Synthetic routes to polyheteroacenes: Characterization of a heterocyclic ladder polymer containing phenoxathiinium-type building blocks

Article abstract of DOI:10.1021/ma010961d

The synthetic routes to ladder polymers that consist of benzenetetrayl subunits with oxo and methylsulfonio linkages are described. As the key intermediate, poly(phenylene oxide)s having pendant methylsulfenyl groups are prepared by copper-catalyzed oxidative polymerization of the corresponding phenols with O₂. The oxidation of the polymer with an equimolar amount of H₂O₂ in the presence of acetic acid effects the high-yielding conversion of methylsulfenyl to methylsulfinyl groups without the formation of the undesired methylsulfonyl groups. The superacidified condensation of the resulting polymer (Swern reaction of aryl sulfoxides) under dilution conditions induces the polymer-analogous intramolecular electrophilic ring-closing reaction of the hydroxymethylphenylsulfonium cation onto the adjacent benzene ring to yield the required ladder polymer, which has proved to be a semiconductor with an intrinsic electric conductivity of 2 × 10^-5 S/cm. A comparison of the spectroscopic properties of the ladder polymer with those of the model compounds such as 5-methylphenoxathiinium triflate and phenoxathiin discloses π-electron delocalization over the methylsulfonio linkages, demonstrating the efficacy of the ladderization for p-π/d-π interactions in arylsulfonium moieties. This synthetic approach permits the thio and alkylsulfonio ladder linkages for a variety of phenyl ethers to form in high yields.

Full text of DOI:10.1021/ma010961d

Macromolecules 2002, 35, 67-78
67
Synthetic Routes to Polyheteroacenes: Characterization of a
Heterocyclic Ladder Polymer Containing Phenoxathiinium-type
Building Blocks
Ken ich i Oya izu , Ta k efu m i Mik a m i, F u m io Mitsu h a sh i, a n d Eish u n Tsu ch id a *,†
Department of Polymer Chemistry, Advanced Research Institute for Science and Engineering,
Waseda University, Tokyo 169-8555, J apan
Received J une 4, 2001; Revised Manuscript Received September 12, 2001
ABSTRACT: The synthetic routes to ladder polymers that consist of benzenetetrayl subunits with oxo
and methylsulfonio linkages are described. As the key intermediate, poly(phenylene oxide)s having pendant
methylsulfenyl groups are prepared by copper-catalyzed oxidative polymerization of the corresponding
phenols with O2. The oxidation of the polymer with an equimolar amount of H2O2 in the presence of
acetic acid effects the high-yielding conversion of methylsulfenyl to methylsulfinyl groups without the
formation of the undesired methylsulfonyl groups. The superacidified condensation of the resulting polymer
(Swern reaction of aryl sulfoxides) under dilution conditions induces the polymer-analogous intramolecular
electrophilic ring-closing reaction of the hydroxymethylphenylsulfonium cation onto the adjacent benzene
ring to yield the required ladder polymer, which has proved to be a semiconductor with an intrinsic electric
conductivity of 2 × 10-5 S/cm. A comparison of the spectroscopic properties of the ladder polymer with
those of the model compounds such as 5-methylphenoxathiinium triflate and phenoxathiin discloses
π-electron delocalization over the methylsulfonio linkages, demonstrating the efficacy of the ladderization
for p-π/d-π interactions in arylsulfonium moieties. This synthetic approach permits the thio and
alkylsulfonio ladder linkages for a variety of phenyl ethers to form in high yields.
Sch em e 1
In tr od u ction
Herein we report a novel synthetic approach to
preparing π-conjugated laddertype poly(phenylene ox-
ide)s containing methylsulfonio linkages and demon-
strate the synthetic utility of aryl sulfoxides as the
precursor for heterocyclic compounds. The synthetic
concept consists of a polymer-analogous condensation
of aryl sulfoxides as outlined in Scheme 1. This type of
reaction yields a soluble ladder polymer 1 with ben-
zenetetrayl repeating units bridged by oxo and sulfonio
groups. Specifically, the spectroscopic results reveal the
π-electron delocalization over the methylsulfonio moiety
in the ladder polymer.
The interest in rigid-rod ladder (ribbon) polymers,1
especially in the π-conjugated acene series,2 has per-
sisted over several decades due to their potential ap-
plication as materials with thermal, mechanical, and
chemical stability,3 optical nonlinearity,4 and electric
conductivity upon oxidative or reductive doping.5 The
classical methods available for the synthesis of the
ladder polymers are (1) a concerted route with repetitive
cycloadditions,6 which typically involve a regiospecific
Diels-Alder cyclization,7 and (2) a multistep route in
which the single-stranded precursor can undergo poly-
mer-analogous cyclization reactions.8 Recently, some
effective polymer-analogous reactions of pendant func-
tional groups have been devised to provide π-conjugated
ladder polymers, such as the Schiff base formation
between alternating amine and ketone moieties9a-d and
electrophilic cyclization utilizing 4-alkoxyphenylethynyl
groups.9e-g
sulfoxides as monomers.10 In particular, we have es-
tablished that methyl phenyl sulfoxide (MPS) undergoes
self-polycondensation in CF3SO3H under suitable condi-
tions to produce poly(methylsulfonio-1,4-phenylene tri-
flate) (PPS+) in 100% yield (Scheme 1).11 The protonated
sulfoxide (hydroxylmethylphenylsulfonium cation) elec-
trophilically attacks the terminal phenyl ring (Swern
reaction of aryl sulfoxides)12 to exclusively produce
linear, high molecular-weight PPS+. Interestingly, PPS+
is highly soluble in organic polar solvents and even in
H2O.13 Thus, it seems reasonable to suppose that a
soluble, defect-free polymer 1 should be obtained when
the same reaction is employed as the polymer-analogous
reaction. The synthesis of 1 hinges on the use of the
prepolymer poly(p-phenylene oxide) bearing o-methyl-
sulfenyl groups (3b) as the key intermediate, which is
prepared by copper-catalyzed oxidative polymerization
of an o-methylsulfenylated phenol with O2 followed by
oxidation with H2O2 (Scheme 2). Although a large
number of studies have been made on the oxidative
We have developed the chemistry to prepare a variety
of linear alkylsulfoniophenylene polymers using aryl
* Corresponding author: Tel +813-5286-3120; fax +813-3205-
4740; e-mail eishun@mn.waseda.ac.jp.
† CREST investigator, J ST.
10.1021/ma010961d CCC: $22.00 © 2002 American Chemical Society
Published on Web 12/04/2001

68 Oyaizu et al.
Macromolecules, Vol. 35, No. 1, 2002
Sch em e 2
Sch em e 3
SbF5 in SO2 at the thiocarbonyl sulfur24 and the
extension of the π-conjugation length via the vacant
p-orbital of a boron atom.25
Resu lts a n d Discu ssion
Syn th esis a n d Str u ctu r e of a Mod el Com p ou n d
(5). To confirm the ring-closing reaction by the Swern
condensation of aryl sulfoxides, a model reaction was
carried out (Scheme 3). 2-(Methylsulfinyl)phenyl phenyl
ether (4) was prepared by the Ullmann ether synthesis.
The admixture of phenol and 2-(methylsulfinyl)bro-
mobenzene at 160 °C under basic conditions in the
presence of a copper catalyst afforded 4 in 80% yield.
Upon the exposure of 4 to CF3SO3H, a methylsulfonio
linkage was formed that forced the two benzene units
into planarity. The ring-closing reaction did not proceed
at room temperature and required heating at 80 °C. The
product, 5-methylphenoxathiinium triflate (5), was quan-
titatively obtained in 97% isolated yield. Triflic acid, the
strongest monobasic acid, was found to be the most
effective for the quantitative reaction. The product from
intermolecular condensations was not detected when the
reaction was carried out under dilution conditions.
An alternative synthetic route to 5 was provided by
the superacid-induced transmethylation26 with methyl
formate and phenoxathiin, which yielded 5 in 95% yield
(see Experimental Section). Conversely, the treatment
of 5 with nucleophilic reagents such as pyridine re-
sulted in the conversion of the methylsulfonio linkage
to a sulfide bond yielding phenoxathiin quantitatively
(Scheme 3).
Although a number of crystal structures of the sul-
fonium salts have been reported, such as those of the
dihalosulfonium salts27 and the aurated sulfonium
salt,28 no systemized study has been reported on those
of the arylsulfonium salts, to the best of our knowledge.
In attempts to obtain typical parameters for the bond
lengths and angles and the torsional angles of the
annulated arylsulfonium compounds, the product 5 was
subjected to X-ray crystallographic analysis. Layering
the acetone solution of 5 with diethyl ether afforded
colorless needlelike crystals suitable for an X-ray dif-
fraction study (Table 1) which revealed the structure
of 5 as shown in Figure 1. The S(1) atom covalently
bonded with the three carbon atoms extends 0.829 Å
above the C(1)C(2)C(13) plane. The arrangement of the
four atoms represents a typical trigonal-pyramidal
structure. The S(1)-C(1) bond length (1.813 Å) is
comparable with the value of typical alkylsulfonium
compounds.29 It is known that the bond length between
the sulfur and the phenyl carbon is indicative of the
oxidation state of the sulfur atom (Table 2). The S(1)-
C(2) and S(1)-C(13) bond lengths (1.766 and 1.768 Å,
respectively) are slightly longer than the C-S bond
length of phenoxathiin30 (1.75 Å) due to the decrease in
the electron density of the 3p lone pair, which resonate
with the π electrons of the benzene ring. The cation is
separated by the triflate anion, which is arranged in
the proximity of the cations and occupies a σ crystal-
lographic site symmetry.
polymerization of phenols 2,6-disubstituted with alkyl14
and aryl15 groups and halogen atoms,16 the oxidative
polymerization of alkylsulfenylated phenols is unprec-
edented to our knowledge.
A further important issue is to resolve the problem
of the inherent low solubility of the π-conjugated ladder
polymers, which renders their structure elucidation and
practical application very difficult. Indeed, rigid skel-
etons require flexible alkyl substituents to improve their
solubility and processability, sacrificing the crystallinity
and intermolecular interactions.17 Therefore, the syn-
thesis of a new definable and characterizable π-conju-
gated ladder backbone is an important subject of study.
Our principal findings include the facts that the conver-
sion of 3b to 1 give rises to a distinct bathochromic shift
in the longest wavelength absorption and a drastic
increase in the intrinsic electric conductivity. Thus, the
issue for 1 has to do with whether the benzene ring
could resonate through the cationic site and develop a
π-conjugated ladder framework. The delocalization of
the electron density into the low-lying vacant 3d orbitals
of sulfur has been proposed in sulfur ylides18 (R2S+--
CR′2 T R2SdCR′2) to rationalize the stabilization of the
negative charge of the carbanion by the adjacent sulfur,
though the preferred geometry of the carbon and sulfur
atoms indicates that sulfur ylides do not contain an
appreciable CdS bond character.19 On the other hand,
the p-π/d-π overlap and charge delocalization of aryl-
sulfonium moiety into the aromatic ring has been found
in the dihalo(pentafluorophenyl)sulfonium cation,20 which
is indicated by the significant deshielding of the ortho
and para ring fluorines in 19F NMR. This is related to
the proposed charge delocalization of the protonated
aromatic thioketones into the aromatic ring through the
mercaptocarbenium resonance forms,21 which has been
demonstrated by the protonation-induced deshielding
of the ring carbons and the shielding of the thiocarbonyl
carbons in 13C NMR, in contrast to the deshielding of
the thiocarbonyl carbons in aliphatic thioketones due
to an inductive effect.22 The lower pKa of p-(dimethyl-
sulfonio)phenol (7.30) than that of p-(trimethylammo-
nio)phenol (8.35) is also indicative of the p-π/d-π
interaction in the arylsulfonium moieties,23 which should
contribute to the stabilization of the conjugate base
through the quinoid resonance form. In analogy to these
observations, the NMR spectroscopic studies of 1 and a
model compound, 5-methylphenoxathiinium triflate,
under neutral and superacidic conditions reveal that the
delocalization of the positive charge on the sulfur atom
could also occur into the benzene ring under strongly
acidic conditions and that it could be enhanced with the
ladder framework. This may be reminiscent of the
formation of a novel heteroaromatic system upon the
protonation of vinylene trithiocarbonate with FSO3H-

Macromolecules, Vol. 35, No. 1, 2002
Synthetic Routes to Polyheteroacenes 69
Ta ble 1. Su m m a r y of X-r a y Cr ysta llogr a p h ic Da ta for 5
emp form
fw
cryst syst
space group
a (Å)
C
14H11F3S2O4
absn coeff µ
3.85 cm-1
55.0
4112
4111
2186 [I > 3.00σ(I)]
249
364.35
2θmax (deg)
orthorhombic
Pnma (no. 62)
23.928(2)
no. of reflns cold
no. of unq reflns
no. of obsd reflns
params
b (Å)
18.881(2)
c (Å)
6.961(2)
3144(1)
refln/param ratio
R
8.78
0.054
V (Å3)
Z
8
Rw
0.044
density (calcd)
crystal size (mm)
radiation
1.539 g/cm3
0.1 × 0.1 × 1.2
MoKR (λ ) 0.71069 Å)
goodness-of-fit
max peak in diff map
min peak in diff map
2.82
0.77 e-/Å3
-0.57 e-/Å3
F igu r e 1. ORTEP view (30% probability ellipsoids) of 5.
Ta ble 2. Selected Bon d Len gth s a n d An gles for 5
Ch a r a cter ized by X-r a y Cr ysta llogr a p h ya
F igu r e 2. 1H NMR spectra of (a) 4 in CD2Cl2, (b) 5 in acetone-
d6, and (c) 5 in CF3SO3H. (a, b) TMS was used as the internal
standard. (c) A CDCl3 solution of TMS was used as the external
standard, which was placed near the sample solution by use
of a double tube. Residual proton signals in the deuterated
solvents are marked with asterisks.
atoms
bond length, Å
atoms
bond length, Å
S(1)-C(1)
S(1)-C(13)
O(1)-C(8)
1.813(5)
1.768(4)
1.377(5)
S(1)-C(2)
O(1)-C(7)
1.766(4)
1.393(5)
atoms
angle, deg
101.3(2)
98.3(2)
119.3(4)
118.0(3)
atoms
angle, deg
C(1)-S(1)-C(2)
C(1)-S(1)-C(13)
S(1)-C(2)-C(7)
O(1)-C(7)-C(2)
O(1)-C(8)-C(13)
100.7(2)
119.9(4)
122.7(4)
123.0(4)
the methylsulfenylation of phenols by the Friedel-
Crafts reaction with dimethyl disulfide in the presence
of AlCl3. The reaction proceeded at temperatures higher
than 40 °C, and the desired products were obtained in
the highest yield (ca. 50%) when the reaction was
carried out in m-dichlorobenzene at 100 °C for 5 h. The
products were most conveniently prepared and isolated
with CCl4 as the solvent at 80 °C for 1 h (see Experi-
mental Section). The p-substituted phenols became
the major products in solvents such as C2H5OH and
CH3CN or with a prolonged time of reaction. At higher
temperatures, cresol was eventually converted to 2-
(methylsulfenyl)toluene.
The oxidation of methylsulfenyl to methylsulfinyl
groups was accomplished by the treatment with H2O2
in the presence of CH3CO2H. The product, the o-
methylsulfinylated phenols, were obtained quantita-
tively in 98% isolated yield. Further oxidation to the
undesired o-methylsulfonylated phenols did not take
place when an equimolar amount of H2O2 was used as
the oxidant.
Syn th esis of P r ecu r sor P olym er s. Attempts to
polymerize the o-methylsulfinylated phenols with a
copper catalyst and O2 met with failure (Table 3).
Reasoning that the oxidation of phenols bearing an
electron-withdrawing sulfoxide group might be disfa-
vored because of the high oxidation potential and/or the
undesired coordination of sulfoxide to the copper cata-
lyst, we turned to the polymerization of the o-methyl-
sulfenylated phenols. Thus, polymer 3b was prepared
as outlined in Scheme 2.
C(2)-S(1)-C(13)
S(1)-C(13)-C(8)
C(7)-O(1)-C(8)
a
Estimated standard deviations are given in parentheses.
In 1H NMR, a deshielding effect of 0.68 ppm is
observed for the CH3S+- atoms in 5 relative to the
CH3S(O)- atoms in the precursor 4 (Figure 2). This effect
is rationalized by considering an enhanced electron-
withdrawing (inductive) effect of the sulfur atom upon
the conversion of the sulfoxide into the sulfonium.
Interestingly, the CH3S+- resonance of 5 in 13C NMR
appears at a higher magnetic field (δ ) 36.8 ppm) than
the CH3S(O)- resonance of 4 (δ ) 42.3 ppm).
The optical absorption spectra of 5 and phenoxathiin
were recorded in CH3CN (Figure 3a). The shortening
of the (phenyl)C-S bond upon the conversion of 5 to
phenoxathiin is reflected in the bathochromic shift of
the B band32 near 300 nm, which can be ascribed to the
enhanced auxochromic effect of the sulfide bond relative
to that of the sulfonium center.
Mon om er Syn th esis. We have already established
that methylsulfenyl groups are conveniently introduced
into a variety of aromatic compounds by the supera-
cidified reaction with dimethyl sulfoxide (DMSO) (Swern
reaction of sulfoxides)8,10,13 followed by the treatment
with nucleophilic reagents such as pyridine. However,
phenol and cresol gave undesired p-methylsulfenylated
phenols as major products in this reaction. In attempts
to synthesize the o-substituted phenols, we turned to

70 Oyaizu et al.
Macromolecules, Vol. 35, No. 1, 2002
temperatures. Other oxidants such as nitric acid and
iodosobenzene resulted in the lower yielding conversion
to the sulfoxide.
In 1H NMR of 3b, there is no CH3S- or CH3S(O)2-
resonance (Figure 4a); these typically appear near δ )
2.3 and 3.2 ppm, respectively. The linear oxy-1,4-
phenylene structure of 3b is corroborated by the two
distinct peaks at δ ) 6.80 and 7.26 ppm ascribed to the
phenyl protons.
R in g-Closin g R ea ct ion . The exposure of 3b to
CF3SO3H at 80 °C under dilution conditions induced the
polymer-analogous ring-closing reaction of the pendant
methylsulfinyl groups to afford the planarized polymer
1, which was soluble in acidic media such as CF3SO3H
and fairly soluble in organic solvents such as DMSO.
Polymer 1 is obtained as a black powder whose defect-
free structure is confirmed by cross-polarization magic-
1
angle spinning (CP/MAS) and H NMR. In the CP/MAS
spectra (Figure 5a,b), the CH3S+- resonance of 1 (δ )
29.1 ppm) appears at a higher magnetic field than the
CH3S(O)- resonance of 3b (δ ) 42.4 ppm), consistent
with the spectral change upon the conversion of 4 to 5.
In addition, there is no remaining CH3S(O)- resonance
1
in the H NMR spectra of the lower molecular-weight 1
(Figure 4b) (the higher molecular weight 1 is not
sufficiently soluble in solvents to be clearly examined
by NMR). The IR and NMR spectra indicate that
intermolecular methylsulfonio linkages unlikely formed
in 1; at much higher concentrations (>10 mol/L), an
insoluble and undefinable polymer network resulted due
to the condensation of 3b.
F igu r e 3. Absorption spectra of (a) the model compounds 5
(1 mmol/L) and phenoxathiin (1 mmol/L) in CH3CN and (b) 5
(1 and 20 mmol/L) in CF3SO3H. The optical path length was
0.1 cm.
One could also suppose that the cyclization reaction
does not necessarily occur selectively in the para posi-
tion to the oxo functions. However, spectroscopic results
showed no indication of ortho coupling. The experimen-
tal behavior is supported by the PM3 semiempirical MO
calculation of the model compounds, where the net
charges on the carbon atoms at positions ortho to the
methylsulfinyl and methylsulfonio groups are more
cationic and less susceptible to the electrophilic substi-
tution reaction than the carbon atoms at positions para
to these groups (Figure 6). The regioselectivity in
ladderization is also explained by steric effect. The
cyclization at ortho position to the methylsulfonio group
gives a considerably unstable structure in which hy-
drogen atoms of two methylsulfonio groups can collide
with each other.
Sp ectr oscop ic P r op er ties. The 1H NMR spectra
reveal that the CH3S+- atoms in 1 are deshielded by
only 0.11 ppm compared to the CH3S(O)- atoms in the
precursor 3b. The magnitude of the deshielding dra-
matically decreases for the ladder polymer. In fact, a
deshielding effect of 0.68 ppm is observed for the methyl
protons in 5 relative to those in 4 (Table 5). In the
methylsulfoniophenylene polymer without the oxo link-
age (PPS+), the magnitude of the deshielding effect
relative to the corresponding monomer (MPS) is even
larger (1.1 ppm). On the other hand, a deshielding effect
of ca. 0.9 ppm for the phenyl proton in 1 relative to 3b
is significantly larger than the deshielding effect of ca.
0.56 ppm for those in 5 relative to 4. It follows that the
decrease in the deshielding effect for the CH3S+- atoms
in the case of the ladder polymer cannot be ascribed to
the electron-donating effect of the methyl group on the
benzene ring in 1. These results can be rationalized only
by considering a significant carbenium ion contribution
to the resonance structure of 1 (Scheme 4), the charge
The oxidative polymerization of the monomers with
a copper catalyst bearing a variety of amine ligands was
examined (Table 3). A linear polymer 2b was obtained
from 2-methyl-6-(methylsulfenyl)phenol with a Cu-
tmeda catalyst (tmeda ) N,N,N′,N′-tetramethylethyl-
enediamine) under O2. In particular, a relatively high
molecular weight polymer (Mw ) 35 000, Mn ) 10 000)
was obtained with a ligand/Cu ratio of 10 with nitroben-
zene as the solvent. On the other hand, polymerization
in CH3OH gave the lower molecular weight 2b due to
the precipitation of the oligomer during the reaction;
the product (Mw ) 4000, Mn ) 2000) was also employed
to give 1 with a higher solubility in organic solvents by
taking advantage of the low molecular weight (vide
infra).
The oxidative polymerization of 2-(methylsulfenyl)-
phenol with the copper catalyst and O2 gave polymer
2a with lower yields and molecular weights (Table 3).
1H NMR revealed that the product involved oxy-1,2-
phenylene units and branched structure in addition to
the oxy-1,4-phenylene units, which is undesirable for
the subsequent ring-closing reaction.
The synthesis of a defect-free polymer 1 requires the
quantitative conversion of both the sulfinylation of 2b
and the ring-closing of 3b. A variety of oxidants were
examined to oxidize the pendant methylsulfenyl groups
in 2b (Table 4). The oxidation of polymer 2b with an
equimolar amount of H2O2 in CH3CO2H at room tem-
perature with CH2Cl2 as a solvent effected the high-
yielding conversion of methylsulfenyl to methylsulfinyl
groups without the formation of the undesired methyl-
sulfonyl groups (Table 4). Gel-permeation chromato-
graphic (GPC) analysis of 3b revealed that no molecular
weight degradation occurred during the sulfinylation.
Further oxidation to methylsulfonyl groups tended to
occur in the presence of excess H2O2 or at elevated

Macromolecules, Vol. 35, No. 1, 2002
Synthetic Routes to Polyheteroacenes 71
a
Ta ble 3. Cop p er -Ca ta lyzed Oxid a tive P olym er iza tion of P h en ols w ith O2
a
b
d
Except where noted, solvent ) nitrobenzene, room temperature, 12 h. 0.25 mol/L. c Cu ) CuCl (0.025 mol/L). Insoluble part in
methanol. e Determined by gel-permeation chromatography versus polystyrene standards. f N,N,N′,N′-Tetramethylethylenediamine.
Solvent ) methanol.
g
Ta ble 4. Su lfin yla tion of 2ba
oxidation state (%)b
oxidant
solvent
concn (mol/L)
temp (°C)
time (h)
sulfide
sulfoxide
sulfone
product
H2O2 + CH3CO2H
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CCl4
CH3CN
CH2Cl2
CH2Cl2
0.1
0.1
0.1
2.5
2.5
2.5
0
0
rt
0
rt
40
rt
rt
rt
6
24
24
24
24
24
24
6
85
0
0
0
0
15
100
100
0
0
0
41
45
70
0
0
0
100
100
100
9
3b
3b
c
c
c
0
HNO3 (70%)
C6H5IO
50
55
30
0.12
0.12
0
0
24
a
b
1
0.1 mol/L. Determined by integration of H NMR peaks near δ ) 2.3 (-SCH3), 2.8 [-S(O)CH3], and 3.2 ppm [-S(O)2CH3]. c Poly(oxy-
2-methyl-6-methylsulfonyl-1,4-phenylene).
charge delocalization into the pentafluorophenyl ring
through p-π/d-π interactions.20
The model dimeric system provides further data for
assessing the spectroscopic properties of the polymers.
An important aspect is derived from the comparison of
the crystal structures of 5 and diphenylmethylsulfonium
hexafluoroantimoate,11 the control of 5 without the oxo
linkage between the two benzene rings. Obviously, the
torsions of the best least-squares plane of the adjacent
benzene units in 5 (34.72°) is smaller than that in the
diphenylmethylsulfonium cation11 (83.12°). In addition,
while a comparison of crystal structures of phenox-
athiin30 and diaryl sulfides28 [bis(4-methylphenyl) sul-
fide, 1.75 Å; bis(4-bromophenyl) sulfide, 1.75 Å] reveals
that the oxo linkage seems to have no effect on the
sulfide-C(phenyl) bond lengths, the S+-C(phenyl) bond
lengths in 5 are shorter than those of the diphenyl-
methylsulfonium cation (1.783 and 1.782 Å). Moreover,
the smaller C-S-C bond angles in the diphenylmeth-
ylsulfonium cation11 (103.6°) than in the diaryl sulfides28
[bis(4-methylphenyl) sulfide, 109°; bis(4-bromophenyl)
sulfide, 109°; diphenyl sulfide, 113°], which has been
ascribed to the enhanced p-character of the C-S bond
and the s-character of the sulfonium center,32 does not
F igu r e 4. 1H NMR spectra of (a) 3b in CD2Cl2 and (b) the
lower molecular weight 1 (see text) in DMSO-d6. TMS was
used as the internal standard. Residual proton signals in the
deuterated solvents are marked with asterisks.
delocalization into the aromatic ring causing a decrease
in the deshielding effect for the methyl protons and an
increase in that for the phenyl protons. Such a deshield-
ing effect for the phenyl protons is reminiscent of the
downfield shift of ring fluorine resonances in the 19F
NMR spectrum of dihalo(pentafluorophenyl)sulfonium
cations under strongly acidic conditions due to the

72 Oyaizu et al.
Macromolecules, Vol. 35, No. 1, 2002
linkage act as conjugation barriers. On the other hand,
the CF3SO3H solution of 5 is deep blue and shows new
absorption bands near λmax ) 513 and 578 nm (Figure
3b), due probably to the resonance structure (Scheme
4). No cation radical is detected in the electron spin
resonance (ESR) spectrum of the blue solution. The
formation of the protonated carbonium and oxonium
species is unlikely due to the positive charge on the
sulfur atom of 5. The absorption band in the visible
region is not attributable to the intramolecular charge-
transfer transition because there is no indication of
intermolecular donor-acceptor interactions11 between
the diphenylmethylsulfonium cation and diphenyl ether
in CF3SO3H even at very high concentrations. It seems
reasonable to suppose that 5 has a more planar confor-
mation in strongly acidic medium than in the crystal
state due to the enhanced carbenium ion contribution
to the resonance form (Scheme 4). Neutralization of the
CF3SO3H solution of 5 reinstates the 1H NMR and
optical absorption spectra identical to those in Figures
2b and 3a, respectively, ensuring the reversibility of the
changes upon the superacidification of 5.
Rigid planar conjugated systems are characterized by
a distinct bathochromic shift of the longest wavelength
absorption with the increasing number of fused aro-
matic subunits.33 Furthermore, they generally show
very sharp absorption edges due to their rigid character.8b
The optical absorption data of the polymers (Figure 7a)
were recorded in CH3CN for 2b and 3b and in CF3SO3H
for 1 and a partly ladderized polymer 1′ (see Experi-
mental Section). The absorption band significantly red
shifts upon completion of the ladderization (1′ f 1),
which indicates that π electrons could delocalize through
the polymer backbone. However, the absorption edge
features are different from those expected for rigid
π-conjugated polymers. The longest-wavelength band
of 1 is a broad shoulder near 600 nm, which is close to
the absorption band of 5 under acidic conditions (Fig-
ure 3b). The featureless absorption edge tailing to ca.
940 nm may indicate that the contribution of the
delocalized state to the resonance form of 1 (Scheme 4)
is small and that π electrons cannot delocalize through-
out the backbone, due probably to the relative stability
of the localized quinoidal form. Nevertheless, the small
optical band gap (1.3 eV) estimated from the tailing edge
is comparable to those of other π-conjugated ladder
polymers.9
F igu r e 5. 13C CP/MAS spectra of (a) 3b, (b) 1, and (c) 6.
F igu r e 6. Carbon net charges of oxyphenylene trimer models
for 3b before (a) and during the course of ladderization (b)
obtained by PM3 MO calculation.
hold for the annulated compounds (5, 98.3°; phenox-
athiin, 98°). These characteristics could be an indication
that, with the planarized benzene rings in 5, the
π-electron density is faintly delocalized into the meth-
ylsulfonio linkage.
It must be noted that the electron delocalization
through the ladder polymer backbone, rather than the
mere planarization of the benzene rings, is responsible
for the spectral changes upon ladderization. Preliminary
results has been obtained to indicate that the molecular
length, rather than the tetrasubstituted benzene units,
mainly works on the tailing of the absorption edge of 1
under neutral conditions (Figure 7b); an unpurified two-
unit model, derived from 1,4-bis[oxy(2-methylsulfinyl)-
phenyl]benzene by the ring-closing reaction, showed λmax
at 298 nm without a significant tailing edge in neutral
medium. Added support is also provided by the drastic
change in the electronic properties upon the conversion
of 1 into 6 (vide infra), a planarized analogue that is
incapable of delocalization through the position occupied
by the sulfide moiety; while 1 is a semiconductor with
We hypothesized that the charge delocalization should
be pronounced when the resulting carbenium cations
are stabilized in a strongly acidic medium (Scheme 4).
It was reported by Mu¨llen and co-workers8c that
CF3SO3H acts as a key dehydrating agent to allow the
formation of a carbenium-containing π framework. In
Figure 2c is shown the 1H NMR of 5 dissolved in
CF3SO3H, which reveals a decrease in the deshielding
effect with the magnitude of 0.5 ppm for the CH3S+-
atoms relative to those under neutral conditions con-
sistent with the extensive charge delocalization into the
aromatic rings. Additional evidence supporting this
interpretation is given in Figure 3. In the absence of
acid (Figure 3a), the methylation of phenoxathiin to 5
does not lead to any bathochromic shift of λmax, which
indicates that the methylsulfonio linkage and the sulfide
an intrinsic electric conductivity σ of 2 × 10-5 S cm-1
,
6 is an insulator (σ < 10-11 S cm-1). Polymer 1 and the
model compound 5 show no emission signal; the sulfur
atoms seem to play a role in the exciton quenching.

Macromolecules, Vol. 35, No. 1, 2002
Synthetic Routes to Polyheteroacenes 73
Ta ble 5. 1H a n d 13C NMR Ch em ica l Sh ifts of Meth yl Gr ou p s Bou n d to Su lfu r Atom sa
a
b
δ values are given in parts per million (ppm). Excepts where noted, solvent ) CDCl3. Solvent ) CD2Cl2. c Solvent ) acetone-d6.
Solvent ) DMSO-d6. e Solvent ) CF3SO3H. Standard (external) ) TMS/CDCl3. f CP/MAS. Low molecular weight part. Solvent )
D2O. Solvent ) CD3CN.
d
g
h
i
Sch em e 4
thermic reaction accompanied by a rapid drop in weight
of ca. 70% (Td10% ) 450 °C).34 These polymers are known
to show two complementary types of solid-state proper-
ties. While PPS is a partly crystalline material (Tg )
90 °C, Tc ) 137 °C, and Tm ) 282 °C),35 PPO is mainly
amorphous (Tg ) 205-220 °C, Tm ) 267 °C)36 and
completely miscible with polystyrene. We have already
established that their linear hybrid poly(oxy-1,4-phen-
ylenethio-1,4-phenylene) (PPOS) is a crystalline polymer
with Tm ) 191 °C, Tg ) 88 °C, and Tc ) 137 °C.37 The
Tm of PPOS is ca. 90 °C lower than that of PPS because
of an increase in ∆Sm due to its lower molecular
symmetry. The Td10% of PPOS (535 °C)37 is higher than
that of PPS due to the higher binding energy of the ether
bond than that of the thioether bond. The combination
of PPS and PPO to compound 6 with phenoxathiin-type
building blocks should result in a new material display-
ing interesting thermal properties. These include a high
Td10% due to the double-stranded, rigid, and planar
structure. Indeed, it has been reported38 that, among
polypyromellitimides containing a variety of aromatic
groups in the diamine component, the highest stability
in thermogravimetry is achieved with a polymer con-
taining the phenoxathiin group; all polyimides based on
the same diamines and the anhydrides of diphenyl- or
diphenyloxidetetracarboxylic acids show the same trend,38
which is quite natural since the phenyl rings are
attached by two bonds ensuring the high thermal
stability of the diamine component.
A comparison of the spectroscopic properties of the
sulfonium cations under acidic and neutral conditions
provides additional insights into the π-electron delocal-
ization through the sulfonium center. In the first place,
the lack of noticeable changes upon superacidification
in the 1H NMR and the optical absorption spectra of
the diphenylmethylsulfonium cation and those of PPS+
may demonstrate, conversely, the efficacy of planariza-
tion by the oxo linkages in 5 and 1 for charge delocal-
ization. In the second place, the lack of a noticeable
difference between the spectroscopic properties of 1 in
CF3SO3H and those in neutral medium (Figure 7b)
indicates that the ladder framework also seems to play
a role in the stabilization of the carbenium resonance
forms. In the final place, while 1 is black, PPS+ is a
white powder and colorless in both neutral and supera-
cidic media.
Th er m a l P r op er ties. Poly(phenylene sulfide) (PPS)
and poly(2,6-dimethylphenylene oxide) (PPO) (Chart 1)
are heteroatom-containing polymers with high chemical
and thermal stability. PPS is slowly decomposed above
450 °C (Td10% ) 516 °C), while PPO shows the onset of
decomposition near 420 °C followed by a strong exo-
The high-yielding conversion of 5 to phenoxathiin by
the treatment with pyridine led us to examine the
demethylation of 1. The efficacy of this reaction for use
in polymers has been demonstrated by the successful

74 Oyaizu et al.
Macromolecules, Vol. 35, No. 1, 2002
F igu r e 8. TGA curves of (a) the precursor polymers 2b and
3b and (b) the ladder polymers 1 and 6 under N2. The dotted
lines in panel b represent the temperature for a 10% weight
loss (Td10%). The temperature was scanned from room temper-
ature at a rate of 10 °C/min.
F igu r e 7. (a) Absorption spectra of the polymers (1 mmol unit/
L) before ladderization (2b and 3b in CH3CN), during the
course of the ladderization (1′ in CF3SO3H), and after ladder-
ization (1 in CF3SO3H). (b) Absorption spectrum of the lower
molecular weight 1 (see text) (1 mmol unit/L) in CH3CN. The
optical path length was 0.1 cm.
Polymers 1 and 6 both show no X-ray diffraction peak,
revealing that they are amorphous. The DSC analysis
shows no thermal transition before decomposition,
indicating the lack of glass transition in the temperature
range of interest due to the rigid structure.
Ch a r t 1
Com p a r ison w ith P r eviou s Stu d ies. The problem
of improving the solubility of π-conjugated ladder
polymers has frequently been addressed by derivatizing
ladder structures with suitable side groups to destabilize
the interchain interaction. On the other hand, one could
also consider a polymer electrolyte structure as a
candidate for a highly soluble ladder framework without
such substituents. The first ladder polymer electrolyte,
to our knowledge, is a polycarbenium with thioxanthy-
lium-type repeating units reported by Mu¨llen et al.,8c
which was claimed to be isoelectronically related to poly-
[n]acenes. However, the characterization was impeded
by an insufficient solubility in common solvents.8d
We previously reported the synthesis of two ladder
polymers with methylsulfonio linkages by the polymer-
analogous Swern condensation of aryl sulfoxides and
demonstrated their solubility in protonic acids but failed
to establish the π-electron delocalization into the sul-
fonio moiety due to the following reasons. First, we
reported an oligo(p-phenylene) ladder containing sulfide
and sulfonio linkages, but the extensive π-conjugation
was ascribed rather to the planarization of the benzene
rings than to the p-π/d-π interaction between the
sulfonium moiety and the benzene ring.8a Then, a ladder
polymer containing benzenetetrayl units bridged by
imino and methylsulfonio groups, an analogue of 1
containing imino groups in place of the oxo linkages,
was prepared from poly[imino-1,3-phenyleneimino-4,6-
bis(methylsulfinyl)-1,3-phenylene].8e However, the opti-
cal band gap estimated from the tailing edge of the
absorption spectrum (520 nm, 2.4 eV) indicated that the
π-electron conjugation did not extend throughout the
polymer chain. The localized intramolecular donor-
conversion of PPS+ to PPS.10a-h Polymer 1 was sus-
pended in pyridine, which was refluxed for a sufficiently
long time to ensure the completion of the demethylation
reaction. The product is obtained as a pale brown
powder. The absence of the CH3S+- resonance in CP/
MAS (Figure 5c) and of the IR signals due to triflate
anions establish the structure of 6.
A comparison of the Td10% values of the linear ana-
logues, such as PPS, PPO, and PPOS, with that of 6
reveal the enhancement in stability against thermolysis
by the ladder framework. Figure 7 shows the thermo-
gravimetric analysis (TGA) curves of polymers 1 and 6
and their precursors. In the absence of O2, polymers 2b
and 3b show the onset of decomposition near 350 °C
accompanied by a rapid drop in weight of ca. 30%
(Figure 8a). In contrast, polymer 6 shows the onset of
decomposition near 450 °C followed by only a slight
weight loss (Figure 8b). The thermal stability of the
ladder-type hybrid 6 (Td10% ) 555 °C) is even higher
than that of the linear hybrid PPOS. Polymer 1 is more
easily decomposed upon heating due to the weaker
sulfonio linkages (Figure 8b).

Macromolecules, Vol. 35, No. 1, 2002
Synthetic Routes to Polyheteroacenes 75
117.6, 118.6, 119.7, 124.5, 124.9, 125.3, 130.5, 132.2, 136.6,
153.3, 156.0. IR (KBr, cm-1): 3061 (w), 2920 (νCH, w), 1228
(νCOC, s), 1072 (νSdO, s), 754, 693 (δCH, s). MS: calcd for
acceptor interaction between the imino and methylsul-
fonio moieties was also considered to play a role in the
visible absorption.8e,11 Taking into account the lack of
such donor-acceptor interaction between oxo and meth-
ylsulfonio linkages, one can ascribe the smaller band
gap in 1 only to the π-electron delocalization through
the polymer backbone. MO calculations of 1 including
the d-orbitals of sulfur, with a view to proving the p-π/
d-π interaction, are the subject of our continuing
research.
C
13H12O2S, 232.06; found (m/z), 232 (M+).
Rin g-Closin g Rea ction of 4. A solution of 4 (0.23 g, 1.0
mmol) in CCl4 (2.0 mL) was added dropwise to CF3SO3H (5.0
mL) at rt with vigorous stirring. The resulting black solution
was heated at 80 °C and stirred for 24 h. The reaction was
quenched by pouring the solution into diethyl ether after
cooling to precipitate 5-methylphenoxathiinium triflate (5) as
a pale brown powder that was collected by filtration, washed
thoroughly with diethyl ether, and dried under vacuum (97%
yield). Anal. Calcd for C14H10F3O4S2: C, 46.3; H, 2.77; S, 17.7.
Con clu sion
1
Found: C, 46.7; H, 2.69; S, 17.8. H NMR (acetone-d6, TMS,
The polymer-analogous condensation of aryl sulfox-
ides is proposed as a convenient method to prepare the
ladder polymer containing sulfonio linkages that force
the consecutive aromatic units into planarity. The
ladder polymer 1 has bathochromically shifted absorp-
tions in the electronic spectrum. The bridging methyl-
sulfonio units have a p-π/d-π interaction with the
benzene rings, thus allowing for greater electron delo-
calization between the consecutive benzenetetrayl sub-
units. Because the delocalization of π-electrons through
the sulfonium center is confirmed, the present approach
represents a facile and potentially useful new class of
ladder polymers.
ppm): δ 3.49 (s, 3H, S+CH3), 7.60-8.25 (m, 8H, ArH). 1H NMR
(CF3SO3H, TMS/CDCl3 in double NMR tube, ppm): δ 2.99 (s,
3H, S+CH3), 7.65-8.04 (m, 8H, ArH). 13C NMR (DMSO-d6,
TMS, ppm): δ 36.8 (S+CH3), 107.0, 119.5, 126.1, 131.3, 135.7,
150.9. 13C NMR (CF3SO3H, TMS/CDCl3 in double NMR tube,
ppm): δ 36.0 (S+CH3), 104.88, 104.93, 122.39, 126.92, 130.06,
136.67, 152.36, 152.41. IR (KBr, cm-1): 3023 (m), 2930
(νCH, s), 1222 (νCOC, s), 758 (δCH, s), 638 (νCF, s). UV-vis
(CH3CN, nm): λmax 212, 288. UV-vis (CF3SO3H, nm): λmax 208,
288, 513, 578.
Dem eth yla tion of 5. The dark brown solution of 5 (0.35 g,
1.0 mmol) in pyridine (10 mL) was refluxed for 24 h with
constant stirring. After cooling, the solution was neutralized
with HCl. Extraction with CHCl3 followed by rotating evapo-
ration and drying under vacuum gave phenoxathiin in 98%
yield as a pale brown solid. Anal. Calcd for C12H8OS: C, 72.0;
H, 4.03; S, 16.0. Found: C, 71.9; H, 4.01; S, 15.9. 1H NMR
(CDCl3, TMS, ppm): δ 6.98-7.25 (m, ArH). 13C NMR (CDCl3,
TMS, ppm): δ 117.8, 120.4, 124.5, 126.8, 127.8, 152.1. IR (KBr,
cm-1): 2924 (νCH, m), 1226 (νCOC, s), 751 (δCH, s). MS: calcd
for C12H8OS, 200.03; found (m/z), 200 (M+). UV-vis (CH3CN,
nm): λmax 202, 294.
Exp er im en ta l Section
Ma ter ia ls. Commercial reagents of 2-bromobenzenethiol,
iodomethane, phenol, o-cresol, dimethyl disulfide, AlCl3, NaOH,
HCl, CF3SO3H, the aqueous solution of H2O2, CH3CO2H,
N,N,N′,N′-tetramethylethylenediamine, 2,6-lutidine, CuCl, and
deuterated solvents were used as received. The other solvents
were purified by distillation prior to use.
Meth yla tion of P h en oxa th iin . To a solution of phenox-
athiin (2.0 g, 10 mmol) and methyl formate (1.2 g, 20 mmol)
in CH2Cl2 (7.5 mL) was added CF3SO3H (5.0 mL). The
resulting purple solution was stirred at rt for 12 h. The
reaction was quenched by pouring the solution into diethyl
ether to precipitate 5, which was collected by filtration, washed
with diethyl ether, and dried under vacuum (95% yield).
Syn th esis of th e Mod el Com p ou n d 2-(Meth ylsu lfin yl)-
p h en yl P h en yl Eth er (4). To an aqueous solution (40 mL)
of NaOH (2.0 g, 50 mmol) were added 2-bromobenzenethiol
(5.0 g, 26.5 mmol) and iodomethane (18.8 g, 0.132 mol) with
vigorous stirring. The resulting white suspension was stirred
at 40 °C for 12 h. Extraction with CHCl3 followed by rotary
evaporation afforded 2-(methylsulfenyl)bromobenzene in 98%
yield as a dark brown liquid. 1H NMR (CD2Cl2, TMS, ppm):
δ 2.47 (s, 3H, SCH3), 7.00-7.53 (m, 4H, ArH). 13C NMR
(CD2Cl2, TMS, ppm): δ 15.9 (SCH3), 121.8, 125.7, 126.0, 128.8,
133.0, 140.2. IR (KBr, cm-1): 3057 (m), 2984 (m), 2919 (νCH,
s), 741 (δCH, s). MS: calcd for C7H7BrS, 201.95; found (m/z),
202 (M+). To a solution of 2-(methylsulfenyl)bromobenzene
(2.03 g, 10 mmol) in CH2Cl2 (50 mL) were added an aqueous
solution of H2O2 (30%, 10 mL) and CH3CO2H (2 mL). The
resulting mixture was stirred at rt for 24 h. Extraction with
CHCl3 followed by rotating evaporation and drying under
vacuum afforded 2-(methylsulfinyl)bromobenzene in 97% yield
Mon om er Syn th esis. 2-Methyl-6-(methylsulfenyl)phenol
was prepared by the Friedel-Crafts reaction of o-cresol with
dimethyl disulfide as follows. To a solution of AlCl3 (160 g,
1.2 mol) in CCl4 (300 mL) was added a solution of o-cresol (108
g, 1.0 mol) and dimethyl disulfide (113 g, 1.2 mol) in CCl4 (200
mL). The solution boiled as the reaction progressed and was
then refluxed under N2 for 1 h. After the reaction, a light-
yellow CCl4 solution was separated from the hot reaction
mixture by use of a separatory funnel. The addition of H2O
followed by extraction with CHCl3, dehydration with anhy-
drous Na2SO4, and rotary evaporation afforded a mixture of
2-methyl-6-(methylsulfenyl)phenol, 2-methyl-4-(methylsulfe-
nyl)phenol, 2-methyl-4,6-bis(methylsulfenyl)phenol, 2-(meth-
ylsulfenyl)toluene, and unreacted o-cresol. Distillation of the
mixture (5 mmHg, 75 °C) gave a crude product that still
contained 2-(methylsulfeyl)toluene and o-cresol as contami-
nants. The crude product was dissolved in an aqueous solution
of NaOH, and undissolved 2-(methylsulfenyl)toluene was
filtered out. The filtrate was neutralized with HCl and
extracted with CHCl3. The extract was washed thoroughly
with H2O, dehydrated with anhydrous Na2SO4, and rotary-
evaporated to yield a mixture of o-cresol and the product.
Purification by silica gel column chromatography with CHCl3
as the eluent afforded 2-methyl-6-(methylsulfenyl)phenol (10
g) as a light yellow liquid. 1H NMR (CDCl3, TMS, ppm): δ
2.26 (s, 3H, CH3), 2.28 (s, 3H, SCH3), 6.78 (s, 1H, OH), 6.74-
7.31 (m, 3H, ArH). 13C NMR (CDCl3, TMS, ppm): δ 16.3 (CH3),
19.9 (SCH3), 120.3, 120.6, 124.3, 132.0, 132.3, 154.6. IR (KBr,
cm-1): 3397 (νOH, s), 2912 (νCH, s), 1339 (δOH, m), 1233
(νCO, s), 769 (δCH, m). MS: calcd for C8H10OS, 154.23; found
(m/z), 154 (M+).
1
as a dark brown liquid. H NMR (CDCl3, TMS, ppm): δ 2.81
(s, 3H, SOCH3), 7.34-7.96 (m, 4H, ArH). 13C NMR (CDCl3,
TMS, ppm): δ 41.9 (SOCH3), 118.3, 125.6, 128.7, 132.2, 132.9,
145.4. IR (KBr, cm-1): 3059 (m), 2996 (m), 2914 (νCH, s), 1058
(νSdO, s), 758 (δCH, s). MS: calcd for C7H7BrOS, 217.94;
found (m/z), 218 (M+). A solution of 2-(methylsulfinyl)bro-
mobenzene (1.1 g, 5.0 mmol), copper(I) chloride (0.495 g, 5.0
mmol), and sodium methoxide (0.54 g, 10 mol) in phenol (20
mL) was heated at 160 °C under N2 for 24 h with constant
stirring. After cooling, an aqueous solution of NaOH was added
to the resulting solution to dissolve the unreacted sodium
phenolate into an H2O layer. Extraction with chloroform
followed by a thorough washing with H2O, dehydration with
anhydrous Na2SO4, and rotary evaporation afforded a crude
product in 80% yield as a dark brown liquid. Purification by
silica gel column chromatography with CHCl3 as the eluent
gave 4 as a dark brown solid. Anal. Calcd for C13H12O2S: C,
67.2; H, 5.21; S, 13.8. Found: C, 67.0; H, 5.18; S, 13.9. 1H NMR
(CD2Cl2, TMS, ppm): δ 2.81 (s, 3H, SOCH3), 6.83-7.90 (m,
9H, ArH). 13C NMR (CD2Cl2, TMS, ppm): δ 42.3 (SOCH3),

76 Oyaizu et al.
Macromolecules, Vol. 35, No. 1, 2002
2-(Methylsulfenyl)phenol was prepared from phenol and
dimethyl disulfide by a similar method as follows. To a solution
of phenol (47.1 g, 0.5 mol) in CCl4 (50 mL) were added AlCl3
(66.7 g, 0.5 mol) and dimethyl disulfide (47.1 g, 0.5 mol). The
resulting yellow solution was refluxed for 2 h. The addition of
H2O followed by extraction with CHCl3, dehydration with
anhydrous Na2SO4, and rotary evaporation afforded the crude
product. Purification by distillation (5 mmHg, 75 °C) followed
by silica gel column chromatography with CHCl3 as the eluent
afforded 2-(methylsulfenyl)phenol in 80% yield as a transpar-
ent liquid. 1H NMR (CDCl3, TMS, ppm): δ 2.31 (s, 3H, SCH3),
6.75 (s, 1H, OH), 6.84-7.50 (m, 4H, ArH). 13C NMR (CDCl3,
TMS, ppm): δ 114.7 (SCH3), 120.6, 121.0, 130.5, 134.5, 155.9.
MS: calcd for C7H8OS, 140.03; found (m/z), 140 (M+).
2-Methyl-6-(methylsulfinyl)phenol was prepared by the
oxidation of 2-methyl-6-(methylsulfenyl)phenol with H2O2 as
follows. To a solution of 2-methyl-6-(methylsulfenyl)phenol
(1.54 g, 10 mmol) in CH2Cl2 (50 mL) were slowly added 30%
H2O2 (10 mL) and CH3CO2H (2 mL). The resulting mixture
was vigorously stirred at rt for 24 h. Extraction with CHCl3
followed by rotary evaporation and drying under vacuum
afforded 2-methyl-6-(methylsulfinyl)phenol in 98% yield as a
dark brown liquid. 1H NMR (CDCl3, TMS, ppm): δ 2.26 (s,
3H, CH3), 2.94 (s, 3H, SOCH3), 6.77-7.31 (m, 3H, ArH), 10.45
(s, 1H, OH). 13C NMR (CDCl3, TMS, ppm): δ 15.3 (CH3), 41.72
(SOCH3), 119.2, 122.0, 122.3, 128.9, 134.0, 157.9. IR (KBr,
cm-1): 3448 (νOH, m), 3061, 2922 (νCH, m), 1053 (νSO, s),
761 (δCH, m). MS: calcd for C8H10O2S, 170.23; found (m/z),
170 (M+).
2-(Methylsulfinyl)phenol was prepared by the oxidation of
2-(methylsulfenyl)phenol as follows. To a solution of 2-(meth-
ylsulfenyl)phenol (7.01 g, 50 mmol) in CH2Cl2 (100 mL) were
slowly added 30% H2O2 (50 mL) and CH3CO2H (10 mL). The
resulting mixture was vigorously stirred at rt for 24 h.
Extraction with CHCl3 followed by rotary evaporation and
drying under vacuum afforded the crude product, which was
purified by recrystallization from a solution in CHCl3 and
hexane to give 2-(methylsulfinyl)phenol in 90% yield as a white
powder. Anal. Calcd for C7H8O2S: C, 53.8; H, 5.16; S, 20.5.
Found: C, 53.7; H, 5.20; S, 20.3. 1H NMR (CDCl3, TMS,
ppm): δ 2.96 (s, 3H, SOCH3), 6.90-7.39 (m, 4H, ArH), 10.24
(s, 1H, OH). MS: calcd for C7H8O2S, 156.02; found (m/z), 156
(M+).
CH2Cl2 (50 mL) were added 30% H2O2 (5.0 mL) and CH3CO2H
(1.0 mL). The resulting mixture was vigorously stirred at rt
for 24 h. After the reaction, the mixture was rotary-evaporated
to replace the solvent with CHCl3. The resulting solution was
poured into hexane to precipitate the product, which was
collected by filtration, washed thoroughly with hexane and
H2O, and dried under vacuum to give 3b in 100% yield as a
white powder. Anal. Calcd for C8H8O2S: C, 57.1; H, 4.79; S,
19.1. Found: C, 56.9; H, 4.79; S, 19.5. 1H NMR (CD2Cl2, TMS,
ppm): δ 2.12 (s, 3H, CH3), 2.78 (s, 3H, SOCH3), 6.80 (s, 1H,
ArH), 7.26 (s, 1H, ArH). 13C NMR (CDCl3, TMS, ppm): δ 16.5
(CH3), 42.2 (SOCH3), 119.8, 120.3, 134.4, 141.4, 142.2, 155.3.
CP/MAS (ppm): δ 16.3, 42.4, 122.0, 134.5, 142.7, 155.9. IR
(KBr, cm-1): 3011, 2968, 2904 (νCH, m), 1183 (νCOC, s), 1056
(νSO, s), 752 (δCH, m). UV-vis (CH3CN, nm): λmax 300. GPC
(DMF, PS standard): Mn, 11 000; Mw, 39 000.
La d d er iza tion . Polymer 3b (0.17 g, 1 mmol unit) was
dissolved in CH2Cl2 (2.0 mL). The solution was added dropwise
to CF3SO3H (10 mL) at rt with vigorous stirring. The resulting
black solution was stirred at 80 °C for 24 h. After the reaction,
the homogeneous solution was poured into diethyl ether to
precipitate a black powder, which was collected by filtration,
washed with diethyl ether, aqueous NaOH, and H2O repeat-
edly, and dried under vacuum to yield 1 (0.27 g). Anal. Calcd
for C9H7F3O4S2: C, 36.0; H, 2.35; S, 21.4. Found: C, 36.1; H,
2.33; S, 21.6. CP/MAS (ppm): δ 15.2 (CH3), 29.1 (S+CH3),
119.4, 122.0, 128.6, 130.7, 135.5, 148.7. IR (KBr, cm-1): 3023,
2930 (νCH, m), 1222 (νCOC, s), 1161, 637 (νCF, m), 859, 761
(δCH, m). UV-vis (CF3SO3H, nm): λmax 200, 256, 302. The
partly ladderized polymer 1′ was obtained when the reaction
was quenched for 5 h. UV-vis (CF3SO3H, nm): λmax 278, 374,
404.
Sulfinylation of the lower molecular weight 2b (Mn ) 2000,
Mw ) 4000) followed by ladderization by the same method
yielded the lower molecular weight 1, which was soluble in
DMSO. Anal. Calcd for C9H7F3O4S2: C, 36.0; H, 2.35; S, 21.4.
Found: C, 35.8; H, 2.29; S, 21.9. 1H NMR (DMSO-d6, TMS,
ppm): 2.73 (s, 3H, CH3), 2.89 (s, 3H, S+CH3), 7.95 (s, 1H, ArH).
IR (KBr, cm-1): 2931 (νCH, m), 1261 (νCOC, s), 1171, 640
(νCF, m), 859, 761 (δCH, m).
Dem eth yla tion of 1. Polymer 1 (1.5 g, 3.3 mmol unit) was
dispersed in pyridine (100 mL), which was refluxed for 1 week.
The resulting pale brown powder was collected by filtration,
washed thoroughly with CH3OH, and dried under vacuum to
give 6 in 100% yield (0.9 g). Anal. Calcd for C7H4OS: C, 61.7;
H, 2.96; S, 23.5. Found: C, 61.9; H, 2.94; S, 22.9. CP/MAS
(ppm): δ 13.8, 123.4, 148.0. IR (KBr, cm-1): 2920 (νCH, m),
1267 (νCOC, s), 850 (δCH, m).
Oxid a tive P olym er iza tion . To a solution of 2-methyl-6-
(methylsulfenyl)phenol (1.54 g, 10 mmol) in nitrobenzene (20
mL) was added a solution of N,N,N′,N′-tetramethylethylene-
diamine (1.16 g, 10 mmol) and CuCl (0.099 g, 1.0 mmol) in
nitrobenzene (20 mL). Upon mixing, the color of the solution
became dark brown. The resulting solution was stirred under
O2 for 12 h. After the reaction, the solution was poured into
CH3OH (200 mL) containing 5% HCl to precipitate the product,
which was collected by filtration, washed with CH3OH, and
dried under vacuum to yield 2b in 98% yield as a white
powder. Anal. Calcd for C8H8OS: C, 63.1; H, 5.30; S, 21.1.
Found: C, 63.3; H, 5.28; S, 21.0. 1H NMR (CDCl3, TMS,
Mea su r em en ts. 1H and 13C NMR spectra were recorded
1
on a J eol J NM-LA500 (500 MHz H, 125 MHz 13C) spectrom-
eter with chemical shifts downfield from tetramethylsilane as
the internal standard. 13C CP/MAS spectra were obtained on
a J eol GSX-400 spectrometer. Infrared spectra were obtained
on a J asco FT-IR 5300 spectrometer with potassium bromide
pellets. UV-vis spectra were recorded on a Shimadzu UV-2100
spectrometer. Thermogravimetry and differential thermal
analysis were performed on a Seiko TG-DTA 220 instrument
at a heating rate of 10 °C/min under nitrogen at a flow rate of
300 mL/min. A 5 mg sample was used for each thermal
analysis. Molecular weight measurements were done by gel-
permeation chromatography (GPC) on a Shimadzu LC-9A
liquid chromatograph equipped with a SPD-6AV UV-vis
spectrophotometric detector set at 275 nm. DMF containing 1
wt % LiBr was used as the eluent. Calibration was done with
polystyrene standards. Elemental analyses were performed on
a Perkin-Elmer PE-2400 II and a Metrohm 645 multi-DOSI-
MAT. Two parallel analyses were performed for each sample.
Mass spectra were obtained on a Shimadzu GCMS-QP5050
spectrometer.
4
ppm): δ 2.07 (s, 3H, CH3), 2.32 (s, 3H, SCH3), 6.38 (d, 1H, J
) 2.4 Hz, ArH), 6.59 (d, 1H, 4J ) 2.4 Hz, ArH). 13C NMR
(CDCl3, TMS, ppm): δ 14.6 (CH3), 16.8 (SCH3), 110.1, 113.0,
132.6, 134.4, 143.5, 155.1. IR (KBr, cm-1): 2979, 2918, 2855
(νCH, m), 1590, 1458 (νCdC, s), 1186 (νCOC, s), 753 (δCH,
m). GPC (DMF, PS standard): Mn, 10 000; Mw, 35 000. UV-
vis (CH3CN, nm): λmax 290.
A lower molecular-weight 2b was obtained in 25 wt % yield
as an off-white powder when the same reaction was performed
in CH3OH instead of nitrobenzene. Anal. Calcd for C8H8OS:
1
C, 63.1; H, 5.30; S, 21.1. Found: C, 63.0; H, 5.36; S, 20.8. H
NMR (CDCl3, TMS, ppm): δ 2.06 (s, 3H, CH3), 2.32 (s, 3H,
SCH3), 6.39 (d, 1H, 4J ) 2.4 Hz, ArH), 6.58 (d, 1H, 4J ) 2.4
Hz, ArH). 13C NMR (CDCl3, TMS, ppm): δ 14.5 (CH3), 16.8
(SCH3), 110.2, 113.0, 132.5, 134.4, 143.4, 155.1. IR (KBr, cm-1):
2981, 2915, 2850 (νCH, m), 1589, 1455 (νCdC, s), 1181
(νCOC, s), 751 (δCH, m). GPC (DMF, PS standard): Mn, 2000;
Mw, 4000.
X-r a y Cr ysta llogr a p h y. Colorless needlelike crystals of 5
were grown from acetone solutions of the desired compound
after layering with diethyl ether. Following microscopic ex-
amination in air, a suitable crystal was mounted on a glass
fiber at room temperature. All measurements were done on a
Rigaku AFC7R diffractometer with a 7.5 kW rotating-anode
Su lfin yla tion of 2b. Polymer 2b was oxidized with H2O2
to 3b as follows. To a solution of 2b (0.76 g, 5 mmol unit) in

Macromolecules, Vol. 35, No. 1, 2002
Synthetic Routes to Polyheteroacenes 77
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generator and graphite-monochromated MoKR radiation (λ )
0.71069 Å). Unit cell parameters and an orientation matrix
for data collection were determined by least-squares refine-
ments with the setting angles of 25 carefully centered reflec-
tions in the range 28.70° < 2θ < 29.96°. The data were
collected at a temperature of 23 °C by the ω-2θ scan technique
to a maximum 2θ value of 55.0°. Scans were done at a speed
of 16.0°/min (in ω). The weak reflections [I < 10.0σ(I)] were
rescanned (up to two scans). The intensities of three repre-
sentative reflections were measured after every 150 reflections.
No decay correction was applied. An empirical absorption
correction based on the azimuthal scans of several reflections
was applied that resulted in transmission factors ranging from
0.89 to 1.00. The data were corrected for Lorentz and polariza-
tion effects. A correction for the secondary extinction was
applied (coefficient ) 4.61690 × 10-7).
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Str u ctu r e Solu tion a n d Refin em en t. The structure was
solved by direct methods (SHELXS86)39 and expanded by
Fourier techniques. Some non-hydrogen atoms were refined
anisotropically, while the rest were refined isotropically. The
hydrogen atoms were refined isotropically. The final cycle of
full-matrix least-squares refinement40 was based on 2186
observed reflections [I > 3.00σ(I)] and 249 variable parameters
and converged with unweighted and weighted agreement
factors of R ) Σ||Fo| - |Fc||/Σ|Fo| and Rw ) (Σw(|Fo| - |Fc|)2/
2
ΣwFo
)
1/2 as listed in Table 1. The plots of Σw(|Fo| - |Fc|)2 versus
|Fo|, reflection order in data collection, sin θ/λ, and various
classes of indices showed no unusual trends. The data collec-
tion and structure solution parameters and conditions are
listed in Table 1. The selected bond lengths and angles are
listed in Table 2. All calculations were performed with the
teXsan crystallographic software package from Molecular
Structure Corp.41
Ack n ow led gm en t. This work was partially sup-
ported by a Grant-in-Aid for Scientific Research
(11650878) from the Ministry of Education, Science,
Sports, and Culture in J apan.
Su p p or tin g In for m a tion Ava ila ble: Five tables giving
atomic coordinates, anisotropic displacement parameters, and
equivalent isotropic thermal parameters for 5. This informa-
tion is available free of charge via the Internet at http://
pubs.acs.org.
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MA010961D