-quaterthiophene
(3). The key reagent (1-diazo-2-oxopropyl)phosphonate)41 was
synthesized freshly prior to use according the following literature
protocol: A suspension of 115 mg of sodium hydride (2.9 mmol, 10
equiv) in 30 mL of dry tetrahydrofuran was cooled to 0 °C, and 382
μL of dimethyl(2-oxopropyl)phosphonate (2.8 mmol, 9.6 equiv) was
added dropwise to the solution. The resulting mixture was stirred at 0
°C for 1 h. Then 567 mg (2.8 mmol, 10 equiv) of tosyl azide was
added and the reaction mixture was stirred for another 10 min at 0 °C.
The reaction mixture then was quickly passed through a short filtration
column (silica gel, eluent ethyl acetate) and the solvent was removed
in vacuo to give (1-diazo-2-oxopropyl)phosphonate as a colorless oil.
The reagent was dissolved in 14 mL of dry tetrahydrofuran and added
to a previously prepared suspension of 716 mg of potassium carbonate
(5.2 mmol, 18 equiv) and 200 mg of 2 (287.7 μmol, 1 equiv) in 8 mL
of dry methanol. The resulting intensely yellow mixture was stirred
under argon overnight. The solvent was removed in vacuo. The
residue was redissolved in dichloromethane and was washed with a
saturated solution of ammonium chloride. The layers were separated,
and the aqueous layer was repeatedly extracted with dichloromethane.
The combined organic layers were dried over Na2SO4, which was
filtered off, and the solvent was removed in vacuo. The crude product
was put onto silica gel and was purified by column chromatography
(silica gel, hexane as eluent) to yield 178 mg (257.5 μmol, 90%) of the
desired product 3 as a bright yellow oil. 1H NMR (400 MHz, CDCl3):
δ = 7.18 (d, 3J(H‑5‴,H‑4‴) = 5.14 Hz, 1H, H- 5‴), 7.12 (m, 3H, H-3″, H-
4″, H-3′), 7.03 (m, 2H, H-4′, H-4), 6.95 (d, 3J(H‑5‴,H‑4‴) = 5.24, 1H, H-
4‴), 3.39 (s, 1H, acetylene-H), 2.76 (m, 4H, Ha), 1.64 (m, 4H, Hb),
1.26 (m, 36H, Hc‑k), 0.88 (“t”, 3J(H‑l,H‑k) = 6.82 Hz, 6H, Hl). 13C NMR
(100 MHz, CDCl3): δ = 139.9, 139.4, 137.5, 136.4, 136.0, 135.6,
134.0, 132.5, 130.2, 130.1, 127.0, 126.5, 124.1, 123.9, 123.8, 119.7, 82.0
(C-B), 76.9 (C-A), 31.9, 30.7, 30.4, 30.0, 29.7, 29.7, 29.6, 29.6, 29.5,
29.5, 29.4, 29.4, 29.4, 29.3, 29.2, 22.7, 14.1. MS (MALDI-TOF,
dithranol): m/z [M + H]+ = 690.3 (calcd for C42H58S4 690.3), m/z [M
− 16]+ = 674.2, m/z [M + dithranol + Na]+ = 940.4. FT-IR (KBr), ν
(cm−1): 3309, 2923, 2852, 2101, 1645, 1465, 834, 791, 656, 587.
Analytical HPLC: analytical nitrophenyl-column, 100% hexane as
eluent, 99% purity. UV−vis (CH2Cl2): λmax (ε) = 390 (29 700).
1-tert-Butyl 2-Methyl (2S,4R)-4-[4-(3,3‴-didodecyl-
2,2′:5′,2″:5″,2‴-quaterthien-5-yl)-1H-1,2,3-triazol-1-yl)-
pyrrolidine-1,2-dicarboxylate (7). To a solution of 69 mg (100
μmol, 1 equiv) of 3 in 4 mL of dichloromethane under argon was
added 54 mg (203 μmol, 2 equiv) of 4, 1.3 mg of copper powder (20
μmol, 0.2 equiv), and 7.5 mg of tetrakis(acetonitrile)copper(I)
hexafluorophosphate (20 μmol, 0.2 equiv). The reaction was stirred
at room temperature overnight. The reaction mixture was poured onto
semiconcentrated ammonia, and the layers were separated. The
(4S)-1-tert-Butoxycarbonyl)-4-[4-(3,3‴-didodecyl-
2,2′:5′,2″:5″,2‴-quaterthien-5-yl-1H-1, 2,3-triazol-1-yl]-L-pro-
line (8) and (4R)-1-tert-Butoxycarbonyl)-4-[4-(3,3‴-didodecyl-
2,2′:5′, 2″:5″,2‴-quaterthien-5-yl-1H-1,2,3-triazol-1-yl]-D-pro-
line (9). A representative synthetic procedure is given for both
enantiomers: 86 mg (124 μmol, 1 equiv) of 3 was dissolved in 5 mL of
dichloromethane. Subsequently, under argon atmosphere 64 mg (249
μmol, 2 equiv) of the respective amino acid 5 or 6, 1.6 mg (25 μmol,
0.2 equiv) of copper powder, and 56 mg (149 μmol, 1.2 equiv) of
tetrakis(acetonitrile)copper(I) hexafluorophosphate were added. The
reaction was stirred at room temperature overnight. After 20 h,
another 0.2 equiv of the catalyst was added (9 mg, 25 μmol). After 25
h at room temperature, the reaction mixture was poured onto
semiconcentrated ammonia, and the layers were separated. The
aqueous layer was repeatedly extracted with dichloromethane. The
organic layers were combined, and the solvent was removed in vacuo.
The crude product was purified by RP-HPLC using a ternary gradient
of THF, acetonitrile, and water (t = 0 min, water 50%, acetonitrile
45%, THF 5%; t = 17 min, water 2%, acetonitrile 60%, THF 38%; tR =
11.2 min). For further purification the product was submitted to r-
GPC with THF as eluent and subsequent SEC with dichloromethane.
The desired product was lyophilized from dioxane and was obtained as
an intensely yellow solid in 82% and 92% yield, respectively.
Analytical data for 8. 1H NMR (400 MHz, CDCl3/MeOD 1:1): δ =
7.84 (s, 1H, triazole-H), 6.91 (s, 1H, H-4), 6.87 (d, 3J(H‑5‴,H‑4‴) = 5.20
3
Hz, 1H, H- 5‴), 6.81 (d, J(H‑3′,H‑4′);(H‑4″,H‑3′) = 3.73 Hz, 2H,H-3′, H-
3
3
4″), 6.73 (d, J(H‑3′,H‑4′) = 3.78 Hz, 1H, H-4′), 6.68 (d, J(H‑3″,H‑4″)
=
3
3.77 Hz, 1H, H-3″), 6.60 (d, J(H‑5‴,H‑4‴) = 5.18, 1H, H-4‴), 4.90 (m,
1H, Hγ), 4. 08, 3.86, and 3.57 (m, 3H, Hα, Hδ), 2.69 (m, 1H, Hβ),
2.44 (m, 4H, Ha), 2.37 (m, 1H, Hβ), 1.31(m, 4H, Hb), 1.13 (s, 9H,
3
Boc), 0.90 (m, 36H, Hc‑k), 0.52 (t, J(H‑l,H‑k) = 6.77 Hz, 6H, Hl);
separated signals of the minor conformer, 7.82 (s, 1H, triazole-H),
1.16 (s, 9H, Boc). 13C NMR (126 MHz, CDCl3/MeOD 1:1): δ =
173.3, 173.1, 153.8, 153.5, 142.1, 139.8, 139.3, 136.5, 135.9, 134.9,
134.0, 129.8, 129.6, 129.5, 129.4, 129.3, 127.0, 126.9, 126.1, 125.9,
123.3, 123.3, 123.2, 118.6, 80.8, 80.7, 57.8, 57.3, 57.0, 56.9, 51.0, 50.4,
35.3, 34.5, 31.3, 30.0, 29.9, 29.0, 29.0, 28.9, 28.9, 28.8, 28.7, 28.7, 28.5,
27.4, 27.2, 22.0, 13.2. MS (MALDI-TOF, DCTB): m/z [M + H]+ =
946.6 (calcd for C52H74N4O4S4 946.4). Anal. Calcd (%) for
C52H74N4O4S4: C 65.92, H 7.87, N 5.91. Found: C 66.20, H 8.00,
N 5.85.
4519
dx.doi.org/10.1021/cm4020767 | Chem. Mater. 2013, 25, 4511−4521

Chemistry of Materials
Article
1
Analytical NMR data for 9. H NMR (400 MHz, CDCl3/MeOD
1:1): δ = 7.83 (s, 1H, triazole-H), 6.90 (s, 1H, H-4), 6.86 (d,
ACKNOWLEDGMENTS
■
3J(H‑5‴,H‑4‴) = 5.20 Hz, 1H, H-5‴), 6.78 (d, J(H‑3′,H‑4′);(H‑4″,H‑3′) = 3.73
3
This work has been supported by the Volkswagen foundation
(Project AZ. 85101-85103).
3
Hz, 2H, H-3′, H-4″), 6.71 (d, J(H‑3′,H‑4′) = 3.78 Hz, 1H, H-4′,), 6.66
3
3
(d, J(H‑3″,H‑4″) = 3.77 Hz, 1H, H-3″), 6.59 (d, J(H‑5‴,H‑4‴) = 5.18, 1H,
H-4‴), 4.89 (m, 1H, Hγ), 4.11, 3.84, and 3.56 (m, 3H, Hα, Hδ), 2.68
(m, 1H, Hβ), 2.43 (m, 4H, Ha), 2.36 (m, 1H, Hβ), 1.31 (m, 4H, Hb),
REFERENCES
■
(1) Handbook of Thiophene-Based Materials: Applications in Organic
Electronics and Photonics; Perepichka, I. F., Perepichka, D. F., Eds.;
Wiley-VCH: Weinheim, Germany, 2009.
3
1.12 (s, 9H, Boc), 0.89 (m, 36H, Hc‑k), 0.51 (t, J(H‑l,H‑k) = 6.77 Hz,
6H, Hl); separated signals of the minor conformer, 7.81 (s, 1H,
triazole-H), 1.15 (s, 9H, Boc). 13C NMR (126 MHz, CDCl3/MeOD
1:1): δ = 173.3, 173.0, 153.8, 153.5, 142.1, 139.8, 139.2, 136.4, 135.9,
134.9, 134.0, 129.8, 129.6, 129.5, 129.4, 129.3, 126.9, 126.9, 126.0,
125.8, 123.2, 123.2, 118.5, 80.8, 80.6, 57.8, 57.3, 57.0, 56.9, 51.0, 50.3,
35.3, 34.5, 31.3, 30.0, 29.8, 29.0, 29.0, 28.9, 28.9, 28.8, 28.8, 28.7, 28.5,
27.3, 27.2, 22.0, 13.2. MS (MALDI-TOF, DCTB): m/z [M + H]+ =
946.6 (calcd for C52H74N4O4S4 946.4). Anal. Calcd (%) for
C52H74N4O4S4: C 65.92, H 7.87, N 5.91. Found: C 65.93, H 7.93,
N 5.81.
(4R)-1-tert-Butoxycarbonyl)-4-[4-(3,3‴-didodecyl-
2,2′:5′,2″:5″,2‴-quaterthien-5-yl)-1H-1,2,3-triazol-1-yl]-L-pro-
line (10). To a solution of 41 mg (43 μmol, 1 equiv) of 7 in 2 mL of
aqueous dioxane/methanol 1:1 was added 9 mg (213 μmol, 5 equiv)
of lithium hydroxide monohydrate. The reaction was stirred for 2.5 h
at 40 °C. The solvent was removed in vacuo and the residue was taken
up in dichloromethane. Acetic acid (5%, pH 2) was added, and the
two-phase system was stirred vigorously for 30 min. The layers were
separated, and the aqueous layer was repeatedly extracted with
dichloromethane. Then the solvent was removed in vacuo. The crude
product was purified by RP-HPLC using a ternary gradient of THF,
acetonitrile, and water (t = 0 min, water 50%, acetonitrile 45%, THF
5%; t = 17 min, water 2%, acetonitrile 60%, THF 38%; tR = 11.5 min).
After lyophylization from dioxane, 30 mg (31.7 μmol, 74%) of the
(2) Sirringhaus, H.; Brown, P. J.; Friend, R. H.; Nielsen, M. M.;
Bechgaard, K.; Langeveld-Voss, B. M. W.; Spiering, A. J. H.; Janssen, R.
A. J.; Meijer, E. W.; Herwig, P.; de Leeuw, D. M. Nature 1999, 401,
685−688.
(3) Hoofmann, R. J. O. M.; de Haas, M. P.; Siebbeles, L. D. A.;
Warman, J. M. Nature 1998, 392, 54−56.
(4) Bauerle, P.; Fischer, T.; Bidlingmeier, B.; Rabe, J. P.; Stabel, A.
̈
Angew. Chem., Int. Ed. 1995, 34, 303−307.
(5) Kirschbaum, T.; Azumi, R.; Mena-Osteritz, E.; Bauerle, P. New J.
̈
Chem. 1999, 241−250.
(6) Azumi, R.; Gotz, G.; Debaerdemaeker, T.; Bauerle, P. Chem.
̈
̈
Eur. J. 2000, 6, 735−744.
(7) Mena-Osteritz, E.; Meyer, A.; Langeveld-Voss, B. M. W.; Janssen,
R. A. J.; Meijer, E. W.; Bauerle, P. Angew. Chem., Int. Ed. 2000, 39,
̈
2679−2684.
(8) Mena-Osteritz, E. Adv. Mater. 2002, 14, 609−616.
(9) Kilbinger, A. F. M.; Schenning, A. P. H. J.; Goldoni, F.; Feast, W.
J.; Meijer, E. W. J. Am. Chem. Soc. 2000, 122, 1820−1821.
(10) Schenning, A. P. H. J.; Kilbinger, A. F. M.; Biscarini, F.;
Cavallini, M.; Cooper, H. J.; Derrick, P. J.; Feast, W. J.; Lazzaroni, R.;
Leclere, P.; McDonell, L. A.; Meijer, E. W.; Meskers, S. C. J. J. Am.
Chem. Soc. 2002, 124, 1269−1275.
1
̀
(11) Leclere, P.; Surin, M.; Viville, P.; Lazzaroni, R.; Kilbinger, A. F.
desired product 10 was obtained as a bright yellow solid. H NMR
(400 MHz, CDCl3/MeOD 1:1): δ = 7.76 (s, 1H, triazole-H), 6.93 (s,
M.; Henze, O.; Feast, W. J.; Cavallini, M.; Biscarini, F.; Schenning, A.
P. H. J.; Meijer, E. W. Chem. Mater. 2004, 16, 4452−4466.
(12) Henze, O.; Feast, W. J.; Gardebien, F.; Jonkheijm, P.; Lazzaroni,
R.; Leclere, P.; Meijer, E. W.; Schenning, A. P. H. J. J. Am. Chem. Soc.
2006, 128, 5923−5929.
3
1H, H-4), 6.87 (d, J(H‑5‴,H‑4‴) = 5.18 Hz, 1H,H- 5‴), 6.82 (d,
3J(H‑3′,H‑4′);(H‑4″,H‑3′) = 3.71 Hz, 2H, H-3′, H-4″), 6.74 (d, J(H‑3′,H‑4′)
=
3
3.79 Hz, 1H, H-4′), 6.69 (d, 3J(H‑3″,H‑4″) = 3.78 Hz, 1H, H-3″), 6.60 (d,
3J(H‑5‴,H‑4‴) = 5.21, 1H, H-4‴), 4.97 (m, 1H, Hγ), 4.20 (m, 1H, Hα),
3.73 and 3.59 (m, 2H, Hδ), 2.64 (m, 1H, Hβ), 2.46 (m, 4H, Ha), 2.30
(m, 1H, Hβ), 1.33 (m, 4H, Hb), 1.11 (s, 9H, Boc), 0.90 (m, 36H,
(13) Wolffs, M.; Korevaar, P. A.; Jonkheijm, P.; Henze, O.; Feast, W.
J.; Schenning, A. P. H. J.; Meijer, E. W. Chem. Commun. 2008, 4613−
4615.
(14) Westenhoff, S.; Abrusci, A.; Feast, W. J.; Henze, O.; Kilbinger,
A. F. M.; Schenning, A. P.H. J.; Silva, C. Adv. Mater. 2006, 18, 1281−
1285.
(15) Leclere, P.; Surin, M.; Lazzaroni, R.; Kilbinger, A. F. M.; Henze,
̀
O.; Jonkheijm, P.; Biscarini, F.; Cavallini, M.; Feast, W. J.; Meijer, E.
W.; Schenning, A. P. H. J. J. Mater. Chem. 2004, 14, 1959−1963.
(16) Nilsson, K. P. R.; Olsson, J. D. M.; Konradsson, P.; Inganas, O.
3
Hc‑k), 0.51 (t, J(H‑l, H‑k) = 6.76 Hz, 6H, Hl); separated signals of the
minor conformer, 7.75 (s, 1H, triazole-H), 1.13 (s, 9H, Boc). 13C
NMR (126 MHz, CDCl3/MeOD 1:1): δ = 174.0, 173.6, 154.0, 153.7,
142.1, 139.9, 139.4, 136.6, 136.0, 135.0, 134.1, 129.9, 129.9, 129.6,
129.5, 129.4, 129.4, 127.0, 126.2, 125.9, 123.3, 123.3, 123.2, 118.6,
118.5, 80.8, 80.6,58.257.9, 57.7, 57.4, 51.4, 51.2, 35.7, 34.9, 31.3, 30.0,
29.9, 29.0, 29.0, 28.9, 28.8, 28.8, 28.7, 28.5, 27.4, 27.3, 22.0, 13.2. MS
(MALDI-TOF, DCTB): m/z [M + H]+ = 946.7 (calcd for
C52H74N4O4S4 946.4). Anal. Calcd (%) for C52H74N4O4S4: C 65.92,
H 7.87, N 5.91. Found: C 65.92, H 7.88, N 5.75.
̈
Macromolecules 2004, 37, 6316−6321.
(17) Nilsson, K. P. R.; Herland, A.; Hammarstrom, P.; Inganas, O.
Biochemistry 2005, 44, 3718−3724.
̈
(18) Melucci, M.; Barbarella, G.; Gazzano, M.; Cavallini, M.;
Biscarini, F.; Bongini, A.; Piccinelli, F.; Monari, M.; Bandini, M.;
Umani-Ronchi, A.; Biscarini, P. Chem.Eur. J. 2006, 12, 7304−7312.
(19) Whitesides, G. M.; Grzybowski, B. Science 2002, 295, 2418−
2421.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra of compounds 2, 3, 7−10 (PDF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
(20) Schenning, A. P. H. J.; Meijer, E. W. Chem. Commun. 2005,
3245−3258.
(21) Schillinger, E.-K.; Jatsch, A.; Schmid, S.; Bauerle, P. J. Mater.
̈
Chem. 2010, 20, 3563−3578.
AUTHOR INFORMATION
■
(22) Klok, H. A.; Rosler, A.; Gotz, G.; Mena-Osteritz, E.; Bauerle, P.
̈
̈
̈
Org. Biomol. Chem. 2004, 2, 3541−3544.
Corresponding Author
*E-mail: peter.baeuerle@uni-ulm.de.
(23) Diegelmann, S. R.; Gorham, J. M.; Tovar, J. D. J. Am. Chem. Soc.
2008, 130, 13840−13841.
Present Addresses
(24) Tsai, W.-W.; Li, L.-s.; Cui, H.; Jiang, H.; Stupp, S. I. Tetrahedron
2008, 64, 8504−8514.
§BASF Coatings GmbH, D-48165 Munster, Germany.
̈
∥Bachem AG, Hauptstrasse 144, 4416 Bubendorf, Switzerland.
(25) Stone, D. A.; Hsu, L.; Stupp, S. I. Soft Matter 2009, 5, 1990−
1993.
Notes
(26) Gus’kova, O. A.; Khalatur, P. G.; Bauerle, P.; Khokhlov, A. R.
̈
The authors declare no competing financial interest.
Chem. Phys. Lett. 2008, 461, 64−70.
4520
dx.doi.org/10.1021/cm4020767 | Chem. Mater. 2013, 25, 4511−4521

Chemistry of Materials
Article
(27) Gus’kova, O. A.; Khalatur, P. G.; Khokhlov, A. R. Macromol.
Theory Simul. 2009, 18, 219−246.
(57) Lightner, D. A.; Gurst, J. E Organic Conformational Analysis and
Stereochemistry from Circular Dichroism Spectroscopy, Wiley-VCH, New-
York, 2000; p 423 ff.
(58) Anderson, N. G.; Lust, D. A.; Colapret, K. A.; Simpson, J. H.;
Malley, M. F.; Gougoutas, J. Z. J. Org. Chem. 1996, 61, 7955−7958.
(59) Webb, T. R.; Eigenbrot, C. J. Org. Chem. 2002, 56, 3009−3016.
(28) Gus’kova, O. A.; Schillinger, E.; Khalatur, P. G.; Bauerle, P.;
̈
Khokhlov, A. R. Polym. Sci. Ser. A 2009, 51, 430−445.
(29) (a) Tian, L.; Szilluweit, R.; Marty, R.; Bertschi, L.; Zerson, M.;
Spitzner, E.-C.; Magerle, R.; Frauenrath, H. Chem. Sci. 2012, 3, 1512−
1521. (b) Spitzner, E.-C.; Riesch, C.; Szilluweit, R.; Tian, L.;
Frauenrath, H.; Magerle, R. ACS Macro Lett. 2012, 1, 380−383.
(30) Kumar, R. J.; MacDonald, J. M.; Singh, Th. B.; Waddington, L.
J.; Holmes, A. B. J. Am. Chem. Soc. 2011, 133 (22), 8564−8573.
(31) Lehrman, J. A.; Cui, H.; Tsai, W.-W.; Moyer, T. J.; Stupp, S. I.
Chem. Commun. 2012, 48, 9711−9713.
(32) (a) Wall, B. D.; Diegelmann, S. R.; Zhang, S.; Dawidczyk, T. J.;
Wilson, W. L.; Katz, H. E.; Mao, H.-Q.; Tovar, J. D. Adv. Mater. 2011,
23, 5009−5014. (b) Sanders, A. M.; Dawidcyzk, T. J.; Katz, H. E.;
Tovar, J. D. ACS Macro Lett. 2012, 1, 1326−1329.
(33) Schillinger, E.-K.; Mena-Osteritz, E.; Hentschel, J.; Borner, H.
̈
G.; Bauerle, P. Adv. Mater. 2009, 21, 1562−1567.
̈
(34) Shaytan, A. K.; Schillinger, E.-K.; Khalatur, P. G.; Mena-Osteritz,
E.; Hentschel, J.; Borner, H. G.; Bauerle, P.; Khokhlov, A. R. ACS
̈
̈
Nano 2011, 5, 6894−6909.
(35) Sonntag, L.-S.; Schweizer, S.; Ochsenfeld, C.; Wennemers, H. J.
Am. Chem. Soc. 2006, 128, 14697−14703.
(36) Erdmann, R. S.; Kumin, M.; Wennemers, H. Chimia 2009, 63,
̈
197−200.
(37) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed.
2001, 40, 2004−2021.
(38) Tornøe, C. W.; Christensen, C.; Meldal, M. Org. Chem. 2002,
67, 3057−3062.
(39) Rabanal, F.; Ludevid, M. D.; Pons, M.; Giralt, E. Biopolymers
1993, 33, 1019−1028.
(40) Engel, J.; Schwarz, G. Angew. Chem., Int. Ed. 1970, 9, 389−400.
(41) Ghosh, A. K.; Bischoff, A.; Cappiello, J. Eur. J. Org. Chem. 2003,
5, 821−832.
(42) Kumin, M.; Sonntag, L.-S.; Wennemers, H. J. Am. Chem. Soc.
̈
2007, 127, 466−467.
(43) (a) Kuemin, M.; Schweizer, S.; Ochsenfeld, C.; Wennemers, H.
J. Am. Chem. Soc. 2009, 131, 15474−15482. (b) Kuemin, M.; Nagel, Y.
A.; Schweizer, S.; Monnard, F. W.; Ochsenfeld, C.; Wennemers, H.
Angew. Chem. Int. Ed. 2010, 49, 6324−6327.
(44) Kuemin, M.; Engel, J.; Wennemers, H. J. Pept. Sci. 2010, 16,
596−600.
(45) Nagel, Y.; Kuemin, M.; Wennemers, H. Chimia 2011, 65, 264−
267.
(46) Upert, G.; Bouiller
2012, 51, 4231−4234.
(47) (a) Callant, P.; D’Haenens, L.; Vandewalle, M. Synth. Commun.
̀
e, F.; Wennemers, H. Angew. Chem., Int. Ed.
1984, 14, 155. (b) Roth, G. J.; Liepold, B.; Muller, S. G.; Bestmann, H.
̈
J. Synthesis 2004, 1, 59−62.
(48) Jatsch, A.; Kopyshev, A.; Mena-Osteritz, E.; Bauerle, P. Org. Lett.
̈
2008, 10, 961−963.
(49) Kraatz, H. B.; Leek, D. M.; Houmam, A.; Enright, G. D.;
Lusztyk, J.; Wayner, D. D. M. J. Organomet. Chem. 1999, 589, 38−49.
(50) Xu, Y.; Saweczko, P.; Kraatz, H.-B. J. Organomet. Chem. 2001,
637−639, 335−342.
(51) Adams, N. R. Electrochemistry at Solid Electrodes; Dekker: New
York, 1969.
(52) Jatsch, A. Ph.D. thesis, Ulm University, 2010.
(53) Harada, N.; Nakanishi, K. Circular Dichroism Spectroscopy 
Exciton Coupling in Organic Stereochemistry; University Science Books:
Mill Valley, CA, 1983.
(54) Tucker, S. A.; Bates, H. C.; Amszi, V. L.; Acree, W. E., Jr.; Lee,
H.; Di Raddo, P.; Fetzer, R. G. J. C.; Dyker, G. Anal. Chim. Acta 1993,
278, 269−274.
(55) Wade, D. A.; Tucker, S. A. Talanta 2000, 53, 571−578.
(56) Melavanki, R. M.; Kusanur, R. A.; Kulakarni, M. V.;
Kadadevarmath, J. S. J. Lumin. 2008, 128, 573−577.
4521
dx.doi.org/10.1021/cm4020767 | Chem. Mater. 2013, 25, 4511−4521