Electroactive polymers containing pendant harmane, phenoxazine or carbazole rings as host materials for OLEDs

Article abstract of DOI:10.1016/j.dyepig.2014.04.034

Polystyrenes containing electronically isolated harmane, phenoxazine or carbazole rings were synthesized and characterized by NMR spectroscopy, elemental analysis and gel permeation chromatography. The new polymers represent amorphous materials of high th

Full text of DOI:10.1016/j.dyepig.2014.04.034

Dyes and Pigments 108 (2014) 121e125
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Electroactive polymers containing pendant harmane, phenoxazine
or carbazole rings as host materials for OLEDs
E. Zaleckas a, R. Griniene a, B. Stulpinaite a, J.V. Grazulevicius a, L. Liu b, Z. Xie b,
,
,
a,
*
E. Schab-Balcerzak c d, E. Kamarauskas e, B. Zhang b , S. Grigalevicius
*
a Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu plentas 19, LT50254 Kaunas, Lithuania
b State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
130022 Changchun, China
c Institute of Chemistry, University of Silesia, 9 Szkolna Street, 40-006 Katowice, Poland
d Centre of Polymer and Carbon Materials, Polish Academy of Sciences, 34 M. Curie-Sklodowska Street, 41-819 Zabrze, Poland
e Department of Solid State Electronics, Vilnius University, Sauletekio aleja 9, LT10222 Vilnius, Lithuania
a r t i c l e i n f o
a b s t r a c t
Article history:
Polystyrenes containing electronically isolated harmane, phenoxazine or carbazole rings were synthe-
sized and characterized by NMR spectroscopy, elemental analysis and gel permeation chromatography.
The new polymers represent amorphous materials of high thermal stability with glass-transition tem-
peratures of 139e179 ꢀC. The electron photoemission spectra of layers of the synthesized polymers
showed ionization potentials of about 5.6e6.0 eV. The polymers were tested as host materials in
phosphorescent green OLEDs with bis(2-phenylpyridine)(acetylacetonato)iridium(III) as the guest. The
device based on polymer containing phenoxazine fragments exhibited the best overall performance with
a turn-on voltage of 2.8 V, maximum photometric efficiency of about 17 cd/A and maximum brightness
of 2920 cd/m2.
Received 5 March 2014
Received in revised form
19 April 2014
Accepted 25 April 2014
Available online 6 May 2014
Keywords:
Vinyl monomer
Electroactive material
Polystyrene
Ó 2014 Elsevier Ltd. All rights reserved.
Ionization potential
Host
Light emitting diode
1. Introduction
carbazole- and indole-based derivatives demonstrate rather
large triplet energies and are potential host materials for
Improvements in the performance of organic light emitting di-
odes (OLEDs) over the past decade have resulted in commercially
available products. The efficiencies of OLED devices have advanced
rapidly in recent years because of the development of efficient
emitters [1e5] as well as efficient phosphorescent guest molecules
containing transition metals [6e8]. In the phosphorescent devices,
to reduce quenching associated with relatively long excited-state
lifetimes of triplet emitters and tripletetriplet annihilation, the
emitters are normally used as emitting guests in a host material,
and thus suitable host materials are of equal importance for
electro-phosphorescent OLEDs. The triplet level of the hosts should
be larger than that of the triplet emitter to prevent energy transfer
from the guest back to the host and to confine effectively triplet
excitons to the guest molecules [9e11]. It was reported earlier that
electro-phosphorescent devices [12e14]. Here, we report on new
electroactive polymers containing electronically isolated pendant
harmane, phenoxazine or carbazole rings. The fragments of aro-
matic heterocyclic compounds are attached to long and neural alkyl
chains of the macromolecules and have not an electronic interac-
tion. The polymers should have high triplet energy and are suitable
as polymeric hosts for large area OLED devices.
2. Experimental
2.1. Instrumentation
1H NMR spectra were recorded using a Varian Unity Inova
(300 MHz) instrument. Mass spectra were obtained on a Waters ZQ
2000 spectrometer. UV spectra were measured with a Spectronic
GenesysÔ 8 spectrometer. Fluorescence (FL) spectra were recorded
with a Hitachi MPF-4 spectrometer.
* Corresponding authors.
E-mail addresses: bhzhang512@ciac.ac.cn (B. Zhang), saulius.grigalevicius@ktu.lt
(S. Grigalevicius).
The molecular weights of polymers were determined by a gel
permeation chromatography (GPC) system including GMHHR-M
http://dx.doi.org/10.1016/j.dyepig.2014.04.034
0143-7208/Ó 2014 Elsevier Ltd. All rights reserved.

122
E. Zaleckas et al. / Dyes and Pigments 108 (2014) 121e125
columns and Bischoff LAMBDA 1000 detector. Polystyrene stan-
dards were used for calibration of the columns and THF was chosen
as an eluent.
Differential scanning calorimetry (DSC) measurements were
carried out using a Bruker Reflex II thermosystem. Thermogravi-
metric analysis (TGA) was performed on a TGAQ50. The TGA and
DSC curves were recorded in a nitrogen atmosphere at a heating
rate of 10ꢀC/min.
The ionization potentials of the layers of the compounds syn-
thesized were measured by the electron photoemission method in
air [15]. The samples for the ionization potential measurement
were prepared as we described earlier [16].
10-(4-Vinylbenzyl)phenoxazine (5) was prepared by similar
procedure as described for monomer 4. 10H-phenoxazine (2) (2 g,
10.9 mmol) and 4-vinylbenzyl chloride (1.87 g, 12.3 mmol) were
stirred in acetone (50 ml) and heated to 75 ꢀC. Then powdered so-
dium hydroxide (0.49 g, 12.3 mmol) and a catalytic amount of TBAS
(0.08 g) were added to the mixture, and it was stirred for 14 h at
75 ꢀC. After TLC control the mixture was filtered, the solvent was
evaporated and the product was purified by column chromatog-
raphy with silica gel using hexane/ethyl acetate (vol. ratio 2:1) as an
eluent. Yield: 62% (2.2 g) of colourless crystals. M.p.: 85 ꢀC (DSC).
MS (APCIþ, 20 V): 300.5 ([M þ 1], 100%). 1H NMR spectrum
(400 MHz, CDCl3, d, ppm): 7.39e7.23 (m, 4H, Ar); 6.73e6.64 (m, 7H,
The devices were fabricated on glass substrates and consisted of
multiple layers sandwiched between the bottom indium tin oxide
(ITO) anode and the top metal cathode (Al). The device structure
used was ITO/PEDOT:PSS(40 nm)/host 7, 8 or 9 doped with 10 wt%
of Ir(ppy)2(acac) (40 nm)/SPPO13(45 nm)/LiF (1 nm)/Al (100 nm).
The PEDOT:PSS layer was deposited onto the pre-cleaned ITO
substrate via spin-coating (Convac 1001 spin-coater, 2500 rpm,
30 s) and annealed at 120 ꢀC for 45 min in air. The emissive layer
was subsequently spin-coated (Convac 1001 spin-coater, 2900 rpm,
20 s) onto the PEDOT:PSS layer from chlorobenzene solution and
annealed at 100 ꢀC for 30 min in glove box. The layers of SPPO13,
LiF and Al were deposited in a vacuum chamber at a base pressure
of less than 4 ꢁ 10ꢂ4 Pa.
Ar and eCH]CH2); 6.32 (d, 2H, J ¼ 7.6 Hz, Ar); 5.73 (d, 1H,
J ¼ 17.6 Hz, eCH]CH2); 5.22 (d, 1H, J ¼ 11.2 Hz, eCH]CH2); 4.75 (s,
2H, NeCH2). Elemental analysis for C21H17NO % Calc.: C 84.25, H
5.72, N 4.68; % Found: C 84.19, H 5.78, N 4.61.
9-(4-Vinylbenzyl)carbazole (6) was prepared by similar proce-
dure as described for monomer 4. 9H-carbazole (3) (5 g, 30 mmol)
and 4-vinylbenzyl chloride (5 g, 30.4 mmol) were stirred in THF
(50 ml) and heated to 75 ꢀC. Then powdered sodium hydroxide
(1.3 g, 32.5 mmol) and a catalytic amount of TBAS (0.22 g) were
added to the mixture, and it was stirred for 24 h at 75 ꢀC. After TLC
control the mixture was filtered, the solvent was evaporated and
the product was purified by column chromatography with silica gel
using hexane/ethyl acetate (vol. ratio 5:1) as an eluent. After crys-
tallization from the eluent yield of the product was 20% (1.7 g).
M.p.: 186 ꢀC (DSC).
Luminance of the resulting OLEDs was measured using a
Keithley source measurement unit (Keithley 2400 and Keithley
2000) with a calibrated silicon photodiode. The EL spectra of the
devices were measured using a SpectroScan PR650 spectropho-
tometer. All the devices were characterized without encapsulation
and all the measurements were carried out under ambient
condition.
MS (APCIþ, 20 V): 284.5 ([M þ 1], 100%). 1H NMR spectrum
(300 MHz, CDCl3,
d
, ppm): 8.12 (d, 2H, J ¼ 7.8 Hz, Ar); 7.40 (t, 2H,
J ¼ 7.5 Hz, Ar); 7.33 (d, 2H, J ¼ 8.1 Hz, Ar); 7.29e7.05 (m, 6H, Ar); 6.62
(dd,1H, J1 ¼10.8 Hz, J2 ¼17.7Hz, eCH]CH2); 5.65 (dd,1H, J1 ¼0.9 Hz,
J2 ¼17.7 Hz, eCH]CH2); 5.45 (s, 2H, NeCH2); 5.17 (dd,1H, J1 ¼0.9 Hz,
J2 ¼ 10.8 Hz, eCH]CH2). Elemental analysis for C21H17N % Calc.: C
89.01, H 6.05, N 4.94; % Found: C 88.94, H 6.08, N 4.91.
2.2. Materials
Homopolymers 7e9 were synthesized by free radical polymer-
ization of the vinyl monomers 4, 5 and 6 using AIBN as an initiator.
A corresponding monomer and initiator were charged in a Schlenk
flask and subjected to three vacuum/nitrogen refill cycles.
Anhydrous N-methyl-2-pyrrolidone (NMP) was added sequentially
then the mixture was heated at 75 ꢀC for 24 h, and poured into
methanol. The crude polymer was purified by extracting with
methanol for 24 h using a Soxhlet extractor. Mn, Mw and poly-
dispersity index (PDI) of the polymers were estimated from results
of gel permeation chromatography.
1-Methyl-9H-pyrido[3,4-b]indole (harmane) (1), 10H-phenox-
azine (2), 9H-carbazole (3), 4-vinylbenzyl chloride, sodium
hydroxide, tetrabutylammonium hydrogen sulphate (TBAS), 2,20-
azoisobutyronitrile (AIBN) and organic solvents were purchased from
Aldrich and used as received. 2,7-Bis(diphenylphosphoryl)-9,90-spi-
robi[fluorene] (SPPO13), bis(2-phenylpyridine)(acetylacetonato)iri-
dium(III) [Ir(ppy)2(acac)] were purchased from Luminescence
Technology Corp.
1-Methyl-9-(4-vinylbenzyl)pyrido[3,4-b]indole (4) was pre-
pared by the reaction of 1-methyl-9H-pyrido[3,4-b]indole (har-
mane) (1) with an excess of 4-vinylbenzyl chloride under basic
conditions in the presence of a phase transfer catalyst e TBAS.
Harmane (1) (0.44 g, 2.4 mmol) and 4-vinylbenzyl chloride (0.41 g,
2.7 mmol) were stirred in acetone (20 ml) and heated to 75 ꢀC. Then
powdered sodium hydroxide (0.11 g, 2.8 mmol) and a catalytic
amount of TBAS (0.02 g) were added to the mixture, and it was
stirred for 4 h at 75 ꢀC. After TLC control the mixture was filtered,
the solvent was evaporated and the product was purified by col-
umn chromatography with silica gel using hexane/ethyl acetate
(vol. ratio 2:1) as an eluent. Yield: 46% (0.34 g) of colourless crystals.
M.p.: 177 ꢀC (DSC).
Poly{1-methyl-9-(4-vinylbenzyl)pyrido[3,4-b]indole} (7). 1-Me
thyl-9-(4-vinylbenzyl)pyrido[3,4-b]indole (4) (0.32 g, 1.1 mmol)
was polymerized in NMP (0.5 ml) using AIBN (6 mol%, 10.4 mg) as
initiator. After precipitation and extraction yield of the product was
63% (0.2 g). Mw ¼ 8370, Mn ¼ 5900. 1H NMR spectrum (400 MHz,
CDCl3, d, ppm): 8.31e8.05 (m, 1H, Ar); 8.02e7.78 (m, 1H, Ar); 7.77e
7.47 (m, 1H, Ar); 7.24e6.60 (m, 3H, Ar); 6.50e5.70 (m, 4H, Ar);
5.51e4.81 (m, 2H, NeCH2); 2.74e2.26 (m, 3H, CH3); 1.71e1.24 (m,
1H, eCHeCH2e); 1.17e0.72 (m, 2H, eCHeCH2e). Elemental anal-
ysis for (C21H18N2)n % Calc.: C 84.53, H 6.08, N 9.39; % Found: C
84.49, H 6.12, N 9.32.
Poly[10-(4-vinylbenzyl)phenoxazine] (8). One gram of 10-(4-
vinylbenzyl)phenoxazine (5) (3.2 mmol) was polymerized in NMP
(1 ml) using AIBN (6 mol%, 31.2 mg) as initiator. After precipitation
and extraction yield of the product was 30% (0.3 g). Mw ¼ 13,400,
MS (APCIþ, 20 V): 299.6 ([M þ 1], 100%). 1H NMR spectrum
(300 MHz, CDCl3,
d
, m.d): 8.36 (d, 1H, J ¼ 6.8 Hz, Ar); 8.17 (d, 1H,
J ¼ 10.4 Hz, Ar); 7.88 (d, 1H, J ¼ 7.2 Hz, Ar); 7.61e7.52 (m, 1H, Ar);
7.37e7.27 (m, 4H, Ar); 6.99e6.93 (m, 2H, Ar); 6.65 (dd, 1H,
J1 ¼ 6.4 Hz, J2 ¼ 18.0 Hz, eCH]CH2); 5.79 (s, 2H, NeCH2); 5.69 (dd,
1H, J1 ¼ 1.0 Hz, J2 ¼ 23.6 Hz, eCH]CH2); 5.21 (dd, 1H, J1 ¼ 1.0 Hz,
J2 ¼ 14.4 Hz, eCH]CH2); 2.89 (s, 3H, CH3). Elemental analysis for
Mn ¼ 6700. 1H NMR spectrum (400 MHz, CDCl3,
d, ppm): 8.30e8.05
(m, 1H, Ar); 8.02e7.78 (m, 1H, Ar); 7.77e7.47 (m, 1H, Ar); 7.24e6.60
(m, 3H, Ar); 6.50e5.70 (m, 4H, Ar); 5.51e4.81 (m, 2H, NeCH2);
2.74e2.26 (m, 3H, CH3); 1.70e1.24 (m, 1H, eCHeCH2e); 1.17e0.72
(m, 2H, eCHeCH2e). Elemental analysis for (C21H17NO)n % Calc.: C
84.25, H 5.72, N 4.68; % Found: C 84.17, H 5.81, N 4.62.
C
21H18N2 % Calc.: C 84.53, H 6.08, N 9.39; % Found: C 84.59, H 6.12,
N 9.41.

E. Zaleckas et al. / Dyes and Pigments 108 (2014) 121e125
123
Poly[9-(4-vinylbenzyl)carbazole] (9). 9-(4-Vinylbenzyl)carba-
zole (6) (0.83 g, 2.9 mmol) was polymerized in NMP (2 ml) using
AIBN (6 mol%, 28.6 mg) as initiator. After precipitation and
extraction yield of the product was 82% (0.68 g). Mw ¼ 2880,
Molecular weights and polydispersities of the synthesized
polymers were estimated by GPC. The number-average molecular
weights (Mn), weight-average molecular weights (Mw) as well as
the polydispersity indexes (PDI) are summarized in Table 1. The
molecular weights of the polymers depend on the nature of elec-
trophores attached to the polymeric chain. The monomer 8 con-
taining phenoxazine rings yielded polymers with the highest
molecular weight. Carbazole-based monomer 6 yielded mostly
oligomers with polymerization degree (PD) of about 9. The
different PD of these polymers could probably be explained by the
different solubility of the formed materials in NMP.
Mn ¼ 2570. 1H NMR spectrum (400 MHz, CDCl3,
d, ppm): 8.29e7.89
(m, 2H, Ar); 7.80e6.87 (m, 6H, Ar); 6.77e6.24 (m, 2H, Ar); 6.17e5.70
(m, 2H, Ar); 5.50e4.58 (m, 2H, NeCH2); 1.76e1.24 (m, 1H, eCHe
CH2e); 1.19e0.52 (m, 2H, eCHeCH2e). Elemental analysis for
(C21H17N)n % Calc.: C 89.01, H 6.05, N 4.94; % Found: C 88.95, H 6.11,
N 4.89.
The thermal behaviour of the polymers 7e9 was studied by DSC
and TGA. All the materials demonstrated rather high thermal sta-
bility. The temperatures at which initial loss of mass (T5%) was
observed are 340 ꢀC for 7, 297 ꢀC for 8, and 305 ꢀC for 9. DSC
measurements confirmed that the polymers are amorphous ma-
terials with high glass-transition temperatures. When samples of
the materials were subjected to DSC heating scans the glass-
transitions were observed at 179 ꢀC for 7, at 165 ꢀC for 8 and at
139 ꢀC for 9, and no peaks due to crystallization and melting
appeared on further cooling and heating cycles between ꢂ30 ꢀC
and 250 ꢀC.
UV absorption and FL spectra of dilute solutions of the synthe-
sized polymers were recorded. The values of lmax are presented in
Table 2. For comparison the corresponding spectral data of the
monomers 4e6 are presented in the table. The electronic absorp-
tion energies of the polymers 7e9 are comparable, and the lmax
values are in the range of 241e352 nm. FL maxima of the polymers
appear in the region of wavelengths from 363 to 392 nm.
3. Results and discussion
The synthesis of the polymers containing electronically isolated
harmane, phenoxazine or carbazole rings (7e9) was carried out by
the synthetic route shown in Scheme 1. Monomers 4e6 were
prepared by a nucleophilic substitution reaction between the cor-
responding aromatic heterocyclic compound (harmane, 10H-phe-
noxazine, 9H-carbazole) and an excess of 4-vinylbenzyl chloride
under basic conditions with TBAS as a phase transfer catalyst.
Polymers 7e9 were obtained by radical polymerization of the vinyl
monomers (4e6) in N-methyl-2-pyrrolidone solutions using 2,20-
azoisobutyronitrile as an initiator. Low-molar-mass fractions of the
products of polymerizations were removed by Soxhlet extraction of
the raw polymers with methanol.
The new derivatives were identified by mass spectrometry (for
monomers), 1H NMR spectroscopy and elemental analyses. The
data were found to be in good agreement with the proposed
structures. The synthesized materials were soluble in common
organic solvents, such as chloroform and THF at room temperature.
Transparent thin films of these materials could be prepared by
spin-coating from solutions.
The comparison of the UV absorption and FL spectra of the
polymers with those of the corresponding monomers did not
reveal any considerable bathochromic shift of the spectra of poly-
mers with respect to those of the monomers. This observation
demonstrates that considerable intra-molecular interactions are
not observed in solutions of the polymers and they should
demonstrate high triplet energies.
n
H
( b )
N
( a )
Ionization potentials (Ip) of thin amorphous films of the poly-
mers were determined from electron photoemission spectra of the
layers. The spectra as well as the values of Ip are presented in Fig. 1.
It is seen that layers of polymer 8 have the lowest Ip and could be
used as hole injecting/transporting layers in optoelectronic devices
as well as hole transporting hosts for phosphorescent OLEDs. Ip of
polymers 7 and 9 are rather close and reach 6.0 eV. These values are
rather similar to that of other derivatives containing unsubstituted
carbazolyl or indolyl fragments [17]. These Ip values suggest that an
additional hole injecting layer would be necessary for application of
the polymers 7 and 9 as host materials for phosphorescent OLEDs.
To evaluate the performance of the polymers 7e9 as hosts,
green phosphorescent OLEDs were fabricated using green emitter
Ir(ppy)2(acac) as the guest. The device structure used was ITO/
PEDOT:PSS/host 7, 8 or 9 doped with 10 wt% of Ir(ppy)2(acac)/
SPPO13/LiF/Al. The conducting polymer poly(3,4-ethylenedioxy
thiophene): poly(styrenesulfonate) (PEDOT:PSS) was used as the
hole-injection layer, hosts 7e9 doped with the green phosphores-
cent bis(2-phenylpyridine)(acetylacetonato)iridium(III) [Ir(ppy)2
(acac)] were used as the emitting layer, 2,7-bis(diphenylphos
phoryl)-9,90-spirobi[fluorene] (SPPO13) was applied as electron-
N
N
N
1
N
N
7
4
n
H
( a )
( b )
N
O
N
N
2
O
O
5
8
n
H
N
( a )
( b )
Table 1
N
N
Molecular weights and PDI of the polymers synthesized.
3
Polymer
Mw
8370
13,400
2880
Mn
PDI
9
6
7
8
9
5900
6700
2570
1.4
2.0
1.1
Scheme 1. (a) 4-Vinylbenzyl chloride, NaOH, TBAS; (b) 2,20-azoisobutyronitrile (AIBN),
NMP.

124
E. Zaleckas et al. / Dyes and Pigments 108 (2014) 121e125
Table 2
The wavelengths of UV absorption and FLa maxima of the synthesized derivatives.
Compound
UV: lmax (nm)
FL: lmax (nm)
4
5
6
7
8
9
241, 278, 288, 337, 352
241, 325
259, 294, 329, 343
242, 279, 290, 338, 353
242, 326
387
391
363
389
392
364
262, 295, 330, 343
a
Excitation wavelength 290 nm.
transporting layer and LiF was used as the electron-injecting layer.
In all the formed devices containing hosts of 7e9, the electro-
phosphorescence was found to originate only from the guest at
different bias voltages. No host and doped transport molecular
emission were visible from the OLEDs, indicating an efficient en-
ergy transfer or charge transfer from the hosts to the guest as well
as the effective injection of both holes and electrons into the
emitting layer.
Fig. 2 shows characteristics of the formed devices. The OLEDs
exhibit turn-on voltages of 2.8e6.1 V, maximum brightness of
1940e2920 cd/m2 and photometric efficiencies of 4.7e17 cd/A. The
unusual OLED’s characteristics of the material 9-based device are
related to the inefficient charge transport behaviour and high
charge injection barrier from film of PEDOT:PSS into emitting layer
due to high Ip of the polymeric host. The distinct efficiency roll-off
rate at high current density was observed for all the devices. This
typical behaviour of phosphor-doped devices could be related to
tripletetriplet annihilation, excitonepolaron quenching effect as
well as charge imbalance at high current density regions during
operation. The charge imbalance conditions exist especially for
unipolar charge transport host materials. An optimization, such as
host engineering by adding electron-transporting host materials,
could solve this problem and could be planed for preparation of
optimized devices.
The device prepared using phenoxazine-based polymer 8 as the
host exhibited the best overall performance with a low turn-on
voltage of 2.8 V, maximum brightness of 2920 cd/m2 and
maximal photometric efficiency of about 17 cd/A. For the techni-
cally important brightness of 100 cd/m2, the efficiency of the device
containing host 8 was above 14.5 cd/A These findings look rather
promising when compared to the similar devices containing
Fig. 2. OLED characteristics of the devices containing hosts of 7, 8 or 9.
poly(9-vinylcarbazole) as a host [18]. It should be pointed out that
these characteristics were obtained in non-optimized test devices
under ordinary laboratory conditions. Some of the synthesized
polymers could be used for preparation of optimized and incap-
sulated devices. The experiments will be other part of this research
and device stability will be investigated at this stage.
In conclusion, polystyrenes containing pendant electroactive
harmane, phenoxazine or carbazole rings were synthesized from
the corresponding vinyl monomers by radical polymerization in
solution. The amorphous polymers show high thermal stability and
glass-transition temperatures of 139e179 ꢀC. The electron photo-
emission spectra of the layers of the materials showed ionization
Fig. 1. Electron photoemission spectra of the layers of polymers 7e9.

E. Zaleckas et al. / Dyes and Pigments 108 (2014) 121e125
125
[6] Adachi C, Baldo MA, Thompson ME, Forrest SR. Nearly 100% internal phos-
potentials of 5.6 eV for the polymer with phenoxazine rings and
of 6.0 eV for other polymers. The synthesized materials were
tested as hosts in phosphorescent OLEDs with bis(2-
phenylpyridine)(acetylacetonato)iridium(III) as the guest. The de-
vice with the host polymer containing pendant phenoxazinyl
fragments exhibited the best overall performance (turn-on voltage:
2.8 V; maximum photometric efficiency: w17 cd/A; maximum
brightness: 2920 cd/m2).
phorescence efficiency in an organic light-emitting device.
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Acknowledgements
[10] Jou JH, Yang YM, Chen SZ, Tseng JR, Peng SH, Hsieh CY, et al. High-efficiency
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Postdoctoral fellowship (Dr. Ernestas Zaleckas) is being funded
by European Union Structural Funds project “Postdoctoral Fellow-
ship Implementation in Lithuania”. Dr. Baohua Zhang is financially
supported by the National Natural Science Foundation of China (No.
51103147). Habil. Dr. V. Gaidelis is thanked for the help in ionization
potential measurements.
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based high triplet energy glass-forming electroactive molecular materials.
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