Facile transformation of perylene tetracarboxylic acid dianhydride into strong donor-acceptor chromophores

Article abstract of DOI:10.1021/ol302519q

An efficient synthesis of 9,10-dibromo-1,6,7,12-tetrachloro-perylene-3,4- dicarboxylic acid monoimides from easily available 1,6,7,12-tetrachloro- perylene-3,4,9,10-tetracarboxylic acid dianhydride is reported. Therefrom, unprecedented perylene monoimides

Full text of DOI:10.1021/ol302519q

ORGANIC
LETTERS
XXXX
Vol. XX, No. XX
000–000
Facile Transformation of Perylene
Tetracarboxylic Acid Dianhydride into
Strong DonorꢀAcceptor Chromophores
Yulian Zagranyarski,† Long Chen,† Yanfei Zhao,† Henrike Wonneberger,‡ Chen Li,†
,†
€
and Klaus Mullen*
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz,
Germany, and BASF SE, 67056 Ludwigshafen, Germany
muellen@mpip-mainz.mpg.de
Received September 12, 2012
ABSTRACT
An efficient synthesis of 9,10-dibromo-1,6,7,12-tetrachloro-perylene-3,4-dicarboxylic acid monoimides from easily available 1,6,7,12-tetrachloro-
perylene-3,4,9,10-tetracarboxylic acid dianhydride is reported. Therefrom, unprecedented perylene monoimides with pronounced donorꢀ
acceptor character were obtained via twofold aromatic amination. The halogen substituents in the 1,6,7,12-positions of perylene were removed
under basic conditions. To the best of our knowledge, this is the first efficient synthetic route toward 9,10-doubly functionalized perylene-3,4-
dicarboxylic acid monoimides.
The electronic absorption window is one of the most im-
portantcriteria in dyestuffchemistry.1 Great efforts have
been continuously made to achieve near-infrared (NIR) or
even infrared (IR) absorbers for potential applications in
optical recording, NIR photography, laser welding, mark-
ing, bioimaging, and solar cells.2 Several strategies have been
utilized toward this goal. Among these are (i) extension of
the π-conjugation,3 (ii) polymerization,4 (iii) formation of
quinoid structures,6 and (iv) incorporation of donor and
acceptor substituents.5 The design of pushꢀpull systems
has proven to be one of the most efficient ways to obtain
large bathochromic shifts of the optical absorption.
Perylene-3,4-dicarboxylic acid monoimides (PMIs) and
perylene-3,4,9,10-tetracarboxylic acid diimides (PDIs) are
known as key chromophores in dye chemistry. Typically,
they possess one or two imide entities as auxochromic
groups which are responsible for their outstanding optical
and electronic properties. Therefore, PMIs and PDIs play
an important role as colorants and active components of
organic electronic devices,7 especially solar cells.8,9 Under
† Max Planck Institute for Polymer Research.
‡ BASF SE.
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r
10.1021/ol302519q
XXXX American Chemical Society

harsh imidization conditions in quinoline, using aliphatic
or aromatic amines and Zn(OAc)2, commercially available
perylene tetracarboxylic acid dianhydride (PTCDA) can
be directly transformed into PMI in reasonable yield.10
Subsequently, the PMI can be either monobrominated
(9-position) or tribrominated (1,6,9-position).11 A method
to selectively brominate the two peri-positions (9,10-position)
is hitherto elusive. Via further nucleophilic substitution or
metal-catalyzed coupling reactions, 9-monohalogenated
PMIs can be functionalized with various substituents such
as thiophene,12 aromatic or aliphatic amines,13 phenol,14
carboxylic acid,4a and cyanide.15 Our group, for example,
has introduced different donors with varying electron-
donating strength in the 9-position of PMI.16 The resulting
dyes exhibit absorption bands covering the whole visible
and even parts of the NIR region.
9-donor-substituted PMIs,16 due to increased electron
density in the molecule. Very recently, a twofold donor
functionalization of both peri-positions has been reported
by Valiyaveettil.17 However, the authors could not selec-
tively introduce those functionalities but had to work with
a mixture of isomers and tolerate bay-substitution. Donor
functionalization of just the two peri-positions of PMI has
not been reported yet and remains a great challenge due to
the lack of a versatile building block. Bromination at the
9,10-positions of PMI is always accompanied by bromina-
tion of one or both bay-positions (1,6-position).17 Addi-
tionally, the subsequent reactions of the brominated PMI
normally take place first in the bay-positions. Here, for the
first time, we describe a facile synthetic method toward 9,10-
functionalized PMIs (Figure 1). To simultaneously intro-
duce two donor groups in the peri-positions of the PMI
skeleton, a selective Hunsdiecker reaction was carried out by
a simple procedure, using inexpensive reagents i.e. sodium
hydroxide, acetic acid, and bromine, as shown in Scheme 1.
Scheme 1. Synthesis of Double Donor PMI 5 and PMI 8
Figure 1. Design concept: comparison of conventional PMI and
this work.
Besides the introduction of stronger donors in the 9-
position, a donor functionalization of both peri-positions
(9,10-position) would be a second promising way to en-
hance the pushꢀpull character, compared to the current
€
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(d) Wonneberger, H.; Pschirer, N.; Bruder, I.; Schoneboom, J.; Ma,
Due to its flat and rigid core, the unsubstituted PTCDA
is normally used as a pigment and is not soluble in most
solvents. To ensure sufficient solubility of the intermedi-
ates, another commercially available 1,6,7,12-tetrachloro-
PTCDA 1 was selected. The four chlorine substituents
induce a twist in the perylene core and thus improve the
solubility of 1 and its derivatives. The key building block,
9,10-dibromo-functionalized perylene monoanhydride 2,
€
€
C. Q.; Erk, P.; Li, C.; Bauerle, P.; Mullen, K. Chem.;Asian J. 2011, 6,
1744–1747.
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B
Org. Lett., Vol. XX, No. XX, XXXX

was prepared in a high yield of 85% by a simple Hunsdiecker
reaction,18 by sequentially adding sodium hydroxide, acetic
acid, and bromine to the PTCDA 1. Compound 2 was
slightly soluble in common organic solvents such as CH2Cl2,
CHCl3, THF, etc. The following one-pot reaction of 2, in an
excess amount of aniline, led to twofold aromatic amination
and imidation, affording compound 3 in 70% yield. Subse-
quently, a methylene bridge between the amine donors was
introduced (4) and the chlorine substituents were cleaved to
give 5. Compound 4 was prepared by cyclization with para-
formaldehyde using catalytic amounts of trifluoroacetic
acid (yield = 96%). In the following step, 5 was obtained
by dechlorination of 4 using potassium hydroxide in ethyl-
ene glycol in 63% yield. Complete removal of the chlorine
atoms was confirmed by both mass and NMR measure-
ments (see Supporting Information).
It is known that aromatic diamines with adjacent amino
groups can react with the anhydrides to form amidines.19
For example, the reaction of 2 with 1,2-diaminobenzene in
NMP produces benzimidazole due to the condensation of
diamine and dicarboxylic acid anhydride, which addition-
ally results in an unprecedented seven-membered ring
formation by nucleophilic substitution of the two bromo-
groups of 2 and 1,2-diaminobenzene. To avoid the con-
densation of dicarboxylic acid anhydride and 1,2-diami-
nobenzene, 2 was first transformed into its imide analogue
6 by imidation with pentadecan-8-amine in NMP at
110 °C. The following twofold aromatic amination of 6
with 1,2-diaminobenzene afforded PMI 7 in 43% yield.
Further dechlorination of 7 was carried out using similar
conditions as in the case of 4, affording 21% of 8.
The UV/vis absorption spectra of compounds 3ꢀ5, 7,
and 8 were recorded in CH2Cl2 solution. All double donor
PMIs with 9,10-double functionalization exhibit broad
absorption bands which is typical for pushꢀpull type
molecules. Compound 3 displays an absorption maximum
around 612 nm. However, after bridging the nitrogen with
a methylene group (compound 4), not only is the absorp-
tion maximum shifted toward longer wavelengths (λmax
=
635 nm) but alsothe absorption band showsaconsiderably
enhanced molar absorption coefficient (Table 1). Interest-
ingly, the dechlorinated product 5 possesses a similar
absorption spectrum as the unsubstituted PMIs (e.g., N-(2,6-
diisopropylphenyl)-perylene-3,4-dicarboxylic acid mono-
imide, Figure 2 black curve) with two maxima at ca. 626
and 660 nm, which display a bathochromic shift of about
150 nm. In comparison to the unsubstituted PMI, 5 ex-
hibits a similarly shaped absorption band, however, with
a large bathochromic shift and strongly enhanced molar
absorption coefficient, which indicates a synergistic push-
ingeffectfromthetwo symmetricdonor groups inthe9,10-
positions. Due to the pushꢀpull effect, the fluorescence of
compounds 5 and 8 is almost quenched. When excited at
660 nm, compound 5 shows a weak emission band with a
maximum at 729 nm in CH2Cl2 solution and a quantum
yield of 0.7%, while compound 8 exhibits an emission
maximum at 677 nm when excited at 590 nm with a
quantum yield of 0.2% (Figure S1, using Cresyl violet in
ethanol as standard). These results indicate that an effi-
cient photoinduced intramolecular electron transfer (PET)
takes place in both compounds. The broad absorption
bands in the visꢀNIR region and additionally strong PET
behavior show that 5 and 8 are outstanding candidates for
application in photovoltaics, especially in dye-sensitized
solar cells.
Figure 2. UVꢀvis spectra of PMIs 3ꢀ5, 7, and 8 in di-
chloromethane.
Figure 3. Cyclic voltammograms of 4, 5, 7, and 8 in CHCl2 with
0.1 M Bu4NPF6 as the electrolyte, AgCl/Ag as the reference
electrode, Au disk as the working electrode, and Pt wire as the
(18) Johnson, R. G.; Ingham, R. K. Chem. Rev. 1956, 56, 219–269.
(19) (a) Langhals, H.; Sprenger, S.; Brandherm, M. T. Liebigs Annalen
1995, 481–486. (b) Langhals, H.; Jaschke, H. Chem.;Eur. J. 2006, 12,
2815–2824.
counter electrode with a scan rate of 100 mV sꢀ1
.
Org. Lett., Vol. XX, No. XX, XXXX
C

To elucidate the influence of the two phenylamino
groups in the peri-positions on the energy levels of the
molecular orbitals, the electrochemical properties of dou-
ble donor PMI 4, 5, 7, and 8 were investigated by cyclic
voltammetry in CH2Cl2 (Figure 3). The onset potentials
together with the calculated values for the HOMOꢀ
LUMO energy levels of 4, 5, 7, and 8 are summarized in
Table 1. For example, compound 4 shows two reversible
oxidation curves at 0.48, 1.07 V and one reduction curve
at ꢀ1.19 V (vs Fcþ/Fc), indicating stepwise formation of
radical cations and dications upon oxidation and radical
anions by reduction. In contrast, the dechlorinated com-
pound 5 exhibits two reversible oxidation peaks with
onsets at 0.18 and 0.88 V where the first oxidation onset
is 0.3 V lower than that of 4, suggesting that 5 is oxidized
more easily than 4. A similar decrease of oxidation and
reduction potentials is observed for PMI 8 when compared
to its chlorinated analogue 7.
In summary, we have presented the synthesis of two double
donor substituted PMIs based on the versatile building block
9,10-dibromo-1,6,7,12-tetrachloro-perylene-3,4-dicarboxylic
acid monoanhydride 2, obtained by a selective Hunsdiecker
reaction. This twofold peri-functionalization strategy opens
up a new chapter in perylene chemistry regarding novel
dyes, as well as perylene-based organic electronic materials.
Remarkable pushꢀpull systems with strong absorption
toward the NIR can be achieved. Moreover, the different
halogen functionalities in the peri- and bay-positions allow
Table 1. Optical and Electronic Properties of PMIs
ε
λmax
[nm]
Ered1
[V]b
Eox1
[V]b
LUMO
[eV]c
HOMO
[eV]d
PMI
[Mꢀ1 cmꢀ1 a
]
4
5
7
8
54200
45300
40500
30200
635
660
588
591
ꢀ1.19
ꢀ1.40
ꢀ1.21
ꢀ1.55
0.48
0.18
0.47
0.11
ꢀ3.61
ꢀ3.40
ꢀ3.59
ꢀ3.25
ꢀ5.28
ꢀ4.98
ꢀ5.27
ꢀ4.91
a Measured at λmax b Onset potentials, determined by cyclic voltam-
.
metric measurements in 0.1 M solution of Bu4NPF6 in CH2Cl2 vs Fcþ/
Fc. c Estimated vs vacuum level from ELUMO = ꢀ4.80 eV ꢀ Ered1
.
d Estimated vs vacuum level from EHOMO = ꢀ4.80 eV þ Eox1
.
convenient fine-tuning of the molecular energy levels by
further functionalization (e.g., phenoxylation, arylation or
amination) instead of dechlorination. Imidation of 4 and
7 with designated anchoring groups such as glycine would
allow use of these strong pushꢀpull chromophores in
dye-sensitized solar cells.20 Introduction of such anchoring
groups as well as a variety of other functional groups in the
two peri-positions is currently underway in our laboratory.
Acknowledgment. We gratefully acknowledge financial
support from the DFG Priority Program SPP 1355 and
BASF SE. L.C. gratefully acknowledges funding by the
Alexander von Humboldt Foundation.
Supporting Information Available. Full experimental
details and characterization data. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
€
(20) (a) Mishra, A.; Fischer, M. K. R.; Bauerle, P. Angew. Chem., Int.
Ed. 2009, 48, 2474–2499. (b) Haid, S.; Marszalek, M.; Mishra, A.;
Wielopolski, M.; Teuscher, J.; Moser, J. E.; Humphry-Baker, R.;
€
Zakeeruddin, S. M.; Gratzel, M.; Bauerle, P. Adv. Funct. Mater. 2012,
22, 1291–1302.
The authors declare no competing financial interest.
D
Org. Lett., Vol. XX, No. XX, XXXX