Synthesis and solid-state investigations of oligo-phenylene-ethynylene structures with halide end-groups

Article abstract of DOI:10.1002/ejoc.201200033

In the field of material science functionalization of substrate surfaces (e.g. metal, graphite) with organic molecules is of increasing interest. Desirable targets are molecules with functional groups providing for two-dimensional assembly and three-dimen

Full text of DOI:10.1002/ejoc.201200033

FULL PAPER
DOI: 10.1002/ejoc.201200033
Synthesis and Solid-State Investigations of Oligo-Phenylene–Ethynylene
Structures with Halide End-Groups
Nicolas M. Jenny,[a][‡] Hong Wang,[b,c][‡] Markus Neuburger,[a] Harald Fuchs,[b,d]
Lifeng Chi,*[b] and Marcel Mayor*[a,d]
Keywords: Materials science / Crystal engineering / Surface analysis / Electrostatic interactions / Cross-coupling / Synthetic
methods
In the field of material science functionalization of substrate
surfaces (e.g. metal, graphite) with organic molecules is of
increasing interest. Desirable targets are molecules with
functional groups providing for two-dimensional assembly
and three-dimensional crystal growth. We have synthesized
structures particular interesting and challenging. Here we
probe the interplay of halide end-groups and the backbone
of an OPE to investigate the intermolecular interactions in
both solution depositions (2D) and X-ray crystal structures
(3D). The STM images and the crystal structures of each OPE
a series of halogen-end-capped oligo-phenylene-ethynyl- reveal striking packing similarities. For each molecule, a
enes (OPEs) to study the interactions at the solid/liquid inter-
face and in crystal structures. Organohalides can be involved
in a wide variety of intermolecular interactions such as C–
X···H, C–X···X–C and C–X···π-orbitals. The range of halogen-
based interactions and the diversity of intermolecular forces
along different crystal axes makes the investigation of such
plane in the crystal structure with an arrangement of mole-
cules resembling its two-dimensional packing on a flat sur-
face was found. These results support the hypothesis of
sheet-by-sheet crystal growth and suggest that flat surfaces
would be ideal interfaces to promote crystal growth for hal-
ide-end-capped OPEs.
tions.[6] The self-assembly of organic molecules at the solid/
liquid interface leads to large organized molecular patterns
on surfaces. These laterally controlled supramolecular
architectures can provide surface properties useful for bot-
tom-up synthetic strategies.[7] Of particular interest are self-
assembled systems yielding porous networks that provide
well-defined two-dimensional patterns as templates for
functional guests.[8–13] We previously reported on the self-
assembly of fluorinated rods[14] and branched fluorinated
stars[15] where the fluorine-hydrogen as well as molecule-
substrate interactions dictated the assembly of a lateral net-
work. Inspired by these large-area self-assembled patterns
we became interested in the organizing power of
halide···hydrogen interactions. To explore the influence of
various halides for lateral self-assembly on a flat substrate
and for three-dimensional arrangement in single crystals,
we designed molecular rods 1–3 (Figure 1). These rods con-
sist of flat and rigid OPE backbones that favor
molecule···substrate interactions.[14,16] Terminal halides
groups (Cl, Br and I) are expected to direct the lateral as-
sembly by a wide variety of intermolecular interac-
tions[4,17,18] such as C–X···H, C–X···X–C and C–X···π-or-
bital. The differences in electrostatic potentials and size of
the halides are expected to vary the strength of the intermo-
lecular interactions and might be reflected in the resulting
self-assembled structures. Because halides have both posi-
tive and negative electrostatic potentials, they can be at-
tracted by other negative halides (or π-orbitals) or electro-
Introduction
In the field of material science the functionalization of
metal and graphite surfaces with organic molecules is of
increasing interest. Being able to control the electrochemical
and physical properties of surfaces such as conductivity, re-
sistance and hydrophilic or hydrophobic properties has
made many new applications possible.[1,2] To alter the prop-
erties of an entire surface homogenously the molecules must
be arranged in a periodic manner. The easiest way to
achieve this is by solution deposition of molecules able to
control their orientation with respect to their neighbors.
This self-assembly process depends on intermolecular inter-
actions including hydrogen bonding,[3] hydrogen-halogen or
halogen···halogen interactions,[4] Van-der-Waals interac-
tions[5] and dipole···dipole (molecule···substrate) interac-
[a] Department of Chemistry, University of Basel,
St. Johanns-Ring 19, 4056 Basel, Switzerland
Fax: +41-61-267-1016
E-mail: marcel.mayor@unibas.ch
[b] Physical Institute, University of Münster,
Wilhelm-Klemm-Strasse 10, 48149 Münster, Germany
[c] Department of Chemistry, College of Chemistry and Chemical
Engineering, Xiamen University,
Xiamen 361005, China
[d] Karlsruhe Institute of Technology (KIT), Institute of
Nanotechnology,
P. O. Box 3640, 76021 Karlsruhe, Germany
[‡] These authors contributed equally to this work.
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201200033.
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Investigations on Oligo-Phenylene-Ethynylenes
Figure 1. The model compounds were assembled at the solid/liquid interface and crystallized. The lateral arrangement of the molecules
at the surface and in “sheets” in the solid-state structure were investigated.
positive hydrogen atoms.[4,17,19] Two hexyl substituents on molecular interactions in all three directions in the crystal
the central phenyl units of the OPE rods enable the process- is a very difficult task. Alternative organic building blocks
ability of the molecular building blocks. These alkyl substit- are aromatic structures.[29,30] Two-dimensional structural
uents are expected to reduce the molecular density of the control is easily achieved in the planes of the aromatic rings
rod on the substrate but should be small enough to allow whereas the packing of the sheets in the third dimension is
tight molecular packing directed by the terminal halogens. less controlled. The aromatic rings impart some interactions
The spontaneous formation of laterally ordered flat sheets of their own (π···π, C–H···O) which may contribute to or-
of densely packed molecules is of particular interest as a dered staples. However, such crystals differ considerably in
potential motif for a tightly packed 3D molecular assembly. the strength of the interactions of molecules within and be-
The stacking of such sheets might result in a crystal-like 3D tween the sheets. The combination of the diversities of halo-
order providing a perfect interface between a flat substrate gen-based interactions and of the intermolecular forces
material and the molecules’ crystalline state.
In the field of crystal engineering various intermolecular such structures particular interesting and challenging.
interactions have been studied extensively.[20] Strong and di-
Here we systematically investigate halide-based interac-
along different crystal axes makes crystal engineering with
rectional hydrogen bonds (e.g. O–H···O or N–H···O) have tions by comparing the self-assembly of terminally halogen-
been investigated in detail.[21] Of particular interest are substituted OPE rods 1–3 at the solid-liquid interface (2D)
halogen bonds because of the two-fold role of the halogen and in a single crystal (3D), and examine the extent of simi-
atom. On one hand the halide substituent can interact with larity of the patterns obtained by intermolecular interac-
a lone-pair provided by a heteroatom in proximity and act tions.
as the hydrogen does in a hydrogen bond;[22] and on the
other hand the halide can provide lone-pairs for electron
deficient atoms of neighboring molecules. Consequently,
Results and Discussion
various interactions (e.g. C–X···X–C and C–X···Y–C) can
be observed with halogen substituents.[23,24,25] This diversity
The OPE target structures consist of a π-conjugated
of possible interactions increases the complexity in con- backbone and either chlorine, bromine or iodine end-
trolling the crystal growth by the molecules’ design. In a groups. The target structures were synthesized by either a
crystal engineering approach the strength of intermolecular convergent or divergent approach.[31] Attempts to synthe-
interactions is tuned by controlling the spatial arrangement size these structures directly failed (Scheme 1) owing to po-
of various substituents by the molecules’ backbone struc- lymerization, homo-coupling and poor solubility of the tar-
ture.[26,27] A major design challenge in engineering crystals get structures. Hexyl chains were introduced to the central
comprising exclusively organic molecules is that molecules unit of the OPE structure to increase the solubility and pro-
with functional groups pointing in all three dimensions are cessability of the target structures.
required.[28] Variation of modular functionalities along one
axis and, at the same time, maintaining equally weak inter- shown in Scheme 2. Both rods were assembled by using a
The assembly of dichloro-OPE 1 and dibromo-OPE 2 is
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Scheme 1. One-step synthetic strategy to terminally halogen-functionalized OPE rods.
pseudo-high-dilution strategy profiting from the increased cyclo[5.4.0]undec-7-ene, as a non-nucleophilic base and
reactivity of aryl iodides in Sonogashira coupling chemis- small traces of water were used to slowly deprotect the
try.[32] 1,4-Diiodo-2,5-dihexylbenzene (4) was synthesized TMS-acetylenes 5 and 6. The low concentration of free
following a literature procedure.[33] With building block 4 acetylene favored its reaction with the Pd-activated aryl iod-
and the commercially available compounds (4-chlorophen- ide and provided the desired rods 1 and 2 in reasonable
ylethynyl)trimethylsilane (5) and (4-bromophenylethynyl)- yields. Dichloro-OPE 1 and dibromo-OPE 2 were isolated
trimethylsilane (6) in hand, assembly of target structures in 65 and 73% yield, respectively.
1 and 2 was achieved through Sonogashira cross-coupling
reactions (Scheme 2). An in situ deprotection method[32]
was chosen to minimize the amount of free acetylene in the
reaction mixture and prevent homocoupling. 1,8-Diazabi-
For the synthesis of diiodo-OPE derivative 3 various dif-
ferent strategies were explored (Scheme 3). The strategy de-
scribed for 1 and 2, on the basis of increased reactivity of
iodine as a leaving group in the Sonogashira cross coupling
reaction,[34,35] gave polymeric products instead of desired
rod 3.
Initially a halide exchange reaction was attempted with
dibromo-OPE 2 [Scheme 3 (A)].[36,37] Treatment of 2 with
butyllithium and 1,2-diiodoethane led to a mixture of prod-
ucts. The isolation of diiodo-OPE 3 turned out to be chal-
lenging owing to very similar polarities of the dibromo-
OPE 2 and the corresponding iodo-bromo-OPE. However,
the target structure 3 was isolated in a low yield (22%) as
an off-white solid by column chromatography.
Masking strategies were considered to improve the yield
and purity of the target structure. An ideal masking group
would be readily available, stable to a variety of chemical
Scheme 2. Synthesis of dichloro-OPE 1 and dibromo-OPE 2.
Scheme 3. Synthesis of diiodo-OPE 3 by using various strategies ranging from halide exchange (A), to functional group interconversion
and masking strategies (B–D).
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Investigations on Oligo-Phenylene-Ethynylenes
conversions, and conveniently transformed under mild con- role strategy of 41%. However, the considerably increased
ditions and in a high yield to form the desired aryl iod- temperature required during the triazene strategy might be
ide.[31]
a drawback when additional functional groups are present.
An amine is suitable for functional group interconver-
All target structures and intermediates were charac-
1
sion. Diamino-OPE 8 was synthesized for subsequent con- terized by H and 13C NMR spectroscopy and mass spec-
version to diiodo-OPE 3, see Scheme 3 (B).[38] The idea was trometry, and by elemental analysis where applicable. In the
to profit from the polarity differences between starting ma- case of the target structures, the identity was corroborated
terial 8 and product 3. This strategy was first reported by by X-ray analysis.
Sandmeyer[39] and has been improved over the course of the
last century.[38,40] Compound 8 was synthesized by using a
Crystal Structures and Surface Images
Sonogashira coupling reaction in a yield of 90% with build-
ing blocks 4 and 7.[41,42] The product was then converted
into a diazonium salt by using sulfuric acid and sodium
nitrite in acetonitrile at 0 °C. After 24 h the reaction was
quenched with sodium iodide to afford diiodo-OPE 3 in
an improved yield of 50%.[40] However, during the reaction
considerable amounts of partially dehalogenated OPEs
were formed that again made isolation of 3 challenging.
Dimethylpyrroles were proposed as base-stable masking
groups for iodines under Sandmeyer-type conditions, see
Scheme 3 (C).[43,40] Building block 10 was obtained by using
a literature procedure starting from 4-iodoaniline (9).[44]
The second diacetylene, building block 11, was obtained in
90% yield by using standard cross-coupling conditions.[45]
Assembling masked OPE 12 by using a divergent approach
gave an overall yield of 58%. The final Sandmeyer-type re-
action, undertaken in a water/acetonitrile mixture as sol-
vent, gave the diiodo-OPE 3 in a yield of 72%. Simple fil-
tration through a short silica plug (40:1 hexane:tert-butyl-
methylether), gave product 3 in an overall yield of 41% as
a white crystalline solid. Interestingly, side products with
similar polarities were not observed. The increased solubil-
ity of the dimethylpyrrole-OPE 12 in the water/acetonitrile
mixture, may have improved the formation of the diazo-
nium salt during the Sandmeyer reaction. As in the case of
diamino-OPE 8 – see part B of Scheme 3 – the slow forma-
tion of the diazonium salt in the heterogeneous dispersion
is assumed to be responsible for the large quantity of side
products.
The crystals for X-ray analysis were either grown by slow
cooling of a saturated cyclohexane solution to 4 °C or by
slow evaporation of cyclohexane at room temperature. All
three compounds crystallize in the centro-symmetric space
group P1. The unit cells of OPEs 1 and 2 each contain one
molecule, whereas that of 3 contains two molecules and a
¯
cyclohexane molecule. In all three structures the molecules
¯
are located on an inversion center of the space group P1.
Thus, in the case of 1 and 2 the molecules are arranged
parallel to each other. In the case of 3 the two molecules
and the solvent molecule are located on different inversion
¯
centers of the space group P1 permitting the formation of
a fishbone-like arrangement in the direction I···I of the two
different orientations forming an angle of about 90°.
All the STM measurements were taken with a Nano-
scope IIIa Scanning tunneling microscope, and the STM tip
was prepared by mechanically cutting Pt/Ir wire (90:10).
The molecules were dissolved in 1-phenyloctane to make
saturated solutions. The solution was subsequently dropped
on a freshly cleaved highly oriented pyrolytic graphite
(HOPG) surface. The HOPG/1-phenyloctane interface was
investigated by STM. All STM images were performed in
constant current mode.
Dichloro-OPE 1 and Dibromo-OPE 2
The crystal structures of both OPEs 1 and 2 show a par-
Finally, alkylated triazenes were explored as masking allel arrangement of the rods (see parts a in Figures 2 and
groups for iodines [Scheme 3 (D)].[46,47] Triazenes can be 3) forming several layers shifted by 5.2 and 5.7 Å, respec-
directly substituted with iodine by using methyl iodide in a tively. By looking at a planar cut through the crystal struc-
sealed tube at 120 °C, and alkylated triazenes are stable tures similar Cl···Cl (Figure 2, b, 5.0 and 4.8 Å) and Br···Br
towards strong bases and high temperatures. Pyrrolidine- (Figure 3, b, 4.8 and 5.1 Å) distances were observed. Cl···H
triazenes are known for favorable crystallization properties as well as Br···H interactions could be observed where the
and we hoped this property might improve the isolation of terminal halogen interacted with two hydrogen atoms com-
these intermediates. Triazene building block 13 was synthe- ing from two different rods. The area of the unit cell (in a
sized following a procedure reported by Godt.[48] Ditriaz- plane) comprising a single OPE molecule is about 1.84 nm2
ene-OPE 14 was synthesized by using a cross-coupling reac- for dichloro-OPE 1 and about 1.93 nm2 for dibromo-OPE
tion in very poor yield (7%). Even changing the disconnec- 2 (see Supporting Information).
tion strategy and putting the acetylenes on the central unit
Parts c in Figures 2 and 3 show the STM images of a
did not improve the yield. Instead diamino-OPE 8 was monolayer of OPEs 1 and 2 on a HOPG surface. A lamellar
transformed into ditriazene-OPE 14 and isolated by structure, where the rods lie parallel to each other, was ob-
crystallization in 80% yield. OPE 14 was subsequently served in each case. The unit cell for dichloro-OPE 1 was
transformed into diiodo-OPE 3 in a yield of 75%. Simple determined with a = (2.0Ϯ0.1) nm, b = (1.0Ϯ0.1) nm and
filtration through silica (cyclohexane) gave the pure prod- α = (76Ϯ2)° whereas the unit cell for dibromo-OPE 2 was
uct. The overall yield for the triazene strategy was 54%, determined with a = (2.0Ϯ0.1) nm, b = (1.0Ϯ0.1) nm and
which represents a slight increase over the yield for the pyr- α = (75Ϯ4)°. The unit cells, which contain one molecule,
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L. Chi, M. Mayor et al.
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Figure 2. (a) The crystal structure of dichloro-OPE 1 reveals a par-
allel arrangement of rods. Hexyl chains and hydrogen atoms have
been removed for clarity. (b) Planar cut through the crystal struc-
ture of 1. The slightly larger distance of 5.0 Å is shown in blue and
the slightly shorter distance of 4.8 Å is shown in black. The Cl···H
interactions (3.4 Å) are shown in green. (c) STM image of a HOPG
surface covered with 1.
Figure 3. (a) The crystal structure of dibromo-OPE 2 reveals a par-
allel arrangement of rods. Hexyl chains and hydrogen atoms have
been removed for clarity. (b) Crystal structure of 2 showing the
parallel order. The larger distance of 5.1 Å is shown in blue and the
shorter distance of 4.8 Å is shown in black. The Br···H interactions
(3.3 Å) are shown in green. (c) STM image of a HOPG surface
covered with 2.
have a surface area of about 1.94 nm2 for 1 and 1.93 nm2
for 2.
By comparing the individual molecular arrangements of
a planar cut through the crystal structure (see b in Figures 2
and 3) with the molecular arrangements at the solid liquid
interface (see c in Figures 2 and 3) an exact match of the
parallel crystal arrangement was observed. The same zigzag
arrangement of the chlorines and the bromines was found.
X···H interactions as well as alkyl-chain interdigitations
could be observed on the surface. Eight X···H interactions
per molecule were observed (see b in Figure 2 and 3, indi-
cated in green) in the crystal structure and at the solid li-
quid interface.
(Figure 4, b) a perpendicular arrangement of the rods is
observed. This arrangement leads to the formation of two
cavities. The distance between the iodines within these cavi-
ties is 14.2 and 8.3 Å, respectively. The angles of the perpen-
dicular rods are between 92.3 and 93.7°. The central benz-
ene units of the rods are situated in the corners of the unit
cell at a distance of 15.0 and 15.3 Å to one another. The
area of the unit cell (in a plane) comprising two molecules
and a cyclohexane is about 4.54 nm2 (see Supporting Infor-
mation).
The terminal iodine has a strong positive electrostatic po-
tential along the molecular axis and a negative electrostatic
potential off the axis forming a “belt” around the iodine.[4]
Diiodo-OPE 3
The packing order of the crystal structure reveals several Therefore, it can interact with electron donors such as other
layers of molecules (Figure 4, a). Looking at the unit cell, halogens and π-orbitals as well as electron acceptors includ-
three planar sheets are observed having a total height of ing hydrogen atoms.[17] The perpendicular arrangement of
7.3 Å. When looking at that planar cut through the crystal the rods comes from a strong I···π-orbital interaction where
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Investigations on Oligo-Phenylene-Ethynylenes
perpendicular to each other forming large and small cavi-
ties.
The molecular arrangement observed in a planar cut
through the crystal (Figure 4, b) and the arrangement at the
solid/liquid interface (Figure 4, c) match almost perfectly.
The area of two molecules in the crystal structure is about
4.5 nm2, which is similar to the surface coverage at the so-
lid/liquid interface of 4.2 nm2. The same interactions where
a terminal iodine interacts with a π-orbital and two hydro-
gen atoms were identified. These interactions clearly dictate
the two-dimensional assembly in both the crystal structure
and at the solid-liquid interface, whereas alkyl chain inter-
digitation[16] plays a smaller part. This situation could be
due to the eight I···H and four I···π-orbital interactions per
molecule.
Remarkable similarity between a planar cut through the
crystal structure and the assembly at the solid-liquid inter-
face was found for OPEs 1–3. However, each OPE shows
considerable variation in their arrangement induced by the
terminal halide. Similar arrangements were found for
dichloro-OPE 1 and dibromo-OPE 2. The halides show a
zigzag line coming from X···H interactions and alkyl chain
interdigitations (Figures 2 and 3). It seems that these are
the only interactions to control molecular arrangement. We
were able to measure that dichloro-OPE rods 1 were not
commensurable with the graphite sheet and therefore we
can assume that the assembly was mainly controlled by
intermolecular interactions. Monolayers of dibromo-OPE 2
and diiodo-OPE 3 were not stable enough to determine
their commensurability. This indicates that intermolecular
interactions dominate their assembly.
For diiodo-OPE 3 a quite different arrangement was ob-
served. The halides interact with electropositive hydrogen
atoms from neighboring rods and also with an electronega-
tive π-orbital, leading to a perpendicular arrangement (Fig-
ure 4). Presumably the larger size of the iodine together
with the larger electropositive potential is responsible for
this change in molecular packing. In particular, the latter is
assumed to form an interaction with the acetylene π-system
resulting in the perpendicular arrangement of the molecular
rods.
Figure 4. (a) The crystal structure of diiodo-OPE 3 reveals a per-
pendicular arrangement of rods forming large and small cavities.
Solvent, hexyl chains and hydrogen atoms have been removed for
clarity. (b) Planar cut through the crystal structure of 3 showing
the square cavities. The larger iodine-iodine distance of 14.2 Å is
shown in blue and the shorter iodine-iodine distance of 8.3 Å is
shown in black. The I···H (3.2 Å and 3.3 Å) and the I···π-orbital
(4.1 Å) interactions are shown in green. (c) STM image of a HOPG
surface covered with 3.
Differences on the molecular packing of the three struc-
tures suggest X···H bonds are the dominating intermo-
lecular interactions which becomes weaker with increasing
the electropositive potential of the iodine interacts with an size and decreasing electronegativity of the halogen atom
electronegative π-orbital of a second rod (Figure 4, a). The (Cl Ͼ Br Ͼ I).[49] In the case of 3 the X···H bonds are weak
central benzene unit undergoes π-π stacking with another enough that the X···π-system interaction begins to compete.
rod that is perpendicular. This crystal structure reveals that
the functional groups (I, H, CϵC) within the molecule dic-
tate the two-dimensional arrangement. The central benzene
unit controls the three-dimensional arrangement.
Conclusions
Figure 4 (c) shows the STM image of a monolayer of
A series of halide-end-functionalized OPEs were synthe-
diiodo-OPE 3 at the solid/liquid interface. The molecules sized to investigate their packing properties in single crys-
form a highly ordered network with large and small pores. tals and on atomically flat graphite substrates. In spite of
The unit cell was determined with a = (2.1Ϯ0.1) nm, b = their structural simplicity and similarity, the synthesis of
(2.0Ϯ0.1) nm and α = (90Ϯ4)°. The unit cell contains two target structures 1–3 was more challenging than expected.
molecules with a surface area of about 4.2 nm2. By looking OPEs 1 and 2 were synthesized in good yields through an
at the molecular arrangement on the surface the rods lie in situ deprotection method to prevent the formation of side
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L. Chi, M. Mayor et al.
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water (0.0115 mL) was added and the reaction mixture was stirred
at room temperature for 48 h. The mixture was concentrated under
reduced pressure and the residue was dissolved in CH2Cl2 and
washed with water (2ϫ20 mL). The organic layer was dried with
MgSO4, filtered and concentrated under reduced pressure to afford
the crude product as yellow oil. The oil was purified by column
products. Various synthetic strategies for OPE 3 were inves-
tigated. Functional group interconversion was superior for
yield and isolation properties of the target structure and
efficient syntheses were developed. Although the triazene
masking strategy gave the highest overall yield and a very
pure product, the dimethylpyrrole masking-group worked
considerably better than the free amine functional group
interconversion and requires lower reaction temperatures.
The STM images and the crystal structures for OPEs 1–3
chromatography (cyclohexane) to afford 1 (158 mg, 61.3%) as a
3
white solid. 1H NMR (400 MHz, CDCl3): δ = 7.45 (dt, JH,H
=
4
3
4
8.8, JH,H = 2 Hz, 4 H), 7.35 (s, 2 H); 7.34 (dt, JH,H = 8.8, JH,H
3
= 2 Hz, 4 H), 2.78 (t, JH,H = 8 Hz, 4 H), 1.70–1.66 (m, 4 H),
revealed a structural similarity for each rod. In their crystal 1.39–1.30 (m, 12 H), 0.88 (t, JH,H = 6.8 Hz, 6 H) ppm. 13C NMR
3
(100 MHz, CDCl3): δ = 142.5 (2 C, Cq), 134.4 (2 C, Cq), 132.8 (4
C, Ct), 132.5 (2 C, Ct), 128.9 (4 C, Ct), 122.5 (2 C, Cq), 122.1 (2 C,
Cq), 93.0 (2 C, Cq), 89.5 (2 C, Cq), 34.3 (2 C, Cs), 32.9 (2 C, Cs),
30.8 (2 C, Cs), 29.4 (2 C, Cs), 22.8 (2 C, Cs), 14.3 (2 C, Cp) ppm.
MS (EI): m/z (%) = 514.2 (100) [M]+, 443.2 (12.5) [M – 2Cl]+.
structures a slice plane with a molecular arrangement re-
sembling their two-dimensional packing on a flat surface
was found for each compound. These results support the
hypothesis of slice-by-slice crystal growth and suggest flat
surfaces as ideal interfaces to promote crystal growth. Of
particular interest was the arrangement of diiodo-OPE 3.
The STM image and the crystal structure revealed a porous
network of alternating pore sizes. This assembly can be ra-
1,4-Bis[2-(4-bromophenyl)ethynyl]-2,5-dihexylbenzene
(2):
A
Schlenk tube was purged with argon, charged with Pd(PPh3)2Cl2
(34.12 mg, 0.048 mmol, 0.06 equiv.), CuI (30.5 mg, 0.16 mmol,
tionalized by I···H and I···π-orbital interactions. This per- 0.2 equiv.) and [(4-bromophenyl)ethynyl]trimethylsilane (6, 405 mg,
1.6 mmol, 2 equiv.), and purged again. Dry benzene (8 mL) and
triethylamine (1.35 mL) were added. The suspension was degassed
for 10 min. 1,4-dihexyl-2,5-diiodobenzene[33] (4, 400 mg, 0.8 mmol,
pendicular arrangement might pave the way to porous crys-
tals grown on flat substrates.
In summary, halides have a large influence on the pack-
ing of OPE rods. This is rationalized by their differences
in electrostatic potentials. Understanding these interactions
will enable controlled surface functionalization and open
the door to controlled crystal growth on flat substrates.
1 equiv.)
and
1,8-diazabicyclo[5.4.0]undec-7-ene
(2.9 mL,
19.2 mmol, 24 equiv.) were added, and the resulting solution turned
green. Deionized water (0.0115 mL) was added and the reaction
mixture was stirred at room temperature for 36 h. The mixture was
concentrated under reduced pressure and the residue was dissolved
in CH2Cl2 and washed with water (2ϫ20 mL). The organic layer
was dried with MgSO4, filtered and concentrated under reduced
pressure to afford the crude product as a dark oil. The oil was
purified by column chromatography (hexane) to afford 2 (354 mg,
Experimental Section
1
73.2%) as a white solid. H NMR (250 MHz, CDCl3): δ = 7.498
General Remarks: All purchased chemicals were used as received
without further purification. Dry solvents and compounds 5, 6 and
7 were purchased from Sigma–Aldrich. All oxygen-sensitive reac-
tions were performed under an argon atmosphere. Glassware was
heated to 120 °C and cooled under a flow of argon. Silica gel
(60 μm) was purchased from Sigma–Aldrich. TLC plates (silica gel
60 F254) were purchased from Merck. All 1H and 13C NMR spectra
were recorded on a Bruker DPX-NMR (400 MHz/100.6 MHz) or
on a Bruker DRX-500 (500 MHz/125 MHz) spectrometer. Chemi-
cal shifts are given in ppm relative to residual solvent or trimethyl-
silane as internal standards. NMR solvents were obtained from
Cambridge Isotope Laboratories, Inc. (Andover, MA, USA). The
measurements were recorded at room temperature. All protons
were assigned by using COSY and NOESY experiments. All car-
bons were assigned by using DEPT, HMQC and HMBC experi-
ments. Mass spectra were recorded on a Bruker esquire 3000 plus
for ESI, a Finnigan MAT 95Q for EI or a finnigan MAT 8400 for
FAB. HRMS (ESI) spectra were recorded with a LTQ Orbitrap XL
(Thermo Fisher Scientific) by using a nanoelectrospray ion source.
Elemental analyses were measured with a Perkin–Elmer Analysator
240.
3
4
(dt, JH,H = 8.25, JH,H = 2.25 Hz, 4 H), 7.43–7.24 (m, 6 H), 2.78
3
(t, JH,H = 7.5 Hz, 4 H), 1.73–1.52 (m, 4 H), 1.36–1.28 (m, 12 H)
0.88 (t, JH,H = 6.75 Hz, 6 H) ppm. 13C NMR (100 MHz, CDCl3):
3
δ = 142.3 (2 C, Cq), 132.9 (4 C, Ct), 131.8 (4 C, Ct), 122.5 (2 C,
Cq), 122.4 (2 C, Cq), 122.3 (2 C, Cq), 92.9 (2 C, Cq), 89.5 (2 C, Cq),
34.1 (2 C, Cs), 31.7 (2 C, Cs), 30.6 (2 C, Cs), 29.2 (2 C, Cs), 22.6 (2
C, Cs), 14.1 (2 C, Cp) ppm. MS (EI): m/z (%) = 604.1 (100) [M]+.
C34H36Br2 (604.5): calcd. C 67.56, H 6.00; found C 67.4, H 5.95.
1,4-Bis[2-(4-aminophenyl)ethynyl]-2,5-dihexylbenzene (8): A 25 mL
Schlenk tube was purged with argon and charged with 1,4-diiodo-
2,5-dihexylbenzene[33] (4, 996 mg, 2 mmol, 1 equiv.), Pd(PPh3)2Cl2
(141 mg, 0.2 mmol, 0.1 equiv.), CuI (39.9 mg, 0.2 mmol, 0.1 equiv.),
4-ethynylaniline (7, 604 mg, 5 mmol, 2.5 equiv.), triethylamine
(7 mL) and dry THF (10 mL). The resulting mixture was degassed
for 10 min. and stirred for 16 h at room temperature. The mixture
was diluted with tert-butylmethyl ether (tBME) and filtered
through celite. The filtrate was concentrated under reduced pres-
sure and the residue was purified by column chromatography (cy-
clohexane/tBME, 1:2) to afford 8 as a brown solid (858 mg, 90%).
3
4
1H NMR (400 MHz, CD2Cl2): δ = 7.308 (dt, JH,H = 8.4, JH,H
=
3
4
1,4-Bis[2-(4-chlorophenyl)ethynyl]-2,5-dihexylbenzene
(1):
A
2.4 Hz, 4 H), 7.31 (s, 2 H), 6.65 (dt, JH,H = 8.4, JH,H = 2.4 Hz, 4
Schlenk tube was purged with argon, charged with Pd(PPh3)2Cl2
(21.3 mg, 0.03 mmol, 0.06 equiv.), CuI (19 mg, 0.1 mmol,
0.2 equiv.) and [(4-chlorohenyl)ethynyl]trimethylsilane (5, 221 mg,
1.02 mmol, 2.05 equiv.), and purged again. Dry benzene (5 mL)
and triethylamine (0.84 mL) were added. The brown suspension
was degassed for 10 min. 1,4-dihexyl-2,5-diiodobenzene[33] (4,
249 mg, 0.5 mmol, 1 equiv.) and 1,8-diazabicyclo[5.4.0]undec-7-ene
(1.0 mL, 12 mmol, 24 equiv.) were added to the solution. Deionized
H), 3.94 (s, 4 H), 2.77 (t, 3JH,H = 7.6 Hz, 4 H), 1.70–1.64 (m, 4 H),
1.36–1.33 (m, 12 H), 0.89 (t, JH,H = 6.8 Hz, 6 H) ppm. 13C NMR
3
(100 MHz, CD2Cl2): δ = 147.5 (2 C, Cq), 143.2 (2 C, Cq), 133.0 (4
C, Ct), 132.2 (2 C, Ct), 122.9 (2 C, Cq), 114.9 (4 C, Ct), 112.8 (2 C,
Cq), 94.9 (2 C, Cq), 86.6 (2 C, Cq), 34.5 (2 C, Cs), 32.2 (2 C, Cs),
31.0 (2 C, Cs), 29.6 (2 C, Cs), 23.0 (2 C, Cs), 14.3 (2 C, Cp) ppm.
MS (EI): m/z (%) = 476.3 (100) [M]+. C34H40N2 (476.7): calcd. C
85.67, H 8.46, N 5.88; found C 85.39, H 8.38, N 5.91.
2744
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 2738–2747

Investigations on Oligo-Phenylene-Ethynylenes
1,4-Bis{2-[4-(2,5-dimethyl-1H-pyrrol-1-yl)phenyl]ethynyl}-2,5-dihex-
ylbenzene (12): A 25 mL Schlenk tube was purged with argon,
charged with Pd(PPh3)2Cl2 (42.5 mg, 0.06 mmol, 0.06 equiv.), CuI
(38.1 mg, 0.2 mmol, 0.2 equiv.) and TMS-protected acetylene 11[45]
(439 mg, 1.0 mmol, 1 equiv.), and purged again. Dry benzene
(10 mL) and triethylamine (1.7 mL) were added. The yellow sus-
pension was degassed for 10 min resulting in a brown solution. Di-
methylpyrrole derivative 10[44] (624 mg, 2.1 mmol, 2.1 equiv.) and
1,8-diazabicyclo[5.4.0]undec-7-ene (3.6 mL, 24.0 mmol, 24 equiv.)
were added to the solution. Deionized water (0.0144 mL) was
added and the reaction mixture was stirred at room temperature
for 100 h. The reaction mixture was diluted with tBME and washed
with water (2ϫ20 mL) and brine. The organic layer was dried with
MgSO4, filtered and concentrated under reduced pressure to afford
the crude product as a dark oil. The oil was purified by column
chromatography (cyclohexane/tBME, 40:1) to afford 12 (367 mg,
organic layers were combined, washed with brine, dried with
MgSO4 and concentrated under reduced pressure to afford the
crude product. Ethyl acetate was added and the slurry was put in
an ultrasonic bath for 5 min. The mixture was then filtered and the
solid product was dried under vacuum to afford 14 (558 mg, 82%)
as a yellow solid. 1H NMR (400 MHz, CDCl3): δ = 7.481 (dt, 3JH,H
4
3
4
= 8.8, JH,H = 2 Hz, 4 H), 7.41 (dt, JH,H = 8.8, JH,H = 2 Hz, 4
3
H), 7.34 (s, 2 H), 3.80 (s, 8 H), 2.80 (t, JH,H = 7.6 Hz, 4 H), 2.04
3
(m, 8 H), 1.72–1.68 (m, 4 H), 1.41–1.31 (m, 12 H), 0.878 (t, JH,H
= 7.2 Hz, 6 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 151.4 (2
C, Cq), 142.3 (2 C, Cq), 132.4 (4 C, Ct), 132.3 (2 C, Ct), 122.8 (2
C, Cq), 120.6 (4 C, Ct), 120.0 (2 C, Cq), 94.7 (2 C, Cq), 88.6 (2 C,
Cq), 34.4 (Cs, C4), 32.0 (2 C, Cs), 30.0 (2 C, Cs), 29.5 (2 C, Cs),
24.0 (2 C, Cs), 22.9 (4 C, Cs), 14.4 (2 C, Cp) ppm. MS (EI): m/z
(%) = 640.4 (5.5) [M+], 543.3 (40.5) [M+ – C4H8N3], 445.2 (100)
[M+ – C8H16N6]. HRMS (ESI): calcd. for C42H52N6 [M + H]+
641.4326; found 641.4337.
1
58%) as a white solid. H NMR (400 MHz, CDCl3): δ = 7.62 (dt,
4
3
3JH,H = 8.4, JH,H = 1.6 Hz, 4 H), 7.39 (s, 2 H); 7.22 (dt, JH,H
=
1,4-Bis[2-(4-iodophenyl)ethynyl]-2,5-dihexylbenzene (3)
4
3
8.4, JH,H = 1.6 Hz, 4 H), 5.92 (s, 4 H), 2.83 (t, JH,H = 7.6 Hz, 4
Halide Exchange: A 25 mL two-necked flask was purged with ar-
gon, charged with 1,4-bis[2-(4-bromophenyl)ethynyl]-2,5-dihex-
ylbenzene (2, 100.00 mg, 0.165 mmol, 1 equiv.) and THF
(3.00 mL), and the resulting mixture was cooled to –100 °C. nBuLi
(0.23 mL, 0.350 mmol, 2.12 equiv., 1.6 m in hexane) was slowly
added to the colorless suspension so that the temperature did not
exceed –90 °C. The reaction mixture turned green and then yellow.
The mixture was then stirred for 45 min before more nBuLi
(0.05 mL, 0.080 mmol, 0.5 equiv., 1.6 m in hexane) was added. The
reaction mixture was added dropwise with a syringe to a precooled
(–78 °C) solution of 1,2-diiodoethane (98.7 mg, 0.350 mmol,
2.12 equiv.) in THF (1.50 mL) and stirred overnight. The dark
brown reaction mixture was poured onto an aqueous solution of
Na2S2O3 (15%) under a layer with diethyl ether. The ether layer
was washed twice with an aqueous solution of Na2S2O3 (15%). The
aqueous layer was extracted with diethyl ether (3ϫ10 mL). The
combined organic extracts were dried with MgSO4, filtered and
concentrated under reduced pressure to gave a yellow residue. The
crude product was purified by column chromatography (hexane) to
afford 3, (26.02 mg, 22%) as an off-white solid.
H), 2.06 (s, 12 H), 1.74–1.71 (m, 4 H), 1.43–1.26 (m, 12 H), 0.88
3
(t, JH,H = 6.8 Hz, 6 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
142.6 (2 C, Cq), 132.7 (2 C, Cq), 132.4 (4 C, Ct), 129.3 (2 C, Ct),
129.0 (4 C, Cq), 128.5 (4 C, Ct), 123.0 (2 C, Cq), 122.7 (2 C, Cq),
106.3 (4 C, Ct), 93.4 (2 C, Cq), 89.6 (2 C, Cq), 34.4 (2 C, Cs), 32.0
(2 C, Cs), 30.9 (2 C, Cs), 29.5 (2 C, Cs), 22.9 (2 C, Cs), 14.3 (2 C,
Cp), 13.3 (4 C, Cp) ppm. MS (EI): m/z (%) = 632.4 (100) [M]+.
HRMS (ESI): calcd. for C46H52N2 [M + H]+ 633.4203; found
633.4211.
1,4-Bis{2-[4-(3,3-tetramethylenetriazeno)phenyl]ethynyl}-2,5-di-
hexylbenzene (14)
Pathway
1:
Bis(triphenylphosphine)palladium(II)
chloride
(42.1 mg, 0.06 mmol, 0.06 equiv.), CuI (47.6 mg, 0.25 mmol,
0.2 equiv.) and 1-(4-trimethylsilylethynylphenyl)-3,3-tetramethyl-
enetriazene[48] (13, 679 mg, 2.5 mmol, 2.5 equiv.) were added to a
50 mL Schlenk tube and purged with argon. Benzene (12 mL) and
triethylamine (1.7 mL) were added. The resulting solution was de-
gassed for 10 min and 1,4-dihexyl-2,5-diiodobenzene[45] (4, 498 mg,
1.0 mmol, 1 equiv.)
and 1,8-diazabicyclo[5.4.0]undec-7-ene
(4.48 mL, 30 mmol, 30 equiv.) were added. Water (18 μL,
1.0 mmol, 1 equiv.) was added and the reaction mixture turned
green. The resulting mixture was stirred for 24 h at room tempera-
ture. The reaction mixture was concentrated under reduced pres-
sure and the residue was dissolved in CH2Cl2 (60 mL), extracted
with water (2ϫ20 mL) and washed with brine (30 mL). The or-
ganic layer was then dried with MgSO4, filtered and concentrated
under reduced pressure to afford a red-brown solid. The residue
was purified by column chromatography (hexane/tBME, 2:1 + 3%
triethylamine) to afford 14 (45 mg, 7%) as a yellow powder.
Pyrrole Strategy: A 50 mL two-necked round-bottomed flask was
purged with argon and charged with 1,4-bis{2-[4-(2,5-dimethyl-1H-
pyrrol-1-yl)phenyl]ethynyl}-2,5-dihexylbenzene
(12)
(100 mg,
0.158 mmol, 1 equiv.), MeCN (4.5 mL) and H2SO4 (3.32 mL, 2 m,
6.64 mmol, 42 equiv.). The mixture was cooled to –5 °C. Sodium
nitrite (65.4 mg, 0.948 mmol, 6 equiv.) dissolved in water (1 mL)
was added dropwise at –5 °C and the mixture was stirred overnight
before sodium iodate (189 mg, 1.26 mmol, 8 equiv.) dissolved in
water (1 mL) was added. The reaction mixture was then allowed to
warm to room temperature over 1 h. The mixture was heated
briefly to 60 °C and then stirred at room temperature for 4 h. The
mixture was neutralized with a saturated solution of Na2CO3 and
then extracted with ethyl acetate (3ϫ40 mL). The combined or-
ganic extracts were washed with Na2S2O3 (1 n, 2ϫ50 mL) and
water (20 mL), dried with MgSO4 and concentrated under reduced
pressure. The crude product was purified by column chromatog-
raphy (hexane/tBME, 40:1) to afford 3 (79 mg, 72%) as a white
solid.
Pathway 2: A 25 mL two-necked round-bottomed flask was purged
with argon and charged with 1,4-bis[2-(4-aminophenyl)ethynyl]-
2,5-dihexylbenzene (8, 501 mg, 1.05 mmol, 1 equiv.), water
(1,5 mL), acetonitrile (1.5 mL) and hydrochloric acid (37%,
0.803 mL, 9.45 mmol, 9 equiv.). The resulting mixture was cooled
to 0 °C and stirred for 1 h. A solution of sodium nitrite (145 mg,
2.1 mmol, 2 equiv.) in water (3.5 mL) was added and the mixture
was again stirred for 1 h at 0 °C. The mixture was then transferred
into another flask containing potassium carbonate (1.466 mg,
10.5 mmol, 10 equiv.), water/acetonitrile, 2:1 (3 mL) and pyrrol-
Triazene Strategy: A 10 mL MW-pressure tube was purged with
argon and charged with 1,4-bis{2-[4-(3,3-tetramethylenetriazeno)-
idine (0.345 mL, 4.2 mmol, 4 equiv.). The resulting mixture was phenyl]ethynyl}-2,5-dihexylbenzene (14, 60.9 mg, 0.095 mmol,
stirred for 1 h at 0 °C and a further 2 h at room temperature. The
mixture was then diluted with CH2Cl2 (100 mL). The aqueous
phase was separated and washed with CH2Cl2 (2ϫ50 mL). The
1 equiv.) and iodomethane (4 mL). The sealed tube was heated to
120 °C and stirred for 12 h. The reaction mixture was then concen-
trated under reduced pressure. The residue was dissolved in cyclo-
Eur. J. Org. Chem. 2012, 2738–2747
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2745

L. Chi, M. Mayor et al.
FULL PAPER
hexane and filtered through silica to afford 1,4-bis[2-(4-iodophen-
yl)ethynyl]-2,5-dihexylbenzene (3) (52 mg, 78.2%) as a white solid.
was solved by direct methods by using the program Superflip.
Least-squares refinement against F was carried out on all non-hy-
drogen atoms by using the program CRYSTALS. R = 0.0558 (ob-
3
4
1H NMR (400 MHz, CD2Cl2): δ = 7.73 (dt, JH,H = 8.8, JH,H
=
3
4
2 Hz, 4 H), 7.37 (s, 2 H), 7.26 (dt, JH,H = 8.8, JH,H = 2 Hz, 4 H), served data), wR = 0.1018 (all data), GOF = 1.0652. Minimal/
3
2.80 (t, JH,H = 7.6 Hz, 4 H), 1.70–4.64 (m, 4 H), 1.42–1.31 (m, 12
maximal residual electron density: –1.41/2.39 eÅ–3. Chebychev
polynomial weights were used to complete the refinement. Plots
H), 0.88 (t, JH,H = 6.8 Hz, 6 H) ppm. 13C NMR (100 MHz,
3
CDCl3): δ = 143.0 (2 C, Cq), 138.2 (4 C, Ct), 133.5 (4 C, Ct), 132.9 were produced by using CAMERON.
(2 C, Ct), 123.5 (2 C, Cq), 123.0 (2 C, Cq), 94.6 (2 C, Cq), 93.6 (2
CCDC-849687 (for 1), -849688 (for 2) and -849689 (for 3) contain
C, Cq), 90.3 (2 C, Cq), 34.6 (2 C, Cs), 32.3 (2 C, Cs), 31.2 (2 C, Cs),
29.8 (2 C, Cs), 23.2 (2 C, Cs), 14.5 (2 C, Cp) ppm. MS (EI): m/z
(%) = 697.9 (100) [M+], 572.1 (12.5) [M+ – I].
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Crystal Data
Supporting Information (see footnote on the first page of this arti-
1
cle): H and 13C NMR spectra of compounds 1–3, 8, 12, and 14;
Dichloro-OPE 1: Crystal data for 1: formula C34H36Cl2,
large-area STM images and planar cuts through the crystal struc-
tures of compounds 1–3; experimental procedures of compounds
4, 10, 11 and 13.
M
=
515.57, F(000)
=
274, colorless plate, size
3
¯
0.030ϫ0.070ϫ0.180 mm , triclinic, space group P1, Z = 1, a =
5.6220(7) Å, b = 8.0932(11) Å, c = 15.495(2) Å, α = 86.859(9)°, β
= 83.191(9)°, γ = 87.654(9)°, V = 698.59(16) Å3, dcalcd.
=
1.225 Mg·m–3. The crystal was measured on a Bruker Kappa
Apex2 diffractometer at 123 K by using graphite-monochromated
Mo-Kα radiation with λ = 0.71073 Å, Θmax = 30.032°. Minimal/
maximal transmission 0.98/0.99, μ = 0.253 mm–1. The Apex2 suite
has been used for data collection and integration. From a total of
13850 reflections, 4056 were independent (merging r = 0.050). From
these, 2222 were considered as observed [IϾ2.0σ(I)] and were used
to refine 163 parameters. The structure was solved by direct meth-
ods by using the program Superflip. Least-squares refinement
against F was carried out on all non-hydrogen atoms by using the
program CRYSTALS. R = 0.0402 (observed data), wR = 0.0823 (all
data), GOF = 1.1125. Minimal/maximal residual electron density:
–0.26/0.28 eÅ–3. Chebychev polynomial weights were used to com-
plete the refinement. Plots were produced by using CAMERON.
Acknowledgments
We thank the University of Basel and the Karlsruhe Institute of
Technology for ongoing support. Financial support by the Swiss
National Science Foundation (SNF) and by the Sinergia program
“Electromechanical Systems” of the SNF are gratefully acknowl-
edged. H. W. thanks the support of the China Scholarship Council.
[1] D. Bonifazi, S. Mohnani, A. Llanes-Pallas, Chem. Eur. J. 2009,
15, 7004–7025.
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2010, 22, 3506–3520.
Dibromo-OPE 2: Crystal data for 2: formula C34H36Br2,
M
=
604.47, F(000)
=
310, colorless needle, size
3
¯
0.040ϫ0.060ϫ0.270 mm , triclinic, space group P1, Z = 1, a =
5.7434(8) Å, b = 8.0996(8) Å, c = 15.4925(16) Å, α = 86.096(5)°, β
= 82.539(5)°, γ = 87.253(4)°, V = 712.38(14) Å3, dcalcd.
=
1.409 Mg·m–3. The crystal was measured on a Bruker Kappa Apex2
diffractometer at 123 K by using graphite-monochromated Mo-Kα
radiation with λ = 0.71073 Å, Θmax = 37.784°. Minimal/maximal
transmission 0.84/0.89, μ = 2.866 mm–1. The Apex2 suite has been
used for data collection and integration. From a total of 27787
reflections, 7551 were independent (merging r = 0.033). From these,
4999 were considered as observed [IϾ2.0σ(I)] and were used to
refine 163 parameters. The structure was solved by direct methods
by using the program Superflip. Least-squares refinement against
F was carried out on all non-hydrogen atoms by using the program
CRYSTALS. R = 0.0251 (observed data), wR = 0.0471 (all data),
GOF = 1.0921. Minimal/maximal residual electron density: –0.35/
0.44 eÅ–3. Chebychev polynomial weights were used to complete
the refinement. Plots were produced by using CAMERON.
[8] A. S. Klymchenko, J. Sleven, K. Binnemans, S. De Feyter,
Langmuir 2006, 22, 723–728.
[9] T. Takami, D. P. Arnold, A. V. Fuchs, G. D. Will, R. Goh,
E. R. Waclawik, J. M. Bell, P. S. Weiss, K.-I Sugiura, W. Liu, J.
Jiang, J. Phys. Chem. B 2006, 110, 1661–1664.
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Veciana, D. Ruiz-Molina, Chem. Commun. 2006, 2866–2868.
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H. Uji-i, M. Sonoda, K. Hirose, F. C. De Schryver, S.
De Feyter, Y. Tobe, J. Am. Chem. Soc. 2008, 130, 6666–6667.
[12] S. Lei, K. Tahara, X. Feng, S. Furukawa, F. C. De Schryver,
K. Müllen, Y. Tobe, S. De Feyter, J. Am. Chem. Soc. 2008, 130,
7119–7129.
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F. C. De Schryver, Y. Tobe, S. De Feyter, J. Am. Chem. Soc.
2006, 128, 3502–3503.
Diiodo-OPE 3: Crystal data for 3: formula C37H42I2, M = 740.55,
F(000) = 740, colorless block, size 0.040ϫ0.130ϫ0.230 mm3, tri-
[14] Z. Mu, L. Shu, H. Fuchs, M. Mayor, L. Chi, Langmuir 2011,
¯
clinic, space group P1, Z = 2, a = 7.2908(9) Å, b = 15.0277(16) Å,
27, 1359–1363.
[15] Z. Mu, L. Shu, H. Fuchs, M. Mayor, L. Chi, J. Am. Chem.
Soc. 2008, 130, 10840–10841.
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8725–8726.
c = 15.3177(15) Å, α = 88.906(6)°, β = 78.977(7)°, γ = 82.784(7)°,
V = 1634.2(3) Å3, dcalcd. = 1.505 Mg·m–3. The crystal was measured
on a Bruker Kappa Apex2 diffractometer at 123 K by using graph-
ite-monochromated Mo-Kα radiation with λ = 0.71073 Å, Θmax
=
30.242°. Minimal/maximal transmission 0.78/0.93, μ = 1.947 mm–1.
The Apex2 suite has been used for data collection and integration.
From a total of 32598 reflections, 9576 were independent (merging
r = 0.055). From these, 5270 were considered as observed
[IϾ2.0σ(I)] and were used to refine 353 parameters. The structure
2746
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 2738–2747

Investigations on Oligo-Phenylene-Ethynylenes
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Received: January 11, 2012
Published Online: April 4, 2012
Eur. J. Org. Chem. 2012, 2738–2747
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