Blue phosphorescence of trifluoromethyl- and trifluoromethoxy-substituted cationic iridium(III) isocyanide complexes

Article abstract of DOI:10.1021/om300557d

We report the first comprehensive comparative synthetic, structural, electrochemical, and spectroscopic study of an extended series of fluorocarbon-modified iridium(III) complexes. We prepared seven new cationic Ir(III) complexes with tert-butyl isocyanid

Full text of DOI:10.1021/om300557d

Article
pubs.acs.org/Organometallics
Blue Phosphorescence of Trifluoromethyl- and Trifluoromethoxy-
Substituted Cationic Iridium(III) Isocyanide Complexes
Nail M. Shavaleev,*,† Filippo Monti,‡ Rosario Scopelliti,† Nicola Armaroli,*,‡ Michael Gratzel,†
̈
and Mohammad K. Nazeeruddin*,†
†
́
Laboratory of Photonics and Interfaces, Ecole Polytechnique Fed
́
er
́
ale de Lausanne, CH-1015 Lausanne, Switzerland
Consiglio Nazionale delle Ricerche, Via P. Gobetti,
‡Molecular Photoscience Group, Istituto per la Sintesi Organica e la Fotoreattivita,
101, 40129, Bologna, Italy
́
S
* Supporting Information
ABSTRACT: We report the first comprehensive comparative synthetic,
structural, electrochemical, and spectroscopic study of an extended series
of fluorocarbon-modified iridium(III) complexes. We prepared seven new
cationic Ir(III) complexes with tert-butyl isocyanide and trifluoromethyl-
or trifluoromethoxy-substituted cyclometalating 2-phenylpyridines,
[(C∧N)2Ir(CNtBu)2](CF3SO3), and characterized five of them by crystal
structure analysis. The redox potentials and photophysical properties of
Ir(III) complexes are determined by the type, position, and number of
fluorocarbon groups in the cyclometalating ligand. The complexes exhibit pale blue to yellow-green phosphorescence at room
temperature with quantum yields and excited-state lifetimes up to 73% and 84 μs in solution (under argon) and 7.5% and 4.3 μs
in neat solid (under air). The structured and solvent-independent phosphorescence spectra, with 0−0 emission transition at
445−467 nm, and the long calculated radiative lifetimes, 43−160 μs, indicate that the complexes emit from a cyclometalating-
ligand-centered triplet excited state. Bulky fluorocarbon groups prevent intermolecular interaction (aggregation) of the
complexes, thereby minimizing red-shift of phosphorescence color in going from solution to neat solid.
exhibit green-blue/pale blue phosphorescence in solution.13 In
INTRODUCTION
■
neat solid, however, the phosphorescence of 9 was quenched
and its color was red-shifted, because H/F substituents in 9 did
not provide sufficient steric bulk to prevent aggregation.13,15
Bulky and electron-withdrawing fluorocarbon groups with
inert C(sp3)−F bonds tune electronic properties, improve
solubility, and reduce intermolecular interaction of metal
complexes;10,16,17 however, fluorocarbons were rarely used in
organometallic Ir(III) complexes.5−8,10,11,17 Here, we report a
comparative synthetic, structural, electrochemical, and spectro-
scopic study of phosphorescent Ir(III) isocyanide complexes
with trifluoromethyl- or trifluoromethoxy-substituted cyclo-
metalating 2-phenylpyridines (Schemes 1 and 2). To our
knowledge, this is the first comprehensive study of an extended
series of fluorocarbon-modified organometallic complexes in
general10,16 and Ir(III) complexes in particular.5−8,10,11,17 We
demonstrate that the fluorocarbons change electrochemical and
photophysical properties of organometallic Ir(III) complexes
and that the fluorocarbon-modified Ir(III) complexes can
exhibit blue phosphorescence in solution/neat solid at ambient
conditions.
High-energy emitters,1−3 in particular phosphorescent iridium-
(III) complexes,4−8 are required for generation of blue and
white light in electroluminescent devices.9 One of the ways to
blue-shift the phosphorescence color of a cyclometalated Ir(III)
complex is to modify the electron-rich part of the ligand with an
electron-withdrawing fluoro4−7,10−13 or trifluoromethyl5−8,10
group to stabilize the HOMO and to increase the HOMO−
LUMO gap.14
An Ir(III) complex must exhibit blue phosphorescence in
neat solid or in a solid matrix in order to be of use in blue-
electroluminescent devices.9 Intermolecular interaction (aggre-
gation) between Ir(III) complexes often causes the broadening
and red-shift of the phosphorescence spectrum in going from
solution to neat solid.13,15 For example, we recently reported
that cationic bis-cyclometalated Ir(III) complexes 9 with
strong-field electron-withdrawing isocyanide ligands (Chart 1)
Chart 1. Reference Ir(III) Complexes13
RESULTS AND DISCUSSION
Synthesis. 2-Phenylpyridines L1−L8 were prepared by
Suzuki−Miyaura coupling of arylboronic acids with 2-
■
Received: June 19, 2012
© XXXX American Chemical Society
A
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cyclometalation of L4 occurred only at C6′.19 In contrast,
cyclometalation of L8 occurred at C2′ and C6′ to give a
mixture of [(C∧N)2Ir(μ-Cl)]2 complexes (the same outcome
was reported for 3-methoxyphenyl-substituted C∧N ligands19);
therefore, further experiments with L8 were not performed.
Seven new iridium(III) complexes [(C∧N)2Ir(CNtBu)2]-
(CF3SO3), 1−7, were prepared by reaction of [(C∧N)2Ir(μ-
Cl)]2 (C∧N = L1−L7) with silver triflate (to remove the
chloride anion) and with tert-butyl isocyanide (Scheme
2).13,20,21 Purification by column chromatography on silica
gave 1−7 as air- and moisture-stable yellow or pale yellow
solids that are soluble in polar organic solvents.
a
Scheme 1. Synthesis of 2-Phenylpyridines
1H and 19F NMR spectra of 1−7 exhibit a single set of signals
for the C∧N and CNtBu ligands and indicate that 1−7 have a
1
C2-symmetry in solution. Integration of H peaks confirms the
1:1 ratio of C∧N to CNtBu. 19F NMR confirms the presence of
the CF3/OCF3 groups and of the CF3SO3 anion. ESI+ TOF
−
mass spectra contain a peak of the [(C∧N)2Ir(CNtBu)2]+
cation.
a
Reaction conditions: (a) K2CO3, Pd(PPh3)4, THF/water (3:1),
Review of non-patent literature reveals that until now Ir(III)
complexes with L2 and L6−L8 or a combination of L1−L8 and
an isocyanide were not known, that charged Ir(III) complexes
were described only for L1 (with neutral N∧N ligands),11 and
that neutral Ir(III) complexes were reported only for L122 and
L3−L5.5,6 Moreover, there was only one example of the use of
a trifluoromethoxy/perfluoroalkoxy-modified cyclometalating
ligand for Ir(III),5 while no such examples are known for
precious metals Ru, Os, Rh, Pd, Pt, and Au.
under Ar, 85 °C.
a
Scheme 2. Synthesis of New Ir(III) Complexes
Structural Characterization. The following features are
observed in the X-ray structures of 1 and 4−7 (Figures 1−3
Figure 1. Structure of 1 (50% probability ellipsoids; co-crystallized
molecule of dichloromethane, H atoms, triflate anion, and the disorder
of the tert-butyl group omitted; ORTEP). Heteroatom color codes: N,
blue; F, green; Ir, black.
a
Reaction conditions: (a) cyclometalating ligand, 2-ethoxyethanol/
water (3:1), under Ar, 120 °C; (b) under Ar, RT (i) AgCF3SO3,
CH3OH/CH2Cl2; (ii) tert-butyl isocyanide, CH2Cl2. The numbering
of the phenyl ring is indicated in the structures of 1 and 6.
and Table 1): (i) The Ir(III) ion is in a distorted octahedral
[(C∧N)2Ir(C)2]+ coordination environment, and the two
nitrogen atoms of the C∧N ligands are in trans-position to
each other. (ii) The Ir−C bonds with the isocyanides are
shorter than are those with the C∧N ligands. (iii) The Ir−
(C∧N) bond lengths in 1, 4, 6, and 7 are 2.042(6)−2.078(14)
Å for Ir−C and 2.048(12)−2.076(5) Å for Ir−N. Steric clash
between the 5′-CF3 group and Ir in complex 5 causes
elongation of the Ir−(C∧N) bonds to 2.12 Å for Ir−C and
2.069(3)−2.079(4) Å for Ir−N. (iv) The Ir−C (C∧N) bonds in
1, 4−7, and their analogues13,20,21 are longer than are those in
bromopyridine (Scheme 1). Reaction of L1−L8 with
IrCl3·3H2O gave the cyclometalated complexes [(C∧N)2Ir(μ-
Cl)]2 (Scheme 2).18 The complexes with 2′-substituted ligands
L2 and L7 are insoluble in noncoordinating solvents; the rest of
the complexes are soluble in dichloromethane.
The Ir−C bond with the 3′-substituted ligands L4 and L8
could form either at the 2′ or 6′ phenyl carbon; however,
B
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Figure 3. Structures of 6 (top) and 7 (bottom) (50% probability
ellipsoids; H atoms and triflate anion omitted; the disorder of the
trifluoromethyl groups in 6 omitted; only one of the two independent
molecules shown for 6 [Ir(1)]; ORTEP). Heteroatom color codes: O,
red; N, blue; F, green; Ir, black.
Figure 2. Structures of 4 (top) and 5 (bottom) (50% probability
ellipsoids; H atoms and triflate anion omitted; the disorder of the
trifluoromethyl groups in 5 omitted; only one of the two independent
molecules shown for 5 [Ir(2)]; ORTEP). Heteroatom color codes: N,
blue; F, green; Ir, black.
a
Table 1. Structural Parameters of Ir(III) Complexes
bond lengths (Å)
Ir(III) complexes with weak-field N/O-ligand(s) [(C∧N)2Ir-
20
(N/O)n]0/+
.
We consider the elongation of Ir−C (C∧N)
isocyanide
C∧N
angles (deg)
bonds in [(C∧N)2Ir(CNtBu)2]+ to be caused by the trans-
influence of strong-field isocyanide ligands. (v) The Ir−
isocyanide fragments are not linear, and the angles are
165.5(5)−178.4(2)° for Ir−CN or 158.9(9)−176.4(5)° for
CN−C. (vi) The C∧N ligands are nearly planar, and the
dihedral angles between the phenyl and pyridyl are 2.4−14.4°.
The largest deviation from planarity is observed when a
fluorocarbon is placed at the position 2′ (7) or 5′ (5), where it
clashes with the 3-H (pyridyl) or Ir. (vii) Replacing a 4′-CF3
group (1) by a 4′-OCF3 one (6) does not alter the structure of
the complex. (viii) Bulky CF3, OCF3, and tBu groups prevent
face-to-face π−π stacking of the complexes. The shortest Ir···Ir
distances are 8.8−9.5 Å. Structural parameters of 1 and 4−7 are
similar to those of their analogues.13,20,21
complex
Ir−C
Ir−C
Ir−N
Ph−Py
1
2.022(14)
2.031(15)
2.025(2)
2.020(2)
2.012(4)
2.015(4)
2.015(5)
2.021(4)
2.018(7)
2.028(7)
2.034(6)
2.023(6)
2.065(13)
2.078(14)
2.045(2)
2.050(2)
2.120(4)
2.124(4)
2.121(4)
2.122(5)
2.057(6)
2.066(6)
2.042(6)
2.049(6)
2.048(12)
2.070(12)
2.0604(18)
2.0678(19)
2.072(3)
2.069(3)
2.079(4)
2.076(4)
2.076(5)
2.068(5)
2.061(5)
2.060(4)
6.01
8.28
4
2.39
5.72
b
5 (Ir1)
10.67
6.07
b
5 (Ir2)
12.12
14.05
9.64
b
6 (Ir1)
9.01
7
14.38
8.51
a
Each row corresponds to one ligand. tert-Butyl isocyanide in trans-
b
position to the carbon atom of the C∧N ligand in the same row. Two
independent molecules, Ir(1) and Ir(2), are present in the unit cell of
5 and 6. The data for the disordered Ir(2) molecule of 6 are not
shown.
Electrochemistry. Redox potentials of 1−7 were measured
with cyclic voltammetry relative to Fc+/Fc23 in acetonitrile and
DMF (Table 2 and Figure 4; Table S2 and Figures S1 and S2,
Supporting Information).
Trifluoromethyl-substituted complexes 1−5 undergo a
reduction at −1.74 to −2.23 V, which is irreversible for 4
and 5 or quasi-reversible for 1 and 2. In contrast, 3 is the first
Ir(III) isocyanide complex to exhibit a reversible reduc-
tion.13,20,21 The 2′,4′-substituted complexes 1−3 have less
negative reduction potentials than do the 3′,5′-analogues 4 and
5 (Table 2). Addition of a second CF3 group shifts the
C
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a
Table 2. Redox Properties
c
cd
,
Eox, V
e
Ered, V
ΔE, V
b
f
f
complex
R′
DMF
ACN
ACN
ACN
g
1
4′-CF3
2′-CF3
−2.10 (83)
−2.05 (117)
−1.74 (78)
−2.22
−2.10
−2.25
−2.21
−2.38
−2.34
g
2
g
g
3
2′,4′-(CF3)2
3′-CF3
3′,5′-(CF3)2
4′-OCF3
2′-OCF3
H
−1.79 (83)
−2.23
4
5
−2.12
−2.28
−2.23
−2.38
6
1.50
1.50
1.23
1.42
3.78
3.73
3.61
3.76
7
h
9H
h
9F
4′-F
−2.34
a
Relative to Fc+/Fc. On glassy carbon working electrode, in the presence of 0.1 M (NBu4)PF6, at scan rate 100 mV/s. Estimated error: 50 mV. The
b
anodic/cathodic peak separation for the standard, Fc+/Fc couple was 73−93 mV. Substituents on the phenyl ring of the cyclometalating ligand.
c
d
Irreversible process (unless stated otherwise); the oxidation or reduction peak potentials are reported. Oxidation of the complexes was outside of
the electrochemical window of the solvent for 1−7 in DMF (>1.0 V relative to Fc+/Fc) and for 1−5 in acetonitrile (ACN) (>1.5 V relative to Fc+/
e
f
g
Fc). Redox gap: ΔE = Eox − Ered. Cyclic voltammograms of 1 and 2 in ACN at 100 mV/s were not informative. Reversible (3) or quasi-reversible
(1 and 2) process; E1/2 is reported; the anodic/cathodic peak separation is given in parentheses. Data from the literature.13
h
red
results suggest that the irreversibility of electrochemical
processes in 1−7 arises from a chemical reaction that follows
the electron transfer.24
The irreversible character of most of the observed electro-
chemical processes prevented us from determining the formal
redox potentials of 1−7; nevertheless, we consider that the
peak potentials and the redox gap correctly reproduce the
qualitative trends in the energy of the HOMO, LUMO, and
HOMO−LUMO gap of 1−7.13,25
The reduction and oxidation of 1−7 take place on the pyridyl
and on the Ir−aryl fragment, respectively.13 We explain the
highly positive oxidation potentials of 1−7 by the cationic
charge of the complexes and by the presence of the electron-
withdrawing fluorocarbons5−8 and the strong-field electron-
withdrawing isocyanides.13,20,21,26,27 1−7 have less negative
redox potentials than do the non-substituted/mono-fluorinated
analogues 913 (Chart 1 and Table 2); therefore, fluorocarbons
in 1−7 stabilize the HOMO and the LUMO of the complexes
to a greater extent than do the H/F groups in 9. The redox gap
in 6 and 7 is larger than that in 9H, and it is similar to that in
9F (Table 2).
Absorption Spectroscopy. The infrared absorption
spectra of 1−7 in neat films feature two peaks at 2217−2175
cm−1 separated by 20 cm−1 that are characteristic of stretching
vibrations of the tert-butyl isocyanide CN bond (Table 3 and
Figure S3 in the Supporting Information).13 The presence of
two intense IR peaks confirms the cis-geometry of the
Figure 4. Cyclic voltammograms of 1−7 in DMF (glassy carbon
working electrode, 0.1 M NBu4PF6, 100 mV/s). The unit on the
vertical axis is 10 μA. CVs in acetonitrile are shown in the Supporting
Information.
reduction potential to the less negative values: this shift is larger
for the 2′,4′-bis-substitution (0.31−0.36 V from 1 or 2 to 3)
than it is for the 3′,5′-bis-substitution (0.12 V from 4 to 5)
(Table 2). The oxidation of 1−5 is outside of the electro-
chemical window of DMF and acetonitrile.
Table 3. UV−Vis and IR Absorption Maxima
Trifluoromethoxy-substituted complexes 6 and 7 undergo an
irreversible reduction at −2.21 to −2.28 V and an irreversible
oxidation at 1.50 V (Table 2). Complexes 6 and 7 exhibit more
negative redox potentials than do the CF3 analogues 1 and 2
(Table 2); therefore, we conclude that the OCF3 group is a
weaker electron-withdrawing substituent than is the CF3 group.
We note that (i) the reduction potentials of 3−7 are solvent-
independent at a cyclic voltammetry scan rate of 100 mV/s in
DMF and acetonitrile (Table 2), (ii) the reduction of 4, 6, and
7, which is irreversible at 100 mV/s, becomes quasi-reversible at
scan rate 1 V/s in acetonitrile (Figure S2 and Table S2,
Supporting Information), and (iii) the trends in redox
potentials and redox gaps (ΔE = Eox − Ered) of 1−7 do not
change when the scan rate is increased from 100 mV/s to 1 V/s
(Table 2 and Table S2 in the Supporting Information). These
a
bc
,
complex
IR, cm−1
λabs, nm (ε, 103 M−1 cm−1
)
1
2
3
4
5
6
7
2195, 2175
2201, 2181
2209, 2190
2201, 2180
2217, 2198
2195, 2175
2202, 2181
252 (33), 298 (16), 309 (15), 346 (7.6)
348 (8.8)
290 (16), 339 (8.4)
297 (13), 307 (13), 330 (8.2)
304 (13), 312 (12, sh)
253 (34), 297 (14), 308 (13, sh), 332 (11)
253 (33), 300 (16), 309 (17), 335 (7.8)
a
Infrared absorption bands of solid films of the neat complex in the
b
region of the CN stretching vibrations. In dichloromethane, at
room temperature, at 250−600 nm. Errors: 2 nm for λabs
;
5% for ε.
c
Lowest energy transition in 1−7 is a composite band with a broad
main maximum and lower energy shoulder(s) (Figure 5).
D
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isocyanide ligands in 1−7.28 The frequency (wavenumber) of
the CN peaks in isocyanide complexes reflects the strength
of both the σ bonding and the π back-bonding between the
isocyanide ligand and the metal;29 therefore, variation of this
frequency cannot be correlated to the change of only one of
these two bonding interactions.29
Electronic spectra of 1−7 in dichloromethane exhibit the
lowest energy band, which we assign to an (Ir-aryl)-to-pyridyl
charge transfer (CT) transition,13 at 320−400 nm with molar
absorption coefficients (ε) of about 10 × 103 M−1 cm−1 (Table
3 and Figure 5). The 4′-substituted complexes 1 and 6 have CT
Figure 6. Corrected and normalized luminescence spectra of 1−7 at
room temperature in dichloromethane solution (DCM, blue trace)
and in neat solid film (red trace).
Figure 5. Absorption spectra of 1−7 in dichloromethane solution. The
unit on the vertical axis is 5 × 103 M−1 cm−1. The spectra (1−3; 4 and
5; 6 and 7) are shifted with respect to one another along the vertical
axis by 10 × 103 M−1 cm−1. Additional absorption spectra are shown in
the Supporting Information.
transition at higher energy than do the 2′-substituted analogues
2 and 7, respectively (Figure 5). Addition of a second CF3
group blue-shifts the CT transition from 4 (3′) to 5 (3′,5′); in
contrast, a red-shift is observed from 1 (4′) to 3 (2′,4′), and no
shift from 2 (2′) to 3 (2′,4′) (Figure 5). We expect the energy
of the CT transition to exhibit direct correlation with the
redox/HOMO−LUMO gap (ΔE, Table 2),13 and, indeed, this
is the case for 6 and 7 (ΔE could be measured only for these
two complexes).
At higher energies, π−π* electronic transitions of 2-
phenylpyridines dominate the spectrum with ε = (13−34) ×
103 M−1 cm−1 (Figure 5 and Table 3; Figures S4−S6 in the
Supporting Information).
Figure 7. Corrected and normalized luminescence spectra of 1−7 at
room temperature in acetonitrile solution (ACN, blue trace) and in
PMMA film (1 wt % of the complex, red trace).
one emissive center; (iv) the emission quantum yields (Φ) and
the observed excited-state lifetimes (τ) are 27−73% and 24−84
μs (Table 4); (v) the calculated radiative lifetimes, τrad = τ/Φ,
are 43−160 μs (Table 4).
Luminescence Spectroscopy. Complexes 1−7 exhibit
pale blue to yellow-green phosphorescence at room temper-
ature in solution and in neat solid (Figures 6 and 7, Table 4).
The phosphorescence of 1−7 is quenched by air/oxygen,
especially in liquid solutions.
Complexes 1−7 are brightly emissive in solution and exhibit
a narrow variation of quantum yields in a given solvent: 27−
47% in dichloromethane or 45−73% in acetonitrile under argon
or 46−58% in PMMA under air (Table 4). The quantum yields
and excited-state lifetimes of 1−7 do not show extreme
dependence on the type or number of fluorocarbon(s);
moreover, Φ and τ of 1−7 are better than or similar to those
of the reported analogues;13,20,21 therefore, we conclude that
modification with fluorocarbon(s) does not facilitate non-
radiative processes in Ir(III) complexes. The photophysical
properties of 1−7 in 1 wt % PMMA under air are similar to
those in 10−5 M liquid solutions under argon; therefore, we
consider that 1−7 in solid PMMA matrix do not form
aggregates and are not quenched by oxygen.
In solution, in 10−5 M dichloromethane and acetonitrile
(under argon) and in 1 wt % poly(methyl methacrylate)
(PMMA, drop-cast film, under air), (i) the emission spectra of
1−7 are solvent-independent and exhibit a vibronic structure
that becomes better resolved at 77 K (Figures 6−8); (ii) the
vibronic peaks are less resolved (even at 77 K) for complexes 2,
3, and 5, which have a CF3 group in the hindered 2′ or 5′
position (Figures 6−8); (iii) the luminescence decays are
single-exponential functions suggesting the presence of only
E
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Table 4. Photophysical Properties
a
b
c
d
e
f
complex
medium
λ0−0, nm
λmax, nm
Φ, % τ, μs τrad, μs
1
DCM
ACN
455
455
455
459
454
489
488
488
491
454
499
497
496
504
495
503
504
503
503
500
479
478
477
479
445
482
482
479
483
481
482
480
481
479
447
481
479
479
485
446
516
452
484, 509
447
44
67
46
24
41
25
55
61
54
PMMA
solid
5.1
DCM, 77 K
DCM
33
26
41
27
2
3
4
5
6
7
42
57
49
62
72
55
ACN
PMMA
solid
5.8
DCM, 77 K
DCM
464
38
25
33
24
37
45
49
68
73
49
ACN
PMMA
solid
7.5
DCM, 77 K
DCM
467
448
446
447
450
445
455
454
449
32
27
49
32
45
70
55
60
70
58
Figure 8. Corrected and normalized luminescence spectra of 1−7 in
dichloromethane solution at 77 K.
ACN
PMMA
solid
3.8
DCM, 77 K
DCM
48
42
84
45
OCF3 (7/6) group in 2-phenylpyridine. This blue-shift must
arise from the stabilization of the HOMO by the fluorocarbon,
because Eox (4, 6, 7) ≫ Eox (9H). Addition of a second CF3
group strongly stabilizes the LUMO (Ered becomes less
negative), thereby red-shifting the phosphorescence color
from 1 or 2 to 3 and from 4 to 5 (the ground-state absorption
spectrum, however, is blue-shifted from 4 to 5). The shorter
wavelength of the 0−0 transition at 77 K (Table 4)
corresponds to the more negative reduction potential (higher
LUMO energy) in 1−7 and to the larger redox/HOMO−
LUMO gap in 6, 7, and 9 (Table 2, Figures S7 and S8,
Supporting Information).
27
53
47
160
160
96
ACN
PMMA
solid
5.0
DCM, 77 K
DCM
451
452
449
450
448
447
449
449
450
457
446
456
452
456
447
84
30
58
34
40
68
55
75
85
62
ACN
PMMA
solid
6.3
DCM, 77 K
DCM
53
24
42
25
47
73
58
51
58
43
ACN
The structured and solvent-independent phosphorescence
spectra and the long radiative lifetimes indicate that 1−7 emit
from a cyclometalating-ligand-centered (LC) excited
state.13,14,30,31 The radiative lifetime of 1−7 is solvent-sensitive
and varies, but by no more than a factor of 1.7, in the order
acetonitrile ≥ dichloromethane ≥ PMMA (Table 4). This
solvent dependence of τrad can arise from the change in the
degree of mixing between the (solvatochromic) charge-transfer
and the (non-solvatochromic) cyclometalating-ligand-centered
excited states in 1−7 (the greater contribution of the CT
excited state to the LC one is expected to shorten the radiative
lifetime of the complex).30,31 We suggest that the elongation of
Ir−(C∧N) bonds in complex 5 caused by the 5′-CF3 group
(Table 1) decouples the Ir-to-ligand-charge-transfer excited
state from the cyclometalating-ligand-centered one. We
consider that this decoupling is reflected in the longer radiative
lifetime of 5 (96−160 μs) when compared with the other
complexes (43−85 μs) (Table 4). Long radiative lifetimes cause
high sensitivity to the triplet−triplet interaction/oxygen
quenching that can limit the use of 1−7 in electroluminescent
devices, but can make 1−7 excellent oxygen sensors.21
PMMA
solid
5.3
DCM, 77 K
solid
37
g
9H
4.4
2.6
DCM, 77 K
solid
g
9F
DCM, 77 K
a
Dichloromethane (DCM) or acetonitrile (ACN) solution at room
temperature under argon (10−5 M). PMMA solution (1 wt % of the
complex, drop-cast film) or neat solid complex (spin-coated film) at
room temperature under air. Frozen dichloromethane solution at 77 K.
b
Highest energy vibronic luminescence peak (0−0 transition).
c
d
e
Maximum of the luminescence spectrum. λexc = 320 nm. The
luminescence decay is a biexponential function in neat complex: the
f
two components are 0.8−1.9 and 2.8−4.3 μs. Calculated radiative
lifetime: τrad = τ/Φ. Data from the literature.13
g
The phosphorescence color of 1−7 is determined by the
type, position, and number of fluorocarbon groups in the 2-
phenylpyridine ligand. The wavelength of the 0−0 transition
(λ0−0) at 77 K correctly characterizes the variation of
phosphorescence color of 1−7 at room temperature (Table
4; λ0−0 peaks at room temperature are often not resolved). λ0−0
at 77 K is observed at 445−467 nm, and it increases in the
order 3′-CF3 (4) ≤ 2′-OCF3 (7) ≤ 4′-OCF3 (6) = 4′-F (9F) <
3′,5′-(CF3)2 (5) ≤ H (9H) < 4′-CF3 (1) < 2′-CF3 (2) < 2′,4′-
(CF3)2 (3) (Table 4 and Figure 8). The strongest blue-shift of
phosphorescence color in 1−7 (against a reference 9H13) is
achieved by a single substitution with a 3′-CF3 (4) or 2′-/4′-
In going from solution to neat solid (spin-coated film, under
air) the quenching by oxygen and the aggregation/self-
quenching13,15 of 1−7 cause the following changes: (i) the
emission spectrum broadens (Figure 6); (ii) the 0−0 transition
loses intensity and the long-wavelength transitions gain
intensity (Figure 6); (iii) the luminescence decay becomes
biexponential; (iv) the quantum yield and excited-state lifetime
decrease to 3.8−7.5% and 0.8−4.3 μs (Table 4). Bulky
F
dx.doi.org/10.1021/om300557d | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
and its color changed from yellow to nearly colorless. It was stirred at
RT under argon for 96 h to give a pale yellow solution. It was directly
loaded on the chromatography column (silica, 15 g) to avoid rotor-
evaporating foul-smelling tert-butyl isocyanide. Elution with 0.5−1.0%
CH3OH in CH2Cl2 removed the impurities. Elution with 1.0−2.0%
CH3OH in CH2Cl2 recovered the pure product as a pale yellow eluate.
The complexes were often isolated as oils that solidified on standing.
Further details are provided below.
Complex 1. [(L1)2Ir(μ-Cl)]2 (104 mg, 0.079 mmol), AgCF3SO3
(46 mg, 0.179 mmol), and tert-butyl isocyanide (0.5 mL, 365 mg, 4.4
mmol) gave a pale yellow solid that exhibits bluish-green
phosphorescence in solution and in powder: 133 mg (0.14 mmol,
88%). Anal. Calcd for C35H32F9IrN4O3S (MW 951.92): C, 44.16; H,
3.39; N, 5.89. Found: C, 44.03; H, 3.45; N, 5.69. 1H NMR (400 MHz,
CD2Cl2): δ 9.02 (d, J = 5.6 Hz, 2H), 8.25−8.15 (m, 4H), 7.86 (d, J =
8.0 Hz, 2H), 7.57 (td, J = 6.4, 2.0 Hz, 2H), 7.38−7.31 (m, 2H), 6.36
(s, 2H), 1.40 (s, 18H, tert-butyl) ppm. 19F NMR (376 MHz, CD2Cl2):
δ −63.37 (6F, Ph−CF3), −78.84 (3F, triflate) ppm. ESI+ TOF MS: m/
z 803.1 ({M − CF3SO3}+, 100%).
fluorocarbons reduce intermolecular interaction of 1−7,
thereby minimizing the red-shift of the emission color in
going from solution to neat solid, especially for 6 (4′-OCF3)
and the bis-CF3-substituted complexes 3 and 5 (Figure 6 and
Table 4).
Conclusions. Trifluoromethyl- and trifluoromethoxy-modi-
fied bis-cyclometalated cationic Ir(III) isocyanide complexes
1−7 exhibit bright phosphorescence at ambient conditions.
Substitution with a single fluorocarbon group in the C∧N ligand
can blue-shift the phosphorescence color of an Ir(III) complex;
for example, we observe pale blue phosphorescence (λ0−0
=
446−452 nm) in solution from 4 (3′-CF3), 6 (4′-OCF3), and 7
(2′-OCF3) (Φ = 40−73%) and in neat solid from 6 (4′-OCF3)
(Φ = 6.3%). The wavelength and efficiency of blue
phosphorescence of 4, 6, and 7 are one of the best reported
for cationic bis-cyclometalated Ir(III) complexes.13 In contrast,
bis-CF3 substitution in the C∧N ligand red-shifts the
phosphorescence color of the complex (3 and 5, Table 4 and
Figures 6−8) and introduces steric strain (5, Table 1 and
Figure 2).
Photophysical properties of 1−7 in solution are better than
or similar to those of the reported analogues.13,20,21 Bulky
fluorocarbon groups (1−7) minimize intermolecular inter-
action and offer better control over the phosphorescence color
and efficiency of an Ir(III) complex in neat solid than do the
H/F groups (913). The trifluoromethoxy group gives better
blue-phosphorescent Ir(III) complexes (6, 7) than does a
fluoro (9F13) or trifluoromethyl (1, 2) group. We expect
fluorocarbon-modified cyclometalating ligands to gain applica-
tion in phosphorescent organometallic complexes32 of iridium-
(III),31 platinum(II),33 and gold(III).34
Complex 2. [(L2)2Ir(μ-Cl)]2 (100 mg, 0.074 mmol), AgCF3SO3
(45 mg, 0.175 mmol), and tert-butyl isocyanide (0.5 mL, 365 mg, 4.4
mmol) gave a yellow glass that exhibits yellow-green phosphorescence
in solution and in powder: 112 mg (0.118 mmol, 79%). Anal. Calcd
for C35H32F9IrN4O3S (MW 952.17): C, 44.16; H, 3.39; N, 5.89.
1
Found: C, 44.36; H, 3.23; N, 5.65. H NMR (400 MHz, CD2Cl2): δ
9.09 (dd, J = 5.2, 0.8 Hz, 2H), 8.48 (d, J = 8.4 Hz, 2H), 8.16 (td, J =
8.4, 1.2 Hz, 2H), 7.56−7.49 (m, 2H), 7.49 (d, J = 8.0 Hz, 2H), 7.07−
6.99 (m, 2H), 6.33 (d, J = 7.6 Hz, 2H), 1.36 (s, 18H, tert-butyl) ppm.
19F NMR (376 MHz, CD2Cl2): δ −57.10 (6F, Ph−CF3), −78.84 (3F,
triflate) ppm. ESI+ TOF MS: m/z 803.16 ({M − CF3SO3}+, 100%).
Complex 3. [(L3)2Ir(μ-Cl)]2 (100 mg, 0.062 mmol), AgCF3SO3
(35 mg, 0.136 mmol), and tert-butyl isocyanide (0.5 mL, 365 mg, 4.4
mmol) gave a yellow glass that exhibits yellow-green phosphorescence
in solution and in powder: 114 mg (0.105 mmol, 85%). Anal. Calcd
for C37H30F15IrN4O3S (MW 1087.92): C, 40.85; H, 2.78; N, 5.15.
1
Found: C, 41.15; H, 2.93; N, 4.91. H NMR (400 MHz, CD2Cl2): δ
EXPERIMENTAL SECTION
9.20 (d, J = 5.2 Hz, 2H), 8.53 (d, J = 8.4 Hz, 2H), 8.30−8.22 (m, 2H),
7.76−7.67 (m, 4H), 6.47 (s, 2H), 1.42 (s, 18H, tert-butyl) ppm. 19F
NMR (376 MHz, CD2Cl2): δ −57.56 (6F, Ph−CF3), −63.99 (6F,
Ph−CF3), −78.78 (3F, triflate) ppm. ESI+ TOF MS: m/z 939.2 ({M −
CF3SO3}+, 100%).
Complex 4. [(L4)2Ir(μ-Cl)]2 (100 mg, 0.074 mmol), AgCF3SO3
(42 mg, 0.163 mmol), and tert-butyl isocyanide (0.5 mL, 365 mg, 4.4
mmol) gave a pale yellow solid that exhibits pale blue (in solution) or
pale blue-green (in powder) phosphorescence: 119 mg (0.125 mmol,
84%). Anal. Calcd for C35H32F9IrN4O3S (MW 951.92): C, 44.16; H,
3.39; N, 5.89. Found: C, 44.26; H, 3.53; N, 5.46. 1H NMR (400 MHz,
CD2Cl2): δ 9.01 (d, J = 6.0 Hz, 2H), 8.24−8.13 (m, 4H), 7.96 (s, 2H),
7.56 (td, J = 6.4, 2.0 Hz, 2H), 7.17 (dd, J = 8.0, 0.8 Hz, 2H), 6.33 (d, J
= 8.0 Hz, 2H), 1.41 (s, 18H, tert-butyl) ppm. 19F NMR (376 MHz,
CD2Cl2): δ −62.6 (6F, Ph−CF3), −78.8 (3F, triflate) ppm. ESI+ TOF
MS: m/z 803.3 ({M − CF3SO3}+, 100%).
Complex 5. [(L5)2Ir(μ-Cl)]2 (100 mg, 0.062 mmol), AgCF3SO3
(35 mg, 0.136 mmol), and tert-butyl isocyanide (0.5 mL, 365 mg, 4.4
mmol) gave a pale yellow glass that exhibits bluish-green
phosphorescence in solution and in powder: 106 mg (0.097 mmol,
79%). Anal. Calcd for C37H30F15IrN4O3S (MW 1087.92): C, 40.85; H,
2.78; N, 5.15. Found: C, 40.63; H, 2.75; N, 5.19. 1H NMR (400 MHz,
CD2Cl2): δ 9.05 (d, J = 5.6 Hz, 2H), 8.21−8.08 (m, 6H), 7.73 (s, 2H),
7.58−7.49 (m, 2H), 1.34 (s, 18H, tert-butyl) ppm. 19F NMR (376
MHz, CD2Cl2): δ −60.1 (6F, Ph−CF3), −63.1 (6F, Ph−CF3), −78.8
(3F, triflate) ppm. ESI+ TOF MS: m/z 939.1 ({M − CF3SO3}+,
100%).
■
Elemental analyses were performed by Dr. E. Solari, Service for
Elemental Analysis, Institute of Chemical Sciences and Engineering
(ISIC EPFL). 1H, 13C, and 19F NMR spectra were recorded with
Bruker AV400 (400 MHz), AV200 (200 MHz), and AVIII-400 (400
MHz) spectrometers. Mass spectra were recorded with Q-TOF Ultima
(Waters) and TSQ7000 (Thermo Fisher) spectrometers (Mass-
Spectroscopy Service, ISIC EPFL).
Purification, crystal growth, and handling of all compounds were
carried out under air. All products were stored in the dark. Chemicals
from commercial suppliers were used without purification. Chroma-
tography was performed on a column with an i.d. of 30 mm on silica
gel 60 (Fluka, No. 60752). The progress of reactions and the elution of
products were followed on TLC plates (silica gel 60 F254 on aluminum
sheets, Merck).
Further experimental details are provided in the Supporting
Information.
Synthesis of Ir(III) Isocyanide Complexes 1−7. The structures
of 1−7 are shown in Scheme 2. The syntheses of L1−L8 (Scheme 1)
and [(C∧N)2Ir(μ-Cl)]2 are described in the Supporting Information.
The reactions were performed under argon and in the absence of light.
The solvents were deoxygenated by bubbling with Ar, but they were
not dried. CAUTION: tert-butyl isocyanide is a foul-smelling volatile
liquidensure adequate ventilation! The cyclometalated Ir(III)
precursor [(C∧N)2Ir(μ-Cl)]2 was suspended (for C∧N = L2, L3,
L7) or dissolved (for other C∧N) in CH2Cl2 (20 mL) at RT. A
solution of AgCF3SO3 (excess, Aldrich) in CH3OH (10 mL) was
added dropwise. The reaction mixture was stirred (24 h for C∧N = L2
and L7; 4 h for the other C∧N) to give a yellow solution containing
the white precipitate of AgCl. It was filtered through a paper filter to
remove AgCl and evaporated to dryness (these operations were done
under air). The resulting Ir(III) solvento complex was suspended or
dissolved in degassed CH2Cl2 (20 mL), and tert-butyl isocyanide (large
excess, Aldrich) was added. The reaction mixture became a solution,
Complex 6. [(L6)2Ir(μ-Cl)]2 (100 mg, 0.071 mmol), AgCF3SO3
(40 mg, 0.156 mmol), and tert-butyl isocyanide (0.4 mL, 292 mg, 3.5
mmol) gave a pale yellow solid that exhibits pale blue phosphor-
escence in solution and in powder: 130 mg (0.132 mmol, 93%). Anal.
Calcd for C35H32F9IrN4O5S (MW 983.92): C, 42.72; H, 3.28; N, 5.69.
1
Found: C, 43.08; H, 3.16; N, 5.67. H NMR (400 MHz, CD2Cl2): δ
8.92 (d, J = 5.6 Hz, 2H), 8.13 (td, J = 7.6, 1.2 Hz, 2H), 8.06 (dd, J =
G
dx.doi.org/10.1021/om300557d | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
8.4, 1.2 Hz, 2H), 7.78 (d, J = 7.8 Hz, 2H), 7.50−7.44 (m, 2H), 6.97−
6.91 (m, 2H), 5.93 (dd, J = 2.0, 1.2 Hz, 2H), 1.38 (s, 18H, tert-butyl)
ppm. 19F NMR (376 MHz, CD2Cl2): δ −57.8 (6F, OCF3), −78.9 (3F,
triflate) ppm. ESI+ TOF MS: m/z 835.3 ({M − CF3SO3}+, 100%).
Complex 7. [(L7)2Ir(μ-Cl)]2 (100 mg, 0.071 mmol), AgCF3SO3
(45 mg, 0.175 mmol), and tert-butyl isocyanide (0.5 mL, 365 mg, 4.4
mmol) gave a yellow solid that exhibits pale blue (in solution) or
yellow-green (in powder) phosphorescence: 116 mg (0.118 mmol,
83%). Anal. Calcd for C35H32F9IrN4O5S (MW 983.92): C, 42.72; H,
3.28; N, 5.69. Found: C, 43.05; H, 3.03; N, 5.48. 1H NMR (400 MHz,
CD2Cl2): δ 9.04 (dd, J = 6.0, 1.2 Hz, 2H), 8.64 (d, J = 8.0 Hz, 2H),
8.20−8.12 (m, 2H), 7.53−7.46 (m, 2H), 7.03−6.96 (m, 4H), 6.12−
6.05 (m, 2H), 1.37 (s, 18H, tert-butyl) ppm. 19F NMR (376 MHz,
CD2Cl2): δ −57.08 (6F, OCF3), −78.86 (3F, triflate) ppm. ESI+ TOF
MS: m/z 835.18 ({M − CF3SO3}+, 100%).
(7) (a) Takizawa, S.-y.; Nishida, J.-i.; Tsuzuki, T.; Tokito, S.;
Yamashita, Y. Inorg. Chem. 2007, 46, 4308. (b) Yang, C.-H.; Cheng, Y.-
M.; Chi, Y.; Hsu, C.-J.; Fang, F.-C.; Wong, K.-T.; Chou, P.-T.; Chang,
C.-H.; Tsai, M.-H.; Wu, C.-C. Angew. Chem., Int. Ed. 2007, 46, 2418.
(c) Chiu, Y.-C.; Hung, J.-Y.; Chi, Y.; Chen, C.-C.; Chang, C.-H.; Wu,
C.-C.; Cheng, Y.-M.; Yu, Y.-C.; Lee, G.-H.; Chou, P.-T. Adv. Mater.
2009, 21, 2221.
(8) (a) Ionkin, A. S.; Marshall, W. J.; Roe, D. C.; Wang, Y. Dalton
Trans. 2006, 2468. (b) Ionkin, A. S.; Wang, Y.; Marshall, W. J.; Petrov,
V. A. J. Organomet. Chem. 2007, 692, 4809. (c) Xu, M.; Zhou, R.;
Wang, G.; Xiao, Q.; Du, W.; Che, G. Inorg. Chim. Acta 2008, 361,
2407. (d) Lee, S.-C.; Kim, Y. S. Mol. Cryst. Liq. Cryst. 2009, 505, 325.
(9) (a) Slinker, J. D.; Rivnay, J.; Moskowitz, J. S.; Parker, J. B.;
Bernhard, S.; Abruna, H. D.; Malliaras, G. G. J. Mater. Chem. 2007, 17,
̃
2976. (b) Ulbricht, C.; Beyer, B.; Friebe, C.; Winter, A.; Schubert, U.
S. Adv. Mater. 2009, 21, 4418. (c) Xiao, L.; Chen, Z.; Qu, B.; Luo, J.;
Kong, S.; Gong, Q.; Kido, J. Adv. Mater. 2011, 23, 926. (d) Hu, T.; He,
L.; Duan, L.; Qiu, Y. J. Mater. Chem. 2012, 22, 4206.
(10) (a) Babudri, F.; Farinola, G. M.; Naso, F.; Ragni, R. Chem.
Commun. 2007, 1003. (b) Chou, P.-T.; Chi, Y. Chem.Eur. J. 2007,
13, 380.
ASSOCIATED CONTENT
* Supporting Information
■
S
Synthesis and characterization of L1−L8 and [(C∧N)2Ir(μ-
Cl)]2 (C∧N = L1−L8); NMR spectra; experimental
techniques; crystallographic data (Table S1); cyclic voltammo-
grams (Table S2 and Figures S1 and S2); absorption spectra
(Figures S3−S6); λ0−0−Ered and λ0−0−ΔE plots (Figures S7
and S8); CIF of the crystal structures of 1 and 4−7, CCDC
892860−892864. This material is available free of charge via the
Internet at http://pubs.acs.org.
(11) Sykes, D.; Tidmarsh, I. S.; Barbieri, A.; Sazanovich, I. V.;
Weinstein, J. A.; Ward, M. D. Inorg. Chem. 2011, 50, 11323.
(12) Ladouceur, S.; Fortin, D.; Zysman-Colman, E. Inorg. Chem.
2011, 50, 11514.
(13) Shavaleev, N. M.; Monti, F.; Costa, R.; Scopelliti, R.; Bolink, H.;
Ortí, E.; Accorsi, G.; Armaroli, N.; Baranoff, E.; Gratzel, M.;
̈
Nazeeruddin, Md. K. Inorg. Chem. 2012, 51, 2263.
(14) Avilov, I.; Minoofar, P.; Cornil, J.; De Cola, L. J. Am. Chem. Soc.
2007, 129, 8247.
AUTHOR INFORMATION
Corresponding Author
■
(15) Kawamura, Y.; Brooks, J.; Brown, J. J.; Sasabe, H.; Adachi, C.
Phys. Rev. Lett. 2006, 96, 017404.
*Tel: +41 21 693 6124. Fax: +41 21 693 4111. E-mail: nail.
shavaleev@epfl.ch; nicola.armaroli@cnr.it; mdkhaja.
nazeeruddin@epfl.ch.
(16) (a) Springer, C. S., Jr.; Meek, D. W.; Sievers, R. E. Inorg. Chem.
1967, 6, 1105. (b) Miller, M. T.; Gantzel, P. K.; Karpishin, T. B.
Angew. Chem., Int. Ed. 1998, 37, 1556. (c) Hasegawa, Y.; Ohkubo, T.;
Sogabe, K.; Kawamura, Y.; Wada, Y.; Nakashima, N.; Yanagida, S.
Angew. Chem., Int. Ed. 2000, 39, 357.
Notes
The authors declare no competing financial interest.
(17) Leung, S.-K.; Liu, H.-W.; Lo, K. K.-W. Chem. Commun. 2011,
47, 10548.
(18) (a) Nonoyama, M. Bull. Chem. Soc. Jpn. 1974, 47, 767.
(b) Sprouse, S.; King, K. A.; Spellane, P. J.; Watts, R. J. J. Am. Chem.
Soc. 1984, 106, 6647.
ACKNOWLEDGMENTS
■
We thank the European Union (CELLO, STRP 248043;
https://www.cello-project.eu/) and the CNR (MACOL,
PM.P04.010) for financial support.
(19) (a) Li, L.; Brennessel, W. W.; Jones, W. D. Organometallics
2009, 28, 3492. (b) Davies, D. L.; Lowe, M. P.; Ryder, K. S.; Singh, K.;
Singh, S. Dalton Trans. 2011, 40, 1028.
(20) Li, J.; Djurovich, P. I.; Alleyne, B. D.; Yousufuddin, M.; Ho, N.
N.; Thomas, J. C.; Peters, J. C.; Bau, R.; Thompson, M. E. Inorg. Chem.
2005, 44, 1713.
(21) Habibagahi, A.; Mebarki, Y.; Sultan, Y.; Yap, G. P. A.; Crutchley,
R. J. ACS Appl. Mater. Interfaces 2009, 1, 1785.
(22) Dedeian, K.; Djurovich, P. I.; Garces, F. O.; Carlson, G.; Watts,
R. J. Inorg. Chem. 1991, 30, 1685.
(23) (a) Willard, H. H.; Boldyreff, A. W. J. Am. Chem. Soc. 1929, 51,
REFERENCES
■
(1) Wen, S.-W.; Lee, M.-T.; Chen, C. H. J. Display Technol. 2005, 1,
90.
(2) (a) Deaton, J. C.; Place, D. W.; Brown, C. T.; Rajeswaran, M.;
Kondakova, M. E. Inorg. Chim. Acta 2008, 361, 1020. (b) Liao, S.-H.;
Shiu, J.-R.; Liu, S.-W.; Yeh, S.-J.; Chen, Y.-H.; Chen, C.-T.; Chow, T.
J.; Wu, C.-I. J. Am. Chem. Soc. 2009, 131, 763.
(3) (a) Adamovich, V.; Brooks, J.; Tamayo, A.; Alexander, A. M.;
Djurovich, P. I.; D’Andrade, B. W.; Adachi, C.; Forrest, S. R.;
Thompson, M. E. New J. Chem. 2002, 26, 1171. (b) Unger, Y.; Meyer,
D.; Strassner, T. Dalton Trans. 2010, 39, 4295. (c) Li, K.; Guan, X.;
Ma, C.-W.; Lu, W.; Chen, Y.; Che, C.-M. Chem. Commun. 2011, 47,
9075.
(4) (a) Yang, C.-H.; Li, S.-W.; Chi, Y.; Cheng, Y.-M.; Yeh, Y.-S.;
Chou, P.-T.; Lee, G.-H.; Wang, C.-H.; Shu, C.-F. Inorg. Chem. 2005,
44, 7770. (b) Ragni, R.; Plummer, E. A.; Brunner, K.; Hofstraat, J. W.;
Babudri, F.; Farinola, G. M.; Naso, F.; De Cola, L. J. Mater. Chem.
2006, 16, 1161. (c) Dedeian, K.; Shi, J.; Forsythe, E.; Morton, D. C.;
Zavalij, P. Y. Inorg. Chem. 2007, 46, 1603. (d) Zhu, Y.-C.; Zhou, L.; Li,
H.-Y.; Xu, Q.-L.; Teng, M.-Y.; Zheng, Y.-X.; Zuo, J.-L.; Zhang, H.-J.;
You, X.-Z. Adv. Mater. 2011, 23, 4041. (e) Zheng, Y.; Batsanov, A. S.;
Edkins, R. M.; Beeby, A.; Bryce, M. R. Inorg. Chem. 2012, 51, 290.
(5) Grushin, V. V.; Herron, N.; LeCloux, D. D.; Marshall, W. J.;
Petrov, V. A.; Wang, Y. Chem. Commun. 2001, 1494.
471. (b) Gagne,
́
R. R.; Koval, C. A.; Lisensky, G. C. Inorg. Chem. 1980,
19, 2854. (c) Gritzner, G.; Kuta, J. Pure Appl. Chem. 1984, 56, 461.
̊
(d) Tsierkezos, N. G. J. Solution Chem. 2007, 36, 289.
(24) Nicholson, R. S.; Shain, I. Anal. Chem. 1964, 36, 706.
(25) Cardona, C. M.; Li, W.; Kaifer, A. E.; Stockdale, D.; Bazan, G. C.
Adv. Mater. 2011, 23, 2367.
(26) (a) Connor, J. A.; Meyer, T. J.; Sullivan, B. P. Inorg. Chem. 1979,
18, 1388. (b) Indelli, M. T.; Bignozzi, C. A.; Marconi, A.; Scandola, F.
J. Am. Chem. Soc. 1988, 110, 7381.
(27) Stoyanov, S. R.; Villegas, J. M.; Cruz, A. J.; Lockyear, L. L.;
Reibenspies, J. H.; Rillema, D. P. J. Chem. Theory Comput. 2005, 1, 95.
(28) Leung, C.-F.; Ng, S.-M.; Xiang, J.; Wong, W.-Y.; Lam, M. H.-W.;
Ko, C.-C.; Lau, T.-C. Organometallics 2009, 28, 5709.
(29) Sarapu, A. C.; Fenske, R. F. Inorg. Chem. 1975, 14, 247.
(6) Coppo, P.; Plummer, E. A.; De Cola, L. Chem. Commun. 2004,
1774.
(30) Colombo, M. G.; Hauser, A.; Gudel, H. Inorg. Chem. 1993, 32,
3088.
̈
H
dx.doi.org/10.1021/om300557d | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(31) Flamigni, L.; Barbieri, A.; Sabatini, C.; Ventura, B.; Barigelletti,
F. Top. Curr. Chem. 2007, 281, 143.
(32) (a) Evans, R. C.; Douglas, P.; Winscom, C. J. Coord. Chem. Rev.
2006, 250, 2093. (b) Wong, W.-Y.; Ho, C.-L. Coord. Chem. Rev. 2009,
253, 1709. (c) Yam, V. W.-W.; Wong, K. M.-C. Chem. Commun. 2011,
47, 11579.
(33) Williams, J. A. G.; Develay, S.; Rochester, D. L.; Murphy, L.
Coord. Chem. Rev. 2008, 252, 2596.
(34) (a) Garg, J. A.; Blacque, O.; Fox, T.; Venkatesan, K. Inorg. Chem.
2010, 49, 11463. (b) Au, V. K.-M.; Wong, K. M.-C.; Zhu, N.; Yam, V.
W.-W. Chem.Eur. J. 2011, 17, 130.
I
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