Efficient green-light-emitting electrochemical cells based on ionic iridium complexes with sulfone-containing cyclometalating ligands

Article abstract of DOI:10.1002/chem.201300457

A new approach to obtain green-emitting iridium(III) complexes is described. The synthetic approach consists of introducing a methylsulfone electron-withdrawing substituent into a 4-phenylpyrazole cyclometalating ligand in order to stabilize the highest-occupied molecular orbital (HOMO). Six new complexes have been synthesized incorporating the conjugate base of 1-(4-(methylsulfonyl)phenyl)-1 H-pyrazole as the cyclometalating ligand. The complexes show green emission and very high photoluminescence quantum yields in both diluted and concentrated films. When used as the main active component in light-emitting electrochemical cells (LECs), green electroluminance is observed. High efficiencies and luminances are obtained at low driving voltages. This approach for green emitters is an alternative to the widely used fluorine-based substituents in the cyclometalating ligands and opens new design possibilities for the synthesis of green emitters for LECs. Green enlightenment: Electron-withdrawing sulfone groups introduced into the cyclometalating phenylpyrazole ligands lead to very efficient green-emitting ionic iridium complexes. Green electroluminescence from efficient light-emitting chemical cells is obtained (see figure). Copyright

Full text of DOI:10.1002/chem.201300457

FULL PAPER
DOI: 10.1002/chem.201300457
Efficient Green-Light-Emitting Electrochemical Cells Based on Ionic Iridium
Complexes with Sulfone-Containing Cyclometalating Ligands
[
a]
[b]
[a]
Daniel Tordera, Andreas M. Bꢀnzli, Antonio Pertegꢁs,
[
a]
[b]
[b]
Josꢂ M. Junquera-Hernꢁndez, Edwin C. Constable, Jennifer A. Zampese,
[b]
[a]
[a]
Catherine E. Housecroft,* Enrique Ortꢃ,* and Henk J. Bolink
Abstract: A new approach to obtain
green-emitting iridium(III) complexes
is described. The synthetic approach
consists of introducing a methylsulfone
electron-withdrawing substituent into a
pyrazole as the cyclometalating ligand.
The complexes show green emission
and very high photoluminescence
quantum yields in both diluted and
concentrated films. When used as the
main active component in light-emit-
ting electrochemical cells (LECs),
green electroluminance is observed.
High efficiencies and luminances are
obtained at low driving voltages. This
approach for green emitters is an alter-
native to the widely used fluorine-
based substituents in the cyclometalat-
ing ligands and opens new design possi-
bilities for the synthesis of green emit-
ters for LECs.
AHCTUNGTRENNUNG
4-phenylpyrazole
cyclometalating
ligand in order to stabilize the highest-
occupied molecular orbital (HOMO).
Six new complexes have been synthe-
sized incorporating the conjugate base
Keywords: cyclometalation · densi-
ty functional calculations · iridium ·
LEC devices · photophysical prop-
erties
of
1-(4-(methylsulfonyl)phenyl)-1H-
Introduction
cy, and stability in one device. Recently, LECs based on cat-
ionic iridium complexes were reported showing instant turn-
on, high luminance, and long lifetime with reasonable effi-
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
Light-emitting electrochemical cells (LECs) are a type of
electroluminescent device consisting of a luminescent mate-
rial that can be either a conjugated polymer with an added
[5]
ciency when using a pulsed bias. Another of the main
drawbacks of Ir-iTMC LECs is that most emit in the
[
1]
[6]
electrolyte in a blended structure (PLEC) or an ionic tran-
sition-metal complex (iTMC) that performs the roles of in-
yellow–orange region with fewer examples emitting red,
[6a,7]
[8]
blue,
or green light.
[2]
jection, transport, and light emission. The main advantages
of this type of device are their simple structure, as they usu-
ally consist of a single layer processed from solution, and
their insensitivity to the work function of the electrodes em-
Previous works have shown that the highest occupied mo-
lecular orbitals (HOMOs) are located on the phenyl groups
III
of the cyclometalating ligands and the 5d orbitals of the Ir
ion, whereas the lowest unoccupied molecular orbitals
[
3]
[8d,9]
ployed. This is a result from the presence of ions, which
migrate towards the electrodes when a bias is applied, low-
ering the injection barrier and allowing for efficient injec-
(LUMOs) are found on the ancillary ligands.
Hence,
tuning the emission towards green can be obtained by stabi-
[2a–c]
lizing the HOMO or destabilizing the LUMO.
For the
[
1,4]
tion.
been evaluated, mainly by using iridium
core due to its high photoluminescence efficiency and tuna-
In the case of iTMC LECs, many complexes have
former, the main route adopted consists on attaching fluo-
rine-based electron-withdrawing substituents onto the cyclo-
AHCTUNGTR(ENNNUG III) as the metal
[8a,c,e]
metalating ligands.
stituents on the ancillary ligand have been used;
examples, the fluorine-based substituents on the cyclo-
metalating ligands are also present. Therefore, the use of
For the later, electron-donating sub-
[2b,c]
[8b,d]
ble color emission.
Classically, one of the major draw-
backs of this type of devices has been the difficulty to
obtain simultaneously fast turn-on, high luminance, efficien-
in these
A
H
U
T
E
N
N
ACHTUNGTRENNUNG
fluorine-based substituents in order to obtain a blue shift of
the emission of the complex has been widely employed.
In this work, we present a new way to obtain green-emit-
[
a] D. Tordera, A. Pertegꢀs, Dr. J. M. Junquera-Hernꢀndez, Prof. E. Ortꢁ,
Dr. H. J. Bolink
Instituto de Ciencia Molecular
ting iridium ACHNTUGRNENUG( III) complexes, based on an electron-withdraw-
Universidad de Valencia
C/Catedrꢀtico J. Beltrꢀn 2, 46980 Paterna (Spain)
E-mail: enrique.orti@uv.es
ing sulfone substituent attached to the cyclometalating phe-
nylpyrazole ligand, which opens a new range of synthetic
possibilities. Six new complexes incorporating this substitu-
ent have been synthesized and their electrochemical and
photophysical properties have been characterized with the
help of density functional theory calculations. The electrolu-
minescent properties of the new complexes have been inves-
tigated showing green emission with very good efficiencies
[
b] A. M. Bꢂnzli, Prof. E. C. Constable, Dr. J. A. Zampese,
Prof. C. E. Housecroft
Department of Chemistry, University of Basel,
Spitalstrasse 51, 4056 Basel (Switzerland)
E-mail: catherine.housecroft@unibas.ch
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201300457.
Chem. Eur. J. 2013, 19, 8597 – 8609
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
8597

at high luminance levels in simple LEC devices driven at
different current densities.
Results and Discussion
Synthesis and NMR spectroscopic characterization: The
method for preparing 1-[4-(methylsulfonyl)phenyl]-1H-pyra-
zole (Hmsppz) was based upon literature routes to related
[7b]
compounds
and involved treatment of 4-bromophenyl
methyl sulfone with pyrazole in the presence of CuI under
basic conditions. The electrospray mass spectrum of Hmsppz
+
showed a peak at m/z=223.0 corresponding to [M+H] ,
1
13
and the H and C NMR spectra were in accordance with
the structure shown in Scheme 1. The dimer [{Ir(msppz) (m-
A
H
U
G
R
N
N
ACHTUNGTRENNUNG
2
2 6
Scheme 2. Synthetic route to the complexes [Ir ACHTUNGTRNEUNGN( msppz) ACHUTNRGENNU(G N^N)] ACHTUNGTRENNUNG[ PF ].
Conditions: addition of ligand 1–6 in MeOH, 1208C, 2 h in a microwave
reactor, followed by anion exchange.
1
13
The room temperature solution H and C NMR spectra
of [Ir(msppz)2 A( N^N)][PF ] (N^N=1–6) were assigned by
using COSY, NOESY, HMQC, and HMBC methods. For li-
A
H
U
G
R
N
U
G
C
U
G
R
N
U
G
ACHTUNGTRENNUNG
6
+
gands 1–4, [Ir ACHTUNGETRNN(UNG msppz) ACHTNUGTRENNU(GN N^N)] possesses C symmetry; the
2 2
introduction of the pendant phenyl substituent in 5 and 6
lowers the symmetry resulting in an inequivalence of the
ꢀ
[
msppz] ligands and of the two rings of the bipyridine
(
bpy) unit. The ring labeling (Scheme 1) allows direct com-
parison of the NMR signals in all six complexes. In the four
Me
A4
Me
A6
C -symmetric complexes, NOESY H /H and H /H
2
A4
A3
cross peaks, a COSY H /H cross peak, and a NOESY
H /H cross peak allowed H to be distinguished from
H . For [Ir ACHNTUGRENNUG( msppz) (5)] ACHTUGNTRENNUGN[ PF ] and [Ir ACHTUNGERTNNU(GN msppz) (6)] ACHTUNGRTNUNEGN[ PF ], as-
2 6 2 6
A3
B3
B3
B5
signments of the proton signals started with rings E and F,
and NOESY cross peaks were used to distinguish between
resonances for pairs of corresponding protons in rings A/C
Scheme 1. Structure of Hmsppz and the complexes, with ring and atom
numbering for the NMR spectroscopic assignments. The ligand number-
ing changes upon coordination.
and B/D. As observed for related complexes, for example
ꢀ
those containing the [dfppz]
cyclometalating ligand
[13]
(
Hdfppz=1-(2,4-difluorophenyl)-1H-pyrazole), the signal
for H appears at significantly lower frequency than that
for H . C NMR chemical shift assignments from HMQC
C6
A6 13
Cl)} ] was prepared following the method of Watts and cow-
2
orkers for the related compound [{Ir
A
H
U
G
R
N
U
G
A
H
U
G
E
N
N
(m-Cl)} ] (Hppy=
and HMBC spectra were compared with those for similar
2
2
[10]
1
13
ꢀ
[13]
2-phenylpyridine) and the H and C NMR spectra were
complexes with the [dfppz] cyclometalating ligand
similarities in the chemical shifts for analogous C nuclei
across a series of complexes provided additional support for
and
1
3
consistent with the structure shown in Scheme 2. Following
[
11]
a standard methodology,
treatment of [{Ir AHCTUNGTRENNUNG( msppz) ACHTNUGTRENNUNG( m-
2
[12]
Cl)} ] with the bipyridines 1–6
followed by exchange of
the chloride for hexafluoridophosphate ion (Scheme 2) re-
sulted in the formation of six new complexes [Ir(msppz) -
(N^N)][PF ] (N^N=1–6). The electrospray mass spectrum
the correct assignments. In [Ir ACHTUNGTRENNUN(G msppz) (5)] ACHTUNTGRENNNU[G PF ] and [Ir-
2 6
2
A
H
U
G
R
N
N
ACHTUNGTRENNUNG
2
6
A
H
U
G
E
N
N
dered rotation on the NMR timescale at 295 K. We have de-
scribed an analogous behavior in a number of [Ir(C^N) -
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
ACHTUNGTRENNUNG
6
2
+
of each complex showed a peak envelope corresponding to
ACHTUNGTRENNGNU( N^N)] complexes in which the N^N ligand bears a 6-
The resonance for H is only slight-
ly broadened, whereas that for H appears as a broad
+
[13,14]
G4
the [MꢀPF ] ion with an isotope pattern consistent with
phenyl substituent.
6
G3
that calculated.
8598
www.chemeurj.org
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 8597 – 8609

Efficient Green Light-Emitting Electrochemical Cells
FULL PAPER
signal (d=6.83 ppm, FWHMꢁ75 Hz (FWHM=full width
+
at half maximum) for [Ir
FWHMꢁ70 Hz for [Ir
A
H
U
G
R
N
U
G
2
+
ACHTUNGTNRENUNG( msppz) (6)] ). An extremely broad
2
signal is also observed in the spectrum of each complex (d=
6
6
.02 ppm, FWHMꢁ130 Hz for [Ir
.04 ppm, FWHMꢁ120 Hz for [Ir(msppz) (6)] ). Cooling a
(msppz) (6)]
ACHTUNGTNERNUN(G msppz) (5)] and d=
2
+
CD CN solution of [Ir
A
H
U
G
R
N
U
G
ACHTUNGTNERNUN[G PF ] from 295 to 250 K
6
3
leads to a collapse of the resonance at d=6.82 ppm (marked
with an asterisk in Figure 1) and evolution of two signals,
1
Figure 1. Variable-temperature H NMR spectra (500 MHz, CD
3
CN) of a
part of the aromatic region of [Ir
A
H
U
G
R
N
U
G
2
(6)]
A
H
U
G
R
N
U
G
6
]. See Scheme 1 for
ring labeling. The significance of the star (*) and dot (*) characters is ex-
plained in the text.
which appear at 250 K as broad triplets (d=6.94 and
+
Figure 2. a) Structure of the [Ir
A
H
U
G
R
N
U
G
2
(6)] cation in [Ir
A
H
U
G
R
N
N
(msppz)
2
(6)]-
G3/G5
6.70 ppm) and are assigned to H
(Figure 1). The very
.
6
AHCTUNGTRNENUG[ PF ] MeCN with hydrogen atoms omitted for clarity and ellipsoids plot-
broad resonance at d=6.04 ppm (marked with a * in
Figure 1) at 295 K sharpens on cooling to a signal at d=
ted at 40% probability level. Selected bond lengths and angles: Ir1ꢀ
C28=1.9999(16), Ir1ꢀC18=2.0171(16), Ir1ꢀN3=2.0175(14), Ir1ꢀN5=
2.0182(14),
Ir1 N1=2.1261(14),
ꢀ
Ir1ꢀN2=2.1885(14),
N3ꢀN4=
C6
5
.96 ppm (overlapping that for proton H ). The latter is as-
1
.3708(19), N5ꢀN6=1.368(2), C8ꢀS1=1.7434(17), S1ꢀC17=1.7985(19),
C22ꢀS2=1.7630(17), O1ꢀS2=1.4409(14), O2ꢀS2=1.4440(14), S3ꢀO3=
1.4403(15),
S3ꢀO4=1.4418(15), S3ꢀC37=1.756(2), S3ꢀC32=
1.7651(18) ꢄ; N1
G2
G6
signed to either H or H , and the variable-temperature
experiment reveals the second signal of this pair as a broad-
ened doublet at d=7.20 ppm. Figure 1 confirms that coales-
ꢀ
Ir1ꢀN2=76.15(5), C18ꢀIr1ꢀN3=79.97(6), C28ꢀIr1ꢀ
G2
G6
N5=80.41(6), N3ꢀIr1ꢀN5=171.43(6), C18ꢀIr1ꢀN1=178.63(6), C28ꢀ
Ir1ꢀN2=166.17(6), C8ꢀS1ꢀC17=103.28(9), O1ꢀS2ꢀO2=117.45(9), O3ꢀ
cence for exchange of H and H is not achieved at 295 K,
and it is noteworthy that, at this temperature, only one of
the two signals is observed because of the overlap of the
S3ꢀO4=118.55(9)8. b) Face-to-face stacking of the phenyl ring of ligand
ꢀ
6
with the [msppz] ligand containing atom C22.
C3
C4
second signal with the resonances for H and H (marked
with a * in Figure 1).
phenyl and the pyrazole ring planes are 11.4 and 8.28). In
the coordinated ligand 6, the bpy domain is non-planar
(angle between the pyridine rings=15.88) and the phenyl
ring is twisted through 55.08 with respect to the pyridine
ring containing atom N2. The latter distortions are associat-
ed with the intra-cation face-to-face p stacking between the
.
Single-crystal structure of [Ir
Ray quality crystals of [Ir(msppz) (6)]
grown from a MeCN solution of the compound layered with
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
2
6
.
A
H
U
G
R
N
U
G
ACHTUNGTNERNGNU[ PF ] MeCN were
6
Et O. Figure 2a shows the structure of the [Ir ACHTUNGTERNNUN(G msppz) (6)]
2
ion and important bond parameters are given in the caption.
Atom Ir1 is octahedrally sited and the cation is chiral; the
2
ꢀ
phenyl ring in 6 and the phenyl ring in the [msppz] ligand
complex crystallizes in the monoclinic space group P2 /c
containing atom C22 (Figure 2b). The rings are offset with
respect to one another (inter-centroid separation=3.59 ꢄ)
and the angle between their least square planes is 12.78, re-
sulting in a moderately efficient interaction. This example
adds to the growing number of similar complexes that we
have recently described in which the presence of the p inter-
1
with both enantiomers in the unit cell. As anticipated, atoms
N3 and N5 of the cyclometalated ligands are mutually trans.
The crystal structure confirms the presence of the methyl
[15]
ꢀ
sulfone substituents. The ring framework of each [msppz]
ligand deviates slightly from planarity (angles between the
Chem. Eur. J. 2013, 19, 8597 – 8609
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8599

C. E. Housecroft, E. Orti et al.
action is engineered to enhance the lifetime of the excited
state of the complex.
electron-withdrawing effects of the sulfone- and difluoro-
substituted C^N ligands are similar.
[13,16]
Each sulfone unit is oriented so that one SꢀO bond is
The absorption spectra of solutions of [Ir
ACHTUNGTRNENUNG( msppz) ACHTUNGTRENNUNG( N^N)]-
2
twisted towards the plane of the aromatic ring to which it is
ACHTUNGTREN[NGNU PF ] (N^N=1–6) in acetonitrile are shown in Figure 3 and
6
attached. This permits intra-cation CꢀH···O hydrogen-bond
data are given in Table 2. For ligands 1, 2, 5, and 6, the spec-
formation, consistent with general observations for organic
[17]
sulfones. Relevant torsion angles are C21ꢀC22ꢀS2ꢀO1=
ꢀ
20.5(2) and C33ꢀC32ꢀS3ꢀO3=15.9(2)8 with hydrogen-
bond distances of O1···H21a=2.61 and O3···H33a=2.56 ꢄ.
ꢀ
Both the [PF ] ion and the MeCN solvent molecule are or-
6
dered. Packing in the lattice is dominated by CꢀH···NMeCN
,
CꢀH···F, and CꢀH···O contacts.
Preliminary crystallographic data for [Ir
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
2
6
[
Ir
(msppz) (4)] ACHTUNGTRENNUNG[ PF ] confirm the gross structural features of
6
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (2)]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[PF ],
[Ir
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
and
[Ir-
2
6
2
6
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
each complex (octahedral iridium ACHTUNGRNENUG( III), cyclometalation of
Hmsppz, and the chelating ligand 1–4). However, twinning
of all crystals screened limited the quality of the data.
Electrochemical and photophysical studies: Each of the [Ir-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(N^N)]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[PF ] complexes is redox active and Table 1
Figure 3. Electronic absorption spectra of [Ir
A
H
U
G
E
N
N
2A
H
U
G
R
N
U
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[PF ]
2
6
6
(
N^N=1 (&), 2 (*), 3 (~), 4 (
&
gives the cyclic voltammetric data. The complexes exhibit
ꢀ
5
ꢀ3
1
0
moldm ).
Table 1. Cyclic voltammetric data with respect to ferrocene/ferrocenium
+
(
Fc/Fc ); CH
3
CN solutions with [tBu
4
N]
A
H
U
T
E
N
N
[PF
6
] as supporting electrolyte
2 6
Table 2. Photophysical properties measured for [Ir ACHTUNGRTENUNGN( msppz) ACHUTNRGENNU(G N^N)] ACHTUNGTRENNUNG[ PF ]
with N^N=1–6.
ꢀ
1
and a scan rate of 0.1 Vs ; unless otherwise stated, the electrochemical
processes are reversible or near-reversible (ir=irreversible; qr=quasi-re-
versible).
[
a]
Solution
Diluted
Device
configuration
[b]
[c]
film
ox
=2
red
1=2
E1 [V]
E
[V]
DE1/2 [V]
max
abs
max
max
em
max
l
l
t
Fem
l
Fem
l
Fem
em
em
ir
ir
ir
ir
ir
[Ir
[Ir
[Ir
[Ir
[Ir
[Ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz)
(msppz)
(msppz)
(msppz)
(msppz)
(msppz)
2
2
2
2
2
2
(1)]
(2)]
(3)]
(4)]
(5)]
(6)]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[PF
[PF
[PF
[PF
[PF
[PF
6
6
6
6
6
6
]
]
]
]
]
]
+1.27, +1.77
+1.19, +1.77
ꢀ1.68, ꢀ2.37
ꢀ1.85, ꢀ2.49
ꢀ1.74, ꢀ2.32
ꢀ2.17
2.95
3.04
2.93
3.22
3.02
2.94
[nm] [nm] [ns] [%] [nm] [%] [nm]
[%]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
ACHTUNGTRENNUNG
[Ir
[Ir
[Ir
[Ir
[Ir
[Ir
A
H
N
T
E
N
N
2
2
2
2
2
2
(1)]
(2)]
(3)]
(4)]
(5)]
(6)]
A
T
N
T
N
U
G
6
6
6
6
6
6
] 252 518
] 252 504
92 71
85 80
495 92
487 91
505 94
493 65
495 86
506 92
508
497
518
510
503
519
85
53
60
30
53
51
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
+1.19
A
H
U
G
E
N
N
ACHTUNGTRENNUNG
qr
ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
+1.05 , +1.52
+1.24
A
H
U
G
E
N
N
A
H
N
T
E
N
G
] 266 516 116 77
ir
ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
ꢀ1.78, ꢀ2.39
ꢀ1.73, ꢀ2.32
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
] 262 492
] 259 506
76 50
99 38
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
+1.21
A
H
N
R
N
U
G
ACHTUNGTRENNUNG
A
H
U
T
N
U
G
A
H
N
T
E
U
G
] 258 516 136 66
ꢀ5
ꢀ3
[
a] MeCN solution (2.50ꢅ10 moldm ). [b] 5% by weight in a poly-
ylmethacrylate (PMMA) matrix. lexc =314 nm. [c] Mixed with the
liquid 1-butyl-3-methylimidazolium hexafluoridophosphate
[PF ] in a 4:1 molar ratio. lexc =314 nm.
A
H
U
G
R
N
N
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
one or more bpy-centered reduction processes. Reductions
ꢀ
A
H
U
G
R
N
U
G
6
centered on the [msppz] ligand are not observed within the
accessible solvent window (to ꢀ3 V); replacing pyridine by
pyrazole in the C^N ligand produces a significant increase
in the level of the LUMO. In Table 1, the first or only oxida-
tion wave is assigned to an iridium-based process and is re-
versible or quasi-reversible in all cases. On going from [Ir-
tra are similar and exhibit intense absorptions with l
the range 252–266 nm arising from ligand-based p* p tran-
in
max
!
sitions. The presence of the SMe or NMe substituents in li-
2
+
+
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(ppy) (1)] to [Ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (1)] , this oxidation shifts from
gands 3 and 4 results in an increased intensity of the ligand-
2
[
2
18]
+
0.84 to +1.27 V, which is consistent with the electron-
based absorptions in [Ir
ACTHUNGTRENNUN(G msppz) (3)] ACHTUNGTRENUNN[G PF ] and [Ir-
2 6
withdrawing effects of the sulfone groups in the cyclometa-
A
H
U
G
R
N
N
ACHTUNGTRENNUNG
2
6
lated ligand. A shift to less positive potentials is observed
the bpy-centered p system.
Solutions of the [Ir(msppz) ACHTUNGTRENNNU(G N^N)] AHCTUNGTRENNNU[G PF ] complexes in
2 6
acetonitrile are emissive when excited at approximately
360 nm and the emission maxima are given in Table 2. The
photoluminescence (PL) bands are broad and unstructured
+
for the iridium oxidation on going from [Ir
A
H
U
G
R
N
U
(msppz) (1)] to
A
H
U
G
R
N
U
G
2
+
+
[Ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (2)] or [Ir
A
H
U
G
E
U
(msppz) (4)] as electron-donating
2
2
tBu or NMe2 substituents are introduced into the N^N
ligand. The SMe groups in 3 also decrease the oxidation po-
tential. A comparison can also be made between the com-
(Figure 4). By taking [Ir ACHTUNTGNERNUG( msppz) (1)] ACTHUNGTERNNNUG[ PF ] as a benchmark,
2 6
+
ꢀ
ꢀ
pounds [Ir
Hdfppz=1-(2,4-difluorophenyl)-1H-pyrazole). For the
former, oxidation of the metal center occurs at +1.24 V
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(C^N) (5)] with C^N=[msppz] or [dfppz]
Figure 4 illustrates that introduction of the NMe substitu-
2
2
(
ents into the bpy ligand causes a blue shift in lem from 518
(1) to 492 nm (4). A small blue shift is also observed upon
introducing tert-butyl substituents on going from [Ir-
[14b]
compared to +1.21 V for the latter,
indicating that the
8600
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Chem. Eur. J. 2013, 19, 8597 – 8609

Efficient Green Light-Emitting Electrochemical Cells
FULL PAPER
Figure 4. Room temperature, solution emission spectra of [Ir
A
H
U
G
R
N
U
G
2
-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(N^N)]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[PF
6
] (N^N=1 (&), 2 (*), 3 (~), 4 (
.50ꢅ10 moldm ).
&
3
ꢀ
5
ꢀ3
2
ACHTUNGTRENNUNG( msppz) (1)] ACHTUNGTRENNUNG[ PF ] (518 nm) to [Ir ACHTUNGTRNENU(GN msppz) (2)] ACHTUNGRTUNNEGN[ PF ] (504 nm)
2 6 2 6
or [Ir
ACHTUNGTRENNUNG( msppz) (5)] ACHTUNGTRENNUNG[ PF ] (506 nm). This is consistent with the
2 6
electron-donating properties of the tBu and NMe groups.
2
We note that the emission maximum of [Ir
492 nm) is essentially the same as that of [Ir ACHTUNGTERNNUN(G dfppz) (4)]-
2
ACTHUNGTRNENUN(G msppz) (4)] ACHTUNRTGENNNU[G PF ]
2 6
(
[14b]
A[ PF ] (493 nm),
C
H
T
U
N
G
T
R
E
N
N
U
N
G
indicating that the electron-withdrawing
6
ꢀ
ability of the methylsulfone group in [msppz] is comparable
ꢀ
to that of the fluoro-substituents in [dfppz] ; this is also sup-
2
Figure 5. Photoluminescence spectra in thin-films of [Ir AHCTUNGERTNNUNG( msppz) ACHTUNGTRENNUNG( N^N)]-
AHCTUNGTERNNUNG[ PF ), 4 (
6
] (N^N=1 (&), 2 (*), 3 (~
&
), 5 (*), and 6 (~)): a) 5% in
ported by the electrochemical data described above. The
presence of SMe substituents in the N^N ligand has a negli-
gible effect upon the emission (lem =516 nm in both [Ir-
weight in PMMA and b) mixed with the ionic liquid 1-butyl-3-methylim-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
H
U
G
R
N
U
G
A
T
N
T
E
N
N
A
H
U
G
R
N
U
G
6
ACHTUNGTRENNUNG( msppz) (3)] ACHTUNGTRENNUNG[ PF ] and [Ir ACHTUNGTERNNNU(G msppz) (6)] ACHTUNTGNERNU[G PF ]).
2 6 2 6
The photoluminescence quantum yields (Fem or PLQY)
of degassed solutions of the [Ir(msppz) (N^N)][PF ] com-
plexes in acetonitrile are listed in Table 2. They exhibit
quantum yields of 50, 38, and 66% for complexes with
N^N=4, 5, and 6, respectively, and notably high PLQYs of
corporating tert-butyl substituents (2 and 5) are more blue
shifted. The red shift of the PL maxima when comparing the
films in a device configuration with the films in a diluted
configuration can be attributed to concentration effects. The
measured PLQYs are 92, 91, 94, 65, 86, and 92% for N^N=
1–6, respectively, in the diluted configuration, and 85, 53, 60,
30, 53, and 51% for N^N=1–6, respectively, in the device
configuration. These quantum yields are amongst the high-
A
H
U
G
R
N
N
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
2
6
71, 80 and 77% for complexes containing N^N=1, 2, and 3,
respectively. It is noteworthy that degassing the complex-
containing acetonitrile solutions with argon for 15 min led
to PLQY values that increase by a factor up to ten. This in-
dicates a strong quenching of the phosphorescence by
oxygen.
The PL spectra and quantum yields of the complexes
were also studied in thin solid films in both diluted and
device configuration. In the diluted configuration, the com-
III
est reported for green-emitting Ir complexes. The PLQY
values in the device configuration remain high, yet they are
significantly lower than in the diluted configuration because
of the increased self-quenching between neighboring com-
plexes. Surprisingly, in the device configuration, the quan-
tum yield for the complex with N^N=1, despite having no
substituent on the ancillary ligand, remains extremely high
when compared to the other complexes. This higher quan-
tum yield translates into a higher efficacy in the electrolumi-
nescent device as is shown below. The reason for this is not
clear, because no bulky group is present, and it is most
likely due to differences in the packing of the complexes in
the film.
plexes were dispersed 5% by weight in a poly
rylate (PMMA) matrix. The device configuration consisted
of the complex mixed with the ionic liquid (IL) 1-butyl-3-
methylimidazolium hexafluoridophosphate [BMIM][PF ] in
ACHTUNGERTNNUNmG eth ACHTUNRTGENNUNyG l ACHTUNGTERNNNUmG eth ACHTUNGERTNNUGNa c-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
AHCTUNGTRENNUNG
6
a 4:1 molar ratio, which corresponds to the configuration
used in LEC devices.
The thin-film solid-state PL spectra exhibit unstructured
broad emissions (Figure 5) typical for complexes containing
a combination of cyclometalated and neutral diimine li-
Theoretical calculations: To gain further insight into the
[19]
gands, the maxima are given in Table 2. A slight red shift
is observed for the complexes incorporating thiomethyl sub-
stituents on the ancillary ligand (3 and 6), whereas those in-
electrochemical and photophysical properties, the molecular
+
and electronic structures of the [Ir
A
H
U
G
R
N
U
G
A
H
U
G
E
N
N
(N^N)] ions, in
2
both ground and excited states, were investigated by per-
Chem. Eur. J. 2013, 19, 8597 – 8609
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8601

C. E. Housecroft, E. Orti et al.
+
forming density functional theory (DFT) calculations at the
B3LYP/(6-31G**+LANL2DZ) level in the presence of the
solvent (acetonitrile).
ACHTUNGTNERNU(GN msppz) (2)] , for which the phenyl group is lacking, is
2
almost planar (1.48). Complexes with N^N=1, 2, and 4 also
show nearly planar bpy ligands.
Calculations on the electronic ground state (S ) correctly
reproduce the near-octahedral coordination of the Ir metal
Figure 6 shows the energies calculated for the HOMO
and LUMO of all complexes, and Figure 7 compares the
molecular orbital distribution found for complexes [Ir-
0
and predict the geometric parameters in good accord with
+
the experimental data. For instance, for the [Ir ACHTUNGTRENN(UNG msppz) (6)]
2
ion, the values computed for the bite angles formed by the
N^N and C^N ligands with the Ir center (N1ꢀIr1ꢀN2: 74.6,
N3ꢀIr1ꢀC18: 79.1, and N5ꢀIr1ꢀC28: 79.48) are in good
agreement with the X-ray data (76.15(5), 79.97(6), and
80.41(6)8, respectively). The optimized values calculated for
the bond distances and the bond angles defining the coordi-
nation sphere of the iridium center are collected in Table S1
(
see the Supporting Information) for all the complexes. The
sulfone units are always obtained to be oriented so that the
methyl group is perpendicular to the plane of the aromatic
ring to which they are attached and the two SꢀO bonds
form intra-cation CꢀH···O hydrogen bonds with average dis-
Figure 6. Energy diagram showing the energies (in [eV]) calculated for
+
the HOMOs and LUMOs of [Ir
A
H
U
G
R
N
U
G
2
A
H
U
G
R
N
U
(N^N)] (N^N=1–6).
tances of 2.55 and 2.66 ꢄ, respectively. This is consistent
with the experimentally determined crystal structure of [Ir-
+
+
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (6)]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[PF ].
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
2
6
2
2
For complexes with N^N=5 and 6, calculations correctly
predict the intra-cation face-to-face p stacking of the pend-
ant phenyl substituent of the bpy ligand with the phenyl ring
ples. Despite the fact that the HOMO is localized on the Ir
center and the phenyl rings of the cyclometalated C^N li-
gands (see Figure 7), the substitution pattern of the ancillary
ligand has a measurable effect on the energy of this orbital
and therefore on the oxidation potential. The attachment of
ꢀ
of the adjacent [msppz] ligand. The inter-centroid distance
+
computed for [Ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (6)] (3.80 ꢄ) slightly overesti-
2
mates the X-ray value (3.59 ꢄ) likely due to the packing
forces acting in the crystal. The angle between the pyridine
rings in the bpy domain (16.68) and the angle between the
planes of the phenyl ring and the nearest pyridine ring
the electron-donating tBu and NMe2 groups to the bpy
ligand slightly destabilizes the HOMO of [Ir ACHTUNGTRENN(UNG msppz) (2)]
2
+
+
(ꢀ5.79 eV) and [Ir
A
H
U
G
R
N
N
(msppz) (4)] (ꢀ5.73 eV) compared with
2
+
[Ir
A
T
N
T
E
N
G
2
(
58.58) reproduce well the X-ray values (15.8 and 55.08, re-
the progressive cathodic shift observed for the first oxida-
+
spectively). The non-planarity of the coordinated bpy ligand
tion potential on going from [Ir ACHUTNGTNERNUG( msppz) (1)] (+1.27 V) to
2
+
+
is due to the steric effects introduced by the phenyl substitu-
[Ir ACHTNUGERTNNNUG( msppz) (2)] (+1.19 V) and [Ir ACHTNUGTRENNU(GN msppz) (4)] (+1.05 V)
2 2
+
ent. For instance, complex [Ir
A
H
U
G
R
N
U
G
(Table 1). The introduction of the pendant phenyl ring in
2
ing angle of 16.58 for the bpy domain, which is similar to
the complex with N^N=5 partially compensates the effect
+
+
that calculated for [Ir
A
H
U
G
E
N
N
(msppz) (6)] , whereas complex [Ir-
of the tBu groups and the [Ir
A
H
U
G
R
N
U
G
2
2
ꢀ
3
Figure 7. Schematic representation showing the electron-density contours (0.03 ebohr ) and the energy values (in [eV]) calculated for the highest occu-
+
pied and lowest unoccupied molecular orbitals of [Ir
clarity.
2
ACHTUNGTRENNUN(G msppz) ACHUTNGTRENNNU(G N^N)] with N^N=1 (left) and N^N=4 (right). Hydrogen atoms have been omitted for
8602
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Efficient Green Light-Emitting Electrochemical Cells
FULL PAPER
+
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (5)] complexes present similar HOMO energies
NMe groups and may lead to changes in the nature of the
2
2
(
ꢀ5.87 and ꢀ5.85 eV, respectively) and close oxidation po-
emitting state.
tentials (+1.27 and +1.24 V, respectively).
The nature of the emitting excited state was investigated
by fully optimizing the electronic and molecular structures
of the lowest triplet state (T ) by using the spin-unrestricted
UB3LYP approach. After full-geometry relaxation, the T1
state is computed to lie in the range 2.66–2.84 eV above S0
(adiabatic energy differences, DE in Figure 8a). These ener-
The substitution pattern of the ancillary N^N ligand has a
larger effect on the energy of the LUMO (see Figure 6) be-
cause this orbital fully resides on the bpy ligand (see
Figure 7 for complexes with N^N=1 and 4). The energy of
the LUMO significantly increases by passing from N^N=1
1
(
ꢀ2.17 eV) to 2 (ꢀ1.99 eV) and especially to 4 (ꢀ1.62 eV)
gies are similar to those obtained for analogous [Ir ACHTUNGTRENNUNG( dfppz) -
2
due to the attachment of the electron-donating tBu and
NMe groups. This justifies the cathodic shift measured for
2
+
the first reduction potential of [Ir
and [Ir
A
H
U
G
R
N
U
G
2
+
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (4)]
(ꢀ2.17 V) compared with [Ir-
2
+
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (1)] (ꢀ1.68 V). The SMe groups present in com-
2
plexes with N^N=3 and 6 have no significant effect on the
energies of the HOMO and LUMO (Figure 6). The
HOMO–LUMO energy gap therefore has a value of ap-
proximately 3.70 eV for complexes with N^N=1, 3, and 6,
presents an intermediate value of approximately 3.85 eV for
complexes with N^N=2 and 5, and increase to 4.10 eV for
the complex with N^N=4 that incorporates the most elec-
tron-donating NMe2 groups. This trend fully justifies the
evolution of the electrochemical gap, which increases from a
value of approximately 2.94 V for N^N=1, 3, and 6, to
about 3.03 V for N^N=2 and 5, and finally to 3.22 V for the
complex with N^N=4 (Table 1) and is in agreement with
the blue shifts observed in the emission spectra (Table 2).
The energies obtained for the HOMO (ꢀ5.73 eV), the
Figure 8. a) Schematic energy diagram showing the adiabatic energy dif-
ference (DE) between the S and T states and the emission energy (Eem
from T calculated for complexes [Ir
paired-electron spin density contours (0.003 ebohr ) calculated for b)
0
1
)
LUMO (ꢀ1.62 eV), and the HOMO–LUMO gap (4.10 eV)
+
1
2
ACHTUNGTRENNUN(G msppz) ACHTNUGTRENNNU(G N^N)] (N^N=1–6). Un-
+
ꢀ3
for [Ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (4)] are almost identical to those previously
2
+
+
+
1 2 2
the fully relaxed T state of [Ir ACHTNUGTRENNUG(N msppz) (1)] and c) [Ir ACHTUNGRNNEG(U msppz) (4)] .
reported for the complex [IrACHTGNUTRENNUNG
.07 eV, respectively).
trochemical potentials obtained for [Ir
2
[14b]
4
This explains the very similar elec-
+
ox
1=2
A
H
U
G
R
N
U
G
=
+
2
red
+
+
(
1.05, E1 =ꢀ2.17, DE1/2 =3.22 V) and [Ir
(dfppz) (4)]
A
H
U
G
R
N
U
G
complexes (2.69–2.84 eV) incorporating the
=2
ox
=2
red
ꢀ
E1 =+1.04, E =ꢀ2.15, DE =3.19 V), and demonstrates
[dfppz] ligand and are significantly larger than that calcu-
1=2
1/2
+
[14b]
that the electron-withdrawing sulfone substituent attached
to the ppz ligands has an effect on the electronic structure
lated for [Ir
A
H
U
G
R
N
N
(ppy) (1)] (2.40 eV).
For [Ir ACHTUNGENTRNUNG( msppz) -
2
2
+
AHCTUNGTREGUN(NN N^N)] complexes with N^N=1–3, 5, and 6, the T state
1
of the complex equivalent to that obtained when using
mainly results from the HOMO!LUMO monoexcitation
and implies an electron transfer from the Ir–msppz environ-
ment to the bpy ligand. This is illustrated in Figure 8b by
ꢀ
[dfppz] ligands, where two fluorine atoms are introduced in
the 2- and 4-position.
The atomic orbital composition calculated for the HOMO
and the LUMO suggests that the lowest-energy triplet state
should correspond to a mixed metal-to-ligand/ligand-to-
ligand charge-transfer (MLCT/LLCT) state as already re-
the unpaired-electron spin density distribution calculated for
+
[Ir
A
H
U
G
R
N
U
G
2
fectly matches the topology of the HOMO!LUMO excita-
tion (see Figure 7, left). Similar spin density distributions
are obtained for complexes with N^N=2, 3, 5, and 6 (see
Figure S1 in the Supporting Information). The electron
+
[6b,14b,16d–-
ported for analogous [Ir ACHUTNGRENNU(G C^N) ACHUTNGTRENNNU(G N^N)] complexes.
2
f,19a,20]
However, the molecular orbital distribution is not the
+
same for all the [Ir
A
H
U
G
R
N
N
(msppz)
A
T
N
T
N
N
(N^N)] (N^N=1–6) com-
transfer associated with the excitation to the T state causes
2
1
plexes. As depicted in Figure 7, the HOMOꢀ1 and
a small contraction of the coordination sphere of the iridium
centre (Table S1 in the Supporting Information) and de-
creases the twisting of the bpy ligand for complexes with
N^N=5 and 6 (10.48), for which the intra-cation p stacking
is preserved.
+
HOMOꢀ2 of [Ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (1)] are well separated in energy
2
from the HOMO and are located on the Ir–pyrazole envi-
ronment. This is also the case for complexes with N^N=2,
3
, 5, and 6. In contrast, the HOMOꢀ1 and HOMOꢀ2 of the
+
complex [Ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (4)] are nearly degenerate with the
Therefore, the calculations suggest that the emitting T1
state for complexes with N^N=1–3, 5, and 6 has a mixed
2
HOMO and correspond to combinations of Ir-(t ) and p or-
2
g
3
3
bitals of the ancillary ligand (see Figure 7, right). The high
energy of these orbitals is due to the electron-donating
MLCT/ LLCT character in agreement with the broad and
unstructured aspect of the emission bands (Figure 4). How-
+
ever, this is not the case for [Ir ACHTGNUTERNN(UNG msppz) (4)] , for which the
2
Chem. Eur. J. 2013, 19, 8597 – 8609
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8603

C. E. Housecroft, E. Orti et al.
3
T state converges to a p–p* ligand-centered ( LC) triplet of
1
the 4,4’-dimethylamino-2,2’-bipyridine ligand with a small
contribution from the metal (0.11 e) (see Figure 8c). As dis-
+
cussed above, the difference for [Ir
A
H
U
G
R
N
U
G
2
this complex the HOMOꢀ1 and HOMOꢀ2, which are
mostly concentrated on the ancillary ligand, lie very close in
energy (ꢀ5.74 eV) to the HOMO (ꢀ5.73 eV) (see Figure 7,
right). As a consequence, the HOMOꢀ2!LUMO and
3
HOMOꢀ1!LUMO excitations give rise to LC states
lower in energy than the HOMO!LUMO excitation (see
TD-DFT results in Table S2 in the Supporting Information)
3
and the emitting T state has a predominant LC character.
1
This can explain the lower PLQY values measured experi-
Figure 9. Electroluminescence spectra of films composed of the complex
+
mentally for [Ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (4)] .
2
2 6
[ AHCTNUGTRENNNGU( msppz) ACHTUGNTREUNN(G N^N)] ACHTGNRUETNNUG[ PF
] (N^N=1 (&), 2 (*), 3 (~), 5 (*), and 6 (~))
Ir
mixed with the ionic liquid 1-butyl-3-methylimidazolium hexafluorido-
phosphate [BMIM][PF ] in a molar ratio of 4:1.
To estimate the phosphorescence emission energy, the ver-
tical energy difference between T and S was computed by
A
H
U
G
R
N
U
G
6
1
0
performing a single-point calculation of S at the optimized
0
minimum-energy geometry of T (E in Figure 8a). The cal-
1
em
culations lead to vertical emission energies that shift to the
blue in passing from complexes with N^N=1 (515 nm), 3
tive to fluorine-based substituents in order to obtain green-
emitting complexes.
(
(
525 nm), and 6 (521 nm) to complexes with N^N=2
490 nm), 4 (487 nm), and 5 (492 nm), which is in good
To determine the performance of the devices, the LECs
were operated under a block-wave pulsed-current driving
scheme at 1000 Hz with 50% duty cycle and average (over
the on- and off-pulse) current densities of 100, 50, and
agreement with the experimental emission maxima recorded
in solution (Table 2). The emission energies again demon-
strate that the sulfone substituent affects the electronic
structure of the complex in a similar way to the attachment
of fluorine atoms. For instance, the emission energy calculat-
ed for [Ir
to that obtained for [Ir
which is in perfect agreement with experimental measure-
ments (492 and 493 nm, respectively).
use of sulfone electron-withdrawing groups as an alternative
strategy to blue shift the emission of the complex.
ꢀ
2
25 Am . This operation mode is preferred over the one
using a constant voltage as it leads to higher stabilities and
faster turn-on. The performance of the LECs follows the
same trend independent on the complex employed. For
clarity, the luminance, voltage, and efficiency are depicted
versus the operation time for the best performing device
(Figure 10). The figures of merit of the LECs using the
other complexes are summarized in Table 3. Upon turning-
on the device, the average applied voltage drops rapidly
over the first seconds and then remains almost constant for
the duration of the experiment. This is due to the high initial
barriers for electron and hole injection that require a higher
voltage to sustain the current density applied. When this
high voltage is applied, fast ionic motion is induced that re-
duces the injection barriers and leads to a gradual decrease
of the operation voltage to the value needed for the bulk
transport.
The luminance decreases with a decreasing current densi-
ty. This decrease is not in all devices proportional to the de-
crease in the current density, which leads to differences in
the current efficiency or efficacy. For the LECs using com-
plexes with N^N=3, 5, and 6, the efficacy is independent
on the current density. This is remarkably different for the
LECs using complexes with N^N=1 and 2, for which the ef-
ficacy increases strongly upon reducing the current density.
Therefore, it appears that the devices using complexes with
N^N=1 and 2 are rather optimized and, upon reducing the
current density, less quenching of excitons occurs leading to
a higher relative luminance and hence efficiency. It appears
therefore that in LECs using complexes with N^N=3, 5,
and 6, the efficiency is limited by other factors. This assump-
tion is in agreement with the lower values obtained for
these devices.
+
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz) (4)] (2.54 eV, 487 nm) is nearly identical
2
+
ACHTUNGTRENNUNG( dfppz) (4)] (2.53 eV, 488 nm),
2
[14b]
This supports the
Electroluminescent devices: To study the electroluminescent
behavior of complexes [Ir
–3, 5, and 6, LEC devices were prepared. A 90 nm layer of
poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)
PEDOT:PSS) was spin-coated on top of a patterned
indium tin oxide (ITO) coated glass substrate followed by a
0 nm emitting layer consisting of one of the complexes and
the ionic liquid [BMIM][PF ] at a molar ratio of 4:1. The
ACHTUNGTRENNUNG( msppz) ACHUTNGERTNNUNG( N^N)] ACHNUTGTERNNUN[G PF ] with N^N=
2 6
1
(
9
A
H
U
G
R
N
U
G
6
latter was added to reduce the turn-on time. The devices
were moved into an inert atmosphere glovebox and were
annealed at 1008C during one hour. A 70 nm aluminium
layer was thermally evaporated as the top electrode contact.
Devices from complex with N^N=4 were not prepared due
to the low PLQY obtained in the thin-film device configura-
tion.
The electroluminescence (EL) spectra are shown in
Figure 9. The spectra are rather similar to those obtained by
photo-excitation (Figure 5). The CIE coordinates are (0.31,
0
.53), (0.27, 0.50), (0.33, 0.56), (0.29, 0.50), and (0.33, 0.55)
for complexes with N^N=1–3, 5, and 6, respectively. All
the complexes are found in the green region of the CIE co-
ordinate map showing that the attachment of methylsulfone
substituents to the cyclometalating ligands is a good alterna-
8604
www.chemeurj.org
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 8597 – 8609

Efficient Green Light-Emitting Electrochemical Cells
FULL PAPER
[8c]
as the number of fluorine atoms is increased. In the case
of LECs using [Ir(msppz) (N^N)][PF ] complexes, there are
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
2
6
no fluorine atoms and yet the stability is also low. This sug-
gests that the presence of fluorine substituents in the com-
plex is not the only reason for the poor stabilities of green
and blue LECs.
Conclusion
III
A series of green-emitting Ir complexes incorporating sul-
fone substituents on the cyclometalating ligand has been
presented. The electron-withdrawing sulfone group leads to
a blue-shifted emission when compared to complexes based
on the unsubstituted phenylpyridine ligand. Six complexes,
all having identical cyclometalating phenylpyrazole ligands
but differently substituted bipyridine ancillary ligands, were
prepared and evaluated. They exhibit very high photolumi-
nescence quantum yields (>80%) when dispersed in a thin
film of PMMA, with the exception of the complex contain-
ing the 4,4’-dimethylamino-2,2’bipyridine ligand (4). Quite
remarkable is the very small decrease in the photolumines-
cence quantum yield with an increasing concentration of the
complex in the thin film. The best complex when prepared
in a thin film with more than 90% in weight still has a pho-
toluminescent quantum efficiency above 85%. This indicates
a very low exciton quenching between the different com-
plexes. When evaluated in LECs, the devices exhibit green
emission with good efficiencies at high luminance values.
Even though no fluoride substituent is used on the com-
plexes, also in these LECs the stability is not very good.
Hence, the low device stability observed for LECs contain-
ing wide-band-gap iTMCs is not only due to the presence of
fluorine atoms.
Figure 10. Device performance of the LEC using [Ir
2 6
ACHTUNGTRENUNNG( msppz) (1)] ACHTUNGRETNNUN[G PF ] at
different average current densities (100 (squares), 50 (dots), and
ꢀ
2
2
5 Am (triangles)). Top: Luminance (closed symbols) and average volt-
age (open symbols). Bottom: Efficacy (closed symbols) and power effi-
ciency (open symbols).
Table 3. Performance of the LEC devices of complexes [Ir
2
ACHTUNGTNERUNNG( msppz) -
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(N^N)][PF ] with N^N=1–3, 5, and 6 biased with a block-wave-pulsed
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
6
current at a frequency of 1000 Hz and a duty cycle of 50% at different
current densities.
[
a]
Current
density
t
on
Lummax
t
1/2
Efficacy
Power
EQE
[%]
ꢀ
2
ꢀ1
[b]
[s]
A[ cdm
C
H
T
U
N
G
T
R
E
N
N
U
N
G
]
A
H
U
G
R
N
N
[min]
A[ cdA
H
U
G
R
N
U
]
efficiency
ꢀ
2
ꢀ1
A[ Am
C
H
T
U
N
G
T
R
E
N
N
U
N
G
]
A
H
U
G
R
N
U
G
]
1
2
3
5
6
25
<5
<5
<5
<5
7
<5
<5
19
<5
<5
<5
<5
350
<5
334
657
1127
80
890
992
125
254
790
238
338
853
43
54
23
14
13.5
12.8
10.4
2.7
15.5
9.3
5.1
4.7
7.2
9.4
6.8
6.4
5.0
0.9
5.7
3.0
2.5
2.0
2.2
4.4
3.1
3.2
0.4
2.4
4.3
4.1
3.3
0.9
4.9
2.9
1.6
1.4
2.2
2.9
2.1
2.5
0.2
2.3
5
0
1
1
1
00
25
0.2
3.0
3.0
7.7
4.0
1.5
12
5.4
3.3
35
5
0
Experimental Section
00
25
1
13
5
0
General: H and C NMR spectra were recorded on a Bruker Avance
III-500 NMR spectrometer (chemical shifts with respect to d(TMS)=
00
25
ACHTUNGTRENNUNG
0 ppm). Solution electronic absorption and emission spectra were record-
ed on an Agilent 8453 spectrophotometer and Shimadzu 5301PC spectro-
fluorophotometer, respectively. A Shimadzu 8400S instrument with
5
0
6.8
8.1
0.8
7.3
1
00
50
00
golden gate accessory was used to record the FTIR spectra of solid sam-
1
796
3.1
ples. Electrospray ionization (ESI) mass spectra were measured by using
plus
a Bruker esquire 3000
mass spectrometer. Electrochemical measure-
ꢀ
2
[
a] Taken as the time needed to reach 100 cdm . If the maximum lumi-
ments were carried out by using cyclic voltammetry and were recorded
by using a VersaSTAT 3 potentiostat from Princeton Applied Research
with glassy carbon working and platinum auxiliary electrodes; a silver
wire was used as a pseudo-reference electrode. Solvent was dry, purified
ꢀ
2
nance (Lummax) is less than 100 cdm , ton is taken as the time to reach
maximum luminance. [b] EQE=external quantum efficiency.
MeCN and 0.1m [nBu
4 6 2
N] ACHTUNGERTUNNNG[ PF ] was used as supporting electrolyte. Cp Fe
The turn-on time of the complexes is in the range of sec-
onds, as a result of the pulsed-current driving. The lifetime
of the devices (t , defined to be the time for the luminance
to decay from the maximum to half of the maximum) is
rather short. This is also observed with most other green-
and green-blue-emitting LECs. In previous studies it has
been suggested that the stability is related to the number of
fluorine atoms in the complex with a decrease in the lifetime
(
Cp=cyclopentadienyl) was used as internal reference. A Biotage Initia-
tor 8 reactor was used for the syntheses under microwave conditions.
Melting points were measured by using a Krꢂss Optronic Melting Point
Meter M5000. Fluka silica 60 and Merck alumina 90 were used for
column chromatography. NH
used without further purification.
1/2
4 6
PF was purchased from Alfa Aesar and
Hmsppz: 4-Bromophenyl methyl sulfone (5.00 g, 21.1 mmol, 1 equiv),
pyrazole (2.15 g, 31.6 mmol, 1.5 equiv), CuI (0.401 g, 2.11 mmol,
0.1 equiv), K CO (8.73 g, 63.2 mmol, 3 equiv), and l-proline (0.485 g,
2 3
Chem. Eur. J. 2013, 19, 8597 – 8609
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8605

C. E. Housecroft, E. Orti et al.
4
.21 mmol, 0.2 equiv) were combined in dry DMSO (120 mL) under an
inert atmosphere and the mixture was heated at 1308C for 24 h. After
this time, aqueous NH OH (25%, 200 mL) and H O (100 mL) were
added. A precipitate formed, which was separated by filtration, dissolved
in CH Cl , washed with aqueous NH OH (25%) and H O (twice), and
dried over MgSO . Residual solvent was evaporated under reduced pres-
sure and the product was purified by column chromatography (Fluka
silica gel 60, 0.040–0.063 mm, CH Cl /ethyl acetate 5:1). Hmsppz was iso-
lated as an off-white solid (2.60 g, 0.012 mmol, 56%). M.p. 138.38C;
(Merck alumina 90 standardized, CH
100:1 changing to 100:5, followed by Fluka silica gel 60, 0.040–0.063 mm,
CH Cl changing to CH Cl /MeOH 100:1 changing to 100:5). Recrystalli-
zation in MeCN/Et O yielded [Ir(msppz) (2)][PF ] as a yellow solid
(55 mg, 0.053 mmol, 35%). H NMR (500 MHz, CD CN, 295 K): d=8.50
2 2 2 2
Cl changing to CH Cl /MeOH
4
2
2
2
2
2
2
A
H
U
G
R
N
U
2
A
H
U
G
E
N
N
6
1
2
2
4
2
3
E3
B3
(d, J=3.0 Hz, 2H; H ), 8.49 (d, J=2.0 Hz, 2H; H ), 7.95 (d, J=5.9 Hz,
4
E6
A3+A4
2H; H ), 7.66 (overlapping m, 4H; H
), 7.51 (dd, J=5.9, 2.0 Hz,
E5
B5
A6
2H; H ), 7.11 (d, J=2.3 Hz, 2H; H ), 6.75 (d, J=1.8 Hz, 2H; H ),
2
2
B4
Me
6.70 (dd, J=2.9, 2.4 Hz, 2H; H ), 2.94 (s, 6H; H ), 1.42 ppm (s, 18H;
1
B3/B5
Bu
13
E4
E2
H NMR (500 MHz, CD
3
CN): d=8.26 (dd, J=2.5, 0.4 Hz, 1H; H
), 7.77 (d, J=1.6 Hz, 1H; H
),
), 6.57 (dd, J=2.6,
CN):
3
H ); C NMR (126 MHz, CD CN, 295 K): d=165.6 (C ), 157.0 (C ),
A2A3
B3/B5
E6
A2
B5
A5
A1
A6
8
1
.01 (s, 4H; H
151.8 (C ), 147.9 (C ), 141.1 (C ), 139.2 (C ), 134.5 (C ), 131.8 (C ),
B4
Me
13
B3
E5
A4
E3
A3
B4
.7 Hz, 1H; H ), 3.09 ppm (s, 3H; H ); C NMR (126 MHz, CD
3
130.8 (C ), 126.0 (C ), 124.3 (C ), 122.8 (C ), 113.6 (C ), 110.2 (C ),
A1
B3/B5
A4
A2/A13
B3/B5
Me
CtBu
tBu
d=144.6 (C ), 143.2 (C
1
C
), 139.0 (C ), 130.0 (C
), 128.8 (C
),
44.5 (C ), 36.5 (C ), 30.4 ppm (C ); IR (solid) n˜ =3126 (w), 2955
A2/A13
B4
Me
19.7 (C
), 109.7 (C ), 44.6 ppm (C ); MS (ESI): m/z calcd for
S: 223.1; found: 223.0 [M+H] ; elemental analysis calcd (%)
(w), 2874 (w), 1615 (m), 1577 (w), 1477 (m), 1411 (m), 1387 (w), 1367
+
(
(
7
w), 1341 (w), 1315 (w), 1295 (m), 1274 (m), 1253 (m), 1145 (s), 1119
10
H
11
N
2
O
2
m), 1093 (m), 1070 (m), 1057 (m), 1026 (w), 955 (m), 898 (w), 831 (s),
for C10
H
10 2 2
N O S (222.26): C 54.04, H 4.54, N 12.60; found: C 53.99, H
ꢀ
1
90 (s), 745 (s), 723 (m), 607 (m), 583 (m), 555 cm (s); UV/Vis
4
.53, N 12.28.
{Ir(msppz) (m-Cl)}
.37 mmol) were heated under reflux in 2-ethoxyethanol (70 mL) and
ꢀ
5
ꢀ3
(
(
1
CH
3
CN, 2.50ꢅ10 mol dm ): l=252 ((e=48000), 273 (sh, 36000), 309
[
9
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2 3 2
]: IrCl ·H O (1.00 g, 3.35 mmol) and Hmsppz (1.86 g,
3
ꢀ1
ꢀ1
19000), 332 nm (sh, 10000 dm mol cm ); emission (CH
3
CN, 2.50ꢅ
ꢀ
5
ꢀ3
0
mol dm , lexc =362 nm): lem =504 nm; MS (ESI): m/z calcd for
water (25 mL) for 24 h. The reaction mixture was allowed to cool to
room temperature and then H O (75 mL) was added and extracted three
times with CH Cl . The combined organic layers were washed with H
3ꢅ75 mL) and the resulting precipitate was collected by filtration. The
+
C
38
H
42IrN
%) for C38
3.53, H 4.27, N 7.76.
Ir(msppz) (3)][PF ]: The procedure was the same as the one for [Ir-
(msppz) (2)][PF but starting with [{Ir(msppz) (m-Cl)} (100 mg,
.075 mmol) and 3 (37.2 mg, 0.15 mmol). [Ir(msppz) (3)][PF ] was isolat-
6
O
4
S
2
: 903.2; found: 903.3 [MꢀPF
6
] ; elemental analysis calcd
2
(
4
H
42
F
6
IrN PS
6
O
4
2
(1048.09): C 43.55, H 4.04, N 8.02; found: C
2
2
2
O
(
[
A
H
U
G
R
N
U
G
2
A
H
U
G
R
N
U
G
6
remaining CH
2
Cl
2
was evaporated to dryness and the residue was washed
O to give [{Ir(msppz) (m-Cl)} ] as a pale yellow solid
1.50 g, 1.12 mmol, 67%). The dimer was used in the following reactions
A
T
N
R
N
U
2
A
H
U
G
R
N
N
6
]
A
H
U
G
E
N
N
2
A
T
N
T
N
N
2
]
with H
(
2
O and Et
2
A
H
U
G
R
N
U
G
2
A
H
U
G
R
N
U
2
0
A
H
U
G
R
N
U
G
2
1
A
T
N
T
E
N
N
6
1
ed as a yellow solid (110 mg, 0.107 mmol, 72%). H NMR (500 MHz,
CD CN, 295 K): d=8.50 (dd, J=3.0, 0.4 Hz, 2H; H ), 8.28 (d, J=1.9 Hz,
2H; H ), 7.76 (d, J=6.1 Hz, 2H; H ), 7.66 (overlapping m, 4H;
H
H
H
CD CN, 295 K): d=157.4 (C ), 155.8 (C ), 150.7 (C ), 147.9 (C ),
3
1
1
after verification by NMR spectroscopy.
H NMR (500 MHz,
B3
B3
3
[
D
6
]acetone, 295 K): d=8.96 (d, J=2.6 Hz, 1H; H ), 7.90 (d, J=1.9 Hz,
E3
E6
B5
A3
1
H
2
1
1
H; H ), 7.73 (d, J=8.3 Hz, 1H; H ), 7.42 (dd, J=8.3, 2.0 Hz, 1H;
), 7.05 (dd, J=3.0, 2.0 Hz, 1H; H ), 6.54 (d, J=2.0 Hz, 1H; H ),
.80 ppm (s, 3H; H ); C NMR (126 MHz, CD CN): d=148.1 (C ),
3
42.8 (C ), 138.1 (C ), 130.9 (C ), 130.4 (C ), 128.9 (C ), 123.1 (C ),
A3+A4
E5
A4
B4
A6
), 7.28 (dd, J=6.1, 2.1 Hz, 2H; H ), 7.21 (dd, J=2.2, 0.4 Hz, 2H;
B5
A6
Me
13
A2
), 6.73 (dd, J=1.9, 0.5 Hz, 2H; H ), 6.71 (dd, J=2.9, 2.2 Hz, 2H;
B4
Me
SMe
13
B5
A5
A6
B3
A1
A4
), 2.93 (s, 6H; H ), 2.62 ppm (s, 6H; H ); C NMR (126 MHz,
E4
E2
E6
A2
A3
B4
Me
12.3 (C ), 109.4 C ), 44.4 ppm (C ).
(msppz) (1)][PF ]: suspension of [{Ir
.075 mmol) and 1 (23.4 mg, 0.150 mmol) in MeOH (20 mL) was reacted
B5
A5
A1
A6
B3
A4
41.3 (C ), 139.1 (C ), 134.1 (C ), 131.8 (C ), 130.8 (C ), 124.3 (C ),
[
Ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
6
A
A
H
U
G
R
N
U
(msppz)
2
A
H
U
G
R
N
U
G
2
]
(100 mg,
E5
E3
A3
B4
Me
23.9 (C ), 121.5 (C ), 113.6 (C ), 110.1 (C ), 44.5 (C ), 14.4 ppm
0
SMe
(
1
1
C
); IR (solid): n˜ =3136 (w), 2973 (w), 2926 (w), 2849 (w), 1599 (m),
530 (w), 1475 (m), 1467 (m), 1415 (m), 1396 (m), 1386 (m), 1341 (w),
313 (w), 1291 (s), 1273 (m), 1146 (s), 1119 (m), 1091 (m), 1070 (m), 1055
in a microwave reactor for 2 h at 1208C. The greenish solution was al-
lowed to reach room temperature and NH PF (122 mg, 0.750 mmol) was
added and the reaction mixture was stirred for 30 min. The product pre-
cipitated on the addition of another 100 mg of NH PF . Recrystallization
from MeOH followed by addition of another two equivalents of NH PF
and washing with a minimum amount of cold MeOH afforded [Ir-
4
6
(
7
m), 1021 (w), 958 (s), 917 (w), 889 (w), 877 (w), 841 (s), 827 (s), 816 (s),
4
6
ꢀ1
94 (s), 744 (s), 709 (w), 668 (m), 653 (w), 586 (m), 564 (s), 555 cm (s);
4
6
ꢀ5
ꢀ3
3
UV/Vis (CH CN, 1.00ꢅ10 moldm ): l=266 (e=79000), 291 (sh,
5
(
3
ꢀ1
ꢀ1
0000), 325 (sh, 24000), 352 nm (sh, 15000 dm mol cm ); emission
1
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz)
2
(1)]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[PF
6
] as a yellow solid (75.0 mg, 0.080 mmol, 54%). H NMR
ꢀ5
ꢀ3
CH
3
CN, 1.00ꢅ10 moldm , lexc =366 nm): lem =516 nm; MS (ESI):
E3
(
500 MHz, CD
3
B3
CN, 295 K): d=8.52 (d, J=8.2 Hz, 2H; H ), 8.50 (d, J=
.0 Hz, 2H; H ), 8.17 (td, J=8.0, 1.4 Hz, 2H; H ), 8.08 (d, J=5.0 Hz,
+
m/z calcd for C32
analysis calcd (%) for C32
N 8.03; found: C 36.87, H 3.37, N 7.77.
Ir(msppz) (4)][PF ]: The method was the same as the one for [Ir-
(msppz) (2)][PF but starting with [{Ir(msppz) (m-Cl)} (100 mg,
.075 mmol) and 4 (36.3 mg, 0.150 mmol). Purification was performed by
using two chromatographic columns (Fluka silica gel 60, 0.040–0.063 mm,
CH Cl /acetone 4:1, followed by Merck alumina 90 standardized, CH Cl
acetone 4:1). Recrystallization from MeCN/Et O yielded [Ir(msppz) (4)]-
[PF as pale yellow solid (25 mg, 0.025 mmol, 16%). H NMR
500 MHz, CD
lapping m, 4H; H
H
30IrN
6
O
4
S
4
: 883.1; found: 883.2 [MꢀPF
6
] ; elemental
E4
3
2
0
H
H
30
F
6
IrN PS ·H
6
O
4
4
2
O (1046.07): C 36.74, H 3.08,
E6
A3+A4
H; H ), 7.66 (overlapping m, 4H; H
), 7.52 (ddd, J=7.2, 5.4,
E5
B5
.8 Hz, 2H; H ), 7.15 (d, J=2.2 Hz, 2H; H ), 6.75 (d, J=1.6 Hz, 2H;
[
A
H
U
G
R
N
U
G
2
A
H
U
G
R
N
U
G
6
A6
B4
Me
13
), 6.69 (t, J=2.6 Hz, 2H; H ), 2.94 ppm (s, 6H; H ); C NMR
A
T
N
T
E
N
N
2
A
H
U
G
R
N
N
6
]
A
H
U
G
E
N
N
2
A
T
N
T
N
N
2
]
E2
E6
A2
(
(
(
3
126 MHz, CD CN, 295 K): d=157.2 (C ), 152.4 (C ), 147.8 (C ), 141.4
C
C
0
B5
E4
A5
A1
A6
B3
), 140.8 (C ), 139.1 (C ), 133.9 (C ), 131.8 (C ), 130.8 (C ), 129.1
E5
E3
A4
A3
B4
Me
), 125.5 (C ), 124.4 (C ), 113.6 (C ), 110.2 (C ), 44.5 ppm (C );
2
2
2
2
/
IR (solid): n˜ =3148 (w), 2937 (w), 1628 (w), 1602 (w), 1556 (w), 1477 (m),
1
1
2
A
H
U
G
E
N
N
2
471 (m), 1447 (m), 1409 (m), 1386 (m), 1344 (w), 1316 (m), 1301 (s),
286 (s), 1273 (m), 1246 (w), 1218 (w), 1145 (s), 1120 (m), 1093 (m), 1072
1
A
H
U
G
E
N
G
6
]
a
B3
(
3
CN, 295 K): d=8.48 (d, J=2.7 Hz, 2H; H ), 7.63 (over-
(
m), 1056 (m), 1046 (m), 1024 (w), 1008 (w), 956 (m), 916 (w), 832 (s),
A3+A4
E3+E6
), 7.45 (overlapping m, 4H; H
), 7.13 (d, J=
8
6
25 (s), 789 (s), 779 (s), 761 (s), 743 (s), 731 (s), 724 (s), 668 (m), 643 (m),
B5
A6
2
2
2
(
(
(
.0 Hz, 2H; H ), 6.76 (d, J=1.9 Hz, 2H; H ), 6.70 (dd, J=3.0, 2.3 Hz,
H; H ), 6.57 (dd, J=6.7, 2.8 Hz, 2H; H ), 3.15 (s, 12H; H ),
.92 ppm (s, 6H; H ); C NMR (126 MHz, CD CN, 295 K): d=157.3
3
ꢀ1
ꢀ5
ꢀ3
09 (w), 584 (s), 548 cm (s); UV/Vis: (CH
(e=47000), 272 (sh, 38000),
10000 dm mol cm ); emission (CH
3
CN, 2.50ꢅ10 moldm ):
B4
E5
NMe
l=252
(
312
(19000),
331
Me
13
3
ꢀ1
ꢀ1
ꢀ5
ꢀ3
3
CN, 2.50ꢅ10 mol dm
,
l
exc
=
E2
E4
E6
A2
B5
A5
C
C
C
), 156.1 (C ), 150.1 (C ), 148.2 (C ), 140.6 (C ), 138.9 (C ), 136.2
3
66 nm): lem =518 nm; MS (ESI): m/z calcd for C30
H
26IrN
6
O
4
S
2
: 791.1;
A1
A6
B3
A4
A3
B4
), 131.9 (C ), 130.4 (C ), 123.7 (C ), 113.3 (C ), 109.9 (C ), 109.8
+
found: 791.0 [MꢀPF
IrN PS ·H
H 3.04, N 8.71.
6
] ; elemental analysis calcd (%) for
E5
E3
NMe
Me
), 106.6 (C ), 44.5 (C ), 40.0 ppm (C ); IR (solid): n˜ =3145 (w),
C
30
H
26
F
6
6
O
4
2
2
O (953.89): C 37.77, H 2.96, N 8.81; found: C 37.95,
2
935 (w), 1703 (w), 1615 (s), 1544 (w), 1522 (w), 1475 (m), 1433 (w), 1411
(
m), 1381 (m), 1341 (w), 1314 (w), 1285 (s), 1225 (w), 1187 (w), 1144 (s),
[
0
Ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(msppz)
2
(2)]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[PF
6
]:
A
suspension of [{Ir
A
H
U
G
E
N
N
(msppz)
2
A
T
N
T
E
N
N
(m-Cl)}
2
]
(100 mg,
1118 (m), 1092 (w), 1068 (w), 1055 (m), 1033 (m), 1016 (m), 954 (m), 916
(w), 831 (s), 825 (s), 815 (s), 790 (s), 744 (m), 723 (w), 668 (w), 587 (m),
.075 mmol) and 2 (40.2 mg, 0.150 mmol) in MeOH (20 mL) was reacted
ꢀ
1
ꢀ5
ꢀ3
in a microwave reactor for 2 h at 1208C. The greenish solution was al-
lowed to cool to room temperature and NH PF (122 mg, 0.750 mmol)
was added and the mixture was stirred for 30 min. The suspension was
evaporated to dryness and purified twice by column chromatography
555 (s), 550 (s), 519 cm (s); UV/Vis (CH CN, 1.00ꢅ10 moldm ): l=
3
4
6
262 (e=78000), 279 (sh, 62000), 298 (sh, 42000), 334 (sh, 17000), 381
3
ꢀ1
ꢀ1
ꢀ5
ꢀ3
3
(sh, 8000 dm mol cm ); emission (CH CN, 2.50ꢅ10 moldm , lexc =
8 4 2
366 nm): lem =492 nm; MS (ESI): m/z calcd for C34H36IrN O S : 877.2;
8606
www.chemeurj.org
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 8597 – 8609

Efficient Green Light-Emitting Electrochemical Cells
FULL PAPER
+
+
found: 877.3 [MꢀPF
IrN PS ·2H
8.77, H 3.40, N 10.60.
Ir(msppz) (5)][PF ]: The procedure was the same as the one for [Ir-
(msppz) (2)][PF but starting with [{Ir(msppz) (m-Cl)} (100 mg,
.075 mmol) and 5 (36.3 mg, 0.150 mmol). Purification of the product was
performed by using column chromatography twice (Merck alumin 90
standardized; CH Cl changing to CH Cl /MeOH 100:1, followed by
Fluka silica gel 60, 0.040–0.063 mm, CH Cl changing to CH Cl /MeOH
00:1). Recrystallization from MeCN/Et O afforded [Ir(msppz) (5)][PF
as a pale yellow solid (106 mg, 0.094 mmol, 63%). H NMR (500 MHz,
6
] ; elemental analysis calcd (%) for
C
37
H
32IrN
6
O
H
4
S
3
: 913.1; found: 913.2 [MꢀPF
6
] ; elemental analysis calcd
.
C
3
34
H
36
F
6
8
O
4
2
2
O (1058.04): C 38.60, H 3.81, N 10.59; found: C
(%) for C37
found: C 43.03, H 3.29, N 8.77.
32
F
6
IrN
6
O
4
PS
3
CH
3
CN (1099.12): C 42.62, H 3.21, N 8.92;
[
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
6
Crystallography: Data were collected on a Bruker–Nonius KappaAPEX
diffractometer with data reduction, solution, and refinement by using the
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
6
]
A
H
U
G
R
N
U
G
2
A
T
N
T
E
N
N
2
]
[
21]
[22]
[23]
0
programs APEX2
draw ORTEP-style diagrams and to analyze the structure.
Ir(msppz) (6)][PF ]: IrN PS M=1099.14; yellow block;
monoclinic; space group: P2 /c; a=12.6915(12), b=11.9740(11), c=
and SHELXL97.
Mercury v. 2.4
was used to
2
2
2
2
[
A
H
U
G
R
N
N
A
T
N
T
E
U
C
39
H
F
O
3
;
2
6
35
6
7
4
2
2
2
2
1
1
2
A
H
U
G
R
N
U
G
2
A
T
N
T
E
N
G
6
]
3
2
1
1
7.620(3) ꢄ;
.774 Mgm ; m
b=101.419(5)8;
(MoKa)=3.515 mm ; T=123 K; total 117704 reflections;
1974 unique reflections; Rint =0.0381; refinement of 11023 reflections
V=4114.2(7) ꢄ ;
Z=4;
calcd
1 =
1
ꢀ3
ꢀ1
ACHTUNGTRENNUNG
D3+F3
CD
1
1
H
7
(
1
H
3
CN, 295 K): d=8.49 (overlapping m, 2H; H
H; H ), 8.34 (dd, J=3.1, 0.6 Hz, 1H; H ), 8.05 (dd, J=5.9, 0.6 Hz,
H; H ), 7.57 (d, J=1.9 Hz, 1H; H ), 7.54 (dd, J=2.4, 0.6 Hz, 1H;
), 7.51 (overlapping m, 2H; H
), 8.45 (d, J=1.8 Hz,
E3
B3
(
554 parameters) with I>2s(I) converged at final R1=0.0185 (R1 all
E6
F5
data=0.0220); wR2=0.0413 (wR2 all data=0.0429); GOF=1.028.
CCDC 910854 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
D5
A4+E5
A3
), 7.45 (d, J=8.4 Hz, 1H; H ),
C3+C4
G4
.12 (overlapping m, 2H; H
), 6.98 (tt, J=7.5, 1.3 Hz, 1H; H ), 6.90
D4
G3
dd, J=3.0, 2.3 Hz, 1H; H ), 6.83 (broad, H ), 6.66 (dd, J=3.0, 2.3 Hz,
B4
B5
H; H ), 6.44 (dd, J=2.4, 0.5 Hz, 1H; H ), 6.40 (d, J=2.0 Hz, 1H;
Thin film photoluminescence: The photoluminescence spectra and quan-
tum yields of the thin films were measured with a Hamamatsu C9920-02
Absolute PL Quantum Yield Measurement System (lexc =314 nm). The
system is made up of an excitation light source, consisting of a xenon
lamp linked to a monochromator, an integration sphere, and a multi-
channel spectrometer.
A6
G2
C6
), 6.02 (very broad, H , see text), 5.93 (dd, J=1.6, 0.8 Hz, 1H; H ),
Mering A/C
Mering A/C
tBuring F
2
1
1
1
1
.87 (s, 3H; H
.42 ppm (s, 9H; H
), 2.86 (s, 3H; H
), 1.51 (s, 9H; H
),
tBuring E
13
); C NMR (126 MHz, CD CN, 295 K): d=
3
F6
F4
E4
F2
E2
E6
65.9 (C ), 165.8 (C ), 165.5 (C ), 158.8 (C ), 158.2 (C ), 151.1 (C ),
47.3 (C ), 147.1 (C ), 141.7 (C ), 141.1 (C ), 140.1 (C ), 139.2 (C ),
A2
C2
D5
B5
G1
A5
C5
C1
A1
A6+C6
B3
37.4 (C ), 135.0 (C ), 131.4 (C ), 131.2 (C
), 130.7 (C ), 130.6
D3
G4
F5
E5
A4
E3
Theoretical calculations: Density functional calculations (DFT) were car-
ried out with the C.01 revision of the Gaussian 09 program package by
using Beckeꢆs three-parameter B3LYP exchange-correlation functional
(
(
(
(
(
(
C
), 130.2 (C ), 127.1 (C ), 125.6 (C ), 124.3 (C ), 123.3 (C ), 122.4
[
24]
C4
F3
A3
C3
B4
D4
C
C
C
), 121.2 (C ), 113.3 (C ), 113.1 (C ), 110.4 (C ), 110.3 (C ), 44.50
[
25]
Mering A/C
Mering A/C
CtBuring E/F
CtBuring E/F
), 44.47 (C
), 30.3 ppm (C
), 36.55 (C
), C
), 36.5 (C
), 30.4
[26]
tBuring E/F
tBuring E/F
G2/G3
together with the 6-31G** basis set for H, C, N, O, and S
and the
double-z” quality LANL2DZ basis set for the element Ir. The geome-
tries of the singlet ground state (S ) and of the lowest-energy triplet state
) were fully optimized without imposing any symmetry restriction.
not resolved; IR (solid): n˜ =2961
[
27]
“
w), 2923 (w), 2874 (w), 1611 (w), 1579 (w), 1543 (w), 1480 (m), 1411
w), 1388 (w), 1369 (w), 1339 (w), 1315 (w), 1294 (s), 1253 (w), 1206 (w),
145 (s), 1121 (m), 1092 (w), 1071 (w), 1057 (w), 1028 (w), 954 (m), 915
w), 874 (w), 831 (s), 790 (m), 744 (m), 722 (w), 700 (m), 666 (w), 653
w), 643 (w), 582 (m), 555 cm
0
(T
1
1
The geometry of the first triplet state was calculated at the spin-unre-
stricted UB3LYP level with a spin multiplicity of three. All the calcula-
tions were performed in the presence of the solvent (acetonitrile). Sol-
vent effects were considered within the self-consistent reaction field
(SCRF) theory by using the SMD keyword that performs a polarized
(
(
1
ꢀ1
(s); UV/Vis (CH
3
CN, 2.50ꢅ
ꢀ
5
ꢀ3
3
ꢀ1
ꢀ1
0
moldm ): l=259 (e=49000), 318 nm (21000 dm mol cm ); emis-
ꢀ
5
ꢀ3
sion (CH
ESI): m/z calcd for C44
mental analysis calcd (%) for C44
3
CN, 2.50ꢅ10 moldm
,
l
exc =360 nm):
l
em =506 nm; MS
+
(
H
46IrN
6
O
4
S
2
: 979.3; found: 979.3 [MꢀPF
6
] ; ele-
[
28]
continuum model (PCM) calculation by using the solvation model of
H
46
F
6
IrN PS
6
O
4
2
(1124.19): C 47.01, H
[
29]
Thrular et al. The SMD solvation model is based on the polarized con-
tinuous quantum chemical charge density of the solute (the “D” in the
name stands for “density”). Time-dependent DFT (TD-DFT) calcula-
tions of the lowest-lying 50 triplets were performed in the presence of
the solvent at the minimum-energy geometry optimized for S
4
.12, N 7.48; found: C 46.66, H 4.20, N 7.79.
Ir(msppz) (6)][PF ]: The procedure was the same as the one for [Ir-
(msppz) (2)][PF but starting from [{Ir(msppz) (m-Cl)} (100 mg,
.075 mmol) and 6 (41.7 mg, 0.150 mmol). The product was purified by
column chromatography (Merck alumina 90 standardized; CH Cl chang-
ing to CH Cl /MeOH 100:1, followed by Fluka silica gel 60, 0.040–
.063 mm, CH Cl changing to CH Cl /MeOH 100:1). Recrystallization
from MeCN/Et O gave [Ir(msppz) (6)][PF ] as a yellow solid (78.0 mg,
.074 mmol, 49%). H NMR (500 MHz, CD CN, 295 K): d=8.51 (d, J=
[
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
6
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
6
]
A
H
U
G
R
N
U
G
2
A
T
N
T
E
N
N
2
]
[30]
0
0
.
2
2
To investigate the influence of the basis set used for the element iridium,
2
2
+
the geometries of the S
0
and T
1 2
states of complexes [Ir ACHNUTRTGENNUNG( msppz) (1)] and
0
2
2
2
2
+
[Ir ACHTNUGTERNUNNG( msppz) (4)] were also optimized by using the high-quality, “triple-
2
2
A
H
N
T
E
U
G
2
A
H
U
G
E
N
N
6
[
31]
1
z+polarization” def2-TZVP basis set for Ir. The more extended def2-
TZVP basis set has almost no effect on the coordination sphere of the iri-
dium center, leading to maximum differences of 0.013 ꢄ for bond lengths
and 0.38 for bond angles (Table S3 in the Supporting Information). It has
also a negligible effect on the molecular orbital energies, on the TD-DFT
0
8
H
7
3
D3
E3
.4 Hz, 1H; H ), 8.48 (d, J=3.0 Hz, 1H; H ), 8.34 (d, J=3.0 Hz, 1H;
B3
F3
E4+E6
), 8.29 (d, J=2.0 Hz, 1H; H ), 8.16 (overlapping m, 2H; H
),
), 7.45 (d,
J=8.4 Hz, 1H; H ), 7.34 (d, J=1.9 Hz, 1H; H ), 7.12 (overlapping m,
D5
A4+E5
.54 (d, J=2.2 Hz, 1H; H ), 7.50 (overlapping m, 2H; H
A3
F5
C3+C4
G4
D4
vertical excitation energies and on the emission energies from T
Supporting Information for further details).
1
(see the
2
H; H
), 6.98 (t, J=7.4 Hz, 1H; H ), 6.89 (t, J=2.6 Hz, 1H; H ),
.82 (broad, H ), 6.75 (d, J=2.3 Hz, 1H; H ), 6.67 (t, J=2.6 Hz, 1H;
), 6.38 (d, J=1.9 Hz, 1H; H ), 6.04 (very broad, H , see text), 5.94
G3
B5
6
H
(
2
B4
A6
G2
Device preparation: The solvents were supplied by Aldrich. The thick-
ness of the films was determined with an Ambios XP-1 profilometer.
C6
Mering A
Mering C
d, J=1.4 Hz, 1H; H ), 2.86 (s, 3H; H
), 2.84 (s, 3H; H
),
ꢀ
1
SMe
13
Indium tin oxide (ITO) coated glass plates (15 W& ) were patterned by
conventional photolithography (http://www.naranjosubstrates.com). The
substrates were cleaned by sonication in water-soap, water, and 2-propa-
nol baths, in that order. After drying, the substrates were placed in a UV-
ozone cleaner (Jelight 42-220) for 20 min.
.69 ppm (s, 3H; H ); C NMR (126 MHz, CD CN, 295 K): d=164.7
3
F6
F4
F2
E2
E6
A2
(
(
(
(
(
(
(
(
(
C
), 157.7 (C ), 157.6 (C ), 158.2 (C ), 151.8 (C ), 147.3 (C ), 147.0
C2
C5
D5
B5
E4
G1
A5
C
C
C
C
C
), 141.9 (C ), 141.4 (C ), 140.6 (C ), 139.6 (C ), 139.1 (C ), 137.4
C1
A1
C6
B3
A6
), 134.5 (C ), 131.3 (C ), 131.2 (C ), 130.7 (C ), 130.7 (C ), 130.6
D3
C4
G4
E5
E3
F5
A4
), 130.3 (C ), 128.6 (C ), 125.9 (C ), 124.8 (C ), 124.4 (C ), 122.5
F3
A3
C3
B4
D4
), 119.9 (C ), 113.3 (C ), 113.1 (C ), 110.4 (C ), 110.3 (C ), 44.5
The electroluminescence devices were made as follows. First, a 90 nm
layer of PEDOT:PSS (CLEVIOS P VP AI 4083, aqueous dispersion, 1.3–
1.7% solid content, Heraeus) was spin-coated on the ITO glass substrate
to improve the reproducibility of the devices and to prevent the forma-
tion of pinholes. Then, 90 nm transparent films of the complexes [Ir-
Merings A+C
SMe
G2/G3
), 14.4 ppm (C ), C
not resolved; IR (solid): n˜ =3128
w), 2928 (w), 1603 (w), 1588 (m), 1528 (w), 1477 (m), 1411 (m), 1390
w), 1341 (w), 1317 (w), 1301 (m), 1287 (m), 1274 (m), 1145 (s), 1121
m), 1093 (m), 1071 (w), 1060 (m), 1029 (w), 1004 (w), 955 (s), 926 (w),
9
16 (w), 894 (w), 880 (w), 841 (s), 826 (s), 821 (s), 789 (m), 775 (m), 765
6
ACHTUNGTNERNUNG( msppz)2 AHCTUNGERTNNGNU( N^N)] ACHNTUTGRENNUNG[ PF ] with N^N=1–6 and the ionic liquid 1-butyl-3-
(
m), 743 (s), 698 (m), 673 (w), 650 (w), 634 (w), 608 (w), 587 (s), 563 (s),
methylimidazolium hexafluoridophosphate (>98.5%, Sigma–Aldrich) in
a 4:1 molar ratio were spin-coated from 20 mgmL acetonitrile solution
at 1000 rpm for 20 s. The devices were transferred in an inert atmosphere
2 2
glovebox (<0.1 ppm O and H O, MBraun) and were annealed at 1008C
ꢀ
1
ꢀ5
ꢀ3
ꢀ1
5
2
1
55 cm (s); UV/Vis (CH
73 (sh, 46000), 317 nm (sh, 24000 dm mol cm ); emission (CH CN,
.00ꢅ10 moldm , lexc =366 nm): lem =516 nm; MS (ESI): m/z calcd for
3
CN, 1.00ꢅ10 moldm ): l=258 (e=51000),
3
ꢀ1
ꢀ1
3
ꢀ
ꢀ3
Chem. Eur. J. 2013, 19, 8597 – 8609
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8607

C. E. Housecroft, E. Orti et al.
during a time of one hour. The Al electrode (70 nm) was thermally
evaporated by using a shadow mask under a vacuum (<1ꢅ10 mbar)
[8] a) H. J. Bolink, E. Coronado, R. D. Costa, N. Lardiꢇs, E. Ortꢁ, Inorg.
Chem. 2008, 47, 9149–9151; b) J. D. Slinker, C. Y. Koh, G. G. Mallia-
ras, M. S. Lowry, S. Bernhard, Appl. Phys. Lett. 2005, 86, 173506;
c) D. Tordera, M. Delgado, E. Ortꢁ, H. J. Bolink, J. Frey, M. K. Na-
zeeruddin, E. Baranoff, Chem. Mater. 2012, 24, 1896–1903; d) M. S.
Lowry, J. I. Goldsmith, J. D. Slinker, R. Rohl, R. A. Pascal, G. G.
Malliaras, S. Bernhard, Chem. Mater. 2005, 17, 5712–5719; e) H. C.
Su, F. C. Fang, T. Y. Hwu, H. H. Hsieh, H. Chen, G. Lee, S. Peng,
K. T. Wong, C. C. Wu, Adv. Funct. Mater. 2007, 17, 1019–1027.
[9] R. Terki, L. P. Simoneau, A. Rochefort, J. Phys. Chem. A 2009, 113,
ꢀ
6
with an Edwards Auto500 evaporator integrated in the glovebox. The
2
area of the device was 6.534 mm . The devices were not encapsulated
and were characterized inside the glovebox at room temperature.
LEC characterization: An Avantes luminance spectrometer was used to
measure the EL spectrum. The device lifetime was measured by applying
pulsed currents and monitoring the voltage and luminance by a True
Colour Sensor MAZeT (MTCSiCT Sensor) with a Botest OLT OLED
Lifetime-Test System.
5
34–541.
10] S. Sprouse, K. A. King, P. J. Spellane, R. J. Watts, J. Am. Chem. Soc.
984, 106, 6647–6653.
11] F. Neve, A. Crispini, S. Campagna, S. Serroni, Inorg. Chem. 1999,
8, 2250–2258.
12] G. J. ten Brink, I. W. C. E. Arends, M. Hoogenraad, G. Verspui,
R. A. Sheldon, Adv. Synth. Catal. 2003, 345, 497–505.
13] K. H. Lee, P. E. Schwenn, A. R. G. Smith, H. Cavaye, P. E. Shaw, M.
James, K. B. Krueger, I. R. Gentle, P. Meredith, P. L. Burn, Adv.
Mater. 2011, 23, 766–770.
[
[
[
[
1
3
Acknowledgements
This work has been supported by the European Union (CELLO, Grant
STRP 248043; https://www.cello-project.eu/), the Spanish Ministry of
Economy and Competitiveness (MINECO) (MAT2011-24594, CSD2007-
0
0010, CTQ2009-08790, and CTQ2012-31914), the Generalitat Valenci-
[
14] a) J. Fang, P. Matyba, L. Edman, Adv. Funct. Mater. 2009, 19, 2671–
ana (Prometeo/2012/053), the European Research Council (Advanced
Grant 267816 LiLo) and the Swiss National Centre of Competence in
Research (NCCR) “Nanoscale Science”. D.T. and A.P. acknowledge
MECD (Spanish Ministry of Education, Culture, and Sport) and
MINECO for FPU and FPI grants, respectively. We thank Rochꢇ M.
Walliser for recording the 500 MHz NMR spectra. We acknowledge help-
ful discussions with Dr. David Vonlanthen, and we thank Dr. Imenne
Bouamaied for providing ligand 6.
2
676; b) E. Baranoff, H. J. Bolink, E. C. Constable, M. Delgado, D.
Haussinger, C. E. Housecroft, M. K. Nazeeruddin, M. Neuburger, E.
Ortꢁ, G. E. Schneider, D. Tordera, R. M. Walliser, J. A. Zampese,
Dalton Trans. 2013, 42, 1073–1087.
[
[
15] C. Janiak, J. Chem. Soc. Dalton Trans. 2000, 3885–3896.
16] a) H. J. Bolink, E. Coronado, R. D. Costa, E. Ortꢁ, M. Sessolo, S.
Graber, K. Doyle, M. Neuburger, C. E. Housecroft, E. C. Constable,
Adv. Mater. 2008, 20, 3910–3913; b) S. Graber, K. Doyle, M. Neu-
burger, C. E. Housecroft, E. C. Constable, R. D. Costa, E. Ortꢁ, D.
Repetto, H. J. Bolink, J. Am. Chem. Soc. 2008, 130, 14944–14945;
c) R. D. Costa, E. Ortꢁ, H. J. Bolink, S. Graber, C. E. Housecroft, M.
Neuburger, S. Schaffner, E. C. Constable, Chem. Commun. 2009,
[
[
1] Q. Pei, G. Yu, C. Zhang, Y. Yang, A. J. Heeger, Science 1995, 269,
086–1088.
2] a) J. D. Slinker, J. Rivnay, J. S. Moskowitz, J. B. Parker, S. Bernhard,
H. D. AbruÇa, G. G. Malliaras, J. Mater. Chem. 2007, 17, 2976–2989;
b) T. Hu, L. He, L. Duan, Y. Qiu, J. Mater. Chem. 2012, 22, 4206–
1
2
029–2031; d) R. D. Costa, E. Ortꢁ, H. J. Bolink, S. Graber, S.
Schaffner, M. Neuburger, C. E. Housecroft, E. C. Constable, Adv.
Funct. Mater. 2009, 19, 3456–3463; e) R. D. Costa, E. Ortꢁ, H. J.
Bolink, S. Graber, C. E. Housecroft, E. C. Constable, Adv. Funct.
Mater. 2010, 20, 1511–1520; f) R. D. Costa, E. Ortꢁ, H. J. Bolink, S.
Graber, C. E. Housecroft, E. C. Constable, J. Am. Chem. Soc. 2010,
4
215; c) R. D. Costa, E. Ortꢁ, H. J. Bolink, F. Monti, G. Accorsi, N.
Armaroli, Angew. Chem. 2012, 124, 8300–8334; Angew. Chem. Int.
Ed. 2012, 51, 8178–8211; d) J. D. Slinker, A. A. Gorodetsky, M. S.
Lowry, J. Wang, S. Parker, R. Rohl, S. Bernhard, G. G. Malliaras, J.
Am. Chem. Soc. 2004, 126, 2763–2767; e) F. Dumur, D. Bertin, D.
Gigmes, Int. J. Nanotechnol. 2012, 9, 377–395.
3] a) J. D. Slinker, J. A. DeFranco, M. J. Jaquith, W. R. Silveira, Y.
Zhong, J. M. Moran-Mirabal, H. G. Graighead, H. D. AbruÇa, J. A.
Marohn, G. G. Malliaras, Nat. Mater. 2007, 6, 894–899; b) P.
Matyba, K. Maturova, M. Kemerink, N. D. Robinson, L. Edman,
Nat. Mater. 2009, 8, 672–676.
4] a) S. van Reenen, P. Matyba, A. Dzwilewski, R. A. J. Janssen, L.
Edman, M. Kemerink, J. Am. Chem. Soc. 2010, 132, 13776–13781;
b) M. Lenes, G. Garcꢁa-Belmonte, D. Tordera, A. Pertegꢀs, J. Bis-
quert, H. J. Bolink, Adv. Funct. Mater. 2011, 21, 1581–1586; c) Q.
Pei, Yang, G. Yu, C. Zhang, A. J. Heeger, J. Am. Chem. Soc. 1996,
1
32, 5978–5980; g) R. D. Costa, E. Ortꢁ, H. J. Bolink, S. Graber,
C. E. Housecroft, E. C. Constable, Chem. Commun. 2011, 47, 3207–
209.
17] O. Malinkiewicz, M. Lenes, H. Brine, H. J. Bolink, RSC Adv. 2012,
, 3335–3339.
18] R. D. Costa, E. Ortꢁ, D. Tordera, A. Pertegꢀs, H. J. Bolink, S.
Graber, C. E. Housecroft, L. Sachno, M. Neuburger, E. C. Consta-
ble, Adv. Energy Mater. 2011, 1, 282–290.
3
[
[
[
2
[
[
19] a) H. J. Bolink, L. Cappelli, S. Cheylan, E. Coronado, R. D. Costa,
N. Lardiꢇs, M. K. Nazeeruddin, E. Ortꢁ, J. Mater. Chem. 2007, 17,
5
032–5041; b) J. Li, P. I. Djurovich, B. D. Alleyne, M. Yousufuddin,
N. N. Ho, J. C. Thomas, J. C. Peters, R. Bau, M. E. Thompson, Inorg.
Chem. 2005, 44, 1713–1727.
1
18, 3922–3929.
[
[
[
5] a) D. Tordera, S. Meier, M. Lenes, R. D. Costa, E. Ortꢁ, W. Sarfert,
H. J. Bolink, Adv. Mater. 2012, 24, 897–900; b) D. Tordera, A. Per-
tegꢀs, N. M. Shavaleev, R. Scopelliti, E. Ortꢁ, H. J. Bolink, E. Baran-
off, M. Grꢈtzel, M. K. Nazeeruddin, J. Mater. Chem. 2012, 22,
[20] M. S. Lowry, W. R. Hudson, R. A. Pascal, S. Bernhard, J. Am.
Chem. Soc. 2004, 126, 14129–14135.
[21] Analytical X-ray Systems, I. Bruker, APEX2, version 2, User
Manual, M86-E01078, Madison, WI, 2006.
1
9264–19268.
[22] G. M. Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 112–122.
[23] a) M. Panigrahi, S. Dash, S. Patel, B. K. Mishra, Tetrahedron 2012,
68, 781–805; b) C. F. Macrae, I. J. Bruno, J. A. Chisholm, P. R. Edg-
ington, P. McCabe, E. Pidcock, L. Rodrꢁguez-Monge, R. Taylor, J.
van de Streek, P. A. Wood, J. Appl. Crystallogr. 2008, 41, 466–470.
[24] Gaussian 09, Revision C.01, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V.
Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X.
Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Son-
nenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.
Montgomery, J. A., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd,
E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Nor-
6] a) L. He, J. Qiao, L. Duan, G. Dong, D. Zhang, L. Wang, Y. Qiu,
Adv. Funct. Mater. 2009, 19, 2950–2960; b) A. B. Tamayo, S. Garon,
T. Sajoto, P. I. Djurovich, I. Tsyba, R. Bau, M. E. Thompson, Inorg.
Chem. 2005, 44, 8723–8732; c) R. D. Costa, P. M. Viruela, H. J.
Bolink, E. Ortꢁ, THEOCHEM 2009, 912, 21–26.
7] a) C. H. Yang, J. Beltrꢀn, V. Lemaur, J. Cornil, D. Hartmann, W.
Sarfert, R. Frohlich, C. Bizzarri, L. De Cola, Inorg. Chem. 2010, 49,
9
891–9901; b) L. He, L. Duan, J. Qiao, R. Wang, P. Wei, L. Wang,
Y. Qiu, Adv. Funct. Mater. 2008, 18, 2123–2131; c) B. Chen, Y. Li,
W. Yang, W. Luo, H. Wu, Org. Electron. 2011, 12, 766–773; d) M.
Mydlak, C. Bizzarri, D. Hartmann, W. Sarfert, G. Schmid, L.
De Cola, Adv. Funct. Mater. 2010, 20, 1812–1820.
8608
www.chemeurj.org
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 8597 – 8609

Efficient Green Light-Emitting Electrochemical Cells
FULL PAPER
mand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J.
Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Strat-
mann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochter-
ski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P.
Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, ꢉ. Farkas,
J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian, Inc.,
Wallingford CT, Gaussian, Inc., Wallingford CT, 2010.
[28] a) J. Tomasi, M. Persico, Chem. Rev. 1994, 94, 2027– 2094; b) C. S.
Cramer, D. G. Truhlar, Solvent Effects and Chemical Reactivity,
Kluwer, Dordrecht, 1996, pp. 1–80; c) J. Tomasi, B. Mennucci, R.
Cammi, Chem. Rev. 2005, 105, 2999–3093.
[29] A. V. Marenich, C. J. Cramer, D. G. Truhlar, J. Phys. Chem. B 2009,
113, 6378–6396.
[30] C. Adamo, D. Jacquemin, Chem. Soc. Rev. 2013, 42, 845–856.
[31] F. Weigend, R. Ahlrichs, Phys. Chem. Chem. Phys. 2005, 7, 3297–
3305.
[
[
25] C. T. Lee, W. T. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785–789.
26] M. M. Francl, W. J. Pietro, W. J. Hehre, J. S. Binkley, M. S. Gordon,
D. J. Defrees, J. A. Pople, J. Chem. Phys. 1982, 77, 3654–3665.
27] P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 299–310.
Received: February 5, 2013
Published online: May 6, 2013
[
Chem. Eur. J. 2013, 19, 8597 – 8609
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8609