A novel class of photo- and electroactive polymers containing oxadiazole and amine moieties in a side chain

Article abstract of DOI:10.1021/ma021406u

A new class of photo- and electroactive polymer materials showing an liquid-crystalline (LC) phase were designed and synthesized: four kinds of polymers with both oxadiazole and arylamine moieties as carrier-transporting groups in the side chain. Among th

Full text of DOI:10.1021/ma021406u

Macromolecules 2003, 36, 3457-3464
3457
Articles
A Novel Class of Photo- and Electroactive Polymers Containing
Oxadiazole and Amine Moieties in a Side Chain
Hir oyu k i Moch izu k i,† Ta k a h ir o Ha su i,† Ma su k i Ka w a m oto,† Tom ik i Ik ed a ,*,†
Ch ih a ya Ad a ch i,‡ Yosh io Ta n igu ch i,‡ a n d Ya su h ik o Sh ir ota §
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, J apan, Faculty of Textile Science and Technology, Shinshu University,
Ueda, Nagano 386-8567, J apan, and Faculty of Engineering, Osaka University, Yamadaoka,
Suita, Osaka 565-0871, J apan
Received August 29, 2002; Revised Manuscript Received J anuary 22, 2003
ABSTRACT: A new class of photo- and electroactive polymer materials showing an liquid-crystalline
(LC) phase were designed and synthesized: four kinds of polymers with both oxadiazole and arylamine
moieties as carrier-transporting groups in the side chain. Among them, the polymers with a dimethylamine
and a methylcarbazole moiety show LC phases. Furthermore, all the polymers emitted strong blue
fluorescence, and their fluorescent quantum yields were over 0.6. The aligned sample of the polymer
with the carbazole moiety emitted polarized fluorescence at room temperature. One-layer type electrolu-
minescent (EL) devices were fabricated by using the polymer with a triphenylamine moiety, which
exhibited the highest quantum yield (∼0.82), and found to emit the EL emission at blue region.
1. In tr od u ction
We have investigated EL devices using molecularly
doped host LCs and evaluated in detail emission be-
havior of the EL devices.4 In this system, electronic
properties and electrooptical properties were able to be
tuned by using various dyes, carrier transport materials
and host low molecular-weight LCs.
Electroluminescent (EL) devices based on organic thin
layers have attracted much interest because of their
possible application as large-area light-emitting dis-
plays.1 Electroluminescence in such systems is gener-
ated by recombination of holes and electrons in the
emitting layer, which produces excited states in the
emitter material. These EL devices, which consist of a
doubled layer structure with an organic hole transport
layer and a luminescent electron transport layer, show
emission with an low-operating voltage. However, the
device structure with two organic layers contains an
interface between the two layers where only a weak van
der Waals force exists; therefore, one-layer-type device
may achieve an improvement of structural stability
because of the absence of these interfaces.2
However, the EL devices consisting of these LCs, like
the molecularly doped EL materials using LC matrices
and a novel class of LC compounds showing both strong
fluorescence and a charge-transporting ability, always
require glass cells, so that low molecular-weight LCs
are not necessarily promising from the standpoint of
material processability.
Currently, polymeric materials are generally expected
to be suitable for EL devices because they have good
processability and intrinsically high durability. In ad-
dition, several one-layer devices with bipolar polymers
as well as bipolar dye-dispersed polymers have been
reported.5 The bipolar polymers are classified into two
types: p-conjugated polymers1e,6 and polymers with
chromophores.7 Chromophores are incorporated into the
latter polymers on a skeleton and/or on a side chain and
the resulting polymers have been shown to be applicable
to EL devices as a new class of polymer materials. It
was found that there was a very little difference in the
driving mechanism between sublimed-dye multilayer
and bipolar polymer systems. In addition, from the
standpoint of ease of molecular design and synthesis,
polymers with chromophores have advantages over fully
p-conjugated polymers.
Liquid crystals (LCs) are promising materials in
terms of a unique self-organizing nature and fluidity.
Several low molecular-weight LCs containing either hole
(benzothiazole) or electron (oxadiazole) conducting groups
as mesogens have been synthesized,3 and some have
been investigated as charge transport and, in some
cases, EL emission materials. These LCs show high
electron and/or hole drift mobilities based on aligned
and stacked structures in a smectic (Sm) phase. It was
reported that EL devices using these LCs exhibited
polarized EL emissions.3(d)
* To whom correspondence should be addressed. E-mail:
tikeda@res.titech.ac.jp. URL: http://www.res.titech.ac.jp/polymer.
Telephone: +81-45-924-5240; +81-45-924-5275.
† Tokyo Institute of Technology.
In many areas of material science such as molecular
electronics and photonics, the controlled alignment of
photoactive chromophores with p-electron conjugation
is essential in the application. As decribed above, among
‡ Shinshu University.
§ Osaka University.
10.1021/ma021406u CCC: $25.00 © 2003 American Chemical Society
Published on Web 04/19/2003

3458 Mochizuki et al.
Macromolecules, Vol. 36, No. 10, 2003
Sch em e 1. Syn th etic Rou te for th e P olym er s Used in
Th is Wor k
heated and stirred, while 6-bromo-1-hexanol (36.2 g, 0.20 mol)
was added slowly. The reaction mixture was heated under
reflux for 24 h, and then the solvent was removed by evapora-
tion under reduced pressure. Water (300 mL) was added, and
the mixture was made strongly acidic with the addition of
hydrochloric acid. The precipitate was isolated and recrystal-
lized from methoxyethanol.
1
Yield: 22.6 g (72.0 mmol, 40%). Mp: 210-212 °C. H NMR
(δ, DMSO-d6): 1.40-1.87 (8H, m), 4.10 (2H, t), 4.22 (2H, t),
7.12 (2H, d), 7.74 (2H, d), 7.81 (2H, d), 8.09 (2H, d). Anal. Calcd
for C19H22O4 (314): C, 72.59; H, 7.05. Found: C, 72.70; H, 6.90.
4-(4-(2-Hyd r oxyeth oxy)p h en yl)ben zoic Acid . The title
compound was prepared by the same procedure as 4-(4-(6-
hydroxyhexyloxy)phenyl)benzoic acid.
Yield: 20.9 g (81.0 mmol, 45%). Mp: 222-224 °C. 1H NMR
(δ, DMSO-d6): 4.40 (2H, t), 4.61 (2H, t), 7.12 (2H, d), 7.74 (2H,
d), 7.81 (2H, d), 8.09 (2H, d). Anal. Calcd for C15H14O4 (258):
C, 60.76; H, 5.46. Found: C, 60.99; H, 5.50.
4-(4-(11-Hyd r oxyu n d ecyloxy)p h en yl)ben zoic Acid . The
title compound was prepared by the same procedure as 4-(4-
(6-hydroxyhexyloxy)phenyl)benzoic acid.
Yield: 27.7 g (72.0 mmol, 40%). Mp: 198-200 °C. 1H NMR
(δ, DMSO-d6): 1.40-1.87 (18H, m), 4.12 (2H, t), 4.21 (2H, t),
7.12 (2H, d), 7.74 (2H, d), 7.81 (2H, d), 8.09 (2H, d). Anal. Calcd
for C24H32O4 (385): C, 74.97; H, 8.39. Found: C, 75.00; H, 8.41.
4′-(6-Me t h a c r yloyloxy-1-h e xyloxy)b ip h e n yl-4-c a r -
boxylic Acid . A mixture of 4′-(6-hydroxyhexyloxy)biphen-
yl-4-carboxylic acid (9.40 g, 0.03 mol), methacrylic acid (21.5
g, 0.25 mol), hydroquinone (1.70 g, 0.02 mol), 4-toluenesulfonic
acid monohydrate (1.70 g, 0.01 mol), and benzene (200 mL)
was heated under reflux in a Dean-Stark apparatus for 24 h.
Water was added to the cooled resultant mixture, and then
the solvent was removed by evaporation under reduced pres-
sure. The crude product was redissolved in chloroform. The
solution was filtered, washed with water and dried over
anhydrous magnesium sulfate. The solvent was removed very
carefully by evaporation under reduced pressure (maximum
water bath temperature was 40 °C) to prevent the formation
of oligomers. The crude product was recrystallized from
ethanol.
Sch em e 2. Syn th etic Rou te for Va r iou s Tetr a zole
Der iva tives Used in Th is Wor k
Yield: 4.36 g (11.4 mmol, 38%). Mp: 140-142 °C. 1H NMR
(δ, CDCl3): 1.40-1.87 (8H, m), 1.95 (3H, s), 3.99 (2H, t), 4.16
(2H, t), 5.55 (1H, s), 6.10 (1H, s), 6.96 (2H, d), 7.55 (2H, d),
7.60 (2H, d), 8.12 (2H, d). Anal. Calcd for C23H26O5 (382): C,
72.23; H, 6.85. Found: C, 72.30; H, 6.90.
4′-(2-Met h a cr yloyloxyet h oxy)b ip h en yl-4-ca r b oxylic
Acid . The title compound was prepared by the same procedure
as 4′-(6-methacryloyloxy-1-hexyloxy)biphenyl-4-carboxylic acid.
Yield: 3.91 g (12.0 mmol, 40%). Mp: 148-150 °C. 1H NMR
(δ, CDCl3): 1.96 (3H, s), 4.26 (2H, t), 4.53 (2H, t), 5.60 (1H, s),
6.16 (1H, s), 7.00 (2H, d), 7.57 (2H, d), 7.63 (2H, d), 8.13 (2H,
d). Anal. Calcd for C19H18O5 (326): C, 69.93; H, 5.56. Found:
C, 70.00; H, 5.61.
various molecular alignment techniques, cooperative
alignment of chromophores in LC media has been
intensively studied due to effective alignment and easy
processing.8 However, in a host/guest system, the chro-
mophore content is limited to maintain LC properties
of the matrix.
In this work, we report the synthesis of a novel class
of polymeric materials which show LC phases and
consist of multifunctional mesogens with photo- and
electroactive properties. These mesogens are composed
of oxadiazole and arylamine moieties as thermally,
photochemically, and electrochemically inert moieties.
4′-(11-Meth a cr yloyloxy-1-u n d ecyloxy)bip h en yl-4-ca r -
boxylic Acid . The title compound was prepared by the same
procedure as 4′-(6-methacryloyloxy-1-hexyloxy)biphenyl-4-car-
boxylic acid.
Yield: 4.75 g (10.5 mmol, 35%). Mp: 134-136 °C. 1H NMR
(δ, CDCl3): 1.40-1.87 (18H, m), 1.95 (3H, s), 3.99 (2H, t), 4.16
(2H, t), 5.55 (1H, s), 6.10 (1H, s), 6.96 (2H, d), 7.55 (2H, d),
7.60 (2H, d), 8.12 (2H, d). Anal. Calcd for C28H36O5 (453): C,
74.31; H, 8.02. Found: C, 74.42; H, 8.11.
2. Exp er im en t
2.1. P r ep a r a tion of Com p ou n d s. The oxadiazole mono-
mers in this study were prepared starting from 4-(4-hydroxy-
phenyl)benzoic acid by a synthetic route shown in Scheme 1,
and various tetrazole derivatives were prepared by a procedure
shown in Scheme 2 with abbreviations. All regents were
purchased from Tokyo Kasei Co. and Aldrich Co. The com-
4-Dim et h yla m in ob en zot et r a zole (R ea ct ion A). 4-Di-
methylaminobenzonitrile (5.00 g, 34 mmol) was dissolved in
dry DMF (80 mL), and then sodium azide (36.0 g, 0.55 mol)
and ammonium chloride (29.0 g, 0.55 mol) were added to the
solution. The solution was stirred and heated under reflux for
10 h. The cooled solution was then added to aqueous hydro-
chloric acid. The precipitate was collected and washed with
water. The recrystallization from toluene/ethyl acetate gave
the desired product as a white solid.
1
pounds were identified by H NMR, absorption spectroscopy,
and elemental analysis.
2.2. Ma ter ia ls. 4-(4-(6-Hyd r oxyh exyloxy)p h en yl)ben -
zoic Acid . 4-(4-(6-Hydroxyhexyloxy)phenyl)benzoic acid (38.6
g, 0.18 mol) was dissolved in a mixture of ethanol (60 mL),
potassium hydroxide (27.0 g, 0.48 mol), and water (30 mL). A
trace of potassium iodide was added, and the solution was
Yield: 5.20 g (27.2 mmol, 80%). Mp: 81-83 °C. 1H NMR
(δ, DMSO-d6): 2.99 (s, 6H), 6.85 (d, 2H), 7.83 (d, 2H). Anal.
Calcd for C9H12N5 (189): C, 57.13; H, 5.86; N, 37.01. Found:
C, 57.10; H, 5.86; N, 37.00.

Macromolecules, Vol. 36, No. 10, 2003
Photo- and Electroactive Polymers 3459
3-F or m yl-9-m eth ylca r ba zole (Rea ction B). Phosphoryl
chloride (8.00 g, 0.05 mol) was added slowly into DMF (10.0
g, 0.14 mol), which was purged with nitrogen and cooled to 0
°C. The reactant was warmed to room temperature and stirred
for 1 h and then cooled again to 0 °C. To this mixture was
added N-methylcarbazole (5.00 g, 0.03 mol) in 1,2-dichloro-
ethane (13 mL). In 1 h, the reaction temperature was raised
to 90 °C and then kept for 8 h. The cooled solution was poured
into ice water and extracted with dichloromethane and dried
with anhydrous magnesium sulfate. The crude product was
purified by column chromatography on silica gel (eluent:
dichloromethane/hexane ) 3/1). Recrystallization from hexane/
ethanol gave the desired product.
was purified by column chromatography on silica gel (eluent:
chloroform/THF ) 1/10). Recrystallization from ethanol/
toluene gave the desired product.
1
Yield: 2.51 g (4.80 mmol, 60%). Mp: 115-118 °C. H NMR
(δ, CDCl3): 1.25-1.89 (8H, m), 1.95 (3H, s), 3.08 (6H, s), 4.00
(2H, t), 4.20 (2H, t), 5.55 (1H, s), 6.11(1H, s), 6.78 (2H, d), 7.04
(2H, d), 7.55 (2H, d), 7.67 (2H, d), 8.05 (2H, d), 8.16 (2H, d).
Anal. Calcd for C32H35N3O4 (523): C, 73.12; H, 6.71; N, 7.99.
Found: C, 73.20; H, 6.60; N, 7.93.
2-(4′-Met h a cr yloyloxyet h oxyb ip h en yl-4-yl)-5-(4-N,N-
d im eth yla m in op h en yl)-1,3,4-oxa d ia zole (M2-OXD-MA).
The title compound was prepared by the same procedure as
M6-OXD-MA.
Yield: 7.84 g (22.5 mmol, 75%). Mp: 71-73 °C. 1H NMR
(δ, CDCl3): 3.89 (3H, s), 7.30-8.1 (4H, m), 8.05 (1H, d), 8.15
(1H, d), 8.60 (1H, s), 10.10 (1H, s). Anal. Calcd for C14H11NO
(209): C, 80.36; H, 5.30; N, 6.69. Found: C, 80.30; H, 5.36; N,
6.74.
Yield: 2.40 g (5.12 mmol, 64%). Mp: 100-102 °C. 1H NMR
(δ, CDCl3): 1.95 (3H, s), 3.05 (6H, s), 4.15 (2H, t), 4.45 (2H, t),
5.55 (1H, s), 6.11(1H, s), 6.68 (2H, d), 6.94 (2H, d), 7.50 (2H,
d), 7.62 (2H, d), 7.90 (2H, d), 8.10 (2H, d). Anal. Calcd for
C
28H27N3O4 (470): C, 71.63; H, 5.80; N, 8.95. Found: C, 71.57;
3-F or m yl-9-p h en ylca r ba zole. The title compound was
prepared by the same procedure as 3-formyl-9-methylcarba-
zole.
H, 5.95; N, 8.90.
2-{4′-(11-Met h a cr yloyloxy-1-u n d ecyloxy)b ip h en yl-4-
yl}-5-(4-N,N-d im eth yla m in op h en )-1,3,4-oxa d ia zole (M11-
OXD-MA). The title compound was prepared by the same
procedure as M6-OXD-MA.
Yield: 5.70 g (21.0 mmol, 70%). Mp: 105-107 °C. 1H NMR
(δ, CDCl3): 7.30-8.15 (9H, m), 8.40 (1H, d), 8.17 (1H, d), 8.62
(1H, s), 10.5 (1H, s). Anal. Calcd for C19H13NO (271): C, 84.11;
H, 4.83; N, 5.16. Found: C, 84.23; H, 4.75; N, 5.14.
3-Cya n o-9-m eth ylca r ba zole (Rea ction C). A mixture of
3-formyl-9-methylcarbazole (3.00 g, 14 mmol), hydroxyamine
hydrochloride (1.20 g, 17 mmol), acetic acid (3.00 g, 0.05 mol),
pyridine (2.00 g, 25 mmol), and DMF (10 mL) was stirred and
heated at 140 °C for 5 h. The crude product was extracted with
dichloromethane and washed with water. The product was
purified by column chromatography on silica gel (eluent:
chloroform/toluene) and recrystallized from hexane/ethanol.
Yield: 2.14 g (10.3 mmol, 74%). Mp: 91-93 °C. 1H NMR
(δ, CDCl3): 3.89 (3H, s), 7.25-8.1 (5H, m), 8.15 (1H, d), 8.60
(1H, s). Anal. Calcd for C14H10N2 (206): C, 81.53; H, 4.89; N,
13.58. Found: C, 81.50; H, 5.00; N, 13.50.
Yield: 2.76 g (4.64 mmol, 58%). Mp: 114-116 °C. 1H NMR
(δ, CDCl3): 1.25-1.86 (18H, m), 1.95 (3H, s), 3.05 (6H, s), 4.15
(2H, t), 4.45 (2H, t), 5.55 (1H, s), 6.11(1H, s), 6.68 (2H, d), 6.94
(2H, d), 7.50 (2H, d), 7.62 (2H, d), 7.90 (2H, d), 8.10 (2H, d).
Anal. Calcd for C37H45N3O4 (596): C, 74.59; H, 7.61; N, 7.05.
Found: C, 74.57; H, 7.64; N, 7.00.
2-{4′-(6-Meth a cr yloyloxy-1-h exyloxy)bip h en yl-4-yl}-5-
(4-N,N-diph en ylam in oph en yl)-1,3,4-oxadiazole (M6-OXD-
P A). 4′-(6-Methacryloyloxy-1-hexyloxy)biphenyl-4-carboxylic
acid (3.00 g, 7.85 mmol) was added to thionyl chloride (30 mL)
and stirred on heating at 60 °C for 2 h. Excess thionyl chloride
was removed under reduced pressure, and then the residue
was reacted with (4-tetrazolylphenyl)diphenylamine (4.10 g,
13 mmol) in dry pyridine (40 mL) at 155 °C. The cooled solution
was poured into water, and the crude product was extracted
with dichloromethane and washed with water three times. The
product was purified by column chromatography on silica gel
(eluent: chloroform/THF ) 1/15). Recrystallization from etha-
nol/toluene gave the desired product.
3-Cya n o-9-p h en ylca r ba zole. The title compound was
prepared by the same procedure as 3-cyano-9-methylcarbazole.
Yield: 2.55 g (9.53 mmol, 68%). Mp: 175-177 °C. 1H NMR
(δ, CDCl3): 7.26-7.72 (11H, m), 8.18 (1H, d), 8.45 (1H, s). Anal.
Calcd for C19H12N2 (268): C, 85.05; H, 4.51; N, 10.44. Found:
C, 85.06; H, 4.32; N, 10.62.
Yield: 3.02 g (4.64 mmol, 58%). Mp: 115-118 °C. 1H NMR
(δ, CDCl3): 1.25-1.89 (8H, m), 1.98 (3H, s), 4.05 (2H, t), 4.20
(2H, t), 5.56 (1H, s), 6.11(1H, s), 6.97 (2H, d), 7.10-7.40 (12H,
m), 7.56 (2H, d), 7.72 (2H, d), 7.95 (2H, d), 8.16 (2H, d). Anal.
3-Tetr a zolyl-9-m eth ylca r ba zole. A mixture of 3-cyano-
9-methylcarbazole (3.00 g, 15 mmol), sodium azide (15.1 g, 0.23
mol), ammonium chloride (12.4 g, 0.23 mol), and dry DMF (110
mL) was stirred and heated at 140 °C for 10 h. The cooled
solution was slowly poured into water. The precipitate was
collected and washed with water. Recrystallization from
toluene/methanol gave the desired product.
Calcd for
C42H39N3O4 (650): C, 75.88; H, 6.02; N, 7.17.
Found: C, 75.70; H, 6.00; N, 7.23.
2-{4′-(11-Met h a cr yloyloxy-1-u n d ecyloxy)b ip h en yl-4-
yl}-5-(4-N,N-diph en ylam in oph en yl)-1,3,4-oxadiazole (M11-
OXD-P A). The title compound was prepared by the same
procedure as M6-OXD-PA.
1
Yield: 3.11 g (12.9 mmol, 86%). Mp 264-266 °C. H NMR
(δ, DMSO-d6): 3.89 (3H, s), 7.30-8.1 (4H, m), 8.05 (1H, d),
8.15 (1H, d), 8.60 (1H, s). Anal. Calcd for C14H11N5 (249): C,
67.46; H, 4.45; N, 28.09. Found: C, 67.52; H, 4.40; N, 28.08.
3-Tetr a zolyl-9-p h en ylca r ba zole. The title compound was
synthesized and purified by the same procedure as 3-tetrazolyl-
9-methylcarbazole.
Yield: 3.45 g (4.80 mmol, 60%). Mp: 91-93 °C. 1H NMR
(δ, CDCl3): 1.25-1.89 (18H, m), 1.98 (3H, s), 4.05 (2H, t), 4.20
(2H, t), 5.56 (1H, s), 6.11(1H, s), 6.97 (2H, d), 7.10-7.40 (12H,
m), 7.56 (2H, d), 7.72 (2H, d), 7.95 (2H, d), 8.16 (2H, d). Anal.
Calcd for
C47H49N3O4 (720): C, 78.41; H, 6.86; N, 5.84.
Yield: 5.56 g (12.6 mmol, 84%). Mp: 155-157 °C. 1H NMR
(δ, DMSO-d6): 7.30-8.2 (10H, m), 8.09 (1H, d), 8.33 (1H, d),
8.94 (1H, s). Anal. Calcd for C19H13N5 (311): C, 73.30; H, 4.21;
N, 22.49. Found: C, 73.14; H, 4.31; N, 22.55.
Found: C, 78.60; H, 6.66; N, 6.00.
2-{4′-(6-Meth a cr yloyloxy-1-h exyloxy)bip h en yl-4-yl}-5-
(3-N-p h en ylca r b a zoyl)-1,3,4-oxa d ia zole (M6-OXD-P Cz).
The title compound was prepared by the same procedure as
M6-OXD-PA.
(4-Tetr a zolylp h en yl)d ip h en yla m in e.9,10 4-Tetrazolyltri-
phenylamine was prepared and purified as reported previ-
ously.
Yield: 2.85 g (4.40 mmol, 55%). Mp: 118-120 °C. 1H NMR
(δ, CDCl3): 1.45-1.89 (8H, m), 1.96 (3H, s), 3.90 (3H, s), 4.04
(2H, t), 4.18 (2H, t), 5.55 (1H, s), 6.11(1H, s), 6.99 (2H, d), 7.33-
7.75 (8H, m), 8.25 (4H, m), 8.89 (1H, s). Anal. Calcd for
Mon om er . 2-{4′-(6-Meth a cr yloyloxy-1-h exyloxy)bip h e-
n yl-4-yl}-5-(4-N,N-d im et h yla m in op h en yl)-1,3,4-oxa d ia -
zole (M6-OXD-MA).10 4′-(6-Methacryloyloxy-1-hexyloxy)bi-
phenyl-4-carboxylic acid (3.00 g, 7.85 mmol) was added to
thionyl chloride (30 mL) and stirred on heating at 60 °C for 2
h. Excess thionyl chloride was removed by evaporation under
reduced pressure, and then the residue was reacted with
4-dimethylaminobenzotetrazole (2.30 g, 12 mmol) in dry py-
ridine (40 mL) at 135 °C. The cooled solution was poured into
water, and the crude product was extracted with dichlo-
romethane and washed with water three times. The product
C
42H37N3O4 (648): C, 77.88; H, 5.76; N, 6.49. Found: C, 77.70;
H, 5.90; N, 6.32.
2-{4′-(6-Meth a cr yloyloxy-1-h exyloxy)bip h en yl-4-yl}-5-
(3-N-m eth ylca r ba zoyl)-1,3,4-oxa d ia zole (M6-OXD-MCz).
The title compound was prepared by the same procedure as
M6-OXD-PA.
Yield: 2.91 g (4.96 mmol, 62%). Mp: 140-142 °C. 1H NMR
(δ, CDCl3): 1.45-1.89 (8H, m), 1.96 (3H, s), 4.03 (2H, t), 4.18
(2H, t), 5.55 (1H, s), 6.11(1H, s), 6.98 (2H, d), 7.30-7.75 (13H,

3460 Mochizuki et al.
Macromolecules, Vol. 36, No. 10, 2003
F igu r e 1. Chemical structures of monomers synthesized in
this work.
m), 8.21 (4H, m), 8.91 (1H, s). Anal. Calcd for C37H35N3O4
(586): C, 75.88; H, 6.02; N, 7.17. Found: C, 75.80; H, 6.00; N,
7.12.
P olym er iza tion . A solution of monomer (1.00 g) and 2,2′-
azobis(isobutyronitrile) (1 mol % of monomer) in dry DMF (5
mL) or dry THF (5 mL) was degassed by three freeze-pump-
thaw cycles and then sealed off. The mixture was stirred and
heated in a sealed tube at 80 °C for 10 h. The cooled solution
was poured into 500 mL of hexane with stirring to precipitate
the polymer. The polymer obtained was purified by reprecipi-
tation from dichloromethane into hexane three times and dried
under vacuum for 48 h.
F igu r e 2. Chemical structures of a new class of polymers
prepared in this work.
Yield: (PM2-OXD-MA, 0.45 g, 45%; PM6-OXD-MA, 0.55 g,
55%; PM11-OXD-MA, 0.57 g, 57%; PM6-OXD-PA, 0.61 g, 61%;
PM11-OXD-PA, 0.63 g, 63%; PM6-OXD-MCz, 0.38 g, 38%;
PM6-OXD-PCz, 0.60 g, 60%).
2.3. LC P h a se Beh a vior . LC behavior and phase transition
behavior of the prepared polymers were examined on
a
polarizing microscope (Olympus model BH-SP) equipped with
a hot stage (Mettler EP-82) and by X-ray diffractometry (MAC
Science MXP with a thermal controller, model 5301). Ther-
modynamic properties and Tg were determined with a dif-
ferential scanning calorimeter (DSC: Seiko I&E SSC 5000)
at a heating rate of 10 °C/min. At least four scans were
performed for each sample to check reproducibility.
Order parameters (S) were evaluated from the polarized
absorption spectra recorded with a UV spectrometer with the
aid of a polarizer. Aligned samples for polarized absorption
spectroscopy were prepared by annealing the polymers above
Tg on a glass plate whose surface was coated with polyimide
(PI: 50 nm). The PI surface was mechanically rubbed prior to
the spin-coating of polymers on the glass substrate.
2.4. Op tica l P r op er ties. Absorption spectra were mea-
sured with a J asco V-550 spectrometer and a Shimadzu UV-
200 spectrometer. Photoluminescence spectra were taken with
a Hitachi F-4000 fluorescence spectrometer. Fluorescent quan-
tum yields (Φf) were evaluated spectroscopically using quinine
sulfate as a standard at room temperature.
F igu r e 3. (a) DSC heating thermogram (10 °C/min) of PM6-
OXD-MA. (b) X-ray diffraction pattern of PM11-OXD-MA at
150 °C in the SmA phase.
The number-average molecular weights (Mn) were
determined by GPC using polystyrenes as standards.
The Mn and the molecular weight distribution (Mw/Mn)
of each polymer were described as follows. Mn and Mw/
Mn: PM2-OXD-MA, 20,000, 1.3; PM6-OXD-MA, 12,000,
1.6; PM11-OXD-MA, 13,000, 1.7; PM6-OXD-PA, 31,000,
1.2; PM11-OXD-PA, 32,000, 1.3; PM6-OXD-PCz, 20,000,
1.4; PM6-OXD-MCz, 9,800, 1.7.
3.1. LC P h a se Beh a vior . In the present work, each
polymer was characterized by its LC phase behavior.
Figure 3 indicates a DSC thermogram of PM6-OXD-MA
on heating. Tg was observed at around 97 °C, and then
an endothermic peak due to an LC-isotropic (I) phase
transition appeared at around 211 °C. These results
indicate that PM6-OXD-MA exhibits a typical DSC
curve of a polymer LC showing an LC phase ranging
wider than 100 °C.
3. Resu lts a n d Discu ssion
Figures 1 and 2 show the chemical structures of the
monomers and the polymers synthesized in this study.
Four kinds of polymers containing an oxadiazole and
various arylamine moieties were prepared: poly[2-{4′-
(m-methacryloyloxy-1-alkyloxy)biphenyl-4-yl}-5-(4-N,N-
dimethylaminophenyl)-1,3,4-oxadiazole] is abbreviated
as PMm-OXD-MA (m is alkyl spacer length); similarly,
poly[2-{4′-(m′-methacryloyloxy-1-alkyloxy)biphenyl-4-
yl}-5-(4-N,N-diphenylaminophenyl)-1,3,4-oxadiazole] as
PMm′-OXD-PA, and poly[2-{4′-(6-methacryloyloxy-1-
hexyloxy)biphenyl-4-yl}-5-(3-N-phenylcarbazoyl)-1,3,4-
oxadiazole] as PM6-OXD-PCz, and poly[2-{4′-(6-meth-
acryloyloxy-1-hexyloxy)biphenyl-4-yl}-5-(3-N-methyl-
carbazoyl)-1,3,4-oxadiazole] as PM6-OXD-MCz.

Macromolecules, Vol. 36, No. 10, 2003
Photo- and Electroactive Polymers 3461
F igu r e 5. Polarized absorption spectra of PM6-OXD-MA at
23 °C.
F igu r e 4. LC behavior of the oxadiazole polymers prepared
in this study.
Ta ble 1. Dich r oic Ra tios (R) a n d Or d er P a r a m eter s (S) of
Figure 4 summarizes the results of evaluation of LC
phase behavior. In PMm-OXD-MA, the LC phase be-
havior was significantly affected by the alkyl spacer
length (m). Namely, PM2-OXD-MA with m ) 2 did not
show any LC phase (showed only Tg at 143 °C), while
PM6-OXD-MA exhibited a nematic (N) phase (G 97 N
211 I), and PM11-OXD-MA showed a smectic A (SmA)
phase (G 77 SmA 205 I). We have performed a definition
of LC phase by observation of a polarizing microscope
and an X-ray scattering. PM6-OXD-MA showed a Schlier-
en texture at 150 °C, suggesting that it shows a N phase.
On the other hand, in measurement of the X-ray
scattering for PM11-OXD-MA at 150 °C, a narrow single
peak at around 2θ ) 2.5 ° and a diffuse halo in a wide
angle region were observed, meaning a layer structure
(Figure 3b). This result indicates that PM11-OXD-MA
shows an SmA phase. It can be seen that PMm-OXD-
MA showed more highly ordered and wider LC phases
as the m increased. In addition, Tg’s of PMm-OXD-MA
were affected by the alkyl spacer length. Tg of PM6-
OXD-MA was 97 °C and lower by 46 °C than that of
PM2-OXD-MA. Furthermore, Tg of PM11-OXD-MA at
77 °C was lower by 20 °C than that of PM6-OXD-MA.
A large drop in Tg of the polymers on increase of the
spacer length is commonly observed, and this phenom-
enon is interpreted as a result of plasticization by the
side-chain alkyl moietiy. On the other hand, in PMm′-
OXD-PA containing triphenylamine as an end group in
the side chain, PM6-OXD-PA and PM11-OXD-PA did
not exhibit any LC phase regardless of the value of m‘:
PM6-OXD-PA and PM11-OXD-PA showed only Tg at
124 and 95 °C, respectively. It seems that steric
hindrance between two clusters of benzene rings in the
end group of PMm′-OXD-PA may prevent the formation
of an LC phase. Furthermore, PM6-OXD-PCz also did
not exhibit any LC phase; it showed only Tg at 132 °C.
These results indicate that the occupied volume of the
end group in the side chain is an important factor to
show the LC phases. In contrast, it is interesting to note
that PM6-OXD-MCz possessing a bent-shaped structure
shows an N phase (G 119 N 202 I).
th e Oxa d ia zole P olym er s Syn th esized in Th is Stu d y
polymer
R
S
PM6-OXD-MA
PM11-OXD-MA
PM6-OXD-MCz
2.84
3.40
3.10
0.38
0.44
0.41
Table 1. With this geometry of the molecular long axis
and the transition moments, S can be calculated by the
equation S ) (R - 1)/(R + 2), where R is the dichroic
ratio, defined by R ) A|/A . S values of PM6-OXD-MA,
PM11-OXD-MA and PM6-OXD-MCz were 0.38, 0.44 and
0.41, respectively. It was found that S of PM11-OXD-
MA showing an SmA phase was higher than that of
PM6-OXD-MA exhibiting an N phase.
3.2. Op tica l P r op er ties. Figure 6 shows absorption
spectra of the polymers in dichloromethane (10-5 M):
the extinction coefficients of the entire polymers were
40 000-45 000. Optical properties are very important
to evaluate basic characteristics like an energy band-
gap of a compound for EL devices.11-13
PM2-OXD-MA, PM6-OXD-MA, and PM11-OXD-MA
showed absorption maxima at around 345 and 280 nm.
PM6-OXD-MA exhibited the same spectrum as PM11-
OXD-MA regardless of the alkyl spacer length. Simi-
larly, the absorption spectrum of PM6-OXD-PA was the
same as that of PM11-OXD-PA showing absorption
maxima at around 366 and 345 nm. On the other hand,
PM6-OXD-PCz and PM6-OXD-MCz containing a car-
bazole moiety as the end group revealed absorption
peaks at around 336 nm, shifted to a shorter wavelength
region than that of PM6-OXD-MA and PM6-OXD-PA.
Figure 7 displays fluorescence spectra of the polymers
in dichloromethane (10-6 M). It was found that all the
polymers emitted strong blue fluorescence. In PMm-
OXD-MA, the fluorescence spectrum of PM6-OXD-MA
(λex ) 345 nm) was the same as that of PM11-OXD-MA
(λex ) 345 nm) with a peak at around 455 nm. However,
PM2-OXD-MA showed a fluorescence maximum at
around 460 nm (λex ) 345 nm), shifting by 5 nm to
longer wavelength than that of PM6-OXD-MA.
The polymers showing LC phases, namely, PM6-OXD-
MA, PM11-OXD-MA and PM6-OXD-MCz, were evalu-
ated on the molecular alignment. Figure 5 shows
polarized absorption spectra of PM6-OXD-MA below Tg.
The absorbance parallel to the rubbing direction was
much higher than that perpendicular to the rubbing
direction. This means that the mesogens of PM6-OXD-
MA are aligned parallel to the rubbing direction. S
values of the polymers, which were evaluated by the
polarized absorption spectroscopy, are summarized in
With respect to PMm′-OXD-PA, PM6-OXD-PA showed
a fluorescence peak at around 450 nm and the same
spectrum as that of PM11-OXD-PA.
On the other hand, PM6-OXD-MCz and PM6-OXD-
PCz, which contained carbazole moieties as an end
group in the side chain, showed fluorescence peaks at
shorter wavelength than that of PM6-OXD-MA and
PM6-OXD-PA. This means that introduction of the
carbazole moiety into the side chain affects optical
properties, namely, shifts the absorption and fluores-

3462 Mochizuki et al.
Macromolecules, Vol. 36, No. 10, 2003
F igu r e 7. Fluorescence spectra of the prepared oxadiazole
polymers in dichloromethane.
F igu r e 6. Absorption spectra of the prepared oxadiazole
polymers in dichloromethane.
Ta ble 2. P h otolu m in escen t Qu a n tu m Yield s of th e
P olym er s in Dich lor om eth a n e
cence peaks to the shorter wavelength. We presumed
that the incorporation of carbazole moieties into the side
chain leads to the extended π-conjugation, which causes
red shifts of the absorption and fluorescence peaks. If
π-conjugation were extended by introduction of the
carbazole moiety, absorption and fluorescence maxima
of both PM6-OXD-PCz and PM6-OXD-MCz would shift
to longer wavelength even in solution. However, PM6-
OXD-PCz and PM6-OXD-MCz actually showed absorp-
tion and fluorescence with a peak shifted to a shorter
wavelength region than our expectation. As the carba-
zole derivatives is assumed to aggregated in solution,
at present, a detailed reason for the blue shift in
photophysics of the derivatives is under investigation
but not clear.
3.3. Qu a n tu m Yield of F lu or escen ce of th e P oly-
m er . Φf is a very important factor to evaluate a
characteristic of compounds for an EL device.14 The
results of Φf measurements of PM6-OXD-MA, PM6-
OXD-PA, PM6-OXD-PCz, and PM6-OXD-MCz are shown
in Table 2. It was found that all the samples exhibited
high yields (over 0.6). Especially, PM6-OXD-PA showed
the highest Φf value (0.82), and the Φf value of PM6-
OXD-MCz showing an LC phase was 0.72.
polymer
Φfa
λex (nm)b
liquid crystalc
PM6-OXD-MA
PM6-OXD-PA
PM6-OXD-PCz
PM6-OXD-MCz
0.60
0.82
0.73
0.72
345
364
336
336
O
O
Quantum yields. b Excitation wavelength. c Open circle: showed
an LC phase.
a
on a glass substrate whose surface was coated with
mechanically rubbed polyimide films. The homoge-
neously aligned films were obtained after annealing in
the N phase at 145 °C for 2 h.
Figure 8 shows polarized fluorescence spectra of an
aligned film of PM6-OXD-MCz. In this case, the excita-
tion wavelength was 336 nm with unpolarized light. It
was found that the intensity of fluorescence polarized
parallel to the rubbing direction was much higher than
that polarized perpendicular to the rubbing direction.
A dichroic ratio (I|/I ) was estimated as 3.5 at 430 nm.
3.5. EL Em ission of P M6-OXD-P A. A one-layer type
EL device using PM6-OXD-PA, which showed the high-
est quantum yield, was fabricated. The structure of the
EL device is shown in Figure 9. A patterned ITO-coated
glass substrate was used as a transparent anode. On
the ITO anode, PM6-OXD-PA film was spin-coated from
3.4. P ola r ized F lu or escen ce. Aligned films of PM6-
OXD-MCz were prepared by spin-coating from solution

Macromolecules, Vol. 36, No. 10, 2003
Photo- and Electroactive Polymers 3463
F igu r e 8. Polarized fluorescence spectra of PM6-OXD-MCz.
I|, fluorescence polarized parallel to the rubbing direction; I ,
fluorescence polarized perpendicular to the rubbing direction.
F igu r e 10. Current density-voltage characteristic of the EL
device consisting of PM6-OXD-PA (a) and luminance-voltage
characteristic of the EL device (b).
a maximum current density of 43 mA/cm2 was obtained
at 28 V.
In Figure 10b, luminance-voltage characteristic of
the EL device is shown. The EL device had a turn-on
voltage of luminance at 10 V as well as the current
density. Compared with other EL polymers with an
active moiety in a side chain,15 a single layered EL
devices consisting of PM6-OXD-PA showed a lower turn
on voltage. The luminance intensity increased with
increasing the applied voltage and a maximum lumi-
nance of 30 cd/m2 was obtained at 27 V.
F igu r e 9. Configuration of EL devices using PM6-OXD-PA
(a) and photoluminescence and electroluminescence spectra of
PM6-OXD-PA (b).
a 1 wt % dichloromethane solution, and the polymer film
was dried and annealed at 140 °C for 1 h. The thickness
of the polymer film was 100 nm. Furthermore, a
magnesium/silver (10/1) alloy cathode, 100 nm in thick-
ness, was directly deposited on top of the polymer film
under vacuum (6 × 10-6 Pa). The emitting area of the
EL devices was 2 × 2 mm2.
4. Con clu sion
A novel class of functional polymers were designed
and synthesized. Among the materials, the polymers
containing a dimethylamine moiety as an end group in
the side chain and the polymer introducing a carbazole
unit as an end group in the side chain showed LC
phases: PM6-OXD-MA and PM11-OXD-MA showed an
N phase and an SmA phase, respectively, and PM6-
OXD-MCz exhibited an N phase. All the polymers
emitted strong blue fluorescence and exhibited high
quantum yields (over 0.6). In addition, PM6-OXD-MCz
showed the fluorescence anisotropy, and the one-layer
type EL device using PM6-OXD-PA, which exhibited the
highest quantum yield of fluorescence, emitted EL
emission at a blue region. These compounds, therefore,
are potential for multifunctional LC materials for many
elecroactive devices.
Figure 9 compares the EL spectrum from the EL
device with the photoluminescence spectrum of the film
of PM6-OXD-PA. In the EL device, the bright blue EL
emission was observed. The EL peak was found to be
located at 453 nm, which corresponded well to the
photoluminescence peak. The shape of the EL spectrum
was almost the same as that of the photoluminescence
spectrum, except for a small difference at the longer
wavelength region. It is clear that charge recombination
and emission occur on the chromophore of PM6-OXD-
PA.
The current density-voltage relationship in the EL
devices is shown in Figure 10 a. The EL device had a
turn-on voltage of the current density at 10 V. The
current density increased with the applied voltage and
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