Synthesis of diketopyrrolopyrrole (DPP) derivatives comprising bithiophene moieties

Article abstract of DOI:10.1016/j.tet.2010.01.027

Herein we disclose an easily applicable method for the synthesis of diketopyrrolopyrrole (DPP) derivatives comprising bithiophene moieties, with different substituents on the nitrogen atoms (Me, n-octyl, 3,5-di-tert-butylbenzyl, Boc) and on the thiophene rings (C₆H₁₃, C₁₂H₂₅), in good yields and purities. A comparison is made between the previously described method from literature and our more efficient approach regarding number of steps, overall yields and ease of synthesis and purification.

Full text of DOI:10.1016/j.tet.2010.01.027

Tetrahedron 66 (2010) 1837–1845
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of diketopyrrolopyrrole (DPP) derivatives comprising bithiophene
moieties
,
Sara Stas a, Sergey Sergeyev b, Yves Geerts a
*
a Universite´ Libre de Bruxelles (ULB), Faculte´ des Sciences, Laboratoire de Chimie des Polyme`res, CP 206/01, Boulevard du Triomphe, 1050 Brussels, Belgium
b University of Antwerp (UA), Department of Chemistry, Groenenborgerlaan 171, 2020 Antwerp, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
Herein we disclose an easily applicable method for the synthesis of diketopyrrolopyrrole (DPP) derivatives
comprising bithiophene moieties, with different substituents on the nitrogen atoms (Me, n-octyl, 3,5-di-
tert-butylbenzyl, Boc) and on the thiophene rings (C6H13, C12H25), in good yields and purities. A comparison
is made between the previously described method from literature and our more efficient approach re-
garding number of steps, overall yields and ease of synthesis and purification.
Received 10 December 2009
Accepted 7 January 2010
Available online 13 January 2010
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
devices, it is necessary to derivatize the DPP chromophore in order
to prepare soluble and film forming compounds. To increase the
3,6-Diaryl-2,5-dihydro-1,4-diketopyrrolo[3,4-c]pyrroles (DPPs)
are known as high performance organic pigments used in paints,
inks, lacquers, printings and plastics.1 They are endowed with
brilliant shades ranging from yellowish green to bluish red,
depending on the aryl group attached to the chromophore unit, and
exhibit outstanding chemical resistance, thermal stability, light and
weather fastness, indicating high quality of colour retention.2 Be-
sides being a chromophore, DPP is also a fluorophore emitting in
the visible region with a high fluorescence quantum yield.3–5
The DPP molecule is virtually planar, the two aryl rings being
twisted out of the chromophore plane by merely a few degrees (e.g.,
7ꢀ for phenyl). These heterocyclic compounds have been the object
of several crystallographic studies and it was shown that the solid-
state arrangement of DPP molecules occurs in parallel sheets.6–9
The colour derives not only from the molecular structure, but also
solubility, the NH group of the DPP unit can be substituted and
DPPs can be derivatized by incorporation in different materials
such as conjugated polymers, liquid crystals and metal com-
plexes.16,17 In particular, DPP-containing conjugated polymers
have been used as functional materials in OLEDs, OTFTs18–20 and
solar cells.21–27
Herein, we report the synthesis of DPP derivatives 1 compris-
ing bithiophene moieties (Fig. 1). Previously reported syntheses of
these DPP derivatives described in scientific journals15–17,20,22,28
or patents29–32 often lack experimental details. Moreover, in our
hands certain synthetic steps were not reproducible. Therefore,
we set out first to optimize the existing synthetic method and
then to develop alternative pathways towards DPP derivatives 1.
Our goal is to develop a versatile and high-yielding synthesis of
DPP molecules bearing bithiophene units. This synthetic pathway
should also allow an easy derivatization by incorporating different
substituents on the terminal thiophene units and on the N-atoms
of the DPP moiety in order to modulate supramolecular order in
solid state.
from the supramolecular order (p–p-interactions between the
layer of molecules), since the colour in solid state differs from the
colour in very dilute solutions.10 The hydrogen bonding between
neighbouring lactam-nitrogen and carbonyl-oxygen atoms is cru-
cial for pigments in order to limit solubility. In fact, DPPs are in-
soluble in most common organic solvents, except in polar aprotic
solvents (e.g., NMP, DMSO, DMF).
There is an increasing interest in DPP compounds for more
advanced applications such as their use as charge-generating
materials for laser printers, erasable optical information carriers
or as electroluminescent elements.11–15 To use DPPs in electronic
* Corresponding author.
E-mail addresses: sara.stas@vub.ac.be (S. Stas), ygeerts@ulb.ac.be (Y. Geerts).
Figure 1. Structure of DPP derivatives discussed in this paper.
0040-4020/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.01.027

1838
S. Stas et al. / Tetrahedron 66 (2010) 1837–1845
2. Results and discussion
derivatized DPPs where O-alkylation of the amide34 occurred instead
of N-alkylation. Another explanation for the low yields, besides the
formation of side products, can be the lack of experimental data given
in the experimental part of the patents, preventing accurate repetition
of the synthetic procedure. Alkylation with 2-hexyldecyl meth-
anesulphonate, a more reactive alkylating agent (Scheme S1, Supple-
mentary data), was unsuccessful and produced a very complex
mixture of products. Because alkylations of the DPP nitrogen with
branched alkyl chains did not takeplace verysmoothly, N-methylation
was investigated. Reaction of DPP 3 with MeI (K2CO3, NMP, 55 ꢀC)
afforded the methylated derivative 4b in 86% yield.35,36 However, 4b
was very poorly soluble in organic solvents and therefore, N-methyl-
ation was not used anymore. Since methylated DPP 4b was synthe-
sized in good yield, but suffers from low solubility, and since alkylation
witha branched alkylchainoffers goodsolubilitytothecorresponding
DPP 4a, although it wasproduced in low yields, it wastried to combine
the positive aspects of both reactions by N-alkylation with a longer
linear alkyl chain.3,11,15,16 Reaction of n-octyliodide with DPP 3 (K2CO3,
NMP, 140 ꢀC) gave rise to dioctyl derivative 4c, which precipitated as
a dark red solid upon aqueous work-up (64% yield).15,16 As expected,
this compound was soluble in most organic solvents.
2.1. Re-evaluation and optimization of previously reported
synthetic route
The synthesis of 3,6-di(2,20-bithiophen-5-yl)-1,4-diketo-
pyrrolo[3,4-c]pyrroles 1 described in literature is summarized in
Scheme 1.15–17,20,31 We started with the careful re-investigation
and, if needed, optimization of the published procedures for all
synthetic steps.
In contrast to the N-alkylations, some other reported N-function-
alizations ofDPP 3 werewellreproducible. Derivative 4d was obtained
from reaction of 3with3,5-bis-tert-butylbenzylbromide(K2CO3, NMP,
140 ꢀC) in 74% yield.37,38 Boc-protected DPP 4e was prepared from 3,
N,N-dimethylaminopyridine (DMAP) and di-tert-butyl dicarbonate
(THF, rt) in 68% yield.9,22,39 Both DPPs (4d and 4e) were isolated by
simple precipitation from MeOH and the bulky substituents render
these DPP derivatives well soluble in organic solvents.
Scheme 1. Synthesis of 3,6-di(2,20-bithiophen-5-yl)-1,4-diketopyrrolo[3,4-c]pyrroles 1
as described in literature. Reagents and conditions: (i) 0.5 equiv (CH2)2(COOEt)2,
1.7 equiv NaOC(CH3)2(CH2CH3), tert-amyl alcohol, reflux, 2 h, Ar-atmosphere, 72%; (ii)
4 equiv base, excess alkylating agent, Ar-atmosphere; (iii) 2.1 equiv NBS, anhydrous
CHCl3, rt, 48 h, Ar-atmosphere, dark; (iv) 20 mol % Pd(PPh3)4, 2.5 equiv 6, anhydrous
toluene, reflux, 2.5 h, Ar-atmosphere.
The next step towards DPP derivatives 1 comprising bithiophene
moieties is the bromination of the soluble DPP derivatives 4. The
previously reported bromination procedures15,16,20,22,31 were slightly
modified in order to obtain better yields. Bromination of DPP 4 with
2.1 equiv NBS occurred in dry CHCl3 in 48 h, and gave moderate to
good yields (5a, 20%; 5c, 80%; 5d, 51%; 5e, 73%).15 Precipitation of
DPP 5 in methanol was sufficient to obtain highly pure compounds.
For the conversion of brominated DPPs 5 to bithiophene con-
taining DPPs 7, two cross coupling reactions were reported, namely
the Suzuki coupling12–15,22,23 and the Stille coupling16,20,27,31, the
former one being more abundantly described. We have selected
the Stille coupling since it is generally the more efficient reaction for
the synthesis of oligothiophenes.40 Published Stille couplings with
linear16 and branched20,31 alkyl-DPP compounds resulted in yields of
60–90%. Repeating the same literature method, led to yields of
maximum 30% in our hands. Therefore, optimization of the reaction
between dibromide 5e and stannic compound 6a41 was undertaken.
Different combinations of solvents, reaction temperatures and re-
action times were evaluated (Table S2, Supplementary data). Yields
of bithiophene containing DPP 7ea (the first letter refers to R1 and
the second to R2) given in Table S2, were obtained after precipitation
of the product in methanol. The best result was achieved after reflux
in toluene for 3 h. Longer times gave rise to side products, shorter
reactions resulted in incomplete conversion (mono-coupled prod-
uct). Optimized conditions were applied for the coupling of bromi-
nated DPPs 5c, 5d and 5e with stannane 6a to give the corresponding
products 7ca, 7da and 7ea in 73%, 78% and 85% yield, respectively.
In the final synthetic step, bromination of 7 was done in the
same manner as bromination of 4 and yields between 50 and 60% of
DPP derivatives 1 were obtained, while in literature yields of 83–
97% are published.20,31
The first step consists of a condensation of thiophene-2-car-
bonitrile (2) with diethylsuccinate. We found the published pro-
cedure to be well reproducible,15,28,30 yielding DPP 3 as a red solid
(72% found versus 75% reported). Since DPP 3 is only soluble in
polar aprotic solvents, it was in a second step solubilized by
substituting the lactam-NH group.
Inafirstattempt, itwastriedtoderivatizeDPPchromophore3with
a branched alkyl chain in the same way as described in litera-
ture.17,20,23,27,31 Therefore 1-bromo-2-hexyldecane was used as alky-
lating agent (Scheme S1, Supplementary data). According to the
literature, potassium carbonate operates as base to deprotonate the
amide-NH and alkylation in DMF20 or NMP31 results in yields around
45% of dialkylated DPP 4a. Surprisingly, yields of only 12% in DMF and
19% in NMP of DPP 4a were obtained in our hands. It was tried to
optimize the reaction (Table S1, Supplementary data) by testing sev-
eral aprotic solvents at different reaction temperatures (NMP, DMSO
and DMF in a range of 120–150 ꢀC) and by varying the base (K2CO3,
Cs2CO3 and NaH), but the yields of pure 4a, obtained after flash
chromatography on silica gel, were always considerably lower than
the yields claimed in literature. The highest yield of DPP 4a (25%) was
obtained in DMSO under Ar-atmosphere, with K2CO3 as base and with
6 equiv of alkyl bromide (Table S1, entry 14). The low yields can be
explained by the multiple side reactions, which compete with the
nucleophilic substitution of the alkyl bromide by deprotonated DPP
(Scheme S2, Supplementary data). 2-Hexyl-1-decanol, probably
formed via hydrolysis of the corresponding bromide with traces of
water, and 7-methylenepentadecane, formed by elimination of HBr,
were isolated as side compounds, as well as unreacted alkyl bromide.
In the reactions in DMSO, 2-hexyl-1-decanal was present as side
compound, resulting from reaction between the alkyl bromide and
DMSO, which is mechanistically closely related to the Swern oxida-
tion.33 One ormore otherDPPderivatives were formedbesides desired
DPP compound 4a. The structure of these products has not yet been
identified since not very pure samples were isolated by chromatog-
raphy. Possible DPP side compounds are monoalkylated DPP and
For the first pathway towards 3,6-di(2,20-bithiophen-5-yl)-1,4-
diketopyrrolo[3,4-c]pyrroles 1, which already has been described in
literature, following conclusions can be drawn. Several steps of the
originally published synthesis were difficult to reproduce and re-
quired considerable optimization. Still, we were often unable to
produce the reported yields. The synthetic route exists of five steps

S. Stas et al. / Tetrahedron 66 (2010) 1837–1845
1839
for which we obtained overall yields between 11 and 17%, while the
overall yields described in literature are slightly higher (26–33%).
Because of these not satisfying yields, we decided to develop
alternative synthetic pathways. These pathways should possess
high overall yields, high purities of the end product, a low number
of steps and they should be easily applicable. Since several syn-
thetic transformations (in particular the N-functionalization) on
the DPP core proved problematic, our idea was to postpone the
formation of DPP core to the later steps of the synthesis.
used to generate the DPP core. This would also lead to a route
consisting of only four steps (Scheme 3). Synthesis of bithiophene
10 was accomplished by Stille coupling of 5-bromothiophene-2-
carbonitrile (8) with stannic compounds 6, resulting in yields of
80% for 10a and 92% for 10b. Using the bithiophene building blocks
10 in a reaction with diethyl succinate and sodium tert-amyl alco-
holate yielded 41% and 45% of the corresponding DPP compounds
11a and 11b. Subsequent derivatization with Boc2O was carried out
by the same method as described for the Boc-protection of DPP
chromophore 3 and gave rise to yields of 91% for 7ea and 89% for
7eb. The final step is a bromination with NBS, which was executed
by the same experimental method as the bromination of DPPs 4,
leading to DPP analogues 1 (1ea, 94%; 1eb, 87%). Pathway B consists
of four steps with an overall yield for 1ea of 28% and for 1eb of 32%.
In a last proposed pathway (pathway C) towards bithiophene
containing DPPs 1 (Scheme 4), bithiophene 10b was also formed in
a first step (yield of 92%), but was then quantitatively brominated
into bithiophene 12b before it was used in a reaction with dieth-
ylsuccinate and base towards DPP derivative 13b (yield of 59%). The
final step in this synthetic route was the N-functionalization of the
DPP core. Towards this end, the same optimized conditions were
applied as for the derivatization of DPP chromophore 3 into DPPs 4,
giving rise to DPPs 1bb, 1cb, 1db and 1eb with yields of 77%, 69%,
84% and 69%, respectively. Pathway C consists of four steps with an
overall yield for 1bb of 42%, for 1cb of 37%, for 1db of 46% and for
1eb of 37%.
2.2. New synthetic routes towards DPP derivatives 1
A first alternative method (Pathway A) starts with the ring
closure towards the DPP core with commercially available 5-bro-
mothiophene-2-carbonitrile (8) (Scheme 2). This would immedi-
ately afford DPP chromophore 9 with bromo atoms on the
thiophene units, decreasing the total number of steps from five to
four. However, the ring closure towards DPP 9 did not occur
smoothly. Analysis of the reaction mixture by 1H NMR (DMSO-d6)
and MALDI-MS showed that besides desired DPP 9 a side product
with DPP core (in ratio 1:1) was present, probably formed by nu-
cleophilic aromatic substitution of the bromo atom on the thio-
phene unit by the deprotonated diethyl succinate. Since the first
step in pathway A would already require intensive purification to
remove the large amount of side product and thus would lead to
a low yield of DPP core 9, this route was not further explored.
The overall yields of 3,6-di(2,20-bithiophen-5-yl)-1,4-diketo-
pyrrolo[3,4-c]pyrroles 1 in pathway B (28–32%) and pathway C (37–
46%) were higher than the overall yields in the optimized method
from literature (Scheme 1, 11–17%). Moreover, pathways B and C
consist only of four steps instead of five. The bottleneck in these
new routes is the generation of the DPP cores (yields of only 41% to
59%). The lower yields of DPP compounds 11 and 13 compared to
DPP chromophore 3 prepared from unfunctionalized nitrile 2 in
72% yield, may be related to the presence of more bulky carbonitrile
containing bithiophenes, causing more sterical hindrance and
impeding ring closure towards the DPP core. Another problem
encountered throughout this reaction is the fact that 40-alkyl-2,20-
bithiophene-5-carbonitriles 10b and 12b are solid at room tem-
perature. Therefore the described method for the synthesis of DPP 3
could not be performed, since it requires adding dropwise a mix-
ture of diethyl succinate and (liquid) cyanothiophene to a boiling
solution of base in tert-amyl alcohol.39 After some experimenting,
we discovered that highest yields of the corresponding DPPs (11b
or 13b) were obtained by adding diethyl succinate and base si-
multaneously and dropwise to a boiling solution of carbonitrile in
Scheme 2. Pathway
A towards DPP derivatives 1. Reagents and conditions: (i)
0.5 equiv (CH2)2(COOEt)2, 1.7 equiv NaOC(CH3)2(CH2CH3), tert-amyl alcohol, reflux, 2 h,
Ar-atmosphere.
A second alternative pathway (Pathway B) starts with the syn-
thesis of carbonitrile containing bithiophene unit 10, which is then
Scheme 3. Pathway B towards DPP derivatives 1. Reagents and conditions: (i) 10 mol % Pd(PPh3)4, 1.3 equiv 6, anhydrous DMF, 80 ꢀC, 4.5 h, Ar-atmosphere; (ii) 0.5 equiv
(CH2)2(COOEt)2, 1.7 equiv NaOC(CH3)2(CH2CH3), tert-amyl alcohol, reflux, 2 h, Ar-atmosphere; (iii) 4 equiv base, excess alkylating agent Ar-atmosphere; (iv) 2.1 equiv NBS, anhy-
drous CHCl3, rt, 48 h, Ar-atmosphere, dark.

1840
S. Stas et al. / Tetrahedron 66 (2010) 1837–1845
Scheme 4. Pathway C towards DPP derivatives 1. Reagents and conditions: (i) 10 mol % Pd(PPh3)4, 1.3 equiv 6, anhydrous DMF, 80 ꢀC, 4.5 h, Ar-atmosphere; (ii) 2.1 equiv NBS,
anhydrous THF, 0 ꢀC 1 h to rt 18 h, Ar-atmosphere, dark; (iii) 0.5 equiv (CH2)2(COOEt)2, 1.7 equiv NaOC(CH3)2(CH2CH3), tert-amyl alcohol, reflux, 2 h, Ar-atmosphere; (iv) 4 equiv
base, excess alkylating agent, Ar-atmosphere.
the alcohol or by heating a one-pot mixture of all the compounds
under reflux. The same procedures were applied by Horn et al. to
synthesize pyrrolo[3,4-c]pyrrole-1,4-dione units from solid 4-cya-
nobiphenyls.42 From this publication it can also be concluded that
DPP core formation from solid biaryl carbonitriles results in lower
yields (35%) than from liquid cyanoaryls (60–70%). This observation
supports the presence of lower yields in the ring closing reactions
of bithiophene carbonitriles 10b and 12b towards corresponding
DPP units 11b and 13b. Additionally, we came across a difficult
characterization of DPP molecules 11 and 13. Since they are in-
soluble in most common organic solvents, it was not possible to
record a proton NMR spectrum (tested deuterated solvents: CDCl3,
CD2Cl2, THF-d8, TFA-d, CDCl3þfew drops of TFA-d, DMSO-d6, DMF-
d7, D2O, MeOD, CS2þfew drops of CDCl3, benzene-d6, NO2Ph-d5)
and only MALDI-HRMS proved the formation of the desired
bithiophene containing DPPs. Several interactions take place be-
efficient synthetic route towards DPP derivatives comprising
bithiophene moieties. Moreover, our research showed that syn-
thetic transformations on the DPP core proved problematic, but by
applying pathway C, the formation of the DPP core is postponed to
the one before last step and N-functionalization completes the
synthesis. Route C allows an easy derivatization by incorporating
different substituents on the terminal thiophene units and on the
N-atoms of the DPP moiety in order to modulate supramolecular
order in solid state. With this method, the desired functionalized
DPPs 1 become available in large scale and with high purities,
which are useful characteristics for further polymerization towards
donor semiconducting materials that can be used in the de-
velopment of photovoltaics.
4. Experimental
tween adjacent molecules, such as
p–p-interactions between the
4.1. General methods
layer of molecules, hydrogen bonding between neighbouring lac-
tam-N and carbonyl-O atoms and van der Waals contacts between
therminal aryl groups. The same interactions are present for
monothiophene comprising DPPs, but in case of bithiophene
High resolution 1H NMR (300 MHz) and 13C NMR (75 MHz)
spectra were recorded in CDCl3 or DMSO-d6 on a Bruker Avance 300
spectrometer. Chemical shifts are reported in parts per million
downfield from TMS, coupling constants (J) are given in Hertz. 13C
NMR assignments were made using DEPT, HMQC and HMBC
spectra. 2D-spectra were recorded on a Varian VNMRS 400 spec-
trometer. MALDI-HRMS measurements were made on a Waters
MALDI-QTOF Premier mass spectrometer using a 350 mW laser and
dithranol (1,8-dihydroxy-9,10-dihydroanthracen-9-one) as matrix.
Infrared spectra were recorded with an Avatar 370 FTIR apparatus
(Thermo Nicolet), using the attenuated total reflection technology
(ATR). UV–vis absorption spectra were recorded on an Agilent 8453
spectrophotometer in a quartz cell (optical path of 1 cm). Melting
points were measured by means of a Wild M3B Heerbrugg Swit-
zerland microscope in combination with a Mettler Hot Stage (FP82)
and a Mettler Central processor (FP80). Column chromatography
comprising DPPs even stronger
p–p-interactions are present be-
tween the bithiophene units of adjacent molecules, resulting in
very strong aggregates, insoluble in most common organic sol-
vents. The formation of DPPs 11 and 13 was however not deniable
when analyzing the results of the next step in the pathway: func-
tionalization of these insoluble molecules on the nitrogen atom
gave rise to perfectly soluble DPP derivatives 7 and 1 of which
NMRs could easily be obtained (CDCl3).
3. Conclusion
The best yields and highest purities of DPP derivatives 1 com-
prising bithiophene moieties were obtained in pathway C (Scheme
4), starting from commercially available 5-bromothiophene-2-car-
bonitrile (8). Stille coupling with stannic compounds 6 gave rise to
intermediate products 40-alkyl-2,20-bithiophene-5-carbonitrile 10
(up to 92% yield). Subsequent bromination yielded quantitatively
bromides 12, which were then used in a reaction with diethyl
succinate to form corresponding DPP chromophores 13 (up to 59%
yield). In the last step, N-functionalization of 13 produced the target
DPP derivatives 1 with yields of 69–84%.
was performed using Merck silica (diameter 40–63
mm) or Merck
neutral alumina Brockmann grade I (diameter 50–200
mm), which
was turned into activity grade III-IV by adding 8 wt % of water. TLC-
analysis was performed on aluminium backed sheets (Merck)
coated with 0.2 mm silica with UV-indicator 60F254 or on plastic
backed sheets (Merck) coated with 0.2 mm neutral alumina with
UV-indicator 60F254
. Several anhydrous solvents were used
throughout this work and they were dried as follows. THF was
distilled from sodium metal, using benzophenone as indicator.
2-Methylbutan-2-ol (¼tert-amyl alcohol) was dried by heating
under reflux (Tb¼102 ꢀC) with sodium metal for 2 h followed by
distillation on 4 Å molecular sieves. Freshly purchased NMP was
This four-step pathway gave overall yields of 37–46% of DPP
compounds 1, which are much higher than the yields obtained in
the optimized five-step pathway previously described in literature
(11 to 17%). Therefore we believe that pathway C is the most

S. Stas et al. / Tetrahedron 66 (2010) 1837–1845
1841
kept on molecular sieves (4 Å) under argon. Chloroform (HPLC-
grade) was stored on CaCl2. Anhydrous DMF (99.8%) and anhydrous
DMSO (99.9%) were purchased from Aldrich.
(2H, t, J¼7.7 Hz,
C
quat.thiopheneCH2(C5H11)), 1.65–1.60 (2H, m,
Cquat.thiopheneCH2CH2(CH2)3CH3), 1.40–1.27 (3ꢂ2H, m, Cquat.thiophene
CH2CH2(CH2)3CH3), 0.90 (3H, t, J¼6.9 Hz, Cquat.thiophene(CH2)5CH3).
13C NMR (75 MHz, CDCl3):
d (ppm) 145.2 (Cquat.thiophene(5)), 144.7
(Cquat.thiophene(4)), 138.2 (CHthiophene(7)), 134.4 (Cquat.thiophene(2)),
127.3 (CHthiophene(6)), 123.1 (CHthiophene(3)), 121.7 (CHthiophene(2)),
114.3 (CN), 107.1 (Cquat.thiophene(8)), 31.6 (Cquat.thiopheneCH2), 30.4,
30.3, 28.9 (Cquat.thiopheneCH2(CH2)3CH2CH3), 22.6 ((CH2)4CH2CH3),
14.1 ((CH2)5CH3).
4.2. Pathway B towards DPP derivatives comprising
bithiophene moieties 1
4.2.1. Tributyl(4-hexylthiophen-2-yl)stannane
(6a)41. Tributyl(4-
hexylthiophen-2-yl)stannane (6a) was synthesized according to
the reported literature.41 Yield: 72%, light yellow liquid. Complete
spectral characterization: see Supplementary data.
4. 2. 3. 2. 40-Dodecyl-2,20-bithiophene-5-carbonitrile
(10b). Compound (10b) was isolated from the reaction mixture by
adding MeOH and storing the flask overnight in the fridge in order
to fully precipitate the compound. The white precipitate was fil-
tered off and washed with MeOH to yield 92% of 40-dodecyl-2,20-
bithiophene-5-carbonitrile (10b) (3.30 g). 1H NMR (300 MHz,
4.2.2. Tributyl(4-dodecylthiophen-2-yl)stannane (6b). Tributyl(4-
docedylthiophen-2-yl)stannane (6b) was synthesized by an
analogues method as described for the synthesis of tributyl(4-
hexylthiophen-2-yl)stannane (6a).41
To a solution of 3-dodecylthiophene (20 mmol, 5.05 g, 5.6 ml) in
anhydrous THF (40 ml) cooled to ꢁ78 ꢀC under argon, LDA in THF/
ethylbenzene/heptane (1.8 M, 1 equiv, 20 mmol, 11.1 ml) was added
dropwise. At the end of the addition the mixture was allowed to
reach 0 ꢀC in 3 h. The mixture was then cooled back down to ꢁ78 ꢀC
and Bu3SnCl (1 equiv, 20 mmol, 6.51 g, 5.4 ml) was added in one
portion. The mixture was kept for 15 min at ꢁ78 ꢀC before it was
allowed to reach room temperature at which temperature it was
stirred for 2.5 h. Hexane (40 ml) was added and the reaction mix-
ture was washed with water (4ꢂ20 ml). The water phase was
extracted once again with hexane (40 ml) and the organic fractions
were combined, dried (MgSO4), filtered and evaporated. Kugelrohr
distillation was performed as purification method. Unreacted
Bu3SnCl (Tb¼171–173 ꢀC/25 mmHg) and 3-dodecylthiophene
(Tb¼290 ꢀC/760 mmHg) were distilled off at 170 ꢀC/8.5 mmHg. The
light yellow tributyl(4-dodecylthiophen-2-yl)stannane (7.98 g, 74%
yield) distilled at 220 ꢀC/8.5 mmHg and was stored at 2–4 ꢀC. 1H
CDCl3):
d
(ppm) 7.50 (1H, d, J¼3.9 Hz, CHthiophene(6)), 7.11 (1H, d,
J¼1.3 Hz, CHthiophene(1)), 7.09 (1H, d, J¼3.9 Hz, CHthiophene(7)), 6.93
(1H, d, J¼1.3 Hz, CHthiophene(3)), 2.59 (2H, t, J¼7.8 Hz, Cquat.thiophene
CH2(C11H23)), 1.67–1.57 (2H, m, Cquat.thiopheneCH2CH2(CH2)9CH3),
1.37–1.26 (9ꢂ2H, m, Cquat.thiopheneCH2CH2(CH2)9CH3), 0.88 (3H, t,
J¼6.7 Hz, Cquat.thiophene(CH2)11CH3). 13C NMR (75 MHz, CDCl3):
d
(ppm) 145.2 (Cquat.thiophene(5)), 144.8 (Cquat.thiophene(4)), 138.3
(CHthiophene(7)), 134.5 (Cquat.thiophene(2)), 127.4 (CHthiophene(6)),
123.2 (CHthiophene(3)), 121.8 (CHthiophene(2)), 114.4 (CN), 107.2
(Cquat.thiophene(8)), 32.0 (Cquat.thiopheneCH2), 30.5 (Cquat.thiophene
CH2CH2), 29.9, 29.87, 29.85, 29.8, 29.7, 29.54, 29.48, 29.37
((CH2)2(CH2)8CH2CH3), 22.8 ((CH2)10CH2CH3), 14.2 ((CH2)11CH3).
4.2.4. Synthesis of 3,6-bis(40-alkyl-2,20-bithiophen-5-yl)pyrrolo[3,4-
c]pyrrole-1,4(2H,5H)-dione (11)
4.2.4.1. 3,6-Bis(40-hexyl-2,20-bithiophen-5-yl)pyrrolo[3,4-c]pyr-
role-1,4(2H,5H)-dione (11a). The same procedure as described for
the synthesis of 3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-
1,4(2H,5H)-dione (3) was applied.39
NMR (300 MHz, CDCl3):
d
(ppm) 7.19 (1H, d, J¼0.8 Hz, SCHthiophene
Cquat.thiopheneC12H25), 6.96 (1H, d, J¼0.8 Hz, SCquat.thiophene
(Sn)CHthiophene), 2.65 (2H, t, J¼7.8 Hz, Cquat.thiopheneCH2(C11H23)),
1.67–1.51 (12H, m, 3ꢂSnCH2(CH2)2CH3), 1.40–1.26 (10ꢂ2H, m,
Cquat.thiopheneCH2(CH2)10CH3), 1.14–1.05 (3ꢂ2H, m, 3ꢂSnCH2), 0.89
(3ꢂ3H, t, J¼7.2 Hz, 3ꢂSnCH2(CH2)2CH3), 0.88 (3H, t, J¼6.6 Hz,
A
mixture of 40-hexyl-2,20-bithiophene-5-carbonitrile (10a)
(4 mmol, 1.10 g) and 0.5 equiv diethyl succinate (2 mmol, 348 mg)
was added dropwise over 1.3 h to a solution of 1.7 equiv sodium
tert-amyl alcoholate (1 N solution, 6.8 mmol, 6.8 ml,) in boiling dry
2-methylbutan-2-ol (8 ml) under argon atmosphere. Stirring was
continued for 1.5 h under reflux. The mixture was then cooled to
room temperature before it was added to an ice-cooled mixture of
methanol (25 ml) and concentrated (12.5 M) hydrochloric acid
(1 ml). The mixture was stirred for 30 min and then left overnight
in the fridge (2–3 ꢀC) in order to fully precipitate the DPP derivative
11a. The black precipitate was filtered off, washed with methanol
and water, and then an overnight Soxhlet extraction with MeOH
was performed to remove all MeOH-soluble side compounds. After
drying of the solid in vacuo, 3,6-bis(40-hexyl-2,20-bithiophen-5-
yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (11a) was obtained as
a dark blue solid in 41% yield (520 mg). IR (ATR, cmꢁ1): nmax 3127
(aromatic C–H bending), 2955, 2924, 2850 (CH alkane stretch),1641
(C]O amide stretch), 1595 (NH amide stretch), 1439, 1419 (aro-
Cquat.thiophene(CH2)11CH3). 13C NMR (75 MHz, CDCl3):
d (ppm) 144.4
(Cquat.thiopheneSn), 136.9 (SCHthiopheneCquat.thiopheneC12H25), 136.2
(Cquat.thiopheneC12H25), 125.5 (SCquat.thiophene(Sn)CHthiophene), 31.9
(Cquat.thiopheneCH2(C11H23)), 30.7, 30.0, 29.8, 29.69, 29.66, 29.6,
29.52, 29.49, 29.4, 29.0 (Cquat.thiopheneCH2(CH2)10CH3), 27.3 (3ꢂ
SnCH2CH2CH2CH3), 22.7 (3ꢂSnCH2CH2CH2CH3), 14.1 (Cquat.thiophene
(CH2)11CH3), 13.7 (3ꢂSn(CH2)3CH3), 10.7 (3ꢂSnCH2(CH2)2CH3).
4.2.3. Synthesis of 40-alkyl-2,20-bithiophene-5-carbonitrile (10). A
mixture of 5-bromothiophene-2-carbonitrile (8) (10 mmol, 1.88 g),
Pd(Ph3P)4 (0.1 equiv, 1 mmol, 1.16 g) and stannane 6 (1.3 equiv,
13 mmol) in anhydrous DMF (60 ml) was brought under argon at-
mosphere and heated during 4.5 h at 80 ꢀC. After cooling the
mixture to room temperature, a saturated solution of NH4Cl
(100 ml) was added, and the medium was then extracted with
CH2Cl2 (70 ml/50 ml/20 ml). The organic layers were combined,
washed with water (50 ml), dried over and concentrated under
vacuum.
matic C]C stretch), 1350 (CH alkane bending). UVmax(THF): l (nm)
239, 346, 388, 554, 595. HRMS (MALDI): m/z calcd for C34H36N2O2S4
(Mꢃþ) 632.1660; found 632.1673; ppm: 2.1. Mp: >300 ꢀC.
4 . 2 . 3 .1. 4 0- H e x y l - 2 , 2 0- b i t h i o p h e n e - 5 - c a r b o n i t r i l e
(10a). Compound (10a) was purified from the reaction mixture by
flash chromatography on neutral alumina (Brockmann grade III-IV)
with nHex/CH2Cl2 (8:2) as eluents (Rf¼0.31) resulting in 80% of 40-
hexyl-2,20-bithiophene-5-carbonitrile (10a) (2.21 g) as a light yel-
4.2.4.2. 3,6-Bis(40-dodecyl-2,20-bithiophen-5-yl)pyrrolo[3,4-
c]pyrrole-1,4(2H,5H)-dione (11b). A mixture of 40-dodecyl-2,20-
bithiophene-5-carbonitrile (10b) (2.5 mmol, 899 mg), 1.7 equiv
sodium tert-amyl alcoholate (1 N, 4.25 mmol, 4.25 ml, 4,25 mmol)
and 0.5 equiv diethyl succinate (1.25 mmol, 218 mg) in anhydrous
2-methylbutan-2-ol (5 ml) was stirred under reflux under argon
atmosphere during a period of 2.5 h. The mixture was added to an
ice-cooled mixture of methanol (15 ml) and concentrated (12.5 M)
low liquid. 1H NMR (300 MHz, CDCl3):
d
(ppm) 7.51 (1H, d, J¼3.9 Hz,
CHthiophene(6)), 7.12 (1H, d, J¼1.4 Hz, CHthiophene(1)), 7.10 (1H, d,
J¼3.9 Hz, CHthiophene(7)), 6.94 (1H, d, J¼1.4 Hz, CHthiophene(3)), 2.60

1842
S. Stas et al. / Tetrahedron 66 (2010) 1837–1845
hydrochloric acid (0.75 ml). The mixture was stirred for 30 min and
then stored overnight in the fridge (2–3 ꢀC) in order to fully pre-
cipitate 3,6-bis(40-dodecyl-2,20-bithiophen-5-yl)pyrrolo[3,4-c]pyr-
role-1,4(2H,5H)-dione (11b). The dark purple precipitate was
filtered off, washed with methanol and water, and then dried in
vacuo. An overnight Soxhlet extraction with MeOH was performed
to remove all MeOH-soluble side compounds and after drying of
the dark blue solid in vacuo, 45% (449 mg) of 3,6-bis(40-dodecyl-
2,20-bithiophen-5-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (11b)
was yielded. IR (ATR, cmꢁ1): nmax 3125 (aromatic C–H bending),
2918, 2849 (CH alkane stretch), 1636 (C]O amide stretch), 1595
(NH amide stretch), 1452, 1431, 1413 (aromatic C]C stretch), 1351
(2ꢂ18H, m, Cquat.thiopheneCH2CH2(CH2)9CH3), 0.88 (2ꢂ3H, t, J¼6.6 Hz,
Cquat.thiophene(CH2)5CH3). 13C NMR (75 MHz, CDCl3):
(ppm) 159.1 (CO
d
pyrrole-2-one), 148.9 (CO Boc), 144.7 (Cquat.thiophene(2)), 144.6
(Cquat.(9)), 136.7 (Cquat.thiophene(5)), 135.7 (Cquat.thiophene(4)), 135.2
(CHthiophene(6)), 127.7 (Cquat.(8)), 126.9 (CHthiophene(3)), 124.2
(CHthiophene(7)), 121.4 (CHthiophene(1)), 110.2 (Cquat.(10)), 86.0 (Cquat.
tBu), 31.9 ((CH2)9CH2CH2CH3), 30.43, 30.38, 29.68, 29.67, 29.66, 29.60,
29.45, 29.36, 29.29 ((CH2)9CH2CH2CH3), 27.7 (CH3 tBu), 22.7
((CH2)10CH2CH3), 14.1 ((CH2)11CH3). IR (ATR, cmꢁ1): nmax 3111, 3083
(aromatic C–H bending), 2956, 2916, 2850 (CH alkane stretch), 1741
(C]O ester stretch), 1685 (C]O amide stretch), 1561, 1545, 1433 (ar-
omatic C]C stretch),1365,1297 (CH alkane bending),1213,1149,1100
(CH alkane bending). UVmax(THF):
l
(nm) 238, 353, 375, 552, 597.
(C–O ester stretch). UVmax(CH2Cl2): l (nm) 231, 333, 405, 572. HRMS
HRMS (MALDI): m/z calcd for C46H60N2O2S4 (Mꢃþ) 800.3538; found
800.3527; ppm: 1.4. Mp: >300 ꢀC.
(MALDI): m/z: calcd for C56H76N2O6S4 (Mꢃþ): 1000.4586; found:
1000.4581; ppm: 0.5. Mp: >300 ꢀC, Boc-deprotection 147–152 ꢀC.
4.2.5. Boc-protection of 3,6-bis(40-alkyl-2,20-bithiophen-5-yl)pyr-
rolo[3,4-c]pyrrole-1,4(2H,5H)-dione (11). The Boc-protection of 11
was executed as described for the Boc-protection of DPP chromo-
phore 3, which was executed according to the reported literature.22
In a two-necked, oven-dried round bottom flask, 3,6-bis(40-al-
kyl-2,20-bithiophen-5-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione
(11) (2 mmol) was dissolved in 20 ml anhydrous THF and the
resulting solution was purged with argon for 10 min. Then,
2.5 equiv of N,N-dimethylaminopyridine (5 mmol, 611 mg) dis-
solved in 7 ml anhydrous THF were added and the reaction mixture
was stirred 15 min under argon atmosphere at room temperature.
Next, 5 equiv of di-tert-butyl dicarbonate (10 mmol, 2.3 ml) were
added (rinsed with 3 ml THF) and the mixture was stirred for 24 h
at room temperature under argon. The mixture was concentrated
under vacuum and the residue was dissolved in 12 ml MeOH and
stored for 30 min in the fridge at 2–3 ꢀC before the dark blue pre-
cipitate was filtered off. The precipitate was washed with MeOH
and dried under vacuum to give pure dark blue Boc-protected DPP
derivative 7.
4.2.6. Bromination of di-tert-butyl-3,6-bis(40-alkyl-2,20-bithiophen-
5-yl)-1,4-dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate
7. Bromination of 7 was executed by an analogue method as de-
scribed for the bromination of DPP compound 4e.22
In a two-necked, oven-dried 25 ml round bottom flask covered
with aluminium foil, di-tert-butyl-3,6-bis(40-alkyl-2,20-bithiophen-
5-yl)-1,4-dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate
7
(0.4 mmol) was dissolved in 24 ml anhydrous chloroform and
stirred under argon for 15 min. 2.1 equiv of N-bromosuccinimide
(0.84 mmol, 150 mg) were added in one portion at room temper-
ature and the mixture was stirred for 48 h at rt. The reaction
mixture was poured into 60 ml MeOH and the resulting suspension
was stirred for 20 min at rt. The precipitation was completed in the
fridge during 15 min. DPP derivatives 1 were collected as dark blue
solids by vacuum filtration and were washed with several portions
of hot distilled water and hot MeOH.
4.2.6.1. Di-tert-butyl-3,6-bis(50-bromo-40-hexyl-2,20-bithiophen-
5-yl)-1,4-dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate
(1ea). Yield¼91% (377 mg). 1H NMR (300 MHz, CDCl3):
d (ppm)
4.2.5.1. Di-tert-butyl-3,6-bis(40-hexyl-2,20-bithiophen-5-yl)-1,4-di-
8.18 (2ꢂ1H, d, J¼4.1 Hz, CHthiophene(6)), 7.15 (2ꢂ1H, d, J¼4.1 Hz,
CHthiophene(7)), 7.00 (2ꢂ1H, s, CHthiophene(3)), 2.55 (2ꢂ2H, t,
J¼7.5 Hz, Cquat.thiopheneCH2(CH2)4CH3), 1.66–1.57 (2ꢂ2H, m,
oxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate (7ea). Yield¼91%
(608 mg).1H NMR (300 MHz, CDCl3):
d
(ppm) 8.21 (2ꢂ1H, d, J¼4.1 Hz,
t
CHthiophene(6)), 7.21 (2ꢂ1H, d, J¼4.1 Hz, CHthiophene(7)), 7.14 (2ꢂ1H, d,
J¼1.2 Hz, CHthiophene(3)), 6.92 (2ꢂ1H, d, J¼1.2 Hz, CHthiophene(1)), 2.59
Cquat.thiopheneCH2CH2(CH2)3CH3), 1.63 (2ꢂ9H, s, 2ꢂ Bu), 1.38–1.28
(2ꢂ6H, m, Cquat.thiopheneCH2CH2(CH2)3CH3), 0.90 (2ꢂ3H, t, J¼6.5 Hz,
t
(2ꢂ2H, t, J¼7.6 Hz, Cquat.thiopheneCH2(CH2)4CH3),1.64(2ꢂ9H, s, 2ꢂ Bu),
Cquat.thiophene(CH2)5CH3). 13C NMR (75 MHz, CDCl3):
d (ppm) 159.0
1.63–1.61 (2ꢂ2H, m, Cquat.thiopheneCH2CH2(CH2)3CH3), 1.32–1.26
(2ꢂ6H, m, Cquat.thiopheneCH2CH2(CH2)3CH3), 0.90 (2ꢂ3H, t, J¼6.4 Hz,
(CO pyrrole-2-one), 148.9 (CO Boc), 143.6 (Cquat.thiophene(2)), 143.3
(Cquat.(9)), 136.6 (Cquat.thiophene(4)), 135.5 (Cquat.thiophene(5)), 135.1
(CHthiophene(6)), 128.1 (Cquat.thiophene(8)), 126.2 (CHthiophene(3)),
124.3 (CHthiophene(7)), 110.4 (Cquat.(10)), 109.6 (Cquat.thiophene(1)),
86.1 (Cquat. tBu), 31.6 ((CH2)3CH2CH2CH3), 29.58, 29.57, 28.9
((CH2)3CH2CH2CH3), 27.8 (CH3 tBu), 22.6 ((CH2)4CH2CH3), 14.1
((CH2)5CH3). IR (ATR, cmꢁ1): nmax 3065, 3052 (aromatic C–H
bending), 2952, 2925, 2855 (CH alkane stretch), 1748 (C]O ester
stretch), 1680 (C]O amide stretch), 1561, 1546 (aromatic C]C
stretch),1367,1301 (CH alkane bending),1213,1145,1100 (C–O ester
Cquat.thiophene(CH2)5CH3).13C NMR (75 MHz, CDCl3):
d (ppm) 159.1 (CO
pyrrole-2-one), 148.9 (CO Boc), 144.7 (Cquat.thiophene(2)), 144.6
(Cquat.(9)), 136.7 (Cquat.thiophene(4)), 135.7 (Cquat.thiophene(5)), 135.2
(CHthiophene(6)), 127.7 (Cquat.thiophene(8)), 126.9 (CHthiophene(3)), 124.2
(CHthiophene(7)), 121.4 (CHthiophene(1)), 110.2 (Cquat.(10)), 86.0 (Cquat.
tBu), 31.6 ((CH2)3CH2CH2CH3), 30.4, 30.3, 28.9 ((CH2)3CH2CH2CH3),
27.7 (CH3 tBu), 22.6 ((CH2)4CH2CH3),14.1 ((CH2)5CH3). IR (ATR, cmꢁ1):
nmax 3124, 3095 (aromatic C–H bending), 2953, 2920, 2851 (CH alkane
stretch), 1740 (C]O ester stretch), 1685 (C]O amide stretch), 1559,
1540, 1431 (aromatic C]C stretch), 1366, 1305 (CH alkane bending),
stretch). UVmax(CH2Cl2):
l (nm) 232, 342, 393, 572. MALDI-HRMS:
m/z: calcd for C44H50N2O6S4Br2 (Mꢃþ): 988.0918; found: 988.0930;
ppm: 1.2. Mp: >300 ꢀC, Boc-deprotection 174–177 ꢀC.
1215, 1148, 1095 (C–O ester stretch). UVmax(CH2Cl2):
l (nm) 230,
332, 405, 567. MALDI-HRMS: m/z: calcd for C44H52N2O6S4 (Mꢃþ):
832.2708; found: 832.2708; ppm: 0.0. Mp: >300 ꢀC, Boc-depro-
tection 167–173 ꢀC.
4.2.6.2. Di-tert-butyl-3,6-bis(50-bromo-40-dodecyl-2,20-bithio-
phen-5-yl)-1,4-dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate
(1eb). Yield¼87% (483 mg). 1H NMR (300 MHz, CDCl3):
d (ppm)
4.2.5.2. Di-tert-butyl-3,6-bis(40-dodecyl-2,20-bithiophen-5-yl)-1,4-
8.18 (2ꢂ1H, d, J¼4.1 Hz, CHthiophene(6)), 7.15 (2ꢂ1H, d, J¼4.1 Hz,
CHthiophene(7)), 6.99 (CHthiophene(3)), 2.54 (2ꢂ2H, t, J¼7.4 Hz,
Cquat.thiopheneCH2(CH2)10CH3), 1.69–1.63 (2ꢂ2H, m, Cquat.thiophene
dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate(7eb). Yield¼89%
(712 mg). 1H NMR (300 MHz, CDCl3):
d
(ppm) 8.21 (2ꢂ1H, d, J¼4.1 Hz,
t
CHthiophene(6)), 7.21 (2ꢂ1H, d, J¼4.1 Hz, CHthiophene(7)), 7.14 (2ꢂ1H, d,
J¼1.2 Hz, CHthiophene(3)), 6.91(2ꢂ1H, d, J¼1.2 Hz, CHthiophene(1)), 2.59
CH2CH2(CH2)9CH3), 1.63 (2ꢂ9H, s, 2ꢂ Bu), 1.36–1.26 (2ꢂ18H, m,
Cquat.thiopheneCH2CH2(CH2)9CH3), 0.88 (2ꢂ3H, t, J¼6.6 Hz, Cquat.thio-
t
(2ꢂ2H, t, J¼7.7 Hz, Cquat.thiopheneCH2(CH2)10CH3),1.63 (2ꢂ9H, s,2ꢂ Bu),
phene(CH2)11CH3). 13C NMR (75 MHz, CDCl3):
d (ppm) 159.0 (CO
1.66–1.57 (2ꢂ2H, m, Cquat.thiopheneCH2CH2(CH2)9CH3), 1.32–1.26
pyrrole-2-one), 148.9 (CO Boc), 143.6 (Cquat.thiophene(2)), 143.3

S. Stas et al. / Tetrahedron 66 (2010) 1837–1845
1843
(Cquat.(9)), 136.6 (Cquat.thiophene(4)), 135.5 (Cquat.thiophene(5)), 135.1
(CHthiophene(6)), 128.1 (Cquat.thiophene(8)), 126.2 (CHthiophene(3)),
124.3 (CHthiophene(7)), 110.4 (Cquat.(10)), 109.6 (Cquat.thiophene(1)),
86.1 (Cquat. tBu), 31.9 ((CH2)9CH2CH2CH3), 29.65, 29.57, 29.4, 29.4,
29.2 ((CH2)9CH2CH2CH3), 27.8 (CH3 tBu), 22.7 ((CH2)10CH2CH3),14.1
((CH2)11CH3). IR (ATR, cmꢁ1): nmax 3063 (aromatic C–H bending),
2981, 2920, 2851 (CH alkane stretch), 1742 (C]O ester stretch),
1681 (C]O amide stretch), 1560, 1539, 1435 (aromatic C]C
stretch), 1366, 1300 (CH alkane bending), 1215, 1149, 1101 (C–O
alkane stretch), 1641 (C]O amide stretch), 1600 (NH amide
stretch), 1453, 1420 (aromatic C]C stretch), 1340 (CH alkane
bending). HRMS (MALDI): m/z calcd for C46H58N2O2S4Br2 (Mꢃþ
956.1748; found 956.1751; ppm: 0.3. Mp: >300 ꢀC.
)
4.3.3. Functionalization of DPPs 13 at the nitrogen position
4.3.3.1. N-methylation of DPP 13b towards 3,6-bis(50-bromo-40-
dodecyl-2,20-bithiophen-5-yl)-2,5-dimethylpyrrolo[3,4-c]pyrrole-
1,4(2H,5H)-dione (1bb). The same method was applied as described
for the N-methylation of DPP 3 into DPP derivative 4b. This method
is derived from a modified literature procedure.35,36
ester stretch). UVmax(CH2Cl2):
l (nm) 230, 341, 406, 572. MALDI-
HRMS: m/z: calcd for C56H74N2O6S4Br2 (Mꢃþ): 1156.2796; found:
1156.2834; ppm: 3.3; m/z: calcd for C46H58N2O6S4Br2
([Mꢃþ]ꢁ(2ꢂBoc)): 956.1748; found: 1156.1768; ppm: 2.1. Mp:
>300 ꢀC, Boc-deprotection 173–178 ꢀC.
A solution of 3,6-bis(50-bromo-40-dodecyl-2,20-bithiophen-5-
yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (13b) (0.125 mmol,
120 mg) and potassium carbonate (4 equiv, 0.5 mmol, 69 mg) in
4 ml anhydrous NMP was brought under argon atmosphere and
was stirred for 1 h at rt. Then, 12.8 equiv of iodomethane
(1.6 mmol, 227 mg) were added in one portion. The mixture was
stirred for 1 h at rt and then brought at 60 ꢀC and 10 additional
equivalents of MeI were added (177 mg) since MeI is very volatile
(bp around 45 ꢀC). The mixture was stirred for 2 h at 60 ꢀC and
then another 10 equiv of MeI (177.4 mg) were added and the
mixture was left at 60 ꢀC overnight (18 h). The mixture was cooled
down to room temperature, washed with water (15 ml) and
extracted with EtOAc (15 ml/10 ml/10 ml). The organic layers were
collected and evaporated. The residue was suspended in 15 ml
MeOH and a dark blue precipitate is formed. The mixture was
stored in the fridge for 1 h and then the precipitate was filtered off,
washed with fresh MeOH and dried in vacuo. A fast purification
over alumina with CH2Cl2 as eluents was executed (Rf¼0.67),
resulting in 77% (95 mg) of 3,6-bis(50-bromo-40-dodecyl-2,20-
bithiophen-5-yl)-2,5-dimethylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-
4.3. Pathway C towards DPP derivatives comprising
bithiophene moieties 1
4.3.1. Synthesis of 50-bromo-40-dodecyl-2,20-bithiophene-5-carbon-
itrile (12b). 40-Dodecyl-2,20-bithiophene-5-carbonitrile (5 mmol,
1.80 g) was dissolved in anhydrous THF (50 ml), covered from light
with aluminium foil and cooled down to 0 ꢀC. 1.06 equiv of N-bro-
mosuccinimide (5.3 mmol, 943 mg) were added portionwise over
aperiodof1 h.Thereactionmixturewasstirredfor1 hintheice-water
bath before it was allowed to reach room temperature at which
temperature the reaction was overnight stirred. The mixture is
quenched with water (50 ml) and hexane (50 ml) is added. The
organic phase was additionally extracted three times with water
(3ꢂ50 ml). The combined water phase was once back-extracted with
hexane (50 ml). The organicphases were combined, dried over MgSO4
and concentrated in vacuo. 50-Bromo-40-dodecyl-2,20-bithiophene-5-
carbonitrile (12b) was obtained as a light yellow solid in quantitative
yield (2.19 g).1H NMR (300 MHz, CDCl3):
d
(ppm) 7.50 (1H, d, J¼3.9 Hz,
dione (1bb). 1H NMR (300 MHz, CDCl3):
d
(ppm) 8.83 (2ꢂ1H, d,
CHthiophene(6)), 7.04 (1H, d, J¼3.9 Hz, CHthiophene(7)), 6.97 (1H, s,
CHthiophene(3)), 2.55 (2H, t, J¼7.7 Hz, Cquat.thiopheneCH2(C11H23)), 1.64–
1.54 (2H, m, Cquat.thiopheneCH2CH2(CH2)9CH3), 1.33–1.26 (9ꢂ2H, m,
Cquat.thiopheneCH2CH2(CH2)9CH3), 0.88 (3H, t, J¼6.6 Hz, Cquat.thiophene
J¼3.8 Hz, CHthiophene(6)), 7.23 (2ꢂ1H, d, J¼3.8 Hz, CHthiophene(7)),
7.03 (2ꢂ1H, s, CHthiophene(3)), 3.64 (2ꢂ3H, s, 2ꢂN–CH3), 2.55
(2ꢂ2H, t, J¼7.6 Hz, Cquat.thiopheneCH2(CH2)10CH3), 1.67–1.60
(2ꢂ2H, m, Cquat.thiopheneCH2CH2(CH2)9CH3), 1.35–1.27 (2ꢂ18H, m,
Cquat.thiopheneCH2CH2(CH2)9CH3), 0.88 (2ꢂ3H, t, J¼6.4 Hz,
(CH2)11CH3). 13C NMR (75 MHz, CDCl3):
d (ppm) 143.9 (Cquat.thiophene
(5)),143.6 (Cquat.thiophene(2)),138.2(CHthiophene(7)),134.2(Cquat.thiophene
(4)), 126.7 (CHthiophene(3)), 123.3 (CHthiophene(6)), 114.0 (CN), 110.7
(Cquat.thiophene(1)),107.6 (Cquat.thiophene(8)), 31.9(Cquat.thiopheneCH2), 29.7
(Cquat.thiopheneCH2CH2), 29.66, 29.63, 29.60, 29.50, 29.36, 29.35, 29.20,
29.18 ((CH2)2(CH2)8CH2CH3), 22.7 ((CH2)10CH2CH3), 14.1 ((CH2)11CH3).
Cquat.thiophene(CH2)11CH3). 13C NMR (75 MHz, CDCl3):
d (ppm) 158.7
(CO pyrrole-2-one), 144.4 (Cquat.thiophene(2)), 140.9 (Cquat.(9)), 137.8
(Cquat.thiophene(4)), 136.6 (Cquat.thiophene(5)), 132.0 (CHthiophene(6)),
125.0 (CHthiophene(3)), 120.2 (Cquat.thiophene(8)), 115.5 (CHthiophene
(7)), 109.6 (Cquat.(10)), 103.4 (Cquat.thiophene(1)), 31.9 ((CH2)9
CH2CH2CH3), 29.7 (N–CH3), 29.63, 29.59, 29.51, 29.45, 29.41, 29.36,
29.25, 29.21, 29.18 ((CH2)9CH2CH2CH3), 22.7 ((CH2)10CH2CH3), 14.1
((CH2)11CH3). IR (ATR, cmꢁ1): nmax 3069, 3043 (aromatic C–H
bending), 2919, 2850 (CH alkane stretch), 1644 (C]O amide
4.3.2. Synthesis of 3,6-bis(50-bromo-40-dodecyl-2,20-bithiophen-5-
yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione
(13b). 50-Bromo-40-
dodecyl-2,20-bithiophene-5-carbonitrile (12b) (7.40 mmol, 3.25 g)
was suspended in 15 ml 2-methylbutan-2-ol under argon and the
mixture is brought to 102 ꢀC (bp tert-amyl alcohol). (When the
mixture reached 70 ꢀC, carbonitrile 12b was dissolved in the alco-
hol.) Diethyl succinate (0.5 equiv, 3.70 mmol, 0.6 ml) and sodium
tert-amyl alcoholate (1.7 equiv,1 N,12.6 mmol,12.6 ml) were added
dropwise to the boiling solution during a period of 2 h (12 portions
of þ/ꢁ1 ml base and þ/ꢁ0.05 ml succinate). The mixture was then
further refluxed for 3 h. The mixture was cooled to room temper-
ature (30 min) and added to an ice-cooled mixture of methanol
(50 ml) and concentrated (12.5 M) hydrochloric acid (2 ml). The
mixture was stirred for 10 min and then overnight put in the fridge
at 2–3 ꢀC in order to fully precipitate DPP 13b. The dark purple
precipitate was filtered off, washed with methanol and water, and
then dried in vacuo. The dried precipitate was put in a Soxhlet
cellulose thimble and extracted overnight with MeOH in order to
remove all the MeOH-soluble side compounds. After drying the
solid in vacuo, 59% 3,6-bis(50-bromo-40-dodecyl-2,20-bithiophen-5-
yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (2.11 g) was obtained. IR
(ATR, cmꢁ1): nmax 3128 (aromatic C–H bending), 2917, 2851 (CH
stretch), 1561, 1446, 1424 (aromatic C]C stretch). UVmax(CH2Cl2):
l
(nm) 235, 355, 408, 581, 622. MALDI-HRMS: m/z: calcd for
C48H62N2O2S4Br2 (Mꢃþ): 984.2061; found: 984.2053; ppm: 0.8. Mp:
203.7–206.1 ꢀC.
4.3.3.2. N-octylation of DPP 13b towards 3,6-bis(50-bromo-40-
dodecyl-2,20-bithiophen-5-yl)-2,5-dioctylpyrrolo[3,4-c]pyrrole-
1,4(2H,5H)-dione (1cb). The same method was applied as described
for N-octylation of DPP 3 into DPP derivative 4c.15,16
A solution of 3,6-bis(50-bromo-40-dodecyl-2,20-bithiophen-5-
yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione
(13b)
(0.3 mmol,
288 mg) and potassium carbonate (1.2 mmol, 166 mg) in 8 ml an-
hydrous NMP was brought under argon atmosphere and was
heated to 140 ꢀC. After 30 min at that temperature, 3 equiv of
n-octyliodide (0.9 mmol, 216 mg) were added in one portion. The
mixture was further mixed at 140 ꢀC during 5 h. The mixture was
cooled down to room temperature (10 min) and then quenched
with water (16 ml). A precipitate was formed and the mixture was
stored in the fridge overnight to fully precipitate the compound.

1844
S. Stas et al. / Tetrahedron 66 (2010) 1837–1845
The dark blue/black precipitate was filtered off, washed with water
and MeOH and dried in vacuo. A fast purification over alumina with
CH2Cl2 as eluents was executed (Rf¼0.76), resulting in 69% (302 mg)
of 3,6-bis(50-bromo-40-dodecyl-2,20-bithiophen-5-yl)-2,5-dioctyl-
pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (1cb). 1H NMR (300 MHz,
(Cquat. tBu), 31.9 ((CH2)9CH2CH2CH3), 31.4 (CH3 tBu), 29.68, 29.67,
29.66, 29.64, 29.63, 29.56, 29.41, 29.36, 29.25 ((CH2)9CH2CH2CH3),
22.7 ((CH2)10CH2CH3), 14.1 ((CH2)11CH3). IR (ATR, cmꢁ1): nmax 3072,
3018 (aromatic C–H bending), 2952, 2923, 2854 (CH alkane stretch),
1654 (C]O amide stretch), 1560, 1508, 1445, 1426 (aromatic C]C
CDCl3):
d
(ppm) 8.85 (2ꢂ1H, d, J¼4.2 Hz, CHthiophene(6)), 7.22 (2ꢂ1H,
stretch), 1396, 1361, 1344 (CH alkane bending). UVmax(CH2Cl2): l
d, J¼4.2 Hz, CHthiophene(7)), 7.01 (2ꢂ1H, s, CHthiophene(3)), 4.07 (2ꢂ2H,
t, J¼7.3 Hz, NCH2(CH2)6CH3), 2.56 (2ꢂ2H, t, J¼7.7 Hz, Cquat.thiophene
CH2(CH2)10CH3), 1.79–1.73 (2ꢂ2H, m, NCH2CH2(CH2)5CH3), 1.64–1.54
(2ꢂ2H, m, Cquat.thiopheneCH2CH2(CH2)9CH3), 1.44–1.24 (2ꢂ16H, m,
NCH2CH2(CH2)5CH3þCquat.thiopheneCH2CH2(CH2)9CH3), 0.88 (2ꢂ3H, t,
J¼5.7 Hz, N(CH2)7CH3), 0.87 (2ꢂ3H, t, J¼6.7 Hz, Cquat.thiophe-
(nm) 230, 356, 399, 582, 619. MALDI-HRMS: m/z: calcd for
C76H102N2O6S4Br2 (Mꢃþ): 1360.5191; found: 1360.5167; ppm: 1.8.
Mp: 187–193 ꢀC.
4.3.3.4. Boc-protection of DPP 13b towards di-tert-butyl-3,6-
bis(50-bromo-40-dodecyl-2,20-bithiophen-5-yl)-1,4-dioxopyrrolo[3,4-
c]pyrrole-2,5(1H,4H)-dicarboxylate (1eb). The Boc-protection of
13b was executed as described for the Boc-protection of DPP
chromophore 3, which was executed according to the reported
literature.22
ne(CH2)11CH3).13C NMR (300 MHz, CDCl3):
d (ppm) 161.2 (CO pyrrole-
2-one), 143.6 (Cquat.thiophene(2)), 142.0 (Cquat.(9)), 138.9 (Cquat.thiophene
(4)), 136.3 (Cquat.thiophene(5)), 135.5 (CHthiophene(6)), 128.2 (Cquat.
thiophene(8)), 125.9 (CHthiophene(3)), 124.8 (CHthiophene(7)), 110.1
(Cquat.(10)), 108.3 (Cquat.thiophene(1)), 42.3 (NCH2(CH2)6CH3), 31.9, 31.8,
30.0, 29.9, 29.71, 29.67, 29.66, 29.62, 29.58, 29.41, 29.36, 29.32, 29.26,
29.20, 26.9 (NCH2(CH2)5CH2CH3þCquat.thiophene(CH2)10CH2CH3), 22.7,
22.6 (N(CH2)6CH2CH3þCquat.thiophene(CH2)10CH2CH3), 14.13, 14.12
(N(CH2)7CH3þCquat.thiophene(CH2)11CH3). IR (ATR, cmꢁ1): nmax 2954,
2918, 2849 (CH alkane stretch), 1656 (C]O amide stretch), 1556,
1545, 1510 (aromatic C]C stretch), 1450, 1407, 1367 (CH alkane
In a two-necked, oven-dried round bottom flask, 3,6-bis(50-
bromo-40-dodecyl-2,20-bithiophen-5-yl)pyrrolo[3,4-c]pyrrole-1,4-
(2H,5H)-dione (13b) (0.5 mmol, 480 mg) was dissolved in 15 ml
anhydrous THF and the resulting solutionwas purged with argon for
10 min. Then, 2.5 equiv of N,N-dimethylaminopyridine (1.25 mmol,
153 mg) dissolved in 5 ml anhydrous THF were added and the re-
action mixture was stirred for 15 min under argon atmosphere at
room temperature. Next, 5 equiv of di-tert-butyl dicarbonate
(2.5 mmol, 546 mg) were added (rinsed with 5 ml THF) and the
mixture was stirred for 24 h at room temperature under argon. The
mixture was concentrated under vacuum and the residue was dis-
solved in 20 ml MeOH and a very sticky dark blue precipitate was
formed, which upon sonication broke up in small particles. The
mixture was stored overnight in the fridge at 2–3 ꢀC in order to fully
precipitate the DPP before it was filtered off. A fast purification over
alumina with CH2Cl2 as eluents was executed (Rf¼0.82) resulting in
69% (406 mg) of di-tert-butyl-3,6-bis(50-bromo-40-dodecyl-2,20-
bithiophen-5-yl)-1,4-dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicar-
boxylate (1eb). Spectral analysis: vide supra.
bending). UVmax(CH2Cl2):
l (nm) 231, 356, 381, 582, 621. MALDI-
HRMS: m/z: calcd for C50H66N2O2S4Br2 (Mꢃþ): 1012.2374; found:
1012.2335; ppm: 3.9. Mp: 117–118 ꢀC.
4.3.3.3. N-benzylation of DPP 13b towards 3,6-bis(50-bromo-40-
dodecyl-2, 20-bithiophen-5-yl)-2, 5-bis(3,5-di-tert-bu-
tylbenzyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (1db). The same
method was applied as described for the N-benzylation of DPP 3
into DPP derivative 4d. This method is derived from a modified
literature procedure.37,38
A
solution of 3,6-bis(50-bromo-40-dodecyl-2,20-bithiophen-5-
yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (13b) (0.4 mmol, 384 mg)
and potassium carbonate (4 equiv, 1.6 mmol, 221 mg) in 12 ml an-
hydrous NMP was brought under argon atmosphere and was heated
to 60 ꢀC. After 30 min at that temperature, 3 equiv of 1-(bromo-
methyl)-3,5-di-tert-butylbenzene (1.2 mmol, 340 mg) were added in
one portion as a solution in 3 ml NMP (3,5-di-tert-butylbenzyl bro-
mide is a white solid). The mixture was further mixed at 60 ꢀC during
2 h and then it was brought at 80 ꢀC and further stirred for 18.5 h. The
mixture was cooled down to room temperature, washed with water
(45 ml) and extracted with EtOAc (45 ml/30 ml/20 ml). The organic
layers were collected and evaporated. The residue was suspended in
40 ml MeOH and a dark blue precipitate was formed. The mixture
was overnight stored in the fridge in order to fully precipitate the DPP
and then the precipitate was filtered off, washed with fresh MeOH
and dried in vacuo. Further purification was not necessary and 3,6-
bis(50-bromo-40-dodecyl-2,20-bithiophen-5-yl)-2,5-bis(3,5-di-tert-
butylbenzyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (1db) was
Acknowledgements
The research leading to these results has received funding from
the European Community’s Seventh Framework Programme (FP7/
2007–2013) under grant agreement NO 212311 of the ONE-P
project.
Supplementary data
Methods for the synthesis of all the described compounds in
Scheme 1 were slightly modified compared to the literature pro-
cedures. Moreover, full spectral characterization (1H NMR, 13C NMR,
IR, HRMS and UV–vis absorption) of all these products was per-
formed. Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tet.2010.01.027.
obtained in 84% (465 mg) yield. 1H NMR (300 MHz, CDCl3):
d (ppm)
8.60 (2ꢂ1H, d, J¼4.2 Hz, CHthiophene(6)), 7.28 (2ꢂ1H, t, J¼1.6 Hz, tBu-
Carom.quat.CHarom.Carom.quat.-tBu), 7.11 (2ꢂ1H, d, J¼4.2 Hz, CHthiophene
(7)), 7.10 (2ꢂ2H, t, J¼1.6 Hz, CHarom.Carom.quat.(CH2)CHarom.), 6.91
(2ꢂ1H, s, CHthiophene(3)), 5.34 (2ꢂ2H, s, CH2Benzyl), 2.51 (2ꢂ2H, t,
J¼7.6 Hz, Cquat.thiopheneCH2(CH2)10CH3), 1.63–1.55 (2ꢂ2H, m,
Cquat.thiopheneCH2CH2(CH2)9CH3), 1.34–1.26 (2ꢂ18H, m, Cquat.thiophene
References and notes
1. Hao, Z. M.; Iqbal, A. Chem. Soc. Rev. 1997, 26, 203.
2. Wallquist, O.; Lenz, R. Macromol. Symp. 2002, 187, 617.
3. Vala, M.; Weiter, M.; Vynuchal, J.; Toman, P.; Lunak, S., Jr. J. Fluoresc. 2008, 18,
1181.
4. Guo, E. Q.; Ren, P. H.; Zhang, H. C.; Yang, W. J. Chem. Commun. 2009, 859.
5. Metten, B.; Martinez, K.; Thomas, J.; Qin, W.; Smet, M.; Boens, N.; Dehaen, W.
Org. Biomol. Chem. 2007, 5, 2587.
6. Mizuguchi, J.; Grubenmann, A.; Wooden, G.; Rihs, G. Acta Crystallogr., Sect. B:
Struct. Sci. 1992, 48, 696.
7. Langhals, H.; Potrawa, T.; Noth, H.; Linti, G. Angew. Chem., Int. Ed. Engl.1989, 28, 478.
8. Closs, F.; Gompper, R. Angew. Chem., Int. Ed. Engl. 1987, 26, 552.
9. MacLean, E. J.; Tremayne, M.; Kariuki, B. M.; Cameron, J. R. A.; Roberts, M. A.;
Harris, K. D. M. Cryst. Growth Des. 2009, 9, 853.
t
CH2CH2(CH2)9CH3), 1.26 (4ꢂ9H, s, 4ꢂ Bu), 0.88 (2ꢂ3H, t, J¼6.6 Hz,
Cquat.thiophene(CH2)11CH3). 13C NMR (75 MHz, CDCl3):
d (ppm) 161.5
(CO pyrrole-2-one), 151.1 (Carom.quat.tBu), 143.5 (Cquat.thiophene(2)),
142.4 (Cquat.thiophene(5)), 139.5 (Cquat.(9)), 138.7 (NCH2CHarom.quat.),
135.8 (CHthiophene(6)), 135.7 (Cquat.thiophene(4)), 128.2 (Cquat.thiophene
(8)), 125.8 (CHthiophene(3)), 124.6 (CHthiophene(7)), 121.2 (tBu-
C
arom.quat.CHarom.Carom.quat.-tBu),
120.7
(CHarom.Carom.quat.(CH2)
10. Song, B.; Wang, Z. Q.; Chen, S. L.; Zhang, X.; Fu, Y.; Smet, M.; Dehaen, W. Angew.
Chem., Int. Ed. 2005, 44, 4731.
CHarom.),110.0 (Cquat.(10)),108.1 (Cquat.thiophene(1)), 45.8 (NCH2), 34.8

S. Stas et al. / Tetrahedron 66 (2010) 1837–1845
1845
11. Zhu, Y.; Heim, I.; Tieke, B. Macromol. Chem. Phys. 2006, 207, 2206.
12. Rabindranath, A. R.; Zhu, Y.; Heim, I.; Tieke, B. Macromolecules 2006, 39, 8250.
13. Zhu, Y.; Rabindranath, A. R.; Beyerlein, T.; Tieke, B. Macromolecules 2007, 40, 6981.
14. Zhang, K.; Tieke, B. Macromolecules 2008, 41, 7287.
15. Zou, Y.; Gendron, D.; Badrou-Aı¨ch, R.; Najari, A.; Tao, Y.; Leclerc, M. Macro-
molecules 2009, 42, 2891.
28. Iqbal, A.; Jost, M.; Kirchmayr, R.; Pfenninger, J.; Rochat, A.; Wallquist, O. Bull.
Soc. Chim. Belg. 1988, 97, 615.
29. Iqbal, A.; Cassar, L. U.S. Patent US4415685, 1983.
30. Yamamoto, H.; Norihisa, D. WIPO Patent WO2004/090046, 2004.
31. Turbiez, M.; Janssen, R. A. J.; Wienk, M. M.; Kirner, H. J.; Dueggeli, M.; Tieke, B.;
Zhu, Y. WIPO Patent WO2008/000664, 2008.
16. Zou, Y.; Gendron, D.; Neagu-Plesu, R.; Leclerc, M. Macromolecules 2009, 42, 6361.
17. Zhou, E.; Yamakawa, S.; Tajima, K.; Yang, C.; Hashimoto, K. Chem. Mater. 2009,
21, 4055.
32. Hao, Z.; Schmidhal, B.; Budry, J.-L.; Fontana, M.; Turbiez, M.; Bienewald, F.;
dueggeli, M.; Aebischer, O.F.; Hayoz, P.; Fonrodona, T.M. WIPO Patent WO2009/
047104, 2009.
18. Yan, H.; Chen, Z.; Zheng, Y.; Newman, C.; Quinn, J. R.; Dotz, F.; Kastler, M.;
Facchetti, A. Nature 2009, 457, 679.
19. Bijleveld, J. C.; Zoombelt, A. P.; Mathijssen, S. G. J.; Wienk, M. M.; Turbiez, M.; de
Leeuw, D. M.; Janssen, R. A. J. J. Am. Chem. Soc. 2009, 131, 16616.
20. Burgi, L.; Turbiez, M.; Pfeiffer, R.; Bienewald, F.; Kirner, H. J.; Winnewisser, C.
Adv. Mater. 2008, 20, 2217.
21. Wienk, M. M.; Turbiez, M.; Gilot, J.; Janssen, R. A. J. Adv. Mater. 2008, 20, 2556.
22. Tamayo, A. B.; Walker, B.; Nguyen, T.-Q. J. Phys. Chem. C 2008, 112, 11545.
23. Tamayo, A. B.; Dang, X.-D.; Walker, B.; Seo, J.; Kent, T.; Nguyen, T.-Q. Appl. Phys.
Lett. 2009, 94, 103301.
24. Yu, C.-Y.;Chen, C.-P.;Chan, S.-H.;Hwang, G.-W.;Ting, C.Chem.Mater. 2009, 21, 3262.
25. Chen, J.; Cao, Y. Acc. Chem. Res. 2009, 42, 1709.
33. Sweat, F. W.; Epstein, W. W. J. Org. Chem. 1967, 32, 835.
34. Challis, B. C.; Challis, J. A. In The Chemistry of Amides; Zabicky, J., Ed.; Wiley: New
York, NY, 1970; p 734.
35. Colonna, G.; Pilati, T.; Rusconi, F.; Zecchi, G. Dyes Pigm. 2007, 75, 125.
36. Fukuda, M.; Kodama, K.; Yamamoto, H.; Mito, K. Dyes Pigm. 2004, 63, 115.
37. Smet, M.; Metten, B.; Dehaen, W. Tetrahedron Lett. 2001, 42, 6527.
38. Verheijen, W.; Hofkens, J.; Metten, B.; Vercammen, J.; Shukla, R.; Smet, M.;
Dehaen, W.; Engelborghs, Y.; De Schryver, F. Macromol. Chem. Phys. 2005, 206,
25.
39. Morton, C. J. H.; Gilmour, R.; Smith, D. M.; Lightfoot, P.; Slawin, A. M. Z.;
MacLean, E. J. Tetrahedron 2002, 58, 5547.
40. Ba¨uerle, P. In Electronic Materials: The Oligomer Approach; Mu¨llen, K., Wegner, G.,
Eds.; Wiley-VCH: Weinheim, 1998; p 105.
26. Walker, B.; Tamayo, A. B.; Dang, X.-D.; Zalar, P.; Seo, J. H.; Garcia, A.; Tantiwiwat,
M.; Nguyen, T.-Q. Adv. Funct. Mater. 2009, 19, 3063.
27. Huo, L.; Hou, J.; Chen, H.-Y.; Zhang, S.; Jiang, Y.; Chen, T. L.; Yang, Y. Macro-
molecules 2009, 42, 6564.
41. Bundgaard, E.; Krebs, F. C. Polym. Bull. 2005, 55, 157.
42. Horn, M.; Hepuzer, Y.; Yagci, Y.; Bilgin-Eran, B.; Cernenco, U.; Harabagiu, V.;
Pinteala, M.; Simionescu, B. C. Eur. Polym. J. 2002, 38, 2197.