Charge-transfer interactions in a multichromophoric hexaarylbenzene containing pyrene and triarylamines

Article abstract of DOI:10.1021/jo300924x

Two different hexaarylbenzenes with three pyrene and three triarylamine substituents in different positions (trigonal symmetric and asymmetric arrangement) were synthesized, and their charge-transfer states were investigated by optical spectroscopy. In these multichromophoric systems triarylamine acts as the electron donor and pyrene as the electron acceptor. A reference chromophore with only one donor-acceptor pair was also investigated. All these chromophores form charge-transfer states upon photoexcitation which relax with a moderate fluorescence quantum yield to the ground state. The compounds do not differ significantly concerning most of their fluorescence properties, which shows that the fluorescent charge-transfer state is very similar in all chromophores. This observation indicates symmetry breaking for the symmetric chromophore within fluorescence lifetime of several tens of ns. This interpretation was substantiated by fluorescence excitation anisotropy measurements in a sucrose octaacetate matrix.

Full text of DOI:10.1021/jo300924x

Article
pubs.acs.org/joc
Charge-Transfer Interactions in a Multichromophoric
Hexaarylbenzene Containing Pyrene and Triarylamines
Christoph Lambert,* Julia Ehbets, Dirk Rausch, and Markus Steeger
Institut fur Organische Chemie, Universitat Wurzburg, Wilhelm Conrad Rontgen Research Center for Complex Material Systems,
̈
̈
̈
̈
Wurzburg, Center for Nanosystems Chemistry, Am Hubland, 97074 Wurzburg, Germany
̈
̈
S
* Supporting Information
ABSTRACT: Two different hexaarylbenzenes with three pyrene and three
triarylamine substituents in different positions (trigonal symmetric and
asymmetric arrangement) were synthesized, and their charge-transfer states
were investigated by optical spectroscopy. In these multichromophoric systems
triarylamine acts as the electron donor and pyrene as the electron acceptor. A
reference chromophore with only one donor−acceptor pair was also investigated.
All these chromophores form charge-transfer states upon photoexcitation which
relax with a moderate fluorescence quantum yield to the ground state. The
compounds do not differ significantly concerning most of their fluorescence
properties, which shows that the fluorescent charge-transfer state is very similar
in all chromophores. This observation indicates symmetry breaking for the
symmetric chromophore within fluorescence lifetime of several tens of ns. This
interpretation was substantiated by fluorescence excitation anisotropy measure-
ments in a sucrose octaacetate matrix.
vibrational progression and is polarized along the long axis of
INTRODUCTION
■
pyrene. This refers to a HOMO→LUMO transition. Despite
the long fluorescence lifetime, the fluorescence quantum yield
of unsubstituted pyrene is relatively high (0.64 in toluene)2
because intersystem crossing (kISC = 105 s−1) is even slower
than the rate of fluorescence (kf = 106 s−1). Owing to these
facts, pyrene has recently gained much attention because its
luminescent properties may be used in organic light-emitting
diodes (OLEDs)5−7 and other optoelectronic devices,8 as well
as for biolabeling.9,10
Triarylamines are important hole-conducting materials for
optoelectronic devices, most importantly for OLEDs but also
for electrophotography.11−16 The donor strength can easily be
tuned by substituents in ortho- and para-positions whose
presence is also a prerequisite for making triarylamine radical
cations chemically stable as these tend to dimerize at the
otherwise unblocked para-position.17,18 Furthermore, the
relatively small reorganization energy of the triarylamines
supports fast electron-transfer processes.
Pyrene is a versatile chromophore that may act both as an
electron donor and an electron acceptor.1 In this paper, we
combine three pyrene units with three triarylamine moieties in
a hexaarylbenzene (HAB) superchromophore assembly in
order to probe charge-transfer processes and energy migration
within this system. The triarylamines are strong electron donors
that force the pyrenes to be the acceptors.
Pyrene itself shows some unique optical properties: a long
fluorescence lifetime (354 ns),2 delayed fluorescence as a
consequence of triplet−triplet annihilation, and excimer
formation in concentrated solution are only the highlights.3
Most of these properties are the consequence of a very weak
S1←S0 transition (Lb band in Platt’s terminology) at ca. 370 nm
which is polarized perpendicularly to the long axis4 and which is
due to a combination of HOMO-1→LUMO and HOMO→
LUMO+1 excitation (see Figure 1).2 The most prominent
absorption at 334 nm, however, shows a pronounced
Interactions between amines and pyrene have been
investigated quite intensively in the past. These studies mostly
refer to either fluorescence quenching by photoinduced
electron transfer from the amine to the unsaturated hydro-
carbon19−25 or to charge-transfer processes in which the two
redox chromophores were involved.1,26−28 While in the former
process fluorescence from the S1 state of pyrene is quenched by
the formation of pyrene radical anions, in the latter CT states
Received: May 8, 2012
Published: June 25, 2012
Figure 1. Optical transitions in pyrene.
© 2012 American Chemical Society
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Figure 2. Charge-transfer interactions in the multidimensional chromophores 1−3.
Scheme 1. Synthesis of 1−3
are formed from which fluorescence now occurs in a much
different way than from pyrene’s local S1 state. In the majority
of these works pyrene is substituted at its 1-position because of
easier synthetic accessibility. However, following the work of
Marder et al.,29,30 substitution at the 2-position is readily
achieved and will be used in this work.
meric” analogue 3 where only one donor−acceptor pair is
present.
RESULTS AND DISCUSSION
■
Synthesis. The HAB chromophores 1 and 2 were
synthesized by cobalt-catalyzed cyclotrimerization47 of an
appropriately substituted tolan precursor molecule 4. The
cyclotrimerization is sensitive to steric hindrance, which might
explain the low yield of isomer mixture of 25%. For statistical
reasons, one expects the yields of the 1,3,5-isomer 2 and the
1,2,4-isomer 1 to have a 1:3 ratio which was found in similar
cases before.33,48 Indeed, pure asymmetric compound 1 could
be isolated in 18% yield from the isomer mixture by
precipitation from acetone. If the residue contained only
compound 2 in 7% yield, this would lead to the expected ratio
of 7:8≈1:3. However, in the present case we experienced
problems in isolating 2 and the residue had to be purified by
HPLC on a silica gel NUCLEOSIL 120−5 phase with
dichloromethane to give only 2% of pure 2. In this context it
proved critical to use dichloromethane from J. T. Baker
stabilized with amylene.
In the study presented here, we focus on through-space
charge-transfer interactions between triarylamine donors and
pyrene acceptors in multidimensional chromophores. As a
scaffold we use hexaarylbenzene (HAB).31 Recently, HABs
have often been used as a scaffold in complex chromophore
systems in order to study energy or electron-transfer processes
or interchromophore interactions in general or they have been
used for light-harvesting purposes.5,32−46 In the HABs, six
phenyl rings are arranged around a central benzene ring in a
propeller-like fashion. The dihedral angle between the phenyl
substitutents and the benzene ring is ca. 60° which reduces
direct orbital overlap and, thus, conjugational effects via the
benzene core. In the chromophores 1 and 2 studied here, three
triarylamines and three pyrenes are attached to the central
benzene and, thus, are an integral part of the HAB. Owing to
the pyrenes being attached to the central benzene at their 2-
position conjugational effects are minimized by the fact that the
HOMO and the LUMO of pyrene possess nodes along the
long molecular axis (see Figure 1).2 Thus, the interaction
between pairs of triarylamines and pyrene is mainly through-
space. In the symmetric chromophore 2 with the triarylamines
in 1-, 3-, and 5-position of the central benzene ring there are six
through-space interactions indicated by red arrows in Figure 2.
In the asymmetric isomer 1 there are only four such
interactions. For comparison we also investigated a “mono-
The reference chromophore 3 was synthesized by a Diels−
Alder reaction of tetraphenylcyclopentadienone and tolan 4 in
57% yield. The synthesis of the tolan 4 proved to be tricky.
Several attempts to use either 2-bromo-, 2-OTos-, or 2-OTf-
substituted pyrene in Sonogashira or Stille reactions led to 20%
yield at best. Finally, the synthesis of 4 was accomplished by a
Sonogashira reaction of 2-chloropyrene 5 and triarylamine
alkyne 6 in a microwave oven in 58% yield. The chloro
compound 5 in turn was prepared from 2-pyreneboronic acid
pinacol ester 7 in 97% yield. A similar reaction using 2-
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Figure 3. (a) Absorption spectra of 1−3 in THF; (b) magnified CT band of 2.
iododpyrene yielded 62% of 4 but because the synthesis of 2-
iodopyrene from pyrene-2-boronic acid49 is associated with
only moderate yields (30%) the route via 2-chloropyrene is
preferred and presented here (Scheme 1).
and the pyrene acceptor. Fluorescence excitation spectra are
practically identical to the absorption spectra and prove the CT
emission originating from the state which corresponds to the
lowest energy CT absorption band at ca. 25400 cm−1
irrespective of the excitation energy. A plot of the reduced
UV/vis and Fluorescence Spectroscopy. The absorption
spectra of 1−3 are very similar and show several distinct
features (see Figure 3a): a broad and structureless band around
36000 cm−1 is mainly due to a localized π−π* excitation of the
triarylamine moieties. At 29100 cm−1, we identify the La-
transition of the pyrene chromophores. This band has a
pronounced vibronic progression as found in many pyrene
derivatives.4 Between 26000 and 28000 cm−1 there is the weak
pyrene Lb band visible. Because of the localized nature of these
transitions, all these bands are hardly solvatochromic. However,
at ca. 25400 cm−1 (in cyclohexane) there is an even weaker but
broad and structureless band which shows a positive
solvatochromism as can be seen from the different band
maximum in acetonitrile: 25800 cm−1 (see Figure 3b). We
assign this band to a charge-transfer (CT) excitation between
the triarylamine donor and the pyrene acceptor. Accordingly,
this band is more intense for 2 where six CT interactions are
possible than for 1 with four such interactions, while 3 shows
the weakest CT band with only one interaction.
emission (intensity divided by v3) and absorption spectra
̃
(intensity divided by v)50 of 3 in cyclohexane allows us to
̃
create a mirror image of the fluorescence CT band and to
identify more clearly the CT band in the absorption spectra
(Figure 5). The 00-energy was determined as the intersection
between both bands and is 24300 cm−1.
The fluorescence quantum yields ϕf of 1−3 were determined
in different solvents (see Table 1) and do not differ significantly
between the chromophores. However, the quantum yield
strongly depends on the solvent polarity and ranges between ca.
7% in acetonitrile up to ca. 30% in cyclohexane. Fluorescence
lifetimes of 1−3 were determined by a gated detection
technique with pulsed LED at either 340 or 372 nm. In all
cases, monoexponential decays were observed (see Figure 6)
and the lifetimes were obtained by deconvolution of the decay
curves with the instrument response function. The lifetimes are
between ca. 45 ns in acetonitrile and ca. 25 ns in cyclohexane
but again do not differ significantly for the three chromophores.
With eqs 1 and 2 we calculated the rate constants for the
radiative deactivation kf and for the nonradiative deactivation
knr. With kf and the Strickler−Berg51 eq 3 we derived the
transition moments μfl which characterize the individual CT
transitions. In stark contrast, it is difficult to extract the CT
bands from the absorption spectra for two reasons: first, in 1
and 2 there are four and six CT transitions at similar energy,
and second, the CT band overlap strongly with the Lb bands.
The fluorescence of 1−3 also shows a pronounced positive
solvatochromism, e.g., the broad and featureless emission band
of 3 has a maximum at 22900 cm−1 in cyclohexane but at 17200
cm−1 in acetonitrile (see Figure 4). This behavior contrasts
those of unsubstituted triarylamines and of pyrene and is
attributed to the CT transition between the triarylamine donor
ϕ
τf
f
kf =
(1)
1 − ϕ
f
knr
=
τf
(2)
ge v−3I dv
∫
̃
̃
3hε0
9
f
μf2l =
·
·
·
kf
n(n2 + 2)2
16·106π3
gg
I dv
∫
̃
f
(3)
In eq 3, h is Planck’s constant, ε0 is the electric field constant, n
is the index of refraction of the solvent, gg and ge are the degree
of degeneracy of ground and excited state, and If is the
fluorescence intensity. From Table 1 it is obvious that the
transition moments are very similar for all compounds but
Figure 4. Fluorescence spectra of 3 in different solvents.
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Figure 5. (a) Reduced absorption and fluorescence spectra of 3 in cyclohexane. (b) Magnification of the gray shaded area of (a).
a
Table 1. Fluorescence Data of 1−3
also show fluorescence with a similar lifetime and quantum
yield. However, the fluorescence solvatochromism is much
stronger in the borane based HABs than in 1−3 which,
together with the somewhat lower CT state energy, indicates
that the triarylborane is a much better electron acceptor than
pyrene. However, the electronic coupling might also be
stronger in the boron HABs. Both effects may enhance the
dipole moment difference upon excitation and, thus, the
solvatochromism.52,53
Fluorescence Excitation Anisotropy. In order to gain a
more detailed insight into the energy-transfer processes in 1
and 2 we measured the fluorescence excitation anisotropy of
these chromophores in sucrose octaacetate which forms a
nonpolar solid glass matrix at rt.54,55 Fluorescence anisotropy r
is defined by eq 4 in which IVV and IVH is the fluorescence
intensity with excitation and emission polarizer set vertically or
horizontally, respectively, and G is an apparatus dependent
correction factor. The anisotropy r can be related to the angle
Θ of absorption and emission transition moment. Depending
on this angle, r can vary between 0.4 (Θ = 0°) and −0.2 (Θ =
90°).56−58
kf
knr
v
(107
)
(107
μfl
̃
fl
(cm−1
)
ϕf
τf (ns)
s−1
s−1
)
(D)
b
MeCN
1
2
3
1
2
3
1
2
3
1
2
3
17200
17200
17200
19300
19300
19400
21300
21300
21600
22600
22500
22900
0.06
0.07
0.07
0.15
0.16
0.15
0.21
0.24
0.26
0.22
0.31
0.28
44.6
0.13
0.17
0.15
0.39
0.39
0.37
0.85
0.71
0.76
0.86
1.18
0.93
2.11
2.22
2.02
2.22
2.07
2.11
3.20
2.24
2.15
3.05
2.63
2.39
0.66
0.76
0.71
0.89
0.89
0.86
1.13
1.04
1.06
1.02
1.20
1.04
c
41.9
c
45.7
b
THF
38.3
c
40.6
c
40.2
b
n-Bu2O
cyclohexane
24.7
b
33.9
b
34.4
b
25.6
b
26.2
b
30.1
a
v , fluorescence energy; ϕ , quantum yield; τ , lifetime; k , fluorescence
rate constant; knr, nonradiative rate constant; μfl, transition moment of
fluorescence. Excitation at 340 nm. Excitation at 372 nm.
̃
fl
f
f
f
b
c
2 3cos2 Θ − 1
IVV − IVH·G
IVV + 2·IVH·G
r =
=
·
5
2
(4)
The excitation anisotropy spectra of 1−3 are given in Figure 8.
The reference compound 3 shows anisotropy of almost 0.4 at
the low energy foot of the CT absorption band. Thus, emission
and absorption transition moments are almost parallel, that is,
excitation is into the state from which also emission occurs.
Deviations from the ideal r = 0.4 may be observed because of
partial energy transfer between different molecules or because
of molecular rearrangement during the excited state lifetime. At
higher energy r decreases to 0.3 at 25000 cm−1 which is due to
increasing overlap with the Lb band. At the energy of the Lb
band (26000−28000 cm−1) the anisotropy is around 0.2 which
indicates an angle between the Lb transition moment and the
Figure 6. Fluorescence decay profile of 2 at 340 nm excitation and
monoexponential fit (residues are given in blue).
increase with decreasing solvent polarity from ca. 0.7 D in
acetonitrile to ca. 1.1 D in cyclohexane. The smaller transition
moment in the more polar solvent is in agreement with a more
complete charge transfer in acetonitrile since a 100% charge
separation would require a vanishing orbital overlap between
donor and acceptor and, thus, an also vanishing transition
moment. The dipole moments on the order of 1 D are very
similar to those recently observed in a HABs chromophore with
triarylamine donors and triarylborane acceptors.48 These HABs
CT transition of ca. 35
5°. From this angle, we derive a
dihedral twisting angle of the pyrene chromophore and the
central benzene ring of ca. 32°. However, we stress that this
angle value is associated with a very large error. At the energies
of the La band the anisotropy drops further to ca. r = 0 and
follows nicely the vibronic progression of this band. This
anisotropy corresponds to a ca. 55
5° angle between the
transition moments of the CT and the La band. If we assume
the CT proceeding from the center of the triarylamine to the
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center of the pyrene we may indeed derive an angle of ca. 60°
between this CT transition moment and the La transition
moment which is polarized along the pyrene long axis. Strong
overlap of higher energy pyrene bands with those of the
triarylamine precludes further interpretation of the anisotropy
above 33000 cm−1.
in an anisotropy of r = 0.156,57 as indeed observed in the energy
region of the Lb and La bands between 25000 and 33000 cm−1.
However one must be cautious with this interpretation because
such a depolarization can also be caused accidentally by band
overlap. Excitation at the red edge of the CT band (red arrow
in Figure 7) populates the lowest energy state only from which
emission with maximal anisotropy (r → 0.4) is expected
because the transition moments between excitation and
emission are parallel (Θ = 0°): a “red-edge excitation effect”
results.
The anisotropies of 1 and 2 are very similar. They start at
somewhat lower values than in 3 but decrease steadily and
much stronger than in 3 down to r = 0.1 at ca. 25000 cm−1.
Such a “red-edge excitation effect”59−62 has frequently been
observed in multidimensional chromophores and is caused by
energy transfer between different states of slightly different
energy within one chromophore molecule: in symmetric
chromophores like 2 exciton coupling theory63 tells us that
the six equivalent CT states (see Figure 2) interact and produce
a set of two pairs of degenerate CT states and two totally
symmetric CT states.64 Because of the small transition moment
of the CT states (on the order of 1 D), these energy splittings
will be rather small. However, even in such seemingly
symmetric chromophores symmetry breaking may be induced
by an asymmetric matrix (or solvent) environment which lifts
the degeneracy of the CT states and leads to slightly different
energies; see Figure 7.65 If the higher energy states are excited
CONCLUSIONS
■
Sonogashira reaction of the now readily available 2-chloropyr-
ene with ethynyltriarylamine allowed the synthesis of tolan
derivatives with pyrene attached at the 2-position. Cobalt-
catalyzed trimerization of these tolans led to two different HAB
chromophores which form CT states upon photoexcitation.
This means that in combination with triarylamine donors
pyrene acts as the electron acceptor. These CT states relax with
moderate fluorescence quantum yields to the ground state. The
compounds 1−3 do not differ significantly concerning most of
their fluorescence properties which indicates that the
fluorescent CT state is very similar in all chromophores. For
the superficially symmetric HAB 2, this requires symmetry
breaking within the fluorescence lifetime of several tens of ns,
that is, after photon absorption the excitation may travel around
all donor−acceptor pairs but finally gets trapped within
fluorescence lifetime in one donor−acceptor pair from which
emission then occurs. Because of the “round-trip”66 through all
donor−acceptor pairs depolarization with r = 0.1 within two
dimensions is found at higher energies. At the lowest energy of
the CT band (red edge) only those donor−acceptor pairs
whose matrix surrounding and conformational orientation are
energetically optimal are excited. These states fluoresce
preferentially with high anisotropy (r → 0.4) because energy
transfer to higher lying CT states is unfavorable. The
asymmetric HAB 1 is very similar to 2 in all optical
characteristics which supports the above made conclusions.
Model chromophore 3 shows a somewhat more detailed
anisotropy which allows deducing the relative orientation of the
pyrene moiety.
Figure 7. Six degenerate charge-transfer states in 2 couple to yield two
sets of degenerate CT states and two nondegenerate CT states (within
hexagonal symmetry). Symmetry breaking lifts the degeneracy. Blue
arrow: excitation into higher lying states. Dashed arrows: energy
transfer. Red arrows: absorption and emission into and from the
lowest energy CT state.
EXPERIMENTAL SECTION
■
UV/vis/NIR spectra were measured in 1 cm quartz cuvettes with a
JASCO V-670 spectrometer using Uvasol solvents from Merck.
Absorption spectra were recorded at ca. 1 × 10−5 M.
Fluorescence measurements were performed with a Photon
Technology International (PTI) QM fluorescence spectrometer.
Standard 1 cm cuvettes were used and spectra were recorded in
Uvasol solvents from Merck after purging the samples for 15 min with
argon gas. As a fluorescence standard, quinine sulfate in 1 M sulfuric
acid (ϕf = 0.546) was used and the following equation was applied to
determine the quantum yields:67
I(v)·OD ·(n20)2
̃
⎛
⎜
⎝
⎞
⎟
⎠
Figure 8. Fluorescence excitation anisotropy in sucrose octaacetate at
rt (red, green and blue triangles). The absorption and fluorescence
spectra are those of 3 in dibutyl ether.
̃
ref
D
ϕ = ϕ
f
f,ref
I(v)ref ·OD·(nD20)2ref
̃
where ϕf is the quantum yield of the sample, I(ν) the integrated
emission band, OD the optical density of the absorption band at the
excitation wavelength, and nD is the refraction index of the solvent.
Fluorescence lifetimes were measured with a PTI TM fluorescence
lifetime spectrometer with either a pulsed 340 nm or a 372 nm LED
for excitation. Colloidal silica in deionized water was used as scatter
solution to determine the instrument response. Lifetimes were
determined by fitting the decay curves with an exponential decay
(blue arrow in Figure 7), energy transfer between these states
leads to the population of the lowest energy state from which
emission occurs. This process causes a depolarization if the
energy transfer is faster than the fluorescence lifetime which is a
reasonable assumption given the long lifetime on the order of
10−30 ns. A total depolarization within two dimensions results
20
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function. Solvents and cuvette were used as in the steady state
fluorescence experiments.
purified by HPLC (VP 250/10 NUCLEOSIL 120-5) in DCM to yield
the symmetric isomer 2.
Fluorescence Excitation Anisotropy. These measurements were
done with the PTI fluorescence spectrometer described above. For
polarized excitation and detection, two Glan−Thompson polarizers
were used. The emission was detected at 21200 cm−1. For the
measurements at rt sucrose octaacetate (SOA) was used as the solid
matrix.55 SOA was purchased from a commercial supplier and
recrystallized from ethanol. SOA and the analyte were dissolved in
dichloromethane (Uvasol) and filtered through a PTFE-filter (0.2 μm
pore size). After purging with argon for 10 min, the solution was
concentrated in vacuo and a colorless oil was obtained. This oil was
filled in a 1 cm quartz cuvette and kept at 100 °C for 1 h and at 150 °C
for 4 h in an oven in order to remove excess solvent.
Synthesis. All reagents were commercially available in standard
quality and used as received. Solvents were purified according to
standard procedures. Reactions requiring inert-gas conditions were
carried out in flame-dried Schlenk vessels. Silica gel (40−63 μm) was
obtained from a commercial supplier. Purity of the synthesized
compounds was checked by inspection of the 13C NMR spectra.
Microwave reactions were performed in MLS μCHEMIST microwave
oven using a closed pressure vessel.
Asymmetric isomer 1: yield 150 mg (18%) of a colorless solid;
C114H81N3O6 [1588.88]; mp 318−322 °C (DCM-d2); 1H NMR
(600.1 MHz, dichloromethane-d2, δ) 8.22 (d, 2 H), 8.09−8.00 (−, 7
H), 7.96−7.85 (−, 14 H), 7.77−7.71 (−, 4 H), 6.86 (AA′, 2 H), 6.79
(AA′, 2 H), 6.74 (AA′, 2 H), 6.53 (AA′, 4 H, MeO-Ph-), 6.45 (AA′, 4
H, MeO-Ph-), 6.42−6.38 (−, 6 H), 6.34 (BB′, 2 H), 6.32 (BB′, 4 H,
MeO-Ph-), 6.17 (AA′, 4 H, MeO-Ph-), 6.11 (BB′, 2 H), 6.08 (BB′, 4 H,
MeO-Ph-), 3.58 (s, 6 H), 3.55 (s, 6 H), 3.44 (s, 6 H); 13C NMR (151
MHz, dichloromethane-d2, δ) 155.4 (Cq), 155.3 (Cq), 155.0 (Cq),
146.4 (Cq), 146.3 (Cq), 146.2 (Cq), 141.9 (Cq), 141.8 (Cq), 141.47
(Cq), 141.46 (Cq), 141.40 (Cq), 141.35 (Cq), 141.32 (Cq), 141.2 (Cq),
140.8 (Cq), 139.5 (Cq), 139.4 (Cq), 139.2 (Cq), 134.6 (Cq), 134.5
(Cq), 134.4 (Cq), 132.7 (CH), 132.6 (CH), 132.5 (CH), 131.6 (Cq),
131.37 (Cq), 131.34 (Cq), 130.14 (Cq), 130.09 (Cq), 130.08 (Cq),
129.4 (CH), 129.3 (CH), 129.2 (CH), 127.9 (CH), 127.65 (CH),
127.59 (CH), 127.2 (CH), 127.15 (CH), 127.12 (CH), 126.0 (CH),
125.92 (CH), 125.89 (CH), 125.4 (CH), 125.3 (CH), 125.0 (CH),
124.95 (CH), 124.92 (CH), 124.89 (Cq), 124.87 (CH), 124.63 (Cq),
124.60 (Cq), 122.7 (Cq), 122.59 (Cq), 122.57 (Cq), 121.7 (CH), 121.4
(CH), 121.3 (CH), 114.43 (CH), 114.37 (CH), 114.1 (CH), 55.59
(CH3), 55.58 (CH3), 55.5 (CH3); ESI-MS pos (high resolution) m/z
calcd for C114H81N3O6 1587.61199, found 1587.61302, Δ = 0.65 ppm.
Symmetric isomer 2: yield 17.0 mg (2%) of a colorless solid;
C114H81N3O6 [1588.88]; mp >350 °C (DCM); 1H NMR (600.1 MHz,
acetone-d6, δ) 8.31 (d, 6 H, H-7), 8.15 (d, 6 H, H-4), 8.07 (m, 3 H, H-
8), 8.00 (s, 6 H, H-2), 7.93 (d, 6 H, H-5), 6.87 (AA′, 6 H, H-15),
6.25−6.15 (−, 30 H, H-14 and MeO-Ph-), 3.47 (s, 18 H, H-21); 13C
NMR (151 MHz, acetone-d6, δ) 155.8 (Cq), 147.0 (Cq), 142.4 (Cq),
141.74 (Cq), 141.70 (Cq), 140.0 (Cq), 135.3 (Cq), 133.4 (CH), 132.2
(Cq), 130.8 (Cq), 130 (CH), 128.4 (CH), 127.9 (CH), 126.8 (CH),
125.8 (CH), 125.42 (Cq), 125.37 (CH), 123.3 (Cq), 122.3 (CH),
114.8 (CH), 55.4 (CH3); ESI-MS pos (high resolution) m/z calcd for
C114H81N3O6 1587.61199, found 1587.61318, Δ = 0.75 ppm.
1-(Pyrenyl)-2-(4-(bis-N,N-(4-methoxy)phenyl)amine)-3,4,5,6-
(tetraphenyl)benzene 3. Compound 4 (87.0 mg, 164 μmol) and
2,3,4,5-tetraphenylcyclopenta-2,4-dienone (95.0 mg, 246 μmol) were
dissolved in Ph2O (15 mL) under inert-gas atmosphere. The mixture
was refluxed for 7 d, the solvent was removed in vacuo, and the residue
was purified by flash chromatography on silica gel (petroleum ether/
dichloromethane 2:3): yield 83 mg (57%) of a colorless solid;
C66H47NO2 [886.09]; mp 301−304 °C (DCM/PE); 1H NMR (600.1
MHz, dichloromethane-d2, δ) 8.14 (d, 2 H, H-7), 7.99−7.95 (-, 3 H,
H-4, H-8), 7.78 (d, 2 H, H-5), 7.71 (s, 2 H, H-2), 6.99−6.85 (m, 17 H,
phenyl), 6.78−6.74 (−, 2 H, phenyl), 6.71−6.67 (−, 1 H, phenyl),
6.62 (AA′, 2 H, H-15), 6.33 (AA′, 4 H, MeO-Ph-), 6.28 (BB′, 4 H,
MeO-Ph-), 6.19 (BB′, 2 H, H-14), 3.55 (s, 6 H, H-21); 13C NMR (151
MHz, dichloromethane-d2, δ) 155.4 (Cq), 146.2 (Cq), 141.5 (Cq),
141.4 (Cq), 141.20 (Cq), 141.19 (Cq), 141.15 (Cq), 141.09 (Cq),
141.08 (Cq), 140.8 (Cq), 140.74 (Cq), 140.68 (Cq), 140.6 (Cq), 139.4
(Cq), 134.3 (Cq) 132.4 (CH), 131.9 (CH), 131.82 (CH), 131.80 (2 ×
CH), 131.5 (Cq), 130(Cq), 129 (CH), 127.7 (CH), 127.2 (CH),
126.98 (CH), 126.94 (CH), 126.92 (2 × CH), 126.0 (CH), 125.64
(CH), 125.61 (CH), 125.59 (CH), 125.3 (2 × CH), 125.1 (CH),
124.8 (Cq), 122.5 (Cq), 121.1 (CH), 114.3 (2 × CH), 55.6 (CH3) (4
× CH-signals of phenyl rings overlap which can be seen by integration
of the appropriate signals); ESI-MS pos. (high resolution) m/z calcd
for C66H47NO2 885.36013, found 885.36059, Δ = 0.52 ppm.
2-Chloropyrene 5. Similar to ref 68. 2-Pyreneboronic acid
pinacole ester (43.0 mg, 131 μmol) was dissolved in MeOH (2
mL), and a solution of CuCl2 (53.0 mg, 393 μmol) in H2O (2 mL)
was added. The green mixture was stirred at 65 °C for 6 h and
extracted with Et2O (3 × 5 mL). The organic phases were washed with
brine (3 × 15 mL) and dried over Na2SO4.The solvent was removed in
vacuo, and the residue was purified by flash chromatography on silica
gel with petroleum ether: yield 30.0 mg (97%) of a colorless solid;
1
C16H9Cl [236.69]; mp 136−145 °C (DCM/PE); H NMR (600.1
MHz, chloroform-d, δ) 8.20 (d, 2 H, H-7), 8.12 (s, 2 H, H-2), 8.10 (d,
2 H, H-4), 8.03 (t, 3 H, H-8) 7.97 (d, 2 H, H-5); 13C NMR (151
MHz, chloroform-d, δ) 132.4 (Cq), 131.8 (Cq), 130.8 (Cq), 128.6
(CH), 126.3 (CH), 126.1 (CH), 125.7 (CH), 124.23 (Cq), 124.17
(CH), 123.0 (CH).
N,N-Di(4-methoxyphenyl)-N-[4-[2-(pyrenyl)ethynyl]phenyl]-
amine 4. Alkyne 669 (127 mg, 384 μmol), 2-chloropyrene 5 (91.0 mg,
384 μmol), Cs2CO3 (125 mg, 384 μmol), and Pd(PPh3)2Cl2 (5.40 mg,
7.69 μmol) were dissolved in DMF (10 mL) and purged with nitrogen
for ca. 5 min. After the addition of DBU (5.79 μL, 38.0 μmol) and
PtBu3 (1 M in toluene, 15.0 μL, 15.0 μmol), the mixture was heated at
150 °C in a microwave oven for 10 min. After being cooled to rt, ethyl
acetate (10 mL) was added and the mixture was filtered over Celite
and then washed with brine. The aqueous phase was extracted with
ethyl acetate (3 × 5 mL), and the combined organic phases were dried
over Na2SO4. The solvent was removed in vacuo, and the residue was
purified by flash chromatography on silica gel (petroleum ether/ethyl
acetate 9:1): yield 118 mg (58%) of a yellow solid; C38H27NO2
1
[529.62]; mp 180-184 °C (hexane); H NMR (600.1 MHz, acetone-
d6, δ) 8.38 (s, 2 H, H-2), 8.30 (d, 2 H, H-7), 8.21 (d, 2 H, H-4 o. H-5),
8.17 (d, 2 H, H-4 o. H-5), 8.08 (m, 1 H, H-8), 7.45 (AA′, 2 H, H-14 o.
H-15), 7.15 (AA′, 4 H, MeO-Ph-), 6.97 (BB′, 4 H, MeO-Ph-), 6.84
(BB′, 2 H, H-14 o. H-15), 3.82 (s, 6 H, H-21); 13C NMR (151 MHz,
acetone-d6, δ) 157.9 (Cq), 150.3 (Cq), 140.7 (Cq), 133.3 (CH), 132.2
(Cq), 132.1 (Cq), 129.1 (CH), 128.5 (CH), 128.1 (CH), 127.8 (CH),
127.4 (CH), 126.4 (CH), 125.0 (Cq), 124.6 (Cq), 122.4 (Cq), 119.0
(CH), 115.8 (CH), 114.0 (Cq), 91.5 (Cq), 89.2 (Cq), 55.7 (CH3);
ESI-MS pos (high resolution) m/z calcd for C38H27NO2 529.20363,
found 529.20371, Δ = 0.15 ppm.
1,2,4-(Pyrenyl)-3,4,6-(4-(bis-N,N-(4-methoxy)phenyl)-
anilino)benzene 1 and 1,3,5-(Pyrenyl)-2,4,6-(4-(bis-N,N-(4-
methoxy)phenyl)anilino)benzene 2. Compound 4 (280 mg, 529
μmol) was dissolved in 1,4-dioxane (12 mL) under inert-gas
atmosphere, and Co2(CO)8 (27.0 mg, 79.0 μmol) was added. The
reaction mixture was refluxed for 7 d. The solvent was removed in
vacuo, and the residue was purified by flash chromatography on silica
gel (petroleum ether/dichloromethane 2:3) to give crude product as
an isomer mixture. The asymmetric isomer 1 was obtained by
precipitation from a concentrated solution in acetone. The residue was
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR and mass spectra. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: christoph.lambert@uni-wuerzburg.de.
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Article
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Deutsche Forschungsgemein-
schaft (La 991/13-1). We acknowledge the assistance of M.
Moos for help with the NMR spectra and the mathematical
evaluation of polarization anisotropy data.
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