π-conjugated poly(dithiafulvene)s and poly(diselenafulvene)s: Effects of side alkyl chains on optical, electrochemical, and conducting properties

Article abstract of DOI:10.1021/ma011939n

Electron-donating π-conjugated polymers with dithiafulvene moiety (4) or with diselenafulvene moiety (5) were prepared by cycloaddition polymerization of chalcogenoketenes derived from aromatic diynes (3). The solubilities of the polymers strongly depende

Full text of DOI:10.1021/ma011939n

Macromolecules 2002, 35, 3539-3543
3539
π-Conjugated Poly(dithiafulvene)s and Poly(diselenafulvene)s: Effects of
Side Alkyl Chains on Optical, Electrochemical, and Conducting
Properties
Ken su k e Na k a ,* Ta k a sh i Uem u r a , a n d Yosh ik i Ch u jo*
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University,
Yoshida, Sakyo-ku, Kyoto, 606-8501, J apan
Received November 6, 2001; Revised Manuscript Received February 12, 2002
ABSTRACT: Electron-donating π-conjugated polymers with dithiafulvene moiety (4) or with diselena-
fulvene moiety (5) were prepared by cycloaddition polymerization of chalcogenoketenes derived from
aromatic diynes (3). The solubilities of the polymers strongly depended on the structures. The
diselenafulvene polymers (5) showed lower solubilities than the corresponding dithiafulvene polymers
(4). Attachment of long alkyl chains enhanced the solubilties in nonpolar solvents. The structures of the
polymers were confirmed by IR and 1H NMR spectra. UV-vis measurements indicated that π-conjugations
of the polymers were expanded; in particular, those of polymers containing the long alkoxy side chains
were developed effectively. All the polymers showed electron-donating properties in cyclic voltammometry
measurements and formed soluble charge-transfer complexes with 7,7,8,8-tetracyano-p-quinodimethane
(TCNQ). After the complexation with TCNQ, the conductivities of the polymers increased.
In tr od u ction
between the dichalcogenafulvenes and π-acceptors are
incorporated into conjugated polymers, electron mobility
along the polymer backbone via π-conjugation as well
as along the stacking direction via π-orbital overlap
would be improved (high dimension of conducting
state).8 Furthermore, inter- and intramolecular Cou-
lombic repulsions between the charged species would
be suppressed to enhance the stacking CT formations
due to the large number of chalcogene atoms in the
π-conjugated dichalcogenafulvene-based polymers.7a,8
We have reported9 on a series of π-conjugated polymer
with the dithiafulvene unit, which formed CT complexes
with TCNQ. Resulting polymer CT complexes showed
highly improved electrical conductivities. In this article,
we report on a general synthesis of π-conjugated poly-
(dichalcogenafulvene)s by cycloaddition polymerizations
of chalcogenoketenes. Comparison between the new
poly(dithiafulvene)s and poly(diselenafulvene)s is in-
teresting. We also studied effects of the polymer side
chains on chemical and physical properties of the poly-
(dichalcogenafulvene)s.
Dichalcogenafulvene derivatives have been widely
used as electron donor components in the preparation
of charge-transfer (CT) complexes and radical ion salts.1
In the chemistry of the dichalcogenafulvenes, especially
the focus has been centered on derivatives of tetrathia-
fulvalene (TTF, 1). Since the discoveries of a high
electrical conductivity in a chloride salt of TTF2 and
metallic behavior in the charge-transfer (CT) complex
with 7,7,8,8-tetracyano-p-quinodimethane (TCNQ),3 there
have been many studies of TTF-based materials that
possess unusual electronic and magnetic properties.4
The recent developments in synthetic TTF chemistry
have allowed the ready preparation of large quantities
of derivatized TTFs, which are utilized not only for
components of the molecular conductor but also for
π-rich redox-active supramolecular systems.5 Mean-
while, replacement of sulfur by chalcogens with more
diffuse orbitals (Se, Te) would enhance the interstack
interaction to increase dimensionality of the conduction
state. The resulting high dimensionality improves the
conducting performance of such organic metals at low
temperature. For example, cation radicals of tetra-
methylselenafulvalene (TMTSF, 2) have been reported
to exhibit superconductivity below 5 K due to the
Se-Se interaction between the units.6
Resu lts a n d Discu ssion
P olym er Syn th esis. We employed three monomers
(3a -c) with different side alkyl chains to prepare the
poly(dichalcogenafulvene)s (4, 5). Cycloaddition poly-
merizations of chalcogenoketenes and their alkynechal-
cogenol tautomer derived from 3 in situ successfully
produced the poly(dithiafulvene)s 4 and the poly(disel-
enafulvene)s 5 (Scheme 1). End-capping by piperidine
to convert thioamides or selenoamides resulted in better
solubilities of the obtained polymers than those of the
polymers without end-capping. Synthetic details of poly-
(dithiafulvene) 4a were reported in 1999.9b The report
showed that molecular weights of the poly(dithiaful-
vene)s varied with the change of the reaction solvent,
and Et2O was the best reaction medium to achieve
satisfactory degrees of the polymerization. In present
work, Et2O was the most effective solvent to synthesize
the poly(dithiafulvene)s 4b and 4c, but the poly(disel-
Hybridization between the dichalcogenafulvene de-
rivatives and π-conjugated polymers is an attraction.7,8
The association of structural characters and properties
may contribute to mutual fertilization by development
of new materials of fundamental and technological
interest. The conjugated polymers are basically low-
dimensional conductors, similar to the dichalcogena-
fulvene-based CT salts. When intermolecular CT units
10.1021/ma011939n CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/22/2002

3540 Naka et al.
Macromolecules, Vol. 35, No. 9, 2002
Sch em e 1
Ta ble 1. P r ep a r a tion of P oly(d ich a lcogen a fu lven e)s
The structures of the new poly(dithiafulvene)s (4b,
1
4c) were confirmed by IR and H NMR spectroscopies
compared with those of the model compounds reported
previously(6, 7).9b To support the structures of the poly-
(diselenafulvene)s, two model compounds (8, 9) were
synthesized. 2,6-Bisphenyl-1,4-diselenafulvene (8)10 was
used as a model compound for the diselenafulvene unit
of 5 and selenoamide (9)10 as a model for the terminal
unit of the poly(diselenafulvene)s. In the IR spectrum
of 8, peaks corresponding to the double bonds of the
diselenafulvene moiety appeared at 1576 and 1558
cm-1. The IR spectra of the soluble parts as well as
insoluble parts of the poly(diselenafulvene)s 5 showed
similar peaks between 1550 and 1580 cm-1, suggesting
that the structures of both parts of 5 are basically the
same containing diselenafulvene moieties in the struc-
tures. The model diselenafulvene compound 8 was
observed to show less solubility than 6, and the molec-
ular weights of 5 were lower than those of the corre-
sponding poly(dithiafulvene)s 4, suggesting that strong
Se-Se interactions might induce interunit stackings
between the diselenafulvene moieties to give the low
yield
(%)
mol wt
(Mn)
entry
compd
solubility
DMSO, DMF
DMSO, DMF
CHCl3, CH2Cl2, THF
insoluble
partially soluble in DMSO
partially soluble in CHCl3,
THF
1
2
3
4
5
6
4a
4b
4c
5a
5b
5c
76
37
68
95
85
98
6810a
3090a
8870
2110a,c
5220b,d
a
GPC was carried out by using DMSO as an eluent at 50 °C
b
after calibration with standard poly(ethylene glycol). GPC were
performed in chloroform at 25 °C by use of polystyrene standard
d
samples. c DMSO-soluble part. Chloroform-soluble part.
enafulvene)s 5 could not be obtained in Et2O; however,
in THF polymerization toward 5 underwent smoothly.
Solubilities of the polymers are summarized in Table
1. Similar to 4a , the poly(dithiafulvene) 4b was soluble
in aprotic polar solvents such as DMSO and DMF.
Because of the long alkoxy chains, polymer 4c showed
good solubility in CHCl3, CH2Cl2, and THF and was
hardly soluble in DMSO and DMF. Solubilities of the
poly(diselenafulvene)s were found to be very limited;
e.g., polymer 5a was completely insoluble in any solvent,
preventing further investigations of its chemical and
physical properties. Despite the long alkoxy substitu-
tions on the phenylene unit, polymers 5b and 5c showed
partial solubilities in organic solvents. 31% of 5b was
soluble in DMSO, and the CHCl3-soluble part of 5c was
46%. The polymers obtained in this work were subjected
to gel permeation chromatography (GPC) measurement
to determine molecular weights (Table 1). In the case
of the poly(diselenafulvene)s, the soluble parts of the
polymers were examined.
1
solubilities of 5. The H NMR spectrum of the DMSO-
d6 soluble part of 5b showed a broad peak corresponding
to diselenole ring proton at 7.5 ppm and peaks for the
terminal selenoamide moiety at 3.6, 4.3, and 4.4 ppm.
1
In the H NMR spectrum of the CDCl3-soluble part of
5c, satisfactory peaks attributed to the diselenafulvene
protons and the terminal selenoamide moiety were
observed.
Op tica l P r op er ties. The UV-vis absorption of the
polymers in the solution is seen in Figure 2. The peaks
due to π-π* transitions of 4 and the soluble parts of 5
were located at longer wavelengths than those of the
corresponding model compounds, indicating efficient
π-electron delocalizations in the polymer systems. In the
series of the poly(dithiafulvene)s, methyl substitution
on benzene ring gave rise to a blue shift from the
absorption of 4a due to a steric distortion of 4b in CH3-
CN. UV-vis measurement of 4c showed a notable
feature of the conjugation. The π-conjugation system of
4c in CHCl3 was the most effectively expanded among
those of the poly(dithiafulvene)s. Each soluble part of
the poly(diselenafulvene) (5b in CH3CN, 5c in CHCl3)

Macromolecules, Vol. 35, No. 9, 2002
Poly(dithiafulvene)s and Poly(diseleafulvene)s 3541
F igu r e 1. 1H NMR spectrum of the soluble part of 5b in DMSO-d6.
Ta ble 2. P h ysica l P r op er ties of
P oly(d ich a lcogen a fu lven e)s
conductivityd
UV λmax oxidation nondoped,
TCNQ
complex, S/cm
entry compd
(nm)
peak (V)c
S/cm
1
2
3
4
5
6
7
4a
4b
4c
5b
5c
6
398a
366a
451b
377a
429b
358b
341b
0.60
0.55
0.74
0.59
0.79
0.40
0.44
3 × 10-7
8 × 10-7
<10-7
2 × 10-4
9 × 10-4
4 × 10-6
2 × 10-4
4 × 10-6
2 × 10-6
1 × 10-7
8
a
b
UV spectra were measured in CH3CN. UV spectra were
measured in CHCl3. c Cyclic voltamograms were obtained in
CH3CN solution containing 0.1 M [NEt4]BF4. Scan rates were 300
mV/s. Electrical conductivities were measured at room temper-
d
ature by the two-probe technique.
The effective π-conjugations in 4c and 5c should be
induced by electron-donating effects of the alkoxy
groups. Several examples have shown that the intro-
duction of strong electron-donating alkoxy groups sig-
nificantly reduces the band gaps of poly(thiophene) and
poly(thienylene vinylene).11
Electr och em ica l Stu d y. The electrochemical redox
behaviors of the donors were studied by cyclic voltam-
metry (CV) (Table 2). The model compounds 6 and 8
showed single oxidation peaks at 0.40 and 0.44 V vs Ag/
Ag+, respectively. The value of the oxidation peak for
the dithiafulvene 6 was less positive by 0.04 V than that
of 8, indicating that the electron-donating ability of 6
is slightly stronger than that of 8. The cast films of the
polymers (4 and 5) showed irreversible broad oxidation
waves between 0.5 and 0.8 V vs Ag/Ag+. UV-vis and
CV measurements suggested that the oxidation poten-
tial and the π-electron delocalizations of the polymers
are correlative. The oxidation potentials of the polymers
shifted positively with the development of the π-conju-
gations and may also be finely tuned by substituents
on the benzene ring in the systems of the poly(dichal-
cogenafulvene)s.
F igu r e 2. UV-vis absorption spectra of (A) 4a and 4b in CH3-
CN, 4c and 6 in CHCl3 and (B) the soluble part of 5b in CH3-
CN, the soluble part of 5c and 8 in CHCl3.
TCNQ Com p lexes. The poly(dichalcogenafulvene)s
formed CT complexes with TCNQ. After adding an
excess amount of TCNQ to a polymer solution, it
gradually turned to be dark green. The unreacted TCNQ
was filtered off, and then the filtrate was evaporated to
had an absorption with a similar peak position to its
analogous poly(dithiafulvene). The π-conjugation system
of 5c was also highly developed by the long alkoxy chain.

3542 Naka et al.
Macromolecules, Vol. 35, No. 9, 2002
hexane (0.65 mL, 1.04 mmol) was added at 0 °C. The reaction
mixture was kept at 0 °C for 0.5 h, and powder of sulfur or
selenium (1.00 mmol) was added. After stirring the mixture
for 2 h at 0 °C, water (18 mg) was carefully added at -55 °C.
The temperature of the mixture was allowed to rise at room
temperature, and the reaction mixture was stirred for 3 h. The
mixture was then poured into a large quantity of Et2O or
hexane. The obtained precipitate was washed with water to
remove inorganic salts. After drying under reduced pressure,
the polymeric compound was obtained.
obtain a dark green powder as a polymer CT complex.
The resulting complexes derived from 4a , 4b, and 5b
were soluble in acetonitrile, DMSO, DMF, acetone, and
MeOH. The CT complexes composed of 4c or 5c were
soluble in THF, CHCl3, and CH2Cl2. The UV-vis
absorptions of the polymer CT complexes exhibited λmax
at 845, 762, and 745 nm, which were responsible for the
anion radical of TCNQ.12 The conductivities of the
polymers were measured at room temperature by the
two-probe technique and are summarized in Table 2.
After complexation with TCNQ, the conductivities of the
polymers increased remarkably. In the case of 4a and
4b, the values raised approximately 1000 times higher
than those of the uncomplexed polymers. The relatively
low conductivities of 4c and 5c complexes suggested
incomplete complexations with TCNQ in the solid states
because of the steric hindrances of the long alkoxy
groups.
4b. Yield: 37%. 1H NMR (DMSO-d6, ppm): δ 1.2-1.6 (CH2
of piperidine unit), 2.3 (-CH3 on phenyl moiety), 3.6 (N-CH2
of piperidine unit), 4.2 (N-CH2 of piperidine unit and -CH2C-
(dS)N ), 6.7 (benzylidene and aromatic protons), 7.2 (aromatic
and 1,3-dithiole ring protons). IR (KBr, cm-1): 1576, 1550,
1290, 1262.
1
4c. Yield: 68%. H NMR (CDCl3, ppm): δ 0.9 (-OC11H22
-
CH3), 1.1-1.6 (-OC2H4-C9H18-CH3 and CH2 of piperidine
unit), 1.8 (-OCH2-CH2-C10H21), 3.8-4.2 (-OCH2-C11H23 and
N-CH2 of piperidine unit), 4.3 (N-CH2 of piperidine unit and
-CH2C(dS)N ), 6.8 (benzylidene and aromatic protons), 7.0-
7.2 (aromatic and 1,3-dithiole ring protons). IR (KBr, cm-1):
1580, 1288, 1262.
Con clu sion
5a . Yield: 95%. IR (KBr, cm-1): 1575, 1556.
We presented here the synthesis and properties of the
π-conjugated polymers with the electron-donating dichal-
cogenafulvene units. UV absorption analysis indicated
that π-conjugations in 4 and 5 were developed ef-
ficiently. In particular, the most effective π-conjugations
were achieved in the systems of the polymers attaching
the long alkoxy side chains. The polymers acted as good
electron donors, similarly to the low molecular weight
model compounds. The polymers formed semiconducting
CT complexes with TCNQ. Some polymers showed
highly improved conductivities (3 orders of magnitude
greater than the uncomplexed polymers) upon TCNQ
complexation.
1
5b. Yield: 85%. H NMR (DMSO-d6 soluble part, ppm): δ
1.2-1.5 (CH2 of piperidine unit), 2.2 (-CH3 on phenyl moiety),
3.6 (N-CH2 of piperidine unit), 4.3 (N-CH2 of piperidine unit),
4.4 (-CH2C(dS)N ), 6.7-7.4 (benzylidene and aromatic pro-
tons), 7.5 (1,3-diselenole ring proton). IR (KBr, cm-1): 1576,
1553, 1292.
1
5c. Yield: 68%. H NMR (CDCl3, ppm): δ 0.9 (-OC11H22
-
CH3), 1.1-1.5 (-OC2H4-C9H18-CH3 and CH2 of piperidine
unit), 1.8 (-OCH2-CH2-C10H21), 3.8-4.1 (-OCH2-C11H23 and
N-CH2 of piperidine unit), 4.2 (N-CH2 of piperidine unit and
-CH2C(dS)N ), 6.9 (aromatic protons), 7.1 (benzylidene pro-
ton), 7.5 (1,3-diselenole ring protons). IR (KBr, cm-1): 1577,
1555, 1291.
Mod el Rea ction s. a . 2,6-Bisp h en yl-1,4-d iselen a fu lven e
(8).10 A 1.6 M solution of n-butyllithium in hexane (0.65 mL,
1.04 mmol) was added to a stirred solution of phenylacetylene
(102 mg, 1 mmol) in THF (2 mL), cooled at 0 °C. When the
addition was completed, the reaction mixture was stirred at 0
°C for 0.5 h, and powder of selenium (79 mg, 1.00 mmol) was
added. After stirring the mixture for an additional 2 h at 0
°C, water (1 mL) was carefully added at -78 °C. The temper-
ature of the mixture was allowed to rise at room temperature,
and the two layers were separated. The organic solution was
dried with MgSO4, and the solvent was removed, yielding the
Exp er im en ta l Section
Ma ter ia ls. Unless stated otherwise, all reagents and chemi-
cals were obtained from commercial sources and used without
further purification. Solvents were dried and distilled under
N2. 1,4-Diethynyl-2,5-dimethylbenzene (3b)13 and 1,4-dieth-
ynyl-2,5-bis(dodecyloxy)benzene (3c)14 were synthesized ac-
cording to the literature. Syntheses of the dithiafulvene 6 and
the thioamide 7 have been described in a previous paper.9b
Mea su r em en ts. 1H NMR and IR spectra were recorded on
a J EOL J NM-EX270 spectrometer and a Perkin-Elmer 1600
spectrometer, respectively. GPC measurements of 4b and 5b
were carried out on TSK gel a-3000 by using DMSO as an
eluent at 50 °C after calibration with standard poly(ethylene
glycol) samples. GPC of 4c and 5c were performed with a
Shodex K-803 in chloroform at 25 °C by use of polystyrene as
standard samples. UV-vis spectra were obtained on a J ASCO
V-530 spectrophotometer. Cyclic voltammetry was carried out
with a BAS CV-50W electrochemical analyzer in CH3CN
solution of 0.1 M [NEt4]BF4 as a supporting electrolyte.
Platinum wire auxiliary electrode and Ag/AgCl RE-5 reference
electrode were used in the CV measurements. For the CV of
the polymers, thin polymer films were prepared on indium tin
oxide (ITO) coated glass electrodes by casting from their
solutions. The electrodes were dried under vacuum. For the
CV of the model compounds, they were dissolved in the CH3-
CN solution containing the supporting electrolyte. A platinum
working electrode was used, instead of ITO. Electrical con-
ductivities were measured at room temperature by the two-
probe technique using a Keithley 2400 source meter. The
polymer films were prepared by dropping of the polymer
solutions onto glass plates equipped with platinum electrodes,
followed by drying in vacuo.
diselenafulvene 8 (146 mg, 81%). IR (NaCl): 1576, 1558 cm-1
.
1H NMR (270 MHz, DMSO-d6): δ 7.23-7.48 (m, 11H), 7.85
(s, 1H).
b. 1-(2-P h en yl-1-selen oxoeth yl)p ip er id in e (9).10 To a
solution of piperidine (2.5 mL, 25 mmol) in Et2O (1 mL) was
added 1.6 M solution in hexane of n-butyllithium (1.56 mL,
2.50 mmol) at -30 °C. Phenylacetylene (255 mg, 2.50 mmol)
was added to the reaction mixture. The temperature of the
mixture was allowed to rise to 80 °C. The powder of selenium
(197 mg, 2.5 mmol) was added, the mixture was stirred for 2
h, and then 1 N HCl (5 mL) was added. The brown organic
layer was separated, and the aqueous phase was extracted
with Et2O. The combined organic phase was dried over
anhydrous MgSO4 and evaporated to give the yellow product
(604 mg, 91%). 1H NMR (CDCl3): δ 1.28 (m, 2H), 1.73 (m, 4H),
3.55 (t, 2H), 4.39 (t, 2H), 4.52 (s, 2H), 7.35 (m, 5H).
Ack n ow led gm en t. This work was supported by
Grants-in-Aid for Scientific Research (No. 12650865)
from the Ministry of Education, Culture, Sports, Sci-
ence, and Technology, Government of J apan. T.U.
appreciates Research Fellowship of the J apan Society
for the Promotion of Science for Young Scientists for
financial support.
P olym er iza tion . A typical procedure was as follows. To a
solution of a diethynyl compound (0.50 mmol) in a solvent
(Et2O or THF, 4.0 mL), 1.6 M solution of n-butyllithium in

Macromolecules, Vol. 35, No. 9, 2002
Poly(dithiafulvene)s and Poly(diseleafulvene)s 3543
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