Synthesis and characterization of 5-octylthieno[3,4-c ]pyrrole-4,6-dione derivatives as new monomers for conjugated copolymers

Article abstract of DOI:10.1021/ol1027514

An efficient route for the synthesis of 1-iodo-5-octyl-4H-thieno[3,4-c] pyrrole-4,6(5H)-dione as a key intermediate to build new electron-deficient monomers and related conjugated polymers is reported. Along these lines, two new low bandgap copolymers were synthesized from Stille or Suzuki coupling. These polymers were characterized and their properties compared to those of analogous conjugated polymers.

Full text of DOI:10.1021/ol1027514

ORGANIC
LETTERS
2011
Vol. 13, No. 1
38-41
Synthesis and Characterization of
5-Octylthieno[3,4-c]pyrrole-4,6-dione
Derivatives As New Monomers for
Conjugated Copolymers
Philippe Berrouard, Franc¸ois Grenier, Jean-Re´mi Pouliot, Eric Gagnon,
Christian Tessier, and Mario Leclerc*
Canada Research Chair on ElectroactiVe and PhotoactiVe Polymers, De´partement de
Chimie, UniVersite´ LaVal, Que´bec City, Que´bec, G1K 7P4, Canada
mario.leclerc@chm.ulaVal.ca
Received September 30, 2010
ABSTRACT
An efficient route for the synthesis of 1-iodo-5-octyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione as a key intermediate to build new electron-deficient
monomers and related conjugated polymers is reported. Along these lines, two new low bandgap copolymers were synthesized from Stille or
Suzuki coupling. These polymers were characterized and their properties compared to those of analogous conjugated polymers.
The synthesis of new low bandgap semiconducting polymers
has become a very intense research field.1 Recently, poly-
(thieno[3,4-c]pyrrole-4,6-dione), p(TPD), derivatives have
attracted a lot of attention since they can lead to high-power
conversion efficiencies when used as active components in
bulk heterojunction (BHJ) solar cells.2-6 Furthermore, the
synthesis of the TPD unit is simple and its relatively low
cost increases its potential for commercial applications. To
expand its versatility and utility, we wanted to develop an
(3) Zhang, Y.; Hau, S. K.; Yip, H.-L.; Sun, Y.; Acton, O.; Jen, A. K.-
Y. Chem. Mater. 2010, 22, 2696
(4) Zhang, G.; Fu, Y.; Zhang, Q.; Xie, Z. Chem. Commun. 2010, 46,
4997.
.
(1) Leclerc, M.; Morin, J. F. Design and Synthesis of Conjugated
Polymers; Wiley-VCH Verlag: Weinheim, Germany, 2010.
(5) Piliego, C.; Holcombe, T. W.; Douglas, J. D.; Woo, C. H.; Beaujuge,
P. M.; Fre´chet, J. M. J. Am. Chem. Soc. 2010, 132, 7595.
(6) Yuan, M.-C.; Chiu, M.-Y.; Liu, S.-P.; Chen, C.-M.; Wei, K.-H.
Macromolecules 2010, 43, 6936.
(2) Zou, Y.; Najari, A.; Berrouard, P.; Beaupre´, S.; A¨ıch, B. R.; Tao,
Y.; Leclerc, M. J. Am. Chem. Soc. 2010, 132, 5330
.
10.1021/ol1027514  2011 American Chemical Society
Published on Web 11/29/2010

efficient methodology to synthesize new TPD derivatives.
We believe that these new monomeric units should lead to
fully conjugated polymers with lower LUMO, HOMO, and
bandgap together with a better processability and stability.
TPD-based conjugated polymers were first reported by
Tour et al. in 1997.7 A few years later, Pomerantz et al.
reported a study on a dimer of TPD.8 Their synthetic
procedures were based on the bromination of the TPD unit
with 1 equiv of NBS. We tried to repeat these procedures
but with limited success (see Scheme S6 in the Supporting
Information). This is probably due to a reaction called
halogen dance9 that makes the conditions hard to control to
obtain the desired product with a good yield. To keep the
advantage of an easy synthesis of TPD derivatives, we
decided to develop a new synthetic route based on a Gewald-
type reaction.10 This reaction allows compound 2 to form
with an amine at the 2-position and two ester functions at
the 3- and 4-positions. Those functions were strategically
placed to reach our target 4 (see Scheme 1). Then, we
Figure 1. X-ray structure of compound 5.
As seen in Figure 1, the dimer adopts an anti-coplanar
conformation probably related to the formation of strong
noncovalent interactions between the oxygen atoms and the
sulfur atoms.12 One can assume that such favorable interac-
tions will exist into related polymeric structures, probably
leading to better intermolecular interactions. Such electron-
deficient units should also lead to lower LUMO energy levels
and bandgaps together with a better processability due to
the presence of solubilizing side chains.
Scheme 1. Synthetic Route for 1-Iodo-5-octyl-4H-thieno[3,4-c]pyr-
role-4,6(5H)-dione and 1,1′-Dibromo-5,5′-dioctyl-
[3,3′]bi[thieno[3,4-c]pyrrolyl]-4,6,4′,6′-tetraone
Scheme 2. Synthesis of 1,1′-(2,1,3-Benzothiadiazole-4,7-diyl)bis(3-
bromo-5-octyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione)
We envisioned that compound 4 can also be used to
elaborate a large number of new conjugated monomers. For
instance, we synthesized 4,4-di(3,3-dibromo-5-octylthieno[3,4-
c]pyrrole-4,6-dione)benzodiathiadiazole (compound 8) by
performing a Suzuki cross-coupling reaction under micro-
wave conditions on compound 4 followed by a bromination
reaction (Scheme 2).
substituted the amine of 2 by an iodide with a Sandmeyer-
type reaction. To obtain 3, we performed an hydrolysis, in
acidic conditions, of the two ester functions. We finally
closed the pyrroledione ring with the same conditions
previouly used by Koeckelberghs et al.11
This approach has resulted in an efficient method to obtain
the key intermediate 4, which can then lead to the desired
TPD dimers with an Ullmann reaction. To understand the
solid-state behavior of TPD dimers, we elucidated the X-ray
crystallographic structure of compound 5.
(7) Zhang, Q. T.; Tour, J. M. J. Am. Chem. Soc. 1997, 119, 5065.
(8) Pomerantz, M.; Amarasekara, A. S. Synth. Met. 2003, 257, 135.
(9) Mayers, B. T.; Fry, A. J. Org. Lett. 2006, 8, 411.
(10) Sabnis, R. W.; Rangnekar, D. W.; Sonawane, N. D. J. Heterocycl.
Chem. 1999, 36, 333.
Figure 2. X-ray structure of compound 8.
To understand the solid-state behavior of compound 8, we
solved its X-ray crystallographic structure. As seen in Figure
(11) Cornelis, D.; Peeters, H.; Zrig, S.; Andrioletti, B.; Rose, E.; Verbiest,
T.; Koeckelberghs, G. Chem. Mater. 2008, 20, 2133.
Org. Lett., Vol. 13, No. 1, 2011
39

Scheme 3. Synthesis of P1 and P2
2, 8 shows a coplanar conformation for the three conjugated
moieties. It is highly possible that this conformation also
would be present in a polymer material containing this unit.
Both compounds 6 and 8 were then utilized to make two
new low bandgap copolymers. We decided to prepare
polymers P1 and P2 since their respective analogues,
PBDTTPD2-5 and PCDTBT,13,14 have shown remarkable
properties when used in BHJ solar cells. As discussed above,
it is assumed that new P1 and P2 should exhibit better
stability (lower HOMO), lower LUMO energy levels, and
bandgaps. These properties could lead to good polymeric
donors as well as allowing the design of new polymeric
acceptors. As shown in Scheme 3, P1 was synthesized by
Stille coupling whereas P2 was obtained through a Suzuki
reaction.
P1 and P2 were then characterized and their properties
were compared with those previously reported for PBDTTPD
and PCDTBT (Scheme 4). P1 and P2 are thermally stable
up to 456 and 330 °C, respectively. We observed a glass
transition at 178 °C for P1 and at 206 °C for P2. No
crystallization and melting peaks were observed for P1 and
P2.
We measured a Mn of 29 000 g/mol and Mw of 70 000
g/mol for P1 and a Mn of 6 200 g/mol and Mw of 16 000
g/mol for P2. The optical and electrochemical properties of
P1 and P2 (Table 1) were determined in parallel with their
Table 1. Electronic Properties of P1, P2, and Their Analogues
Obtained by Cyclic Voltemperometry and UV-Vis (see Figures
S1-S4, Supporting Information)
bandgap (eV)
polymers HOMO (eV) LUMO (eV) electrochemical optical
P1
PBDTTPD
P2
-5.57
-5.64
-5.98
-5.51
-3.94
-3.83
-4.13
-3.59
1.63
1.81
1.85
1.92
1.67
1.81
1.85
1.89
PCDTBT
analogues. In the case of P2, we observed a lower bandgap
than that reported for PCDTBT by about 0.1 eV. Adding
the BTPD instead of the TPD in P1 has a significant
influence on the LUMO and a slight one on the HOMO
energy level. Although P2 and PCDTBT have comparable
bandgaps, the HOMO and LUMO orbitals of the former are
considerably lower (0.47 eV for the HOMO and 0.54 eV
for the LUMO). This kind of substitution can be really useful
for a fine-tuning of the electronic properties of various
conjugated polymers.
Scheme 4
.
The New Conjugated Polymers P1 and P2 and Their
Respective Analogues
In conclusion, a new efficient synthetic route was elabo-
rated for the preparation of the 1-iodo-5-octyl-4H-thieno[3,4-
c]pyrrole-4,6(5H)-dione. From this building block, we were
able to expand the TPD-based copolymer family. Two new
polymers were compared to their analogues and show
significant modulation of the energy levels. In our future
(12) Pomerantz, M. Tetrahedron. Lett. 2003, 44, 1563.
(13) Blouin, N.; Michaud, A.; Leclerc, M. AdV. Mater. 2007, 19, 2295.
(14) Blouin, N.; Michaud, A.; Gendron, D.; Wakim, S.; Blair, E.; Neagu-
Plesu, R.; Belleteˆte, M.; Durocher, G.; Tao, Y.; Leclerc, M. J. Am. Chem.
Soc. 2008, 130, 732.
40
Org. Lett., Vol. 13, No. 1, 2011

work, we will test these materials in BHJ solar cells as donors
and acceptors. We will also synthesize a full series of
derivatives to continue to expand the TPD-based copolymer
family.
for the crystallographic data of compound 8, and David
Gendron, Pierre-Luc Boudreault, Ahmed Najari, and Ying-
ping Zou of our research group for their assistance.
Supporting Information Available: Experimental pro-
cedures, electrochemical measurement, spectroscopic data,
NMR spectra, and X-ray crystallographic details. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. This work was supported by grants
from NSERC and a research contract from the Sustainable
Development Technology Canada (SDTC) Program. The
authors thank Thierry Maris of Universite´ de Montre´al for
the crystallographic data of compound 5, Professor Fre´de´ric
Georges Fontaine and Christian Garon of Universite´ Laval
OL1027514
Org. Lett., Vol. 13, No. 1, 2011
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