Synthesis and self-assembly of rod-coil molecules with n-shaped rod building block

Article abstract of DOI:10.1002/pola.23909

The rod-coil molecules with n-shaped rod building block, consisting of an anthracene unit and two biphenyl groups linked together with acetylenyl bonds at the 1,8-position of anthracene as a rigid rod segment, and the alkyl or alkyloxy chains with various

Full text of DOI:10.1002/pola.23909

Synthesis and Self-Assembly of Rod-Coil Molecules with n-Shaped Rod
Building Block
KE-LI ZHONG,1 ZHEGANG HUANG,2 ZHIJIN MAN,1 LONG YI JIN,1,3 BINGZHU YIN,1 MYONGSOO LEE2
1Key Laboratory for Organism Resources of the Changbai Mountain and Functional Molecules, Ministry of Education and
Department of Chemistry, College of Science, Yanbian University, No. 977 Gongyuan Road, Yanji 133002,
People’s Republic of China
2Department of Chemistry, Seoul National University, Seoul 151-747, Korea
3School of Natural Sciences, University of California, Merced, California 95343
Received 1 December 2009; accepted 18 December 2009
DOI: 10.1002/pola.23909
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: The rod-coil molecules with n-shaped rod building
block, consisting of an anthracene unit and two biphenyl groups
linked together with acetylenyl bonds at the 1,8-position of an-
thracene as a rigid rod segment, and the alkyl or alkyloxy chains
with various length (i.e., methoxy- (1), octyl- (2), hexadecyl- (3))
at the 10-position of anthracene and poly(ethylene oxide) with
the number of repeating units of 7 connected with biphenyl as
coil segments were synthesized. The molecular structures were
characterized by 1H NMR and MALDI-TOF mass spectroscopy.
The self-assembling behavior of new type of molecules 1–3 was
investigated by means of DSC, POM, and SAXS at the bulk state.
These molecules with a n-shaped rod building block segment
self-assemble into supramolecular structures through the com-
bination of p–p stacking of rigid rod building blocks and micro-
phase separation of the rod and coil blocks. SAXS studies reveal
that molecules 1 and 2 show hexagonal columnar and rectangu-
lar columnar structures in the liquid crystalline phase, respec-
tively; meanwhile, molecules 1–3 self-organize into lamellar
structures in the crystalline state. In addition, self-assembling
studies of molecules 1–3 by DLS and TEM indicated that these
molecules self-assemble into elongated nanofibers in aqueous
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medium.
2010 Wiley Periodicals, Inc. J Polym Sci Part A:
Polym Chem 48: 1415–1422, 2010
KEYWORDS: n-shaped; rod-coil; SAXS; self-assembly; supramo-
lecular structures
INTRODUCTION Self-assembly of conjugated molecular sys-
tems through noncovalent forces including hydrophobic and
hydrophilic effects, electrostatic interaction, hydrogen bond-
ing, and microphase segregation can be widely used because
of their remarkable potentials as advanced functional materi-
als in areas of biochemistry, molecular electronics, biomi-
metic chemistry, and materials science.1–5 Among self-assem-
bling molecular systems, conjugated rod-coil block molecules
facile provide the spontaneous generation of a well-defined
supramolecular architecture.6 The supramolecular structures
can be precisely controlled by systematic variation of the
molecular shape and volume fraction of specific segments.7–9
The self-assembling studies concerning supramolecular
structures and the intriguing properties have been reported,
focusing on various shapes of rigid conjugated rod segment,
such as Y shaped,10–12 T shaped,13,14 O shaped,15 K shaped,16
propeller shaped,17 and dumbbell like.18 The results showed
that incorporation of flexible coil segments into the conju-
gated rod building block lead to various shaped molecules
and these molecules self-organize into unique self-assem-
bling or aggregation structures, such as 1D lamellar, 2D co-
lumnar, cylinders, discrete bundles, ribbons, and vesicles.
One example is that we have systematically studied a dumb-
bell-shaped molecule that can self-assemble into a capsule
structure with responsive gated nano-pores undergoing a
transition from the open state to the closed state upon heat-
ing, which is capable of blocking cargo transport.18 Hence,
such a system has the potential to be developed as the gated
plasma membrane of an artificial cell. In particular, there is
growing interest in the design of synthetic rod-coil molecules
with conjugated n-shaped rod building block that are able to
self-assemble into supramolecular nanostructures for appli-
cation in biochemistry and materials science.
With this in mind, for the first time, we synthesized rod-coil
molecules 1–3 (see Scheme 1) with conjugated n-shaped rod
building blocks and investigated their self-assembling behav-
iors in bulk state and an aqueous solution by using differen-
tial scanning calorimetry (DSC), thermal polarized optical
Additional Supporting Information may be found in the online version of this article. Correspondence to: L. Y. Jin (E-mail: lyjin@ybu.edu.cn) or M.
Lee (E-mail: myongslee@snu.ac.kr)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 1415–1422 (2010) 2010 Wiley Periodicals, Inc.
ROD-COIL MOLECULES WITH n-SHAPED ROD BUILDING BLOCK, ZHONG ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthetic route of molecules 1–3.
microscopy (POM), small-angle X-ray scatterings (SAXS), and
transmission electron microscopy (TEM).
2-pol optical polarized microscope, equipped with a Mettler
FP82 hot-stage and a Mettler FP90 central processor, was
used to observe the thermal transitions and to analyze the
anisotropic texture. Matrix-assisted laser desorption ioniza-
tion time-of-flight mass spectroscopy (MALDI-TOF-MS) was
performed on a perceptive Biosystems Voyager-DE STR using
a 2-cyano-3-(4-hydroxyphenyl) acrylic acid (CHCA) as matrix.
The UV–vis and the fluorescence spectra were obtained from
a Shimadzu UV-1650PC spectrometer and a Hitachi F-4500
fluorescence spectrometer, respectively. Dynamic light scat-
tering (DLS) measurements were performed by using a
UNIPHASE He-Ne laser operating at 632.8 nm. The transmis-
sion electron microscope (TEM) was performed at 120 kV
using JEOL 1020. Sample was stained by depositing a drop
of 2 wt % uranyl acetate aqueous solution onto the surface
EXPERIMENTAL
Materials
Poly(ethylene glycol) methyl ether (Mw ¼ 350), toluene-p-
sulfonyl chloride (TsCl, 98%), 2-methyl-3-butyn-2-ol, cuprous
iodide, sodium iodide, copper powder, 1-bromopentadecane,
1-bromooctane (all from Aldrich), tetrakis(triphenylphos-
phine) palladium(0), sodium borohydride, 4-hydroxy-40-iodo-
biphenyl, 1,8-dichloro-anthraquinone (all from TCI), and the
conventional reagents were used as received. Molecules 4
and 8–12 were prepared according to the procedures
described elsewhere (see Supporting Information).19–21
ꢀ
of the sample-loaded grid and dried at 45 C.
Measurements
1H NMR spectra were recorded from CDCl3 solutions on a
Bruker AM 300 spectrometer. A Perkin–Elmer Pyris Diamond
differential scanning calorimeter was used to determine the
thermal transitions, which were reported as the maxima and
minima of their endothermic or exothermic peaks; the heat-
ing and cooling rates were controlled to 10 ꢀC/min. X-ray
scattering measurements were performed in transmission
mode with synchrotron radiation at the 3C2 X-ray beam line
at Pohang Accelerator Laboratory, Korea. A Nikon Optiphot
Synthesis of Compound 5
Excess K2CO3, 4-hydroxy-40-iodobiphenyl (3.0 g, 10 mmol),
and compound 4 (5.5 g, 11 mmol) were dissolved in abso-
lute acetonitrile (120 mL). The mixture was further refluxed
for 12 h. The solvent was removed in a rotary evaporator
and washed by water, and then the mixture was extracted
with ethyl acetate and dried over anhydrous magnesium sul-
fate and filtered. After the solvent was removed in a rotary
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ARTICLE
evaporator, the crude product was purified by silica gel chro-
matography (EA as eluent) to yield 5.3 g of a yellow ropy
liquid (85%).
1H NMR (300 MHz, CDCl3, d, ppm) 9.62(s, 1H, 9-anthracene-
H), 8.24(d, 2H, 4,5-anthracene-H), 7.76(d, 2H, 2,7-anthra-
cene-H), 7.49(m, 6H, 3,6-anthracene-H and o to phenyl-CC),
7.33(d, 8Ar-H, m to phenyl-CC), 6.84(d, 4Ar-H, o to CH2O-
phenyl), 4.10(t, 4H, phenylOCH2CH2O), 3.82(t, 4H, phenyl-
OCH2CH2O), 3.51–3.70(m, 50H, AOCH2CH2OA and anthra-
cene-CH2), 3.34(s, 6H, OCH3), 1.78(m, 2H, anthracene-
CH2CH2), 1.55(m, 2H, anthracene-CH2CH2CH2), 1.22–1.30(m,
24H, ACH2CH2ACH3), 0.86 (t, 3H, CH3). MALDI-TOF-MS m/z
(M)þ 1434, (MþNa)þ 1457.
1H NMR (300 MHz, CDCl3,d, ppm) 7.73(d, 2Ar-H,o to phenyl-
I, J ¼ 11.3 Hz),7.47(d, 2Ar-H,m to phenyl-OCH2, J ¼ 8.6 Hz),
7.29 (d, 2Ar-H, m to phenyl-I, J ¼ 11.3 Hz), 6.98 (d, 2Ar-H, o
to phenylAOCH2, J ¼ 8.6 Hz), 4.17 (t, 2H, phenylOCH2CH2O,
J ¼ 4.8 Hz), 3.88(t, 2H, phenylOCH2CH2O, J ¼ 4.8 Hz), 3.54–
3.74(m, 24H, AOCH2 CH2OA), 3.38(s, 3H, OCH3).
Synthesis of Compound 6
Molecule 2
1
Compound 5 (3.09 g, 5 mmol), 2-methyl-3-butyn-2-ol (1.26
g, 15 mmol), Et3N (20 mL), CuI (15 mg, 0.08 mmol), and
Pd(PPh3)4 (50 mg, 0.04 mmol) were dissolved in THF
(30 mL). The mixture was refluxed for 12 h under Ar, and
then the solution was concentrated and washed by water.
The mixture was extracted with ethyl acetate and 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 (CH2Cl2/CH3OH ¼ 20/1
as eluent) to yield 1.72 g of a yellow ropy liquid (62%).
Yield:52%; H NMR (300 MHz, CDCl3, d, ppm) 9.66(s, 1H, 9-
anthracene-H), 8.28(d, 2H, 4,5-anthracene-H), 7.82(d, 2H,
2,7-anthracene-H), 7.54(m, 6H,3,6-anthracene-H and o to
phenyl-CC), 7.35(d, 8Ar-H, m to phenyl-CC), 6.84(d, 4Ar-H, o
to CH2Ophenyl), 4.14(t, 4H, phenylOCH2CH2O), 3.88(t, 4H,
phenylOCH2CH2O), 3.51–3.70(m, 50H, AOCH2CH2OA and an-
thracene-CH2), 3.36(s, 6H, OCH3), 1.80(m, 2H, anthracene-
CH2CH2), 1.59(m, 2H, anthracene-CH2CH2CH2), 1.20–1.30(m,
24H, ACH2CH2ACH3), 0.87(t, 3H, CH3). MALDI-TOF-MS m/z
(M)þ 1319, (MþNa)þ 1342.
1H NMR (300 MHz, CDCl3, d, ppm) 7.42–7.52(m, 6Ar-H, m to
OCH2phenyl, m to phenyl-CC, o to phenyl-CC), 6.97(d, 2Ar-H, o
to CH2Ophenyl), 4.17(t, 2H, phenyl OCH2CH2O), 3.87(t, 2H,
phenylOCH2CH2O), 3.54–3.74(m, 24H, AOCH2 CH2OA), 3.37(s,
3H, OCH3), 1.63(s, 6H, CH3).
Molecule 1
1
Yield:58%; H NMR (300 MHz, CDCl3, d, ppm) 9.50(s, 1H, 9-
anthracene-H), 8.32(d, 2H, 4,5-anthracene-H), 7.80(d, 2H,
2,7-anthracene-H), 7.52(m, 6H,3,6-anthracene-H and o to
phenyl-CC), 7.38(d, 8Ar-H, m to phenyl-CC), 6.84(d, 4Ar-H, o
to CH2Ophenyl), 4.17(m, 7H, anthranene-OCH3 and phenyl-
OCH2CH2O), 3.87(t, 4H, phenylOCH2CH2O), 3.53–3.74(m,
48H, AOCH2 CH2OA), 3.36(s, 6H, OCH3). MALDI-TOF-MS m/z
(M)þ 1236, (MþNa)þ 1259.
Synthesis of Compound 7
Compound 6 (1.7 g, 3.0 mmol) and NaOH (1.2 g, 30 mmol)
were dissolved in toluene (50 mL). The mixture was refluxed
for 10 h, and then the solvent was removed and washed by
water. The mixture was extracted with ethyl acetate and
dried over anhydrous magnesium sulfate and filtered. After
the solvent was removed in a rotary evaporator, the crude
product was purified by chromatography on silica
gel(EA:CH3OH ¼ 5:1 as eluent) to yield 1.1 g of a yellow liq-
uid (70%).
RESULTS AND DISCUSSION
Synthesis of Molecules 1–3
The synthetic route of the rod-coil molecules with a n-
shaped rod building block, consisting of an anthracene unit
and two biphenyl groups linked together with acetylenyl
bonds at the 1,8-position of anthracene as a rigid rod seg-
ment, and the alkyl or alkyloxy chains with various length
(methoxy- (1), octanyl- (2), hexadecyl- (3)) at the 10-posi-
tion of anthracene and poly(ethylene oxide) with the number
of repeating units of 7 connected with biphenyl as coil seg-
ments was outlined in Scheme 1. Compound 7 was obtained
from successive reactions of tosylation, nucleophilic substitu-
tion, sonogashira coupling, and demethylation using poly
(ethylene glycol) methyl ether (Mw ¼ 350), 4-hydroxy-40-
iodobiphenyl and 2-methyl-3-butyn-2-ol as starting materi-
als. 4,5-Diiodo-9-anthrone (9), 1,8-diiodo-10-methoxyanthra-
cene (10), 1,8-diiodo-10-octylanthracene (11), and 1,8-
diiodo-10-hexadecanylanthracene (12) were synthesized
according to the literature reported elsewhere.19,20 Sonoga-
shira coupling reaction of compound 7 with compound 10,
11, 12 successfully afforded rod-coil molecules 1, 2, 3 with
n-shaped rod segment, respectively. The resulting block mol-
ecules were purified by silica gel column chromatography
and then further purified by recycling preparative high per-
formance liquid chromatography. The structure of molecules
1–3 were characterized by 1H NMR and MALDI-TOF mass
1H NMR (300 MHz, CDCl3, d, ppm) 7.45–7.49(m, 6Ar-H, m to
OCH2phenyl, m to phenyl-CC, o to phenyl-CC), 6.94(d, 2Ar-H,
o to CH2Ophenyl), 4.13(t, 2H, phenylOCH2CH2O), 3.86(t, 2H,
phenylOCH2CH2O), 3.50–3.70(m, 24H, AOCH2 CH2OA),
3.34(s, 3H, OCH3), 3.11(s, 1H, CCAH).
Synthesis of Molecules 1–3
Molecules 1–3 were synthesized by the same procedure. A
representative example is described for 3. Compound 12
(0.14 g, 0.21 mmol), Compound 7 (0.15 g, 0.5 mmol), CuI(15
mg, 0.08 mmol), and Pd(PPh3)4(50 mg, 0.04 mmol) were dis-
solved in THF(40 mL) and Et3N(20 mL). The mixture was
refluxed for 30 h under Ar, then was concentrated by evapo-
ration and washed by water. The mixture was extracted with
ethyl acetate and dried over anhydrous magnesium sulfate
and filtered. After the solvent was removed in a rotary evap-
orator, the crude product was purified by silica gel chroma-
tography (EA/CH3OH ¼ 4/1 as eluent). The product was fur-
ther purified by recycle gel permeation chromatography
(JAI) to yield 100 mg of a yellow solid (48%).
ROD-COIL MOLECULES WITH n-SHAPED ROD BUILDING BLOCK, ZHONG ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 1 Thermal Transitions of n-shaped Molecules (Data Are
from Heating and Cooling Scans)
Phase Transition (ꢀC)
Molecule
fcoil
Heating
Cooling
1
2
3
0.57
0.60
0.63
L 142.5 Colh 163.2 i
L 100.1 Colr 106.4 i
L 106.5 i
i 160.5 Colh 141 L
i 105.3 Colr 89.2 L
i 99.4 L
L, lamellar phase; Colh, hexagonal columnar phase; Colr, rectangular co-
lumnar phase; I, isotropy; fcoil, coil volume fraction.
curves together with optical texture preliminarily confirmed
the presence of an ordered columnar phase. To identify the
detailed self-organizing structures, X-ray scattering studies
were performed. Several peaks with the ratio of 1:H3:H4:H9
in the small-angle region shown in Figure 3(b) can be
indexed as the 100, 110, 200, 300 reflections of a 2D hexag-
onal columnar structure (see supporting information). From
the observed d spacing of the 100 reflection, the lattice pa-
rameter of 2D hexagonal columnar phase of 1 is calculated
to be 4.64 nm. From the experimental values of the unit cell
parameters (a, b, c, and c) and the density (q), the average
number of molecules per cross-sectional slice of the column
can be calculated according to eq 1, where M is the molecu-
lar mass and NA is Avogadro’s number. According eq 1, the
average number (n) of molecules in each bundle of 1 is cal-
culated to be ꢁ4. On the basis of the data, the schematic
representation of the hexagonal columnar structure of 1 can
be illustrated as shown in Figure 4(b).
FIGURE 1 DSC traces (10 ꢀC/min) recorded during the
second heating scan (a), the first cooling scan (b) of 1; the sec-
ond heating scan (c), the first cooling scan (d) of 2; and the
second heating scan (e) and the first cooling scan (f) of 3.
spectroscopy (see Supporting Information Figures S1, S2)
and were shown to be in full agreement with the structure
presented in Scheme 1.
Structures of Bulk State
The self-assembling behavior of molecules 1–3 was investi-
gated by DSC, thermal POM, and SAXS, Figure 2 shows the
DSC heating and cooling traces and thermal transitions of
the molecules 1–3. Molecule 1, connected with a methoxy
group at 10 position of anthracene, shows an ordered bulk-
state organization with bright birefringence, which trans-
abc sin c
n ¼
(1)
ꢀ
forms into an isotropic liquid at 163.2 C [Fig. 1(a) and Table
M=qNA
1]. On slow cooling of 1, from the isotropic liquid to liquid
crystalline mesophase, the focal conical spherulitic fan tex-
ture was observed by POM experiment [Fig. 2(a)]. The DSC
In addition, the small-angle X-ray diffraction patterns of the
crystalline phases of 1 display several sharp reflections
FIGURE 2 Representative optical polarized micrograph (ꢂ100) of the texture exhibited by (a) hexagonal columnar structure of 1
and (b) rectangular columnar structure of 2 at the transition from the isotropic liquid. [Color figure can be viewed in the online
issue, which is available at www.interscience.wiley.com.]
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ꢀ
phase at 106.4 C [Fig. 1(c) and Table 1]. Upon cooling from
the isotropic liquid, a leaf-like texture with the characteristic
of a columnar mesophase can be observed by using an opti-
cal polarized microscope [Fig. 2(b)]. The detailed liquid crys-
talline structure of 2 is also confirmed by small-angle X-ray
scattering experiments. The ꢀsmall-angle X-ray scattering of 2
measured at cooling to 100 C displays four sharp reflections
that can be indexed as the 100, 010, 200, 300 that corre-
spond to a two-dimensional rectangular columnar structure
with lattice constants a ¼ 6.6 nm and b ¼ 3.7 nm [see Fig.
3(d) and Supporting Information]. This dimension implies
that the more rod-like rigid segments arrange axially with
their preferred direction within a cross-sectional slice of the
column in which octyl chains pack in an interdigitated fash-
ion. The average number of molecules in each supramolecu-
lar aggregate is calculated to be nearly 4 by eq 1 and the
schematic representation of the rectangular columnar struc-
ture characterized by POM and SAXS can be illustrated as
shown in Figure 4(d). Similar to molecule 1, the structure of
crystalline phase of molecule 2 also shows monomolecule
layer with the interlayer spacing of 4.1 nm [Figs. 3(c) and
4(c)].
FIGURE 3 Small-angle X-ray diffraction patterns of 1, 2, and 3
measured in solid state and melt state plotted against q (¼ 4p
sin y/k). (a) in the lamellar phase for 1 at 80 ꢀC, (b) hexagonal
columnar phase for 1 at 150 ꢀC, (c) lamellar phase for 2 at 70
ꢀC, (d) rectangular columnar phase for 2 at 100 ꢀC, and (e) la-
mellar phase for 3 at 25 ꢀC.
In sharp contrast to molecule 1, molecule 3 contained a hex-
adecyl chain at 10 position of anthracene, only displays a 1D
lamellar crystalline phase. There is only one endothermic
and exothermic peak showed on DSC curves [Fig. 1(e,f)]. The
small-angle X-ray diffraction patterns display several sharp
reflections which correspond to equidistant q-spacings [Fig.
3(e)] and can be indexed to a lamellar lattice with the layer
spacing of 8.6 nm. Considering the layer thickness obtained
from the X-ray diffraction pattern is much larger than the
estimated molecular length (6.2 nm by CPK model) and
effect of the space filling requirement of n-shaped building
block, bilayer arrangement of the rigid segments is expected
which correspond to equidistant q-spacings and thus index
to a lamellar lattice. The layer spacing of 4.0 nm is very
close to the corresponding estimated molecular length
(4.5 nm by Corey-Pauling-Koltun (CPK) molecular model) in-
dicative of a monomolecule layer structure in which rod seg-
ments are fully interdigitated [Figs. 3(a) and 4(a)].
Molecule 2, incorporating an octyl group at 10 position of
anthracene, also displays a columnar mesophase. Molecule 2
exhibits a birefringent liquid crystalline phase at a melting
state (100.1 ꢀC), followed by transformation to an isotropic
FIGURE 4 Schematic representation of self-assembly of (a) monolayer structure for 1, (b) hexagonal columnar structure for 1, (c)
monolayer structure for 2, (d) rectangular columnar structure for 2, and (e) bilayer structure for 3.
ROD-COIL MOLECULES WITH n-SHAPED ROD BUILDING BLOCK, ZHONG ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 Characterization of the Thermotropic Liquid
acterization of the self-assembling behavior of n-shaped mol-
Crystalline Behavior of Molecules 1–3 in Bulk State
ecules 1–3 in bulk state was summarized in Table 2.
Liquid Crystalline Phase
Crystalline
Aggregation Behavior in Aqueous Solution
Molecules 1–3 can be considered as a novel class of amphi-
philes because it consists of hydrophilic flexible chain and
hydrophobic rigid aromatic segment.22,23 Aggregation behav-
ior of molecules 1–3 was subsequently studied in aqueous
solution using UV–vis and fluorescence spectra [Fig. 5(a)].
The absorption spectrum of 3 in aqueous solution (0.002 wt
%) exhibits a broad transition with a maximum at 272 nm,
resulting from the conjugated rod block. The fluorescence
spectrum of 3 in chloroform solution (0.002 wt %) exhibits
a strong emission maximum at 449 nm and 476 nm. How-
ever, the emission maximum in aqueous solution is blue-
shifted with respect to that observed in chloroform solution,
and the fluorescence is significantly quenched, indicative of
aggregation of the conjugated rod segments [Fig. 5(a)].
Hexagonal
Columnar
Rectangular
Columnar
Phase
Lamellar
Molecule d (nm)
a (nm) b(nm)
n
a (nm) b (nm)
n
1
2
3
4.0
4.1
8.6
4.64
4.64
4
6.6
3.7
4
a, b, the lattice constants; n, the average number of molecules per
cross-sectional slice of the column; d, the layer spacing.
to be the best way to pack the hydrophobic segment, leading
to a lamella structure [see Fig. 4(e)]. Furthermore, one inter-
esting point is that the peak intensity associated with the
(002) reflection appears to be the most intense, implying
that distance of the rod segment within bilayer domain is
4.3 nm. On the basis of the DSC, POM, and XRD studies, char-
DLS experiments of 3 were performed in aqueous solution
to further investigate the aggregation behavior over a scat-
tering angular range of 30ꢀ–130ꢀ [Fig. 5(b)]. The CONTIN
FIGURE 5 (a) Absorption and emission spectra of 3 in CHCl3 and aqueous solution (0.002 wt %), (b) autocorrelation functions of 3 in
aqueous solution (0.01 wt %), (c) hydrodynamic radius distribution of 3, and (d) angular dependence of diffusion coefficient for 3.
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FIGURE 6 TEM images (negatively stained with uranyl acetate) of sample cast from aqueous solution of (a) 1, (b) 2, and (c) 3 (scale
bar ¼ 100 nm).
analysis of the autocorrelation function at a scattering angle
of 90ꢀ showed a broad peak corresponding to an average
hydrodynamic radius (Rh) of ꢁ295 nm [Fig. 5(c)]. The angu-
lar dependence of the apparent diffusion coefficient was
measured because the slope is related to the shape of the
diffusing species. As shown in Figure 5(d), the slope value of
0.025 is consistent with the value predicted for elongated
nonspherical micelles (0.03).24 Molecules 1 and 2 showed
similar aggregation behavior to that of 3 and their Rh value
showed to be 112 nm and 260 nm, respectively.
assemble into elongated nanofibers with several micrometers
length. The nanofibers consist of hydrophobic aromatic inner
cores surrounded by hydrophilic flexible segments that are
exposed to an aqueous environment. Within the core, the
extended aromatic segments are stacked with a radial
arrangement to release steric hindrance from bulky chains.
CONCLUSIONS
Molecules 1–3 with a n-shaped rigid block segment, consist-
ing of a anthracene unit, alkyl chain, and poly(ethylene ox-
ide), were successfully synthesized and their self-assembling
behavior in bulk and an aqueous solution was investigated.
In the melt state, molecule 1 with a methoxy group at 10
position of anthracene self-assembles into a hexagonal co-
lumnar structure, Whereas molecule 2 with an octyl group
at 10 position of anthracene self-organizes into rectangular
columnar structure. Further increasing the length of alkyl
chain suppresses a liquid crystalline phase and exhibits only
a lamellar structure at solid state as in the case of 3. The
variation in the supramolecular structure can be explained
by considering the microphase separation between the dis-
similar parts of the molecule and the space-filling require-
ment of the flexible hydrophobic chains. Molecule 1 based
on a methoxy group at the end of the rod segment can be
packed with interdigitation of the rod segments, and
To further confirm the aggregation structure, TEM experi-
ments have been performed with an aqueous solution (Fig. 6).
TEM micrograph of 3, which obtained from a 0.01 wt % aque-
ous solution cast onto a TEM grid, clearly shows 1-dimen-
sional nanofibers with a uniform diameter of 11.0 nm. Most of
the strands have lengths up to several hundred nanometers.
Considering the fully extended molecular length of the mole-
cule 3 is estimated to be about 5.4 nm, the 11.0 nm width is
consistent with sum of two molecular of 3. Hence, the sche-
matic representation of the nanofiber structure of 3 can be
illustrated as shown in Figure 7. Remarkably, molecules 1 and
2 also self-assemble to elongated nanofibers with a uniform
diameter of 7.0 nm and 9.0 nm, respectively, (Fig. 7).
On the basis of the results described above, the amphiphiles
with a n-shaped aromatic segment can be considered to self-
FIGURE 7 Schematic representa-
tion of the proposed self-assem-
bly of molecule
3 in aqueous
solution. [Color figure can be
viewed in the online issue, which
is available at www.interscience.
wiley. com.]
ROD-COIL MOLECULES WITH n-SHAPED ROD BUILDING BLOCK, ZHONG ET AL.
1421

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
10 Ryu, J. H.; Lee, E.; Lim, Y. B.; Lee, M. J Am Chem Soc 2007,
increasing the length of the hydrophobic chain prohibits mo-
lecular interaction of the rod segments due to phase separa-
tion between aromatic rods and alkyl chains, resulting in the
formation of 1D lamellar structure. In aqueous medium, mol-
ecules 1–3 can self-assemble into elongated nanofiber struc-
ture with a radial arrangement of the aromatic segments.
129, 4808–4814.
11 Jang, C. J.; Ryu, J. H.; Lee, J. D.; Sohn, D.; Lee, M. Chem
Mater 2004, 16, 4226–4231.
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6375–6378.
This work was supported by Program for New Century Excel-
lent Talents in University, Ministry of Education, China, National
Natural Science Foundation of China, and the National Creative
Research Initiative Program of the Korean Ministry of Science
and Technology.
13 Moon, K. S.; Kim, H. J.; Lee, E.; Lee, M. Angew Chem Int Ed
2007, 46, 6807–6810.
14 Liu, L. B.; Moon, K. S.; Gunawidjaja, R.; Lee, E.; Tsukruk, V.
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15 Ryu, J. H.; Oh, N. K.; Lee, M. Chem Commun 2005,
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