Derivatives of 4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9- dione: Synthesis and properties

Article abstract of DOI:10.1021/jo0704311

(Chemical Equation Presented) A new family of organic semiconducting materials (1-4) integrating the structural components of thiophene and fluorene into a single molecular entity was synthesized and characterized. Optical and electrochemical properties of these previously unknown 4,9-dihydro-s-indaceno[1, 2-b:5,6-b′]dithiophene-4,9-dione derivatives were studied in detail. These materials possess unique optical properties with the longest wavelength absorption maxima around 500-800 nm, which gradually reached a saturation limit with the total number of thiophene units approaching eight. They also display dramatic change in the redox properties with increasing conjugation chain lengths. A thin film of oligomer 3 prepared by a solution-casting method showed a well-ordered solid-state structure according to X-ray diffraction analysis.

Full text of DOI:10.1021/jo0704311

Derivatives of
4,9-Dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione: Synthesis
and Properties
Chunchang Zhao,† Yong Zhang,‡ and Man-Kit Ng*,†
Departments of Chemistry and Chemical Engineering, UniVersity of Rochester,
Rochester, New York 14627
ng@chem.rochester.edu
ReceiVed March 15, 2007
A new family of organic semiconducting materials (1-4) integrating the structural components of thiophene
and fluorene into a single molecular entity was synthesized and characterized. Optical and electrochemical
properties of these previously unknown 4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione deriva-
tives were studied in detail. These materials possess unique optical properties with the longest wavelength
absorption maxima around 500-800 nm, which gradually reached a saturation limit with the total number
of thiophene units approaching eight. They also display dramatic change in the redox properties with
increasing conjugation chain lengths. A thin film of oligomer 3 prepared by a solution-casting method
showed a well-ordered solid-state structure according to X-ray diffraction analysis.
Introduction
virtue of their electron-richness, structurally well-defined and
solution-processable oligothiophenes normally behave as hole-
transporting (p-type) semiconductors in most aforementioned
applications. The vastly rich chemistry of thiophene and its
derivatives has continued to fuel the development of new types
of oligomeric systems, especially those that possess a comple-
mentary electronic demand. A recent surge of interest in this
Organic semiconductors based on rigid and linear π-conju-
gated systems have been well-investigated owing to their
potential use as active organic semiconductor layers in a variety
of organic electronic devices.1 Among the various π-conjugated
homoaromatic and heteroaromatic systems, oligomers and
polymers derived from thiophene and its derivatives have
emerged as highly promising candidates for applications in
organic field-effect transistors,2 photovoltaic cells,3 and high-
performance charge-transporting materials4 owing to their
demonstrably high charge-carrier mobility in the solid state. By
(2) (a) Torsi, L.; Dodabalapur, A.; Rothberg, L. J.; Fung, A. W. P.; Katz,
H. E. Science 1996, 272, 1462-1464. (b) Katz, H. E.; Bao, Z.; Gilat, S. L.
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Luscombe, C.; Kavulak, D.; Frechet, J. M. J.; Kline, R. J.; McGehee, M.
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Marks, T. J. AdV. Mater. 2005, 17, 1705-1725. (f) Sirringhaus, H. AdV.
Mater. 2005, 17, 2411-2425. (g) Zen, A.; Bilge, A.; Galbrecht, F.; Alle,
R.; Meerholz, K.; Grenzer, J.; Neher, D.; Scherf, U.; Farrell, T. J. Am.
Chem. Soc. 2006, 128, 3914-3915. (h) Sun, Y.; Liu, Y.; Zhu, D. J. Mater.
Chem. 2005, 15, 53-65.
† Department of Chemistry.
‡ Department of Chemical Engineering.
(1) (a) Tour, J. M. Chem. ReV. 1996, 96, 537-554. (b) Roncali, J. Chem.
ReV. 1997, 97, 173-206. (c) Schwab, P. F. H.; Smith, J. R.; Michl, J. Chem.
ReV. 2005, 105, 1197-1279.
10.1021/jo0704311 CCC: $37.00 © 2007 American Chemical Society
Published on Web 07/18/2007
6364
J. Org. Chem. 2007, 72, 6364-6371

4,9-Dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-diones
FIGURE 1. Structures of some polycyclic diketone molecules and target molecules.
direction has resulted in the discovery of electronically comple-
mentary, n-type oligothiophene-based materials based on con-
version to the corresponding (S,S)-dioxide5 or functionalization
of the oligothiophene backbone with potent electron-withdraw-
ing perfluoroalkyl,6 pentafluorophenyl,7 or dicyanomethylene
substituents.8 These results clearly suggest that novel p-type and
n-type organic materials could be produced by introducing
electron-donating or electron-accepting functionalities into the
oligothiophene core, and interesting ambipolar behavior may
be achieved within a single multifunctional material.
Fluorene-containing compounds9 represent another important
class of aromatic system that has also received considerable
attention due to their unique photophysical properties and
feasibility for chemical modification. Fluorene and its derivatives
are rigid and planar molecules (when there is no alkyl substitu-
tion at the 9-position) that are usually associated with relatively
large band gaps and low HOMO energy levels, rendering them
highly stable toward photodegradation and thermal oxidation
during device operation. Correspondingly, organic devices
derived from fluorene-based materials generally exhibit good
device properties and desirable longevity when compared to
those fabricated from thiophene-based semiconducting materials.
The extension of the parent fluorene and of fluorenone to their
elongated analogues leads to the corresponding structurally
related indenofluorene and indenofluorene-6,12-dione family.10
These expanded and elongated conjugated systems would be
expected to lead to even more interesting electronic and optical
properties attributable to a planar and more extensively conju-
gated structure (Figure 1).
Although significant research effort has been devoted to the
design and synthesis of π-conjugated molecular systems based
on oligothiophenes and fluorene-containing derivatives as two
separate families of semiconducting materials, reports on the
integration of these structural components into a single molecular
entity are rather limited. The previously unknown 4,9-dihydro-
s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione (Figure 1, center)
appears to us as an appealing synthetic target with potentially
interesting photophysical properties owing to its unique struc-
tural feature that is highly reminiscent of indenofluorene-6,12-
dione (Figure 1, left). In this paper, we focus on the design of
a new family of soluble organic semiconducting materials based
on 4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione
derivatives, with thiophene rings replacing the two phenyl rings
in the parent indenofluorene-6,12-dione molecule (Figure 1).
To improve the solubility properties of oligomers 1-4, alkyl
groups have been introduced into the central core and/or the
terminal R-position in each oligomeric derivative. Herein, the
synthesis and characterization of the derivatives of 4,9-dihydro-
s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione along with their
unique optical and electronic properties are reported.
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Results and Discussion
Synthesis. The reactions used for the preparation of com-
pounds 1a, 1b, 2a, 2b, 3, and 4 are outlined in Schemes 1-3.
In light of the decreasing solubility of this oligomer series upon
(7) (a) Facchetti, A.; Yoon, M. H.; Stern, C. L.; Katz, H. E.; Marks, T.
J. Angew. Chem., Int. Ed. 2003, 42, 3900-3903. (b) Letizia, J. A.; Facchetti,
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J. Am. Chem. Soc. 2001, 123, 9214-9215. (b) Meng, H.; Zheng, J.;
Lovinger, A. J.; Wang, B. C.; Van Pattern, P. G.; Bao, Z. Chem. Mater.
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J. Org. Chem, Vol. 72, No. 17, 2007 6365

Zhao et al.
SCHEME 1. Synthesis of Oligomer 1a
SCHEME 2. Synthesis of Oligomer 1b
chain elongation, a hexyl side group has been introduced on
each of the terminal thienyl units in compounds 1a, 2a, 3, and
4. The key cross-coupling partners for ready access to com-
pounds 1a, 1b, 2a, 2b, and 3, namely, 4,5-dihexyl-2-tributyl-
stannylthiophene, 3-hexyl-2-trimethylsilyl-5-tributylstannylth-
iophene, and 5′-hexyl-5-tributylstannyl-2,2′-bithiophene, were
conveniently prepared from a facile lithiation of 2,3-dihexylth-
iophene, 3-hexyl-2-trimethylsilylthiophene,11a and 5-hexyl-2,2′-
bithiophene,11b respectively, with n-butyllithium in ether or
tetrahydrofuran, followed by quenching with tributyltin chloride
and aqueous workup. A two-folded palladium-catalyzed Stille
cross-coupling between methyl 2,5-diiodoterephthalate and 4,5-
dihexyl-2-tributylstannylthiophene or 3-hexyl-2-trimethylsilyl-
5-tributylstannylthiophene furnished dithienyl-substituted tereph-
thalate diesters 6 and 9 in 52 and 61% yields, respectively.
Selective removal of the TMS group on the R-position of the
(11) (a) Spivey, A. C.; Turner, D. J.; Turner, M. L.; Yeates, S. Org.
Lett. 2002, 4, 1899-1902. (b) Nicolas, Y.; Blanchard, P.; Levillain, E.;
Allain, M.; Mercier, N.; Roncali, J. Org. Lett. 2004, 6, 273-276.
6366 J. Org. Chem., Vol. 72, No. 17, 2007

4,9-Dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-diones
SCHEME 3. Synthesis of Oligomers 2a, 2b, 3, and 4
thienyl units in 9 was achieved upon treatment with trifluoro-
acetic acid (TFA, CH2Cl2, 25 °C) to afford compound 10 in
99% yield. Saponification of the resulting diesters 6 and 10
(NaOH, 9:1 v/v EtOH/H2O, reflux) smoothly provided 2,5-bis-
[2′-(4′,5′-dihexylthienyl)]terephthalic acid 7 (81%) and 2,5-bis-
[2′-(4′-hexylthienyl)]terephthalic acid 11 (93%), which were
readily transformed into the corresponding acid dichlorides 8
and 12 (oxalyl chloride, CH2Cl2, 25 °C, 12 h). Upon removal
of the volatile materials in vacuo, a Lewis acid-promoted
intramolecular Friedel-Crafts cyclization (3 equiv of AlCl3,
CH2Cl2) of 8 and 12 took place smoothly to give the hitherto
unknown conjugated diketones 1a and 1b in 88 and 63% yield,
respectively.
5-tributylstannyl-2,2′-bithiophene, respectively, to form the
corresponding oligomer 2a (79%), 2b (80%), or 3 (51%) in
acceptable yields. Dibromo intermediate 14 was obtained in a
procedure similar to that employed for 13, which was then
subjected to a cross-coupling reaction with 5′-hexyl-5-tributyl-
stannyl-2,2′-bithiophene to furnish oligomer 4 in 50% yield.
Overall, all of the new compounds synthesized exhibit good
solubility characteristics in common organic solvents such as
CH2Cl2, CHCl3, THF, toluene, and chlorobenzene under ambient
conditions.
The thermal properties of oligomers 1a, 1b, 2a, 2b, 3, and 4
were evaluated by means of thermogravimetric analyses (TGA)
under a nitrogen atmosphere at a heating rate of 10 °C/min,
and the results are summarized in Table 1 and Figure S1 in
Supporting Information. It is apparent that these materials
exhibited excellent thermal stability with decomposition tem-
peratures (corresponding to 5% weight loss) at 326 °C for 1a,
Bromination of diketone 1b (2 equiv of NBS, 1/1 v/v CHCl3/
AcOH) readily provided dibromo intermediate 13, which was
further subjected to a Stille cross-coupling with 5-hexyl-2-
tributylstannylthiophene, 2-tributylstannylthiophene, or 5′-hexyl-
J. Org. Chem, Vol. 72, No. 17, 2007 6367

Zhao et al.
TABLE 1. Some Physical Properties of Oligomers 1a, 1b, 2a, 2b,
3, and 4
displayed weak lowest-energy absorptions around 500-800 nm.
On the other hand, in 1-butanol, these absorptions were shifted
toward longer wavelengths as expected for the π-π* transition
of ketones from a nonpolar to a more polar solvent (Figure S2).
It is worth mentioning that the absorption maxima of 1a (338,
617 nm) or 2a (385, 649 nm) were observed at a slightly longer
wavelength compared to those of 1b (330 nm, 576 nm) or 2b
(380, 627 nm), indicating that the extra alkyl groups in 1a and
2a are able to exert a moderate electron-donating effect. With
the same central chromophore present in oligomers 2 and 3,
the longer conjugated chains of the oligothiophene in these
oligomers progressively resulted in longer absorption maxima
(λmax ) 617 nm for 1a, 649 nm for 2a, and 654 nm for 3) along
the series. These absorption maxima also rapidly reached a
saturation limit, as the change was 32 nm from 1a to 2a but
only 5 nm was observed from 2a to 3. It could be envisaged
that elongation with additional oligothiophene units would not
extend the longest wavelength absorption maxima to any
significant extent. As expected, continual addition of two more
thiophene units did not change the longest absorption maximum
by comparing the λmax values for 3 and 4 (Table 1), although
there was still an observable bathochromic shift for their short
wavelength absorptions (412 nm for 3 to 423 nm for 4). To
illustrate the effect of chain elongation and end capping of each
thienyl terminus with an electron-donating alkyl substituent, the
λmax for π-π* transition of the conjugated backbone was
continuously red-shifted by about 90 nm from 1b to 4. Similarly,
the weak longest wavelength absorption maxima were batho-
chromically shifted by about 80 nm and gradually reached a
saturation limit with the total number of thiophene units
approaching eight in oligomer 4.
1/2
1/2
E1
b, E2
ox
ox
oligomer
λmaxa (nm)
(V vs Fc/Fc+)
Tdd (°C)
1a
338
617
330
576
332
385
649
327
380
627
352
412
654
423
653
0.82
326
297
1b
2a
0.72c
0.63, 0.90
0.38c
396
339
2b
3
0.45
0.36
397
399
4
a Measured in dichloromethane. b Performed in Bu4NPF6/CH2Cl2 solu-
tion, V ) 100 mV/s. c Only Epc observed. d Temperature of decomposition
corresponding to 5% weight loss from TGA analysis under N2 at a heating
rate of 10 °C/min.
The absorption spectra of 1-4 essentially cover the full
ultraviolet-visible region from 280 to 800 nm, but their
absorption coefficients between 500 and 800 nm are much
smaller when compared to those in the 300-500 nm range.
These observations show that our materials are not readily
optimized to be used as efficient solar light absorbers in the
construction of organic-based solar cell devices. It is known
that oligothiophenes with additional dicyanovinyl or tricyanovi-
nyl substituents at a terminal R,ω position can dramatically shift
their absorption bands to longer wavelength with larger absorp-
tion coefficients.13 Such an alternative design strategy with
dicyanovinyl groups attached to the R,ω position of oligomers
1-4 is currently under investigation.
Electrochemical Properties. The redox properties of oligo-
mers 1-4 (measured at a concentration of 10-3 M) were
investigated by cyclic voltammetry in dichloromethane contain-
ing 0.01 M of tetrabutylammonium hexafluorophosphate as
supporting electrolyte at a scan rate of 100 mV/s at room
temperature (Table 1, Figure 3 and Figure S3). A platinum wire
was used as the working electrode. Another Pt wire was used
as the counter electrode, and Ag/AgNO3 was used as the
reference electrode. All reported potentials are calibrated against
the ferrocene/ferrocenium (Fc/Fc+) couple, which was used as
the internal standard. All oligomers displayed oxidative pro-
cesses under the experimental conditions. The data in Table 1
showed the effects of varying numbers of oligothiophene
substituents on the redox behaviors of 1-4. A clear trend of
FIGURE 2. UV-vis absorption spectra of compounds 1a, 1b, 2a,
2b, 3, and 4 in CH2Cl2.
297 °C for 1b, 396 °C for 2a, 339 °C for 2b, 397 °C for 3, and
399 °C for 4.
Optical Properties. The UV-vis absorption spectra of
oligomers 1-4 were measured in dichloromethane solutions
(Table 1, Figure 2). As shown in Figure 2, each of the thiophene-
based diketone compounds exhibits intense absorption bands
attributable to the π-π* transition of the conjugated backbone.
By increasing the number of thiophene units in the series of
oligomers 1-4, the absorption maxima (λmax) of the π-π*
transition in CH2Cl2 are bathochromically shifted from 338 nm
for 1a to 385 nm for 2a, to 412 nm for 3, and finally to 423 nm
for 4, in good agreement with the formation of a more
delocalized and extended π-conjugated system. Particularly
noteworthy is the appearance of broad absorption peaks at longer
wavelength, which can be assigned to a π-π* transition, and
the π-π* nature of this transition is supported by studying the
solvent effects.12 In cyclohexane, these diketone oligomers
(13) (a) Bader, M. M.; Custelcean, R.; Ward, M. D. Chem. Mater. 2003,
15, 616-618. (b) Pappenfus, T. M.; Burand, M. W.; Janzen, D. E.; Mann,
K. R. Org. Lett. 2003, 5, 1535-1538. (c) Pappenfus, T. M.; Chesterfield,
R. J.; Frisbie, C. D.; Mann, K. R.; Casado, J.; Miller, L. L. J. Am. Chem.
Soc, 2002, 124, 4184-4185.
(12) (a) Koster, P. B.; Runsink, J.; Janssen, M. J. J. Chem. Soc., Perkin
Trans. 2 1979, 393-397. (b) Lambert, T. L.; Ferraris, J. P. J. Chem. Soc.,
Chem. Commun. 1991, 752-754. (c) Ferraris, J. P.; Lambert, T. L. J. Chem.
Soc., Chem. Commun. 1991, 1268-1270.
6368 J. Org. Chem., Vol. 72, No. 17, 2007

4,9-Dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-diones
FIGURE 4. X-ray diffraction spectrum of the thin film of oligomer 3
deposited at room temperature and annealed at 120 °C for 4 h.
maintaining good film-forming properties, we have investigated
the solid-state structure of the thin film of oligomer 3 (cast from
chloroform solution onto Si wafer) by using a wide-angle X-ray
diffraction method (Figure 4). Sharp reflection peaks are readily
observed in the X-ray diffractogram of the annealed (120 °C,
4 h) thin film of 3. The appearance of clearly resolved and
intense diffraction peaks indicates that 3 forms a well-ordered
layered structure on the silicon wafer substrate as observed for
R,ω-dihexyloligothiophenes.15 The d-spacing obtained from the
first reflection peak at 3.85° corresponds to a value of 2.29 nm.
Conclusion
In summary, new and soluble 4,9-dihydro-s-indaceno[1,2-b:
5,6-b′]dithiophene-4,9-dione derivatives 1-4 have been syn-
thesized and characterized. The thermal, optical, and electro-
chemical properties of these oligomers have been studied in
detail. Oligomers 1-4 exhibited excellent thermal stability with
decomposition temperatures (corresponding to 5% weight loss)
at 326 °C for 1a, 297 °C for 1b, 396 °C for 2a, 339 °C for 2b,
397 °C for 3, and 399 °C for 4. These materials possess unique
optical properties with the longest energy absorption maxima
at around 500-800 nm, which reached a saturation limit with
increasing number of thiophene units. They also displayed
dramatic change in the redox properties with increasing chain
lengths, as shown by the gradual decrease of oxidative peak
potentials. In addition, this class of materials can be readily
fabricated into well-ordered thin films by solution-based
methods according to X-ray diffraction analysis.
FIGURE 3. Cyclic voltammograms of 2a, 3, and 4 (c ) 10-3 M) in
CH2Cl2 containing Bu4NPF6 (0.01 M) as supporting electrolyte at room
temperature, with a scan rate of 100 mV/s. Potentials are versus the
ferrocene/ferrocenium (Fc/Fc+) couple (internal standard).
oxidative peak potentials was observed where the oxidative
potential becomes smaller in the order of 1, 2, 3, and 4. While
an irreversible oxidation wave (E1/2 ) 0.82 V vs Fc/Fc+) was
observed for compound 1a, the elongated oligomer 2a displays
two quasi-reversible oxidation waves with their peak potentials
shifted to 0.63 and 0.90 V. Continual addition of two more
thiophene units further reduces the E1/2 value to 0.45 V for
oligomer 3. For the longest and most electron-rich oligomer 4,
the oxidative potential was finally shifted to 0.36 V. The
oxidative peak potentials decrease in the order of 1, 2, 3, and
4, which can be attributed to the enhanced π-electron delocal-
ization with continuously increasing conjugation length by
adding thiophene units.
Experimental Section
2,3-Dihexylthiophene. To a suspension of magnesium turnings
(0.98 g, 41 mmol) in 10 mL of anhydrous ether and several drops
of 1,2-dibromoethane was added a solution of 1-bromohexane
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(15) (a) Garnier, F.; Yassar, A.; Hajlaoui, R.; Hotowitz, G.; Deloffre,
F.; Servet, B.; Ries, S.; Alnot, P. J. Am. Chem. Soc. 1993, 115, 8716-
8721. (b) Moret, M.; Campione, M.; Borghesi, A.; Miozzo, L.; Sassella,
A.; Trabattoni, S.; Lotz, B.; Thierry, A. J. Mater. Chem. 2005, 15, 2444-
2449.
The feasibility of solution-processable fabrication of ordered
organic thin films on substrates is an important parameter when
evaluating organic semiconducting materials for use in low-
cost electronic devices.14 As the ultimate goal of this work is
to prepare new materials that are solution-processable while
J. Org. Chem, Vol. 72, No. 17, 2007 6369

Zhao et al.
(6.1 g, 37 mmol) in 40 mL of ether. The reaction mixture was then
refluxed for 15 h. The Grignard solution was transferred via cannula
to an addition funnel and added dropwise to a mixture of Ni(dppp)-
Cl2 (28 mg, 0.05 mmol) and 2-bromo-3-hexylthiophene (7.16 g,
29 mmol) in ether (20 mL) at 0 °C. The resulting mixture was
refluxed for 16 h, cooled to room temperature, hydrolyzed with
1 N HCl (30 mL) and 70 mL of ice water followed by extraction
with ether. The combined organic extracts were dried (Na2SO4),
and the solvent was removed in vacuo to afford a yellow oil, which
was purified by distillation under high vacuum to give 4.71 g (64%)
of analytically pure compound: 1H NMR (400 MHz, CDCl3) δ
7.02 (d, 1H), 6.81 (d, 1H), 2.71 (t, 2H), 2.50 (t, 2H), 1.66-1.50
(m, 4H), 1.41-1.26 (m, 12H), 0.91-0.88 (m, 6H); 13C NMR
(100 MHz, CDCl3) δ 138.7, 137.6, 128.6, 120.8, 31.9, 31.7, 31.6,
30.8, 29.2, 28.9, 28.2, 27.7, 22.6, 22.5, 14.0; HRMS (ESI) calcd
for C16H28S: 252.1906. Found: 252.1915.
4,5-Dihexyl-2-tributylstannylthiophene (5). To a stirred solu-
tion of 2,3-dihexylthiophene (2.52 g, 10 mmol) in 35 mL of
anhydrous ether at 0 °C was added dropwise a solution of n-BuLi
(2.5 M, 5.2 mL). The resulting solution was stirred for 20 min at
0 °C and warmed to room temperature over 30 min. The mixture
was cooled to 0 °C, and tributyltin chloride (4.89 g, 15 mmol) was
added dropwise. The resulting mixture was stirred at 0 °C for
10 min, warmed to room temperature over 30 min, poured into
water, and extracted with ether. The combined organic extracts were
washed with saturated NaCl, dried, and filtered, and the filtrate
was concentrated under reduced pressure to afford organostannane
5. This crude product was used for next step without further
purification: 1H NMR (400 MHz, CDCl3) δ 6.84 (s, 1H), 2.72 (t,
2H), 2.50 (t, 2H), 1.64-1.51 (m, 10H), 1.39-1.27 (m, 18H), 1.13-
1.06 (m, 6H), 0.92-0.82 (m, 15H).
131.2, 130.2, 52.5, 31.8, 31.8, 31.5, 29.4, 22.6, 14.1, 0.4; HRMS
(ESI) calcd for C36H54O4S2Si2: 670.3002. Found: 693.2910 [M +
Na]+.
Dimethyl 2,5-bis[2′-(4′-hexylthienyl)]-1,4-benzenedicarboxy-
late (10). To a stirred solution of 9 (6.71 g, 10 mmol) in CH2Cl2
at 0 °C was added slowly a solution of trifluoroacetic acid (2 mL)
in 20 mL of CH2Cl2. The resulting mixture was further stirred for
1 h at 0 °C, washed with water, dried over Na2SO4, and filtered,
and the filtrate was concentrated to give 5.25 g (99%) of 10: 1H
NMR (400 MHz, CDCl3) δ 7.77 (s, 2H), 6.96 (d, 2H), 6.92 (d,
2H), 3.77 (s, 6H), 2.61 (t, 4H), 1.64-1.54 (m, 4H), 1.35-1.29 (m,
12H), 0.88 (t, 6H); 13C NMR (100 MHz, CDCl3) δ 168.4, 143.7,
139.9, 133.4, 133.2, 131.4, 128.2, 121.3, 52.5, 31.6, 30.44, 30.41,
28.9, 22.6, 14.0; HRMS (ESI) calcd for C30H38O4S2: 526.2212.
Found: 527.2301 [M + H]+.
2,5-Bis[2′-(4′,5′-dihexylthienyl)]-1,4-benzenedicarboxylic acid
(7). A mixture of 6 (940 mg, 1.35 mmol) and sodium hydroxide
(216 mg, 5.4 mmol) in 27 mL of ethanol and 3 mL of water was
refluxed overnight. The solvent was evaporated under vacuum to
about half of its original volume. Water was added, and the resulting
aqueous layer was treated with HCl to obtain a solid, which was
filtered and dried to afford 730 mg (81%) of 7: 1H NMR
(400 MHz, DMSO-d6) δ 14.39 (b, 2H), 7.55 (s, 2H), 6.97 (s, 2H),
2.70 (t, 4H), 2.45 (t, 4H), 1.60-1.48 (m, 8H), 1.36-1.27 (m, 24H),
0.92-0.80 (m, 12H); 13C NMR (100 MHz, DMSO-d6) δ 169.6,
140.5, 138.9, 135.5, 134.3, 131.3, 129.7, 128.9, 31.7, 31.5, 31.4,
30.6, 28.9, 28.7, 28.0, 27.5, 22.5, 22.4, 14.4, 14.3; LRMS (APCI)
calcd for C40H58O4S2: 666.4. Found: 667.6 [M + H]+.
2,5-Bis[2′-(4′-hexylthienyl)]-1,4-benzenedicarboxylic acid (11).
Compound 11 was prepared by saponification of 10 in 93% yield
according to the procedure for 7: 1H NMR (400 MHz, DMSO-d6)
δ 13.39 (b, 2H), 7.62 (s, 2H), 7.23 (s, 2H), 7.09 (s, 2H), 2.54 (t,
4H), 1.58-1.50 (m, 4H), 1.27 (m, 12H), 1.07 (t, 6H); LRMS (APCI)
calcd for C28H34O4S2: 498.2. Found: 497.2 [M - H]-.
2,5-Bis[2′-(4′,5′-dihexylthienyl)]-1,4-benzenedicarboxylic acid
dichloride (8). A solution of 7 (360 mg, 0.54 mmol) and oxalyl
chloride (0.5 mL, 5.7 mmol) in 30 mL of dry CH2Cl2 and several
drops DMF was stirred for 12 h at room temperature. The solvent
was removed under vacuum to obtain the crude acid dichloride,
which was used for next step without further purification.
2,5-Bis[2′-(4′-hexylthienyl)]-1,4-benzenedicarboxylic acid dichlo-
ride (12). Compound 12 was prepared from 11 according to the
procedure for 8.
2,3,7,8-Tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]-
dithiophene-4,9-dione (1a). A solution of acid dichloride (380 mg,
0.54 mmol) in 30 mL of CH2Cl2 was added to a suspension of
anhydrous AlCl3 (216 mg, 1.62 mmol) in 10 mL of CH2Cl2 at 0
°C. The resulting mixture was further stirred for 20 min, then at
room temperature for 3 h. The reaction mixture was poured into
ice water and 1 M hydrochloric acid and extracted with CH2Cl2,
dried over Na2SO4, filtered, and the solvent was removed in vacuo.
The crude product was purified by flash chromatography (silica
gel, eluent: hexane/CH2Cl2 ) 5:1) to afford 300 mg (88%) 1a:
1H NMR (400 MHz, CDCl3) δ 7.06 (s, 2H), 2.70 (t, 4H), 2.62 (t,
4H), 1.65-1.56 (m, 8H), 1.40-1.26 (m, 24H), 0.97-0.90 (m, 12H);
13C NMR (100 MHz, CDCl3) δ 187.0, 154.7, 1444.9, 140.2, 139.9,
139.4, 135.2, 113.5, 31.6, 31.58, 31.5, 30.0, 29.1, 28.8, 28.1, 26.3,
22.6, 22.5, 14.03, 14.0; HRMS (ESI) calcd for C40H54O2S2:
630.3560. Found: 630.3558.
3,8-Dihexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-
4,9-dione (1b). Compound 1b was prepared from acid chloride 12
in 63% yield according to the procedure for 1a: 1H NMR
(400 MHz, CDCl3) δ 7.19 (s, 2H), 6.80 (s, 2H), 2.72 (t, 4H), 1.67-
1.62 (m, 4H), 1.37-1.28 (m, 12H), 0.88 (t, 6H); 13C NMR
(100 MHz, CDCl3) δ 186.4, 158.3, 140.8, 140.5, 139.5, 139.4,
124.4, 114.2, 31.5, 29.3, 28.9, 28.3, 22.5, 14.0; HRMS (ESI) calcd
for C28H30O2S2: 462.1682. Found: 462.1688.
3-Hexyl-2-trimethylsilyl-5-tributylstannylthiophene. This com-
pound was prepared form 3-hexyl-2-trimethylsilylthiophene ac-
cording to the procedure for 5: 1H NMR (400 MHz, CDCl3) δ
7.07 (s, 1H), 2.70 (t, 2H), 1.58-1.36 (m, 8H), 1.35-1.29 (m, 12H),
1.10-1.08 (m, 6H), 0.91-0.87 (m, 12H), 0.33 (s, 9H).
5′-Hexyl-5-tributylstannyl-2,2′-bithiophene. This compound
was prepared form 5-hexyl-2,2′-bithiophene according to the
procedure for 5: 1H NMR (400 MHz, CDCl3) δ 7.21 (d, 1H), 7.03
(d, 1H), 6.97 (d, 1H), 6.66 (d, 1H), 2.77 (t, 2H), 1.67-1.53 (m,
8H), 1.39-1.26(m, 12H), 1.12-1.08(m, 6H), 0.97-0.86 (m, 12H).
Dimethyl 2,5-bis[2′-(4′,5′-dihexylthienyl)]-1,4-benzenedicar-
boxylate (6). Dimethyl 2,5-diido-1,4-benzenedicarboxylate
(1.115 g, 2.5 mmol) was added to a solution of 5 (5.41 g, 10 mmol)
in anhydrous DMF (30 mL), and the resulting mixture was purged
with N2 for 30 min. A mixture of Pd(PPh3)2Cl2 (53 mg, 0.075 mmol)
and PPh3 (40 mg, 0.15 mmol) was then added, and the reaction
mixture was heated to 100 °C overnight. Excess DMF was removed
under high vacuum, and the residue was dissolved in ethyl acetate
and treated with 10% aqueous KF. The mixture was filtered through
a pad of Celite. The filtrate was dried over Na2SO4, filtered, and
the solvent removed in vacuo. The crude product was purified by
flash chromatography (silica gel, eluent: hexane/CH2Cl2 ) 7:1) to
afford 0.9 g (52%) of 6: 1H NMR (400 MHz, CDCl3) δ 7.69 (s,
2H), 6.79 (s, 2H), 3.77 (s, 6H), 2.72 (t, 4H), 2.48 (t, 4H), 1.67-
1.58 (m, 8H), 1.41-1.26 (m, 24H), 0.97-0.95 (m, 12H); 13C NMR
(100 MHz, CDCl3) δ 168.9, 140.8, 138.5, 135.6, 133.0, 132.7,
130.9, 128.4, 52.4, 31.7, 31.7, 31.6, 30.8, 29.1, 28.9, 28.2, 27.9,
22.6, 22.5, 14.0; HRMS (ESI) calcd for C42H62O4S2: 694.4084.
Found: 694.4089.
Dimethyl 2,5-bis[2′-(4′-hexyl-5′-trimethylsilylthienyl)]-1,4-
benzenedicarboxylate (9). Compound 9 was prepared by the
coupling of dimethyl 2,5-diido-1,4-benzenedicarboxylate with
3-hexyl-2-trimethylsilyl-5-tributylstannylthiophene in 61% yield
according to the procedure for 6: 1H NMR (400 MHz, CDCl3) δ
7.76 (s, 2H), 7.01 (s, 2H), 3.77 (s, 6H), 2.65 (t, 4H), 1.66-1.54
(m, 4H), 1.40-1.31 (m, 12H), 0.90 (t, 6H), 0.34 (s, 18H); 13C NMR
(100 MHz, CDCl3) δ 168.6, 150.8, 144.0, 134.8, 133.1, 132.9,
2,7-Dibromo-3,8-dihexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]-
dithiophene-4,9-dione (13). To a solution of 1b (925 mg, 2 mmol)
6370 J. Org. Chem., Vol. 72, No. 17, 2007

4,9-Dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-diones
in 60 mL of CHCl3/AcOH (1:1) was added N-bromosuccinimide
(NBS) (818 mg, 4.6 mmol) in small portions at room temperature
and stirred for 12 h. The reaction mixture was poured into water
and extracted with CHCl3. The combined organic layers were
washed with saturated NaHCO3, Na2S2O3, water, and dried over
anhydrous Na2SO4. The solvent was removed in vacuo to afford
1.24 g (100%) of 13, which was pure enough for the next step: 1H
NMR (400 MHz, CDCl3) δ 7.16 (s, 2H), 2.71 (t, 4H), 1.62-1.58
(m, 4H), 1.37-1.30 (m, 12H), 0.88 (t, 6H); 13C NMR (100 MHz,
CDCl3) δ 185.3, 156.3, 139.6, 139.46, 139.45, 137.9, 114.5, 113.3,
31.5, 28.9, 28.8, 27.2, 22.6, 14.1; HRMS (ESI) calcd for C28H28O2S2-
Br2: 617.9892. Found: 617.9895.
3,8-Dihexyl-2,7-bis[2′-(5′-hexylthienyl)]-4,9-dihydro-s-indaceno-
[1,2-b:5,6-b′]dithiophene-4,9-dione (2a). To a solution of 13
(410 mg, 0.66 mmol) in 50 mL of toluene/DMF (4:1) was added
5-hexyl-2-(tributylstannyl)thiophene (905 mg, 1.98 mmol), and the
resulting mixture was purged with N2 for 30 min. A mixture of
Pd(PPh3)2Cl2 (28 mg, 0.04 mmol) and PPh3 (21 mg, 0.08 mmol)
was then added, and the reaction mixture was heated to 100 °C for
36 h. Excess solvent was removed under high vacuum The crude
product was purified by flash chromatography (silica gel, eluent:
hexane/CH2Cl2 ) 5:1) to get 330 mg (79%) of 2a: 1H NMR
(400 MHz, CDCl3) δ 7.15 (s, 2H), 6.96 (d, 2H), 6.75 (d, 2H), 2.87-
2.80 (t, 8H), 1.72-1.54 (m, 8H), 1.40-1.26 (m, 24H), 0.92-0.86
(m, 12H); 13C NMR (100 MHz, CDCl3) δ 186.7, 155.2, 147.4,
140.5, 140.3, 139.5, 136.5. 136.1, 132.0, 126.3, 124.5, 114.0, 31.5,
30.1, 29.9, 29.2, 28.7, 26.9, 22.5, 14.0; HRMS (ESI) calcd for
C48H58O2S4: 794.3314. Found: 794.3326.
was prepared by coupling of 13 with 5′-hexyl-5-tributylstannyl-
2,2′-bithiophene in 51% yield according to the procedure for 2a:
1H NMR (400 MHz, CDCl3) δ 7.17 (s, 2H), 7.04 (m, 4H), 7.01 (d,
2H), 6.70 (d, 2H), 2.90 (t, 4H), 2.80 (t, 4H), 1.70-1.65 (m, 8H),
1.40-1.37 (m, 8H), 1.33-1.29 (m, 16H), 0.91-0.87 (m, 12H);
13C NMR (100 MHz, CDCl3) δ 186.5, 155.3, 146.1, 140.7, 140.4,
139.4, 138.7, 136.5, 135.9, 133.9, 132.8, 127.0, 124.9, 123.7, 123.2,
114.1, 31.5, 30.2, 29.9, 29.2, 28.8, 27.1, 22.6, 22.6, 14.09, 14.07;
HRMS (ESI) calcd for C56H62O2S6: 958.3069. Found: 958.3080.
3,8-Dihexyl-2,7-bis[2′-(5′-bromothienyl)]-4,9-dihydro-s-in-
daceno[1,2-b:5,6-b′]dithiophene-4,9-dione (14). Compound 14 was
prepared from 2b in 89% according to the procedure for 13: 1H
NMR (400 MHz, CDCl3) δ 7.20 (s, 2H), 7.05 (d, 2H), 6.91 (d,
2H), 2.83 (t, 4H), 1.64-1.52 (m, 4H), 1.40-1.35 (m, 4H), 1.31-
1.29 (m, 8H), 0.91-0.87 (m, 6H).
2,7-Bis[2′-(5′′′-hexyl-5′,2′′;5′′,2′′′-terthienyl)]-3,8-dihexyl-4,9-
dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione (4). Com-
pound 4 was prepared by coupling of 14 with 5′-hexyl-5-
tributylstannyl-2,2′-bithiophene in 50% yield according to the
procedure for 2a: 1H NMR (400 MHz, CDCl3) δ 7.11 (s, 2H),
7.04 (d, 2H), 7.03 (d, 2H), 7.01 (d, 2H), 6.97-6.95 (m, 4H), 6.66
(d, 2H), 2.88 (t, 4H), 2.77 (t, 4H), 1.69-1.54 (m, 8H), 1.43-1.29
(m, 24H), 0.92-0.91 (m, 12H); 13C NMR (100 MHz, CDCl3) δ
186.5, 155.4, 145.9, 140.7, 140.4, 137.8, 134.6, 134.3, 133.4, 127.0,
124.9, 124.5, 123.6, 123.5, 114.1, 31.5, 30.2, 29.9, 29.2, 28.8, 27.2,
22.61, 22.58, 14.12, 14.08, 13.98; HRMS (ESI) calcd for
C64H66O2S8: 1122.2823. Found: 1122.2784.
3,8-Dihexyl-2,7-bis(2′-thienyl)-4,9-dihydro-s-indaceno[1,2-b:
5,6-b′]dithiophene-4,9-dione (2b). Compound 2b was prepared by
coupling of 13 with 2-(tributylstannyl)thiophene in 80% yield
according to the procedure for 2a: 1H NMR (400 MHz, CDCl3) δ
7.37 (dd, 2H), 7.18 (s, 2H), 7.16 (dd, 2H), 7.09 (dd, 2H), 2.87 (t,
4H), 1.66-1.61 (m, 4H), 1.40-1.37 (m, 4H), 1.31-1.27 (m, 8H),
0.92-0.86 (m, 6H); 13C NMR (100 MHz, CDCl3) δ 186.5, 155.6,
140.5, 140.4, 139.5, 136.8, 135.8, 134.7, 127.5, 126.7, 126.3, 114.2,
31.5, 29.9, 29.2, 27.0, 22.5, 14.0; HRMS (ESI) calcd for
C36H34O2S4: 626.1436. Found: 626.1436.
Acknowledgment. We wish to thank the University of
Rochester, ACS PRF, and NYSTAR James D. Watson Inves-
tigator Program for financial support.
Supporting Information Available: List of materials and
general experimental methods; NMR spectra of the new compounds,
cyclic voltammograms, and TGA spectra. This material is available
free of charge via the Internet at http://pubs.acs.org.
2,7-Bis[2′-(5′’-hexyl-5′,2′′-bithienyl)]-3,8-dihexyl-4,9-dihydro-
s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione (3). Compound 3
JO0704311
J. Org. Chem, Vol. 72, No. 17, 2007 6371