Polymerizable cationic iridium(III) complexes exhibiting color tunable light emission and their corresponding conducting metallopolymers

Article abstract of DOI:10.1016/j.poly.2009.06.014

Cyclometalated iridium(III) complexes have been synthesized for use in a variety of photophysical applications, including polymer light emitting diodes (PLEDs). A series of new complexes with one electrochemically polymerizable ligand and two phenylpyridine(ppy)-based ligands have been prepared: [Ir(ppy)₂L][PF₆](1), [Ir(F-mppy)₂L][PF₆](2), and [Ir(Br-mppy)₂L][PF₆](3), where L = 3,8-bis(2,2′-bithien-5-yl)-1,10-phenanthroline. The ancillary ppy ligands can be easily varied synthetically to tune emission color of the monomer from blue-green to red. The solid state structure of complex 1 has been obtained by single crystal X-ray crystallography. Conducting polymer materials have been prepared by electropolymerization of monomers and were characterized through XPS analysis and spectroscopic studies.

Full text of DOI:10.1016/j.poly.2009.06.014

Polyhedron 29 (2010) 110–115
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Polymerizable cationic iridium(III) complexes exhibiting color tunable light
emission and their corresponding conducting metallopolymers
Travis W. Hesterberg, Xiaoping Yang, Bradley J. Holliday *
Department of Chemistry and Biochemistry, Center for Electrochemistry, The University of Texas at Austin, 1 University Station, A5300, Austin, TX 78712-0165, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 12 June 2009
Cyclometalated iridium(III) complexes have been synthesized for use in a variety of photophysical appli-
cations, including polymer light emitting diodes (PLEDs). A series of new complexes with one electro-
chemically polymerizable ligand and two phenylpyridine(ppy)-based ligands have been prepared:
0
Keywords:
[Ir(ppy) L][PF ](1), [Ir(F-mppy) L][PF ](2), and [Ir(Br-mppy) L][PF ](3), where L = 3,8-bis(2,2 -bithien-5-
2
6
2
6
2
6
Polymer light emitting diodes (PLEDs)
Iridium(III) complexes
Electropolymerization
Metallopolymer
yl)-1,10-phenanthroline. The ancillary ppy ligands can be easily varied synthetically to tune emission
color of the monomer from blue–green to red. The solid state structure of complex 1 has been obtained
by single crystal X-ray crystallography. Conducting polymer materials have been prepared by electropo-
lymerization of monomers and were characterized through XPS analysis and spectroscopic studies.
Ó 2009 Elsevier Ltd. All rights reserved.
Conducting polymer
1
. Introduction
The development of solid state light emitting materials has
Due to this, doping cyclometalated iridium(III) complexes into a
host has been an effective way to achieve highly efficient elec-
trophosphorescent devices and reduce phosphorescence quench-
ing [11,15–20]. Another approach involves the coupling of an
iridium metal center directly to a polymer backbone. This route en-
ables more efficient energy transfer from the ligand/polymer to the
metal center due to the proximity of the components.
been a focus of extensive research in recent years [1]. Polymer light
emitting diodes (PLEDs) have been heavily researched since their
initial fabrication in 1990 where a conjugated polymer was utilized
as an electroluminescent material [2,3]. Compared to other inor-
ganic electroluminescent materials, polymer materials have many
desirable characteristics including ease of processing, mechanical
properties, and portability [4,5].
Our approach involves the design and synthesis of iridium(III)
complexes that have the ability to be readily electropolymerized
into conducting metallopolymers giving a material with direct
communication between the metal center and the polymer back-
bone and show strong photophysical properties that can be tuned
synthetically. A bithiophene substituted 1,10-phenanthroline li-
gand which possesses a metal binding site and polymerizable
end groups was chosen for its ability to efficiently transfer energy
directly to the iridium metal center. Ancillary phenylpyri-
dine(ppy)-based ligands were chosen for this study due to ease
of synthesis and the ability to make predictable electronic changes
of the metal complexes based on simple variation of substituent
groups which will result in variable color emission. Herein, we
report the design, synthesis and characterization of a series of
iridium(III) complexes that exhibit light emission ranging from
blue–green to red and their corresponding metallopolymers.
The photophysical properties of cyclometalated iridium(III)
complexes have been widely studied both fundamentally and to-
wards specific applications [6,7]. For example, due to their high
luminescence quantum yields and short phosphorescent lifetimes,
these compounds are suitable for application in light emitting de-
vices. Through simple synthetic and structural changes of the li-
gands that result in electronic changes in the complexes, the
emission profile of this class of complexes can be selectively tuned
to emit light over the visible spectrum [6–10]. Strong spin–orbital
coupling in these systems promotes an efficient inter-system
crossing from the singlet to triplet excited state, which has the po-
tential to result in high electroluminescence efficiency by harness-
ing both singlet and triplet excitons formed by charge injection [3].
Previous reports have shown that iridium(III) complexes in
dilute solution at room temperature show strong photolumines-
cence, however, at high concentrations, intermolecular interac-
tions lead to dimer, excimer, or aggregate formation which can
quench the phosphorescence emission in the solid state [11–14].
2
. Experimental
2.1. Materials and physical measurements
Air- and moisture-sensitive reactions were carried out in flame-
dried glassware using standard Schlenk techniques under an inert
argon atmosphere. Dry DMF was used as received from EMD as
*
Corresponding author. Tel.: +1 512 471 8491; fax: +1 512 471 8648.
E-mail address: bholliday@cm.utexas.edu (B.J. Holliday).
0
277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.06.014

T.W. Hesterberg et al. / Polyhedron 29 (2010) 110–115
111
sure-seal bottles. Bromine was obtained from EMD. 1,10-Phenan-
2.3. Spectroscopy
throline and tri-n-butlytin chloride were purchased from Alfa
Aesar. trans-Dichlorobis(triphenylphosphine)palladium(II) was
obtained from Strem. Dry solvents were obtained from an Innova-
tive Technologies Pure-Solv 400 solvent purification system. All
other chemicals were used as received from commercial suppliers.
NMR spectra were recorded with a Varian Unity + 300 and were
referenced to residual solvent peaks. All coupling constants are
listed in Hertz (Hz). Mass spectrometry was carried out using a
Thermo Finngan TSQ 700. X-ray photoelectron spectroscopy
All spectroscopic data was obtained in DCM solutions unless
otherwise noted. Absorption spectra were recorded on a Varian
Cary 6000i UV–Vis–NIR Spectrophotometer with Starna Quartz
Fluorometer Cells with a pathlength of 10 mm. Luminescent mea-
surements were recorded on a Photon Technology International
QM 4 spectrophotometer equipped with a 6-in. diameter K
Sphere-B integrating sphere. For quantum yield measurements,
the integrating sphere was used. For quantum yield determination,
(
XPS) was carried out on a PHI 5700 XPS system equipped with
kmax of the excitation profile was used as the excitation wave-
dual Mg X-ray source and monochromatic Al X-ray source com-
plete with depth profile and angle-resolved capabilities. 3,8-Dibro-
mo-1,10-phenanthroline was prepared from 1,10-phenanthroline
by Yamamoto’s method [21]. 5-(Tributylstannyl)-2,2-bithiophene
length. Quantum yield was calculated by dividing the area under
the emission peak of the complex by the difference between the
area under the excitation peak of the sample from that of a blank
solution (Aem sample/(Aex blank ꢁ Aex sample), where A = area under
peak) [24].
was prepared by Swager’s method [22]. The target ligand,
0
3
,8-bis(2,2 -bithien-5-yl)-1,10-phenanthroline, (BT)
2
phen, was
prepared according to modification of literature procedures
23]. 5-Methyl-2-(4-fluoro-phenyl)-pyridine, 5-methyl-2-(4-bro-
mo-phenyl)-pyridine, tetrakis-5-methyl-2-(5-fluoro-phenyl)-pyri-
dine)-bis-( -chloro)-diiridium(III), tetrakis-5-methyl-2-(5-bromo-
phenyl)-pyridine)-bis-( -chloro)-diiridium(III), tetrakis-(2-phenyl-
pyridine)-bis-( -chloro)-diiridium(III) were prepared according to
the literature methods [6].
2.4. Preparation of iridium complexes
[
The complexes were synthesized from a general procedure de-
l
scribed below and is shown in Scheme 1. A solution of tetrakis-(R
-ppy)-bis-( -chloro)-diiridium(III) (21.1 mg, 0.0196 mmol) in
MeOH (8 mL) was added to a solution of (BT) phen in 1,2-dichloro-
ethane (4 mL). The solution was heated to reflux for 2 h. After cool-
ing to room temperature, a saturated aqueous solution of KPF
1
,
l
R
2
l
l
2
6
2
.2. Electrochemistry
(5 mL) was added. The reaction mixture was filtered and washed
with water and diethyl ether. The solid was purified by recrystalli-
zation from DCM and ether, followed by recrystallization from
DCM and hexanes.
Electrochemical syntheses and studies were performed in a dry-
box under a nitrogen atmosphere using a GPES system from Eco.
Chemie B.V. All the electrochemical experiments were carried out
in a three-electrode cell with Ag/AgNO
wire dipped in a 0.01 M silver nitrate solution with 0.1 M Bu
in CH CN), a Pt working electrode, and Pt wire coil counter elec-
trode. Potentials were relative to this 0.01 M Ag/AgNO reference
electrode. Ferrocene was used as an external reference to calibrate
the reference electrode before and after experiments were per-
formed and that value was used to correct the measured poten-
tials. All electrochemistry was performed in dichloromethane
3
reference electrode (silver
2.4.1. [Ir(ppy)
Prepared according to general procedure using tetrakis-(2-
phenylpyridine)-bis-( -chloro)-diiridium(III). After purification,
an orange–red solid was obtained, 1 (76%). H NMR (300 MHz,
CDCl ) d 8.76 (d, 2H, J = 1.8), 8.38 (d, 2H, J = 1.8), 8.16 (s, 2H),
2 2 6
((BT) phen)][PF ] (ppy = 2-phenypyridine) (1)
4
NPF
6
3
l
1
3
3
8.06 (d, 2H, J = 8.1), 7.88 (d, 2H, J = 6.9), 7.79 (t, 2H, J = 2.4), 7.62
(d, 2H, J = 5.4), 7.42 (d, 2H, J = 3.6), 7.23 (m, 6H), 7.09 (m, 6H),
1
3
1
6.90 (t, 2H, J = 6.0), 6.48 (d, 2H, J = 7.2). C { H} NMR could not
(
DCM) solutions using 0.1 M [(n-Bu)
porting electrolyte. The TBAPF was purified by recrystallization
three times from hot ethanol before being dried for 3 days at
00–150 °C under active vacuum prior to use. Polymer films were
4
N][PF
6
] (TBAPF
6
) as the sup-
be obtained due to poor solubility of the compound. MS (CI): Anal.
+
6
Calc. for C50
H
32IrN
4
S
4
(M ): 1009.29. Found: 1009. m.p.: 250–
258 °C.
1
prepared on Delta Technologies ITO-coated glass for spectroscopic
measurement and on stainless steel for XPS. Electrosyntheses of
the polymer films were preformed from 1 ꢀ 10 M monomer
solutions by continuous cycling between ꢁ1.5 and 1.5 V at
v = 100 mV/s. The films obtained were then washed with fresh
DCM before further experiments.
2.4.2. [Ir(F-mppy)
(4-fluoro-phenyl)-pyridine) (2)
Prepared according to general procedure using tetrakis-(5-
methyl-2-(4-fluoro-phenyl)-pyridine)-bis-( -chloro)-diiridium(III).
After purification, an orange–red solid was obtained, 2 (78%). H NMR
(300 MHz,CDCl )d8.99(d, 2H, J = 3.0),8.66(d, 2H, J = 1.8),8.44(d,2H,
2 2 6
((BT) phen)][PF ] (F-mppy = 5-methyl-2-
ꢁ
3
l
1
3
Scheme 1. Synthesis of iridium(III) complexes.

1
12
T.W. Hesterberg et al. / Polyhedron 29 (2010) 110–115
0
J = 1.8), 8.20 (s, 2H), 7.83 (m, 4H), 7.60 (d, 2H, J = 6.9), 7.46 (s, 2H), 7.18
2,2 -bithiophene (BT) as a polymerizable group, was prepared
according to a modified literature procedure [23]. The ligand was
obtained as an orange solid. The ancillary ppy ligands were varied
in the series of complexes to provide a broad range of color emis-
sion from the metal complexes and were either commercially
available or synthesized according to the literature procedures
(
m, 8H), 6.95 (t, 2H, J = 2.4), 6.10 (dd, 2H, J = 9.3, J = 2.7), 2.03 (s, 6H).
1
3
1
C { H} NMR couldnot be obtained due to poor solubilityof the com-
+
pound. MS (CI): Anal. Calc. for C52
1
H F IrN S
34 2 4 4
(M ): 1073.13. Found:
073. m.p.: 315–321 °C.
2
.4.3. [Ir(Br-mppy)
bromo-phenyl)-pyridine) (3)
Prepared according to general procedure using tetrakis-(5-
methyl-2-(4-bromo-phenyl)-pyridine)-bis-( -chloro)-diiridium(III).
After purification, a red solid was obtained, 3 (75%). H NMR
300 MHz, CDCl ) d 8.99 (d, 2H, J = 3.0), 8.66 (d, 2H, J = 2.1), 8.44 (d,
H, J = 2.1), 8.20 (s, 2H), 7.88 (m, 4H), 7.61 (d, 2H, J = 7.5), 7.45 (s,
2
((BT)
2
phen)][PF
6
] (Br-mppy = 5-methyl-2-(4-
[6]. IrCl
to form the chlorine bridged dimmer according to the literature
procedure [6]. The dimer was then reacted with the BT (phen) li-
gand to produce monomers 1–3 (Scheme 1). All compounds,
including monomers, were obtained in good yield and are slightly
soluble in common organic solvents. All solution, gas-phase, and
solid state data obtained for the monomers are consistent with
the proposed molecular structures.
3
ꢂH
2
O was reacted with two equivalents of the ppy ligands
2
l
1
(
2
2
3
H), 7.37-7.08 (m, 10H), 6.51 (d, 2H, J = 1.8), 2.03 (s, 6H). 1 C { H}
3
1
NMR could not be obtained due to poor solubility of the compound.
+
MS (CI): Anal. Calc. for C52H34Br IrN S
2 4 4
(M ): 1195.14. Found: 1195.
3.2. Structure of complex 1
m.p.: 201–207 °C.
The solid state structure of monomer 1 was determined by X-
ray diffraction analysis and the resulting ORTEP representation
can be seen in Fig. 1. The six-coordinate Ir(III) lies in the center
of a slightly distorted octahedral environment as the N3–Ir–N1
bond angle is 97.0° and the N3 –Ir–N1 angle is 96.0°. These angles
are slightly increased due to the steric bulk of the bithiophene
2
.5. X-ray crystal structure analysis
Single crystals of 1 suitable for X-ray diffraction analysis were
0
grown by slow liquid diffusion of diethyl ether into a concentrated
solution of 1-chlorobenzene. Crystallographic and structural
refinement data are provided in Table 1. Diffraction data for 1
was collected on a Nonius Kappa CCD diffractometer with graphite
groups on the polymerizable ligand so that no interaction between
the ppy ligands and the (BT) phen occurs. The coordination envi-
2
monochromated Mo K
a
radiation (k = 0.71073 Å) at 153 K. An
ronment around the metal center is defined by two carbon and
two nitrogen atoms from the ppy ligands and by two nitrogen
atoms from the (BT) phen ligand. The Ir–N1(phen) bond distance
2
(2.168 Å) is slightly longer than the Ir–N3(ppy) bond distance
(2.065 Å), which is consistent with the data of the parent complex
2 6
[Ir(ppy) (1,10-phen)][PF ], which does not contain the bithiophene
polymerizable groups (Ir–Nphen 2.164 Å; Ir–Nppy 2.060 Å) [27]. A
dihedral angle of 16.4° is seen between the planes of the thiophene
rings, while that between the thiophene and phenanthroline rings
is 13.5°. The relatively small dihedral angles between the aromatic
rings are consistent with a large amount of conjugation across the
absorption correction was applied using GAUSSIAN. The structure
was solved by direct methods and refined anisotropically using
full-matrix least-squares method with the SHELX97 program pack-
age [25]. The coordinates of the non-hydrogen atoms were refined
anisotropically, while hydrogen atoms were included in the calcu-
lation isotropically but not refined. Neutral atom scattering factors
were taken from Cromer and Waber [26].
3
. Results and discussion
.1. Synthesis and characterization of complexes
The polymerizable ligand, (BT) phen, in which the 1,10-phe-
(
2
BT) phen ligand, and does not perturb electronic properties of the
3
aromatic system [28]. The remaining structural parameters that
were determined agree well with the parent complex. Selected
bond lengths and angles are given in Table 2.
2
nanthroline(phen) moiety serves as a metal binding site and the
3.3. Spectroscopic properties of monomers 1–3
Table 1
The photophysical properties of the series of three monomers
Crystal data and structure refinement for complex 1.
and polymers have been studied in a variety of conditions. The data
of the three complexes are summarized in Table 3. The absorption
spectra of 1, 2, and 3 (Fig. 2a) correspond primarily to the absorp-
Formula
Formula weight
Crystal system
Space group
a (Å)
C
50
H
32
F
6
N
4
PS
4
Irꢂ2H
2
O
1190.24
monoclinic
P2(1)/n
16.810(3)
13.806(3)
22.468(5)
94.02(3)
5201.5(18)
4
tion of the (BT)
2
phen ligand (Table 3), however, the metal com-
plexes display a red-shift from that of the free ligand. This shift
b (Å)
c (Å)
b (°)3
V (Å )
Z
D
calc (g cm 3
ꢁ
)
1.520
T (K)
153(1)
F(0 0 0)
l
2360
2.821
(mmꢁ1)
h Range (°)
Reflection measured
Reflection used
2.93–25.00
26 927
8955
Parameters
613
a
R
(I > 2
r(I))
R
1
= 0.0986
wR = 0.2055
= 0.2572
wR = 0.2861
2
Ra (all data)
R
1
2
S
0.993
Fig. 1. ORTEP diagram of
probability level. Hydrogen atoms, solvent molecules, and counter ions are omitted
for clarity.
1 showing the labeling scheme of atoms at 30%
a
2
2
2
2)2]]1/2. w = 1/[
2(F 2
R
1
=
R
|F
o
| ꢁ |F
c
|R
|F
o
|. wR
2
= [
,0) + 2F
R
w[(F
o
ꢁ F
c
) ]/
R
|[w(F
o
r
o
) +
2
2
2
(
0.075P) ], where P = [max(F
o
c
]/3.

T.W. Hesterberg et al. / Polyhedron 29 (2010) 110–115
113
Table 2
the excitation of the complex [6]. Emission studies were also con-
ducted at 77 K in frozen 2-methyltetrahydrofuran solutions, giving
a qualitatively stronger emission with no distinguishable change in
emission wavelength.
Selected bond lengths (Å) and angles (°) for 1.
Ir(1)–C(39)
Ir(1)–N(3 )
Ir(1)–N(3)
Ir(1)–C(39 )
Ir(1)–N(1)
Ir(1)–N(2)
C(39)–Ir(1)–N(3 )
2.00(2)
2.02(2)
2.065(19)
2.07(2)
2.13(2)
2.168(18)
92.1(9)
79.7(9)
170.3(7)
90.2(8)
81.9(8)
92.9(8)
176.0(8)
91.4(7)
97.0(8)
92.2(8)
100.6(8)
96.0(8)
90.6(7)
169.1(8)
77.1(8)
0
0
3.4. Electrochemistry/electropolymerization
0
Monomers 1–3 were electropolymerized to form poly-1, 2, and
C(39)–Ir(1)–N(3)
3
(Scheme 2) as electrode-confined films on ITO-coated glass for
0
N(3 )–Ir(1)–N(3)
emission studies and stainless steel for X-ray photoelectron spec-
0
0
C(39)–Ir(1)–C(39 )
0
troscopy (XPS) analysis. Cyclic voltammetry of 1, 2, and 3 in a win-
N(3 )–Ir(1)–C(39 )
+
0
dow from +1.5 to ꢁ1.5 V (versus Fc/Fc ) showed growth of a
N(3)–Ir(1)–C(39 )
C(39)–Ir(1)–N(1)
polymer film. The first scan of the CV for poly-1 showed oxidation
at 0.9 V, corresponding to irreversible oxidation of the monomer.
Sequential scans show a reversible wave with E1/2 = 0.57 V corre-
sponding to the redox properties of the electrode-confined poly-
mer, which is deposited on the working electrode, and 0.9 V
0
N(3 )–Ir(1)–N(1)
N(3)–Ir(1)–N(1)
0
C(39 )–Ir(1)–N(1)
C(39)–Ir(1)–N(2)
0
N(3 )–Ir(1)–N(2)
N(3)–Ir(1)–N(2)
(
continued monomer oxidation), whose positions steadily become
0
C(39 )–Ir(1)–N(2)
more positive as the number of scans is increased. Fig. 3a shows
the CV of 1 as a representative example of this series of complexes.
The inset of Fig. 3a, shows a linear relationship between current in-
crease/decrease and the number of scans during polymerization
indicating uniform growth of the polymer up to 20 scans. A scan
rate dependence study was conducted on poly-1 which is shown
in Fig. 3b. As shown in the inset of Fig. 3b, the current of the elec-
trode-confined film has a linear relationship to the electrochemical
scan rate up to 100 mV/s. This result indicates a strongly adsorbed
electroactive material that is not limited by the ionic flux of coun-
ter ions and also implies conductivity of the polymer film. At high-
er scan rates there is a decrease in charge mobility through the
polymer backbone resulting in less facile ion transport and a devi-
ation from the linear relationship. Thinner polymer films may give
N(1)–Ir(1)–N(2)
is due to the extended conjugation of the ligand as it planarizes
when bound to the metal as seen by the small dihedral angles be-
tween the thiophene and phen rings (vide supra). The p–p* transi-
tion near 270 nm originates from the ancillary ppy ligands and is
also red-shifted from that of the free ligand. The emission spectra
of 1, 2, and 3 (Fig. 2b) display strong, broad emission peaks which
shift in maxima due to the change in ancillary ppy ligands. The
trend in the shift of emission wavelength (3 > 1 > 2) is consistent
with that of previous reports when considering the electron rich
2
nature of the (BT) phen ligand which is primarily responsible for
Table 3
2
kmax of UV–Vis and photoluminescence data of compounds (BT) phen, 1, 2, and 3.
Compound
BT) Phen
1
2
3
Absorbancea
kmax (nm) (
e)
Excitationa
k
max (nm)
Emissiona
k
max (nm)
Ua
(
2
257(12 000), 307(9000), 396(18 000)
264(38 000), 352(24 000), 442(33 000)
273(57 000), 361(23 000), 461(33 000)
273(57 000), 408(42 000) 467(35 000)
400
425
400
320
480
547
512
589
0.2453
0.0039
0.0784
0.0041
a
ꢁ1
ꢁ1
All data were obtained in a DCM solution at RT. Unit of
e is M cm .
Fig. 2. UV–Vis absorption (a) and emission (b) spectra of complexes 1–3 taken in DCM at room temperature.

1
14
T.W. Hesterberg et al. / Polyhedron 29 (2010) 110–115
Scheme 2. Electrochemical polymerization of iridium-containing monomers to form conducting metallopolymers.
Fig. 3. (a) Cyclic voltammogram of 1. Inset: plot of current versus numbers of scans. (b) Scan rate dependence study of 1. Inset: plot of current versus scan rate.
a more linear response than those studied. Similar data was ob-
served for poly-2, and poly-3 and can be found in Supplementary
data.
3.5. Characterization of polymers
In order to characterize the polymer films, XPS studies were
conducted to determine the elemental composition of the polymer
through survey scans of the film. Quantitative XPS analysis of poly-
1
reveals that the film has an atomic ratio of iridium (4f):sulfur
(
2p) = 1:5.02, which is consistent with the stoichiometric molar ra-
tio found in the monomer by the same technique, 1:4.86, and pro-
posed film structure, 1:4. Results for poly-2 showed the polymer
having an Ir:S ratio of 1:7.06, which is higher than the theoretical
value, but is an average of three separate sample studies all having
similar data. The atomic ratio for poly-3 is 1:5.04, which is similar
to the results of poly-1 and the theoretical value. Similar devia-
tions in the molar ratios from the theoretical values of the poly-
mers have been previously reported [29]. Data plots of XPS
results can be seen in Supplementary data.
Fig. 4. UV–Vis absorption spectra of poly-1, -2, -3 on ITO-coated glass at room
temperature.
3.6. Spectroscopic properties of polymers
Fig. 4 shows the UV–Vis absorption spectra of poly-1, poly-2,
matic system of a conjugated metallopolymer structure. The
and poly-3 deposited on ITO-coated glass. These polymers display
absorption is red-shifted from that of 1, 2, 3 and of the (BT)
2
phen
very broad absorption bands characteristic of the extended aro-
ligand. Emission spectra of the polymers were recorded with an

T.W. Hesterberg et al. / Polyhedron 29 (2010) 110–115
115
Acknowledgements
We gratefully acknowledge the Robert A. Welch Foundation (F-
631), the Petroleum Research Fund administered by the American
1
Chemical Society (47022-G3), the National Science Foundation
CHE-0639239, CHE-0741973 and CHE-0847763), the American
(
Heart Association (0765078Y), the UT-CNM and UT-Austin for
financial support of this research. TWH would like to acknowledge
the Division of Inorganic Chemistry Student Travel Award that al-
lowed him to present a portion of this work at the Fall 2008 ACS
meeting.
Appendix A. Supplementary data
Fig. 5. Energy level diagram of complexes 1 (blue), 2 (red), 3 (black), (BT)
poly-(BT) phen. (For interpretation of the references to colour in this figure legend,
the reader is referred to the web version of this article.)
2
phen and
2
CCDC 730383 contains the supplementary crystallographic data
for 1. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2009.06.014.
excitation wavelength of 400 nm and showed no observable emis-
sion. With this result, copolymerizations with a metal-containing
monomer to bithiophene ratio of 1:50 and 1:100 were conducted.
This was done to determine if the spacing of the metal centers in
the polymer chain and the overall density of the metal complexes
in the films had any role in quenching of the emission. The electro-
chemical and spectroscopic data for these experiments can be
found in the Supplementary data. UV–Vis absorption and emission
spectra were taken on ITO-coated glass, but no observable emis-
sion was detected from the copolymer films. Energy level determi-
nation studies were conducted on the monomers and the polymers
in order to establish the thermodynamic favorability of charge
transfer to the metal center in these complexes. Fig. 5 shows the
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4
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