Synthesis and structure-property correlations of dicyanovinyl-substituted oligoselenophenes and their application in organic solar cells

Article abstract of DOI:10.1002/adfm.201201018

The convergent synthesis of a series of acceptor-donor-acceptor (A-D-A) type dicaynovinyl (DCV)-substituted oligoselenophenes DCVnS (n = 3-5) is presented. Trends in thermal and optoelectronic properties are studied, in dependence on the length of the con

Full text of DOI:10.1002/adfm.201201018

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Synthesis and Structure–Property Correlations of
Dicyanovinyl-Substituted Oligoselenophenes and their
Application in Organic Solar Cells
Stefan Haid, Amaresh Mishra,* Matthias Weil, Christian Uhrich, Martin Pfeiffer,
and Peter Bäuerle*
the theoretical investigation of oligose-
lenophenes.[1–4] The synthesis of a series
of oligoselenophenes up to a hexamer
was first published by Nakanishi et al.
in 1997.[5,6] The authors showed that oli-
goselenophenes could be synthesized by
the same C–C cross coupling reactions
as oligothiophenes. Furthermore, the
systematic changes of the optoelectronic
properties in a series of oligoselenophenes
were similar to those for oligothiophenes.
The investigated oligoselenophenes exhib-
ited red-shifted absorption spectra and
lower bandgaps compared to their oli-
gothiophene analogs. To date, this series
remained the only systematically investi-
gated series of oligoselenophenes.
Polyselenophenes, on the other hand,
have been investigated more widely in
recent years, both theoretically and experi-
mentally. Some promising properties,
especially for application in organic solar
cells (OSC), were predicted and confirmed
by experiments, i.e., lower bandgaps, red-
shifted absorption and better polarizability
compared to polythiophenes.[1,2,7–11] Due
The convergent synthesis of a series of acceptor–donor–acceptor (A-D-A)
type dicaynovinyl (DCV)-substituted oligoselenophenes DCVnS (n = 3–5) is
presented. Trends in thermal and optoelectronic properties are studied, in
dependence on the length of the conjugated backbone. Optical measure-
ments reveal red-shifted absorption spectra and electrochemical investiga-
tions show lowering of the lowest unoccupied molecular orbital (LUMO)
energy levels for DCVnS compared to the corresponding thiophene analogs
DCVnT. As a consequence, a lowering of the bandgap is observed. Single
crystal X-ray structure analysis of tetramer DCV4S provides important insight
into the packing features and intermolecular interactions of the molecules,
further corroborating the importance of the DCV acceptor groups for the
molecular ordering. DCV4S and DCV5S are used as donor materials in planar
heterojunction (PHJ) and bulk-heterojunction (BHJ) organic solar cells.
The devices show very high fill factors (FF), a high open circuit voltage,
and power conversion efficiencies (PCE) of up to 3.4% in PHJ solar cells
and slightly reduced PCEs of up to 2.6% in BHJ solar cells. In PHJ devices,
the PCE for DCV4S almost doubles compared to the PCE reported for the
oligothiophene analog DCV4T, while DCV5S shows an about 30% higher PCE
than DCV5T.
to the predicted favorable properties, several polyselenophenes
and selenophene containing co-polymers have been applied
in OSCs in the last few years and power conversion efficien-
cies of up to 6.87% were achieved.[12–20] Selenophene-based
oligomers, on the other hand, have only scarcely been used in
solar cells. Some selenophene-containing sensitizers for dye-
sensitized solar cells were investigated.[21,22] A series of selen-
ophene- and biselenophene-substituted diketopyrrolopyrroles
was used in solution-processed bulk-heterojunction (BHJ) solar
cells, whereby PCEs of 1.5% were achieved.[23] To the best of
our knowledge, oligoselenophenes longer than a trimer have
not been implemented in organic solar cells so far.
During the past years, the emergence of novel strategies in
the design of conjugated small molecules and oligomers as
well as the development of new device architectures has led to
remarkable improvements in the performance of OSCs.[24] In
our group, a number of acceptor-donor-acceptor (A-D-A) oli-
gothiophenes have been synthesized and studied in vacuum-
processed solar cells.[25–35] In particular, dicyanovinyl (DCV)-
substituted oligothiophenes showed very good efficiencies,
1. Introduction
In contrast to oligothiophenes, oligoselenophenes are still a
rather unexplored class of organic π-conjugated materials.
This is mainly due to the less developed chemistry and higher
price of selenophene. Therefore, some studies focused only on
S. Haid, Dr. A. Mishra, Prof. P. Bäuerle
Institute of Organic Chemistry II and Advanced Materials
University of Ulm
Albert-Einstein-Allee 11, D-89081 Ulm, Germany
E-mail: amaresh.mishra@uni-ulm.de;
peter.baeuerle@uni-ulm.de
Dr. M. Weil
Institut für Chemische Technologien und Analytik
Abteilung Strukturchemie, Technische Universität Wien
Getreidemarkt 9/164-SC, 1060 Vienna, Austria
Dr. C. Uhrich, Dr. M. Pfeiffer
Heliatek GmbH, Treidlerstr. 3, 01139 Dresden, Germany
DOI: 10.1002/adfm.201201018
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Scheme 1. Dicyanovinyl-substituted oligoselenophenes (left) and oligothiophenes (right).
and the best value of up to 5.2% was obtained with a DCV-
2. Results and Discussion
substituted quinquethiophene (DCV5T) in BHJ solar cells.[27]
In a very recent work, we investigated DCV-substituted selen-
ophene-thiophene co-oligomers containing butyl side chains,
which showed good PCEs of 2.5–3.0%.[28]
2.1. Synthesis
The synthesis of DCV3S started with 2,2′:5′,2′′-terselenophene
1,[5] which was formylated in a Vilsmeier-Haack reaction with
N,N-dimethylformamide (DMF)/phosphoryl chloride (POCl3)
to obtain dialdehyde 2 in 63% yield (Scheme 2). Dialdehyde 2
was reacted with malononitrile and β-alanine in a Knoevenagel
condensation and after recrystallization from chlorobenzene
DCV3S was obtained in 72% yield. Due to their expected low
solubility, DCV4S and DCV5S were synthesized by a conver-
gent approach developed recently in our laboratory.[27] Thus,
Encouraged by these results, we present now in this work
the synthesis of a series of DCV-substituted oligoselenophenes
DCVnS . Their thermal and optoelectronical properties and their
application in OSCs will be discussed and compared to the pre-
viously reported oligothiophenes (DCVnT ) (Scheme 1).[27] Fur-
thermore, the single crystal structure analysis of the tetrameric
DCV4S will be discussed and compared to its thiophene analog
DCV4T.
Scheme 2. a) POCl3/DMF (20 equiv), dichloroethane, reflux, 5 d; b) malononitrile, β-alanine, dichloroethane/ethanol, reflux, 2 d; c) Pd(PPh3)2Cl2,
DMF, 80 °C, overnight; d) NBS (1 equiv), DMF, −25 °C, 3 d; e) malononitrile, β-alanine, dichloroethane/ethanol, reflux, 2 h; f) Pd(PPh3)4, DMF, 80 °C,
overnight.
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DCV4S was obtained by Stille cross-coupling of bisstannylated
biselenophene 3[36] and DCV-substituted bromoselenophene
4
[28] using Pd(PPh3)2Cl2 as catalyst. After Soxhlet extraction with
chlorobenzene, pure DCV4S was obtained in 80% yield. For the
synthesis of DCV5S, DCV-substituted bromobiselenophene 7
was synthesized from 2,2′-biselenophene-5-carbaldehyde 5[5] by
monobromination with N-bromosuccinimide (NBS) in DMF at
−25 °C, which afforded bromo derivative 6 in 88% yield. Sub-
sequent Knoevenagel condensation with malononitrile gave
diselenophene 7 in 95% yield. Stille cross-coupling of 7 with
2,5-bis(trimethylstannyl)selenophene 8, which had been synthe-
sized from 2,5-dibromoselenophene[28] by lithiation with n-butyl
lithium (n-BuLi) and subsequent quenching with trimethyltin
chloride, afforded DCV5S in 74% yield after Soxhlet extraction
with chlorobenzene.
2.2. Thermal Properties
Figure 1. DSC curves for DCV3S-DCV5S measured under argon flow at a
heating rate of 10 oC min−1
.
Oligoselenophenes DCV3S-DCV5S were designed for applica-
tion in vacuum-processed solar cells and therefore need to be
stable at the higher temperatures used for thermal evaporation.
This thermal stability was investigated by Differential Scanning
Calorimetry (DSC) under an argon atmosphere (Figure 1). The
DSC curve of each compound showed one endothermic peak
indicating the melting point and one exothermic peak at higher
temperatures, indicating beginning decomposition. The melting
points for all three compounds (282–358 °C) are substantially
higher than those of the corresponding oligothiophenes[27]
(ΔTm = 17–38 °C, see Table 1). The oligoselenophenes showed
the same odd-even effect as the analogous oligothiophenes. As
a consequence, we found a significantly higher melting point
for even numbered DCV4S (358 °C) than for odd-numbered
DCV3S (282 °C) and DCV5S (324 °C). The decomposition tem-
peratures of all oligomers were above 370 °C, a temperature
which typically is sufficient for vacuum sublimation.
compared to the data for the corresponding oligothiophenes.
The absorption spectrum of DCV3S showed a broad peak with a
maximum at 521 nm. With increasing number of selenophene
units, the absorption maximum is bathochromically shifted
(DCV4S: λmax,abs = 547 nm; DCV5S: λmax,abs = 565 nm) due
to extended π-conjugation. The emission spectrum of DCV3S
clearly showed a structured band with a maximum at 599 nm
and a vibronic shoulder at 638 nm. The spectra of DCV4S
(λmax,em = 654 nm) and DCV5S (λmax,em = 695 nm) were red-
shifted, but lost fine structure. Compared to the corresponding
oligothiophenes (DCVnT ), the absorption maxima are red-
shifted by 25–35 nm. For the emission maxima, this trend is
slightly more pronounced with shifts between 30 and 45 nm.
In contrast to DCVnT , no clear trend for the molar extinction
coefficients could be observed for DCVnS . The molar extinction
coefficients of DCV3S (ε = 62 200 L mol−1 cm−1 ) and DCV5S
(ε = 63 500 L mol−1 cm−1 ) are found to be in the same region.
For DCV4S, however, no extinction coefficient could be deter-
mined because of its poor solubility.
2.3. Optical Spectroscopy
The optical properties of DCVnS were investigated by UV-vis
absorption and emission spectroscopy in dichloromethane
solution (Figure 2a). In Table 1, the data are summarized and
Thin films were prepared for DCV4S and DCV5S by vacuum
sublimation on glass substrates and their UV-vis absorption
T a b le 1 . Optical data of DCVnS in comparison with their thiophene analogs DCVnT .
solution
film
a)
Compound
Tm
Egopt b)
Egopt c)
λabs
λem
λabs
λem
[°C]
[eV]
[eV]
[nm]
[nm]
[nm]
[nm]
DCV3S
DCV4S
DCV5S
DCV3Td)
DCV4Td)
DCV5Td)
282
358
324
265
320
287
521
547
565
495
518
530
599
654
695
564
612
663
2.08
1.95
1.89
2.20
2.09
2.02
–
–
–
581
596
528
560
570
797
822
695
670
767
1.68
1.60
1.85
1.78
1.69
a)Melting temperature determined from DSC; b)Estimated using the onset of the UV-vis spectra in DCM; c)Estimated using the onset of the thin film UV-vis spectra;
d)Values taken from ref. [27].
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Figure 3. Differential pulse voltammograms of DCVnS measured in
dichloromethane at 25 °C (DCV3S) or tetrachloroethane at 80 °C (DCV4S,
DCV5S). Supporting electrolyte TBAPF6 (0.1 M), scan rate 100 mV s−1
,
potentials versus Fc/Fc+.
Figure 2. a) UV-vis absorption and emission spectra of DCV3S-DCV5S
measured in dichloromethane. b) UV-vis absorption and emission spectra
of DCV4S and DCV5S in thin films deposited by vacuum sublimation on
glass substrates.
internal standard. DPVs of all three compounds are shown in
Figure 3. The data are summarized and compared to the cor-
responding oligothiophenes in Table 2.
All three compounds showed one reduction and two oxida-
tion processes. For DCV4S, a second reduction wave was vis-
ible. The oxidation potentials are shifted to more negative values
with increasing chain length of the oligoselenophene. The first
oxidation potential decreased from 0.99 V for DCV3S to 0.57 V
for DCV5S, whereas the second one shifted from 1.28 V for
DCV3S to 0.85 V for DCV5S. For the longer oligomers the redox
waves are reversible, indicating the formation of stable radical
cations and dications due to the extended conjugated system.
Compared to the corresponding oligothiophenes, the oxidation
potentials were lower by 0.1 V. The reduction potentials shifted
as well to more negative values with increasing number of
selenophenes (from –1.17 V for DCV3S to –1.38 V for DCV5S).
From the onset of the first oxidation and reduction potential,
HOMO (highest occupied molecular orbital) and LUMO (lowest
unoccupied molecular orbital) energy values were calculated for
each compound by subtracting the respective value from the
Fc/Fc+ energy level (–5.1 eV vs. vacuum).[37] The difference of
the thus determined HOMO and LUMO energies corresponds
to the electrochemical bandgap (EgCV). The data are summa-
rized in Table 2 and compared with the values for the oligothi-
ophene analogs. The HOMO energy was raised with increasing
number of selenophenes from –6.02 eV for DCV3S to –5.60 eV
and emission spectra were measured (Figure 2b). Compared
to the solution spectra, the absorption spectra in thin films
are significantly broadened and the maxima are bathochromi-
cally shifted by ≈30 nm due to planarization and ordering of
the molecules in the solid state. The emission maxima are even
further red-shifted by 130–140 nm. The broad and red-shifted
absorptions result in reduced optical bandgaps for DCV4S
opt
and DCV5S compared to those in solution (ΔEg ≈ 0.29 eV).
Both, in solution and in thin film, the bandgaps of the oligose-
lenophenes are by 0.1–0.15 eV lower than those of the corre-
sponding oligothiophenes.
2.4. Electrochemical Characterization
The redox properties of DCV3S were measured by cyclic vol-
tammetry (CV) and differential pulse voltammograms (DPV)
at room temperature in dichloromethane solution with
0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6)
as supporting electrolyte. Due to their poor solubility in
dichloromethane, DCV4S and DCV5S were investigated in tet-
rachloroethane/TBAPF6 solutions at 80 °C. All measurements
were carried out with the ferrocene/ferrocenium couple as
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T a b le 2 . Electrochemical data for DCVnS compared to their thiophene analogs DCVnT .
compound
E0
[V]
E0
[V]
E0
red1
[V]
HOMOa)
[eV]
LUMOa)
[eV]
EgCV
[eV]
ox1
ox2
DCV3Sb)
DCV4Sc)
DCV5Sc)
DCV3Td)
DCV4Td)
DCV5Td)
0.99
0.81
0.57
1.06
0.84
0.64
1.28
1.11
0.85
–
–1.17
–1.25
–1.38
–1.25
–1.41
–1.37
–6.02
–5.81
–5.60
–6.09
–5.85
–5.62
–4.00
–3.96
–3.84
–3.90
–3.87
–3.73
2.02
1.85
1.76
2.19
1.98
1.89
1.20
0.93
a)Set Fc+/Fc EHOMO = −5.1 eV;[37] b)Measured in DCM/TBAPF6 (0.1 M), 25 °C, V = 100 mV s−1 , vs. Fc+/Fc; c)Measured in tetrachloroethane/TBAPF6 (0.1 M), 80 °C, V =
100 mV s−1 , vs. Fc+/Fc; d)Values according to ref. [27].
for DCV5S. For the LUMO energies we see the same trend,
but somewhat smaller (–4.00 eV for DCV3S to –3.84 eV for
DCV5S). Consequently, the electrochemical bandgap decreased
from 2.02 eV for DCV3S to 1.76 eV for DCV5S. Compared to
the oligothiophene analogs, the HOMO values of the oligose-
lenophenes are relatively similar while the LUMO values are
lower by about 0.1 eV. Due to these lower LUMO energies, the
electrochemical bandgap of the oligoselenophenes were 0.1–
0.15 eV smaller compared to the oligothiophenes. The same
trend was observed for the optical bandgaps (see above). The
lower ionization potential[38] of selenium (9.75 eV) compared to
sulfur (10.36 eV) could be the main reason for the lower LUMO
energies of the investigated oligoselenophenes compared to
their thiophene analogs. This is in accordance with theoretical
studies, which have shown that upon replacement of sulfur
by selenium the HOMO should remain relatively unaffected,
whereas the LUMO should be stabilized by any heteroatom
with a lower ionization potential.[39]
Due to the low HOMO energy of −6.02 eV, DCV3S rather
shows an n-type semiconducting character and is not suitable as
donor material in organic solar cells. On the other hand, DCV4S
(EHOMO = −5.81 eV) and DCV5S (EHOMO = −5.60 eV) should
be suitable p-type materials for OSCs with C60 as acceptor.
The large difference between the HOMO of DCVnS and the
LUMO of C60 (ELUMO = −4.08 eV)[40] should provide reasonably
high open circuit voltages (VOC) as the VOC depends mainly on
the energy difference between the LUMO of the acceptor and
HOMO of the donor materials.
planar (rms deviation 0.116 Å) with dihedral angles between
the selenophene units below 4.5°. The terminal DCV-groups
are slightly twisted out of the molecular plane with nitrogen-
plane distances of up to 0.33 Å.
The bond lengths of the oligoselenophene backbone are
summarized in Table 3 and the inter- and intramolecular
non-bonding atom distances shorter than the sum of the cor-
responding van der Waals radii are collected in Table 4. The
values for the selenophenic C=C double bonds (1.362–1.378 Å),
C–C single bonds (1.402–1.409 Å) and the C–C interring bonds
(1.438–1.446 Å) are comparable with those of the corresponding
oligothiophene DCV4T. The C–Se bonds (1.872–1.892 Å), how-
ever, are substantially longer than the C–S bonds (1.730–1.745 Å)
in DCV4T due to the larger selenium atom. These values are in
good agreement with the values for the respective monomeric
selenophene (1.855 Å) and thiophene (1.714 Å).[41,42]
The unit cell comprises four molecules divided into two
centrosymmetric pairs of antiparallelly arranged molecules
(Figure 5). In the crystal, molecules extend in layers parallel to
the (9 3 21) plane with channels parallel to [100] that contain
disordered molecules. It was not possible to resolve this dis-
order satisfactorily (for treatment of the disorder see details in
the experimental section). Although the crystal structure looks
very similar to that of DCV4T, some differences can be rec-
ognized by comparison of the intra- and intermolecular short
contacts (Table 4 and Figure 4). Interestingly, no intramolecular
short contacts between hydrogen and sulfur atoms are observed
for DCV4T, while each selenium atom in DCV4S interacts with
the hydrogen atoms of the adjacent selenophene ring(s). This is
a consequence of the larger van der Waals radius of selenium
(1.90 Å) compared to sulfur (1.80 Å).[43] In contrast to DCV4T,
no intermolecular short distances between H2 and H11 are
observed. However, there is an additional intermolecular inter-
action between Se3 and N2. For DCV4T, no intermolecular
interactions between sulfur and nitrogen atoms were observed.
The nitrogen atoms N2-N4 of DCV4S interact with hydrogens
H7, H17 and H21 via weak non-classical C-H…N hydrogen
bonds, but the bond lengths of the hydrogen bonds, especially
the N2…H7 bond, are slightly larger compared to DCV4T, indi-
cating slightly weaker hydrogen bonding.
2.5. Single Crystal Structure Analysis
Lath-like single crystals of DCV4S suitable for structural analysis
were obtained after gradient sublimation at 1.75 · 10−6 mbar
and 325 °C. The crystals belong to the monoclinic space group
P21/n with 4 molecules in the unit cell. The unit cell para-
meters are: a = 3.92030(10), b = 27.6816(9), c = 22.7887(7) Å,
β = 93.181(2)°. Figure 4 shows the molecular structure of DCV4S
in the crystal. The crystal structure is isostructural to that of the
thiophene analog DCV4T.[27] The selenophene units show an
all trans conformation while the DCV groups are in an all cis
conformation relative to the selenium atoms of the adjacent
selenophene ring. The configuration of the molecule is almost
DCV4S does not exhibit a herringbone structure in the crystal
which was observed for the parent 2,2′:5′,2′′:5′′,2′′′-quaterselen-
ophene.[44] The π-conjugated backbones of the molecules are
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Figure 4. a) Molecular structure of DCV4S (front view) with atomic numbering scheme. Inter- and intramolecular short contact distances are depicted
by gray lines, respectively. Torsion angles between adjacent selenophene rings: A-B 178.7°, B-C 175.5°, C-D 178.4°, N4-A 9.3°, D-N1 6.2°. b) Side
view.
oriented parallel to one another, as it is seen in the view from
the [010] direction (Figure 6). The intermolecular distances,
“d”, are 3.563 Å compared to 3.512 Å for DCV4T, indicating
a slightly less compact packing and π–π stacking of the selen-
ophene backbones due to the larger van der Waals radius of
selenium compared to sulfur. In the perpendicular direction,
the molecules (Figure 5) are lying in approximate coplanarity
with a small offset between neighboring molecules (Δ =
1.085 Å; Figure 6). As in the case of DCV4T, weak non-classical
hydrogen bonding interactions caused by the terminal nitrile
T a b le 3 . Bond lengths [Å] in the oligoselenophene moiety in DCV4S single crystals (Se-C bond lengths are shown in bold).
N1
C23
N2
C24
C22
C21
C4
C23
C22
C24
C22
C21
C4
1.141(4)
1.427(4)
1.151(4)
1.434(4)
1.363(4)
1.425(3)
1.883(2)
1.381(4)
1.410(3)
1.379(3)
1.880(2)
1.439(2)
1.875(2)
1.370(3)
1.407(3)
1.371(4)
1.886(2)
1.445(3)
C9
Se3
C10
C11
C12
Se3
C13
Se4
C14
C15
C16
Se4
C17
C18
C19
C20
N3
1.875(2)
1.367(3)
1.405(3)
1.366(3)
1.880(2)
1.439(3)
1.874(2)
1.376(3)
1.402(4)
1.370(4)
1.892(2)
1.414(3)
1.357(4)
1.437(3)
1.439(4)
1.147(3)
1.152(4)
C9
C10
C11
C12
C12
C13
C13
C14
C15
C16
C16
C17
C18
C18
C19
C20
Se1
C3
C4
C2
C3
C2
C1
C1
Se1
C1
C5
C5
Se2
C5
C6
C6
C7
C7
C8
C8
Se2
C9
N4
C8
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T a b le 4 . Short inter- (left) and intra- (middle and right) molecular contacts [Å], below the sum of the van der Waals radii, in DCV4S single crystals.
C23…C24a)
N2…Se3b)
N2…H7c)
Se1…C23
Se1…N1
Se1…H6
Se2…H2
Se2…H10
Se3…H7
Se3…H14
Se4…C20
Se4…N4
Se4…H11
3.345
3.428
2.689
2.504
2.526
3.116
3.328
2.948
2.962
2.968
2.986
2.952
3.147
3.319
2.967
N3…H17d)
N4…H21e)
Symmetry codes: a)–1 + x, y, z; b)1.5 + x, 1/2 - y, ½ + z; c)–1.5 + x, 1/2 - y, –1/2 + z; d)–3 + x, y, 1 + z; e)1 – x, 1 – y, 1 – z.
residues seem to be the main driving forces for the parallel
ordering of the π-conjugated system in DCV4S. This explains
the same packing features of both compounds. In summary,
the general packing pattern is controlled by the DCV groups
while the intermolecular π–π distances are increased by incor-
poration of selenium into the conjugated backbone.
the respective donor (DCV4S or DCV5S) and C60 as acceptor on
a heated substrate. The device with DCV4S was fabricated at a
substrate temperature of 70 °C and a blend ratio of 1:1, while
DCV5S was deposited at 90 °C with a blend ratio of 2:1. These
conditions had turned out to be optimal for the corresponding
oligothiophenes.[26,27]
The current density-voltage (J–V) curves of the PHJ and BHJ
devices and the external quantum efficiency (EQE) spectra are
shown in Figure 6 and Figure 7, respectively. The photovoltaic
parameters are summarized in Table 5. The dark curves in PHJ
solar cells showed very good rectification behavior, while larger
leakage currents were observed in BHJ devices.
For both device architectures, the layer thicknesses do not
significantly influence the overall device efficiencies. The short
circuit current density (JSC) increases with increased layer
thickness, but the fill factor (FF) decreases leading to an almost
unchanged overall efficiency. DCV5S gave better PCEs (PHJ:
3.4%; BHJ: 2.6%) compared to DCV4S (PHJ: 2.4%; BHJ: 1.7%).
All devices showed a high VOC, as VOC is generally determined
by the energetic difference between the LUMO of the acceptor
C60 and the HOMO of the donor.[45] In DCV4S and DCV5S-
based PHJ devices, the VOC decreases from 0.95 V to about
0.91 V. In this architecture, the change of VOC represents in a
first approximation the HOMO energy level difference between
the two donor materials in the solid state.[46] This difference can
2.6. Photovoltaic Performance
Due to the low-lying HOMO energy level and the possible n-type
character DCV3S was not used for solar cell fabrication. DCV4S
and DCV5S, however, were implemented as donor material in
combination with fullerene C60 as electron acceptor, both in
planar heterojunction (PHJ) and in bulk-heterojunction (BHJ)
solar cells. The devices were fabricated by vacuum sublimation
on glass substrates coated with indium tin oxide (ITO). For the
PHJ devices, the following layer sequence was used: ITO coated
glass, 15 nm C60 as acceptor, 6 nm or 10 nm DCV4S or DCV5S
as donor, 5 nm undoped 9,9-bis[4-(N,N-bis-biphenyl-4-ylamino)-
phenyl]-9H-fluorene (BPAPF), 50 nm BPAPF doped with
10 wt% NDP9 as hole transporting layer (HTL), 1 nm NDP9,
50 nm gold as top electrode. For the BHJ devices, a 20 nm or
30 nm mixed donor-acceptor layer was used instead of the pris-
tine donor layer. This layer was prepared by co-evaporation of
Figure 5. Molecular packing of DCV4S in the single crystal viewed from the direction normal to the (9 3 21) plane.
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Figure 6. Molecular packing of DCV4S in the single crystal view from the [010] direction showing the π–π stacking [d] of the molecules.
also be expected from the electrochemically determined energy
levels (ΔEHOMO ≈ 0.2 eV) as shown in Table 2. One explana-
tion for the deviation of the energetic shift could be that the
latter values were obtained for single molecules in solution,
whereas the values in the devices were shifted due to molecular
packing in the solid state. Since the HOMO values of DCVnS
are very similar to those of DCVnT , the VOC values for the oli-
goselenophenes are comparable to those of the corresponding
oligothiophenes.
In the PHJ devices, JSC increased with increasing layer thick-
ness from 6 to 10 nm. This result shows that the exciton dif-
fusion length is larger than 6 nm in both materials. The PHJ
solar cells with DCV5S showed slightly higher JSC values of
7.1 mA cm−2 . This can be correlated to the EQE spectra of the
DCV5S devices which are broad and red-shifted compared
to DCV4S. The DCV5S spectra showed an onset at ≈800 nm
reaching a maximum of ≈0.35, while the maximum for DCV4S
lies below 0.3 with an onset at ≈750 nm (Figure 8a). Thus, more
charge carriers are generated in the DCV5S device, leading to
an increased photocurrent.
The PHJ devices with DCV4S showed lower FF and larger
saturation values compared to the devices with DCV5S. Both
effects originate from a voltage dependent photo-generated
charge carrier recombination. One explanation could be an
insufficient energetic LUMO offset between DCV4S and C60
leading to inefficient and voltage-dependent exciton separation
at this interface.
For both compounds, the PHJ devices showed better PCEs
than the BHJ devices. This difference in performance was
mainly due to the slightly increased JSC values and significantly
higher FFs for the PHJ devices. This trend is in contrast to
Figure 7. J–V characteristics of a) planar heterojunction solar cells (6 nm
donor layer) and b) bulk-heterojunction solar cells (20 nm bulk layer) with
DCV4S and DCV5S as donor materials.
previous results with corresponding oligothiophenes in which
BHJ devices outperformed PHJ solar cells.[27] All BHJ devices
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T a b le 5 . Photovoltaic parameters of PHJ and BHJ solar cells containing DCV4S and DCV5S.
Saturationb)
Incident light intensity
PCE
[%]
a)
Oligomers
Device structure
Substrate temperature
Layer thickness
[nm]
JSC,ap,100
V OC
[V]
FF
[°C]
[mA cm−2
]
[mW cm−2
]
DCV4S
DCV4S
DCV5S
DCV5S
DCV4S
DCV4S
DCV5S
DCV5S
PHJ
PHJ
PHJ
PHJ
BHJ
BHJ
BHJ
BHJ
r.t.
r.t.
r.t.
r.t.
70
70
90
90
6
4.8
5.3
6.3
7.1
4.6
4.8
6.1
6.4
0.95
0.95
0.90
0.91
0.89
0.88
0.90
0.89
0.53
0.47
0.59
0.53
0.41
0.39
0.47
0.45
1.24
1.30
1.16
1.20
1.44
1.43
1.48
1.45
96
96
2.4
2.4
3.3
3.4
1.7
1.6
2.6
2.6
10
6
92
10
20
30
20
30
92
97
97
105
105
a)Measured with mask; b)Defined as J(–1 V)/JSC
.
showed non-optimal rectifying behavior. Increasing the blend
layer thickness from 20 to 30 nm only slightly affected the
photovoltaic parameters of the BHJ solar cells, which are sum-
marized in Table 4. One explanation for both effects could be
a strong crystallization and phase separation of the oligoselen-
ophenes and C60 when deposited on a heated substrate. As a
consequence, the generated photocurrent is strongly limited by
exciton diffusion, leading to stagnation of JSC with increasing
blend layer thickness. At the same time, comparably low FF
and high saturation values point towards non-optimal charge
carrier transport in these particular blend layers.
Compared to the previously investigated oligothiophenes
DCV4T and DCV5T, the PHJ device efficiencies (6 nm
donor layer) of DCV4S and DCV5S are higher. In the case of
the tetramers, the PCE of DCV4S (2.4%) is twice as high as the
PCE for DCV4T (1.2%).[27] This is mainly a consequence of the
much higher JSC (5.2 vs 2.9 mA cm−2 ). For the pentamers, the
efficiency increases from 2.6% for DCV5T to 3.4% for DCV5S
due to both, higher JSC and FF values.
In BHJ devices (20 nm active layer) the PCE for DCV4S
(1.7%) is very similar to that of DCV4T (1.5%).[26] However,
a considerable decrease of the efficiency was observed for
DCV5S (2.6%) compared to DCV5T (3.9%).[27] The main reason
for this decrease is the lower FF (0.45 for DCV5S vs. 0.61 for
DCV5T), which could be a result of less efficient charge carrier
extraction.
In order to improve the device performance, further detailed
studies are necessary on the optimization of substrate tempera-
ture and fabrication conditions. In our previous investigation,
we also observed that the efficiency of DCV-endcapped
thiophene-selenophene co-oligomers dropped with increasing
selenophene content due to poorer phase separation.[28]
3. Conclusion
We reported on the synthesis of a series of longer oligoselen-
ophenes with terminal acceptor groups (DCVnS ). The influ-
ence of selenium in the conjugated oligomers on optoelectronic
properties and solar cell performance has been explored in
detail and compared with the corresponding oligothiophenes
DCVnT . Thermal, optical and electrochemical properties of
Figure 8. External quantum efficiency (EQE) spectra of a) PHJ solar cells
and b) BHJ devices with DCV4S and DCV5S.
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collected (θmax = 38.1°) and merged to 13421 independent data (Rint
0.050); final R indices: R1(I > 2σ(I)) = 0.0481, wR2 (all) = 0.1109.
Detailed crystallographic data for the structure of DCV4S have
been deposited with the Cambridge Crystallographic Data Centre as
supplementary publication CCDC 874137.
Optical measurements in solution were carried out in 1 cm cuvettes
with Merck Uvasol grade solvents. Absorption spectra were recorded
on a Perkin Elmer Lambda 19 spectrometer and corrected fluorescence
=
DCVnS exhibited similar chain length dependence as the cor-
responding oligothiophenes. Red-shifted absorption bands and
lowering of the bandgap were observed for DCVnS in compar-
ison with DCVnT . The replacement of sulfur by selenium led
to a lowering of the LUMO energy level, while the HOMO level
stayed relatively unaffected. The single crystal structure analysis
of tetramer DCV4S confirmed the important role that the DCV
groups play for molecular ordering, whereas the introduction of
selenium resulted in increased intermolecular distances com-
pared to DCV4T. Oligomers DCV4S and DCV5S were imple-
mented as donor materials in vacuum-processed PHJ and BHJ
solar cells with C60 as acceptor. This is the first time that longer
oligoselenophenes were used as donor materials in small mol-
ecule organic solar cells (SMOSC). In PHJ devices, the oligose-
lenophenes showed higher PCEs than their thiophene analogs,
the best efficiency being 3.4% for DCV5S. In BHJ devices, the
PCE for DCV5S was lower than for DCV5T, but there is still
room for improvement by optimization of the fabrication con-
ditions. Nevertheless, these results demonstrate the successful
application of acceptor-functionalized oligoselenophenes as
donor materials for efficient SMOSC.
spectra were recorded on
a Perkin Elmer LS 55 fluorescence
spectrometer. Cyclic voltammetry experiments were performed with a
computer-controlled Autolab PGSTAT30 potentiostat in a three-electrode
single-compartment cell with a platinum working electrode, a platinum
wire counter electrode, and an Ag/AgCl reference electrode. All potentials
were internally referenced to the ferrocene/ferrocenium couple.
Thin Film and Device Fabrication: Thin films and heterojunction solar
cell devices were prepared by thermal vapor deposition in ultra high
vacuum at a base pressure of 10−7 mbar onto the substrate at room
temperature. Thin films for absorption and emission measurements
were prepared on quartz substrates, solar cells on tin-doped indium
oxide (ITO) coated glass (Thin Film Devices, USA, sheet resistance of
30 Ω sq−1 ). Layer thicknesses were determined during evaporation by
using quartz crystal monitors calibrated for the respective material.
The thin films prepared for absorption and emission measurements
are approximately 30 nm thick. Thin film absorption spectra were
recorded on a Shimadzu UV-2101/3101 UV–Vis spectrometer. The thin
film emission spectra were recorded with an Edinburgh Instruments
FSP920 fluorescence spectrometer. Planar heterojunction and bulk-
heterojunction solar cells were prepared layer by layer without breaking
the vacuum. The layer structure of the bulk-heterojunction solar cells is
as follows: ITO/15 nm C60/20 or 30 nm blend layer of respective DCVnS
and C60 (ratio 1:1 or 2:1 in volume) prepared by co-evaporation on heated
substrate (70 or 90 °C)/5 nm BPAPF/50 nm BPAPF doped with 10 wt%
NDP9 (Novaled AG, Dresden, Germany)/1 nm NDP9/50 nm gold.
The planar heterojunction devices were built up as follows: ITO/15 nm
C60/6 nm or 10 nm donor layer of respective DCVnS /5 nm BPAPF/50 nm
BPAPF doped with 10 wt% NDP9 (purchased from Novaled AG, Dresden,
Germany)/1 nm NDP9/50 nm gold. The dopant material NDP9 was
purchased from the company Novaled AG, Dresden, Germany, and can
be available by directly contacting the company.
Photovoltaic Characterization: J–V and EQE measurements were carried
out in a glove box with nitrogen atmosphere. J–V characteristics were
measured using a source-measure unit (Keithley SMU 2400) and an AM
1.5G sun simulator (KHS Technical Lighting SC1200). The intensity was
monitored with a silicon photodiode (Hamamatsu S1337) which was
calibrated at Fraunhofer ISE. The mismatch between the spectrum of the
sun simulator and the AM 1.5G spectrum was not taken into account.
For well defined active solar cell areas, aperture masks (2.76 mm2)
were used. Simple EQE measurements were carried out using the
sun simulator in combination with color filters for monochromatic
illumination. The illumination intensities were measured with a silicon
reference diode (Hamamatsu S1337).
Materials: Dimethylformamide (DMF, Merck) was dried under
reflux over phosphorous pentoxide (Merck). Dichloromethane
(DCM), dichloroethane (DCE), ethanol (EtOH) and ethyl acetate were
purchased from Merck and distilled prior to use. All synthetic steps
were carried out under an argon atmosphere (except Knoevenagel
condensations). β-Alanine, N-bromosuccinimide (NBS), phosphoryl
chloride, sodium hydrogencarbonate and sodium sulfate were
purchased from Merck. Pd(PPh3)2Cl2 and Pd(PPh4)3 were purchased
from Acros. 2,5-dibromoselenophene,[28] 2,2′:5′,2′′-terselenophene 1,[5]
2,5-bis(trimethylstannyl)selenophene 3,[50] 2-((5-bromoselenophen-2-yl)-
methylene)malononitrile 4[28] and 2,2′-biselenophene-5-carbaldehyde 5[5]
were synthesized according to literature procedures.
[2,2′:5′,2′′-Terselenophene]-5,5′′-dicarbaldehyde (2): DMF (2.29 g,
31.3 mmol) was dissolved under argon in DCE (30 mL) and POCl3
(4.72 g, 30.8 mmol) was slowly added at 0 °C. The mixture was stirred
at r.t. for 2 h. It was added to a solution of 2,2′:5′,2″-terselenophene 1
(595 mg, 1.53 mmol) in DCE (30 mL) and the resulting red mixture was
4. Experimental Section
Instruments and Measurements: NMR spectra were recorded on a
Bruker AMX 500 (1H NMR: 500 MHz, 13C NMR: 125 MHz) or an Avance
400 spectrometer (1H NMR: 400 MHz, 13C NMR: 100 MHz) at 25 °C
unless otherwise noted. Chemical shift values (δ) are expressed in
parts per million using residual solvent protons (1H NMR, δH = 7.26 for
CDCl3, δH = 5.32 for CD2Cl2, δH = 5.92 for C2D2Cl4, δH = 2.50 for DMSO-
d6; 13C NMR, δC = 77.0 for CDCl3, δC = 53.84 for CD2Cl2) as internal
standard. The splitting patterns are designated as follows: s (singlet),
d (doublet), t (triplet), and m (multiplet). The assignments are Sel-H
(selenophene protons), -CHO (aldehyde protons), DCV-H (dicyanovinyl
protons). Melting points were determined using a Mettler Toledo DSC
823e and were not corrected. Elemental analyses were performed on
an Elementar Vario EL. Thin layer chromatography was carried out on
aluminum plates, pre-coated with silica gel, Merck Si60 F254. Preparative
column chromatography was performed on glass columns packed with
silica gel, Merck Silica 60, particle size 40–63 μm. EI mass spectra were
recorded on a Varian Saturn 2000 GC-MS and MALDI-TOF mass spectra
on a Bruker Daltonics Reflex III.
X-ray diffraction data of
a dark-red DCV4S single crystal were
collected in a stream of nitrogen at 100(2) K on a Bruker APEX-II CCD
area detector diffractometer using graphite-monochromated Mo Kα
radiation. Absorption correction based on a semi-empirical method was
performed with the SADABS algorithm.[47] The structure was solved by
direct methods with SHELXS-97,[48] revealing all atoms of the selenophene
backbone. Additional atoms were located from difference Fourier maps
during refinement on F2 with SHELXL-97.[48] In the structure, voids
in the asymmetric unit with a volume of ca. 97 Å3 are present. These
voids represent ca. 17% of the overall volume and are filled with heavily
disordered DCV4S molecules, clearly discernible from the smeared electron
density (maximum electron density within the voids 11.2 e−). It was not
possible to resolve this disorder satisfactorily. Therefore, all electron
density associated with peaks in these voids was eventually omitted by
applying the PLATON/SQUEEZE option.[49] For the final model, all non-H
atoms were refined anisotropically. H atoms were placed in calculated
positions riding the parent C atom with CϪH distance constraints of
0.95 Å, and with Uiso(H) = 1.2Ueq(C). DCV4S: C24H10N4Se5, Mr = 670.20,
dark-red lath, 0.65 × 0.24 × 0.10 mm3, monoclinic, P21/n, a = 3.9203(1) Å,
b = 27.6816(9) Å, c = 22.7887(7) Å, β = 93.181(2) °, V = 2469.22(13) Å3,
Z = 4, μ = 5.961 mm−1 , dx = 1.803 g·cm−3 , T = 100(2) K. 49820 reflections
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refluxed for 5 d. A sat. NaHCO3 solution (150 mL) was added and the
mixture was stirred for 1.5 h. It was extracted with DCM (5 × 200 mL).
The combined organic layers were dried over Na2SO4 and the solvent was
removed. The crude product was purified by column chromatography
(flash silica; monoaldehyde eluted with DCM, dialdehyde eluted with
DCM/ethyl acetate 8:2). The pure product 2 (426 mg, 0.957 mmol, 63%)
2-((5′-Bromo-2,2′-biselenophen-5-yl)methylene)malononitrile
(7):
5′-Bromo-2,2′-biselenophene-5-carbaldehyde 6 (1.40 g, 3.82 mmol),
malononitrile (763 mg, 11.5 mmol) and β-alanine (33 mg, 0.37 mmol)
were suspended in an ethanol/DCE mixture (1:1 v/v, 15 mL) and the
mixture was stirred at 80 °C for 2 h. The resulting red crystals were
filtered off, washed with methanol and dried in high vacuum to afford
1.51 g (3.63 mmol, 95%) of product 7. Mp. 208 °C; 1H NMR (400 MHz,
1
was obtained as an orange solid. Melting point (Mp.) 215 °C; H NMR
3
(400 MHz, CDCl3, δ): 9.76 (s with 77Se-satellites, JSe-H = 4.6 Hz, 2H,
3
CD2Cl2, δ): 7.87 (s, 1H, DCV-H), 7.77 (d, J = 4.3 Hz, 1H, Sel-H), 7.29-
3
7.26 (m, 3H, Sel-H); 13C NMR (100 MHz, CD2Cl2, δ): 156.74, 154.04,
144.93, 144.79, 138.84, 135.21, 130.51, 127.62, 119.92, 114.71, 114.41,
77.14; EIMS (m/z (%)): 418 (100, M), 337 (21, M-Br); Anal. calcd. for
C12H5BrN2Se2: C 34.73, H 1.21, N 6.75; found: C 34.89, H 1.31, N 6.80.
2,5-Bis(trimethylstannyl)selenophene (8): 2,5-Dibromoselenophene
(3.09 g, 10.7 mmol) was dissolved under argon in dry diethyl ether
(50 mL) and the solution was cooled to −78 °C. n-BuLi (1.6 M in
hexane, 14.0 mL, 22.3 mmol) was added dropwise within 10 min and
the mixture was stirred below −70 °C for 50 min. Trimethyltin chloride
(4.69 g, 23.5 mmol, dissolved in 5 mL diethyl ether) was added and
stirring was continued for 1.5 h. The mixture was poured into a sat.
NaHCO3 solution (80 mL) and extracted with diethyl ether (100 mL). The
combined organic layers were dried over Na2SO4 and the solvent was
removed to obtain 4.78 g of an off-white solid. The crude product was
washed with methanol to obtain 8 as white crystals (3.24 g, 7.09 mmol,
66%). 1H NMR (400 MHz, CDCl3, δ): 7.68 (s, 2H, Sel-H), 0.37 (s with
-CHO), 7.90 (d, J = 4.0 Hz, 2H, Sel-H-4,4’’), 7.40 (s, 2H, Sel-H-3′,4′),
7.38 (d, 3J = 4.0 Hz, 2H, Sel-H-3,3′′); 13C NMR (100 MHz, CDCl3, δ):
184.14, 153.60, 148.71, 145.20, 140.43, 130.37, 128.02; MS (MALDI-TOF,
m/z): [M+] = calcd. for C14H8O2Se3, 445.8; found 445.9; Anal. calcd. for
C14H8O2Se3: C 37.78, H 1.81; found: C 38.03, H 2.12.
2,2′-([2,2′:5′,2′′-Terselenophene]-5,5′′-diylbis(methanylylidene))-
dimalononitrile (DCV3S): [2,2′:5′,2′′-Terselenophene]-5,5′′-dicarbaldehyde
2 (392 mg. 0.881 mmol), malononitrile (400 mg, 6.05 mmol) and
β-alanine (10.8 mg, 0.121 mmol) were dissolved in a DCE/EtOH mixture
(75 mL, 2:1 v/v) and the mixture was refluxed for 43 h. The mixture was
cooled to r.t. and the solvent was reduced to half of its volume. The
resulting solid was filtered off and washed thoroughly with ethanol,
methanol and diethyl ether to obtain 390 mg of crude product. It was
recrystallized from chlorobenzene (80 mL) and the resulting blackish
crystals were filtered off, washed with ethanol and methanol and dried
in high vacuum. 343 mg (0.634 mmol, 72%) of pure product DCV3S
was obtained. Mp. 282 °C; 1H NMR (500 MHz, DMSO-d6, 360 K, δ):
2
Sn-satellites, JH-Sn = 56 Hz, 18 H, Sn-Me); 13C NMR (100 MHz, CDCl3,
3
4
δ): 150.16, 138.68, −7.79; EIMS (m/z (%)): 444 (100, [M-CH3]+); Anal.
calcd. for C10H10SeSn2: C 26.30, H 4.41; found: C 26.42, H 4.30.
2,2′-([2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′-Quinqueselenophene]-5,5′′′′-
diylbis(methanylylidene))-dimalononitrile (DCV5S): In a Schlenk tube,
8.55 (s, 2H, DCV-H), 8.11 (dd, J = 4.5 Hz, J = 0.5 Hz, 2H, Sel-H-4,4″),
7.78 (s, 2H, Sel-H-3′,4′), 7.68 (d, J = 4.5 Hz, 2H, Sel-H-3,3″); 13C NMR
3
(125 MHz, DMSO-d6, 360 K, δ): 154.28, 154.12, 144.54, 144.10, 138.55,
131.56, 128.21, 113.68, 113.41, 74.83; MS (MALDI-TOF, m/z): [M+]
calcd. for C20H8N4Se3, 543.8; found: 543.9; Anal. calcd. for C20H8N4Se3:
C 44.39, H 1.49, N 10.35; found: C 44.19, H 1.62, N 10.45.
2,5-bis(trimethylstannyl)selenophene
8
(201 mg, 0.440 mmol),
2-((5-bromo-2,2-biselenophen-5-yl)methylene)malononitrile 7 (384 mg,
0.925 mmol) and Pd(PPh3)4 (27 mg, 23.4 μmol, 5 mol%) were dissolved
in dry DMF (12 mL) and the solution was degassed. It was stirred at
80 °C for 20 h. The resulting solid was filtered off, washed with THF and
methanol and dried in high vacuum to obtain 317 mg of a green solid.
It was further purified by Soxhlet extraction with chlorobenzene for 4 d
to afford 260 mg (0.325 mmol, 74%) of DCV5S as a green solid. Mp.
324 °C; 1H NMR (500 MHz, C2D2Cl4, 340K, δ): 7.74 (s, 2H, DCV-H),
7.72 (d, 3J = 4.5 Hz, 2H, Sel-H), 7.42 (d, 3J = 4.0 Hz, 2H, Sel-H), 7.27 (d,
2,2′-([2,2′:5′,2′′:5′′,2′′′-Quaterselenophene]-5,5′′′-diyl-
bis(methanylylidene))dimalononitrile (DCV4S): In
a
Schlenk tube,
5,5′-bis(trimethylstannyl)-2,2′-biselenophene 3 (396 mg, 0.676 mmol)
and 2-((5-bromoselenophen-2-yl)methylene)malononitrile 4 (482 mg,
1.69 mmol) were dissolved in dry DMF (6 mL) and the solution was
degassed. Pd(PPh3)2Cl2 (23.5 mg, 33.5 μmol) was added, the solution
was degassed again and stirred at 80 °C for 3 d. The solution was cooled
to r.t. and the resulting solid was filtered off. It was washed with THF
and methanol and dried in high vacuum to obtain DCV4S as a green
solid (364 mg, 0.543 mmol, 80%). The compound was further purified
by Soxhlet extraction with chlorobenzene for 3 weeks. Mp. 358 °C; 1H
NMR (500 MHz, DMSO-d6, 360 K, δ): 8.54 (s, 2H, DCV-H), 8.11 (d, 3J =
4.5 Hz, 2H, Sel-H), 7.75 (d, 3J = 4.5 Hz, 2H, Sel-H), 7.64 (d, 3J = 4.5 Hz,
2H, Sel-H), 7.55 (d, 3J = 4.5 Hz, 2H, Sel-H); MS (MALDI-TOF, m/z): [M+]
calcd. for C24H10N4Se4: 671.8; found: 671.4; Anal. calcd. for C24H10N4Se4:
C 43.01, H 1.50, N 8.36; found: C 43.33, H 1.71, N 8.55.
3
3J = 4.0 Hz, 2H, Sel-H), 7.23 (s, 2H, Sel-H-3″,4″), 7.21 (d, J = 4.0 Hz,
2H, Sel-H); MS (MALDI-TOF, m/z): [M+] calcd. for C28H12N4Se5: 799.7;
found, 799.7). Anal. calcd. for C28H12N4Se5: C 42.08, H 1.51, N 7.01;
found: C 42.08, H 1.60, N 6.89.
Acknowledgements
5′-Bromo-2,2′-biselenophene-5-carbaldehyde (6): 2,2′-biselenophene-5-
carbaldehyde 5 (1.29 g, 4.47 mmol) was dissolved in DMF (10 mL) and
NBS (800 mg, 4.49 mmol) was dissolved in 5 mL DMF. The solutions
were put in the freezer for 3 h. They were mixed and put back in the
freezer for 3 d. The resulting crystals were filtered off and washed with
methanol to obtain orange crystals (780 mg). The filtrate was put in
the freezer over the weekend. The resulting precipitate was filtered off
and another 280 mg of a yellow solid were obtained. Water was added
to the filtrate and the mixture was extracted with DCM (3 × 25 mL).
The combined organic layers were washed with water (3 × 20 mL),
dried over Na2SO4 and the solvent was removed. The resulting solid
was washed with methanol and dried in high vacuum to afford 385 mg
of a yellow solid. All fractions contained pure product 6 and were
combined to obtain an overall yield of 1.45 g (3.94 mmol, 88%). Mp.
The authors would like to thank the German Ministry of Education and
Research (BMBF) for financial support in the frame of project OPEG 2010.
Received: April 11, 2012
Published online:
[1] S. S. Zade, N. Zamoshchik, M. Bendikov, Acc. Chem. Res. 2011, 44,
14.
[2] S. S. Zade, N. Zamoshchik, M. Bendikov, Chem. Eur. J. 2009, 15,
8613.
[3] S. S. Zade, M. Bendikov, Chem. Eur. J. 2008, 14, 6734.
[4] S. Millefiori, A. Alparone, Synth. Met. 1998, 95, 217.
[5] H. Nakanishi, S. Inoue, T. Otsubo, Mol. Cryst. Liq. Cryst. 1997, 296,
335.
[6] S. Inoue, H. Nakanishi, K. Takimiya, Y. Aso, T. Otsubo, Synth. Met.
1997, 84, 341.
1
3
153 °C; H NMR (400 MHz, CD2Cl2, δ): 9.71 (s, 1H, -CHO), 7.87 (d, J
3
3
= 4.0 Hz, 1H, Sel-H-4), 7.28 (d, J = 4.0 Hz, 1H, Sel-H-3), 7.23 (d, J
= 4.0 Hz, 1H, Sel-H-3’), 7.17 (d, J = 4.0 Hz, 1H, Sel-H-4’); 13C NMR
3
(100 MHz, CDCl3, δ): 183.88, 153.47, 147.85, 140.12, 134.10, 128.92,
127.23, 117.92; EIMS (m/z (%)): 368 (100, M), 339 (16, M-CHO), 260
(32, M-CHO-Br); Anal. calcd. for C9H5BrOSe2: C 29.46, H 1.37; found:
C 29.58, H 1.41.
[7] A. Patra, Y. H. Wijsboom, G. Leitus, M. Bendikov, Chem. Mater.
2011, 23, 896.
©
wileyonlinelibrary.com
Adv. Funct. Mater. 2012,
DOI: 10.1002/adfm.201201018
2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
11

www.afm-journal.de
www.MaterialsViews.com
[8] L. Li, J. Hollinger, A. A. Jahnke, S. Petrov, D. S. Seferos, Chem. Sci.
2011, 2, 2306.
[9] Y. H. Wijsboom, A. Patra, S. S. Zade, Y. Sheynin, M. Li,
L. J. W. Shimon, M. Bendikov, Angew. Chem. 2009, 121, 5551;
Angew. Chem. Int. Ed. 2009, 48, 5443.
[27] R. Fitzner, E. Reinold, A. Mishra, E. Mena-Osteritz, H. Ziehlke,
C. Körner, K. Leo, M. Riede, M. Weil, O. Tsaryova, A. Weiß, C. Uhrich,
M. Pfeiffer, P. Bäuerle, Adv. Funct. Mater. 2011, 21, 897.
[28] S. Haid, A. Mishra, C. Uhrich, M. Pfeiffer, P. Bäuerle, Chem. Mater.
2011, 23, 4435.
[10] M. Heeney, W. Zhang, D. J. Crouch, M. L. Chabinyc, S. Gordeyev,
R. Hamilton, S. J. Higgins, I. McCulloch, P. J. Skabara, D. Sparrowe,
S. Tierney, Chem. Commun. 2007, 5061.
[11] A. Patra, Y. H. Wijsboom, S. S. Zade, M. Li, Y. Sheynin, G. Leitus,
M. Bendikov, J. Am. Chem. Soc. 2008, 130, 6734.
[12] D. Bhattacharyya, K. K. Gleason, J. Mater. Chem. 2012, 22, 405.
[13] W.-H. Lee, S. K. Lee, S. K. Son, J.-E. Choi, W. S. Shin, K. Kim,
S.-H. Lee, S.-J. Moon, I.-N. Kang, J. Polym. Sci., Part A 2012, 50,
551.
[14] S. D. Oosterhout, M. M. Wienk, M. Al-Hashimi, M. Heeney,
R. A. J. Janssen, J. Phys. Chem. C 2011, 115, 18901.
[15] A. Maurano, C. G. Shuttle, R. Hamilton, A. M. Ballantyne, J. Nelson,
W. Zhang, M. Heeney, J. R. Durrant, J. Phys. Chem. C 2011, 115,
5947.
[29] A. Mishra, C. Uhrich, E. Reinold, M. Pfeiffer, P. Bäuerle, Adv. Energy
Mater. 2011, 1, 265.
[30] S. Steinberger, A. Mishra, E. Reinold, J. Levichkov, C. Uhrich,
M. Pfeiffer, P. Bäuerle, Chem. Commun. 2011, 47, 1982.
[31] S. Steinberger, A. Mishra, E. Reinold, C. M. Müller, C. Uhrich,
M. Pfeiffer, P. Bäuerle, Org. Lett. 2010, 13, 90.
[32] D. Wynands, B. Männig, M. Riede, K. Leo, E. Brier, E. Reinold,
P. Bäuerle, J. Appl. Phys. 2009, 106, 054509.
[33] K. Schulze, M. Riede, E. Brier, E. Reinold, P. Bäuerle, K. Leo, J. Appl.
Phys. 2008, 104, 074511.
[34] K. Schulze, C. Uhrich, R. Schüppel, K. Leo, M. Pfeiffer, E. Brier,
E. Reinold, P. Bäuerle, Adv. Mater. 2006, 18, 2872.
[35] C. Uhrich, R. Schüppel, A. Petrich, M. Pfeiffer, K. Leo, E. Brier,
P. Kilickiran, P. Bäuerle, Adv. Funct. Mater. 2007, 17, 2991.
[36] H. Kong, D. S. Chung, I.-N. Kang, J.-H. Park, M.-J. Park, I. H. Jung,
C. E. Park, H.-K. Shim, J. Mater. Chem. 2009, 19, 3490.
[37] C. M. Cardona, W. Li, A. E. Kaifer, D. Stockdale, G. C. Bazan, Adv.
Mater. 2011, 23, 2367.
[16] M. I. Ozkut, S. Atak, A. M. Onal, A. Cihaner, J. Mater. Chem. 2011,
21, 5268.
[17] D. S. Chung, H. Kong, W. M. Yun, H. Cha, H.-K. Shim, Y.-H. Kim,
C. E. Park, Org. Electron. 2010, 11, 899.
[18] H. A. Saadeh, L. Lu, F. He, J. E. Bullock, W. Wang, B. Carsten, L. Yu,
ACS Macro Lett. 2012, 1, 361.
[38] D. R. Lide, CRC Handbook of Chemistry and Physics, 84 ed., Boca
Raton, FL 2003.
[19] A. M. Ballantyne, L. Chen, J. Nelson, D. D. C. Bradley, Y. Astuti,
A. Maurano, C. G. Shuttle, J. R. Durrant, M. Heeney, W. Duffy,
I. McCulloch, Adv. Mater. 2007, 19, 4544.
[39] H. O. Villar, P. Otto, M. Dupuis, J. Ladik, Synth. Met. 1993, 59, 97.
[40] Q. Xie, F. Arias, L. Echegoyen, J. Am. Chem. Soc. 1993, 115,
9818.
[20] R. Yang, R. Tian, J. Yan, Y. Zhang, J. Yang, Q. Hou, W. Yang, C. Zhang,
Y. Cao, Macromolecules 2004, 38, 244.
[41] J. Schatz, Science of Synthesis, Vol. 9, Thieme Verlag, Stuttgart 2000,
p. 287.
[21] F. Gao, Y. Cheng, Q. Yu, S. Liu, D. Shi, Y. Li, P. Wang, Inorg. Chem.
2009, 48, 2664.
[42] J. Schatz, Science of Synthesis, Vol. 9, Thieme Verlag, Stuttgart 2000,
p. 423.
[22] R. Li, X. Lv, D. Shi, D. Zhou, Y. Cheng, G. Zhang, P. Wang, J. Phys.
Chem. C 2009, 113, 7469.
[23] K. A. Mazzio, M. Yuan, K. Okamoto, C. K. Luscombe, ACS Appl.
Mater. Interfaces 2011, 3, 271.
[24] A. Mishra, P. Bäuerle, Angew. Chem. Int. Ed. 2012, 51, 2020; Angew.
Chem. 2012, 124, 2060.
[25] S. Steinberger, A. Mishra, E. Reinold, E. Mena-Osteritz, H. Müller,
C. Uhrich, M. Pfeiffer, P. Bäuerle, J. Mater. Chem. 2012, 22,
2701.
[43] A. Bondi, J. Phys. Chem. 1964, 68, 441.
[44] H. Nakanishi, S. Inoue, Y. Aso, T. Otsubo, Synth. Met. 1999, 101, 639.
[45] D. Cheyns, J. Poortmans, P. Heremans, C. Deibel, S. Verlaak,
B. P. Rand, J. Genoe, Phys. Rev. B 2008, 77, 165332.
[46] C. Uhrich, D. Wynands, S. Olthof, M. K. Riede, K. Leo, S. Sonntag,
B. Männig, M. Pfeiffer, J. Appl. Phys. 2008, 104, 043107.
[47] G. M. Sheldrick, SADABS. University of Göttingen, Germany 2008.
[48] G. M. Sheldrick, Acta Cryst. A 2008, 64, 112.
[49] A. L. Spek, Acta Cryst. D 2009, 65, 148.
[26] R. Fitzner, C. Elschner, M. Weil, C. Uhrich, C. Körner, M. Riede,
K. Leo, M. Pfeiffer, E. Reinold, E. Mena-Osteritz, P. Bäuerle, Adv.
Mater. 2012, 24, 675.
[50] D. J. Crouch, P. J. Skabara, M. Heeney, I. McCulloch, D. Sparrowe,
S. J. Coles, M. B. Hursthouse, Macromol. Rapid Commun. 2008, 29,
1839.
©
12 wileyonlinelibrary.com
2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2012,
DOI: 10.1002/adfm.201201018