Phosphorescent side-chain functionalized poly(norbornene)s containing iridium complexes

Article abstract of DOI:10.1021/ma0512298

Norbornenes containing phosphorescent iridium complexes based on Ir(ppy)₃ and Ir(ppy)₂-(bpy)(PF₆) were synthesized and copolymerized with alkylnorbornenes via ring-opening metathesis polymerization in nonpolar solvents usi

Full text of DOI:10.1021/ma0512298

9000
Macromolecules 2005, 38, 9000-9008
Articles
Phosphorescent Side-Chain Functionalized Poly(norbornene)s
Containing Iridium Complexes
Joseph R. Carlise, Xian-Yong Wang, and Marcus Weck*
School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400
Received June 10, 2005; Revised Manuscript Received August 24, 2005
ABSTRACT: Norbornenes containing phosphorescent iridium complexes based on Ir(ppy)3 and Ir(ppy)2-
(bpy)(PF6) were synthesized and copolymerized with alkylnorbornenes via ring-opening metathesis
polymerization in nonpolar solvents using ruthenium initiators. The luminescent properties of the resulting
polymers both in solution and in the solid state were tested. The polymers were found to retain the optical
properties of the phosphorescent small molecule analogues with emission maxima in the yellow/green,
quantum yields from 0.23 to 0.24 for Ir(ppy)2(bpy)(PF6) analogues, 0.02 to 0.03 for mer-Ir(ppy)3 analogues,
and 0.20 to 0.24 for fac-Ir(ppy)3 analogues, and lifetimes of 0.41 to 0.55 µs for Ir(ppy)2(bpy)(PF6) analogues,
0.22 to 0.62 µs for mer-Ir(ppy)3 analogues, and 1.28 to 1.48 µs for fac-Ir(ppy)3 analogues. By combining
the phosphorescent properties of these emissive molecules with the solution processability and ease of
synthesis of polynorbornene backbones, these materials might be highly useful in the field of light-emitting
devices and emissive display technology.
Introduction
ogy.5 To meet the needs of the rapidly expanding scope
of applications that have been suggested for polymer-
supported, highly emissive phosphorescent complexes,
further optimization is necessary. This includes syn-
thesizing increasingly robust and durable, yet easily
modifiable, polymeric scaffolds in order to facilitate the
tuning of materials. Ring-opening metathesis polymer-
ization (ROMP) has been shown to fulfill these criteria.6
It typically employs straightforward, facile monomer
syntheses resulting in a versatile library of monomers.6
Furthermore, the ruthenium-carbene complexes that
catalyze ROMP are extremely efficient as well as highly
functional group tolerant.6 Finally, ROMP is often living
and highly controlled allowing for the highest degree
of control over the resulting polymer properties such as
molecular weight and polydispersity and for the syn-
thesis of block copolymers.
ROMP has also been shown to be an effective method
for polymerization and solution processing of such
important fluorescent complexes as Alq3 and Ru(bpy)3-
(PF6)2.7 Thus, ROMP is an excellent route toward the
study, realization, and optimization of the ever-expand-
ing field of polymer-supported phosphorescent materi-
als. In this work, we demonstrate the synthesis of
phosphorescent iridium complexes covalently bound to
norbornene, the homo- and copolymerization of these
monomers, and finally the persistent adherence of the
luminescence activity to the known values of the small
molecule analogues throughout the entire process for
the polymers in solution as well as in the solid state.
Organic light-emitting diodes (OLEDs) are in high
demand today in nearly every facet of the technological
world. It is proposed that the next generation of OLED
material will be based on phosphorescent materials
instead of the current fluorescence-based systems due
to the significantly higher quantum yields that are
possible.1 One shortcoming of current OLEDs as well
as future systems is their lengthy device fabrication. In
this paper, we describe the synthesis and photophysical
characterization of a new class of polymer-supported
phosphorescent materials, poly(norbornene)-supported
iridium complexes. This material can be synthesized in
a highly controlled fashion as a result of the polymer-
ization method employed and combines the possibility
of solution film processing with phosphorescence.
Phosphorescent coordination complexes, including the
class of iridium compounds studied in this paper,
already feature prominently in various materials and
devices as the emissive species, as a result of their high
quantum efficiencies and strong photo- and electrolu-
minescence.1 In current device technologies, the lumi-
nescent molecules are either vacuum-deposited as low
molecular weight compounds or doped into a polymeric
matrix,2 requiring lengthy and expensive fabrication of
devices.3 To simplify this fabrication process, recent
efforts have been aimed at direct incorporation of the
emissive species, via covalent attachment, to a solution-
processable polymer backbone.4 Examples to date in-
clude the attachment to poly(dimethylsiloxane)s, poly-
(fluorene)s, and poly(styrene)s, showing promising results
in areas such as solution processing and sensor technol-
Results and Discussion
Monomer Design. Monomers were designed based
on choice of phosphorescent complex as well as durabil-
ity and ease of synthesis. All monomers were synthe-
* Corresponding
chemistry.gatech.edu.
author.
E-mail:
marcus.weck@
10.1021/ma0512298 CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/01/2005

Macromolecules, Vol. 38, No. 22, 2005
Poly(norbornene)s Containing Iridium Complexes 9001
Scheme 1. Synthesis of 1a
a (a) Lithium diisopropylamide, THF, -78 °C; (b) propylene
oxide, THF, 0 °C, 73%; (c) exo-5-norbornene-2-carboxylic acid,
DCC, DMAP, CH2Cl2, 42%; (d) [Ir(ppy)2Cl]2, ethylene glycol,
150 °C, 72%; (e) NH4PF6(aq).
addition of NH4PF6(aq) to provide iridium-containing
monomer 1 in 72% yield (Scheme 1).
Commercially available 4-(2-pyridine)benzaldehyde
was reduced with LiAlH4 to give the corresponding
alcohol 6 in 94% yield, which was then esterified with
exo-5-norbornene-2-carboxylic acid using DCC/DMAP,
as described for 1, to give compound 7 in 80% yield.
Simultaneously, [Ir(ppy)2Cl]2 was treated with silver
trifluoromethanesulfonate (AgOTf) to transform the
chloro complex into the more labile iridium triflate
species which is the precursor for the meridional
coordination with a third ppy-type ligand. The resulting
triflate complex was treated with 7 in acetone at room
temperature overnight to give the meridionally oriented
iridium-containing monomer mer-2 in 43% yield (Scheme
2).9
Monomer fac-2 was obtained by the reduction of the
previously reported formylphenyl-substituted iridium
complex Ir(ppy)2fppy2c with LiAlH4 to give compound
8, fac-Ir(ppy)2(hmppy) (hmppy ) hydroxymethyl-ppy)
which contains a single hydroxymethyl group as a
chemical handle. Esterification with exo-5-norbornene-
2-carboxylic acid using DMAP and DCC yielded the
facially oriented monomer 2 in 40% yield (Scheme 3).
The yield-limiting step is the facial coordination of the
ligands onto the iridium metal center. This step occurs
typically in less than 30% whereas meridional orienta-
tion can be achieved in yields as high as70%.9 Monomer
3 was obtained as described in the literature.10
Figure 1. (top) Monomers employed in this study: 1, bpy-
based, charged iridium complex; 2, ppy-based, neutral iridium
complex; 3, alkyl spacer-based monomer. (bottom) Grubbs’
third-generation catalyst.
sized in three steps or less from commercially available
starting materials. The emissive complex is attached to
the polymerizable unit by a short alkyl linker to a
norbornenyl ester which has been shown to be highly
stable under a variety of conditions.8 To investigate the
optical effects on the properties of the resulting poly-
mers, both a charged monomer and a neutral monomer
are included in this study as well as an alkyl-chain
based monomer that can serve to space out the lumi-
nescent inorganic complexes and aid polymer solubility
(Figure 1).
Monomer Synthesis. Monomers 1-3 were readily
synthesized in three steps or less in overall good yields.
The synthesis of monomer 1 started with the treatment
of commercially available 4,4′-dimethyl-2,2′-dipyridyl
(dMbpy) with 1 equiv of lithium diisopropylamide
(LDA), followed by the addition of 1 equiv of propylene
oxide, to give compound 4 in 73% yield. Ring-opening
addition of the propylene oxide to form 4 occurred
exclusively by the attack of the dMbpy anion on the less
substituted carbon of the epoxide. No attack onto the
more substituted carbon was detected. Compound 4 was
esterified with exo-5-norbornene-2-carboxylic acid, using
dicyclohexylcarbodiimide (DCC) and a catalytic amount
of (dimethylamino)pyridine (DMAP) to afford compound
5 in 42% yield. In a modification to a previously
published procedure,2g 5 was then combined with [Ir-
(ppy)2Cl]2 at 150 °C in ethylene glycol, followed by the
Polymerization. Homo- and copolymerizations were
carried out using a standard protocol for all monomers.
Monomers 1 and 2 were homo- and copolymerized with
3 in various ratios in dichloromethane and precipitated
into either diethyl ether or methanol. All polymeriza-
tions were complete within 2-3 min, using Grubbs’
third-generation benzyldine initiator as the ROMP
catalyst (Figure 1).11 The target degree of polymeriza-

9002 Carlise et al.
Scheme 2. Synthesis of mer-2a
Macromolecules, Vol. 38, No. 22, 2005
a (a) Lithium aluminum hydride, THF, 94%; (b) exo-5-
norbornene-2-carboxylic acid, DCC, DMAP (cat.), CH2Cl2, 80%;
(c) [Ir(ppy)2OTf]2, acetone, ambient temperature, 43%.
Scheme 3. Synthesis of fac-2a
Figure 2. Copolymers poly-1-co-3 (top) and poly-2-co-3 (bot-
tom).
was thus employed in this study as a means of control-
ling the chromophore density in the solid state as well
as an aid to polymer solubility.
Although all homopolymers of 1, mer-2, and 310 were
fully soluble in dichloromethane, dichloromethane solu-
tions of poly-1 or poly-2 when mixed with a solution of
poly-3 would either become turbid or cause full precipi-
tation of the iridium-containing polymers from solution.
This is consistent with observations in the literature
that polymers containing metal complexes are often
insoluble in strongly nonpolar environments,12 although
it is also possible that the precipitation may have been
caused by the formation of polymer aggregates. How-
ever, attempts at block copolymerizations of 3 with
either 1 or 2 caused the same phenomena, i.e., a 50-
fold excess of monomer 3 was added to a homogeneous
solution of a short chain polymer (∼20 mer, catalyst was
1
still fully initiated and living as observed by H NMR
of the carbene signal) of 1 or 2. Upon addition of this
second monomer, turbidity or precipitation occurred
instantly. Both poly-1 and poly-2 also precipitated
quickly in hexanes or diethyl ether, giving the same
result as the addition of an excess of alkyl monomer 3.
Copolymers of 1 or 2 with 3 only remained fully soluble
when they were copolymerized in a random fashion.
Therefore, although the rates of polymerization with the
catalyst we employed are very fast, the observed solu-
bility of the copolymers suggests a random nature for
the copolymers used in this system.
Gel-permeation chromatography (GPC) was employed
for all polymers (Table 1). All GPC traces of poly-mer-2
and its copolymer analogues were multimodal, showing
approximately the same elution times as their fac-
counterparts, but in all cases for poly-mer-2 and its
corresponding copolymers there were two highly over-
lapping, non-baseline-resolved signals. Therefore, while
clearly polymers were formed, we are not able to
a (a) Lithium aluminum hydride, THF, 99%; (b) exo-5-
norbornene-2-carboxylic acid, DCC, DMAP, THF, 40%.
tion was 50 for poly-1 and poly-2 and all copolymers,
and copolymer ratios consisted of both 20:1 and 2:1 for
the mixtures of both monomers 3:1 and 3:2 (Figure 2).
Poly-1 and poly-mer-2, in contrast to previously
published homopolymers that contain charged transi-
tion metal complexes on every repeating unit,7 were
fully soluble in dichloromethane without the aid of alkyl
spacers or alkylated ligands. In contrast, poly-fac-2
precipitated out during the polymerization and could
not be redissolved in any organic solvent. Monomer 3

Macromolecules, Vol. 38, No. 22, 2005
Poly(norbornene)s Containing Iridium Complexes 9003
Table 1. Polymer Characterization Data
more evenly around the periphery of the complex while
maintaining the positive metal center on the interior.
These solubility problems were not observed in the case
of the monomer fac-2, or any of its copolymers with 3,
indicating that the insolubility is directly an effect of
restraining these complexes into very close proximity
with each other in nonpolar solvents, as is the case with
the homopolymer only.
There were no distinct glass transition temperatures
observable for any of the homopolymers as well as the
1:20 copolymers of 3 with 1 or 2. However, for the 1:20
copolymer of fac-2 with 3, a glass transition of -44 °C
was observed. The 1:2 copolymers of 3 with 1, mer-2,
and fac-2 all exhibited distinct Tg values of 10, -43, and
-53 °C, respectively. These values may reflect the
differences caused by incorporation of a charged polymer
(poly-1 series) compared with a neutral polymer (mer-
and fac-poly-2 series). In all cases, the polymers exhib-
ited progressively higher decomposition temperatures
as the amount of comonomer 3 increased.
Photophysical Properties. The agreement of the
luminescent data between the well-studied small phos-
phorescent iridium complexes and our polymeric mate-
rial in solution and in the solid state is crucial to the
potential development and realization of polymeric
OLEDs. In acetonitrile, Ir(ppy)2(bpy)(PF6) has been
reported to emit strongly at 606 nm,16 while tert-butyl
substitution at the bipyridinyl 4- and 4′-positions gives
rise to an emission maximum at 581 nm,2g suggesting
that alkylation at the para-positions of the bipyridine
has a blue-shifting effect on the emissive properties of
the complex. We measured an emission maximum of 555
nm for compound 1 (Table 2, Figure 3), suggesting that
the employment of the norbornenyl ester in close
proximity to the emissive complex is responsible for the
observed change in wavelength. Poly-1 has an emission
maximum of 556 nm, as do all copolymers of 1 with alkyl
spacer monomer 3 (Table 2, Figure 3). The emission
quantum yield for 1 of 0.236 is nearly identical to
previously reported values in the literature of 0.235 for
the tert-butyl analogue,2g while the luminescence life-
time for 1 (534 ns) was also similar to the small molecule
analogue (557 ns). In the solid state, poly-1 exhibited
an emission at 545 nm for the homopolymer and 540
and 531 nm for the copolymers as incorporation of 3
increased (Table 3, Figure 4). This observation is
consistent with previously reported trends that show
that the emission wavelength is strongly dependent
upon the local environment and that a blue shift is
observed upon dilution of the luminescent monomer
concentration in a copolymer.2g,7b,17 Similar shifts in
polymer
Mn
Mw
PDI Tg, °C Td, °C
poly-1
31 000 43 100 1.39
11 200 19 300 1.71
18 500 47 000 2.55
330
339
347
248
298
336
poly-1-co-3 (1:2)
poly-1-co-3 (1:20)
poly-mer-2
poly-mer-2-co-3 (1:2)
poly-mer-2-co-3 (1:20)
poly-fac-2
10
-43
poly-fac-2-co-3 (1:2)
poly-fac-2-co-3 (1:20)
26 300 30 500 1.16
44 100 54 300 1.23
-53
-44
358
374
determine molecular weights and polydispersities. The
fact that all polymers eluted fully to give baseline-
resolved mono- or multimodal signals was unexpected,
as it is commonly known for most charged metal-
containing polymers that if any sample comes through
the columns at all the data will likely be entirely
undecipherable due to the formation of either ag-
gregates or at least strong interactions of the metal
complex with the stationary phase.13 This problem can
be circumvented for polymers containing a single metal
complex by doping the mobile phase with ammonium
hexafluorophosphate.13 However, poly-1 could be fully
characterized using GPC in methylene chloride, with
no dopant added to the mobile phase, even though every
repeat unit contains a charged moiety. The homopoly-
mer poly-1 showed the lowest polydispersity index (PDI)
with 1.39. A PDI of 1.71 was observed for the 1:2
copolymer of 1 with 3, while a PDI of 2.55 was observed
for the 1:20 copolymer. Copolymers of fac-2 with 3
showed more narrow distributions and lower PDI’s. The
1:2 copolymer had a PDI of 1.16, and the 1:20 copolymer
had a PDI of 1.23.
The insolubility of the homopolymer of fac-2 was
unexpected on the basis of the good solubility of poly-
mer-2. This polymer’s insolubility may be due to several
factors. First, because of the anionic nature of the
phenylpyridine ligand, a relatively strong dipole is
created in the facial configuration since the anionic
carbon bound to the metal exists on the same face of
the molecule for all three ligands. In fact, for the small
molecule fac-Ir(ppy)3, a quite large dipole moment of 6.5
D has been calculated.14 In the homopolymer, when
these complexes are forced to be in close proximity along
the backbone, aggregation may occur as a result.
Conversely, the meridional configuration has anionic
carbons that are trans to each other, canceling out any
dipolar effects created by two out of the three ligands.
This trans effect also causes lengthening of these
carbon-iridium organometallic bonds (2.07-2.08 Å),15
thus distributing the anionic character of the ligands
Table 2. Solution Photophysical Data for Compounds 1-3 and Their Corresponding Polymers
complex
λabs,g nm
λem, nm
Φh
τ (µs)e
τ (µs)f
1
556,a 551b
0.236a
0.278a
0.225a
0.238a
0.034a
0.022a
0.025a
0.022b
0.219a
0.145
0.207
0.138
0.148
0.049
0.031
0.041
0.048
0.033
0.534
0.549
0.413
0.486
0.498
0.619
0.222
0.350
1.48
poly-1i
555,a 551b
poly-1-co-3 (1:2)
poly-1-co-3 (1:20)
mer-2
556,a 552b
557,a 554b
546,a 543,b 537,c 540d
519,a 538,b 511,c 545d
517,a 541b
mer-poly-2
388a
385a
385b
373a
mer-poly-2-co-3 (1:2)
mer-poly-2-co-3 (1:20)
fac-2
540b
543,a 515b
fac-poly-2
fac-poly-2-co-3 (1:2)
fac-poly-2-co-3 (1:20)
293,a 377a
377b
517,a 515b
514b
0.243b
0.201b
0.045
0.045
1.28
1.43
a Acetonitrile. b Dichloromethane. c Toluene. d Dimethyl sulfoxide. e THF, ambient conditions. f THF, degassed. g Most samples showed
broad absorbance range with no clear local maximum. h Relative to Ru(bpy)3(PF6)2. i Lifetimes measured in dichloromethane.

9004 Carlise et al.
Macromolecules, Vol. 38, No. 22, 2005
Figure 5. Solid-state PL emission spectra of (from right to
left): mer-poly-2, mer-poly-2-co-3 (1:2), and mer-poly-2-co-3 (1:
20) (ex 380 nm).
Figure 3. Solution PL emission spectra of (from top to
bottom): 1, poly-1, poly-1-co-3 (1:2), and poly-1-co-3 (1:20) in
dichloromethane (ex 400 nm).
Figure 6. Solid-state PL emission spectra of (from right to
left): fac -poly-2-co-3 (1:2) and fac-poly-2-co-3 (1:20) (ex 380
nm).
Figure 4. Solid-state PL emission spectra of (right to left):
poly-1, poly-1-co-3 (1:2), and poly-1-co-3 (1:20) (ex 400 nm).
Table 3. Solid-State Photophysical Data for All Polymers
polymer
λem (nm)
polymer
λem (nm)
1
545
540
531
550
543
mer-2-co-3 (1:20)
fac-2
fac-2-co-3 (1:2)
fac-2-co-3 (1:20)
534
1-co-3 (1:2)
1-co-3 (1:20)
mer-2
521
513
mer-2-co-3 (1:2)
solid-state emission were observed for polymers of both
mer-2 (Figure 5) and fac-2 (Figure 6) as well.
It has been well documented that in dichloromethane,
at room temperature, fac-Ir(ppy)3 emits strongly at 510
nm,18 with emission quantum yields as high as 0.40,
while mer-Ir(ppy)3 emits at 512 nm with lower quantum
yields of 0.036.15 This difference in emission quantum
yields, brought about by the large discrepancy in non-
radiative decay rates (more than an order of magnitude
between facial and meridional Ir(ppy)3), lessens signifi-
cantly as the temperature decreases from 298 to 77 K,
where both complexes are strongly luminescent.15 We
observed similar differences in our observations of the
luminescent intensities of polymers containing mer-2
(Figure 7) vs polymers containing fac-2 (Figure 8) in
solution as well as in the solid state at room tempera-
ture. In accordance with the aforementioned literature
trends, fac-2 was significantly more emissive, with an
Figure 7. Solution PL emission spectrum of (from top to
bottom): mer-2, mer-poly-2, mer-poly-2-co-3 (1:2), and mer-
poly-2-co-3 (1:20) in dichloromethane (ex 380 nm).
emission quantum yield of 0.219 in acetonitrile. Copoly-
mers of fac-2 with 3 in a 1:2 ratio and 1:20 ratio gave
quantum yields of 0.243 and 0.201, respectively. mer-

Macromolecules, Vol. 38, No. 22, 2005
Poly(norbornene)s Containing Iridium Complexes 9005
Figure 8. Solution PL emission spectrum of (from top to
bottom): fac-2, fac-poly-2-co-3 (1:2), and fac-poly-2-co-3 (1:20)
in dichloromethane (ex 380 nm).
Figure 9. Solvent dependence for mer-poly-2: A (toluene), C
(acetonitrile), D (dichloromethane), E (dimethyl sulfoxide), B
(fac-2 in dichloromethane, for comparison).
2, however, showed a much lower emission quantum
yield of 0.034 in acetonitrile. Both homo- and copolymers
containing this complex showed slightly lower quantum
yields of 0.022-0.025.
Table 4. Lifetimes (in µs) Measured for mer-2 and
Poly-mer-2 in Various Solvents, Both in Ambient
Conditions and Degassed
The emission maximum for mer-2 and its polymers
in acetonitrile was shifted substantially from that
expected from the small molecule analogue mer-Ir(ppy)3.
The only structural difference between mer-2 and the
previously reported mer-Ir(ppy)3 complex is the addition
of the norbornenyl ester para to the pyridine on the
phenyl group of one of the ppy ligands, although it is
electronically separated from the metal complex by a
methylene linkage. Despite the expected insulating
effect of the methylene unit, a red shift of the emission
wavelength from that reported in the literature for the
unsubstituted mer-Ir(ppy)3 complex (512 nm) to 543 nm
is observed. However, when comparing emission spectra
for mer-2 and its polymers in various solvents, it be-
comes evident that the emission from the mer-complex
is comprised of two different emission maxima: one
occurring in the expected range of 510-515 nm and
another occurring in the range of 538-546 nm. Depend-
ing on the choice of solvent, the intensities of each vary
with respect to one another (Figure 9). In dichlo-
romethane (538 nm) or dimethyl sulfoxide (545 nm), the
emission for poly-mer-2 is broad and significantly red-
shifted from that expected on the basis of the literature
reported small molecule by as much as 30 nm in some
instances. There is a small shoulder to the left, appear-
ing in the range normally expected for the major signal
in the previously reported small molecule. Conversely,
in toluene, the emission (510 nm) closely resembles that
of the facial complex. It is narrower, with a shoulder to
the right, in the range of the other signal observed for
the more polar solvents described above. Finally, in
acetonitrile, there is a broad emission maximum ob-
served, which appears to span nearly equally the two
different emissions observed for the other solvents
(516-540 nm). It is interesting to note that in the case
of mer-2 this solvent dependence was not observed, and
the emission maximum in all four solvents mentioned
above remained in the range of 537 nm (toluene) to 546
nm (acetonitrile). Table 4 lists the corresponding life-
times for each of the aforementioned solvents. In the
case of the two solvents that exhibit the most strongly
red-shifting effects on the emission, namely dichloro-
methane and dimethyl sulfoxide, the lifetimes are also
mer-2
degassed
mer-poly-2
solvent
air
air
degassed
CH2Cl2
DMSO
CH3CN
toluene
0.069
0.211
0.022
0.036
0.516
0.62
0.481
0.348
0.042
0.145
0.002
0.028
0.133
0.286
0.717
0.791
markedly different from the other entries, both showing
a significant decrease. Neither toluene nor acetonitrile
showed the same lowering effect on the excited-state
lifetimes for poly-mer-2.
In the mer-configuration of Ir(ppy)3, when one ligand
is modified as in the case with mer-2, there are two
diastereomers possible. However, since the monomer
mer-2 does not show the same solvent-dependent be-
havior as in the polymer, the observed differences in
emission for mer-poly-2 are more likely due to confor-
mational differences in the polymer architecture brought
about by the changes in the environment as a result of
varying the solvent. Specifically, acetonitrile is a good
solvent for the emissive complex but a poor solvent for
the poly(norbornene) backbone. Both dichloromethane
and dimethyl sulfoxide are good solvents for both the
metal complex and the polymer backbone, and toluene
is a poor to average solvent for both the complex and
the backbone. The various combinations above can
create a wide variety of polymer conformations in
solution, causing differences in interchromophore dis-
tances, potentially giving rise to the observed variations
in emission wavelength.
Conclusions
We have demonstrated the ROMP polymerization of
several iridium complex containing monomers, their
solubility in nonpolar solvents, and the retention of
luminescent properties by the emissive complexes both
as polymers in both solution and the solid state. The
results described herein lay the foundation for further
steps into device fabrication using these materials,
providing simplification and improvements to the pro-
cess of polymerizing highly emissive phosphorescent
iridium complexes.

9006 Carlise et al.
Macromolecules, Vol. 38, No. 22, 2005
137.4, 137.3, 136.2, 136.1, 136.0, 133.1, 130.1, 130.0, 124.1,
124.0, 122.2, 122.1, 120.1, 120.0, 119.4, 119.0, 118.9, 66.6, 49.8,
45.9, 43.5, 42.8, 29.4. Elemental analysis for C42H43IrN3O2:
Calcd: C, 62.67; H, 4.26; N, 5.22. Found: C, 62.19; H, 4.35;
N, 4.89.
Experimental Section
General Methods. All reagents were purchased either from
Acros Organics or Aldrich and used without further purifica-
tion. DMF and CDCl3 were distilled from calcium hydride and
degassed prior to use. THF was dried via passage through
copper oxide and alumina columns. NMR spectra were taken
using a 300 MHz Varian Mercury spectrometer. All spectra
are referenced to residual proton solvent. Mass spectral
analyses were provided by the Georgia Tech Mass Spectrom-
etry Facility using a VG-70se spectrometer. Gel permeation
chromatography (GPC) analyses were carried out using a
Waters 1525 binary pump coupled to a Waters 2414 refractive
index detector with methylene chloride as an eluant on
American Polymer Standards 10 µm particle size, linear mixed
bed packing columns. All GPCs were calibrated using poly-
(styrene) standards. Atlantic Microlabs, Norcross, GA, per-
formed all elemental analyses. UV/vis absorption measure-
ments were taken on a Shimadzu UV-2401 PC recording
spectrophotometer. Emission measurements were acquired
using a Shimadzu RF-5301 PC spectrofluorophotometer. Life-
time measurements were taken using a PTI model C-72
fluorescence laser spectrophotometer with a PTI GL-3300
nitrogen laser. DSC data were collected using a Seiko model
DSC 220C. TGA data were collected using a Seiko model TG/
DTA 320.
fac-exo-Bis(2-phenyl-pyridine)iridium(II) Bicyclo[2.2.1]-
hept-5-ene-2-carboxylic Acid 4-Pyridin-2-yl-benzyl Ester
(fac-2). Compound 8 (200 mg, 0.24 mmol), exo-5-norbornene-
2-carboxylic acid (40 mg, 0.24 mmol), and dimethylaminopy-
ridine (DMAP) (17 mg, 0.12 mmol) were combined in 15 mL
of dichloromethane. A solution of dicyclohexylcarbodiimide
(DCC) (60 mg, 0.24 mmol) in 5 mL of dichloromethane was
added, and the reaction was stirred under argon at ambient
temperature for 24 h. The solvent was evaporated, and the
residue was purified via column chromatography (neutral
alumina, 1:1 hexane/dichloromethane) to give fac-2 as a bright
yellow powder in 40% yield. 1H NMR (CDCl3, 300 MHz): δ )
7.79-7.75 (m, 3H); 7.64-7.59 (m, 3H); 7.50-7.39 (m, 6H);
6.92-6.85 (m, 8H); 6.83-6.77 (m, 3H); 6.17-6.08 (m, 2H); 4.98
(d, 1H, J ) 12.8 Hz); 4.92 (dd, 1H, J1 ) 12.7 Hz, J2 ) 1.8 Hz);
2.99 (s, br, 1H); 2.90 (s, br, 1H); 2.20 (dd, 1H, J1 ) 10.1 Hz, J2
) 4.4 Hz); 1.93-1.86 (m, 1H); 1.56 (m, 1H); 1.47 (m, 2H). 13C
NMR (CDCl3, 100 MHz): δ ) 176.3, 166.8, 166.4, 161.8, 161.3,
161.0, 147.2, 144.0, 143.9, 138.4, 138.2, 137.4, 137.3, 137.3,
136.2, 135.9, 130.1, 130.0, 129.9, 128.9, 124.1, 122.3, 122.2,
120.2, 120.1, 119.5, 119.0, 67.0, 64.1, 46.9, 46.7, 43.5, 43.4, 41.9,
30.7, 30.6, 30.5, 27.2. Elemental analysis for C42H43IrN3O2:
Calcd: C, 62.67; H, 4.26; N, 5.22. Found: C, 62.30; H, 4.36;
N, 4.88.
exo-Bis(2-phenyl-pyridine)iridium(III) Bicyclo[2.2.1]-
hept-5-ene-2-carboxylic Acid 1-Methyl-3-(3-methyl-[2,3′]-
bipyridinyl-4′-yl)propyl Ester Hexafluorophosphate (1).
Compound 5 (910 mg, 2.51 mmol) and [Ir(ppy)2Cl] (615 mg,
2
4-(Methyl-[2,3′]bipyridinyl-4′-yl)-butan-2-ol (4). Diiso-
propylamine (1.41 g, 13.9 mmol) was dissolved in 30 mL of
dry THF under argon and cooled to 0 °C. n-Butyllithium (10
M solution in hexanes, 1.39 mL, 13.9 mmol) was added, and
the reaction was stirred for 20 min. The resulting in-situ-
generated lithium diisopropylamide was then cooled to -78
°C, and a solution of 4,4′-dimethyl-2,2′-dipyridyl (2.5 g, 13.6
mmol) was added dropwise over a period of 10 min. The
reaction was stirred for 30 min, allowed to warm to 0 °C, and
then cooled to -20 °C. A solution of propylene oxide (788 mg,
13.6 mmol) in 70 mL of THF was added dropwise over a period
of 30 min, and the reaction was stirred for 1 h. The reaction
mixture was quenched by slow addition of 10 mL of water,
followed by 70 mL of aqueous pH 7 phosphate buffer. The
mixture was extracted three times with diethyl ether, the
combined organic layers dried with MgSO4, the solvent
removed, and the resulting residue subject to column chro-
matography (neutral alumina, 1:1 hexane/EtOAc) to remove
less polar impurities (rf 0.5), while the product remained on
the baseline. Pure 4 was subsequently eluted (rf 0.5) by
flushing the column with a 20:1 mixture of EtOAc/EtOH to
give 2.40 g (9.90 mmol, 73%) of the target compound as a
1.14 mmol Ir) were combined in degassed ethylene glycol (10
mL) and refluxed for 24 h under an argon atmosphere. The
reaction mixture was then removed from the heat and allowed
to cool to room temperature followed by the addition of NH4-
PF6 (1.7 mL of a 1.0 mM aqueous solution). The reaction
mixture was then extracted with methylene chloride and
washed three times with water and dried with MgSO4, and
the solvent was removed to give crude 1, which was purified
via column chromatography (silica, 98:2 CH2Cl2/EtOH) to give
compound 1 as a bright yellow powder (830 mg, 0.82 mmol,
1
72%). H NMR (CDCl3, 300 MHz): δ ) 8.48 (m, 2H); 7.91 (s,
br, 1H); 7.88 (s, br, 1H); 7.80-7.71 (m, 4H); 7.66 (d, 2H, J )
7.5 Hz); 7.54-7.49 (m, 2H); 7.21-7.17 (m, 2H); 7.06-7.02 (m,
2H); 6.99 (dt, 2H, J1 ) 7.4 Hz, J2 ) 0.9 Hz); 6.88 (dt, 2H, J1 )
7.5 Hz, J2 ) 1.1 Hz); 6.29 (dd, 2H, J1 ) 7.4 Hz, J2 ) 3.8 Hz);
6.13-6.08 (m, 2H); 4.93 (m, 1H); 3.02 (s, 1H); 2.90 (m, 3H);
2.57 (s, 3H); 2.08-1.96 (m, 2H); 1.92-1.85 (m, 1H); 1.70 (s,
br, 1H); 1.49 (m, 1H); 1.36 (m, 2H); 1.28 (dt, 3H, J1 ) 6.2 Hz,
J2 ) 1.7 Hz). 13C NMR (CDCl3, 100 MHz): δ ) 176.2, 168.0,
167.9, 156.0, 155.5, 155.4, 152.5, 150.8, 150.0, 149.8, 148.8,
143.8, 138.3, 138.2, 136.0, 132.0, 131.9, 130.9, 129.1, 128.3,
128.3, 126.1, 125.2, 124.9, 123.6, 122.7, 119.8, 70.0, 46.9, 46.6,
46.5, 43.6, 41.9, 41.8, 35.7, 31.4, 30.6, 30.6, 21.6, 20.0. MS (ESI)
863.3 (M - loss of PF6-). Elemental analysis for C45H42F6-
IrN4O2P: Calcd: C, 53.62; H, 4.20; N, 5.56. Found: C, 53.63;
H, 4.21; N, 5.42.
1
slightly yellow oil. H NMR (CDCl3, 300 MHz): δ ) 8.49 (dd,
2H, J1 ) 8.1 Hz, J2 ) 5.0 Hz); 8.18 (d, 2H, J ) 4.2 Hz); 7.09
(dt, 2H, J1 ) 4.9 Hz, J2 ) 1.6 Hz); 3.78 (sextet, 1H, J ) 6.1
Hz); 2.76 (m, 2H); 2.39 (s, 3H); 1.80 (m, 2H), 1.17 (d, 3H, J )
6.2 Hz). 13C NMR (CDCl3, 100 MHz): δ ) 156.3, 156.2, 152.6,
149.3, 149.1, 148.5, 124.9, 124.2, 122.3, 121.6, 67.2, 39.8, 31.9,
24.0, 21.4. MS (ESI) 243.1 (M + 1).
mer-exo-Bis(2-phenyl-pyridine)iridium(II) Bicyclo-
[2.2.1]hept-5-ene-2-carboxylic Acid 4-Pyridin-2-yl-benzyl
Ester (mer-2). [Ir(ppy)2Cl] (100 mg, 0.187 mmol Ir) was
exo-Bicyclo[2.2.1]hept-5-ene-2-carboxylic Acid 1-Meth-
yl-3-(3-methyl-[2,3′]bipyridinyl-4′-yl)propyl Ester (5). Com-
pound 4 (2.00 g, 8.25 mmol), exo-5-norbornene-2-carboxylic acid
(1.14 g, 8.25 mmol), and DMAP (50 mg, 0.41 mmol) were
combined in 50 mL of dichloromethane at ambient tempera-
ture under argon. A solution of DCC (1.74 g, 8.42 mmol) in 30
mL of dichloromethane was added, and the reaction mixture
was stirred overnight. The resulting white precipitate was
filtered off, and the solvent was removed. The residue was
purified using column chromatography (neutral alumina, 5:1
hexane/EtOAc) to yield two distinct compounds that eluted
together. The impurity was removed by repeated reprecipita-
tion from hot hexanes, while pure 5 remained fully soluble.
Compound 5 was collected as a slightly yellow oil (1.27 g, 3.50
2
treated with silver triflate in 5 mL of refluxing acetone for 2
h in the dark. The reaction mixture was then filtered, and the
filtrate was combined with compound 7 (114 mg, 0.37 mmol).
Immediately, 0.1 mL of triethylamine was added, causing the
reaction to turn instantly from light yellow to deep orange and
turbid. The reaction was left to stir under argon at ambient
temperature overnight. Then the solvent was removed, and
the residue was purified via column chromatography (neutral
alumina, 1:1 hexane/dichloromethane) to give mer-2 in 43%
1
yield. H NMR (CDCl3, 300 MHz): δ ) 8.08 (d, 1H, J ) 5.8
Hz); 7.92 (m, 1H); 7.78 (m, 2H); 7.63 (m, 2H); 7.63 (m, 1H);
7.57 (m, 1H); 7.49 (m, 2H); 6.93 (m, 3H); 6.81 (m, 1H); 6.71
(m, 1H); 6.60 (m, 1H); 6.39 (m, 1H); 6.11 (m, 2H); 4.95 (m,
2H); 2.97 (s, br, 1H); 2.89 (s, br, 1H); 2.18 (m, 1H); 1.89 (m,
1H); 1.34 (m, 3H). 13C NMR (CDCl3, 100 MHz): δ ) 167.0,
166.5, 161.7, 161.3, 161.0, 147.3, 147.2, 143.9, 143.8, 137.5,
1
mmol, 42%). H NMR (CDCl3, 300 MHz): δ ) 8.55 (m, 2H);
8.23 (s, br, 2H); 7.13 (m, 2H); 6.13 (m, 2H); 4.98 (sextet, 1H, J
) 6.3 Hz); 3.03 (d, br, 1H, J ) 4.5 Hz); 2.92 (s, br, 1H), 2.75

Macromolecules, Vol. 38, No. 22, 2005
Poly(norbornene)s Containing Iridium Complexes 9007
(m, 2H); 2.44 (s, 3H); 2.20 (m, 1H); 1.96 (m, 3H); 1.52 (m, 1H),
1.39 (m, 2H); 1.27 (dd, 3H, J1 ) 6.3 Hz, J2 ) 1.1 Hz). 13C NMR
(CDCl3, 100 MHz): δ ) 175.9, 156.4, 156.0, 151.8, 149.3, 149.0,
148.3, 138.2, 135.9, 124.9, 124.0, 122.2, 121.1, 70.4, 47.0, 46.7,
43.8, 43.7, 42.0, 37.0, 36.9, 31.9, 30.7, 21.6, 20.5. MS (ESI)
363.2 (M + 1). Elemental analysis for C23H26N2O2: Calcd: C,
76.21; H, 7.23; N, 7.73. Found: C, 75.56; H, 7.38; N, 7.73.
130.7, 129.2, 128.4, 125.7, 125.0, 124.9, 123.6, 122.7, 120.0,
65.9, 37.3, 35.8, 31.5, 21.4, 21.3, 20.1, 19.9, 19.8.
Poly-1-co-3 (1:2). H NMR (CD2Cl2, 300 MHz): δ ) 8.42
1
(m, 0.6H); 7.95 (m, 0.6H); 7.87-7.73 (m, 1.3H); 7.53 (m, 0.6H);
7.25 (m, 0.6H); 7.03 (m, 0.9H); 6.94 (m, 0.6H); 6.34 (m, 0.6H);
5.50-5.15 (m, 2H); 4.95 (m, 0.4H); 3.99 (m, 1.2H); 3.16 (0.6H);
2.90-2.65 (m, 1.8H); 2.41 (m, 1.5H), 1.97 (m, 2H); 1.82-1.48
(m, 2H); 1.30 (m, 5.5H); 0.91 (m, 1.9H). 13C NMR (CDCl3, 100
MHz): δ ) 175.7, 174.8, 168.0, 156.0, 155.5, 152.3, 150.7,
150.4, 150.1, 148.8, 144.0, 138.3, 134.7, 133.6, 132.9, 131.9,
130.8, 129.2, 128.4, 125.7, 125.0, 124.7, 123.5, 122.7, 120.0,
64.4, 48.7, 41.5, 36.8, 32.0, 31.4, 29.4, 28.9, 26.3, 26.2, 22.9,
21.4, 15.3, 14.1.
(4-Pyridin-2-yl-phenyl)methanol (6). A solution of 4-py-
ridin-2-yl-benzaldehyde (2.00 g, 10.9 mmol) in 20 mL of dry
THF was added dropwise over a period of 10 min to a stirred
suspension of lithium aluminum hydride (829 mg, 21.8 mmol)
in 80 mL of dry THF at 0 °C under an argon atmosphere. After
complete addition, the reaction mixture was allowed to warm
to room temperature and stirred for 4 h. The solution was then
cooled again to 0 °C, and the reaction mixture was carefully
quenched by the slow addition of 10 mL of 1 N HCl. The
mixture was diluted with diethyl ether, washed twice with
neutral phosphate buffer (pH 7.0) and once with brine, and
dried over MgSO4, the solvent was removed, and the residue
was purified by column chromatography (silica gel, ethyl
acetate/hexanes 1:2) to yield 6 as a slightly yellow oil (1.90 g,
10.2 mmol, 94%). 1H NMR (CDCl3, 300 MHz): δ ) 8.66 (ddd,
1H, J1 ) 4.9 Hz, J2 ) 1.7 Hz, J3 ) 0.9 Hz); 7.91 (d, 2H, J )
8.3 Hz); 7.72 (m, 2H); 7.41 (d, 2H, J ) 8.4 Hz); 7.22 (ddd, 1H,
J1 ) 6.9 Hz, J2 ) 4.8 Hz, J3 ) 1.6 Hz); 4.71 (s, 2H); 2.82 (s,
1H). 13C NMR (CDCl3, 100 MHz): δ ) 157.4, 149.6, 142.3,
142.2, 138.5, 138.4, 137.1, 127.4, 127.2, 122.3, 121.0, 64.9. MS
(ESI) 185.9 (M + 1).
exo-Bicyclo[2.2.1]hept-5-ene-2-carboxylic Acid 4-Pyri-
din-2-ylbenzyl Ester (7). Compound 6 (1.50 g, 8.10 mmol),
exo-5-norbornene-2-carboxylic acid (1.12 g, 8.10 mmol), and
DMAP (10 mg, 0.081 mmol) were combined in 50 mL of
dichloromethane under argon. Then a solution of DCC (1.68
g, 8.18 mmol) in 30 mL of dichloromethane was added, and
the reaction mixture was stirred overnight at ambient tem-
peratures. A white precipitate formed during the reaction
which was filtered off. The solvent was removed and the
residue subject to column chromatography (basic alumina, 7:1
hexane/EtOAc) to yield 7 as a clear oil (1.98 g, 6.48 mmol,
80%). 1H NMR (CDCl3, 300 MHz): δ ) 8.69 (ddd, 1H, J1 ) 4.8
Hz, J2 ) 1.7 Hz, J3 ) 1.0 Hz); 8.00 (d, 2H, J ) 8.4 Hz); 7.74
(m, 2H); 7.45 (d, 2H, J ) 8.4 Hz); 7.23 (ddd, 1H, J1 ) 7.1 Hz,
J2 ) 4.9 Hz, J3 ) 2.2 Hz); 6.12 (m, 2H); 5.19 (s, 2H); 3.08 (s,
1H); 2.93 (s, 1H); 2.30 (m, 1H); 1.95 (dt, 1H, J1 ) 11.8 Hz, J2
) 3.6 Hz); 1.54 (m, 1H); 1.39 (m, 1H). 13C NMR (CDCl3, 100
MHz): δ ) 176.1, 157.1, 149.9, 139.4, 138.3, 137.2, 137.0,
135.9, 128.6, 127.3, 122.4, 120.7, 66.2, 47.0, 46.7, 43.5, 42.0,
30.8. MS (ESI) 306.1 (M + 1). Elemental analysis for C20H19-
NO2: Calcd: C, 78.66; H, 6.27; N, 4.59. Found: C, 78.35; H,
6.36; N, 4.63.
fac-Bis(2-phenylpyridine)-p-hydroxymethyl-2-(pyridyl)-
benzene Iridium (III) (8). fac-Ir(ppy)2(fppy) (0.20 mg, 0.29
mmol) was dissolved in 30 mL of tetrahydrofuran (THF), and
8.8 mL (3-fold excess) of lithium aluminum hydride (0.1 M
solution in THF) was added dropwise, upon which the solution
turned immediately from bright orange-red to yellow-green.
The reaction mixture was stirred at ambient temperatures for
1 h and then quenched by the addition of ethyl acetate. The
crude material, which showed no remaining aldehyde signal
by 1H NMR, was dissolved in dichloromethane and washed
three times with water, dried with MgSO4, and used without
further purification.
General Polymerization Procedure. Polymerizations
were carried out under argon, at ambient temperatures, in
dichloromethane, at concentrations of 0.2 M in monomer. All
polymers were synthesized on an ∼50 mg scale with a
monomer-to-catalyst ratio of 50:1. All polymers were purified
by precipitation into either methanol or diethyl ether.
Poly-mer-2. 1H NMR (CD2Cl2, 300 MHz): δ ) 9.27 (d, 1H,
J ) 5.7 Hz); 8.05 (m, 1H); 7.97-7.88 (m, 2H); 7.82 (t, 1H, J )
7.7 Hz); 7.68 (m, 2H); 7.58 (d, 2H, J ) 7.8 Hz); 7.46-7.07 (m,
2H); 7.00-6.71 (m, 7H); 6.65-6.50 (m, 3H); 6.38 (m, 1H); 5.90
(d, 1H, J ) 7.7 Hz); 5.40-4.81 (m, 2H); 3.13 (m, 2H); 2.73-
2.31 (m, 2H); 2.10-1.78 (m, 2H); 1.62 (m, 2H); 1.18 (m, 1H).
13C NMR (CD2Cl2, 100 MHz): δ ) 168.2, 151.7, 145.0, 144.2,
136.9, 130.6, 129.3, 124.4, 123.9, 122.8, 121.6, 118.9, 47.1, 8.7.
Poly-mer-2-co-3 (1:2). 1H NMR (CDCl3, 300 MHz): δ )
9.22 (d, 0.3H, J ) 5.5 Hz); 8.08 (m, 0.2H); 7.87 (m, 0.4H); 7.73
(m, 0.5H); 7.54 (m, 0.6H); 7.22 (m, 0.4H); 6.95-6.68 (m, 1.2H);
6.55 (m, 0.3H); 6.37 (m, 0.2H); 5.92 (d, 0.2H, J ) 7.8 Hz); 5.50-
4.79 (m, 2H); 3.99 (m, 1.3H); 3.06 (m, 0.8H); 2.85 (m, 0.9H);
2.50 (m, 0.5H); 1.98 (m, 1H); 1.74 (m, 0.4H); 1.60 (m, 1.1H);
1.32 (m, 7.1H); 0.88 (m, 1.8H). 13C NMR (CDCl3, 100 MHz): δ
) 174.8, 168.7, 153.4, 151.8, 145.5, 143.9, 137.4, 136.5, 134.7,
133.5, 132.9, 130.8, 130.2, 129.9, 129.3, 126.5, 124.4, 123.9,
122.4, 121.5, 118.8, 118.6, 64.6, 48.7, 47.0, 43.1, 40.8, 36.3, 32.0,
29.4, 28.9, 26.3, 26.2, 22.9, 14.4, 8.9.
Acknowledgment. Financial support has been pro-
vided by Halliburton Energy Services and by the Office
of Naval Research (MURI, Award N00014-03-1-0793).
M.W. gratefully acknowledges a 3M Untenured Faculty
Award, a DuPont Young Professor Award, an Alfred P.
Sloan Fellowship, a Camille Dreyfus Teacher/Scholar
Award, and a Blanchard Assistant Professorship.
Supporting Information Available: Absorption spectra
for all functionalized polymers. This material is available free
of charge via the Internet at http://pubs.acs.org.
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