Pyridylpyrazole N∧N ligands combined with sulfonyl-functionalised cyclometalating ligands for blue-emitting iridium(III) complexes and solution-processable PhOLEDs

Article abstract of DOI:10.1039/c7dt02289a

A series of blue iridium(iii) complexes (12-15) comprising sulfonyl-functionalised phenylpyridyl cyclometalating ligands and pyridylpyrazole N^N ligands are reported, with an X-ray crystal structure obtained for 12. The complexes are highly emissive with photoluminescence quantum yields of 0.52-0.70 in dichloromethane solutions: two of the complexes (12 and 14) show emissions at λ^PL_max 457 nm which is considerably blue-shifted compared to the archetypal blue emitter FIrpic (λ_max 468 nm). The short excited state lifetimes (1.8-3.3 μs) and spectral profiles are consistent with phosphorescence from a mixture of ligand-centred and MLCT excited states. Density functional (DFT) and time dependent DFT (TD-DFT) calculations are in agreement with the electrochemical properties and the blue phosphorescence of the complexes. The additional mesityl substituent on the pyridylpyrazole ligand of 12 and 13 enhances the solubility of the complexes facilitating thin film formation by solution processing. Phosphorescent organic light-emitting diodes (PhOLEDs) have been fabricated using 12 or 13 in a solution-processed single-emitting layer using either poly(vinylcarbazole) (PVK) or 1,3-bis(N-carbazolyl)benzene (mCP) as host. The most blue-shifted electroluminescence (λ^EL_max 460 nm, CIE_x,y 0.15, 0.21) is obtained for an OLED containing complex 12 and mCP, with a brightness of 5400 cd m^-2 at 10 V which is high for PhOLEDs with similar blue CIE coordinates using a solution-processed emitter layer.

Full text of DOI:10.1039/c7dt02289a

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Pyridylpyrazole N^N ligands combined with
sulfonyl-functionalised cyclometalating ligands
for blue-emitting iridium(III) complexes and
solution-processable PhOLEDs†
Cite this: DOI: 10.1039/c7dt02289a
a
a
a
b
Helen Benjamin, Mark A. Fox,
Andrei S. Batsanov, Hameed A. Al-Attar,
c
c
b
a
Chensen Li, Zhongjie Ren,
Andrew P. Monkman and Martin R. Bryce
*
A series of blue iridium(III) complexes (12–15) comprising sulfonyl-functionalised phenylpyridyl cyclo-
metalating ligands and pyridylpyrazole N^N ligands are reported, with an X-ray crystal structure obtained
for 12. The complexes are highly emissive with photoluminescence quantum yields of 0.52–0.70 in
dichloromethane solutions: two of the complexes (12 and 14) show emissions at λPL 457 nm which is
max
considerably blue-shifted compared to the archetypal blue emitter FIrpic (λmax 468 nm). The short
excited state lifetimes (1.8–3.3 μs) and spectral profiles are consistent with phosphorescence from a
mixture of ligand-centred and MLCT excited states. Density functional (DFT) and time dependent DFT
(TD-DFT) calculations are in agreement with the electrochemical properties and the blue phospho-
rescence of the complexes. The additional mesityl substituent on the pyridylpyrazole ligand of 12 and 13
enhances the solubility of the complexes facilitating thin film formation by solution processing.
Phosphorescent organic light-emitting diodes (PhOLEDs) have been fabricated using 12 or 13 in a solu-
tion-processed single-emitting layer using either poly(vinylcarbazole) (PVK) or 1,3-bis(N-carbazolyl)
Received 23rd June 2017,
Accepted 27th July 2017
benzene (mCP) as host. The most blue-shifted electroluminescence (λEL 460 nm, CIEx,y 0.15, 0.21) is
max
DOI: 10.1039/c7dt02289a
obtained for an OLED containing complex 12 and mCP, with a brightness of 5400 cd m−2 at 10 V which is
rsc.li/dalton
high for PhOLEDs with similar blue CIE coordinates using a solution-processed emitter layer.
lised mostly on the iridium atom and the phenyl ring, and the
lowest unoccupied MO (LUMO) is on the pyridyl ring. This
Introduction
The varied applications of luminescent transition metal com- spacial separation of HOMO and LUMO means that the
1
plexes include biological labelling probes, ion sensors, water emission wavelength of the complexes, which occurs from a
3
splitting, solar cells and emitters for phosphorescent organic mixture of triplet metal-to-ligand charge-transfer ( MLCT)
2
–8
14,15
light-emitting diodes (OLEDs)
ing.
and for solid-state light- states and π–π* transitions of the ligands,
can be tuned
9
,10
Cyclometalated iridium(III) complexes are especially with precision by the presence of electron-withdrawing or elec-
prominent in the OLED field due to their ability to harvest tron-donating substituents at specific sites on the ppy frame-
both singlet and triplet excitons, which can result in internal work. Additional attractive features are that the complexes gen-
1
1–13
quantum efficiencies approaching 100%.
Many complexes erally emit with high quantum yields and relatively short
incorporate cyclometalated 2-phenylpyridine (ppy) ligands excited state lifetimes on the microsecond timescale, and they
1
1–13
where the highest occupied molecular orbital (HOMO) is loca- possess high photochemical and chemical stability.
Blue emitting iridium complexes are important current
1
6,17
targets.
shifting the emission of iridium complexes towards the blue.
These are: (1) Lowering the HOMO with respect to the LUMO
Four main approaches are known to be effective in
1
8
a
Department of Chemistry, Durham University, Durham DH1 3LE, UK.
E-mail: m.r.bryce@durham.ac.uk
1
9
b
Department of Physics, Durham University, Durham DH1 3LE, UK
by introducing electron-withdrawing groups, such as fluorine
c
20
20
21
State Key Laboratory of Chemical Resource Engineering, Beijing University of
sulfonyl, phosphoryl, perfluoroalkyl, perfluoroalkyl car-
Chemical Technology, Beijing 100029, China
22
13
bonyl, and cyano substituents at specific positions on the
phenyl ring. (2) Raising the LUMO by either adding electron-
†
Electronic supplementary information (ESI) available: Thermogravimetric data;
NMR spectra; additional computational and CV data. CCDC 1495066. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c7dt02289a
2
3,24
donating groups such as methoxy to the pyridyl ring,
or
replacing the pyridyl ring with another heterocycle with higher
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2
5
LUMO energy. (3) Using electron-withdrawing N^N ligands, parison with 14 and 15, thereby facilitating film formation by
e.g. pyridyl-azole, to modulate the electron density around the solution processes without affecting the emission colour.
2
6–28
metal centre, thereby affecting the HOMO energy.
(4)
Using strong σ-donor ligands, e.g. carbenes, to increase the
crystal field splitting, thereby widening the HOMO–LUMO gap
and shifting non-emissive d–d* metal-centred (MC) states to
Synthesis and characterisation
1
9
The route to ligand 9 is shown in Scheme 1. 2-Acetyl-4-chloro-
pyridine 6 was synthesised by reaction between 4-nitro-
α-picoline-N-oxide 3 and acetyl chloride to give 4 in 23%
yield. An intermediate oxime has been proposed in this step.
The N-oxide was reduced using PCl3 to produce 5 in 73%
higher energies.
The present study combines a pyridylpyrazole-based N^N
4
3
2
9
ligand with sulfonyl-containing cyclometalating ligands to
4
3
obtain the new heteroleptic complexes 12–15 with emission
4
3
1
6
blue-shifted compared to the archetypal blue emitter, FIrpic,
and the analogous picolinate-complexes 1 and 2
2
9
yield, followed by reaction with methyl magnesium chloride to
(Fig. 1).
4
4
give 6 in 92% yield. The mesityl group was then introduced
via a Suzuki coupling of 6 with 2,4,6-trimethylphenylboronic
acid to give 7 in 52% yield. The final steps, described in the lit-
Pyridylpyrazole ligands blue-shift the emission due to their
high acidity, reducing the electron density around the Ir centre
3
0
and hence reducing the HOMO level relative to the LUMO.
They have also been exploited as the chromophoric ligands in
4
5
erature for other analogues, involved a crossed Claisen con-
densation reaction with ethyl trifluoroacetate to give a pre-
sumed diketone intermediate 8, followed by a ring closing con-
densation reaction with hydrazine hydrate to give 9 in 20%
yield.
3
1
N-heterocyclic carbene complexes and in conjunction with
3
2–34
other ligands.
The strongly electron-withdrawing CF
3
group on the pyrazole ring should further blue shift the emis-
3
5
sion. The p-tolylsulfonyl and methylsulfonyl groups (com-
plexes 1 and 2) both blue shift the emission to the same
The desired complexes 12 and 13 were then synthesised
4
6,47
2
9
under standard conditions;
namely, reaction of the ligand
extent, and methoxy substituents can lead to a blue shift
2
9
3
6,37
10 with IrCl
3
·3H
2
O and ligand 11
2
with [Ir(COD)Cl] in
depending on their position on the ppy ligand.
Reducing
2
-ethoxyethanol to give a species presumed to be the bridged
the number of aromatic fluorine substituents, e.g. by selective
replacement with methoxy, can maintain the blue colour and
reduce chemical degradation of a complex during device oper-
μ-dichloro diiridium dimer [Ir(L) Cl] . This intermediate
species was then reacted in situ with ligand 9 to give the
desired complexes 12 and 13 (Scheme 2). The attempted syn-
thesis of 13 using IrCl ·3H O failed to yield any product and
the ligand 11 could not be recovered. Difficulties in the cyclo-
metalation of ligands containing methoxy substituents using
IrCl ·3H O have been reported previously.
2
2
3
8
ation. Complexes 12–15 incorporate a mesityl substituent at
C4 of the ppy ligand; it is known that a mesityl group at this
position enhances the quantum yields of some complexes by
reducing triplet–triplet quenching without affecting blue
3
2
2
9,36
3
9–42
Complexes 14
colour purity.
We also report the new mesityl substituted
3
2
and 15 were synthesised from 10 and 11 by analogous reac-
tions with 3-trifluoromethyl-5-(2-pyridyl)pyrazole ligand 16.
pyridylpyrazole ligand 9 which achieves the desired aims of
increasing the solubility of the complexes 12 and 13, in com-
30
Thermal gravimetric analysis (TGA) shows that all the complexes
possess good thermal stability (Table S5 in ESI†), suggesting the
complexes should be stable under device operation.
X-Ray crystal structure
The single crystal X-ray structure of the highly-functionalised
complex 12 (Fig. 2) shows a distorted octahedral coordination
3
2
of the Ir atom, similar to that in its analogues. The two Ir–C
bonds are in cis positions to one another and trans to the Ir–N
Fig. 1 Previously reported picolinate complexes.
Scheme 1 Synthesis of ligand 9. Reagents and conditions: i, CH
3
COCl, 60 °C; ii, PCl
3
, CHCl
3
, reflux; iii, (1) CH
3
MgCl, ether, 0 °C, (2) dilute HCl; iv,
·H O, ethanol, reflux.
t
Pd(OAc) , PPh , 2,4,6-trimethylphenylboronic acid, Na CO , DME/water, reflux; v, KO Bu, F
2
3
2
3
3
CCO Et, THF, reflux; vi, N
2
2
H
4
2
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bonds of the N^N ligand, which are, therefore, elongated com-
pared to the mutually trans bonds Ir–N(4) and Ir–N(5). The
mesityl groups are near-perpendicular to the corresponding
pyridyl rings. The crystal packing of 12 is dominated by edge-
to-face contacts between arene groups, without π–π stacking.
Photophysical and electrochemical
properties
The absorption and emission spectra of complexes 12–15
Scheme 2 Synthesis of complexes 12–15. Reagents and conditions: i, (Fig. 3) are consistent with pyridylpyrazole subtly lowering the
IrCl
3
5
3
·3H
-trifluoromethyl-5-(2-pyridyl)pyrazole 16 (for 14 and 15) DCM/ethanol,
5 °C; ii, [Ir(COD)Cl] , 2-ethoxyethanol, 130 °C, followed by 9 or 16,
2
O, 2-ethoxyethanol, 130 °C, followed by 9 (for 12 and 13) or
energy of the HOMO. All the complexes show strong absorp-
tion bands in the 250–325 nm region, assigned to the π–π*
2
1
6,18
transitions on the ligands.
Absorption bands with lower
DCM/ethanol, 55 °C.
extinction coefficients in the 350–450 nm range are ascribed to
1
singlet and triplet metal-to-ligand charge-transfer ( MLCT and
3
48,49
MLCT) states.
Here, we see differences between the picoli-
2
9
1
nate complexes 1 and 2, and complexes 12–15; the MLCT
bands move to higher energies on replacing the picolinate
ligands with ligands 9 or 16, suggesting the pyridylpyrazole
has indeed decreased the energy of the metal d-orbitals. The
emission spectra of the complexes are shown in Fig. 3b.
Complexes 12–15 emit in the blue region, and display a
similar emission profile to that of FIrpic and the analogous
picolinate complexes 1 and 2. A notable feature is that the λmax
value for 12 and 13 is blue-shifted by 7 and 8 nm relative to
their analogous picolinate complexes 1 and 2, respectively.
This represents a blue-shift of 11 nm and 2 nm relative to that
1
6
of the benchmark sky-blue emitter FIrpic. The impressive
1 nm shift for complex 12 is primarily a consequence of the
1
combined benefits of the sulfone substituents and the N^N
ligand. The UV-Vis absorption and emission of complexes 14
and 15 are similar to those of complexes 12 and 13, indicating
the introduction of the mesityl substituent on the N^N ligand
does not impact the emission colour.
Fig. 2 X-ray molecular structure of 12. H atoms and the disorder of CF
group are omitted; thermal ellipsoids are drawn at the 30% probability
level. Bond distances (Å): Ir–N(1) 2.102(6), Ir–N(3) 2.142(8), Ir–N(4) 2.040
3
The photoluminescence quantum yield (PLQY) and lifetime
(
6), Ir–N(5) 2.057(6), Ir–C(10) 2.006(7) and Ir–C(22) 1.991(9). Interplanar data are listed in Table 1. The PLQYs for complexes 12–15 are
angles (°): i/ii 7, ii/iii 90, iv/v 7, iv/vi 74, vii/viii 4, vii/ix 89.
comparable to their pic analogues 1 and 2, with lifetimes and
Fig. 3 (a) UV-Vis absorption spectra of the complexes in DCM [<10− M]. Inset shows an expansion of the 350–475 nm region. (b) Emission spectra
5
in deaerated DCM, λex = 380 nm.
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Table 1 Photophysical data for the iridium complexes
abs
(ε) /nm (×10 M cm−1
a
3
−1
em
b
a,c
a,d
5
−1
5 −1
Complex
FIrpic
λ
)
λ
/nm
PLQY/ΦPL
τ
P
/μs
k
r
/10 s
knr/10 s
max
max
277 (50.1), 301 (34.2), 304 (32.6), 337 (13.8, sh), 357 (8.9, sh), 468, 496, 531 (sh) 0.67
00 (6.2), 454 (0.8)
258 (s sh, 108.5), 271 (128.6), 297 (123.4), 307 (sh, 112.5),
39 (s sh, 29.2), 379 (15.7), 450 (1.0)
275 (104.4), 291 (101.9), 324 (sh, 47.8), 381 (14.5),
05 (sh, 7.9), 456 (0.9)
1.72
1.78
2.13
3.90
3.76
2.72
1.92
1.85
1.97
4
2
9
1
2
464, 490, 524 (sh) 0.67
474, 497, 536 (sh) 0.58
3
2
9
4
1
1
2
3
274 (144.4), 293 (136.7), 370 (19.4), 419 (sh, 2.7), 447 (0.7)
255 (sh, 100.4), 277 (125.8), 292 (133.5), 321 (59.6) (sh),
457, 486, 521 (sh) 0.62
466, 494, 531 (sh) 0.52
2.30
3.13
2.70
1.66
1.65
1.53
3
75 (16.3), 406 (sh, 5.1), 454 (0.8)
1
1
4
5
274 (171.0), 291 (161), 374 (17.9), 418 (2.1), 450 (0.5)
276 (129.3), 295 (122.75), 325 (50.8), 371 (18.2), 411 (3.2),
457, 486, 522 (sh) 0.70
467, 494, 531 (sh) 0.64
2.74
3.30
2.55
1.94
1.09
1.09
4
54 (0.7)
a
b
c
Data obtained in DCM solution at 20 °C. Data obtained in degassed DCM solution with λex = 380 nm. Measured relative to Ir(ppy)
3
ΦPL = 0.46
d
in degassed DCM at 20 °C; estimated error ±5%. Estimated error ±5%.
spectral profiles consistent with phosphorescence from a
mixture of ligand-centred and MLCT excited states.
As complexes 12–15 contain a pyridylpyrazole-based ligand
it is assumed the second oxidation occurs either on this ligand
1
8,49
The electrochemical behaviour of complexes 12–15 was or is due to an interaction of this ligand with the metal.
n
investigated by cyclic voltammetry (CV) in a 0.1 M N Bu
4
PF
6
Exchanging the picolinate ancillary ligand for pyridylpyrazole
acetonitrile solution, and compared to FIrpic and picolinate results in an increase in the first oxidation potential by only
2
9
analogues 1 and 2. The voltammograms of FIrpic, 12–15 are 10–20 mV (1 vs. 12, 2 vs. 13), consistent with pyridylpyrazole
shown in Fig. 4 and S13,† and the key parameters are listed in subtly lowering the energy of the HOMO. The presence of the
Table 2. Whereas the picolinate complexes (FIrpic, 1 and 2) mesityl group on the N^N ligand (complexes 12 and 13)
show a single quasi-reversible oxidation wave, complexes decreases the oxidation potentials by ca. 50 mV compared to
1
2–15 show two oxidation waves. In the case of 12 and 13 the the unsubstituted complexes 14 and 15. No reduction waves
two waves are irreversible, whereas for 14 and 15 the first oxi- were observed within the solvent window to −2.0 V. This is
dation wave is quasi-reversible.
consistent with the calculated large HOMO–LUMO gap
Table 2).
(
Computations
Electronic structure calculations were carried out on the four
new iridium complexes 12–15 to explore the frontier orbitals
(
Fig. 5 and Tables S1–S4†) in order to support the electro-
chemical and photophysical observations. The full geometries
were optimised at B3LYP/LANL2DZ:3-21G* to compare directly
29
with computed data of FIrpic, 1 and 2 reported earlier. The
optimised geometries are denoted as 12′–15′ to identify them
as computed models and distinguish the predicted data from
experimental data. Comparison between optimised (12′) and
Fig. 4 Cyclic voltammograms of the iridium complexes.
Table 2 Cyclic voltammetric data of the iridium complexes
ox1
a
ox2
1=2
a
c
d
Complex
E
/V
E
/V
Obs E(HOMO) /V
Complex
Calc. HOMO/eV
Calc. LUMO/eV
Calc. HLG /eV
1
=2
2
9
FIrpic
0.89
1.01
0.89
1.02
0.91
1.07
0.97
—
—
—
1.28
1.17
1.41
1.28
−5.69
−5.81
−5.69
−5.82
−5.71
−5.87
−5.77
FIrpic′
1′
2′
12′
13′
14′
15′
−5.49
−5.64
−5.53
−5.74
−5.62
−5.77
−5.64
−1.87
−1.94
−1.89
−1.83
−1.77
−1.89
−1.84
3.62
3.70
3.64
3.91
3.85
3.88
3.80
2
2
9
9
1
2
1
1
1
1
b
b
b
b
b
b
2
3
4
5
a
n
+ 50 b
Not reversible. E(HOMO) = −4.8 − E 1o x1
c
Redox data were obtained in 0.1 M N Bu
4
PF
6
acetonitrile solutions and are reported vs. FcH/FcH .
=2
+
d
with respect to the FcH/FcH couple at 4.8 V. HLG = HOMO–LUMO energy gap.
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which is consistent with the observed blue-shifted emissions
of 12–15 compared to FIrpic. The LUMOs in 13′ and 15′
contain more pyridylpyrazole character than ppy character
(
Fig. 5) which is explained by the increased number of elec-
tron-donating methoxy groups present in the ppy ligands of
these complexes.
TD-DFT computations were carried out on the S optimised
0
geometries of 12′–15′ to predict emission wavelengths of these
complexes. The initial excitation is assumed to give the lowest
energy singlet excited state S
iridium centre results in intersystem crossing (ISC) to form the
triplet excited state T and phosphorescence is observed from
the S ← T process. The small Stokes shifts observed for these
complexes suggest that the T1 geometry is similar to the
corresponding S geometry. The reverse process S ← T is
Fig. 5 Frontier molecular orbitals for 12’ and 13’. All contours are thus considered to have the same nature as the computed S
1
which in the presence of the
1
0
1
0
0
1
0
3
1/2
plotted at ±0.04 (e per bohr ) . Ir : phenyl : pyrazolyl : pyridyl(pypz) :
→
T1 process with the predicted emission wavelength adjusted
to take into account the Stokes shift. Table 3 shows there is
close agreement between the predicted S ← T wavelengths
pyridyl(ppy) % orbital contribution ratio are listed for each orbital.
0
1
and the observed emission wavelengths for all the complexes.
X-ray determined (12) geometry reveals good agreement with
differences in bond lengths below 0.04 Å.
Complexes 12′–15′ have HOMOs similar to FIrpic with the
HOMO on iridium and phenyl (ppy) (Fig. 5). The lower HOMO
energies on the complexes 12′–15′, compared to FIrpic, reflect
the electron-withdrawing properties of the sulfone groups.
Frontier orbital energies for all complexes are listed in Table 2
for direct comparison with the observed CV data. The trends
in observed and computed HOMO energies are in very good
agreement. The iridium contributions (32–33%, Table 3) in the
HOMOs of 12′–15′ are lower than the corresponding contri-
bution in FIrpic′ (44%) suggesting increased ligand contri-
butions in the MLCT transitions involved in the emissions of
Phosphorescent organic light-emitting
devices
PhOLEDs containing complex 12, 13 or 2 as the dopant
complex were fabricated to compare directly with our reference
devices containing FIrpic and 1. The initial standard device
architecture comprised of a simple single-emissive-layer which
was a blend of poly(vinylcarbazole) (PVK) as the host material,
OXD-7 (an electron-transporting material) and the Ir complex
to give the architecture: ITO/PEDOT:PSS (45 nm)/PVK:OXD-7
(
(
30 wt%):Ir complex (15 wt%) (60 nm)/TPBi (30 nm)/LiF
1 nm)/Al (100 nm). The emissive layer was spin-coated from
1
2′–15′ with respect to MLCT transitions for FIrpic′.
The LUMOs in 12′–15′ have substantial contributions from
chlorobenzene solution to prevent possible degradation of the
the pyridyl groups of the ppy and the pyridylpyrazole ligands
which raise their orbital energies compared to FIrpic′ where
the LUMO is entirely located on the pyridyl group of the ppy
ligands. The pyridylpyrazole ligands are, therefore, not ancil-
lary. Consequently, the HOMO–LUMO energy gaps (HLGs) in
complexes 12′–15′ are larger than the HLG in FIrpic′ (Table 2)
complexes which is known to occur during thermal evapor-
38,51–54
ation of complexes which have fluorinated ligands.
TPBi
was used as an additional electron transporting layer adjacent
to the cathode to improve charge balance and to ensure that
55
excitons are confined in the emitter layer. The efficiency and
luminance data of the devices are summarised in Table 4 and
the electroluminescence (EL) spectra are shown in Fig. 6a. The
EL and PL spectra are similar for all the complexes due to
Table 3 Iridium atom contributions in HOMOs and predicted (TD-DFT)
emission wavelengths of iridium complexes
efficient exciton confinement on the emissive molecules. The
EL
max
λ
of complex 12 is significantly bluer (by 6 nm) than the
corresponding pic complex 1. However, as a trade-off, 12 has
lower brightness (panel e), lower EQE (panel c), and lower
current and power efficiencies (panels d and f). Based on the
electrochemical data, the HOMO of 12 is lower in energy than
1, which could be partially responsible for the reduced per-
formance. Complex 13, however, performed better than 2, with
Observed
a
1
em
b
Complex
% Ir HOMO
S
0
← T
/nm
Complex
λ
/nm
max
2
9
FIrpic′
44
39
40
33
33
32
32
471
467
473
455
459
454
459
FIrpic
1
2
12
13
14
15
471
464
474
457
466
457
467
2
2
9
9
1
2
1
1
1
1
′
′
2′
3′
4′
5′
comparable brightness and turn-on voltage (panel e), and with
EL
superior EQE, current and power efficiencies. The λ
of 13 is
max
also blue-shifted relative to 2; however, this is offset by a
broader emission resulting in similar CIE coordinates for both
complexes. The additional mesityl substituent on the N^N
a
0
Values from TD-DFT data on S optimised geometries with scaling
b
energy factor of 0.945 based on DCM at 298 K. Observed highest
energy band from emission spectra (Table 1).
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Table 4 Summary of device data
Brightness
/nm (max, and at 10 V)/cd m
Current
Turn-on voltage /V EQEmax/% efficiency/cd A
Power
efficiency/lm W
CIE
EL
max
−2
c
−1
−1
d
Complex
λ
coordinates/(x,y)
a
FIrpic
475
470
478
464
473
460
7340, 2380
2072, 175
516, 160
1066, 55
456, 195
6.2
8.5
8.5
9.5
7.9
6.2
5.4
3.5
1.2
2.3
1.7
6.3
12.2
6.1
2.6
4.1
3.9
6.9
5.1
1.9
0.9
1.2
1.4
3.5
(0.19, 0.38)
(0.16, 0.30)
(0.22, 0.40)
(0.17, 0.28)
(0.23, 0.40)
(0.15, 0.21)
a
1
2
a
a
1
1
1
2
3
2
a
b
5428, 5400
a
In PVK host. In mCP host. Measured at a brightness of 10 cd m−2
b
c
d
. Measured at 12 V.
Fig. 6 Electroluminescent device data for complexes FIrpic, 1, 2, 12 and 13 in PVK host and for 12 in mCP host.
ligand of 12 and 13 enhances the solubility of the complexes layer and Tm3PyBP serves as an additional hole/exciton-block-
5
6
facilitating thin film formation by solution processing.
ing layer to optimise the device structure. Compared to the
We further explored the bluest complex 12 using mCP as a 12:PVK device, the 12:mCP device displayed a significantly
wide energy gap host which is more appropriate for a deep lower turn-on voltage and further blue shifted electrolumines-
EL
max
blue emitter in the architecture: ITO/TAPC (45 nm)/mCP:Ir cence to λ
460 nm, CIEx,y (0.15, 0.21) with an increased
complex 12 (15 wt%) (45 nm)/Tm3PyBP (5 nm)/TPBi (30 nm)/ maximum EQE of 6.3% and increased brightness at 10 V of
LiF (1 nm)/Al (100 nm). TAPC served as a hole-transporting 5400 cd m− which is high compared to reported PhOLEDs
2
Dalton Trans.
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Paper
with similar blue CIE coordinates using a solution-processed trode. Experiments were conducted in dry acetonitrile solution
5
7
n
emitter layer.
with N Bu PF (0.1 M) as the supporting electrolyte at a scan
4 6
rate of 100 mV s− . The reference electrode was assumed to be
stable and was referenced externally to ferrocene (Cp Fe) and
decamethylferrocene (Cp* Fe) which displayed potentials (E1/2)
1
2
Conclusions
2
of −0.41 V and +0.10 V, respectively, versus Ag/AgNO
3
under
To summarise, replacing the picolinate ancillary ligand of the these conditions. It was not possible to use Cp Fe or Cp* Fe as
2
2
heteroleptic iridium complexes 1 and 2 with a pyridylpyrazole- an internal reference because their addition to the solutions of
based ligand affords the new complexes 12–15 with blue the complexes resulted in a distortion of the redox waves of
shifted emission. This is ascribed to a reduction of electron the complexes.
density around the metal centre which results in a lowering of
Solution state photophysical data were obtained using
the energy of the HOMO of the complexes, as observed in the freshly prepared solutions of the complexes in DCM. Emission
solution electrochemical data. (TD-)DFT calculations are in and lifetime measurements used thoroughly degassed solu-
excellent agreement with the observed photophysical and tions achieved by three freeze–pump–thaw cycles, and quartz
electrochemical properties of the complexes. Blue-emitting cuvettes with a path length of 1 cm. The solutions had absor-
PhOLEDs have been fabricated with a solution-processed emis- bance below 0.10 to minimise inner filter effects. UV-vis
sive layer structure. Notably, devices of complex 12 possess absorption measurements were recorded using a Unicam UV2-
EL
λ
460 nm and CIE (0.15, 0.21) with brightness at 10 V of 100 spectrometer operated with Unicam Vision (ver. 3.50) soft-
max
x,y
400 cd m− . This study demonstrates that the rational design ware. Baseline correction was achieved by reference to pure
2
5
of new complexes with specific functionalities on the cyclo- solvent in the same cuvette. Absorption measurements were
metalating and the N^N ligands is an effective route to new obtained using quartz cuvettes with a path length of 2 cm.
efficient blue emitters and PhOLEDs using relatively simple Excitation and emission spectra were recorded on a Jobin–
device architectures.
Yvon–Horiba SpexFluoromax 3 Spectrometer. Solutions of the
complexes in degassed DCM [<10− M] were used for decay
measurements. Samples were excited with a pulsed nitrogen
laser emitting at 337.1 nm. Emission was focused onto a
spectrograph and detected on a sensitive gated iCCD camera
5
Experimental section
Materials, synthesis and characterisation
(
Stanford Computer Optics) with sub-nanosecond resolution.
Solution PLQYs were recorded in degassed solvent, and deter-
mined using the relative method, with Ir(ppy) (ΦPL = 0.46 in
degassed dichloromethane, determined in-house vs. ΦPL
.546 in 0.5 M H SO ) as the reference. The PLQYs were calcu-
All commercially available chemicals were used without
further purification. Reactions requiring an inert atmosphere
were performed under a blanket of argon gas, which was dried
over a phosphorus pentoxide column. Anhydrous solvents
were dried through an HPLC column on an Innovative
Technology Inc. solvent purification system. Column chrom-
atography was performed using 40–60 μm mesh silica gel.
Analytical TLC was performed on plates pre-coated with silica
gel (Merck, silica gel 60F254) and visualised using UV light
3
=
0
2
4
lated according to the following equation:
ꢀ
ꢁ
2
Gradx
Gradref
ηx
Φx ¼ Φref
:
ηref
where subscripts ‘x’ and ‘ref’ denote the material being
measured and the reference, respectively. Φ represents the
PLQY, Grad is the gradient from the plot of integrated fluo-
rescence intensity vs. absorbance, and η is the refractive index
of the solvent.
(
254, 315, 365 nm). NMR spectra were recorded on a Bruker
Avance 400 MHz spectrometer. Chemical shifts are referenced
to tetramethylsilane [TMS, Si(CH ] at 0.00 ppm. Melting
3 4
)
points were determined in open-ended capillaries using a
Stuart Scientific SMP3 melting point apparatus at a ramping
rate of 1 °C min− and were recorded to the nearest 0.1 °C. ESI
and MALDI mass spectra were recorded on a Thermo-Finnigan
LTQ FT (7.0 T magnet) spectrometer. ASAP mass spectra were
recorded on a Waters Xevo QTOF spectrometer. GCMS spectra
were recorded on a Thermo-Finnigan Trace GCMS (EI and CI
ion sources). Elemental analyses were obtained on an Exeter
Analytical Inc. CE-440 elemental analyzer.
1
Thermal analyses
Thermogravimetric analysis (TGA) was performed in a nitrogen
atmosphere using a PerkinElmer Pyris 1 TGA instrument. The
complexes were heated at a rate of 10 °C min− from room
temperature up to 600 °C.
1
Computational studies
Solution electrochemistry and photophysics
All calculations were carried out with the Gaussian 09
5
8
0
Cyclic voltammetry experiments were recorded using a BAS package. All optimised S geometries for 12′–15′ were carried
CV50 W electrochemical analyzer fitted with a three-electrode out using B3LYP with the pseudopotential (LANL2DZ) for
5
9
60
6
1
system consisting of a Pt disk (∅ = 1.8 mm) as the working iridium and 3-21G* basis set for all other atoms. This model
electrode, a Pt wire as an auxiliary electrode and an Ag/AgNO chemistry was selected for direct comparison with computed
0.1 M [NEt ][ClO ] in CH CN) system as the reference elec- data on FIrpic′, 1′ and 2′. Electronic structure and TD-DFT
3
2
9
(
4
4
3
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calculations were also from the optimised geometries at emissive layer and annealed at 80 °C for 30 min to remove the
B3LYP/LANL2DZ:3-21G*. The MO diagrams and orbital contri- residual solvent. Finally, a 5 nm-thick hole/exciton blocking
6
2
butions were generated with the aid of Gabedit
GaussSum packages, respectively.
and layer of Tm3PyPB was vacuum deposited followed by a 30 nm-
thick electron-transporting layer (ETL) of TPBi, and a cathode
composed of a 1 nm-thick layer of LiF and aluminum (100 nm)
6
3
Phosphorescent organic light-emitting devices (PhOLEDs)
PhOLEDs with poly(vinylcarbazole) (PVK) host were fabricated pressure of 10− Torr. The OLED devices had a pixel sise of
was sequentially deposited through shadow masking at a
6
on indium tin oxide (ITO)-coated glass substrates of thickness 4 mm × 4 mm. All measurements were performed at room
1
25 nm and possessing a sheet resistance of 15 Ω per square. temperature under ambient conditions.
Poly(3,4-ethylenedioxythiophene) doped with high work func-
tion hole injection layer poly(styrenesulfonic acid) (PEDOT:
PSS) (HIL1.3) from CLEVIOS was spin-coated at 2500 rpm for
Synthesis of ligands and complexes
1-(4-Mesitylpyridin-2-yl)ethanone 7. 2-Acetyl-4-chloro-
4
4
6
0 s to produce a ∼50 nm thick hole-injecting/transporting pyridine 6 (1.5 g, 9.68 mmol), 2,4,6-trimethylphenylboronic
layer (HTL). The PEDOT:PSS layer was annealed at ca. 200 °C acid (1.75 g, 10.67 mmol) and PPh (657 mg, 2.50 mmol) were
3
for 5 min to remove any residual water. A chlorobenzene solu- dissolved in DME (70 mL) and the solution was degassed for
tion of 25 mg ml− of poly(vinylcarbazole) (PVK) (M
1
= 90 000) 20 min by bubbling with argon. Separately, an aqueous solu-
w
was doped with 30% w/w of (1,3-phenylene)bis[5-(4-tert-butyl- tion of Na CO (4.18 g, 39.43 mmol in 17 mL) was degassed.
2
3
phenyl)-1,3,4-oxadiazole] (OXD-7). Blended devices were made The solutions were combined and Pd(OAc)
2
(130 mg,
by mixing 15% w/w of the Ir complexes. The prepared mixtures 0.58 mmol) was added. The mixture was heated to reflux over-
were filtered with a 0.45 μm pore filter and spin-coated at 2500 night under an atmosphere of argon. The solution was then
rpm for 1 min on the top of the PEDOT:PSS layer and baked cooled to RT, and the majority of the solvent was removed
for 10 min at 120 °C. Each sample was shadow masked to in vacuo. DCM and water were added, and the organic layer
produce four identical devices of area 4 × 5 mm; the samples separated. The aqueous layer was extracted with additional
were then introduced into a nitrogen glove box, where 30 nm DCM, and the extracts combined and the solvent removed
of 2,2′,2″-(1,3,5-benzenetriyl)tris-[1-phenyl-1H-benzimidazole] in vacuo. The crude residue was purified by column chromato-
(
TPBi) was evaporated as an electron injection/hole blocking graphy (DCM), followed by recrystallisation from hexane to
−
1
layer at a rate of ∼1 A s under vacuum at a pressure of ca. 1 × give 1-(4-mesitylpyridin-2-yl)ethanone 7 (1.2 g, 52%); m.pt.
−
6
1
0
Torr, followed by 0.8 nm LiF and a 100 nm capping layer 118.9–119.9 °C; δ
of aluminium under the same evaporation conditions. 7.88 (1H, dd, J 1.7, 0.8), 7.31 (1H, dd, J 4.9, 1.7), 6.95–6.94 (2H,
Therefore, the device configuration for all complexes was: ITO/ m), 2.79 (3H, s), 2.33 (3H, s), 1.97 (6H, s); δ (101 MHz; CDCl
PEDOT:PSS (50 nm)/PVK:OXD-7 (35%):Ir-complex (15%)/TPBi 200.07, 153.73, 151.14, 149.18, 138.05, 135.64, 135.08, 128.61,
30 nm)/LiF (0.8 nm)/Al (100 nm). All samples were encapsu- 128.41, 123.06, 26.19, 21.19, 20.72; HRMS (FTMS + ESI): calcd
H 3
(400 MHz; CDCl ) 8.74 (1H, dd, J 4.9, 0.8),
C
3
)
(
+
lated inside a glove box using DELO UV cured epoxy for [C16
H17NO + H] : 240.1388. Found: 240.1388.
(KATIOBOND) and capped with a 1.2 × 1.2 cm microscope 4-Mesityl-2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridine 9.
glass slide then exposed to UV light for 3 min. Current–voltage A solution of 4-mesityl-2-acetylpyridine 7 (1.20 g, 5.01 mmol)
data, device efficiency, brightness and electroluminescence in THF (15 mL) was added dropwise to a stirred suspension of
t
spectra were measured in a calibrated Labsphere LMS-100 inte- KO Bu (0.68 g, 6.06 mmol) in dry THF solution (30 mL) which
grating sphere. A home written NI LabVIEW programme was was cooled in an ice bath. After 5 min ethyl trifluoroacetate
used to control an Agilent 6632B DC power supply, and the (0.65 mL, 5.51 mmol) was added slowly. The solution was
emission properties of the device were measured using an allowed to stir at 0 °C for 15 min before being removed from
Ocean Optics USB4000 CCD fibre optic spectrometer. The the ice bath. The mixture was heated to reflux overnight before
thicknesses of the various layers in the device were measured being cooled, and the solvent was removed under reduced
with a J A Woolam VASE Ellipsometer using thin films which pressure. Water (30 mL) was added to the resulting solid to
had been spin-coated on Si/SiO2 substrates under the same form a suspension which was neutralised with conc. HCl. The
conditions as the device films.
solution was then extracted with DCM. The organic phase was
and the solvent removed to give the pre-
Devices with 1,3-bis(N-carbazolyl)benzene (mCP) host were dried over MgSO
4
fabricated as follows. TAPC (1,1-bis{4-[N,N-di(p-tolyl)amino] sumed 1,3-dione intermediate 8 (not characterised). This was
phenyl}cyclohexane), TPBi, and Tm3PyPB (1,3,5-tris(3-pyridyl- dissolved in ethanol (30 mL) and hydrazine hydrate (0.34 mL,
3
-phenyl)benzene) were obtained from commercial sources. 95%) was added. The solution was heated to reflux overnight
Indium tin oxide (ITO)-coated glass with a sheet resistance of before the solvent was removed in vacuo. The residue was dis-
0 Ω per square was used as the substrate. Before device fabri- solved in DCM and washed with water to remove unreacted
1
cation, the ITO-coated glass substrate was precleaned and hydrazine hydrate. The solvent was removed, and the oily
exposed to UV-ozone for 15 min. PEDOT:PSS was then spin- residue was redissolved in ethanol and conc. HCl (0.5 mL) was
coated onto the clean ITO substrate as a hole-injection layer. added (to promote complete dehydration). The solution was
Next a mixture of complex 12 and mCP in chlorobenzene was heated to reflux for 5 h, before being cooled and the solvent
−
1
spin-coated (10 mg mL ; 3000 rpm) to form a ca. 45 nm thick removed. The crude solid was dissolved in DCM and washed
Dalton Trans.
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Paper
with water, before being dried over MgSO
in vacuo. The crude solid was purified by column chromato- masked using PLATON SQUEEZE program.
4
and concentrated ordered along infinite channels parallel to the x axis) was
6
7,68
The large
graphy (1 : 3 EtOAc : DCM v/v) followed by recrystallisation atomic displacement parameters, together with practical
from hexane to give an off-white solid, 4-mesityl-2-(3-(trifluoro- absence of Bragg diffraction at 2θ > 50°, indicate severe
methyl)-1H-pyrazol-5-yl)pyridine
71.1–172.9 °C; δ (400 MHz; CDCl
1H, dd, J 5.0, 0.9), 7.47 (1H, dd, J 1.5, 0.9), 7.15 (1H, dd, J 5.0, added to a stirred solution of 2-(2,4-dimethoxy-3-(methyl-
9
(277 mg, 20%); m.pt. internal strain, probably caused by partial solvent loss.
1
H
3
) 11.95 (1H, br s), 8.70 Iridium complex 13. [Ir(COD)Cl] (90 mg, 0.13 mmol) was
2
(
1
2
9
.5), 6.96–7.00 (2H, m), 6.91 (1H, s), 2.35 (3H, s), 2.02 (6H, s); sulfonyl)phenyl)-4-mesitylpyridine 11 (226 mg, 0.55 mmol)
δ
F
(376 MHz; CDCl ) −62.34 (3F, s); δ (101 MHz; CDCl in 2-ethoxyethanol (5 mL). The solution was heated to 130 °C
3
C
3
)
1
1
1
51.57, 149.86, 146.91, 144.42 (q, J 38.4), 143.10, 138.08, under an argon atmosphere overnight before being cooled to
35.43, 134.97, 128.52, 125.07, 121.40, 121.14 (q, J 267.9), RT. Water was added and a yellow precipitate formed which
01.34, 21.06, 20.57; HRMS (FTMS
+
ESI): calcd for was filtered, washed with more water and dried. The precipi-
tate, presumed to be the intermediate dichloro bridged dimer,
+
[C
18
H
16
N
3
F
3
+ H] : 332.1375. Found: 332.1379.
Iridium complex 12. IrCl ·3H O (66 mg, 0.19 mmol) was was dissolved in DCM/ethanol (40 mL, 3 : 1 v/v) and 4-mesityl-
3
2
added to a stirred solution of 2-(2-fluoro-4-methoxy-3-tosyl- 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridine
phenyl)-4-mesitylpyridine 10
2
9
(90 mg,
(169 mg, 0.38 mmol) in 0.27 mmol) was added and the solution was heated at 55 °C
-ethoxyethanol (5 mL). The solution was heated to 130 °C overnight under an argon atmosphere. The solution was
2
9
under an argon atmosphere overnight, during which time a cooled and the solvent was removed in vacuo. The residue was
bright yellow precipitate formed, presumed to be the dichloro purified by column chromatography (EtOAc in DCM: gradient
bridged dimer. The solvent was removed in vacuo and the elution from 0% to 15%) to give a yellow solid, iridium
precipitate was redissolved in DCM/ethanol (20 mL, 3 : 1 v/v). complex 13 (98 mg, 27%); Anal. calc. for C64
-Mesityl-2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridine C, 57.21; H, 4.73; N, 5.21. Found: C, 57.17; H, 5.07; N, 4.68;
77 mg, 0.28 mmol) was added and the solution was heated at δH (400 MHz; CD Cl ) 8.47 (1H, d, J 1.4), 8.38 (1H, d, J 1.4),
63 3 5 8 2
H F IrN O S :
4
9
(
2
2
6
0 °C overnight under an argon atmosphere. The solution was 7.80–7.74 (3H, m), 7.65 (1H, dd, J 1.8, 0.8), 6.98 (5H, s), 6.95
cooled and the solvent was removed in vacuo. The residue was (2H, s), 6.91 (1H, dd, J 5.7, 1.8), 6.84 (1H, dd, J 5.9, 1.9), 6.81
purified by column chromatography (EtOAc in DCM, 2.5% (1H, dd, J 5.9, 1.9), 6.03 (1H, s), 6.01 (1H, s), 3.88 (3H, s), 3.85
increased to 4%) to give a yellow solid, iridium complex 12 (3H, s), 3.61 (3H, s), 3.60 (3H, s), 3.22 (3H, s), 3.19 (3H, s), 2.33
(190 mg, 70%); Anal. calc. for C74
H
65
F
5
IrN
5 6 2
O S : C, 60.39; H, (3H, s), 2.32 (3H, s), 2.31 (3H, s), 2.09 (3H, s), 2.06 (3H, s), 2.05
4
.45; N, 4.76. Found: C, 60.53; H, 4.71; N, 4.50; δH (400 MHz; (3H, s), 2.01 (3H, s), 1.88 (3H, s), 1.85 (3H, s); δF (376 MHz;
CDCl
3
) 8.12–8.17 (1H, m), 8.03–8.08 (1H, m), 7.89 (2H, d, CDCl
3
)
−58.48 (s); HRMS (FTMS
+
ESI): calcd for
Ir + H] : 1342.3754. Found: 1342.3802.
2-(3-(Trifluoromethyl)-1H-pyrazol-5-yl)pyridine
1
91
+
63 3 5 8 2
J 8.2), 7.88 (2H, d, J 8.2), 7.67 (1H, d, J 5.9), 7.64 (1H, d, J 5.9), [C64H F N O S
7
7
5
2
1
.59 (1H, dd, J 1.7, 0.8), 7.57 (1H, d, J 5.9), 7.27 (4H, t, J 8.7),
16.
.02–6.89 (8H, s), 6.78 (2H, td, J 6.1, 1.8), 5.79 (1H, s), 2-Acetylpyridine (1.00 g, 8.25 mmol) and ethyltrifluoroacetate
.74 (1H, s), 3.47 (3H, s), 3.44 (3H, s) 2.39 (3H, s), 2.38 (3H, s), (2.35 g, 16.51 mmol) were added dropwise simultaneously to a
.34 (3H, s), 2.33 (6H, s), 2.09 (3H, s), 2.01 (3H, s), 1.98 (3H, s), stirred suspension of NaH (396 mg, 16.51 mmol) in THF
.97 (3H, s), 1.86 (6H, s); δ
F 3
(376 MHz; CDCl ) −59.87 (3F, s), (20 mL, dry) with caution (gas evolution). The mixture was
−
110.50 (1F, s), −111.36 (1F, s); HRMS (FTMS + ESI): calcd for stirred at RT for 30 min before being heated to reflux over-
1
91
+
[C H N F O S
Ir + H] : 1470.3981. Found: 1470.3995. night. The reaction was cooled and quenched with water. The
7
4
65 5 5 6 2
Single crystals of 12·3CH Cl for X-ray study were grown by reaction mixture was acidified to pH 6 with dilute HCl (2 M)
2
2
layering of hexane over a DCM solution of 12; they instantly and then extracted with EtOAc (3 × 60 mL). The organic phases
decomposed when taken out of the solvent. The X-ray experi- were combined, dried over MgSO , filtered and the solvent was
4
ment was carried out at T = 120 K on a D8 Venture (Bruker removed in vacuo to give the crude 1,3-dione. The dione was
AXS) 3-circle diffractometer equipped with a IμS Mo micro- dissolved in ethanol (20 mL) and N
2
H
4
·H
2
O (4 mL) was
¯
source (Mo-Kα radiation, focussing mirrors, λ = 0.71073 Å) added. The solution was heated to reflux overnight before
and a PHOTON 100 CMOS area detector. The structure being cooled to RT. The solvent was removed in vacuo
6
4
was solved by direct methods (SHELXS v. 2013/1 program ) and the residue was purified by column chromatography
and refined by full-matrix least squares using SHELXL v. (hexane : EtOAc 3 : 2 v/v) to give an off-white solid, 2-(3-(tri-
6
6
2
014/7 (ref. 65) and OLEX2
software. Crystal data: fluoromethyl)-1H-pyrazol-5-yl)pyridine 16 (1.31 g, 75%);
C
74
H
67
F
5
IrN ·3CH Cl , M = 1726.40, triclinic, space group
5
O
6
S
2
2
2
δ
H
(400 MHz; CDCl ) 11.74 (1H, s), 8.65 (1H, ddd, J 4.9, 1.8,
3
P ˉ1 (no. 2), a = 14.209(1), b = 18.215(1), c = 18.780(1) Å, α = 1.0), 7.82 (1H, td, J 7.8, 1.7), 7.65 (1H, dt, J 7.9, 1.1), 7.33 (1H,
3
6
D
5
2
7.984(2), β = 86.202(2), γ = 69.653(2)°, V = 4213.6(5) Å , Z = 2, ddd, J 7.6, 4.9, 1.1), 6.96 (1H, s); δ
F
(376 MHz; CDCl
3
) −62.35 (s).
= 1.361 g cm− , μ = 1.89 mm , 57 359 reflections with 2θ ≤
0°, 14 940 unique, R = 0.048, R = 0.069 [11 521 data with I ≥ mesitylpyridine 10
3
−1
Iridium complex 14. 2-(2-Fluoro-4-methoxy-3-tosylphenyl)-4-
c
2
9
(110 mg, 0.23 mmol) and IrCl ·3H O
3 2
int
2
σ(I)], wR(F ) = 0.201 (all data). CCDC 1495066.† The structure (37 mg, 0.10 mmol) were combined in 2-ethoxyethanol (5 mL),
contains DCM of crystallisation, of which 1.5 molecules per and the mixture was heated to reflux overnight under a nitro-
asymmetric unit were located and the rest (presumably dis- gen atomosphere. The reaction was the cooled to RT, and the
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solvent removed in vacuo. The residue was redissolved in DCM/
EtOH (3 : 1 v/v, 20 mL) and 2-(3-(trifluoromethyl)-1H-pyrazol-5-
3 H. Yersin, Highly Efficient OLEDs with Phosphorescent
Materials, Wiley-VCH, Darmstadt, 2008.
yl)pyridine 16 (28 mg, 0.13 mmol) and Na
0
6
2
CO
.10 mmol) were added. The solution was heated to 55 °C for
h, before being cooled to RT and the solvent removed
3
(11 mg,
4 M. S. Lowry and S. Bernhard, Chem. – Eur. J., 2006, 12,
7970.
5 K. K.-W. Lo, W.-K. Hui, C.-K. Chung, K. H.-K. Tsang, D.
C.-M. Ng, N. Zhu and K.-K. Cheung, Coord. Chem. Rev.,
2005, 249, 1434.
6 K. Müllen and U. Scherf, Organic Light Emitting Devices:
Synthesis, Properties and Applications, Wiley-VCH Verlag
GmbH & Co. KGaA, 2006.
7 R. Mertens, The OLED Handbook. A Guide to OLED
Technology, Industry and Market, 2014: http://www.oled-info.
com/handbook.
in vacuo. The residue was purified by column chromatography
0–3% EtOAc in DCM) to give the product as a yellow solid,
iridium complex 14 (109 mg, 77%); Anal. calc. for
IrN : C, 57.68; H, 4.10; N, 5.17. Found: C, 57.84;
H, 4.33; N, 4.92; δ (400 MHz, CDCl ) 8.11 (1H, s), 8.05 (1H, s),
.95–7.78 (6H, m), 7.70–7.64 (1H, m), 7.56 (1H, d, J 6.0),
(
C
65
H
55
F
5
5 6 2
O S
H
3
7
7
7
.50–7.43 (2H, m), 7.29 (1H, d, J 0.8), 7.26–7.22 (2H, m),
.18–7.11 (1H, m), 7.01 (1H, s), 6.93 (4H, d, J 6.4), 6.77 (1H, dd,
J 5.9, 1.8), 6.71 (1H, dd, J 6.0, 1.8), 5.72 (1H, s), 5.70 (1H, s),
8 Z.-R. Li and H. Meng, Organic Light-Emitting Materials and
Devices, CRC Press, Boca Raton, Florida, 2006.
9 M. Du, Y. Feng, D. Zhu, T. Peng, Y. Liu, Y. Wang and
M. R. Bryce, Adv. Mater., 2016, 28, 5963.
3
1
−
.44 (3H, s), 3.41 (3H, s), 2.39 (3H, s), 2.38 (3H, s), 2.33 (6H, s),
.99 (3H, s), 1.97 (6H, s), 1.93 (3H, s); δ (376 MHz; CDCl
59.85 (3F, s), −110.73 (1F, s); −111.48 (1F, s); HRMS (FTMS +
F
3
)
1
91
+
ESI): calcd for [C65
H
55
N
5
O
6
F
5
S
2
Ir + H] : 1352.3198. Found: 10 L. Ying, C.-L. Ho, H. Wu, Y. Cao and W.-Y. Wong, Adv.
1
352.3193.
Mater., 2014, 26, 2459.
Iridium complex 15. 2-(2,4-Dimethoxy-3-(methylsulfonyl) 11 E. Holder, B. M. W. Langeveld and U. S. Schubert, Adv.
2
9
phenyl)-4-mesitylpyridine 11
(198 mg, 0.48 mmol) and
Mater., 2005, 17, 1109.
[
Ir(COD)Cl]
nol (5 mL), and the mixture was heated to reflux overnight 13 X. Yang, G. Zhou and W.-Y. Wong, Chem. Soc. Rev., 2015,
under a nitrogen atmosphere. The reaction was the cooled to 44, 8484.
2
(79 mg, 0.12 mmol) were combined in 2-ethoxyetha- 12 P. T. Chou and Y. Chi, Chem. – Eur. J., 2007, 13, 380.
RT, and the solvent removed in vacuo. The residue was redis- 14 Y. You and S. Y. Park, Dalton Trans., 2009, 1267.
solved in DCM/EtOH (3 : 1 v/v, 20 mL) and 2-(3-(trifluoro- 15 S. Ladouceur and E. Zysman-Colman, Eur. J. Inorg. Chem.,
methyl)-1H-pyrazol-5-yl)pyridine 16 (63 mg, 0.30 mmol) and
Na CO (50 mg, 0.47 mmol) were added. The solution was 16 E. Baranoff and B. F. Curchod, Dalton Trans., 2015, 44,
heated to 55 °C for 5 h, before being cooled to RT and the 8318.
solvent removed in vacuo. The residue was purified by column 17 S. H. Kim, J. Jang, S. J. Lee and J. Y. Lee, Thin Solid Films,
chromatography (0–10% EtOAc in DCM) to give the product as 2008, 517, 722.
a yellow solid, iridium complex 15 (28 mg, 56%); Anal. calc. for 18 S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq,
2013, 2985.
2
3
C
55
H
53
F
3
IrN
5
O
8
S
2
: C, 53.91; H, 4.36; N, 5.72. Found: C, 53.48;
(400 MHz, CDCl ) 8.46 (1H, d, J 1.8), 8.40
R. Kwong, I. Tsyba, M. Bortz, B. Mui, R. Bau and
M. E. Thompson, Inorg. Chem., 2001, 40, 1704.
H, 4.43; N, 5.55; δ
H
3
(1H, d, J 1.8), 7.88 (2H, m), 7.82 (1H, d, J 5.9), 7.75 (1H, d, 19 T. Sajoto, P. I. Djurovich, A. Tamayo, M. Yousufuddin,
J 5.6), 7.52 (1H, d, J 5.9), 7.16 (1H, td, J 6.0, 2.6), 7.04 (1H, s),
.98 (2H, s), 6.96 (2H, s), 6.85 (1H, dd, J 5.9, 1.9), 6.72 (1H, dd,
R. Bau, M. E. Thompson, R. J. Holmes and S. R. Forrest,
Inorg. Chem., 2005, 44, 7992.
6
J 5.9, 1.9), 5.96 (1H, s), 5.89 (1H, s), 3.91 (3H, s), 3.91 (3H, s), 20 C. Fan, Y. Li, C. Yang, H. Wu, J. Qin and Y. Cao, Chem.
3
2
−
.60 (3H, s), 3.58 (3H, s), 3.30 (3H, s), 3.27 (3H, s), 2.35 (6H, s),
.03 (6H, s), 2.01 (3H, s), 1.97 (3H, s); δ (376 MHz; CDCl
Mater., 2012, 24, 4581.
21 J. B. Kim, S. H. Han, K. Yang, S. K. Kwon, J. J. Kim and
Y. H. Kim, Chem. Commun., 2015, 51, 58.
22 S. Lee, S. O. Kim, H. Shin, H. J. Yun, K. Yang, S. K. Kwon,
J. J. Kim and Y. H. Kim, J. Am. Chem. Soc., 2013, 135,
F
3
)
1
91
60.00 (s); HRMS (FTMS + ESI): calcd for [C H N O F S
Ir
5
5
53 5 8 3 2
+
+
H] : 1224.2972. Found: 1224.2987.
14321.
2
3 L.-L. Wu, C.-H. Yang, I. W. Sun, S.-Y. Chu, P.-C. Kao and
H.-H. Huang, Organometallics, 2007, 26, 2017.
Acknowledgements
We thank EPSRC grant EL/L02621X/1 for funding the work in 24 H. Oh, K.-M. Park, H. Hwang, S. Oh, J. H. Lee, J.-S. Lu,
Durham.
S. Wang and Y. Kang, Organometallics, 2013, 32, 6427.
5 E. Orselli, G. S. Kottas, A. E. Konradsson, P. Coppo,
R. Frohlich, L. de Cola, A. van Dijken, M. Buchel and
H. Borner, Inorg. Chem., 2007, 46, 11082.
6 J. Li, P. I. Djurovich, B. D. Alleyne, M. Yousufuddin,
N. N. Ho, J. C. Thomas, J. C. Peters, R. Bau and
M. E. Thompson, Inorg. Chem., 2005, 44, 1713.
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