Synthesis and characterization of thermally cross-linkable oligophenothiazine

Article abstract of DOI:10.1080/15421406.2012.703446

A series of 10-butylphenothiazine trimer (3-PTVB) and pentamer (5-PTVB) with in-situ thermally cross-linkable vinyl benzene were synthesized successfully. The TGA thermograms revealed that 3-PTVB and 5-PTVB were stable up to 430 and 370C, respectively. In the first heating scan of DSC thermograms, 3-PTVB and 5-PTVB showed glass transition temperature (T_g) at 113C and 95.3C (143C). Both 3-PTVB and 5-PTVB showed broad endothermic process in the region of 185-220C, which is thermally cross-linking temperature. In the second heating process, Tg and endothermic process were not observed. Wavelength of UV-visible maximum absorption of thermally cured 3-PTVB is 340nm, which is same as the UV-visible maximum absorption of 5-PTVB. The thermally cured films showed no damage nor any discernible change in the UV-visible spectrum after washing with organic solvents such as methylene chloride (MC), chloroform, and toluene. Thermally cured 3-PTVB and 5-PTVB films were electrochemically very stable. The HOMO energy level of 3-PTVB and 5-PTVB were 4.98 and 4.86eV, respectively. Double layer structured polymer light-emitting diodes based on in-situ thermally cured 3-PTVB and 5-PTVB were fabricated. The maximum luminance efficiency of devices based on 3-PTVB and 5-PTVB were 1.004 cd/A at 14.0V and 1.074 cd/A at 16.5V, respectively, which are much higher than that of the device without thermally cured 3-PTVB or 5-PTVB (0.348 cd/A at 15.0V).

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Synthesis and Characterization
of Thermally Cross-Linkable
Oligophenothiazine
Mi Young Jo a & Joo Hyun Kim a
a Department of Polymer Engineering, Pukyong National University,
Yongdang-Dong , Nam-Gu , Busan Korea
Published online: 17 Sep 2012.
To cite this article: Mi Young Jo & Joo Hyun Kim (2012) Synthesis and Characterization of Thermally
Cross-Linkable Oligophenothiazine, Molecular Crystals and Liquid Crystals, 567:1, 178-186, DOI:
10.1080/15421406.2012.703446
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Mol. Cryst. Liq. Cryst., Vol. 567: pp. 178–186, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.703446
Synthesis and Characterization of Thermally
Cross-Linkable Oligophenothiazine
MI YOUNG JO AND JOO HYUN KIM∗
Department of Polymer Engineering, Pukyong National University,
Yongdang-Dong, Nam-Gu, Busan Korea
A series of 10-butylphenothiazine trimer (3-PTVB) and pentamer (5-PTVB) with in-
situ thermally cross-linkable vinyl benzene were synthesized successfully. The TGA
◦
thermograms revealed that 3-PTVB and 5-PTVB were stable up to 430 and 370 C,
respectively. In the first heating scan of DSC thermograms, 3-PTVB and 5-PTVB showed
◦
◦
◦
glass transition temperature (Tg) at 113 C and 95.3 C (143 C). Both 3-PTVB and
5-PTVB showed broad endothermic process in the region of 185–220 ◦C, which is
thermally cross-linking temperature. In the second heating process, Tg and endothermic
process were not observed. Wavelength of UV-visible maximum absorption of thermally
cured 3-PTVB is 340 nm, which is same as the UV-visible maximum absorption of
5-PTVB. The thermally cured films showed no damage nor any discernible change
in the UV-visible spectrum after washing with organic solvents such as methylene
chloride (MC), chloroform, and toluene. Thermally cured 3-PTVB and 5-PTVB films
were electrochemically very stable. The HOMO energy level of 3-PTVB and 5-PTVB
were −4.98 and −4.86 eV, respectively. Double layer structured polymer light-emitting
diodes based on in-situ thermally cured 3-PTVB and 5-PTVB were fabricated. The
maximum luminance efficiency of devices based on 3-PTVB and 5-PTVB were 1.004
cd/A at 14.0 V and 1.074 cd/A at 16.5 V, respectively, which are much higher than that
of the device without thermally cured 3-PTVB or 5-PTVB (0.348 cd/A at 15.0 V).
Keywords in-situ thermally curable oligomer; phenothiazine; p-type organic semicon-
ductor; Hole injection material
1. Introduction
Conjugated polymers have been studied in polymer light-emitting diodes (PLEDs) [1–4],
polymer solar cells (PSCs) [5–7], thin film transistors (TFTs) [8–13], and electrochromic
devices (ECDs) [14,15] Among these, PLEDs and PSCs have been focused tremendously
because of easiness of process. To get highly efficient devices, multi-layer structured devices
are fabricated with charge (hole and electron) injection and transporting layer. The charge
(hole and electron) injection and transporting processes are crucial factors for improving the
performances of polymer light-emitting diodes (PLEDs) and polymer solar cells (PSCs).
In order to fabricate multi-layer structured device, the hole injection/transporting layer
should have good solvent resistance to successive layer coating. Recently, in-situ thermally
∗Address correspondence to Joo Hyun Kim, Department of Polymer Engineering, Pukyong
National University, Yongdang-Dong, Nam-Gu, Busan 608-739, Korea. Tel: 82–51-629-6452, Fax:
82–51-629-6429. E-mail: jkim@pknu.ac.kr
[380]/178

Synthesis and Characterization of Thermally
[381]/179
polymerizable hole injection materials based on triarylamine, alkylphenothiazine, alkylcar-
bazole have been studied [16–23]. The devices based on reported hole injection materials
exhibited excellent performances.
Poly(10-hexyl-10H-hexylphenothiazin-3,7-diyl) (PT) is well known very strong elec-
tron donor and has high-lying ionization potential so that PT can be used as hole injection
material [24,25]. In our previous report [22], PT with in-situ thermally polymerizable methyl
methacrylate showed good hole injection properties. However, lacks of reproducibility in
polymerization reaction and purification process were problem. The purification and repro-
ducibility in the synthesis of oligomers such as trimer or pentamer are much easier than
those of analogues’ polymers. Here, we report the synthesis and physical properties of
trimer and pentamer of 10-butylphenothiazine with in-situ polymerizable vinyl benzene.
2. Experimental Section
2.1 Materials and Synthesis
Tetrahydrofuran (THF) was distilled over sodium/benzophenone. Methylene chloride (MC)
was distilled over CaH2. All other chemicals were purchased from Sigma-Aldrich Co, Tokyo
Chemical Industry (TCI) or Alfa Aesar (A Johnson Matthey Company) and were used as
received unless otherwise described.
2.1.1. 7-[4-(4-vinyl-benzyloxy)-phenyl]-{7ꢀ-[4-(4-vinyl-benzyloxy)-phenyl]-10-butyl-
10H-phenothiazine-3-yl}-10,10ꢀ-dibutyl-10H,10ꢀH-3,3ꢀ-biphenothiazine (3-PTVB). A
solution of 4-vinyl benzyl chloride (64.0 mg, 0.420 mmol) was added dropwise to a portion
of compound 126 (150 mg, 0.170 mmol) and potassium carbonate (580 mg, 0.420 mmol)
◦
in DMF (20 mL) under nitrogen atmosphere at 40 C. After stirring for overnight, a
portion of 50 mL of water was added to the reaction mixture and extracted three times
with EA. The combined organic layer was dried over anhydrous MgSO4 and evaporation
the solvent using a rotary evaporator. The crude product was purified by recrystallization
◦
using methanol/MC. The yield of yellow solid is 87.1% (0.17 g). mp: 211.3 C. MS
(MALDI-TOF): [M-H] +, m/z 1176.8. H-NMR (400 MHz, CDCl3, ppm): δ 7.43∼7.42
1
(b, 14H), 7.33∼7.31 (b, 10H), 7.01∼7.00 (d, J = 8.8 Hz, 4H), 6.88 (b, 4H), 6.77∼6.70
(dd, J1 = 17.6 Hz, J2 = 11.0 Hz, 2H), 5.79∼5.75 (dd, J1 = 17.6 Hz, J2 = 0.7 Hz, 2H),
5.28∼5.25 (dd, J1 = 11.0 Hz, J2 = 0.7 Hz, 2H), 5.08 (s, 4H), 3.90∼3.87 (t, J = 6.9 Hz,
6H), 1.86∼1.79 (m, 6H), 1.54∼1.45 (m, 6H), 0.99∼0.95 (t, 9H), 13C-NMR (100 MHz,
CDCl3, ppm): δ 158.05, 144.06, 143.98, 143.79, 137.33, 136.52, 136.43, 135.10, 134.29,
134.24, 132.91, 127.66, 127.52, 126.43, 125.45, 125.23, 125.16, 115.62, 115.40, 115.15,
114.08, 69.85, 47.21, 29.69, 28.98, 20.20, 13.84. Anal. Calcd. for C78H71N3O2S3: C,
79.49; H, 6.07; N, 3.57; O, 2.71; S, 8.16. Found: C, 77.31; H, 4.044; N, 6.337; S, 10.41.
2.1.2. 3,6-bis-{10,10ꢀ-dibutyl-7ꢀ-[4-(4-vinyl-venzyloxy)-phenyl]-10H,10Hꢀ-
[3,3ꢀ]biphenothiazinyl}-10-hexyl-10H-phenothiazine (5-PTVB). A solution of 4-vinyl
benzyl chloride (32.0 mg, 0.210 mmol) was added dropwise to a portion of compound 226
(100 mg, 0.070 mmol) and potass◦ium carbonate (290 mg, 0.210 mmol) in DMF (20 mL)
under nitrogen atmosphere at 40 C. After stirring for overnight, a portion of 50 mL of
water was added to the reaction mixture and extracted three times with EA. The combined
organic layer was dried over anhydrous MgSO4 and evaporation the solvent using a rotary
evaporator. The crude product was purified by recrystallization using methanol/MC. The
o
+
,
yield of yellow solid is 71.8% (0.086 g). mp: 131.2 C. MS (MALDI-TOF): [M-H]

180/[382]
M. Young and J. H. Kim
1
m/z 1712.3. H-NMR (400 MHz, CDCl3, ppm): δ 7.45∼7.41 (m, 14H), 7.31 (b, 20H),
7.02∼7.00 (d, J = 8.8 Hz, 6H), 6.89 (b, 6H), 6.73 (dd, J1 = 17.6 Hz, J2 = 11.0 Hz,
2H), 5.79∼5.74 (dd, J1 = 17.6 Hz, J2 = 1.1 Hz, 2H), 5.27∼5.25 (dd, J1 = 11.0 Hz,
J2 = 0.7 Hz, 2H), 5.08 (s, 4H), 3.91∼3.88 (t, J = 6.9 Hz, 10H), 1.87∼1.79 (m, 10H),
1.52∼1.47 (m, 14H), 0.99∼0.95 (t, J = 7.4 Hz, 15H), 13C-NMR (100 MHz, CDCl3, ppm):
δ 158.04, 144.02, 143.94, 143.75, 137.31, 136.51, 136.43, 135.05, 134.23, 132.87, 127.65,
127.50, 126.41, 125.44, 125.22, 125.13, 124.76, 124.70, 115.40, 115.14, 114.07, 69.82,
47.55, 47.19, 31.47, 28.96, 26.83, 26.67, 22.60, 20.19, 14.01, 13.84. Anal. Calcd. for
C112H105N5O2S5: C, 78.51; H, 6.18; N, 4.09; O, 1.87; S, 9.36. Found: C, 80.06; H, 4.577;
N, 6.066; S, 10.36.
2.2. Device Fabrication
ITO-coated glass substrates were cleaned with deionized water, acetone, methanol, 2-
propanol in ultrasonic bath. A solution of 3-PTVB or 5-PTVB (5 mg/mL in chloro-
form:chlorobenzene (1:1 by volume)) layer was spin-coated as a hole injection layer (HIL)
onto the ITO. Before spin-coating, 3-PTVB or 5-PTVB was filtered through 0.20-µm PTFE
◦
syringe filter. After spin coating, the thin film was heated up to 185 C for 2 hours. The
typical thickness of 3-PTVB or 5-PTVB film was 5 ∼ 10 nm. The green emitting polymer
(PF9B)27 were dissolved in toluene and filtered through 0.20-µm PTFE syringe filter be-
fore spin coating. The typical thickness of emissive layer was 60 nm. Al was evaporated as
cathode onto the surface of the emissive polymer film by thermal evaporation technique at
2.0 × 10−6 torr. The typical active area of the devices was 6 mm2.
2.3. Measurements
1
Synthesized compounds were characterized by H-NMR and 13C-NMR spectrum, which
were obtained with a JEOL JNM ECP-400 spectrometer. The elemental and MASS analyses
of synthesized compounds were carried out on a Elementar Vario macro/micro elemen-
tal analyzer and Shimadzu GC-MS QP-5050A spectrometer. Thermogravimetric analysis
◦
(TGA) was carried out under nitrogen atmosphere at a heating rate of 10 C/min with a
Perkin-Elmer TGA 7 thermal analyzer. Differential scanning calorimetry (DSC) was mea-
sured by a Perkin Elmer (Pyris 1, Diamond) under nitrogen atmosphere at a scan rate of
10 ◦C/min. UV-Visible spectrum were recorded using a JASCO V-530 UV/VIS Spectropho-
tometer. Cyclic voltammetry was performed by a EG&G 362 Scanning Potentiostat with a
three electrode cell in a solution of Bu4NPF6 (0.1 M) in freshly distilled methylene chloride
at a scan rate of 100 mV/s. Pt wires were used as the counter and working electrode and a
Ag/Ag+ electrode was used as the reference electrode. Prior to each measurement, the cell
was deoxygenated with argon. The current density-voltage-brightness (J-V-B) characteris-
tics were measured using a source meter (KEITHLEY 2400) and a luminometer (Minolta
LS110).
3. Results and Discussion
3.1 Synthesis and Characterization of oligomers
Scheme 1 shows the synthetic procedures for thermally cross-linkable phenothiazine
(PT) trimer and pentamer, which are synthesized by the well-known palladium-catalyzed
Suzuki coupling reaction between brominated PT and borylated PT to extend length of

Synthesis and Characterization of Thermally
[383]/181
HO
N
S
OH
Cl
O
N
S
O
S
N
S
N
S
N
S
N
K2CO3 / DMF
1
3-PTVB
N
S
N
S
N
S
S
N
S
HO
OH
N
2
N
S
N
S
N
S
Cl
S
N
S
N
O
O
K2CO3 / DMF
5-PTVB
Scheme 1. Synthesis of thermally cross-linkable 10H-butylphenothiazine oligomers.
π-conjugation. All the compounds were well characterized by elemental analysis, MASS,
1H-NMR, and 13C-NMR.
Figure 1 shows the TGA thermaograms of 3-PTVB and 5-PTVB. Phenothiazine trimer
and pemtamer with vinyl benzene (VB) are thermally stable because points of 5%-weight
loss in TGA thermogram of 3-PTVB and 5-PTVB appear at 403 and 370 ◦C, respectively.
In order to investigate, thermal behavior of 3-PTVB and 5-PTVB, we performed differential
scanning calorimetry (DSC). As shown in Figure 2 (a), in the first heating scan, glass tran-
sition temperature (Tg) of 3-PTVB shows at 113 ◦C and 3-PTVB shows broad endothermic
process in the region of 185–220 ◦C with a peak at 217 ◦C. In the second heating process,
3-PTVB does not have Tg and endothermic process, because the thermally curing reaction
is completed in the first heating scan. From the DSC thermogram one can easily notice
◦
that the endothermic process at 217 C in the first scan is due to thermally cross-linking
reaction of VB group. In the first heating scan of 5-PTVB, it shows endothermic process
in the region of 183–213 ◦C with a peak at 200 ◦C. In the first scan of 5-PTVB seems to
◦
be show two glass transition processes at 95.3 and 143 C. From the DSC thermogram,
Figure 1. TGA thermorgrams of (a) 3-PTVB and (b) 5-PTVB.

182/[384]
M. Young and J. H. Kim
Figure 2. DSC thermorgrams of (a) 3-PTVB and (b) 5-PTVB.
we confirm that Tg of 5-PTVB is higher than that of 3-PTVB. We cannot observe the
endothermic process in the second heating scan of 5-PTVB.
Figure 3 shows the UV-visible absorption spectrum of 3-PTVB and 5-PTVB. The
absorbance of thermally cured 3-PTVB film was slightly decreased than that of pristine
film, because the molecules in the cured film are more close-packed than pristine film.
The absorbance of thermally cured 3-PTVB did not show big difference on washing with
organic solvent such as MC. In the optical properties of 5-PTVB film, similar features were
observed (Figure 3 (b)). Also, the shapes of the spectrum of before and after cured films
were almost identical to those of pristine 3-PTVB and 5-PTVB films.
Figure 3. UV-Visible spectrum of (a) 3-PTVB and (b) 5-PTVB. (rectangular: before cross-link,
triangle: after cross-link, circle: washed cross-linked film with MC)

Synthesis and Characterization of Thermally
[385]/183
Figure 4. Cyclic voltammogram of thermally cross-linked (a) 3-PTVB and 5-PTVB film on ITO
coated glass.
3.2 Electrochemical and electroluminescent properties
The HOMO energy levels were estimated from the oxidation onset potential by the energy
level of ferrocene is – 4.8 eV. Cyclic voltammograms (CVs) of thermally cured 3-PTVB
and 5-PTVB film on ITO coated glass show quasi-reversible behavior (Figure 4). Two
oxidation peaks at 0.41 and 0.60 V vs. Fc/Fc+ were observed in the CV of 3-PTVB (Figure
4 (a)). Also, the CV of 5-PTVB were observed two oxidation peaks at 0.40 and 0.71 V
vs. Fc/Fc+ were observed (Figure 4 (b)). The thermally cured 3-PTVB and 5-PTVB films
on ITO don’t change in the cathodic and anodic peak current upon repeated redox scans
in 0.1 M Bu4NPF6 in MC. This is also indicating that cured 3-PTVB and 5-PTVB exhibit
good electrochemical stability and solvent resistance. The HOMO energy level of cured
3-PTVB figured out –4.98 eV from the oxidation onset potential of the first scan of the
CV, which is very similar to that of cured 5-PTVB film (-5.86 eV). This is very similar
to that of poly(hexylphenothiazine)24,25 and thermally cured poly(alkylphenothiazine)22,
whose HOMO energy level are −4.9 ∼ −5.0 eV.
In order to investigate hole injection and transporting properties of cured 3-PTVB and
5-PTVB, we fabricated double layer structured device, ITO/cured 3-PTVB (10 nm)/PF9B
(60 nm)/Al (device I, Figure 5 (b)) and ITO/cured 5-PTVB (10 nm)/PF9B (60nm)/Al
(device II, Figure 5 (c)). The thickness of films was measured by Alpha-Step IQ surface
Table 1. Optical, electrochemical, and thermal properties of 3-PTVB and 5-PTVB.
UVmax
(nm)
Egap
(eV)
Eox,peak
(V)
Eonset (V),
HOMO (eV)a Td (◦C)b Tg (◦C)c
Cured 3-PTVB
Cured 5-PTVB
340
340
2.64
2.67
0.41, 0.60
0.40, 0.71
0.18, −4.98
0.06, −4.86
403
370
113
95.3, 143
aestimated from the oxidation onset potential by the energy level of ferrocene is – 4.8 eV
bthe point of 5%-weight loss, measured using uncured oligomer
cmeasured using uncured oligomer

184/[386]
M. Young and J. H. Kim
Figure 5. I-V-L curves of the device (a) ITO/PF9B/Al, (b) ITO/cured 3-PTVB/PF9B/Al, and (c)
ITO/cured 5-PTVB/PF9B/Al.
profiler. Figure 5 shows current density (J) and brightness (B) as a function of applied
voltage (V) of the device I and device II. The device performances are summarized in
Table 2. The J-V curves of the devices show typical rectification properties. The turn-on
voltage (defined as the voltage required to give a luminescent of 1 cd/m2) of the device I
and II were 7.5 V. In order to compare the performances with device I and device II, we also
fabricated the device without cured 3-PTVB or 5-PTVB (ITO/PF9B/Al, Figure 5 (a)). The
turn-on voltage of device without cured 3-PTVB or 5-PTVB was 9.5 V, which was much
Table 2. Device performances of LEDs prepared with thermally cured 3-PTVB and 5-
PTVB.
Von (V)a
LE100 (cd/A)b
LEmax (cd/A)c
Bmax (cd/m2)d
ITO/PF9B/Al
ITO/cured
9.5
7.5
0.372 @ 14.0 V 0.348 @ 15.0 V 496 @ 15.0 V
0.844@ 12.0 V 1.004@ 14.0 V 2906@ 17.0 V
3-PTVB/PF9B/Al
ITO/cured
7.5
0.972@ 11.5 V 1.074@ 13.5 V 3165@ 16.5 V
5-PTVB/PF9B/Al
adefined as the voltage required to give a luminescent of 1 cd/m2.
bluminance efficiency at 100 cd/m2.
cmaximum luminescence efficiency.
dmaximum brightness

Synthesis and Characterization of Thermally
[387]/185
higher than device I and device II. The maximum brightness and maximum efficiency of
device I and device II were dramatically improved than the device without cured 3-PTVB
or 5-PTVB. From the electroluminescent properties, cured 3-PTVB and 5-PTVB show
good hole injection and transporting properties. In addition, the maximum luminescence
efficiency and brightness of device II were 1.074 cd/A and 3165 cd/m2, which were higher
than those of device I (1.004 cd/A and 2906 cd/m2). Because cured 5-PTVB has longer
π-conjugation length compared to that of cured 3-PTVB.
4. Conclusions
We synthesized new π-conjugated trimer (3-PTVB) and pentamer (5-PTVB) based on
10-butylphenothiazine with vinyl benzene as thermally cross-linkable unit by well known
palladium catalyzed the Suzuki reaction. From the UV-Visible spectroscopy, thermally
cured 3-PTVB and 5-PTVB are safe to the successive layer coating by the solution process.
Also, we confirm that the cured oligomers are electrochemically stable. The performances
of double layer structured devices exhibited superior performances than those of the de-
vice without 3-PTVB or 5-PTVB. In addition, turn-on voltages of the device based on
cured oligomers were much lower than that of the device without cured oligomers. From
the results, thermally cured 3-PTVB and 5-PTVB are potential materials for hole injec-
tion/transporting layer.
Acknowledgment
This research was supported by Converging Research Center Program through the Ministry
of Education, Science and Technology (2012K001279) and Basic Science Research Pro-
gram through the National Research Foundation of Korea (NRF) funded by the Ministry
of Education, Science and Technology (2012-0001356).
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