Synthesis of dopant with phenothiazine moiety and polymer electroluminescence device properties

Article abstract of DOI:10.1080/15421400490506009

(N-2-ethylhexyyl-3(6)-phenothiazinylene vinylene-co-9, 10-anthrylene vinyleone), KPD-1, as a new low molecular weight dopant was synthesized. Poly(1,12-dodecanedioxy-2-methoxy-1,4-phenylene-1,2-ethenylene-1, 1′-biphenyl-4,4′-ylene-1,2-ethenylene-3-methoxy-1,4-phenylene), /Poly(BFMP₁₂AV)/, as a matrix polymer was also prepared by Honer-Emmons condensation. Single- and multi-layered PLKDs were fabricated with a mixture of dopant/matrix polymer as an emissive layer. The effect of dopant/matrix polymer and device structures on the energy transfer and electro-optical properties of doped PLKDs was discussed in terms of emission color changes and luminescence efficiency of doped PLEDs. Copyright Taylor & Francis Inc.

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Synthesis of Dopant with
Phenothiazine Moiety and
Polymer Electroluminescence
Device Properties
a
a
a
Lee Park , Byeung Jang , Jeong Baek , Young
a
b
c
Jung , Younghwan Kwon & Hyun Cho
a
Department of Polymer Science , Kyungpook
National University , Daegu, Korea
b
Department of Chemical Engineering , Daegu
University , Gyeongbuk, Korea
c
Electronic Materials and Devices Research Center ,
KIST , Seongbuk-gu, Seoul, Korea
Published online: 18 Oct 2010.
To cite this article: Lee Park , Byeung Jang , Jeong Baek , Young Jung , Younghwan
Kwon & Hyun Cho (2004) Synthesis of Dopant with Phenothiazine Moiety and Polymer
Electroluminescence Device Properties, Molecular Crystals and Liquid Crystals, 424:1,
119-126, DOI: 10.1080/15421400490506009
To link to this article: http://dx.doi.org/10.1080/15421400490506009
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Mol. Cryst. Liq. Cryst., Vol. 424, pp. 119–126, 2004
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400490506009
SYNTHESIS OF DOPANT WITH PHENOTHIAZINE
MOIETY AND POLYMER ELECTROLUMINESCENCE
DEVICE PROPERTIES
Lee Soon Park, Byeung Jo Jang, Jeong Ju Baek, and Young Chul Jung
Department of Polymer Science, Kyungpook National University,
Daegu 702-701, Korea
Younghwan Kwon
Department of Chemical Engineering, Daegu University,
Gyeongbuk, 712-714, Korea
Hyun Nam Cho
Electronic Materials and Devices Research Center, KIST,
Seongbuk-gu, Seoul, 136-791, Korea
(N-2-ethylhexyl)-3(6)-phenothiazinylene vinylene-co-9,10-anthrylene vinyl-
ene), KPD-1, as a new low molecular weight dopant was synthesized.
0
Poly(1,12-dodecanedioxy-2-methoxy-1,4-phenylene-1,2-ethenylene-1,1 -biphe-
0
nyl-4,4 -ylene-1,2-ethenylene-3-methoxy-1,4-phenylene), [Poly(BFMP12-AV)],
as a matrix polymer was also prepared by Honer-Emmons condensation.
Single- and multi-layered PLEDs were fabricated with
a mixture of
dopant=matrix polymer as an emissive layer. The effect of dopant=matrix
polymer and device structures on the energy transfer and electro-optical
properties of doped PLEDs was discussed in terms of emission color changes
and luminescence efficiency of doped PLEDs.
Keywords: conjugated polymer; dopant=matrix system; energy transfer; Horner-Emmons
condensation; light-emitting diode
Received 1 October 2003; accepted 16 January 2004.
This work was supported by grant No. (R12-2002-055-01003-0) from the Basic Research
Program of the Korea Science & Engineering Foundation.
Address correspondence to Lee Soon Park, Department of Polymer Science, Kyungpook
National University, Sangyuk-dong, Buk-gu, Daegu 702-701, Korea. Tel.: (þ82)53-950-5627,
Fax: (þ82)53-950-6616, E-mail: lspark@knu.ac.kr
119

1
20
L. S. Park et al.
INTRODUCTION
Research into conjugated polymers have been motivated by their
promising application in light-emitting diodes (LEDs), since R. H.
Friend et al. reported LED made from poly( p-phenylenevinylene)
[
1,2]. It has been generally accepted [3,4] that the electrochemical
structure and nanostructures of conjugated polymers has played a
key role on the electro-optical properties of LEDs. However, a few
of conjugated polymers have been satisfied with the required perform-
ance. It has been reported that electroluminescent properties in
PLEDs are improved either by contructing multi-layer devices or by
incorporating low molecular weight dopant in the emissive layer.
Therefore, the use of proper dopant with high color purity and energy
transfer capability could be one approach to improve electro-optical
properties of PLEDs.
In this work we synthesized a new low molecular weight dopant with
both phenothiazine and anthracene moieties which had similar structure
with poly(BFMP -AV) matrix polymer reported by our laboratory [5].
12
Single- and double-layered PLEDs were fabricated with polymeric matrix=
dopant layer as an emissive layer and evaluated in terms of emission color
and luminescence efficiency.
EXPERIMENTAL
Synthesis
Synthesis of (N-2-ethylhexyl)-3(6)-phenothiazinylene vinylene-co-9,10-
anthrylene vinylene) (KPD-1). Firstly N-(2-ethylhexyl)phenothiazine
(EHPZ) was synthesized from the reaction of phenothiazine (6 g,
0
sodium hydroxide (7.2 g, 0.18 mol) in dimethylsulfoxide (60 ml) at room
.03 mol) and 2-ethylhexylbromide (5.8 g, 0.03 mol) in the presence of
1
temperature for 3 h [11]. Yield: 73%. H NMR(CDCl ), d: 6.87, 7.12 (m,
3
8
H, Ar-H), 3.70 (m, 2H, N-CH –), 1.93 (t, 1H, CH–), 1.22–1.44 (m, 9H,
2
ꢀ1
–
CH –), 0.83–0.87 (m, 6H, –CH ), IR (KBr), cm : 3064 (Ar CH), 2926
2
3
(
aliphatic CH), 2857 (N–CH –), 1593, 1485 (Ar C¼C).
2
N-(2-Ethylhexyl)-3(6)-formylphenothiazine (EHFZ) was synthesized
using modified Vilsmeier-Haack formylation in the second step [6,7].
Yield : 45%, H NMR(CDCl ), d: 9.73 (m, 2H, aldehydic hydrogen), 6.88,
1
3
7
CH–), 0.76–0.82 (m, 6H, –CH ), IR (KBr), cm : 3048 (Ar CH; weak sig-
.56 (m, 6H, Ar H), 3.73 (t, 2H, N–CH –), 1.17–1.85 (m, 9H, –CH –,
2 2
ꢀ
1
3
nal), 2927 (aliphatic CH), 2857 (N–CH –), 2724 (aldehydic hydrogen),
2
1
688 (C¼O), 1600, 1465 (Ar C¼C).

Synthesis of Dopant with Phenothiazine Moiety
121
SCHEME 1

1
22
L. S. Park et al.
9
,10-(Chloromethyl)anthracene (4.8 g, 0.014 mol) was reacted with
ꢁ
triethylphosphite (30 g, 0.18 mol) at 120 C for 12 h. The unreacted triethyl-
phosphite was removed under reduced pressure [12]. 9,10-Bis(diethoxy-
phosphinylmethyl)antrhracene (PHAN) was obtained as yellow crystal.
1
Yield: 92%. H NMR (CDCl ), d: 7.57, 8.38 (m, 8H, Ar H), 4.23 (d, 8H,
3
–
CH O–P–), 3.84 (m, 4H, Ar–CH –P), 1.06 (t, 12H, –CH ), IR (KBr),
2 2 3
ꢀ1
cm : 3026 (Ar CH), 2983 (aliphatic CH), 1251 (P¼O).
As presented in Scheme 1(a), KPD-1 was synthesized with adding
potassium tert-butoxide (4.73 g, 0.04 mol) solution into a mixture of EHFZ
(
1.70 g, 0.005 mol) and PHAN (1.20 g, 0.0025 mol) in THF, and then stirring
1
at room temperature for 7 h. Yield: 51%, H NMR (CDCl ), d: 6.94
(
(
3
ꢀ
1
m, 4H,¼CH–), IR (KBr), cm : 3021 (Ar CH), 2924 (aliphatic CH), 2855
N–CH –), 1578, 1471 (Ar C¼C), 965 (trans vinylene).
2
Poly(BFMP -AV) alternating copolymer, as shown in Scheme 1(b), was
1
2
obtained by Horner-Emmons condensation reaction [5,8,9].
Fabrication of PLED
The emissive layer (EML) was formed on ITO glass by spin coating of mix-
ture solution of KPD-1 dopant and poly(BFMP -AV) in trichloroethylene.
1
2
˚
AL electrode (2000 A thickness) was vacuum deposited by electron-beam
ꢀ
5
method using thermal evaporator (2.0 ꢂ 10 torr, KVT-420, Korea Vacuum
Co.). For multi-layered PLED, PEDOT as a hole transporting layer (HTL)
˚
was spin coated to give a thickness of 500 A or Alq as an electron trans-
3
˚
porting layer (ETL) was vacuum deposited to a thickness of 300 A.
Measurements
1
H-NMR and FT-IR spectra of synthesized compounds were taken on a
Varian Unity Plus 300 and Jasco FT=IR-620 spectrometer, respectively.
UV-visible absorption spectra were obtained from Shimadzu UV-2100.
Photoluminescence (PL) spectra were obtained by optical multichannel
analyzer (OMA system, Lazer Photonics). Excitation source was He-Cd
laser (325 nm). Electroluminescence (EL) spectra and color coordinates
were measured by using Spectroscan PR 704 (Photoresearch Inc.). Current
and luminance vs. voltage profiles were obtained by using a dc power
supply connected with model 8092A digital multimeter (Hyun Chang
Product Co. Ltd) and luminance meter (Minolta LS-100), respectively.
RESULTS AND DISCUSSION
UV-Vis absorption maximum (kmax,UV) and PL maximum (kmax,PL) of
poly(BFMP -AV) were measured to be at 299 nm and 338 nm, respectively,
12

Synthesis of Dopant with Phenothiazine Moiety
123
as shown in Figure 1. KPD-1 exhibited kmax,UV at 322 nm, which was over-
lapped to a relatively large extent with PL peaks of poly(BFMP -AV). KPD-
12
1
of poly(BFMP -AV)=KPD-1 mixtures were measured as a function of the
showed kmax,PL at 374 nm, when excited at its kmax,UV. UV-Vis and PL spectra
12
KPD-1 content in mixtures, as shown in Table 1. It was observed that while
kmax,UV values of poly(BFMP -AV)=KPD-1 mixtures remained unchaged,
12
kmax,PL of the mixtures clearly were measured to be in the range of 564–
5
sition of poly(BFMP -AV)=KPD-1 (97=3 wt.=wt.) exhibited the highest
86 nm, higher than kmax,PL of KPD-1 itself. Of the mixtures used, the compo-
12
kmax,PL among them. It has been well known that the emission by exciplex for-
mation is observed in longer wavelength than normal emission peak [10,11].
Therefore, large shift of PL emission by poly(BFMP -AV)=KPD-1 may be
12
due to the enhanced exciplex formation between the matrix polymer and
the dopant at this composition (3 wt.% of KPD-1).
Luminescence vs. voltage profiles of PLEDs such as single-layered
ITO=[poly(BFMP -AV)=KPD-1]=Al (S-2 EL device), and double-layered
ITO=PEDOT=[poly(BFMP -AV)=KPD-1]=Al (D-1 EL device), ITO=[poly
1
2
12
(BFMP -AV)=KPD-1]=Alq =Al (D-2 EL device) were shown in Figure 2.
ITO=[poly(BFMP -AV)=KPD-1]=Alq =Al (D-2 EL device) had a maximum
12 3
1
2
3
2
luminance of 89 cd=m (16 V) and a maximum luminance efficiency of
FIGURE 1 UV-Vis and PL spectra in THF; (a) UV-Vis and (b) PL of Poly(BFMP12
AV), (c) UV-Vis and (d) PL of KPD-1.
-

1
24
L. S. Park et al.
TABLE 1 Electro-optic Data of Matrix=Dopant System
Sample
kmax,UV (nm=eV)
kmax,PL (nm=eV)
Poly(BFMP12-AV)
KPD-1
299=4.16
322=3.83
309=4.01
305=4.06
305=4.06
338=3.66
374=3.31
564=2.19
586=2.11
565=2.19
Poly(BFMP12-AV) : KPD-1 99 : 1 (w=w)
Poly(BFMP12-AV) : KPD-1 97 : 3 (w=w)
Poly(BFMP12-AV) : KPD-1 95 : 5 (w=w)
0.183 lm=W (12 V). The luminance efficiency (g, lm=W) was calculated by
using the following equation:
g ¼ ðpLÞ=ðVJÞ
ð1Þ
2
2
where L(cd=m ), V(V), and J(A=m ) are luminance intensity, applied volt-
age, and current density, respectively. This result indicated that hole and
electron trnasporting rate in D-2 device was well balanced by introducing
Alq as an ETL. As presented in Figure 3, D-2 device also exhibited k
3
max,EL
6
04 nm, longer wavelength than other PLEDs. EL emission colors of
FIGURE 2 Luminance vs. voltage profile of single- and double-layered PLEDs; S-2
&), D-1 ( , D-2 (^).
(
~

Synthesis of Dopant with Phenothiazine Moiety
125
FIGURE 3 EL spectra of single- and double-layered PLEDs.
FIGURE 4 Color coordinates of PLEDs.

1
26
L. S. Park et al.
PLED’s are shown in Figure 4, according to the NTSC chromaticity
diagram. The EL emission of PLED’s showed green (x¼0.5128, y¼
0
.4730) for S-2, yellowish-orange (x¼0.5455, y¼0.4485) for D-1, and
orange (x¼0.5605, y¼0.4380) for D-2 devices, respectively.
CONCLUSIONS
KPD-1 dopant possessing both phenothiazine and antracene moieties were
synthesized by using Horner-Emmons reaction and were used as a dopant
in the polymer matrix, poly(BFMP -AV). The optimized weight ratio of
12
poly(BFMP -AV)=KPD-1 (97=3 w=w) dopant system exhibited a maxium
1
2
red-shift of PL emission. PLEDs were fabricated with the same composition
of matrix=dopant as a light emitting layer. Double-layered ITO=[poly
(BFMP -AV)=KPD-1]=Alq =Al (D-2 EL device), which contained Alq
12 3 3
layer as an ETL, exhibited enhanced EL emission and efficiency compared
to those of other PLEDs by stopping the holes transported and enhancing
injection of electrons to the emitting layer.
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