New series of blue-emitting and electron-transporting copolymers based on fluorene

Article abstract of DOI:10.1021/ma011593g

A novel series of conjugated copolymers having oxadiazole, quinoline, quinoxaline, and phenylenecyanovinylene moieties in the main chain based on fluorene were synthesized in good yields by palladium-catalyzed Suzuki coupling reaction, a new approach different from the traditional polyhydrazide precursor route (oxadiazole-containing polymers), acid-catalyzed Friedlaender condensation reaction (polyquinolines), and Knoevenagel condensation polymerization (poly(phenylenecyanovinylene)). The thermal, electrochemical, and optical properties of these copolymers were examined. All these polymers possess excellent thermal stability with glass transition temperatures of 114-208 °C and onset decomposition temperatures of 387-415 °C. Cyclic voltammetry studies reveal that these copolymers possess low-lying LUMO energy levels ranging from -3.01 to -3.37 eV and low-lying HOMO energy levels ranging from -6.13 to -6.38 eV and may be promising candidates for electron-transporting or hole-blocking materials in light-emitting diodes. The polymers in thin films emit strong blue luminance around 414-476 nm with narrow bandwidth upon photoexcitation. Photoluminescence spectra of the polymers in the films are only red-shifted by 7-11 nm compared to those in the solution, indicating that the aggregation and the excimer fluorescence are suppressed.

Full text of DOI:10.1021/ma011593g

Macromolecules 2002, 35, 2529-2537
2529
New Series of Blue-Emitting and Electron-Transporting Copolymers
Based on Fluorene
Xia ow ei Zh a n , Yu n qi Liu ,* Xia Wu , Sh u a i Wa n g, a n d Da oben Zh u *
Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100080, China
Received September 10, 2001; Revised Manuscript Received December 19, 2001
ABSTRACT: A novel series of conjugated copolymers having oxadiazole, quinoline, quinoxaline, and
phenylenecyanovinylene moieties in the main chain based on fluorene were synthesized in good yields
by palladium-catalyzed Suzuki coupling reaction, a new approach different from the traditional
polyhydrazide precursor route (oxadiazole-containing polymers), acid-catalyzed Friedla¨nder condensation
reaction (polyquinolines), and Knoevenagel condensation polymerization (poly(phenylenecyanovinylene)).
The thermal, electrochemical, and optical properties of these copolymers were examined. All these polymers
possess excellent thermal stability with glass transition temperatures of 114-208 °C and onset
decomposition temperatures of 387-415 °C. Cyclic voltammetry studies reveal that these copolymers
possess low-lying LUMO energy levels ranging from -3.01 to -3.37 eV and low-lying HOMO energy
levels ranging from -6.13 to -6.38 eV and may be promising candidates for electron-transporting or
hole-blocking materials in light-emitting diodes. The polymers in thin films emit strong blue luminance
around 414-476 nm with narrow bandwidth upon photoexcitation. Photoluminescence spectra of the
polymers in the films are only red-shifted by 7-11 nm compared to those in the solution, indicating that
the aggregation and the excimer fluorescence are suppressed.
In tr od u ction
ing the steric interactions in the polymer backbone.10
As a result, homopolymers and copolymers of fluorene
have emerged as the most attractive blue-emitting
materials due to their high efficiency and good thermal
stability.11-13 To our knowledge, electron-transporting
polymers based on fluorene are still rare.14 No effort has
been devoted to synthesis of fluorene-based conjugated
electron-transporting electroluminescent polymers con-
taining oxadiazole, quinoxaline, and phenylenecyanovi-
nylene.
In this work, we describe the synthesis of a novel
series of electron-deficient oxadiazole-, quinoline-, qui-
noxaline-, and phenylenecyanovinylene-containing con-
jugated copolymers based on fluorene in hope of com-
bining both excellent electron-affinitive properties of the
formers and blue light-emitting and high quantum
efficiency of the latter into a polymer. Moreover, we
introduced sterically hindered substituents into fluorene
moiety to enhance processability and amorphicity of
polymers. These copolymers possess good solubility,
excellent thermal stability, low-lying LUMO energy
levels, and blue-emitting properties.
Since the discovery of an electroluminescent (EL)
polymer in 1990, EL conjugated polymers have attracted
much interest in recent years because of potential
application in large-area flat panel displays.1 It is
established that high quantum efficiency EL devices can
be obtained by achieving both efficient charge injection
and balanced mobility of both charge carriers inside the
EL materials. In general, most of the EL polymers inject
and transport holes more efficiently than electrons due
to their inherent richness of π-electrons. Thus, synthesis
of novel efficient electron transport (ET) polymers is
needed to improve device performance. Polyquinolines
and polyquinoxalines have recently been demonstrated
as ET layers in light-emitting diodes (LEDs) due to their
high thermal and oxidative stability, outstanding me-
chanical property, and good film-forming ability.2,3
However, polyquinolines and polyquinoxalines possess
poor solution processability.
2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiaz-
ole (PBD) is one of the most widely used electron
injection/transport or hole-blocking materials.4 Its func-
tion is believed to result from the high electron affinity
of the oxadiazole ring in the molecule. Several oxadia-
zole-containing polymers have been synthesized as
electron-transporting materials;5 oxadiazole-containing
light-emitting polymers have also been prepared in
recent years.6-8 Poly(p-phenylenecyanovinylene) (CN-
PPV) and its derivatives are well-known electron-
transporting electroluminescent polymers.9
Exp er im en ta l Section
Ma ter ia ls. 3,3-Diaminobenzidine (Acros), phenylacetylene
(Fluka), 1,4-diacetylbenzene (Acros), ethyl 4-bromobenzoate
(Acros), dimethyl terephthalate (Acros), 4-bromophenylaceto-
nitrile (Acros), and 4-bromobenzaldehyde (Acros) were used
as received without further purification. 2,7-Dibromo-9,9-bis-
(2-ethylhexyl)fluorene,15 2-amino-5-bromobenzophenone,16 tet-
rakis(triphenylphosphine)palladium(0),17 and bis(triphenylphos-
phine)palladium dichloride17 were synthesized by literature
methods. Toluene was freshly distilled from sodium benzo-
phenone ketyl under nitrogen prior to use. Triethylamine was
dried over CaH2 and distilled under a N2 atmosphere prior to
use. m-Cresol was purified by distillation under reduced
pressure.
Fluorene derivatives show interesting and unique
chemical and physical properties because they contain
a rigid planar biphenyl unit, and the facile substitution
at the remote C9 position can improve the solubility and
processability of polymers without significantly increas-
Mon om er Syn th esis. 9,9-Bis(2-ethylhexyl)fluorene-2,7-bis-
(trimethylene boronate) was synthesized according to our
previous literature.15 The synthesis of other monomers is
shown in Scheme 1.
* To whom correspondence should be addressed. E-mail: liuyq@
infoc3.icas.ac.cn.
10.1021/ma011593g CCC: $22.00 © 2002 American Chemical Society
Published on Web 02/16/2002

2530 Zhan et al.
Macromolecules, Vol. 35, No. 7, 2002
Sch em e 1. Syn th etic Rou te to th e Mon om er s
2,7-Bis(ph en yleth yn yl)-9,9-bis(2-eth ylh exyl)flu or en e (2).
To a solution of 2,7-dibromo-9,9-bis(2-ethylhexyl)fluorene (1)
(2.2 g, 4 mmol) in dry triethylamine (30 mL) was added
phenylacetylene (1.1 mL, 10 mmol). After the solution was
degassed with nitrogen for 30 min while stirring, Pd(PPh3)2-
Cl2 (70 mg, 0.10 mmol) and CuI (38.0 mg, 0.20 mmol) were
added. The reaction mixture was then refluxed under nitrogen
for 24 h. After the reaction was complete, the crude mixture
was filtered at room temperature to remove triethylammonium
bromide precipitate. The precipitate was rinsed with diethyl
ether, and the combined filtrates were evaporated to dryness.
The residue was purified by flash column chromatography
(silica gel, 20% ethyl acetate in petroleum ether) to give
compound 2 (2.1 g, 87%) as an orange oil. Anal. Calcd for
C
45H50: C, 91.47; H, 8.53. Found: C, 91.05; H, 8.68%. 1H NMR
(300 MHz, CDCl3): δ 7.69 (d, 2H), 7.58 (m, 8H), 7.38 (m, 2H),
7.28 (d, 2H), 7.20 (d, 2H), 2.05 (d, 4H), 1.32 (s, 2H), 0.94-0.75
(m, 22H), 0.59 (t, 6H). MS (EI) 590.89 (calcd for C45H50), 590
(found). FT-IR (Nujol mulls): ν 2958, 2926, 2857, 1597, 1493,
1462, 1378, 822, 755, 690 cm-1
.
2,7-Bis(p h e n yloxoa ce t yl)-9,9-b is(2-e t h ylh e xyl)flu o-
r en e (3). To a solution of 2 (2.4 g, 4 mmol) in 20 mL of
dichloromethane was added 200 mg of tetrabutylammonium
bromide, 40 mL of water, 0.8 g of NaHCO3, and 4.0 g of
KMnO4. After vigorous stirring at room temperature for 48 h,
sodium bisulfite (6 g) and hydrochloric acid (3.0 mL) were

Macromolecules, Vol. 35, No. 7, 2002
Copolymers Based on Fluorene 2531
slowly added to reduce excess oxidizing agents. The mixture
was extracted with CH2Cl2 and washed with water, and the
organic layer was dried over magnesium sulfate. The solvent
was evaporated to afford a yellow viscous oil (2.6 g, 97%). Anal.
Calcd for C45H50O4: C, 82.53; H, 7.70. Found: C, 82.08; H,
(50 mg) in ethanol (30 mL) under a nitrogen atmosphere. The
reaction mixture was stirred at room temperature for 1 h. The
product was obtained as a precipitate, was filtered, and was
washed with water to give a yellow powder (3.30 g, 91%). Anal.
Calcd for C15H9Br2N: C, 49.63; H, 2.50; N, 3.86. Found: C,
1
1
7.68%. H NMR (300 MHz, CDCl3): δ 8.06 (m, 4H), 7.92 (m,
49.64; H, 2.54; N, 3.80%. H NMR (300 MHz, CDCl3): δ 7.77
2H), 7.82 (m, 2H), 7.57 (m, 4H), 7.47-7.38 (m, 4H), 1.98 (d,
4H), 1.18 (s, 2H), 0.81-0.57 (m, 22H), 0.36 (t, 6H). 13C NMR
(50 MHz, CDCl3): δ 194.4, 152.5, 145.7, 134.8, 133.6, 132.9,
132.2, 130.0, 129.7, 129.4, 128.9, 128.3, 125.3, 121.3, 55.6, 43.7,
34.6, 33.7, 27.9, 26.9, 22.5, 13.8, 10.1. MS (FAB) 654.89 (calcd
for C45H50O4), 654 (found). FT-IR (Nujol mulls): ν 2959, 2928,
2872, 2858, 1671, 1601, 1579, 1452, 1319, 1206, 1162, 889, 750,
(d, 2H), 7.62-7.52 (m, 6H), 7.45 (s, 1H). 13C NMR (50 MHz,
CDCl3): δ 140.9, 132.8, 132.2, 130.5, 127.3, 125.1, 123.6, 117.2,
111.0. MS (EI) 363.05 (calcd for C15H9Br2N), 363 (found).
P olym er Syn th esis. The two synthetic routes to copoly-
mers are illustrated in Scheme 2. The quinoxaline-containing
copolymer (P F Qx) was prepared by a condensation reaction
between 2,7-bis(phenyloxoacetyl)-9,9-bis(2-ethylhexyl)fluorene
and 3,3-diaminobenzidine in m-cresol. Other polymers were
synthesized through a palladium-catalyzed Suzuki coupling
reaction between diboronate and dibromide in toluene.
P oly{[9,9-bis(2-eth ylh exyl)flu or en e-2,7-d iyl]-a lt-[6,6′-
bis(3-p h en ylqu in oxa lin e)-2,2′-d iyl]} (P F Qx). Equimolar
amounts of monomer 3 (654 mg, 1.0 mmol) and 3,3-diami-
nobenzidine (18) (214 mg, 1.0 mmol) were dissolved in 4 mL
of freshly distilled m-cresol in a 50 mL three-necked flask. The
reaction mixture was stirred under nitrogen purge at 100 °C
for 48 h during which progressive increase of the solution
viscosity was observed. After cooling to room temperature, the
reaction mixture was poured into 100 mL of methanol to give
a precipitate. The obtained solid was redissolved in m-cresol
and reprecipitated from methanol, followed by Soxhlet extrac-
tion with ethanol for 24 h to give a pale yellow powder (600
mg, 75%). Anal. Calcd for (C57H56N4)n: C, 85.89; H, 7.08.
Found: C, 85.35; H, 7.18%. 1H NMR (300 MHz, CDCl3): δ 8.72
(m, 2H), 8.41 (m, 4H), 7.87 (m, 2H), 7.64 (m, 6H), 7.41 (m,
8H), 2.00 (d, 4H), 1.26 (s, 2H), 1.02-0.62 (m, 28H). 13C NMR
(50 MHz, CDCl3): δ 154.2, 154.0, 153.6, 151.6, 141.6, 141.1,
140.7, 139.4, 137.8, 129.8, 129.3, 129.2, 128.9, 128.4, 127.5,
127.3, 125.7, 119.6, 55.0, 44.5, 34.9, 33.7, 28.2, 26.9, 22.9, 14.1,
10.5. FT-IR (KBr): ν 3060, 2957, 2925, 2856, 1733, 1613, 1537,
1463, 1383, 1342, 1261, 1193, 1059, 1029, 827, 805, 769, 697
715, 689, 649 cm-1
.
2,2′-(p-P h en ylen e)bis(6-br om o-4-p h en ylqu in olin e) (6).
Under nitrogen atmosphere, 2-amino-5-bromobenzophenone
(4) (5.52 g, 20 mmol), 1,4-diacetylbenzene (5) (1.62 g, 10 mmol),
sulfuric acid (0.1 mL), and acetic acid (10 mL) were placed in
a three-necked flask and refluxed for 18 h. After cooling, the
mixture was slowly added to a stirred mixture of crushed ice
(40 g) and 25% ammonia solution in water (15 mL) to give a
precipitate. The obtained solid was washed with hot water,
ethanol, and chloroform to afford a white solid (5.33 g, 83%);
mp >300 °C. Anal. Calcd for C36H22Br2N2: C, 67.31; H, 3.45;
N, 4.36. Found: C, 67.09; H, 3.53; N, 4.22%. 1H NMR (300
MHz, CF3COOD): δ 8.56 (s, 2H), 8.42 (d, 4H), 8.35 (m, 6H),
7.76 (m, 10H). 13C NMR (50 MHz, CF3COOD): δ 152.1, 139.8,
137.7, 135.1, 134.1, 131.9, 130.2, 129.6, 129.2, 128.1, 126.1,
122.2, 121.9. MS (FAB) 642.39 (calcd for C36H22Br2N2), 642
(found).
4-Br om oben zoic Hyd r a zid e (8). To a solution of ethyl
4-bromobenzoate (7) (5.7 g, 25 mmol) in 25 mL of methanol
was added hydrazine monohydrate (4.7 mL, 75 mmol), and
then the mixture was refluxed for 16 h under a nitrogen
atmosphere. After the reaction was complete, water was
poured into the mixture and extracted with ethyl acetate. The
solvent was evaporated to give white needlelike crystals (5.1
g, 95%); mp 166-167 °C. Anal. Calcd for C7H7BrN2O: C, 39.10;
H, 3.28; N, 13.03. Found: C, 39.23; H, 3.27; N, 13.12%. 1H
NMR (300 MHz, DMSO-d6): δ 9.88 (s, 1H), 7.79 (d, 2H), 7.68
(d, 2H), 4.54 (s, 2H).
cm-1
.
P oly{[9,9-bis(2-eth ylh exyl)flu or en e-2,7-d iyl]-a lt-[2,2′-
(p -p h en ylen e)b is(4-p h en ylq u in olin e)-6,6′-d iyl]} (P F Q).
Under a nitrogen atmosphere, 9,9-bis(2-ethylhexyl)fluorene-
2,7-bis(trimethylene boronate) (19) (280 mg, 0.5 mmol), 6 (320
mg, 0.5 mmol), Pd(PPh3)4 (6.0 mg, 0.005 mmol), toluene (5 mL),
and 2 M K2CO3 (5 mL) were placed in a three-necked flask
and refluxed for 72 h. After cooling, the mixture was diluted
with CHCl3 (20 mL) and washed with water, and the organic
layer was dried over magnesium sulfate. The solvent was
evaporated to 2 mL and then poured into methanol to give a
precipitate. The obtained solid was redissolved in CHCl3 and
reprecipitated from methanol, followed by Soxhlet extraction
with the same solution for 24 h to give a pale yellow powder
(426 mg, 98%). Anal. Calcd for (C65H62N2)n: C, 89.61; H, 7.17.
Found: C, 89.29; H, 7.23%. 1H NMR (300 MHz, CDCl3): δ 8.43
(d, 4H), 8.05 (m, 4H), 7.91 (s, 2H), 7.68 (m, 2H), 7.59-7.36
(m, 16H), 2.12 (d, 4H), 1.15 (s, 2H), 0.70-0.36 (m, 28H). 13C
NMR (50 MHz, CDCl3): δ 155.7, 151.5, 140.5, 140.0, 138.9,
138.2, 130.1, 129.6, 128.8, 128.2, 126.5, 126.4, 126.2, 123.2,
120.1, 119.9, 55.2, 44.4, 34.5, 33.8, 28.0, 27.0, 22.6, 13.9, 10.3.
FT-IR (KBr): 2957, 2924, 2855, 1588, 1546, 1470, 1383, 1354,
Bis(4-br om op h en yl)h yd r a zin e (9). Equimolar amounts
of 8 (2.15 g, 10 mmol) and 4-bromobenzoic chloride (2.19 g, 10
mmol) were dissolved in 50 mL of pyridine. The reaction
mixture was refluxed for 6 h under a nitrogen atmosphere.
After cooling to room temperature, the mixture was poured
into 200 mL of ethanol and was frozen to afford white plate
crystals (3.2 g, 80%); mp 319-320 °C. Anal. Calcd for C14H10
-
Br2N2O2: C, 42.24; H, 2.53; N, 7.04. Found: C, 42.01; H, 2.57;
N, 7.12%. 1H NMR (300 MHz, DMSO-d6): δ 10.63 (s, 2H), 7.85
(d, 4H), 7.77 (d, 4H).
2,5-Bis(4-br om op h en yl)-1,3,4-oxa d ia zole (10). A solution
of 9 (4.0 g, 10 mmol) in SOCl2 (10 mL) was refluxed for 5 h
under nitrogen atmosphere. Excess SOCl2 was distilled off, and
then the residue was slowly poured into 50 mL of water to
give a precipitate. The crude produce was purified by sublima-
tion to yield white crystals (2.7 g, 71%); mp 258 °C. Anal. Calcd
for C14H8Br2N2O: C, 44.25; H, 2.12; N, 7.37. Found: C, 44.08;
H, 2.17; N, 7.31%. 1H NMR (300 MHz, CDCl3): δ 8.00 (d, 4H),
7.68 (d, 4H). 13C NMR (50 MHz, CDCl3): δ 164.0, 132.5, 128.3,
126.6, 122.6. MS (EI) 380.04 (calcd for C14H8Br2N2O), 380
(found).
1,4-Bis[5-(4-b r om op h en yl)-1,3,4-oxa d ia zole-2-yl]b en -
zen e (14). This compound was prepared by a procedure
similar to that of 10, using dimethyl terephthalate (11) instead
of ethyl 4-bromobenzoate (7), and the product was isolated as
a white crystalline solid (64%); mp >300 °C. Anal. Calcd for
1262, 1095, 1066, 1018, 874, 818, 701 cm-1
.
P oly{[9,9-b is(2-et h ylh exyl)flu or en e-2,7-d iyl]-a lt-[2,5-
bis(p-p h en ylen e)-1,3,4-oxa d ia zole]} P F Ox. This polymer
was prepared by a procedure identical to P F Q using 10 instead
of 6; the product was isolated as an off-white powder in a yield
of 75%. Anal. Calcd for (C43H48N2O)n: C, 84.83; H, 7.95.
Found: C, 85.44; H, 8.17%. 1H NMR (300 MHz, CDCl3): δ 8.21
(d, 4H), 7.78 (m, 6H), 7.63 (d, 4H), 2.08 (d, 4H), 1.19 (s, 2H),
0.81-0.46 (m, 28H). 13C NMR (50 MHz, CDCl3): δ 164.6, 151.6,
145.0, 140.9, 138.3, 127.6, 127.4, 126.8, 126.3, 122.8, 122.4,
120.4, 119.8, 55.2, 44.4, 34.8, 34.0, 28.2, 27.2, 22.7, 14.0, 10.4.
FT-IR (KBr): 2961, 2926, 2872, 2857, 1613, 1500, 1465, 1408,
C
22H12Br2N4O2: C, 50.41; H, 2.31; N, 10.69. Found: C, 50.13;
H, 2.36; N, 10.77%. 1H NMR (300 MHz, DMSO-d6): δ 8.04 (m,
4H), 7.85 (m, 4H), 7.75 (m, 4H). MS (EI) 524.17 (calcd for
C
22H12Br2N4O2), 524 (found).
1,2-Bis(4-br om op h en yl)-1-cya n ovin ylen e (17). 4-Bro-
1378, 1262, 1098, 1018, 852, 817, 804, 752 cm-1
.
mophenylacetonitrile (15) (1.96 g, 10 mmol) and 4-bromoben-
zaldehyde (16) (1.85 g, 10 mmol) were dissolved in ethanol (50
mL). To the mixture was added dropwise a solution of NaOH
P oly{[9,9-b is(2-et h ylh exyl)flu or en e-2,7-d iyl]-a lt-{1,4-
bis[5-(p-ph enylen e)-1,3,4-oxadiazole-2-yl]ben zen e}}P F2Ox.
This polymer was prepared by a procedure identical to P F Q

2532 Zhan et al.
Macromolecules, Vol. 35, No. 7, 2002
Sch em e 2. Syn th etic Rou te to th e P olym er s
using 14 instead of 6; the product was isolated as an off-white
powder in a yield of 95%. Anal. Calcd for (C51H52N4O2)n: C,
81.35; H, 6.96. Found: C, 81.94; H, 7.13%. 1H NMR (300 MHz,
CDCl3): δ 8.22 (m, 8H), 7.80 (m, 4H), 7.74 (m, 6H), 2.06 (d,
4H), 1.17 (s, 2H), 0.80-0.44 (m, 28H). FT-IR (KBr): 2961,
151.5, 143.8, 141.2, 140.7, 138.4, 129.9, 127.6, 127.5, 127.2,
126.8, 126.4, 126.2, 122.7, 120.3, 55.3, 44.5, 34.7, 33.8, 28.1,
27.1, 22.7, 14.0, 10.4. FT-IR (KBr): 3031, 2957, 2926, 2871,
2857, 2215, 1605, 1518, 1465, 1409, 1378, 1260, 1099, 1016,
894, 847, 817, 742 cm-1
.
2913, 2854, 1601, 1509, 1462, 1267, 1091, 805, 464 cm-1
.
In str u m en ta tion . FT-IR spectra were taken on a Perkin-
Elmer System 2000 FT-IR spectrometer with KBr pellets or
Nujol mulls. UV-vis spectra in chloroform solution and in thin
films on quartz substrates were recorded on a Hitachi U-3010
UV-vis spectrophotometer. Photoluminescence (PL) spectra
of the polymers in chloroform solution and in thin films on
quartz substrates were measured on a Hitachi F-4500 spec-
trophotometer. 1H NMR spectral data are expressed in ppm
relative to internal standard tetramethylsilane and were
P oly{[9,9-b is(2-et h ylh exyl)flu or en e-2,7-d iyl]-a lt-[1,2-
bis(p-p h en ylen e)-1-cya n ovin ylen e]} P F CNP V. This poly-
mer was prepared by a procedure identical to P F Q using 17
instead of 6; the product was isolated as a greenish-yellow
powder in a yield of 79%. Anal. Calcd for (C44H49N)n: C, 89.29;
H, 8.34. Found: C, 88.64; H, 8.29%. 1H NMR (300 MHz,
CDCl3): δ 8.06 (s, 1H), 7.96-7.51 (m, 14H), 2.07 (d, 4H), 1.26
(s, 2H), 0.88-0.58 (m, 28H). 13C NMR (50 MHz, CDCl3): δ

Macromolecules, Vol. 35, No. 7, 2002
Copolymers Based on Fluorene 2533
obtained in CDCl3 or other deuterated solvents on a Bruker
dmx 300 NMR spectrometer. 13C NMR spectra were observed
in deuterated solvents (20% w/v) on a Varian Unity 200 MHz
NMR spectrometer. Mass spectra were determined with the
instruments AEI-MS50 for EI-MS and KYKY-ZH-P-5 for FAB-
MS. Elemental analyses were carried out by a Carlo Erba
model 1106 elemental analyzer. Thermal gravimetric analysis
(TGA) measurements were performed on Perkin-Elmer series
7 thermal analysis system under N2 at a heating rate of 20
°C/min. Differential scanning calorimetry (DSC) measure-
ments were performed on Perkin-Elmer DSC 7 under N2 at a
heating rate of 20 °C/min. The weight-average molecular
weights (Mw) and polydispersity indices (Mw/Mn) of the poly-
mers were measured on a PL-GPC model 210 chromatograph
at 35 °C, using THF as eluent and standard polystyrene as
reference. For study on electrochemical behavior, a polymer
thin film was prepared on a platinum wire as a working
electrode, using a platinum wire as the counter electrode and
Ag/Ag+ as the reference electrode in a solution of tetrabutyl-
ammonium hexafluorophosphate (0.1 M) in acetonitrile. The
reference electrode potential vs normal hydrogen electrode
(NHE) is 0.2223 V.18 The cyclic voltammogram was recorded
on a computer-controlled EG&G potentiostat/galvanostat model
283. The lowest unoccupied molecular orbital (LUMO) and the
highest occupied molecular orbital (HOMO) energy levels of
the polymers were converted from the onset reduction and
oxidation potentials, respectively, with the assumption that
the energy level of ferrocene/ferrocenium (Fc) is 4.8 eV below
vacuum.19
and 2. First of all, we synthesized a new bisquinoline
monomer 6 by acid-catalyzed condensation reaction
between o-aminoketone 4 and diacetylbenzene 5. Then
we prepared the polymer P F Q composed of fluorene and
quinoline units using palladium-catalyzed Suzuki cou-
pling reactions between fluorene diboronate and quino-
line dibromide in toluene. The polymer P F Q was
obtained as a pale yellow powder in a high yield of 98%.
In contrast to polyquinolines reported in the literature,16
P F Q is completely soluble in common organic solvents,
such as chloroform and tetrahydrofuran, due to the
2-ethylhexyl side chain attached to the fluorene moiety.
The copolymer constituted of fluorene and quinoxa-
line, P F Qx, was synthesized according to Scheme 2. The
monomer 3 was prepared according to Scheme 1. Phen-
ylacetylene and 2,7-dibromofluorene (1) were cross-
coupled in a palladium-catalyzed Heck reaction to
compound 2. The compound 2 could easily be oxidized
to the tetraketone 3 with KMnO4 in CH2Cl2 according
to the procedure for the oxidation of 2,5-bis(phenylethy-
nyl)thiophene described by J enekhe.3d The route to the
tetraketone 3 avoids the use of highly toxic selenium
dioxide as the oxidizing agent.3c The last step is the
polycondensation of the tetraketone 3 and 3,3-diami-
nobenzidine 18 in m-cresol, leading to the new substi-
tuted polyquinoxaline P F Qx. The obtained polyquinox-
aline P F Qx is a pale yellow powder. In contrast to
polyquinoxalines reported in the literature,3d P F Qx is
completely soluble in common organic solvents, such as
chloroform, tetrahydrofuran, and m-cresol. This was
partially due to the 2-ethylhexyl side chain attached to
the fluorene moiety.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of P olym er s.
The synthesis of aromatic poly(1,3,4-oxadiazole) com-
pounds has been reviewed recently.20 The widespread
route involves the preparation of polyhydrazide precur-
sors followed by cyclodehydration. However, this syn-
thetic route has some disadvantages. One is the difficult
purification of the polyhydrazide precursors because of
their poor solubility in common organic solvents, result-
ing in impurity of the final polymers. It should be
emphasized that purity of the polymers is an important
criterion of EL materials since the impurity of the
polymers leads to the poor performance of the EL
devices. Another is the incompleteness of the heteroge-
neous cyclodehydration reaction because of low solubil-
ity of the precursors and their corresponding final
polymers in dehydrating solvents such as POCl3.7b We
used a different synthetic approach which is outlined
in Schemes 1 and 2. At first we synthesized easily
purified (by sublimation) 1,3,4-oxadiazole-containing
monomers 10 and 14. Finally, we prepared polymers
by employing palladium-catalyzed Suzuki coupling re-
actions between fluorene diboronate and 1,3,4-oxadia-
zole dibromide in toluene. Two oxadiazole-containing
polymers P F Ox and P F 2Ox were synthesized success-
fully in good yields of 75% and 95%. These polymers
are off-white powders. Polymer P F Ox has good solubil-
ity in common organic solvents such as chloroform and
tetrahydrofuran (THF), while polymer P F 2Ox has poor
solubility in chloroform and THF because of higher
1,3,4-oxadiazole content in the latter.
The established synthetic route to poly(p-phenyl-
enecyanovinylene) (CN-PPV) involves Knoevenagel con-
densation polymerization of terephthalaldehyde with
benzenediacetonitrile.9a However, the molecular weight
of the CN-PPV obtained by the above method is not
high; for example, the number-average molecular weight
(Mn) of the CN-PPV synthesized by Greenham et al. is
4000 by gel permeation chromatography (GPC) against
polystyrene standard.9a Here, we report a different
synthetic route which is outlined in Schemes 1 and 2.
We synthesized a phenylenecyanovinylene monomer 17
by base-catalyzed condensation reaction between 4-bro-
mophenylacetonitrile (15) and 4-bromobenzaldehyde
(16) in ethanol. Then we prepared the polymer P F C-
NP V consisting of fluorene and phenylenecyanovinylene
units using palladium-catalyzed Suzuki coupling reac-
tions between fluorene diboronate and phenylenecy-
anovinylene dibromide in toluene. The polymer P F C-
NP V was obtained as a greenish-yellow powder in a
yield of 79%. The prepared P F CNP V is soluble in
chloroform and THF. The Mn of P F CNP V was mea-
sured to be 13 140 by GPC on the basis of polystyrene
standard, 3 times that for the reported CN-PPV.9a
The molecular weights of these polymers were deter-
mined by gel permeation chromatography using poly-
styrene as the standard and are listed in Table 1. These
copolymers have weight-average molecular weights (Mw)
of 20 000-81 400 with polydispersity indices (Mw/Mn)
of 2.3-2.9. The thermal properties of the polymers were
determined by TGA and DSC measurements. Figure 1
gives thermogravimetric curve of the polymer P F Qx.
TGA reveals good thermal stability of this polymer with
the onset decomposition temperature (Td) of 415 °C
under nitrogen. As shown in Table 1, all these polymers
possess excellent thermal stability with Td ranging from
In general, polyquinolines were synthesized by acid-
catalyzed Friedla¨nder condensation reaction between
bis(o-aminoketone) and diacetylaryl compound in m-
cresol.14,21 m-Cresol is known to catalyze the polycon-
densation. However, the use of the high boiling and
polar m-cresol has one disadvantage, that is, the poor
removability of the solvent from bulk material or cast
films for LED applications. Here, we employed a dif-
ferent synthetic route which is outlined in Schemes 1

2534 Zhan et al.
Macromolecules, Vol. 35, No. 7, 2002
Ta ble 1. Molecu la r Weigh ts a n d Th er m a l P r op er ties of
th e P olym er s
Ta ble 2. Absor p tion a n d Em ission Sp ectr a l Da ta of th e
P olym er s in Ch lor ofor m a n d in Th in Solid F ilm s
a
a
polymer
yield (%)
Mw
Mw/Mn
Tdb (°C) Tgc (°C)
absorption
emission
λmaxa (nm)
λmaxc (nm)
band
fwhmd
(nm)
P F Ox
P F 2Ox
P F Q
P F Qx
P F CNP V
75
95
98
75
79
20 000
20 100
66 100
81 400
38 110
2.3
2.2
2.5
2.9
2.9
399
394
387
415
411
137
194
146
208
114
polymers solution film gapb (eV) solution film
P F Ox
P F 2Ox
P F Q
P F Qx
P F CNP V
366
349
391
404
399
369
352
394
402
403
3.02
3.09
2.81
2.80
2.66
405
428
432
448
465
414
422
441
455
476
76
82
115
80
a
Weight-average molecular weight (Mw) and polydispersity
index (Mw/ Mn) determined by means of GPC in THF on the basis
65
b
of polystyrene calibration. Onset decomposition temperature
Absorption maxima in solution (chloroform, 10-4 mol/L) and
a
measured by TGA under N2. c Glass transition temperature
measured by DSC under N2.
b
in films on quartz substrates. Optical band gap derived from film
absorption spectra. c Emission maxima in solution (chloroform,
10-4 mol/L) and in films on quartz substrates; the excitation
d
wavelength corresponds to the absorption maximum. Full width
at half-maximum of the film PL spectra.
F igu r e 1. Representative TGA curve (P F Qx).
F igu r e 3. Absorption spectra of the polymers in chloroform
solution.
and in the solid state. The absorption and emission
spectral data for the polymers in solution and in the
films casting from solution in CHCl3 are summarized
in Table 2. The absorption spectra of the polymers
obtained for diluted CHCl3 solution are illustrated in
Figure 3 to reveal the effects of changing the polymer
backbone structure on band gap and π-π* transition
maximum (λmax). All the polymers show the maximum
absorptions in the range 349-404 nm, attributed to
π-π* transition of the polymers. The optical band gaps
(Eg) of the polymers were determined to be 2.66-3.09
eV from the film absorption spectra. Compared to the
absorption spectrum of the polymer containing one
oxadiazole ring per repeated unit, i.e., P F Ox, the
introduction of an additional oxadiazole ring in the
polymer P F 2Ox containing two oxadiazole rings per
repeated unit brings about change to the absorption
peak in the short wavelength region. Replacing the
oxadiazole moiety in P F Ox with quinoline or phenyl-
enecyanovinylene moiety results in a bathochromic shift
in λmax and a reduction in Eg. Further red shift and
smaller Eg are induced when the quinoline ring in P F Q
is replaced by the quinoxaline ring. In other words, the
electronic structures and properties of the fluorene-
based polymers can be readily tuned by molecular
engineering of a counit in the main chain. Figure 4
shows the absorption spectra of the thin solid films of
the polymers, which are similar to those measured in
the solution. Thus, the electronic transitions of the
polymers are primarily determined by their molecular
structures, which are insignificantly affected by their
aggregation states.
F igu r e 2. DSC chart of P F Qx.
387 to 415 °C. The DSC thermogram of P F Qx (Figure
2) shows a clear glass transition at 208 °C. The glass
transition temperature (Tg) of the polymers ranges from
114 to 208 °C (Table 1). These Tg values are much
higher than that of typical polyfluorene (∼55 °C),22
indicating that the incorporation of oxadiazole, quino-
line, and quinoxaline rings and phenylenecyanovinylene
unit significantly enhances the thermal stability of the
fluorene-based polymers. The Tg of the polymer contain-
ing two oxadiazole rings per repeated unit, i.e., P F 2Ox,
is 194 °C, higher than that of its cousin containing one
oxadiazole ring per repeated unit, i.e., P F Ox (137 °C).
The Tg of the quinoxaline-containing polymer, i.e.,
P F Qx, is 208 °C, higher than that of its cousin contain-
ing quinoline ring, i.e., P F Q (146 °C). Clearly, the glass
transition temperature increases as the chain rigidity
of the polymer increases.
P h otop h ysica l P r op er ties. The photophysical char-
acteristics of the polymers were investigated in solution

Macromolecules, Vol. 35, No. 7, 2002
Copolymers Based on Fluorene 2535
F igu r e 4. Absorption spectra of the polymers in thin films.
F igu r e 6. Photoluminescence spectra of the polymers in thin
solid films.
F igu r e 5. Fluorescence spectra of the polymers in chloroform
solution.
F igu r e 7. Cyclic voltammograms of P F Ox recorded from a
thin film deposited on
a platinum wire electrode in an
electrolyte solution of Bu4NPF6 (0.1 M) in CH3CN at a scan
rate of 50 mV/s. The potentials were measured relative to Ag/
Ag+ reference electrode.
The great similarity between PL and EL spectra of
many light-emitting materials suggests that similar
mechanisms are at play or that the same emitting
species (a singlet exciton) is involved in each case.23
Because of the simplicity of the PL measurements, we
first checked the PL behaviors of the polymers. Figure
5 shows the PL spectra of the polymers in chloroform
solution. All the polymers in chloroform solution emit
strong blue fluorescence around 405-465 nm under
ultraviolet irradiation. Compared to those of the oxa-
diazole-containing polymers (P F Ox and P F 2Ox), the
PL spectra of the polymers containing quinoline or
quinoxaline units (P F Q and P F Qx) locate in the longer
wavelength region. Further a red shift is observed in
the PL spectrum of the polymer P F CNP V containing
a CN-PPV unit. CN-PPV is a red-emitting material,
while our copolymer P F CNP V consisting of CN-PPV
and fluorene units is a blue-emitting material.
The PL spectra of the polymers in thin solid films are
illustrated in Figure 6. All the polymers in thin films
emit strong blue luminance around 414-476 nm upon
photoexcitation. In comparison with its solution fluo-
rescence, P F 2Ox as solid films has emission blue-
shifted by 6 nm. It is worth noting that the PL maxima
of the polymers films except for P F 2Ox are only red-
shifted by 7-11 nm compared to those of the polymers
solution. Full width at half-maximum (fwhm) of the film
PL spectra is in the range of 65-82 nm except for P F Q.
It should be emphasized that polyfluorene derivatives
trend to undergo various degrees of aggregation and the
excimer formation in the films, leading to concentration-
dependent EL quenching, emission band broadening,
and bathochromic shift.13a In contrast to the polyfluo-
rene derivatives reported in the literature, our copoly-
mers based on fluorene emit narrow-peak blue light
with slight red shifts. We explain this interesting
phenomenon by the assumption that sterically demand-
ing groups such as 2-ethylhexyl prevent “disklike”
molecules from stacking on top of each other, and
consequently excimer fluorescence is suppressed.
Electr och em ica l P r op er ties. Cyclic voltammetry
(CV) was employed to investigate the redox behaviors
of the polymers. Regarding the energy level of the
ferrocene/ferrocenium (Fc) reference, one can calculate
the LUMO and HOMO energies with the assumption
that the energy level of Fc is 4.8 eV below vacuum.19
Since the energy level of Fc is determined by photoelec-
tron spectroscopy in the solid state, this method can only
be considered to be a rough approximation. It is worth
mentioning that obtaining absolute HOMO and LUMO
levels from electrochemical data in combination with the
energy gap is still in debate. An example of typical cyclic
voltammograms is shown in Figure 7. Quasi-reversible
oxidation and reduction waves were revealed for P F Ox
(Figure 7). On sweeping the polymer cathodically, the
onset of the reduction occurs at about ca. -1.67 V vs
Ag/Ag+ above which the cathodic current quickly in-
creases, and a cathodic peak appears at -2.00 V. A
corresponding reoxidation peak appears at -1.74 V. For
oxidation, the onset potential is ca. 1.56 V and an anodic
peak occurs at 1.79 V with the corresponding rereduc-

2536 Zhan et al.
Macromolecules, Vol. 35, No. 7, 2002
Ta ble 3. Electr och em ica l P oten tia ls a n d En er gy Levels of
th e P olym er s
that the aggregation and the excimer fluorescence are
suppressed. Intensive studies on the electroluminescent
and electron-transporting/hole-blocking properties of
these polymers in LED devices are in progress.
a
b
Ered (V vs Eox (V vs
polymers
Ag/Ag+)
Ag/Ag+) LUMOc (eV) HOMOd (eV)
P F Ox
P F 2Ox
P F Q
P F Qx
P F CNP V
-1.67
-1.49
-1.44
-1.31
-1.60
1.56
1.70
1.58
1.51
1.45
-3.01
-3.19
-3.24
-3.37
-3.08
-6.24
-6.38
-6.26
-6.19
-6.13
Ack n ow led gm en t. This work was supported by
National Natural Science Foundation of China, the
Major State Basic Research Development Program, and
Chinese Academy of Sciences.
a
b
Reduction potentials measured by cyclic voltammetry. Oxi-
dation potentials measured by cyclic voltammetry. c Calculated
from the reduction potentials assuming the absolute energy level
Refer en ces a n d Notes
of ferrocene/ferrocenium to be 4.8 eV below vacuum.19 Calculated
d
(1) (a) Blasse, G.; Grabmaier, B. C. Luminescent Materials;
Springer-Verlag: Berlin, 1994. (b) Organic Electrolumines-
cent Materials and Devices; Miyata, S., Nalwa, H. S., Eds.;
Gordon and Breach Publishers: Amsterdam, 1997. (c) Friend,
R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J . H.; Marks,
R. N.; Taliani, C.; Bradley, D. D. C.; dos Santos, D. A.; Bre´das,
J . L.; Lo¨gdlund, M.; Salaneck, W. R. Nature (London) 1999,
397, 121.
(2) (a) J enekhe, S. A.; Zhang, X.; Chen, X. L.; Choong, V. E.; Gao,
Y.; Hsieh, B. R. Chem. Mater. 1997, 9, 409. (b) Parker, I. D.;
Pei, Q.; Marrocco, M. Appl. Phys. Lett. 1994, 65, 1272. (c)
Chen, T. A.; J en, A. K.-Y.; Cai, Y. M. Chem. Mater. 1996, 8,
607. (d) J en, A. K.-Y.; Wu, X. M.; Ma, H. Chem. Mater. 1998,
10, 471.
(3) (a) Fukuda, T.; Kanbara, T.; Yamamoto, T.; Ishikawa, K.;
Takezeo, H.; Fukuda, A. Appl. Phys. Lett. 1996, 68, 2346. (b)
O’Brien, D.; Weaver, M. S.; Lidzey, D. G.; Bradley, D. D. C.
Appl. Phys. Lett. 1996, 69, 881. (c) J andke, M.; Strohriegl,
P.; Berleb, S.; Werner, E.; Bru¨tting, W. Macromolecules 1998,
31, 6434. (d) Cui, Y.; Zhang, X.; J enekhe, S. A. Macromol-
ecules 1999, 32, 3824.
(4) (a) Adachi, C.; Tsutsui, T.; Saito, S. Appl. Phys. Lett. 1989,
55, 1489. (b) Adachi, C.; Tsutsui, T.; Saito, S. Appl. Phys. Lett.
1990, 56, 799.
from the oxidation potentials assuming the absolute energy level
of ferrocene/ferrocenium to be 4.8 eV below vacuum.19
tion peak at 1.70 V. As shown in Figure 7, after 10 scans
for the same polymer film, only slight changes for both
the potentials and the current intensities of the redox
process were observed, demonstrating that the polymer
is stable to cycling through the reduction and oxidation.
The HOMO and LUMO energy levels are summarized
in Table 3. Their LUMO levels range from -3.01 to
-3.37 eV. These reduction potentials are lower than
those of PBD (∼-2.4 eV) and other oxadiazole-contain-
ing materials7 and comparable with that of CN-PPV
(-3.10 eV), which shows good electron-transporting
ability in polymeric LEDs.9 Such energy levels may
provide a closer match to the work function of Al when
they are used as electron-transporting materials in
polymer LEDs. The HOMO energy levels of these
polymers range from -6.13 to -6.38 eV, much lower
than those of most currently known EL materials. Thus,
all these polymers can also be employed as hole-blocking
materials in LEDs.
The LUMO level of P F Ox is -3.01 eV, while the
LUMO level of P F 2Ox is -3.19 eV. It is clear that the
higher the oxadiazole content, the lower the LUMO level
of the polymer and therefore the better the electron
injection properties. The LUMO level of P F Q is -3.24
eV, comparable to that of polyquinolines reported in the
literature.14 It is believed that the low-lying LUMO of
polyquinolines originates from the electron-deficient
nature of the quinoline ring. The increased electron
deficiency of the quinoxaline ring due to an additional
imine nitrogen, compared to the quinoline ring, brings
about the lower LUMO level of P F Qx (-3.37 eV).
(5) Strukelj, M.; Papadimitrakopoulos, F.; Miller, T. M.; Roth-
berg, L. J . Science 1995, 267, 1969.
(6) (a) Pei, Q.; Yang, Y. Chem. Mater. 1995, 7, 1568. (b)
Buchwald, E.; Meier, M.; Karg, S.; Po¨sch, P.; Schmidt, H.-
W.; Strohriegel, P.; Riess, W.; Schwoerer, M. Adv. Mater.
1995, 7, 839.
(7) (a) Yu, W.-L.; Meng, H.; Pei, J .; Huang, W. J . Am. Chem.
Soc. 1998, 120, 11808. (b) Huang, W.; Yu, W.-L.; Meng, H.;
Pei, J .; Li, S. F. Y. Chem. Mater. 1998, 10, 3340. (c) Yu, W.-
L.; Meng, H.; Pei, J .; Lai, Y.-H.; Chua, S.-J .; Huang, W. Chem.
Commun. 1998, 1957. (d) Yu, W.-L.; Meng, H.; Pei, J .; Huang,
W.; Li, Y.; Heeger, A. J . Macromolecules 1998, 31, 4838. (e)
Huang, W.; Meng, H.; Yu, W.-L.; Pei, J .; Chen, Z.-K.; Lai,
Y.-H. Macromolecules 1999, 32, 118.
(8) (a) Peng, Z.; Bao, Z.; Galvin, M. E. Chem. Mater. 1998, 10,
2086. (b) Peng, Z.; Zhang, J . Chem. Mater. 1999, 11, 1138.
(9) (a) Greenham, N. C.; Moratti, S. C.; Bradley, D. D. C.; Friend,
R. H.; Holmes, A. B. Nature (London) 1993, 365, 628. (b) Liu,
Y.; Li, Q.; J iang, X.; Zhu, D. Synth. Met. 1997, 85, 1279. (c)
Peng, Z.; Galvin, M. E. Chem. Mater. 1998, 10, 1785.
Con clu sion s
(10) (a) Klaerner, G.; Miller, R. D. Macromolecules 1998, 31, 2007.
(b) J enekhe, S. A.; Osaheni, J . A. Science 1994, 265, 765.
We synthesized a novel series of conjugated copoly-
mers having oxadiazole, quinoline, quinoxaline, and
phenylenecyanovinylene moieties in the main chain
based on fluorene by palladium-catalyzed Suzuki cou-
pling reaction, a new approach different from the
traditional polyhydrazide precursor route (polyoxadia-
zoles), acid-catalyzed Friedla¨nder condensation reaction
(polyquinolines), and Knoevenagel condensation poly-
merization (CN-PPV). These copolymers possess good
solubility and excellent thermal stability. Cyclic volta-
mmetry reveals that these polymers have a low-lying
LUMO energy level ranging from -3.01 to -3.37 eV and
a low-lying HOMO energy levels ranging from -6.13
to -6.38 eV and may be attractive candidates for
electron-transporting or hole-blocking materials in LEDs.
The polymers in thin films emit strong blue luminance
with narrow bandwidth upon photoexcitation. PL spec-
tra of the polymers in the films are only red-shifted by
7-11 nm compared to those in the solution, indicating
(11) (a) Yang, Y.; Pei, Q. J . Am. Chem. Soc. 1996, 118, 7416. (b)
He, Y.; Gong, S.; Hattori, R.; Kanicki, J . Appl. Phys. Lett.
1999, 74, 2265. (c) Yu, W.; Cao, Y.; Pei, J .; Huang, W.; Heeger,
A. J . Appl. Phys. Lett. 1999, 75, 3270. (d) Yu, W.; Pei, J .; Cao,
Y.; Huang, W.; Heeger, A. J . Chem. Commun. 1999, 1837.
(e) Liu, B.; Yu, W.; Lai, Y.; Huang, W. Chem. Commun. 2000,
551.
(12) (a) Redecker, M.; Bradley, D. D. C.; Inbasekaran, M.; Woo,
E. P. Appl. Phys. Lett. 1998, 73, 1565. (b) J anietz, S.; Bradley,
D. D. C.; Grell, M.; Giebeler, C.; Inbasekaran, M.; Woo, E. P.
Appl. Phys. Lett. 1998, 73, 2453. (c) Grell, M.; Bradley, D. D.
C.; Inbasekaran, M.; Woo, E. P. Adv. Mater. 1997, 9, 798. (d)
Grell, M.; Knoll, W.; Lupo, D.; Meisel, A.; Miteva, T.; Neher,
D.; Nothofer, H.; Scherf, U.; Yasuda, A. Adv. Mater. 1999,
11, 671. (e) Virgili, T.; Lidzey, D. G.; Bradley, D. D. C. Adv.
Mater. 2000, 12, 58.
(13) (a) Sainova, D.; Miteva, T.; Nothofer, H.; Scherf, U.; Glowacki,
I.; Ulanski, J .; Fujikawa, H.; Neher, D. Appl. Phys. Lett. 2000,
76, 1810. (b) Weinfurtner, K.; Fujikawa, H.; Tokito, S.; Taga,
Y. Appl. Phys. Lett. 2000, 76, 2502. (c) J iang, X.; Liu, S.; Ma
H.; J en, A. K.-Y. Appl. Phys. Lett. 2000, 76, 1813.

Macromolecules, Vol. 35, No. 7, 2002
Copolymers Based on Fluorene 2537
(14) (a) Kim, J . L.; Kim, J . K.; Cho, H. N.; Kim, D. Y.; Kim, C. Y.;
Hong, S. II. Macromolecules 2000, 33, 5880. (b) Kim, J . L.;
Cho, H. N.; Kim, J . K.; Hong, S. II. Macromolecules 1999,
32, 2065. (c) Kim, J . L.; Kim, J . K.; Cho, H. N.; Kim, D. Y.;
Hong, S. II. Synth. Met. 2000, 114, 97.
(15) Zhan, X.; Liu, Y.; Zhu, D.; Huang, W.; Gong, Q. Chem. Mater.
2001, 13, 1540.
(16) Sybert, P. D.; Beever, W. H.; Stille, J . K. Macromolecules
1981, 14, 493.
(17) (a) Coulson, D. R. Inorg. Synth. 1972, 13, 121. (b) Tayim, H.
A.; Bouldoukian, A.; Awad, F. J . Inorg. Nucl. Chem. 1970,
32, 3799.
(19) Pommerehne, J .; Vestweber, H.; Guss, W.; Mahrt, R. F.;
Bassler, H.; Porsch, M.; Daub, J . Adv. Mater. 1995, 7,
551.
(20) Schulz, B.; Bruma, M.; Brehmer, L. Adv. Mater. 1997, 9, 601.
(21) Liu, Y.; Ma, H.; J en, A. K.-Y. Chem. Mater. 1999, 11, 27.
(22) Fukuda, M.; Sawada, K.; Yoshino, K. J . Polym. Sci., Polym.
Chem. 1990, 31, 2465.
(23) Li, X.-C.; Moratti, S. C. In Photonic Polymer Systsms:
Fundamentals, Methods, and Applications; Wise, D. L.,
Wnek, G. E., Trantolo, D. J ., Cooper, T. M., Gresser, J . D.,
Eds.; Marcel Dekker: New York, 1998; Chapter 10, pp
335-371.
(18) Milazzo, G.; Caroli, S. Tables of Standard Electrode Poten-
tials; Wiley-Interscience: New York, 1977.
MA011593G