Iridium luminophore complexes for unimolecular oxygen sensors

Article abstract of DOI:10.1021/ja049872h

In this study, a series of novel luminescent cyclometalated Ir(III) complexes has been synthesized and evaluated for use in unimolecular oxygen-sensing materials. The complexes Ir(C6)₂(vacac), 1, Ir(ppy)₂-(vacac), 2, fac-Ir(ppy)₂(vppy), 3, and mer-Ir(ppy)₂(vppy), 4, where C6 = Coumarin 6, vacac = allylaceto-acetate, ppy = 2-phenylpyridine, and vppy = 2-(4-vinylphenyl) pyridine, all have pendent vinyl or allyl groups for polymer attachment via the hydrosilation reaction. These luminophore complexes were characterized by NMR, absorption, and emission spectroscopy, luminescence lifetime and quantum yield measurements, elemental analysis, and cyclic voltammetry. Complex 1 was structurally characterized using X-ray crystallography, and a series of 1-D (¹H, ¹³C) and 2-D (¹H-¹H, ¹H-¹³C) NMR experiments were used to resolve the solution structure of 4. Complexes 1 and 3 displayed the longest luminescence lifetimes and largest quantum efficiencies in solution (τ = 6.0 μs, φ = 0.22 for 1; τ = 0.4 μs, φ = 0.2 for 3) and, as result, are the most promising candidates for future luminescence-quenching-based oxygen-sensing studies.

Full text of DOI:10.1021/ja049872h

Published on Web 05/26/2004
Iridium Luminophore Complexes for Unimolecular Oxygen
Sensors
†
‡
§
,‡
Maria C. DeRosa, Derek J. Hodgson, Gary D. Enright, Brian Dawson,*
,
§
,†
Christopher E. B. Evans,* and Robert J. Crutchley*
Contribution from the Ottawa-Carleton Chemistry Institute, Carleton UniVersity,
Ottawa, Ontario, K1S 5B6, Canada, Centre for Biologics Research, Biologics and Genetic
Therapies Directorate, Health Canada, Tunney’s Pasture, Ottawa, Ontario, Canada K1A 0L2,
and National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6
Received January 8, 2004; E-mail: robert_crutchley@carleton.ca; brian_dawson@hc-sc.gc.ca; chris.evans@coven.net
Abstract: In this study, a series of novel luminescent cyclometalated Ir(III) complexes has been synthesized
and evaluated for use in unimolecular oxygen-sensing materials. The complexes Ir(C6)
2 2
(vacac), 1, Ir(ppy) -
(
vacac), 2, fac-Ir(ppy) (vppy), 3, and mer-Ir(ppy) (vppy), 4, where C6 ) Coumarin 6, vacac ) allylaceto-
2
2
acetate, ppy ) 2-phenylpyridine, and vppy ) 2-(4-vinylphenyl)pyridine, all have pendent vinyl or allyl groups
for polymer attachment via the hydrosilation reaction. These luminophore complexes were characterized
by NMR, absorption, and emission spectroscopy, luminescence lifetime and quantum yield measurements,
elemental analysis, and cyclic voltammetry. Complex 1 was structurally characterized using X-ray
1
13
1
1
1
13
crystallography, and a series of 1-D ( H, C) and 2-D ( H- H, H- C) NMR experiments were used to
resolve the solution structure of 4. Complexes 1 and 3 displayed the longest luminescence lifetimes and
largest quantum efficiencies in solution (τ ) 6.0 µs, φ ) 0.22 for 1; τ ) 0.4 µs, φ ) 0.2 for 3) and, as result,
are the most promising candidates for future luminescence-quenching-based oxygen-sensing studies.
Introduction
sensing are based on cyclometalated iridium(III) complexes, and
several have recently been investigated for PSP applications.3
Luminescence-quenching-based oxygen sensors find applica-
tions in a variety of areas from medicine to chemical and
environmental analysis.1 One notable application of these
materials is in flow visualization; in this field, these sensors
are commonly known as pressure-sensitive paints (PSPs). PSPs
are gaining widespread acceptance as the technology of choice
for use in surface pressure distribution measurements for
The dispersed nature of the luminescent molecules in many
PSP formulations can lead to problems of aggregation within
the paint or leaching from the oxygen-permeable matrix.4
Recently, work from Manners and Winnik et al. has established
that the covalent attachment of a luminophore to the polymer
matrix can help lessen these problems and can result in improved
5
behavior over analogous dispersed systems. In an earlier work,
2
aerodynamic applications. These paints are typically composed
we have shown that the hydrosilation reaction is an effective
methodology for the creation of unimolecular oxygen sensors
from nonionic vinyl-bearing luminophores and hydride-
of an oxygen-sensitive luminescent compound dispersed in an
oxygen-permeable polymer matrix. An ideal luminophore
complex for oxygen sensing should fulfill several key require-
ments: efficient emission (high quantum yield) for improved
sensitivity, long excited state lifetime (from hundreds of
nanoseconds to microseconds) to be quenched efficiently by
oxygen, as well as excellent photostability and resistance to
singlet oxygen. Ancillary properties such as a large Stokes shift
and long wavelength excitation energies, that is, in the visible
range, improve the applicability of a luminophore to oxygen
sensing. Some of the most promising luminophores for oxygen
6
terminated siloxane polymers. This study describes a series of
cyclometalated Ir(III) complexes for use in pressure-sensitive
paints: Ir(C6)2(vacac), 1, Ir(ppy)2(vacac), 2, fac-Ir(ppy)2(vppy),
3
)
, and mer-Ir(ppy)2(vppy), 4, where C6 ) Coumarin 6, vacac
allylacetoacetate, ppy ) 2-phenylpyridine, and vppy ) 2-(4-
vinyl)-phenylpyridine. These compounds represent the two main
types of complex luminophores currently employed in PSP,
those with ligand-based emission, and those with charge-transfer
(
3) (a) Vander Donckt, E.; Camerman, B.; Hendrick, F.; Herne, R.; Vandeloise,
R. Bull. Soc. Chim. Belg. 1994, 103, 207. (b) Amao, Y.; Ishikawa, Y.;
Okura, I. Anal. Chim. Acta 2001, 445, 177. (c) Gao, R.; Ho, D. G.;
Hernandez, B.; Selke, M.; Murphy, D.; Djurovich, P. I.; Thompson, M. E.
J. Am. Chem. Soc. 2002, 124, 14828. (d) Carlson, B.; Khalil, G.; Gouterman,
M.; Dalton, L. Polym. Prepr. 2002, 43, 590.
(4) (a) Lu, X.; Manners, I.; Winnik, M. A. Macromolecules 2001, 34, 1917.
(b) Klimant, I.; Wolfbeis, O. S. Anal. Chem. 1995, 67, 3160. (c) Hubner,
J. P.; Carroll, B. F.; Schanze, K. S.; Ji, H. F. Exp. Fluids 2000, 28, 21.
(5) Wang, Z.; McWilliams, A. R.; Evans, C. E. B.; Lu, X.; Chung, S.; Winnik,
M. A.; Manners, I. AdV. Funct. Mater. 2002, 12, 415.
(6) DeRosa, M. C.; Mosher, P. J.; Yap, G. P. A.; Focsaneanu, K.-S.; Crutchley,
R. J.; Evans, C. E. B. Inorg. Chem. 2003, 42, 4864.
†
Carleton University.
Health Canada.
National Research Council of Canada.
‡
§
(
1) Amao, Y. Microchim. Acta 2003, 143, 1 and references therein.
2) (a) Bell, J. H.; Schairer, E. T.; Hand, L. A.; Mehta, R. D. Annu. ReV. Fluid
Mech. 2001, 33, 155. (b) Hubner, J. P.; Caroll, B. F.; Schanze, K. S.; Ji,
H. F.; Holden, M. S. AIAA J. 2001, 39, 654. (c) Engler, R. H.; Klein, C.;
Trinks, O. Meas. Sci. Technol. 2000, 11, 1077. (d) Taghavi, R.; Raman,
G.; Bencic, T. Exp. Fluids 1999, 26, 481. (e) Dowgwillo, R. M.; Morris,
M. J.; Donovan, J. F.; Benne, M. E. J. Aircr. 1996, 33, 109.
(
10.1021/ja049872h CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 7619-7626
9
7619

A R T I C L E S
i.e., metal-to-ligand or ligand-to-metal)-based emission. In
addition, these luminophores are functionalized with pendent
vinyl or allyl groups to allow for the covalent attachment of
these complexes to hydride-containing silicones via transition-
metal-catalyzed hydrosilation.
DeRosa et al.
1
(
284 K, operating at 16.35 T (corresponding to 700.13 MHz for H and
1
76.07 13C), processed using XWIN NMR 3.0. All experiments used
2 2 6
CD Cl or acetone-d from Cambridge Isotopes Ltd. and Sigma-Aldrich
and were referenced to solvent resonances at 5.32 and 2.05 ppm,
respectively. Elemental analyses were performed by Canadian Mi-
croanalytical Service, Ltd. of Delta, B. C., Canada. Electron impact
mass spectrometry (EI-MS) was performed at the University of Ottawa
Mass Spectrometry Center. Absorption and steady-state emission spectra
X-ray crystallography has been established as the principal
technique in structure determination, and one seldom finds a
study of any novel inorganic or organometallic complex that
does not include a crystal structure in its characterization.
Unfortunately, the process of growing an X-ray quality crystal
is an arduous one, and many systems are not conducive to crystal
growth. In these instances, alternate methods of structural
characterization must be explored. NMR spectroscopy is
undoubtedly one of the most powerful techniques in structure
elucidation with its 1-D and 2-D experiments routinely employed
to resolve the molecular structure of proteins and DNA
2 2
were acquired in dry CH Cl or dry toluene on a Cary 5 UV-vis-
NIR spectrophotometer and a Photon Technology International version
1.23 luminescence spectrometer, respectively, at ambient temperatures.
Time-resolved fluorescence decays were obtained by excitation with
the third harmonic of a Surelite Nd:YAG laser (355 nm, 6 ns, e25
2
mJ). All experiments were done in static 0.7 × 0.7 cm fused silica
2
cuvettes, following purging with N gas for 15 min. For the quantum
yield determinations, the N
2
purged samples were optically matched
to an Ir(ppy) standard using a Varian Cary 1E spectrophotometer.
Toluene was used as the solvent for all lifetime and quantum yield
measurements.
3
7
complexes. Organometallic and coordination chemists typically
1
13
apply H and C NMR spectroscopy to confirm the presence
of organic ligands on their complexes, but there are few
examples where NMR spectroscopy is used to determine the
[
Ir(C6)
2
(vacac)], 1. [Ir(C6)
2
Cl]
2
(0.2 g, 0.17 mmol, FW 1154.20 g
-1
-1
mol ) and silver triflate (0.09 g, 0.35 mmol, 256.06 g mol ) were
dissolved in acetone (40 mL) and refluxed under argon for 2 h. The
cloudy orange solution was cooled to room temperature and gravity-
filtered to remove AgCl. To the filtrate was added allylacetoacetate
(vacac) (64 µL, 0.43 mmol) and triethylamine (0.5 mL). The solution
was stirred overnight at room temperature under argon. Solvent-
stripping to dryness yielded a deep orange solid which was purified
using a short silica gel column, eluting with diethyl ether. The first
bright orange band was collected and solvent-stripped to dryness. The
product was recrystallized by slow diffusion of hexanes into a
concentrated dichloromethane solution, yielding red-orange X-ray
8
three-dimensional structure of their systems. In this study, we
1
13
also present a unique example where a series of 1-D ( H, C)
1
1
1
13
and 2-D ( H- H, H- C) NMR experiments served to resolve
the solution structure of mer-Ir(ppy)2(vppy), 4.
Experimental Section
Iridium(III) chloride hydrate was purchased from Strem, and
2-phenylpyridine, silver triflate, allylacetoacetate, and Coumarin 6 were
purchased from Aldrich. [Ir(ppy)
according to published procedures.
2
Cl]
2
and [Ir(C
6
2
) Cl]
2
were prepared
quality crystals of [Ir(C6)
2
(vacac)], 1 (120 mg, 0.12 mmol, 34% yield,
FW 1032.23 g mol ). Anal. Calcd as the monosolvate C35 Ir‚
CH Cl : C, 51.61; H, 4.06; N, 5.02. Found: C, 51.94; H, 4.02; N,
9
-
1
26 3
H N
Cyclic voltammetry was performed with a BAS CV-27 voltammo-
graph and a BAS X-Y recorder. A double-jacketed cell was fitted with
a Teflon lid incorporating the three electrodes and an argon bubbler
and was attached to a Haake D8-G circulating bath to maintain the
temperature at 25 °C. Platinum disk working and counter electrodes
2
2
1
5
.17. H NMR (acetone-d
6
, 400 MHz): 7.98 (t, 2H, 8 Hz), 7.58 (d,
H, 8 Hz), 7.46 (d, 1H, 8 Hz), 7.23 (m, 4H), 6.19 (t, 2H, 2 Hz), 6.02
dd, 2H, 9 Hz, 2 Hz), 5.91 (m, 2H), 5.65 (m, 1H), 4.97 (m, 2H), 4.38
qtd, 2H, 17 Hz, 5 Hz, 1.5 Hz), 4.28 (s, 1H), 3.21 (dq, 8H, 7 Hz, 2.6
Hz), 1.55 (s, 3H), 0.90 (dt, 12H, 7 Hz, 2.5 Hz). UV-vis: ꢀ445 ) 7.79
1
(
(
(BAS, 1.6 mm diameter), a silver wire pseudo-reference with ferrocene
as an internal reference, and 0.1 M tetrabutylammonium hexafluoro-
phosphate (TBAH; twice recrystallized in 1:1 EtOH/water) as the
supporting electrolyte were all used. NMR spectra were acquired either
on a Bruker AMX-400 at ambient temperatures processed using X-32
computer software UXNMR 920801 or on a Bruker Avance 700 at
4
-1
-1
4
-1
-1
×
10 M cm ; ꢀ473 ) 8.65 × 10 M cm . CV: 0.69 V vs ferrocene
(
MeCN, 0.1 M TBAH).
X-ray Structural Determination of 1. The single-crystal diffraction
data were collected at 173 K on a Bruker SMART CCD diffractometer
with Mo KR radiation (0.71073 Å). The program SMART was used
for collecting frames of data, indexing reflections, and determination
of lattice parameters; SAINT was used for integration of the intensity
of reflections and scaling. SADABS was used for absorption correction,
and SHELXTL was used for space group and structure determination,
and least-squares refinements on F . Hydrogen atoms were placed in
calculated positions and constrained to ride with the atoms with which
they were bonded. Problems in refinement convergence were largely
due to solvent disorder.
(
7) For example, see: (a) Radha, P. K.; Patel, P. K.; Hosur, R. V. Biochemistry
1
998, 37, 9952. (b) Gelasco, A.; Lippard, S. J. Biochemistry 1998, 37,
230. (c) Kurutz, J. W.; Lee, K. Y. C. Biochemistry 2002, 41, 9627. (d)
9
Hemmi, H.; Yoshida, T.; Kumazaki, T.; Nemoto, N.; Hasegawa, J.;
Nishioka, F.; Kyogoku, Y.; Yokosawa, H.; Kobayashi, Y. Biochemistry
2
10
2
002, 41, 10657. (e) Dowd, T. L.; Rosen, J. F.; Li, L.; Gundberg, C. M.
Biochemistry 2003, 42, 7769. (f) Ying, J.; Ahn, J.-M.; Jacobsen, N. E.;
Brown, M. F.; Hruby, V. J. Biochemistry 2003, 42, 2825. (g) Ojha, R. P.;
Dhingra, M. M.; Sarma, M. H.; Shibata, M.; Farrar, M.; Turner, C. J.;
Sarma, R. H. Eur. J. Biochem. 1999, 265, 35. (h) Eichm u¨ ller, C.; Tollinger,
M.; Kr a¨ utler; B.; Konrat, R. J. Biomol. NMR 2001, 20, 195. (i) Chen, J.
M.; Nelson, F. C.; Levin, J. I.; Mobilio, D.; Moy, F. J.; Nilakantan, R.;
Zask, A.; Powers, R. J. Am. Chem. Soc. 2000, 122, 9648. (j) Mondelli, R.;
Scaglioni, L.; Mazzini, S.; Bolis, G.; Ranghino, G. Magn. Reson. Chem.
[Ir(ppy)
2
(vacac)], 2. [Ir(ppy)
2
Cl]
2
(0.5 g, 0.47 mmol, FW 1072.11
g mol-1) and silver triflate (0.13 g, 0.94 mmol, FW 256.06 g mol
-1
)
were dissolved in acetone (40 mL) and refluxed under nitrogen for 2
h. The cloudy yellow solution was cooled and gravity-filtered to remove
AgCl. Allylacetoacetate (vacac) (174 µL, 1.18 mmol, FW 142.16 g
mol ) and triethylamine (0.5 mL) were added to the filtrate. The
solution was then stirred overnight at room temperature under nitrogen.
After solvent-stripping to dryness, the dark yellow solid was purified
on a short silica gel column, eluting with dichloromethane. The first
bright yellow band was collected and solvent-stripped to dryness. The
product was recrystallized by slow diffusion of hexanes into a
2
000, 38, 229.
(
8) (a) Bortolin, M.; Bucher, U. E.; R u¨ egger, H.; Venanzi, L. M.; Albinati,
A.; Lianza, F.; Trofimenko, S. Organometallics 1992, 11, 2514. (b) Kortes,
R. A.; Stringfield, T. W.; Ward, M. S.; Lin, F.-T.; Shepherd, R. E. Inorg.
Chim. Acta 2000, 304, 60. (c) Reger, D. L.; Gardinier, J. R.; Smith, M. D.;
Pellechia, P. J. Inorg. Chem. 2003, 42, 482. (d) Proudfoot, E. M.; Mackay,
J. P.; Karuso, P. Dalton Trans. 2003, 2, 165. (e) Macchioni, A. Eur. J.
Inorg. Chem. 2003, 2, 195. (f) Zuccaccia, C.; Bellachioma, G.; Cardaci,
G.; Macchioni, A. J. Am. Chem. Soc. 2001, 123, 11020.
-
1
(
9) (a) Sprouse, S.; King, K. A.; Spellane, P. J.; Watts, R. J. J. Am. Chem.
Soc. 1984, 106, 6647-6653. (b) Nonoyama, M. Bull. Chem. Soc. Jpn. 1974,
4
7, 767-768. (c) Nonoyama, M. J. Organomet. Chem. 1974, 82, 271-
76. (d) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee,
2
H.-E.; Adachi, C.; Burrows, P. E.; Forrest, S. R.; Thompson, M. E. J. Am.
Chem. Soc. 2001, 123, 4304-4312.
(10) Blessing, R. Acta Crystallogr. 1995, A51, 33-38.
7620 J. AM. CHEM. SOC.
9
VOL. 126, NO. 24, 2004

Iridium Luminophore Complexes
A R T I C L E S
d, 1H, 7.56 Hz), 7.71 (P3′, dd, 1H, 7.89 and 1.31 Hz), 7.68 (N 4, ddd,
concentrated dichloromethane solution, yielding a golden yellow
v
microcrystalline solid [Ir(ppy)
yield, FW 641.75 g mol ). Anal. Calcd as the semihydrate C35H N -
2
(vacac)], 1 (330 mg, 0.514 mmol, 55%
1H, 7.81, 7.78, and 1.72 Hz), 7.65 (N6′, d, 1H 5.89 Hz), 7.61 (N4,
ddd, 1H, 7.78, 7.76, and 1.63 Hz), 7.57 (N4′, ddd, 1H, 7.79, 7.76, and
-
1
26 3
Ir‚0.5H
2
O: C, 53.53; H, 4.03; N, 4.30. Found: C, 53.41; H, 3.83; N,
1.49 Hz), 7.12 (P
7.39, 7.53, and 1.38 Hz), 6.96 (P5, ddd, 1H, 7.19, 7.21, and 1.23 Hz),
6.94 (N 5, ddd, 1H, 7.28, 5.82, and 1.38 Hz), 6.93 (P4′, ddd, 1H, 7.43,
7.31, and 1.54 Hz), 6.91 (P 6, d, 1H, 1.90 Hz), 6.86 (P5′, ddd, 1H,
v
4, dd, 1H, 8.10 and 1.94 Hz), 7.01 (P4, ddd, 1H,
1
4
7
6
.34. H NMR (acetone-d
.93 (m, 2H), 7.65 (d, 2H, 8 Hz), 7.35 (m, 2H), 6.76 (t, 2H, 7.6 Hz),
.60 (m, 2H), 6.23 (d, 2H, 7.6 Hz), 5.67 (m, 1H), 4.98 (m, 2H), 4.73
6
, 400 MHz): 8.64 (m, 2H), 8.08 (m, 2H),
v
v
(
ꢀ
s, 1H), 4.25 (qtd, 2H, 12 Hz, 5.6 Hz, 1.5 Hz), 1.72 (s, 3H). UV-vis:
257 ) 4.32 × 10 M cm ; ꢀ400 ) 3.92 × 10 M cm . CV: 0.47
7.38, 7.36, and 1.40 Hz), 6.81 (N5′, ddd, 1H, 7.40, 5.99, and 1.41 Hz),
6.80 (N5, ddd, 1H, 7.36, 5.96, and 1.43 Hz), 6.61 (P6, dd, 1H, 7.20
and 1.36 Hz), 6.51 (PvA, dd, 1H, 17.64 and 10.892 Hz), 6.45 (P6′, dd,
1H, 7.64 and 1.21 Hz), 5.52 (PvC, dd, 1H, 17.63 and 1.28 Hz), 5.06
4
-1
-1
3
-1
-1
V vs ferrocene (MeCN, 0.1 M TBAH).
-(4-Vinylphenyl)pyridine (vppyH). Potassium-tert-butoxide (21.8
2
(PvB, dd, 1H, 10.22 and 1.27 Hz). 13C NMR (CD
(P 1), 175.18 (P1), 170.60 (N2), 168.10 (N 2), 167.98 (N2′), 159.71
(P1′), 153.59 (N6), 151.61 (N 6), 148.26 (N6′), 146.02 (P 2), 145.26
(P2), 142.73 (P2′), 138.34 (PvA), 138.22 (P 5), 137.12 (N 4), 136.35
(P 6), 136.20 (N4), 134.78 (N4′), 132.96 (P6), 130.80 (P6′), 130.23
(P5), 129.92 (P5′), 124.84 (P 3), 124.59 (P3), 124.44 (P3′), 122.83 (N
or N5′), 122.69 (N5), 121.91 (N5′ or N 5), 121.35 (P4), 119.70 (N 3),
119.51 (P 4), 119.291 (P4′), 119.18 (N3 or N3′), 118.93 (N3 or N3′),
mL, 1.0 M solution in THF) was added dropwise through a septum
into a flame-dried Schlenk flask containing a cloudy white suspension
of methyl triphenylphosphonium bromide (3.9 g, 10.91 mmol, FW
2
2
Cl , 176 MHz): 177.76
v
v
v
v
-
1
3
57.24 g mol ) in diethyl ether (100 mL). The yellow mixture was
v
V
cooled in an ice/water bath and stirred for 30 min. A solution of 4-(2-
pyridyl)benzaldehyde (1 g, 5.46 mmol, FW 183.21 g mol-1) in diethyl
ether (15 mL) was then added slowly over 10 min via cannula. The
resultant solution was shielded from light, allowed to gradually warm
to room temperature, and stirred overnight. Distilled water (50 mL)
was added to the solution, and the ether layer was separated and washed
three times with aliquots of distilled water (3 × 50 mL). The yellow
V
v
V
5
v
v
v
4
-1
-1
113.37 (PvBC). UV-vis: ꢀ274 ) 4.86 × 10 M cm ; ꢀ390 ) 7.99 ×
10 M cm-1. CV: 0.25 V vs ferrocene (CH
3
-1
2
2
Cl , 0.1 M TBAH).
Results and Discussion
4
ether layer was then dried over MgSO . Solvent-stripping to dryness
resulted in a pale yellow oil which was purified by column chroma-
tography on silica gel, eluting with 15% diethyl ether in hexanes (0.47
Synthesis of 1-4. The reaction of the chloride-bridged dimer
Ir(C6)2Cl]2 with the vacac ligand in the presence of silver
[
-
1
1
g, 2.6 mmol, 47% yield, FW 180.23 g mol ). H NMR (CD
2 2
Cl , 400
triflate led to the synthesis of the mononuclear iridium complex
. Complex 2 was synthesized in a similar fashion using [Ir-
(ppy)2Cl]2 as a starting material. In both cases, the dimers were
confirmed by NMR spectroscopy to be in the trans configura-
tion.
MHz): 8.66 (1H, m), 8.00 (2H, d, 8.3 Hz), 7.77 (2H, m), 7.53 (2H, d,
1
8
1
.5 Hz), 7.23 (1H, m), 6.78 (1H, dd, 17.6 Hz, 10.9 Hz), 5.85 (1H, dd,
7.6 Hz, 0.8 Hz), 5.30 (1H, m). MS (EI): M ) 181.
+
fac-[Ir(ppy)
2
(vppy)], 3. 2-(4-Vinylphenyl)pyridine (1.0 g, 5.5 mmol,
-
1
FW 180.23 g mol ), [Ir(ppy)
2
Cl]
2
(0.8 g, 0.75 mmol, FW 1072.11 g
-1
-1
mol ), and silver triflate (0.38 g, 1.5 mmol, FW 256.06 g mol ) were
all dissolved in 2-ethoxyethanol (15 mL) and heated using an oil bath
under nitrogen to 95 °C overnight. The deep yellow solution was cooled
and gravity-filtered to remove the gray AgCl precipitate. The filtrate
was solvent-stripped to dryness and was purified by column chroma-
tography (silica gel) using 2:1 hexanes/diethyl ether as the eluent to
remove unreacted vppy. The mobile phase was switched to 1:1 hexanes/
diethyl ether to elute the bright yellow product band, which was solvent-
stripped to dryness to yield [Ir(ppy)
1
2
(vppy)], 3 (0.09 g, 0.13 mmol,
8% yield, FW 680.83 g mol ). Anal. Calcd as the monohydrate
Ir‚H O: C, 60.15; H, 4.04; N, 6.01. Found: C, 60.56; H, 4.12;
N, 5.64. H NMR (CD Cl , 700 MHz): 7.95 (m, 3H), 7.69 (m, 6H),
.59 (m, 3H), 7.04 (m, 1H), 6.94 (m, 5H), 6.81 (m, 5H), 6.46 (dd, 1H,
7.49 and 10.84 Hz), 5.49 (d, 1H, 17.60 Hz), 5.03 (d, 1H, 10.87 Hz).
-
1
C
35
H
26
N
3
1
2
2
2
7
1
4
-1
-1
4
-1
-1
UV-vis: ꢀ287 ) 4.24 × 10 M cm ; ꢀ290 ) 1.13 × 10 M cm
CV: 0.31 V vs ferrocene (CH Cl , 0.1 M TBAH).
mer-[Ir(ppy) (vppy)], 4. [Ir(ppy) Cl] (0.5 g, 0.47 mmol, FW
072.11 g mol ) and silver triflate (0.13 g, 0.94 mmol, FW 256.06 g
.
2
2
2
1
2
2
-
1
-
1
Complex 3 was synthesized from the addition of vppyH to
the chloride-bridged dimer [Ir(ppy)Cl]2 in 2-ethoxyethanol at
elevated temperatures (95 °C), using silver triflate to scavenge
the chloride ions. The low yield of 3 (18%) prompted a
modification of the reaction conditions. The solvent was changed
to acetone, and triethylamine was added to help deprotonate
the vppyH ligand. These new reaction conditions led to the
synthesis of the novel complex 4 in good yield (70%). Elemental
mol ) were dissolved in acetone (40 mL) and refluxed under nitrogen
for 2 h. The cloudy yellow solution was cooled and gravity-filtered to
remove AgCl. To the filtrate were added vinylpyridine (vppyH) (0.35
g, 1.9 mmol, FW 180.23 g mol-1) and triethylamine (0.5 mL). The
solution was then stirred overnight at room temperature under nitrogen.
After being solvent-stripped to dryness, the dark yellow solid was
purified on a short silica gel column, eluting with dichloromethane.
The first bright yellow/orange band was collected and solvent-stripped
to dryness. The product was recrystallized by slow diffusion of hexanes
into a concentrated dichloromethane solution, yielding a golden yellow
1
analysis and H NMR spectroscopy confirmed the purity and
formula of the two complexes, and thus the possibility that 3
and 4 were analogous to the facial and meridional isomers of
Ir(ppy)3 was explored.
Tris-complexes with asymmetric ligands present the possibil-
ity of preparing either facial (fac) or meridional (mer) isomers.
A recent study by Thompson et al. has been the only study of
microcrystalline solid [Ir(ppy)
2
(vppy)], 4 (220 mg, 0.33 mmol, 70%
yield, FW 680.83 g mol ). Anal. Calcd as the solvate C35 Ir‚
14): C, 62.29; H, 4.16; N, 6.02. Found: C, 62.51; H, 4.56; N,
-
1
26 3
H N
0
5
6
.2(C H
1
.48. H NMR (CD
3, d, 1H, 8.25 Hz), 7.96 (N
.87 (N3, N3′, d, 2H, 8.13 Hz), 7.77 (P
2 2
Cl , 700 MHz): 8.14 (N6, dd, 1H, 5.86 and 1.59
Hz), 7.98 (N
7
v
v
6, dd, 1H, 5.54 and 1.60 Hz),
v
3, d, 1H, 5.56 Hz), 7.75 (P3,
J. AM. CHEM. SOC.
9
VOL. 126, NO. 24, 2004 7621

A R T I C L E S
DeRosa et al.
mer isomers of d trischelates to date.11 In this case, high
temperatures (refluxing glycerol ∼200 °C) were required to
synthesize the fac isomer, while the mer isomer could be
prepared using glycerol at 140-145 °C. Because the synthesis
of 4 is carried out at low temperature, it can be suggested that
this is the kinetically favored product, while the higher reaction
temperature used in 2-ethoxyethanol allows for 3, the thermo-
dynamically favored product, to be formed. A fac isomer would
have all three phenyl ligands on the same face of the molecule,
trans to a pyridyl nitrogen. This is likely the more thermody-
namically favored structure due to the strong trans influence of
the anionic phenyl ligand. Further confirmation of this is shown
in the sections on electronic spectroscopy and cyclic voltam-
metry.
6
Figure 1. ORTEP diagram of 1‚(CH2Cl2) (30% probability). Hydrogen
atoms and molecules of solvation have been removed for clarity. Selected
bond lengths (Å) and angles (deg): Ir-C41, 1.9912(13); Ir-C11, 1.981-
(2); Ir-N1, 2.0488(14); Ir-N31, 2.0386(14); Ir-O61, 2.1246(11); Ir-O64,
2
.1404(17); O61-Ir-O64, 87.68(6); N1-Ir-O61, 82.74(5); C41-Ir-O61,
72.37(7); C11-Ir-N1, 80.29(7).
1
Table 1. X-ray Crystallographic Data for 1‚(CH2Cl2)
empirical formula
formula weight
crystal system
48 45 2 4 7 2
C H Cl IrN O S
-
1
1117.10 g mol
monoclinic
P21/c
space group
unit cell dimensions
a ) 14.5249(9) Å; â ) 124.978(10)°
b ) 17.4530(11) Å
c ) 22.1208(14) Å
3
volume
4594.8(5) Å
Structural Analysis of 1 and 4. Single crystals of 1 were
grown by diffusion of hexanes into concentrated dichlo-
romethane solutions, and its structure was unambiguously
confirmed by X-ray crystallography. The molecular structure
of 1‚(CH2Cl2) is given as Figure 1, and X-ray crystallographic
data have been placed in Table 1.
calculated density
l
1.615 Mg/m3
0.71073 Å
0.0434
0.1034
4
2
R1 (Fo )
wR2 (Fo )
2
Z
-
1
absorption coefficient
3.169 mm
Attempts to grow X-ray quality crystals of 3 and 4 to confirm
the structure of the two isomers have so far yielded only
powders. We attempted to apply 1-D and 2-D NMR techniques
using a 700 MHz instrument to determine the structures of 3
and 4, particularly to verify that they were indeed “mer” and
in the Supporting Information, Figures S2 and S3, respectively.
One key feature of all the H NMR spectra is the presence of
resonance assigned to the vinyl and allyl groups that are crucial
to the hydrosilation attachment reaction.
1
The suspected “mer” isomer 4 was investigated using a series
“
fac” isomers. The effective C3 symmetry of the fac isomer
1
13
of H and C NMR experiments. Each of the proton resonances
was assigned using a combination of 1-D and 2-D techniques.
1
should lead to a simpler H NMR spectrum, while the C1
symmetry of the mer isomer would yield a much more
complicated pattern. Unfortunately, the spectral overlap present
in the fac isomer precluded complete NMR analysis. The H
and 13C NMR spectra of 3 can be found in Figures 2 and S1,
1
The 1-D H NMR spectrum of the complex (Figure 3) confirmed
the correct number of protons (26) and displayed minimal
overlap among the peaks, which is essential to the unambiguous
assignment of the structure. The signals at 6.51, 5.53, and 5.07
ppm are representative of the vinyl protons PvA, PvC, and PvB,
respectively (see Chart 1). These peaks were easily assigned
due to their large coupling constants through the double bond
1
1
respectively. The H NMR spectra of 1 and 2 can also be found
(
11) Tamayo, A. B.; Alleyne, B. D.; Djurovich, P. I.; Lamansky, S.; Tsyba, I.;
Ho, N. N.; Bau, R.; Thompson, M. E. J. Am. Chem. Soc. 2003, 125, 7377-
3
3
7
387.
( Jtrans ) 17 Hz, and Jcis ) 10 Hz). The signal at 6.91 was
7622 J. AM. CHEM. SOC.
9
VOL. 126, NO. 24, 2004

Iridium Luminophore Complexes
A R T I C L E S
Figure 2. 1H NMR spectrum (700 MHz) of 3 in CD2Cl2. The resonances corresponding to the vinyl moiety are highlighted.
Figure 3. 1H NMR spectrum (700 MHz) of 4 in CD2Cl2. The resonances corresponding to the vinyl moiety are highlighted.
assigned to Pv6 as it is split solely by a meta proton with a 4J
coupling constant of ca. 1.5 Hz. The remaining protons were
assigned to their position in the bicyclic system via their splitting
patterns and coupling constants. The protons that are in the 4th
and 5th positions in a phenyl ring have a splitting pattern of
doublet of triplets (dt), or a doublet of doublet of doublets (ddd),
whereas those in the 3rd and 6th positions show a doublet of
doublet (dd) pattern. The protons at the 3rd and 6th positions
of the pyridine portion of the ring system were distinguished
related spectroscopy (COSY; Figure S4) and total correlated
spectroscopy (TOCSY; Figure S5).
The 13C NMR spectrum of 4 confirmed the presence of 23
unique carbons in the molecule (Figure S6). Through the use
of DEPT 135 (distortionless enhancement by polarization
transfer; Figure S7), each carbon resonance was identified as
either quaternary, CH, or CH . Only one CH carbon was found,
2
2
with a chemical shift of 113.37 ppm, assigned to the vinyl
carbon (PvBC). Heteronuclear multiple quantum coherence
(HMQC; Figure S8) was used to assign the carbon shifts to the
corresponding proton shift, while the assignment of the qua-
ternary carbons and the attachment of the rings in each bicyclic
3
using the difference in coupling constants ( J ) 5-6 Hz for
3
protons adjacent to the nitrogen, and J ) 7-8 Hz for the other
protons). The proton assignments were confirmed using cor-
J. AM. CHEM. SOC.
9
VOL. 126, NO. 24, 2004 7623

A R T I C L E S
DeRosa et al.
Chart 1. Diagram of mer-[Ir(ppy)2(vppy)], 4, Indicating the
interactions can only occur in the meridional structural isomer
shown in Figure 5 and its mirror image.
1
Numbering Scheme Used in Assigning the H NMR Spectrum (All
Resonances Are Assigned in Table 2)
Electrochemistry of 1-4. All complexes showed quasi-
reversible oxidations in acetonitrile or dichloromethane (see
Table 3) that ranged from 0.25 to 0.69 V vs the ferrocene/
ferrocenium redox couple, in agreement with literature data.9
Oxidation of Ir(III) cyclometalated compounds tends to be
reversible when iridium centered, while oxidation of HOMOs
with considerable σ-bond orbital contributions are irreversible;14
thus, these oxidations are assigned to the iridium(IV/III) couple.
The trend in the electrochemistry data corresponds well with
the emission data for the complexes with predominantly metal-
to-ligand charge-transfer (MLCT)-based emission (see section
on solution electronic spectroscopy).
d,11,13
mer-Ir(III) tris-cyclometalates have been shown to be easier
to oxidize than their facial analogues by 50-100 mV.11 The
electrochemistry of 3 and 4 (Table 3) concurs with these findings
with a 60 mV difference in Ir(IV/III) couples, which could be
rationalized by their difference in ligand field strength. In the
mer isomer, the two anionic phenyl ligands lie trans to one
another, which could lead to a lengthening of the Ir-C bonds
and a destabilization of the HOMO, allowing for more facile
oxidation of the metal center.
Photophysical Properties of 1-4. The photophysical prop-
erties of 1 are dominated by the C6 ligand (see Table 4 and
Figure 6). The C6 molecule is a fluorescent laser dye that is
emissive at room temperature but shows no noticeable phos-
phorescence. By cyclometalating C6 with Ir to produce complex
Table 2. 1H and 13C Chemical Shifts for 4 and Assignments
1H chemical
13C chemical
shift (ppm)
assignment
N6
shift (ppm)
assignment
Pv1
8.14
7.98
7.96
7.87
7.77
7.75
7.71
7.68
7.65
7.61
7.57
7.12
7.01
6.96
6.94
6.93
6.91
6.86
6.81
6.80
6.61
6.51
6.45
5.52
5.06
177.76
175.18
170.60
168.10
167.98
159.71
153.59
151.61
148.26
146.02
145.26
142.73
138.34
138.22
137.12
136.35
136.20
134.78
132.96
130.80
130.23
129.92
124.84
124.59
124.44
Nv3
Nv6
N3 and N3′
Pv3
P3
P1
N2
Nv2
N2′
P1′
N6
Nv6
N6′
Pv2
P2
P2′
PvA
Pv5
Nv4
Pv6
N4
N4′
P6
P6′
P5
P5′
Pv3
P3
P3′
N5′ or Nv5
N5
N5′ or Nv5
P4
Nv3
Pv4
P3′
Nv4
N6′
N4
N4′
Pv4
P4
P5
Nv5
P4′
Pv6
P5′
N5′
N5
P6
PvA
P6′
1
, the emission energy shifts from 500 nm for the free dye to
568 nm. Intersystem crossing into the triplet levels of the ligand,
assisted by the presence of the heavy iridium center, leads to
ligand-based phosphorescence and is responsible for the dra-
matic energy red-shift seen here and in other C6 complexes.9d
The electronic spectrum of 1 is characterized by two intense
ligand-based absorbances in the blue region.
PvC
PvB
The absorption spectra of 2-4 (see Figure 6) were assigned
9,13,15
by analogy to similar phenylpyridine-based complexes
and
122.83
122.69
121.91
121.35
119.70
119.51
119.29
119.18
118.93
113.37
show intense spin-allowed phenyl- and pyridyl-based π-π*
bands from 260 to 290 nm with metal-to-ligand (MLCT)
transitions from 380 to 450 nm. The MLCT transitions consist
1
of the spin-allowed MLCT at higher energies and the formally
3
P4′
spin-forbidden MLCT at lower energies. The extinction coef-
N3 or N3′
N3 or N3′
PvBC
ficients for the two are comparable in all cases, because the
3
1
MLCT can “steal” intensity from the MLCT through spin-
orbit coupling induced by the heavy iridium center. Comparison
of the absorption spectra of the facial and meridional isomers
3 and 4 reveals several differences. The π-π* absorbance in 3
is less intense than in 4 and shows a more pronounced shoulder
at lower energy, while the MLCT band envelope of 3 is more
sharply defined. These differences mirror those seen in the
system were determined by heteronuclear multiple bond coher-
1
13
ence (HMBC; Figure S9). See Table 2 for a list of H and
C
chemical shifts and their assignments.
Once all resonances were assigned, it was then possible to
use ROESY experiments (rotating frame Overhauser spectros-
copy; see Figure 4) to determine through-space interring
interactions and, in turn, the configuration of the ligands about
the iridium center. Figure 5 shows the key inter-ring correlations
used to assign the final structure. For a correlation to exist, the
1
1
literature for Ir(III) fac and mer isomers.
The trend in emission energy for complexes 2-4 resembles
the trend in their Ir(IV/III) redox couples: the more positive
the redox potential, the higher the emission energy. This suggests
1
2
two interacting protons must be within 5 Å of one another.
(
13) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Kwong, R.;
Using this technique, the following interactions could be
established: N6 with P6′ and Pv6, P6 with N6′ and Nv6. These
Tsyba, I.; Bortz, M.; Mui, B.; Bau, R.; Thompson, M. E. Inorg. Chem.
2001, 40, 1704-1711.
(14) Neve, F.; Crispini, A.; Campagna, S.; Serroni, S. Inorg. Chem. 1999, 38,
2250-2258.
(
12) Frienkiel, T. A. In NMR of Macromolecules: A Practical Approach;
(15) Colombo, M. G.; Brunold, T. C.; Riedener, T.; G u¨ del, H. U.; F o¨ rtsch, M.;
Roberts, G. C. K., Ed.; Oxford University Press: Oxford, 1993; p 35-70.
B u¨ rgi, H.-B. Inorg. Chem. 1994, 33, 545-550.
7624 J. AM. CHEM. SOC.
9
VOL. 126, NO. 24, 2004

Iridium Luminophore Complexes
A R T I C L E S
Figure 4. ROESY spectrum (700 MHz) of 4 in CD2Cl2 in the region of 6.5-8.2 ppm. The full ROESY spectrum can be found in the Supporting Information
Figure S10).
(
Table 3. CV Data for Complexes 1-4
complex
E
1/2 (V vs Fc/Fc
+
)
p
∆E (mV)
Ir(C6)2(vacac), 1a
Ir(ppy)2(vacac), 2a
fac-Ir(ppy)2(vppy), 3
0.69
0.47
0.31
0.25
150
60
75
b
mer-Ir(ppy)2(vppy), 4b
75
a
In acetonitrile (0.1 M TBAH). b In CH2Cl2 (0.1 M TBAH).
Table 4. Electronic Spectroscopy Data for Complexes 1-4
λ
max
λ
max
λ
max
τ (µs)
298 Ke
a
b
φe
π−π* (ꢀ)
MLCT (ꢀ)
emission
d
4
e
c,e
1
2
3
4
445 (7.79 × 10 )
568, 613
6.0 0.22
0.1 0.02
0.4 0.2
0.2 0.03
Figure 5. Proposed structure of 4 based on 2-D NMR analysis. Only
hydrogens at the 6 positions are shown. Dashed green and red lines indicate
key interring correlations determined by ROESY.
d
4
4
74 (8.69 × 10 )
257 (4.32 × 10 ) 400 (3.92 × 10 ) 520f
d 4
d
3
d
3
4
48 (2.76 × 10 )
f
4
f
4
e
e
c,e
287 (4.24 × 10 ) 384 (1.13 × 10 ) 514, 542, 580
40 (3.90 × 10 )
the emissive state in these complexes has a large contribution
of MLCT character, a reasonable assumption because the
emissive states of similar Ir(III) complexes tend to be chiefly
MLCT based.15,16 Complexes 3 and 4 show more structured
emission and thus may have some ligand contribution to the
emissive state. This is especially seen in the case of 4, whose
f
3
4
d
4
d
3
d
c,d
274 (4.86 × 10 ) 390 (7.99 × 10 ) 535, 572
45 (3.86 × 10 )
d
3
4
a
Wavelengths in nm. b ꢀ has units of L mol cm-1. c Low-energy
-1
shoulder. d In dichloromethane. e In toluene. In acetonitrile.
f
1
7
emission profile is markedly different from that of Ir(ppy)3.
The vinyl group in vinylphenylpyridine leads to greater con-
3
jugation in this ligand; thus, its (π-π*) excited state should
be at slightly lower energy than in the phenylpyridine system
(
16) Colombo, M. G.; Hauser, A.; G u¨ del, H. U. Inorg. Chem. 1993, 32, 3088-
092.
17) King, K. A.; Spellane, P. J.; Watts, R. J. J. Am. Chem. Soc. 1985, 107,
431-1432.
and may contribute to the emissive state.
Table 4 also lists luminescence lifetimes and quantum
efficiencies for complexes 1-4. Compound 1 has not only the
3
(
1
J. AM. CHEM. SOC.
9
VOL. 126, NO. 24, 2004 7625

A R T I C L E S
DeRosa et al.
Figure 6. Solution absorption (1, 2, 4-CH2Cl2; 3-acetonitrile) and emission (1, 3-toluene; 2-acetonitrile; 4-CH2Cl2) profiles of 1-4 (1-black, 2-green,
-blue, 4-red).
3
longest lifetime and highest quantum efficiency of all complexes,
it also enjoys the added advantages of a sizable Stokes shift
try), and spectroscopically (absorption and emission). On the
basis of the photophysical properties of the luminophores in
solution, sensors based on complexes 1 and 3 are the most
promising candidates for PSP studies. Future studies will
describe the covalent attachment of these luminophores to
hydride-containing silicones and illustrate the advantages of
these unimolecular systems over analogous dispersed systems
for use in pressure-sensitive paints.
-1
(3500 cm ) and intense absorption in the visible which should
allow for efficient excitation at longer wavelengths, making it
a very promising candidate for future PSP studies.
As expected, the meridional isomer 4 has a shorter lumines-
cence lifetime and a lower quantum yield as compared to its
facial analogue 3. The poorer photophysical properties of 4 could
be partially attributed to higher nonradiative rate constants
1
1
caused by dissociation of the Ir-C bond in the excited state.
Acknowledgment. We thank Dr. Youssef M e´ barki for his
assistance with the oxygen sensitivity experiments and Prof. J.
C. Scaiano for the use of his equipment for the luminescence
lifetime measurements. Financial support by the Natural Science
and Engineering Research Council of Canada (NSERC) in the
form of a Discovery Grant (R.J.C.) and a postgraduate scholar-
ship (MCD) is gratefully acknowledged. C.E.B.E. thanks the
NRC for supporting his research through the Research Associate
Program.
While 3 possesses a high quantum efficiency and long lifetime
as compared to the other phenylpyridine-based complexes in
this study, its photophysical properties are less ideal as compared
to those of Ir(ppy)3 (τ ) 2 µs, φ ) 0.4),17 which has recently
been investigated as a luminescent oxygen sensor.3 Excited-
state reactions of the vinyl group could be responsible for an
increase in nonradiative decay. The covalent attachment of this
luminophore to a hydride-containing silicone polymer via the
hydrosilation reaction will result in the saturation of this vinyl
group and may lead to improved photophysical properties.
a,b
Supporting Information Available: 1-D and 2-D NMR
spectra of complexes 1-4. Additional figures and X-ray
crystallographic files in CIF format for compound 1. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Conclusions
A series of luminescent cyclometalated Ir(III) complexes with
suitable pendent ligands for polymer attachment has been
synthesized and characterized structurally (X-ray crystallography
and NMR spectroscopy), electrochemically (cyclic voltamme-
JA049872H
7626 J. AM. CHEM. SOC.
9
VOL. 126, NO. 24, 2004