Synthesis and properties of poly(10-octylphenothiazine-CO-2′, 3′,6′,7′-tertrakis-octyloxy-9-spirobifluorene) for OLEDs

Article abstract of DOI:10.1080/15421400601013429

Many attempts have been focused on polymer light-emitting diodes (PLEDs) for large area display application. We report synthesis and properties of new phenothiazyl polymer derivatives, Poly(10-octyl-10H-phenothiazine-3,7-diyl) (POP), Poly(2',3',6',7'-tert

Full text of DOI:10.1080/15421400601013429

Mol. Cryst. Liq. Cryst., Vol. 462, pp. 267–276, 2007
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400601013429
Synthesis and Properties of Poly(10-Octylphenothiazine-
CO-2’,3’,6’,7’-Tertrakis-Octyloxy-9-Spirobifluorene)
for OLEDs
Ji-Soung Kang
Jong-Wook Park
Department of Chemistry=Display Research Center, The Catholic
University of Korea, Puchon, Kyonggi, Korea
Ji-Hoon Lee
Department of Polymer Engineering=Chung-Ju National University,
Chung-Ju, Chungbuk, Korea
Se-Young Oh
Department of Chemical Engineering, Sogang University, Mapo,
Seoul, Korea
Many attempts have been focused on polymer light-emitting diodes (PLEDs) for
large area display application. We report synthesis and properties of new phe-
nothiazyl polymer derivatives, Poly(10-octyl-10H-phenothiazine-3,7-diyl) (POP),
Poly(20,30,60,70-tertrakis-octyloxy-9-spirobifluorene-2,7-diyl) (PTOSF), and their
random copolymers, Poly(10-octylphenothiazine-co-20,30,60,70-tertrakis-octyloxy-9-
spirobifluorene) (POTOSF), which were polymerized by Yamamoto reaction. The
obtained compound was identified by 1H-NMR, UV-Visible spectroscopy and
GPC data. Weight average molecular number (Mn) of the polymers ranged from
17,000 to 300,000 g=mol with polydispersity indices of 1.6ꢀ6.5. Maximum UV-Vis-
ible absorption of the polymers was distributed from 285 to 403 nm. PL emission of
POP, PTOSF and POTOSF copolymer were found to be 480, 434 and 484 nm,
respectively. EL emission peak of double-layer EL device of POTOSF was at
494 nm (bluish green).
Keywords: electroluminescence; phenothiazine; polymer light-emitting diodes (PLEDs);
Yamamoto reaction
This work was supported by grant No. R01-2006-00010196-0 from the Basic Research
Program of the Korea Science & Engineering Foundation.
Address correspondence to Jong-Wook Park, Department of Polymer Science=Display
Research Center, Catholic University of Korea, Puchon, Kyonggido, Korea. E-mail:
hahapark@catholic.ac.kr
267

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INTRODUCTION
Polymer light-emitting diodes (PLEDs) have attracted much atten-
tion from academia and industry because of their applications in
large area flat-panel displays [1,2]. In particular, interest in
PLEDs fabricated from conjugated Polymers [3,4] has augmented
because such PLEDs have properties that are well-suited to flat
panel displays: good processability, low operating voltages, fast
response times, and facile color tunability over the full visible
range.
On the other hand, a number of issues, such as low electrolumi-
nescent (EL) efficiencies and luminescent stability, which need to
be resolved, currently spoil their commercial applications, although
many light-emitting polymers have been synthesized and investi-
gated, and the performance of PLEDs has been improved greatly
in recent years. Therefore, investigation for new p-conjugated poly-
mers with higher luminescent performance remains one of the
major challenges in the area. Among the many kinds of conjugated
polymers, PPV and its derivatives are the most extensively investi-
gated polymers employed as emitting layers in PLEDs [5,6].
Recently, dendrimer-type Ir complexes, having large molecular
weight, have been investigated so that the thin film of these mate-
rials can be fabricated by the solution process [7]. Phenothiazine is
a well-known heterocyclic compound with electron-rich sulfur and
nitrogen heteroatoms. Molecules and polymers [8,10,11] containing
phenothiazine moieties have recently attracted much research
interest because of their unique electro-optical properties and their
resulting potential in diverse applications such as light-emitting
diodes [9,11]. It has been suggested that inclusion of phenothiazine
into a polyfluorene should improve the hole-transporting properties
of the polyfluorene and thus improve the EL device efficiency.
recently synthesized an alternating copolymer of phenothiazine
and fluorene by the Suzuki coupling reaction and characterized
its properties [11].
In this paper, we have synthesized phenothiazine homopolymer
and spriofluorene copolymer. Poly(10-octyl-10H-phenothiazine-3,7-
diyl) (POP), Poly(20,30,60,70-tertrakis-octyloxy-9-spirobifluorene-2,7-diyl)
(PTOSF), and their random copolymers, Poly(10-octylphenothiazine-co-
20,30,60,70-tertrakis-octyloxy-9-spirobifluorene) (POTOSF), were synthe-
sized through Yamamoto polymerization. Optical properties of these poly-
mers were characterized by UV-visible and photoluminescence (PL)
spectra. Moreover, double-layer EL device was fabricated using POTOSF
as emitting materials.

Synthesis and Properties of POTOSF for OLEDs
269
EXPERIMENT
Instrument
1H-NMR spectra was recorded on a Brucker DPX-300 MHz spec-
trometer at room temperature. The molecular weights of the polymers
were determined by gel permeation chromatography (GPC) analysis
using a Waters high pressure GPC assembly Model M410. The optical
absorption spectra were measured by a Hewlett Packard 8453 Spec-
trometer. Perkin Elmer luminescence spectrometer LS50 (Xenon flash
tube) was used for photo- and EL spectroscopy. For EL devices, poly-
mer film was prepared by spin coating a solution containing 0.7 wt%
of the polymer in toluene. Smooth and pinhole free film with a thick-
ness around 70 nm was easily obtained from the polymer solutions.
For double layered device, a modified water dispersion of PEDOT
[poly(3,4-ethylenedioxy-thiophene)] doped with poly(styrene sulfo-
nate) (PSS) (Bayer AG, Germany) was used as the hole-injection=tran-
transport layer. Cathode (LiF=Al) was deposited with 10ꢁ6 torr give an
emitting area of 9 mm2. Current-Voltage (I-V) characteristic of the film
was measured using Keithley 2400 electrometer. Light intensity was
obtained by Minolta CS-1000.
Synthesis
10-octyl-10H-phenothiazine (1)
Phenothiazine of 10 g (50 mmol) and potassium hydroxide of 8 g
(147 mmol) were dissolved in dimethyl sulfoxide of 300 ml under nitro-
gen. After stirring for 1 hour, 1-bromo-octane of 9.5 ml (54 mmol) was
added. The mixture was refluxed for 24 hours. After reaction mixture
was worked up by silica gel chromatography to have colorless liquid of
11 g (72% reaction yield).
1H NMR: d: 7.12(m, 4H), 6.88(d, 4H), 3.80(t, 2H), 1.81(m, 2H), 1.40
(m, 2H), 1.26(m, 8H), 0.86(t, 3H)
3,7-dibromo-10-octyl-10H-phenothiazine (2)
10-Octyl-10H-phenothiazine of 11 g (35 mmol) was dissolved in chlor-
form of 200 ml under nitrogen and cooled to 5–10ꢂC with ice-water
bath. After N-bromosuccinimide (NBS) of 14 g (80 mmol) was added
slowly. The mixture stirred for 2 hours at room temperature. The
crude product was purified by column chromatography using a cosol-
vent (hexane=ethyl acetate¼10:1) as the eluent., yellow liquid of 9 g
(65% yield).
1H NMR: d: 7.34(m, 4H), 6.95(d, 2H), 3.81(t, 2H), 1.62(m, 2H), 1.31
(m, 2H), 1.19(m, 8H), 0.81(t, 3H).

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1,2-bis(octyloxy)benzene (3)
Pyrocatechol of 15 g (130 mmol), K2CO3 of 47 g (340 mmol) and KI of
2.1 g (13 mmol) were dissolved in acetonitrile of 300 ml under nitrogen.
After stirring for 1 hour, 1-bromo-otane of 62 ml (320 mmol) was added.
The mixture was refluxed for 40 hours. After the reaction mixture was
worked up by silica gel chromatography to have colorless liquid of 43 g
(95% yield).
1H NMR: d: 6.78(m, 2H), 6.70(m, 2H), 3.77(t, 4H), 1.54(m, 4H),
1.13(m, 20H), 0.73(t, 6H).
4-bromo-1,2-bis(octyloxy)benzene (4)
The redish liquid product was obtained by reacting 1,2-bis(octylox-
y)benzene of 43 g (120 mmol) with NBS of 23 g (130 mmol) with 94%
yield (50 g).
1H NMR: d: 6.95(s, 1H), 6.87(d, 1H), 6.73(d, 1H), 3.80(m, 4H), 1.54
(m, 4H), 1.11(m, 20H), 0.72(t, 6H).
2-(3,4-bis(octyloxy)phenyl)-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (5)
4-Bromo-1,2-bis(octyloxy)benzene of 20 g (48 mmol) was dissolved
in anhydrous THF of 300 ml and cooled to ꢁ78ꢂC and then n-BuLi of
38 ml (62 mmol) was added. After 2 hours, 2-isopropoxy-4,4,5,5-tetra-
methyl-1,3,2-diozaborolane of 12 ml (62 mmol) was added slowly to
reaction mixture. The product was obtained reddish liquid of 20 g
(90% yield).
1H NMR: d: 7.03(d, 1H), 6.93(m, 2H), 4.01(m, 4H), 1.77(m, 4H),
1.37(m, 32H), 0.87(t, 6H).
3,4,3 04 0-tetrakis-octyloxy-biphenyl (6)
Pd(OAC)2 of 0.97 g (4.3 mmol) and (tri-O-tolyl)3 phosphine of 1.3 g
(4.3 mmol) were dissolved in dimethylether of 150 ml and H2O of
100 ml under nitrogen. After 4-bromo-1,2-bis(octyloxy)benzene of
21 g (51 mmol) and 2-(3,4-bis(octyloxy)phenyl)-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane of 20 g (43 mmol) were injected, and then K2CO3
of 15 g (100 mmol) and H2O (100 ml) added. The mixture was refluxed
for 3 hours. The product was obtained by recrystallization with ethyl
acetate=ethanol (white solid of 17 g, 60%yield).
1H NMR: d: 7.17(s, 2H), 7.11(d, 2H), 6.99(d, 2H), 4.06(m, 8H),
1.77(m, 8H), 1.51(m, 8H), 1.48(m, 32H), 0.89(m, 12H).
2-bromo-4,5,3 0,4 0-tetrakis-octyloxy-biphenyl (7)
The product was obtained by bromination of 3,4,30,40-tetrakis-octy-
loxy-biphenyl of 17 g (26 mmol) with NBS of 5 g (28 mmol). It was

Synthesis and Properties of POTOSF for OLEDs
271
obtained by recrystallization with methylene chloride=ethanol (white
solid of 16 g, 60%yield).
1H NMR: d: 7.18(s, 1H), 6.98(s, 2H), 6.89(s, 1H), 6.87(d, 1H), 4.06
(m, 8H), 1.77(m, 8H), 1.51 (m, 8H), 1.48(m, 32H), 0.89 (m, 12H).
2,7-dibromo-9-(4,5,3’,4’-tertrakis-octyloxy-biphenyl-2-yl)-9H-
fluoren-9-ol (8)
2-Bromo-4,5,30,40-tetrakis-octyloxy-biphenyl of 16 g (22 mmol) was
dissolved in anhydrous THF of 300 ml under nitrogen and cooled to
ꢁ78ꢂC, and then t-BuLi of 31 ml (53 mmol) was added. After 1 hour,
2,7-dibromo-9H-fluoren-9-one of 9 g (26 mmol) was added slowly to
reaction mixture. The product was purified by column chromato-
graphy using a cosolvent (hexane=EA ¼ 50:1) as the eluent to have
yellowish viscous liquid of 9 g (40% yield).
1H NMR: d: 7.17(d, 2H), 7.12(m, 4H), 6.98(m, 5H), 4.06(m, 8H),
1.83(m, 9H), 1.34(m, 40H), 0.87(m, 12H).
2,7-dibromo-2 0,3 0,6 0,7 0-tertrakis-octyloxy-9-spirobifluoren (9)
3,6-dibromo-9-(4,5,30,40-tertrakis-octyloxy-biphenyl-2-yl)-9H-fluoren-
9-ol of 9 g (8.8 mmol) was dissolved in acetic acid of 200 ml under cooled
to 0–5ꢂC. And then HCl of 10 ml was added slowly. The product was
purified by column chromatography using a cosolvent (hexane=ethyl
acetate¼50:1) as the eluent to have white solid of 5 g (60% yield).
1H NMR: d: 7.64(d, 2H), 7.46(m, 2H), 7.19(s, 2H), 6.84(s, 2H),
6.13 (s, 2H), 4.10(t, 4H), 3.71(t, 4H), 1.84(m, 4H), 1.34(m, 44H),
0.87(m, 12H).
Polymerization
POP, PTOSF and POTOSF, which were polymerized by Yamamoto
reaction. Each Schlenk tube containing 5 ml of DMF, bis(1,5-cycloocta-
dienyl)nickel(0), 2,2-dipyridyl and 1,5-cyclooctadiene (the last three in a
molar ratio of 1:1:1) was kept under nitrogen at 80ꢂC for 30 min. 5 ml of
anhydrous toluene was then added to the monomer. Polymerization was
maintained at 80ꢂC for 48 hours, and then bromopentafluorobenzene
(0.1 mol% of monomer) was dissolved in toluene and added to the reac-
tion mixture for end-capping. When the reaction had finished, each
polymer was precipitated from an equivolume mixture of concentrated
HCl, methanol, and acetone. The isolated polymers were dissolved
in toluene and precipitated in methanol. Finally, the resulting poly-
mers were purified by soxhlet extraction by using acetone and then
dried in a vacuum. All polymer yields ranged from 10 to 75% after
purification [12].

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SCHEME 1 Synthetic route of POP.
RESULTS AND DISCUSSION
Synthesized polymer structures are shown in Scheme 1–3. The num-
ber average molecular weights (Mn) of POP, PTOSF and POTOSF
copolymer were determined by gel-permeation chromatography
(GPC) using a polystyrene standard with THF solvent and found to
be range from 17,000 to 300,000 g=mol with polydispersity indices of
1.6ꢀ6.5. Although molecular weights of synthesized polymers were
high, their polydispersity was wide. These results are summarized
in Table 1.
SCHEME 2 Synthetic route of PTOSF.

Synthesis and Properties of POTOSF for OLEDs
273
SCHEME 3 Synthetic route of POTOSF.
POP homopolymer showed low molecular weight with good polydis-
persity value. POTOSF copolymer exhibited high molecular weight of
300,000 (Mn) and 1,440,000 (Mw) g=mol. The reason why phenothia-
zine moiety of 10% was introduced into spirofluorene moiety is that
phenothiazine could be working as charge carrier moiety to emitter
of spirofluorene group.
UV-visible absorption spectra of thin films of POP, PTOSF and
POTOSF copolymer are depicted in Figure 1. Each spectrum was nor-
malized to the peak maximum for more accurate comparison of wave-
length. The maximum UV-visible absorption and absorption onset of
POP, PTOSF and POTOSF copolymer exhibited at around 370, 391,
403 nm and 466, 434, 436 nm, respectively, which are originated from
p-pꢃ transition of conjugated polymer backbone. The optical band gaps
of the polymers were determined from the analysis of absorption edge
with a plot of (hv) vs. (ahv)2, where a, h, and v are absorbance, Plank’s
constant, and the frequency of light. The optical band gap of POP,
PTOSF and POTOSF copolymer were found to be 2.76, 2.91 and
2.90 eV.
TABLE 1 Average Molecular Weight and Polydispersity Indices of Synthe-
sized Polymer
Feed mole ratio
Feed mole ratio
of spirofluorene of phenothiazine
unit (%)
unit (%)
Mn
Mw
Polydispersity
POP
PTOSF
POTOSF
–
100
90
100
–
10
17,000
71,000
300,000 1,440,000
28,000
460,000
1.63
6.48
4.78

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J.-S. Kang et al.
FIGURE 1 UV-visible spectra of POP (a, circle), PTOSF (b, square), and
POTOSF (c, triangle) copolymer films on glass.
Figure 2 shows the PL emission spectra of polymer thin films. Two
homopolymer of POP and PTOSF showed its own characteristic PL
maximum value as 480 nm and 434 nm including 454 nm shoulder
FIGURE 2 PL spectra of POP (a, square), PTOSF (b, circle), and POTOSF
(c, triangle) copolymer films on glass.

Synthesis and Properties of POTOSF for OLEDs
275
TABLE 2 Electronic Levels of POP, PTOSF and POTOSF Copolymer
HOMO
LUMO
Optical band gap
POP
PTOSF
POTOSF
5.26
5.63
5.64
2.50
2.72
2.74
2.76
2.91
2.90
peak. Copolymer POTOSF which contained POP (10%) and PTOSF
(90%) exhibited PL maximum value of 484 nm, which means that
the exciton energy of PTOSF unit in POTOSF might be transferred
to POP unit. As shown in Scheme III, the feed ratio of POP moiety
and PTOSF moiety in synthesis of POTOSF was 9:1 and polymeriza-
tion yield was always more than 50%. It means that POTOSF contains
PTOSF moiety and POP moiety together. Therefore the reason why
Figure 2(c) of POTOSF is similar to Figure 2(a) of POP is that exciton
energy in copolymer can be transferred from PTOSF moiety having
relatively wide band gap energy to POP moiety.
The electrochemical characteristics of the polymers were investi-
gated by using cyclic voltammetric analysis. The first oxidation poten-
tial was used to determine the HOMO energy level. Ferrocene was
used as an internal standard for calibrating the potential. This data
accounts that we could get HOMO level. Based on UV-visible data
FIGURE 3 EL spectrum of ITO=PEDOT:PSS(50 nm)=POTOSF(70 nm)=
LiF(1 nm)=Al(200 nm) device at 20 mA=cm2.

276
J.-S. Kang et al.
and CV data, all electronic levels of HOMO, LUMO and band gaps are
summarized in Table 2.
Even though POP has smaller band gap than PTOSF and POTOSF,
it shows higher LUMO level of 2.5 eV. We believe that there is energy
barrier to inject electron from cathode compared to PTOSF and
POTOSF in device. Also PTOSF and POTOSF showed similar band
gap value and HOMO and LUMO level values, but they showed quite
different PL spectrum because of energy transfer as shown in Figure 2.
Double-layer EL device was fabricated using POTOSF copolymer
such as ITO=PEDOT:PSS (50 nm)=POTOSF (70 nm)=LiF (1 nm)=Al
(200 nm) device. EL spectrum of POTOSF device is shown in
Figure 3. Emission peak of copolymer POTOSF device exhibited EL
maximum value of 494 nm, which matched with its PL emission peak
of 484 nm.
Further studies of synthetic compounds devices optimization are
under way. We will report the EL efficiency and life time data in other
paper.
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