Quaterthiophenes with terminal Indeno[1,2-b]thiophene units as p-type organic semiconductors

Article abstract of DOI:10.1021/jo802028n

Quaterthiophenes 4T, Oct-4T, and Tol-4T based on a central 2,2′-bithiophene core α,ω-terminated with 4,4-unsubstituted and 4,4-disubstituted n-octyl or p-tolyl indeno[1,2-b]thiophene have been synthesized by Stille or Miyaura-Suzuki couplings. Compound 4T

Full text of DOI:10.1021/jo802028n

Quaterthiophenes with Terminal Indeno[1,2-b]thiophene Units as
p-Type Organic Semiconductors
Laurent Pouchain, Olivier Ale´veˆque, Yohann Nicolas,† Agathe Oger, Charles-Henri Le Re´gent,
Magali Allain, Philippe Blanchard,* and Jean Roncali
UniVersity of Angers, CNRS, CIMA, Linear Conjugated Systems Group,
2 BouleVard LaVoisier, 49045 Angers, France
Philippe.Blanchard@uniV-angers.fr
ReceiVed September 12, 2008
Quaterthiophenes 4T, Oct-4T, and Tol-4T based on a central 2,2′-bithiophene core R,ω-terminated with
4,4-unsubstituted and 4,4-disubstituted n-octyl or p-tolyl indeno[1,2-b]thiophene have been synthesized
by Stille or Miyaura-Suzuki couplings. Compound 4T was also synthesized by an alternative route
involving a soluble precursor bearing solubilizing trimethylsilyl groups which have been eliminated in
the last step. The electronic properties of the compounds have been analyzed by cyclic voltammetry,
UV-vis absorption and fluorescence emission spectroscopy. Thermal evaporation of 4T and Oct-4T
leads to crystalline thin films and UV-vis absorption and X-ray diffraction data for these films suggest
that the molecules adopt a quasi-vertical orientation onto the substrate. Strong π-π intermolecular
interactions have been observed for 4T but not for molecules Oct-4T due to the presence of n-octyl
chains. Sublimed thin films of Tol-4T show an amorphous character. The characterization of field-effect
transistors fabricated from these three materials gave a hole-mobility of 2.2 × 10-2 cm2 V-1 s-1 with an
on/off ratio of 2.2 × 104 for 4T while no field-effect was observed for Oct-4T and Tol-4T.
Introduction
derived from linear π-conjugated systems are a focus of intense
research effort.5,10-16 Whereas acenes1,10,17,18 and thiophene1,19-22
Organic field-effect transistors (OFETs) are intensively
investigated in view of their potential applications in active
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† Permanent address: University of Bordeaux 1, CNRS, ISM, 351 cours de
la libe´ration, 33405 Talence, France.
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10.1021/jo802028n CCC: $40.75 2009 American Chemical Society
Published on Web 01/12/2009

Quaterthiophenes as p-Type Organic Semiconductors
oligomers still represent some of the most widely investigated
classes of organic semiconductors, recent years have witnessed
the emergence of various classes of hybrid conjugated
systems.20,23
Thiophene-phenylene hybrid oligomers have attracted special
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Pouchain et al.
CHART 1
CHART 2
Results and Discussion
Synthesis. Compounds 4T, Oct-4T and Tol-4T have been
synthesized by Stille42 or Miyaura-Suzuki43 coupling of
appropriate 2,2′-bithiophenes and 2-halogeno or 2-trialkylstannyl
derivatives of indeno[1,2-b]thiophene. The synthesis of the latter
compounds is shown in Scheme 1. Indeno[1,2-b]thiophene 5
was prepared according to the McDowell procedure.44 The
synthesis of 2 has been significantly improved by reacting
methyl 2-bromobenzoate 1 with 2-tributylstannylthiophene in
the presence of a Pd(0) catalyst. Saponification of ester 2
followed by acidification led to acid 3, which was subsequently
converted into acid chloride. Further intramolecular Friedel-Crafts
acylation afforded ketone 4. Compound 5 was obtained after a
Wolf-Kishner reduction of ketone 4 and was then selectively
iodinated or brominated at the 2-position by 1 equiv of
N-iodosuccinimide or N-bromosuccinimide in DMF to give
compounds 6 and 7, respectively.45 Owing to the relative acidity
of the protons of the methylene bridge of 5, the 2-tributylstannyl
derivative 8 was synthesized by lithium-bromine exchange on
compound 7 and reaction with tributylstannyl chloride.
The synthesis of the unsubstituted quaterthiophene 4T has
been carried out in different conditions summarized in Scheme
2. A Miyaura-Suzuki coupling between 2 equiv of iodo
derivative 6 and pinacolato boronic ester 946 led to 4T in 32%
yield. Alternatively, Stille couplings between bromo derivative
7 (2.5 equiv) and 5,5′-bis(tributylstannyl)-2,2′-bithiophene 1047
or stannyl derivative 8 (2.5 equiv) and 5,5′-dibromo-2,2′-
bithiophene 1148 gave 4T in comparable yields close to 45%.
As a result of its low solubility in THF or toluene, 4T
precipitated in the reaction mixture and was recovered by
filtration. Purification of 4T consisted of successive washings
with different solvents and further Soxhlet extractions with
solvents in the following order: hexane, acetone, dichlo-
romethane, toluene, and finally chlorobenzene. The major part
of 4T was extracted with chlorobenzene while some amount of
4T was recovered from toluenic extracts. The lack of solubility
in common deuterated organic solvents (see Experimental
Section and Supporting Information) did not allow for NMR
analysis at room temperature. The identity of 4T was confirmed
by the MALDI-TOF mass spectrum of the chlorobenzene
extracts, which essentially showed one main peak at m/z ) 506
(100%, M+•), associated with the related less intense isotope
peaks at m/z ) 507 (35%) and 508 (19%) (Figure S2, Supporting
Information). However, another system of weak intensity was
also observed with the main peak at m/z ) 670 (6% relative to
the peak at m/z ) 506) assigned to the presence of a small
amount of sexithiophene derivative 6T. This byproduct results
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phenyl ring by a thiophene will limit steric interactions on one
side and contribute to reduce the overall aromaticity of the
system and thus the HOMO-LUMO gap.34
We report here the synthesis of a series of quaterthiophenes
4T, Oct-4T and Tol-4T bearing R,ω-terminal 4,4-unsubstituted
or 4,4-disubstituted indeno[1,2-b]thiophene as well as parent
oligomers obtained as side product of the synthesis (Chart 2).
The electronic properties of the new compounds have been
analyzed by cyclic voltammetry, UV-vis and fluorescence
emission spectroscopy. Thin films of 4T, Oct-4T and Tol-4T
prepared by thermal evaporation have been characterized by
UV-vis and fluorescence emission spectroscopy and X-ray
diffraction and preliminary results on the use of these com-
pounds in OFETs are presented.
1056 J. Org. Chem. Vol. 74, No. 3, 2009

Quaterthiophenes as p-Type Organic Semiconductors
SCHEME 1
SCHEME 2
from an initial homocoupling of bithiophene derivatives 9-11
during Stille or Miyaura-Suzuki reaction. Such Stille homo-
coupling has already been observed during the synthesis of other
oligothiophenes.49 Interestingly the MALDI-TOF data of the
toluenic extracts show the presence of only 4T (Figure S2,
Supporting Information). Similarly, the indenothiophene com-
pounds 6-8 used in the synthesis of 4T were also subjected to
homocouplings leading to the formation of bithiophene 2T.
With the aim of developing an alternative route to 4T free
of 6T, the soluble precursor 13 was synthesized by reacting
2.5 equiv of stannyl compound 8 with 1 equiv of 3,3′-
bis(trimethylsilyl)-5,5′-dibromo-2,2′-bithiophene 1223h (Scheme
3). As recently reported,23h the bulky trimethylsilyl groups of
these intermediate compounds strongly enhance their solubility.
Purification of 13 was performed by successive silica gel column
chromatography and preparative thick layer chromatography to
get rid of sexithiophene traces. The subsequent cleavage of the
trimethylsilyl groups of 13 in the presence of fluoride anions
led to pure 4T, which was recovered by simple filtration. As
expected, the MALDI-TOF spectrum of 4T confirmed the
absence of 6T. Moreover, the mass spectrum recorded between
m/z ) 0 and 1500 shows only the presence of the molecular
ion peak at m/z ) 506 with the corresponding isotope peaks,
thus suggesting a good purity for this sample (Figure S3,
Supporting Information). The 1H NMR spectrum of 4T recorded
in CDCl3 at 55 °C or in DMSO-d6 at 90 °C (Figures S18 and
S19, Supporting Information), respectively, shows a very weak
singlet at 3.72 or 3.80 ppm corresponding to the protons of the
two methylene bridges, suggesting that compound 4T is pure.
(49) Van Hal, P. A.; Beckers, E. H. A.; Meskers, S. C. J.; Janssen, R. A. J.;
Jousselme, B.; Blanchard, P.; Roncali, J. Chem. Eur. J. 2002, 8, 5415–5429.
J. Org. Chem. Vol. 74, No. 3, 2009 1057

Pouchain et al.
SCHEME 3
SCHEME 5
SCHEME 4
TABLE 1. UV-vis Absorption, Fluorescence Emission, and Cyclic
Voltammetric Data for Oligothiophenes
compd
λ
max, nma
380, 397, 417 440, 466, 495
442 512, 545, 595
λ
em, nmb
Φ, % Epa1, Vc Epa2, Vc
2T
4T
6
26
4
0.85
1.33 (irr)
Oct-2T 391, 408, 427 451, 477, 510
0.84
0.75
0.68
0.79
1.30 (irr)
0.93
Oct-4T 450
Oct-6T 470
Tol-4T 452
516, 550, 600
544, 582, 640
517, 550, 600
31
18
27
0.82
1.00
a Absorption maxima in CH2Cl2. b Emission maxima in CH2Cl2 with
perylene (Φ ) 92% in EtOH) as standard. Bold numbers represent the
more intense absorption or emission bands. c 1 mM substrate in 0.10 M
n-Bu4NPF6/CH2Cl2, scan rate 100 mV s-1, Pt working electrode, ref
SCE.
of Pd(PPh3)4 (Scheme 5). Compound 19 was obtained from 18
by lithium-bromine exchange and reaction with trimethylstan-
nyl chloride. Bromination of compound 17 with N-bromosuc-
cinimide in DMF gave the bromo derivative 18.50 Compound
17 was prepared by reacting p-tolyllithium, generated by reaction
of n-BuLi on p-bromotoluene, with ester 2 to give an intermedi-
ate alcohol which was then cyclized into 17 in acidic conditions.
Electrochemical and Optical Properties. The electrochemi-
cal properties of new compounds have been analyzed by cyclic
voltammetry (CV) in dichloromethane in the presence of
tetrabutylammonium hexafluorophosphate as supporting elec-
trolyte. Table 1 lists CV, UV-vis absorption, and fluorescence
emission data for oligothiophenes derivatives. The CV of 4T
could not be recorded because of insufficient solubility. The
CV of 2T presents a one-electron reversible oxidation peak at
Epa1 ) 0.85 V corresponding to the generation of a stable radical
cation followed by an irreversible oxidation peak at more
positive potential (Figure S4, Supporting Information).
However, assignment of the aromatic protons is still prevented
by the weakness of the NMR signals.
Analogs more soluble than 4T have been obtained by
substitution at the methylene bridges by n-octyl chains and
p-tolyl groups leading to compounds Oct-4T and Tol-4T,
respectively. Compound Oct-4T was prepared either by
Miyaura-Suzuki coupling of iodinated compound 15 with
pinacolato boronic ester 9 or by Stille coupling of stannyl
derivative 16 with 5,5′-dibromo 2,2′-bithiophene 11 (Scheme
4). Compound 16 was obtained from 15 after successive
lithium-iodine exchange and reaction with trimethylstannyl
chloride. Compound 15 was prepared from 5 by double
alkylation with n-octylbromide in basic conditions leading to
the 4,4-substituted indenothiophene 14, which was then iodi-
nated using N-iodosuccinimide.
In the case of the Suzuki coupling, Oct-4T was obtained in
modest yield (24%), whereas the main product was 2,2′-
bithiophene Oct-2T (27%). Only traces of sexithiophene Oct-
6T were observed. The use of Stille conditions improved the
yield of Oct-4T to 66%, while 16% yield of sexithiophene Oct-
6T and traces of bithiophene Oct-2T were obtained.
Figure S5 in Supporting Information shows the CV traces of
Oct-2T, Oct-4T, and Oct-6T. Compound Oct-2T exhibits a
one-electron reversible oxidation peak at Epa1 ) 0.84 V and an
ill-defined irreversible oxidation wave around 1.30 V (not
shown). The CV of Oct-4T shows two reversible one-electron
oxidation peaks at Epa1 ) 0.75 V and Epa2 ) 0.93 V, associated
with the formation of stable radical cation and dication. As
expected, insertion of additional thiophene rings from Oct-2T
1
to Oct-4T and Oct-6T produces a negative shift of Epa and
Based on the preceding results, compound Tol-4T was
prepared in 53% yield by Stille reaction between 5,5′-dibromo-
2,2′-bithiophene 11 and the stannyl derivative 19 in the presence
(50) Wong, K.-T.; Hwu, T.-Y.; Balaiah, A.; Chao, T.-C.; Fang, F.-C.; Lee,
C.-T.; Peng, Y.-C. Org. Lett. 2006, 8, 1415–1418.
1058 J. Org. Chem. Vol. 74, No. 3, 2009

Quaterthiophenes as p-Type Organic Semiconductors
FIGURE 1. Normalized absorption and photoluminescence spectra of Oct-2T (dotted line), Oct-4T (dashed-dotted line), and Oct-6T (solid line)
in CH2Cl2.
2
1
Epa2, while the difference ∆Epa ) Epa - Epa decreases from
Oct-4T (180 mV) to Oct-6T (140 mV) due to the smaller
Coulombic repulsion in the dicationic state as chain length
increases. Replacement of n-octyl chains of Oct-4T by p-tolyl
groups in Tol-4T leads to a positive shift of 40 mV and 70 mV
of the Epa1 and Epa2 values, respectively (Figure S6, Supporting
Information).
The absorption and emission spectra of 4T are shown in
Figure S7, Supporting Information. A broad absorption band
attributed to a π-π* transition is observed at λmax ) 442 nm,
while the emission spectrum exhibits a more resolved vibronic
structure with the most populated 0-0 transition at 512 nm, a
less intense peak at 545 nm, and a shoulder at 595 nm. Similar
spectra are observed for Oct-4T and Tol-4T, although substitu-
tion of the indeno[1,2-b]thiophene heterocycle leads to a slight
red shift of absorption and emission maxima (Table 1).
The UV-vis spectrum of compound 13 shows an absorption
maximum at 379 nm, and the ∼63 nm blue shift compared to
4T agrees well with the restricted conjugation imposed by the
twisted structure of the molecule (Figure S7, Supporting
Information).
Figure 1 shows the absorption and emission spectra of
oligothiophenes of the octyl series. As expected, increasing the
length of the π-conjugated system from two to six thiophene
rings leads to a progressive red shift of the maximum of
absorption associated with the reduction of the HOMO-LUMO
gap (∆E). The latter can be estimated from the absorption edges
in the UV-vis spectra of Oct-2T (∆E ) 2.7 eV), Oct-4T
(∆E ) 2.4 eV), and Oct-6T (∆E ) 2.3 eV).
Theoretical Calculations. Theoretical calculations on 4T and
a reference compound fluorene-thiophene-thiophene-fluorene
(FTTF) (Chart 2), which has recently demonstrated great
potential as active material in OFETs,37,38 have been performed
at the ab initio density functional level with the Gaussian 03
program. Becke’s three-parameter gradient corrected functional
(B3LYP) with a polarized 6-31G(d,p) basis was used for all
full geometry optimizations. In both cases, the oligothiophene
chain adopts an anti conformation. As expected, 4T presents a
more planar structure than FTTF. While the dihedral angles
between the thiophene rings of the central bithiophene core are
comparable for 4T (13°) and for FTTF (10°), the dihedral angles
between the terminal indeno[1,2-b]thiophene unit (14°) or the
terminal fluorene unit (25°) and the vicinal thiophene ring differ
significantly (Figure 2). This difference results in a decrease of
the calculated ∆E from 3.18 eV for FTTF to 2.74 eV for 4T,
FIGURE 2. Optimized structures and energy levels of HOMO and
LUMO of FTTF and 4T.
which stems from the concomitant +0.19 eV increase of the
HOMO level and -0.25 eV decrease of the LUMO level.
Interestingly, the LUMO level is more affected than the HOMO
level. The HOMO and LUMO of both molecules show typical
aromatic and quinoid characters, respectively, with an extension
of π-conjugation over the whole conjugated backbone.
Film Characterizations. Films of 4T, Oct-4T, and Tol-4T
have been grown on glass by sublimation of 4T, Oct-4T, or
Tol-4T under high vacuum. The absence of degradation of the
molecules during vacuum sublimation was confirmed by check-
ing the UV-vis absorption spectrum of the redissolved films.
Although 4T, Oct-4T, and Tol-4T show similar UV-vis
spectra in solution, those of the corresponding thin films exhibit
three drastically different behaviors. Thus, comparison of the
solution and the solid-state spectra of 4T reveals a 57 nm blue
shift of λmax and the appearance of a weak electronic transition
at 510 nm for the film (Figure 3, top). As already observed for
J. Org. Chem. Vol. 74, No. 3, 2009 1059

Pouchain et al.
FIGURE 4. X-ray diffraction diagrams of films of 50 nm thickness of
4T (top) and Oct-4T (bottom) on glass.
The solid-state optical spectrum of Oct-4T shows a well-
resolved vibronic structure. However, in contrast to 4T, a red
shift in absorbance typical of the formation of J aggregates52
and a broadening of the absorption band of Oct-4T are observed
in the solid state (Figure 3, middle), suggesting weaker
intermolecular π-interactions and a different molecular arrange-
ment. On the other hand, the similarity of the UV-vis spectrum
of Tol-4T obtained in solution or as film indicates limited
π-intermolecular interactions in the solid state (Figure 3,
bottom).
In addition, the quenching of the fluorescence for the film of
4T and the persistence of fluorescence properties for films of
Oct-4T and Tol-4T (Figure S9, Supporting Information) agree
well with the expected weaker intermolecular π-interactions in
the two latter cases.
Films of 50 nm thickness of 4T, Oct-4T, and Tol-4T have
been analyzed by X-ray diffraction in reflection mode. The XRD
diagram of a film of Tol-4T shows the absence of diffraction
peaks indicating an amorphous character (Figure S10, Support-
ing Information). By contrast, films of 4T and Oct-4T show a
FIGURE 3. Absorption spectra of 4T (top), Oct-4T (middle), and Tol-
4T (bottom) as films on glass (solid line) or in CH2Cl2 (dashed-dotted
line).
other oligothiophenes,1,19,20,21a,c,22,51 this behavior results from
a Davydov splitting of the singlet excited state that is generally
associated with strongly interacting π-conjugated systems in the
solid state.
(52) (a) Mishra, A.; Behera, R. K.; Behera, P. K.; Mishra, B. K.; Behera,
G. B. Chem. ReV. 2000, 100, 1973–2011. (b) Dautel, O. J.; Wantz, G.; Almairac,
R.; Flot, D.; Hirsch, L.; Le`re-Porte, J.-P.; Parneix, J.-P.; Serein-Spirau, F.; Vignau,
L.; Moreau, J. J. E. J. Am. Chem. Soc. 2006, 128, 4892–4901.
(51) Roncali, J.; Fre`re, P.; Blanchard, P.; de Bettignies, R.; Turbiez, M.;
Roquet, S.; Leriche, P.; Nicolas, Y. Thin Solid Films 2006, 511-512, 567–575.
1060 J. Org. Chem. Vol. 74, No. 3, 2009

Quaterthiophenes as p-Type Organic Semiconductors
FIGURE 6. IDS versus VDS characteristics at different VG values for
an OFET based on an evaporated layer of 4T, channel length L ) 50
µm and channel width W ) 5 mm.
a p-type semiconductor. A field-effect mobility µ of 2.2 × 10-2
cm2 V-1 s-1 corresponding to an average of eight devices was
obtained at a drain voltage of -80 V. The transfer characteristics
and the log(IDS) versus VG curve (Figure S11, Supporting
Information) give an average threshold voltage VT of -16.9 V
and an average on/off ratio of 2.2 × 104, respectively. Using
similar conditions, Bao et al. have reported a field-effect mobility
of 2-3 × 10-2 cm2 V-1 s-1 with on/off ratios of 105-106 for
OFETs based on FTTF.37
FIGURE 5. Possible structures for films of 4T (top) and Oct-4T
(bottom).
crystalline character and are highly ordered as evidenced by
sharp diffraction peaks (Figure 4). The XRD diagram for 4T
exhibits various peaks among them three different first order
diffraction peaks (001), (001′), and (001′′) at 2θ values of 3.83°,
4.76°, and 4.84°, which correspond to the respective d-spacings
of 23.0, 18.5, and 18.2 Å (λCu-R ) 1.5406 Å). Assuming a fully
extended linear structure for 4T with all vicinal thiophene rings
in an anti conformation, the MM2 minimized length of 4T was
estimated to 25 Å. Hence, these results suggest that three
crystalline domains coexist in the film where the long axis of
molecules 4T is tilted relative to the normal of the surface with
the angle values of 23°, 42°, and 43°. Figure 5 (top) represents
a schematic description of the film structure of 4T.
The XRD diagram of a film of Oct-4T shows one intense
diffraction peak (001) at 2θ ) 3.65° and two weak peaks
corresponding to higher orders of diffraction. These peaks lead
to a molecular layer of 24.2 Å of thickness. Using the molecular
length calculated for 4T, molecules Oct-4T adopt a quasivertical
orientation relative to the surface with an estimated tilt angle
of 15° with, however, weaker intermolecular π-interactions due
to the presence of the n-octyl chains, (Figure 5, bottom) in
agreement with UV-vis results.
OFET Fabrication and Measurements. TGA and DSC
measurements (see Supporting Information) showed that qua-
terthiophenes 4T, Oct-4T, and Tol-4T presented high thermal
stability compatible with a sublimation process. On this basis,
top-contact OFETs were made by deposition of a film of 50
nm thickness of 4T, Oct-4T, and Tol-4T onto a substrate kept
at 20 °C of a heavily doped silicon with a 200 nm thick SiO2
layer as dielectric, and the devices were completed by gold top
contact source and drain electrodes.
Devices realized from the octyl (Oct-4T)- and tolyl (Tol-
4T)-substituted quaterthiophenes did not show any field-effect
behavior, as could be expected from the already discussed weak
intermolecular interactions. Figure 6 presents the drain current
versus drain-source voltage (IDS/VDS) curves at different gate
voltages (VG) of an OFET based on 4T. The drain current
increases with increasing negative gate voltage, as expected for
Conclusion
Quaterthiophene derivatives 4T, Oct-4T, and Tol-4T based
on a central 2,2′-bithiophene core with two terminal 4,4-
unsubstituted or 4,4-disubstituted indeno[1,2-b]thiophene het-
erocycles have been synthesized using Stille or Miyaura-Suzuki
couplings. While complete characterization of the unsubstituted
derivative 4T of the series was prevented because of its lack of
solubility in common organic solvents, the introduction of
n-octyl chains or p-tolyl groups at the 4-positions of the
indeno[1,2-b]thiophene moiety led to more soluble compounds
Oct-4T and Tol-4T. Moreover, a detailed study of the synthesis
of quaterthiophene Oct-4T has evidenced the formation of
byproduct such as bithiophene Oct-2T and sexithiophene Oct-
6T resulting from homocoupling reactions. These side reactions
that make the purification of insoluble derivative 4T difficult
led us to adopt an alternative synthetic route involving a soluble
precursor for the synthesis of 4T.
Optical and X-ray diffraction results show that sublimed films
of 4T and Oct-4T are highly crystalline with molecules adopting
a quasivertical orientation on the substrate, whereas films of
Tol-4T are amorphous. Strong π-π intermolecular interactions
in the case of 4T allow for the realization of OFET with
interesting hole-mobilities and on/off ratios, while such interac-
tions are hindered by the presence of the n-octyl chains of
Oct-4T.
Work focused on the development of new conjugated systems
based on the indenothiophene building block and combining
solubility and strong intermolecular interactions is now under-
way and will be reported in future publications.
Experimental Section
Devices Preparation and Characterization. Organic FETs were
prepared by evaporation of 4T, Oct-4T, and Tol-4T under a vacuum
J. Org. Chem. Vol. 74, No. 3, 2009 1061

Pouchain et al.
of 6 × 10-7 mbar and subsequent deposition of a 50 nm thick
organic layer at a rate of 0.2 nm s-1 onto Si n++ wafer with a 200
nm thick SiO2 layer (ACM) with a substrate temperature of 20 °C.
As source and drain top contacts, 50 nm of Au were evaporated
through a homemade shadow mask, defining a channel of 5000
µm width and 50 µm length. The characterization was carried out
in a glovebox using an Agilent 4155C semiconductor parameter
analyzer. The contacts were obtained by W tips (Signatone). For
evaluation of the mobility (µ) in the saturation regime, the following
equation was used:
mL) was degassed with N2 for 10 min before addition of Pd2dba3
(015 g, 0.16 mmol). The reaction mixture was refluxed for 18 h
under a N2 atmosphere. After concentration under reduced pressure,
the residue was filtered on silica gel (eluent, CH2Cl2). Further
purification was performed by a first column chromatography on
silica gel with a mixture cyclohexane/CH2Cl2 9:1 as eluent and
another one with cyclohexane as solvent (Rf ) 0.37). Finally, a
preparative thick layer chromatography on silica gel led to 13 (0.43
1
g, 31% yield) as a yellow solid. Mp 193-194 °C. H NMR (500
MHz, CDCl3): δ 0.19 (s, 18H), 3.71 (s, 4H), 7.18 (s, 2H), 7.21 (t,
2H, 3J ) 7.5 Hz), 7.23 (s, 2H), 7.34 (t, 2H, 3J ) 7.3 Hz), 7.47 (d,
2H, 3J ) 7.5 Hz), 7.49 (d, 2H, 3J ) 7.5 Hz). 13C NMR (125 MHz,
CDCl3): δ 0.06, 34.3, 118.8, 119.8, 124.93, 124.99, 127.0, 128.7,
138.78, 138.81, 139.1, 140.3, 142.2, 143.5, 145.6, 147.7. MS
MALDI-TOF 650 [M+•]. UV-vis (CH2Cl2): λmax ) 379 nm.
IDS(sat) ) (W ⁄ 2L)µCi(VG - VT)2
(1)
where IDS is the drain current, VG is the gate voltage, VT is the
extrapolated threshold voltage, µ is the field-effect mobility, L and
W are the channel length and width, respectively, and Ci is the
insulator capacitance per unit area.
5,5′-Bis(4H-indeno[1,2-b]thien-2-yl)-2,2′-bithiophene (4T).
Miyaura-Suzuki Coupling. A solution of Na2CO3 (1.3 g, 12
mmol) in water (10 mL) and Aliquat 336 (480 mg, 1.2 mmol) was
added to a mixture of diboronic ester 946 (500 mg, 1.2 mmol) and
iodo derivative 6 (720 mg, 2.4 mmol) in toluene (15 mL). This
mixture was degassed with N2 for 15 min before addition of a
catalytic amount of Pd(PPh3)4 (87 mg, 75 µmol) and subsequent
refluxing for 48 h. The reaction mixture was then poured into MeOH
(100 mL) leading to the formation of a brown precipitate, which
was filtered and washed successively with toluene, an aqueous
solution of HCl 5%, water, hot MeOH (4 × 75 mL) and hot acetone
(3 × 75 mL). After drying, the brown precipitate was subjected to
successive Soxhlet extractions with hexane (5 h), acetone (15 h),
dichloromethane (15 h), toluene (24 h), and finally chlorobenzene
(2 × 48 h). The orange precipitate observed in the toluenic extract
was filtered to give 75 mg of compound 4T as demonstrated by
MALDI-TOF mass spectrometry and UV-vis spectroscopy. In
addition the extracts obtained from chlorobenzene were concentrated
and the resulting residue was triturated with acetone and filtered,
washed with acetone and hexane, and dried to afford 120 mg of
compound 4T, accompanied by traces of 6T as observed by
MALDI-TOF mass spectrometry (ca. 32% of overall yield). Note
that some amount of 2T as slightly yellow powder (65 mg) resulting
from homocoupling of compound 6 was obtained by evaporation
of the dichloromethane extracts and further purification by dissolu-
tion in hot CHCl3 and precipitation using EtOH.
Stille Coupling between 7 and 10. A mixture of 5,5′-bis(tribu-
tylstannyl)-2,2′-bithiophene 1047 (1 g, 1.34 mmol) and bromo
derivative 7 (0.84 g, 3.35 mmol) in anhydrous toluene (30 mL)
was degassed with N2 for 10 min before addition of Pd(PPh3)4 (150
mg, 0.13 mmol). The reaction mixture was refluxed for 16 h under
a N2 atmosphere. At room temperature, the resulting orange
precipitate was filtered, successively washed with toluene and
pentane and dried to give 0.53 g of orange powder. The same
sequence of Soxhlet extractions as Miyaura-Suzuki coupling was
carried out on the orange powder leading to 80 mg of 4T obtained
from the precipitate of the toluenic extracts while the extracts of
chlorobenzene gave 220 mg of 4T, accompanied by traces of 6T
as observed by MALDI-TOF mass spectrometry (ca. 44% of overall
yield).
2-Iodo-4H-indeno[1,2-b]thiophene (6). A solution of N-io-
dosuccinimide (2.7 g, 12.7 mmol) in DMF (60 mL) was added
dropwise to a solution of 5 (2 g, 11.6 mmol) in DMF (60 mL)
cooled to 0 °C and protected from the daylight. The reaction mixture
was stirred for 1 h at 0 °C and then allowed to reach room
temperature. Water (450 mL) was added, and the resulting white
precipitate was filtered and washed with water (2 × 50 mL) giving,
after drying, 6 (3.06 g, 88% yield) as white powder. Mp 91-92
°C. 1H NMR (500 MHz, CDCl3): δ 3.69 (s, 2H), 7.21 (t, 1H, 3J )
7.5 Hz), 7.29 (s, 1H), 7.32 (t, 1H, 3J ) 7.5 Hz), 7.44 (d, 1H, 3J )
7.5 Hz), 7.48 (d, 1H, 3J ) 7.5 Hz). MS (70 eV, EI) m/z
(I%) ) 298 (M+•, 100), 171 (55).
2-Bromo-4H-indeno[1,2-b]thiophene (7). A solution of N-
bromosuccinimide (1.08 g, 6.1 mmol) in DMF (30 mL) was added
dropwise to a solution of 5 (1 g, 5.8 mmol) in DMF (30 mL) cooled
to 0 °C and protected from the daylight. The resulting solution was
stirred for 1 h at 0 °C and then was allowed to reach room
temperature. The mixture was concentrated under reduced pressure.
After dilution with Et2O (50 mL), the solution was washed with
water (3 × 50 mL), dried over MgSO4, and concentrated to give a
residue that was purified by chromatography over silica gel
(cyclohexane) to give 7 as light-yellow crystals (1.41 g, 97% yield).
1
Mp 58-59 °C. H NMR (500 MHz, CDCl3): δ 3.69 (s, 2H), 7.12
3
3
(s, 1H), 7.22 (t, 1H, J ) 7.4 Hz), 7.32 (t, 1H, J ) 7.5 Hz), 7.43
3
3
(d, 1H, J ) 7.4 Hz), 7.48 (d, 1H, J ) 7.3 Hz). MS (70 eV, EI)
m/z (I%) ) 252 (M+•, 90), 250 (M+ •, 100), 171 (90).
2-Tributylstannyl-4H-indeno[1,2-b]thiophene (8). Under a N2
atmosphere, a solution of n-BuLi 1.6 M in hexanes (2.85 mL, 4.56
mmol) was added dropwise to a solution of 7 (1.10 g, 4.38 mmol)
in anhydrous Et2O (125 mL) cooled to -78 °C. After 0.5 h of
stirring at this temperature, Bu3SnCl 96% (1.77 mL, 6.26 mmol)
was added, and the reaction mixture was then allowed to warm
slowly to room temperature. After dilution with Et2O (150 mL),
the mixture was washed successively with a saturated aqueous
solution of NH4Cl (40 mL) and brine (2 × 100 mL). The organic
phase was separated by decantation and concentrated under reduced
pressure. The residue was diluted with EtOAc (40 mL), and a
saturated aqueous solution of NaF (30 mL) was added leading, after
20 min of stirring, to the precipitation of Bu3SnF, which was
separated by filtration. The filtered solution was washed with brine
(50 mL), dried over MgSO4, and concentrated to dryness. The
obtained oil (2.03 g) was sufficiently pure (>90%) and hence was
Stille Coupling between 8 and 11. A mixture of 5,5′-dibromo-
2,2′-bithiophene 1148 (0.27 g, 0.83 mmol) and stannyl derivative 8
(1.02 g, 2.21 mmol) in anhydrous toluene (30 mL) was degassed
with N2 for 10 min before addition of Pd(PPh3)4 (100 mg, 0.09
mmol). The reaction mixture was refluxed for 21 h under a N2
atmosphere. At room temperature, the resulting orange precipitate
was filtered, successively washed with toluene and pentane and
dried to give 0.35 g of orange powder. The same sequence of
Soxhlet extractions as Miyaura-Suzuki coupling was carried out
leading to 50 mg of 4T obtained from the precipitate of the toluenic
extracts while the extracts of chlorobenzene gave 150 mg of 4T,
accompanied by traces of 6T as observed by MALDI-TOF mass
spectrometry (ca. 48% of overall yield).
1
used in the next step without further purification. H NMR (500
3
MHz, CDCl3): δ 0.91 (t, 9H, J ) 7.2 Hz), 1.08-1.25 (m, 6H),
1.34-1.39 (m, 6H), 1.56-1.65 (m, 6H), 3.68 (s, 2H), 7.15 (s, 1H),
3
3
7.16 (t, 1H, J ) 7.4 Hz), 7.30 (t, 1H, J ) 7.4 Hz), 7.46 (d, 1H,
3J ) 7.0 Hz), 7.48 (d, 1H, J ) 7.4 Hz).
3
5,5′-Bis(4H-indeno[1,2-b]thien-2-yl)-3,3′-bis(trimethylsilyl)-
2,2′-bithiophene (13). A mixture of 3,3′-bis(trimethylsilyl)-5,5′-
dibromo-2,2′-bithiophene 1223h (1 g, 2.14 mmol) and stannyl
derivative 8 (2.53 g, 5.41 mmol) in the presence of AsPh3 (0.35 g,
1.14 mmol) and CuI (0.10 g, 0.53 mmol) in anhydrous toluene (60
1062 J. Org. Chem. Vol. 74, No. 3, 2009

Quaterthiophenes as p-Type Organic Semiconductors
Elimination of Trimethylsilyl Groups of 13. A solution of
n-Bu4NF 1 M in THF (1 mL) was added to a solution of 13 (100
mg, 0.15 mmol) in pyridine (10 mL) and the reaction mixture was
stirred at 20 °C for 20 h. The resulting precipitate was filtered,
washed successively with water (3 × 50 mL), acetone (3 × 50
mL) and Et2O (2 × 50 mL) and dried affording 4T (40 mg, 51%
yield).
A saturated aqueous solution of NH4Cl was added to the mixture
and, after vigorous stirring for 0.5 h, the organic phase was separated
by decantation, dried over MgSO4 and concentrated. The viscous
oil was dissolved in EtOAc (50 mL) and was vigorously stirred
for 0.5 h after addition of a saturated aqueous solution of NaF to
get rid of the unreacted trimethyltin chloride. The resulting
precipitate was filtered over celite which was rinsed with EtOAc.
The filtrated solution was washed with brine (50 mL), water (50
mL), dried over MgSO4 and concentrated. The resulting oil (1.80
g) consisted of a mixture of ca. 80% of 16 and ca. 20% of 14 as
1
4T: Mp 356 °C. H NMR analysis was prevented due to the
lack of solubility of 4T in CDCl3, pyridine-d5, THF-d8, DMSO-d6,
DMF-d7, benzene-d6 and chlorobenzene-d5 at 20 °C. However, one
singlet was observed for the two methylene bridges at 3.72 ppm in
hot CDCl3 (55 °C) or at 3.80 ppm in hot DMSO-d6 (90 °C) (see
Supporting Information). MS MALDI-TOF 506 [M+•]. ESI+
HRMS: cald for C30H18S4 506.02914; found 506.0293. UV-vis
(CH2Cl2): λmax ) 442 nm.
1
determined by H NMR. This crude product was used in the next
step without further purification.
5,5′-Bis(4,4-dioctyl-4H-indeno[1,2-b]thien-2-yl)-2,2′-bithio-
phene (Oct-4T). Miyaura-Suzuki Coupling between 15 and
9. A solution of Na2CO3 (0.65 g, 6 mmol) in water (5 mL) was
added to a mixture of boronic ester 946 (0.25 g, 0.6 mmol),
compound 15 (630 mg, 1.2 mmol) and Aliquat 336 (240 mg, 0.6
mmol) in toluene (10 mL). This mixture was degassed with N2 for
0.5 h before addition of Pd(PPh3)4 (50 mg, 45 µmol) and subsequent
refluxing for 65 h under a N2 atmosphere. Water (100 mL) was
added and the reaction mixture was extracted with Petroleum Ether
(3 × 100 mL). The organic phases were gathered, washed with an
aqueous solution of HCl 1 M (100 mL), brine (100 mL), dried
over MgSO4 and concentrated under reduced pressure. Chroma-
tography on silica gel (eluent: Petroleum Ether) led to a fraction
corresponding to Oct-2T as a yellow oil (Rf ) 0.62, 80 mg, 27%
yield) and to a fraction corresponding to Oct-4T as an orange-red
powder (Rf ) 0.49, 140 mg, 24% yield).
1
2T: Mp 124-125 °C. H NMR (500 MHz, CDCl3): δ 3.72
3
3
(s, 4H), 7.21 (t, 2H, J ) 7.5 Hz), 7.25 (s, 2H), 7.33 (t, 2H, J )
7.5 Hz), 7.47 (d, 2H, 3J ) 7.5 Hz), 7.49 (d, 2H, 3J ) 7.5 Hz). 13
C
NMR: 2T was too insoluble in CDCl3, pyridine-d5 and DMSO-d6
to obtain a 13C NMR spectrum. MS MALDI-TOF 342 [M+ •]. ESI+
HRMS: cald for C22H14S2 342.05369; found 342.0535. UV-vis
(CH2Cl2): λmax ) 380 nm (sh), 397 nm, 417 nm (sh).
4,4-Dioctyl-4H-indeno[1,2-b]thiophene (14). Potassium hy-
droxide (2.5 g) was added to a mixture of 5 (2.4 g, 13.9 mmol),
1-bromooctane (5.97 g, 11 mmol) and potassium iodide (70 mg,
0.4 mmol) in DMSO (60 mL) cooled to 0 °C. The resulting solution
was allowed to reach room temperature overnight. Water (100 mL)
was slowly poured into the reaction mixture previously cooled to
0 °C. The mixture was extracted with Et2O (2 × 80 mL), and the
combined organic extracts were washed with water, brine, an
aqueous saturated solution of NH4Cl, dried over MgSO4 and
concentrated under vacuum. The residual 1-bromooctane was
distilled using a Kugelrohr apparatus. The resulting brown oil was
purified by chromatography of silica gel (eluent: Petroleum Ether)
Stille Coupling between 16 and 11. Pd(PPh3)4 (120 mg, 0.11
mmol) was added to a N2 degassed solution of 16 (1.80 g, 80%
pure, 2.6 mmol) and dibromobithiophene 1148 (360 mg, 1.1 mmol)
in toluene (50 mL). The reaction mixture was refluxed for 24 h,
and then water (60 mL) was added at room temperature. The
mixture was diluted with Petroleum Ether (50 mL), washed with
brine (50 mL), dried over MgSO4 and concentrated. The viscous
red oil was purified by chromatography on silica gel (eluent:
Petroleum Ether) to give Oct-4T as an orange-red solid (Rf ) 0.49,
690 mg, 66% yield). Compound Oct-6T (Rf ) 0.27, 120 mg, 16%
yield) was also isolated as bright red powder.
1
to give 14 as a colorless oil (3.4 g, 60% yield). H NMR (500
3
MHz, CDCl3): δ 0.72-0.85 (m, 4H), 0.84 (t, 6H, J ) 7.3 Hz),
2
3
1.06-1.25 (m, 20 H), 1.84 (dt, 2H, J ) 13.0 Hz, J ) 4.8 Hz),
2
3
3
1.94 (dt, 2H, J ) 13.0 Hz, J ) 4.8 Hz), 6.97 (d, 1H, J ) 4.8
3
4
Hz), 7.18 (dt, 1H, J ) 7.4 Hz, J ) 1 Hz), 7.24-7.30 (m, 3 H),
Oct-2T: 1H NMR (500 MHz, CDCl3): δ 0.71-098 (m, 8H), 0.82
7.40 (d, 1H, J ) 7.4 Hz). 13C NMR (125 MHz, CDCl3): δ 14.1,
3
3
(t, 12H, J ) 7.2 Hz), 1.06-1.30 (m, 40H), 1.85 (m, 4H), 1.94
22.6, 24.1, 29.2, 29.3, 30.1, 31.8, 39.0, 53.8, 118.6, 121.5, 122.6,
124.9, 126.7, 127.1, 138.2, 141.1, 153.9, 155.4. MS (70 eV, EI)
m/z (I%) ) 396 (M·+, 100%). Anal. Calcd for C27H40S: C, 81.74;
H, 10.16. Found: C, 81.71; H, 10.42.
3
(m, 4H), 7.09 (s, 2H), 7.18 (t, 2H, J ) 7.5 Hz,), 7.26 (m, 4 H),
3
7.36 (d, 2H, J ) 7.5 Hz). MS MALDI-TOF 790 [M+•]. UV-vis
(CH2Cl2): λmax ) 391 nm (sh), 408 nm, 427 nm (sh).
Oct-4T: Mp 101-102 °C. 1H NMR (500 MHz, CDCl3): δ
0.75-0.92 (m, 8 H), 0.83 (t, 12H, 3J ) 7.2 Hz), 1.11-1.26
2-Iodo-4,4-dioctyl-4H-indeno[1,2-b]thiophene (15). A solution
of N-iodosuccinimide (580 mg, 2.6 mmol) in DMF (30 mL) was
added dropwise to a solution of 14 (1 g, 2.5 mmol) in DMF (20
mL) cooled to 0 °C and protected from the daylight. The resulting
solution was stirred for 1 h at 0 °C, and then allowed to reach
room temperature. Water (400 mL) was added and the resulting
mixture was extracted with CH2Cl2 (4 × 100 mL). The organic
layers were gathered, washed with water (4 × 60 mL), dried over
magnesium sulfate and concentrated. A chromatography on silica
gel (eluent: cyclohexane) afforded 15 (1.2 g, 92% yield) as a
2
(m, 40H), 1.85 (dt, 4H, J ) 13.0 Hz,3J ) 4.6 Hz), 1.94 (dt, 4H,
2J ) 13.0 Hz,3J ) 4.6 Hz), 7.04-7.14 (m, 6H), 7.20 (t, 2H,3J )
7.5 Hz), 7.25-7.30 (m, 4H), 7.39 (d, 2H,3J ) 7.5 Hz). 13C NMR
(125 MHz, CDCl3): δ 14.1, 22.7, 24.2, 29.32, 29.35, 30.1, 31.8,
39.0, 54.4, 118.2, 118.7, 122.5, 123.7, 124.2, 125.3, 126.9, 135.5,
137.4, 138.0, 139.1, 140.4, 153.4, 156.1. MS MALDI-TOF 954
[M+•]. UV-vis (CH2Cl2): λmax ) 450 nm. Anal. Calcd for C62H82S4:
C, 77.93; H, 8.65. Found: C, 77.72; H, 8.72.
Oct-6T: Mp 147-148 °C. 1H NMR (500 MHz, CDCl3): δ
1
colorless oil. H NMR (500 MHz, CDCl3): δ 0.66-0.77 (m, 4H),
3
3
0.73-0.93 (m, 8H), 0.83 (t, 12H, J ) 7.2 Hz), 1.08-1.26 (m,
0.84 (t, 6H, J ) 7.2 Hz), 1.05-1.32 (m, 20 H), 1.76-1.91 (m, 4
40H), 1.86 (dt, 4H, 2J ) 13.0 Hz, 3J ) 4.6 Hz), 1.94 (dt, 4H, 2J )
13.0 Hz,3J ) 4.6 Hz), 7.04-7.15 (m, 10H), 7.20 (t, 2H,3J ) 7.5
Hz), 7.25-7.30 (m, 4H), 7.39 (d, 2H,3J ) 7.5 Hz). 13C NMR (125
MHz, CDCl3): δ 14.2, 22.7, 24.2, 29.3, 29.4, 30.1, 31.9, 39.0, 54.4,
118.2, 118.7, 122.6, 123.7, 124.3, 124.5, 124.5, 125.3, 127.0, 135.3,
135.9, 136.2, 137.6, 138.0, 139.1, 140.4, 153.5, 156.1. ESI+ HRMS:
calcd for C62H82S4 1118.50538; found 1118.5036. UV-vis
(CH2Cl2): λmax ) 470 nm.
3
3
H), 7.13 (s, 1H), 7.19 (t, 1H, J ) 7.5 Hz), 7.24 (t, 1H, J ) 7.5
Hz), 7.25 (d, 1H, J ) 7.5 Hz), 7.33 (d, 1H, J ) 7.5 Hz). 13C
NMR (125 MHz, CDCl3): δ 14.3, 22.8, 24.2, 29.4, 29.4, 30.1, 31.9,
39.0, 54.5, 74.3 (C-I), 118.9, 122.8, 125.5, 127.0, 131.2, 137.8,
146.4, 153.0, 156.0. MS (70 eV, EI) m/z (I%) ) 522 (M·+, 100).
2-Trimethylstannyl-4,4-dioctyl-4H-indeno[1,2-b]thiophene (16). A
solution of n-BuLi 2.5 M in hexanes (1.75 mL) was added dropwise
to a solution of 15 (2.1 g, 4.02 mmol) in anhydrous Et2O (50 mL)
under inert atmosphere at -70 °C. The reaction mixture was then
allowed to reach 0 °C and then cooled to -50 °C before addition
of a solution of trimethyltin chloride (920 mg, 4.62 mmol) in
anhydrous Et2O (10 mL). The reaction mixture was allowed to reach
room temperature and was diluted with Petroleum Ether (100 mL).
3
3
2-Trimethylstannyl-4,4-di-p-tolyl-4H-indeno[1,2-b]thiophene
(19). A solution of n-BuLi 1.6 M in hexanes (1.2 mL, 1.92 mmol)
was added dropwise to a solution of 18 (0.77 g, 1.78 mmol) in
anhydrous THF (35 mL) cooled to -75 °C under an inert
atmosphere. After 0.5 h of stirring at this temperature, a solution
J. Org. Chem. Vol. 74, No. 3, 2009 1063

Pouchain et al.
of Me3SnCl 1 M in THF (2.2 mL, 2.2 mmol) was added to the
reaction mixture, which was then allowed to warm to room
temperature and stirred for 12 h. After dilution with Et2O (150 mL),
the reaction mixture was washed with a saturated aqueous solution
of NH4Cl (100 mL) and concentrated under reduced pressure. The
residue was diluted with EtOAc (30 mL) and a saturated aqueous
solution of NaF (25 mL) was added. This mixture was stirred for
20 min and filtered on celite, and the filtered solution was washed
with a saturated aqueous solution of NaCl (15 mL), dried over
MgSO4, and concentrated to dryness. The resulting oil (0.77 g)
consisted of a mixture of ca. 70% of 19 and ca. 30% of 17 as
Hz), 7.17 (dt, 2H, 3J ) 7.6 Hz,4J ) 1.1 Hz), 7.28 (dt, 2H, 3J ) 7.5
Hz, 4J ) 0.8 Hz), 7.34 (d, 2H, 3J ) 7.5 Hz), 7.42 (d, 2H, 3J ) 7.4
Hz). 13C NMR (125 MHz, CDCl3): δ 21.0, 63.2, 119.4, 119.5, 124.0,
124.2, 124.3, 124.5, 125.09, 126.14, 127.6, 127.8, 129.1, 135.7,
136.5, 136.96, 137.01, 140.0, 140.1, 141.6, 153.3, 156.4. MS (70
eV, EI) m/z (I%) ) 866 (M+., 100), 433 (80). ESI+ HRMS: calcd
for C58H42S4 866.21694; found 866.2168. UV-vis (CH2Cl2): λmax
) 452 nm.
Acknowledgment. The Conseil Ge´ne´ral of Maine and Loire
and the city of Angers are acknowledged for providing a Ph.D.
grant for L.P. and Y.N., respectively. The authors thank the
Service Central d′Analyses Spectroscopiques de l’Universite´
d’Angers for the characterization of organic compounds.
1
determined by H NMR. This crude product was used in the next
step without further purification.
5,5′-Bis(4,4-di-p-tolyl-4H-indeno[1,2-b]thien-2-yl)-2,2′-bithio-
phene (Tol-4T). A mixture of 5,5′-dibromo-2,2′-bithiophene 11
(0.19, 0.59 mmol) and stannyl derivative 19 (0.77 g, 80% pure,
1.20 mmol) in anhydrous toluene (30 mL) was nitrogen degassed
for 15 min before addition of Pd(PPh3)4 (0.17 g, 0.15 mmol). The
reaction mixture was refluxed for 21 h under an inert atmosphere.
After concentration under reduced pressure, the resulting residue
was subjected to two successive column chromatographies on silica
gel (eluent, cyclohexane/CH2Cl2 90:10) to give a orange-red solid,
which was further recrystallized from a mixture of CH2Cl2 and
EtOH leading to Tol-4T as an orange-red crystalline powder (0.27
Supporting Information Available: Synthetic procedures
for compounds 2-5, 17, and 18; thermal stability data for 4T,
Oct-4T, and Tol-4T; MALDI-TOF mass spectra of 4T; cyclic
voltammograms of 2T and Tol-4T; absorption and emission
spectra of Tol-4T; emission spectrum of a film of Oct-4T;
transfer characteristic and log(IDS) vs VG plot of an OFET based
on 4T; 1H and 13C NMR spectra of new compounds; and
crystallographic data for Tol-4T presented in CIF format. This
material is available free of charge via the Internet at
http://pubs.acs.org.
1
g, 53% yield). Mp 212-214 °C. H NMR (500 MHz, CDCl3): δ
3
3
2.30 (s, 12H), 7.03 (d, 2H, J ) 4.1 Hz), 7.05 (d, 8H, J ) 8.2
Hz), 7.07 (d, 2H, 3J ) 4.1 Hz), 7.08 (s, 2H), 7.13 (d, 8H, 3J ) 8.3
JO802028N
1064 J. Org. Chem. Vol. 74, No. 3, 2009