Diphenylamine end-capped diketopyrrolopyrroles with phenylene-vinylene conjugation extension

Article abstract of DOI:10.1016/j.tetlet.2014.03.080

Two pyrrolo[3,4-c]pyrrole-1,4-diones (diketopyrrolopyrroles, DPP) with 4″-diphenylamino-stilben-4′-yl substituents at the 3- and 3,6-positions of the DPP heterocycle are synthesized. The ¹H and ¹³C NMR spectra of their soluble deriva

Full text of DOI:10.1016/j.tetlet.2014.03.080

Accepted Manuscript
Diphenylamine end-capped diketopyrrolopyrroles with phenylene-vinylene
conjugation extension
Štěpán Frebort, Martin Vala, Stanislav Luň ák Jr., Jana Honová, Tomá š
Mikysek, Zdeněk Eliá š, Antonín Lyčka
PII:
S0040-4039(14)00501-2
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.03.080
TETL 44402
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
17 October 2013
24 February 2014
18 March 2014
Please cite this article as: Frebort, Š., Vala, M., Luň ák, S. Jr., Honová, J., Mikysek, T., Eliá š, Z., Lyčka, A.,
Diphenylamine end-capped diketopyrrolopyrroles with phenylene-vinylene conjugation extension, Tetrahedron
Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.2014.03.080
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Diphenylamine end-capped diketopyrrolopyrroles with phenylene-vinylene
conjugation extension
Štěpán Frebort a, Martin Vala b*, Stanislav Luňák Jr. b, Jana Honová b, Tomáš Mikysek c,
Zdeněk Eliáš c,d, Antonín Lyčka a
a Centre for Organic Chemistry Ltd., Rybitví 296, CZ-533 54 Rybitví, Czech Republic
b
Materials Research Centre, Faculty of Chemistry, Brno University of Technology,
Purkyňova 118, 612 00 Brno, Czech Republic
c Faculty of Chemical Technology, University of Pardubice, Studentská 573, CZ-532010
Pardubice, Czech Republic
d Synthesia, a. s., Semtín 103, CZ-530 02 Pardubice, Czech Republic
Graphical abstract
N
N
N
H3C CH3
O
CH3
O
R-Br, DMF,
K2CO3, 120 0C
Na, tert-AmOH
O
O
+
RN
O
HN
O
R =
O
H3C O
NR
NH
O
O
H3C CH3
CN
H3C
H3C
N
N
*Corresponding author: Martin Vala
E-mail address: vala@fch.vutbr.cz
1

Abstract
Two pyrrolo[3,4-c]pyrrole-1,4-diones (diketopyrrolopyrroles, DPP) with 4′′-diphenylamino-
stilben-4′-yl substituents at the 3- and 3,6-positions of the DPP heterocycle are synthesized.
1
The H and 13C NMR spectra of their soluble derivatives, N(2) and N(5)-dialkylated by 2-
ethylhexyl bromoacetate, were completely assigned. Soluble DPPs show photovoltaic activity
in bulk heterojunction solar cells. Their electrochemistry, and absorption and fluorescence
spectra were studied.
Keywords
diketopyrrolopyrrole, alkylation, NMR, organic photovoltaics
Symmetrical
pyrrolo[3,4-c]pyrrole-1,4-diones
(1,4-diketopyrrolo[3,4-c]pyrroles,
abbreviated as DPP) with the same substituents at the 3- and 6-positions form a promising
class of electron donors in bulk heterojunction (BHJ) solar cells.1 Asymmetrical push-pull
substituted DPPs were successfully used in dye-sensitised solar cells (DSSC).2 The common
feature of DPP dyes used in both types of organic photovoltaics (OPVs) is the presence of a 2-
thienyl substituent at the 3- or 3,6-positions,3 and their good solubility obtained following
N(2), N(5)-dialkylation with branched alkyl groups.
There are generally two synthetic routes to obtain the final soluble dyes.4a The first consists of
a complete synthesis of a conjugated system and final alkylation, while the second starts with
the synthesis of a DPP core with only one ring at each of the 3,6-positions, then alkylation and
final conjugation extension of the soluble precursor by halogenation followed by coupling
reactions. The latter route is generally preferred, especially for DPPs with highly extended
conjugation, such as DPP dimers.1b,4b The disadvantage of this synthetic strategy is the
absence of a parent pigment, which could be modified simply by various alkyl groups in order
to optimise the properties of the final material. 5 On the other hand, the preparation of DPP
pigments by classical6 and industrial7 syntheses from aromatic nitriles and a succinic ester (or
pyrrolinone8 in the case of asymmetrical DPPs) is complicated by their extreme insolubility,
making traditional purifying procedures such as recrystallization or column chromatography
impossible.
2

Scheme 1: Preparation of symmetrical (a) and non-symmetrical (b) DPPs and followed by
alkylation (the products are drawn for R′ = NPh2 - see text, tert-AmOH = tert-amyl alcohol).
a)
N
N
R´
H3C CH3
O CH3
O
R-Br, DMF,
K2CO3, 120 0C
Na, tert-AmOH
O
O
+
RN
HN
R =
O
H3C O
NR
NH
O
O
O
O
H3C CH3
CN
H3C
H3C
N
N
1a
1
b)
R´
R-Br, DMF,
K2CO3, 120 0C
Na, tert-AmOH
O
O
O
+
RN
O
HN
O
HN
O
O
R =
NR
NH
O
CH3
O
CN
H3C
H3C
N
N
2a
2
Both phenylene and phenylene-vinylene conjugation extension of the parent 3,6-
diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione (C.I. Pigment Red 255) and its
peripheral electron-donating substitution results in a bathochromic shift.9 Phenylene
conjugation extension of dimethylamino end-capped DPP brings a further, but a relatively
3

small, red shift in absorption.10 Furthermore, the synthesis of such an extended pigment was
carried out by an indirect route involving a coupling reaction and final thermal decomposition
of the so-called latent pigment.10a Consequently, the first aim of the present Letter is to report
the preparation of extended DPPs end-capped by a strong electron-donating substituent and to
test whether such an enlarged conjugated system could be synthesized by a direct route.
Phenylene-vinylene conjugation extension was chosen as it gives a higher red shift compared
to the phenylene example9b (Scheme 1). N(2),N(5)-dialkylation of DPP pigments with
branched alkyl groups is necessary to obtain processable materials with good morphology of
layers and/or good phase separation in BHJ devices. Nevertheless, this reaction is also
accompanied by O-alkylated by-products necessitating careful purification of the product.11
On the other hand, no unwanted by-products were observed during alkylation with more
reactive ethyl bromoacetate.12 Thus the second aim of this work was to combine both the
higher reactivity of esters and solubility-inducing branched alkyl groups in a 2-ethylhexyl
bromoacetate alkylating agent (Scheme 1), which has never been used previously in the
syntheses of soluble derivatives of organic pigments. The spectral and electrochemical
properties of the synthesized compounds were studied and their ability to produce
photovoltaic effects was tested.
The reaction of 4-dimethylamino-4′-cyano-stilbene (R′ = NMe2) with succinic ester
according to Scheme 1a, gave the resulting pigment in low yield (1%) and in poor purity. On
the other hand, when starting from 4-diphenylamino-4′-cyano-stilbene (R′ = NPh2), a well-
defined product 113 was obtained in moderate yield (39%). A slightly higher yield (40%) was
obtained for asymmetrical DPP pigment 2,14 synthesized according to Scheme 1b. Compound
1 thus represents the largest DPP pigment prepared by a direct route ever reported, to the best
of our knowledge, with the distance between the two amino nitrogens being 27.993 Å
according to DFT (B3LYP/6-311G(d,p)) calculations.15 On the other hand, the course of the
reaction starting with a dimethylamino derivative shows the limits of this synthetic strategy.
We consider that this difference results from a sterically demanding propeller-like
diphenylamino (DPA) group partially hindering aggregation (stacking) of the pigment, and
also limiting the packing of starting compounds inside these aggregates.
The N(2),N(5)-dialkylation with 2-ethylhexyl bromoacetate proceeded as expected.
Compounds 1a,16 and 2a,17 were produced in moderate yields (24%, and 55%) and good
selectivity. Detailed NMR studies of compounds 1a and 2a were performed18 including
application of 2D experiments (COSY, NOESY, HMQC, and HMBC). The existence of
cross-peaks between H(2′) and NCH2COO in the NOESY spectra, and protons H(5′) and
4

carbons C(3′) as well as protons H(6′) and carbons C(8′) in the HMBC were of key
1
importance for the assignments. The H and 13C chemical shifts of compounds 1a and 2a are
reported in Table S1 in the Supporting information.
Table 1
Studied and supporting compounds19 (EH = 2-ethylhexyl, DPA = diphenylamino) and their
optical properties in DMSO.
O
R
N
N
n
R´
N
R
O
m
Compound
1
H
1a
2
H
2a
3
H
3a
4
H
H
0
4a
R
CH2COOEH
CH2COOEH
CH2COOEt
CH2COOEt
R′
DPA
1
DPA
H
H
1
DPA
0
DPA
0
H
0
n
m
1
1
1
1
0
0
0
0
0
0
λabs (nm)
586
530
-
546
772
498
-
569
597
538
614
542
593
508
603
λems (nm) 764
Stokes
178
-
226
-
28
76
51
95
shift (nm)
The absorption spectra of non-alkylated compounds 1–4 in DMSO show a similar
shape with maxima corresponding to 0-0 vibronic transitions (Figure 1). These bands
correspond to HOMO-LUMO excitation accompanied by pronounced charge (electron)
transfer from the peripheral triphenylamine to the central DPP core (Figure 2 for compound
1). Conjugation extension induces a bathochromic shift 17 nm (3 → 1), and 4 nm (4 → 2). On
the other hand, while the fluorescence spectra of 3 and 4, in DMSO show moderate Stokes
shifts (800 cm-1 and 1700 cm-1), approximately mirror-symmetry between the absorption and
5

emission for 3, and relatively high fluorescence quantum yields (φF = 0.41 and 0.22), the
fluorescence of compounds 1 and 2 show very similar maxima (Table 1), being weak (φF <
0.01 for both), with considerable Stokes shifts (4000 cm-1 and 5300 cm-1) and the vibronic
structures are blurred. Such behaviour may indicate an excited state symmetry-breaking20 for
quadrupolar compound 1 and twisted intramolecular charge-transfer21 for both 1 and dipolar
2, i.e., the phenomena which were observed only for distorted N(2),N(5)-dialkylated
piperidino-phenyl DPP derivatives,12 but not for their pigment precursors.9a The poor
solubilities of all four pigments did not allow a study of the solvent dependence of the
absorption and fluorescence spectra.
Figure 1. Absorption and fluorescence spectra of compounds 1–4 in DMSO.
6

Figure 2. Kohn-Sham frontier orbitals of compound 1 (DFT B3LYP/6-311G(d,p), isovalue =
0.02).
The absorption spectra of 1a and 2a in DMSO show one structureless band with
maxima at 530 nm and 498 nm, respectively, indicating the loss of planarity induced by N(2),
N(5)-dialkylation.12 While 4-diphenylamino derivatives 3a and 4a show weak, but easily
detectable fluorescence in DMSO, in a similar manner to their 4-piperidino analogues,12 the
fluorescence of 1a and 2a could not be detected at all. Such total absence of fluorescence of
DPP derivatives in solution is reported for the first time, to the best our knowledge. On the
other hand, both 1a and 2a show fluorescence in weakly polar toluene at room temperature
and highly polar, but rigid 2-methyltetrahydrofuran solvent glass at 77 K, i.e., the non-
radiative excited state deactivation process requires both high solvent polarity and a fluid
environment, which allows the conformational changes.
The solid-state absorption edge (Figure 3), which is important for solar cell efficiency,
was estimated as 640 nm for 1a and 560 nm for 2a from thin film absorption, giving thus an
optical band gap in compound 1a 0.21 eV lower compared to 2a., i.e., a bit higher than the
difference derived from the absorption maxima in DMSO solution (0.16 eV). Both, 1a and 2a
show weak solid-state fluorescence in thin films.
7

Figure 3: Solid-state absorption spectra of 1a and 2a.
Table 2
Electrochemical first redox potentials and band gaps obtained by cyclic and rotating disc
voltammetry in DMF (or acetonitrile).22 HOMO and LUMO energies were obtained using
EHOMO/LUMO = Eox1/red1 + 4.350 for DMF, and +4.429 for acetonitrile.23
Compound
E1/2 ox [V]
0.87a
EHOMO [eV]
-5.22
E1/2 red [V]
-1.06
EHOMO [eV]
-3.29
∆E [V]
1.93
1a
2a
3a
4a
0.85
-5.20
-1.09
-3.26
1.94
0.84a (0.78a) -5.19 (-5.21) -1.07 (-1.24)
-3.28
1.91
0.97 (0.93) -5.32 (-5.36) -1.19 (-1.22)
-3.16
2.16
a Two-electron process
The optical band gaps of 4-diphenylamino substituted compounds 3a and 4a, derived
from the absorption maxima in DMSO, do not differ from the values of their 4-piperidino
analogues by more than 0.03 eV.12 On the other hand, the absolute values of their HOMO and
LUMO energies represented by the first oxidation and reduction potentials in acetonitrile
(Table 2) are considerably stabilized.24 The stabilization of the HOMO by about 0.2 eV is
crucial for power conversion efficiency (PCE) of organic bulk heterojunction (BHJ) solar
cells, as its Uoc factor represents the difference between the HOMO of the DPP donor and the
8

LUMO of the C61 PCBM acceptor in the solid-state.1b Conversely, the LUMO is stabilized
slightly less and not sufficiently to allow back electron transfer from fullerene to the DPP
environment and following recombination in BHJ solar cells. While addition of the second
DPA group, when going from 4a to 3a, brings a considerable lowering of the first oxidation
potential in DMF, i.e., a destabilization of the HOMO energy by 0.13 eV (Table 2), no such
effect was observed when going from asymmetrical 2a to 1a (the difference is 0.02 eV in
favour of 1a).
Compounds 1a and 2a show sufficient solubility to be processed from chloroform to
form good phase separation in blends with C61 PCBM in BHJ solar cells. Using branched
alkyl bromoacetates as alkylating agents thus represents an interesting alternative for
increasing solubility based on derivatization with branched halo-alkanes, probably for a wider
variety of substrates than just DPPs.
BHJ solar cells were prepared by a standard procedure.25 Preliminary results without
any optimization of the parameters show moderate power conversion efficiency (PCE) =
0.75% for compound 1a, with a short circuit current (Jsc) = 3.90 mA.cm-2, an open circuit
voltage (Uoc) = 593 mV and a fill-factor (FF) = 32.5%. When asymmetrical DPP 2a was used:
PCE = 0.25%, with Jsc = 1.92 mA.cm-2, Uoc = 531 mV and FF = 24.1%. There is a series of
consecutive optical and electronic processes, which allow observation of photovoltaic
behaviour, however, the inability to employ light from 560 to 640 nm (Figure 3) may be one
of the reasons for the lower PCE of our compound 2a.
Although the PCE for symmetrical 1a is considerably lower than the value for
DPP(TBFu)2, i.e., the best photovoltaic material between small (non-polymeric) DPPs in BHJ
OPV applications, with optimized PCE = 4.1 – 4.8% in combination with C71 PCBM,26 and
PCE = 3.13% (3.4% by our measurement) with C61 PCBM,27 the value for 1a is probably the
highest published for DPPs not containing a thiophene ring. Extensive optimization of the
ratio of the components, the effect of annealing and additives and other device properties is
now in progress and will be discussed in a forthcoming full paper.
In conclusion, two extended DPP pigments have been synthesized by a direct base-
catalyzed reaction of an aromatic nitrile and succinic, and pyrrolinone esters. Their
derivatives, prepared with high selectivity by alkylation using a branched ester of bromoacetic
acid, show sufficient solubility to be processed from solution. The structures of both soluble
1
derivatives were confirmed by full assignment of the H and 13C NMR chemical shifts.
Moderate power conversion efficiencies in BHJ solar cells with these DPPs as electron donors
9

were found. Electrochemical and spectral data rationalize some aspects of the photovoltaic
performance.
Acknowledgements
Access to computing and storage facilities owned by parties and projects contributing
to the National Grid Infrastructure MetaCentrum, provided under the programme "Projects of
Large Infrastructure for Research, Development, and Innovations" (LM2010005) is highly
appreciated by S.L. J.H. is a Brno Ph.D. Talent Scholarship Holder. T.M. is indebted to the
Ministry of Education, Youth and Sports of the Czech Republic (CZ.1.07/2.3.00/30.0021).
This work was supported by the Ministry of Industry and Trade of the Czech Republic
(project FR-TI1/144), Grant Agency of the Czech Republic (projects P205/10/2280 and 13-
29358S) and by the Ministry of Education, Youth and Sports of the Czech Republic (projects
7E09061 and LO1211).
References and notes
1.
2.
(a) Walker B.; Kim Ch.; Nguyen T.-Q. Chem. Mater. 2011, 23, 470-482; (b) Walker
B.; Liu J.; Kim Ch.; Welch G. C.;Park J. K.; Lin J.; Zalar P.; Proctor C. M.; Seo J. H.;
Bazan G. C.; Nguyen T. Q. Energ. Environ. Sci. 2013, 6, 952-962
(a) Qu S.; Tian H. Chem. Commun. 2012, 48, 3039-3051; (b) Qu S.; Qin Ch.; Islam
A.; Wu Y.; Zhu W.; Hua J.; Tian H.; Han L. Chem. Commun. 2012, 48, 6972-6974;
(c) Zhang F.; Jiang K.-J.; Huang J.-H.; Yu Ch.-Ch.; Li S.-G.; Chen M.-G.; Yang L.-
M.; Song Y.-L. J. Mater. Chem. A. 2013, 1, 4858-4863
3.
4.
(a) Yum J.-H.; Holcombe T. W.; Kim Y.; Yoon J.; Raktys K.; Nazeeruddin M. K.;
Grätzel M. Chem. Commun. 2012, 48, 10727-10729; (b) Holcombe T. W.; Kim Y.;
Yum J.-H.; Yoon J.; Gao P.; Marszalek M.; Di Censo D.; Raktys K.; Nazeeruddin M.
K.; Grätzel M. Chem. Commun. 2012, 48, 10724-10726
(a) Stas S.; Sergeyev S.; Geerts Y. Tetrahedron 2010, 66, 1837–1845; (b) Stas S.;
Balandier J.-Y.; Lemaur V.; Fenwick O.; Tregnano G.; Quist F.; Cacialli F.; Cornil J.;
Geerts Y.-H. 2013, 9, 198-208
5.
6.
Naik M. A.; Venkatramaiah N.; Kanimozhi C.; Patil S. J. Phys. Chem. C 2012, 116,
26128-26137
(a) Iqbal A.; Jost M.; Kirchmayr R.; Pfenninger J.; Rochat A.; Wallquist O. Bull. Soc.
Chim. Belg. 1988, 97, 615-643; (b) Wallquist O. In High Performance Pigments,
Smith H. H., Ed.; Wiley-VCH: Weinheim, 2002; pp. 159-183
7.
Herbst W.; Hunger K. Industrial Organic Pigments; Wiley-VCH: Weinheim, 2004
10

8.
9.
Morton C. J. H.; Gilmour R.; Smith D. M.; Lightfoot P.; Slawin A. M.; MacLean E. J.
Tetrahedron 2002, 58, 5547–5565
(a) Luňák Jr. S.; Vyňuchal J.; Vala M.; Havel L.; Hrdina R. Dyes Pigments 2009, 82,
102-108; (b) Luňák Jr. S.; Havel L.; Vyňuchal J.; Horáková P.; Kučerík J.; Weiter M.;
Hrdina R. Dyes Pigments 2010, 85, 27-36
10.
11.
(a) Beninatto R.; Borsato G.; De Lucchi O.; Fabris F.; Lucchini V.; Zendri E. Dyes
Pigments 2013, 96, 679-685; (b) Vala M.; Vyňuchal J.; Toman P.; Weiter M.; Luňák
Jr. S. Dyes Pigments 2010, 84, 176-182
(a) Frebort Š.; Eliáš Z.; Lyčka A.; Luňák Jr. S.; Vyňuchal J.; Kubáč L.; Hrdina R.;
Burgert L. Tetrahedron Lett. 2011, 52, 5769-5773; (b) Zhao B.; Sun K.; Xue F.;
Ouyang J. Org. Electron. 2012, 13, 2516-2524
12.
13.
Luňák Jr. S.; Vala M.; Vyňuchal J.; Ouzzane I.; Horáková P.; Možíšková P.; Eliáš Z.;
Weiter M. Dyes Pigments 2011, 91, 269-278
Synthesis of 3,6-bis(4′-diphenylaminostilben-4-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-
dione (1). Sodium metal (0.93 g, 0.041 mol), with surface oxide removed by cutting
and washing in tert-amyl alcohol, was diluted in 30 ml of tert-amyl alcohol under
heating in the presence of a catalytic amount of anhydrous ferrous chloride. When the
sodium had completely dissolved, the temperature was set to 105 ˚C, and the light
yellow solution was charged with 4-diphenylamino-4′-cyano-stilbene (5.00 g, 0.013
mol). Addition of the di-tert-butyl ester of succinic acid (1.55 g, 0.007 mol) was
started promptly in the form of a solution in tert-amyl alcohol (15 ml). The mixture
was heated to reflux for 2 h, cooled to 80 ˚C and poured into demineralized H2O (200
ml). The mixture was stirred for another 2 h at 80 ˚C and the crude product isolated by
filtration. Purification by Soxhlet extraction of the crude pigment using MeOH (3x8 h)
and acetone (3x8 h), gave 2.20 g of a dark-brown dust (yield 40%).
m. p. > 400 ˚C. Anal. Calcd. for C58H42N4O2: C 84.24; H 5.12; N 6.77. Found: C
83.29; H 4.98; N 6.61.
14.
Synthesis
of
3-phenyl-6-(4′-diphenylaminostilben-4-yl)pyrrolo[3,4-c]pyrrole-
1,4(2H,5H)-dione (2). Sodium metal (0.60 g, 0.027 mol), with surface oxide removed
by cutting and washing in tert-amyl alcohol, was diluted in 60 ml of tert-amyl alcohol
with a catalytic amount of anhydrous ferrous chloride. After the sodium had dissolved,
the light yellow solution was heated to reflux and 4-diphenylamino-4′-cyano-stilbene
(5.00 g, 0.013 mol) was added. When the starting nitrile had dissolved, the ethyl ester
of 2,3-dihydro-2-oxo-5-phenyl-1H-pyrrol-4-carboxylic acid (3.10 g, 0.013 mol) was
added in the form of a suspension in 30 ml of tert-amyl alcohol. Addition was
followed by 2 h of reflux, pouring into demineralized H2O (300 ml) and isolation of
the crude product by suction filtration. The major impurities were removed by Soxhlet
extraction with MeOH (3x8 h) and acetone (3x8 h). The product (3.00 g) was obtained
as a rusty-brown powder (yield 40%).
m. p. > 400 ˚C. Anal. Calcd. for C38H27N3O2: C 81.85; H 4.88; N 7.54. Found: C
81.79; H 4.83; N 7.50.
11

15.
Gaussian 09, Revision C.01, Frisch M. J.; Trucks G. W.; Schlegel H. B.; Scuseria G.
E.; Robb M. A.; Cheeseman J. R.; Scalmani G.; Barone V.; Mennucci B.; Petersson
G.A.; Nakatsuji H.; Caricato M.; Li X.; Hratchian H. P.; Izmaylov A. F.; J. Bloino G.
A.; Zheng G.; Sonnenberg J. L.; Hada M.; Ehara M.; Toyota K.; Fukuda R.; Hasegawa
J.; Ishida M.; Nakajima T.; Honda Y.; Kitao O.; Nakai H.; Vreven T.; Montgomery, Jr.
J. A.; Peralta J. E.; Ogliaro F.; Bearpark M.; Heyd J. J.; Brothers E.; Kudin K. N.;
Staroverov V. N.; Keith T.; Kobayashi R.; Normand J; Raghavachari K.; Rendell A.;
Burant J. C.; Iyengar S. S.; Tomasi J.; Cossi M.; Rega N.; Millam J. M.; Klene M.;
Knox J. E.; Cross J. B.; Bakken V.; Adamo C.; Jaramillo J.; Gomperts R.; Stratmann
R. E.; Yazyev O.; Austin A. J.; Cammi R.; Pomelli C.; Ochterski J. W.; Martin R. L.;
Morokuma K.; Zakrzewski V. G.; Voth G. A.; Salvador P.; Dannenberg J. J.; Dapprich
S.; Daniels A. D.; Farkas O.; Foresman J. B.; Ortiz J. V.; Cioslowski J.; Fox D. J.
Gaussian, Inc., Wallingford CT, 2010.
16.
3,6-Bis(4'-diphenylaminostilben-4-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione
(1)
(3.00 g, 3.633 mmol) was suspended in NMP (70 ml). The mixture was heated and the
temperature maintained at 120 ˚C during the reaction. K2CO3 (2.01 g, 14.511 mmol)
was added and the mixture became darker and lost its fluorescence. The 2-ethylhexyl
ester of bromoacetic acid (3.64 g, 14.511 mmol) was added slowly over 1 h and the
mixture was heated for another 2 h. After cooling to room temperature, the mixture
was poured into demineralized H2O (150 ml) to form a stable emulsion. The emulsion
was extracted with CHCl3 (3x100 mL). Separation of the phases was possible only
after addition of NaCl to the H2O phase. The organic solution was dried over MgSO4
and the solvent removed by distillation. The liquid residue was recrystallized from
cyclohexane and gave 1.03 g of dark-brown crystals of E-bis(2-ethylhexyl) 2,2′-(3,6-
bis{4-[4-(diphenylamino)styryl]phenyl}-1,4-dioxopyrrolo[3,4-c]pyrrole-2,5-(1H,4H)-
diyl diacetate (1a) (yield 24%).
m. p. 168 – 170 ˚C. Anal. Calcd. for C78H78N4O6: C 80.24; H 6.73; N 4.80. Found: C
79.72; H 6.71; N, 4.65.
17.
3-Phenyl-6-(4'-diphenylaminostilben-4-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (2)
(1.00 g, 1.793 mmol) was suspended in DMF (70 ml), together with K2CO3 (1.00 g,
7.173 mmol) and the temperature of the mixture was increased to 120 ˚C. Over the
next 60 min, the 2-ethylhexyl ester of bromoacetic acid (1.75 g, 7.173 mol) was added
dropwise. After an additional 1 h, the reaction was cooled to room temperature and
poured into brine (700 ml). The product, E-bis(2-ethylhexyl) 2,2′-(3-{4-[4-
(diphenylamino)styryl]phenyl}-1,4-dioxo-6-phenylpyrrolo[3,4-c]pyrrole-2,5-(1H,4H)-
diyl diacetate (2a) was precipitated and isolated by filtration. Chromatographic
purification gave 0.90 g of a red microcrystalline solid (yield 55%).
m. p. 70-74 ˚C. Anal. Calcd. for C58H63N3O6: C 77.56; H 7.07; N 4.68. Found: C
76.18; H 6.98; N 4.51.
1
18.
NMR spectra were recorded on a Bruker Avance II spectrometer (400.13 MHz for H
and 100.62 MHz for 13C) in CDCl3. The 1H and 13C NMR chemical shifts are given on
the δ scale (ppm) and are referenced to internal TMS. All 2D experiments (gradient-
selected (gs)-COSY, (gs)-NOESY, gs-HMQC, gs-HMBC) were performed using the
manufacturer’s software (TOPSPIN 2.1).
12

19.
20.
The synthesis and analytical data of supporting compounds 3, 3a, 4 and 4a will be
described in a forthcoming full paper.
Terenziani F.; Painelli A.; Katan C.; Charlot M.; Blanchard-Desce M. J. Am. Chem.
Soc. 2006, 128, 15742-15755
21.
22.
Grabowski Z. R.; Rotkiewicz K.; Rettig W. Chem. Rev. 2003, 103, 3899-4031
Electrochemical measurements were carried out in DMF (for all compounds) and in
MeCN (for 3a and 4a) containing 0.1 M Bu4NPF6 in a three electrode cell by cyclic
voltammetry (CV) and rotating disc voltammetry (RDV). The working electrode was a
platinum disc (2 mm in diameter) for CV and RDV experiments, respectively. A
saturated calomel electrode (SCE) was used as the reference electrode separated from
the measured solution by a bridge filled with supporting electrolyte. A Pt wire served
as an auxiliary electrode. Voltammetric measurements were performed using a
potentiostat PGSTAT 128N (Metrohm Autolab B.V., Utrecht, The Netherlands)
operated via NOVA 1.10 software from the same manufacturer
23.
24.
Isse A. A.; Gennaro A. J. Phys. Chem. B 2010, 114, 7894–7899.
Luňák Jr. S.; Eliáš Z.; Mikysek T.; Vyňuchal J.; Ludvík J. Electrochim. Acta 2013,
106, 351-359
25.
Bulk heterojunction solar cells were prepared on ITO patterned substrates. The
substrates were cleaned in a hot ultrasonic bath in NaOH for 4 min, then washed twice
with deionized H2O, immersed in isopropanol for 5 min and dried. PEDOT:PSS
(Heraeus Clevios™ P VP AI 4083) was dynamically spin-coated over the ITO
contacts at 5000 rpm and annealed for 5 min at 150 °C on a hotplate in a nitrogen
glovebox to remove solvent residues. The organic semiconducting layer was spin-
coated from DPP:PCBM solution with a total concentration of solids of 15 mg/ml,
donor:acceptor mass ratio = 30:70 at 2000 rpm. No annealing was performed. Both,
PEDOT:PSS, and the semiconducting mixture were gently wiped off the cathode strip.
The top aluminum contact was evaporated on top of the structure. Six OPV devices
are defined on each structure. Current voltage characteristics were measured with a
Keithley 2601B electrometer. Efficiency was calculated from IV-characteristics under
illumination with a calibrated AAA solar simulator (LOT Oriel) providing irradiance
of 1 sun (100 mW/cm2) and a standard AM 1.5 spectrum, simulating sunlight after
passing through the atmosphere. The variation of efficiency within devices on one
structure was maximally 10%.
26.
27.
(a) 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, 3063-3069; (b) Liu J; Walker B.;
Tamayo A.; Zhang Y.; Nguyen T.-Q. Adv. Funct. Mater. 2013, 23, 47-56; (c)
Bürckstümmer H.; Tulyakova E.V.; Deppisch M.; Lenze M. R.; Kronenberg N. M.;
Gsänger M.; Stolte M.; Meerholz K.; Würthner F. Angew. Chem. Int. Ed. 2011, 50,
11628-11632
(a) Ripaud E.; Demeter D.; Rousseau T.; Boucard-Cétol E.; Allain M.; Po R.; Leriche
P.; Roncali J. Dyes Pigments 2012, 95, 126-133; (b) Top PCE = 3.4% (Jsc = 11.23
13

mA.cm-2, Uoc = 606 mV and FF = 49.8), the value was obtained for a 60:40
DPP(TBFu)2 : C61 PCBM mixing ratio and 10 minutes annealing at 80 °C.
14