Conjugated copolymers comprised cyanophenyl-substituted spirobifluorene and tricarbazole-triphenylamine repeat units for blue-light-emitting diodes

Article abstract of DOI:10.1002/pola.23783

A series of conjugated blue-light-emitting copolymers, PTC-1, PTC-2, and PTC-3, comprised different ratios of electron-withdrawing segments (spirobifluorene substituted with cyanophenyl groups) and electron-donating segments (tricarbazole-triphenylamines), has been synthesized. The structures of these polymers were characterized and their thermal, photophysical, electrochemical, and electroluminescence properties were measured. Incorporation of rigid spirobifluorene units into the copolymers led to blue-shifted absorption peaks in dilute toluene solution. Cyclic voltammetric measurement indicated the bandgaps of the polymers were in the range of 2.77-2.94 eV. It was found that increasing cyanophenyl-spirobifluorene content in the polymer backbone lowered both the HOMO and LUMO energy levels of the copolymers, which was beneficial for electron injection/ transporting in the polymer layer of the device. OLED device evaluation indicated that all the polymers emitted sky blue to deep blue light when the pure polymers were used as the emissive layers in the devices with a configuration of ITO/ PEDOT:PSS/polymers/CsF/Ca/Al. The devices have been optimized by doping 30 wt % PBD into the polymer layers. Among the doped devices, PTC-2 showed the best performance with the turn-on voltage of 3.0 V, maximum brightness of 7257 cd/m², maximum current efficiency of 1.76 cd/A, and CIE coordinates of (0.15, 0.14).

Full text of DOI:10.1002/pola.23783

Conjugated Copolymers Comprised Cyanophenyl-Substituted
Spirobifluorene and Tricarbazole-Triphenylamine Repeat
Units for Blue-Light-Emitting Diodes
YING LIN,1,2 ZHI-KUAN CHEN,1 TENG-LING YE,3 YAN-FENG DAI,1,3 DONG-GE MA,3 ZHUN MA,1
QIN-DE LIU,1 YU CHEN2
1Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602, Singapore
2Department of Chemistry, Lab for Advanced Materials, East China University of Science and Technology, 130 Meilong Road,
Shanghai 200237, People’s Republic of China
3State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of
Sciences, Graduate School of the Chinese Academy of Sciences, Changchun 130022, People’s Republic of China
Received 27 August 2009; accepted 8 October 2009
DOI: 10.1002/pola.23783
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A series of conjugated blue-light-emitting copoly-
mers, PTC-1, PTC-2, and PTC-3, comprised different ratios of
electron-withdrawing segments (spirobifluorene substituted with
cyanophenyl groups) and electron-donating segments (tricarba-
zole-triphenylamines), has been synthesized. The structures of
these polymers were characterized and their thermal, photophys-
ical, electrochemical, and electroluminescence properties were
measured. Incorporation of rigid spirobifluorene units into the
copolymers led to blue-shifted absorption peaks in dilute toluene
solution. Cyclic voltammetric measurement indicated the band-
gaps of the polymers were in the range of 2.77—2.94 eV. It was
found that increasing cyanophenyl-spirobifluorene content in the
polymer backbone lowered both the HOMO and LUMO energy lev-
els of the copolymers, which was beneficial for electron injection/
transporting in the polymer layer of the device. OLED device
evaluation indicated that all the polymers emitted sky blue to
deep blue light when the pure polymers were used as the emis-
sive layers in the devices with
a configuration of ITO/
PEDOT:PSS/polymers/CsF/Ca/Al. The devices have been opti-
mized by doping 30 wt % PBD into the polymer layers. Among
the doped devices, PTC-2 showed the best performance with the
turn-on voltage of 3.0 V, maximum brightness of 7257 cd/m2,
maximum current efficiency of 1.76 cd/A, and CIE coordinates of
C
V
(0.15, 0.14).
2009 Wiley Periodicals, Inc. J Polym Sci Part A:
Polym Chem 48: 292–301, 2010
KEYWORDS: charge transporting; conjugated polymers; cyano-
phenyl-spirobifluorene; doped devices; fluorescence; photo-
physics; polymer light-emitting diodes (PLEDs); tricarbazole-
triphenylamine; UV-Vis spectroscopy
INTRODUCTION Fluorene-based polymers and oligomers
have been considered as the candidates in organic electronic
devices,1 such as light-emitting diodes (LEDs),2 solar cells,3
and field-effect transistors (FETs).4 Especially in LEDs, poly-
fluorenes have been broadly used as the emissive materials
in polymeric light-emitting diodes (PLEDs) because of their
good thermal stability, film-forming ability, and high electro-
luminescence (EL) efficiencies.2 However, the classical poly
(alkylfluorene) homopolymers suffer from poor spectral sta-
bility associated with keto defects in the polymer backbone
or excimer emission.5 The common strategies, to address
this issue, are introduction of bulky groups to the C-9 posi-
tion of the fluorene unit, e.g., spirobifluorene, or copolymer-
ization with suitable comonomers.6 The structural feature of
90ꢀ angle between the two connected fluorene moieties in
spirobifluorene can significantly suppress the side effect of
molecular packing.7 Attachment of additional substituents
onto one fluorene unit of the spirobifluorene as the polymer
side-chain can further retard the main-chain aggregation.
Tang et al.7(d) reported spirobifluorene trimers with periph-
eral carbazole groups, which exhibited pure blue emission
with high quantum yield and good spectral stability. How-
ever, the device performance is not high, probably because
of the unbalanced charge injection and transport. In this
case, injection and transporting of holes are much easier
than electrons due to the carbazole segments. To enhance
the electron injection and transport, introduction of electron-
withdrawing components into the polymers is proven to be
effective. Among all the electron-withdrawing groups, cyano
group, which possesses strong electron-withdrawing prop-
erty and excellent luminescence efficiency,8 has been well
investigated. Taranekar et al.9 reported a series of alternated
Additional Supporting Information may be found in the online version of this article. Correspondence to: Z.-K. Chen (E-mail: zk-chen@imre.a-star.
edu.sg) or Y. Chen (E-mail: chentangyu@yahoo.com)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 292–301 (2010) 2009 Wiley Periodicals, Inc.
292
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
SCHEME 1 Synthetic route for M1.
polymers with cyanofluorene groups emitted green to blue
light with low turn-on voltages. Very recently, Zhen et al.
reported a series of deep blue-light-emitting oligofluorenes
containing carbazole-phenylamines and cyanophenyl groups.
The carbazole-phenylamine and cyanophenyl segments bal-
anced the hole and electron transport, thus resulted in very
high efficient blue-light emission.10 In fact, carbazole and tri-
phenylamine, as building blocks for light-emitting materials,
not only help to enhance hole-transporting property but also
improve thermal stability of the materials.11
troluminescence (EL) performances of these copolymers were
evaluated using two device configurations: ITO/PEDOT:PSS/
polymers/CsF/Ca/Al (Device A) and ITO/PEDOT:PSS/poly-
mers:PBD/CsF/Ca/Al (Device B). Device A used the pure poly-
mer as the emissive layer, and the other doped 30% of 2-(4-
tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) in the
emissive layer to further improve the device performance.12 All
the Device B exhibited better performance in comparison to
Device A.
In this work, we report the synthesis of a series of copoly-
mers PTC-1, PTC-2, and PTC-3, containing cyanophenyl sub-
stituted spirobifluorene and tricarbazole-triphenylamine with
well-defined chemical structures and the characterization of
the thermal, photophysical, electrochemical, and electrolumi-
nescent properties of the copolymers. The copolymers were
prepared via the Suzuki coupling reaction with three comono-
mers: 20,70-dibromo-2,7-bis(40-cyanophenyl)-9,90-spirobifluorene
(M1), 4-(3,6-(di-9H-carbazol-9-yl)-9H-carbazol-9-yl)-40,400-dibro-
motriphenylamine (M2), and 9,9-dihexylfluorene-2,7-bis(tri-
methyleneborate) (M3). In M1, two cyanophenyl groups were
attached onto one fluorene unit of the spirobifluorene. Such a
design can not only enhance the electron transporting property
but also suppress the intra- and intermolecular interaction. In
M2, two carbazole segments were linked onto C-3 and C-6
positions of another carbazole incorporated with triphenyl-
amine, so called tricarbazole-triphenylamine. The two mono-
mers were not only conjugated but also separated by the alkyl
substituted fluorene (M3), which could reduce the intramolecu-
lar interaction between the segments containing electron trans-
porting moieties and hole-transporting moieties. With different
feed ratios of M1 and M2, random copolymers PTC-1, PTC-2,
and PTC-3 were synthesized to optimize the charge transport-
ing properties of the copolymers. For comparison, two refer-
ence copolymers PSF and PTCF were also prepared. The elec-
EXPERIMENTAL
General Information
Molecular weights [number–average (Mn) and weight–
average (Mw)] were determined with a Waters 2690 gel per-
meation chromatography (GPC) using a polystyrene standard
eluting with tetrahydrofuran. Nuclear magnetic resonance
(NMR) spectra were recorded on a Bruker 400 spectrometer
at a resonance frequency of 400 MHz for 1H and 100 MHz
for 13C in deuterated solution with a tetramethylsilane
(TMS) as a reference for the chemical shifts. Elemental analy-
ses were conducted on a Flash 1112 Series elemental ana-
lyzer. Thermogravimetric analysis (TGA) and differential
scanning calorimetry (DSC) were carried out using TA instru-
ments TGA-Q500 and DSC-Q100 modules, respectively. The
glass-transition temperature (Tg) was recorded on the sec-
ond heating curve. The UV-vis absorption and photolumines-
cence (PL) spectra were recorded on a Shimadzu UV-3101
scanning spectrophotometer and on a Perkin-Elmer LS 55
fluorescence spectrometer, respectively. Cyclic voltammetric
measurements were conducted on a three-electrode AUTO-
LAB (model PGSTAT30) workstation in
a solution of
nBu4NPF6 (0.10 M) in acetonitrile at a scan rate of 100 mV/s
at room temperature.
SCHEME 2 Synthetic route for M2.
CONJUGATED BLUE-LIGHT-EMITTING COPOLYMERS, LIN ET AL.
293

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 3 Synthetic route of the conjugated polymers.
3,6-Dibromo-9-(4-nitrophenyl)-9H-carbazole (3) were synthe-
sized according to the literature reported.13 2,7-Dibromo-9,90-
spirobifluorene (1) was purchased from Pacific ChemSource. 4-
Cyanophenylboronic acid and phenylboronic acid were bought
from Boron Molecular. Copper(I) iodine and 1,10-phenanthro-
line were from Merck and Lancaster, respectively. Tin(II) chlo-
ride was obtained from Riedel deHaen. Tetrakistriphenylphos-
phine palladium(0) [Pd(PPh3)4] and palladium (II) acetate
[Pd(OAc)2] were purchased from Strem Chemicals. 1-Bromo-4-
iodobenzene was bought from Alfa Aesar. Iron(III) chloride,
20,70-Dibromo-2,7-bis(40-cyanophenyl)-9,90-
spirobifluorene (M1)
To a solution of 2,7-bis(40-cyanophenyl)-9,90-spirobifluorene
ꢀ
(2) (1.04 g, 2.0 mmol) in 25 mL of dichloromethane at 0 C,
40 mg (0.3 mmol) of iron(III) chloride was added. A solution
of bromine (0.71 g, 4.4 mmol) in 10 mL of dichloromethane
was added into the stirring mixture dropwise at 0 ꢀC. After
stirring at room temperature for 48 h, the solution was
ꢀ
cooled to 0 C again, and an aqueous solution of sodium sul-
fite was added slowly till the dark color disappeared. The or-
ganic layer was separated, and the aqueous layer was
extracted with dichloromethane. The combined organic layer
was washed with brine and dried over sodium sulfate. The
solvent was removed, and the residue was purified by col-
umn chromatography eluting with n-hexane/ethyl acetate
(5:1) followed by recrystallization with ethanol to give M1
(1.12 g, 82.5%).
1,10-bis(diphenylphosphino)-ferrocene,
tetrabutylammonium
bromide, and 9,9-dihexylfluorene-2,7-bis(trimethyleneborate)
were obtained from Aldrich. Bromine was obtained from Spec-
trum. Carbazole, sodium tert-butoxide and bromobenzene were
purchased from Fluka. Sodium carbonate and potassium car-
bonate were bought from Fisher Scientific. All the solvents
were A.R. grade and used without further purification.
1H NMR (CDCl3, 400 MHz, ppm) d 7.99 (d, J ¼ 8.0 Hz, 2H),
7.72 (d, J ¼ 8.0 Hz, 2H), 7.69 (dd, J ¼ 1.6, 8.0 Hz, 2H), 7.64
(d, J ¼ 8.4 Hz, 4H), 7.53–7.57 (m, 6H), 6.91 (dd, J ¼ 2.0, 6.8
Hz, 4H). 13C NMR (CDCl3, 100 MHz, ppm) d 149.75, 148.66,
144.93, 141.37, 139.72, 139.67, 132.47, 131.64, 127.90,
127.72, 127.36, 122.75, 122.20, 121.73, 121.23, 118.74,
111.09, 65.71. m/z: 676 (Mþ, 100%), 679 (15%), 678
(42%), 677 (33%), 675 (19%), 674 (47%), 598 (11%), 597
(24%), 596 (12%), 595 (23%), 516 (15%), 515 (19%). Anal.
Calcd. for C39H20Br2N2: C, 69.25; H, 2.98; N, 4.14. Found: C,
69.59; H, 3.02; N, 4.20.
Synthesis of Monomers
2,7-Bis(40-cyanophenyl)-9,90-spirobifluorene (2)
To a mixture of 2,7-dibromo-9,90-spirobifluorene (1) (1.76 g,
3.7 mmol) and 4-cyanophenylboronic acid (2.04 g, 13.9 mmol),
Pd(PPh3)4 (0.23 g, 0.20 mmol) was added in argon atmos-
phere. Toluene (32 mL) and 2 M Na2CO3 aqueous solution (16
mL) was added into the mixture and heated to reflux with
continuous stirring in the dark for 24 h under the protection
of nitrogen. After cooling to room temperature, the organic
layer was separated and the aqueous layer was extracted with
ethyl acetate. The combined organic layer was washed with
water, brine, and dried over sodium sulfate. The solvent was
removed under reduced pressure, and the crude product was
purified by silica gel column chromatography eluting with n-
hexane/ethyl acetate (5:1) to give 2 as white powders (1.94 g,
3,6-(Di-9H-carbazol-9-yl)-9-(4-nitrophenyl)-
9H-carbazole (4)
A mixture of 3,6-dibromo-9-(4-nitrophenyl)-9H-carbazole (3)
(4.30 g, 9.6 mmol), carbazole (3.67 g, 21.9 mmol), copper(I)
iodide (375 mg, 1.97 mmol), 1,10-phenanthroline (710 mg,
3.94 mmol), and potassium carbonate (5.98 g, 43.3 mmol)
was purged with nitrogen and 28 mL of anhydrous DMF was
added. The mixture was heated to reflux for 24 h. After
cooled to room temperature, the dark solution was poured
into ice-water. After filtration, the yellow solid obtained was
recrystallized in dichloromethane/methanol to give 4 (5.10
g, 85.5%).
1
77.5%). H NMR (CDCl3, 400 MHz, ppm) d 7.98 (d, J ¼ 8.0 Hz,
2H), 7.89 (d, J ¼ 7.6 Hz, 2H), 7.64 (dd, J ¼ 1.6, 8.0 Hz, 2H),
7.60 (d, J ¼ 8.4 Hz, 4H), 7.52 (d, J ¼ 8.4 Hz, 4H), 7.41 (t, J ¼
7.6 Hz, 2H), 7.14 (t, J ¼ 7.6 Hz, 2H), 6.94 (s, 2H), 6.80 (d, J ¼
7.6 Hz, 2H). 13C NMR (CDCl3, 100 MHz, ppm) d 150.43,
147.96, 145.17, 141.85, 141.51, 139.29, 132.39, 128.15,
128.08, 127.63, 127.26, 124.08, 122.76, 120.90, 120.28,
118.79, 110.87, 66.11. Anal. Calcd. for C39H22N2: C, 90.32; H,
4.28; N, 5.40. Found: C, 90.35; H, 4.41; N, 5.53.
294
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
1H NMR (CD2Cl2, 400 MHz, ppm) d 8.61 (d, J ¼ 9.2 Hz, 2H),
8.34 (d, J ¼ 1.6 Hz, 2H), 8.18 (d, J ¼ 8.0 Hz, 4H), 8.02 (d, J
¼ 8.8 Hz, 2H), 7.80 (d, J ¼ 8.8 Hz, 2H), 7.70 (dd, J ¼ 1.8, 8.6
Hz, 2H), 7.43 (d, J ¼ 3.6 Hz, 8H), 7.30 (m, 4H). 13C NMR
(CDCl3, 100 MHz, ppm) d 146.62, 143.18, 141.65, 139.71,
131.66, 127.14, 126.74, 125.97, 125.86, 124.87, 123.33,
120.17, 120.02, 119.91, 111.14, 109.56. Anal. Calcd. for
Synthesis of Polymers
Taking the preparation of PTC-2 as an example: To a 25-mL
round bottom flask charged with M1 (270.6 mg, 0.40 mmol),
M2 (359.5 mg, 0.40 mmol), 9,9-dihexylfluorene-2,7-bis(tri-
methyleneborate) (M3) (401.8 mg, 0.80 mmol), potassium
carbonate (396.2 mg, 2.90 mmol), and tetrabutylammonium
bromide (61.4 mg, 0.19 mmol) was added tetrakis(triphenyl-
phosphine) palladium (2 mg) in glove-box. Degassed toluene
(6.4 mL) and water (1.5 mL) was added into the mixture by
syringe. After heating the mixture at 83 ꢀC under nitrogen
atmosphere for 42 h, excess phenylboronic acid and bromo-
benzene were added as end-capping reagents sequentially in
12 h interval. The mixture was extracted with chloroform for
three times, and the combined organic extracts were washed
with water, brine, and dried over sodium sulfate. The salt was
filtered off, and the filtrate was concentrated into a small vol-
ume. The polymer solution was added dropwise into stirred
methanol. After filtration, the collected solid was purified by
reprecipitating into methanol and then Soxhlet extraction with
acetone. The polymer was then dried under vacuum to give
557.2 mg of pale yellow solid with a yield of 72.4%. GPC
(THF) Mn ¼ 29.5 kDa, Mw ¼ 48.0 kDa, PDI ¼ 1.63.
C42H26N4O2: C, 81.54; H, 4.24; N, 9.06. Found: C, 81.55; H,
4.27; N, 9.01.
4-[(3,6-Di-9H-carbazol-9-yl)-9H-carbazol-
9-yl]aniline (5)
To a solution of 4 (3.71 g, 6.0 mmol) in 250 mL of dry THF/
ethanol (1:1), added SnCl2 (5.69 g, 30.0 mmol). The mixture
was heated to reflux for 24 h. The solvent was removed
under reduced pressure then the residue was neutralized
slowly with cool 40 wt % NaOH. After the mixture became
alkaline, 300 mL of toluene was added with stirring. The
solid was removed by filtration and the aqueous layer of the
filtrate was extracted with toluene twice (150 mL each
time). The combined organic layer was washed with brine
and dried over sodium sulfate. After the solvent was
removed, off-white solid 5 was obtained (3.22 g, 91.4%).
1H NMR (CD2Cl2, 400 MHz, ppm) d 8.32 (s, 2H), 8.18 (d, 4H,
J ¼ 7.6 Hz), 8.03–8.09 (m, 4H), 7.29–7.74 (m, 52H), 7.09–
7.16 (m, 4H), 1.93–2.01 (m, 8H), 0.92–1.09 (m, 24H), 0.52–
0.77 (m, 20H). Anal. Calcd. for [C143H118N6]n: C, 89.43; H,
6.19; N, 4.38. Found: C, 88.81; H, 6.25; N, 4.25.
1H NMR (CD2Cl2, 400 MHz, ppm) d 8.29 (s, 2H), 8.17 (d, 4H,
J ¼ 7.6 Hz), 7.62 (d, 4H, J ¼ 1.2 Hz), 7.48 (d, 2H, J ¼ 8.8
Hz), 7.42 (d, 8H, J ¼ 3.6 Hz), 7.29 (m, 4H), 6.99 (d, 2H, J ¼
8.8 Hz), 4.06 (s, 2H). 13C NMR (CD2Cl2, 100 MHz, ppm) d
147.44, 142.28, 141.85, 130.24, 128.82, 127.50, 126.35,
126.27, 123.97, 123.48, 120.53, 120.01, 119.93, 116.24,
111.75, 110.15. Anal. Calcd. for C42H28N4: C, 85.69; H, 4.79;
N, 9.52. Found: C, 85.64; H, 5.20; N, 9.16.
PSF. M1 (270.5 mg, 0.40 mmol) and M3 (200.9 mg, 0.40
mmol) were used for preparation of PSF and 283.0 mg of
light-yellow solid were obtained with a yield of 83.3%. GPC
(THF) Mn ¼ 4.6 kDa, Mw ¼ 5.9 kDa, PDI ¼ 1.28.
4-(3,6-(Di-9H-carbazol-9-yl)-9H-carbazol-9-yl)-
40,400-dibromotriphenylamine (M2)
1H NMR (CD2Cl2, 400 MHz, ppm) d 8.01–8.10 (m, 4H), 7.35–7.76
(m, 18H), 7.05–7.15 (m, 4H), 1.92 (br, 4H), 0.92–0.99 (m, 12H),
0.52–0.71 (m, 10H). Anal. Calcd. for [C64H52N2]n: C, 90.53; H, 6.17;
N, 3.30. Found: C, 90.41; H, 6.41; N, 3.17.
A mixture of 5 (2.24 g, 3.8 mmol), 1-bromo-4-iodobenzene
(2.80 g, 9.9 mmol), Pd(OAc)2 (171 mg, 0.76 mmol), 1,10-bis
(diphenylphosphino)-ferrocene (845 mg, 1.52 mmol), and so-
dium tert-butoxide (1.46 g, 15.2 mmol) was purged with
nitrogen and then added dry toluene (35 mL). The mixture
was refluxed for 36 h in the dark and cooled to room tem-
perature. The suspension was dispersed in 300 mL toluene
and filtered to remove the solid. The filtrate was washed
with water, brine, and dried over sodium sulfate. After the
solvent was removed, the residue was purified by column
chromatography with n-hexane/dichloromethane (4:1) to
give M2 as off-white solid (1.76 g, 51.4%).
1H NMR (CD2Cl2, 400 MHz, ppm) d 8.32 (s, 2H), 8.18 (d, 4H,
J ¼ 8.0 Hz), 7.73 (d, 2H, J ¼ 8.4 Hz), 7.63–7.67 (m, 4H), 7.48
(d, 4H, J ¼ 8.8 Hz), 7.42 (d, 8H, J ¼ 4.0 Hz), 7.38 (d, 2H, J ¼
8.8 Hz), 7.28–7.33 (m, 4H), 7.13 (d, 4H, J ¼ 8.8 Hz). 13C
NMR (CD2Cl2, 100 MHz, ppm) d 146.83, 146.28, 141.84,
140.89, 132.62, 131.78, 130.29, 128.17, 126.16, 126.11,
125.89, 124.83, 123.93, 123.13, 120.17, 119.68, 119.67,
116.28, 111.36, 109.70. m/z (EI) 898 (Mþ, 100%), 902
(11%), 901 (29%), 900 (59%), 899 (56%), 897 (29%), 896
(47%), 822 (6%), 821 (18%), 820 (30%), 819 (19%), 818
(29%). Anal. Calcd. for C54H34Br2N4: C, 72.17; H, 3.81; N,
6.23. Found: C, 72.32; H, 4.08; N, 5.95.
PTC-1. M1 (202.9 mg, 0.30 mmol), M2 (134.8 mg, 0.15
mmol) and M3 (226.0 mg, 0.45 mmol) were used for prepa-
ration of PTC-1 and 314.3 mg of pale yellow solid were
obtained with a yield of 75.6%. GPC (THF) Mn ¼ 11.0 kDa,
Mw ¼ 16.5 kDa, PDI ¼ 1.50.
1H NMR (CD2Cl2, 400 MHz, ppm) d 8.32 (s, 2H), 8.18 (d, 4H,
J ¼ 7.6 Hz), 8.02–8.12 (m, 8H), 7.26–7.76 (m, 70H), 7.07–
7.16 (m, 8H), 1.92–2.10 (m, 12H), 0.92–1.05 (m, 36H), 0.63–
0.77 (m, 30H). Anal. Calcd. for [C207H170N8]n: C, 89.77; H,
6.19; N, 4.05. Found: C, 89.73; H, 6.32; N, 3.95.
PTC-3. M1 (101.5 mg, 0.15 mmol), M2 (269.6 mg, 0.30
mmol), and M3 (226.0 mg, 0.45 mmol) were used for prepa-
ration of PTC-3, and 339.7 mg of pale yellow solid were
obtained with a yield of 75.7%. GPC (THF) Mn ¼ 15.6 kDa,
Mw ¼ 25.0 kDa, PDI ¼ 1.60.
1H NMR (CD2Cl2, 400 MHz, ppm) d 8.32 (s, 4H), 8.18 (d, 8H,
J ¼ 7.6 Hz), 8.05–8.11 (m, 4H), 7.306–7.82 (m, 86H), 7.07–
7.16 (m, 4H), 2.01–2.10 (d, br, 12H), 0.92–1.10 (m, 36H),
0.53–0.77 (m, 30H). Anal. Calcd. for [C222H184N10]n: C, 89.12;
H, 6.20; N, 4.68. Found: C, 89.01; H, 6.34; N, 4.66.
CONJUGATED BLUE-LIGHT-EMITTING COPOLYMERS, LIN ET AL.
295

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
PTCF. M2 (359.5 mg, 0.40 mmol) and M3 (200.9 mg, 0.40
mmol) were used for preparation of PTCF, and 178.6 mg of
pale yellow solid were obtained with a yield of 41.7%. GPC
(THF) Mn ¼ 17.1 kDa, Mw ¼ 27.4 kDa, PDI ¼ 1.60.
via the Suzuki coupling reaction. The feed molar ratios
between M1 and M2 were 1:0, 2:1, 1:1, 1:2, and 0:1 in PSF,
PTC-1, PTC-2, PTC-3, and PTCF, respectively. The yields
were 41.7–83.3%. All the polymers showed good solubility
in toluene, dichloromethane, chloroform, and tetrahydrofuran
and could be spin coated into high-quality films for device
fabrication. The number–average molecular weights (Mn)
and weight–average molecular weights (Mw) of the polymers
were in the range of 4600–29,500 and 5900–48,000, respec-
tively, with the polydispersity indexes of 1.28–1.63. PSF,
which was composed of M1 and M3, precipitated from solu-
tion during the polymerization propagation. It is easy to
understand that PSF demonstrated the lowest molecular
weight (Mw/Mn ¼ 5900/4600) compared with other poly-
mers due to its poor solubility. The chemical structures of
the intermediates and monomers were characterized by 1H
and 13C NMR spectra. The 1H NMR spectra of the copoly-
mers were consistent with their statistic chemical structures.
We found that the actual molar ratio of the monomers in
each polymer calculated from 1H NMR is in good agreement
with the corresponding feed molar ratio. The 1H and 13C
NMR spectra are shown in the Supporting Information (SI).
Thermal properties of the polymers were evaluated by ther-
mogravimetric analysis (TGA) and differential scanning calo-
rimetry (DSC) under a nitrogen atmosphere. The spectra are
shown in Figures 1 and 2. The decomposed temperatures
(Tds, 5 wt % loss) of the polymers are higher than 400 ꢀC.
The first ꢃ20% weight loss from 400 to 480 ꢀC is assigned
to the decomposition of alkyl groups. The glass-transition
temperatures (Tgs) are all higher than 250 ꢀC. The TGA and
DSC results indicate that the polymers possess extremely
good thermal stability. The physical properties of all the
polymers are summarized in Table S1.
1H NMR (CD2Cl2, 400 MHz, ppm) d 8.31 (s, 2H), 8.17 (d, br,
4H), 7.29–7.80 (m, 34H), 2.10 (d, br, 4H), 1.10 (br, 12H),
0.77 (br, 10H). Anal. Calcd. for [C79H66N4]n: C, 88.56; H, 6.21;
N, 5.23. Found: C, 88.59; H, 6.38; N, 5.06.
Device Fabrication and Performance Measurements
The PLEDs were fabricated on indium tin oxide (ITO)-coated
glass substrates. The substrates were precleaned sequentially
in detergent solution, distilled water, acetone, and methanol
in an ultrasonic bath. The cleaned substrates were treated
with oxygen-argon plasma and spin coꢀated with 50nm of
(PEDOT:PSS), followed by drying at 120 C in air for 30 min
to remove residual water. For Device A, as shown in the
inset of Figure 5(a), the polymers were spin coated from a
chloroform solution onto the ITO/PEDOT:PSS surface and
annealed at 120 ꢀC for 30 min to form a 80-nm thick
emitting layer. For Device B, as shown in the inset of
Figure 6(a), a solution of 70 wt % polymer and 30 wt %
PBD in chloroform, which was prefiltered through Teflon fil-
ter (0.45 lm), was then spin coated on top of the PEDOT:PSS
layer followed by annealing at 120 ꢀC for 30 min to form a
80-nm thick emitting layer. A 1-nm thick CsF buffer layer
was grown through thermal sublimation in a vacuum of 1 ꢁ
10ꢂ5 Pa onto the emitting layer both in Devices A and B.
The cathode was composed of 10 nm Ca and 100 nm Al,
which were successively thermally deposited. The corre-
sponding configuration of Device A was ITO/PEDOT:PSS
(50 nm)/polymers (80 nm)/CsF (1 nm)/Ca (20 nm)/Al
(100 nm), whereas that of Device B was ITO/PEDOT:PSS
(50 nm)/polymers:PBD (80 nm)/CsF (1 nm)/Ca (20 nm)/Al
(100 nm). The steady-state current–voltage–luminance (I–V–
L) characteristics were recorded using a Keithley 2400
source meter with a calibrated Si photodiode. The EL spectra
were measured by a PR650 SpectraScan spectrophotometer.
All measurements were carried out at room temperature
under ambient conditions.
Optical and Photoluminescence Properties
The normalized UV-vis absorption and photoluminescence
(PL) spectra of the polymers in dilute (10ꢂ6 M) toluene solu-
tion are shown in Figure 3(a). The absorption maxima are in
the range of 359–372 nm corresponding to the p–p* transi-
tion of the polymer backbone. The absorption bands are red
shifted gradually with increasing the content of tricarbazole-
triphenylamines. Thus, PTCF, which is composed of only tri-
carbazole-triphenylamine repeating unit and 9,9-dihexylfluor-
ene repeating unit, shows the absorption maximum at 372
nm, which is the longest wavelength among the polymers,
suggesting relatively longest p-conjugation.14 The absorption
shoulders at about 346 nm of PTC-1, PTC-2, PTC-3, and
PTCF could be ascribed to the carbazole absorption.15 In PL
emission spectra, PSF has the shortest emission peak at 414
nm with a vibronic shoulder at around 436 nm. The other
four polymers have the main emission peaks at 422–423 nm
with small shoulders at 443 nm. From the absorption and
PL emission spectra, the Stokes shifts of PTC-1, PTC-2, and
PTC-3 were calculated to be 61, 57, and 54 nm, respectively,
which are larger than that of PSF and PTCF. The larger
Stokes shifts in the three copolymers might suggest that
incorporation of both M1 and M2 into the polymer backbone
causes a larger geometric conformation change from the
RESULTS AND DISCUSSION
Synthesis and Characterization
The synthetic routes to the monomers (M1 and M2) and
polymers are shown in Schemes 1–3. 2,7-Dibromo-9,90-spiro-
bifluorene (1) reacted with 4-cyanophenylboronic acid to
afford 2,7-bis(40-cyanophenyl)-9,90-spirobifluorene (2) using
Suzuki coupling reaction at the presence of palladium (0)
catalyst. M1 was obtained through bromination of Com-
pound 2 by using appropriate amount of bromine catalyzed
by FeCl3. 3,6-(Di-9H-carbazol-9-yl)-9-(4-nitrophenyl)-9H-car-
bazole (4) was prepared by the Ullmann reaction between
3,6-dibromo-9-(4-nitrophenyl)-9H-carbazole (3) and carba-
zole. 4 was reduced to 4-[(3,6-di-9H-carbazol-9-yl)-9H-carba-
zol-9-yl]aniline (5) by using SnCl2. The key monomer M2
was obtained by Ullmann reaction between 5 and 1-bromo-
4-iodobenzene, using palladium(II) acetate as a catalyst. The
polymers with different ratios of comonomers were prepared
296
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
FIGURE 1 TGA curves of the polymers recorded under flowing
nitrogen conditions. [Color figure can be viewed in the online
issue, which is available at www.interscience.wiley.com.]
ground states to excited states in solutions:16 higher content of
M1, larger geometric conformation caused. The corresponding
fluorescence quantum yields (Uf) of the polymers were deter-
mined by using quinine sulfate (U ¼ 0.55) as a reference
according to the method reported.17 The fluorescence and
absorption of quinine sulfate were measured in a 0.1 M sulfuric
acid aqueous solution. PL quantum yields of the polymers were
measured in dilute toluene solution. As shown in Table S1, the
fluorescence quantum yields of PSF, PTC-1, PTC-2, PTC-3, and
PTCF are 0.79, 0.75, 0.82, 0.66, and 0.60, respectively.
FIGURE 3 UV-Vis absorption and PL emission spectra for the
polymers (a) in dilute toluene solution (10ꢂ6 mol/L) and (b) in
thin film. [Color figure can be viewed in the online issue, which
is available at www.interscience.wiley.com.]
Figure 3b shows the normalized UV-vis and PL spectra of
the copolymers in thin films. The absorption maxima are in
the range of 370–375 nm. The maximum absorption wave-
length shifts of PSF, PTC-1, PTC-2, PTC-3, and PTCF from
dilute solutions to thin films are 13, 10, 5, 2, and 3 nm,
respectively, indicating that weak aggregation effect existed
in the PSF film could be fully suppressed by incorporation of
tricarbazole-triphenylamine segments into the polymer back-
bone. In the emission spectra, 10–23 nm of red shifts were
observed in the solid states compared with that in dilute solu-
tions, indicating the excitons could transfer the energy to
lower energy site before radiation occurred in the solid
state.18 The copolymer PTC-1, PTC-2, and PTC-3 showed
more red-shifted emissions and larger Stokes shifts than both
PSF and PTCF, which could be ascribed to larger geometric
conformation change from the ground states to excited states
in thin films as explained above. Moreover, the red shifts of
PTC-1, PTC-2, and PTC-3 in comparison with the homopoly-
mers are only observed in emission spectra but not in absorp-
tion spectra and also suggest that no intramolecular charge
transfer (ICT) from the electron-donating component to elec-
tron-withdrawing component exists in the copolymers.19
Electrochemical Properties
Cyclic voltammetry (CV) experiments were carried out to
investigate the electrochemical properties of the polymers.
The CV curves of PSF, PTC-1, PTC-2, PTC-3, and PTCF are
shown in Figure 4. Both the reduction and oxidation cycles
of the polymer films were measured in acetonitrile conduct-
ing with tetrabutylammonium hexafluorophosphate as the
electrolyte. Polymer solutions were coated on the surface of
FIGURE 2 DSC measurements of the polymers recorded under
flowing nitrogen atmosphere.
CONJUGATED BLUE-LIGHT-EMITTING COPOLYMERS, LIN ET AL.
297

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
from ꢂ5.18 to ꢂ5.71 eV using the equation of HOMO¼ ꢂ4.8
ox
onset
ꢂ (E
ꢂ 0.51) eV. Meanwhile, the calculated LUMO levels
of the polymers lay between ꢂ2.25 and ꢂ2.94 eV. The elec-
trochemical measurement results were summarized in Table
S2. When tricarbazole-triphenylamine units were incorpo-
rated into the copolymers, both HOMO and LUMO levels
increased significantly, compared with homopolymer PSF.
The HOMOs and LUMOs for PTC-1, PTC-2, and PTC-3 are in
the range of ꢂ5.18 to ꢂ5.32 eV and ꢂ2.25 to ꢂ2.41 eV,
respectively, which are lowered by about 0.5 eV and 0.7 eV
than that for PSF, suggesting that the HOMO/LUMO energy
levels of the copolymers are dominated by the electron-
donating moieties in the polymer backbones.
Electroluminescence Properties
To investigate the electroluminescence properties of the
polymers, two types of devices were fabricated: one used
pure polymer films as the emissive layer and the other used
PBD-doped polymers. The corresponding device structures
are ITO/PEDOT:PSS/polymers/CsF/Ca/Al (Device A) and
ITO/PEDOT:PSS/polymers:PBD/CsF/Ca/Al (Device B). In
both device configurations, poly (ethylenedioxy)thiophene
mixed with poly(styrene sulfonic acid) (PEDOT:PSS) was
used as the hole injection layer (50 nm). The emissive layer
was 80 nm, and cesium-fluoride (CsF) (1 nm) was used as
the electron-injection layer. The 20 nm of Ca and 100 nm of
Al were deposited onto CsF layer as the cathode. With the
configuration of Device A, as summarized in Table S3, the
reference polymer PTCF presented the highest turn-on volt-
age and brightness but the lowest maximum current effi-
ciency and power efficiency, which should be ascribed to the
poor electron transporting property of the polymer. Another
reference polymer PSF showed the lowest maximum lumi-
nance because of poor hole transporting. Incorporation of
both M1 and M2 into the polymers facilitates the tunability
of the electroluminescence properties such as the turn-on
voltages, luminance, current and power efficiencies, EL spec-
tra, and CIE coordinates. Among the five polymers, PTC-1
showed the highest current efficiency of 0.99 cd/A, which is
ꢃ50% higher than that for the devices based on the two ref-
erence polymers, suggesting relatively balanced electron/
hole transportation. All these polymers exhibit good spectral
stability during device operated at different voltages. Figure
5(d) shows the EL spectra of these polymers at the applied
voltage of 8 V. It can be observed that the EL maxima of the
polymers are all red shifted compared with their PL spectra
in thin films. The difference between the PL and EL spectra
is caused by the different emission mechanism: the PL emis-
sion only involves exciton migration and relaxation, but in
EL both charge migration and energy transfer are involved.20
In addition, the formation of eximers could be another rea-
son. The EL maxima of PSF (488 nm), PTC-1 (488 nm), and
PTC-2 (484 nm) are in the sky blue region.
FIGURE 4 Cyclic voltammograms of the polymers in solid
states, collected in 0.1 M nBu4NPF6 acetonitrile solution at
room temperature. Scan rate: 100 mV sꢂ1
.
the working electrode by drop-casting method. All the poly-
mers displayed reversible reduction and oxidation processes,
suggesting good electrochemical stability for the electron-
withdrawing/donating segments in the polymers. The onset
oxidation potentials of the polymers measured from the CV
traces are in the range of 0.89–1.42 V. The onset reduction
potentials of the polymers changed from ꢂ1.35 to ꢂ2.04 V
with decreasing content of cyanophenyl-spirobifluorene
units. The PSF, whose structure is dominated by the elec-
tron-withdrawing units, has the highest onset reduction
potential of ꢂ1.35 V, indicating the strongest electron-with-
drawing property. PTC-2, PTC-3, and PTCF, containing more
tricarbazole-triphenylamine units than cyanophenyl-spirobi-
fluorene units, demonstrate very close onset reduction/
oxidation potentials, indicating they have similar charge
injecting and transporting properties. The bandgaps of the
polymers were calculated based on the onset reduction and
onset oxidation potentials and found to be from 2.77 to 2.94
eV. The bandgaps were tuned by the ratios of M1 and M2:
the polymer without M2 had the lowest bandgap whereas
incorporation of M2 into the polymer backbone could raise
the bandgaps compared with PSF. This indicates that incor-
poration of M2 moieties into the polymer backbone can
To obtain higher performance, devices with optimized struc-
tures (Device B) with the configuration of ITO/PEDOT:PSS/
polymers:PBD/CsF/Ca/Al were fabricated in which the emis-
sive layer contained 70% of polymers and 30% of PBD [5-
improve the color quality for blue-light emission. With ferro-
ox
onset
cene as the external standard (E
was found to be 0.51
V), the HOMO levels of the polymers were calculated to be
biphenyl-2-(4-tert-butyl)phenyl-1,3,4-oxadiazole)],
because
298
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

FIGURE 5 (a) Current density versus applied bias voltage (inset: device configuration of ITO/PEDOT:PSS/polymers/CsF/Ca/Al); (b)
luminance versus applied bias voltage; (c) current efficiency versus current density; and (d) the normalized EL spectra of the
polymers recorded at the voltage of 8 V.
FIGURE 6 (a) Current density versus applied bias voltage (inset: device configuration of ITO/PEDOT:PSS/polymers:PBD/CsF/Ca/
Al); (b) luminance versus applied bias voltage; (c) current efficiency versus current density for devices; and (d) the normalized
EL spectra of the polymers mixed with PBD recorded at the voltage of 8 V.

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
PBD can help to confine the holes in the emissive layer by
blocking the holes migrating to cathode side. In addition,
PBD can narrow the emissive spectrum to achieve better
color quality for blue emission.12 The results of the devices
doped with PBD were summarized in Table S4 and the I–V–L
plots were shown in Figure 6(a–c). As expected, the doped
devices exhibited improved performances in comparison
with the pure polymer-based devices: higher luminance,
higher current efficiencies and power efficiencies, and deeper
blue EL spectra. Except PTC-1, all the polymers showed
lower turn-on voltages. Compared with the pure polymer-
based devices, the maximum brightness has been raised by
25–174%; the highest current efficiencies were improved by
0.3–1.3 times. Among them, PTC-1 and PTC-2 demonstrated
similar current efficiency. However, PTC-2 showed higher
luminance and better power efficiency. The EL spectra of the
optimized devices driven at 8 V are shown in Figure 6(d).
All the polymers showed blue-shifted emissions. The x þ y
values of the CIE coordinates of the undoped devices are in
the range of 0.36–0.53. The values are significantly reduced
to 0.26–0.40 in Device B. All the polymers, except PTC-1,
emitted pure blue to deep blue light in Device B. All the
results indicated that doping PBD was an effective approach
to improve the device performance and suppress the forma-
tion of excimers in the emissive layer. Among the polymers,
PTC-2 showed the best performance with the turn-on volt-
age of 3.0 V, maximum brightness of 7257 cd/m2, current
efficiency of 1.76 cd/A, power efficiency of 1.30 lm/W, and
EL emission peak at 460 nm with the CIE coordinates of
(0.15, 0.14).
layers. In comparison with the pure polymer-based devices,
the polymers in Device B with 30 wt % of PBD in the active
layers showed improved device performance. The maximum
current efficiencies were improved by 0.3–1.3 folds, and the
brightnesses were increased by 25–174%. In addition, all the
polymers emitted deep blue light with x þ y values of about
0.30. Among all the polymers, PTC-2 demonstrated the best
performance with the highest brightness of 7257 cd/m2, max-
imum current efficiency of 1.76 cd/A, power efficiency of 1.30
lm/w, and CIE coordinates of (0.15, 0.14).
REFERENCES AND NOTES
1 (a) Geng, Y.; Trajkovska, A.; Katsis, D.; Ou, J. J.; Culligan, S. W.; Chen,
S. H. J Am Chem Soc 2002, 124, 8337–8347; (b) Scherf, U.; List, E. J.
W. Adv Mater 2002, 14, 477–487; (c) Geng, Y.; Culligan, S. W.; Traj-
kovska, A.; Wallace, J. U.; Chen, S. H. Chem Mater 2003, 15, 542–549;
(d) Kulkarni, A. P.; Tonzola, C. J.; Babel, A.; Jenekhe, S. A. Chem Mater
2004, 16, 4556–4573; (e) Li, J. Y.; Ziegler, A.; Wegner, G. Chem Eur J
2005, 11, 4450–4457; (f) Tang, W; Ke, L.; Tan, L.; Lin, T.; Kietzke, T.;
Chen, Z. K. Macromolecules 2007, 40, 6164–6171; (g) Grisorio, R.;
Piliego, C.; Cosma, P.; Fini, P.; Mastrorilli, P.; Gigli, G.; Suranna, G. P.;
Nobile, C. F. J Polym Sci Part A: Polym Chem 2009, 47, 2093–2104.
(h) Li, H.; Wang, L.; Zhao, B.; Shen, P.; Tan S. J Polym Sci Part A: Polym
Chem 2009, 47, 3296–3308; (i) Jeong, E; Kim, S. H.; Jung, I. H.; Xia, Y.;
Lee, K.; Suh, H.; Shim, H.-K.; Woo, H. Y. J Polym Sci Part A: Polym
Chem 2009, 47, 3467–3479.
2 (a) Chen, X.; Liao, J. L.; Liang, Y.; Ahmed, M. O.; Tseng, H. E.; Chen, S.
A. J Am Chem Soc 2002, 125, 636–637; (b) Mu¨ller, C. D.; Falcou, A.;
Reckefuss, N.; Rojahn, M.; Wiederhirn, V.; Rudati, P.; Frohne, H.;
Nuyken, O.; Becker, H.; Meerholz, K. Nature 2003, 421, 829–833; (c)
Shu, C. F.; Dodda, R.; Wu, F. I.; Liu, M. S.; Jen, A. K. Y. Macromolecules
2003, 36, 6698–6703; (d) Liu, J.; Zhou, Q.; Cheng, Y.; Geng, Y.; Wang,
L.; Ma, D.; Jing, X.; Wang, F. Adv Mater 2005, 17, 2974–2978; (e) Tu,
G. L.; Mei, C. Y.; Zhou, Q. G.; Cheng, Y. X.; Geng, Y. H.; Wang, L. X.; Ma,
D. G.; Jing, X. B.; Wang, F. S. Adv Funct Mater 2006, 16, 101–106; (f)
Peng, Q.; Yan, L. S.; Chen, D. Z.; Wang, F. Z.; Wang, P.; Zou, D. Chun J
Polym Sci Part A: Polym Chem 2007, 45, 5296–5307; (g) Park, M. J.;
Lee, J.; Park, J. H.; Lee, S. K.; Lee, J. I.; Chu, H. Y.; Hwang, D. H.; Shim, H.
K. Macromolecules 2008, 41, 3063–3070; (h) Hsieh, B.-Y.; Chen, Y. J
Polym Sci Part A: Polym Chem 2009, 47, 833–844.
CONCLUSIONS
A series of conjugated blue-light-emitting copolymers PTC-1,
PTC-2, and PTC-3 containing cyanophenyl substituted spiro-
bifluorenes and tricarbazole-triphenylamines has been
designed and synthesized. For comparison, two reference
polymers PSF and PTCF were also prepared. The feed ratios
of two monomers (20,70-dibromo-2,7-bis(40-cyanophenyl)-
9,90-spirobifluorene and 4-(3,6-(di-9H-carbazol-9-yl)-9H-
carbazol-9-yl)-40,400-dibromotriphenylamine) in PSF, PTC-1,
PTC-2, PTC-3, and PTCF were varied from 1:0, 2:1, 1:1, 1:2,
to 0:1, respectively. TGA and DSC analyses indicated that all
the polymers had good thermal stabilities: the decomposed
temperatures (Tds, 5 wt % loss) and the glass-transition tem-
peratures (Tgs) of the polymers are higher than 400 ꢀC and
3 (a) Snaith, H. J.; Arias, A. C.; Morteani, A. C.; Silca, C.; Friend, R. H.
Nano Lett 2002, 2, 1353–1357; (b) Svensson, M.; Zhang, F. L.; Veen-
stra, S. C.; Verhees, W. J. H.; Hummelen, J. C.; Kroon, J. M.; Inganas, O.;
Andersson, M. R. Adv Mater 2003, 15, 988–991; (c) Wang, X. J.; Per-
zon, E.; Oswald, F.; Langa, F.; Admassie, S.; Andersson, M. R.; Inganas,
O. Adv Funct Mater 2005, 15, 1665–1670; (d) Ashraf, R. S.; Hoppe,
H.; Shahid, M.; Gobsch, G.; Sensfuss, S.; Klemm, E. J Polym Sci Part A:
Polym Chem 2006, 44, 6952–6961; (e) Mcneill C. R.; Halls, J. J. M.;
Wilson, R.; Whiting, G. L.; Berkebile, S.; Ramsey, M. G.; Friend, R. H.;
Greenham, N. C. Adv Funct Mater 2008, 18, 2309–2321; (f) Tang, W.;
Chellappan, V.; Liu, M.; Chen, Z.-K.; Ke, L. ACS Appl Mater Interfaces
2009, 1, 1467–1473; (g) Park, J. S.; Ryu, T. L.; Song, M.; Yoon, K.-J.;
Lee, M. J.; Shin, I. A.; Lee, G.-D.; Lee, J. W.; Gal, Y.-S.; Jin, S.-H. J Polym
Sci Part A: Polym Chem 2008, 46, 6175–6184.
ꢀ
250 C, respectively. The fluorescence quantum yields of the
polymers measured in dilute toluene solution are in the range
of 60–82%. Investigation of the cyclic voltammetric behaviors
of the polymer films revealed that the band gaps of the poly-
mers are from 2.77 to 2.94 eV. The higher the content of the
cyanophenyl-spirobifluorene, the lower HOMO and LUMO
energy levels were obtained. The EL performances of the three
copolymers and two reference polymers were evaluated with
two device configurations: ITO/PEDOT:PSS/polymers/CsF/
Ca/Al (Device A) and ITO/PEDOT:PSS/polymers(70%):PBD
(30%)/CsF/Ca/Al (Device B). The polymers emitted sky blue
light when the pure polymers were used as the emissive
4 (a) Babel, A.; Jenekhe, S. A. Macromolecules 2003, 36, 7759–7764;
(b) Chen, M.; Crispin, X.; Perzon, E.; Andersson, M. R.; Pullerits, T.;
Andersson, M.; Ingana¨s, O.; Berggren, M. Appl Phys Lett 2005, 87,
252105–252107; (c) Zaumseil, J.; Donley, C. L.; Kim, J. S.; Friend, R.
300
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
H.; Sirringhaus, H. Adv Mater 2006, 18, 2708–2712; (d) Lim, E.; Kim,
Y. M.; Lee, J.-I.; Jung, B.-J.; Cho, N. S.; Lee, J.; Do, L.-M.; Shim, H.-K. J
Polym Sci Part A: Polym Chem 2006, 44, 4709–4721; (e) Charas, A.;
Alcacer, L.; Pimentel, A.; Conde, J. P.; Morgado, J. Chem Phys Lett
2008, 455, 189–191.
9 Taranekar, P.; Abdulbaki, M.; Krishnamoorti, R.; Phanichphant, S.;
Waenkaew, P.; Patton, D.; Fulghum, T.; Advincula, R. Macromolecules
2006, 39, 3848–3854.
10 Zhen, C. G.; Chen, Z. K.; Liu, Q. D.; Dai, Y. F.; Shin, R. Y. C.; Chang, S.
Y. Kieffer, J. Adv Mater 2009, 21, 2425–2429.
5 (a) Jenekhe, S. A.; Osaheni, J. A. Science 1994, 265, 765–768; (b)
Grell, M.; Bradley, D. D. C.; Ungar, G.; Hill, J.; Whitehead, K. S. Macro-
molecules 1999, 32, 5810–5817.
11 Lu, J.; Tao, Y.; D’iorio, M.; Li, Y.; Ding, J.; Day, M. Macromolecules
2004, 37, 2442–2449.
12 (a) Cao, Y.; Parker, I. D.; Yu, G.; Zhang, C.; Heeger, A. J. Nature 1999,
397, 414–417; (b) Kim, B. S.; Kim, C. G.; Oh, J. J.; Kim, M. S.; Kim, G. W.;
Park, D. K. Macromol Res 2006, 14, 343–347.
6 (a) Kla¨rmer, G.; Lee, J. I.; Lee, V. Y.; Chan, E.; Chen, J. P.; Nelson, A.;
Markiewicz, D.; Siemens, R.; Scott, J. C.; Miller, R. D. Chem Mater
1999, 11, 1800–1805; (b) Ego, C.; Grimsdale, A. C.; Uckert, F.; Yu, G.;
Srdanov, G.; Mu¨llen, K. Adv Mater 2002, 14, 809–811; (c) Yoon, K.-J.;
Park, J. S.; Lee, S.-J.; Song, M.; Shin, I. A. Lee, J. W.; Gal, Y.-S.; Jin,
S.-H. J Polym Sci Part A: Polym Chem 2008, 46, 6762–6769. (d)
Horst, S.; Evans, N. R.; Bronstein, H. A.; Williams, C. K. J Polym Sci
Part A: Polym Chem 2009, 47, 5116–5125; (e) Chen, R.-T.; Chen,
S.-H.; Hsieh, B.-Y.; Chen, Y. J Polym Sci Part A: Polym Chem 2009,
47, 2821–2834. (f) Bondarev, D.; Zednı´k, J.; Vohlı´dal, J.; Podha´jecka´,
13 Kulasi, A.; Yi, H.-N.; Iraqi, A. J Polym Sci Part A: Polym Chem
2007, 45, 5957–5967.
14 Mikroyannidis, J. A.; Gibbons, K. M.; Kulkarni, A. P.; Jenekhe, S. A.
Macromolecules 2008, 41, 663–674.
15 Li, B. L.; Liu, Z. T.; He, Y. M.; Pan, J.; Fan, Q. H. Polymer 2008, 49,
1527–1537.
ˇ
K.; Sedla´cek, J.
J Polym Sci Part A: Polym Chem 2009, 47,
16 (a) Dreuw, A. J Phys Chem A 2006, 110, 4592–4599; (b) Jiang, Z.;
Zhang, W.; Yao, H.; Yang, C.; Cao, Y.; Qin, J.; Yu, G.; Liu, Y. J Polym Sci
Part A: Polym Chem 2009, 47, 3651–3661.
4532–4546.
7 (a) Johansson, N.; Salbeck, J.; Bauer, J.; Weisso¨rtel, F.; Bro¨ms, P.;
Andersson, A.; Salaneck, W. R. Adv Mater 1998, 10, 1136–1141; (b)
Yu, W. L.; Pei, J.; Huang, W.; Heeger, A. J. Adv Mater 2000, 12,
828–831; (c) Wu, F. I.; Dodda, R.; Reddy, D. S.; Shu, C. F. J Mater
Chem 2002, 12, 2893–2897; (d) Tang, S.; Liu, M.; Gu, C.; Zhao, Y.;
Lu, P.; Liu, L.; Shen, F.; Yang, B.; Ma, Y. J Org Chem 2008, 73,
4212–4218.
17 (a) Huang, W.; Yu, W. L.; Meng, H.; Pei, J.; Li, S. F. Y. Chem Mater
1998, 10, 3340–3345; (b) Chen, Z. K.; Wang, L. H.; Kang, E. T.; Huang,
W. Phys Chem Chem Phys 1999, 1, 3789–3795; (c) Huang, C.; Zhen,
C. G.; Su, S. P.; Chellappan, V.; Balakrisnan, B.; Auch, M. D. J.; Loh, K. P.;
Chen, Z. K. Polymer 2006, 47, 1820–1829.
18 Kim, J.-S.; Lu, L.; Sreearunothat, P.; Seeley, A.; Yim, K.-H.; Petrozza, A.;
8 (a) Xiao, Y.; Yu, W. L.; Pei, J.; Chen, Z. K.; Huang, W.; Heeger, A. J.
Synth Met 1999, 106, 165–170; (b) Pucci, A.; Biver, T.; Ruggeri, G.;
Itzel Meza, L.; Pang, Y. Polymer 2005, 46, 11198–11205; (c) Jin, Y.;
Ju, J.; Kim, J.; Lee, S.; Kim, J. Y.; Park, S. H.; Son, S. M.; Jin, S. H.; Lee,
K. Suh, H. Macromolecules 2003, 36, 6970–6975; (d) Grisorio, R.;
Piliego, C.; Fini, P.; Cosma, P.; Masterorilli, P.; Gigli, G.; Suranna, G.
Murphy, C. E.; Beljonne, D. J Am Chem Soc 2008, 130, 13120–13131.
19 Liu, J.; Zou, J.; Yang, W.; Wu, H.; Li, C.; Zhang, B.; Peng, J.; Cao, Y.
Chem Mater 2008, 20, 4499–4506.
20 (a) Mal’tsev, E. I.; Brusentseva, M. A.; Berendyaev, V. I.; Kolesni-
kov, V. A.; Lunina, E. V.; Kotovb, B. V.; Vannikova, A. V. Mendeleev
Commun 1998, 8, 31–32; (b) Hsieh, B. Y.; Chen, Y. J Polym Sci
Part A: Polym Chem 2008, 46, 3703–3713.
P.; Nobile, C. F.
6051–6063.
J Polym Sci Part A: Polym Chem 2008, 46,
CONJUGATED BLUE-LIGHT-EMITTING COPOLYMERS, LIN ET AL.
301