Poly(spirobifluorene)s containing nonconjugated diphenylsulfone moiety: Toward blue emission through a weak charge transfer effect

Article abstract of DOI:10.1021/ma500407m

Instead of conjugated dibenzothiophene-S,S-dioxide (DBTSO), we have introduced nonconjugated diphenylsulfone (DPSO) as the electron-deficient unit into the main chain of poly(spirobifluorene)s (PSFs). Because of the weaker electron affinity of DPSO relative to DBTSO, the charge transfer from the pendant 2,3,6,7-tetraoctyloxyfluorene to the main chain can be effectively prevented. Consequently, the resultant polymers containing DPSO moiety show pure blue emissions, which is different from DBTSO-based PSFs that exhibit undesired green emissions. With a single-layer device configuration, a peak luminous efficiency of 2.90 cd/A and a maximum luminescence of 14130 cd/m² have been realized for the polymer PSFDPSO03. The corresponding CIE coordinates are (0.17, 0.18), nearly independent of the applied current density from 2 to 592 mA/cm². These results indicate that tuning the electron affinity of the incorporated electron-deficient units is a very promising strategy to control the charge transfer strength for the development of blue-emitting PSFs with high efficiency and stability.

Full text of DOI:10.1021/ma500407m

Article
pubs.acs.org/Macromolecules
Poly(spirobifluorene)s Containing Nonconjugated Diphenylsulfone
Moiety: Toward Blue Emission Through a Weak Charge Transfer
Effect
Xuchao Wang,†,‡ Lei Zhao,†,‡ Shiyang Shao,† Junqiao Ding,*,† Lixiang Wang,*,† Xiabin Jing,†
and Fosong Wang†
†State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun, 130022, P. R. China
‡University of Chinese Academy of Sciences, Beijing, 100049, P. R. China
S
* Supporting Information
ABSTRACT: Instead of conjugated dibenzothiophene-S,S-dioxide (DBTSO),
we have introduced nonconjugated diphenylsulfone (DPSO) as the electron-
deficient unit into the main chain of poly(spirobifluorene)s (PSFs). Because of
the weaker electron affinity of DPSO relative to DBTSO, the charge transfer
from the pendant 2,3,6,7-tetraoctyloxyfluorene to the main chain can be
effectively prevented. Consequently, the resultant polymers containing DPSO
moiety show pure blue emissions, which is different from DBTSO-based PSFs
that exhibit undesired green emissions. With a single-layer device configuration,
a peak luminous efficiency of 2.90 cd/A and a maximum luminescence of 14130
cd/m2 have been realized for the polymer PSFDPSO03. The corresponding
CIE coordinates are (0.17, 0.18), nearly independent of the applied current
density from 2 to 592 mA/cm2. These results indicate that tuning the electron
affinity of the incorporated electron-deficient units is a very promising strategy
to control the charge transfer strength for the development of blue-emitting PSFs with high efficiency and stability.
octyloxy-9-spirobifluorene) reported by Bo Z. et al. reveals no
green emission even after annealed at 200 °C for 3 h in air.7
However, PSFs still suffer from poorer device efficiency
compared with PFs.8
1. INTRODUCTION
Polymer light-emitting diodes (PLEDs) have attracted lots of
industrial and scientific interests due to their low-cost wet-
processing capability for display and illumination applications.1
To realize full-color displays, three primary color emitting
polymers, i.e., blue, green, and red, are highly desirable.2
Among them, it is a great challenge to produce blue-emitting
polymers with long-term stability and high efficiency.3 To date,
polyfluorenes (PFs) have been recognized as the most
promising blue emitters because of their high solid-state
quantum yields.4 Unfortunately, a blue to greenish blue color
change is often observed for PFs associated with the appearance
of a novel low energy green band emission during device
operation or thermal annealing in air. The origin of this green
emission is generally believed to be from the aggregation or
keto-defects in PFs according to the literatures.5
To solve this problem, spirobifluorene is adopted as a
building block to design blue-emitting polymers.6 Through a
spiro linkage at the 9-position of fluorene, the possibility of the
fluorene repeat unit into fluorenone is avoided, and thus the
chemical stability of poly(spirobifluorene)s (PSFs) is enhanced.
Meanwhile, the orthogonal configuration between backbone
and side groups in PSFs can bring about a large steric hindrance
of the individual polymer chains, and further prevent their
aggregation in the solid state. As a result, different from PFs,
PSFs have excellent spectral stability. For example, poly(2′-
It is believed that the hypervalent sulfur atom obtained by
oxidation can lead to an electron deficiency of the S,S-dioxide
based backbones.9 Particularly, dibenzothiophene-S,S-dioxide
(DBTSO) has been recently demonstrated as an excellent
electron-deficient moiety by the Cao group to improve the
luminous efficiency and stability of PFs.10 In view of this, we
decided to introduce the same DBTSO unit into the main chain
of PSFs. Nevertheless, our initial attempt failed because an
undesired green emission was obtained with Commission
Internationale de L’Eclairage (CIE) coordinates of (0.27, 0.46)
for PSFDBTSO05 (Figure 1).11 This was caused by the strong
charge transfer (CT) from pendant 2,3,6,7-tetraoctyloxyfluor-
ene to DBTSO in the main chain. Therefore, aiming at blue
emitters, it is necessary to weaken the strong CT effect
observed in PSFs containing DBTSO.
In this paper, by finely tailoring the structure of the electron-
deficient moiety, we have realized blue-emitting PSFs with high
efficiency and stability. As depicted in Figure 1, in place of
Received: February 24, 2014
Revised: April 9, 2014
Published: April 17, 2014
© 2014 American Chemical Society
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Figure 1. Molecular design of PSFs with different electron-deficient units.
a
Scheme 1. Synthetic Route of the Polymers
a
Reagents and conditions: (a) C8H17Br, Bu4NBr, NaOH, THF/H2O, 80 °C, 84%; (b) NBS, DMF, 94%; (c) Mg, LiCl, FeCl3, 1,2-dibromoethane,
THF, 57%; (d) NBS, DMF/CHCl3, 60%; (e) Mg, LiCl, 2,7-dibromofluorenone, THF, 62%; (f) HCl, CH3COOH, 60%; (g) PdCl2(dppf),
bis(pinacolato)diboron, KOAc, DMF, 80 °C, 75%; (h) CuI, Na2S·9H2O, K2CO3, DMF, 60%; (i) H2O2, CH3COOH, 90%; (j) Pd2(dba)3, 2-
dicyclohexylphosphino-2′,6′-dimethoxybiphenyl, Aliquat 336, K2CO3, H2O, toluene, 85−95%.
DBTSO whose electron cloud could be delocalized into the
whole conjugated backbone through 3,7-linkage, a non-
conjugated analogue, diphenylsulfone (DPSO), is incorporated
into the main chain of PSFs. Unlike PSFDBTSO05, the CT
strength can be effectively inhibited because of the lower
electron affinity energy of DPSO relative to DBTSO, and pure
blue emissions are achieved for the DPSO-based polymers
including PSFDPSO01, PSFDPSO03, PSFDPSO05,
PSFDPSO07, and PSFDPSO10 (Figure 1). Additionally, their
electron injection barriers are reduced by about 0.1−0.4 eV
after the introduction of DPSO. On the basis of a simple single-
layer device structure, PSFDPSO03 gives a promising luminous
efficiency of 2.90 cd/A together with CIE coordinates of (0.17,
0.18), which is almost independent of the applied current
density.
2. RESULTS AND DISCUSSION
2.1. Synthesis and Characterization. Scheme 1 shows
the synthetic route of the polymers. Starting from 1,2-
benzenediol, alkylation, bromination, and iron-catalyzed
homocoupling reactions12 were performed in sequence to
give the intermediate 3. After bromination of 3, the
corresponding Grignard reagent was prepared in the presence
of magnesium power and LiCl,13 followed by quenching with
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2,7-dibromofluorenone to afford the tertiary alcohol 5. Further
treatment of 5 with HCl/HOAc gave the key monomer 6,
which was further converted to the desired boronic ester 7 in a
yield of 75% via a palladium-catalyzed cross-coupling reaction.
On the other hand, another comonomer, di(4-bromophenyl)
sulfone (9), was easily obtained after the oxidation of di(4-
bromophenyl) sulfide that was derived from 4-bromoiodoben-
zene under Na2S·9H2O and CuI catalyst. With 6, 7 and 9 in
hand and simultaneously tuning the feed ratio of 9, the blue-
emitting polymers, PSFDPSO00, PSFDPSO01, PSFDPSO03,
PSFDPSO05, PSFDPSO07, and PSFDPSO10 were finally
synthesized via the Suzuki polycondensation. The actual
content of DPSO in the polymers could be estimated according
readily soluble in common organic solvents, such as toluene,
xylene, chloroform, THF, etc., ensuring the formation of their
high quality films by spin-coating. Their thermal properties
were also studied by thermogravimetric analysis (TGA) and
differential scanning calorimetry (DSC). The polymers
PSFDPSO00−PSFDPSO10 exhibit the same decomposition
temperature of 360 °C, corresponding to a 5% weight loss
(Figure 3). And in the range of 25 to 280 °C, no glass transition
1
to their H NMR spectra. As shown in Figure 2, the peaks at
Figure 3. TGA curves of the polymers.
or melting is detected for all polymers (Figure S1, Supporting
Information). According to the literature reports,6g,7 the glass
transition temperatures are reported to be 121 and 293 °C for
PSFs that contain one and two alkyloxy groups, respectively.
Hence we can speculate that the glass transition temperatures
of PSFDPSO00−PSFDPSO10 with four octyloxy chains may
be close to or even higher than the decomposition temperature,
indicative of the good thermal stability of their formed films.14
2.2. Electrochemical Properties. Cyclic voltammetry
(CV) and differential pulse voltammetry (DPV) were used to
explore the electrochemical properties of the polymers
PSFDPSO00−PSFDPSO10. With regard to the energy level
of the ferrocene reference (4.8 eV below the vacuum level),
their highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) levels are estimated
according to the equations of HOMO = −e(Eox + 4.8 V) and
LUMO = −e(Ered + 4.8 V), where Eox and Ered are taken from
the first oxidation and reduction peak in DPV curves,
respectively (Figure 4). All the polymers display nearly the
same HOMO level of about −5.40 eV, independent of the
DPSO content.
1
Figure 2. H NMR spectra of the polymers.
7.67 ppm are assigned to the protons of the homopolymer
PSFDPSO00, while the signals at 7.83 and 7.49 ppm are
attributed to the protons of DPSO. By comparing the integral
of these two sets of signals, the DPSO loading is calculated, and
the data are listed in Table 1. It is found that the actual content
Table 1. Physical Properties of the Polymers
DPSO content in the
polymers (mol %)
a
b
b
c
polymer
feed ratio actual content Mn (kDa) PDI Td (°C)
PSFDPSO00
PSFDPSO01
PSFDPSO03
PSFDPSO05
PSFDPSO07
PSFDPSO10
0
1
0
101
147
105
89
4.0
4.8
4.5
4.0
4.5
3.7
360
360
360
360
360
360
1.23
3.61
4.76
6.98
10.11
3
5
7
155
107
10
a
b
Calculated from the 1H NMR spectra. Determined by GPC in THF
c
using polystyrene standards. 5% weight loss temperature determined
by TGA in N2.
Figure 4. Cyclic voltammograms (a) and differential pulse
voltammetry (b) of the polymers in films.
of DPSO is very close to the feed ratio, suggesting that DPSO
has been fully incorporated into the main chain of the polymers
during polymerization.
The number-average molecular weight (Mn) and polydisper-
sity index (PDI) of these polymers, determined by gel
permeation chromatography (GPC), are in the range of 89−
155 kDa and 3.7−4.8, respectively (Table 1). Furthermore, in
the presence of four octyloxy chains, all the polymers are
In striking contrast, the LUMO level gradually decreases as
the content of DPSO rises. For instance, PSFDPSO10 has a
LUMO level of −2.65 eV, which is 0.43 eV lower than that of
PSFDPSO00 (−2.22 eV), implying that the electron injection
barrier can be effectively modulated to facilitate the electron
injection/transport with the insertion of DPSO into the
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Figure 5. Absorption and PL spectra of the polymers in toluene (a) and PL spectra of the polymers in films (b).
polymeric backbone. Noticeably, the LUMO level of
PSFDPSO10 is still higher than that of PFs copolymer
containing the planar conjugated DBTSO fragment (−2.82
eV).10a The result further verifies that the nonconjugated
DPSO unit possesses much weaker electron-withdrawing
capability compared with DBTSO,15 which may be favorable
for the tuning of CT degree as will be discussed later.
fluorene unit to the electron-withdrawing DPSO unit. To
confirm this CT effect, the PL spectra with different solvent
polarity were recorded for these copolymers. Taking
PSFDPSO05 as an example, the emission maxima is slightly
red-shifted from 452 nm in toluene to 478 nm in THF, and
correspondingly the full width at half-maximum (fwhm) is
increased from 78 to 100 nm (Figure S2).
2.3. Optical Properties. Figure 5a depicts the UV−vis and
photoluminescence (PL) spectra of the polymers
PSFDPSO00−PSFDPSO10 in dilute toluene solutions (data
are given in Table 2). As can be clearly seen, all the polymers
On going from solution to solid state, the 0−2 emission is
further intensified (Figure 5b). Consequently, its intensity is
comparable to that of the 0−1 counterparts for PSFDPSO07
and PSFDPSO10. Taking into account that PSFDPSO00 has
similar PL spectra in solution and film, aggregation could be
excluded due to the inherent orthogonal configuration.
Therefore, in this case both the intra- and intermolecular CT
are proposed for the enhancement of 0−2 emission. It is
worthy noting that, the developed copolymers are basically blue
emissive even for PSFDPSO10 with high content of DPSO, for
they all show well-defined vibronic peaks including 0−0, 0−1,
and 0−2 transitions. This is quite different from green-emitting
PSFDBTSO05, where a structureless CT emission dominates
the whole spectrum (Figure 5b).11 The significant difference
correlates well with the theoretical calculations performed on
the pentamers DSBF−DPSO−DSBF and DSBF−DBTSO−
DSBF, where two spirobifluorene dimers are bridged by DPSO
and DBTSO, respectively, and the octyloxy side chains are
truncated into methoxy groups. In DSBF−DBTSO−DSBF, as
shown in Figure S3, the LUMO is mainly distributed on the
central DBTSO moiety. However, due to the weaker electron-
withdrawing ability of DPSO relative to DBTSO, the LUMO
further extends into the neighboring spirobifluorene backbones
at both ends of DPSO for DSBF−DPSO−DSBF. The less
separation between HOMO and LUMO means a weak CT
character in DPSO-containing polymers, which results in their
pure blue emissions.
2.4. Electroluminescent Properties. PLEDs with a single-
layer device structure of ITO/PEDOT:PSS (40 nm)/EML (80
nm)/Ca (20 nm)/Al (100 nm) were fabricated to investigate
the electroluminescent (EL) properties of the polymers
PSFDPSO00−PSFDPSO10. The EL spectra for all the
polymers are shown in Figure 6 and the corresponding device
data are summarized in Table 3. After the inclusion of DPSO in
the backbone, the CIE coordinates gradually red-shift from
(0.16, 0.14) of PSFDPSO00 to (0.18, 0.22) of PSFDPSO10.
Interestingly, compared with the film PL counterparts (Figure
5b), the 0−2 emissions are greatly alleviated under electric
excitation. The reason is not very clear now, but we believe that
PL and EL spectra are measured under different environments,
and the lower radiative decay constant of CT states relative to
local excited states may contribute to the suppression of 0−2
emissions.17
Table 2. Optical and Electronic Properties of the Polymers
λ
λ
λ
HOMO
d
LUMO
d
abs a
(nm)
em a
em b
c
polymer
(nm)
(nm)
Φem
(eV)
(eV)
PSFDPSO00 344, 383,
399
452
437,
455
0.20
0.33
0.24
0.24
0.22
0.20
−5.39
−5.40
−5.40
−5.38
−5.39
−5.38
−2.22
−2.33
−2.45
−2.58
−2.62
−2.65
PSFDPSO01 344, 383,
399
452
452
453
455
456
456
457
464
PSFDPSO03 344, 383,
399
PSFDPSO05 343, 383,
396
PSFDPSO07 343, 383,
396
465,
480
PSFDPSO10 343, 381,
395
468,
481
a
b
Measured in toluene solution of 10−6 M at 298 K. Measured in solid
c
film at 298 K and the excitation wavelength is 360 nm. Solid state
fluorescence quantum yield measured by integrating-sphere method.
d
HOMO = −e(Eox + 4.8 V) and LUMO = −e(Ered + 4.8 V), where Eox
and Ered are the first oxidation and reduction peak taken from the DPV
curves, respectively.
exhibit two similar absorption bands in the ranges 360−430
and 310−360 nm. The former absorption originates from the
π−π* transition of the polymeric backbone and the latter is
related to the spiro-conjugated system between the backbone
and side fluorene attached with four alkoxyl groups.16 However,
their PL spectra are obviously influenced by the DPSO content,
as indicated in Figure 5a. The homopolymer PSFDPSO00 with
no DPSO unit shows an emission maxima at 452 nm
accompanied by a shoulder at 425 nm, corresponding to the
0−1 and 0−0 transitions, respectively.16 While for the
copolymers PSFDPSO01, PSFDPSO03, PSFDPSO05,
PSFDPSO07, and PSFDPSO10, a discernible 0−2 vibronic
peak at around 481 nm appears in their PL spectra, and its
intensity increases with the increasing DPSO content. Owing to
the existence of the spiro-conjugation in PSFs, the observed
spectral changes may be reasonably ascribed to the intra-
molecular CT from the electron-donating 2,3,6,7-tetraoctyloxy-
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PSFDPSO10. Correspondingly, the brightness goes initially
from 7749 cd/m2 of PSFDPSO00 upward to 14130 cd/m2 of
PSFDPSO03, and then downward to 3914 cd/m2 of
PSFDPSO10. As a consequence, among the polymers
PSFDPSO00−PSFDPSO10, PSFDPSO01 and PSFDPSO03
show the best device performance with a maximum luminous
efficiency of 2.74 cd/A (1.79 lm/W, 1.82%) and 2.90 cd/A
(1.80 lm/W, 1.78%), respectively. These values are very
promising and are comparable to those of state-of-art blue-
emitting PSFs.1c
To evaluate the spectral stability of these polymers,
PSFDPSO03 is taken as an example, and its EL spectra are
recorded driving at different applied current densities (Figure
8). With the increasing current density from 2 to 592 mA/cm2
Figure 6. EL spectra of the polymers at 5 V.
Table 3. Devices Characteristic of PLEDs Based on the
Polymers
a
b
Von
Lmax
ηl,max
ηp, max
ηext,max
(%)
CIE
(x, y)
polymer
(V) (cd/m2) (cd/A) (lm/W)
PSFDPSO00
3.4
3.0
3.0
3.0
3.0
2.8
7749
13 425
14 130
11 555
8442
1.12
2.74
2.90
2.35
1.70
0.77
0.37
1.79
1.80
1.71
1.27
0.62
0.76
1.82
1.78
1.48
1.03
0.43
(0.16,
0.14)
PSFDPSO01
PSFDPSO03
PSFDPSO05
PSFDPSO07
PSFDPSO10
(0.16,
0.16)
(0.17,
0.18)
(0.17,
0.18)
(0.17,
0.19)
Figure 8. EL spectra of PSFSO03 under different applied current
3914
(0.18,
0.22)
densities.
a
b
Turn-on voltage at a brightness of 1 cd/m2. Measured at a
brightness of 1000 cd/m2. Lmax: maximum brightness; ηl, max: maximum
(corresponding to the brightness from 54 cd/m2 to 12169 cd/
m2), the EL spectra remain nearly unchanged, and only a slight
variation of CIE coordinates is observed from (0.17, 0.18) to
(0.16, 0.16). Most importantly, no long wavelength emission
that is usually detected for PFs appears during device operation.
These observations indicate that the DPSO-based polymers do
have good color stability.
luminous efficiency; ηp, max: maximum power efficiency; ηext, max
maximum external quantum efficiency.
:
Parts a and b of Figure 7 show the current density−
voltage−luminescence characteristics of the polymers
PSFDPSO00−PSFDPSO10, and their current density depend-
ence of luminous efficiency, respectively. Except for
PSFDPSO00, the current density at the same driving voltage
seems to substantially increase from PSFDPSO01 to
PSFDPSO10. With the increasing DPSO loading, the above-
mentioned LUMO levels of the polymers can be efficiently
tuned to facilitate electron injection, and thus lead to the
enhanced current density. In addition, when the feed ratio of
DPSO increases from 0% to 3% (Figure 7b and Table 3), the
luminous efficiency is first increased from 1.12 cd/A of
PSFDPSO00 to 2.90 cd/A of PSFDPSO03, which comes
from the much more balanced carriers in PSFDPSO03 induced
by the improved electron injection. The further enhancement
of the DPSO content would interrupt the obtained charge
balance, resulting in lower efficiency of 0.77 cd/A for
3. CONCLUSION
A series of blue-emitting PSFs have been successfully designed
and synthesized by incorporating a nonconjugated DPSO
moiety into the polymer backbone rather than the conjugated
DBTSO. The relative weaker electron affinity of DPSO to
DBTSO is demonstrated to contribute to the prevention of the
strong CT effect, thereby leading to pure blue emissions for
DPSO-based PSFs. At the same time, their electron injection
abilities are improved with the loading of DPSO. In comparison
to the homopolymer PSFDPSO00, a more than 2-fold
enhancement of the device efficiency is attained for
PSFDPSO03. Under different applied current densities,
moreover, such DPSO-based PSFs display nearly unchanged
Figure 7. Current density−voltage−luminance curves of the devices (a) and their current density dependence of luminous efficiency (b).
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poured into 500 mL water and extracted with dichloromethane three
times. The organic layer was combined and dried over Na2SO4. After
removal of the solvent, the product was separated by column
chromatography to have colorless liquid (43.0 g, yield 84%). 1H NMR
(400 MHz, CDCl3, δ): 6.88 (s, 4 H), 3.99 (t, J = 6.7 Hz, 4 H), 1.86−
1.75 (m, 4 H), 1.51−1.42 (m, 4 H), 1.40−1.22 (m, 16 H), 0.88 (t, J =
6.8 Hz, 6 H).
EL spectra without long wavelength emissions. In terms of the
pure blue emission, high color stability, and promising device
performance, we believe that, the PSFs containing DPSO
moiety would have great potential applications for full-color
displays.
4. EXPERIMENTAL SECTION
4-Bromo-1,2-bis(octyloxy)benzene (2). 1,2-Bis(octyloxy)benzene
(43.0 g, 120.00 mmol) was dissolved in 150 mL of CHCl3 at 0 °C.
NBS (23.0 g, 130.00 mmol) dissolved in 250 mL of DMF was added
dropwise at 0 °C. After that, the resulting mixture was stirred at room
temperature for 12 h. Then the solution was poured into 2000 mL of
water and extracted with dichloromethane three times. The organic
layer was combined and dried over Na2SO4. After removal of the
solvent the product was separated by column chromatography to
afford colorless liquid (50 g, yield 94%). 1H NMR (400 MHz, CDCl3,
δ): 7.02−6.94 (m, 2 H), 6.76−6.69 (m, 1 H), 3.95 (m, 4 H), 1.80 (m,
4 H), 1.51−1.39 (m, 4 H), 1.38−1.23 (m, 16 H), 0.96−0.83 (m, 6 H).
3,4,3′,4′-Tetrakis(octyloxy)biphenyl (3). The compound 2 (33.1 g,
80.00 mmol) in 150 mL of THF was slowly added dropwise to 15 mL
of THF containing anhydrous LiCl (3.7 g, 86.40 mmol), iodide, and
magnesium turnings (2.9 g, 120.00 mmol) at room temperature. Then
the solution was stirred for 12 h at 50 °C. The solution then added
dropwise to a 20 mL THF, containing FeCl3 (389.0 mg, 2.40 mmol)
and 1,2-dibromoethane (15.0 g, 80.00 mmol) at room temperature.
The whole procedure was carried under an argon atmosphere. The
resulting mixture was stirred at room temperature for 12 h and then
hydrolyzed with a 1 M aqueous HCl solution (100 mL). After
extraction with dichloromethane three times, the organic layer was
combined and dried over Na2SO4. After removal of the solvent, the
white solid product was obtained by recrystallization from petroleum
ether (15.0 g, yield 57%). 1H NMR (400 MHz, CDCl3, δ): 7.09−7.02
(m, 4 H), 6.92 (d, J = 8.9 Hz, 2 H), 4.16−3.87 (m, 8 H), 1.97−1.74
(m, 8 H), 1.58−1.43 (m, 8 H), 1.38−1.19 (m, 32 H), 0.89 (m, 12 H).
2-Bromo-4,5,3′,4′-tetrakis(octyloxy)biphenyl (4). The compound
3 (17.0 g, 26.00 mmol) was dissolved in 200 mL CHCl3 at 0 °C. NBS
(5.0 g, 28.00 mmol) dissolved in 70 mL of DMF was slowly added
dropwise at 0 °C. After that, the solution was stirred at room
temperature for 12 h. Then the resulting mixture was poured into 700
mL of water and extracted with dichloromethane three times. The
organic layer was combined and dried over Na2SO4. After removal of
the solvent, the white solid of product was obtained by recrystallization
from petroleum ether (16 g, yield 60%). 1H NMR (400 MHz, CDCl3,
δ): 7.10 (s, 1 H), 6.95 (s, 1 H), 6.90 (s, 2 H), 6.84 (s, 1 H), 4.15−3.88
(m, 8 H), 1.94−1.73 (m, 8 H), 1.53−1.41 (m, 8 H), 1.39−1.20 (m, 32
H), 1.02−0.77 (m, 12 H).
1
4.1. Characterization. H and 13C NMR spectra were recorded
with a Bruker Avance 400 NMR spectrometer. Molecular weight of the
polymers were determined by gel permeation chromatography (GPC)
on a Waters 410 instrument with polystyrene as a standard and THF
as the eluent. Elemental analysis was performed on a Vario EL
elemental analyzer. MALDI/TOF (matrix-assisted laser desorption
ionization/time-of-flight) mass spectra were performed on AXIMA
CFR MS apparatus (COMPACT). GC-MS was recorded on an
Agilent 5975 GC-MS spectrometer. Melting point was measured with
Beijing Tech X-4 digital melting-point apparatus with optical
microscope. Thermal gravimetric analysis (TGA) and differential
scanning calorimetry (DSC) were performed under a flow of nitrogen
with PerkinElmer-TGA 7 and PerkinElmer-DSC 7 system, respec-
tively. UV−visible absorption and photoluminescent spectra were
measured with a PerkinElmer Lambda 35 UV−vis spectrometer and a
PerkinElmer LS 50B spectrofluorometer, respectively. The PL
quantum yields of solid state films on the quartz plate were measured
using a quantum yield measurement system (C10027, Hamamatsu
Photonics) excited at 360 nm. Cyclic voltammetry (CV) and
differential pulse voltammetry (DPV) were measured in anhydrous
acetonitrile with Bu4NClO4 (0.1 mol/L) as the electrolyte on a
CHI660a electrochemical analyzer at a scan rate of 100 mV/s. A glass
carbon electrode, a saturated calomel electrode, and a Pt wire were
used as the working electrode, the reference electrode, and the counter
electrode, respectively. The polymers were spin-coated on the working
electrode for the measurement. Theoretical calculations were
performed using the Gaussian 09 package, and the model geometries
of oligomers were fully optimized by density functional theory (DFT)
using Beck’s three-parametrized Lee−Yang−Parr exchange functional
(B3LYP) with 6-31G* basis sets.
4.2. Device Fabrication and Measurements. The device
structure was ITO/PEDOT:PSS (35 nm)/polymer (80 nm)/Ca (20
nm) /Al (100 nm). The indium tin oxide (ITO) (20 Ω per square)
samples were cleaned with acetone, detergent, and distilled water and
then were cleaned in an ultrasonic solvent bath. After baking in a
heating chamber at 130 °C for 2 h, the ITO-glass substrates were
treated with O2 plasma for 25 min. Subsequently, poly(3,4-
ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS, Ba-
tron-P4083, Bayer AG) was spin-coated on top of the ITO at a
speed of 5000 rpm for 60 s and then baked at 120 °C for 45 min.
Then, solutions of the polymers in toluene were filtered through a
filter (0.45 μm) and spin-coated on PEDOT:PSS as the emissive layer
(EML) at a speed of 1500 rpm for 60 s. Successively, the substrate was
annealed at 100 °C for 0.5 h inside a nitrogen-filled glovebox and then
transferred to a vacuum thermal evaporator. On top of the EML, the
calcium was thermally deposited the cathode through a shadow mask
with an array of 70 mm2 openings at a pressure of 4.0 × 10−4 Pa.
Finally, aluminum was deposited subsequently as the protective layer
for calcium at a pressure of 1.0 × 10−3 Pa. The EL spectra and CIE
coordinates were measured using a PR650 spectra colorimeter. The
current−voltage and brightness−voltage curves of devices were
measured using a Keithley 2400/2000 source meter and a calibrated
silicon photodiode. All the measurements were carried out at room
temperature under ambient conditions.
2,7-Dibromo-9-(4,5,3′,4′-tertrakis(octyloxy)biphenyl-2-yl)-9H-flu-
oren-9-ol (5).18 The compound 4 (16.4 g, 20.00 mmol) in 200 mL of
THF was slowly added dropwise to 20 mL of THF containing
anhydrous LiCl (924.0 mg, 22.00 mmol), iodide, and magnesium
turnings (528.0 mg, 22.00 mmol) at room temperature. Then the
solution was stirred for 8 h at 50 °C. The solution then added
dropwise to a 30 mL of THF, containing 2,7-dibromofluorenone (7.4
g, 20.00 mmol) at room temperature. The reaction mixture was stirred
for 8 h. The whole procedure was carried under an argon atmosphere.
At last, the resulting mixture was poured into 300 mL of water and
extracted with dichloromethane three times, the organic layer was
combined and washed with water and dried over Na2SO4. After
removal of the solvent, the product was separated by column
1
chromatography to afford a colorless liquid (12.4 g, yield 62%). H
NMR (400 MHz, CDCl3, δ): 7.10 (s, 1 H), 6.95 (s, 1 H), 6.90 (s, 2
H), 6.84 (s, 1 H), 4.15−3.88 (m, 8 H), 1.94−1.73 (m, 8 H), 1.53−1.41
(m, 8 H), 1.39−1.20 (m, 32 H), 1.02−0.77 (m, 12 H).
2,7-Dibromo-2′,3′,6′,7′-tertrakis(octyloxy)-9,9′-spirobifluorene
(6). The compound 5 (9.0 g, 8.80 mmol) was dissolved in acetic acid
(200 mL) at 10 °C. And then 10 mL of HCl was added slowly. The
solution was stirred for 10 h at room temperature. After the reaction
was complete, the mixture was poured into 2000 mL of water and
extracted with dichloromethane three times. The organic layer was
combined and dried over Na2SO4. After removal of the solvent, the
4.3. Materials. All chemicals and reagents were used as received
from commercial sources without further purification. Solvents for
chemical synthesis were purified according to the standard procedures.
1,2-Bis(octyloxy)benzene (1). 1,2-Benzenediol (17.0 g, 154.00
mmol), NaOH (37.0 g, 924.00 mmol), Bu4NBr (5.0 g, 15.40
mmol), and 1-bromootane (73 mL, 273.00 mmol) were dissolved in
300 mL of THF and 100 mL of water under nitrogen. Then the
solution was stirred at 80 °C. After 3 h, the resulting mixture was
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product was purified by column chromatography and recrystallized
from ethanol there times to produce a white solid (5.0 g, yield 60%).
1H NMR (400 MHz, CDCl3, δ): 7.64 (d, J = 8.1 Hz, 2 H), 7.47 (d, J =
H), 7.20 (s, 2.4 H), 6.83 (s, 2.4 H), 6.12 (s, 2.6 H), 4.09 (s, 4.0 H),
3.61 (s, 3.7 H), 1.85 (s, 5.6 H), 1.60−1.46 (br, 11.9 H), 1.38−1.13 (br,
51.3 H), 0.94−0.86 (m, 8.8 H), 0.85−0.78 (m, 8.1 H). 13C NMR (101
MHz, CDCl3, δ): 150.2, 149.3, 148.6, 140.9, 140.6, 140.3, 135.0, 126.9,
122.2, 119.9, 109.6, 104.9, 69.5, 69.3, 31.9, 31,7, 29.5, 29.3, 29.2, 26.2,
25.9, 22.7, 22.6, 14.1, 14.0. Anal. Calcd for PSFSO01 (%): C, 82.56; H,
9.72; S, 0.04. Found: C, 82.71; H, 9.25; S, 0.11.
6.8 Hz, 2 H), 7.20 (s, 2 H), 6.85 (d, J = 1.4 Hz, 2 H), 6.14 (s, 2 H),
4.12 (s, 4 H), 3.72 (s, 4 H), 1.93−1.83 (m, 4 H), 1.71−1.62 (m, 4 H),
1.58−1.19 (m, 40 H), 0.93−0.82 (m, 12 H). 13C NMR (101 MHz,
CDCl3, δ): 150.7, 149.5, 148.4, 138.9, 138.8, 134.6, 130.4, 126.9,
121.3, 120.7, 109.4, 104.6, 69.1, 31.3, 31,2, 29.0, 28.9, 28.8, 28.7, 25.6,
25.5, 22.2, 22.1, 13.6. Anal. Calcd for 6 (%): C, 69.36; H, 7.97. Found:
C, 69.74; H, 7.88. MALDI−TOF MS: m/z 984.4. Melting point: 76−
78 °C.
PSFDPSO00. Green fiber, 370 mg. Yield: 90%. Monomer 7 (270.3
mg, 0.25 mmol) and monomer 6 (246.8 mg, 0.25 mmol) were used.
1H NMR (400 MHz, CDCl3, δ): 7.65 (br, 2.6 H), 7.19 (s, 2.9 H), 6.82
(s, 3.2 H), 6.11 (s, 2.8 H), 4.08 (s, 4.0 H), 3.60 (s, 3.7 H), 1.84 (s, 5.8
H), 1.58−1.45 (br, 14.6 H), 1.39−1.11 (br, 63.2 H), 0.92−0.85 (m,
10.4 H), 0.84−0.77 (m, 10.9 H). 13C NMR (101 MHz, CDCl3, δ):
149.7, 148.9, 148.1, 140.1, 134.5, 126.4, 121.7, 119.4, 108.9, 104.5,
69.1, 68.8, 31.4, 31.3, 29.0, 28.8, 28.7, 25.7, 25.4, 22.2, 22.1, 13.6. Anal.
Calcd for PSF (%): C, 82.56; H, 9.72. Found: C, 82.81; H, 9.62.
PSFDPSO03. Green fiber, 385 mg. Yield: 95%. Monomer 7 (270.3
mg, 0.25 mmol), monomer 6 (232.0 mg, 0.235 mmol), and monomer
2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)-2′,3′,6′,7′-
tertrakis(octyloxy)-9,9′-spirobifluorene (7). The compound 6 (7.0 g,
7.10 mmol), PdCl2(dppf) (350.0 mg, 0.43 mmol), KOAc (2.0 g, 20.40
mmol), and bis(pinacolato)diboron (4.0 g, 15.80 mmol) were
dissolved in 40 mL of dry DMF and then stirred at 80 °C for 24 h
under an argon atmosphere. After the reaction was complete, the
mixture was poured into 200 mL of water and extracted with
dichloromethane three times. The organic layer was combined and
dried over Na2SO4. After removal of the solvent, the product was
separated by column chromatography and recrystallized from ethanol
1
9 (5.6 mg, 0.015 mmol) were used. H NMR (400 MHz, CDCl3, δ):
7.81 (br, 0.4 H), 7.66 (br, 1.8 H), 7.48 (br, 0.3 H), 7.19 (s, 2.5 H),
6.83 (s, 2.3 H), 6.11 (s, 2.4 H), 4.08 (s, 4.0 H), 3.61 (s, 3.6 H), 1.85 (s,
5.0 H), 1.63−1.46 (br, 11.4 H), 1.42−1.10 (br, 48.8 H), 0.95−0.85
(m, 8.2 H), 0.84−0.76 (m, 7.9 H). 13C NMR (101 MHz, CDCl3, δ):
150.2, 149.3, 148.6, 140.8, 140.5, 140.2, 135.0, 127.7, 126.9, 122.1,
119.8, 109.5, 104.9, 69.5, 69.3, 31.8, 31,7, 29.4, 29.3, 29.1, 26.1, 25.9,
22.7, 22.6, 14.1, 14.0. Anal. Calcd for PSFSO03 (%): C, 82.43; H, 9.68;
S, 0.12. Found: C, 82.70; H, 9.32; S, 0.18.
1
to give a white solid (5.8 g, yield 75%). H NMR (400 MHz, CDCl3,
δ): 7.84 (s, 4 H), 7.17 (d, J = 12.5 Hz, 4 H), 6.12 (s, 2 H), 4.12 (s, 4
H), 3.66 (s, 4 H), 1.96−1.79 (m, 4 H), 1.69−1.46 (m, 8 H), 1.42−1.15
(m, 60 H), 0.94−0.79 (m, 12 H). 13C NMR (101 MHz, CDCl3, δ):
149.0, 148.7, 148.1, 143.7, 140.3, 135.0, 133.8, 129.9, 128.3, 118.9,
109.8, 104.5, 83.2, 69.1, 31.3, 31,2, 29.0, 28.9, 28.8, 28.7, 25.6, 25.4,
24.3, 22.2, 22.1, 13.6, 13.5. Anal. Calcd for 7 (%): C, 76.65; H, 9.51.
Found: C, 77.15; H, 9.18. MALDI−TOF MS: m/z 1080.8. Melting
point: 142−144 °C.
PSFDPSO05. Green fiber, 357 mg. Yield: 90%. Monomer 7 (270.3
mg, 0.25 mmol), monomer 6 (222.1 mg, 0.225 mmol), and monomer
1
Di(4-bromophenyl) Sulfide (8).15 4-Bromoiodobenzene (11.3 g,
40.00 mmol), Na2S·9H2O (5.8 g, 24.00 mmol), CuI (760.0 mg, 4.00
mmol), and K2CO3 (5.5 g, 40.00 mmol) in 80 mL of DMF under
argon were stirred at 120 °C for 18 h. Then the resulting mixture was
poured into 200 mL of water and extracted with dichloromethane. The
combined organic layer was dried with Na2SO4 and then concentrated
under vacuum. The residue was purified by column chromatography to
give a white solid (4.1 g, yield 60%). 1H NMR (400 MHz, CDCl3, δ):
7.43 (d, J = 8.3 Hz, 4 H), 7.19 (d, J = 8.3 Hz, 4 H).
9 (9.4 mg, 0.025 mmol) were used. H NMR (400 MHz, CDCl3, δ):
7.82 (br, 0.5 H), 7.66 (br, 1.6 H), 7.52−7.45 (br, 0.5 H), 7.19 (br, 2.4
H), 6.83 (br, 2.3 H), 6.11 (s, 2.3 H), 4.09 (s, 4.0 H), 3.61 (s, 3.8 H),
1.85 (s, 4.8 H), 1.61−1.46 (br, 11.2 H), 1.38−1.10 (br, 46.2 H), 0.92−
0.86 (m, 7.8 H), 0.84−0.77 (m, 7.5 H). 13C NMR (101 MHz, CDCl3,
δ): 150.2, 149.3, 148.6, 140.8, 140.5, 140.4, 135.0, 127.8, 126.9, 122.2,
119.9, 109.6, 104.9, 69.5, 69.3, 31.8, 31,7, 29.4, 29.3, 29.1, 26.1, 25.9,
22.7, 22.6, 14.1, 14.0. Anal. Calcd for PSFSO05 (%): C, 82.33; H, 9.65;
S, 0.20. Found: C, 82.98; H, 9.33; S, 0.23.
PSFDPSO07. Green fiber, 344 mg. Yield: 88%. Monomer 7 (270.3
mg, 0.25 mmol), monomer 6 (212.2 mg, 0.215 mmol), and monomer
9 (13.2 mg, 0.035 mmol) were used. 1H NMR (400 MHz, CDCl3, δ):
7.82 (br, 0.7 H), 7.66 (br, 1.5 H), 7.52−7.45 (br, 0.6 H), 7.19 (br, 2.4
H), 6.95−6.77 (br, 2.3 H), 6.16−6.09 (br, 2.3 H), 4.08 (s, 4.0 H), 3.61
(s, 3.8 H), 1.85 (s, 5.3 H), 1.67−1.45 (br, 12.2 H), 1.42−1.12 (br, 53.6
H), 0.91−0.86 (m, 10.2 H), 0.84−0.79 (m, 8.6 H). 13C NMR (101
MHz, CDCl3, δ): 150.2, 149.3, 148.6, 141.0, 140.6, 140.3, 135.0, 127.9,
126.9, 122.2, 119.9, 109.6, 104.9, 69.5, 69.3, 31.8, 31,7, 29.5, 29.3, 29.2,
26.2, 25.9, 22.7, 22.6, 14.1, 14.0. Anal. Calcd for PSFSO07 (%): C,
82.24; H, 9.62; S, 0.29. Found: C, 82.58; H, 9.40; S, 0.33.
Di(4-bromophenyl) Sulfone (9). Di(4-bromophenyl)sulfide (3.4 g,
9.88 mmol), 30% hydrogen peroxide (50 mL), and CH3COOH (100
mL) were stirred continuously at 100 °C for 10 h. Then the resulting
mixture was poured into 500 mL of water and extracted with
dichloromethane. The combined organic layer was dried with Na2SO4.
After removal of the solvent, the product was purified by column
chromatography and recrystallized from hexane to give a white solid
1
(3.4 g, yield 90%). H NMR (400 MHz, CDCl3, δ): 7.78 (d, J = 8.0
Hz, 4 H), 7.65 (d, J = 8.0 Hz, 4 H). 13C NMR (101 MHz, CDCl3, δ):
139.7, 132.2, 128.7, 128.3. Anal. Calcd for 9 (%): C, 38.33; H, 2.14.
Found: C, 38.50; H, 2.45. GC−MS: m/z 374, 376, 378. Melting point:
171−172 °C.
PSFDPSO10. Green fiber, 324 mg. Yield: 85%. Monomer 7 (270.3
mg, 0.25 mmol), monomer 6 (197.4 mg, 0.20 mmol), and monomer 9
General Procedures of Suzuki Polycondensation Taking
PSFDPSO01 as an Example. A mixture of monomer 7 (270.3 mg,
0.25 mmol), monomer 6 (241.8 mg, 0.245 mmol), monomer 9 (1.9
mg, 0.005 mmol), Pd2(dba)3 (0.9 mg), Aliquat 336 (20.0 mg), and 2-
dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (3.2 mg) were dis-
solved in a mixture of toluene (6 mL) and water (2 mL) under an
argon atmosphere. The mixture was heated to 95 °C and stirred for 2
h. Benzeneboronic acid (15 mg) in 3 mL of toluene was subsequently
added and the mixture was refluxed for 5 h. Finally, 1 mL of
bromobenzene was added, and the mixture was refluxed for 5 h. Then
sodium diethyldithiocarbamate trihydrate (1.0 g) and deionized water
(20 mL) were added into the mixture. The solution was kept at 80 °C
with vigorous stirring under argon for 24 h. After cooling, the resulting
polymer was resolved in dichloromethane, and then washed three
times with deionized water. After removal of the solvent, the resulting
polymers were received by precipitation in methanol. The final
purification was carried out by Soxhlet extraction with acetone for
about 24 h and then precipitated in methanol (370.0 mg, yield 90%).
1H NMR (400 MHz, CDCl3, δ): 7.86−7.79 (br, 0.3 H), 7.66 (br, 1.8
1
(18.8 mg, 0.05 mmol) were used. H NMR (400 MHz, CDCl3, δ):
7.82 (br, 0.8 H), 7.71−7.63 (br, 1.6 H), 7.53−7.47 (br, 0.8 H), 7.19
(br, 2.3 H), 6.98−6.77 (br, 2.3 H), 6.11 (br, 2.3 H), 4.09 (s, 4.0 H),
3.61 (s, 3.9 H), 1.85 (s, 4.7 H), 1.66−1.45 (br, 10.9 H), 1.37−1.10 (br,
44.6 H), 0.91−0.86 (m, 7.4 H), 0.84−0.79 (m, 7.1 H). 13C NMR (101
MHz, CDCl3, δ): 150.2, 149.3, 148.6, 140.9, 140.5, 140.3, 135.0, 127.7,
126.9, 122.2, 119.9, 109.6, 104.9, 69.5, 69.3, 31.8, 31,7, 29.4, 29.3, 29.1,
26.1, 25.9, 22.7, 22.6, 14.1, 14.0. Anal. Calcd for PSFSO10 (%): C,
82.09; H, 9.58; S, 0.42. Found: C, 82.34; H, 9.25; S, 0.44.
ASSOCIATED CONTENT
■
S
* Supporting Information
DSC curves of the polymers, solution PL spectra, HOMO and
LUMO distributions, and 1H NMR and 13C NMR spectra. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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AUTHOR INFORMATION
■
Corresponding Authors
*(J.D.) E-mail: junqiaod@ciac.ac.cn.
*(L.W.) E-mail: lixiang@ciac.ac.cn.
(c) Johansson, N.; Salbeck, J.; Bauer, J.; Weissortel, F.; Broms, P.;
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by the 973 Project (No.
2009CB623601), and the National Natural Science Foundation
of China (Nos. 21174144, 51322308 and 91333205).
(7) Wu, Y. G.; Li, J.; Fu, Y. Q.; Bo, Z. S. Org. Lett. 2004, 6, 3485−
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