Quaterthiophene-based dimers containing an ethylene bridge: Molecular design, synthesis, and optoelectronic properties

Article abstract of DOI:10.1016/j.tet.2011.10.020

Two quaterthiophene-based dimers including an ethylene bridge have been designed and efficiently prepared; experimental and computational studies show a promising potential as semiconducting material with a charge transport of higher dimensionality compared to quaterthiophene.

Full text of DOI:10.1016/j.tet.2011.10.020

Tetrahedron 68 (2012) 349e355
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Quaterthiophene-based dimers containing an ethylene bridge: molecular design,
synthesis, and optoelectronic properties
a
a
a
a
a
a
ˇ
Maud Jenart , Claude Niebel , Jean-Yves Balandier , Julie Leroy , Alix Mignolet , Sara Stas ,
b
b
a,
*
ꢀ
Antoine Van Vooren , Jerome Cornil , Yves Henri Geerts
Universite Libre de Bruxelles (ULB), Laboratory of Polymer Chemistry, C.P. 206/01, Boulevard du Triomphe, 1050 Brussels, Belgium
a
ꢀ
b
ꢀ
Universite de Mons, Laboratory for Chemistry of Novel Materials, Place du Parc 20, 7000 Mons, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
Two quaterthiophene-based dimers including an ethylene bridge have been designed and efficiently
prepared; experimental and computational studies show a promising potential as semiconducting ma-
terial with a charge transport of higher dimensionality compared to quaterthiophene.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 1 September 2011
Received in revised form 6 October 2011
Accepted 7 October 2011
Available online 20 October 2011
Keywords:
Oligothiophene synthesis
Organic electronics
Quantum-chemical calculations
Charge transport dimensionality
1. Introduction
hand, dyads composed of two identical organic redox centers
linked by a conjugated bridging unit have also been extensively
Charge transfer between two distant redox centers is of crucial
interest in the field of life science as well as organic electronics.1
Organic donor-bridge-acceptor systems have been widely studied
to determine the parameters influencing the charge transfer. The
use of Marcus theory to describe covalently linked redox centers
pointed out the importance of the electronic coupling and of the
reorganization energy.2 The numerous investigations made on or-
ganic and organometallic donor-bridge-acceptor dyads have con-
tributed to this fundamental understanding. To cite only a few:
Miller et al. have reported the experimental evidences of the
inverted region predicted by the Marcus theory.3 Paddon-Row et al.
have studied the photoinduced charge separation in norbonylogous
based donor-bridge-acceptor bichromophores (Fig. 1a).4 Wasie-
lewski and co-workers have shown the control of the electron
transfer using cross-conjugated bridges in dyads made from
anthracenyljulolidine and naphthalenedicarboximide (Fig. 1b), re-
spectively, as donor and acceptor.5 The study of organic donor-
bridge-acceptor systems has also allowed the distinction between
intramolecular charge transfer through superexchange or hopping
mechanisms.3,5,6 It has also been instrumental in the fine tuning of
HOMOeLUMO band gap of organic semiconductors.7,8 On the other
studied to promote charge delocalization.9,10 The investigations
made on the photoexcited species of these bridged dimers, also
known as mixed valence systems, allowed the introduction of
a useful classification to characterize the intramolecular charge
delocalization.9 Class I groups together the completely localized
* Corresponding author. Tel.: þ32 2650 5390; fax: þ32 2650 5410; e-mail
Fig. 1. Example of bridged
p
-systems studied by Paddon-Row (a),4 Wasielewski (b),5
€
13
14
address: ygeerts@ulb.ac.be (Y.H. Geerts).
Lambert12 and Bredas (c), Mullen (d).
ꢀ
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.10.020

350
M. Jenart et al. / Tetrahedron 68 (2012) 349e355
systems, fully delocalized systems are class III, and the compounds
in between belong to class II.9,11
The radical cations of N,N,N0,N0-tetraanisyl-p-phenylenediamine
(TAPDþ) for instance is one of the most studied mixed valence
system at the borderline of class II and class III (Fig. 1c).12,13 Dif-
ferent p-conjugated spacers have also been introduced in the TAPD
core to analyze their influence on the overall charge de-
localization.9 If much of the attention has been paid to the influence
of
p-conjugated bridges on the electronic delocalization in mixed
valence systems, investigations have also been made on non-
€
conjugated spacers. Noteworthy, Mullen and co-workers have
studied the intramolecular electron transfer through a non-
conjugated bridge linking two anthryl electrophores (Fig. 1d).14
This study concluded that the mode of linking drastically affects
the rate of electron transfer processes from anthryl radical mono-
anions as well as the charge storage behavior.14 The organic redox
dimers linked by a non-conjugated spacer have been so far studied
in solution as mixed valence systems. Surprisingly enough, their
use for charge transport purposes is comparatively less docu-
mented. In a recent review paper, Roncali has pointed out the es-
sential role of the charge transport dimensionality as a design
principle for organic semiconductors with higher performance.15 In
this paper, we introduce the concept that a saturated covalent
Fig. 2. Structures of quaterthiophene derivatives 1, 2, 7, and 13. A vanishingly weak
electronic coupling occurs between adjacent molecules of 1 and 2 since the frontier
orbitals poorly overlap. The ethylene bridge in 7 and 13 promotes a large electronic
coupling between the
p-systems to increase the dimensionality of charge transport.
bridge connecting two
p-conjugated systems could increase the
dimensionality of charge transport. This concept relies on a rational
molecular design based on quantum-chemical calculations that are
introduced in Section 2. Sections 3 and 4 report the synthesis and
molecular
characterization
of
two
complementary
quaterthiophene-based dimers containing an ethylene bridge.
2. Molecular design
Among the variety of oligomers used in the synthesis of semi-
conducting materials, oligothiophenes have received a high in-
terest, mainly due to the
p-electron delocalization, high
polarizability of sulfur atoms, and supramolecular organization
coupled with an acceptable synthetic accessibility.16 In particular,
alkylated quaterthiophene derivatives present a good solubility in
organic solvents in addition to interesting electronic properties due
to their solid-state arrangement.16,17 The 3,300-didodecylquater-
thiophene crystals, for instance, form a lamellar-type structure
containing parallel rows of oligothiophenes.17 3,3000-Didodecylqua-
terthiophene (1) films present a one-dimensional charge trans-
porting ability resulting from this lamellar arrangement. This type
of alkylated quaterthiophene derivatives appears as a suitable
building block for the elaboration of bridged dimer for enhanced
charge transport properties (see Fig. S11 in Supplementary data).
Fig. 3. Evolution of the electronic coupling as a function of the torsion angle q for 1 and 7.
has been calculated here as half the splitting of the HOMO and
LUMO levels of the individual units in the dimer.20
The evolution of the electronic coupling in these systems as
a function of the torsion angle q is presented in Fig. 3, as calculated
at the widely used semi-empirical HartreeeFock INDO level.21
For the bridged systems, the electronic coupling presents
a maximum around 90ꢀ for both HOMO and LUMO levels, as ex-
pected from a previous theoretical study.22 In absolute value, there
are also two maxima around 0ꢀ and 180ꢀ and zero values around
30ꢀ and 150ꢀ. The increase by about one order of magnitude of the
electronic coupling when introducing the bridge is clearly evi-
denced in Fig. 2, thus demonstrating the high potential of bridged
systems for enhanced dimensionality for charge transport. The
electronic coupling is found to increase when reducing the size of
the conjugated backbone due to an increase of the electronic
density on the atom connected by the bridge. On the contrary, this
electronic coupling reduces when increasing the size of the satu-
rated bridge due to an exponential distance dependence.22 The
introduction of a vinylene bridge such as in 6, vide infra, allows for
a complete electronic delocalization together with a rigidification
of the molecule. However, the charges will be localized in the
center of the system, thus yielding the charge transport into a sin-
The s-covalent bridge introduces a link of fixed length between
the two oligothiophene moieties and is expected to promote the
electronic communication via through-bond coupling in the sys-
tem,18,19 so that an additional dimension is open for charge trans-
port (Fig. 2).
In order to validate this concept, we have calculated the elec-
tronic coupling between two unsubstituted quaterthiophene units
connected by an ethylene bridge (Fig. 3). The structure has been
initially optimized at the semi-empirical HartreeeFock AM1 level
while keeping the chromophores planar and parallel. The torsion
angles between the thienyl units and the bridge have then been
varied together in opposite directions by steps of 15ꢀ, without
further geometry optimizations, so that both chromophores are
kept parallel to one another. In addition, we took geometries gen-
erated in this way and removed the bridge while saturating the cut
bond with a hydrogen atom to create non-bridged systems with the
same relative position of the chromophores as in the bridged
structure (structures 1 and 2, Fig. 2). Doing so, we can assess the
increase in the electronic coupling induced by the bridge. The latter
gle direction. The use of a
s-covalent ethylene bridge therefore
appears as the best choice for extension of charge transport

M. Jenart et al. / Tetrahedron 68 (2012) 349e355
351
dimensionality in bridged quaterthiophene-based systems. It is
noteworthy that the electronic coupling of 19 meV calculated at
q
¼90ꢀ for compound 7 is of the same order of magnitude as the one
calculated between adjacent molecules of dinaphtho[2,3-b:20,30-f]
thieno[3,2-b]thiophene (DNTT), which is among the best organic
semiconductors known to date.23
Besides the benefit of the covalent bridge, the position of the alkyl
side chains in the quaterthiophene core also plays a role on the
charge transport dimensionality. Quaterthiophene derivatives
present a tunable supramolecular self-assembly induced by the
length, the branching, and the position of the alkyl side chains.17,24,25
Whereas the
mellar-type structure with a one-dimensional charge transport
ability,17 the crystals of its
-dialkylated analogues such as the
5,5000-dihexylquaterthiophene show a more conventional ‘herring-
bone’ arrangement with a 2-D charge transport.26 Thus
- or
b-dialkylated didodecylquaterthiophene forms a la-
Scheme 2. Synthesis of quaterthiophene derivative 5 and target bridged dimer 7.
Reagents and conditions: (i) Zn, TiCl4, THF, 0 ꢀC to reflux, 2.5 h; (ii) NH2eNH2, KOH,
pentan-1-ol, reflux, 20 h; (iii) Rh(I), H2 (4 atm), 60 ꢀC, 24 h.
a,u
b
a-
hydrogen was unsuccessful leading to complete recovery of the
alkylated quaterthiophene represents complementary building
blocks for the introduction of a covalent ethylene bridge between
starting p-conjugated dimer 6, whether using NaBH4/AcOH in the
presence of Pd/C30 or the methyl-borane sulfur complex.31 The
same results were obtained for a catalytic hydrogenation carried
out at atmospheric pressure, using classic Pd/C or Wilkinson cata-
lyst (Rh(PPh3)Cl).32 The target bridged dimer 7 was finally quanti-
tatively produced using not less than 30 mol % of Wilkinson catalyst
in a 24 h hydrogenation reaction under a pressure of 4 atm.33 In
addition, the same reaction conditions applying Pd/C as catalyst
provided a conversion of only 50%. It is worth noting that the use of
a smaller amount of Wilkinson catalyst also led to incomplete hy-
drogenation, producing an inseparable mixture of 6 and 7.
two cores. The
the charge transport dimensionality from 1-D to 2-D, while the
derivative would evolve from 2-D to 3-D. The availability of two
systems, using the same -system but differing by their anticipated
b-dimer derivative would allow an enhancement of
a-
p
transport dimensionality, is important for demonstrating the bridge
concept. In this purpose, we decided to prepare the
quaterthiophene-based dimers 7 and 13 containing an ethylene
bridge. Their synthesis and characterization are reported below.
3. Synthesis
3.2. Synthesis of quaterthiophene derivative 13
3.1. Synthesis of quaterthiophene derivative 7
The precedent MacMurry-mediated procedure was not thought
to be efficient for the preparation of bridged dodecylquaterthio-
phene dimer 13. Indeed, this synthetic pathway implies the final
reduction of 13 corresponding unsaturated precursor, which is
likely to be poorly soluble in organic solvent and consequently
difficult to hydrogenate. We therefore decided to prepare 13 using
more convenient intermediates. The chosen synthetic procedure
starts with the preparation of the didodecylterthiophene 10
(Scheme 3). Ziener and co-workers described the synthesis of 10
through the lithiation of terthiophene followed by the addition of
1-bromodidodecane.25 However, this procedure leads to a rather
low yield of only 24%. We therefore decided to prepare 10 differ-
ently, starting from the easily accessible bromothiophene 8 and
commercially available bithiophene borane 9.
The bridged quaterthiophene dimer 7 was prepared starting from
the corresponding didodecylquaterthiophene 1, which is obtained in
two steps from commercially available 3-dodecylthiophene.18
Compound 1 was first involved in a formylation reaction (Scheme
1). Our first attempts using the lithiation procedure27 with
1.1 equiv of n-BuLi followed by an excess of dry DMF resulted in only
37% of the desired mono-aldehyde 3, about 8% of the dialdehyde 4,
and 48% of unreacted starting material 1. The VilsmeiereHaack
conditions28 were found to be more efficient in this case, allowing
the preparation of the target aldehyde 3 in 51% yield together with
the formation of less than 5% of the symmetric diformylated qua-
terthiophene 4.
Scheme 1. Formylation of quaterthiophene 1. Reagents and conditions: (i) n-BuLi,
DMF, ꢁ78 ꢀC to rt, overnight; (ii) POCl3/DMF, 0 ꢀC to rt, 24 h.
The conjugated dimer 6 was then produced in 93% yield by
MacMurry coupling,29 using low valent Ti as catalyst (Scheme 2). 1H
NMR, UVevis, and IR analysis of 6 showed that only the E-isomer
was formed during this coupling, which could certainly be
explained by the steric hindrance introduced by the dodecyl side
chains. A simple WolffeKishner reduction of quaterthiophene al-
dehyde 3 also allowed the preparation of the methyl derivative 5,
used as a reference for the UVevis discussion. Different reduction
conditions were tried to prepare the target bridged dimer 7 from its
vinyl precursor 6. Reduction involving in situ production of
Scheme 3. Synthesis of quaterthiophene dimer 13. Reagents and conditions: (i) 9,
Pd(PPh3)4, Aliquat 336, K2CO3aq, 80 ꢀC, 20 h; (ii) n-BuLi, 2-isopropoxy-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane, ꢁ78 ꢀC to rt, overnight; (iii) 12, Pd(PPh3)4, Aliquat
336, K2CO3aq, 80 ꢀC, 20 h.
A SuzukieMiyaura coupling34 performed in toluene afforded
the desired terthiophene 10 in an acceptable yield of 48%. Next, the

352
M. Jenart et al. / Tetrahedron 68 (2012) 349e355
Table 1
borane 11 was efficiently produced in 88% yield through the
quenching of 10 mono-lithiated derivative with tetramethyldiox-
oborolane. The SuzukieMiyaura coupling of 11 with bridged thio-
phene dimer 12 finally allowed the production of the target
quaterthiophene 13 in 37% yield. This rather low yield is certainly
due to the decomposition of starting borane 11 during the coupling,
since a non negligible amount of terthiophene 10 was recovered.
Different reaction conditions were tried by changing the reaction
temperature from 80 ꢀC to reflux, but without better results.
Compound 13 appears to be poorly soluble in organic solvent
Molar extinction coefficients
3
, absorption (lmax(abs)) and fluorescence
max
(
lmax(em)) maximum of 1, 5, 6, 7, and 13 in 10ꢁ5 M solution in THF
3
lmax(abs)
lmax(em)
max
(Mꢁ1 cmꢁ1
)
(nm/eV)
(nm/eV)
1
5
6
7
31 000
33 000
77 000
61 000
22 000
376/3.30
382/3.25
458/2.71
384/3.23
422/2.94
453/2.74
457/2.72
546/2.27
458/2.71
508/2.44
13
compared to its
in THF or chloroform even at room temperature. This feature is in
agreement with the known solubility trend between -alkylated
quaterthiophenes and their
-alkylated analogues.18,25
b-alkylated analogue 7, which was perfectly soluble
gap. The reduction of the vinyl bridge in 6 breaks this
gation between the two quaterthiophene cores, inducing the
lmax(abs) blue shift observed after hydrogenation. The presence of
p-conju-
a,u
b
a
weaker absorption band in the spectrum of 6 around
4. Photophysical properties in dilute solution
lmax¼350 nm (Fig. 4a), is not consistent with the presence of the 6
Z stereoisomer in addition to 6 E, since the lmax of this transition is
lower than the lmax(abs) of 1. The bathochromic shift of 8 nm
observed between 1 and its bridged dimer 7 could not be assigned
to an additional electronic coupling in 7 through the ethylene
bridge. Indeed, an analogue shift of 6 nm is already present be-
tween 1 and its methyl derivative 5, which rather points to an
inductive effect. In addition, another bathochromic shift is ob-
The absorption spectra of the five oligothiophenes 1, 5, 6, 7, and
13 in THF present typical oligothiophene features with a predom-
inant absorption band known to correspond to the HOMOeLUMO
transition.35,36 All these bands are structureless (Fig. 4a), indicating
that the quaterthiophene cores are flexible and rotate around the
inter-ring bonds in the ground state.
served when passing from the b-alkylated dimer 7 to its a-alky-
lated analogue 13. This feature is in agreement with the
observation made by Faccheti et al. in their comparison of the
optical properties of
This shift to lower energy values is explained by steric in-
teractions generated by the -substitution, which distorts the oli-
a,u- and b,b
0-alkylated quaterthiophenes.36
b
gothiophene conjugated backbone from the planarity in solution.
Moreover, it seems that the quaterthiophene dimer 13 was not
totally soluble in THF, which explains the remaining absorption
observed above 520 nm certainly due to a scattering of the in-
cident light by insoluble particles. A filtration of the analyte solu-
tion through an HPLC pad led to a complete disappearance of this
remaining absorption (see Supplementary data) together with
a decrease in
3 , which confirms our assumption. The
3
value
measured for 13 is therefore very approximative. All fluorescence
spectra (Fig. 4b), also measured in THF solutions, show a vibra-
tional structure due to the rigidity of the excited molecules. In-
deed, oligothiophenes in the S1 state adopt a quinoid structure,37
where the thiophene cores are linked by C]C double bonds,
thus inducing a planarization of the molecules upon excitation. As
it is the case for the UVevis absorption, a light bathochromic shift
is observed when going from lmax(em) of 1 to lmax(em) of 5 or 7,
and a larger one is seen between lmax(em) of dimers 7 and 13,
respectively.
5. Conclusion
In conclusion, computational studies demonstrate the interest
of introducing an ethylene bridge between two quaterthiophene
cores to access an enhanced charge transport dimensionality. Based
on this molecular design, we successfully synthesized two novel
oligothiophene dimers 7 and 13 both containing an ethylene spacer.
Their overall yields, 47% and 16%, respectively, are sufficient to scale
up their synthesis, and hence produce larger amounts for physical
studies. The next steps, beyond the scope of this synthetic paper,
involve the fabrication and characterization of thin films to mea-
sure charge carrier mobility in field-effect transistors. This en-
compasses the resolution of the crystal structure to access the
conformation of the ethylene bridge that is anticipated to control
the extent of the electronic coupling between quaterthiophene
units.
Fig. 4. Absorption (a) and fluorescence (b) spectra of oligothiophenes 1, 5, 6, 7, and 13
in solution in THF.
Besides, a red shift of the lmax(abs) is observed when going
from 1 to its dimer 6 (Table 1), which is explained by the extension
of the conjugation in the dimer and thus a lower HOMOeLUMO

M. Jenart et al. / Tetrahedron 68 (2012) 349e355
353
6. Experimental section
9:1 v/v) affording 5 (0.181 g, 0.27 mmol, 92%) as an orange oil,
which solidify upon cooling. Rf (hexane): 0.35; mp: 33.8e35.5 ꢀC;
6.1. Materials and methods
1H NMR (CDCl3, 300 MHz)
d
: 7.18 (d, 1H, J¼5.2 Hz, H5000), 7.11 (d, 1H,
J¼3.6 Hz, H300), 7.10 (d, 1H, J¼3.6 Hz, H40), 7.01 (d, 1H, J¼3.6 Hz,
H400), 6.95 (d, 1H, J¼3.6 Hz, H30), 6.94 (d, 1H, J¼5.2 Hz, H4000), 6.61 (s,
1H, H4), 2.78 (t, 2H, J¼7.8 Hz, CthiopheneeCH2e), 2.70 (t, 2H,
J¼7.8 Hz, CthiopheneeCH2e), 2.45 (s, 3H, CthiopheneeCH3), 1.71e1.55
(m, 4H, CthiopheneeCH2eCH2e), 1.42e1.19 (m, 36H, e(CH2)9eCH3),
Unless otherwise noted, all chemicals were purchased from
Aldrich or Acros and used without further purification. THF was
dried by conventional method (Na/benzophenone distillation pro-
cedure under argon) and collected with glass syringes. TLC: SiO2
Silica gel 60F254 on aluminum sheet (Merck). Column chromatog-
raphy: Silica gel 60 (particle size 0.063e0.200 mm, Merck). 1H NMR
(300 MHz) and 13C NMR (75 MHz) were recorded on Bruker Avance
300 at room temperature. Chemical shifts are given in parts per
million and coupling constants J in hertz. The residual signal of the
solvent was taken as internal reference standard. EI-HRMS mea-
surements were made on a Waters AutoSpec 6 and MALDI-TOF
experiments on a Waters QToF Premier. Absorption spectra were
recorded on an Agilent 8453 spectrophotometer in a quartz cell
(optical path of 1 cm) in tetrahydrofuran (concentration solutions
of 10ꢁ5 M were used). Emission spectra were measured on an
Aminco Bowman series 2 luminescence spectrophotometer.
0.88 (t, 6H, J¼6.8 Hz, e(CH2)9eCH3); 13C NMR (CDCl3, 75 MHz)
d:
140.01, 139.99, 138.5, 137.1, 136.3, 135.9, 135.3, 130.5, 130.2, 128.7,
128.0, 126.7, 126.0, 123.9, 123.8, 32.1, 30.8, 29.83, 29.77, 29.71, 29.69,
ꢂ
29.6, 29.5, 29.4, 22.9, 15.4, 14.3; HRMS (MALDI-TOF): [Mþ ] calcd for
C41H60S4 m/z 680.3578, found 680.3572.
6.2.3. (E)-1,2-Bis(3,3000-didodecyl-2,20:50,200:500,2000-quaterthiophen-5-
yl)ethene (6). To a solution of Zn-powder (0.223 g, 3.41 mmol) in
dry THF (10 mL) was added dropwise TiCl4 (0.19 mL, 1.71 mmol) at
0 ꢀC under argon atmosphere. The reaction mixture was stirred for
20 min at 0 ꢀC before the addition of a solution of quaterthiophene
mono-aldehyde 3 (0.988 g, 1.42 mmol) in dry THF (10 mL). The
mixture was stirred further for 5 min at 0 ꢀC, and then refluxed for
2 h. The mixture was cooled down to room temperature, poured
into water (40 mL), and extracted with dichloromethane. The ex-
tracts were washed with water, dried over MgSO4, and concen-
trated under reduced pressure. The residue was suspended into
MeOH, and the insoluble crude product was recovered by filtration.
It was then purified by column chromatography on silica gel (tol-
uene) to give 6 (0.902 g, 0.66 mmol, 93%) as a yellow solid. Rf
6.2. Synthetic procedures
6.2.1. 3,3000-Didodecyl-2,20:50,200:500,2000-quaterthiophene-5-carbox-
aldehyde (3). To prepare the Vilsmeier reagent, POCl3 (0.31 mL,
3.30 mmol) was added at 0 ꢀC to DMF (1.0 mL, 12.97 mmol) under
argon. The resulting solution was stirred for 2 h at room tempera-
ture. It was added dropwise to a solution of quaterthiophene 1
(2.00 g, 3.0 mmol) in dry 1,2-dichloroethane (30 mL) under inert
atmosphere. The reaction mixture was stirred further for 24 h at
room temperature. It was then poured into ice/water, neutralized
with aqueous Na2CO3, and extracted with dichloromethane. The
combined organic layers were washed with water and brine, dried
over MgSO4, and concentrated under reduced pressure. The residue
was purified by column chromatography on silica gel (toluene) to
give 3 (1.06 g, 1.52 mmol, 51%) and 4 (0.09 g, 0.12 mmol, 4%) both as
red solids.
(toluene): 1.00; mp: 87.5e90.1 ꢀC; 1H NMR (THF-d8, 300 MHz)
d:
7.29 (d, 2H, J¼5.2 Hz, H5000), 7.21 (d, 4H, J¼3.8 Hz, H40, H300), 7.11 (d,
2H, J¼3.8 Hz, H400), 7.07 (d, 2H, J¼3.8 Hz, H30), 7.00 (s, 4H, H4,
eCH]CHe), 6.97 (d, 2H, J¼5.2 Hz, H4000), 2.85e2.75 (m, 8H,
C
thiopheneeCH2e), 1.74e1.60 (m, 8H,
CthiopheneeCH2eCH2e),
1.46e1.23 (m, 72H, e(CH2)9eCH3), 0.88 (t,12H, J¼6.7 Hz, eCH3); 13
C
NMR (THF-d8, 75 MHz) d: 141.5, 141.4, 140.9, 137.8, 137.6, 136.6,
136.4, 131.2, 131.04, 130.99, 130.6, 127.6, 127.4, 125.2, 125.13, 125.08,
122.2, 33.1, 31.8, 31.4, 30.82, 30.79, 30.76, 30.60, 30.55, 30.5, 30.4,
ꢂ
For 3: Rf (toluene): 0.78; mp: 55.6e57.8 ꢀC; 1H NMR (CDCl3,
30.2, 23.8, 14.3; HRMS (MALDI-TOF): [Mþ ] calcd for C82H116S8 m/z
300 MHz)
d
: 9.83 (s, 1H, eCHO), 7.59 (s, 1H, H4), 7.22e7.14 (m, 4H,
1356.6843, found 1356.6830.
H30, H40, H300, H5000), 7.03 (d, 1H, J¼3.8 Hz, H400), 6.95 (d, 1H,
J¼5.2 Hz, H4000), 2.87e2.74 (m, 4H, CthiopheneeCH2e), 1.76e1.59 (m,
4H, CthiopheneeCH2eCH2e), 1.46e1.20 (m, 36H, e(CH2)9eCH3), 0.88
6.2.4. 1,2-Bis(3,3000-didodecyl-2,20:50,200:500,2000-quaterthiophen-5-yl)
ethane (7). Tris(triphenylphosphine)chloro-rhodium (I) (0.094 g,
0.10 mmol) was added to a solution of 6 (0.446 g, 0.33 mmol) in dry
toluene (7 mL), in a glass tube fitted with a septum. The resultant
mixture was degassed with argon for 15 min. The septum was then
pierced with needles and the mixture was placed in a Parr appa-
ratus. The hydrogenation was carried out at 60 ꢀC for 24 h, at
a pressure of 4 atm. Purification by column chromatography on
silica gel, using dichloromethane as eluent, quantitatively yielded
the dimer 7 (0.441 g, 0.32 mmol, quant.) as a light yellow solid. Rf
(t, 6H, J¼6.7 Hz, eCH3); 13C NMR (CDCl3, 75 MHz)
d: 182.4, 140.9,
140.4, 140.2, 140.1, 139.1, 139.0, 136.2, 136.0, 133.6, 130.1, 130.0,
128.2, 126.6, 124.5, 124.1, 124.0, 31.9, 30.6, 30.2, 29.64, 29.59, 29.56,
ꢂ
29.5, 29.44, 29.41, 29.35, 29.3, 22.7, 14.1; HRMS (MALDI-TOF): [Mþ
]
calcd for C41H58OS4 m/z 694.3371, found 694.3383.
For 4: Rf (toluene): 0.32; mp: 81.0e82.8 ꢀC; 1H NMR (CDCl3,
300 MHz) d
: 9.83 (s, 2H, CHO), 7.63 (s, 2H, H4, H4000), 7.25 (s, 4H, H30,
H40, H300, H400), 2.84 (t, 4H, J¼7.8 Hz, CthiopheneeCH2e), 1.76e1.64 (m,
4H,
C
thiopheneeCH2eCH2e), 1.43e1.18 (m, 36H, e(CH2)9eCH3),
(CH2Cl2): 0.95; mp: 55.6e58.7 ꢀC; 1H NMR (THF-d8, 300 MHz)
d:
0.90e0.83 (m, 6H, eCH3); 13C NMR (CDCl3, 75 MHz)
d: 183.1, 141.5,
7.28 (d, 2H, J¼5.2 Hz, H5000), 7.18 (d, 2H, J¼3.7 Hz, H40 or H300), 7.17 (d,
2H, J¼3.7 Hz, H300 or H40), 7.05 (d, 2H, J¼3.8 Hz, H400), 7.01 (d, 2H,
J¼3.8 Hz, H30), 6.96 (d, 2H, J¼5.2 Hz, H4000), 6.74 (s, 2H, H4),
3.13(s, 4H, CthiopheneeCH2eCH2eCthiophene), 2.80 (t, 4H, J¼7.7 Hz,
141.2, 140.7, 139.7, 138.8, 135.1, 128.9, 125.4, 32.5, 30.8, 30.3, 30.2,
ꢂ
30.1, 30.0, 23.3, 14.5; HRMS (MALDI-TOF): [Mþ
] calcd for
C42H58O2S4 m/z 722.3320, found 722.3340.
C
thiopheneeCH2e), 2.75 (t, 4H, J¼7.7 Hz, CthiopheneeCH2e), 1.74e1.58
6.2.2. 3,3000-Didodecyl-5-methyl-2,20:50,200:500,2000-quaterthiophene
(5). To a solution of hydrazine hydrate (0.70 mL, 14.43 mmol) and
quaterthiophene mono-aldehyde 3 (0.200 g, 0.29 mmol) in pentan-
1-ol (15 mL) was added potassium hydroxide (0.321 g, 5.73 mmol).
The reaction mixture was stirred under reflux for 20 h. It was then
cooled to room temperature, poured into water, and extracted with
dichloromethane. The combined organic layers were successively
washed with water and brine, dried over MgSO4, and concentrated
under reduced pressure. The crude product was purified by column
chromatography on silica gel (petroleum ether/dichloromathene
(m, 8H, CthiopheneeCH2eCH2e), 1.44e1.22 (m, 72H, e(CH2)9eCH3),
0.92e0.84 (m,12H, eCH3); 13C NMR (CDCl3, 75 MHz)
d: 143.3,140.8,
140.6, 137.8, 137.3, 136.8, 136.3, 131.2, 131.0, 129.3, 129.2, 127.6, 127.1,
125.1,124.93,124.85, 33.1, 32.9, 31.8, 31.7, 30.8, 30.6, 30.5, 30.4, 30.2,
ꢂ
23.8, 14.6; HRMS (MALDI-TOF): [Mþ ] calcd for C82H118S8 m/z
1358.6999, found 1358.6951.
6.2.5. 5-Dodecyl-2,20:50,200-terthiophene (10). A solution of bromo-
thiophene 8 (1.164 g, 3.52 mmol), bithiophene borane 9 (1.030 g,
3.52 mmol), and Aliquat 336 (few drops) in toluene (20 mL) was

354
M. Jenart et al. / Tetrahedron 68 (2012) 349e355
degazed with argon for 20 min. Tetrakis triphenylphosphine palla-
dium (0.400 g, 0.34 mmol) was then added to the reaction mixture,
could not be recorded due to the poor solubility of 13 in organic
solvent at room temperature.
followed by
a degazed 2 M K2CO3 aqueous solution (4 mL,
8.00 mmol). The reaction mixture was stirred at 80 ꢀC overnight. It
was then cooled at room temperature, poured into water, and
extracted with dichloromethane. The combined organic layers were
successively washed with water and brine, dried over MgSO4, and
concentrated under reduced pressure. The crude product was fil-
tered over silica gel using dichloromethane as eluent and further
purified by recrystallization in toluene/methanol yielding 10
(0.705 g,1.69 mmol, 48%) as a yellow powder. The NMR and physical
properties of this compound correspond to the one previously de-
scribed by Ellinger et al.25 Rf (hexane): 0.16; mp: 74.0 ꢀC; 1H NMR
Acknowledgements
This work has been financially supported by the Belgian Federal
Science Policy Office (PAI SF2), by a concerted research action of the
French Community of Belgian (ARC Nꢀ 20061), and by the Belgian
National Fund for Scientific Research (FNRS). The authors also
would like to thank Pr. Ivan Jabin and Marc Pamart for their help
respectively with the hydrogenation step and the mass spectrom-
etry. J.C. is a senior researcher of FNRS.
(CDCl3, 300 MHz)
d
: 7.20 (dd,1H, J¼5.1 and 1.1 Hz, H500), 7.16 (dd,1H,
Supplementary data
J¼3.5 and 1.1 Hz, H300), 7.07e7.04 (m,1H, H3), 7.03e6.98 (m, 3H, H30,
H40, H400), 6.68 (d, 1H, J¼3.5 Hz, H4), 2.79 (t, 2H, J¼7.5 Hz,
1H and 13C spectra of all described compounds. Supplementary
data associated with this article can be found in online version, at
doi:10.1016/j.tet.2011.10.020.
C
thiopheneeCH2e), 1.73e1.63 (m, 2H,
CthiopheneeCH2eCH2e),
1.33e1.27 (m, 18H, e(CH2)9eCH3), 0.91e0.86 (m, 3H, eCH3); 13C
NMR (CDCl3, 75 MHz) : 145.8,137.5,137.0,135.6,134.6,128.0,125.0,
d
124.4, 123.6, 123.5, 32.1, 31.8, 30.4, 29.8, 29.7, 29.5, 29.2, 22.9, 14.3.
References and notes
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phene 10 (1.0 g, 2.40 mmol) in dry THF (50 mL) was added drop-
wise n-butyllithium (1.6 M in hexane, 1.44 mL, 3.60 mmol) at
ꢁ78 ꢀC and under argon. The reaction mixture was stirred at ꢁ78 ꢀC
for 15 min, then the cold bath was removed and the mixture was
warmed to room temperature. It was cooled again to ꢁ78 ꢀC before
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was washed with methanol affording the desired terthiophene
borane 11 (1.140 g, 2.10 mmol, 88%) as a green solid. The product
was used in the next step without further purification. 1H NMR
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