Molecular triangles: Synthesis, self-assembly, and blue emission of cyclo-7,10-tris-triphenylenyl macrocycles

Article abstract of DOI:10.1002/asia.201100258

A set of cyclo-7,10-tris-triphenylenyl macrocycles have been prepared by a Yamamoto cyclotrimerization protocol. In these novel macrocycles, three triphenylene units are covalently linked to each other, resulting in the formation of triangular-shaped molecules. The fully planar derivative revealed pronounced self-assembly behavior. NMR spectroscopy was used to determine the association constant in solution. 2D wide-angle X-ray scattering was applied to the study of the liquid crystallinity of this new discotic mesogen in the bulk state. Furthermore, nonplanar, laterally substituted derivatives were successfully tested as blue emitters in organic light-emitting diodes owing to their unique optoelectronic properties and their high stability. In this case, substitution with sterically demanding phenyl groups was efficiently used to suppress intermolecular packing, thus preventing undesired quenching effects.

Full text of DOI:10.1002/asia.201100258

DOI: 10.1002/asia.201100258
Molecular Triangles: Synthesis, Self-Assembly, and Blue Emission of Cyclo-
7,10-tris-triphenylenyl Macrocycles
Matthias Georg Schwab,[a, b] Tianshi Qin,[a] Wojciech Pisula,[a] Alexey Mavrinskiy,[a]
Xinliang Feng,[a] Martin Baumgarten,[a] Hun Kim,[a] Frꢀdꢀric Laquai,[a] Sebastian Schuh,[c]
Roman Trattnig,[c] Emil J. W. List,*[c, d] and Klaus Mꢁllen*[a]
Abstract: A set of cyclo-7,10-tris-tri-
phenylenyl macrocycles have been pre-
pared by a Yamamoto cyclotrimeriza-
tion protocol. In these novel macrocy-
cles, three triphenylene units are cova-
lently linked to each other, resulting in
the formation of triangular-shaped
molecules. The fully planar derivative
revealed pronounced self-assembly be-
havior. NMR spectroscopy was used to
determine the association constant in
solution. 2D wide-angle X-ray scatter-
ing was applied to the study of the
liquid crystallinity of this new discotic
mesogen in the bulk state. Further-
more, nonplanar, laterally substituted
derivatives were successfully tested as
blue emitters in organic light-emitting
diodes owing to their unique optoelec-
tronic properties and their high stabili-
ty. In this case, substitution with steri-
cally demanding phenyl groups was ef-
ficiently used to suppress intermolecu-
lar packing, thus preventing undesired
quenching effects.
Keywords: blue emission · liquid
crystals
·
macrocycles
·
self-
assembly · triphenylenes
Introduction
egies for the buildup of substituted derivatives are avail-
able.[3,4] Monomeric TP derivatives received considerable in-
terest when their liquid-crystalline nature was first report-
ed,[5] spurring research in 2,3,6,7,10,11-hexasubstituted TP
mesogens in particular.[6–11] Liquid crystallinity is driven by
the strong p-stacking tendency of the planar TP core and
van der Waals interactions of lateral side chains. Hexa-
Triphenylene (TP) is a polycyclic aromatic hydrocarbon
(PAH) that has been widely studied in chemistry and mate-
rials science owing to a manifold of fascinating properties.
The triangular-shaped molecule owes its particular chemical
stability to the fully benzenoid character of the aromatic
system.[1,2] TP chemistry is well developed and various strat-
AHCTUNGTREGaNNUN lkoxytriphenylenes are of significant interest as fast photo-
conductors for applications in xerography.[9] In addition,
polymers[12–15] and dendrimers[16–19] based on TP are also
known to exhibit pronounced self-assembly behavior. A
second major field of application is devoted to the optoelec-
tronic properties of the molecule. TP is a famous blue emit-
ter and has recently been investigated in organic optoelec-
tronic devices.[13,15–17,20–22] Surprisingly, only a few macrocy-
cles containing TP have been reported and so far little is
known about the self-assembly of these cyclic systems in so-
lution, on surfaces, and in the bulk state.[23–28] Moreover, the
direct covalent linkage of three TP units within a macrocy-
cle would raise the question to what degree the moderate
luminescence yields of below 6% of monomeric TPs[29] can
be boosted in a cyclic conjugated arrangement. It is hy-
pothesized that this will enhance the transition dipole
moment of the otherwise symmetry-forbidden S0!S1 transi-
tion.[30] This assumption is based on similar approaches, in
which the symmetry in TP is broken by means of monofunc-
tionalization using cyano substituents, leading to a threefold
[a] Dr. M. G. Schwab, Dr. T. Qin, Dr. W. Pisula, Dr. A. Mavrinskiy,
Dr. X. Feng, Dr. M. Baumgarten, H. Kim, Dr. F. Laquai,
Prof. Dr. K. Mꢀllen
Max Planck Institute for Polymer Research
Ackermannweg 10,D-55128 Mainz (Germany)
Fax : (+49)6131-379100
E-mail: muellen@mpip-mainz.mpg.de
[b] Dr. M. G. Schwab
BASF SE
Carl-Bosch-Straße 38, 67063 Ludwigshafen (Germany)
[c] S. Schuh, R. Trattnig, Prof. E. J. W. List
NanoTecCenter Weiz Forschungsgesellschaft mbH
Franz-Pichler-Straße 32, A-8160 Weiz (Austria)
[d] Prof. E. J. W. List
Institute of Solid State Physics
Graz University of Technology
Petersgasse 16, A-8010 Graz (Austria)
E-mail: e.list@tugraz.at
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201100258.
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FULL PAPERS
increase in the luminescence yield,[31] or by symmetric
methyl substitution, forcing the molecule to adopt a twisted
conformation instead of a symmetric planar one.[32] Aryl–
aryl cross-coupling macrocycles can be thought of as a tool-
box. Frequently, macrocyclic systems are built up from two
or more complementarily functionalized constituents follow-
ing A2B2-type synthetic protocols, such as Suzuki–Miyaura
or Sonogashira–Hagihara coupling reactions. However, AA-
functionalized building units as well as BB-functionalized
counterparts need to be synthesized prior to macrocycle for-
mation.[33–36] In contrast, the cyclotrimerization of a single
AA-functionalized precursor can significantly shorten the
synthetic route and thereby enhance the overall yield. Ex-
amples of successful cyclotrimerization reactions involve the
copper(II)-mediated reaction of Grignard reagents derived
from biphenyl,[37] ortho-terphenyl,[38] and phenanthrene[39,40]
and the trimerization of Lipshutz cuprates.[41] We have re-
cently introduced the concept of a Yamamoto-based cyclo-
trimerization, which relied on the selective assembly of 3,6-
dibromo-9,10-diarylphenanthrenes with halogen sites that
included an ideal angle of 1208.[42,43]
for charge transport in organic field-effect transistors
(OFETs).[7,44–46] Whereas strong intermolecular packing was
desired for macrocycle 9, the two derivatives 10a/10b were
designed with respect to their use as fluorophores in organic
light-emitting diodes (OLEDs). There, aggregation in the
solid state is prevented to avoid self-quenching effects aris-
ing from intermolecular packing as well as bathochromic
shifts in the emission spectrum due to excimer forma-
tion.[47,48] As such, the versatility of this design concept has
been recently demonstrated for polymeric[13,14] and dendrit-
ic[16,17] materials containing TP units of identical topology.
Hence, macrocycles 10a/10b are characterized by shorter
alkyl chains and additional twisted benzene units. Macrocy-
cle 10a contains six regularly distributed propyl chains,
whereas a statistical hexyl substitution pattern is applied to
10b to further suppress the aggregation of this derivative.
In the first step, the preparation of the functionalized TP
precursors 4, 8a, and 8b was realized according to the two
synthetic pathways depicted in Scheme 1. The functionalized
and symmetrically substituted TP 4 was synthesized from
1,2-dibromo-4,5-bis(dodecyloxy)benzene (1)[49] by adopting
a reported procedure for the analogous alkyl derivatives.[50]
A double Suzuki–Miyaura coupling of 1 with phenyl boronic
acid yielded the functionalized ortho-terphenyl 2. The key
step of this route consisted of building the TP backbone
through the oxidative photocyclization of 2, yielding 2,3-
bis(dodecyloxy)triphenylene (3), which can be considered a
model compound for the macrocycle itself, in 73%. The
final bromination to yield 7,10-dibromo-2,3-bis(dodecyloxy)-
triphenylene (4) was achieved by treatment of 3 with bro-
mine in the presence of catalytic amounts of iron and
iodine.
Results and Discussion
Synthesis of Macrocycles
In this study, we extend the scope of suitable monomers to
functional TPs successfully applied for the buildup of a set
of triangular cyclo-7,10-tris-triphenylenyl macrocycles (9,
10a/10b; Figure 1). Our motivation for the synthesis of
these new cyclic trimers is twofold. A strong tendency to
self-organize into stacked molecular aggregates can be an-
ticipated from the flat dodecyloxy-substituted core of mac-
rocycle 9. Columnar mesophases adopted by discotic mole-
cules in the bulk state have found great interest due to the
possible application of such highly organized superstructures
Regarding the synthesis of precursors 8a and 8b, another
strategy had to be applied to realize phenyl substitution in
the 1,4-position (Scheme 1). The point of departure was the
bromination of phenanthrene-9,10-dione (5), according to a
route established in the literature.[51] Subsequent Knoevena-
gel condensation of 3,6-dibromophenanthrene-9,10-dione
(6) with diphenylacetone gave the functionalized phency-
clone derivative 7. In a final Diels–Alder [4+2] cycloaddi-
tion of 7 with oct-4-yne or oct-1-yne, the functionalized TPs
8a (symmetric) and 8b (asymmetric) were obtained, respec-
tively, in high yields.
The cyclotrimerization reaction to yield the cyclo-7,10-
tris-triphenylenyl macrocycles 9 and 10a/10b was achieved
by following standard Yamomoto conditions.[52,53] Hence, the
catalyst was prepared under glovebox conditions, activated,
and then the solution containing the TP precursor was
added dropwise to guarantee pseudo-dilution conditions.
Typically, the reaction was run at 60 (9) or 808C (10a/10b)
for 3 days in the dark. Quenching and decomposition of
nickel residues was achieved by dropping the reaction mix-
ture into a dilute solution of hydrochloric acid in methanol.
The reaction products were isolated by using a combination
of column chromatography on silica and recycling gel per-
meation chromatography (rGPC).
Figure 1. Conformation and geometric parameters of macrocycles 9 (left)
and 10a/10b (right), as derived from quantum chemical analysis (B3LYP,
6-311G*, side-chains are omitted).
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Molecular Triangles
Scheme 1. Synthetic route to the macrocycles 9 and 10a/10b, conditions: a) phenylboronic acid, [PdACHTNUTRGNEUNG(PPh3)4], K2CO3, 1,4-dioxane, 1008C, 87%; b) hn, I2,
propylene oxide, toluene, RT, 73%; c) Br2, Fe/I2, ꢀ58C, 66%; d) hn, Br2, nitrobenzene, 1008C, 45%; e) 1,3-diphenylpropan-2-one, KOH/MeOH, 808C,
74%; f) 8a: oct-4-yne, diphenyl ether, 2208C, 81%; 8b: octy-1-ne, ortho-xylene, 1708C, 92%; g) 9: [Ni
608C, 21%; 10a: 808C, 70%; 10b: 808C, 77%. DMF=N,N-dimethylformamide.
ACHTUNGRTENUN(NG cod)2] (cod,=2,2’-bipyridine), toluene/DMF,
Quantum chemical calculations (B3LYP, 6-311G*) carried
out on macrocycle 9 indicated a propeller-like structure with
C3 symmetry. As seen in the side-view representation in
Figure 1, this manifests in a dihedral angle of 24.08 between
two neighboring TP units. A cavity diameter of 5.9 ꢂ was
derived. Similar geometric parameters (22.28, 5.9 ꢂ) were
found by computational analysis of the core of 10a/10b
(Figure 1). However, the aforementioned twisted arrange-
ment of the lateral benzene rings is clearly visible and also
induces a bent, nonplanar conformation of the three TP
units.
spectroscopy. The spectra obtained were in agreement with
the highly symmetric structure of 9 and 10a/10b (see the
Supporting Information). All three macrocycles displayed
high solubility in common organic solvents.
Self-Assembly in Solution
The strong aggregation tendency of 9 became evident
during handling and purification. Upon concentrating solu-
tions of this macrocycle, turbidity appeared long before visi-
ble precipitation set in, indicating scattering effects from
molecular aggregates. Furthermore, to suppress pronounced
signal broadening, NMR spectroscopy analysis of 9 was per-
formed at elevated temperatures in 1,1,2,2-tetrachloroethane
([D2]TCE). Increasing the temperature resulted in a pro-
gressive downfield shift of the aromatic signals (see the Sup-
porting Information). The strong temperature dependency
Matrix-assisted laser desorption/ionization time-of-flight
(MALDI-TOF) spectroscopy, after purification of 9 and
10a/10b, indicated the successful construction of the macro-
cycles. In all cases, the signal of the target compound was
exclusively observed (see the Supporting Information). The
mass spectra recorded of the crude products revealed the
presence of the de-halogenated monomer and dimer as
major side products of the reaction. Further analysis of the
1
seen in the H NMR spectra motivated us to investigate the
solution aggregation properties further. Temperature- and
concentration-dependent NMR spectroscopy experiments
1
macrocycles was carried out by means of H and 13C NMR
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are known to be effective for the elucidation of the associa-
tion constant, KA, of disc-like aromatic systems in solu-
tion.[33,54,55]
onene (HBC) derivatives (457 Lmolꢀ1),[55] highlighting
strong p stacking for the cyclic TP trimer. Indeed, the
number of benzene rings is 12 for macrocycle 9 and 13 for
HBC, reflecting the similar size of the total p surface of
both discs.
The underlying theory is based on the observation that
the chemical shift of a particular proton in a polymolecular
stack is different from that of the single molecule. Thus, a
dilution series from 8.0ꢃ10ꢀ3 to 7.0ꢃ10ꢀ5 m was performed
in [D2]TCE at 808C and the chemical shift of the protons in-
dicating the macrocycle cavity was plotted as a function of
concentration (Figure 2). A typical sigmoidal curve resulted,
which was analyzed by using an attenuated K model accord-
ing to a procedure described elsewhere.[33,54] From this
model, a KA value of 444 Lmolꢀ1 was calculated for the
macrocycle 9. This number is only slightly lower than that
known for hexadodecyl-substituted hexa-peri-hexabenzocor-
Liquid Crystallinity
Monomeric, alkyl-substituted TPs have also been widely
studied in the field of discotic liquid crystals owing to the
formation of mesophases that are generally characterized by
a high degree of organization.[6,7,9–11] This structural perfec-
tion arises from the highly symmetric, disc-like aromatic
core of TPs, which readily promotes their liquid crystallinity
when decorated with peripheric alkyl chains. We were inter-
ested in the thermotropic behavior and the long-range self-
assembly of the macrocyclic homologue 9, which preserved
several important features of TP-based liquid crystals. This
refers in particular to the triangular shape reminiscent of TP
itself and the positioning of six alkoxy substituents at the pe-
riphery of the molecule. Hence, the bulk-phase properties of
macrocycle 9 were determined by two-dimensional wide-
angle X-ray scattering (2D-WAXS) experiments and corre-
lated to results from the thermal analysis by differential
scanning calorimetry (DSC) (Figure 3).
The DSC trace showed two phase transitions that were
fully reversible. Upon second heating, a minor endothermic
peak was detected at TH1 =64.38C and a second major endo-
thermic transition occurred at TH2 =109.18C. Both were
found to reappear as exothermic transitions at TC1 =55.58C
and TC2 =103.68C, respectively, when the sample was cooled
down again (Figure 3A). 2D-WAXS measurements carried
out on a mechanically extruded fiber of 9[45] indicated that,
above the phase transition temperature of 109.18C, a liquid-
crystalline hexagonal columnar organization (Colh) is adopt-
ed.[7] The equatorial reflections in the corresponding pattern
(Figure 3B) revealed that the molecules pack in columnar
structures, which assembled within a hexagonal unit cell de-
fined by a parameter of ahex =3.55 nm. In the columns, the
Figure 2. Concentration dependence of the 1H NMR spectroscopy signal
shift of macrocycle 9 in [D2]TCE at 808C. TCE=1,1,2,2-tetrachloro-
ethane.
Figure 3. a) DSC trace of macrocycle 9 upon second heating (red) and cooling (blue); b) 2D-WAXS patterns of an extruded fiber of macrocycle 9 at
1308C; c) schematic illustration of the proposed molecular packing of 9 in columnar structures, side-chains are omitted for clarity.
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Molecular Triangles
macrocycles stack on top of each other with a typical p-
stacking distance of p=0.35 nm.[44,45] The molecular plane is
arranged orthogonal to the columnar axis, as depicted in the
schematic illustration of Figure 3C. Characteristic for the
liquid-crystalline phase, an amorphous halo appeared that
could be attributed to the disordered dodecyloxy chains.
Cooling the sample to 308C, this halo remained unaffected,
while the columnar arrangement changed to a rectangular
unit cell with art =2.96 nm and brt =2.03 nm. When the tem-
peratures of the phase transitions are compared to the ther-
motropic data of 2,3,6,7,10,11-hexakis(dodecyloxy)tripheny-
lene,[11] an increased intermolecular packing can be deduced
for macrocycle 9. Hence, for the monomeric TP containing
an identical number of six dodecyloxy chains, the transition
to Colh occurred at a much lower temperature of 558C and
the clearing point was reached at 638C.[11] The significantly
stronger aggregation of macrocycle 9 is not only evidenced
by higher phase transition temperatures, but also by the fact
that heating the compound to temperatures of 400–4508C
does not lead to isotropization of the sample and is ulti-
mately limited by the thermal decomposition of the macro-
cycle. A comparably broad liquid-crystalline phase width
has also been reported for a related cyclo-3,6-trisphenan-
threnyl macrocycle.[42]
emission, PL quantum yield (PLQY), and absorption prop-
erties. All relevant values are summarized in Table 1.
In general, according to Clar, the bands in the absorption
spectra of PAHs can be classified as a, b, and p bands.[1,2] As
for parent TP,[56] these characteristic bands manifest in the
Table 1. Summary of relevant optical properties for 9, 10a, and 10b as
determined in toluene (1.1ꢃ10ꢀ4 m). The previously reported data for
parent TP and TPTP is given for comparison.
In solution
Thin films
[a]
[b]
lem (max) [nm]
FPL [%]
lem (max) [nm]
FPL [%]
TP[c]
TPTP[d]
9
10a
10b
376
401
421
422
430
6
5
64
68
38
–
–
–
<1
13
43
402
479
480
425
[a] Taking quinine sulfate dehydrate as a standard reference. [b] Taking
poly(fluorene) as standard reference. [c] Data taken from refer-
A
a
ence [56]. [d] TPTP=1,2,4-triphenyltriphenylene; data taken from refer-
ence [16].
absorption spectrum of all macrocycles and appear at similar
wavelengths owing to the common aromatic structure of the
cyclic backbone (Figure 4). For instance, the bands are locat-
ed at lb =302, lp =346, and la =386 nm in the case of 9. The
high degree of vibronic fine structure is also mirrored in the
corresponding PL emission spectra depicted in Figure 4 for
solution measurements. The corresponding maximum
values, lem, are found at 421 (9), 422 (10a), and 430 nm
(10b). With respect to monomeric TP with its emission max-
imum located at 376 nm,[56] as well as 1,2,4-triphenyltriphe-
nylene (TPTP) with an emission maximum at 401 nm,[16] the
observed bathochromic shift of the three macrocycles can
be clearly attributed to the cyclic conjugated arrangement.
All three compounds exhibit an intense blue PL that is lo-
cated close to the ideal value for blue-emitting
OLEDs.[13,15–17,20–22] Comparing the limited PLQY, FPL, of
6.0% for parent TP[29] and only 5.0% for TPTP (a phenyl-
substituted, twisted, non-planar TP)[16] to those of 9 and
10a/10b, up to a tenfold improvement in the PLQY for the
macrocyclic arrangement can be observed. Macrocycles 9
and 10a exhibit a PLQY of 64 and 68%, respectively,
whereas for 10b a PLQY of 38% was determined. This
result clearly confirms the original hypothesis for this work
and the aim to increase the transition dipole moment of the
otherwise symmetry-forbidden S0!S1 transition through a
cyclic conjugated arrangement.[30] By this reasoning, the
PLQY of the TP unit is greatly enhanced, while the transi-
tion energy (emission maximum) is only slightly changed
from the near UV to the center of the blue region of the
spectrum. Similar to other systems, the oscillator strength of
the emissive transition is enhanced by the macrocycle ap-
proach because the overall symmetry of the TP unit is effec-
tively broken (Figure 1).[31] Moreover, this new molecular
design forces the TPs to adopt a contorted instead of a fully
planar conformation, which further influences the transition
dipole of the molecule.[32] In addition, the overall increased
Optoelectronic Properties
We then investigated the optical and optoelectronic proper-
ties of macrocycles 9 and 10a/10b, which strongly differed
in the degree of planarity and symmetry, as seen in Figure 1.
To characterize the basic optical properties and study the
aggregation behavior, macrocycles 9 and 10a/10b were in-
vestigated in solution (Figure 4) and as thin films (Figure 6,
see below) with respect to their photoluminescence (PL)
Figure 4. Normalized UV/Vis absorption spectra and normalized PL
emission spectra of macrocycles 9, 10a, and 10b in toluene (1.1ꢃ10ꢀ4 m).
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E. J. W. List, K. Mꢀllen et al.
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transition dipole, and thereby, enhanced radiative decay rate
should also make the impact of intersystem crossing to the
triplet manifold on the total excited-state lifetime less domi-
nant, as examined in the following discussion.
cies has decayed. The second broad and longer-lived compo-
nent of the spectrum is a consequence of the high tendency
of macrocycle 9 to aggregate, even in dilute solutions at con-
centrations as low as 1.1ꢃ10ꢀ4 m.
Regarding the nature of the excited states of single fluo-
rophores and aggregates in solution, important information
can be derived from time-resolved PL measurements, as re-
cently exemplified by a series of oligothiophenes.[57] In com-
Also, the fluorescence decay transient of 9 is indicative of
a second contribution to the overall emissive behavior. In
fact, two different decay channels are identified, since the
decay transient can be sufficiently well described by a sum
of two exponentials, similar to previously reported results
on TP liquid crystals and dendrimers (Figure 5B).[8,19] The
first component has a lifetime of t1 =3.7 ns and an ampli-
tude of 0.87, whereas the second component is characterized
by t2 =11.2 ns and an amplitude of 0.13. The former can be
ascribed to the fluorescence of the individual macrocycles,
whereas the latter arises from aggregated species. This as-
signment was further supported by experiments at higher
and lower analyte concentrations, since the amplitude of the
shorter-lived component was found to increase upon dilu-
tion and to decrease at higher concentration, thus reflecting
the impact of aggregation. The broad and featureless, as
well as slightly redshifted, spectrum further supports the as-
signment of the emission as fluorescence from aggregates
present in solution.
1
bination to the analysis carried out by means of H NMR
spectroscopy (Figure 2), the pronounced solution aggrega-
tion behavior of 9 was thus studied in more detail and also
compared with that of the monomeric model compound 2,3-
bis(dodecyloxy)triphenylene (3). The measurements were
performed in toluene at a concentration of 1.1ꢃ10ꢀ4 m, thus
at a concentration at which mainly the fluorescence of iso-
lated molecules can be expected with a small contribution
from aggregates. Figure 5A shows a comparison of time-re-
Finally, a closer comparison of the fluorescence lifetimes
of macrocycle 9 with model compound 3 by time-resolved
PL spectroscopy revealed that the fluorescence lifetime re-
duced from 10.0 ns for 3 (see the Supporting Information)
to 3.7 ns, as obtained from the fits depicted above. This
strongly supports the previous conclusion of stronger elec-
tronic coupling of the lowest p–p* singlet excited state to
the ground state in the cyclic trimer than in model com-
pound 3.
Device Results
The solid-state PL spectra obtained by measurements of
thin films prepared by spin-coating indicated significant dif-
ferences for the three macrocycles (Figure 6). As clearly ob-
served for 9 and 10a, the PL emission maximum undergoes
a dramatic bathochromic shift from about 420 to 480 nm.
The shift of the PL maximum is accompanied by a severe
broadening of the emission spectrum, a loss of the vibronic
structure, and a significant decrease in PLQY in the solid
state (Table 1). All three observations are a clear indication
of aggregation in the bulk state and excimer formation due
to intermolecular packing.[47,48] On the contrary, macrocycle
10b, containing three statistically arranged hexyl side chains,
does not show this strong alteration of the emission spec-
trum upon changing from solution to the solid state. Here
only a very moderate redshift of 5 nm is observed for the
emission maximum, no loss of the vibronic features is found,
and no significant quenching of the PLQY in the solid state
is observed. Macrocycle 10b exhibits a PLQY that is about
Figure 5. a) Normalized time-resolved PL spectra of 9 immediately after
excitation (black) and at a delay of 21 ns (gray) in toluene at a concentra-
tion of 1.1ꢃ10ꢀ4 m. b) PL decay transient (gray circles) of 9 and biexpo-
nential fit (black) to the data with decay times of t1 =3.7 ns and t2 =
11.2 ns.
solved PL spectra of 9 at different delay times after excita-
tion and Figure 5B depicts a fluorescence decay transient of
9 fitted to a biexponential decay pattern. These results were
derived from streak camera experiments by using femtosec-
ond laser pulse excitation.
The spectrum straight after excitation exhibits virtually
the same vibronic features as the steady-state measurements
shown in Figure 4a with a maximum lem at 421 nm and vi-
bronic replica at 395 and 445 nm. However, after 21 ns, the
spectrum has evolved into a broad and featureless emission
with the maximum redshifted by 11 nm with respect to the
early spectrum, now centered at 433 nm. Clearly, a second
fluorescent species is present at this concentration; however,
its longer lifetime and less-efficient emission allow observa-
tion only after the intense fluorescence of the isolated spe-
40% of that of polyACTHNUTRGNEUNG(fluorene) (PF)—a blue emitting poly-
mer with a similar emission spectrum and a state-of-the-art
PLQY and documented good OLED performance.
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Molecular Triangles
trum were observed when keeping the current densities in
the device below 2500 Amꢀ12. When driving the device
above this current density value, a redshift of the emission
was observed. This was attributed to a thermally induced re-
organization of the active layer as a consequence of the
Joule heating during operation of the device. It can be sup-
posed that the increased molecular mobility at higher tem-
perature results in an undesired cofacial orientation of the
molecular cores despite the bulkiness of the lateral substitu-
ents. For comparison, macrocycle 10a was also tested in EL
devices (not shown) and the device exhibited a green-emis-
sion EL spectra similar to those observed in PL with a maxi-
mum of 600 cdmꢀ12 at 6.5 V and CIE (xy)=(0.20, 0.31). The
experiments carried out on the TP macrocycles demonstrat-
ed the great potential of this new class of blue emitters for
solution-processed, small-molecule OLED applications.
Benchmarking the attained performance against results ob-
tained for devices based on polymers[12–15] and dendrim-
ers[16–19] using TP building blocks clearly revealed that the
cyclic TP trimers exhibited a strongly improved PLQY; an
essential parameter of high-performance OLEDs. However,
the materials need to be further improved in terms of ther-
mal stability to avoid reorganization/recrystallization before
further device optimization work can take place.
Figure 6. Comparison of a normalized solution (1.1ꢃ10ꢀ4 m) in toluene
and solid-state PL emission spectra of 9, 10a, and 10b obtained from
spin-coated thin films.
Therefore, macrocycle 10b was chosen as an active blue
emitter in a simple two-layer, solution-processed OLED
configuration with 1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-
yl)phenyl (TPBi) as an electron-transport layer in a indium
tin oxide (ITO)/poly(3,4-ethylenedioxythiophene)–poly(styr-
Conclusion
Three new cyclo-7,10-tris-triphenylenyl macrocycles were
successfully prepared by using a Yamamoto-type cyclotrime-
rization approach. This flexible synthetic protocol allowed
for the buildup of molecular triangles in which the TP units
were directly linked to each other. By introducing long
alkoxy side chains to the core of the macrocycle, strong self-
assembly can be induced that is in analogy to the properties
of monomeric alkyl-substituted TPs. As such, a high associa-
tion constant, KA, that was of the same order of magnitude
as those of HBC derivatives could be derived from NMR
spectroscopy solution experiments. The liquid crystallinity of
the discotic molecule was studied by means of 2D-WAXS
and correlated to its thermal properties. The highly organ-
ized columnar superstructures adopted by this fully planar-
ized macrocycle could be applied as charge-carrier pathways
in OFET devices. The comparative study of the optical
properties of the three cyclic trimers revealed significant dif-
ferences that could be correlated to the nature of the pe-
ripheral groups and their substitution pattern. On the one
hand, all three compounds showed deep-blue emission in so-
lution and a tenfold increase in the PLQYs with respect to
parent TP as a result of conjugation along the cyclic back-
bone, which strongly increased the transition dipole moment
of the otherwise symmetry-forbidden S0!S1 transition. On
the other hand, the intrinsic intermolecular packing tenden-
cy could only be sufficiently disrupted to confine the favora-
ble PL properties to the solid state for one derivative that
was composed of two regioisomers. The macrocycle was
tested successfully as an active component in the emissive
enesulfonate) (PEDOT:PSS)/10b
(10 nm)/Al device.[17] The results are depicted in Figure 7.
The electroluminescence (EL) onset for the device is ob-
ACHUTGTNRENN(GU 50 nm)/TPBiACHTUNGTRENN(UGN 10 nm)/Ca-
ACHTUNGTRENNUNG
served at 3.9 V. The maximum luminance is found to be
200 cdmꢀ12 at 6.5 V; macrocycle 10b shows a narrow deep-
blue emission similar to PL with Commission Internationale
De LꢄEclairage (CIE) (xy)=(0.16, 0.07). All devices fabri-
cated from 10b showed good stability over time and no ag-
gregation effects and related changes in the emission spec-
Figure 7. Voltage/current (gray) and voltage/luminance (black) character-
istics of ITO/PEDOT:PSS/10b (50 nm)/TPBi (10 nm)/Ca (10 nm)/Al
diode; the inset shows the corresponding EL spectrum of 10b.
Chem. Asian J. 2011, 6, 3001 – 3010
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3007

E. J. W. List, K. Mꢀllen et al.
FULL PAPERS
ed by filtration, washed with methanol, and used for the next step with-
layer of an OLED and showed promising performance both
regarding emissive properties and device stability. However,
for future studies, even more bulky side groups should be at-
tached to the TP moieties to further suppress the observed
thermal reassembly at a high driving current if OLED appli-
cations of the macrocycles are envisaged.
out further purification. Compound 2 was obtained as a white solid
1
(5.17 g, 8.63 mmol, 87%). H NMR (300 MHz, CD2Cl2): d=7.24–7.08 (m,
10H), 6.93 (s, 2H), 4.04 (t, J=6.6, 4H), 1.82 (p, 4H), 1.56–1.18 (m, 36H),
0.88 ppm (t, J=6.7, 6H); 13C NMR (75 MHz, CD2Cl2): d=149.08, 142.32,
133.75, 130.57, 128.36, 126.71, 116.94, 70.11, 32.56, 30.33, 30.27, 30.05,
29.99, 26.69, 23.31, 14.49 ppm; MS (FD, 8 kV): m/z (%): 595.0 (100.0)
[M+].
Synthesis of 3
Experimental Section
Compound 2 (0.50 g, 0.83 mmol) and iodine (0.23 g, 0.91 mmol) were dis-
solved in toluene (120.0 mL). Then propylene oxide (0.4 mL, 5.72 mmol)
was added. The solution was irradiated with 300 nm (40 W) for 48 h at
room temperature. The crude product was purified by column chroma-
tography (hexane/ethyl acetate=20/1) to yield 3 as a white solid (0.36 g,
0.61 mmol, 73%). 1H NMR (300 MHz, CD2Cl2): d=8.66 (d, J=8.6, 2H),
8.52 (d, J=8.7, 2H), 8.03 (s, 2H), 7.70–7.57 (m, 4H), 4.24 (t, J=6.6, 4H),
1.93 (p, 4H), 1.65–1.18 (m, 36H), 0.88 ppm (t, J=6.6, 6H); 13C NMR
(75 MHz, CD2Cl2): d=150.3, 130.1, 129.6, 127.6, 126.8, 124.7, 123.9,
123.4, 107.3, 69.9, 32.5, 30.7, 30.3, 30.3, 30.1, 30.0, 26.7, 23.3, 14.5 ppm;
MS (FD, 8 kV): m/z (%): 593.5 (100.0) [M+]; elemental analysis calcd
(%) for C42H62O2: C 84.51, H 10.13; found: C 87.21, H 10.98.
Techniques
1H and 13C NMR spectra were recorded on Bruker DPX250 and
DRX500 spectrometers, respectively, and referenced to residual signals
of the deuterated solvent. Field-desorption mass spectra (FD/MS) were
performed with a VG Instruments ZAB 2-SE-FDP spectrometer using
8 kV accelerating voltage. MALDI-TOF mass spectra were measured by
using a Bruker Reflex II instrument utilizing a 337 nm nitrogen laser,
calibrated against poly(ethylene glycol) (3000 gmolꢀ1). The 2D-WAXS
experiments of orientated filaments were performed by means of a rotat-
ing anode (Rigaku 18 kW) X-ray beam with a pinhole collimation and a
2D Siemens detector with a beam diameter of 1.0 mm. A double graphite
monochromator for the CuKa radiation (l=0.154 nm) was used. The pat-
terns were recorded with vertical orientation of the filament axis and
with the beam perpendicular to the filament.
Synthesis of 4
Compound 3 (1.00 g, 1.68 mmol) was dissolved in CH2Cl2 (18.0 mL) and
a catalytic amount of iron powder and iodine was added. Then, a solution
of bromine (1.08 g, 6.76 mmol) in CH2Cl2 (7.2 mL) was added dropwise
at a temperature of ꢀ58C. The reaction was allowed to proceed at this
temperature for 3 h after what it was stopped by the addition of a 10%
solution of sodium thiosulfate. The crude product was recrystallized from
CH2Cl2 to yield 4 as a white crystalline solid (0.84 g, 1.11 mmol, 66%).
1H NMR (300 MHz, THF): d=8.83 (s, 2H), 8.50 (d, J=8.8, 2H), 8.03 (s,
2H), 7.73 (d, J=8.7, 2H), 4.23 (t, J=6.1, 4H), 1.89 (p, 4H), 1.43 (m,
36H), 0.89 ppm (t, J=6.6, 6H); 13C NMR (75 MHz, THF): d=151.7,
131.5, 130.9, 130.2, 127.3, 126.1, 124.8, 121.5, 107.7, 70.0, 33.1, 30.9, 30.9,
30.8, 30.6, 30.5, 27.3, 23.7, 14.6 ppm; MS (FD, 8 kV): m/z (%): 754.2
(100.0) [M+]; elemental analysis calcd (%) for C42H60O2Br2: C 66.84, H
7.75; found: C 64.19, H 5.12.
For time-resolved PL spectroscopy, the materials were dissolved in tolu-
ene at a concentration of 0.2 mgmLꢀ1 and the solutions were transferred
into quartz glass cuvettes with a thickness of 1 mm. The samples were ex-
cited at 300 nm with the output of a commercial laser system consisting
of an optical parametric amplifier (Coherent OPerA Solo) itself pumped
by the output of a titanium:sapphire femtosecond amplifier (Coherent
LIBRA HE) operating at a repetition rate of 1 kHz with a pulse width of
100 fs. The emitted light was collected by an optical telescope and fo-
cused into a spectrograph for spectral dispersion and detected by a
C4742 Hamamatsu Streak Camera system.
For the OLED devices, ITO-covered glass substrates were cleaned with
acetone, toluene, and isopropanol and subsequently exposed to oxygen
plasma. PEDOT:PSS layers were spin-coated under ambient conditions
and dried under an inert atmosphere. Subsequently, the active material
Synthesis of 7
dissolved in toluene (5.0 gLꢀ1
) was spin-coated on top of the PE-
DOT:PSS layer, resulting in a film thickness of about 50 nm, which was
dried at 1208C under a dynamic vacuum less than 1ꢃ10ꢀ5 mbar. The mul-
tilayer cathode and TPBi was thermally deposited in a vacuum coating
unit at base pressures less than 3ꢃ10ꢀ6 mbar. The luminescence/voltage
measurements were performed by using an integrating sphere equipped
with a silicon photodiode and a computer controlled Keithley 237 source
measurement unit. Spectral characterization was done with a Lot-Oriel
Multispec equipped with a DB 401-UV CCD camera from Andor. The
quantum chemical calculations were performed by the DFT approach
with B3LYP hybrid functionals using the 6-31G* basis set.[58]
3,6-Dibromophenanthrene-9,10-dione (6; 0.88 g, 2.40 mmol) and 1,3-di-
phenyl-2-propanone (0.75 g, 3.57 mmol) were dissolved in anhydrous
MeOH (50.0 mL) under an argon atmosphere. Then, a solution of KOH
(0.15 mL) in MeOH (2m) was added dropwise and the mixture was
heated to 808C for 5 min. The brown mixture was fast frozen to 08C and
HCl (1.9 mL; 1.25m in MeOH) was added with stirring to neutralize the
solution to pH 5. The green precipitate was filtered off, washed with cold
MeOH, and purified by column chromatography (hexane/CH2Cl2 =2/1),
affording 7 as a dark green powder (0.95 g, 1.75 mmol, 74%). 1H NMR
(250 MHz, CD2Cl2): d=7.93 (d, J=1.9 Hz, 2H), 7.43 (dd, J=7.4, 5.5 Hz,
6H), 7.39–7.29 (m, 6H), 7.11ppm (dd, J=8.6, 1.9 Hz, 2H). 13C NMR
(62.5 MHz, CD2Cl2): d=197.8, 147.4, 137.8, 136.2, 134.4, 133.0, 132.6,
132.1, 130.2, 129.0, 128.7, 128.6, 128.2, 127.1, 126.7, 124.2, 123.8,
106.8 ppm. MS (FD, 8 kV): m/z (%): 540.2 (100.0) [M+].
Materials
1,2-Dibromo-4,5-bis(dodecyloxy)benzene (1)[49] and 3,6-dibromophenan-
threne-9,10-dione (6)[51] were synthesized according to the literature pro-
cedures. All other chemicals and solvents were purchased from commer-
cial sources and used without further purification. Solvents for synthesis
were purified according to standard procedures. Reactions were carried
out under an argon atmosphere.
Synthesis of 8a
6,9-Dibromophencyclone (7; 450 mg, 0.83 mmol) and oct-4-yne (183 mg,
1.66 mmol) were dissolved in diphenyl ether (10.0 mL) in a microwave
tube. The argon-bubbled mixture was stirred at 2208C under 300 W mi-
crowave irradiation for 8 h. After cooling to room temperature, the reac-
tion mixture was precipitated into MeOH, and further purified by
column chromatography (hexane/CH2Cl2 =4/1), affording 8a (418 mg,
0.67 mmol, 81%). 1H NMR (300 MHz, CD2Cl2): d=8.43 (d, J=2.1 Hz,
2H), 7.53–7.39 (m, 8H), 7.33 (dd, J=7.3, 2.0 Hz, 4H), 7.10 (dd, J=9.1,
2.1 Hz, 2H), 2.90–2.73 (m, 4H), 1.37–1.16 (m, 4H), 0.70 ppm (t, J=
7.3 Hz, 6H). 13C NMR (75 MHz, CD2Cl2): d=143.3, 140.6, 138.5, 132.2,
131.5, 130.5, 129.4, 129.1, 129.1, 127.5, 126.1, 120.4, 115.4, 32.8, 24.8,
Synthesis of 2
1,2-Dibromo-4,5-bis(dodecyloxy)benzene (1, 6.00 g, 9.92 mmol) and phe-
nylboronic acid (3.63 g, 29.77 mmol) were dissolved in toluene
(150.0 mL). Then,
a 2m aqueous solution of potassium carbonate
(40.0 mL) and a few drops of Aliquat 336 were added. After degassing
by argon bubbling, tetrakis(triphenylphosphine)palladium(0) (2.29 g,
1.98 mmol) were added and the resulting mixture was heated to reflux
for 24 h. The precipitate that was formed during the reaction was collect-
3008
www.chemasianj.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3001 – 3010

Molecular Triangles
14.5 ppm; MS (FD, 8 kV): m/z (%): 622.2 (100.0) [M+]; elemental analy-
(%): 1387.33 (100.0) [M+]; elemental analysis calcd (%): C 93.46, H
sis calcd (%) for C36H30Br2: C 69.47, H 4.86; found: C 69.53, H 4.80.
6.54; found: C 93.48, H 6.49.
Synthesis of 8b
6,9-Dibromophencyclone (7; 450 mg, 0.83 mmol) and 1-octyne (183 mg,
1.66 mmol) were dissolved in ortho-xylene (10.0 mL) in a microwave
tube. The argon bubbled mixture was stirred at 1708C under 300 W mi-
crowave irradiation for 8 h. After cooling to room temperature, the reac-
tion mixture was precipitated into MeOH and further purified by column
chromatography (hexane/CH2Cl2 =4:1), affording 8b (475 mg, 0.76 mmol,
92%). 1H NMR (300 MHz, CD2Cl2): d=8.48 (t, J=2.4 Hz, 2H), 7.55 (t,
J=4.5 Hz, 2H), 7.51–7.38 (m, 9H), 7.30 (dd, J=7.4, 2.0 Hz, 2H), 7.15
(ddd, J=15.6, 9.0, 2.0 Hz, 2H), 2.77–2.58 (m, 2H), 1.52 (s, 2H), 1.18 (d,
J=7.4 Hz, 6H), 0.82 ppm (t, J=6.8 Hz, 3H). 13C NMR (75 MHz,
CD2Cl2): d=144.6, 142.3, 141.4, 138.9, 132.8, 132.5, 131.8, 131.7, 131.4,
129.8, 129.6, 129.4, 129.3, 129.1, 127.73, 127.65, 126.2, 120.9, 33.8, 31.8,
31.6, 29.6, 22.9, 14.2 ppm; MS (FD, 8 kV): m/z (%): 622.2 (100.0) [M+];
elemental analysis calcd (%) for C36H30Br2: C 69.47, H 4.86; found: C
69.51, H 4.72.
Acknowledgements
M.G.S. thanks the “Graduate School Materials Science in Mainz” for a
scholarship. H.K. acknowledges funding from the IRTG1404: Self-organ-
ized materials for optoelectronics provided by the DFG. F.L. thanks the
Max Planck Society for funding of a Max Planck Research Group. R.T.
thanks the BMWFJ and the Christian Doppler Society for the financial
support. We would like to thank Lei Dou for the computational analysis
of the NMR spectroscopy data.
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Synthesis of 9
The catalyst solution was prepared inside the glovebox by adding DMF
(6.0 mL) and toluene (12.0 mL) to a mixture of bis(cyclooctadiene)nick-
el(0) (0.12 g, 0.47 mmol), 2,2’-bipyridine (0.07 g, 0.47 mmol) and cyclooc-
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tography on silica gel (CH2Cl2/methanol=10/1). Further purification was
achieved by preparative gel permeation chromatography (chloroform) to
yield 9 as a white solid (25 mg, 0.014 mmol, 21%). 1H NMR (300 MHz,
CDCl3): d=7.95 (s, 6H), 7.35 (d, J=7.6, 6H), 7.16 (d, J=8.1, 6H), 7.03
(s, 6H), 3.75 (t, J=4.1, 12H), 1.79 (p, 12H), 1.55–1.28 (m, 108H),
0.91 ppm (t, J=6.7, 18H); 13C NMR (75 MHz, CDCl3): d=148.3, 133.2,
128.2, 128.0, 123.2, 122.1, 121.9, 117.7, 105.4, 68.4, 31.8, 29.7, 29.6, 29.33,
29.29, 26.1, 22.5, 13.9 ppm; MS (MALDI-TOF): m/z (%): 1783.39 (100.0)
[M+].
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Synthesis of 10a
Bis(cyclooctadiene)nickel(0) (286 mg, 1.04 mmol), cyclooctadiene
(0.13 mL, 1.04 mmol), and 2,2’-bipyridine (162 mg, 1.04 mmol) were dis-
solved in dry toluene (1.0 mL) and dry DMF (2.0 mL) in a Schlenk tube
under glovebox conditions. The resulting solution was stirred for 20 min
at 608C and then a solution of 8a (270 mg, 0.43 mmol) in dry toluene
(12.0 mL) was added dropwise over 30 min. The reaction mixture was
stirred for 12 h at 808C under the exclusion of light. After cooling to
room temperature, the reaction mixture was precipitated into MeOH,
and further purified by column chromatography (hexane/CH2Cl2 =3/1),
affording 10a (142 mg, 0.10 mmol, 70%). 1H NMR (300 MHz, CD2Cl2):
d=9.35 (s, 6H), 8.53 (s, 6H), 7.54 (s, 6H), 7.47–7.29 (m, 30H) 2.79 (s,
12H), 1.37–1.16 (m, 12H), 0.70 ppm (t, J=7.3 Hz, 18H); 13C NMR
(125 MHz, THF): d=143.9, 139.2, 138.6, 135.5, 135.3, 131.9, 131.6, 129.5,
128.5, 126.8, 122.5, 119.9, 119.7, 32.5, 29.7, 13.7 ppm; MS (MALDI-TOF):
m/z (%): 1387.14 (100.0) [M+]; elemental analysis calcd (%) for C108H90
C 93.46, H 6.54; found: C 93.50, H 6.47.
:
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Same procedure as that used for 10a, yielding 10b as a solid (153 mg,
0.11 mmol, 77%). The final product contained two inseparable isomers
(1,1’,1’’ and 1,1’,2’’ hexyl-substituted). 1H NMR (300 MHz, CD2Cl2): d=
9.46 (s, 6H), 8.70–8.28 (m, 6H), 7.70–7.59 (m, 6H), 7.53–7.23 (m, 33H),
2.83–2.60 (m, 6H), 1.63–1.10 (m, 24H), 0.80 ppm (t, J=6.8 Hz, 9H);
13C NMR (125 MHz, THF): d=142.6, 139.8, 139.0, 138.5, 138.4, 137.4,
131.7, 131.6, 131.0, 130.9, 130.1, 129.4, 128.8, 126.8, 124.5, 124.38, 124.36,
122.4, 121.8, 33.4, 31.4, 29.2, 22.4, 13.4 ppm; MS (MALDI-TOF): m/z
Chem. Asian J. 2011, 6, 3001 – 3010
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3009

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Received: March 13, 2011
Published online: July 14, 2011
3010
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