Small D-π-A systems with o-phenylene-bridged accepting units as active materials for organic photovoltaics

Article abstract of DOI:10.1002/chem.201301054

Donor-acceptor (D-π-A) systems that combine triarylamine donor blocks and dicyanovinyl (DCV) acceptor groups have been synthesized. Starting from the triphenylamine (TPA)-thiophene-DCV compound (1) as a reference system, various synthetic approaches have

Full text of DOI:10.1002/chem.201301054

FULL PAPER
DOI: 10.1002/chem.201301054
Small D–p–A Systems with o-Phenylene-Bridged Accepting Units as Active
Materials for Organic Photovoltaics
Antoine Leliꢀge, Jꢁrꢁmie Grolleau, Magali Allain, Philippe Blanchard,* Dora Demeter,
Thꢁodulf Rousseau, and Jean Roncali*[a]
Abstract: Donor–acceptor (D–p–A)
systems that combine triarylamine
donor blocks and dicyanovinyl (DCV)
acceptor groups have been synthesized.
Starting from the triphenylamine
sion of the p-conjugating spacer group
lead to the modulation of the HOMO
level. On the other hand, the fusion of
the DCV group onto the vicinal thio-
phene ring by an ortho-phenylene
bridge allows for a specific fine-tuning
of the LUMO level. The electronic
properties of the molecules were ana-
lyzed by using UV/Vis spectroscopy
and cyclic voltammetry and the com-
pounds were evaluated as donor mate-
rials in basic bilayer planar heterojunc-
tion solar cells by using C60 as acceptor
material. The relationships between the
electronic properties of the donors and
the performance of the corresponding
photovoltaic devices are discussed. Bi-
layer planar heterojunction solar cells
that used reference compound 1 and
C70 afforded power-conversion efficien-
cies of up to 3.7%.
À
À
(TPA) thiophene DCV compound (1)
as a reference system, various synthetic
approaches have been developed for
controlling the light-harvesting proper-
ties and energy levels of the frontier or-
bitals in this molecule. Thus, the intro-
duction of methoxy groups onto TPA,
the replacement of one phenyl ring of
TPA by a thiophene ring, or the exten-
Keywords: bridging ligands · chro-
mophores · cyclic voltammetry · do-
nor–acceptor systems · solar cells
Introduction
major tool for the definition of guidelines for the molecular
engineering of new active materials.[1]
Over the past few years, we have witnessed the emergence
of small conjugated molecules at the forefront of research
on solution-processed and vacuum-deposited donor–accept-
or heterojunction organic solar cells (OSCs).[1] Whilst bulk
heterojunction (BHJ) OSCs[2] that are based on soluble,
low-band-gap p-conjugated co-polymers and PC71BM fuller-
ene have reached conversion efficiencies exceeding 9.0%,[3]
the inherent polydispersity of polymers is a source of varia-
bility in the composition, molecular weight, and electronic
properties of the final material and, thus, of the perform-
ance of the resulting OSCs.[1] In this regard, the use of con-
jugated molecules in OSCs presents several advantages. Be-
sides straightforward synthesis and purification processes
and, hence, more-reproducible photovoltaic performance,
well-defined chemical structures allow a more precise analy-
sis of the structure–property relationships that remain a
Over the past few years, this molecular approach has led
to the synthesis and evaluation of many classes of donor ma-
terials that are based on a wide range of chemical structures,
such as triphenylamines,[4] oligothiophenes,[5] squaraines,[6]
quinacridones,[7] cyanines,[8] diketopyrrolopyrroles,[9] boron-
dipyrromethenes,[10] indigo,[11] porphyrins,[12] and various tail-
ored 1D, 2D, or 3D architectures.[1,13]
Intensive research effort that focused on the design of
new active materials and on the optimization of the fabrica-
tion of OSCs by, for example, the application of thermal
treatments,[9] the introduction of additives,[14] or the insertion
of additional intermediate buffer layers,[3a,5] has led to rapid
progress and conversion efficiencies (PCEs) exceeding
7.0% for BHJ cells that are based on hybrid oligothio-
phenes as donors and PC71BM as an acceptor.[14] These re-
sults demonstrate that molecule-based OSCs are now capa-
ble of rivaling their parent polymer-based devices. More-
over, in addition to solution processes, small molecules can
also be deposited by using vacuum techniques.[5a–d,15,16]
The structure of efficient molecular donors typically in-
volves a combination of donor (D) and acceptor (A) groups
to create an internal charge-transfer, which produces an ex-
tension of the spectroscopic response of the OSC, an in-
crease in the open-circuit voltage, and enhanced stability of
the molecule against oxidation.[4a,17] Over the past few years,
many donor materials that are based on D–A combinations
have been synthesized, including symmetrical D–A–D or A–
D–A systems, star-shaped molecules, or more-complex mo-
[a] Dr. A. Leliꢀge, M. Sc. J. Grolleau, M. Sc. M. Allain, Dr. P. Blanchard,
Dr. D. Demeter, Dr. T. Rousseau, Dr. J. Roncali
LUNAM, University of Angers
CNRS UMR 6200, MOLTECH-Anjou
Linear Conjugated Systems Group
2 Bd Lavoisier, 49045 Angers (France)
E-mail: Philippe.Blanchard@univ-angers.fr
Jean.Roncali@univ-angers.fr
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201301054.
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lecular architectures.[1,4–14] In spite of their efficiency, some
of these systems contain a sophisticated molecular structure,
thereby requiring relatively complex syntheses, and their
molecular weights sometimes exceed 1500 gmolÀ1. In this
context, the question of the minimization of the complexity,
size, and molecular weight of donor molecules represents an
interesting problem. In fact, beyond being a challenge for
experimental and theoretical chemists, these various points
could have important implications in terms of the cost and
environmental impact of future industrial synthesis, purifica-
tion, and processing of active materials for OSCs.[18] In this
regard, recent work has shown that interesting photovoltaic
performances can be achieved with donors of relatively
small spatial extension and low molecular weight.[8a,15,16]
A few years ago, we reported the first examples of star-
shaped triphenylamine (TPA)-based molecules with periph-
eral dicyanovinyl (DCV) acceptor groups and we showed
that these systems could lead to efficient solution-processed
or vacuum-deposited OSCs with high open-circuit voltage-
s.[1e,4a] More recently, we have shown that unsymmetrical
TPA-based systems with two (or even only one) DCV
groups can produce interesting results.[4c] Herein, consider-
ing the DA3 molecule[4a] as a starting model (Scheme 1), we
have synthesized a simple D–A molecule (1) as a reference
system for an analysis of the structure–property relation-
ships of a series of parent compounds (2–6) in which the
energy levels of the frontier orbitals have been modulated
by using various synthetic principles. Thus, the modification
of the HOMO level has been achieved by the introduction
of methoxy groups onto the TPA block, by replacement of
one phenyl group of TPA by a thiophene cycle, or by exten-
sion of the p-conjugating spacer. On the other hand, control
of the LUMO level has been sought through the modulation
of the electron-withdrawing effect of the DCV group by co-
valent bridging. We have extensively investigated rigidifica-
tion as an efficient approach for the synthesis of low-band-
gap p-conjugated systems or push–pull chromophores for
nonlinear optics.[19] In the specific case of molecular donors,
this approach can represent an interesting tool for the con-
trol of electronic properties at a moderate cost in terms of
increasing the molecular weight.
Preliminary results along this line were recently reported
in a short communication.[20] Herein, we present a more-ex-
tended account of the synthesis and electronic properties of
molecules that were designed according to these synthetic
principles. Moreover, their potential as donor materials in
organic solar cells is discussed with an emphasis on struc-
ture–property relationships.
Results and Discussion
The synthesis of compounds 2–6 is described in Scheme 3
and Scheme 4. Reference compound 1 was prepared accord-
ing to a literature procedure.[20,21] All of these compounds
were prepared by Pd-catalyzed cross-coupling reactions as
initially reported by Effenberger et al. for analogous donor–
acceptor-substituted oligothiophenes.[22]
Scheme 2 shows the synthesis of the ortho-phenylene-
bridged acceptor units. Ketone 7[20,23] was brominated at the
free a position of the thiophene ring by using bromine as a
reagent. Lower yields were obtained with NBS. A Knoeve-
nagel condensation reaction of compound 8 with malonodi-
nitrile gave dicyano compound 9 in 98% yield. Bromination
of ketone 10[24] with NBS gave compound 11 in 77% yield.
Scheme 2. Synthesis of the acceptor building blocks: i) Br2/NaHCO3,
CHCl3 (87%); ii) CH2(CN)2, NaOAc, EtOH (98%); iii) NBS/DMF
(77%). NBS=N-bromosuccinimide.
Scheme 1. Structures of the D–A molecules.
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Small D–p–A Systems with o-Phenylene-Bridged Accepting Units
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Scheme 3. Synthesis of compounds
Bu3SnCl, THF; ii) compound 9, [Pd(PPh3)4], toluene, reflux (87% yield
from compound 12); iii) nBuLi, À788C then isopropoxytetramethyldioxa-
borolane, THF (42%); iv) compound 8, [Pd(PPh3)4], Aliquat 336,
2
and 3: i) nBuLi, À788C then
AHCTUNGTRENNUNG
Scheme 4. Synthesis of compounds 4, 5, and 6: i) nBuLi, À78CC then
AHCTUNGTRENNUNG
Bu3SnCl, THF; ii) compound 8, [PdACTHNURTGNEUNG(PPh3)4], toluene, reflux (75% yield
Na2CO3, toluene/water 1:1, reflux (88%); v) CH2(CN)2, Et3N, CHCl3
for compound 21 from compound 17, 79% yield for compound 22 from
compound 18, and 78% yield for compound 25 from compound 23);
iii) CH2(CN)2, Et3N, CHCl3 (75% yield for compound 4, 75% yield for
compound 5, and 92% yield for compound 6).
(90% yield for compound 2, 67% yield for compound 3); vi) compound
11, [PdACHTUNGTRENNUNG(PPh3)4], Aliquat 336, Na2CO3, toluene/water 1:1, reflux (86%).
Compound 2 was synthesized by a Suzuki coupling of bro-
moketone 8 with the boronic ester of TPA 14, followed by a
Knoevenagel condensation reaction of extended carbonyl
compound 15 with malonodinitrile (Scheme 3). Interestingly,
a Stille coupling reaction between the stannyl derivative of
TPA 13 and bromo compound 9 led to a more-straightfor-
ward route to compound 2.[20] Compounds 13 and 14 were
obtained from compound 12 after lithium/bromine exchange
with nBuLi at low temperatures, followed by the addition of
Bu3SnCl and isopropoxytetramethyldioxaborolane, respec-
tively. Isomeric compound 3 was prepared in an analogous
manner by treating compound 14 with bromoketone 11,
thus giving the intermediate ketone (16), which was subject-
ed to a Knoevenagel condensation reaction with malonodi-
nitrile.
single crystals of sufficient quality for X-ray analysis. Nota-
bly, the preparation of single crystals of open-chain com-
pound 1 was much more tedious. This result is not surprising
considering the well-known tendency of TPA derivatives to
form amorphous materials.[30] These results also suggest that
rigidification by covalent bridging improves their aptitude
for crystallization.
Figure 1 shows the molecular structures of compounds 1,
2, 3, and 4 (see the Supporting Information, Table S1).[39]
The DCV group of compound 1 adopts a cis conformation
relative to the sulfur atom of the vicinal thiophene, as previ-
ously observed for a,w-oligothiophenes that were end-
capped with DCV groups.[5b] With the exception of the two
outermost phenyl rings of the TPA unit, the rest of the mol-
ecule adopts a quasi-planar conformation, as shown by a di-
hedral angle of 3.18 (C7-C8-C9-C10) between the inner ben-
zene ring of TPA and the thiophene unit and a dihedral
angle of 2.98 between the thiophene ring and the DCV
group (C6-C1-C2-C3).
For compounds 2 and 4, the cis conformation of the DCV
group relative to the sulfur atom of the vicinal thiophene
group is imposed by the covalent bridging. Compared to
compound 1, the dihedral angle (C2-C1-C15-C20) between
the inner benzene ring of TPA and the thiophene unit de-
creases to 0.28, whereas the dihedral angle (C3-C4-C5-C6)
exhibits a value of 0.98. As expected, the indenothiophene
moiety is completely planar. All of these data indicate
slightly better planarity of compound 2 compared to refer-
ence compound 1.
The synthesis of compounds 4–6 is described in Scheme 4.
Selective deprotonation at the a position of the thiophene
ring of compounds 17,[25] 18,[26] and 23[27] with nBuLi, fol-
lowed by the addition of Bu3SnCl, gave stannyl derivatives
19, 20, and 24.[28,29] These compounds were directly em-
ployed in a Stille coupling reaction with bromoketone 8 in
the presence of catalytic amount of [PdACHTNURTGNEUNG(PPh3)4], thus lead-
ing to the formation of extended ketones 21, 22, and 25 in
75–79% yields. Finally, Knoevenagel condensation reactions
of compounds 21, 22, and 25 with malonodinitrile led to
compounds 4, 5, and 6, respectively.
Single crystals suitable for X-ray diffraction were grown
by the slow evaporation of solutions of bridged compounds
2, 3, and 4 in CH2Cl2. The slow diffusion of MeOH into a
solution of compound 1 in CH2Cl2 led to the growth of
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P. Blanchard, J. Roncali et al.
Figure 1. Molecular structures of compounds 1, 2, 3, and 4 as obtained by X-ray diffraction.
One major difference between the structures of com-
pounds 2 and 3 is the considerably larger dihedral angle
(C2-C1-C15-C20) in compound 3 (15.48), which leads to a
less-planar p-conjugated system. In compound 4, the two ad-
jacent thiophene rings generate rotational conformers in the
unit cell with the thiophene rings in anti (4a) or syn confor-
mations (4b) and dihedral angles smaller than 48.
The electronic properties of compounds 1–6 have been
analyzed by using cyclic voltammetry and UV/Vis spectro-
scopy. The cyclic voltammograms (CVs) in CH2Cl2
in Epa (10 mV), but a large positive shift in Epr (430 mV).
These results show that the ortho-phenylene bridge has a
small influence on the HOMO level, but leads to a large de-
crease in the LUMO level. The large positive shift of the Epr
value and the transition from an irreversible to a reversible
reduction process as observed for all of the bridged com-
pounds can be interpreted by stabilization of the reduced
state that is associated with the formation of an aromatic cy-
clopentadienyl anion radical upon reduction (Scheme 5).
in the presence of Bu4NPF6 as a supporting electro-
lyte show that all of these compounds can be rever-
sibly oxidized (Figure 2). On the other hand, the re-
duction process that leads to the formation of the
radical anion is reversible for bridged compounds
2–6, whereas this process appears to be irreversible
for open-chain compound 1 (Figure 2).
Table 1. Cyclic voltammetry data for compounds 1–6 versus SCE in 0.10m Bu4NPF6/
CH2Cl2 (scan rate: 100 mVsÀ1).
[a]
[a]
Compd
Epa
A
1
Epr1
[V/SCE]
DE
[V]
EHOMO
[eV]
ELUMO
[eV]
EHOMOÀELUMO
G
[eV]
1
2
3
4
5
6
1.01
1.00
0.92
0.81
0.70
0.85
À1.23[b]
À0.80
À0.83
À0.78
À0.79
À0.76
2.24
1.80
1.75
1.59
1.49
1.61
À5.89
À5.87
À5.79
À5.67
À5.56
À5.75
À4.06
À4.33
À4.29
À4.34
À4.32
À4.36
1.83
1.54
1.50
1.33
1.24
1.39
The CV of compound 1 exhibits a reversible oxi-
dation wave with an anodic peak potential (Epa) at
1.01 V and an irreversible reduction wave with a
maximum at Epr =À1.23 V (Table 1). A comparison
of the data of compounds 1 and 2 shows that the
[a] The energy levels of the HOMO and LUMO were determined from the onset of
the oxidation and reduction waves, respectively, by using an offset of 4.99 eV for the
bridging of the DCV unit leads to a small decrease SCE versus the vacuum level.[31]
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Figure 2. Cyclic voltammograms of compounds 1 (0.5 mm), 2 (1 mm), 3 (0.5 mm), 4 (1 mm), 5 (1 mm), and 6 (<0.5 mm) in 0.10m Bu4NPF6/CH2Cl2 (scan
rate: 100 mVsÀ1).
the Epa value (90 mV) but still produces a positive shift of
the Epr value of 400 mV. This former observation can be re-
lated to an extension of the whole p system, which results
from a connection of the terminal phenyl ring on the 2-posi-
tion of the thiophene ring.
On the other hand, the significant positive shift in the Epr
value of compound 3 shows that, although the DCV group
is not directly conjugated to the donor part of the molecule,
thereby generating a much weaker internal charge transfer
(as shown by the UV/Vis data discussed below), the bridging
Scheme 5. Formation of a cyclopentadienyl anion upon electrochemical
reduction.
DCV group still exerts a strong influence on the LUMO
level. In fact, as in the case of its isomer (2), the reduced
state of compound 3 can be also stabilized by the formation
A comparison of the CV data for compounds 1 and 3
shows that, when connected at the 3-position of the thio-
phene ring, the DCV group leads to a moderate decrease in
of an aromatic cyclopentadienyl radical anion (Scheme 5).
This result confirms the strong localization of the LUMO on
the acceptor part of the molecule.
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As expected, the replacement of the TPA moiety of com-
pound 2 by a diphenylthienylamine unit (compound 4) and
the further introduction of methoxy groups (compound 5)
produce negative shifts in the Epa value of 190 and 300 mV,
respectively, whereas the Epr values are positively shifted by
only 10–20 mV. These results are consistent with a HOMO
that is essentially localized on the donor part of the mole-
cule.
Finally, the CV data for compound 6 show that the inser-
tion of an additional thiophene ring into the conjugating
spacer of compound 2 produces a 0.15 V decrease in the Epa
value but has almost no effect on the Epr value, thus further
confirming the strong localization of the LUMO on the ac-
ceptor part of the molecule.
Figure 3. UV/Vis absorption spectra in CH2Cl2. Dotted line (1), solid line
(2), and dashed line (3).
To summarize, these CV results show that the introduc-
tion of methoxy groups or the replacement of a phenyl
group by a thienyl group in the TPA block significantly in-
creases the HOMO level, with little or no effect on the
LUMO level. Conversely, the ortho-phenylene bridging of
the DCV group has practically no effect on the HOMO, but
essentially affects the LUMO level. All of these results are
consistent with strongly localized HOMO and LUMO, the
energy levels of which can be specifically tuned by using ap-
propriate synthetic approaches.
(e). For compound 3, the ICT band is hardly discernible.
This result can be explained by the fact that, when connect-
ed at the 3-position of the thiophene ring, the DCV group is
no longer directly conjugated with the donor part of the
molecule, which results in an almost-complete annihilation
of the ICT, even if the absorption onset can still be dis-
cerned at about 700 nm. This result provides further indirect
confirmation of the ICT origin of the long-wavelength ab-
sorption band for this class of D–A compounds.
The optical properties of these D–A compounds have
been investigated by using UV/Vis spectroscopy in solution
and as thin films that were spin-cast onto glass from their
solutions (10 mgmLÀ1) in CHCl3. Table 2 lists the main opti-
The spectra of compounds 2, 4, and 5 (Figure 4) show that
replacing the inner phenyl ring of TPA by a thiophene unit
Table 2. UV/Vis absorption data for compounds 1–6 as solutions in
CH2Cl2 or as thin films that were spin-cast onto glass from solutions in
CHCl3 and thermal data.
Compd lmax (ICT) e (ICT)
lmax (film) Eg
[nm]
[eV][a]
M.p.
[8C]
Td
[8C]
[nm]
G
]
1
2
3
4
5
6
501
610
600
664
710
621
33900
16200
500
17600
23100
17100
523 1.98
633 1.58
178 292
249 334
262 338
228 324
200 379
>260 397
392 (644)[b] 2.70 (1.70)[b]
688 1.42
738 1.28
638 1.50
[a] Eg was estimated from the onset of absorption at low energies.
[b] Values in parentheses correspond to the weak ICT band.
Figure 4. UV/Vis absorption spectra in CH2Cl2. Solid line (2), dotted line
(4), and dashed line (5).
cal properties of the various compounds, together with their
melting points and decomposition temperatures, as meas-
ured by using TGA. These data show that all of these com-
pounds present a relatively high decomposition temperature.
The spectra of all of these D–A compounds show a first ab-
sorption band within the region 300–400 nm and a second
band at longer wavelengths, which is assigned as an internal
charge transfer (ICT).[4a,32]
Figure 3 shows the UV/Vis spectra of compounds 1, 2,
and 3. A comparison of the spectra of compounds 1 and 2
clearly shows that the ortho-phenylene bridge produces a
large bathochromic shift of the maximum of the ICT band
(about 100 nm). However, this shift is accompanied by a
substantial decrease in the molecular absorption coefficient
leads to a 54 nm red-shift of lmax, whilst a further 46 nm red
shift is obtained by the introduction of methoxy groups at
the para positions of the two phenyl rings. Furthermore,
these changes are accompanied by a significant increase in
À
the intensity of the ICT band relative to the p p* electronic
transition. On the other hand, a comparison of the data for
compounds 2 and 6 shows that the extension of the conju-
gating spacer by the insertion of an additional thiophene
ring only has a minor influence on the optical gap (see the
Supporting Information, Figure S1). In agreement with the
CV data, the narrowing of the optical gap in compounds 4
and 5 compared to compound 2 is due to an increase in the
HOMO level (Table 1).
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À
The optical band gap in these compounds (Eg) was esti-
mated from the long-wavelength absorption edge of the
spectra of their spin-cast thin films on glass substrates. For
most of these compounds, their solid-state spectra present a
broadening of the absorption band and a red-shift of lmax
(Table 2 and the Supporting Information, Figure S2). The Eg
values follow the same trend as indicated by the lmax values
and show that gaps smaller than 1.50 eV are reached for
compounds 4–6.
ly localized on the thiophene DCV block for compound 1
and is further extended onto the ortho-phenylene ring in
compounds 2 and 3.
To summarize, these theoretical results are in full agree-
ment with the experimental data, that is, the ortho-phenyl-
ene bridges specifically affect the LUMO level of the D–A
systems, thus confirming the interest in this synthetic ap-
proach for the fine-tuning of the energy levels of D–A sys-
tems.
To gain further insight into the effects of covalent bridg-
ing on the electronic properties of these compounds, theo-
retical calculations based on density functional methods
were performed with the Gaussian 09 program for the non-
bridged compound (1) and ortho-phenylene-bridged com-
pounds 2 and 3.[33] Becke’s three-parameter[34] gradient-cor-
rected functional (B3LYP) with the 6-31GACTHUNRTGNEUNG(d,p) basis set
were used to optimize their geometries and to compute
their electronic structures at the observed minima.
Apart from the two outermost phenyl units of TPA, all of
the molecules exhibit a quasi-planar structure. In agreement
with the X-ray data, the DCV moiety of compound 1 adopts
a syn conformation relative to the sulfur atom of the thio-
phene ring, whereas this conformation is imposed by the
bridging in compound 2. Figure 5 shows the HOMO and
These D–A compounds have been evaluated as donor
materials in basic bilayer planar heterojunctions by using
C60 as an acceptor. Although solution-processed molecular
BHJs that incorporate C70 derivatives as acceptor molecules
and some additives can achieve high PCE values,[14] the opti-
mization of the multiple experimental variables that are in-
volved in such cells is a rather tedious task that requires
large amounts of the donor compound and, therefore, this
kind of devices does not appear to be the most convenient
for the analysis of structure–property relationships in a large
series of compounds.
The donor layer (thickness ꢀ35 nm) was spin-cast from a
solution of the compound in CHCl3 (10 mgmLÀ1) onto ITO
slides that were pre-coated with a PEDOT:PSS film (thick-
ness: 40 nm). Then, the slides were introduced in a glove
box that was equipped with a vacuum chamber, a layer of
C60 (thickness: 30 nm) was deposited by thermal evapora-
tion, and the devices were completed by the vacuum deposi-
tion of an aluminum electrode (thickness: 100 nm). Each
batch comprised two or three slides with two cells of size
0.28 cm2 on each slide. For all of these compounds, thermal
treatment for 5 min was found to significantly improve their
PCE values through increasing their short-circuit current
densities (Jsc), open-circuit voltages (Voc), or filling factors
(FFs; Table 3 and the Supporting Information, Table S2).
Figure 6 and the Supporting Information, Figure S3 show
the effect of thermal treatment on the plot of current densi-
ty versus voltage of the of PHJ cells that were based on
compounds 1–5. However, attempts to detect some thermal-
ly induced material reorganization with eventual crystalliza-
tion by using X-ray diffraction and UV/Vis absorption spec-
troscopy of spin-cast films of the donors were unsuccessful.
Although reorganization, such as reorientation of push–pull
molecules upon thermal treatment, as has been recently re-
ported,[35] cannot be ruled out, this result suggests that the
observed increase in the PCE might be due to a thermally
induced extension of the area of the D/A interfacial contact
zone, thus leading to an enhanced interpenetration of the
donor and acceptor materials.[36] This hypothesis needs to be
confirmed, although it is consistent with the higher efficien-
cy of mixed co-evaporated cells compared to simple bilayer
cells.[15b,16,37]
Figure 5. HOMO and LUMO energy levels and their representations for
compounds 1, 2, and 3 after optimization with Gaussian 09 at the B3LYP/
6-31GACHTUNGTRENNUNG(d,p) level of theory.
LUMO energy levels of these molecules. The ortho-phenyl-
ene bridge leads to a small increase in the HOMO level of
compounds 2 and 3, but to a large decrease in the LUMO
level. As already discussed, this result agrees well with the
significant positive shift of the Epr value as observed by
cyclic voltammetry for compounds 2 and 3 compared to
compound 1. The HOMO level of compound 3 increases
slightly compared to that of compound 2, in agreement with
the lower Epa value for compound 3. Figure 5 also shows
that, whereas the HOMO of compounds 1–3 is essentially
Table 3 lists the photovoltaic parameters of the devices
under AM 1.5 simulated solar illumination. A comparison of
the data for the cells that were based on donors 1 and 2
shows that the ortho-phenylene bridge produces an im-
provement in the FF value from 0.43 to 0.52 and in the Voc
value from 0.92 to 0.97 V, which result in an increase in the
À
present on the TPA thiophene moiety, the LUMO is strong-
Chem. Eur. J. 2013, 00, 0 – 0
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P. Blanchard, J. Roncali et al.
Figure 6. Left: Plots of current density versus voltage of PHJ cells that were based on donors 1 (top) and 2 (bottom) with C60 in the dark (white circles)
and under white-light illumination with an incident power light of 90 mWcmÀ2 before (gray circles) and after thermal treatment (black circles). Right:
External quantum efficiency of the cells under monochromatic irradiation after thermal treatment (solid line) and UV/Vis spectra of thin-films of the
donors (dashed lines).
due to the large decrease in Voc value (for example, to
Table 3. Photovoltaic parameters after 5 min thermal treatment of bilayer
0.55 V for compound 5), which is caused by an increase in
the HOMO level, owing to the introduction of thiophene
and methoxy groups into the structure.
donor/acceptor cells based on donors 1–5 under white-light illumination
at a power density of 90 mWcmÀ2
.
Donor/
acceptor
VOC
[V]
JSC
[mAcmÀ2
FF
[%]
PCE
[%]
G
]
On the basis of the best performance of the compounds
reported above, compounds 1 and 2 were chosen for the
preparation of bilayer planar heterojunctions with C70 as ac-
ceptor material under the same conditions. After thermal
treatment at 1208C for 5 min, the cells gave PCE values of
2.37 for compound 1 and 2.46 for compound 2 (see the Sup-
porting Information, Figure S4). As presented in Table 3,
the replacement of C60 by C70 significantly increased the Jsc
value, which could be related to the better absorption prop-
erties of C70 over C60.[38] However, the Voc value decreased
by 110 mV and 140 mV for compounds 1 and 2, respectively,
thus leading to PCEs that were comparable to those meas-
ured with C60.
All of these results show that, in spite of their simple
structures, these small D–A compounds can lead to efficient
photovoltaic conversion. To gain further information on the
potential of this class of compounds, some device optimiza-
tion was performed by using the simplest compound (1) as a
donor. To this end, a layer of the donor (thickness: 25 nm)
and a layer of C70 (thickness: 20 nm) were successively de-
posited by thermal evaporation onto an ITO slide that was
coated with PEDOT:PSS. The simple aluminum cathode
[a]
1/C60
0.92
0.97
0.71
0.73
0.55
0.81
0.83
5.77
5.32
2.07
3.83
4.97
7.52
6.20
43
52
35
44
52
35
43
2.53
2.97
0.57
1.35
1.57
2.37
2.46
[a]
2/C60
[b]
3/C60
[a]
4/C60
[c]
5/C60
[a]
1/C70
[a]
2/C70
[a] Thermal treatment at 1208C. [b] Thermal treatment at 1508C.
[c] Thermal treatment at 1408C.
PCE value from about 2.50 to 3.00%. However, this in-
crease in efficiency is essentially due to a spectroscopic ex-
tension of the photoresponse, as shown by the EQE spec-
trum of compound 2 in Figure 6. This latter EQE spectrum
also shows the contribution of the ICT absorption band of
films of compound 2 to the photocurrent. As expected, com-
pound 3, in which the ICT is almost eliminated, leads to the
lowest PCE among this series. Finally, a comparison of the
results that were obtained with compounds 2, 4, and 5 shows
that, despite their lower band gap, compounds 4 and 5 lead
to lower PCE values. Besides lower Jsc values, this result is
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Small D–p–A Systems with o-Phenylene-Bridged Accepting Units
FULL PAPER
level, whereas a modulation of the HOMO level can be ach-
ieve by using some more-classical synthetic principles.
The potential use of these molecular donors for photovol-
taic conversion has been evaluated in basic planar hetero-
junction solar cells by using C60 fullerene as an acceptor.
The photovoltaic results have shown that some of these
simple compounds can lead to efficiencies that are compara-
ble to those obtained with more complex heavier molecules,
a conclusion that is supported by some preliminary attempts
at device optimization.
Work that is aimed at the design and synthesis of new
series of molecular donors of smaller size, taking into ac-
count the conclusions of the above analyses of structure–
property relationships, is underway.
Experimental Section
General: NMR spectra were recorded on Bruker AVANCE III 300 (1H:
300 MHz, 13C: 75 MHz) or Bruker AVANCE DRX 500 spectrometers
(1H: 500 MHz, 13C: 125 MHz). Chemical shifts are given in ppm relative
to TMS. IR spectra were recorded on a Bruker Vertex 70 spectrometer
and UV/Vis spectra were recorded on Perkin–Elmer Lambda 19 or 950
spectrometers. Melting points are uncorrected. Matrix-assisted laser-de-
sorption/ionization mass spectrometry was performed on a Bruker Dal-
tonics BIFLEX III spectrometer by using dithranol as the matrix.
Cyclic voltammetry was performed in 0.10m Bu4NPF6/CH2Cl2 (HPLC
grade) on a Biologic SP-150 potentiostat with positive feedback compen-
sation. Solutions were degassed by nitrogen bubbling prior to each ex-
periment. The experiments were carried out in a one-compartment cell
that was equipped with a platinum electrode (diameter: 2 mm) as work-
ing electrode, a platinum wire counter electrode, and a silver wire in a
0.01m solution of AgNO3 in MeCN as a reference electrode. The ferrici-
Figure 7. Top: Plots of current density versus voltage of a PHJ cell that
was based on ITO/PEDOT-PSS/donor 1/C70/Ca/Al in the dark (white cir-
cles) and under white-light illumination with an incident power light of
100 mWcmÀ2 before (gray circles) and after thermal treatment (black cir-
cles). Bottom: External quantum efficiency of the cells before (gray cir-
cles) and after thermal treatment (black circles).
nium/ferrocenium couple was used as internal reference (E8ACHTUNGTRENNUNG
(Fc+/Fc)=
0.405 V/SCE in 0.1m Bu4NPF6/CH3CN or CH2Cl2 and the potentials were
expressed versus a saturated calomel electrode (SCE) as a reference. Ele-
mental analysis was performed on a thermoelectron instrument. Purifica-
tion by column chromatography was carried out on Acros silica gel Si 60
(35–70 mm). Differential scanning calorimetry (DSC) and thermogravi-
metric analysis (TGA) were performed on instruments from TA Instru-
ments.
was replaced by calcium (thickness: 40 nm) and aluminum
(thickness: 100 nm).
After thermal treatment at 1008C for 30 min, the EQE
spectrum of the cell presents a broad spectroscopic response
with a maximum of about 65% at 540 nm (Figure 7). The
plot of J versus V, recorded under AM 1.5 simulated solar il-
lumination, affords a Jsc value of 9.81 mAcmÀ2, which, com-
bined with a Voc value of 0.96 V and a FF of 40%, leads to a
PCE of 3.70%.
Device preparation: Glass slides (24ꢂ25ꢂ1.1 mm2) that were coated with
indium tin oxide with a surface resistance of 10 W/& were purchased
from Praezisions Glas & Optik GmbH. Part of the ITO layer was etched
away with a 37% aqueous solution of HCl and Zn. Then, the ITO elec-
trodes were successively cleaned in an ultrasound bath with Deconex
(VWR international GmbH), distilled water (15.3 MWcmÀ1), acetone,
EtOH, and distilled water again for 10 min each and dried in an oven at
1008C. Then, the electrodes were modified by spin-casting a layer of PE-
DOT:PSS (Clevios P VP. AI 4083, HC-Starck; filtered through a 0.45 mm
membrane just prior to use) at 5000 rpm (r=10 s, t=60 s) and the elec-
trode was dried at 1308C for 15 min. Films of the donor materials (thick-
ness: 30–35 nm) were spin-cast under atmospheric conditions from
10 mgmLÀ1 solutions of the donors in CHCl3 (6000 rpm for 3 s and
10000 rpm for 9 s). CHCl3 (HPLC grade) was distilled over P2O5 before
use. After film deposition, the devices were introduced in an Ar-filled
glove box (200B, MBraun) that was equipped with a vacuum chamber
and a film of C60 fullerene (>99%, thickness: 30 nm, MER Corporation)
and an aluminum electrode (thickness: 100 nm) were thermally evaporat-
ed on top of the donor film under a pressure of 2ꢂ10À6 mbar through a
mask that defined two cells (diameter: 6.0 mm, 0.28 cm2) on each ITO
electrode. C70 (>99%) was purchased from MER Corporation and used
as received.
Conclusion
To summarize, small D–A conjugated systems that were
based on triarylamine and DCV groups have been synthe-
sized. The simplicity of their structures, combined with the
strong localization of the frontier orbitals, make these mole-
cules interesting model systems for the analysis of structure–
properties relationships and, thus, for the definition of some
synthetic guidelines for the selective tuning of the energy
levels of frontier orbitals. Thus, it has been shown that the
bridging of the DCV group can significantly narrow the op-
tical band gap, owing to a strong decrease in the LUMO
Chem. Eur. J. 2013, 00, 0 – 0
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P. Blanchard, J. Roncali et al.
The plots of J versus V of these devices were recorded in a glove box in
the dark and under illumination by using a Keithley 236 source-measure
unit and a home-made acquisition program. The light source was an
AM1.5 Solar Constant 575 PV simulator (Steuernagel Lichttecknik) that
was equipped with a metal-halogen lamp. The light intensity was meas-
ured by a broad-band power meter (13PEM001, Melles Griot). The devi-
ces were illuminated through the ITO electrode side. The efficiency
values reported herein are not corrected for the possible spectroscopic
mismatch of the solar simulator. External quantum efficiency (EQE) was
measured by using a halogen lamp (Osram) on an Action Spectra Pro
150 monochromator, a lock-in amplifier (Perkin–Elmer 7225), and a
S2281 photodiode (Hamamatsu).
1H NMR (300 MHz, CDCl3): d=7.66 (d, J=8.6 Hz, 2H), 7.28–7.24 (m,
4H), 7.14–7.06 (m, 6H), 7.05–7.01 (m, 2H), 1.33 ppm (s, 12H).
2-(4-(Diphenylamino)phenyl)-8H-indeno
G
A
solution of Na2CO3 (540 mg, 5.1 mmol) in water (5 mL) and Aliquat 336
(200 mg) were added to a solution of ketone 8 (130 mg, 0.51 mmol) and
boronate ester 14 (190 mg, 0.51 mmol) in a Schlenk tube. The mixture
was degassed with argon for 15 min, [PdACTHNUTRGNEUNG(PPh3)4] (60 mg, 0.05 mmol, 5%
mol) was added, and the mixture was heated at reflux under an argon at-
mosphere for 48 h. After the addition of water (20 mL) at room tempera-
ture, the mixture was extracted with toluene (2ꢂ20 mL). The organic
phases were washed with a saturated aqueous solution of NH4Cl (20 mL)
and water (3ꢂ20 mL), dried over MgSO4, and concentrated to dryness.
The product was purified by column chromatography on silica gel (petro-
leum ether/EtOAc, 5:1) to give compound 15 as a red solid (190 mg,
88%). M.p. 210–2128C; 1H NMR (300 MHz, CDCl3): d=7.51 (d, J=
8.9 Hz, 2H), 7.47 (d, J=6.6 Hz, 1H), 7.36–7.27 (m, 5H), 7.24 (s, 1H),
7.21–7.04 ppm (m, 10H); 13C NMR (75 MHz, CDCl3): d=185.6, 159.7,
159.6, 149.2, 147.1, 139.7, 138.1, 133.8, 133.5, 129.6, 128.4, 127.0, 126.7,
125.3, 124.0, 123.7, 122.5, 119.6, 114.9 ppm; IR (neat): n˜ =1721, 1684 cmÀ1
(C=O); UV/Vis (CH2Cl2): lmax (e)=484 nm (12700 LmolÀ1 cmÀ1); MS
(EI): m/z: 428.8 [M]+; HRMS (ESI): m/z calcd for C29H19NOS:
430.12601; found: 430.12589; elemental analysis calcd (%) for
C29H19NOS: C 80.09, H 4.46, N 3.26, C 80.32, H 4.57, N 3.12.
Synthesis: 2-Bromo-8H-indenoACHTUNTGRNE[UGN 2,1-b]thiophen-8-one (8): Br2 (0.19 mL,
3.70 mmol) was added dropwise into a solution of ketone 7 (0.5 g,
2.68 mmol) and NaHCO3 (241 mg, 2.87 mmol) in CHCl3 (20 mL) at 08C.
The reaction mixture was allowed to warm to room temperature and stir-
red for 7 h. After the addition of water, the mixture was extracted with
CH2Cl2. The organic phase was washed with a saturated aqueous solution
of NaHCO3 and water, dried over MgSO4, and concentrated under
vacuum. Column chromatography on silica gel (petroleum ether/CH2Cl2,
1:1) gave
a yellow-orange powder (0.62 g, 87%). M.p. 135–1368C;
1H NMR (300 MHz, CDCl3): d=7.47 (ddd, J=7.2, 1.2, 0.7 Hz, 1H), 7.34
(td, J=7.2, 1.2 Hz, 1H), 7.19 (td, J=7.2, 1.0 Hz, 1H), 7.17 (s, 1H),
7.13 ppm (ddd, J=7.2, 0.9, 0.7 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=
184.7, 157.7, 139.2, 136.8, 136.5, 133.9, 128.8, 128.1, 124.5, 123.6,
119.9 ppm; IR (neat): n˜ =1726, 1685 cmÀ1 (C=O); UV/Vis (CH2Cl2): lmax
(e)=408 nm (800 LmolÀ1 cmÀ1); MS (EI): m/z: 263.6/266.0 [M]+; elemen-
tal analysis calcd (%) for C11H5BrOS: C 49.83, H 1.90; found: C 49.76,
H 2.06.
2-(4-(Diphenylamino)phenyl)-4H-indeno
G
A
solution of Na2CO3 (290 mg, 2.7 mmol) in water (2.5 mL) and Aliquat
336 (100 mg) were added to a solution of bromoketone 11 (70 mg,
0.27 mmol) and Suzuki reagent 14 (100 mg, 0.27 mmol) in a Schlenk tube.
The mixture was degassed with argon for 15 min, [PdACTHNUTRGNE(UNG PPh3)4] (30 mg,
0.026 mmol, 5 mol%), and the mixture was heated at reflux under an
argon atmosphere for 48 h. After the addition of water at room tempera-
ture, the mixture was extracted with toluene. The combined organic
phases were washed with a saturated aqueous solution of NH4Cl, water,
dried over MgSO4, and concentrated to dryness. Column chromatography
on silica gel (petroleum ether/EtOAc, 1:5) gave a red solid (100 mg,
86%). M.p. 212–2148C; 1H NMR (300 MHz, CDCl3): d=7.47–7.39 (m,
3H), 7.37–7.26 (m, 5H), 7.22 (s, 1H), 7.20–7.03 ppm (m, 10H); 13C NMR
(75 MHz, CDCl3): d=187.9, 156.7, 149.1, 148.2, 147.3, 142.7, 139.3, 136.0,
134.1, 129.6, 128.5, 127.3, 126.5, 124.9, 123.6, 123.2, 119.2, 115.7 ppm; IR
(neat): n˜ =1701 cmÀ1 (C=O); UV/Vis (CH2Cl2): lmax (e)=488 nm
(1600 LmolÀ1 cmÀ1); MS (EI): m/z: 428.5 [M]+; MS (MALDI-TOF): m/z:
429.2 [M]+; HRMS (ESI): m/z calcd for C29H19ONS: 429.11819; found:
429.11849.
2-(2-Bromo-8H-indenoACHTUNGTRENNUNG[2,1-b]thiophen-8-ylidene)malononitrile (9): Malo-
nonitrile (124 mg, 1.88 mmol) was added to a solution of compound 8
(250 mg, 0.94 mmol) and CH3COONa (100 mg, 1.22 mmol) in EtOH
(10 mL). The reaction mixture was heated at reflux for 1.5 h and cooled
in an ice bath. The precipitate was recovered by filtration and washed
with EtOH to give a brown powder (290 mg, 98%). M.p. 254–2588C;
1H NMR (300 MHz, CD2Cl2): d=8.12 (d, J=7.7 Hz, 1H), 7.39 (td, J=
7.5, 1 Hz, 1H), 7.29 (d, J=7.4 Hz, 1H), 7.27 (s, 1H), 7.24 ppm (td, J=
7.6, 1.3 Hz, 1H); 13C NMR (75 MHz, CD2Cl2): d=157.9, 154.4, 138.2,
136.7, 136.1, 134.1, 129.0, 128.8, 127.1, 124.1, 121.4, 114.2, 113.0,
+
74.0 ppm; IR (neat): n˜ =2220 cmÀ1 (C N); MS (EI): m/z: 311.7 [M] ; ele-
ꢁ
mental analysis calcd (%) for C32H19N3S: C 53.69, H 1.61, N 8.95; found:
C 53.23, H 1.61, N 8.83.
2-Bromo-4H-indenoACHTUNGTRENNUNG[1,2-b]thiophen-4-one (11): In the absence of light, a
2-(5-(N,N-Diphenylamino)thiophen-2-yl)-8H-indenoACHTNUTRGNE[NUG 2,1-b]thiophen-8-one
solution of NBS (110 mg, 0.61 mmol) in DMF (2 mL) was added drop-
wise to a solution of ketone 10[24] (100 mg, 0.54 mmol) in DMF (4 mL) at
08C. The reaction mixture was stirred 12 h at room temperature. After
the addition of an aqueous solution of HCl (10%), the mixture was ex-
tracted with CH2Cl2. The organic phase was washed with a saturated
aqueous solution of Na2S2O3 and water, dried over MgSO4, and concen-
trated under vacuum. Column chromatography on silica gel (petroleum
ether/CH2Cl2, 1:1) gave an orange powder (0.11 g, 77%). M.p. 104–
1058C; 1H NMR (300 MHz, CDCl3): d=7.43 (d, J=7.2 Hz, 1H); 7.32 (t,
J=7.8 Hz, 1H); 7.18 (t, J=7.8 Hz, 1H); 7.11 ppm (s, 1H); 7.06 (d, J=
7.2 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=186.1, 158.6, 140.7, 138.5,
134.7, 134.1, 128.8, 124.0, 123.9, 119.3, 115.5 ppm; IR (neat): n˜ =
1710 cmÀ1 (C=O); UV/Vis (CH2Cl2): lmax =273, 435 nm; MS (ESI): m/z:
264.8/266.8 [M+H]+.
(21): Under an argon atmosphere, a 2.5m solution of nBuLi in n-hexane
(0.35 mL, 0.87 mmol) was added dropwise to a solution of compound
17[25] (200 mg, 0.79 mmol) in anhydrous THF (15 mL) in a Schlenk flask
at À788C in the dark. The reaction mixture was stirred at this tempera-
ture for 0.5 h before the addition of Bu3SnCl (0.27 mL, 0.99 mmol). After
5 min at À788C, the mixture was allowed to warm to room temperature
and then stirred for 2 h. After dilution with Et2O (50 mL), the organic
phase was washed with a saturated aqueous solution of NaF, water, dried
over MgSO4, and evaporated to give Stille reagent 19 as a light-yellow
oil, which was directly used in the next step. A mixture of compounds 19
and 8 (200 mg, 0.80 mmol) in toluene (10 mL) in a Schlenk flask was de-
gassed with argon for 15 min before the addition of [PdACTHUNTRGNE(UNG PPh3)4] (46 mg,
0.04 mmol). The reaction mixture was heated at reflux for 14 h under an
argon atmosphere. After the addition of water, the mixture was extracted
with toluene. The organic phase was washed with a saturated aqueous
solution of NH4Cl, water, dried over MgSO4, and evaporated. Column
chromatography on silica gel (CH2Cl2) gave a purple solid (260 mg,
75%). M.p. 170–1728C; 1H NMR (300 MHz, CDCl3): d=7.45 (d, J=
7.2 Hz, 1H), 7.36–7.27 (m, 5H), 7.24–7.08 (m, 9H), 7.01 (s, 1H),
6.55 ppm (d, J=4.0 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=185.2,
159.4, 154.4, 152.9, 147.3, 139.4, 138.2, 133.4, 132.8, 129.6, 128.5, 127.9,
125.1, 124.3, 123.7, 123.6, 119.6, 118.8, 114.8 ppm; IR (neat): n˜ =1715,
N,N-Diphenyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline (14):
Under an argon atmosphere, a 1.6m solution of nBuLi in n-hexane
(1.15 mL, 1.84 mmol) was added dropwise into a solution of 4-bromo-
N,N-diphenylaniline (400 mg, 1.23 mmol) in anhydrous THF (2 mL) in a
Schlenk flask at À788C. After stirring for 0.5 h at this temperature, 2-iso-
propoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (0.38 mL, 1.86 mmol)
was added dropwise and the stirring was continued for a further 1.5 h at
À788C. The reaction mixture was allowed to warm to room temperature
and stirred for a further 4 h. The solvent was evaporated and the result-
ing oil was purified by column chromatography on silica gel (n-hexane/
EtOAc, 5:1) to give compound 14 as a yellow oil (190 mg, 42%).
1666 cmÀ1
(C=O);
UV/Vis
(CH2Cl2):
lmax
(e)=516 nm
(12700 LmolÀ1 cmÀ1); MS (MALDI-TOF): m/z: 435.2 [M]+; HRMS
(ESI): m/z calcd for C27H17ONS2: 435.07461; found: 435.07480.
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Small D–p–A Systems with o-Phenylene-Bridged Accepting Units
FULL PAPER
2-(5-(Bis(4-methoxyphenyl)amino)thiophen-2-yl)-8H-indeno
G
8.8 Hz, 2H), 7.40–7.27 (m, 7H),; 7.21 (m, J=7.3, 1.7 Hz, 1H), 7.19–7.09
(m, 6H), 7.04 ppm (d, J=8.8 Hz, 2H); 13C NMR (75 MHz, CDCl3): d=
161.5, 157.5, 156.3, 149.9, 146.8, 138.2, 138.1, 133.2, 132.8, 129.7, 128.4,
127.2, 126.3, 125.9, 125.6, 124.4, 121.9, 120.8, 114.7, 114.4, 113.5,
phen-8-one (22): Compound 22 was prepared according to the same pro-
cedure as for compound 21, starting from compound 18[26] (300 mg,
0.96 mmol),
a 2.5m solution of nBuLi (0.4 mL, 1 mmol), Bu3SnCl
70.7 ppm; IR (neat): n˜ =2219 cmÀ1 (C N); UV/Vis (CH2Cl2): lmax (e)=
(0.27 mL, 0.99 mmol), and compound 8 (250 mg, 0.94 mmol), as a purple
solid (370 mg, 79%). M.p. 153–1548C; 1H NMR (300 MHz, CDCl3): d=
7.42 (d, J=7.1 Hz, 1H), 7.34–7.24 (m, 2H), 7.21–7.11 (m, 5H), 7.10–7.04
(m, 2H), 6.92 (s, 1H), 6.87 (d, J=9.0 Hz, 4H), 6.27 (d, J=4.1 Hz, 1H),
3.81 ppm (s, 6H); 13C NMR (75 MHz, CDCl3): d=185.1, 159.5, 156.9,
153.6, 140.4, 139.4, 138.427, 133.2, 131.8, 128.4, 126.0, 125.6, 124.3, 123.5,
119.5, 114.9, 113.9, 113.5, 55.7 ppm; IR (neat): n˜ =1713, 1666 cmÀ1 (C=
O); UV/Vis (CH2Cl2): lmax (e)=542 nm (15700 LmolÀ1 cmÀ1); MS
(MALDI-TOF): m/z: 495.3 [M]+; HRMS (ESI): m/z calcd for
C29H21O3NS2: 495.09574; found: 495.09544.
ꢁ
610 nm (16200 LmolÀ1 cmÀ1); MS (EI): m/z: 477.1 [M]+; HRMS (ESI):
m/z calcd for C32H20N3S: 478.13724; found: 478.13720; elemental analysis
calcd (%) for C32H19N3S: C 80.48, H 4.01, N 8.80, S 6.71; found: C 80.08,
H 3.99, N 8.72, S 6.61.
2-(2-(4-(Diphenylamino)phenyl)-4H-indenoACTHNUTRGNEU[GN 1,2-b]thiophen-4ylidene)ma-
lononitrile (3): Two drops of Et3N were added to a mixture of compound
16 (100 mg, 0.23 mmol) and malonitrile (30 mg, 0.46 mmol) in CHCl3
(15 mL). The reaction mixture was heated at reflux for 14 h. The solvent
was evaporated under vacuum and the crude product was triturated with
hot EtOH (10 mL), filtered, and washed with EtOH (2ꢂ10 mL) to give
compound 3 as a dark green powder (90 mg, 67%). M.p. 262–2648C;
1H NMR (300 MHz, CDCl3): d=8.08 (d, J=8.3 Hz, 1H), 7.61 (s, 1H),
7.43 (d, J=8.9 Hz, 2H), 7.36–7.27 (m, 5H), 7.19–7.04 ppm (m, 10H);
13C NMR (75 MHz, CDCl3): d=157.9, 151.9, 149.5, 148.6, 147.2, 140.7,
138.1, 136.4, 134.2, 129.6, 128.2, 126.7, 126.6, 126.6, 125.0, 123.8, 123.0,
2-(5-(4-(Diphenylamino)phenyl)thiophen-2-yl)-8H-indenoACTHNUTRGNE[UNG 2,1-b]thiophen-
8-one (25): Under an argon atmosphere, a 2.5m solution of nBuLi in n-
hexane (0.28 mL, 0.7 mmol) was added dropwise to a solution of N,N-di-
phenyl-4-(thiophen-2-yl)aniline (23,[27] 190 mg, 0.58 mmol) in anhydrous
THF (8 mL) in a Schlenk flask at À788C. After stirring for 1 h at this
temperature, Bu3SnCl (95% of purity, 0.20 mL, 0.7 mmol) was added
dropwise. After 5 min, the reaction mixture was allowed to warm to
room temperature and stirred for a further 1 h. After evaporation of the
solvent, EtOAc (25 mL) was added and the organic layer was washed
with a saturated aqueous solution of NaF, a saturated aqueous solution
of NaCl, dried over MgSO4, and concentrated to dryness to give an
orange oil that corresponded to compound 24, which was used in the
next step without further purification.
120.2, 117.1, 113.5, 113.0, 75.2 ppm; IR (neat): n˜ =2224 cmÀ1 (C N); UV/
ꢁ
Vis (CH2Cl2): lmax (e)=600 nm (500 LmolÀ1 cmÀ1); MS (MALDI-TOF):
m/z: 477.2 [M]+; HRMS (ESI): m/z calcd for C32H20N3S: 478.13724;
found: 478.13752.
2-(2-(5-(Diphenylamino)thiophen-2-yl)-8H-indenoACTHNUGRTNEUNG[2,1-b]thiophen-8-ylide-
ne)malononitrile (4): Two drops of Et3N were added to a mixture of ma-
lonitrile (25 mg, 0.36 mmol) and compound 21 (60 mg, 0.14 mmol) in
CHCl3 (15 mL). The reaction mixture was heated at reflux overnight.
The solvent was evaporated and the residue was purified four times by
column chromatography on silica gel (CH2Cl2) to give a green solid
In a Schlenk flask, a mixture of stannyl derivative 24 (430 mg, 0.7 mmol)
and compound 8 (200 mg, 0.75 mmol) in toluene (30 mL) was degassed
with argon for 15 min. After the addition of [PdACHTNUTRGNE(UNG PPh3)4] (45 mg,
0.04 mmol), the Schlenk flask was sealed and the reaction mixture was
stirred at 1108C for 3 days. After the addition of water, the organic phase
was separated and the aqueous phase was extracted with toluene. The or-
ganic phases were combined, washed with a saturated aqueous solution
of NaCl, dried over MgSO4, and concentrated under vacuum. Column
1
(50 mg, 75%). M.p. 228–2318C; H NMR (300 MHz, CDCl3): d=7.95 (d,
J=7.3 Hz, 1H), 7.40–7.30 (m, 4H), 7.29–7.07 (m, 10H), 6.87 (s, 1H),
6.48 ppm (d, J=4.0 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=156.7,
156.3, 156.1, 146.9, 138.3, 137.8, 132.9, 131.4, 129.8, 128.5, 126.7, 126.2,
126.0, 125.0, 124.4, 120.7, 117.1, 114.7, 114.2, 113.7, 69.7 ppm; IR (neat):
ꢁ
chromatography on silica gel (cyclohexane/CH2Cl2, 7:3) gave
powder (300 mg, 78%). M.p. 210–2128C; 1H NMR (300 MHz, CDCl3):
d=7.50–7.43 (m, 3H), 7.37–7.26 (m, 6H), 7.22–7.11 (m, 8H), 7.11–7.03
(m, 4H); IR (neat): n˜ =1720, 1681 cmÀ1 (C=O); UV/Vis (CH2Cl2): lmax
(e)=499 nm (10500 LmolÀ1 cmÀ1); MS (MALDI-TOF): m/z: 510.6 [M]+;
HRMS (ESI): m/z calcd for C33H21ONS2: 511.10591; found: 511.10526.
n˜ =2217 cmÀ1
(C N);
UV/Vis
(CH2Cl2):
lmax
(e)=664 nm
(17600 LmolÀ1 cmÀ1); MS (MALDI-TOF): m/z: 483.3 [M]+; HRMS
(ESI): m/z calcd for C30H17N3S2: 483.08584; found: 483.08534.
2-(2-(5-(Bis(4-methoxyphenyl)amino)thiophen-2-yl)-8H-indenoACHTUNGTRENUNG[2,1-b]thio-
phen-8-ylidene)malononitrile (5): Three drops of Et3N were added to a
mixture of compound 22 (205 mg, 0.41 mmol) and malonitrile (54 mg,
0.82 mmol) in CHCl3 (30 mL). The reaction mixture was heated at reflux
for 12 h. The solvent was evaporated under vacuum and the crude prod-
uct was triturated with hot EtOH (10 mL), filtered, and washed with
EtOH (2ꢂ10 mL) to give compound 5 as a green powder (200 mg, 90%).
M.p. 200–2028C; 1H NMR (300 MHz, CDCl3): d=8.03 (d, J=8.3 Hz,
1H), 7.30–7.11 (m, 8H), 6.93–6.85 (m, 5H), 6.24 (d, J=4.2 Hz, 1H),
3.83 ppm (s, 6H); 13C NMR (75 MHz, CDCl3): d=159.0, 157.5, 156.3,
155.7, 140.0, 139.8, 138.6, 137.7, 132.6, 128.4, 127.6, 126.6, 125.8, 124.4,
120.6, 115.0, 114.7, 114.0, 113.3, 113.3, 112.1, 68.3, 55.7 ppm; IR (neat):
ꢁ
2-(2-(4-(Diphenylamino)phenyl)-8H-indenoACTHUNTGRENNG[U 2,1-b]thiophen-8-ylidene)ma-
lononitrile (2): Route 1: Under an argon atmosphere, a 2.5m solution of
nBuLi in n-hexane (0.50 mL, 1.25 mmol) was added dropwise to a solu-
tion of compound 12 (250 mg, 0.77 mmol) in anhydrous THF (15 mL) in
a Schlenk flask at À788C in the dark. The reaction mixture was stirred at
this temperature for 0.5 h before the addition of Bu3SnCl (0.25 mL,
0.92 mmol). After 5 min at À788C, the mixture was allowed to warm to
room temperature and then stirred for a further 2 h. After dilution with
Et2O, the organic phase was washed with a saturated aqueous solution of
NaF and water and dried over MgSO4. Evaporation of the solvent gave
compound 13 as slightly yellow oil, which was directly used in the next
step.
n˜ =2211 cmÀ1
(C N);
UV/Vis
(CH2Cl2):
lmax
(e)=710 nm
(23100 LmolÀ1 cmÀ1); MS (MALDI TOF): m/z: 543.0 [M]+; HRMS
To a mixture of compound 13 and compound 9 (240 mg, 0.77 mmol) in
toluene (10 mL) in a degassed Schlenk flask was added [PdACTHUNTRGNE(UNG PPh3)4]
(ESI): m/z calcd for C32H21O2N3S2: 543.10697; found: 543.10593.
2-(2-(5-(4-(Diphenylamino)phenyl)thiophen-2-yl)-8H-indenoACTHNUGRTNEUNG[2,1-b]thio-
(50 mg, 0.04 mmol) and the mixture was heated at reflux for 12 h under
an argon atmosphere. After the addition of water, the mixture was ex-
tracted with toluene. The organic phase was washed with a saturated
aqueous solution of NH4Cl and water, dried over MgSO4, and evaporated
under vacuum. The residue was purified twice by column chromatogra-
phy on silica gel (CH2Cl2) to give a dark-blue solid (320 mg, 87%).
Route 2: Two drops of Et3N were added to a mixture of compound 15
(90 mg, 0.21 mmol) and malonitrile (28 mg, 0.42 mmol) in CHCl3
(15 mL). The reaction mixture was heated at reflux for 14 h. The solvent
was evaporated under vacuum and the crude product was triturated with
hot EtOH (10 mL), filtered, and washed with EtOH (2ꢂ10 mL) to give
compound 2 as a dark-blue powder (90 mg, 90%). M.p. 249–2518C;
1H NMR (300 MHz, CD2Cl2): d=8.07 (d, J=7.6 Hz, 1H), 7.55 (d, J=
phen-8-ylidene)malononitrile (6): Four drops of Et3N were added to a
mixture of malonitrile (60 mg, 0.90 mmol) and compound 25 (200 mg,
0.39 mmol) in CHCl3 (15 mL). The reaction mixture was heated at reflux
overnight. The solvent was evaporated under vacuum and the crude
product was triturated with hot EtOH (10 mL), filtered, and washed with
EtOH (2ꢂ10 mL) to give compound 6 as a green powder (180 mg, 83%).
M.p.>2608C; 1H NMR (300 MHz, CDCl3): d=8.12 (d, J=7.5 Hz, 1H),
7.47 (d, J=8.7 Hz, 2H), 7.39 (d, J=4.0 Hz, 1H), 7.36–7.18 (m, 11H),
7.17–7.03ppm (m, 6H); IR (neat): n˜ =2213 cmÀ1 (C N); UV/Vis
ꢁ
(CH2Cl2): lmax (e)=620 nm (17100 LmolÀ1 cmÀ1); MS (MALDI-TOF): m/
z: 558.6 [M]+; HRMS (MALDI-TOF): m/z calcd for C36H21N3S2:
559.1177; found: 559.1186.
Chem. Eur. J. 2013, 00, 0 – 0
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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Acknowledgements
The Ministꢀre de la Recherche is acknowledged for a PhD grant to A.L.
We thank the PIAM of the University of Angers for performing the char-
acterization of the organic compounds.
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Small D–p–A Systems with o-Phenylene-Bridged Accepting Units
FULL PAPER
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J. A. Montgomery, J. E. Peralta, F. Ogliaro, V. Bearpark, J. J. Heyd,
E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Nor-
mand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J.
Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Strat-
mann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochter-
ski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P.
Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas,
Received: March 19, 2013
Published online: && &&, 0000
Chem. Eur. J. 2013, 00, 0 – 0
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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P. Blanchard, J. Roncali et al.
Good things in small packages: The
bridging of a dicyanovinyl group to the
vicinal thiophene by an ortho-phenyl-
ene bridge leads to a new electron-
withdrawing building block, which has
been used for the synthesis of small
donor–p–acceptor molecular donors
with tailored electronic properties.
Efficient planar heterojunction solar
cells based on these donors of reduced
molecular size and C60 or C70 are
reported.
Donor–Acceptor Systems
A. Leliꢀge, J. Grolleau, M. Allain,
P. Blanchard,* D. Demeter,
T. Rousseau, J. Roncali* . . . . &&&& — &&&&
Small D–p–A Systems with o-
Phenylene-Bridged Accepting Units as
Active Materials for Organic Photo-
voltaics
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www.chemeurj.org
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!