Stepwise unidirectional synthesis of oligo phenylene vinylenes with a series of monomers. Use in plastic solar cells

Article abstract of DOI:10.1021/jo0506783

Four new monomers for directional stepwise synthesis of oligophenylenevinylenes (OPVs) (4-{2-[4-(5,5-dimethyl[1,3]dioxan-2-yl)-2,5- dipropoxyphenyl]vinyl}benzyl)phosphonic acid diethyl ester, (5-{2-[4-(5,5- dimethyl[1,3]dioxan-2-yl)-2,5-dipropylphenyl]vinyl}thiophene-2-ylmethyl) phosphonic acid diethyl ester, (5-{2-[4-(5,5-dimethyl[1,3]dioxan-2-yl)-2,5- dipropoxyphenyl]vinyl}thiophene-2-ylmethyl)phosphonic acid diethyl ester, and (7-{2-[4-(5,5-dimethyl[1,3]dioxan-2-yl)-2,5-dipropylphenyl]-vinyl}benzo[1,2,5] thiadiazol-4-ylmethyl)phosphonic acid diethyl ester have been prepared. Trimeric OPVs were then synthesized and tested as active materials in photovoltaic cells. Conversion efficiencies in the range of 0.5-1% were obtained in blends with the soluble C₆₀ derivative PCBM. A terpyridine end-functionalized trimer and a heterotrimer with a mixed composition of monomers were also prepared.

Full text of DOI:10.1021/jo0506783

Stepwise Unidirectional Synthesis of Oligo Phenylene Vinylenes
with a Series of Monomers. Use in Plastic Solar Cells
Mikkel Jørgensen* and Frederik C. Krebs
The Polymer Department, Risø National Laboratory, P.O. Box 49, DK-4000 Roskilde, Denmark
mikkel.joergensen@risoe.dk
Received April 6, 2005
Four new monomers for directional stepwise synthesis of oligophenylenevinylenes (OPVs) (4-{2-
[4-(5,5-dimethyl[1,3]dioxan-2-yl)-2,5-dipropoxyphenyl]vinyl}benzyl)phosphonic acid diethyl ester,
(5-{2-[4-(5,5-dimethyl[1,3]dioxan-2-yl)-2,5-dipropylphenyl]vinyl}thiophene-2-ylmethyl)phosphon-
ic acid diethyl ester, (5-{2-[4-(5,5-dimethyl[1,3]dioxan-2-yl)-2,5-dipropoxyphenyl]vinyl}thiophene-
2-ylmethyl)phosphonic acid diethyl ester, and (7-{2-[4-(5,5-dimethyl[1,3]dioxan-2-yl)-2,5-dipropylphenyl]-
vinyl}benzo[1,2,5]thiadiazol-4-ylmethyl)phosphonic acid diethyl ester have been prepared. Trimeric
OPVs were then synthesized and tested as active materials in photovoltaic cells. Conversion
efficiencies in the range of 0.5-1% were obtained in blends with the soluble C60 derivative PCBM.
A terpyridine end-functionalized trimer and a heterotrimer with a mixed composition of monomers
were also prepared.
Introduction
methods (Figure 1). Single oligomers are much better
defined than polymers, and properties can therefore be
correlated with structure far easier.1 To realize this
potential, we need a toolbox of diverse monomers and a
reliable sequential reaction scheme to assemble them.
The latter requirement is fulfilled by monomers that can
be joined using a two-step procedure. An obvious choice
is to create the vinylene groups using the Horner-
Wadsworth-Emmons (HWE) reaction (also called the
Horner-Wittig reaction) between a benzyl phosphonate
ester and a benzaldehyde. To avoid uncontrolled polym-
erization, the requisite aldehyde functionality must be
protected as an acetal until needed. Each cycle in our
synthesis thus has a HWE reaction followed by a depro-
tection step as outlined in Scheme 1.
Stepwise and unidirectional oligomerization of OPVs
has not been widely exploited presumably due to the
added work required to prepare monomers such as 1.
Some groups have prepared a number of both sym-
metrical and unsymmetrical OPVs with varying end
groups with 6-12 phenylene vinylene fragments using
the HWE,8 Siegrist,9 Heck,10 and Suzuki-Miyaura11 type
reactions. The group of Yu et al. has prepared OPVs
through stepwise reactions with two different monomers
Phenylene vinylene oligomers (OPVs) and the corre-
sponding polymers (the PPVs) have been extensively
investigated both in regard to their synthesis and mate-
rial properties as conducting elements and as light
harvesting antennas.1-6 A smaller subset of these inter-
esting materials are OPVs of a unidirectional nature that
can be prepared using a stepwise strategy, as we have
shown in a previous paper.7 Such a strategy allows us to
fine-tune the properties to the level that have only been
realized in natural oligomers such as peptides and
oligonucleotides, which are also prepared using similar
(1) (a) Mu¨llen, K.; Wegner, G. Electronic Materials: The Oligomer
Approach; Wiley-VCH: Weinheim, 1998. (b) Wong, M. S.; Li, Z. H. Pure
Appl. Chem. 2004, 76, 1409-1419.
(2) Granstro¨m, M.; Petritsch, K.; Arias, A. C.; Lux, A.; Anderson,
M. R.; Friend, R. H. Nature 1998, 395, 257-260.
(3) Brabec, C. J.; Sariciftci, N. S.; Hummelen, J. C. Adv. Funct.
Mater. 2001, 11, 15-26.
(4) Spangaard, H.; Krebs, F. C. Sol. En. Mater. Sol. Cells 2004, 83,
125-146.
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Friend, R. H. Science 2001, 293, 1119-1122.
(6) Meier, H.; Gerold, J.; Kolshorn, H.; Mu¨ling, B. Chem. Eur. J.
2004, 10, 360-370.
(7) Jørgensen, M.; Krebs, F. C. J. Org. Chem. 2004, 69, 6688-6696.
10.1021/jo0506783 CCC: $30.25 © 2005 American Chemical Society
Published on Web 06/24/2005
6004
J. Org. Chem. 2005, 70, 6004-6017

Synthesis of Oligo Phenylene Vinylenes with a Series of Monomers
CHART 1. Generalized Monomer Structure Where
AR1 Is a Dipropyl- or Dipropoxyphenyl Group and
AR2 Can Be 1,4-Phenyl, Thiophenyl, or
Benzothiadiazole Substituentsa
FIGURE 1. Concept of unidirectional stepwise oligomeriza-
tion. A monomer has two different end groups that can be
coupled in a sequential manner. One group is protected during
coupling and then deprotected to allow the next cycle. In the
first reaction, the monomer is end-capped with a monofunc-
tional reagent.
SCHEME 1. Unidirectional and Stepwise
Synthesis of OPV Oligomers Based on HWE
Reactions with Monomer 1 Followed by
Deprotection of the Acetal Groupa
a Three general synthetic strategies have been investigated with
the principal disconnections (a-c) shown around the central double
bond.
in the context of organic solar cells.13 Another interesting
possibility is to use the control over the synthesis to
create molecules with a gradual change in electronic
levels along the conjugated backbone. Compounds such
as these could find widespread use as active materials
in polar devices such as organic light emitting diodes and
plastic solar cells. Materials with a directional buildup
may be much more appropriate to use in contact with
electrode surfaces or with a variation of the electronic
levels that sets a preferred orientation for electron/hole
transport or even charge separation.
a In the first step, the monomer is typically reacted with
4-methoxybenzaldehyde which then becomes the R group.
Results and Discussion
utilizing the Heck and HWE reactions alternately.12
Previously, we have described the simpler strategy using
only one type of monomer summarized in Scheme 1,
where the extension of the oligomer is carried out with a
HWE reaction followed by deprotection of the acetal
function. The unidirectional nature allows end-function-
alization to study the effects of attaching functional
groups that can interact, e.g., with a surface or with other
molecules. This concept have previously been explored
Monomer Synthesis. Chart 1 shows the general
layout of the monomer stilbene type structure composed
of two aryl groups linked by a vinylene bridge. At one
end is a methyl phosphonate ester group and at the other
an acetal-protected aldehyde group. Also shown in Chart
1 are the three possible bond disconnections of the central
vinylene fragment in the monomer. The syntheses of the
monomers 1 and 2 using the Heck reaction are examples
of the (a) type disconnection. Since our first paper on the
subject we have extended the list of monomers to
members with more electron-donating/accepting groups.
Two types of AR1 groups, either dipropyl- or dipropoxy-
substituted, have been utilized. The alkyl groups give the
OPVs some degree of solubility at least up to the “trimer”
stage with seven benzene rings. Three different AR2
groups were investigated with either benzene, thiophene
(8) (a) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem., Int.
Ed. 1998, 37, 402-428. (b) Yang, J. P.; Heremens, P. L.; Haefnagels,
R.; Tachelet, W.; Dielteens, P.; Blockhuys, F.; Giese, H. J.; Borghs, G.
Synth. Met. 2000, 108, 95-100. (c) Meier, H.; Gerold, J.; Kolshorn,
H.; Baumann, W.; Bletz, M. Angew. Chem., Int. Ed. 2002, 41, 292-
295.
(9) Detert, H.; Stalmach, U. J. Prakt. Chem. 2000, 342, 10-16.
(10) Van Hutten, P. F.; Wildeman, J.; Meetsma, A.; Hadziioannou,
G. J. Am. Chem. Soc. 1999, 121, 5910-5918.
(11) Babudri, F.; Farinola, G. M.; Lopez, L. C.; Martinelli, M. G.;
Naso, F. J. Org. Chem. 2001, 66, 3878-3885.
(13) Nierengarten, J.-F.; Eckert, J.-F.; Felder, D.; Nicoud, J.-F.;
Armaroli, N.; Marconi, G.; Vicinelli, V.; Boudon, C.; Gisselbrecht, J.-
P.; Gross, M.; Hadziioannou, G.; Karsnikov, V.; Ouali, L.; Echegoyen,
L.; Liu, S.-G. Carbon 2000, 38, 1587-1598.
(12) (a) Li, W.; Wang, H.; Yu, L.; Morkved, T. L.; Jaeger, H. M.
Macromolecules 1999, 32, 3034-3044. (b) Maddux, T.; Li, W.; Yu, L.
J. Am. Chem. Soc. 1997, 119, 844-845.
J. Org. Chem, Vol. 70, No. 15, 2005 6005

Jørgensen and Krebs
SCHEME 2. Synthesis of the Monomers 1 and 2a
SCHEME 3. Synthesis of the
Thiophene-Containing Monomers 3 and 4 through
Two Different Routes (Top)a
a Key: (i) Pd2dba3, Et3N, P(t-Bu)3‚HBF4, dioxane; (ii) 2,2-
dimethylpropanediol, TsOH, toluene.
or benzothiadiazole moieties totaling in all five different
monomers (1-5). Both the AR1 and AR2 groups influence
the OPV electronic structure, which allow us to vary, e.g.,
the optical band gap. The diverse nature of these mono-
mers also prompted us to investigate a number of
different synthetic routes that will be discussed in the
following. These routes explore the principal disconnec-
tions (a), (b), and (c) to form the double bond using the
Heck-, HWE-, and the Stille-type reactions.
Disconnection (a). As described previously, the mono-
mer 1 with a stilbene motif was prepared via the Heck
reaction from 4-bromo-2,5-dipropylbenzaldehyde 7 and
diethyl 4-vinyl-benzyl phosphonate ester followed by
acetalization with 2,2-dimethylpropane-1,3-diol as shown
in Scheme 2. The best conditions for the Heck reaction
were optimized in the previous study to be Pd2dba3 and
tri-tert-butylphosphine as the catalyst system in dioxane
as solvent and triethylamine as the base at reflux similar
to the system devised by Litke and Fu.14
This method has now been extended to prepare the
monomer 2 with propoxy groups instead of propyl on the
AR1 ring. The 4-bromo-2,5-dipropoxybenzaldehyde (8),
needed for this step, was prepared from 1,4-dibromo-2,5-
dipropoxybenzene by halogen-to-lithium exchange fol-
lowed by reaction with dimethylformamide as described
by Meier and Aust.15 Careful control over the reaction
conditions are necessary, especially the choice of diethyl
ether as solvent, to limit the amount of dilithiation
resulting in an inseparable mixture of aldehydes and
starting material. Otherwise, the concomitant Heck
reaction with diethyl 4-vinylbenzyl phosphonate ester
followed by acetalisation to prepare monomer 2 was
completely analogous to the synthesis of monomer 1.
Purification was achieved by chromatography.
Disconnection (b). A few symmetrical OPVs with
alternating benzene and thiophene groups have been
described by Xue and Luo as promising red light-emitting
materials in OLED’s.16 Thiophene is not so easy to
introduce since a thiophene analogue to diethyl 4-vinyl-
benzyl phosphonate ester is not known. Somewhat dif-
ferent strategies were therefore adopted for the mono-
mers 3 and 4 as shown in Scheme 3.
a The syntheses of 2-(diethylphosphonylmethyl)thiophene
and 2,5-bis(diethylphosphonylmethyl)thiophene are also shown
(bottom).
13 and 14 as light yellow recrystalizable solids. While
diethyl thiophene methyl phosphonate ester17a and the
bis phosphonate ester17b are known compounds, a modi-
fied procedure was used in this study and details of the
synthetic procedure can be found in the Experimental
Section. An unusual type of alkylation procedure was
then employed to add the methyl phosphonate ester
group at the thiophene moiety. Dalton and Wang18 and
later Fre`re et al.19 developed a reaction where a thiophene-
copper reagent is derivatized with diethyl iodomethyl
phosphonate ester. We applied this reaction to the
thiophene derivatives 13 and 14 to obtain the monomers
3 and 4. Unfortunately, it was rather difficult to obtain
pure materials by this procedure because the reaction
did not go to completion and also due to difficulties in
removing dark-colored copper impurities. A somewhat
longer route also shown in Scheme 3 was therefore
explored. The compounds 13 and 14 were transformed
into the crystalline aldehydes 15 and 16 by lithiation with
butyllithium followed by reaction with dimethyl forma-
mide. Reduction to the corresponding hydroxymethyl
The partially acetal protected dipropyl- or dipropoxy-
terephthaldehydes 11 and 12 were prepared from the
bromophenyldioxolanes 9 and 10 via bromine-to-lithium
exchange with butyllithium in THF followed by reaction
with dimethyl formamide. A HWE reaction with diethyl
thiophene methyl phosphonate ester gave the compounds
(17) (a) Masatome, I.; Milton, L. L.; Castle, R. J. Heterocycl. Chem.
1980, 17, 1259-1264. (b) Berlin, A.; Bradamante, S.; Ferraccioli, R.;
Pagani, G. A.; Sannicolo, F. J. Chem. Soc., Perkin Trans. 1 1987, 2631-
2636.
(18) Wang, C.; Dalton, L. R. Tetrahedron Lett. 2000, 41, 617-620.
(19) Fre`re, P.; Raimundo, J.-M.; Blanchard, P.; Delaunay, J.; Rich-
omme, P.; Sauvajol, J.-L.; Orduna, J.; Roncali, J. J. Org. Chem. 2003,
68, 7254-7265.
(14) Littke, A.; Fu, G. J. Am. Chem. Soc. 2001, 123, 6989-7000.
(15) Meier, H.; Aust, H, J. Prakt. Chem. 1999 341, 466-471.
(16) Xue, C.; Luo, F.-T. Tetrahedron 2003, 59, 5193-5198.
6006 J. Org. Chem., Vol. 70, No. 15, 2005

Synthesis of Oligo Phenylene Vinylenes with a Series of Monomers
SCHEME 4. Synthesis of the Thiadiazole Moiety
of Monomers 5 and 6
thiophene compounds was accomplished with sodium
borohydride in a mixture of ethanol and THF. A Mit-
sunobu reaction with carbon tetrabromide and triphenyl
phosphine was then used to convert the hydroxymethyl
group into the corresponding thiophenylmethyl bromide.
Finally, the phosphonate ester groups were introduced
by an Arbusov reaction with triethyl phosphite. Purifica-
tion of the monomers 3 and 4, using column chromatog-
raphy with diethyl ether as eluent and then became much
easier.
Disconnection (c). Work on the synthesis of 4-meth-
yl-2,1,3-benzothiadiazole (17) was reported by Michaelis
as early as 1893 by reaction of 3-methylphenylene-1,2-
diamine and thionyl chloride in benzene followed by
steam distillation.20 Later work by Pilgram et al. on the
preparation of 17 used thionylaniline with good yield.21
Vanelle et al. compared the thionyl chloride route and
the thionylaniline route and while the latter generally
gives a higher yield the workup is tedious.22 Recent work
on derivatization of the benzothiadiazole skeleton in-
cludes amination using both nitration and palladium
catalysis.23 We prepared 17 by a combination of the
Michaelis and the Vanelle route employing stannous
chloride reduction of 2-amino-3-nitrotoluene followed by
reaction with thionyl chloride and subsequent steam
distillation of the product. The bromination of 17 in HBr-
(aq) using bromine gave 18 by a procedure similar to the
one described.21,22 The use of excess bromine has been
reported to give 19 directly21 while allylic bromination
using NBS in CCl4 is preferable.22 All of the literature
procedures20-23 have analytical data limited to elemental
analysis and boiling points/melting points. Except for 18
SCHEME 5. Synthesis of the Dipropyl- and
Dipropoxyphenylvinylstannane Reagents
1
1
where H NMR data is given there are no reported H
NMR and 13C NMR data for these compounds. Reaction
of 19 with triethyl phosphite gave the phosphonic ester
20 directly. The preparations of the ethynyl compounds
23 and 24 were attempted in different ways. The simplest
approach was a Sonogashira coupling using trimethylsilyl
acetylene and copper/palladium catalysis followed by
removal of the TMS groups using either Bu4NF or K2-
CO3 in MeCl2/MeOH. The latter method proved to be
most efficient allowing for easy workup. The Sonogashira
reaction was, however, very sluggish, and attempts to
convert the bromine into iodine gave no improvement.
It was then decided to prepare the acetylene from the
vinyl compound by bromine addition and elimination
using potassium tert-butoxide instead. Addition of tri-
butyltin hydride to arylacetylenes have been studied in
the literature and gives rise to both R and â addition and
cis and trans addition.24-27 The best method for the
addition was found to be the mixing of the two compo-
nents neat and stirring gently under argon while follow-
ing the progress of the reaction using NMR.
The coupling of stannanes with aryl halides has been
reported with the use of copper,28 palladium,29 nickel,30
and manganese31 catalysis. We chose copper catalysis
with sodium chloride as cocatalyst for the subsequent
coupling of the vinylstannane with 20 in NMP (Scheme
4). While the addition of Bu3SnH to the acetylene was
about 60% trans, this was reflected in the product after
coupling as being a mixture of cis and trans (Scheme 5).
To overcome this, (PPh3)4Pd(0) was added at the end of
the coupling reaction followed by heating to reflux. This
efficiently transformed all the double bonds into the trans
form. Monomer 5 was prepared sufficiently pure using
this route, while it proved impossible to separate 6 from
a larger amount of starting materials and byproducts
(Scheme 6).
Synthesis and Characterization of OPV Oligo-
mers. With the monomers (1-5) in hand it was now
possible to explore a number of different experiments
with oligomers. A simple extension of our previous work
was to make trimers of each of the monomers and
investigate the difference in absorption maxima. The
(20) Michaelis, A. Ann. Chem. 1893, 273, 173-268 (p 263).
(21) Pilgram, K.; Zupan, M.; Skiles, R. J. Heterocycl. Chem. 1970,
7, 629-633.
(22) Vanelle, P.; Liegois, C. T.; Meuche, J.; Maldonado, J.; Crozet,
M. P. Heterocycles 1997, 45, 955-962.
(23) Liu, Y.; Prashad, M.; Repie`, O.; Blacklock, T. J. J. Heterocycl.
Chem. 2003, 40, 713-716.
(24) Leusink, A. J.; Budding, H. A.; Marsman, J. W. J. Organomet.
Chem. 1967, 9, 285-294.
(28) Kang, S.-K.; Kim, J.-S.; Yoon, S.-K.; Lim, K.-H.; Yoon, S.-S.
Tetrahedron Lett. 1998, 39, 3011-3012.
(25) Leusink, A. J.; Budding, H. A. J. Organomet. Chem. 1967, 11,
533-539.
(29) Roth, G. P.; Farina, V.; Liebeskind, L. S.; Pen˜a-Cabrera, E.
Tetrahedron Lett. 1995, 36, 2191-2194.
(26) Kikukawa, K.; Umekawa, H.; Wada, F.; Matsuda, T. Chem. Lett.
1988, 881-884.
(30) Shirakawa, E.; Yamasaki, K.; Hiyama, T. Synthesis 1998, 10,
1544-1549.
(27) Allred, G. D.; Liebeskind, L. S. J. Am. Chem. Soc. 1996, 118,
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(31) Kang, S.-K.; Kim, J.-S.; Choi, S.-C. J. Org. Chem. 1997, 62,
4208-4209.
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Jørgensen and Krebs
SCHEME 6. Final Assembly of the Thiadiazole-Type Monomers 5 and 6 through Stille Coupling of the
Components 20 with 25 or 26
CHART 2. Structures of the Four Different Types of “Homo” Oligomers Prepared in This Study Based on
the Monomers 2-5a
a In the first step, each of the monomers was end-capped by a HWE reaction with 4-methoxybenzaldehyde followed by hydrolysis of the
acetal function. Stepwise elongation with the monomers then gave the corresponding dimers and trimers.
maxima are an expression of the optical band gap that
is related to the various donor/acceptor groups in the
molecules.
of the product in the HWE reaction between monomer 5
and 4-methoxybenzaldehyde the 4-{2-[4-(5,5-dimethyl-
[1,3]dioxan-2-yl)-2,5-dipropyl-phenyl]-vinyl}-7-[2-(4-meth-
oxy-phenyl)-vinyl]-benzo[1,2,5]thiadiazole 37 was isolated
and characterized as described in the Experimental
Section (Chart 2).
End-Functionalization. The present synthetic strat-
egy makes it straightforward to add end-groups that can
give further functionality to the molecules. Adding a
ligand group such as a terpyridine moiety would allow
us to create metal complexes attached to a conjugated
“wire” OPV. A similar terpyridine-OPV architecture has
been reported recently.32
The monomers 3 and 4 were designed to give oligomers
with alternating benzene and thiophene moieties. Smaller
symmetrical OPVs of this type have recently been studied
by Xue and Luo for their potential as red light-emitting
materials.16 Thiophene-containing conducting polymers
and oligomers are of interest as low band-gap materials.
Reactions with the monomer 5 proved to be difficult and
gave only low yields (20-30%) of products in the HWE
reaction. A possible side reaction is nucleophilic attack
on the benzothiadiazole moiety and as a consequence
sodium hydride was used as the base in the reactions
with 5 instead of potassium tert-butoxide. The trimer 36
was obtained in very low yield and contaminated with
both dimeric and tetrameric products. It could be purified
by size exclusion chromatography (SEC) to show that it
is a low band gap material with absorption maximum at
500 nm extending out to 600 nm. To prove the identity
The synthesis of the terpyridine end-functionalized
trimer 40 began with a HWE reaction between the
terpyridine phosphonate ester 38 and the aldehyde 12
(32) El-ghayoury, A.; Schenning, A. P. H. J.; van Hal, P. A.; Weidl,
C. H.; van Dongen, J. L. J.; Janssen, R. A. J.; Schubert, U. S.; Meijer,
E. W. Thin Solid Films 2002, 403-404, 97-101.
6008 J. Org. Chem., Vol. 70, No. 15, 2005

Synthesis of Oligo Phenylene Vinylenes with a Series of Monomers
SCHEME 7. Synthesis of a “Trimer” OPV with a Terpyridine End Group 40
resulting in the end-capped monomer 39 (Scheme 7).
Although Zang et al. and others have described terpyri-
dine phosphonate ester 38 previously, no specific details
on the synthesis and compound properties were given.33-35
These have therefore been included in the Experimental
Section. Extension of compound 39 with the monomer 2
was carried out twice using the HWE reaction followed
by deprotection of the acetal function to give the target
terpyridine trimer 40.
Tapering the Electronic Levels. In principle it is
possible to control the nature and substituents of each
aromatic ring along the OPV. This level of specificity is
similar to that found in peptide synthesis where the order
of amino acid residues can be controlled. Choosing
different monomers with different electronic levels would
allow us to create OPVs were these properties vary along
the backbone. A preferred direction of electron or hole
conduction could be envisaged. To demonstrate the
present level of control that is possible with the set of
monomers and the stepwise oligomerization reactions we
prepared a “hetero-trimer” 43 using three different
monomers as shown in Scheme 8. The assembly began
with the end capping of monomer 4 with piperonal
creating the electron-rich part of the molecule. In the
second step, monomer 1 was chosen as a bridge and
finally, the monomer 5 was added to create the electron
deficient region. Inspection will show that each of the
seven aromatic rings in the structure is substituted
differently. A disconnection scheme would show that
virtually every bond with the exception of the rings
themselves and the propyl groups have been created
along the synthetic pathway. Only the last step adding
monomer 5 proved to be troublesome resulting in a very
low yield.
Spectral Properties. The absorption spectra of the
trimers, measured in chloroform solution, seen in Figure
2 show the effect of the substitutions on the optical band
gap. Changing the propyl substituents on the AR1 ring
into propoxy groups when, AR2 is a benzene or a
thiophene ring, red shifts the absorption maximum 44
and 63 nm, respectively (original trimer f 29 and 32 f
35). Exchanging benzene for thiophene in AR2 similarly
affects red shifts of 57 and 50 nm (original trimer f 32
and 29 f 35). The effect of substituting the AR2 benzene
ring in the original trimer with a benzothiadiazole ring
is more dramatic with a red shift of 91 nm (original
trimer f 36). Changing the end group from a 4-meth-
oxyphenyl to a terpyridine group (29 f 40) on the other
hand has almost no effect. The absorption maximum is
still at 451 nm with a slightly broader shoulder toward
higher wavelengths.
Photovoltaic Behavior. The materials prepared here
were also investigated with respect to their photovoltaic
properties. It was, however, found that the materials with
propoxy sidegroups formed very poor films and it was
only possible to prepare photovoltaic devices of 32 and
35. One reason for this observation could be that the
torsion angle between the aryl group and the alkoxy
substituent is close to 0° whereas the torsion angle
between the aryl group and an alkyl group is close to
90°.36 In the solid a planar geometry is more easily
achieved with alkoxy groups and packing is easier. This
could explain the poor solubility for the alkoxy com-
(33) Zhang, Y.; Murphy, C. B.; Jones, W. E., Jr. Macromolecules
2002, 35, 630-636.
(34) Collin, J.-P.; Guillerez, S.; Sauvage, J.-P.; Barigelletti, F.; De
Cola, L.; Flamigni, L.; Balzani, V. Inorg. Chem. 1991, 30, 4230-4238.
(35) Spahni, W.; Calzaferri, G. Helv. Chim. Acta 1984, 67, 450.
J. Org. Chem, Vol. 70, No. 15, 2005 6009

Jørgensen and Krebs
SCHEME 8. Synthesis of the Hetero Trimer 43 Starting from Piperonala
a All seven aromatic rings in this compound are differently substituted showing the versatility of the stepwise oligomerization scheme.
FIGURE 2. Normalized absorption spectra of the original trimer prepared from monomer 1 and the trimers 29, 32, 35, 36, and
40 dissolved in chloroform.
pounds based on a PPV backbone. Fortunately, this is
not the case for the oligophenylenevinylenethien-
ylenevinylene backbone. Photovoltaic cells based on 32
and 35 and their mixtures with the soluble fullerene
derivative PCBM37 were prepared on glass substrates
with a layer of PEDOT/PSS covered ITO. The active layer
was coated on top by spin-coating and the device was
completed by evaporation of an aluminum electrode. The
devices were then tested under a sun simulator (AM1.5)
with an incident power in the range of 1000 W m-2 and
the IV-curves were recorded. The results have been
summarized in Table 1.
(36) Krebs, F. C.; Jørgensen, M. Macromolecules 2003, 36, 4374-
4384.
(37) Hummelen, J. C.; Knight, B. W.; LePeq, F.; Wudl, F.; Yao, J.;
Wilkins, C. L. J. Org. Chem. 1995, 60, 532-538.
Good dark rectification characteristics and diode be-
havior were only obtained with a high concentration of
6010 J. Org. Chem., Vol. 70, No. 15, 2005

Synthesis of Oligo Phenylene Vinylenes with a Series of Monomers
TABLE 1. Photovoltaic Data for the Materials Studied
material
rectification |1V|
Voc (V)
Isc (mA cm-2
)
FF (%)
PIncident (W m-2
)
η (%)
32
0.92
1.04
9.84
0.94
3.46
12.4
0.155
0.290
0.499
0.080
0.625
0.505
-0.005
-0.596
-2.639
-0.007
-1.875
-3.926
25
27
34
24
34
38
931
931
970
945
945
935
0.0002
0.0500
0.4662
0.0001
0.4216
0.8140
32/PCBM (1:1)
32/PCBM (1:4)
35
35/PCBM (1:1)
35/PCBM (1:4)
a The device geometry was ITO/PEDOT:PSS/material/aluminum. The devices were tested under a sun simulator with a spectrum
approximating AM1.5 and were not corrected for mismatch. The active area of the devices was 3 cm2.
FIGURE 4. Photovoltaic action spectrum in terms of the short
circuit current (Isc) for a photovoltaic cell based on a mixture
of 35 and PCBM (1:4) with an active area of 3 cm2. The UV-
vis spectrum of the device film is also shown.
FIGURE 3. IV curves of the device based on 35 and PCBM
(1:4) in the dark and under illumination with a sun simulator
Conclusion
at 935 W m-2 approximating AM1.5 conditions.
Four new stilbene-type monomers with an acetal
masked aldehyde group connected to a dipropyl- or
dipropoxy-substituted benzene ring, and a phosphonate
ester group connected to either benzene, thiophene, or a
benzothiadiazole ring, have been prepared. Several new
synthetic strategies had to be developed to be able to
obtain the monomers. With these at hand together with
an existing monomer from a previous study, directional
stepwise synthesis of oligomers up to the trimer stage
were made having seven aryl groups connected by six
ethylene bridges. End group functionalization was in-
vestigated using a terpyridine group with the promise
of easy access to metal coordinated OPVs. Access to the
five different monomers also made it possible to prepare
a mixed trimer with differently substituted rings in effect
a tapering of the electronic levels along the molecule. The
convergent synthetic strategy chosen allows for the
preparation of gram quantities of the trimers where
many of the bonds have been created during the synthetic
pathway. The varied nature of the different trimers was
reflected in the UV-vis absorption spectra with maxima
in the 400-500 nm range. Exchanging the propyl groups
in the AR1 ring for propoxy groups and benzene to
thiophene in the AR2 ring thus affects a redshift of 100
nm allowing some control over the optical band gap.
Photovoltaic devices could be made from two of the
trimers 32 and 35 with alternating benzene and thiophene
groups. Mixed with the soluble C60 derivative PCBM
these cells converted the incident light to electric power
with efficiencies in the range of 0.5 to 1% with trimer 35
having the highest efficiency and the lowest band gap.
PCBM (80 wt %) as shown in Figure 3 for 35. The fill
factors (FF) obtained increased with increasing PCBM
concentration as expected. The maximum value obtained
was 38% and thus considerably lower than typical
literature values exceeding 50% for small area devices
(active areas of a few mm2). Our devices had a large
active area (3 cm2) and the sheet resistance of the
electrodes could contribute significantly to the serial
resistance of the device. A higher serial device resistance
leads to a lowering of the FF. The presence of film
imperfections and parasitic or shunt resistances lowers
the parallel device resistance and would thus also lead
to a lowering of the FF. We attribute the low values for
FF to the choice of a large device area. The possibility of
achieving functional devices over large area are however
paramount for future applications and an active area of
a few square centimeters must be considered as an
absolute minimum for devices when considering the
future potential of the technology.
The photovoltaic action spectrum was symbatic with
the absorption spectrum as shown in Figure 4.
The maximum incident photon current efficienciy
(IPCE) that is a measure of how many of the incident
photons that are converted into electrons in the external
circuitry was 16% for a 1:4 mixture of 35 and PCBM at
the maximum (440 nm). This shows that the photovoltaic
conversion is highly efficient in a narrow range. All
photovoltaic characterization was performed in the ambi-
ent atmosphere.
J. Org. Chem, Vol. 70, No. 15, 2005 6011

Jørgensen and Krebs
140.7. MS: m/z 534.2457, calcd for C29H43O5PS (MNa+)
534.2461. Anal. Calcd for C29H43O5PS: C, 65.14; H, 8.11.
Found: C, 65.41; H, 8.22.
Experimental Section
(4-{2-[4-(5,5-Dimethyl[1,3]dioxan-2-yl)-2,5-dipropoxy-
phenyl]vinyl}benzyl)phosphonic Acid Diethyl Ester (2)
(Monomer 2). 4-Bromo-2,5-dipropoxybenzaldehyde (30 g, 0.1
mol) and 4-vinylbenzylphosphonic acid diethyl ester (25,5 g,
0.10 mol) were dissolved in dioxane (200 mL) together with
triethylamine (40 mL) and purged with argon for 5 min. Then
catalyst Pd2(dba)3 (0.4 g) and tri-tert-butylphosphine tetrafluo-
roboric acid salt (0.55 g) were added, and the dark mixture
was heated to reflux under argon for 3 h. The next day, dioxane
and excess triethylamine was removed in a vacuum, the
remaining dark oil was partitioned between diethyl ether (400
mL) and dilute hydrochloric acid (200 mL), the water phase
was extracted once with diethyl ether (200 mL), and the
combined organic phase was washed with dilute hydrochloric
acid, dried over magnesium sulfate, filtered, and evaporated.
The oil was dissolved in diethyl ether, silica (ca. 100 mL) was
added, and the ether was evaporated. Meanwhile, a large
column of silica (ca. 300 mL) slurried in diethyl ether was
made up. The crude product/silica mixture was placed on top
and eluted with diethyl ether (ca. 2L) to remove a dark band
(catalyst and starting material). The product was the eluted
with THF. The solvent was removed in a vacuum to give ca.
41 g of yellow oil.
The oil was dissolved in toluene (300 mL) together with 2,2-
dimethyl-1,3-propanediol (10.5 g, 0.1 mol) and a catalytic
amount of p-toluenesulfonic acid and heated to reflux for 1h
in a flask equipped with a water separator. The mixture was
cooled and filtered through a small layer of potassium carbon-
ate to remove the acid and a small amount of palladium black.
The toluene was removed in a vacuum to give a tan oil. Yield:
47.8 g, 99%. 1H NMR (CDCl3, 250.1 MHz) δ: 0.87 (s, 3H), 1.05
(t, 3H, J ) 7 Hz), 1.07 (t, 3H, J ) 7 Hz), 1.24 (t, 6H, J ) 7
Hz), 1.32 (s, 3H), 1.84 (heptuplet, 4H, J ) 7 Hz), 3.14 (d, 2H,
JPH ) 22 Hz), 3.65 (d, 2H, J ) 11 Hz), 3.75 (d, 2H, J ) 11 Hz),
3.9-4.0 (m, 8H), 5.74 (s, 1H), 7.06 (d, 1H, J ) 16 Hz), 7.08 (s,
1H), 7.18 (s, 1H), 7.26 (dd, 2H, J1 ) 2 Hz, J2 ) 8 Hz), 7.45 (d,
1H, J ) 16 Hz), 7.46 (d, 2H, J ) 8 Hz). 13C NMR (CDCl3, 62.9
MHz) δ: 10.6, 10.7, 16.3, 16.4, 21.4, 21.8, 22.6, 22.8, 23.2, 30.3,
32.4, 34.6, 36.5, 62.2, 62.3, 70.9, 71.2, 77.9, 97.0, 110.8, 111.6,
123.6, 126.6, 126.7, 127.4, 127.7, 128.6, 129.9, 130.1, 130.5,
130.6, 136.6, 136.7, 150.3, 151.1 ppm. MS: m/z 583.2818, calcd
for C31H45O7P (MNa+) 583.2795.
(5-{2-[4-(5,5-Dimethyl[1,3]dioxan-2-yl)-2,5-dipropoxy-
phenyl]vinyl}thiophene-2-ylmethyl)phosphonic Acid Di-
ethyl Ester (Monomer 4). Prepared from the aldehyde 16
1
as above. Yield: 37%. H NMR (CDCl3, 250.1 MHz) δ: 0.80
(s, 3H), 1.06 (t, 3H, J ) 7 Hz), 1.08 (t, 3H, J ) 7 Hz), 1.30 (t,
6H, J ) 7 Hz), 1.33 (s, 3H), 1.83 (heptuplet, 4H, J ) 8 Hz),
3.34 (d, 2H, JHP ) 21 Hz), 3.65 (d, 2H, J ) 11 Hz), 3.76 (d, 2H,
J ) 11 Hz), 3.96 (t, 3H, J ) 7 Hz), 3.99 (t, 3H, J ) 7 Hz), 4.09
(pentuplet, 4H, J ) 8 Hz), 5.74 (s, 1H), 6.84-6.89 (m, 2H),
7.00 (s, 1H), 7.17 (s, 3H). 13C NMR (CDCl3, 62.9 MHz) δ: 10.6,
10.7, 16.3, 21.8, 22.8, 23.2, 28.5 (JCP ) 2 Hz), 30.2, 63.0 (JCP
)
1 Hz), 70.8, 71.1, 77.8, 97.0, 110.6, 111.6, 122.4, 123.2, 125.8,
127.3, 127.8, 131.4, 143.2, 150.3, 151.0 ppm. MS: m/z 589.2336,
calcd for C29H43O7PS (MNa+) 589.2350.
(7-{2-[4-(5,5-Dimethyl[1,3]dioxan-2-yl)-2,5-dipropyl-
phenyl]vinyl}benzo[1,2,5]thiadiazol-4-ylmethyl)phos-
phonic Acid Diethyl Ester (Monomer 5). The crude product
mixture of compound 25 (26.6 mmol) was mixed with NaCl
(1.6 g, 26.6 mmol) in NMP (60 mL) and CuI (0.506 g, 2.66
mmol, 10 mol %). The mixture was heated to 90 °C and became
dark brown. The phosphonate ester (9.71 g, 26.6 mmol)
dissolved in NMP (60 mL) was added slowly. The color soon
changed to light yellow/brown and was stirred overnight at
90 °C while adding the phosphonate slowly over about 1 h.
The following day, (PPh3)4Pd (300 mg) was added and the
mixture heated to reflux. The mixture was poured into water
and extracted with ether. The ether phase was passed through
silica and washed with ether (2 L). It was then washed with
THF (2 L). Evaporation of the THF gave a dark red oil. Yield:
1
6.5 g (42%). H NMR (250 MHz, 300 K, TMS, CDCl3) δ: 0.80
(s, 3H), 1.01 (t, 3H, J ) 7 Hz), 1.18 (t, 3H, J ) 7 Hz), 1.66
(heptuplet, 4H, J ) 8 Hz), 2.69 (t, 2H, J ) 7 Hz), 2.78 (t, 2H,
J ) 7 Hz), 3.65 (d, 2H, J ) 11 Hz), 3.74 (d, 2H, JPH ) 22 Hz),
3.78 (d, 2H, J ) 11 Hz), 4.04 (pentet, 4H, J ) 7 Hz), 5.53 (s,
1H), 7.41 (d, 1H, J ) 16 Hz), 7.47 (s, 1H), 7.51 (s, 1H), 7.60 (s,
2H), 8.31 (d, 1H, J ) 16 Hz); 13C NMR (63 MHz, 300 K, TMS,
CDCl3) δ: 14.2, 16.2, 16.3, 17.6, 21.9, 23.2, 24.6, 24.7, 30.3,
34.3, 35.8, 49.3, 62.1, 62.2, 77.9, 99.9, 123.7, 123.9, 125.2, 126.6,
127.0, 129.8, 129.9, 131.6, 135.7, 136.1, 137.9, 138.8, 153.2,
155.4. MS: m/z 609.2508, calcd for C31H43N2O5PS (MNa+)
609.2523.
(5-{2-[4-(5,5-Dimethyl[1,3]dioxan-2-yl)-2,5-dipropyl-
phenyl]vinyl}thiophene-2-ylmethyl)phosphonic Acid Di-
ethyl Ester (Monomer 3). Compound 15 (10 g, 24 mmol) was
dissolved in THF (100 mL) and ethanol (50 mL) and treated
with sodium borohydride (5 g, excess) for 30 min. The solvents
were removed in a vacuum, and the oily residue was separated
between water (100 mL) and diethyl ether (100 mL) the
organic phase was dried over magnesium sulfate, filtered, and
evaporated to dryness. The semisolid was taken up in THF
(100 mL) and treated with carbon tetrabromide (8.8 g, 1.1
equiv) and triphenylphosphine (6.9 g, 1.1 equiv) for 1 h. The
solvent was removed, and the residue taken up in diethyl ether
and filtered through a 5 cm layer of silica to remove most of
the triphenylphosphine oxide. Diethyl ether was then removed
in a vacuum, and the remaining oil was mixed with an excess
of triethyl phosphite. The reaction mixture was heated to
reflux for 10 min and the excess triethyl phosphite removed
in a vacuum. The raw product was purified by chromatography
on silica with diethyl ether as eluent. Yield: 3.2 g, 25% as oil.
1H NMR (CDCl3, 250.1 MHz) δ: 0.77 (s, 3H), 0.95 (t, 3H, J )
7 Hz), 0.97 (t, 3H, J ) 7 Hz), 1.28 (t, 6H, J ) 8 Hz), 1.31 (s
3H), 1.61 (heptuplet, 4H, J ) 7 Hz), 2.64 (p, 4H, J ) 7 Hz),
3.31 (d, 2H, JHP ) 21 Hz), 3.62 (d, 2H, J ) 11 Hz), 3.75 (d, 2H,
J ) 11 Hz), 4.08 (p, 4H, J ) 7 Hz), 5.48 (s, 1H), 6.8-6.9 (m,
2H), 6.98 (d, 1H, J ) 16 Hz), 7.06 (d, 1H, J ) 16 Hz), 7.30 (s,
1H), 7.40 (s, 1H). 13C NMR (CDCl3, 62.9 MHz) δ: 14.1, 14.2,
16.3, 21.8, 23.2, 24.4, 24.6, 25.4, 30.1, 34.2, 35.2, 77.9, 100.0,
122.7, 124.3, 125.4, 125.7, 126.3, 127.6, 127.8, 128.0, 131.3,
132.0, 132.1, 132.5, 132.8, 135.2, 135.5, 137.8, 138.0, 138.2,
2-(4-Bromo-2,5-dipropylphenyl)-5,5-dimethyl[1,3]-
dioxane (9). 4-Bromo-2,5-dipropylbenzaldehyde (52 g, 0.19
mol) was mixed with 2,2-dimethyl-1,3-propanediol (22 g, 1.1
equiv) and p-toluenesulfonic acid (200 mg, cat) in toluene (500
mL) in a flask equipped with a Dean-Stark water separator
and heated to reflux for 2 h. The cooled mixture was washed
with a solution of sodium hydrogen carbonate, dried over
magnesium sulfate, filtered, and evaporated to dryness.
Yield: 66 g, 96%. 1H NMR (CDCl3, 250.1 MHz) δ: 7.51 (s, 1H),
7.35 (s,1H), 5.49 (s, 1H), 3.78 (d, 2H, J ) 11 Hz), 3.64 (d, 2H,
J ) 11 Hz), 2.70 (t, 2H, J ) 7 Hz), 2.63 (t, 2H, J ) 8 Hz), 1.65
(m, 4H), 1.33 (s, 3H), 0.99 (double triplet, 6H, J ) 8 Hz), 0.81
(s, 3H). 13C NMR (CDCl3, 62.9 MHz) δ: 14.0, 14.2, 21.9, 23.3,
24.4, 30.2, 33.7, 37.9, 77.9, 99.5, 124.8, 128.1, 133.4, 135.3,
139.4, 139.6.
2-(4-Bromo-2,5-dipropoxyphenyl)-5,5-dimethyl[1,3]-
dioxane (10). 4-Bromo-2,5-dipropoxybenzaldehyde (47 g, 0.15
mol) was dissolved in toluene (300 mL together with 2,2-
dimethyl-1,3-propanediol (16 g, 0.15 mol) and p-toluenesulfonic
acid (cat.) and heated to vigorous reflux for 1 h in flask
equipped with a Dean-Stark trap to remove water. The cooled
reaction mixture was washed with sodium hydrogencarbonate
solution dried over MgSO4, filtered, and finally evaporated.
Yield: 57 g, 98%. 1H NMR (CDCl3, 250.1 MHz) δ: 7.21 (s, 1H),
7.07 (s, 1H), 5.69 (s, 1H), 3.99 (t, 2H, J ) Hz), 3.88 (t, 2H, J )
Hz), 3.75 (d, 2H, J ) Hz), 3.64 (d, 2H, J ) Hz), 1.7-1.9 (m,
4H), 1.31 (s, 3H), 1.06 (t, 3H, J ) Hz), 1.03 (t, 3H, J ) Hz),
0.79 (s, 3H). 13C NMR (CDCl3, 62.9 MHz) δ: 150.5, 149.9,
6012 J. Org. Chem., Vol. 70, No. 15, 2005

Synthesis of Oligo Phenylene Vinylenes with a Series of Monomers
127.2, 117.8, 113.1, 112.6, 96.7, 77.84, 71.6, 71.1, 30.3, 23.2,
22.7, 22.6, 21.8, 10.6, 10.6.
22.8, 21.9, 10.8, 10.7 ppm. Anal. Calcd for C24H32O4S: C, 69.20;
H, 7.74. Found: C, 69.15; H, 7.75.
5-{2-[4-(5,5-Dimethyl[1,3]dioxan-2-yl)-2,5-dipropyl-
phenyl]vinyl}thiophene-2-carbaldehyde (15). Compound
13 (16 g, 42 mmol) was dissolved in THF (250 mL) and cooled
on a dry ice-acetone bath. At -50 °C, butyllithium (30 mL,
1.5 M in hexanes) was added, and the temperature was
allowed to reach 0 °C in 30 min. Cooling was applied while
adding DMF (25 mL, excess) to keep the temperature below
-30 °C. Stirring at ambient temperature was continued for 1
h to complete the reaction, and water (100 mL) was added.
The solvents were removed in a vacuum, and the residue was
taken up in diethyl ether. The ether phase was separated and
evaporated to give a tan oil that was triturated with methanol
(50 mL) and scratched to induce crystallization. Yield: 13.4
g, 78%. Mp: 113-115 °C. 1H NMR (CDCl3, 250.1 MHz) δ: 0.82
(s, 3H), 0.99 (t, 3H, J ) 7 Hz), 1.01 (t, 3H, J ) 7 Hz), 1.34 (s,
3H), 2.6-2.7 (m, 4H), 3.66 (d, 1H, J ) 11 Hz), 3.79 (d, 1H, J
) 11 Hz), 5.52 (s, 1H), 7.10 (d, 1H, J ) 16 Hz), 7.14 (d, 2H, J
) 4 Hz), 7.38 (s, 1H), 7.41 (d, 1H, J ) 16 Hz), 7.47 (s, 1H),
7.66 (d, 2H, J ) 4 Hz). 13C NMR (CDCl3, 62.9 MHz) δ: 14.1,
14.2, 21.9, 23.2, 24.7, 30.2, 35.2, 77.9, 99.8, 121.7, 126.3, 126.7,
127.9, 130.7, 134.5, 136.4, 137.1, 138.1, 138.9, 141.4, 153.0,
182.5. MS: m/z 327.1423, calcd for C20H22O2S (MH+) 327.1413.
5-{2-[4-(5,5-Dimethyl[1,3]dioxan-2-yl)-2,5-dipropoxy-
phenyl]vinyl}thiophene-2-carbaldehyde (16). Prepared
from 14 as above. Yield: 76%. Mp: 128-129 °C. 1H NMR
(CDCl3, 250.1 MHz) δ: 0.80 (s, 3H), 1.04 (t, 3H, J ) 7 Hz),
1.09 (t, 3H, J ) 7 Hz), 1.33 (s, 3H), 1.85 (heptuplet, 4H,J ) 8
Hz), 3.66 (d, 2H, J ) 11 Hz), 3.76 (d, 2H, J ) 11 Hz), 5.74 (s,
1H), 7.02 (s, 1H), 7.12 (d, 2H, J ) 4 Hz), 7.21 (s, 1H), 7.25 (d,
1H, J ) 16 Hz), 7.50 (d, 1H, J ) 16 Hz), 7.64 (d, 2H, J ) 4
Hz), 9.84 (s, 1H); 13C NMR (CDCl3, 62.9 MHz) δ: 10.6, 10.7,
21.8, 22.8, 23.7, 30.3, 70.8, 71.1, 77.9, 111.2, 111.6, 121.3, 126.0,
126.1, 128.3, 137.2, 141.3, 150.3, 151.6, 153.5, 182.5.
4-Methylbenzo-2,1,3-thiadiazole (17). 3-Methyl-1,2-phen-
ylenediamine (0.66 mol), prepared by reduction of 2-amino-3-
nitrotoluene using SnCl2 in concentrated HCl, was stirred in
benzene (500 mL) when SOCl2 (200 mL, excess) was added
over 30 min with vigorous stirring. HCl(g) was evolved, and
the evaporation cooled the solution. The mixture was heated
gently. After 3 days, the black mixture with a yellow transmis-
sion color was hydrolyzed carefully with water. The benzene
was evaporated, and the mixture was steam distilled. After 2
L of steam had distilled, the distillation was stopped and the
distillate was saturated with NaCl and extracted with ether.
Evaporation gave 65 g (65%). 1H NMR (250 MHz, 300 K, TMS,
CDCl3): δ 2.65 (s, 3H), 7.10 (d, J ) 7 Hz, 1H), 7.36 (dd, J1)7
Hz, J2)9 Hz, 1H), 7.30 (d, J ) 9 Hz, 1H); 13C NMR (63 MHz,
300 K, TMS, CDCl3): δ 17.6, 118.8, 127.7, 129.3, 131.5, 154.9,
155.4. Elemental analysis in accordance with ref 20.
4-(5,5-Dimethyl[1,3]dioxan-2-yl)-2,5-dipropylbenzalde-
hyde (11). Compound 9 (114 g, 0.321 mol) was dissolved in
dry THF and cooled to -78 °C on a dry ice acetone bath under
argon. Butyllithium (1.5 M in hexanes, 240 mL) was added in
one portion, and the reaction mixture was stirred in the cold
for another 10 min to complete the reaction. Then DMF (100
mL, excess) was added, and the cooling bath was removed.
After 1 h at ambient temperature, water (200 mL) was added,
and the solvents were removed in a vacuum. The remaining
oil water mixture was taken up in diethyl ether, dried over
magnesium sulfate, filtered, and evaporated again. The oil was
1
distilled. Yield: 84.6 g, 74%. H NMR (CDCl3, 250.1 MHz) δ:
0.82 (s, 3H), 0.99 (t, 3H, J ) 7 Hz), 1.34 (s, 3H), 1.61-1.7 (m,
4H), 2.70 (t, 2H, J ) 8 Hz), 2.98 (t, 2H, J ) 8 Hz), 3.66 (d, 2H,
J ) 11 Hz), 3.79 (d, 2H, J ) 11 Hz), 5.55 (s, 1H), 7.57 (s, 1H),
7.64 (s, 1H), 10.27 (s, 1H). 13C NMR (CDCl3, 62.9 MHz) δ: 14.0,
14.1, 21.8, 23.2, 24.3, 25.6, 30.2, 33.8, 34.0, 77.9, 99.2, 128.9,
132.0, 133.7, 138.4, 141.2, 143.1, 192.1.
4-(5,5-Dimethyl[1,3]dioxan-2-yl)-2,5-dipropoxybenzal-
dehyde (12). Prepared from 10 as above. Yield: 82% as a
white solid. Could be recrystallized with loss from ethanol.
Mp: 76-77 °C. 1H NMR (CDCl3, 250.1 MHz) δ: 10.47 (s, 1H),
7.30 (broad s, 2H), 5.74 (s, 1H), 4.06 (t, 2H, J ) 8 Hz), 3.95 (t,
2H, J ) 8 Hz), 3.75 (d, 2H, J ) 11 Hz), 3.69 (d, 2H, J ) 11
Hz), 1.84 (m, 4H), 1.32 (s, 3H), 1.06(t, 3H, J ) 7 Hz), 1.03 (t,
3H, J ) 7 Hz), 0.81 (s, 3H). 13C NMR (CDCl3, 62.9 MHz) δ:
189.580, 156.304, 150.115, 134.652, 125.293, 112.140, 110.299,
96.505, 77.875, 70.641, 70.596, 30.349, 23.210, 22.596, 22.555,
21.830, 10.577, 10.527. Anal. Calcd for C19H28O5: C, 67.83; H,
8.39. Found: C, 67.69; H, 8.40.
2-[2,5-Dipropyl-4-(2-thiophene-2-ylvinyl)phenyl]-5,5-
dimethyl[1,3]dioxane (13). Prepared using the same proce-
dure as for compound 14 (below). Yield: 45%. Mp: 80-81 °C.
1H NMR (CDCl3, 250.1 MHz) δ: 0.82 (s, 3H), 1.00 (t, 3H, J )
7 Hz), 1.01 (t, 3H, J ) 7 Hz), 1.35 (s, 3H), 1.66 (heptuplet, 4H,
J ) 7 Hz), 2.6-2.75 (m, 4H), 3.65 (d, 2H, J ) 11 Hz), 3.79 (d,
2H, J ) 11 Hz), 5.53 (s, 1H), 7.01 (dd, 1H, J ) 4 Hz, J ) 5
Hz), 7.09 (d, 1H, J ) 16 Hz), 7.07 (dd, 1H, J ) 1.0 Hz, J ) 4
Hz), 7.18 (d, 1H, J ) 16 Hz), 7.19 (d, 1H, J ) 5 Hz), 7.35 (s,
1H), 7.41 (s, 1H). 13C NMR (CDCl3, 62.9 MHz) δ: 14.2, 14.3,
21.9, 23.3, 24.5, 24.7, 30.2, 34.3, 35.3, 77.9, 100.0, 122.7, 124.1,
125.7, 126.2, 126.5, 127.6, 135.2, 135.7, 137.8, 138.2, 143.4.
Anal. Calcd for C24H32O2S: C, 74,95; H, 8,39. Found: C, 75,-
04; H, 8,47.
2-[2,5-Dipropoxy-4-(2-thiophene-2-ylvinyl)phenyl]-5,5-
dimethyl[1,3]dioxane (14). Dioxolane aldehyde starting
material (43.5 g, 0.129 mol) and thiophenemethyl phosphonate
ester (30 g, 1 equiv) were mixed in THF (500 mL) under argon.
Potassium tert-butoxide (20 g, excess) was dissolved in THF
and added to the reaction mixture in small portions. The
reaction was exothermic and a gel formed. The mixture was
then heated to reflux for 1 h during which time the mixture
became a thin slurry. The cooled reaction mixture was diluted
with water and the solvent evaporated. The yellow oil was
partitioned between water (100 mL) and diethyl ether (250
mL). The organic phase was dried over MgSO4, filtered, and
evaporated to give 52 g oil that solidified on standing. The solid
was triturated with methanol (150 mL) and filtered to give
34 g of moist yellow crystalline material. 1H NMR showed that
this material was slightly impure with a small amount of the
starting aldehyde. The raw material was therefore recrystal-
lized from 150 to 200 mL methanol. Yield: 23 g, 42%. Mp:
113-114 °C. 1H NMR (CDCl3, 250.1 MHz) δ: 0.81 (s, 3H), 1.07
(t, 3H, J ) Hz), 1.10 (t, 3H, J ) Hz), 1.34 (s, 3H), 1.85 (m,
4H), 3.67 (d, 2H, J ) Hz), 3.77 (d, 2H, J ) Hz), 4.00 (m, 4H),
5.75 (s, 1H), 6.99-7.06 (m, 3H), 7.18 (d, 1H, J ) Hz), 7.20 (s,
1H), 7.27 (s, 2H); 13C NMR (CDCl3, 62.9 MHz) δ: 151.1, 150.3,
143.7, 127.5, 127.4, 125.6, 125.6, 124.1, 123.7, 122.4, 115.2,
111.7, 110.9, 97.1, 77.9, 77.030, 76.9, 76.5, 71.1, 71.0, 30.3, 23.2,
4-Bromo-7-methylbenzo-2,1,3-thiadiazole (18). Com-
pound 17 (15 g, 0.1 mol) was dissolved in HBr(aq) 47% (100
mL). The mixture was stirred while bromine (16 g (0.1 mol)
was added. The mixture was stirred and heated. After 5 min,
a solid precipitated. After 30 min, the color of bromine had
disappeared and a colorless sticky adduct had formed. The
mixture was heated to vigorous reflux with vigorous stirring.
A sudden evolution of HBr(g) was observed indicating the
elimination of HBr. Crystals gradually formed on the sides of
the flask. After 16 h, the reaction was stopped. Some of the
product had deposited in the condenser. The colorless product
was extracted with CH2Cl2, and the organic phase was dried
(MgSO4) and evaporated to give the pure product. Yield: 19.75
1
g (86%). Mp: 135-137 °C. H NMR (250 MHz, 300 K, TMS,
CDCl3) δ: 2.57 (s, 3H), 7.06 (d, J ) 7 Hz, 1H), 7.56 (d, J ) 7
Hz, 1H). 13C NMR (63 MHz, 300 K, TMS, CDCl3) δ: 17.4,
111.1, 128.3, 131.1, 131.8, 153.0, 155.0. Anal. Calcd for C7H5-
BrN2S: C, 36.70; H, 2.20; N, 12.24. Found: C, 36.74; H, 1.79;
N, 11.96.
4-Bromo-7-bromomethylbenzo-2,1,3-thiadiazole (19).
Compound 18 (19.7 g, 0.086 mol) was mixed with NBS (15.3
J. Org. Chem, Vol. 70, No. 15, 2005 6013

Jørgensen and Krebs
g, 0.086 mol) and benzoyl peroxide (50 mg) in CCl4 (500 mL).
The mixture was heated to reflux when 33% HBr in AcOH (1
mL) was added. The reaction usually started within a few
minutes and was complete in 30 min. The mixture was
evaporated, and the solids were dissolved in CH2Cl2 (1 L). The
organic phase washed with water (3 × 500 mL), dried over
MgSO4, and evaporated to dryness. The solid could be recrys-
tallized from CCl4 but was sufficiently pure for use in the
subsequent step. Yield: 25.6 g (97%). Mp: 138-140 °C. 1H
NMR (250 MHz, 300 K, TMS, CDCl3) δ: 4.92 (s, 2H), 7.51 (d,
J ) 7 Hz, 1H), 7.79 (d, J ) 7 Hz, 1H). 13C NMR (63 MHz, 300
K, TMS, CDCl3) δ: 27.6, 114.8, 129.8, 130.3, 131.9, 152.9,
153.5. Anal. Calcd for C7H4Br2N2S: C, 27.30; H, 1.31; N, 9.10.
Found: C, 27.51; H, 1.05; N, 9.06.
2,5-Dipropyl-4-(5,5-dimethyl-1,3-dioxan-2-yl)phenylacet-
ylene (23). Compound 21 (34.5 g, 114 mmol) was dissolved
in ether (500 mL) containing pyridine (0.5 mL). The mixture
was cooled to 0 °C. Bromine (5.85 mL, 114 mmol) was added
with stirring. After 10 min, the mixture was evaporated. THF
(500 mL) was added and the product dissolved under argon.
tBuOK (30 g, excess) was added and the mixture heated to
reflux. After 1 h, the reaction was complete. The mixture was
cooled, and water (500 mL) was added. The organic phase was
separated and dried. Evaporation gave an oil that was distilled
on a microdistillation apparatus. A prefraction (1 g) boiling
up to 170 °C was discarded. The fraction boiling at 170-176
°C/0.007mbar was collected. Yield: 17.25 g (40%). 1H NMR
(250 MHz, 300 K, TMS, CDCl3) δ: 0.81 (s, 3H), 0.99 (t, J ) 8
Hz, 6H), 1.34 (s, 3H), 1.60-1.75 (m, 4H), 2.63 (t, J ) 7 Hz,
2H), 2.77 (t, J ) 7 Hz, 2H), 3.21 (s, 1H), 3.65 (d, J ) 11 Hz,
2H), 3.79 (d, J ) 11 Hz, 2H), 5.55 (s, 1H), 7.31 (s, 1H), 7.51 (s,
1H). 13C NMR (63 MHz, 300 K, TMS, CDCl3) δ: 14.09, 14.15,
21.8, 23.2, 23.9, 24.3, 30.2, 33.7, 36.3, 77.9, 80.1, 82.6, 99.6,
121.7, 126.5, 133.8, 136.5, 137.4, 142.9. Anal. Calcd for
C20H28O2: C, 79.96; H, 9.39. Found: C, 80.12; H, 9.60.
2,5-Dipropoxy-4-(5,5-dimethyl-1,3-dioxan-2-yl)phen-
ylacetylene (24). Compound 22 (38.1 g, 114 mmol) was
dissolved in ether (500 mL) containing pyridine (0.5 mL). The
mixture was cooled to 0 °C, and bromine (5.83 mL, 114 mmol)
was added slowly. The color of the bromine disappeared
immediately. A solid precpipitated. The mixture was evapo-
rated and dissolved in THF (500 mL). tBuOK (30 g, excess)
was added with cooling. The mixture was heated to reflux.
After 1 h, the reaction was complete. The mixture was cooled,
and water was added. The organic phase was separated and
dried. Evaporation gave an oil that was distilled on a micro-
distillation apparatus discarding a small prefraction boiling
below 160 °C/4 × 10-3 mbar. The fraction boiling at 160-180
°C/4 × 10-3 mbar was collected. Yield: 18.5 g (54%). 1H NMR
(250 MHz, 300 K, TMS, CDCl3) δ: 0.77 (s, 3H), 0.99-1.07 (m,
6H), 1.30 (s, 3H), 1.73-1.86 (m, 4H), 3.26 (s, 1H), 3.63 (d, J )
11 Hz, 2H), 3.73 (d, J ) 11 Hz, 2H), 3.88 (t, J ) 6 Hz, 2H),
4.01 (t, J ) 6 Hz, 2H), 5.71 (s, 1H), 6.96 (s, 1H), 7.19 (s, 1H);
13C NMR (63 MHz, 300 K, TMS, CDCl3) δ: 10.48, 10.54, 21.8,
22.6, 23.1, 30.2, 70.8, 71.0, 77.8, 80.1, 81.1, 96.7, 111.7, 112.6,
117.7, 129.0, 149.6, 154.7. Anal. Calcd for C20H28O4: C, 72.26;
H, 8.49. Found: C, 71.94; H, 8.74.
1-Tributylstannyl-2-(2,5-dipropyl-4-(5,5-dimethyl-1,3-
dioxan-2-yl)phenyl)ethylene (25). The ethyne (8 g, 26.6
mmol) was mixed with tributylstannyl hydride (8 g, slight
excess) neat and heated under argon to 50 °C. The reaction
was followed using NMR and was found to proceed smoothly
over a few hours. The appearance of two doublets and
disappearance of the acetylenic proton is easy to follow. After
3 h, tributylstannyl hydride (1.5 g) was added and the
temperature increased to 100 °C for 30 min. This completed
the reaction that would seem to be a 2:1 mixture of cis and
trans (or trans and cis). The mixture was used directly.
HWE Reactions of the Monomers (1-5) with Aromatic
Aldehydes and Extension to the Dimers and Trimers.
General Procedure. 4-(2-{4-[2-(4-Methoxyphenyl)vinyl]-
phenyl}vinyl)-2,5-dipropoxybenzaldehyde (27). Monomer
2 (1.3 g, 2.3 mmol) and 4-methoxybenzaldehyde (0.52 g, 3.8
mmol, excess) were dissolved in THF (50 mL), and the mixture
was heated to reflux and treated with potassium tert-butoxide
(0.7 g, excess). The reaction mixture was stirred at reflux for
30 min to complete the HWE reaction. Concentrated hydro-
chloric acid (5 mL) was added and reflux continued for 30 min
to hydrolyze the acetal function. The solvent was removed in
a vacuum and the residue mixed with water (25 mL). The solid
product was filtered off, washed with water (2 × 25 mL) and
ethanol (2 × 25 mL), and finally dried in a vacuum. Yield: 0.81
g, 76%. A small sample was recrystallized from acetonitrile.
Mp: 168-9 °C. 1H NMR (CDCl3, 250.1 MHz) δ: 1.10 (t, 6H, J
) 7 Hz), 1.89 (p, 4H, J ) 7 Hz), 3.83 (s, 3H), 4.00 (t, 2H, J )
7 Hz), 4.07 (t, 2H, J ) 6 Hz), 6.91, (d, 2H, J ) 9 Hz), 6.97 (d,
4-Bromo-7-(diethylphosphonomethyl)benzo-2,1,3-thia-
diazole (20). Compound 19 (25.6 g, 0.083 mol) was refluxed
in triethyl phosphite (100 mL) for 1 h. Evaporation of the
triethyl phosphite gave a yellow oil that was distilled using a
microdistillation apparatus. The product was collected as a
yellow oil discarding two prefractions. Bp: 220-232 °C/0.01
1
× 10-3 bar. Yield: 22.9 g (73%). H NMR (250 MHz, 300 K,
TMS, CDCl3) δ: 1.07 (t, J ) 7 Hz, 6H), 3.57 (d, J ) 22 Hz,
2H), 3.94 (q, J ) 7 Hz, 4H), 7.36 (dd, J1 ) 7 Hz, J2 ) 4 Hz,
1H), 7.65 (d, J ) 7 Hz, 1H). 13C NMR (63 MHz, 300 K, TMS,
CDCl3) δ: 16.68 (d, J ) 6 Hz), 29.30 (d, J ) 140 Hz), 62.65 (d,
J ) 6 Hz), 113.06 (d, J ) 5 Hz), 125.54 (d, J ) 10 Hz), 130.38
(d, J ) 7 Hz), 132.35 (d, J ) 4 Hz), 153.40 (d, J ) 2 Hz), 154.73
(d, J ) 6 Hz). Anal. Calcd for C11H14BrN2O3PS: C, 36.18; H,
3.86; N, 7.67. Found: C, 35.80; H, 3.39; N, 7.69.
2,5-Dipropyl-4-(5,5-dimethyl-1,3-dioxan-2-yl)styrene
(21). Compound 11 (45.6 g, 150 mmol) was mixed with
triphenylphosphonium bromide (60 g, excess) in dry THF (500
mL) under argon. tBuOK (20 g, excess) was added slowly in
portions. The mixture acquired a yellow color and became
warm. The mixture was stirred under argon for 24 h. The
mixture was poured into water (1 L), and the THF was
evaporated. The mixture was extracted with ether, and the
ether phase was dried and evaporated to a volume of 250 mL
and passed through a column packed with silica (10 cm Ø ×
10 cm). The product eluted first and was obtained as a light
1
yellow oil. Yield: 36.75 g (81%). H NMR (250 MHz, 300 K,
TMS, CDCl3) δ: 0.81 (s, 3H), 0.95-1.03 (m, 6H), 1.34 (s, 3H),
1.5-1.7 (m, 4H), 2.58-2.70 (m, 4H), 3.65 (d, J ) 11 Hz, 2H),
3.78 (d, J ) 11 Hz, 2H), 5.25 (dd, J1 ) 2 Hz, J2 ) 11 Hz, 1H),
5.62 (dd, J1)2 Hz, J2)17 Hz, 1H), 5.53 (s, 1H), 6.96 (dd, J1 )
11 Hz, J2 ) 17 Hz, 1H), 7.28 (s, 1H), 7.43 (s, 1H). 13C NMR
(63 MHz, 300 K, TMS, CDCl3) δ: 14.18, 14.23, 21.9, 23.2, 24.3,
24.7, 30.2, 34.2, 35.1, 77.9, 100.0, 114.9, 126.8, 127.2, 134.7,
135.2, 136.6, 137.7, 137.8. Anal. Calcd for C20H30O2: C, 79.42;
H, 10.00. Found: C, 78.55; H, 10.19.
2,5-Dipropoxy-4-(5,5-dimethyl-1,3-dioxan-2-yl)-
styrene (22). Compound 12 (50 g, 149 mmol) was mixed with
triphenylphosphonium bromide (60 g, excess) in dry THF (500
mL) under argon. tBuOK (20 g, excess) was added slowly in
portions. The mixture became a little more yellow and warm.
The mixture was stirred under argon for 24 h. Water (100 mL)
was added, and the mixture was evaporated. Ether was added,
and the mixture was washed with water. A solid was some-
times observed to crystallize from the aqueous phase (this was
found to be triphenylphosphine oxide). The ether phase was
passed through silica. The product runs in the front and
triphenylphosphine oxide was retained. The pure product was
obtained as a yellow oil. Yield: 45 g (90%). 1H NMR (250 MHz,
300 K, TMS, CDCl3) δ: 0.79 (s, 3H), 1.05 (t, J ) 8 Hz, 6H),
1.33 (s, 3H), 1.74-1.86 (m, 4H), 3.65 (d, J ) 11 Hz), 3.76 (d, J
) 11 Hz), 3.89-4.00 (m, 4H), 5.25 (dd, J1 ) 2 Hz, J2 ) 11 Hz,
1H), 5.72 (dd, J1 ) 2 Hz, J2 ) 18 Hz, 1H), 5.75 (s, 1H), 7.00 (s,
1H), 7.06 (dd, J1 ) 11 Hz, J2 ) 18 Hz, 1H), 7.18 (s, 1H); 13C
NMR (63 MHz, 300 K, TMS, CDCl3) δ: 10.63, 10.67, 21.8, 22.8,
23.2, 30.2, 70.7, 71.0, 77.8, 97.0, 110.8, 111.3, 114.2, 127.5,
128.0, 131.7, 150.2, 150.8. Anal. Calcd for C20H30O4: C, 71.82;
H, 9.04. Found: C, 71.49; H, 9.12.
6014 J. Org. Chem., Vol. 70, No. 15, 2005

Synthesis of Oligo Phenylene Vinylenes with a Series of Monomers
1H, J ) 16 Hz), 7.10 (d, 1H, J ) 16 Hz), 7.17 (s, 1H), 7.24 (d,
1H, J ) 16 Hz), 7.33 (s, 1H), 7.4-7.6 (m, 7H), 10.47 (s, 1H).
13C NMR (CDCl3, 62.9 MHz) δ: 10.6, 10.7, 22.6, 55.3, 70.6,
70.7, 110.1, 110.5, 114.2, 122.5, 124.2, 126.0, 126.6, 127.2,
127.8, 128.5, 130.0, 131.9, 134.4, 136.2, 137.7, 150.7, 156.2,
159.4, 189.0. MS: m/z 456.2312, calcd for C30H32O4 (MH+)
456.2301.
138.3, 138.4, 140.8, 141.5, 142.2, 142.4, 142.5, 143.1, 143.6,
159.4, 191.7. MS: m/z 1019.4937, calcd for C68H74O2S3 (MH+)
1019.4924.
4-(2-{5-[2-(4-Methoxyphenyl)vinyl]thiophene-2-yl}vinyl)-
2,5-dipropoxybenzaldehyde (33). Prepared from 4-meth-
oxybenzaldehyde and monomer 4 as above. Recrystallized from
ethanol to give red powder. Yield: 67%. Mp: 134-135 °C. UV-
vis [chloroform, λmax(ꢀ)]: 440 (42 700). 1H NMR (CDCl3, 250.1
MHz) δ: 1.09 (t, 3H, J ) 7 Hz), 1.11 (t, 3H, J ) 7 Hz), 1.81-
1.96 (m, 4H), 3.82 (s, 3H), 3.99 (t, 2H, J ) 6 Hz), 4.05 (t, 2H,
J ) 6 Hz), 6.49 (d, 1H, J ) 4 Hz), 6.91 (d, 2H, J ) 4 Hz),
6.98-7.01 (m, 3H), 7.08 (broad singlet, 1H), 7.20 (d, 1H, J )
16 Hz), 7.31 (s, 1H), 7.37 (d, 1H, J ) 16 Hz), 7.41 (d, 2H, J )
9 Hz), 10.44 (s, 1H). 13C NMR (CDCl3, 62.9 MHz) δ: 10.6, 10.7,
22.6, 55.3, 70.6, 70.7, 110.2, 110.5, 114.2, 119.7, 122.3, 124.1,
125.6, 126.4, 127.7, 128.2, 128.7, 129.6, 133.9, 141.4, 143.5,
150.7, 156.2, 159.5, 188.9. MS: m/z 463.1935, calcd for
C28H30O4S (MH+) 463.1938.
4-[2-(4-{2-[4-(2-{4-[2-(4-Methoxyphenyl)vinyl]phenyl}-
vinyl)-2,5-dipropoxyphenyl]vinyl}phenyl)vinyl]-2,5-dipro-
poxybenzaldehyde (28). The methoxy-terminated monomer
27 from above (0.81 g, 1.7 mmol) and monomer 2 (1.3 g, 2.3
mmol, excess) were reacted as above with potassium tert-
butoxide to give the methoxy-terminated dimer product.
Yield: 1.1 g, 82%. Mp: 191-3 °C. Could be recrystallized from
1
a small amount of benzene. H NMR (CDCl3, 250.1 MHz) δ:
1.11 (t, 6H, J ) 7 Hz), 1.15 (t, 6H, J ) 7 Hz), 1.92 (p, 8H, J )
7 Hz), 3.84 (s, 3H), 3.99-4.12 (m, 8H), 6.89 (d, 2H, J ) 8 Hz),
6.97 (d, 1H, J ) 16 Hz), 7.10 (d, 1H, J ) 16 Hz), 7.12-7.22
(m, 5H), 7.26 (d, 1H, J ) 16 Hz), 7.34 (s, 1H), 7.37 (s, 1H),
7.5-7.6 (m, 12H), 10.48 (s, 1H). MS: m/z 776.3923, calcd for
C52H56O6 (MH+) 776.4077.
4-[2-(5-{2-[4-(2-{5-[2-(4-Methoxyphenyl)vinyl]thiophene-
2-yl}vinyl)-2,5-dipropoxyphenyl]vinyl}thiophene-2-yl)-
vinyl]-2,5-dipropoxybenzaldehyde (34). Prepared from
compound 33 and monomer 4. Yield: 76%. Mp 119-120 °C.
4-{2-[4-(2-{4-[2-(4-{2-[4-(2-{4-[2-(4-Methoxyphenyl)vinyl]-
phenyl}vinyl)-2,5-dipropoxyphenyl]vinyl}phenyl)vinyl]-
2,5-dipropoxyphenyl}vinyl)phenyl]vinyl}-2,5-dipropoxy-
benzaldehyde (29). Compound 28 (1.0 g, 1.3 mmol) and
monomer 2 (1,3 g, 2.3 mmol, excess) were reacted as above to
give the trimer product as an orange powder. Yield: 1.20 g,
83%. Mp: 236-8 °C. UV-vis [chloroform, λmax(ꢀ)]: 452
(142 000). Could be recrystallized from DMF. 1H NMR (CDCl3,
250.1 MHz) δ: 1.08-1.20 (m, 18H), 1.92 (p, 12H, J ) 7 Hz),
3.83 (s, 3H), 3.99-4.1 (m, 12H), 6.91 (d, 2H, J ) 9 Hz), 6.97
(d, 1H, J ) 16 Hz), 7.09 (d, 1H, J ) 16 Hz), 7.1-7.2 (m, 9H),
1
UV-vis [chloroform, λmax(ꢀ)]: 484 (82 200). H NMR (CDCl3,
250.1 MHz) δ: 1.05-1.18 (m, 12H), 1.91 (heptuplet, 8H, J )
7 Hz), 3.83 (s, 3H), 3.99-4.01 (m, 8H), 6.84-7.01 (m, 11H),
7.21-7.28 (m, 5H), 6.86 (d, 2H, J ) 8 Hz), 7.42 (d, 2H, J ) 9
Hz), 10.45 (s, 1H). 13C NMR (CDCl3, 62.9 MHz) δ: 10.6, 10.7,
10.8, 22.6, 22.9, 55.3, 70.7, 70.8, 71.1, 110.7, 114.2, 119.9, 122.5,
124.2, 126.9, 127.6, 129.8, 134.0, 141.8, 142.3, 144.1, 150.8,
151.1, 151.2, 156.2, 159.4, 188.9. MS: m/z 788.3166, calcd for
C48H52O6S2 (MH+) 788.3205.
4-{2-[5-(2-{4-[2-(5-{2-[4-(2-{5-[2-(4-Methoxyphenyl)vinyl]-
thiophene-2-yl}vinyl)-2,5-dipropoxyphenyl]vinyl}-
thiophene-2-yl)vinyl]-2,5-dipropoxyphenyl}vinyl)-
thiophene-2-yl]vinyl}-2,5-dipropoxybenzaldehyde (35).
Prepared from compound 34 and monomer 4. Yield: 89%.
Mp: 120-125 °C. UV-vis [chloroform, λmax(ꢀ)]: 502 (118 000).
1H NMR (CDCl3, 250.1 MHz) δ: 1.04-1.2 (m, 18H), 1.8-2.0
(m, 12H), 3.83 (s, 3H), 4.0-4.1 (m, 12H), 6.8-7.1 (m, 15H),
7.2-7.4 (m, 13H), 10.45 (s, 1H). 13C NMR (CDCl3, 62.9 MHz)
δ: 10.6, 10.7, 10.8, 22.7, 22.9, 55.3, 70.6, 70.7, 71.1, 110.2,
110.5, 114.2, 120.0, 122.5, 123.3, 123.4, 124.1, 125.6, 126.8,
127.6, 128.0, 129.8, 134.0, 141.8, 142.2, 142.3, 144.1, 150.7,
151.1, 151.2, 156.2, 159.4, 188.9. MS: m/z 1115.4611, calcd
for C68H74O8S3 (MH+) 1115.4619.
4-[2-(7-{2-[4-(2-{7-[4-(2-{7-[2-(4-Methoxyphenyl)vinyl]-
benzo[1,2,5]thiadiazol-4-yl}vinyl)-2,5-dipropylphenyl]-
vinyl}benzo[1,2,5]thiadiazol-4-yl}vinyl)-2,5-dipropyl-
phenyl]vinyl}benzo[1,2,5]thiadiazol-4-yl)vinyl]-2,5-di-
propylbenzaldehyde (36). Prepared from monomer 5 and
4-methoxybenzaldehyde in three steps using sodium hydride
as the base. Unfortunately, the yield in each step was rather
poor and the final product was contaminated with some lower
and higher molecular weight components, presumably the
dimer and tetramer. This crude product was purified using
size-exclusion chromatography which left only enough material
for mass spectroscopy and absorption spectroscopy. UV-vis
[chloroform, λmax(ꢀ)]: 310, 499. MS: m/z 1174.5081, calcd for
C74H74N6O2S3 (MH+) 1174.5030.
7.29 (s, 1H), 7.35 (s, 1H), 7.4-7.6 (m, 19 H), 10.48 (s, 1H). 13
C
NMR (CDCl3, 62.9 MHz) δ: 10.6, 10.7, 10.8, 22.7, 22.9, 55.3,
70.6, 70.8, 71.1, 110.2, 110.6, 114.2, 123.2, 124.3, 126.3, 126.6,
126.8, 127.0, 127.2, 127.7, 128.0, 128.5, 130.2, 134.4, 136.4,
136.8, 137.0, 137.1, 137.3, 138.1, 150.8, 151.1, 156.2, 159.3,
189.0 ppm. MS: m/z 1110.6213, calcd for C75H83NO7 (MH+)
1110.6242.
4-(2-{5-[2-(4-Methoxyphenyl)vinyl]thiophene-2-yl}vinyl)-
2,5-dipropylbenzaldehyde (30). Prepared as above from
4-methoxybenzaldehyde and monomer 3. Recrystallized from
ethanol. Yield: 54%. Mp: 98-100 °C. 1H NMR (CDCl3, 250.1
MHz) δ: 1.02 (t, 6H, J ) 7 Hz), 1.59-1.78 (m, 4H), 2.76 (t,
2H, J ) 8 Hz), 3.00 (s, 2H, J ) 8 Hz), 3.84 (s, 3H), 6.9-7.1 (m,
10H), 7.24 (d, 1H, J ) 16 Hz), 7.4-7.5 (m, 3H), 7.64 (s, 1H),
10.23 (s, 1H). 13C NMR (CDCl3, 62.9 MHz) δ: 13.9, 14.0, 24.0,
25.5, 34.2, 34.9, 55.3, 114.3, 119.7, 124.3, 125.5, 126.5, 127.4,
127.7, 128.3, 128.8, 129.6, 132.5, 132.8, 138.3, 140.8, 141.0,
143.1, 143.4, 159.5, 191.7 ppm. MS: m/z 430.1962, calcd for
C28H30O2S (MH+) 430.1967.
4-[2-(5-{2-[4-(2-{5-[2-(4-Methoxyphenyl)vinyl]thiophene-
2-yl}vinyl)-2,5-dipropylphenyl]vinyl}thiophene-2-yl)-
vinyl]-2,5-dipropylbenzaldehyde (31). Prepared from the
methoxyterminated monomer 30 and monomer 3. Used di-
rectly in the next step. Yield: 52%. Mp: 167 °C. 1H NMR
(CDCl3, 250.1 MHz) δ: 1.02 (t, 6H, J ) 7 Hz), 1.04 (t, 6H, J )
6 Hz), 1.61-1.76 (m, 8H), 2.7-2.8 (m, 6H), 3.00 (t, 2H, J ) 7
Hz), 3.84 (s, 3H), 6.8-7.4 (m, 14H), 7.4-7.5 (m, 5H), 7.64 (s,
1H), 7.24 (s, 1H).
4-{2-[5-(2-{4-[2-(5-{2-[4-(2-{5-[2-(4-Methoxyphenyl)vinyl]-
thiophene-2-yl}vinyl)-2,5-dipropylphenyl]vinyl}thio-
phene-2-yl)vinyl]-2,5-dipropylphenyl}vinyl)thiophene-2-
yl]vinyl}-2,5-dipropylbenzaldehyde (33). Prepared from
the dimer 32 and monomer 3. Yield: 67%. Mp: 195-8 °C. UV-
vis [chloroform, λmax(ꢀ)]: 465 (146 000). 1H NMR (CDCl3, 250.1
MHz) δ: 0.97-1.08 (m, 18H), 1.6-1.8 (m, 12H), 2.7-2.8 (m,
10H), 3.01 (t, 2H, J ) 8 Hz), 3.84 (s, 3H), 6.8-7.3 (m, 23H),
7.4-7.5 (m, 7H), 7.65 (s, 1H), 10.24 (s, 1H). 13C NMR (CDCl3,
62.9 MHz) δ: 14.0, 24.1, 25.5, 34.3, 34.9, 35.3, 55.3, 114.2,
119.9, 122.2, 122.6, 124.6, 125.5, 126.5, 126.6, 127.0, 127.6,
128.2, 128.3, 129.8, 132.5, 132.8, 134.4, 134.5, 134.7, 134.8,
4-{2-[4-(5,5-Dimethyl-[1,3]dioxan-2-yl)-2,5-dipropyl-
phenyl]vinyl}-7-[2-(4-methoxyphenyl)vinyl]benzo-
[1,2,5]thiadiazole (37). Monomer 5 (300 mg, 0.5 mmol) and
4-methoxybenzaldehyde (150 mg, 1.1 mmol) were dissolved in
THF (50 mL), sodium hydride (100 mg, 60% dispersion in
mineral oil) was added, and the mixture was heated to reflux
for 1 h. The cooled reaction mixture was then filtered through
a layer of silica to remove excess monomer and basic residues.
The solvent was removed in a vacuum, and the orange red
residue was triturated with hot ethanol (50 mL) and cooled.
The product was filtered off, washed with ethanol (25 mL) and
petroleum ether (2 × 50 mL), and finally dried in a vacuum.
1
Yield: 80 mg 28%. Mp: 126-128 °C. H NMR (CDCl3, 250.1
J. Org. Chem, Vol. 70, No. 15, 2005 6015

Jørgensen and Krebs
MHz) δ: 0.83 (s, 3H), 1.04 (t, 6H, J ) 7 Hz), 1.36 (s, 3H), 1.71
(heptuplet, 4H, J ) 7 Hz), 2.73 (t, 2H, J ) 8 Hz), 2.82 (t, 2H,
J ) 8 Hz), 3.68 (d, 2H, J ) 11 Hz), 3.81 (d, 2H, J ) 11 Hz),
3.86 (s, 3H), 5.56 (s, 1H), 6.94 (d, 2H, J ) 8 Hz), 7.4-7.6 (m,
6H), 7.65 (s, 2H), 7.93 (d, 1H, J ) 16 Hz), 8.34 (d, 1H, J ) 16
Hz). 13C NMR (CDCl3, 62.9 MHz) δ: 14.3, 21.9, 23.3, 24.6, 24.8,
30.2, 34.3, 35.5, 55.3, 77.9, 100.0, 114.2, 122.5, 125.5, 126.2,
126.5, 127.3, 127.7, 128.2, 129.4, 129.6, 130.4, 131.1, 132.7,
135.6, 136.3, 137.9, 138.9, 153.9, 159.8.
(4-[2,2′;6′,2′′]Terpyridin-4′-yl-benzyl)phosphonic Acid
Diethyl Ester (38).33 4′-p-Tolyl[2,2′;6′,2′′]terpyridine was pre-
pared according to the solventless method developed by Cave
and Raston38 and subsequently reacted with N-bromosuccin-
imide (NBS). The 4′-(4-bromomethylphenyl)[2,2′:6′,2′′]terpy-
ridine34 (6.2 g, 15.4 mmol) was mixed with triethyl phosphite
(10 mL, excess) and heated to reflux for 30 min. On cooling,
the product separated as an off-white powder that was
triturated with petroleum ether and filtered off. Yield: 6.3 g,
89%. Mp: 93-94 °C. 1H NMR (CDCl3, 250.1 MHz) δ: 1.24 (t,
6H, J ) 7 Hz), 3.18 (d, 2H, J ) 21 Hz), 4.01 (heptuplet, 4H, J
) 7 Hz), 7.28 (ddd, 2H, J ) 1 Hz, J ) 5 Hz, J ) 7 Hz), 7.41
(dd, 2H, J ) 2 Hz, J ) 8 Hz), 7.77-7.84 (m, 4H), 8.61 (D, 2H,
J ) 8 Hz), 8.68 (d, 2H, J ) 8 Hz), 8.69 (s, 2H).
2,5-Dipropoxy-4-[2-(4-[2,2′;6′,2′′]terpyridin-4′-ylphenyl)-
vinyl]benzaldehyde (39). Prepared from terpyridine benzyl
phosphonate ester and aldehyde 12. Recrystallized from etha-
nol. Yield: 87%. Mp: 222-224 °C. 1H NMR (250 MHz, 300 K,
DMSO-d6-CDCl3 1:1) δ: 1.04 (t, 3H, J ) 7 Hz), 1.06 (t, 3H, J
) 7 Hz), 1.81 (pentuplet, 4H, J ) 7 Hz), 3.96 (t, 2H, J ) 6
Hz), 4.09 (t, 2H, J ) 6 Hz), 7.17 (s, 1H), 7.44 (d, 1H, J ) 17
Hz), 7.52 (d, 1H, J ) 17 Hz), 8.02 (t, 2H, J ) 6 Hz), 8.05 (s,
1H), 8.16 (d, 2H, J ) 8 Hz), 8.59 (t, 2H, J ) 7 Hz), 9.02 (d, 2H,
J ) 5 Hz), 9.07 (s, 2H), 9.24 (d, 2H, J ) 8 Hz), 10.32 (s, 1H).
13C NMR (CDCl3 with 4 dr CF3COOH, 62.9 MHz) δ: 10.4, 22.4,
71.0, 107.7, 112.3, 116.8, 121.3, 123.0, 123.3, 124.9, 125.2,
127.9, 128.0, 134.0, 135.6, 140.0, 142.5, 146.2, 146.8, 148.0,
150.8, 153.6, 157.5, 158.4, 159.1, 159.7, 160.4. MS: m/z
556.2590, calcd for C36H33N3O3 (MH+) 556.2595.
4-[2-(4-{2-[4-(2-{4-[2-(2,5-Dipropoxy-4′-[2,2′;6′,2′′]ter-
pyridin-4′-yl-biphenyl-4-yl)vinyl]phenyl}vinyl)-2,5-di-
propoxyphenyl]vinyl}phenyl)vinyl]-2,5-dipropoxybenz-
aldehyde (40) (Trimer Terpyridin). Prepared from com-
pound 39 and monomer 2 in two HWE reaction/acetal depro-
tection cycles in 43% yield as an orange powder. Mp: 267-
268 °C. UV-vis [chloroform, λmax(ꢀ)]: 451 (126 000). 1H NMR
(250 MHz, 300 K, CDCl3) δ: 1.0-1.2 (m, 18H), 1.8-2.0 (m,
12H), 4.0-4.1 (m, 12H), 7.1-7.4 (m, 14H), 7.47-7.69 (m, 14H),
7.86-7.96 (m, 4H), 8.67-8.78 (m, 6H) 10.47 (s, 1H). 13C NMR
(CDCl3, 62.9 MHz) δ: 10.6, 10.7, 10.8, 22.6, 22.9, 70.7, 71.2,
110.8, 118.5, 121.3, 123.7, 123.7, 126.9, 127.0, 127.2, 127.5,
128.6, 134.4, 136.8, 137.2, 138.9, 149.1, 149.7, 151.2, 156.0,
156.2, 156.4. MS: m/z 1196.6162, calcd for C80H81N3O7 (MH+)
1196.6147.
product above and monomer 1. Yield: 85%. Mp: 144-146 °C.
1H NMR (CDCl3, 250.1 MHz) δ: 1.02 (t, J ) 7 Hz), 1.04 (t, J
) 7 Hz), 1.15 (t, J ) 7 Hz), 1.16 (t, J ) 7 Hz), 1.6-1.8 (m, 4H),
19-2.0 (m, 4H), 2.78 (t, 2H, J ) 8 Hz), 3.02 (t, 2H, J ) 8 Hz),
4.0-4.1 (m, 4H), 5.98 (s, 2H), 6.8-7.2 (m, 11H), 7.26 (s + s,
2H), 7.37 (d, 1H, J ) 16 Hz), 7.5-7.6 (m, 6H), 7.66 (s, 1H),
10.25 (s, 1H). 13C NMR (CDCl3, 62.9 MHz) δ: 10.8, 14.0, 22.9,
24.0, 25.6, 34.2, 34.9, 71.0, 71.1, 101.2, 105.3, 108.5, 110.6,
120.4, 121.4, 126.7, 126.9, 127.2, 127.9, 128.1, 131.6, 132.5,
132.7, 136.2, 138.1, 138.4, 141.3, 141.9, 142.5, 143.1, 147.4,
148.2, 151.1, 151.2, 191.8 ppm. MS: m/z 764.3530, calcd for
C50H52O5S (MH+) 764.3535
Hetero Trimer (43). Prepared from compound 42 and
monomer 5. Yield: 21%. Mp: 198 °C dec. UV-vis [chloroform,
1
λmax(ꢀ)]: 460 (86 000). H NMR (CDCl3, 250.1 MHz) δ: 0.8-
1.2 (m, 18H), 1.6-2.0 (m, 12H), 4.0 (m, 12H), 5.96 (s, 2H), 6.7-
7.7 (m, 28H), 8.41 (d, 1H, J ) 9 Hz), 10.27 (s, 1H). MS: m/z
1111.5112, calcd for C72H74N2O5S2 (MH+) 1111.5112.
Diethyl 2-Thiophene-yl-2-methylphosphonate Ester
and Bisester. Thiophene (84 g, 1 mol) was mixed with
paraformaldehyde (33 g, 1.1 mol) in acetic acid (250 mL) and
cooled using an ice-ethanol bath. HBr (185 mL, ca. 1 mol,
33% in acetic acid) was added in one portion with vigorous
stirring. The temperature increased to 30 °C and then declined
back to 5 °C. After being stirred at that temperature for 1 h,
the mixture was allowed to reach ambient temperature and
then poured into water (2 L). The organic phase was separated,
diluted with chloroform (300 mL), washed with saturated
sodium hydrogen carbonate solution (1 L), dried over magne-
sium sulfate, filtered, and dried. The solvent was removed in
a vacuum to give an oil (110 g) with the approximate composi-
tion 85/15 of 2-bromomethylthiophene and 1,4-bis-bromo-
methylthiophene that was mixed directly with triethyl phos-
phite (200 g, excess) and heated to reflux for 1 h and then
distilled in a vacuum. Yield: 95.3 g of diethyl 2-thiophene-yl-
2-methylphosphonate ester, 40% based on thiophene, bp 112-6
°C at 3 × 10-3 mbar. Continued distillation gave the tetraethyl
thiophene 2,5-bis (methylphosphonate ester). Yield: 24 g.
Bp: 210-45 °C at 3 × 10-3 mbar.
Photovoltaic Characterization. Photovoltaic devices were
prepared on PEDOT/PSS-coated ITO substrates as reported
elsewhere.7 The concentration of the solutions were typically
20 mg mL-1 in chlorobenzene. In the case of the oligomer/
PCBM mixtures this implied a varying absorption intensity
of the oligomer component for the device (see the Supporting
Information). The film absorbencies were in the range 0.7-
0.2. All manipulations were carried out in air. The samples
were then transferred to the vacuum chamber of the evapora-
tor and pumped to a pressure <2 × 10-6 mbar and left for 1 h
before the aluminum electrode (100 nm) was applied by
thermal evaporation. After cooling, the system was purged
with argon and the samples were mounted with silver epoxy
and the thermosetting silver epoxy hardened in an oven at 75
( 5 °C for 15 min. The samples were then analyzed im-
mediately after hardening the silver epoxy. The active area of
the devices was 3 cm-2. The electrical measurements were
carried out using a Keithley 2400 Sourcemeter. The wave-
length dependence of the photovoltaic response was measured
using a high power spectrometer comprised of a 150W water-
cooled Xenon lamp, a blazed diffraction grating, and a movable
arm with the sample. The setup has been described earlier
(see also the Supporting Information).39 The photovoltaic
response under simulated sunlight (AM1.5) was performed
using a Solar Constant 575 from Steuernagel Lichttechnik
GmBH, Germany. The spectrum of the solar simulator was
determined in the wavelength range 180-1100 nm using an
optical spectrum analyzer and was found to have larger
abundance of UV-photons and a smaller abundance of IR
photons. The use of a UV filter was found necessary to
4-{2-[5-(2-Benzo[1,3]dioxol-5-ylvinyl)thiophene-2-yl]-
vinyl}-2,5-dipropoxybenzaldehyde (41). Prepared from
1
piperonal and monomer 4. Yield: 82%. Mp: 137-138 °C. H
NMR (CDCl3, 250.1 MHz) δ: 1.09 (t, 3H, J ) 7 Hz), 1.11 (t,
3H, J ) 7 Hz), 1.87 (p, 2H, J ) 7 Hz), 1.90 (p, 2H, J ) 7 Hz),
4.00 (t, 2H, J ) 6 Hz), 4.06 (t, 2H, J ) 6 Hz), 5.98 (s, 2H), 6.79
(d, 1H, J ) 8 Hz), 6.85 (d, 1H, J ) 16 Hz), 6.89-7.05 (m, 5H),
7.08 (s, 1H), 7.20 (d, 1H, J ) 16 Hz), 7.31 (s, 1H), 7.37 (d, 1H,
J ) 16 Hz), 10.45 (s, 1H). 13C NMR (CDCl3, 62.9 MHz) δ: 10.6,
10.7, 22.6, 70.6, 70.7, 101.2, 105.3, 108.5, 110.2, 110.5, 120.2,
121.5, 122.5, 124.1, 125.6, 126.7, 128.2, 128.8, 131.4, 133.9,
141.6, 143.1, 147.5, 148.2, 150.7, 156.2, 188.9 ppm. MS: m/z
477.1724, calcd for C28H28O5S (MH+) 477.1730.
4-(2-{4-[2-(4-{2-[5-(2-Benzo[1,3]dioxol-5-ylvinyl)thio-
phene-2-yl]vinyl}-2,5-dipropoxyphenyl)vinyl]phenyl}-
vinyl)-2,5-dipropylbenzaldehyde (42). Prepared from the
(38) Cave, G. W. V.; Raston, C. L. J. Chem. Soc., Perkin Trans. 1
2001, 3258-3264.
(39) Krebs, F. C.; Jørgensen, M. Rev Sci. Instrumen. 2003, 74, 3438-
3442.
6016 J. Org. Chem., Vol. 70, No. 15, 2005

Synthesis of Oligo Phenylene Vinylenes with a Series of Monomers
approximate AM1.5 conditions in the wavelength range rel-
evant for this study. The simulated sunlight was then adjusted
to approximately 900-1000 W m-2 using a bolometric precision
pyranometer from Eppley laboratories. The exact incident
power was recorded during each experiment. The temperature
of the devices during measurement was 72 ( 2 °C. The results
were not corrected for mismatch of the spectral response. The
photovoltaic response degraded quickly in the atmosphere for
the pure oligomers and somewhat slower for the oligomer/
PCBM mixtures (see the Supporting Information). In the latter
case, half-lives of the order of 24 h were observed under
illumination (1000 W m-2, AM1.5). The degradation of the
photovoltaic response with time is well-known and mechanistic
studies have been reported recently.40 Reaction with both
oxygen from the atmosphere and the aluminum electrode is
responsible for the degradation.41 Other possible factors
include humidity from the atmosphere.
Acknowledgment. We thank Niller Fagerberg for
technical assistance with the synthesis of 4-methyl-
benzo-2,1,3-thiadiazole. This work was supported by the
Danish Technical Research Council (STVF 26-02-0174,
STVF 2058-03-0016), the Danish Strategic Research
Council (DSF 2104-04-0030), and Public Service Obliga-
tion (PSO 103032 FU 3301).
Supporting Information Available: IV curves, wave-
length scans, and device film UV-vis spectra for all devices
studied. This material is available free of charge via the
Internet at http://pubs.acs.org.
JO0506783
(40) Krebs, F. C.; Carle´, J. E.; Cruys-Bagger, N.; Andersen, M.;
Lilliedal, M. R.; Hammond, M. A.; Hvidt, S. Sol. En. Mater. Sol. Cells
2005, 86, 499-516.
(41) Norrman, K.; Krebs, F. C. Sol. En. Mater. Sol. Cells 2005, web
release April 18, 2005.
J. Org. Chem, Vol. 70, No. 15, 2005 6017