Fine tuning of the electronic properties of linear π-conjugated oligomers by covalent bridging

Article abstract of DOI:10.1002/chem.200500853

A series of oligothienylenevinylenes, π-conjugated oligomers rigidified by ethylene bridges attached at different sites of the conjugated backbone, have been constructed by multistep synthetic methodologies. Electronic absorption spectra show that the rigidification of the conjugated system produces a bathochromic shift of the absorption maximum and a narrowing of the HOMO-LUMO energy gap, as compared to the spectra of an open-chain reference compound. The cyclic voltammograms of all oligomers show that these compounds can be reversibly oxidized into their cation radicals and dications and that rigidification produces a large negative shift of the first oxidation potential, which is indicative of a considerable increase of the HOMO level. Electrochemical data confirm that covalent bridging strongly affects the HOMO and LUMO levels and these data demonstrate that the sites of fixation of the bridges on the π-conjugated backbone exert a determining effect on the relative stability of the cation radical and dication. Examination of these various results in the light of theoretical calculations shows that in addition to a local control of bond length alternation, and hence of the HOMO-LUMO gap, the fixation of covalent bridges at selected positions of the π-conjugated system limits the deformation of the π-conjugated structure upon oxidation to the charged states.

Full text of DOI:10.1002/chem.200500853

DOI: 10.1002/chem.200500853
Fine Tuning of the Electronic Properties of Linear p-Conjugated Oligomers
by Covalent Bridging
Philippe Blanchard,* Patrick Verlhac, Laurent Michaux, Pierre Fr›re, and Jean Roncali*[a]
Abstract: A series of oligothienylenevi-
nylenes, p-conjugated oligomers rigidi-
fied by ethylene bridges attached at
different sites of the conjugated back-
bone, have been constructed by multi-
step synthetic methodologies.Electron-
ic absorption spectra show that the ri-
gidification of the conjugated system
produces a bathochromic shift of the
absorption maximum and a narrowing
of the HOMO–LUMO energy gap, as
compared to the spectra of an open-
chain reference compound.The cyclic
voltammograms of all oligomers show
that these compounds can be reversibly
oxidized into their cation radicals and
dications and that rigidification produ-
ces a large negative shift of the first ox-
idation potential, which is indicative of
a considerable increase of the HOMO
level.Electrochemical data confirm
that covalent bridging strongly affects
the HOMO and LUMO levels and
these data demonstrate that the sites of
fixation of the bridges on the p-conju-
gated backbone exert a determining
effect on the relative stability of the
cation radical and dication.Examina-
tion of these various results in the light
of theoretical calculations shows that in
addition to a local control of bond
length alternation, and hence of the
HOMO–LUMO gap, the fixation of
covalent bridges at selected positions
of the p-conjugated system limits the
deformation of the p-conjugated struc-
ture upon oxidation to the charged
states.
Keywords: conjugation · electronic
properties · oligomers · structure–
property relationships · thiophene
chemistry
Introduction
of the HOMO–LUMO gap of conjugated polymers and
oligomers and hence of the band gap of the resulting materi-
als have received considerable research efforts during the
past two decades.[4–8]
The control of the electronic properties of thiophene-based
p-conjugated systems is currently subject to high interest
motivated by the applications of these systems in organic
devices such as field-effect transistors (OFETs), light-emit-
ting diodes (OLEDs), and solar cells.[1–3] In this context, the
structural control of quantities such as absorption and emis-
sion spectra, oxidation and reduction potentials, or lumines-
cence efficiency represents a key issue.Since most of these
parameters depend on the levels of the frontier orbitals and
their energy gap, synthetic approaches aimed at the control
The HOMO–LUMO gap of linear p-conjugated systems
containing (hetero)aromatic units is governed by various
structural factors such as bond length alternation, planarity,
aromatic resonance energy, and electronic effects of eventu-
al substituents.[4] On these grounds, band-gap engineering
has been developed along different approaches, such as the
increase of the quinonoid character of the ground state as in
poly(benzo[c]thiophene),[5] the introduction of electron-
withdrawing groups on the p-conjugated backbone,[6] or the
synthesis of conjugated systems containing alternant donor
and acceptor groups.[7] Although this latter approach has led
to conjugated polymers with the smallest optical band gaps
known to date,[7] bulk heterojunction solar cells in which
such low-band-gap polymers serve as donor material are
still less efficient than those based on more “classical” poly-
mers of the poly(p-phenylenevinylene) or poly(thiophene)
series.[8] This limited success clearly underlines the need to
pursue research aimed at the parallel development of strat-
egies for band-gap engineering based on different synthetic
principles.
[a] Dr.P.Blanchard, P.Verlhac, L.Michaux, Prof.P.Fr›re,
Dr.J.Roncali
Groupe Syst›mes ConjuguØs LinØaires, CIMMA
CNRS UMR 6200, UniversitØ dꢀAngers
2 Boulevard Lavoisier, 49045 Angers Cedex (France)
Fax : (+33)2-4173-5405
E-mail: philippe.Blanchard@univ-angers.fr
jean.roncali@univ-angers.fr
Supporting information for this article (1H NMR spectra of com-
pounds 3, 4, and 16c, 13C NMR spectrum of compound 3) is available
on the WWW under http://www.chemeurj.org/ or from the author.
1244
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Chem. Eur. J. 2006, 12, 1244 – 1255

FULL PAPER
Extensive studies on oligothienylenevinylenes (nTVs)
have shown that the limitation of rotational freedom and
the reduction of overall aromaticity associated with the in-
sertion of double bonds between thiophene rings confer on
these systems the smallest HOMO–LUMO gap (DE) among
extended p-conjugated oligomers.[9] On such as basis, nTVs
represent a particularly interesting basic structure for the
development of synthetic approaches aimed at fine control
of the electronic properties of p-conjugated systems and of
the corresponding molecular materials.
We have shown already that covalent bridging of the cen-
tral double bond of dithienylethylene (DTE) leads to a sig-
nificant reduction of the HOMO–LUMO gap of the mole-
cule and of the band gap of the resulting polymers.[10] A par-
ticularly demonstrative illustration of the interest of this ap-
proach is provided by the threefold increase of the second-
harmonic-generation efficiency of push–pull NLO-phores
based on bridged-DTE conjugating spacers as compared to
their open-chain analogues.[11]
As a further step, we describe here the synthesis of ex-
tended nTVs in which covalent fasteners have been intro-
duced at various sites of the conjugated structure (2–5).De-
spite its conceptual simplicity, such a task requires the devel-
opment of rather complex and tedious chemistry due to the
need to 1) increase the solubility of the intermediate and
final compounds and 2) define synthetic approaches allow-
ing the fixation of the covalent bridges at various defined
sites of the conjugated system.
The optical and electrochemical properties of these
oligomers have been analyzed by UV/Vis spectroscopy and
cyclic voltammetry and the relationships between the geom-
etry of the p-conjugated structures and their electronic
properties are discussed with the aid of theoretical calcula-
tions.It is shown that, through a proper choice of localiza-
tion of the molecular fasteners and solubilizing side chains,
it is possible to achieve fine tuning of the HOMO and
LUMO levels and of their energy gap.
Results and Discussion
synthesized by two routes.Knoevenagel condensation of al-
dehyde 9 with malonic acid gave the acrylic acid derivative
10, which was subsequently reduced to 13 in the presence of
sodium amalgam.However, due to the hazards inherent in
the large-scale use of this reagent, an alternative route was
Synthesis: The reference open-chain compound 1 was syn-
thesized as already reported.[9,12] Depending on their solubil-
ity, the various bridged oligothienylenevinylenes (2–5) were
synthesized by either McMurry dimerization or Horner–
Wadsworth–Emmons olefination with cyclic ketones 14a–c
as starting materials.The synthesis of 14a and 14b has al-
ready been described,[10c] while that of 14c is depicted in
Scheme 1.Bromination of 3- n-octylthiophene with bromine
in the presence of a catalytic amount of iron powder gave
2,4,5-tribromo-3-octylthiophene (6) in 94% yield.3-Bromo-
4-n-octylthiophene (7) was obtained in 94% yield by treat-
ment of 6 with two equivalents of nBuLi followed by addi-
tion of water.Reaction of 7 with CuCN in refluxing DMF[13]
gave the nitrile derivative 8 in 97% yield.Aldehyde 9 was
obtained in 93% yield by reduction of the nitrile group with
DIBAl-H followed by hydrolysis.The carboxylic acid 13 was
developed.Horner–Wadsworth–Emmons olefination of
9
with triethylphosphonoacetate in the presence of n-butyl-
lithium gave ester 11, which was then hydrogenated to give
compound 12.Saponification of the ester group followed by
acidification gave acid 13 in an overall yield of 91%, based
on 9.The cyclic ketone 14c was prepared from 13 either by
direct intramolecular Friedel–Crafts acylation or by inter-
mediate conversion of 13 into the corresponding acid chlo-
ride, with the latter two-step method giving better yields.
McMurry dimerization[14] of cyclopenta[b]thiophen-6-ones
14a–c gave the various bridged DTEs 16a–c (Scheme 2).
Whereas compounds 16a and 16b were obtained as pure E
isomers,[10c] compound 16c was obtained as a mixture of E
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1245

P.Blanchard, J.Roncali et al.
Scheme 1.Synthesis of cyclic ketone 14c.Oct =octyl, DMF=N,N-di-
methylformamide, DIBAl-H=diisobutylaluminum hydride, PPA=poly-
phosphoric acid, DME=dimethoxyethane.
Scheme 2.Synthesis of compounds 2–5.1,2-DCE =1,2-dichloroethane.
was synthesized by Wittig olefination of dialdehyde 17c
with phosphonium salt 15a.The cyclic Wittig reagent 15a
was obtained by reduction of ketone 14a into the related al-
cohol with NaBH4,[15] followed by reaction with triphenyl-
phosphonium hydrobromide[16] in acetonitrile.
UV/Vis spectroscopy: Table 1 lists the UV/Vis spectro-
scopic data for compounds 1–5.As generally observed for
nTVs,[9] all the spectra exhibit a well-resolved vibronic fine
and Z isomers which were separated by recrystallization and
column chromatography.The target compounds 2–5 were
synthesized according to two different routes depending on
the solubility of the final compound.The most soluble com-
pound 3 was prepared by McMurry coupling of aldehyde
18b and purified by column chromatography.Due to the
creation of a stereogenic center consecutive to the grafting
of the butyl chains at the ethylene bridge, compound 3 was
obtained as a mixture of stereoisomers.
Table 1.Optical data of compounds 1–5 in dichloromethane.
Owing to their poor solubility, compounds 2 and 4 were
prepared by an alternative route based on the Horner–
Wadsworth–Emmons olefination.Aldehydes 18a–c were ob-
tained by Vilsmeier formylation of the corresponding deriv-
atives 16a–c.Dialdehyde 17c was prepared from 16c by the
same method by using an excess of DMF and POCl3.Reduc-
tion of 18a and 18c with NaBH4 gave the intermediate alco-
Compound
l0–2 [nm]
l0–1 [nm]
l0–0 [nm]
DE [eV]
1
2
3
4
5
429
456
460
466
450
458
485
489
495
478
487
520
523
531
513
2.55
2.38
2.37
2.34
2.42
hols.Reaction of the latter compounds with PBr produced
3
the corresponding highly unstable bromo derivatives which
were immediately treated with the anion of diethyl phos-
phate to give phosphonates 19a and 19c.Compounds 2 and
4 were then prepared in 69% and 93% yields, respectively,
by Horner–Wadsworth–Emmons olefination of 18a and 18c
structure with three maxima in the 430–530 nm region
(Figure 1).The quasi constant energy spacing of these
maxima (ꢀ0.16 eV) is consistent with a coupling of the vi-
bronic C=C stretching mode to the electronic structure.[17]
Comparison of the electronic absorption data of the
bridged compound 2 to those of the open-chain reference
with phosphonates 19a and 19c, respectively.Compound
5
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Bridged p-Conjugated Oligomers
FULL PAPER
Figure 1.Electronic absorption spectra of the oligomers in CH 2Cl2.
Dotted line: 1; dotted and dashed line: 2; solid line: 4.
compound 1 reveals a 27 nm bathochromic shift of the ab-
sorption maximum (l0–1) and a 33 nm shift of the maximum
of the 0–0 transition (l0–0), which corresponds to a 0.17 eV
decrease of the HOMO–LUMO gap (DE; Table 1).It is
worth noting that this decrease of DE is two times larger
than that observed between dithienylethylene and its bridg-
ed analogue 16a,[10] but smaller than the 0.40 eV band-gap
reduction observed between the corresponding polymers.[10]
This result confirms that, as expected, the effects of rigidifi-
cation are cumulative and effective on extended oligomers.
Introduction of butyl chains at the ethylene bridge (in 3)
produces a further 3–4 nm red shift of the band maxima.A
slightly larger red shift (ꢀ10 nm) is observed for compound
4 due to the stronger inductive electron-releasing effect of
the alkyl chain when attached at the 3 position of thiophene.
The combined effects of rigidification and inductive effects
result in an overall decrease of the HOMO–LUMO gap of
0.21 eV between oligomers 1 and 4.
Figure 2.Cyclic voltammograms of compounds 1 (top), 4 (middle), and 5
(bottom).Concentration: approximately 0.5 m
m in 0.10m Bu4NPF6/
CH2Cl2, Pt electrodes, scan rate 100 mVsꢁ1
.
Table 2.Cyclic voltammetry data for compounds 1–5.[a]
Compound
E01 [V]
E02 [V]
E0 ꢁE01 [mV]
log K
2
1
2
3
4
5
0.78
0.45
0.44
0.33
0.29
0.94
0.60
0.59
0.51
0.60
160
150
150
180
310
2.71
2.54
2.54
3.05
5.25
Although the structures of all the bridged compounds 2–5
contain four ethylene bridges, the data in Table 1 show that
the red shift of the absorption maxima and the decrease of
DE are noticeably smaller for 5 than for compounds 2–4.
This result clearly evidences the major influence of the posi-
tion of the covalent bridges along the p-conjugated structure
on the delocalization of the p electrons.
[a] Conditions: Concentration=0.05 mm in 0.10m Bu4NPF6/CH2Cl2, Pt
electrodes, scan rate 100 mVsꢁ1, reference electrode Ag/AgCl.
Cyclic voltammetry: The electrochemical properties of
the oligomers were analyzed by cyclic voltammetry in meth-
ylene chloride with tetrabutylammonium hexafluorophos-
phate as the supporting electrolyte.A low substrate concen-
tration (approximately 5”10ꢁ5 m) was used for all com-
pounds because of the low solubility of compounds 2 and 4.
The cyclic voltammetry results of all oligomers exhibit
two reversible one-electron oxidation processes correspond-
ing to the successive generation of the cation radical and di-
cation at redox potentials E0 and E0 (Figure 2).Compari-
and E0 values for compounds 2 and 3 shows that alkyl sub-
2
stituents at the ethylene bridge have little effect on the
HOMO level of the p-conjugated system.By contrast, intro-
duction of octyl chains at the b positions of thiophene as
achieved in compound 4 produces a further 120 mV nega-
tive shift of the E0 value compared to the unsubstituted
1
bridged compound 2.However, the E0 value shifts only by
2
90 mV, which results in an increase of the potential differ-
ence E0 ꢁE0 from 150 to 180 mV.
1
2
2
1
son of the electrochemical data for compounds 1 and 2
(Table 2) shows that covalent bridging of the open-chain
compound 1 induces negative shifts in the E0 and E0 values
Comparison of the data for compound 4 and 5 shows that,
despite the removal of two octyl chains, movement of the
ethylene bridges from the outer to the inner sides of the two
median thiophene rings induces a further negative shift of
1
2
of 330 and 340 mV, respectively.The similarity of the E0
1
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P.Blanchard, J.Roncali et al.
the E0 value from 0.33 V for 4 to 0.29 V for 5, thereby indi-
logues (4’ and 5’’, respectively), while an unsubstituted ana-
logue of 5 (5’) was also computed for comparison with com-
pound 2 (Scheme 3).After optimization, all computed mole-
cules retain a fully planar geometry with an E configuration
and s-trans conformation.
1
cating a further increase of the HOMO level.To the best of
our knowledge, the oxidation potential of compound 5 is the
lowest reached for a p-conjugated chain of comparable
length in the absence of electronic effects due to electron-
donating substituents.For example, this potential is approxi-
mately 0.60 V lower than that of 3’,3’’’’’-dialkylsexithio-
phene[18] although this latter compound contains 12 double
bonds versus the 11 in compounds 1–5.On the other hand,
further comparison of the data for compounds 4 and 5
shows that moving two ethylene bridges from the outer to
the inner sides of the two median thiophene rings leads to a
90 mV positive shift of the E0 value.The two opposite
2
shifts of the E0 and E0 values result in an increase of the
1
2
difference E0 ꢁE0 from 180 to 310 mV.This result shows
2
1
that the position of the bridging groups exerts a considera-
ble influence on the relative stability of the cation radical
versus the dication.In fact, the increase in the E0 ꢁE0
2
1
value corresponds to an increase of more than two orders of
magnitude in equilibrium constant K corresponding to the
disproportionation of the cation radical into the neutral and
dication states (expressed as log K=0.059/E0 ꢁE0 ;
Scheme 3.Structures of the methyl-substituted analogues 4’ and 5’ and
the unsubstituted analogue 5’’.
2
1
Table 1).[19,20]
Figure 3 summarizes the computed energies of the fron-
tier molecular orbitals.These results show that covalent
bridging of the open-chain compound 1 produces an in-
crease of both the HOMO and LUMO levels.However, the
larger increase of the HOMO level results in a narrowing of
the HOMO–LUMO gap.
The calculated values agree well with those derived from
optical and electrochemical data and they confirm that the
lowest DE value is reached for compound 4’, whereas the al-
ternative localization of the ethylene bridges in compound 5
induces a larger upshift of the LUMO level.
Whatever the position of the ethylene bridges, the intro-
duction of alkyl substituents at the b position of thiophene
produces a further upshift of all frontier orbitals.As expect-
ed, the largest effects are observed for 4’ in which four alkyl
groups are added instead of the two in compound 5’’.On
Examination of the values of the HOMO–LUMO gap de-
termined from optical data in the light of the cyclic voltam-
metry data clearly shows that the reduction of the DE value
induced by covalent bridging is associated with a considera-
ble increase (ꢀ0.40–0.50 V) of the HOMO level. However,
the fact that this increase is larger than the corresponding
reduction of the DE value (ꢀ0.20 eV) implies that the cova-
lent bridging of the conjugated system simultaneously in-
creases the HOMO and LUMO levels, with the net reduc-
tion of the DE value resulting from a faster increase of the
HOMO level.
Theoretical calculations: To gain more detailed informa-
tion on the electronic properties of the bridged compounds,
the geometry of oligomers 1–5 was optimized at the DFT//
B3LYP/6-31G** level[21] by using the Gaussian 98 pro-
gram.[22] When not imposed by
covalent bridging, an s-trans
conformation
was
initially
chosen for all single bonds con-
necting a thiophene ring to a
double bond.In all cases, an
E
configuration was also imposed
for all ethylenic linkages.In
fact, these geometrical features
precisely correspond to those
found in the crystal structure of
several
related
com-
pounds.[9d,10b,10c,23] In order to
reduce the computing time
while taking into account the
inductive effect of the alkyl
groups in compounds 4 and 5,
calculations were performed on
Figure 3.B3LYP/6-31G** one-electron energy diagram around the frontier molecular orbitals of 1, 2, 4’, 5’,
their methyl-substituted ana- and 5’’.
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Chem. Eur. J. 2006, 12, 1244 – 1255

Bridged p-Conjugated Oligomers
FULL PAPER
the other hand, compound 5’’ shows the highest HOMO
as for the cation radical, the formation of the dication is
easier for the bridged compounds.
level, a result in agreement with the lowest E0 value found
1
for compound 5.
Examination of the bond lengths of the neutral and charg-
ed states (Table 3) shows that oxidation to the cation radical
and dication leads to a shortening of the single bonds and a
stretching of the double bonds, which results in a progres-
sive inversion of BLA in the dication.However, the struc-
ture of the cation radical remains essentially aromatic and
full transition to a quinonoid structure occurs only for the
dication, as recently demonstrated in the case of oligothio-
phenes.[27] Interestingly, further examination of the changes
of bond lengths upon oxidation shows that covalent bridging
contributes to limit the overall deformation of the conjugat-
ed system.Thus, the average absolute value of bond-length
changes upon oxidation to the cation radical decreases from
0.0185 Š for compound 1 to 0.0179 and 0.0175 Š for com-
pounds 2 and 5’, respectively.
Figure 4 shows the variation of the absolute value of the
bond-length difference jdlj between the neutral and dica-
tion states versus bond number for the three compounds
(Scheme 4).In every case the largest deformation occurs in
the median part of the molecule while the bond lengths of
the external thiophene rings remain practically unchanged.
For the open-chain compound 1, the magnitude of deforma-
tion progressively increases toward the middle of the mole-
cule and the largest bond-length contraction involves the
exocyclic median bonds 10 and 12, which decrease in length
by 0.07 Š when converted into double bonds.
For the bridged compound 2, the largest changes also in-
volve bonds 10 and 12 but the bond-length contraction de-
creases from 0.07 to 0.05 Š. Another noticeable difference
is that upon conversion into single bonds, the two lateral
ethylenic double bonds 5 and 17 in 2 undergo a larger
stretching than those in compound 1.For compound 5’,
bonds 9, 10, 12, and 13 undergo large deformations; howev-
er, the largest stretching is now observed for the median
double bond 11.
Comparison of the average absolute value of bond-length
changes between the neutral and dication states shows that
this quantity decreases from 0.041 Š for compound 1 to
0.037 Š for the bridged compounds 2 and 5’.This result,
Previous crystallographic data have shown that the cova-
lent bridging of DTE into 16b produces a decrease of bond
length alternation (BLA; defined as the difference between
the average length of single and double bonds) from 0.095
to 0.078 Š.[10b,c] As confirmed by experimental and theoreti-
cal results, this reduced BLA is associated with a decrease
of the HOMO–LUMO gap, with an important increase of
the HOMO level.
Optimization of the geometry of DTE and 16b with the
procedure already used for compounds 1–5 leads to calculat-
ed BLA values of 0.063 and 0.061 Š for DTE and 16b, re-
spectively.These results show that the B3LYP/6-31G** level
leads to a substantial underestimation of the BLA.With this
reservation in mind, BLA values of 0.055, 0.053, and
0.054 Š have been calculated for compounds 1, 2, and 5’, re-
spectively.The values are lower than those found for DTE
and 16b, a finding in agreement with previous results show-
ing that chain-length extension tends to reduce the BLA
value.[23] On the other hand, these BLA values are, as ex-
pected, intermediate between those based on crystallograph-
ic data for polyenes (ꢀ0.100 Š)[24] and oligothiophenes
(0.051 Š for sexithiophene).[25] Although modest, the calcu-
lated BLA differences between the open-chain and bridged
oligomers are in qualitative agreement with previous results
and confirm that the reduction of the DE value produced by
covalent bridging of the open-chain system 1 results from a
decrease of bond length alternation.
Oxidation of linear p-conjugated systems with a nonde-
generated ground state, such as poly(p-phenylene) or poly-
(thiophene), into their cation-radical and dication states is
accompanied by a transition from an aromatic to a quino-
noid structure of the aromatic benzene or thiophene ring.[26]
Of course, such a transition implying the inversion of BLA
is accompanied by a major reorganization of the geometry
of the conjugated structure.From this viewpoint, the cova-
lent fastening of several single and double bonds of the con-
jugated backbone can be expected to significantly affect the
geometrical relaxation of the structure.In order to analyze
this question, the geometry of
the cation-radical and dication
Table 3.Bond lengths and BLA values for the neutral, cation-radical, and dication states of the open-chain
compound 1 and the bridged compounds 2 and 5’.
states of compounds 1, 2, and 5’
has been optimized by using
the same base as for the neutral
state.
Compound
Bond number[a]
5/17 6/16 7/15
BLA
1/21
2/20
3/19
4/18
8/14
9/13
10/12 11
1
1.369 1.422 1.383 1.442 1.356 1.436 1.386 1.411 1.386 1.435 1.360
1.377 1.410 1.393 1.422 1.372 1.417 1.407 1.387 1.409 1.406 1.384
1.390 1.396 1.411 1.401 1.395 1.397 1.431 1.368 1.432 1.364 1.410 ꢁ0.026
0.055
0.017
The energy of the singly oc-
1+C
1++
cupied
molecular
orbital
(SOMO) of the cation radical
increases from ꢁ7.62 eV for
compound 1 to ꢁ7.07 eV for
2
1.373 1.420 1.381 1.443 1.359 1.439 1.384 1.409 1.390 1.435 1.361
1.377 1.413 1.392 1.425 1.379 1.416 1.408 1.386 1.411 1.407 1.383
1.384 1.403 1.409 1.406 1.403 1.396 1.432 1.368 1.432 1.383 1.410 ꢁ0.021
0.053
0.017
2+C
2++
compounds
2
and 5’.This
result, which is consistent with
5’
1.372 1.422 1.377 1.444 1.360 1.437 1.392 1.408 1.384 1.438 1.362
1.375 1.415 1.388 1.428 1.376 1.416 1.411 1.386 1.409 1.407 1.392
1.384 1.405 1.404 1.408 1.399 1.395 1.433 1.368 1.434 1.384 1.422 ꢁ0.020
0.054
0.019
a decrease of the E0 value
5’+C
5’++
2
from 0.94 V for 1 to 0.60 V for
2 and 5 (Table 2), confirms that, [a] Bond numbering as shown in Scheme 4.
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P.Blanchard, J.Roncali et al.
Scheme 4.Bond numbering system for the oligomers.
Conclusion
Oligothienylenevinylenes with covalent fasteners attached at
different positions of the p-conjugated backbone have been
synthesized.The relationships between the structure and the
electronic properties of these oligomers have been analyzed
by UV/Vis spectroscopy, cyclic voltammetry and theoretical
calculations with reference to an open-chain compound.
These various investigations show that covalent bridging in-
duces an increase of the energy levels of the frontier orbitals
with a faster upshift of the HOMO, which results in a reduc-
tion of the HOMO–LUMO gap.Experimental and theoreti-
cal results have revealed the importance of the sites of fixa-
tion of the covalent bridges along the p-conjugated structure
for the fine tuning of the energy levels of the neutral and
charged states.An analysis of the geometrical changes asso-
ciated with the oxidation processes has shown that covalent
bridging limits the structural relaxation of the conjugated
structure.This latter result suggests that, besides control of
the energy gap, rigidification of p-conjugated systems by co-
valent bridging represents an interesting tool to reduce the
reorganization energy associated with the charge-transport
process in organic semiconductors.
Experimental Section
1H NMR and 13C NMR spectra were recorded with a Bruker Avance
DRX 500 spectrometer at 500.13 and 125.7 MHz, respectively; Chemical
shift (d) values are given in ppm (relative to TMS) and coupling con-
stants (J) are given in Hz.IR spectra were recorded with a Perkin–
Elmer 841 spectrophotometer by using samples embedded in KBr discs
or thin films between NaCl plates.UV/Vis spectra were recorded with a
Perkin–Elmer Lambda 2 spectrometer by using dichloromethane as the
solvent (HPLC grade from SDS).Melting points are uncorrected.Ele-
mental analyses were performed by the Service Central dꢀAnalyses of the
CNRS (Vernaison, France).Column chromatography purifications were
carried out on Merck Si 60 silica gel (40–63 mm).
Figure 4.Variation of the absolute value of the bond-length difference
between the neutral and the dication states versus bond number for com-
pounds 1 (top), 2 (middle), and 5’ (bottom).
Mass spectrometry analyses were performed on a JMS-700 (JEOL LTD,
Akishima, Tokyo, Japan) double-focusing mass spectrometer with re-
versed geometry, equipped with a pneumatically assisted electrospray-
ionization (ESI) source.Nitrogen was used as the nebulizer gas.The
sample, diluted in a chloroform solution or in a CHCl3/CH3CN (70:30)
mixture, was introduced into the ESI interface through a syringe pump
(PHD 2000 infusion; Harvard Apparatus, Holliston, MA, USA) at a
40 mLminꢁ1 flow rate.A 5 kV acceleration voltage was applied and the
elemental composition of ions was checked by high-resolution measure-
ments by using an electric-field scan with a mixture of poly(ethylene gly-
cols) as the internal standard with nominal molecular weights centered
around 1000.Matrix-assisted laser desorption/ionization MS was per-
formed on a MALDI-TOF MS BIFLEX III Bruker Daltonics spectrome-
ter with dithranol as the matrix.
which confirms the smaller deformation of the bridged p-
conjugated backbone, suggests that the inner-sphere reor-
ganization energy associated with oxidation of bridged con-
jugated systems should be smaller than for the open-chain
analogue.Since this parameter is known to play a major
role in the charge-carrier mobility of the resulting organic
semiconductors,[28] the above results provide a strong incite-
ment to pursue the development of synthetic strategies
aimed at the rigidification of p-conjugated systems.
1250
www.chemeurj.org
ꢁ 2006 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
Chem. Eur. J. 2006, 12, 1244 – 1255

Bridged p-Conjugated Oligomers
FULL PAPER
Cyclic voltammetry was performed in dichloromethane solutions pur-
chased from SDS (HPLC grade).Tetrabutylammonium hexafluorophos-
phate (0.1 or 0.2m as the supporting electrolyte) was purchased from
Acros and used without purification.Solutions were deaerated by nitro-
gen bubbling prior to each experiment that was run under a nitrogen at-
mosphere.Experiments were done in a one-compartment cell equipped
with a platinum working microelectrode (1=1 mm) and a platinum wire
counterelectrode.An Ag/AgCl electrode checked against the ferrocene/
ferricinium couple (Fc/Fc+) before and after each experiment was used
as a reference.Electrochemical experiments were carried out with a
PAR 273 potentiostat with positive feedback compensation.
2 h at ꢁ58C, the reaction mixture was carefully hydrolyzed at ꢁ58C by
addition of a 2:1 mixture of an aqueous solution of 2m HCl and MeOH
(100 mL).The mixture was then warmed to 20 8C and stirred overnight.
After filtration of the mixture and separation of the organic phase, the
aqueous phase was extracted with CH2Cl2.The organic phases were col-
lected, washed with an aqueous solution of 2m HCl, dried over Na2SO4,
and evaporated in vacuo.After purification by filtration on silica gel
(eluent: CH2Cl2), compound 9 was obtained as a yellow oil (20.8 g, 93%
yield): 1H NMR (CDCl3): d=0.88 (t, 3H, 3J=6.9 Hz), 1.30 (m, 10H),
1.59 (m, 2H), 2.89 (t, 2H, 3J=7.7 Hz), 6.98 (d, 1H, 3J=3.3 Hz), 8.07 (d,
1H, 3J=3.3 Hz), 9.98 ppm (s, 1H); 13C NMR (CDCl3): d=14.07, 22.62,
29.14, 29.22, 29.36, 29.96, 31.84, 122.76, 139.39, 140.28, 143.70,
185.70 ppm; EI MS: m/z (%): 224 [M+C] (50), 139 (38), 126 (100), 97
(44); IR (NaCl): n˜ =1687 cmꢁ1 (CꢂO); elemental analysis calcd (%) for
C13H20OS: C 69.59, H 8.98, O 7.13, S 14.29; found: C 69.89, H 9.11, O
7.85, S 13.51.
DFT calculations were carried out by means of the Gaussian 98 pro-
gram.[22] We used the Beckeꢀs three-parameter exchange functional com-
bined with the LYP correlation functional (B3LYP).[21] The 6-31G* basis
for carbon and sulfur atoms and 6-31G basis for hydrogen atoms were
used to optimize the geometry and to compute the electronic structure at
the minima found.The geometry of computed molecules was obtained
by using the Molekel-4.0 program.
(E)-3-(4-n-Octyl-3-thienyl)propenoic acid (10): A mixture of compound 9
(6 g, 26.5 mmol) and malonic acid (5.52 g, 53 mmol) in anhydrous pyri-
dine (30 mL) in the presence of piperidine (1.2 mL) was heated to 1108C
for 2.5 h and then refluxed for 0.5 h. When cooled to 208C, the reaction
mixture was poured into water (100 mL) and an aqueous solution of
25% HCl was dropwise added until the pH value became lower than 7.
The resulting white precipitate was recovered by filtration and dried to
2,4,5-Tribromo-3-n-octylthiophene (6): In the absence of light, bromine
(20.3 mL, 0.3962 mol) was added dropwise over a period of 1.5 h to a so-
lution of 3-n-octylthiophene (25 g, 0.1275 mol) in anhydrous CHCl3
(300 mL) in the presence of a catalytic amount of iron powder (0.72 g,
0.0129 mol). The reaction mixture was stirred for 2 h. After careful addi-
tion of water (50 mL), the mixture was slowly neutralized by an aqueous
solution of 2m NaOH (150 mL).The organic phase was separated by de-
cantation and the aqueous phase was extracted with CH2Cl2 (2”100 mL).
The organic phases were collected and washed with a saturated aqueous
solution of Na2S2O3, dried over Na2SO4, and concentrated to dryness to
afford an orange oil (51.8 g, 94% yield): 1H NMR (CDCl3): d=0.91 (t,
3H, 3J=7.05 Hz), 1.28–1.32 (m, 12H), 2.73 ppm (t, 2H, 3J=7.5 Hz);
13C NMR (CDCl3): d=14.09, 22.65, 28.44, 29.18, 29.25, 29.68, 30.80,
31.84, 108.03, 109.71, 115.76, 141.56 ppm.
1
give 10 as a white powder (6.68 g, 94% yield). M.p. 142–1438C; H NMR
(CDCl3): d=0.89 (t, 3H, 3J=7.05 Hz), 1.31 (m, 10H), 1.61 (m, 2H), 2.68
(t, 2H, 3J=7.5 Hz), 6.32 (d, 1H, 3J=16.0 Hz), 6.98 (d, 1H, 3J=2.8 Hz),
7.63 (d, 1H, 3J=2.8 Hz), 7.76 ppm (d, 1H, 3J=16.0 Hz); 13C NMR
(CDCl3): d=14.09, 22.65, 29.01, 29.22, 29.36, 29.97, 31.84, 117.03, 121.78,
126.48, 135.65, 139.44, 142.55, 172.57 ppm; EI MS: m/z (%): 266 [M+C]
ꢁ1
ꢁ
(32), 168 (100), 123 (33); IR (KBr): n˜ =3000–2400 (O H), 1676 cm (C=
O); elemental analysis calcd (%) for C15H22O2S: C 67.33, H 8.32, O
12.01, S 12.03; found: C 66.88, H 8.41, O 11.70, S 11.73.
3-Bromo-4-n-octylthiophene (7): Under an N2 atmosphere, 2.5m nBuLi
in hexane (84 mL, 0.21 mol) was slowly added over a period of 2 h to a
solution of compound 6 (43.30 g, 0.10 mol) in anhydrous Et2O (220 mL)
cooled to ꢁ58C.After 20 min of additional stirring at ꢁ58C, the reaction
mixture was carefully hydrolyzed at ꢁ58C with vigorous stirring by addi-
tion of an aqueous solution of 4m HCl (50 mL).The mixture was diluted
with Et2O (50 mL) and slowly warmed to 208C.The aqueous phase was
separated and extracted with Et2O (2”100 mL).The organic phases were
collected and washed with water (2”150 mL), dried over Na2SO4, and
evaporated to dryness.The oily residue was purified by chromatography
on silica gel (eluent: petroleum ether) to afford a slightly yellow oil
(25.8 g, 94% yield): 1H NMR (CDCl3): d=0.91 (t, 3H, 3J=7.05 Hz),
1.10–1.43 (m, 10H), 1.50–1.70 (m, 2H), 2.60 (t, 2H, 3J=7.5 Hz), 6.95 (d,
1H, 3J=3.3 Hz), 7.22 ppm (d, 1H, 3J=3.3 Hz); 13C NMR (CDCl3): d=
14.09, 22.65, 29.27, 29.30, 29.36, 29.68, 29.86, 31.85, 112.80, 120.54, 122.59,
128.29 ppm.
(E)-Ethyl-3-(4-n-Octyl-3-thienyl)propenoate (11): A solution of 2.5m
nBuLi in hexane (78 mL, 0.195 mol) was added dropwise over a period
of 1 h to a solution of triethylphosphonoacetate (40 mL, 0.202 mol) in an-
hydrous THF (100 mL) cooled to ꢁ508C under an N2 atmosphere.After
additional stirring for 0.5 h at ꢁ508C, a solution of aldehyde 9 (22.4 g,
0.1 mol) in anhydrous THF (100 mL) was added dropwise over 1 h and
then the reaction mixture was allowed to warm up to 208C overnight.
After addition of a saturated aqueous solution of NH4Cl (140 mL) and
an aqueous solution of 1m HCl (100 mL) and dilution with Et2O
(200 mL), the organic phase was separated, washed with water, dried
(Na2SO4), and concentrated to dryness.The resulting oil was purified by
chromatography on silica gel (eluent: CH2Cl2) to give a yellow oil
(28.36 g, 96% yield): 1H NMR (CDCl3): d=0.88 (t, 3H, 3J=6.9 Hz),
1.25–1.37 (m, 10H), 1.33 (t, 3H, 3J=7.1 Hz), 1.61 (m, 2H), 2.66 (t, 2H,
3J=7.7 Hz), 4.26 (q, 2H, 3J=7.1 Hz), 6.29 (d, 1H, 3J=15.9 Hz), 6.95 (d,
4
4
3
1H, J=3.2 Hz), 7.55 (d, 1H, J=3.2 Hz), 7.65 ppm (d, 1H, J=15.9 Hz);
13C NMR (CDCl3): d=14.07, 14.30, 22.63, 29.01, 29.21, 29.33, 29.36,
29.916, 31.81, 60.37, 118.10, 121.52, 125.37, 135.97, 137.07, 142.39,
167.18 ppm; EI MS: m/z (%): 294 [M+C] (58), 196 (100); IR (NaCl): n˜ =
1712 cmꢁ1 (C=O); elemental analysis calcd (%) for C17H26O2S: C 69.35,
H 8.91, S 10.87, O 10.87; found: C 69.17, H 8.81, S 11.87, O 10.95.
3-Cyano-4-n-octylthiophene (8):
A mixture of compound 7 (25.7 g,
93.4 mmol) and CuCN (9.25 g, 103.3 mmol) in anhydrous DMF (190 mL)
was refluxed for 38 h.The reaction mixture was cooled to 60 8C before a
solution of FeCl3 (31.9 g, 196.5 mmol) in an aqueous solution of 8n HCl
(130 mL) was added.The mixture was then cooled to 20 8C and extracted
with CH2Cl2.The organic phases were washed with water, dried over
Na2SO4, and evaporated in vacuo.The resulting red oil was purified by
column chromatography on silica gel (eluent: CH2Cl2/petroleum ether
(2:8)) to afford 8 as an orange oil (20 g, 97% yield): 1H NMR (CDCl3):
d=0.88 (t, 3H, 3J=6.8 Hz), 1.16–1.41 (m, 10H), 1.61 (m, 2H), 2.73 (t,
2H, 3J=7.7 Hz), 7.01 (d, 1H, 3J=3.1 Hz), 7.86 ppm (d, 1H, 3J=3.1 Hz);
13C NMR (CDCl3): d=14.06, 22.60, 29.04, 29.11, 29.16, 29.24, 29.71,
31.79, 111.99, 115.04, 121.74, 135.40, 144.51 pm; EI MS: m/z (%): 221
[M+C] (11), 150 (7), 136 (8), 123 (100), 57 (11); IR (NaCl): n˜ =2227 cmꢁ1
(C=N); elemental analysis calcd (%) for C13H19NS: C 70.54, H 8.65, N
6.33, S 14.48; found: C 70.44, H 8.67, N 6.25, S 14.47.
Ethyl-3-(4-n-Octyl-3-thienyl)propanoate (12): A mixture of compound 11
(50 g, 0.170 mol) and 10% palladium on activated carbon (5 g) in abso-
lute EtOH (300 mL) was allowed to react with H2 (70 bar, 158C) for
24 h.The mixture was filtered over celite and the solution was concen-
trated to dryness to afford an almost pure product.Further purification
by filtration over silica gel (eluent: CH2Cl2) led to a pure yellow oil
(49.32 g, 98%): 1H NMR (CDCl3): d=0.89 (t, 3H, 3J=6.9 Hz), 1.24–1.39
(m, 10H), 1.28 (t, 3H, 3J=7.2 Hz), 1.59–1.65 (m, 2H), 2.52 (t, 2H, 3J=
7.8 Hz), 2.64 (t, 2H, 3J=7.8 Hz), 2.86 (t, 2H, 3J=7.8 Hz), 4.12 (q, 2H,
3J=7.2 Hz), 6.91 (d, 1H, 4J=3.8 Hz), 6.92 ppm (d, 1H, 4J=3.8 Hz);
13C NMR (CDCl3): d=14.08, 14.18, 22.64, 23.95, 28.72, 29.25, 29.45,
29.55, 29.56, 31.85, 34.16, 60.45, 120.32, 139.73, 141.86, 172.97 ppm; EI
MS: m/z (%): 296 [M+C] (27), 198 (100), 124 (77); IR (NaCl): n˜ =
1734 cmꢁ1 (C=O); elemental analysis calcd (%) for C17H28O2S: C 68.87,
H 9.52, S 10.81, O 10.79; found: C 68.48, H 9.63, S 12.11, O 10.51.
3-Formyl-4-n-octylthiophene (9): A solution of 1m diisobutylaluminum
hydride in CH2Cl2 (130 mL, 0.13 mol) was slowly added to a solution of
compound 8 (22.1 g, 0.1 mol) in anhydrous CH2Cl2 (500 mL) cooled be-
tween ꢁ5 and ꢁ108C under an N2 atmosphere.After being stirred for
Chem. Eur. J. 2006, 12, 1244 – 1255
ꢁ 2006 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
www.chemeurj.org
1251

P.Blanchard, J.Roncali et al.
3-(4-n-Octyl-3-thienyl)propanoic acid (13): Method A: 3% sodium amal-
gam, prepared from sodium (1.56 g, 67.8 mmol) and mercury (50.3 g),
was added portionwise to a solution of compound 10 (6.6 g, 24.8 mmol)
dissolved in an aqueous solution of 2% NaOH (50 mL).After 20 h of
stirring, the resulting mercury was separated by decantation, then the
mixture was cooled to 08C and acidified with an aqueous solution of 1m
HCl.The resulting white precipitate was filtered off and dissolved in
CH2Cl2 and the solution was dried over Na2SO4.After the solution was
evaporated to dryness, compound 13 was obtained as white powder
(6.60 g, 99% yield). Method B: An aqueous solution of 3.5m NaOH
(350 mL, 1.225 mol) was added to a solution of compound 12 (49.13 g,
0.166 mol) in EtOH (250 mL). The reaction mixture was stirred at 908C
for 4 h and then cooled to 08C before concentrated HCl (100 mL) was
carefully added.The resulting white precipitate was recovered by filtra-
tion, washed thoroughly with an aqueous solution of 4m HCl, and dried.
The product was dissolved in CH2Cl2, then the resulting solution was
dried over Na2SO4 and concentrated to dryness to afford compound 13 as
a white powder (43.03 g, 97%). M.p. 92–958C; 1H NMR (CDCl3): d=
48% HBr and PPh3[16]) was added portionwise to this solution over a
period of 10 min.The reaction mixture was then cooled to room temper-
ature.After addition of water (30 mL) and extraction with CH 2Cl2, the
organic phases were washed with water, dried (MgSO4), and concentrat-
ed to dryness.Purification by chromatography on silica gel (eluent:
CH2Cl2 and then MeOH) led to an orange foam (0.99 g, 66% yield):
M.p.=122–1278C; 1H NMR (CDCl3): d=1.54–1.61 (m, 1H), 2.55–2.2.66
(m, 2H), 3.62–3.71 (m, 1H), 6.61 (d, 1H, 3J=4.9 Hz), 6.99 (dd, 1H,
3JH,H =7.2, 2JH,P =8.7 Hz), 7.17 (dd, 1H, 3JH,H =4.9, 5JH,P =3.2 Hz), 7.61–
7.65 (m, 6H), 7.76–7.81 ppm (m, 9H).
6,6’-Bi(4,5-dihydro-6H-3-n-octyl-cyclopenta[b]thienylidene) (16c): After
the dropwise addition of TiCl4 (4.20 mL, 38.2 mmol) to anhydrous THF
(150 mL) cooled to 08C under an N2 atmosphere, zinc powder (4.99 g,
76.3 mmol) was added portionwise. The mixture was successively warmed
to room temperature, refluxed for 30 min, and cooled again to 08C,
before a solution of compound 14c (4.83 g, 19.3 mmol) in anhydrous
THF (120 mL) was added.The reaction mixture was then refluxed for
5 h.At 20 8C, the reaction mixture was filtered over celite.After washing
of the cake of celite with THF, water (100 mL) was added to the solution.
The organic phase was separated by decantation and the aqueous phase
was extracted with CH2Cl2.At this step, the beige precipitate observed at
the interface between the aqueous and the CH2Cl2 organic phase was re-
covered by filtration and washed with Et2O to give a white powder
(0.78 g). The previous cake of celite was also thoroughly washed with hot
CH2Cl2 and all organic phases were collected, washed with water, dried
over Na2SO4, and evaporated to afford a yellow solid (3.77 g). Independ-
ent recrystallizations of the two fractions from CH2Cl2 afforded beige
needles of pure (E)-16c isomer (2.07 g). The filtered solutions were col-
lected and concentrated to dryness and the residue was purified by chro-
matography on silica gel (eluent: CH2Cl2/cyclohexane (5:95)).The result-
ing fraction corresponding to an E/Z mixture was triturated with petrole-
um ether to afford a beige solid (0.88 g) that was a mixture of (E)- and
(Z)-16c isomers.The overall yield of the reaction was 65%, with the E/Z
ratio being approximately 5:1.It was possible to isolate the pure ( Z)-16c
isomer from the mixture by successive recrystallizations from CH2Cl2 to
separate as much as possible of the (E)-16c isomer followed by chroma-
tography on silica gel (adsorption of the mixture on silica gel and elution
with cyclohexane).( E)-16c isomer: Rf =0.62 (cyclohexane); m.p. 118–
1208C; 1H NMR (CDCl3): d=0.88 (t, 6H, 3J=6.9 Hz), 1.25–1.35 (m,
20H), 1.56–1.61 (m, 4H), 2.52 (t, 4H, 3J=7.7 Hz), 2.89–2.91 (m, 4H),
3.21–3.23 (m, 4H), 6.90 ppm (s, 2H); 13C NMR (CDCl3): d=14.03, 22.65,
26.76, 29.25, 29.42, 29.47, 31.88, 32.94, 34.95, 124.04, 126.29, 138.38,
143.58, 149.94 ppm; EI MS: m/z (%): 468 [M+C] (3), 235 (100), 137 (47);
UV/Vis (CH2Cl2): lmax (log e)=367 (3.64), 347 (3.72), 331 nm (3.59); ele-
mental analysis calcd (%) for C30H44S2: C 76.86, H 9.46, S 13.68; found:
C 76.78, H 9.58, S 13.23; (Z)-16c isomer: Rf =0.51 (cyclohexane); m.p.=
65–678C; 1H NMR (CDCl3): d=0.88 (t, 6H, 3J=6.9 Hz), 1.25–1.35 (m,
20H), 1.56–1.61 (m, 4H), 2.51 (t, 4H, 3J=7.7 Hz), 2.81–2.84 (m, 4H),
3.09–3.12 (m, 4H), 6.89 ppm (s, 2H).
3
0.88 (t, 3H, J=7.04 Hz), 1.28 (m, 10H), 1.62 (m, 2H), 2.51 (m, 2H), 2.69
(m, 2H), 2.86 (m, 2H), 6.95 (d, 1H, 3J=2.6 Hz), 7.28 ppm (d, 1H, 3J=
2.6 Hz); 13C NMR (CDCl3): d=14.09, 22.65, 23.64, 28.72, 29.25, 29.45,
29.54, 31.85, 33.82, 65.03, 120.47, 120.54, 139.33, 141.82, 178.96 ppm; EI
MS: m/z (%): 268 [M+C] (22), 170 (100), 123 (30), 111 (20); IR (KBr):
ꢁ1
ꢁ
n˜ =3600–2500 (O H), 1696 cm (C=O); elemental analysis calcd (%)
for C15H24O2S: C 67.12, H 9.01, O 11.92, S 11.94; found: C 66.68, H 9.15,
O 12.21, S 11.78.
4,5-Dihydro-6H-3-octylcyclopenta[b]thiophen-6-one (14c): Method A: A
mixture of compound 13 (6.6 g, 24.06 mmol) and polyphosphoric acid
(6 g) in anhydrous dimethoxyethane (100 mL) was refluxed for 24 h.The
reaction mixture was cooled to 208C and poured into water (200 mL).
After extraction with Et2O (3”200 mL), the organic phases were collect-
ed, washed with water (200 mL), dried over Na2SO4, and concentrated in
vacuo.The residue was purified by column chromatography on silica gel
(eluent: CH2Cl2) to afford an orange oil (2.8 g, 45% yield). Method B: A
mixture of compound 13 (22 g, 82.09 mmol) and thionyl chloride (26 mL,
0.356 mol) in dry Et2O (200 mL) was refluxed for 4 h under an N2 atmos-
phere.After evaporation of the solvent and the excess thionyl chloride,
the resulting oil (25.10 g), the acyl chloride, was directly engaged in the
next step.Thus, a solution of the acyl chloride in CS (150 mL) was
2
added dropwise to a suspension of AlCl3 (13.85 g, 0.1039 mol) in CS2
(200 mL) under an N2 atmosphere.The reaction mixture was refluxed for
16 h, cooled to 208C, and then poured into a mixture of ice (400 mL) and
concentrated HCl (200 mL).After extraction of the aqueous solution
with CH2Cl2, the organic phases were collected, dried over Na2SO4, and
evaporated in vacuo.The residue was purified by chromatography on
silica gel, with CH2Cl2 as the eluent for the first column and a mixture of
CH2Cl2/petroleum ether (3:7) as the eluent for a second column, to
afford a yellow oil (13.75 g, 67% yield): 1H NMR (CDCl3): d=0.87 (t,
3H, 3J=7.0 Hz), 1.18–1.40 (m, 10H), 1.61 (m, 2H), 2.56 (t, 2H, 3J=
7.7 Hz), 2.90–3.00 (m, 4H), 7.48 ppm (s, 1H); 13C NMR (CDCl3): d=
14.10, 22.65, 23.33, 28.31, 29.22, 29.28, 29.35, 31.85, 40.91, 135.27, 139.22,
140.87, 168.72, 197.58 ppm; EI MS: m/z (%): 250 [M+C] (22), 165 (6), 152
(100), 123 (10); IR (NaCl): n˜ =1698 cmꢁ1 (C=O); UV/Vis (CH2Cl2): lmax
(log e)=263 nm (4.58); elemental analysis calcd (%) for C15H22OS: C
71.95, H 8.86, S 12.80; found: C 72.17, H 8.93, S 11.74.
Isomerization of (Z)-16c to (E)-16c: A solution of (Z)-16c isomer
(1.08 g, 2.31 mmol) in CH2Cl2 (30 mL) in the presence of p-toluenesulfon-
ic acid monohydrate (40 mg, 0.21 mmol) was stirred at 208C.The ( E)-16c
isomer slowly started to precipitate and complete conversion to the (E)-
16c isomer was achieved after 2 days, as checked by TLC (SiO2/cyclohex-
ane).Water (50 mL) was added and the mixture was extracted with
CH2Cl2 (4”50 mL).The organic phases were dried (Na 2SO4) and evapo-
rated in vacuo to give a residue, which was adsorbed on silica gel by
evaporation of a CH2Cl2 solution and then purified by chromatography
on silica gel (eluent: cyclohexane) to afford pure (E)-16c isomer (0.76 g,
70% yield).
5,6-Dihydro-4H-cyclopenta[b]thiophen-6-yl triphenylphosphonium bro-
mide (15a): NaBH4 (0.35 g, 9.2 mmol) was added in small amounts over
a period of 10 min to a solution of ketone 14a (0.55 g, 4 mmol) in anhy-
drous EtOH (20 mL) cooled to 08C and the reaction mixture was stirred
at 208C for 7 h.After addition of Et 2O (100 mL) and water (30 mL), the
aqueous phase was separated by decantation and extracted with Et2O
(2”30 mL).The organic phases were collected, washed with a saturated
aqueous solution of NaCl, dried (Na2SO4), and concentrated to dryness.
Chromatography on silica gel (eluent: CH2Cl2) gave the intermediate al-
(E)-2,2’-Diformyl-6,6’-bi(4,5-dihydro-6H-3-n-octyl-cyclopenta[b]thienyli-
dene) (17c): POCl3 (0.37 mL, 4 mmol) was added dropwise to a solution
of compound 16c (0.47 g, 1 mmol) and anhydrous DMF (0.46 mL,
6 mmol) in anhydrous 1,2-dichloroethane (20 mL) under an N2 atmos-
phere.The reaction mixture was refluxed for 16 h and then cooled to
208C before an aqueous solution of 2m sodium acetate (30 mL) was
added and the mixture was stirred for a further 3 h.After extraction with
CH2Cl2, the organic fractions were washed with water, dried over
1
cohol as a yellow oil (0.45 g, 80% yield): H NMR (CDCl3): d=2.09 (brs,
1H), 2.31–2.34 (m, 1H), 2.65–2.69 (m, 1H), 2.84–2.93 (m, 2H), 5.29 (brs,
1H), 6.81 (d, 1H, 3J=4.9 Hz), 7.33 ppm (d, 1H, 3J=4.9 Hz).[15] The rela-
tively unstable alcohol compound was directly dissolved in hot MeCN
(30 mL), then HPPh3Br (1.15 g, 3.35 mmol; prepared from a solution of
1252
www.chemeurj.org
ꢁ 2006 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
Chem. Eur. J. 2006, 12, 1244 – 1255

Bridged p-Conjugated Oligomers
FULL PAPER
Na2SO4, and evaporated in vacuo.The residue was purified by chroma-
tography on silica gel (by adsorption of the residue on silica gel and elu-
tion with CH2Cl2/petroleum ether (1:1)).Dialdehyde 17c was obtained as
a yellow-orange solid (0.35 g, 67% yield). M.p. 191–1948C; 1H NMR
(CDCl3): d=0.88 (t, 6H, 3J=6.9 Hz), 1.26–1.36 (m, 20H), 1.58–1.65 (m,
of THF and MeOH (1:1; 80 mL) and the reaction mixture was stirred
overnight at 208C.After partial concentration of the solvents, an aqueous
solution of 2m HCl (40 mL) was added and the mixture was extracted
with CH2Cl2.The organic phases were thoroughly washed with water,
dried (Na2SO4), and concentrated to dryness to give the intermediate al-
cohol compound as a beige solid (0.84 g, 92% yield). M.p.>1408C
(decomp.); 1H NMR (CDCl3): d=2.90–3.05 (m, 4H), 3.10–3.20 (m, 4H),
3
4H), 2.88 (t, 4H, J=7.7 Hz), 3.00 (brs, 4H), 3.28 (brs, 4H), 9.95 ppm (s,
2H); 13C NMR (CDCl3): d=14.12, 22.66, 26.62, 27.70, 29.21, 29.37, 29.42,
30.62, 31.85, 34.72, 131.82, 142.77, 147.84, 151.60, 153.65, 182.01 ppm; EI
MS: m/z (%): 524 [M+C] (100), 439 (8); HRMS: calcd for C32H44O2S2:
524.278275; found: 524.277643; IR (KBr): n˜ =1646 cmꢁ1 (C=O).
3
3
4.81 (s, 2H), 6.86 (s, 1H), 6.92 (d, 1H, J=4.7 Hz), 7.32 ppm (d, 1H, J=
4.7 Hz); IR (KBr): n˜ =3100–3600 cmꢁ1 (O H); elemental analysis calcd
ꢁ
(%) for C15H14OS2: C 65.66, H 5.14, S 23.37, O 5.83; found: C 65.73, H
5.32, S 21.81, O 6.11. A solution of 1m PBr3 in CH2Cl2 (0.75 mL,
0.75 mmol) was added to a solution of alcohol (0.40 g, 1.46 mmol) in an-
hydrous THF (35 mL) cooled between ꢁ58C and ꢁ108C under an N2 at-
mosphere.After 5 min of additional stirring at between ꢁ58C and
ꢁ108C (the complete conversion of the alcohol was confirmed by TLC),
this solution was rapidly poured onto a solution of NaPO(OEt)2 in anhy-
drous THF at ꢁ108C (freshly prepared by dropwise addition of a solution
of HPO(OEt)2 (0.75 mL, 5.81 mmol) in anhydrous THF (5 mL) to a sus-
pension of 60% NaH dispersion in oil (0.23 g, 5.81 mmol) in anhydrous
THF (10 mL) cooled to ꢁ108C, with the reaction being stirred for 1 h be-
tween ꢁ58C and ꢁ108C under an N2 atmosphere).The reaction mixture
was stirred at 08C for 2 h and was slowly warmed to 208C overnight.
After addition of water (40 mL) and extraction with CH2Cl2, the organic
phases were washed with water, dried (Na2SO4), and evaporated in
vacuo.The oily residue was purified by chromatography on silica gel
(eluent: CH2Cl2/EtOAc (9:1)) to afford a beige solid (0.26 g, 45% yield).
M.p. 123–1268C; 1H NMR (CDCl3): d=1.32 (t, 6H, 3J=7.2 Hz), 2.90–
3.06 (m, 4H), 3.13–3.28 (m, 4H), 3.37 (d, 2H, 2JH,P =21.1 Hz), 4.11 (m,
4H), 6.83 (d, 1H, 4JH,P =3.8 Hz), 6.91 (d, 1H, 3J=4.9 Hz), 7.31 ppm (d,
(E)-2-Formyl-6,6’-bi(4,5-dihydro-6H-cyclopenta[b]thienylidene)
(18a):
POCl3 (0.23 mL, 2.46 mmol) was added dropwise to a solution of bridged
DTE 16a (0.54 g, 2.21 mmol) and anhydrous DMF (0.20 mL, 2.46 mmol)
in anhydrous 1,2-dichloroethane (70 mL) at 08C under an N2 atmosphere.
The reaction mixture was refluxed for 18 h and then cooled to 208C
before an aqueous solution of 2m sodium acetate (50 mL) was added and
the mixture was stirred for a further 3 h.After extraction with CH 2Cl2,
the organic fractions were dried over Na2SO4 and evaporated in vacuo to
give a solid, which was purified by chromatography on silica gel (eluent:
CH2Cl2) to give a yellow-orange powder (540 mg, 83% yield): M.p.=
184–1868C; 1H NMR (CDCl3): d=3.03 (m, 4H, CH2), 3.25 (m, 4H,
CH2), 6.95 (d, 1H, 3J=4.8 Hz), 7.43 (d, 1H, 3J=4.8 Hz), 7.51 (s, 1H),
9.77 ppm (s, 1H, CHO); 13C NMR (CDCl3): d=26.8, 27.4, 34.5, 35.8,
123.2, 125.1, 131.8, 131.9, 133.3, 143.3, 146.6, 150.1, 153.3, 154.1,
182.4 ppm; EI MS: m/z (%): 272 [M+C] (100); IR (KBr): n˜ =1642 cmꢁ1
(C=O); UV (CH2Cl2): lmax =434 nm.
(E)-2-Formyl-6,6’-bi(4-n-butyl-4,5-dihydro-6H-cyclopenta[b]thienylidene)
(18b): POCl3 (0.16 mL, 1.68 mmol) was added dropwise to a solution of
compound 16b (0.50 g, 1.40 mmol) and anhydrous DMF (0.13 mL,
1.68 mmol) in anhydrous 1,2-dichloroethane (17 mL) under an N2 atmos-
phere.The reaction mixture was refluxed for 18 h and then cooled to
208C before an aqueous solution of 2m sodium acetate (30 mL) was
added and the mixture was stirred for a further 3 h.After extraction with
CH2Cl2, the organic fractions were dried over Na2SO4 and evaporated in
vacuo to give a residue, which was purified by chromatography on silica
gel (eluent: CH2Cl2/petroleum ether (1:1)) to give a yellow-orange oil
(0.46 g, 85% yield): 1H NMR (CDCl3): d=0.89–1.10 (m, 6H), 1.30–1.82
(m, 12H), 2.79–2.93 (m, 2H), 3.25–3.51 (m, 4H), 6.97 (d, 1H, 3J=
4.9 Hz), 7.43 (d, 1H, 3J=4.9 Hz), 7.55 (s, 1H), 9.79 ppm (s, 1H);
13C NMR (CDCl3): d=14.04, 22.77, 29.54, 29.71, 36.19, 36.27, 40.07,
40.65, 41.53, 42.87, 124.44, 131.69, 131.72, 132.73, 142.49, 146.47, 153.51,
154.19, 157.43, 182.54 ppm; EI MS: m/z (%): 384 [M+C] (100), 327 (100);
IR (KBr): n˜ =1658 cmꢁ1 (C=O); UV (CH2Cl2): lmax (log e)=434 nm
(4.58); elemental analysis calcd (%) for C23H28S2O: C 71.83, H 7.34, S
16.67, O 4.16; found: C 72.01, H 7.48, S 16.61, O 4.72.
3
1H, J=4.9 Hz); EI MS: m/z (%): 394 [M+C] (38), 257 (100).
Diethylphosphonate 19c: NaBH4 (0.19 g, 5 mmol) was added in small
amounts to a solution of aldehyde 18c (2 g, 4.03 mmol) in a mixture of
THF (120 mL) and MeOH (30 mL) cooled to 08C and the reaction mix-
ture was stirred overnight at 208C.After partial concentration of the sol-
vents, an aqueous solution of 1m HCl (40 mL) was added and the mix-
ture was extracted with CH2Cl2.The organic phases were thoroughly
washed with water, dried (Na2SO4), and concentrated to dryness.Recrys-
tallization from iPr2O gave a beige solid (1.60 g, 80% yield). M.p. 122–
1
1248C; H NMR (CDCl3): d=2.90–3.05 (m, 4H), 3.10–3.20 (m, 4H), 4.81
(s, 2H), 6.86 (s, 1H), 6.92 (d, 1H, 3J=4.7 Hz), 7.32 ppm (d, 1H, 3J=
4.7 Hz); EI MS: m/z (%): 498 [M+C] (32), 482 (75), 480 (85), 382 (100);
IR (KBr): n˜ =3393 cmꢁ1 (O H); elemental analysis calcd (%) for
ꢁ
C31H46OS2: C 74.64, H 9.29, S 12.85, O 3.21; found: C 74.38, H 9.46, S
12.56, O 3.27.
A solution of 1m PBr3 in CH2Cl2 (0.33 mL, 0.33 mmol) was added to a
solution of alcohol (0.50 g, 1 mmol) in anhydrous THF (20 mL) cooled to
08C under an N2 atmosphere.After 5 min of additional stirring at 0 8C
(complete conversion of the alcohol was confirmed by TLC), this solu-
tion was rapidly poured onto a solution of NaPO(OEt)2 in anhydrous
THF at ꢁ208C (freshly prepared by dropwise addition of a solution of
HPO(OEt)2 (0.86 mL, 6.67 mmol) in anhydrous THF (10 mL) to a sus-
pension of 60% NaH dispersion in oil (0.27 g, 6.75 mmol) in anhydrous
THF(10 mL) cooled to ꢁ208C, with the reaction being stirred successive-
ly for 1 h at ꢁ208C and 2 h at 208C, then cooled to ꢁ208C under an N2
atmosphere).The reaction mixture was stirred at ꢁ108C for 1 h and was
slowly warmed to 208C overnight.The mixture was poured onto ice
(100 mL) and Et2O (50 mL) was added.The organic phase was separated
by decantation and the aqueous phase was extracted with CH2Cl2.The
organic phases were dried (Na2SO4) and evaporated in vacuo.The resi-
due was purified by flash chromatography on silica gel (eluents: CH2Cl2,
CH2Cl2/EtOAc (9:1), and CH2Cl2/EtOAc (7:3)) to afford a brown solid
(0.22 g, 35% yield): M.p.=116–1198C; 1H NMR (CDCl3): d=1.32 (t,
6H, 3J=6.9 Hz), 1.27–1.32 (m, 28H), 1.48–1.53 (m, 2H), 2.49–2.53 (m,
4H), 2.88–2.90 (m, 4H), 3.14–3.21 (m, 4H), 3.31 (d, 2H, 2JH,P =21.0 Hz),
4.06–4.12 (m, 4H), 6.89 ppm (s, 1H); EI MS: m/z (%): 618 [M+C] (100),
481 (33); HRMS: calcd for C35H55O3S2P: 618.333028; found: 618.328264.
(E)-2-Formyl-6,6’-bi(4,5-dihydro-6H-3-n-octyl-cyclopenta[b]thienylidene)
(18c): POCl3 (0.50 mL, 5.36 mmol) was added dropwise to a solution of
compound 16c (2.20 g, 4.70 mmol) and anhydrous DMF (0.50 mL,
6.47 mmol) in anhydrous 1,2-dichloroethane (85 mL) under an N2 atmos-
phere.The reaction mixture was refluxed for 4 h and then cooled to
208C before an aqueous solution of 2m sodium acetate (50 mL) was
added and the mixture was stirred for a further 3 h.After extraction with
CH2Cl2, the organic fractions were dried over Na2SO4 and evaporated in
vacuo to give a solid, which was purified by chromatography on silica gel
(by adsorption of the solid on silica gel and elution with CH2Cl2/petrole-
um ether (1:1)).Aldehyde 18c was obtained as yellow crystals after re-
crystallization from iPr2O (1.99 g, 85% yield): M.p.=128–1328C;
1H NMR (CDCl3): d=0.86–0.89 (m, 6H), 1.26–1.35 (m, 20H), 1.60–1.63
(m, 4H), 2.53 (t, 2H, 3J=7.7 Hz), 2.85 (t, 2H, 3J=7.7 Hz), 2.92–2.95 (m,
4H), 3.22–3.27 (m, 4H), 7.04 (s, 1H), 9.90 ppm (s, 1H); 13C NMR
(CDCl3): d=14.13, 14.15, 22.67, 22.70, 26.3, 26.97, 27.72, 29.19, 29.22,
29.29, 29.39, 29.44, 30.63, 31.87, 31.91, 34.14, 35.64, 125.16, 126.76, 133.75,
138.69, 140.92, 142.93, 148.02, 151.04, 153.21, 153.29, 181.55 ppm; UV/Vis
(CH2Cl2): lmax (log e): 437 nm (4.55); elemental analysis calcd (%) for
C31H44OS2: C 74.95, H 8.93, S 12.91, O 3.22; found: C 74.87, H 8.87, S
12.79, O 3.35; IR (KBr): n˜ =1649 cmꢁ1 (C=O).
Diethylphosphonate 19a: NaBH4 (0.24 g, 6.32 mmol) was added in small
amounts to a solution of aldehyde 18a (0.91 g, 3.34 mmol) in a mixture
Compound 2: tBuOK (45 mg, 0.40 mmol) was added in small amounts to
a solution of aldehyde 18a (50 mg, 0.21 mmol) and freshly purified phos-
Chem. Eur. J. 2006, 12, 1244 – 1255
ꢁ 2006 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
www.chemeurj.org
1253

P.Blanchard, J.Roncali et al.
phonate derivative 19a (80 mg, 0.20 mmol) in anhydrous THF (15 mL)
cooled to 08C under an N2 atmosphere.The solution rapidly became
dark red and the mixture was stirred at 208C for 5 h.The solvent of the
reaction was partially evaporated under reduced pressure before MeOH
(25 mL) was added.The resulting precipitate was recovered by filtration
and successively washed with water, MeOH, and Et2O to give a dark
[1] a) C.D. Dimitrakopoulos, P.R.L. Malenfant,
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99; b) J.A. Rogers, Z. Bao, A. Dodabalapur, B.Crone, V.R. Raju,
H.E.Katz, V.Kuck, K.J.Ammundson, P.Drzaic,
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Proc. Natl. Acad.
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red-brown powder (72 mg, 69% yield).Mp.269–272
8C; UV/Vis
(CH2Cl2): lmax (log e)=456 (4.26), 485 (4.32), 520 nm (4.25); EI MS: m/z
(%): 512 [M+C] (100), 482 (33), 384 (24), 257 (31); HRMS: calcd for
C30H24S4: 512.076088; found: 512.075522.
[2] a) A.Kraft, AC. .Grimsdale, AB. .Holmes,
Angew. Chem. 1998,
110, 416; Angew. Chem. Int. Ed. 1998, 37, 402; b) U.Mitschke, P.
Bäuerle, J. Mater. Chem. 2000, 10, 1471.
[3] a) C.J. Brabec, N.S. Sariciftci, J.C. Hummelen,
Compound 3: After the dropwise addition of TiCl4 (0.16 mL, 1.43 mmol)
to anhydrous THF (20 mL) cooled to 08C under an N2 atmosphere, zinc
powder (0.19 g, 2.86 mmol) was added in one portion. The mixture was
successively warmed up to room temperature, refluxed for 30 min, and
Adv. Funct. Mater.
Solar Energy
2001, 11, 15; b) C.Videlot, A.El Kassmi, D.Fichou,
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1939.
cooled again to 08C before
a solution of compound 18b (0.50 g,
Adv. Mater. 2003, 15,
1.30 mmol) in anhydrous THF (50 mL) was added. The reaction mixture
was then refluxed for 1.5 h (completion of the reaction was checked by
TLC with CH2Cl2/petroleum ether (1:9) as the eluent).At 20 8C, water
(40 mL) was added and the mixture was extracted with CH2Cl2.The or-
ganic phases were washed with water, dried (Na2SO4), and concentrated
to dryness.The residue was purified by chromatography on silica gel
(deposition of the residue dissolved in pure CH2Cl2 or THF and elution
with CH2Cl2/cyclohexane (4:6)).The product was then dissolved in the
minimum amount of THF and precipitated with an excess of MeOH
after 1 h at 48C to give a dark red powder (0.33 g, 69% yield) which was
[4] J.Roncali, Chem. Rev. 1997, 97, 173.
[5] F.Wudl, M.Kobayashi, A.J.Heeger,
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1268; b) A.H.Ho, H.Brisset, P.Fr›re, J.Roncali,
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[7] a) E.E.Havinga, W.Ten Hoeve, H.Wynberg, Synth. Met. 1993, 55–
57, 299; b) M.Kozaki, S.Tanaka, Y.Yamashita, J. Org. Chem. 1994,
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59, 442; c) C.Kitamura, S.Tanaka, Y.Yamashita,
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1
1996, 8, 570; d) M.Karikomi, C.Kitamura, S.Tanaka, Y.Yamashita,
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4923; g) I.F.Perepichka, E.Levillain, J.Roncali,
2004, 14, 1679.
a mixture of diastereomers.Mp. .229–232 8C; H NMR (CDCl3): d=0.90–
1.00 (m, 12H), 1.25–1.85 (m, 24H), 2.70–2.94 (m, 4H), 3.15–3.52 (m,
8H), 6.85 (s, 2H), 6.94 (d, 2H, 3J=4.9 Hz), 7.00 (s, 2H), 7.31 ppm (d,
2H, 3J=4.9 Hz); 13C NMR (CDCl3): d=14.11, 22.86, 29.66, 29.71, 29.76,
36.36, 36.44, 40.52, 41.60, 42.38, 120.73, 121.80, 122.73, 125.63, 126.25,
129.39, 142.20, 143.30, 147.22, 154.63, 154.71; EI MS: m/z (%): 736 [M+C]
(42), 370 (100), 313 (86); HRMS: calcd for C46H56S4: 736.326489; found:
736.326242; UV/Vis (CH2Cl2): lmax (log e): 460 (4.55), 489 (4.72), 523 nm
(4.67); elemental analysis calcd (%) for C46H56S4: C 74.95, H 7.66; found:
C 75.02, H 7.52.
J. Mater. Chem.
[8] a) C.Winder, N.S.Sariciftci, J. Mater. Chem. 2004, 14, 1077; b) C.J.
Brabec, C.Winder, N.S.Sariciftci, J.C.Hummelen, A.Dhanabalan,
P.van Hal, R.A.J.Janssen,
Adv. Funct. Mater. 2002, 12, 709; c) F.
Zhang, E.Perzon, X.Wang, W.Mammo, M.R.Andersson, O.Inga-
näs, Adv. Funct. Mater. 2005, 15, 745.
[9] a) J.Roncali, Acc. Chem. Res. 2000, 33, 147; b) E.H. Elandaloussi,
Compound 4: tBuOK (90 mg, 0.80 mmol) was added in small amounts to
a solution of aldehyde 18c (170 mg, 0.34 mmol) and freshly purified
phosphonate derivative 19c (210 mg, 0.34 mmol) in anhydrous THF
(15 mL) cooled to 08C under an N2 atmosphere.The solution rapidly
became dark red and the mixture was stirred at 208C for 5 h.After addi-
tion of MeOH, the resulting precipitate was recovered by filtration and
successively washed with water, MeOH, Et2O, and MeOH to give a dark
P.Fr›re, P.Richomme, J.Orduna, J.Garín, J.Roncali,
J. Am. Chem.
Soc. 1997, 119, 10774; c) I.Jestin, P.Fr›re, P.Blanchard, J.Roncali,
Angew. Chem. 1998, 110, 990; Angew. Chem. Int. Ed. 1998, 37, 942;
d) I.Jestin, P.Fr›re, N.Mercier, E.Levillain, D.Stievenard, J.Ron-
cali, J. Am. Chem. Soc. 1998, 120, 8150.
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J.
1
Chem. Soc. Chem. Commun. 1994, 2249; b) H.Brisset, P.Blanchard,
B.Illien, A.Riou, J.Roncali, Chem. Commun. 1997, 569; c) P.Blan-
red-brown powder (305 mg, 93% yield).Mp. .202–204 8C; H NMR (CS2/
C6D6): d=0.81 (brs, 12H), 1.20 (brs, 40H), 1.48 (brs, 8H), 2.38–2.46 (m,
8H), 2.76 (brs, 8H), 2.99–3.12 (m, 8H), 6.69 ppm (s, 4H); HRMS (ESI):
calcd for C62H88S4: 960.576890; found: 960.5821; UV/Vis (CH2Cl2): lmax
(log e): 466 (4.46), 495 (4.61), 531 nm (4.54).
chard, H.Brisset, B.Illien, A.Riou, J.Roncali,
J. Org. Chem. 1997,
62, 2401.
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chaux, J.Roncali, Chem. Commun. 2000, 1597; b) J.-M. Raimundo,
P.Blanchard, N.Gallego-Planas, N.Mercier, I.Ledoux-Rak, R.
Hierle, J.Roncali, J. Org. Chem. 2002, 67, 205.
Compound 5: tBuOK (130 mg, 1.14 mmol) was added in small amounts
to a solution of dialdehyde 17c (100 mg, 0.19 mmol) and phosphonium
salt 15a (270 mg, 0.57 mmol) in a mixture of anhydrous THF (30 mL)
and anhydrous CH3CN (20 mL) cooled to 08C under an N2 atmosphere.
After concentration to dryness, the residue was purified by two succes-
sive filtrations on silica gel (eluent: CH2Cl2) to afford an orange-brown
powder (20 mg, 14% yield): M.p.=130–1328C; 1H NMR (CS2/C6D6): d=
0.78–0.81 (m, 6H), 1.15–1.24 (m, 20H), 1.32–1.50 (m, 4H), 2.47 (t, 4H,
3J=7.6 Hz), 2.78–2.80 (m, 4H), 2.86–2.88 (m, 4H), 3.08 (brs, 4H), 3.22–
3.24 (m, 4H), 6.49 (brs, 2H), 6.66 (d, 2H, 3J=4.7 Hz), 7.01 ppm (d, 2H,
3J=4.7 Hz); MALDI-TOF MS: calcd for C46H56S4: 736.3264; found:
736.32 [M+C]; UV/Vis (CH2Cl2): lmax (log e): 450 (4.44), 478 (4.57),
513 nm (4.48).
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Sci. B 1987, 25, 1071; b) O.Inganäs, W.Salaneck, J.E.Osterholm, J.
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Received: July 20, 2005
Published online: November 10, 2005
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