Synthesis of conjugated polymers bearing pendant bipyridine ruthenium complexes

Article abstract of DOI:10.1016/j.reactfunctpolym.2015.02.008

Abstract Conjugated polymers bearing pendant bipyridine groups, PM1PT-x, were synthesized in high yield from a carefully designed dibromocarbazole monomer M1 using a Suzuki coupling reaction with a phenothiazine diborate monomer. PM1PT-x, where x is the mole percentage of M1 in the total feed of dibromo-monomers and varied to levels of 25%, 50%, 75% and 100%, was reacted with a ruthenium complex to yield conjugated polymers bearing pendant bipyridine ruthenium complexes, PM1PT-x-Ru. The introduction of ruthenium complexes extended the absorption of PM1PT-x-Ru to the visible light region. Furthermore, these polymers demonstrated sufficient stability and suitable energy levels to potentially be highly efficient photoactive materials for polymeric solar cells.

Full text of DOI:10.1016/j.reactfunctpolym.2015.02.008

Reactive & Functional Polymers 90 (2015) 7–14
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Synthesis of conjugated polymers bearing pendant bipyridine ruthenium
complexes
Yuxia Jin a,b, Yingliang Liu , Wenbo Wu , Qiong Wu , Hongyan Gao , Chenxu Wang , Shengang Xu
⇑
,
Shaokui Cao
a
a
a
a
a
a
a,
a,
⇑
School of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450052, Henan Province, PR China
School of Materials Engineering, Zhengzhou Technical College, Zhengzhou 450121, Henan Province, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Conjugated polymers bearing pendant bipyridine groups, PM1PT-x, were synthesized in high yield from a
carefully designed dibromocarbazole monomer M1 using a Suzuki coupling reaction with a phenoth-
iazine diborate monomer. PM1PT-x, where x is the mole percentage of M1 in the total feed of
dibromo-monomers and varied to levels of 25%, 50%, 75% and 100%, was reacted with a ruthenium com-
plex to yield conjugated polymers bearing pendant bipyridine ruthenium complexes, PM1PT-x-Ru. The
introduction of ruthenium complexes extended the absorption of PM1PT-x-Ru to the visible light region.
Furthermore, these polymers demonstrated sufficient stability and suitable energy levels to potentially
be highly efficient photoactive materials for polymeric solar cells.
Received 22 November 2014
Received in revised form 25 February 2015
Accepted 26 February 2015
Available online 22 March 2015
Keywords:
Conjugated polymer
Ruthenium complex
Carbazole
Ó 2015 Elsevier B.V. All rights reserved.
Phenothiazine
1
. Introduction
Polymeric materials have played increasingly important roles in
incorporating transition metal complexes into organic conjugated
polymers to improve their optical absorption have also been found,
as shown in Chart 1. In most of these strategies, transition metal
complexes were incorporated in the polymer main chain (types a
and b, Chart 1). However, the charge transfer ability of the
conjugated main chain would be affected by the blocking of the
embedded metal complexes, which may decrease the PCE in some
instances [21–24]. An alternative approach is to link the metal
complexes to the side chain of the conjugated polymers through
a flexible linkage (type c, Chart 1), which allows for simultaneous
extended absorption and high PCE because the charge transfer
ability of the main chain and the light harvesting ability of the
metal complex would not interfere with each other. However, this
approach is rarely used in literature [25,26], possibly due to
difficulty in synthesis. As reported in the literature [25], no poly-
mer was obtained directly by the polymerization of monomers
containing a metal complex. Thus, it is vital to develop an
appropriate and simple way to synthesize this type of polymer.
In this paper, we prepared a series of conjugated polymers,
PM1PT-x-Ru, with metal complexes linked as pendant groups via
a flexible chain. The conjugated main chains consisted of carbazole
and phenothiazine moieties, giving the polymers good hole-trans-
porting ability [27,28]. The ruthenium complex, which is one of the
most studied metal complexes in this area due to its potential in
solar energy conversion [15,29], is linked to the conjugated main
chain via a flexible spacer. Thus, the light harvesting ability of
ruthenium complexes is combined with the excellent charge
meeting the requirements of modern society due to their tunable
optoelectronic properties, flexibility, ease of processing and good
cost efficiency [1–5]. For synthetic chemists, it is important to
design new strategies to simplify the synthesis of functional
polymers in order to increase development in corresponding
applications. With an increasing demand for cheap renewable
energy sources, synthetic polymers have been thoroughly explored
as photovoltaic materials [6–8] in recent years. In comparison with
their traditional inorganic counterparts, polymeric solar cells
(
PSCs) have the potential advantage of fabrication on flexible and
lightweight substrates using roll-to-roll solution processing,
providing cost-effective production [9–11]. However, their power
conversion efficiency (PCE), the most important parameter for
solar cells, is still insufficient for many practical applications. The
relatively mismatched and narrow absorption band of most
polymers is one of the main reasons for the low PCE [12–14].
It is well known that some transition metal complexes show
strong broad absorption in the visible light region, and these
complexes have been frequently used as photosensitizers in
dye-sensitized solar cells [15–20]. In literature, several strategies
⇑
Corresponding authors. Tel./fax: +86 371 6776 3561.
E-mail addresses: xusg@zzu.edu.cn (S. Xu), caoshaokui@zzu.edu.cn (S. Cao).
http://dx.doi.org/10.1016/j.reactfunctpolym.2015.02.008
381-5148/Ó 2015 Elsevier B.V. All rights reserved.
1

8
Y. Jin et al. / Reactive & Functional Polymers 90 (2015) 7–14
Chart 1. The original idea of this work and different types of conjugated polymers containing metal complexes.
transfer ability of the conjugated backbone in one molecule.
Encouragingly, thin films of the obtained polymers showed a broad
absorption peak centered at approximately 540 nm. Furthermore,
these polymers demonstrated good stability and suitable energy
level. Coupled with their extended absorption spectra, these
polymers should be suitable candidates for fabricating PSCs. Herein,
we present the synthesis and characterization of these polymers.
carefully designed and not previously reported. A low molar mass
ruthenium complex, Ru-bpy, was also synthesized as a model
compound.
2.3.1. Synthesis of monomer M1
A mixture of compound 1 (0.976 g, 2.00 mmol), compound 2
(
0.400 g, 2.00 mmol), potassium hydroxide (0.281 g, 5.00 mmol),
potassium iodide (13 mg), 18-crown-6 (11 mg), and DMF (20 mL)
2
. Experiment
was stirred at 105 °C for 24 h under argon. The mixture was then
poured into water and extracted using CHCl
with water. The organic phase was separated and dried overnight
with anhydrous MgSO . Solvents were removed by evaporation,
and the obtained residue was purified by silica gel column chro-
matography using a mixed solvent of hexane, ethyl acetate and tri-
3
, followed by washing
2
.1. Materials
4
0
0
4
,4 -Dimethyl-2,2 -bipyridine and [RuCl
2
(p-cymene)]
2
were
purchased from Acros. 2-Isopropoxy-4,4,5,5-tetramethyl-1,3,
2
-dioxaborolane was purchased from Alfa Aesar. 3,6-Dibromo-9-
ethylamine (1:1:0.01, v/v/v) as eluent to give a white powder of
0
1
(
2
2
6-bromohexyl) carbazole (1) [30], 4-hydroxymethyl-4 -methyl-2,
M1 (1.060 g, Yield: 87.3%). H NMR (400 MHz, CDCl
3
, d, ppm):
0
-bipyridine (2) [31], monomers M2 [32] and M3 [32], and 2,
8.63 (d, J = 4.9 Hz, 1H, ArH), 8.50 (d, J = 4.9 Hz, 1H, ArH), 8.32 (s,
1H, ArH), 8.23 (s, 1H, ArH), 8.13 (d, J = 1.5 Hz, 2H, ArH), 7.53 (dd,
J = 8.7, 1.6 Hz, 2H, ArH), 7.29 (d, J = 4.7 Hz, 1H, ArH), 7.24 (s, 2H,
0
0
-bipyridine-4,4 -dicarboxydiethylester (6) [33] were synthesized
according to literature procedures. All other reagents were used as
received.
ArH), 7.12 (d, J = 4.8 Hz, 1H, ArH), 4.56 (s, 2H, ArACH
2
OA), 4.24
(
(
1
t, J = 7.1 Hz, 2H, ACH
s, 3H, ArACH A), 1.83 (m, 2H, ACH
.49–1.27 (m, J = 10.4 Hz, 4H, ACH
d, ppm): 156.3, 155.8, 149.3, 149.0, 148.3, 139.3, 129.1, 124.8,
2
N), 3.48 (t, J = 6.3 Hz, 2H, ACH OA), 2.44
2
A), 1.60 (m, 2H, ACH
A). C NMR (100 MHz, CDCl ,
2
A),
2.2. Instruments
3
2
1
3
2
3
1H NMR and 13C NMR spectra were recorded on a Bruker DRX-
00 (400 MHz) NMR spectrometer. FT-IR spectra were conducted
with a Nicolet Protégé 460 infrared spectrometer on a KBr disc.
Elemental analyses were carried out on an EA 1110 CHNSO
elemental analysis system. Mass spectra were recorded on a
1
2
23.5, 123.3, 122.1, 121.9, 119.4, 112.0, 110.4, 71.4, 70.8, 43.2,
9.5, 28.8, 27.0, 26.0, 21.2. MS (ES-TOF) Calcd for
4
[
C
30
H
29
N
3
OBr
OBr
.83; N, 6.89.
2
+ H] 608.39; found 608.07. Anal. Calcd for
C
4
H
30 29
N
3
2
: C, 59.33; H, 4.81; N, 6.92. Found: C, 59.16; H,
Micromass
Q-Tof
mass
spectrometer.
Gel
permeation
chromatography (GPC) analysis was performed on an HLC-8220
liquid chromatograph calibrated with polystyrene standards using
THF as eluent. Thermogravimetric analysis (TGA) was determined
2
.3.2. Synthesis of the model compound, Ru-bpy
The synthesis of the low molar mass ruthenium complex
with
a
NETZSCH DSC-204 calorimeter at
a
heating rate of
with a nitrogen flow from room temperature to
00 °C. UV–vis absorption spectra were obtained on a Shimadzu
Ru-bpy was conducted similarly to as described in literature
ꢀ1
1
6
0 °C min
[
(
34]. Compound 2 (60 mg, 0.30 mmol) was added to a DMF
30 mL) solution of compound 5 (87 mg, 0.15 mmol) in a flask
UV-3010 instrument. Cyclic voltammetry (CV) was measured on a
RST 3000 electrochemistry workstation with a three-electrode sys-
tem, consisting of a Teflon-shrouded 3 mm glassy carbon electrode,
a saturated calomel electrode and a platinum wire as the working,
reference and counter electrodes, respectively. Distilled dimethylfor-
mamide (DMF) was used as the solvent, which was deoxygenated
with argon prior to the measurement. Then, 0.1 M of tetrabuty-
protected by argon flushing, and stirred at 80 °C for 4 h without
exposure to light. Subsequently, compound 6 (83 mg, 0.30 mmol)
was added and the reaction mixture was stirred at 140 °C for 4 h.
4
Finally, an excess of NH NCS (46 mg, 0.60 mmol) was added to
the resulting deep black solution and the reaction continued for
another 4 h at the same temperature. Subsequently, the reaction
mixture was cooled to room temperature and the solvent was
removed. Water was added to resuspend the precipitate, which
was collected and washed with water and ethanol several times,
and then dried under vacuum to yield a black powder of Ru-bpy.
lammonium tetrafluoroborate (TBABF
electrolyte, and the scan rate of all measurements was 100 mV s
4
) was used as the supporting
ꢀ1
.
1
2.3. Synthesis of intermediates and monomers
(136 mg, Yield: 83.1%). From the H NMR spectrum, the product
of Ru-bpy could be recognized as a mixture of stereoisomers. 1
H
The synthesis of different intermediates and monomers are pre-
sented in Scheme 1. The monomer M1 is a dibromo-carbazole
linked with a bipyridine group via a flexible spacer, which was
NMR (400 MHz, DMSO, d, ppm): 9.50 (d, J = 5.5 Hz, 2H, ArH), 9.21
(m, 2H, ArH), 9.09–8.97 (m, 4H, ArH), 8.68 (s, 2H, ArH), 8.52 (s,
2H, ArH), 8.36 (m, 2H, ArH), 8.03–7.78 (m, 4H, ArH), 7.74–7.54

Y. Jin et al. / Reactive & Functional Polymers 90 (2015) 7–14
9
Scheme 1. Synthesis of the monomers M1–M3 and the model compound Ru-bpy.
(
(
m, 4H, ArH), 7.30 (s, 2H, ArH), 7.19 (d, J = 11.2 Hz, 2H, ArH), 7.06
s, 2H, ArH), 5.89 (s, 1H, AOH), 5.64 (s, 1H, AOH), 4.90 (s, 2H,
significantly reduced. Therefore, the conjugated polymers bearing
pendant bipyridine groups via flexible spacer, PM1PT-x,
were synthesized using Suzuki coupling reaction of the
dibromo-monomers M1 and M2 in different molar ratios with
the diborate monomer M3 using Pd(PPh as catalyst. The
resulting polymers were named as PM1PT-x, with x-values of 25,
50, 75 and 100, representing the molar percentage of M1 in the
total feed dibromo-monomers.
a
ArACH
(
ArACH
6
2
A), 4.61 (s, 2H, ArACH
d, J = 7.0 Hz, 2H, ACH A), 2.68 (s, 3H, ArACH
), 1.45 (t, J = 6.7 Hz, 6H, ACH ), 1.30 (dd, J = 17.5, 11.4 Hz,
2 2
A), 4.51 (s, 2H, ACH A), 4.37
a
2
3
), 2.41 (s, 3H,
3
3
3 4
)
ꢀ
ꢀ1
1
H, ACH
723 cm
3
1
). IR (KBr disc):
m
(SCN): 2102 cm
, m (C@N): 1613 cm , m (C@C): 1400 cm .
,
m
(COO):
ꢀ
ꢀ1
1
2
.4. Synthesis of polymers bearing pendant bipyridine groups,
Taking PM1PT-25 as an example, the typical synthetic procedure
was as follows. M1 (0.152 g, 0.25 mmol), M2 (0.352 g, 0.75 mmol),
M3 (0.563 g, 1.00 mmol), tetrakis(triphenylphosphine)palladium
(0) (26 mg) and tetrabutylammonium bromide (0.200 g) were
mixed in a Schlenk tube under argon atmosphere. THF (20 mL)
was added and the mixture was degassed by freeze-pump-thaw
cycle three times. Cesium carbonate aqueous solution (2.00 g in
3 mL water) was added and the mixture was heated at 60 °C for
7 days. Then, the mixture was dropped into methanol and filtered.
PM1PT-x
Some carbazole-based copolymers have been synthesized upon
Suzuki coupling reaction between dibromo-monomers and dibo-
rate monomer using palladium as catalyst [35,36]. Jayakannan
et al. [37] reported that polymers obtained using Pd(OAc)
catalyst contain chains with various combinations of end groups.
While using Pd(PPh the number of different end groups was
2
as
3 4
)

1
0
Y. Jin et al. / Reactive & Functional Polymers 90 (2015) 7–14
The polymer was dissolved in THF and re-precipitated from metha-
nol three times, and finally dried in vacuum oven overnight.
reaction. PM1PT-50-Ru was obtained as a brownish black powder
ꢀ1
(0.403 g, Yield: 85.4%). IR (KBr disc):
m
(SCN): 2100 cm
, m (COO):
ꢀ1
PM1PT-25 was obtained as a pale yellow powder (0.547 g, Yield:
1720 cm . Anal. Calcd for (C54H N O S2.5Ru0.5): C, 68.39; H,
59 5 2.5
1
8
4
(
(
3.2%). H NMR (400 MHz, CDCl
3
, d, ppm): 8.73–6.78 (ArH),
OA), 4.39–4.20 (carbazoleANCH A), 3.86–3.64
A), 3.56–3.38 (ACH OA),
), 2.11–1.15 (ACH A), 0.98–0.73 (ACH ). M
6.23; N, 7.39. Found: C, 67.76; H, 6.30; N, 7.29.
PM1PT-75-Ru Compound 5 (0.175 g, 0.30 mmol), compound 6
4
(0.166 g, 0.60 mmol), NH NCS (0.092 g, 1.20 mmol) and PM1PT-
.63–4.49 (ArACH
2
2
phenothiazineANCH
ArACH
2
2
2.52–2.35
= 6.36 ꢁ 10 ,
3
3
2
3
w
75 (0.484 g, 0.50 mmol bipyridine units) were charged for the
reaction. PM1PT-75-Ru was obtained as a black powder (0.615 g,
PDI = 1.94 (GPC). Anal. Calcd for (C42.5
49.5 2.5 0.25
H N O S1.75): C, 77.92;
ꢀ
1
H, 7.32; N, 5.35. Found: C, 77.81; H, 7.08; N, 5.17.
PM1PT-50. M1 (0.304 g, 0.50 mmol), M2 (0.235 g, 0.50 mmol)
and M3 (0.563 g, 1.00 mmol) were charged for the polymerization.
Yield: 83.6%). IR (KBr disc):
m
(SCN): 2101 cm
, m (COO):
ꢀ1
1720 cm . Anal. Calcd for (C61H N O S2.75Ru0.75): C, 65.86;
64.5 6.5 3.75
H, 5.80; N, 8.19. Found: C, 65.46; H, 5.96; N, 7.85.
PM1PT-50 was obtained as a pale yellow powder (0.434 g, Yield:
PM1PT-100-Ru Compound 5 (0.175 g, 0.30 mmol), compound 6
1
8
4
1.2%). H NMR (400 MHz, CDCl
3
, d, ppm): 8.68–6.78 (ArH), 4.63–
OA), 4.39–4.20 (carbazoleANCH A), 3.86–3.64
A), 3.56–3.38 (ACH OA),
), 2.11–1.12 (ACH A), 0.98–0.73 (ACH ). M
4
(0.166 g, 0.60 mmol), NH NCS (0.092 g, 1.20 mmol) and PM1PT-
.49 (ArACH
2
2
100 (0.381 g, 0.50 mmol bipyridine units) were charged for the
(
(
phenothiazineANCH
ArACH
2
2
2.52–2.35
= 4.46 ꢁ 10 ,
reaction. PM1PT-100-Ru was obtained as
(0.553 g, Yield: 86.3%). IR (KBr disc):
a
black powder
3
ꢀ1
3
2
3
w
m
(SCN): 2102 cm
,
m
ꢀ1
PDI = 1.57 (GPC). Anal. Calcd for (C45
.40; N, 6.10. Found: C, 78.26; H, 7.39; N, 6.07.
PM1PT-75. M1 (0.456 g, 0.75 mmol), M2 (0.118 g, 0.25 mmol)
H
51
N
3
O
0.5
S1.5): C, 78.37; H,
70 8 5 3
(COO): 1720 cm . Anal. Calcd for (C68H N O S Ru): C, 64.04; H,
7
5.49; N, 8.78. Found: C, 64.56; H, 5.60; N, 8.09.
and M3 (0.563 g, 1.00 mmol) were charged for the polymerization.
3
. Results and discussion
PM1PT-75 was obtained as a pale yellow powder (0.573 g, Yield:
1
7
4
(
(
8.8%). H NMR (400 MHz, CDCl
3
, d, ppm) 8.68–6.78 (ArH), 4.63–
OA), 4.39–4.20 (carbazoleANCH A), 3.86–3.64
A), 3.56–3.38 (ACH OA),
), 2.11–1.12 (ACH A), 0.98–0.73 (ACH ). M
3.1. Synthesis of monomer M1
.49 (ArACH
2
2
phenothiazineANCH
ArACH
2
2
2.52–2.35
= 3.23 ꢁ 10 ,
3
The synthetic routes to the monomers and polymers are pre-
sented in Schemes and 2. M1 was synthesized using
Williamson reaction between compounds 1 and 2 in the presence
of potassium hydroxide, potassium iodide and 18-crown-6. When
2 3
only using strong alkali NaH or weak alkali K CO in DMF without
3
2
3
w
1
a
PDI = 1.50 (GPC). Anal. Calcd for (C47.5
52.5 3.5 0.75
H N O S1.25): C, 78.95;
H, 7.27; N, 6.78. Found: C, 78.43; H, 7.31; N, 6.25.
PM1PT-100. M1 (0.608 g, 1.00 mmol) and M3 (0.563 g,
1
.00 mmol) were charged for the polymerization. PM1PT-100
1
potassium iodide and 18-crown-6, the yield of M1 was very low.
When M1 was synthesized by a Williamson reaction between
was obtained as a pale yellow powder (0.560 g, Yield: 73.6%).
NMR (400 MHz, CDCl
ArACH OA), 4.39–4.20 (carbazoleANCH
iazineANCH A), 3.56–3.38 (ACH OA), 2.52–2.35 (ArACH
.05 (ACH A), 0.98–0.73 (ACH
GPC). Anal. Calcd for (C50 OS): C, 79.16; H, 7.12; N, 7.39.
Found: C, 78.86; H, 7.08; N, 7.17.
H
3
,
d, ppm) 8.73–6.82 (ArH), 4.63–4.49
A), 3.86–3.64 (phenoth-
), 2.19–
= 7.78 ꢁ 10 , PDI = 1.98
6
-bromohexyl carbazole and compound 2, then brominated by
(
2
2
1
NBS, the post-treatment of M1 was very difficult. The H NMR
spectrum of M1 is shown in Fig. 1. The peaks at 3.49 ppm and
2
2
3
3
1
(
2
3 w
). M
4
.57 ppm may be assigned to the protons of the alkoxy group
linked to the hexyl group (A(CH ACH OA, marked i in Fig. 1)
and bipyridine (AOCH Abpy, marked j in Fig. 1), respectively.
54 4
H N
2
)
5
2
2
Their integrated area ratio was 1:1, which is consistent with the
theoretical value, indicating the successful synthesis of M1.
Furthermore, the chemical structure of M1 was also confirmed
2
.5. Synthesis of Ru-containing polymers, PM1PT-x-Ru
As shown in Scheme 2, the Ru-containing polymers PM1PT-x-
Ru were synthesized by adding compound 6, NH SCN and
1
3
by C NMR, elemental analysis and MS measurements.
4
PM1PT-x in sequence to the DMF solution of Ru-complex 5. The
obtained polymers PM1PT-x-Ru, where x = 25, 50, 75 and 100,
were extracted in a Soxhlet extractor to remove the unreacted
low molar mass compounds.
3.2. Synthesis of polymers bearing pendant bipyridine groups, PM1PT-
x
Taking PM1PT-25-Ru as an example, compound 6 (0.083 g,
The conjugated polymers were prepared by Suzuki polycon-
densation between the dibromo-monomers M1 and M2 and the
diborate monomer M3. The obtained conjugated polymers were
named as PM1PT-25, PM1PT-50, PM1PT-75 and PM1PT-100,
corresponding to the molar percentage of M1 in the dibromo-
0
(
.30 mmol) was added to a DMF (30 mL) solution of compound 5
0.087 g, 0.15 mmol) in a flask protected by argon flushing, and
stirred at 80 °C for 4 h under reduced light. Subsequently,
NH NCS (0.046 g, 0.60 mmol) was added, and the reaction mixture
was refluxed for 4 h. Finally, polymer PM1PT-25 (0.658 g,
.25 mmol bipyridine units) was added to the resulting black
4
1
monomer feed. Fig. 1 shows the H NMR spectra of monomer M1
1
0
and all PM1PT-x polymers. In the H NMR spectra of the polymers,
solution, and the reaction mixture was refluxed for another 4 h.
The reaction mixture was cooled to room temperature and added
dropwise into 150 mL methanol. The polymer precipitate was
collected by filtration and washed with large amount of water,
methanol and acetone. The product was further purified by
washing it with a mixed solution (methanol/acetone = 1:1) in a
Soxhlet extractor for 2 days to remove any residual low molar mass
compounds. PM1PT-25-Ru was obtained as a brownish black
the chemical shifts were consistent with the proposed polymer
structure as demonstrated in Scheme 2, although they demon-
strated a tendency for signal broadening due to polymerization.
Furthermore, the content of relative monomers was also
calculated from the integration ratios of the peaks to be
2
4.35 ppm (carbazoleANCH A, marked m in Fig. 1) and 3.83 ppm
(phenothiazineANCH A, marked n in Fig. 1). The mole ratio of car-
2
bazole units to phenothiazine units of PM1PT-25, PM1PT-50,
PM1PT-75 and PM1PT-100 were estimated to be 1:7.01, 1:3.02,
0.6:1, and 1:1, respectively, and thus were very close to the calcu-
lated values x:(2 ꢀ x) expected from the corresponding M1 in the
dibromo-monomer feed (x = 25%, 50%, 75%, and 100%). The integra-
tion value of the signals originating from the bipyridine moiety of
M1 is 8.3–8.7 ppm, increasing with the increase of M1 content in
ꢀ1
powder (0.627 g, Yield: 80.1%). IR (KBr disc):
m (SCN): 2100 cm , m
ꢀ1
(
53.5 3.5 1.25
COO): 1720 cm . Anal. Calcd for (C47H N O S2.25Ru0.25): C,
7
1.96; H, 6.83; N, 6.25. Found: C, 71.62; H, 6.80; N, 6.09.
PM1PT-50-Ru Compound 5 (0.087 g, 0.15 mmol), compound 6
(
0.083 g, 0.30 mmol), NH
4
NCS (0.046 g, 0.60 mmol) and PM1PT-
5
0 (0.268 g, 0.25 mmol bipyridine units) were charged for the

Y. Jin et al. / Reactive & Functional Polymers 90 (2015) 7–14
11
Scheme 2. Synthesis of polymers PM1PT-x and PM1PT-x-Ru.
Fig. 1. 1H NMR spectra of monomer M1 and polymers PM1PT-x in CDCl
3
.
the feed. This is more evident for successful polymerization.
Furthermore, all elemental analyses of PM1PT-x were consistent
with their corresponding calculated values according to the
x = 25%, 50%, 75%, and 100%, further confirming the successful
polymerization. The data of weight-averaged molecular weight
(M
w
) and polydispersity index (PDI) measured by GPC were
values ranged from 3230 to
compositional formulae [C(40+10x)
H
(48+6x)
N
(2+2x)
O
x
S(2ꢀx)], where
summarized in Table 1. The M
w

1
2
Y. Jin et al. / Reactive & Functional Polymers 90 (2015) 7–14
7
780, and the PDI values were in the range of 1.50–1.98, which are
similar to the results of reported polymers prepared through
Suzuki polycondensation [38–40].
3.3. Synthesis of Ru-containing polymers, PM1PT-x-Ru
The polymers PM1PT-x-Ru were prepared by a one-pot post-
functionalization method. To avoid the occurrence of inter-chain
crosslinking through macromolecular ligand chelation with metal
ions, the feeding order of reagents was carefully arranged. First,
dichloro-(p-cymene) ruthenium (II) dimer and compound 6 in
4
DMF were added to a flask, and then NH NCS was added. At this
stage, four of the six coordination sites of the ruthenium ion had
been occupied by one bipyridine ligand and two thiocyanate
ligands, and only two coordination sites were left for the coordina-
tion with the pendant bipyridine groups in the polymers PM1PT-x.
Therefore, crosslinking through inter-chain coordination of macro-
molecular ligand with ruthenium ion could be avoided effectively.
The Ru-containing polymers PM1PT-x-Ru were obtained in high
yields, above 80%, and show fairly good solubility in some organic
solvents, which could be further indication that inter chain
coordination was avoided. Thus, by modifying the synthetic
procedure, polymers PM1PT-x-Ru have been synthesized by a
one-pot post-functionalization reaction, which is a novel simplified
strategy to prepare this type of conjugated polymers with metal
complexes linked to the pendant ligand through a flexible chain.
Fig. 2 is the FT-IR spectra of PM1PT-x-Ru. Compared to the
metal-free polymers PM1PT-x, PM1PT-x-Ru have very strong
Fig. 2. FT-IR spectra of PM1PT-x-Ru (x = 25, 50, 75 and 100) in KBr disc.
d
M1 units increased, the T of PM1PT-x showed a tendency to
decrease, which might result from the ether linkage between the
carbazole and bipyridine moieties in the monomer M1 [41].
Fig. 3(b) shows the TGA curves of the Ru-containing polymers
PM1PT-x-Ru and the model compound Ru-bpy with the tempera-
d d
ture at 5% weight loss (T ) summarized in Table 2. The T values of
PM1PT-x-Ru are in the range of 220–282 °C, much lower than
those of the ligand polymer PM1PT-x. This decrease may possibly
be due to the prior detachment of the thiocyanate ligands on the
ꢀ1
ꢀ1
absorption bands at approximately 2100 cm
and 1720 cm
,
ruthenium complex [41]. With the increase in Ru content, the T
d
which could be ascribed to the -SCN group and ACOOA group
stretching vibration of the ruthenium complex, indicating
the ruthenium complexes had been successfully introduced
into the polymer. Furthermore, the elemental analysis results
of PM1PT-x-Ru were very close to the theoretical value,
indicating that almost all the bipyridine ligands in the polymers
PM1PT-x have been converted into the corresponding ruthenium
complexes.
of PM1PT-x-Ru also showed a tendency to decrease. Fortunately,
the thermal stability of these Ru-containing polymers is much
better than the model compound Ru-bpy, indicating the con-
tribution of the conjugated polymeric main chain. Furthermore,
this observation also indicated that our strategy to prepare this
type of polymer was successful in some sense; otherwise, the
thermal stability of the obtained polymers would be similar to
that of the model compound Ru-bpy.
3.4. Solubility and thermal properties
3.5. UV–vis absorption spectra
The metal-free polymers PM1PT-x showed good solubility in
common organic solvents such as CHCl , THF, DMF, DMAc and
3
Fig. 4(a) shows the UV–vis absorption spectra of PM1PT-x in
THF solution. A strong absorption peak centered at 285 nm and a
shoulder peak in the range of 325–440 nm were observed. The peak
at 285 nm resulted from the absorption of bipyridine-centered
transitions. The shoulder peak may be assigned to the absorption
of the conjugated main chain. With the increase of the carbazole
moieties in PM1PT-x, the shoulder peak shifted from 370 nm to
DMSO. After coordinating with the ruthenium complex, the
solubility of corresponding PM1PT-x-Ru decreased to some extent,
but they are still soluble in some polar solvents such as DMF, DMAc
and DMSO, indicating again that the modification of the synthetic
procedure avoided inter-chain crosslinking of macromolecular
ligands.
The thermal stability of the polymers under nitrogen atmo-
sphere was evaluated by thermogravimetric analysis (TGA).
Fig. 3(a) shows the TGA curves of ligand polymers PM1PT-x, with
3
38 nm, indicating the decreased effective conjugation length.
Fig. 4(b) shows the UV–vis absorption spectra of PM1PT-x-Ru,
PM1PT-100 and Ru-bpy in films. The polymer thin films were
prepared by spin-coating DMF solution (6 mg/mL) onto
a
d
the temperature at 5% weight loss (T ) summarized in Table 1. The
indium-tin-oxide (ITO) coated glass substrates at a rotating speed
of 1200 RPM at room temperature, then drying the coated glass
substrates in the oven. Compared with PM1PT-100, PM1PT-100-Ru
showed a new broad peak centered at 528 nm with the full width
at half maximum (FWHM) of 163 nm. This new peak of PM1PT-
T
d
of PM1PT-x was in the range of 317–356 °C. With the content of
Table 1
Results of GPC, TGA and UV–vis measurements for all PM1PT-x.
1
00-Ru is similar to the absorption peak at 556 nm of the model
a
PDIa
b
k
abs (nm)c
PM1PT-x
M
w
T
d
(°C)
compound Ru-bpy, which was ascribed to the metal-to-ligand
charge transfer (MLCT) of Ru-complex linked to the polymer chain
PM1PT-25
PM1PT-50
PM1PT-75
PM1PT-100
6360
4460
3230
7780
1.94
1.57
1.50
1.98
356
340
331
317
283, 370
285, 363
286, 351
286, 338
[
22,29]. The MLCT absorption peak is due to the promotion of an
electron from the metal-centered d orbital to an unfilled ligand-
centered
complex moieties have been successfully incorporated into the
polymer chain. Therefore, the objective of enhancing the
photosensitivity of the polymeric materials into the visible region
⁄
p
orbital. This result also indicated that the ruthenium
a
Estimated by GPC using THF as eluent calibrated by polystyrene standard.
The temperature at 5% weight loss (T ) determined by TGA under nitrogen
d
atmosphere at a heating rate of 10 °C/min.
b
c
The UV–vis absorption in a 2 mg/mL THF solution.

Y. Jin et al. / Reactive & Functional Polymers 90 (2015) 7–14
13
Fig. 3. The TGA curves of PM1PT-x (a), PM1PT-x-Ru and Ru-bpy (b) under nitrogen atmosphere at a heating rate of 10 °C minꢀ1.
Table 2
Data of TGA, UV–vis and CV measurements for PM1PT-x-Ru (x = 25, 50, 75, 100) and
Ru-bpy.
ox
onset
red
onset
PM1PT-x-
Ru
T
(°C)
d
k
abs
E
HOMO
(eV)c
LUMO
(eV)c
E
g
(eV)
E
a
b
d
(nm)
PM1PT-
282
298, 350, 0.60
550
298, 349, 0.61
546
298, 347, 0.62
540
298, 346, 0.69
528
ꢀ0.79 ꢀ5.34
ꢀ0.75 ꢀ5.35
ꢀ0.74 ꢀ5.36
ꢀ0.73 ꢀ5.43
ꢀ0.74 ꢀ5.47
ꢀ0.43 ꢀ5.38
ꢀ3.95
ꢀ3.99
ꢀ4.00
ꢀ4.01
ꢀ4.00
ꢀ4.31
1.39
1.36
1.36
1.42
1.47
1.07
2
5-Ru
PM1PT-
0-Ru
PM1PT-
5-Ru
PM1PT-
268
241
220
317
170
5
7
1
00-Ru
PM1PT-
296, 351
0.73
1
00
Ru-bpy
297, 341, 0.64
55
5
Fig. 5. CV curves of PM1PT-100-Ru, Ru-bpy and PM1PT-100 dissolved in 0.1 M
ꢀ
1
a
b
c
4
DMF-TBABF with a scanning rate of 100 mV s .
Determined by TGA under nitrogen atmosphere at a heating rate of 10 °C/min.
The UV–vis absorption maxima in solid film.
ꢀ1
Tested in 0.1 M DMF-TBABF
4
solution at 100 mV s scan rate.
d
Calculated by E
g
= (ELUMO–EHOMO) eV.
3.6. Electrochemical properties
Fig. 5 shows the cyclic voltammetry (CV) curves of Ru-bpy,
PM1PT-100, and PM1PT-100-Ru, which were measured by CV
was realized through the introduction of ruthenium complexes. The
⁄
using SCE as reference electrode in 0.1 M DMF-TBABF solution
above characteristic d–
p
MLCT transitions of all PM1PT-x-Ru
4
ꢀ1
at 100 mV s scanning rate. The HOMO/LUMO energies were cal-
culated from the oxidation and reduction potentials according to
polymers appeared at approximately 540 nm with FWHM in the
range of 156–163 nm. The intensity of the MLCT bands increased
with the increase in ruthenium complex content in PM1PT-x-Ru.
In addition, the absorption maximum of the MLCT band shifted
to shorter wavelengths when the ruthenium content increased,
which was mainly attributed to the presence of intra- and
inter-chain charge transfer complexes (CTC) in the condensed film
state [42].
ox
red
an empirical formula, EHOMO = ꢀ(Eon + 4.74) (eV), ELUMO = ꢀ(Eon
+
4.74) (eV) [43], and summarized in Table 2. The quasi-reversible
oxidation waves of Ru-bpy complex could be assigned to the
Ru(II/III) couple [26], and the reversible reduction waves could be
assigned to the ligand-centered reduction of substituted
bipyridines. The HOMO/LUMO of Ru-bpy was evaluated to be
Fig. 4. UV–vis absorption spectra of PM1PT-x in THF solution (a) and PM1PT-x-Ru, PM1PT-100 and Ru-bpy in films (b).

1
4
Y. Jin et al. / Reactive & Functional Polymers 90 (2015) 7–14
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5.38 eV and ꢀ4.31 eV, respectively. As for polymers PM1PT-100
Am. Chem. Soc. 135 (2013) 8464–8467.
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and ꢀ5.43 eV, respectively. The band gaps of PM1PT-100 and
PM1PT-100-Ru were calculated to be 1.47 eV and 1.42 eV,
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[
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[
A series of conjugated polymers PM1PT-x with pendant bipyri-
8
dine groups were synthesized successfully via Suzuki coupling
polycondensation using carbazole and phenothiazine as the main
chain moieties. Through a one-pot post-functionalization reaction,
ruthenium complexes were introduced into the polymer through
a flexible spacer in high yields, which lead to a new simplified strat-
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Furthermore, after the incorporation of ruthenium complexes, the
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