Blue phosphorescent N-heterocyclic carbene chelated Pt(ii) complexes with an α-duryl-β-diketonato ancillary ligand

Article abstract of DOI:10.1039/c4dt03085k

C^C chelated Pt(ii) compounds that contain an N-heterocyclic carbene (NHC) donor have recently attracted great interest as blue or white phosphorescent emitters for organic light-emitting devices (OLEDs). To overcome the tendency for excimer formation in Pt(ii) compounds, an α-duryl-β-diketonato ligand was selected as the ancillary ligand for blue phosphorescent C^C chelated Pt(ii) compounds. Using this approach, a series of NHC-based C^C chelated Pt(ii) compounds has been designed and synthesized. The chelate ligands used in the new C^C chelated Pt(ii) compounds include 1-phenylimidazol-2-ylidene in Pt1, 1-phenyl-1,2,4-triazol-5-ylidene in Pt2, p-TMS-1-phenylimidazol-2-ylidene in Pt3, and p-TMS-1-phenyl-1,2,4-triazol-5-ylidene in Pt4. A single-crystal X-ray diffraction analysis revealed that the presence of the α-duryl-β-diketonato ligand in the Pt(ii) compounds effectively suppresses the dimer formation in the crystal lattice. Pt1, Pt2, Pt3, and Pt4 display blue phosphorescence at room temperature. The p-TMS substituted complex Pt3 was found to display the most efficient blue phosphorescence at λ_em = 468 nm with a Φ_PL of 0.68. Spectroscopic and computational studies established that the blue phosphorescence in the phenyl-imidazolylidene chelated complexes originates mainly from a ³MLCT state while that in the phenyl-triazolylidene chelated compounds arises from a ³ILCT state. Electroluminescent devices using Pt1 and Pt3 as the dopant were fabricated which display both monomer and exciplex emission, leading to pure white light electroluminescence with CIE coordinates of (0.32, 0.31).

Full text of DOI:10.1039/c4dt03085k

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ARTICLE TYPE
Blue Phosphorescent N-Heterocyclic Carbene Chelated Pt(II)
Complexes with an
α-Duryl-β-Diketonato Ancillary Ligand
a‡
a‡
b
a
b
a
Soo-Byung Ko, Hee-Jun Park, Shaolong Gong, Xiang Wang, Zheng-Hong Lu, and Suning Wang*
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
C^C* chelated Pt(II) compounds that contain an Nꢀheterocyclic carbene (NHC) donor have recently
attracted great interest as blue or white phosphorescent emitters for organic lightꢀemitting devices
(OLEDs). To overcome the tendency of excimer formation in Pt(II) compounds, an αꢀdurylꢀβꢀdiketonato
ligand was selected as the ancillary ligand for blue phosphorescent C^C* chelated Pt(II) compounds.
Using this approach, a series of NHCꢀbased C^C* chelated Pt(II) compounds have been designed and
synthesized. The chelate ligands used in the new C^C* chelated Pt(II) compounds include 1ꢀ
phenylimidazolꢀ2ꢀylidene in Pt1, 1ꢀphenylꢀ1,2,4ꢀtriazolꢀ5ꢀylidene in Pt2, pꢀTMSꢀ1ꢀphenylimidazolꢀ2ꢀ
ylidene in Pt3, and p-TMSꢀ1ꢀphenylꢀ1,2,4ꢀtriazolꢀ5ꢀylidene in Pt4. Singleꢀcrystal Xꢀray diffraction
1
1
2
0
5
0
analysis revealed that the presence of the αꢀdurylꢀβꢀdiketonato ligand in the Pt(II) compounds effectively
suppresses the dimer formation in the crystal lattice. Pt1, Pt2, Pt3, and Pt4 display blue phosphorescence
at room temperature. The pꢀTMS substituted complex Pt3 was found to display the most efficient blue
phosphorescence at λem = 468 nm with an ΦPL of 0.68. Spectroscopic and computational studies
established that the blue phosphorescence in the phenylꢀimidazolylidene chelated complexes originates
3
mainly from a MLCT state while that in the phenylꢀtriazolylidene chelated compounds arises from a
3
ILCT state. The electroluminescent devices using Pt1 and Pt3 as the dopant were fabricated, which
display both monomer and exciplex emission, leading to pure white light electroluminescence with CIE
coordinates of (0.32, 0.31).
Pt(C^C*), have recently emerged as a promising class of blue
1
3,14
Introduction
phosphorescent emitters.
The strong ligand field exerted by
the NHC ligands cannot only raise the energy of the metal
centered nonꢀradiative dꢀd excited states, thus effectively
reducing thermal quenching, but also increase the stability of
the cyclometalated complexes through the strong metalꢀNHC
bond. Although examples of Pt(C^C*) complexes are known
previously, only a few tridentate and tetradentate complexes have
Phosphorescent cyclometalated platinum(II) complexes have
attracted great attention because of their potential applications in
2
3
3
4
4
5
0
5
0
5
15
5
5
6
6
7
0
5
0
5
0
1
2
small cation or anion sensing, photocatalysis, photoisomeriꢀ
3
4
zation, and photoelimination. The high spinꢀorbit coupling
ꢀ
1 5
(SOC) constant of the platinum atom (χ = 4881 cm ) promotes
intersystem crossing from singlet to triplet excited states,
resulting in increased harvesting ability for both electroꢀgenerated
singlet and triplet excitons. 2ꢀarylpyridinate (C^N) ligands are
among the most commonly used chromophore ligands for Pt(II)
compounds because they provide a relatively strong ligandꢀfield
to the Pt(II) ion, and minimize the nonꢀradiative decay through
the dꢀd excited state.
acetylacetonato (acac) and dipivaloylmethane (dpm) are among
the most commonly used ancillary ligands for phosphorescent
Pt(II) compounds because they provide excellent thermal stability,
volatility, and solubility to the complex, highly desired for the use
in organic lightꢀemitting diodes (OLEDs). Based on this class of
materials, greenishꢀblue,
phosphorescent Pt(II) compounds have been demonstrated for use
in OLEDs. Nonetheless, stable and efficient blue emitters based
on Pt(II) compounds remain rare and are most in demand. Nꢀ
Heterocyclic carbene (NHC) cyclometalated Pt(II) complexes,
13,16,17
18
been demonstrated to produce deep blue
phosphorescent OLEDs. Bidentate Pt(C^C*) complexes with
diketonato ancillary ligands that display blue emission at room
or white
β
ꢀ
19ꢀ21
temperature are known.
However, the emission quantum
efficiencies are low for Pt(II) compounds with simple C^C*
ligands such as Pt(C^C*)(acac) in Chart 1 (R = H, QE = 0.07),
unless bulky substituent groups are introduced on the imidazolyl
ring to minimize intermolecular quenching,
applications of blue phosphorescent Pt(C^C*) in OLEDs remain
problematic due to the wide energy band gap (E ) and the poor
confinement of triplet excitons in the host materials. We
reported recently that Pt(II) complexes, Pt(BMes -C^C*)(acac)
20a
6
βꢀDiketonato ligands such as
19d
and the
g
20
7
8
,9
10
11
12
2
green,
orange,
and white
with BMes ꢀfunctionalized NHC chelating ligands display highly
efficient blue or greenishꢀblue phosphorescence and electroꢀ
phosphorescence. Nevertheless, the synthetic procedures for
2
21
Pt(BMes -C^C*)(acac)
are
challenging
and
their
2
electroluminescence (EL) spectra show considerable red shift and
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nd
broadening relative to the photoluminescence (PL) spectra. We
therefore investigated the alternative and simpler nonꢀborylated
when TsOH was added (which was intended to remove the 2
methyl on the Pt(II) center). All Pt(II) complexes were
C^C*ꢀchelated Pt(II) compounds by using a bulky diketonato 50 characterized by NMR spectroscopic and elemental analyses.
ligand, 4ꢀhydroxyꢀ3ꢀ(2,3,5,6ꢀtetramethylphenyl)pentꢀ3ꢀenꢀ2ꢀone
5
0
5
(αꢀdurylꢀβꢀdiketonato), as the ancillary ligand. This approach has
led to the discovery of a series of bright blue phosphorescent
C^C*ꢀchelated Pt(II) compounds (Pt1 – Pt4 in Chart 1).
Although the use of a related bulky diketonato ligand (
ꢀdiketonato) in C^Nꢀchelated Pt(II) compounds was reported
previously, the ꢀphenylꢀ ꢀdiketonato ligand was found to be
ineffective in preventing excimer emission. In contrast, our new
ꢀdurylꢀ ꢀdiketonato based C^C*ꢀchelated Pt(II) compounds
αꢀphenylꢀ
β
1
α
β
2
2
α
β
display consistent monomer blue emission in solution and in the
solid state, demonstrating the effectiveness of this simple
approach in achieving blue phosphorescent Pt(II) compounds.
The details are presented herein.
1
Scheme 1. Synthesis of the ligands and the Pt(II) compounds.
Structures
Chart 1. Blue phosphorescent NHC cyclometalated Pt(II) complexes.
Crystal structures of Pt1 and Pt3 were determined by singleꢀ
crystal Xꢀray diffraction analysis and are shown in Fig. 1 and 2,
respectively, along with important bond lengths and angles.
Details of the crystal data are given in the Electronic
Supplementary Information (ESI). Both compounds have a
typical square planar geometry around the Pt(II) atom. The bond
length between the PtꢀC(carbene) (1.953(3) Å in Pt1, 1.938(10)
Results and Discussions
55
Syntheses
20
25
30
35
40
45
The
αꢀdurylꢀβꢀdiketone ancillary ligand was synthesized using a
modified procedure reported by Ramirez and coworkers (Scheme
23
24
1
).
Lithiation of 3ꢀbromoꢀ1,2,4,5ꢀtetraꢀmethylbenzene ,
followed by quenching the aryllithium using anhydrous DMF 60 Å in Pt3) is slightly shorter than the corresponding PtꢀC(phenyl)
produced 2,3,5,6ꢀtetramethylbenzaldehyde (1), which, after
reacting with neat 2,2,2ꢀtrimethoxyꢀ4,5ꢀdimethylꢀ1,3ꢀ
dioxaphosphoꢀlene under heating produced diketone, 4ꢀhydroxyꢀ
ꢀ(2,3,5,6ꢀtetramethylphenyl)pentꢀ3ꢀenꢀ2ꢀone (2) in a moderate
(1.993(3) Å in Pt1, 1.953(9) Å in Pt3). In both structures, the
oxygen atom (O(1)) that is trans to the carbene C(1) atom has a
shorter PtꢀO bond length than the one (O(2)) that is trans to the
phenyl ring by about 0.04 Å. The same trend was also observed
3
yield. The aryl functionalized imidazolium salts and 1,2,4ꢀ 65 in previously reported Pt(C^C*)(acac) compounds and attributed
1
9ꢀ21
triazolium salts were prepared according to the procedures shown
in Scheme 1. The starting materials 1ꢀarylimidazole (3 and 5) and
to the stronger trans effects exerted by the phenyl ring.
An
interesting observation is the close contact between the OH group
of a methanol solvent molecule and the Pt(II) atom in Pt1 as
shown in Fig. 1. The Pt(1)⋅⋅⋅O(3) distance is 3.274(1) Å and the
1
ꢀarylꢀ1Hꢀ1,2,4ꢀtrizole (4 and 6) were synthesized by CuI
25
catalyzed Ullmann condensation in the presence of Cs CO .
2
3
The C^C* chelated Pt(II) complexes were obtained according to a 70 Pt(1)⋅⋅⋅H distance is approximately 2.44 Å. This could be
26
28
modified oneꢀpot synthetic procedure we reported recently. The
Ag(I) carbene intermediate generated by the reaction of the iodide
salts with Ag O in CH Cl was transmetalated with
described as agostic Pt⋅⋅⋅H interactions and is quite interesting
since most previously reported examples of agostic Pt⋅⋅⋅H
interactions are intramolecular in nature in which the H atom is
part of the ligand bound to the Pt(II) center. The most important
2
7
2
2
2
[
PtMe (SMe )] in THF. After the removal of AgI solid and
2 2 2
o
heating at 50 ~ 55 C for 2 hrs to further facilate cyclometalation 75 feature of these complexes is that the duryl ring of the ancillary
of the phenyl ring in the chromophore ligand, pꢀtolyl sulfonic
acid (TsOH) and the ancillary ligand 2 were added along with
Na CO in methanol, generating the corresponding Pt(II)
ligand is nearly perpendicular to the Pt(II) square plane with a
o
dihedral angle of 95.7° and 98.3 in Pt1 and Pt3, respectively.
2
3
The orthogonal arrangement of the duryl ring with respect to the
Pt(II) unit is expected to reduce intermolecular stacking
complexes as white solids, which were purified by column
chromatography on silica gel. The isolated yields of the phenylꢀ 80 interactions of the Pt(II) compounds. Nonetheless, for Pt1,
triazolylidene chelated complexes Pt2 and Pt4 are low (12 ~
13%), compared to those of the phenylꢀimidazolylidene based
complexes Pt1 and Pt3 (45 ~ 55%), which may be caused by
competing protonation of the nitrogen site in the triazolylidene
extended stacking interactions with short intermolecular contacts
involving the Pt(II) central core are observed in the crystal lattice,
as shown in Fig. 3. The shortest atomic separation distance
between two partially stacked phenylꢀimidazolyl ligands is ~3.33
2
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Å while the shortest Pt⋅⋅⋅Pt separation distance is 5.483(1) Å,
which is much longer than the Pt⋅⋅⋅Pt separation distances
Pt3. The shortest Pt⋅⋅⋅Pt separation distance is 5.645(1) Å
between the discrete pair of molecules shown in Fig. 4. The
reported for C^Nꢀchelated Pt(II) compounds that contain an αꢀ 25 shortest atomic contact distance within this pair is ~3.51 Å.
2
2b
phenylꢀβꢀdiketonato ligand, an indication that the αꢀdurylꢀβꢀ
diketonato ligand is more effective in reducing stacking
interactions than the αꢀphenylꢀβꢀdiketonato ligand.
Besides this discrete pair, which does have the exact parallel
arrangement (not related by an inversion center), molecules of
Pt3 do not have the extended parallel arrangement in the crystal
lattice as that observed for Pt1, supporting that TMS group in Pt3
indeed can reduce intermolecular interactions.
5
30
Fig. 1. The crystal structure of Pt1 with 50% thermal ellipsoids and
labeling schemes. Bond lengths (Å) and angles (°): Pt(1)ꢀC(1) 1.953(3),
Pt(1)ꢀC(5) 1.993(3), Pt(1)ꢀO(1) 2.0360(18), Pt(1)ꢀO(2) 2.0779(18), C(1)ꢀ
Pt(1)ꢀC(5) 79.99(11), O(1)ꢀPt(1)ꢀO(2) 88.59(7). C(1)ꢀPt(1)ꢀO(1)
1
0
1
72.68(9), C(5)ꢀPt(1)ꢀO(2) 178.51(9).
Fig. 4. Intermolecular interactions of Pt2.
Phosphorescence
UVꢀVis absorption and phosphorescence spectra of all Pt(II) com
pound are shown in Fig. 5 ꢀ 7. As shown in Fig. 5, all Pt(II) comꢀ
plexes display one broad absorption band in the 300 ~ 375 nm
region with moderate extinction coefficients. The weaker low
energy shoulder band at about 350 nm may be assigned to metalꢀ
toꢀligand charge transfer (MLCT) transitions mixed with intraꢀ
ligand charge transfer (ILCT) transitions, which is supported by
TDꢀDFT calculation results (see the TDꢀDFT section). The
imidazolylidene chelated complexes Pt1 and Pt3 have a stronger
absorption band than their corresponding triazolylidene analogues
Pt2 and Pt4. The TMS group in Pt3 and Pt4 increases the
absorption intensity and redꢀshifts the absorption band, an
3
4
4
5
5
5
0
5
0
5
Fig. 2. The crystal structure of Pt3 with 50% thermal ellipsoids and
labeling schemes. Bond lengths (Å) and angles (°): Pt(1)ꢀC(1) 1.938(10),
Pt(1)ꢀC(6) 1.953(9), Pt(1)ꢀO(1) 2.022(7), Pt(1)ꢀO(2) 2.078(7), C(1)ꢀPt(1)ꢀ
C(6) 79.2(4), O(1)ꢀPt(1)ꢀO(2) 87.3(3), C(1)ꢀPt(1)ꢀO(1) 172.2(4), C(6)ꢀ
∧
indication that the C C*ꢀchelate ligand is likely a major
contributor to the HOMO level of the molecule, which can be
1
5
29
destabilized by electron donating groups.
Pt1, Pt2, Pt3, and Pt4 display weak phosphorescence (ΦPL
<
0.001) in CH Cl2 solution at room temperature under N2
2
atmosphere probably due to the thermal quenching by solvent
molecules. However, in a more "rigid" environment such as
PMMA thin films, these molecules show bright blue
phosphorescent emission with λmax = 458 – 468 nm and ΦPL
=
0.16 to 0.55 at ambient temperature (Fig. 6 and Table 1). The
∧
*
nature of the C C ꢀchelate ligands was found to have a significant
impact on the phosphorescent properties. For example, the
imidazolylidene chelated compounds Pt1 and Pt3 show a broad
and featureless emission peak at λmax = 467 ~ 468 nm, while the
Pt(1)ꢀO(2) 179.0(4).
Fig. 3. Intermolecular stacking interactions of Pt1
60 triazolylidene chelated complexes Pt2 and Pt4 display an
emission peak that is about 10 nm blue shifted (λmax = 458 ~ 459
nm) with distinct vibronic features. Most notably, the ΦPL of the
imidazolylidene chelated complexes is more than 1.6 times
greater than those of the triazolylidene chelated systems. The
2
0
The introduction of the TMS group substitution in Pt3 further
reduces intermolecular stacking interactions. Indeed, as shown in
Fig. 4, there is no extended πꢀstacking interaction in the lattice of
6
5
TMS substitution was also found to have a significant impact on
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Table 1. Absorption and Luminescence Data
b
b,c
a
Emission 77 K
Emission, 298 K
Absorption
Complex
4
ꢀ1 ꢀ1
5 wt% PMMA
10 wt% PMMA
λ
max (nm),
ε
(10 cm M )
λ
max (nm)
τ
p
(ꢀs)
d
d
λ
max (nm)
467
Φ
p
λ
max (nm)
468
Φ
p
Pt1
Pt2
Pt3
Pt4
318 (1.33), 336 (0.46)
313 (0.97), 320 (0.98), 340 (0.42)
321 (1.58), 343 (0.52)
449
446
449
454
8.7
11.5
9.4
0.30
0.16
0.55
0.18
0.38
0.24
0.68
0.29
458
459
467
468
318 (1.31), 323 (1.32), 343 (0.62)
13.8
459
459
a
ꢀ5
b
c
The spectra were measured in degassed THF solution: [M] = 1.0 × 10 . Measured in 2ꢀmethyltetrahydrofuran solution. All the complexes solution in
d
2 2
CH Cl show weak emission (Φ < 0.001). Solid state quantum yields were measured using an integration sphere. All quantum yields are ± 10%.
1
1
2
2
0
5
0
5
from Pt1 to Pt3, although it is much less obvious for Pt2 and Pt4.
This could be attributed to the greater steric shielding provided by
the TMS group. Interestingly, the TMS group has no effect on the
emission energy of the Pt(II) compounds. The other important
observation is that the ΦPL of all Pt(II) compounds increases
substantially with increasing doping concentration in PMMA and
no spectral shift or excimer emission peak was observed. In fact,
the neat solids of these Pt(II) compounds display the same blue
emission peak as that observed in the PMMA films and no
excimer emission was observed (see the ESI). Compared to the
simple Pt(3ꢀmethylꢀ1ꢀphenylꢀ1Hꢀimidazolylidene)(acac) comꢀ
plex, which has a ΦPL of 0.07 in 2% PMMA, the new Pt1 to Pt4
are much more efficient blue emitters, which could only be
explained by the steric shielding provided by the duryl group in
the ancillary ligand. With a ΦPL of 0.68 in 10% PMMA, the TMS
substituted Pt3 complex is the most efficient blue emitter among
the four new compounds we investigated.
20
Fig. 5. UVꢀVis absorption spectra of Pt1, Pt2, Pt3, and Pt4 complexes in
THF (1.0 × 10 M).
ꢀ5
5
Fig. 7. Phosphorescent spectra of Pt1, Pt2, Pt3, and Pt4 in 2ꢀMeꢀTHF at
7
7 K (λex = 320 nm, delay time =110 ꢀs).
To further clarify the origin of the emissive states for these
30
complexes, the time resolved phosphorescence emission spectra
at 77 K were recorded in 2ꢀMeꢀTHF frozen glass for all
compounds and the data are shown in Fig. 7 and Table 1. The 77
K spectra of these compounds display 5 ~ 20 nm rigidochromic
blue shift when compared with those of PMMA thin films
Fig. 6. Photographs showing the emission colours of Pt1, Pt2, Pt3, and
Pt4 complexes in 10 wt% PMMA film (top) and their emission spectra
(bottom) [λex = 320 nm].
phosphorescence, as evidenced by the substantial ΦPL increase 35 recorded at room temperature. Bright blue phosphorescence was
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observed for all compounds at 77 K. The emission spectra of Pt1
and Pt3 at 77 K remain broad and with λmax = ~450 nm, an
the ancillary ligand with large contributions from the d orbital of
the Pt(II) center (17 ~ 28%). In contrast, the LUMO and
indication that the emission is likely from a MLCT transition. In
contrast, the spectra of both Pt2 and Pt4 show wellꢀresolved 55 C Cꢀchelated ligand and the ancillary ligand (see the ESI). These
LUMO+1 levels are mainly the πꢀorbital contributions of the
∧
5
0
5
vibrational features with λmax = 446 and 454 nm, respectively, an
indication that the emission is likely from transitions localized on
the chelate ligands. The phosphorescent decay lifetime of Pt1 and
results indicate that MLCT and ILCT transitions are likely
responsible for the phosphorescence of Pt1, Pt2, Pt3, and Pt4.
Pt3 (τp = 8.7 ꢀ 9.4 ꢀs) are shorter than those of Pt2 and Pt4 ( p
τ =
1
1.5 13.8 ꢀs), further indication that the phenylꢀ
ꢀ
a
1
imidazolylidene based complexes have more Pt(II) involvement
in the phosphorescence than the phenyltriazolylidene based
compounds, which may be responsible for their higher emission
quantum efficiencies. The estimated triplet energy values of all
Pt(II) compounds are in the 3.02 ~ 3.05 eV range, based on the 77
K emission spectra.
Fig. 8. DFT optimized structures of the P1, Pt2, Pt3, and Pt4 in the
1
Electrochemical Properties
The electrochemical behavior of the Pt(II) compounds was
investigated by cyclic voltammetry (CV) using ferroceniꢀ
um/ferrocene as the internal standard. The data are summarized in
Table 2. During the cathodic scan in THF, all complexes
exhibited an irreversible reduction with the reduction potential
ranging from ꢀ2.23 to ꢀ2.27 V. The reduction potentials of Pt2
and Pt4 are 0.20 ~ 0.25 V more positive than those of Pt1 and
Pt3, which may be attributed to the greater electron affinity of the
triazolylidene unit in Pt2 and Pt4.
In addition, the reduction potential of the paraꢀTMS
substituted Pt3 and Pt4 is less negative than their nonꢀsubstituted
counterpart. Using the reduction potentials and the UVꢀVis
absorption spectra, the HOMO and LUMO energy levels of all
these complexes were estimated and shown in Table 2.
2
2
3
0
5
0
a
Table 2. Electrochemical Data
a
Complex
E
red (V)
Optical gap
HOMO
(eV)
LUMO
(eV)
b
c
d
(eV)
ground state.
Pt1
Pt2
Pt3
Pt4
ꢀ2.57
ꢀ2.37
ꢀ2.53
ꢀ2.23
3.33
3.31
3.32
3.30
ꢀ4.95
ꢀ5.13
ꢀ4.98
ꢀ5.26
ꢀ1.62
ꢀ1.82
ꢀ1.66
ꢀ1.96
60 Fig. 9. The isodensity surface plots and energies for the frontier molecular
orbitals of P1, Pt2, Pt3, and Pt4 in the ground state (isocontour value =
0.04).
a
4 6
The CV were recorded in THF solution containing 0.10 M (nꢀBu) PF as
0
+
b
the electrolyte, relative to E (Fc/Fc ) = 0.61 V. Estimated from the UVꢀ
Vis spectra. Estimated from the optical energy gap and the LUMO
energy. Estimated from the reduction potentials.
N
c
Al (100 nm)
d
3
5
LiF (1 nm)
N
N
N
TmPyPb ( 40 nm)
POPCPA or 26mCPy:
x% Pt (15 nm)
DFT Computational study
TAPC (60 nm)
MoO3 (1 nm)
TAPC
N
N
TmPyPb
To further understand the photophysical properties of the Pt(II)
30
complexes Pt1, Pt2, Pt3, and Pt4, DFT and TDꢀDFT
computational study was performed for all Pt(II) compounds by
ITO (70 nm)
O
N
P
Glass Substrate
N
N
3
1
32
4
4
5
0
5
0
using Gaussian 09 software based DFT methods at B3LYP
level using LANL2DZ basis set for platinum metal and 6ꢀ31G(d)
POPCPA
26mCPy
3
3
-1.62
-1.62
basis set for all other atoms. The optimized structures shown in
Fig. 8 agree well with the crystal structures with the duryl group
being perpendicular to the plane of all the Pt(II) square plane. The
key frontier molecular orbitals (FMOs) diagrams in the ground
state are depicted in Fig. 9. Further details and complete diagrams
-
1.84
-2.00
TAPc
-2.00
-
2.30
Pt
4.95
Pt
-
2.78
-2.78
LiF/Al
LiF/Al
TAPc
-
-4.95
POPCCA TmPyPb
-5.24
TmPyPb
-6.68
ITO/MoO3
ITO/MoO3
-
5.60
-5.60 26mCPy
-6.00
are provided in the ESI. As shown in Table 3, the calculated S →
0
S and S → T transitions of all complexes involve mainly three
-6.68
1
0
1
transition configurations (HOMO
LUMO+1, or HOMOꢀ1 → LUMO). The HOMO and HOMOꢀ1
levels are mainly from πꢀorbitals of the C C ꢀchelate ligand and
→
LUMO, HOMO
→
Fig. 10. EL device structure and materials used.
∧
*
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Dynamic Article Links ►
View Article Online
DOI: 10.1039/C4DT03085K
DOI: 10.1039/c0xx00000x
www.rsc.org/xxxxxx
ARTICLE TYPE
a
Table 3. DFT/TDꢀDFT calculation results
b
b
c
Complex
Pt1
HOMO (eV)
ꢀ5.54
LUMO (eV)
ꢀ0.95
E
g
(T
2.93
1
, eV)
S
0
→ T
1
E
g
(S
3.82
1
, eV)
S
0
→ S
1
f
Hꢀ1 → L (34%)
H → L (42%)
Hꢀ1 → L+1
H → L (31%)
H → L+1
42%)
0.0032
(
Pt2
ꢀ5.65
ꢀ1.10
2.94
3.71
0.0137
H → L (61%)
H → L+1
21%)
H → L (45%)
H → L+1
(
21%)
H → L (26%)
Hꢀ1 → L (25%)
H → L (34%)
Hꢀ1 → L+1
30%)
H → L+1
29%)
(
Pt3
Pt4
ꢀ5.53
ꢀ5.65
ꢀ0.96
ꢀ1.15
2.93
2.94
3.78
3.67
0.0078
0.0184
(
28%)
H → L (73%)
(
(
a
b
c
The calculations were performed at the B3LYP level using LANL2DZ basis set for Pt and 6ꢀ31G(d) basis set for all other atoms. in the Ground state.
Oscillator strength.
5
10
15
20
25
Fig. 11. EL spectra and luminanceꢀcurrent densityꢀvoltage (LꢀJꢀV) diagrams of POPCPA host based EL devices using Pt1 (top) or Pt3 (bottom) as a single
30
dopant.
35
that these two compounds have relatively high phosphorescent
quantum yields. Because of the high LUMO level and the large
HOMOꢀLUMO gap of Pt1 or Pt3, it was difficult to find a
suitable host material for them in EL devices. We selected both
(4ꢀ{1ꢀ[4ꢀ(diphenylphosꢀphoryl)phenyl]ꢀcycloꢀhexyl}ꢀphenyl)bisꢀ
Electroluminescence
To evaluate the potential of the new class of blue phosphorescent
emitters for applications in OLEDs, EL devices using Pt1 or Pt3
as the blue dopant were fabricated, based on the consideration
This journal is © The Royal Society of Chemistry [year]
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DOI: 10.1039/C4DT03085K
3
4
(
4ꢀmethylphenyl)amine (POPCPA) and 2,6ꢀdi(9Hꢀcarbazolꢀ9ꢀ
device structure.
3
5
yl)pyridine (26mCpy) as the host because of their high triplet
energy (2.93 eV and 2.80 eV, respectively) and the relatively
high LUMO in case of POPCPA. 1,1ꢀBis[(diꢀ4ꢀ
torylamino)phenyl cyclohexane (TAPC) was used as the hole
transport material because its energy levels match well those of
the host materials. For the electron transporting layer, 1,3,5ꢀtri[(3ꢀ
pyridyl)ꢀphenꢀ3ꢀyl]benzene (TmPyPb) was employed due to its
relative high triplet energy. The structure of the EL device is as
Experimental Section
60
General Information
5
0
5
0
5
0
5
All reactions were carried out under a dry nitrogen atmosphere
using standard Schlenk techniques. Tetrahydrofuran (THF) was
distilled by using sodium and benzophenone as an indicator under
nitrogen prior to use. The starting materials, 1ꢀphenylꢀ1Hꢀ
2
5
25
1
1
2
2
3
3
follows: ITO (70 nm)/MoO3 (1 nm) / TAPC (60 nm) / 65 imdazole (3),
1ꢀphenylꢀ1ꢀHꢀ1,2,4ꢀtriazole (4),
(4ꢀbromoꢀ
2
4
POPCPA(or 26mCpy): Ptꢀemitter (5 or 10 wt%, 15 nm) /
TmpyPb (40 nm) / LiF (1 nm) / Al (100 nm) (see Fig. 10). As
shown by the EL data for 5% and 10% devices for Pt1 and Pt3
with POPCPA as the host in Fig. 11, the performance of the EL
phenyl)trimethylsilane, 1ꢀ(4ꢀ(triꢀmethylsilyl)phenyl)ꢀ1Hꢀimidaꢀ
zole (5), 3ꢀmethylꢀ1ꢀphenylꢀ1Hꢀimidazolꢀ3ꢀium iodide (7), 4ꢀ
24
20
1
9b
methylꢀ1ꢀphenylꢀ1Hꢀ1,2,4ꢀtriazolꢀ4ꢀium iodide (8),
and [Ptꢀ
2
7
Me (SMe )] (bis[dimethyl( ꢀdimethylsulfide)platinum(II)])
ꢀ
2
2
2
devices is poor due to the poor confinement of excitons within 70 were synthesized according to literature procedures. Deuterated
the emitter layer. The EL spectra of all devices for Pt1 and Pt3
display dual emission peaks, one blue emission peak at ~ 470 nm
from the Pt(II) compounds (except for the 5% device of Pt3 that
has considerable host emission contributions) and one orange
emission peak at ~ 590 nm from either excimer or exciplex. As a 75 Water GCT Time of Flight (TOF) mass spectrometer and Thermo
consequence of the dual emission, the emission color of the
POPCPA host based devices is very closed to the true white light
solvents CDCl3 and DMSO were purchased from Cambridge
1
Isotopes and used as acquired without further purification. The H
13
and C NMR spectra were recorded on a Bruker Avance 400
MHz spectrometers. HRꢀEIMS were measured by Micromass /
Scientific Orbitrap Velos Pro mass spectrometer. Elemental
analyses were performed at the elemental analysis laboratory,
University of Montreal, Montreal, Quebec, Canada. UVꢀVis
spectra were obtained on Varian Cary 50 UVꢀVisible spectroꢀ
(e.g. the 5% doped devices of Pt1 has a CIE (xy) coordinates of
(0.32, 0.31). Because no excimer emission peak was observed in
the PL spectrum of either neat film or 50% POPCPA film of Pt1 80 photometer. Cyclic voltammetry (CV) was performed using a
or Pt3 (see the Fig. S7 ꢀ S8 in the ESI), the EL emission peak at
90 nm is likely from exciplex formed between the host and the
charge transport materials. The performance of EL devices using
6mCpy as the host is comparable to those of the POPCPA based
BAS CVꢀ50W voltammetric analyzer with 100 mV/s scan rates.
The electrolytic cell used was a conventional three compartment
cell, with a Pt working electrode, Pt wire auxiliary electrode, and
Ag/AgCl reference electrode. The CV measurements were
5
2
devices except that the host emission is much greater. Further 85 performed at room temperature using 0.10 M NBu PF in THF as
4
6
details can be found in the ESI. These data indicated that in order
the supporting electrolyte under N2 atmosphere. The ferroꢀ
cenium/ferrocene couple (E = 0.61 V) was used as the internal
standard. Excitation and emission spectra were recorded on a
Photon Technologies International QuantaMaster Model 2 specꢀ
∧
*
0
to reveal the true potential of the new C C ꢀchelated Pt(II)
compounds in OLEDs, new and better host/charge transport
materials that have a high triplet energy and a high LUMO level
to match those of the Pt(II) compounds are necessary, which is a 90 trometer. Phosphorescent lifetimes were measured on a Photon
key problem in the research of blue electrophosphorescent
devices.
Technology International Phosphorescent lifetime spectrometer,
Timemaster Cꢀ631F equipped with a xenon flash lamp, and
digital emission photon multiplier tube for both excitation and
emission. The optical energy gap was estimated by the absorption
edge of the absorption spectra. The solution quantum efficiencies
Conclusions
95
We have shown that the use of an
αꢀdurylꢀ
β
ꢀdiketonate ancillary
36
were measured using FIrpic (ΦPL = 0.60) as a standard in
4
4
5
5
0
5
0
5
ligand can improve the blue phosphorescent quantum efficiencies
CH Cl at room temperature under N atmosphere. The emitter
∧
2
2
2
of C C*ꢀchelated Pt(II) compounds based on phenylꢀ
films were prepared by spin coating method for a solution of 5 or
0 wt% Pt complex in a PMMA / THF solution. The solid
imidazolylidene or phenylꢀtriazolylidene chromophores, because
of the greatly reduced intermolecular interactions. A TMS
substituent group on the phenylꢀimidazolylidene chromophore
ligand was found to further enhance the phosphorescent quantum
efficiency of the Pt(II) compounds. The cyclometalated ligands
have an impact on the phosphorescent properties of the Nꢀ
heterocyclic carbene Pt(II) complexes, leading to enhanceꢀments
1
1
1
1
00 quantum efficiencies were measured by an integration sphere in
the air.
DFT computations were performed using Gaussian09, revision
31
B.01 software package and the High Performance Computing
Virtual Laboratory (HPCVL) at Queen’s University. The groundꢀ
32
05 state geometries were fully optimized at the B3LYP level using
of the quantum efficiency as
a blue emitter. The blue
LANL2DZ basis set for platinum metal and 6ꢀ31G(d) basis set
phosphorescence of the Pt(II) complexes based on the phenylꢀ
33
for all other atoms. The initial geometric parameters of Pt1 and
3
imidazolylidene ligand appears to have a much greater MLCT
Pt3 in the calculations were employed from crystal structure data
for geometry optimization. Timeꢀdependent density function
10 theory (TDꢀDFT) calculations were performed to obtain the
vertical singlet and triplet excitation energies. The polarizable
continuum model (PCM) was used to take into account of the
solvent (THF) effect. Density difference plots were produced
character than those based on the phenylꢀtriazolylidene ligand in
3
which the phosphorescence mainly arises from
a
ILCT
transition. Although the EL performance of the new Pt(II)
compounds is poor, the pure white EL color produced by these
compounds is interesting, which deserves further research efforts
to understand the origin of the exciplex emission and optimize the
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 7

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View Article Online
DOI: 10.1039/C4DT03085K
with Gaussview using the iso ontour value of 0.04 au.
1.664 mmol) (5) was reacted with iodomethane (207 ꢀL, 3.33
mmol) in 2 mL of THF for 20 h at 100 C according to general
o
60
Synthesis
procedure. Compound 9 was isolated as a white solid in 95%
1
2
,3,5,6-Tetramethylbenzaldehyde (1): 3ꢀbromoꢀ1,2,4,5ꢀ
yield (566 mg, 1.58 mmol). H NMR (400 MHz, DMSOꢀd , δ,
6
tetramethylbenzene (0.42 g, 2.0 mmol) dissolved in 30 mL of
THF was cooled to ꢀ78 C and nꢀBuLi (1.6 M, 1.3 mL, 2.1 mmol)
ppm): 9.75 (s, 1H, NCHN), 8.29 (s, 1H, NCHC), 7.95 (s, 1H,
o
5
0
5
0
5
0
5
0
5
0
5
CCHN), 7.79 (d, JHꢀH = 7.8 H, 2H, CH ), 7.74 (d, J
= 8.3 H,
Ar
HꢀH
1
3
was added dropwise. After stirring for 1 hour, DMF (0.3 mL, 4.0 65 2H, CH ), 3.95 (s, 3H, NCH ), 0.30 (s, 9H, SiCH ). C NMR
Ar
3
3
o
mmol) was added and stirred for 1 hour at ꢀ78 C. The reaction
(100 MHz, CDCl , δ, ppm): 142.3 (CH ), 135.9 (NCHN), 135.2
3 Ar
was warmed to room temperature and quenched with water. The
reaction mixture was then extracted three times with diethyl ether
(3 x 30 mL). The combined organic phases were washed with
(CH ), 135.0 (CH ), 124.5 (NCHN), 121.0 (CH ), 120.9
Ar Ar Ar
(CCHN), 36.2 (NCH ), ꢀ1.3 (SiCH ).
3
3
1
1
2
2
3
3
4
4
5
5
4-methyl-1-(4-(trimethylsilyl)phenyl)-1H-1,2,4-triazol-4-
water, dried over magnesium sulfate (MgSO ), and then filtered. 70 ium iodide (10): 6 (300 mg, 1.38 mmol) was reacted with
4
The crude product was purified by column chromatography on
iodomethane (172 ꢀL, 2.76 mmol) in 2 mL of THF for 20 h at
o
silica gel (petroleum ether: ethyl acetate = 99: 1 v/v). Yield: 0.14
100 C according to general procedure. Compound 10 was
1
g (0.86 mmol, 43%). H NMR (400 MHz, CDCl ): δ 10.66 (s, 1
isolated as a pale yellowish solid in 82 % yield (405 mg, 1.13
3
1
3
1
H), 7.14 (s, 1 H), 2.42 (s, 6 H), 2.28 (s, 6 H). C NMR (100
mmol). H NMR (400 MHz, DMSOꢀd , δ, ppm): 10.85 (s, 1H,
6
MHz, CDCl ): δ 195.94, 135.77, 135.42, 134.72, 134.47, 19.79, 75 NCHN), 9.37 (s, 1H, NCHN), 7.87 (d, JHꢀH = 8.6 Hz, 2H, CHAr),
3
+
1
5.18; HRꢀEIMS (m/z) [M ] calcd for C H O 162.1045; found,
7.83 (d, JHꢀH = 8.6 Hz, 2H, CH ), 3.99 (s, 3H, NCH ), 0.31 (s,
Ar 3
1
1
14
13
1
62.1039.
-Hydroxy-3-(2,3,5,6-tetramethylphenyl)pent-3-en-2-one
9H, SiCH3). C NMR (100 MHz, CDCl , δ, ppm ): 145.8
3
4
(NCHN), 143.3 (NCHN), 142.1 (CH ), 135.4 (CH ), 135.0
Ar
Ar
(2): The reaction mixture of 1 (0.14 g, 0.86 mmol) and 2,2,2ꢀ
trimethoxyꢀ4,5ꢀdimethylꢀ1,3,2ꢀdioxaphosphole (0.91 g, 4.3
mmol) in a 8 mL vial with no solvent added was stirred for 2 days
(CH ), 119.6 (CH ), 34.3 (NCH ), ꢀ1.4 (SiCH ).
Ar
Ar
3
3
80
General Procedure for Pt(II) Compounds: Imidazolium (or
triazolium) iodide and silver(I) oxide were dissolved/suspended
in dry CH Cl (5 mL) and stirred for 5 h in the dark at room
o
at 70 C. After the addition of methanol (2 mL), the reaction
2
2
o
mixture was stirred for another 6 hrs at 70 C. Methanol was
temperature. After filtration, the solvent was removed under
removed under vacuum and the crude product was purified by
reduced pressure. The resulting white solid with [PtMe (SMe ) ]
2
2 2
o
column chromatography on silica gel (nꢀhexane: ethyl acetate = 85 were dissolved in THF (5 mL) and further heated to 55 C for
1
2
0: 1, v/v). Yield: 0.13 g (0.56 mmol, 65%). H NMR (300 MHz,
another 2 h. After cooling to ambient temperature, the reaction
mixture was stirred for 1 h and filtered. The solution of pꢀtolyl
sulfonic acid monohydrate in THF (2 mL) was added dropwise
and the mixture was stirred for 0.5 h. Afterwards a mixture of 2
CDCl δ, ppm): 16.61 (s, 1 H), 6.98 (s, 1 H), 2.27 (s, 6 H), 2.05
3
,
1
3
(
s, 6 H), 1.75 (s, 6 H). C NMR (75 MHz, CDCl , δ, ppm):
3
190.69, 135.24, 133.97, 133.43, 131.11, 112.95, 23.31, 20.31,
+
1
2
6.42. HRꢀEIMS (m/z) [M ] calcd for C H O 232.1463; found, 90 and Na CO in MeOH (2 mL) was added. After stirring for 5 ~ 10
15 20 2
2 3
32.1470.
-(4-(trimethylsilyl)phenyl)-1H-1,2,4-triazole (6): A Schlenk
flask was charged with CuI (0.17 g, 0.87 mmol), Cs CO (2.84 g,
h, all the solvent was removed under reduced pressure and then
the resulting mixture was extracted with CH Cl (3 x 30 mL). The
1
2
2
2
3
combined organic phases were washed with water, dried over
8.72 mmol), (4ꢀbromophenyl)ꢀtrimethylsilane (1.00 g, 4.36
MgSO , filtered, and concentrated. The residue was purified by
4
mmol), 1Hꢀ1,2,4ꢀtriazole (0.42 g, 6.10 mmol), and DMF (10 mL) 95 column chromatography on silica gel to provide the desired Pt(II)
o
under N atmosphere. The reaction mixture was heated at 120 C
complex.
Pt1: 3ꢀMethylꢀ1ꢀphenylꢀ1Hꢀimidazolꢀ3ꢀium iodide (123 mg,
0.43 mmol) (3), silver(I) oxide (50 mg, 0.22 mmol),
2
for 40 hrs, then cooled to room temperature. After extracting the
product with ethyl acetate and washing with water, the organic
phase was dried over MgSO . After the removal of the solvent,
[PtMe (SMe ) ] (124 mg, 0.22 mmol), pꢀtoluenesulfonic acid
4
2
2 2
the resulting residue was purified by column chromatography on 100 monohydrate (82 mg, 0.43 mmol), 2 (82 mg, 0.43 mmol), and
silica gel to yield compound 6 as a white solid in 50% yield
Na CO3 (46 mg, 0.43 mmol) were reacted according to the
2
1
(
0.47 g, 2.18 mmol). H NMR (400 MHz, CDCl , δ, ppm): 8.56
general procedure. The reaction mixture was purified by column
3
(
s, 1H, NCHN), 8.11 (s, 1H, NCHN), 7.68ꢀ7.62 (m, 4H, CH ),
chromatography on silica gel (CH Cl as eluent) to obtain Pt1
Ar
2
2
1
3
1
0.31 (s, 9H, SiCH3). C NMR (100 MHz, CDCl , δ, ppm)δ:
complex as white solid (138 mg, 0.24 mmol) in 55% yield. H
3
1
1
52.8 (CH ), 141.3 (NCHN), 141.0 (CH ), 137.5 (NCHN), 105 NMR (400 MHz, CDCl , δ, ppm ): 7.83 (dd, pseudoꢀsat, J
=
=
Ar
Ar
3
HꢀPt
+
34.9 (CH ), 119.4 (CH ), ꢀ1.05 (SiCH ). HRꢀEIMS (m/z) [M ]
20.2 Hz, JHꢀH = 6.8 Hz, JHꢀH = 2.0 Hz, 1H, CH ), 7.26 (d, J
Ar HꢀH
Ar
Ar
3
calcd for C H N Si 217.1035; found, 217.1052.
2.0 Hz, 1H, NCHN), 7.06ꢀ6.98 (m, 2H, CH ), 6.96 (d, J = 2.0
11
15
3
Ar
HꢀH
General Procedure for Imidazolium Iodides: A Jꢀyoung
type tube was charged with imidazole (or triaozle) and
Hz, 1H, CH ), 6.94 (s, 1H, CH ), 6.82 (d, J = 2.0 Hz, 1H,
HꢀH
Ar
Ar
NCHN), 4.11 (s, 3H, NCH ), 2.25 (s, 6H, C CH ), 2.07 (s, 6H,
3 Ar 3
1
3
iodomethane. After addition of dry THF, the reaction mixture 110 C CH ), 1.68 (s, 3H, COCH ), 1.59 (s, 3H, COCH ). C NMR
Ar
3
3
3
o
was stirred at 100 C for 20 h. After cooling to room temperature,
(100 MHz, CDCl , δ, ppm ): 183.8 (CO), 183.7 (CO), 147.2
3
the solvent was removed under reduced pressure. The residue was
precipitated by using dichloromethane and nꢀhexane. The
generated solid is filtered off, washed with nꢀhexane and diethyl
ether, and dried under vacuum.
(NCN) 140.0 (PtC), 134.0 (CH ), 133.8 (CH ), 131.8 (CH ),
Ar
Ar
Ar
130.5 (CH ), 125.3 (CH ), 124.3 (CH ), 123.6 (CH ), 120.8
Ar
Ar
Ar
Ar
(NCHC), 114.5 (NC ), 114.1 (CCHN), 110.1 (COCCO), 34.9
Ar
115 (NCH ), 27.8 (COCH ), 27.7 (COCH ), 20.6 (CCH ), 16.7
3
3
3
3
3
-methyl-1-(4-(trimethylsilyl)phenyl)-1H-imi-dazol-3-ium
(CCH ). Anal. Calcd for C H N O Pt: C, 51.45; H, 4.84; N,
3 25 28 2 2
iodide (9): 1ꢀ(4ꢀ(Trimethylsilyl)phenyl)ꢀ1Hꢀimidazole (360 mg,
8
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

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DOI: 10.1039/C4DT03085K
4
.80. Found: C, 51.48; H, 4.89; N, 4.82.
Pt2: 4ꢀmethylꢀ1ꢀphenylꢀ1Hꢀ1,2,4ꢀtriazolꢀ4ꢀium iodide (246
49.38; H, 5.37; N, 6.40. Found: C, 49.40; H, 5.41; N, 6.44.
EL Device Fabrication
60
mg, 0.86 mmol) (4), silver(I) oxide (100 mg, 0.43 mmol),
PtMe (SMe ) ] (248 mg, 0.43 mmol), pꢀtoluenesulfonic acid
[
Devices were fabricated in a threeꢀchamber evaporator (ELꢀOEL
2
2 2
ꢀ
5
5
0
5
0
5
0
5
0
5
0
5
monohydrate (164 mg, 0.86 mmol), 2 (164 mg, 0.86 mmol), and
Na CO (92 mg, 0.86 mmol) were reacted according to the
general procedure. The reaction mixture was purified by column
cluster tool) with a base pressure of ~1 × 10 Pa without breaking
vacuum. The ITO anode is commercially patterned and coated on
2
3
2
glass substrates 50 × 50 mm with a sheet resistance less than 15
chromatography on silica gel (nꢀhexane : ethyl acetate = 8 : 1, 65 ꢁ. Substrates were ultrasonically cleaned with a standard
v/v) to obtain Pt2 complex as white solid (65 mg, 0.11 mmol) in
regiment of Alconox, acetone, and methanol followed by UV
1
1
1
2
2
3
3
4
4
5
5
13% yield. H NMR (400 MHz, CDCl , δ, ppm): 7.88 (s, 1H,
ozone treatment for 15 min. The active area for all devices was 2
3
2
NCHN), 7.84 (dd, pseudoꢀsat, JHꢀPt = 28.4 Hz, JHꢀH = 5.2 Hz, JHꢀH
mm . The film thickness were monitored by a calibrated quartz
=
3.2 Hz, 1H, CH ), 7.30 (dd, J = 7.2 Hz, JHꢀH = 1.6 Hz, 1H,
crystal microbalance and were further verified for singleꢀcarrier
Ar
HꢀH
CH ), 7.10ꢀ7.09 (m, 2H, CH ), 6.95 (s, 1H, CH ), 4.13 (s, 3H, 70 devices using capacitanceꢀvoltage measurements (Agilent
Ar
Ar
Ar
NCH ), 2.26 (s, 6H, C CH ), 2.07 (s, 6H, C CH ), 1.71 (s, 3H,
4294A). IꢀV characteristics were measured using a HP4140B
picoammeter in ambient air. Luminance measurements and EL
spectra were taken using a Minolta LSꢀ110 luminance meter and
Ocean Optics USB200 spectrometer with bare fiber, respectively.
3
Ar
3
Ar
3
1
3
COCH ), 1.61 (s, 3H, COCH ). C NMR (100 MHz, CDCl , δ,
3
3
3
ppm): 184.8 (CO), 183.9 (CO), 154.3 (NCN) 141.6 (PtC), 134.1
(
(
(
NCHN), 133.7 (CH ), 131.3 (CH ), 130.6 (CH ), 125.5
Ar Ar Ar
CH ), 124.1 (CH ), 112.4 (CH ), 111.7 (COCCO), 32.9 75 Additional details regarding device fabrication and characꢀ
Ar
Ar
Ar
37
NCH ), 27.8 (COCH ), 20.6 (C CH ), 16.7 (C CH ). Anal.
terization have been described elsewhere.
3
3
Ar
3
Ar
3
Calcd for C H N O Pt: C, 49.31; H, 4.66; N, 7.19. Found: C,
24
27
3
2
4
9.34; H, 4.68; N, 7.22.
Pt3: Compound 9 (304 mg, 0.85 mmol), silver(I) oxide (98
Acknowledgment
We thank the Natural Sciences and Engineering Research
Council for financial support. S. Wang thanks the Canada
Council for the Arts for the Killam Research Fellowship.
mg, 0.42 mmol), [PtMe (SMe ) ] (244 mg, 0.42 mmol), pꢀ
toluenesulfonic acid monohydrate (161 mg, 0.85 mmol), 2 (197
2
2 2
80
mg, 0.85 mmol), and Na CO (135 mg, 1.27 mmol) were reacted
2
3
according to the general procedure. The reaction mixture was
purified by column chromatography on silica gel (nꢀhexane :
CH Cl = 2 : 1, v/v) to obtain Pt3 complex as white solid (125
Notes and references
a
Department of Chemistry, Queen's University, Kingston, Ontario, K7M
2
2
1
3
N6, Canada. E-mail: suning.wang@chem.queensu.ca; Fax: (+1) 613-
33-6669; Tel: (+1) 613-533-6941.
Department of Materials Science and Engineering, University of
mg, 0.19 mmol) in 45% yield. H NMR (400 MHz, CDCl , δ,
3
5
ppm): 8.02 (d, pseudoꢀt, JHꢀPt = 23.0 Hz, JHꢀH = 6.8 Hz, 1H,
b
8
5
CH ), 7.26 (s, JHꢀH = 2.0 Hz, 1H, NCHN), 7.20ꢀ7.18 (d, JHꢀH
=
Ar
Toronto, Toronto, Ontario, M5S 3E4, Canada.
6
4
1
.8 Hz, 1H, CH ), 6.95ꢀ6.93 (m, 2H, CH ), 6.81 (s, 1H, CH ),
Ar Ar Ar
† Electronic Supplementary Information (ESI) available: NMR spectra,
electrochemical data, crystal structural data, TDꢀDFT computational data,
and EL data. See DOI: 10.1039/b000000x/
.10 (s, 3H, NCH ), 2.26 (s, 6H, C CH ), 2.08 (s, 6H, C CH ),
3
Ar
3
Ar
3
.68 (s, 3H, COCH ), 1.58 (s, 3H, COCH ), 0.28 (s, 9H, SiCH ).
3
3
3
1
3
90 ‡ These authors contributed equally.
C NMR (100 MHz, CDCl , δ, ppm): 183.7 (CO), 151.1 (NCN),
3
1
(a) S. J. Farley, D. L. Rochester, A. L. Thompson, J. A. K. Howard
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1
47.8 (CH ) 140.0 (PtC), 136.4, (CH ), 135.8 (CH ), 134.0
Ar Ar Ar
(CH ), 133.8 (CH ), 130.5 (CH ), 129.0 (CH ), 124.3 (CH ),
Ar Ar Ar Ar Ar
1
3
20.8 (NCHC), 114.4 (NC ), 114.1 (CCHN), 109.5 (COCCO),
Ar
95
4.9 (NCH ), 27.9 (COCH ), 27.8 (COCH ), 20.6 (CCH ), 16.7
3
3
3
3
(CCH ), ꢀ0.69 (SiCH ). Anal. Calcd for C H N O PtSi: C,
3
3
28 36
2
2
5
1.28; H, 5.53; N, 4.27. Found: C, 51.30; H, 5.57; N, 4.32.
1
0089; (f) A. DorazcoꢀGonzalez, Organometallics, 2014, 33, 868.
Pt4: Compound 10 (350 mg, 0.97 mmol), silver(I) oxide (113
2
3
(a) Q. Xu, W. –F. Fu, G. Zhang, Z. Bian, J. Zhang, X. Han and W.
Xu, Catal. Commun., 2008, 10, 49; (b) G. –J. Zhang, X. Gan, Q. –Q.
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8584; (b) Y. ꢀL. Rao and S. Wang, Organometallics, 2011, 30, 4453;
mg, 0.49 mmol), [PtMe (SMe ) ] (280 mg, 0.49 mmol), pꢀ 100
2
2 2
toluenesulfonic acid monohydrate (185 mg, 0.97 mmol), 2 (226
mg, 0.97 mmol), and Na CO (155 mg, 1.46 mmol) were reacted
2
3
according to general procedure. The reaction mixture was
purified by column chromatography on silica gel (nꢀhexane : 105
(c) C. ꢀJ. Lin, Y. ꢀH. Liu, S. –M. Peng, J. –S. Yang, J. Phys. Chem. B,
ethyl acetate = 10 : 1, v/v) to obtain Pt4 complex as white solid
1
2012, 116, 8222; (d) N. Wang, S. ꢀB. Ko, J. –S. Lu, L. D. Chen and S.
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(
77 mg, 0.12 mmol) in 12% yield. H NMR (400 MHz, CDCl , δ,
3
ppm): 8.04 (dd, pseudoꢀt, JHꢀPt = 24.9 Hz, 1H, CH ), 7.87 (s, 1H,
Ar
4
5
NCHN), 7.30 (d, JHꢀH = 3.6 Hz, 2H, CH ), 6.96 (s, 1H, CH ),
Ar
Ar
110
4
1
.13 (s, 3H, NCH ), 2.26 (s, 6H, C CH ), 2.07 (s, 6H, C CH ),
3 Ar 3 Ar 3
6
(a) F. Barigelletti, D. Sandrini, M. Maestri, V. Balzani, A. V.
Zelewsky, L. Chassot, P. Jolliet and U. Maeder, Inorg. Chem., 1988,
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3
3
3
1
3
C NMR (100 MHz, CDCl , δ, ppm): 183.8 (CO), 180.4.9 (CO),
3
2
7, 3644; (b) H. Yersin and D. Donges, Top. Curr. Chem., 2001, 214,
152.6 (NCN) 146.9 (PtC), 141.6 (NCHN), 134.1 (CH ), 133.8
Ar
115
81.
(
(
(
CH ), 130.6 (CH ), 129.5 (CH ), 113.1 (CH ), 111.1
7
(a) J. Brooks, Y. Babaya, S. Lamansky, P. I. Djurovich, I. Tsyba, R.
Bau and M. E. Thompson, Inrog. Chem., 2002, 41, 3055; (b) B. Yin,
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Ar
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COCCO), 32.9 (NCH ), 27.8 (COCH ), 20.6 (C CH ), 16.7
3
3
Ar
3
C CH ), ꢀ0.71 (SiCH ). Anal. Calcd for C H N O PtSi: C,
Ar
3
3
27 35
3
2
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