Macrocyclic amphiphiles with 1,8-anthrylene fluorophores: Synthesis and attempts toward two-dimensional organization

Article abstract of DOI:10.1021/ol100877g

(Figure presented) New macrocyclic amphiphiles with two or three integrated 1,8-anthrylenes have been synthesized by an iterative Sonogashira cross-coupling protocol. The final cyclization has been conducted with 80% yield under cuprous-free dilution conditions. Formation of a monolayer at the air/water interface has also been demonstrated. These results open the intriguing possibility to construct large 2D supramolecular/macromolecular systems for which unique photophysical and -chemical properties are expected.

Full text of DOI:10.1021/ol100877g

ORGANIC
LETTERS
2010
Vol. 12, No. 12
2778-2781
Macrocyclic Amphiphiles with
1,8-Anthrylene Fluorophores: Synthesis
and Attempts toward Two-Dimensional
Organization
Patrick Kissel,† Jeroen van Heijst,† Raoul Enning,‡ Andreas Stemmer,‡ A.
Dieter Schlu¨ter,*,† and Junji Sakamoto*,†
Laboratory of Polymer Chemistry, Department of Materials, ETH Zurich,
Wolfgang-Pauli-Strasse 10, HCI J541, CH-8093 Zurich, Switzerland, and
Nanotechnology Group, Department of Mechanical and Process Engineering,
Tannenstrasse 3, CLA J13, CH-8092 Zurich, Switzerland
schlueter@mat.ethz.ch; sakamoto@mat.ethz.ch
Received April 16, 2010
ABSTRACT
New macrocyclic amphiphiles with two or three integrated 1,8-anthrylenes have been synthesized by an iterative Sonogashira cross-coupling
protocol. The final cyclization has been conducted with 80% yield under cuprous-free dilution conditions. Formation of a monolayer at the
air/water interface has also been demonstrated. These results open the intriguing possibility to construct large 2D supramolecular/macromolecular
systems for which unique photophysical and -chemical properties are expected.
Photophysical and -chemical properties of anthracene deriva-
tives are attractive for applications in photofunctional devices
and materials.1 Construction of single molecular or supramo-
lecular/macromolecular systems in which anthracene units
are integrated with a well-defined order is of particular
interest. To control such functionality in terms of position
and orientation, the use of macrocyclic scaffolds would be
advantageous because of their reduced conformational free-
dom.2
We introduce here the synthesis of new macrocyclic am-
phiphiles, M3 (1) and M2 (2), in which three or two 1,8-
anthrylene units are embedded, respectively (Figure 1). A barrel-
like shape is expected for these compounds, whereby the
hydroxyl groups are positioned at a rim on the side opposite to
the anthrylene moieties. By taking advantage of this unique
amphiphilic structure, feasibility of monolayer formation has
been tested for M3 at the air/water interface aiming at two-
dimensional organization. Note that such a 2D supramolecular
structure containing the 1,8-anthrylene fluorophores in well-
defined order may not only serve for sensing guest molecules,
relaying energy/electron transfer, but also be converted into a
2D covalent periodic network (2D polymers), e.g., by [4 +
4]-cycloaddition between the anthrylenes.3,4
† ETH Zurich Wolfgang-Pauli-Strasse 10.
‡ Nanotechnology Group.
(1) (a) Becker, H.-D. Chem. ReV. 1993, 93, 145. (b) Bouas-Laurent,
H.; Desvergne, J.-P.; Castellan, A.; Lapouyade, R. Chem. Soc. ReV. 2000,
29, 43. (c) Bouas-Laurent, H.; Desvergne, J.-P.; Castellan, A.; Lapouyade,
R. Chem. Soc. ReV. 2001, 30, 248.
(2) For example, see: (a) Grave, C.; Schlu¨ter, A. D. Eur. J. Org. Chem.
2002, 3075. (b) Sakamoto, J.; Schlu¨ter, A. D. Eur. J. Org. Chem. 2007,
2700.
For the synthesis (Scheme 1), compounds 3-5 were
selected as starting materials and prepared according to
10.1021/ol100877g  2010 American Chemical Society
Published on Web 05/25/2010

conditions to furnish the desired final product 1 in 80%
isolated yield (180 mg) after purification by recycling gel-
permeation chromatography (rGPC).2b,4b
Scheme 1. Syntheses of M3 (1) and M2 (2) from the Three
Starting Compounds 3-5 by Iterative Use of the Sonogashira
Coupling
Figure 1. Macrocyclic amphiphiles M3 (1) and M2 (2) in which
three or two 1,8-anthrylene units are embedded, respectively. The
hydroxyl groups are positioned at a rim on the side opposite to the
1,8-anthrylene units.
reported procedures5,6 on a scale of 15, 15, and 7 g,
respectively. The Sonogashira cross-coupling reaction7 was
iteratively used for the subsequent build-up process with
removal of the silyl protecting group. Note that no protection
of the hydroxyl groups was required throughout the present
scheme except for purification of 2 (see below) which
facilitated the synthesis considerably. First, one molar
equivalent of 3 was subjected to the Sonogashira coupling
with 4 and 5 separately. These reactions afforded 8 and 9 as
major products, respectively, together with 6 as common
minor product. All these three compounds, 8, 9, and 6, were
prepared on the several gram scale and subsequently used
for the syntheses of M3 (1) and M2 (2), respectively.
Regarding target 1, compound 9 was first subjected to
deprotection of the triisopropylsilyl (TIPS) group to give 10,
which was then followed by the Sonogashira coupling with
8 to afford 11. Note that this coupling reaction took place
selectively at the iodo carbon because of its higher reactivity
than the bromo one.8 Next, compound 11 was subjected to
TIPS deprotection to give 12, followed by the Sonogashira
coupling with 8 to furnish 13 which is a linear precursor of
1 (3 g). The final intramolecular cyclization was carried out
with in situ deprotection of the triisopropylsilyl (TIPS) groups
(13 to 14) in a dilute solution (0.7 mM). Cuprous iodide
was not used as cocatalyst for the Sonogashira reaction9 due
to the detrimental effect on cyclization expected from our
previous results.2b Instead, an increased amount (20 mol %)
of palladium(0) catalyst was used to accelerate the reaction.
The cyclization proceeded efficiently under the present
(3) (a) Zhang, A.; Sakamoto, J.; Schlu¨ter, A. D. Chimia 2008, 62, 776.
(b) Sakamoto, J.; van Heijst, J.; Lukin, O.; Schlu¨ter, A. D. Angew. Chem.,
Int. Ed. 2009, 48, 1030
.
(4) (a) Mu¨nzenberg, C.; Rossi, A.; Feldman, K.; Fiolka, R.; Stemmer,
A.; Kita-Tokarczyk, K.; Meier, W.; Sakamoto, J.; Lukin, O.; Schlu¨ter, A. D.
Chem.sEur. J. 2008, 14, 10797. (b) Kissel, P.; Schlu¨ter, A. D.; Sakamoto,
J. Chem.sEur. J. 2009, 15, 8955
(5) Kissel, P.; Weibel, F.; Federer, L.; Sakamoto, J.; Schlu¨ter, A. D.
Synlett 2008, 1793
(6) Kissel, P.; Breitler, S.; Reinmu¨ller, V.; Lanz, P.; Federer, L.; Schlu¨ter,
A. D.; Sakamoto, J. Eur. J. Org. Chem. 2009, 2953
(7) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975,
.
.
.
16, 4467.
Regarding target 2, the compound 6 (300 mg) was
subjected to an intermolecular cyclization with 5 (90 mg).
(8) For example, see: Opris, D. M.; Franke, P.; Schlu¨ter, A. D. Eur. J.
Org. Chem. 2005, 822.
Org. Lett., Vol. 12, No. 12, 2010
2779

The Sonogashira reaction was performed with in situ
deprotection of the TIPS groups (6 to 7) in a dilute solution
(0.7 mM), whereby 7 partially precipitated. The reaction was
nevertheless continued for 10 days. Since the product mixture
including 2 was poorly soluble in chloroform, the hydroxyl
groups were acetylated prior to rGPC purification using
chloroform (Supproting Information). Di-O-acetylated cyclic
product 15 was isolated in 22% yield (49 mg). Because of
the solubility problem, the cyclization conditions still need
to be optimized.10 The targeted compound 2 (33 mg) was
finally furnished by deacetylation of 15 and subsequent
precipitation from methanol. Note that all structures were
1
confirmed by H and 13C NMR as well as high-resolution
mass spectrometry (Supporting Information).
Both M3 (1) and M2 (2) could be recrystallized from
chloroform and dioxane/water, and the crystals were found
to exhibit yellowish green and yellow colors, respectively.
The M2 single crystals could be grown large enough to be
analyzed by X-ray diffraction revealing a structure of M2
with a triclinic unit cell (Supporting Information). It was
found that M2 is nearly flattened within the single crystal
structure to close the cavity (Figure 2). Given the consider-
able rotational freedom at the acetylene axes of M2, this was
expected from related results reported by Toyota et al.11 The
crystal structure of M3 has not been elucidated yet because
the crystal size is still too tiny to analyze (Supporting
Information). It is nevertheless anticipated that M3 can hardly
close its cavity in a way similar to M2 because this would
cause increasing distortion due to the length mismatch
between TAT and ATA (Note: “A” and “T” represent the
anthrylene and the m-terphenylene bridge for which distances
between the connection sites are ∼5.0 and ∼7.7 Å, respec-
tively).
Figure 2. Conformation of 2 found in its X-ray single crystal
structure obtained by recrystallization from 1,4-dioxane/water.
Views from the side (a) and from the bottom (b) are presented
with both stick (left) and space-filling display modes (right).
Figure 3 shows UV-vis absorption and emission spectra
obtained from dilute solutions of M3 and M2 in THF. They
are typical for isolated anthracenes and support that the
anthrylene units, despite their close proximity in the mac-
rocycle, retain their intrinsic photophysical properties. While
the M3 emission exhibits some tailing whose nature is not
yet clarified, dominant monomer emission suggests that
intramolecular face-to-face stacking of the anthrylenes is
unlikely.4b,11
Next, monolayer formation of M3 was investigated. A
chloroform solution was spread at the air/water interface on
a Langmuir trough (Figure 4a). The monolayer was vertically
transferred at 10 mN/m lateral pressure onto mica and gold
substrates12 for atomic force microscopy (AFM) and scan-
ning tunneling microscopy (STM) analyses, respectively.
Figure 3. UV-vis absorption (solid lines) and emission spectra
(broken lines) of 1 (black) and 2 (gray) in THF. Concentrations
for absorption: 10 µM for 1 and 15 µM for 2. Concentrations for
emission: 2 µM for 1 and 3 µM for 2. Excitation wavelength: 365
nm.
The square area in the AFM image (Figure 4b, recorded
in tapping mode) was artificially created by scratching the
monolayer away with the AFM tip under contact mode.13
A
(9) (a) Dieck, H. A.; Heck, F. R. J. Organomet. Chem. 1975, 93, 259.
For the Sonogashira reaction without cuprous iodide, two different names
are being used in the literature, namely, “copper-free Sonogashira reaction”
and “Heck alkynylation.” For comments on this matter, see: (b) Ljungdahl,
T.; Pettersson, K.; Albinsson, B.; Martensson, J. J. Org. Chem. 2006, 71,
1677. (c) Chinchilla, R.; Na´jera, C. Chem. ReV. 2007, 107, 874. We tend
to agree to these comments, however, and as the former name is used much
more often in the literature we will use it here as well.
height profile across the scratched area (Figure 4c) was
recorded along the line indicated in the image providing a
step height of approximately 1.3 nm. This proved the mica
substrate to be covered with a film having this thickness
which is in good agreement with the height of the M3
molecule and hence with the thickness of a monolayer.
(10) As an alternative, the linear compound 12 can also be considered
as a precursor of 2 instead of 7 (with 4 or 5).
(11) (a) Toyota, S.; Goichi, M.; Kotani, M. Angew. Chem., Int. Ed. 2004,
43, 2248. (b) Toyota, S.; Goichi, M.; Kotani, M.; Takezaki, M. Bull. Chem.
Soc. Jpn. 2005, 78, 2214. (c) Toyota, S.; Suzuki, S.; Goichi, M. Chem.sEur.
J. 2006, 12, 2482.
(12) Heger, M.; Wagner, P.; Semenza, G. Surf. Sci. 1993, 291, 39.
(13) For example, see: (a) Ton-That, C.; Shard, A. G.; Bradley, R. H.
Langmuir 2000, 16, 2281. (b) Anariba, F.; DuVall, S. H.; McCreery, R. L.
Anal. Chem. 2003, 75, 3837.
2780
Org. Lett., Vol. 12, No. 12, 2010

molecular dimension of M3. These dots also form one-
dimensional parallel arrays. The periodicity within the lines
is ∼1.4 nm, and the one vertically across the lines is ∼1.7
nm. Because it is difficult to propose a molecular model at
the present stage, Figure 4d contains only some characteristic
distances between constituents. The reason of the unexpected
anisotropic pattern is not yet clear. Because of the length
scale differences between typical Au-Au distances and those
given in Figure 4d, the line formation does not seem to be
associated with a gold surface pattern.12 It might be due to
a reorientation of the M3 molecules while transferring.14
Further investigations are underway using fluorescence
spectroscopy and high-resolution microscopies including
STM, AFM, and transmission electron microscopy (TEM).
Acknowledgment. The authors deeply thank Dr. W. B.
Schweizer (ETHZ) for X-ray crystallographic analysis, Dr.
X. Zhang and L. Bertschi (ETHZ) for mass measurements,
PhD candidate P. Wolfer (ETHZ) for his kind help in
polarization optical microscopy, and PhD candidate T. Bauer
(ETHZ) for his skillful help in the experiments with the
Langmuir trough. Financial support by the ETH grant (TH-
05 07-1) and the Swiss National Fund (200021-129660) are
gratefully acknowledged.
Figure 4. Preparation and structural analysis of the monolayer
of M3. (a) Surface pressure/area isotherm of M3 at the air/water
interface. (b) AFM tapping-mode image of the monolayer on a
mica substrate after contact-mode scratching. (c) Height profile
along the line indicated in the AFM image. (d) STM image of
the monolayer on a gold substrate12 with indication of period-
icities.
Supporting Information Available: All experimental
procedures, NMR & HR-MS data, GPC elution curves of
cyclization experiments, optical microscopy images of
crystals, and crystallographic data (CIF file).15 This material
is available free of charge via the Internet at http://pubs.acs.org.
OL100877G
To gain insight into the molecular arrangement within this
monolayer, the film was also analyzed by STM. It could be
observed that white dots in the image (Figure 4d) have the
(14) To address this issue, various modifications of M3 at the hydroxyl
groups are now in progress.
(15) CCDC 772825.
Org. Lett., Vol. 12, No. 12, 2010
2781