Self-assembly of cationic pyrene nanotubes

Article abstract of DOI:10.1039/c2jm15997j

The controlled preparation of organic nanotubes via self-assembly of polycyclic aromatics is a contemporary challenge for supramolecular science. Here, we show that the self-assembly of pyrene-containing cationic amphiphiles, 3-(4-(pyren-6-yl)phenoxy)propan-1-ammonium salts (PyPA-Cl, PyPA-Br, and PyPA-SO₄), can form high aspect ratio nanotubes with a uniform diameter distribution. We have also demonstrated that the counter anions also play an important role in the self-assembling results. The self-assembly of pyrene-containing cationic amphiphilic molecules with monovalent anions (Cl ^- and Br^-) forms exclusively uniform nanotubes; whereas the self-assembly of amphiphiles with bivalent counter anions (SO ₄^2-) forms exclusively high aspect ratio nanoribbons. Furthermore, we have found that the diameter of the PyPA-Br nanotubes is larger than that of the PyPA-Cl nanotubes. The research results reported herein represent an important step towards the preparation of functional nanostructures with controlled 1D architectures.

Full text of DOI:10.1039/c2jm15997j

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links <
C
Journal of
Materials Chemistry
Cite this: J. Mater. Chem., 2012, 22, 4927
www.rsc.org/materials
PAPER
Self-assembly of cationic pyrene nanotubes
*
Yulan Chen, Bo Zhu, Yang Han and Zhishan Bo
Received 18th November 2011, Accepted 4th January 2012
DOI: 10.1039/c2jm15997j
The controlled preparation of organic nanotubes via self-assembly of polycyclic aromatics is
a contemporary challenge for supramolecular science. Here, we show that the self-assembly of pyrene-
containing cationic amphiphiles, 3-(4-(pyren-6-yl)phenoxy)propan-1-ammonium salts (PyPA-Cl,
PyPA-Br, and PyPA-SO4), can form high aspect ratio nanotubes with a uniform diameter distribution.
We have also demonstrated that the counter anions also play an important role in the self-assembling
results. The self-assembly of pyrene-containing cationic amphiphilic molecules with monovalent anions
(Clꢀ and Brꢀ) forms exclusively uniform nanotubes; whereas the self-assembly of amphiphiles with
bivalent counter anions (SO42ꢀ) forms exclusively high aspect ratio nanoribbons. Furthermore, we have
found that the diameter of the PyPA-Br nanotubes is larger than that of the PyPA-Cl nanotubes. The
research results reported herein represent an important step towards the preparation of functional
nanostructures with controlled 1D architectures.
playsanimportantroleinthe self-assembly result. Self-assembly of
Introduction
PyPA-X with monovalent counteranions such as Clꢀ and Brꢀ
afforded exclusively nanotubes with tunable dimensions; whereas
self-assembly of PyPA-X with bivalent counteranions such as
SO42ꢀ gave rise to well-defined high aspect ratio nanoribbons.
The supramolecular assembly of synthetic organic molecules into
well-ordered nanostructures with controllable morphology is
currently a subject of great interest.1–4 The principles of supra-
molecular chemistry provide us not only the possibility of probing
into the complexity of nature, but also many potential applica-
tions in various fields.5–8 The use of planar aromatic building
blocks, especially polycyclic aromatics, for supramolecular self-
assembly is of particular importance for achieving nanoobjects
with tunable electronic and photonic properties.5,9–11 The self-
assembled 1D nanoobjects from planar aromatics are excellent
candidate for electronic and optoelectronic devices owing to the
charge-transporting and energy-migrating pathway provided by
the p–p interactions between the piled planar aromatics.3,12–16
Besides p–p interactions, by appropriate functionalization,
various noncovalent intermolecular forces, such as hydrogen-
bonding, amphiphilic, and charge-transfer interactions, have been
utilized as secondary forces to tailor the molecular arrangement of
the polycyclic aromatics.17–21 In comparing with other 1D nano-
structures such as nanoribbons and fibrils, examples of p-conju-
gated systems that assemble into high aspect nanotubes are
relatively uncommon, since strict conditions are required.22–28
Herein, we present the supramolecular self-assembly of a series
of cationic amphiphilic molecules, 3-(4-(pyren-6-yl)phenoxy)
propanammonium salts, abbreviated as PyPA-X as shown in
Fig. 1, with a hydrophobic polycyclic aromatic disc (pyrene) and
aprotonatedaminogroupconnectedwithaspacer, whereXstands
for different anions. The counteranion of the ammonium group
Experimental
Materials and methods
The catalyst precursor Pd(PPh3)4 was prepared according to the
literature procedure29 and stored in a Schlenk tube under
nitrogen.
4,4,5,5-Tetramethyl-2-(pyren-6-yl)-1,3,2-dioxabor-
olane (4) was prepared according to the literature.30 Tert-butyl-3-
chloropropylcarbamate (1) was purchased from Synwit Tech-
nology. All other chemicals were purchased from Aldrich or
Acros and used without further purification. Tetrahydrofuran
(THF) was distilled over sodium and benzophenone. All reactions
were performed under an atmosphere of nitrogen and monitored
by TLC with silica gel 60 F254 (Merck, 0.2 mm). Column chro-
matography was carried out on silica gel (200–300 mesh).
Characterization
1H and 13C NMR spectra were recorded on a Bruker AV400
spectrometer in CDCl3 or DMSO-d6. Combustion analyses were
Institute of Polymer Chemistry and Physics, College of Chemistry, Beijing
Normal University, Beijing, 100875, P.R. China. E-mail: zsbo@bnu.edu.
cn; Fax: +86 10 62206891; Tel: + 86 10 62206891
Fig. 1 Chemical structures of PyPA-X (X ¼ Cl, Br, and SO4).
J. Mater. Chem., 2012, 22, 4927–4931 | 4927
This journal is ª The Royal Society of Chemistry 2012

View Article Online
performed on a Flash EA 1112 analyzer. Scanning electron
microscopy (SEM) was performed on a JEOL model JSM-6700F
FE-SEM and a Hitachi S-4800 FE-SEM operating at 5 kV.
Samples for SEM measurement were prepared by dropping the
suspension onto a silicon substrate followed by air drying and
coating with Pt; transmission electron microscopy (TEM) was
obtained on a Hitachi H-800 electron microscope and a JEOL
model JEM-1011 electron microscope operating at 100 kV.
Samples for TEM measurement were prepared by dropping the
suspension onto 200 mesh copper grids followed by air-drying.
EDX spectra were recorded with a Hitachi S-4800 SEM equip-
ped with Horiba-EMAX450 energy dispersive X-ray analyzer
operating at an accelerating voltage of 15 kV. Powder X-ray
diffraction data were collected on a Rigaku model RINT Ultima
III diffractometer by depositing powder on glass substrate, from
2q ¼ 1.5ꢁ to 60ꢁ with 0.02ꢁ increments at 25 ꢁC. UV-vis
absorption spectra were obtained on a Shimadzu UV-vis spec-
trophotometer model UV-1601 PC. Fluorescence spectra were
recorded on a Hitachi F-4500 spectrometer.
overnight. A large amount of precipitate was formed. Filtration
and washing with acetone afforded PyPA-Cl as a colorless solid
(0.49 g, 95%). 1H NMR (400 MHz, DMSO-d6, ppm): d 8.42–8.11
(m, 11H), 8.07 (d, 1H), 7.81 (d, 2H), 7.22 (d, 2H), 4.25 (t, 2H),
3.06 (br, 2H), 2.18 (m, 2H). 13C NMR (100 MHz, DMSO-d6,
ppm): d 158.50, 137.49, 133.29, 132.06, 131.62, 131.04, 130.50,
128.31, 128.18, 128.02, 127.89, 127.02, 125.91, 125.56, 125.51,
125.29, 124.83, 124.71, 115.29, 65.25, 36.77, 27.37.
Synthesis of PyPA-Br. To a solution of 5 (0.10 g, 0.22 mmol) in
THF (3.0 mL) hydrobromic acid (1.0 mL, 10 M) was added. The
mixture was stirred at room temperature for 12 h. After the
addition of acetone (30.0 mL), the mixture was placed in a fridge
overnight. A large amount of precipitate was formed. Filtration
and washing with acetone afforded PyPA-Br as a colorless solid
1
(0.086 g, 90%). H NMR (400 MHz, DMSO-d6, ppm): d 8.39–
8.01 (m, 9H), 7.92 (s, 3H), 7.60 (d, 2H), 7.22 (d, 2H), 4.24 (t, 2H),
3.09 (t, 2H), 2.16 (m, 2H). 13C NMR (100 MHz, DMSO-d6,
ppm): d 158.50, 137.55, 133.42, 132.13, 131.70, 131.11, 130.58,
128.39, 128.24, 128.08, 127.97, 127.08, 125.98, 125.62, 125.57,
125.33, 124.91, 124.79, 115.39, 65.44, 37.12, 27.57.
Synthesis of tert-butyl 3-(4-bromophenoxy)propyl-carbamate
(3). A mixture of 1 (10.0 g, 0.052 mol), 2 (11.0 g, 0.064 mol), KI
(5.0 g, 0.030 mol), K2CO3 (30.0 g, 0.217 mol) and butanol
(300 mL) was heated to reflux and stirred under a nitrogen
atmosphere overnight; CH2Cl2 was added. The mixture was
washed with a large portion of aqueous NaOH solution several
times, and the organic layer was separated and dried over
anhydrous Na2SO4. After the removal of the solvent, the residue
was recrystallized in n-hexane and ethyl ether to afford 3 as
Synthesis of PyPA-SO4. To a solution of 5 (0.10 g, 0.22 mmol)
in THF (3.0 mL) concentrated sulfuric acid (1.0 mL, 10 M) was
added. The mixture was stirred at room temperature for 24 h.
After the addition of acetone (30.0 mL), the mixture was placed
in a fridge overnight. A large amount of precipitate was formed.
Filtration and washing with acetone afforded PyPA-SO4 as
a colorless solid (0.074 g, 83%). 1H NMR (400 MHz, DMSO-d6,
ppm): d 8.40–8.02 (m, 9H), 7.84 (s, 3H), 7.61 (d, 2H), 7.22
(d, 2H), 4.24 (t, 2H), 3.09 (br, 2H), 2.14 (m, 2H). 13C NMR
(100 MHz, DMSO-d6, ppm): d 158.50, 137.55, 133.43, 132.13,
131.70, 131.11, 130.59, 128.40, 128.24, 128.08, 127.97, 127.10,
125.99, 125.62, 125.58, 125.33, 124.91, 124.79, 115.39, 65.41,
37.21, 27.59.
1
a colorless solid (11.2 g, 66%). H NMR (400 MHz, CDCl3,
ppm): d 7.36 (d, 2H), 6.77 (d, 2H), 4.72 (s, 1H), 3.98 (t, 2H), 3.31
(m, 2H), 1.95 (m, 2H), 1.44 (s, 9H). 13C NMR (100 MHz, CDCl3,
ppm): d 158.03, 156.15, 132.43, 116.41, 113.10, 93.92, 66.14,
38.01, 29.66, 28.56. Anal. calcd. for C14H20BrNO3: C, 50.92; H,
6.10; N, 4.24. Found: C, 50.91; H, 6.21; N, 4.46.
Synthesis of tert-butyl 3-(4-(pyren-6-yl)phenoxy)propyl-carba-
mate (5). A mixture of 3 (1.0 g, 3.0 mmol), 4,4,5,5-tetramethyl-2-
(pyren-6-yl)-1,3,2-dioxaborolane 4 (1.2 g, 3.6 mmol), NaHCO3
(0.5 g, 6.0 mmol), THF (25 mL), and H2O (11 mL) was carefully
degassed before and after Pd(PPh3)4 (35 mg, 0.030 mmol) was
added. The mixture was heated to reflux and stirred under
a nitrogen atmosphere overnight. CH2Cl2 (150 mL) and brine
was added, and the organic layer was separated and dried over
anhydrous Na2SO4. After the removal of the solvent, the residue
was purified by chromatography on a silica gel column eluting
Results and discussion
The synthesis of PyPA-X (X ¼ Cl, Br, and SO4) is quite
straightforward and the synthetic route is shown in Fig. 2. Mono
bromide 3 carrying a tert-butyloxycarbonyl (Boc) protected
amino group was prepared by the reaction of commercially
available tert-butyl-3-chloropropylcarbamate 1 and 4-bromo-
phenol 2 under Williamson etherification conditions with K2CO3
as the base, KI as the catalyst, and butanol as the solvent. Boc
protected compound 5 was synthesised in a yield of 81% by
Suzuki–Miyaura cross-coupling of pyrene mono boronic acid
ester 4 and mono bromide 3 in a biphasic mixture of THF and
aqueous NaHCO3 with Pd(PPH3)4 as a catalyst precursor. After
deprotection of compound 5 with concentrated aqueous HCl,
HBr or H2SO4, the desired molecules PyPA-Cl, PyPA-Br and
PyPA-SO4, were obtained in yields of 95%, 90% and 83%,
respectively. The structures of all new compounds were unam-
1
with CH2Cl2 to afford 5 as a green solid (1.1 g, 81%). H NMR
(400 MHz, CDCl3, ppm): d 8.22–8.15 (m, 4H), 8.09 (s, 2H), 8.03–
7.96 (m, 3H), 7.56 (d, 2H), 7.10 (d, 2H), 4.82 (s, 1H), 4.16 (t, 2H),
3.41 (m, 2H), 2.04 (m, 2H), 1.48 (s, 9H). 13C NMR (100 MHz,
CDCl3, ppm): d 158.35, 156.24, 137.57, 133.87, 131.75, 131.16,
130.53, 128.73, 127.84, 127.50, 126.14, 125.50, 125.00, 119.13,
114.56, 46.97, 38.42, 29.81, 28.61. Anal. calcd. for C30H29NO3:
C, 79.80; H, 6.47; N, 3.10. Found: C, 79.47; H, 6.52; N, 3.30.
1
biguously confirmed by H and 13C NMR spectroscopy, and all
except for the cationic ammonium salts PyPA-Cl, PyPA-Br and
PyPA-SO4 were also verified by elemental analysis.
Synthesis of PyPA-Cl. To a solution of 5 (0.60 g, 1.33 mmol) in
THF (5.0 mL) hydrochloric acid (1.0 mL, 10 M) was added. The
mixture was stirred at room temperature for 12 h. After the
addition of acetone (30.0 mL), the mixture was placed in a fridge
The precipitation technique is a very useful method in the self-
assembly of nanostructures. Nanosized aggregates can be formed
by slowly diffusing a poor solvent into a solution of good solvent.
4928 | J. Mater. Chem., 2012, 22, 4927–4931
This journal is ª The Royal Society of Chemistry 2012

View Article Online
Fig. 2 Synthesis of PyPA-X (X ¼ Cl, Br, SO4).
PyPA-X was not soluble in water while they displayed a good
solubility (for PyPA-Cl and PyPA-Br, up to 1 mg mLꢀ1 and for
PyPA-SO4, up to 0.4 mg mLꢀ1) in ethanol. The controlled self-
assembly of PyPA-X took place upon slow diffusion of water
vapor into hot ethanol solutions of PyPA-X (1.0 mg mLꢀ1 for
PyPA-Cl and PyPA-Br and 0.4 mg mLꢀ1 for PyPA-SO4) at
60 ꢁC. White aggregates formed quickly after 10 min of diffusion.
After standing for 1 h, the wet precipitates were transferred onto
silicon and copper grids by a dip-coating method for scanning
electron microscopy (SEM) and transmission electron micros-
copy (TEM) observation, respectively. As shown in Fig. 3a–d,
low and high resolution SEM images revealed that precipitates of
PyPA-Cl and PyPA-Br are composed exclusively of entangled
nanosized fibrils with high aspect ratio. These fibrils were several
micrometres in length and several tens of nanometres in width.
TEM studies showed that these fibril assemblies were of tubular
structures (Fig. 3e and f). The centrifugation of the suspension,
the dispersion of the remaining wet solid in a small amount of
water, and finally freeze-drying led exclusively to nanotubes. In
the dry form, the self-assembled nanotubes are stable and can be
kept in air for at least six months. It is worth noting that
changing the counteranions brings about significant changes in
morphology. The nanotubes formed by PyPA-Br are larger in
diameter than those formed by PyPA-Cl. The width of the
nanotubes from PyPA-Br is about 70 nm and the wall thickness
is about 30 nm, while the nanotubes from PyPA-Cl have
a uniform width of about 30 nm, and a wall thickness of about 10
nm. In contrast with the nanotubes obtained from PyPA-Cl and
PyPA-Br, PyPA-SO4 with a binary anion self-assembled into
ribbon-like aggregates with a width of about 150 nm and length
of several tens of micrometres (Fig. 3g and h).
Fig. 3 SEM images of self-assembled nanotubes by (a), (b) PyPA-Cl;
(c), (d) PyPA-Br; TEM images of self-assembled nanotubes by (e) PyPA-
Cl; and (f) PyPA-Br; (g) and (h) SEM images of self-assembled nano-
ribbons by PyPA-SO4.
corresponds to the p–p stacking distance between the pyrene
units.10 The observed three equidistant peaks with d-spacings of
1.99, 1.03, and 0.52 nm, respectively, are characteristic of
a lamellar structure.31,32 Considering that the actual molecular
length of PyPA-Cl is approximately 1.0 nm (optimized by
Materials Studio software as shown in Fig. 5a), each lamella may
consist of bilayers with an unsymmetrical head-to-head confor-
mation (Fig. 5b).33,34 The XRD pattern of self-assembled PyPA-
Br exhibited the first and the second order reflection peaks with
d-spacings of 0.97 and 0.49 nm, indexing to a lamellar structure.
These values are consistent with the actual molecular length of
PyPA-Br. This result could be rationalized by the presence of
a stable monolayer lipid membrane within the assembly. The
larger Brꢀ anions cause the antiparallel organization of the
rod-like cores inside the layers (Fig. 5b).33 The sharp peak with
a d-spacing of 0.65 nm is most probably due to the distance
between the anions, and the d-spacing of 0.39 nm is because of
the dense stacking of the pyrene units. For PyPA-Cl and PyPA-
Br, the curvature of the lamellar structure may emerge from the
large hydrophobic/hydrophilic ratio, which may enforce
membrane curvature to reduce the surface edges exposed to water,
thus self-assembled into nanotubes.27 In contrast, nanoribbons
The morphological differences among PyPA-Cl, PyPA-Br,
and PyPA-SO4 suggest different packing modes for the three
molecules, which is further supported by powder X-ray diffrac-
tion (PXRD) measurements of their freeze-dried aggregates.
Well-resolved XRD patterns of the nanostructures from PyPA-
Xs were observed, demonstrating both the long range and short
range ordering of molecules (Fig. 4a and b).31 The XRD profile
of self-assembled nanotubes from PyPA-Cl displayed a peak
centered at 21.2ꢁ corresponding to a d-spacing of 0.42 nm, which
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 4927–4931 | 4929

View Article Online
Fig. 4 XRD patterns of (a) self-assembled nanotubes by PyPA-Cl and
PyPA-Br, and (b) self-assembled nanoribbons by PyPA-SO4.
Fig. 5 (a) Simulated molecular conformation (by Material Studio
software) of PyPA-X; (b) schematic illustration of the formation of
nanotubes from PyPA-Cl and PyPA-Br; and (c) schematic illustration of
the formation of nanoribbons from PyPA-SO4.
formed by PyPA-SO4 exhibiting a mixture of two different
diffraction patterns (Fig. 5c), adopt lamellar structures with both
bilayer and monolayer conformations. Based on the experi-
mental results of SEM, TEM, and PXRD, we put forward
a rational assumption about the self-assembled structures and
possible packing models of PyPA-Cl, PyPA-Br, and PyPA-SO4
as shown in Fig. 5.
investigated. The self-assembly process was carried out by slow
diffusion of water vapor to an ethanol solution of PyPA-X (X ¼
Cl, Br, and SO4) to afford 1D nanostructures in a controllable
manner. The self-assembly of PyPA-X with monovalent coun-
teranions such as Clꢀ and Brꢀ afforded high aspect nanotubes
The optical properties of pyrene derivatives are very sensitive
to their physical state. Solution and film UV-vis and fluorescence
spectra of PyPA-Cl are shown in Fig. 6. In the ultraviolet region,
the highly dilute ethanol solution of PyPA-Cl (1.0 mg mLꢀ1
)
showed an absorption peak at 343 nm, characteristic of 1-phenyl
substituted pyrene in solution; in the film, the absorption peak of
PyPA-Cl broadened, indicating the aggregation of pyrene units.
The highly dilute ethanol solution of PyPA-Cl (1.0 mg mLꢀ1
)
exhibited typical monomer emission of 1-phenyl substituted
pyrene with two peaks at 387 and 403 nm; the PyPA-Cl nanotube
film exhibited a broad emission peak centered at 456 nm, char-
acteristic of pyrene excimer emission, indicating the aggregation
of pyrene units in nanotubes.9,35
Conclusions
In summary, we have demonstrated that the use of designing
supramolecular assembly method could afford new nanotubes
from simple starting materials. The self-assembly behavior of
cationic pyrene amphiphiles PyPA-X (X ¼ Cl, Br, and SO4) was
Fig. 6 Normalized UV-vis and fluorescence spectra of PyPA-Cl in film
and in dilute ethanol solution (1 mg mLꢀ1).
4930 | J. Mater. Chem., 2012, 22, 4927–4931
This journal is ª The Royal Society of Chemistry 2012

View Article Online
16 L. E. Sinks, B. Rybtchinski, M. Iimura, B. A. Jones, A. J. Goshe,
X. Zuo, D. M. Tiede, X. Li and M. R. Wasielewski, Chem. Mater.,
2005, 17, 6295–6303.
17 J. Barbera, M. G. Debije, J. Piris and Y. H. Geerts, Adv. Mater., 2003,
15, 1614–1618.
with a uniform width distribution. The dimension of nanotubes
formed by PyPA-Br is larger than that of nanotubes formed by
PyPA-Cl. Changing the counterion from the monovalent anions
2ꢀ
Clꢀ and Brꢀ to the bivalent anion SO4 led to a significant
18 V. Percec, M. Glodde, M. Peterca, A. Rapp, I. Schnell, H. W. Spiess,
T. K. Bera, Y. Miura, V. S. K. Balagurusamy, E. Aqad and
P. A. Heiney, Chem.–Eur. J., 2006, 12, 6298–6314.
19 J. van Herrikhuyzen, A. Syamakumari, A. Schenning and
E. W. Meijer, J. Am. Chem. Soc., 2004, 126, 10021–10027.
change in morphology of the aggregate from nanotubes to
nanoribbons. Possible packing styles were described based on
X-ray diffraction results. The nanoobjects reported herein are
expected to be useful in the fields of bio/chem-sensors and
optoelectronic devices.
€
20 D. Wu, W. Pisula, V. Enkelmann, X. Feng and K. Mullen, J. Am.
Chem. Soc., 2009, 131, 9620–9621.
21 C. Wang, S. Yin, S. Chen, H. Xu, Z. Wang and X. Zhang, Angew.
Chem., 2008, 120, 9189–9192; C. Wang, S. Yin, S. Chen, H. Xu,
Z. Wang and X. Zhang, Angew. Chem., Int. Ed., 2008, 47, 9049–
9052.
22 T. Shimizu, M. Masuda and H. Minamikawa, Chem. Rev., 2005, 105,
1401–1443.
23 D. T. Bong, T. D. Clark, J. R. Granja and M. R. Ghadiri, Angew.
Chem., 2001, 113, 1016–1041; D. T. Bong, T. D. Clark,
J. R. Granja and M. R. Ghadiri, Angew. Chem., Int. Ed., 2001, 40,
988–1011.
Acknowledgements
This work is supported by Nature Science Foundation of China
(20834006), 973 Program (2011CB935703 and 2009CB623603),
and the Fundamental Research Funds for the Central
Universities.
24 T. Yamamoto, T. Fukushima and T. Aida, Adv. Polym. Sci., 2008,
220, 1–27.
Notes and references
€
25 D. Wu, L. Zhi, G. J. Bodwell, G. Cui, N. Tsao and Klaus Mullen,
Angew. Chem., 2007, 119, 5513–5516; D. Wu, L. Zhi, G. J. Bodwell,
1 J.-M. Lehn, Science, 1985, 227, 849–856.
2 G. W. Whitesides and B. Grzybowski, Science, 2002, 295, 2418–2421.
3 F. J. M. Hoeben, P. Jonkheijm, E. W. Meijer and
A. P. H. J. Schenning, Chem. Rev., 2005, 105, 1491–1546.
4 J. A. A. W. Elemans, A. E. Rowan and R. J. M. Nolte, J. Mater.
Chem., 2003, 13, 2661–2670.
€
G. Cui, N. Tsao and Klaus Mullen, Angew. Chem., Int. Ed., 2007,
46, 5417–5420.
26 W.-Y. Yang, E. Lee and M. Lee, J. Am. Chem. Soc., 2006, 128, 3484–
3485.
€
5 A. C. Grimsdale and K. Mullen, Angew. Chem., Int. Ed., 2005, 44,
27 H. Shao, J. Seifert, N. C. Romano, M. Gao, J. J. Helmus,
C. P. Jaroniec, D. A. Modarelli and J. R. Parquette, Angew. Chem.,
2010, 122, 7854–7857; H. Shao, J. Seifert, N. C. Romano, M. Gao,
J. J. Helmus, C. P. Jaroniec, D. A. Modarelli and J. R. Parquette,
Angew. Chem., Int. Ed., 2010, 49, 7688–7691.
5592–5629.
6 V. Balzani, A. Credi, F. M. Raymo and J. F. Stoddart, Angew. Chem.,
Int. Ed., 2000, 39, 3348–3391.
7 J. Rebek, Jr, Acc. Chem. Res., 1999, 32, 278–286.
8 J.-H. Ryu, D.-J. Hong and M. Lee, Chem. Commun., 2008, 1043–
1054.
28 C. Park, I. H. Lee, S. Lee, Y. Song, M. Rhue and C. Kim, Proc. Natl.
Acad. Sci. U. S. A., 2006, 103, 1199–1203.
29 C. A. Tolman, W. C. Seidel and D. H. Gerlach, J. Am. Chem. Soc.,
1972, 94, 2669–2676.
30 M. Beinhoff, W. Weigel, M. Jurczok, W. Rettig, C. Modrakowski,
9 Y. Kamikawa and T. Kato, Langmuir, 2007, 23, 274–278.
10 Y. Kamikawa and T. Kato, Org. Lett., 2006, 8, 2463–2466.
€
11 F. Wurthner, Z. J. Chen, F. J. M. Hoeben, P. Osswald, C. C. You,
€
I. Bruedgam, H. Harti and A. D. Schluter, Eur. J. Org. Chem.,
P. Jonkheijm, J. von Herrikhuyzen, A. P. H. J. Schenning,
P. P. A. M. van der Schoot, E. W. Meijer, E. H. A. Beckers,
S. C. J. Mes-kers and R. A. J. Janssen, J. Am. Chem. Soc., 2004,
126, 10611–10618.
2001, (20), 3819–3829.
31 S. Laschat, A. Baro, N. Steinke, F. Giesselmann, C. Hagele, G. Scalia,
€
R. Judele, E. Kapatsina, S. Sauer, A. Schreivogel and M. Tosoni,
Angew. Chem., 2007, 119, 4916–4973; S. Laschat, A. Baro,
€
12 E. W. Meijer and A. P. H. J. Schenning, Nature, 2002, 419, 353–354.
13 Y. Yamamoto, T. Fukushima, Y. Suna, N. Ishii, A. Saeki, S. Seki,
S. Tagawa, M. Taniguchi, T. Kawai and T. Aida, Science, 2006,
314, 1761–1764.
N. Steinke, F. Giesselmann, C. Hagele, G. Scalia, R. Judele,
E. Kapatsina, S. Sauer, A. Schreivogel and M. Tosoni, Angew.
Chem., Int. Ed., 2007, 46, 4832–4887.
32 H. Sakashita, A. Nishitani, Y. Sumiya, H. Terauchi, K. Otha and
I. Yamamoto, Mol. Cryst. Liq. Cryst., 1988, 163, 211–219.
33 X. Cheng, X. Bai, S. Jing, H. Ebert, M. Prehm and C. Tschierske,
Chem.–Eur. J., 2010, 16, 4588–4601.
34 M. Masuda and T. Shimizu, Langmuir, 2004, 20, 5969–5977.
35 F. M. Winnik, Chem. Rev., 1993, 93, 587–614.
€
14 D. Wu, R. Liu, W. Pisula, X. Feng and K. Mullen, Angew. Chem.,
2011, 123, 2843–2846; D. Wu, R. Liu, W. Pisula, X. Feng and
€
K. Mullen, Angew. Chem., Int. Ed., 2011, 50, 2791–2794.
15 C. F. Van Nostrum, S. J. Picken and R. J. M. Nolte, Angew. Chem.,
1994, 106, 2298–2300; C. F. Van Nostrum, S. J. Picken and
R. J. M. Nolte, Angew. Chem., Int. Ed. Engl., 1994, 33, 2173–2175.
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 4927–4931 | 4931