Deep-blue emitting poly(2′,3′,6′,7′-tetraoctyl-2,7-spirosilabifluorene) simultaneously with good color purity and high external quantum efficiency

Article abstract of DOI:10.1016/j.orgel.2018.04.046

A deep-blue emitting poly(2′,3′,6′,7′-tetraoctyl-2,7-spirosilabifluorene), namely PSSiBF, has been newly developed for PLEDs. Unlike the previously-reported alkyl-functionalized P27SiF, the unwanted aggregation can be effectively prevented in PSSiBF due t

Full text of DOI:10.1016/j.orgel.2018.04.046

Accepted Manuscript
Deep-blue emitting poly(2′,3′,6′,7′-tetraoctyl-2,7-spirosilabifluorene) simultaneously
with good color purity and high external quantum efficiency
Xiushang Xu, Keyan Bai, Junqiao Ding, Lixiang Wang
PII:
S1566-1199(18)30210-6
10.1016/j.orgel.2018.04.046
ORGELE 4654
DOI:
Reference:
To appear in: Organic Electronics
Received Date: 28 March 2018
Revised Date: 25 April 2018
Accepted Date: 25 April 2018
Please cite this article as: X. Xu, K. Bai, J. Ding, L. Wang, Deep-blue emitting poly(2′,3′,6′,7′-
tetraoctyl-2,7-spirosilabifluorene) simultaneously with good color purity and high external quantum
efficiency, Organic Electronics (2018), doi: 10.1016/j.orgel.2018.04.046.
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Graphic Abstract
The introduced spiro-linkage into the silicon-containing polymer has been
demonstrated to effectively prevent the unwanted aggregation, leading to deep-blue
electroluminescence with CIE coordinates of (0.16, 0.06).

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Deep-Blue Emitting Poly(2',3',6',7'-tetraoctyl-2,7-
spirosilabifluorene) Simultaneously with Good Color Purity and
High External Quantum Efficiency
Xiushang Xu,a,b Keyan Bai,a,b Junqiao Ding,*,a Lixiang Wang*,a
a State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China
b University of Chinese Academy of Sciences, Beijing 100049, P. R. China
Abstract:
A deep-blue emitting poly(2',3',6',7'-tetraoctyl-2,7-spirosilabifluorene), namely PSSiBF,
has been newly developed for PLEDs. Unlike the previously-reported alkyl-functionalized
P27SiF, the unwanted aggregation can be effectively prevented in PSSiBF due to the
perpendicular arrangement between two spiro-linked dibenzosilole moieties. Compared with
P27SiF (ΦPL = 0.62), consequently, an improved PLQY of 0.84 is obtained for the film of
PSSiBF accompanied by a significant reduction of the long-wavelength emission in the range
of 450-550 nm. Based on a double-layer device configuration, PSSiBF gives a bright deep-
blue electroluminescence, revealing a state-of-art EQE of 2.8% and CIE coordinates of (0.16,
0.06). The simultaneous realization of good color purity and high EQE clearly implies that the
silicon-containing polymers do have the great potential in efficient PLEDs.
Keywords: PLEDs; aggregation; color purity; deep-blue; silicon-containing polymers

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1. Introduction
Poly(dibenzosilole), where the vulnerable C-9 carbon in polyfluorene is replaced by silicon,
has attracted much attention in polymer light-emitting diodes (PLEDs) since 2005 [1-3].
Because silicon belongs to the same periodic group as carbon, its solubility in common
organic solvents is expected to be close to polyfluorene, ensuring the excellent wet
processibility during device fabrication [4]. Secondly, unlike the easily-oxidized C-9 carbon
atom in polyfluorene [5-7], the silicon atom is difficult to be oxidized. So the unwanted low
energy green emission band caused by the keto defects could be avoided in
poly(dibenzosilole) to improve the blue light spectral stability [1, 4, 8-9]. Thirdly, the silicon
atom with relatively low-lying σ* orbitals can enter into the π* orbitals of diene [10-11].
Benefitting from such a σ*-π* conjugation, the lowest unoccupied molecular orbital (LUMO)
energy level of poly(dibenzosilole) turns out to be deeper than that of polyfluorene, thus
favoring the effective electron injection and transporting [4, 8]. Given these advantages, a
series of 3,6- or 2,7-linked poly(dibenzosilole)s have been independently reported for
applications in PLEDs by A. B. Holmes and Y. Cao groups [2, 3, 12-17].
At the early stage, the alkyl-functionalized poly(dibenzosilole)s including P27SiF (Figure
1) were demonstrated to show extremely stable blue electroluminescence with a moderate
external quantum efficiency (EQE) up to 0.66% [13]. Unfortunately, the corresponding
Commission Internationale de L’Eclairage (CIE) coordinates are (0.20, 0.19), significantly
deviating from the s-RGB standard for blue (0.15, 0.06). According to the literature [18], the
C-Si bond (1.89 Å) is longer than the C-C bond (1.53 Å), allowing more efficient interchain
stacking owing to the absence of steric hindrance between the alkyl groups and the polymeric
backbone. The resultant aggregation may be responsible for the enhanced emission from the
vibronic shoulders in the range of 450-550 nm [1, 13], leading to both low device
performance and poor color purity of blue light [19, 20]. To solve this problem, the bulky
aryl substitutes instead of alkyl ones were then selected as the side chains to afford poly(9,9-

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dialkoxyphenyl-2,7-silafluorene) (PSF) [21]. Because of the suppression of aggregation, its
CIE coordinates moved towards (0.17, 0.13) along with an elevated EQE of 2.21%. On the
other hand, when the 3,6-silafluorene unit was introduced into the P27SiF main chain, the
copolymer P36-27SiF90 realized further blue-shifted CIE coordinates of (0.16, 0.08) but with
a slightly reduced EQE of 1.95% relative to PSF [13]. Despite these achievements, novel
molecular design rules are still required for the development of blue emissive silicon-
containing polymers simultaneously with good color purity and high EQE.
With this idea in mind, here we newly develop a deep-blue emitting poly(2',3',6',7'-
tetraoctyl-2,7-spirosilabifluorene) (PSSiBF). As depicted in Figure 1, the perpendicular
arrangement between two spiro-linked dibenzosilole moieties can prevent the interchain
interactions [22], so that the aggregation-induced long wavelength emission and luminescence
quenching are anticipated to be weakened to some degree. Compared with the previously-
reported alkyl-functionalized P27SiF, the 0-0 peak of PSSiBF in solid state is blue-shifted by
about 8 nm associated with a considerable reduction of 0-1 emission and an improved
photoluminescence quantum yield (PLQY) of 0.84. As a result, ongoing from P27SiF to
PSSiBF, the CIE coordinates of the single-layer devices are tuned from (0.18, 0.15) to (0.16,
0.06), and the EQE is correspondingly increased from 0.5% to 1.3%. Further introduction of
an additional hole-transporting layer leads to an optimized EQE of 2.8% for PSSiBF while its
CIE coordinates remain nearly unchanged. The simultaneous achievement of both good color
purity and high EQE clearly indicates the great potential of PSSiBF applied in efficient blue-
emitting PLEDs.
2. Results and Discussion
2.1 Synthesis and Characterization
The synthetic route of PSSiBF is plotted in Scheme 1. Starting from the commercially
available 1,2-dichlorobenzene that reacted with octyl magnesium bromide, 1,2-dioctylbenzene

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(1) was prepared, followed by a bromination [23-24]. The resultant 1,2-dioctyl-4,5-
dibromobenzene (2) was homo-coupled under n-BuLi to give 2,2'-dibromo-4,4',5,5'-
tetraoctyl-1,1'-biphenyl (3) [25]. On the other hand, a copper-catalyzed Ullmann homo-
coupling was performed between 2,5-dibromonitrobenzene to afford 4,4'-dibromo-2,2'-
dinitrobiphenyl (4), which was converted to 4,4'-dibromo-2,2'-diiodobiphenyl (6) through a
reduction and a Sandmeyer reaction successively. After lithiation, 6 was further cyclized to
form 2,7-dibromo-9,9-dichlorosilafluorene (8). In this case, an extremely low temperature of -
o
100 C and four equivalent of n-BuLi were used to ensure the selective and complete
lithiation of 6 not on the bromide groups but on the iodide ones. Meanwhile, a large amount
of SiCl4 (10 equiv relative to 6) was required to be added into the reaction mixture in one
portion so as to eliminate the accompanied by-product 2,2',7,7'-tetrabromo-9,9’-silabifluorene.
Finally, the key monomer 2,7-dibromo-2',3',6',7'-tetraoctyl-spirosilabifluorene (9) was
obtained by a reaction between 8 and the 3’s bilithiated product 7 in a yield of 40%.
Prior to polymerization, the dibromide monomer 9 was converted to its respective
diboronic ester monomer 10 in a yield of 78%. With both 9 and 10 in hand, the homopolymer
PSSiBF was synthesized via a typical Suzuki polymerization. With Pd2(dba)3 as the catalyst
and SPhos as the ligand, the polymerization was completed in less than 60 min, and excess
monomers and/or oligomers were removed by Soxhlet extraction with acetone. After
purification, the number- and weight-average molecular weights (Mn and Mw) of PSSiBF,
determined by high-temperature gel permeation chromatography (GPC), were 33.5 and 192.5
kDa, respectively. For comparison, P27SiF was also prepared as the reference polymer (Mn =
28.6 kDa, Mw = 66.8 kDa).
Although PSSiBF has poor solubility in tetrahydrofuran (THF), it is well soluble in toluene,
chloroform, xylene and chlorobenzene. This is favorable for the generation of high quality
film by spin-coating. In addition, PSSiBF possesses a decomposition temperature
o
(corresponding to a 5% weight loss) as high as 430 C (Figure 2), which is close to that of

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o
P27SiF (436 C). But different from P27SiF with a glass transition temperature at 249 oC, no
o
obvious glass transition or melting is detected for PSSiBF in the range of 25 to 300 C.
Similar to poly(spirobifluorene)s [26-29], the observation may be reasonably attributed to the
o
glass transition temperature higher than 300 C, indicating the more rigidity and better
thermal stability of PSSiBF with regard to P27SiF.
2.2 Photophysical properties
Figure 3 shows the UV-Vis and photoluminescent (PL) spectra of P27SiF and PSSiBF
measured in 10-5 M toluene. As can be clearly seen, PSSiBF possesses a major absorption
band peaked at about 350 nm. Compared to P27SiF (382 nm), a hypsochromic shift of nearly
30 nm is observed for PSSiBF due to the possible larger torsion between two repeating units
in PSSiBF than in P27SiF. In addition, the PL spectra of both P27SiF and PSSiBF in dilute
solutions exhibit well-defined vibronic structures including 0-0 and 0-1 transitions. And the
corresponding emissions are blue-shifted from 417 and 440 nm of P27SiF to 414 and 436nm
of PSSiBF.
To further evaluate the interchain interactions in P27SiF and PSSiBF, the dependence of the
concentration on their PL spectra is also studied. Similar to the literature [1, 13], there exists
an obvious aggregation in P27SiF. With the increasing concentration, the 0-0 emission is
considerably red-shifted from 417 to 428 nm for P27SiF (Figure 4a). Meanwhile, its long
wavelength 0-1 emission is found to be gradually enhanced, and finally becomes dominant in
solid state. By contrast, the 0-0 emission of PSSiBF still dominates the whole PL, and gives a
smaller bathochromic shift of only 6 nm (Figure 4b). The difference implies that the
aggregation could be effectively prevented in PSSiBF attributable to the characteristic
orthogonal configuration [19]. This point is further confirmed by the PLQY measurement. As
listed in Table 1, a close PLQY of 0.88 and 0.87 is determined in solution for P27SiF and

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PSSiBF. However, in film, the PLQY of PSSiBF (ΦPL = 0.84) remains nearly unchanged,
whereas P27SiF shows a reduced PLQY of 0.62.
2.3 Electrochemical properties
Cyclic voltammetry (CV) was used to explore the electrochemical properties of PSSiBF as
well as P27SiF. During the anodic and cathodic scanning (Figure 5), the PSSiBF film displays
an irreversible oxidation and reduction waves, respectively. With regard to the ferrocene
reference (4.8 eV below the vacuum level), the highest occupied molecular orbital (HOMO)
and LUMO energy levels of PSSiBF are estimated to be -6.10 and -2.40 eV, lower than those
of P27SiF (-5.90 and -2.27 eV). The observation means that the electron injection is favored
for PSSiBF relative to P27SiF, whereas the hole injection becomes more difficult. Moreover,
compared with P27SiF (3.63 eV), the electrochemical bandgap of PSSiBF (3.70 eV) is found
to be elevated by about 0.07 eV, which is in well agreement with the above-mentioned
hypsochromic shift for both the absorption and PL spectra of PSSiBF.
2.4 Electroluminescent properties
To investigate the electroluminescent (EL) properties of PSSiBF, firstly, a simple single-
layer device was fabricated with a structure of ITO/PEDOT:PSS (40 nm)/PSSiBF (80 nm)/Ca
(20 nm)/Al. At the same time, a control device was also prepared for comparison by using
P27SiF as the emitting layer (EML) in place of PSSiBF. Consistent with their PL counterparts,
a similar trend is observed for the EL spectra of P27SiF and PSSiBF (Figure 6a). That is,
compared with P27SiF, PSSiBF shows a blue-shifted EL accompanied by a significant
reduction of long-wavelength emission above 450 nm. Accordingly, the corresponding CIE
coordinates are varied from (0.18, 0.15) of P27SiF to (0.16, 0.06) of PSSiBF. It should be
noted that the CIE coordinates of PSSiBF match well with the s-RGB standard for blue (0.15,
0.06), indicative of the much better color purity of PSSiBF than P27SiF. Meanwhile, the

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maximum EQE is greatly enhanced from 0.5% of P27SiF to 1.3% of PSSiBF (Figure 6b). As
discussed above, the prevented aggregation in PSSiBF reasonably contributes to the
simultaneous realization of good color purity and high EQE.
Considering the large hole injection barrier in PSSiBF, subsequently, a double-layer device
was further assembled to optimize its device performance by introducing an additional 30 nm
thickness of poly(9-vinylcarbazole) (PVK) as the hole-transporting layer. Because the HOMO
level of PVK (-5.9 eV) [30] lies between those of PEDOT:PSS (-5.2 eV) [31] and PSSiBF (-
6.1 eV), a cascade hole injection and transporting could be expected from the anode to the
EML through PVK (Inset in Figure 7a). As a consequence, ongoing from single-layer device
to double-layer one, the turn-on voltage at 1 cd/m2 is down from 8.2 to 6.0 V, and the
maximum luminance is up from 410 to 5560 cd/m2 (Table 2). Correspondingly, the peak EQE
is improved to 2.8% while the CIE coordinates keep almost unchanged (Figure 7a). The
obtained performance is well comparable with those of polyfluorenes and
poly(dibenzosilole)s with CIEy < 0.10 (Table S1), suggesting that the spiro linkage is a
promising strategy to develop efficient deep blue polymers. In addition, PSSiBF shows an
excellent color stability, and the EL spectra are found to be independent on the current density
ranging from 87 to 271 mA/cm2 (Figure 7b).
3. Conclusions
In summary, a novel deep-blue emitting PSSiBF has been successfully designed and
synthesized for efficient PLEDs based on two spiro-linked dibenzosilole moieties. Owing to
the characteristic orthogonal configuration, the unwanted aggregation can be effectively
prohibited to not only weaken the long-wavelength emission but also increase the film PLQY.
Compared with the alkyl-functionalized P27SiF (CIE: (0.18, 0.15); EQE: 0.5%), the single-
layer device of PSSiBF reveals an improved EQE of 1.3% and better CIE coordinates of (0.16,
0.06). Moreover, the EQE can be further optimized to be 2.8% without changing the CIE

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coordinates after the insertion of an additional hole-transporting PVK. This work, we believe,
will shed light on the development of silicon-containing blue polymers simultaneously with
good color purity and high EQE.
4. Experimental section
4.1 Measurements and Characterization.
13
1H and C NMR spectra were recorded with a Bruker Avance 400 NMR spectrometer.
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). Molecular weights of the polymers were determined by
high-temperature GPC on a PL-GPC 220 instrument with polystyrene as the standard and
trichlorobenzene as the eluent in 130 oC. Thermal gravimetric analysis (TGA) and differential
scanning calorimetry (DSC) were performed under a flow of nitrogen with PerkinElmer-TGA
7 and PerkinElmer-DSC7 system, respectively. UV−Vis absorption and PL spectra were
measured with a PerkinElmer Lambda 35 UV−Vis spectrometer and a PerkinElmer LS 50B
spectrofluorometer, respectively. The PLQYs of the polymers in toluene solutions were
measured with polyfluorene as the reference (ΦPL = 0.90 in toluene). And the PLQYs of films
on the quartz plate were measured using a quantum yield measurement system (C10027,
Hamamatsu Photonics) excited at 360 nm. CV was performed on aCHI660a electrochemical
analyzer in anhydrous acetonitrile with Bu4NClO4 (0.1 mol/L) as the electrolyte 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 directly spin-coated on the working electrode for the measurement, and all the
potentials were calibrated by Fc/Fc+.
4.2 Device Fabrication and Measurements

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The indium tin oxide (ITO) (20 Ω per square) substrates were cleaned with acetone,
detergent, distilled water and then 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.
Firstly, poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT: PSS, Batron-
P4083, Bayer AG) was spin-coated on top of the ITO at a speed of 5000 rpm for 60 s and
baked at 120 °C for 45 min. Then the PVK solution in chlorobenzene was filtered through a
filter (0.45 µm) and spin-coated on PEDOT: PSS as the hole transporting layer at a speed of
1500 rpm for 60 s. After annealed at 80 °C for 2 h inside a nitrogen-filled glove-box, solutions
of the polymers in toluene were spin-coated on PVK as the emissive layer at a speed of 1500
rpm for 60 s, and annealed at 80 °C for 0.5 h. Finally, the substrate was transferred to a
vacuum thermal evaporator, and calcium and aluminum were thermally deposited as the
cathode through a shadow mask with an array of 14 mm2 at a pressure of 10-3 ~ 10−4 Pa. Also,
the single-layer devices were fabricated according to the same procedure as the double-layer
ones but without the usage of PVK. 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.
4.3 Synthesis
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-dioctylbenzene (1): A flam-dried 500 mL round-bottom flask was charged with Mg
(7.46 g, 0.31 mol) under argon atmosphere. The diethyl ether solution of 1-bromooctane (42
mL, 0.259 mol) was added together with a small amount of I2 to initiate the reaction. The
reaction mixture was refluxed for 2 h, cooled to room temperature and filtered under an inert

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atmosphere to remove any unreacted Mg metal. Under an argon atmosphere, the obtained
octylmagnesium bromide was added dropwisely to the stirred mixture of 1, 2-dichlorobenzene
o
(11.0 mL, 0.10 mol) and Ni(dppe)Cl2 (1.2 g, 2.2 mmol) in drydiethyl ether (160 mL) at 0 C.
After addition, the reaction was allowed to reflux and stirred overnight. The mixture was
cooled to room temperature and poured into 300 mL 6M HCl solution with ice. The diethyl
ether layer was separated and washed several times with H2O, NaHCO3 and NaCl saturated
solution and dried over Na2SO4. The solvent was removed under vacuum, and the resultant oil
was purified by distillation to afford 1 (colorless oil, 15.86 g, yield 51%). 1H NMR (400 MHz,
CDCl3) δ 7.12 (m, 4H ), 2.59 (t, J = 8.0 Hz 4H ), 1.20-1.70 (m, 24H), 0.88 (t, J = 6.6 Hz, 6H).
1,2-dibromo-4,5-dioctylbenzene (2): Br2(14.20 mL, 284.75 mmol) was added dropwise to
the mixture of 1 (17.20 g, 56.95 mmol) and I2(0.15 g, 0.57 mmol) in CHCl3 (280 mL) at 0 oC
under an argon atmosphere. The reaction was stirred at room temperature overnight, and
quenched with the aqeous Na2SO3. The organic phase was washed with water and brine, dried
over Na2SO4, and concentrated to give the crude product under reduced pressure. The crude
1
product was purified by distillation to afford 2 (colorless oil, 24.80 g, yield 95%) H NMR
(400 MHz, CDCl3) δ 7.36 (s, 2H), 2.52 (t, J = 8.4 Hz, 4H), 1.20-1.70(m, 24H), 0.85(t, J =
6.4Hz, 6H).
2,2'-dibromo-4,4’,5,5’-tetraoctyl-1,1’-biphenyl (3): To a stirring solution of 2 (3.00 g, 6.55
mmol) in dry THF (100 mL), n-BuLi (1.25 mL, 3.20 mmol, 2.5 M in n-hexane) was added
dropwise slowly at -78 oC. The reaction mixture was allowed to rise to room temperature and
stirred overnight. After quenched with dilute HCl and extracted with diethyl ether (3×50 mL),
the organic layer was dried over Na2SO4, and concentrated to give the crude product under
reduced pressure. The by-product was removed by distillation, and the pure product 3 was

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afforded (colorless oil, 1.20 g, yield 48%). 1H NMR (400 MHz, CDCl3) δ 7.01 (s, 2H ), 7.40
(s, 2H ), 2.56 (t, J = 7.7Hz, 8H), 1.20-1.70 (m, 48H ), 0.85 (t, J = 6.4Hz, 12H).
4,4’-Dibromo-2,2’-dinitrobiphenyl (4): To a solution of 2,5-dibromonitrobenzene (50.00 g,
0.18 mol) in DMF (500 mL) was added copper powder (27.00 g, 0.42 mol), and the reaction
o
mixture was heated to 125 C for 3 h. After cooled to room temperature, toluene (200 mL)
was added. The insoluble inorganic salts were removed by filtration through celite and the
filtrate was evaporated to dryness. The crude material was vigorously washed with methanol
(3×200 mL) and redissolved in toluene (200 mL). The remaining inorganic salts were again
removed by filtration through celite, and the filtrate was evaporated to yield the title
compound 4 as yellow crystals (26.2 g, yield 85%). 1H NMR (400 MHz, CDCl3) δ 7.16 (d, J
= 8.2 Hz, 2H) 7.82 (dd, J = 8.2, 1.9 Hz, 2H ), 8.38 (d, J = 1.9Hz, 2H).
4,4’-Dibromobiphenyl-2,2'-diamine (5): To a solution of 4 (15.00 g, 37.30 mmol) in ethanol
(186 mL) was added 32 % w/w aqueous HCl (124 mL). Tin powder (17.60 g, 147.00 mmol)
was added portion-wise over 10 minutes, and the reaction mixture was heated to reflux at 100
oC for 2 h. After cooling, the mixture was poured into ice water (400 mL) and then basified
with 20% w/w aqueous NaOH solution (150 mL). The product was extracted with diethyl
ether, and the organic layer was washed with brine, dried over anhydrous Na2SO4 and
evaporated to dryness. Purification by recrystallization from ethanol afforded the title
1
compound 5 as light brown crystals (8.3 g, yield 65%). H NMR (400 MHz, DMSO- d6) δ
6.83 (d, J = 8.2Hz, 2H), 6.75 (dd, J = 8.2, 1.9 Hz, 2H ), 6.95 (d, J = 1.9 Hz, 2H), 4.67 (s, 4H ).
4,4’-Dibromo-2,2’-diiodobiphenyl (6) : A three-necked flask equipped with a low
temperature thermometer was charged with 5 (1.00 g, 2.60 mmol), aqueous HCl (10 mL, 32%
w/w), H2O (40 mL) and acetonitrile (40 mL). The mixture was warmed and stirred until 5 was

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dissolved. After cooled to -10 oC, a solution of sodium nitrite (0.92 g, 13.40 mmol) in H2O (5
mL) was added slowly to the reaction mixture, keeping the reaction temperature between -10
and -5 oC. The reaction was stirred at this temperature for 1 h, and then a solution of KI (4.44
g, 26.70 mmol) in H2O (30 mL) was dropwise via cannula to the reaction mixture with
o
vigorous stirring, whilst maintaining the reaction temperature between -15 and -10 C. Once
addition was completed, the reaction was warmed to room temperature and then heated to 60
oC for 16 h. The product was extracted with chloroform (3×100 mL) and the combined
organic phase was washed with aqeous Na2S2O3 (200 mL), H2O (200 mL) and brine (200 mL),
dried by Na2SO4 and evaporated to dryness. Purification by column chromatography on silica
gel using n-hexane as eluent, followed by recrystallization from n-hexane yielded the title
compound 6 as colorless needles (0.45 g, yield 30%). 1H NMR (400 MHz, CDCl3) δ7.02 (d, J
= 8.2Hz, 2H ), 7.55 (dd, J = 8.2, 1.9 Hz, 2H), 8.08 (d, J = 1.9 Hz, 2H).
3',7'-dibromo-2,3,7,8-tetraoctyl-5,5'-spirosilabifluorene (9) : 2.09 mL of n-Butyllithium
(5.22 mmol, 2.5 M in n-hexane) was added over 30 min to a solution of 6 (0.73 g, 1.31 mmol)
o
o
in 80 mL dry THF at -100 C under argon atmosphere. After stirred for 2 h at -100 C, the
SiCl4 (3 mL, 26.20 mmol) was added in one portion.The mixture was stirred for a further 4 h
at -100 oC, and eventually allowed to rise to room temperature. The solvent and excess SiCl4
was stripped by the vacuum distillation to afford 9, 9-dichloro-2,7-dibromosilafluorene (8)
without further purification.
On the other hand, 1.0 mL of n-butyllithium (2.50 mmol, 2.5 M in n-hexane) was added
dropwise to a solution of 3 (1.00 g, 1.31 mmol) in 80 mL diethyl ether at -78 oC. To ensure the
complete conversion to the 3’s bilithiated product 7, the mixture was allowed to rise to room
o
temperature for overnight. After cooled to -78 C, the solution of 8 prepared above was
dissolved in 70 mL THF, and added dropwise. The reaction mixture was stirred at room
temperature overnight, and quenched with aqueous NH4Cl. The aqueous layer was extracted

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with diethyl ether for three times, and the combined organic layer was dried over Na2SO4 and
concentrated. The crude product was purified by silica gel chromatography and further
purified by recrystallization in Et2O/MeCN to afford the monomer 9 as white solid (0.49 g,
yield 40%). 1H NMR (400 MHz, CDCl3) δ7.73 (d, J = 8.3 Hz, 2H), 7.64 (s, 2 H), 7.59 (dd, J =
8.3, 2.0 Hz, 1 H), 7.52 (d, J = 2.0 Hz, 1 H), 7.11 (s, 2 H), 2.74 – 2.62 (m, 4 H), 2.60 – 2.42 (m,
13
4H ), 1.65 -1.47 (m, 48H), 0.90 (t, J = 6.6 Hz, 6H), 0.84 (t, J = 6.7 Hz, 6H). C NMR (101
MHz, CDCl3) δ 137.02, 134.97, 134.04, 122.70, 122.46, 121.76, 33.44, 32.71, 31.90, 31.38,
29.95, 29.39, 22.67, 14.09. MALDI−TOF MS: m/z 936.4. Anal. Calcd. for C56H78Br2Si: C,
71.62; H, 8.37; Found: C, 71.72; H, 8.44.
2,3,7,8-tetraoctyl-3',7'-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-5,5'-
spirosilabifluorene (10): The monomer 9 (0.50 g, 0.53 mmol), Pd(dppf)2Cl2 (26 mg, 0.03
mmol), KAc (0.31 g, 3.20 mmol), and bis(pinacolato)diboron (0.32 g, 1.28 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 completed, the mixture was poured into 200 mL of water and extracted
with diethyl ether three times. The organic layer was combined and dried over Na2SO4. After
removal of the solvent, the crude product was purified by column chromatography and
1
recrystallized from Et2O/CH3CH2OH to give a white solid 10 (0.42 g, yield 78%). H NMR
(400 MHz, CDCl3) δ 7.99 – 7.91 (m, 4H), 7.89 (s, 2H ), 7.57 (d, J = 4.5 Hz, 2H), 7.04 (d, J =
13
8.3 Hz, 2H), 2.72 – 2.61 (m, 4H), 2.58-0.99 (m, 48H), 0.94 – 0.86 (m, 12H). C NMR (101
MHz, CDCl3, δ) 152.36, 148.23, 143.75, 141.07, 139.91, 137.69, 135.04,133.65, 129.32,
121.51, 120.61, 83.74, 33.42, 32.77, 31.92, 31.38, 29.99, 29.66, 29.35, 29.39, 24.83, 22.67,
14.11. MALDI−TOF MS: m/z 1032.7. Anal. Calcd. For C68H102B2O4Si: C, 79.05; H, 9.95;
Found: C, 79.13; H, 9.66.

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Poly(2',3',6',7'-tetraoctyl-2,7-spirosilabifluorene) (PSSiBF) : A mixture of monomer 9
(187.3 mg, 0.20 mmol), monomer 10 (206.4 mg, 0.20 mmol), Pd2(dba)3 (0.9 mg), Aliquat 336
(20.0 mg), and SPhos (3.2 mg) were dissolved in a mixture of toluene (8 mL) and aqueous
K2CO3 (2 mL, 2 M) under an argon atmosphere. The mixture was heated to 95 °C and stirred
for 1 h. Benzeneboronic acid (15 mg) in 3 mL of toluene was subsequently added and the
mixture was refluxed for 5 h. Finally, 0.5 mL of bromobenzene was added, and the mixture
was refluxed for 5 h. Then sodium diethyldithiocarbamatetrihydrate (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 to give the desired polymer PSSiBF (150.0 mg, yield 50%). 1H NMR
(400 MHz, C6D4Cl2) δ 8.10-7.48 (m, 4H), 7.64-7.48 (m, 6H), 3.28-3.26 (m, 8H), 2.20-1.21 (m,
13
36H), 1.20-0.61 (m, 24H). C NMR (101 MHz, C6D4Cl2, δ) 133.22, 132.82, 130.96, 130.62,
130.35, 130.11, 33.09, 32.85, 32.66, 31.80, 31.11,30.95, 29.85, 29.34, 22.52, 22.33, 13.93,
13.77. Anal. Calcd. for (C56H78Si)n: C, 86.08; H, 10.32; Found: C, 86.39; H, 10.78.
Author Information:
Corresponding authors: junqiaod@ciac.ac.cn; lixiang@ciac.ac.cn
Acknowledgements
The authors acknowledge the financial support from the National Key Research and
Development Program (2016YFB0401301), the 973 Project (2015CB655001) and the
National Natural Science Foundation of China (Nos. 51573183 and 21474106).

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Figure 1. Molecular structures of selected silicon-containing polymers with blue or deep-blue
emissions.

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Scheme 1. Synthetic route of PSSiBF. Reagents and conditions: (a) n-C8H17Br, Mg, I2, 2 h;
then Ni(dppe)Cl2, reflux, 12 h; (b) Br2 (5 equiv.), I2 (0.01equiv.); (c) n-BuLi (0.5 equiv.), -78
oC, THF (dry); (d) Cu, 125 oC, DMF, 3 h; (e) Sn, HCl, 100 oC, EtOH; (f) HCl, NaNO2, -10 to-
5 oC, MeCN, H2O, 1 h; then KI, 60 oC, 16 h; (g) n-BuLi, -78oC, Et2O (dry); (h) n-BuLi, -100
o
o
o
oC, THF, 2 h; then SiCl4 (10 equiv.), -100 C for 4 h; 25 C, overnight; (i) 25 C, 12 h; (j)
o
o
KAc, Pd(dppf)2Cl2, 80 C, DMF; (k) Pd2(dba)3, Aliquant336, SPhos, K2CO3 (2 M), 95 C,
toluene.

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Figure 2. TGA (a) and DSC curves (b) of PSSiBF compared with P27SiF.

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Figure 3. UV-Vis and PL spectra of P27SiF and PSSiBF measured in 10-5 M toluene.

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Figure 4. Dependence of the concentration on the PL spectra for P27SiF (a) and PSSiBF (b).

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Figure 5. CV curves of PSSiBF compared with P27SiF.

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Figure 6. Single-layer device performance of PSSiBF compared with P27SiF: (a) EL spectra
at 10 V; (b) EQE as a function of current density.

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Figure 7. (a) EQE as a function of current density for the double-layer device of PSSiBF.
Inset: energy level alignment of double layer device; (b) EL spectra at different current density.

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Table 1. Physical properties of PSSiBF compared with P27SiF.
a
a
a
b
b
d
e
λabs
λem
ΦPL
λem
ΦPL
HOMO c LUMOc
Td
Tg
[nm]
382
[nm]
[%]
[nm]
[%]
[eV]
[eV]
[oC] [oC]
P27SiF
PSSiBF
417, 440 0.88 428, 448 0.62
414, 436 0.87 420, 442 0.84
-5.90
-2.27
436
430
249
n.d.
347
-6.10
-2.40
b
c
a Measured in toluene at a concentration of 10-5 M; Measured in film; HOMO = −e(Eox +
4.8 V) and LUMO = −e(Ered + 4.8 V), where Eox and Ered are the first oxidation and reduction
d
onset values taken from the CV curves, respectively;
Decomposition temperature
e
corresponding to 5% weight loss; Glass transition temperature determined from the second
heating cycle in DSC curves.

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Table 2. Device performance of PSSiBF compared with P27SiF.
c
d
d
Von
Lmax
ηc
ηp
EQE d
(%)
CIE
(x, y)
Polymer
(V) (cd/m2)
(cd/A)
0.62
(lm/W)
0.13
P27SiF a
PSSiBF a
PSSiBF b
8.6
8.2
6.0
2500
410
0.5
(0.18, 0.15)
0.42
0.92
0.15
0.19
1.3
2.8
(0.16, 0.06)
(0.16, 0.06)
5560
a
b
c
d
Single-layer device; Double-layer device; Turn-on voltage at 1 cd/m2; Maximum
values for current efficiency (ηc), power efficiency (ηP) and EQE.