Hierarchical superstructures with control of helicity from the self-assembly of chiral bent-core molecules

Article abstract of DOI:10.1002/chem.201200057

Herein, two asymmetric chiral bent-core molecules, 3-[(4-{[4-(heptyloxy) benzoyl]oxy}benzoyl)oxy]-phenyl-4-[(4-{[(1R)-1-methylheptyl]oxy}benzoyl)oxy] benzoate (BC7R) and 3-[(4-{[4-(heptyloxy)benzoyl]oxy}benzoyl)oxy]-phenyl-4-[(4- {[(1S)-1-methylheptyl]oxy}benzoyl)oxy] benzoate (BC7S), were synthesized to demonstrate control of the helicity of their self-assembled hierarchical superstructures. Mirror-imaged CD spectra showed a split-type Cotton effect after the formation of self-assembled aggregates of BC7R and BC7S, thereby suggesting the formation of intermolecular exciton couplets with opposite optical activities. Both twisted and helical ribbons with preferential helicity that corresponded to the twisting character of the intermolecular exciton couplet were found in the aggregates. The formation of helical ribbons was attributed to the merging of twisted ribbons through an increase in width to improve morphological stability. As a result, control of the helicity of hierarchical superstructures from the self-assembly of bent-core molecules could be achieved by taking advantage of the transfer of chiral information from the molecular level onto the hierarchical scale.

Full text of DOI:10.1002/chem.201200057

FULL PAPER
DOI: 10.1002/chem.201200057
Hierarchical Superstructures with Control of Helicity from the Self-Assembly
of Chiral Bent-Core ACHTNUTGRNEUNGMolecules
Shih-Chieh Lin,[a] Rong-Ming Ho,*[a] Chin-Yen Chang,[b] and Chain-Shu Hsu*[b]
Abstract: Herein, two asymmetric
chiral bent-core molecules, 3-[(4-{[4-
(heptyloxy)benzoyl]oxy}benzoyl)oxy]-
phenyl-4-[(4-{[(1R)-1-methylheptyl]-
oxy}benzoyl)oxy] benzoate (BC7R)
and 3-[(4-{[4-(heptyloxy)benzoyl]oxy}-
benzoyl)oxy]-phenyl-4-[(4-{[(1S)-1-
the formation of self-assembled aggre-
gates of BC7R and BC7S, thereby sug-
gesting the formation of intermolecular
exciton couplets with opposite optical
activities. Both twisted and helical rib-
bons with preferential helicity that cor-
responded to the twisting character of
the intermolecular exciton couplet
were found in the aggregates. The for-
mation of helical ribbons was attribut-
ed to the merging of twisted ribbons
through an increase in width to im-
prove morphological stability. As
a result, control of the helicity of hier-
archical superstructures from the self-
assembly of bent-core molecules could
be achieved by taking advantage of the
transfer of chiral information from the
molecular level onto the hierarchical
scale.
methylheptyl]oxy}benzoyl)oxy]
ben-
zoate (BC7S), were synthesized to
demonstrate control of the helicity of
their self-assembled hierarchical super-
structures. Mirror-imaged CD spectra
showed a split-type Cotton effect after
Keywords: aggregation · bent-core
molecules · chirality · helical struc-
tures · self-assembly
Introduction
trinsic chiral compounds, unique phase-chirality could also
be acquired from the self-assembly of achiral bent-core mol-
ecules.[42–44] The macroscopic chirality of the achiral bent-
core molecules could be built on the basis of their character-
istic mesophases, such as the B2 phase (also named the
SmCP phase, it is a smectic structure with layered chirality
that is determined by the direction of polarity and the tilting
of the molecular director with respect to the layer
normal),[45,46] the B4 phase (a helical structure in which the
helical axis lies parallel to the smectic layer as the twisted-
grain-boundary (TGB) phase),[47–49] and the B7 phase (a
spiral filament and more-complicated chiral textures with
polarization-modulated/undulated-layer (PM/UL) struc-
tures).[50–53] Watanabe and co-workers suggested that the for-
mation of phase chirality from achiral bent-core molecules
was attributed to the asymmetric twist conformation that re-
sulted from the ester linkages that connected the central
phenyl ring to the side wings.[54–64] Moreover, the twisting
power that was induced by an offset to the macroscopic po-
larization and an enantiomorphoic structure that was con-
structed by tilting the molecules with respect to the layer
normal were proposed as the origins of phase chirality.[65–67]
More recently, in contrast to the unique chiral mesophases
that were formed from achiral bent-core molecules, Hough,
Clark, and co-workers also studied the B4 phase, and found
helical nanofilament phases with right- and left-handedness
from twisted smectic layers.[68]
Nature uses self-assembly as a convenient tool to construct
materials into highly ordered structures through cooperative
secondary interactions, such as hydrogen bonding, amphi-
philic effects, electrostatic interactions, metal coordination,
À
van der Waals interactions, p p stacking, steric hindrance,
and chirality.[1–4] Biological molecules and macromolecules
can form different kinds of self-assembled superstructures
that have specific functions through the interplay of these
non-covalent bonding forces.[5] Among the biological archi-
tectures that are constructed by self-assembly in nature, the
helical morphology is perhaps the most-fascinating tex-
ture.[6,7] Molecular chirality is considered to be one of the
most-important driving forces for the formation of helical
morphologies of different lengths.[8–41] In contrast to the for-
mation of helical morphologies from the self-assembly of in-
[a] S.-C. Lin, Prof. R.-M. Ho
Department of Chemical Engineering
National Tsing Hua University
No. 101, Section 2, Kuang-Fu Road
Hsinchu, Taiwan 30013 (R.O.C)
Fax : (+886)3-571-5408
E-mail: rmho@mx.nthu.edu.tw
[b] C.-Y. Chang, Prof. C.-S. Hsu
Department of Applied Chemistry
National Chiao Tung University
No. 1001, University Road, Hsinchu
Taiwan 30013 (R.O.C.)
Although the mechanism for the formation of helical
phases of bent-core molecules from the molecular level
have been well-studied and rationalized, the control of helic-
ity in these helical morphologies remains challenging.[69–72]
Thus, the development of methods to control the helicity of
Fax : (+886)3-572-3764
E-mail: cshsu@mail.nctu.edu.tw
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200057.
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helical superstructures is attracting much attention. Recent-
ly, by taking advantage of the ferroelectronic-switching
property of the B2 phase, the formation of one-handed heli-
cal phases in achiral bent-core molecules was achieved by
applying an electronic field to induce a symmetry-breaking
transition.[73–81] Moreover, helical phases with preferential
helicity were obtained by introducing small amounts of
enantiomerically pure chiral dopants into an achiral
host.[82–87] Watanabe and co-workers synthesized a series of
bent-core molecules to clarify the B4 phase and they demon-
strated the formation of helical structures.[82] Two different
domains with opposite optical rotations, which gave intense
CD peaks at around 430 nm with opposite signs, were found
under uncrossed polarizers, thus suggesting that right- and
left-handed helical phases could be formed simultaneously.
Most interestingly, one-handed helical structures could be
selectively formed by introducing chiral dopants into the
host compound. Although controlling the helicity of hier-
archical superstructures and phases from the self-assembly
of achiral bent-core molecules could be achieved by using
physical and external approaches, the formation of one-
handed helical morphologies by the directly assembly of
bent-core molecules remains challenging. In our previous
work, we formed both left- and right-handed helical super-
structures from the self-assembly of achiral bent-core mole-
cule 1,3-phenylene bis[4-(4-n-heptyloxybenzoyloxy)ben-
zoates] (BC7).[88]
Results and Discussion
Self-assembly of chiral bent-core molecules: Figure 1 shows
the UV/Vis and CD spectra of dilute solutions of BC7R and
BC7S in isopropyl alcohol (IPA). According to the chemical
Figure 1. a) CD and b) UV/Vis spectra of BC7R (solid line) and BC7S
(dashed line) in dilute IPA solutions (1 mg/4 mL, 0.032 wt.%, 3.1ꢁ
10À4 m).
Herein, we wanted to control the helicity of hierarchical
superstructures from the self-assembly of two asymmetric
chiral bent-core molecules, 3-[(4-{[4-(heptyloxy)benzoyl]-
oxy}benzoyl)oxy]-phenyl-4-[(4-{[(1R)-1-methylheptyl]oxy}-
benzoyl)oxy] benzoate (BC7R) and 3-[(4-{[4-(heptyloxy)-
benzoyl]oxy}benzoyl)oxy]-phenyl-4-[(4-{[(1S)-1-methylhep-
tyl]oxy}benzoyl)oxy] benzoate (BC7S; Scheme 1). Unlike
structures of BC7R and BC7S, which were composing of
several para-substituted benzoate groups in a bent-core
structure, the main absorption in the UV/Vis spectra was at-
À
tributed to the p p* transitions in the benzoate chromo-
phore. In the CD spectra, a positive Cotton effect was clear-
ly identified in the BC7R solution at the same wavelength
(263 nm), which corresponded to the absorption band in the
UV/Vis spectrum, whereas a negative Cotton effect was
found in the BC7S solution, thereby suggesting the existence
of the opposite chiral entity in each enantiomer. In contrast
to the specific Cotton effect from the configurational chirali-
ty of the chiral bent-core molecules in dilute solution,
mirror-imaged CD spectra with
a significant split-type
Cotton effect (Figure 2a) were observed for BC7R and
BC7S after their aggregation from IPA solutions. The IPA
solvent played a role as the theta-solvent for BC7R and
BC7S, that is, the solubility of the chiral bent-core molecules
in IPA largely decreased on lowering the temperature so as
to result in the formation of self-assembled chiral aggre-
gates. Thus, it was reasonable to suggest that the significant
changes and enhancement in the CD signals were due to in-
termolecular incorporation. Comparing the CD and UV/Vis
spectra of the self-assembled chiral aggregates, the theoreti-
cal anaclastic point, which was calculated from the splitting
between the doubly intense CD bands at 247 nm and
289 nm, was located at 268 nm, which corresponded well
with the maximum absorption band in the UV/Vis spectra
(Figure 2b), thereby indicating that the CD signals were
indeed due to the molecular absorption of the constituent
Scheme 1. Chemical structures of chiral bent-core molecules BC7R (top)
and BC7S (bottom).
the control of helicity through physical and external ap-
proaches, the control of helicity during the forming of heli-
cal superstructures from BC7R and BC7S was achieved by
directly introducing chiral entities into the chemical struc-
tures of the bent-core molecules for self-assembly; there-
fore, one-handed helical superstructures were formed with
control of their helicity through the transfer of chiral infor-
mation from the molecular level onto the hierarchical scale.
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Figure 3. Electronic-transition dipoles along the long axis of the benzoate
chromophores (shown as arrows) in BC7S and its aggregates.
gregates were examined by TEM. Figure 4 shows TEM
images of chiral superstructures that resulted from the self-
assembly of BC7R and BC7S into right- and left-handed
Figure 2. a) CD and b) UV/Vis absorption spectra of self-assembled
aggregates of BC7R (solid line) and BC7S (dashed line) in IPA (1 mg/
2 mL, 0.064 wt.%, 6.2ꢁ10À4 m).
chiral bent-core molecules and that the splitting of the
Cotton effect was mainly due to intermolecular interactions.
To further investigate the above-mentioned intermolecu-
lar incorporation into self-assembled chiral aggregates of
BC7R and BC7S, the split-type Cotton effect was rational-
ized by using the exciton-chirality method.[89] Typically, the
À
benzoate chromophore exhibited three kinds of p p* transi-
1
tions in the UV region: A1g–1B2u (lLb), an intramolecular
charge-transfer transition, and A1g–1B1u (1La).[90,91] The first
1
and second absorption bands were due to the electronic-
transition dipoles along the short and long axis of the ben-
zoate chromophore, respectively. The dibenzoate Cotton
À
effect that was due to p p* intramolecular charge-transfer
transitions may have been red-shifted owing to the influence
of para substituents.[92] Consequently, by considering the
type of para substitution in the benzoate chromophore ex-
amined herein and by calculating the e value from the UV/
Vis spectra, the absorption at 263 nm was attributed to in-
tramolecular charge-transfer transitions. Moreover, this elec-
tronic-transition dipole was approximately parallel to the al-
Figure 4. TEM images of self-assembled superstructures of BC7R (a–c)
and BC7S (d–f) in IPA (1 mg/2 mL): a) Right- and d) left-handed twisted
ribbons; b) right- and e) left-handed helical ribbons; c,f) tubular struc-
tures.
twisted ribbons (Figure 4a,d), right- and left-handed helical
ribbons (Figure 4b,e), and tubular superstructures with spe-
cific helical trace lines on the exterior (Figure 4c,f). The
handedness of the helical superstructure corresponded well
with the sign of the exciton couplet of the benzoate chromo-
phores (i.e., positive or negative chirality), thus indicating
a correlation between the sign of intermolecular exciton
coupling and the helicity of the formed helical superstruc-
ture. That is, the helicity of the self-assembled morphologies
could be controlled by introducing a chiral entity onto the
chemical structure of the bent-core molecules. These spectra
showed the successful transfer of chirality from configura-
tional chirality on the molecular level into superstructural
chirality on the hierarchical scale through self-assembly.
Interestingly, the morphological evolution from twisted
ribbons into helical ribbons was occasionally observed by
TEM (Figure 5). Morphological transition owing to the
fusion of one-handed twisted ribbons onto helical ribbons
À
coholic (C O) bond so that the dihedral angle between the
transition dipoles of the adjacent benzoate chromophores
was too small to result in the occurrence of an exciton cou-
plet.[90] As a result, we suggested that the formation of the
split-type Cotton effect (Figure 2a) was mainly due to inter-
molecular interactions. The aggregation of self-assembled
BC7S gave rise to the formation of dipole–dipole interac-
tions between the benzoate chromophores at which the elec-
tronic-transition dipoles would be perpendicular to the heli-
cal axis of self-assembled superstructure so as to result in
the occurrence of an exciton couplet (Figure 3).
Self-assembled superstructures with control over their helici-
ty: To further examine the hierarchical superstructures of
BC7R and BC7S from the self-assembly of the chiral bent-
core molecules in IPA solution, the self-assembled chiral ag-
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R.-M. Ho, C.-S. Hsu et al.
suggested that the molecular packing in the aggregates was
due to the bent-core structure and that the chiral entity on
the terminal chain would determine the twist direction of
the packing. Similar diffraction results were found in the
helical ribbon (Figure 6d,f), regardless of enantiomeric
character; the unit cell possessed the same dimensions as
that of the twisted ribbon, thus indicating that the molecular
packing in the crystalline state of the aggregates was identi-
cal, regardless of the assembled hierarchical morphologies.
Moreover, the SAED pattern exhibited symmetrical arcs
that consisted of a series of reflections. This arc-like diffrac-
tion pattern, which was comprised of a series of single-crys-
talline-like reflections (i.e., diffraction spots) was possible
evidence to support the twisting and bending mechanisms
for the formation of helical superstructures, similar to our
previous studies in BC7.[88]
Proposed mechanism for the formation of helical architec-
tures: Figure 7 shows a hypothetical model for the formation
of helical superstructures from the self-assembly of chiral
bent-core molecules. On the basis of the geometry optimiza-
tion of the bent-core molecules, the adjacent benzoate
groups should rotate at different angles with respect to each
other by twisting the ester linkages so as to result in the for-
mation of the optimum molecular geometry with a twist
(Figure 7a). Subsequently, the solvophobic interactions
would result in the formation of closely packed molecules as
crystallites with higher stability, as confirmed by the scatter-
ing results (Figure 6). Furthermore, the packing of these
bent-core molecules would give rise to significant intermo-
lecular interactions between adjacent benzoate chromo-
phores (Figure 8) and would also result in the accumulation
of free energy in the molecular packing. Consequently, the
twisting driving force for ordering would be triggered by
a lowering of the steric hindrance so as to form the twisted
crystallite, that is, the twisted-ribbon superstructures (Fig-
ure 7b). With the increase in the population of twisted rib-
bons during aggregation, these twisted ribbons would begin
to merge together and fuse into a wide ribbon with continu-
ous growth. However, the increase in the width of the
ribbon would cause instability in the energetic state owing
to the saddle-like curvature with double twists in the twisted
ribbon (Figure 7c). Consequently, a wide ribbon should
transform into a helical ribbon with cylindrical curvature for
improved morphological stability.[99–102] The formation of
helical ribbons was attributed to these twisting and bending
mechanisms owing to the combination of width-growth and
chiral effects. Eventually, consistent with the predictions of
TCLB theory, the helical ribbon may further scroll to form
tubular superstructures, which would be the most-stable
morphology, to lower the energetic penalty from the lateral
surfaces.
Figure 5. TEM images of the morphological transition from the fusion of
one-handed twisted ribbons to the helical ribbon with same helicity to
afford self-assembled aggregates of BC7R (top) and BC7S (bottom) in
IPA.
with the same helicity was identified for the self-assembled
aggregates of BC7R (left) and BC7S (right) in IPA. That is,
the formation of helical ribbons was attributed to the merg-
ing of twisted ribbons so as to reach a morphological state
with higher thermodynamic stability.[93–95] This morphologi-
cal transformation from the self-assembly of chiral bent-
core molecules was in line with the predictions of tilted
chiral lipid bilayer (TCLB) theory.[96–98] By considering the
morphological stability, the spherical vesicles that were or-
ganized with chiral lipid molecules may have transformed
into twisted strips and further become wound-ribbon helical
structures that eventually formed the tubular texture
through a scrolling mechanism for the reduction of lateral
surface free energy. To investigate the molecular disposi-
tions in each chiral superstructure, SAED experiments were
performed to examine the structural packing of the self-as-
sembled morphologies. Figure 6a shows a TEM image of
the twisted ribbons of self-assembled BC7R aggregates from
which a [00L] zonal SAED pattern was obtained (Fig-
ure 6b). The basal unit-cell dimensions were a=1.02 nm
and b=0.80 nm with an orthorhombic lattice, which was
close to the previously reported unit-cell dimensions of the
achiral bent-core molecule (i.e., BC7).[88] These ED results
Co-assembly of enantiomeric chiral mixtures and the race-
mate: To further demonstrate that the control over the hel-
icity of helical superstructures was based on the configura-
tional chirality of the self-assembly of bent-core molecules,
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Self-Assembly of Chiral Bent-Core Molecules
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right-
and
left-handedness
(Figure 9). No helical ribbons
were formed from the self-as-
sembly of the racemic mixture.
We speculated that, for enantio-
merically pure chiral bent-core
molecules, the twist character
of the intermolecular interac-
tions (i.e., exciton couplet)
could be executed by following
the same chirality of the bent-
core molecules, which would
result in the lowest energetic
penalty in molecular packing so
as to form the same handed
twisted ribbons and eventually
develop as helical ribbons, as
predicted by TCLB theory.
However, the energetic penalty
in molecular packing would
have become significant owing
to the incompatible steric hin-
drance that would have been
caused by the enantiomer with
an opposite twist in its molecu-
lar geometry. Consequently, it
would be much-more difficult
to reach the most-stable mor-
phology (i.e., helical ribbons)
for the chiral superstructures
that consisted of the enantio-
mers. That is, the minor enan-
tiomer played the role of a de-
fective unit for the formation of
the co-assembled chiral super-
structures by the transformation
of their optimum molecular ge-
ometry into the opposite one
for packing.
Conclusion
Figure 6. TEM images of a) right-handed twisted ribbons, c) right-handed helical ribbon from BC7R, and
e) left-handed helical ribbon from BC7S in IPA. b,d,f) Selected area electron diffraction (SAED) patterns of
the circled regions in (a), (c), and (e), respectively. Straight lines and dashed lines in (d) and (f) indicate the
coordinates of the upper and lower layers of the helical superstructure in (c) and (e), respectively.
The helicity of hierarchical su-
perstructures of bent-core mol-
ecules could be control by
simply introducing
a
chiral
a racemic mixture was also prepared for co-assembly. There
was no optical activity in a racemic mixture. The absence of
a CD signal for the racemic mixture was attributed to the
co-existing of equal amount of enantiomers in the solution
so as to result in an equal population of helical morpholo-
gies with opposite handedness (i.e., the equal and opposite
signs of the intermolecular exciton couplets) owing to the
lack of preferential chirality (i.e., chiral bias from the enan-
tiomers). TEM analysis further confirmed that these co-as-
sembled aggregates exhibited twisted ribbons with both
entity onto the chemical structure. Both twisted and helical
ribbons with preferential one-handed helicity were obtained
through the self-assembly of BC7R and BC7S. Helical rib-
bons were formed from the merging of twisted ribbons with
increasing width so as to afford higher morphological stabili-
ty. In contrast, both right- and left-handed twisted ribbons
with equal populations could be observed as a racemic mix-
ture. The lack of preferential helicity was attributed to the
presence of equal amounts of the enantiomers so as to
result in equivalent an opposite signs in the intermolecular
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R.-M. Ho, C.-S. Hsu et al.
Figure 7. Hypothetic formation of left-handed helical superstructures in
the self-assembly of BC7S: a) optimal molecular geometry with a twist of
the chiral bent-core molecule, that is, the conformational chirality, results
in the formation of one-handed twisted-ribbon superstructures (b). Once
the twisted ribbons merge together, a wide ribbon is formed and further
scrolls into a helical ribbon with the same helicity through twisting and
bending mechanisms to afford higher morphological stability (c).
Figure 9. TEM images of a) right- and b) left-handed twisted ribbons
from a racemic mixture of BC7R and BC7S in IPA solution.
Figure 8. Correlation between the sign of intermolecular exciton coupling
and the helicity of the helical superstructure.
a transparent state). To acquire fully aggregated samples with more-
stable morphologies owing to self-assembly, the solution was left to stand
under ambient conditions for about 1 month before the aggregates were
collected for UV/Vis and CD spectroscopic measurements and TEM
analysis.
exciton couplet. The absence of the formation of helical
ribbon superstructures may have been due to higher mor-
phological instability because of the energetic penalty for
the molecular packing of the enantiomers.
Acknowledgements
Experimental Section
This work was supported by the National Science Council (NSC 99–
2120m-007–003).
Characterization: UV/Vis absorption and CD spectra were obtained si-
multaneously on a JASCO J-815 spectrometer in a cylindrical quartz cuv-
ette with 1 mm light path. TEM was carried out on a JEOL JEM-2100
LaB6 at an accelerating voltage of 200 kV. Bright-field TEM images were
obtained by using the mass-thickness contrast from shadowing with Pt/
Pb=4:1 at a tilt angle of 308 to the sample surface. Molecular simulations
were carried out by using HyperChem 7 with the OPLS force field to ex-
ecute the geometric optimization of the bent-core molecules.
[1] G. M. Whitesides, J. P. Mathias, C. T. Seto, Science 1991, 254, 1312–
1319.
[2] M. Muthukumar, C. K. Ober, E. L. Thomas, Science 1997, 277,
1225–1232.
[3] J.-M. Lehn, Science 2002, 295, 2400–2403.
[4] G. M. Whitesides, B. Grzybowski, Science 2002, 295, 2418–2421.
[5] D. Philp, J. F. Stoddart, Angew. Chem. 1996, 108, 1242–1286;
Angew. Chem. Int. Ed. Engl. 1996, 35, 1154–1196.
[6] J. D. Watson, F. H. C. Crick, Nature 1953, 171, 737–738.
[7] S. H. Kim, G. J. Quigley, F. L. Suddath, A. McPherson, D. Sneden,
J. J. Kim, J. Weinzierl, A. Rich, Science 1973, 179, 285–288.
[8] J. J. L. M. Cornelissen, J. J. J. M. Donners, R. Gelder, W. S. Gras-
winckel, G. A. Metselaar, A. E. Rowan, N. A. J. M. Sommerdijk,
R. J. M. Nolte, Science 2001, 293, 676–680.
[9] J.-S. Park, H.-S. Lee, J. R. Lai, B. M. Kim, S. H. Gellman, J. Am.
Chem. Soc. 2003, 125, 8539–8545.
[10] P. Wittung, P. E. Nielsen, O. Buchardt, M. Egholm, B. Nordꢂn,
Nature 1994, 368, 561–563.
Sample preparation: The syntheses of chiral bent-core molecules BC7R
and BC7S are described in detail in the Supporting Information. For the
self-assembly studies, a sample of the bent-core molecule (1 mg) was
added to isopropyl alcohol (IPA) with 2 mL and 4 mL for dilute and self-
assembled aggregates of solution, respectively. The solution was heated
until the solution became transparent (approximately 808C for 5 min).
After complete dissolution, the solution was cooled to ambient tempera-
ture to induce aggregation (i.e., either self-assembly or co-assembly). To
prepare the dilute solutions for the single-chain measurements, the trans-
parent solution was left under ambient conditions for 30 min to eliminate
the temperature fluctuation for absorption and then the solution was ex-
amined by CD spectroscopy (i.e., the experiment was carried out in
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[11] H. Nakako, Y. Mayahara, R. Nomura, M. Tabata, T. Masuda, Mac-
romolecules 2000, 33, 3978–3982.
[12] M. Fujiki, J. Am. Chem. Soc. 1994, 116, 6017–6018.
[13] E. Yashima, T. Matsushima, Y. Okamoto, J. Am. Chem. Soc. 1995,
117, 11596–11597.
[14] E. Yashima, K. Maeda, Y. Okamoto, Nature 1999, 399, 449–451.
[15] N. Nakashima, S. Asakuma, T. Kunitake, J. Am. Chem. Soc. 1985,
107, 509–510.
[16] J.-H. Fuhrhop, P. Schnieder, E. Boekema, W. Helfrich, J. Am.
Chem. Soc. 1988, 110, 2861–2687.
[17] J. H. Jung, G. John, K. Yoshida, T. Shimizu, J. Am. Chem. Soc.
2002, 124, 10674–10675.
[18] C.-H. Sung, L.-R. Kung, C.-S. Hsu, T.-F. Lin, R.-M. Ho, Chem.
Mater. 2006, 18, 352–359.
[19] T.-F. Lin, R.-M. Ho, C.-H. Sung, C.-S. Hsu, Chem. Mater. 2006, 18,
5510–5519.
[20] T.-F. Lin, R.-M. Ho, C.-H. Sung, C.-S. Hsu, Chem. Mater. 2008, 20,
1404–1409.
[21] T.-F. Lin, R.-M. Ho, C.-H. Sung, M.-S. Ho, C.-S. Hsu, Chem. Eur. J.
2010, 16, 7385–7388.
[22] J. Song, Q. Cheng, S. Kopta, R. C. Stevens, J. Am. Chem. Soc. 2001,
123, 3205–3213.
[23] B. W. Messmore, P. A. Sukerkar, S. I. Stupp, J. Am. Chem. Soc.
2005, 127, 7992–7993.
[24] Y. Lin, A. Wang, Y. Qiao, C. Gao, M. Drechsler, J. Ye, Y. Yan, J.
Huang, Soft Matter 2010, 6, 2031–2036.
[25] C. Y. Li, D. Yan, S. Z. D. Cheng, F. Bai, T. He, L.-C. Chien, F. W.
Harris, B. Lotz, Macromolecules 1999, 32, 524–527.
[26] C. Y. Li, S. Z. D. Cheng, X. Weng, J. J. Ge, F. Bai, J. Z. Zhang,
B. H. Calhoun, F. W. Harris, L.-C. Chien, B. Lotz, J. Am. Chem.
Soc. 2001, 123, 2462–2463.
[27] J. J. L. M. Cornelissen, M. Fischer, N. A. J. M. Sommerdijk, R. J. M.
Nolte, Science 1998, 280, 1427–1430.
[28] K. T. Kim, M. A. Winnik, I. Manners, Soft Matter 2006, 2, 957–965.
[29] C.-K. Chen, S.-C. Lin, R.-M. Ho, Y.-W. Chiang, B. Lotz, Macromo-
lecules 2010, 43, 7752–7758.
[30] D. Pijper, M. G. M. Jongejan, A. Meetsma, B. L. Feringa, J. Am.
Chem. Soc. 2008, 130, 4541–4552.
[31] D. Maillard, R. E. Prud’homme, Macromolecules 2006, 39, 4272–
4275.
[32] K. L. Singfield, J. M. Klass, G. R. Brown, Macromolecules 1995, 28,
8006–8015.
[33] R.-M. Ho, Y.-W. Chiang, C.-C. Tsai, C.-C. Lin, B.-T. Ko, B.-H.
Huang, J. Am. Chem. Soc. 2004, 126, 2704–2705.
[34] R.-M. Ho, C.-K. Chen, Y.-W. Chiang, Macromol. Rapid Commun.
2009, 30, 1439–1456.
[35] R.-M. Ho, Y.-W. Chiang, C.-K. Chen, H.-W. Wang, H. Hasegawa,
S. Akasaka, E. L. Thomas, C. Burger, B. S. Hsiao, J. Am. Chem.
Soc. 2009, 131, 18533–18542.
[36] C.-C. Chao, C.-K. Chen, Y.-W. Chiang, R.-M. Ho, Macromolecules
2008, 41, 3949–3956.
[46] D. M. Walba, E. Kçrblova, R. Shao, J. E. Maclennan, D. R. Link,
M. A. Glaser, N. A. Clark, Science 2000, 288, 2181–2184.
[47] F. Araoka, N. Y. Ha, Y. Kinoshita, B. Park, J. W. Wu, H. Takezoe,
Phys. Rev. Lett. 2005, 94, 137801.
[48] D. M. Walba, L. Eshdat, E. Kçrblova, R. K. Shoemaker, Cryst.
Growth Des. 2005, 5, 2091–2099.
[49] S.-W. Choi, S. Kang, Y. Takanishi, K. Ishikawa, J. Watanabe, H.
Takezoe, Angew. Chem. 2006, 118, 6653–6656; Angew. Chem. Int.
Ed. 2006, 45, 6503–6506.
[50] G. Pelzl, S. Diele, A. Jꢃkli, Ch. Lischka, I. Wirth, W. Weissflog,
Liq. Cryst. 1999, 26, 135–139.
[51] A. Jꢄkli, C. Lischka, W. Weissflog, G. Pelzl, A. Saupe, Liq. Cryst.
2000, 27, 1405–1409.
[52] H. N. S. Murthy, B. K. Sadashiva, Liq. Cryst. 2003, 30, 1051–1055.
[53] D. A. Coleman, J. Fernsler, N. Chattham, M. Nakata, Y. Takanishi,
E. Kçrblova, D. R. Link, R.-F. Shao, W. G. Jang, J. E. Maclennan,
O. Mondainn-Monval, C. Boyer, W. Weissflog, G. Pelzl, L.-C.
Chien, J. Zasadzinski, J. Watanabe, D. M. Walba, H. Takezoe, N. A.
Clark, Science 2003, 301, 1204–1211.
[54] T. Sekine, T. Niori, M. Sone, J. Watanabe, S.-W. Choi, Y. Takanishi,
H. Takezoe, Jpn. J. Appl. Phys. 1997, 36, 6455–6463.
[55] E. Gorecka, M. Nakata, J. Mieczkowski, Y. Takanishi, K. Ishikawa,
J. Watanabe, H. Takezoe, S. H. Eichhorn, T. M. Swager, Phys. Rev.
Lett. 2000, 85, 2526–2529.
[56] T. Imase, S. Kawauchi, J. Watanabe, J. Mol. Struct. 2001, 560, 275–
281.
[57] J. Thisayukta, H. Niwano, H. Takezoe, J. Watanabe, J. Am. Chem.
Soc. 2002, 124, 3354–3358.
[58] H. Kurosu, M. Kawasaki, M. Hirose, M. Yamada, S. Kang, J. Thi-
sayukta, M. Sone, H. Takezoe, J. Watanabe, J. Phys. Chem. A 2004,
108, 4674–4678.
[59] H. Niwano, M. Nakata, J. Thisyukta, D. R. Link, H. Takezoe, J. Wa-
tanabe, J. Phys. Chem. B 2004, 108, 14889–14896.
[60] R. Y. Dong, J. Xu, G. Benyei, K. Fodor-Csorba, Phys. Rev. E 2004,
70, 011708.
[61] J. Xu, R. Y. Dong, V. Domenici, K. Fodor-Csorba, C. A. Veracini,
J. Phys. Chem. B 2006, 110, 9434–9441.
[62] D. M. Walba, E. Korblova, C.-C. Huang, R. Shao, M. Nakata, N. A.
Clark, J. Am. Chem. Soc. 2006, 128, 5318–5319.
[63] R. Y. Dong, A. Marini, J. Phys. Chem. B 2009, 113, 14062–14072.
[64] H. S. Jeong, S. Tanaka, D. K. Yoon, S.-W. Choi, Y. H. Kim, S. Ka-
wauchi, F. Araoka, H. Takezoe, H.-T. Jung, J. Am. Chem. Soc.
2009, 131, 15055–15060.
[65] T. Sekine, T. Niori, J. Watanabe, T. Furukawa, S. W. Choi, H. Take-
zoe, J. Mater. Chem. 1997, 7, 1307–1309.
[66] J. Watanabe, T. Niori, T. Sekine, H. Takezoe, Jpn. J. Appl. Phys.
1998, 37, L139–L142.
[67] G. Heppke, D. Moro, Science 1998, 279, 1872–1873.
[68] L. E. Hough, H. T. Jung, D. Krꢅerke, M. S. Heberling, M. Nakata,
C. D. Jones, D. Chen, D. R. Link, J. Zasadzinski, G. Heppke, J. P.
Rabe, W. Stocker, E. Kçrblova, D. M. Walba, M. A. Glaser, N. A.
Clark, Science 2009, 325, 456–460.
[37] R.-M. Ho, Y.-W. Chiang, S.-C. Lin, C.-K. Chen, Prog. Polym. Sci.
2011, 36, 376–453.
[69] E. Gorecka, D. Pociecha, F. Araoka, D. R. Link, M. Nakata, J. Thi-
sayukta, Y. Takanishi, K. Ishikawa, J. Watanabe, H. Takezoe, Phys.
Rev. E 2000, 62, R4524-R4527.
[70] J. P. F. Lagerwall, F. Giesselmann, M. D. Wand, D. M. Walba,
Chem. Mater. 2004, 16, 3606–3615.
[38] S. J. George, A. Ajayaghosh, P. Jonkheijm, A. P. H. J. Schenning,
E. W. Meijer, Angew. Chem. Int. Ed. 2004, 43, 3422–3425.
[39] A. Ajayaghosh, C. Vijayakumar, R. Varghese, S. J. George, Angew.
Chem. 2006, 118, 470–474; Angew. Chem. Int. Ed. 2006, 45, 456–
460.
[71] R. A. Reddy, B. K. Sadashiva, U. Baumeister, J. Mater. Chem. 2005,
15, 3303–3316.
[72] C. V. Yelamaggad, I. S. Shashikala, G. Liao, D. S. S. Rao, S. K.
Prasad, Q. Li, A. Jakli, Chem. Mater. 2006, 18, 6100–6102.
[73] M. Zennyoji, Y. Takanishi, K. Ishikawa, J. Thisayukta, J. Watanabe,
H. Takezoe, J. Mater. Chem. 1999, 9, 2775–2778.
[74] D. Shen, A. Pegenau, S. Diele, I. Wirth, C. Tschierske, J. Am.
Chem. Soc. 2000, 122, 1593–1601.
[75] G. Dantlgraber, A. Eremin, S. Diele, A. Hauser, H. Kresse, G.
Pelzl, C. Tschierske, Angew. Chem. 2002, 114, 2514–2518; Angew.
Chem. Int. Ed. 2002, 41, 2408–2412.
[40] A. Ajayaghosh, R. Varghese, S. Mahesh, V. K. Praveen, Angew.
Chem. 2006, 118, 7893–7896; Angew. Chem. Int. Ed. 2006, 45,
7729–7732.
[41] V. K. Praveen, S. S. Babu, C. Vijayakumar, R. Varghese, A. Ajaya-
ghosh, Bull. Chem. Soc. Jpn. 2008, 81, 1196–1211.
[42] G. Pelzl, S. Diele, W. Weissflog, Adv. Mater. 1999, 11, 707–724.
[43] R. A. Reddy, C. Tschierske, J. Mater. Chem. 2006, 16, 907–961.
[44] H. Takezoe, Y. Tahanishi, Philipp. J. Vet. Med. Jap. J. Appl. Phys.
2006, 45, 597–625.
[45] D. R. Link, G. Natale, R. Shao, J. E. Maclennan, N. A. Clark, E.
Kçrblova, D. M. Walba, Science 1997, 278, 1924–1927.
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
7
&
ÞÞ
These are not the final page numbers!

R.-M. Ho, C.-S. Hsu et al.
[76] M. W. Schrçder, S. Diele, G. Pelzl, W. Weissflog, ChemPhysChem
2004, 5, 99–103.
[88] S.-C. Lin, T.-F. Lin, R.-M. Ho, C.-Y. Chang, C.-S. Hsu, Adv. Funct.
Mater. 2008, 18, 3386–3394.
[89] K. Nakanishi, N. Berova, Circular Dichroism: Principles and Appli-
cations (Eds: K. Nakanishi, N. Berova, R. W. Woody) VCH, New
York 1994, Ch. 13.
[77] R. A. Reddy, M. W. Schrçder, M. Bodyagin, H. Kresse, S. Diele, G.
Pelzl, W. Weissflog, Angew. Chem. 2005, 117, 784–788; Angew.
Chem. Int. Ed. 2005, 44, 774–778.
[90] J. Tanaka, Bull. Acad. Vet. Fr. Bull. Chem. Soc. Jap. 1963, 36, 833–
847.
[78] R. A. Reddy, V. A. Raghunathan, B. K. Sadashiva, Chem. Mater.
2005, 17, 274–283.
[91] N. Harada, K. Nakanishi, Acc. Chem. Res. 1972, 5, 257–263.
[92] N. Harada, K. Nakanishi, J. Am. Chem. Soc. 1968, 90, 7351–7352.
[93] H. Cui, T. Muraoka, A. G. Cheetham, S. I. Stupp, Nano Lett. 2009,
9, 945–951.
[94] I. A. Nyrkova, A. N. Semenov, A. Aggeli, N. Boden, Eur. Phys. J. B
2000, 17, 481–497.
[95] A. Aggeli, I. A. Nyrkova, M. Bell, R. Harding, L. Carrick, T. C. B.
McLeish, A. N. Semenov, N. Boden, Proc. Natl. Acad. Sci. USA
2001, 98, 11857–11862.
[96] O.-Y. Zhong-can, L. Ji-xing, Phys. Rev. Lett. 1990, 65, 1679–1682.
[97] O.-Y. Zhong-can, L. Ji-xing, Phys. Rev. A 1991, 43, 6826–6836.
[98] J. V. Selinger, J. M. Schnur, Phys. Rev. Lett. 1993, 71, 4091–4094.
[99] R. Oda, I. Huc, M. Schmutz, S. J. Candau, F. C. MacKintosh,
Nature 1999, 399, 566–569.
[79] C. Keith, R. A. Reddy, A. Hauser, U. Baumeister, C. Tschierske, J.
Am. Chem. Soc. 2006, 128, 3051–3066.
[80] C. Keith, R. A. Reddy, M. Prehm, U. Baumeister, H. Kresse, J. L.
Chao, H. Hahn, H. Lang, C. Tschierske, Chem. Eur. J. 2007, 13,
2556–2577.
[81] Y. Zhang, M. J. OꢆCallaghan, U. Baumeister, C. Tschierske, Angew.
Chem. 2008, 120, 6998–7002; Angew. Chem. Int. Ed. 2008, 47,
6892–6896.
[82] J. Thisayukta, Y. Nakayama, S. Kawauchi, H. Takezoe, J. Wata-
nabe, J. Am. Chem. Soc. 2000, 122, 7441–7448.
[83] J. Thisayukta, H. Niwano, H. Takezoea, J. Watanabe, J. Mater.
Chem. 2001, 11, 2717–2721.
[84] M. Nakata, D. R. Link, J. Thisayukta, Y. Takanishi, K. Ishikawa, J.
Watanabe, H. Takezoe, J. Mater. Chem. 2001, 11, 2694–2699.
[85] A. Jꢄkli, G. Liao, I. Shashikala, U. S. Hiremath, C. V. Yelamaggad,
Phys. Rev. E 2006, 74, 041706.
[86] M. Lee, S.-T. Hur, H. Higuchi, K. Song, S.-W. Choi, H. Kikuchib, J.
Mater. Chem. 2010, 20, 5813–5816.
[87] S. Taushanoff, K. V. Le, J. Williams, R. J. Twieg, B. K. Sadashiva, H.
Takezoe, A. Jꢄkli, J. Mater. Chem. 2010, 20, 5893–5898.
[100] A. Brizard, C. Aimꢂ, T. Labrot, I. Huc, D. Berthier, F. Artzner, B.
Desbat, R. Oda, J. Am. Chem. Soc. 2007, 129, 3754–3762.
[101] E. T. Pashuck, S. I. Stupp, J. Am. Chem. Soc. 2010, 132, 8819–8821.
[102] L. Ziserman, H.-Y. Lee, S. R. Raghavan, A. Mor, D. Danino, J.
Am. Chem. Soc. 2011, 133, 2511–2517.
Received: January 6, 2012
Published online: && &&, 2012
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Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Self-Assembly of Chiral Bent-Core Molecules
FULL PAPER
Helical Structures
S.-C. Lin, R.-M. Ho,* C.-Y. Chang,
C.-S. Hsu* ..................... &&&& — &&&&
Hierarchical Superstructures with
Control of Helicity from the Self-
Assembly of Chiral Bent-Core
AHCTUNGTRENNMGUN olecules
Letꢀs twist again: The helicity of
assembly. The formation of helical rib-
bons was attributed to the merging
together of twisted ribbons (see
figure).
twisted and helical ribbons was con-
trolled by introducing chiral entities
into bent-core molecules for their self-
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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9
&
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These are not the final page numbers!