Effect of chain extension on the electrochemical and electronic properties of π-conjugated soluble thienylenevinylene oligomers

Article abstract of DOI:10.1021/ja9722739

Thienylenevinylene oligomers (nTVs) containing up to 10 thiophene rings and bearing solubilizing hexyl groups at the α-position of the end thiophene rings or octyl or dibutyl chains at the 3-position or the 3- and 4-positions of the thiophene rings have been synthesized by a combination of formylation reaction, Wittig-Horner olefination, and McMurry dimerization. Owing to the good solubility imparted by alkyl chains, the electrochemical behavior of nTVs has been analyzed for the first time. Chain extension leads to;a negative shift of the peak potentials corresponding to the formation of the cation radical and dication and to a decrease of their difference. For the octamers the dication is formed directly through a two-electron transfer while the system can be reversibly charged up to the tetracationic state. Electronic absorption spectra show the expected bathochromic shift of λ(max) and decrease of the HOMOLUMO gap with extension of the conjugation length. Thus, solution-cast films of octamers exhibit band-gap values electrochemical and optical data to infinite chain length suggests that the oxidation potential and:intrinsic band gap of a defect-free PTV could be significantly smaller than the present experimental values.

Full text of DOI:10.1021/ja9722739

10774
J. Am. Chem. Soc. 1997, 119, 10774-10784
Effect of Chain Extension on the Electrochemical and
Electronic Properties of π-Conjugated Soluble
Thienylenevinylene Oligomers
El Hadj Elandaloussi,† Pierre Fre`re,† Pascal Richomme,‡ J. Orduna,§
J. Garin,§ and Jean Roncali*,†
Contribution from the Inge´nierie Mole´culaire et Mate´riaux Organiques, CNRS UMR 6501,
UniVersite´ d’Angers, 2 Bd LaVoisier, F-49045 Angers, France, SC RMN, UniVersite´ d’Angers,
2 Bd LaVoisier, F-49045 Angers, France, and Laboratorio de Quimica Organica UniVersidad de
Zaragoza, Zaragoza, Spain
ReceiVed July 8, 1997X
Abstract: Thienylenevinylene oligomers (nTVs) containing up to 10 thiophene rings and bearing solubilizing hexyl
groups at the R-position of the end thiophene rings or octyl or dibutyl chains at the 3-position or the 3- and 4-positions
of the thiophene rings have been synthesized by a combination of formylation reaction, Wittig-Horner olefination,
and McMurry dimerization. Owing to the good solubility imparted by alkyl chains, the electrochemical behavior of
nTVs has been analyzed for the first time. Chain extension leads to a negative shift of the peak potentials corresponding
to the formation of the cation radical and dication and to a decrease of their difference. For the octamers the dication
is formed directly through a two-electron transfer while the system can be reversibly charged up to the tetracationic
state. Electronic absorption spectra show the expected bathochromic shift of λmax and decrease of the HOMO-
LUMO gap with extension of the conjugation length. Thus, solution-cast films of octamers exhibit band-gap values
comparable to or even smaller than that of the parent poly(thienylenevinylene) (PTV). Extrapolation of the
electrochemical and optical data to infinite chain length suggests that the oxidation potential and intrinsic band gap
of a defect-free PTV could be significantly smaller than the present experimental values.
Introduction
analysis of the electrochemical and electronic properties of the
corresponding polymers. Thus, the evolution of the electronic
and electrochemical properties of oligothiophenes (nTs) as a
function of chain length has been analyzed by several groups,
and the data obtained have been extrapolated to predict the
oxidation potential, absorption maximum, and band gap of an
infinite defect-free poly(thiophene) (PT) chain.5
More recently, the potentialities of π-conjugated oligomers
as molecular wires6 for future development in molecular
electronics and logic7 has received special attention. Such an
application puts specific requirements on the structure and
properties of the envisioned linear π-conjugated system which
must simultaneously possess precisely controlled structure and
dimensions, good stability, and optimal electron transmission
properties. From this latter viewpoint, simple polyenic struc-
tures should in principle exhibit optimal π-electron delocaliza-
tion as exemplified by the high performances of the derived
push-pull chromophores in nonlinear optics (NLO).8 However,
due to the lack of thermal and photothermal stability of polyenes,
the synthesis of models for molecular wires has been focused
on the more stable p-phenylene,9 phenylene-ethynylene and
thiophene-ethynylene oligomers.10 However, due to excessive
Conjugated oligomers with a well-defined chemical structure
are aquiring a growing importance in the field of organic
conductors. From a technological viewpoint, electronic proper-
ties of these compounds that approach and sometimes even
surpass those of the corresponding polydisperse polymers1-5
have been used in the fabrication of electronic and optoelectronic
devices such as diodes,2 field-effect transistors,3 and light-
emitting diodes (LEDs).4
At a more fundamental level, conjugated oligomers have
attracted considerable interest as model compounds for the
* Author to whom correspondence should be addressed. E-mail: jean.
roncali@univ-angers.fr.
† Inge´nierie Mole´culaire et Mate´riaux Organiques, CNRS UMR 6501,
Universite´ d’Angers.
‡ SC RMN, Universite´ d’Angers.
§ Laboratorio de Quimica Organica Universidad de Zaragoza.
X Abstract published in AdVance ACS Abstracts, October 15, 1997.
(1) Electronic Materials, The Oligomer Approach; Wegner, G., Mu¨llen,
K., Eds.; Wiley: New York, 1996.
(2) (a) Tasaka, S.; Katz, H. E.; Hutton, R. S.; Orenstein, J.; Frederickson,
G. H.; Wang, T. T. Synth. Met. 1986, 16, 17. (b) Fichou, D.; Nishikitani,
Y.; Horowitz, G.; Roncali, J.; Garnier, F. Synth. Met. 1989, 28, C729.
(3) (a) Garnier, F.; Yassar, A.; Hajlaoui, R.; Horowitz, G.; Deloffre, F.;
Servet, B.; Ries, S.; Alnot, P. J. Am. Chem. Soc. 1993, 115, 8716. (b) Katz,
H. E.; Dodabalapur, A.; Torsi, L.; Elder, D. Chem. Mater. 1995, 7, 2238.
(c) Katz, H. E. J. Mater. Chem. 1997, 7, 369.
(6) (a) Lehn, J. M. Angew. Chem., Int. Ed. Engl. 1988, 27, 90. (b)
Effenberger, F.; Schlosser, H.; Ba¨uerle, P.; Maier, S.; Port, H.; Wolf, H. C.
Angew. Chem., Int. Ed. Engl. 1988, 27, 281. (c) Guay, J.; Diaz, A.; Wu,
R.; Tour, J. M. J. Am. Chem. Soc. 1993, 115, 1869. (d) Wu, R.; Schumm,
J. S.; Pearson, D. L.; Tour, J. M. J. Org. Chem. 1996, 61, 6906 and
references therein.
(4) Geiger, F.; Stoldt, M.; Schweizer, R.; Ba¨uerle, P.; Umbach, E. AdV.
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V.; Corbin, D. R. J. Am. Chem. Soc. 1991, 113, 600. (c) ten Hoeve, W.;
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Diaz, A.; Wu, R.; Tour, J. M.; Dao, L. H. Chem. Mater. 1992, 4, 1097. (f)
Ba¨uerle, P.; Segelbacher, U.; Gaudl, K.-U.; Huttenlocher, D.; Mehring, M.
Angew. Chem., Int. Ed. Engl. 1993, 32, 76. (g) Ba¨uerle, P.; Fisher, T.;
Bidlingmeier, B.; Stabel, A.; Rabe, J. P. Angew. Chem., Int. Ed. Engl. 1995,
34, 303.
(7) Aviram, A. J. Am. Chem. Soc. 1988, 110, 5687.
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M.; Bloy, V.; Alain, V. Chem. Phys. 1995, 199, 253. Shu, C.-F.; Tsai, W.
J.; Jen, A. K.-Y.; Zhang, Y.; Chen, T.-A. Chem. Commun. 1996, 2279.
(9) Beley, M.; Chodorowski-Kimmes, S.; Collin, J. P.; Laine´, P.; Launay,
J. P.; Sauvage, J. P. Angew. Chem., Int. Ed. Engl. 1994, 33, 1775.
Grosshenny, V.; Harriman, A.; Ziessel, R. Angew. Chem., Int. Ed. Engl.
1995, 34, 1100.
S0002-7863(97)02273-7 CCC: $14.00 © 1997 American Chemical Society

π-Conjugated Soluble Oligomers
J. Am. Chem. Soc., Vol. 119, No. 44, 1997 10775
Chart 1
Scheme 1a
π-electron confinement, these systems exhibit a rapid saturation
of effective conjugation with chain length.
Poly(thienylenevinylene) (PTV) is known to have a smaller
band gap than PT.11,12 In fact, the presence of double bonds of
defined configuration leads to (i) a decrease of the overall
aromatic character of the system and hence of π-electron
localization and (ii) a limitation of the rotational disorder
inherent to nTs,13 which contributes to increasing the band gap.14
Although the good π-electron delocalization of thienylenevi-
nylene oligomers (nTVs) has been used in the design of NLO
chromophores15 and extended tetrathiafulvalene analogs,16 the
synthesis and the characterization of the electronic properties
of nTVs have attracted much less attention than those of nTs.
Kossmehl first reported the synthesis of nTVs up to the heptamer
by means of a succession of formylation and Wittig reactions.17
More recently, the same compounds have been synthesized by
other groups,18,19 while some cyclic versions of nTVs have been
described by Cava et al.20 As shown in these previous works,
the rapid drop of solubility caused by chain extension has
represented a major obstacle to the development of longer nTVs
and to the detailed investigation of their electronic and
electrochemical properties.17,18
We report here the synthesis and characterization of nTVs
substituted by alkyl chains either at the R-position of the terminal
thiophene rings (Chart 1) or at the â-position or the â,â′-
positions of each thiophene (Charts 2 and 3).21 The enhanced
solubility imparted by substitution allowed extension of the chain
a Reagents and conditions: (a) n-BuLi, DMF/THF, room tempera-
ture; (b) t-BuOK/THF, room temperature; (c) TiCl4, Zn/THF, reflux;
(d) NBS/CHCl3-AcOH, 1:1, room temperature; (e) n-BuLi/Et2O -100
°C, then DMF room temperature; (f) POCl3, DMF/DCE, reflux; (g)
n-BuLi, TMEDA/hexane, reflux, then -40 °C, DMF/THF room
temperature.
(10) Tormos, G.; Nugara, P. N.; Lakshmikantham, M. V.; Cava, M. P.
Synth. Met. 1993, 53, 271. Tour, J. M. Trends Polym. Sci. 1994, 2, 332.
(11) (a) Yamada, S.; Tokito, S.; Tsuisui., T.; Saito, S. J. Chem. Soc.,
Chem. Commun. 1987, 1448. (b) Barker, J. Synth. Met. 1989, 32, 43. (c)
Eckhardt, H.; Shacklette, L. W.; Jen, K. Y.; Elsenbaumer, R. L. J. Chem.
Phys. 1989, 91, 1303.
length up to the octamer and decamer, which are the longest
nTVs reported so far. Owing to this improved solubility, the
electrochemical properties of nTVs have been investigated for
the first time. Electrochemical and optical data are discussed
with regard to their implications for the electronic properties
of PTV as well as for future applications of linear π-conjugated
systems.
(12) Roncali, J. Chem. ReV. 1992, 92, 711.
(13) (a) Alberti, A.; Favaretto, L.; Seconi, G. J. Chem. Soc., Perkin Trans.
2 1990, 931. (b) Barbarella, G.; Zambianchi, M.; Bongini, A.; Antolini, L.
AdV. Mater. 1993, 5, 834. (c) Chadwick, J. E.; Kohler, B. E. J. Phys. Chem.
1994, 98, 3631. (d) Belleteˆte, M.; Leclerc, M.; Durocher, G. J. Phys. Chem.
1994, 98, 9450. (e) Distefano, G.; Da Colle, M.; Jones, D.; Zambianchi,
M.; Favaretto, L.; Modelli, A. J. Phys. Chem. 1993, 97, 3504. (f) Orti, E.;
Viruela, P. M.; Sanchez-Marin, J.; Tomas, F. J. Phys. Chem. 1995, 99,
4955. (g) Horne, J. C.; Blanchard, G. J.; LeGoff, E. J. Am. Chem. Soc.
1995, 117, 955.
Results and Discussion
Three series of nTVs were synthesized. In a first set of
experiments the synthesis of nTVs bearing hexyl chains at the
R-position of the end thiophene rings was carried out (Chart
1). However, due to the limited solubility of these oligomers,
two other series of nTVs based on 3-octylthiophene (series a)
or 3,4-dibutylthiophene (series b) were synthesized (Charts 2
and 3).
(14) Roncali, J. Chem. ReV. 1997, 97, 173.
(15) (a) Rao, V. P.; Jen, A. K.-Y.; Wong, K. Y.; Drost, K. J. Tetrahedron
Lett. 1993, 34, 1747. (b) Rao, V. P.; Cai, Y. M.; Jen, A. K.-Y. J. Chem.
Soc., Chem. Commun. 1994, 1689.
(16) (a) Elandaloussi, E.; Fre`re, P.; Roncali, J.; Richomme, P.; Jubault,
M.; Gorgues, A. AdV. Mater. 1995, 7, 390. (b) Elandaloussi, E.; Fre`re, P.;
Roncali, J. Tetrahedron Lett. 1996, 37, 6121.
(17) (a) Kossmehl, G., Ber. Bunsen-Ges. Phys. Chem. 1979, 83, 417.
(b) Kossmehl, G.; Ha¨rtel, M.; Manecke, G. Makromol. Chem. 1970, 131,
15.
(18) Nakayama, J.; Fujimori, T. Heterocycles 1991, 32, 991.
(19) (a) Spangler, C. W.; Liu, P.-K. Synth. Met. 1991, 44, 259. (b)
Spangler, C. W.; Bryson, P.; Liu, P.-K.; Dalton, L. R. J. Chem. Soc., Chem.
Commun. 1992, 253.
Commercially available 2-hexylthiophene (11) (Lancaster)
was converted into the corresponding 5-carboxaldehyde 12 in
94% yield by lithiation followed by reaction with DMF (Scheme
1). Wittig olefination of 12 using diethyl (2-thienylmethyl)-
(21) Preliminary communication: Elandaloussi, E.; Fre`re, P.; Roncali,
J. Chem. Commun. 1997, 301.
(20) Hu, Z.; Atwood, J. L.; Cava, M. P. J. Org. Chem. 1994, 59, 8071.

10776 J. Am. Chem. Soc., Vol. 119, No. 44, 1997
Elandaloussi et al.
Chart 2
phosphonate (1)22 afforded compound 13a in 87% yield.
Carboxaldehyde 13b was then obtained in 82% yield using the
same method as for 12. Wittig olefination of 13b with 1
afforded 14a (88%), which was subsequently converted into
aldehyde 14b in 73% yield. The target compounds containing
four and six thiophene rings 4h and 6h were then obtained in
41% and 21% yields, respectively, by McMurry coupling of
aldehydes 13b and 14b using low-valent titanium.23
The synthesis of oligomers substituted at the 3-position or
the 3- and 4-positions of the thiophene rings is depicted in
Scheme 2. 3-Octylthiophene (15a) and 3,4-dibutylthiophene
(15b) were synthesized from the corresponding bromothiophenes
by nickel-catalyzed cross coupling with alkyl Grignard re-
agents.24 Regioselective bromination of 15a with NBS gave
15c in 91% yield. Treatment of 15c with n-butyllithium and
reaction with DMF afforded aldehyde 16a in 96% yield.
Vilsmeier formylation of 15b gave aldehyde 16b in 96% yield
while 3,4-dibutyl-2,5-thiophenedicarbaldehyde (16c) was syn-
thesized in 58% yield by reaction of DMF on the dilithiated
derivative of 15b prepared in the presence of TMEDA.25
McMurry coupling of aldehydes 16a and 16b afforded dithi-
enylethylenes 2a and 2b in 89% and 67% yields, respectively.
Vilsmeier formylation of 2a and 2b gave aldehydes 17a and
17b in 70% and 92% yields. Vilsmeier formylation was found
more selective for the preparation of the monoaldehydes than
reaction of DMF on the lithio derivatives, which always gave
a mixture of mono- and dicarboxaldehyde presumably because
of the difficulty of selectively performing metallation at a single
position. 3b with a substituted median thiophene was prepared
in 79% yield by a double Wittig reaction of the dialdehyde 16c
with 1. Conversion of 3b into the monoaldehyde 18b was
achieved in 69% yield by Vilsmeier formylation. McMurry
coupling of aldehydes 17a and 17b afforded 4a and 4b in 71%
and 78% yields, respectively. These compounds were then
converted into the corresponding monoaldehydes 19a and 19b
and dialdehyde 19c by Vilsmeier formylation (yields 38%, 46%,
and 83%, respectively). Oligomers containing six thiophenes
(6a,b) were synthesized by two different routes. Wittig
olefination of dialdehyde 19c with 1 gave 6a in 82% yield, while
6b was obtained by McMurry dimerization of the monoaldehyde
18b (yield 25%). The target compounds 8a and 8b were
synthesized in 25% and 52% yields, respectively, by McMurry
dimerization of aldehydes 19a and 19b. Vilsmeier formylation
of 8b gave the dialdehyde 20b (81%), which was converted
into the longest oligomer 10b by a double Wittig olefination
with 1. All nTVs were satisfactorily characterized by NMR,
(22) Seeboth, H.; Andreae, S. Z. Chem. 1977, 16, 399.
(23) McMurry, J. E. Chem. ReV. 1989, 89, 1513. Fu¨rstner, A.; Bogdanov-
ic, B. Angew. Chem., Int. Ed. Engl. 1996, 35, 2443.
(24) Tamao, K.; Odama, S.; Nakasima, I.; Kumada, M.; Minato, A.;
Suzuki, K. Tetrahedron 1982, 8, 3347.
(25) Ferringa, B. L.; Hulst, R.; Rickers, R.; Bradsma, L. Synthesis 1968,
316.

π-Conjugated Soluble Oligomers
J. Am. Chem. Soc., Vol. 119, No. 44, 1997 10777
Chart 3
1
mass, and UV-vis spectroscopies. For 6b and 8a, H NMR
spectra recorded in C6D6 + CDCl3 (2:1) allowed the separation
of ethylenic and aromatic protons (Figure 1), thus confirming
the all-trans configuration. However, due to their sensitivity
toward oxygen, especially for the longest ones, correct combus-
tion analyses were difficult to obtain in some cases. Therefore,
electrochemical and spectroscopic experiments were performed
on samples purified by column chromatography immediately
before use.
values of the difference Epa(2)-Epa(1) indicate stronger Cou-
lombic repulsion between positive charges in the dication for
4h and 6h. These differences can be related to the smaller
number of alkyl substituents leading to a smaller overall +I
effect. Similarly, nTVs of the b series exhibit less positive Epa
values than those of series a due to the cumulative electron-
releasing effect of the twice larger number of alkyl substituents.
The effect of chain extension on the electrochemical behavior
of nTVs is illustrated in Figures 2-5. The cyclic voltammo-
gram (CV) of 2b exhibits two successive oxidation waves with
Epa(1) and Epa(2) at 0.97 and 1.32 V, respectively. While the
CVs of 2a and 2b exhibit an irreversible first oxidation wave
indicative of a followup chemical reaction, only 2a gives rise
to the formation of a polymeric film upon subsequent redox
cycling. This polymer has already been investigated by
Catellani et al.26 and was not further characterized. The lack
of electropolymerization of 2b is probably related to the
combined effects of the stabilization of the cation radical, as
Cyclic Voltammetry. Table 1 lists the values of the anodic
peak potentials Epa(1) and Epa(2) corresponding to the successive
generation of the cation radical and dication for the various series
of nTVs. Comparison of the data for oligomers 4 and 6 which
are available for three types of substitution shows that, for a
given chain length, nTVs substituted at the â-positions of the
thiophene ring (series a and b) exhibit less positive Epa(1) and
Epa(2) values than their analogs substituted at the R-position of
the end thiophene ring 4h and 6h. Furthermore, the larger

10778 J. Am. Chem. Soc., Vol. 119, No. 44, 1997
Elandaloussi et al.
Scheme 2a
a Reagents and conditions: (a) n-BuLi, DMF/THF, room temperature; (b) t-BuOK/THF, room temperature; (c) TiCl4, Zn/THF, reflux; (d) NBS/
CHCl3-AcOH, 1:1, room temperature; (e) n-BuLi/Et2O -100 °C, then DMF room temperature; (f) POCl3, DMF/DCE, reflux; (g) n-BuLi, TMEDA/
hexane, reflux, then -40 °C, DMF/THF room temperature.
indicated by the ca. 0.10 V lower Epa(1) value, and of the steric
hindrance to planarity during the coupling process caused by
interactions bewteen the butyl groups.12,27
extension leads also to an increase of the number of accessible
oxidation states, and as appears in the CV of 8b (Figure 5), the
two-electron wave is followed by two successive one-electron
waves at 0.78 and 0.93 V (Epa(3) and Epa(4)) indicating that
the system can be charged up to the tetracationic state. Further
chain extension to 10b causes a negative shift of Epa(3) to 0.63
V, but the rather poor definition of the CV due to the low
solubility did not allow us to decide whether this wave involves
one or two electrons.
For both series of nTVs chain extension leads to an increase
of the reversibility of the two oxidation waves, a negative shift
of Epa(1) and Epa(2), and a decrease of the difference Epa(2) -
Epa(1) which reflects the reduction of the on-site Coulombic
repulsion between positive charges in the dicationic state. For
8a and 8b, this evolution results in the coalescence of the two
successive one-electron oxidation peaks into a single-step two-
electron wave, as confirmed by the 30 mV difference between
Epa(1) and the corresponding cathodic peak potential. Chain
Previous studies on different series of substituted thiophene
oligomers from the monomer to the octamer have shown than
nTs are oxidized to the dication state by means of two successive
one-electron oxidation steps.5d,e Extrapolation of the CV data
to an infinite chain length led to different views concerning the
ultimate electrochemical properties of the polymer. The dif-
ference Epa(2) - Epa(1) was predicted either to cancel5d or to
(26) Catellani, M.; Luzzati, S.; Musco, A.; Speroni, F. Synth. Met. 1994,
62, 223.
(27) Roncali, J.; Garreau, R.; Garnier, F.; Lemaire, M. J. Chem. Soc.,
Chem. Commun. 1987, 1500.

π-Conjugated Soluble Oligomers
J. Am. Chem. Soc., Vol. 119, No. 44, 1997 10779
Figure 1. 1H NMR spectrum of 6b in C6D6 + CDCl3 (2:1).
Figure 3. Cyclic voltammogram of 10-4 M 4b in 0.1 M Bu4NPF6/
CH2Cl2: scan rate 100 mV s-1, reference SCE.
Table 1. Cyclic Voltammetric Data for nTVs, 10-4 M Substrate in
a
10-1 M TBAHP in CH2Cl2
Epa(1)
(V)
Epa(2)
(V)
Epa(2) - Epa(1)
Epa(3), Epa(4)
compd
(V)
(V)
4h
6h
2a
4a
6a
0.68
0.66
1.06
0.70
0.60
0.92
0.84
1.39
0.88
0.70
0.24
0.18
0.33
0.18
0.10
0.00
0.35
0.36
0.18
0.12
0.00
0.00
8a
0.56
2b
3b
4b
6b
8b
10b
0.97
0.84
0.60
0.57
1.32
1.20
0.78
0.69
0.45
0.43
0.78, 0.93
0.63
a Pt electrodes, reference SCE, scan rate 100 mV s-1
.
Figure 4. Cyclic voltammogram of 10-4 M 6b in 0.1 M Bu4NPF6/
CH2Cl2: scan rate 100 mV s-1, reference SCE.
corresponding to a third electron transfer was also observed,
thus providing the first evidence for formation of a radical
trication.
In this context, the above results appear particularly interesting
as they provide the first unequivocal evidence for direct
formation of a dication on a conjugated oligomer of homoge-
neous chemical structure. Furthermore the difference between
Epa(1) and the peak corresponding to the formation of the radical
trication (Epa(3)) (0.35 V for 8b and 0.20 V for 10b) is much
smaller than the 0.65 V observed for the pyrrole-thiophene
heptamer.28 This result indicates that the larger chain extension
and the less overall aromatic character of nTVs leads to smaller
Coulombic repulsion between positive charges, thus making
multicationic higher oxidation states more easily accessible, as
confirmed by the tetracationic state reached by 8b.
In a number of recent papers Miller et al. have reported
evidence for the formation of cation radical π-dimers for nTs
and discussed their possible role as alternatives for bipolarons
in particular in the process of interchain charge transport in PT.29
Such cation radical π-dimers have also been observed for the
Figure 2. Cyclic voltammogram of 10-4 M 2b in 0.1 M Bu4NPF6/
CH2Cl2: scan rate 100 mV s-1, reference SCE.
converge to a limit of 0.18 V.5e In fact CV data for the longest
known nTs (16-mer) seem to indicate the occurrence of two
oxidation steps.5f As far as we know, the only evidence for
formation of a dication by a single-step two-electron transfer
in a conjugated heterocyclic oligomer has been reported by
Parakka et al. for a heptamer containing four thiophene cycles
and three pyrrole rings.28 A second reversible one-electron wave
(28) Parakka, J. P.; Jeevarajan, J. A.; Jeevarajan, A. S.; Kispert, L. D.;
Cava, M. P. AdV. Mater. 1996, 8, 54.

10780 J. Am. Chem. Soc., Vol. 119, No. 44, 1997
Elandaloussi et al.
Figure 6. Electronic absorption spectrum of 8a in CH2Cl2.
600-700 nm region in the spectra previously reported for
unsubstituted hexamer and heptamer18 was not observed here.
For a given chain length, nTVs of series b absorb at longer
wavelengths and show smaller ∆E values than those of series
a; these differences reflect the effect of the larger number of
alkyl substituents on the electronic density of the π-conjugated
system. Apart from these modest differences, the spectra of
oligomers of the two series are very similar in shape and exhibit
a well-resolved vibronic fine structure. This fine structure and
the absence of a cis band in these spectra bring further support
to a rigid and all-trans geometry.30 The spectrum of 8a (Figure
6) shows two maxima at 517 and 552 nm and several well-
defined shoulders around 450, 480, and 595 nm. This spectrum
is in agreement with a vibronic structure with a 0-0 transition
at 595 nm and vibronic side bands at higher energy as already
observed for other conjugated polymers and oligomers.31 The
energy difference between two consecutive maxima lies in the
range 0.15-0.17 eV, which is consistent with a CdC stretching
mode strongly coupled to the electronic structure.32
Figure 5. Cyclic voltammogram of 10-4 M 8b in 0.1 M Bu4NPF6/
CH2Cl2: scan rate 100 mV s-1, reference SCE.
Table 2. UV-Visible Spectroscopic Data for nTVs in CH2Cl2
compd
λ
max (nm)
∆E (eV)
4h
6h
2a
4a
6a
465
511
354
473
526
552
556
360
423
488
522
572
580
2.25
2.06
2.94
2.09
1.93
1.84
1.70
2.94
2.52
2.13
1.99
1.78
1.72
8a
8af
2b
3b
4b
6b
8b
10b
As shown in Table 2, the longest oligomers 8a, 8b, and 10b
show HOMO-LUMO gaps (∆E) around 1.70-1.80 eV. These
∆E values are already smaller than the band gap of PT12 and
close to that of PTV.11 In order to confirm this conclusion the
preparation of thin films by solution casting has been attempted.
Oligomers of series b were found less soluble than those of
series a, and solubility decreased dramatically for 10b. Fur-
thermore, films cast from 8b solutions were of limited optical
quality due to their polycrystalline structure. In contrast, 8a
exhibits excellent film-forming properties. The optical spectrum
of a solution-processed film is shown in Figure 7. The
persistence of the vibronic fine structure is consistent with a
well-ordered material while absorption onset indicates a band
gap of ca. 1.70 eV. This value, similar to or even slightly
smaller than that for PTV synthesized by the soluble precursor
route (1.70-1.80 eV),11 suggests that the mean effective
conjugation length of PTV is limited to ca. eight TV units.
Contrary to the spectrum of 8a, that of PTV shows significant
residual absorption in the 2.50-3.50 eV region, which corre-
sponds to the absorption domain of the nonconjugated precursor.
This difference suggests the presence of conjugation defects in
PTV prepared by thermal elimination. In fact, several recent
studies on the parent poly(p-phenylenevinylene) synthesized by
longest nTs (16-mer).5g Although due to the direct access to
the dication such a process seems less probable for long nTVs,
the occurrence of additional one-electron oxidation waves
(radical trication and tetracation) beyond the first two-electron
wave seems difficult to reconcile with the bipolaron theory since,
in this case, a (multi)dicationic state should represent the
ultimate oxidation state. Although such a debate is clearly far
beyond the scope of this paper, the above results pose intriguing
questions regarding either the mechanisms of charge transport
in conducting polymers or the limits of the use of oligomers as
models for the corresponding conjugated polymers.
UV-Vis Spectroscopy. Table 2 lists the main electronic
absorption data for the various nTVs. For each series, chain
extension leads as expected to a bathochromic shift of the
absorption maximum λmax and to a narrowing of the HOMO-
LUMO gap (∆E) estimated from the low-energy absorption
edge. Oligomers with n-hexyl chains at the R-position of the
end thiophene rings absorb at shorter wavelengths and exhibit
larger ∆E values than their â-substituted analogs. The λmax
values for 4h and 6h (465 and 511 nm) are very close to those
reported for unsubstituted nTVs, namely, 460 and 510 nm.17,18
This similarity suggests that introduction of alkyl chains at the
R-position of the end thiophene rings has little influence on the
electronic structure of the π-conjugated system. On the other
hand, it is noteworthy that the additional weak shoulder in the
(30) Jaffe´, H. H.; Orchin, M. Theory and Applications of UltraViolet
Spectroscopy; Wiley: New York, 1962.
(31) Roncali, J.; Korri Youssoufi, H.; Garreau, R.; Garnier, F.; Lemaire,
M. J. Chem. Soc., Chem. Commun. 1990, 414. Li, H. S.; Garnier, F.; Roncali,
J. Solid State Commun. 1991, 77, 811. Yassar, A.; Horowitz, G.; Valat, P.;
Wintgens, V.; Hmyene, M.; Deloffre, F.; Srivastava, P.; Lang, P.; Garnier,
F. J. Phys. Chem. 1995, 99, 9155.
(29) Hill, M. G.; Mann, K. R.; Miller, L. L.; Penneau, J. F. J. Am. Chem.
Soc. 1992, 114, 2728. Hill, M. G.; Mann, K. R.; Miller, L. L.; Penneau, J.
F.; Zinger, B. Chem. Mater. 1992, 4, 1106. Zinger, B.; Mann, K. R.; Hill,
M. G.; Miller, L. L. Chem. Mater. 1992, 4, 1113. Yu, Y.; Gunic, E.; Zinger,
B.; Miller, L. L. J. Am. Chem. Soc. 1996, 118, 1013.
(32) Rughooputh, S. D. D. V.; Hotta, S.; Heeger, A. J.; Wudl, F. J. Polym.
Sci. 1987, 25, 1071.

π-Conjugated Soluble Oligomers
J. Am. Chem. Soc., Vol. 119, No. 44, 1997 10781
Figure 9. Variation of Epa(1) Vs the reciprocal number of carbons in
the conjugated chain for oligomers of series b.
Figure 7. Optical spectrum of a film of 8a cast from a CH2Cl2 solution.
(7.0) than for nTs (5.4, not shown). Interestingly, the slope in
Figure 9 is about twice smaller than that of Figure 8. Since
Epa(1) is related to the HOMO energy level,34 this twice smaller
slope indicates that the gap reduction resulting from chain
extension involves symmetrical changes of the HOMO and
LUMO energies with respect to mid-gap.
As already discussed, one of the most interesting opportunities
offered by linear π-conjugated systems is their use as molecular
wires or as conjugating spacers in NLO chromophores. In this
context, it is interesting to compare the above results with the
performances of other known systems. Thus for nTs saturation
occurs for 8-12 thiophene rings (Cn ) 32-48) with a λmax
around 460-465 nm.5 For dialkoxy-substituted oligo(phen-
ylene-ethylene)s the limit occurs around 9-10 phenyl rings
(Cn ) 52-58, λmax ) 475-480 nm).35 For oligo(1,4-phen-
ylene-ethynylene)s and -(2,5-thiophene-ethynylene)s satura-
tion occurs around the tetramer (Cn ) 22, λmax ) 370 nm) and
octamer (Cn ) 46, λmax ) 440 nm), respectively.10
The effective conjugation and hence HOMO-LUMO gap
of linear π-conjugated systems are related to the average
delocalization (or confinement) length of π-electrons.36 Whereas,
for polyenes, this parameter depends essentially on the degree
of bond length alternation, in polyaromatic systems, other factors
such as planarity and aromatic resonance energy plays also a
determining role.14 Thus, for nTs statistical rotational disorder
is one of the main limiting factors.13,14,37 The larger HOMO-
LUMO gap of oligo(phenyleneethylene)s compared to nTVs
reflects the higher resonance energy of benzene, while excessive
π-electron confinement within aromatic rings and acetylenic
linkages can account for the very limited effective conjugation
of oligo(1,4-phenylene-ethynylene)s and -(2,5-thiophene-
ethynylene)s.10
Figure 8. Variation of the HOMO-LUMO gap Vs the reciprocal
number of carbons in the conjugated chain for oligomers of series b.
the same route have clearly evidenced the strong effect of the
conditions of thermal elimination (temperature and leaving
group) on the effective conjugation as well as on the perfor-
mances of LEDs based on these polymers.33
The data in Table 2 show that for both series chain extension
produces a steady decrease of ∆E with no apparent saturation.
The dependence of ∆E versus the reciprocal number of carbons
in the conjugated chain (1/Cn) leads to a straight line with a
slope of 15 (Figure 8). The location of the points corresponding
to 3b and 6b above the line is due to the presence of
unsubstituted thiophene rings. For nTs, a similar analysis done
using literature data5 gives a slope of 11.5 (not shown). The
higher slope found for nTVs indicates that a similar increment
in the number of carbons in the conjugated chain is more
efficient in terms of increase of effective conjugation length
and gap reduction for the nTVs than for the nTs series.
Extrapolation to 1/Cn ) 0 gives a ∆E of 1.45 eV for an infinite
PTV chain. Comparison of this value with the band gap of
PTV (1.70-1.80 eV)11,14 and that of the 8a film (1.70 eV)
suggests that longer nTVs may exhibit even smaller band gaps.
As shown in Figure 9, Epa(1) scales linearly with 1/Cn except
again for 3b and 6b. Intercept leads to an extrapolated Epa(1)
value of 0.30 V for an infinite chain length. As for optical
data, the slope of Epa(1) Vs 1/Cn is higher for the nTV series
In this context the optical data of nTVs indicate that they are
at present the heterocycle-based oligomeric system with the
highest ratio of effective conjugation/topological conjugation
and hence may be well-suited as molecular wires in nanoscopic
systems.
Conclusion
Soluble thienylenevinylene oligomers have been synthesized.
Whereas substitution at the R-positions of the end thiophene
(34) Parker, V. D. J. Am. Chem. Soc. 1976, 98, 98. Lyons, L. E. Aust.
J. Chem. 1980, 33, 1717. Loutfy, R. O.; Cheng, Y. C. J. Chem. Phys. 1980,
73, 2902.
(35) Stalmach, U.; Kolshorn, H.; Brehm, I.; Meier, H. Liebigs Ann. 1996,
1449.
(36) Hernandez, V.; Castiglioni, C.; Del Zopo, M.; Zerbi, G. Phys. ReV.
B 1994, 50, 9815.
(33) Stenger-Smith, J. D.; Lenz, R. W.; Wegner, G. Polymer 1989, 30,
1048. Shah, H. V.; McGhie, A. R.; Arbuckle, G. A. Thermochim. Acta
1996, 287, 319. Herold, M.; Gmeiner, J.; Schwoerer, M. Acta Polym. 1996,
47, 436. Mertens, R.; Nagels, P.; Callaerts, R. Synth. Met. 1997, 84, 977.
(37) Roncali, J.; Thobie-Gautier, C. AdV. Mater. 1994, 6, 846.

10782 J. Am. Chem. Soc., Vol. 119, No. 44, 1997
Elandaloussi et al.
NMR (DMSO-d6) 144.7, 141.9, 139.4, 127.9, 126.8, 126.3, 125.2,
124.8, 121.5, 119.9; 30.95, 30.9, 29.6, 28.1, 22.1, 13.9 ppm.
rings has little influence on the solubility and electronic
properties, mono- or disubstitution at the â-positions of the
thiophene ring leads to a strong enhancement of solubility, thus
allowing the synthesis of the longest oligomers reported so far.
In addition to a steady decrease in oxidation potential, chain
extension leads to an increase of the number of oxidation states
and to a reduction of the difference between the potential of
formation of the cation radical and dication. For the octamers,
a first conclusive evidence for direct generation of the dication
through a two-electron transfer has been obtained while the
tetracationic state is reached below 1.0 V/SCE. Chain extension
leads to a steady decrease of the HOMO-LUMO gap without
apparent saturation. Consequently some solution-processed
films exhibit a band gap similar to or even smaller than that of
PTV. Extrapolation of the HOMO-LUMO gap Vs chain length
leads to a predicted gap value ca. 0.30 eV smaller than the
present experimental value for PTV, suggesting that the
synthesis of longer nTVs may allow further band-gap reduction.
Comparison of these results with data for other conjugated
oligomers indicates that nTVs represent the system with the
highest ratio of effective conjugation Vs number of carbons in
the chain. These results, which can already have important
implications for further analyses of the mechanisms of charge
transport in π-conjugated polymers or for further design of
molecular wires or NLO chromophores, provide a strong
incitement to develop longer nTVs. Work in this direction is
now in progress in our laboratory and will be reported in the
near future.
(E)-1-(5-Formyl-2-thienyl)-2-(5′-hexyl-2′-thienyl)ethylene (13b).
This compound was prepared using the procedure described for 12 from
13a (2.76 g, 10 mmol), n-BuLi (7.5 mL, 12 mmol), and DMF (1.2
mL, 15.5 mmol) in 25 mL of dry THF. The crude product was purified
by silica gel column chromatography (PE/CH2Cl2 (1:1) to leave a yellow
solid, which after recrystallization from hexane gave 2.5 g (82%) of
13b. Mp: 49.5-50 °C. MS (EI): M+ 304 (100). 1H NMR (DMSO-
3
3
d6): δ 9.84 (s, 1H); 7.91 (d, 1H, J ) 3.29 Hz); 7.39 (d, 1H, J ) 16
3
3
Hz); 7.35 (d, 1H, J ) 3.52 Hz); 7.12 (d, 1H, J ) 3.52 Hz); 7.04 (d,
3
3
3
1H, J ) 16 Hz); 6.78 (d, 1H, J ) 3.29 Hz); 2.75 (t, 2H, J ) 7.5
Hz); 1.61-1.56 (m, 2H); 1.26 (broad signal, 6H); 0.84 (t, 3H, 3J ) 6.5
Hz). 13C NMR (DMSO-d6): 183.5, 151.4, 147.0, 140.7, 139.0, 138.6,
129.0, 127.1, 126.1, 125.6, 118.9 , 30.95, 30.9, 29.6, 28.1, 22.0, 13.9
ppm.
(E,E)-2-(5′-Hexyl-2′-thienylvinyl)-5-(2′′-thienylvinyl)thiophene (14a)-
. This compound was obtained using the procedure described for 13a
from 1.52 g (5 mmol) of 13b, 1.4 g (6 mmol) of 1, and 0.78 g (7
mmol) of t-BuOK. The crude product was purified by column
chromatography (silica gel PE/CH2Cl2, 4:1) and recrystallized from PE
to yield 1.7 g (88%) of a yellow solid. Mp: 74 °C. MS (EI): M+
384 (100). 1H NMR (DMSO-d6): δ 7.46 (d, 1H, 3J ) 5.17 Hz); 7.21
3
3
(d, 1H, J ) 3.52 Hz); 7.11 (d, 1H, J ) 3.76 Hz); 7.09 (s, 2H); 7.06
3
3
3
(d, 1H, J ) 3.76 Hz); 7.04 (d, 1H, J ) 16 Hz); 7.02 (d, 1H, J )
3
3
3.76 Hz); 7.01 (d, 1H, J ) 3.76 Hz); 6.94 (d, 1H, J ) 16 Hz); 6.75
(d, 1H, 3J ) 3.52 Hz); 2.76 (t, 2H, J ) 7.5 Hz); 1.63-1.55 (m, 2H);
3
1.28 (broad signal, 6H); 0.85 (t, 3H, J ) 6.5 Hz, CH3). 13C NMR
3
(DMSO-d6): 145.2, 141.7, 141.0, 140.5, 139.4, 128.1, 128.0, 127.6,
127.1, 126.9, 125.4, 125.0, 121.9, 121.1, 120.0, 119.9, 30.9, 29.6, 28.1,
22.0, 13.9 ppm. Anal. (calcd): C, 68.26 (68.70); H, 6.26 (6.29).
(E,E)-2-(5′-Formyl-2′-thienylvinyl)-5-(5′′-hexyl-2′′-thienylvinyl)-
thiophene (14b). This compound was prepared similarly to 13b from
14a (1.3 g, 3.4 mmol), n-BuLi (2.65 mL, 4.24 mmol), and DMF (0.5
mL). The crude product was purified by column chromatography (silica
gel, PE/CH2Cl2, 2:1) and recrystallized from PE/CH2Cl2 (4:1) to give
1.03 g (73%) of red-orange crystals. Mp: 116-117 °C. MS (EI):
M+ 412 (100). 1H NMR (DMSO-d6): δ 9.85 (s, 1H), 7.94 (d, 1H, 3J
Experimental Section
Electrochemical experiments were carried out with a PAR 273
potentiostat-galvanostat in a three-electrode single-compartment cell
equipped with platinum microelectrodes of 7.85 × 10-3 cm2 area, a
platinum wire counter electrode, and a saturated calomel reference
electrode (SCE). Cyclic voltammetry was performed in methylene
chloride solutions (HPLC grade) containing 0.1 M tetrabutylammonium
hexafluorophosphate (TBAHP) (Fluka puriss). Solutions were deaer-
ated by nitrogen bubbling prior to each experiment which was run under
a nitrogen atmosphere. UV-visible absorption spectra were recorded
on a Lambda 2 Perkin-Elmer spectrophotometer.
3
3
) 3.76 Hz); 7.45 (d, 1H, J ) 16 Hz); 7.40 (d, 1H, J ) 3.76 Hz);
3
3
7.25 (d, 1H, J ) 3.76 Hz); 7.15 (d, 1H, J ) 3.76 Hz); 7.14 (d, 1H,
3
3
3J ) 16 Hz); 7.05 (d, 1H, J ) 3.76 Hz); 7.02 (d, 1H, J ) 16 Hz);
3
3
3
7.00 (d, 1H, J ) 16 Hz); 7.08 (d, 1H, J ) 3.76 Hz); 2.76 (t, 2H, J
) 7.5 Hz); 1.64-1.56 (m, 2H); 1.28 (broad signal, 6H); 0.85 (t, 3H, 3J
) 6.5 Hz). Anal. (calcd): C, 66.92 (66.95); H, 5.99 (5.86).
3-Octylthiophene (15a),24 3,4-dibutylthiophene (15b),24 2-bromo-3-
octylthiophene (15c), and diethyl (2-thienylmethyl)phosphonate22 (1)
were prepared according to know procedures.
(E,E,E)-1,2-Bis[5-(5′-hexyl-2′-thienylvinyl)-2-thienyl]ethylene (4h).
To a suspension of low-valent Ti prepared from TiCl4 (0.66 mL, 6
mmol)) and Zn (0.78 g, 12 mmol) in 30 mL of dry THF under N2 at
0 °C was added a dry solution of 13b (1.52 g, 5 mmol) in 10 mL of
THF. After 2 h of refluxing, the mixture was cooled to room
temperature, poured into water, and then extracted with CH2Cl2. The
organic phase was washed with water and dried over MgSO4. After
solvent removal, the crude solid was recrystallized from CHCl3/hexane
to give 0.6 g (41%) of a red solid. Mp: 146 °C. MS (EI): 576 (100).
5-Hexyl-2-thiophenecarboxaldehyde (12). To a stirred THF solu-
tion (40 mL) containing 2-hexylthiophene (11) (Lancaster) (3.36 g, 20
mmol) was slowly added 15.6 mL of n-BuLi (1.6 M in hexanes, 25
mmol) at 0 °C under a N2 atmosphere, and the solution was stirred for
15 min. DMF (2.3 mL, 30 mmol) was added, and the mixture was
allowed to warm to room temperature. The mixture was poured into
an aqueous solution of ammonium chloride (1 N) and extracted with
CH2Cl2. The organic layer was washed with water, dried over MgSO4,
and evaporated. The residue was purified by column chromatography
(silica gel, petroleum ether (PE)/CH2Cl2, 4:1) to give 3.71 g (94%) of
3
1H NMR (CDCl3): δ 6.95 (d, 2H, J ) 15.7 Hz); 6.92 (s, 2H); 6.89
(d, 2H, 3J ) 4 Hz); 6.87 (d, 2H); 6.86 (d, 2H, 3J ) 15.7 Hz); 6.84 (d,
3
3
3
2H, J ) 3.76 Hz); 6.65 (d, 2H, J ) 3.76 Hz); 2.78 (t, 4H, J ) 7.3
Hz); 1.70-1.65 (m, 4H); 1.33 (br, 12H); 0.90 (t, 6H, 3J ) 6.4 Hz). 13
C
3
a yellow oil. 1H NMR (CDCl3): δ 9.82 (s, 1H); 7.55 (d, 1H, J ) 4
Hz); 6.83 (d, 1H, 3J ) 4 Hz); 2.85 (t, 2H, 3J ) 7.5 Hz); 1.40-1.28 (m,
NMR (DMSO-d6): 145.8, 141.8, 141.0, 140.0, 127.2, 126.7, 126.4,
127.7, 122.2, 121.4, 120.2, 31.5, 31.4, 30.4, 28.7, 22.5, 14.0 ppm. Anal.
(calcd): C, 69.95 (70.81); H, 6.94 (7.00); S, 21.81 (22.20).
(E,E,E,E,E)-1,2-Bis{5-[5′-(5′′-hexyl-2′′-thienylvinyl)-2′-thienylvi-
nyl]-2-thienyl}ethylene (6h). This compound was prepared using the
procedure described for 4h from 14b (0.74 g, 1.8 mmol), TiCl4 (0.24
mL, 2.19 mmol), and Zn (0.29 g, 4.40 mmol) in THF. The usual
workup and recrystallization from CH2Cl2 gave 0.15 g (21%) of a dark
red solid. Mp: 248 °C dec. MS (EI): M+ 792 (100). Solubility was
too low to perform spectroscopic analyses.
3-Octyl-2-thiophenecarboxaldehyde (16a). A solution of n-BuLi
(2.5 M in hexanes, 16.8 mL, 42 mmol) was added dropwise at -100
°C under N2 to a stirred solution of 15c (11g, 40 mmol in 60 mL of
ether). During the whole addition, the reaction temperature was kept
at -100 °C and then was allowed to gradually rise to -60 °C. At this
3
8H); 0.87 (t, 3H, J ) 6.5 Hz).
(E)-1-(5-Hexyl-2-thienyl)-2-(2′-thienyl)ethylene (13a). To a stirred
solution of 12 (3.53 g, 18 mmol) and 1 (5.05 g, 21.6 mmol) in dry
THF (80 mL) was added t-BuOK (3 g, 27 mmol) portionwise under
N2 at room temperature. After 30 min of stirring, the reaction mixture
was poured into water and extracted with CH2Cl2. The organic phase
was washed, dried over MgSO4, and evaporated under reduced pressure
to leave an oil, which after chromatography on silica gel with PE/CH2-
Cl2 (2:1) gave 4.33 g (87%) of the title compound as an orange viscous
oil which crystallizes at + 4 °C. 1H NMR (DMSO-d6): δ 7.40 (d,
1H, 3J ) 5.2 Hz); 7.16 (d, 1H, 3J ) 3.3 Hz); 7.05 (d, 1H, 3J ) 16 Hz);
3
3
3
7.03 (d, 1H, J ) 3.5 Hz); 6.97 (d, 1H, J ) 3.5 Hz); 6.96 (d, 1H, J
) 16 Hz); 6.72 (d, 1H, 3J ) 3.3 Hz); 2.73 (t, 2H, 3J ) 7.5 Hz); 1.58-
1.54 (m, 2H); 1.30 (broad signal, 6H); 0.84 (t, 3H, 3J ) 6.5 Hz). 13C

π-Conjugated Soluble Oligomers
J. Am. Chem. Soc., Vol. 119, No. 44, 1997 10783
temperature, DMF (4.65 mL, 60 mmol) was slowly added and the
mixture allowed to warm to room temperature. The mixture was poured
into a 1 M aqueous solution of NH4Cl and extracted with CH2Cl2. The
organic layer was washed with water, dried over MgSO4, and evaporated
under reduced pressure. The residue was passed through a short column
(silica gel, CH2Cl2) to give 8.6 g (96%) of yellow oil. 1H NMR
(E)-1-(5-Formyl-3,4-dibutyl-2-thienyl)-2-(3′,4′-dibutyl-2′-thienyl)-
ethylene (17b). Compound 17b was prepared similarly to 17a from
2b (3.85 g, 9.25 mmol), DMF (0.93 mL, 12.03 mmol), and POCl3 (1.03
mL, 11.1 mmol) in 1,2-dichloroethane (30 mL). The crude product
was purified by column chromatography (silica gel, PE/CH2Cl2, 1:1)
to give 3.78 g (92%) of the title compound as an orange viscous oil
which crystallized at +4 °C. C27H40OS2 MS (EI): M•+ 444 (100). 1H
3
3
(CDCl3): δ 9.99 (s, 1H); 7.59 (d, 1H, J ) 5 Hz); 6.97 (d, 1H, J )
5 Hz); 2.91 (t, 2H, 3J ) 7.5 Hz); 1.62-1.59 (m, 2H); 1.27-1.23 (br,
3
NMR (CDCl3): δ 9.97 (s, 1H); 7.27 (d, 1H, J ) 15.5 Hz); 6.96 (d,
3
10H); 0.83 (t, 3H, J ) 6.5 Hz). 13C NMR (CDCl3): 182.0, 152.7,
1H, 3J ) 15.5 Hz); 6.84 (s, 1H); 2.85 (t, 2H, 3J ) 7.5 Hz); 2.63-2.47
(m, 6H); 1.63-1.36 (m, 16H); 1.00-0.90 (m, 12H). 13C NMR
(CDCl3): 181.82, 152.9, 147.1, 143.6, 142.2, 140.2, 135.9, 134.5, 124.2,
119.7, 117.8, 34.3, 33.3, 31.8, 31.7, 28.5, 26.8, 26.7, 26.0, 22.8, 22.7,
22.6, 22.5, 14.0, 13.9, 13.8, 13.7 ppm.
137.4, 134.2, 130.5, 31.6, 31.2, 29.1, 29.0, 28.9, 28.2, 22.4, 13.9 ppm.
3,4-Dibutyl-2-thiophenecarboxaldehyde (16b). POCl3 (6.1 mL,
65.3 mmol) was added at 0 °C to a stirred solution of 15b (8 g, 40.8
mmol) and dry DMF (5.7 mL, 73.7 mmol) in 40 mL of 1,2-
dichloroethane under N2. After 2 h of refluxing, the mixture was cooled
to room temperature and neutralized with a sodium acetate solution (1
M). The organic layer was separated and the aqueous layer extracted
with CH2Cl2. The combined extracts were washed with water, dried
over MgSO4, and evaporated under reduced pressure. The oily residue
was purified by column chromatography (silica gel, PE/CH2Cl2, 3:2)
to give 8.48 g (92%) of a yellow oil. 1H NMR (CDCl3): δ 9.93 (s,
(E,E)-2,5-Bis(2′-thienylvinyl)-3,4-dibutylthiophene (3b). This com-
pound was prepared by Wittig-Horner bis-olefination using the
procedure described for 13a from 16c (1 g, 4 mmol), 1 (2.8 g, 12 mmol),
and t-BuOK (1.57 g, 14 mmol). The crude product was purified by
column chromatography (silica gel, PE/CH2Cl2, 4:1) and recrystallized
from PE to give 1.3 g (79%) of orange crystals. Mp: 68 °C. MS
3
(EI): M+ 412 (100). 1H NMR (CDCl3): δ 7.17 (d, 2H, J ) 5 Hz);
3
3
3
3
1H); 7.26 (s, 1H), 2.88 (t, 2H, J ) 8 Hz); 2.53 (t, 2H, J ) 8 Hz);
7.06 (d, 2H, J ) 15.5 Hz); 7.02 (br 2H); 6.99 (dd, 2H, J ) 4 Hz);
3 3
3
1.60-1.45 (m, 8H); 0.87 (t, 6H, J ) 7 Hz).
6.98 (d, 2H, J ) 15.5 Hz); 2.59 (t, 4H, J ) 7.6 Hz); 1.46-1.24 (m,
8H); 0.98 (t, 6H, 3J ) 7 Hz). 13C NMR (CDCl3): 142.4, 141.1, 134.0,
127.2, 125.2, 123.5, 120.2, 119.5, 32.9, 28.7, 22.1, 13.4 ppm. Anal.
(calcd): C, 70.37 (69.88); H, 6.79 (6.85); S, 23.35 (23.27).
3,4-Dibutyl-2,5-thiophenedicarbaldehyde (16c). n-BuLi (20.6 mL,
32.9 mmol) was added dropwise to a solution of 15b (2.69 g, 13.7
mmol) and TMEDA (5 mL, 32.9 mmol) in 10 of mL hexane. The
resulting mixture was refluxed for 30 min, then THF (50 mL) was
added, and the mixture was cooled to -40 °C and treated with an excess
of DMF (3.2 mL, 41.1 mmol). The reaction mixture was allowed to
warm to room temperature and then poured into 300 mL of HCl solution
(0.5 M). Saturated NaHCO3 solution was added until neutrality of the
aqueous layer. The organic phase was separated and the aqueous layer
extracted with 2 × 60 mL of CH2Cl2. The organic layer was dried
over MgSO4 and evaporated under reduced pressure to leave a dark
orange oil. Chromatography (silica gel, CH2Cl2/PE, 1:1) afforded a
yellow solid, which after recrystallization from PE gave 2.03 g (58%)
of white crystals. Mp: 65 °C. MS (EI): M+ 252 (96); 223 (100,
-CHO). 1H NMR (CDCl3): δ 10.12 (s, 2H); 2.92 (t, 4H, 3J ) 8 Hz);
(E,E)-2-(5′-Formyl-2′-thienylvinyl)-5-(2′′-thienylvinyl)-3,4-dibu-
tylthiophene (18b). This compound was prepared by Vilsmeier
formylation of 3b (1 g, 2.42 mmol), using POCl3 (0.36 mL, 3.88 mmol)
and DMF (0.34 mL, 4.36 mmol) as already described for 16b. After
the usual workup, the crude product was purified by column chroma-
tography (silica gel, eluting first with PE/CH2Cl2 (4:1) to separate the
unreacted starting material (0.22 g), then with PE/CH2Cl2 (1:1) to afford
0.74 g (69%) of the title compound as a red solid). Recrystallized
from ethanol: mp 72-73 °C. MS (EI): M+ 440 (100). 1H NMR
3
(DMSO-d6): δ 9.85 (s, 1H); 7.95 (d, 1H, J ) 3.78 Hz); 7.47 (d, 1H,
3J ) 14.8 Hz); 7.46 (d, 1H, 3J ) 3.78 Hz); 7.45 (d, 1H, 3J ) 14.8 Hz);
3
3
7.37 (d, 1H, J ) 3.5 Hz); 7.28 (d, 1H, J ) 3.5 Hz); 7.10-6.98 (m,
3
3
3
1.61-1.43 (m, 8H); 0.97 (t, 6H, J ) 7.3 Hz). 13C NMR (CDCl3):
3H); 2.63 (t, 4H, J ) 7.6 Hz); 1.47-1.38 (m, 8H); 0.93 (t, 6H, J )
7 Hz). Anal. (calcd): C, 68.12 (68.16); H, 6.39 (6.41); S, 21.59
(21.79).
183.2, 151.6, 143.2 , 34.2, 26.3, 22.7, 13.7 ppm.
(E)-1,2-Bis(3-octylthienyl)ethylene (2a). This compound was
prepared from 16a (8.52 g, 38 mmol), TiCl4 (5 mL, 45.6 mmol), and
Zn (6 g, 91.2 mmol) using the procedure described for 4h and purified
by column chromatography (silica gel, PE/CHCl3, 6:1) to give 7.05 g
(E,E,E)-1,2-Bis[5-(3′-octyl-2′-thienylvinyl)-4-octyl-2-thienyl]eth-
ylene (4a). This compound was prepared from 17a (14 g, 31.5 mmol),
TiCl4 (4.15 mL, 37.8 mmol), and Zn (5 g, 75.6 mmol) as already
described for 4h. The crude product was purified by column chro-
matography (silica gel, PE/CH2Cl2, 1:1) and recrystallized from hexane
to yield 9.56 g (71%) of a red solid. Mp: 120 °C. MS (FAB): M+
1
(89%) of an orange solid. Mp: 35 °C. MS (EI): M+ 416 (100). H
3
NMR (CDCl3): δ 7.08 (d, 2H, J ) 5.17 Hz); 7.01 (s, 2H); 6.86 (d,
3
3
2H, J ) 5.17 Hz); 2.67 (t, 4H, J ) 7.5 Hz); 1.63-1.57 (m, 4H);
1.35-1.25 (m, 20H); 0.88 (t, 6H, J ) 6.5 Hz). 13C NMR (CDCl3):
856. 1H NMR (CDCl3): 7.09 (d, 2H, J ) 5.17 Hz); 6.97 (s, 4H);
3
3
3
3
140.7, 136.3, 129.7, 122.5, 119.5, 31.9, 30.6, 31.0, 29.5, 29.2, 28.4,
22.7, 14.1 ppm.
6.91 (s, 2H), 6.86 (d, 2H, J ) 5.17 Hz); 6.77 (s, 2H); 2.67 (t, 4H, J
3
) 7.5 Hz); 2.61 (t, 4H, J ) 7.5 Hz); 1.65-1.56 (m, 8H); 1.35-1.25
(m, 40H); 0.89 (m, 12H). 13C NMR (CDCl3): 142.2, 141.4, 139.9,
136.8, 136.2, 130.4, 129.9, 123.2, 121.8, 119.9, 119.5, 32.4, 32.3, 31.4,
31.2 30.0, 29.9, 29.8, 29.7, 28.9, 28.8, 23.1, 14.6 ppm. Anal. (calcd):
C, 75.85 (75.66); H, 9.91 (9.41); S, 14.95 (14.93).
(E)-1,2-Bis[2-(3,4-dibutylthienyl)]ethylene (2b). This compound
was prepared using the procedure described for 4h from TiCl4 (4.7
mL, 42.85 mmol) and Zn (5.6 g, 85.7 mmol). After the usual workup,
the residue was purified by column chromatography (silica gel, PE)
and recrystallized from pentane to yield 5 g (67%) of the title product
as light yellow crystals. Mp: 88 °C. MS (EI): M+ 416 (100). 1H
(E,E,E)-1,2-Bis[5-(3′,4′-dibutyl-2′-thienylvinyl)-3,4-dibutyl-2-thi-
enyl]ethylene (4b). This compound was obtained using the same
procedure from 17b (3.6 g, 8.1 mmol), TiCl4 (1.07 mL, 9.72 mmol),
and Zn (1.27 g, 19.45 mmol). The crude product was chomatographed
(silica gel, CH2Cl2) and recrystallized from hexane to yield 2.7 g (78%)
of red crystals. Mp: 162 °C. MS (EI): M+ 856 (100). 1H NMR
(CDCl3): δ 6.99 (s, 4H); 6.97 (s, 2H); 6.76 (s,2H); 2.7-2.56 (m, 16H);
1.65-1.40 (m, 32H); 0.98-0.93 (m, 24H). 13C NMR (CDCl3): 143.8,
141.9, 141.8, 140.5, 137.5, 135.5, 135.4, 120.4, 119.8, 119.6, 118.4,
33.9, 33.7, 32.3, 31.4, 29.1, 27.2, 27.1, 23.2, 23.1, 14.5, 14.4 ppm.
Anal. (calcd): C, 75.27 (75.66); H, 9.50 (9.41); S, 15.07 (14.93).
(E,E,E)-1-[5-(5′-Formyl-3′-octyl-2′-thienylvinyl)-4-octyl-2-thienyl]-
2-[5′′-(3′′′-octyl-2′′′-thienylvinyl)-4′′-octyl-2′′-thienyl]ethylene (19a).
This compound was prepared similarly to 16b from 4a (1.46 g, 1.7
mmol), DMF (0.16 mL, 2.07 mmol), and POCl3 (0.16 mL, 1.7 mmol).
After the usual workup, the crude product was purified by column
chromatography (silica gel, eluting first with PE/CH2Cl2, 7:3, to recover
the unreacted starting material (0.72 g), then with PE/CH2Cl2, 1:1) to
afford 0.57 g (38%) of a dark red solid Recrystallized from hexane:
3
NMR (CDCl3): δ 7.01 (s, 2H); 6.76 (s, 2H); 2.62 (t, 4H, J ) 8 Hz);
3
3
2.51 (t, 4H, J ) 8 Hz); 1.66-1.40 (m, 16H); 0.97 (t, 12H, J ) 7.3
Hz). 13C NMR (CDCl3): 143.3, 139.7, 136.9, 119.6, 117.6, 33.2, 31.8,
28.7, 26.6, 22.7, 22.6, 14.0, 13.9 ppm.
(E)-1-(5-Formyl-3-octyl-2-thienyl)-2-(3′-octyl-2′-thienyl)ethyl-
ene (17a). This compound was prepared from 2a (20 g, 48 mmol),
DMF (5.6 mL, 72 mmol), and POCl3 (5.65 mL, 60.5 mmol) in 1,2-
dichloroethane (200 mL) using the procedure described for 16b. The
crude product was purified by column chromatography (silica gel, PE/
CH2Cl2, 3:2) to give 15 g (70%) of the title compound as a dark orange
viscous oil. C27H40OS2 MS (EI): M+ 444 (100). 1H NMR (CDCl3):
3
δ 9.80 (s, 1H); 7.51 (s, 1H); 7.26 (d, 1H, J ) 15.5 Hz); 7.17 (d, 1H,
3J ) 5.17 Hz); 6.96 (d, 1H, 3J ) 15.5 Hz); 6.88 (d, 1H, 3J ) 5.17 Hz);
3
2.67 (t, 4H, J ) 7.5 Hz); 1.65-1.57 (m, 4H); 1.32-1.22 (m, 20H);
0.87 (m, 6H). 13C NMR (CDCl3): 182.4, 146.9, 143.2, 141.5, 139.1,
138.9, 135.3, 130.1, 124.4, 123.7, 117.8, 31.8, 31.0, 30.5, 29.3, 29.2,
28.4, 22.6, 14.0 ppm.

10784 J. Am. Chem. Soc., Vol. 119, No. 44, 1997
Elandaloussi et al.
3
mp 114 °C. MS (FAB): M+ 884. 1H NMR (CDCl3): δ 9.80 (s, 1H);
NMR (C6D6 + CDCl3 (2:1)): δ 7.30 (d, 4H, J ) 16 Hz, 4H ethyl);
7.15 (d, 4H, 3J ) 16 Hz, 4H ethyl); 6.95 (s, 2H, 2H ethyl, centr); 6.77
(d, 2H, 3J ) 3.4 Hz, 2H′ thioph); 6.73 (d, 2H, 3J ) 4.5 Hz, 2H′′′ thioph);
6.66 (dd, 2H, 3J ) 4.5 Hz and 3J ) 3.4 Hz, 2H′′′ thioph); 6.62 (d 2H,
3
3
7.51 (s, 1H); 7.22 (d, 1H, J ) 15.5 Hz); 7.09 (d, 1H, J ) 5.17 Hz);
3
3
7.00 (d, 1H, J ) 15.5 Hz); 6.96 (d, 1H, J ) 15.5 Hz); 6.95 (d, 1H,
3J ) 15.5 Hz); 6.93 (d, 1H, 3J ) 15.5 Hz); 6.92 (d, 1H, 3J ) 15.5 Hz);
6.86 (d, 1H, 3J ) 5.17 Hz); 6.79 (s, 2H); 2.67-2.59 (m, 8H); 1.60 (br,
8H); 1.29 (br, 40H); 0.86 (m, 12H). 13C NMR (CDCl3): 182.4, 147.0,
144.4, 141.7, 141.6, 141.5, 141.2, 141.0, 139.2 (C-3′), 139.1 138.9,
136.3, 134.6, 129.9 129.4, 129.3, 123.4, 122.9, 122.4, 120.9, 119.7,
118.9, 117.7, 31.9, 31.8, 30.9, 30.8, 30.7, 30.6, 29.5, 29.4, 29.3, 29.2,
28.4, 28.2, 22.6, 14.1, 14.0 ppm. Anal. (calcd): C, 74.40 (74.62); H,
9.25 (9.12); S, 14.32 (14.46); O, 1.83 (1.81).
3J ) 4.3 Hz, 2H thioph, centr); 6.55 (d, 2H J ) 4.3 Hz, 2H thioph).
3
(E,E,E,E,E,E,E)-1,2-Bis{5-[5′-[5′′-(3′′′-octyl-2′′′-thienylvinyl)-4′′-
octyl-2′′-thienylvinyl]-(3′-octyl-2′-thienylvinyl]-4-octyl-2-thienyl}-
ethylene (8a). This compound was prepared using the procedure
described for 4h from 19a (1.6 g, 1.8 mmol), TiCl4 (0.4 mL, 3.6 mmol),
and Zn (0.47 g, 7.2 mmol). After the usual workup, the crude product
was recrystallized from CHCl3 to give 0.4 g (25%) of a dark blue solid.
Mp: 180 °C dec. MS (FAB): M + 1 1737. 1H NMR (CDCl3): δ
(E,E,E)-1-[5-(5′-Formyl-3′,4′-dibutyl-2′-thienylvinyl)-3,4-dibutyl-
2-thienyl]-2-[5′′-(3′′′,4′′′-dibutyl-2′′′-thienylvinyl)-3′′,4′′-dibutyl-2′′-
thienyl]ethylene (19b). This compound was prepared from 4b (1.53g,
1.78 mmol), DMF (0.16 mL, 2.07 mmol), and POCl3 (0.17 mL, 1.78
mmol) using the procedure described for 16b. After the usual workup,
the crude product was purified by chromatography (silica gel), eluting
first with PE/CH2Cl2, 7:3, to recover the unreacted starting material
(0.5 g) and then with PE/CH2Cl2, 1:1, to afford 0.74 g (46%) of the
title product as a dark solid (purple in solution). Recrystallized from
hexane: mp 153 °C. MS (EI): M+ 884 (100). 1H NMR (CDCl3): δ
3
7.08 (d, 2H, J ) 5.17 Hz); 6.97 (s, 4H); 6.93 (s, 4H); 6.91 (s, 6H);
3
6.85 (d, 2H, J ) 5.17 Hz); 6.78 (s, 6H); 2.62-2.57 (m, 16H); 1.61
(br 16H); 1.30-1.26 (br 80H); 0.95-0.88 (m, 24H). 1H NMR (C6D6
+ CDCl3 (2:1)): δ 7.30 (d, 4H, 3J ) 15.5 Hz); 7.15 (d, 4H, 3J ) 15.5
3
3
Hz); 6.95 (s, 2H); 6.78 (d, 2H, J ) 3.1 Hz); 6.73 (d, 2H, J ) 4.5
Hz); 6.67 (dd, 2H, J ) 4.5 Hz, J ) 3.1 Hz); 6.61 (d, 2H, J ) 3.7
Hz); 6.55 (d, 2H, J ) 3.7 Hz); 2.60 (t, 8H, J ) 7.5 Hz); 1.56-1.47
(m, 16H), 1.07-0.96 (m, 12 H).
3
3
3
3
3
(E,E,E,E,E,E,E)-1,2-Bis{5-[5′-[5′′-(3′′′,4′′′-dibutyl-2′′′-thienylvinyl)-
3′′,4′′-dibutyl-2′′-thienylvinyl]-3′,4′-dibutyl-2′-thienylvinyl]-3,4-dibu-
tyl-2-thienyl}ethylene (8b). This compound was prepared similarly
to 4h from 19b (0.884 g, 1 mmol), TiCl4 (0.22 mL, 2 mmol), and Zn
(0.26 g, 4 mmol). After 12 h of refluxing, the mixture was cooled to
room temperature and poured into a 10% K2CO3 solution. The resulting
mixture was vigorously stirred for 30 min to deposit a solid material,
which was filtered, washed with acetone in a Soxhlet extractor for 6 h,
and then extracted with CH2Cl2 for 20 h. The extract was evaporated
under reduced pressure to leave a dark blue solid material, which was
washed again with hot acetone, filtered, and recrystallized from CHCl3/
hexane to afford 0.45 g (52%) of the pure title compound as a dark
blue solid. Mp: 180 °C dec. MS (FAB): (M + 1)+ 1737. 1H NMR
(CDCl3): δ 6.99 (s, 14H); 6.76 (s, 2H); 2.62-2.50 (m, 32H); 1.62-
1.43 (m, 64H); 1.03-0.94 (m, 48H). Anal. (calcd): C, 75.59 (75.99);
H, 9.24 (9.28); S, 14.64 (14.72).
3
3
9.98 (s, 1H), 7.27 (d, 1H, J ) 15.5 Hz); 7.04 (d, 1H, J ) 15.5 Hz);
3
3
7.03 (d, 1H, J ) 15.5 Hz); 6.97 (d, 2H, J ) 15.5 Hz); 6.95 (d, 1H,
3J ) 15.5 Hz); 6.77 (s, 1H); 2.85 (t, 2H, 3J ) 7.5 Hz); 2.62-2.50 (m,
14H); 1.62-1.38 (m, 32H); 1.02-0.94 (m, 24H). 13C NMR (CDCl3):
182.3, 153.5, 147.8, 144.5, 143.5, 142.5, 142.1, 141.8, 140.6, 137.6,
137.4, 136.0, 135.1, 135.0, 134.4, 124.2, 120.9, 120.7, 119.5, 118.5,
118.4, 34.86, 34.08, 33.94, 33.888, 33.85, 33.76, 33.67, 33.62, 32.26,
29.14, 27.33, 27.28, 27.20, 27.16, 27.11, 26.55, 23.25, 23.20, 23.08,
23.02, 22.91, 14.43, 14.40, 14.32 ppm.
(E,E,E)-1,2-Bis-[5-(5′-formyl-3′-octyl-2′-thienylvinyl)-4-octyl-2-
thienyl]ethylene (19c). This compound was prepared from 4a (0.428
g, 0.5 mmol), POCl3 (0.2 mL, 2 mmol), and DMF (0.25 mL, 3 mmol)
in 1,2-dichloroethane (15 mL) using the procedure already described
for 16b. The crude product was purified by column chromatography
(silica gel, CH2Cl2) and then recrystallized from CHCl3/hexane to give
0.38 g (83%) of mauve crystals. Mp: 98 °C dec. MS (FAB): M+
912 (100). 1H NMR (CDCl3): δ 9.79 (s, 2H); 7.50 (s, 2H); 7.21 (d,
(E,E,E,E,E,E,E)-1,2-Bis{5-[5′-[5′′-(5′′′-formyl-3′′′,4′′′-dibutyl-2′′′-
thienylvinyl)-3′′,4′′-dibutyl-2′′-thienylvinyl]-3′,4′-dibutyl-2′-thienylvi-
nyl]-3,4-dibutyl-2-thienyl}ethylene (20b). This compound was pre-
pared as described for 16b by Vilsmeier formylation of 8b (0.15 g,
8.6 × 10-2 mmol), DMF (excess, 1 mL), and POCl3 (60 mL, 8 equiv)
in 1,2-dichloroethane (30 mL). After the usual workup, the crude
product was recrystallized from CHCl3 to afford 0.125 g (81%) of the
title compound as a dark blue solid, which was directly used for the
next step.
3
3
2H, J ) 15.5 Hz); 6.93 (s, 2H); 6.91 (d, 2H, J ) 15.5 Hz); 6.81 (s,
3
3
2H); 2.67 (t, 4H, J ) 7.5 Hz); 2.59 (t, 4H, J ) 7.5 Hz); 1.63-1.57
(m, 8H); 1.29 (br, 40H); 0.90-0.86 (m, 12H). 13C NMR (CDCl3):
182.8, 147.3, 144.8, 142.2, 141.5, 139.7, 139.3, 135.5, 130.3, 123.6,
122.4, 118.5, 32.3, 31.2, 31.0, 29.9, 29.8, 29.7, 29.6, 28.8, 28.7, 23.1,
14.5 ppm. Anal. (calcd): C, 73.66 (73.64); H, 8.93 (8.84); S, 13.87
(14.02); O, 3.36 (3.51).
(E,E,E,E,E)-1,2-Bis{5-[5′-(2′′-thienylvinyl)-(3′-octyl-2′-thienylvi-
nyl]-4-octyl-2-thienyl}ethylene (6a). This compound was prepared
by using the procedure described for 3b from 19c (91.2 mg, 0.1 mmol),
1 (120 mg, 0.5 mmol), and t-BuOK (80 mg, 0.7 mmol) in 20 mL of
dry THF. After 2 h of stirring at room temperature, the solvent was
evaporated under reduced pressure and the solid residue was purified
by column chromatography (silica gel, CH2Cl2) to yield 88 mg (82%)
(E,E,E,E,E,E,E,E,E)-1,2-Bis{5-[5′-[5′′-[5′′′-(2′′′′-thienylvinyl)-
3′′′,4′′′-dibutyl-2′′′-thienylvinyl]-3′′,4′′-dibutyl-2′′-thienylvinyl]-3′,4′-
dibutyl-2′-thienylvinyl]-3,4-dibutyl-2-thienyl}ethylene (10b). This
compound was prepared using the procedure described for 3b, from
20b (0.1 g, 5.6 × 10-2 mmol), 1 (70 mg, 0.56 mmol), and t-BuOK (94
mg, 0.84 mmol) in 15 mL of dry THF. After 2 h of stirring at room
temperature, the solvent was evaporated under reduced pressure and
the solid residue was taken up with methanol, filtered, and washed
several times with methanol and then with ether. Recrystallization from
CH2Cl2 afforded 95 mg (87%) of 10b as a dark blue solid. Mp: >260
°C, MS (FAB): (M + 2)+ 1954 (100), (M + 1)+ 1953 (66). 1H NMR
(CDCl3): δ 7.06-7.01 (m, 6H); 6.99 (s, 16 H); 6.97 (s, 2H); 2.62-
2.59 (m, 32H); 1.60 (br, 64 H); 1.01-0.89 (m, 48 H).
1
of a dark mauve solid. Mp: 123 °C. MS (FAB): M+ 1072 (69). H
NMR (CDCl3): δ 7.19 (d, 2H, 3J ) 5 Hz); 7.10-6.90 (m, 14 H); 6.81-
3
3
6.79 (2s, 2H); 2.67 (t, 4H, J ) 7.5 Hz); 2.61 (t, 4H, J ) 7.5 Hz);
1.65-1.56 (m, 8H); 1.35-1.25 (m, 40H); 0.89, (m 12H). Anal.
(calcd): C, 74.28 (73.84); H, 8.45 (8.27).
(E,E,E,E,E)-1,2-Bis{5-[5′-(2′′-thienylvinyl)-3′,4′-dibutyl-2′-thien-
ylvinyl]-2-thienyl}ethylene (6b). This compound was obtained as
described for 4h from 18b (0.52 g, 1.18 mmol), TiCl4 (0.26 mL, 2.36
mmol), and Zn (0.31 g, 4.72 mmol). After the usual workup, the crude
product was recrystallized from CHCl3 to yield 125 mg (25%) of a
Supporting Information Available: 1H NMR spectra for
compounds 4h, 4a, 4b, 8a, and 8b (9 pages). See any current
masthead page for ordering and Internet access instructions.
1
dark mauve solid. Mp: 235 °C dec. MS (FAB): M+ 848 (100). H
3
NMR (CDCl3): δ 7.18 (d, 2H, J ) 5 Hz) 7.09-6.89 (m, 18H); 2.60
3
(t, 8H, J ) 7.5 Hz); 1.56-1.42 (m, 16H); 1.02-0.96 (m, 12H). 1H
JA9722739