Synthesis and structural, electronic, and optical properties of oligo(thienylfuran)s in comparison with oligothiophenes and oligofurans

Article abstract of DOI:10.1021/jo048282z

(Chemical Equation Presented) Alternate thiophene/furan oligomers having four and six heterocycles, i.e., oligo(thienylfuran) dimer and trimer 2 (n = 4 and 6), were newly synthesized by repetitive Stille coupling reactions. The structural, electronic, and optical properties of these oligomers were investigated by X-ray crystallography (for n = 4), cyclic voltammetry (CV), UV-vis and fluorescence spectroscopy, and DFT calculations, and the results were compared with those of corresponding oligothiophenes (1) and oligofurans (3). The inter-ring torsional energy profiles calculated for bithiophene 1 (n = 2), thienylfuran 2 (n = 2), and bifuran 3 (n = 2) at the B3LYP/6-31G(d) level indicated that the most stable conformers of 2 (n = 2) and 3 (n = 2) are fully coplanar with transoid structure while that of 1 (n = 2) is twisted with a dihedral angle of 158°. In accord with this, X-ray crystallographic analysis of 2 (n = 4) revealed that the π-conjugated system is nearly planar with the inter-ring C=C-C=C dihedral angles between the thiophene and furan rings of 173.6(7)°, -177.0(7)°, and 172.6(6)°. In the packing structure, these nearly planar molecules are arranged in a herringbone pattern. The CV on a series of oligo(thienylfuran)s 2 showed irreversible oxidation peaks at +0.90, +0.42, and +0.29 V vs Fc/Fc⁺ for n = 2, 4, and 6, which were 0.15-0.18 V lower than those for corresponding oligothiophenes 1 and were closer to those for oligofurans 3. On the other hand, the UV-vis spectra of 2 showed the longest wavelength absorption to be almost identical with those of the corresponding 1, and more bathochromically shifted than those of the corresponding 3. The results of CV and UV-vis measurements were supported by DFT calculations (B3LYP/ 6-311+G(2d,p)//B3LYP/6-31G(d)). Thus, oligo(thienylfuran)s 2 have HOMOs which are higher than those of oligothiophenes 1 and close to those of 3, and HOMO-LUMO gaps which are close to those of 1 and smaller than those of 3. In fluorescence spectra, the quantum yield of 2 increased with elongation of the π-system (n = 2 (3.5%), 4 (19%), 6 (24%)).

Full text of DOI:10.1021/jo048282z

Synthesis and Structural, Electronic, and Optical Properties of
Oligo(thienylfuran)s in Comparison with Oligothiophenes and
Oligofurans
Yasuo Miyata, Tohru Nishinaga, and Koichi Komatsu*
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
komatsu@scl.kyoto-u.ac.jp
Received September 29, 2004
Alternate thiophene/furan oligomers having four and six heterocycles, i.e., oligo(thienylfuran) dimer
and trimer 2 (n ) 4 and 6), were newly synthesized by repetitive Stille coupling reactions. The
structural, electronic, and optical properties of these oligomers were investigated by X-ray
crystallography (for n ) 4), cyclic voltammetry (CV), UV-vis and fluorescence spectroscopy, and
DFT calculations, and the results were compared with those of corresponding oligothiophenes (1)
and oligofurans (3). The inter-ring torsional energy profiles calculated for bithiophene 1 (n ) 2),
thienylfuran 2 (n ) 2), and bifuran 3 (n ) 2) at the B3LYP/6-31G(d) level indicated that the most
stable conformers of 2 (n ) 2) and 3 (n ) 2) are fully coplanar with transoid structure while that
of 1 (n ) 2) is twisted with a dihedral angle of 158°. In accord with this, X-ray crystallographic
analysis of 2 (n ) 4) revealed that the π-conjugated system is nearly planar with the inter-ring
CdC-CdC dihedral angles between the thiophene and furan rings of 173.6(7)°, -177.0(7)°, and
1
72.6(6)°. In the packing structure, these nearly planar molecules are arranged in a herringbone
pattern. The CV on a series of oligo(thienylfuran)s 2 showed irreversible oxidation peaks at +0.90,
+
+
0.42, and +0.29 V vs Fc/Fc for n ) 2, 4, and 6, which were 0.15-0.18 V lower than those for
corresponding oligothiophenes 1 and were closer to those for oligofurans 3. On the other hand, the
UV-vis spectra of 2 showed the longest wavelength absorption to be almost identical with those
of the corresponding 1, and more bathochromically shifted than those of the corresponding 3. The
results of CV and UV-vis measurements were supported by DFT calculations (B3LYP/
6
-311+G(2d,p)//B3LYP/6-31G(d)). Thus, oligo(thienylfuran)s 2 have HOMOs which are higher than
those of oligothiophenes 1 and close to those of 3, and HOMO-LUMO gaps which are close to those
of 1 and smaller than those of 3. In fluorescence spectra, the quantum yield of 2 increased with
elongation of the π-system (n ) 2 (3.5%), 4 (19%), 6 (24%)).
Introduction
Oligothiophenes have attracted considerable attention
as the active component of organic electronic devices.
Particularly, R-oligothiophenes (1) and their R-alkylated
derivatives are among the most intensively investigated
2
organic materials for light-emitting diodes (LED) and
1-3
field-effect transistors (FET).2 For construction of these
devices with oligothiophenes 1 (n ) 6 and 8), which are
the well-investigated oligothiophenes, high-vacuum depo-
-5
(1) For recent reviews, see: (a) Hotta, S. In Handbook of Organic
Conductive Molecules and Polymers: Nalwa, H. S., Ed.; Wiley: Chich-
ester, UK, 1997; Vol. 2, Chapter 8. (b) Ba u¨ erle, P. In Electronic
Materials: The Oligomeric Approach; M u¨ llen, K., Wegner, G., Eds.;
Wiley-VCH: Weinheim, Germany, 1998; Chapter 2. (c) Handbook of
Oligo- and Polythiophenes; Fichou, D., Ed.; Wiley-VCH: Weinheim,
Germany, 1999. (d) Otsubo, T.; Aso, Y.; Takimiya, K. Bull. Chem. Soc.
Jpn. 2001, 74, 1789.
(4) (a) Garnier, F.; Hajlaoui, R.; Yassar, A.; Srivastava, P. Science
1994, 265, 1684. (b) Sirringhaus, H.; Tessler, N.; Friend, R. H. Science
1998, 280, 1741. (c) Waldauf, C.; Schilinsky, P.; Perisutti, M.; Hauch,
J.; Brabec, C. J. Adv. Mater. 2003, 15, 2084. (d) Murphy, A. R.; Fr e´ chet,
J. M. J.; Chang, P.; Lee, J.; Subramanian, V. J. Am. Chem. Soc. 2004,
126, 1596. (e) Ong, B. S.; Wu, Y.; Liu, P.; Gardner, S. J. Am. Chem.
Soc. 2004, 126, 3378.
(
(
2) Fichou, D. J. Mater. Chem. 2000, 10, 571.
3) (a) Dodabalapur, A.; Torsi, H.; Katz, H. E. Science 1995, 268,
2
70. (b) Horowitz, G.; Hajlaoui, M. E. Adv. Mater. 2000, 12, 1046.
1
0.1021/jo048282z CCC: $30.25 © 2005 American Chemical Society
Published on Web 01/15/2005
J. Org. Chem. 2005, 70, 1147-1153
1147

Miyata et al.
sition is typically utilized because of their insolubility.
The improvement of solubility of these organic materials
is quite important because it can provide the possibility
4
of low-cost processing of thin films by spin coating and
5
inkjet printing. The introduction of appropriate substit-
uents to thiophene rings is one approach to increase the
solubility of oligothiophenes, and recently high-perfor-
mance FETs have been demonstrated by using such
4
d
4b,e
soluble oligo- and polythiophenes.
As another ap-
proach, replacement of sulfur atoms of some of the
thiophene units by other heteroatoms may also be useful.
As such, mixed π-conjugated oligomers made of
thiophenes and other five-membered heterocycles such
6
6e,7
8
9
as furan, pyrrole, silole, and phosphole have recently
been investigated. Hucke and Cava have synthesized
oligomers composed of alternately connected furan and
thiophene rings, but their detailed properties have not
been fully examined except for UV-vis and electrochemi-
cal data. Compared with oligothiophenes 1, the solubil-
ity of these furan-containing oligomers is significantly
enhanced. Therefore, further comparison of the structural
and electronic properties of these “heterooligomers” with
FIGURE 1. Inter-ring torsional energy profiles for 1 (n ) 2)
(
(
red), 2 (n ) 2) (green), and 3 (n ) 2) (blue) (B3LYP/6-31G-
d)).
features and electronic and optical properties, including
absorption and emission, as well as redox properties,
were investigated by means of X-ray crystallographic
study, theoretical calculations, cyclic voltammetry, and
UV-vis and fluorescence spectroscopy. The results are
discussed in comparison with the properties of corre-
sponding oligothiophenes 1 and oligofurans 3.
6c
“
3
homooligomers” such as oligothiophene 1 and oligofuran
appears important to explore the potential of these
oligomers for the use in electronic devices. The mixed
thiophene/furan oligomers so far reported consist of an
odd number of five-membered rings,6 and no series of
oligomers with an even number has been reported.
Results and Discussion
c
Synthesis. In general, the functionalization involving
halogenation and lithiation of the C-H bonds at the R-
position in the π-conjugated oligomers of five-membered
heterocycles becomes less regio-selective with extension
of the chain length.6
c,10
Thus, a TMS group was used to
protect one side for the selective bromination of the other
11
and also as a “tag” for selective iodination at this position.
As shown in Scheme 1, silylated thienylfuran 5 pre-
pared by Stille coupling of 2-bromo-5-(trimethylsilyl)-
thiophene12 with 2-(trimethylstannyl)furan in the pres-
In this paper, we report synthesis and fundamental
electronic properties of oligo(thienyfuran)s 2 with an even
number of five-membered-ring heterocycles (n ) 2, 4, 6).
These were synthesized by repetitive oligomerization,
using Stille cross-coupling reactions. Then, the structural
13
14
ence of copper(II) oxide was brominated by NBS in the
presence of a catalytic amount of benzoyl peroxide (BPO)
in toluene to give 6 (n ) 2) in 92% yield. Then, the TMS
group of 6 (n ) 2) was transformed into an iodo group
with ICl to give 7, while the bromo group of 6 (n ) 2)
was transformed into a stannyl group by lithiation
followed by addition of trimethyltin chloride to give 8 (n
) 2). Iodide 7 was quite unstable and was immediately
used in the next cross-coupling reaction without purifica-
tion. The cross-coupling reaction of 7 and 8 was carried
out without copper(II) oxide, because the reaction was,
otherwise, too fast to be controlled for the selective
formation of 6 (n ) 4). Debromination and desilylation
of 6 (n ) 4) afforded thienylfuran dimer 2 (n ) 4) as a
yellow solid. By the coupling reaction carried out simi-
larly above, 6 (n ) 6) was synthesized in 37% yield, from
which was obtained thienylfuran trimer 2 (n ) 6) as an
orange solid by debromination and desilylation.
(5) (a) Sirringhaus, H.; Kawase, T.; Friend, R.; Shimoda, T.; In-
basekaran, M.; Wu, W.; Woo, E. Science 2000, 290, 2123. (b) Speakman,
S. P.; Rozenberg, G. G.; Clay, K. J.; Milne, W. I.; Ille, A.; Gardner, I.
A.; Bresler, E.; Steinke, J. Org. Electron. 2001, 2, 65.
(
6) (a) Chen, L.-H,; Wang, C.-Y.; Luo, T.-M. H. Heterocycles 1994,
3
8, 1393. (b) Parakka, J. P.; Cava, M. P. Synth. Met. 1995, 68, 275. (c)
Hucke, A.; Cava, M. P. J. Org. Chem. 1998, 63, 7413. (d) Garzino, F.;
Meou, A.; Brun, P. Helv. Chim. Acta 2002, 85, 1989. (e) Seixas de Melo,
J.; Elisei, F.; Becker, R. S. J. Chem. Phys. 2002, 117, 4428.
(7) (a) Groenendaal, L.; Niziurski-Mann, R. E.; Cava, M. P. Adv.
Mater. 1993, 5, 547. (b) Kozaki, M.; Parakka, J. P.; Cava, M. P.
Tetrahedron Lett. 1995, 36, 6835. (c) van Haare, J. A. E. H.;
Groenendaal, L.; Peerlings, H. W. I.; Havinga, E. E.; Vekemans, J. A.
J. M.; Janssen, R. A. J.; Meijer, E. W. Chem. Mater. 1995, 7, 1984. (d)
Peerlings, H. W. I.; Havinga, E. E.; Vekemans, J. A. J. M.; Meijer, E.
W. Synth. Met. 1995, 69, 467. (e) Parakka, J. P.; Jeevarajan, J. A.;
Jeevarajan, A. S.; Kispert, L. D.; Cava, M. P. Adv. Mater. 1996, 8, 54.
(
3
f) Kozaki, M.; Parakka, J. P.; Cava, M. P. J. Org. Chem. 1996, 61,
657.
8) (a) Tamao, K.; Yamaguchi, S.; Ito, Y.; Matsuzaki, Y.; Yamabe,
(
T.; Fukushima, M.; Mori, S. Macromolecules 1995, 28, 8668. (b) Tamao,
K.; Uchida, M.; Izumizawa, T.; Furukawa, K.; Yamaguchi, S. J. Am.
Chem. Soc. 1996, 118, 11974. (c) Yamaguchi, S.; Goto, T.; Tamao, K.
Angew. Chem., Int. Ed. 2000, 39, 1695. (d) Zhang, G.; Ma, J.; Jiang,
Y. Macromolcules 2003, 36, 2130.
In contrast to the intractably low solubility of oligoth-
iophene 1 (n ) 6), oligo(thienylfuran) 2 (n ) 6) is readily
(10) Eachern, A. M.; Soucy, C.; Leitch, L. C.; Arnason, J. T.; Morand,
P. Tetrahedron 1988, 44, 2403.
(
9) (a) Hay, C.; Fischmeister, C.; Hissler, M.; Toupet, L.; Reau, R.
Angew. Chem., Int. Ed. 2000, 39, 1812. (b) Hay, C.; Hissler, M.;
Fischmeister, C.; Rault-Berthelot, J.; Toupet, L.; Nyulaszi, L.; Reau,
R. Chem. Eur. J. 2001, 7, 4222. (c) Delaere, D.; Nguyen, M. T.;
Vanquickenborne, L. G. J. Phys. Chem. A 2003, 107, 838. (d) Hay, C.;
Fave, C.; Hissler, M.; Rault-Berthelot, J.; Reau, R. Org. Lett. 2003, 5,
(11) Hensel, V.; Schl u¨ ter, A. D. Chem. Eur. J. 1999, 5, 421.
(12) Wu, R.; Schumm, J. S.; Pearson, D. L.; Tour, J. M. J. Org. Chem.
1996, 61, 6906.
(13) Pinhey, J. T.; Roche, E. G. J. Chem. Soc., Perkin Trans. 1 1988,
2415.
3
467. (e) Fave, C.; Cho, T.-Y.; Hissler, M.; Chen, C.-W.; Luh, T.-Y.;
(14) Gronowitz, S.; Bj o¨ rk, P.; Malm, J.; H o¨ rnfeldt, A.-B. J. Orga-
nomet. Chem. 1993, 460, 127.
Wu, C.-C.; Reau, R. J. Am. Chem. Soc. 2003, 125, 9254.
1148 J. Org. Chem., Vol. 70, No. 4, 2005

Oligo(thienylfuran)s
SCHEME 1
TABLE 1. Comparison of the Main Features of
TABLE 2. KS HOMO and LUMO Levels and
HOMO-LUMO Gapsa
Torsional Energy Profiles for 1 (n ) 2), 2 (n ) 2), and 3 (n
a
)
2)
HOMO-LUMO
dihedral angle (deg)
energy (kcal mol-1)
energy barrier
compd
HOMO (eV)
LUMO (eV)
gap (eV)
1 (n ) 2)
-5.84
-5.28
-5.10
-5.69
-5.14
-4.96
-5.62
-5.07
-4.89
-1.60
-2.24
-2.47
-1.43
-2.04
-2.26
-1.12
-1.76
-1.99
4.24
3.04
2.63
4.26
3.10
2.70
4.50
3.31
2.90
1
1
2
(n ) 4)
(n ) 6)
(n ) 2)
trans relative cis to trans to
compd
cis
trans
to cis
trans
cis
1
2
3
(n ) 2)
(n ) 2)
(n ) 2)
30
0
0
158
180
180
-0.7
-0.1
-1.8
2.0
4.1
3.5
2.7
4.2
5.3
2 (n ) 4)
2 (n ) 6)
3 (n ) 2)
3
3
(n ) 4)
(n ) 6)
a
B3LYP/6-31G(d).
a
B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d).
soluble in common organic solvents such as dichloro-
methane and benzene in a concentration of approxi-
mately 20 mg/mL or slightly higher. Also, melting points
of 2 (n ) 4 (76.5-77.0 °C) and 6 (143.4-144.7 °C)) are
dihedral angles of the most stable cisoid conformers of 1
n ) 2), 2 (n ) 2), and 3 (n ) 2) are 30°, 0°, and 0°,
(
respectively. Again, only 1 (n ) 2) is not planar due to
the same steric reason. These results are in reasonable
agreement with the recent report on calculations for 1
significantly lower than those of corresponding oligoth-
iophenes 1 (n ) 4 (208-210 °C) and 6 (302-307 °C)).15
Theoretical Calculations. To predict differences in
the structural and electronic properties of 1, 2, and 3,
theoretical calculations were carried out at the B3LYP/
1
6
(
n ) 2) and 2 (n ) 2) at the HF/6-31G(d,p) level.
Next, Kohn-Sham (KS) HOMO and LUMO levels, and
the HOMO-LUMO gaps of 1-3 (B3LYP/6-311+G(2d,p)//
B3LYP/6-31G(d)), were calculated to give the results
summarized in Table 2. Upon comparison of analogues
with the same number of rings, the HOMO levels of oligo-
6
-31G(d) level. First, the inter-ring torsional energy
profiles of 1-3 (n ) 2) were obtained by calculating the
energy for each conformer upon changing the inter-ring
CdC-CdC torsion angle by 10° (Figure 1). From the
results shown in Figure 1 and Table 1, the most stable
conformer of 2 (n ) 2) and 3 (n ) 2) is found to be the
one with fully coplanar and transoid structure, while that
of 1 (n ) 2) is twisted with the optimized dihedral angle
of 158° (Table 1). This twisting of 1 (n ) 2) is ascribed to
the steric repulsion between the sulfur atom and a
â-hydrogen of the adjacent thiophene ring. Also, the
(
thienylfuran)s 2 are higher than those of corresponding
thiophenes 1 by 0.14-0.15 eV, while the values for
oligofurans 3 are higher than those of 2 by 0.07 eV. The
donor abilities of 2 and 3 are predicted to be higher than
that of 1. On the other hand, the HOMO-LUMO gap of 2
is quite close to that of 1, while it is smaller than that of
3
by 0.20-0.24 eV. This implies that the excitation
(
15) Katz, H. E.; Torsi, L.; Dodabalapur, A. Chem. Mater. 1995, 7,
(16) Diaz-Quijada, G. A.; Weinberg, N.; Holdcroft, S.; Pinto, B. M.
J. Phys. Chem. A 2002, 106, 1266.
2
235.
J. Org. Chem, Vol. 70, No. 4, 2005 1149

Miyata et al.
FIGURE 2. (a) Packing structure within the bc plane of 2 (n ) 4). (b) The herringbone angle and the intermolecular distances
within the ab plane of 2 (n ) 4). One of the disordered molecules is shown by an asterisk. Sulfur and oxygen atoms are shown
in red and blue, respectively.
energy of 2 is comparable to that of 1 and is smaller than
that of 3.
center of molecules is 4.62 Å, (iii) the intermolecular
distance along the a axis is 5.68 Å, and (iv) the intermo-
lecular distance along the b axis is 7.28 Å) of 2 (n ) 4)
are smaller than those of pentacene (53°, (i) 2.63 Å, (iii)
6.27 Å, and (iv) 7.78 Å)18 and of 1 (n ) 6) (65°, (i) 3 Å, (ii)
4.9 Å, (iii) the intermolecular distance along the b axis
is 6.0 Å, and (iv) the intermolecular distance along the c
axis is 7.9 Å),18 indicating a more densely packed
structure of 2 (n ) 4). In fact, the shortest intermolecular
contacts between heavy atoms were shown to be 3.32 Å
between C6 and C8 of the adjacent molecules and 3.35
Å between C7 and C8 of the adjacent molecules, both of
which are shorter than the sum of the van der Waals
Crystal Structure of Thienylfuran Dimer 2 (n )
4
). Recently, a considerable number of single crystals of
oligothiophenes were successfully obtained by sublima-
tion under a very low pressure of inert gas and their
X-ray structures were determined.2
,17
Similarly, the
single crystals of 2 (n ) 4) were obtained by sublimation
at 80 °C under a reduced pressure of nitrogen (ca. 3
mmHg) for 10 days, using an apparatus reported by
Azumi and co-workers.1 The crystal structure of 2 (n )
7e
4
) was determined by X-ray crystallography at -173 °C.
The ORTEP drawing exhibited an all-transoid and highly
planar structure (see Supporting Information). The tor-
sion angles (C3-C4-C5-C6, C7-C8-C9-C10, and C11-
C12-C13-C14) between thiophene and furan rings were
found to be 173.6(7)°, -177.0(7)°, and 172.6(6)°, respec-
tively.
2
radii of sp -carbon atoms (3.40 Å). This distance is even
smaller than the shortest intermolecular heavy atom
contact in the crystal structures of 1 (n ) 4) (C-S, 3.58
17c
Å). Thus, replacement of some of the sulfur atoms of
oligothiophene by smaller oxygen atoms seems to cause
denser packing, which would be advantageous for effec-
tive electron transfer.
In the crystal packing structure shown in Figure 2, the
molecules marked with an asterisk involved the statisti-
cal disorder along the long axis of the molecule. However,
the disordered molecules are on the same plane, and the
packing structure is in a herringbone arrangement
Electrochemistry. It has been reported that oligo-
furans 3 have lower oxidation potentials than oligoth-
iophenes 1 of the corresponding sizes, indicating that
1
7,18
21
similar to the case of oligothiophenes
as well as
HOMO levels of 3 are higher than those of 1. Then, the
18
pentacene, which has shown the best FET performance
so far. Figure 2b illustrates the herringbone packing
cyclic voltammetry (CV) of oligo(thienylfuran)s 2 was
1
9
2 2
carried out in CH Cl to compare their oxidation poten-
of 2 (n ) 4) within an ab plane of the crystal together
tials with those of 1 and 3. As summarized in Table 3,
the CV of 2 (n ) 2, 4, 6) showed irreversible oxidation
peaks at the potential of +0.90, +0.42, and +0.29 V vs
with values of the herringbone angle and the intermo-
lecular distances.1
8,20
The observed herringbone angle
+
(
50°) and the intermolecular distances ((i) the distance
Fc/Fc , respectively, which are 0.15-0.18 V lower than
between planes is 2.66 Å, (ii) the distance between the
the oxidation potentials of 1 of the corresponding sizes.
Although care must be taken because of the difference
of the solvent and reference electrode,2
1,22
there seems
(
17) (a) Horowitz, G.; Bachet, B.; Yassar, A.; Lang, P.; Demanze,
F.; Fave, J.-L.; Garnier, F. Chem. Mater. 1995, 7, 1337. (b) Kloc, Ch.;
Simpkins, P. G.; Siegrist, T.; Laudise, R. A. J. Cryst. Growth 1997,
to be a tendency that the oxidation potentials of 2 (n )
and 6) are rather closer to the values for 3 (n ) 4 and
4
1
82, 416. (c) Siegrist, T.; Kloc, Ch.; Laudise, R. A.; Katz, H. E.; Haddon,
R. C. Adv. Mater. 1998, 10, 379. (d) Antolini, L.; Horowitz, G.; Kouki,
F.; Garnier, F. Adv. Mater. 1998, 10, 382. (e) Azumi, R.; Goto, M.;
Honda, K.; Matsumoto, M. Bull. Chem. Soc. Jpn. 2003, 76, 1561.
6) than those of 1. This tendency is in agreement with
the result of DFT calculations shown in Table 2. Hucke
and Cava have reported that an oligomer with a thiophene
(
18) Cornil, J.; Beljonne, D.; Calbert, J. P.; Br e´ das, J. L. Adv. Mater.
001, 13, 1053.
19) Nelson, S. F.; Lin, Y.-Y.; Gundlach, D. J.; Jackson, T. N. Appl.
Phys. Lett. 1998, 72, 1854.
2
(
(21) Distefano, G.; Jones, D.; Guerra, M.; Favaretto, L.; Modelli, A.;
Mengoli, G. J. Phys. Chem. 1991, 95, 9746.
+
(
20) The herringbone angle and the intermolecular distances of the
(22) The value vs SCE is corrected to that vs Fc/Fc by addition of
other disordered packing structure are equal to that of the packing
structure shown in Figure 2b.
3 4 6
0.40 V (CH CN/[NBu ][PF ]). See: Connelly, N. G.; Geiger, W. E. Chem.
Rev. 1996, 96, 877.
1150 J. Org. Chem., Vol. 70, No. 4, 2005

Oligo(thienylfuran)s
FIGURE 3. (a) Electronic absorption spectra and (b) fluorescence spectra of 2 (n ) 2 (red), 4 (green), and 6 (blue)) measured in
THF.
TABLE 3. Oxidation Potential (Epa), Longest
Wavelength Absorption (λab), and Fluorescence
Wavelength (λem) of 1, 2, and 3
compd
Epa (V)a
λab (nm)
λem (nm)
362d
437, 478
b
c
1
(n ) 2)
(n ) 4)
(n ) 6)
(n ) 2)
(n ) 4)
(n ) 6)
(n ) 2)
(n ) 4)
(n ) 6)
+1.05
302
b
c
d
1
1
2
2
2
3
3
3
+0.60
390
e
c
f
d,f
+0.45
432
298
469, 510
b
g
g
+0.90
354, 358
b
387g
431, 457g
+0.42
b
g
g
+0.29
432i
484, 514
+0.67h
282
361
298, 313
i
h
i
i
+0.44
391, 413
e
399f
f
f
+0.36
436, 463
a
V vs Fc/Fc+. b In CH2Cl2. c In CHCl3: ref 23. d In dioxane; ref
f
2
4. e Predicted value based on a 1/n vs Epa plot. Predicted value
FIGURE 4. Correlation between electronic transition energies
based on a 1/n vs Emax plot. In THF. h Converted from the E vs
g
23
(
E) and inverse ring numbers (1/n) of oligothiophene 1 (red),
SCE: refs 21 and 22. i In CH3CN: ref 25.
25
oligo(thienylfuran) 2 (green), and oligofuran 3 (blue).
ring connected to the furan terminus of 2 (n ) 4) and an
oligomer with a furan ring connected to the thiophene
terminus of 2 (n ) 4) exhibit reversible and irreversible
oxidation peaks at E1/2 +0.39 V and Epa +0.35 V vs Fc/
plotted against 1/n (inverse ring number) to give the
correlations shown in Figure 4. In this plot, a linear
relationship is theoretically predicted26 and the slope
reflects the effectiveness of the π-conjugation, which
involves structural factors such as bond alternation,
planarity, and aromaticity.27 In the case of oligo(thienyl-
furan)s 2, a good linearity was observed, and the slope
+
6c,22
Fc , respectively (converted from the E vs SCE).
These
data demonstrate that oxidation potentials decrease with
an increase in the number of furan rings. Qualitatively,
oxidation potentials also decrease with an increase in the
chain length of oligomers with both even and odd
numbers of heterocycles. Thus, the irreversible oxidation
peak potential mentioned above is located between the
(
3.87) was found to be slightly larger than that (3.71) for
, and almost equivalent to that (3.86) for 3. This result
1
suggests that the π-conjugation in 2 is slightly more
effective than that in 1. This would be ascribed to the
E
pa values for 2 (n ) 4) (+0.42 V) and 2 (n ) 6) (+0.29 V)
2
8
lower aromaticity of furan than that of thiophene and/
or higher planarity of 2 than 1 as already mentioned
above. On the other hand, if we assume that the linear
plot can be extrapolated to 1/n ) 0, the longest wave-
length absorption for the poly(thienylfuran) with an
infinite chain length could be predicted to appear at λmax
observed in the present work.
Absorption and Fluorescence Spectra. The UV-
vis absorptions of oligo(thienylfuran)s 2 exhibited clear
bathochromic shift with increasing number of hetero-
cycles as shown in Table 3 and in Figure 3a. The observed
maximum absorptions are quite close to the values for
corresponding oligothiophenes 1, and bathochromically
shifted by 16-33 nm as compared with those of oligo-
furans 3 of the corresponding ring numbers. These
results indicate that HOMO-LUMO gaps of 2 are close
to those of 1 and smaller than those of 3, which is also
consistent with the results of theoretical calculations
)
556 nm (2.23 eV).
(
24) Becker, R. S.; Seixas de Melo, J.; Ma c¸ anita, A. L.; Elisei, F.
Pure Appl. Chem. 1995, 67, 9.
25) Seixas de Melo, J.; Elisei, F.; Gartner, C.; Alioisi, G. G.; Becker,
R. S. J. Phys. Chem. A 2000, 104, 6907.
26) Lahti, P. M.; Obrzut, J.; Karasz, F. E.; Macromolecules 1987,
0, 2023.
(
(
2
(
Table 2).
(
27) Fr e` re, P.; Raimundo, J.-M.; Blanchard, P.; Delaunay, J.; Rich-
To compare the effectiveness of π-conjugation in 1, 2,
omme, P.; Sauvajol, J.-L.; Orduna, J.; Garin, J.; Roncali, J. J. Org.
Chem. 2003, 68, 7254.
and 3, the values of E (π-π*-transition energy) were
(
28) (a) Bernardi, A.; Bottoni, A.; Venturini, A. J. Mol. Struct.
(
THEOCHEM) 1988, 163, 173 and references therein. (b) Schleyer, P.
(
23) van Pham, C.; Burkhardt, A.; Shabana, R.; Cunningham, D.
D.; Mark, H. B., Jr.; Zimmer, H. Phosphorus, Sulfur Silicon 1989, 46,
53.
v. R.; Freeman, P. K.; Jiao, H.; Goldfuss, B. Angew. Chem., Int. Ed.
Engl. 1995, 34, 337. (c) Delaere, D.; Nguyen, M. T.; Vanquickenborne,
L. G. Phys. Chem. Chem. Phys. 2002, 4, 1522.
1
J. Org. Chem, Vol. 70, No. 4, 2005 1151

Miyata et al.
Some furan-containing oligomers and polymers are
known to exhibit characteristic fluorescence.29 We have
examined the fluorescence spectra of 2 (n ) 2, 4, 6), and
the results are shown in Figure 3b. The maximum
emission bands (λem) of 1, 2, and 3 are summarized in
Table 3. According to the extension of the chain length,
the quantum yields of 2 were found to increase (n ) 2
2-{2-(5-trimethysilyl)thienyl}furan (5). A mixture of
1
2
2-bromo-5-(trimethylsilyl)thiophene
(5.47 g, 23.4 mmol),
Pd(PPh
3 4
) (1.35 g, 1.17 mmol), and CuO (1.86 g, 23.4 mmol)
1
4
in 60 mL of DMF was stirred at 100 °C. After 5 min, a
1
3
solution of 2-(trimethlstannyl)furan (7.56 g, 32.7 mmol) in 5
mL of DMF was added via a cannula. The mixture was stirred
at 100 °C for 1 h and then cooled to room temperature. The
precipitates were filtered off, and the volatiles of the filtrate
were removed in vacuo. The residue was purified by flash
(
(
3.5%), 4 (19%), 6 (24%)). In particular, 2 (n ) 4) and 2
n ) 6) emitted strong blue and green light, respectively.
chromatography over SiO
2
with hexane as an eluent to afford
1
5
1
(4.91 g, 94.4%) as a colorless oil: H NMR (C
6 6
D ) δ 7.30 (d,
H, J ) 3.5 Hz), 7.02 (dd, 1H, J ) 2.1, 0.9 Hz), 6.99 (d, 1H, J
Conclusion
) 3.5 Hz), 6.35 (dd, 1H, J ) 3.3, 0.9 Hz), 6.07 (dd, 1H, J )
13
3
1
.3, 2.1 Hz), 0.22 (s, 9H); C NMR (C
39.5, 135.4, 124.7, 112.3, 105.9, 0.23; HRMS (EI) calcd for
14OSSi 222.0535, found 222.0544.
Thienylfuran Monomer 2 (n ) 2). To a stirred solution
of 5 (0.462 g, 2.08 mmol) in 30 mL of wet THF was added a
THF solution of Bu NF (1.0 M, 2.2 mL, 2.2 mmol) under air.
6 6
D ) δ 150.5, 142.3, 139.7,
In summary, a series of oligo(thienylfuran) 2 (n ) 2,
4
)
, and 6) were synthesized. The crystal structure of 2 (n
11
C H
4) revealed that the π-system is almost planar with
more densely packed herringbone structure than that of
oligothiophene 1 (n ) 4). On the basis of the results of
cyclic voltammetry and electronic spectral measure-
ments, the HOMO levels of 2 were found to be close to
those of oligofuran 3 and higher than those of 1 while
the HOMO-LUMO gaps were shown to be close to those
of 1 and smaller than those of 3. These experimental
observations are in qualitative agreement with the
results of DFT calculations. Also it is to be noted that
the solubility of 2 (n ) 6) in common solvents is much
better than that of 1 (n ) 6). Thus, it is interesting to
study the FET character of 2 (n ) 4, 6), particularly
because of the denser packing of 2 (n ) 4), higher donor
ability, and better solubility than 1. The investigation
into fabrication and evaluation of such devices with oligo-
4
The reaction mixture was stirred for 15 min, quenched by
adding water (10 mL), and extracted with ether, and the
organic layer was dried over MgSO
in vacuo, and the residue was purified by column chromato-
graphy over SiO with hexane as an eluent to afford 2 (n ) 2)
(0.266 g, 85.1%) as a colorless oil: H NMR (C D ) δ 7.11 (dd,
1H, J ) 3.5, 1.2 Hz), 6.98-6.97 (m, 1H), 6.72-6.65 (m, 2H),
4
. The solvent was removed
2
1
6
6
1
3
6.25 (d, 1H, J ) 3.3 Hz), 6.03 (dd, 1H, J ) 3.3, 2.1 Hz);
C
NMR (C ) δ 150.3, 142.1, 134.6, 128.1, 124.7, 123.3, 112.2,
05.6. The H and C NMR spectral data were identical with
6
D
6
1
13
1
those of commercially available reagent.
Compound 6 (n ) 2). To a stirred solution of 5 (1.18 g,
.32 mmol) and a small portion of benzoyl peroxide in toluene
5
(
30 mL) was gradually added NBS (0.95 g, 5.32 mmol) at -10
C under air. After being stirred for 0.5 h at -10 °C, the
mixture was evaporated under reduced pressure. The residue
was subjected to flash chromatography over SiO with hexane
as an eluent to afford 6 (n ) 2) (1.48 g, 92.3%) as a colorless
°
(thienylfuran)s is currently underway.
2
Experimental Section
1
6 6
solid: mp 37.2-38.0; H NMR (C D ) δ 7.16 (d, 1H, J ) 3.6
Hz), 6.91 (d, 1H, J ) 3.6 Hz), 6.07 (d, 1H, J ) 3.3 Hz), 5.91 (d,
General Procedure. All reactions were carried out under
an argon atmosphere unless otherwise noted. THF was
distilled from sodium benzophenone ketyl. Hexane was dis-
tilled over sodium metal. Dichloromethane, carbon tetrachlo-
1
3
1
1
H, J ) 3.3 Hz), 0.20 (s, 9H); C NMR (C
38.3, 135.4, 125.0, 121.8, 114.1, 108.1, 0.16; HRMS (EI) calcd
13BrOSSi 299.9640, found 299.9650.
Compoun 6 (n ) 4). To a stirred solution of 6 (n ) 2) (2.58
g, 8.5 mmol) in CCl (70 mL) cooled at 0 °C was added a
solution of iodine monochloride in CH Cl (1.0 M, 8.6 mL, 8.6
6 6
D ) δ 152.3, 140.0,
for C11H
2 3
ride, and DMF were distilled over CaH . One drop of Et N was
added to all solvents used for the workup procedures. All
commercially available materials were of reagent grade unless
4
2
2
1
2
mmol) dropwise over 20 min. The reaction mixture was stirred
for 1 h at -10 °C and then for 4 h at room temperature. The
reaction was quenched with a 10% aqueous solution of sodium
thiosulfate (20 mL) and the mixture was extracted with
dichloromethane. The organic layer was washed with brine
otherwise noted. 2-Bromo-5-(trimethylsilyl)thiophene and
-(trimethylstannyl)furan13 were synthesized according to
2
literature procedure.
Computational Method. All calculations were conducted
30
with the Gaussian 98 programs. Geometry optimization and
calculations on inter-ring torsional energy profiles were per-
formed with the restricted Becke hybrid (B3LYP) at the
and water and dried over MgSO
in vacuo, and the residue was purified by flash chromatogra-
phy over SiO with hexane as an eluent to afford crude iodide
4
. The solvent was removed
2
6
-31G(d) level. The HOMO and LUMO levels were estimated
1
7
3
5
6 6
(2.37 g) as a yellow oil: H NMR (C D ) δ 6.68 (d, 1H, J )
at single-point calculations (B3LYP/6-311+(2d,p)), using the
.9 Hz), 6.41 (d, 1H, J ) 3.9 Hz), 5.80 (d, 1H, J ) 3.6 Hz),
.77 (d, 1H, J ) 3.6). Because of the instability, the crude 7
geometries optimized at the B3LYP/6-31G(d) levels.
was used in the next step without further purification.
(29) For example, see: (a) Saadeh, H.; Goodson, T.; Yu, L. Macro-
A solution of n-butyllithium in hexane (1.60 M, 2.8 mL, 4.48
mmol) was added dropwise to a stirred solution of 6 (n ) 2)
1.23 g, 4.08 mmol) in THF (50 mL) at -78 °C. After the
molecules 1997, 30, 4608. (b) Yang, C.; Abley, M.; Holdcroft, S.
Macromolecules 1999, 32, 6889. (c) Lee, C.-F.; Liu, C.-Y.; Song, H.-C.;
Luo, S.-J.; Tseng, J.-C.; Tso, H.-H.; Luh, T.-Y. Chem. Commun. 2002,
(
2
824.
30) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
mixture was stirred at -78 °C for 30 min, a THF solution of
trimethyltin chloride (1.0 M, 4.9 mL, 4.9 mmol) was added.
The reaction mixture was stirred at -78 °C for 1 h, and then
at room temperature overnight. To this mixture, a solution of
crude 7 in 20 mL of THF was added, followed by a solution of
(
Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.,
Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.;
Daniels, A. D.; Kubin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M.; Head-Gordon, M.; Replogle,
E. S.; Pople, J. A. Gaussian 98, revision A.5; Gaussian, Inc.: Pitts-
burgh, PA, 1998.
Pd(PPh
via cannula. The reaction mixture was stirred for 12 h at 70
C. The solvent was removed in vacuo, and the residue was
purified by column chromatography over SiO eluted with
3 4
) (0.49 g, 0.43 mmol) in 20 mL of THF both added
°
2
2 2
hexane-CH Cl (9:1) to afford 6 (n ) 4) (1.16 g, 63.3%) as a
yellow solid. An analytically pure sample was obtained by
1
recrystallization from hexane: mp 100.1-100.5 °C; H NMR
1152 J. Org. Chem., Vol. 70, No. 4, 2005

Oligo(thienylfuran)s
(
C
6
D
6
) δ 7.31 (d, 1H, J ) 3.5 Hz), 7.03 (d, 1H, J ) 3.5 Hz),
.92 (d, 1H, J ) 3.5 Hz), 6.86 (d, 1H, J ) 3.5 Hz), 6.32 (d, 1H,
J ) 3.3 Hz), 6.22 (d, 1H, J ) 3.3 Hz), 5.98 (d, 1H, J ) 3.3 Hz),
obtained by reprecipitation from hexane and CH
2
Cl
) δ 7.14 (dd, 1H, J ) 3.5, 1.2
Hz), 7.02-6.99 (m, 5H), 6.75-6.68 (m, 2H), 6.28-6.20 (m, 5H),
2
: mp
1
6
6 6
143.4-143.7 °C; H NMR (C D
.90 (d, 1H, J ) 3.3 Hz), 0.25 (s, 9H); 13C NMR (C
49.8, 148.9, 140.0, 139.1, 135.5, 133.0, 131.6, 124.9, 124.3,
23.9, 121.9, 114.2, 108.5, 108.3, 108.1, 0.24; HRMS (FAB)
D
) δ 151.8,
13
5
1
1
6
6
6 6
6.06 (dd, 1H, J ) 3.3, 1.8 Hz); C NMR (C D ) δ 149.9, 149.6,
149.1, 149.0, 142.4, 134.0, 133.2, 132.7, 132.5, 132.4, 129.2,
128.6, 128.3, 127.6, 124.9, 124.2, 124.1, 124.0, 123.6, 112.4,
calcd for C19
H
17BrO
2
S
2
2
Si 447.9623, found 447.9627. Anal.
14 3 3
108.4, 108.3, 108.1, 106.1; HRMS calcd (FAB) for C24H O S
Calcd for C19
H
17BrO
2
S
Si: C, 50.77; H, 3.81. Found: C, 50.55;
446.0105, found 446.0101. Anal. Calcd for C24
64.49; H, 3.14. Found: C, 64.08; H, 3.29.
14 3 3
H O S : C,
H, 3.87.
Thienylfuran Dimer 2 (n ) 4). A solution of n-butyl-
lithium in hexane (1.60 M, 0.8 mL, 1.28 mmol) was added
dropwise to a stirred solution of 6 (n ) 4) (0.52 g, 1.15 mmol)
in THF (30 mL) at -78 °C. After the solution was stirred at
X-ray Structural Analysis. Single crystals suitable for
X-ray crystallography were obtained by sublimation at 80 °C
under a reduced pressure of nitrogen (ca. 3 mmHg) for 10
17e
days. Intensity data were collected at 100 K with Mo KR
-
78 °C for 30 min, the reaction was quenched with water (10
mL), and the mixture was extracted with ether and dried over
MgSO . The solvent was removed in vacuo, and the residue
was redissolved in 20 mL of wet THF. To the solution was
added a solution of Bu NF in THF (1.0 M, 1.3 mL, 1.3 mmol)
radiation (λ ) 0.71073 Å) and a graphite monochromator. The
structure was solved by direct methods (SHELXTL) and
2
4
refined by full-matrix least-squares on F (SHELXL-97). Non-
hydrogen atoms were refined anisotropically. All hydrogen
4
atoms were placed by using AFIX instructions. The Z value of
under air. The reaction mixture was stirred for 15 min,
quenched with water (10 mL), and extracted with ether, and
1
compound 2 (n ) 4) is 6 in sprite of the monoclinic P2 /n space
group because it has 1.5 nonidentical molecules in the unit
cell. Although one of them was disordered in 1:1 ratio having
a pseudocenter of symmetry in the middle of the disordered
molecules, the disorder was solved adequately by using
PART-1 instructions. The structural parameters of the disor-
dered molecules were restrained to have geometries similar
to each other by using SAME instruction. The anisotropic
temperature factors of disordered molecules were restrained
the organic layer was dried over MgSO
4
. The solvent was
removed in vacuo, and the residue was purified by column
2 2 2
chromatography over SiO eluted with hexane-CH Cl (20:1)
to afford 2 (n ) 4) (0.30 g, 87.4%) as a yellow solid. An
analytically pure sample was obtained by recrystallization
1
from hexane: mp 76.5-76.9 °C; H NMR (C
6
D
6
) δ 7.12 (dd,
1
H, J ) 3.6, 1.5 Hz), 7.01-6.97 (m, 3H), 6.74-6.67 (m, 2H),
13
6
.26-6.19 (m, 3H), 6.04 (dd, 1H, J ) 3.3, 1.8 Hz); C NMR
) δ 149.9, 149.5, 148.9, 142.3, 134.0, 133.0, 132.5, 128.3,
24.8, 124.0, 123.9, 123.5, 112.4, 108.2, 108.0, 106.0; HRMS
by using SIMU, DELU, and ISOR instructions. C16
10 2 2
H O S ;
(
C
6
D
6
3
FW ) 298.36, crystal size 0.20 × 0.05 × 0.05 mm , monoclinic
1
P2 /n, a ) 5.676(10) Å, b ) 21.665(4) Å, c ) 16.651(3) Å, â )
1
(
FAB) calcd for C16
H
10 2 2
10
O
2
S
2
298.0122, found 298.0126. Anal.
3
-3
9
4.057(3)°, V ) 2042.3(6) Å , Z ) 6, D
refinement converged to R
GOF ) 1.094.
c
) 1.456 g cm . The
Calcd for C16
H O S : C, 64.35; H, 3.35. Found: C, 64.43; H,
) 0.0852, wR ) 0.2019 (I > 2σ(I)),
1 2
3.82.
Compound 6 (n ) 6). A solution of tert-butyllithium in
Cyclic Voltammetry. Cyclic voltammetry (CV) at room
temperature was performed with use of a standard three-
electrode cell consisting of a glassy-carbon working electrode,
hexane (1.42 M, 2.85 mL, 4.05 mmol) was added dropwise to
a stirred solution of 6 (n ) 4) (203.5 mg, 0.45 mmol) in hexane
(
30 mL) at 0 °C. After the solution was stirred for 3 h at 0 °C,
3 3
a Pt-wire counter electrode, and a Ag/AgNO (CH CN) refer-
tributyltin chloride (1.3 mL, 4.6 mmol) was added. The reaction
mixture was stirred for 1 h at 0 °C, and then at room
temperature overnight.
The solvent of the mixture was removed in vacuo. To this
mixture, a solution of crude 7 (606 mg) in 20 mL of THF was
3 4
added, followed by a solution of Pd(PPh ) (126.4 mg, 0.11
ence electrode under argon atmosphere. The CV measure-
ments were carried out by using 1.0 mM solutions of samples
with tetrabutylammonium perchlorate as the supporting
electrolyte (0.1 M) in all measurements. The observed anodic
peak potentials were calibrated with ferrocene added after
each measurement.
mmol) in 20 mL of THF both added via cannula. The reaction
mixture was stirred for 17 h at 70 °C. The solvent was removed
in vacuo, and the residue was purified by flash chromatogra-
Acknowledgment. This work was supported by
Grant-in-Aid for Young Scientists ((B) No. 14740347,
and (A) No. 16685005) from the Ministry of Education,
Culture, Sports, Science, and Technology of Japan.
Computation time was provided by the Supercomputer
Laboratory, Institute for Chemical Research, Kyoto
University. The authors thank Dr. Takahiro Sasamori
2 2 2
phy over SiO eluted with hexane-CH Cl (1:4). The eluted
product was further purified by preparative GPC eluted with
toluene to afford 6 (n ) 6) (100.4 mg, 37.3%) as an orange solid.
An analytically pure sample was obtained by reprecipitation
1
from hexane and CH
2
Cl
2
: mp 147.0-147.6 °C; H NMR (C
6 6
D )
δ 7.33 (d, 1H, J ) 3.8 Hz), 7.04 (d, 2H, J ) 3.8 Hz), 7.01 (d,
H, J ) 3.8 Hz), 6.90 (d, 1H, J ) 3.8 Hz), 6.87 (d, 1H, J ) 3.8
Hz), 6.35 (d, 1H, J ) 3.6 Hz), 6.29 (d, 1H, J ) 3.6 Hz), 6.22 (d,
H, J ) 3.6 Hz), 6.19 (d, 1H, J ) 3.6 Hz), 5.98 (d, 1H, J ) 3.6
1
(Institute for Chemical Research, Kyoto University) for
his help in X-ray structural analysis, and they also
thank Mr. Teruhiko Umehara (Institute for Chemical
Research, Kyoto University) for his help in UV-vis and
fluorescence spectroscopic measurements.
1
1
3
Hz), 5.89 (d, 1H, J ) 3.6 Hz), 0.25 (s, 9H); C NMR (C
6
D
6
) δ
1
1
1
51.8, 149.8, 149.3, 149.1, 148.9, 140.5, 139.1, 135.5, 132.9,
32.8, 132.4, 131.7, 124.9, 124.4, 124.2, 124.1, 124.0, 121.9,
14.2, 108.6, 108.4, 108.3 108.2, 108,1, 0.25; HRMS (FAB) calcd
for C27
H
21BrO
3
S
3
Si 595.9605, found 595.9607. Anal. Calcd for
Si: C, 54.21; H, 3.51. Found: C, 54.06; H, 3.81.
Thienylfuran Trimer 2 (n ) 6). The procedures used for
the synthesis of 2 (n ) 4) were applied for the synthesis of 2
n ) 6). The use of 6 (n ) 6) (220 g, 0.37 mmol), n-butyllithium
in hexane (1.60 M, 0.25 mL, 0.4 mmol), and a THF solution of
Bu NF (1.0 M, 0.40 mL, 0.40 mmol) gave 2 (n ) 6) as an orange
solid (140 mg, 84.7%). An analytically pure sample was
Supporting Information Available: 1H and 13C NMR
C
27
H
21BrO
3
S
3
1
spectra of 5 and 6 (n ) 2), and H NMR spectrum of 7; X-ray
crystallographic data for crystals 2 (n ) 4); and Cartesian
coordinates and total energies for the optimized structures of
all calculated molecules. This material is available free of
charge via the Internet at http://pubs.acs.org.
(
4
JO048282Z
J. Org. Chem, Vol. 70, No. 4, 2005 1153