How to build fully π-conjugated architectures with thienylene and phenylene fragments

Article abstract of DOI:10.1002/ejoc.200601114

A series of small-sized model π-conjugated oligomers have been prepared from thienylene and phenylene or dimethyl-or dimethoxy-substituted phenylene units. Crystallographic data for the methoxylated compound show a quasi-planar conformation with a non-covalent S-O interaction. The resulting strong conjugation in the gas phase has also been highlighted by UV/photoelectron spectroscopy and theoretical calculations (DFT). Indeed, for these compounds there is a large energy gap ΔE^π arising from the interaction between the molecular orbitals of the isolated thienylene-phenylene species. This can be explained in terms of the energies of the two π orbitals of the dimethoxyphenylene unit, the shape of these molecular orbitals in a three-orbital interaction diagram and by the presence of the S...O interaction which reduces the inter-ring angle between the two aromatic cycles. The nature of the sulfur-oxygen interaction, discussed from a theoretical point of view, is mainly electrostatic, the orbital contribution from the only correctly directed orbitals n_O^σ and σ*_S-C being slightly stabilising. These results show extensive conjugation of the π system corroborated by a small HOMO-LUMO gap. These studies, carried out in the solid state and in the gas phase, show how important it is to combine thienylene and dialkoxyphenylene fragments to obtain oligomers with a strong electronic delocalisation. Thus, these compounds are of interest in the fields of electronic and optoelectronic devices. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200601114

FULL PAPER
DOI: 10.1002/ejoc.200601114
How to Build Fully π-Conjugated Architectures with Thienylene and Phenylene
Fragments
Sandrine Lois,[a] Jean-Charles Florès,[a] Jean-Pierre Lère-Porte,*[a]
Françoise Serein-Spirau,*[a] Joël J. E. Moreau,[a] Karinne Miqueu,*[b]
Jean-Marc Sotiropoulos,*[b] Patrick Baylère,[b] Monique Tillard,[c] and Claude Belin[c]
Keywords: Sulfur heterocycles / Noncovalent interactions / Photoelectron spectroscopy / Density functional calculations
A series of small-sized model π-conjugated oligomers have
been prepared from thienylene and phenylene or dimethyl-
or dimethoxy-substituted phenylene units. Crystallographic
data for the methoxylated compound show a quasi-planar
conformation with a non-covalent S–O interaction. The re-
sulting strong conjugation in the gas phase has also been
highlighted by UV/photoelectron spectroscopy and theoreti-
cal calculations (DFT). Indeed, for these compounds there is
a large energy gap ∆Eπ arising from the interaction between
the molecular orbitals of the isolated thienylene-phenylene
species. This can be explained in terms of the energies of the
two π orbitals of the dimethoxyphenylene unit, the shape of
these molecular orbitals in a three-orbital interaction dia-
duces the inter-ring angle between the two aromatic cycles.
The nature of the sulfur–oxygen interaction, discussed from
a theoretical point of view, is mainly electrostatic, the orbital
contribution from the only correctly directed orbitals nOσ and
σ*S–C being slightly stabilising. These results show extensive
conjugation of the π system corroborated by a small HOMO–
LUMO gap. These studies, carried out in the solid state and
in the gas phase, show how important it is to combine thieny-
lene and dialkoxyphenylene fragments to obtain oligomers
with a strong electronic delocalisation. Thus, these com-
pounds are of interest in the fields of electronic and optoelec-
tronic devices.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
gram and by the presence of the S···O interaction which re- Germany, 2007)
effect mobilities.[4] More recently, highly regioregular thien-
Introduction
ylene-2,5-dialkoxyphenylene copolymers have been devel-
oped and have shown very interesting properties: the pres-
ence of polar dialkoxy chains ensured excellent glass ad-
hesion and enabled the formation of homogeneous thin-
film coatings. These materials are highly fluorescent in solu-
tion and this fluorescence could be polarised by ordering
these polymers by coating them on an oriented Teflon de-
posit.[5] Moreover, very low band gaps and low oxidation
potentials were recorded which are indicative of highly con-
jugated π systems.[6] Finally, one such polymer exhibited
self-organisation properties leading to lamellar structures
with favourable π-stacking interactions between two consec-
utive conjugated chains characterised by an interchain dis-
tance of 3.8 Å.
π-Conjugated organic polymers have received much at-
tention for several years because of the large variety of ap-
plications directly associated with the existence of an ex-
tended conjugated π-system along the polymer backbone.
They have attracted much interest in the design of electronic
and optoelectronic devices such as organic field-effect tran-
sistors (OFET), organic light-emitting diodes (OLED) or
solar cells because of their remarkable electronic and elec-
tro-optical properties[1,2] which are easy to tune as a result
of their molecular and supramolecular chemistry. Among
the more notable examples, the regioregular poly(3-alkyl-
thiophene) exhibits excellent chain planarity and extended
conjugation lengths as a result of its head-to-tail regiochem-
istry,[3] leading to highly conjugated sheets with high field-
In the search for novel materials with transport proper-
ties resulting from optimised π-conjugation, oligo(pheny-
lenethienylene)s have been developed as a new class of or-
ganic semi-conductor.[7] Interesting electronic mobilities in
organic field-effect transistors formed from this kind of
stable and easily processable compound[8] have demon-
strated that these compounds have extended conjugation.
However, building oligo(phenylenethienylene)s consisting of
more than five-to-six consecutive rings leads to fairly insol-
uble compounds and prevents advantage being taken of this
extended conjugation. To overcome the solubility problem,
[a] Hétérochimie Moléculaire et Macromoléculaire, UMR CNRS
5076, Ecole Nationale Supérieure de Chimie de Montpellier,
8, rue de l’Ecole Normale, 34296 Montpellier Cedex 05, France
E-mail: lere@enscm.fr
[b] Equipe de Chimie-Physique, IPREM-UMR CNRS 5254 Ave-
nue de l’Université,
B. P. 1155, 64013 Pau Cedex, France
E-mail: jean-marc.sotiro@univ-pau.fr
[c] Laboratoire des Agrégats Moléculaires et Matériaux Inor-
ganiques, UMR CNRS 5072, Université Montpellier II,
2 Place Eugène Bataillon, 34095 Montpellier Cedex 5, France
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Eur. J. Org. Chem. 2007, 4019–4031
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4019

J.-P. Lère-Porte, J.-M. Sotiropoulos et al.
FULL PAPER
alkyl or alkoxy chains can be introduced into the conju- from a sensitive and non-storable thienylzinc chloride inter-
gated backbone leading to oligo(2Ј-thienylene-2,5-dialk- mediate, itself elaborated from the corresponding organo-
oxyphenylene) nanostructures. To improve and better tune lithium derivative and rigorously dried zinc dichloride.[9]
the optoelectronic properties of these regioregular alternat- Concerning the access to 2, the protocol proposed herein is
ing sequences of thienylene and 2,5-dialkoxyphenylene moi- an efficient alternative to the reaction of thiophene in the
eties and in particular to explore whether such models are presence of a catalytic amount of concentrated sulfuric acid
potentially interesting as compounds with high field-effect with a cis/trans mixture of 3,6-dimethoxy-3,6-dimethylcy-
mobilities, it was important to examine if such sequences clohexa-1,4-diene (ca. 1:1), itself obtained by electrochemi-
are appropriate for building fully conjugated chains.
cal oxidation of p-xylene.[10] Moreover, the preparative
In this work, we have studied the electronic properties method described herein was very convenient for the prepa-
of poly(phenylenethienylene) compounds and the effect of ration of the three-ring compounds 4–6 and avoided the
phenylene 2,5-disubstitution by alkoxy groups on the conju- elaboration of specific reactive species such as 2-thienylbis-
gation. We focused our attention on understanding the ori- (isobutyloxy)borane to prepare 4 in 72% yield in a 24 h
gin of the planarity of these compounds. What is the main Suzuki coupling or 2-thienylcadmium chloride, prepared
factor leading to this planarity? Is it an intrinsic property from toxic but more easily dried and stored cadmium chlo-
bestowed by the alkoxy groups or a consequence of the ride, to obtain 5 in 57% yield.[9] Finally, 6 was selectively
packing effect in the solid state? The answers to these prob- prepared according to Scheme 1, whereas use of 2-thienyl-
lems could only be found in an experimental study in the zinc chloride in a palladium(0)-catalysed cross-coupling
gas phase in which the molecular entities are fully isolated with 1,4-dimethoxybenzene yielded a five-ring byproduct
from each other. Small-sized thienylene-2,5-disubstituted- (14%) besides the desired three-ring oligomer synthesised
phenylene oligomers have been elaborated as models to in 49% yield.[9] To prepare 7, 2,5-dimethoxyphenol[11] was
study by UV/photoelectron spectroscopy (UV/PES) in the O-alkylated in 93% yield with one equivalent of benzyl bro-
gas phase and by density functional calculations (DFT). mide in the presence of K2CO3 in refluxing acetonitrile
Analysis of the results obtained in the gas and condensed (Scheme 2).[12] The obtained 1-benzyloxy-2,5-dimethoxy-
phases has allowed us to understand the crucial role played benzene (8) was then selectively iodinated in 86% yield in
by the intramolecular S···O interaction in determining the the 4-position of the phenylene with 1.05 equivalent of N-
planarity of these oligomers.
iodosuccinimide activated by 0.3 equivalent of trifluoro-
acetic acid.[13] The resulting 1-benzoyloxy-4-iodo-2,5-di-
Results and Discussion
Synthesis
Seven model compounds containing the thienylene-2,5-
disubstituted-phenylene system were elaborated using Stille
or the Suzuki palladium(0)-catalysed cross-coupling. Six of
them were prepared according to the synthetic pathways
described in Scheme 1: equimolar amounts of monobromi-
nated benzene and tributylstannylthiophene for 1–3
(Scheme 1, a) and a half equimolar amount of a dibromi-
nated benzene moiety relative to 2-tributylstannylthiophene
for 4–6 (Scheme 1, b).
This general synthetic pathway is efficient and easier to
implement than those reported in the literature for some
compounds: for instance, phenylthiophene 1 has been pre-
Scheme 2. Synthesis of 1-benzyloxy-2,5-dimethyl-4-(2-thienyl)ben-
pared via a catalysed palladium(0) Negishi cross-coupling zene 7.
Scheme 1. Synthesis of thienylene-1,4-disubstituted phenylenes 1–6.
4020
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 4019–4031

How to Build Fully π-Conjugated Architectures
FULL PAPER
methoxybenzene was immediately treated with 1.2 equiva- that the two units 61 and 62 adopt an anti conformation in
lent of 2-thiopheneboronic acid in a Pd0-catalysed Suzuki the crystal state, the intramolecular (S···O) interactions be-
cross-coupling to afford 7 in 71% yield
ing optimised. Such S···O interactions, which are the driving
The seven thienylene-2,5-disubstituted-phenylene oligo- force for the stabilisation of the conjugated segment in the
mers were isolated as solids except for 2 and 3 which are trans conformation for the thienylene rings, have been ob-
colourless or light-yellow oils.
served in the X-ray crystallographic structure of a variety
of oligo(3,4-ethylenedioxythiophene)s.[14]
Such S···O interactions have been evidenced in the crystal
state of thiazole nucleosides,[15] acetazolamide, thiadiazoli-
nethione,[16] dimethyl 1,3-dithiolan-2-ylidenemalonate,[17]
dimethyl 2,2Ј-bithiophene-3,4Ј-dicarboxylate, dimethyl 2,2Ј-
bithiophene-3,3Ј-dicarboxylate[18] and extended conjugated
systems containing at least two consecutive (3,4-ethylene-
dioxythiophene) entities.[14,19] From radiocrystallographic
data, all the authors who observed the intramolecular non-
covalent S···O interaction attribute to it the self-rigidifica-
tion of the molecular structure in a privileged conforma-
tion. Since a radiocristallographic study can be realised
with monocrystals of suitable compounds, such intramolec-
ular non-covalent S···O interactions have been evidenced
but, to the best of our knowledge, have never been ex-
plained. Hence DFT calculations were carried out to pro-
vide more information on this interaction. Moreover, in or-
der to understand the role played by the alkoxyphenylene
substituent in the observed planarity of 6 and 7 and to
avoid the packing effect in the crystal, the calculations were
realised considering the compounds as completely individ-
ual species, that is, as in the gas phase. Moreover, quantum
calculations on model oligomers 1–6 were carried out to
gain information on the geometrical properties of the thien-
ylene-2,5-disubstituted-phenylene sequences. Additionally,
the electronic properties of these compounds will be con-
solidated by UV/PES. These properties provide information
on the π–π orbital interactions, and hence on the magnitude
of the conjugation and also on the position of the HOMO
orbital which can be correlated with the oxidation poten-
tial.
Structural Study in the Solid State by X-ray Diffraction
Experiments
After slow recrystallisation from an ethanol/toluene solu-
tion, white needle-shaped monocrystals of 6 and 7 were ob-
tained and studied by X-ray diffraction.
The asymmetric unit of 7 consists of one molecule and
the orthorhombic P212121 unit cell contains four molecules.
The P2/c monoclinic unit cell of 6 also contains four mole-
cules located at inversion centres in such a way that the
asymmetric unit consists of two independent half molecules
(Figure 1).
C(thiophene)–C(phenylene) bond lengths, distances be-
tween the sulfur and the oxygen and the dihedral angles
between the thienylene and the phenylene rings have been
examined and the recorded values for 6 and 7 are reported
in Table 1.
Table 1. X-ray-diffraction determined structural data for 6 and 7.
7
61
62
Φ [°]
d(CTh–CPh) [Å]
d(S–O) [Å]
5.85
1.459
2.705
10.49
1.470
2.700
11.88
1.476
2.715
As expected, in the two compounds 6 and 7, the inter-
ring CTh–CPh bond length reveals a character between a
single and a double bond and tends to decrease with the
inter-ring torsion angle. The low values of the dihedral an-
gle (Φ) recorded in the crystal state indicate quasi-planar
conformations and are the signature of a high level of con-
jugation between the aromatic rings. Moreover, the ob-
served sulfur–oxygen distances are considerably shorter
(2.7 Å) than the sum of the van der Waals radii of sulfur
and oxygen (1.85+1.5 = 3.35 Å): these observations are
Quantum Chemical Study in the Gas Phase
The π–π interactions in the gas phase between the thien-
consistent with the existence of non-covalent intramolecu- ylenes and phenylenes moieties were first determined in the
lar sulfur–oxygen interactions (S···O) which induce self- smaller systems 1–3 and then this study was extended to
rigidification of the conjugated system in quasi-planar con- systems substituted by one more thienylene ring 4–6
formations with an extended conjugation. It is worth noting (Scheme 3).
Figure 1. ORTEP diagrams of (a) 7 and (b) 6. Intramolecular S···O interactions are indicated by dotted lines.
Eur. J. Org. Chem. 2007, 4019–4031
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4021

J.-P. Lère-Porte, J.-M. Sotiropoulos et al.
FULL PAPER
Structural Study of the Three-Ring Compounds
The geometrical parameters for 4–6 computed by the
DFT method are presented in Table 2. Compound 6 adopts
a privileged conformation with a short S···O distance
(2.786 Å) and the two oxygen lone-pairs point towards the
sulfur (Scheme 3), in agreement with the experimental crys-
tallographic data. The main result of this study is the
change in the inter-ring angles upon substitution of the
phenyl ring and the lengthening of the conjugated skeleton.
The addition of a thienylene entity onto a phenylene-thieny-
lene fragment leads to a decrease in the inter-ring angle.
Moreover, as previously observed in the two-ring series, the
smallest inter-angle value in the three-ring series is obtained
for the dimethoxylated compound 6 (21.1°). These geomet-
rical parameters determined in the gas phase are in quite
good agreement with the theoretical parameters previously
reported by Pan et al.[20] at the HF/3-21G* level. However,
for these three compounds, the inter-ring angles determined
by DFT are smaller than those determined by HF calcula-
tions because electronic correlation is taken into account in
the DFT, but not in the HF calculations.
Scheme 3. Privileged conformations of compounds 1–6 studied in
the gas phase.
Structural Study of the Two-Ring Compounds
UV/Photoelectron Spectroscopic Study in the Gas Phase
For compounds 1–3, calculations with the B3LYP hybrid
functional and the 6-31G(d,p) basis set were carried out
(see the Theoretical Section in the Experimental Section).
The privileged conformers are presented in Scheme 3 and
the geometrical parameters are reported in Table 2. For 1,
only one conformer exists on the potential energy surface.
The two rings are slightly twisted with a 28.5° inter-ring
angle Φ and the CTh–CPh bond length of about 1.47 Å is
between a single and a double bond. In contrast, two rota-
mers were found on the potential energy surface for 2, but
with no significant energy gap (0.43 kcalmol–1). The more
stable rotamer corresponds to the arrangement with the
lower steric hindrance (see Supporting Information for the
other rotamer). The angle between the two units is the high-
est observed (41.5°) for these compounds. For 3, the global
minimum (for all the other rotamers see the Supporting In-
formation) adopts a conformation with a short S···O dis-
tance of 2.798 Å, less than the sum of the van der Waals
radii, and has the smallest inter-ring angle of 24.2°. The
UV/photoelectron spectroscopy has proved to be an ex-
cellent experimental tool for revealing the electronic struc-
ture and bonding features of molecules.[21] In the present
study of these π-conjugated systems, this spectroscopic
method can provide an evaluation of the effect of the phen-
ylene substituents (H, CH3, OCH3) on the electronic prop-
erties of the thienylene-phenylene compounds. Experimen-
tally, thanks to UV/photoelectron spectroscopy, the posi-
tion of the HOMO orbital can be obtained as well as infor-
mation on the π–π splitting (∆Eπ) which corresponds to the
magnitude of the interaction. This latter value depends on
the orbital overlap, but also on the energies of the isolated
fragments. So, if we consider the experimental energies of
the π orbitals of the phenylene fragments[22] (benzene: πPh
,
1
πPh2: 9.2 eV; dimethylbenzene: πPh1: 8.6 eV, πPh2: 9.2 eV; di-
methoxybenzene: πPh1: 7.9 eV, πPh2: 9.2 eV), they are quite
close to the π orbitals of thiophene [πTh1: 8.9 eV and πTh
2
(nSπ): 9.2 eV].[23] Consequently, the π–π interactions be-
tween these two types of units are expected to be strong.
Scheme 4 shows in a simple way the correlation between
the orbital interactions of the isolated fragments and the
corresponding photoelectron spectrum.
C
Th–CPh bond length is 1.470 Å, similar to that observed
for 1 and 2, and consequently does not seem to provide
much information on the inter-ring conjugation.
Electronic Properties of the Two-Ring Compounds
The photoelectron spectra were recorded at 40 °C for 1
and at 120 °C for 2 and 3 (p = 10–5 mbar, beam tempera-
ture).
The photoelectron (PE) spectrum of 1 (Figure 2) exhibits
three well-resolved bands at 8.1, 9.2 and 9.8 eV and then
broad bands between 11.4 and 15 eV. Considering the ex-
perimental ionisation potentials (IP) of the two fragments
benzene[22] and thiophene,[23] the first IP of 1 (8.1 eV) sug-
Table 2. Geometrical parameters for 1–6.
Compound
1
2
3
4
5
6
d(CTh–CPh) [Å] 1.469
1.475
–41.5
–
0.45
0.24
1.470
–24.2
2.798
0.49
1.466 1.473
26.2
–
0.45
0.24
1.467
–21.1
2.786
0.49
Φ [°]
–28.5
–
0.45
0.24
–39.7
–
0.45
0.24
d(S–O) [Å]
[a]
qS
[a]
qX
–0.53
–0.53
[a] Total natural charges from the NBO analysis: qS: charge on
sulfur; qX: charge on hydrogen or oxygen (facing the sulfur atom). gests a strong interaction between the π systems of the two
4022
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 4019–4031

How to Build Fully π-Conjugated Architectures
FULL PAPER
Scheme 4. Schematic π–π interactions (∆Eπ) illustrated for phenylthiophene 1 with experimental ionisation energies in eV. The correspond-
ing photoelectron spectra are qualitatively simulated.
rings. From such considerations, this spectrum can be easily
For 2, the experimental ∆Eπ is only about 1.2 eV and
described with a two-orbital interaction diagram: the first corresponds to the energy gap between the ionisations rep-
and the third bands are assigned to the ejection of electrons resented by the two shoulders at 8.2 and 9.4 eV. The nature
localised in the molecular orbitals (MO) resulting from the of the others ionisations are presented under the spectrum
interaction between the πPh and πTh orbitals since only in the Supporting Information. Conversely, the replacement
1
1
the πPh orbital possesses electron density on the carbon of hydrogen by a methoxy group in the same positions,
1
atom linked to the thienyl ring (Scheme 4). These orbitals leads to a lowering of the first IP and to an increase in ∆Eπ.
correspond to the π– (out-of-phase) and π+ (in-phase) com- Plots of the first, second and fourth MOs clearly show a
bination of orbitals, respectively, and are named π1 and mixing between the two π orbitals of the dimethoxybenzene
1
π1 . The middle band, more intense, is associated with two and the πTh orbital of the thiophene. In this case, the ex-
4
1
ionisations from the πph and πth orbitals. For this com- perimental ∆Eπ, which corresponds to the difference be-
2
2
pound, the experimental ∆Eπ is about 1.7 eV and is in per- tween the first and fourth bands, is about 1.9 eV and agrees
fect accord with the theoretical value (1.7 eV).
with the theoretically determined value (2.1 eV). Among
These semi-empirical assignments were confirmed by de- the values of ∆Eπ recorded for compounds 2 and 3, the
termination of the Kohn–Sham energies, the nature of the methoxy disubstitution at the 2,5-positions of the phenylene
Kohn–Sham orbitals (KS) and the estimated vertical ionis- contributes to an enhancement of the π–π interaction be-
ation energies (see Supporting Information for the Kohn– tween the phenylene and the thienylene fragments.
Sham energies and Figure 2 for a plot of the Kohn–Sham
orbitals and the estimated vertical ionisation energies).
In order to understand why this π–π gap is maximal in 3,
we examined the two factors that influence ∆Eπ, the energy
When methyl or methoxy substituents are introduced difference between the involved orbitals of the two isolated
into the benzene ring the PE spectra are modified. In the fragments and the through-space orbital overlap, which de-
case of 2, two intense bands appear at 8.6 and 9.1 eV, with pends on the dihedral angle Φ between the two rings. To
two shoulders at about 8.2 and 9.4 eV (Figure 3), whereas estimate the incidence of the proximity of the energy levels
the spectrum of 3 displays a different shape with five sharp of the isolated fragments, the same torsion angle Φ between
peaks below 10.5 eV (7.6, 8.3, 8.9, 9.5 and 10.1 eV) and a the two rings was imposed and ∆Eπ for compounds 1–3
massif between 11 and 16 eV (Figure 4).
(Table 3) were then compared. For the same inter-ring tor-
A more complex interaction diagram arises from phenyl sion angle Φ (0, 45, 135 or 180°), for compounds 1 and 2
substitution (Figure 5). Indeed, the two π orbitals of the ∆Eπ is the same and varies in the same way when Φ is modi-
aryl group πPh and πPh are localised on the carbon atom fied. In contrast, for 3 the ∆Eπ value is always higher than
1
2
linked to the thienylene cycle and not only πPh1, as observed those for 1 and 2. This means that the difference between
for the phenyl group. Consequently, the πTh orbital inter- the energies of the isolated fragments has an important ef-
1
acts with the πPh1 and πPh2 orbitals of the phenylene group, fect on the ∆Eπ splitting. In fact, the highest ∆Eπ value
inducing better delocalisation on three orbitals [πx , πx , πx
observed for 3 can be ascribed to the energy of the πph
1
2
4
1
with x = 2 (Me) or 3 (OMe)] instead of two as in 1 (π1 , orbital [πph for dimethoxybenzene (–5.31 eV) is higher in
1
1
π1 ). In this way, for 2 and 3, we estimate the π–π interac- energy than πph for dimethylbenzene (–6.14 eV) and πph
4
1
1
tion by considering the out-of-phase and in-phase combina- for benzene (–6.72 eV)] and also to the involvement of the
tions (πx and πx ), as for 1. πph orbital in this interaction (see Supporting Information
1
4
2
Eur. J. Org. Chem. 2007, 4019–4031
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4023

J.-P. Lère-Porte, J.-M. Sotiropoulos et al.
FULL PAPER
Figure 3. Photoelectron spectra of 2 and 5. Experimental and theo-
retical (italics) IP [eV] values, experimental and theoretical (in
brackets) ∆Eπ values [eV], with ∆Eπ being the energy difference
between the MOs involved in the π–π interaction. MOLEKEL
plots of the orbitals involving in the π-delocalisation are shown.
Figure 2. Photoelectron spectra of 1 and 4. Experimental and theo-
retical (italics) IP [eV] values, experimental and theoretical (in
brackets) ∆Eπ values [eV], with ∆Eπ being the energy difference
between the MOs involved in the π–π interaction. MOLEKEL
plots of the orbitals involving in the π-delocalisation are shown.
Table 3. Experimental and theoretical ∆Eπ values for the privileged
conformers. Theoretical ∆Eπ values for the other conformers (Φ =
0, 180, 45, 135°).
for the Kohn–Sham orbital energies and Figure 5). These
energetic positions lead to better delocalisation.
Concerning the effect of the dihedral angle, the small
value calculated for the inter-ring torsion angle Φ for 3
(24.2°), compared with those calculated for 1 (28.5°) and 2
(41.5°), also contributes to an enhanced splitting ∆Eπ. The
results presented in Table 3 clearly show that for 1 and 2
the geometry of the structure that undergoes π-orbital over-
lap is the main factor influencing the magnitude of ∆Eπ and
consequently that of the conjugation: indeed, the highest
inter-ring angle observed for 2 (41.5°) is probably a result
of the steric effect of the methyl substituents and corre-
1
2
3
Φ = 28.5°
Φ = 41.5°
Φ = 24.2°
∆Eπ
∆Eπ
[eV]
[eV]
1.7
1.7
1.2
1.4
1.9
2.1
exp.
theo.
Φ = 0, 180°
1.9
∆Eπ
∆Eπ
[eV]
[eV]
1.9
1.4
2.2
1.8
theo.
theo.
Φ = 45, 135°
1.4
4024
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 4019–4031

How to Build Fully π-Conjugated Architectures
FULL PAPER
Another parameter that gives information on the de-
localisation over the molecular structure is the HOMO–
LUMO gap. The energy gap between the two frontier orbit-
als, summarised in Table 4, gives a rough estimate of the
lowest electronic excitation energy. In the UV/Vis spectra
an absorption is identified as a π–π* transition. It is note-
worthy that the smallest HOMO–LUMO gap is calculated
for 3 and it corresponds to the highest absorption wave-
length maximum (λmax). The destabilisation of the HOMO,
associated with the lowest ionisation potential for 3 (7.6 eV
for 3 vs. 8.1 eV for 1 and 8.2 eV for 2), leads to the smallest
HOMO–LUMO gap which makes easier the electron trans-
fer.
Table 4. Experimental and theoretical ∆Eπ, ∆E(HOMO–LUMO)
and absorption wavelength maxima λmax
.
1
2
3
4
5
6
∆Eπ
∆Eπ
[eV]
[eV]
1.7
1.7
4.8
285
1.2
1.4
4.9
275
1.9
2.1
4.4
315
2.4
2.4
4.0
325
1.5
1.9
4.3
294
2.7
2.7
3.7
358
exp.
theo.
∆E(H–L)theo. [eV]
λmax [nm]
In summary, by considering the value of ∆Eπ, corre-
sponding to the HOMO–HOMO-3 gap and related to the
π conjugation as well as the HOMO–LUMO gap, disubsti-
tution in the 2,5-positions by methoxy groups leads to a
more delocalised system in the gas phase. Moreover, this
low IP (high energy of the HOMO) corresponds to a low
oxidation potential.
Electronic Properties of the Three-Ring Compounds
In order to see if the previous results can be generalised
when the conjugated chain is lengthened by the addition of
a thienylene group in the 4-position of the phenylene moi-
ety, we studied 4–6 in the gas phase. For these compounds,
the PE spectra (Figure 2, Figure 3 and Figure 4) were re-
corded between 170 and 180 °C (p = 10–5 mbar, beam tem-
perature) and present similar shapes. The photoelectron
spectrum of compound 4 displays a first broad and small
band at 7.7 eV separated from the next two recorded at 8.7
and 9.2 eV, respectively, the latter one being intense. The
fourth broad but small band is at 10.1 eV.
The same spectral shape arises from 5. In this case, the
first band is shifted towards a higher ionisation potential
(8 eV). The positions of the second and third bands are
quasi-unchanged (8.6 and 9.1 eV, respectively). The fourth
band (9.5 eV) emerges as a shoulder of the third intense
band at 9.1 eV.
Figure 4. Photoelectron spectra of 3 and 6. Experimental and theo-
retical (italics) IP [eV] values, experimental and theoretical (in
brackets) ∆Eπ values [eV], with ∆Eπ being the energy difference
between the MOs involved in the π–π interaction. MOLEKEL
plots of the orbitals involving in the π-delocalisation are shown.
(a) Superposition of the He(II) (grey) and He(I) (black) spectra of
the frame part.
The spectrum of 6 shows similar band intensities. The
sponds to the smallest ∆Eπ (1.2 eV experimental and 1.4 eV first ionisation potential is the smallest IP observed for the
theoretical). For 3, if we compare the relative stabilities of six studied models and appears at 7.3 eV. The second IP is
the more probable conformers, the global energy minimum recorded at 8.4 eV, the third is an intense band at 8.9 eV
is not for the conformer in which the sulfur and oxygen and the fourth a weaker and broader one at 9.8 eV.
atoms are in opposite positions (Φ = 25.6°), but in which
Analysis of the experimental and theoretical results al-
the methoxy group is directed towards the sulfur (Φ = lowed us to assign the different bands in the PE spectra.
24.2°). Consequently, the presence of a non-covalent S···O For 4 and 5 the ionisations that arise from the removal of
attractive interaction seems to reduce the dihedral angle be- an electron from the π orbitals delocalised over the three
tween the two rings.
rings can be assigned to the first and fourth bands (respec-
Eur. J. Org. Chem. 2007, 4019–4031
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4025

J.-P. Lère-Porte, J.-M. Sotiropoulos et al.
FULL PAPER
Figure 5. Interaction diagram for 3 and 6. The main interactions are presented as bold dotted lines and secondary ones as grey dotted
lines. Estimated ionisation energies [eV] are shown.[38]
tively, 7.7 and 10.1 eV for 4 and 8.0 and 9.5 eV for 5). For the fourth bands, respectively, at 7.3 and 9.8 eV. These
the second and third bands the assignments are presented bands arise from ionisations of π orbitals delocalised over
under the figures in the Supporting Information. As pre- the thienylene and phenylene units. In this case, for sym-
Th
viously observed in the two-ring series, the experimental metry reasons, only the antibonding π1 orbital can inter-
value of ∆Eπ for the dimethylated compound 5 of about act with the π phenylene orbitals. Here again, the MO plot
1.5 eV is smaller than that of the unsubstituted phenyl com- (Figure 5) clearly shows that the first, second and sixth or-
pound 4 (2.4 eV).
bitals arise from mixing of the πTh1/πPh and πPh orbitals.
1 2
The highest ∆Eπ is observed for 6 and is about 2.5 eV. It In contrast, the second band at 8.4 eV and the third one at
is in very good agreement with the theoretical value and 8.9 eV represent ionisations from orbitals localised only on
corresponds to the energy difference between the first and the thienylene or the phenylene rings (see the MO plot un-
4026
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 4019–4031

How to Build Fully π-Conjugated Architectures
FULL PAPER
der the spectrum in the Supporting Information). He(I)/ only the σ oxygen lone-pair by a second-order perturbation
He(II) changes are in agreement with the proposed in- theory analysis (NBO calculation).
terpretations of the spectra. Indeed, it is well known that
The atomic charges on the S and O atoms in 3 and 6
the relative intensity of bands assigned to molecular orbit- are, respectively, 0.49 and –0.53 and suggest, for the S···O
als with substantial participation of the sulfur lone-pair de- interaction, a significant electrostatic interaction between a
crease in an He(II) spectra.[24] To illustrate these modifica- positively charged S atom and a negatively charged O atom.
tions, the superimposed He(I) and He(II) photoelectron This is in agreement with the short calculated S···O dis-
spectra are presented in Figure 4a for 6 and clearly show tance. This electrostatic interaction probably leads to the
the important decrease in the intensity of the third band good planarity of these compounds. Conversely, for 2 and
(8.9 eV), indicative of the participation of sulfur 3s/3p 5, the atomic charges on the S and H atoms are positive, at
atomic orbitals in the π molecular orbitals concerned.
0.45 and 0.24, respectively, and so repulsive. Considering
Comparing the two series of compounds, the lengthening the orbital interaction, the calculated stabilising energies re-
of the conjugated chain leads to a decrease in the first ionis- veal that the interaction between the two correctly directed
σ
ation potential of around 0.4 eV and a more significant nO and σ*S–C orbitals is weak (2–3 kcal/mol) and so it
splitting ∆Eπ for 4–6, corresponding to the π1–π6 gap, than would make a slight contribution to the stabilisation of the
that recorded for 1–3, corresponding to the π1–π4 gap (Fig- S···O interaction.
ure 2–Figure 4). This result is consistent with enhanced π
conjugation in the thienylene-phenylene-thienylene com-
pounds compared with that observed in the thienylene-
phenylene ones. Moreover, the greatest ∆Eπ gap and the
smallest HOMO–LUMO gap (3.70 eV calcd. for 6 vs.
Conclusions
4.04 eV for 4 and 4.32 eV for 5) are observed when the
To build fully π-conjugated architectures it is important
phenyl ring is substituted by methoxy groups. These to elaborate an alternating sequence of thienylene and 2,5-
HOMO–LUMO gaps agree with the measured maximum dialkoxyphenylene entities: a high inter-ring conjugation,
absorption wavelength (Table 4) and are coherent with the which occurs from such a combination, is revealed by a
fact that 6 is the more delocalised π system.
small π–π* gap and a high experimental ∆Eπ between the
In summary, the six PE spectra suggest that π conjuga- π orbitals delocalised over the two thienylene and 2,5-dialk-
tion takes place in all the compounds and is greater in the oxyphenylene fragments of 6. The small HOMO–LUMO
dimethoxylated compounds 3 and 6 than in the unsubsti- gap, which leads to an absorption in the visible spectrum,
tuted 1 and 4 or in the dimethylated compounds 2 and 5, is mainly due to a high HOMO level which induces a small
as shown by the splittings of the π+ and π– ionisation bands oxidation potential. The very high value of ∆Eπ is due, on
Ph
Ph
and the ∆E(HOMO–LUMO) gaps. Moreover, for 3 and 6 the one hand, to the energies and shape (π1 and π2 are
the first IP is the weakest observed; they correspond to the localised on the carbon linked to the thienylene group close
lowest oxidation potentials. All these parameters indicate to π1Th) of the isolated fragments and, on the other hand,
that dimethoxyphenylene-thienylene sequences are highly π- to the presence of an S···O interaction which favours a small
conjugated systems. Consequently, the strong π conjugation dihedral angle between the two rings and consequently a
observed in the gas phase for 3 and 6 seems to be mainly good π-orbital overlap. In these systems, this intramolecular
due to an intrinsic property of the compounds.
attractive non-bonding S···O interaction seems essentially
of electrostatic nature even if a weak negative hyperconju-
gation nOσǞσ*S–C probably contributes to the interaction.
It is noteworthy that non-substituted or 2,5-dialkoxy-substi-
tuted thienylene-phenylenes have very closed geometric and
Character of the S···O Interaction
We previously demonstrated the importance of the pres- electronic characteristics. In contrast to alkyl chains which
ence of 2,5-dialkoxy substituents on phenylene for ob- confer solubility but damage conjugation, the alkoxy sub-
taining highly conjugated systems with small inter-ring stituents provide good solubility and improve the inter-ring
angles, strong π delocalisation and small HOMO–LUMO conjugation.
gaps. The presence of the non-covalent S···O interaction ob-
Moreover, between such planar nanostructures, intermo-
served in isolated molecules 3 and 6 seems to be of great lecular π-stacking interactions will be particularly favoured
importance. Other authors have investigated by theoretical and this type of arrangement favours superior transport
methods the intramolecular interactions between chalcogen properties in organic materials resulting in, for example,
and oxygen or chlorine atoms in systems other than high field-effect mobilities that can be exploited for use in
thienylene-phenylene sequences.[25–28] These authors ex- organic transistors or photovoltaic cells. In addition, the
plained such types of interaction either by orbital and/or importance of the association of the thienylene and 2,5-di-
electrostatic interactions. Which factor makes the main con- alkoxyphenylene moieties clearly appears to lead, even for
tribution in our specific case? To answer this we determined very short oligomers, to relatively high absorption maxima
the total natural charges on compounds 1–6 coming from and so one can envisage, with longer analogous oligomers,
an NBO analysis of the more stable conformers (Table 2). their application in optoelectronic devices such as electrolu-
We also investigated the stabilising interaction involving minescent diodes or solar cells.
Eur. J. Org. Chem. 2007, 4019–4031
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4027

J.-P. Lère-Porte, J.-M. Sotiropoulos et al.
FULL PAPER
silica gel column (pentane/diethyl ether, 90:10) to give 2 as a colour-
less oil in 80% yield (2.405 g). H NMR (200 MHz, CDCl3): δ =
Experimental Section
1
General Procedures: DMF, THF, CH3CN and toluene were dried
and distilled under nitrogen prior to use. Bromobenzene, benzyl
bromide 1-bromo-2,5-dimethylbenzene, 1-bromo-2,5-dimethoxy-
benzene, 1,4-dibromobenzene, 1,4-dibromo-2,5-dimethylbenzene,
1,4-dibromo-2,5-dimethoxybenzene, 2-tributylstannylthiophene, 2-
thiopheneboronic acid, N-iodosuccinimide, triphenylphosphane,
7.32 (dd, J = 5, J = 1.4 Hz, 1 H, HTh), 7.23–7.03 (m, 5 H, HTh
+
HPh), 2.37 (s, 3 H, HMe), 2.34 (s, 3 H, HMe) ppm. 13C NMR
(200 MHz, CDCl3): δ = 143.4 (CTh), 135.4 (CPh), 134.0 (CPh), 133.0
(CPh), 130.9 (CTh), 130.7 (CTh), 128.9 (CTh), 127.9 (CPh), 126.3
(CPh), 125.0 (CPh), 20.7 (CMe), 20.6 (CMe) ppm. IR (KBr): ν = 3107,
˜
3070, 3015, 2952, 2915, 2865, 1728, 1612, 1496, 1437, 1379, 1254,
1220, 1168, 1041, 888, 833, 810, 696, 602, 557 cm–1. MS (FAB+):
m/z (%) = 189 (60) [M + 1]+, 149 (90). Absorption (CHCl3): λmax
= 270 nm.
bis(triphenylphosphane)dichloropalladium,
(dibenzylidene-
acetone)palladium were purchased (Alfa and Aldrich) and used
without further purification. 1H and 13C NMR spectra were re-
corded with a Bruker AC 200 spectrometer. Chemical shifts (in δ
units, ppm) are referenced to TMS using CHCl3 (δ = 7.27 ppm)
and CDCl3 (δ = 77.70 ppm) as the internal standards, respectively,
for 1H and 13C NMR spectra. IR spectra were recorded with a
Perkin-Elmer 1000 spectrophotometer and absorption spectra with
a Hewlett–Packard 8453 spectrophotometer. Melting points were
measured with an Electrothermal 9100 apparatus. Mass spectrome-
try was carried out with a JEOL JMS-DX 300 apparatus in FAB+
ionisation mode. C,H elemental analyses were performed by the
Service Central d’Analyses du CNRS (Vernaison, France).
The spectroscopic data agree with those reported in the litera-
ture.[10]
2-(2,5-Dimethoxyphenyl)thiophene (3): Compound 3 was prepared
according to the same procedure as 2 with 1-bromo-2,5-dimethoxy-
benzene
(13.8 mmol,
2.99 g),
2-(tributylstannyl)thiophene
(13.8 mmol, 5.149 g), bis(triphenylphosphane)dichloropalladium
(194 mg, 2 mol-%) and triphenylphosphane (579 mg, 2.21 mmol).
After the reaction, the crude product was purified over a chromato-
graphic silica gel column (pentane/diethyl ether, 90:10) to give 3 as
a pale yellow oil in 90% yield (2.735 g). 1H NMR (200 MHz,
CDCl3): δ = 7.49 (dd, J = 3.7, J = 1.3 Hz, 1 H, HTh), 7.32 (dd, J
= 5.1, J = 1.3 Hz, 1 H, HTh), 7.22 (d, J = 2.8 Hz, 1 H, HPh), 7.09
(dd, J = 5.1, J = 3.7 Hz, 1 H, HTh), 6.92 (d, J = 10 Hz, 1 H, HPh),
6.81 (dd, J = 10, J = 2.8 Hz, HPh), 3.84 (s, 3 H, HOMe), 3.78 (s, 3
H, HOMe) ppm. 13C NMR (200 MHz, CDCl3): δ = 143.4 (CTh),
135.4 (CPh), 134.0 (CPh), 133.0 (CPh), 130.9 (CTh), 130.7 (CTh),
128.9 (CTh), 127.9 (CPh), 126.3 (CPh), 125.0 (CPh), 20.6 (CMe), 20.7
The photoelectron spectra were recorded with a Perkin–Elmer 0018
instrument equipped with a 127° cylindrical analyser and analysed
using a microcomputer supplemented with a digital analogue con-
verter. The spectra were calibrated using the known autoionisation
of helium at 4.99 eV [He(II)/He(I)] and xenon ionisations at 12.13
and 13.44 eV. All the products were vaporised by the heat of the
beam. Consequently, the different temperatures presented in this
publication correspond to the beam temperature and not the sam-
ple temperature. We maintained a stable temperature of the beam
in order to vaporise enough of the compounds and to obtain in-
tense spectra.
(CMe) ppm. IR (KBr): ν = 3082, 2996, 2944, 2826, 1609, 1576,
˜
1473, 1355, 1285, 1222, 1041, 831, 798, 695, 618 cm–1. MS (FAB+):
m/z (%) =220 (100) [M]+, 205 (90) [M – 15]+, 177 (10), 162 (10),
134 (10). Absorption (CHCl3): λmax = 325 nm. C12H12O2S (220.29):
calcd. C 65.42, H 5.49; found C 65.63, H 5.71.
2-Phenylthiophene (1): In a 250 mL round-bottomed flask, bromo-
benzene (30 mmol, 4.710 g), 2-tributylstannylthiophene (30 mmol,
11.195 g), bis(triphenylphosphane)dichloropalladium (421 mg,
2 mol-%) and triphenylphosphane (1.26 g, 4.8 mmol, 16 mol-%)
were introduced under nitrogen into an anhydrous solvent mixture
(THF/DMF, 1:1, 60 mL). The medium was stirred at 80 °C for 18 h
and treated, after removing THF, with 250 mL of an ammonium
fluoride solution (3 ) and diethyl ether (250 mL). The mixture was
vigorously stirred for 1 h, and the organic phase was extracted with
diethyl ether (3ϫ50 mL), filtered, washed with ammonium fluoride
solution (50 mL) and then with a saturated sodium chloride solu-
tion (50 mL). After drying over sodium sulfate, it was concentrated
and the orange liquid was distilled under vacuum to give phenyl-
thiophene as a white bright solid in 80% yield (3.84 g). M.p. 34–
1,4-Di(2-thienyl)benzene (4): Compound 4 was prepared according
to the same procedure as 2 with 1,4-dibromobenzene (16 mmol,
3.84 g), 2-tributylstannylthiophene (32 mmol, 11.95 g), bis(triphen-
ylphosphane)dichloropalladium (224 mg, 2 mol-%) and tri-
phenylphosphane (672 mg). After the reaction, the crude product
was purified by recrystallisation from ethanol/CH2Cl2 (95:5) to give
1
4 as a yellow solid in 80% yield (2.405 g). M.p. 206 °C. H NMR
(200 MHz, CDCl3): δ = 7.58 (s, 4 H, HPh), 7.28 (dd, J = 3.6, J =
1.2 Hz, 2 H, HTh), 7.23 (dd, J = 5.1, J = 1.2 Hz, 2 H, HTh), 7.02
(dd, J = 5.1, J = 3.6 Hz, 2 H, HTh) ppm. 13C NMR (200 MHz,
CDCl3): δ = 143.9 (CTh), 135.1 (CTh), 129.4 (CTh), 128.1 (CTh),
125.7 (CPh), 123.5 (CPh) ppm. IR (KBr): ν = 3088, 3066, 3031,
˜
1589, 1492, 1427 1265, 1110, 1056, 958, 852, 814, 696 cm–1. MS:
m/z (%) = 242 (55) [M]+, 154 (100), 137 (100). Absorption (CHCl3):
λmax = 325 nm.
1
36 °C; Eb(5ϫ10–2 57 °C. H NMR (200 MHz, CDCl3): δ = 7.66 (d,
)
J = 7.8 Hz, 2 H, HTh), 7.43–7.28 (m, 5 H, HPh), 7.11 (dd, J = 3.6,
J = 5.0 Hz, HTh) ppm. 13C NMR (200 MHz, CDCl3): δ = 144.9
(CTh), 134.9 (CPh), 129.3 (CPh), 128.4 (CPh), 127.9 (CTh), 126.4
The spectroscopic data agree with those reported in the literature.[9]
(CPh), 125.2 (CTh), 123.5 (CTh) ppm. IR (KBr): ν = 3073, 1680,
1,4-Dimethyl-2,5-di(2-thienyl)benzene (5): Compound 5 was pre-
pared according to the same procedure as 2 with 1,4-dibromo-2,5-
dimethylbenzene (16 mmol, 4.22 g), 2-(tributylstannyl)thiophene
(32 mmol, 11.95 g), bis(triphenylphosphane)dichloropalladium
(224 mg, 2 mol-%) and triphenylphosphane (672 mg). After the re-
action, the crude product was purified over a chromatographic sil-
ica gel column (pentane/diethyl ether, 90:10) to give 5 as a white
solid in 75% yield (3.24 g). 1H NMR (200 MHz, CDCl3): δ = 7.38–
7.35 (m, 4 H), 7.14–7.12 (m, 4 H), 2.47 (s, 6 H, Me) ppm. 13C
NMR (200 MHz, CDCl3): δ = 134.0 (CTh), 133.8 (CPh = C1 and
C4), 133.2 (CPh = C2 and C5), 133.1 (CPh = C3 and C6), 127.6 (CTh),
˜
1601, 1489, 1447, 1377, 1257, 850, 826, 755, 693 cm–1. MS (FAB+):
m/z (%) = 160 [M]+. Absorption (CHCl3): λmax = 285 nm.
The spectroscopic data agree with those reported in the litera-
ture.[9,29]
2-(2,5-Dimethylphenyl)thiophene (2): Compound 2 was prepared ac-
cording to the same procedure as 1 with 2-bromo-p-xylene
(16 mmol, 2.96 g), 2-(tributylstannyl)thiophene (16 mmol, 5.970 g),
bis(triphenylphosphane)dichloropalladium (224 mg, 2 mol-%) and
triphenylphosphane (672 mg, 2.56 mmol) under nitrogen in an an-
hydrous solvent mixture (THF/DMF, 1:1, 30 mL). After the reac-
tion, the crude product was purified through a chromatographic
126.9 (CTh), 125.6 (CTh), 21.0 (CMe) ppm. IR (KBr): ν = 3069,
˜
3005, 2952, 2919, 2857, 1490, 1451, 1432, 1379, 1040, 1032, 957,
4028
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 4019–4031

How to Build Fully π-Conjugated Architectures
FULL PAPER
892, 829, 701 cm–1. MS (FAB+): m/z (%) = 270 (100) [M]+, 255
(40) [M – CH3]+. Absorption (CHCl3): λmax = 294 nm.
After cooling, THF was removed and the medium diluted with
dichloromethane. The organic phase was washed several times with
water, dried with sodium sulfate and concentrated in vacuo to give
a black oil purified over a chromatographic silica gel column eluted
with a pentane/diethyl ether mixture (90:10). Compound 7 was ob-
The spectroscopic data agree with those reported in the literature.[9]
1,4-Dimethoxy-2,5-di(2-thienyl)benzene (6): Compound 6 was pre-
pared according to the same procedure as 2 with 1,4-dibromo-2,5-
dimethoxylbenzene (16 mmol, 4.73 g), 2-(tributylstannyl)thiophene
(32 mmol, 11.95 g), bis(triphenylphosphane)dichloropalladium
(224 mg, 2 mol-%) and triphenylphosphane (672 mg). After the re-
action, the crude product was purified over a chromatographic sil-
ica gel column (pentane/diethyl ether, 90:10) to give 6 as a white
solid in 76% yield (3.67 g). M.p. 135–136 °C. 1H NMR (200 MHz,
CDCl3): δ = 7.55 (dd, J = 3.7, J = 1.3 Hz, 2 H, HTh), 7.36 (dd, J
= 5.2, J = 1.2 Hz, 2 H, HTh), 7.26 (s, 2 H, HPh), 7.12 (dd, J = 5.2, J
= 3.6 Hz, 2 H, HTh), 3.95 (s, 6 H, MeO) ppm. 13C NMR (200 MHz,
CDCl3): δ = 150.1 (CPh), 139.2 (CTh), 127.0 (CTh), 125.8 (CTh),
1
tained as a white solid in 71% yield (2.5 g). M.p. 89 °C. H NMR
(200 MHz, CDCl3): δ = 7.78 (s, 1 H, HTh = H5), 7.50–7.25 (m, 7
H, OCH2Ph + 2HTh), 7.06 (m, 1 H, HPh = H3), 6.59 (s, 1 H, HPh
= H6), 5.19 (s, 2 H, OCH2Ph), 3.89 (s, 3 H, MeO), 3.77 (s, 3 H,
MeO) ppm. 13C NMR (200 MHz, CDCl3): δ = 150.1 (C1), 148.2
(C5), 144.1 (C2), 139.4 (CPh), 136.9 (CTh), 128.6 (2CPh), 128.0 (CTh),
127.4 (CPh), 126.7 (CTh), 124.6 (CPh), 124.4 (CPh), 116.1 (C4), 113.0
(C3), 101.3 (C6), 71.5 (OCH2Ph), 56.9 (CMe), 56.5 (CMe) ppm. IR
(KBr): ν = 3069, 1608, 1212, 760 cm–1. HRMS (FAB+): calcd. for
˜
C19H18O3S 326.0976; found 326.0975.
Theoretical Section
125.6 (CTh), 123.1 (CPh), 112.4 (CPh), 56.4 (CMe) ppm. IR (KBr): ν
˜
Calculations were performed with the Gaussian 98 program[30,31]
using the density functional theory method.[32] The various struc-
tures were fully optimised at the B3LYP level.[33] This functional
was built using Becke’s three-parameter exchange functional[34a]
and the Lee–Yang–Parr correlation functional.[33c] The 6-31G(d,p)
basis set was used. All atoms were augmented with a single set of
polarisation functions. Several publications have shown that the
hybrid functional B3LYP is adequate for studying the electronic
structures of π-conjugated systems such as those involving a phos-
phole moiety,[34] EDOT[35] or π-conjugated oligomers.[36]
= 3092, 3065, 2993, 2964, 2940, 2872, 2829, 1534, 1488, 1462, 1454,
1393, 1290, 1217, 1171, 1062, 1038, 843, 815, 760, 700 cm–1. MS
(FAB+): m/z (%) = 302 (100) [M]+, 154 (95), 136 (60). Absorption
(CHCl3): λmax = 358 nm.
The spectroscopic data agree with those reported in the literature.[9]
2,5-Dimethoxyphenol: This compound was prepared according to
the literature.[11]
1-Benzoyloxy-2,5-dimethoxybenzene (8): In
a round-bottomed
flask, 2,5-dimethoxyphenol (3 g, 19.4 mmol, 1 equiv.), benzyl bro-
mide (3.3 g, 19.4 mmol, 1 equiv.) and potassium carbonate (4 g,
29 mmol, 1.5 equiv.) were refluxed in acetonitrile (100 mL) for 3 h.
After cooling and filtration of the potassium carbonate, the solvent
was removed in vacuo and the residue was dissolved in dichloro-
methane. The organic phase was washed with water, dried with
sodium sulfate and concentrated. A white solid precipitated and,
after washing with pentane, 8 was obtained in 93% yield (4.4 g).
Second derivatives were calculated in order to check that the op-
timised structures are true minima on the potential energy surface.
All total energies have been zero-point-energy (ZPE) and tempera-
ture-corrected using unscaled density functional frequencies.
NBO population analysis[37] was performed in order to determine
the total charges for each atom and to check if strong or weak
stabilising interactions between a filled orbital and an empty or-
bital exist for the studied systems.
1
M.p. 36 °C. H NMR (200 MHz, CDCl3): δ = 7.50–7.25 (m, 5 H,
HPh), 6.82 (d, J = 8.8 Hz, 1 H, H6), 6.53 (d, J = 2.7 Hz, 1 H, H3),
6.42 (dd, J = 8.8, J = 2.7 Hz, 1 H, H5), 5.13 (s, 2 H, OCH2Ph),
3.83 (s, 3 H, MeO), 3.72 (s, 3 H, MeO) ppm. 13C NMR (200 MHz,
CDCl3): δ = 154.1 (C2), 149.2 (C1), 144.0 (C3), 137 (CPh), 129 (CPh),
128 (CPh), 127 (CPh), 113 (CPh), 104 (CPh), 103 (CPh), 71 (OCH2Ph),
55.7 (CMe), 55.5 (CMe) ppm.
Ionisation energies[38] were calculated as suggested previously by
Stowasser and Hoffmann.[39] Other authors, like Arduengo and co-
workers[40] or Werstiuk and Rademacher and their co-workers,[41]
used this method in order to assign different PE spectra.
Molecular orbital diagrams were plotted using the MOLEKEL
package.[42]
The spectroscopic data agree with those reported in the litera-
ture.[12]
X-ray Crystal Structure Determinations
1-Benzoyloxy-2,5-dimethoxy-4-(2-thienyl)benzene (7): In a round-
bottomed flask, 8 (3.2 g, 13 mmol, 1 equiv.), N-iodosuccinimide
(3.3 g, 14.7 mmol, 1.1 equiv.) and trifluoroacetic acid (0.5 g,
4 mmol, 0.3 equiv.) were diluted in acetonitrile (100 mL) and vigor-
ously stirred for 12 h. Subsequently, the solvent was evaporated and
the medium was dissolved in dichloromethane. The organic phase
was washed a sodium hydroxide solution (1 ), dried with sodium
sulfate and concentrated to give 1-benzoyloxy-2,5-dimethoxy-4-
iodobenzene as a yellow powder in 86% yield (4.1 g). This product
was used in the next step without further purification. 1H NMR
(200 MHz, CDCl3): δ = 7.50–7.30 (m, 5 H, HPh), 7.23 (s, 1 H, HPh),
6.49 (s, 1 H, HPh), 5.15 (s, 2 H, CH2), 3.83 (s, 3 H, MeO), 3.72 (s,
3 H, MeO) ppm.
Crystals were selected and inserted inside thin-wall Lindemann
capillaries for X-ray diffraction analyses. The best diffracting single
crystals were used for data collection at 173 K. Diffracted inten-
sities were measured over a full sphere of the reciprocal space on
an Xcalibur CCD (Oxford Diffraction) diffractometer using mono-
chromated Mo-Kα radiation (λ = 0.71073 Å). CrysAlisCCD and
CrysAlisRed software packages[43] were used for data acquisition,
extraction and reduction. The structures were solved using the di-
rect methods provided by SHELXS-97[44] and subsequent Fourier
analyses. Refinement of atomic positions and anisotropic displace-
ment parameters for all non-hydrogen atoms were carried out by
the full-matrix least-squares method based on F2 (program
SHELXL-97[45]). Hydrogen atoms attached to carbon were placed
in geometrically idealised positions and constrained to ride on their
parent atoms. They were given an isotropic displacement parameter
equal to 1.2 times the Ueq of their C parent.
Under nitrogen, 1-benzoyloxy-4-iodo-2,5-dimethoxybenzene (4 g,
1 equiv., 10.8 mmol), 2-thiopheneboronic acid (1.65 g, 1.2 equiv.,
12.9 mmol) and Na2CO3 (2.3 g, 2 equiv., 21.6 mmol) were intro-
duced into a Schlenk tube containing bis(dibenzylideneacetone)
palladium (200 mg, 3.2 mol-%) and triphenylphosphane (225 mg,
8 mol-%). The mixture was heated at 60 °C whilst stirring for 12 h.
Crystal Data for 6: C16H14O2S2, M = 302.39, monoclinic, space
group P2/c, a = 11.212(1), b = 7.586(1), c = 18.723(1) Å, β =
116.34(2)°, V = 1427.1(2) Å3, T = 173 K, Z = 4, Dc = 1.407 gcm–3,
Eur. J. Org. Chem. 2007, 4019–4031
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4029

J.-P. Lère-Porte, J.-M. Sotiropoulos et al.
FULL PAPER
yellow, 0.31ϫ0.38ϫ0.47 mm, µ = 0.37 mm–1, 25658 reflections
[12] T. Capecchi, C. B. de Koning, J. P. Michael, J. Chem. Soc. Per-
kin Trans. 1 2000, 2681–2688.
measured (2θmax = 64°), 4647 unique, Rint = 0.133. Final R1
=
[13]
A.-S. Castanet, F. Colobert, P.-E. Broutin, Tetrahedron Lett.
2002, 43, 5047–5048.
0.0566 and wR2 = 0.1483 for 181 refined parameters and 1885 ob-
served data points with IϾ3σ(I). Goodness of fit = 0.912, electron
density residuals 0.31/–0.38 eÅ–3.
[14]
a) M. Turbiez, P. Frère, J. Roncali, J. Org. Chem. 2003, 68,
5357–5360; b) M. Turbiez, P. Frère, M. Allain, C. Videlot, J.
Ackermann, J. Roncali, Chem. Eur. J. 2005, 11, 3742–3752; c)
I. F. Perepichka, S. Roquet, P. Leriche, J.-M. Raimundo, P.
Frère, J. Roncali, Chem. Eur. J. 2006, 12, 2960–2966; d) A.
Dkhissi, F. Louwet, L. Groenendaal, D. Beljonne, R. Lazza-
roni, J. L. Brédas, Chem. Phys. Lett. 2002, 359, 466–472.
F. T. Burling, B. M. Goldstein, J. Am. Chem. Soc. 1992, 114,
2313–2320.
Y. Nagao, T. Honjo, H. Iimori, S. Goto, S. Sano, M. Shiro, K.
Yamaguchi, Y. Sei, Tetrahedron Lett. 2004, 45, 8757–8761.
K. M. Kim, Y.-A. Lee, O.-S. Jung, Y. S. Sohn, Bull. Korean
Chem. Soc. 1996, 17, 93–95.
M. Pomerantz, A. S. Amarasekara, H. V. R. Dias, J. Org.
Chem. 2002, 67, 6931–6937.
a) M. Turbiez, P. Frère, P. Blanchard, J. Roncali, Tetrahedron
Lett. 2000, 41, 5521–5525; b) J.-M. Raimundo, P. Blanchard,
P. Fr ère, N. Mercier, I. Ledoux-Rak, R. Hierle, J. Roncali, Tet-
rahedron Lett. 2001, 42, 1507–1510.
Crystal Data for 7: C19H18O3S, M = 326.39, orthorhombic, space
group P212121, a = 5.3220(5), b = 8.5420(5), c = 35.178(2) Å, V
= 1599.2(2) Å3, T = 173 K, Z = 4, Dc = 1.356 gcm–3, colourless,
0.21ϫ0.33ϫ0.65 mm, µ = 0.21 mm–1, 20675 reflections measured
(2θmax = 50°), 2815 unique, Rint = 0.082. Flack parameter =
0.04(1). Final R1 = 0.0549 and wR2 = 0.1163 for 211 refined param-
eters and 2726 observed data points with IϾ2σ(I). Goodness of fit
= 1.074, electron density residuals = 0.25/–0.27 eÅ–3.
[15]
[16]
[17]
[18]
[19]
CCDC-616271 (for 7) and -616272 (for 6) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supporting Information (see also the footnote on the first page of
this article): Structural and electronic properties of the rotamers,
full description of the PE spectra and Z-matrix.
[20]
[21]
J.-F. Pan, S.-J. Chua, W. Huang, Chem. Phys. Lett. 2002, 363,
18–24.
See for example: a) J. W. Rabalais, Principles of Ultraviolet
Photoelectron Spectroscopy, John Wiley & Sons, New York,
1977; b) U. Lottermoser, P. Rademacher, M. Mazik, K. Kow-
ski, Eur. J. Org. Chem. 2005, 522–531; c) P. Rademacher, Chem.
Rev. 2003, 103, 933–976.
Acknowledgments
The authors gratefully acknowledge financial support from the
“Ministère de la Recherche” and the Centre National de la Recher-
che Scientifique (CNRS). We thank the Institut du Developpement
de Ressources en Informatique Scientifique (IDRIS, Orsay,
France), administered by the CNRS, for the use of calculation facil-
ities and Dr Pfister-Guillouzo for fruitful discussions.
[22]
[23]
[24]
C. N. R. Rao, P. K. Basu, M. S. Hegde, Systematic Organic UV
Photoelectron Spectroscopy, Marcel Dekker, New York, 1979.
See for example: H. Bock, B. Roth, Phosphorus Sulfur 1983,
14, 211–223.
a) J.-J. Yeh, Atomic Calculation of Photoionisation Cross-Sec-
tions and Asymmetry Parameters, Gordon and Breach Science
Publishers, Langhorne, PE, 1993; b) I. P. Csonka, G. Vass, L.
Szepes, D. Szabo, I. Kapovits, J. Mol. Struct. (THEOCHEM)
1998, 455, 141–159.
[1] J. R. Sheats, H. Antoniadis, M. Hueschen, W. Leonard, J.
Miller, R. Moon, D. Roitman, A. Stocking, Science 1996, 273,
884–888.
[2] a) T. A. Stockheim, R. L. Elsenbaumer, J. R. Reynolds (Eds.),
Handbook of Conducting Polymers, Marcel Dekker, New York,
1998; b) H. S. Nalwa (Ed.), Handbook of Organic Conductive
Molecules and Polymers, vol. 1–3, John Wiley & Sons, New
York, 1997.
[3] R. D. Mc Cullough, P. C. Ewbank in Handbook of Conducting
Polymers (Eds.: T. A. Stockheim, R. L. Elsenbaumer, J. R.
Reynolds), Marcel Dekker, New York, 1998, chapter 9, pp.
225–258.
[4] H. Sirringaus, P. J. Brown, R. H. Friend, M. M. Nielsen, K.
Bechgaard, B. M. W. Langeveld-Voss, A. J. H. Spiering,
R. A. J. Janssen, E. W. Meijer, P. Herwig, D. M. De Leeuw, Na-
ture 1999, 401, 685–687.
[5] J.-P. Lère-Porte, J. J. E. Moreau, F. Serein-Spirau, C. Torreilles,
A. Righi, J.-L. Sauvajol, M. Brunet, J. Mater. Chem. 2000, 10,
927–932.
[6] R. A. Silva, F. Serein-Spirau, M. Bouachrine, J.-P. Lère-Porte,
J. J. E. Moreau, J. Mater. Chem. 2004, 14, 3043–3050.
[7] a) S. Hotta, S. A. Lee, Synth. Met. 1999, 101, 551–552; b) S.
Hotta, S. A. Lee, T. Tamaki, J. Heterocycl. Chem. 2000, 37, 25–
29; c) S. Hotta, S. A. Lee, H. Kimura, J. Heterocycl. Chem.
2000, 37, 25–29.
[25]
[26]
[27]
[28]
[29]
[30]
V. I. Minkin, R. M. Minyaev, Mendeleev Commun. 2000, 5,
167–206.
G. D. Markham, C. W. Bock, J. Mol. Struct. (THEOCHEM)
1997, 418, 139–154.
M. Iwaoka, H. Komatsu, T. Katsuda, S. Tomoda, J. Am.
Chem. Soc. 2004, 126, 5309–5317.
A. F. Cozzolino, I. Vargas-Baca, S. Mansour, A. H. Mahmoud-
khani, J. Am. Chem. Soc. 2005, 127, 3184–3190.
J. Wolfe, R. Singer, B. Yang, S. Buchwald, J. Am. Chem. Soc.
1999, 121, 9550–9561.
M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Mont-
gomery, R. E. Stratman, J. C. Burant, S. Dapprich, J. M. Mil-
lam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J.
Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pom-
elli, C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P. Y.
Ayala, Q. Cui, K. Morokuma, D. K. Malick, A. D. K. Rabuck,
K. Raghavachari, J. B. Foresman, J. Cioslowswi, J. V. Ortiz,
A. G. Baboul, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz,
I. Komaromi, R. Gomperts, R. Martin, D. J. Fox, T. Keith,
M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C. Gonzalez,
M. Challacombe, P. M. W. Gill, B. Jonhson, W. Chen, M. W.
Wong, J. L. Andres, M. Head-Gordon, E. S. Replogle, J. A. Po-
ple, Gaussian 98, Revision A.7, Gaussian, Inc., Pittsburgh, PA,
2001 (A.11.1) or 2002 (A.11.3).
[8] a) M. Mushrush, A. Fachetti, M. Lefenfeld, H. E. Katz, T. J.
Marks, J. Am. Chem. Soc. 2003, 125, 9414–9423; b) A. Fach-
etti, J. Letizia, M.-H. Yoon, M. Mushrush, H. E. Katz, T. J.
Marks, Chem. Mater. 2004, 16, 4715–4727.
[31]
[32]
W. J. Hehre, L. Radom, P. v. R. Schleyer, J. A. Pople, Ab initio
Molecular Orbital Theory, John Wiley & Sons, New York,
1986.
R. G. Parr, W. Yang, Functional Theory of Atoms and Molecules
(Eds.: R. Breslow, J. B. Goodenough), Oxford University Press,
New York, 1989.
[9] A. Pelter, I. Jenkins, D. Jones, Tetrahedron 1997, 53, 10357–
10400.
[10] F. Alonso, M. Yus, Tetrahedron 1991, 47, 313–316.
[11] U. Wriede, M. Fernandez, K. F. West, D. Harcourt, H. W.
Moore, J. Org. Chem. 1987, 52, 4485–4489.
4030
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 4019–4031

How to Build Fully π-Conjugated Architectures
[33] a) A. D. Becke, Phys. Rev. A 1988, 38, 3098–3100; b) A. D. [40] A. J. Arduengo III, H. Bock, H. Chen, M. Denk, D. A. Dixon,
FULL PAPER
Becke, J. Chem. Phys. 1993, 98, 5648–5652; c) C. Lee, W. Yang,
R. G. Parr, Phys. Rev. B 1988, 37, 785–789.
[34] a) M. A. De Oliveira, H. F. Dos Santos, W. B. De Almeida,
Phys. Chem. Chem. Phys. 2000, 2, 3373–3380; b) D. Delaere,
M. T. Nguyen, L. G. Vanquickenborne, J. Phys. Chem. A 2003,
107, 838–846.
J. C. Green, W. A. Hermann, N. L. Jones, M. Wagner, R. West,
J. Am. Chem. Soc. 1994, 116, 6641–6649.
[41] a) H. M. Muchall, P. Rademacher, J. Mol. Struct. 1997, 435,
157–167; b) H. M. Muchall, P. Rademacher, J. Mol. Struct.
1998, 471, 189–194; c) H. M. Muchall, N. H. Werstiuk, B.
Choudhurry, Can. J. Chem. 1998, 76, 221–227; d) H. M. Much-
all, N. H. Werstiuk, B. Choudhurry, J. Ma, J. Warkentin, J. P.
Pezacki, Can. J. Chem. 1998, 76, 238–240.
[35] D. Delaere, M. T. Nguyen, L. G. Vanquickerborne, J. Phys.
Chem. A 2003, 107, 838–846.
[36] P. Blanchard, P. Verlhac, L. Michaux, P. Frère, J. Roncali,
Chem. Eur. J. 2006, 12, 1244–1255.
[37] a) A. E. Reed, L. A. Curtiss, F. Weinhold, J. Chem. Rev. 1988,
88, 899–926; b) J. P. Foster, F. Weinhold, J. Am. Chem. Soc.
1980, 102, 7211–7218.
[42] a) P. F. Flükiger, “Development of the molecular graphics
package MOLEKEL and its application to selected problems
in organic and organometallic chemistry”, Ph.D. Dissertation,
University of Geneva, 1992; b) MOLEKEL: An Interactive
Molecular Graphics Tool: S. Portmann, H. P. Lüthi, Chimia
2000, 54, 766–770.
[43] CrysAlisCCD and CrysAlisRed 169 software package, 2001, Ox-
ford Diffraction, Ltd., Abingdon, UK.
[44] G. M. Sheldrick, SHELXS-97: A Program for Crystal Struc-
tures Solution, 1997, University of Göttingen, Germany.
[45] G. M. Sheldrick, SHELXL-97: A Program for Refining Crystal
Structures, 1997, University of Göttingen, Germany.
Received: December 21, 2006
[38] Estimated IPs (except for IP1) were calculated by applying a
uniform shift at the different Kohn–Sham energies [shift: x =
IP1exp + εKS (HOMO)], where εKS(HOMO) is the highest occu-
pied B3LYP/6-31G** Kohn–Sham MO energy of the ground-
exp
state molecule and IP1 is the lowest experimental IP of the
molecule, as suggested previously by Stowasser and
Hoffmann.[39] The first estimated IP is taken to be equal to the
first experimental ionisation potential.
[39] R. Stowasser, R. Hoffmann, J. Am. Chem. Soc. 1999, 121,
Published Online: June 25, 2007
3414–3420.
Eur. J. Org. Chem. 2007, 4019–4031
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4031