Toward Sustainable Organic Semiconductors from a Broad Palette of Green Reactions

Article abstract of DOI:10.1002/ejoc.201700317

New conjugated materials, based on the triphenylamine-thiophene moiety and integrating azomethine bonds with a dibenzofuran unit or a cyanovinyl bond with a phenylthiophene or bithiophene unit, have been synthesized by using a wide range of green reaction

Full text of DOI:10.1002/ejoc.201700317

A Journal of
Accepted Article
Title: Toward sustainable organic semiconductors from a broad palette
of green reactions
Authors: Alexandre Faurie, Jérémie Grolleau, Frédéric Gohier, Magali
Allain, Stéphanie Legoupy, and Pierre Frère
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201700317
Link to VoR: http://dx.doi.org/10.1002/ejoc.201700317
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10.1002/ejoc.201700317
European Journal of Organic Chemistry
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Toward sustainable organic semiconductors from a broad palette
of green reactions
Alexandre Faurie,[a] Jérémie Grolleau,[a] Frédéric Gohier,[a] Magali Allain,[a] Stéphanie Legoupy*[a] and
Pierre Frère*[a]
Abstract: New conjugated materials, based on triphenylamine-
thiophene moiety and integrating azomethine bonds with
dibenzofuran unit or cyanovinyl bond with phenyl-thiophene and
bithiophene units, have been synthesized by using a wide range of
green reactions such as direct heteroarylation coupling reaction,
Knoevenagel and Schiff base condensations and Stille cross coupling
reaction from ionic liquid supported thiophenstannane. The electronic
properties of the new molecules were analyzed by using UV/Vis
spectroscopy and cyclic voltammetry. The potential use of the
molecules as donor materials for photovoltaic conversion were
evaluated in simple bilayer solar cells by using C60 fullerene as
acceptor material.
Schiff base chemistry allowing to develop ethylenic or imine
bonds,[5] (ii) direct C-H arylation reactions for the extension of
heterocycle systems by avoiding organometallic coupling
reactions.[6] However, to merit the sustainable appellation, the
green synthetic procedures must involve all the synthetic steps
and do not have to limit to the last step. Moreover, basic concepts
must be respected, as the non-use of chlorinated solvents or the
non-formation of by-products, especially if toxic, needing
laborious purifications using large amounts of solvent.
As a further step in our contribution on the synthesis of organic
semiconductors via green approaches,[7] we have explored the
synthesis of new conjugated materials by exploiting a wide range
of various green reactions. Within the class of conjugated
materials, the donor-acceptor (D/A) approach with electron-
donating (D) and electron acceptor (A) blocks in the conjugated
backbone is currently one of the most widely investigated
materials for the development of electronic plastics.[8] Thus we
have focused on the synthesis of D/A molecules I and IIa,b
including the triphenylamine (TPA) -thiophene moiety for the
donor block (Figure 1). For molecule I, the central acceptor part is
constituted by an imino-pentafluorobenzodifuran moiety, while for
unsymmetrical compounds IIa,b the acceptor block corresponds
to a cyanovinyl unit. The electronic properties of the new
derivatives and the results of prototype of bilayer solar cells
performed with I and IIa,b as donor and C60 as acceptor materials
are also presented.
Introduction
Extended conjugated systems are the focus of extensive
researches motivated by their potentials as organic
semiconductor materials used for the development of large area,
lightweight and flexible optoelectronic devices such as organic
field-effect transistors (OFET), organic electroluminescent diodes
(OLED) and organic photovoltaic cells (OPC).[1] Currently in the
field of organic photovoltaics, a large part of the works focuses on
the design of new conjugated materials for increasing the
performances of the devices,[2] thus leading to more complex
extended molecular structures, polymers or small molecules.[3]
The conception of most conjugated materials induces long
synthetic routes and the formation of more and more wastes,
making difficult to claim the green and low cost criteria for the
synthesis of organic-semiconductors. For three years, several
reviews emphasized the importance of integrating the green
chemistry concepts to the conception of organic semiconductor
materials.[4] It has evidenced that cleaner and cheaper routes
toward conjugated systems can be achieved by handling: (i)
green condensation reactions such as Knœvenagel reactions or
[a]
Dr A. Faurie§, Dr J. Grolleau§, Dr F. Gohier, M. Allain, Dr S. Legoupy
and Prof. P. Frère
MOLTECH-Anjou
Université d’Angers
Figure 1. Structures of new conjugated systems I and II based on TPA moiety.
2 Boulevard Lavoisier, 49045 Angers cedex, France
E-mail: stepahnie.legoupy@univ-angers.fr, pierre.frere@univ-
angers.fr
[§]
These authors contributed equally to this work
Results and Discussion
Supporting information, including the electrical characteristic of the
solar cells (Figure S1) and NMR spectra of compounds I, IIa,b, is
given via a link at the end of the document.
The eco-friendly synthetic pathways for preparing I and IIa,b,
presented in Scheme 1, are based for the first step on the
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10.1002/ejoc.201700317
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synthesis of aldehyde of the TPA-thiophene unit 1, easily and
rapidly obtained via a direct heteroarylation coupling reaction. The
last steps correspond to condensation reactions with
diaminobenzodifurane 2 or thiophene-aryl-acetonitrile 3.
aldehyde 1. We have sought to simplify the procedure by using a
heterogeneous catalyst such as Pd(OH)2/C (Pearlman’s
catalyst).[7b, 13] Thus by using stoichiometric amount of thiophene
carbaldehyde and TPA-Br, potassium acetate (3 equiv.) and
Scheme 1. Synthetic pathways of I and IIa,b .
palladium hydroxide on carbon (3% mol. in Pd(OH)2) in
dimethylacetamide (DMA) at 150 °C, the compound 1 was
isolated in 60 % yield after simple filtration on a small plug of silica
gel. Between the two methods, on the one hand the use of
homogeneous catalysis allows to less heating for obtaining 1 in a
slight better yield, on the other hand with the Pearlman's catalyst
there is no need to use the expensive phosphine derivative and
the purification is easier allowing to handle less solvent.
The first titled compound I has been obtained by a double
condensation between the diaminobenzodifurane 2 and 2 equiv.
of aldehyde 1 performed at room temperature in ethyl lactate as
green solvent with acid catalysis (trifluroacetic acid 5% mol.).[7a]
Addition of water in the mixture favors the precipitation, then the
filtered solid is washed three times with ethanol to give I as a red
solid in 70 % yield. As already described, the diamino compound
2 is rapidly obtained in one step by a double Michael addition
between benzoquinone and 2 equiv. of pentafluoroacetonitrile in
the presence of aqueous ammoniac solution in ethanol.[14]
These last derivatives are obtained in one step by green
reactions; double Michael addition for 2 and Stille cross coupling
with ionic liquid supported organotin reagents.
Since the first demonstration of direct arylation of thiophene with
aryl-halide by Ohta and coworkers in 1990,[9] this methodology is
more and more used for the development of extended conjugated
materials based on thiophene moiety for optoelectronic
applications. In 2011, Fagnou et al. demonstrated that TPA-
Thiophene carbaldehyde 1 could be synthesized by direct
arylation route from 2-formyl thiophene[10] instead of Stille[11] or
Suzuki[12] reactions. The direct coupling proceeded in 72 % yield
by heating at 100°C in toluene for 16h a stoichiometric mixture of
Br-TPA and thiophene carboxaldehyde in presence of phosphine
derivative PCy3.HBF4 (10 - 12 mol %), pivalic acid (30 mol %),
K2CO3 (3 equiv.) and Pd(OAc)2 (6 mol %).[7c] Without phosphine
in the same conditions, the yield fell to less of 5%. A column
chromatography on silica gel was necessary to purify the
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10.1002/ejoc.201700317
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Single crystal of I, obtained by slow evaporation of chloroform
solution, has been analyzed by X-ray diffraction. The latter
crystallizes in the triclinic P-1 space group. The phenyl of the TPA
connected to the thiophene and the azomethine junction in a E
configuration are in the plane defined by the benzodifuran
systems (Figure 2). Each lateral pentafluorophenyl cycle
assumes a torsional angle of 54° with respect to the benzodifuran
plane. The molecules stack along the b axe such as the central
benzodifurane moiety of a molecule overlaps the iminothiophene
part of the molecules above and below. The distance between two
consecutive planes formed by BDF units is of 3.80 Å.
supported thiophenstannane on brominated acetonitrile
derivatives 4a,b have been tested without solvent in presence of
Pd(OAc)2 as precatalyst. After 18h heating at 80°C, the target
coupling products 3a,b were obtained by extraction with diethyl
ether in 45 % and 50 % yields respectively. The reaction has also
been performed by using toluene as solvent at 80 °C. After 18h
stirring the solvent was removed and the coupling products 3a,b
were isolated in 50 and 53 % yields respectively, by simple
extraction with diethyl ether.
The Knoevenagel condensations between aldehyde 1 and the
acetonitrile derivatives 3a,b were performed in ethanol as solvent
in presence of a catalytic amount of tBuONa. After 18h stirring at
room temperature, the precipitate was filtered then washed with
ethanol to give the pure target molecules IIa and IIb as red solids
in 70 and 80 % yields respectively.
The electronic properties of the titled molecules have been
evaluated by theoretical calculations and analysed by UV-Vis
spectroscopy and cyclic voltammetry. Theoretical and
experimental data are gathered in Table 1.
Theoretical calculations were performed at the ab initio density
functional level with the gaussian09 package by using Becke’s
three parameter gradient corrected functional (B3LYP) with a
polarized 6.31G(d,p) for the HOMO and LUMO determinations.
The optimized structures and the contours of the orbitals for the
HOMO and LUMO levels are presented in Figure 3.
Figure 2. X-ray structure of I
The syntheses of the acetonitrile derivatives 3a,b from bromo-
arylacetonitrile 4a,b have been already reported, either by direct
arylation coupling with an excess of thiophene (3a in 62% yield)[15]
or by Suzuki reaction with the thiophene boronic acid derivative
(3b in 38% yield).[16] In this work, we have explored the use of
thiophenstannane supported on ionic liquid[17] in Stille cross-
coupling reaction as a new method for synthesizing 3a,b. The
Stille reaction is extensively used for the synthesis of conjugated
materials[18] due to many advantages of the organostannanes
compared to other organometallics such as their readily
syntheses, their water- and air-stability and their tolerance
towards many functional groups. Moreover, the Stille reaction
requires mild reaction conditions without additive of expensive
ligand to give high yields.[19] However, organic tin chemistry
presents disadvantages such as pollution of obtained conjugated
materials by tin salts and difficulties of separation. Efforts have
been made to overcome these problems, leading, for example, to
the development of synthetic methods using organotin reagents
supported [20] on polymers [21] or ionic liquids.[22] On the other hand,
it has been shown that Stille cross-coupling reactions with
organotin reagents supported on ionic liquid could be performed
without solvent or additive by using commercially available
catalysts.[22-23] The cross-coupling products were obtained by
using simple purification techniques and the contamination by tin
wastes was limited. Organotin compound was recycled five times
with good yield and reused in Stille cross-coupling reactions
without loss of reactivity. The Stille reaction with ionic liquid
Figure 3. Calculated HOMOs and LUMOs (B3LYP/6-31G(d,p). and energy
levels for the compounds I and IIa,b.
The optimized structure of I is very close to that obtained from X-
ray, ie good planarity of the conjugated system including the
benzodifurane moiety and the two imino-thiophene units while the
lateral pentafluorophenyl cycles have a torsional angle of 49° with
the benzodifurane plane. The HOMO is allocated on the TPA units
and on all the conjugated system. The LUMO is delocalized on
the benzodithiophene and the two thiophene-imino units. For the
two compounds IIa,b, the structures are almost identical and, they
present planar structures of the conjugated backbones and a
torsion of the outermost phenyl units of TPA. The HOMOs are
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10.1002/ejoc.201700317
European Journal of Organic Chemistry
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allocated on the TPA – thiophene units and extended to the
phenyl or thienyl cyanovinyl units. The LUMOs are mainly
delocalized on the central part of the molecules including
thiophene-cyanovinyl-thiophene or phenyl units. Compound I with
the longer extended system presents the lowest band gap E =
2.32 eV. Between IIa and IIb, the replacement of the external
phenyl-thiophene in IIa by a bithiophene in IIb unit allows both to
destabilize the HOMO and stabilize the LUMO leading to a
reduction of the band gap of 2.72 to 2.54 eV.
Cyclic voltammetry (CV) was performed in methylene chloride in
the presence of 0.1 M tetrabutylammonium hexafluorophosphate
as supporting electrolyte. The CV of I (Figure 5 top) presents two
oxidation waves with anodic peaks Eox1 and Eox2 at 0.84 and 1.20
V respectively. The analysis of the oxidation processes shows
that the difference between the anodic and the cathodic peaks
(Ep = Eaox1 – Ecox1) of the reversible oxidation waves is 40 mV
for the first oxidation process and 70 mV for the second.
Considering the theoretical 60 mV expected for a mono-electronic
process, we can stipulate for the first oxidation wave, a bi-
electronic process giving directly a dication I++,[24] followed by
another one-electron oxidation in I+3.. The large extended
conjugated structure of compound I favours the access to
Table 1. Theoretical band gap, experimental absorption data and cyclic
voltammetry data of compounds I and IIa,b.
[a]
[b]
[c]
[d]
[d]
[d]
[e]
ETheo
Cpds
max
Eopt
eV
Eox1
V
Eox2
V
Ered
V
EElec
eV
polycationic state. In reduction compound
irreversible peak at Ered = -1.30 V.
I presents an
nm
eV
I
2.32
2.72
2.54
303
536
1.90
2.38
2.25
0.84
1.06
0.97
1.26
1.24
1.05
-1.20
-1.28
-1.22
2.04
2.34
2.19
IIa
IIb
301
431
304
451
[a] B3LYP/6-31G(d,p). [b] 2 10-5 M in CH2Cl2 [c] Optical band gap calculated from
the edge of the absorption band. [d]10-3 M in 0.1 M Bu4NPF6/CH2Cl2, scan rate
100 mV s-1, Pt working electrode, ref. SCE. [e] Electrochemical band gap EElect
= Eox1 – Ered.
The UV-vis absorption spectra of I and IIa,b in CH2Cl2 exhibit two
distinct absorption bands (Figure 4). The high-energy band with a
maximum around 300 nm could be assigned to the specific
transition involving TPA. The second band around 430-450 nm for
IIa,b and at 534 nm for I corresponds to the classical *. The
smallest band gap calculated from the foot of the absorption band
is 1.90 eV for the more extended compound I. Between
compounds IIa,b, the red shift observed for IIb corresponds to a
better electronic delocalization through thiophene cycle, less
aromatic than the phenyl.
Figure 5. CVs of I (top) and IIa (bottom) 10-3 mol L-1 in 0.1 M Bu4NPF6 in CH2Cl2,
v = 100 mV s-1
For the less extended compounds IIa,b, the two one-electron
oxidation processes (Figure 5 bottom for IIa) correspond to the
formation of radical cation II+. and dication II++. Compared to I, the
Figure 4. UV-Vis absorption spectra of compounds I and IIa,b in CH2Cl2.
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10.1002/ejoc.201700317
European Journal of Organic Chemistry
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values of the first oxidation potentials Eox1 are positively shifted at
1.06 V and 0.90 V for IIa and IIb respectively indicating a
stabilization of the HOMO level, thus confirming the theoretical
calculations. Between IIa and IIb, the replacement of phenyl by
thienyl cycle leads to a slight cathodic shift of 160 mV for IIb
indicating a better electronic delocalization. Both IIa,b show
irreversible reduction peaks at -1.28 and -1.22 V respectively.
the compound I. The cell based on IIa presents a first peak at 355
nm following by a broad band extending up to 580 nm with the
highest contribution for the photocurrent at 420 nm corresponding
to the absorption of IIa.
The potentialities of these molecules as donor materials in
photovoltaic devices have been evaluated in basic bilayer planar
heterojunction solar cells (PHJ) by using C60 as acceptor
materials. The cells of 0.28 cm2 area were fabricated using the
classical procedure. The electrical characteristic of the solar cells
under AM 1.5-stimulated solar irradiation at 80 mW cm−2 are
gathered in Table 2 and Figure S1 (in supporting information)
presents the plots of current density versus voltage of PHJ cells
based on I and IIa.
Table 2. Photovoltaic characteristics of PHJ cells based on donors I and IIa,b
under 1.5 simulated solar illumination at 80 mW cm-2.
[a]
Entry
Cpd
T annealed
°C
Voc
V
JSC
mA cm-2
FF
PCE
%
1
2
3
4
5
I
0.84
0.77
0.72
0.68
0.58
4.13
4.36
2.85
4.69
3.17
0.40
0.35
0.44
0.48
0.30
1.73
1.56
1.11
1.92
0.46
Figure 6. External quantum efficiency (EQE) of the cells produced with donors
I (solid line) and IIa (dashed line).
I
100
130
IIa
IIa
IIb
Conclusions
Two series of conjugated small molecules have been synthesized
by exploiting various green reactions. The coupling reactions of
heterocycles have been carried out by seeking either to limit the
formation or to suppress the diffusion of metallic by-products. For
the first case, direct heteroarylation coupling reaction has been
realized between TPA and thiophene carbaldehyde using an
extremely simple procedure with heterogeneous [Pd] catalysis.
For the second case, Stille cross coupling were performed from
thiophenstannane supported on ionic liquid, not generating small
brominated stannyl byproducts. The synthetic procedures were
realized without solvent or in presence of small amount of toluene
while the target compounds were purified by a simple extraction
with diethyl ether. All the other reactions, Michael addition,
Knoevenagel and Schiff base condensations giving only water as
by-products were carried out at room temperature and in green
solvents such as ethanol or ethyl lactate. Moreover, one the main
interest of this approach resides in the ease and rapidity of
obtaining the target molecules. The study of the electronic
properties shows that these small molecules, based on TPA-
thiophene moieties and integrating azomethine bonds with
dibenzofuran unit or cyanovinyl bond with phenyl-thiophene and
bithiophene units, present optical properties and energy levels
adapted to be used as donor materials for photovoltaic conversion.
The compatibility of the new small molecules for the OPV has
been shown with the first attempts in simple bilayer solar cells by
using C60 as acceptor materials leading to performances reaching
up to 2% of PCE.
[a] After 5 min annealing.
For compound I, the cells before annealing (entry 1) present a
photovoltaic effect with an open circuit voltage (Voc) of ca 0.84 V,
a short-circuit current density (JSC) of 4.13 mA.cm-2 and a fill factor
(FF) of 0.36, resulting in an average PCE of 1.73 %. Tests of
annealing at different temperatures (example at 100 °C, entry 2)
showed decreased performances of the cells due to
a
concomitant decrease of Voc and FF. After prolonged annealing,
a significant deterioration of the films was observed. For
compounds IIa,b, high difference in the photovoltaic effects were
obtained. Cells built with IIb (entry 5) presented small PCE of
0.46 % with a small fill factor of 0.30 and the smaller Voc of 0.58V.
A rapid deterioration of the cells was observed during the tests of
annealing. By using IIa as donor material, the PCE raised to
1.11 % (entry 3) with a Voc of 0.72 V and a FF of 0.44. For this
material, annealing at 130 °C during 5 min allowed to enhance the
performance to reach a PCE of 1.92 % due to a large enhancing
of the current density that increased from a value of 2.84 to 4.69
mA cm-2. The external quantum efficiency (EQE) spectra for the
best cells built with I and IIa were recorded under monochromatic
irradiation (Figure 6). For the cell based on I, the spectrum shows
a broad wave extending from 350 to 650 nm with a maximum at
390 nm, probably corresponding in part to the contribution of C60
to the photocurrent, followed by a shoulder around 600 nm due to
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Compound 3b
Experimental Section
M.p. 62 °C; 1H NMR (300 MHz, CDCl3, TMS):  [ppm] = 7.24 (dd, 1H, J =
5.1 Hz, J=1.0 Hz); 7.13 (dd, 1H J=3.6 Hz, J=1.0 Hz), 7.03 -7.01 (m, 2H);
6.97-6.96 (m, 1H); 3.89 (d, 2H, J=1.0 Hz); 13C NMR (75 MHz, CDCl3,
TMS):  [ppm] =138.1, 136.4, 129.5, 127.8, 127.7, 124.9, 124.1, 123.5,
116.6, 18.7; HRMS – CI : Calculated for C10H7NS2 205.0020; found
205.0017.
Synthesis
Preparation of 1 by Direct C-H heteroarylation with heterogeneous
catalysis
To a solution of 4-bromo-N,N-diphenylaniline (300 mg, 0.91 mmol),
potassium acetate (277 mg, 2.82 mmol, 3.1 eq), palladium hydroxide on
carbon (20 wt. % loading) (71 mg, 10% mol) in dimethylacetamide (6 ml)
General procedure for preparation of IIa and IIb by Knoevenagel reaction
To a solution of aldehyde 1 (100 mg, 0.28 mmol) and acetonitrile derivative
3a (56 mg, 0.28 mmol) or 3b (58 mg, 0.28 mmol) in 10 mL of EtOH was
added a catalytic amount of sodium tert-butoxide. After night stirring at RT,
the crude was filtered and triturated with cold EtOH to give red powders.
degassed
with
argon
during
20
min
was
added
2-
thiophenecarboxaldehyde (85 µL, 0.91 mmol). The mixture was stirred at
150°C during 16h, cooled and poured into water (50 mL). The organic layer
was extracted with ethyl acetate (30 mL), dried over anhydrous MgSO4
and solvent was removed. The residue was purified by
chromatography over 2cm silica gel (Hexane/AcOEt: 60/40) to afford a
yellow solid (195 mg, yield: 60%).
a flash
Compound IIa. Yield 70 %.
M.P. 187 °C; 1H (300 MHz, CDCl3, TMS):  [ppm] =7.66 – 7.50 (m, 7H),
7.38 – 7.25 (m, 7H), 7.15-7.05 (m, 10 H); 13C NMR (75 MHz, CDCl3, TMS):
 [ppm] = 149.4, 148.5, 147.2, 143.4, 136.2, 134.7,134,4, 133.8, 133.1,
129.9, 129.4, 128.3, 127.0, 126.9, 126.4, 126.0,125.5, 125.0, 123.7, 123.6,
122.9, 122.7, 106.2; HRMS (FAB) calcd for C35H24N2S2 [M+]: 536.1375,
found: 536.1375.
m.p. 88-90 °C; 1H NMR (300 MHz, CDCl3, TMS):  [ppm] = 9.85 (s, 1H);
7.71 (d, 1H, J=4.0Hz); 7.52 (d, 2H, J=8.8Hz); 7.34-7.26 (m, 5H); 7.17-7.04
(m, 8H); 13C NMR (75 MHz, CDCl3, TMS):  [ppm] = 182.8, 154.8, 149.4,
147.2, 141.6, 137.9, 129.7, 127.5, 126.4, 125.4, 124.1, 123.1, 122.6;
HRMS (FAB) calcd for C23H17NOS [M+]: 355.1031, found: 355.1028
Compound IIb. Yield 80 %.
M.p.: 210 °C; 1H (300 MHz, CDCl3, TMS):  [ppm] = 7.54 – 7.05 (m, 22 H).
13C NMR (75 MHz, CDCl3, TMS):  [ppm] = 149.4, 148.5, 147.2, 137.8,
137.6, 136.7, 135.9, 134.1, 130.1, 131.6, 129.5, 128.1, 127.4, 127.0, 125.3,
125.0, 124.4, 124.3, 123.6, 122.9, 122.8, 122.6, 101.4; HRMS (FAB) calcd
for C33H22N2S3 [M+]: found: 542.0945.
Preparation of I by Schiff base condensation
To a solution of 1 (220 mg,0.62 mmol) in ethyl lactate (8 ml) stirred at room
temperature was added diaminobenzofuran (150 mg, 0.29 mmol) and a
catalytic amount of trifluoroacetic acid (0.1 ml). After a night at RT, water
(20 ml) was added and the precipitate was filtered and triturated with
methanol to give a red solid (240 mg, yield 70%).
Structure Refinement and crystal data for I
m.p. > 260 °C;1H (300 MHz, C2D2Cl4, TMS):  [ppm] = 8.96 (s, 1H); 7.57 –
7.52 (m, 6H); 7.44 (s,2H); 7.34-7.29 (m, 10H), 7.17-7.05 (m, 16H); 19F
(CDCl3): -137.0 (dd, 4F, J=21.8 Hz, J = 7.0 Hz); -154.6 (t, 2F, J=21 Hz), -
162.2 (td, 4F, J = 21.8 Hz, J= 7.0 Hz); HRMS (MALDI-TOF) calcd for
C66H36N4O2S2 [M+]: 1194.2120, found: 1194.2112.
Single crystals of I suitable for X-ray diffraction analysis were obtained by
slow evaporation of a mixture of chlorobenzene - chloroform solution. The
compound crystallizes in the triclinic P-1 space group. X-ray single-crystal
diffraction data were collected at 150K on an Agilent SuperNova
diffractometer equipped with Atlas CCD detector and mirror
monochromated micro-focus Cu-Kα radiation (λ = 1.54184 Å). The
structure was solved by direct methods and refined on F2 by full matrix
least-squares techniques using SHELX97 programs (G.M. Sheldrick,
1998). All non-H atoms were refined anisotropically and multiscan
empirical absorption was corrected using CrysAlisPro program
(CrysAlisPro, Agilent Technologies, V1.171.37.35g, 2014). The H atoms
were included in the calculation without refinement.
General procedure for the Stille coupling with ionic liquid supported
organotin reagents
1-(6-(Dibutyl(thiophen-2-yl)stannyl)hexyl)-3-ethyl-1H-imidazol-3-ium
bromide has been prepared as already described.[17]
Under inert atmosphere, a mixture of ionic liquid (1 equiv.), aryl bromide
(1equiv.) and palladium acetate (0.05 equiv.) without toluene or with 5 mL
of toluene was heated at 80 °C or 110 °C during 17h. The mixture was
cooled, the co-solvent was evaporated in vacuo then the residue was
treated with diethyl ether to extract the compound and the crude product
was purified via flash chromatography over 2cm silica gel (Hexane/AcOEt:
60/40).
C68H36F10N4O2S2, M = 1195.13, brown needle, 0.31 × 0.09 × 0.03 mm3,
triclinic, space group P-1, a = 7.6536(11) Å, b = 12.286(3) Å, c =15.052(2)
Å, α = 82.317(15)°, β = 79.867(12)°, γ = 79.896(15)°, V =1364.0(4) Å3, Z
=1, ρcalc =1.455 g/cm3, μ(Cu Kα) = 1.639 mm−1, F(000) = 610, θmin = 3.00°,
θmax = 73.11°, 9759 reflections collected, 5184 unique (Rint = 0.0951),
parameters/restraints = 388/0, R1 = 0.0825 and wR2 = 0.1885 using 3047
reflections with I > 2σ(I), R1 = 0.1335 and wR2 = 0.2157 using all data,
GOF = 0.999, −0.602 < Δρ < 0.457 e.Å−3. CCDC- 1530104
Compound 3a
M.p. 102 °C; 1H NMR (300 MHz, CDCl3, TMS):  [ppm] = 7.63 (d, 2H, J =
8.2 Hz); 7.35-7.30 (m, 4H); 7.10 (dd, 1H J= 5.0 Hz, J=3.7 Hz), 3.77 (s, 2H);
13C NMR (75 MHz, CDCl3, TMS):  [ppm] =143.3, 134.4, 128.9, 128.5,
128.2, 126.6, 125.3, 123.6, 117.7, 23.4; HRMS – CI : Calculated for
C12H9NS 199.0456; found 199.0451.
Preparation of the solar cells
Indium-tin oxide coated glass slides of 24×25×1.1 mm with a sheet
resistance of RS = 10 Ω/sq were purchased from VisionTek Systems Ltd.
The substrates were scrubbed using dishwashing soap before being
cleaned by a series of ultrasonic treatments for 15 min in distilled water,
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10.1002/ejoc.201700317
European Journal of Organic Chemistry
FULL PAPER
acetone, and isopropanol. Once dried under a steam of nitrogen, a UV-
ozone plasma treatment (UV/Ozone ProCleaner Plus, Bioforce
Nanosciences) was performed for 15 min. A filtered aqueous solution of
poly(3,4-ethylenedioxy-thiophene)-poly(styrenesulfonate) (PEDOT:PSS;
Clevios P VP. AI 4083) through a 0.45 μm RC membrane (Millex®) was
spun-cast onto the patterned ITO surface at 5000 rpm for 40 s before being
baked at 115°C for 15 min. The films of donor materials I, IIa or IIb were
spun-cast from 2-methyltetrahydrofurane[25] solutions containing 8 mg/mL
of material then the cells were completed by the successive thermal
deposition of C60 (30 nm) and aluminum (80 nm) at a pressure of 10-6 Torr
through a shadow mask defining two cells of 27 mm2 each. J vs V curves
were recorded in the dark and under illumination using a Keithley 236
source-measure unit and a home-made acquisition program. The light
source is an AM1.5 Solar Constant 575 PV simulator (Steuernagel
Lichttecknik, equipped with a metal halogen lamp). The light intensity was
measured by a broad-band power meter (13PEM001, Melles Griot). EQE
was recorded under ambient atmosphere using a halogen lamp (Osram)
with an Action Spectra Pro 150 monochromator, a lock-in amplifier (Perkin-
Elmer 7225) and a S2281 photodiode (Hamamatsu).
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10.1002/ejoc.201700317
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Entry for the Table of Contents (Please choose one layout)
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Alexandre Faurie, Jérémie Grolleau,
Frédéric Gohier, Magali Allain,
Stéphanie Legoupy* and Pierre Frère*
Page No. – Page No.
Toward sustainable organic
semiconductors from a broad palette
of green reactions
Text for Table of Contents
New conjugated materials, based on triphenylamine-thiophene moiety and integrating azomethine
bonds with dibenzofuran unit or cyanovinyl bond with phenyl-thiophene and bithiophene units, have
been synthesized by using a wide range of green reactions
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