Synthesis and optical and electrochemical properties of a bispyrimidinium-dibenzothiophene-S,S-dioxide-based cationic conjugated polymer

Article abstract of DOI:10.1016/j.tet.2017.03.062

A novel n-type cationic conjugated polymer (PFSOmiCl), consisting of bispyrimidinium-dibenzothiophene-S,S-dioxide and fluorene scaffolds, was developed from its polymeric precursor (PFSOmi) through an intramolecular cyclization reaction. In comparison with PFSOmi, PFSOmiCl exhibits significant bathochromical absorption and photoluminescence spectra in both solution and film form, as well as a more hydrophilic film surface. Cyclic voltammetry tests demonstrate that PFSOmiCl possesses a deep lowest unoccupied molecular orbital (LUMO) energy level of??4.18?eV, which is comparable to the LUMO energy levels of common fullerene derivatives. These unique properties endow PFSOmiCl with great utilization potential in organic optoelectronic devices. Moreover, this research offers a novel guideline for designing new conjugated polyelectrolytes.

Full text of DOI:10.1016/j.tet.2017.03.062

Tetrahedron xxx (2017) 1e7
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Tetrahedron
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Synthesis and optical and electrochemical properties of a
bispyrimidinium-dibenzothiophene-S,S-dioxide-based cationic
conjugated polymer
Guiting Chen, Wei Yang, Bin Zhang*
Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of
Technology, Guangzhou 510640, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel n-type cationic conjugated polymer (PFSOmiCl), consisting of bispyrimidinium-dibenzothio-
phene-S,S-dioxide and fluorene scaffolds, was developed from its polymeric precursor (PFSOmi) through
an intramolecular cyclization reaction. In comparison with PFSOmi, PFSOmiCl exhibits significant
bathochromical absorption and photoluminescence spectra in both solution and film form, as well as a
more hydrophilic film surface. Cyclic voltammetry tests demonstrate that PFSOmiCl possesses a deep
lowest unoccupied molecular orbital (LUMO) energy level of ꢀ4.18 eV, which is comparable to the LUMO
energy levels of common fullerene derivatives. These unique properties endow PFSOmiCl with great
utilization potential in organic optoelectronic devices. Moreover, this research offers a novel guideline for
designing new conjugated polyelectrolytes.
Received 18 January 2017
Received in revised form
15 March 2017
Accepted 20 March 2017
Available online xxx
Keywords:
Dibenzothiophene-S,S-dioxide
Pyrimidinium
© 2017 Elsevier Ltd. All rights reserved.
n-type
Polyelectrolyte
Conjugated polymer
1. Introduction
abundance.23e25
In past decades, water/alcohol-soluble conjugated polymers
Conjugated polymers have been widely used in organic elec-
tronic devices, such as organic light-emitting diodes (OLEDs),1e3
organic photovoltaics (OPVs),4e6 organic field-effect transistors7e9
and bio/chemosensors,10,11 as a result of their significant advan-
tages, including light weight, low cost, flexibility and large-scale
solution processing. In comparison with the rapid development of
p-type (hole-transporting) conjugated polymers,12e14 the lack of
high-performance n-type (electron-transporting) polymeric semi-
conductors has significantly hindered the improvement in perfor-
mance of organic photoelectric devices. For instance, as only a small
amount of n-type conjugated polymers and small molecules can
adequately serve as electron acceptors in OPVs,15e17 researchers
have been forced to use high-cost fullerene derivatives as acceptors
in order to improve efficiencies.18 Alternatively, in the bio/chemo-
sensor field, investigations have been mainly focused on synthe-
sizing electron-donating polymers to detect electron-deficient
analytes.19e22 However, reports of electron-withdrawing poly-
mers for the detection of electron-rich analytes are not in
(WSCPs) have attracted significant attention and been extensively
utilized in OLEDs,26,27 OPVs28,29 and bio/chemosensors.30 By
incorporating surfactant-like polar groups (e.g., ammonium,31,32
sulfonate and33 phosphonate groups34), conjugated polymers can
be dissolved in highly polar solvents, such as water, dimethyl
sulfoxide (DMSO), methanol and so on. This kind of unusual solu-
bility offers an opportunity to fabricate multilayer optoelectronic
devices via orthogonal solvent processing techniques without
interfacial erosion problems, when WSCPs are used as electrode
interfacial layers in OLEDs and OPVs.27,28 In addition, solubility in
aqueous media, which is an essential property for biosensors,
makes WSCPs capable of interacting with biomacromolecules that
are only soluble in aqueous solution.30 However, most of the re-
ported WSCPs are based on electron-rich backbones, and ideally, n-
type WSCPs with electron-deficient backbones are more efficient
for electron transportation and extraction in organic electronic
devices.35 Hence, it is necessary to develop new n-type WSCPs to
improve the performance of OPVs, OLEDs and perovskite solar cells
(PVSCs), as well as to detect electron-donating analytes.
Recently, the Swager group synthesized a series of cationic
conjugated polymers composed of bispyridinium-phenylene
* Corresponding author.
E-mail address: msbzhang@scut.edu.cn (B. Zhang).
http://dx.doi.org/10.1016/j.tet.2017.03.062
0040-4020/© 2017 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Chen G, et al., Synthesis and optical and electrochemical properties of a bispyrimidinium-dibenzothiophene-
S,S-dioxide-based cationic conjugated polymer, Tetrahedron (2017), http://dx.doi.org/10.1016/j.tet.2017.03.062

2
G. Chen et al. / Tetrahedron xxx (2017) 1e7
scaffolds that showed high electron affinities and con-
ductivities.24,25,36e38 Because of their significant electron-
withdrawing abilities, some of these WSCPs exhibited admirable
sensing performance when they were used to detect electron-
donating analytes (e.g., volatile amines and caffeine).24,25 Su and
co-workers prepared three n-type conjugated small molecules
containing bispyridiniumephenylene units, and used one of them
for improving the cathode interfacial contact of an OPV.39 Inter-
estingly, they found that their material could create an interfacial
dipole between the active layer and metal cathode, which was
consistent with the research of Kim and co-workers.40 This dipole
could reduce the work function of cathode and thus increase the
built-in potential across the device. As a result, the short-circuit
current (Jsc), open-circuit voltage (Voc) and fill factor (FF) of the
OPV were simultaneously enhanced. Based on the above results,
cationic conjugated polymers and small molecules containing bis-
pyridinium units may be a class of high-performance materials for
organic photoelectric devices and sensors.
seven rings, which displayed high thermal stabilities and photo-
luminescence quantum yields.46
Previously, we demonstrated the successful synthesis of two
novel cationic conjugated small molecules based on bispyridinium-
FSO or bispyrimidinium-FSO segments, and their photoelectronic
properties were investigated in detail.47 Herein, we report the
design and synthesis of a novel n-type cationic conjugated polymer
(PFSOmiCl), consisting of bispyrimidinium-FSO and fluorene scaf-
folds. The bispyrimidinium-FSO unit endows the polyelectrolyte
with high electrophilicity and a planar structure for
p-electron
delocalization. In addition, the pyrimidinium rings offer this poly-
mer versatile solubility and processability in highly polar solvents.
The octyl group side chains within a fluorene repeating unit grant
the polymer good film-forming ability. Therefore, this type of WSCP
may be a potential material for organic electronic devices, such as
OLEDs, OPVs, PVSCs and bio/chemosensors.
2. Results and discussion
Dibenzothiophene-S,S-dioxide (FSO) is a well-known n-type
aromatic heterocycle that exhibits good thermal stability, high
fluorescence efficiency, high electron affinity and electron-
transporting ability.41e44 Previously, we synthesized a family of
blue, green and red light-emitting polyfluorenes (PFs) containing
FSO units.1 These polymers exhibited excellent electroluminescent
performance with maximal efficiencies of 7.0,17.6 and 6.1 cd Aꢀ1 for
the blue, green and red light-emitting polymers, respectively.
Subsequently, we introduced FSO moieties into the backbones of
alcohol-soluble PFs containing amino groups.45 When these poly-
mers were utilized as cathode interlayers in OLEDs and OPVs, some
of them displayed better modification performance than the
famous interfacial material, poly[(9,9-bis(3-(N,N-dimethylamino)
propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)], which was
attributed to enhancements in the electron-transporting properties
of these polymers by the FSO units. In addition, we also obtained a
series of novel polycyclic aromatic compounds based on FSO-fused
2.1. Synthesis
The synthetic route of PFSOmiCl is shown in Scheme 1. Com-
pound 1 was reacted with n-BuLi in anhydrous tetrahydrofuran
(THF) at ꢀ78 ꢁC, after which the reaction was quenched by 1-
bromo-2-methoxyethane. Compound 3 was obtained as a white
solid by oxidizing 2 with a H2O2 aqueous solution. Subsequently,
bromination of 3 with N-bromobutanimide in the mixed solvent of
concentrated H2SO4 and AcOH (3:1, v/v) offered compound 4. It was
found that the presence of concentrated H2SO4 was indispensable
for improving the reaction yield. Compound 4 could be separated
from the byproducts by column chromatography on silica gel with
ethyl/petroleum (1/1, v/v) as the eluent. Then, elimination of the
methyl groups within the side chains of 4 by BBr3 generated 5.
Compound 5 has poor solubility in common organic solvents (THF,
CHCl3, toluene and so on). Compound 6 was obtained through the
Scheme 1. Synthetic routes for the monomers and polymers.
Please cite this article in press as: Chen G, et al., Synthesis and optical and electrochemical properties of a bispyrimidinium-dibenzothiophene-
S,S-dioxide-based cationic conjugated polymer, Tetrahedron (2017), http://dx.doi.org/10.1016/j.tet.2017.03.062

G. Chen et al. / Tetrahedron xxx (2017) 1e7
3
reaction between 5 and t-butyldimethylchlorosilane (TBDMSCl) in
anhydrous THF at 0 ꢁC. The reaction yield was as high as 92% and
the solubility of 6 is much higher than that of 5, due to the intro-
duction of TBDMS groups. The chemical structures of compounds
1e6 were verified by 1H NMR, 13C NMR (Figures S1eS6), atmo-
spheric pressure chemical ionization mass spectrometry (APCI-MS)
and elemental analysis. Intermediate 7 was obtained through the
Pd-catalyzed SuzukieMiyama coupling reaction between 6 and
bis(pinacolato)diboron at 85 ꢁC. The crude product of 7 was
extracted by fast column chromatography on neutral Al2O3 with
ethyl acetate/petroleum ether (1/1, v/v) as the eluent. It was diffi-
cult to exhaustively obtain pure 7 by further purifications, and the
further purifications were accompanied by a great loss of 7, so the
crude product of 7 was used for the next step directly. Monomer 8
was prepared through the common Pd-catalyzed Suzuki cross-
coupling reaction between intermediate
7
and 2,5-
dibromopyrimidine, and its structure was also confirmed by 1H
NMR, 13C NMR (Figure S7), APCI-MS and elemental analysis. The
other monomer 9, 2,7-bis(4,4,5,5-tertramethyl-[1,3,2]-dioxabor-
olan-2-yl)-9,9-dioctyl-fluorene, was synthesized according to a
literature procedure.48 The copolymerization between 8 and 9
through the standard Pd-catalyzed Suzuki cross-coupling reaction
afforded the precursor polymer poly[2,7-(9,9-dioctylfluorene)-alt-
5,5-(30,70-di-2-pyrimidinyl-20,80-bis(2-(tert-butyldimethylsilany-
loxy)ethyl)-dibenzothiophene-S,S-dioxide)] (PFSOmi). PFSOmi is
readily soluble in common organic solvents, such as THF and CHCl3,
but insoluble in highly polar solvents (water, DMSO, methanol and
so on). Its number average molecular weight (Mn) tested by gel
permeation chromatography (GPC) is 16900 Da, with a poly-
dispersity index of 1.5. The conjugated polyelectrolyte (CPE),
PFSOmiCl, was prepared from PFSOmi via two steps.36 Firstly,
PFSOmi was treated with SOCl2, during which the TBDMSO groups
within PFSOmi were substituted by chlorine atoms from SOCl2 and
thus intermediate 10 was generated. Secondly, the intramolecular
nucleophilic substitution reaction of 10 took place, which finally
formed the target CPE, PFSOmiCl. PFSOmiCl is readily soluble in
DMSO, and partly soluble in methanol and N,N-dimethylforma-
mide, but is insoluble in water and low polarity solvents such as
CHCl3, THF and toluene. This unique solubility endows PFSOmiCl
with excellent application potential as a cathode interlayer in
solution-processed multilayer OLEDs, OPVs and PVSCs, since the
adjacent layers are usually deposited from low-polarity solvents.29
The 1H NMR spectra of PFSOmi and PFSOmiCl agree with their
chemical structures, as shown in Figures S8 and S9. The signals of
the protons adjacent to the nitrogen atoms are located at 9.19 ppm
in the spectrum of PFSOmi. Whereas the responses of the protons
adjacent to the nitrogen cations or nitrogen atoms shift to 10.26 or
10.14 ppm, respectively, in the spectrum of PFSOmiCl, due to the
generation of electron-withdrawing Nþ cations. The signals of the
other protons within the aromatic rings of PFSOmiCl also possess
higher chemical shifts compared to those of PFSOmi. The reso-
nances at 3.68 and 5.13 ppm are induced by the protons within the
ethylene bridges in the spectrum of PFSOmiCl. The intense peaks at
about 0.91 and 0.02 ppm, which are induced by the TBDMS groups,
disappear in the spectrum of PFSOmiCl. These results indicate that
the CPE could be readily prepared from its precursor.
Fig. 1. Thermo-gravimetric analysis curve of PFSOmiCl.
decomposition process is about 293 ꢁC. The results imply good
thermal stability of PFSOmiCl.
2.3. Optical properties
The UVevis absorption and photoluminescence (PL) spectra of
PFSOmi and PFSOmiCl in solution and film form are shown in
Fig. 2, and the details of the optical properties are summarized in
Table 1. As shown in Fig. 2(a), PFSOmi exhibits a single absorption
peak at 375 nm in THF solution, and a bathochromical band at
394 nm in film state. Alternatively, the absorption spectrum of
PFSOmiCl in DMSO shows a slight band at about 346 nm, which
2.2. Thermal properties
The thermal properties of PFSOmiCl were investigated by
thermo-gravimetric analysis (TGA). The results are shown in Fig. 1.
The scanning temperatures were ramped from 50 to 800 ꢁC with a
consistent increasing rate of 10 ꢁC minꢀ1. PFSOmiCl exhibits two
main degradation processes that probably result from the cleavage
of octyl groups and ethylene bridges, and the onset temperature of
Fig. 2. UVevis absorption (a) and PL (b) spectra of PFSOmi and PFSOmiCl.
Please cite this article in press as: Chen G, et al., Synthesis and optical and electrochemical properties of a bispyrimidinium-dibenzothiophene-
S,S-dioxide-based cationic conjugated polymer, Tetrahedron (2017), http://dx.doi.org/10.1016/j.tet.2017.03.062

4
G. Chen et al. / Tetrahedron xxx (2017) 1e7
Table 1
Table 2
UVevis absorption and PL properties of PFSOmi and PFSOmiCl.
Electrochemical properties of PFSOmi and PFSOmiCl.
a
Polymer
labs (nm)
lPL (nm)
Eogpt (eV)
Polymer
Ered (V)
Eox (V)
LUMO (eV)
HOMO (eV)
Eg (eV)
Solution
Film
Solution
Film
PFSOmi
PFSOmiCl
ꢀ1.41
ꢀ0.21
1.35
1.42
ꢀ2.98
ꢀ4.18
ꢀ5.74
ꢀ5.81
2.76
1.63
PFSOmi
PFSOmiCl
375
346
453
394
363
460
451
583
468
604
2.80
2.33
a
Eg ¼ LUMO ꢀ HOMO.
ferrocenium (Fc/Fcþ) was measured to be 0.41 V using a SCE
reference electrode under the same experimental conditions. Since
the redox potential of Fc/Fcþ has an absolute energy level
of ꢀ4.80 eV to the vacuum energy level,51 the highest occupied
molecular orbital (HOMO) and the lowest unoccupied molecular
orbital (LUMO) energy levels can be calculated according to the
empirical equations: HOMO ¼ -e (Eox þ 4.8e0.41) (eV), LUMO ¼ -e
(Ered þ 4.8e0.41) (eV), where Eox and Ered are the onset oxidation
and reduction potential vs. SCE, respectively. As shown in Fig. 3 and
Table 2, PFSOmi exhibits Ered and Eox values of about ꢀ1.41 and
1.35 V, respectively, and the LUMO and HOMO energy levels are
thus ꢀ2.98 and ꢀ5.74 eV, respectively. For PFSOmiCl, the reduction
onset at about ꢀ0.29 V is attributed to the reduction of one of the
Nþ cations,36 and the more negative reduction band is caused by
the reduction of H2O within the testing system, as observed in our
blank test under the same conditions. In addition, the oxidation
behavior at the positive voltage side is ascribed to the oxidation of
the fluorene unit.26 The Ered and Eox values of PFSOmiCl are located
at ꢀ0.21 and 1.42 V, respectively, so the LUMO and HOMO energy
levels are about ꢀ4.18 and ꢀ5.81 eV, respectively. Note that in
comparison with PFSOmi, PFSOmiCl shows deeper LUMO and
HOMO levels, which is attributed to the introduction of electron-
withdrawing pyrimidinium salts.52 Furthermore, it is well known
that in a donor-acceptor (D-A) copolymer, the HOMO level of the
copolymer mainly depends on the D unit, and the LUMO level is
mainly related to the A unit.52 Since PFSOmi and PFSOmiCl own
the same D units (fluorene), their HOMO levels are close to each
other, but their A units (bispyrimidinium-FSO) are distinctly
different, which results in the significant difference in their LUMO
levels. Moreover, it is interesting to note that the LUMO energy level
of PFSOmiCl is very close to the LUMO energy levels of common
fullerene derivatives, such as [6,6]-phenyl-C61-butyric acid methyl
ester and [6,6]-phenyl-C70-butyric acid methyl ester (in the range
of ꢀ3.8 to ꢀ4.3 eV),53e55 which suggests that PFSOmiCl can form
an ohmic contact with these fullerene derivatives, and this is
helpful for electron transportation and extraction when PFSOmiCl
is applied as cathode modification layer in OPVs or PVSCs.35
Moreover, the relatively deep-lying HOMO energy level is able to
prevent hole carriers from flowing towards the cathode, which can
improve the performance of OLEDs, OPVs and PVSCs.16
can be attributed to the p-p* transition of the conjugated backbone,
and an intense peak at about 453 nm that results from the intra-
molecular charge-transfer (ICT) effect. The absorption peaks of
PFSOmiCl in film bathochromically shift to 363 and 460 nm, due to
the intermolecular aggregation in the solid film state. It is inter-
esting to note that the absorption spectra of PFSOmiCl are obvi-
ously red-shifted compared with those of PFSOmi in both solution
and film form. This is because the newly formed ethylene bridges
enforce the planar conformation of the bispyrimidinium-FSO
scaffold, which decreases the torsion angles between pyr-
imidinium and FSO rings, and thus enhances the molecular orbital
overlap, as well as the delocalization of electrons.36,49 In addition,
the formation of pyrimidinium salts can improve the electron-
withdrawing ability of the bispyrimidinium-FSO segment, and
thus promote the ICT within conjugated backbones and decrease
the band gap of PFSOmiCl.37,50 The optical band gaps (Eogpts) of
PFSOmi and PFSOmiCl, calculated from the absorption onsets in
films, are 2.80 and 2.33 eV, respectively.
In order to achieve a more insightful understanding of the op-
tical properties of PFSOmi and PFSOmiCl, their PL spectra were
also recorded in both solution and film form, as shown in Fig. 2(b).
PFSOmi displays emission peaks at 451 and 468 nm in solution and
film form, respectively. The locations of the PL peaks of PFSOmiCl
bathochromically shift to 583 and 604 nm in DMSO and film,
respectively. Similarly, the reason for the red shifts of PL spectra can
be assigned to the more planar conformation and stronger ICT of
PFSOmiCl compared with PFSOmi. Moreover, relative to PFSOmi,
PFSOmiCl reveals broader PL spectra in both solution and film form
that is also due to the stronger ICT effect in PFSOmiCl.39
2.4. Electrochemical properties
Cyclic voltammetry (CV) was used to investigate the electro-
chemical properties of PFSOmi and PFSOmiCl. The results are
shown in Fig. 3 and Table 2. The redox potential (E1/2) of ferrocene/
2.5. Wetting properties
The wetting properties of the precursor polymer and poly-
electrolyte were estimated by measuring the water contact angle
(q
) on each surface of the PFSOmi and PFSOmiCl films, and the
images were recorded with a digital camera. As shown in Fig. 4, the
value of PFSOmi film is 103.6ꢁ, yet the surface of PFSOmiCl layer
becomes more hydrophilic with a
of 87.0ꢁ. This is probably due to
q
q
the accumulation of the ionic components in the topmost surface of
PFSOmiCl film, as observed for other CPE films.56 It was reported
that in OPV devices, when covered with a perylene diimide-based
cathode interlayer containing phosphate groups (PDIP), the active
layer became more hydrophilic with a decreased q, which eased the
inherent incompatibility between the metal cathode and organic
Fig. 3. Cyclic voltammogram of PFSOmiCl in film measured in 0.1 M Bu4NPF6 in
acetonitrile at a scan rate of 50 mV sꢀ1
.
layer.57 They found that the improved wettability of the active layer
Please cite this article in press as: Chen G, et al., Synthesis and optical and electrochemical properties of a bispyrimidinium-dibenzothiophene-
S,S-dioxide-based cationic conjugated polymer, Tetrahedron (2017), http://dx.doi.org/10.1016/j.tet.2017.03.062

G. Chen et al. / Tetrahedron xxx (2017) 1e7
5
UPLC equipped with Waters Acquity TQ detector (Thermo Finnigan
LCQ Fleet system). Elemental analyses were performed on a Vario
EL elemental analysis instrument (Elementar Co.). Molecular
weight of the precursor polymer was determined by a Waters GPC
2410 in THF using a calibration curve with polystyrene standards.
Thermo-gravimetric analysis (TGA) was conducted using
a
NETZSCH TG 209 at a heating rate of 10 ꢁC minꢀ1 and a nitrogen
flow rate of 20 mL minꢀ1. UVevis absorption spectra were per-
formed on a HP 8453 spectrophotometer. PL spectra were recorded
on an Instaspec IV CCD spectrophotometer (Oriel Co.). Cyclic vol-
tammetry (CV) were characterized on a CHI600D electrochemical
workstation with a standard three electrodes cell based on a Pt wire
counter electrode and a platinum (Pt) working electrode, against
saturated calomel electrode (SCE) as reference electrode at a scan
rate of 50 mV sꢀ1 within a nitrogen-saturated anhydrous solution of
0.1 mol Lꢀ1 tetrabutylammonium hexafluorophosphates (Bu4NPF6)
in acetonitrile, versus ferrocene/ferrocenium (Fc/Fþc ) as the internal
reference.
Fig. 4. Water contact angle images of PFSOmi (a) and PFSOmiCl (b) layers.
with cathode by PDIP could reduce the contact resistance and thus
improve the OPV performance. Similarly, the increased hydrophi-
licity of organic light-emitting layers in OLEDs and organic
electron-transporting layers in PVSCs by cathode interlayers could
also optimize the compatibility between organic layers and metal
cathodes, and thus improve the device performance.58,59 Therefore,
when PFSOmiCl is employed as a cathode interlayer in OPVs,
OLEDs or PVSCs, its hydrophilic surface is expected to improve the
wettability of organic layer with inorganic cathode that is impor-
tant for reducing the contact resistance and increasing the device
performance.
4.2. Synthetic procedures
4.2.1. 2,8-Dibromo-dibenzothiophene (1)
Into a mixture of dibenzothiophene (50.0 g, 272 mmol), Fe
(1.00 g, 18.0 mmol) and CHCl3 (400 mL) was added Br2 (35.0 mL,
680 mmol) (diluted with CHCl3 (100 mL)) slowly at 0 ꢁC. The
mixture was gradually warmed to room temperature with vigor-
ously stirring overnight. Then aqueous solution of NaHSO3 (28.3 g,
272 mmol) was added to quench the reaction. The mixture was
filtered, and the residue was washed with water and purified by
recrystallization from THF to afford 1 as a white crystal (39.0 g,
3. Conclusions
41.9%). 1H NMR (300 MHz, CDCl3)
7.72e7.69 (d, J ¼ 8.4 Hz, 2H), 7.59e7.56 (dd, J ¼ 8.4 Hz, J ¼ 2.0 Hz,
2H). 13C NMR (75 MHz, CDCl3)
(ppm): 138.75, 136.30, 130.43,
d
(ppm): 8.23 (d, J ¼ 1.8 Hz, 2H),
A
novel n-type cationic conjugated polymer (PFSOmiCl)
composed of bispyrimidinium-FSO and fluorene building blocks
has been designed and synthesized. In comparison with its poly-
meric precursor (PFSOmi), PFSOmiCl shows distinctive optical and
wetting properties as a result of the generation of electron-
deficient pyrimidinium salts. In both solution and film form,
PFSOmiCl exhibits significantly bathochromical UVevis absorption
and PL spectra, as well as broader PL bands, when compared with
PFSOmi. The hydrophilic and wetting properties of the PFSOmiCl
film are also dramatically better than those of the PFSOmi film.
Moreover, PFSOmiCl displays a deep-lying LUMO energy level
of ꢀ4.18 eV that is comparable to the LUMO energy levels of
common fullerene derivatives, which means the probable forma-
tion of ohmic contact at the PFSOmiCl/fullerene interface in OPVs
and PVSCs. These unique features including good thermal stability,
polar-solvents solubility, nice hydrophilicity, high electron affinity
and large conjugated plane signify that PFSOmiCl may be a
promising material candidate for organic electronic applications.
d
124.86, 124.33, 118.76. MS (APCI) calculated for C12H6Br2S: 342.1,
found: 343.0. Elemental analysis calculated for C12H6Br2S: C, 42.14;
H, 1.77; S, 9.37, found: C, 41.62; H, 1.99; S, 9.86.
4.2.2. 2,8-Bis(2-methoxyethyl)-dibenzothiophene (2)
Into the solution of 1 (3.42 g, 10.0 mmol) in anhydrous THF
(200 mL) was slowly added n-BuLi (2.4 M in n-hexane, 10.4 mL)
at ꢀ78 ꢁC under argon, and the reaction mixture was stirred
at ꢀ78 ꢁC for 1 h followed by quenching with 1-bromo-2-
methoxyethane (2.80 mL, 30.0 mmol). The solution was then
freely warmed to room temperature and stirred overnight. Distilled
water (50 mL) was added slowly and the aqueous layer was
extracted with CH2Cl2 for three times. The combined organic layer
was washed with brine before dried over anhydrous MgSO4. The
crude product was collected by evaporating off the solvent and then
purified by column chromatography on silica gel with CH2Cl2/pe-
troleum ether (1/1, v/v) as eluent to afford 2 as a colorless oil
4. Experimental section
(975 mg, 32.5%). 1H NMR (300 MHz, CDCl3)
d (ppm): 8.02 (s, 2H),
7.77e7.74 (d, J ¼ 8.1 Hz, 2H), 7.33e7.30 (dd, J ¼ 8.1 Hz, J ¼ 1.2 Hz,
4.1. General procedures
2H), 3.73e3.68 (t, J ¼ 6.9 Hz, 4H), 3.41 (s, 6H), 3.10e3.05 (t,
J ¼ 6.9 Hz, 4H). 13C NMR (75 MHz, CDCl3)
d (ppm): 137.77, 135.71,
All reagents, unless otherwise specified, were purchased from
Aladdin Chemical Co., Sigma Aldrich Chemical Co., Alfa Aesar
Chemical Co. or J&K Chemical Co., and were used as received.
Anhydrous THF and toluene used for polymerization were further
purified by normal procedures and distilled before used. All air and
water sensitive synthetic manipulations were performed under dry
argon or nitrogen atmosphere.
135.32, 127.82, 122.70, 121.81, 73.94, 58.81, 36.35. MS (APCI)
calculated for C18H20O2S: 300.4, found: 301.0. Elemental analysis
calculated for C18H20O2S: C, 71.96; H, 6.71; S, 10.67, found: C, 71.54;
H, 6.95; S, 10.55.
4.2.3. 2,8-Bis(2-methoxyethyl)-dibenzothiophene-S,S-dioxide (3)
30% aqueous solution of H2O2 (10.0 mL, 88.2 mmol) was added
into the solution of 2 (1.40 g, 4.67 mmol) in AcOH (35 mL) at 110 ꢁC
and the reaction was refluxed for 5 h. After cooled to room tem-
perature, the mixture was poured into distilled water with vigor-
ously stirring. The precipitate was then collected and father
1H NMR and 13C NMR measurements were carried out on a
Bruker AV-300 spectrometer operating at 300 MHz (for 1H) and
75 MHz (for 13C) with tetramethylsilane (TMS) as the internal
reference. APCI-MS analyses were obtained from an Acquity Waters
Please cite this article in press as: Chen G, et al., Synthesis and optical and electrochemical properties of a bispyrimidinium-dibenzothiophene-
S,S-dioxide-based cationic conjugated polymer, Tetrahedron (2017), http://dx.doi.org/10.1016/j.tet.2017.03.062

6
G. Chen et al. / Tetrahedron xxx (2017) 1e7
purified by column chromatography on silica gel with ethyl acetate/
petroleum ether (1/1, v/v) as eluent to afford 3 as a white solid
analysis calculated for C28H42Br2O4SSi2: C, 48.69; H, 6.13; S, 4.64,
found: C, 48.03; H, 6.49; S, 4.98.
(1.32 g, 85.5%). 1H NMR (300 MHz, CDCl3)
d (ppm): 7.74e7.71 (d,
J ¼ 7.8 Hz, 2H), 7.65e7.64 (d, J ¼ 0.6 Hz, 2H), 7.38e7.35 (dd,
4.2.7. 3,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,8-bis
[2-(tert-butyldimethylsilanyloxy)ethyl]-dibenzothiophene-S,S-
dioxide (7)
J ¼ 7.8 Hz, J ¼ 1.2 Hz, 2H), 3.68e3.63 (t, J ¼ 6.5 Hz, 4H), 3.36 (s, 6H),
3.01e2.96 (t, J ¼ 6.6 Hz, 4H). 13C NMR (75 MHz, CDCl3)
d (ppm):
146.25, 136.25, 132.08, 130.95, 122.24, 122.18, 72.85, 58.97, 36.59.
MS (APCI) calculated for C18H20O4S: 332.4, found: 333.5. Elemental
analysis calculated for C18H20O4S: C, 65.04; H, 6.06; S, 9.65, found:
C, 65.48; H, 6.29; S, 9.32.
6 (5.00 g, 7.23 mmol), AcOK (4.96 g, 50.6 mmol) and
4,4,5,5,40,40,50,50-octamethyl-[2,2']bi[[1,3,2]dioxaborolanyl] (5.51 g,
21.7 mmol) were mixed with Pd(dppf)Cl2 (0.16 g, 0.2 mmol) in 1,4-
dioxane (100 mL) under argon. Then the reaction mixture was
stirred at 85 ꢁC overnight under argon. Distilled water was poured
into the reaction after cooled to room temperature. Ethyl acetate
was used to extract the aqueous layer for three times. The com-
bined organic layer was washed with brine before dried over
anhydrous MgSO4. Then the solvent was evaporated off and the
crude product was gotten by fast column chromatography on Al2O3
using ethyl acetate/petroleum ether (1/1, v/v) as eluent. The crude
product was used to synthesize 8 without further purification. MS
(APCI) calculated for C40H66B2O8SSi2: 784.8, found: 785.5.
4.2.4. 3,7-Dibromo-2,8-bis(2-methoxyethyl)-dibenzothiophene-
S,S-dioxide (4)
Into the mixture of 3 (3.32 g, 10.0 mmol), H2SO4 (90 mL) and
AcOH (30 mL) was added N-bromosuccinimide (3.91 g, 22.0 mmol)
slowly at 0 ꢁC in the absence of light. Then the reaction was allowed
to warm to room temperature and stirred overnight. After the re-
action mixture was poured slowly into ice water, the mixture was
filtered and the precipitate was purified by column chromatog-
raphy on silica gel with ethyl acetate/petroleum ether (1/1, v/v) as
eluent to afford 4 as a white solid (3.50 g, 71.2%). 1H NMR (300 MHz,
4.2.8. 3,7-Bis(5-bromopyrimidin-2-yl)-2,8-bis[2-(tert-
CDCl3)
d
(ppm): 7.94 (s, 2H), 7.68 (s, 2H), 3.69e3.65 (t, J ¼ 6 Hz, 4H),
butyldimethylsilanyloxy)ethyl]-dibenzothiophene-S,S-dioxide (8)
The crude product 7 (1.00 g), 2,5-dibromopyrimidine (730 mg,
3.10 mmol), TBAB (30 mg), toluene (15 mL), aqueous solution of
K2CO3 (2 M, 4.00 mL) and Pd(PPh3)4 (45.0 mg, 0.0400 mmol) were
added into a 50 mL of three-neck flask under argon. The reaction
was heated to 85 ꢁC and stirred overnight. Then the reaction was
cooled to room temperature and mixed with distilled water
(35 mL). The aqueous layer was extracted with ethyl acetate for
three times. The combined organic layer was washed with distilled
water and brine before dried over anhydrous MgSO4. The organic
solvent was distilled and the crude product was purified by column
chromatography with ethyl acetate/petroleum ether (1/1, v/v) as
eluent to afford 8 as a white solid (500 mg). 1H NMR (300 MHz,
3.37 (s, 6H), 3.15e3.10 (t, J ¼ 7.5 Hz, 4H). 13C NMR (75 MHz, CDCl3)
d
(ppm): 145.41, 137.15, 130.20, 126.61, 126.39, 124.25, 70.91, 59.02,
37.13. MS (APCI) calculated for C18H18Br2O4S: 490.2, found: 491.6.
Elemental analysis calculated for C18H18Br2O4S: C, 44.10; H, 3.70; S,
6.54, found: C, 43.81; H, 3.99; S, 6.29.
4.2.5. 3,7-Dibromo-2,8-bis(2-hydroxyethyl)-dibenzothiophene-S,S-
dioxide (5)
In the absence of light, BBr3 (4.80 mL, 50.0 mmol) was dropped
slowly into the mixture of CH2Cl2 (200 mL) and 4 (4.90 g,
10.0 mmol) at room temperature. After stirred overnight, the re-
action was quenched with distilled water (10 mL) slowly. The sol-
vent was evaporated off and ethyl acetate was added to solve the
solid. The organic layer was washed with dilute aqueous solution of
NaOH and brine before dried over anhydrous MgSO4. The crude
product was collected by evaporating off the solvent and purified
by column chromatography on silica gel with ethyl acetate/petro-
leum ether (5/1, v/v) as eluent to afford 5 as a white solid (3.99 g,
CDCl3)
J ¼ 3 Hz, 4H), 3.35e3.32 (t, J ¼ 4.5 Hz, 4H), 0.87 (s, 18H), ꢀ0.03 (s,
12H). 13C NMR (75 MHz, CDCl3)
(ppm): 163.41, 157.83, 145.72,
d (ppm): 8.92 (s, 4H), 8.47 (s, 2H), 7.85 (s, 2H), 3.93e3.91 (t,
d
138.96, 136.82, 131.54, 125.59, 125.21, 119.08, 63.68, 37.82, 25.94,
18.30, ꢀ5.37. MS (APCI) calculated for C36H46Br2N4O4SSi2: 846.8,
found: 847.4. Elemental analysis calculated for C36H46Br2N4O4SSi2:
C, 51.06; H, 5.48; N, 6.62; S, 3.79, found: C, 51.68; H, 5.99; N, 6.36; S,
3.52.
86.4%). 1H NMR (300 MHz, DMSO-d6)
d (ppm): 8.30 (s, 2H), 8.19 (s,
2H), 4.95e4.92 (t, J ¼ 5.3 Hz, 2H), 3.75e3.68 (m, 4H), 3.02e2.97 (t,
J ¼ 6.6 Hz, 4H). 13C NMR (75 MHz, DMSO-d6)
d (ppm): 145.87,
136.33, 129.45, 126.07, 126.00, 125.23, 59.69, 59.58. MS (APCI)
calculated for C16H14Br2O4S: 462.2, found: 463.4 Elemental analysis
calculated for C16H14Br2O4S: C, 41.58; H, 3.05; S, 6.94, found: C,
41.03; H, 3.77; S, 6.12.
4.2.9. Poly[2,7-(9,9-dioctylfluorene)-alt-5,5-(30,70-di-2-
pyrimidinyl-20,80- bis(2-(tert-butyldimethylsilanyloxy)ethyl)-
dibenzothiophene-S,S-dioxide)] (PFSOmi)
Monomer
8
(169.0 mg, 0.2000 mmol), 2,7-bis(4,4,5,5-
(9)
tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctyl-fluorene
4.2.6. 3,7-Dibromo-2,8-bis[2-(tert-butyldimethylsilanyloxy)ethyl]-
dibenzothiophene-S,S-dioxide (6)
(128.5 mg, 0.2000 mmol), toluene (7.0 mL), aqueous solution of
K2CO3 (2 M, 0.50 mL) and Pd(PPh3)4 (8.0 mg) were mixed in a 50 mL
of two-neck flask under argon protection. The reaction was stirred
at 80 ꢁC for 24 h under argon atmosphere. After cooled to room
temperature, the mixture was poured into methanol (200 mL). The
precipitate was collected by filtration and then washed with
methanol and acetone successively in a Soxhlet. The obtained solid
T-butyldimethylchlorosilane (TBDMSCl) (3.91 g, 25.9 mmol) was
added in one portion into the mixture of 5 (5.00 g, 10.8 mmol),
anhydrous THF (200 mL) and imidazole (2.21 g, 32.4 mmol) at 0 ꢁC
under argon. After stirring overnight, 200 mL of water was added
into the mixture. Then the aqueous layer was extracted with ethyl
acetate for three times. The combined organic layer was washed
with brine before dried over anhydrous MgSO4. The solution was
concentrated and the crude product was father purified by column
chromatography on silica gel with ethyl acetate/petroleum ether
was dissolved in THF (8 mL) and filtered through a 0.45 mm poly-
tetrafluoroethylene (PTFE) filter. The solution was concentrated
followed by precipitation from methanol (150 mL) to get the target
polymer (179.0 mg, 83%). 1H NMR (300 MHz, CDCl3)
d (ppm): 9.19
(1/5, v/v) as eluent to afford 6 as a white solid (6.83 g, 91.5%). 1
NMR (300 MHz, CDCl3) (ppm): 7.95 (s, 2H), 7.67 (s, 2H), 3.90e3.85
(t, J ¼ 6.5 Hz, 4H), 3.10e3.05 (t, J ¼ 6.3 Hz, 4H), 0.86 (s, 18H), ꢀ0.02
(s, 12H). 13C NMR (75 MHz, CDCl3)
(ppm): 145.60, 137.10, 129.90,
H
(s, 4H), 8.60 (s, 2H), 7.95 (br, 2H), 7.91e7.68 (m, 6H), 4.02 (br, 4H),
3.46 (br, 4H), 2.27e1.99 (m, 4H), 1.25e0.79 (m, 48H), 0.02 (s, 12H).
Elemental analysis calculated for C65H86N4O4SSi2: C, 72.58; H, 8.06;
N, 5.21; S, 2.98, found: C, 71.93; H, 8.42; N, 5.44; S, 2.75. GPC (THF,
d
d
126.54, 126.41, 124.44, 61.69, 40.04, 26.00, 18.36, ꢀ5.30. MS (APCI)
polystyrene standard) analysis showed
PDI ¼ 1.514.
a
Mn
¼
16900 and
calculated for C28H42Br2O4SSi2: 690.7, found: 691.8. Elemental
Please cite this article in press as: Chen G, et al., Synthesis and optical and electrochemical properties of a bispyrimidinium-dibenzothiophene-
S,S-dioxide-based cationic conjugated polymer, Tetrahedron (2017), http://dx.doi.org/10.1016/j.tet.2017.03.062

G. Chen et al. / Tetrahedron xxx (2017) 1e7
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1H NMR (300 MHz, DMSO-d6)
d (ppm): 10.26 (br, 2H), 10.14 (br, 2H),
8.98 (s, 2H), 8.69 (br, 2H), 8.47e8.09 (m, 6H), 5.13 (br, 4H), 3.68 (br,
4H), 2.27e1.97 (m, 4H), 1.23e0.75 (m, 30H). Elemental analysis
calculated for C53H56Cl2N4O2S: C, 72.01; H, 6.39; N, 6.34; S, 3.63,
found: C, 71.53; H, 7.00; N, 6.82; S, 3.41.
Acknowledgements
This work was financially supported by the National Nature
Science Foundation of China (nos. 51273069, 91333206), General
Financial Grant from the China Postdoctoral Science Foundation
(no. 2015M582409) and Shenzhen Fundamental R&D Program (no.
JCYJ20160520175355048).
Appendix A. Supplementary data
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Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2017.03.062.
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Please cite this article in press as: Chen G, et al., Synthesis and optical and electrochemical properties of a bispyrimidinium-dibenzothiophene-
S,S-dioxide-based cationic conjugated polymer, Tetrahedron (2017), http://dx.doi.org/10.1016/j.tet.2017.03.062