Synthesis and characterization of poly(silole-pyridine)

Article abstract of DOI:10.1080/15421406.2014.935974

New poly(silole-pyridine) was designed and synthesized. Polymer was obtained by Yamamoto coupling reaction. The structure of obtained polymer was characterized by the spectroscopic methods such as FT-IR and ¹H-NMR. The resulting polymer was sol

Full text of DOI:10.1080/15421406.2014.935974

Mol. Cryst. Liq. Cryst., Vol. 599: pp. 125–131, 2014
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2014.935974
Synthesis and Characterization
of Poly(silole-pyridine)
1
2
2
YE RIM CHEON, YUN-JI LEE, JEONG CHEOL PARK,
1
1
JAEYOUNG HWANG, SUNG-CHUL SHIN,
AND YUN-HI KIM1
,∗
1
Department of Chemistry, Gyeongsang National University, Jinju, Korea
School of Materials Science and Engineering and ERI, Gyeongsang National
2
University, Jinju, Korea
New poly(silole-pyridine) was designed and synthesized. Polymer was obtained by
Yamamoto coupling reaction. The structure of obtained polymer was characterized by
1
the spectroscopic methods such as FT-IR and H-NMR. The resulting polymer was
soluble in common organic solvents such as toluene, tetrahydrofurane, chloroform,
chlorobenzene, etc. The obtained polymer showed good thermal stabilities, which was
characterized by TGA and DSC.
Keywords Polymer organic light-emitting diode; pyridine; polysilole; energy transfer
Introduction
Organic light-emitting diodes (OLEDs) [1–8] have been profitably employed in small-sized
flat panel display [9]. Polymer light-emitting diodes (PLEDs) [10–12] have also attracted
considerable interest due to their applications in large-area flat panel displays [13] with
high-efficiency. For the highly efficient PLED devices, charge injection and transport from
both the anode and cathode should be balanced at the emitting layer to yield maximum
exciton formation [14,15].
∗
∗
Silole-containg molecules have low LUMO energy level by a σ →π conjugation
and increase their electron affinities [16–18] and have been used as electron-transporting
[19,20] by the high electron mobility. Pyridine is very useful moiety in OLED and PLED,
which was important factor in determining the electro-injection properties and OLED
properties. To enhance the electron mobility of organic semiconductors, aza-aromatics
such as phenanthroline, quinoline, pyridine and triazole have been incorporated into π-
conjugated systems [21–25].
In this study, we designed the polymer which is composed of pyridine and silole unit as
possessing high electron transport ability. We studied the physical, optical, electrochemical
and thermal properties of new obtained polymer.
∗
Address correspondence to Y. H. Kim, Department of Chemistry, Gyeongsang National Uni-
Ev e- rms iat iyl ,: GK ai jmw @a - gd no un .ga ,c J. ki nr ju 404-516, Korea (ROK). Tel.: (+82)55-772-1491; Fax: (+82)55-772-1489.
Color versions of one or more of the figures in the article can be found online at
www.tandfonline.com/gmcl.
[467]/125

126/[468]
Y. R. Cheon et al.
1
Figure 1. The spectrum of polymer (a) FT-IR, (b) H-NMR.
Experimental
Synthesis
Synthesis of bis(phenylacetyl)diphenylsilane. n-Butyllithium (2.5 M in hexane, 70.8 mL,
0
.761 mol) was slowly added to phenyl acetylene (13.9 g, 0.136 mol) in anhydrous
◦
tetrahydrofuran (THF) (200 mL) at −78 C. After 1 h stirring at room temperature,
diphenyl dichlorosilane (15 g, 0.059 mol) was slowly dropped into the mixture at
◦
−
78 C and stirred at room temperature. After 12 h, the reaction was terminated by
the addition of ice water and extracted with ethyl acetate (EA). The crude product
was purified by column chromatography and re-crystallization with hexane/EA: 20/1
◦
−1
as eluent. Yield: 13 g (57%). m.p: 174 C. FT-IR (KBr) (cm ): 3069-3000 (aromatic
C H), 1487, 1441, 1426 (aromatic C C), 2148 (C C), 1112 (Si C); H NMR (300 MHz,
1
CDCl3, ppm) δ = 7.89 ∼ 7.92 (dd, 4H), 7.60 ∼ 7.74 (dd, 4H), 7.35 ∼ 7.51 (m, 6H), 7.09
∼
7.28 (m, 6H). Anal. Calcd. for C28H20Si: C, 87.45; H, 5.24. Found: C, 86.85; H, 5.30.
2,5-Di(bromopyridyl)-1,1-diph-enyl-3,4-diphenylsilole was synthesized in the second
step. Lithium (0.032 g, 0.004 mol) and naphthalene (4.2 g, 0.032 mol) in THF (50 mL) were
stirred for 6 h. Bis(phenylacetyl)diphenylsilane (3 g, 0.007 mol) in THF was dropped to the
◦
mixture at −78 C. After 1 h stirring at room temperature, 1 M ZnCl2 was slowly added to

Synthesis and Characterization of Poly(silole-pyridine)
[469]/127
Table 1. The thermal, optical and electrochemical properties of the polymer
UV PL
Tg T5% (nm) (nm)
HOMO LUMO Eonsetred
◦
◦
Mn
Mw PDI ( C) ( C) film
film
(eV)
(eV)
(V)
Poylmer 5,300 5,800 1.09 92 292 400
511
–
−3.0
−1.40
◦
the mixture at 0 C and stirred for further an hour. 2,6-Dibromopyridine (3.8 g, 0.016 mol)
◦
and PdCl2(PPh3)2 was added and the result solution was refluxed for 16 h at 85 ∼ 90 C.
Once the reaction was completed, the crude product was worked up with water. The product
was extracted with EA. The crude product was purified by column chromatography with
Figure 2. The thermal properties of polymer (a) TGA and (b) DSC curve.

128/[470]
Y. R. Cheon et al.
Table 2. Solubility of polymer
Ethyl
Methylene
Solvent n-Hexane Methanol acetate DMF chloride Chloroform Toluene THF Chlorobenzene
Poylmer ++ −+ ++ ++ ++ ++ ++
−
−
++: soluble, −+: partially soluble, −: insoluble.
hexane/EA: 20/1 as eluent and re-crystallization with methylene chloride (MC) and hexane.
◦
−1
Yield: 2 g (36%). m.p: 244 ∼ 255 C. FT-IR (KBr) (cm ): 3046 (aromatic C H), 1465,
1
1
427 (aromatic C C), 1566 (C N), 1116 (Si C), 1023 (C Br); H NMR (300 MHz,
CDCl3, ppm) δ = 7.9 (d, 4H), 7.3 ∼ 7.45 (m, 6H), 7.12 ∼ 7.2 (t, 6H), 7.09 ∼ 6.9 (m, 8H),
6
.35 ∼ 6.45 (m, 2H). Anal. Calcd. for C38H26Br2N2Si: C, 65.34; H, 3.75; N, 4.01. Found:
C, 55.14; H, 3.85, N, 4.26.
Bis(1,5-cyclooctadiene) nickel(0) (Ni(COD)2) (0.70 g, 2.541 mmol), dipyridyl (0.40 g,
2
.562 mmol), 1,5-cyclooctadiene (0.3 g, 2.771 mmol) in anhydrous DMF (10 mL) and
◦
toluene (10 mL) was refluxed for 30 min at 80 C. 2,5-Di(bromopyridinyl)-1,1-diphenyl-
3
,4-diphenyl silole (1 g, 1.453 mmol) was added to the mixture and refluxed for further
◦
72 h at 80 C. Bromobenzene was injected into the reaction mixture and the reaction was
stirred for 24 h. The crude mixture was worked up with HCl/acetone/methanol : 1/1/1 (v/v).
After precipitation from methanol, the desired polymer was obtained. We can get poly(2,5-
−
1
dipyridyl-1,1-diphenyl-3,4-diphenylsilole). Yield: 0.3 g (37%). FT-IR (KBr) (cm ): 3046
(
1
aromatic C H), 1413 (aromatic C C), 1560 (C N), 1112 (Si C); H NMR (300 MHz,
CDCl3, ppm) δ = 7.9 (d, 6H), 7.34 ∼ 7.42 (m, 6H), 7.14 ∼ 7.19 (t, 6H), 7.05 ∼ 6.96 (m,
H), 6.48 ∼ 6.51 (m, 2H).
8
UV
PL
300 350 400 450 500 550 600 650 700 750
Wavelength (nm)
Figure 3. The optical properties of copolymer (a) UV-visible spectra in film, (b) PL spectra in film.

Synthesis and Characterization of Poly(silole-pyridine)
[471]/129
n-BuLi
Si
Si
Cl
Cl
THF
LiNaph
THF
Si
ZnCl
2
Si
Li
Li
ClZn
ZnCl
THF
Br
N
Br
Br
Br
N
N
PdCl (PPh )
Si
2
3 2
THF
(
a)
Br
Br
N
N
Si
N
Si
N
Ni(COD) , 2',2'-Dipyridyl
2
1,5-cydooctadiene
DMF/Toluene
(
b)
Scheme 1.
Measurements
1H nuclear magnetic resonance (NMR) spectra were recorded using DRX 300 MHz Bruker
spectrometer and chemical shifts in spectra were reported in parts per million (ppm) units
with tetramethylsilane as internal standard. Infrared (IR) studies of the samples were
carried out using a Genesis II FT-IR spectrometer. A Jeol JMS-700 mass spectrometer
was used to obtain the mass spectra of the samples. Thermogravimetric analysis (TGA)
was performed under nitrogen using a TA instrument 2025 thermogravimetric analyzer.
◦
◦
◦
The sample was heated from 50 C to 800 C with a heating rate of 10 C/min. Differential
scanning calorimeter (DSC) studies were carried out under nitrogen using a TA instrument
◦
◦
2
100 differential scanning calorimeter. The sample was heated from 30 C to 300 C with
a heating rate of 10 C/min. UV-visible absorption and photoluminescence (PL) studies
at room temperature were carried out using Perkin Elmer LAMBDA-900 UV/VIS/NIR
◦

130/[472]
Y. R. Cheon et al.
spectrometer and LS-50B lumininescence spectrophotometer. Cyclic voltammogram (CV)
of the sample was recorded using a Epsilon E3 at room temperature in a 0.1 M solution of
tetrabutylammonium perchlorate (Bu4NClO4) in acetonitrile under nitrogen environment
at a scan rate of 50 mV/s. Molecular weights and polydispersities of the polymers were
determined by gel permeation chromatography (GPC) analysis with polystyrene standard
calibration (waters high-pressure GPC assembly Model M515 pump, u-Styragel columns
of HR4, HR4E, HR5E, with 500 and 100 Å, refractive index detectors, solvent THF).
Results and Discussion
The synthetic scheme of polymer was prepared as depicted in scheme 1. Polymer was
obtained by Yamamoto coupling reaction using (Ni(COD)2). The obtained polymer was
purified by precipitation using methanol. The structure of polymer was confirmed by FT-
1
IR and H-NMR (Fig. 1). The FT-IR spectrum of the polymer indicated that the chemical
−1
structure. C-Br peak (1023 cm ) of 2,5-di(bromopyridyl)-1,1-diph-enyl-3,4-diphenylsilole
was not founded in this spectrum. The structure was confirmed by the proton peak at
1
7
.9∼6.28 ppm in H-NMR. Gel permeation chromatography (GPC) analysis determined
the weight average molecular weight (MW) to be 5,800 with a polydispersity index (PDI)
of around 1.09, against polystyrene standards. The molecular weights and polydispersity
indexes of the polymer was summarized in Table 1. The polymer showed good solubility
in common organic solvents, such as methylene chloride, tetrahydrofuran, chloroform,
toluene and chlorobenzene (Table 2).
The thermal properties of the polymer were evaluated by thermal gravimetric analysis
(
TGA) and differential scanning calorimetry (DSC). The 5% weight loss of the polymer
◦
was observed at 292 C. From the DSC data of the polymer the glass transition temperature
(
◦
Tg) was observed at 92 C (Fig. 2).
The UV-visible absorption and photoluminescence spectra of the polymer in film state
are shown in Fig. 3. The UV-visible absorption was indicated at 400 nm in film and the
PL absorption was indicated at 511 nm, at film. The electrochemical behaviors of these
polymers were investigated by cyclic voltammetry (CV). They were summarized in Table 1.
LUMO energy level was −3.0 eV. The polymer shows low LUMO energy level because of
electron-withdrawing property of silole moiety and pyridine. [26, 27] The polymer OLED
will be characterized by using obtained polymer as emitting layer as well as electron
transporting layer.
Conclusions
The new polymer composed of silole and pyridine was synthesized by Yamamoto coupling
reaction. The LUMO level of polymer was very low because of introduction of non-
copolanar silole unit and pyridine unit, which are good electron transporting.
Funding
This research was supported by Industrial Strategic Technology Development Program
(10045269) by MOTIE/KEIT.

Synthesis and Characterization of Poly(silole-pyridine)
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