A New Approach Way for White OLED Based on Single Emitting Layer and Large Stokes Shift
Kim et al.
UV-VIS-NIR spectrometer. Perkin Elmer luminescence
spectrometer LS55 (Xenon flash tube) was used for photo-
luminescence spectroscopy. The redox potentials of the
compounds were determined with cyclic voltammetry
(CV) using a AUTOLAB/PG-STAT128N model system
with a scanning rate of 100 mV/s. We used synthesized
material coated ITO as working electrode, a saturated
Ag/AgNO3 as a reference electrode and Acetonitrile (AN)
with 0.1 M tetrabutylammonium tetrafluoroborate (TBAT)
as an electrolyte. Ferrocene was used for potential calibra-
tion and for reversibility criteria.
The reaction was checked with TLC, and when the reac-
tion was completed, purified by using column chromatog-
raphy with benzene and recrystallization was performed
with chloroform and methanol. As a result, pure pur-
ple compounds were obtained. The final yield was 15%.
1H NMR (300 MHz, THF-d8ꢁ: ꢂ (ppm) 10.34 (s, 2 H),
9.42 (d, 4 H), 9.11 (d, 4 H), 8.30 (m, 4 H), 7.83 (m, 6 H),
−3ꢃ11 (s, 2 H).
2.2.3. [1,5-Diphenyl-porphyrinato]Zinc(II) (DPPZ)
Diphenylporphyrin 1 g (2.162 mmol) and zinc chloride
1.1 g (8.65 mmol) were mixed in a round flask of 250 mL
which was refluxed by using dimethylformamide of 50 mL
as solvent for 4 hour. The reaction was checked with TLC,
and when the reaction was completed, washing with dis-
tilled water, methanol and isopropyl alcohol. and recrystal-
lization was performed with chloroform and hexane. As a
result, pure purple compounds were obtained. The final
EL devices were fabricated as the following struc-
ture: ITO/2-TNATA (60 nm)/NPB (15 nm)/TATa + DPPZ
(50%:50%, 30 nm)/Bphen (30 nm)/LiF (1 nm)/Al
(200 nm), where Tris(N-(naphthalen-2-yl)-N-phenyl-
amino) triphenylamine (2-TNATA) was used as hole injec-
tion layer, N,Nꢀ-bis(naphthalen-1-yl)-N,Nꢀ-bis(phenyl)
benzidine (NPB) as hole transporting layer, 4,7-Diphenyl-
1,10-phenanthroline (Bphen) as electron transporting layer,
the TATa + DPPZ as emitting layer, LiF as electron injec-
tion layer, ITO as anode and Al as cathode. The organic
layer was vacuum-deposited using thermal evaporation at
a vacuum base pressure of 10−6 torr and the rate of depo-
sition being 1 Å/s to give an emitting area of 4 mm2, and
the aluminum layer was continuously deposited under the
same vacuum condition. The current–voltage–luminance
(I–V –L) characteristics of the fabricated EL devices were
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yield was 70%. H NMR (300 MHz, THF-d8ꢁ: ꢂ (ppm)
10.34 (s, 2 H), 9.46 (d, 4 H), 9.16 (d, 4 H), 8.28 (m, 4 H),
7.81 (m, 6 H). FAB-Mass 524 m/z.
3. RESULTS AND DISCUSSION
Scheme 1 shows the chemical structures of TATa and
DPPZ which are used for OLED emitter.
TATa showed UV-Vis and PL maximum values of
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403 nm and 445 nm in film state (see Table I and Fig. 1).8
obtained by Keithley 2400 electrometer. Light intensity
IP: 182.71.110.82 On: Tue, 23 Feb 2016 05:27:31
TATa has high Tg value, above 130 ꢁC. A high Tg indicates
that the morphology of the material is not easily changed
by the high temperatures generated by the operation of
OLED device, and is closely correlated with good OLED
device lifetime.9ꢄ10 Also, as we mentioned in introduction,
large-stokes shift for red dopant is useful approach way
to realize two-color white OLEDs. In this concept, the
main requirement issue for large-stokes shift is no optical
absorption of red dopant in the wavelength range of blue
host emission. Based on this approach way, new DPPZ
was synthesized as shown in Scheme 2.
Copyright: American Scientific Publishers
was obtained by Minolta CS-1000.
2.2. Synthesis of [1,5-Diphenyl-Porphyrinato]
Zinc(II) (DPPZ)
2.2.1. Synthesis of Dipyrromethane ꢀDPMꢁ
Paraformaldehyde 1.73 g (0.0576 mol) and pyrrole 100 mL
(1.44 mol) were mixed in a round flask of 250 mL which
wasꢁ nitrogen atmosphere. Mixture stirred and heated to
60 C. After 30 minute, reduced the heating and added
trifluoroacetic acid 0.44 ml (5.76 mmol) and stirred for
4 h. The reaction was checked with TLC, and when
the reaction was completed, extraction was performed by
using water and ethyl acetate, and moisture was removed
by using anhydrous MgSO4. By distillation, extra pyr-
role was reduced, and pure white dipyrromethane solid
For the optical and electrical data, UV-Vis. spectroscopy
and cyclic voltammetry (CV) were carried out. Based
1
was obtained. The yield was 26%. H NMR (300 MHz,
CDCl3):ꢂ (ppm) 7.88 (s, 2 H), 6.66 (d, 2 H), 6.16 (d, 2 H),
6.03 (s, 2 H), 3.98 (s, 2 H).
N
N
N
N
N
Zn
2.2.2. 1,5-Diphenyl-Porphyrin (DPP)
Dipyrromethane 1 g (6.84× mmol) and benzaldehyde
0.76 ml (6.84 mmol) were mixed in a round flask of
2 L and then boron trifluoride diethyl etherate 0.48 ml
was added, which was stirred by using chloroform of
1 L as solvent. After 1 hour, 2,3-Dichloro-5,6-dicyano-
p-benzoquinone (DDQ) 2.33 g (10.26 mmol) was added
and stirred for 5 hour, and then triethylamine was added.
(a)
(b)
Scheme 1. The chemical structures of 4-(10-(30,50-diphenylbiphenyl-
4-yl)anthracen-9-yl)-N,N-diphenylaniline ((a) TATa) and [5,15-
Diphenylporphyrinato]zinc(II) ((b) DPPZ).
5492
J. Nanosci. Nanotechnol. 14, 5491–5494, 2014