Solution-processable flower-shaped hierarchical structures: Self-assembly, formation, and state transition of biomimetic superhydrophobic surfaced

Article abstract of DOI:10.1002/chem.201000332

Superhydrophobic surfaces inspired by biological microstructures attract considerable attention from researchers because of their potential applications. In this contribution, two kinds of microscale flower-shaped morphologies with nanometer petals formed

Full text of DOI:10.1002/chem.201000332

FULL PAPER
DOI: 10.1002/chem.201000332
Solution-Processable Flower-Shaped Hierarchical Structures: Self-Assembly,
Formation, and State Transition of Biomimetic Superhydrophobic Surfaces
Jie Yin,[a] Jing Yan,[a] Min He,[b] Yanlin Song,*[b] Xiaoguang Xu,[a] Kai Wu,*[a] and
Jian Pei*[a]
Abstract: Superhydrophobic surfaces
inspired by biological microstructures
attract considerable attention from re-
searchers because of their potential ap-
plications. In this contribution, two
kinds of microscale flower-shaped mor-
phologies with nanometer petals
formed from the hierarchical self-as-
sembly of benzothiophene derivatives
bearing long alkyl chains have been de-
veloped as superhydrophobic surfaces.
The intermediate stages of the assem-
blies demonstrated a new formation
mechanism for such flower-shaped
morphologies. The hierarchical mor-
phologies of the film exhibited excel-
lent water-repelling characteristics as
superhydrophobic surfaces, which were
prepared by means of a simple solution
process. The transition process from
the Cassie state to Wenzel state was
easily realized owing to the slight mi-
crostructural differences in the two
kinds of flowers caused by their differ-
ent chemical structures. The superhy-
drophobicity of such functional materi-
als might be beneficial for applications
in electrical devices in which the pres-
ence of water would influence their
performance.
Keywords: hydrophobic effect
·
materials science · photophysics ·
self-assembly
surfaces
· superhydrophobic
Introduction
bled structures for their implementation in special applica-
tions is still a great challenge.
Diverse nanostructures formed through self-assembly of
small aromatic molecules have attracted considerable atten-
tion because of their fascinating optical and electronic appli-
cations.[1] Noncovalent forces such as hydrogen bonding, p–
p stacking, and van der Waals interactions provide the driv-
ing force for molecular self-assembly. With the help of new
synthetic protocols and characterization techniques, a varie-
ty of novel supramolecular architectures have been created.
However, full control over the morphologies of self-assem-
The wettability of a solid surface is an important scientific
and practical issue in daily life.[2] Recently, superhydropho-
bic surfaces inspired by biological microstructures have at-
tracted considerable interest. The morphology of the surface
has played a more important role than the chemical compo-
sition in determining wettability.[3] In particular, the binary
surface structure (micro- and nanostructures) has proven to
be optimum for superhydrophobicity.[4] Many approaches,
including chemical vapor deposition,[5] laser or plasma etch-
ing processes,[6] phase separation,[7] and electrochemical dep-
osition,[8] have been employed to prepare superhydrophobic
surfaces. However, self-assembled morphologies using the
weak van der Waals interaction have attracted increasing in-
terest in this field.[9,10] Due to the simplicity in their prepara-
tion and the diversity of their physical and chemical proper-
[a] J. Yin, J. Yan, Dr. X. Xu, Prof. K. Wu, Prof. J. Pei
Beijing National Laboratory for Molecular Sciences
The Key Laboratory of Bioorganic Chemistry and Molecular
Engineering of the Ministry of Education College of Chemistry
and Molecular Engineering Department
Peking University, Beijing 100871 (China)
Fax : (+86)10-62758145
E-mail: jianpei@pku.edu.cn
ties, solution-processable organic materials represent
promising type of material for self-cleaning applications.
a
Many organic/polymeric materials have been fabricated
as superhydrophobic surfaces; however, they usually lack
special functionality, since they consist mainly of aliphatic
chains. Recently, Nakanishiꢀs group developed a functional
superhydrophobic surface by incorporating C60 units into a
flower-shaped morphology.[9] To introduce more functions
into superhydrophobic surfaces, herein we describe the in-
[b] M. He, Prof. Y. Song
CAS Key Laboratory of Organic Solids
Institute of Chemistry Chinese Academy of Science
Beijing 100190 (China)
Fax : (+86)10-62529684
E-mail: ylsong@iccas.ac.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000332.
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corporation of a p-conjugated system into such materials.
More specifically, we focused on benzothiophene deriva-
tives, which performed excellently in various devices, such
as organic field-effect transistors (OFETs), organic light-
emitting diodes (OLEDs), and photovoltaic cells.[11] So far,
they have not yet been applied to the formation of hydro-
phobic surfaces. Therefore, we present new solution-pro-
cessed flowerlike assemblies formed by these benzodithio-
phene derivatives, and their applications as superhydropho-
bic surfaces. The paper is structured as follows: first, we de-
scribe the design and synthesis of the molecules used for the
self-assembly; second, we detail the morphological studies
on our hierarchical micrometer- and nanometer-sized
flower-shaped assemblies. By using different characteriza-
tion techniques, we further investigate the relative role of
aliphatic chains and aromatic planes in directing the self-as-
sembly. We also describe in detail the mechanism of how
such flowerlike supramolecular structures form. Finally, su-
perhydrophobic surfaces are prepared from the two flower-
like assemblies formed by these benzothiophene derivatives.
Our investigation indicates that these flower-shaped mor-
phologies exhibit excellent water-repellent characteristics. In
addition, because of the slight
ACHTUNGTRENoNUGN xy chains, respectively, were prepared through four steps
from the commercially available 1,4-dibromo-2,5-diiodoben-
zene as shown in Scheme 1. The presence of the conjugated
core and long hydrocarbon side chains is expected to facili-
tate the cooperative interactions of the noncovalent forces
between the molecules.
Morphology studies of the self-assemblies: Compounds 1
and 2 were readily soluble in common organic solvents such
as THF, CHCl3, and CH2Cl2. Compound 1 showed various
morphologies after precipitating from different organic sol-
vents as shown in Figure 1. A mixture (CHCl3/EtOH 1:2,
v/v) was chosen in the following experiments. Self-assem-
bled morphologies were prepared as follows: first, a suspen-
sion of 1 or 2 in the above-mentioned mixture at a concen-
tration of 2 mgmLÀ1 was heated until it formed a transpar-
ent solution, and was then allowed to cool slowly to room
temperature. Precipitates formed in nearly quantitative
yield. For 1, the images obtained from field-emission scan-
ning electron microscopy (FESEM; Figure 2a and b) and
transmission electron microscopy (TEM; Figure 2c and d)
revealed an interesting hierarchical structure: an overall
microstructure differences in
the two kinds of flowers, caused
by structural differences be-
tween their molecular struc-
tures, the transition from the
Cassie state with low adhesion
to the Wenzel state with high
adhesion can be realized. Ach-
ieving superhydrophobicity of
such functional materials would
also be beneficial for their ap-
plications in electrical devices
in which the presence of water
would influence their perfor-
mance.
Results and Discussion
Design and synthesis of the
benzodithiophene derivatives:
The “bottom-up” approach sug-
gests that tuning the molecular
chemical structures can create
new
supramolecular
struc-
tures.[12] To obtain organic
three-dimensional self-assem-
blies, benzodithiophene deriva-
tives with the same aromatic
skeleton but different in the
substituted
positions
and
number of alkyl chains were
synthesized. Compounds 1 and
2 bearing six and two dodecyl- Scheme 1. The synthetic approaches to compounds 1 and 2.
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Flower-Shaped Hierarchical Structures
FULL PAPER
Figure 3. Morphology of self-assembled 2. a) SEM images of flower-
shaped supramolecular assemblies of 2 obtained from CHCl3/EtOH (1:2
v/v). b) SEM and c),d) TEM images of pillarlike petals of the flower-
shaped objects.
flowerlike morphology obtained by 2 was much larger than
that of 1 (20–50 mm) and consisted of longer pillarlike petals
of approximately 5 mm in length and 200 nm in diameter.
Figure 3d displays the multilayer structures of the petals,
which clearly indicates that the obtained precipitates are
formed by hierarchical self-assembly.
Figure 1. SEM images of 1 precipitated from a),b) n-hexane; c),d) 1,4-di-
oxane; e),f) n-dodecane; and g),h) CHCl3/EtOH (1:2 v/v).
Hierarchical organization studies of the flower-shaped struc-
tures: The molecular arrangements inside the flower struc-
tures were studied by using Fourier transform infrared
(FTIR) spectroscopy and powder X-ray diffraction (XRD);
their photophysical properties were also investigated. The
role of the aliphatic chains in directing crystal-structure for-
mation was reflected in FTIR spectroscopic experiments.
FTIR spectra of the flower-shaped supramolecular assem-
blies 1 and 2 on KBr plates (Figure 4a) showed CH2 stretch-
ing vibrations at 2920 cmÀ1 (nanti) and 2850 cmÀ1 (nsym), which
indicates crystalline packing of alkyl chains.[13] Powder XRD
patterns showed that these flower-shaped objects had a cer-
tain degree of crystalline order (Figure 4b). Due to the
flower-shaped morphologies, all crystal planes were on aver-
age equally exposed, so preferential orientation was not ex-
pected. Still, there are strong diffraction signal peaks in the
small-angle region corresponding to d spacings of 38.7 and
27.0 ꢂ for 1 and 2, respectively. For 1, the measured spacing
was somewhat smaller than the actual molecular size
(47.3 nm horizontally and 44.7 nm vertically), which indi-
cates a certain degree of tilting. Due to the smaller number
of alkyl chains, 2 was more anisotropic in shape, so the dif-
fraction pattern was completely different. Typical peaks for
aromatic–aromatic stacking (around 3.5 ꢂ) were not ob-
served, because the central parts of the molecules were not
planar due to the large torsional angle of aryl groups on the
vertical axis;[14] this can be established by viewing the molec-
ular structures calculated by utilizing the Gaussian 03 pro-
gram (see the Supporting Information).[15,16]
Figure 2. Morphology of self-assembled 1. a) SEM and c) TEM images of
flower-shaped supramolecular assemblies of 1 obtained from CHCl3/
EtOH (1:2 v/v). b) SEM and d) TEM images of triangular-like petals of
the flower-shaped objects.
flowerlike morphology of several micrometers in size (4–
20 mm), built up by numerous triangular-like petals of nano-
meter size (200–400 nm in length). These petals were acute
and arranged closely. In addition, fluorescence microscopy
showed that the flower-shaped assemblies exhibited blue
fluorescence owing to the p-conjugated aromatic skeleton
(Figure S1 in the Supporting Information). For 2, flower-
shaped assemblies with two-tier nanostructures were also
observed (Figure 3a and b). In comparison, the size of the
On the other hand, the importance of the central aromatic
unit in the self-assembly is revealed from the change in the
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Y. Song, K. Wu, J. Pei et al.
and 360 nm as shown in Figure S2 in the Supporting Infor-
mation. The UV-visible features of a drop-cast film of the
flower-shaped structures of 1 showed an absorption maxi-
mum at 400 nm, which redshifted 30 nm relative to that in
its dilute solution (1ꢃ10À5 m) in chloroform, as shown in Fig-
ure 5a. Such a large redshift indicates strong interactions
among conjugated plains in the solid state, which changed
its photophysical properties.[17,18] Upon heating the mixture
of 1 in CHCl3/EtOH (1:2 v/v) to 608C, the redshifted band
of the absorption maximum disappeared and the original
band at 360 nm recurred. Such behavior was also demon-
strated by its emission features in Figure 5b, in which the
emission maximum (lmax) also showed a considerable red-
shift on going from the solution to the solid state. Similar to
1, the absorption and emission spectra of 2 under the above-
mentioned conditions also experience similar changes (Fig-
ure 5c and d). These observations revealed that in chloro-
form and in the CHCl3/EtOH (1:2 v/v) mixture at 608C, 1
and 2 were in their monomeric form. However, as the solu-
tion temperature decreased from 608C to room tempera-
ture, the formation of self-assembled species occurred.[19]
In general, based on these results obtained from FTIR
spectroscopy, XRD, optical properties, and micrograph anal-
yses, we tentatively conclude that the self-assembly of 1 and
2 was assisted by the electronic interaction of the aromatic
skeleton and the weak van der Waals interactions of long
aliphatic chains. The exact crystal structure of these precipi-
tates remains unknown at this stage.
Figure 4. a) FTIR spectra (KBr) and b) powder X-ray diffraction data of
1 (c) and 2 (a) precipitated from CHCl3/EtOH (1:2 v/v).
absorption and emission spectra on going to the solid state.
In various dilute organic solutions, 1 showed almost identi-
cal absorption features with two major bands at about 290
~
Figure 5. a) Normalized absorption and b) emission spectra of 1; and c) normalized absorption and d) emission spectra of 2 in CHCl3
(
) ([1]=1ꢃ
10À5 m), CHCl3/EtOH (1:2 v/v) at 608C (&) ([1]=1ꢃ10À5 m), and drop-cast films ( ) of the suspension of flower-shaped structures.
*
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Flower-Shaped Hierarchical Structures
FULL PAPER
The formation mechanism of flower-shaped supramolecular
assemblies: It is interesting to trace the formation mecha-
nism of the flower-shaped objects. First, we slowly cooled
down a homogeneous mixture of the compounds in CHCl3/
EtOH (1:2 v/v) from 608C to room temperature, which
yielded intermediate assembled structures of the precipi-
tates. Then, one drop of the suspension of the assembled ob-
jects was deposited on Si, and excess solvent on the silicon
plate was quickly drained off with filter paper.
As shown in Figure 6, only platelike and elliptical precur-
sors were observed at the initial stage for 1. We note that
such flat objects consisted of stacked layers instead of a
single layer (also observed in ref. [9a]), as supported by con-
trol experiments mentioned later. The edges of such precur-
sors started to bifurcate in every direction (Figure 6a, b, and
c), and then to roll up to minimize the total elastic energy.[20]
When the rolling-up behavior proceeded continuously, the
inner layers had more space to consequently bifurcate (Fig-
ure 6d and e), resulting in a 3D flower-shaped object. After
enough bifurcation growth at the edges and folding in the
plate, the transformation was complete. Rapid cooling from
60 to 08C produced only platelike, elliptical assemblies (Fig-
ure 6g, h, and i). Obviously, because of the rapid cooling
process, those precursors had no time for the bifurcation
and rolling-up, resulting in exclusive formation of intermedi-
ate assembled structures, which are very rare in surfactant
assemblies. In addition to individual flower-shaped objects,
we also observed “clustered flowers” (Figure 6j, k, and l) in
our samples. It was unlikely that these flowers experienced
only physical entanglement, judging from the SEM pictures.
We suspected that some large plates (precursors) were con-
nected together at the initial stage and later evolved into
such large clusters.
Similarly, rapid cooling of the homogeneous mixture of 2
in CHCl3/EtOH (1:2 v/v) to 08C produced multilayered, mi-
crometer-sized belts, which indirectly proved that the sheet
precursors (Figure 7a) obtained by slow cooling to 508C
were also multilayered. As the slow aging proceeds continu-
ously, the objects start to bifurcate all around (Figure 7b),
which results in the assemblies with scrolled petals (Fig-
ure 7c and d). Then every scrolled petal was stretched until
the whole system was energetically stable (Figure 7e and f),
leading to the final structures of the flower-shaped three-di-
mensional objects.
The formation mechanism described above indicates that
the formation of the microscopic flower-like assemblies was
determined by both the spatial and energy factors during
the growth process. In addition, slow aging was essential for
the formation of flower-shaped assemblies.
The properties of superhydro-
phobic surfaces: The surface of
a lotus leaf consists of papillose
epidermal cells on a microme-
ter scale with
a branchlike
nanostructure on every papil-
la.[4b,21] Such a dual-scale rough-
ness gives the surface excellent
superhydrophobicity:
water
droplets can roll off the surfa-
ces with dirt and contamination
without wetting the surfaces.
Because of the resemblance of
our hierarchical structures to
that of the lotus leaf, we tried
to obtained superhydrophobic
surfaces using our new flower-
shaped objects.
Both of the morphologies we
obtained can be easily fabricat-
ed on various substrates (e.g.,
silicon, metal, and glass) by
drop-casting. Under these con-
ditions, flower-shaped objects
formed densely packed films
(Figure 8b). Figure 8a is an
image of a water droplet (6 mL)
lying on a thin film of 1. The
static contact angle (CA) of
water on the thin film was mea-
sured to be 156.58 (Figure 8c).
The water droplet could roll on
Figure 6. SEM images of intermediates of flower-shaped supramolecular assemblies of 1 when slowly cooling a
hot homogeneous solution of 1 in CHCl3/EtOH from 608C to a) 508C ; b) 458C ; c) 408C ; d) 358C (the arrow
shows the possible precursor for the flower formation); e) 308C ; f) 258C. g)–i) SEM images of multilayer as-
semblies of 1 formed by rapid cooling from 60 to 08C. j)–l) SEM images of “clustered flowers”.
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Y. Song, K. Wu, J. Pei et al.
face morphology prepared for a
large amount of flower objects
of 2 looked different to that of
1 (Figure 8b). There were many
microscale pillar-shaped micro-
structures on the superhydro-
phobic surfaces of 2 (Figure 9a
and b). This demonstrated that
water could easily penetrate
into the grooves on the surface
of 2, because of the strong ca-
pillary force of the pillar-
shaped microstructures, result-
ing in the superhydrophobicity
with high adhesive force (Wen-
zelꢀs state; Figure 10).[25] The
result was exactly what we ex-
pected: water droplets stayed
pinned to the surface of 2 when
the surface was tilted (Fig-
ure 9e) or even when it was
turned upside down (Figure 9f).
In addition, a series of pic-
tures, following the time se-
quence, of a water droplet strik-
ing our superhydrophobic surfa-
ces showed the differences of
Figure 7. SEM images of intermediates of flower-shaped supramolecular assemblies of 2 when slowly cooling a
hot homogeneous solution of 2 in CHCl3/EtOH from 608C to a),b) 508C; c),d) 408C; e) 358C ; f) 258C. g)–
i) SEM images of multilayer assemblies of 2 formed by rapid cooling from 60 to 08C.
the thin film freely when being pulled with a needlepoint. In
contrast, a spin-coated film of 1 from a solution in chloro-
form onto silicon resulted in a smooth layer with a low sur-
face roughness (2 nm as measured by atomic force microsco-
py (AFM); Figure 8d), and exhibited a static contact angle
of only 102.78 (inset of Figure 8d), even though they were
formed by the same chemical structure. In the same way,
self-assembled 2 also had a binary surface structure (micro-
and nanostructures), and the surface of 2 showed the super-
hydrophobicity with a water CA of 155.88 (Figure 9d), in
contrast to the CA of 103.18 (Figure 9c) on the spin-coated
film from the solution of 2 in CHCl3. This striking contrast
demonstrated the importance of the rough, two-tier surface
structures on the wettability of the solid structure.
the two surfaces more vividly (Figure 11). The shape of the
water droplet changes dramatically during striking as its ki-
netic energy transforms into potential energy due to the de-
formation of its shape.[26] Despite these deformations, the
droplets falling from the same height toward the two differ-
ent surfaces could return to their round shape and both
bounced back in 16 ms because the surfaces were very water
repellent. However, during the second stroke in succession,
because of the high adhesion force, the water droplet on the
surface of the flower-shaped 2 became almost static (Fig-
ure 11b), whereas it could rebound several times on the sur-
face of 1 (Figure 11a). The facts also indicate the difference
of surface adhesion caused by the two dual-scale microstruc-
tures.
Contact-angle hysteresis, which is determined by the air–
liquid–solid three-phase contact line, can be used to infer
the sliding behavior of a water droplet on a surface. Gener-
ally, there are two superhydrophobic states on a rough sur-
face: Wenzelꢀs state and Cassieꢀs state.[22,23] Water droplets
in Wenzel wetting are found to be highly adhesive (the high
CA hysteresis); on the other hand, those in a Cassie wetting
state can roll off easily (low CA hysteresis). Figure 8e shows
that the sliding angle (SA) in the thin film formed from
flower-shaped objects 1 was smaller than 38. The small slid-
ing angle indicated that the water droplet was suspended by
the air trapped on the composite contact surface[24] and
could easily roll down the surface when tilted, just like the
lotus surface in a Cassieꢀs state. In contrast to the morpholo-
gies of 1, the size of hierarchical micro- and nanostructures
of 2 were both larger than those of 1. Accordingly, the sur-
The static contact angle and sliding angle of the obtained
films of globular objects did not change with time for at
least two weeks at room temperature, thus showing some
degree of stability. The fractal morphologies of the prepared
superhydrophobic films could be stabilized below their melt-
ing points (104.1 and 187.38C for 1 and 2, respectively; Fig-
ure S3 in the Supporting Information).[27] In addition, it is
noteworthy that compared with other methods used for the
preparation of superhydrophobic surfaces, our films were
readily prepared by means of an easy solution process, and
could be readily re-formed, re-used, or washed away.
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Flower-Shaped Hierarchical Structures
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Figure 8. a) Picture of a water droplet on a film of 1. b) SEM image of a
film of 1 on Si deposited from CHCl3/EtOH (1:2 v/v). c) Photograph of a
water droplet on the surface (contact angle of 156.58). d) AFM image of
1 on Si spin-coated film from the solution of 1 in CHCl3 (the roughness
in height was about 2 nm), and a photograph (inset) of a water droplet
on the spin-coated film (contact angle of 102.78). e) Images obtained
during sliding angle measurement, which indicate that a water droplet
can roll down the thin film of the globular object’s surface easily.
Figure 9. a),b) SEM images of a film of 2 on Si deposited from CHCl3/
EtOH (1:2 v/v). c) Behavior of water droplet on a spin-coated film from
a solution of 2 in CHCl3 (CA of 103.18). Shapes of water droplets on a
film of 2 on Si deposited from its solution in CHCl3/EtOH (1:2 v/v) with
different tilt angles: d) 08, CA of 155.88C, e) 908, f) 1808.
Conclusion
In summary, by means of a slight adjustment of alkyl chains
of the molecular structure, two kinds of microscale flower-
shaped morphologies with nanometer petals have been
formed through hierarchical self-assemblies of benzodithio-
phene derivatives. By capturing intermediate stages of the
assemblies, we have proposed a new formation mechanism
for such a flower-shaped morphology. The hierarchical mor-
phologies of the films allowed us to fabricate superhydro-
phobic surfaces by means of a simple solution process. Two
different surfaces with a Cassie state and Wenzel state have
been realized. The water-repelling characteristics of surfaces
formed by 1 are comparable to that of the lotus leaf (contact
angle larger than 161.08 and sliding angle of about 28), and
another surface has a high adhesive property as the flower’s
petals. The superhydrophobicity of the surfaces was vividly
visualized through the investigation of the free-falling water
droplets striking the films. The comparison of these results
with that of a flat film formed with the same molecular
structure but without the dual-scale roughness, demonstrates
the importance of the hierarchical structure. We are now ex-
Figure 10. A schematic illustration for describing the local interaction of
a drop of water in contact with the film of flower objects.
ploring other applications of the as-prepared films, such as
chemical sensors[28] and supramolecular templates,[29] with an
aim to develop new functional devices that can work in am-
bient conditions or even in water.
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Y. Song, K. Wu, J. Pei et al.
Water-repellent and adhesive proper-
ties: The sessile drop method was used
for CA measurements with a dataphy-
sics OCA20 contact angle system at
228C. The water droplet size used for
measurements was 3.0 mL. The contact
angles were measured at five different
points of each sample.
Compound 3:
A mixture of THF
(50 mL) and triethylamine (15 mL)
was added to a mixture of 1,4-dibro-
mo-2,5-diiodobenzene
2.05 mmol), 1,2-bis(dodecyloxy)-4-
ethynylbenzene (1.97 g, 4.2 mmol),
[PdCl2A(PPh3)2] (115 mg, 0.12 mmol),
(1.00 g,
CTHUNGTRENNUNG
and CuI (11 mg, 0.06 mmol) under ni-
trogen using syringes. After it had
been stirred overnight at room tem-
perature under nitrogen, the mixture
was poured into saturated aqueous
NH4Cl solution (100 mL). Aqueous
layers were extracted with EtOAc.
The combined organic layers were
washed with brine, and then dried
over Na2SO4. After removal of the sol-
vents under reduced pressure, the resi-
due was purified by column chroma-
tography (silica gel, petroleum ether/
chloroform 5:1) to give 3 as a white
solid. Yield: 1.92 g, 80%; 1H NMR
(300 MHz, CDCl3): d=7.74 (s, 2H),
7.16–7.12 (dd, J=8.4, 1.8 Hz, 2H),
7.05–7.04 (d, J=1.8 Hz, 2H), 6.85–6.83
(d, J=8.4 Hz, 2H), 4.03–3.99 (m, 8H),
1.85–1.78 (m, 8H), 1.47–1.27 (m,
72H), 0.95–0.86 ppm (t, J=6.9 Hz,
12H); 13C NMR (75 MHz, CDCl3): d=
150.5, 148.8, 135.7, 126.3, 125.4, 123.4,
116.8, 114.4, 113.2, 97.2, 85.6, 69.3,
69.1, 31.9, 29.69, 29.66, 29.63, 29.41,
29.36, 29.23, 29.18, 26.0, 22.7,
14.1 ppm; HRMS (ESI): m/z calcd for
Figure 11. Selected snapshots of a water droplet striking our superhydrophobic surfaces of a) 1 and b) 2.
Experimental Section
C70H109Br2O4: 1171.6692 [M+1]+; found: 1171.6706.
Compound 4: nBuLi (2.5m in hexane, 0.6 mL) was added dropwise to a
solution of compound (500 mg, 0.43 mmol) in anhydrous Et2O
Reagents and instrumentation: All commercially available chemicals
were used without further purification unless otherwise noted. CH2Cl2
was distilled from CaH2 under nitrogen. THF was freshly distilled from
sodium and benzophenone ketyl under nitrogen prior to use. Column
chromatography was performed with silica gel (0.063–0.2 mm). All yields
given refer to isolated yields. 1H and 13C NMR spectra were recorded on
Mercury plus 300 MHz and Bruker 400 MHz instruments using CDCl3 as
3
(100 mL) under nitrogen at À788C. After 10 min at À788C, the mixture
was stirred at 08C for 1 h, and then dimethyl disulfide (160 mg,
1.7 mmol) was added using a syringe. The mixture was stirred at room
temperature for 4 h, and then poured into an aqueous NH4Cl solution.
The organic layer was washed with saturated NH4Cl, brine, and then
dried over Na2SO4. After removal of the solvents under reduced pres-
sure, the residue was purified by column chromatography (silica gel, pe-
troleum ether/dichloromethane 8:1) to give 4 as a yellow solid. Yield:
350 mg, 73%; 1H NMR (300 MHz, CDCl3): d=7.16–7.14 (dd, J=8.4,
1.8 Hz, 2H), 7.074–7.069 (d, J=1.8 Hz, 2H), 6.85–6.83 (d, J=8.4 Hz,
2H), 4.03–3.95 (m, 8H), 2.52 (s, 6H) 1.86–1.79 (m, 8H), 1.49–1.26 (m,
72H), 0.90–0.86 ppm (t, J=6.9 Hz, 12H); 13C NMR (100 MHz, CDCl3):
d=150.1, 148.8, 137.3, 127.7, 125.2, 122.1, 116.7, 114.9, 113.2, 113.1, 97.8,
85.3, 69.3, 69.2, 69.1, 31.9, 29.7, 29.65, 29.62, 29.61, 29.4, 29.35, 29.3, 29.2,
29.18, 29.1, 26.0, 25.99, 22.7, 15.4, 14.1 ppm; HRMS (ESI): m/z calcd for
C72H115O4S2: 1107.8231 [M+1]+; found: 1107.8230.
1
solvent unless otherwise noted. H NMR chemical shifts were referenced
to TMS (d=0 ppm) or CHCl3 (d=7.26 ppm), and 13C NMR chemical
shifts were referenced to CDCl3 (d=77.00 ppm). High-resolution (HR)
ESI mass spectra were recorded on a Bruker Apex IV FTMS. Differen-
tial scanning calorimetry (DSC) analyses were performed on a Mettler
Toledo Instrument DSC822e calorimeter. Powder X-ray diffraction analy-
ses were recorded on a D/max-RA high-power rotating anode 12 kW X-
ray diffractometer. All AFM experiments were carried out with a Nano-
scope IIIa microscope (Multimode, Digital Instruments) under ambient
conditions. Absorption spectra were recorded on
a Perkin–Elmer
Lambda 35 UV-visible spectrometer. Photoluminescence (PL) spectra
were carried out on a Perkin–Elmer LS55 luminescence spectrometer.
Compound 5: Iodine (367 mg, 1.44 mmol) was added to a solution of
compound 4 (400 mg, 0.36 mmol) in CHCl3 (100 mL). After 1 h, aqueous
sodium thiosulfate (2m, 10 mL) was added. The organic layer was washed
with brine, and then dried over Na2SO4. After removal of the solvents
under reduced pressure, the residue was recrystallized in CHCl3/CH2Cl2
Scanning electron microscopy (SEM) was performed on
a Philips
XL30W/TMP operating at 1 kV. Transmission electron microscopy
(TEM) was recorded on a Philips model Tecnai F20 electron microscope
operating at 120 kV.
7316
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Chem. Eur. J. 2010, 16, 7309 – 7318

Flower-Shaped Hierarchical Structures
FULL PAPER
to give 5 as a yellow solid. Yield: 433 mg, 90%; 1H NMR (300 MHz,
CDCl3): d=8.21 (s, 2H), 7.32–7.31 (d, J=2.1 Hz, 2H), 7.27–7.23 (dd, J=
1.8, 8.4 Hz, 2H), 6.97–6.95 (d, J=8.4 Hz, 2H), 4.12–4.04 (m, 8H), 1.89–
1.84 (m, 8H), 1.50–1.26 (m, 72H), 0.90–0.85 ppm (m, J=6.9 Hz, 12H);
13C NMR (75 MHz, CDCl3): d=150.1, 148.8, 143.5, 140.7, 136.7, 126.9,
122.9, 119.1, 115.6, 115.5, 113.2, 69.6, 69.56, 69.47, 69.2, 31.9, 29.7, 29.6,
29.5, 29.44, 29.36, 29.28, 26.1, 22.7, 14.1 ppm; HRMS (ESI): m/z calcd for
C70H108I2O4S2: 1330.5772 [M+1]+; found: 1330.5778.
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Compound 1: Deionized water (1 mL) was added to a mixture of 5
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(200 mg, 0.15 mmol), NaOH (60 mg, 1.5 mmol), 3-dodecyloxyphenylbor-
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had been left at reflux at 808C for 10 h, the mixture was poured into
water (100 mL). The aqueous layer was extracted with EtOAc. The com-
bined extracts were washed with saturated NH4Cl, brine, and then dried
over Na2SO4. After removal of the solvents under reduced pressure, the
residue was purified by column chromatography over silica gel (petro-
leum ether/CHCl3 7:1) to give 1 as a yellow solid. Yield: 205 mg, 85%;
1H NMR (400 MHz, CDCl3): d=7.95 (s, 2H), 7.38–7.34 (m, 2H), 7.00–
6.93 (m, 8H), 6.79 (s, 2H), 6.77 (s, 2H), 3.98–3.95 (t, J=6.6 Hz, 4H),
3.93–3.89 (t, J=6.6 Hz, 4H), 3.64–3.61 (t, J=6.6 Hz, 4H), 1.83–1.61 (m,
12H), 1.44–1.26 (m, 108H), 0.90–0.86 ppm (m, 18H); 13C NMR (75 MHz,
CDCl3): d=159.6, 148.8, 148.4, 139.9, 139.3, 137.5, 135.8, 131.1, 129.9,
126.8, 122.7, 121.8, 116.3, 115.8, 114.5, 113.9, 113.1, 69.1, 68.7, 68.1, 31.9,
29.74, 29.68, 29.65, 29.62, 29.43, 29.36, 29.2, 29.0, 26.1, 25.99, 25.92, 22.7,
14.1 ppm; HRMS (ESI): m/z calcd for C106H166O6S2: 1599.2120 [M+1]+;
found: 1599.2131.
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Compound 2: The preparation of compound 2 was carried out on a scale
of 0.15 mmol using the same procedure as for the preparation of com-
pound 1. Yield: 104 mg, 80%; 1H NMR (400 MHz, CDCl3): d=8.05 (s,
2H), 7.37–7.33 (m, 6H), 7.27–7.23 (m, 6H), 6.97–6.92 (m, 6H), 3.92–3.88
(t, J=6.6 Hz, 4H), 1.77–1.70 (m, 4H), 1.41–1.26 (m, 36H), 0.89–0.85 ppm
(m, 6H); 13C NMR (75 MHz, CDCl3): d=159.4, 140.0, 139.2, 136.9, 136.2,
134.3, 132.1, 129.8, 129.5, 128.3, 127.8, 122.7, 116.3, 116.25, 114.2, 68.1,
31.9, 29.7, 29.63, 29.60, 29.57, 29.4, 29.3, 29.2, 26.0, 22.7, 14.1 ppm; HRMS
(ESI): m/z calcd for C58H70O2S2: 862.4812 [M]+; found: 862.4829.
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Acknowledgements
This work was supported by the Major State Basic Research Develop-
ment Program (nos. 2006CB921602 and 2009CB623601) from the Minis-
try of Science and Technology, and National Natural Science Foundation
of China. We thank Professor Yizhuang Xu for fluorescence microscopy
measurements.
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Received: February 8, 2010
Published online: May 12, 2010
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Chem. Eur. J. 2010, 16, 7309 – 7318