New star-shaped molecules derived from thieno[3,2-b]thiophene unit and triphenylamine

Article abstract of DOI:10.1016/j.tetlet.2010.10.082

A series of new substituted triphenylamine (TPA) derivatives with alkyl thieno[3,2-b]thiophene and thiophene units were synthesized in a combinatorial manner. Suzuki coupling of a dioxaborolane TPA derivative and 2-bromo-3-nonylthieno[3,2-b]thiophene or S

Full text of DOI:10.1016/j.tetlet.2010.10.082

Tetrahedron Letters 51 (2010) 6673–6676
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Tetrahedron Letters
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New star-shaped molecules derived from thieno[3,2-b]thiophene unit
and triphenylamine
⇑
N. Metri, X. Sallenave, L. Beouch, C. Plesse, F. Goubard , C. Chevrot
Laboratoire de Physicochimie des Polymères et des Interfaces (LPPI), Université de Cergy-Pontoise, Institut des matériaux, 5 mail Gay-Lussac, Neuville-sur-Oise, 95031
Cergy-Pontoise Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 July 2010
Revised 12 October 2010
Accepted 13 October 2010
Available online 21 October 2010
A series of new substituted triphenylamine (TPA) derivatives with alkyl thieno[3,2-b]thiophene and thi-
ophene units were synthesized in a combinatorial manner. Suzuki coupling of a dioxaborolane TPA deriv-
ative and 2-bromo-3-nonylthieno[3,2-b]thiophene or Stille coupling of fresh stannyl thieno[3,2-
b]thiophene was used. All compounds were characterized by 1H and 13C NMR, HRMS, UV–vis spectrom-
etry and DSC measurements. It was demonstrated that the optical and thermal properties of these mate-
rials can be tuned by varying both the conjugation length and thienothiophene and thiophene
combination on the TPA branches. Moreover, the measured molar extinction coefficients were increasing
from 63,000 (kmax = 354 nm) to 131,000 L molÀ1 cmÀ1 (kmax = 428 nm) for TPA-thienothiophenes and
TPA-bithiophene thienothiophenes, respectively. Some of them showed molecular glass behavior.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Triphenylamine
Thieno[3,2-b]thiophene
Thiophene
Molecular glasses
Among several organization states, amorphous molecular sys-
tems have constituted a new class of functional organic materials
for use in various applications.1–3 Despite their tendency to crystal-
lization, small organic molecules can also form stable amorphous
glasses above room temperature if their molecular structures are
properly designed.4 Among them, well-defined triphenylamine
derivatives (TPA) have been studied intensively for their
interesting physical properties, including good charge transport,
electroluminescence, and improved thermal and morphological
stabilities.5,6 Recent studies of the synthesis of TPA derivatives
having pseudo-three-dimensional conjugated architecture and
their applications as advanced materials for photovoltaic sys-
tems7–12 and organic light-emitting diodes4,13,1 were carried out
as well. Furthermore, the McCullough group has showed that the
incorporation of heterocyclic thieno[3,2-b]thiophene into a poly-
thiophene backbone led to the synthesis of polymers exhibiting
charge carrier mobilities up to 0.15 cm2/V with lifetimes of several
months.14 Indeed, the incorporation of rigid thieno[3,2-b]thio-
phene units in conjugated oligomers or polymers has been
developed to improve their electronic properties and to optimize
the performance of the corresponding devices.15
and thermal properties of a new series of five molecules 1–5
(Scheme 1) based on the TPA core derivatized with various combi-
nations of alkyl thieno[3,2-b]thiophen/thiophene branches. Be-
cause of the higher degree of unsaturation in the fused rings,
relatively long nonyl chains were used to increase the solubility
of the resultant compounds 1–5 in different organic solvents, espe-
cially in chlorinated ones such as chloroform, chlorobenzene, or
dichlorobenzene. The suggested structures differed in
p-conju-
gated branch length and in the relative position of alkyl chain. It
is noteworthy that in compound 1 the alkyl chain is located on
the inner thiophene ring of the thieno[3,2-b]thiophen unit (named
‘interior’), whereas in compounds 2–5 it is located on the outer ring
of this unit (named ‘exterior’).
The synthetic routes for the different target molecules are
outlined in Scheme 2. 3-Nonylthieno[3,2-b]thiophene, 6, and
2-bromo-3-nonylthieno[3,2-b]thiophene, 8, were prepared by
following the synthetic methods similar to those described in
Ref. 16 while molecules 10 and 11 by procedures close to Ref. 4.
Two coupling methods were used according to the position of
the alkyl chain relative to the TPA core. Compound 1 was synthe-
sized via Suzuki coupling between the dioxaborolane derivative
and 2-bromo-3-nonylthieno[3,2-b]thiophene 8 in 61% yield after
column chromatography. To introduce the alkyl chain on the outer
ring, Stille coupling was applied to obtain compound 2. According
to the reactivity of the different entities, two experimental condi-
tions were used. For compound 2, phenyl-thiophene coupling
was achieved by the reaction of fresh stannyl thieno[3,2-b]thio-
phene 9, and 7 with Pd(PPh3)4 as the catalyst in toluene at reflux.
The resulting compound 2 was isolated in 62% yield.
The original idea of the presented work was to combine both
discussed approaches and to synthesize novel compounds having
triphenylamine groups and thieno[3,2-b]thiophene moieties in
one molecule. Thus, here we report the synthesis and the optical
⇑
Corresponding author. Tel.: +33 134257022.
E-mail address: fabrice.goubard@u-cergy.fr (F. Goubard).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.10.082

6674
N. Metri et al. / Tetrahedron Letters 51 (2010) 6673–6676
S
S
S
C9H19
S
S
C9H19
C9H19
S
S
S
C9H19
C9H19
N
N
S
S
2
1
S
S
C9H19
S
S
S
S
S
C9H19
C9H19
C9H19
S
S
N
S
S
S
S
S
S
3
S
C9H19
C9H19
S
S
S
N
S
N
S
S
C9H19
S
S
5
S
S
S
S
S
S
4
S
C9H19
C9H19
S
S
S
S
C9H19
Scheme 1. Molecular structure of compounds 1–5.
A similar procedure was used to obtain molecules 10, 11. and 5
from 7, 10-Br, and 3-Br, respectively, It is necessary to mention
that the isolated yields were quite high and varied in the range
of 70–85% after precipitation. For coupling between two thiophene
parts, the Pd(PPh3)2Cl2 was used as the catalyst in THF at reflux.
Such procedure was utilized for the preparation of compounds 3
and 4. 10-Br, 11-Br, and 3-Br were prepared by bromination of
10, 11, and 3, respectively, with N-bromosuccinimide in a mixture
of chloroform and acetic acid at room temperature.
The high e
values (63,000–131,000 L molÀ1 cmÀ1) can be as-
signed to the combined effect of high molecular weights
(>1000 g molÀ1) and of the presence of three conjugated branches
per molecule.
Otherwise, the comparison of absorption signals for compounds
4 and 5, containing the thienothiophene and thiophene units com-
bined in a different order, revealed insignificant differences with a
slight increases of kmax and ekmax for compound 5 probably due to
greater planarity (Table 1, entries 4 and 5).
Figure 1 shows the molar extinction coefficient spectra of 1 to 5
in CHCl3 solution. The spectra of the oligothienyl-thienothiophene-
triphenylamines, 2, 3, and 4, revealed a progressive bathochromic
shift of the absorption maximum with the increase of the conju-
gated system’s length, from 386 (2) to 422 (4) nm, correspond-
ingly. Simultaneously, the optical band gaps, which were
determined from the lower-energy onset of the absorption band,
gradually decreased from 2.99 to 2.53 eV (Table 1). At the same
time the molar extinction coefficients were practically doubled in
going from thienothiophene 2 to bithiophene thienothiophene 4
(Table 1, entries 2 and 4). This trend was found to be in accordance
with a previously reported homologous series of conjugated oli-
gothiophenes.17–19
The thermal properties of all the compounds were examined
using thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) under an argon atmosphere. The temperatures
corresponding to 2% weight loss (T2d%) and the glass transition tem-
peratures (Tg), are summarized in Table 1. All compounds showed
significant thermal stability, with T2d% values higher than 300 °C.
Compound 4 demonstrated the lowest stability due to the presence
of two adjacent thiophene rings (Table 1, entry 4). In contrast, com-
pound 5, with a thieno[3,2-b]thiophene unit between the thio-
phenes, exhibited the decomposition temperature as high as
444 °C. DSC analysis revealed that compounds 3 to 5 can be ob-
tained as molecular glasses with glass transitions ranging from
27 to 57 °C.
Compound 1 had the shortest kmax of absorption among this
group probably due to the deplanarization caused by the
repulsive interactions between the nonyl chain and the phenyl
group (Table 1, entry 1). Displacing the nonyl chain to the exterior
position in compound 2 causes a lower deviation from planarity
resulting in a bathochromic effect with an increase of 20% in
absorption.
In summary, synthesis, optical, and thermal properties of no-
vel substituted thieno[3,2-b]thiophene molecules with triphenyl-
amine core were investigated in detail. The synthetic method
allowed the preparation of trisubstituted triphenylamine deriva-
tives of thieno[3,2-b]thiophene and thiophene in a combinatorial
manner starting from tris(4-bromophenyl)amine in relatively
good yields. The newly suggested molecules (1–5) exhibited

N. Metri et al. / Tetrahedron Letters 51 (2010) 6673–6676
6675
C9H19
S
6
S
(i) TMEDA, n-BuLi,THF, 0°C
(ii) Me3SnCl
(i) n-BuLi, THF, -78°C
Br
Br
C9H19
Me3Sn
S
O
O B
then
O
N
9
S
1
2
7
C9H19
Br
Pd(PPh3)4, Toluene, reflux
S
, K2CO3
(ii)
S
THF/H2O (3/1)
Br
8
SnBu3
S
Pd(PPh3)4, Toluene
Reflux
X
S
X
S
N
C9H19
S
X
X
SnBu3
Pd(PPh3)4
Toluene
reflux
S
9, Pd(PPh3)2Cl2
THF, Reflux
S
S
S
S
X
S
X = H, 10
X = Br, 10-Br
NBS
N
X = H,
3
N
NBS
X = Br, 3-Br
S
S
S
S
S
X
S
C9H19
S
X = H, 11
X = Br, 11-Br
NBS
S
X
S
X
S
C9H19
9, Pd(PPh3)2Cl2
X
THF, Reflux
SnBu3
S
Pd(PPh3)4, Toluene
Reflux
4
5
Scheme 2. Synthetic routes of molecules 1–5.
Table 1
Optical and thermal properties of star-shaped targets 1–5
Ma (g molÀ1
)
kmax (nm)
ekmax (L molÀ1 cmÀ1
)
Eg (eV)
Tg (°C)
b
T2d% (°C)
c
Compound
1
2
3
4
5
1037
1037
1283
1529
1529
354
386
396
422
428
63,000
77,000
106,000
128,000
131,000
2.99
2.90
2.65
2.53
2.53
À3
3
27
52
57
361
344
354
305
444
a
b
c
Molecular weight of the compound.
Glass transition temperature is given according to DSC analysis with a heating rate of 20 °C/min.
Temperature of 2 wt % loss according to TGA.

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N. Metri et al. / Tetrahedron Letters 51 (2010) 6673–6676
References and notes
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100000
80000
60000
40000
20000
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p-conjugation with high molar extinction coeffi-
cients and some of them (3–5) demonstrated molecular glass
behavior.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2010.10.082.