Introduction of two anthracene moieties into perylenebis(dicarboximide) Core by suzukimiyaura coupling toward construction of donoracceptordonor arrays

Article abstract of DOI:10.1246/cl.2011.970

To create new φ-conjugated compounds having a donoracceptordonor array, two 4-(9-anthrylethynyl)phenyl groups were introduced into a perylenebis(dicarboximide) structure at 1,6- or 1,7-positions by the SuzukiMiyaura coupling of corresponding dibromoperyle

Full text of DOI:10.1246/cl.2011.970

doi:10.1246/cl.2011.970
970
Published on the web September 5, 2011
Introduction of Two Anthracene Moieties into Perylenebis(dicarboximide) Core
by Suzuki-Miyaura Coupling toward Construction
of Donor-Acceptor-Donor Arrays
Tetsuo Iwanaga,1 Hiroko Ida,1 Makoto Takezaki,2 and Shinji Toyota*1
1Department of Chemistry, Faculty of Science, Okayama University of Science,
1-1 Ridaicho, Kita-ku, Okayama 700-0005
2Department of Applied Chemistry, Faculty of Engineering, Okayama University of Science,
1-1 Ridaicho, Kita-ku, Okayama 700-0005
(Received May 30, 2011; CL-110458; E-mail: stoyo@chem.ous.ac.jp)
To create new ³-conjugated compounds having a donor-
(AEP) groups at 1,6- and 1,7-positions, respectively, by the
Suzuki-Miyaura coupling. As far as we surveyed, anthracene
units have not been adopted at the bay positions in functional PBI
materials.7 We expected that the rod-like units should not only
extend the ³-conjugation but also result in strong absorption and
photoinduced electron transfer. We herein report the synthesis and
spectroscopic data of the new D-A-D type PBI derivatives.
Features in their electronic spectra and electrochemical data were
compared with those of phenyl analogs 1b and 2b to evaluate the
role of the anthracene units.
acceptor-donor array, two 4-(9-anthrylethynyl)phenyl groups
were introduced into a perylenebis(dicarboximide) structure at
1,6- or 1,7-positions by the Suzuki-Miyaura coupling of
corresponding dibromoperylenebis(dicarboximide) and boronic
acid ester derivatives. The UV-vis and fluorescence spectra and
the electrochemical data of these donor-acceptor-donor type
compounds suggested weak electronic interactions between the
anthracene units and the perylenebis(dicarboximide) unit.
Target compounds 1a and 2a were synthesized by the
Suzuki-Miyaura coupling (Figure 1).8 A mixture of dibromo-PBI
derivatives 3 and 4 in a 1:4 ratio, which were difficult to separate,
was prepared by bromination followed by imidation of perylene-
tetracarboxylic dianhydride by a known method.9 Boronic
acid ester 5a was prepared by the Sonogashira coupling of
2-(4-iodophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane10 and
9-ethynylanthracene.11 The Suzuki-Miyaura coupling of 3 and
4 with 5a was carried out in a conventional manner with
[Pd(PPh3)4] and K2CO3 (aq) in THF. From the reaction products,
1a and 2a could be separated by chromatography on silica gel in
24 and 52% yields, respectively. Compounds 1a and 2a were
obtained as a dark green solid and a purple solid, respectively, and
were stable under ambient conditions. Phenyl analogs 1b and 2b
were similarly synthesized from 3, 4, and 5b in 12 and 50%
yields, respectively. These compounds were reasonably charac-
terized by NMR and mass spectrometry.12
Perylenebis(dicarboximide) (PBI) units have been extensive-
ly utilized in the molecular design of various functional molecules
because of their abilities as ³-acceptor as well as effective
chromophores and fluorophores (Figure 1).1 It is noted that the
properties of PBI derivatives are readily tunable by the introduc-
tion of substituents at aromatic moieties and imide-nitrogen
atoms. Substituents at the bay positions (1,6,7,12-C) are known to
greatly influence the electronic properties of the perylene moiety.
In particular, the attachment of donor moieties to form a donor-
acceptor (D-A) array2 is a fascinating motif for organic dyes,3
FETs,1b,1c,4 and solar cell devices.5 In order to synthesize such
molecules, brominated PBIs are convenient starting materials that
can be used for various cross-coupling reactions. For example,
phthalocyanine and porphyrin units have been successfully
introduced via acetylene linkers by the Sonogashira coupling.6
In order to create new types of PBI derivatives as candidates for
functional molecules, we introduced two rod-like donor units
involving electron-rich anthracene moieties into a PBI center to
construct a rigid D-A-D array that tends to form segregated
tabular assemblies in the solid state. Therefore, we synthesized
compounds 1a and 2a having two 4-(9-anthrylethynyl)phenyl
The regioisomers were readily identified from the signal
patterns of the 1H NMR spectra based on the differences in
molecular symmetry. Compound 1a of C2v symmetry gave two
sets of signals due to N-CH2 protons at ¤ 4.14 and 4.23, whereas
2a of C2h symmetry gave one set of signals at ¤ 4.11. Signals
Figure 1. Synthesis of donor-acceptor-donor type PBI derivatives 1 and 2.
Chem. Lett. 2011, 40, 970-971
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

971
Table 1. Fluorescence and electrochemical data of PBI derivatives
and reference compounds
Compound
-
em/nm (Φf)a
¸f/nsb
E1/2red/Vc
1a
2a
1b
2b
7
594 (0.03)
600 (0.02)
612 (0.76)
617 (0.78)
571 (0.02)
527 (0.91)
2.99
2.60
7.98
5.30
4.64
3.65
¹1.03, ¹1.21
¹1.04, ¹1.18
¹1.01, ¹1.18
¹1.05, ¹1.20
¹1.05, ¹1.20
¹0.97, ¹1.11d
6
aAbsolute fluorescence quantum yields. bFluorescence lifetimes.
¹1
cMeasured in CH2Cl2 (1.0 mmol L
)
with n-Bu4NBF4
(0.10 mol L¹1) as supporting electrolyte, Ag/Ag+ as reference
electrode. Values for compound 4 instead of the parent PBI 6.
d
Figure 2. Absorption spectra of PBI derivatives and reference
compounds in CHCl3 at 1.2-2.5 © 10¹5 M.
1a, 2a, 1b,
2b, 7, and 6.
twisting structure between the PBI unit and the attaching
phenylene unit.
In conclusion, we synthesized new PBI derivatives with two
AEP groups by the Suzuki-Miyaura coupling. The photophysical
properties were influenced by the rod-like donor units for several
factors involving electron-transfer interactions. These properties
can be further tuned by the introduction of various substituents,
and cross-coupling reactions are powerful tools for the function-
alization of PBI derivatives. Further studies of the synthesis of
other PBI derivatives and the assembly of the D-A-D type
molecules for use in organic devices are in progress.
assignable the perylene protons were observed as one singlet and
two doublets for both compounds. Those signals were shifted
upfield by 0.3-1.0 ppm upon the introduction of AEP units,
because the protons are located in the shielding region of the
attaching phenylene groups. This structural requirement is
supported by the DFT calculation of 1a¤ and 2a¤, where the
N-alkyl groups are methyl groups instead of alkyl groups. The
structural optimization at the B3LYP/6-31G* level suggested that
dihedral angles between the central PBI unit and the attaching
phenylene units were 50-55° for both model compounds.12
The absorption spectra of 1a, 2a, and related compounds were
measured in CHCl3 (Figure 2). In the longest wavelength region,
the absorption spectra of 1a and 2a gave broad bands with a
shoulder extending to 600 nm. Meanwhile, the absorption spec-
trum of parent PBI 6 gave structured bands with a maximum at
523 nm, whereas the corresponding bands were shifted to the long-
wavelength region in the order of monosubstituted analog 7,12
1a and 2a, accompanied with broadened bands. This means that
the ³ system is extended as more AEP units are introduced,13
even though the perylene and phenyl moieties are nonplanar, as
mentioned above. As for the disubstituted compounds, the
bathochromic effect was slightly larger in the absorption spectrum
of 1,7-substitution than in that of 1,6-substitution. In the
absorption spectrum of 2a, the intensity of the broad band at
500-600 nm was significantly decreased in aromatic solvents, such
as benzene and toluene (see Supporting Information; SI12). We
could not elucidate the cause of this characteristic solvent effect
from available data.
Fluorescence spectra were measured in CHCl3 (Table 1). The
fluorescence quantum yields of 1a and 2a (Φf ¼ 0.03) are much
lower than those of phenyl analogs 1b and 2b and the reference
compound 6. The fluorescence lifetimes of 1a and 2a are shorter
than those of the other compounds. These findings are attributed
to the efficient photoinduced electron transfer from AEP units to
PBI unit. The presence of 9-anthryl groups rather than phenyl
groups at the tips of the rod-like units plays an important role in
the quenching process. We also measured cyclic voltammograms
in CH2Cl2 to evaluate the redox properties in solution (see SI12).
All PBI derivatives gave two reversible reduction waves and
irreversible oxidation waves. The reduction potentials listed in
Table 1 indicate that the values are comparable for 1 and 2, the
absolute values of which are slightly smaller than those of 4. This
trend is consistent with the weak electronic coupling due to the
This work was partly supported by a Grant-in-Aid for Young
Scientists (B) No. 20750038 from MEXT (Ministry of Education,
Culture, Sports, Science and Technology) and a matching fund
subsidy for private universities from MEXT.
This paper is in celebration of the 2010 Nobel Prize awarded
to Professors Richard F. Heck, Akira Suzuki, and Ei-ichi Negishi.
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Chem. Lett. 2011, 40, 970-971
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/