Synthesis and EL properties of light-emitting polymers by Gilch polymerization

Article abstract of DOI:10.1080/15421400500374575

A new class of soluble PPV derivatives containing dimethyldodecylsilylphenyl unit as a pendant was synthesized by Gilch polymerization method. The resulting electroluminescent polymers showed good solubility, good film-forming ability onto the ITO substra

Full text of DOI:10.1080/15421400500374575

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Synthesis and EL Properties
of Light-Emitting Polymers by
Gilch Polymerization
Sung-Ho Jin a , Hwan-Hee Jeong a , Chan-Koo Hwang
a , Seong-Bae Moon a , Jae Wook Lee b , Jin-Taek
Hwang c , Yeong-Soon Gal d & Jin-Kook Lee e
a Department of Chemistry Education and Center
for Plastic Information System , Pusan National
University , Busan, Korea
b Department of Chemistry , Dong-A University ,
Busan, Korea
c Department of Materials Science and Engineering ,
Gwangju Institute of Science and Technology ,
Gwangju, Korea
d Polymer Chemistry Laboratory , Kyungil
University , Hayang, Korea
e Department of Polymer Science and Engineering ,
Pusan National University , Busan, Korea
Published online: 20 Aug 2006.
To cite this article: Sung-Ho Jin , Hwan-Hee Jeong , Chan-Koo Hwang , Seong-Bae
Moon , Jae Wook Lee , Jin-Taek Hwang , Yeong-Soon Gal & Jin-Kook Lee (2006)
Synthesis and EL Properties of Light-Emitting Polymers by Gilch Polymerization,
Molecular Crystals and Liquid Crystals, 444:1, 1-11, DOI: 10.1080/15421400500374575
To link to this article: http://dx.doi.org/10.1080/15421400500374575
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Mol. Cryst. Liq. Cryst., Vol. 444, pp. 1–11, 2006
Copyright # Taylor & Francis LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400500374575
Synthesis and EL Properties of Light-Emitting Polymers
by Gilch Polymerization
Sung-Ho Jin
Hwan-Hee Jeong
Chan-Koo Hwang
Seong-Bae Moon
Department of Chemistry Education and Center for Plastic
Information System, Pusan National University, Busan, Korea
Jae Wook Lee
Department of Chemistry, Dong-A University, Busan, Korea
Jin-Taek Hwang
Department of Materials Science and Engineering, Gwangju
Institute of Science and Technology, Gwangju, Korea
Yeong-Soon Gal
Polymer Chemistry Laboratory, Kyungil University, Hayang, Korea
Jin-Kook Lee
Department of Polymer Science and Engineering, Pusan National
University, Busan, Korea
A new class of soluble PPV derivatives containing dimethyldodecylsilylphenyl unit
as a pendant was synthesized by Gilch polymerization method. The resulting elec-
troluminescent polymers showed good solubility, good film-forming ability onto
the ITO substrate, and exhibited an amorphous morphology due to dimethyldode-
cylsilylphenyl branched group linked to the polymer backbone. The weight average
molecular weights and polydispersities of the present EL polymers were in the
range of 8.0–80.0 ꢀ 104 and 2.67–7.80, respectively. The resulting EL polymers
revealed a high thermal stability of up to 355–410ꢁC. Their glass transition tem-
peratures were in the range of 104–251ꢁC. The emission colors could be tuned from
green to orange-red colors by changing the MEH-PPV contents in copolymer
systems. The turn-on voltages of the EL polymers were in the range of 1.8–4.0 V.
We gratefully acknowledge the Ministry of Information & Communications, Korea,
under the Information Technology Research Center (ITRC) Support Program.
Address correspondence to Sung-Ho Jin, Department of Chemistry Education and
Center for Plastic Information System, Pusan National University, Busan 609-735,
Korea. E-mail: shjin@pusan.ac.kr
1

2
S.-H. Jin et al.
Keywords: electroluminescence; Gilch polymerization; light-emitting diode; poly
(p-phenylenevinylene)
INTRODUCTION
Organic light-emitting diodes (OLEDs) have attracted much attention
because of their wide viewing angle, fast switching time compared to
conventional flat panel liquid crystal displays (LCDs) and their poten-
tial application for large-area flat panel display that can be driven at
low voltage [1–3]. Since Tang and VanSlyke have demonstrated a high
efficiency LED consisting of light-emitting layers and carrier transport
layers [4], various kinds of electroluminescent (EL) polymers as well as
organic fluorescent dyes have been developed in order to obtain high
efficiency, long lifetime and even white-color emission materials for
LCD backlight [5]. Among the conjugated polymers, poly(p-phenylene-
vinylene) (PPV) and its derivatives are known as the most promising
materials for the application of polymer LEDs. These materials have
been synthesized by precursor routes or the dehydrohalogenation
method leading to soluble and high molecular weight polymers.
Recently, there has been increasing interest in the silyl-substituted
luminescent polymers, in which silyl moieties are introduced either
as side chains or as a segment integrated into the polymer backbones
[6–8]. A systematic study on the synthesis of polymers combining silyl
side chains and substitution on the chemical, physical, and optoelectro-
nic properties of the polymers is interesting to materials scientists
and synthetic organic chemists. The attractive properties of silyl-
substituted PPVs are their extremely high PL quantum efficiency, good
solubility, and uniform film morphology in the film state [9,10]. There-
fore, it is meaningful to design and synthesis of silyl substituted PPVs
with the aim of keeping or even further enhancing the PL efficiency
and the processability by a highly branched side group associated with
the larger atom size of Si and the longer bond length of CꢂSi [11].
Recently, we have synthesized a novel EL polymer, such as alkoxy-
phenyloxy substituted PPVs and blending systems with oxadiazole
containing electron transport polymer, to improve the device perform-
ance [12,13]. In the present article, we report a new series of color
tunable PPV derivatives containing dimethyldodecylsilylphenyl side
group by Gilch polymerization for high molecular weight and good
thermal stability. In order to improve the EL efficiency, the bulky
dimethyldodecylsilyl group was introduced into the ortho-position of
phenyl substituent, which increases intramolecular steric hindrance
between dimethyloctylsilylphenyl group and vinylic proton to afford
amorphous morphology and good solubility behaviors.

Synthesis and EL Properties of Light-Emitting Polymers
3
EXPERIMENTAL
Synthesis of 1-bromo-2-(dimethyldodecylsilyl)benzene (1)
A round bottom flask was placed 1,2-dibromobenzene (19.4 g, 82 mmol)
and dry THF (250 mL) under N2 atmosphere. The flask was cooled
to ꢂ78ꢁC. While stirring, n-BuLi (51.44 mL, 1.6 M n-hexane solution,
82 mmol) was added dropwise causing a lightening of the yellow color.
After 1 hr stirring at ꢂ78ꢁC, the mixture was allowed to room tem-
perature and stirred for an additional 1 hr. After cooling to ꢂ78ꢁC,
chlorododecyldimethylsilane (21.6 g, 82 mmol) was added dropwise,
and the system was allowed to slowly warm to room temperature
and stirred for an additional 3 hrs. Most of solvent was evaporated
under a reduced pressure. The resulting oily product was further
purified by column chromatography on silica gel using hexane as an
1
eluent. (Yield: 30%). H-NMR (CDCl3): d 0.27 (s, 6H, Si(CH3)2), 0.77
(t, 2H, SiCH2), 0.92 (t, 3H, ꢂCH3), 1.27 (m, 20H, (CH2)10), 7.21
and 7.49 (d, 4H, aromatic protons).
Synthesis of 2-(4,4,5,5-tetramethyl-2-
isopropoxydioxaborolanyl)-1,4-xylene (2)
A round bottom flask was placed 2-bromo-p-xylene (20 g, 0.11 mol) and
dry THF (200 mL) under N2 atmosphere. While stirring, n-BuLi
(71 mL, 1.6 M n-hexane solution, 0.11 mol) was added dropwise at
ꢂ78ꢁC. When dropping was finished, the mixture was stirred at the
same temperature for 2 hrs. And then, 2-isopropoxy-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane (24.2 g, 0.13 mol) was added dropwise
to the solution at ꢂ78ꢁC. The solution was allowed to slowly warm to
room temperature and stirred for an additional 24 hrs. The reaction
mixture was quenched by water and extracted with ether. The
combined organic layers were dried over anhydrous MgSO4 and
filtered. The solvent was removed by evaporation under reduced press-
ure. The product was purified by chromatography on silica gel using
hexane=ethyl acetate (9=1) as an eluent. (Yield: 90%). 1H-NMR
(CDCl3, ppm): d 7.6 (s, 1H), 7.15 (d, 1H), 7.1 (d, 1H), 2.5 and 2.3
(s, 6H, 2CH3 on aromatic ring), 1.3 (s, 12H).
Synthesis of 1,4-dimethyl-2-(20-dimethyldodecylsilylphenyl)-
benzene (3)
To a stirred solution of compound 1 (9.98 g, 26 mmol) in DME,
Pd(PPh3)4 (0.45 g, 0.39 mmol) was added at room temperature under
N2 atmosphere. After 10 min at room temperature, compound 2

4
S.-H. Jin et al.
(9.06 g, 39 mmol) was added and followed by NaHCO3 (1.0 M, 95 ml).
And then, the mixture was refluxed for 5 hrs. The catalyst was filtered
off, and the phases were separated. The water phase was extracted
twice with ether. The resulting organic extracts were combined and
washed with water, dried over anhydrous MgSO4 and evaporated.
The resulting oily product was purified by column chromatography
on silica gel using hexane as an eluent. (Yield: 56%). 1H-NMR
(CDCl3): d 0.31 (s, 6H, Si(CH3)2), 0.77 (t, 2H, SiCH2), 0.93 (t, 3H,
ꢂCH3), 1.56 (m, 20H, (CH2)10), 2.28 and 2.4 (s, broad, 6H, 2CH3 on
aromatic ring), 7.05–7.55 (m, 7H, aromatic protons).
Synthesis of 1,4-bis(bromomethyl)-2-(2-dimethyldodecyl-
silylphenyl)benzene (4)
A mixture of 1,4-dimethyl-2-(2-dimethyldodecylsilylphenyl)benzene 3
(10.4 g, 25.4 mmol), N-bromosuccinimide (9.95 g, 55.9 mmol), and benzoyl
peroxide (12 mg, 0.05 mmol) in CCl4 (200mL) was heated to reflux
for 3 hrs under N2 atmosphere. A bright red solution with precipitated
succinimidewasproduced.Thewarmreactionmixturewasfilteredunder
suction and washed with a little hot CCl4. The combined organics were
dried over anhydrous MgSO4. After removing of the solvent, the residue
was subjected to purification by chromatography on silica gel using
1
hexane as an eluent. (Yield: 40%). H-NMR (CDCl3): d 0.29 (s, 6H,
Si(CH3)2), 0.79 (t, 2H, SiCH2), 0.91 (t, 3H, ꢂCH3), 1.31 (m, 20H,
(CH2)10), 4.1–4.63 (m, 4H, 2-CH2Br), 7.29–7.62 (d, 7H, aromatic protons).
Synthesis of poly[2-(2-dimethyldodecylsilylphenyl)-1,
4-phenylenevinylene], (o-SiPhPPV)
To a 100 mL Schlenk flask, the monomer 4 (0.2 g, 0.35 mmol) and dry
THF (20 mL) were placed and cooled in an ice bath under N2 atmos-
phere. With stirring, the potassium tert-butoxide (2.13 mL, 1.0 M
THF solution, 2.13 mmol) was added dropwise for 20 min. After
2 min, the reaction mixture turned to yellow and cloudy, and then a
bright yellowish green viscous solution was formed. The reaction mix-
ture was stirred additionally for 3 hrs. The polymerization solution
was precipitated into 400 mL of MeOH with stirring. The crude poly-
mer was Soxhlet extracted with MeOH. The resulting polymer was
redissolved in chloroform and reprecipitated into MeOH. After
filtration and drying under vacuum, a bright yellow polymer was
obtained (0.07 g, 75%). The obtained polymer has the following
1H-NMR spectral characteristics in CDCl3: d 0.30 (s, 6H, Si(CH3)2),
0.70–0.98 (m, 5H, SiCH2 and ꢂCH3), 1.10–1.52 (m, 20H, (CH2)10),

Synthesis and EL Properties of Light-Emitting Polymers
5
7.10–7.80 (br, 9H, aromatic protons and vinylic protons); Anal. Calcd
for C28H40Si: C, 83.10; H, 9.96. Found: C, 82.90; H, 9.86.
Synthesis of poly[2-(2-dimethyldodecylsilylphenyl)-1,4-
phenylenevinylene-co-2-methoxy-5-(2-ethylhexyloxy)-1,4-
phenylenevinylene], (o-SiPhPPV-co-MEH-PPV)
A solution of 3.6 mL of potassium tert-butoxide (1.0 M THF solution,
3.6 mmol) was slowly added over 1 hr using a syringe pump to a stirred
solution of monomer (0.102 g, 0.18 mmol) and 1,4-bis(chloromethyl)-
2-(2-ethylhexyloxy)-5-methoxybenzene (0.14 g, 0.42 mmol) in 20 mL
of dry THF that was cooled to ꢂ5ꢁC. The reaction mixture gradually
increased its viscosity with orange-red fluorescence and was stirred
for 3 hrs. The polymerization solution was precipitated into 600 mL
of MeOH and the crude polymer was Soxhlet extracted with MeOH
to remove the impurities and oligomers. The resulting polymer was
redissolved in chloroform and reprecipitated into MeOH. After
filtration and drying under vacuum, bright red fibrous polymer,
o-SiPhPPV-co-MEH-PPV (50:50 mol%) was obtained. (Yield: 50%)
1H-NMR (CDCl3): d 0.28 (s, 6H, Si(CH3)2), 0.70–0.91 (m, 11H, SiCH2,
and ꢂCH3 ꢀ 3), 1.10–1.60 (m, 31H, methylene and methine protons),
3.8–4.2 (m, 5H, ꢂOCH2, and –OCH3), 7.10–7.60 (br, 13H, aromatic
protons and vinylic protons).
RESULTS AND DISCUSSION
The synthetic procedure for the monomer and the corresponding poly-
mers are depicted in Scheme 1. All synthetic steps for the monomer
are facile and can be easily controlled. In order to improve the proces-
sability and amorphous morphology of the present polymers, dodecyl-
dimethylsilyl group was introduced into the ortho-positions of the
phenyl side group. Compound 3 was synthesized using a Pd(PPh3)4-
mediated carbon-carbon coupling reaction. The monomer was finally
obtained using the bromination of compound 3 and the yield of mono-
mer was about 40%. Polymerization of the monomer 4 was performed
with an excess of potassium tert-butoxide in cooled THF in an ice
water bath under N2 atmosphere. The collected polymer, o-SiPhPPV
was further purified by Soxhlet extraction through MeOH and chloro-
form to remove the oligomers and inorganic impurities.
In order to increase the molecular weight and to improve the device
performance, the copolymerization was carried out with various initial
monomer concentration of bis(chloromethyl)-2-(2-ethylhexyloxy)-5-
methoxybenzene according to the similar method for the synthesis of

6
S.-H. Jin et al.
SCHEME 1
o-SiPhPPV. Table 1 summarizes the polymerization results and
molecular weights of the o-SiPhPPV, MEH-PPV and their copolymers,
o-SiPhPPV-co-MEH-PPV. The weight average molecular weights (Mw)
and polydispersities of the o-SiPhPPV, o-SiPhPPV-co-MEH-PPV and

Synthesis and EL Properties of Light-Emitting Polymers
7
TABLE 1 Polymerization Results and Molecular Weights of o-SiPhPPV and
o-SiPhPPV-co-MEH-PPV
Polymer
Yield (%)
Maw (ꢀ10ꢂ3
)
Mw=Mn
o-SiPhPPV
50
54
50
74
80
80
200
100
490
800
3.30
7.80
6.67
2.74
2.67
o-SiPhPPV-co-MEH-PPV (70:30 mol%)b
o-SiPhPPV-co-MEH-PPV (50:50 mol%)b
o-SiPhPPV-co-MEH-PPV (30:70 mol%)b
MEH-PPV
aGPC in THF using polystyrene standards.
bComposition determined from 1H-NMR spectroscopy.
MEH-PPV for comparison were in the range of 8.0–80.0 ꢀ 104 and 2.67–
7.80, respectively.
The resulting EL polymers were completely soluble in common
organic solvents, such as chloroform, chlorobenzene, toluene, THF,
xylene, and easily spin-coated onto the ITO coated glass substrate.
The excellent solubility behavior of the o-SiPhPPV and o-SiPhPPV-
co-MEH-PPV compared to alkyl- or alkoxy-substituted PPVs is attrib-
uted to the long chain alkylsilyl pendant group. Compared with alkyl-
or alkoxy-substituted PPVs, the side chains linked to the polymer
backbone through the silicon atom can enhance the flexibility of the
polymer, due to the larger atom size of silicon than carbon or oxygen
and longer bond length of SiꢂC than CꢂC or CꢂO. The larger atom
size and longer bond length result in lower barriers to SiꢂC bond
rotation, which leads to enhanced flexibility of the resulting polymers.
The structure and thermal stability of the o-SiPhPPV, o-SiPhPPV-co-
MEH-PPV and MEH-PPV were identified by 1H-NMR, UV-visible
spectroscopy and TGA thermograms. The disappearance of the charac-
teristic benzylic proton peaks at 4.45 and 4.50 ppm of the monomer
and the appearance of new vinylic proton peaks at 7.10 ppm with aro-
matic phenyl protons in polymer confirmed the complete polymeriza-
1
tion. The H-NMR spectrum of the o-SiPhPPV-co-MEH-PPV showed
a signal at 0.28 ppm for dimethyl groups on silicon atom and at
3.8–4.2 ppm for methylene next to oxygen and methoxy groups in side
chains. From the comparison of the peak areas at 0.28 and
3.8–4.2 ppm, compositions of the o-SiPhPPV-co-MEH-PPV were calcu-
lated. The compositions of o-SiPhPPV-co-MEH-PPV are about 70:30,
50:50, and 30:70 mol% with o-SiPhPPV and MEH-PPV units. The
TGA thermograms of the o-SiPhPPV and o-SiPhPPV-co-MEH-PPV
revealed a high thermal stability of up to 355–410ꢁC. The high ther-
mal stability of the o-SiPhPPV and o-SiPhPPV-co-MEH-PPV prevents

8
S.-H. Jin et al.
FIGURE 1 UV-visible absorption spectra of o-SiPhPPV, o-SiPhPPV-co-MEH-
PPV and MEH-PPV in thin film.
the deformation of the polymer morphology and degradation of the
polymeric emitting layer by applied electric fields of the LED.
Figure 1 shows optical absorption spectra of the o-SiPhPPV,
o-SiPhPPV-co-MEH-PPV and MEH-PPV thin films. Absorption maxi-
mum of the o-SiPhPPV is shown at about 420 nm. The maximum
absorption spectra of the o-SiPhPPV-co-MEH-PPV are more red-
shifted than that of o-SiPhPPV. This is due to the introduction of
MEH-PPV segment and the extension of the effective conjugation
length in copolymers.
Figure 2 shows the emission spectra of the o-SiPhPPV, o-SiPhPPV-
co-MEH-PPV, and MEH-PPV thin films under excitation at the
absorption maximum wavelength of corresponding polymer. The emis-
sion maximum of the o-SiPhPPV showed two peaks at about 500 and
530 nm with a shoulder at about 570 nm. As increasing the MEH-PPV
contents, the emission peaks of the o-SiPhPPV-co-MEH-PPV were red-
shifted from 500 and 530 nm to 588 nm. The maximum peaks of the
o-SiPhPPV-co-MEH-PPV are similar to that of MEH-PPV thin film.
The tuning of emission maximum is due to the efficient energy trans-
fer via intramolecular chain interaction in thin film state. The EL
spectra were essentially identical to the PL spectra of the resulting

Synthesis and EL Properties of Light-Emitting Polymers
9
FIGURE 2 PL spectra of o-SiPhPPV, o-SiPhPPV-co-MEH-PPV, and MEH-
PPV in thin film.
FIGURE 3 Luminescence-voltage (L-V) characteristics of ITO=PEDOT=
polymer=Al devices.

10
S.-H. Jin et al.
EL polymers. EL spectra also show a red-shifted upon going from
o-SiPhPPV to o-SiPhPPV-co-MEH-PPV, which is similar to the PL
and absorption spectra. Figure 3 shows the luminescence-voltage
(L-V) characteristics of ITO=PEDOT=polymer=Al devices. The turn-on
voltage of the o-SiPhPPV is approximately 4.0 V. However, the turn-
on voltages of the o-SiPhPPV-co-MEH-PPV were observed 1.8–4.0 V,
which trend to follow that of MEH-PPV. The luminance intensity of
the o-SiPhPPV and o-SiPhPPV-co-MEH-PPV exponentially increased
with an increased voltage.
CONCLUSIONS
We have synthesized and characterized a new class of soluble PPV
derivatives containing alkylsilylphenyl unit as a pendant. The result-
ing EL polymers showed good solubility, good film-forming ability on
ITO substrate, and amorphous properties due to the branching struc-
ture of dimethyldodecylsilyl group linked to the polymer backbone as
well as enhanced flexibility of side chain originated from the larger
size of Si atom and longer bond length of CꢂSi compared with corre-
sponding carbon or oxygen counterparts. Emission spectrum of the
o-SiPhPPV showed two peaks at 500 and 530 nm in the green emission
region. As increasing the MEH-PPV content, the emission peaks of the
copolymers, o-SiPhPPV-co-MEH-PPV were red-shifted to 588 nm. The
emission colors could be tuned from green to orange-red colors by
changing the MEH-PPV content. The turn-on voltages of the polymers
were observed 1.8–4.0 V.
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