A Diketopyrrolopyrrole-Based Dimer as a Blue Pigment

Article abstract of DOI:10.1002/chem.201806121

1,4-Diketopyrrolo[3,4-c]pyrroles (DPPs) constitute a class of hydrogen-bonded pigments covering a color range from yellow–orange to dark violet. We report facile dimerization of a Boc-substituted 3,6-dithienyl-DPP. The formed dimer shows brilliantly blue color as a result of the expansion of the chromophore. The soluble dimer acts as latent pigment and is converted to the corresponding pigment either via thermocleavage or acidic deprotection of the Boc groups. The synthesized pigment is characterized by high migrational stability in a polymer matrix and a clear blue color.

Full text of DOI:10.1002/chem.201806121

A Journal of
Accepted Article
Title: A Diketopyrrolopyrrole-based Dimer as Blue Pigment
Authors: Manuela Casutt, Benedikt Dittmar, Hanna Makowska,
Tomasz Marszalek, Soh Kushida, Uwe H. F. Bunz, Jan
Freudenberg, Daniel Jaensch, and Klaus Müllen
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201806121
Link to VoR: http://dx.doi.org/10.1002/chem.201806121
Supported by

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COMMUNICATION
A Diketopyrrolopyrrole-based Dimer as Blue Pigment
[
a,b]
[a]
[c]
[d]
[a]
Manuela Casutt,
Benedikt Dittmar, Hanna Makowska, Tomasz Marszalek, Soh Kushida, Uwe
H. F. Bunz,[ Jan Freudenberg, Daniel Jänsch,
a,e]
[a,b]
[a,b]
and Klaus Müllen*
[d]
Abstract: 1,4-Diketopyrrolo[3,4-c]pyrroles (DPPs) constitute a class
of hydrogen-bonded pigments covering a color range from yellow-
orange to dark violet. We report facile dimerization of a Boc-
substituted 3,6-dithienyl-DPP. The formed dimer shows brilliantly blue
color as a result of the expansion of the chromophore. The soluble
dimer acts as latent pigment and is converted to the corresponding
pigment either via thermocleavage or acidic deprotection of the Boc
groups. The synthesized pigment is characterized by high migrational
stability in a polymer matrix and a clear blue color.
substituted DPP is described as blackish due to increased overlap
of the aromatic units,[9a, 9b] it is commercially available[10] as a dark
red pigment with a light purple shade (Figure S1, SI), emphasizing
the dependence of the respective polymorph on color.[11] A blue
color, however, remained scare for DPP-based pigments - it is
hinted that this color may be obtained through further p-extension
of the 3,6-arylated DPP chromophore.[
8a, 12]
Even though many
inorganic blue pigments are available, e.g. aquamarines or the
recently discovered YInMn Blue,[13] only few representatives of
commercial organic blue pigments are known such as indigo,
phthalocyanines and indanthrone. These show higher absorptivity
and are more environment-friendly than their inorganic
counterparts.[14]
Among
organic
high-performance
pigments,
1,4-
[
1]
diketopyrrolo[3,4-c]pyrrole (DPP) adopts a special role. Since
the serendipitous discovery of 1,4-diketopyrrolo[3,4-c]pyrrole
DPP) by Farnum et al.[2] in 1974, its synthesis was optimized by
(
Ciba-Geigy Company, which commercialized DPP pigments in
986.[ DPP’s major benefits as organic high-performance
3]
1
pigment are color brilliance, resistance to chemicals, high thermal
stability as well as light and weather fastness.[4] Its pigmentary
character results from strong intermolecular forces, hydrogen
bonds between the lactam units[5] and π-π-stacking between the
planar core structure.[4c, 6] Packing in the solid state and optical
properties of the pigments are widely tunable through substitution
of the 3,6-positions of the DPP scaffold with different aryl-groups
Figure 1. Schematic illustration of the known color spaces of DPP pigments (bp =
p-biphenylyl).
Upon oligomerization of N-alkyl-solubilized diaryl-DPP-based
functional materials, the conjugation length increases, while the
HOMO-LUMO energy gap decreases. Absorption bands are
bathochromically shifted and already short oligomers exhibit a
blue color.[15] As electron-accepting co-monomer, DPP is used in
conjugated polymers, which are primarily applied in the field of
(
Fig. 1). DFT calculations predict a dihedral angel of 27° between
phenyl substituents and the DPP core, caused by steric hindrance
of the α-hydrogen atoms, while smaller thienyl substituents are
nearly coplanar with a dihedral angle of only 12°, induced by
favorable intramolecular sulfur-oxygen interaction.[7]
organic electronics,[ e.g. for solar cells, bulk heterojunction
solar cells (BHJ)[18] and organic field effect transistors (OFETs).[19]
Soluble latent DPP pigments are obtained by N-substitution of the
lactam nitrogen with tert-butyloxycarbonyl (Boc) protecting groups,
16]
[17]
As a result of structural variations and resulting modification
of the solid state packing, arylated DPPs cover a color range from
yellow-orange to dark violet.[8] While most substituents at the
phenyl rings of 3,6-diphenyl-DPP furnish orange-red
which are eliminated by acid treatment or thermally at 190°C to
give the corresponding hydrogen-bonded pigments.[11, 20] Thus,
(λmax = 501 nm to 518 nm) colors, substitution with bromine or the
electron-rich dimethylamino groups causes a bathochromic shift
dispersibility and generation of different polymorphs of the same
pigment can be controlled.[11, 20b, 20c]
to λmax = 533 nm or 562 nm, respectively, resulting in a red-blue
or violet-blue color. (Fig. 1).[9] Although 3,6-bis(p-biphenylyl)
Utilizing the strongly redshifted absorption maximum of bis-
arylated DPP upon dimerization and, revisiting the concept of
latent pigments, we designed and synthesized an organic DPP-
based blue pigment 5 which, in contrast to literature, was not
acessable by variation of substituents. The decoration of its
precursor 4 with thermocleavable or acid-cleavable solubility-
mediating Boc side-chains ensured facile purification and
processing. Pigment 5 exhibited a brilliant blue color and high
migrational stability in a polymer matrix.
[
a]
M. Casutt, B. Dittmar, S. Kushida, Prof. U. H. F. Bunz, Dr. J.
Freudenberg, D. Jänsch
Organisch-Chemisches Institut, Ruprecht-Karls-Universität
Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
M. Casutt, Dr. J. Freudenberg, D. Jänsch
InnovationLab, Speyerer Straße 4, 69115 Heidelberg, Germany
H. Makowska,
[
b]
c]
[
Department of Molecular Physics, Faculty of Chemistry, Lodz
University of Technology, Zeromskiego 116, 90-924 Lodz, Poland
Dr. T. Marszalek, Prof. K. Müllen
Starting from the readily available 3,6-dithienyl-DPP (DPP*) 1
(
Scheme 1),[21] the lactam nitrogen atoms were substituted with
[
d]
e]
Boc-groups to obtain 2 in a yield of 43%.[
22]
Subsequent
Max-Planck-Institute for Polymer Research, Ackermannweg 10,
55128 Mainz, Germany
bromination of one thienyl substituent with NBS (1.00 equiv.) gave
mono-brominated 3 in 32%, accompanied by the corresponding
dibrominated species and starting material as a statistical mixture,
significantly improving literature yield of solely 8%.[20a]
Dimerization proved synthetically challenging: Although
Yamamoto conditions were frequently applied,[15a] in our case,
Email: muellen@mpip-mainz.mpg.de
Prof. U. H. F. Bunz
Centre of Advanced Materials
[
Im Neuenheimer Feld 225, 69120 Heidelberg, Germany
Supporting information for this article is given via a link at the end of
the document
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dimerization of 3 only resulted in yields of up to 10% of 4.
Alternative approaches comprising C-H activation[23] of 2 or 3
were precluded, as these involve the use of acids (e.g. TFA,
PivOH, AcOH),[23-24] cleaving the sensitive Boc protecting groups.
Even under less acidic conditions for oxidative C-H/C-H coupling
The latter exhibited only resonances assignable to pigment 5 (see
SI for full spectrum). A comparison of the powder IR spectra of 4
and 5 (Fig. S5, SI) revealed complete cleavage of the solubilizing
groups. Latent pigment 4 showed an intensively pronounced C=O
stretching vibration of the Boc-side chain and the DPP core at
1686 cm-1 and 1747 cm , which disappeared completely upon
of 2 (AgNO
3
, KF) [20a] deprotection was observed. To circumvent
-1
-1
these issues we developed an in-situ Stille coupling protocol
utilizing hexamethyldistannane providing 4 in satisfactory yields
of 56%. The conversion of the blue latent pigment to its hydrogen-
bonded insoluble counterpart 5 through quantitative cleavage of
the Boc-groups was achieved thermally and via acid-treatment,
either in bulk or from solution (vide infra).
deprotection. Pigment 5 in turn absorbed at 1640 cm and
-1
1590 cm , attributed to the C=O stretching vibration of the DPP
core and the deformation vibration of the newly generated –NH –
the valence vibration absorption of the latter is visible between
2500 cm-1 and 3200 cm-1.
1
3
1
4
1
2
2
S
O
11
7
9
10
NH
8
HN
1-4,
6
5
11-14
4
O
S
3
7-8
1
2
6, 9
5, 10
1
76
168
160
152
144
136
128
120
Chemical Shift (ppm)
Figure 2. Solid state 13C MAS NMR spectra of 5 obtained through microwave
treatment.
Figure
3 depicts photographs and UV-Vis spectra of
compounds 2 to 5 as solutions/microsuspensions in N-Methyl-2-
pyrrolidone (NMP). Note that whereas extinction coefficients are
shown for 2 to 4, only the normalized absorption spectrum is
depicted for micro-suspended 5. Monomers 2 and 3 exhibit typical
absorption and emission properties (see SI) for diaryl-DPP dyes,
with a yellow to orange color and absorption maxima of
4
-1
-1
λ
(
max = 492 nm and 500 nm for 2 (ε = 2.75∙10 M cm ) and 3
Scheme 1. Synthesis of the blue DPP pigment 5: (i) DMAP, di-tert-butyl dicarbonate,
4
-1
-1
ε = 3.63∙10 M cm ). Solutions of dimer 4 in NMP are blue with
THF, rt, 16 h, 43%; (ii) NBS, CHCl
Pd(PPh , toluene, 110°C, 16 h, 56% (iv) 190°C, 1 h or TFA, rt, 5 min, both
quantitative.
3
, rt, 16 h, 32%; (iii) hexamethyldistannane,
4
-1
-1
)
3 4
an absorption maximum of λmax = 602 nm (ε = 7.38∙10 M cm ).
Dimerization causes a bathochromic shift of the absorption
maximum by 110 nm in NMP and doubles the molar extinction
coefficient ε (cf. compound 4) compared to DPP-based monomer
The thermal cleavage of the Boc groups to afford 5 occurred
at 172°C, as determined by thermogravimetric analysis (TGA)
and dynamic differential calorimetry (DSC) (Fig. S2, SI). The
estimated mass loss observed during TGA was in good
agreement with the calculated one, indicating a quantitative
removal of the Boc groups. A second heating cycle confirmed
completion as no further mass loss was observed. The
decomposition temperature of 5 was determined to 542°C by TGA
and DSC (Fig. S2, SI). Besides the, microwave-assisted
thermocleavage[25] various acids were tested for Boc group
cleavage. Trifluoromethylsulfonic acid (TFA) ensured a complete
removal of the Boc group, resulting in 5, which directly
precipitated from solution. Hydrochloric or acetic acid lead to
incomplete cleavage, while sulfuric acid removed the protecting
groups sufficiently, while dissolving the obtained pigment 5
through protonation (vide infra).
-1
2
. The bathochromic shift in emission of 4 (Δ 푣̃ 푠푡표푘푒푠 = 2467 cm )
is accompanied by a dramatic loss in quantum yield (see
Supporting Information).
After loss of the Boc protecting groups, the blue color is
retained for pigment 5. The deviation from the absorption
spectrum of 4 is caused by aggregates, as 5 is insoluble in
common organic solvents and only partially dissolves in NMP
after ultrasonication for 10 min. Thus, the second absorption
maximum at 640 nm and the tail in the NIR range at 700 nm are
attributed to non-molecularly dissolved aggregates. Dissolution of
5 in concentrated sulfuric acid resulted in a green solution with an
4
-1
-1
absorption maxima of 680 nm (ε = 3.06∙10 M cm , see SI). The
observed color change, attributed to protonation, is reversible
upon neutralization, excluding sulfonation or degradation, as
indicated by IR analysis of the re-isolated pigment (see SI).
Completion of the cleavage and generation of 5, both from
acid media and by thermally induced deprotection in the bulk, was
confirmed, apart from TGA and DSC, by mass spectrometry (Fig.
S3, Supporting Information), infrared spectroscopy (IR),
1
3
elemental analysis (EA) and solid state C MAS NMR (Figure 2).
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than in solution. In contrast, the absorption UV-Vis spectra of thin
films of 5 before and after irradiation in a photoreactor (350 nm)
for 1 h did not show notable spectral changes.
8
7
6
5
4
3
2
1
x104
x104
x104
x104
x104
x104
x104
x104
0
2
3
4
5
1
.0
0.5
0.0
400
600
800
Wavelength [nm]
Figure 3. Top: From left to right: Photographs of compounds 2-4 in NMP and 5
as a micro-suspension in NMP under ambient light. Bottom: UV-Vis absorption
spectra of 2-5 in NMP.
Thin films of well soluble latent pigment 4 were spin coated on
glass substrates (CHCl
the solid state the absorption maximum of
3
solution, 10 mg/mL, 30 s, 800 rpm). In
shifts
4
bathochromically to 618 nm (Fig. 4, bottom). Heating the thin film
on a hot plate (190°C for 30 minutes) liberates 5. The successful
cleavage was demonstrated by immersion of the film in
chloroform before and after thermal annealing. Whereas the as-
cast film re-dissolves, the treated film was fully solvent-resistant
(
Fig. 4, top). IR spectra of the thermally treated film 5 confirmed
the quantitative cleavage of the Boc side chain, while no signals
of the solubilizing groups were observed (Fig. S6, SI). The
absorption maximum of the resulting film was redshifted to
Figure 4. Top: Dissolution experiments of latent pigment 4 (left) and pigment 5
(middle), spin coated on glass substrates, by immersing in chloroform solution
and a photograph of the PVC sheet (right). Center: Photograph of 5 as powder
and smeared pigment on white paper. Bottom: UV-Vis absorption spectra of 4
spin cast from chloroform and 5 generated through thermal annealing on glass
substrates.
644 nm. Additionally, the solid state spectra reveal a more
pronounced shoulder at 717 nm, similar to the one observed in
NMP (vide supra). Both effects can be attributed to increased
packing effects caused by hydrogen bond formation, also as
reflected in the polarized optical micrographs. While the films of 4
are amorphous, crystallinity is observed for films of 5 obtained
after thermocleavage, testimony to the order endowed on the
material after hydrogen-bonded network formation. Note that both
compounds do not emit in the solid state, e.g. as thin films.
Scanning electron micrographs were taken after dropcasting
pigments 1 and 5 (Figure 5). 1 shows platelet-shaped structures
with dimensions smaller than 1 µm, but the appearance of 5
varies with cleavage conditions. Deprotection with sulfuric acid
gives amorphous aggregates, while cleavage with TFA affords a
network of microfibers. Thermocleavage generates a network of
spatially isolated rod-shaped structures with lateral dimensions of
up to 2 µm, beneficial for pigment processing and application.[
The influence of thermal annealing on the morphology of
pigments 1 and 5 obtained from TFA, was studied by heating it to
Light stability tests of 5 were conducted in solution and solid
state. The microsuspension of 5 in NMP was completely
degraded after one week at ambient conditions - the dark blue
suspension turned purple. The resulting solution was filtered and
exhibits an absorption maximum hypsochromically shifted by
26]
190 °C. While 2 does not change the morphology, particles from
5
stick together and do not show any ordered structure (see SI).
>70 nm as compared to 5 (see SI). Already after 24 hours the
corresponding peak evolved at 512-535 nm besides the
characteristic main transition at 602 nm. In addition, 5 was
irradiated for one hour in a photoreactor (350 nm) as a solid,
under ambient conditions as well as under nitrogen atmosphere.
After suspension in NMP, both UV-Vis spectra exhibit a slight
shoulder at similar wavelengths, indicating initial degradation and
an intramolecular decomposition pathway, although much slower
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COMMUNICATION
color difference (ΔE) with respect to a white background indicates
a barely visible but still perceptible change in color (for details see
SI). 5 is well dispersible in the PVC matrix and possesses an
excellent migrational stability therein.
In summary, we established a facile synthesis of the dimeric
DPP* 4, which, either by acid or by thermal cleavage, was easily
transformed into the blue pigment 5, with an absorption maximum
of ~640 nm in solution/micro-suspension and the solid state. SEM
images of the thermally generated pigment 5 display a network of
spatially isolated rod-shaped structures indicating its good
processability, demonstrated in homogeneous PVC sheets.
Furthermore, the pigment is exhibiting high migrational stability.
Over all this is the first DPP-based blue pigment, it is a promising
conceptual start that suggests the dimerization of 3,6-dithienyl-
DPP chromophores as a powerful concept to achieve attractive
2 4
Figure 5. SEM images of 1 (top left); 5 obtained from H SO followed by
neutralization with water (top right), from TFA (bottom left) and after microwave
heating (bottom right). All samples were prepared via dropcasting of
suspension in isopropanol on SiO
a
blue-colored pigments. In further studies, we will improve
photostability utilizing a stabilizing polymer matrix[29] or by
2
.
encapsulation of the pigment, [30] allowing its application in
lacquers, printing inks, coating colors or as textile colorant.[
Furthermore, as highly ordered hydrogen-bonded assemblies are
known to perform well in OFETs,[31] the application of both our
latent and blue pigment in transistors is currently under
investigation.
Powder X-Ray Diffraction experiments (XRD) were performed
to obtain deeper information about the internal structure and
crystallinity of soluble precursor 4 and the pigment 5 (Fig. S11,
SI). One dimensional XRD measurements of 4 reveal moderate
crystallinity (Fig. S11a, SI). A small angle reflection located at
26]
6.68° corresponded to a d-spacing of 12.9 Å which is assigned to
width of the molecules (calculated with the Boc group). Low
intensity of this reflection and a lack of higher order reflections
indicated short range order and relatively poor interstack
orientation. Low intensity Bragg reflection located in wide angle
range at 25.34° (3.5 Å) of 4 might be assigned to the weak π-π
interaction, due to the steric hindrance between single molecules
induced by Boc group. The observed π-stacking distance of 4 is
closely comparable to DPP* dimers with a β-bridged alkyl side
chains which showed a π-stacking distance from mainly 3.5 Å.[27]
In contrast to 4, which showed only a low degree of crystallinity,
the resulting compound 5 is much more crystalline. The pigment
without any substituents showed different distribution of the XRD
patterns. First of all, in small angle region the diffraction peak at
Experimental Section
Tetra-tert-butyl
6,6'-([2,2'-bithiophene]-5,5'-diyl)bis(1,4-dioxo-3-
(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate) (4)
3
(500 mg, 862 μmol, 1.00 eq) was dissolved in degassed toluene
(15.0 mL). Hexamethylditin (178 μL, 283 mg, 862 μmol, 1.00 eq) was
added and the reaction mixture was degassed for 20 min. Afterwards
tetrakis(triphenylphosphine)palladium(0) (49.9 mg, 43.1 µmol, 0.05 eq)
was added and the reaction was carried out overnight at 110°C. The
solvent was evaporated in vacuo and the crude product was further
purified by column chromatography eluting with dichloromethane (DCM).
The obtained product 4 (240 mg, 240 μmol, 56%) is a dark blue solid. M.p.:
172°C (dec.). 1H NMR (400 MHz, CDCl
8.26 (m, 2H), 7.65 (dd, J = 5.04 Hz, J = 0.92 Hz, 2H), 7.37 (d, J = 4.35 Hz,
2H), 7.21 (m, 2H), 1.65 (s, 18H), 1.61 (s, 18H). 13C NMR (101 MHz, CDCl
3
2
.06° indicated a lamellar structure with an interlayer distance of
5.2 Å. Secondly higher order reflections 200 and 300 (according
3
): δ = 8.34 (d, J = 4.12 Hz, 2H),
to Miller index – 12.5 Å and 6.3 Å, respectively) are well recorded.
Additionally diffraction peak assigned to the π-π interaction visible
at 26.62° increased significantly and the π-stacking distance
decreased up to 3.34 Å. This suggest much stronger inter-
molecular interactions due to the possible formation of hydrogen
bonds between the pigment molecules.
3
)
δ = 159.2, 159.1, 149.2, 149.0, 142.4, 138.1, 137.0, 135.6, 134.2, 132.1,
130.2, 130.0, 128.3, 126.3, 111.3, 110.6, 86.3, 86.2, 28.0, 27.9. IR (neat):
풗ꢀ = 3101, 3083, 2979, 2361, 1747, 1686, 1558, 1437, 1306, 1147, 1100,
1025, 749 cm-1
+
.
HRMS (DART): [M+H]
m/z = 999.2068, found:
: C, 57.70; H,
m/z = 999.2089. Elemental anal. Calcd for C48
46 4 12 4
H N O S
The microwave generated pigment 5 was embedded in a soft
polyvinyl chloride (PVC) sheet (see SI for details and Fig. 4, top
right) and characterized. Using 0.1 w% of pigment, the foil was
homogenous in color. Colorimetric measurements gave the
coordinates of the CIELAB color system as L* = 10.3, a* = 11.3
and b* = -18.7. Compared to one of the most widely used organic
blue pigments, copper phthalocyanine (CuPc), 5 has a similar
brightness (*L = 16.2 for CuPc), but smaller values of the green-
4
.64; N, 5.61. Found: C, 57.74; H, 5.18; N, 5.34.
6,6'-([2,2'-Bithiophene]-5,5'-diyl)bis(3-(thiophen-2-yl)-2,5-dihydro-
pyrrolo[3,4-c]pyrrole-1,4-dione) (5)
.) 4 (100 mg, 100 µmol) was heated up in the microwave to 190°C for 1 h
to obtain the desired product 5 (59.6 mg, 99.6 µmol, 99%) as a dark solid.
.) 4 (100 mg, 100 µmol) was suspended in TFA and the precipitated solid
was filtered, washed with a saturated solution of NaHCO , methanol and
chloroform to afford pigment 5 (58.7 mg, 98.1 µmol) as a dark solid. M.p.:
1
2
3
red coordinates (a* = 44.4 for CuPc) and yellow-blue (b* = -64.9
for CuPc), indicating a less deep blue tone.[28] The sheets are
exposed to white light for 400 h and revealed a moderate light
>
1
350°C. 13C NMR (101 MHz, CDCl
31.4 (1-4, 11-14), 115.5 (6-9). IR (neat): 푣̃ = 3110, 3069, 2983, 2790,
3
) δ = 168.4 (7-8), 146.9 (5, 10), 141.2-
fastness,
in
between
the
photostability
in
2361, 1635, 1587, 1427, 1276, 1129, 750. HRMS (MALDI): [M]+
solution/microsuspension and the solid state (vide supra). The
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Chemistry - A European Journal
10.1002/chem.201806121
COMMUNICATION
J. 2017, 23, 13718-13723; c) T. Mukhopadhyay, B. Puttaraju, S. P.
Senanayak, A. Sadhanala, R. Friend, H. A. Faber, T. D. Anthopoulos, U.
Salzner, A. Meyer, S. Patil, ACS Appl. Mater. Inferfaces 2016, 8, 25415-
m/z = 597.989, found: m/z
= 597.980. Elemental anal. Calcd for
28 14 4 4 4
C H N O S : C, 56.17; H, 2.36; N, 9.36. Found: C, 56.07; H, 2.18; N,
9.27.
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Acknowledgements
The authors acknowledge Dr. Helmut Reichelt and his colleagues
at BASF SE for the preparation of the PVC sheet, as well as the
evaluation of the colorimetric measurements and the fruitful
discussions.
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Keywords: 1,4-diketopyrrolo[3,4-c]pyrrole (DPP) • blue pigment •
dimerization • latent pigment • tert-butyloxycarbonyl (Boc)
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Chemistry - A European Journal
10.1002/chem.201806121
COMMUNICATION
Entry for the Table of Contents
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COMMUNICATION
Manuela Casutt, Benedikt Dittmar,
Hanna Makowska, Tomasz Marszalek,
Soh Kushida, Uwe H. F. Bunz, Jan
Freudenberg, Daniel Jänsch and Klaus
Müllen*
A Boc substituted 3,6-dithienyl-DPP furnished a soluble latent pigment, which can be
deprotected to give the blue dimeric DPP pigment.
Page No. – Page No.
A Diketopyrrolopyrrole Dimer as Blue
Pigment
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