386
Chemistry Letters 2002
Syntheses of Vinyl Polymers Containing Phenylanthracene Pendants
and Their Application ro Organic EL Device
Satoshi Shirai and Junji Kidoꢀ
Graduate School of Science and Engineering, Yamagata University, Yonezawa, Yamagata 992-8510
(Received November 19, 2001; CL-011164)
Fluorescent vinyl polymers containing 9-phenylanthracene
of Pd(PPh3)4 as a catalyst under nitrogen for 24 hours. The residue
pendants were synthesized and examined as an emitter layer in
organic electroluminescent devices. The single layer polymer EL
device using the homopolymer emitted green light originating
from the excimer of the anthracene units. On the other hand, blue
emission was observed from the devices using thecopolymer with
vinylcarbazole.
was chromatographed on silica-gel using chloroform-hexane
(1 : 5) as eluent to yield the light yellow solid VPA (45%). Anal.
Calcd for (C22H16): C, 94.25; H, 5.75%. Found: C, 94.03; H,
5.85%. mp 159.6–160.5 ꢁC. 1H NMR (CDCl3, 270 MHz, ppm): d
5.4–5.9 (2H, m, CH2), d 6.8–6.9 (1H, m, CH), d 7.2–8.0 (12H, m,
Ar-H), d 8.5 (1H, s, Ar-H). The homopolymer and copolymer
with N-vinylcarbazole (90 mol%) were synthesized by radical
polymerization. 2,20-Azobis (isobutyronitrile) (AIBN) as an
initiator and the corresponding monomers reacted at 65 ꢁC in
THF under nitrogen for 24 h. The polymers were then dissolved in
THF and precipitated into methanol, washed with methanol, and
dried under vacuum at 60 ꢁC to give light yellow polymers.
Homopolymer: Anal. Calcd for (C22H16): C, 94.25; H, 5.75%.
Found: C, 93.81; H, 5.85%. The composition of copolymer,
molecular ratio of carbazole unit and phenylanthracene unit, was
determined to be 9 : 1 (VK : VPA) from elemental analysis.
Found: C, 87.46; H, 5.48; N, 6.25%. Molecular weights were
determined by GPC using polystyrene as a standard. Weight
average molecular weight of the homopolymer and copolymer
were 12000 and 11300 with polydispersibilities of 1.92 and 1.88,
respectively. The homopolymer and copolymer showed the glass
transition temperatures at 173 and 168 ꢁC, and decomposition
temperatures at 427 and 405 ꢁC, respectively.
In organic electroluminescent devices (OELDs), two types of
organic materials, small molecules and polymers, are used in
device fabrication. Among polymers, ꢀ-conjugated polymers,
such as poly(1,4-phenylenevinylene)1 and its derivertives2{4 have
been widely used as the emitting layer in OELDs. However, it is
still difficult to obtain blue emission due to extended ꢀ-
conjugation. On the other hand, non-conjugated polymers such
as poly(N-vinylcarbazole) (PVK)5 emit in purplish blue region.
In addition, emission color can be changed to various colors by
doping fluorescent dyes. For example, we demonstrated white
emission from the device using PVK doped with red, green and
blue dyes.6 In this case, hole-transporting PVK was doped with
electron-transporting material, 2-(4-biphenylyl)-5-(4-tert-butyl-
phenyl)-1,3,4-oxadiazole (PBD) to inject electrons to the PVK
emitter layer.
The polymers were examined as an emitter layer in single-
layer-type devices. The device structure is a glass substrate/
indium-tin-oxide (ITO)/polyethylenedioxithiophene (PEDOT)
In this study, our objective is to develop non-conjugated
polymers and their OELDs emiting blue light. We synthesized
vinyl polymers containing blue fluorescent 9-phenylanthracene
pendants.
9-(4-Vinyl phenyl)anthracene (VPA) was synthesized by
palladium-catalyzed Suzuki cross-coupling reaction as shown in
Scheme 1. 9-Bromoanthracene was reacted at 55 ꢁC with 1,4-
vinylphenylboronic acid in tetrahydrofuran (THF) in the presence
ꢀ
ꢀ
ꢀ
ꢀ
(600 A)/emitting polymer (1000 A)/LiF (5 A)/Al (1000 A). ITO-
coated glass substrates were cleaned in a ultrasonic bath using
several solvents and were treated in a UV-ozone chamber just
before device fabrication. The organic layers were formed by spin
coating from the solution onto ITO, and LiF and Al top electrode
were deposited at 5 Â 10À6 Torr. PEDOT, doped with polystyr-
ene sulfonic acid, was received from Bayer Co. Ltd. ITO-coated
glasses were received from Asahi Glass Co. Ltd. Luminance was
measured using a Topcon BM-8 luminance meter and electro-
luminescence (EL) spectra were taken on a Hamamatsu photonics
PMA-10 optical multi channel analyzer and photoluminescence
(PL) spectra were taken on a fluorescence spectrometer,
Instruments SA Fluoro Max-2. Ionization potential (Ip) was
measured by atmosphere ultra violet photoelectron analysis using
a Riken Keiki AC-1 under ambient atmosphere.
Scheme 1. Synthesis of a monomer.
Figure 2 shows the EL spectra of the devices, which are
identical with the PL spectra. Green EL from the homopolymer
peaking at 490 nm was obtained from the devices as shown in
Figure 2 (a), while, blue EL peaking at 435 nm was obtained from
the device using copolymer as shownin Figure 2 (b). These results
indicate that the decreasing of anthracene units in the copolymer
composition suppresses the formation of the excimer of
anthracene moiety.
Figure 1. The molecular structures of polymers.
Copyright Ó 2002 The Chemical Society of Japan
Shirai, Satoshi
