Synthesis, photophysical and electrophosphorescent properties of fluorene-based platinum(II) complexes

Article abstract of DOI:10.1002/chem.201001570

A series of platinum(II) complexes bearing tridentate cyclometalated C^N^N (C^N^N=6-phenyl-2,2'-bipyridine and π-extended R-C^N^N=3-[6'-(naphthalen-2''- yl)pyridin-2'-yl]isoquinoline) ligands with fluorene units have been synthesised and their photophysic

Full text of DOI:10.1002/chem.201001570

FULL PAPER
DOI: 10.1002/chem.201001570
Synthesis, Photophysical and Electrophosphorescent Properties of Fluorene-
Based Platinum(II) Complexes
Mai-Yan Yuen, Steven C. F. Kui, Kam-Hung Low, Chi-Chung Kwok,
Stephen Sin-Yin Chui, Chun-Wah Ma, Nianyong Zhu, and Chi-Ming Che*[a]
Abstract: A series of platinum(II) com-
plexes bearing tridentate cyclometalat-
ed C^N^N (C^N^N=6-phenyl-2,2’-bi-
pyridine and p-extended R-C^N^N=
3-[6’-(naphthalen-2’’-yl)pyridin-2’-yl]-
structured emission bands with lmax
=
platinum(II) complexes are soluble in
organic solvents, have high thermal sta-
bility with decomposition temperature
>3508C, and can be thermally
vacuum-sublimed or solution-processed
as phosphorescent dopants for the fab-
rication of organic light-emitting
558–601 nm, and high emission quan-
tum yields up to 0.76 in degassed di-
chloromethane. Their emissions are
tentatively assigned to excited states
with mixed 3IL/3MLCT parentage
ACHTUNGTRENNUNGisoquinoline) ligands with fluorene
units have been synthesised and their
photophysical properties have been
studied. The fluorene units are incor-
porated into the cyclometalated ligands
by a Suzuki coupling reaction. An in-
crease in the p-conjugation of the cy-
clometalated ligands confers favoura-
ble photophysical properties compared
to the 6-phenyl-2,2’-bipyridine ana-
logues. The fluorene-based platin-
(IL=intra
G
G
MLCT=metal-to-
ligand charge transfer). The crystal
structures of these platinum(II) com-
plexes reveal extensive PtII···p and/or
p–p interactions. The fluorene-based
diodes (OLEDs).
A
monochromic
OLED with 3d as dopant (2 wt%) fab-
ricated by vacuum deposition gave a
current efficiency of 14.7 cdAꢀ1 and
maximum brightness of 27000 cdmꢀ2.
A high current efficiency (9.2 cdAꢀ1)
has been achieved in a solution-pro-
cessed OLED using complex 3 f
(5 wt%) doped in a PVK (poly(9-vinyl-
carbazole)) host.
Keywords: charge transfer · cyclo-
metalation
·
electrophosphores-
cence · fluorenes · organic light-
emitting diodes · platinum
ACHTUNGTRENNUNGum(II) complexes display vibronic-
Introduction
lution-processable light-emitting materials for polymer light-
emitting diodes (PLEDs),[4] due to the low fabrication cost
for large-area displays through spin-coating, inkjet-printing,
or spray-coating techniques.[5] Recently, several groups have
reported efficient phosphorescent or fluorescent OLEDs
prepared by spin-coating solutions of small organic mole-
Since the first report on organic light-emitting diodes
(OLEDs) by Tang,[1] the quest for new electroluminescent
materials has become a main focus in materials science.[2]
Although significant advances have been made in the design
and fabrication of high performance OLEDs,[3] the fabrica-
tion of OLEDs by vacuum deposition is costly. Conjugated
polymers and oligomers have been studied extensively as so-
ACTHNUTRGNEUNG
cules[6] or iridium(III) complexes.[7] The blending of small
molecules into the polymer host offers an alternative route
for solution-processed OLEDs. However, the differences in
both entropy and enthalpy values between the polymer and
the small molecules in the polymer blend may result in
phase separation, which leads to the formation of traps for
charge carriers. In addition, the HOMOs and LUMOs of
the polymer host are different from those of the small mole-
cules, leading to incomplete energy transfer from host to
dopant. Therefore, there has been considerable interest in
the design of emissive small molecules which are suitable
for blending with the polymer host.
[a] Dr. M.-Y. Yuen, Dr. S. C. F. Kui, Dr. K.-H. Low, Dr. C.-C. Kwok,
Dr. S. S.-Y. Chui, C.-W. Ma, N. Zhu, Prof. C.-M. Che
Department of Chemistry
Institute of Molecular Functional Materials
HKU-CAS Joint Laboratory on New Materials
and State Key Laboratory on Synthetic Chemistry
The University of Hong Kong
Pokfulam Road, Hong Kong (China)
Fax : (+852)2915-5176
p-Conjugated organic oligomers coordinated to transi-
tion-metal ions have emerged as a new class of molecular
electronic materials.[7] In particular, oligomeric organic li-
E-mail: cmche@hku.hk
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201001570.
Chem. Eur. J. 2010, 16, 14131 – 14141
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
14131

gands coordinated to heavy metal ions are of importance, as
they can be utilised as solution-processing phosphorescent
materials.[8] Because intersystem crossing (ISC) becomes ef-
ficient as a result of spin-orbit coupling, emission from both
singlet and triplet states can be harvested, and 100% inter-
nal quantum efficiency (IQE) can, in principle, be achieved.
Using phosphorescent transition-metal complexes as light-
emitting materials, a number of cyclometalated iridiumACHTUNTRGNEUNG(III)
complexes of 2-phenylpyridine have been studied as dopants
in polymeric light-emitting devices.[9] In contrast, there have
been no literature reports on utilising phosphorescent cyclo-
metalated platinum(II) complexes as molecular dopants for
either vacuum-deposited OLEDs or solution-processed
PLEDs. Square-planar d8 cyclometalated platinum(II) com-
plexes have attracted much attention as phosphorescent
dopant materials.[2g] Among them, platinum(II) complexes
containing aromatic N-donor and/or cyclometalated ligands
are known to display a variety of emissive excited states,[10]
including ligand-field (LF), metal-to-ligand charge transfer
Figure 1. Cyclic voltammogram of complex 3d in DMF.
tended R-C^N^N (Types 3–6) ligands. The cyclometalated
ligands were prepared according to literature procedures,[11a]
comprising several steps involving: 1) alkylation of the
methylene (fluorene) motif; 2) bromination; 3) acetylation,
4) Suzuki coupling for the synthesis of fluorene units; and
5) formation of cyclometalated (C^N^N) ligands. In all
cases, the C^N^N ligand is connected to the 2- and/or 2,7-
positions of the fluorene unit(s) (Scheme 1). The experimen-
tal procedures and characterisation data of the ligands and
starting materials are given in the Supporting Information.
The platinum(II) complexes were obtained in high yields by
heating K2PtCl4 under reflux with the corresponding ligands
in a mixture of glacial acetic acid and CHCl3 (v:v, 10:1).
Compared to other cyclometalated PtII complexes, the fluo-
rene-based cyclometalated PtII complexes exhibit better sol-
ubility in common organic solvents, including toluene and
chlorobenzene. This is important for applications involving
ink-jet printing, spin coating and blending with a polymer
host for solution-processed OLEDs. Each ligand and corre-
sponding platinum(II) complex have been characterised by
(MLCT), intra
G
G
metal-metal-to-ligand charge-transfer (MMLCT) states. The
relative energy of these excited states can be tuned by vary-
ing the ligands coordinated to the PtII ion.
We are attracted to the prospect of incorporating fluorene
units in the design of cyclometalated platinum(II) com-
plexes. Previous studies have revealed that, by increasing
the p-conjugation of cyclometalated ligands, the structural
distortion of the triplet excited state is minimised, resulting
in an enhancement of the phosphorescence quantum
yield.[11] Whereas there are many reports on fluorene-based
iridiumACHTUNGTRENNUNG
(III) complexes,[9] there are only a few studies on lu-
minescent platinum(II) complexes containing ligands with
fluorene units.[12] We envisage that by connecting fluorene
units to cyclometalated C^N^N ligands, the high emission
quantum yields of the PtACTHNUTRGNE(NUG C^N^N) complexes could be re-
tained, and their solubility in common organic solvents
could be improved.[13] The fluorene-based platinum(II) com-
plexes could easily be blended with the polymer host to pro-
duce morphologically stable thin films through ink-jet print-
ing or spin coating. Very recently, Shao et al. reported the
photophysical and nonlinear optical properties of platinu-
m(II) complexes of 6-phenyl-4-(9,9-dihexylfluorene-2yl)-
2,2’-bipyridine.[12] Herein we describe the synthesis, crystal
structures and photophysical properties of platinum(II) com-
plexes containing fluorene unit(s) incorporated into the cy-
clometalated 6-phenyl-2,2’-bipyridine (C^N^N complex
types 1 and 2) or 3-[6’-(naphthalen-2’’-yl)pyridin-2’-yl]iso-
1
1H, H-1H COSY and NOESY NMR spectroscopy, EIMS or
fast-atom bombardment (FAB) (+ve) mass spectrometry
1
and elemental analyses. The H NMR spectra of 1, 2, 3a, 5a
and 6a together with proton assignments are depicted as
representative examples in Figures S5–S9 of the Supporting
Information.
1
The H NMR spectra of the as-prepared complexes 4a–d
(Supporting Information, Figures S10–S14) revealed two
species with approximately 1:1 molar ratio in each of the
cases examined. Further investigation through 2D NMR
(1H-1H COSY and NOESY) and 195Pt NMR experiments
confirmed two isomeric forms generated in the course of the
reactions between K2PtCl4 and the fluorene-based cyclome-
talated ligands (Figure 1, Type 4). For complexes 4a–d, the
platinum(II) ion is coordinated by the p-extended R-
C^N^N ligand through the C2 or C10 atom, giving rise to
the linear form (Pt···C2, Isomer A) or bent form (Pt···C10,
Isomer B) (Scheme 1). The Pt···C10 coordination (Isomer
B) causes the C8 and H8 atoms to be in close proximity to
ACHTUNGTRENNUNGquinoline ligands (R-C^N^N complex types 3–6). Com-
plexes 3a, 3d, 3 f, 3g, 5b, 5c and 6c (Scheme 1) have been
tested for the fabrication of vacuum-sublimated and solu-
tion-processed OLEDs.
Results and Discussion
Synthesis and characterisation: Fluorene units are incorpo-
rated in the periphery of C^N^N (Types 1 and 2) and p-ex-
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Chem. Eur. J. 2010, 16, 14131 – 14141

Properties of Fluorene-Based Platinum(II) Complexes
FULL PAPER
Scheme 1. Evolutional scheme of fluorene-based platinum(II) complexes.
the platinum(II) ion, thus, there
1
is a shift of the H NMR signal
Table 1. Summary of electrochemical data and decomposition temperature for complexes 1, 2, 3a–g, 4a–d,
5a–c and 6a–c.
of H8 to the downfield region
(4a: 9.62 ppm in CD2Cl2; 4b:
10.03 ppm in d7-DMF; 4c:
9.48 ppm in CD2Cl2 and 4d:
9.36 ppm in CD2Cl2) (Fig-
ures S10–S14). The structure of
isomeric form A of 4c has been
revealed by X-ray crystal analy-
sis (Figures S29 and S30). The
problem of structural isomerism
can be avoided by changing the
ligand from 3-(6’-(naphthalen-
2’’-yl)pyridin-2’-yl)isoquinoline
(Type 4) to 3-(6’-phenylpyridin-
2’-yl)isoquinoline (Type 5).
Ered [V][a]
Eox [V][a]
HOMO
[eV][b]
LUMO
[eV][b]
Electrochemical
bandgap [eV]
Td
[8C]
onset
E1/2
onset
Epeak
1
2
ꢀ1.62
ꢀ1.60
ꢀ1.80
ꢀ1.77
ꢀ1.79
ꢀ1.72
ꢀ1.72
ꢀ1.77
ꢀ1.71
ꢀ1.70
ꢀ1.68
ꢀ1.68
ꢀ1.71
ꢀ1.71
ꢀ1.71
ꢀ1.68
ꢀ1.71
ꢀ1.66
ꢀ1.72
ꢀ1.73
ꢀ1.71
ꢀ1.89
ꢀ1.85
ꢀ1.91
ꢀ1.85
ꢀ1.84
ꢀ1.88
ꢀ1.82
ꢀ1.81
ꢀ1.80
ꢀ1.78
ꢀ1.81
ꢀ1.83
ꢀ1.79
ꢀ1.80
ꢀ1.83
ꢀ1.77
ꢀ1.80
0.27
0.36
0.43
–
0.60
0.47
0.68
–
ꢀ5.07
ꢀ5.16
ꢀ5.23
n/a[c]
ꢀ3.18
ꢀ3.20
ꢀ3.00
ꢀ3.03
ꢀ3.01
ꢀ3.08
ꢀ3.08
ꢀ3.03
ꢀ3.09
ꢀ3.10
ꢀ3.12
ꢀ3.12
ꢀ3.09
ꢀ3.09
ꢀ3.09
ꢀ3.12
ꢀ3.09
ꢀ3.14
ꢀ3.08
1.89
1.96
2.23
n/a[c]
2.09
2.10
2.02
2.21
2.10
2.05
1.98
2.00
2.05
2.05
2.03
2.04
2.15
2.03
2.08
451
448
433
463
436
448
443
466
451
452
384
448
427
444
419
473
438
392
419
3a
3b
3c
3d
3e
3 f
3g
4a
4b
4c
4d
5a
5b
5c
6a
6b
6c
0.30
0.38
0.30
0.44
0.39
0.35
0.30
0.32
0.34
0.34
0.32
0.36
0.44
0.37
0.36
0.51
0.59
0.51
0.62
0.56
0.61
0.58
0.54
0.63
0.48
0.52
0.59
0.56
0.53
0.55
ꢀ5.10
ꢀ5.18
ꢀ5.10
ꢀ5.24
ꢀ5.19
ꢀ5.15
ꢀ5.10
ꢀ5.12
ꢀ5.14
ꢀ5.14
ꢀ5.12
ꢀ5.16
ꢀ5.24
ꢀ5.17
ꢀ5.16
Thermogravimetric analysis
(TGA) of the cyclometalated
platinum(II) complexes was
performed, and the data are
summarised in Table 1. The de-
composition temperatures of all
[a] Determined in DMF at 298 K with 0.1m nBu4NPF6 as supporting electrolyte; scanning rate: 50 mVsꢀ1
values are versus Cp2Fe0/+. [b] The HOMO and LUMO level were calculated from onset potentials using
;
of the complexes (384–4738C) Cp2Fe0/+ values of 4.8 eV below the vacuum level.[14] [c] n/a= not applicable .
Chem. Eur. J. 2010, 16, 14131 – 14141
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14133

C.-M. Che et al.
are comparable to those of previously reported cyclometa-
lated [PtCl(p-extended R-C^N^N)][11a] and [PtCl
(O^N^N)]
C^N^N ligands (complexes 3a–g, 4a–d, 5a–c and 6a–c,
which range from ꢀ1.77 to ꢀ1.91 V). Comparison of the re-
duction potentials among the different types (Types 3–6) of
fluorene-based [Pt-(C^N^N)] complexes reveals that the E1/
AHCTUNGTRENNUNG
complexes[15] (H-O^N^N=2-(6’-(pyridin-2’-yl)pyridine-2’-
yl)phenol). The cyclic voltammograms of complexes 1, 2,
3a–g, 4a–d, 5a–c and 6a–c in DMF (0.1 moldmꢀ3
nBu4NPF6) reveal one quasi-reversible reduction couple
with E1/2 at ꢀ1.71 to ꢀ1.91 V vs. E1/2 of the Cp2Fe0/+ couple
and an irreversible oxidation wave at 0.47 to 0.68 V. The
electrochemical data are summarised in Table 1. Complex
3b shows no oxidation wave within the electrochemical
window of the DMF solvent. With reference to previously
reported cyclometalated platinum(II) complexes of C^N^N
ligands,[10–12] the reduction couple is assigned to the ligand-
centred reduction of the fluorene-based C^N^N ligand. The
reduction potentials of complexes 1 and 2 (ꢁꢀ1.7 V) are
less cathodic than those of related cyclometalated platinu-
m(II) complexes containing extended p-conjugated R-
of the reduction couple is less sensitive to the number of
2
fluorene units.
X-ray crystallography: Crystallographic data of 2, 3a, 3d
and 4c, intermolecular p–p and Pt···Pt distances, and select-
ed bond lengths and angles are given in the Supporting In-
formation.[16] Perspective views and crystal-packing diagrams
of 2, 3a and 3d are depicted in Figure 2, and those for 4c
are given in the Supporting Information (Figure S29). The
coordination geometries of complexes 2, 3a, 3d and 4c are
similar to those of [PtClACHTNUTGRNEUNG
(C^N^N)][10a] and [PtCl(p-extended
R-C^N^N)].[11a] In each of the complexes, the Pt ion adopts
ꢀ
a distorted square-planar geometry, as revealed by the N
Figure 2. Perspective views of a) 2, b) 3a, c) 3d and d) molecular packing diagram of 3d highlighting the p–p interactions between the molecules (the
two crystallographically inequivalent molecules are represented in black and grey).
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Properties of Fluorene-Based Platinum(II) Complexes
FULL PAPER
ꢀ
Pt C angles of 161.498 (2), 162.108 (3a), 162.108 (3d) and
158.078 (4c), all of which deviate significantly from the ideal
structured absorption bands at 325–355 nm, the absorption
maximum of which is red-shifted with an increasing number
of fluorene units. The molar extinction coefficient (e) of the
free ligand also increases with an increasing number of fluo-
rene units incorporated, consistent with an increase in p-
conjugation. A similar red shift and increase in molar ex-
tinction coefficient have also been observed in the absorp-
tion spectra of the corresponding platinum(II) complexes.
For complexes 1 and 2 containing the related 6-phenyl-2,2’-
bipyridine (C^N^N) ligand, the extinction coefficients (e) in
the UV region are substantially lower than those of other
complexes containing the p-extended C^N^N ligands. With
reference to other related platinum(II) complexes,[10–12,15] the
moderately intense bands at 400–420 nm are tentatively as-
ꢀ
ꢀ
value of 1808. The Pt Npyridine and Pt Nisoquinoline (3a, 3d and
4c) or Pt Npyridine (2) distances of the complexes are similar
ꢀ
ꢀ
ꢀ
ꢀ
(Pt Npyridine: 1.942–1.969 ꢁ; Pt Nisoquinoline/Pt Npyridine: 2.051–
2.102 ꢁ) and are comparable to those of previously reported
(R-C^N^N)][10,11] complexes. The Pt C distances of 3a
ꢀ
[PtCl
(1.974 ꢁ) and 3d (1.969 ꢁ) are slightly shorter, and the plat-
inum(II) ion in each case is ligated by the deprotonated
carbon atom (Cꢀ) of the fluorene unit. In their crystal struc-
tures, complexes 2, 3a and 4c are packed in a head-to-tail
fashion, with substantial p overlap of the fluorene-based
C^N^N ligands. The interplanar distances between two [Pt-
ACHTUNGTRENNUNG(C^N^N)] moieties are in the range of 3.28–3.40 ꢁ, reveal-
1
ing the presence of p–p interactions. In all of these cases,
the shortest Pt···Pt distances between the molecules are
>4 ꢁ, revealing no Pt···Pt interactions.
signed to the electronic transitions with mixed MLCT/3IL
characters. Similar electronic absorption spectra were re-
ported by Shao et al. in the study of platinum(II) complexes
The crystal structure of 3d consists of two crystallographi-
cally inequivalent molecules per asymmetric unit (Fig-
ure S27, denoted by Pt1 and Pt2). In contrast to 2, 3a and
4c, in which the molecules in each case are packed as head-
to-tail dimers, two molecules of 3d are staggered with a tor-
sional angle Npyridine-Pt-Pt-Npyridine of 127.28. Extensive inter-
molecular p–p interactions align the molecules into a 1D
column with alternate interplanar distances of 3.373–3.395 ꢁ
(Figure 2d). One salient feature is the presence of Pt···p in-
of
6-phenyl-4-(9,9-dihexylfluoren-2-yl)-2,2’-bipyridine.[12]
The effect of solvent polarity on the UV/Vis absorption
spectra of 3a (Figure S39) and 6a (Figure 4) has been inves-
tigated. The low-energy absorption band lmax of 3a is blue-
shifted with increasing solvent polarity: 433 nm in toluene;
431 nm in CH2Cl2; 431 nm in ethyl acetate; and 426 nm in
DMF. Likewise, the low-energy absorption peak maximum
of 6a displays a similar shift (lmax): 450 nm in toluene;
442 nm in CH2Cl2; 428 nm in ethyl acetate; 418 nm in
CH3CN; and 417 nm in DMF. Such a blue shift in the ab-
sorption energy suggests that the polarity of the ground
state is higher than that of the excited state; similar features
have been observed in other cyclometalated platinum(II)
complexes.[10,11,15]
teractions between the staggered molecules, with
Pt···CC^N^N distance of 3.407 ꢁ.
a
Small single crystals of 4c were obtained by slow cooling
of saturated solution of 4c in hot DMF. The X-ray diffrac-
tion data collected at 100 K are of sufficient quality for lo-
cating the fluorene-based C^N^N ligand and the Pt and Cl
atoms, but are not good enough for the identification of the
exact location and orientation of the n-hexyl chains. The so-
lution of the X-ray crystal structure using this set of X-ray
diffraction data revealed isomer A (linear form; coordina-
tion through Pt···C2) for 4c; molecules of 4c are packed as
dimers in a head-to-tail fashion, with an interplanar distance
of 3.371 ꢁ (Figure S30).
Complexes 1, 2, 3a–g, 4a–d, 5a–c and 6a–c are strongly
emissive, with emission quantum yields (F) up to 0.73 in de-
gassed dichloromethane at 298 K. The emission lifetimes (t)
of the complexes are in the microsecond time regime, sug-
gesting that the emission in each case originates from the
triplet excited state. Complexes 1 and 2 display a structure-
less emission band at lmax =588 and 568 nm, respectively,
and with emission quantum yields of 0.16 and 0.07, respec-
tively, both of which are substantially higher than that of the
Photophysical properties: The UV/Vis absorption spectra of
complexes 1, 2, 3a–g, 4a–d, 5a–c and 6a–c in dichlorome-
thane at 298 K exhibit an intense vibronic-structured ab-
sorption band, with peak maxima at 310–350 nm, e values of
104–105 dm3 molꢀ1 cmꢀ1, and a moderately intense absorption
shoulder at 400–420 nm (Table 2). The absorption lmax
values resemble those of other cyclometalated C^N^N
[PtClACTHGNUTERNNUG
(C^N^N)] complex (lmax =565 nm, F=0.025).[10a] The
emission spectra and excited-state lifetimes for complexes 1
and 2 are similar to those of the platinum(II) complexes
with fluorenyl-substituted C^N^N ligands recently reported
by Shao et al.[12] One point worth addressing is the effect of
the fluorene substitution on the emission wavelength and
quantum yield of complexes 1 and 2. By incorporating a flu-
orenyl C donor to give the cyclometalated 6-[(9,9-dihexyl-
fluoren-2-yl)pyridin-2-yl]isoquinoline ligand, the emission
lmax is red-shifted from 563 nm in 3a to 588 nm in 3g with
increased emission quantum yield. This phenomenon is at-
tributed to the stronger s-donor properties of the fluorenyl
carbanion C donor compared to the aryl carbanion C
donor; the former subsequently raises the ds* of the PtII ion
and increases the energy gap between the MLCT and non-
emissive d–d states. More importantly, the emission quan-
tum yield is further increased to 0.73 (3d) when the pyridine
platinACHTUNGTRENNUNG
um(II) complexes,[10–12,15] but with increased absorption
extinction coefficients. The photophysical data of 1, 2, 3a–g,
4a–d, 5a–c and 6a–c are summarised in Table 1, and the
corresponding electronic absorption spectra are depicted in
Figure 3 and Figures S32–S40. As revealed in Figure 3, the
intense absorption bands in the UV region (310–350 nm)
are derived from intra
A
N
fluorene-based C^N^N ligands, because similar transitions
are also present in the free ligands (Figure S31). The cyclo-
metalated ligands containing fluorene units display vibronic-
Chem. Eur. J. 2010, 16, 14131 – 14141
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14135

C.-M. Che et al.
Table 2. Photophysical data of complexes 1, 2, 3a–g, 4a–d, 5a–c and 6a–c.
UV/Vis absorption[a] lmax [nm]
Photoluminescence Data
Quantum Solid state, 298 K Solid state, 77 K
yield F[b] lmax [nm] (t [ms])
lmax [nm] (t [ms])
Solution[a]
Glassy solution, 77 K[c]
lmax [nm] (t [ms])
(e [molꢀ1 dmꢀ3 cmꢀ1])
lmax [nm] (t [ms])
1
2
294 (14300), 311 (14200), 330 (13900),
376 (9800), 445 (2000)
216 (144600), 281 (30337), 330 (22800), 568 (1.0)
352 (25400), 432 (7320)
588 (2.2)
0.16
0.07
0.35
0.07
0.02
0.73
0.23
0.73
0.10
0.18
0.12
0.46
0.22
587 (3.1), 626 (2.9) 587 (21.2), 638 (19.7) 556 (31.7), 603 (31.1)
604 (0.1)
558 (8.0), 625 (8.0),
670 (6.3)
558 (22.8), 603 (21.7),
664 (21.1)
3a 243 (43800), 284 (21400), 314 (38400),
349 (40400), 382 (17000), 418 (sh, 5600)
3b 316 (28800), 356 (34500), 383 (23400),
409 (95400), 446 (sh, 2480)
3c 302 (18900), 341 (16200), 390 (18900),
471 (sh, 4960)
3d 319 (48700), 350 (41000), 387 (19100),
418 (8040)
3e 322 (39300), 351 (32100), 387 (15600),
422 (6210)
563 (9.1)
566 (4.3)
601 (3.3)
563 (3.1), 604 (3.0), 561 (4.1), 607 (3.9),
660 (1.2) 661 (1.2)
584 (2.6), 617 (2.5), 580 (6.1), 633 (5.7),
672 (1.7) 694 (5.2)
594 (1.2), 639 (1.2), 594 (5.4), 643 (5.2),
688 (1.1) 709 (4.2)
572 (1.2), 611 (1.1), 570 (4.3), 620 (3.7),
553 (26.5), 575 (21.4),
600 (21.2), 650 (18.4)
560 (20.8), 608
659 (19.7)
ACHTUNGTRENNUNG(20.4),
594 (10.9), 634 (9.3),
693 (8.9)
560 (11.2), 609 (10.5),
673 (10.3)
564 (9.3), 610 (9.1),
666 (8.4)
568 (2.6), 611 (2.5),
668 (2.5)
568 (3.6)
670 (0.6)
587 (1.2)
673 (3.4)
580 (5.6), 630 (5,1),
691 (3.7)
3 f 327 (42200), 355 (33200), 430 (6700)
568 (9.8), 609 (7.8),
666 (5.6)
588 (7.6), 604 (5.9)
564 (3.2), 608 (2.9), 565 (7.3), 608 (7.2),
666 (2.2) 666 (5.0)
557 (15.3), 601 (13.5),
654 (11.8)
3g 306 (43500), 346 (41800), 411 (21800),
482 (3500)
4a 286 (38200), 342 (51200), 399 (15800),
420 (12600), 469 (sh, 2020)
4b 290 (37600), 342 (53200), 397 (16100),
424 (11700), 465 (sh, 1920)
4c 316 (87400), 348 (98600), 379 (85000),
423 (45600), 472 (sh, 3230)
588 (2.3), 674 (1.9) 594 (3.3), 640 (2.8),
709 (2.6)
579 (13.6), 628 (12.8),
685 (11.9)
603 (8.7), 658 (8.0)
603 (7.6)
619 (8.8), 671 (6.9) 619 (12.5), 673 (10.1) 560 (55.8), 601 (51.2),
665 (44.8)
627 (4.2), 677 (2.9) 625 (11.6), 678 (11.1) 542 (28.8), 590 (26.1),
638 (22.9)
604 (5.8), 625 (5.0) 606 (11.8), 667 (11.3) 563 (26.4), 597 (26.2),
647 (20.18)
621 (4.3), 662 (4.2) 594 (11.0), 659 (11.0), 582 (58.8), 633 (53.3)
699 (9.8)
568 (6.2), 603 (5.1)
604 (7.3), 656 (7.0)
4d 342 (54300), 352 (58800), 418 (12000),
453 (sh, 2310)
5a 249 (38900), 291 (24200), 3454 (32100), 558 (13.2), 598 (12.9), 0.47
554 (0.3), 582 (0.2) 558 (6.0), 600 (5.4),
661 (3.8)
548 (20.1), 591 (19.8),
641 (18.2)
421 (7900), 449 (1480)
665 (12.5)
5b 292 (29600), 346 (39300), 422 (10100),
473 (sh, 2430)
561 (12.6), 605 (12.3), 0.26
674 (11.8)
559 (0.7), 605 (0.7) 569 (5.8), 618 (9.4),
673 (8.5)
547 (25.6), 589 (25.4),
638 (18.9)
5c 253 (41600), 303 (33300), 329 (38600),
570 (22.9), 616 (22.1), 0.34
551 (0.1), 594 (0.1), 566 (5.5), 609 (6.0),
568 (46.7), 606 (40.3),
671 (34.7)
562 (28.1), 609 (28.0),
667 (28.0)
563 (15.4), 612 (12.6),
668 (11.3)
584 (32.1), 631 (32.0),
681 (30.2)
373 (35900), 426 (16500), 483 (sh, 2070) 676 (19.8)
6a 252 (127900), 343 (64900), 388 (25100), 572 (9.9), 612 (9.8),
420 (16000), 442 (10900), 472 (sh, 2350) 673 (9.5)
6b 257 (52000), 349 (73200), 424 (15500),
463 (2880)
666 (0.1)
571 (0.1), 617 (0.1), 575 (5.3), 662 (5.2),
673 (0.1) 676 (4.8)
576 (1.3), 621 (1.2), 592 (9.4), 635 (9.4),
682 (1.1) 692 (6.3)
583 (0.8), 533 (0.8), 591 (5.7), 637 (4.0),
687 (0.6) 696 (3.8)
674 (8.5)
0.33
0.32
570 (9.0), 614 (8.8),
675 (8.5)
6c 253 (56900), 335 (70800), 375 (86400),
468 (4680)
586 (12.1), 631 (11.6) 0.36
[a] Determined in degassed dichloromethane solution. [b] Absolute emission quantum yield was measured by the optical dilute method with [Ru-
(bpy)3]Cl2 (bpy=2,2’-bipyridine) in degassed acetonitrile as standard (fr =0.062) and calculated by: fs =fr (Br/Bs)
(ns/nr)2 (Ds/Dr), in which the subscripts
A
ACHTUNGTRENNUNG
s and r refer to sample and reference standard solution respectively, n is the refractive index of the solvents, D is the integrated intensity and f is the lu-
minescence quantum yield. The excitation intensity B is calculated by: B=1ꢀ10ꢀAL, in which A is the absorbance at the excitation wavelength and L is
the optical path length (L=1 cm in all cases). The refractive indices of the solvents at room temperature were taken from standard sources. Errors for f
values (ꢂ10%) are estimated. [c] In DMF: MeOH: EtOH mixture (v:v:v=1:1:4).
ring in C^N^N is replaced by isoquinoline. A previous
study on structurally related [PtCl(p-extended R-C^N^N)]
complexes (p-extended (R-C^N^N)=3-(6’-(naphthalen-2’’-
yl)pyridin-2’-yl)isoquinoline) using DFT calculations[11b] re-
vealed that the isoquinoline ring increases the p-conjugation
of the cyclometalated ligand. This extended p-conjugation
leads to a destabilisation of the HOMO dxz(Pt) orbital, con-
sequently removing the degeneracy of the dxz and dxy orbi-
bronic progression ꢁ1300 cmꢀ1, which are characteristic of
the C=C and C=N stretching frequencies of the fluorene
unit and the C^N^N ligand. This indicates the involvement
of the fluorene-based cyclometalated ligand in the excited
state. We found that the emission energies of 3a and 6a are
only slightly affected by solvent polarity. The emission maxi-
mum is blue-shifted from 567 nm (in toluene) to 563 nm
(CH2Cl2), 561 nm (ethyl acetate) and 559 nm (DMF) for 3a
and from 576 nm (toluene) to 572 nm (CH2Cl2), 570 nm
(ethyl acetate), 567 nm (CH3CN) and 566 nm (DMF) for 6a
(Figure S40). The vibronic-structured emission in solution at
tals. Thus, the [PtClACTHUNGTRENNG(U R-C^N^N)] complexes (R-C^N^N=
extended p-conjugated cyclometalated ligands) do not un-
dergo excited-state Jahn–Teller distortion and the C^N^N-
Pt-Cl plane remains coplanar upon excitation, resulting in
the enhancement of the emission quantum yield.[11b] Com-
plexes 1, 2, 3a–g, 4a–d, 5a–c and 6a–c display vibronic-
structured emissions with lmax =558–604 nm and with vi-
room temperature is consistent with the mixing of intraACHTUNGTRENNUNGli-
A
With reference to previous studies,[11a] we tentatively assign
the solution emission to mixed 3IL/3MLCT excited states.
14136
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Chem. Eur. J. 2010, 16, 14131 – 14141

Properties of Fluorene-Based Platinum(II) Complexes
FULL PAPER
their solid-state emission spectra are given in the Supporting
Information (Figures S41–S59). In general, the complexes
display vibronic-structured emission bands with emission en-
ergies similar to those observed in dichloromethane. For ex-
ample, the emission of 3a exhibits peak maxima lmax at 553,
575, 600 and 650 nm (vibronic progression ꢁ1300 cmꢀ1) in
DMF:MeOH:EtOH glassy solution (v:v:v=1:1:4) at 77 K.
The solid-state emission maxima of complexes 1, 2, 3a–g,
4a–d, 5a–c and 6a–c at room temperature are in the range
from 560 to 650 nm. The vibronic structures are better re-
solved after cooling the solid samples to 77 K. These emis-
sion bands are similarly assigned to mixed 3IL/3MLCT
states.
OLED fabrication and electroluminescent properties: The
fluorene-based cyclometalated platinum(II) complexes dis-
play high emission quantum yields and high thermal stabili-
ty, both of which are required features of advanced materi-
als for OLED applications. The OLEDs studied in this work
were prepared by vacuum deposition and spin-coat methods.
Monochromic OLEDs were fabricated with 2–8 wt% of
platinum(II) complexes as the emitting dopant and with the
following configurations: ITO (indium tin oxide)/NPB (4,4’-
bis[N-(1-naphthyl)N-phenylamino]biphenyl,
40 nm)/CBP
(4,4’-N,N’,-dicarbazolebipenyl): PtII complex (2–8 wt%,
30 nm)/BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline,
15 nm)/Alq3 (tris(8-quinolinolato)aluminium, 30 nm)/LiF
(0.5 nm)/Al (100 nm). The spin-coat device adopted a simi-
lar configuration: ITO/PEDOT:PSS/PVK: PtII complex
(5 wt%, 80 nm)/BCP (15 nm)/Alq3 (30 nm)/LiF (0.5 nm)/Al
(100 nm). Schematic cross-section diagrams of the device
structure are depicted in the Supporting Information (Fig-
Figure 3. UV/Vis absorption (top) and emission (bottom) spectra of cy-
clometalated platinum(II) complexes containing fluorene unit(s).
AHCTUNGTREGuNNUN res S60 and S61), and a summary of the device performan-
ces is given in Table 3.
Devices A–G gave yellow or orange light with similar
CIE coordinates. These OLED devices displayed a strong
emission with peak maxima at 560–585 nm and a shoulder
at about 610–630 nm (Figure 5). Both the band shape and
emission maximum of the electroluminescence (EL) are
similar to that of the corresponding photoluminescence
(PL). The EL is tentatively assigned to the same mixed
3IL/3MLCT excited state as that for the corresponding PL of
the platinum(II) complex. The EL spectra of devices A–G
remained unchanged at a high operation voltage of 15–20 V.
In all cases, there was no undesirable emission from the host
material or Alq3 layer, revealing efficient energy transfer
from the CBP or PVK host material to the dopant com-
plexes.
Figure 4. UV/Vis absorption spectra of 6a in different solvents.
The turn-on voltages for the vacuum-deposited devices
were in the range of 5 to 6 V. The maximum brightness of
29000 cdmꢀ2 was achieved at 17 V for device D. The opera-
tion voltages for devices A–D are similar to the reported
There is a small red shift in the emission lmax along the
series: complexes 5a (one fluorene) to 5c (two fluorene
units) from 558 to 570 nm; and complexes 6a (two fluorene
units) to 6c (four fluorene units) from 572–586 nm by in-
creasing the number of fluorene units. The emission spectra
of 1, 2, 3a–g, 4a–d, 5a–c and 6a–c in glassy solutions
(DMF:MeOH:EtOH mixture, v:v:v=1:1:4) at 77 K and
values found for related [PtClACHTUNGTRNEUNG
(R-C^N^N)][11a] and [PtCl-
AHCTUNGTRENNUNG
(O^N^N)][15]-based OLEDs. Device B was found to display
a similar maximum brightness (27000 cdmꢀ2), with a maxi-
mum current efficiency and power efficiency of 14.7 cdAꢀ1
and 9.2 LmWꢀ1, respectively (Table 3, Figure 6). The current
Chem. Eur. J. 2010, 16, 14131 – 14141
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14137

C.-M. Che et al.
Table 3. Electroluminescence data for 3a, 3d, 3 f, 3g, 5d, 5c and 6c.
[b]
[d]
[e]
[f]
Device
(Complex)
x[a]
[%]
Bmax
A
CIE[c]
x, y
/
hcmax
[cdAꢀ1
hpmax
[lmWꢀ1
]
EQEmax
[%]
Fabrication
method
G
[cdmꢀ2
]
N
]
U
A (3a)
B (3d)
C (5b)
D (5c)
E (3 f)
F (3g)
G (6c)
4
2
3.5
8
5
27000
27000
8300
29000
3500
0.53, 0.45
0.53, 0.46
0.52, 0.43
0.44, 0.54
0.52, 0.47
0.56, 0.42
0.55, 0.43
10.6
14.7
3.8
13.9
9.2
5.3
9.2
1.7
5.5
3.7
1.3
0.8
3.3
5.5
1.3
4.2
3.4
1.5
1.0
vacuum deposition
vacuum deposition
vacuum depostion
vacuum deposition
spin-coating
5
5
1000
1900
3.2
2.5
spin-coating
spin-coating
[a] Dopant concentration of PtII complex. [b] Maximum brightness. [c] Commission Internationale de L’Eclairage coordinates. [d] Maximum current effi-
ciency. [e] Maximum power efficiency. [f] Maximum external quantum efficiency.
Figure 5. Electroluminescence of devices A–G.
Figure 6. Current–voltage–brightness (J-V-B) relationship of device
B
(Complex 3d).
Figure 7. Current efficiency for vacuum-deposited OLED devices A–D
(top) and spin-coated OLED devices E–G (bottom).
efficiency and current density relationships for devices A–G
are depicted in Figure 7. The brightness and device efficien-
turn-on voltage of the spin-coated devices E–G are in the
range of 6 to 7 V, similar to that of PVK-hosted IrIII complex
devices.[17] The relatively higher driving voltage compared to
the vacuum-deposited devices could be attributed to the
thicker light-emitting layer in the spin-coated devices
(PVK:Pt, 80 nm; CBP:Pt, 30 nm). A maximum brightness of
3500 cdmꢀ2 was achieved for device E with a good current
efficiency (9.2 cdAꢀ1). Although a number of highly effi-
cient OLED devices have been fabricated using cyclometa-
lated platinum(II) complexes as phosphorescent dopants
using the vacuum deposition technique,[10,11,15] the results de-
cy are comparable to those devices fabricated with [PtClACHTUNGTRENNUNG
C^N^N)][11a] and [PtCl
rescent dopants.
ACHTUNGTRENNUNG
Solution-processed OLEDs were fabricated using poly(9-
vinylcarbazole) (PVK) as host material. The increased solu-
bility imparted by the two n-hexyl chains on each fluorene
unit could facilitate homogeneous film formation with the
polymer host (Figure S72). It is known that the crystallisa-
tion process leads to the formation of traps for charge carri-
ers, which decreases the OLED device performance. The
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Chem. Eur. J. 2010, 16, 14131 – 14141

Properties of Fluorene-Based Platinum(II) Complexes
FULL PAPER
ing electrolyte at room temperature. All solutions for electrochemical
studies were deaerated with pre-purified argon gas before measurements.
The reference electrode was Ag/AgNO3 (0.1m in acetonitrile), the work-
ing electrode was a glassy carbon electrode and a platinum wire was used
as the counter electrode. Ferrocene was used as the internal reference.
scribed in this work represent the first study of platinum(II)
complexes as suitable phosphorescent dopants in both
vacuum-deposited organic light-emitting diodes as well as
solution-processed devices with polymeric host materials.
Further studies on the use of different host materials, device
thicknesses, and the use of additional electron transport ma-
terial(s) would provide information for improving the per-
formance of the solution-processed OLEDs using platin-
Synthesis of fluorene-based C^N^N ligands and corresponding platin-
AHCTUNGERTGuNNUN m(II) complexes: The fluorene-based C^N^N ligands were prepared by
in situ generation of the pyridine ring through the cyclisation of ketone
with ammonium salt,[11a] followed by a Suzuki coupling reaction. The syn-
thetic scheme and procedures, and the characterisations of the starting
materials (S1–S29) and ligands are described in the Supporting Informa-
tion. The platinum(II) complexes were prepared by heating under reflux
a mixture of K2PtCl4 and the corresponding fluorene-based C^N^N li-
gands in a chloroform/glacial acetic acid mixture (v:v 1:9, 50 mL) for
24 h. The orange solid was filtered, washed with water and diethyl ether
and recrystallised in CH2Cl2 to give an orange crystalline solid. Both li-
gands and corresponding platinum(II) complexes were characterised by
1H NMR spectroscopy, FAB or ESI mass spectrometry and elemental
ACHTUNGTRENNUNGum(II) complexes as dopants.
Conclusion
In summary, a series of new C^N^N cyclometalated ligands
containing fluorene units and their corresponding platin-
ACHTUNGTRENNUNGum(II) complexes have been synthesised and characterised.
1
1
analyses. H NMR spectra were assigned with H–1H COSY and NOESY
experiments.
The crystal structures of the platinum(II) complexes reveal
extensive intermolecular p–p interactions among the fluo-
rene-containing C^N^N ligands. The electronic absorption
and emission spectra of the platinum(II) complexes have
been studied. Vibronic-structured emission bands have been
observed, which are tentatively assigned to triplet excited
Complex 1: Yield: 86%; 1H NMR (400 MHz, CDCl3): d=0.77–0.86 (m,
10H; -CH2- and -CH3), 1.12–1.18 (m, 12H; -CH2-), 1.97–2.02 (m, 4H;
-CH2-), 7.17 (s, 1H; H13), 7.22–7.34 (m, 5H; H7, H8, H9, H15 and H21),
7.47–7.51 (m, 2H; H26 and H27), 7.52 (d, J=7.5 Hz, 1H; H6), 7.62–7.73
(m, 2H; H17 and H25), 7.81 (s, 1H; H3), 7.89 (t, J=7.5 Hz, 1H; H22), 7.98
(d, J=7.2 Hz, 1H; H23), 8.71 ppm (s, 1H; H20); FAB-MS (+ve): m/z: 793
[M+]; elemental analysis calcd (%) for C41H43N2PtCl: C 61.99, H 5.46, N
3.53; found: C 61.84, H 5.64, N 3.54.
states having mixed intraACTHUNTGRENNUGliCAHTUGTNRENNUG
gand (3IL) p–p* and metal-to-
ligand charge transfer (3MLCT) character. When the
number of fluorene units increases from one to two (3a–g;
5a–c) and from two to four (6a–c), a small red shift in emis-
sion energy is observed. These highly emissive platinum(II)
complexes display good thermal stability, rendering them
suitable materials for OLED applications. Their high solu-
bility in common organic solvents such as toluene enable
the complexes to be doped into a polymer host by various
solution-processing techniques, such as ink-jet printing or
the spin-coating method. These complexes are yellow to
orange dopants for OLEDs with good device efficiencies.
The performances of the vacuum-deposited or solution-pro-
cessed OLED are comparable to those of the related
PtII-[10,11,15] or IrIII-based devices.[7,17]
Complex 2: Yield: 86%; 1H NMR (400 MHz, CDCl3): d=0.66–0.89 (m,
10H; -CH2- and -CH3), 1.11–1.31 (m, 12H; -CH2-), 2.06–2.16 (m, 4H;
-CH2-), 2.09–2.20 (m, 2H; -CH2-), 6.91 (t, J=7.0 Hz, 1H , H5), 7.15–7.19
(m, 3H; H6, H8 and H14) 7.33 (d, J=7.3 Hz, 1H , H3), 7.39–7.43 (m, 2H;
H4 and H22), 7.78–7.81 (m, 4H; H6, H10, H25 and H29), 7.82 (d, J=7.4 Hz,
1H , H19), 7.90–8.10 (m, 2H; H15 and H16), 8.95 ppm (d, J=4.8 Hz, 1H ,
H13); FAB-MS (+ve): m/z: 793 [M+]; elemental analysis calcd (%) for
C41H43N2PtCl: C 61.99, H 5.46, N 3.53; found: C 61.95, H 5.50, N 3.51.
1
Complex 3a: Yield: 90%; H NMR (500 MHz, CD2Cl2): d=0.66–0.81 (m,
4H; CH2), 0.77 (t, J=7.1 Hz, 6H; -CH3), 1.04–1.17 (m, 12H; -CH2-),
1.98–2.08 (m, 12H; -CH2-), 7.32 (s, 1H; H13), 7.32–7.39 (m, 4H; H7, H8,
H9 and H15), 7.63 (d, J=7.4 Hz, 1H; H17), 7.69 (t, J=7.8 Hz, 1H; H23),
7.72 (t, J=7.9 Hz, 1H; H16), 7.81 (d, J=7.5 Hz, 1H; H6), 7.85 (t, J=
8.1 Hz, 1H; H24), 7.93 (d, J=8.2 Hz, 1H; H22), 7.96 (d, J=8.1 Hz, 1H;
H25), 7.98 (s, 3JH-Pt=21.1 Hz, 1H; H3), 8.33 (s, 1H; H27), 9.46 ppm (s,
1H; H20); FAB-MS: m/z: 767 [M+]; elemental analysis calcd (%) for
C39H41N2PtCl: C 60.97, H 5.38, N 3.65; found: C 61.94, H 5.34, N 3.62.
Complex 3b: Yield: 90%; 1H NMR (500 MHz, CD2Cl2): d=0.74–0.89
(m, 10H; -CH2-, -CH3), 1.12–1.23 (m, 12H; -CH2-), 2.00–2.06 (m, 4H;
-CH2-), 7.21 (t, J=7.8 Hz, 1H; H13), 7.30–7.51 (m, 6H; H30, H31 and H33),
7.60–7.75 (m, 4H; H32 and H35), 7.76–7.80 (m, 2H; H15 and H17), 7.81 (d,
J=7.1 Hz, 1H; H23), 7.87 (t, J=7.9 Hz, 1H; H16), 7.99 (d, J=7.2 Hz, 1H;
H6), 8.00 (d, J=8.3 Hz, 2H; H3 and H24), 8.24 (d, J=8.2 Hz, 1H; H25),
8.35 (s, 1H; H22), 8.52 (s, 1H; H27), 9.52 ppm (s, 1H; H20); FAB-MS (+
ve): m/z: 944 [M+]; elemental analysis calcd (%) for C53H49N2PtCl: C
67.40, H 5.23, N 2.97; found: C 67.39, H 5.21, N 3.01.
Experimental Section
Instrumentation: Electron-impact (EI) and fast atom bombardment
(FAB) mass spectra were obtained on a Finnigan Mat 95 mass spectrom-
eter. 1H and 13C NMR spectra were recorded on Bruker AVANCE 600,
DRX 400 and 300 FT-NMR spectrometers. 1H and 13C NMR chemical
shifts were referenced to TMS (TMS=tetramethylsilane) and residual
proton/carbon atoms of CDCl3, CD2Cl2 and d7-DMF. Peak assignments
1
Complex 3c: Yield: 90%; H NMR (500 MHz, CD2Cl2): d=0.71–0.83 (m,
were based on H–1H correlation and NOESY 2D NMR experiments. El-
1
10H; -CH2- and -CH3), 1.11–1.24 (m, 12H; -CH2-), 1.99–2.03 (m, 4H;
-CH2-), 6.88–6.98 (m, 2H; H7 and H+), 7.02 (d, J=7.3 Hz, 1H; H29),
7.15 (s, 1H; H9), 7.30–7.47 (m, 2H; H35 and H41), 7.49 (t, J=7.9 Hz, 1H;
H36), 7.51 (t, J=8.1 Hz, 1H; H40), 7.52–7.63 (m, 4H; H6, H16, H17 and
H24), 7.72–7.84 (m, 4H; H3, H23, H25 and H39), 7.91 (t, J=7.0 Hz, 2H; H22
and H37), 8.01 (d, J=7.9 Hz, 1H; H34), 8.32 (s, 1H; H27), 9.36 ppm (s, 1H;
H20); FAB-MS (+ve): m/z: 984 [M+]; elemental analysis calcd (%) for
C55H52N3PtCl: C 67.03, H 5.32, N 4.26; found: C 66.93, H 5.27, N 4.38.
emental analyses were performed at the Institute of Chemistry at the
Chinese Academy of Science, Beijing. UV/Vis spectra were obtained
with a Hewlett–Packard 8452 A spectrophotometer. Excitation and emis-
sion spectra were recorded on Spex Fluorolog-3 model fluorescence spec-
trofluorometer. All solutions for photophysical studies were degassed on
a vacuum line with no fewer than three successive freeze-pump-thaw
cycles. Excited-state lifetimes were measured using a Nd:YAG laser. Lu-
minescence quantum yields were measured using [Ru
(bpy)3]Cl2 in de-
Complex 3d: Yield: 85%; 1H NMR (400 MHz, CD2Cl2): d=0.65–0.86
(m, 10H; -CH2- and -CH3), 1.12–1.24 (m, 12H; -CH2-), 2.02–2.09 (m, 4H;
-CH2-), 7.13 (s, 1H; H15), 7.18 (s, 1H; H13), 7.30–7.34 (m, 3H; H30 and
H31), 7.44–7.49 (m, 6H; H7, H8, H24, H25 and H29), 7.63 (s, 1H; H3), 7.73–
7.81 (m, 3H; H6, H9 and H23), 7.90 (s, 1H; H17), 7.90 (d, J=8.2 Hz, 1H;
gassed acetonitrile as reference. Cyclic voltammetric measurements were
performed using a Princeton Applied Research electrochemical analyser
with a conventional three-compartment cell. Electrochemical measure-
ments were performed in DMF with 0.1m nBu4NPF6 (TBAH) as support-
Chem. Eur. J. 2010, 16, 14131 – 14141
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14139

C.-M. Che et al.
H22), 8.36 (s, 1H; H27), 9.09 ppm (s, 1H; H20); FAB-MS: m/z: 844 [M+];
elemental analysis calcd (%) for C45H45N2PtCl: C 64.01, H 5.37, N 3.32;
found: C 64.08, H 5.31, N 3.26.
ve): m/z: 844 [M+]; elemental analysis calcd (%) for C45H45N2PtCl: C
64.01, H 5.37, N 3.32; found: C 63.98, H 5.33, N 3.27.
Complex 5b: Yield: 86%; 1H NMR (400 MHz, CD2Cl2): d=0.72–0.81
(m, 10H; -CH2- and -CH3), 1.11–1.22 (m, 12H; -CH2-), 2.02–2.09 (m, 4H;
-CH2-), 2.02–2.13 (m, 2H; -CH2-), 2.19–2.25 (m, 2H; -CH2-), 6.94 (t, J=
7.2 Hz, 1H; H4), 6.99 (t, J=7.2 Hz, 1H; H5), 7.23 (d, J=7.0 Hz, 1H; H6),
7.30 (s, 1H; H8), 7.47 (d, J=7.4 Hz, 1H; H3), 7.55–7.63 (m, 3H; H22, H27
and H29), 7.72–7.76 (m, 2H; H18 and H26), 7.82 (t, J=7.5 Hz, 1H; H17),
7.86–7.93 (m, 5H; H10, H15, H16, H23 and H33), 8.39 (s, 1H; H20), 9.33 ppm
(s, 1H; H13); FAB-MS (+ve): m/z: 923 [M+]; elemental analysis calcd
(%) for C45H44N2BrPtCl: C 58.54, H 4.80, N 3.03; found: C 58.57, H 4.81,
N 3.05.
1
Complex 3e: Yield: 79%; H NMR (400 MHz, CD2Cl2): d=0.62–0.78 (m,
10H; -CH2- and -CH3), 1.08–1.15 (m, 12H; -CH2-), 2.00–2.11 (m, 4H;
-CH2-), 7.43–7.47 (m, 5H; H13, H15, H30 and H31), 7.49–7.56 (m, 5H; H7,
H24, H25, H29), 7.65 (m, 1H; H3), 7.81–7.85 (m, 3H; H6, H9 and H23), 7.88
(s, 1H; H17), 8.02 (d, J=7.6 Hz, 1H; H22), 8.47 (s, 1H; H27), 9.43 ppm (s,
1H; H20); FAB-MS (+ve): m/z: 984 [M+]; elemental analysis calcd (%)
for C55H52N3PtCl: C 75.86, H 6.08, N 4.83; found: C 75.81, H 6.03, N
4.91.
1
Complex 3 f: Yield: 85%; H NMR (400 MHz, CD2Cl2): d=0.65–0.86 (m,
1
Complex 5c: Yield: 86%; H NMR (400 MHz, CD2Cl2): d=0.76–0.87 (m,
10H; -CH2- and -CH3), 1.12–1.24 (m, 12H; -CH2-), 2.02–2.09 (m, 4H;
-CH2-), 7.20 (s, 1H; H13), 7.24–2.29 (m, 4H; H7, H8, H9 and H15), 7.47 (t,
J=7.2 Hz, 1H; H24), 7.58 (s, 1H; H31), 7.62 (s, 3H; H6 and H29), 7.68–7.72
(m, 3H; H17, H23 and H25), 7.90 (d, J=8.1 Hz, 1H; H22), 7.94 (s, 1H; H3),
8.33 (s, 1H; H27), 9.48 ppm (s, 1H; H20); FAB-MS (+ve): m/z: 955 [M+];
elemental analysis calcd (%) for C53H61N2PtCl: C 64.01, H 5.37, N 3.32;
found: C 64.08, H 5.33, N 3.29.
10H; -CH2- and -CH3), 1.01–1.38 (m, 12H; -CH2-), 2.06–2.15 (m, 2H;
-CH2-), 2.23–2.33 (m, 2H; -CH2-), 7.08 (m, 2H , H40 and H41), 7.37 (t, J=
7.5 Hz, 1H , H5), 7.42 (m, 1H; H2), 7.49 (t, J=7.3 Hz, 1H; H42), 7.57 (s,
1H; H8), 7.60–7.63 (m, 2H; H35 and H39), 7.64–7.77 (m, 6H; H4, H22, H27,
H29, H36 and H46), 7.83–8.02 (m, 8H; H10, H15, H16, H17, H18, H23, H26 and
H33), 8.48 (s, 1H; H20), 9.56 ppm (s, 1H; H13); FAB-MS (+ve): m/z: 1175
[M+]; elemental analysis calcd (%) for C70H77N2PtCl: C 58.54, H 4.80, N
3.03; found: C 58.58, H 4.83, N 2.99.
1
Complex 3g: Yield: 80%; H NMR (400 MHz, CD2Cl2): d=0.70–0.97 (m,
20H; -CH2- and -CH3), 1.08–1.29 (m, 24H; -CH2-), 2.02–2.25 (m, 8H;
-CH2-), 7.19 (s, 1H; H15), 7.23 (s, 1H; H13), 7.31–7.39 (m, 3H; H38, H39
and H40), 7.47–7.55 (m, 5H; H24, H25, H30 and H31), 7.59 (d, J=8.0 Hz,
1H; H33), 7.65–7.68 (m, 3H; H3, H34 and H44), 7.72 (s, 1H; H17), 7.73 (d,
J=8.0 Hz, 1H; H37), 7.76–7.85 (m, 6H; H6, H7, H9, H23 and H29), 7.92 (d,
J=8.3 Hz, 1H; H22), 8.37 (s, 1H; H27), 9.15 ppm (s, 1H; H20); FAB-MS:
m/z: 1177 [M+]; elemental analysis calcd (%) for C70H77N2PtCl: C 71.44,
H 6.59, N 2.38; found: C 71.31, H 6.60, N 2.42.
1
Complex 6a: Yield: 80%; H NMR (400 MHz, CD2Cl2): d=0.70–0.97 (m,
20H; -CH2- and -CH3), 1.08–1.29 (m, 24H; -CH2-), 2.02–2.25 (m, 8H;
-CH2-), 7.33–7.38 (m, 3H; H34, H35and H36), 7.40–7.52 (m, 3H; H7, H8
and H9), 7.52 (s, 1H; H3), 7.79–7.97 (m, 9H; H6, H13, H15, H23, H24, H29,
H30, H33 and H40), 8.05 (d, J=8.2 Hz, 1H; H25), 8.10 (s, 1H; H17), 8.18 (d,
J=8.1 Hz, 1H; H25), 8.55 (s, 1H; H27), 9.81 ppm (s, 1H; H20); FAB-MS
(+ve): m/z: 1100 [M+]; elemental analysis calcd (%) for C64H73N2PtCl:
C 69.83, H 6.68, N 2.54; found: C 69.71, H 6.70, N 2.56.
Complex 4a: Obtained as a 1:1 mixture of structural isomers A and B.
Yield: 75%; 1H NMR (400 MHz, CD2Cl2): d=0.72–0.95 (m, 20H; -CH2-
and -CH3), 1.12–1.30 (m, 24H; -CH2-), 1.99–2.24 (m, 8H; -CH2-), 7.37–
7.49 (m, 10H; Ar-H), 7.61 (m, 2H; Ar-H), 7.68–7.83 (m, 6H; Ar-H),
7.85–7.86 (m, 18H; Ar-H), 8.11–8.23 (m, 2H; Ar-H), 8.43 (s, 1H; H24),
8.51 (s, 1H; H24’), 9.71 (d, J=7.3 Hz, 1H; H8’), 9.79 (s, 1H; H17’),
10.02 ppm (s, 1H; H17); FAB-MS (+ve): m/z: 893 [M+].
Complex 6b: Yield: 80%; 1H NMR (400 MHz, CD2Cl2): d=0.70–0.97
(m, 20H; -CH2- and -CH3), 1.08–1.29 (m, 24H; -CH2-), 2.02–2.25 (m, 8H;
-CH2-), 7.33–7.38 (m, 3H; H34, H35 and H36), 7.40–7.52 (m, 3H; H7, H8
and H9), 7.52 (s, 1H; H3), 7.79–7.97 (m, 9H; H6, H13, H15, H23, H24, H29,
H30, H33 and H40), 8.05 (d, J=8.2 Hz, 1H; H25), 8.10 (s, 1H; H17), 8.18 (d,
J=8.1 Hz, 1H; H25), 8.55 (s, 1H; H27), 9.81 ppm (s, 1H; H20); FAB-MS
(+ve): m/z: 1256 [M+]; elemental analysis calcd (%) for
C64H71N2Br2PtCl: C 61.07, H 5.69, N 2.23; found: C 60.95, H 5.63, N 2.23.
Complex 4b: Obtained as a 1:0.5 mixture of isomers A and B. Yield:
77%; 1H NMR (400 MHz, d7-DMF): d=0.75–0.93 (m, 12H; -CH2- and
-CH3), 1.14–1.28 (m, 15H; -CH2-), 2.53–2.60 (m, 6H; -CH2-), 7.52–7.69
(m, 3H; Ar-H), 7.72 (d, J=7.6 Hz, 1.5H; Ar-H), 7.89 (d, J=7.3 Hz, 1H;
Ar-H), 7.91–7.97 (m, 2.5H; Ar-H), 8.02 (s, 1H; Ar-H), 8.32–8.47 (m, 7H;
Ar-H), 8.48 (s, 1H; Ar-H), 8.49–8.52 (m, 4H; Ar-H), 8.67–8.73 (m, 4H;
Ar-H), 8.92 (s, 1.5H; Ar-H), 9.12 (s, 1H; Ar-H), 8.52 (s, 1H; H24), 8.52 (s,
0.5H; H24’), 10.02 (s, 1H; H17’), 10.08 (d, J=7.2 Hz, 0.5H; H8’),
10.25 ppm (s, 1H; H17); FAB-MS (+ve): m/z: 971 [M+].
1
Complex 6c: Yield: 80%; H NMR (400 MHz, CD2Cl2): d=0.63–0.92 (m,
20H; -CH2- and -CH3), 1.06–1.33 (m, 24H; -CH2-), 2.04–2.25 (m, 8H;
-CH2-), 7.31–7.41 (m, 6H; H47, H48, H49, H60, H61 and H62), 8.08 (d, J=
8.4 Hz, 1H; H22), 8.14 (s, 1H; H17), 8.18 (d, J=8.0 Hz, 1H; H25), 8.58 (s,
1H; H27), 9.82 ppm (s, 1H; H20); FAB-MS (+ve): m/z: 1765 [M+]; ele-
mental analysis calcd (%) for C114H137N2PtCl: C 77.54, H 7.82, N 1.59;
found: C 77.60, H 7.85, N 1.54.
Single-crystal structure determination: X-ray diffraction data of com-
plexes 2, 3c and 4c were collected on a Bruker X8 Proteum diffractome-
ter using CuKa radiation (1.54178 ꢁ), and the X-ray diffraction data of 3a
were collected on a Bruker Smart CCD 1000 using graphite monochro-
matised MoKa radiation (0.71073 ꢁ). The images were interpreted and in-
tensities were integrated using the PROTEUM2 suite or DENZO pro-
gram. The structure was solved by the direct method employing the
SHELXS-97 program. Full-matrix least-squares refinements on F2 were
used in the structure refinement. The positions of H atoms were calculat-
ed on the basis of the riding mode with thermal parameters equal to 1.2
times those of the associated C atoms, and participated in the calculation
of final R indices. In the final stage of the least-square refinements, all
non-hydrogen atoms were refined anisotropically.
Complex 4c: Obtained as a 1:1 mixture of isomers A and B. Yield: 72%;
1H NMR (400 MHz, CD2Cl2): d=0.65–0.92 (m, 42H; -CH2- and -CH3),
1.15–1.32 (m, 44H; -CH2-), 2.01–2.18 (m, 8H; -CH2-), 2.27–2.43 (m, 8H;
-CH2-), 7.11 (d, J=7.3 Hz, 1H; Ar-H), 7.22–7.34 (m, 2H; Ar-H), 7.38–
7.49 (m, 16H; Ar-H), 7.58–7.70 (m, 8H; Ar-H), 7.74–7.82 (m, 6H; Ar-
H), 7.83–7.91 (m, 4H; Ar-H), 7.96–8.01 (m, 6H; Ar-H), 8.06 (s, 1H; H24),
8.12 (s, 1H; H24’), 9.29 (s, 1H; H17’), 9.46 (d, J=7.4 Hz, 1H; H8’),
9.58 ppm (s, 1H; H17); FAB-MS (+ve): m/z: 1225 [M+].
Complex 4d: Obtained as a 1:1 mixture of isomers A and B. Yield: 82%;
1H NMR (400 MHz, CD2Cl2): d=0.68–0.82 (m, 9H; -CH2-), 0.82–0.91 (m,
11H; -CH2-,-CH3), 1.13–1.28 (m, 24H; -CH2-), 2.12–2.27 (m, 8H; -CH2-),
6.97 (d, J=7.1 Hz, 1H; Ar-H), 7.02 (s, 1H; Ar-H), 7.17–7.38 (m, 14H;
Ar-H), 7.52–7.68 (m, 18H; Ar-H), 7.78 (d, J=7.3 Hz, 1H; Ar-H), 7.83 (d,
J=7.4 Hz, 1H; Ar-H), 7.92 (s, 1H; H24), 8.02 (s, 1H; H24’), 8.89 (s, 1H;
H17’), 9.18 (s, 1H; H17), 9.43 ppm (d, J=7.3 Hz, 1H; H8’); FAB-MS (+
ve): m/z: 971 [M+].
OLED fabrication: The vapour-deposited- and spin-coated OLED devi-
ces fabricated utilised a multilayer sandwich device structure. Indium tin
oxide (ITO) was used as anode and ITO glass was cleaned according to
the following procedure before OLED fabrication. ITO glass was soni-
cated in detergent solution for 10 min at 608C for degreasing, then soni-
cated in deionised water to remove the detergent. It was subsequently so-
nicated in ethanol, toluene and acetone for 10 min at 608C, dried with a
nitrogen blowgun, and heated at 1208C for 1 h. The ITO glass was treat-
ed in a UV ozone cleaner for 25 min before loading onto the vacuum
deposition chamber. All materials were deposited onto the ITO glass by
thermal deposition at a pressure of 1ꢂ10ꢀ6 Torr. The vacuum-deposited
1
Complex 5a: Yield: 86%; H NMR (400 MHz, CD2Cl2): d=0.69–0.89 (m,
10H; -CH2- and -CH3), 1.08–1.39 (m, 12H; -CH2-), 2.08–2.16 (m, 4H;
-CH2-), 7.13 (t, J=7.5 Hz, 1H; H28), 7.18 (t, J=6.4 Hz, 1H; H27), 7.39–
7.45 (m, 3H; H3, H4 and H5),7.50 (d, J=7.5 Hz, 1H; H29), 7.69 (t, J=
6.4 Hz, 1H; H17), 7.785–7.85 (m, 3H; H6, H22 and H33), 7.92–7.96 (m, 2H;
H16 and H23), 7.98 (s, 1H; H10), 8.04 (d, J=8.2 Hz, 1H; H15), 8.11 (d, J=
8.0 Hz, 1H , H18), 8.51 (s, 1H; H20), 9.70 ppm (s, 1H; H13); FAB-MS (+
14140
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 14131 – 14141

Properties of Fluorene-Based Platinum(II) Complexes
FULL PAPER
devices were fabricated by the following procedures: N,N’-bis(1-naph-
thyl)-1,1’-biphenyl-4,4’-diamine (NPB, 30 nm) was first deposited onto
the ITO glass as hole transport layer, followed by a light-emitting layer
with 4,4’-N,N,’-dicarbazolebipenyl (CBP, 30 nm) as host and 2–8 wt% of
platinum complex as phosphorescent dopant. The dopant level was con-
trolled by the deposition rates. The 2,9-dimethyl-4,7-diphenyl-1,10-phe-
nanthroline exciton confining layer (BCP, 15 nm) and electron transport
and injection layers (Alq3, 30 nm), LiF (0.5 nm) and Al (100 nm) were
subsequently deposited. The spin-coated devices were fabricated by the
following procedures: a layer of poly(3,4-ethylenedioxythiophene)/poly-
H. Vestweber, H. Schenk, K. Treacher, Synth. Met. 2001, 122, 105–
110; c) B.-J. de Gans, P. C. Duineveld, U. S. Schubert, Adv. Mater.
2004, 16, 203–213; d) F. So, B. Krummacher, M. K. Mathai, D. Pop-
lavskyy, S. A. Choulis, V.-E. Choong, J. Appl. Phys. 2007, 102,
091101.
[6] K. Watanabe, D. Kumaki, T. Tsuzuki, E. Tokunaga, S. Tokito, J.
Photopolym. Sci. Technol. 2007, 20, 39–42.
[7] a) J.-H. Jou, M.-C. Sun, H.-H. Chou, C.-H. Li, Appl. Phys. Lett.
2005, 87, 043508–043508; b) X. Yang, D. Neher, D. Hertel, T. K.
Dꢄubler, Adv. Mater. 2004, 16, 161–166; c) X. Yang, D. C. Mꢅller,
D. Neher, K. Meerholz, Adv. Mater. 2006, 18, 948–954; d) X. H.
Yang, D. Neher, Appl. Phys. Lett. 2004, 84, 2476–2478.
[8] a) A. L. Kanibolotsky, R. Berridge, P. J. Skabara, I. F. Perepichka,
D. D. C. Bradley, M. Koeberg, J. Am. Chem. Soc. 2004, 126, 13695–
13702; b) Q.-D. Liu, J. Lu, J. Ding, M. Day, Y. Tao, P. Barrios, J.
Stupak, K. Chan, J. Li, Y. Chi, Adv. Funct. Mater. 2007, 17, 1028–
1036; c) W.-Y. Lai, Q.-Y. He, R. Zhu, Q.-Q. Chen, W. Huang, Adv.
Funct. Mater. 2008, 18, 265–276; d) Q. Xin, X.-T. Tao, F.-Z. Wang,
J.-L. Sun, D.-C. Zou, F.-J. Wang, H.-J. Liu, Z. Liu, Y. Ren, M.-H.
Jiang, Org. Electron. 2008, 9, 1076–1086.
ACHTUNGTRENNUNG(styrenesulfonate) (PEDOT/PSS) was spin-coated onto the substrate at
8000 rpm and baked at 908C for 45 min. Fluorene-based platinum(II)
complexes (2–8 wt%) and the PVK polymer host were dissolved in chlor-
obenzene. The resulting solutions were filtered through 0.45 mm filters
prior to use. The solutions were spin-cast at 2000 rpm for 30 s and baked
at 908C for 1 h. The film thicknesses were determined to be in the ap-
proximate range of 1000–1200 ꢁ by ellipsometry. The BCP, Alq3, LiF and
Al layers were subsequently deposited under the same vacuum deposi-
tion conditions as the vacuum-deposited OLEDs.
[9] a) X. Zeng, M. Tavasli, I. F. Perepichka, A. S. Batsanov, M. R.
Bryce, C-J. Chiang, C. Rothe, A. P. Monkman, Chem. Eur. J. 2008,
14, 933–943; b) M. Tavasli, S. Bettington, I. F. Perepichka, A. S. Bat-
sanov, M. R. Bryce, C. Rothe, A. P. Monkman, Eur. J. Inorg. Chem.
2007, 4808–4814; c) B. Liang, L. Wang, Y. Xu, H. Shi, Y. Cao, Adv.
Funct. Mater. 2007, 17, 3580–3589; d) M. Tavasli, S. Bettington,
M. R. Bryce, H. A. Al Attar, F. B. Dias, S. King, A. P. Monkman, J.
Mater. Chem. 2005, 15, 4963–4970; e) A. Tsuboyama, H. Iwawaki,
M. Furugori, T. Mukaide, J. Kamatani, S. Igawa, T. Moriyama, S.
Miura, T. Takiguchi, S. Okada, M. Hoshino, K. Ueno, J. Am. Chem.
Soc. 2003, 125, 12971–12979; f) J. C. Ostrowski, M. R. Robinson,
A. J. Heeger, G. C. Bazan, Chem. Commun. 2002, 784–785.
[10] a) T.-C. Cheung, K.-K. Cheung, S.-M. Peng, C.-M. Che, J. Chem.
Soc. Dalton Trans. 1996, 1645–1651; b) W. Staroske, M. Pfeiffer, K.
Leo, M. Hoffmann, Phys. Rev. Lett. 2007, 98, 197402; c) B.-P. Yan,
C. C. C. Cheung, S. C. F. Kui, H.-F. Xiang, V. A. L. Roy, S.-J. Xu, C.-
M. Che, Adv. Mater. 2007, 19, 3599–3603; d) M. Cocchi, D. Virgili,
V. Fattori, D. L. Rochester, J. A. G. Williams, Adv. Funct. Mater.
2007, 17, 285–289; e) L. Murphy, J. A. G. Williams, Top Organomet.
Chem. 2010, 28, 75–111.
[11] a) S. C. F. Kui, I. H. T. Sham, C. C. C. Cheung, C.-W. Ma, B. Yan, N.
Zhu, C.-M. Che, W.-F. Fu, Chem. Eur. J. 2007, 13, 417–435; b) G. S.-
M. Tong, C.-M. Che, Chem. Eur. J. 2009, 15, 7225–7237.
[12] a) P. Shao, Y. Li, J. Yi, T. M. Pritchett, W. Sun, Inorg. Chem. 2010,
49, 4507–4517; b) G.-J. Zhou, Q. Wang, W.-Y. Wong, D. Ma, L.
Wang, Z. Lin, J. Mater. Chem. 2009, 19, 1872–1883; c) G.-J. Zhou,
W.-Y. Wong, B. Yao, Z. Xie, L. Wang, J. Mater. Chem. 2008, 18,
1799–1809; d) G.-J. Zhou, X.-Z. Wang, W.-Y. Wong, X.-M. Yu, H.-S.
Kwok, Z. Lin, J. Organomet. Chem. 2007, 692, 3461–3473.
Acknowledgements
We gratefully acknowledge financial support from the Innovation and
Technology Commission of the HKSAR Government (ITF/016/08NP),
the University Grants Committee of the Hong Kong SAR (AoE/P-03/
08), the Research Grants Council of Hong Kong SAR (HKU 7008/09P),
the National Natural Science Foundation of China/Research Grants
Council Joint Research Scheme (N HKU 752/08) and the Chinese Acad-
emy of Sciences: Croucher Foundation Funding Scheme For Joint Labo-
ratories. Dr. S. C. F. Kui acknowledges the small project funding
(200807176030) and the postdoctoral fellow scholarship from The Univer-
sity of Hong Kong. Dr. M.-Y. Yuen acknowledges the postgraduate stu-
dentship from The University of Hong Kong.
[1] First OLED: C. W. Tang, S. A. VanSlyke, Appl. Phys. Lett. 1987, 51,
913–915.
[2] a) T. Watanabe, H. S. Nalwa, S. Miyata in Organic Electrolumines-
cent Materials and Devices (Ed: S. Miyata, H. S. Nalwa), Gordon
and Breach, Amserdam, 1997, pp. 459–482; b) F. Hide, M. A. Dꢃaz-
Garcꢃa, B. J. Schwartz, A. J. Heeger, Acc. Chem. Res. 1997, 30, 430–
436; c) R. H. Friend, Pure Appl. Chem. 2001, 73, 425–430; d) W. Lu,
B.-X. Mi, M. C. W. Chan, Z. Hui, N. Zhu, S.-T. Lee, C.-M. Che,
Chem. Commun. 2002, 206–207; e) C.-M. Che, S.-C. Chan, H.-F.
Xiang, M. C. W. Chan, Y. Liu, Y. Wang, Chem. Commun. 2004,
1484–1485; f) S.-W. Lai, C.-M. Che, Top. Curr. Chem. 2004, 241, 27–
63; g) H.-F. Xiang, S.-W. Lai, P. T. Lai, C.-M. Che in Highly Efficient
OLEDs with Phosphorescent Materials (Ed.: H. Yersin), Wiley-
VCH, Weimheim, 2007, pp. 259–282; h) C.-M. Che, C.-C. Kwok, S.-
W. Lai, A. F. Rausch, W. J. Finkenzeller, N. Zhu, H. Yersin, Chem.
Eur. J. 2010, 16, 233–247.
[3] a) C. Adachi, M. A. Baldo, M. E. Thompson, S. R. Forrest, J. Appl.
Phys. 2001, 90, 5048–5051; b) M. Ikai, S. Tokito, Y. Sakamoto, T.
Suzuki, Y. Taga, Appl. Phys. Lett. 2001, 79, 156–158; c) S. Tokito, T.
Iijima, Y. Suzuri, H. Kita, T. Tsuzuki, F. Sato, Appl. Phys. Lett. 2003,
83, 569–571.
[4] a) P. F. van Hutten, V. V. Krasnikov, G. Hadziioannou, Acc. Chem.
Res. 1999, 32, 257–265; b) Z. I. Niazimbetova, A. Menon, M. E.
Galvin, Polym. Prepr. 2003, 44, 659–660; c) I. F. Perepichka, D. F.
Perepichka, H. Meng, F. Wudl, Adv. Mater. 2005, 17, 2281–2305;
d) J. M. Hancock, A. P. Gifford, R. D. Champion, S. A. Jenekhe,
Macromolecules 2008, 41, 3588–3597.
[13] C. M. Che, C. F. Kui, C. C. Kwok, US non-provisional patent appli-
cation No. 12/485,388, 2009.
[14] J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt, H. Bꢄssler, M.
Porsch, J. Daub, Adv. Mater. 1995, 7, 551–554.
[15] C.-C. Kwok, H. M. Y. Ngai, S.-C. Chan, I. H. T. Sham, C.-M. Che, N.
Zhu, Inorg. Chem. 2005, 44, 4442–4444.
[16] CCDC-776826 (2), 774058 (3a) and 776825 (3c) contain the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
[17] S. Lamansky, P. I. Djurovich, F. Abdel-Razzaq, S. Garon, D. L.
Murphy, M. E. Thompson, J. Appl. Phys. 2002, 92, 1570–1575.
[5] a) D. A. Pardo, G. E. Jabbour, N. Peyghambarian, Adv. Mater. 2000,
12, 1249–1252; b) H. Becker, H. Spreitzer, W. Kreuder, E. Kluge,
Received: June 4, 2010
Published online: October 19, 2010
Chem. Eur. J. 2010, 16, 14131 – 14141
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