Columnar self-assembly in electron-deficient heterotriangulenes

Article abstract of DOI:10.1002/chem.201300253

A series of soluble carbonyl-bridged heterotriangulenes, in which flexible n-dodecyl chains are attached through different spacers to the planar nitrogen-centered polycyclic core, have been synthesized. The introduction of triisopropylsilylethynyl moieties enabled, for the first time, the characterization of single-crystal columnar packing of a substituted heterotriangulene by X-ray crystallography. Electrochemical studies disclosed the carbonyl-bridged heterotriangulene core as a reasonably strong acceptor for a reversible two-electron transfer. The tendency of substituted heterotriangulenes to self-assemble in solution, on surfaces, and in the bulk appeared to sensitively depend on the nature of the lateral substituents, their steric demand, and the applied solution processing conditions. It can be concluded that 1) additional phenylene moieties between the heterotriangulene core and the n-dodecyl chains facilitate self-assembly by extending the π-conjugated polycyclic disc, 2) the rod-like ethynylene spacers introduce some additional flexibility and hence lower the overall aggregation tendency, and 3) the combination of both features in the phenylene-ethynylene moieties induces thermotropic liquid crystallinity. Playing the triangle: A series of electron-deficient heterotriangulenes with pendant alkyl chains has been synthesized and their propensity for self-assembly in solution, on a surface, and in the bulk was studied (see figure). A pronounced dependence of the self-assembly behavior on the nature of the spacer between the rigid heterotriangulene core and the flexible alkyl chains was identified. Copyright

Full text of DOI:10.1002/chem.201300253

FULL PAPER
DOI: 10.1002/chem.201300253
Columnar Self-Assembly in Electron-Deficient Heterotriangulenes
Milan Kivala,*[a, c] Wojciech Pisula,[a] Suhao Wang,[a] Alexey Mavrinskiy,[a]
Jean-Paul Gisselbrecht,[b] Xinliang Feng,[a] and Klaus Mꢀllen*[a]
Abstract: A series of soluble carbonyl-
bridged heterotriangulenes, in which
flexible n-dodecyl chains are attached
through different spacers to the planar
nitrogen-centered polycyclic core, have
been synthesized. The introduction of
triisopropylsilylethynyl moieties ena-
bled, for the first time, the characteri-
zation of single-crystal columnar pack-
ing of a substituted heterotriangulene
by X-ray crystallography. Electrochem-
ical studies disclosed the carbonyl-
bridged heterotriangulene core as a
reasonably strong acceptor for a rever-
sible two-electron transfer. The tenden-
cy of substituted heterotriangulenes to
self-assemble in solution, on surfaces,
and in the bulk appeared to sensitively
depend on the nature of the lateral
substituents, their steric demand, and
the applied solution processing condi-
tions. It can be concluded that 1) addi-
tional phenylene moieties between the
heterotriangulene core and the n-do-
decyl chains facilitate self-assembly by
extending the p-conjugated polycyclic
disc, 2) the rod-like ethynylene spacers
introduce some additional flexibility
and hence lower the overall aggrega-
tion tendency, and 3) the combination
of both features in the phenylene–ethy-
nylene moieties induces thermotropic
liquid crystallinity.
Keywords: electrochemistry · het-
ACHUTNGRENeNUG roACHTUNGTRENtNGUN riangulenes · liquid crystals ·
polycyclic aromatic hydrocarbons ·
self-assembly
Introduction
ing materials in organic field-effect transistors (OFETs) and
photovoltaics.[4,5]
Rigid p-conjugated discs decorated with lateral flexible
alkyl substituents are known to self-assemble into columnar
superstructures driven by co-facial p–p stacking and local
phase separation between the rigid core and the flexible
substituents.[1] The alkyl chains ensure solubility, which is
important for easy material processing, and more important-
ly, allow for facile control over the thermotropic liquid crys-
talline behavior and self-assembly on surfaces.[2,3] The effi-
cient p-orbital overlap of neighboring molecules in such col-
umnar aggregates enables one-dimensional (1D) charge-car-
rier transport, which qualifies these systems as semiconduct-
Whereas the vast majority of known organic semiconduct-
ing materials are based on electron-rich, p-type conjugated
cores (hole-transporting), such as triphenylenes,[6] hexa-peri-
hexabenzocoronenes, and even larger polycyclic aromatic
hydrocarbons (PAHs),[3,4a] their n-type counterparts (elec-
tron-transporting) are still rather scarce. Rylene diimides[7]
and hexaazatriphenylene derivatives[8] are the most promis-
ing candidates among various electron-deficient scaffolds in-
vestigated to date. Efficient and stable n-type materials are
essential for p-n junction diodes, organic photovoltaics, and
complementary organic circuits with greater operation
speed and lower power dissipation.[9] However, in spite of
considerable research efforts in this area, n-type organic
semiconductors suitable for real-world applications remain
rather scarce owing to their often limited stability and poor
solubility. To realize useful n-type materials, functionaliza-
tion of intrinsically p-type acenes, oligothiophenes, phenyl-
enes, and larger PAHs with electron-withdrawing moieties,
such as cyano, fluoro, perfluoroalkyl, imide, and carbonyl
groups, is usually applied.[10]
[a] Dr. M. Kivala, Dr. W. Pisula, S. Wang, Dr. A. Mavrinskiy,
Dr. X. Feng, Prof. Dr. K. Mꢀllen
Max Planck Institute for Polymer Research
Ackermannweg 10, 55128 Mainz (Germany)
Fax : (+49)6131-379-350
E-mail: muellen@mpip-mainz.mpg.de
[b] Dr. J.-P. Gisselbrecht
Laboratoire dꢁElectrochimie
et de Chimie Physique du Corps Solide
Institut de Chimie–UMR 7177, C.N.R.S
Universitꢂ de Strasbourg, 4, rue Blaise Pascal
67081, Strasbourg Cedex (France)
For example, the propeller-shaped triphenylamine moiety
was locked into a virtually planar conformation by the intro-
duction of sp3-hybridized dimethylmethylene tethers without
affecting its electron-rich nature.[11] The resulting compound
[c] Dr. M. Kivala
Present address: Department Chemie und Pharmazie
Friedrich-Alexander-Universitꢃt Erlangen-Nꢀrnberg
Henkestrasse 42, 91054 Erlangen (Germany)
E-mail: milan.kivala@fau.de
1a (4,4,8,8,12,12-hexamethyl-4H,8H,12H-benzo
ACHTUNGERTN[NUNG 1,9]ACHTUNGTRENNUNGquinACHTUNGTRENNUNGoACHTUNGTRENNUNGli-
A
ACHTUNGTRENNUNG
been shown to act, after appropriate functionalization, as a
promising hole-transporting and hole-injecting material with
excellent thermal and morphological stability, useful for or-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201300253.
Chem. Eur. J. 2013, 00, 0 – 0
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ganic light-emitting devices.[12] Although the dimethylmethy-
lene bridges improve the materials properties and processa-
bility, they disrupt full p-conjugation within the polyaromat-
ic core. The replacement of these tetrahedral moieties by
carbonyl groups leads to a perfectly planar heterotriangu-
bridging carbonyls thus leading to various undesired prod-
ucts. The Suzuki–Miyaura coupling of 7 with 4-dodecylphen-
ylboronic acid[17] catalyzed by palladium(II) acetate with
2-dicyclohexylphosphino-2’,6’-dimethoxybiphenyl (SPhos)
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ligand delivered 3 in a moderate yield of 43%.[18] Although
several catalytic systems and various reaction conditions
have been explored, higher yields of 3 could not be ob-
tained. Also, the attempted Pd-catalyzed Negishi cross-cou-
pling of 7 with 4-dodecylphenylzinc bromide afforded 3 in
only 21% yield. The ethynylated derivatives 4–6 were ob-
tained in good yields ranging from 73 to 88% by the Sono-
gashira cross-coupling of iodinated 7 with the corresponding
terminal alkyne.[19] In addition, derivative 8 decorated with
the triisopropylsilyl (TIPS)-ethynyl moieties has been syn-
thesized to investigate the solid-state molecular structure of
a substituted heterotriangulene. The TIPS groups are known
to provide sufficient solubility, whereas at the same time, fa-
cilitate the growth of single crystals suitable for X-ray crys-
tallographic analysis (see below).[20]
lene scaffold 1b (4H,8H,12H-benzo
ACHTUNGTREN[UNG 1,9]ACHTUNTGRENqNNGU uinACHTNUTRGENNUNGoHCATUNGTRENUNlNG iACHTUNTGERNUGzN ino-
ACHTUNGTRENNUNG
electron-withdrawing carbonyls greatly reduce the electronic
density of its p-conjugated framework, which makes it po-
tentially interesting as a building block for the construction
of various n-type discotic mesogens. Recently, several star-
shaped derivatives of 1b with peripheral carbazole moieties
for the application in organic light-emitting diodes
(OLEDs) have been prepared and their photophysical and
redox properties studied.[14] Also, derivatives of 1b decorat-
ed with 4-alkoxyphenylethynyl substituents of different alkyl
chain lengths showing a pronounced ability to form one di-
mensional (1D) nano- and microstructures by self-assembly
have been synthesized. We have recently reported on fiber
growth of the n-dodecyl-substituted threefold symmetric
heterotriangulene 2 induced by a solution-based dip-coating
method.[15]
All newly prepared compounds 2–6 and 8 form yellow to
orange solids that are stable at ambient temperature under
air and are reasonably soluble in most organic solvents, with
the exception of methanol or acetone. Consequently, com-
pounds 2–6 and 8 were purified by column chromatography
(SiO2, hexanes/CH2Cl2 mixtures) followed by precipitation
from CH2Cl2 solutions upon addition of MeOH (for 2–6).
The identity of 2–6 and 8 was confirmed by MALDI-TOF
mass spectrometry, which displayed the corresponding mo-
1
lecular ion, H and 13C NMR spectroscopy, elemental analy-
sis, and X-ray crystallography (for 8).
Single crystals of 8 suitable for X-ray crystallographic
analysis were obtained by slow diffusion of hexanes into
CH2Cl2 solution at 258C (Figure 1a). The compound crystal-
Stimulated by these promising findings, we report herein
the synthesis and properties of a series of new heterotrian-
gulene derivatives 2–6 bearing flexible n-dodecyl chains at-
tached through different spacers to the polycyclic core. The
thermotropic and self-assembly properties of these com-
pounds have been studied to gain an insight into the rela-
tionships between the molecular structure and the resulting
propensity for self-assembly.
¯
lizes in the triclinic space group P1 with two independent
molecules of 8 in the unit cell (denoted as A and B). The
N-centered heterotriangulene core in the two independent
molecules is practically planar with a maximum deviation
from the corresponding mean plane passing through the
atoms C11-C23-C17 of about 0.17 and 0.11 ꢅ, respectively.
The angles at the nitrogen atoms add up to 360.08 in both
independent molecules, which indicates no pyramidalization
À
Results and Discussion
at these atoms. Furthermore, the average N CACTHNGUTERNNUG
(sp2) bond
length of 1.41 ꢅ does not differ significantly from that in tri-
ꢀ À
Synthesis: As shown in Scheme 1, the key building block for
the synthesis of all substituted heterotriangulenes 2–6 is the
iodinated compound 7, which was prepared according to the
literature.[14] All reactions involving 7 were performed in tol-
uene at elevated temperatures to enhance its solubility.
Thus, the n-dodecyl-substituted derivative 2 was prepared
by the Pd-catalyzed Negishi cross-coupling of 7 with n-do-
ACTHNGUTERNNUG
phenylamine (1.42 ꢅ).[21] The peripheral C C C(sp2) moiet-
ies are slightly bent as expressed by the corresponding bond
angles ranging from 172.2 to 175.48. This is presumably due
to crystal packing effects induced by the sterically demand-
ing TIPS groups. The independent molecules within the
asymmetric unit are virtually parallel to each other with an
average distance of 3.35 ꢅ and an offset angle of 22.38
A
N
ACHTUNGTREN(NGNU Figure 1b). These values are in good agreement with
here that the attempted Pd-catalyzed Kumada cross-cou-
pling of 7 with the corresponding Grignard reagent deliv-
ered only a complex mixture of products. Taking into ac-
count the higher nucleophilicity of the organomagnesium
species when compared to its organozinc counterpart it can
be assumed that n-dodecylmagnesium bromide attacks the
3.46 ꢅ and 21.18, respectively, observed in the p-stacks con-
sisting of the unsubstituted heterotriangulene 1b.[13b] In con-
trast to 1b, however, the molecules of 8 are rotated by 608
with respect to each other to minimize the contacts between
the bulky TIPS moieties (Figure 1b). In the crystal, the mol-
ecules of 8 pack in “stair-like” p-stacks in which the asym-
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Columnar Self-Assembly
FULL PAPER
Scheme 1. Synthesis of substituted heterotriangulene discs 2–6 and 8. a) n-C12H25ZnBr (0.5m in THF), [PdCl2ACHTUNGTRENNUNG
(dppf)]·CH2Cl2, toluene, 608C, 23 h, 80%
2A(PPh3)2], CuI, iPr2NH, toluene,
(PPh3)2], CuI, iPr2NH, toluene, THF, 708C, 21 h, 85% (5). e) 1,3-Bis(dodecyloxy)-4-ethynyl-
(PPh3)2], CuI, iPr2NH, toluene, 708C, 24 h, 73% (6). f) Triisopropylsilylacetylene, [PdCl2A(PPh3)2], CuI, iPr2NH, toluene, 608C, 17 h, 87%
(8). SPhos=2-dicyclohexylphosphino-2’,6’-dimethoxybiphenyl; dppf=1,1’-bis(diphenylphosphino)ferrocene.
(2). b) 4-Dodecylphenylboronic acid, [Pd
708C, 48 h, 88% (4). d) 1-Dodecyl-4-ethynylbenzene, [PdCl
benzene, [PdCl2A
A
CHTUNGTRENNUNG
CTHUNGTRENNUNG
C
CHTUNGTRENNUNG
metric unit repeats with an average distance of 3.24 ꢅ
(Figure 1c).
the star-shaped heterotriangulenes with carbazole donors.[14]
N
In that case, the longest-wavelength absorption maxima
were assigned to the intramolecular charge-transfer interac-
tions between the electron-deficient heterotriangulene core
and the lateral donors.
UV/Vis spectroscopy: The UV/Vis absorption spectra of the
substituted heterotriangulenes 2–6 and 8 in chloroform
A
To prove the aggregation tendency of the substituted het-
erotriangulenes in solution, concentration-dependent
UV/Vis absorption spectra (concentration range from 7ꢆ
10À5 to 1ꢆ10À7 m) of the n-dodecyl derivative 2 were record-
ed at room temperature in chloroform. Whereas the intensi-
ty of both absorption maxima of 2 at 267 and 427 nm in-
creased with concentration, no shifts or new bands originat-
ing from the aggregate formation were observed within the
studied concentration range (see the Supporting Informa-
tion). Nevertheless, the pronounced deviation from the
from the p–p* transitions of the heterotriangulene core and
the lateral p-conjugated substituents (Figure 2).[13] The addi-
tional lower energy absorption bands appear in all cases
bathochromically shifted when compared with the unsubsti-
tuted parent heterotriangulene 1b with a lmax of 411 nm
(3.02 eV).[13a] This reflects the extension of the p-conjugated
system upon the attachment of the peripheral substituents
and, in the same time, their electron-donating ability, which
is in agreement with the behavior reported previously for
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M. Kivala, K. Mꢀllen et al.
Figure 1. a) Molecular structure of 8 (molecule A), arbitrary numbering, hydrogen atoms omitted for clarity. Atomic displacement parameters obtained
at 153 K are drawn at the 50% probability level. Selected bond lengths (ꢅ) and bond angles (8): C1-C2 1.219(8), C1-C11 1.439(8), C11-C12 1.394(7),
C12-C13 1.387(7), C13-C14 1.469(7), C13-C29 1.406(7), C14-O1 1.237(6), C29-N1 1.398(6), C2-C1-C11 173.6(5), C29-N1-C30 120.7(4), C15-C14-C13
115.7(5). b) Arrangement of the two independent molecules (A and B) in the asymmetric unit of 8. c) Columnar arrangement of neighboring molecules
in the crystal packing of 8 showing co-facial p–p interactions.
1
evidenced by concentration-dependent H NMR spectrosco-
py (see below).
Electrochemistry: The redox properties of the substituted
heterotriangulenes 2–6 and 8 were studied by cyclic voltam-
metry (CV) and rotating disc voltammetry (RDV). The
measurements were carried out in CH2Cl2 with n-Bu4NPF6
(0.1m) as the supporting electrolyte. All potentials are given
against the Fc+/Fc (ferrocenium/ferrocene) couple as an in-
ternal reference and are summarized in Table 1.
Most of the studied heterotriangulenes gave well-resolved
voltammograms with the irreversible oxidations near the
electrolyte discharge (see the Supporting Information). For
compounds 5 and 6, electrode inhibition due to the forma-
tion of insoluble reduction products hindered the full elec-
trochemical characterization. By comparing the oxidation
potential of 6 (+0.95 V) with that of methoxyphenyl-substi-
Figure 2. UV/Vis absorption spectra of heterotriangulenes 2–6 and 8 re-
corded in CHCl3 at room temperature. Given are the maxima of the lon-
gest-wavelength absorption bands.
tuted tetraethynylethenes, which showed an irreversible oxi-
dation step at +0.98 V,[22] it can be concluded that the ob-
served electron-transfer corresponds to the oxidation of the
3,5-bis(dodecyloxy)phenyl donors in 6. To the best of our
Beer–Lambert law, expressed as the nonlinearity of the con-
centration-versus-absorbance plot, suggested the occurrence
of self-association phenomena in solution which was further
knowledge, the redox behavior of the central nitrogen atom
in the insoluble parent heterotriangulene 1b has not been
described to date. Interestingly, the related triphenylamine-
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Columnar Self-Assembly
FULL PAPER
Table 1. Cyclic voltammetry (CV; scan rate v=0.1 VsÀ1) and rotating
disk voltammetry (RDV) data of compounds 2–6, 8 and 9 in CH2Cl2
(with 0.1m n-Bu4NPF6).[a]
Self-assembly in solution: The pronounced deviation from
the Beer–Lambert law observed for 2 by using concentra-
tion-dependent UV/Vis spectroscopy indicated its propensi-
ty for self-assembly in chloroform. This finding stimulated
us to further investigate the solution behavior of 2–5 by
1H NMR spectroscopy in 1,1,2,2-[D2]tetrachloroethane be-
tween 10À1 and 10À5 m at 303 K.[3b,26] In general, the ring cur-
rent induced within the aromatic core influences the reso-
nances of the neighboring molecules and as the disc-shaped
polyaromatic molecules tend to aggregate in an offset face-
to-face arrangement; this self-aggregation leads to an up-
CV
RDV
E8
DEp
Ep
E1/2
Slope
[V][b]
[mV][c]
[V][d]
[V][e]
[mV][f]
2
+1.43
À1.61
À1.81
À1.57
À1.76
À1.48
À1.74
À1.37
À1.73
70
75
70
60
60
80
85
140
À1.66 (1eÀ)
À1.86 (1eÀ)
À1.60 (1eÀ)
À1.79 (1eÀ)
À1.47 (1eÀ)
À1.75 (1eÀ)
À1.40 (1eÀ)
À1.84[g]
65
60
60
60
60
80
50
3
4
5
6
8
1
field shift of the aromatic H NMR resonances.
From our investigations, the following features become
obvious: 1) the chemical shifts of the heterotriangulene pro-
tons showed a distinct concentration dependence (Figure 3),
2) the more distant a-CH2 units of the n-dodecyl chains re-
mained almost unaffected (see the Supporting Information),
and 3) the electron-withdrawing nature of the carbonyl-
bridged core was further illustrated by a downfield shift of
d=0.3 ppm of the directly attached a-CH2 resonances in 2
relative to 3–5 with various spacers. For compound 3, bear-
ing the 4-dodecylphenyl moieties, a dramatic upfield shift of
d=1.6 ppm was observed for the heterotriangulene protons
upon increasing the concentration from 10À5 (d=9.3 ppm)
to 10À1 m (d=7.7 ppm). Also an upfield shift of d=0.2 ppm
for the a-CH2 units in 3 was the largest of all studied com-
pounds. The enlargement of the p-conjugated core by the
peripheral phenylene moieties in 3 makes the co-facial p–p
interactions more efficient, which is in agreement with the
previously observed behavior of extended n-dodecylphenyl-
substituted hexa-peri-hexabenzocoronenes.[3c] Interestingly,
the additional p-conjugated acetylenic spacers between the
heterotriangulene core and the 4-dodecylphenyl unit did not
further enhance the aggregation tendency. Thus, only an up-
field shift of d=0.8 ppm was observed for the heterotriangu-
lene protons in 5 within the studied concentration range.
+0.95
À1.47
+1.44
À1.58
70
À1.44
À1.64
80
70
À1.44 (1eÀ)
À1.66 (1eÀ)
75
65
9[h]
+1.00
[a] All potentials are given versus the Fc+/Fc couple
used as internal standard. [b] E8=(Epc +Epa)/2, in
which Epc and Epa correspond to the cathodic and
anodic peak potentials, respectively. [c] DEp =EpaÀEpc.
[d] Ep =Irreversible peak potential. [f] Slope=Slope
of the linearized plot of E versus log[I/
G
which Ilim is the limiting current and I the current.
[g] Small amplitude signal compared with the first re-
duction. [h] Taken from ref. [23].
derived heterohelicene 9 involving two bridging carbonyls
was oxidized to the corresponding radical cation at approxi-
mately +1.00 V.[23,24] This corresponds to an anodic shift of
more than 400 mV induced by the insertion of the third car-
bonyl bridge when going from helical 9 to planar 2 (+1.43)
or 8 (+1.44 V). Even more dramatic is the comparison be-
tween triphenylamine, forming an unstable radical cation at
0.53 V,[12c] and the heterotriangulenes 2 and 8. The introduc-
tion of the three electron-withdrawing carbonyl moieties
with the concurrent planarization of the triphenylamine
scaffold results in a spectacular anodic shift of more than
900 mV.
Except compound 6, all studied species displayed two re-
versible one-electron reduction steps located at the hetero-
triangulene core (Table 1, see the Supporting Information).
Considering the development of the reversible first reduc-
tion potentials on going from 4-dodecylphenylethynyl-sub-
stituted 5 (À1.37) to 2 (À1.61 V) decorated with the n-do-
decyl moieties it can be established that 1) the extension of
the p-conjugated framework with the electron-withdrawing
acetylenic spacers in 4 (À1.48), 5 (À1.37), and 8 (À1.44 V)
facilitates the first one-electron uptake and 2) the n-dodecyl
moieties acting as moderate electron-donors attached direct-
ly to the heterotriangulene core in 2 (À1.61 V) shift the first
reduction cathodically. Overall, the substituted heterotrian-
gulenes 2–6 and 8 act as fairly strong reversible two-elec-
tron-acceptors comparable with, for instance, 9,10-anthra-
quinone, which is reduced at approximately À1.40 V under
similar conditions.[25]
Figure 3. Concentration-dependent 1H NMR chemical shifts of the pro-
tons located at the heterotriangulene core in 2–5 recorded at 303 K in
1,1,2,2-[D2]tetrachloroethane; the lines are eye guides.
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M. Kivala, K. Mꢀllen et al.
The comparably flat concentration dependence of
d=0.4 ppm observed for 2 bearing the n-dodecyl chains at-
tached directly to the heterotriangulene core further sup-
ports the fact that extended discs undergo p–p interactions
more efficiently,[2] which is further corroborated by the re-
sults of self-assembly studies on surfaces and in the bulk
(see below).
and 5 on the surface, solvent vapor diffusion (SVD) was
used. This procedure is based on exposing a drop-cast solu-
tion to a saturated solvent vapor atmosphere in an airtight
container. One of the advantages of SVD is the fine adjust-
ment of the evaporation rate of the solution by the right
choice of the saturated solvent vapor. It has been shown
that this can significantly reduce the dewetting effect, which
causes discontinuous patches and aggregates during drop-
casting.[27] The fibrous microstructures obtained after SVD
for 3 and 4 are rather similar due to the comparable steric
demand of the substituents (Figure 4a and c). Under the
same processing conditions the fibers observed by AFM for
3 are only slightly longer than for 4 (Figure 4d and f). Since
the acetylenic spacer is smaller than the phenylene moiety,
one could expect growth of longer fibers for 4. Interestingly,
this finding is in line with the lower clearing point deter-
mined for 4 by differential scanning calorimetry (DSC) sug-
gesting indeed higher steric impact of the acetylene-based
substituents on the reduction of the molecular interactions.
This variation might be related to somewhat more flexible
alkyl chains attached at the acetylene spacer in comparison
to the rigid phenylene ring. This observation is also in good
agreement with the results obtained by concentration-de-
pendent 1H NMR spectroscopy (see above).
In contrast to 3 and 4, the 4-dodecylphenylethynyl-substi-
tuted compound 5 is liquid crystalline at ambient tempera-
tures (see below). Correspondingly, the microstructure ob-
tained for 5 differs significantly from the fibers observed for
3 and 4. An identical tribal-shaped pattern has been previ-
ously reported for hexa-peri-hexabenzocoronene-perylene
diimide (HBC-PDI) dyad, which showed also a liquid crys-
talline (LC) phase already at ambient temperatures.[27] In
both cases, the microstructure consists of a continuous phase
with almost infinite branches that are well interconnected
with each other. We assume that this might be a general
phenomenon after SVD for ambient temperature LCs. Pre-
sumably spinodal dewetting is responsible for the formation
of this kind of microstructure on the surface.[28]
Self-assembly on surfaces: After having gained information
about the solution behavior of the heterotriangulenes 2–5,
we became interested in how these results translate into
their self-assembly during the solution deposition on sur-
ACHTUNGTRENNUNGfaces. This is an important aspect, as the nano- and micro-
structures obtained by solution processing of organic materi-
als are of potential use in molecular electronics. The images
obtained from the optical microscopy (OM) studies and by
using atomic force microscopy (AFM) experiments in the
tapping mode are summarized in Figure 4. When the thin
films were prepared by dip-coating from a chloroform solu-
tion onto SiO2 substrate, only n-dodecyl-substituted
2
formed long-range well-aligned fibers.[15] In contrast, for 3,
4, and 5, only macroscopically disordered patches were ob-
served (see the Supporting Information). The sterically
more-demanding substituents in 3–5 most likely reduce the
molecular interactions and hence lead to less-defined self-
assembly on surfaces. To enhance the self-assembly of 3, 4,
Thermotropic properties: To investigate the technologically
relevant columnar self-assembly of the substituted hetero-
triangulenes 2–6 in the bulk, we first determined their ther-
mal properties by differential scanning calorimetry (DSC;
Table 2). The DSC scans point towards to a strong impact of
the length of the spacer between the aromatic core and the
n-dodecyl chains on the thermal behavior (see the Support-
ing Information). For example, the clearing point increases
with a longer spacer from 93 for 2 to 1588C for 5 carrying
the phenylene–ethynylene bridge. The extension of the
spacer decreases the steric demand of the side chains and in
this way improves the molecular p-stacking interactions.
The comparison between 4 and 3 indicates that also the type
of the spacer plays a significant role. Despite the compara-
ble length, compound 3 carrying the more rigid phenylene
shows a significantly larger increase in the clearing tempera-
ture than 4 with the ethynylene spacer. Moreover, multiple
crystalline phase transitions appear for the latter. The phen-
Figure 4. OM and AFM images of films obtained by SVD of a), b) 3, c),
d) 4, and e), f) 5. The scale bars correspond to 20 mm in the OM and
5 mm in the AFM images.
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Columnar Self-Assembly
FULL PAPER
Table 2. Thermal data obtained from the second DSC heating cycle at a
rate of 108C minÀ1. The assignment of the phases is based on the results
from 2D-WAXS and POM.
The optical textures of 5 and 6 differ significantly from
those obtained for the purely crystalline compounds 2–4.
Both derivatives reveal a LC texture with a typical dendritic
morphology (Figure 6a). Further cooling of 5 into the crys-
T
Enthalpy
[JgÀ1
Phase
[8C]
G
]
transition
2
3
4
93
152
48
À54.6
À34.5
À5.9
À21.7
À25.8
À26.8
À5.5
À1.1
–
Cr–I
Cr–I
Cr1–Cr2
Cr2–Cr3
Cr3–I
Cr–Colh
Colh–I
Colh–Colh
Colh–I
85
111
127
158
57
5
6
240[a]
[a] Determined by POM. Abbreviations: Cr=crystalline; Colh =col-
ACHTUNGTRENNUNGumnar hexagonal liquid crystalline; I=isotropic.
ACHTUNGTRENNUNGylene–ethynylene moiety in 5 induces a liquid crystalline
(LC) phase at elevated temperatures, whereas increasing the
alkyl chain fraction in 6 lowers the LC phase even down to
ambient temperatures.
The assignment of the phases was performed on the basis
of optical textures obtained by polarized optical microscopy
(POM) for thin films sandwiched between two glass slides
and subsequently cooled from the isotropic phase by
Figure 6. POM images of 5 at a) 1408C and b) 308C, c) 6 at 308C, and
d) schematic illustration of the homeotropic alignment.
ACHTUNGTRENNUNG
0.18C minÀ1. The POM images for 2 and 3 show characteris-
tic crystalline, highly birefringent textures (Figure 5a and b).
talline phase results in a characteristic high birefringent
image (Figure 6b). The lack of birefringence in the LC
phases between crossed polarizers of both compounds
AHCTUNGTREG(NNUN Figures 6a and c) indicates a homeotropic alignment in
which the molecules adopt a face-on arrangement and the
columns are oriented along the normal axis towards the sur-
face ACHTNUGRTNEUNG
(Figure 6d).[29] The mechanism for this spontaneous
self-alignment is still discussed in literature. However, it
should be noted that both 5 and 6 carry the most bulky sub-
stituents in comparison to the other three derivatives 2–4.
Initially, it was expected that homeotropic alignment of dis-
cotics towards the surface is rather rare behavior. Recently,
Geerts and co-workers found that “just” a mesophase is nec-
essary for this characteristic arrangement of the mole-
cules.[30] This observation is in line with our study: com-
pounds 5 and 6 show a LC phase, whereas 2, 3, and 4 are
purely crystalline. We conclude from this series that the het-
erotriangulene-based discotics align homeotropically when
an LC phase is present.
To characterize the solid-state organization, we oriented
each compound macroscopically by extrusion into a fiber,
mounted the fiber vertically towards a 2D detector and in-
vestigated it by wide-angle X-ray scattering (WAXS); exper-
imental details can be found elsewhere.[3a] Typically, disc-
shaped molecules assemble into the columnar structures,
which are oriented along the extrusion direction.
Figure 5. POM images of a) 2, b) 3 both at 308C, and 4 at c) 308C and
d) 1008C.
For 2, crystalline band-like structures are visible, whereas
macroscopically large spherulites appear for 3. Both textures
do not change after crystallization from the isotropic melt.
Compound 4 reveals also a typical crystalline optical texture
at 308C (Figure 5c), however, above the phase transition at
858C a mixture of small crystalline needles and LC textures
of circular, but also elongated, domains is identified
(Figure 5d). This minor difference between the high and
low temperature crystalline state of 4 is also obvious in the
X-ray scattering results discussed below.
The 2D-WAXS data confirm the high crystallinity for 2–4,
which are organized in a typical herringbone fashion within
the columnar structures (Figure 7a–c). For all three cases,
the wide-angle reflection in the meridional plane of the 2D
pattern and at the off-meridional positions indicate the mo-
lecular tilting towards the stack axis.[31] Thereby, the intensi-
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M. Kivala, K. Mꢀllen et al.
Compound 5 reveals more versatile thermotropic proper-
ties (Figure 8). Before annealing at high temperature, the
molecules form a staggered arrangement in a non-tilted
Figure 8. 2D-WAXS patterns and the corresponding models for the or-
ganization of 5 at a) 308C before annealing, b) 1408C and c) 308C after
annealing (side chains are omitted for clarity).
fashion within the stacks (Figure 8a). An additional reflec-
tion corresponding to a spacing of 0.68 nm appears in the
meridional plane, which is twice the simple p-stacking dis-
tance of 0.34 nm. This indicates that every second molecule
possesses an identical positional order resulting from a mo-
lecular rotation by 608 of the C3-symmetric discs towards its
neighbor and hence the corresponding phase is assigned as
plastic crystalline.[2a,32] The observed arrangement strongly
resembles the single crystal packing of 8 decorated with the
bulky triisopropylsilylethynyl moieties (see above).
In the liquid crystalline phase at 1278C, the staggered
packing diminishes, while the molecules adopt a characteris-
tic mesophase packing (Figure 8b). Upon cooling the
sample back, however, the initial organization is not recov-
ered. Instead, a well-ordered crystalline herringbone pack-
ing is formed as described above for 2–4 (Figure 8c). Thus,
two different packing motifs are obtained for 5 when pro-
Figure 7. 2D-WAXS patterns of a) 2, b) 3 both at 308C, and 4 at c) 308C
and d) 1008C.
ty of these off-meridional scattering intensities varies be-
tween the compounds due to differences in intracolumnar
order. Interestingly, the reflections for 4 attributed to the
molecular packing are slightly blurred in the high-tempera-
ture crystalline phase above 858C (Figure 7d). This observa-
tion is in agreement with the POM image in Figure 4d,
which slightly differs from the low-temperature crystalline
state. We assume that the molecular motion, especially of
the alkyl side chains, increases at higher temperature. How-
ever, due to the molecular tilting and the large number of
higher order reflections, we assigned this phase as crystal-
line. The small-angle reflections on the equatorial plane are
related to the columnar arrangement. The positions of the
reflections are used to determine the 2D unit cell, which de-
scribes the intercolumnar organization (Table 3).
AHCTUNGTREGcNNNU essed from solution or after thermal treatment. This is
quite uncommon, because typically processing can only
affect the mesoscopic organization and not the molecular ar-
rangement. We assume that during cooling from the meso-
phase the n-dodecyl side chains crystallize and induce tilting
of the molecules. When the compound is processed from
solution, the alkyl chains are rather disordered, as indicated
by the amorphous halo in the 2D-WAXS pattern in Fig-
ure 8a. This permits a more favorable arrangement of the
triangular discs to each other resulting in the staggered or-
ganization. This example also emphasizes the important role
of the side chain crystallinity on the packing. Initially, we
have expected a staggered packing for the whole compound
series. However, because 2–4 are typical crystals, only a her-
ringbone organization is found. Due to the bulky 3,5-bis(do-
Table 3. Unit-cell parameters derived from 2D-WAXS measurements for
each phase.
Phase
Unit cell
2D parameter
[nm]
Packing
[nm][a]
2
3
4
Cr
Cr
square
oblique
a=2.28
0.37 (ꢁ408)
a=3.25; b=2.05; g=1058
a=3.22; b=1.97
a=3.23; b=1.83
a=3.29; b=1.84; g=978
a=2.60; b=2.10
a=3.46
0.36 ([c]
)
Cr1
Cr2
Cr3
Cr[b]
Colh
Colh
Colh
rectangular
rectangular
oblique
rectangular
hexagonal
hexagonal
hexagonal
0.36 (ꢁ408)
0.36 (ꢁ408)
0.36 (ꢁ408)
0.35 (ꢁ408)
0.34 (08)
5
6
decyloxy)phenyl substituents
6 forms two LC phases
a=3.50
a=3.50
0.43 (08)
0.43 (08)
(Figure 9). Interestingly, the LC state above 578C is more
ordered in comparison to the low temperature phase. This
could again be related to the chain flexibility at higher tem-
peratures which results in closer molecular packing.
[a] p-Stacking distance; the molecular tilting angle towards the columnar
axis is in parentheses. [b] After annealing. [c] Tilt angle not assignable
due to misalignment.
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Columnar Self-Assembly
FULL PAPER
of relatively weak self-assembly with low steric demand of
the substituents facilitates the formation of fibrous micro-
structures. This seems reasonable, as only the molecules that
are not too tightly bound to each other have enough free-
dom to find the most favorable arrangement during the dep-
osition process.[2b]
The highly organized columnar superstructures formed by
these derivatives by various processing methods could be of
interest as potential charge-carrier pathways for organic mo-
lecular devices. This is even more interesting in light of the
electrochemical data that identified the carbonyl-bridged
heterotriangulenes as fairly strong reversible two-electron
acceptors comparable to 9,10-anthraquinone. Based on our
findings, we believe that the carbonyl-bridged heterotriangu-
lene is an important electron-deficient building block that
will, after further synthetic modifications, provide technolog-
ically relevant n-type organic materials able to compete
with the well-established classes of compounds such as
rylene diimides or hexaazatriphenylene derivatives.
Figure 9. 2D-WAXS patterns of 6 at a) 308C and b) 1208C.
The above-discussed results suggest that the phenylene–
ethynylene linkages are essential for thermotropic liquid
crystallinity in the carbonyl-bridged heterotriangulenes.
These moieties extend the p-conjugated core and reduce the
steric crowding by increasing the distance between the core
and its n-dodecyl pendants which enhances the supramolec-
ular order within the column.[2b] Indeed, the clearing tem-
peratures increase when going from 2 (938C) to extended 5
(1588C), which supports the aforementioned statement.
Experimental Section
Materials and general methods: Reagents and solvents were purchased
as reagent grade from Acros, Sigma–Aldrich, Alfa Aesar, and Rieke
Metals (n-C12H25ZnBr) and used as received. All reactions were per-
formed under an inert atmosphere by applying a positive pressure of N2
Conclusion
We prepared a series of new carbonyl-bridged heterotrian-
gulenes 2–6 with the lateral n-dodecyl chains attached
through different spacers to the polycyclic core and showed
that, owing to their appealing properties, these compounds
could be of interest for application in organic devices. We
found that their propensity to undergo columnar self-assem-
bly in solution, on surfaces, and in the bulk, was greatly in-
fluenced by the nature of the lateral substituents, their steric
demand, and by the applied solution processing conditions,
which is in agreement with the literature data obtained for
different types of disc-shaped molecules.[2] In addition, we
identified a columnar arrangement in the single-crystal
packing of 8 with the bulky triisopropylsilylethynyl moieties.
To the best of our knowledge, this is the first X-ray crystal-
lographic study of a substituted carbonyl-bridged hetero-
triangulene.
From our observations it can be concluded that 1) addi-
tional phenylene moieties between the heterotriangulene
core and the alkyl pendants are beneficial for the self-as-
sembly both in solution and in the bulk state by extending
the conjugated core which increases the p-orbital overlap (3
and 5), 2) the rod-like ethynylene spacers apparently intro-
duce some additional flexibility and hence diminishes the
self-assembly tendency in solution (e.g., 3 vs. 5), and 3) the
combination of both features in the phenylene–ethynylene
moieties induces thermotropic liquid crystallinity (5 and 6).
Although 2, with the n-dodecyl chains attached directly to
the heterotriangulene core, shows the lowest self-association
in solution and the lowest clearing temperature, which is in
line with the conclusions above, it forms well-aligned fibers
already by simple dip-coating. Apparently the combination
using anhydrous solvents. 2,6,10-Triiodo
AHCTUNGTRENNUNG
ACHTUNGTRENN[UNG 1,9]chinolizino[3,4,5,6,7-defg]-
acridin-4,8,12-trione (7),[14] 4-dodecylphenylboronic acid,[17] 1-dodecyl-4-
ethynylbenzene,[33] and 1,3-bis(dodecyloxy)-5-ethynylbenzene[34] were
synthesized according to literature procedures. Column chromatography
(CC) and plug filtrations were carried out with SiO2 60 (particle size
0.040–0.063 mm, 230–400 mesh) and distilled technical solvents. Thin-
layer chromatography (TLC) was conducted on aluminum sheets coated
with SiO2 60 F254 obtained from Macherey–Nagel; visualization with a
UV lamp (254 or 366 nm). Melting points (m.p.) were measured on a
Bꢀchi B-540 melting-point apparatus in open capillaries and are uncor-
rected. “Decomp” refers to decomposition. 1H NMR and 13C NMR spec-
tra were measured on a Bruker AMX300 or on a Bruker DRX500 spec-
trometer at room temperature. Chemical shifts (d) are reported in ppm
relative to the signal of tetramethylsilane (TMS). Residual solvent signals
in the 1H and 13C NMR spectra were used as an internal reference. Cou-
pling constants (J) are given in Hz. The apparent resonance multiplicity
is described as s (singlet), brs (broad singlet), d (doublet), t (triplet), q
(quartet), and m (multiplet). Infrared spectra (IR) were recorded on a
Varian 660-IR FT-IR spectrometer; signal designations: s (strong), m
(medium), w (weak). UV/Vis spectra were recorded on a Perkin–Elmer
Lamda 15 spectrophotometer. The spectra were measured in CHCl3 in a
quartz cuvette (1 cm) at room temperature. The absorption maxima
(lmax) are reported in nm with the extinction coefficient (e) MÀ1 cmÀ1 in
brackets; shoulders are indicated as sh. Field-desorption mass spectra
were recorded on a VG Instruments ZAB 2-SE-FPD spectrometer and
MALDI-TOF mass spectra were recorded on a Bruker Reflex II-TOF
spectrometer using 7,7,8,8-tetracyanoquinodimethane (TCNQ) or 1,8-di-
hydroxy-9,10-dihydroanthracene-9-one (dithranol) as matrix. Elemental
analyses were performed on a Foss Heraeus-Vario EL (Johannes Guten-
berg University Mainz).
Electrochemistry: The electrochemical measurements were carried out at
208C in CH2Cl2, containing 0.1m n-Bu4NPF6 in a classical three-electrode
cell. CH2Cl2 was purchased in spectroscopic grade from Merck, dried
over molecular sieves (4 ꢅ), and stored under Ar prior to use.
n-Bu4NPF6 was purchased in electrochemical grade from Fluka and used
as received. The working electrode was a glassy carbon disk electrode
(3 mm in diameter) used either motionless for cyclic voltammetry (0.1 to
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M. Kivala, K. Mꢀllen et al.
10 VsÀ1) or as rotating-disk electrode for rotating disk voltammetry
(RDV). The auxiliary electrode was a Pt wire, and the reference elec-
trode was a platinum wire used as a pseudo-reference electrode. All po-
tentials are referenced to the ferrocenium/ferrocene (Fc+/Fc) couple,
used as an internal standard, and are uncorrected from ohmic drop. The
cell was connected to Autolab PGSTAT30 potentiostat (Eco Chemie BV,
Utrecht, The Netherlands) controlled by the GPSE software running on
a personal computer.
(s), 1646 (s), 1592 (s), 1466 (s), 1353 (m), 1292 (s), 1162 (w), 918 (w), 861
(w), 800 (m), 721 cmÀ1 (m); UV/Vis (CHCl3): lmax (e)=267 (41000), 403
(sh, 8800), 427 nm (17800mÀ1 cmÀ1); MALDI-TOF (dithranol): m/z calcd
for C57H81NO3+: 828.26 [M]+; found: 828.96; elemental analysis calcd
(%) for C57H81NO3 (828.26): C 82.66, H 9.86, N 1.69; found: C 82.03,
H 10.21, N 1.68.
2,6,10-Tris(4-dodecylphenyl)benzo
ACHTUNGTRENNUNG
4,8,12-trione (3): A Schlenk flask was charged with [PdAHCTUNGTRENNUNG
Mesophase characterization: Thermal transition temperatures were deter-
mined by differential scanning calorimetry (DSC) on a Mettler Toledo
DSC822e. The samples underwent a temperature cycle with a first heat-
ing, first cooling, and a second heating at a rate of 58C minÀ1 (atmo-
0.015 mmol), SPhos (6.0 mg, 0.015 mmol), 4-dodecylphenylboronic acid
(194 mg, 0.67 mmol), and anhydrous K3PO4 (283 mg, 1.33 mmol). Dry tol-
uene (3 mL) was added and the mixture was stirred at room temperature
for 2 min. The iodinated 7 (105 mg, 0.15 mmol) was added and the reac-
tion mixture was heated at 1008C for 72 h. The mixture was diluted with
CH2Cl2 (50 mL), washed with H2O (3ꢆ20 mL) and dried (MgSO4). The
solvents were removed in vacuo and the residue was purified by column
chromatography (SiO2, hexanes/CH2Cl2 =1:1) followed by precipitation
from CH2Cl2/MeOH to afford 3 (68 mg, 43%) as a yellow solid. Rf =0.35
(SiO2, hexanes/CH2Cl2 1:1); m.p. 142–1448C; 1H NMR (300 MHz,
CDCl3): d=0.91 (t, J=6.7 Hz, 9H), 1.26–1.42 (m, 54H), 1.63–1.67 (m,
6H), 2.59 (t, J=7.7 Hz, 6H), 7.00 (d, J=8.0 Hz, 6H), 7.05 (d, J=8.0 Hz,
6H), 8.02 ppm (s, 6H); 13C NMR (75 MHz, CDCl3): d=14.39, 22.97,
29.68, 29.91, 29.97, 29.99, 30.05, 30.08, 31.84, 32.22, 36.00, 122.06, 127.02,
129.26, 131.76, 134.24, 134.46, 137.66, 143.53, 174.54 ppm (20 signals out
of 21 expected); IR (neat): n˜ =2920 (s), 2849 (m), 1652 (s), 1594 (m),
1461 (s), 1345 (w), 1292 (m), 1021 (m), 924 (w), 836 (w), 797 cmÀ1 (m);
UV/Vis (CHCl3): lmax (e)=277 (55700), 313 (41500), 424 (sh, 10300),
449 nm (17200mÀ1 cmÀ1); MALDI-TOF (dithranol): m/z calcd for
C75H94NO3+: 1057.55 [M+H]+; found: 1057.31; elemental analysis calcd
(%) for C57H93NO3·H2O (1074.56): C 83.83, H 8.91, N 1.30 found:
C 83.88, H 8.87, N 1.29.
ACHTUNGTRENNUNG
sphere N2; flow 35 mLminÀ1). The 2D-WAXS measurements were per-
formed using a custom setup consisting of the Siemens Kristalloflex
X-ray source (copper anode X-ray tube, operated at 35 kV/20 mA),
Osmic confocal MaxFlux optics, two collimating pinholes (1.0 and
0.5 mm, Owis, Germany) and an antiscattering pinhole (0.7 mm, Owis,
Germany). The patterns were recorded on a MAR345 image plate detec-
tor (Marresearch, Germany). The samples were prepared as a thin fila-
ment of 0.7 mm diameter by filament extrusion using a custom-built mini
extruder. Each sample was positioned perpendicular to the incident
X-ray beam and vertical to the 2D detector. The optical textures were in-
vestigated using a Zeiss polarizing optical microscope (POM) equipped
with digital temperature control system UNKAM TMS 591. Each sample
was sandwiched between glass slides to form a thin film and was after-
wards heated above the melting point using a heating stage. AFM images
were obtained with a Digital Instruments Nanoscope IIIa AFM in tap-
ping mode.
Self-assembly from solution: Dip-coating was performed at a speed of
20 mmsÀ1 from a chloroform solution with a concentration of 0.6 mgmLÀ1
onto SiO2 substrates. Solvent vapor diffusion was carried out from
chloroform as both solvent (0.6 mgmLÀ1) and vapor (60 mL chloroform
in 100 mL airtight container).
2,6,10-Tri(tetradec-1-ynyl)benzo
ACHTUNGTREN[NUNG 1,9]chinolizino[3,4,5,6,7-defg]acridin-
4,8,12-trione (4): [PdCl2A(PPh3)2] (10 mg, 0.014 mmol) and CuI (5 mg,
CTHUNGTRENNUNG
0.028 mmol) were added to a degassed mixture of 7 (200 mg, 0.28 mmol)
and tetradec-1-yne (250 mg, 1.28 mmol) in iPr2NH and toluene (1:3 v/v;
12 mL). The mixture was stirred at 708C for 48 h, diluted with CH2Cl2
(50 mL) and passed through a plug (SiO2, CH2Cl2). The solvents were re-
moved in vacuo, and the residue was purified by column chromatography
(SiO2, hexanes/CH2Cl2 =20:1) followed by precipitation from CH2Cl2/
MeOH to afford 4 (226 mg, 88%) as a yellow solid. Rf =0.30 (SiO2, hex-
anes/CH2Cl2 20:1); m.p. 104–1058C; 1H NMR (300 MHz, CDCl3): d=
0.86 (t, J=6.6 Hz, 9H), 1.27–1.35 (m, 54H), 1.67 (quint, J=7.2 Hz, 6H),
2.47 (t, J=7.2 Hz, 6H), 8.51 ppm (s, 6H); 13C NMR (75 MHz, CDCl3):
d=14.10, 22.69, 28.59, 29.13, 29.20, 29.27, 29.38, 29.48, 29.61, 29.68, 29.73,
31.93, 77.78, 94.60, 122.34, 122.70, 135.30, 136.55, 174.30 ppm; IR (neat):
n˜ =2916 (s), 2848 (m), 1655 (s), 1585 (m), 1460 (s), 1280 (s), 1222 (w),
925 (m), 801 (m), 720 cmÀ1 (m); UV/Vis (CHCl3): lmax (e)=257 (39100),
274 (41300), 309 (32900), 415 (sh, 10200), 443 nm (18900mÀ1 cmÀ1);
MALDI-TOF (dithranol): m/z calcd for C63H82NO3+: 901.33 [M+H]+;
found: 901.08; elemental analysis calcd (%) for C63H81NO3 (900.32):
C 84.04, H 9.07, N 1.56 found: C 83.47, H 9.10, N 1.54.
X-ray crystallographic analysis: Single crystals (yellow needles) of 8 were
obtained by slow diffusion of hexanes into a solution of 8 in CH2Cl2. A
suitable crystal was selected and mounted on a loop on a SuperNova,
Dual, Cu at zero, Atlas diffractometer. By using OLEX2,[35] the structure
was solved with the ShelXS-97[36] structure solution program by using
direct methods and refined with the ShelXL-97[36] refinement package
using least squares minimization. All non H-atoms were refined aniso-
tropically; H-atoms were refined with fixed isotropic temperature factors
in the riding model.
X-ray crystal structure of 8: Crystal data at 153.1(3) K for C54H69NO3Si3,
¯
Mw =864.37, triclinic, space group P1 (no. 2), a=7.5881(8), b=
19.6115(19), c=34.853(4) ꢅ, a=101.351(9)8, b=90.942(8)8, g=
94.006(8)8, V=5070.3(9) ꢅ3, Z=4, 1calcd =1.132 gcmÀ3
mACHTUNGTRENNUNG
,
2qmax =121.28,
(CuKa)=1.175 mmÀ1, 11116 reflns measured, 9065 unique (Rint =0.0242),
which were used in all calculations. The final wR2 was 0.2108 (all data)
and R1 was 0.0726 (>2s(I)).
CCDC-920629 (8) contains the supplementary crystallographic data for
this paper (excluding structure factors). These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif
2,6,10-Tris[(4-dodecylphenyl)ethynyl]benzo
ACHUTNGTRENNUG[1,9]chinolizinoACHTUNGTRENN[UGN 3,4,5,6,7-
defg]acridin-4,8,12-trione (5): [PdCl2A(PPh3)2] (8 mg, 0.011 mmol) and CuI
A
CHTUNGTRENNUNG
(4 mg, 0.021 mmol) were added to a degassed mixture of 7 (150 mg,
0.21 mmol) and 1-dodecyl-4-ethynylbenzene (260 mg, 0.96 mmol) in
iPr2NH and toluene (1:3 v/v; 10 mL),. The mixture was stirred at 708C
for 21 h, diluted with CH2Cl2 (50 mL), and passed through a plug (SiO2,
CH2Cl2). The solvents were removed in vacuo, and the residue was puri-
fied by CC (SiO2, hexanes/CH2Cl2 =1:1) followed by precipitation from
CH2Cl2/MeOH to afford 5 (206 mg, 85%) as a yellow solid. Rf =0.52
(SiO2, hexanes/CH2Cl2 1:1); m.p. 154–1558C; 1H NMR (300 MHz,
CDCl3): d=0.88 (t, J=6.7 Hz, 9H), 1.27 (s, 54H), 1.56 (brs, 6H), 2.51 (t,
J=7.7 Hz, 6H), 6.95 (d, J=8.0 Hz, 6H), 7.21 (d, J=8.0 Hz, 6H),
8.47 ppm (s, 6H); 13C NMR (75 MHz, CDCl3): d=14.35, 22.93, 29.62,
29.70, 29.80, 29.91, 29.96, 31.34, 32.17, 36.20, 85.90, 93.54, 119.31, 121.97,
122.95, 128.55, 131.95, 135.49, 136.43, 144.32, 174.20 ppm (21 signals out
of 23 expected); IR (neat): n˜ =2919 (s), 2849 (m), 1656 (s), 1585 (m),
1509 (m), 1458 (s), 1289 (s), 1120 (w), 1018 (w), 921 (m), 874 (m), 801
(m), 720 cmÀ1 (m); UV/Vis (CHCl3): lmax (e)=279 (45600), 293 (sh,
2,6,10-Tridodecylbenzo
ACHTUNGTRENNUNG[1,9]chinolizino[3,4,5,6,7-defg]acridin-4,8,12-trione
(2): [PdCl2A(dppf)]·CH2Cl2 (29 mg, 0.04 mmol) and n-dodecylzinc bromide
CHTUNGTRENNUNG
(0.5m in THF; 3.0 mL, 1.5 mmol) were added to a degassed suspension
of 7 (250 mg, 0.36 mmol) in toluene (35 mL). After stirring at 608C for
23 h, sat. aq. NaHCO3 (20 mL) was added and the mixture was extracted
with CH2Cl2 (3ꢆ60 mL). The combined organic layers were washed with
H2O (1ꢆ60 mL), dried (MgSO4), filtered, and the solvents were removed
in vacuo. The crude product was purified by CC (SiO2, hexanes/CH2Cl2 =
1:1) followed by precipitation from CH2Cl2/MeOH to afford 2 (235 mg,
80%) as a yellow solid. Rf =0.55 (SiO2, hexanes/CH2Cl2 1:1); m.p. 94–
1
968C; H NMR (300 MHz, CDCl3): d=0.86 (t, J=6.7 Hz, 9H), 1.25–1.38
(m, 54H), 1.79 (quint, J=7.5 Hz, 6H), 2.90 (t, J=7.5 Hz, 6H), 8.68 ppm
(s, 6H); 13C NMR (75 MHz, CDCl3): d=14.11, 22.68, 29.30, 29.35, 29.47,
29.58, 29.64, 29.66, 31.14, 31.91, 35.14, 123.02, 134.12, 135.52, 140.59,
176.32 ppm (16 signals out of 17 expected); IR (neat): n˜ =2917 (s), 2847
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Columnar Self-Assembly
FULL PAPER
43000), 327 (sh, 38000), 343 (39000), 428 (sh, 12000), 454 nm
Y. H. Geerts, Chem. Soc. Rev. 2007, 36, 1902–1929; c) S. Laschat, A.
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systems, see: a) X. Feng, V. Marcon, W. Pisula, M. R. Hansen, J.
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+
(18300mÀ1 cmÀ1); MALDI-TOF (dithranol): m/z calcd for C81H94NO3
:
1129.62 [M+H]+; found: 1129.50; elemental analysis calcd (%) for
C81H93NO3 (1128.61): C 86.20, H 8.31, N 1.24 found: C 85.83, H 8.69,
N 1.22.
2,6,10-Tris
[3,4,5,6,7-defg]
0.004 mmol) and CuI (2 mg, 0.010 mmol) were added to a degassed mix-
ture of (60 mg, 0.09 mmol) and 1,3-didodecyloxy-5-ethynylbenzene
A
R
ACHTUNGTRENNUNG
A
R
CHTUNGTRENNUNG
7
(120 mg, 0.25 mmol) in iPr2NH and toluene (1:3 v/v; 6 mL). The mixture
was stirred at 708C for 24 h, diluted with CH2Cl2 (50 mL), and passed
through a plug (SiO2, CH2Cl2). The solvents were removed in vacuo, and
the residue was purified by column chromatography (SiO2, hexanes/
EtOAc=10:1) followed by precipitation from CH2Cl2/MeOH to afford 6
(107 mg, 73%) as an orange solid. Rf =0.43 (SiO2, hexanes/EtOAc=
10:1); m.p. 241–2448C; 1H NMR (300 MHz, CDCl3): d=0.84 (m, 18H),
1.23–1.37 (m, 108H), 1.62 (m, 12H), 3.69 (m, 12H), 6.34 (s, 9H),
8.74 ppm (s, 6H); 13C NMR (75 MHz, CDCl3): d=14.32, 22.92, 26.31,
29.57, 29.66, 29.72, 29.78, 30.53, 32.13, 69.04, 73.39, 85.99, 93.07, 109.60,
116.62, 121.28, 123.51, 136.42, 139.04, 152.78, 175.21 ppm (21 signals out
of 23 expected); IR (neat): n˜ =2920 (s), 2852 (m), 1656 (s), 1587 (m),
1499 (s), 1464 (s), 1419 (m), 1361 (m), 1323 (s), 1285 (m), 1234 (s), 1112
(s), 1001 (m), 922 (m), 827 (m), 803 cmÀ1 (m); UV/Vis (CHCl3): lmax
(e)=272 (69300), 335 (sh, 98100), 352 (119600), 458 nm (21100mÀ1 cmÀ1);
MALDI-TOF (dithranol): m/z calcd for C117H166NO9+: 1730.57 [M+H]+;
found: 1730.29; elemental analysis calcd (%) for C117H165NO9·3H2O
(1783.61): C 78.79, H 9.66, N 0.79 found: C 78.51, H 9.61, N 0.71.
ˇ
´
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2,6,10-Tris[(triisopropylsilyl)ethynyl]benzoACHTUNGTNER[NUNG 1,9]chinolizino[3,4,5,6,7-
defg]acridin-4,8,12-trione (8): [PdCl2A(PPh3)2] (15 mg, 0.02 mmol) and CuI
CTHUNGTRENNUNG
(8 mg, 0.04 mmol) were added to a degassed mixture of 7 (300 mg,
0.43 mmol) and triisopropylsilylacetylene (350 mg, 1.92 mmol) in iPr2NH
and toluene (1:3 v/v; 40 mL). The mixture was stirred at 608C for 17 h,
diluted with CH2Cl2 (50 mL), and passed through a plug (SiO2, CH2Cl2).
The solvents were removed in vacuo, and the residue was purified by
column chromatography (SiO2, hexanes/CH2Cl2 =2:1) to give 8 (322 mg,
87%) as a yellow fluffy solid. Rf =0.42 (SiO2, hexanes/CH2Cl2 2:1);
m.p.>3508C (decomp.); 1H NMR (300 MHz, CDCl3): d=1.19 (s, 63H),
9.02 ppm (s, 6H); 13C NMR (75 MHz, CDCl3): d=11.29, 18.70, 95.68,
103.40, 122.03, 123.32, 136.63, 137.66, 175.12 ppm; IR (neat): n˜ =2939
(m), 2862 (m), 1659 (s), 1585 (m), 1454 (s), 1334 (m), 1283 (m), 1070 (w),
993 (m), 964 (m), 924 (m), 873 (s), 793 (s), 677 cmÀ1 (s); UV/Vis
(CHCl3): lmax (e)=263 (70000), 274 (sh, 65200), 315 (58100), 414 (sh,
12500), 438 nm (25300mÀ1 cmÀ1); MALDI-TOF (dithranol): m/z calcd for
C54H70NO3Si3+: 865.39 [M+H]+; found: 865.21; elemental analysis calcd
(%) for C54H69NO3Si3 (864.39): C 75.03, H 8.05, N 1.62; found: C 74.88,
H 8.38, N 1.60.
Acknowledgements
Bettina Gliemann (FAU Erlangen-Nꢀrnberg) is gratefully acknowledged
for reproducing the synthesis and the crystal growth of compound 8, and
Dr. Volker Enkelmann (MPI-P Mainz) and Dr. Frank Hampel (FAU
ACHTUNGTRENNUNGErlangen-Nꢀrnberg) for its X-ray crystallographic analysis. Dr. Manfred
Wagner (MPI-P Mainz) is acknowledged for the measurement of concen-
tration-dependent NMR data. This work was supported by the German
Science Foundation (Korean-German IR TG), the European Communi-
tyꢁs Seventh Framework Program ONE-P (grant agreement no. 212311),
DFG Priority Program SPP 1355, DFG MU 334/32–1, DFG Priority Pro-
gram SPP 1459, and ESF Project GOSPEL (Ref Nr: 09-Euro
ACHTUNGTRNEGNUNG RAPH-
ACHTUNGTRENNUNGENE-FP-001). The Swiss National Science Foundation and the Alexand-
er von Humboldt Foundation are acknowledged for postdoctoral fellow-
ships to M.K.
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Chem. Eur. J. 2013, 00, 0 – 0
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Received: January 23, 2013
Published online: && &&, 2013
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Columnar Self-Assembly
FULL PAPER
Playing the triangle: A series of elec-
tron-deficient heterotriangulenes with
pendant alkyl chains have been synthe-
sized and their propensity for self-
assembly in solution, on a surface, and
in the bulk was studied (see figure). A
pronounced dependence of the self-
assembly behavior on the nature of the
spacer between the rigid heterotrian-
gulene core and the flexible alkyl
chains was identified.
Self-Assembly
M. Kivala,* W. Pisula, S. Wang,
A. Mavrinskiy, J.-P. Gisselbrecht,
X. Feng, K. Mꢀllen* ......... &&&& — &&&&
Columnar Self-Assembly in Electron-
Deficient Heterotriangulenes
Chem. Eur. J. 2013, 00, 0 – 0
ꢄ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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