Pt(II) metal complexes tailored with a newly designed spiro-arranged tetradentate ligand; Harnessing of charge-transfer phosphorescence and fabrication of sky blue and white OLEDs

Article abstract of DOI:10.1021/acs.inorgchem.5b00281

Tetradentate bis(pyridyl azolate) chelates are assembled by connecting two bidentate 3-trifluoromethyl-5-(2-pyridyl)azoles at the six position of pyridyl fragment with the tailored spiro-arranged fluorene and/or acridine functionalities. These new chelates were then utilized in synthesizing a series of Pt(II) metal complexes [Pt(Ln)], n = 1-5, from respective chelates L1-L5 and [PtCl₂(DMSO)₂] in 1,2-dimethoxyethane. The single-crystal X-ray structural analyses were executed on 1, 3, and 5 to reveal the generalized structures and packing arrangement in crystal lattices. Their photophysical properties were measured in both solution and solid state and are discussed in the context of computational analysis. These L1-L5 coordinated Pt(II) species exhibit intense emission, among which complex 5 shows remarkable solvatochromic phosphorescence due to the dominant intraligand charge transfer transition induced by the new bis(pyridyl azolate) chelates. Moreover, because of the higher-lying highest occupied molecular orbital of acridine, complex 5 can be considered as a novel bipolar phosphor. Successful fabrication of blue and white organic light-emitting diodes (OLEDs) using Pt(II) complexes 3 and 5 as the phosphorescent dopants are reported. In particular, blue OLEDs with 5 demonstrated peak efficiencies of 15.3% (36.3 cd/A, 38.0 lm/W), and CIE values of (0.190, 0.342) in a double-emitting layer structure. Furthermore, a red-emitting Os(II) complex and 5 were used to fabricate warm-white OLEDs to achieve peak external quantum efficiency, luminance efficiency, and power efficiency values as high as 12.7%, 22.5 cd/A, and 22.1 lm/W, respectively.

Full text of DOI:10.1021/acs.inorgchem.5b00281

Article
pubs.acs.org/IC
Pt(II) Metal Complexes Tailored with a Newly Designed Spiro-
Arranged Tetradentate Ligand; Harnessing of Charge-Transfer
Phosphorescence and Fabrication of Sky Blue and White OLEDs
†
†
,†
‡
∥
‡
,‡
Kuan-Yu Liao, Che-Wei Hsu, Yun Chi,* Ming-Kuan Hsu, Szu-Wei Wu, Chih-Hao Chang,*
§
§
,§
,∥
Shih-Hung Liu, Gene-Hsiang Lee, Pi-Tai Chou,* Yue Hu, and Neil Robertson*
†
Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan
‡
Department of Photonics Engineering, Yuan Ze University, Chungli 32003, Taiwan
§
Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan
∥
EaStCHEM, School of Chemistry, University of Edinburgh, King’s Buildings, West Mains Road, Edinburgh EH9 3 FJ, U.K.
*
S Supporting Information
ABSTRACT: Tetradentate bis(pyridyl azolate) chelates are
assembled by connecting two bidentate 3-trifluoromethyl-5-(2-
pyridyl)azoles at the six position of pyridyl fragment with the
tailored spiro-arranged fluorene and/or acridine functionalities.
These new chelates were then utilized in synthesizing a series
of Pt(II) metal complexes [Pt(Ln)], n = 1−5, from respective
chelates L1−L5 and [PtCl (DMSO) ] in 1,2-dimethoxy-
2
2
ethane. The single-crystal X-ray structural analyses were executed on 1, 3, and 5 to reveal the generalized structures and
packing arrangement in crystal lattices. Their photophysical properties were measured in both solution and solid state and are
discussed in the context of computational analysis. These L1−L5 coordinated Pt(II) species exhibit intense emission, among
which complex 5 shows remarkable solvatochromic phosphorescence due to the dominant intraligand charge transfer transition
induced by the new bis(pyridyl azolate) chelates. Moreover, because of the higher-lying highest occupied molecular orbital of
acridine, complex 5 can be considered as a novel bipolar phosphor. Successful fabrication of blue and white organic light-emitting
diodes (OLEDs) using Pt(II) complexes 3 and 5 as the phosphorescent dopants are reported. In particular, blue OLEDs with 5
demonstrated peak efficiencies of 15.3% (36.3 cd/A, 38.0 lm/W), and CIE values of (0.190, 0.342) in a double-emitting layer
structure. Furthermore, a red-emitting Os(II) complex and 5 were used to fabricate warm-white OLEDs to achieve peak external
quantum efficiency, luminance efficiency, and power efficiency values as high as 12.7%, 22.5 cd/A, and 22.1 lm/W, respectively.
INTRODUCTION
the ligand-centered ππ* in the lowest-energy excited states. This
reduced MLCT character may allow other less-common
transition processes, such as intraligand charge transfer
■
Recently, there has been a great research effort into third-row
luminescent metal complexes due to high emission quantum
yields and long-lived excited states caused by the efficient, heavy
(
ILCT), to play a dominant role in the lower-lying electronic
1
−7
transition. Similar behavior was documented in the 2-vinyl-
pyridine-type Pt(II) complexes, for which the excited-state
characteristics and emission color have been successfully tuned
by attachment of different main-group substituents on the
metal atom-induced fast singlet/triplet intersystem crossing.
The capability to design and prepare strongly luminescent
materials facilitates their applications in organic light emitting
devices (OLEDs) as well as other technologies, such as chemical,
14
8
−13
chelating cyclometalate.
pressure, and oxygen sensors,
all via the enhanced
Very recently, we described a new kind of tetradentate chelate
participation of the lowest-energy triplet excite states. As a
result, emphasis has been switched from organic fluorescent
materials to transition-metal-based phosphors with cyclometalat-
ing chelates; the latter include those with the octahedral Os(II)
and Ir(III) metal complexes with d -electronic configuration and
the square-planar Pt(II) complexes bearing d -configuration.
One important characteristic of the Os(II) and Ir(III) metal
phosphors is the easily accessible Os(III) and Ir(IV) oxidation
states, which render a greater amount of metal-to-ligand charge
transfer (MLCT) character upon excitation. On the other hand,
the oxidation of Pt(II) to Pt(III) is less preferred, meaning that
the MLCT contribution should be less influential versus that of
(
LPhN), which utilizes a single phenylamido appendage to
connect the pyridyl unit of two bidentate 2-pyridyl pyrazoles
15
(
Chart 1). This design is feasible as it can be assembled using a
6
synthetic protocol similar to those reported for its bidentate
counterpart. Moreover, the phenylamido unit provides a flexible
skeletal arrangement with the desired tetradentate motif, such
that both the reaction intermediate and product may be formed
in a stepwise and controllable manner. However, the Pt(II)
8
Received: February 5, 2015
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.5b00281
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Inorganic Chemistry
Article
a
Chart 1. Structural Drawing of Tetradentate Chelates Based
on 2-Pyridyl Pyrazole
Scheme 1. Synthetic Procedures for L1
a
Experimental conditions: (i) n-BuLi, −78 °C, (ii) (MeCO) O, HCl,
2
reflux, (iii) H O , MeCO H, (iv) Me SiCN, (v) NH Cl, NaOMe, (vi)
2
2
2
3
4
CF CONHNH .
3
2
in glacial acetic acid and cyanation using Me SiCN afforded the
3
25
6
,6′-(9-fluorenylidene)dipicolinonitrile (Scheme 1). Conver-
complexes bearing this class of chelates are highly insoluble in
common organic solvents, which has hampered the subsequent
studies on their basic photophysics and application such as
fabrication of OLEDs. Apparently, the phenylimido appendage is
incapable of shielding the intermolecular ππ interaction between
the square-planar Pt(II) coordination frameworks. This
disadvantage makes development of alternative ligand design
an urgent task.
sion to bitriazole chelate L1 was then achieved by treatment of
the as-synthesized dipicolinonitrile with NH Cl in methanol to
afford the pyridinecarboximidamide, followed by treatment
with trifluoroacetic acid hydrazide in a stainless steel digestion
bomb.
Scheme 2 shows the preparation procedures to the
corresponding fluorene-bridged pyrid-2-yl pyrazole, (L2), R =
4
26
Herein, we report the preparation of a new series of
tetradentate chelates using spiro-arranged fluorene and acridine
linking to the pyrid-2-yl triazole (or pyrazole) units; also see
Chart 1. It is thus expected that the perpendicular arranged spiro-
fluorene and acridine should provide enough steric hindrance to
reduce the intermolecular ππ-stacking interaction between this
class of square-planar Pt(II) complexes, give suitable solubility
for the measurement of photophysical data, and, hence, give
better processability for the fabrication of OLEDs. Moreover,
since acridine is a stronger electron-donating moiety than
a
Scheme 2. Synthetic Procedures for L2 and L3
1
6−19
fluorene,
we expected that, under suitable conditions, its
electron-rich nature would alter the photophysical properties and
convert the transition characteristics from ligand-centered ππ*
state to an ILCT state. Phosphors with such an inherent electron-
donating (or hole-transporting) functional group were occasion-
20−23
ally referred to as bipolar phosphors.
Furthermore, because
of the large variation in electric dipolar vector, notable
solvatochromism in emission was observed by changing the
solvent polarity, achieving an exceedingly broad range of color
tunability. Elaborated below are the preparation and the
associated studies on the photophysical properties and OLED
devices involving this new class of luminescent Pt(II) complexes
with tetradentate chelates.
a
i
Experimental conditions: (i) n-BuLi, −78 °C, PrOC(O)Cl, −78 °C−
RT, (ii) n-BuLi, −78 °C, (iii) (MeCO) O, HCl, reflux, (iv) NaH,
THF, CF CO Et, reflux, (v) N H , EtOH, reflux.
2
3
2
2
4
t
H; (L3), R = Bu. In this synthetic protocol, we first used 6-
bromo-2-(2-methyl-1,3-dioxolan-2-yl)pyridine as the starting
material to prepare the key intermediate, bis[3-(2-methyl-
1,3dioxolan-2-yl)pyridin-2-yl]methanone. It was then reacted
with 2-lithiobiphenyl generated in situ to afford the correspond-
RESULTS AND DISCUSSION
27
■
Synthesis and Characterization. All required tetradentate
chelates L1−L5 contain either a spiro-fluorene or acridine unit
linked to two bidentate pyrid-2-yl triazole (or pyrazole)
fragments at the six position of their pyridyl sites. Scheme 1
depicts the schematic synthetic pathways leading to the fluorene-
bridged pyrid-2-yl triazole (L1). First, the key intermediate, 2,2′-
t
ing coupling products, R = H, Bu. Subsequent dehydration and
deprotection in acidic media gave formation of both the spiro-
fluorene linkage and the acetylpyridine units in a single step.
After this, these intermediates can be converted to the desired
pyrazole chelates L2 and L3 by Claisen condensation with ethyl
trifluoroacetate and subsequent cyclization with hydrazine. With
these synthetic procedures, the corresponding spiro-acridine
chelates, (L4), R = H and (L5), R = Bu, were then synthesized
upon employment of acridine precursors, namely, 2-bromo-N,N-
diphenylaniline and 2-bromo-4-(t-butyl)-N,N-bis(4-t-
(
9-fluorenylidene)dipyridine, was synthesized by a two-step
processes involving the combination of di(pyridin-2-yl)-
methanone and an in situ-generated 2-lithiobiphenyl, followed
by dehydration in a mixture of acetic anhydride and hydrochloric
t
2
4
acid. Subsequent pyridine oxidation using hydrogen peroxide
B
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Article
Chart 2. Structural Drawing of the Studied Pt(II) Metal Complexes 1−5
butylphenyl)aniline, while keeping all of the synthetic
16
procedures and conditions unaltered. The structural drawings
of L4 and L5 are depicted in Chart 1 of the introduction section.
The Pt(II) metal complexes 1−5 were then synthesized using
respective chelates L1−L5 and [PtCl (DMSO) ] in 1,2-
2
2
dimethoxyethane, during which excess of Na CO was added
2
3
to induce deprotonation for optimization of yields. Their
structural drawings are depicted in Chart 2. Moreover, it was
noted that the t-butyl-substituted Pt(II) complexes 3 and 5
showed better solubility in organic solvents versus those without
the t-butyl substituents (cf. 1, 2, and 4), a result of the lipophilic
character of the introduced t-butyl substituents.
The X-ray structural analyses of 1, 3, and 5 were conducted to
disclose their structural arrangement and packing behavior. As
indicated in Figures 1−3, the Pt(II) coordination sphere adopts a
Figure 2. Structural drawing of 3 with thermal ellipsoids shown at 50%
probability level, selected bond distances: Pt−N(1) = 2.020(3), Pt−
N(2) = 1.980(3), Pt−N(4) = 2.014(3), Pt−N(5) = 1.991(3), and Pt···
Pt = 3.455 Å; selected bond angles N(1)−Pt−N(2) = 80.86(13), N(1)−
Pt−N(5) = 176.38(13), N(2)−Pt-N(4) = 176.17(13), N(1)−Pt−N(4)
=
95.36(13), N(2)−Pt−N(5) = 102.76(13), N(4)−Pt−N(5) =
8
1.02(13), C(2)−C(1)−C(11) = 123.3(3), and C(20)−C(1)−C(31)
o
=
101.2(3) . Fluorine atoms of CF fragments were removed for clarity.
3
Figure 1. Structural drawing of 1 with thermal ellipsoids shown at 50%
probability level, selected bond distances: Pt−N(1) = 2.012(4), Pt−
N(2) = 1.975(4), Pt−N(5) = 2.011(4), Pt−N(6) = 1.975(4), and Pt···
Pt = 3.759 Å; selected bond angles N(1)−Pt−N(2) = 80.37(15), N(5)−
Pt−N(6) = 80.44(15), N(1)−Pt−N(6) = 176.25(15), N(2)−Pt−N(5)
=
176.34(15), N(1)−Pt−N(5) = 96.08(14), and N(2)−Pt−N(6) =
o
1
03.09(16) . Fluorine atoms of CF fragments were removed for clarity.
3
Figure 3. Structural drawing of 5 with thermal ellipsoids shown at 50%
probability level, selected bond distances: Pt−N(1) = 2.003(5), Pt−
N(2) = 1.982(5), Pt−N(4) = 2.006(5), and Pt−N(5) = 1.967(5) Å;
selected bond angles N(1)−Pt−N(2) = 80.69(19), N(4)−Pt−N(5) =
81.03(19), N(1)−Pt−N(5) = 176.79(19), N(2)−Pt−N(4) =
distorted square-planar geometry, for which the average (av) Pt−
distance to the azolate fragments (1.975(4) Å in 1 vs
N
az
1
.985(3) Å in 3 and 1.975(5) Å in 5) is found to be slightly
shorter than the av Pt−N distance to the pyridine fragments
py
(2.012(4) Å in 1 vs 2.017(3) Å in 3 and 2.005(5) Å in 5). This
1
75.61(19), N(1)−Pt−N(4) = 96.24(19), and N(2)−Pt−N(5) =
o
difference is undoubtedly caused by the anionic character of the
triazolate (or pyrazolate) units, for which the Coulomb
interaction would be expected to strengthen the associated
Pt−N bonding interaction. Moreover, the N −Pt−N angle
102.1(2) .
the pyridyl units (95.36° in 1 vs 80.86° in 3 and 96.24° in 5),
showing the bond-angle expanding effect introduced by either
the spiro-fluorene or acridine unit.
az
az
between the azolate fragments (103.09° in 1 vs 95.36° in 3 and
02.1° in 5) is also larger than the N −Pt−N angle between
1
py
py
C
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Inorganic Chemistry
Article
Finally, as indicated in their respective packing diagrams, both
Pt(II) complexes 1 and 3 exhibited a dimer-like packing motif in
the crystal lattice, with the spiro-bridged fluorene unit being
tilted away from the second molecule, probably to avoid
excessive steric encumbrance. Moreover, the Pt···Pt contact in
Pt(II) complexes with pyrazolate chelates, that is, 2−5, showed
ππ* absorption at ∼326 nm, with higher extinction coefficient for
the acridine derivatives 4 and 5 due to the greater conjugation
versus the fluorene derivatives 2 and 3.
In addition to the ππ* absorption, all of these Pt(II) complexes
show a weak band at the longer wavelength, which is tentatively
assigned to the transition incorporating a mixed state involving
3
(3.455 Å) is found to be shorter than that of 1 (3.759 Å),
suggesting that the t-butyl group fails to exert the anticipated
effect of pushing apart the weakly associated dimer. This can be
explained by the relative location of the spiro-fluorene unit, as it
seems to occupy space further from the cis-coordinated azolate
fragments and, hence, exerts almost no steric interference
between the pair of dimer molecules. In sharp contrast, the
acridine moiety in 5 is much larger than the spiro-fluorene in
both 1 and 3, hence, greatly increasing the spatial separation of
1
both singlet and triplet metal−ligand charge transfer ( MLCT
3
3
and MLCT) and, to a certain extent, the ligand-centered ππ or
3
ILCT transitions. The absorption onset of these lower-energy
bands follows the ascending order of 1 < 2 ≈ 3 < 4 ≪ 5 in terms
of wavelength, together with a gradual increase in corresponding
absorptivity. This trend in spectral shift showed good agreement
with the onset of their emission spectra, in which the emission
the PtN framework between adjacent molecules, allowing the
peak maximum (or the E peak for emission exhibiting vibronic
4
00
formation of only a monomer in the solid state.
fine structure, see Figure 4b) is in the order of 1 (452 nm) < 2
(460 nm) ≈ 3 (461 nm) < 4 (465 nm) ≪ 5 (520 nm, only one
peak). As listed in Table 1, the radiative lifetime of >1 μs and
quenching of the emission by oxygen (not shown here)
demonstrate the phosphorescence origin of the emission.
Remarkably, as shown in Figure 5a, the emission of acridine
Pt(II) complex 5 exhibits significant solvatochromism, which is
indicated by the observation of a structured emission profile with
E0−0 of 469 nm in cyclohexane and a broadened structureless
emission with a maximum centered between 497−537 nm in the
more polar solvents, for example, tetrahydrofuran (THF),
CH Cl , and ethanol. These observations lead us to conclude
Photophysical Data. The UV−vis absorption and emission
spectra of Pt(II) complexes 1−5 in CH Cl solution at room
2
2
temperature (RT) are shown in Figure 4, while the peak
wavelengths of absorptions, emissions, and other important
photophysical data are summarized in Table 1.
2
2
the occurrence of charge transfer and hence gigantic changes of
dipole moment in the excited state versus ground state happen.
The quantum yield Φ and lifetime τ were recorded, and the
associated radiative (k ) and nonradiative (k ) decay rates were
r
nr
deduced from the Φ and τ data using the following equations.
These data are listed in Table 2 and can contribute to an in-depth
understanding of the solvatochromic effect.
(
k + k ) = 1/τ and Φ(%) = k /(k + k )
r
nr
obs
r
r
nr
As can be seen, a lowered quantum yield Φ = 0.13 and long
lifetime τ = 20.1 μs were observed in cyclohexane at RT, which
3
gave the radiative and nonradiative rate constants, k of 6.3 × 10
r
4
and k of 4.3 × 10 . However, increased emission quantum yield
Φ = 0.88 and 0.52 and shorter lifetime τ = 2.9 and 2.7 μs were
nr
recorded upon switching to more polar solvents such as CH Cl
2
2
and ethanol, from which the substantially increased radiative rate
5
5
constants k of 3.0 × 10 and 1.9 × 10 were deduced. These
r
increased k values and disappearance of the vibronic fine
r
structures versus those recorded in cyclohexane can be ascribed,
in part, to the involvement of ILCT excited states that effectively
harness the triplet emission property. Such a change of emission
character from ligand-centered ππ*/MLCT to ILCT/MLCT
was previously observed in a series of Pt(II) alkynyl complexes
with distinctive tridentate pincer ligands, for which the excited-
state characters were controlled by the structural design of pincer
ligand. In sharp contrast, a simple change of solvent polarity
seems to be highly effective in causing the associated variation of
excited-state character in Pt(II) complex 5.
Figure 4. UV/vis absorption and emission spectra of the spiro-arranged
Pt(II) metal complexes 1−5 in CH Cl at RT. The emission spectra
2
2
28
were acquired in the degassed solution. The excitation wavelength for
each compound is at the peak position.
The dependence of phosphorescence on solvent polarity can
be specified quantitatively according to the dielectric polarization
theory. The shift of emission upon increasing solvent polarity
depends on the differences in the static dipole moments between
the ground (S ) and (T ) excited states. The difference of the
As revealed in Figure 4a, obviously the strong absorption
bands in the UV region (≤330 nm) are derived from a typical
ligand-centered ππ* transition since the corresponding tran-
sitions were also documented for the free ligands. As can be seen,
the Pt(II) complex 1 displays the most blue-shifted peak
wavelength, attributed to the dual triazolate chelates with the
enlarged ππ* energy gap. On the other hand, the other four
0
1
S −T dipole moment can be estimated by the Lippert−Mataga
0
1
29
equation incorporating the luminescence solvatochromic shift.
Considering that the dipole moment of the solute can be
D
DOI: 10.1021/acs.inorgchem.5b00281
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Inorganic Chemistry
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Table 1. Photophysical Data of the Studied Pt(II) Complexes
abs λ in nm (ε × 10−3 M−1 cm−1
a
)
em λ (nm)
a
Q.Y. (%)
τobs (μs)
kr (s−1)
knr (s−1
)
max
max
5.2 × 104
3.5 × 10
3.5 × 10
2.3 × 10
6.7 × 10
4.2 × 10
4
1
2
3
4
5
260 (31), 315 (19), 360 (3), 377 (1.7)
452, 481, 511
460, 488, 521
461, 487, 521
465, 492, 527
520
60
67
82
58
88
11.5
9.3
7.8
6.3
2.9
4
4
4
4
4
270 (32), 326 (23.9), 368 (5.1), 391 (2.0)
271 (31.8), 327 (22.8), 370 (4.8), 390 (2)
267(35), 325 (30.2), 368 (8), 388 (4.2)
270 (41), 326 (30.5), 367 (6.8), 385 (5.3)
7.2 × 10
1.1 × 105
4
9.2 × 10
3.0 × 105
a
Recorded in CH Cl at RT.
2
2
⃗ ⃗
diluted gas phase, respectively. The μg and μ are the dipole
e
moment vectors of the ground and T excited states, and Δf is the
1
solvent polarity parameter expressed as Δf = ((ε − 1)/(2ε + 1)),
where ε stands for the static dielectric constant of the solvent.
The Lippert plot of the phosphorescence as a function of Δf
for Pt(II) complex 5 is shown in Figure 5b. As predicted by eq 1, a
linear relationship is found from cyclohexane to ethanol, and
−1
slope is deduced to be as steep as −9395 cm . The a in eq 1 was
0
estimated to be 9.73 Å by the density functional theory (DFT)
Hartree−Fock method (see Experimental Section). Conse-
quently, the change of dipole moment between S and T was
0
1
calculated to be as large as 29.33 D, firmly supporting the charge
transfer character in the T state of 5. Similar solvent-dependent
1
3
0,31
phosphorescence has been reported in the literature,
which
normally requires the orthogonal orientation and large
separation in distance between donor and acceptor ligands to
enhance significant changes of dipole moment. For transition
metal complexes, the phosphorescence solvatochromism may be
observable in the case of either ILCT or ligand-to-ligand charge
transfer (LLCT) transition but is much less significant in the case
2
,32
of ligand-centered ππ* transition.
To gain further fundamental insight into the above
experimentally observed absorption and emission spectra, we
performed time-dependent density functional theory (TD-DFT)
calculations (see Experimental Section). For the Pt(II)
complexes 1−5, the frontier molecular orbitals (i.e., highest
occupied molecular orbital (HOMO) and lowest unoccupied
molecular orbital (LUMO)) involved in the lowest singlet and
triplet optical transitions are displayed in Table 3 and Figure 6
Figure 5. (a) Emission spectra of spiro-acridine Pt(II) complex 5 in
various degassed solvents at RT. (b) The Lippert−Mataga plot of
phosphorescence as a function of solvent polarity Δf.
(
HOMO−1, HOMO, and LUMO). The calculated lowest-lying
transition in terms of wavelengths and the charge characters of
Table 2. Photophysical Data of spiro-Acridine Pt(II) Complex
5
in Various Solvents
Table 3. Calculated Energy Levels and Orbital Transition
Analyses of Pt(II) Complexes 1−5
a
em λ
τobs
(μs)
max
(
nm)
Φ (%)
kr (s−1)
knr (s−1
)
state λ (nm)
f
assignments
0.0019 HOMO → LUMO (96%)
0 HOMO−1 → LUMO (73%)
MLCT
3
4
5
5
4.3 × 104
cyclohexane
THF
469
497
520
537
13
64
88
52
20.1
11.8
2.9
6.3 × 10
5.4 × 10
3.0 × 10
1.9 × 10
3.1 × 104
1
2
S
1
371.3
428.3
370.6
−3.47%
16.29%
9.76%
4
T
1
CH Cl2
4.2 × 10
2
1.8 × 105
S
1
0.0301 HOMO → LUMO (77%)
ethanol
2.7
HOMO−1 → LUMO (16%)
a
Recorded at RT.
T1
439.3
0
HOMO → LUMO (57%)
HOMO−1 → LUMO (13%)
HOMO−3 → LUMO+1 (7%)
7.60%
approximated by a point dipole in the center of a spherical cavity
3
4
S1
375.6
438.9
0.0006 HOMO → LUMO (96%)
−4.53%
11.50%
of radius a , on the basis of small solvent-dependent absorption
0
T1
0
HOMO−1 → LUMO (70%)
HOMO−3 → LUMO+1(6%)
and negligible solute polarizability, one can thus use eq 1
expressed below to describe the emission solvatochromism.
S1
430.2
441.2
0.0001 HOMO → LUMO (99%)
−5.59%
10.04%
2
(μ
⃗
− μ
⃗
)2
T
1
0
HOMO−1 → LUMO (66%)
HOMO−2 → LUMO+2 (11%)
HOMO−2 → LUMO+1 (6%)
e
g
vac
v
̃
= vf
̃
−
Δf
f
hca03
(1)
vac
5
S1
458.1
459.5
0.0002 HOMO → LUMO (100%)
−5.61%
−5.50%
where v
̃
and v
̃
are the spectral position of the steady-state
f
f
−1
T1
0 HOMO → LUMO (98%)
phosphorescence (in cm ) and the value extrapolated to the
E
DOI: 10.1021/acs.inorgchem.5b00281
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
We made an attempt to further calculate the lowest singlet and
triplet emissions for 5 in four solvents, namely, cyclohexane,
THF, CH Cl , and ethanol (Table 4). The solvent polarity is in
2
2
Table 4. Calculated Wavelengths of the Lowest-Energy Singlet
and Triplet Absorptions and Emissions (nm) for Pt(II)
Complex 5 in Various Solvents
a
solvent
ε
S0 → S1
S0 → T1
T → S0
1
S1 → S0
cyclohexane
THF
2.0
7.4
440.2
456.9
458.1
463.9
454.2
458.4
459.5
465.2
515.0
525.3
526.8
532.4
502.8
517.7
520.3
526.6
CH Cl2
8.9
2
ethanol
24.9
a
ε is the dielectric constant.
an increasing order of cyclohexane < THF < CH Cl < ethanol.
2
2
The calculation was performed via executing the geometry
optimization in the respective lowest excited state, that is, S or
1
T state, followed by a vertical (Franck−Condon) transition
1
Figure 6. Frontier molecular orbitals (HOMO−1, HOMO, and
from S (or T ) to the ground state (S ). As a result, the
1
1
0
LUMO) in the lowest-energy optical transitions for Pt(II) complexes
calculated S → S fluorescence and T → S phosphorescence in
1
0
1
0
1−5.
cyclohexane, THF, CH Cl , and ethanol are (502.8 and 515.0
2
2
nm), (517.7 and 525.3 nm), (520.3 and 526.8 nm), and (526.6
and 532.4 nm), respectively. Interestingly, the calculated
phosphorescence, in terms of wavelength, is relatively insensitive
to the solvent polarity. This result may not be too surprising
because of the application of Onsager solvation model, for
which the treatment of continuum spherical shape for solvent
molecules lacks the anisotropic dipole orientation; thus, the
calculated solvatochromism effect is relatively much smaller than
that of the experimental observation.
the five lowest singlet and triplet optical transitions as well as the
corresponding molecular orbitals are listed in Table 3 and
Supporting Information, Tables S1−S5 and Figures S1−S5,
respectively.
33
The calculated wavelengths of the S → S transitions for 1:
71.3 nm, 2: 370.6 nm, 3: 375.6 nm, 4: 430.2 nm, and 5: 458.1
0
1
3
nm (in CH Cl ) are close to the observed onsets of each
2
2
corresponding absorption spectrum (in CH Cl , see Figure 4 and
Organic Light-Emitting Diode Device Fabrication. Pt
complexes 3 and 5 were used as dopants for the fabrication of
blue phosphorescent OLEDs (PhOLEDs) due to their higher
emission quantum efficiencies. On the basis of our previous
2
2
Table 3). Moreover, the calculated wavelengths of the S → T1
0
transitions for 1: 428.3 nm, 2: 439.3 nm, 3: 438.9 nm, 4: 441.2
nm, and 5: 459.5 nm also correlate well to the emission band in
Figure 4. The electron density distributions of the key frontier
molecular orbitals for Pt(II) complex 1 are mainly localized at the
triazolate chelate (for HOMO−1 and LUMO) and fluorene
fragment (for HOMO). Similarly, the electron density
distributions for Pt(II) complexes 2−5 are mainly located at
the pyrazolate chelate and fluorene/acridine (for HOMO−1 and
HOMO) and at the pyrazolate chelate (for LUMO). The S → S
34−36
experience in fabrication of true-blue PhOLEDs,
we chose a
double-layered design with the following architecture: ITO/
TAPC (40 nm)/mCP doped with 8 wt % of Pt complex (17
nm)/DPEPO doped with 8 wt % of Pt complex (3 nm)/ DPEPO
(3 nm)/ TmPyPB (50 nm)/LiF (0.8 nm)/Al (150 nm). Figure 7
presents structural drawings of the employed materials and
device architecture. The procedure involved dispersing dopants
into hosts with opposite transport properties, so that the carrier
recombination zone can be enlarged compared with the single
emitting layer (EML). Thus, two wide triplet-energy-gap host
materials, 3-bis(9-carbazolyl)benzene (mCP) and bis(2-
(diphenylphosphino)phenyl)ether oxide (DPEPO), for which
0
1
and S → T optical transitions for Pt(II) complexes 1−4 are
0
1
assigned to the HOMO → LUMO or HOMO−1 → LUMO, and
their MLCT character is within the range from −5.59% (S state
1
of 4) to 16.29% (T state of 1). The negative sign indicates that
1
the charge transfer, in part, involves ligand-to-metal charge
transfer (LMCT) or ILCT processes. However, for the T state,
the respective triplet energy gaps (E ) are reported to be 2.9 and
1
T
37−42
which is the origin of the phosphorescence, frontier orbital
analyses indicate that all Pt(II) complexes 1−4 are dominated by
the distinctive ligand-centered ππ* transition. In sharp contrast,
both S and T of complex 5 possess a great portion of charge
3.0 eV, were applied in this approach.
In addition, mCP
−4
shows the hole and electron mobilities to be 1.2 × 10 and 3.4 ×
−
5
2
10 cm /(V s), respectively. The former is an order of
37−39
magnitude higher.
Therefore, the electron-transporting
1
1
transfer character from acridine (HOMO) to the pyrazolate
chelates, that is, a typical ILCT transition, but in a mutual
orthogonal orientation, resulting in a large separation of electron
density between two corresponding moieties. The computa-
tional results thus firmly support the experimental observation,
DPEPO was used to combine with mCP to form the second
EML and the subsequent exciton confining layer. On the other
hand, di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC)
was used as the hole-transport layer, because it possesses a triplet
gap of 2.8 eV, a higher hole mobility of 1 × 10− cm /V s, and an
upper-lying LUMO level capable of blocking the electron
injection, while 1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene
(TmPyPB) was used as the electron-transport layer due to the
2
2
expecting the large change of dipole moment between T and S0
1
states and thus remarkable phosphorescence solvatochromism
for 5. Conversely, the phosphorescence of the other complexes
−3
2
(
i.e., 1−4) mainly involves ligand-centered ππ*, which is rather
higher carrier-transport capability of 1 × 10 cm /V s and large
43−46
insensitive to the solvent polarity.
triplet gap (E ) of 2.78 eV.
T
F
DOI: 10.1021/acs.inorgchem.5b00281
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 7. (a) Structural drawing of the materials and (b) schematic structures of the tested blue and white OLEDs.
Figure 8. (a) EL spectra of devices A and B, (b) EL spectra of device WA at different luminance levels, (c) EL spectra of device WB at different luminance
levels, (d) current density−voltage−luminance (J−V−L) characteristics, (e) external quantum efficiency vs luminance, (f) power efficiencies/
luminance efficiencies vs luminance for devices A, B, WA, and WB.
Figure 8 and Table 5 show the electroluminescence (EL)
characteristics and the associated numerical data for the devices
employing 3 and 5. As shown in Figure 8a, devices A and B
exhibited solely the emission of 3 and 5. No interfering emission
from either hosts or carrier-transport materials was observed,
implying the occurrence of effective exothermic energy transfer
to the dopant. Their EL spectra exhibited stable emission at
different luminance, indicating that the exciton formation zones
shift insignificantly with increasing voltages. This reduced
susceptibility to environmental influence is remarkable. The
slightly wider full width at half-maximum (fwhm) of the EL
spectra versus that of the photluminescence (PL) spectra results
G
DOI: 10.1021/acs.inorgchem.5b00281
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 5. EL Characteristics of Tested Devices with Different Emitters
emission color
sky blue
white
device
A
B
WA
WB
dopant
3
5
3 + Os
5 + Os
12.7
external quantum efficiency (%)
a
b
a
b
a
b
c
12.3
15.3
10.1
9.4
12.8
7.8
10.0
luminescence efficiency (cd/A)
power efficiency (lm/W)
Von (V)
27.1
36.3
16.9
22.5
20.6
30.4
14.2
17.8
26.6
38.0
16.6
22.1
11.7
21.1
7.9
11.7
3.5
3.2
3.5
3.4
2
max luminance (cd/m ) [voltage]
1924 [10.4 V]
(0.190, 0.342)
(0.189, 0.342)
(0.189, 0.342)
4121 [9.8 V]
(0.194, 0.391)
(0.193, 0.390)
(0.193, 0.389)
1945 [10.6 V]
3710 [10.4]
CIE1931 coordinates/CCT (K)/CRI (Ra14)
b
d
e
(0.360, 0.366) 4549 K/70.2
(0.355, 0.362) 4695 K/69.2
(0.355, 0.362) 4684 K/68.3
(0.382, 0.375) 3900 K/64.2
(0.369, 0.375) 4313 K/65.1
(0.365, 0.376) 4438 K/65.4
a
b
2
2
c
2
d
2
e
2
Maximum efficiency. Recorded at 1 × 10 cd/m . Turn-on voltage measured at 1 cd/m . Measured at 500 cd/m . Measured at 1000 cd/m .
from concentration-induced red-shift as well as the effect of
optical interference. Overall, both devices A and B showed sky-
blue emission colors and similar CIE coordinates of (0.190,
Figure 8b,c shows the EL spectra at different luminance. Both
devices presented stable warm-white emission and a minimized
variation of CIE coordinates, that is, (−0.005, −0.004) and
(−0.017, 0.001) for devices WA and WB, respectively. The
0.342) and (0.194, 0.391), respectively.
According to the J−V−L curves shown in Figure 8d, device B
correlated color temperatures (CCT) and color rendering index
2
(
CRI) at 100 cd/m were respectively estimated to be (4549 K,
exhibits a higher current density than device A (8.1 vs 25.9 mA/
2
7
0) and (3900 K, 64) for WA and WB. The lowered CCTs and
cm ) at driving voltage of 8 V. The higher current density of 5
CRI values for WB are due to the red-shifted PL emission of 5. As
shown in Figure 8d both WOLEDs gave similar current densities,
maximum luminescence, and turn-on voltages, respectively.
Their maximum efficiencies reached 10.1% (16.9 cd/A, 16.6 lm/
W) and 12.7% (22.5 cd/A, 22.1 lm/W) for WA and WB,
respectively. In addition, WA exhibited EL efficiencies of 7.8%,
indicates better carrier-transport properties, which is also
confirmed by the lower turn-on voltage and higher luminance.
The corresponding turn-on voltages of A and B obtained at 1 cd/
2
m were recorded to be 3.5 and 3.2 V, respectively. Moreover,
2
device A gave a maximum luminance of 1924 cd/m at 10.4 V,
while device B achieved a much higher luminance of 4121 cd/m2
1
1
4.2 cd/A, and 7.9 lm/W, while WB exhibited efficiencies of
at a lower driving voltage of 9.8 V. Peak EL efficiencies of up to
2
0.0%, 17.8 cd/A, and 11.7 lm/W, both recorded at 1 × 10 cd/
12.3%, 27.1 cd/A, and 26.6 lm/W were recorded for A, and the
2
m . These data are summarized in Figure 8e,f.
efficiencies remained high at ∼9.4%, 20.6 cd/A, and 11.7 lm/W
2
2
at a practical brightness of 1 × 10 cd/m . Under identical
conditions, device B exhibited a maximum efficiency of 15.3%,
CONCLUSION
■
3
6.3 cd/A, and 38.0 lm/W and slightly reduced forward
In conclusion, we report the rational design and syntheses of a
new series of tetradentate bis(pyridyl azolate) chelates. These
chelates offer an orthogonal configuration per se between
fluorene and acridine and two bidentate 3-trifluoromethyl-5-(2-
pyridyl) azolate chelates that offer four binding sites for the
central Pt(II) metal ion. Five Pt(II) metal complexes 1−5 were
thus successfully synthesized, for which the Pt(II)−Pt(II)
interaction has been minimized due to the intrinsic steric
hindrance introduced by the chelates, resulting in the formation
of dimeric structure, rather than the one-dimensional chainlike
oligomer geometry. These complexes with a well-protected
Pt(II) core exhibit intense emission intensity, among which 5
shows remarkable solvatochromism of phosphorescence due to
the dominant ILCT transition in orthogonal orientation, as also
firmly evidenced by the computational approach. These robust
Pt(II) complexes can serve as effective sky blue phosphors for
OLEDs. The peak efficiencies of OLEDs with Pt(II) dopants 3
and 5 were recorded at 12.3% (27.1 cd/A, 26.6 lm/W) and 15.3%
2
efficiencies of 12.8%, 30.4 cd/A, and 21.1 lm/W at 1 × 10 cd/
m . Given the similarity of the PL Φ for both complexes, the
2
better efficiency and the suppressed efficiency roll-off observed in
device B was certainly attributed to the superior carrier transport
of 5.
Encouraged by the aforementioned performances, we made
further attempts to attain white OLEDs (WOLEDs) based on
the blue OLED architecture. A red-emitting Os-
(
fptz) (PPh Me) can provide a complementary color with
2 2 2
respect to the blue emission of 3 and 5 and was thus chosen as the
4
7
second emitter. In general, the color variation and carrier
balance are significantly influenced by both the location and
concentration of red EML layer because of the lower energy
4
8−51
gap.
To stabilize the resulting emission at different voltages,
a thin layer (i.e., 1 nm) of red dopant was sandwiched between
the double layers of blue dopant and constituted the principal
52,53
carrier recombination zone (RZ) in EML.
As shown in
(
36.3 cd/A, 38.0 lm/W), respectively. Furthermore, the red-
Figure 8b, the WOLEDs with blue/red/blue EMLs are depicted
as follows: ITO (120 nm)/TAPC (40 nm)/mCP doped with 8.0
wt % 3 or 5 (16 nm)/mCP doped with 2.0 wt % Os (1 nm)/
DPEPO doped with 8.0 wt % 3 or 5 (3 nm)/DPEPO (3 nm)/
TmPyPB (50 nm)/LiF (0.8 nm)/Al (150 nm). Therefore, the
low HOMO level of the red dopant will help to localize the RZ,
mitigating the color variation induced by the RZ shift as voltage
increases.
emitting Os(II) complex, Os(fptz) (PPh Me) , was combined
2
2
2
with 3 or 5 to fabricate WOLEDs. Devices WA (i.e., 3 + Os)
produced a maximum efficiency of 10.1% and ultrastable warm-
white emission with CIE coordinates (0.360, 0.366) at 100 cd/
2
m , while WB (i.e., 5 + Os) achieved even higher peak efficiency
of 12.7% and warm-white emission with CIE coordinates (0.382,
2
0.375) at 100 cd/m . The orthogonality between the auxiliary
and intimate coordination framework also offers versatility to
H
DOI: 10.1021/acs.inorgchem.5b00281
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
form metal complexes endowed with unique photophysical
properties. These outcomes pinpoint the great potential of these
series of tetradentate chelates in the coordination chemistry as
well as lighting and solar energy research fields.
Spectral data of 4: H NMR (400 MHz, CD
2
Cl
2
, 298 K): δ 7.87 (t, J =
7
=
=
8
1
.9 Hz, 2 H), 7.77 (t, J = 7.4 Hz, 2 H), 7.66 (t, J = 7.4 Hz, 1 H), 7.60 (d, J
7.9 Hz, 2 H), 7.50−7.47 (m, 2 H), 7.35 (d, J = 7.4 Hz, 2 H), 7.17 (dd, J
7.6, 1.7 Hz, 2 H), 7.05−7.00 (m, 4 H), 6.76−6.71 (m, 2 H), 6.42 (d, J =
.4 Hz, 2 H). 13C NMR (175 MHz, THF-d , 298 K): δ 162.7, 152.4,
8
2
49.8, 142.2 (q, J
= 35.9 Hz), 140.2, 139.3, 138.0, 131.3, 130.9,
C−F
1
EXPERIMENTAL SECTION
130.8, 128.9, 128.5, 127.7, 125.6, 122.5 (q, J
16.9, 115.7, 102.4 (q, J
CD Cl , 298 K): δ −60.96. MS [FAB], m/z 871.6, M . Anal. Calcd for
C H F N Pt: C, 50.92; H, 2.43; N, 11.24. Found: C, 50.86; H, 2.99; N,
= 266.5 Hz), 121.8,
■
C−F
3
19
1
= 2.2 Hz), 64.4. F NMR (376 MHz,
General Procedures. All solvents were dried over appropriate
drying agents and distilled prior to use. Commercially available reagents
were used without further purification, unless otherwise stated. All
reactions were performed under a nitrogen atmosphere and monitored
by using precoated thin-layer chromatography plates (0.20 mm with
fluorescent indicator UV254). Mass spectra were obtained on a JEOL
SX-102A instrument operating in electron impact (EI) or fast atom
bombardment (FAB) mode. All NMR spectra were recorded on a
Varian Mercury-400, VNMR-700, or an INOVA-500 instrument.
Elemental analysis was performed with a Heraeus CHN-O Rapid
Elementary Analyzer.
C−F
+
2
2
37 21
6
7
1
0.85%.
Synthesis of [Pt(L5)] (5). This complex was prepared from
Pt(DMSO) Cl and L5 using procedures and conditions similar to
2
2
those described for 1. Yield: 55%.
1
Spectral data of 5: H NMR (400 MHz, CD Cl , 298 K): δ 7.85 (t, J =
2
2
8
=
(
.5 Hz, 2 H), 7.73 (d, J = 6.8 Hz, 2 H), 7.59 (d, J = 7.9 Hz, 2 H), 7.33 (d, J
8.5 Hz, 2 H), 7.23 (s, 2 H), 7.05 (d, J = 9.1 Hz, 2 H), 7.01 (s, 2 H), 6.36
d, J = 9.1 Hz, 2 H), 1.46 (s, 9 H), 1.01 (s, 18 H). 13C NMR (100 MHz,
2
DMSO-d , 298 K): δ 162.8, 152.3, 150.3, 144.8, 142.8 (q, J
Hz), 139.2, 137.1, 136.3, 130.1, 128.2, 127.7, 126.9, 126.1, 123.9, 122.3
= 36.5
Synthesis of [Pt(L1)] (1). A mixture of Pt(DMSO) Cl (65 mg, 0.15
6
C−F
2
2
mmol), Na CO (82 mg, 0.77 mmol), and L1 (100 mg, 0.17 mmol) in
2
3
1
3
(
3
q, J = 266.8 Hz), 117.2, 115.7, 102.6 (q, J = 2.5 Hz), 65.6, 65.1,
1
,2-dimethoxyethane (DME) was refluxed for 5 h. After removal of
C−F C−F
19
4.8, 33.9, 31.1, 30.8. F NMR (376 MHz, CD Cl , 298 K): δ −60.99.
MS [FAB], m/z 1041.3, M . Anal. Calcd for C H F N Pt: C, 56.63; H,
.36; N, 9.42. Found: C, 56.33; H, 4.52; N, 9.39%.
Selected crystal data of 5: C H Cl F N O Pt; M = 1190.02; T =
50(2) K; λ(Mo Kα) = 0.710 73 Å; orthorhombic; space group = Pbca;
a = 14.5851(5), b = 25.7640(9), c = 26.9502(9) Å; V = 10127.1(6) Å ; Z
DME, the residue was extracted with CH Cl , and the CH Cl solution
2
2
2
2
2
2
+
was washed with water, dried over Na SO , and concentrated. The
49 45
6
7
2
4
4
obtained crude product was purified by SiO column chromatography
2
using CH Cl and hexane (15:1) as eluent, followed by recrystallization
52 55
2
6
7
2
2
2
1
from a mixed solution of CH Cl and hexane to obtain a pale yellow
2
2
3
solid (62 mg, 51.2%).
−3
−1
1
= 8; ρcalcd = 1.561 Mg·m ; μ = 2.947 mm ; F(000) = 4784; crystal size
3
Spectral data of 1: H NMR (400 MHz, CD Cl , 298 K): δ 8.03 (dd, J
2
2
=
0.40 × 0.13 × 0.08 mm ; 63 788 reflections collected, 11 632
=
7.8, 1.5 Hz, 2 H), 7.98 (d, J = 7.5 Hz, 2 H), 7.91 (d, J = 7.5 Hz, 2 H),
independent reflections (Rint = 0.0989), max and min transmission =
0.7984 and 0.3853, restraints/parameters =7/646, GOF = 1.066, final
R [I > 2σ(I)] = 0.0504, and wR (all data) = 0.1295.
7
(
.77 (t, J = 7.8 Hz, 2 H), 7.58−7.54 (m, 2 H), 7.43−7.40 (m, 2 H), 6.75
dd, J = 8.6, 1.1 Hz, 2 H). 1 F NMR (376 MHz, CDCl , 298 K): δ
9
3
+
−
64.26. MS [FAB], m/z 784.1, M . Anal. Calcd for C H F N Pt: C,
1
2
29
14
6
8
X-ray Crystallography. All single-crystal X-ray diffraction data were
4
4.45; H, 1.80, N, 14.30. Found: C, 45.03; H, 1.92; N, 13.88%.
measured on a Bruker Smart CCD diffractometer using λ (Mo Kα)
radiation (λ = 0.710 73 Å). The data collection was executed using the
SMART program. Cell refinement and data reduction were made with
the SAINT program. The structure was determined using the
SHELXTL/PC program and refined using full matrix least-squares.
All non-hydrogen atoms were refined anisotropically, whereas hydrogen
atoms were placed at the calculated positions and included in the final
stage of refinements with fixed parameters.
Selected crystal data of 1: C H Cl F N Pt; M = 868.50; T = 150(2)
30
16
2
6
8
K; λ(Mo Kα) = 0.710 73 Å; monoclinic; space group = P2 /c; a =
1
9
2
1
6
.5855(5), b = 25.5533(14), c = 11.7334(6) Å, β = 91.4351(13)°; V =
3
−3
−1
873.1(3) Å ; Z = 4; ρcalcd = 2.008 Mg·m ; μ = 5.148 mm ; F(000) =
3
672; crystal size = 0.20 × 0.10 × 0.08 mm ; 18 640 reflections collected,
606 independent reflections (Rint = 0.0460), max and min transmission
=
0.6835 and 0.4258, restraints/parameters =18/434, GOF = 1.037,
final R [I > 2σ(I)] = 0.0355, and wR (all data) = 0.0760.
1
2
Organic Light-Emitting Diode Fabrication. All commercial
materials and indium tin oxide (ITO)-coated glass were purchased from
Nichem and Lumtec. Glass substrates were cleaned by exposure to a
UV−ozone atmosphere for 5 min. The bottom-emitting OLED devices
were fabricated using ITO-coated glass substrates (<15 Ω) as the anode,
followed by the deposition of multiple organic layers, topped by metal
cathode layer. The organic and metal layers were consecutively
deposited onto the substrates by thermal evaporation in a vacuum
Synthesis of [Pt(L2)] (2). This complex was prepared from
Pt(DMSO) Cl and L2 using procedures similar to those described
2
2
for 1. Yield: 59.8%. 1
Spectral data of 2: H NMR (400 MHz, acetone-d , 298 K): δ 8.21 (d,
6
J = 7.8 Hz, 2 H), 8.11−8.09 (m, 4 H), 7.94 (t, J = 8.4 Hz, 2 H), 7.58 (t, J =
7
.6 Hz, 2 H), 7.46 (t, J = 8.0 Hz, 2 H), 7.42 (s, 2 H), 6.59 (d, J = 8.4 Hz, 2
19
H). F NMR (376 MHz, acetone-d , 298 K): δ −58.97. MS [FAB], m/z
7
6
+
81.0, M . Anal. Calcd for C H F N Pt: C, 47.64; H, 2.06; N, 10.75.
31 16 6 6
−6
chamber with a base pressure of <1 × 10 Torr without breaking the
Found: C, 48.06; H, 2.39; N, 10.35%.
Synthesis of [Pt(L3)] (3). This complex was prepared from
vacuum. The deposition rate was kept at ∼0.1 nm/s. The active area of
2
the device was set to 2 × 2 mm , as defined by the shadow mask used for
Pt(DMSO) Cl and L3 using procedures similar to those described
2
2
cathode deposition. Current density−voltage−luminance character-
ization was measured using a Keithley 238 current source-measure unit
and a Keithley 6485 picoammeter equipped with a calibrated Si-
photodiode. The electroluminescent spectra of the devices were
recorded using an Ocean Optics spectrometer.
for 1. Yield: 61.2%.
Spectral data of 3: H NMR (400 MHz, CD Cl , 298 K): δ 7.99 (s, 2
H), 7.79 (d, J = 7.6 Hz, 2 H), 7.65 (d, J = 4.1 Hz, 4 H), 7.58 (d, J = 8.2 Hz,
1
2
2
19
2
H), 6.99 (s, 2 H), 6.59 (t, J = 4.1 Hz, 2 H), 1.26 (s, 18 H). F NMR
+
(
376 MHz, CDCl , 298 K): δ −61.02. MS [FAB], m/z 894.7, M . Anal.
3
Calcd for C H F N Pt: C, 52.41; H, 3.61; N, 9.40. Found: C, 51.96; H,
39
32
6
6
3
.82; N, 9.11%.
ASSOCIATED CONTENT
■
Selected crystal data of 3: C H Cl F N Pt; M = 978.72; T = 150(2)
40
34
2
6
6
K; λ(Mo Kα) = 0.710 73 Å; monoclinic; space group = P2 /c; a =
*
S
Supporting Information
1
1
3
1
8
1.2393(5), b = 21.0560(11), c = 16.0806(8) Å, β = 92.1010(10)°; V =
General experimental procedures, synthesis procedures, NMR
and MS data of synthesized compounds, X-ray crystallographic
data file (CIF) of Pt(II) complexes 1, 3, and 5, procedures for
ligand preparation, illustrated frontier molecular orbitals,
absorption and emission spectra, additional references, and
results concerning the TD-DFT calculation of all Pt(II)
complexes. This material is available free of charge via the
Internet at http://pubs.acs.org.
3
−3
−1
803.0(3) Å ; Z = 4; ρcalcd = 1.709 Mg·m ; μ = 3.898 mm ; F(000) =
3
928; crystal size = 0.23 × 0.20 × 0.12 mm ; 24 645 reflections collected,
737 independent reflections (Rint = 0.0444), max and min transmission
=
0.6520 and 0.4675, restraints/parameters = 0/502, GOF = 1.089, final
1
Synthesis of [Pt(L4)] (4). This complex was prepared from
R [I > 2σ(I)] = 0.0366, and wR (all data) = 0.0791.
2
Pt(DMSO) Cl and L4 using procedures similar to those described
for 1. Yield: 51.2%.
2
2
I
DOI: 10.1021/acs.inorgchem.5b00281
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(
29) Bagchi, B.; Oxtoby, D. W.; Fleming, G. R. Chem. Phys. 1984, 86,
AUTHOR INFORMATION
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*
*
*
*
2
(
57.
30) Yu, J.-K.; Cheng, Y.-M.; Hu, Y.-H.; Chou, P.-T.; Chen, Y.-L.; Lee,
Corresponding Authors
E-mail: ychi@mx.nthu.edu.tw.
E-mail: chc@saturn.yzu.edu.tw.
E-mail: chop@ntu.edu.tw.
S.-W.; Chi, Y. J. Phys. Chem. B 2004, 108, 19908.
(31) Li, S.-W.; Cheng, Y.-M.; Yeh, Y.-S.; Hsu, C.-C.; Chou, P.-T.; Peng,
S.-M.; Lee, G.-H.; Tung, Y.-L.; Wu, P.-C.; Chi, Y.; Wu, F.-I.; Shu, C.-F.
Chem.Eur. J. 2005, 11, 6347.
E-mail: Neil.Robertson@ed.ac.uk.
(
(
(
32) Vogler, A.; Kunkely, H. Coord. Chem. Rev. 2000, 208, 321.
33) Klamt, A. J. Phys. Chem. 1995, 99, 2224.
34) Chiu, Y.-C.; Hung, J.-Y.; Chi, Y.; Chen, C.-C.; Chang, C.-H.; Wu,
Notes
The authors declare no competing financial interest.
C.-C.; Cheng, Y.-M.; Yu, Y.-C.; Lee, G.-H.; Chou, P.-T. Adv. Mater.
ACKNOWLEDGMENTS
2009, 21, 2221.
■
(
35) Chang, C.-H.; Chen, C.-C.; Wu, C.-C.; Yang, C.-H.; Chi, Y. Org.
Electron. 2009, 10, 1364.
36) Lin, C.-H.; Chang, Y.-Y.; Hung, J.-Y.; Lin, C.-Y.; Chi, Y.; Chung,
This work was supported by the Ministry of Science and
Technology of Taiwan under Grant No. NSC-101-2113-M-007-
13-MY3. The computation was conducted at the National
Center for High-Performance Computing. Y.H. thanks the
China Scholarship Council for a studentship.
(
0
M.-W.; Lin, C.-L.; Chou, P.-T.; Lee, G.-H.; Chang, C.-H.; Lin, W.-C.
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DOI: 10.1021/acs.inorgchem.5b00281
Inorg. Chem. XXXX, XXX, XXX−XXX