Synthesis and properties of highly efficient electroluminescent green phosphorescent iridium cored dendrimers

Article abstract of DOI:10.1021/ma030383w

A simple convergent procedure has been developed for the preparation of solution processable phosphorescent dendrimers with biphenyl-based dendrons and fac-tris(2-phenylpyridyl)iridium(III) cores. We found that the attachment point and branching of the de

Full text of DOI:10.1021/ma030383w

Macromolecules 2003, 36, 9721-9730
9721
Synthesis and Properties of Highly Efficient Electroluminescent Green
Phosphorescent Iridium Cored Dendrimers
S.-C. Lo,† E. B. Na m d a s,‡ P . L. Bu r n ,*,† a n d I. D. W. Sa m u el*,‡
The Dyson Perrins Laboratory, University of Oxford, South Parks Rd, Oxford, OX1 3QY, UK, and
Organic Semiconductor Centre, School of Physics and Astronomy, University of St. Andrews,
North Haugh, St. Andrews, Fife, KY16 9SS, UK
Received J uly 14, 2003; Revised Manuscript Received September 10, 2003
ABSTRACT: A simple convergent procedure has been developed for the preparation of solution processable
phosphorescent dendrimers with biphenyl-based dendrons and fac-tris(2-phenylpyridyl)iridium(III) cores.
We found that the attachment point and branching of the dendrons are important for controlling the
color of the light emission. Photoluminescence excitation measurements showed that energy could be
transferred efficiently from the dendrons to the core. Solution photoluminescence quantum yield (PLQY)
measurements of the dendrimers were of order 70%, showing that the attachment of the dendron did not
decrease the luminescence efficiency of the core iridium complex. The PLQYs of the neat dendrimer films
increased with generation with the second-generation dendrimer having a neat film PLQY of 31%, 11/2
times higher than the first-generation dendrimers and almost 3 times that of the nondendritic iridium
complex, demonstrating the power of the dendrimer architecture to control intermolecular interactions.
Electrochemical experiments showed that charge was injected directly into the core of the dendrimers.
In tr od u ction
tively short triplet lifetime and the ability to modify
their structure to tune the color of emission.13 In
common with fluorescent small molecules most studies
on phosphorescent emitters have concentrated on
molecular materials which are also processed by
evaporation. More recently, there has been more
effort on developing solution-processed phosphorescent
materials.8-11,14 Of these routes we have demonstrated
that solution processed phosphorescent dendrimers can
give very efficient single and bilayer OLEDs.9-11,15
The phosphorescent dendrimers used as the light-
emitting component in these highly efficient OLEDs
have all been comprised of 2-ethylhexyloxy surface
groups, biphenyl-based dendrons, and fac-tris(2-phenyl-
pyridyl)iridium(III) (Irppy3) cores. In our previous re-
ports on these materials we have compared the effect
of generation,10 attachment point of the dendron,11 and
device architecture9,15 on OLED performance. In this
paper we describe the syntheses of these highly efficient
dendrimers and illustrate the modularity of the ap-
proach. We also discuss the effect of dendrimer genera-
tion and dendron attachment point on the physical,
photophysical, and electrochemical properties of the
dendrimers and compare the properties of the dendri-
mers with the molecular Irppy3.
One of the revolutions in organic conjugated materials
was the discovery that those, which were luminescent
in the solid state, could be used as the light-emitting
layer in organic light-emitting diodes (OLEDs). The first
materials used in OLEDs were fluorescent small mol-
ecules, and these materials are processed by evapora-
tion.1 The discovery that conjugated polymers could be
used as the light-emitting element in OLEDs introduced
the idea that solution processing could also be used for
making large-area OLEDs.2 More recently, dendritic
macromolecules have been developed as an alternative
class of materials for solution-processed light emitters.3-5
Light-emitting dendrimers consist of surface groups,
dendrons, and cores with the latter usually being the
emissive chromophore. Although conjugated polymers
have made excellent progress, dendrimers have a num-
ber of potential advantages for OLEDs formed by
solution processing. First, the electronic and processing
properties can be optimized independently. Second, a
convergent synthesis allows a modular approach to their
preparation, meaning that different dendrimer struc-
tures can be formed in a simple manner from common
dendron intermediates.6 Third, the dendrimer genera-
tion can be used to control the intermolecular interac-
tions, which are key to governing OLED performance.7
Finally, phosphorescent dendrimers can be easily
accessed.8-11 The advantage of phosphorescent emitters
is that they give the opportunity to provide OLEDs with
internal efficiencies of 100% due to their ability to
harness both singlet and triplet excited states. In
contrast, fluorescent emitters tend to suffer from a
substantial loss of efficiency due to triplet formation.12
The main molecular phosphorescent materials studied
have been based on iridium(III) complexes.13 The iri-
dium complexes have been used to form highly efficient
OLEDs, and their success has been due to their rela-
Resu lts a n d Discu ssion
Syn th esis. The properties of dendrimers can be
affected by the position of attachment of the dendron
to the core as well as the generation of the dendrimer.
In this new field of phosphorescent dendrimers we have
investigated the first-generation dendrimers 12 and 14
(Scheme 2) to explore the effect of the dendron attach-
ment position on the properties of the core Irppy3
complex. Dendrimers 12 and 14 differ in that the
dendron in 12 is attached meta to the pyridyl moiety
on the ligand phenyl ring whereas for 14 the dendron
is para to the pyridyl ring. These different positions
have been denoted as 3-G1-IrppyD for 12 and 4-G1-
IrppyD for 14 in Scheme 2. We have also studied the
† University of Oxford.
‡ University of St. Andrews.
10.1021/ma030383w CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/03/2003

9722 Lo et al.
Macromolecules, Vol. 36, No. 26, 2003
Sch em e 1a
a
Key: (A) tert-Butyllithium, tetrahydrofuran, dry ice/acetone bath, Ar then 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
and rt; (B) tetrakis(triphenylphosphine)palladium(0), aqueous sodium carbonate, ethanol, toluene, reflux, Ar.
second-generation dendrimer 13, which has the same
attachment point as 12 and is denoted 3-G2-IrppyD
(Scheme 2), to elucidate the effect of dendrimer genera-
tion on the properties of the core. There are a number
of elegant routes to biphenyl-based dendrons and den-
drimers.16 We chose a convergent strategy for the
formation of the dendrimers with the steps shown in
Schemes 1 and 2. The basic synthetic strategy was to

Macromolecules, Vol. 36, No. 26, 2003
Green Phosphorescent Iridium Cored Dendrimers 9723
Sch em e 2a
product, 1,3,5-tris[4′-(2′′-ethylhexyloxy)phenyl]benzene,
was also isolated in a 27% yield. 3 was then transformed
into the first-generation boronate ester 4 in a 75% yield
by metalation at low temperature and reaction with
IPTDB. To complete the syntheses of the first-genera-
tion ligands 6 (3-G1-Lig) and 8 (4-G1-Lig), 4 was coupled
with 2-(3′-bromophenyl)pyridine (5)19 and 2-(4′-bro-
mophenyl)pyridine (7)20 using tetrakis(triphenylphos-
phine)palladium(0) in an ethanol/toluene mixture heated
at reflux. Under these conditions 6 and 8 were formed
in 99% and quantitative yields, respectively.
The strategy for making the second-generation ligand
11 (3-G2-Lig) was slightly different (Scheme 1). The
normal method to form the second-generation “den-
dronized” ligand would be to couple 2 equiv of 4 with
1,3,5-tribromobenzene followed by boronate ester for-
mation and subsequent palladium-catalyzed coupling to
2-(3′-bromophenyl)pyridine (5). Although this route is
feasible, we found that the procedure illustrated in
Scheme 1 was more efficient. The first step in the
alternative procedure was to form the boronate ester
of 2-(3′-bromophenyl)pyridine (5). The boronate ester
[Lig-B(OCMe2)2] (9) was formed by metalation of 5 with
tert-butyllithium at low temperature followed by reac-
tion with IPTDB with 9 being isolated in a 50% yield. 9
was then coupled with 1.2 equiv of 1,3,5-tribromoben-
zene under palladium catalysis to give the dibromophe-
nyl derivative 10 (Lig-DiBrPh) in a 66% yield. The final
step in the formation of the second-generation ligand
was the coupling of 2.8 equiv of the first-generation
dendron 4 with 10. Using the same palladium catalysis
conditions as in the earlier steps, the second-generation
ligand 11 (3-G2-Lig) was formed in a 98% yield. There-
fore, the sequence used for making the dendrons re-
quired only two reaction types: the formation of borate
esters and their subsequent palladium-catalyzed cou-
pling with aryl bromides.
The iridium complexes were then formed from iridium
chloride trihydrate using the same two-step procedure
used for molecular iridium complexes (Scheme 2).21 The
first step for the dendritic complexes involved heating
iridium chloride trihydrate with an excess of the req-
uisite dendritic ligand in aqueous 2-ethoxyethanol.
Although we could isolate the corresponding intermedi-
ate iridium dimers, we found it simpler to just collect
the excess ligand from the initial reaction and react it
with the crude iridium dimer using silver trifluorom-
ethylsulfonate to drive the reaction forward. This second
step was carried out in the melt at temperatures in the
region of 130-145 °C depending on the dendrimer.
Using this protocol, the first-generation dendrimers 12
(with the dendron in the 3-position; 3-G1-IrppyD) and
14 (with the dendron in the 4-position; 4-G1-IrppyD)
and second-generation dendrimer 13 (with the dendron
in the 3-position; 3-G2-IrppyD) were formed in 39%,
49%, and 41% yield, respectively. These yields are over
two steps and are based on the amount of iridium
chloride trihydrate used in the first step. The final
complexation step could lead to either facial or meridi-
onal isomers of the dendrimers. Under the conditions
used in the final complexation step, from the iridium
dimer to the tris complex, the facial isomer is normally
formed. The facial nature of all three dendrimers was
a
Key: (A) Iridium(III) chloride trihydrate, water, 2-ethoxy-
ethanol, heat then 6, 8, or 11, silver trifluoromethanesulfonate,
heat, Ar.
attach the dendrons to the 2-phenylpyridyl ligand and
then complex the “dendronized” ligands to the iridium-
(III) cation. 2-Ethylhexyloxy groups were chosen as the
surface groups for the dendrimers as they have been
successfully used for the formation of spin-coated thin
films of conjugated polymers.17 The key intermediate
in the synthesis of all the dendrimers was the first-
generation boronate ester [G1-B(OCMe2)2], 4 (Scheme
1). 4 is a first-generation dendron as there is one level
of branching from the phenyl group attached to the
boronate ester. 4 was formed in three steps from
1-bromo-4-(2′-ethylhexyloxy)benzene (1).18 The first step
was the formation of the “zeroth”-generation boronate
ester [G0-B(OCMe2)2] (2) from 1, which was achieved
in a 69% yield by metalation of 1 with tert-butyllithium
at low temperature followed by reaction with the 2-iso-
propoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (IPT-
DB). The first-generation bromo-focused dendron (G1-
Br) 3 was then formed by reaction of 2.2 equiv of 2 with
1,3,5-tribromobenzene, using palladium catalysis, in a
60% yield. In addition to the desired 3, the trisubstituted
1
confirmed by H NMR by comparison with the spectra
reported for fac-Irppy3 and mer-Irppy3.21b,c
P h ysica l P r op er ties. We first studied the physical
properties of the dendrimers. All three dendrimers could

9724 Lo et al.
Macromolecules, Vol. 36, No. 26, 2003
be spin-coated to form good-quality thin films. In
addition, we found that the film-forming characteristics
of the dendrimers could be extended to the formation
of films containing blends of molecular materials such
as 4,4′-bis(N-carbazolyl)biphenyl (CBP).9-11 Gel perme-
ation chromatography (GPC) showed that 12, 13, and
14 were monodisperse. To estimate the hydrodynamic
radii (Rh) of the dendritic ligands and dendrimers, we
used the Mh v determined by GPC and the Hester-
Mitchell equation and Mark-Houwink relationship.22
The Mh v’s of dendritic ligands 6, 8, and 11 and dendrim-
ers 12, 13, and 14 were 743, 809 and 1481, and 2238,
3562 and 1681, respectively. These correspond to hy-
drodynamic radii of 5.4, 5.7, and 8.0 Å for 6, 8, and 11
and 10.2, 13.3, and 8.6 Å for 12, 13, and 14. For 3-G1-
IrppyD (12), the increase in hydrodynamic volume was
≈7 times that of the dendron. This is more than 2 times
larger than might be expected for simply connecting
three dendritic ligands to the iridium(III) cation. We
believe that the larger than expected hydrodynamic
volume is due to the more three-dimensional nature of
the dendrimer imparted by the facial arrangement of
the octahedral complex when compared with the den-
dron. For 3-G2-IrppyD (13), the increase in volume
moving from dendron to dendrimer is ≈4.5. This is
closer to the expected increase in volume and is because
the dendritic ligand is itself more three-dimensional in
nature due to the larger number of nonplanar biphenyl
units. However, for 4-G1-IrppyD (14), the increase in
hydrodynamic volume in moving from the dendron to
the dendrimer was only ≈3.4. This value is close to the
approximate 3-fold increase in volume that might be
expected for connecting the dendritic ligands to the
iridium cation and clearly demonstrates that the at-
tachment point of the dendron has a significant effect
on the three-dimensional shape of the dendrimers. The
different three-dimensional shapes can clearly affect the
morphology or packing of the dendrimers in a film.
F igu r e 1. Solution UV-vis absorption spectra of Irppy3, 12,
13, and 14 in toluene.
ligand.23 We first compared the solution UV-vis ab-
sorption spectra of Irppy3, 3-G1-IrppyD (12), and 3-G2-
IrppyD (13) (Figure 1). The spectra of Irppy3 can be
divided into two regions. The first region at around 280
nm corresponds to absorption due to the π to π*
transitions of the ligands with the longer wavelength
overlapping absorptions between 325 and 475 nm aris-
ing from the metal complex. The absorption at around
380 nm has been assigned to the metal to ligand singlet
charge transfer state (MLCT1).24 On adding the biphenyl
dendrons to the 3-position of the complex, there is little
change in either the strength or position of the absorp-
tions of the metal complex. However, there is a large
change in the molar absorptivity in going from Irppy3
to the first- and second-generation dendrimers 12 and
13 at around 280 nm. The increase in the molar
extinction coefficient at this wavelength corresponds to
the presence of the biphenyl units within the dendrons
for 12 and 13 with the difference in absorptivity between
12 and 13 being due to the increased number of the
biphenyl units in the second-generation dendrons. The
fact that there is little change in the wavelength of the
absorptions or molar absorptivities of the metal complex
core for either generation illustrates that the meta
arrangement around the branching phenyls to a first
approximation breaks the conjugation both within the
dendron and to the pyridine of the 2-phenylpyridyl
ligand. In contrast for 4-G1-IrppyD (14) the first phenyl
ring of the dendron is in conjugation with the pyridyl
moiety in the ligand. The increased conjugation length
gives rise to a small red shift, of order 18 nm, for the
metal complex absorptions when compared to 12 and
13. The absorption spectra of the dendrimers were found
to shift slightly in different solvents.
Thermal gravimetric analysis was carried out at a
heating rate of 10 °C/min under nitrogen. In each case
no significant weight loss was seen below 300 °C, and
even at 400 °C only a 5% weight loss was observed. This
shows that the attachment of the dendrons to the
2-phenylpyridine iridium(III) core in either the 3- or
4-position of the phenyl group attached to the iridium
does not have a detrimental effect on the thermal
stability of the complex. The weight loss does not
correspond to sublimation of the dendrimers. We also
studied the thermal properties of the dendrimers by
differential scanning calorimetry. We found that we
needed fast scan rates of order 200-300 °C/min to
observe the glass transition temperatures (Tgs) of the
dendrimers. The Tgs of 3-G1-IrppyD (12) and 3-G2-
IrppyD (13) were found to be around 132 and 189 °C,
respectively. The increase in Tg with generation is
expected and follows the increase in dendrimer molec-
ular weight. The first-generation dendrimer 4-G1-Irp-
pyD (14) had a Tg at around 138 °C, and hence for the
first-generation dendrimers the position to which the
dendron is attached to the core complex has only a small
effect on the thermal properties of the materials. Criti-
cally, the Tgs of all the dendrimers were sufficiently high
to allow the formation of morphologically stable films
suitable for device applications.
The solution photoluminescence (PL) spectra of Ir-
ppy3, 3-G1-IrppyD (12), 3-G2-IrppyD (13), and 4-G1-
IrppyD (14) are shown in Figure 2. For Irppy3, 12, and
13 the PL spectra all contain the same features, a peak
at 514 nm and a shoulder at 545 nm. For 14 there was
a small red shift of ≈20 nm in the PL spectrum due to
an increase in conjugation length caused by the first
phenyl ring of the dendron being in conjugation with
the pyridyl moiety via the phenyl ring of the ligand. The
Commission Internationale de l’Eclairage (C.I.E.) coor-
dinates for solution PL spectra for Irppy3, 12, and 13
P h otop h ysica l P r op er ties. The optoelectronic prop-
erties of the fac-(2-phenylpyridyl)iridium(III) complexes
can be changed by the attachment of substituents to the

Macromolecules, Vol. 36, No. 26, 2003
Green Phosphorescent Iridium Cored Dendrimers 9725
the 4-position rather than the 3-position, the change in
the PL spectra is less in going from solution to the film
than observed for 12. The two peaks are still well-
defined, and each is only shifted a small amount (4 nm)
to the red. The C.I.E. coordinates further illustrate the
movement of the color of the spectra with the coordi-
nates of Irppy3, 12, and 13 being (0.41, 0.56), (0.36, 0.60),
and (0.35, 0.61), respectively, and 14 having (0.42, 0.56).
These results clearly show that the dendron generation
and position of attachment assists in controlling the
intermolecular interactions that can lead to changes in
luminescence.
We probed these intermolecular interactions further
by photoluminescence quantum yield (PLQY) measure-
ments. For 3-G1-IrppyD (12) and 3-G2-IrppyD (13) it
was found that the PLQY of the second-generation
dendrimer at 31% was approximately 1.5 times higher
than the first generation.9,10 This is consistent with
reduced intermolecular core-core interactions for the
second-generation dendrimer. However, we have mea-
sured the PLQY of both 12 and 13 in degassed toluene
and found them to be 70% and 69%, respectively, which
indicates that even with the second-generation den-
drimer there are still significant intermolecular interac-
tions in the film that cause PL quenching. For 4-G1-
IrppyD (14) the solution PLQY was 74% and the film
PLQY was 24%.11 The decrease in PLQY is similar to
that seen for 3-G1-IrppyD (12). By using the dendrimer
in a host matrix, the detrimental intermolecular inter-
actions can be controlled. For example, when 20 wt %
of 3-G1-IrppyD (12) was incorporated into a CBP host,
the PLQY was found at 78% to be similar to the solution
PLQY.10 When 3-G2-IrppyD (13) and 4-G1-IrppyD (14)11
were blended with CBP at the same weight percent, the
measured PLQYs were 80% and 68%. For the PLQY
measurement of the blends the excitation wavelength
of 325 nm excited both the CBP host and the dendrimer
guests. However, PL emission was only observed from
the dendrimers, indicating efficient energy transfer from
the CBP host to the dendrimer guests. Therefore, the
fact that the PLQY of the films is at least as high as
the solution measurements indicates that in the solid
solution of the film the dendrimers are not aggregating.
The remarkable aspect of these blend films is that it is
the dendrimers that provide the good film-forming
properties even though they are the minority component
in the blend. A final aspect of the PL study was to
determine whether energy could be transferred ef-
ficiently from the dendrons to the core. For all three
dendrimers the film UV-vis absorption and photolu-
minescence excitation (PLE) spectra were collected with
that of 4-G1-IrppyD (14) shown in Figure 4 by way of
example. For 14 the emission was observed at 540 nm,
and the excitation wavelength was scanned from 700
to 260 nm. As expected, the direct excitation of the core
metal complex (325-425 nm) gives rise to efficient core
luminescence. In addition, the PLE spectrum matches
the absorption spectrum at short wavelengths where the
dendrons and the ligands absorb. This shows that
energy absorbed by the biphenyl units in the dendrons
is transferred to the core. If energy was not transferred
efficiently from the dendrons to the core, then the PLE
spectrum would mirror the absorption spectrum of the
core complex and hence look similar to the absorption
spectrum of Irppy3 in Figure 1. For 12 and 13 the PLE
spectra also followed their respective UV-vis absorption
spectra closely over both wavelength ranges. This
F igu r e 2. Solution photoluminescence spectra of Irppy3, 12,
13, and 14 in toluene (excitation wavelength ) 360 nm). The
spectra have been normalized and offset vertically for clarity.
F igu r e 3. Film photoluminescence spectra of Irppy3, 12, 13,
and 14 (excitation wavelength ) 325 nm).
are all (0.32, 0.62), and the red shift in the spectrum of
14 is reflected in coordinates of (0.38, 0.60). This again
illustrates the importance of the connection point of the
dendron to the ligand. The film PL spectra of Irppy3 and
the three dendrimers are shown in Figure 3. In going
to the solid state, there is a significant difference in the
emission spectra of the compounds. The PL spectrum
of the neat film of Irppy3 is featureless with the peak of
the emission red-shifted by 30 nm. In addition, the
spectrum contains a long red tail, which is at least in
part due to aggregate emission.25 The attachment of the
first-generation dendron onto the Irppy3 core in the
3-position causes the PL spectrum to look more like the
emission spectrum in solution although the peak and
shoulder are still red-shifted by around 15 nm with
respect to the solution spectrum. The decrease in red
shift of the spectrum relative to Irppy3 is due to the
dendrons on 12 decreasing the intermolecular interac-
tions of the emissive cores within the film. Attachment
of the second-generation dendron enhances the effect,
and there is only a small difference between the solution
and film PL spectra. For 14 which has the dendron in

9726 Lo et al.
Macromolecules, Vol. 36, No. 26, 2003
F igu r e 4. Film UV-vis absorption and photoluminescence
excitation spectra (PLE) (observed at 540 nm) of 14.
indicates that energy transfer from the dendrons to the
core was independent of the point of attachment of the
dendrons to the core and, at these low generations, the
generation.
Electr och em ica l P r op er ties. The final part of the
study on the materials was electrochemical analysis of
their electronic properties. Although the PLE spectra
indicated that energy transfer from the dendrons to the
core was efficient, their wide band gap suggests that
charge should be injected directly in the organometallic
core. The cyclic voltammagrams of the three dendrimers
are shown in Figure 5. 3-G1-IrppyD (12) had one
chemically reversible oxidation at 0.24 V and three
chemically reversible reductions at -2.91, -3.10, and
-3.28 V. Each of the redox processes corresponded to
one electron, and the potentials at which the oxidation
and reductions of 12 occurred were essentially the same
as those reported for Irppy3.23 The electrochemical
results in conjunction with the optical studies show that
the attachment of the dendrons in the 3-position or para
to the metal carbon bond does not change the absolute
energies of the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital
(LUMO) or the HOMO-LUMO energy gap appreciably.
During this study we were surprised to find that the
singly oxidized 12 was remarkably stable to oxygen and
moisture during the electrochemical experiment. The
electrochemical experiments were normally carried out
under anhydrous conditions and an inert atmosphere,
but we found that even after the addition of water and
allowing air into the cell the oxidation of 12 was still
chemically reversible. In contrast, the reduction pro-
cesses of 12 were very sensitive to moisture and oxygen.
For 3-G2-IrppyD (13) and 4-G1-IrppyD (14) the chemi-
cally reversible oxidations were easily seen at 0.26 and
0.27 V. The oxidation potentials of 12, 13, and 14 are
similar despite the slight red shift (0.1 eV in the PL
spectra). This can be understood by the fact that the
HOMO of iridium(III) complexes contains substantial
iridium character21c which does not change significantly
between the three dendrimers. In contrast, the LUMO
for this type of iridium(III) complex is comprised of the
π* orbitals21c of the ligand, and therefore the red shift
in the PL emission for 14 must be due to a decreased
LUMO energy leading to a more positive reduction
potential. However, under identical conditions used for
F igu r e 5. (a) Oxidation cyclic voltammograms of 12, 13, and
14. Scan rate ) 40 mV/s, solvent ) dichloromethane, concen-
tration ) 1 mM, platinum working electrode. (b) Reduction
cyclic voltammogram of 12. Scan rate ) 120 mV/s, solvent )
tetrahydrofuran, concentration ) 1 mM, glassy carbon working
electrode.
12 we were unable to observe clear chemically reversible
reductions for 13 and 14. Indeed for 14 on applying a
negative switching potential (≈-3.6 V) a dark green
compound was observed to form near the working
electrode, suggesting that a chemically irreversible
process was occurring. A final interesting observation
from the electrochemical study was that the difference
between the E1/2 of the first oxidation and reduction for
12 was 3.15 V, and this corresponds to the absorption
wavelength (394 nm) of the MLCT1 in the absorption
spectrum. This indicates that charge can be injected
directly into the orbitals associated with the MLCT
singlet state.
Con clu sion
We have developed a simple synthetic route to solu-
tion processable iridium complex cored dendrimers that
have been demonstrated to give highly efficient OLEDs.
We have demonstrated that the dendrons can be used
to give processability to molecular materials and can
control the important intermolecular interactions for

Macromolecules, Vol. 36, No. 26, 2003
Green Phosphorescent Iridium Cored Dendrimers 9727
benzene18 (1) (1.01 g, 3.54 mmol) in anhydrous tetrahydrofuran
(7 mL) that had been cooled in an dry ice/acetone bath under
argon. The mixture was stirred at -78 °C for 1 h. 2-Isopropoxy-
4,4,5,5-tetramethyl-1,3,2-dioxaborolane (0.87 mL, 4.26 mmol)
was added rapidly to the cold mixture, and the mixture was
stirred at -78 °C for 2 h. The mixture was allowed to warm
room temperature and then stirred at room temperature for
65 h. The reaction was quenched with water (3 mL), and the
two layers were separated. The aqueous layer was extracted
with ether (3 × 7 mL), and then the organic layer and the
ether extracts were combined, dried over anhydrous magne-
sium sulfate, and filtered. The solvent was completely removed
and the residue purified by column chromatography over silica
gel using ethyl acetate-light petroleum (0:1 to 1:10) as eluent
to give 2 (806 mg, 69%). Anal. Calcd for C20H33BO3: C, 72.3;
H, 10.0. Found: C, 72.15; H, 10.05. λmax (CH2Cl2)/nm: 244 (log
ꢀ/dm3 mol-1 cm-1 4.33), 271 (3.15), and 282 (2.98). δH (400.1
MHz; CDCl3): 0.87-0.97 (6 H, m, Me), 1.30-1.58 (20 H, m,
CH2 and Me), 1.70-1.78 (1 H, m, CH), 3.88 (2 H, m, ArOCH2),
6.91 and 7.76 (4 H, AA′BB′, ArH). δC (100.6 MHz; CDCl3): 11.1,
14.1, 23.0, 23.8, 24.8, 29.0, 30.5, 39.3, 70.2, 83.5, 113.9, 136.4,
and 162.0. m/z [EI] 332.3 (M+).
G1-Br (3). A mixture of 2 (380 mg, 1.14 mmol), 1,3,5-
tribromobenzene (163 mg, 0.520 mmol), tetrakis(triphenylphos-
phine)palladium(0) (33 mg, 0.029 mmol), aqueous sodium
carbonate (2 M, 0.5 mL), ethanol (0.5 mL), and toluene (1.5
mL) was deoxygenated and then heated at reflux under argon
for 24 h. The mixture was allowed to cool, and water (3 mL)
and ether (4 mL) were added. The organic layer was removed,
and the aqueous layer was extracted with ether (3 × 5 mL).
The organic layer and the ether extracts were combined, dried
over anhydrous magnesium sulfate, and filtered, and then the
solvent was completely removed. The residue was purified by
column chromatography over silica gel using dichloromethane-
light petroleum (0:1 to 1:10) as eluent to give 3 (202 mg, 60%).
Anal. Calcd for C34H45BrO2: C, 72.2; H, 8.0. Found: C, 71.85;
H, 7.9. λmax (CH2Cl2)/nm: 274 (log ꢀ/dm3 mol-1 cm-1 4.70). δH
(400.1 MHz; CDCl3): 0.87-1.03 (12 H, m, Me), 1.32-1.63 (16
H, m, CH2), 1.76-1.86 (2 H, m, CH), 3.93 (4 H, m, ArOCH2),
7.03 and 7.56 (8 H, AA′BB′, sp H), and 7.66 (3 H, m, G1-bp
H). δC (100.6 MHz; CDCl3): 11.2, 14.2, 23.1, 23.9, 29.1, 30.5,
39.4, 70.5, 114.9, 123.2, 123.9, 127.8, 128.2, 132.0, 143.3, and
159.5. m/z [MALDI: DHB] 564.4 and 566.3 (M+). 1,3,5-Tri[4′-
(2′′-ethylhexyloxy)phenyl]benzene (96 mg, 27%) was also
isolated. δH (200 MHz; CDCl3): 0.82-1.02 (18 H, m, Me), 1.25-
1.63 (24 H, m, CH2), 1.70-1.83 (3 H, m, CH), 3.90 (6 H, d. J )
5.5, ArOCH2), 7.01 and 7.62 (12 H, AA′BB′, sp H), and 7.65 (3
H, s, cp H). m/z [APCI+] 691.5 (MH+).
G1-B(OCMe2)2 (4). tert-Butyllithium (1.5 M, 4.8 mL, 7.2
mmol) was added to a solution of 3 (2.02 g, 3.57 mmol) in
anhydrous ether (12 mL) that had been cooled in a dry ice/
acetone bath under argon. The mixture was stirred at -78 °C
for 1.5 h, and then 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (0.9 mL, 4.4 mmol) was added rapidly to the
mixture. The mixture was allowed to warm to room temper-
ature over 3 h and then stirred at room temperature for further
62 h before being quenched with water (5 mL). The organic
layer was removed, and the aqueous layer was extracted with
ether (3 × 5 mL). The organic layer and the ether extracts
were combined, dried over anhydrous magnesium sulfate, and
filtered, and then the solvent was completely removed. The
residue was purified by column chromatography over silica gel
using ethyl acetate-light petroleum (1:10) and then ethyl
acetate-light petroleum (0:1 to 1:30) as eluent to give 4 (1.63
g, 75%). Anal. Calcd for C40H57BO4: C, 78.4; H, 9.4. Found:
C, 78.4; H, 9.4. λmax (CH2Cl2)/nm: 269 (log ꢀ/dm3 mol-1 cm-1
4.61). δH (500.0 MHz; CDCl3): 0.91-1.00 (12 H, m, Me), 1.31-
1.64 (28 H, m, CH2 and Me), 1.73-1.82 (2 H, m, CH), 3.91 (4
H, m, ArOCH2), 7.00 and 7.63 (8 H, AA′BB′, sp H), 7.85 (1 H,
m, G1-bp H), and 7.97 (2 H, m, G1-bp H). δC (125.7 MHz;
CDCl3): 11.0, 14.0, 23.0, 23.8, 24.8, 29.0, 30.4, 39.3, 70.5, 83.8,
114.6, 128.0, 128.2, 131.3, 133.3, 140.7, and 158.9. m/z [EI]
612.3 (M+).
phosphorescent dendrimers in a manner similar to
fluorescent dendrimers. The dendrimers are thermally
stable, and photoluminescence excitation experiments
show that energy can be transferred efficiently from the
dendrons to the emissive core whereas cyclic voltam-
metry reveals that charge is injected directly into the
core.
Exp er im en ta l Section
Mea su r em en ts. NMR spectra were recorded on Bruker
DPX 400 MHz, AMX 500 MHz, or Varian Gemini 200 MHz
spectrometers: sp ) surface phenyl; bp ) branch phenyl; L )
ligand. All J values are in hertz. UV-vis spectra were recorded
on a Perkin-Elmer UV-vis Lambda 14P spectrometer and
were recorded as solutions in toluene or spectroscopic grade
dichloromethane. Mass spectra were recorded on a VG Au-
tospec for EI or a Micromass TofSpec 2E for matrix-assisted
laser desorption/ionization-time-of-flight (MALDI-TOF) from
dithranol (DITH) or 2,5-dihydroxybenzoic acid (DHB) in re-
flectron mode or a VG Platform for APCI. Melting points were
recorded on a Gallenkamp melting point apparatus and are
uncorrected. Microanalyses were carried out in the Inorganic
Chemistry Laboratory, Oxford, UK. Gel permeation chroma-
tography was carried out using PLgel Mixed-A columns (600
mm + 300 mm lengths, 7.5 mm diameter) from Polymer
Laboratories calibrated with polystyrene narrow standards (Mp
) 580 to 3.2 × 106) in tetrahydrofuran with toluene as flow
marker. The tetrahydrofuran was degassed with helium and
pumped at a rate of 1 mL/min at 30.0 °C. Thermal gravimetric
analysis was performed on a Perkin-Elmer thermogravimetric
analyzer TGA 7. Glass transition temperatures were measured
on a Perkin-Elmer differential scanning calorimeter Pyris 1.
Light petroleum refers to the fraction of boiling point 40-60
°C, unless otherwise stated. When solvent mixtures are used
for chromatography over silica, the proportions are given by
volume.
Electrochemistry was performed using an EG&G Princeton
Applied Research potentiostat/galvanostat model 263A. All
measurements were made at room temperature on samples
dissolved in dichloromethane or tetrahydrofuran, with 0.1 M
tetra-n-butylammonium tetrafluoroborate as the electrolyte.
The tetrahydrofuran was distilled from sodium wire and
benzophenone under argon and then distilled from lithium
aluminum hydride under argon. HPLC grade dichloromethane
was used for the oxidation studies. The electrolyte was purified
by recrystallization from ethyl acetate. The solutions were
deoxygenated with argon. A glassy carbon or platinum working
electrode, platinum wire counter electrode, and Ag/3 M NaCl/
AgCl(sat) reference electrode was used. The ferricenium/
ferrocene couple was used as standard,26 and the ferrocene was
purified by sublimation or recrystallization from ethanol. All
potentials are quoted relative to the ferricenium/ferrocene
couple. In all cases several scans were carried out to confirm
the chemical reversibility of the redox processes.
Solution photoluminescence quantum yields (PLQYs) were
measured by a relative method using quinine sulfate in 0.5 M
sulfuric acid which has a photoluminescence quantum yield
of 0.51, as the standard.27 The dendrimers were dissolved in
toluene and freeze-thaw degassed. Photoluminescence spectra
were recorded in a J Y Horiba Fluoromax 2 fluorimeter, with
the dendrimer solutions excited at 360 nm. The optical
densities of the standard and sample were similar and small
(less than/equal to 0.1). The accuracy of these measurements
is estimated to be (10%.
Films were spin-coated from chloroform solutions with a
dendrimer concentration of 10 mg/mL at 900 rpm for 1 min to
give a thickness of about 150 nm. Their PLQY was measured
using an integrating sphere in accordance with Greenham et
al.28 using a Helium Cadmium laser (Kimmon) as the excita-
tion source. The excitation power was 0.05 mW at 325 nm and
the sphere was purged with nitrogen.
G0-B(OCMe2)2 (2). tert-Butyllithium (1.5 M, 3.8 mL, 5.66
mmol) was added to a solution of 1-bromo-4-(2′-ethylhexyloxy)-
3-G1-Lig (6). A mixture of 4 (100 mg, 0.163 mmol), 2-(3′-
bromophenyl)pyridine (5)19 (32 mg, 0.137 mmol), tetrakis-

9728 Lo et al.
Macromolecules, Vol. 36, No. 26, 2003
(triphenylphosphine)palladium(0) (11 mg, 0.010 mmol), aque-
ous sodium carbonate (2 M, 0.1 mL), ethanol (0.1 mL), and
toluene (0.3 mL) was deoxygenated and then heated at reflux
under argon for 20 h. The mixture was allowed to cool to room
temperature, and water (4 mL) and ether (4 mL) were added.
The organic layer was removed, and the aqueous layer was
extracted with ether (3 × 5 mL). The organic layer and the
ether extracts were combined, washed with brine (8 mL), dried
over anhydrous sodium sulfate, and filtered, and then the
solvent was completely removed. The residue was purified by
chromatotron over silica gel using dichloromethane-light
petroleum (1:50 to 1:10) as eluent to give 6 (87 mg, 99%). Anal.
Calcd for C45H53NO2: C, 84.5; H, 8.4; N, 2.2. Found: C, 84.2;
H, 8.5; N, 2.2. λmax (CH2Cl2)/nm: 270 (log ꢀ/dm3 mol-1 cm-1
4.84). δH (400.1 MHz; CDCl3): 0.92-1.03 (12 H, m, Me), 1.32-
1.67 (16 H, m, CH2), 1.76-1.86 (2 H, m, CH), 3.95 (4 H, m,
ArOCH2), 7.06 and 7.68 (8 H, AA′BB′, sp H), 7.28 (1 H, m, L
H), 7.62 (1 H, t, J ) 7.5, L H), 7.75-7.88 (6 H, m, L H and
G1-bp H), 8.05 (1 H, d, J ) 7.8, L H), 8.37 (1 H, d, J ) 1.6, L
H), and 8.77 (1 H, m, L H). δC (100.6 MHz; CDCl3): 11.2, 14.1,
23.1, 23.9, 29.1, 30.6, 39.4, 70.6, 114.9, 120.7, 122.2, 124.3,
124.5, 126.0, 128.0, 128.3, 129.2, 133.4, 136.8, 140.0, 141.97,
141.99, 142.1, 149.7, 157.4, and 159.2. m/z [APCI+] 640.5
(MH+).
83.9, 120.7, 122.0, 128.2, 129.9, 133.2, 135.3, 136.6, 138.7,
149.6, 154.6, and 157.5. m/z [APCI+] 282.2 (MH+).
Lig-DiBr P h (10). A mixture of the 9 (5.15 g, 18.3 mmol),
1,3,5-tribromobenzene (6.92 g, 22.0 mmol), tetrakis(triph-
enylphosphine)palladium(0) (846 mg, 0.732 mmol), aqueous
sodium carbonate (2 M, 12 mL), ethanol (12 mL), and toluene
(48 mL) was deoxygenated and then heated at reflux under
argon for 19.5 h. The mixture was allowed to cool, and water
(10 mL) and ether (20 mL) were added. The organic layer was
removed, and the aqueous layer was extracted with ether (3
× 20 mL). The organic layer and the ether extracts were
combined, dried over anhydrous sodium sulfate, and filtered,
and then the solvent was completely removed. The residue was
purified by column chromatography over silica gel using ethyl
acetate-light petroleum (0:1 to 1:20) as eluent to give 8 (4.70
g, 66%). Anal. Calcd for C17H11Br2N: C, 52.5; H, 2.9; N, 3.6.
Found: C, 52.6; H, 2.5; N, 3.6. λmax(CH2Cl2)/nm 249 (log ꢀ/dm3
mol-1 cm-1 4.50) and 274 sh (4.32). δH (400.1 MHz; CDCl3):
7.29 (1 H, m, L H), 7.57 (2 H, m, L H), 7.67 (1 H, t, J ) 1.7,
G1-bp H), 7.75 (2 H, d, J ) 1.7, G1-bp H), 7.79 (2 H, m, L H),
7.99 (1 H, m, L H), 8.19 (1 H, m, L H), and 8.74 (1 H, m, L H).
δC (100.6 MHz; CDCl3): 120.7, 122.5, 123.2, 125.7, 126.9, 127.6,
129.1, 129.4, 132.7, 136.9, 138.9, 140.2, 144.6, 149.8, and 156.8.
m/z [APCI] 388.0 (MH+).
4-G1-Lig (8). A mixture of 4 (100 mg, 0.163 mmol), 2-(4′-
bromophenyl)pyridine (7)18 (32 mg, 0.137 mmol), tetrakis-
(triphenylphosphine)palladium(0) (11 mg, 0.010 mmol), aque-
ous sodium carbonate (2 M, 0.1 mL), ethanol (0.1 mL), and
toluene (0.3 mL) was deoxygenated and then heated at reflux
under argon for 21.5 h. The mixture was allowed to cool to
room temperature, and water (4 mL) and ether (5 mL) were
added. The organic layer was separated, and the aqueous layer
was extracted with ether (3 × 5 mL). The organic layer and
the ether extracts were combined, washed with brine (10 mL),
dried over anhydrous sodium sulfate, and filtered, and then
the solvents were completely removed. The residue was
purified by chromatotron over silica gel using dichloromethane-
light petroleum (0:1 to 1:20) as eluent to give 8 (87 mg, 100%)
as a colorless oil, which crystallized on standing; mp 97-98
°C. Anal. Calcd for C45H53NO3: C, 84.5; H, 8.4; N, 2.2. Found:
C, 84.1; H, 8.3; N, 2.3. λmax (CH2Cl2)/nm 283 (log ꢀ/dm3 mol-1
cm-1 4.81). δH (400.1 MHz; CDCl3): 0.94-1.03 (12 H, m, Me),
1.32-1.64 (16 H, m, CH2), 1.77-1.88 (2 H, m, CH), 3.90-3.97
(4 H, m, ArOCH2), 7.05 and 7.66 (8 H, AA′BB′, sp H), 7.27 (1
H, m, L H), 7.75-7.85 (7 H, m, G1-bp H and L H), 8.15 (2 H,
1/2AA′BB′, L H), and 8.76 (1 H, m, L H). δC (100.6 MHz;
CDCl3): 11.1, 14.1, 23.1, 23.9, 29.1, 30.5, 39.4, 70.5, 114.8,
120.5, 122.2, 124.0, 127.3, 127.7, 128.3, 133.4, 136.8, 138.4,
141.6, 141.8, 142.1, 149.7, 157.0, and 159.2. m/z [APCI+] 640.4
(MH+).
3-G2-Lig (11). A mixture of 4 (132 mg, 0.215 mmol), 10 (30
mg, 0.077 mmol), tetrakis(triphenylphosphine)palladium(0) (7
mg, 6 µmol), aqueous sodium carbonate (2 M, 0.1 mL), ethanol
(0.1 mL), and toluene (0.3 mL) was deoxygenated and then
heated at reflux under argon for 18 h. The mixture was allowed
to cool to room temperature, and water (4 mL) and ether (5
mL) were added. The organic layer was removed, and the
aqueous layer was extracted with ether (3 × 5 mL). The
organic layer and the ether extracts were combined, washed
with brine (8 mL), dried over anhydrous sodium sulfate, and
filtered, and then the solvent was completely removed. The
residue was purified by chromatotron over silica gel using
dichloromethane-light petroleum (0:1 to 1:4) as eluent to give
11 (91 mg, 98%). Anal. Calcd for C85H101NO4: C, 85.0; H, 8.5;
N, 1.2. Found: C, 84.8; H, 8.7; N, 1.1. λmax (CH2Cl2)/nm 270
(log ꢀ/dm3 mol-1 cm-1 5.27). δH (400.1 MHz; CDCl3): 0.92-
1.02 (24 H, m, Me), 1.33-1.60 (32 H, m, CH2), 1.74-1.84 (4
H, m, CH), 3.94 (8 H, m, ArOCH2), 7.05 (8 H, 1/2AA′BB′, sp
H), 7.28 (1 H, m, L H), 7.62-7.73 (9 H, m, sp H and L H),
7.77-7.89 (9 H, m, G2-bp H and L H), 8.02 (3 H, m, G1-bp H),
8.07 (1 H, d, J ) 7.9, ArH), 8.38 (1 H, m, L H), and 8.76 (1 H,
s, L H). δC (101.6 MHz; CDCl3): 11.1, 14.1, 23.1, 23.9, 29.1,
30.5, 39.4, 70.5, 114.9, 120.8, 122.3, 124.4, 124.7, 125.7, 126.1,
126.2, 128.0, 128.4, 129.4, 133.3, 136.8, 140.1, 141.6, 142.1,
142.2, 142.4, 142.7, 149.7, 157.3, and 159.2. m/z [MALDI:
DITH] 1200.6 (MH+).
Lig-B(OCMe2)2 (9). tert-Butyllithium (1.7 M, 36.6 mL, 62
mmol) was added to a solution of 2-(3′-bromophenyl)pyridine
(5)19 (8.10 g, 34.6 mmol) in anhydrous tetrahydrofuran (130
mL) that had been cooled in a dry ice/acetone bath under
argon. The mixture was stirred at -78 °C for 2 h, and
2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (9 mL)
was added rapidly to the cold mixture. The reaction was stirred
at -78 °C for 2 h, allowed to warm to room temperature, and
then stirred at room temperature for further 20 h. The reaction
was quenched with water (30 mL), and the organic layer was
removed. The aqueous layer was extracted with ether (3 × 40
mL). Saturated sodium bicarbonate solution (40 mL) was then
added to the aqueous layer, and then the aqueous layer was
extracted with ether (2 × 40 mL). The organic layer and the
ether extracts were combined, dried over anhydrous sodium
sulfate, and filtered, and then the solvent was completely
removed. The residue was purified by column chromatography
over silica gel using dichloromethane-light petroleum (0:1 to
3-G1-Ir p p yD (12). A mixture of 6 (294 mg, 0.459 mmol),
iridium chloride trihydrate (41 mg, 0.12 mmol), water (1.0 mL),
and 2-ethoxyethanol (3.0 mL) was heated (bath temperature:
125-135 °C) under argon for 39 h. After cooling, the resultant
mixture was passed through a column of silica gel using ethyl
acetate-light petroleum (0:1 to 1:10), dichloromethane, and
then methanol as eluents. The filtrate was collected (≈600 mL)
and concentrated to about 50 mL. An orange-yellow solid
precipitated and was collected by filtration. The residue was
washed with methanol (≈10 mL). The bright yellow solid was
dried (177 mg) and then reprecipitated from
a dichlo-
romethane-methanol mixture to give impure iridium dimer
(125 mg). Excess 5 was collected from the filtrate, and the two
products were used without further purification for the next
step. A mixture of the above-obtained iridium complex, re-
cycled 5, and silver trifluoromethanesulfonate (34 mg, 0.133
mmol) was heated (bath temperature: 130 °C) for 3.5 days
under argon. The reaction was then allowed to cool to room
temperature, and the mixture was purified by column chro-
matography over silica gel using dichloromethane-ethyl ac-
etate-light petroleum (0:1:10 to 1:1:10) as eluent to give 12
(95 mg, 39%), TGA(5%) 400 °C. Tg 132 °C (scan rate ) 200 °C/
min). Anal. Calcd for C135H156IrN3O6: C, 76.9; H, 7.5; N, 2.0.
Found: C, 76.7; H, 7.2; N, 2.1. λmax (CH2Cl2)/nm 279 (log ꢀ/dm3
mol-1 cm-1 5.26), 325 sh (4.69), 389 sh (4.17), 414 sh (4.01),
1:30) as eluent to give 9 (4.92 g, 50%). Anal. Calcd for C17H20
-
BNO2: C, 72.6; H, 7.2; N, 5.0. Found: C, 72.6; H, 7.2; N, 5.0.
λmax (CH2Cl2)/nm 250 (log ꢀ/dm3 mol-1 cm-1 4.08) and 279
(4.04). δH (400.1 MHz; CDCl3): 1.37 (12 H, s, Me), 7.23 (1 H,
m, PyH), 7.51 (1 H, m, PhH), 7.76 (1 H, m, PyH), 7.80 (1 H,
m, PyH), 7.87 (1 H, m, PhH), 8.14 (1 H, m, PyH), 8.40 (1 H,
m, PhH), and 8.71 (1 H, m, PyH). δC (100.6 MHz; CDCl3): 24.9,

Macromolecules, Vol. 36, No. 26, 2003
Green Phosphorescent Iridium Cored Dendrimers 9729
458 sh (3.55), and 488 sh (3.16). δH (400.1 MHz; CD2Cl2): 0.92-
1.03 (36 H, m, Me), 1.31-1.66 (48 H, m, CH2), 1.73-1.86 (6
H, m, CH), 3.95 (12 H, m, ArOCH2), 7.00-7.13 (18 H, m, sp H
and L H), 7.30 (3 H, m, L H) 7.67-7.83 (27 H, m, sp H, G1-bp
H, and L H), 8.10 (3 H, d, J ) 1.7, L H), and 8.15 (3 H, d, J )
8.4, L H). δC (100.6 MHz; CDCl3): 11.7, 14.7, 23.9, 24.6, 29.9,
31.3, 40.2, 71.35, 115.5, 120.0, 123.4, 123.6, 123.8, 124.2, 129.0,
129.7, 134.0, 134.3, 137.4, 138.1, 142.5, 144.1, 145.4, 148.2,
160.0, 161.5, and 167.0; m/z [MALDI: DITH] Anal. Calcd for
H, d, J ) 8.3, L H). δC (100.6 MHz; CDCl3): 11.2, 14.2, 23.1,
23.8, 29.1, 30.5, 39.4, 70.2, 114.4, 118.7, 119.0, 122.0, 123.4,
123.7, 124.7, 127.8, 133.3, 135.7, 135.9, 141.37, 141.43, 142.6,
143.5, 147.3, 158.8, 162.0, and 166.4; m/z [MALDI: DITH].
Anal. Calcd for C135H156IrN3O6: 2106.2 (37%), 2107.2 (57%),
2108.2 (95%), 2109.2 (100%), 2110.2 (81%), 2111.3 (40%),
2112.3 (17%), 2113.5 (5%). Found: 2106.2 (35%), 2107.1 (55%),
2108.3 (93%), 2109.2 (100%), 2110.2 (78%), 2111.3 (41%),
2112.3 (18%), 2113.4 (5%) (M+).
C
135H156IrN3O6: 2106.2 (30%), 2107.2 (48%), 2108.2 (89%),
2109.2 (100%), 2110.2 (70%), 2111.2 (34%), 2112.2 (15%),
2113.2 (5%). Found: 2105.3 (16%), 2106.3 (45%), 2107.3 (71%),
2108.3 (100%), 2109.3 (100%), 2110.3 (77%), 2111.4 (38%),
2112.4 (18%), 2113.4 (7%) (M+). In addition excess 6 (121 mg)
was recovered.
Ack n ow led gm en t. We thank CDT Oxford Ltd. for
financial support. I.D.W.S. is a Royal Society Research
Fellow.
Refer en ces a n d Notes
3-G2-Ir p p yD (13). A mixture of 11 (2.97 g, 2.47 mmol),
iridium chloride trihydrate (174 mg, 0.50 mmol), water (4 mL),
and 2-ethoxyethanol (13 mL) was heated (bath temperature:
107 °C) under argon for 60 h before being allowed to cool. The
resultant precipitate was collected by filtration and purified
by column chromatography over a silica gel using dichlo-
romethane-light petroleum (1:30 to 1:10) as eluent to give the
chloro-bridged iridium dimer (900 mg). 11 (1.96 g) was
recovered from the filtrate after purification by column chro-
matography over silica gel using ethyl acetate-light petroleum
(1:30 to 1:10) as eluent. A mixture of the chloro-bridged iridium
dimer (900 mg), 11 (1.96 g), and silver trifluoromethane-
sulfonate (300 mg, 1.17 mmol) was heated (bath tempera-
ture: 145 °C) under argon for 7 days. The reaction was allowed
to cool to room temperature, and the mixture was purified by
column chromatography over silica gel using dichloromethane-
light petroleum (1:20) as eluent to give 13 (774 mg, 41%),
TGA(5%) 400 °C. Tg 189 °C (scan rate ) 300 °C/min). Anal. Calcd
for C255H300IrN3O12: C, 80.8; H, 8.0; N, 1.1. Found: C, 80.7;
H, 8.0; N, 1.1. λmax(CH2Cl2)/nm 272 (log ꢀ/dm3 mol-1 cm-1 5.64),
336 sh (4.76), 388 sh (4.22), 413 sh (4.06), 458 sh (3.57), and
488 sh (3.18). δH (400.1 MHz; CD2Cl2): 0.90-1.00 (72 H, m,
Me), 1.30-1.61 (96 H, m, CH2), 1.70-1.83 (12 H, m, CH), 3.91
(24 H, m, ArOCH2), 7.00-7.12 (30 H, sp H and L H), 7.22 (3
H, d, J ) 7.9, L H), 7.43 (3 H, m, L H), 7.70-7.77 (27 H, m, sp
H and L H), 7.77 (3 H, m, L H), 7.82 (6 H, s, G2-bp H), 7.93
(12 H, s, G2-bp H), 8.02 (3 H, s, G1-bp H), 8.09 (6 H, s, G1-bp
H), and 8.18 (6 H, m, L H). m/z [MALDI: DITH] 3791 (broad)
(M+). In addition excess 11 (676 mg) was recovered.
(1) Tang, C. W.; Van Slyke, S. A. Appl. Phys. Lett. 1987, 51, 913.
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dichloromethane as eluent. The fractions containing the chloro-
bridged iridium dimer and excess ligand were combined, and
the solvent was completely removed. The residue was dissolved
in dichloromethane (2 mL), and methanol (2 mL) was added.
The chloro-bridged dimer that precipitated was collected (≈238
mg) and used without further purification for the next step.
The solvent was removed from the filtrate to give crude
unreacted ligand (≈244 mg). A mixture of the chloro-bridged
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0.313 mmol), and silver trifluoromethanesulfonate (70 mg, 0.27
mmol) was heated (bath temperature: 130-140 °C) for 88 h
under argon. The reaction was allowed to cool to room
temperature, and the mixture was purified by column chro-
matography over silica gel using dichloromethane-ethyl ac-
etate-light petroleum mixture (0:1:10 to 1:1:10) as eluent to
give 14 (200 mg, 49%) as an orange-yellow solid; TGA(5%) 410
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°C; Tg 138 °C (scan rate ) 250 °C/min). Anal. Calcd for C135H156
IrN3O6: C, 76.9; H, 7.5; N, 2.0. Found: C, 76.8; H, 7.5; N, 2.0.;
max(CH2Cl2)/nm 265 sh (log ꢀ/dm3 mol-1 cm-1 5.26), 282 (5.29),
-
λ
391 (4.24), 436 sh (3.83), 472 sh (3.54), and 510 sh (2.86). δH
(400.2 MHz; CDCl3): 0.90-0.97 (36 H, m, Me), 1.29-1.55 (48
H, m, CH2), 1.61-1.70 (6 H, m, CH), 3.66-3.72 (12 H, m,
ArOCH2), 6.62 and 7.37 (24 H, AA′BB′, sp H), 6.87 (3 H, m, L
H), 7.41 (3H, m, L H), 7.50-7.60 (9 H, m, G1-bp H and L H),
7.68 (6 H, s, G1-bp H), 7.75-7.80 (6 H, m, L H), and 7.87 (1

9730 Lo et al.
Macromolecules, Vol. 36, No. 26, 2003
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Burn, P. L. J . Phys. Chem. B, accepted.
MA030383W