Y. Lin et al. / Polymer 51 (2010) 1270–1278
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and good luminescence efficiency [19,20]. Polymers containing
only electron-donating segment or only electron-withdrawing
segment showed poor device performance. Jenekhe et al. [16e]
compared the performances of poly[fluorenevinylene–dipheny-
loxadiazole], poly[fluorenevinylene–triphenylamine] and the
polymer comprised both functional segments, and found that the
bipolar copolymer showed better efficiency (1.34 cd/A) over those
of poly(oxadiazole–fluorene) (0.83 cd/A) and poly(triphenylamine-
fluorene) (0.80 cd/A), when the poly(N-vinylcarbazole) (PVK) was
used as the host material. Jin et al [17c] reported three copolymers
composed of fluorene units and strong electron-withdrawing cyano
groups. The copolymers emitted yellow to orange light rather than
blue light. These ‘‘hole-only’’ or ‘‘electron-only’’ materials showed
either low efficiencies or undesirable emitting color. Therefore, the
polymers containing both electron-donating and electron-with-
drawing segments could overcome the drawbacks of the materials
discussed above.
Synthesis of 2,7-Bis(40-cyanophenyl)-9,90-spirobifluorene (2) [21]:
mixture of 2,7-dibromo-9,90-spirobifluorene (1) (1.76 g,
To
a
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 atmosphere.
Toluene (32 mL) and 2 M Na2CO3 (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 with n-hexane/ethyl acetate (5:1) as
eluent to give 2 as a white powder (1.94 g, 77.5%). 1H 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,
In this work, we report a series of fluorene-based copolymers,
consisting of cyanophenyl groups as electron transporting pendants
and carbazole-triphenylamines comonomer as hole transporting
segments. The copolymers were prepared via the Suzuki coupling
reaction with three comonomers: 20,70-dibromo-2,7-bis(40-cyano-
phenyl)-9,90-spirobifluorene (M1), 4-(9H-carbazol-9-yl)-40,400-dib-
romotriphenylamine (M2), and 9,9-dihexylfluorene-2,7-bis(trime-
thyleneborate) (M3). In the monomer M1 [21], the two cyano groups
are attached onto one of the fluorene units in spirobifluorene through
a phenylene group. Such a design can enhance the electron trans-
porting property of the polymer but avoid strong intramolecular
interaction. Generally, strong intra- and/or inter-molecular inter-
action will lead to large red shift of emission spectrum and reduced
efficiency, and is thus undesirable for blue light emitting materials.
M2, containing the carbazole-triphenylamine basic structure, has
outstanding hole transporting character. These two monomers were
conjugated but also separated by the alkyl substituted fluorene
(M3), which can further reduce the intramolecular interaction. With
different feed ratios of M1 and M2, random copolymers PCC-1, PCC-
2, and PCC-3 were synthesized. For comparison, two reference
copolymers PSF and PCF were also prepared. The electrolumines-
cence (EL) performances of these copolymers were evaluated using
two device configurations: ITO/PEDOT:PSS/polymers/CsF/Ca/Al and
ITO/PEDOT:PSS/polymers:PBD/CsF/Ca/Al. One used the pure poly-
mer as the emissive layer, and the other used 30% of 2-(4-tert-
butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) doped in the
polymer to form the emissive layer to raise the device performance,
such as the color purity and EL efficiency [22]. With the later device
configuration, maximum luminance of 6369 cd/m2 and the highest
current efficiency of 1.97 cd/A for PCC-2 were achieved.
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.
Synthesis of 20,70-Dibromo-2,7-bis(40-cyanophenyl)-9,90-spirobi-
fluorene (M1) [21]: 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 sulfite was added slowly till the
dark color disappeared. The organic 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 column
chromatography eluting with n-hexane/ethyl acetate (5:1) fol-
lowed by recrystalization with ethanol to give M1 (1.12 g, 82.5%).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. 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 4-(9H-Carbazol-9-yl)-40,400-dibromotriphenylamine
(M2): A mixture of 4-carbazol-9-yl-aniline (3) (1.29 g, 5.0 mmol), 1-
bromo-4-iodobenzene (3.39 g, 12.0 mmol), Pd(OAc)2 (224.5 mg,
1.0 mmol), 1,10-bis(diphenylphosphino)–ferrocene(1.11 g, 2.0 mmol)
and sodium tert-butoxide (1.92 g, 20.0 mmol) was purged with
nitrogen, and then dry toluene (20 mL) was added. The mixture was
refluxed for 24 h in the dark under nitrogen protection. The
suspension was dispersed in 100 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/dichloro-
methane (4:1) to give M2 as white solid (464 mg, 16.3%).1H NMR
2. Experimental section
2.1. Materials
2,7-Dibromo-9,90-spirobifluorene (1) was purchased from
Pacific ChemSource. 4-Carbazol-9-yl-phenylamine (4) was synthe-
sized according to the literature reported [14a]. 4-Cyanophe-
nylboronic acid and phenylboronic acid were bought from Boron
Molecular. Tetrakistriphenylphosphine palladium [Pd0(PPh3)4] and
palladium acetate [Pd(OAc)2] were purchased from Strem Chem-
icals. 1-Bromo-4-iodobenzene was bought from Alfa Aesar. 1,10-
Bis(diphenylphosphino)-ferrocene, tetrabutylammonium bromide,
and 9,9-dihexylfluorene-2,7-bis(trimethyleneborate) were
obtained from Aldrich. Sodium tert-butoxide and bromobenzene
were commercial available from Fluka. All the solvents were A.R.
grade and used without further purification.
(CD2Cl2, 400 MHz, ppm)
d
8.16 (d, J ¼ 7.6 Hz, 2H), 7.45 (m, 10H), 7.30
(m, 4H), 7.09 (d, J ¼ 8.8 Hz, 4H). 13C NMR (CD2Cl2, 100 MHz, ppm)
d
146.39,146.11,141.00,132.66,132.50,128.05,125.90,125.88,124.99,
123.25, 120.18, 119.85, 115.95, 109.72. Anal. Calcd for C30H20Br2N2: C,
63.40; H, 3.55; N, 4.93. Found: C, 64.34; H, 3.70; N, 4.96.
General Procedures for Suzuki Polymerization Taking PSF as an
Example: To a 25 mL round bottom flask charged with M1 (270.5 mg,
0.40 mmol), 9,9-dihexylfluorene-2,7-bis(trimethyleneborate) (M3)
(200.9 mg, 0.40 mmol), potassium carbonate (198.1 mg, 1.45 mmol)
and tetrabutylammonium bromide (30.72 mg, 0.10 mmol) was
added Pd(PPh3)4 (1.2 mg) in glove-box. Degassed toluene (3.5 mL)
and water (0.8 mL) was added into the mixture by syringe. After