More efficient spin-orbit coupling: Adjusting the ligand field strength to the second metal ion in asymmetric binuclear platinum(ii) configurations

Article abstract of DOI:10.1039/d0dt00939c

Two types of asymmetric binuclear platinum(ii) complexes (Pt-1 and Pt-3) bearing bridging ligands of 2-(2,4-difluorophenyl)-5-(pyridin-2-yl)pyridine and 2-(2,4-difluorophenyl)-4-(pyridin-2-yl)pyridine as well as their corresponding mononuclear counterparts (Pt-2, Pt-4, and Pt-5) were synthesized and characterized. Different chelating constructions of the second platinum(ii) ions and the bridging ligands in Pt-1 and Pt-3 gave rise to two kinds of electron-transition pathway during their photophysical processes. The meta-/para-carbon of nitrogen on the center pyridyl segments set different levels of ligand field strength to the second platinum(ii) ions, lowering their occupied d orbital to varying degrees. Pt-1 showed an enhanced spin-orbit coupling (SOC), caused by the additional metal component through direct orbital hybridization at higher states, where the fixed molecular skeleton induced by the additional metal-ligand bonding also helped to suppress molecular distortion in the excited state, ensuring a high quantum yield (Φ, 0.89 in toluene), which is among the best results in bimetallic complexes. While the second platinum(ii) ion in Pt-3 seemed to make no contribution to the radiative transition, and only contributed to the HOMO, it provided a benefit by enlarging the conjugate system. Solution-processed organic lighting emitting devices (OLEDs) fabricated with the bimetallic Pt-1 emitter achieved superior efficiencies and up to 21percent external quantum efficiency (EQE) in the Kelly-green region. This journal is

Full text of DOI:10.1039/d0dt00939c

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DOI: 10.1039/D0DT00939C
More Efficient Spin-Orbit Coupling: Adjusting Ligand Field
Strength to the Second Metal Ion in Asymmetric Binuclear
Platinum(II) Configurations
Zhaoran Hao,b Kai Zhang,a Kuan Chen,c Pu Wang,b Zhiyun Lu,c*
Weiguo Zhu, a* and Yu Liua,b*
a
School of Materials Science and Engineering, Jiangsu Collaboration Innovation
Center of Photovoltaic Science and Engineering, Jiangsu Engineering Laboratory
of Light-Electricity-Heat Energy-Converting Materials and Applications, National
Experimental Demonstration Center for Materials Science and Engineering,
Changzhou University, Changzhou 213164, China.
b
College of Chemistry, Key Lab of Environment-Friendly Chemistry and
Application in Ministry of Education, Xiangtan University, Xiangtan 411105,
China.
c
Key Laboratory of Green Chemistry and Technology of Ministry of Education,
College of Chemistry, and State Key Laboratory of Polymer Materials Engineering,
Sichuan University, Chengdu 610065, China.
Email:
(Y. L.) liuyu03b@126.com，
(G. Z.) zhuwg18@126.com,
(Z. L.) luzhiyun@scu.edu.cn

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ABSTRACT: Two types of asymmetric binuclear platinum(II) complexes (DPOtI-:110.a10n3d9/D0DT00939C
Pt-3) bearing bridging ligands of 2-(2,4-difluorophenyl)-5-(pyridin-2-yl)pyridine and
2-(2,4-difluorophenyl)-4-(pyridin-2-yl)pyridine as well as their corresponding
mononuclear counterparts (Pt-2, Pt-4, and Pt-5) were synthesized and characterized.
Different chelating constructions of the second platinum(II) ions and the bridging
ligands in Pt-1 and Pt-3 gave rise to two kinds of electron transition pathway during
their photophysical processes. The meta-/para- carbon of nitrogen on the center
pyridyl segments set different levels of ligand field strength to the second platinum(II)
ions, lowering their occupied d orbital to varying degrees. Pt-1 showed an enhanced
spin-orbit coupling (SOC) that caused by the additional metal component through
direct orbital hybridization at higher states, a fixed molecular skeleton induced by the
additional metal-ligand bonding also helped to suppress molecular distortion in
excited state, ensured its high quantum yield (Φ, 0.89 in toluene) represented among
the best results in bimetallic complexes. While the second platinum(II) ion in Pt-3
seemed had no contribution to the radiative transition, only contributed to HOMO and
benefit to an enlarged conjugate system. Solution processed organic lighting emitting
devices (OLEDs) fabricated with bimetallic Pt-1 emitter achieved superior
efficiencies and up to 21% external quantum efficiency (EQE) in the kelly-green
region.
KEYWORDS: Binuclear platinum(II) complexes; Asymmetric bridging ligand;
Ligand field strength; Spin-orbit coupling; OLEDs

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INTRODUCTION
Bimetallic complexes here refer to those homo-/hetero- multinuclear metal complexes
with their unique bridging ligands possessing two coordination sites, which usually
possess a ‘one-ligand-two-metal’ configuration.1-18 Different from many other
bimetallic complexes with two metal ions close to each other and possessing
metal-metal-to-ligand charge transfer (MMLCT) characteristics,19-21 this kind of
complexes don’t have direct d-d orbital hybridization, only have electron interaction
with the bridging ligands of their each metal component, so that always resemble
photophysical features of the corresponding mononuclear counterparts. For this kind
of complexes usually have following features: 1) Enhanced SOC characteristics
formed by the increased metal component with redshift absorption/emission1-10 or
similar spectra profiles.11 2) Possessing multiple thermal equilibrated/non-equilibrated
triplet states formed by two metal centres and resulting in dual emission or have
12-15
features of the corresponding lower-lying energy monomer;
just as two
independent existence in a dendritic structure.16-18 For the second type,12-18 two metal
ions are usually separated by a relatively remote distance, each unit is largely
unperturbed by the bridging ligand, hence each ‘metal-ligand’ component can be seen
as an individual portion. However, for the first type,1-11 two metal ions are mostly
incorporated to the same aromatic ring, forming a construction that permit electron
delocalization occurred on both the bridging ligand and two metal ions
simultaneously, which means that two metal centres should be considered as a whole.
Consequently, this type of complexes can take full advantage of the hybridization

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between the bridging ligand and greater metal components, forming a more accessible
triplet state with enhanced SOC characteristics, and usually possessing much higher Φ
values when compared with their mononuclear counterparts. Since the additional
metal ion can always raise complexes’ highest occupied molecular orbital (HOMO)
and lower their lowest unoccupied molecular orbital (LUMO) levels via the additional
incorporated dπ orbital,1-10 these types of complexes are especially favored by the
lower energy labeled red/near-infrared emitters. For example, some recently emerging
binuclear platinum(II),3 iridium(III),6,7 and copper(I)22 complexes of this type of
materials had achieved high EQEs above 10%.
However, the fact of the consistent red-shift emission induced by the second
metal ion of these bimetallic complexes hasn’t been yet explained clearly, and most
studies ascribed that to an extension of conjugation, intuitively.1-10 Besides, all the
mentioned bimetallic complexes possessed symmetric molecular configurations and
had their two metal ions placed in similar surroundings, which is a structure limitation
to fully understand this type of complexes. To further to investigate the photophysical
mechanism of that, recently, we synthesized a new type of bimetallic platinum(II)
complex (BuPyrDPy)[Pt(dpm)]2 with an asymmetric donor–acceptor–acceptor (D–A–
A) bridging ligand framework,11 which enable its two metal ions placed in different
surroundings. Interestingly, this unique bimetallic complex had nearly consistent
photophysical profiles to its corresponding mononuclear counterpart (except for an
obviously enhanced metal–to–ligand charge transfer (MLCT) emission band at higher
energy). Although the lowest excited state of (BuPyrDPy)[Pt(dpm)]2 performed

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largely ligand-centered characteristics, however, the d orbital of its two platinum(II)
ions occupied different HOMO stages, and didn’t contributed to the extension of
molecular conjugation.
Based on that, a further study that focused on adjusting the coordination
environment of the second platinum(II) ion was conducted in this paper (Molecular
structures see Chart 1). Pt-1 and Pt-3 possessed two isomerized asymmetric
difluorophenyl-pyridyl-pyridine bridging ligand frameworks, which would prefer to
provide different coordination environments to the second platinum(II) ions through
the chelated meta-/para- carbon of nitrogen on their center pyridyl segments.
Interestingly, very large difference existed during their photophysical processes: Pt-3
exhibited spectra features that are quite typical of the traditionally symmetric
bimetallic complexes, with obviously redshift absorption/emission profiles that
induced by the additional platinum(II) ion; while Pt-1 showed very similar
photophysical characteristcs to its mononuclear counterpart. A key factor that account
for the above was due to the different energy levels of the second platinum(II) ions’ d
orbital, which suffered different ligand field strength through the connected
meta-/para- carbon on the center pyridyl segments. Finally, the second platinum(II)
ions in both two complexes could extend the conjugation on different
HOMOs/LUMOs stages, while the first platinum(II) ions that chelated with the
electron-rich phenylpridyl segments would more perfer to contribute to the HOMO.
The increased metal components major helped to their fixed molecular skeleton to
suppress distortion in excited state, especially for Pt-1 with barely bathochromic shift

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emission profile. OLEDs fabricated with Pt-1 and Pt-3 achieved 21.38% and 16.30%
EQEs in the kelly-green and orange region, respectively, with device performance
superior or comparable to their mononuclear counterparts.
Chart 1. Chemical structures of complexes.
RESULTS AND DISCUSSION
Synthesis and Characterizations. Chart 1 listed two new types of asymmetric
bimetallic complexes (Pt-1/Pt-3) with the terminal pyridyl units on their bridging
ligands substituted at different positions of the center pyridyl segments
(5/4-substituted), as well as their corresponding mononuclear counterparts (Pt-2, Pt-4
and Pt-5). The bridging ligands of 2-(2,4-difluorophenyl)-5-(pyridin-2-yl)pyridine
(L1) and 2-(2,4-difluoro-phenyl)-4-(pyridin-2-yl)pyridine (L2) were obtained by a
common Suzuki coupling reaction with high yields. Both L1 and L2 possessed two
possible coordination sites that could undergo cyclometallation, and all five
platinum(II) complexes were synthesized using an one-pot method.1-11 For the
5-substituted mononuclear complex, only one kind of configuration was obtained
(Pt-2), whose metal ion was only chelated to the electron rich phenylpyridyl portion,

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and the yield was equal to its corresponding bimetallic complex (Pt-1);DOfIo: 1r0.1t0h3e9/D0DT00939C
4-substituted mononuclear complex, two types of configurations were obtained (Pt-4
and Pt-5), together with their corresponding bimetallic complex (Pt-3) with nearly
equal yields. Complexes were fully by characterized by 1H NMR, 13C NMR, and MS,
details synthesis was shown in Scheme 1.
Scheme 1. Synthetic route of complexes.
Reagent and conditions: a) 2,5-dibromopyridine, Pd(PPh3)4, 2M K2CO3 (aq), THF, 80 oC; b)
bis(pinacolato)diboron, potassium acetate, Pd(dppf)Cl2, 1,4-dioxane, 110 °C; c) 2-bromopyridine,
Pd(PPh3)4, 2M K2CO3 (aq), THF, 80 oC; d) 2,4-dibromopyridine, Pd(PPh3)4, 2M K2CO3 (aq), THF, 80
oC; e) 2-(tributylstannyl)pyridine, Pd(PPh3)4, N,N-dimethylformamide, 140 °C; f) K2PtCl4, acetic acid,
120 oC; g) 2,2,6,6-tetramethyl- 3,5-heptanedione, K2CO3, THF, 80 oC.
Single-Crystal Structures. Figure 1 shows molecular structures (a) and their
packing modes (b) of five platinum(II) complexes that determined by single-crystal
X-ray diffraction. From which we could see all three mononuclear complexes (Pt-2,
Pt-4 and Pt-5) possessed somewhat distortion between their terminal pyridyl/phenyl
segments to their principle metal centres. And in terms of the binuclear complexes,

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Pt-1 adopted a locked rigid planar construction by incorporating with the second
platinum ion, while the rigid configuration seemed much more twisted between two
auxillary ligands in Pt-3. Meanwhile, the Pt-C distances in five complexes were close
to each other, with values in region of 1.95~1.98 Ao, which means a similar
coordination ability to metal ions of each bridging ligands. All complexes adopted
staggered face-to-face packing mode, except for Pt-5 with a face-to-edge stacking
pattern.
Figure 1. a) Single-Crystal structures of complexes, the thermal ellipsoids are drawn with 50%
probability, and the hydrogen atoms and the solvent are omitted for clarity. Element (color):
platinum (purple), oxygen (red), carbon (gray), nitrogen (blue), fluorine (yellow). Inset shows the
chelated Pt-C distances. Pt-5 shows a dimer with different orientation of the terminal pyidine. b)
Molecular packing of complexes in different configurations in a crystal unit cell. Pt-3 shows two
perspectives images from which we can see a tight π–π interaction between two nearby ligands
with barely of overlap.
Photophysical Properties. Absorption spectra of the five platinum(II)
complexes in dichloromethane at 298 K (Figure 2a and Table 1) showed typical
characteristics of phenylpyridine platinum(II) species.23 For all five complexes, the
intense absorption bands in the range of 250–350 nm should typically be assigned to
the π–π* transitions of their chelating ligands. Weaker absorption bands at around
350–450 nm were attributed to the mixed singlet/triplet intraligand and metal–to–

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3
ligand charge transfer (1ILCT/1MLCT and ILCT/3MLCT). Of these CT bands, Pt-1,
Pt-3 and Pt-4 performed somewhat bathochromatic shift compared with other two
complexes, which might be caused by the greater electron donating capacity of their
platinum(II) ion through incorporating with an additional metal ion and/or a more
delocalized electron distribution. As for Pt-3, an emerging absorption band extended
to 500 nm at lower energy should be a new state and characterized by the metal–
ligand–metal interacting, which was absent in Pt-1. For nearly all the former reports
based on kinds of bimetallic complexes with symmetric bridging ligands ascribed that
1
new emerging bands to enhanced MLCT induced by the second metal ion,1-10
however, both two metal ions occupied the HOMO/LUMO in their formed molecular
orbitals and participated the lowest states transitions, as their DFT/TD-DFT
calculations performed. Combined with this work, we defined that low absorption
band to charge transfer on metal–ligand–metal hybridized orbital (1MLMCT).
Interestingly, the absent of that band in Pt-1 type are very likely associated with an
orbital mismatching between the second metal ion and the bridging ligand. Specific
discussion based on that vide infra.
The photoluminescent spectra of the five complexes in dichloromethane at 298 K
(Figure 2b, Table 1) are also quite typical of the phenylpyridine platinum(II) species
(except for Pt-3). Especially for Pt-1 and Pt-2, both with structured emission peaked
at around 510 nm along with vibrational shoulders at longer wavelength, which
illustrated their largely dominated π–π* transitions characteristics. The nearly
consistent emissive features of the two complexes agreed with our previously reported

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asymmetric mono/di-metallic complexes,11 which at least indicated that the additional
platinum ion set no conjugate extension on Pt-1’s HOMO/LUMO stages. The similar
Pt-C distances of the two platinum ions in Pt-1 also refuted a hypothesis of a very
weak connection between the second platinum(II) ion and the bridging ligand in
Pt-1(Figure 1). Besides, Pt-1 performed much increased Φ to Pt-2, with values of 0.89
and 0.20, respectively. While the two complexes performed similar excited-states
lifetimes (5.4 μs and 4.1μs) (Figure S2), it could be expected the second platinum(II)
ion had a large enhancement on the radiative transition rate (kr) and nearly an order of
magnitude of decrement on the non-radiative transition rate (knr) of the former (Table
1). Therefore, an increasing effectivity of SOC as well as a fixed molecular skeleton
to suppress distortion in excited state should be expected in Pt-1. Since Pt-1 showed
no bathochromic shift absorption/emission profiles to Pt-2, we could expect that the
second platinum(II) ion in Pt-1 would more prefer to participate in the HOMO+n
(n≥1) and facilitate higher energy states transitions. Pt-4 had a 15 nm bathochromic
shift emission peak to Pt-5, of two isomers with their platinum ions located at
different surroundings, both performed less structured emission profile and implied
more obvious charge transfer characteristics. The relatively lower-lying emissive state
of Pt-4 to Pt-5 was mostly caused by the larger effective conjugate of the former that
induced by its corresponding dπ orbital. Besides, two complexes had similar kr values
in dilute degassed toluene solutions, while a more than two folder decreased knr value
for Pt-5 to Pt-4 might illustrated a larger vibrational configuration change from
ground state to excited state of the former and resulted in a poorer Φ value. However,

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this disadvantage would disappear in doped films, with a more rigid environment to
restrict molecular distortion (see Electroluminescence properties). As for the
corresponding binuclear complex Pt-3, it performed a much bathochromic shift
3
emission band that peaked at around 572 nm with a typical lower-lying MLMCT
emissive feature of symmetric bimetallic complexes.1-10 The molar absorption
coefficient of Pt-3 (5000 M−1 cm−1) at the lower energy showed much reduction to
Pt-4 (22200 M−1 cm−1) and Pt-5 (30500 M−1 cm−1), which means a relatively lower
allowedness of transition dipole moment between ground state and excited state and
primarily to the disadvantage of the kr value of the former. However, the relatively
smaller knr value of Pt-3 to Pt-4 and Pt-5 should also be caused by the molecular
skeleton fixing that induced by the additional platinum(II) ion, just as that in Pt-1
specie. When in thin films, all complexes showed somewhat bathochromic shift at
their either emission peaks. Obvious excimer emission above 600 nm were also
observed in most complexes due to their easily accumulate planar structures (Figure
2c;Table 1). The formed excimer emission can be convinced by the corresponding
excitation spectra that excited at both main emission folder and excimer portion (see
Figure S2.3). 24-26 However, as for Pt-3, which performed much twisted rigid structure
that induced by the steric hindrance between its two auxillary ligands (see Figure 1),
tended to present a broad structureless emission profile with no excimer formation in
solid state.

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Figure 2. Absorption (a) and emission spectra of complexes measured in dilute CH2Cl2 solutions
at 298 K (b); in thin films at 298 K (c); in 2-MeTHF at 77 K (d).
Structured emission profiles of all five complexes become highly resolved with
increasing emission energies at 77 K in their 2-MeTHF matrixes (Figure 2d;Table 1).
The vibrational shoulders observed in emission spectra were caused by different
vibronic transitions,27,28 and one can expect the degree of structural distortion of
complexes for a specific vibrational modes from the integral intensity ratio of the 0-1
vibrational shoulder peak to the 0-0 peak, according to Huang-Rhys factor (SM).29,30
SM values of Pt-1 and Pt-3 for the 1492 cm−1 and 1378 cm−1 fundamentals were much
smaller than other three mononuclear complexes, in accordance with their smaller knr
values that caused by the more rigid structures bonded by the additional metal ions as
the above mentioned. Besides, Pt-5 had the largest SM value amounts to 2.13
estimated at r.t., while the corresponding value decreased seriously as temperature

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drops, which may be ascribed to a thermal population of metal-centered dd* state that
localized more closer to the emissive state of the former.
Table 1. Photophysical properties of five complexes.
e
a
a
c
d
λabs
λPL
Φ b
τ b
λPL
λPL
kr/knr
f
complex
SM
[×105s−1]
[nm], (ε[×104 M−1 cm−1])
[nm]
[%]
[μs]
[nm]
[nm]
504,
253(5.85), 305(6.42),
403(2.63)
511, 550,
596
518, 556,
636
1.30
Pt-1
Pt-2
Pt-3
Pt-4
Pt-5
89
20
27
26
13
5.4(0.80)
4.1(0.52)
5.4(0.43)
2.7(0.30)
1.2(0.59)
1.65/0.20
545, 593
(1.40)
503,
254(8.88), 296(8.17),
334(4.24), 380(1.99)
510, 548,
593
524, 564,
614
1.47
0.50/1.94
0.50/1.35
0.98/2.73
1.08/7.25
544, 586
(1.49)
554,
270(7.90), 297(7.87),
396(2.49), 464(0.50)
1.51
572, 611
519, 548
504, 529
583
601, 656
(1.56)
500,
523, 553,
613
1.76
278(16.55), 394(2.22)
537, 578
(1.41)
488,
252(9.70), 288(8.96),
334(2.96), 381(3.05)
495, 532,
660
2.13
523, 560
(1.41)
a Measured in dilute DCM solutions at r.t. b Φ is the absolute photoluminescence quantum yields measured in degassed
toluene solutions (values in parentheses were measured in air-equilibrated solution), τ is the excited-state lifetime. c kr and
knr are rate constants calculated by using the equations kr=Φ/τ and knr=(1-Φ)/τ, assuming that ΦISC = 1(ISC = intersystem
e
f
crossing). d Measured in solid thin films. Measured in 2-MeTHF matrix at 77 K. Huang-Rhys factor calculated at r.t.
(calculated at 77K in parentheses).
Electrochemical Properties. Cyclic voltammetry (CV) measurement can
provide further information to the orbital participating of platinum(II) ions, where the
lowest energy electron transition process can often be reflected on complexes’ initial
oxidation/reduction processes. Figure 3 and Table 2 provide information of the
corresponding electrochemical properties of five platinum(II) complexes. Just as the
absorption edge performed above, Pt-3 had the narrowest energy gap, especially for
its much more negative onset oxidation potential in comparison with Pt-4 and Pt-5.
The two discernible irreversible oxidation waves of Pt-3 illustrated a continuous redox
process on its two platinum(II) centers,1-10 from which we could see that the second
platinum(II) ion would enlarge the conjugation on complex’s HOMO/LUMO stages.

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Pt-4 performed both cathodically shift oxidation and reduction wave by 0.11 V and
0.06 V compared with Pt-5, which was caused by the more electron-rich feature of its
bridging ligand (through connecting with metal ion at the electron-deficient center
pyridyl segment rather than the electron-rich phenyl group). However, the absence of
two discernible oxidation processes in Pt-1 stated a lack of contribution to the HOMO
stage of the second platinum(II) ion. The similar redox wave form of Pt-1 and Pt-2
illustrated a similar HOMO/LUMO distributions in two complexes, the latter
performed negative oxidation and positive reduction potentials both around only 0.1
eV to the former, which was attributed to the increased electron density on the
bridging ligand of this bimetallic complex. So, here the CV measurement also
reflected the orbitals mismatching between the second metal ion and the bridging
ligand in Pt-1 specie.
Figure 3. Cyclic voltammograms of platinum(II) complexes in CH3CN solutions.
Table 2. Electrochemical properties of complexes.
Eox
(V)a
Ered
(V)a
HOMO/LUMOexp
(eV)b
ΔEg
(eV)c
HOMO/LUMOcal
(eV)d
ΔEg
(eV)d
Complex
Pt-1
0.41
-1.87
-5.21/-2.93
2.28
-5.47/-2.13
3.34

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Pt-2
Pt-3
Pt-4
Pt-5
Pt-0
0.53
0.27
0.49
0.60
-1.95
-1.72
-1.90
-1.84
-5.33/-2.85
-5.07/-3.08
-5.29/-2.90
-5.40/-2.96
2.48
-5.65/-1.96
-5.39/-2.33
-5.48/-2.00
-5.60/-2.12
-5.75/-1.93
DOI:310.6.19039/D0DT00939C
1.99
2.39
2.44
3.06
3.48
3.48
3.82
a
The data are estimated from the onset oxidation/reduction curve referenced to the Fc/Fc+ (Fc is
ferrocene). b Deduced from the equation EHOMO = -4.8-Eox, ELUMO = -4.8-Ered. c Calculated from
onset oxidation/reduction potential. d Calculated by DFT.
Theoretical Calculations. DFT and TDDFT calculations (Figure 4, S3, Table 3,
S1) further proved the case of metal participation in two kinds of bimetallic
platinum(II) complexes. Figure 4a performed the HOMO and LUMO distributions of
the five complexes. For mononuclear complexes of Pt-2 and Pt-5, the HOMO orbitals
were mainly contributed by the electron donating phenyl groups and the platinum(II)
ions, while the LUMO orbitals were largely localized on the electron deficient
dipyridyl segment. Pt-4 had somewhat destabilized HOMO/LUMO levels compared
with Pt-5, because of the enhanced π donation from both phenyl and pyridyl moieties
that contributed to the HOMO of the latter. For Pt-3, the HOMO orbital were formed
from a combination of the phenylpyridyl segement and both two metal ions in an
antibonding fashion, the additional metal ion in Pt-3 had a highly coplanarity with the
bridging ligand, which would render electron delocalization occured on an enlarged
π-conjugated framework and endow complex with a much narrower energy gap.
However, as for another bimetallic specie of Pt-1, the second platinum(II) ion of that
performed far less participation to the HOMO distribution and seemed more prefer to
contribute to the LUMO, nearly no additional π-conjugate extension occurred on the

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HOMO/LUMO stage and was quite uncommon in MLCT dominated metallic
complexes.31,32 To investigate the impact of the bridging ligand on the second
platinum(II) ion in Pt-1, we picked another corresponding hypothetical mononuclear
struture Pt-0 through DFT calculation as a reference (Figure 4b). Encouragingly, its
HOMO orbital was mainly localized on the platinum(II) ion and the electron deficient
center pyridyl unit with a low energy level of -5.75 eV, in sharp contrast to Pt-4,
whose HOMO was largely distributed on the platinum(II) ion and the electron rich
phenylpyridyl portion with a much higher energy level of -5.48 eV. This illustrated
that the dπ orbital of the platinum(II) ion in Pt-0 might suffer a larger ligand field
strength and localized at a much lower energy level. When considered deeper
occupied orbitals for five complexes (Figure S3, Table S1), with regard to Pt-1, there
existed two kinds of independent single-metallic hybridization with the bridging
ligand on different HOMOs stages. The second platinum(II) ion showed much less
participation on the HOMO and HOMO-1, only showed up at the lower-lying
HOMO-2 orbital with a low energy of -5.91 eV that close to the HOMO level in Pt-0,
which further illustrated a much deeper dπ orbital energy level of the second
platinum(II) ion in Pt-1. For Pt-3, the highest three occupied orbitals showed both two
metal ions’ major participation, the first platinum(II) ion exhibited contribution ratios
around 3~4 times of the second platinum(II) ion, which might illustrated a more
efficient orbital coupling of the former with the bridging ligand. In terms of the SOC
characteristics of the five complexes, Pt-1 and Pt-5 performed greater contribution of
the 5d orbital in the HOMO or HOMO-1 that ascribed to the lowest triplet state

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transitions (Table 3). However, both two bimetallic complexes Pt-1 and Pt-3
performed much multiplicity of HOMO distributions, especially for Pt-1 with much
smaller energy differences between HOMO and HOMO-2, which would also
facilitate efficient singlet and triplet states mixing.33 The much larger contribution of π
orbitals in HOMO-2 in Pt-1 and Pt-3 that raised by the additional platinum(II) ion
gave rise to a stronger oscillator strength (f) of S4 (HOMO-2 → LUMO), from which
the T1 state borrowed its intensity and contributed to the radiative rate constant
according to “one-center spin-orbit coupling” principle.34 However, the weakened
phosphorescence of Pt-3 with smaller kr value might partly originated from the mixing
between S1 (HOMO → LUMO) and T1 (54% HOMO → LUMO, 35% HOMO-1 →
LUMO), where the oscillator strength of S1 (HOMO → LUMO) in Pt-3 with value of
0.0294 showed much weaker to its mononuclear counterparts, and might probably be
caused by the relatively poorer overlap between HOMO/LUMO distributions that
raised by the second platinum(II) ion.
Figure 4. Calculated orbital distributions and energy levels for the HOMO and LUMO plots of

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five platinum(II) complexes at their optimized ground state geometries. inset shows a hyDpOoIt:h1e0.t1i0c3a9l/D0DT00939C
complex Pt-0 for comparison.
Table 3. Excited states of five complexes calculated using the TDDFT approach.
Complex
state (E, λ)
Dominant excitations
H→ L(0.97)
oscillator strength (f)
0.1151(singlet)
0.0692(singlet)
0.0805(singlet)
0.0000(triplet)
0.1051(singlet)
0.0764(singlet)
0.0024(singlet)
0.0000(triplet)
0.0294(singlet)
0.0893(singlet)
0.0648(singlet)
0.0000(triplet)
0.0501(singlet)
0.0031(singlet)
0.0487(singlet)
0.0000(triplet)
0.0401(singlet)
0.1143(singlet)
0.0016(singlet)
Character
S1
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT
(2.85 eV, 434 nm)
S2
H-1→ L(0.91)
H-2→ L(0.95)
(2.98 eV, 416 nm)
Pt-1
S4
(3.26 eV, 380 nm)
T1
H-1→ L (0.52)
H→ L(0.22)
(2.46 eV, 505 nm)
S1
H→ L(0.90)
H-1→ L(0.84)
H-2→ L(0.95)
(3.10 eV, 400 nm)
S2
(3.37 eV, 367 nm)
Pt-2
S3
(3.47 eV, 357 nm)
T1
H-1→ L (0.55)
H→ L(0.27)
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT
(2.55 eV, 486 nm)
S1
H→ L(0.92)
H-1→ L(0.90)
H-2→ L(0.92)
(2.51 eV, 494 nm)
S2
(2.76 eV, 449 nm)
Pt-3
S4
(3.04 eV, 408 nm)
T1
H-1→ L (0.35)
H→ L(0.54)
(2.13 eV, 583 nm)
S1
H→ L(0.93)
H-2→ L(0.98)
H-1→ L(0.89)
H→ L(0.84)
(2.88 eV, 431 nm)
S2
(3.29 eV, 376 nm)
Pt-4
S3
MLCT /LLCT
(3.34 eV, 371 nm)
T1
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT
(2.41 eV, 514 nm)
S1
H→ L(0.83)
(2.91 eV, 425 nm)
S2
Pt-5
H-1→ L(0.81)
H-2→ L(0.98)
(3.19 eV, 389 nm)
S3
(3.27 eV, 379 nm)

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T1
H-1→ L (0.69)
0.0000(triplet)
MLCDTO/II:L10C.1T03/L9/LD0CDTT00939C
(2.58 eV, 481 nm)
As a common sense, nitrogen atom is an meta-director in a pyridine ring,
electron density is much deficient at its ortho- or para- position while its meta- site
performs electron rich (Figure 5b, top). The para- hydrogen on the center pyridyl
segment in L1 had its chemical shift to a low field of 8.41 ppm, while the meta-
hydrogen’s chemical shift localized at higher field of 7.86 ppm in L2, of two sites that
would chelate to the second platinum(II) ions. Besides, sites that should be permitted
to chelate to the first platinum(II) ions on the difluorophenyl segments of both two
bridging ligands had similar hydrogen’s chemical shifts to 7.84-7.90 ppm, which were
comparable to the value of the meta- hydrogen in L2 but much smaller than the para-
hydrogen’s shift in L1 (Figure 5a) (This was also reflected in the synthesis procedure,
since we didn’t obtain any mononuclear complex that with platinum ion coordinated
with the dipyridyl portion of L1). From which we can see that both two platinum(II)
ions in Pt-3 suffered similar ligand field strength, hence, they had nearly consistent
lowered occupied d orbital energy levels and contributed to the parallel high-lying
HOMO, which would be reflected on the extended conjugation on the HOMO/LUMO
stages (bathochromic shift spectrum). While in Pt-1, center pyridyl performed a much
stronger ligand field strength to the second platinum(II) ion, the electron deficient
meta- carbon could push the occupied d orbital of the second platinum(II) ion to a
much lower energy level, of which types usually be used to develop broad energy gap
deep blue emitters.35,36 Thus the lower-lying dπ orbital of the second platinum(II) ion
would mismatching the high-lying ML orbital that composed of the first platinum(II)

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ion and the bridging ligand, only mainly occupied HOMO-2, as a result, no
hybridized orbital formed by metal-ligand-metal three components occurred at the
lowest-lying absorption/emission states. Besides, since the second platinum(II) ion
connected with the electron deficient para- carbon, it would also be expected to suffer
an electron-cloud density decrease and performed a much more participation to
LUMO than the first platinum(II) ion.
Figure 5. Brief explanation and photophysical mechanism in two types of bimetallic Pt-1 and
1
Pt-3 complexes (left: marked H NMR shift of two bridging ligands; right: electron density
distribution in pyridine and the corresponding ligand field intensity to metal ions, photophysical
mechanism of Pt-1 and Pt-3).
Electroluminescence Properties. All platinum(II) complexes emitters were
tested in solution processed devices with a device structure of ITO/PEDOT:PSS (40
nm)/(PVK:OXD-7)7:3]:emitter (7 wt%, 50 nm)/ DPEPO (10 nm)/TmPyPB (40
nm)/CsF (1.2 nm)/Al (120 nm) (Figure S4). All devices adopt a 7 wt% doping
concentration to minimize the formation of excimers. Figure 6 presented their device
performances while the corresponding data are listed in Table 4. Electroluminescence

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(EL) spectra of all five platinum(II) complexes (Figure 6a) were similar to the PL
spectra in their dilute CH2Cl2 solutions, with negligible contribution from the matrix,
which means efficient energy transfer from hosts to dopants. All devices performed
moderate turn-on voltage in the region of 4.4~7.2 eV. Interestingly, the turn-on volage
of Pt-1 based device performed a 0.8 V smaller to device based on Pt-2, even though
Pt-1 has a 0.18 eV higher HOMO level and a 0.17 eV lower LUMO level to the latter,
which generally means a larger energy gap of Pt-1 to host and usually should be more
harder for exciton injection. Here, such anomalies of the smaller Von in Pt-1 based
device may be charged by the wider band gap that induced by the second platinum(II)
ion (e.g. raised HOMO-1 level induced by the additional dπ orbital, which just lying
above the HOMO level of PVK host, see Figure S3), and a more smooth exciton
injection pathway should be formed by the multiple states of Pt-1 through internal
conversion. Also, the largest Von of Pt-4 based device was mostly caused by the large
HOMOs levels separation between Pt-4 emitter and PVK host. Besides, the lower Von
of Pt-2 to Pt-5 was caused by the more neighboring LUMO levels of the former to
OXD-7. So, it seemed that exciton capture way here was largely corresponded to
charge trapping mechanism in five devices. Device based on Pt-1 emitter performed
the highest efficiencies with the maximum luminance value of 14650 cd/m2, current
efficiency (CE) of 68.31 cd/A and EQE of 21.38%. All parameters based on Pt-1
emitter were superior to the device performance of the corresponding mononuclear
counterpart Pt-2 emitter (with values of 7540 cd/m2, 55.69 cd/A, and 16.01%), which
can be attributed to the increased metal component and somewhat lower Von of the

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former. For another series, Pt-3 and Pt-5 based devices performed consistent
efficiencies, with values of 7294 cd/m2, 41.11 cd/A, and 16.30% for Pt-3; and 11520
cd/m2, 53.66 cd/A, and 16.49% for Pt-5. Besides, the weakened non-radiation
transition rate in a rigid host matrix seemed do much increase to Pt-5 emitter’s
efficiencies. Pt-4 based device performed poorest efficiencies among all five devices,
which may be related to its higher turn-on voltage that caused by the poor matching of
energy levels to host.
Figure 6. a) EL spectra, b) J−V−R characteristics, c) CE−current density, d) EQE−current density
curves for PHOLEDs based on five platinum(II) complexes.
Table 4. Electroluminescence Characteristics of the devices based on five complexes.
b
c
d
f
e
CIE
Von
λEL
Lmax
CEmax
PEmax
EQEmax
(%)
Dopant a
(cd/m2)
14650
7540
(cd/A)
68.31
55.69
41.11
21.36
53.66
[lm W−1]
38.25
25.69
16.13
6.98
(X, Y)
(V)
4.4
5.2
6.8
7.2
6.4
(nm)
514,552,594
514,552,592
572,612
21.38
16.01
16.30
5.99
(0.36, 0.59)
(0.36, 0.59)
(0.54, 0.45)
(0.35, 0.59)
(0.29, 0.59)
Pt-1
Pt-2
Pt-3
Pt-4
Pt-5
7294
521,549
6722
22.15
503,532
11520
16.49

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a Dopant is devices based on complexes Pt-1 to Pt-5; Von is Turn-on voltage. c maximum lDuOmI:i1n0a.1n0c3e9;/D0DT00939C
d maximum current density; e maximum external quantum efficiency; f maximum power efficiency.
CONCLUSIONS
In conclusion, we prepared two new types of asymmetric bimetallic complexes with
isomerized asymmetric difluorophenyl-pyridyl-pyridine bridging ligand frameworks.
Combined with electrochemical and photophysical studies, we found a new
lower-lying state existed in Pt-3 specie while Pt-1 resembled most photophysical
features to its mononuclear counterpart Pt-2. Further investigated by DFT calculations
and compared with many previous studies based on symmetric bimetallic complexes,
we concluded that Pt-3 had a three-components lowest transition characteristic
(MLMCT), which was mainly attributed to its two associated high-lying dπ orbitals.
While the occupied d orbital of the second platinum(II) ion in Pt-1 suffered much
stronger ligand field strength that induced by the more electron-deficient para- carbon
of the center pyridyl segment, and mainly contributed to the lower-lying HOMO-2.
Pt-1 had enhanced SOC that caused by the additional metal component through direct
orbital hybridization at the higher states, while the second platinum(II) ion in Pt-3
seemed had no contribution to the radiative transition and only benefit to a fixed
molecular skeleton to suppress distortion in excited state. OLEDs fabricated with the
Pt-1 bimetallic emitter achieved superior efficiencies with 21% EQE in the
kelly-green region, which was caused by its higher radiative transition rate as well as
more matched energies to host. This work states a new explanation to kinds of
photophysical processes for bimetallic complexes, and provide a new strategy to

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design both broad or narrow HOMO-LUMO gap bimetallic emitters with high
efficiencies.
EXPERIMENTAL SECTION
General Characterization. Chemicals and reagents were purchased from
commercial sources and used directly. All reactions were conducted under N2
atmosphere. Purification of complexes were carried on column chromatography using
200-300 mesh silica gel. Single crystals of Pt-1 to Pt-5 were grown from solvent
diffusion in their dichloromethane/n-hexane (v/v, 1/2) solutions, complexes exhibit
yellow columnar (Pt-1, Pt-2, and Pt-5), green globular (Pt-4), orange columnar (Pt-3)
1
crystals. H and 13C NMR spectra were recorded on Bruker Avance-400 (III)
spectrometer at 400/126 Hz, with CDCl3 as the solvent and tetramethylsilane (TMS)
as the internal standard. Mass spectrometry (MS) were obtained on a Bruker Autoflex
MALDI-TOF instrument and a Agilent GC-MS instrument. Platinum(II) complexes
Pt-1 (CCDC 1965376), Pt-2 (CCDC 1965377), Pt-3 (CCDC 1965378), Pt-4 (CCDC
1965379) and Pt-5 (CCDC 1965380) were determined by a Bruker SMART Apex
CCD single-crystal X-ray diffractometer equipped with graphite monochromatized
(Mo K α).
Spectroscopic and CV Measurements. Ultraviolet-visible (UV-Vis) absorption
and photoluminescent (PL) spectra were recorded with a Varian Cray 50 UV-vis
spectrophotometer and Perkin-Elmer Ls 50 B luminescence spectrometer,
respectively. Absolute photoluminescence quantum efficiency (Φ) was recorded on a
Horiba Jobin Yvon Fluorolog-3 fluorescence spectrometer equipped with an

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integrating sphere, the measurement was carried on in a degassed tolueneDsOoI:l1u0t.1i0o3n9/D0DT00939C
with nitrogen purging for 30 min. Time-resolved spectroscopy were recorded using a
HORIBA TEMPRO-01 and a spectra 370 laser source on Horiba Jobin Yvon
Fluorolog-3 fluorescence spectrometer through time-corrected single-photon-counting
(TCSPC) measurement. 77 K phosphorescence spectra were obtained using a
HORIBA FluoroMax+ spectrometer at 77 K in a 2-MeTHF matrix. SM value can be
Iv
determined by using the simple expression SM =
wherein v is the vibrational
퐼푣 ― 1
quantum number and Iv is the intensity of the respective progression member. Cyclic
voltammetry measurement was conducted with a CHI620 voltammetric analyzer,
using a standard three-electrode configuration (platinum disk working electrode,
platinum wire counter electrode, and Ag/AgCl reference electrode). Supporting
electrolyte was a 0.1 M n-Bu4NPF6, and external standard was ferrocene/ferrocenium
(Fc/Fc+). Measurements were carried out in degassed acetonitrile solution with a scan
rate of 0.1 V/s. All potentials were quoted vs the Fc+/Fc couple onset oxidation value.
Theoretical Calculations. DFT and time-dependent DFT (TD-DFT) were used
to calculate the ground and excited electronic states of complexes. The
HOMO/LUMO distributions were calculated on the basis of their optimized ground
states. Metal ion’s participations were calculated using Hirshfeld method in Multiwfn.
All calculations were conducted with the Gaussian 09 program package.37 The
B3LYP functional and 6-31G* basis set were used for C, H, N, O and LANL2DZ
basis set for Pt,38 however, it should be note that an alternative theoretical approach to
describe MLCT effects well have been reported by the Kozlowski group.39,40

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Fabrication and Characterization of OLEDs. OLEDs were fabricateDdOIw: 10it.1h03a9/D0DT00939C
process of: a 40 nm poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(styrene
sulfonate) (PSS) mixed electron transporting layer (ETL) was spin-coated onto a
pre-cleaned ITO substrate and dried in vacuum. Then a 50 nm mixed emitting layer
(EML) was spin coated on top of the ETL from its prepared chlorobenzene solution
followed by an annealing treatment at 120 °C for 20 min. After that, a 10 nm hole
bloking layer bis(2-(di(phenyl)phosphino)-phenyl)ether oxide (DPEPO) and then a 40
nm hole transporting layer (HTL) 1,3,5-tri(pyrid-3-yl-phenyl)benzene (TmPyPB) was
evaporated on top of the EML at a deposition rate of 0.5–1.0 nm/s under a pressure of
10−5 mbar orderly. At last, the cathode CsF (1.2 nm)/Al (120 nm) layer was evaporated
on the HTL with a shadow mask at a pressure of 3×10−4 Pa. The
current-voltage-luminance (J–V-L) character were measured with a Keithley 236
source measurement and a Lambertian distribution. The EL spectra and CIE coordinates
wer obtained by Photo Research PR705 optical analyzer. The EQEs were calculated on the
premise of a Lambertian distribution by using the EL spectra, luminance, and current
densities. All the measurements were carried out at room temperature under ambient
conditions.
Synthesis of M1. M1 was synthesized according to the published procedure.41 1
H
NMR (400 MHz, CDCl3) δ 8.76 (d, J = 2.1 Hz, 1H), 8.00 (td, J = 8.9, 6.6 Hz, 1H),
7.88 (dd, J = 8.5, 2.4 Hz, 1H), 7.67 (dd, J = 8.5, 1.4 Hz, 1H), 7.01 (td, J = 8.7, 3.3 Hz,
1H), 6.92 (ddd, J = 11.3, 8.7, 2.5 Hz, 1H). GC-MS MS: m/z found 269.0, calcd for
C11H6BrF2N 268.965.

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Synthesis of M2. A mixture of M1 (1.17 g, 4.37 mmol), bis(pinacolato) diboron
(2.0 g, 7.87 mmol), potassium acetate (1.28 g, 13.15 mmol) and Pd(dppf)Cl2 (120 mg,
0.162 mmol) in 20 mL 1,4-dioxane was stirred at 110 °C for 12 h under the protection
of nitrogen. The reaction mixture was filtered, and the filtrate was concentrated by
evaporation. The residue was dissolved in dichloromethane, washed with water and
dried under anhydrous magnesium sulfate. After evaporation of solvent, the crude
product was purified through passing a flash silica gel column using dichloromethane
as the eluent to give a white solid (820 mg, yield 59%). 1H NMR (400 MHz, CDCl3) δ
9.03 (s, 1H), 8.12 (dd, J = 7.9, 1.7 Hz, 1H), 8.03 (td, J = 8.8, 6.7 Hz, 1H), 7.74 (dd, J
= 7.9, 1.6 Hz, 1H), 7.01 (td, J = 8.3, 2.5 Hz, 1H), 6.91 (ddd, J = 11.3, 8.8, 2.5 Hz, 1H),
1.37 (s, 12H). MALDI-TOF MS: m/z found 318.188 [M+H]+, calcd for
C17H18BF2NO2 317.140.
Synthesis of L1. A mixture of M2 (800 mg, 2.5 mmol), 2-bromopyridine (396
mg, 2.5 mmol), aqueous K2CO3 (2 M, 3 mL), and Pd(PPh3)4 (80 mg, 0.07 mmol) in
15 mL tetrahydrofuran was stirred at 80 °C for 24 h under the protection of nitrogen.
The reaction mixture was concentrated by evaporation and the residue was dissolved
in dichloromethane, washed with water and dried under anhydrous magnesium sulfate.
The solvent was removed by rotary evaporation and the residue was passed through a
flash silica gel column using dichloromethane/tetrahydrofuran as the eluent to give a
white solid (580 mg, yield 86%). 1H NMR (400 MHz, CDCl3) δ 9.29 (s, 1H), 8.75 (d,
J = 4.6 Hz, 1H), 8.40 (d, J = 8.3 Hz, 1H), 8.10 (dd, J = 16.5, 7.9 Hz, 1H), 7.88 (d, J =

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8.3 Hz, 1H), 7.81 (s, 2H), 7.32 (t, J = 5.4 Hz, 1H), 7.03 (t, J = 7.9 Hz, 1HD),OI6: 1.09.1703–9/D0DT00939C
6.90 (m, 1H). GC-MS MS: m/z found 268.1, calcd for C16H10F2N2 268.081.
Synthesis of M3. Similar to the synthesis of M1, we achieved a white solid with
yield of 36%, this low yield was due to nearly equal amount isomer was generated
during the reaction process. 1H NMR (400 MHz, CDCl3) δ 8.52 (d, J = 5.3 Hz, 1H),
8.01 (td, J = 8.8, 6.7 Hz, 1H), 7.95 (s, 1H), 7.44 (dd, J = 5.3, 1.7 Hz, 1H), 7.01 (td, J =
7.9, 1.6 Hz, 1H), 6.93 (ddd, J = 11.2, 8.9, 2.4 Hz, 1H). GC-MS MS: m/z found 268.9,
calcd for C11H6BrF2N 268.965.
Synthesis of L2.
A
mixture of M3 (800 mg, 2.5 mmol),
2-(tributylstannyl)pyridine (920 mg, 2.5 mmol), and Pd(PPh3)4 (80 mg, 0.07 mmol) in
15 mL N,N-dimethylformamide was stirred at reflux temperature for 12 h under the
protection of nitrogen. The reaction mixture was concentrated by evaporation and the
residue was dissolved in dichloromethane, washed with water and dried under
anhydrous magnesium sulfate. The solvent was removed by rotary evaporation and
the residue was passed through
a
flash silica gel column using
dichloromethane/tetrahydrofuran as the eluent to give a white solid (480 mg, yield
71%). 1H NMR (400 MHz, CDCl3) δ 8.82 (d, J = 5.2 Hz, 1H), 8.77 (d, J = 4.7 Hz,
1H), 8.35 (s, 1H), 8.04 (td, J = 8.8, 6.7 Hz, 1H), 7.86 (ddd, J = 11.6, 5.7, 1.6 Hz, 3H),
7.37 (ddd, J = 6.1, 4.9, 2.7 Hz, 1H), 7.03 (td, J = 8.0, 2.1 Hz, 1H), 6.95 (ddd, J = 11.2,
8.8, 2.5 Hz, 1H). GC-MS MS: m/z found 268.1, calcd for C16H10F2N2 268.081.
Synthesis of Pt-1 and Pt-2. A mixture of L1 (134 mg, 0.5 mmol) and K2PtCl4
(207 mg, 0.5 mmol) were dissolved in 10 mL acetic acid and stirred at reflux

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temperature under nitrogen atmosphere for 24 h. The suspension was filtered and the
orange solid was washed with water and methanol then dried under high vacuum. The
platinum intermediate mixture was used for the next step without any purification and
analysis.
The
platinum
intermediate
mixture
(200
mg),
2,2,6,6-tetramethyl-3,5-heptanedione (440 mg, 2.4 mmol), and 2M K2CO3 (5 mL)
were suspended in 20 mL tetrahydrofuran solution and stirred at reflux temperature
for 24 h under nitrogen atmosphere. After cooled to RT, the mixture was washed with
water and extracted with dichloromethane, the organic layer was dried over anhydrous
magnesium sulfate. The solvent was removed by rotary evaporation and the residue
was purified by column chromatography using silica gel and a mixture of petroleum
ether/dichloromethane as the eluent to give both a yellow solid binuclear complex
Pt-1 (20 mg, 4%) and a yellow solid mononuclear complex Pt-2 (20 mg, 6%). Pt-1,
1H NMR (400 MHz, CDCl3) δ 9.08 (d, J = 5.3 Hz, 1H), 9.01 (s, 1H), 8.35 (d, J = 9.8
Hz, 1H), 7.92 (d, J = 6.7 Hz, 1H), 7.61 (d, J = 7.5 Hz, 1H), 7.30 (d, J = 7.7 Hz, 1H),
7.12 (d, J = 9.0 Hz, 1H), 6.60 – 6.54 (m, 1H), 5.90 (s, 1H), 5.83 (s, 1H), 1.35 (s, 9H),
1.34 (s, 9H), 1.30 (s, 9H), 1.29 (s, 9H).. MALDI-TOF MS: m/z found 1027.017
[M+Li]+, calcd for C38H46F2N2O4Pt2 1021.270. 13C{1H}NMR (126 MHz, CDCl3)
δ195.60 (s), 194.73 (d, J = 6.7 Hz), 193.99 (s), 164.87 (s), 155.42 (s), 147.61 (s),
144.38 (d, J = 7.6 Hz), 139.87 (s), 138.68 (s), 124.00 (d, J = 18.1 Hz), 122.36 (s),
118.27 (s), 112.56 (d, J = 17.8 Hz), 99.17 (t, J = 26.5 Hz), 93.67 (s), 93.56 (s), 41.53
(s), 41.50 (s),41.16 (s), 41.08 (s), 28.66 (s), 28.61 (s), 28.52 (s), 28.43 (s). Pt-2, 1H
NMR (400 MHz, CDCl3) δ 9.78 (s, 1H), 8.72 (s, 1H), 8.52 (d, J = 8.1 Hz, 1H), 8.08 –