Hierarchical self-assembly of polycyclic heteroaromatic stars into snowflake patterns

Article abstract of DOI:10.1002/anie.201204006

Seeing stars: The two-dimensional patterns of the polycyclic heteroaromatic star molecules 1 on graphite vary with the side chain length. For n=12, frustrated self-assembly leads to hierarchically organized superstructures: up to 10?molecules form triangu

Full text of DOI:10.1002/anie.201204006

Angewandte
Chemie
DOI: 10.1002/anie.201204006
Supramolecular Networks
Hierarchical Self-Assembly of Polycyclic Heteroaromatic Stars into
Snowflake Patterns**
Stefan-S. Jester,* Eva Sigmund, Lisa M. Rçck, and Sigurd Hçger*
Molecular self-assembly has been established as a key con-
cept for the formation of functional monolayer patterns
decorating solid surfaces. The field of two-dimensional (2D)
crystal engineering relates the adlayer structure with the
nature of the substrate and with the geometry and function-
ality of the adsorbed molecules. Shape-persistent molecules
having a one-dimensional (1D; rigid rod oligomers)[1] or two-
dimensional (polycyclic aromatic hydrocarbons (PAHs)[2] as
well as rigid macrocycles)[3] structure and carrying flexible
alkyl/alkoxy side chains have attracted considerable attention
recently. They are adjustable in size with atomic-scale
precision and can contain various functionalities. Moreover,
the geometries and lattice dimensions of the surface patterns
are transferred to the functional unit arrangements, thus
giving rise to potential applications in single-molecule-based
devices. However, to address that functionality on a single-
molecule level by existing lithographic techniques, the
amplitude of these structures has to have mesoscopic
dimensions. A key problem is that the lattice parameters
are generally close to the size of the molecules, and the time
and effort required for the synthesis of defined molecules of
that size is rather high.
matic corner unit, which fulfills these size requirements
ideally (the distance between the alkoxy chains of neighbor-
ing benzene rings measures 0.98 nm), and their symmetry
matches perfectly with the underlying substrate.[5a]
However, despite considerable progress in the under-
standing of the basic principles that govern the 2D self-
assembly of such molecules, the creation of surface patterns
by a single component with more than one or a few molecules
in the unit cell based on pure van der Waals interactions is still
in its infancy.[7]
In this work we describe D3h-symmetric polycyclic heter-
oaromatic structures with alkoxy chains of different lengths
and their self-organization on HOPG (Figure 1). The com-
pounds are rather easily accessible by condensation of
Several self-assembly approaches are therefore explored
to obtain 2D superstructures with large (tens of nanometers)
lattice constants, and the approaches are based on either the
homo- or co-assembly of molecules. In most cases, strong and
directional noncovalent intermolecular interactions such as
hydrogen bonding, dipole–dipole interaction, or metal coor-
dination are the driving forces for the attraction between the
molecules adsorbed to a (metal) surface.[4] Additionally,
porous network structures and densely packed multicompo-
nent architectures with large lattice constants have been
obtained by utilizing intermolecular alkyl-chain interactions
on highly oriented pyrolytic graphite (HOPG).[5] To maximize
these interactions, adjacent alkyl chains on the same side of
the molecule should be about 0.8–1.0 nm apart from each
other, thus allowing their intermolecular interdigitation.[6]
Intriguing examples are triangular phenylene–ethynylene
macrocycles bearing two alkoxy substituents on each aro-
Figure 1. Chemical structures of the star-shaped molecules [1]n;
n defines the length of the alkoxy side chains.
hexaamino triphenylene with dialkoxyphenanthrene qui-
nones. All molecules contain six alkoxy side groups with
À
O O distances of 0.99 nm for oxygen atoms on the same
dibenzoquinoxaline unit and 0.95 nm for oxygen atoms
framing the molecular bay regions. The orientation of the
side chains of this rigid structure is widely adaptable and
coordination numbers (CNs) from two to six can be adopted
for the interaction (through side chains) with neighboring
molecules (Figure 2a).[8] Depending on the specific orienta-
tion of the long flexible substituents, two, one, or no side
chains of adjacent molecules may interdigitate (Figure 2b,c).
We therefore expected a packing behavior of the molecules
that would lead to long-range ordered networks. Our study
was motivated by the question as to how structural motifs of
the adlayer patterns vary with the chain length, n = 10–14, 16.
Scanning tunneling microscopy (STM) investigations of
adlayer patterns of [1]n were performed at the interface of
1,2,4-trichlorobenzene (TCB) and HOPG. In all images,
regions covered with conjugated backbones and alkoxy side
chains are observed with high and low tunneling current,
[*] Dr. S.-S. Jester, Dr. E. Sigmund, L. M. Rçck, Prof. Dr. S. Hçger
Kekulꢀ-Institut fꢁr Organische Chemie und Biochemie
Rheinische Friedrich-Wilhelms-Universitꢂt Bonn
Gerhard-Domagk-Strasse 1, 53121 Bonn (Germany)
E-mail: stefan.jester@uni-bonn.de
hoeger@uni-bonn.de
[**] Financial support by the DFG, the SFB 624, and the
VolkswagenStiftung is gratefully acknowledged.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201204006.
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Figure 2. a) Selected examples of molecular models for [1]n (here:
n=16), thus illustrating different relative orientations of the alkoxy
side chains and related side chain coordination numbers (CN=2–6).
b,c) Alkoxy side-chain interdigitation motifs for [1]n. Two, one, or no
side chain (brightly grey, from adjacent molecules) interdigitating with
two side chains framing a dibenzoquinoxaline unit (b) and a bay
region (c) of [1]n. The latter consequently adopt distances d2, d1, and
d0.
Figure 3. STM images as well as molecular and schematic models of
the a) dense (d2) and b) porous (h1) patterns of [1]16 at the TCB/
HOPG interface. For (a): d2: 26.3ꢃ26.3 nm2; c=2ꢃ10À6 m,
VS =À0.8 V, It =8 pA; a=(4.8Æ0.2) nm, b=(4.3Æ0.1) nm,
g(a,b)=(67Æ2)8; p1; for (b): h1 ((63) tiling): 25.7ꢃ25.7 nm2;
c=10À6 m, VS =À0.6 V, It =6 pA; a=(6.0Æ0.2) nm, b=(5.9Æ0.2) nm,
g(a,b)=(61Æ2)8; p6. The red and white lines denote unit cells and
HOPG main axis directions, respectively.
which are encoded in bright and dark colors, respectively.[9]
All adsorbed alkoxy side chains which contribute to the
packing are oriented along the directions of the main axes of
the HOPG substrate.[6] Depending on the concentration and
sample preparation parameters, all compounds form domains
of distinct dense and porous polymorphs.
With the exception of [1]13, all compounds [1]n self-
assemble into densely packed oblique surface patterns (plane
group p1) which can be viewed as dumbbell-shaped pairs of
molecules (n = 10, 11; denoted as d1) or rows of alternately
oriented molecules (n = 12, 14, 16; named d2) separated by
interdigitating alkoxy side chains, thus showing that the
overall packing concept of the backbones is maintained
throughout all chain lengths. A dense pattern for [1]16 is
representatively shown in Figure 3a.
Simultaneously, [1]n where n = 13, 14, and 16, form porous
hexagonal adsorbate patterns (denoted as h1, plane group p6)
with identical packing but different backbone distances,
depending on the side-chain length. Representatively for
the h1 patterns, an STM image and the packing model of [1]16
are shown in Figure 3b. Two alkoxy side chains (i.e., framing
the bay regions) of two dibenzoquinoxaline units of each
molecule are aligned in parallel. All bay regions of adjacent
molecules point towards each other so that four alkoxy side
chains interdigitate. In such way, each molecule is connected
to three adjacent molecules (CN = 3) so that the polycyclic
heteroaromatic backbones are separated from each other.
The resulting pores can be viewed as hexagonal honeycombs
where the backbones (representing the corners) are con-
nected by the alkoxy chains (forming the sides). The resulting
cavity diameters vary from 4.4 to 5.3 nm (corner to opposite
corner), and their distances range from 5.3 to 6.0 nm (pore
center to pore center). In a schematic approach aiming at
a more abstract description, the pattern is reduced to
a honeycomb line grid where each crossing point (vertex) is
formed by three adjacent regular hexagonal tiles (see Fig-
ure 3b and the Supporting Information). By adapting
a nomenclature that was introduced in discrete geometry
for k-uniform tilings we denote the h1 pattern as (63)
tiling.[10,11a,12,13]
For [1]n, where n = 10, 12, a different hexagonal adsorbate
pattern (denoted as h22, with a plane group p6) is observed
(Figure 4a and the Supporting Information). At first glance
this structure (again) appears to be a pattern of honeycomb-
shaped nanopores, each formed by six (here densely packed)
aromatic backbones of the molecules. The (hexagonal) nano-
pores are separated from each other by alkoxy side chains and
are 7.5 nm ([1]10) and 7.8 nm ([1]12) apart (Table 1). Alter-
natively, the pattern can be viewed as densely packed
triangular molecular assemblies, each of which consists of
three molecules at the corners which interact through
interdigitating alkoxy side chains, thus forming triangular
pores in their inside. Four of the six alkoxy side chains of each
molecule interact with (side chains of) adjacent molecules in
two directions (with an angle of 608) so that a CN = 2
(Figure 5a) occurs. The remaining side chains are disordered
in the nanopore or point into the solution phase. Conse-
quently, hexagonal pores of densely packed backbones can
even be formed without having functional groups elsewhere
to facilitate a directed interaction, for example, carboxylic
acids.[14] The observation that [1]n (n = 13, 14, 16) forms the h1
pattern while [1]n (n = 10, 12) forms the h22 pattern can be
rationalized by a higher tendency of the longer side chains to
be completely adsorbed to the graphite at the cost of a lower
surface coverage.[5a] The fact that [1]n can form hexagonal (h1
pattern) as well as hexagonal and triangular pores (h2m
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Figure 4. a–d) STM images as well as molecular and schematic models of the porous adlayer patterns h2m (m=2–4) and varying m (also m=5)
for [1]12 at the TCB/HOPG interface. For (a): h22 (3.4.6.4): 28.5ꢃ28.5 nm2, c=5ꢃ10À6 m, VS =À1.2 V, It =18 pA, a=(7.8Æ0.2) nm,
b=(7.8Æ0.2) nm, g(a,b)=(60Æ2)8; p6; for (b): h23 (33.42; 3.4.6.4): 55.5ꢃ55.5 nm2, c=3ꢃ10À6 m, VS =À1.6 V, It =5 pA; a=(11.2Æ0.3) nm,
b=(10.9Æ0.3) nm, g(a,b)=(60Æ2)8; p6; for (c): h24 (36; 33.42; 3.4.6.4): 58.8ꢃ58.8 nm2, c=3ꢃ10À6 m, VS =À1.0 V, It =18 pA;
a=(15.5Æ0.3) nm, b=(15.5Æ0.3) nm, g(a,b)=(60Æ2)8; p6; for (d): h2m: 86.1ꢃ86.1 nm2, cꢀ10À6 m, VS =À1.2 V, It =20 pA. The red and white
lines denote unit cells and HOPG main axis directions, respectively. The white dotted hexagon in (d) indicates the region transcribed by the
molecular model. The black dots in the line patterns of (a)–(c) point out distinct vertices of each tiling.[15]
Table 1: Pattern structures for [1]n (n=10–14, 16), [2]16, and [3]16.
a [nm]
b [nm]
g [8]
N[a]
[1]10
[1]11
[1]12
d1
h22
d1
am.
d2
h22
h23
h24
(h25)[b]
h1
d2
h1
d2
h1
d
h3
d’
d’’
5.6Æ0.2
7.5Æ0.2
4.9Æ0.2
3.2Æ0.1
7.5Æ0.2
3.9Æ0.2
53Æ2
60Æ2
67Æ2
2
6
2
6.0Æ0.1
7.8Æ0.2
11.1Æ0.3
15.5Æ0.3
(18.8Æ0.4)
5.3Æ0.2
5.0Æ0.2
5.8Æ0.2
4.8Æ0.2
6.0Æ0.2
4.7Æ0.1
7.7Æ0.2
4.9Æ0.1
8.8Æ0.2
3.8Æ0.1
7.8Æ0.2
11.1Æ0.3
15.5Æ0.3
(18.8Æ0.4)
5.3Æ0.2
4.1Æ0.1
5.8Æ0.2
4.3Æ0.1
6.0Æ0.2
4.0Æ0.1
7.7Æ0.2
2.8Æ0.1
5.1Æ0.1
60Æ2
60Æ2
60Æ2
60Æ2
(60Æ2)
60Æ2
66Æ2
60Æ2
67Æ2
60Æ2
76Æ2
60Æ2
90Æ2
51Æ2
2
6
12
20
(30)
3
2
3
2
3
[1]13
[1]14
[1]16
[2]16
[3]16
2
6
2
4
Figure 5. Molecular and schematic models of supramolecular aggre-
gates showing the tiles of the adlayer patterns a) h22, b) h23, c) h24
(shown in Figures 4a–c, respectively), and d) h25 (only observed in
random mixed patterns with varying m; see Figure 4d). The digits at
the vertices of the line grids indicate coordination numbers of the
respective molecular building blocks.[8,16]
[a] Molecules per unit cell. [b] Only observed in co-occurrence with other
assemblies (of varying m); nominal unit cell given.
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patterns, here: m = 2, where m describes the number of
molecules that form the triangle side), both through side-
chain interdigitation, is clearly a result of the adaptive
behavior of the molecules with respect to number and
direction of the interdigitating substituents. As discussed at
the end of the previous paragraph, an abstraction towards
a line network leads to vertices formed by triangular,
rectangular, and hexagonal tiles, more precisely a (3.4.6.4)
tiling (see Figure 4a and the Supporting Information).
Of special interest is the observation that the molecules
[1]12 simultaneously form the “inflated” structures h23, h24,
and h25 (Figure 4b–d).[4] In each case, another row with n+1
molecules is added to the triangle that—in the case of h23 and
h24—forms half a unit cell (Figure 5). Within such a triangle
the molecules are connected/linked by interdigitating alkoxy
side chains. The coordination number of the molecules within
the triangles depends on their position. Molecules at the
corners are only connected to two other molecules (by alkoxy
chain interdigitation; CN = 2), while molecules at the edges
have the CN = 4, and molecules in the inner part of the
triangle adopt CN = 6 (Figure 5a–d). These triangles are
closely packed at the surface, and each triangle corner
forms—with the corners of five adjacent triangles—a hexag-
onal pore as discussed before. The pore diameter (of 2.8 nm)
is equal in all structures, while the pore distances range from
7.8 nm (h22) up to 15.5 nm (h24) and nominally 18.8 nm (h25),
and consequently very large unit cells with 20 (h24) and
nominally 30 (h25) molecules are indexed. The packing
behavior of [1]12 is rather surprising. [1]16 forms a porous
network of isolated molecules where all side chains are
adsorbed to the surface, while [1]10 forms a network of
triangular assemblies leading to a higher grafting density at
the cost of the possibility for all alkoxy chains to lie on the
graphite. In the case of [1]12 we are in the medium-chain-
length regime. We did not observe only the expected
coexistence of these two polymorphs in separate domains,
but additionally we found adsorbate patterns which contain
elements of both packing motifs and are combined into
a frustrated structure. The molecules are able to assemble to
superstructures that hierarchically form crystalline patterns
with very large unit cells. For this superstructure formation, it
is highly important that the side chains of the molecules are
widely adaptable and a variety of distinct coordination
numbers and interaction motifs become possible. A compar-
ison with [2]16, which contains four long alkoxy side chains at
two dibenzoquinoxaline units (Figure 6 and the Supporting
Information), shows that it cannot form a porous network
structure (like [1]16; Figure 3b), as the molecule lacks
a threefold symmetry. In contrast, [3]16 has only two long
alkoxy side chains enforcing the formation of trimeric
clusters. These self-assemble, as expected, into a porous
network similar to that of [1]n (n = 10, 12), h22, but no higher-
ordered complex superstructures could be observed that
require also building blocks with higher coordination num-
bers.[17]
Figure 6. a) STM image as well as molecular and schematic models of
an adlayer pattern of [3]16 at the TCB/HOPG interface (44.1ꢃ44.1 nm2;
c=2ꢃ10À4 m, VS =À1.0 V, It =5 pA; a=(7.7Æ0.2) nm,
b=(7.7Æ0.2) nm, g(a,b)=(60Æ2)8; p6). The red and white lines
denote unit cells and HOPG main axis directions, respectively.
b) Chemical structures of [2]16 and [3]16.
hydrogen bonding).[4] In those cases the unit cells are
connected by strong bonds, and the intermolecular bonds
between the molecules within the unit cells are weaker.[4c]
In the case presented here, we show that higher-order
honeycomb network structures with increasing interpore
distance can also be observed for C3-symmetric molecules
purely by van der Waals attraction. A key element in these
networks is the ability of the molecules to adapt the number
and direction of the interdigitating substituents such that they
can hierarchically build up complex superstructures.
Conclusively, we have described star-shaped polycyclic
heteroaromatic molecules, substituted with six (four, two)
alkoxy side chains. The length and number of the substituents
determines which crystal patterns the molecules assemble
into, and distinct packing motifs were observed for long and
short side chains. For the intermediate-chain-length regime,
a frustrated structure having very large unit cell parameters
was observed. As far as we know this is the first time that such
large superstructures of one compound on HOPG have been
observed, wherein the molecules are held together only by
van der Waals attraction. Ongoing studies focus on the
question of the molecular requirements for the inflated
structure formation and how this can be controlled.
Received: May 23, 2012
Revised: June 22, 2012
Published online: && &&, &&&&
Higher-order network structures have been observed for
other C3-symmetric molecules as a result of commensurability
criteria of the adlayer and the substrate,[18] or through
a combination of strong and directional forces (for example,
Keywords: hydrocarbons · interfaces · polycycles ·
scanning tunneling microscopy · self-assembly
.
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adjacent molecules are adsorbed on the HOPG surface to
interact interdigitatively.
[1] For self-assembled monolayers (SAMs) of shape-persistent
linear oligomers, see: a) P. Samorꢀ, N. Severin, K. Mꢁllen, J. P.
Rabe, Adv. Mater. 2000, 12, 579; b) J.-R. Gong, J.-L. Zhao, S.-B.
Lei, L.-J. Wan, Z.-S. Bo, X.-L. Fan, C.-L. Bai, Langmuir 2003, 19,
10128; c) Z. Mu, X. Yang, Z. Wang, X. Zhang, Langmuir 2004,
20, 8892; d) Z.-Y. Yang, L.-H. Gan, S.-B. Lei, L.-J. Wan, C. Wang,
J.-Z. Jiang, J. Phys. Chem. B. 2005, 109, 19859; e) J.-R. Gong, H.-
J. Yan, Q.-H. Yuan, L.-P. Xu, Z.-S. Bo, L.-J. Wan, J. Am. Chem.
Soc. 2006, 128, 12384; f) K. Yoosaf, P. V. James, A. R. Ramesh,
C. H. Suresh, K. G. Thomas, J. Phys. Chem. C 2007, 111, 14933;
g) M. Wielopolski, A. Atienza, T. Clark, D. M. Guldi, N. Martꢀn,
Chem. Eur. J. 2008, 14, 6379; h) D. Mçssinger, S.-S. Jester, E.
Sigmund, U. Mꢁller, S. Hçger, Macromolecules 2009, 42, 7974;
i) Z. Mu, S. Lijin, H. Fuchs, M. Mayor, L. Chi, Langmuir 2011,
27, 1359.
[9] R. Lazzaroni, A. Calderone, J. L. Brꢅdas, J. P. Rabe, J. Chem.
Phys. 1997, 107, 99.
[10] Each molecular backbone is located at a vertex position. The
alkoxy side chains link the backbones—similar as the polygon
edges connect the vertices and thus define the tiles. For details
see the Supporting Information.
[11] k-uniform tilings: a) J. Kepler, Harmonices Mundi, 1619;
b) D. M. Y. Sommerville, Trans. Roy. Soc. Edin. 1905, 41, 725
(k = 1); c) O. Krçtenheerdt, Math.-Natur. Reihe 1969, 18, 273; O.
Krçtenheerdt, Math.-Natur. Reihe 1970, 19, 19; O. Krçtenheerdt,
Math.-Natur. Reihe 1970, 19, 97 (k = 2); d) D. Chavey, Comp.
Math. Appl. 1989, 17, 147 (k = 3).
[12] An overview is found in: B. Grꢁnbaum, G. C. Shepherd, Tilings
and Patterns, W. H. Freeman & Company, New York, 1986.
[13] In a chemical context, this nomenclature was applied for
a description of mesostructures of block copolymers. See: T.
Asari, S. Arai, A. Takano, Y. Matsushita, Macromolecules 2006,
39, 2232; Y. Matsushita, Macromolecules 2007, 40, 771.
[14] a) M. Lackinger, S. Griessl, W. M. Heckl, M. Hietschold, G. W.
Flynn, Langmuir 2005, 21, 4984; b) K. G. Nath, O. Ivasenko,
J. A. Miwa, H. Dang, J. D. Wuest, A. Nanci, D. F. Perepichka, F.
Rosei, J. Am. Chem. Soc. 2006, 128, 4212; c) K. G. Nath, O.
Ivasenko, J. M. MacLeod, J. A. Miwa, J. D. Wuest, A. Nanic,
D. F. Perepichka, F. Rosei, J. Phys. Chem. C 2007, 111, 16996;
d) N. T. N. Ha, T. G. Gopakumar, R. Gutzler, M. Lackinger, H.
Tang, M. Hietschold, J. Phys. Chem. C 2010, 114, 3531; e) V. V.
Korolkov, S. Allen, C. J. Roberts, S. J. B. Tendler, J. Phys. Chem.
C 2012; DOI: org/10.1021/jp212388c.
[2] For recent publications about SAMs of PAHs with alkyl/alkoxy
side chains, see: J. M. Mativetsky, M. Kastler, R. C. Savage, D.
Gentilini, M. Palma, W. Pisula, K. Mꢁllen, P. Samorꢂ, Adv. Funct.
Mater. 2009, 19, 2486.
[3] For SAMs of shape-persistent macrocycles, see: a) S. Hçger, K.
Bonrad, A. Mourran, U. Beginn, M. Mçller, J. Am. Chem. Soc.
2001, 123, 5651; b) E. Mena-Osteritz, P. Bꢃuerle, Adv. Mater.
2001, 13, 243; c) D. Borissov, A. Ziegler, S. Hçger, W. Freyland,
Langmuir 2004, 20, 2781; d) V. Kalsani, H. Ammon, F. Jꢃckel,
J. P. Rabe, M. Schmittel, Chem. Eur. J. 2004, 10, 5481; e) S. Lei,
K. Tahara, F. C. De Schryver, M. Van der Auweraer, Y. Tobe, S.
De Feyter, Angew. Chem. 2008, 120, 3006; Angew. Chem. Int.
Ed. 2008, 47, 2964; f) F. Schlosser, V. Stepanenko, F. Wꢁrthner,
Chem. Commun. 2010, 46, 8350; g) S. K. Maier, S.-S. Jester, U.
Mꢁller, M. M. Mꢁller, S. Hçger, Chem. Commun. 2011, 47,
11023.
[15] The average relative abundances qrel by the different polymorphs
at c = 3 ꢆ 10À6 m (adsorption at RT) are: qrel(d2) = 64.1%; qrel
-
[4] a) G. Pawin, K. L. Wong, K.-Y. Kwon, L. Bartels, Science 2006,
313, 961; b) Y. Ye, W. Sun, Y. Wang, X. Shao, X. Xu, F. Cheng, J.
Li, K. Wu, J. Phys. Chem. C 2007, 111, 10138; c) W. Xiao, X.
Feng, P. Ruffieux, O. Grçning, K. Mꢁllen, R. Fasel, J. Am. Chem.
Soc. 2008, 130, 8910; d) J. Zhang, B. Li, X. Cui, B. Wang, J. Yang,
G. J. Hou, J. Am. Chem. Soc. 2009, 131, 5885; e) S. Clair, M.
Abel, L. Porte, Angew. Chem. 2010, 122, 8413; Angew. Chem.
Int. Ed. 2010, 49, 8237.
(h22) = 6.8%; qrel(h23) = 6.6%; qrel(h24) = 2.0%; qrel(h2m) =
20.5% (with varying m). Domain sizes are: A(d2) = (4208 Æ
3615) nm2;
1005) nm2;
A(h22) = (1858 Æ 1044) nm2;
A(h24) = (1615 Æ 812) nm2;
A(h23) = (1571 Æ
A(h2m) = (2377 Æ
1251) nm2 (with varying m). However, these are first data and
do not allow an interpretation of the phase behavior with regard
to concentration, temperature, and ripening effects. Details are
given in the Supporting Information.
[5] a) K. Tahara, C. A. Johnson II, T. Fujita, M. Sonoda, F. C.
De Schryver, S. De Feyter, M. M. Haley, Y. Tobe, Langmuir
2007, 23, 10190; b) K. Tahara, S. Okuhata, J. Adisoejoso, S. Lei,
T. Fujita, S. De Feyter, Y. Tobe, J. Am. Chem. Soc. 2009, 131,
17583; c) J. Adisoejoso, K. Tahara, S. Okuhata, S. Lei, Y. Tobe, S.
De Feyter, Angew. Chem. 2009, 121, 7489; Angew. Chem. Int.
Ed. 2009, 48, 7353.
[6] a) T. Yang, S. Berber, J.-F. Liu, G. P. Miller, D. Tomꢄnek, J.
Chem. Phys. 2008, 128, 124709; b) B. Ilan, G. M. Florio, M. S.
Hybertsen, B. J. Berne, G. W. Flynn, Nano Lett. 2008, 8, 3160.
[7] S.-S. Jester, E. Sigmund, S. Hçger, J. Am. Chem. Soc. 2011, 133,
11062.
[16] Alkoxy side chains that do not contribute to the packing but are
either randomly adsorbed or point into the solution phase are
not shown.
[17] As a result, we can compel another arrangement for the
polycyclic heteroaromatic stars with -OC16H33 side chains from
the h1 packing (shown in Figure 3b) to a packing similar to h22
(Figure 4a) by chemically adjusting the coordination number.
[2]16 does not form a trimeric superstructure, because most
probably the position at which the alkoxy chains are attached
differs from the positional requirement for the trimer formation
in [1]12; see the Supporting Information.
[18] a) G. Schull, R. Berndt, Phys. Rev. Lett. 2007, 99, 226105; b) Y.
Wei, S. W. Robey, J. E. Reutt-Robey, J. Phys. Chem. C 2008, 112,
18537.
[8] In the context of this work, coordination numbers are defined as
numbers of directions along which the alkoxy side chains of
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
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.
Angewandte
Communications
Communications
Supramolecular Networks
S.-S. Jester,* E. Sigmund, L. M. Rçck,
S. Hçger*
&&&& — &&&&
Hierarchical Self-Assembly of Polycyclic
Heteroaromatic Stars into Snowflake
Patterns
Seeing stars: The two-dimensional pat-
terns of the polycyclic heteroaromatic star
molecules 1 on graphite vary with the side
chain length. For n=12, frustrated self-
assembly leads to hierarchically organ-
ized superstructures: up to 10 molecules
form triangular aggregates which pack
densely into hexagonal patterns with very
large (15.5 nm) lattice constants.
6
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!