Platinum(ii) polymetallayne-based phosphorescent polymers with enhanced triplet energy-transfer: Synthesis, photophysical, electrochemistry, and electrophosphorescent investigation

Article abstract of DOI:10.1039/c5ra03697f

Two series of new phosphorescent copolymers with bicarbazole-based platinum(ii) polymetallayne backbones have been successfully prepared through Sonogashira cross-coupling with different Ir^III ppy-type (ppy = 2-phenylpyridine anion) complexes as phosphorescent centers. The photophysical investigations not only indicate a highly efficient triplet energy-transfer process from the polymetallayne segments to the phosphorescent units in the polymer solution, but also figure out the structure-property relationship between the triplet energy-transfer process and the energy-levels of different excited states. In addition, the phosphorescent copolymers can produce yellow-emitting phosphorescent OLEDs (PHOLEDs) with high EL efficiencies and a current efficiency (η_L) of 11.49 cd A^-1, an external quantum efficiency (η_ext) of 4.38%, a power efficiency (η_P) of 3.78 lm W^-1, and red-emitting PHOLEDs with a η_L of 5.86 cd A^-1, η_ext of 10.1%, and a η_P of 2.29 lm W^-1, representing very decent electroluminescent performances achieved by the phosphorescent copolymers. Herein, this work not only furnishes very important clues for further polishing of this category novel phosphorescent polymer, but also provides a new approach to the design and synthesis of highly efficient phosphorescent copolymers.

Full text of DOI:10.1039/c5ra03697f

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DOI: 10.1039/C5RA03697F
Table of Content Page
Platinum(II) Polymetallayne-Based Phosphorescent Polymers with Enhanced Triplet
Energy-Transfer: Synthesis, Photophysical, Electrochemistry, and Electrophosphorescent
Investigation
Zuan Huang, Boao Liu, Jiang Zhao, Yue He, Xiaogang Yan, Xianbin Xu, Guijiang Zhou,*
Xiaolong Yang,* Zhaoxin Wu*
Promoting triplet energy-transfer in novel phosphorescent polymers with platinum(II)
–
1
of 11.49 cd A ,
polymetallayne backbones to achieve high EL performances with
η
L
ηext of
–
1
4
.38% and ηP of 3.78 lm W .

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Platinum(II) Polymetallayne-Based PhosphorescDO
e
I:
n
10.1039/C5RA03697F
t
Polymers with Enhanced Triplet Energy-Transfer: Synthesis,
Photophysical, Electrochemistry, and
Electrophosphorescent Investigation
Zuan Huang, Boao Liu, Jiang Zhao, Yue He, Xiaogang Yan, Xianbin Xu, Guijiang
Zhou,* Xiaolong Yang,* Zhaoxin Wu*
MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter,
State Key Laboratory for Mechanical Behavior of Materials,
Institute of Chemistry for New Energy Material,
Department of Chemistry, Faculty of Science,
Xi’an Jiaotong University, Xi’an 710049, P.R. China.
E-mail: zhougj@mail.xjtu.edu.cn.
Fax: +86-29-8266-3914
Prof. Z. Wu
Key Laboratory of Photonics Technology for Information,
School of Electronic and Information Engineering,
Xi'an Jiaotong University, Xi'an 710049, P.R. China.
E-mail: zhaoxinwu@mail.xjtu.edu.cn.

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Abstract:
DOI: 10.1039/C5RA03697F
Two series of new phosphorescent copolymers with bicarbazole-based platinum(II)
polymetallayne backbone have been successfully prepared through Sonogashira cross-coupling
III
with different Ir ppy-type (ppy=2-phenylpyridine anion) complexes as phosphorescent centers.
The photophysical investigations not only indicate highly efficient triplet energy-transfer
process from the polymetallayne segments to the phosphorescent units in the polymer solution,
but also figure out the structure-property relationship between the triplet energy-transfer process
and the energy-levels of different excited states. In addition, the phosphorescent copolymers can
furnish yellow-emitting phosphorescent OLEDs (PHOLEDs) with high EL efficiencies with
–
1
current efficiency ( ) of 11.49 cd A , external quantum efficiency ( ) of 4.38%, power
L
ext
–
1
–1
efficiency ( ) of 3.78 lm W , and red-emitting PHOLEDs with  of 5.86 cd A ,  of
P
L
ext
–1
1
0.1%,  of 2.29 lm W , representing very decent electroluminescent performances ever
P
achieved by the phosphorescent copolymers. This work herein not only furnishes very important
clues for further polishing this category novel phosphorescent polymer, but also provides a new
approach to design and synthesis of highly efficient phosphorescent copolymers.
1
. Introduction
Phosphorescent polymers can properly compromise the high electroluminescent (EL) efficiency
1
-3
and easy device fabrication. Hence, these luminescent polymers have received increasing
interest in the field of organic light-emitting devices/diodes (OLEDs), since they can effectively
enhance the EL efficiencies of solution-processed OLEDs compared with their fluorescent
4
,5
counterparts. As the most important component in these polymers, the phosphorescent blocks,
typically ppy-type iridium(III) complexes (ppy = 2-phenylpyridine anion), can either be
6
-10
11-16
imbedded into main chain
or attached to the backbones as side chains
of the obtained

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phosphorescent polymers. Playing the same role of the host materials in the ph
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OLEDs with small molecular triplet emitters, the organic segments in the phosphorescent
polymers can act as the host of the phosphorescent blocks. Thus, the emission layer (EML) in
PHOLEDs can be easily constructed by directly spin-coating a solution of the phosphorescent
polymers, which can greatly simplify the device fabrication. Similar to their fluorescent
counterparts, PHOLEDs also relates to the charge carrier injection/transporting in their EMLs.
Thus, it seems that the phosphorescent polymers with conjugated backbones are preferred to
promote the charge carrier injection/transporting in the EML of PHOLEDs. Another critical
issue should be addressed in PHOLEDs based on conjugated phosphorescent polymers is
blocking the undesired reverse energy-transfer from the emissive triplet states of the
phosphorescent units to the non-emissive triplet states of the conjugated backbones in the
5
phosphorescent polymers. In order to achieve high EL performance in PHOLEDs, the reverse
energy-transfer process should be restrained as far as possible. With the aim to fulfill this
purpose, increasing the triplet energy level of the backbones of phosphorescent polymers should
be a feasible way. Hence, the phosphorescent polymers with nonconjugated backbones have also
been prepared. Clearly, this type polymer backbone seems unfavorable for charge carrier
injection/transporting. In order to overcome the weakness associated with the nonconjugated
backbones of phosphorescent polymers, functional moieties, such as aromatic silane, have been
1
7
introduced to the polymer backbone to furnish high triplet energy level. Despite of all these
endeavors, only handful phosphorescent polymers with judicious molecular design can show
1
6,18,19
good performance.
small molecular triplet emitters involved in PHOLEDs made by vacuum deposition method.
So, novel molecular designs are really needed to further polish the EL performance of the
and most of them still show much lower EL efficiencies compared with
20

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phosphorescent polymers.
DOI: 10.1039/C5RA03697F
From what mentioned above, it might conclude that maintaining the optimized trade-offs
between high triplet energy level and the good charge carrier injection/transporting of the
backbones should represent effective strategy to enhance the EL capacity of the phosphorescent
polymers. For organic conjugated backbone, the twisted configuration should be required to
furnish high triplet energy level. Obviously, it should disfavor the charge carrier transporting by
the hopping mechanism. Maybe it is time to broke away from conventions and develop new
phosphorescent polymers based on totally different backbones. Recently, owing to their diverse
photophysical properties, platinum(II) polymetallaynes can find important applications in
2
1,22
23,24
optical power limiting
and photovoltaics,
etc. In addition, some bithiazole-based
2
5
platinum(II) polymetallaynes can serve as fluorescent emitters in OLEDs. Different from the
π-π conjugations in backbones of the traditional conjugated polymers, i.e. polymers with pure
5
organic or metal-free conjugated backbones, the d-π conjugation between platinum(II) ions and
2
6-28
the organic spacers,
i.e. aromatic alkynes shows relatively weaker conjugation extending
ability to furnish the backbones of the platinum(II) polymetallaynes with high triplet energy
2
9
level. Meanwhile, the conjugation of the backbones of platinum(II) polymetallaynes can be
maintained to benefit charge carrier injection/transporting. Hence, platinum(II) polymetallaynes
should show great potential to overcome the drawbacks associated with the traditional
30
conjugated phosphorescent polymers, which has been shown by our recent preliminary results.
The concerned novel phosphorescent polymers with platinum(II) polymetallayne backbone can
–
1 30
show high EL performance with current efficiency ( ) of 9.17 cd A . It is well accepted that
L
the energy-transfer from the polymer backbones to the phosphorescent units can play critical
role in determine the EL performances of the concerned phosphorescent polymers. Thus,

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optimizing the energy-transfer processes aforementioned in this novel kind of ph
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polymer should be of great importance in obtaining the structure-property relationship
information to provide valuable clues for the design and synthesis new high-performance
phosphorescent polymers. So, in this paper, two series of phosphorescent polymers with
bicarbazole-based platinum(II) polymetallayne backbones and ppy-type iridium(III)
phosphorescent centers have been developed (Chart 1). It has been found that the
energy-transfer from the polymetallayne backbones to the phosphorescent blocks could be
greatly affected by the triplet energy-level difference the between backbone and phosphorescent
center, which will furnish important information of the structure-property relationship of these
novel phosphorescent polymers. Furthermore, the concerned results also provide valuable clue
to optimize the EL performances of these phosphorescent polymers.
N
N
O
O
O
O
Ir
Ir
Ir
N
N
Phosphorescence
Pt Ir
Triplet Energy-transfer
Pt
Pt
S1p
Pt
ISC
Pt Ir
Pt
Pt
Pt
Pt
Pt
Pt
T1p
Pt
Triplet Energy-transfer
Ir
3MLCT
Fluorescence
N
Phosphorescence
Phosphorescence
So
N
Hole Injection/Transporting Ability
Chart 1 The schematic diagram for the chemical structure of the novel phosphorescent
polymers and the sketch of the energy-transfer process involved.
2
. Experimental Section
2
.1. General Information
The commercially available reagents were used directly as received unless otherwise stated. All

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reactions were preceded under inert atmosphere. The solvents were purified
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methods under dry nitrogen before use. The reactions were monitored by thin-layer
chromatography (TLC) with Merck pre-coated aluminum plates. Flash column chromatography
and preparative TLC were carried out using silica gel for small molecular compounds. All
Sonogashira copolymerization reactions were carried out with Schlenk techniques under
nitrogen atmosphere.
2
.2. Physical Characterization
1
13
H NMR and C NMR spectra were measured in CDCl with a Bruker AXS 400MHz
3
spectrometer with the chemical shifts quoted relative to tetramethylsiliane (TMS). Fast atom
bombardment (FAB) mass spectra were recorded on a Finnigan MAT SSQ710 system. UV-Vis
spectra were recorded with a Shimadzu UV-2250 spectrophotometer. The photoluminescent (PL)
properties of the copolymers were measured with an Edinburgh Instruments FLS920
spectrophotometer. The lifetimes for the excited states were measured by a single photon
counting spectrometer from Edinburgh Instruments FLS920 with a 360 nm picosecond LED
lamp as the excitation source, while those at 77 K were obtained by with excitation from a
xenon flash lamp. Differential scanning calorimetry (DSC) was performed with a NETZSCH
o
–1
DSC 200 PC unit under a nitrogen flow at a heating rate of 10 C min . Thermogravimetric
analysis (TGA) was conducted with a NETZSCH STA 409C instrument under nitrogen with a
o
–1
heating rate of 20 C min . The molecular weights of the copolymers were determined by
Waters 2695 GPC in THF. The weights were estimated by using a calibration curve of
polystyrene standards. Cyclic voltammetry (CV) measurement for the sample solution was
performed on Princeton Applied Research model 2273A potentiostat with a glassy carbon
working electrode, a platinum counter electrode, and a platinum-wire reference electrode at a

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scan rate of 100 mV s . The solvent was deoxygenated dichloromethane, and th
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/Cti
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g
electrolyte was 0.1M [nBu N][BF ]. Ferrocene (Fc) was added as an internal calibrant for the
4
4
+
measurement, and all potentials reported were quoted with reference to the Fc-Fc couple. The
polymer films on quartz substrate were obtained by spin-coating their chlorobenzene solution
(ca. 20 mg/mL) and their thickness was determined by Nanoview SE MF-1000 Ellipsometer.
The PL spectra and lifetimes at 77 K were obtained by dipping the degassed sample CH Cl
2
2
solution in thin quartz tube into liquid nitrogen Dewar and recorded the data after standing 3
minutes.
2
.3. Synthesis
The synthetic details of the key compounds L1 and L2, organic monomer MC, IrBr1, IrBr2
and the model polymer P-BC were presented in the Supporting Information (SI).
IrSi1
To the mixture of IrBr1 (0.76 g, 1.00 mmol), Pd(PPh ) Cl (20 mg, 0.071 mmol), CuI (13 mg,
3
2
2
0
.071 mmol) and Et N/CH Cl (30 mL v:v = 1:1), trimethylsilylacetylene (0.5 mL) was added at
3 2 2
room temperature. After stirring one hour at room temperature, the reaction mixture was
o
allowed to proceed at 70 C for 30 h. After cooling to room temperature, the reaction mixture
was concentrated under vacuum to give the crude product, which was further purified by silica
gel column chromatography with petroleum ether/CH Cl (1:1, v/v) as eluent to get the pure
2
2
1
product as orange solid (0.60 g, 75.8%). H NMR 8.56 (s, 2H), 7.76 (s, 4H), 7.52 (d, J = 7.6 Hz,
2
H), 6.79 (t, J = 7.2 Hz, 2H), 6.70 (t, J = 7.2 Hz, 2H), 6.25 (d, J = 7.6 Hz, 2H), 5.26 (s, 1H),1.81
1
3
(
s, 6H), 0.27 (s, 9H).; C NMR (100 MHz, CDCl , δ, ppm): 184.90, 168.12, 151.10, 148.55,
3
1
1
43.99, 133.12, 129.69, 124.52, 120.99, 117.67, 100.98, 100.82, 98.88, 31.61, 28.81, 22.68,
+
4.16, -0.19; FAB-MS (m/z): 792 [M] . Elemental analysis calcd (%) for C H IrN O Si : C
3
7
39
2
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5
6.10, H 4.96, N 3.54; found: C 56.39, H 4.75, N 3.38.
DOI: 10.1039/C5RA03697F
IrM1
The solution of tetrabutylammonium fluoride trihydrate (80 mg, 0.25 mmol) in CH Cl (3 mL)
2
2
was added to the mixture of IrSi1 (0.10 g, 0.13 mmol) and CH Cl (15 mL). After stirring 30
2
2
min at room temperature, the reaction mixture was washed with water (3 × 20 mL). The organic
phase was dried over MgSO and passed through a short silica gel pad quickly. After
4
concentration, the residue was precipitated in hexane. The product was obtained as orange-red
1
solid (72 mg, 85.9%). H NMR (400 MHz, CDCl , δ, ppm): 8.59 (s, 2H), 7.79 (s, 4H), 7.52 (d, J
3
=
7.8 Hz, 2H), 6.83 (t, J = 7.8 Hz, 2H), 6.72 (t, J = 7.2 Hz, 2H), 6.26 (d, J = 7.6 Hz, 2H), 5.26 (s,
1
3
1
1
2
3
H), 3.27 (s, 2H), 1.82 (s, 6H); C NMR (100 MHz, CDCl , δ, ppm):184.95, 168.62, 151.15,
3
48.53, 143.84, 140.04, 133.12, 129.77, 124,61, 121,03, 117.73, 116.42, 100.80, 81.08, 77.20,
+
8.76; FAB-MS (m/z): 648 [M] . Elemental analysis calcd (%) for C H IrN O : C 57.48, H
3
1
23
2
2
.58, N 4.32; found: C 57.27, H 3.49, N 4.18.
P-YC-1
Under N atmosphere, MC (95.0 mg, 0.193 mmol), IrM1 (5.0 mg, 0.007 mmol) and
2
trans-[PtCl (PBu ) ] (135.0 mg, 0.20 mmol) were mixed in a solvent mixture of degassed
2
3 2
Et N/CH Cl (10 mL/20 mL) under stirring. After the monomers were completed dissolved, CuI
3
2
2
(10 mg) was added. The mixture was stirred for 18 h at room temperature. The reaction mixture
was then stirred for 5 h after adding phenylacetylene (5.0 mg, 0.05 mmol). Then the reaction
mixture was concentrated and precipitated in methanol. The precipitation was collected and
dissolved in CH Cl . The copolymer solution was filtered by 0.45 μm PTFE syringe filter. After
2
2
concentration, the copolymer was purified by precipitation twice in methanol and washed with
methanol in a Soxhlet apparatus for 72 h, and dried under vacuum. It was obtained as light

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orange solid (Yield: 80%). H NMR (400 MHz, CDCl , δ, ppm): 8.39 (s), 8.27 (s),
DO
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(
.1
s
0
)
3
,
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8
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.
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3
(s), 8.09 (s), 8.07 (s), 7.82–7.80 (m), 7.65–7.62 (m), 7.46–7.42 (m), 4.30 (br), 2.26 (br), 1.88
3
1
(
br), 1.75–1.72 (br), 1.53–1.40 (m), 1.00–0.93 (m); P NMR (161.9 MHz, CDCl , δ, ppm): 3.32,
3
2
1
.82; Gel permeation chromatography (GPC): number-average molecular weight (M ) = 3.8 ×
n
4
–1
0 g mol , polydispersity index (PDI) = 1.6 (against polystyrene standards).
P-YC-2
It was prepared from MC (90.0 mg, 0.183 mmol), IrM1 (10.0 mg, 0.015 mmol),
trans-[PtCl (PBu ) ] (133.0 mg, 0.198 mmol) and CuI (10 mg), following the same procedure as
2
3 2
1
for P-YC-1. The copolymer was obtained as orange solid (Yield: 83%). H NMR (400 MHz,
CDCl , δ, ppm): 8.40 (s), 8.28 (s), 8.22 (s), 8.15 (s), 8.11 (s), 8.09 (s), 7.83–7.77 (m), 7.64 (br),
3
3
1
7
.48–7.43 (m), 4.30 (br), 2.27 (br), 1.88 (br), 1.75–1.72 (br), 1.53–1.40 (m), 1.00–0.93 (m); P
4
–1
NMR (161.9 MHz, CDCl , δ, ppm): 3.24, 2.81; GPC: M = 3.6 × 10 g mol , PDI = 1.6 (against
3
n
polystyrene standards).
P-YC-3
It was prepared from MC (85.0 mg, 0.172 mmol), IrM1 (15.0 mg, 0.023 mmol),
trans-[PtCl (PBu ) ] (131.0 mg, 0.195 mmol) and CuI (10 mg), following the same procedure as
2
3 2
1
for P-YC-1. The copolymer was obtained as orange solid (Yield: 85%). H NMR (400 MHz,
1
CDCl , δ, ppm): H NMR (400 MHz, CDCl , δ, ppm): 8.39 (s), 8.28 (s), 8.22 (s), 8.15 (s), 8.10
3
3
(s), 8.08 (s), 7.83–7.77 (m), 7.64 (br), 7.47–7.43 (m), 4.30 (br), 2.27 (br), 1.88 (br), 1.75–1.72
3
1
(
br), 1.53–1.40 (m), 1.00–0.93 (m); P NMR (161.9 MHz, CDCl , δ, ppm): 3.23, 2.84; GPC: M
3
n
4
–1
=
3.5 × 10 g mol , PDI = 1.7 (against polystyrene standards).
P-YC-4
It was prepared from MC (80.0 mg, 0.162 mmol), IrM1 (20.0 mg, 0.027 mmol),

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trans-[PtCl (PBu ) ] (127.0 mg, 0.189 mmol) and CuI (10 mg), following the same
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for P-YC-1. The copolymer was obtained as orange solid (Yield: 82%). H NMR (400 MHz,
CDCl , δ, ppm): 8.38 (s), 8.26 (s), 8.20 (s), 8.13 (s), 8.08 (s), 7.79–7.77 (m), 7.64 (br), 7.47–7.43
3
3
1
(
m), 4.29 (br), 2.24 (br), 1.87 (br), 1.75–1.72 (br), 1.53–1.40 (m), 0.98–0.92 (m); P NMR
4
–1
(
161.9 MHz, CDCl , δ, ppm): 3.22, 2.83; GPC: M = 3.3 × 10 g mol , PDI = 1.8 (against
3
n
polystyrene standards).
IrSi2
To the mixture of IrBr2 (0.6 g, 0.70 mmol), Pd(PPh ) Cl (20 mg, 0.029 mmol) and CuI (5 mg,
3
2
2
0
.029 mmol) and Et N/CH Cl (20 mL v:v = 1:1), trimethylsilylacetylene (0.5 mL) was added at
3 2 2
room temperature. After stirring one hour at room temperature, the reaction mixture was
o
allowed to proceed at 70 C for 30 h. After cooling to room temperature, the reaction mixture
was concentrated under vacuum to give the crude product, which was further purified by silica
gel column chromatography with petroleum ether/CH Cl (1:1, v/v) as eluent to get the pure
2
2
1
product as red solid (0.45 g, 72.1%). H NMR (400 MHz, CDCl , δ, ppm): 8.60 (s, 2H), 7.47 (t,
3
J = 7.2 Hz, 4H), 7.83 (dd, J = 8.4, 2.0 Hz, 2H), 7.62 (d, J = 7.2 Hz, 2H), 7.46 (t, J = 7.0 Hz, 2H),
7
.26 (t, J = 7.4 Hz, 2H), 7.04 (d, J = 8.4 Hz, 2H), 6.25 (d, J = 8.4 Hz, 2H), 5.31 (s,1H), 1.83
13
(
s,6H), 0.27 (s, 18H).; C NMR (100 MHz, CDCl , δ, ppm):185.14, 168.62, 157.14, 151.49,
3
1
1
39.64, 137.61, 132.02, 131.80, 131.17, 129.81, 129.25, 126.60, 122.49, 121.40, 121.15, 116.20,
+
01.02, 100.83, 98.88, 28.69, -0.20; FAB-MS (m/z): 892 [M] . Elemental analysis calcd (%) for
C H IrN O Si : C 60.58, H 4.86, N 3.14; found: C 60.39, H 4.65, N 3.08.
45
43
2
2
2
IrM2
The solution of tetrabutylammonium fluoride trihydrate (75 mg, 0.24 mmol) in CH Cl (3 mL)
2
2
was added to the mixture of IrSi2 (0.10 g, 0.11 mmol) and CH Cl (15 mL). After stirring 30
2
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min at room temperature, the reaction mixture was washed with water (3 × 20 mL)
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phase was dried over MgSO and passed through a short silica gel pad quickly. After
4
concentration, the residue was precipitated in hexane. The product was obtained a red solid (69
1
mg, 82.3%). H NMR (400 MHz, CDCl , δ, ppm): 8.63 (s, 2H), 8.49 (dd, J = 8.8, 4.0 Hz, 4H),
3
7
2
.87 (d, J = 8.8 Hz, 2H), 7.62 (d, J = 8.0 Hz, 2H), 7.46 (t, J = 7.6 Hz, 2H), 7.26 (t, J = 7.4 Hz,
H), 7.05 (d, J = 8.4 Hz, 2H), 6.28 (d, J = 8.4 Hz, 2H), 5.30 (s,1H), 3.28 (s,2H), 1.83 (s, 6H);
1
3
C NMR (100 MHz, CDCl , δ, ppm): 185.19, 169.22, 157.21, 151.54, 140.05, 132.01, 131.18,
3
1
29.88, 129.44, 126.69, 122.54, 121.51, 121.11,109.99, 100.82, 81.08, 77.23, 28.74; FAB-MS
+
(
m/z): 748 [M] . Elemental analysis calcd (%) for C H IrN O : C 62.63, H 3.64, N 3.75; found:
39
27
2
2
C 62.34, H 3.35, N 3.28.
P-RC-1
It was prepared from MC (95.0 mg, 0.193 mmol), IrM2 (5.0 mg, 0.007 mmol),
trans-[PtCl (PBu ) ] (134.0 mg, 0.200 mmol) and CuI (10 mg), following the same procedure as
2
3 2
1
for P-YC-1. The copolymer was obtained as orange solid (Yield: 83%). H NMR (400 MHz,
CDCl , δ, ppm): 8.48 (s), 8.39 (s), 8.32 (s), 8.27 (s), 8.21 (s), 8.17 (s), 8.14 (s), 8.11-8.07 (br),
3
7
.82–7.76 (m), 7.64 (br), 7.51–7.42 (m), 4.30 (br), 2.27 (br), 1.88 (br), 1.75–1.72 (br), 1.53–1.40
31
4
(
m), 1.00–0.93 (m); P NMR (161.9 MHz, CDCl , δ, ppm): 3.23, 2.83; GPC: M = 3.5 × 10 g
3
n
–1
mol , PDI = 1.5 (against polystyrene standards).
P-RC-2
It was prepared from MC (90.0 mg, 0.183 mmol), IrM2 (10.0 mg, 0.013 mmol),
trans-[PtCl (PBu ) ] (131.0 mg, 0.196 mmol) and CuI (10 mg), following the same procedure as
2
3 2
1
for P-YC-1. The copolymer was obtained as orange solid (Yield: 83%). H NMR (400 MHz,
CDCl , δ, ppm): 8.48 (s), 8.39 (s), 8.32 (s), 8.28 (s), 8.21 (s), 8.17 (s), 8.14 (s), 8.11-8.07 (br),
3

Page 13 of 37
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7
(
.82–7.76 (m), 7.65 (br), 7.51–7.42 (m), 4.30 (br), 2.27 (br), 1.88 (br), 1.75–1.72 (b
D
r
O
),I:
1
10
.
.
5
10
3
3
–
9/
1
C
.
5RA03697F
4
0
31
4
m), 1.00–0.93 (m); P NMR (161.9 MHz, CDCl , δ, ppm): 3.24, 2.81; GPC: M = 3.3 × 10 g
3
n
–1
mol , PDI = 1.6 (against polystyrene standards).
P-RC-3
It was prepared from MC (85.0 mg, 0.172 mmol), IrM2 (15.0 mg, 0.020 mmol),
trans-[PtCl (PBu ) ] (130.0 mg, 0.192 mmol) and CuI (10 mg), following the same procedure as
2
3 2
1
for P-YC-1. The copolymer was obtained as orange solid (Yield: 81%). H NMR (400 MHz,
CDCl , δ, ppm): 8.48 (s), 8.39 (s), 8.32 (s), 8.27 (s), 8.21 (s), 8.17 (s), 8.14 (s), 8.11-8.07 (br),
3
7
.82–7.76 (m), 7.64 (br), 7.52–7.42 (m), 4.30 (br), 2.27 (br), 1.88 (br), 1.75–1.72 (br), 1.53–1.40
31
4
(
m), 1.00–0.93 (m); P NMR (161.9 MHz, CDCl , δ, ppm): 3.23, 2.84; GPC: M = 3.4 × 10 g
3
n
–1
mol , PDI = 1.7 (against polystyrene standards).
P-RC-4
It was prepared from MC (80.0 mg, 0.162 mmol), IrM2 (20.0 mg, 0.027 mmol),
trans-[PtCl (PBu ) ] (127.0 mg, 0.189 mmol) and CuI (10 mg), following the same procedure as
2
3 2
1
for P-YC-1. The copolymer was obtained as orange solid (Yield: 82%). H NMR (400 MHz,
CDCl , δ, ppm): 8.48 (s), 8.39 (s), 8.32 (s), 8.28 (s), 8.22 (s), 8.14 (s), 8.12-8.07 (br), 7.83–7.76
3
(m), 7.64 (br), 7.58–7.42 (m), 4.30 (br), 2.27 (br), 1.88 (br), 1.75–1.72 (br), 1.53–1.40 (m),
3
1
4
–1
1
.00–0.93 (m); P NMR (161.9 MHz, CDCl , δ, ppm): 3.22, 2.82; GPC: M = 3.2 × 10 g mol ,
3 n
PDI = 1.7 (against polystyrene standards).
2
.4. OLED Fabrication and Measurements
The methods of OLED Fabrication and Measurements are similar to those of our previous
3
0
study. The pre-cleaned ITO glass substrates were treated with ozone for 20 min. Then, the
PEDOT:PSS was deposited on the surface of ITO glass by spin-coating method to form a 45

RSC Advances
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nm-thick hole-injection layer. After being cured at 120 °C for 30 min in the air,
D
t
O
h
I:
e
10
e
.10
m
39
i
/
t
C
ti
5
n
RA03697F
g
layer (35 nm) was obtained by spin-coating a chlorobenzene solution of each phosphorescent
polymer. The ITO glass was dried in a vacuum oven at 50 C for 20 min and it was transferred
to the deposition system for organic and metal deposition. TPBi (45 nm), LiF (1 nm) and Al
–
6
cathode (100 nm) were successively evaporated at a base pressure less than 10 Torr. The EL
spectra and CIE coordinates were measured with a PR650 spectra colorimeter. The L–VJ
curves of the devices were recorded by a Keithley 2400/2000 source meter and the luminance
was measured using a PR650 SpectraScan spectrometer. All the experiments and measurements
were carried out under ambient conditions.
3
. Results and Discussion
3
.1. Synthesis and Characterization
As the most critical component, the synthetic details for the phosphorescent monomers IrM1
and IrM2 are shown in Figure 1. The organic ligands L1 and L2 have been prepared by Suzuki
cross-coupling between 5-bromo-2-iodopyridine and the corresponding arylboronic acid under
o
lower temperature (ca. 90 C) in high yield. The precursor complexes IrBr1 and IrBr2 were
prepared according to the well-established two-step strategy by the cyclometalation of
IrCl ∙nH O with the corresponding organic ligands, followed by coordination of the
3
2
acetylacetone (acac) anion in the presence of Na CO . After undergoing Sonogashira coupling
2
3
reaction, IrBr1 and IrBr2 were converted respectively to IrSi1 and IrSi2, which went through
the cleaving of trimethylsilane groups to obtain IrM1 and IrM2 in high purity as colored solid
(Figure 1). Serving as the aromatic spacers, the organic monomer MC was prepared through
Sonogashira coupling reaction between BCBr and trimethylsilylacetylene, followed by the

Page 15 of 37
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trimethylsilane cleaving of BCSi with [nBu N]F (Scheme S1 in the Supporting Info
D
r
O
m
I:
a
10
t
.
i
1
o
03
n
9
,
/C
S
5
I
RA03697F
)
.
4
Due to the excellent hole injection/transporting (HI/HT) features associated with carbazole unit,
the bicarbazole moiety has been employed in MC with the aim to improve the EL performance
of the final phosphorescent polymers.
Br
N
Br
O
B(OH)2
Ir
N
O
Br
I
N
Br
N
.
L1
i) IrCl3 nH O
2
Trimethylsilylacetylene
Pd(PPh ) Cl , CuI, Et N
IrBr1
ii) Acetylacetone
Pd(PPh3)4
Br
3 2
2
3
B(OH)2
2
M Na CO3
Na CO3
2
2
Br
N
N
O
O
Ir
L2
N
Br
IrBr2
Si
N
N
O
O
O
Ir
Ir
O
N
N
Si
[
nBu N]F
4
IrSi1
IrM1
Si
N
N
O
O
O
O
Ir
Ir
N
N
Si
IrSi2
IrM2
Figure 1. The synthetic pathways for the phosphorescent monomers.
After obtaining all the key monomers, the designed phosphorescent copolymers can be easily

RSC Advances
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prepared by the Sonogashira cross-coupling procedure among the phosphoresce
D
n
O
t
I: 1
m
0.1
o
0
n
39
o
/C
m
5RA03697F
e
r
IrM1 or IrM2, organic monomer MC and trans-[PtCl (PBu ) ] (Figure 2). The mount of the
2
3 2
yellow-emitting phosphorescent monomer IrM1 was set to maintain its weight percentage ca.
.1, 4.3, 6.5, and 8.7-wt% in the final phosphorescent polymers, corresponding to the different
2
feed ratios of MC and IrM1 as follows: m : n = 193 : 7 for P-YC-1, m : n = 183 : 15 for
P-YC-2, m : n = 172 : 23 for P-YC-3, and m : n = 162 : 27 for P-YC-4, respectively (Figure 2).
Similarly, he content of the red-emitting phosphorescent monomer IrM2 was set to weight
percentage ca. 2.1, 4.3, 6.5, and 8.8-wt% in the final phosphorescent copolymers. Based on the
feed ratios bewteen MC and IrM2, the obtained copolymers are named P-RC-1 (m : n = 193 :
5
), P-RC-2 (m : n = 183 : 13), P-RC-3 (m : n = 172 : 20), and P-RC-4 (m : n = 162 : 27),
respectively (Figure 2).

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DOI: 10.1039/C5RA03697F
N
O
N
P
P
Pt
Ir
O
Pt
P
N
P
N
P-YC-1: m : n =193 : 7
P-YC-2: m : n =183 : 15
P-YC-3: m : n =172 : 23
P-YC-4: m : n =162 : 31
m
n
CuI, Et N
3
N
N
N
P
O
O
O
Ir
O
Cl Pt Cl
P
Ir
N
N
N
MC
trans-[PtCl (PBu ) ]
2 3 2
IrM1
IrM2
CuI, Et N
3
N
O
N
P
Pt
P
Pt
O
Ir
P
N
P
N
P-RC-1: m : n =193 : 5
P-RC-2: m : n =183 : 13
P-RC-3: m : n =172 : 20
P-RC-4: m : n =162 : 27
m
n
Figure 2. The synthetic protocol for the phosphorescent copolymers.
The platinum(II) polymetallayne P-BC has also been prepared through Sonogashira
cross-coupling between MC and trans-[PtCl (PBu ) ] (Scheme S1) as model polymer. In order
2
3 2
to investigate the photophysical and electrochemical properties of these phosphorescent
copolymers, P-BC can properly represent the photophysical and electrochemical behaviors of
III
the backbones in these phosphorescent polymers due to the low content of the Ir
phosphorescent units.

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3
.2. Thermal characters, photophysical properties and electrochemistry
DOI: 10.1039/C5RA03697F
The thermal properties of these platinum(II) polymetallayne-based phosphorescent copolymers
have been investigated by thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) under nitrogen atmosphere. The TGA results show very good thermal
stability of these phosphorescent copolymers with high 5% weight-reduction temperature (ΔT )
5
%
ranging from ca. 310 °C to 330 °C (Table 1). Furthermore, these phosphorescent copolymers
show good ability in maintaining morphology stability due to their high glass-transition
temperatures (T ) over 150 °C (Table 1), which can be ascribed to their rigid polymetallayne
g
III
backbone with highly twisted configuration afforded by both bicarbazole and Ir
phosphorescent units. Thus, the good thermal properties will benefit their application in the field
of OLEDs. It has been taken for granted that carbon-carbon triple bonds exhibit poor thermal
stability disfavoring the application of the concerned compounds in the field of EL. However,
recent results have shown that the emitters with carbon-carbon triple bonds can still furnish very
3
1
good EL performances in OLEDs. Hence, the problem associated with the triple-bond
containing EL materials should be case by case. In this case, the good thermal properties should
guarantee the proper application of these phosphorescent copolymers as emitters in PHOLEDs.
Table 1 Photophysical and thermal data for the phosphorescent copolymers.
a
b
Polymers
Absorption λabs (nm)
Emission λem (nm)
ΔT5%/Tg
o
2
98K
Solution at 298 K / film at 298 K / low temperature at 77 K
( C)
P-YC-1
P-YC-2
P-YC-3
P-YC-4
P-RC-1
P-RC-2
P-RC-3
P-RC-4
261, 294, 325, 342, 440
410(0.22 ns), 555(1.0 μs), 598 / 556, 597 / 506, 549(13.0 μs), 597
410(0.21 ns), 555(0.9 μs), 597 / 556, 597 / 506, 550(13.7 μs), 597
412(0.18 ns), 555(0.8 μs), 597 / 556, 597 / 506, 550(12.0 μs), 597
412(0.19 ns), 555(0.8 μs), 598 / 558, 597 / 506, 551(11.3 μs), 507
425(0.22 ns), 632(0.8 μs), 688 / 630, 683 / 458, 539, 626(21.4 μs), 685
426(0.21 ns), 632(0.9 μs), 688 / 630, 683 / 457, 539, 628(20.1 μs), 686
429(0.18 ns), 632(0.7 μs), 688 / 633, 687 / 456, 540, 627(19.9 μs), 685
429(0.19 ns), 632(0.7 μs), 688 / 635, 685 / 456, 540, 629(19.0 μs), 687
325/150
334/155
341/157
348/159
312/155
311/153
313/155
320/160
260, 295, 324, 343, 440, 478
262, 294, 325, 343, 441, 479
260, 294, 323, 345, 440, 480
260, 294, 324, 343, 505
260, 294, 324, 343, 478, 506
261, 295, 324, 342, 478, 506
261, 294, 324, 343, 478, 506

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P-BC
257, 293, 323, 345
420(0.22 ns) / 424 / 456(29.6 μs), 481, 504
View Article Online
330/145
a
b
DOI: 10.1039/C5RA03697F
Measured in CH Cl at a concentration of 0.02 mg/mL. Measured in CH Cl at a concentration of 0.02 mg/mL. The lifetimes in the
2
2
2
2
parentheses are provided behind the corresponding emission band. The excitation wavelength for the measure was set at 360 nm.
3
2
2
1
1
0
0
.0
.5
.0
.5
.0
.5
.0
3.0
2.5
2.0
1.5
1.0
0.5
0.0
(a)
(b)
P-YC-1
P-YC-2
P-YC-3
P-YC-4
P-BC
P-RC-1
P-RC-2
P-RC-3
P-RC-4
P-BC
2
50
300
350
400
450
500
550
600
650
250
300
350
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
1
1
500
1
1
500
200
900
600
300
0
(
c)
(
d)
P-YC-1
P-YC-2
P-YC-3
P-YC-4
P-BC
P-RC-1
P-RC-2
P-RC-3
P-RC-4
P-BC
200
9
6
3
00
00
00
0
4
00
500
600
700
400
500
600
700
Wavelength (nm)
Wavelength (nm)
Figure 3. The absorption and photoluminescent spectra for the CH Cl solutions of the
2
2
phosphorescent polymers at 298 K.
In their UV-Vis absorption spectra (Figure 3a, 3b and Table 1), the phosphorescent
copolymers possess two kinds of absorption bands. The strong absorption bands located before
ca. 370 nm can be safely assigned to the bicarbazole-based platinum(II) polymetallayne
backbones due to their great resemblance to those of the model polymer P-BC. These strong
absorption bands should be induced by the metal disturbed π–π* transitions from the bicarbazole
units. Clearly, the content increasing of phosphorescent units will lower the amount of the
bicarbazole blocks in the obtained phosphorescent copolymers. As a result, the strong

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absorption bands of these phosphorescent copolymers are weakened (Figure 3a an
D
d
O
F
I: 1
i
0
g
.
u
10
r
3
e
9/C
3
5
b
RA03697F
)
.
However, the much weaker absorption bands appear in long wavelength region with increasing
the content of phosphorescent units (ca. 440 nm for P-YC-1 –P-YC-4 and ca. 506 nm for
P-RC-1 –P-RC-4) (Figure 3a, 3b and Table 1). The model polymer P-BC exhibits no weak
absorption bands at long wavelength. Clearly, these inconspicuous absorption bands with very
low intensity should be assigned to the metal-to-ligand charge transfer states for both singlet
1
3
III
(
MLCT) and triplet ( MLCT) from the Ir phosphorescent units (Figure 3a, 3b and Table 1).
III
Due to the low content of the Ir phosphorescent units in the copolymers, the π–π* transition
absorption from their organic ligands should give inessential contribution to the strong
absorption bands of the copolymers.
The photoluminescent (PL) spectra for the two series of phosphorescent copolymers are
recorded in CH Cl solution with the excitation wavelength at 360 nm (Figure 3c, 3d and Table
2
2
1
). For the copolymers P-YC-1 –P-YC-4, the predominant yellow phosphorescent emission
band at ca. 555 nm can be observed (Figure 3c and Table 1), while the copolymers P-RC-1
–
P-RC-4 furnish red emission band at ca. 632 nm. All these emission bands should be induced
III
by the Ir phosphorescent centers in the polymer backbone due to their microsecond lifetime
(Table 1). The intensity of these phosphorescent bands is enhanced with the increasing of the
III
content of the Ir phosphorescent units. Apart from the phosphorescent emission bands located
in long wavelength region, these copolymers also show high-energy emission band (Figure 3c,
3
d and Table 1). According to their nanosecond lifetime (ca. 0.2 ns) together with the PL
spectrum of the model polymer P-BC (Table 1 and Figure 3b), these high-energy emission
bands should be induced by the singlet states of the bicarbazole-based polymetallayne segments
in the copolymers. It is worth to note that these novel phosphorescent copolymers can exhibit

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strong phosphorescent emission even in the solution (Figure 3c, 3d). Differently, thDO
e
I:
t
1
r
0
a
.1
d
0
i
3
t
9
i
/
o
C
n
5RA03697F
a
l
conjugated phosphorescent polymers typically give dominated high-energy emissions from the
singlet states of the backbones, while very weak or even no phosphorescent signal can be
detected in the solution. Clearly, there should be much more efficient energy-transfer process
involved in these phosphorescent polymers, which should be incurred by the polymetallayne
backbones. Obviously, if there is only energy-transfer process from the singlet states of the
III
polymetallayne backbones to the Ir phosphorescent units, these copolymers should show
similar PL behavior in the solution to that of the traditional conjugated phosphorescent polymers.
Hence, the most likely efficient energy-transfer process involved should come from the triplet
states of the polymetallayne backbones, representing their most significant difference from the
organic conjugated backbones. If the expected efficient energy-transfer process from the triplet
III
states of the polymetallayne backbones to the Ir phosphorescent units do happen, the
phosphorescent signal associated with the bicarbazole-based polymetallayne backbones should
III
be effectively quenched. In addition, the lifetime of the phosphorescent band from the Ir
phosphorescent units in these copolymers should be longer than that of the corresponding free
phosphorescent monomers IrM1 and IrM2. In order to confirm this issue, the low temperature
PL spectra at 77 K for both phosphorescent copolymers and model polymer P-BC (Figure 4)
III
have been obtained together with the excited-state lifetimes. Even with low content of the Ir
phosphorescent units (< 9 wt%), the phosphorescent signal at ca. 460 nm from the
polymetallayne backbones can be effectively quenched with respect to that of the model
polymer P-BC. Furthermore, the phosphorescent lifetimes (τ ) of the phosphorescent
p
copolymers are also compared with those of the phosphorescent monomers. At 298 K in
degassed CH Cl , the τ corresponding the phosphorescent band at ca. 555 nm for P-YC-1 –
2
2
p

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P-YC-4 is about 1.0 μs, which is much longer than that of the corresponding ph
monomer IrM1 (0.25 μs). At low temperature 77K in CH Cl glass, P-YC-1 – P-YC-4 show τ
p
D
o
O
s
I
p
: 1
h
0
o
.10
r
3
9
s
/
c
C
e
5RA03697F
n
t
2
2
III
ca. 12 μs for the phosphorescent band from the Ir phosphorescent units, much longer than that
of the phosphorescent monomer IrM1 (3.1 μs) as well. Furthermore, the low temperature τ for
p
P-YC-1 – P-YC-4 is quite close to that of model polymer P-BC. The similar results are
obtained for the copolymers P-RC-1 – P-RC-4: τ ca. 1.0 μs for P-RC-1 – P-RC-4 vs. τ ca. 0.3
p
p
μs for IrM2 at 298 K; τ ca. 20 μs for P-RC-1 – P-RC-4 vs. τ ca. 2.7 μs for IrM2 at 77 K. The
p
p
lifetime data together with the PL spectra at 77 K clearly indicate the energy-transfer process
III
from the triplet states of the polymetallayne backbones to the Ir phosphorescent centers in
these novel phosphorescent polymers. Obviously, this new efficient energy-transfer process
should be absent in the traditional conjugated phosphorescent polymer solutions under
photo-excitation, since the pure organic conjugated backbones prefer to generate singlet excited
states rather than the triplet ones in photo-excitation process.
2
2
1
1
500
000
500
000
2
2
1
1
500
000
500
000
(a)
P-YC-1
P-YC-2
P-YC-3
P-YC-4
P-BC
(b)
P-RC-1
P-RC-2
P-RC-3
P-RC-4
P-BC
5
00
0
5
00
0
4
50
500
550
600
650
700
450
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
Figure 4. The photoluminescent (PL) spectra at 77 K for the phosphorescent copolymers and
their model polymer P-BC.
According to the results aforementioned together with the UV-vis absorption and PL spectra
in Figure 5, the energy-transfer processes involved in these phosphorescent copolymers can be

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figured out. Under the excitation of 360 nm light, the polymetallayne backb
D
o
O
n
I:
e
10
s
.10
o
39
f
/C
t
5
h
RA03697F
e
p
copolymers will generate the first singlet states (S ) based on the UV-vis absorption spectrum
1
of the model polymer P-BC (Figure 5). Then, there should be cascade energy-transfer process
p
1
Y
1
R
from S to MLCT (singlet states of MLCT in IrM1) (Figure 6a) and MLCT (singlet states
1
of MLCT in IrM2) (Figure 6b), which are converted via inter-system crossing (ISC) into
3
Y
3
R
emissive MLCT (triplet states of MLCT in IrM1) (Figure 6a) and MLCT (triplet states of
MLCT in IrM2) to induce yellow phosphorescence signal in P-YC-1 – P-YC-4 and red
phosphorescence signal in P-RC-1 – P-RC-4, respectively (Figure 3c and Figure 3d). This
energy-transfer pathway is quite similar to that in conventional phosphorescent polymers with
pure organic conjugated backbones. Differently, the platinum(II) ions along the polymetallayne
p
p
backbones of theses copolymers can effectively induce triplet states (T ) from S through ISC
1
1
process, which have been confirmed the strong phosphorescent signal in the PL spectrum of the
model polymer P-BC at 77 K (Figure 5). Owing to the overlap between the MLCT absorption
p
p
bands of IrM1/IrM2 and emission bands from T , the energy-transfer from T to the emissive
1
1
3
Y 3
R
MLCT / MLCT should be very efficient and hence induce strong yellow phosphorescent
emission in P-YC-1 – P-YC-4 (Figure 6a) and intense red phosphorescent signal in P-RC-1 –
p
P-RC-4 (Figure 6b). Thus, it should be due to the efficient energy-transfer from the T to the
1
3
MLCT of the phosphorescent centers to induce the strong phosphorescent emission of these
copolymers in solution.
III
Additionally, the organic ligands in the Ir phosphorescent units in these copolymers can also
be excited by the 360 nm light according to the absorption spectra of IrM1 and IrM2 (Figure 5).
Y
R
There should be energy-transfer process from the singlet sates S / S of the ligands in the
1
1
1
Y 1
R
yellow/red phosphorescent centers to MLCT / MLCT , which can be converted into emissive

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3
Y 3
R
View Article Online
MLCT / MLCT via ISC to induce yellow/red phosphorescence in P-YC-1DO
–
I: 10
P
.1
-
0
Y
39
C
/C5
-
RA03697F
4
/
P-RC-1 – P-RC-4 as well (Figure 6a and Figure 6b). However, this energy-transfer procedure
should be inessential compared with the two pathways aforementioned due to the following
III
reasons. Owing to the low content of the phosphorescent Ir blocks, their ligands will absorb
too small amount of energy form the excitation light to furnish strong phosphorescent signal.
p
Y
R
Furthermore, possessing higher energy-level than S (Figure 5), S / S can transfer energy to
1
1
1
p
S , which will disfavor the energy-transfer process as well (Figure 6a and Figure 6b).
1
Comparing the PL spectra at both 298 K and 77 K (Figure 3c v.s. Figure 3d and Figure 4a v.s.
Figure 4b), the energy-transfer processes aforementioned in P-YC-1 – P-YC-4 should be more
efficient than those in P-RC-1 – P-RC-4, indicated by the much stronger signals for both
fluorescence (ca. 420 nm) (Figure 3c v.s. Figure 3d) and phosphorescence (ca. 460 nm) (Figure
4
a v.s. Figure 4b) from the polymetallayne backbones in P-RC-1 – P-RC-4. From the UV-vis
absorption spectra for phosphorescent monomers and the PL spectrum of P-BC at room
temperature, the MLCT absorption bands for IrM1 can show better overlap with the fluorescent
emission band of P-BC that that of IrM2 (Figure 5), which should guarantee the more efficient
p
energy-transfer from S1 to the phosphorescent units in P-YC-1 – P-YC-4. Thus, the
copolymers P-YC-1 – P-YC-4 exhibit much weaker fluorescence signals form the
polymetallayne backbones than P-RC-1 – P-RC-4 (Figure 3c v.s. Figure 3d). In addition, the
3
absorption maximum (ca. 510 nm) of the MLCT band of IrM2 also deviates far from the
predominate phosphorescent emission band (ca. 460 nm) of P-BC with respect to that of IrM1
3
(
ca. 480 nm for the MLCT absorption band) (Figure 5). This situation also indicates the less
p
efficient energy-transfer from T1 to the phosphorescent units in P-RC-1 – P-RC-4.
Accordingly, the phosphorescent signal from the polymetallayne backbones in P-RC-1 –

Page 25 of 37
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P-RC-4 is relatively stronger than that of P-YC-1 – P-YC-4 as well (Figure 4a v.s. FDOigI:
u
10
r
.
e
103
4
9
b
/C5RA03697F
)
.
In the low-temperature PL spectra of these novel phosphorescent copolymers (Figure 4), there
are also weaker high-energy emission bands (ca. 505 nm for P-YC-1 – P-YC-4 and ca. 540 nm
for P-RC-1 – P-RC-4). Obviously, compared with the PL spectrum of P-BC at 77 K (Figure 4),
these weak emission bands should come from the phosphorescent units rather than
polymetallayne backbones of the phosphorescent copolymers. In the PL spectra of IrM1 and
IrM2 at 77 K, there are weak high-energy emission bands (ca. 500 nm for IrM1 and ca. 548 nm
1
for IrM2), which should come from the fluorescent emission of the MLCT (Figure S1). These
weak emission bands possess quite similar wavelength to those of the high-energy emission in
the phosphorescent copolymers aforementioned. Hence, high-energy emission bands ca. 505 nm
for P-YC-1 – P-YC-4 and ca. 540 nm for P-RC-1 – P-RC-4 can be assigned to the emission of
1
the MLCT states from the phosphorescent units. According to the UV-vis absorption spectrum
1
Y
of IrM1 (Figure 5), the absorption for lowest MLCT states of the phosphorescent units in
P-YC-1 – P-YC-4 should be ca. 436 nm, corresponding the energy-level of 2.84 eV. This
p
energy-level is higher than the triplet states of the polymetallayne backbones (T ca. 2.73 eV),
1
1
Y
p
which can promote energy-transfer from MLCT to T . Clearly, this energy-transfer process
1
1
Y
will reduce the population of MLCT excited states, which will reduce their chance of decay to
the ground states radiatively (Figure 5). Hence, the concerned emission band at ca. 505 nm is
very weak for P-YC-1 – P-YC-4 (Figure 4a). On the contrary, the situation is different in
1
R
P-RC-1 – P-RC-4. The energy-level of the MLCT states is ca. 2.62 eV corresponding ca. 473
p
p
nm (Figure 5), which is lower T (ca. 2.73 eV). Thus, there should be energy-transfer from T
1
1
1
R
1
R
to MLCT , which will increase the population of the MLCT states in the excitation process
of P-RC-1 – P-RC-4 to enhance their radiative decay to the ground states. Accordingly, the

RSC Advances
Page 26 of 37
1
R
View Article Online
DOI: 10.1039/C5RA03697F
emission band from MLCT in P-RC-1 – P-RC-4 is enhanced (Figure 4b).
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
1.0
0.8
0.6
0.4
0.2
0.0
UV P-BC
PL P-BC at 298 K
PL P-BC at 77K
UV IrM1
UV IrM2
3
00
400
500
600
700
Wavelength (nm)
Figure 5. UV-Vis spectra for model polymer P-BC and phosphorescent monomers together with
the PL spectrum of P-BC in CH Cl at both 298 K and 77 K.
2
2
S1Y
S1p
(a)
ISC
1MLCTY
T1p
ISC
3MLCTY
Fluorescence
Fluorescence
Phosphorescence
So
S1R
S1p
(
b)
ISC
T1p
1MLCTR
ISC
3MLCTR
Fluorescence
Fluorescence
Phosphorescence
So
Figure 6. a) Energy-transfer sketch involved in the phosphorescent copolymers P-YC-1 –
P-YC-4. b) Energy-transfer sketch involved in the phosphorescent copolymers P-RC-1 –
p
p
Y
R
P-RC-4. S /T : Singlet/Triplet states of the polymetallayne backbones; S /S : Singlet sates
1
1
1
1
1
Y 3
Y
of the ligands in IrM1/IrM2; MLCT / MLCT : Singlet/Triplet states of MLCT in IrM1;
MLCT / MLCT : Singlet/Triplet states of MLCT in IrM2.
1
R 3
R

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DOI: 10.1039/C5RA03697F
3
.3. Electrochemical characterization
The electrochemical properties of the two series of phosphorescent copolymers have been
characterized by the cyclic voltammetry (CV) experiments under nitrogen atmosphere with
ferrocene (Fc) as the standard. All the phosphorescent copolymers possess a quasi-irreversible
+
oxidation process in the potential range from ca. 0.33 V to 0.36 V v.s. Fc/Fc (Table 2). Based
III
on the CV results for the Ir ppy-type phosphorescent complexes, the reduction waves for the
N-heterocycle aromatic moieties can be detected. However, no detectable reduction procedure
has been recorded for these phosphorescent copolymers. This result can be ascribed to the low
III
content of the Ir phosphorescent units in the copolymers and the relevant CV signals cannot be
detected properly. With the aim to assign the origin of the oxidation process, the CV
measurement of model polymer P-BC is also carried out. The polymer P-BC exhibits E at ca.
p
0
.33 V, which is quite close to those from the phosphorescent copolymers. Furthermore, the
3
2
platinum(II) centers typically show irreversible oxidation process with E at ca. 0.5 V. Thus,
p
the oxidation peak should be induced by the bicarbazole units in the backbone of the
phosphorescent copolymers. Critically, the low oxidation potentials can furnish these
phosphorescent copolymers with good hole injection (HI) abilities. Together with the excellent
3
3
hole-transporting (HT) characters of the carbazole groups, these phosphorescent copolymers
show exhibit good hole injection/transporting (HI/HT) properties to enhance their EL
performances.

RSC Advances
Page 28 of 37
Table 2 Redox properties of the copolymers
View Article Online
DOI: 10.1039/C5RA03697F
a
b
Copolymers
Ep (V)
Eg (eV)
EHOMO (eV)
ELUMO (eV)
P-YC-1
P-YC-2
P-YC-3
P-YC-4
P-RC-1
P-RC-2
P-RC-3
P-RC-4
0.33
0.33
0.35
0.36
0.33
0.34
0.35
0.35
0.33
3.15
3.15
3.14
3.09
3.18
3.06
3.05
3.05
3.20
-5.13
-5.13
-5.15
-5.16
-5.13
-5.14
-5.15
-5.15
-1.98
-1.98
-2.01
-2.07
-1.95
-2.08
-2.10
-2.10
-1.93
P-BC
-5.13
a
b
Obtained through the onset of the UV-vis absorption spectra. ELUMO = EHOMO + Eg
3
.4. Electrophosphorescence characterization
As aforementioned, there is efficient energy-transfer from the triplet sates of the polymetallayne
III
backbone to the Ir phosphorescent units in these novel phosphorescent copolymers. This
should represent very important characters of these copolymers, since triplet energy-transfer
process can play critical role in the operation of the PHOLEDs. Even for the PHOLEDs based
on traditional conjugated phosphorescent copolymers, there is also predominant energy-transfer
process from the triplet sates of the conjugated backbones to the phosphorescent units in the EL
1
8
process.
Thus, the unique energy-transfer processes aforementioned in these novel
phosphorescent copolymers should benefit their EL process. Additionally, due to the weak
26,27,29,34,35
conjugation-extending ability of the platinum(II) ions,
the polymetallayne backbones
of these copolymers can exhibit high triplet energy-level (ca. 2.73 eV) to effectively block the
reverse energy-transfer process. Furthermore, the phosphorescent copolymers possess good
film-forming ability indicated by the low root mean square (RMS) roughness of c.a. 2.0 nm
(Figure S2). With all the features together with HI/HT ability afforded by the bicarbazole
moieties, these novel phosphorescent copolymers should show great potential in PHOLEDs.
Hence, their EL capacity has been characterized.

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DOI: 10.1039/C5RA03697F
Al (100 nm)
LiF (1 nm)
N
N
N
TPBi (45 nm)
N
Emission layer (35 nm)
PEDOT:PSS (45 nm)
N
N
ITO
Glass
O
O
O
O
TPBi
Device Emission layer component
S
S
+
S
S
+
n
O
O
O
O
Y1
Y2
Y3
Y4
P-YC-1
P-YC-2
P-YC-3
P-YC-4
_
_
SO H SO3
SO H SO3
SO H
3
3
3
R1
R2
R3
R4
P-RC-1
P-RC-2
P-RC-3
P-RC-4
n
PEDOT:PSS
Figure 7. The configuration of the PHOLEDs made from these phosphorescent copolymers and
the chemical structures for the involved functional materials.
The solution-processed PHOLEDs based on these copolymers have be fabricated with the
configuration of ITO/PEDOT:PSS (45 nm)/Emission layer, EML (35 nm)/TPBi (45 nm) /LiF (1
nm)/Al (100 nm) (Figure 7). The PEDOT:PSS layer acts as hole-injection layer (HIL). The
1
,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBi) layer plays the role of both
hole-blocking and electron-transporting, while LiF serves as an electron-injection layer. When
proper voltage was applied to the these PHOLEDs, intense yellow electrophosphorescence at ca.
5
50 nm can be observed from the devices Y1 – Y4 with P-YC-1 – P-YC-4 as emitter, while red
electrophosphorescence at ca. 630 nm can be detected from the devices R1 – R4 with P-RC-1 –
P-RC-4 as emitter (Figure 8). All the devices show EL representing similar line-shape to that of
corresponding copolymers in solid film (Figure S3), indicating the origin of EL is from the