New Pt(II) complex with extra pure green emission for OLED application: synthesis, crystal structure and spectral properties

Article abstract of DOI:10.1016/j.jorganchem.2018.01.037

New (2-(4-methylpyrazol-1-yl)phenyl) platinum(II) (dibenzoylmethane) Pt(mpp)(dbm) complex based on 4-methylpyrazole was synthesized using a simple scheme. Its crystal structure, spectral and electrochemical properties were studied. The extra pure green (CIE chromacity coordinates X = 0.1419, Y = 0.7444) electroluminescence for OLED structures was obtained.

Full text of DOI:10.1016/j.jorganchem.2018.01.037

Accepted Manuscript
New Pt(II) complex with extra pure green emission for OLED application: Synthesis,
crystal structure and spectral properties
Ilya Taidakov, Sergey Ambrozevich, Rasim Saifutyarov, Konstantin Lyssenko,
Roman Avetisov, Elena Mozhevitina, Andrew Khomyakov, Mikhail Khrizanforov, Yulia
Budnikova, Igor Avetissov
PII:
S0022-328X(18)30043-3
10.1016/j.jorganchem.2018.01.037
JOM 20275
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 24 October 2017
Revised Date: 18 January 2018
Accepted Date: 20 January 2018
Please cite this article as: I. Taidakov, S. Ambrozevich, R. Saifutyarov, K. Lyssenko, R. Avetisov, E.
Mozhevitina, A. Khomyakov, M. Khrizanforov, Y. Budnikova, I. Avetissov, New Pt(II) complex with extra
pure green emission for OLED application: Synthesis, crystal structure and spectral properties, Journal
of Organometallic Chemistry (2018), doi: 10.1016/j.jorganchem.2018.01.037.
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ACCEPTED MANUSCRIPT
New Pt(II) complex with extra pure green emission for OLED application: synthesis, crystal
structure and spectral properties
Dedicated to Prof. Irina P. Beletskaya at the occasion of the 85-th birthday.
Ilya Taidakov,a,b*, Sergey Ambrozevichb, Rasim Saifutyarov,a Konstantin Lyssenko,c Roman
Avetisov,d Elena Mozhevitina,a Andrew Khomyakov,a Mikhail Khrizanforov,e Yulia Budnikovae
and Igor Avetissova.
aDmitry Mendeleev University of Chemical Technology of Russia, Department of Chemistry and
Technology of Crystals, 125047, Moscow, Miusskaya pl. 9, Russian Federation.
bP.N. Lebedev Physical Institute of Russian Academy of Sciences, 119991, Moscow, Leninskiy
Prospekt, 53, Russian Federation. e-mail:taidakov@gmail.com
cA. N. Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences,
119991, Moscow, Vavilova st., 28, Russian Federation.
dAROMOLED Ltd., 125047, Moscow, Miusskaya pl. 9/5, Russian Federation.
eA. E. Arbuzov Institute of Organic and Physical Chemistry of Russian Academy of Sciences,
420088, Kazan, A.E. Arbuzov str., 8, Russian Federation
Abstract:
New
(2-(4-methylpyrazol-1-yl)phenyl)
platinum(II)
(dibenzoylmethane)
Pt(mpp)(dbm) complex based on 4-methylpyrazole was synthesized using a simple scheme. Its
crystal structure, spectral and electrochemical properties were studied. The extra pure green (CIE
chromacity coordinates X=0.1419, Y=0.7444) electroluminescence for OLED structures was
obtained.
Keywords: pyrazole; dibenzoyimethane; organic light-emitting diode; platinum (II) complex;
metallocycles
1. Introduction
Cyclometalated complexes of platinum (II) and iridium(III) are the most important
phosphorescent phosphors for organic light-emitting devices [1,2]. Besides, they are extensively
use for various luminescent applications [3,4], in sensors [5,6] and for biomedical purposes [7,8].
They have a number of unique properties such as a wide range of emission colors, high quantum
yields of luminescence, a short lifetime of triplet exited states. The emission of Pt (II) complexes
is attributed to MLCT (metal-to-ligand charge transfer) excited states as well as possible
intraligand π-π* states. ne can assume, that for efficient electroluminescence the LUMO energy

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should match the cathode work function level, while the energy of the highest HOMO should be
close to those of hole-transport layer commonly made from NPB or CBP [9,10]. This leads to a
large variety of ligands, as well as to the types of complexes. To nowadays among all complexes
the C^N, N^N, N^C^N chelate complexes are the most studied and the most efficient [11,12].
In general, for the OLED technology a synthetic accessibility of electroluminescent complexes
may be not less important than the high quantum efficiency. Another significant challenge is a
creation of emitters with fine RGB colors. Theoretically, color of luminescence of Pt(II)
complexes can be precisely adjusted by a proper choice of ligands, but up to now the most
effective way to find such an emitters is screening of complexes libraries [9,10].
Heteroleptic C^NPtL complexes (where L is noncyclometalating ancillary ligand) offer some
advantages over symmetrical bis-C^N complexes. Their physical (such as volatility, solubility,
ets.) and photophysical properties can be independently adjusted by variation of both C^N and
L compositions. An ancillary ligand can also have a significant influence on the electron density
at the metal center. Subsequently, the amount of ground state electron density at Pt-center will
affect to the emission color, due to alterations in nature of the lowest energy transition [13]. An
immense number of combinations of C^NPt blocks and ancillary ligands (L) ave been
investigated to nowadays. They have included, but not limited mainly by derivatives of 2-
phenylpyridine, 2-(2-thienyl)pyridine [13,14], 2-phenylisoquinoline [15], functionaly substituted
2-phenylpyridines [16,17], 2-phenylbenzothiazole [18] and other arylated heterocycles. Simple
1.3-diketones have been used as monoanionic ancillary ligands in the most of abovementioned
complexes, but examples of C^NPt blocks coordinated by diimine (1.10-phenantroline, 2.2-
bipyridyl) [19], chlorine atoms or CO groups [20] have been also known. A lot of reviews,
devoted to different aspects of Pt(II) organometallic chemistry and applications of complexes
have been published to the date [21,22].
Much less attention have been paid to C^N platinum complexes with arylated azoles and 1,3-
diketones as O^O ancillary ligands. Most of the known compounds can be attributed to carbene
complexes with arylimidazole [23, 24] or benzimidazole [25] ligands. Only a few complexes
based on 1-phenylpyrazole as a C^N –ligand and 1,3-diketones were described by Batagoda [26]
and Wu [27], and no other examples of such compounds bearing pyrazole fragment have been
reported up to date. Unfortunately, no attempts to study their electroluminescence were
performed.

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In the present research we have succeed to make Pt(II) complex with extra pure green
electroluminescence based on 4-phenyl-4-methylpyrazole as a cyclometalated ligand and
diphenylpropanedione-1.3 as an ancillary ligand.
2. Experimental Section
2.1 General Information
K2PtCl4 was purchased from Aldrich. All other solvents and reagents were synthetic grade and
purchased form Aldrich and Acros Organics. For spectroscopic measurements solvents were
degassed by purging of He for 30 min before preparation of solutions. OLED grade materials
were purchased from Lumtec Corp. (Taiwan). 4-Methyl-1-phenyl-1H-pyrazole was obtained in 72
% yield by procedure, described by Pavlik [28].
Impurity concentrations were measured by a NexION 300D (Perkin Elmer) inductively coupled
plasma mass-spectrometer. Elemental analysis was performed on an Elementar Vario Micro-
Cube CHNO(S) analyzer. NMR spectra were recorded at 298 K on a Bruker DRX-500
1
instrument operated at 500.13 MHz for Н nucleus, in CDCl3 as solvents. TMS (δ = 0.00 ppm)
was used for 1H and 13C NMR measurements as a standard.
Electrochemical measurements were performed on a BASiEpsilonE2P electrochemical analyzer
(USA) managed by Epsilon-EC-USB-V200 software.
UV-VIS absorption spectra were recorded on a Varian Cary-100 Scan instrument.
Photoluminescent (PL) spectra and decay kinetics of powdered complex and solutions were
obtained using a Fluorolog FL3-22 (Horiba-Jobin-Yvon) spectrofluorimeter equipped by 450 W
Xenon lamp and standard Hamamatsu R-928 PMT. PL quantum yields were measured on the
same setup in the integration sphere (absolute method). The measurements were performed at
least three times and the results were averaged.
The synthesized complexes were purified by vacuum sublimation at dynamic pressure 5×10-6 Pa
and temperature of the complex about 270°C.
Electroluminescent spectra (EL) spectra of OLED devices were recorded by a QE65000
spectrometer The electroluminescent (EL) characteristics were measured with computer
controlled Keithley 2400 source meter in combination with a QE65000 spectrometer (Ocean
Optics, Inc.) supported by optical fiber cable. Integration time was 30 s for the every run in the
300-800 nm wavelength range. A LumiCAM 1300 photometer-colorimeter (Instrument Systems

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Optische Messtechnik, GmbH) was used for measurements of brightness and chromaticity
coordinates of OLED structures. All measurements have been conducted in air without device
encapsulation.
2.2
Synthesis
of
(2-(4-Methylpyrazol-1-yl)phenyl)platinum(II)
(dibenzoylmethane)
(Pt(mpp)(dbm)).
A cyclometallated product was prepared in one step according to the modified procedure of Wu
[27]. In a Schlenk tube under Ar atmosphere 158 mg (1 mmol) of 4-methyl-1-phenyl-1H-
pyrazole and 208 mg (0.5 mmol) of K2PtCl4 in 5 ml of water-2-etoxyethanole mixture (1:3 v/v)
were heated with stirring for 12 h at 100°C. After the cooling, 15 ml of water was added,
precipitate of dimer complex was separated, washed with water and dried at 80°C at 0.1 Torr to a
constant weight. To the resulted solid 5 ml of 2-etoxyethanole was added followed by an
addition of 340 mg (1.51 mmol) of 1,3-diphenylpropane-1,3-dione and 1 g (9.5 mmol) of
Na2CO3. The resulted suspension was stirred at 100°C for 15 h, cooled and decomposed by
dropwise addition of deionized water (15 ml). The dark solid was separated, washed with
deionized water, dried at 80°C at 0.1 Torr and purified by column chromatography (silica
1
gel/CH2Cl2). Yield - 104 mg (39 %) of yellow solid. H NMR (500 MHz, CDCl3) δ: 8.07 (m,
4H), 7.70 (m, 3H), 7.55 (m, 3H), 7.47 (m, 4H), 7.10 (m, 3H), 6.78 (s, 1H), 2.19 (s, 3H). 13C
NMR (500 MHz, CDCl3) δ:178.36, 144.62, 139.93, 137.56, 131.81, 130.89, 130.69, 128.53,
127.07, 124.53, 123.93, 122.03, 116.94, 109.70, 97.14, 9.47. 195Pt NMR (500 MHz, CDCl3) δ: -
2715. Elemental analysis (%) for C25H21N2O2Pt (M = 576.52): calc.: C, 52.08; H, 3.67; N, 4.86;
found: C, 52.12; H, 3.69; N, 4.83.
2.3 X-ray crystallography of Pt(mpp)(dbm) complex
The single crystals of Pt(mpp)(dbm) complex suitable for X-ray analysis, were obtained by slow
diffusion of hexane to the saturated solution of complex in CH2Cl2 under Ar at RT.
At 110K crystals are monoclinic, a =12.3019(7) Ǻ, b =11.4797(7) Ǻ, c = 14.4514(9) Ǻ, β =
103.5574(13)°, V = 1984.0(2) Ǻ3, P21/c space group, Z = 4 (Z’=1). F(000) =1112, GOF = 1.000,
a total of 40185 reflections (2Θmax>58°) were measured with a Smart APEX II CCD
diffractometer [λ(MoKα) = 0.71072 Å, ω-scans, 2Θ<58°], and 5274 independent reflections
(Rint =0.0338) were used in further refinement. The structure was solved by direct methods and
refined by the full-matrix least-squares technique against F2 in the anisotropic-isotropic
approximation. The positions of hydrogen atoms were calculated. Hydrogen atoms were refined
in riding model with Uiso(H) equal to 1.5 Ueq(C) and 1.2 Ueq(C) of the connected methyl and

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other carbon atoms. The refinement converged to wR2 = 0.0621 and GOF = 1.009 for all
independent reflections (R1 = 0.0266 for 4394 observed reflections with I > 2σ(I)). CCDC
1511807 contains the supplementary crystallographic data for this paper.
2.4 Computational studies.
The calculations were performed with the Gaussian 09 program package using the PBE1PBE
functional. A mixed basis set is used where a cc-pVTZ basis set was used for carbon, hydrogen,
nitrogen, oxygen, fluorine atoms and the cc-pVTZ-PP basis set with relativistic effective core
potentials was used for platinum [29]. The conductor-like polarization continuum model CPCM
[30] of CH2Cl2 solvent were applied to all calculations. The obtained structures were confirmed
as the true minima by the absence of imaginary frequencies. TD-DFT computations were carried
out on the optimized ground state S0 geometries.
2.5 Electrochemical measurements
The electrochemical measurements were performed by using a conventional three-electrode
system. In the case of powdered samples a glassy carbon with carbon paste electrode (CPE) was
used as a working electrode. An Ag/AgCl (0.01M) electrode was used as a reference electrode,
and a Pt wire was used as a counter electrode. 0.1 M Et4NBF4 was used as a supporting
electrolyte for the determination of current - voltage characteristics. Acetonitrile was distilled
over P2O5 and KMnO4, and then over molecular sieves After purification, the solvent was stored
under dry Ar atmosphere. Et4NBF4, which was used as a base salt, was recrystallized from
ethanol and dried in a vacuum chamber at 100 °C for 2 days. The preparation of a modified CPE
electrode was as follows. A mixture of graphite powder and phosphonium salt (dodecyl(tri-tert-
butyl)phosphonium tetrafluoroborate) with 90/10 (w/w) ratio was milled in a mortar until the
homogeneous mass of the paste was obtained. This paste then was uniformly distributed of the
surface of a glassy carbon substrate. The detailed description of the technique is given in
Ref.[31,32].
2.6 OLED fabrication
Multilayers OLED devices were fabricated by layer-by-layer vacuum thermal sputtering (<10-5
Pa) on a glass substrate (20x30x3 mm) with ITO conducting layer. The deposition rates of each
layer were no more than 0.03 nm×s-1. The emission layer consisted of CBP: Pt(mpp)(dbm)-
complex (8%) was deposited with the rate ~0.01 nm×s-1 due to low pressure of Pt(mpp)(dbm)
vapor at 250 °C. The OLED structure ITO (anode)/ MoO3 (1 nm) / NPB (N,N′-Di(1-naphthyl)-
N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine, 40 nm) / CBP (4,4′-Bis(N-carbazolyl)-1,1′-

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biphenyl): Pt(mpp)(dbm) complex (8 wt. %) (30 nm) / BCP (2,9-Dimethyl-4,7-diphenyl-1,10-
phenanthroline, 15 nm) / LiF (1.2 nm) /Al (100 nm) was fabricated. Extra pure MoO3 (99.9995
wt% free of W impurity) with controlled oxygen nonstoichiometry [33] was used as a hole
blocking material [9]. NPB was used as one of the most efficient hole-transport materials and it
provided the necessary hole mobility [2,9]. CBP is an up-to-date standard host matrix for
phosphorescent dopants [10]. BCP was used as an electron-transport material with good hole
blocking properties [9].
3. Results and discussion
3.1 Synthesis and structural characterization
Among thousands of known cyclometallated Pt(II) complexes, only few examples of compounds
with simultaneously coordination with 1,3-diketone and 1-phenylpyrazole ligands have been
described [26,27] (Fig.1).
Fig. 1. The known examples of complexes based on 1-phenylpyrazole and 1.3-diketones.
In the both Ref. [16,22] the synthetic approach to cyclometallated complexes was based on two-
step methodology: (i) formation of Pt(II) dimer in the reaction of Pt(II) precursor with
phenylazole and (ii) subsequent cleavage of dimer by the interaction with the large excess of 1.3-
diketone in the presence of the base. We used the same approach for the preparation of
Pt(mpp)(dbm) complex (Fig.2).
Fig. 2. Рreparation of Pt(mpp)(dbm) complex

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The Pt(mpp)(dbm) complex was obtained in 39 % overall yield by the convectional procedure
started from very simple commercial precursors. No palladium-catalyzed cross-coupling
reactions were used. As-synthesized Pt(mpp)(dbm) complex was as pure as 99.9905 wt% (trace
metals) according to the ICP-MS measurements. Taking into account the influence of impurities
on electroluminescence efficiency [34,35] we additionally purified the Pt(mpp)(dbm) complex
by high-vacuum sublimation. The final purity of powdered preparation was 99.9987 wt% (See
Table S1, Fig. S1). The obtained complex composition was proved by NMR, elemental analysis
and its structure was confirmed by X-ray single crystal analysis.
The X-ray diffraction analysis has unambiguously revealed the formation of a desired product
Pt(mpp)(dbm) (Fig. 3). The platinum is characterized by squire-planar geometry with Pt-O, Pt-N
and Pt-C bonds lengths equal to 1.996(3)-2.052(3), 1.961(3) and 1.979(4) Å, respectively. In
crystal molecules are assembled into dimers by stacking interaction between the phenyl group of
β-diketonate and methylpyrazol with the shortest C…C contact equal to 3.38 Å (Fig. S1).
Fig. 3. The general view of molecular structure of Pt(mpp)(dbm) complex (left) in representation
of atoms by thermal ellipsoids (p=50%). Microphotograph of Pt(mpp)(dbm) single crystal (right)
3.2 Photophysical property
The absorption spectra of complex and free ligands were recorded in CH2Cl2 degassed solutions
at 4.5×10-5 mol/L (Fig. 4). The intense band at 280-260 nm is attributed to spin-allowed ligand-
centered transitions of dbm and mpp ligands (π→π* transitions), while relatively weak bands at
320 - 440 nm region are commonly assigned to mixed 3MLCT or LLCT (ligand-to-ligand charge
transfer state) [2,22]. The reason of their origin is strong spin-orbit coupling of the Pt atom. A
strong spin-orbit coupling leads to the mixing of lowest triplet and higher-laying singlet excited
states and this, in turn, causes an increase of phosphorescent quantum efficiency.

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Fig.4. The absorption spectra of complex and free ligands in CH2Cl2 degassed solutions.
The PL spectrum of Pt(mpp)(dbm) complex solution in CH2Cl2 had one band with 535 nm
maximum (Fig.5) which corresponded to green emission (the CIE chromacity coordinates
3
X=0.3581, Y=0.5480). Similar to the other Pt(II) complexes this band resulted from MLCT
3
states, as well as from LLCT [2,22]. The MLCT nature of excited states can be confirmed by
the Gaussian line shape and the relatively long lifetime of the state (τ = 1.8 µs at 535 nm for
degassed 5×10-4 M solution in CH2Cl2). The absolute PL quantum yield (PLQY) was 8.70±0.13
% (λext= 370 nm) for the solution.
Fig. 5. The normalized absorption and emission spectra of Pt(mpp)(dbm) complex in 5×10-5
mol/L degassed CH2Cl2 solution (λext. =370 nm).

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The PL spectrum of the sublimed powdered complex had two small shoulders on the both sides
on the band (Fig.6). The band maximum was shifted to the red wavelength region in comparison
with the solution measurements. This phenomenon is well known [36] for Pt(II) complexes and
usually attributed to formation of partially ordered structures (e.g. by π-π stacking and other
weak interactions) in solid.
Fig. 6. The emission spectrum of sublimed solid Pt(mpp)(dbm) complex (λext = 370 nm).
The nature of this emission band was estimate by means of TD-DFT calculation of the complex.
The optimized geometry for Pt(mpp)(dbm) is rather close to the experimental one. In particular
the Pt-O, Pt-N and Pt-C bonds lengths are 1.993-2.080 1.969 Pt-C 1.968 Å, correspondingly.
TD DFT calculation have revealed the presence of T1-S0 transition with the energy equal to
486.8 nm that is rather close to experimental value (484.5 nm) of 0-0 band i.e. intercrossing of
the absorption and emission spectra (see Fig. 5). The lowest energy transitions (T1-S0) is mainly
HOMO to LUMO, which is the ligand-to-ligand transition (i.e. from phenylpyrazole to 1.3-
diketonate ligand). But, as the both frontier orbitals contain some Pt contributions, than the
transition should be regarded as a mixed metal–ligand to metal–ligand charge transfer (see Table
2).
3.3 Electrochemical property
The Pt(mpp)(dbm) displays a reversible (ipa/ipc∼0.4) Pt-based reduction at -1.53 V(E1/2 an
Esemidif vs.Ag/AgCl). (Fig. 7, Table 1). The Pt(mpp)(dbm) displays a reversible (ipa/ipc∼0.08 and
DEp/2=Ea-Ec/2 = 80mV ) [37] . The oxidation process measured for Pt(mpp)(dbm) in CPE were
not reversible and were ill-defined. Oxidation peak potential is +0.99 V (1Еox. semidif,) vs Ag/AgCl
(Fig. 8, Table 1). General electrochemical characteristics of Pt(mpp)(dbm) are given in Table 1.
The energy levels of the HOMO and LUMO were calculated based on the electrochemical data

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using previously proposed formulas ( ELUMO = − (E[semidif,red vs. Fc+/ Fc] + 4.8), EHOMO = − (E[semidif,red
vs. Fc+/ Fc] + 4.8) [38]. The estimated values for HOMO and LUMO were calculated as -5.34 and -
2.82 eV, respectively. Complex [Pt(MPP)(DBM)] is able to reversibly accept two electrons and
give back one electron (irrev.) according to the Scheme 1.
Scheme 1. Oxidation and reduction steps of the compound [Pt(MPP)(DBM)].
Table 1. Electrochemical properties of [Pt(mpp)(dbm)]
Reduction
с
a
с
a
1Еp /Еp ,
V
2Еp /Еp ,
V
vs.
-1.57/-1.49
-2.02/1.94
-1.98
-2.22/-2.08
-2.67/-2.53
-2.62
Ag/AgCl
vs. Fc/Fc+
Semidif vs.
Fc/Fc+
Oxidation
a
с
a
с
1Еp /Еp ,
V
2Еp /Еp ,
V
vs.
1.15(irrev)
0.70
1.66(irrev)
1.21
Ag/AgCl
vs. Fc/Fc+
Semidif vs.
Fc/Fc+
0.54
1.13
Fig. 7. Cyclic voltammograms (reduction) obtained with a modified CPE of [Pt(mpp)(dbm)]
(graphite + ionic liquid +Pt complex) in 2 ml CH3CN (0.1 M Et4NBF4).

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Fig. 8. Cyclic voltammograms (oxidation) obtained with a modified CPE of [Pt(mpp)(dbm)]
(graphite + ionic liquid + Pt complex) in 2 ml CH3CN (0.1 M Et4NBF4).
3.4 Theoretical calculations
To check how the modification of ligands in the complex studied affects the energy of T1-S0
transition we have performed the DFT calculations for the series of complexes in which we
modified either 1,3-diketonate (i.e. LUMO) or phenylpyrazole (i.e. HOMO) moieties. The
general view of theoretically studied complexes, the frontier orbitals as well as energies of T1-S0
transition are shown in Table 2. As one can see, the rational choice of substituents in 1,3-
diketonates makes possible to vary the energy of triplet state within ~100 nm or HOMO-LUMO
gap by ca. 1.0 eV, while the inclusion of electron withdrawing or π-donor substituents to the
phenylpyrazole fragment doesn't perturb the triplet state. The examination of the energy of
HOMO orbital clearly shows that in the whole series, the energy varies in the rather narrow
range and replace of the fluorine in Pt-III with the methoxy group in Pt-IV costs only ca. 0.01 ev.
While the replace of the methyl substituents in Pt-II with the CF3 ones in Pt-III causes the
increase of the LUMO energy by ca. 0.5 eV. Considering that various 1,3-diketonates are in
general much more available commercially, it seems that such a route of modification of
platinum complexes with a phenylpyrazole fragment can be beneficial for fine tuning of optical
properties of complexes and OLED structures.

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Table 2. View of frontier orbitals (HOMO/LUMO) and calculated values of energy of 0-0
transition for series of complexes.
Complex
HOMO
LUMO
λ (T1-S0 transition), nm
486.9
410.2
519.9
481.3
487.2
484.5 experimental
3.5 OLED performance.
To investigate the performance of new complex as a phosphorescent emitter the OLED with the
structure described in the Section 2.6 was made. The energy level diagram and molecular
structures of additional layers are presented in Fig. 9. One can see that the energy state of
Pt(mpp)(dbm) molecules matches well to the CBP matrix.

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Fig. 9. Energy level diagram (relative to vacuum level) and topology of the fabricated OLED.
As a result the produced OLED structure had typical UC characteristic (Fig S6) with a
comparatively high turn-on voltage of 6.7 V. The maximum values of current efficiency, power
efficiency, and external quantum efficiency were obtained at 32 mA/cm2 (see Fig. S9-S11). The
EL spectrum has two maxima at the region of 510-540 nm most likely due to aggregation of
3
3
complex in the matrix [39,40]. Emissive states are MLCT and LC (3ππ*) as it was stated for
other platinum(II) complexes [2] (Fig.10). The most interesting property of the OLED structures
based on Pt(mpp)(dbm) as an emitting agent is the obtained CIE color coordinates of X=0.1419,
Y=0.7444 which are very close to the standard CIE green color 546.1 nm. The OLED structure
had the uniform distribution of lighting intensity of 400 Cd/m2 at 10 V.

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Fig. 10. Electroluminescence of OLED structure ITO/MoO3 (1 nm)/NPB (35 nm)
/CBP:Pt(MPP)(DBM) (8%) (30 nm)/BCP (15 nm)/LiF (1.2 nm)/Al (100 nm) at 8 V and 3D
intensity brightness map at 10 V.
Conclusion
In conclusion the high pure (2-(4–methylpyrazol-1-yl) phenyl) platinum(II) (dibenzoylmethane)
was synthesized using the simple scheme followed by the vacuum sublimation. The chemical
purity of 99.9987 wt% determined by the ICP-MS and the fine matching let's achieved the extra
pure green emission of the multilayer OLED structure (CIE chromacity coordinates X=0.1419,
Y=0.7444).
Acknowledgements
The research was supported by the Russian Scientific Foundation by grant № 14-13-01074П and
partially- by RFBR grant №18-02-00653. The X-ray diffraction data were obtained using the
equipment of Center for molecules composition studies of INEOS RAS.
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Figure captions
Fig. 1. The known examples of complexes based on 1-phenylpyrazole and 1.3-diketones.
Fig. 2. Рreparation of Pt(mpp)(dbm) complex.
Fig. 3. The general view of molecular structure of Pt(mpp)(dbm) complex (left) in representation
of atoms by thermal ellipsoids (p=50%). Microphotograph of Pt(mpp)(dbm) single crystal
(right).
Fig. 4. The absorption spectra of complex and free ligands in CH2Cl2 degassed solutions.
Fig. 5. The normalized absorption and emission spectra of Pt(mpp)(dbm) complex in 5×10-5
mol/L degassed CH2Cl2 solution (λext = 370 nm).
Fig. 6. The emission spectrum of the sublimed solid Pt(mpp)(dbm) complex (λext = 370 nm).
Fig. 7. Cyclic voltammograms (reduction) obtained with a modified CPE of [Pt(mpp)(dbm)] in
CH3CN (0.1 M Et4NBF4).
Fig. 8. Cyclic voltammograms (oxidation) obtained with a modified CPE of [Pt(mpp)(dbm)] in
CH3CN (0.1 M Et4NBF4).
Fig. 9. Energy level diagram (relative to vacuum level) and topology of the fabricated OLED.
Fig. 10. Electroluminescence of OLED structure ITO/MoO3 (1 nm)/NPB (35 nm)
/CBP:Pt(MPP)(DBM) (8%) (30 nm)/BCP (15 nm)/LiF (1.2 nm)/Al (100 nm) at 8 V and 3D
intensity brightness map at 10 V.
Scheme 1. Oxidation and reduction steps of the compound [Pt(mpp)(dbm)].

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Highlights
New Pt(II) complex with extra pure green emission for OLED application:
synthesis, crystal structure and spectral properties
Ilya Taidakov, Rasim Saifutyarov, Konstantin Lyssenko, Roman Avetisov, Elena Mozhevitina,
Andrew Khomyakov, Mikhail Khrizanforov, Yulia Budnikova and Igor Avetissov.
•
•
•
New (2-(4-methylpyrazol-1-yl)phenyl) platinum(II) (dibenzoylmethane) was made
crystal structure, spectral and electrochemical properties of Pt(MPP)(DBM) were studied
Extra pure green electroluminescence for OLED structures was obtained