Synthesis and photoluminescence properties of heterocycle-containing poly(disubstituted acetylene)s

Article abstract of DOI:10.1016/j.polymer.2012.08.009

The metathesis polymerizations of disubstituted acetylenes containing heterocycles such as thiophene, furan, benzo[b]thiophene, and benzothiazole were examined using NbCl₅, TaCl₅, and WCl₆. Thiophene-containing monomers polymerized to afford relatively high-molecular-weight polymers in moderate yields. Benzo[b]thiophene-containing monomers also polymerized to give polymers with relatively high molecular weights. On the other hand, furan- and benzothiazole-containing monomers exhibited low metathesis polymerizability, and the polymerizations did not provide high-molecular-weight polymers. Poly(1-hexyl-2-arylacetylene)s having heterocycles [poly(1a) and poly(3a), Scheme 1] emitted blue-colored lights, and the emission maxima were around 480 nm. Heterocycle-containing poly(1-phenyl-2-arylacetylene) [poly(1b)] and poly(1-fluorenyl-2-arylacetylene) [poly(3d)] showed green-colored and yellow-colored emissions, and the emission maxima were 520 and 540 nm, respectively. The emission wavelengths of poly(disubstituted acetylene)s having heterocycles were almost the same as those of the corresponding poly(disubstituted acetylene)s without heterocycles. However, heterocycle-containing polymers showed high fluorescence quantum yields compared to the corresponding polymers without heterocycles. Diarylacetylene polymers showed emission red-shifts between the solution and cast film, while the emission maximum of poly(1-hexyl-2-phenylacetylene) [poly(1a)] in the cast film was almost the same as that in the solution. Benzo[b]thiophene-containing poly(1-(4-trimethylsilylphenyl)-2-phenylacetylene) [poly(3b)] and poly(1-(9,9-dimethyl-2-fluorenyl)-2-phenylacetylene) [poly(3d)] afforded the free-standing membranes because of their high molecular weights. The oxygen permeability coefficient (PO₂) of poly(3b) was as large as 1400 barrers. Poly(3d) showed higher gas permeability, and its PO₂ was 5300 barrers.

Full text of DOI:10.1016/j.polymer.2012.08.009

Polymer 53 (2012) 4380e4387
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Synthesis and photoluminescence properties of heterocycle-containing
poly(disubstituted acetylene)s
*
Tatsuoki Muroga, Toshikazu Sakaguchi , Tamotsu Hashimoto
Department of Materials Science and Engineering, Graduate School of Engineering, University of Fukui, Bunkyo 3-9-1, Fukui 910-8507, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The metathesis polymerizations of disubstituted acetylenes containing heterocycles such as thiophene,
furan, benzo[b]thiophene, and benzothiazole were examined using NbCl5, TaCl5, and WCl6. Thiophene-
containing monomers polymerized to afford relatively high-molecular-weight polymers in moderate
yields. Benzo[b]thiophene-containing monomers also polymerized to give polymers with relatively high
molecular weights. On the other hand, furan- and benzothiazole-containing monomers exhibited low
metathesis polymerizability, and the polymerizations did not provide high-molecular-weight polymers.
Poly(1-hexyl-2-arylacetylene)s having heterocycles [poly(1a) and poly(3a), Scheme 1] emitted blue-
colored lights, and the emission maxima were around 480 nm. Heterocycle-containing poly(1-phenyl-
2-arylacetylene) [poly(1b)] and poly(1-fluorenyl-2-arylacetylene) [poly(3d)] showed green-colored and
yellow-colored emissions, and the emission maxima were 520 and 540 nm, respectively. The emission
wavelengths of poly(disubstituted acetylene)s having heterocycles were almost the same as those of the
corresponding poly(disubstituted acetylene)s without heterocycles. However, heterocycle-containing
polymers showed high fluorescence quantum yields compared to the corresponding polymers without
heterocycles. Diarylacetylene polymers showed emission red-shifts between the solution and cast film,
while the emission maximum of poly(1-hexyl-2-phenylacetylene) [poly(1a)] in the cast film was almost
the same as that in the solution. Benzo[b]thiophene-containing poly(1-(4-trimethylsilylphenyl)-2-
phenylacetylene) [poly(3b)] and poly(1-(9,9-dimethyl-2-fluorenyl)-2-phenylacetylene) [poly(3d)] affor-
ded the free-standing membranes because of their high molecular weights. The oxygen permeability
coefficient (PO2) of poly(3b) was as large as 1400 barrers. Poly(3d) showed higher gas permeability, and
its PO2 was 5300 barrers.
Received 22 May 2012
Received in revised form
1 August 2012
Accepted 4 August 2012
Available online 10 August 2012
Keywords:
Poly(disubstituted acetylene)
Heterocycle
Photoluminescence
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
unsubstituted and monosubstituted acetylene polymers show no
or weak luminescence [21e23]. Some studies on luminescence of
Recently, there has been a considerable interest in conjugated
polymers because of their electronic and optical properties [1e5].
Their primary applications are organic light emitting diodes
(OLEDs), field-effect transistors [6e9]. The benefits of conjugated
polymers include low cost processing via solution-based tech-
niques such as spin-coating and inkjet printing methods and ability
to optimize the electronic, optical, and physical properties for
various applications. A number of conjugated polymers such as
polythiophenes [10e12], poly(p-phenylenevinylene)s [13e16],
poly(p-phenyleneethynylene)s [17e20], and their copolymers were
studied and known to emit strong light upon photo- and electro-
excitations. Similarly to such conjugated polymers, disubstituted
acetylene polymers exhibit strong luminescence, although
disubstituted acetylene polymers have been reported [24e31],
however, it has not been clarified that what substituents are suit-
able to high emission and how the substituents affect the lumi-
nescence. Especially, there are few reports on the luminescence of
polyacetylenes containing polar groups.
Disubstituted acetylene polymers are obtained by the metath-
esis polymerization of corresponding acetylene monomers with
NbCl5, TaCl5, and WCl6 [32e34]. These transition metal catalysts are
intolerant toward polar groups, and thus it is difficult to synthesize
disubstituted acetylene polymers containing polar groups by the
metathesis polymerization. Therefore, poly(disubstituted acety-
lene)s with polar groups were generally synthesized through
polymer reaction after the polymerization of nonpolar disubsti-
tuted acetylenes [35e40]. On the other hand, Tang and coworkers
succeeded in the polymerization of disubstituted acetylenes con-
taining polar groups [26,27,41e43]. For instance, poly(1-phenyl-1-
undecyne)s containing esters were successfully synthesized by
* Corresponding author. Tel.: þ81 776 27 9779; fax: þ81 776 27 8767.
E-mail address: sakaguchi@matse.u-fukui.ac.jp (T. Sakaguchi).
0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2012.08.009

T. Muroga et al. / Polymer 53 (2012) 4380e4387
4381
Scheme 1. Metathesis polymerization of heterocycle-containing disubstituted acetylenes.
the metathesis polymerization with WCl6/Ph4Sn catalyst. In this
way, disubstituted acetylenes with relatively low polarity can
polymerize using transition metal catalysts.
curve to the time axis. The solubility coefficient (S) value was
calculated by using equation S ¼ P/D.
In the present study, the metathesis polymerizations of
novel disubstituted acetylenes containing heterocycles such as
thiophene, furan, benzo[b]thiophene, and benzothiazole were
investigated using NbCl5/n-Bu4Sn, TaCl5/n-Bu4Sn, and WCl6/Ph4Sn
(Scheme 1). The absorption and emission spectra of the
heterocycle-containing polymers were studied in CHCl3. Further,
the emission spectra of some polymers in cast film were examined.
On the other hand, poly(disubstituted acetylene)s like poly(-
diphenylacetylene) and its derivatives are known to possess high
gas permeability [33]. Therefore, the membranes of benzo[b]thio-
phene-containing polymers were prepared and their gas perme-
ability was examined.
2.2. Materials
1-Octyne, 1-bromo-4-iodobenzene, chlorobenzene, 2-methyl-
3-butyne-2-ol, iodomethane, 1-bromooctane, and common
organic solvents were commercially obtained from Wako Pure
Chemicals, Ind., Ltd. and used without further purification. 5-
Bromo-2-furaldehyde, 2-bromothiophene, benzo[b]thiophene-
2-ylboronic acid, 2-(4-bromophenyl)benzothiazole, quinoline,
and copper powder were purchased from Tokyo Chemical
Industry (TCI), Ltd. and used without further purification. 2-
Isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborane, niobium (V)
chloride, tantalum (V) chloride, and tungsten (VI) chloride were
commercially obtained from Aldrich Chemistry, Ind., Ltd. and
used without further purification. Toluene which is polymeri-
zation solvent was purified by two times of distillation
in the presence of CaH2. 2-Bromofuran [44], 2-bromo-9,9-
dimethylfluorene [31], and p-n-octyliodobenzene [45] were
prepared according to the literature. Novel monomers were
synthesized as shown in Scheme 2. The detailed procedures and
analytical data are described below.
2. Experimental
2.1. Measurements
The molecular weight distribution (MWD) of polymers was
measured by gel permeation chromatography (GPC) in chloroform
(at a 1.0 mL/min flow rate) at 40 ꢀC on a Shimadzu LC-10AD chro-
matograph equipped with four polystyrene gel columns (Shodex K-
805Lꢁ1 and K-804Lꢁ3) and a Shimadzu RID-6A refractive index
detector. The weight-average molecular weight (Mw) and poly-
dispersity ratio [weight-average molecular weight/number-average
molecular weight (Mw/Mn)] were calculated from chromatograms
based on a polystyrene calibration. 1H (500 MHz) and 13C (125 MHz)
NMR spectra were recorded on Jeol LA-500 instrument in CDCl3 at
room temperature. UVevis absorption was measured with HITACH
U-3900H spectrophotometer and optical emission spectrometry
was measured with Perkin Elmer LS-55 fluorescence spectrometer.
Elemental analyses of monomers were performed at the Microan-
alytical Center of Kyoto University. Gas permeability coefficients
were measured with a Rikaseiki K-315-N gas permeabilityapparatus
at 25ꢀC under 1 atm upstream pressure. Thepermeabilitycoefficient
2.3. Monomer synthesis
2.3.1. 1-Hexyl-2-(4-(2-thiophenyl)phenyl)acetylene (1a)
n-BuLi in hexane (1.6 M, 65 mL, 0.10 mol) was slowly added to
a solution of 2-bromothiophene (11 g, 0.068 mol) in THF (200 mL)
(P) expressed in barrer unit (1 barrer
¼
10ꢂ10 cm3 (STP)
cm cmꢂ2 sꢂ1 cmHgꢂ1) was calculated from the slope of the steady-
state line. The diffusion coefficient (D) value was determined by
the time lag method using the following equation:
D ¼ l2=6
q
here, l is the membrane thickness and
q is the time lag, which is
given by the intercept of the asymptotic line of timeepressure
Scheme 2. Synthesis of monomers.

4382
T. Muroga et al. / Polymer 53 (2012) 4380e4387
at ꢂ78 ꢀC. After stirring for 2 h at this temperature, the mixture was
added to a solution of 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (13 g, 0.068 mol) in 150 mL of THF. The mixture
was warmed to room temperature and stirred overnight. The
reaction was terminated by adding a small amount of methanol and
the resultant solution was washed with water three times. The
solution was dried over anhydrous sodium sulfate, and concen-
trated under reduced pressure. The crude product was purified
by silica gel column chromatography (eluent: hexane) to give
2-(4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)thiophene (11.7 g,
0.056 mol, 82%).
2.3.4. 1-Hexyl-2-[4-(2-benzothiazolyl)phenyl]acetylene (4a)
Monomer 4a was synthesized by the same method as for 1a
using 2-(4-bromophenyl)benzothiazole and 1-octyne (Yield 95%).
1H NMR (CDCl3, ppm): 8.07e7.24 (m, 9H, Ar), 2.42 (t, J ¼ 6.0 Hz, 2H,
C^CeCH2e), 1.65e1.25 (m, 8H, C^CeCH2e(CH2)4eCH3), 0.91 (t,
J ¼ 7.0 Hz, 3H, CH3). 13C NMR (CDCl3, ppm): 167.4, 154.1, 135.1, 127.3,
126.4, 125.2, 123.2, 121.6, 93.4, 80.2, 31.4, 28.7, 22.5, 19.6, 14.0. Anal.
Calcd for C21H21NS: C, 78.95; H, 6.63; N, 4.38; S, 10.04. Found: C,
77.77; H, 6.68; N, 4.13.
2.3.5. 1-(4-Trimethylsilylphenyl)-2-[4-(2-thiophenyl)phenyl]
A 500 mL three-necked flask was equipped with a three-
acetylene (1b)
way stopcock and
a
magnetic stirring bar. Dichlorobis
1-(4-Trimethylsilylphenyl)-2-(4-bromophenyl)acetylene
was
(triphenylphosphine)palladium (II) (0.10 g, 0.14 mmol), cuprous iodide
(0.10 g, 0.53 mmol), and triphenylphosphine (0.10 g, 0.38 mmol) were
put in the flask. After the flask was flushed with nitrogen, 1-bromo-4-
iodobenzene (7.6 g, 0.027 mol) and 1-octyne (3.0 g, 0.027 mol) in
triethylamine (500 mL) were added to it. The mixture was stirred for
16 h at 80 ꢀC. After the triethylamine was evaporated, ether (200 mL)
was added, and the insoluble salt was filtered off. The solution was
washed with HClaq. (1.0 M) three times. The ethereal solution was
dried over anhydrous sodium sulfate. Ether was evaporated, and the
crude product was purified by silica gel column chromatography
(eluent: hexane) to give 1-hexyl-2-(4-bromophenyl)acetylene (7.0 g,
0.026 mol, 98%).
1-Hexyl-2-(4-bromophenyl)acetylene (7.0 g, 0.026 mol), 2-
(4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)thiophene (5.4 g,
0.026 mol), dimethoxyethane (200 mL), ethanol (95 mL), Na2CO3aq
(2.0 M, 95 mL), tetrakis(triphenylphosphine)palladium (0.60 g,
0.48 mmol) were placed in three-necked flask, and the mixture was
stirred at 80 ꢀC overnight. Ether (ca. 200 mL) was added, and the
mixture was washed with water. Ether was evaporated, and the
crude product was purified by silica gel column chromatography
(eluent: hexane) to give 1-hexyl-2-[4-(2-thiophenyl)phenyl]acet-
ylene (1a) (4.5 g, 0.017 mol, 65%). 1H NMR (CDCl3, ppm): 7.53e7.06
(m, 7H, Ar), 2.41 (t, J ¼ 6.0 Hz, 2H, C^CeCH2e), 1.61e1.30 (m, 8H,
C^CeCH2e(CH2)4eCH3), 0.90 (t, J ¼ 7.0 Hz, 3H, CH3). 13C NMR
(CDCl3, ppm): 143.8, 133.4, 128.1, 127.7, 125.5, 123.0, 91.5, 80.3, 31.4,
28.7, 28.6, 22.7, 19.5, 14.1. Anal. Calcd for C18H20S: C, 80.54; H, 7.51;
S, 11.95. Found: C, 78.09; H, 8.28.
prepared by the same method as for 1-phenyl-2-(4-bromophenyl)
acetylene using 4-trimethylsilylphenylacetylene (Yield 96%).
Monomer 1b was synthesized by the same method as for 1a using
1-(4-trimethylsilylphenyl)-2-(4-bromophenyl)acetylene and 2-
(4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)thiophene (Yield 76%).
1H NMR (CDCl3, ppm): 7.59e7.07 (m, 11H, Ar), 0.27 (s, 9H, SiCH3).
13C NMR (CDCl3, ppm): 143.7, 141.1, 134.2, 133.2, 132.1, 130.6, 130.5,
128.5, 128.1, 125.7, 125.4, 123.5, 90.5, 89.7, ꢂ1.2. Anal. Calcd for
C21H20SSi: C, 75.85; H, 6.06; S, 9.64; Si, 8.45. Found: C, 75.44; H,
6.01.
2.3.6. 1-(4-Trimethylsilylphenyl)-2-[4-(2-furanyl)phenyl]acetylene
(2b)
This monomer was synthesized by the same method as for 1b
using 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)furan (Yield
53%). 1H NMR (CDCl3, ppm): 7.65e7.48 (m, 11H, Ar), 0.27 (s, 9H,
SiCH3). 13C NMR (CDCl3, ppm): 142.5, 141.5, 132.0, 130.6, 130.5,
123.5, 122.0, 111.9, 105.9, 90.4, 89.8, ꢂ1.2. Anal. Calcd for
C21H20OSi: C, 79.70; H, 6.37; O, 5.06; Si, 8.87. Found: C, 79.51; H,
6.44.
2.3.7. 1-(4-Trimethylsilylphenyl)-2-[4-(2-benzo[b]thiophenyl)
phenyl]acetylene (3b)
Monomer 3b was synthesized by the same method as for 1b
using benzo[b]thiophene-2-ylboronic acid (Yield 74%). 1H NMR
(CDCl3, ppm): 7.49e7.24 (m, 13H, Ar), 0.27 (s, 9H, SiCH3). 13C NMR
(CDCl3, ppm): 141.4, 139.7, 133.2, 133.0, 131.6, 130.6, 127.9, 123.8,
123.2, 122.3, 90.7, 88.7, ꢂ1.3. Anal. Calcd for C25H22SSi: C, 78.48; H,
5.80; S, 8.38; Si, 7.34. Found: C, 72.51; H, 5.26.
2.3.2. 1-Hexyl-2-[4-(2-furanyl)phenyl]acetylene (2a)
2-(4,4,5,5-Tetramethyl-1,3,2-dioxaborane-2-yl)furan
was
prepared by the same method as for 2-(4,4,5,5-tetramethyl-
1,3,2-dioxaborane-2-yl)thiophene using 2-isopropoxy-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane (Yield 78%). Monomer 2a was
synthesized by the same method as for monomer 1a using 1-
hexyl-2-(4-bromo)phenylacetylene and 2-(4,4,5,5-tetramethyl-
1,3,2-dioxaborane-2-yl)furan (Yield 76%). 1H NMR (CDCl3, ppm):
7.67e7.37 (m, 7H, Ar), 2.41 (t, J ¼ 6.0 Hz, 2H, C^CeCH2e), 1.63e
1.25 (m, 8H, C^CeCH2e(CH2)4eCH3), 0.90 (t, J ¼ 7.0 Hz, 3H,
CH3). 13C NMR (CDCl3, ppm): 142.3, 131.8, 129.8, 123.5, 122.9,
118.6, 111.8, 91.4, 80.5, 31.4, 28.7, 28.6, 22.6, 19.5, 14.0. Anal.
Calcd for C18H20O: C, 85.67; H, 7.99; S, 6.34. Found: C, 85.50; H,
8.51.
2.3.8. 1-(4-Trimethylsilylphenyl)-2-[4-(2-benzothiazolyl)phenyl]
acetylene (4b)
Monomer 4b was synthesized by the same method as for 4a
using 4-trimethylsilylphenylacetylene (Yield 93%). 1H NMR (CDCl3,
ppm): 8.09e7.25 (m, 13H, Ar), 0.28 (s, 9H, SiCH3). 13C NMR (CDCl3,
ppm): 167.2, 154.2, 135.3, 132.2, 130.7, 127.4, 126.4, 125.3, 123.3,
121.6, 92.1, 89.2, ꢂ1.2. Anal. Calcd for C24H21NSSi: C, 75.15; H, 5.52;
N, 3.65; S, 8.36; Si, 7.32. Found: C, 74.99; H, 5.55; N, 3.64.
2.3.9. 1-(4-n-Octylphenyl)-2-[4-(2-thiophenyl)phenyl]acetylene
(1c)
1-(4-n-Octylphenyl)-2-(4-bromophenyl)acetylene was prepared
by the same method as for 1-phenyl-2-(4-bromophenyl)acetylene
using 4-octylphenylacetylene (Yield 98%). Monomer 1c was
synthesized by the same method as for 1b using 1-(4-octylphenyl)2-
(4-bromophenyl)acetylene (Yield 75%).1H NMR (CDCl3, ppm): 7.61e
7.07 (m, 11H, Ar), 2.85 (t, J ¼ 7.7 Hz, 2H, ArCH2e), 2.62 (quint,
J ¼ 7.7 Hz, 2H, ArCH2CH2e), 1.30 (m, 10H, ArCH2CH2e(CH2)5eCH3),
0.88 (t, J ¼ 7.0 Hz, 3H, CH3). 13C NMR (CDCl3, ppm): 143.5, 134.1,
132.1,128.8,128.1,126.3,125.7,120.3, 92.6, 88.6, 35.9, 31.9, 31.2, 29.5,
29.3, 22.7, 14.1. Anal. Calcd for C26H28S: C, 83.82; H, 7.58; S, 8.61.
Found: C, 82.61; H, 7.35.
2.3.3. 1-Hexyl-2-[4-(2-benzo[b]thiophenyl)phenyl]acetylene (3a)
Monomer 3a was prepared by the same method as for 1a using
1-hexyl-2-(4-bromo)phenylacetylene and benzo[b]thiophene-2-
ylboronic acid (Yield 69%). 1H NMR (CDCl3, ppm): 7.82e7.25 (m,
9H, Ar), 2.42 (t, J ¼ 6.0 Hz, 2H, C^CeCH2e), 1.63e1.31 (m, 8H,
C^CeCH2e(CH2)4eCH3), 0.91 (t, J ¼ 7.0 Hz, 3H, CH3). 13C NMR
(CDCl3, ppm): 143.6, 140.7, 139.6, 133.3, 131.3, 126.2, 124.6, 124.5,
124.0, 122.3, 119.7, 92.0, 80.0, 31.4, 28.7, 28.6, 22.6, 19.5, 14.1. Anal.
Calcd for C22H22S: C, 82.97; H, 6.96; S,10.07. Found: C, 83.45; H, 7.19.

T. Muroga et al. / Polymer 53 (2012) 4380e4387
4383
2.3.10. 1-(4-n-Octylphenyl)-2-[4-(2-furanyl)phenyl]acetylene (2c)
Monomer 2c was synthesized by the same method as for 1c
using 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborane-2-yl)furan (Yield
23%). 1H NMR (CDCl3, ppm): 7.68e6.65 (m, 11H, Ar), 2.85 (t,
J ¼ 7.7 Hz, 2H, ArCH2e), 2.62 (quint, J ¼ 7.7 Hz, 2H, ArCH2CH2e),
2.20 (m, 10H, ArCH2CH2e(CH2)5eCH3), 0.98 (t, J ¼ 7.0 Hz, 3H,
CH3). 13C NMR (CDCl3, ppm): 142.5, 142.1, 132.3, 131.8, 128.2, 123.6,
90.5, 89.2, 35.9, 31.9, 31.2, 29.4, 29.3, 22.7, 14.1. Anal. Calcd for
C26H28O: C, 87.60; H, 7.92; O, 4.49. Found: C, 86.50; H, 8.35.
80 ꢀC for 24 h, which was quenched with a small amount of
methanol. The resulting polymer was isolated by precipitation
into a large excess of acetone, and its yield was determined
gravimetrically.
2.5. Preparation and desilylation of membrane
Membranes of poly(3b) and poly(3d) were prepared by
casting their toluene solutions into Petri dishes at room
temperature. The dish was covered with a glass vessel to slow
evaporation of solvent. After a membrane was formed, the
membrane was peel off, and it was immersed in methanol for
24 h and dried to constant weight at room temperature under
atmospheric pressure.
The desilylation of membrane of poly(3b) was carried out
according to the literature [46]. The membrane was immersed in
trifluoroacetic acid at room temperature for 24 h. To remove
residual impurities in polymer matrix, the membrane was
immersed in methanol for 24 h. The membrane was dried at room
temperature under atmospheric pressure. The completion of desi-
lylation was confirmed by the comparison between IR spectra of
membranes before and after reaction (Fig. 1). The spectrum after
reaction showed no absorptions at 1250 and 1120 cmꢂ1 derived
from trimethylsilyl group, which were observed in the spectrum
before reaction.
2.3.11. 1-(4-n-Octylphenyl)-2-[4-(2-benzo[b]thiophenyl)phenyl]
acetylene (3c)
Monomer 3c was synthesized by the same method as for 1c
using benzo[b]thiophene-2-ylboronic acid (Yield 62%). 1H NMR
(CDCl3, ppm): 7.89e7.14 (m, 13H, Ar), 2.84 (t, J ¼ 7.7 Hz, 2H, ArCH2e
), 2.62 (quint, J ¼ 7.7 Hz, 2H, ArCH2CH2e), 1.68 (m, 10H, ArCH2CH2e
(CH2)5eCH3), 0.89 (t, J ¼ 7.0 Hz, 3H, CH3). 13C NMR (CDCl3, ppm):
145.1, 139.7, 132.2, 128.8, 128.4, 123.8, 120.0, 90.8, 87.7, 36.0, 31.9,
31.2, 29.4, 29.3, 22.7, 14.1. Anal. Calcd for C30H30S: C, 85.26; H, 7.15;
S, 7.59. Found: C, 82.08; H, 6.97.
2.3.12. 1-(4-n-Octylphenyl)-2-[4-(2-benzothiazolyl)phenyl]
acetylene (4c)
Monomer 4c was synthesized by the same method as for 4a
using 4-n-octylphenylacetylene (Yield 63%). 1H NMR (CDCl3, ppm):
8.08e7.154 (m, 12H, Ar), 2.87 (t, J ¼ 7.7 Hz, 2H, ArCH2e), 2.63 (quint,
J ¼ 7.7 Hz, 2H, ArCH2CH2e), 1.58 (m, 10H, ArCH2CH2e(CH2)5eCH3),
0.88 (t, J ¼ 7.0 Hz, 3H, CH3). 13C NMR (CDCl3, ppm): 167.2, 154.2,
135.1, 132.1, 128.9, 126.4, 123.3, 92.2, 88.3, 36.0, 31.9, 31.2, 29.4, 29.3,
22.7, 14.1. Anal. Calcd for C29H29NS: C, 82.22; H, 6.90; N, 3.31; S, 7.57.
Found: C, 81.01; H, 7.13; N, 3.13.
2.6. Fractional free volume (FFV) of polymer membranes
The densities of membranes were determined by hydrostatic
weighing using a Mettler Toledo balance and a density determi-
nation kit. In this method, a liquid with known density (r0) is
needed, and the membrane density (
equation:
r) is given by the following
2.3.13. 1-(9,9-Dimethy)-2-fluorenyl)-2-[4-(2-thiophenyl)phenyl]
acetylene (1d)
2-Ethynyl-9,9-dimethylfluorene was prepared by the same
method as for p-ethynyl-n-octylbenzene using 2-bromo-9,9-
dimethylfluorene (Yield 59%). 1-(9,9-Dimethyl-2-fluorenyl)-2-(4-
bromophenyl)acetylene was prepared by the same method as for
r
¼
r0 ꢁ MA=ðMA ꢂ MLÞ
where MA is membrane weight in air and ML is membrane weight in
the auxiliary liquid. An aqueous sodium nitrate was used as the
auxiliary liquid. FFV is calculated by the following equation:
1-phenyl-2-(4-bromophenyl)acetylene
using
2-ethynyl-9,9-
dimethylfluorene (Yield 80%). Monomer 1d was synthesized by
the same method as for 1a using 1-(9,9-dimethyl-2-fluorenyl)-2-
(4-bromophenyl)acetylene (Yield 68%). 1H NMR (CDCl3, ppm):
7.70e7.09 (m, 14H, Ar), 1.50 (s, 6H, CH3). 13C NMR (CDCl3, ppm):
153.6, 143.7, 134.0, 130.7, 128.2, 127.1, 125.9, 125.3, 122.6, 120.3,
120.2, 120.0, 91.2, 89.3, 46.9, 27.0. Anal. Calcd for C27H20S: C, 86.13;
H, 5.35; S, 8.52. Found: C, 85.23; H, 5.60.
À
Áꢀ
À
Áꢀ
FFV ¼ vsp ꢂ v0 vspz vsp ꢂ 1:3vw vsp
where vsp is the polymer specific volume, and v0 is the occupied
volume of the polymer. The occupied volume is typically estimated
as 1.3 times the van der Waals volume (vw), which is calculated
using the group contribution method [47].
2.3.14. 1-(9,9-Dimethy)-2-fluorenyl)-2-[4-(2-benzo[b]thiophenyl)
phenyl]acetylene (3d)
Monomer 3d was synthesized by the same method as for 3a
using 1-(9,9-dimethyl-2-fluorenyl)-2-(4-bromophenyl)acetylene
(Yield 24%). 1H NMR (CDCl3, ppm): 7.70e7.24 (m, 16H, Ar), 1.50 (s,
6H, CH3). 13C NMR (CDCl3, ppm): 153.6, 139.7, 133.0, 130.7, 127.1,
125.9, 122.4, 121.6, 120.3, 120.0, 91.4, 89.4, 46.9, 27.0. Anal. Calcd for
C31H22S: C, 87.28; H, 5.20; S, 7.52. Found: C, 79.62; H, 5.04.
2.4. Polymerization
Polymerization was carried out in a glass tube equipped with
a three-way stopcock under dry nitrogen at 80 ꢀC. A detailed
procedure is as follows. The monomer solution was prepared in
a glass tube by mixing monomer and dry toluene. Another glass
tube was charged with NbCl5, n-Bu4Sn, and dry toluene; this
catalyst solution was aged at 80 ꢀC for 10 min, and then
monomer solution was added to it. Polymerization was run at
Fig. 1. IR spectra of membranes of poly(3b) before and after desilylation.

4384
T. Muroga et al. / Polymer 53 (2012) 4380e4387
Table 1
Table 3
Polymerization of thiophene-containing monomers.a
Polymerization of benzo[b]thiophene-containing monomers.a
Yieldb
%
Mn
Mw/Mn
Monomer
Catalyst
Yieldb
%
Mn
Mw/Mn
c
c
c
c
Monomer
Catalyst
1a
TaCl5
NbCl5
WCl6
TaCl5
NbCl5
WCl6
TaCl5
NbCl5
WCl6
TaCl5
NbCl5
WCl6
33
64
48
38
10
21
22
68
6
1,410,000
1,500,000
12,400
Insoluble
107,000
830
75,600
1810
1230
2.9
2.3
3.9
3a
TaCl5
NbCl5
WCl6
TaCl5
NbCl5
WCl6
TaCl5
NbCl5
WCl6
TaCl5
NbCl5
WCl6
43
59
79
64
18
0
17
6
28
64
23
0
14,700
1470
1860
1,570,000
213,000
20
6.4
44
1.6
3.6
1b
1c
1d
3b
3c
3d
13
3.1
5.6
1.4
1.5
6.0
1.2
2.9
147,000
106,000
1340
190,000
206,000
2.4
2.7
2.4
2.9
1.2
81
35
73
1670
981
1220
a
a
Polymerized in toluene at 80 ꢀC for 24 h; [M]0 ¼ 0.50 M, [Catalyst] ¼ 20 mM,
Polymerized in toluene at 80 ꢀC for 24 h; [M]0 ¼ 0.50 M, [Catalyst] ¼ 20 mM,
[Cocatalyst] ¼ 80 mM.
[Cocatalyst] ¼ 80 mM.
b
b
Methanol-insoluble product.
Measured by GPC.
Methanol-insoluble product.
Measured by GPC.
c
c
3. Results and discussion
molecular weights. All the polymerizations of 2c provided only
oligomers in low yields. Compared to thiophene-containing
monomers, furan-containing monomers are difficult to generate
high-molecular-weight polymers. This may be due to that the
resonance energy of furan is smaller than that of thiophene. When
the metathesis polymerizations of substituted acetylenes are
carried out in the presence of small amount of olefins, oligomers
and low-molecular-weight polymers are produced because the
olefins work as chain transfer agents [48,49]. In the present study,
two double bonds in furan may cause adverse effects on propa-
gating species in the metathesis polymerizations. We demon-
strated the polymerization of equimolar mixture of 1-(4-
trimethylsilylphenyl)-2-phenylacetylene and furan using TaCl5/n-
Bu4Sn. 1-(4-Trimethylsilylphenyl)-2-phenylacetylene is known to
polymerize to afford a high-molecular-weight polymer in high
yield (Mn ¼ 750,000, yield ¼ 85%) [50]. In contrast, the polymer-
ization in the presence of furan gave a low-molecular-weight
polymer in very low yield (Mn ¼ 74,000, yield ¼ 9%).
3.1. Polymerization
The polymerizations of all monomers were carried out by using
TaCl5/n-Bu4Sn, NbCl5/n-Bu4Sn, and WCl6/Ph4Sn catalysts in toluene
at 80 ꢀC. The results of polymerizations of thiophene-containing
monomers 1aed are shown in Table 1. The polymerizations of 1a
with TaCl5 and NbCl5 afforded high-molecular-weight polymers in
moderate yields (Mn: 1,410,000 and 1,500,000, respectively). The
polymerization of 1a with WCl6 gave a low-molecular-weight
polymer, whose Mn was 12,400. Monomer 1b polymerized using
NbCl5 to give a polymer with Mn of 107,000. However, the products
obtained by the polymerization using TaCl5 and WCl6 were an
insoluble polymer and an oligomer, respectively. Monomer 1c
possesses a long alkyl chain, and hence, the alkyl group seemed to
prevent the propagating reaction. The polymerization of 1c with
TaCl5 afforded a relatively low-molecular-weight polymer in low
yield, and the polymerizations with NbCl5 and WCl6 gave just
oligomers. The polymerizations of 1d also provided oligomers,
which may be due to the steric effect of bulky 9,9-
dimethylfluorenyl groups.
Table 3 shows the results of polymerizations of benzo[b]thio-
phene-containing monomers 3aed. Monomer 3a polymerized
using TaCl5, NbCl5, and WCl6 to give polymers with low molecular
weights. The polymerization of 3b with TaCl5 afforded a high-
molecular-weight polymer in good yield. The polymerization of
3b with NbCl5 also gave a relatively high-molecular-weight poly-
mer, but the molecular weight and yield were much lower than
those with TaCl5. Monomer 3c and 3d also polymerized using TaCl5
and NbCl5 to give polymers with relatively high molecular weights.
The WCl6-catalyzed polymerizations of 3bed afforded an oligomer
and no methanol-insoluble product.
The results of polymerizations of benzothiazole-containing
monomers 4aec were shown in Table 4. Monomer 4a hardly
polymerized, and only oligomer was obtained when NbCl5 was
used as a catalyst. The polymerization of 4b with TaCl5 afforded
a relatively high-molecular-weight polymer in good yield, while
the polymerizations with NbCl5 and WCl6 did not proceed. All the
polymerizations of 4c with TaCl5, NbCl5, and WCl6 provided oligo-
mers, whose Mn’s were around 1000.
The results of polymerizations in the present study can be dis-
cussed from two aspects, that is a kind of heterocyclic compound
and a kind of substituent except for heterocycle. The tendency of
polymerization is roughly indicated below. Thiophene- and benzo
[b]thiophene-containing monomers exhibit high polymerizability
compared to furan- and benzothiazole-containing monomers. As
noted, a furan might work as chain transfer agents. In addition, the
low polymerizability of furan- and benzothiazole-containing
monomers can be accounted for by the idea that the carbone
Table
2 shows the results of polymerizations of furan-
containing monomers 2aec. The polymerization of 2a with TaCl5
provided a polymer, and its Mn was 13,800. The molecular weight
is two orders of magnitude lower than that of poly(1a) obtained
by the polymerization with TaCl5. When 2a was polymerized with
NbCl5 and WCl6, oligomers were obtained. The polymerization of
2b with TaCl5 gave an insoluble polymer, and the polymerizations
with NbCl5 and WCl6 gave solvent-soluble products with low
Table 2
Polymerization of furan-containing monomers.a
Yieldb
%
Mn
Mw/Mn
c
c
Monomer
Catalyst
2a
TaCl5
NbCl5
WCl6
TaCl5
NbCl5
WCl6
TaCl5
NbCl5
WCl6
38
26
38
53
51
40
25
27
13
13,800
3160
1430
Insoluble
2240
1220
2150
1700
1080
2.5
5.3
2.4
2b
2c
13
2.5
2.7
3.2
2.0
a
Polymerized in toluene at 80 ꢀC for 24 h; [M]0 ¼ 0.50 M, [Catalyst] ¼ 20 mM,
[Cocatalyst] ¼ 80 mM.
b
Methanol-insoluble product.
Measured by GPC.
c

T. Muroga et al. / Polymer 53 (2012) 4380e4387
4385
Table 4
3.2. Absorption and photoluminescence properties
Polymerization of benzothiazole-containing monomers.a
c
c
Absorption and emission of polymers were investigated in CHCl3
(Fig. 2). Poly(4a) and poly(1b) were examined using the polymer
samples obtained by the polymerization with NbCl5. Poly(2b) were
examined using the polymer samples obtained by the polymeriza-
tion with WCl6. The other polymers were studied using the polymer
samples obtained by the polymerizationwith TaCl5. Fig. 2 [A] and [B]
shows the emission spectra and UVevis absorption spectra of
poly(1-hexyl-2-arylacetylene)s, respectively. The absorption cutoffs
were observed in the spectral region around 400 nm. Upon photo-
excitation, the solutions emitted blue lights with emission maxima
around 480 nm. On the other hand, the absorption cutoffs of pol-
y(diarylacetylene)s were observed in the spectral region beyond
470 nm (Fig. 2 [D] and [F]). These are red-shifted compared to those
of poly(1-hexyl-2-arylacetylene)s because the main chain conju-
gation was widened by attaching phenyl groups instead of alkyl
groups on the main chain. All the emission maxima were around
510 nm, and no clear difference was observed even when the
substituent was different (Fig. 2 [C] and [E]). This suggests that not
only the bulky substituents such as trimethylsilyl and n-octyl groups
but also heterocycles hardly affect absorption and emission wave-
lengths of poly(diarylacetylene) derivatives in dilute solution. The
absorption wavelength of poly[1-(9,9-dimethyl-2-fluorenyl)-2-
arylacetylene] was further red-shifted, and the absorption cutoff
Monomer
Catalyst
Yieldb
%
Mn
Mw/Mn
4a
TaCl5
NbCl5
WCl6
TaCl5
NbCl5
WCl6
TaCl5
NbCl5
WCl6
0
22
0
67
0
953
2.2
15
4b
4c
174,000
0
24
26
61
1550
1020
1270
6.0
1.1
2.0
a
Polymerized in toluene at 80 ꢀC for 24 h; [M]0 ¼ 0.50 M, [Catalyst] ¼ 20 mM,
[Cocatalyst] ¼ 80 mM.
b
Methanol-insoluble product.
Measured by GPC.
c
carbon triple bond in the monomer is prevented from coordinating
to metal carbene by the strong interaction of metal carbene with
furanyl and benzothiazolyl groups, which exhibit stronger basicity
than thiophenyl and benzo[b]thiophenyl groups. Concerning
other substituents, n-octylphenyl and dimethylfluorenyl group-
containing monomers show low polymerizability compared to
hexyl, phenyl, and trimethylsilyl phenyl group-containing mono-
mers because the steric hindrance of bulky substituents prevents
propagation reaction.
Fig. 2. Emission spectra (excitation at 300 nm) and UVevis absorption spectra of polymers in CHCl3 (c ¼ 1 ꢁ 10ꢂ6, 1 ꢁ 10ꢂ5, or 1 ꢁ 10ꢂ4 mol/L).

4386
T. Muroga et al. / Polymer 53 (2012) 4380e4387
Table 5
lowers fluorescence quantum efficiency because the intermolecular
excimers have low transition energy in a nonradiative process [51e
54]. Therefore, poly(diarylacetylene)s generally show low quantum
Molecular weight, maximum emission (Emax), and quantum yield (f
).a
Polymer
Mn
Emax, nm
f, %
yields due to the strong
p-stacking of aryl groups compared to
poly(1a)
poly(2a)
poly(3a)
poly(1b)
poly(3b)
poly(4b)
poly(1c)
poly(3c)
poly(3d)
polyA
1,410,000
13,800
14,700
107,000
1,570,000
174,000
75,600
147,000
190,000
41,100
490
380
472
520
509
397
384
524
536
470
510
510
530
0.69
0.54
eb
poly(1-alkyl-2-phenylacetylene)s. However, poly(1b), poly(3b),
poly(4b), and poly(1c) with bulky trimethylsilyl and n-octyl groups
exhibited relatively high quantum yields. The higher quantum
yields would be due to that the bulky substituents weaken the
intermolecular interaction by the steric hindrance. Poly(3d)
showed relatively high quantum yield, which can be accounted for
by that the methyl groups attached at 9-position of fluorene rings
0.33
0.39
0.67
0.46
eb
0.52
0.62
0.18
0.56
0.30
prevent the intermolecular
p-stacking. Compared to the model
polyB
polyC
polyD
2,060,000
1,160,000
106,000
polymers, the emission maxima of heterocycle-containing poly-
mers were almost the same or slightly red-shifted. This indicates
that heterocycle in poly(diarylacetylene)s is independent on main
chain conjugation. However, the fluorescence quantum yields of
heterocycle-containing polymers were higher than those of the
corresponding model polymers. The reason is not cleared, but the
a
Using quinine sulfate as standard sample.
Could not be measured because of poor solubility in CHCl3.
b
heterocycles might act as bulky substituents for hindrance to
stacking.
p-
Fig. 3 showed emission spectra of poly(1a), poly(3b), poly(4b),
and poly(3d) in chloroform solution and cast film. These polymers
had relatively high molecular weights and afforded thin films by
solution casting onto a quartz plate. The emission maximum of
poly(1a) in cast film was 490 nm, which is the same as that in
solution. This is associated with the long alkyl chains attached to
the main chain which prevents p-stacking of phenyl rings even in
solid state. On the other hand, diarylacetylene polymers exhibited
emission red-shifts between the solution and cast film. For
instance, the emission maxima of poly(3b) in solution and cast film
were 509 and 530 nm, respectively. This is because the increase of
Chart 1. Structures of model polymers.
p-stacking widened the effective conjugation of main chains.
was observed in the spectral region beyond 500 nm (Fig. 2 [H]). The
solution of poly(3d) emitted yellow light, and the emission
maximum was 540 nm (Fig. 2 [G]).
3.3. Gas permeability
Fluorescence quantum yields (f) of the polymer solutions were
Free-standing membranes of poly(3b) and poly(3d) could be
fabricated by casting their toluene solutions, but the other poly-
mers could not afford free-standing membranes because their
molecular weights were relatively low. Desilylated membrane of
poly(3b) [poly(3b)DeSi] was obtained by the reaction of membrane
of poly(3b) with trifluoroacetic acid/hexane. The gas permeability
measured by using quinine sulfate in sulfuric acid (1.0 M) as the
standard. Table 5 shows the data of the present polymers and the
model polymers not-containing heterocycles, whose structures are
shown in Chart 1. The quantum yields of poly(1a) and poly(2a)
were 0.69 and 0.54%, respectively. The intermolecular packing
Fig. 3. Comparison of emission spectra of polymers between the solution and cast film (excitation at 300 nm).

T. Muroga et al. / Polymer 53 (2012) 4380e4387
4387
Table 6
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a
a
b
c
Membrane
PO2
PN2
PCO2
DCO2
SCO2
Density
FFV
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poly(3d)
1400
2300
5300
680
1450
3700
6200
8700
18,000
2.6
2.6
3.3
0.23
0.33
0.53
1.11
1.19
1.05
0.163
0.155
0.309
Measured at 25 ꢀC. In the unit of barrer (1 barrer ¼ 1 ꢁ 10ꢂ10 cm3 (STP) cm
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