Siloles and acetenyl aromatics copolymers: Synthesis, characterization and photophysical properties

Article abstract of DOI:10.1002/cjoc.201400870

Two copolymers, poly(1,1-dimethyl-3,4-diphenylsilole-alt-N-hexyl-3,6-diethynylcarbazole) (PS-DyCz) and poly(1,1-dimethyl-3,4-diphenylsilole-alt-2,7-diethynyl-9,9′-dihexylfluorene) (PS-DyF), were synthesized by Sonogashira coupling reaction of 2,5-dibromo-

Full text of DOI:10.1002/cjoc.201400870

FULL PAPER
DOI: 10.1002/cjoc.201400870
Siloles and Acetenyl Aromatics Copolymers: Synthesis,
Characterization and Photophysical Properties
Zhenhua He,a,b Guoqiao Lai,b Zhifang Li,b Xiao Yuan,a Yongjia Shen,a and Chengyun Wang*,a
a Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science and
Technology, Shanghai 200237, China
b Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou
Normal University, Hangzhou, Zhejiang 310012, China
Two copolymers, poly(1,1-dimethyl-3,4-diphenylsilole-alt-N-hexyl-3,6-diethynylcarbazole) (PS-DyCz) and poly-
(1,1-dimethyl-3,4-diphenylsilole-alt-2,7-diethynyl-9,9'-dihexylfluorene) (PS-DyF), were synthesized by Sonogashira
coupling reaction of 2,5-dibromo-1,1-dimethyl-3,4-diphenylsilole and N-hexyl-3,6-diethynylcarbazole or 2,7-diethy-
nyl-9,9'-dihexylfluorene, respectively. The chemical structures of the copolymers were characterized by NMR, FT-IR
techniques. Their thermal and photophysical properties were evaluated by TGA, DSC, UV-Vis and fluorescence spec-
troscopy, respectively. The weight-averaged molecular weights (Mw) of PS-DyCz and PS-DyF are 1.20×104 and 3.83
×104 Da, respectively. The degree of polymerization is 8 and 22 units. These π-conjugated polymers exhibited lower
band-gap of 2.25 and 2.70 eV due to the presence of silole rings and C≡C triple bonds in their backbone, the results
were consistent with the density functional (DFT) calculations at the B3LYP/6-31G* level.
Keywords silole, acetylene, carbazole, fluorene, conjugated polymer, density functional theory
Introduction
cation because of their structural rigidities, for example,
poly(2,7-fluorene ethynylene)s (PFEs) have high quan-
tum efficiency, broad emission range and low band
gap.[21] Silole-acetylene polymeric systems are particu-
larly interesting because they display unusually narrow
band gaps and high electron affinities.[22-25] If silole-
acetylene building block could be incorporated into
carbazole or fluorene polymeric chain, the new assem-
bly should display improved hole-transport properties,
and suppress the aggregation and/or excimers formation
of molecules.[26,27]
Therefore, we synthesized two copolymers consist-
ing of silole and diethynylcarbazole, or diethynylfluo-
rene moieties in the backbone. And the chemical struc-
tures of two polymers were characterized by NMR,
FT-IR techniques, their thermal and photophysical
properties were evaluated by TGA, DSC, UV-Vis and
fluorescence spectroscopy, and theoretical calculations
were carried out using density functional theory (DFT)
method at B3LYP/6-31G*level.[28]
Silole (silacyclopentadiene) has recently been high-
lighted as an important building block for polymer
light-emitting diodes (PLED),[1-3] field-effect transistors
(FET),[1,2,4] bulk heterojunction (BHJ) solar cells[5-7] and
explosives detection.[8-13] Silole possesses low-lying
LUMO energy level associated with the σ*-π* conjuga-
tion arising from the interaction between the σ* orbital
of two exocyclic σ bonds in the silicon atom and the π*
orbital of the butadiene moiety. Silole also exhibits high
electron affinity and unique aggregation-induced emis-
sion (AIE).[14-16] Therefore, the conjugated polymers
containing silole ring can reduce band-gap value and
enhance carrier mobility.
Carbazole-based polymers have high hole-transport
ability and wide band-gap energy transfer. Meanwhile,
ethynylene group is a key π-spacer for efficient elec-
tronic communication of π-chromophores in the con-
structions of poly(aryleneethynylene)s[17] or poly(diethy-
nylcarbazole-arylene).[18,19] On the other hand, fluorene-
based polymers such as polyfluorenes (PFs) have
emerged as emitting materials suitable for using in
PLEDs because of their highly efficient photolumines-
cence (PL), excellent thermal and oxidative stability,
and good solubility.[20] Fluorene-based polymers con-
taining C≡C triple bond facilitate electronic communi-
Experimental
Materials and instruments
Tetrahydrofuran was distilled from sodium and ben-
zophenone under an Ar atmosphere prior to use. Tri-
*
E-mail: cywang@ecust.edu.cn; Tel./Fax: 0086-021-64252967
Received December 19, 2014; accepted March 4, 2015; published online March 30, 2015.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201400870 or from the author.
550
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Chin. J. Chem. 2015, 33, 550—558

Siloles and Acetenyl Aromatics Copolymers: Synthesis, Characterization and Photophysical Properties
ethylamine was refluxed and distilled over calcium hy-
dride prior to use. Phenylacetylene and 3-methyl-1-
butyn-3-ol were distilled prior to use. Zinc chloride was
dried by refluxing in thionyl chloride and stored in Ar
atmosphere. All other chemicals were purchased from
commercial supplier and used without further purifica-
tion. Reactions were carried out under dry argon at-
mosphere when necessary.
then bubbled with Ar for 30 min. Lithium slice (0.250 g,
36 mmol, 4.5 equiv.) was added to the reaction mixture
under a stream of Ar. The solution was stirred for 6 h
giving a thick dark green LiNaph solution. Bis(phenyl-
ethynyl)dimethylsilane (1, 2.083 g, 8 mmol) was dis-
solved in THF (40 mL), degassed under reduced pres-
sure, and then bubbled with Ar for 30 min, and added
dropwise into LiNaph solution at room temperature over
ca. 20 min. The solution was protected from light by
wrapping the reaction vessel in aluminium foil and
cooled to −10 ℃. Anhydrous ZnCl2 (5.452 g, 40 mmol,
5 equiv.) dissolved in THF (33 mL) was added dropwise
into the naphthalenide/silane mixture over ca. 30 min
and stirred for 20 min at −10 ℃. The suspension was
then cooled to −78 ℃ and N-bromosuccinamide (3.560
g, 20 mmol, 2.5 equiv.) dissolved in THF (16 mL) was
added quickly via syringe. After stirring for 1 h at −78
℃, the cold reaction mixture was poured into vigor-
ously stirred half-saturated aqueous NH4Cl (150 mL)
and extracted with ethyl acetate (50 mL×3). The or-
ganic extracts were combined and washed successively
with half-saturated Na2S2O3 (50 mL), water (100 mL),
brine (50 mL×2), then dried by anhydrous Na2SO4, and
filtered through a thin pad of silica. The naphtha-
lene/dibromosilole mixture was concentrated and sub-
jected to a column chromatograph (silica gel, petroleum
1H and 13C NMR spectra were recorded on a Bruker
Avance III 400 spectrometer. Chemical shifts (δ) are
expressed downfield from tetramethylsilane using the
residual protonated solvent as internal standard (chloro-
1
form-d, H δ 7.26 and 13C δ 77.0). Coupling constants
are expressed in hertz. Molecular weights and polydis-
persity index of polymers were obtained on a Waters
1515 using a calibration of curve of polystyrene stan-
dards, with tetrahydrofuran as the eluent. UV-vis ab-
sorption spectra were measured on a Varian Cary 100
spectrometer. Fluorescence spectra were recorded on a
Varian Cary Eclipse spectrometer. FT-IR spectra were
collected from a Nicolet Magna-IR 550 spectrometer.
Thermogravimetric analysis (TGA) was carried out us-
ing Netzsch STA 409 PC/PG under N2 atmosphere.
Differential scanning calorimetry (DSC) analysis was
made on a Netzsch STA 409 PC/PG under nitrogen at-
mosphere.
1
ether), providing off-white product (1.442 g, 43%). H
Synthesis of bis(phenylethynyl)dimethylsilane (1)
NMR (400 MHz, CDCl3) δ: 7.19－7.15 (m, 6H, ArH),
6.97－6.95 (m, 4H, ArH), 0.46 (s, 6H, Si(CH3)2); 13C
NMR (100 MHz, CDCl3) δ: 156.0, 136.9, 129.0, 127.5,
127.4, 122.7, −6.3. MS (EI) m/z: 419.9 ([M]＋).
Magnesium ribbons were scraped off oxidation lay-
ers, cut into small pieces (2.45 g, 0.1 mol) and activated
with two grains of free iodine. THF (10 mL) was added
via syringe and stirred for 30 min. Bromoethane (10.90
g, 0.1 mol) dissolved in THF (25 mL) was added drop-
wise over ca. 20 min into the magnesium suspension.
Then the mixture was refluxed for 1 h and cooled to
room temperature. Phenylacetylene (10.20 g, 0.1 mol)
dissolved in THF (20 mL) was added dropwise and re-
fluxed for 2 h. Me2SiCl2 (6.45 g, 0.05 mol) dissolved in
THF (20 mL) was added dropwise at room temperature
and refluxed for 3 h. After the mixture was cooled to
room temperature, water (50 mL) and ethyl acetate (50
mL) were added to the flask. The organic phase was
separated and extracted with ethyl acetate (50 mL×2).
The combined extract was dried by anhydrous Na2SO4,
and then the filtrate was concentrated to dryness under a
reduced pressure. The yellow-white solid was dissolved
in a minimal amount of boiling hexane, and then cooled
in a freezer (−30 ℃) for 1 h to give the product as
off-white powder that was collected by vacuum filtra-
tion (9.29 g, 71%). 1H NMR (400 MHz, CDCl3) δ: 7.53
－7.50 (m, 4H, ArH), 7.36－7.29 (m, 6H, ArH), 0.49 (s,
6H, Si(CH3)2); 13C NMR (100 MHz, CDCl3) δ: 132.1,
128.8, 128.2, 122.7, 105.9, 90.6, 0.5.
Synthesis of 3,6-diiodocarbazole (4)
Carbazole (6.0 g, 36 mmol), KI (7.8 g, 47 mmol) and
KIO3 (10.0g, 47 mmol) were dissolved in acetic acid
(150 mL) at room temperature. The reaction mixture
was heated to 80 ℃ for 6 h. Then the mixture was
cooled to room temperature, filtered and washed suc-
cessively with water, saturated Na2CO3, saturated
Na2S2O3 and water. The crude product was recrystal-
lized from ethanol to give a white solid (11.0 g, 73%).
1H NMR (400 MHz, CDCl3) δ: 8.33 (d, J＝1.6 Hz, 2H,
ArH), 8.07 (s, 1H, NH), 7.68 (dd, J＝8.5, 1.7 Hz, 2H,
ArH), 7.21 (d, J＝8.5 Hz, 2H, ArH); 13C NMR (100
MHz, CDCl3) δ: 138.5, 134.8, 129.4, 124.6, 112.7, 82.4.
Synthesis of N-hexyl-3,6-diiodocarbazole (5)
A mixture of 3,6-diiodocarbazole (4, 4.2 g, 10
mmol), 1-bromohexane (2.0 g, 12 mmol) and K2CO3
(7.0 g, 50 mmol) in DMF (35 mL) was stirred at 80 ℃
under argon for 4 h. The mixture was then cooled to
room temperature and poured into 200 mL of water. The
crude product was collected from filtration and washed
completely with water. Recrystallization from hexane
1
Synthesis of 2,5-dibromo-1,1-dimethyl-3,4-diphenyl-
silole (3)
gave pure product as white solid (4.10 g, 82%). H
NMR (400 MHz, CDCl3) δ: 8.32 (d, J＝1.6 Hz, 2H,
ArH), 7.71 (dd, J＝8.6, 1.7 Hz, 2H, ArH), 7.16 (d, J＝
8.6 Hz, 2H, ArH), 4.21 (t, J＝7.2 Hz, 2H, NCH2),
Naphthalene (4.820 g, 37.6 mmol, 4.7 equiv.) was
dissolved in THF (24 mL) and degassed in vacuo, and
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He et al.
FULL PAPER
1
1.85－1.76 (m, 2H, CH2), 1.37－1.23 (m, 6H, CH2),
0.85 (t, J＝7.0 Hz, 3H, CH3); 13C NMR (100 MHz,
CDCl3) δ: 139.5, 134.5, 129.3, 124.0, 110.9, 81.6, 43.2,
31.5, 28.8, 26.9, 22.5, 14.0.
from hexane to give a white solid (9.23 g, 88%). H
NMR (400 MHz, CDCl3) δ: 7.87 (s, 2H, ArH), 7.70 (d,
J＝8.0 Hz, 2H, ArH), 7.49 (d, J＝8.1 Hz, 2H, ArH),
3.83 (s, 2H, CH2).
Synthesis of N-hexyl-3,6-di(3-hydroxy-3-methyl-
butynyl)carbazole (6)
Synthesis of 2,7-diiodo-9,9'-dihexylfluorene (9)
Into 250 mL three-neck flask, 2,7-diiodofluorene (8,
5.016 g, 12 mmol) and DMSO (20 mL) were added, and
heated to 60 ℃. Then, tetra-n-butylammonium bromide
(0.81 g, 2.5 mmol), 50% aqueous NaOH (8 mL) and
1-bromohexane (5.943 g, 36 mmol) were added. The
reaction mixture was stirred at 80 ℃ under Ar atmos-
phere for 8 h, and cooled to room temperature. Then, 80
mL of 1 mol•L−1 HCl was added and the mixture was
extracted with ethyl acetate. The organic layer was
washed by 1 mol•L−1 HCl and water (3 times), and dried
over anhydrous MgSO4. The solvent was then removed
under reduced pressure and the yellow oil was purified
by column chromatography (silica gel, petroleum ether)
N-Hexyl-3,6-diiodocarbazole (5, 2.00 g, 4 mmol)
and 3-methyl-1-butyn-3-ol (1.01 g, 12 mmol) were dis-
solved in Et3N (40 mL), and degassed in vacuo, and
then bubbled with Ar for 30 min. Under a stream of Ar,
Pd(PPh3)2Cl2 (70 mg, 0.1 mmol), PPh3 (80 mg, 0.3
mmol) and CuI (153 mg, 0.8 mmol) were added. The
reaction mixture was refluxed overnight, and cooled to
room temperature. The mixture was filtered and washed
with ethyl acetate (3 times). The solvent was then re-
moved under reduced pressure, and the residual was
purified by column chromatography (silica gel, petro-
leum ether/ethyl acetate, V∶V＝2∶5) to afford a white
solid (1.60 g, 96%). 1H NMR (400 MHz, CDCl3) δ: 8.13
(d, J＝1.00 Hz, 2H, ArH), 7.52 (dd, J＝8.5, 1.5 Hz, 2H,
ArH), 7.30 (d, J＝8.5 Hz, 2H, ArH), 4.24 (t, J＝7.2 Hz,
2H, NCH2), 2.12 (s, 2H, OH), 1.88－1.78 (m, 2H, CH2),
1.67 (s, 12H, (CH3)2), 1.38－1.23 (m, 6H, CH2), 0.85 (t,
J＝7.0 Hz, 3H, hexyl-CH3); 13C NMR (100 MHz,
CDCl3) δ: 140.4, 129.6, 124.2, 122.3, 113.2, 108.8, 92.0,
83.1, 65.8, 43.3, 31.7, 31.5, 28.9, 26.9, 22.5, 13.9.
1
to afford a pale yellow solid (5.758 g, 82%). H NMR
(400 MHz, CDCl3) δ: 7.69－7.61 (m, 4H, ArH), 7.40 (d,
J＝8.5 Hz, 2H, ArH), 1.98－1.81 (m, 4H, ArCCH2),
1.16－1.01 (m, 12H, (CH2)3), 0.79 (t, J＝7.1 Hz, 6H,
CH3), 0.60－0.48 (m, 4H, CH2CH3).
Synthesis of 2,7-bis(trimethylsilyl)-9,9'-dihexyl-fluo-
rene (10)
2,7-Diiodo-9,9'-dihexylfluorene (9, 2.662 g, 4.5
mmol) was dissolved in 40 mL of Et3N under argon
atmosphere. CuI (35 mg) and Pd(PPh3)2Cl2 (58 mg)
were added to the stirred solution. Trimethylsilylacety-
lene (1.340 g, 13.5 mmol, 3 equiv.) dissolved in Et3N
(25 mL) was added dropwise into the mixture and
heated to reflux for 8 h. After the reaction mixture was
cooled to room temperature, the formed precipitate tri-
ethylammonium hydroiodide was filtered off. The sol-
vent was removed under reduced pressure and the crude
product was purified by column chromatography (silica
gel, petroleum ether) to afford a white solid (1.336 g,
Synthesis of N-hexyl-3,6-diethynylcarbazole (7)
With vigorous stirring, a mixture of N-hexyl-3,6-
di(3-hydroxy-3-methylbutynyl)-carbazole (6, 1.0 g, 2.4
mmol) and potassium hydroxide (404 mg, 7.2 mmol) in
60 mL of isopropanol was heated at reflux for 4 h under
Ar atmosphere . Upon cooling, the solvent was removed
under reduced pressure and the crude product was puri-
fied by column chromatography (silica gel, CH2Cl2/
petroleum ether, V∶V＝2∶5) to afford an off-white
1
solid (570 mg, 79%). H NMR (400 MHz, CDCl3) δ:
8.22 (d, J＝0.9 Hz, 2H, ArH), 7.61 (dd, J＝8.5, 1.5 Hz,
2H, ArH), 7.33 (d, J＝8.5 Hz, 2H, ArH), 4.27 (t, J＝7.2
Hz, 2H, NCH2), 3.08 (s, 2H, ≡CH), 1.89－1.80 (m, 2H,
CH2), 1.38－1.23 (m, 6H, CH2), 0.86 (t, J＝7.0 Hz, 3H,
CH3); 13C NMR (100 MHz, CDCl3) δ: 140.6, 130.1,
124.7, 122.2, 112.7, 108.9, 84.7, 75.4, 43.3, 31.5, 28.9,
26.9, 22.5, 14.0; HRMS (ESI) calcd for C22H21N
299.1674, found 299.1666.
1
57%). H NMR (400 MHz, CDCl3) δ: 7.59 (d, J＝7.8
Hz, 2H, ArH), 7.45 (dd, J＝7.9, 1.2 Hz, 2H, ArH), 7.41
(s, 2H, ArH), 1.98－1.89 (m, 4H, ArCCH2), 1.17－0.96
(m, 12H, (CH2)3), 0.77 (t, J＝7.2 Hz, 6H, CH3), 0.61－
0.45 (m, 4H, CH2CH3), 0.28 (s, 18H, SiCH3); 13C NMR
(100 MHz, CDCl3) δ: 150.9, 140.8, 131.2, 126.2, 121.7,
119.8, 106.1, 94.2, 55.2, 40.4, 31.5, 29.7, 23.6, 22.6,
14.0, 0.05.
Synthesis of 2,7-diiodofluorene (8)
Synthesis of 2,7-diethynyl-9,9'-dihexylfluorene (11)
Fluorene (4.155 g, 25 mmol) was dissolved in 130
mL of the mixed solvent (CH3COOH/H2O/H2SO4＝
100/20/3) with mechanical stirrer at 80 ℃ (internal
temperature). Then, periodic acid dihydrate (2.849 g,
12.5 mmol) and iodine (6.345 g, 25 mmol) were quickly
added. The reaction mixture was stirred for 3 h and the
abundant white precipitate was formed. The mixture
was cooled, and the pale yellow solid was collected by
filtration and washed successively with water, saturated
Na2CO3 and water. The crude product was recrystallized
2,7-Bis(trimethylsilyl)-9,9'-dihexylfluorene (10, 527
mg, 1 mmol), CH2Cl2 (10 mL), methanol (10 mL) and
KOH (1 mol•L−1, 4 mL) were added to 100 mL flask,
and stirred at room temperature under argon atmosphere
overnight. Water (30 mL) and diethyl ether (30 mL)
were added to the reaction mixture, the organic layer
was separated and the aqueous layer was extracted with
diethyl ether (20 mL×2). The combined extract was
washed with brine and dried over anhydrous MgSO4.
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Chin. J. Chem. 2015, 33, 550—558

Siloles and Acetenyl Aromatics Copolymers: Synthesis, Characterization and Photophysical Properties
The solvent was removed under reduced pressure to
yield the title compound as off-white solid (360 mg,
94%). H NMR (400 MHz, CDCl3) δ: 7.63 (d, J＝7.8
Grignard reaction and Tamao’s endo-endo intramolecu-
lar reductive cyclization (Scheme 1).[29-31]
1
Hz, 2H, ArH), 7.50－7.45 (m, 4H, ArH), 3.15 (s, 2H,
≡CH), 1.97－1.90 (m, 4H, ArCCH2), 1.15－0.96 (m,
12H, (CH2)3), 0.76 (t, J＝7.2 Hz, 6H, CH3), 0.64－0.50
(m, 4H, CH2CH3); 13C NMR (100 MHz, CDCl3) δ:
151.0, 141.0, 131.2, 126.5, 120.8, 120.0, 84.5, 55.2,
40.2, 31.5, 29.6, 23.6, 22.6, 14.0. HRMS (ESI) cald for
C29H34 382.2661, found 382.2655.
Scheme 1 Synthesis of dibromosilole
Ph
Ph
b
a
Si
1
Ph
ZnCl
Ph
ClZn
Ph
Br
Ph
c
Synthesis of poly(1,1-dimethyl-3,4-diphenylsilole-alt-
N-hexyl-3,6-diethynyl-carbazole) (PS-DyCz)
Br
Si
Si
2,5-Dibromo-1,1-dimethyl-3,4-diphenylsilole
(3,
3
2
420 mg, 1 mmol) and N-hexyl-3,6-diethynylcarbazole
(7, 300 mg, 1 mmol) were dissolved in the mixture of
toluene (10 mL) and Et3N (3 mL), and degassed under
reduced pressure, and then bubbled with Ar over ca. 30
min. Under a stream of argon was added Pd(PPh3)4 (50
mg) and CuI (20 mg). The mixture was heated to 60 ℃,
stirred for 3 d. The mixture was cooled to room tem-
perature and filtered and evaporated to dryness under a
reduced pressure. The residue was dissolved in CHCl3
(3 mL), and precipitated from methanol (35 mL). The
precipitation procedure was repeated three times to re-
move any unreacted monomer and low molecular
weight oligomers. A precipitation was collected by
vacuum filtration and dried in vacuum for 1 h at 60 ℃.
The resultant polymer was obtained as red powder (263
Reagents and conditions: (a) EtMgBr, diethyl ether, reflux, 2 h;
Me2SiCl2, 35 ℃, 3 h. (b) LiNaph, THF, 6 h; ZnCl2/THF, −10 ℃, 20
min. (c) NBS/THF, −78 ℃, 1 h.
The N-hexyl-3,6-diethynylcarbazole (7) was synthe-
sized through four steps (Scheme 2). 3,6-Diiodocarba-
zole (4) was prepared from carbazole by a diiodination
reaction,[19] which was alkylated with 1-bromohexane in
the presence of K2CO3 to afford N-hexyl-3,6-diiodo-
carbzole (5).[4] Then, the Pd/Cu-catalyzed cross-cou-
pling reaction of 5 and 3-methyl-1-butyn-3-ol gave
compound 6, which was deprotected to afford 7 under
KOH/isopropanol condition. The overall yield was 79%.
1
Scheme 2 Synthesis of N-hexyl-3,6-diethynylcarbazole (7)
monomer
mg, 37%). H NMR (400 MHz, CDCl3 ) δ: 8.60－6.80
(m, ArH), 4.22 (br, NCH2), 1.82 (br, CH2CH3), 1.57 (br,
(CH2)3), 0.84 (br, CH3), 0.66 (br, Si(CH3)2); FT-IR (KBr)
ν: 3447 (w), 3056 (w), 2957 (s), 2926 (s), 2853 (m),
2139 (w), 1625 (m), 1595 (m), 1482(s), 1381 (m), 1350
(m), 1284 (m), 1259 (s), 1091 (m), 1022 (m), 802 (s),
695 (m) cm−1. GPC (THF) Mw: 12045, Mn: 4562, PDI:
2.6.
I
I
a
b
N
N
H
H
4
Carbazole
HO
OH
I
I
Synthesis of poly(1,1-dimethyl-3,4-diphenylsilole-alt-
2,7-diethynyl-9,9'-dihexyl-fluorene) (PS-DyF)
c
N
C6H13
N
The polymer was synthesized by the similar method
described in the synthesis of PS-DyCz. 2,5-Dibromo-
1,1-dimethyl-3,4-diphenylsilole (3, 420 mg, 1 mmol),
5
C6H13
6
2,7-diethynyl-9,9'-dihexylfluorene (11, 383 mg,
1
d
mmol), Pd(PPh3)4 (53 mg) and CuI (17 mg) were used
in this case. The resultant polymer was obtained as yel-
lowish brown solid (324 mg, 40%). 1H NMR (400 MHz,
CDCl3) δ: 8.10－7.30 (m, ArH), 7.20－6.70 (m, ArH),
3.12 (br, ≡CH), 2.12－1.78 (m, CH2), 1.20－0.96 (m,
CH2), 0.79 (t, J ＝7.2 Hz, CH3), 0.70 －0.45 (m,
Si(CH3)2); FT-IR (KBr) ν: 3435 (m), 2924 (s), 2851 (m),
2136 (w), 1600 (w), 1460(m), 1414 (w), 1257 (w), 1095
(w), 889 (w), 818 (m), 675 (w) cm−1. GPC (THF), Mw:
38266, Mn: 14277, PDI: 2.7.
N
C6H13
7
Reagents and conditions: (a) KI, KIO3, AcOH, 80 ℃, 6 h. (b)
n-C6H13Br, K2CO3, DMF, 80 ℃, 4 h. (c) 3-Methyl-1-butyn-3-ol,
Pd(PPh3)2Cl2, PPh3, CuI, Et3N, reflux, overnight. (d) KOH, isopro-
panol, reflux, 4 h.
The synthesis of 2,7-diethynyl-9,9'-dihexylfluorene
(11) was similar to the synthesis of 7 (Scheme 3), which
was prepared by diiodination of fluorene, alkylation
with 1-bromohexane in the presence of 50% NaOH aq,
Sonogashira cross-coupling reaction using trimethyl-
silylacetylene as alkynylation reagent and finally de-
Results and Discussion
Synthesis and characterization
The 2,5-dibromosilole monomer was synthesized by
Chin. J. Chem. 2015, 33, 550—558
© 2015 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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553

He et al.
FULL PAPER
protection.[32] Notably, when 3-methyl-1-butyn-3-ol was
used as alkynylation reagent, deprotection of the cross
coupling product under KOH/isopropanol condition
gave fickle results in our laboratory. In contrast, depro-
tection of 2,7-bis(trimethylsilyl)-9,9'-dihexylfluorene
(10) yielded almost quantitatively diethynylfluorene as
white powder. The structures of 7 and 11 were
Scheme 4 Synthesis and structures of copolymers PS-DyCz and
PS-DyF
Ph
Ph
a
3
+
7
Si
n
N
C6H13
1
confirmed by H and 13C NMR, which were consistent
PS-DyCz (12)
with the literature.[21]
Ph
Ph
a
Scheme 3 Synthesis of 2,7-diethynyl-9,9'-dihexylfluorene (11)
11
+
3
Si
n
monomer
C6H13 C6H13
b
PS-DyF (13)
a
Reagents and conditions: (a) Pd(PPh3)4, Et3N, toluene, 60 ℃, 3 d.
I
I
Fluorene
8
Table 1 Molecular weight and thermal properties of copoly-
mers
c
I
I
Copolymer
PS-DyCz
PS-DyF
Mn/Da Mw/Da PDI na Td/℃ Tg/℃
C6H13 C6H13
C6H13 C6H13
Si
Si
b
4562
12045 2.6
8
319
－
10
9
b
14277
38266 2.7 22 341
－
d
a Degree of polymerization, that is the number of PS-DyCz or
PS-DyF repeat units depicted in. No glass transition signals
b
C6H13 C6H13
11
were observed.
Reagents and conditions: (a) I2, H5IO6, AcOH, H2SO4, H2O, reflux,
80 ℃, 3 h. (b) n-C6H13Br, tetrabutylammonium bromide, 50%
aqueous NaOH, DMSO, 80 ℃, 8 h. (c) Trimethylsilylacetylene,
structure of each monomer unit of the alternating co-
polymer. We can assign some characteristic proton
resonance, including one proton resonating at δ 0.60 (br)
for Si－CH3 of silole ring, and one proton resonating at
δ 4.22 (br) for N－CH2 of 7, or at δ 0.79 (t) for
hexyl-CH3 of 11. The NMR results confirmed the
chemical structure of the alternating copolymer (see the
Experimental Section for details).
The FT-IR spectra of PS-DyCz and PS-DyF co-
polymer are shown in Figure 1 and Figure 2, respec-
tively. The C≡C stretching vibration of PS-DyCz and
PS-DyF is observed at 2140 (w) and 2136 (w) cm−1, and
Si－C stretching vibration at 802 (s) and 818 (m) cm−1,
respectively. The strong stretching vibration of Si－C
shows more silole ring incorporated in the chain of co-
polymer.
1
Pd(PPh3)2Cl2, CuI, Et3N, reflux, 8 h. (d) KOH (1 mol•L− ), CH2Cl2,
MeOH, room temperature, overnight.
Both copolymers PS-DyCz and PS-DyF were syn-
thesized by Sonogashira coupling between 2,5-dibromo-
silole and correspondingly equimolar diethynyl com-
pounds in toluene and triethylamine after stirring for 3 d
(Scheme 4). Since the palladium catalyst is quite sensi-
tive to oxygen and 2,5-dibromosilole is easily decom-
pose under light, the polymerization reaction was run in
the dark using a standard Schlenk technique. The co-
polymers are both soluble in common solvents such as
chloroform, toluene, acetone and tetrahydrofuran, etc.
The molecular weight and the polydispersity index (PDI)
were measured by GPC using THF as an eluent and
polystyrene as the standard, and corresponding data are
summarized in Table 1. The weight-averaged molecular
weight (Mw) and PDI are 1.20×104 Da and 2.6 for
PS-DyCz, and 3.83×104 Da and 2.7 for PS-DyF, re-
spectively. The number-average molecular weight (Mn)
is 4.56×103 Da for PS-DyCz and 1.43×104 Da for
PS-DyF, and corresponding degree of polymerization (n)
is 8 and 22 silole-acetenyl aromatics units, respectively.
The difference of their n values was mainly attributed to
the copolymer’s innate structure. PS-DyF is closer to
linear structure, but PS-DyCz tends to spiral structure,[33]
because 3,6-position substitution of carbazole has about
60° angle to produce larger steric hinderance.
The structures of copolymers were also characterized
by 1H NMR and FT-IR. 1H NMR indicates the chemical
Figure 1 FT-IR spectrum of PS-DyCz copolymer.
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Siloles and Acetenyl Aromatics Copolymers: Synthesis, Characterization and Photophysical Properties
thermal stability, which is adequate for their applica-
tions in polymer solar cells (PSCs)[37] and other opto-
electronic devices.
Absorption and emission spectra
The UV-Vis absorption spectra of the copolymers in
THF are shown in Figure 4. The photophysical proper-
ties and optical band gap data of the copolymers are
summarized in Table 2. The polymer concentration
values are calculated based on the molecular weight of a
repeating unit.
Figure 2 FT-IR spectrum of PS-DyF copolymer.
Thermal properties
The thermal behavior of copolymers was investi-
gated by thermogravimetric analysis (TGA) and differ-
ential scanning calorimetry (DSC), and the correspond-
ing data are summarized in Table 1. DSC analysis re-
vealed that no glass transition signals were detected for
all the copolymers. This observation may be due to the
stiffness of the copolymer’s main chain.[34] Thermal
stability is an important criterion for evaluating the can-
didate of polymer for optoelectronic applications due to
the involvement of thermal processes in the device fab-
rications and operations.[35] The TGA plots (Figure 3)
showed that copolymers PS-DyCz and PS-DyF are
thermally stable with only about 5% weight loss (Td) in
a N2 atmosphere at temperatures of 319 ℃and 341 ℃,
respectively, similar to HB-car (Td＝356 ℃)[4] and
aryleneethynylene-carbazole hyperbranched polymer
(Td＝418 ℃).[36] The high decomposition temperatures
of these two copolymers are mainly attributed to ther-
mal stability characteristic of silole rings.[5] Meanwhile,
a little higher decomposition temperature of PS-DyCz
than that of PS-DyF indicated that PS-DyCz existed
branch structure of polymer in some extent. The results
indicated that these two copolymers possessed good
Figure 4 UV-Vis absorption spectra of copolymer PS-DyCz (a)
and PS-DyF (b) in THF solution at two concentration.
The absorption spectra of PS-DyCz (Figure 4)
showed that there were four peaks located at 251, 303,
380, and 467 nm. The absorption peaks observed at 251
and 303 nm are due to the π-π* transitions of the carba-
zole core,[1] and are red-shifted relative to that of
monomer 7 (λ＝290 nm).[38] This phenomenon suggests
the extensive conjugation length in the copolymer. The
peaks at 380 (shoulder) and 467 nm are attributed to
silole ring incorporated in the main chain of
copolymer.[30] With increasing of copolymer contents,
the absorptions are gradually intensified.
In contrast to PS-DyCz, the UV-Vis spectra of
PS-DyF (Figure 4b) exhibited a larger molar absorption
(ε) and narrow absorption range in the solution. The
weaker absorption band at around 250－325 nm is most
probably the absorption band of fluorene.[39] Thus, the
Figure 3 TGA curves of copolymers at a heating rate of 10 ℃/
min under N2 atmosphere.
Chin. J. Chem. 2015, 33, 550—558
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555

He et al.
FULL PAPER
Table 2 Optical band gaps and photophysical properties of copolymers
Absorptiona
Copolymer
Band-gap ΔEb/eV
Fluo-rescence λmaxc/nm
λ
max/nm
ε/(L•mol−1•cm−1)
Onset/nm
550
0.42×105, 0.32×105,
0.22×105, 0.11×105
0.90×105, 1.18×105
PS-DyCz
PS-DyF
251, 303, 380,d 467
391,d 418
2.25
2.70
542, 569
429, 460d
460
a In THF. b Estimated by absorption edge, ΔE＝(1240 eV•nm) (absorption onset−1). c Excited at 460 nm for PS-DyCz and 391 nm for
PS-DyF. d Shoulder peak.
maximum absorptions at 391 (shoulder) and 418 nm in
the Figure 4b arised from the absorption of silole ring.
The εmax (1.18×105 L•mol−1•cm−1) of PS-DyF is about
3 times larger than that of PS-DyCz (εmax, 0.42×105
L•mol−1•cm−1), which is attributed to the longer effec-
tive conjugated chain or larger degree of polymeriza-
tion.[40] Moreover, copolymer containing more ethynyl
units seemed to have relatively larger molar absorption
coefficient compared to the polymer with less ethynyl
units (see Figure 2 and Figure 4b).[33]
The optical band gap of PS-DyCz and PS-DyF is es-
timated to be 2.25 and 2.70 eV based on its solution
onset absorption wavelength. These narrow band gaps
are particularly attributed to low-lying LUMO energy
level of silole-acetylene polymeric systems,[2] which
Figure 6 PL spectra of copolymer PS-DyF in THF solution at
different concentration. Excitation wavelength: 391 nm.
were lower than those of V-shaped carbazole-fluorene
oligomers (2.95 eV)[26,33] or poly(2,7-fluorene ethyny-
lene) (PFE, around 2.88 eV).[21] The characteristic of
enhanced emission (AEE) effect and spiral structure of
copolymer.[33] But the decrease from 6.4×10−5 to 8×
low band-gap suggested their potential application as
10−4 mol•L−1 is mainly due to aggregation-caused
photovoltaics cell and other materials.
The fluorescence emission spectra of PS-DyCz and
quenching (ACQ) effect. Therefore, this change of PL
PS-DyF in THF solution at different concentrations at
intensity is the comprehensive result of AEE and ACQ
room temperature are shown in Figure 5 and Figure 6,
effect. Then, the fluorescence intensity of PS-DyF was
respectively, which showed broad emission bands with
also not monotone increasing relation with concentra-
PL intensity enhancement by increasing concentration.
Figure 5 showed that the broad emission band was over
tion, and maximum intensity is 428 and 455 nm at 1.1×
10−5 mol•L−1. The intensity increased from 2.2×10−7 to
1.1×10−5 mol•L−1 and decreased from 1.1×10−5 to
500－750 nm and maximum emission peaks located at
542 and 569 nm for the THF solution at 6.4×10−5
1.76×10−4 mol•L−1. This phenomenon is the competi-
mol•L−1. The PL intensity of copolymer increased with
tive result of AEE and ACQ effect, which is identical
increasing the concentration of copolymer from 8×10−7
with PL of copolymer PS-DyCz. As same as UV-Vis
to 6.4×10−5 mol•L−1, which is caused by the aggregate-
spectra of PS-DyF, there is not the fluorescence of fluo-
rene observed at 300－350 nm.[41]
Density functional theoretical calculations
Density functional theory (DFT) calculations were
performed at B3LYP/6-31G* level using copolymers’
trimer models, 2,5-bis(2,7-diethynylfluorene)silole and
2,5-bis(3,6-diethynylcarbazole)silole (Figure 7). The
orbital plots suggested that the HOMOs were distributed
over both acetenyl aromatics (diethynylcarbazole and
diethynyl-fluorene) and silole rings, but the LUMOs
were mainly localized in the silole ring and ethynyl
spacer. These characters of silole ring and ethynyl
spacer lowered the band gap between HOMO and
LUMO energy level. The frontier orbital energy of −5.4
eV for PS-DyCz calculated by DFT is 0.3 eV less than
that of PS-DyF (−5.1 eV), but the LUMOs are equiva-
lent. And the calculated bandgaps are obviously greater
Figure 5 PL spectra of copolymer PS-DyCz in THF solution at
different concentration. Excitation wavelength: 460 nm.
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Siloles and Acetenyl Aromatics Copolymers: Synthesis, Characterization and Photophysical Properties
than those estimated by absorption onset values. This
result was mainly caused by the difference of trimer
models used in the DFT calculations and the realistic
polymers;[42] the trimer models are small molecules,
while PS-DyCz or PS-DyF has a degree of polymeriza-
tion of 8 or 22, respectively.
THF solution demonstrated at 380, 467 nm and 391,
418 nm, respectively, and the absorption intensities
were enhanced with the increase of their concentration.
But PS-DyF displayed larger molar absorption coeffi-
cient due to more ethynyl units in the polymer backbone.
The maximum emission peaks of PS-DyCz and PS-DyF
located at 542, 569 nm and 428, 455 nm, and fluores-
cence spectrum showed broad emission bands. Owing to
silole and acetylene incorporated into the main chain of
copolymers, the band gap of PS-DyCz and PS-DyF fell
to 2.25 and 2.70 eV, respectively.
Acknowledgement
The authors are grateful to the financial support from
the National Natural Science Foundation of China (Nos.
20872035, 21076078), and the Hangzhou Normal Uni-
versity.
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We have successfully synthesized and characterized
two novel conjugated copolymers poly(silole-ethynyl
carbazole)s (PS-DyCz) and poly(silole-ethynylfluorene)s
(PS-DyF) by Sonogashira coupling reaction. To inves-
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absorption peaks of PS-DyCz and PS-DyF copolymer in
Chin. J. Chem. 2015, 33, 550—558
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www.cjc.wiley-vch.de
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