Near-infrared emitting pyrazole-bridged binuclear platinum complexes: Synthesis, photophysical and electroluminescent properties in PLEDs

Article abstract of DOI:10.1016/j.dyepig.2016.01.014

Two novel near-infrared emitting binuclear platinum (II) complexes were successfully designed and synthesized with the bridged ancillary ligand of 3,5-dimethyl pyrazol, in which 2-(pyren-1-yl) pyridine and its derivative of 2-(7-(tert-butyl)pyren-1-yl)pyridine were used as cyclometalated ligands, respectively. Their photophysical, thermal, electrochemical, as well as electro-luminescent properties were investigated. The intrinsic near-infrared electro-luminescent spectra peaked at 692 nm with a shoulder at 753 nm was observed in the single-emissive-layer polymer light-emitting diodes using both binuclear platinum (II) complexes as the dopant. The tert-butyl group attached in pyrenyl ring was found to play an important role in improving electroluminescent properties. Better electroluminescent properties were obtained for the platinum complex with 2-(7-(tert-butyl)pyren-1-yl)pyridine in the devices with a maximum external quantum efficiency of 0.15% and a radiant intensity of 19.10 μW cm^-2. To our best knowledge, this is a first reported example on the near-infrared electroluminescence of binuclear platinum complex containing pyrazoline auxiliary ligand.

Full text of DOI:10.1016/j.dyepig.2016.01.014

Accepted Manuscript
Near-Infrared Emitting Pyrazole-Bridged Binuclear Platinum Complexes: Synthesis,
Photophysical and Electroluminescent Properties in PLEDs
Ning Su, Fanyuan Meng, Jianhua Chen, Yafei Wang, Hua Tan, Shijian Su, Weiguo
Zhu
PII:
S0143-7208(16)00025-5
10.1016/j.dyepig.2016.01.014
DYPI 5067
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 20 November 2015
Revised Date: 9 January 2016
Accepted Date: 13 January 2016
Please cite this article as: Su N, Meng F, Chen J, Wang Y, Tan H, Su S, Zhu W, Near-Infrared Emitting
Pyrazole-Bridged Binuclear Platinum Complexes: Synthesis, Photophysical and Electroluminescent
Properties in PLEDs, Dyes and Pigments (2016), doi: 10.1016/j.dyepig.2016.01.014.
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ACCEPTED MANUSCRIPT
Table of Contents
Two novel near-infrared emitting binuclear platinum (II) complexes of
(pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2 were synthesized. The intrin
-sic dual electroluminescent peaks at 692 nm and 753 nm were observed
in their single-emissive-layer doped PLEDs.

ACCEPTED MANUSCRIPT
Near-Infrared Emitting Pyrazole-Bridged Binuclear Platinum
Complexes: Synthesis, Photophysical and Electroluminescent
Properties in PLEDs
Ning Su†, Fanyuan Meng†,‡, Jianhua Chen†, Yafei Wang†*, Hua Tan†,
Shijian Su‡,*, Weiguo Zhu†,*
†College of Chemistry, Key Lab of Environment-Friendly Chemistry and Application in the
Ministry of Education, Xiangtan University, Xiangtan 411105, People’s Republic of China
††Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of
Luminescent Materials and Devices, South China University of Technology, Guangzhou
510640, People’s Republic of China
*To whom correspondence should be addressed:
(W. Z.) zhuwg18@126.com
(S. S.) mssjsu@scut.edu.cn
(Y. W.) wangyf_miracle@hotmail.com
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Abstract: Two novel near-infrared emitting binuclear platinum (II) complexes
were successfully designed and synthesized with the bridged ancillary ligand of
3,5-dimethyl pyrazol, in which 2-(pyren-1-yl) pyridine and its derivative of
2-(7-(tert-butyl)pyren-1-yl)pyridine were used as cyclometalated ligands,
respectively. Their photophysical, thermal, electrochemical, as well as electro-
luminescent properties were investigated. The intrinsic near-infrared electro-
luminescent spectra peaked at 692 nm with a shoulder at 753 nm were observed
in the single-emissive-layer polymer light-emitting diodes using both binuclear
platinum (II) complexes as the dopant. The tert-butyl group attached in pyrenyl
ring was found to play an important role in improving electroluminescent
properties. Better electroluminescent properties were obtained for the platinum
complex with 2-(7-(tert-butyl)pyren-1-yl)pyridine in the devices with a maxi-
mum external quantum efficiency of 0.15% and a radiant intensity of 19.10
ꢀW.cm-2. To our best knowledge, this is a first reported example on the near-
infrared electroluminescence of binuclear platinum complex containing pyrazo-
line auxiliary ligand.
Key Words: Binuclear platinum (II) complex; Near-infrared emission; Electro-
luminescenceꢀPolymer light-emitting diodes
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1.Introduction
Over the last two decades, platinum (II) complexes have achieved huge
success in polymer/organic light-emitting diodes (PLEDs/OLEDs) due to their
100 % internal quantum efficiency and various excited states [1-7]. The strong
metal-to-ligand charge transfer (MLCT) and metal-metal-to-ligand charge
transfer (MMLCT) effect, as well as intermolecular interaction make these plati
-num (II) complexes achieve significantly red-shifted long wavelength emi-
ssion, which is of considerable interest for using as near-infrared (NIR) emit-
ing organic materials, potentially applied in bio-imaging [8-10], telecommu-
nication [11-13], and the dissolved oxygen sensor for microbioreactors [14],
especially in displays [15,16].
To date, several strategies to develop NIR emitting platinum complexes, such
as expanding π-conjugation system and featuring with donor-acceptor (D-A)
framework, have been demonstrated. For instance, Reynolds and his coworkers
reported a series of π-extended mononuclear platinum (II) porphyrins with
photoluminescent (PL) peaks ranging from 773 to 1022 nm [17]. The highest
external quantum efficiency (EQE) of 9.2% with the maximum emission peak
at 773 nm was observed in the vapor-deposited multilayer OLEDs [18].
However, the preparation of the expanded π-conjugation compounds is very
complicated. Furthermore, the devices based on these planar platinum (II)
porphyrins showed a serious efficiency roll-off. Considering that the intense
intramolecular charge transfer (ICT) can provide remarkably red-shifted
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emission in the D-A type fluorophors, we developed one D-A-A mononuclear
platinum (II) complex bearing triphenylamine, benzothiadiazole and pyridine
units, which displayed a NIR emission at 769 nm [19]. Although this mono-
nuclear platinum (II) complex achieved NIR emissions through enhanced ICT
effect, the device performance still has some space to be improved for their
practical application.
Recently, utilization of intense MMLCT transition from platinum complexes
was proved to be an effective strategy to realize NIR emission materials
[20-23]. To this end, we reported a binuclear platinum (II) complex of (piq)2-
Pt2(µ-C8OXT)2 consisting of 1-phenyl-isoquinoline (piq) cyclometalated ligand
and 5-(4-octyloxyphenyl)-1,3,4-oxadiazole-2-thiolate (C8OXT) auxiliary ligand
[24]. This binuclear platinum complex presented an EL emission at 702 nm
with an EQE of 6.3% in the single-emissive-layer (SEL) PLEDs. However, it is
unclear how to effectively construct Pt-Pt band and precisely control the Pt-Pt
distance to achieve the MMLCT transition in these binuclear cyclometalated
platinum (II) complexes.
Inspired by the intriguing photo-induced structural change leading to MM-
LCT transition in the pyrazolate-bridged binuclear cyclometalated platinum (II)
complexes [25-26], it is expected this class of binuclear platinum (II) complex-
es could achieve NIR emission by enlarging cyclometalated ligand structure. In
order to realize this assumption and further make clear the structure-property
relationship of these pyrazolate-bridged binuclear platinum (II) complexes,
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herein, we devoted our efforts to design novel NIR emission materials based on
binuclear cyclometalated platinum (II) complexes containing 3,5-dimethyl-1H-
pyrazol (dmpz). In this contribution, two novel pyrazolate bridged binuclear
cyclometalated platinum (II) complexes of (pypy)2Pt2(dmpz)2 and (tBupypy)2
-Pt2(dmpz)2 were synthesized, in which 2-(pyren-1-yl) pyridine (pypy) and its
tert-butyl derivative (tBupypy) were used as cyclometalated ligands, respective
-ly. Their optical, electrochemical and EL properties were primary investigated.
Isolated dual emissions at about 500 nm and 690 nm were observed for two
binuclear platinum complexes in both dichloromethane solution and solid state.
Employing these binuclear platinum complexes as the dopant, the single-
emissive-layer PLEDs show the stable NIR emission with a peak at 692 nm and
a shoulder at 753 nm at various doping concentrations from 2 wt%, 4 wt% to 8
wt%. The (tBupypy)2Pt2(dmpz)2-based PLEDs possess a better device
performance with the maximum EQE of 0.15% and a radiant intensity of 19.10
ꢀWcm-2. To our best knowledge, this is the first report on the NIR PLEDs
based on the pyrazolate-bridged binuclear platinum (II) complexes.
Experiments
2.1 Methods
All solvents were carefully dried and distilled prior to use. Commercially
available reagents were used without further purification unless otherwise
stated. All reactions were performed under nitrogen atmosphere and were
monitored by thin-layer chromatography. 1H NMR spectra were recorded on a
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Bruker Avance-400 spectrometer at 400 MHz using CDCl3 as solvent and
tetramethylsilane (TMS) as the internal standard unless specified otherwise.
Mass spectra were measured on a Bruker Daltonics BIFL-EX Ш MALDI-TOF
analyzer under MALDI mode. The UV/vis absorption and PL spectra were
measured with a Varian Cray 50 and Perkin-Elmer LS50B luminescence
spectrometer, respectively. The equation of Φs = Φr(ɳs2ArIs/ɳr2AsIr) was used to
calculate the fluorescence quantum yield (Φ) of the binuclear platinum
complex using complex Ru(bpy)3 as the standard compound in N2 atmosphere,
where Φs is the quantum yield of the sample, Φr is the quantum yield of the
reference, ɳ is the refractive index of the solvent, As and Ar are the absorbance
of the sample and the reference at the wavelength of excitation, and Is and Ir are
the integrated areas of emission bands [27]. Fluorescence decay curves were
obtained on FLS920 with time-corrected single-photon-counting (TCSPC)
measurement. The thermogravimetric analysis (TGA) was performed with a
NETZSCH STA449 apparatus from 25 to 600 oC at a heating rate of 10 oC/min
under nitrogen atmosphere. Cyclic voltammetry measurement was conducted
on a CHI620 voltammetric analyzer under argon atmosphere in an anhydrous
acetonitrile solution of tetra(n-butyl) ammonium hexafluorophosphate (BuN4-
PF6, 0.1 M) at a scan rate of 20 mV/s. The platinum plate, platinum wire and
Ag/AgCl electrode were used as working electrode, counter electrode, refe-
rence electrode, respectively. Binuclear platinum complexes were coated on the
surface of platinum plate and all potentials were corrected against ferrocene/
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ferrocenium (Fc/Fc+).
2.2 Device fabrication and characterization
(pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2 were dissolved in chloroben-
zene with a concentration of 5mg/mL at room temperature overnight. Firstly,
poly(ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) was spin-
coated on indium tin oxide (ITO) at 3000 rpm in N2 atmosphere. Then the
emissive layer consisting of polyvinylcarbazole (PVK) and 1,3-bis(5-(4-(tert-
butyl)phenyl)-1,3,4-oxadiazol-2-yl)benzene (OXD-7) was prepared by spin-
coating at 1500 rpm in N2 atmosphere. Finally, 4 nm cathode of Ba and 100 nm
capping layer of Al were successively deposited on the top of emissive layer
through a shadow mask in vacuum. The device structure is ITO/ PEDOT: PSS
(40 nm)/ binuclear platinum complex (x%) + PVK:OXD-7 (50 nm)/ Ba (4 nm)/
Al (100 nm). The doping concentrations of binuclear platinum complexes were
2 wt%, 4 wt% and 8 wt% in the emissive layer, respectively. The ratio of PVK
and OXD-7 was 7:3 in weight. The EL spectra were recorded on miniature
fiberoptic spectrometer (USB 2000, Ocean Optics). The current density-
voltage-radiant emittance (J−V−R) characteristics were recorded on a Keithley
236 source measurement unit and a calibrated silicon photodiode. And EQE
values were calculated based on the reported procedure [28].
2.4 Synthesis of (pypy)2Pt2(dmpz)2
To a suspension of K2PtCl4 (446 mg, 1.08 mmol) in 2-ethoxyethanol (15mL)
and water (5 mL), compound 3a (pypy) (600 mg, 2.15 mmol) were added under
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N2 atmosphere. The mixture was stirred at 80 oC for 24 h. After cooled to room
temperature (RT), the mixture was poured into water (50 mL) and the precipi-
tate was collected and washed with water (2×10 mL). The crude precipitate
was dried in vacuum for 2 h to give chloro-bridged dimmer as dark yellow
solid (750 mg). This dimmer was directly used to next step without any further
purification.
A mixture of chloro-bridged dimmer (750 mg, 0.67 mmol), 3,5-dimethyl-
pyrazole (dmpz) (128 mg, 1.33 mmol) and CH3ONa (362 mg, 6.7 mmol) in
o
dichloromethane (DCM) was stirred at 60 C for 48 h under N2 atmosphere.
After cooled to RT, the suspension was distilled to remove solvent under reduc-
ed pressure. The crude was purified through a flash silica gel column using
petroleum ether (PE)/DCM (V/V = 2/1) as the eluent to give (pypy)2Pt2(dmpz)2
1
as light yellow solid in a yield of 34%. H NMR (400 MHz, CDCl3) δ ppm:
8.71 (d, J = 1.5 Hz, 2H), 8.60 (d, J = 7.6 Hz, 2H), 8.25 (d, J = 6.3 Hz, 2H),
8.09-7.99 (m, 6H), 7.96-7.89 (m, 6H), 7.84 (s, 2H), 7.74 (s, 2H), 6.97 (s, 2H),
6.13 (s, 2H), 2.47 (s, 6H), 2.24 (d, J = 14.6 Hz, 6H). MALDI-MS (m/z) for
C52H38N6Pt2: calcd. 1137.25; found, 1136.317.
2.5 Synthesis of (tBupypy)2Pt2(dmpz)2
(tBupypy)2Pt2(dmpz)2 was synthesized according to the above synthetic
1
procedure of (pypy)2Pt2 (dmpz)2 as dark yellow solid with a yield of 30%. H
NMR (400 MHz, CDCl3) δ ppm: 8.70 (d, J = 3.7 Hz, 2H), 8.61 (d, J = 9.1 Hz,
2H), 8.28 (d, J = 7.7 Hz, 2H), 8.11 (s, 4H), 8.02 (d, J = 9.2 Hz, 2H), 7.93 (d, J
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= 8.8 Hz, 2H), 7.87 (d, J = 8.8 Hz, 2H), 7.80 (s, 2H), 7.78-7.71 (m, 2H), 6.97 (s,
2H), 6.12 (s, 2H), 2.46 (s, 6H), 2.25 (s, 6H), 1.55(s, 18H). MALDI-MS (m/z)
for C60H54N6Pt2: calcd. 1248.37; found, 1248.458.
3. Results and discussion
.
3.1. Synthesis and characterization
The synthetic route of both binuclear platinum complexes is depicted in
Scheme 1. Compound 2 was prepared based on the reported procedure [29].
Suzuki coupling reaction between compound 2 and 2-bromopyridine afforded
t
the cyclometalated ligand 3 (pypy or Bupypy) in the presence of Pd(PPh3)4 in
78% yield. The pyrazolate-bridged binuclear platinum complexes of (pypy)2Pt2
-(dmpz)2 and (tBupypy)2Pt2(dmpz)2 were prepared by a successive two-step
reactions according to the previous reports [23, 30]. The target binuclear plati-
1
num (II) complexes were confirmed with H NMR and MALDI-TOF mass
spectrometry (see ESI).
3.2 Photophysical properties
The UV/vis absorption spectra of (pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2-
(dmpz)2 in DCM solution (10-5 M) at room temperature are shown in Fig. 1.
Similar absorption spectra with two resolved absorption bands are displayed in
the range of 250-500 nm. The high-energy absorption bands at about 286 nm
with an extinction coefficient (ε) of 4.2×105 M-1cm-1 is definitely ascribed to the
spin-allowed ligand-central (1LC) π-π* transition [31]. On the basis of assign-
ments in analogous molecules [25-26], the low-energy absorption bands at
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about 413 nm (2.0×105 M-1cm-1) can be attributed to the spin-allowed intra-
1
ligand (1IL) transition and MLCT transition, to some extend MMLCT transi-
tionꢁwhich were found in those absorption profiles for the mononuclear
platinum (II) complex containing 2-(pyren-1-yl)pyridine ligand [31] and the
butterfly-like binuclear platinum (II) complexes bearing pyrazolate ligands [32].
Compared to the pyrazolate-bridged binuclear platinum complex bearing
difluorophenyl pyridine, both binuclear platinum complexes here show signi-
ficantly red-shifted absorption [33]. In addition, (pypy)2Pt2(dmpz)2 and
(tBupypy)2Pt2(dmpz)2 further exhibit the red-shifted absorption spectra in neat
films instead of in DCM, implying that a stronger intermolecular interaction
exist in neat film (Fig. S1, ESI).
Fig. 2a shows the PL spectra of both binuclear platinum complexes in DCM
(10-5 M) under the excitation wavelength of 410 nm. The relevant data are
summarized in Table 1. Both binuclear platinum complexes exhibit clearly dual
emission at 480 nm and 690 nm in solution under N2 atmosphere. Based on
Maʹs reports, we assumed that the higher energy band is attributed to a singlet
3
1LC excited state, while the lower energy band is assigned to the MLCT
3
excited state with a little contribution of the MMLCT excited state to some
extent [32-33]. In order to further demonstrate this assumption, we measured
the PL emission at the same concentration in the air. The lower energy emission
is obviously quenched by oxygen, which indicates that the emission at 690 nm
origins from triplet excited state. Furthermore, significantly different emission
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lifetimes between 480 nm (ca. 4.40 ns and 5.78 ns) and 690 nm (ca. 3.47 ꢀs and
3.84 ꢀs) also confirmed the different excited state for the PL spectra of
(pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2. Using Ru(bpy)3 as the standard
compound, (pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2 show a fluorescence
quantum yield of 2.58% and 5.90% in degassed DCM, respectively. In order to
explore the effect of different solvent on the PL emission, we measured the PL
spectra for (pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2 in different solvents,
which are showed in Fig. S2 (see ESI) together with the PL profiles of the pypy
t
and Bupypy ligands in DCM. Similar PL profiles with a little blue shift are
observed in different solvents with the increasing polarity for both platinum
complexes. Fig. 2b further shows their PL spectra in a solid-state polystyrene
(PS) matrix. In contrast to the PL profiles in DCM solutions, remarkably
red-shift dual emissions centered at 527 nm and 687 nm with a shoulder at 717
nm are exhibited in the PS matrix. This result suggests that expanding
π-conjugation for cyclometalated ligands can result in dual emission of their
dinuclear platinum complexes in solution and solid state.
3.3 Thermal property
TGA measurement was carried out to evaluate the thermal properties of
binuclear platinum complexes. The recorded TGA curve is shown in Fig. S3
o
o
(see ESI). The decomposition temperatures (Td) of 318 C and 277 C are
observed for (pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2 at 5% weight loss,
respectively. The grafted tert-butyl in pyrenyl moiety has a little negative effect
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on the thermal stability of its binuclear platinum complex.
3.4. Electrochemical property
The CV curve is recorded in Fig. S4. The corresponding data are collected in
Table 2. The irreversible onset oxidation potentials (Eox) of (pypy)2Pt2(dmpz)2
and (tBupypy)2Pt2(dmpz)2 are observed at 0.27 V and 0.23 V vs Fc/Fc+. The
highest occupied molecular orbit (HOMO) energy levels (EHOMO) can be
calculated according to the following equation: EHOMO = -(Eox + 4.8) eV [34].
As a calculated result, the EHOMO values are -5.07 eV and -5.03 eV for
(pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2, respectively. Based on their
opt
corresponding optical energy gaps (Eg ) and EHOMO levels [35], the lowest
unoccupied molecular orbital (LUMO) energy levels (ELUMO) are estimated to
be -2.63 eV for (pypy)2Pt2(dmpz)2 and -2.61 eV for (tBupypy)2Pt2(dmpz)2. It
indicates that the grafted tert-butyl has a little influence on electrochemical
properties in the binuclear platinum complexes.
3.5 Electroluminescent property
Fig. 4 shows the EL spectra of the binuclear platinum complexes-based
devices at the dopant concentrations of 2 wt%, 4 wt% and 8 wt%, respectively.
Almost identified EL spectra are observed for both devices at the same dopant
concentrations. Three isolated emission peaks located at 692 nm, 753 nm and
445 nm were detected. Compared to the PL spectrum of PVK/OXD-7(7:3) as
shown in Fig. S5, the higher energy emission comes from host matrix of PVK/
OXD-7 and the lower energy emission is assigned to platinum complex [36].
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Therefore, the EL emission here is dominated by MMLCT transition. As
increasing the dopant concentrations from 2 wt%, 4 wt% to 8 wt%, the emi-
ssive intensity at about 445 nm is remarkably decreased and up to disappeared,
which demonstrates that the energy transfer from host matrix to dopant is
complete in the device at high dopant concentration. Additionally, it is worth
noted that the tert-butyl substituent plays a positive effect on the energy
transfer from host matrix to guest. Fig. 5 shows the EQE curves of the (pypy)2-
Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2-based devices at different dopant concen-
trations. It is found that the (pypy)2Pt2(dmpz)2-based devices exhibit a decreas-
ed EL efficiency with increasing dopant concentrations from 2 wt% to 8 wt%.
In contrast, the (tBupypy)2Pt2(dmpz)2-based devices display an increased EL
efficiency. This result also confirmed that the bulky steric hindrance of bulky
group has a crucial role on the inhibition of concentration quenching in device.
The highest EQE values of 0.11% and 0.15 % are obtained in the (pypy)2Pt2-
(dmpz)2- and (tBupypy)2Pt2(dmpz)2-based devices, respectively. The current
density-voltage-radiant intensity (J-V-R) characteristics of these devices are
depicted in Fig. 6, and the data are listed in Table 3. The applied voltages and
log functions of current densities exhibit linear relationship while the applied
voltages exceed threshold voltage value [37]. Furthermore, the maximum
radiant intensity of 16.65 and 19.10 ꢀW.cm-2 are obtained in the (pypy)2Pt2-
(dmpz)2- and (tBupypy)2Pt2(dmpz)2-based devices, respectively.
Conclusions
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In summary, two novel 3,5-dimethylpyrazole-bridged binuclear platinum
complexes of (pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2 were obtained and
characterized. Both binuclear platinum complexes showed similar UV-vis
absorption and PL spectra, as well as the analogical electrochemical properties.
Expanded π-conjugation in cyclometalated ligand can control the dual emission
of its platinum complexes in solution and solid state. Furthermore, almost the
same NIR EL profiles peaked at 692 nm with a shoulder at 753 nm were
observed in the PLEDs using both binuclear platinum complexes as the dopant,
respectively. Significantly improved EL properties were obtained in the
(tBupypy)2Pt2(dmpz)2-doped devices with a EQE of 0.15% and a radiant
intensity of 19.10 ꢀW.cm-2. This work proves an efficient strategy for binuclear
platinum complexes to give the NIR EL emission by MMLCT effect in PLEDs.
Acknowledgments
Thanks to the financial supports from the National Natural Science Founda-
tion of China (51473140, 21202139, 51273168), the Program for Innovative
Research Cultivation Team in University of Ministry of Education of China
(1337304), the Innovation Group in Hunan Natural Science Foundation
(12JJ7002), Natural Science Foundation of Hunan (2015JJ2139, 12JJ4019), the
Scientific Research Fund of Hunan Provincial Education Department (12B123,
11CY023), the Scientific Research Fund of Xiangtan University (11QDZ18,
2011XZX08).
Appendix A. Supplementary material
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Supplementary data related to this article can be found at ------.
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Captions of Figures
Scheme 1. Synthetic route of (pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2.
Fig. 1. UV/vis absorption spectra of (pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2 in dilute
DCM (10-5 M) at room temperature.
Fig. 2. PL spectra of (pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2 in dilute DCM solution
(10-5 M) (a) and in the polystyrene film (b) at room temperature.
Fig. 3. Fluorescence decay curves of (pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2 in dilute
DCM (10-5 M) monitored at wavelength of 480 nm and 690 nm in N2 atmosphere.
Fig. 4. EL spectra of the (pypy)2Pt2(dmpz)2- and (tBupypy)2Pt2(dmpz)2-based devices at
different dopant concentrations from 2 wt% to 8 wt%.
Fig. 5. EQE curves of the (pypy)2Pt2(dmpz)2- and (tBupypy)2Pt2(dmpz)2-based devices at
different dopant concentrations from 2 wt% to 8 wt%.
Fig. 6. J-V-R profiles of the (pypy)2Pt2(dmpz)2- and (tBupypy)2Pt2(dmpz)2-based devices at
different dopant concentrations from 2 wt% to 8 wt%.
Table 1. Photophysical, excited state decay and thermal data of (pypy)2Pt2(dmpz)2 and
(tBupypy)2Pt2(dmpz)2.
Table 2. Electrochemical data of (pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2.
Table 3. EL, J-V-R and EQE data of (pypy)2Pt2(dmpz)2 and (tBupypy)2Pt2(dmpz)2.
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Scheme 1
Fig. 1
Fig. 2
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Fig. 3
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Fig. 4
Fig. 5
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Fig. 6
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Table 1
λab /nma
( ε /105 M-1 cm-1) (nm)b (nm)a (nm)c
λab
λPL
λPL
Φd
τe
Td
Complexes
(oC)
318
(pypy)2Pt2(dmpz)2
286 (4.20),
370 (1.44),
410 (1.87)
286 (3.65),
371 (1.19),
413 (1.56)
289
423
480
577
690
480
614
690
526
686
715
526
687
717
2.58%
4.40 ns
3.47 ꢀs
289
425
5.90%
5.78 ns
277
t
( Bupypy)2Pt2(dmpz)2
3.84 ꢀs
c
a Measured in dilute DCM (10-5 M) at room temperature. b Measured in neat film at room temperature.
Measured in polystyrene(PS) film. d Measured in dilute DCM (10-5 M) in N2 atmosphere according to the
e
equation of Φs=Φr(ɳs2ArIs/ɳr2AsIr). Measured in dilute DCM (10-5 M) in N2 atmosphere at wavelength of 480
nm and 690 nm, respectively.
Table 2
Complexes
Eox(V)a
0.27
Egopt (eV)b
2.44
EHOMO (eV)c
-5.07
ELOMO (eV)d
-2.63
(pypy)2Pt2(dmpz)2
(tBupypy)2Pt2(dmpz)2
0.23
2.42
-5.03
-2.61
a The potential of Fc/Fc+ vs Ag/AgCl electrode was measured to be 0.42 V. b Calculated
opt
from the absorption band edge of the films, Eg = 1240/λedge. c Calculated from empirical
equation: EHOMO = -(Eox + 4.8)eV. d Calculated from ELUMO = Egopt + EHOMO.
Table 3
Complexes
Ratio
Vth
(V)
Rmax
(µW.cm-2)
16.65
PLQY
(%)a
0.1
EQEmax
(%)
(%)
2
9.23
10.52
10.31
7.93
8.80
8.10
0.11
0.09
0.07
0.13
0.15
0.14
(pypy)2Pt2(dmpz)2
4
12.38
0.6
8
12.24
0.4
(tBupypy)2Pt2(dmpz)2
2
12.74
0.1
4
12.48
0.8
8
19.10
0.9
aAbsolute quantum yield measured in a PVK/OXD-7(70:30) film.
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Highlights
ꢀ Two pyrazolate-bridged based binuclear platinum complexes are
prepared.
ꢀ Both platinum complexes show a dual emission at 480 and 690 nm in
solution and thin film.
ꢀ NIR emission peak at 692 nm with a shoulder at 753 nm is observed in
the platinum complexes-doped PLEDs.
ꢀ The maximum EQE of 0.15% and a radiant intensity of 19.10 µWcm-2
are obtained in their doped PLEDs.