Changing the Emission Properties of Phosphorescent C^C*-Cyclometalated Thiazol-2-ylidene Platinum(II) Complexes by Variation of the β-Diketonate Ligands

Article abstract of DOI:10.1002/chem.201604456

Cyclometalated thiazol-2-ylidene platinum(II) complexes based on the N-phenyl-4,5-dimethyl-1,3-thiazol-2-ylidene N-heterocyclic carbene (NHC) ligand and seven different β-diketonate ligands have been synthesised and investigated for their structural and p

Full text of DOI:10.1002/chem.201604456

A Journal of
Accepted Article
Title: Changing the Emission Properties of Phosphorescent C^C*
Cyclometalated Thiazol-2-ylidene Platinum(II) Complexes by
Variation of the β-Diketonate Ligands
Authors: Hendrik Leopold, Ute Heinemeyer, Gerhard Wagenblast, Ingo
Muenster, and Thomas Straßner
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Changing the Emission Properties of Phosphorescent C^C*
Cyclometalated Thiazol-2-ylidene Platinum(II) Complexes by
Variation of the β-Diketonate Ligands
Hendrik Leopold,[a] Ute Heinemeyer,[b] Gerhard Wagenblast,[b] Ingo Münster,[b] and Thomas
Strassner*[a]
Abstract: Cyclometalated thiazol-2-ylidene platinum(II) complexes
based on the N-phenyl-4,5-dimethyl-1,3-thiazol-2-ylidene N-
heterocyclic carbene (NHC) ligand and seven different β-diketonate
ligands were synthesized and investigated for their structural and
photophysical properties. The synthesis by an one-pot procedure
starts with in situ formation of the corresponding silver(I) carbene
and transmetalation to platinum. Cyclometalation is then followed by
the reaction with the respective β-diketonate under basic conditions.
All compounds were fully characterized by standard techniques
including 195Pt-NMR. Three solid-state structures revealed quite
different aggregation behaviour depending on the β-diketonate
architecture. The reported complexes show strong phosphorescence
at room temperature in amorphous PMMA films. The emission
wavelength (about 510 nm) is independent from the β-diketonate
ligand, but the use of electronically diverse β-diketonates strongly
100%.[2] This so-called OLED architecture relies on the spin-orbit
coupling (SOC) of the heavy metal atom to promote the
population of the spin-forbidden triplet states after excitation by
intersystem crossing.[3] The following relaxation to the ground-
state proceeds under emission of visible light.[4] Since then, the
concept of triplet harvesting has become one of the most
referred topics in emitter chemistry.[5] High-performance
materials using this concept with high energy-to-photon
conversions were presented to match the prerequisites of
modern day lighting and display technologies.[6]
Platinum(II) complexes were shown to be among the best
emitting materials up until now. Originating from the square-
planar environment and
a coordination number of four
platinum(II) complexes with bidentate,[7] tridentate[8] and even
tetradentate[9] ligands and their devices were presented.[10]
influences the observed quantum yields (QY) and the decay lifetimes. Motifs like C^N cyclometalated platinum metal complexes, e.g.
Theoretical studies employing density functional theory (DFT)
methods support the conclusion of a metal-to-ligand charge transfer
(3MLCT) as the main emission process in accordance to the
reported photophysical properties. Standard organic light emitting
diodes (OLEDs) with unoptimized matrix materials using one of the
complexes showed values of 12.3% external quantum yield (EQE),
24.0 lm W-1 luminous efficacy and 37.8 cd A-1 current efficiency at
300 cd m-2.
based on phenylpyridines, phenylpyrazoles and C^C*
cyclometalating NHC ligands were investigated for their
excellent photophysical properties.[11]
In detail, platinum(II) complexes with bidentate C^N or C^C*
cyclometalating ligands have attracted great scientific interest
due to their high structural and electronic tunability.[12] Especially
platinum(II) complexes with β-diketonate ligands have been
studied intensively (I–V, Scheme 1)[13] since the initial work by
Thompson and co-workers (I, Scheme 1).[14]
Introduction
The discovery of the interaction of stacked layers of different
conducting organic materials, their charge transportation
characteristics and the resulting emission of light from an
organic emitter was
a
major breakthrough for lighting
Scheme 1. General structures of C^N and C^C* cyclometalated bidentate
platinum(II) complexes..
technologies.[1] Shortly after, phosphorescent transition metal
complexes were established as the emitting material and
opened up an elegant way to overcome the classic fluorescence
limit of 25% with the promise of conversion rates of up to
Next to platinum(II) emitters of the basic phenylpyridine-[14] (I,
Scheme 1) and pyrazole-based (II, Scheme 1) motifs,[15] diverse
NHC-based C^C* cyclometalated platinum(II) complexes (III–V,
Scheme 1) provided a new class of emitting materials with high
colour purities and defined emission wavelengths for OLED
application.[13a, 13b, 13h]
To control exciton generation and recombination physics as well
as electron transportation and to avoid emitter aggregations in
OLEDs structurally diverse β-diketonate ligands have been
presented.[6b, 11c, 16] To suppress typical efficiency roll-offs from
aggregation effects followed by thermal quenching and therefore
[a]
H. Leopold, Prof. Dr. T. Strassner
Physikalische Organische Chemie
Technische Universität Dresden 01069 Dresden (Germany)
Fax: (+49) 351-463-39679
E-mail: thomas.strassner@chemie.tu-dresden.de
Homepage: http://www.chm.tu-dresden.de/oc3
Dr. U. Heinemeyer, Dr. G. Wagenblast, Dr. I. Münster
BASF SE 67056 Ludwigshafen (Germany)
[b]
Supporting information for this article can be found under
http://dx.doi.org./10.1002/chem.XXXxxxXXX
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radiationless transitions, the overall architecture of the
followed procedure B. An overview of the synthesized structures
platinum(II) β-diketonate compounds was optimized. In particular, is given in Scheme 3.
C^C* cyclometalated platinum(II) complexes (III and IV, Scheme
1) with sterically demanding and electronically diverse β-
diketonate ligands showed excellent photophysical properties.[13e,
13i]
Recently, the photophysical properties of C^C* cyclometalated
N-aryl-4,5-dimethyl-1,3-thiazol-2-ylidene platinum(II) complexes
with acetylacetonate (acac) as the auxiliary ligand were
presented (V, Scheme 1).[13a] As the N-phenyl-1,3-thiazol-2-
ylidene showed improved photophysical properties compared to
structurally similar imidazole- and triazole-based compounds,[13b,
13h]
we decided to study the influence of electronically and
sterically modified β-diketonates on this new class of platinum
13e]
complexes.[13c,
Especially acetylacetonate derivatives with
aromatic groups led to improved photophysical properties. We
therefore synthesized seven novel, structurally diverse
platinum(II) complexes based on the N-aryl-4,5-dimethyl-1,3-
thiazol-2-ylidene motif to study structural and electronic
influences on the emission properties by variation of the β-
diketonate ligands.
Scheme 2. Synthesis of complexes 9–15: (i) Ag2O, rt to 50 °C, A: DMF (B:
1,4-Dioxane); (ii) Pt(COD)Cl2, rt to 115 °C, A: DMF (B: 1,4-Dioxane,
Butanone); (iii) KOtBu, β-diketonate 2–8, rt to 100 °C, DMF.
Characterization
All complexes were obtained as deeply coloured yellow to
orange solids and were characterized with standard methods.
The complexes show different solubility, which proved to be
beneficial for their purification via flash chromatography, e.g. for
the mesityl- and durylsubstituted compounds 14 and 15 (see
Experimental Section for further details).
Depending on the β-diketonate ligand different thermal
properties were observed. The 3-phenyl- (10), CF3- (11) and
especially the mesityl-substituted complex 14 showed defined
melting points between 238–308 °C, for the other complexes
high decomposition temperatures over 300°C were observed.
The electronic effect of the β-diketonate ligands could also be
observed from the 195Pt-NMR resonance signals which were
found in the typical range between -3314 ppm (9) and -3331
ppm (10) in CDCl3.[13b-d, 13w]
Results and Discussion
Synthesis
The N-phenyl-4,5-dimethyl-1,3-thiazolium hexafluorophosphate
salt 1 (Scheme 2) was prepared by a two step procedure
starting with the synthesis of the corresponding N-Phenyl-4,5-
dimethyl-1,3-thiazol-2-thione. Oxidation in acetic acid followed
by salt metathesis with KPF6 gave the N-phenyl-4,5-dimethyl-
1,3-thiazolium hexafluorophosphate salt 1 as the desired NHC-
precursor.[13a]
The β-diketonate compounds 2, 4–6 (Scheme 2) are
commercially available and were used without further purification.
In an Ullmann-type reaction, 3-phenylpentane-2,4-dione (3) was
synthesized by using copper(I) iodide, L-proline and potassium
carbonate.[17] Friedel-Crafts acylation of the corresponding
substituted benzene derivatives with malonyl chloride and
aluminium(III) chloride yielded the sterically demanding β-
diketonate ligands 1,3-bis(2,4,6-trimethylphenyl)-propane-1,3-
dione (7) and 1,3-bis(2,3,5,6-tetramethylphenyl)propane-1,3-
dione (8).[13c, 18]
The platinum(II) complexes 9–15 were synthesized in an one-
pot procedure by deprotonation of the thiazolium salt 1 with
silver(I) oxide and in situ formation of the corresponding silver(I)
carbene
structure,
transmetalation
to
dichloro(1,5-
cyclooctadiene)- platinum(II) (Pt(COD)Cl2), cyclometalation at
elevated temperatures and reaction with the corresponding
acetylacetonate (acac) derivative using potassium tert-
butanolate as the base (Scheme 2).[13d, 13h]
Over the course of this study we found that dimethylformamide
(DMF) allows to perform the whole reaction without solvent
exchange. Therefore complexes 9–12 were synthesized using
the improved procedure A with yields of up to 36%. The
synthesis of compounds 13–15 with yields of 30% to 41%
Scheme 3. Synthesized complexes 9–15.
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Figure 1. ORTEP representations of complexes 13–15. Thermal ellipsoids are drawn at 50% probability level.
Solid-state structure determination
(see ESI, Figure S1†). The sterically demanding mesityl- and
duryl-groups in compounds 14 and 15 prevent molecular
aggregation and lead to Pt...Pt distances of 7.097(1)–7.273(1) Å
(see Supporting Information, Figure S2-S5). Separated
molecules as found in compounds 14 and 15 are beneficial for
the performance of the OLED as stacking usually reduces the
efficiency of the OLED.[19]
Single-crystals suitable for X-ray diffraction experiments could
be obtained for the platinum(II) complexes with aryl-substituted
acetylacetonate ligands 13–15 as depicted in Fig. 1 (additional
crystal structure data are available from the Supporting
Information, Table S1).
In all three structures the platinum(II) atom is in a square-planar
coordination environment (Table 1) with an O1-Pt1-O2 angle
close to 90° (88.79(12)–91.40(18)°) and an C1-Pt1-C7 angle of
only 79.4(2)–79.9(3)°. The C1-Pt1 distances are the shortest
(1.907(4)–1.918(7) Å) while the Pt1-O1 distances are the
longest (2.073(3)–2.085(4) Å) platinum bonds. The C7-Pt1 bond
distances were found to be 1.972(6)–1.986(6) Å, the Pt1-O2
Photophysical properties
The photophysical properties of all complexes were investigated
in films of 2 wt% emitter concentration in amorphous poly
(methyl methacrylate) (PMMA) at room temperature (RT). The
films were fabricated with a high enough thickness to closely
resemble the amorphous environment in a device. We prefer
this over measurements in solution, since the triplet properties of
transition metal complexes are not independent from their
environment. In previous investigations by our group for the
class of C^C* cyclometalated Pt(II) NHC complexes in solution
using deaerated methylene chloride or 2-methyltetra-hydrofuran
we always observed very similar emission spectra, but
show bond distances of 2.050(3)–2.063(5)
Å (for further
information see ESI, Tables S3–S5†). The bond lengths and
angles are in very good agreement to those previously found in
other solid state structures of C^C* cyclometalated imidazole-
and triazole-based platinum(II) acac complexes.[13c-e, 13i]
Table 1. Selected bond lengths (Å), angles (deg), and dihedral angles (deg) of significantly lower quantum yields. For all these reasons we
complexes 13– 15.
solely focused on solid-state measurements.
The UV/VIS absorption spectra for complexes 9–15 are depicted
13
14
15
in Fig. 2. All complexes show similar bands with strong
absorptions in the high energy region below 275 nm which can
be attributed to π–π*-transitions from the NHC-ligand.[13a, 13c]
The spectra can be divided into two different groups. The
phenyl-, mesityl- and duryl-substituted complexes 13–15 show
higher absorption values together with broader shoulders,
especially in the region between 340 nm to 360 nm. Contrary to
them complexes 9–12 reveal weaker absorptions and sharper
maxima at wavelengths of 360 nm to 365 nm. These
absorptions are described as metal-to-ligand charge transfer
C1–Pt1
1.907(4)
1.981(5)
2.073(3)
2.050(3)
79.4(2)
1.914(6)
1.972(6)
2.080(4)
2.056(4)
79.9(3)
1.918(7)
1.986(6)
2.085(4)
2.063(5)
79.8(3)
C7–Pt1
Pt1–O1
Pt1–O2
C1–Pt1–C7
O1–Pt1–O2
C1–N1–C6–C7
88.79(12)
2.3(6)
90.59(16)
4.1(7)
91.40(18)
-3.2(7)
(1MLCT) states in the literature[13a, 13c]
.
Depending on the bulkiness of the aryl-groups of the β-
diketonate ligand different molecular aggregates and Pt...Pt-
distances can be observed for compounds 13–15. π–π
interactions of molecular pairs, especially of the NHC ligands
with the horizontally oriented phenyl groups, lead to
intermolecular Pt...Pt distances of 5.7971(5) Å for compound 13,
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this position. Similar effects on the QYs have been reported by
Wang and co-workers for imidazole-based platinum(II)
complexes with a 3-duryl-substituted β-diketonate ligand.[13v]
Complexes 12–15 show overall enhanced emission properties
with quantum yields of up to 66 % and decay lifetimes between
5.4–11.4 µs. This beneficial effect of bulky substituents was
previously also found for phenylimidazole- and phenyltriazole
based platinum(II) complexes.[13e, 13i]
Especially, with a QY of 66 % and a decay lifetime of 9.0 µs
complex 14 with 1,3-bis(2,4,6-trimethylphenyl)propane-1,3-
dionato ligand shows the most promising properties for use as
an emitting material in OLEDs.
1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
9
10
12
14
11
13
15
250
275
300
325
350
375
400
wavelength [nm]
Figure 2. Absorption spectra of complexes 9–15 (2 wt% in PMMA, RT).
Table 2. Photoluminescence data (2 wt% in PMMA, RT) of the complexes 9–
15.
Emission spectra for the 2 wt% films of complexes 9, 10 and 12–
15 in PMMA are shown in Fig. 3 (complex 11 is not shown due
to its low quantum yield;[13f] for separate spectra of all complexes
please refer to the ESI, Figures S6–S12†). With the exception of
the CF3-substituted compound 11 all complexes show
phosphorescence at room temperature in the green to yellow
region of the visible spectrum (508–526 nm) with quite different
quantum yields and decay times (Table 2).
#
λexc (nm)a
CIE x;yb
λem (nm)c
ϕd
τ0(µs)e
13.7
9
370
370
340
360
370
370
360
0.29;0.51
0.27;0.52
0.44;0.49
0.26;0.52
0.33;0.57
0.26;0.52
0.26;0.52
509
508
546
508
526
508
508
0.17
0.49
<0.01
0.63
0.57
0.66
0.64
10
11
12
13
14
15
9.6
n.d.f
11.4
5.4
Broad emission bands with a wavelength maximum at about 510
nm, uniquely independent from the β–diketonate ligand, are
revealed (see Fig. 3). Only complex 13 with the 1,3-diphenyl-
9.0
10.7
aExcitation wavelength. bCIE coordinates at RT. cMaximum emission
wavelength. dQuantum yield at λexc; N2 atmosphere. eDecay lifetimes (excited
by laser pulses (355 nm, 1 ns)) given as τ0 = τv/ϕ. fn.d. = not determined.
1,3-propanedionato ligand shows
a
red-shifted emission
maximum at 526 nm due to a change of the lowest unoccupied
molecular orbital (LUMO) from the thiazole ligand onto the β–
diketonate ligand, in agreement with DFT calculations (see DFT
calculations section).[13c]
In addition, the photophysical performance of pure amorphous
emitter films (100 %, RT) was investigated (see ESI, Fig. S13,
S14 and Table S2†). In all cases reduced QYs are observed in
1
9
0,9
10
0,8
the neat films due to aggregation induced quenching effects.[11b,
12
20]
0,7
13
Compared to the data from the 2 wt% films, complex 10 shows a
strongly red-shifted maximum emission wavelength of 675 nm,
which is attributed to a stacking at higher concentrations. On the
other hand the aryl-substituted compounds 14 and 15 retain
0,6
14
0,5
15
0,4
0,3
0,2
0,1
0
their characteristic emission properties with
a maximum
emission wavelength still at about 515 nm. These results are in
good agreement with the data from the solid state structures
where based on the structural data we concluded that they show
a low tendency to stack and are not likely to form Pt...Pt
interactions.
400
450
500
550
600
650
700
750
800
wavelength [nm]
Figure 3. Emission spectra of complexes 9, 10 and 12–15 (2 wt% in PMMA,
In agreement with the broad unstructured emission bands and
RT).
3
the stable emission wavelengths a strong MLCT-participation in
the main emission processes is proposed. The reported
complexes show interesting effects on the photophysical
properties upon changing the β-diketonate ligand, compared to a
similar N-phenyl-1,3-thiazol-2-ylidene platinum(II) complex with
an unsubstituted acac-system.[13a]
For complex 9 with the 3-methylpentane-2,4-dionato ligand a
quantum yield of 17 % was observed. The negative effect of the
additional methyl group in 3-position had been reported before
for imidazole-based systems.[13c] A phenyl group in 3-position
leads to a better quantum yield of 49%, but is still not as good as
what was found for complexes 12-15 with hydrogen atoms in
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DFT calculations
For all complexes 9-15 geometry optimizations were performed
using DFT methods (B3LYP, BP86) on the 6-31G(d) double-ξ
level of theory. The validity of the chosen level of theory can be
seen from the good agreement between the calculated
structures of complexes 13–15 and the solid state structure data
(see ESI, Tables S3–S5†). For these complexes the B3LYP/
6-31G(d) results are in good agreement to the experimental
solid state data, significantly better than the BP86 functional with
the same basis set.
Figure 4. Mixed-matrix device layout. 17
=
2,8-bis(triphenylsilyl)di-
For complexes 9, 11 and 13 the calculated triplet-state
structures show notable distortions relative to their ground-state
structures (see ESI, Tables S6-S9†), which might explain why
these three compounds were experimentally found to show low
QYs attributed to fast non-radiative decays from these pseudo-
Jahn-Teller conformations.[10, 13c]
For all complexes frontier molecular orbitals (FMOs) of the
ground-state structures and the spin densities of the triplet-state
structures were calculated and plotted to further investigate the
emission process (see ESI, Figure S15†). All calculated
structures reveal a strong participation of the NHC-ligand and
the metal centre in agreement with the observed photophysical
properties and emission bands.
As discussed earlier, compound 13 shows a different behaviour.
Here the LUMO is situated on the β-diketonate due to the
orientation of the phenyl groups relative to the plane of the
platinum-NHC-system. As can be seen from the photophysical
properties, this leads to a different emission process compared
to compounds 14 and 15, which is further supported by an
observed triplet distortion and the shifted spin density onto the β-
diketonate.
A previously described model for the prediction of the maximum
emission wavelength applied to these novel complexes revealed
a good agreement of calculated and experimental values (see
ESI, Tables S10 and S11†).[21] In addition to previously reported
predictions[13a] for this class of platinum(II) compounds, and
similar good agreements of calculation and experiment, further
studies can be reliably based on the results from the reported
prediction model.
benzo[b,d]furan, 18 = [Ir(dpbic)3]. ETL = electron-transport layer, HBL = hole-
blocking layer, EML = emission layer, HTL = hole-transport layer, HIL = hole-
injection layer. BCP = 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. LiQ = 8-
hydroxyquinolinolatolithium.
Optimization of the mixed-matrix OLEDs started with an ETL
thickness of 30 nm and a doping concentration of 5% of the
hole-transporter Ir(dpbic)3 (18). The device showed promising
results with an EQE of 9.3%, an operating voltage of 6.6 V, a
current efficiency of 29.6 cd A-1 and a luminous efficacy of 14.2
lm W-1 (see Table 3 for optimization data and Fig. 5 for resulting
graphs). Further doping of the EML with increasing
concentrations of Ir(dpbic)3 (18) lowered the operating voltage,
slightly affecting the overall charge transporting characteristics
as can be seen from the current density plot in Fig. 5. Increasing
the hole-transporter capability furthermore resulted in an overall
increased performance, affecting external quantum yields,
current efficiencies and luminous efficacies.
The optimal architecture and composition was a combination of
a 30 nm thick ETL and a doping concentration of 20% with
Ir(dpbic)3 (18). Said device showed an EQE of 12.3%, a
luminous efficacy of 24.0 lm W-1 and a current efficiency of 37.8
cd A-1 at 300 cd m-2. In addition, this device showed a maximum
luminance as high as 12510 cd m-2 (Fig. 6).
Table 3. Device performance with complex 14a at RT and 300 cd m-2.
Doping
of 18
[%]
Thickness
d of ETL
[nm]
CIE
Voltage
[V]
Curr. eff.
[cd A-1]
Lum.
eff.
EQEb
[%]
[x;y]
Electroluminescence
[lm W-1]
For the fabrication of OLEDs, compound 14 not only revealed
promising thermal properties to be used in the deposition of thin
layers under high vacuum conditions but also showed high
quantum yields with a decay lifetime of 10.0 µs and stable
emission properties in neat films. In addition, the investigation of
the corresponding solid state structure showed a high steric
demand of the single molecule preventing molecular
aggregation and accompanied performance losses.[19] With a
yield of 40% even in a scale of 3.2 mmol, complex 14 was
additionally accessible in high quantities.
5
30
35
30
35
30
35
0.34;0.56
0.32;0.56
0.31;0.55
0.32;0.55
0.30;0.54
0.30;0.54
6.6
6.7
5.8
5.9
5.0
5.0
29.6
24.5
32.5
28.0
37.8
35.6
14.2
11.5
17.6
14.8
24.0
22.4
9.3
7.7
5
10
10
20
20
10.3
8.9
12.3
11.6
aEmission layer was doped with 15% of complex 14. bExternal quantum efficiency
The device architecture is presented in Fig. 4 (see the
Experimental Section for details). To compare our results with
previously reported materials[13c, 13g] the given device setup was
chosen using 2,8-bis(triphenylsilyl)dibenzo[b,d]furan (17) as the
host material.[22]
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Conclusions
In this study seven novel phosphorescent platinum(II)
complexes based on the C^C* cyclometalating ligand 4,5-
dimethyl-3-phenyl-1,3-thiazol-2-ylidene were synthesized and
investigated. The influence of different O^O chelating β-
diketonates on the photophysical properties was demonstrated.
All complexes but the CF3-substituted compound emit at room
temperature with high quantum yields up to 66% and short
decay lifetimes of 5.4–13.7 µs in 2 wt% PMMA films. Emission
spectra showed broad band forms with wavelength maxima in
the green region of the visible spectrum (508-526 nm)
independent from the β-diketonate ligand. In contrast to
previously reported C^C* cyclometalated complexes based on
imidazole or triazole NHCs this emission behaviour is unique for
this class of complexes regarding their photophysical properties.
Investigations of frontier molecular orbitals as well as spin
densities calculated by DFT methods further support the
conclusion for a 3MLCT with a strong participation of the thiazole
NHC ligand as the main emission process. For three complexes
solid-state structures were determined and different molecular
aggregations were revealed, depending on the steric demand of
the β-diketonate ligand. With these novel complexes the
emission properties regarding quantum yields and decay
lifetimes can be fine-tuned without affecting the overall emission
wavelength characteristics.
Figure 5. Mixed-matrix device data at emitter (14) concentrations of 15% with
different concentrations of 18 and varied thickness of the ETL (5% 18, d(ETL)
= 30 nm, black; 5% 18, d(ETL) = 35 nm, red; 10% 18, d(ETL) = 30 nm, green;
10% 18, d(ETL) = 35 nm, blue; 20% 18, d(ETL) = 30 nm, cyan; 20% 18,
d(ETL) = 35 nm, orange) plotted against the voltage.
Previously, the electroluminescent properties of C^C*
cyclometalated platinum(II) complexes based on imidazole NHC
With the most promising complex devices with an EQE as high
as 7.7%, a luminous efficacy of 11.5 lm W-1 and a current
efficiency of 24.5 cd A-1 at 300 cd m-2 with a green emission
colour were prepared. By optimizing the doping concentration of
the emission layer with an iridium hole-transporter and the
thickness of the electron transport layer values of 12.3% EQE,
24.0 lm W-1 and 37.8 cd A-1 at 300 cd m-2 were achieved.
ligands and acetylacetonate derivatives adopting the same
13g]
device architecture were reported.[13c,
The novel device
based on complex 14 shows improved characteristics in
comparison to the previously reported devices (12.6% EQE,
11.9 lm W-1 and 25.2 cd A-1 at 300 cd m-2)[13c] with better
luminous efficacies and current efficiencies while showing a
similar external quantum yield and using only 15% of complex
14 in the EML.
Experimental Section
General considerations
All complex syntheses were performed under an argon atmosphere and
the exclusion of light, using flame dried Schlenk tubes. Solvents of at
least 99.0% purity were used in this study. DMF and 1,4-Dioxane were
dried using standard techniques and stored under an argon atmosphere
over molecular sieves (3 Å). Dichloro(1,5-cyclooctadiene)platinum(II)
23]
(Pt(COD)Cl2),[13h,
3-phenylpentane-2,4-dione (3),[17] 1,3-bis(2,4,6-
trimethylphenyl)propane-1,3-dione
(7)[18]
and
1,3-bis(2,3,5,6-
tetramethylphenyl)propane-1,3-dione (8)[13c] were prepared as described
in the literature. Compound 1 was synthesized according to a procedure
previously described in the literature.[13a] Chemicals were obtained from
common suppliers and used without further purification. 1H-, 13C-, 19F-
and 195Pt-NMR spectra were recorded on Bruker NMR spectrometers.
1H- and 13C-spectra were referenced internally by using the resonances
of the solvent (1H: 7.26 ppm, 13C: 77.0 ppm for CDCl3; 1H: 2.50 ppm, 13C:
39.43 ppm for DMSO-d6). 19F-NMR spectra are referenced externally
against trifluoromethylbenzene as the standard signal. 195Pt-NMR spectra
were referenced externally by using potassium tetrachloroplatinate(II) in
D2O (-1617.2 ppm (PtCl42-), -2654.1 ppm (PtCl2)). Deuterated chloroform
was filtered over basic alumina prior to use. Shifts δ are given in ppm,
coupling constants J in Hz. Electrospray ionization mass spectra of the
complexes 9–15 were measured on a Bruker Esquire MS with ion trap
detector. Elemental analyses were performed on a Hekatech elemental
Figure 6. Mixed-matrix device EQEs plotted against the luminance at emitter
(14) concentrations of 15% with different concentrations of 18 and varied
thickness of the ETL (5% 18, d(ETL) = 30 nm, black; 5% 18, d(ETL) = 35 nm,
red; 10% 18, d(ETL) = 30 nm, green; 10% 18, d(ETL) = 35 nm, blue; 20% 18,
d(ETL) = 30 nm, cyan; 20% 18, d(ETL) = 35 nm, orange).
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10.1002/chem.201604456
Chemistry - A European Journal
FULL PAPER
analyser by the microanalytical laboratory of our institute. Uncorrected
melting points have been determined using a Wagner and Munz Poly
Therm A system. Photoluminescence measurements were performed in
thin PMMA films doped with 2 wt% emitter or from neat emitter films. The
emitter films were prepared by doctor blading a solution of emitter in a 10
wt % PMMA solution in dichloromethane on a quartz substrate with a 60
μm doctor blade. The film was dried, and the emission was measured
under nitrogen. Excitation was conducted at wavelengths of 340−370 nm
(Xe lamp with a monochromator), and the emission was detected with a
calibrated quantum yield detection system (Hamamatsu, model C9920-
02). The uncertainty of the quantum yield is ±2% for quantum yields of
>10%. The phosphorescence decay was measured by excitation with
pulses of a THG-NdYAG laser (355 nm, 1 ns) and time-resolved photon
counting by a multichannel scaling (MCS) technique. The absorption
spectra were measured on a Zeiss MCS601 spectrometer.
for all atoms and anomalous dispersion corrections for the non-hydrogen
atoms were taken from the International Tables for Crystallography.[28] All
calculations were performed with the programs COLLECT,[29] DIRAX,[30]
EVALCCD,[31] SIR92,[26b] SIR97,[26a] SADABS,[25] the SHELXL-97
package,[32] and PLATON.[33] Images of the solid state structures were
generated with ORTEP-3[34] and MERCURY.[35] CCDC 1484566-
1484568 contain the supplementary crystallographic data for compounds
13-15. These data are provided free of charge by The Cambridge
Crystallographic Data Centre.
Computational details
The Gaussian09 package[36] was used to perform all quantum chemical
calculations employing the density functional hybrid model B3LYP[37] and
gradient-corrected BP86.[38] Both functionals were combined with a 6-
31G(d) basis set.[39] In all calculations platinum was described with a
decontracted Hay-Wadt(n+1) ECP and basis set.[40] All given structures
were verified as true minima by vibrational frequency analysis and the
absence of negative eigenvalues. FMOs and spin densities were
visualized by GaussView.[41]
Device fabrication
For the production of the devices and testing, an ITO substrate used as
the anode was first cleaned by commercial detergents for the LCD-
Production (Deconex® 20NS and 25ORGAN-ACID®) followed by
immersion in an acetone/isopropanole-mixture in an ultrasonic bath.
Afterwards the substrate is treated with ozone to remove residues of
organic material. This treatment also improves the hole-injection
properties of the ITO substrate. Then the hole-injection layer is spin-
coated from solution. The devices were fabricated by thermal deposition
of thin layers under high vacuum conditions with rates of approximately
0.5–5 nm min-1 at 10-7 to 10-9 mbar on an indium tin oxide (ITO) coated
glass substrate with a 35 nm spin-coated layer of Plexcore. On top of the
ITO substrate layer of molybdenum oxide blended with tris(1,3-
diphenylbenzo[d]imidazol-2-ylidene)iridium(III) (Ir(dpbic)3, 18) was
deposited as hole-transport layer followed layer of pure Ir(dpbic)3 (18) as
electron blocking layer. The emission layer was mixed with 15% of
emitter 14 and differing concentrations of Ir(dpbic)3 (5%, 10% and 20%)
to improve the charge carrier balance. After deposition of hole-blocking
layer of 2,8-bis(triphenylsilyl)dibenzo[b,d]furan (17) the thickness of the
electron-transport layer of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline
(BCP) blended with 8-hydroxyquinolinolato-lithium (LiQ)[24] was varied
(30 nm and 35 nm) to improve the cavities regarding said devices. Finally
a layer of 0.75 nm lithium fluoride and a 100 nm aluminium electrode are
deposited. All diodes are sealed with glass in an inert nitrogen
atmosphere. For characterization of the OLEDs the electroluminescence
spectra were measured at various currents and voltages. The I–V
characteristic was measured in combination with the emitted light.
Synthesis of complexes 9–15
General Procedure A and B: The General Procedure A employed in
this study starts by adding dry DMF to a mixture of N-phenyl-4,5-
dimethylthiazolium salt 1 and 0.55 eq. of Ag2O in a dry Schlenk tube. The
resulting solution is stirred at room temperature for 2 hours and for 22 h
at 50 °C under the exclusion of light. After addition of 1 eq. Pt(COD)Cl2
further 2 h hours of stirring at room temperature, 22 hours of stirring at
115 °C are followed by addition of 4.0 eq. of the corresponding
acetylacetonate derivative and 4.0 eq. of KOtBu. Afterwards the final
mixture is stirred at room temperature for 24 hours and then heated to
100 °C for 6 hours. All volatiles are removed in vacuo, the remaining
solid is dispersed in 50 ml of distilled water and filtered. The solid residue
is dissolved in dichloromethane and the complex isolated by flash column
chromatography using pure dichloromethane for compounds 9–12 and
an isohexanes/ethyl acetate mixture (5:1) for compound 14 as the eluent.
Subsequent washing with isohexanes and diethylether yielded the pure
complexes. The General Procedure B follows the same time-temperature
sequence but uses dry 1,4-dioxane as the solvent for the reaction of the
N-arylthiazolium salt 1 with Ag2O. In the transmetalation step before the
addition of Pt(COD)Cl2 2-Butanone is added. After 2 h hours of stirring at
room temperature and 22 hours of stirring at 115 °C the solvent is
removed in vacuo and dry DMF, 4.0 eq. the corresponding
acetylacetonate derivative and 4.0 eq. of KOtBu are added. Drying,
washing and remains the same as described above. Complex 13 was
isolated by flash column chromatography using pure dichloromethane.
Compound 14 was isolated as described in General Procedure A.
Compound 15 was purified using an isohexanes/ethyl acetate mixture
(3:1) as the eluent.
X-ray crystallography
Crystals of compound 13 and 15 were grown by slow evaporation of a
saturated dichloromethane solution. Compound 13 crystallized as orange
prisms, whereas compound 15 crystallized as green plates. Slow infusion
of a saturated dichloromethane solution of complex 14 with diethyl ether
yielded the corresponding single crystals as thin yellow needles.
Preliminary examination and data collection were carried out on a
NONIUS κ-CCD diffraction system (FR590) equipped with an Oxford
Cryosystem cooling system at the window of a fine-focus sealed tube
using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). The
reflections were merged and corrected from Lorentz, polarization and
decay effects. Absorption correction was applied using SADABS.[25] The
structures were solved by a combination of direct methods[26] with the aid
of difference Fourier synthesis and were refined against all data using
SHELXL-97.[27] Hydrogen atoms were assigned to ideal positions using
the SHELXL-97 riding model. All non-hydrogen atoms were refined with
anisotropic displacement parameters. Full-matrix least-squares
(SP-4-4)-[4,5-dimethyl-3-phenyl-κC’-1,3-thiazol-2-ylidene-κC]-[3-
methylpentane-1,3-dionato-κO,κO’] platinum(II) (9). According to the
General Procedure A 20 ml of dry DMF were added to a mixture of 268
mg (0.8 mmol) N-phenyl-4,5-dimethylthiazolium salt 1 and 102 mg of
Ag2O (0.44 mmol, 0.55 eq.). Stepwise addition of 299 mg Pt(COD)Cl2
(0.8 mmol, 1 eq.), 384 mg of 3-methylpentane-2,4-dione (2) (3.2 mmol,
4.0 eq.), 359 mg of KOtBu (3.2 mmol, 4.0 eq.) and following General
Procedure A in temperature and workup steps yielded complex 9 as a
yellow powder (87 mg, 21.9 %). M.p.: dec. >305 °C. 1H-NMR (CDCl3,
25 °C, 500 MHz): δ 8.02–7.74 (m, 1H, CHarom), 7.47–7.33 (m, 1H,
CHarom), 7.16–6.98 (m, 2H, CHarom), 2.70 (s, 3H, CH3), 2.26 (s, 3H, CH3),
2.18 (s, 3H, CH3), 2.14 (s, 3H, CH3), 1.99 (s, 3H, CH3) ppm. 13C-NMR
(CDCl3, 25 °C, 125 MHz): δ 185.1 (CO), 183.6 (CO), 178.4 (NCS), 151.4
(Ci-Pt), 136.9 (Ci), 132.5 (CHarom), 128.5 (Ci), 125.4 (CHarom.), 123.4
(CHarom), 123.2 (Ci), 113.3 (CHarom), 105.9 (Ci), 28.4 (CH3;acac), 28.3
2
refinements were carried out by minimizing Σw(Fo − Fc2)2 with the
SHELXL-97 weighting scheme. Details of the structure determinations
are given in the Supporting Information. Neutral-atom scattering factors
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10.1002/chem.201604456
Chemistry - A European Journal
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(CH3;acac), 16.6 (CH3;acac), 14.1 (CH3), 12.7 (CH3) ppm. 195Pt-NMR (65
MHz, 25 °C, CDCl3): δ -3314 ppm. MS (ESI+, m/z, fragment): 497.2
(M+H)+. Anal. Calc. for C17H19NO2PtS: C, 41.13; H, 3.86; N, 2.82; S,
6.45%. Found: C, 40.85; H, 3.82; N, 2.92; S, 6.81%.
According to the General Procedure B 20 ml of dry 1,4-dioxane were
added to
a
mixture of 268 mg (0.8 mmol) N-phenyl-4,5-
dimethylthiazolium salt 1 and 102 mg of Ag2O (0.44 mmol, 0.55 eq.).
Stepwise addition of 299 mg Pt(COD)Cl2 (0.8 mmol, 1 eq.), 732 mg of
1,3-diphenylpropane-1,3-dione (6) (3.2 mmol, 4.0 eq.) and 359 mg of
KOtBu (3.2 mmol, 4.0 eq.) and following General Procedure B in
temperature and workup steps yielded complex 13 as a bright orange
powder (146 mg, 30.0 %). M.p.: dec. >314 °C. 1H-NMR (CDCl3, 25 °C,
300 MHz): δ 8.12 (d, J = 7.9 Hz, 4H, CHarom), 8.07–7.96 (m, 1H, CHarom),
7.58–7.40 (m, 7H, CHarom), 7.21–7.01 (m, 2H, CHarom), 6.84 (s, 1H,
CHacac), 2.73 (s, 3H, CH3), 2.32 (s, 3H, CH3) ppm. 13C-NMR (CDCl3,
25 °C, 75 MHz): δ 180.1 (CO), 180.0 (CO), 177.8 (NCS), 140.1 (2C, Ci),
137.1 (Ci), 132.9 (CHarom), 130.9 (CHarom), 130.8 (CHarom), 128.9 (CHarom),
128.7 (CHarom), 128.5 (3C, CHarom), 127.9 (Ci), 127.3 (3C, CHarom), 127.2
(Ci), 125.7 (CHarom), 123.6 (CHarom), 113.5 (CHarom), 96.7 (CHarom), 14.2
(CH3), 12.8 (CH3) ppm. 195Pt-NMR (65 MHz, 25 °C, CDCl3): δ -3293 ppm.
MS (ESI+, m/z, fragment): 607.2 (M+H)+. Anal. Calc. for C26H21NO2PtS: C,
51.48; H, 3.49; N, 2.31; S, 5.29%. Found: C, 51.34; H, 3.32; N, 2.38; S,
5.38%.
(SP-4-4)-[4,5-dimethyl-3-phenyl-κC’-1,3-thiazol-2-ylidene-κC]-[3-
phenylpentane-2,4-dionato-κO,κO’] platinum(II) (10). According to the
General Procedure A 20 ml of dry DMF were added to a mixture of 268
mg (0.8 mmol) N-phenyl-4,5-dimethylthiazolium salt 1 and 102 mg of
Ag2O (0.44 mmol, 0.55 eq.). Stepwise addition of 299 mg Pt(COD)Cl2
(0.8 mmol, 1 eq.), 564 mg of 3-phenylpentane-2,4-dione (3) (3.2 mmol,
4.0 eq.), 359 mg of KOtBu (3.2 mmol, 4.0 eq.) and following General
Procedure A in temperature and workup steps yielded complex 10 as a
yellow powder (75 mg, 16.8 %). M.p.: 260 °C. 1H-NMR (CDCl3, 25 °C,
500 MHz): δ 7.99–7.79 (m, 1H, CHarom), 7.47–7.33 (m, 3H, CHarom), 7.33–
7.27 (m, 1H, CHarom), 7.24–7.17 (m, 2H, CHarom), 7.16–7.00 (m, 2H,
CHarom), 2.70 (s, 3H, CH3), 2.28 (s, 3H, CH3), 1.83 (s, 3H, CH3), 1.79 (s,
3H, CH3) ppm. 13C-NMR (CDCl3, 25 °C, 125 MHz): δ 185.3 (CO), 184.1
(CO), 177.9 (NCS), 151.4 (Ci-Pt), 141.7 (Ci), 137.0 (Ci), 132.5 (CHarom),
131.9 (2C, CHarom), 128.8 (2C, CHarom), 128.1 (Ci), 126.7 (CHarom), 125.5
(CHarom.), 123.6 (Ci), 123.4 (CHarom), 117.4 (Ci), 113.4 (CHarom.), 29.1
(CH3;acac), 28.9 (CH3;acac), 14.1 (CH3), 12.7 (CH3) ppm. 195Pt-NMR (65
MHz, 25 °C, CDCl3): δ -3331 ppm. MS (ESI+, m/z, fragment): 559.3
(M+H)+. Anal. Calc. for C22H21NO2PtS: C, 47.31; H, 3.79; N, 2.52; S,
5.74%. Found: C, 47.69; H, 3.53; N, 2.54; S, 5.97%.
(SP-4-4)-[4,5-dimethyl-3-phenyl-κC’-1,3-thiazol-2-ylidene-κC]-[1,3-
bis(2,4,6-trimethylphenyl)propane-1,3-dionato-κO,κO’]platinum(II)
(14). According to the General Procedure A 20 ml of dry DMF were
added to
a
mixture of 1262 mg (3.2 mmol) N-phenyl-4,5-
dimethylthiazolium salt 1 and 408 mg of Ag2O (1.76 mmol, 0.55 eq.).
Stepwise addition of 1196 mg Pt(COD)Cl2 (3.2 mmol, 1 eq.), 3.95 g 1,3-
bis(2,4,6-trimethylphenyl)propane-1,3-dione (7) (12.8 mmol, 4.0 eq.),
1.48 g of KOtBu (12.8 mmol, 4.0 eq.) and following General Procedure A
in temperature and workup steps yielded complex 14 as a yellow powder
(874 mg, 39.5 %). According to the General Procedure B 20 ml of dry
1,4-dioxane were added to a mixture of 268 mg (0.8 mmol) N-phenyl-4,5-
dimethylthiazolium salt 1 and 102 mg of Ag2O (0.44 mmol, 0.55 eq.).
Stepwise addition of 299 mg Pt(COD)Cl2 (0.8 mmol, 1 eq.), 987 mg of
1,3-bis(2,4,6-trimethylphenyl)propane-1,3-dione (3.2 mmol, 4.0 eq.) and
359 mg of KOtBu (3.2 mmol, 4.0 eq.) and following General Procedure B
in temperature and workup steps yielded complex 14 as a bright yellow
powder (226 mg, 40.8 %). M.p.: 307-308 °C. 1H-NMR (CDCl3, 25 °C, 300
MHz): δ 7.97–7.65 (m, 1H, CHarom), 7.40 (dd, J = 5.9 Hz, J = 3.4 Hz, 1H,
CHarom), 7.02 (dd, J = 5.8 Hz, J = 3.3 Hz, 2H, CHarom), 6.91–6.80 (m, 4H,
CHarom), 5.68 (s, 1H, CHacac), 2.69 (s, 3H, CH3), 2.42–2.33 (m, 12H),
2.33–2.27 (m, 6H), 2.27–2.18 (m, 3H) ppm. 13C-NMR (CDCl3, 25 °C, 125
MHz): δ 185.8 (CO), 184.8 (CO), 177.7 (NCS), 151.4 (Ci-Pt), 139.3 (2C,
Ci), 137.6 (Ci), 137.6 (Ci), 136.9 (Ci), 134.2 (2C, Ci), 134.1 (2C, Ci), 133.0
(2C, CHarom), 128.2 (CHarom), 128.1 (CHarom), 127.4 (Ci), 125.6 (CHarom),
123.9 (2C, Ci), 123.6 (CHarom), 113.4 (CHarom), 107.5 (CHarom), 21.1 (2C,
CH3), 20.0 (2C, CH3), 19.9 (2C, CH3), 14.1 (CH3), 12.7 (CH3) ppm. 195Pt-
NMR (65 MHz, 25 °C, CDCl3): δ -3296 ppm. MS (ESI+, m/z, fragment):
691.5 (M+H)+. Anal. Calc. for C32H33NO2PtS: C, 55.64; H, 4.82; N, 2.03;
S, 4.64%. Found: C, 55.83; H, 4.91; N, 2.06; S, 4.50%.
(SP-4-4)-[4,5-dimethyl-3-phenyl-κC’-1,3-thiazol-2-ylidene-κC]-
[1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κO,κO’] platinum(II) (11).
According to the General Procedure A 20 ml of dry DMF were added to a
mixture of 268 mg (0.8 mmol) N-phenyl-4,5-dimethylthiazolium salt 1 and
102 mg of Ag2O (0.44 mmol, 0.55 eq.). Stepwise addition of 299 mg
Pt(COD)Cl2 (0.8 mmol, 1 eq.), 666 mg of 1,1,1,5,5,5-hexafluoropentane-
2,4-dione (4) (3.2 mmol, 4.0 eq.), 359 mg of KOtBu (3.2 mmol, 4.0 eq.)
and following General Procedure A in temperature and workup steps
yielded complex 11 as an orange powder (44 mg, 9.3 %). M.p.: 238-
241 °C. 1H-NMR (CDCl3, 25 °C, 600 MHz): δ 7.63–7.45 (m, 1H, CHarom),
7.36–7.26 (m, 1H, CHarom), 7.08–6.96 (m, 2H, CHarom), 6.20 (s, 1H,
CHacac), 2.63 (s, 3H, CH3), 2.25 (s, 3H, CH3) ppm. 13C-NMR (CDCl3,
25 °C, 151 MHz): δ 172.5 (CO), 172.4 (CO), 171.7 (NCS), 150.9 (Ci-Pt),
137.3 (Ci), 132.6 (CHarom), 125.8 (CHarom), 125.2 (Ci), 124.5 (CHarom),
123.8 (Ci), 119.3 (Ci), 117.2 (Ci), 113.8 (CHarom), 93.8 (CHarom), 14.0
(CH3), 12.5 (CH3) ppm. 19F-NMR (DMSO, 25 °C, 284 MHz): δ -76.0, -
75.8 (CF3) ppm. 195Pt-NMR (65 MHz, 25 °C, CDCl3): δ -3307 ppm. MS
(ESI+, m/z, fragment): 591.1 (M+H)+. Anal. Calc. for C16H11F6NO2PtS: C,
32.55; H, 1.88; N, 2.37; S, 5.43%. Found: C, 32.39; H, 1.84; N, 2.43; S,
5.60%.
(SP-4-4)-[4,5-dimethyl-3-phenyl-κC’-1,3-thiazol-2-ylidene-κC]-
[2,2,6,6-tetramethylheptane-3,5-dionato-κO,κO’]platinum(II)
(12).
According to the General Procedure A 20 ml of dry DMF were added to a
mixture of 268 mg (0.8 mmol) N-phenyl-4,5-dimethylthiazolium salt 1 and
102 mg of Ag2O (0.44 mmol, 0.55 eq.). Stepwise addition of 299 mg
Pt(COD)Cl2 (0.8 mmol, 1 eq.), 602 mg of 2,2,6,6-tetramethylheptane-3,5-
dione (5) (3.2 mmol, 4.0 eq.), 359 mg of KOtBu (3.2 mmol, 4.0 eq.) and
following General Procedure A in temperature and workup steps yielded
complex 12 as a yellow powder (164 mg, 36.2 %). M.p.: dec. >337 °C.
1H-NMR (CDCl3, 25 °C, 300 MHz): δ 7.95–7.66 (m, 1H, CHarom), 7.38–
7.23 (m, 1H, CHarom), 7.08–6.89 (m, 2H, CHarom), 5.75 (s, 1H, CHacac),
2.59 (s, 3H, CH3), 2.18 (s, 3H, CH3), 1.21 (s, 9H, CH3), 1.19 (s, 9H, CH3)
ppm. 13C-NMR (CDCl3, 25 °C, 75 MHz): δ 195.5 (CO), 194.7 (CO), 178.9
(NCS), 151.5 (Ci-Pt), 136.8 (Ci), 132.8 (CHarom), 128.9 (Ci), 125.4
(CHarom), 123.5 (Ci), 123.1 (CHarom), 113.3 (CHarom), 92.8 (CHarom), 41.7
(Ci), 41.3 (Ci), 28.6 (3C, CH3), 28.4 (3C, CH3), 14.1 (CH3), 12.7 (CH3)
ppm. 195Pt-NMR (65 MHz, 25 °C, CDCl3): δ -3320 ppm. MS (ESI+, m/z,
fragment): 567.3 (M+H)+. Anal. Calc. for C22H29NO2PtS: C, 46.63; H,
5.16; N, 2.47; S, 5.65%. Found: C, 46.76; H, 5.28; N, 2.35; S, 5.62%.
(SP-4-4)-[4,5-dimethyl-3-phenyl-κC’-1,3-thiazol-2-ylidene-κC]-[1,3-
diphenylpropane-1,3-dionato-κO,κO’]platinum(II) (13).
(SP-4-4)-[4,5-dimethyl-3-phenyl-κC’-1,3-thiazol-2-ylidene-κC]-[1,3-
bis(2,3,5,6-tetramethylphenyl)propane-1,3-dionato-κO,κO’]
platinum(II) (15). According to the General Procedure B 20 ml of dry 1,4-
dioxane were added to a mixture of 268 mg (0.8 mmol) N-phenyl-4,5-
dimethylthiazolium salt 1 and 102 mg of Ag2O (0.44 mmol, 0.55 eq.).
Stepwise addition of 299 mg Pt(COD)Cl2 (0.8 mmol, 1 eq.), 1.08 g 1,3-
bis(2,3,5,6-tetramethylphenyl)propane-1,3-dione (8) (3.2 mmol, 4.0 eq.)
and 359 mg of KOtBu (3.2 mmol, 4.0 eq.) and following General
Procedure B in temperature and workup steps yielded complex 15 as a
yellow powder (97 mg, 16.9 %). M.p.: dec. >317 °C. 1H-NMR (CDCl3,
25 °C, 300 MHz): δ 7.99–7.67 (m, 1H, CHarom), 7.51–7.31 (m, 1H,
CHarom), 7.12–6.98 (m, 2H, CHarom), 6.94 (d, J = 3.3 Hz, 2H, CHarom), 5.63
(s, 1H, CHacac), 2.70 (s, 3H, CH3), 2.39–2.10 (m, 27H) ppm. 13C-NMR
(CDCl3, 25 °C, 75 MHz): δ 187.1 (CO), 186.01 (CO), 177.9 (NCS), 151.4
(Ci-Pt), 142.5 (Ci), 142.4 (Ci), 136.9 (Ci), 133.7 (Ci), 133.6 (Ci), 133.2 (Ci),
133.1 (CHarom), 132.3 (Ci), 131.1 (CHarom), 131.0 (Ci), 129.8 (Ci), 129.7
(Ci), 128.9 (Ci), 127.4 (Ci), 125.6 (CHarom), 124.0 (CHarom), 123.6 (Ci),
This article is protected by copyright. All rights reserved.

10.1002/chem.201604456
Chemistry - A European Journal
FULL PAPER
113.4 (CHarom), 108.0 (CHarom), 29.7 (CH3), 20.5 (CH3), 19.7 (CH3), 19.1
(CH3), 16.5 (CH3), 16.5 (CH3), 15.9 (CH3), 15.3 (CH3), 14.1 (CH3), 12.7
(CH3) ppm. 195Pt-NMR (65 MHz, 25 °C, CDCl3): δ -3305 ppm. MS (ESI+,
m/z, fragment): 719.5 (M+H)+. Anal. Calc. for C34H37NO2PtS: C, 56.81; H,
5.19; N, 1.95; S, 4.46%. Found: C, 56.53; H, 5.29; N, 1.95; S, 4.44%.
4819-4830; f) K. Li, G. Cheng, C. Ma, X. Guan, W.-M. Kwok, Y.
Chen, W. Lu, C.-M. Che, Chem. Sci. 2013, 4, 2630-2644.
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Acknowledgements
We would like thank the ZIH for the generous allocation of
computation time at their high-performance computing facility. Dr.
Eberhardt Herdtweck is acknowledged for his helpful
discussions, as well as his contributions to solve various
crystallographic problems. We are grateful to Dr. Alexander
Tronnier and M.Sc. Piermaria Pinter for synthetic work in the
ligand preparation.
Keywords: phosphorescence • OLED • platinum • thiazole •
NHC
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Entry for the Table of Contents (Please choose one layout)
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Platinum(II) complexes based on the
C^C* cyclometalating thiazol-2-ylidene
motif together with seven different β-
diketonate ligands are investigated
for their structural and emission
properties.
Hendrik Leopold, Ute Heinemeyer,
Gerhard Wagenblast, Ingo Münster,
Thomas Strassner*
Page No. – Page No.
Changing the Emission Properties of
Phosphorescent C^C*
Cyclometalated Thiazol-2-ylidene
Platinum(II) Complexes by Variation
of the β-Diketonate Ligands
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