Synthesis, characterization and photovoltaic properties of platinum-containing poly(aryleneethynylene) polymers with phenanthrenyl- imidazole moiety

Article abstract of DOI:10.1016/j.jorganchem.2011.07.005

A new type of soluble, solution-processable platinum(II) polyyne polymers based on phenanthrenyl-imidazole chromophore and their corresponding diplatinum model complexes were synthesized via the CuI-catalyzed dehydrohalogenation reaction of the platinum(I

Full text of DOI:10.1016/j.jorganchem.2011.07.005

Journal of Organometallic Chemistry 696 (2011) 4112e4120
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterization and photovoltaic properties of platinum-containing
poly(aryleneethynylene) polymers with phenanthrenyl-imidazole moiety
, ,
1
b
,
c
ꢀ ꢁ b
Hongmei Zhan a, Wai-Yeung Wong a , Annie Ng , Aleksandra B. Djurisic
*
**
, Wai-Kin Chan
a Institute of Molecular Functional Materials,1 Department of Chemistry and Centre for Advanced Luminescence Materials, Hong Kong Baptist University,
Waterloo Road, Kowloon Tong, Hong Kong, PR China
b Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, PR China
c Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new type of soluble, solution-processable platinum(II) polyyne polymers based on phenanthrenyl-
imidazole chromophore and their corresponding diplatinum model complexes were synthesized via
the CuI-catalyzed dehydrohalogenation reaction of the platinum(II) chloride precursor and each of the
diethynyl ligands. The photophysical (absorption and emission spectra), thermal, electrochemical and
photovoltaic properties of the polymers were investigated. Both polymers exhibit strong absorption
bands centered at 459e466 nm. The effect of adding thiophene ring along the polymer backbone was
evaluated. Bulk heterojunction solar cells fabricated by blending these metallopolymers with meth-
anofullerene were studied, with the power conversion efficiency reaching 0.39%, although the band gap
energies of the polymers are not low.
Received 21 May 2011
Received in revised form
4 July 2011
Accepted 4 July 2011
Keywords:
Phenanthrenyl-imidazole
Solar cell
Platinum
Thiophene
Ó 2011 Elsevier B.V. All rights reserved.
Metallopolymer
1. Introduction
on narrowing the polymer band gap. One of the most effective
approaches is designing the conjugated polymers containing elec-
In recent years, organic solar cells (OSCs) have received a great
deal of attention in academic and industrial laboratories due to
their advantages such as low cost, light weight, solution-based
processing and flexible devices [1e4]. Conjugated polymers pos-
tron donoreacceptor (DeA) pairs. Intramolecular DeA systems can
enhance the rate of charge transfer within molecules or polymers
[8e13]. There are two kinds of DeA systems: one possesses alter-
nating electron-rich donor and electron-deficient acceptor units
along the polymer main chains, which are usually encountered in
BHJ solar cells and have shown promising performance with the
PCE as high as w3e7% [6,7,14e21]; the other typical architecture is
the electron-deficient acceptor unit as the side chain attached to
the conjugated polymer backbone in a coplanar manner [22e26].
The introduction of an electron acceptor unit as side chain to the
polymeric main chain can also effectively widen the absorption
band and enhance charge transfer ability. This molecular architec-
ture used in BHJ device has the advantage that it allows charge
separation through sequential transfer of electrons from the main
chains to the side chains and then to methanofullerene such as
[6,6]-phenyl C61-butyric acid methyl ester (PCBM) [22,23,27].
sessing delocalized
p-electron systems have been studied exten-
sively for their application in bulk heterojunction (BHJ) solar cells,
in which the photoactive thin film consists of a bicontinuous and
interpenetrating blend of polymeric donors and fullerene acceptors
[5]. The power conversion efficiency (PCE) of OSCs has reached up
to w7e8% [6,7]. For fulfilling the goal of large scale commerciali-
zation as a renewable energy source, the photovoltaic efficiencies of
OSCs must be further enhanced. So, it is necessary to design and
develop new donor materials possessing better absorption prop-
erties in the visible spectrum and high charge carrier mobilities.
In order to harvest more photons and further improve the
photovoltaic efficiencies of OSCs, key developments have focused
Phenanthrenyl-imidazole is a
and the imidazole is an electron-deficient ring used as an acceptor
unit.. Recently, Wei and co-workers reported series of
phenanthrenyl-imidazole-containing regioregular polythiophene
copolymers, which showed relatively better performance with PCE
of w2.8e4.1% [22e24]. In addition, metal-containing conjugated
organic polymers represent an intriguing and promising class of
p-conjugated and planar structure,
a
* Corresponding author. Tel.: þ852 34117074; fax: þ852 34117348.
** Corresponding author. Tel.: þ852 28597946; fax: þ852 25599152.
E-mail addresses: rwywong@hkbu.edu.hk (W.-Y. Wong), dalek@hku.hk
ꢀ ꢁ
(A.B. Djurisic).
1
Areas of Excellence Scheme, University Grants Committee (Hong Kong).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.07.005

H. Zhan et al. / Journal of Organometallic Chemistry 696 (2011) 4112e4120
4113
materials, and platinum alkynyls have been a popular candidate for
inclusion into such a polymeric backbone owing to their potential
applications in molecular electronics and materials science, espe-
cially the platinum metallopolyyne polymers of the general form
trans-[-Pt(L)2C^CRC^C-]n (L is an auxiliary phosphine ligand, and
R is an aromatic spacer unit). The d-orbital of the platinum can
overlap with the p-orbital of the alkyne unit, and hence enhance
3 M KCl) reference electrode. The solvent in all measurements was
deoxygenated acetonitrile, and the supporting electrolyte was
0.1 M [nBu4N]BF4. Thin polymer films were deposited on the
working electrode by dip-coating in chlorobenzene solution
(6 mg mLꢁ1). Where appropriate, the oxidation and reduction
potentials were used to determine the HOMO and LUMO energy
levels using the equations EHOMO ¼ [ꢁ(Eox (vs. Ag/AgCl) ꢁ E(N.H.E. vs. Ag/
the
p-conjugation and
p-electron delocalization along the polymer
AgCl))] ꢁ 4.50 eV and ELUMO ¼ [ꢁ(Ered
Ag/AgCl) ꢁ E(N.H.E.
(vs.
vs. Ag/
backbone [28]. Furthermore, efficient intersystem crossing in such
organometallic species facilitates the formation of triplet excited
states and thus allows extended exciton diffusion lengths [29e35].
These features enable these metallopolymers to be used as the
donor materials in photovoltaic cells, and the mean PCE of 4.1% has
been achieved by the platinum metallopolyyne polymers based on
the benzothiadiazole chromophore [36e38]. The work was also
extended to other heterocyclic spacers [39e43].
AgCl))] ꢁ 4.50 eV, where the potentials for N.H.E. vs. vacuum and
N.H.E. vs. Ag/AgCl are 4.50 and ꢁ0.22 V, respectively [47,48]. The
molecular weights of the polymers were determined by GPC (HP
1050 series HPLC with visible wavelength and fluorescent detec-
tors) using polystyrene standards. Thermal analyses were per-
formed with a PerkineElmer TGA6 thermal analyzer.
2.3. Preparation of compounds
In view of the considerations above, we report here the
synthesis, characterization and photovoltaic properties of two
platinum metallopolyyne polymers based on thiophene chromo-
phore and the electron-deficient phenanthrenyl-imidazole
attached to the thiophene unit as a side chain. The hexyl groups
would improve the solubilities of the polymers. Compared with P1,
polymer P2 possesses two additional thiophene rings in one
building block unit, which is expected to further improve the
absorption properties of polymers and thus enhance the perfor-
mance of polymer solar cells.
2.3.1. Synthesis of PITBr
A mixture of phenanthrenequinone (0.83 g, 4 mmol), 2,5-
dibromo-3-thiophene-carboxaldehyde (1.07 g, 4 mmol), aniline
(1.86 g, 20 mmol), ammonium acetate (1.23 g, 16 mmol), and glacial
acetic acid (25 mL) was charged sequentially in a single-necked
flask and heated in an oil bath to a bath temperature of 123 ꢀC
under nitrogen, maintained at this temperature for 3e5 h. After
cooling, the solvent was removed under reduced pressure. The
residue was dissolved in CH2Cl2 (75 mL) and then the solution was
washed with water and brine. Organic layer was dried by Na2SO4,
filtered and concentrated under reduced pressure. The residue was
purified by silica gel column chromatography to give the crude
product, which was then recrystallized from the mixture solution
of CH2Cl2 and hexane to obtain the pure product PITBr (1.21 g, 57%)
as a wheat-yellow powder.
2. Experimental
2.1. General information
All reactions were carried out under a nitrogen atmosphere by
using standard Schlenk techniques. Solvents were dried and
distilled from appropriate drying agents under an inert atmosphere
prior to use. Glassware was oven-dried at about 120 ꢀC. All reagents
and chemicals, unless otherwise stated, were purchased from
commercial sources and used without further purification. trans-
Pt(PEt3)2(Ph)Cl [44] and trans-Pt(PBu3)2Cl2 [45] were prepared
according to the literature methods. All reactions were monitored
by thin-layer chromatography (TLC) with Merck pre-coated glass
plates. Flash column chromatography and preparative TLC were
carried out using silica gel from Merck (230e400 mesh). Infrared
spectra were recorded as CH2Cl2 solutions using a PerkineElmer
Paragon 1000 PC or Nicolet Magna 550 Series II FTIR spectrometer,
using CaF2 cells with a 0.5 mm path length. Fast atom bombard-
ment (FAB) mass spectra were recorded on a Finnigan MAT SSQ710
system and MALDI-TOF (matrix-assisted laser desorption/ioniza-
tion time-of-flight) spectra were obtained by an Autoflex Bruker
MALDI-TOF mass spectrometer. NMR spectra were measured in
CDCl3 on a Varian Inova 400 MHz FT-NMR spectrometer and
chemical shifts are quoted relative to tetramethylsilane for 1H and
13C nuclei and H3PO4 for 31P nucleus.
Spectral data: 1H NMR (400 MHz, CDCl3,
d/ppm): 8.82 (dd,
J1 ¼8.0 Hz, J2 ¼ 1.0 Hz, 1H, Ar), 8.77 (d, J ¼ 8.4 Hz, 1H, Ar), 8.70 (d,
J ¼ 8.2 Hz, 1H, Ar), 7.74 (t, J ¼ 7.0 Hz, 1H, Ar), 7.68e7.64 (m, 1H, Ar),
7.60e7.57 (m, 4H, Ar), 7.48e7.46 (m, 2H, Ar), 7.30e7.27 (m, 1H, Ar),
7.25e7.22 (m, 1H, Ar), 6.76 (s, 1H, Ar); 13C NMR (100 MHz, CDCl3,
d/
ppm): 144.27, 137.36, 137.23, 132.27, 131.49, 129.91, 129.89, 129.37,
128.34, 128.28, 127.48, 127.42, 127.04, 126.36, 125.79, 125.28, 124.10,
123.11, 122.71, 122.66, 120.96, 114.82, 111.33 (Ar); FAB-MS: m/z
535.0 [M]þ.
2.3.2. Synthesis of L1-HT
To a solution of 2-(2,5-dibromothiophen-3-yl)-1-phenyl-1H-
phenanthro[9,10-d]imidazole (PITBr, 0.27 g, 0.5 mmol) and tribu-
tyl(4-hexyl-thiophen-2-yl)stannane (0.73 g, 1.6 mmol) in dry
toluene (10 mL) under nitrogen was added the catalyst Pd(PPh3)4
(29 mg, 0.025 mmol). The reaction mixture was heated to reflux for
1 day until reaction completion as shown by TLC analysis. The
reaction mixture was cooled to room temperature and the solvent
was removed. The residue was purified by column chromatography
on silica gel eluting with CH2Cl2/hexane (1.5:1, v/v) to give the
compound L1-HT (0.32 g, 84%) as an orange solid.
2.2. Physical measurements
Spectral data: 1H NMR (400 MHz, CDCl3,
d/ppm): 8.87 (dd,
J1 ¼8.0 Hz, J2 ¼ 1.2 Hz, 1H, Ar), 8.77 (d, J ¼ 8.4 Hz, 1H, Ar), 8.72 (d,
J ¼ 8.3 Hz, 1H, Ar), 7.77e7.73 (m, 1H, Ar), 7.68e7.64 (m, 1H, Ar),
7.53e7.49 (m, 1H, Ar), 7.44e7.40 (m, 1H, Ar), 7.36e7.32 (m, 2H, Ar),
7.26e7.24 (m, 1H, Ar), 7.22e7.19 (m, 2H, Ar), 7.09e7.07 (m, 2H, Ar),
6.97 (d, J ¼ 1.3 Hz, 1H, Ar), 6.80 (d, J ¼ 1.0 Hz, 1H, Ar), 6.72 (d,
J ¼ 1.3 Hz, 1H, Ar), 6.69 (s, 1H, Ar), 2.56 (t, J ¼ 7.5 Hz, 2H, C6H13), 2.41
(t, J ¼ 7.5 Hz, 2H, C6H13), 1.64e1.57 (m, 2H, C6H13), 1.46e1.38 (m, 2H,
C6H13), 1.37e1.28 (m, 6H, C6H13), 1.23e1.09 (m, 6H, C6H13), 0.89 (t,
J ¼ 6.6 Hz, 3H, C6H13), 0.82 (t, J ¼ 6.8 Hz, 3H, C6H13); 13C NMR
UV/vis spectra were obtained on an HP-8453 diode array spec-
trophotometer. The solution emission spectra and lifetimes of the
compounds were measured on a Photon Technology International
(PTI) Fluorescence QuantaMaster Series QM1 spectrophotometer.
The quantum yields were determined in degassed CH2Cl2 solutions
at 293 K against coumarin 6 in ethanol (FF ¼ 0.78) [46]. The cyclic
voltammetry measurements were carried out at a scan rate of
100 mV sꢁ1 using a eDAQ EA161 potentiostat electrochemical
interface equipped with a thin film coated ITO covered glass
working electrode, a platinum counter electrode and a Ag/AgCl (in
(100 MHz, CDCl3,
d/ppm): 146.86, 144.18, 143.66, 137.42, 137.38,
136.74, 136.05, 135.62, 134.67, 129.28, 129.08, 128.27, 127.93, 127.61,

4114
H. Zhan et al. / Journal of Organometallic Chemistry 696 (2011) 4112e4120
127.49, 127.34, 127.30, 126.94, 126.46, 126.23, 125.63, 125.31, 125.06,
124.05, 123.13, 122.86, 122.83, 121.11, 121.04, 119.55 (Ar), 31.54,
30.45, 30.35, 30.26, 29.00, 28.83, 28.28, 26.79, 22.53, 17.31, 14.12,
13.66 (C6H13); FAB-MS: m/z 709.4 [M]þ.
2.3.6. Synthesis of L1-TMS and L2-TMS
To an ice-cooled mixture of L1-Br (99 mg, 0.11 mmol) in dry
triethylamine (6 mL) and CH2Cl2 (6 mL) solution mixture were
added CuI (3.8 mg, 0.02 mmol), Pd(OAc)2 (4.5 mg, 0.02 mmol) and
PPh3 (16 mg, 0.06 mmol). After the solution was stirred for 30 min
at 0 ꢀC, trimethylsilylacetylene (54 mg, 0.55 mmol) was then added
and the suspension was stirred for 30 min in an ice-bath before
being warmed to room temperature. After reacting for 30 min at
room temperature, the mixture was refluxed for 20 h. The solution
was then allowed to cool to room temperature and the solvent
mixture was evaporated in vacuo. The residue was purified by
column chromatography on silica gel eluting with a solvent
combination of CH2Cl2/hexane (1:2, v/v) to provide L1-TMS (72 mg,
70%) as an orange solid.
2.3.3. Synthesis of L1-Br
Compound L1-HT (0.11 g, 0.15 mmol) was dissolved in THF
(10 mL). NBS (55 mg, 0.31 mmol) was then added to the solution
and the mixture was stirred overnight at room temperature in
the dark. Until the reaction completion as shown by TLC analysis,
the solvent was removed. The residue was purified by column
chromatography on silica gel eluting with CH2Cl2/hexane (1:1, v/
v) to give the pure compound L1-Br (0.10 g, 75%) as an orange
solid.
Spectral data: 1H NMR (400 MHz, CDCl3,
d
/ppm): 8.86 (d,
Spectral data: 1H NMR (400 MHz, CDCl3,
d/ppm): 8.86 (dd,
J ¼ 7.9 Hz, 1H, Ar), 8.74 (d, J ¼ 8.4 Hz, 1H, Ar), 8.69 (d, J ¼ 8.4 Hz, 1H,
Ar), 7.74 (t, J ¼ 7.8 Hz, 1H, Ar), 7.64 (t, J ¼ 7.7 Hz, 1H, Ar), 7.51e7.42
(m, 2H, Ar), 7.37 (t, J ¼ 7.8 Hz, 2H, Ar), 7.23e7.20 (m, 2H, Ar), 7.14 (d,
J ¼ 7.3 Hz, 2H, Ar), 7.05 (s, 1H, Ar), 6.80 (s, 1H, Ar), 6.67 (s, 1H, Ar),
2.49 (t, J ¼ 7.5 Hz, 2H, C6H13), 2.37 (t, J ¼ 7.5 Hz, 2H, C6H13),
1.57e1.52 (m, 2H, C6H13), 1.41e1.30 (m, 8H, C6H13), 1.19e1.07 (m,
6H, C6H13), 0.89 (t, J ¼ 6.9 Hz, 3H, C6H13), 0.79 (t, J ¼ 6.8 Hz, 3H,
J1 ¼8.0 Hz, J2 ¼1.1 Hz, 1H, Ar), 8.76 (d, J ¼ 8.4 Hz, 1H, Ar), 8.71 (d,
J ¼ 8.3 Hz, 1H, Ar), 7.74 (t, J ¼ 7.1 Hz, 1H, Ar), 7.65 (t, J ¼ 7.7 Hz, 1H,
Ar), 7.52e7.48 (m, 1H, Ar), 7.46e7.42 (m, 1H, Ar), 7.38e7.35 (m, 2H,
Ar), 7.26e7.19 (m, 2H, Ar), 7.16e7.13 (m, 3H, Ar), 6.86 (s,1H, Ar), 6.68
(s, 1H, Ar), 2.63 (t, J ¼ 7.5 Hz, 2H, C6H13), 2.51 (t, J ¼ 7.4 Hz, 2H,
C6H13), 1.62e1.59 (m, 2H, C6H13), 1.45e1.41 (m, 2H, C6H13),
1.36e1.31 (m, 6H, C6H13), 1.23e1.11 (m, 6H, C6H13), 0.89 (t,
J ¼ 6.9 Hz, 3H, C6H13), 0.81 (t, J ¼ 6.8 Hz, 3H, C6H13), 0.25 (s, 9H,
C6H13); 13C NMR (100 MHz, CDCl3,
d/ppm): 145.70, 143.16, 142.63,
137.47, 137.39, 136.06, 135.62, 134.89, 134.24, 129.54, 129.44, 129.32,
128.38, 127.99, 127.57, 127.43, 127.42, 127.40, 127.24, 126.75, 126.31,
125.77, 125.23, 124.94, 124.14, 123.18, 122.84, 122.80, 121.10, 110.40,
108.27 (Ar), 31.64, 31.48, 29.63, 29.37, 28.94, 28.78, 22.63, 22.51,
21.09, 14.52, 14.16, 14.11 (C6H13); FAB-MS: m/z 867.0 [M]þ.
TMS), 0.16 (s, 9H, TMS); 13C NMR (100 MHz, CDCl3,
d/ppm): 149.90,
149.44, 145.88, 137.60, 137.44, 136.62, 135.96, 135.33,134.59, 129.63,
129.49, 129.43, 128.43, 128.08, 127.76, 127.75, 127.53, 127.38, 127.35,
127.30, 126.42, 125.85, 125.31, 125.08, 124.23, 123.27, 122.97, 122.93,
121.18, 119.45, 117.92 (Ar), 103.05, 102.82, 97.22, 97.11 (C^C), 31.68,
31.55, 30.08, 30.01, 29.68, 29.45, 29.02, 28.88, 22.72, 22.62, 14.26,
14.22 (C6H13), 0.07, ꢁ0.00 (TMS); FAB-MS: m/z 901.5 [M]þ. Anal.
Calc. for C55H60N2S3Si2: C, 73.28; H, 6.71; N, 3.11. Found: C, 73.55; H,
6.82; N, 3.32%.
2.3.4. Synthesis of L2-T
The procedure was similar to that of L1-HT.
Orange solid (77%). Spectral data: 1H NMR (400 MHz, CDCl3,
d/
ppm): 8.89 (dd, J1 ¼8.0 Hz, J2 ¼ 1.1 Hz, 1H, Ar), 8.76 (d, J ¼ 8.6 Hz,
1H, Ar), 8.71 (d, J ¼ 8.3 Hz, 1H, Ar), 7.77e7.73 (m, 1H, Ar), 7.68e7.64
(m, 1H, Ar), 7.52e7.35 (m, 4H, Ar), 7.30e7.28 (m, 1H, Ar), 7.24e7.10
(m, 7H, Ar), 7.06e7.04 (m,1H, Ar), 6.98 (s,1H, Ar), 6.95e6.92 (m, 2H,
Ar), 6.74 (s, 1H, Ar), 2.70 (t, J ¼ 7.8 Hz, 2H, C6H13), 2.55 (t, J ¼ 7.7 Hz,
2H, C6H13), 1.65e1.61 (m, 2H, C6H13), 1.42e1.30 (m, 8H, C6H13),
1.10e1.00 (m, 6H, C6H13), 0.89e0.86 (m, 3H, C6H13), 0.75 (t,
The same procedure was used to prepare L2-TMS.
L2-TMS: Orange solid (91%). 1H NMR (400 MHz, CDCl3,
d/ppm):
8.86 (d, J ¼ 7.9 Hz, 1H, Ar), 8.78 (d, J ¼ 8.4 Hz, 1H, Ar), 8.73 (d,
J ¼ 8.4 Hz, 1H, Ar), 7.76 (t, J ¼ 7.1 Hz, 1H, Ar), 7.70 (t, J ¼ 7.0 Hz, 1H,
Ar), 7.54e7.50 (m, 1H, Ar), 7.46 (t, J ¼ 7.5 Hz, 1H, Ar), 7.38 (t,
J ¼ 7.8 Hz, 2H, Ar), 7.26e7.22 (m, 2H, Ar), 7.17e7.15 (m, 4H, Ar), 7.05
(d, J ¼ 3.8 Hz,1H, Ar), 6.97 (s,1H, Ar), 6.95 (d, J ¼ 3.8 Hz,1H, Ar), 6.78
(d, J ¼ 3.8 Hz, 1H, Ar), 6.75 (s, 1H, Ar), 2.71 (t, J ¼ 7.8 Hz, 2H, C6H13),
2.55 (t, J ¼ 7.7 Hz, 2H, C6H13), 1.65e1.61 (m, 2H, C6H13), 1.42e1.31
(m, 8H, C6H13), 1.19e1.01 (m, 6H, C6H13), 0.90 (t, J ¼ 6.5 Hz, 3H,
C6H13), 0.76 (t, J ¼ 7.0 Hz, 3H, C6H13), 0.26 (s, 9H, TMS), 0.22 (s, 9H,
J ¼ 7.2 Hz, 3H, C6H13); 13C NMR (100 MHz, CDCl3,
d/ppm): 146.26,
140.47, 140.08, 137.51, 137.41, 136.16, 135.65, 135.46, 135.25, 134.09,
132.62, 131.58, 130.27, 129.45, 129.38, 129.34, 129.18, 128.34, 128.01,
127.52, 127.49, 127.42, 127.39, 127.28, 126.84, 126.81, 126.26, 126.08,
125.67, 125.61, 125.55, 125.12, 124.11, 123.15, 122.86, 121.12 (Ar),
31.68, 31.46, 30.57, 30.49, 29.34, 29.27, 29.11, 29.07, 22.65, 22.48,
14.19, 14.09 (C6H13); FAB-MS: m/z 873.2 [M]þ.
TMS); 13C NMR (100 MHz, CDCl3,
d/ppm): 146.11, 141.22, 140.81,
137.58, 137.46, 137.36, 137.15, 136.18, 135.23, 134.54, 133.19, 133.10,
131.27, 129.81, 129.65, 129.58, 129.49, 129.33, 128.45, 128.07, 127.63,
127.59, 127.50, 127.32, 127.14, 126.39, 125.81, 125.81, 125.54, 125.27,
124.21, 123.26, 123.01, 122.98, 122.91, 121.21 (Ar), 100.45, 100.37,
97.41, 97.36 (C^C), 31.76, 31.54, 30.52, 30.43, 29.61, 29.35, 29.15,
22.73, 22.55, 14.24, 14.17 (C6H13), ꢁ0.01, ꢁ0.05 (TMS); FAB-MS: m/z
1065.5 [M]þ. Anal. Calc. for C63H64N2S5Si2: C, 71.01; H, 6.05; N, 2.63.
Found: C, 71.32; H, 5.97; N, 2.78%.
2.3.5. Synthesis of L2-Br
The procedure was similar to that of L1-Br.
L2-Br: Orange solid (88%). Spectral data: 1H NMR (400 MHz,
CDCl3,
d/ppm): 8.89 (dd, J1 ¼8.0 Hz, J2 ¼1.2 Hz, 1H, Ar), 8.75 (d,
J ¼ 8.6 Hz, 1H, Ar), 8.70 (d, J ¼ 8.4 Hz, 1H, Ar), 7.76e7.72 (m, 1H, Ar),
7.67e7.63 (m, 1H, Ar), 7.51e7.42 (m, 2H, Ar), 7.38e7.35 (m, 2H, Ar),
7.24e7.21 (m, 2H, Ar), 7.17e7.13 (m, 3H, Ar), 6.98 (d, J ¼ 3.9 Hz, 1H,
Ar), 6.95 (s,1H, Ar), 6.87 (d, J ¼ 3.8 Hz,1H, Ar), 6.83 (d, J ¼ 3.9 Hz,1H,
Ar), 6.75 (s, 1H, Ar), 6.66 (d, J ¼ 3.9 Hz, 1H, Ar), 2.64 (t, J ¼ 7.8 Hz, 2H,
C6H13), 2.50 (t, J ¼ 7.6 Hz, 2H, C6H13), 1.62e1.58 (m, 2H, C6H13),
1.39e1.29 (m, 8H, C6H13), 1.12e1.01 (m, 6H, C6H13), 0.88e0.85 (m,
3H, C6H13), 0.76 (t, J ¼ 7.3 Hz, 3H, C6H13); 13C NMR (100 MHz, CDCl3,
2.3.7. Synthesis of L1 and L2
To a solution of L1-TMS (68 mg, 0.075 mmol) in CH2Cl2 (5 mL)
and MeOH (5 mL) was added K2CO3 (22 mg, 0.158 mmol), and the
solution was stirred at room temperature for 6 h under nitrogen.
After the reaction was complete as shown by TLC analysis, the
solvent was removed under reduced pressure. The residue was
purified by column chromatography on silica gel using CH2Cl2/
hexane (1.5:1, v/v) as eluent to afford compound L1 (40 mg, 71%) as
an orange solid.
d/ppm): 145.94,140.93,140.49,137.44,137.31,137.03,136.81,136.02,
135.06, 134.43, 132.99, 130.69, 130.25, 130.16, 129.41, 129.33, 129.26,
129.19, 129.16, 128.28, 127.91, 127.45, 127.43, 127.33, 127.17, 126.94,
126.74, 126.21, 125.66, 125.11, 124.05, 123.10, 122.74, 121.03, 112.10,
112.05 (Ar), 31.57, 31.38, 30.48, 30.41, 29.24, 29.17, 29.02, 28.98,
22.58, 22.41, 14.10, 14.03 (C6H13); FAB-MS: m/z 1031.2 [M]þ.
Spectral data: IR (KBr):
CDCl3,
/ppm): 8.85 (dd, J1 ¼7.9 Hz, J2 ¼1.2 Hz, 1H, Ar), 8.77 (d,
J ¼ 8.4 Hz, 1H, Ar), 8.73 (d, J ¼ 8.2 Hz, 1H, Ar), 7.77e7.73 (m, 1H, Ar),
n ;
(C^C) 2094 cmꢁ1 1H NMR (400 MHz,
d

H. Zhan et al. / Journal of Organometallic Chemistry 696 (2011) 4112e4120
4115
7.69e7.65 (m, 1H, Ar), 7.54e7.50 (m, 1H, Ar), 7.47e7.43 (m, 1H, Ar),
P2: Orange solid (86%). Spectral data: IR (KBr):
2084 cmꢁ1;1HNMR (400 MHz, CDCl3,
n
(C^C)
7.40e7.36 (m, 2H, Ar), 7.27e7.20 (m, 2H, Ar), 7.16e7.14 (m, 3H, Ar),
6.89 (s, 1H, Ar), 6.70 (s, 1H, Ar), 3.51 (s, 1H, C^CH), 3.39 (s, 1H,
C^CH), 2.65 (t, J ¼ 7.5 Hz, 2H, C6H13), 2.52 (t, J ¼ 7.5 Hz, 2H, C6H13),
1.64e1.57 (m, 2H, C6H13), 1.45e1.38 (m, 2H, C6H13), 1.34e1.30 (m,
6H, C6H13), 1.22e1.09 (m, 6H, C6H13), 0.89 (t, J ¼ 6.5 Hz, 3H, C6H13),
d
/ppm): 8.88 (d, J ¼ 7.8 Hz,1H,
Ar), 8.78 (d, J ¼ 8.5 Hz, 1H, Ar), 8.73 (d, J ¼ 8.4 Hz, 1H, Ar), 7.75 (t,
J ¼ 7.5 Hz, 1H, Ar), 7.67 (t, J ¼ 7.5 Hz, 1H, Ar), 7.52e7.35 (m, 4H, Ar),
7.25e7.23 (m, 2H, Ar), 7.17e7.14 (m, 3H, Ar), 6.95e6.88 (m, 2H, Ar),
6.78e6.71 (m, 2H, Ar), 6.67e6.65 (m, 2H, Ar), 2.71e2.69 (m, 2H,
C6H13), 2.64e2.48 (m, 2H, C6H13), 2.18e2.05 (m, 12H, PBu3),
1.70e1.30 (m, 34H, PBu3 þ C6H13),1.15e0.81 (m, 27H, PBu3 þ C6H13),
0.79 (t, J ¼ 6.8 Hz, 3H, C6H13); 13C NMR (100 MHz, CDCl3,
d/ppm):
150.10, 149.51, 145.63, 137.47, 137.31, 136.38, 136.20, 135.16, 134.86,
129.52, 129.42, 129.33, 128.35, 127.93, 127.87, 127.62, 127.42, 127.30,
127.24, 127.21, 126.30, 125.74, 125.22, 124.92, 124.11, 123.16, 122.82,
122.78, 121.08, 118.01, 116.55 (Ar), 84.93, 84.75, 76.32, 72.36 (C^C),
31.60, 31.44, 30.06, 30.00, 29.54, 29.30, 28.94, 28.78, 22.60, 22.48,
14.13, 14.08 (C6H13); FAB-MS: m/z 757.3 [M]þ. Anal. Calc. for
C49H44N2S3: C, 77.74; H, 5.86; N, 3.70. Found: C, 77.54; H, 6.02;
N, 3.89%.
0.75 (t, J ¼ 7.0 Hz, 3H, C6H13); 31P NMR (162 MHz, CDCl3,
d/ppm):
3.22 (1JPePt ¼ 2329 Hz); Anal. Calc. for (C81H100N2P2S5Pt)n: C, 64.05;
H, 6.64; N, 1.84. Found: C, 64.12; H, 6.76; N, 2.01%; GPC (THF):
Mw ¼ 58370, Mn ¼ 20910, DP ¼ 14, PDI ¼ 2.79.
2.3.9. Synthesis of model complexes M1 and M2
All of them were synthesized following the dehydrohalogenat-
ing coupling between trans-Pt(PEt3)2(Ph)Cl and the corresponding
diterminal alkynes. A typical procedure was given for M1 starting
from L1.
The same procedure as L1 was used to prepare L2.
L2: Orange solid (86%). Spectral data: IR (KBr):
n(C^C)
2097 cmꢁ1 1H NMR (400 MHz, CDCl3,
;
d
/ppm): 8.87 (dd,
J1 ¼7.9 Hz, J2 ¼1.2 Hz, 1H, Ar), 8.76 (d, J ¼ 8.5 Hz, 1H, Ar), 8.72 (d,
J ¼ 8.4 Hz, 1H, Ar), 7.75 (t, J ¼ 7.0 Hz, 1H, Ar), 7.69e7.65 (m, 1H, Ar),
7.53e7.36 (m, 4H, Ar), 7.25e7.14 (m, 6H, Ar), 7.09 (d, J ¼ 3.8 Hz, 1H,
Ar), 6.97 (s, 1H, Ar), 6.96 (d, J ¼ 3.8 Hz, 1H, Ar), 6.79 (d, J ¼ 3.8 Hz,
1H, Ar), 6.76 (s, 1H, Ar), 3.42 (s,1H, C^CH), 3.37 (s,1H, C^CH), 2.70
(t, J ¼ 7.8 Hz, 2H, C6H13), 2.55 (t, J ¼ 7.7 Hz, 2H, C6H13), 1.65e1.60
(m, 2H, C6H13), 1.44e1.38 (m, 8H, C6H13), 1.21e0.99 (m, 6H, C6H13),
0.89 (t, J ¼ 6.7 Hz, 3H, C6H13), 0.76 (t, J ¼ 7.0 Hz, 3H, C6H13); 13C
To a solution of ligand L1 (7.0 mg, 0.01 mmol) and trans-
Pt(PEt3)2(Ph)Cl (11 mg, 0.02 mmol) in triethylamine (3 mL) and dry
CH2Cl2 (3 mL) was added CuI (2 mg) under nitrogen. After stirring
overnight at room temperature, all volatile components were
removed under reduced pressure. The residue was dissolved in
CH2Cl2 and purified by preparative silica TLC plates using CH2Cl2/
hexane (1.8:1, v/v) as eluent to give the pure product M1 as a red
solid (8 mg, 43%).
n ;
(C^C) 2077 cmꢁ1 1H NMR (400 MHz,
NMR (100 MHz, CDCl3,
d/ppm): 145.93, 141.24, 140.80, 137.52,
Spectral data: IR (KBr):
CDCl3,
/ppm): 8.87 (d, J ¼ 7.0 Hz, 1H, Ar), 8.74 (d, J ¼ 8.4 Hz, 1H, Ar),
137.43, 137.31, 136.04, 135.08, 134.53, 133.50, 133.41, 133.10, 130.90,
129.29, 129.45, 129.35, 129.21, 128.31, 127.93, 127.54, 127.46, 127.37,
127.17, 127.03,126.99, 126.26, 125.69, 125.43, 125.39,125.14,124.07,
123.12, 122,76, 121.65, 121.61, 121.06 (Ar), 82.51, 82.43, 76.76, 76.71
(C^C), 31.61, 31.39, 30.41, 30.33, 29.45, 29.21, 29.01, 22.59, 22.41,
14.10, 14.03 (C6H13); FAB-MS: m/z 921.4 [M]þ. Anal. Calc. for
C57H48N2S5: C, 74.31; H, 5.25; N, 3.04. Found: C, 74.44; H, 5.12;
N, 2.96%.
d
8.68 (d, J ¼ 8.4 Hz, 1H, Ar), 7.71 (d, J ¼ 7.3 Hz, 1H, Ar), 7.64 (d,
J ¼ 7.1 Hz, 1H, Ar), 7.52e7.35 (m, 4H, Ar), 7.32e7.26 (m, 2H, Ar),
7.26e7.15 (m, 6H, Ar), 7.06 (s, 1H, Ar), 6.96 (t, J ¼ 7.4 Hz, 2H, Ar), 6.88
(t, J ¼ 7.4 Hz, 2H, Ar), 6.82 (s, 1H, Ar), 6.78 (t, J ¼ 7.3 Hz, 1H, Ar), 6.74
(t, J ¼ 7.2 Hz, 1H, Ar), 6.64 (s, 1H, Ar), 2.61 (t, J ¼ 7.6 Hz, 2H, C6H13),
2.47 (t, J ¼ 7.6 Hz, 2H, C6H13),1.77e1.70 (m,12H, PEt3),1.49e1.29 (m,
24H, PEt3 þ C6H13), 1.25e1.19 (m, 4H, C6H13), 1.12e1.05 (m, 18H,
PEt3), 0.96e0.76 (m, 24H, PEt3 þ C6H13); 31P NMR (162 MHz, CDCl3,
d
/ppm): 10.16 (1JPePt ¼ 2635 Hz), 9.63 (1JPePt ¼ 2626 Hz); MALDI-
2.3.8. Synthesis of polymers P1 and P2
TOF: m/z 1772.6440 [M]þ, Calculated: 1772.6320; Anal. Calc. For
C85H112N2P4S3Pt2: C, 57.61; H, 6.37; N, 1.58. Found: C, 57.45; H, 6.46;
N, 1.67%.
The polymers were prepared by the dehydrohalogenative
polycondensation between trans-Pt (PBu3)2Cl2 and each of L1eL2.
A typical procedure was given for P1 starting from L1.
To a stirred solution mixture of L1 (37 mg, 0.05 mmol) and
trans-Pt(PBu3)2Cl2 (33 mg, 0.05 mmol) in freshly distilled triethyl-
amine (4 mL) and CH2Cl2 (4 mL) was added a small amount of CuI
(3.00 mg). The solution was stirred at room temperature for 24 h
under the nitrogen atmosphere. The solvents were removed on
a rotary evaporator in vacuo. The residue was redissolved in CH2Cl2
and filtered through a short column on neutral aluminum oxide
eluting with CH2Cl2 to remove ionic impurities and catalyst residue.
After removal of the solvent, the crude product was precipitated in
methanol from CH2Cl2. The precipitate was collected via filtration
and washed with copious amounts of methanol and dried under
vacuum for 5 h to afford the polymer P1 (43 mg, 63%).
M2: Orange solid (49%). Spectral data: IR (KBr):
n(C^C)
2081 cmꢁ1; 1H NMR (400 MHz, CDCl3,
d/ppm): 8.89 (d, J ¼ 8.0 Hz,1H,
Ar), 8.78 (d, J ¼ 8.6 Hz, 1H, Ar), 8.73 (d, J ¼ 8.2 Hz, 1H, Ar), 7.74 (t,
J ¼ 7.0 Hz, 1H, Ar), 7.67 (t, J ¼ 7.0 Hz, 1H, Ar), 7.53e7.49 (m, 1H, Ar),
7.47e7.26 (m, 7H, Ar), 7.25e7.23 (m, 2H, Ar), 7.17e7.14 (m, 3H, Ar),
6.99e6.93 (m, 5H, Ar), 6.89 (d, J ¼ 3.8 Hz, 1H, Ar), 6.83e6.79 (m, 3H,
Ar), 6.73 (d, J ¼ 3.8 Hz,1H, Ar), 6.68 (m, 2H, Ar), 2.71 (t, J ¼ 7.8 Hz, 2H,
C6H13),2.55(t, J ¼ 7.7 Hz,2H, C6H13),1.78e1.64(m, 26H, PEt3 þ C6H13),
1.40e1.32 (m, 8H, C6H13), 1.15e1.02 (m, 42H, PEt3 þ C6H13), 0.90 (t,
J ¼ 6.8 Hz, 3H, C6H13), 0.76 (t, J ¼ 7.0 Hz, 3H, C6H13); 31P NMR
(162 MHz, CDCl3,
d
/ppm): 9.98, 9.95 (1JPePt ¼ 2631 Hz); MALDI-TOF:
m/z 1935.3507 [M]þ, Calculated: 1935.6000; Anal. Calc. For
C93H116N2P4S5Pt2: C, 57.69; H, 6.04; N,1.45. Found: C, 57.98; H, 6.15; N,
1.30%.
Spectral data: IR (KBr):
CDCl3,
/ppm): 8.86 (t, J ¼ 7.6 Hz, 1H, Ar), 8.78e8.70 (m, 2H, Ar),
n ;
(C^C) 2083 cmꢁ1 1H NMR (400 MHz,
d
7.73e7.65 (m, 2H, Ar), 7.52e7.50 (m, 1H, Ar), 7.42e7.40 (m, 1H, Ar),
7.36e7.31 (m, 2H, Ar), 7.20e7.13 (m, 4H, Ar), 7.04e7.00 (m, 1H, Ar),
6.81e6.77 (m, 1H, Ar), 6.63e6.58 (m, 1H, Ar), 2.59e2.53 (m, 2H,
C6H13), 2.46e2.41 (m, 2H, C6H13), 2.10e2.07 (m, 3H, PBu3),
1.76e1.74 (m, 6H, PBu3), 1.50e1.43 (m, 8H, PBu3), 1.30e1.09 (m,
33H, PBu3 þ C6H13), 0.94e0.86 (m, 9H, PBu3 þ C6H13), 0.84e0.80
(m, 13H, PBu3 þ C6H13), 0.74e0.70 (m, 4H, PBu3 þ C6H13); 31P NMR
2.4. Solar cell fabrication and characterization
The device structure was ITO/PEDOT:PSS/polymer:PCBM blend/
Al. The ITO glass substrates (10
U per square) were cleaned by
sonication in toluene, acetone, ethanol and deionized water, dried
in an oven, and then cleaned with UV ozone for 300 s. As-received
PEDOT:PSS solution was passed through the 0.45 mm filter and
(162 MHz, CDCl3,
d
/ppm): 3.04 (1JPePt ¼ 2336 and 142 Hz); Anal.
Calc. for (C73H96N2P2S3Pt)n: C, 64.72; H, 7.14; N, 2.07. Found: C,
64.97; H, 7.23; N, 2.32%; GPC (THF): Mw ¼ 76280, Mn ¼ 35430,
DP ¼ 26, PDI ¼ 2.15.
spin-coated on patterned ITO substrates at 5000 r.p.m. for 3 min,
followed by baking in N2 at 150 ꢀC for 15 min. The polymer:PCBM

4116
H. Zhan et al. / Journal of Organometallic Chemistry 696 (2011) 4112e4120
(1:4 by weight) active layer was prepared by spin-coating the
chlorobenzene solution (30 mg per mL) at 800 r.p.m. for 2 min. The
substrates were dried at room temperature in low vacuum (vacuum
oven) for 1 h, and then stored in high vacuum (10ꢁ5e10ꢁ6 Torr)
overnight. Al electrode (100 nm) was evaporated through a shadow
mask to define the active area of the devices (2 mm diameter
circle). All the fabrication procedures (except drying, PEDOT:PSS
annealing and Al deposition) and cell characterization were per-
formed in air. Power conversion efficiency was determined from
JeV curve measurement (using a Keithley 2400 sourcemeter) under
white light illumination (at 100 mW cmꢁ2). For white light effi-
ciency measurements, Oriel 66002 solar light simulator with AM
1.5 filter was used. The light intensity was measured by a Molectron
Power Max 500D laser power meter.
The thermal properties of the polymers were also examined by
thermal gravimetric analysis (TGA) under nitrogen. Polymer P1
exhibits good thermal stability with the decomposition onsets at
w339 ꢀC and the percent weight loss is w15%, indicating that two
butyl groups were removed from the polymer. For polymer P2, two
butyl groups were removed at the lower decomposition tempera-
ture of 238 ꢀC, while elevating the temperature up to 374 ꢀC, six
butyl groups were all removed from polymer, as deduced from the
percentage weight loss of w23% as shown in the TGA curve.
3.2. Photophysical and electrochemical characterization
The absorption and emission spectra of the ligands, polymers
and model complexes were measured in CH2Cl2 solutions at 293 K
(Table 1 and Figs. 1 and 2). All the compounds show two absorption
bands, one sharp and strong peak at about 260 nm and the other
broad and relatively weak peak between 320 and 550 nm [22e24].
The former is caused by the presence of conjugated phenanthrenyl-
imidazole moieties that are not fully coplanar to the thiophene
polymer main chain because of the steric hindrance. The latter is
3. Results and discussion
3.1. Synthetic methodologies and chemical characterization
The chemical structures and synthesis of new platinum(II)
polyyne polymers P1eP2 and their model compounds M1eM2 are
shown in Scheme 1. In the initial attempt, we tried to synthesize the
compound PITBr according to the method reported in the literature
[22], that is, ring closure reaction followed by bromination, but
unfortunately we failed in the second step and it was messy and
difficult to separate the target product from the reaction mixture.
So, we optimized the synthetic methods as follows. Thiophene-3-
carboxaldehyde was first brominated by bromine in the solvent
mixture of 48% aqueous hydrobromic acid and diethyl ether to give
2,5-dibromo-3-formylthiophene. The ring closure reaction
between phenanthrenequinone, 2,5-dibromo-3-formylthiophene
and aniline was carried out in the presence of ammonium acetate
and acetic acid to achieve the key precursor PITBr as a yellow solid.
Following Stille cross-coupling reaction and bromination with N-
bromosuccinimide (NBS), compound L1-Br was obtained in high
yield. Repeating the similar Stille cross-coupling reaction, L2-T was
obtained and sequential bromination gave compound L2-Br. By
Sonogashira coupling reaction, the bromide groups were converted
to the corresponding trimethylsilylethynyl groups in a CH2Cl2/NEt3
mixture using CuI, Pd(OAc)2 and PPh3 as the catalysts. Following
desilylation with potassium carbonate in methanol, the final
diethynyl ligands L1eL2 were obtained as orange solids. Polymers
P1eP2 and their model compounds M1eM2 were prepared by the
Sonogashira-type dehydrohalogenation between each of the
diethynyl precursors and the corresponding platinum precursors
trans-Pt(PBu3)2Cl2 and trans-Pt(PEt3)2(Ph)Cl with the stoichio-
metric ratio of 1:1 and 1:2.1, respectively. Polymers P1eP2 were
purified by flash column chromatography over neutral Al2O3 to
remove ionic impurities and catalyst residues, and repeated
precipitation and isolation.
All of the Pt compounds are thermally- and air-stable solids and
they are soluble in common chlorinated hydrocarbons. From the gel
permeation chromatography (GPC) analysis on P1 and P2, the
number-average molecular weights (Mn) of P1 and P2 calibrated
against polystyrene standards were 3.54 and 2.09 kg mole1, corre-
sponding to the polydispersity indices (PDI) of 2.15 and 2.79,
indicating that P1 and P2 possess 26 and 14 repeating units,
respectively. The structures of polymers P1eP2 and their model
compounds M1eM2 were unequivocally characterized using mass
spectrometry, IR and NMR spectroscopies (see Experimental
section). The NMR data are consistent with the proposed struc-
ture of the polymers and model compounds. The peaks arising from
terminal eC^CH groups are absent in the NMR and IR spectra,
confirming metalealkynyl bond formation.
assigned to the pep* transitions of the conjugated chain [22e24]
and the presence of the phenanthrenyl-imidazole moieties
increases the effective conjugation length of the polythiophene
main chain to some extent. With the extension of the
p-conjuga-
tion system, the second absorption band becomes gradually
stronger and red-shifted to the longer wavelength, as revealed by
a comparison of the absorption spectra of the diethynyl ligands and
the corresponding platinum(II) complexes. Besides, the maximum
absorption peak of L2 is shown at 424 nm, and an obvious red shift
of 28 nm occurs compared with that of L1 at 396 nm, probably
because the introduction of additional thiophene rings results in
the extension of the p-conjugated system. While M1 and M2 show
the same absorption peak at 449 nm, P2 shows a slightly blue-
shifted absorption band compared with that of P1. We speculate
that the blue-shifted absorption peak may be related to the lower
molecular weight and lower degree of polymerization for P2. The
optical band gaps of P1 and P2 are 2.34 and 2.28 eV, respectively.
Presumably, a higher degree of conjugation with the additional
thienyl units reduces the band gap.
All the phenanthrenyl-imidazole-based diethynyl ligands,
model complexes and polymers show photoluminescence proper-
ties in the visible region. Polymers P1 and P2 can emit intense
fluorescence from the singlet excited states at 531 and 560 nm,
respectively, and show a significant red shift compared to the cor-
responding ligands L1 and L2 at 484 and 527 nm, respectively,
which indicates the longer length of
p-conjugation. The emission
properties of M1eM2 are very similar to those of P1eP2, with the
emission maxima at 516 and 562 nm, respectively. The measured
photoluminescence lifetimes for these compounds are very short
(ca. 0.70e2.27 ns), characteristic of the spin-allowed singlet emis-
sion. These results and the small Stokes shift preclude the emitting
state as a triplet but a singlet excited state instead [32,49]. In
addition, the emission density of ligands, dimers and polymers
decreased gradually with the extended
p-conjugation length, as
deduced from the reduced quantum yield values. Therefore, it is
mostly an intramolecular charge transfer (ICT) excited state that
contributes to the effective photoinduced charge separation in
energy conversion for P1eP2 [36,49].
The highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) levels of stable P1eP2 were
determined from electrochemical measurements using cyclic vol-
tammetry. The experiments were performed by casting the poly-
mer films on the glassy-carbon working electrode with a Ag/AgCl
wire as the reference electrode, at a scan rate of 100 mV sꢁ1. The
solvent in all measurements was deoxygenated acetonitrile, and

H. Zhan et al. / Journal of Organometallic Chemistry 696 (2011) 4112e4120
4117
C6H13
Bu3Sn
CHO
CHO
Br
O
O
N
S
Br2, HBr
Et2O
N
N
Br
N
Pd(PPh3)4, toluene
S
S
S
S
NH2
S
Br
Br
CH3COOH, CH3CO2NH4
S
C6H13
C6H13
L1-HT
PITBr
Bu3Sn
Pd(PPh3)4, toluene
N
N
NBS
THF
NBS
THF
S
N
N
S
S
S
S
Br
Br
S
S
S
S
C6H13
C6H13
C6H13
C6H13
L1-Br
L2-T
K2CO3
N
Pd(OAc)2, PPh3, CuI
N
N
N
S
TMS
CH2Cl2, MeOH
TMS
S
S
CH2Cl2, NEt3
S
Br
m
TMS
Br
S
S
S
S
S
S
m
m
m
C6H13
C6H13
C6H13
C6H13
L1-Br m = 0
L2-Br m = 1
L1-TMS
L2-TMS
m = 0
m = 1
N
PBu3
Pt
N
S
S
S
S
S
m
m
n
C6H13
C6H13
PBu3
P1
P2
m = 0
m = 1
N
N
S
S
S
S
S
m
m
C6H13
C6H13
L1
L2
m = 0
m = 1
N
PEt3
Pt
PEt3
Pt
N
S
S
Ph
Ph
S
S
S
m
m
C6H13
C6H13
PEt3
PEt3
M1
m = 0
M2
m = 1
Scheme 1. Chemical structures and synthetic pathways of P1eP2 and M1eM2.

4118
H. Zhan et al. / Journal of Organometallic Chemistry 696 (2011) 4112e4120
Table 1
UV L2
UV M2 1.0
UV P2
PL L2
PL M2
PL P2
Absorption and emission data for diethynyl ligands L1eL2, model complexes
1.0
0.8
0.6
0.4
0.2
0.0
M1eM2 and polymers P1eP2.a
labs [nm] (
3
ꢂ 104 Mꢁ1 cmꢁ1
)
lemi [nm] (
s
F, ns)
FF (%)
0.8
0.6
0.4
0.2
0.0
L1
L2
M1
M2
P1
P2
259 (4.9), 396 (1.7)
259 (5.7), 424 (2.7)
260 (5.4), 449 (2.8)
260 (4.9), 449 (2.7)
259, 466
484 (0.70)
527 (1.18)
516 (1.18), 539 (1.11)
562 (0.99)
531 (0.92), 552 (2.09)
560 (2.27)
4.46
13.40
3.62
9.79
1.03
3.40
259, 459
a
All the photophysical data were measured in CH2Cl2 at 293 K; Quantum yields
were measured with an excitation wavelength of 420 nm using coumarin 6 in
ethanol as the reference (FF ¼ 0.78).
300
400
500
600
700
the supporting electrolyte was 0.1 M [nBu4N]BF4. The relevant data
are collected in Table 2. From the values of reduction potential
(Ered), the LUMO levels of P1eP2 were calculated according to the
following equations ELUMO ¼ ꢁ(Ered þ 4.72) eV (where the unit of
potential is V vs. Ag/AgCl) and EHOMO ¼ ꢁ(Eogpt ꢁ ELUMO) eV. Poly-
mers P1 and P2 show a quasi-reversible reduction wave at ꢁ0.81
and ꢁ0.87 V, respectively, which is attributed to the reduction of
the phenanthrenyl-imidazole moiety. The HOMO level of P2
is ꢁ6.13 eV, which is higher than that of P1 (ꢁ6.25 eV), and the
HOMO energy levels are elevated with the enhanced electron-
donating ability of the donor units.
Wavelength (nm)
Fig. 2. Normalized absorption and emission spectra of L2, M2 and P2 in CH2Cl2 at
293 K.
Table 2
Electrochemical data and photovoltaic performances for polymers P1eP2.a
Polymer
Eogpt
(eV)
Ered/ELUMO
(V)/(eV)
EHOMO
Voc
Jsc
FF
PCE
(%)
(eV)
(V)
(mA cmꢁ2
)
P1
P2
2.34
2.28
ꢁ0.81/ꢁ3.91
ꢁ0.87/ꢁ3.85
ꢁ6.25
ꢁ6.13
0.58
0.53
1.44
2.67
0.33
0.28
0.28
0.39
a
Eogpt ¼ 1240/lonset where lonset is the onset value of absorption spectrum in
CH2Cl2; ELUMO ¼ ꢁ(Ered þ 4.72) eV; EHOMO ¼ ꢁ(Eogpt ꢁ ELUMO) eV.
3.3. Polymer solar cell behavior
Since the generated excitons could readily dissociate into elec-
trons and holes and transfer from the electron-donating polymeric
main chain to the electron-withdrawing moieties in the side-chain-
tethered phenanthrenyl-imidazole conjugated polymers, which
favors the photocurrent generation and photoelectronic energy
conversion in photovoltaic devices, polymer solar cells were
fabricated by using P1 and P2 as the electron donor and PCBM as
the electron acceptor with a blend ratio of 1:4. The hole-collection
electrode consisted of indium tin oxide (ITO) with a spin-coated
0.53 V, a Jsc of 2.67 mA cmꢁ2 and an FF of 0.28, while the device
based on P2/PCBM (1:4) shows a PCE of 0.28% with a Voc of 0.58 V,
a Jsc of 1.44 mA cmꢁ2 and an FF of 0.33 under the same conditions,
mainly due to the higher Jsc for P2 which is almost double that of P1.
It is known that the ICT effect can be strengthened with the
enhancement of electron-donating ability of donor unit or
electron-withdrawing ability of acceptor [50,51]. Therefore, the
addition of thiophene unit in P2 could result in more rapid charge
transfer from the polymeric main chain to the electron-
withdrawing phenanthrenyl-imidazole-tethered side chains and
then to PCBM [23]. P2 has a relatively lower Voc than that of P1,
which is consistent with its higher HOMO energy value, because Voc
is linearly correlated with the difference of the HOMO energy level
of the donor and the LUMO energy level of the acceptor [52].
Among them, the FFs are relatively lower than those of higher
poly(3,4-ethylene-dioxythiophene)/poly(styrene
sulfonate)
(PEDOT/PSS) layer, whereas Al served as the electron-collecting
electrode. The current density (J) vs. voltage (V) curves of the
solar cells with the blend layer of P1/PCBM and P2/PCBM (1:4) are
shown in Fig. 3. The open-circuit voltage (Voc), short-circuit current
density (Jsc), fill factor (FF), and PCE of the devices are summarized
in Table 2.
The higher PCE of 0.39% for this type of polymers was obtained
by the device using P2/PCBM (1:4) as the active layer with a Voc of
1
0
UV L1
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
UV M1
UV P1
PL L1
PL M1
PL P1
-1
-2
P1 : PCBM (1:4)
P2 : PCBM (1:4)
-3
0.0
0.2
0.4
0.6
0.8
300
400
500
600
700
Voltage (V)
Wavelength (nm)
Fig. 1. Normalized absorption and emission spectra of L1, M1 and P1 in CH2Cl2 at
Fig. 3. JeV curves of solar cell devices with P1 and P2:PCBM (1:4) active layers under
293 K.
AM 1.5 G illumination.

H. Zhan et al. / Journal of Organometallic Chemistry 696 (2011) 4112e4120
4119
P2 devices reach 13% and 21% at an incident wavelength of 455 nm,
respectively.
0.4
0.3
0.2
0.1
0.0
P1 : PCBM (1:4)
P2 : PCBM (1:4)
4. Conclusions
In summary, two new DeA side-chain-tethered phenanthrenyl-
imidazole platinum(II) polyyne polymers were synthesized and
characterized. These polymers exhibit a narrow and strong band
around 260 nm and a broad lower energy absorption band in the
visible region. The optical band gaps range from 2.28 eV to 2.34 eV.
The incorporation of additional thiophene fragments into the
polymer chain improves the ICT effect in the DeA
p-conjugation
system, which results in higher Jsc, and thus improves the perfor-
mance of the resulting PSCs to 0.39%. One of the major limiting
parameters is presumably due to the restricted absorption prop-
erties in the visible region. Therefore, it is expected that a contin-
uous optimization of the chemical structures of polymer main
chain by incorporating some special functional chromophores with
stronger electron-donating ability than thiophene rings or the
phenanthrenyl-imidazole side chain modified by strong electron-
withdrawing groups such as F or CF3 would narrow the band
gaps and thus enhance the photovoltaic efficiency of this kind of
metallopolymers.
400
500
600
Wavelength (nm)
700
Fig. 4. Absorption spectra for solar cell devices based on P1 and P2:PCBM (1:4) blends.
performance polymers reported before, partly due to the fact that
all processing (except PEDOT:PSS annealing and electrode deposi-
tion) and measurements have been done in ambient atmosphere
which likely results in the presence of traps. So, we expect FF to
improve for fabrication and characterization to be performed in an
inert gas environment. Comprehensive study of charge transport
and the influence of traps is necessary to further improve FF and
overall device performance. It is worth mentioning that the
photovoltaic efficiency of P1 device was improved to 0.79% when
PC70BM was used as the electron acceptor to optimize the device,
which represents a two-fold increase than that of the P1/PCBM
device.
The absorption spectra of P1:PCBM and P2:PCBM (1:4) blend
films prepared under the same conditions are shown in Fig. 4, and
the EQE curves for these devices are depicted in Fig. 5. The shapes of
EQE curves of these polymers are similar to their corresponding
UV/vis absorption spectra, illustrating that all the light energy
absorbed by the polymer/PCBM blend film is to some extent con-
verted into electricity. The blend films only have relatively strong
absorption between 400 and 535 nm mainly arising from the
organometallic polymers. The limited absorption results in the low
PCE for this kind of polymers. The maximum EQE values for P1 and
Acknowledgements
This work was supported by the University Grants Committee
Areas of Excellence Scheme (AoE/P-03/08), the Faculty Research
Grant from Hong Kong Baptist University (FRG2/09-10/091), the
General Research Fund (HKBU202607) as well as the Collaborative
Research Fund (HKUST2/CRF/10) from the Hong Kong Research
Grants Council. This work was also partly supported by Strategic
Research Theme and University Development Fund of the Univer-
sity of Hong Kong.
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