Facile synthetic approach to novel core-extended perylene carboximide dyes

Article abstract of DOI:10.1039/b509220e

The straightforward synthesis of two new classes of core-extended perylene chromophores, dibenzocoronene tetracarboxdiimide and indenoperylene dicarboxmonoimide, proves that directional enlargement of the aromatic π-system leads to tailored bathochromic a

Full text of DOI:10.1039/b509220e

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Facile synthetic approach to novel core-extended perylene carboximide
dyes{
Sibylle Mu¨ller and Klaus Mu¨llen*
Received (in Cambridge, UK) 30th June 2005, Accepted 5th July 2005
First published as an Advance Article on the web 19th July 2005
DOI: 10.1039/b509220e
Diverse methodologies to functionalize the perylene aromatic
core are a topic of current research to extend the range of
application of these chromophores as functional dyes or improve
their performance in devices. Perylene tetracarboxdiimides,
functionalized in one bay-region using Diels–Alder reactions
followed by reduction or mono-nitration and cyclization are
known.11 Diindenoperylenes are commercially available pigments
which are synthesized by intermolecular oxidative coupling of
fluoranthene units.12
The straightforward synthesis of two new classes of core-
extended perylene chromophores, dibenzocoronene tetracar-
boxdiimide and indenoperylene dicarboxmonoimide, proves
that directional enlargement of the aromatic p-system leads to
tailored bathochromic and hypsochromic shifts.
Rylene tetracarboxdiimides 1–3 as chromophores with an
extended aromatic p-system display exceptional chemical, thermal,
and photochemical stability with high extinction coefficients.1
Their use has been explored for such demanding applications as
optoelectronic devices,2 thermographical processes,3 photovoltaic
devices,4 energy transfer cascades,5 light emitting diodes,6 and NIR
absorbing systems.7 Extension of the aromatic system along the
long molecular axis from perylene-, 1, to terrylene-, 2,8 and
quaterrylene tetracarboxdiimides, 3,9 (Fig. 1) induces a large
bathochromic shift reaching an absorbance maximum at 780 nm
for 3 and a linear increase of the extinction coefficient up to
170,000 M21 cm21. However, enlargement of the p-system does
not always cause a shift to longer wavelengths. The coronene
tetracarboxdiimides 4 can be regarded as perylene tetracarboxdi-
imides expanded along the short molecular axis. Their absorbance
is hypsochromically shifted by 100 nm to a maximum at 428 nm
compared with that of the perylene derivative, leading to a yellow
colour.10 Stable, yellow chromophores with high molar extinction
coefficients are generally difficult to obtain, as e often increases
with the size of the aromatic system, but these usually absorb more
bathochromically.1c Basic chemical modification of the red or
orange perylene core facilitates a shift of colour to either direction,
yellow or violet.
Herein, we report a straightforward, two-step synthesis to
enlarge the aromatic p-system of available perylene derivatives,
leading to two novel chromophores, namely the indenoperylene
dicarboxmonoimide 5 and the dibenzocoronene tetracarboxdi-
imide 6. Both represent a new class of benzo-condensed derivatives
of the perylene core.
1,7-Dibromoperylene tetracarboxdiimide 7 usually contains
various amounts of the corresponding 1,6-isomer.13 An advantage
of this synthesis is that both isomers react to form the same desired
product. The reaction of 1,7-dibromoperylene tetracarboxdi-
imide
7
with 2-bromophenylboronic acid under Suzuki
conditions afforded 8 in 53% yield (Scheme 1). Self-reaction of
Fig. 1 Rylene- and coronene carboximide derivatives.
Scheme 1 Reagents, conditions and yields: a) (i) 2-bromophenylboronic
acid, (Ph3P)4Pd, K2CO3 (aq), toluene, ethanol, 75 uC, 12 h, 53%; (ii)
(Ph3P)2PdCl2, DBU, DMA, 160 uC, overnight, 46%; b) (i) 2-bromophe-
nylboronic acid, (Ph3P)4Pd, K2CO3 (aq), toluene, ethanol, 75 uC, 4 h, 85%;
(ii) (Ph3P)2PdCl2, DBU, DMA, 160 uC, overnight, 30%.
Max-Planck-Institute for Polymer Research, Ackermannweg 10,
D-55128 Mainz, Germany. E-mail: muellen@mpip-mainz.mpg.de;
Fax: +49 6131 379350; Tel: +49 6131 379150
{ Electronic supplementary information (ESI) available: Full experimental
details. See http://dx.doi.org/10.1039/b509220e
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Chem. Commun., 2005, 4045–4046 | 4045

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powder and a reddish-violet hue in chloroform solution. The
indeno-substitution causes a bathochromic shift of the absorbance
maximum by 15 nm compared to the perylene tetracarboxdiimide.
The fluorescence maximum of 5 is at 565 nm.
In summary, the synthesis of two novel classes of chromophores
was detailed, namely the dibenzocoronene tetracarboxdiimides and
the indenoperylene dicarboxmonoimides, via a short and facile
route. The palladium-catalyzed ring annulation reaction has
opened the way to the enlargement of the aromatic p-system
and has thereby led to new chromophores based on core-extended
perylene dyes. The UV/vis spectrum of dibenzocoronene tetra-
carboxdiimide 6 is characterized by sharp absorption bands
between 400 nm and 500 nm, leading to a brilliant greenish-yellow
appearance. Insoluble derivatives of this new class of chromophore
may be useful as new stable yellow pigments. Further, one can
envision use in optoelectronic devices such as field effect
transistors, as good phase forming ability is expected when
decorated with long alkyl chains. The class of indenoperylene
dicarboxmonoimide 5 with an absorbance maximum of 542 nm
represents a new class of violet dyes and pigments. The application
of 5 for frequency doubling in laser welding will be investigated.
Both chromophores have a high photochemical stability and a
bright fluorescence.
Fig. 2 Absorption spectra of 6 (solid line), 4a (dotted line) and 5 (dashed
line) in CHCl3.
2-bromophenylboronic acid is known to not occur under these
conditions.14 One- and two-fold debrominated products of 8 were
observed in minor amounts (ca. 10%) but this mixture was directly
used successfully for the next step, in which palladium-catalyzed
dehydrohalogenation15 with 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU) in dimethyl acetamide (DMA) furnished dibenzocoronene
tetracarboxdiimide 6 in 46% yield. Analogously, the 9-bromoperyl-
Financial support of this work by the BASF AG is gratefully
acknowledged. S. M. thanks the ‘‘Fonds der chemischen
Industrie’’ and the ‘‘Bundesministerium fu¨r Bildung und
Forschung’’ for financial support.
ene dicarboxmonoimide
9
was Suzuki coupled with
2-bromophenylboronic acid under the same conditions and yielded
10 in 85% (also containing ca. 10% of debrominated 10).
Treatment of this mixture with DBU and a palladium catalyst
promoted cyclization to a five-membered ring, resulting in the
indenoperylene dicarboxmonoimide 5 with a yield of 30%.
Both coronene derivatives 6 and 4a are soluble in common
organic solvents such as dichloromethane, chloroform, or toluene.
In the region of shorter wavelengths, up to 400 nm, the spectrum
of 6 shows a sharp band with a defined structure at 349 nm;
whereas, the band with a maximum absorbance of 338 nm in the
spectrum of 4a is broad (Fig. 2). Only one band with the typical
perylene vibronic structure can be seen at longer wavelength with
an absorbance maximum at 494 nm (e 5 66,000 M21 cm21) which
gives rise to the yellow colour. The extinction coefficient of 6 at
494 nm is comparable with the extinction coefficient of 4a at
428 nm (e 5 62,000 M21 cm21).13 The photochemical stability of 6
is much higher than that of 4a: the extinction coefficient of a
chloroform solution of 4a under UV-irradiation16 dropped to 34%
of its initial value after 10 h. Dibenzocoronene 6 still showed an
extinction coefficient maximum of 76% under the same conditions.
Presumably, the aromatic bonds between the 5- and 6-positions
and the 11- and 12-positions in the coronene tetracarboxdiimides 4
have some double bond character, which makes them less stable.
These bonds are stabilized in the dibenzocoronene tetracarboxdi-
imide 6, leading to the higher stability.
Notes and references
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The yellow solution of 6 appears brighter and greener than that
of 4a, given that there is no absorbance above 515 nm for 6.
Dibenzocoronene 6 has a bright fluorescence with a quantum yield
of 80%, high compared with other yellow fluorophores, e.g.
acridine yellow, which has a fluorescence quantum yield of 47%.17
The indenoperylene 5 has an absorption band with a maximum at
542 nm (e 5 65,000 M21 cm21) which also shows the typical
perylene vibronic structure, causing a violet appearance of the
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16 Quarz cuvettes, lmax 5 254 nm, c 5 6 6 105 M.
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4046 | Chem. Commun., 2005, 4045–4046
This journal is ß The Royal Society of Chemistry 2005