Ordered nanostructures from self-assembly of H-shaped coil-rod-coil molecules

Article abstract of DOI:10.1002/pola.27448

A new class of p-conjugated, skewed H-shaped oligomers, consisting of biphenyl, phenylene vinylene, and phenylene ethynylene units as the rigid segment, were synthesized via Sonogashira coupling and Wittig reactions. The coil segments of these molecules were composed of poly(ethylene oxide) (PEO) or PEO with lateral methyl groups between the rod and coil segment, respectively. The experimental results revealed that the lateral methyl groups attached to the surface of the rod and coil segments dramatically influenced the selfassembling behavior of the molecules in the crystalline phase. H-shaped rod-coil molecules containing a lateral methyl group at the surface of the rod and PEO coil segments self-assemble into a two-dimensional columnar or a three-dimensional bodycentered tetragonal nanostructures in the crystalline phase, whereas molecules lacking a lateral methyl group based on the PEO coil chain self-organize into lamellar or hexagonal perforated lamellar nanostructures.

Full text of DOI:10.1002/pola.27448

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Ordered Nanostructures from Self-Assembly of H-Shaped Coil–Rod–Coil
Molecules
Zhuoshi Wang,1 Keli Zhong,2 Yongri Liang,3 Tie Chen,1 Bingzhu Yin,1 Myongsoo Lee,4
Long Yi Jin1,4
1Key Laboratory for Organism Resources of the Changbai Mountain and Functional Molecules and Department
of Chemistry, College of Science, Yanbian University, No. 977 Gongyuan Road, Yanji 133002, China
2College of Chemistry, Chemical Engineering and Food Safety, Bohai University, Jinzhou 121013, China
3College of Materials Science & Engineering, Beijing Institute of Petrochemical Technology, Beijing 102617, China
4State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University,
Changchun 130012, China
Correspondence to: L. Y. Jin (E-mail: lyjin@ybu.edu.cn) or M. Lee (E-mail: mslee@jlu.edu.cn)
Received 12 August 2014; accepted 7 October 2014; published online 28 October 2014
DOI: 10.1002/pola.27448
ABSTRACT: A new class of p-conjugated, skewed H-shaped
oligomers, consisting of biphenyl, phenylene vinylene, and
phenylene ethynylene units as the rigid segment, were synthe-
sized via Sonogashira coupling and Wittig reactions. The coil
segments of these molecules were composed of poly(ethylene
oxide) (PEO) or PEO with lateral methyl groups between the
rod and coil segment, respectively. The experimental results
revealed that the lateral methyl groups attached to the surface
of the rod and coil segments dramatically influenced the self-
assembling behavior of the molecules in the crystalline phase.
H-shaped rod–coil molecules containing a lateral methyl group
at the surface of the rod and PEO coil segments self-assemble
into a two-dimensional columnar or a three-dimensional body-
centered tetragonal nanostructures in the crystalline phase,
whereas molecules lacking a lateral methyl group based on the
PEO coil chain self-organize into lamellar or hexagonal perfo-
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rated lamellar nanostructures. 2014 Wiley Periodicals, Inc. J.
Polym. Sci., Part A: Polym. Chem. 2015, 53, 85–92
KEYWORDS: body-centered tetragonal; coil–rod–coil; H-shaped
molecule; nanostructure; SAXS; self-assembly
Recently, ordered nanostructures in the form of T-shaped,19–21
dumbbell,22–26 and O-shaped27 rod–coil molecules or
copolymers have been reported by Lee and coworkers. The
results imply that various supramolecular nanostructures can be
constructed by controlling the molecular parameters of the dif-
ferent shape of rod–coil molecules.28 One example is the filled
cylindrical and hollow tubular scrolls that are formed through
self-assembly of T-shaped rod–coil molecules consisting of a
penta-p-phenylene-conjugated rod connected to a poly(propyl-
ene oxide) coil laterally attached through an imidazole linkage.29
The authors explained that the structure of the scrolls could be
controlled by adjusting the volume fraction of rod-to-coil seg-
ments of the T-shaped rod–coil molecules in the solid state.
Hence, such a system has the potential for a wide range of appli-
cations in nanoscience. Although, to our knowledge, many
papers reported the self-assembling behavior of the rod–coil
molecular systems, there is no report concerning the synthesis
and self-assembly of H-shaped coil–rod–coil oligomers.
INTRODUCTION An important challenge in the preparation
of self-assembling materials is to control the formation of
supramolecular nanostructures with well-defined shapes and
sizes. These advanced functional materials have remarkable
potential in fields such as biochemistry, molecular electron-
ics, biomimetic chemistry, and materials science.1–7 Self-
assembly of rod–coil block molecules in the bulk state leads
to various supramolecular nanostructures, such as the one-
dimensional (1D) lamellar, two-dimensional (2D) columnar,
and three-dimensional (3D) bundles. These are held together
by noncovalent forces, including hydrophobic and hydro-
philic effects, electrostatic interactions, hydrogen bonding,
and microphase segregation.8–13 It has been reported that
molecular parameters, such as the volume fraction of rod–
to–coil segment, the cross-sectional area of the coil segment,
or the shape of the rigid rod segment, dramatically influence
the tendency of the molecules to form various
nanostructures.14–18
Zhuoshi Wang and Keli Zhong contributed equally to this work.
Additional Supporting Information may be found in the online version of this article.
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Therefore, the design of rod–coil molecules consisting of conju-
gated H-shaped rod building blocks and poly(ethylene oxide)
(PEO) coil segments incorporating lateral methyl groups
between the rod and coil segments is of great interest. Such mol-
ecules are able to self-assemble into various supramolecular
nanostructures that can find applications in biochemistry and
materials science.
reducing the phase transition temperatures of molecules 2a
and 2b in comparison to molecules 1a and 1b.
To identify the self-assembled nanostructures, SAXS experi-
ments were performed for molecules 1 and 2. In the crystal-
line phases of 1a, the small-angle X-ray diffraction patterns
show several sharp reflections, which correspond to equidis-
tant q-spacings and, thus, index to a lamellar lattice [Fig.
2(a)]. The layer spacing at the lower temperature crystalline
phase of 45.4 Å is less than the corresponding estimated
stretching molecular length [61.6 Å by Corey–Pauling–Koltun
(CPK) molecular model], indicative of a monolayer lamellar
structure, in which the rod segments are fully interdigitated.
With this in mind, in this work, we report the synthesis and
structural analysis of H-shaped rod building block oligomers
composed of biphenyl, phenylene vinylene, and phenylene ethy-
nylene units as a rigid segment, and we investigate their self-
assembling behaviors in bulk state by using differential scan-
ning calorimetry (DSC) and small-angle X-ray scattering (SAXS).
In contrast to 1a, coil–rod–coil molecule 1b based on the lon-
ger coil length displays a distinct nanostructure. The X-ray dif-
fraction patterns of 1b shown in Figure 2(b) can be indexed to
the (100), (010), (200), and (300) planes, corresponding to a
2D oblique columnar structure with lattice constants a 5 66.4
Å, b 5 51.4 Å, and a characteristic angle c 5 55ꢀ. From the
experimental values of the unit cell parameters (a, b, c) and the
density (q 5 1.02), the average number (n) of molecules per
cross-sectional slice of the column is calculated to be approxi-
mately 4, according to the following equation, where Mw is the
molecular weight and NA is Avogadro’s number.
RESULTS AND DISCUSSION
Synthesis of H-Shaped Oligomers 1 and 2
The synthetic route for H-shaped coil–rod–coil oligomers con-
sisting of biphenyl, phenylene vinylene, and phenylene ethyny-
lene units as a rigid segment is described in Scheme 1. Coil–
rod–coil molecules 1 and 2 were successfully synthesized
through the Sonogashira coupling reaction between 1,4-
bis(2,5-diethynylstyryl)benzene (molecule 7) and precursor 8.
Molecule 7 with tetraethynyl groups was prepared by the
desilylation of molecules 6. This in turn was obtained via a
Sonogashira coupling reaction between 1,4-bis(5-bromo-2-
iodostyryl)benzene (molecule 5) and trimethylsilylacetylene
(TMSA) with Pd/Cu as a catalyst. 1,4-Bis(5-bromo-2-iodostyr-
yl)benzene was produced by the Wittig–Horner reaction of the
phosphonate ylide 3 and 5-bromo-2-iodobenzaldehyde, using
2-aminobenzoic acid methyl ester and dimethyl terephthalate
as starting materials. The reaction product containing 1 and 2
was purified using silica gel column chromatography and
recycle gel permeation chromatography. The structures of
molecules 1 and 2 were characterized by 1H NMR and matrix-
assisted laser desorption ionization time-of-flight (MALDI-
TOF) mass spectroscopy (see Supporting Information) and
were shown to be in full agreement with the structures pre-
sented in Scheme 1.
n5 ðabc3sin cÞ3q3NA=Mw
(1)
The results described above demonstrate that in the case of
H-shaped rigid building blocks it is much easier to manipu-
late the supramolecular structure using different lengths of
flexible PEO chains than in the case of the linear rod–coil
molecular architecture. The tendency of a lamellar phase to
transform into a 2D columnar phase is consistent with the
results obtained on n-shaped rod–coil systems reported by
our laboratory.30,31 The variation in the supramolecular
structure can be rationalized by considering the microphase
separation between the dissimilar parts of the molecules and
the space-filling requirement of the flexible PEO chains.
Molecules 2a and 2b were synthesized to investigate the influ-
ence of the methyl groups grafted on the surface of the rod
and coil segments on the self-assembly tendency of H-shaped
coil–rod–coil molecules. The SAXS patterns of molecule 2a dis-
played two main peaks together with several reflections, as
shown in Figure 3(a). The observed reflections can be indexed
to the (101), (002), (102), (110), (112), (113), and (230)
planes for 3D hexagonal symmetry (P63/mmc space group
symmetry) with lattice constants a 5 62.2 Å and c 5 81 Å
(see Table 2). An interesting point to be noted here is that the
peak intensity associated with the (002) reflection appears to
be the most intense, implying that the fundamental structure
is lamellar. Hence, the supramolecular structure of 2a can be
characterized as a honeycomb-like crystalline layer of rod seg-
ments with in-plane hexagonal packing of coil perforations.32
From the lattice parameters determined from the X-ray dif-
fraction patterns and the densities of each segment, the perfo-
ration sizes are calculated to be 4.2 nm in diameter (see
Supporting Information).
Structures of Bulk State
The self-assembling behavior of the H-shaped molecules 1
and 2 was investigated by means of DSC and SAXS. Figure 1
shows the DSC heating and cooling traces and the thermal
transitions of the oligomers 1a and 1b and 2a and 2b. The
transition temperatures determined from the DSC scans are
summarized in Table 1. As shown in Table 1, the melting
transition temperatures of the H-shaped molecules decrease
with the increase in PEO coil length. By incorporating methyl
groups into molecules 1 and 2, the melting points of mole-
cules 2a and 2b significantly decreased to values comparable
with those for 1a and 1b. The results clearly prove that
increasing the length of the flexible chain or incorporating
side groups at the surface of the rod and coil leads to a
reduced tendency of self-assembly of the rod segments for
the construction of ordered nanostructures, subsequently
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SCHEME 1 Synthetic route of H-shaped rod–coil molecules 1 and 2.
FIGURE 1 DSC traces (10 ꢀC/min) recorded during the second heating scan and the first cooling scan of the series of molecules 1 and 2.
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TABLE 1 Thermal Transitions and Corresponding Enthalpy
Changes of Molecules 1 and 2
Phase Transition Temperature (ꢀC) and
Corresponding Enthalpy Changes
(kJ/mol)
Molecule
Heating
Cooling
1a
K 217 (9.3) i
i 210 (11.4) k
1b
2a
2b
K 128 (19.8) i
K 92 (20.7) i
K 68 (22.3) i
i 120 (21.3) k
i 63 (23.9) k
i 53 (24.6) k
In contrast to molecule 2a, the SAXS patterns of molecule 2b
showed a sharp, high-intensity reflection at a low angle
together with a number of sharp reflections of low intensity
at higher angles [Fig. 3(b)]. These reflections can be indexed
to the (110), (101), (020), (211), and (220) planes for a 3D
body-centered tetragonal structure with lattice constants of
a 5 69.6 Å and c 5 64.1 Å (c/a 5 0.92) (see Table 3). To
describe the detailed supramolecular nanostructure, it is
desirable to calculate the number of molecules per micelle.
From the lattice constants and the densities, the average
number (n) of molecules per micelle can be calculated to be
approximately 40, according to eq 2, where Mw is the molec-
ular weight, q is the molecular density, and NA is Avogadro’s
number.
FIGURE 3 Small-angle X-ray diffraction patterns of the rod–coil
oligomers 2a and 2b measured in their solid state.
NAq
n5a2c
(2)
2Mw
These results indicate that the methyl groups that are
grafted on the surface of the rod and coil segments lead to
the formation of various supramolecular nanostructures of
the rod–coil molecular system.
On the basis of the above discussion, we reached the follow-
ing conclusions. Molecules 1a and 1b self-assemble into a
lamellar structure and an oblique columnar structure in the
solid state. However, molecules 2a and 2b, which have lat-
eral methyl groups at the surface of the rod and coil seg-
ments, and coil lengths identical with 1a and 1b, self-
organize into a hexagonal perforated lamellar structure and
a 3D body-centered tetragonal structure in the solid state,
respectively (see Table 4). Based on the data presented so
far, a schematic representation of the self-assembled struc-
tures of 1 and 2 is illustrated in Figure 4.
The structures of molecules 1a and 2a or 1b and 2b, con-
sisting of similar rod segments and identical-length coil
chains, show that the lateral methyl groups on the surface of
the rod and coil segments are the main feature that influen-
ces the self-assembling behavior of coil–rod–coil molecules.
The methyl groups at the surface of the rod and coil seg-
ments can lead to lower interactions of p–p stacking and,
subsequently, loosen the packing of the H-shaped rod
FIGURE 2 Small-angle X-ray diffraction patterns of the rod–coil
oligomers 1a and 1b measured in their solid state.
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TABLE 2 Small-Angle X-Ray Diffraction Data for Hexagonal
Perforated Lamellar Structure of Molecule 2a in the Crystalline
Phase, Measured at Room Temperature
methyl groups between the rod and coil segment, respectively.
The experimental results revealed that the lateral methyl
groups grafted on the surface of the rod and coil segments
dramatically influenced the self-assembling behavior in the
crystalline phase. Molecule 1a, with short coil lengths, self-
assembles into a lamellar structure, while molecule 1b, with a
longer PEO coil chain, self-organizes into a 2D rectangular
columnar structure. Molecules 2a and 2b, incorporating
methyl groups between the surface of the coil and rod seg-
ments, spontaneously organize into a perforated lamellar
structure and a 3D body-centered tetragonal structures,
respectively. The strategy described here regarding the incor-
poration of methyl groups onto the surface of the rod and coil
segments could induce the formation of various supramolecu-
lar nanostructures in the rod–coil molecular architecture for
application in nanodevice or nanowire materials.
Hexagonal Perforated Lamellar Structure
h
k
l
qobsd (nm21
)
qcalcd (nm21
)
1
0
1
1.40
1.395
0
1
1
2
0
1
1
0
2
2
3
3
1.55
2.55
3.05
5.08
1.552
2.548
3.051
5.080
qobsd and qcalcd are the scattering vectors of the observed and calcu-
lated reflections for the hexagonal perforated lamellar structure with lat-
tice parameters a 5 6.22 nm, c 5 8.1 nm (k 5 0.154 nm).
segments to produce the more stable 2D columnar or 3D
bundle nanostructures (for WAXS data, see Supporting Infor-
mation). Hence, the strategy of incorporating lateral methyl
or short-chain alkyl groups onto the surface of rod–coil
molecular systems is an effective way to construct various
supramolecular nanostructures for application in nano-
science or materials science. The same is true for incorporat-
ing the lateral chain groups in the middle of the rod
segment. It should be pointed out that we reported previ-
ously16 that the lateral alkyl groups grafted on the center of
the rod segment significantly to influence the self-assembling
behavior of rod–coil molecules. Recently, we have con-
structed the hexagonal-perforate lamellar, columnar, body-
centered tetragonal, and hexagonal closed-packed nanostruc-
tures with various lattice constants, by synthesizing rod–coil
molecules containing lateral alkyl groups in the center of rod
segments.33,34
EXPERIMENTAL
Materials
Di(ethylene glycol) methyl ether 99%, poly(ethylene glyco-
l)methyl ether, tetraethylene glycol 99.5%, toluene-p-sulfonyl
chloride (TsCl, 98%), (2)-ethyl L-lactate, 3,4-dihydro-2H-
pyran, 3,4-dihydro-2H-pyran (99%), p-toluenesulfonic acid
monohydrate(981%), pyridine, phosphorus tribromide,
sodium
hydride,
tetrakis(triphenyl-phosphine)palladium
(99%), copper(I) iodide (98%), triethyl phosphite, 4-
hydroxy-40-iodobiphenyl (981%), 18-crown-6 (99%), lithium
aluminum hydride (97%), methyl 2-aminobenzoate, diisobu-
tylaluminum hydride (1 M solution in hexane), dimethyl ter-
ephthalate, pyridinium chlorochromate (98%) (all from J&K
Chemical and Sigma-Aldrich), and the conventional reagents
were used as received.
Techniques
1H NMR spectra were recorded from CDCl3 solution on a
Bruker AM 300 spectrometer. Column chromatography (silica
gel 100–200) was used to check the purity of the products. A
Perkin Elmer Pyris Diamond differential scanning calorimeter
was used to determine the thermal transitions with the max-
ima and minima of their endothermic or exothermic peaks,
controlling the heating and cooling rates to 10 ꢀC/min. The
X-ray scattering measurements were performed in transmis-
sion mode, with synchrotron radiation at the 1W2A X-ray
beam line, at the Beijing Accelerator Laboratory. The synthe-
sized compounds powdered before preparing the XRD sam-
CONCLUSIONS
A new class of p-conjugated, skewed H-shaped oligomers con-
sisting of biphenyl, phenylene vinylene, and phenylene ethyny-
lene units as
Sonogashira coupling and Wittig reactions. The coil segments
of these molecules were composed of PEO or PEO with lateral
a rigid segment was synthesized, via
TABLE 3 Small-Angle X-Ray Diffraction Data for Body-Centered
Tetragonal Structure of Molecule 2b in the Crystalline Phase,
Measured at Room Temperature
ples. MALDI-TOF-MS was performed on
a Perceptive
Biosystems Voyager-DE STR using a 2-cyano-3-(4-hydroxy-
phenyl) acrylic acid as matrix.
Body-Centered Tetragonal Structure
h
k
l
qobsd (nm21
)
qcalcd (nm21
)
1
1
0
1.28
1.282
Synthesis of Precursors 3, 4, and 8
These compounds were prepared according to the proce-
dures described elsewhere.35,36 For detailed synthetic proce-
dures, see Supporting Information.
1
0
2
2
0
2
1
2
1
0
1
0
1.34
1.81
2.25
2.55
1.338
1.809
2.249
2.548
Synthesis of 1,4-Bis(5-bromo-2-iodostyryl)benzene (5)
Compound 3 (0.09 g, 0.24 mmol) together with sodium
hydride (0.02 mg,0.60 mmol) were put into a two-necked
flask and dissolved in dry tetrahydrofuran (THF; 50 mL).
qobsd and qcalcd are the scattering vectors of the observed and calcu-
lated reflections for the body-centered tetragonal structure with lattice
parameters a 5 6.96 nm, c 5 6.41 nm (k 5 0.154 nm).
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TABLE 4 Characterization of the Self-Assembling Behavior of H-Shaped Molecules 1a and 1b and 2a and 2b in the Bulk State
Molecule
fcoil (%)
Crystalline Phase
Body-Centered
Tetragonal
Lamellar
HPL
Oblique Columnar
d (nm)
a
c
a
b
a
c
1a
1b
2a
2b
50.6
58.0
51.9
60.0
4.54
6.64
5.14
6.22
8.1
6.96
6.41
fcoil, coil volume fraction; d, the layer spacing; HPL, hexagonal perforated layer phase; a, c, lattice constant (nm).
ꢀ
Upon gentle heating at 50 C, the solution gradually turned a
light yellow color. A solution of aldehyde 4 (0.11 g, 0.48
mmol) in THF (15 mL) was added dropwise over 1 h. The
reaction was kept under stirring and heating for another 4 h.
The small excess of sodium hydride was carefully quenched
with diluted hydrochloric acid (10%, 20 mL), and the mix-
ture was extracted several times with methylene chloride.
The organic layer was dried with magnesium sulfate and
concentrated under vacuum, and the crude product was
purified by means of recrystallization to give the pure com-
pound as a yellow solid (63 mg, 50%).
1H NMR (300 MHz, CDCl3): 7.76 (d, J 5 0.9 Hz, 2H), 7.72 (d,
J 5 4.8 Hz, 2H), 7.58 (s, 4H), 7.26 (d, J 5 9.6 Hz, 2H), 7.10
(dd, J 5 5.1, 1.8 Hz, 2H), 6.98 (d, J 5 9.6 Hz, 2H).
Synthesis of 1,4-Bis(2,5-bis(trimethylsilylethynyl)styryl)
benzene (6)
Bis(triphenylphosphine)palladium(II) dichloride (0.53 g, 0.45
mmol) and copper iodide (0.71 g, 0.9 mmol) were added to
a mixture of 5 (2.06 g, 3 mmol), trimethylsilyl acetylene (4.2
mL, 30 mmol), trimethyl amine (Et3N; 5 mL), and THF (30
mL). The mixture was heated to reflux for 19 h under N2
FIGURE 4 Schematic representation of self-assembly of (a) monolayer structure for 1a, (b) oblique columnar structure for 1b, (c)
perforated lamellar structure for 2a, and (d) body-centered tetragonal superlattice for 2b. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
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and kept away from the light. The mixture was then diluted
with methyl chloride, washed with water, and dried over
MgSO4. After filtration, the filtrate was concentrated to about
1.5 mL and precipitated from methanol (50 mL). The solid
was collected by filtration and further purified using flash
column chromatography (4:1 hexane/CH2Cl2) to give 6 (1.54
g, 80%) as a yellow solid.
7.48–7.52 (m, 12 H), 7.38 (d, J 5 9.9 Hz, 2H), 6.68–6.71 (m,
8H), 4.56–4.64 (m, 4H), 3.66–3.75 (m, 74 H), 3.37 (s, 12H), 1.35
(d, J 5 6.2 Hz, 12H). MALDI-TOF-MS m/z (M)1 2045.
Oligomer 2b
Yield: 23.6%; 1H NMR (300 MHz, CDCl3, d, ppm): 7.88 (s,
2H), 7.76 (d, J 5 9.6 Hz, 2H), 7.70–7.74 (m, 16 H), 7.53 (s,
4H), 7.46–7.50 (m, 12 H), 7.42 (d, J 5 9.9 Hz, 2H), 6.68–6.72
(m, 8H), 4.57–4.63 (m, 4H), 3.66–3.75 (m, 108 H), 3.34 (s,
12H), 1.35 (d, J 5 6.2 Hz, 12H). MALDI-TOF-MS m/z (M)1
2397, (M 1 Na)1 2420.
1H NMR (300 MHz, CDCl3): 7.81 (s, 2H), 7.68 (d, J 5 6 Hz, 2H),
7.57 (s, 4H), 7.44 (d, J 5 5.1 Hz, 2H), 7.30 (dd, J 5 4.8, 0.9 Hz,
2H), 7.22 (d, J 5 9.6 Hz, 2H), 0.34 (s, 18H), 0.30 (s, 18H).
Synthesis of 1,4-Bis(2,5-diethynylstyryl)benzene (7)
A solution of 6 (1.54 g, 2.4 mmol) and potassium carbonate
(2 g, 14.4 mmol) in THF/MeOH (30 mL/30 mL) was stirred
at room temperature for 3 h. The mixture was then concen-
trated by evaporation and extracted with dichloromethane.
The combined organic portions were dried over MgSO4 and
filtered. The residue was purified by flash column chroma-
tography with 30% CH2Cl2 in hexanes to give product 7
(1.08 g, 91%) as a yellow solid.
ACKNOWLEDGMENTS
This work was supported by the National Natural Science
Foundation of China (grant nos. 21164013 and 21304009),
the Program for New Century Excellent Talents in Jilin Prov-
ince (201410), China, the Open Projects of State Key Labora-
tory of Supramolecular Structure and Materials, Jilin
University (grant no. sklssm201430), and the State Key Lab-
oratory of Elemento-Organic Chemistry, Nankai University.
The authors are grateful to Bejing Synchrotron Radiation
Facility (BSRF), Institute of High Energy Physics, Chinese
Academy of Sciences for help with the X-ray scattering meas-
urements of molecular structures.
1H NMR (300 MHz, CDCl3): 7.84 (d, J 5 0.9 Hz, 2H), 7.62 (d,
J 5 9.9 Hz, 2H), 7.56 (s, 4H), 7.48 (d, J 5 5.1 Hz, 2H), 7.33
(dd, J 5 4.8, 1.5 Hz, 2H), 7.19 (d, J 5 9.9 Hz, 2H), 3.49 (s,
2H), 3.20 (s, 2H).
Synthesis of the H-Shaped Coil–Rod–Coil Oligomers (1 and 2)
These oligomers were synthesized by the same synthetic
procedures. A representative example was described for 1a.
Compound 7 (0.114 g, 0.3 mmol), compound 8 (0.954 g, 1.8
mmol), CuI (23 mg, 0.12 mmol), and Pd(PPh3)4 (69 mg, 0.06
mmol) were dissolved in absolute THF (30 mL) and Et3N
(20 mL). The mixture was refluxed for 48 h under N2. Then,
it was concentrated by evaporation and washed with water.
The mixture was extracted with dichloroethane, dried over
anhydrous magnesium sulfate, and filtered. After the solvent
was removed in a rotary evaporator, the crude product was
purified by silica gel chromatography (EA:CH3OH, 30:1 to
10:1). The product was further purified by recycle gel per-
meation chromatography (JAI) to yield 0.49 g of yellow solid
(25.7%).
REFERENCES AND NOTES
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Oligomer 1b
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1
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