A helically folded poly(m,p-phenylene)

Article abstract of DOI:10.1016/j.tet.2015.04.102

Abstract Two amphiphilic poly(m,p-phenylene)s were synthesized through Suzuki polycondensation from 1,3-phenylene dibromide bearing solubilizing tri- or tetra(ethylene glycol) chains and 1,4-phenylene diboronic acid diester. Unlike its tri(ethylene glycol

Full text of DOI:10.1016/j.tet.2015.04.102

Accepted Manuscript
A Helically folded poly(m,p-phenylene)
Manuel Burkhalter, Ramchandra Kandre, Oleg Lukin
PII:
S0040-4020(15)00629-8
10.1016/j.tet.2015.04.102
TET 26705
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 18 February 2015
Revised Date: 15 April 2015
Accepted Date: 27 April 2015
Please cite this article as: Burkhalter M, Kandre R, Lukin O, A Helically folded poly(m,p-phenylene),
Tetrahedron (2015), doi: 10.1016/j.tet.2015.04.102.
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A Helically folded poly(m,p-phenylene)
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Manuel Burkhalter, Ramchandra Kandre, Oleg Lukin
Department of Materials, ETH Zurich, Switzerland and Skolkovo Institute of Science and Technology, Skolkovo, Russia

1
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Tetrahedron
journal homepage: www.elsevier.com
A Helically folded poly(m,p-phenylene)†
Manuel Burkhaltera, Ramchandra Kandrea, and Oleg Lukinb
a Institute of Polymers,Department of Materials, ETH Zurich, Wolfgang-Pauli St. 10, HCI, CH-8093 Zurich, Switzerland
b Skolkovo Institute of Science and Technology, Novaya St. 100, Skolkovo, Odintsovsky district, Moscow Region, 143025 Russia
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Two amphiphilic poly(m,p-phenylene)s were synthesized through Suzuki polycondensation
from 1,3-phenylene dibromide bearing solubilizing tri- or tetra(ethylene glycol) chains and 1,4-
phenylene diboronic acid diester. Unlike its tri(ethylene glycol)-functionalized congener the
polymer with tetra(ethylene glycol) chains was shown to possess considerably high molecular
weight (Mw = 15 900 and Mn = 7 300) and good solubility in both polar and nonpolar organic
solvents. Fluorescence spectra of the polymer recorded in CHCl3 and aqueous acetonitrile
revealed that in the latter solution the fluorescence intensity is considerably lower and the band
is redshifted by about 70 nm compared to the former one. This indicates a transition from a
random coil conformation to an ordered compact one. A convincing indication of helical folding
of the polymer came from an induced circular dichroism spectroscopic study of inclusion
complexes of the tubular helical folds with α-pinene enantiomers influencing the sense of the
helix.
Available online
Keywords:
polyphenylenes
amphiphilicity
helical structures
folding
Suzuki polycondensation
2009 Elsevier Ltd. All rights reserved
.
1. Introduction
ethynylene)s equipped with optically active substituents was
recently observed directly by means of atomic force
microscopy.10 Although the helical motif on the basis of the m-
phenylene ethynylene structure has proven to be highly valuable
in many respects there are a few limitations for practical
applicability of oligomers and polymers constructed of these
units. Like any other foldamer, oligo(m-phenylene ethynylene)s
are structurally perfect monodisperse compounds but their
multistep synthesis is time-consuming and costly. Additionally,
low molecular weight oligomers generally find little use in the
production of functional materials. Poly(m-phenylene
ethynilene)s have the advantages of one-step synthesis and high
molecular weights.11 However, diyne defects12 that are often
introduced into the polymer chain during the synthesis would
perturb the folding process and disrupt the tubular helical
structure. Therefore, it is of importance to develop novel helical
polymers with improved structural homogeneity, chemical
stability, and functions. Polyarylenes are suitable candidates in
this regard since they are chemically and thermally robust. There
are a few reports on helical structures formed by oligomeric and
polymeric ortho- and meta-phenylenes.13,14 These compounds
were shown to fold into tight non-tubular helices. However, for
applicative purposes, such as catalysis and chiral discrimination,
hollow tubular nanostructures are essential. As shown in Figure
Helical structures play key roles in a number of biological
functions. This fact has inspired chemists to design many helical
molecules1 to investigate their molecular chirality and to use
them for practical applications such as chiral materials for
asymmetric synthesis,2 separation of enantiomers,3 chiral
building blocks for self-assembled nanomaterials4 and devices5
etc. In this context the design and synthesis of helical polymers
and oligomers (foldamers)6 in which the helix-sense can be
controlled is of significant interest. meta-Connected phenylene
ethynylene is presently one of the most popular structural type
for helical foldamers and polymers. This motif was first
developed by Moore and co-workers,7 who prepared a series of
oligo(m-phenylene ethynilene)s and demonstrated their strong
tendency to fold into a helical conformation in polar solvents
driven by noncovalent solvophobic interactions. This
conformation was shown to possess an internal lipophilic cavity
capable of guest binding. A helicity of the preferred handedness
can be influenced by the formation of inclusion complexes with
chiral guests8 or chiral substituents at the oligomer backbone.9
The formation of helical structure with a preferred handedness of
oligo(m-phenylene ethynylene) foldamers was evidenced by the
appearance of pronounced absorption bands in their circular
dichroism (CD) spectra. The helix formation along with its
1, consideration of molecular models suggests that
a
absolute handedness of amphiphilic poly(m-phenylene
polyphenylene comprising alternating meta- and para-phenylene
———
† The article is dedicated to Professor Artem Oganov on the occasion of his 40th birthday
Corresponding author. Tel.: +7-(495) 280-14-81 ext.3114; fax: +7-(495) 280-14-81; e-mail: o.lukin@skoltech.ru

2
Tetrahedron
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moieties can adopt a tubular helical conformation with an
The preparation of polymer 5a turned out to be problematic.
internal diameter of ca. 1 nm. One of us has recently reported the
synthesis of high molecular weight poly(m,p-phenylene)s
through Suzuki polycondensation.15 Here we present the
synthesis and folding studies of first amphiphilic poly(m,p-
phenylene)s.
The oligomeric product precipitated out from solution during the
polymerization. After isolation 5a was found to be largely
soluble in chloroform at room temperature. The molecular weight
of 5a were determined to be Mw = 6 500 (Pw = 19) and Mn =
2 800 (Pn = 8) by GPC analysis relative to retention times of
polystyrene standards. The low molecular weight of 5a and its
poor solubility in polar solvents preclude the use of the polymer
to study helical folding. Unlike the case with 5a, the
polycondensation of 3b with 4 proceeded smoothly; no
precipitation occurred during the reaction. Polymer 5b was
obtained in nearly quantitative yield and subjected to the GPC
analysis revealing Mw = 15 900 (Pw = 41) and Mn = 7 300 (Pn =
19). Notably, according to the molecular model shown in Figure
1, the determined values of molecular weight of 5b translate to
helices with three to seven full turns (one full turn corresponds to
six repeat units). Structural integrity of the polymers 5a and 5b
was confirmed by solution H and 13C NMR spectroscopy (see
1
Figure 2 showing the corresponding spectra of 3b). Elemental
analyses of the polymers 5 gave satisfactory convergence with
values calculated not including the end groups (see Experimental
section).
Figure 1.Side (left) and top (right) views of an energy-minimized (MMX
force field) helical conformation of an unsubstitutedpoly(m,p-phenylene)
consisting of 96 alternating m- and p-phenylenes (48 repeat units).
2. Results and Discussion
2.1. Synthesis
A common synthetic route to polyphenylenes consists of
Suzuki polycondensation (SPC) of AA and BB types of
monomers bearing pairs of aryl halide and arylboronic
functionalities, respectively. The synthesis of the AA type
monomers 3 is depicted in Scheme 1. The transesterification of
commercially available ethyl ester of 3,5-dibromobenzoic acid 1
with monomethyl ethers of oligo(ethylene glycol)s 2 readily
gives amphiphilic dibromides 3. The latter were subjected to SPC
with 1,4-phenylene diboronic acid diester 4 (BB-type monomer)
under previously reported conditions15 to yield target poly(m,p-
phenylene)s 5 (Scheme 2).
O
OEt
O
OR
reflux
+
HO(CH2CH2O)nCH3
-EtOH
Br
Br
Br
Br
R = -(CH2CH2O)3CH3
1
2a: n = 3
2b: n = 4
3a:
3b: R = -(CH2CH2O)4CH3
Scheme 1. Preparation of the AA monomers 3.
Figure 2.1H (a) and 13C (b) NMR spectra of amphiphilic polyphenylene 5b
recorded in CDCl3. The solvent signals are marked (*).
O
OR
2.2. Folding studies
O
O
O
O
SPC
3
B
B
+
The described analyses of the folding of amphiphilic oligo(m-
phenylene ethynilene)s revealed that these amphiphilic oligomers
exist as random-coiled conformations in chloroform which is a
good solvent for both the lipophilic backbone and the
oligo(ethylene glycol) chains. The amphiphilic oligomers adopt
helical conformations in highly polar solvents that are considered
as bad solvents for the nonpolar oligomer backbone. Acetonitrile
and its mixtures with water were found to be the best folding-
promoting solvents for oligo(m-phenylene ethynylene)s. From a
structure standpoint (nonpolar backbone and polar side chains)
n
4
5a: R = -(CH2CH2O)3CH3
5b: R = -(CH2CH2O)4CH3
Scheme 2. Suzuki polycondensation (SPC) synthesis of amphiphilic
polymers 5. Reagents and conditions: Pd[P(p-tolyl)3]3, NaHCO3, THF/H2O,
80 °C, 96h.
poly(m,p-phenylene)s
5 are expected to have a similar
conformational behavior in the given solvents. Investigation of

3
solubility of polymers 5 in different solvents showed that
polyphenylene 5a could only be dissolved in chloroform. Its
solubility in polar solvents, such as acetonitrile and DMF was
found to be very poor. On the contrary, polyphenylene 5b
exhibited good solubility in both chloroform and the polar
solvents. At concentrations of up to 100 mg·L–1 the polymer was
also soluble in an acetonitrile-water (80:20) solution. However,
an attempt at increasing the water content in the acetonitrile
solution caused precipitation of the polymer. The decreased
solubility of 5b in aqueous acetonitrile compared to that of m-
phenylene ethynylene oligomers is understood taking into
account a larger liphophilic load in the backbone of the former
(six carbons in p-phenylene vs. two carbons in acetylene
linkage). On the basis of the solubility analysis, all further studies
were performed with polyphenylene 5b.
Fluorescence spectroscopy was shown to be a valuable tool for
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study of conformational changes of m-phenylene ethynylenes.16
Therefore, for further conclusions on the conformation of 5b its
fluorescence spectra were recorded.
As shown in Figure 4, the fluorescence intensity of 5b in
aqueous acetonitrile is considerably smaller than that in
chloroform. In addition the fluorescence emission band of the
aqueous acetonitrile sample is redshifted by about 70 nm. Both
the decreased fluorescence intensity and the redshift are
indicative of the compact folded conformation of 5b in aqueous
acetonitrile. After the excitation, the photons emitted by the
phenylene chromophores of 5b in its folded state could get
efficiently absorbed by the phenylene units of spatially adjacent
helical turns leading to the emission decrease. The maximum at
425 nm (the redshift compared with the chloroform sample) can
be attributed to π-stacked aromatic chromophores,17 which is also
in line with the assumption of the helically folded conformation
of 5b. The fluorescence spectrum of 5b in chloroform indicates
an unfolded random coiled structure in which chromophore units
interact more with the solvent rather than with each other
resulting in efficient emission at a shorter wavelength.
UV-spectroscopic measurements of polyphenylene 5b carried
out in different solvents (CHCl3, THF, DMF, CH3CN, aqueous
CH3CN) reveal that the absorption maximum of the polymer does
not depend much on the solvent nature; all observed absorption
maxima lie in the range from 286 to 292 nm. Figure 3 depicts UV
spectra of 5b recorded in pure acetonitrile and in an acetonitrile-
water (80:20) solution. These absorption maxima differing by
only 6 nm are the two “extreme” cases.
Figure 3. UV spectra of polyphenylene 5b (10 mg·L–1) in acetonitrile (solid
line, λmax = 286 nm) and in an acetonitrile-water 80:20 solution (dashed line,
λmax = 292 nm).
Figure 5. CD spectra of the polyphenylene 5b (10 mg·L–1) in an acetonitrile-
water solution (80:20). Dashed line corresponds to the solution of the pure
polymer. Solid line is the spectrum of the polymer in the presence of (1S)-(–)-
α-pinene; dotted line is the spectrum of the polymer in the presence of (1R)-
(+)-α-pinene. The concentration of α-pinene in the solutions was 5 ꢀmol·L–1
that corresponded to a ratio of one α-pinene per one full helical turn (6 repeat
units).
As follows from the molecular modeling (Figure 1) the
helically folded poly(m,p-phenylene) should possess an internal
cavity with a diameter ca. 1 nm. The cavity is hydrophobic and,
therefore, suitable for nonpolar guests of matching size. An
inclusion of a chiral guest should lead to a formation of two
diastereoisomeric complexes with R and S helices. Assuming that
in the solution there is a thermodynamic equilibrium between the
R and S helices, the binding of the chiral guest would shift the
equilibrium to an energetically more favored diastereoisomeric
complex. The prevailing handedness of the helix should manifest
itself in CD spectra. Indeed, the addition of optically pure α-
pinene enantiomers to dilute solutions of polyphenylene 5b in
aqueous acetonitrile results in induced circular dichroism. Figure
5 shows the CD spectra of 5b in presence of both α-pinene
enantiomers. The control CD measurements of the pure 5b did
Figure 4. Fluorescence spectra of polyphenylene 5b (10 mg·L–1) in
chloroform (solid line) and in an acetonitrile-water (80:20) solution (dashed
line). Excitation at 290 nm.
Notably, conformational transitions, such as coil-to-helix, are
rarely evident from the UV spectra of amphiphilic foldamers.

4
Tetrahedron
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4. Experimental section
not reveal any absorbance (the dashed line in Figure 5).
Noteworthy, α-pinene does not absorb in this wavelength
region.8a Therefore, the observed bands in the CD spectra
originate from the helical conformation of the polyphenylene
chain.
4.1. General
NMR spectra were recorded on Bruker Avance 300 and
Bruker Avance 500 spectrometers. TMS was used as an internal
standard. MALDI-TOF measurements were carried out using a
Bruker Ultraflex II mass spectrometer. UV/VIS measurements
were performed on a Perkin Elmer Lambda 20 UV/VIS
spectrometer at 20 °C in 1cm thick quartz cuvettes. Fluorescence
spectra were recorded on a Spex 1681 spectrometer at room
temperature in 1 cm thick quartz cuvettes.Circular dichroism
(CD) spectra were recorded on a Jasco, J-715 spectropolarimeter
at 25 °C.
3. Conclusions and outlook
Amphiphilic poly(m,p-phenylene) 5b presented here is a novel
structural motif capable of helical folding through solvophobic
interactions. Molecular modeling reveals that the helices made up
of the poly(m,p-phenylene) are tubular structures with lipophilic
internal cavity. According to the molecular weight distribution
measured by GPC the polymer can form helices with three to
seven full turns (assuming one turn consists of six repeat units).
The folding into helical conformation occurs in dilute solutions
of the polymer in aqueous acetonitrile and manifests itself best
through induced circular dichroism spectroscopy of the inclusion
complexes of tubular helical folds with enantiomers of α-pinene.
The addition of an optically pure α-pinene shifts the equilibrium
between R and S helices toward the one that forms a more stable
diastereoisomeric inclusion complex with the given α-pinene
enantiomer. The increased population of helices of one
Analytical GPC measurements in chloroform as eluent were
performed at room temperature at a flow rate of 1.0 mL/min. The
column set consisted of SDV columns, and the detectors used
were UV and RI. Polystyrene standards were used for the
calibration. A Viscotek GPC-System equipped with a pump, a
degasser (GPCmax VE2001), RI detector (302 TDA), and three
columns (2×PLGel Mix-C and ViscoGEL GMHHRN 18055,
7.5×300 mm each) was used. Given GPC data refere to low angle
light scattering measurement. Elemental analysis was performed
on a Leco 900 instrument.
handedness is reflected by
Fluorescence spectroscopy is also indicative of the coil-to-helix
conformational transition of the polymer in aqueous acetonitrile.
a pronounced CD activity.
Note, the slightly excessive deviations between the calculated
and measured values in elemental analyses of carbon in polymers
5a and 5b are associated with the polymers’ end groups. Given
the not fully clarified nature and the amount of the latter, we
neglected them in the calculated values of elemental analyses.
Ongoing work in our laboratory is concerned with the design
of monomers for the synthesis of poly(m,p-phenylene)s with
higher molecular weights and an improved hydrophilic-lipophilic
balance. The ability to control the helix sense of high molecular
weight tubular structures might be of importance not only on
account of their chirality-oriented applications but also to keep
the uniform shape of the cylindrical nanoobjects, as
schematically shown in Figure 7.
4.2. 2-(2-(2-Methoxyethoxy)ethoxy)ethyl 3,5-dibromobenzoate
(3a)
A suspension of ethyl 3,5-dibromobenzoate 1 (6.8 g, 21.17
mmol), 2-(2- (2-methoxyethoxy)ethoxy)ethanol 2a (18.3 g, 111.0
mmol) and potassium carbonate (1.0 g, 7.24 mmol) was heated at
85 °C in a distillation system as long as the condensation of
ethanol was complete. The excess of ether 2a was removed by
distillation under reduced pressure. The residue was subjected to
flash chromatography with ethyl acetate/hexane (1:1) as eluent to
give upon evaporation 6.27 g (65%) of colorless oil. [Found: C,
39.39; H, 4.42; C14H18Br2O5 requires C 39.66, H 4.28%]; Rf
(ethyl acetate/hexane 1:1) = 0.2; νmax (liquid film) 3130-3055
(ArH), 2820 (CH), 1729 (C=O), 1120, 1127 (C-O), 1075 (ArBr)
cm-1; H NMR (CDCl3, 300 MHz) δ (ppm): 3.29 (s, 3H, OCH3),
1
Figure 6. Possible mechanisms of helical folding of amphiphilic
polyphenylenes in chiral (A) and achiral (B) environments. The cartoon
representation of the polymer is based on a molecular model of poly(m,p-
phenylene) consisting of 60 repeat units. In a long polymer chain the folding
can occur independently at several places of the chain. Furthermore, in case
of folding in an achiral environment the local helical folds of one polymer
chain may have different handedness.
3.46 (t, 2H, J 3.66 Hz, OCH2), 3.58. –3.63 (m, 6H, OCH2), 3.76
(t, 2H, J 4.17 Hz, OCH2), 4.41 (t, 2H, J 4.28 Hz, OCH2), 7.75 (t,
J 1.8 Hz, 1H, ArH), 8.01 (s, 2H, ArH). 13C NMR (CDCl3, 200
MHz); δ (ppm): 59.00, 64.81, 68.96, 70.59, 70.61, 70.66, 71.92,
122.94, 131.38, 133.31, 138.21, 163.89; m/z (LC-MS, APCI):
M+, found 424. C14H18Br2O5 requires 423.93.
4.3. 2,5,8,11-Tetraoxatridecan-13-yl 3,5-dibromobenzoate (3b)
One can easily imagine the transition of a random coil
conformation of a high molecular weight helically foldable
polymer into a helical conformation that starts independently at
different sites of the macromolecule. In this case an uncontrolled
(with no chiral auxiliary present) folding may lead to the
formation of multiple local helical folds of arbitrary handedness
resulting in a distorted secondary structure, as illustrated in
Figure 7, path B. In an alternative situation in which the folding
is guided by an asymmetric support, e.g., chiral guest, solvent, or
a substituent, the formation of a uniform secondary structure is
more feasible (Figure 7, path A).
A suspension of ethyl 3,5-dibromobenzoate 1 (24.62 g, 15.0
mmol), 2,5,8,11-tetraoxatridecan-13-ol 2b (15.62 g, 75.0 mmol),
and potassium carbonate (0.52 g, 37.5 mmol) was heated at 85 °C
in a distillation system as long as the condensation of ethanol was
complete. The excess of ether 2b was removed by distillation
under reduced pressure. The residue was subjected to flash
chromatography with ethyl acetate/hexane (1:1) as eluent to give
upon evaporation 3.1 g (44%) of colorless oil. [Found: C, 40.75;
H, 4.70; C16H22Br2O6 requires C 40.88, H 4.72%]; Rf (ethyl
acetate/hexane 1:1) = 0.15; νmax (liquid film) 3133–3057 (ArH),
2822 (CH), 1721 (C=O), 1115, 1126 (C-O), 1069 (ArBr) cm-1; 1H
NMR (CDCl3, 300 MHz) δ (ppm): 3.41 (s, 3H, OCH3), 3.53–3.58
(m, 2 H, OCH2), 3.60–3.73 (m, 10 H, OCH2), 3.87 (t, 2H, J 4.8

5
Supplementary data
Hz, OCH ), 4.51 (t, 2H, J 3.8 Hz, OCH ), 7.88 (t, 1H, J 1.8Hz,
ACCEPTED MANUSCRIPT
2
2
ArH), 8.15 (d, 2H, J 1.8 Hz, ArH); 13C NMR (CDCl3, 75 MHz) δ
(ppm): 59.00, 64.84, 68.96, 70.51, 70.62, 70.64, 71.92, 122.96,
131.39, 133.32, 138.23, 163.92; m/z (LC-MS, APCI): M+, found
468. C16H22Br2O6 requires 467.98.
Supplementary data (GPC elution curves for compounds 5a and
5b) associated with this article can be found, in the online
version, at:
4.4. Poly[2-(2-(2-methoxyethoxy)ethoxy)ethyl 4',5-biphenyl-3-
carboxylate] (5a)
References and notes
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Dibromide 3a (2 g, 4.5 mmol) and benzene-1,4-bis(boronic
acid)propane-1,3-diol diester 4 (4.5 mmol) were dissolved in dry
THF (100 mL). A concentrated solution of NaHCO3 in water (30
mL) was added to the reaction mixture and the system was
15
degassed. Freshly prepared Pd[P(p-tolyl)3]3 (3 mg, 0.6 mol%)
was added and the reaction mixture was allowed to stir at 80 °C
for 96 h under nitrogen atmosphere. Then deionized water (200
mL) was added and the emulsion was taken up with
dichloromethane (2×150 mL). The organic layer was separated,
washed with water, brine, dried over Mg2SO4, and evaporated to
give 0.97 g (60%) of polyphenylene 5a as colorless solid.
[Found: C, 69.44; H, 6.60; C20H22O5 requires C 70.15, H 6.48%];
νmax (KBr) 3154–3072 (br, ArH), 2800 (CH), 1690 (C=O), 1111,
1
(C-O); H NMR (CDCl3, 500 MHz) δ (ppm): 3.37 (br. s, 3H,
OCH3), 3.52 (br. s, 2H, OCH2), 3.72 (br. s, 6H, OCH2), 3.94 (br.
s, 2H, OCH2), 4.62 (br. s, 2H, C(O)OCH2), 7.89 (br. s, 4H, ArH),
8.17 (br. s, 1H, ArH), 8.40 (br. s, 2H, ArH);13C NMR (CDCl3,
175 MHz) δ(ppm): 59.00, 64.81, 68.96, 70.59, 70.61, 70.66,
71.92,128.00, 128.29, 130.87, 131.90, 140.22, 141.94, 167.03.
4.5. Poly[2,5,8,11-tetraoxatridecan-13-yl 4',5- biphenyl-3 -
carboxylate] (5b)
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D. Angew. Chem. Int. Ed. 2007, 46, 4956–4959.
Dibromide 3b (1.01 g, 2.14 mmol) and benzene-1,4-
bis(boronic acid)propane-1,3-diol diester 4 (0.526 g, 2.14 mmol)
were dissolved in dry THF (50 mL). A concentrated solution of
NaHCO3 in water (10 mL) was added to the reaction mixture and
the system was degassed. Freshly prepared Pd[P(p-tolyl)3]3 (1.5
mg, 0.6 mol%) was added and the reaction mixture was allowed
to stir at 80 °C for 96 h under nitrogen atmosphere. Then
deionized water (100 mL) was added and the emulsion was taken
up with dichloromethane (2×70 mL). The organic layer was
separated, washed with water, brine, dried over Mg2SO4, and
evaporated to give a highly viscous residue. The latter was
dissolved in chloroform (10 mL) and the solution was poured
into stirred hexane (100 mL). The suspended polymer was
separated by centrifugation as colorless solid. [Found: C, 67.86;
H, 6.93; C22H26O6 requires C 68.37, H 6.78%]; νmax (KBr) 3160–
16. Hecht, S.; Khan, A. Angew. Chem. Int. Ed. 2003, 42, 6021–6024.
17. Khan, A.; Hecht, S. Chem. Eur. J. 2006, 12, 4764–4774.
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3066 (br, ArH), 2807 (CH), 1695 (C=O), 1110 (C-O); H NMR
(CDCl3, 300 MHz) δ (ppm): 3.43 (br. s, 3H, OCH3), 3.52 (br. s,
2H, OCH2), 3.61 (br. s, 2H, OCH2), 3.64 (br. s, 2H, OCH2), 3.69
(br. 2H, OCH2), 3.72 (br. s, 2H, OCH2), 3.76 (br. s 2H, OCH2),
3.93 (br. 2H, OCH2), 4.60 (br. s, 2H, C(O)OCH2), 7.87 (br. 4H,
ArH), 8.15 (br. s, 1H, ArH), 8.38 (br. s, 2H, ArH); 13C NMR
(CDCl3, 300 MHz) δ (ppm): 58.96, 64.43, 69.26, 70.49, 70.65,
71. 89, 127.35, 127.88, 130.14, 131.51, 139.67, 141.54, 166.39.
Acknowledgments
The authors thank Prof. P. Walde (ETH Zurich) for his
professional assistance with UV/Vis, fluorescence, and CD
measurements. We are also grateful to Mr. M. Colussi and Ms.
D. Sutter for carrying out GPC measurements and recording
NMR spectra, respectively. Mr. V. Lukin is acknowledged for
producing the 3D illustrations. Last but not least, we would like
to express our gratitude to Prof. A. D. Schlüter (ETH Zurich) for
his advice and support.

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SUPPLEMENTARY DATA
A Helically folded poly(m,p-phenylene)
Manuel Burkhaltera, Ramchandra Kandrea, and Oleg Lukinb
a Institute of Polymers,Department of Materials, ETH Zurich, Wolfgang-Pauli St. 10, HCI, CH-8093 Zurich, Switzerland
b Skolkovo Institute of Science and Technology, Novaya St. 100, Skolkovo, Odintsovsky district, Moscow Region, 143025 Russia
GPC of polyphenylene 5a
GPC of polyphenylene 5b
Corresponding author. Tel.: +7-(495) 280-14-81 ext.3114; fax: +7-(495) 280-14-81; e-mail: o.lukin@skoltech.ru
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