Toward perylene dyes by the Hundsdiecker reaction

Article abstract of DOI:10.1021/ol5008586

An efficient method to synthesize 3,4,9,10-tetrabromoperylenes is reported under optimized Hunsdiecker conditions. Various octasubstituted perylenes were obtained by reaction of 1,6,7,12-tetrachloro-3,4,9,10-tetrabromoperylene with phenol, trimethylsilyl chloride, cooper cyanide, or sulfur via metal-catalyzed couplings or nucleophilic substitutions. These new perylenes show completely different optical and redox properties, thus opening a facile way to develop new chromophophore structures.

Full text of DOI:10.1021/ol5008586

Letter
pubs.acs.org/OrgLett
Toward Perylene Dyes by the Hundsdiecker Reaction
Yulian Zagranyarski,† Long Chen,† Daniel Jansch,† Thomas Gessner,‡ Chen Li,*,† and Klaus Mullen*,†
̈
̈
†Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
‡BASF SE, 67056 Ludwigshafen, Germany
S
* Supporting Information
ABSTRACT: An efficient method to synthesize 3,4,9,10-
tetrabromoperylenes is reported under optimized Hunsdiecker
conditions. Various octasubstituted perylenes were obtained by
reaction of 1,6,7,12-tetrachloro-3,4,9,10-tetrabromoperylene
with phenol, trimethylsilyl chloride, cooper cyanide, or sulfur
via metal-catalyzed couplings or nucleophilic substitutions.
These new perylenes show completely different optical and
redox properties, thus opening a facile way to develop new
chromophophore structures.
erylene-3,4,9,10-tetracarboxylic acid diimides (PDIs),
which have served as famous dyes, pigments,1 and
Additionally, PMIs can be either monobrominated (in the 9-
position) or tribrominated (in the 1,6,9-positions).11 In
particular, 9-functionalized PMIs are currently under intensive
investigation for application in dye-sensitized solar cells.12
However, until now, only a limited number of perylenes
without carboximides in the 3,4,9,10-positions have been
synthesized (see Scheme 1). 1,6,7,12-Substituted perylenes
with substituents other than carboximide units have not yet
been realized because direct functionalization of perylene only
occurs at the 2,5,8,11-positions.13 Copper-catalyzed decarbox-
ylation to remove anhydrides and subsequent halogenation are
the conventional methods to achieve other functional groups in
the peri-position of 2,5,8,11-subsituted perylenes.14a Another
method to achieve decarboxylative halogenation is through use
of the Hunsdiecker reaction.14b The initial discovery by
Hunsdiecker used dry silver(I) salts of aliphatic carboxylic
acids in a reaction with bromine, resulting in the formation of
alkyl bromides.14c We have previously described an efficient
way to synthesize 9,10-dibromo-1,6,7,12-tetrachloroperylene-
3,4-dicarboxylic acid monoanhydride (2Br-PMA, Scheme 1a)
by a selective Hunsdiecker reaction of 2a.15 Herein, we report
continuous work on a series of symmetric 3,4,9,10-subsituted
perylenes via further developed Hunsdiecker reactions,
establishing a facile method toward new types of chromo-
phores. It is noteworthy to mention that these 3,4,9,10-
substituted perylenes cannot be obtained by the direct
functionlization of perylene. On the other hand, the present
3,4,9,10-funtionalization method not only increases the
solubility of perylene (e.g., 7) but also will induce phase-
forming properties.
P
semiconductors2,3 with various applications,4−7 are normally
synthesized via perylene-3,4,9,10-tetracarboxylic acid dianhy-
drides (PDA 1, Scheme 1) with amines in nitrogen-containing
Scheme 1. Our Previous Work (a) and the Present (b)
Synthesis of 3,4,9,10-Tetrabromo-Substituted Perylenes
a
a
General procedure toward compounds 4 (67%), 5a (83%), 5b
(83%), 5c (6%), and 6 (89%): NaOH, water, Br2, 70 °C, 30 min; 5c:
NaOH, water, THF, Br2, rt.
polar solvents (e.g., quinoline, imidazole, and N-methyl-2-
pyrrolidone) or acidic solutions (e.g., acetic acid and propanoic
acid). On the other hand, under harsh imidization conditions in
quinoline with Zn(OAc)2, 1 can be directly transformed into
perylene monoimides (PMIs) with reasonable yields.8 Higher
homologues of perylene diimides, for instance, terylene
diimides9 and quaterylene diimides,10 have been synthesized
in the last several decades using PMIs as starting materials.
Our synthetic concept uses the Hunsdiecker reaction to
remove the tetracarboxylic acid dianhydride groups, while in
situ introducing halogens into the four peri-positions (Scheme
1b). We selected five perylene dianhydrides as substrates, which
Received: March 22, 2014
© XXXX American Chemical Society
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were PDA (1), 1,6,7,12-tetrachloro-PDA (2a), 1,6,7,12-
tetrabromo-PDA (2b), 1,6,7,12-tetra(tert-octylphenoxy)-PDA
(2c), and the double S-annelated PDA (3). The solubility of
the anhydrides in basic solutions was a critical issue for the
Hunsdiecker reaction. With a flat and rigid core, the
unsubstituted PDA 1 and S-annelated PDA 3 are not soluble
in most solvents. However, for the present purpose, the
substrates must be soluble in aqueous NaOH which is, indeed,
the case at 70 °C for all starting compounds except for the
tetraphenoxy compound 2c. For this reason, the desired
products 5a, 5b, and 6 can be obtained in high yields (>80%).
However, without bay-substituents, the Hunsdiecker reaction of
1 with bromine is very difficult to control. In this case, the main
product is 1,3,4,6(7),9,10-hexabromoperylene 4 with negligible
amounts of 3,4,9,10-tetrabromoperylene. Because of the four
tert-octylphenoxy groups at the 1,6,7,12-positions, 2c is hardly
soluble in aqueous NaOH solution. Therefore, THF was used
as cosolvent to obtain a clear solution of 2c and NaOH in
water. Bromine was then added to the mixture at room
temperature in order to avoid bromination at the phenoxy
groups. Unfortunately, 5c was obtained only in very low yields
(ca. 6%) because most of the starting material 2c precipitated
from the reaction mixture and thus prevented the Hunsdiecker
reaction. Among the perylenes (4−6) discussed above, we are
particularly interested in 1,6,7,12-tetrachloro-3,4,9,10-tetrabro-
moperylene 5a because of its high solubility and abundant
functionalization possibilities.
solubility in common organic solvents. This prompted us to
carry out further functionalization.
Compound 5a was reacted with phenol, trimethylsilyl
chloride, sulfur, and copper cyanide, respectively. All the
reactions took place at the four bromo positions instead of at
the chloro sites. Upon synthesis of 7, conventional phenox-
ylation conditions were used (Scheme 2).10 A mixture of 4-tert-
Scheme 2. Functionalization of 1,6,7,12-Tetrachloro-
a
3,4,9,10-tetrabromoperylene
a
Key: (i) 4-tert-octylphenol, K2CO3, NMP, 120 °C, 5 h, 74%; (ii) n-
A single crystal of 5a was obtained by slow evaporation of its
toluene solution. Its crystal structure confirmed the complete
bromination at the four peri-positions of the perylene (Figure
1a). Compound 5a possesses a strongly twisted perylene
BuLi, THF, −78 °C, TMSCl, 2 h, 48%; (iii) sulfur, NMP, 190 °C, 3 h,
97%; (iv) CuCN, DMF, 130 °C, 2 h, 70%; inset: photos of the
solution of 5a, 7−10 in CH2Cl2.
octylphenol, K2CO3, N-methyl-2-pyrrolidone (NMP), and
compound 5a was reacted at 120 °C to obtain 1,6,7,12-
tetrachloro-3,4,9,10-tetra(p-tert-octylphenoxy)perylene (7) in
74% yield. In addition, the four bromo groups were “protected”
with a trimethylsilyl (TMS) group by reacting 5a with
trimethylsilyl chloride to afford the useful intermediate 9 in
48% yield. This offers many possibilities for further useful
transformations. By simply treating 5a with sulfur powder in a
polar aprotic solvent (NMP) at 190 °C, the S-annelated
perylene 8 was obtained in almost quantitative yield. On the
other hand, four strongly electron-withdrawing cyano groups
were introduced by electrophilic substitution of 5a and CuCN
in DMF, which afforded tetracyanoperylene 10 in 70% yield.
The UV/vis absorption spectra of perylenes 5a and 7−10
were recorded in CH2Cl2 for comparison as shown in Figure
2a. Compound 5a displayed an absorption maximum at 460 nm
with a bathochromic shift of 24 nm when compared to that of
the parent perylene (436 nm).18 After replacement of the
bromo groups with octylphenoxyl, trimethylsilyl (TMS), and
cyano groups, the absorption maxima were shifted to 468 nm
for 7, 447 nm for 9 ,and 473 nm for 10, respectively. To our
surprise, the S-annelated perylene 8 formed a pink solution in
CH2Cl2 and exhibited a significant bathochromic shift of 100
nm compared with that of 5a, with an absorption maximum at
560 nm. The two strong electron-donating disulfur bridges and
four electron-withdrawing chloro groups form a donor−
acceptor system through the perylene core and thus lead to
such a bathochromic shift. Similar to other reported perylenes,
compounds 5a and 7−10 are fluorescent. The fluorescence
spectra recorded in CH2Cl2 are shown in Figure 2b. The
photoluminescence of 5a and 7−10 ranged from cyan, green,
Figure 1. Crystal structure of 5a obtained. (a) Top and (b) side views
shown as ORTEP drawing. (c) Side view of columnar packing diagram
along the c axis. C, gray; H, white; Cl, green; Br, bronze.
skeleton with a dihedral angle of 38.6° between the two
naphthalene planes and an average torsion angle of 40.5° at the
perylene bay-positions. This could be ascribed to the repulsion
between the two bay-substituted chlorine atoms. This twisted
configuration of 5a is comparable to that of octachloroperylene
diimide, where a dihedral angle of 37.2° between the two
naphthalene planes is found.16 Columnar packing was observed
with stacks of molecules oriented along the c axis, probably
driven by the halogen−π interactions (3.47 Å)17 between the
bromine atoms and adjacent naphthalene planes (Figure 1c).
Like other twisted conjugated systems, 5a exhibits good
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onset potentials, together with the calculated values for the
HOMO−LUMO energy levels of 7−10, are summarized in
Table 1. For example, compounds 7 and 8 both displayed two
Table 1. Optical and Electronic Properties of Perylenes
a
b
b
λmax
(nm)
Egap
Ered1
Eox1
LUMO
(eV)
HOMO
(eV)
(V)
(V)
(V)
e
d
7
468
560
447
473
2.46
2.07
2.62
2.48
0.55
0.13
0.93
−2.89
−2.86
−3.11
−4.17
b
−5.35
−4.93
−5.73
−6.65
e
d
8
e
d
9
c
f
10
−0.63
a
Calculated from the onset of UV absorption. Onset potentials,
determined by cyclic voltammetric measurements in 0.1 M solution of
c
Bu4NPF6 in CH2Cl2 vs Fc+/Fc. Estimated vs vacuum level from
d
ELUMO = −4.80 eV − Ered1. Estimated vs vacuum level from EHOMO
=
e
f
−4.80 eV + Eox1. Calculated from ELUMO = EHOMO + Egap. Calculated
from EHOMO = ELUMO − Egap
.
reversible oxidation curves at 0.55, 0.79 V and 0.13, 0.35 V,
respectively, representing the stepwise formation of radical
cations and dications upon oxidation. In contrast, the
trimethylsilyl-substituted perylene 9 only exhibited one
reversible oxidation peak with an onset potential at 0.93 V.
Its first oxidation onset was 0.8 V larger than that of 8,
suggesting that 8 was oxidized much more easily than 9. On the
other hand, in the case of tetracyano-substituted perylene 10,
no oxidation peak was observed, while the material instead
exhibited two reversible reduction curves at −0.63 and −0.96 V.
These results demonstrate a way to tune the electronic
properties of perylene from those of a strong donor (i.e., 8)
to a strong acceptor molecule (i.e., 10). The LUMO energy
level of 10, calculated from the CV measurement, is as low as
−4.17 eV, which is lower than that of the well investigated PDI
(−3.8 eV)19 and even comparable to those of fullerene
derivatives (e.g., C60: −4.5 eV; PCBM: −3.7 eV).20 These
comparsions suggest that 10 could serve as n-type semi-
conductor as well as acceptor material in organic solar cells.
In summary, we have presented the synthesis of 3,4,9,10-
tetrabromo-substituted perylenes and their further functionliza-
tion with sulfur, phenol, CuCN, and trimethylsilyl chloride. The
Hunsdiecker reaction opens a facile and low-cost way to
synthesize nonimide perylene chromophores via perylene
dianhydrides. The new peri-perbrominated and bay-subsituted
perylenes serve as versatile building blocks to make novel
perylene dyes. The potential of these new perylenes for use in
high-tech applications, such as OFET and OPV, is currently
under investigation in our laboratory. Furthermore, the novel
tetrabromoperylene 5a will serve as a versatile building block to
construct rylene-based graphene nanoribbons.21
Figure 2. Normalized (a) UV−vis and (b) fluorescence spectra of
perylenes 5a and 7−10 in CH2Cl2.
yellow, to red depending on their peri-substituents. Perylenes 7,
9, and 10 displayed intense emission peaks at 523, 488, and 510
nm with fluorescence quantum yields (Φ) of 86%, 99%, and
28%, respectively. In contrast, the sulfur-annulated perylene 8
only exhibited very weak fluorescence at 606 nm. These results
indicate that one can conveniently tune the optical properties of
the new perylene derivatives by the substituents at the four peri-
positions, which has not been achieved before.
To elucidate the influence of the substituents in the peri-
positions on the energy levels of the molecular orbitals, the
electrochemical properties of the perylenes 7−10 were
investigated by cyclic voltammetry (CV) (Figure 3). The
ASSOCIATED CONTENT
* Supporting Information
■
S
Full experimental details and characterization data. This
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
■
Figure 3. Cyclic voltammograms of 7−10 in CH2Cl2 (10−3 mol L−1);
*E-mail: lichen@mpip-mainz.mpg.de.
*E-mail: muellen@mpip-mainz.mpg.de.
scan rate 100 mVs−1, vs Fc+/Fc.
C
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Letter
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge financial support from the
Volkswagen Foundation Project (AZ. 85101-85103) and
BASF SE.
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