Twofold C?H Activation Enables Synthesis of a Diazacoronene-Type Fluorophore with Near Infrared Emission Through Isosteric Replacement

Article abstract of DOI:10.1002/chem.202004080

The synthesis and photophysical properties of a soluble amide-embedded coronene is reported. The key step in this synthesis is the twofold C?H activation of diazaperylene by a rhodium(III)Cp* catalyst. This unprecedented structural motif shows intense fluorescence in the near infrared region with a small Stokes shift and a distinct vibronic structure, which exhibits a slight extent of negative solvatochromism. Comparison of this compound with some relevant compounds revealed the importance of the amide incorporation in the peripheral concave region including an angular position to retain high aromaticity reflecting that of parent coronene. Treatment of this compound with Lewis acid B(C₆F₅)₃ formed a bis-adduct, which exhibited enhanced aromaticity as a consequence of the increased double bond character of the amide C?N bonds.

Full text of DOI:10.1002/chem.202004080

Accepted Article
Accepted Article
Title: Twofold C–H Activation Enables Synthesis of a Diazacoronene-
type Fluorophore with Near Infrared Emission through Isosteric
Replacement
Authors: Steffen Greßies, Masato Ito, Mika Sakai, Hiroshi Osaki, Ju
Hyun Kim, Tobias Gensch, Constantin Daniliuc, Naoki Ando,
Shigehiro Yamaguchi, and Frank Glorius
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To be cited as: Chem. Eur. J. 10.1002/chem.202004080
Link to VoR: https://doi.org/10.1002/chem.202004080
01/2020

10.1002/chem.202004080
Chemistry - A European Journal
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Twofold C–H Activation Enables Synthesis of a Diazacoronene-
type Fluorophore with Near Infrared Emission through Isosteric
Replacement
Steffen Greßies,[a],† Masato Ito,[b],† Mika Sakai,[b] Hiroshi Osaki,[b] Ju Hyun Kim,[a] Tobias Gensch,[a]
Constantin Daniliuc,[a] Naoki Ando,[b] Shigehiro Yamaguchi,*[b],[c] and Frank Glorius*[a]
[a]
Dr. S. Greßies, Dr. J. H. Kim, Dr. T. Gensch, Dr. C. Daniliuc, Prof. Dr. F. Glorius
Organisch-Chemisches Institut
Westfälische Wilhelms-Universität Münster
Corrensstraße 40, 48149 Münster (Germany)
E-mail: glorius@uni-muenster.de
[b]
M. Ito, M. Sakai, Dr. H. Osaki, Dr. Naoki Ando, Prof. Dr. S. Yamaguchi
Department of Chemistry, Graduate School of Science, and Integrated Research Consortium on Chemical Sciences (IRCCS),
Nagoya University
Furo, Chikusa, Nagoya 464-8602 (Japan)
E-mail: yamaguchi@chem.nagoya-u.ac.jp
[c]
Prof. Dr. S. Yamaguchi
Institute of Transformative Bio-molecules (WPI-ITbM), Nagoya University
Furo, Chikusa, Nagoya 464-8602 (Japan)
†
S. Greßies and M. Ito contributed equally to this work.
Supporting information for this article is given via a link at the end of the document.
Abstract: The synthesis and photophysical properties of a soluble
amide-embedded coronene is reported. The key step in this synthesis
is the twofold C–H activation of diazaperylene by a rhodium(III)Cp*
catalyst. This unprecedented structural motif shows intense
fluorescence in the near infrared region with a small Stokes shift and
a distinct vibronic structure, which exhibits a slight extent of negative
solvatochromism. Comparison of this compound with some relevant
compounds revealed the importance of the amide incorporation in the
peripheral concave region including an angular position to retain high
aromaticity reflecting that of parent coronene. Treatment of this
compound with Lewis acid B(C6F5)3 formed a bis-adduct, which
exhibited enhanced aromaticity as a consequence of the increased
double bond character of the amide C–N bonds.
Introduction
Organic chromophores with distinct photophysical properties
are constantly used as fluorophores for various applications, such
as organic light-emitting diodes (OLED), sensor technology,
photosensitizers, and fluorescent probes for bioimaging.[1]
Besides chemical modification of known fluorophores by
introducing additional substituents, the development of new
structural motifs is a lasting challenge. One promising approach
to this end is to dope polycyclic aromatic hydrocarbons (PAHs)
with heteroatoms, such as B, N, P, and S atoms,[2] or replace a
part of their double bonds with isosteric bonds. For the latter
strategy, a representative one is to introduce a C=N double bond,
which endows the parent skeleton with an electron-accepting
character (Figure 1a).[3] Replacement with a B–N bond as an
isostere of the C=C double bond has also attracted recent
growing attention.[4] Various intriguing B–N-containing PAHs have
been produced,
Figure 1. (a) A replacement strategy with C=C isosteres for constructing a new
PAH scaffold and chemical structures of amide-embedded PAHs and (b)
relevant compounds 1–4 and a key precursor 5.
which can retain aromaticity in the PAH scaffolds dependent on
the incorporation mode of the B–N bond. A crucial benefit to
introduce these isosteric bonds is to enable reducing the
symmetry of PAHs, perturb the electronic structure, and impart
the skeleton with polarity. In general, PAHs with high symmetry
tend to have their lowest-energy electronic transition with a
forbidden character. In contrast, such replacement strategy would
not only perturb the HOMO–LUMO energy gap, resulting in
1
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10.1002/chem.202004080
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bathochromic shifts of the absorption and emission maxima, but
also alter the electronic transition with the allowed character,
rendering it a promising approach to gain a new fluorophore motif.
Herein we focus our attention on employing an amide bond as
an isosteric replacement of a C=C double bond (Figure 1a).[5-7]
The amide C–N bond has a partial double bond character, which
corresponds to one third of the  bond energy of the C=C bond,
which should have a direct impact on the aromaticity of the PAH
skeletons. Moreover, the amide carbonyl group would generate a
local dipole to the skeleton and thereby give rise to the polarity-
dependent character of the absorption and fluorescent properties.
There are two ways to introduce the amide bond into PAHs: either
replacing the double bond at the outer K-region, or integration of
the amide moiety to the peripheral concave region in a fashion
that the inner angular carbon atom is replaced with the amide
nitrogen atom with three distinct C–N bonds. The latter mode is
particularly of interest because it would more significantly perturb
the electronic structure and aromaticity by participation of the
nitrogen lone pair to a hexagon aromatic ring.
The problem is the synthetic challenge of such structural motif.
Recently, amide-embedded pyrene derivatives 1 have been
synthesized by Gryko and coworkers[6] and our group,[7]
independently (Figure 1b). In detail, we utilized a Co(III)Cp*-
catalyzed C–H activation and subsequent alkylation of 2-
phenylpyridines with diazo compounds followed by Lewis acid-
assisted nucleophilic annulation by the pyridyl nitrogen atom.
Since then, related transformations to this structural motif have
been developed using Co- or Rh-catalysis,[8] as well as Pd-
catalyzed carbonylation strategies.[9] Previously, multi-step
synthesis was required to access this motif.[10] Transition metal-
catalyzed C–H activation emerged as powerful tool for organic
synthesis.[11] Rhodium complexes have been utilized in various
C–H activation reactions as efficient and unique catalysts.[12]
While Rh(II)-catalyzed carbenoid insertion reactions into inert C–
H bonds are well established,[13] the alkylation of C–H bonds
through insertion of a rhodium carbene species into a rhodium(III)-
carbon bond is less explored.[14] We envisioned that our synthetic
strategy via C–H activation would allow us to access more
expanded PAHs and, as an attractive candidate, we designed
bis(amide)-embedded coronene 2.
and electronic structure by complexation with a Lewis acid,
demonstrating an advantage of this design strategy in comparison
with the conventional substitution with the C=N double bond.
Herein we report these properties of 2 together with its X-ray
crystal structures without and with B(C6F5)3.
Results and Discussion
For the synthesis, we envisioned that the bis(amide)-
embedded coronene scaffold could be obtained by the twofold C–
H activation of diazaperylene precursor 5 (Figure 1b), which was
synthesized in four steps from commercially available compounds
(Scheme 1).[17] Thus, treatment of 1,5-diaminoanthraquinone 6
with a slight excess of sodium nitrite and sequential addition of
potassium iodide resulted in the formation of 1,5-
diiodoanthraquinone 7. This reaction showed full conversion of 6.
The relatively low yield was mainly due to the challenging
purification of 7, which was poorly soluble in standard organic
solvents. Treatment of 7 with copper(I) acetylide gave 1,5-
di(hexyn-1-yl)anthraquinone 8 in 82% yield with facile purification
due to the increased solubility owing to the alkyl chains.
Compound 8 was further transformed to dibutyl-substituted
diazaperylene 5 in 91% yield by treatment with an excess amount
of urea at high temperatures in DMF.
Notably, amide-embedded pyrene
1 showed intriguing
negative solvatochromism due to increased aromaticity with
increasing the solvent polarity and, consequently, 1 behaves as
“aza-pyrene” and exhibited blue-shifted absorption and emission
bands in more polar solvents.[6] Our interest in this study is to
demonstrate the efficacy of this design strategy to produce amide-
embedded PAHs as “aza-PAH” analogues. Coronene, consisting
of seven fused 6-membered rings, only shows the symmetry-
forbidden absorption band as the lowest-energy electronic
transition around 425 nm.[15] One example of diazacoronene 3
has been reported by Wang and coworkers, which exhibited the
absorption (abs) and emission (em) maxima at 488 nm and 502
nm, respectively.[16] In stark contrast, the synthesized
diazacoronene analogue 2 exhibits pronouncedly red-shifted abs
and em that reach the near infrared region with a high
fluorescence quantum yield. Theoretical studies in comparison
with some relevant molecules including its regioisomer 4 revealed
that the position of the amide moieties plays a crucial role to gain
these properties and 2 has a substantial contribution of a Clar-
sextet canonical structure (Figure 1). Moreover, the amide
carbonyl groups provide an opportunity to tune the aromaticity
Scheme 1. Synthetic route to bis(amide)-embedded coronene 2. For detailed
conditions, see SI. TFE
Dimethylaminopyridine.
=
2,2,2-Trifluoroethanol. DMAP
=
4-
For the final twofold C–H activation step, 2-diazo-4,4-
dimethyl-3-oxopentanoate was selected as a coupling partner,
since the ester group was required for the C–N bond formation,
while an additional electron-withdrawing keto group adjacent to
the diazo group would stabilize the resulting carbene species.
This stabilization effect is crucial for the reactivity as described
previously.7 We also envisioned that the tert-butylcarbonyl group
would help increasing the solubility of the target molecule 2.
Treatment of 5 with 10 mol% of the cationic Rh(III)Cp*
precursor [Rh(III)Cp*(MeCN)3](SbF6)2 and a slight excess of the
diazo compound in 2,2,2-trifluoroethanol (TFE) at 120 °C for 14 h,
unfortunately, resulted in a mixture of the desired compound 2
and a mono-alkylated, mono-annulated product 9 due to
insufficient nucleophilicity of the nitrogen atom at the electrophilic
2
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carbon of the ester group. In the previous report,7 a Co(III)Cp*
catalyst was used in order to facilitate the carbonyl activation due
to its higher Lewis acidity. However, no conversion was observed
for this transformation using the same Co(III)Cp* catalyst, likely
due to the higher sensitivity of Co(III) to steric effects of the
substrate. In contrast, it was found that simple addition of 10 mol%
of 4-dimethylaminopyridine (DMAP) after 14 h to activate the ester
group and additional heating of the reaction mixture resulted in
the formation of the desired compound 2, which was isolated in
15% yield as dark green crystals.
Compound
2
was unequivocally identified by NMR
spectroscopy and mass spectrometry. Specifically, in the 1H NMR
spectrum in CD2Cl2, the compound showed three kinds of signals
in the aromatic region, including the enamine C–H singlet peak at
7.91 ppm (Figure S12), indicative of retaining high aromaticity
even for the amide-containing hexagon ring (vide infra). The
structure of 2 was further identified by X-ray crystallographic
analysis (Figure 2a). A single crystal suitable for the analysis was
obtained by slow evaporation of a sample dissolved in a mixture
of CH2Cl2/pentane (1:9, v/v).[18] Compound 2 crystallized with one
and a half molecules in the asymmetric unit. Both independent
molecules present similar crystallographic bonds and angles
parameters. Only one molecule (the entire molecule) is discussed
below. The crystal structure showed that the tert-butylcarbonyl
moiety has almost a perpendicular orientation against the
polycyclic plane, which should be responsible for the high
solubility. One of the amide-containing hexagon rings is slightly
deviated from the plane of the polycyclic skeleton to avoid the
steric congestion with the neighbouring exocyclic bonds. Notably,
similar to the structure of parent coronene, the C–C bonds at the
K-region tend to have shorter bond distances around 1.35–1.36
Å compared to those of the C–C bonds at the peripheral concave
region (1.37–1.43 Å) (Figure 2b). The amide moiety also follows
this trend that the amide C–N bond is rather long of 1.449(8) Å
and 1.465(8) Å in contrast to the amide C–C(carbonyl) bond of
1.406(8) Å and 1.405(8) Å, while the carbonyl C=O bonds are
subtly long of 1.236(7) Å and 1.235(7) Å. In the packing structure,
the compound forms dimeric -stacked motifs in an offset fashion
with the short interplane distance of 3.32 Å (Figure S1).
The incorporation of the amide moiety into the PAH skeleton
results in significant alternation of the electronic structure, which
was proven by cyclic voltammetry (Figure 3). In CH2Cl2,
compound 2 exhibited two reversible redox processes for
reduction and one reversible redox process for oxidation. Notably,
both of the two-electron reduction and one-electron oxidation
processes were reversible for at least 10 cycles, indicating that
the thus generated reduced and oxidized species are stable under
the measurement conditions. The half wave potentials (E1/2) in the
reductive region were observed at less negative potential of –1.51
V and –1.92 V (vs Fc/Fc+), while the compound showed a rather
less positive first oxidative potential of 0.31 V (vs Fc/Fc+), implying
Figure 2. (a) Crystal structure of 2 (50% probability for thermal ellipsoids),
where hydrogen atoms are omitted for clarity and (b) comparison in bond
lengths [Å] between 2 (left) and coronene (right).[19]
0.31
–1.51
–1.92
–2.5
–2.0
–1.5
–1.0
–0.5
0
0.5
1.0
Voltage / V vs Fc/Fc+
Figure 3. Cyclic voltammogram of bis(amide)-embedded coronene 2 in CH2Cl2:
scan rate: 0.05 V s–1; supporting electrolyte: [nBu4N][PF6] (0.1 M); all potentials
referenced vs. Fc/Fc+.
In the absorption spectrum in CH2Cl2, compound 2 exhibited
an intense band with a distinct vibronic structure in the NIR region
(Figure 4). The spectral shape is in contrast to a broad and
structureless absorption band of amide-embedded pyrene 1,[6,7]
and more similar to those of coronene derivatives in terms of the
distinct vibronic structure, except the forbidden character for the
lowest-energy absorption band.[15c] The molar absorption
coefficient of 2 exceeds 5  104 M–1 cm–1, demonstrating the
impact of the reduced symmetry by embedding the amide
moieties. The absorption maximum (abs) of 2 was significantly
red-shifted to 673 nm, which is longer by 143 nm and 188 nm than
those of 1 (R = C(O)OCH3, abs 530 nm)7 and diazacoronene 3
(abs 485 nm in CHCl3),[16] respectively. In fluorescence spectrum
in the same solvent, bis(amide)-embedded coronene 2 showed a
mirror-image emission band with a distinct vibronic structure. The
emission maximum (em) is 686 nm with a small Stokes shift of
a
narrow HOMO–LUMO gap. Reflecting this electronic
characteristic, the compound exhibited both the absorption and
emission in the near infrared (NIR) region (vide infra).
3
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8.0
the electronic transition energies for the absorption consistent
with the experimental results. The lowest-energy transition band
is assigned to the –* transition in which the HOMO–LUMO
transition is dominant. Both the HOMO and LUMO are delocalized
over the entire  skeleton including the amide moieties (Figure 5).
Importantly, the oscillator strength for this transition is 0.347,
demonstrating its symmetry-allowed character unlike parent
coronene. Calculated optimized structures of 2' in the S0 and S1
(B3LYP/6-31+G(d) level of theory) suggested a small structural
relaxation in the excited state with subtle bond-length changes.
Franck-Condon analysis for the transition from the zero-point
vibrational energy level in the S1 to the S0 was also conducted.
The simulated fluorescence spectrum is well consistent with the
experimental result. The vertical bending vibrational modes in the
S0 are relevant to the intense and small FWHM emission band at
the shorter wavelength around 690 nm, while the stretching
vibrational modes are involved in the second vibronic band at
around 760 nm (Figures S6–8, Table S2).
The calculations including the solvent effect using the
polarizable continuum model (PCM) reproduced the negative
solvatochromism in the absorption spectra. Namely, the
calculated absorption maximum was blue shifted from 624 nm
(1.99 eV) in toluene to 614 nm (2.02 eV) in CH2Cl2, whereas the
HOMO and LUMO energy levels were essentially unchanged
(Figure 5). Close inspection of the optimized structures in these
solvents showed a slightly elongated amide C=O bond as well as
a slightly shortened amide N–C bond (Figure S9), although the
extent of the structural change is small, indicative of the increased
aromaticity of the amide-embedded hexagon ring in a more polar
solvent in the ground state.
Absorption
Emission
6.0
4.0
2.0
0
300
400
500
600
700
800
900
Wavelength / nm
Figure 4. Absorption and emission spectra of 2 in CH2Cl2. Pictures show 2 in
CH2Cl2 (C = 0.003 M) (left) and under UV irradiation (365 nm) (right).
282 cm–1, which is much smaller than that of 1 (R = C(O)OCH3,
1774 cm–1).[7] The fluorescence quantum yield of 2 was as high
as 0.64 in CH2Cl2 and the full-width-at-half-maximum (FWHM) for
the shorter-wavelength band was 29 nm. The fluorescence
lifetime was determined by the time-resolved fluorescence
spectra to be 13 ns, from which the radiative (kr) and nonradiative
(knr) decay rate constants from the singlet excited state were
determined to be 4.9  107 s–1and 2.8  107 s–1, respectively.
We also studied the solvent effect on the photophysical
properties (Table S1). Going from nonpolar toluene to CH2Cl2,
both the absorption and emission bands exhibited subtle blue
shifts from 682 nm to 673 nm and from 692 nm to 686 nm for the

abs and em, respectively. The fluorescence quantum yield is not
significantly affected by the solvent polarity. The fact that the
negative solvatochromism was observed even in the absorption
spectra implies its less polar structure in a more polar solvent
even in the ground state, although the extent of the blue shift is
smaller than that of 1.[6]
Figure 6. NICS(1)zz values of 1, 2', and 4 in toluene together with those of
pyrene and coronene for comparison, calculated at the B3LYP/6-31+G(d) level
of theory.
To gain insight into the aromatic character of the amide-
embedded PAHs, the nucleus-independent chemical shift (NICS)
calculations were conducted at the B3LYP/6-31+G(d) level of
theory[20] (Figure 6). The results showed that all hexagon rings A–
F in the bis(amide)-embedded coronene 2', except the central ring
G, retain high aromaticity in toluene with the NICS(1)zz values in
the range from –23.3 ppm to –16.2 ppm. This is in stark contrast
to the aromatic character of the mono(amide)-embedded pyrene
1 (R = C(O)CH3), in which the amide-embedded ring B only has
the NICS(1)zz value of –8.60 ppm, while those of the adjacent
rings A and C are highly aromatic with the values of –31.6 ppm
and –28.8 ppm, respectively. This significant difference between
Figure 5. TD-DFT calculation of 2' in toluene and CH2Cl2 calculated at the
PBE0/6-31+G(d) level of theory and the pictorial drawings of Kohn-Sham
HOMO and LUMO for 2' in CH2Cl2.
To assign the electronic transition bands observed for 2, we
conducted theoretical calculations for model compound 2' that
furnishes ethyl groups instead of butyl groups. Time-dependent
(TD) DFT calculation at the PBE0/6-31+G(d) level of theory gave
4
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1 and 2' is rationalized by considering the aromatic character of
the corresponding parent PAHs. In light of the Clar’s rule, the rings
A and C in pyrene have high aromaticity, while that of the ring B
is moderate. In contrast, in coronene, the peripheral rings A retain
high aromaticity, while the central ring B shows less aromaticity.
The aromatic characters of the amide-embedded PAHs follow this
trend and the rings B and E can retain high aromaticity despite
the amide N–C bond in the hexagon ring. In other words, the
amide substitution at the peripheral concave region can alter the
electronic structure without significantly altering the aromatic
character. This implication is worth noting when compared to the
other substitution mode like in 4, where the amide-embedded ring
B does not have high aromaticity by reflecting a dominant
character of the perylene scaffold. The NICS calculation of 2' also
showed that the increase in the solvent polarity from toluene to
CH2Cl2 renders the NICS(1)zz value of the ring B and E slightly
more negative from –17.6 and –16.9 ppm to –18.0 and –17.2 ppm
(Figure S10). This change is likely responsible for the
experimentally observed negative solvatochromism.
demonstrated for various -conjugated systems containing N-
heteroaryls or carbonyl groups, which generally results in
decreasing their LUMO levels, and thereby gives rise to red-
shifted absorption and emission bands.[21] We envisioned that
complexation of our amide-embedded coronene with a Lewis acid
would enhance the double bond character of the amide C–N
bonds and thereby increase the aromaticity of the amide-
embedded hexagon ring. Thus, we treated compound 2 with
B(C6F5)3 in CH2Cl2 and monitored the change in the absorption
spectra. Upon addition of B(C6F5)3 to a solution of 2 (1.17 x 10–5
M), the intense sharp band for 2 at 673 nm gradually decreased
in intensity and a new broad band appeared around 655 nm with
a broad tail in the longer wavelength region. An isosbestic point
was observed at 658 nm and 703 nm until addition of ca. 2.0 equiv
of B(C6F5)3, indicative of partial formation of a mono-B(C6F5)3
adduct. Further increase in the amount of B(C6F5)3 resulted in the
rise of the broad absorption band with the abs of 709 nm while
decreasing the intensity of the absorption bands at 655 nm and
673 nm. We assumed the formation of bis-B(C6F5)3 adduct
2[B(C6F5)3]2, which was ultimately corroborated by the X-ray
crystallographic analysis[18] (vide infra). The resulting CH2Cl2
solution of 2[B(C6F5)3]2 showed no fluorescence.
(a)
The crystal structure of 2[B(C6F5)3]2 showed that two B(C6F5)3
units sit above and below the plane of the amide-embedded
coronene skeleton with the O–B distance of 1.571(6) Å. As a
result of this complexation, the amide-embedded hexagon ring
itself was deviated from the plane to a more extent compared to
that of parent 2. Importantly, the amide N–C bond was shortened
to be 1.418(6) Å, while the amide C–O bond length is elongated
to 1.307(5) Å, indicative of the increased aromaticity by the
complexation with B(C6F5)3. Indeed, the NICS(1)zz value of the
amide-embedded ring, calculated using the crystal structure at
the same level as that for 2', was more negative value of –21.4
ppm compared to those (–17.6 and –16.9 ppm) in 2' (Figure S11).
6.0
B(C6F5)3 / M
0
2.34 × 10–5
2.34 × 10–4
4.0
2.0
0
300
400
500
600
700
800
900
Wavelength / nm
(b)
O
B(C6F5)3
nBu
Conclusion
tBu
N
O
O
N
tBu
(C6F5)3B
We succeeded in synthesizing bis(amide)-embedded
coronene by the twofold C–H activation of a diazaperylene. The
close inspection of its structure and properties in comparison with
some relevant compounds revealed that the amide-replacement
strategy is a useful design to alter the electronic structure of the
PAH skeleton. The installation of the amide bond to the peripheral
concave region is shown to be crucial for the retained high
aromaticity of the parent skeleton. Therefore, the resulting
compound behaves as a diaza-coronene (Figure 1). Notably, the
synthesized bis(amide)-embedded coronene exhibited a far more
significantly red-shifted absorption band compared to the known
diazacoronene 3. Our diazacoronene has a deep green color and
an intense NIR emission with the em of 686 nm and a high
fluorescence quantum yield of 0.64 in CH2Cl2. These properties
demonstrate the efficacy of this design strategy to gain novel
fluorophore skeletons for -electron materials. An additional
feature of this compound class is its capability to tune the
electronic structure by the complexation with a Lewis acid. Taking
advantage of a set of these properties we are currently working
on expanding the application of this structural motif to various
directions including bioimaging.
nBu
O
Figure 7. (a) Absorption spectral change of 2 (1.17  10–5 M) in CH2Cl2 upon
addition of B(C6F5)3 and (b) crystal structure of 2[B(C6F5)3]2 (50% probability of
thermal ellipsoids), where hydrogen atoms and solvent molecules included in
the crystalline lattice are omitted for clarity.
The amide-replacement strategy provides an additional option
to modify the electronic structure of PAH, namely the
complexation with a Lewis acid. Such electronic tuning has been
5
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[9]
a) H. Yu, G. Zhang, H. Huang, Angew. Chem. Int. Ed. 2015, 54, 10912–
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Lett. 2019, 21, 9114–9118.
Acknowledgements
We thank the Deutsche Forschungsgemeinschaft (Leibniz
Award) and the Humboldt Foundation (J.H.K.) for generous
financial support. This work also received generous funding from
JSPS KAKENHI grants (18H05261). We also thank JSPS Core-
to-Core Program, A. Advanced Research Networks. We also
thank Dr. Klaus Bergander for NMR assistance, Prof. T. Yanai
and Mr. N. Inai (Nagoya University) for the discussion about the
Franck-Condon analysis and Prof. T. Sasamori (Nagoya City
University) for the help of the X-ray crystallographic analysis.
[10] T. A. Alanine, W. R. J. D. Galloway, T. M. McGuire, D. R. Spring, Eur. J.
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Keywords: C–H activation • amide • coronene • fluorescence •
aromaticity
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10.1002/chem.202004080
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Twofold C–H activation of diazaperylene by a rhodium catalyst produces a bis(amide)-embedded coronene, which retains high
aromaticity and exhibits an intense near infrared fluorescence with a high quantum yield. Thus, the replacement of C=C double bonds
with amides represents a useful strategy for emissive polycyclic aromatic hydrocarbons (PAH). Further complexation with B(C6F5)3
enhances the aromaticity of the amide-embedded hexagon rings.
Institute and/or researcher Twitter usernames: @GloriusGroup
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