Syntheses, photoluminescence, and electroluminescence of iridium(III) complexes with fluorinated 2-phenylpyridine as main ligands and tertraphenylimidodiphosphinate as ancillary ligand

Article abstract of DOI:10.1002/ejic.201300861

Three green-emitting heteroleptic iridium complexes with 2-(4,5,6-trifluorophenyl)pyridine, 2-(3,4,6-trifluorophenyl)pyridine, and 2-(3,4,5-trifluorophenyl)pyridine as main ligands and tetraphenylimidodiphosphinate (tpip) as the ancillary ligand were synt

Full text of DOI:10.1002/ejic.201300861

Job/Unit: I30861
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DOI:10.1002/ejic.201300861
Syntheses, Photoluminescence, and Electroluminescence of
Iridium(III) Complexes with Fluorinated 2-Phenylpyridine
as Main Ligands and Tertraphenylimidodiphosphinate as
Ancillary Ligand
[
a]
[a]
[a]
[a]
[a]
Cheng-Cheng Wang, Yi-Ming Jing, Tian-Yi Li, Qiu-Lei Xu,
[
a]
[a]
[a]
Song Zhang, Wei-Nan Li, You-Xuan Zheng,* Jing-Lin Zuo,
Xiao-Zeng You, and Xiu-Qiang Wang*
[a]
[b]
Keywords: Iridium / Luminescence / Organic light-emitting diodes / Fluorinated ligands
Three green-emitting heteroleptic iridium complexes with 2-
4,5,6-trifluorophenyl)pyridine, 2-(3,4,6-trifluorophenyl)pyr-
phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBi), 45 nm/LiF
(1 nm)/Al (100 nm)} exhibited good performances. The de-
vice doped with bis[2-(3,4,6-trifluorophenyl)pyridine](tet-
(
idine, and 2-(3,4,5-trifluorophenyl)pyridine as main ligands
and tetraphenylimidodiphosphinate (tpip) as the ancillary
ligand were synthesized and characterized. The positions of
the three fluorine atoms on the phenyl ring affect the emis-
sion properties of the complexes, and the application of Htpip
as the ancillary ligand improves the electron mobility of the
complexes to make it comparable to that of the popular elec-
tron transport material tris(8-hydroxyquinolinato)aluminium
raphenylimidodiphosphinato)iridium
2
[Ir(F3,4,6ppy) (tpip)]
(8 wt.-%) showed superior performance with a peak current
–
1
efficiency (η
c
) of 66.36 cdA and a peak external quantum
efficiency (ηext, EQE) of 25.7% at 5.8 V, a maximum power
–
1
p
efficiency (η ) of 48.20 lmW at 4.4 V, and a maximum lumi-
–
2
nance (Lmax) of 47627 cdm at 12.6 V. Notably, the electrolu-
minescence (EL) efficiency roll-off effects at relatively high
current density in all devices are very mild, which helps them
to obtain high efficiency at brightness. The results suggest
(
3
Alq ) under the same electric fields. The organic light-emit-
ting diodes (OLEDs) based on the above phosphorescent
emitters {indium tin oxide (ITO)/1,1-bis[4-(di-p-tolyl-amino)-
phenyl]cyclohexane (TAPC), 30 nm/Ir complex (x wt.-%)/
N,NЈ-dicarbazolyl-3,5-benzene (mCP), 15 nm/1,3,5-tri(1-
2
that the three complexes, [Ir(F3,4,6ppy) (tpip)] especially,
would have potential applications in OLEDs.
excited states.[2] These IrIII complexes have very strong
spin–orbit coupling, which introduces intersystem crossing
to mix the singlet and triplet exited states and changes the
spin-forbidden radiative relaxation from the triplet exited
state to be allowed. As a result, both singlet and triplet
excitons can be harvested for light emission, and the in-
Introduction
In recent decades, organic light-emitting diodes (OLEDs)
have evolved because of their low power consumption and
the possibility to fabricate large and brilliant flat panel dis-
plays at moderate prices, illuminating wallpapers, and mic-
rodisplays for all types of applications. As the emitters,
phosphorescent Ir complexes play an important part in
[1]
III
ternal quantum efficiency of the Ir complexes can theore-
III
tically achieve 100%.
the fabrication of efficient OLEDs owing to their high
quantum efficiency and the short lifetimes of their triplet
III
In particular, Ir complexes based on 2-phenylpyridine
(ppy) derivatives have drawn much more attention because
they emit red, green, and blue light, which can be tuned by
[
[
a] State Key Laboratory of Coordination Chemistry, Nanjing modifying the ppy main ligands as well as by introducing
National Laboratory of Microstructures, Center for Molecular
Organic Chemistry, School of Chemistry and Chemical
Engineering, Nanjing University,
[3]
diverse ancillary ligands. Different substituents at the dif-
III
ferent positions of the ppy ring in these Ir complexes will
result in various spectral characteristics. For example, Ir
III
Nanjing 210093, P. R. China
E-mail: yxzheng@nju.edu.cn,
complexes that carry fluorinated phenylpyridine ligands
http://hysz.nju.edu.cn/yxzheng/
[
4]
b] School of Life Science, Nanjing University,
Nanjing 210093, Nanjing 210093, P. R. China
E-mail: xqwang@nju.edu.cn
were reported to have good performances, which suggests
that the introduction of the electron-withdrawing groups
improves the performance of OLEDs; the conversion of the
C–H bonds in these complexes to C–F bonds may have sev-
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300861
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eral potential benefits, such as reduction of irradiative exci- Results and Discussion
ton decay, enhancement of photoluminescence (PL) effi-
Single-Crystal Analysis and Thermal Properties
ciency, and electron mobility.[ In 2010, Chi and Chou gave
5]
a critical review on advanced methodologies for the system-
The single-crystal structures of [Ir(F4,5,6ppy)
2
(tpip)],
(tpip)], and [Ir(F3,4,5ppy) (tpip)] are shown in
2
III
atic preparation of Ir -based phosphors that show latent [Ir(F3,4,6ppy)
applications in the field of OLEDs.[6] In 2006, Naso and
De Cola reported the synthesis and performance of OLEDs
of blue homoleptic [Ir(F ppy) ] and heteroleptic [(F ppy) -
2
n
3
n
2
Ir(acac)] complexes [n = 3, F ppy = 2-(3,4,6-trifluoro-
3
phenyl)pyridine; n = 4, F ppy = 2-(3,4,5,6-tetrafluoro-
4
[5d]
phenyl)pyridine; acac = acetylacetonate].
Tao and Lee
also reported highly efficient blue and white phosphores-
cent OLEDs based on an iridium complex with 2-(3,4,5-
trifluorophenyl)pyridine and 2-(4,5,6-trifluorophenyl)pyr-
idine as main ligands and 2-picolinic acid (pic) as ancillary
[
5j,5k]
ligand.
As the electron effects are believed to be one of
III
the ways to finely tune the color of the emission of Ir
complexes, the position and number of the fluorine atoms
substituted at the phenyl ring will mainly affect the emitting
III
[5j,5k]
properties of Ir complexes.
Indeed, these complexes
were expected to show a shift of the emission to higher
frequency, owing to the presence of electron-withdrawing
fluorine substituents on the chelating ligands, which should
decrease the energy of the highest occupied molecular or-
bital (HOMO) and, as a consequence, increase the HOMO–
LUMO (lowest unoccupied molecular orbital) energy gap.
In addition, in most mixed-ligand iridium complexes
[
Ir(CN) (LX)], density functional theory calculations indi-
2
cate that the HOMO is largely metal-centered, whereas the
LUMO is primarily localized on the heterocyclic rings of
the cyclometalated ligands. Though the ancillary ligand is
not directly involved in the lowest excited state, it can alter
the energy of the excited state by modifying the electron
[7]
density at the metal center and affect the carrier mobility
[
8]
of the complexes. Thus, the photophysical, electrochemi-
III
cal, and electroluminescent properties of Ir complexes can
be tuned through controlled functionalization of both the
cyclometalated and ancillary ligands. Our group has re-
ported highly efficient green and blue-green phosphorescent
OLEDs with tetraphenylimidodiphosphinate (tpip) deriva-
tives as an ancillary ligand.[ Compared with the popular
acac ligand, Htpip has more polar P=O bonds and four
bulky aromatic groups, which may improve the electron mo-
bility and lead to larger spatial separation of neighboring
8]
III
molecules of the Ir complex to suppress triplet–triplet an-
nihilation (TTA) and triplet–polaron quenching (TPQ) ef-
[
8b]
fectively.
The performances of the devices suggest that
III
Htpip is a useful ancillary ligand for Ir complexes and
benefits OLED performances.[ To investigate the effects of
the positions of the three fluorine atoms of the phenyl ring
8]
III
of ppy in Ir complexes on their OLED performance and
explore the application of Htpip ligands, we synthesized
three bis-cyclometalated IrIII complexes, namely,
[
Ir(F4,5,6ppy) (tpip)] [F4,5,6ppy = 2-(4,5,6-trifluorophenyl)-
2
pyridine], [Ir(F3,4,6ppy) (tpip)] [F3,4,6ppy = 2-(3,4,6-tri-
2
fluorophenyl)pyridine], and [Ir(F3,4,5ppy) (tpip)] [F3,4,5ppy
2
Figure 1. ORTEP diagrams of [Ir(F4,5,6ppy)
2
(tpip)], [Ir(F3,4,6ppy)
2
-
=
2-(3,4,5-trifluorophenyl)pyridine], and investigated their
[9–11]
(
2
tpip)], and [Ir(F3,4,5ppy) (tpip)].
Ellipsoids are drawn at the
OLED characteristics.
50% probability level. Hydrogen atoms are omitted for clarity.
Eur. J. Inorg. Chem. 0000, 0–0
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Figure 1, the corresponding crystallographic data are sum-
marized in Table 3, and selected bond lengths and angles
are listed in Tables S1–3. Despite the similarity of the struc-
tures of [Ir(F4,5,6ppy) (tpip)], [Ir(F
ppy) (tpip)], and
2
3,4,6
2
[
Ir(F3,4,5ppy) (tpip)], they crystallize in different space
2
groups. [Ir(F4,5,6ppy) (tpip)] and [Ir(F
ppy) (tpip)] be-
2
2
3,4,6
long to the triclinic space group P2 /n, but [Ir(F3,4,5ppy)2-
1
(
tpip)] belongs to the orthorhombic space group P2 /c. The
1
different space groups of the above complexes indicate that
the crystal packing is sensitive to the position of the three
fluorine atoms in the phenyl ring. For [Ir(F4,5,6ppy) (tpip)]
2
and [Ir(F3,4,5ppy) (tpip)], the iridium center adopts a dis-
2
torted octahedral coordination geometry with two CN
cyclometalated ligands and an Htpip ancillary ligand (cis-
C,C and trans-N,N disposition). For [Ir(F3,4,6ppy) (tpip)],
2
the geometry of the iridium center is octahedral. The
average Ir–C, Ir–N, and Ir–O bond lengths are in agreement
with the corresponding parameters described for other simi-
larly constituted complexes (Tables S1–3).
The thermal properties of these iridium complexes were
characterized by thermogravimetric (TG) and differential
scanning calorimetry (DSC) analysis under a nitrogen
stream (Figure S4). The TG-DSC data reveal that all of
the complexes have good thermal stability, and the initial
decomposition temperatures are in the range 390–404 °C.
Furthermore, all of the complexes can be vacuum evapo-
rated easily without degradation and show good film-form-
ing ability, which indicates that the complexes are potential
emitting materials for the fabrication of stable OLEDs.
Photophysical Properties
The absorption spectra of [Ir(F4,5,6ppy) (tpip)],
2
[
Ir(F3,4,6ppy) (tpip)], and [Ir(F
ppy) (tpip)] in CH Cl
3,4,5 2 2 2
2
were recorded at room temperature (Figure 2, a). Like other
phenylpyridine-type heteroleptic iridium complexes, all of
these complexes exhibit two major absorption regions. The
intense bands at high energy (Ͻ340 nm), which resemble
the spectra of the free ligands, are assigned to the spin- Figure 2. (a) UV/Vis absorption spectra of [Ir(F4,5,6ppy) (tpip)],
2
[
(
(
Ir(F3,4,6ppy)
2
(tpip)], and [Ir(F3,4,5ppy)
b) room-temperature and low-temperature (77 K) emission spectra
inset) of complexes in degassed CH Cl , (c) room-temperature
2 2 2
(tpip)] in degassed CH Cl ,
allowed ligand-centered (LC) πǞπ* transitions localized on
ppy. The relatively weak absorption bands in the range 340–
1
3
2
2
4
50 nm are attributed to the mixing of MLCT and MLCT
emission spectra of mCP films doped with the complexes.
(metal-to-ligand charge-transfer) states or ligand-to-ligand
charge-transfer (LLCT) transitions through strong spin–or-
bit coupling of iridium atoms (Figure 2, b).[ The absorp- [Ir(F3,4,6ppy) (tpip)] has two emission peaks at 475 and
12]
2
tion bands and molar extinction coefficients are listed in 501 nm, but the emission peaks of [Ir(F3,4,6ppy) (acac)] are
2
Table 1.
at 465 and 493 nm, respectively. These results suggest that
At room temperature, all of the complexes in deaerated the ancillary ligands can affect the emission properties of
CH Cl solutions show broad emission spectra with max- iridium complexes. In general, the emission bands from
2
2
ima in the range 497–513 nm. The emission peaks are MLCT states are broad and featureless, whereas a highly
3
slightly different to those of the reported complexes based structured emission band mainly originates from the π–π*
on 2-(trifluorophenyl)pyridine as main ligands and pic or state. Accordingly, all of the complexes emit from a mixture
acac as the ancillary ligands.[
5d,5j,5k]
For example, the emis- of MLCT states and the dominant ligand-based π–π* state.
sion peaks of [Ir(F4,5,6ppy) (tpip)] and [Ir(F ppy) (tpip)] Of the three complexes, [Ir(F3,4,6ppy) (tpip)] exhibited the
3
2
3,4,5
2
2
are 499 and 496/526 nm, but [Ir(F4,5,6ppy) (pic)] and broadest spectrum and the highest intensity at the same
2
[
Ir(F3,4,5ppy) (pic)] emit at 483 and 479/509 nm, respec- concentration (10–5 m). The emission quantum efficiency
2
tively. Although tpip has a similar structure to that of acac, yields of the three complexes are 28, 13, and 21%, respec-
Eur. J. Inorg. Chem. 0000, 0–0
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Table 1. Thermal, photophysical, electrochemical, and electron mobility data for [Ir(F4,5,6ppy)
Ir(F3,4,5ppy) (tpip)].
2
2
(tpip)], [Ir(F3,4,6ppy) (tpip)], and
[
2
[a]
[b]
[c]
[d]
[e]
HOMO/LUMO[f]
[eV]
[g]
[10–6 cm V s ]
2
–1 –1
T
m
/T
d
Absorption λ [nm]
λ
em [nm]
τ
p
[μs]
Φ
p
[%]
μ
e
–1
–1
[°C]
(logε [m cm ])
[
Ir(F4,5,6ppy)
2
(tpip)] 304/390
252 (4.14), 298 (3.78),
499 (494/525)
2.19 (2.08) 28
–5.59/–3.08
–5.70/–2.92
–5.58/–3.05
5.00
4.61
5.45
3
88 (3.07)
250 (4.26), 304 (3.88),
79 (3.12)
293 (3.91), 388 (3.19)
[Ir(F3,4,6ppy)
2
(tpip)] 313/404
475/501 (468/500) 2.40 (2.59) 13
496/526 (492/526) 2.52 (2.23) 21
3
[Ir(F3,4,5ppy)
2
(tpip)] 334/391
[
a] T
m
: melting temperature, T
d
: decomposition temperature. [b] Recorded with the complexes in degassed CH
2
Cl
2
at room temperature
–5
–5
at a concentration of 10 m. [c] Recorded with the complexes in degassed CH
values in parentheses were measured at 77 K. [d] Recorded with the complexes in degassed CH
values in parentheses are for the solid complexes at room temperature. [e] Φ: emission quantum efficiency yield referenced to fac-[Ir(ppy)
] (Φ = 0.4), λexc = 400 nm. [f] HOMO/LUMO energy level values calculated based on the cyclovoltammety (CV) diagram with ferrocene
as the internal standard and the UV/Vis spectra in degassed CH Cl . [g] Electron mobility (μ ) values under an electric field of 1300 (V/
2 2
Cl at a concentration of 10 m at room temperature; the
–
5
2
2
Cl at a concentration of 10 m; the
3
p
2
2
e
cm)1
/2
.
tively. Compared with [Ir(dfppy) (tpip)] [dfppy = 2-(4,6-di- range of microseconds (2.19–2.52 μs in CH Cl2 solution
2
2
fluorophenyl)pyridine, Φp = 4%],[ the introduction of and 2.08–2.59 μs in the solid state) at room temperature
more fluorine substituents results in an increase of the (Table 1, Figure S5 and S6) and are indicative of the phos-
phosphorescence quantum yield. There are reports that the phorescent origin for the excited states in each case.
replacement of C–H bonds with C–F bonds can bring
8a]
about a lower vibrational frequency, which leads to an im-
proved PL efficiency.[ As N,NЈ-dicarbazolyl-3,5-benzene Electrochemistry and Theoretical Calculations
4]
(
mCP) is a popular host material in OLEDs, the PL proper-
To calculate the HOMO and LUMO energy levels of the
present heteroleptic iridium complexes, their electrochemi-
cal behaviors were investigated by cyclic voltammetry with
ferrocene as the internal standard (Figure 3). During the
anodic scan, all of the complexes show reversible Ir /Ir
oxidation couples with redox potentials in the region 0.50–
ties of mCP films doped with the three complexes were also
investigated. From Figure 2c, it can be seen that all the
peaks are similar to those of the Ir complexes in CH Cl .
The absence of mCP emission suggests a complete energy
transfer from the mCP host to the iridium complexes ex-
cited by photons. In addition, the [Ir(F3,4,6ppy) (tpip)]-
III
2
2
III IV
2
1
.30 V, which are in accordance with those of previously
doped mCP film also shows the highest emission intensity
of all the films.
III
[14]
reported cyclometalated Ir systems. The HOMO levels
were calculated from the oxidation potentials, and the
LUMO levels were obtained from the HOMO data and the
As shown in Figure 2b (inset), the structured emission at
3
7
7 K reveals that the mixing between the MLCT and the
band gap (E ) obtained from the UV/Vis spectra. The
3
g
LC levels is so effective that an almost ligand-centered
emission is observed upon freezing of the matrix. The rigid-
ity of the solvent dramatically affects the stabilization of the
charge-transfer states, which shift to higher energy at low
temperature, and the electronic mixing of the two states de-
creases. The rigidochromic effect on some transition metal
complexes has been reported.[13] Owing to the low viscosity
of the medium at room temperature, the solvent molecules
in the vicinity of the excited-state molecule readily undergo
reorientation by dipole–dipole interactions within the life-
time of the excited state, which results in the formation of
the fully relaxed excited state. Thus, the room-temperature
emission occurs from the fully relaxed excited state. On the
other hand, the excited state at 77 K emits before the sol-
vent relaxation occurs, which results in the rigidochromic
effects on the emission spectra. Notably, [Ir(F3,4,6ppy)2-
HOMO/LUMO energy levels of [Ir(F4,5,6ppy) (tpip)],
2
[
Ir(F3,4,6ppy) (tpip)], and [Ir(F
ppy) (tpip)] can be esti-
3,4,5 2
2
mated as –5.59/–3.08, –5.70/–2.92, and –5.58/–3.05 eV,
respectively (Table 1), from the empirical formulas E
HOMO
[
15]
=
–e(Eox + 4.4) and ELUMO = EHOMO + Eg. Among the
complexes, [Ir(F3,4,6ppy) (tpip)] shows the lowest HOMO
2
level and the highest LUMO level, in agreement with the
(tpip)] shows green-blue emission with a maximum peak at
468 nm with a blueshift as large as 26 nm relative to the
other two complexes.
The phosphorescence lifetime (τ ) is the crucial factor
p
that determines the rate of triplet–triplet annihilation in
OLEDs. Longer τ values usually cause greater triplet–trip-
p
14]
[
let annihilation.
The lifetimes of [Ir(F4,5,6ppy) (tpip)],
2
Figure 3. Cyclic voltammograms of [Ir(F4,5,6ppy) (tpip)],
2
[
Ir(F3,4,6ppy) (tpip)], and [Ir(F
ppy) (tpip)] are in the [Ir(F3,4,6ppy)
2
2
(tpip)], and [Ir(F3,4,5ppy) (tpip)].
2
3,4,5
2
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spectroscopic data. The obvious difference between tation lifetime relies on the electron transport capability. To
Ir(F3,4,6ppy) (tpip)] and other two complexes confirms the obtain phosphorescent OLEDs with low efficiency roll-off,
[
2
effects of the position of the fluorine atoms on the phenyl it is necessary to synthesize phosphorescent molecular ma-
rings. terials with outstanding electron mobility. As discussed be-
Density functional theory calculations for [Ir(F4,5,6ppy)2- fore, compared with the popular acac ligand, Htpip has
tpip)], [Ir(F3,4,6ppy) (tpip)], and [Ir(F ppy) (tpip)] were more polar P=O bonds and four bulky aromatic groups,
(
2
3,4,5
2
conducted to gain insights into the electronic states and the which may improve the electron mobility and suppress the
[
8b]
orbital distribution by employing the Gaussian09 software. TTA and TPQ effects effectively.
The effects of substitution on the relative energies of the The electron mobility (μ ) values of the iridium com-
HOMO and LUMO levels and selected molecular orbitals plexes were determined by the transient electroluminescence
MOs) of the complexes are shown in Figure 4. The (EL) method based on indium tin oxide (ITO)/ 1,1-bis[4-
e
(
HOMOs of the three complexes involve contributions from (di-p-tolyl-amino)phenyl]cyclohexane (TAPC, 50 nm)/Ir
Ir d orbitals (50.43–53.86%) and from a π orbital localized complex (60 nm)/LiF (1 nm)/Al (100 nm) with short and
[
8b,17]
on the fluorine-substituted ppy ligand (39.65–43.71%). rectangular driving voltage pulses.
In transient EL
Meanwhile, the LUMO is largely dominated by the π* or- measurements, the time-dependent EL response is moni-
bitals of the fluorine-substituted ppy ligand, together with tored upon excitation of the devices with a rectangular volt-
small contributions from Ir and tpip orbitals (Table S4). age pulse. A finite delay time (t ), which is between the ap-
d
Therefore, modification of the phenyl ring changes the en- plication of a voltage pulse and the onset of the EL signal,
ergy of both the HOMO and the LUMO. The close similar- is determined by the arrival of the slower charge carrier of
[
17,18]
ity between the calculated and experimental values reveals the injected carriers at the emission zone.
As shown in
the reliability of our computation.
Figures 5 and S7, after the t , the EL signals gradually rise
d
before reaching the saturated EL intensities. With increas-
ing applied voltage amplitudes from 8 to 10 V, the t values
d
decrease. The electron mobility data can be roughly calcu-
2
lated with the equation μ = d /(t V), in which d is the thick-
e
d
ness of the emitting layer, and V is the driving voltage. For
Ir(F3,4,6ppy) (tpip)], t decreased from 1.32 to 0.78 μs, ac-
[
2
d
companied by a voltage rise from 8 to 10 V. The experimen-
tal results show that the electron mobility values in a 30 nm
–
6
2
–1 –1
[
Ir(F3,4,6ppy) (tpip)] layer are 3.41–4.61ϫ10 cm V s
2
1
/2
under electric fields from 1150 to 1300 (V/cm) , compar-
able to that of the popular electron transport material
Alq
4
under
the
same
electric
fields
(4.74–
3
.86ϫ10–6 cm V s ). In addition, [Ir(F4,5,6ppy) (tpip)]
2
–1 –1 [8b]
2
and [Ir(F3,4,5ppy) (tpip)] also have similar electron mobility
2
values to that of [Ir(F3,4,6ppy) (tpip)] (Table 1, Figure S7).
2
The good electron transport ability of these complexes facil-
itates the injection and transport of electrons, which broad-
ens the recombination zone and balances the distribution
of holes and electrons, particularly for high doping concen-
Figure 4. Isodensity plots of the HOMOs and LUMOs for
trations, and leads to improved recombination probability
[
Ir(F4,5,6ppy)
tpip)].
2
(tpip)], [Ir(F3,4,6ppy)
2
(tpip)], and [Ir(F3,4,5ppy)
2
-
[19]
and suppressed TTA and TPQ.
Therefore, efficient
(
Notably, [Ir(F3,4,6ppy) (tpip)], which has the lowest
2
HOMO and the highest LUMO, exhibits the largest energy
gap compared with the other two complexes. The difference
can be attributed to the replacement of a C–H bond with a
C–F bond at the 5Ј-position of ppy, which shows more ob-
vious electron-withdrawing effect than the other substituent
positions. Thus, in [Ir(F3,4,6ppy) (tpip)], the electron density
2
on the Ir atom decreases and the HOMO level is stabilized.
The consistent tendency and small difference (0.14–0.17 eV)
between the calculation values and the experimental data
reveal the reliability of our theoretical study.
Electron Mobility
As the hole mobility is roughly 2–3 orders of magnitude
Figure 5. Transient EL signals as a function of electrical field for
(tpip)].
higher than the electron mobility in OLEDs,[ their exci- the device based on [Ir(F3,4,6ppy)
16]
2
Eur. J. Inorg. Chem. 0000, 0–0
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FULL PAPER
OLEDs with suppressed efficiency roll-off are expected at (tpip)], BG1 (x = 6 wt.-%), BG2 (8 wt.-%), and BG3
relatively low voltage.
(10 wt.-%) for [Ir(F3,4,6ppy) (tpip)], CG1 (x = 6 wt.-%),
2
CG2 (8 wt.-%), and CG3 (10 wt.-%) for [Ir(F3,4,5ppy)2-
(
tpip)]. The key performance parameters of the devices with
different dopants and concentrations are listed in Table 2.
With [Ir(F4,5,6ppy) (tpip)] and [Ir(F ppy) (tpip)] as the
Electroluminescence Devices
2
3,4,6
2
The electroluminescence properties of [Ir(F4,5,6ppy)2-
emitters, the devices with 8 wt.-% doped concentration
AG2 and BG2) showed superior device efficiencies than
those with other doping concentrations. However, for
Ir(F3,4,5ppy) (tpip)], the device (CG1) with 6 wt.-% doped
(
tpip)], [Ir(F3,4,6ppy) (tpip)], and [Ir(F
ppy) (tpip)] were
2
3,4,5 2
(
investigated in devices comprising ITO/TAPC (30 nm)/Ir
complex (x wt.-%):mCP (15 nm)/1,3,5-tri(1-phenyl-1H-
benzo[d]imidazol-2-yl)phenyl (TPBi, 45 nm)/LiF (1 nm)/Al
[
2
concentration exhibited the best device efficiency. Figure 7
shows the EL spectra, current and power efficiency vs. cur-
rent density (η –J and η –J) curves, and current density–
voltage and luminance–voltage (J–V and L–V) characteris-
tics for devices AG2, BG2, and CG1. All the devices have
turn-on voltages (Vturn-on) below 3.5 V, and the maximum
(100 nm). The energy diagrams of the devices and the
molecular structures of the materials used are shown in
Figure 6. Clearly, the HOMO and LUMO levels of
c
p
[
Ir(F4,5,6ppy) (tpip)],
[Ir(F3,4,6ppy) (tpip)],
and
2
2
[
Ir(F3,4,5ppy) (tpip)] are all within the HOMO and LUMO
2
levels of the host material mCP. Therefore, a good carrier
trapping is expected in these devices, and this is the domi-
nated EL mechanism. Furthermore, holes and electrons will
be well confined within the doped light-emitting layer.
emission peaks for [Ir(F4,5,6ppy) (tpip)], [Ir(F3,4,6ppy)2-
(
2
tpip)], and [Ir(F3,4,5ppy) (tpip)] devices are located at 497,
2
4
97, and 495 nm, respectively. The Commission Internatio-
nale de l’Eclairage (CIE) color coordinates are x = 0.17, y
0.60 for AG2, x = 0.17, y = 0.50 for BG2, and x = 0.17,
=
y = 0.57 for CG1. The similarity of the EL and PL emission
spectra indicates that the EL is caused by emission from the
triplet excited states of the iridium complexes. The absence
of residual emission from mCP suggests a complete energy
transfer from the mCP host to the iridium complexes in
these devices.
For the [Ir(F4,5,6ppy) (tpip)]-based devices, AG2 showed
2
–1
a peak current efficiency of 43.95 cdA , an external quan-
tum efficiency (η , EQE) of 15.1% at 5.1 V, and a maxi-
ext
mum power efficiency of 28.51 lmW–1 at 4.6 V. The peak
ηext was obtained from the current efficiency, EL spectrum,
and the human photopic sensitivity. Of all six devices, AG3
has the maximum luminance (Lmax) of 57193 cdm–2 at
9
.2 V. [Ir(F3,4,6ppy) (tpip)]-based BG2 exhibited the best
2
–1
efficiency: a peak current efficiency of 66.36 cdA and ex-
ternal efficiency of 25.7% at 5.8 V, a power efficiency (η )
p
Figure 6. Device structures and energy level diagrams of HOMO
and LUMO levels (relative to vacuum level) for materials used in
device fabrication.
–1
of 48.20 lmW at 4.4 V, and a maximum luminance of
4
7627 cdm–2 at 12.6 V. Perhaps the broad emission spec-
trum and the high intensity of the [Ir(F3,4,6ppy) (tpip)]-
2
To optimize the device efficiency, concentration-depen-
dence experiments were performed in the range 6–10 wt.-%
to give green-emitting OLEDs named as AG1 (x = 6 wt.-
doped mCP film combine to improve the efficiency of the
devices. The devices with [Ir(F3,4,5ppy) (tpip)] as the emitter
2
showed relatively poor performances with a maximum cur-
%), AG2 (8 wt.-%), and AG3 (10 wt.-%) for [Ir(F4,5,6ppy)2-
–1
rent efficiency of 37.36 cdA and external efficiency of
Table 2. Device performances of [Ir(F4,5,6ppy)
2
(tpip)], [Ir(F3,4,6ppy)
2
(tpip)], and [Ir(F3,4,5ppy)
2
(tpip)] doped OLEDs.
max [cdm–2]
[
a]
η
c,max [cdA ] (V)
[a]
–1
η
p,max [lmW ] (V)
[a]
–1
η
ext,max [%]
[a]
λmax [nm]
[b]
Device
Vturn-on [V]
L
AG1
AG2
AG3
BG1
BG2
BG3
CG1
CG2
CG3
3.3
3.3
3.2
3.3
3.3
3.3
3.2
3.2
3.4
55826
38827
57193
40028
47627
32533
40319
34276
31250
43.62 (5.3)
43.95 (5.1)
24.46 (5.4)
36.43 (5.2)
66.36 (5.8)
36.58 (6.7)
37.36 (6.5)
34.83 (6.5)
32.97 (6.4)
26.29 (5.4)
28.51 (4.6)
15.44 (4.7)
23.94 (4.5)
48.20 (4.4)
20.03 (5.5)
19.11 (5.1)
17.78 (5.7)
18.11 (5.8)
15.0
15.1
8.4
14.1
25.7
13.9
12.8
12.1
11.5
497 (0.17, 0.60)
497 (0.17, 0.50)
495 (0.17, 0.57)
[
a] Maximum values of the devices; the values in parentheses are the corresponding driving voltages. [b] Values were collected at 8 V, and
CIE coordinates (x, y) are shown in parentheses.
Eur. J. Inorg. Chem. 0000, 0–0
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FULL PAPER
1
1
4
2.8% at 6.5 V,
a
maximum power efficiency of
–1
9.11 lmW at 5.1 V, and a maximum brightness of
0319 cdm–2 at 12.7 V. The results show that the positions
of the three F atoms on the phenyl ring can influence both
III
the PL properties and EL performances of the Ir com-
plexes.
Notably, the EL efficiency roll-off effects at relatively
high current density in these devices are very mild. For
BG2, the ηc values at practical luminances of 100 and
000 cdm–2 are 67.55 and 64.37 cdA , respectively, which
–1
1
help to obtain the high efficiency and brightness. This mild
roll-off should be attributed to fluorination of the ppy li-
gand and the application of Htpip as the ancillary ligand,
which can decrease self-quenching and improve the hole–
electron balance in charge injection. Good electron mobility
of the phosphorescent emitters would facilitate the injection
and transport of electrons and, therefore, broaden the re-
combination zone and balance the distribution of holes and
electrons, particularly at high doping concentrations; this
leads to suppressed TTA and TPQ and improved recombi-
nation probability, high device efficiency, and low efficiency
[
19,20]
roll-off effect.
Conclusions
Three heteroleptic iridium complexes with 2-(4,5,6-tri-
fluorophenyl)pyridine, 2-(3,4,6-trifluorophenyl) pyridine,
and 2-(3,4,5-trifluorophenyl)pyridine as the main ligands
and tetraphenylimidodiphosphinate (tpip) as the ancillary
ligand were synthesized. All of the complexes are green
emitters (λmax = 496–501 nm) with PL quantum efficiency
yields of 13–28%. Electrochemistry and DFT calculation
results reveal that the HOMO and LUMO levels
of
[Ir(F4,5,6ppy) (tpip)],
[Ir(F3,4,6ppy) (tpip)],
and
2
2
[
Ir(F3,4,5ppy) (tpip)] are well within the HOMO and
2
LUMO levels of the mCP host material; therefore, good
carrier trapping is expected in devices containing these
complexes. Owing to the good electron mobility values of
III
the Ir complexes, which are improved by the tpip ancillary
–
6
2
–1 –1
ligand [3.41–4.61ϫ10 cm V s
under electric fields
from 1150 to 1300 (V/cm)1 ], all the devices show good
/2
performances. The device based on [Ir(F3,4,6ppy) (tpip)]
2
with 8 wt.-% concentration exhibited superior performance
to the others and has a peak external quantum efficiency
–1
(
ηext) of 25.7%, a peak current efficiency (η ) of 66.36 cdA
c
at 5.8 V, and a maximum power efficiency (η ) of
p
4
8.20 lmW–1 at 4.4 V. The EL efficiency roll-off effects at
relatively high current density in these devices are very mild,
which helps to obtain high efficiency and high brightness.
Experimental Section
Figure 7. Charts for the three devices AG2, BG2, and CG1 doped
with [Ir(F4,5,6ppy) (tpip)], [Ir(F3,4,6ppy) (tpip)], and [Ir(F3,4,5ppy)
tpip)], respectively. (a) Normalized EL spectra, (b) current effi-
ciency as a function of current density, (c) power efficiency as a
function of current density, and (d) current density–voltage and
luminance–voltage curves.
General Information: All commercial chemicals were used without
further purification, except for anhydrous toluene. All reactions
were conducted under a nitrogen atmosphere. H NMR spectra
were recorded with a Bruker AM 500 spectrometer. Mass spec-
trometry (MS) spectra were obtained with an electrospray ioniza-
2
2
2
-
(
1
Eur. J. Inorg. Chem. 0000, 0–0
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FULL PAPER
tion (ESI) mass spectrometer (LCQ fleet, Thermo Fisher Scientific)
for ligands and a matrix-assisted laser desorption/ionization time-
of-flight (MALDI-TOF) mass spectrometer (Bruker Daltonic Inc.)
for complexes. Elemental analyses for C, H, and N were performed
with an Elementar Vario MICRO analyzer. TG-DSC measure-
ments were performed with a DSC 823e analyzer (Mettler). Ab-
sorption and emission spectra were measured with a Shimadzu UV-
Absorption corrections were applied by using SADABS.[23] The
structures were solved by direct methods and refined by full-matrix
2
[24]
least-squares on F by using the program SHELXS-97. The posi-
tions of metal atoms and their first coordination spheres were lo-
cated from direct methods; other non-hydrogen atoms were found
in alternating difference Fourier syntheses and least-squares refine-
ment cycles and, during the final cycles, refined anisotropically. Hy-
drogen atoms were placed in calculated positions and refined as
riding atoms with uniform Uiso values (Table 3).
3100 spectrophotometer and a Hitachi F-4600 luminescence spec-
trophotometer, respectively. The quantum efficiency measurements
were performed at room temperature with degassed toluene solu-
CCDC-908971
{for
[Ir(F4,5,6ppy)
2
(tpip)]},
-908972
{for
3 p
tions and fac-[Ir(ppy) ] (Φ
= 0.4) as a reference.[ Low-tempera-
21]
[
Ir(F3,4,6ppy) (tpip)]}, and -908973 {for [Ir(F3,4,5ppy)
2
2
(tpip)]} con-
ture (77 K) emission spectra were recorded with a Hitachi F-4600
luminescence spectrophotometer with samples in 5 mm diameter
quartz tubes, which were placed in a liquid nitrogen Dewar
equipped with quartz walls. Samples and standard solutions were
degassed with at least three freeze–pump–thaw cycles. PL lifetime
measurements were performed by using an excitation line (370 nm)
of a laser delivering pulses of 25 ns time duration at 20 Hz repeti-
tion rate with an Edinburgh FSL-920 spectrophotometer. Cyclic
voltammograms were recorded at a scan rate of 100 mV/s at room
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Computation Study:[13] The singlet ground-state geometry of the
iridium complexes has been optimized at the density functional
theory (DFT) level from the X-ray crystallographic data. B3LYP
geometry optimizations were performed with the LANL2DZ basis
set for Ir and the 6-31G(d) basis set for C, H, N, O, F, and P atoms.
The characterization of the lowest-lying singlet and triplet excited
states based on the ground-state geometry used the same functional
and basis set. All the geometries were confirmed as stationary
structures by the presence of only real frequencies at the same level
of the theory. All calculations were performed with the Gaussian09
software.
2 2
temperature with CH Cl solutions under nitrogen by using a
three-electrode cell equipped with a Pt disk working electrode, a Pt
wire counterelectrode, and a Pt wire pseudoreference electrode with
a computer-controlled IM6ex electrochemical and chemilumines-
cent system (Zahner); tetrabutylammonium perchlorate (nBu
ClO , 0.1 m) was used as the supporting electrolyte. All potentials
are calibrated with ferrocene in acetonitrile as a reference.
4
N-
4
[8,14]
OLED Fabrication and Measurement:
All OLEDs with an
2
X-ray Crystallographic Analysis: Crystals of the iridium complexes
were obtained by vacuum sublimation. The diffraction data were
collected with a Bruker SMART CCD diffractometer (Bruker Dal-
emission area of 0.1 cm were fabricated on prepatterned ITO-
–
1
coated glass substrates with a sheet resistance of 15 Ωsq . The
substrate was cleaned by ultrasound in organic solvents followed
by ozone treatment for 20 min. All materials used for EL devices
were sublimed in vacuo (2.2ϫ10 Pa) prior to use. The 30 nm hole
transport material of 1,1-bis[4-(di-p-tolyl-amino)phenyl] cyclohex-
ane (TAPC) film was first deposited on the ITO glass substrate.
The phosphor (x wt.-%) and host (mCP, N,NЈ-dicarbazolyl-3,5-
benzene) were co-evaporated to form 15 nm emitting layer from
two separate sources. Successively, 1,3,5-tri(1-phenyl-1H-benzo-
α
tonic Inc.) by using monochromated Mo-K radiation (λ =
–
4
0
.71073 Å) at room temperature. The cell parameters were retrieved
[22]
by using SMART software and refined by using SAINT on all
observed reflections. The data were collected by using a narrow-
frame method with scan widths of 0.30° in ω and an exposure time
of 10 s/frame. The highly redundant data sets were reduced by
using SAINT and corrected for Lorentz and polarization effects.
Table 3. Crystallographic data and structure refinement for [Ir(F4,5,6ppy)
2
(tpip)], [Ir(F3,4,6ppy)
[Ir(F3,4,6ppy) (tpip)]
IrN
2
(tpip)], and [Ir(F3,4,5ppy)
[Ir(F3,4,5ppy) (tpip)]
IrN
2
(tpip)].
[
Ir(F4,5,6ppy)
2
(tpip)]
2
2
Formula
FW
T [K]
C
46
H
30
F
6
IrN
3
O
2
P
2
C
46
H
30
F
6
3
O
2
P
2
C
46
H
30
F
6
3 2 2
O P
1024.87
296(2)
1024.87
296(2)
1024.87
296(2)
Wavelength [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
0.71073
triclinic
P1
0.71073
orthorhombic
Pbca
20.5929(10)
18.8926(9)
20.9574(10)
90.00
90.00
90.00
8153.5(7)
8
1.670
0.71073
triclinic
¯
¯
P1
10.9896(4)
12.5364(6)
16.0015(3)
90.4480(10)
104.177(2)
107.0080(10)
2036.38(13)
2
10.4740(5)
12.2002(6)
17.6273(4)
105.2140(10)
91.522(2)
112.7750(10)
1983.19(14)
2
α [°]
β [°]
γ [°] 3
V [Å ]
Z
ρ
calcd. [g/cm3]
1.665
3.426
1004
1.710
3.518
1004
–1
μ (Mo-K
F(000)
α
) [mm ]
3.424
4032
Range of transmission factors [°]
Reflections collected
1.70–26.00
12433
7969
1.038
0.0520, 0.1350
0.0577, 0.1370
1.76–28.29
10120
7452
1.038
0.0262, 0.0573
0.0472, 0.0669
2.29–28.35
7774
6404
1.051
0.0520, 0.1261
0.0591, 0.1279
Unique reflections
2
GOF on F
[
[
a]
a]
[b]
[b]
R
R
1
,
,
wR
wR
2
[IϾ2σ(I)]
(all data)
1
2
[
a] R = = [Σw(F 2 2)2/Σw(F 2)]1/2
1 o c o 2 o c o
Σ||F | – |F ||/ΣF |. [b] wR – F .
Eur. J. Inorg. Chem. 0000, 0–0
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1
[d]imidazol-2-yl)phenyl (TPBi, 45 nm) as electron transport mate-
F
4,5,6ppy: Yield 78%. H NMR (500 MHz, [D
6
]acetone): δ = 8.74
rial, LiF (1 nm) as electron injection material, and Al (100 nm) as
(d, J = 4.7 Hz, 1 H), 7.95 (td, J = 7.9, 1.6 Hz, 1 H), 7.92–7.82 (m,
the cathode were evaporated. The vacuum was less than 1ϫ10 Pa 2 H), 7.48–7.40 (m, 1 H), 7.39–7.29 (m, 1 H) ppm.
during the deposition of all materials. The current density–voltage
J–V) and luminance–voltage (L–V) characteristics, current effi-
ciency vs. current density (η –J), and power efficiency vs. current
density (η –J) curves of the devices were measured with a com-
–
5
1
F
6
3,4,6ppy: Yield 82%. H NMR (500 MHz, [D ]acetone): δ = 8.74
(
(
(
d, J = 4.7 Hz, 1 H), 8.03 (ddd, J = 11.7, 9.2, 7.2 Hz, 1 H), 7.94
td, J = 7.7, 1.7 Hz, 1 H), 7.90–7.86 (m, 1 H), 7.47–7.37 (m, 2 H)
c
p
ppm.
3,4,5ppy: Yield 87%. H NMR (500 MHz, [D
d, J = 4.7 Hz, 1 H), 8.02 (d, J = 8.0 Hz, 1 H), 8.00–7.90 (m, 3 H),
.46–7.37 (m, 1 H) ppm.
(F-ppy) Ir(μ-Cl)] : A solution of chlorodiphenylphosphine (4.40 g,
0 mmol) and hexamethyldisilazane (1.77 g, 11 mmol) in anhy-
puter-controlled Keithley 2400 source meter with a calibrated sili-
con diode in air without device encapsulation. The EL spectra were
measured with a Hitachi F-4600 photoluminescence spectropho-
tometer. On the basis of the uncorrected PL and EL spectra, the
CIE coordinates were calculated by using a test program of the
Spectra Scan PR650 spectrophotometer.
1
F
(
7
6
]acetone): δ = 8.69
[
2
2
2
drous toluene (30 mL) was heated to reflux under nitrogen for 6 h,
and then the byproducts and toluene were removed at reduced pres-
sure. A solution of H O (2.5 mL, 30 wt.-% in H O) in THF (5 mL)
2 2 2
Syntheses: Htpip, F-ppy (F4,5,6ppy, F3,4,6ppy, and F3,4,5ppy), [(F-
ppy)
previously published literature procedures.[
scheme is shown in Scheme 1. Purified [Ir(F4,5,6ppy)
Ir(F3,4,6ppy) (tpip)], and [Ir(F3,4,5ppy) (tpip)] were obtained by
2 2 2
Ir(μ-Cl)] , and [Ir(F-ppy) (tpip)] were obtained according to
8,15]
The synthesis
(tpip)],
was added in an ice bath. The solution was stirred for 2 h and then
added to diethyl ether (50 mL), whereupon a white precipitate was
obtained. The solid was washed with water and recrystallized from
2
[
2
2
vacuum-evaporation after silica column chromatography.
1
methanol to give the desired product Htpip in 50% yield. H NMR
[
(
(
3 2
500 MHz, (CD ) SO]: δ = 7.73 (dd, J = 11.3, 7.8 Hz, 1 H), 7.52
31
t, J = 7.2 Hz, 20 H), 7.44 (t, J = 6.6 Hz, 1 H) ppm. P NMR
–
3
500 MHz, CDCl ): δ = 19.34 (s) ppm. ESI-MS: m/z = 416 [M] .
To a suspension of Htpip (2.09 g, 5 mmol) in methanol (20 mL)
was added a solution of KOH (2.85 g, 5.2 mmol) in methanol
(
5 mL), and the mixture was stirred for 2 h at room temperature.
Concentration in vacuo precipitated a white solid, which was reco-
vered by filtration and washed with diethyl ether to yield Ktpip
(
1.65 g, 73%).
General Synthesis of [Ir(F4,5,6ppy)
Ir(F3,4,5ppy) (tpip)]: [(F-ppy) Ir(μ-Cl)]
0.27 g, 0.6 mmol) in 2-EtOCH CH OH (10 mL) were heated at
CH OH solvent was removed by
2
(tpip)], [Ir(F3,4,6ppy)
2
(tpip)], and
[
(
1
2
2
2
(0.2 mmol) and Ktpip
2
2
20 °C for 24 h. The 2-EtOCH
2
2
vacuum, and the crude product was chromatographed on a silica
column with an elution gradient (petroleum ether/EtOAc 10:1–7:1)
to produce a brilliant yellow sample of each iridium complex. Fur-
ther purification was achieved by gradient sublimation in vacuo,
and yields of 28–35% were obtained.
1
[
Ir(F4,5,6ppy)
2
(tpip)]: Yield 32%. H NMR (500 MHz, CDCl
3
): δ =
9
1
7
.02 (d, J = 5.6 Hz, 2 H), 8.05 (d, J = 8.3 Hz, 2 H), 7.77 (dd, J =
2.3, 6.9 Hz, 4 H), 7.50 (t, J = 7.8 Hz, 2 H), 7.44–7.30 (m, 10 H),
.18 (t, J = 7.4 Hz, 2 H), 7.01 (td, J = 7.6, 2.8 Hz, 4 H), 6.68 (t, J
Scheme 1. The synthetic route for the ligands and [Ir(F4,5,6ppy)
2
-
= 6.6 Hz, 2 H), 5.66–5.42 (m, 2 H) ppm. MALDI-TOF: m/z =
+
(
tpip)], [Ir(F3,4,6ppy)
Pd(PPh , K CO , THF/H
EtOCH CH OH/H O, reflux, 24 h; (iii) toluene, 105 °C, 6 h; (iv)
, THF; (v) KOH, methanol; (vi) 2-EtOCH CH OH, N
20 °C, 24 h.
2
(tpip)], and [Ir(F3,4,5ppy)
2
(tpip)]. (i)
·3H O, 2-
1024.93 [M] . C H F IrN O P (1024.92): calcd. C 53.90, H 2.95,
4
6
30
6
3
2 2
3
)
4
2
3
2
O, 80 °C, 24 h; (ii) IrCl
3
2
N 4.10; found C 53.86, H 2.93, N 4.12.
2
2
2
1
[
Ir(F3,4,6ppy)
2
(tpip)]: Yield 35%. H NMR (500 MHz, CDCl
3
): δ =
H
2
O
2
2
2
2
,
1
9.02 (d, J = 5.5 Hz, 2 H), 8.05 (d, J = 8.3 Hz, 2 H), 7.77 (dd, J =
1
7
2.3, 6.9 Hz, 4 H), 7.50 (t, J = 7.8 Hz, 2 H), 7.43–7.30 (m, 10 H),
.18 (t, J = 7.4 Hz, 2 H), 7.18 (t, J = 7.4 Hz, 2 H), 7.01 (td, J =
General Synthesis Procedure for F-ppy: The three ligands [F4,5,6ppy:
-(4,5,6-trifluorophenyl)pyridine, 3,4,6ppy: 2-(3,4,6-trifluoro-
7.6, 2.8 Hz, 4 H), 6.68 (t, J = 6.5 Hz, 2 H) ppm. MALDI-TOF:
m/z = 1025.03 [M] . C H F IrN O P (1024.92): calcd. C 53.90,
2
F
+
4
6
30
6
3
2 2
phenyl)pyridine, F3,4,5ppy: 2-(3,4,5-trifluorophenyl) pyridine] were
prepared in good yields through Suzuki coupling reactions. 2-
Bromopyridine (2.40 mL, 25 mmol), trifluorophenyl boronic acid
H 2.95, N 4.10; found C 53.70, H 2.98, N 4.05.
1
[
Ir(F3,4,5ppy)
2
(tpip)]: Yield 28%. H NMR (500 MHz, CDCl
3
): δ =
9.03 (d, J = 5.6 Hz, 2 H), 7.77 (dd, J = 12.3, 7.0 Hz, 4 H), 7.50 (d,
(
5.28 g, 30 mmol), K
phenylphosphine)palladium(0) (0.35 g, 0.3 mmol) were dissolved in
a tetrahydrofuran/H O (THF/H O) mixture (80/60 mL). The solu-
2 3
CO (16.56 g, 120 mmol), and tetrakis(tri-
J = 8.1 Hz, 14 H), 7.50 (d, J = 8.1 Hz, 2 H), 7.17 (t, J = 7.3 Hz, 2
H), 7.00 (td, J = 7.6, 2.8 Hz, 4 H), 6.56 (t, J = 6.5 Hz, 2 H) ppm.
2
2
+
MALDI-TOF: m/z = 1024.79 [M] . C46
H
30
F
6
IrN
3
O
2
P
2
(1024.92):
tion was heated at 80 °C and monitored with TLC. The THF was
removed by vacuum concentration, and then the cooled crude mix-
calcd. C 53.85, H 2.92, N 4.30; found C 53.86, H 2.93, N 4.12.
ture was poured into water and extracted with CH
2
Cl
2
(30 mLϫ
Supporting Information (see footnote on the first page of this arti-
cle): H NMR spectra, MALDI-TOF spectra, selected bond
1
3). Finally, silica column purification (petroleum ether/EtOAc 10:1)
gave a white solid.
lengths and angles, TG-DSC thermograms, photoluminescence life-
Eur. J. Inorg. Chem. 0000, 0–0
9 © 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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/KAP1
Date: 24-09-13 16:23:26
Pages: 12
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FULL PAPER
times of solids and CH
der different electric fields of iridium complexes [Ir(F4,5,6ppy)
tpip)], [Ir(F3,4,6ppy) (tpip)], and [Ir(F3,4,5ppy) (tpip)].
2
Cl
2
solutions, and transient EL signals un-
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Acknowledgments
This work was supported by the Chinese Major State Basic Re-
search Development Program (grant numbers 2011CB808704,
16, 1161–1170; e) S.-Y. Takizawa, J.-I. Nishida, T. Tsuzuki, S.
Tokito, Y. Yamashita, Inorg. Chem. 2007, 46, 4308–4319; f) C.-
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Chem. 2007, 119, 2470; Angew. Chem. Int. Ed. 2007, 46, 2418–
2013CB922101) and the National Natural Science Foundation of
China (NSFC) (grant numbers 21371093 and 21021062).
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Received: July 8, 2013
Published Online: ᭿
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11
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FULL PAPER
Ir-Based OLEDs
C.-C. Wang, Y.-M. Jing, T.-Y. Li, Q.-
L. Xu, S. Zhang, W.-N. Li, Y.-X. Zheng,*
J.-L. Zuo, X.-Z. You, X.-
A
light-emitting diode based on
2
[Ir(F3,4,6ppy) (tpip)] [F3,4,6ppy = 2-(3,4,6-
trifluorophenyl)pyridine, tpip = tetraphen-
ylimidodiphosphinate] exhibited good per-
formance with a peak ηext of 25.7% and a
Q. Wang* ........................................ 1–12
–
1
Syntheses, Photoluminescence, and Elec-
troluminescence of Iridium(III) Complexes
with Fluorinated 2-Phenylpyridine as Main
Ligands and Tertraphenylimidodiphos-
phinate as Ancillary Ligand
peak η
c
of 66.36 cdA at 5.8 V and a peak
–
1
η
p
of 48.20 lmW at 4.4 V.
Keywords: Iridium / Luminescence / Or-
ganic light-emitting diodes / Fluorinated
ligands
Eur. J. Inorg. Chem. 0000, 0–0
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim