Reactive conducting thiepin polymers

Article abstract of DOI:10.1021/jo902079j

(Chemical Equation Presented) We report the design and synthesis of annulated thiepins designed to undergo bent-to-planar transformation driven by aromatization under electrochemical control. Thiepins are conjugated seven-membered ring systems with a thioether in the macrocycle. We synthesized thermally stable thiepins that are electropolymerizable to give rise to thiepin-containing electroactive polymers. Extended thiepin systems undergo sulfur extrusion with oxidation, and this feature has utility in peroxide sensing. 2009 American Chemical Society.

Full text of DOI:10.1021/jo902079j

pubs.acs.org/joc
Reactive Conducting Thiepin Polymers
Changsik Song and Timothy M. Swager*
Department of Chemistry and Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
tswager@mit.edu
Received October 6, 2009
We report the design and synthesis of annulated thiepins designed to undergo bent-to-planar
transformation driven by aromatization under electrochemical control. Thiepins are conjugated
seven-membered ring systems with a thioether in the macrocycle. We synthesized thermally stable
thiepins that are electropolymerizable to give rise to thiepin-containing electroactive polymers.
Extended thiepin systems undergo sulfur extrusion with oxidation, and this feature has utility in
peroxide sensing.
CHART 1. Heteroepins
Introduction
We have had a long-standing interest in the design of
polymers that undergo large conformational changes in
response to an electrochemical stimulus for molecular
actuators and other mechanically responsive applications.1
A powerful driving force for such a conformational change
is the aromatization (4n ( 2 π-electrons) energy gained
from changes in the electronic configuration (oxidation or
reduction) of molecules with 4n π-electrons, which initially
prefer a bent geometry due to antiaromatic destabilization.
Cyclooctatetraene- and thianthrene-based building blocks
have been proposed for this purpose.2 We have become
interested in conjugated seven-membered ring systems
that have a heteroatom with a lone pair of electrons:
heteroepines (Chart 1). With the lone pair electrons
on the heteroatoms heteroepines can be considered to be
8π-electron heteroannulenes, which are antiaromatic acc-
Results and Discussion
Thermal Stability of Thiepins and Design of the Molecular
Scaffold. The chemistries of azepine and oxepin are well
documented,3 but thiepin chemistry is relatively rare due
to thermal instability of the parent molecule.4 Compared
to azepine and oxepin, thiepin is notoriously unstable
and the parent molecule (without any substituents) has
not been detected so far. It easily loses the sulfur atom
and furnishes a benzenoid product. Sulfur extrusion is
believed to occur by valence isomerization to the corres-
ponding thianorcaradiene, followed by the cheletropic
loss of sulfur (Scheme 1).4,5 The pronounced instability
is the result of the low activation energy of the sulfur
extrusion step.
€
ording to Huckel’s rule. Thus, heteroepines are candidates
for molecular actuators that can undergo “bent-to-planar”
transformations under redox control. In this paper, we
describe our efforts in the design of electroactive and
reactive thiepin materials.
€
(3) (a) Vogel, E.; Gunther, H. Angew. Chem., Int. Ed. 1967, 6, 385–401.
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Swager, T. M. Org. Lett. 2008, 10, 3575–3578.
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Swager, T. M. IEEE J. Oceanic Eng. 2004, 29, 692–695.
(b) Dewar, M. J. S.; Trinajstic, N. Tetrahedron 1970, 26, 4269–4267.
(c) Paquette, L. A. Angew. Chem., Int. Ed. 1971, 10, 11–20.
(4) Murata, I.; Nakasuji, K. Top. Curr. Chem. 1981, 97, 33–70.
(5) Gleiter, R.; Krennrich, G.; Cremer, D.; Yamamoto, K.; Murata, I. J.
Am. Chem. Soc. 1985, 107, 6874–6879.
DOI: 10.1021/jo902079j
r
Published on Web 11/13/2009
J. Org. Chem. 2010, 75, 999–1005 999
2009 American Chemical Society

Song and Swager
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SCHEME 1. Sulfur Extrusion of Thiepin and Its Stabilization
by Bulky Side Groups
Stable thiepins have been prepared by the addition of
annulation and steric effects (Scheme 1). When bulky groups
are introduced at the 2- and 7-positions, steric repulsion
disfavors the thianorcaradiene intermediate and the mole-
cules are thermally stable. If aromatic rings are annulated to
thiepin, a substantial resonance energy loss accompanies
valence-isomerization.4
FIGURE 1. (a) Design of an annulated thiepin polymer. (b) Geo-
metry-optimized (B3LYP, 3-21 g) structures of an annulated thiepin
in its neutral (left) and doubly oxidized (right) states.
other heteroepins,7 annulated thiophenes,8 and various aro-
matic thioethers.9 The typical source of sulfur is sulfur
dichloride or bis(phenylsulfonyl) sulfide ((PhSO2)2S). How-
ever, the drawback is the generally low yields, typically
∼30% for cyclic products.
Our design of the thiepin actuating molecular building
block makes use of a stabilized annulated system containing
two thiophenes and one benzene ring (Figure 1a). We chose
thiophene annulation due to its electrochemical stability and
ease of synthetic modification through the R-position of the
annulated thiophenes (C3 and C10). Solubilizing groups
could also be easily attached to the benzene moiety.
We calculated the optimal geometry (B3LYP, 3-21G) of the
simple dithieno[b,f]benzo[d]thiepin (Figure 1b). As expected,
the molecule of the neutral state adopts a bent geometry. The
distance between the outmost carbons (from C3 to C10) is
We first followed the same “dilithio” method starting with
bis(bromothienyl)benzene derivatives 2a-c, which were pre-
pared by selective NBS bromination of compounds 1a-c
(Scheme 2). Compounds 1a-c were synthesized starting
from catechol according to known procedures.10 The dibro-
mides 2a-c were subjected to lithiation followed by sub-
stitution with sulfur sources. We were able to isolate the
desired thiepin products 3a-c, but the yields were less than
30%. Attempts to improve the yield by varying the solvent or
temperature were not successful.
˚
∼6.8 A. The optimized geometry of the doubly oxidized
After noticing that sulfur dichloride could be a good
electrophile in the aromatic electrophilic substitution, we
tried a direct cyclization with compounds 1a-c. This route
was inspired by the preparation of 3,30-dipyrrolyl sulfides
using sulfur dichloride starting from substituted pyrroles.11
In addition, the 2-position of thiophene is highly selective
over 5-position in other electrophilic reactions (e.g.,
bromination). Fortunately, via the direct cyclization we were
able to obtain the desired thiepins in good yields. It should be
noted that sulfur dichloride needs to be freshly distilled just
prior to use because it tends to decompose relatively quickly
to sulfur monochloride (S2Cl2) and chlorine.
molecule is nearly planar presumably due to the energy gain
from its aromatic electronic structure. The distance between
the outmost carbons in the planar conformation enlarges to
˚
∼7.6 A, which is an 11% increase from the neutral state. It
should be noted, however, that the geometry calculations
(DFT) here have been conducted on molecules in a gas phase,
which therefore may produce a certain discrepancy when the
molecules are in a different environment (in solution/solid
amorphous state, for example).
Synthesis of Thiophene-Annulated Thiepins. Yasuike et al.
reported the synthesis of dithieno[b,f]thiepins via dilithium
intermediates but did not investigate any applications.6
Traditionally, annulated thiepins have been prepared by
condensation, elimination, ring expansion or rearrange-
ment, etc.4 However, Yasuike’s approach is modular, and
they were able to prepare dithienoheteroepins containing
group 14, 15, and 16 elements, including thiepins. This
“dilithio” method has been applied to the preparation of
Thiepins 3a-c are pale yellow and are crystalline
powders even with the racemic 2-ethylhexyloxy side chains.
The X-ray crystal structure of the methoxy derivative 3c
(Scheme 2) clearly shows the bent geometry at its neutral
˚
state. The distance between the outmost carbons (6.85 A)
is in good agreement with the value from the DFT cal-
culation.
In orderto examinethe effect of the substitutionpattern, we
synthesized dithieno[3,2-b;20,30-f]benzo[d]thiepin 7, which is
isomeric to 3b (Scheme 3). To incorporate bromines into the
3- and 30-positions, 4 was first tetrabrominated and then
subjected to debromination to compound 6. This route was
necessary because bromination occurs at the 5-positions first,
and moreover, lithium-bromine exchange also favors the less
sterically hindered 5-positions. Following the standard
(6) Yasuike, S.; Nakashima, F.; Kurita, J.; Tsuchiya, T. Heterocycles
1997, 45, 1899–1902.
(7) (a) Yasuike, S.; Ohta, H.; Shiratori, S.; Kurita, J.; Tsuchiya, T. J.
Chem. Soc., Chem. Commun. 1993, 1817–1819. (b) Yasuike, S.; Shiratori,
S.-i.; Kurita, J.; Tsuchiya, T. Chem. Pharm. Bull. 1999, 47, 1108–1114.
(c) Yasuike, S.; Kiharada, T.; Tsuchiya, T.; Kurita, J. Chem. Pharm. Bull.
2003, 51, 1283–1288.
(8) (a) Nenajdenko, V. G.; et al. Synthesis 2003, 124–128. (b) Nenajdenko,
V. G.; Sumerin, V. V.; Chernichenko, K. Y.; Balenkova, E. S. Org. Lett. 2004,
6, 3437–3439. (c) Rajca, A.; Miyasaka, M.; Pink, M.; Wang, H.; Rajca, S. J.
Am. Chem. Soc. 2004, 126, 15211–15222.
(9) (a) Nakayama, J.; Katano, N.; Shimura, Y.; Sugihara, Y.; Ishii, A. J.
Org. Chem. 1996, 61, 7608–7610. (b) Chahma, M.; Hicks, R. G.; Myles, D. J.
T. Macromolecules 2004, 37, 2010–2012. (c) Chahma, M.; Myles, D. J. T.;
Hicks, R. G. Chem. Mater. 2005, 17, 2672–2678.
(10) Tova, J. D.; Rose, A.; Swager, T. M. J. Am. Chem. Soc. 2002, 124,
7762–7769.
(11) Chen, Q.; Dolphin, D. Synthesis 2001, 40–42.
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SCHEME 2. Synthesis of Annulated Thiepinsa
aReagents: (i) K2CO3, 1-bromodecane, acetone, reflux, 1 d, 93%; (ii) Br2, CH2Cl2, room temperature, 2 h, 96%; (iii) 3-thiophene boronic acid, Na2CO3,
Pd(PPh3)4, toluene, EtOH, H2O, reflux, 18 h, 94%; (iv) NBS, CHCl3, acetic acid, room temperature, 89%; (v) t-BuLi, Et2O or THF, then (PhSO2)2S or
SCl2, -78 °C f room temperature, <30%; (vi) SCl2, CH2Cl2, -40 °C, 80%.
SCHEME 3. Synthesis of Isomeric Annulated Thiepin 7a
aReagents: (i) NBS (4 equiv), CHCl3, acetic acid, room temperature, 97%; (ii) n-BuLi, THF, -78 °C, 30 min, then MeOH, 90%; (iii) t-BuLi, Et2O,
(PhSO2)2S, -78 °C f room temperature, 15 h, 31%.
“dilithio” procedure we were able to obtain isomeric thiepin 7,
albeit in a low yield.
Cyclic Voltammograms of Annulated Thiepins. Figure 2
shows the cyclic voltammograms (CVs) of compounds 3c and 7.
The CVs were taken in CH2Cl2 with 0.1 M TBAPF6 as a
supporting electrolyte on a Pt button electrode with a standard
three-electrode configuration under ambient conditions.
Both CVs showed two 1-electron oxidation waves consis-
tent with the oxidation of the thiepin π-systems from 8 to
6 π-electrons. Oxidation of 7 (0.73 V) occurred at a lower
potential than 3c (0.82 V vs Fc/Fcþ, the first half potentials).
This difference can be rationalized by the positions where
electrons or charges reside in the stable canonical resonance
forms (Scheme 4). The radical in 7•þ can be benzylic and also
in the favored R-position of the thiophene, while the benzylic
radical in 3c•þ is at the β-position of the thiophenes.
The reduction waves of 3c and 7 are quite different. The
reduction from 3c2þ to 3c•þ appears as a sharp peak, which
is at a lower potential than expected. We attribute this to
the aromatic energy gain after the second oxidation (8 to
6 π-electrons). In other words, the dication 3c2þ is stabilized
by planarization and a overpotential is required to rereduce
the molecule. The reduction for 72þ was not complete at a
normal potential range, but an additional reduction peak
appeared at the very lower potential (∼-0.5 V vs Fc/Fcþ).
This type of reduction occurs only from the 72þ, not from 7•þ
as evidenced by reversing the scan after first oxidation
(Figure 2b, blue dotted line). The charge trapping observed
FIGURE 2. CVs of 3c (a) and 7 (b) in CH2Cl2 with 0.1 M TBAPF6
as a supporting electrolyte. The red dotted lines represent the first
could be the result of some reversible intermolecular chemi-
cal bonding or a solid state (aggregation) effect.
scans. The blue dotted line (b) shows the behavior when reversed
after the first oxidation wave.
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SCHEME 4. Proposed Charge Delocalization of Thiepin’s
Radical Cation
SCHEME 5. Synthesis of Electropolymerizable Thiepin
Monomersa
In short, both thiepin 3c and 7 showed two 1-electron
redox events, which are reproducible and chemically rever-
sible under the above conditions. The annulation pattern
influences the molecule’s oxidation and reduction potentials.
The sharp reduction from 3c2þ to 3c•þ is consistent with our
proposal of planarization by aromatic energy gain.
Electropolymerization of Extended Thiepins. We focused
on the molecule 3-types of thiepins ([2,3-b]-annulation),
and synthesized electropolymerizable thiepins 9 and 10 by
bromination of 3a, followed by Stille coupling reactions
(Scheme 5).
aReagents: (i) NBS, CHCl3, acetic acid, room temperature, 76%; (ii)
PdCl2(PPh3)2, DMF, 80 °C, 15 h, 78-80%.
under swept potential conditions (Figure 3a). In pure
CH2Cl2 solvent we obtained a polymer growth, but the
resulting polymers were loosely bound to the electrodes
and were washed away with any manipulation. Both mono-
mers 9 and 10 displayed a linear growth in redox currents
with each potential scan. Poly(9) and poly(10) displayed
similar behaviors characteristic of conjugated polymers,
and the electrochemical characterization of poly(9) is shown
in Figure 3. Scan-rate dependence of thin films of poly(9) in
Electropolymerizations successfully yielded thin polymer
films with monomer solutions in 1:1 mixture of CH2Cl2 and
CH3CN with 0.1 M TBAPF6 as a supporting electrolyte
FIGURE 3. (a) Electropolymerization of 9 on a Pt button electrode in a 1:1 mixture of CH2Cl2 and CH3CN. The red dotted line represents the
first scan. (b) CV (dotted line) and in situ conductivity measurement (solid line) of the film of poly(9) on a 5 μm interdigitated Pt microelectrode
in CH3CN. (c) CVs of the film of poly(9) at different scan rates. (d) Electronic absorption spectra of the film of poly(9) on an ITO-coated glass
electrode in CH3CN as a function of oxidation potential from 0.0 to 1.0 V vs Ag/Agþ. TBAPF6 (0.1 M) was used as a supporting electrolyte in
all cases.
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SCHEME 6. Sulfur Extrusion of Thiepin Polymer 11 and Model Compound 12 upon Oxidation
the monomer-free solution (CH3CN) is linear (Figure 3c),
but as the films grow thicker the peak potentials shift at
fast scan rates, suggesting limited ion diffusion. In situ
conductivity measurements revealed the maximum conduc-
tivities were ∼60-70 S/cm for both poly(9) and poly(10)
(Figure 3b). Spectroelectrochemical measurements show
very delocalized electronic structures, especially at high
doping levels (Figure 3d).
Thin electrochemically deposited films are not always easily
characterized. However, we noticed in the CVs that the redox
couple at the low potentials, ∼0.2 V for poly(9) and ∼-0.1 V
for poly(10) (all vs Fc/Fcþ), and the overall electrochemical
behavior was very similar to poly(dithienonaphthalene)s,
which were reported previously in our group by using a
tandem cyclization and polymerization mechanism.10,12 The
molecular structure of dithienonaphthalene is identical to the
structure obtained if the sulfur is extruded in the thiepins.
Moreover, after repeated redox cycling vibrational fine struc-
ture became more evident in the absorption of poly(10) in its
neutral state, which is unusual for this type of (flexible)
polymer. The above observations imply that the polymers
have changed to rigid molecular frames, presumably due to
the sulfur extrusion in the polymers.
Our sulfur extrusion hypothesis with oxidation was con-
firmed with thiepin polymers prepared via cross-coupling
chemistry and model compounds (Scheme 6). Specifically
when we measured the electroactivity of the drop-cast films
of chemically synthesized thiepin polymers (Figure 4) the
onset of the first scan (∼0.9 V) shifted irreversibly to lower
potentials (∼0.3 V, all vs Fc/Fcþ) with oxidative redox
cycling. Furthermore, upon reversing of the high potential
in the first scan, the return current crosses the trace of the
initial anodic potential sweep. This feature shows that we are
creating a species that is more easily oxidized than the parent
material and is suggestive of irreversible reactions. The
profiles of successive scans resembled those of reported
poly(dithienonaphthalene)s,12 the structures that result after
sulfur extrusion from the polymers.
FIGURE 4. CVs of a drop-cast film of polymer 11 on an ITO-
coated glass electrode in CH3CN with 0.1 M TBAPF6 as a support-
ing electrolyte. The dotted line represents the first scan.
reduction by MeOH. We were able to obtain in a high yield
the desufurized product 13, which was confirmed by NMR
and MS (Supporting Information). Thus, based on the above
results, we conclude that oxidized thiophene-annulated thie-
pins are unstable and prone to sulfur extrusion. However, it
should be noted here that as Figure 2 illustrates, thiophene-
annulated thiepins are electrochemically stable when there is
no substitution at 2,20-positions.
Properties of Thiepin 1-Oxide (Sulfoxide). The fact that
substituted annulated thiepins are labile when oxidized pre-
vented the desired electrochemical utility. However, the
sulfur extrusion from the annulated thiepins produces dithie-
nonaphthalenes, which are very rigid, stable, and lumines-
cent. As a result, we can expect a large optical signal change if
we chemically affect this transition from the bent, flexible,
and nondelocalized annulated thiepin. It is also known that
thiepin 1-oxides (sulfoxide) are less thermally stable than
thiepins,13 and even sterically or electronically stabilized
thiepin 1-oxides are easily converted to the benzenoid com-
pounds, presumably through the same valence-isomerization
sulfur-extrusion mechanism. It should be noted that unlike
thiepin 1-oxides, thiepin 1,1-dioxides (sulfones) are known
to be thermally very stable. In fact, the parent thiepin
We also observed sulfur extrusion in a substituted thiepin
model compound with oxidation by nitrosonium ion. Bis-
aryl (4-cyanophenyl)-substituted thiepin compound 12
was prepared and subject to an oxidation, followed by a
(13) (a) Schlessinger, R. H.; Ponticello, G. S. Tetrahedron Lett. 1968, 9,
3017–3020. (b) Hofmann, H.; Gaube, H. Angew. Chem., Int. Ed. 1975, 14,
812–813. (c) Yamazaki, S.; Isokawa, A.; Yamamoto, K.; Murata, I. J. Chem.
Soc., Perkin Trans. 1 1994, 2631–2635.
(12) Tova, J. D.; Swager, T. M. Adv. Mater. 2001, 13, 1775–1780.
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SCHEME 7. Synthesis of Thiepin Oxide 14 and Dithienonaphthalene 15a
aReagents: (i) m-Chloroperoxybenzoic acid, CH2Cl2, -20 °C, 1 h, 55%; (ii) 2-tributylstannylthiophene, PdCl2(PPh3)2, DMF, 80 °C, 15 h, 70%.
1,1-dioxide has been isolated as a stable compound at room
temperature.4,14
Based upon our analysis, if an initially nonemissive or
weakly emissive thiepin molecule encounters peroxides the
thiepins can be converted to thiepin 1-oxide, which will
transform rapidly into a highly fluorescent benzenoid com-
pound. Organic peroxides have been used in explosives (e.g.,
tricycloacetone peroxides or TCAP), and their detection is of
increasing importance. Thus, we decided to investigate the
potential of the annulated thiepins as peroxide sensors.
We first synthesized the thiepin 1-oxide 14 from thiepin 9
by reaction with m-chloroperoxybenzoic acid in CH2Cl2 at
low temperature (Scheme 7). With 1 equiv of peroxide,
thiepin 1,1-dioxide was also formed as a byproduct in
∼15% yield. We were able to isolate the thiepin 1-oxide 14
as a crystalline solid but it slowly decomposed at room
FIGURE 5. Time evolution (total 30 min) of emission spectra from
the oxidation of 9 (Ar = 2-thienyl) in the presence of m-chloroper-
oxybenzoic acid (excess) at room temperature in CH2Cl2 to produce
15. The excitation wavelength was 360 nm.
temperature. However, it was stable enough to be character-
ized, and we obtained a single crystal of unsubstituted
thiepin oxide 14b at -20 °C (Scheme 7).
The molecular structure of thiepin 1-oxide 14b is similar to
that of thiepin 3c with a slight increase in the distance
emission at around 400 nm. However, upon peroxide
exposure, a relatively strong emission at 430 nm emerged,
which matches dithienonaphthalene 15’s fluorescence
(Supporting Information). The fluorescence spectrum of
the intermediate thiepin oxide 14 is similar to that of thiepin
9; thus, the 430 nm fluorescence increased strictly as the
result of the formation of 15. This “turn-on” scheme can be
utilized for a peroxide sensor.
1
between the outmost carbons (6.897 vs 6.853 A). In the H
˚
NMR spectrum there were two sets of signals in a roughly
3:1 ratio, indicating two isomers are present. The X-ray
crystal structure shows the oxygen in the endo(axial)-
position. However, thiepin 1-oxide with the oxygen in the
exo(equatorial)-position is also present. An X-ray structure
of a related benzothiepin 1-oxide with sulfoxide oxygen’s
exo-position was previously reported.15 For comparison,
dithienonaphthalene 15 was prepared by Stille coupling
reaction with compound 16, which was prepared by follow-
ing the literature procedure.10
We examined the fluorescence changes when thiepin 9 was
exposed to a peroxide. In a cuvette containing a CH2Cl2
solution of 9 we added one drop of a CH2Cl2 solution
containing m-chloroperoxybenzoic acid (∼0.05 M, excess)
and monitored the increasing fluorescence intensity as time
progressed (Figure 5). Initially, thiepin 9 displayed a weak
Conclusion
We have designed and synthesized annulated thiepin
systems which undergo bent-to-planar transformation dri-
ven by aromatization under electrochemical control. In the
cyclic voltammetry, annulated thiepin (3c) showed a very
interesting sharp peak at the reduction of its dication,
suggestive of aromatic energy gains in the doubly oxidized
thiepin. Extended thiepin systems, in spite of the thermal
stability in the neutral state, were found to be unstable when
oxidized, and sulfur extrusion is observed. Such a property is
useful in peroxide sensing, and we exploited the fact that the
(14) Mock, W. L. J. Am. Chem. Soc. 1967, 89, 1281–1283.
€
(15) Hofmann, H.; Bohme, R.; Wilhelm, E. Chem. Ber. 1978, 111, 309.
1004 J. Org. Chem. Vol. 75, No. 4, 2010

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JOCFeatured Article
sulfoxide has an even lower extrusion barrier than sulfur
itself. The increased fluorescence originated from the extru-
sion products, which showed a potential as a “turn-on”
sensor for peroxides.
aqueous NH4Cl, KF, and NH4Cl again. After being dried over
MgSO4, the organic layer was evaporated under reduced pressure
and subjected to column chromatography (dichloromethane/
hexane = 1:3). The product was further purified by recrystallization
(dichloromethane/methanol). Yield: 0.270 g (78%) of pale yellow
1
solid. H NMR (400 MHz, CDCl3) δ: 7.24 (dd, 2H, J = 5.1,
Experimental Section
1.0 Hz), 7.18 (s, 2H), 7.16 (dd, 2H, J = 3.6, 1.0 Hz), 7.10 (s, 2H),
7.12 (dd, 2H, J = 5.1, 3.6 Hz), 3.95 (m, 4H), 1.82 (m, 2H),
1.57-1.34 (m, 16H), 0.99-0.91 (m, 12H). 13C NMR (125 MHz,
CDCl3) δ: 149.1, 146.0, 138.1, 136.9, 128.9, 128.1, 127.9, 125.7,
125.2, 124.5, 113.9, 71.8, 39.8, 30.8, 29.4, 24.2, 23.3, 14.3, 11.5.
HR-MS (ESI): calcd for C38H44O2S5 [M þ Na]þ 715.1837, found
715.1869.
Materials. SCl2 was synthesized from S2Cl2 with Cl2 accord-
ing to the literature method16 and freshly distilled with a few
drops of PCl3 prior to use. Anhydrous DMF was purchased
from Aldrich as Sure-Seal Bottles and used as received. THF,
anhydrous CH2Cl2, and toluene were purified by passage
through two alumina columns of an Innovative Technologies
purification system. All other chemicals were of reagent grade
and used as received.
Polymer 11. Compound 8 (0.069 g, 0.1 mmol) and hexabu-
tylditin (0.058 mL, 0.11 mmol) were dissolved in toluene
(1.5 mL) and DMF (1.5 mL). The mixture was degassed with
Ar for 40 min, and Pd(PPh3)4 (2.4 mg, 2 mol %) was added
under gentle Ar stream. The mixture was allowed to stir at
110 °C for 2 d, at which time the mixture was cooled to room
temperature and methanol was added to precipitate. The filtered
solid was redissolved in CHCl3 and added to acetone to pre-
cipitate again. The product was filtered and dried under air.
Yield: 0.041 g (78%) of crimson solid. GPC (polystyrene
6,7-Di(2-ethylhexyloxy)benzo[d]dithieno[2,3-b;30,20-f]thiepin
(3a). Freshly distilled SCl2 (2.1 mL, 16.5 mmol) in CH2Cl2
(100 mL) was added dropwise to a CH2Cl2 (450 mL) solution
of compound 1a (7.48 g, 15 mmol) at -40 °C under Ar. The
mixture was slowly warmed to room temperature and stirred
for 15 h, at which time the mixture was poured into 10%
aqueous NaHCO3. The organic layer was washed with brine,
dried over MgSO4, and evaporated under reduced pressure.
The crude mixture was subjected to column chromatography
(dichloromethane/hexane = 1:10). The product was further
purified by recrystallization (dichloromethane/methanol).
Yield: 6.04 g (76%) of lightly yellow solid. Tm = 87-89 °C.
1H NMR (500 MHz, CDCl3) δ: 7.25 (d, 2H, J = 5.5 Hz), 7.13
(d, 2H, J = 5.5 Hz), 7.05 (s, 2H), 3.96 (m, 4H), 1.82 (m, 2H),
1.57-1.34 (m, 16H), 0.94 (m, 12H). 13C NMR (125 MHz,
CDCl3) δ: 148.9, 145.3, 130.7, 129.4, 128.0, 126.4, 114.1, 71.7,
39.8, 30.8, 29.3, 24.2, 23.3, 14.3, 11.4. HR-MS (ESI): calcd for
1
standard): Mn = 6170, Mw = 7790, PDI = 1.26. H NMR
(300 MHz, CDCl3) δ: 7.15 (aromatic C-H), 7.03 (aromatic C-H),
3.95 (aliphatic C-H), 1.84-0.92 (aliphatic C-H).
6,7-Di(2-ethylhexyloxy)-3,10-bis(thiophene-2-yl)benzo[d]dithieno-
[2,3-b;30,20-f]thiepin 1-Oxide (14). To a CH2Cl2 (1 mL) solution of
9 (0.029 g, 0.042 mmol) was added m-chloroperoxybenzoic acid
(assumed as 72% purity, 0.010 g, 0.042 mmol) in CH2Cl2 (0.5 mL) at
-20 °C, and the mixture was allowed to stir for 1 h. After being
warmed to room temperature, the mixture was diluted with CH2Cl2,
and washed with saturated NaHCO3 and brine. The organic layer
was dried over MgSO4, and evaporated under reduced pressure. The
crude product was purified by column chromatography (ethyl
acetate/hexane/chloroform = 1:7:1). Yield: 0.015 g (51%) of pale
yellow solid. 1H NMR (400 MHz, CDCl3) forendo (axial) δ:7.47(s,
2H), 7.33 (dd, 2H, J = 5.1, 1.0 Hz), 7.33 (s, 2H), 7.29 (dd, 2H, J =
3.6, 1.0 Hz), 7.08 (dd, 2H, J = 5.1, 3.6 Hz), 4.16 (m, 4H), 1.90 (m,
4H), 1.53-1.27 (m, 20H), 0.90 (t, 6H, J = 6.8 Hz). For exo
(equatorial) δ: 7.28 (dd, 2H, J = 5.1, 1.0 Hz), 7.26 (s, 2H), 7.23 (dd,
2H, J = 3.6, 1.0 Hz), 7.10 (s, 2H), 7.05 (dd, 2H, J = 5.1, 3.6 Hz),
4.16 (m, 4H), 1.90 (m, 4H), 1.53-1.27 (m, 20H), 0.90 (t, 6H, J=6.8
Hz). 13C NMR (125 MHz, CDCl3) for endo (axial) δ: 149.4, 141.7,
139.3, 136.3, 135.7, 128.4, 127.1, 126.5, 125.9, 125.4, 114.0, 69.6,
32.0, 29.6, 29.5, 29.5, 26.3, 22.9, 14.3. For exo (equatorial) δ: 149.2,
139.7, 139.6, 135.2, 134.8, 128.3, 126.3, 125.9, 124.8, 118.8, 113.8,
69.6, 32.0, 29.6, 29.5, 29.5, 26.3, 22.9, 14.3. HR-MS (ESI): calcd for
C38H44O3S5 [M þ H]þ 709.1967, found 709.1979.
C
30H40O2S3 [M þ Na]þ 551.2083, found 551.2077.
6,7-Di(decyloxy)benzo[d]dithieno[3,2-b;20,30-f]thiepin (7). To a
cooled (-78 °C) Et2O (50 mL) solution of compound 6 (0.713 g,
1 mmol) was added dropwise t-BuLi (1.7 M in hexane, 2.41 mL,
4.1 mmol). The initially cloudy mixture became clear as lithia-
tion proceeded. After the mixture was stirred at -78 °C for
10 min, (PhSO2)2S was added in portions. The mixture was
allowed to stir at -78 °C for 3 h and then at room temperature
for another 12 h. After being diluted with diethyl ether, the
mixture was washed with 10% aqueous NaHCO3 and brine. The
organic layer was dried over MgSO4 and evaporated under
reduced pressure. The crude mixture was subjected to column
chromatography (chloroform/hexane = 1:7). Yield: 0.181 g
(31%) of light yellow solid. 1H NMR (400 MHz, CDCl3)
δ: 7.29 (d, 2H, J = 5.2 Hz), 7.10 (s, 2H), 6.93 (d, 2H, J = 5.2
Hz), 4.09 (m, 4H), 1.87 (m, 4H), 1.50 (m, 4H), 1.40-1.28 (m,
24H), 0.89 (t, 6H, J = 6.8 Hz). 13C NMR (125 MHz, CDCl3)
δ: 149.2, 143.2, 131.5, 130.7, 125.9, 125.8, 115.4, 69.5, 32.1, 29.9,
29.8, 29.6, 29.6, 29.4, 26.2, 22.9, 14.4. HR-MS (ESI): calcd for
C34H48O2S3 [M þ Na]þ 607.2709, found 607.2711.
Acknowledgment. This work was supported by the U.S.
Army through the Institute for Soldier Nanotechnologies
under contract with the U.S. Army Research Office.
6,7-Di(2-ethylhexyloxy)-3,10-bis(thiophene-2-yl)benzo[d]dithieno-
[2,3-b;30,20-f]thiepin (9). To a degassed solution of DMF (5 mL) of
compound 8 (0.350 g, 0.5 mmol) were added 2-tributylstannylthio-
phene (0.368 mL, 1.1 mmol) and PdCl2(PPh3)2 (18 mg, 5 mol %).
The mixture was allowed to stir at 80 °C for 15 h, at which time the
mixture was cooled to room temperature. Ethyl aceate was added to
the mixture, and the organic layer was washed with saturated
Supporting Information Available: Detailed experimental
procedures for the synthesis of all other compounds. Crystal-
lographic data for 3c and 14b. Cyclic voltammogram of the
chemically synthesized thiepin polymer. Fluorescence spectrum
of dithienonaphthalene 15. 1H and 13C NMR spectra of all
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
(16) Schmeisser, M. In Handbook of Preparative Inorganic Chemistry, 2nd
ed.; Bauer, G., Ed.; Academic: New York, 1963.
J. Org. Chem. Vol. 75, No. 4, 2010 1005