Extreme tuning of redox and optical properties of cationic cyclometalated iridium(III) isocyanide complexes

Article abstract of DOI:10.1021/om300894m

We report seven heteroleptic cationic iridium(III) complexes with cyclometalating N-arylazoles and alkyl/aryl isocyanides, [(C ^aN)₂Ir(CNR)₂](CF₃SO ₃), and characterize two of them by crystal structure analysis. The complexes are air- and moisture-stable white solids that have electronic transitions at very high energy with absorption onset at 320-380 nm. The complexes are difficult to reduce and oxidize; they exhibit irreversible electrochemical processes with peak potentials (against ferrocene) at -2.74 to -2.37 V (reduction) and 0.99-1.56 V (oxidation) and have a large redox gap of 3.49-4.26 V. The reduction potential of the complex is determined by the azole heterocycle (pyrazole or indazole) and by the isocyanide (tert-butyl or 2,6-dimethylphenyl) and the oxidation potential by the Ir-aryl fragment [aryl = 2′,4′-R₂-phenyl (R = H/F), 9′,9′-dihexyl- 2′-fluorenyl]. Three of the complexes exhibit phosphorescence in argon-saturated dichloromethane and acetonitrile solutions at room temperature with 0-0 transitions at 473-478 nm (green color; the emission spectra are solvent-independent), quantum yields of 3-25%, and long excited-state lifetimes of 62-350 μs. All of the complexes are phosphorescent at 77 K with 0-0 transitions at 387-474 nm (blue to green color). The extremely long calculated radiative lifetimes, 0.5-3.5 ms, confirm that the complexes emit from a cyclometalating-ligand-centered excited state.

Full text of DOI:10.1021/om300894m

Article
pubs.acs.org/Organometallics
Extreme Tuning of Redox and Optical Properties of Cationic
Cyclometalated Iridium(III) Isocyanide Complexes
Nail M. Shavaleev,*,† Filippo Monti,‡ Rosario Scopelliti,† Andrea Baschieri,§ Letizia Sambri,§
Nicola Armaroli,*,‡ Michael Gratzel,† and Mohammad K. Nazeeruddin*,†
̈
†
́
Laboratory of Photonics and Interfaces, Ecole Polytechnique Fed
‡Molecular Photoscience Group, Istituto per la Sintesi Organica e la Fotoreattivita,
́
er
́
ale de Lausanne, CH-1015 Lausanne, Switzerland
Consiglio Nazionale delle Ricerche, Via P. Gobetti,
̀
101, 40129, Bologna, Italy
§Department of Organic Chemistry “A. Mangini”, University of Bologna, Viale Risorgimento 4, 40136, Bologna, Italy
S
* Supporting Information
ABSTRACT: We report seven heteroleptic cationic iridium(III) complexes with cyclometalating N-
arylazoles and alkyl/aryl isocyanides, [(C∧N)2Ir(CNR)2](CF3SO3), and characterize two of them by
crystal structure analysis. The complexes are air- and moisture-stable white solids that have electronic
transitions at very high energy with absorption onset at 320−380 nm. The complexes are difficult to
reduce and oxidize; they exhibit irreversible electrochemical processes with peak potentials (against
ferrocene) at −2.74 to −2.37 V (reduction) and 0.99−1.56 V (oxidation) and have a large redox gap of
3.49−4.26 V. The reduction potential of the complex is determined by the azole heterocycle (pyrazole
or indazole) and by the isocyanide (tert-butyl or 2,6-dimethylphenyl) and the oxidation potential by the
Ir−aryl fragment [aryl = 2′,4′-R2-phenyl (R = H/F), 9′,9′-dihexyl-2′-fluorenyl]. Three of the complexes
exhibit phosphorescence in argon-saturated dichloromethane and acetonitrile solutions at room temperature with 0−0 transitions
at 473−478 nm (green color; the emission spectra are solvent-independent), quantum yields of 3−25%, and long excited-state
lifetimes of 62−350 μs. All of the complexes are phosphorescent at 77 K with 0−0 transitions at 387−474 nm (blue to green
color). The extremely long calculated radiative lifetimes, 0.5−3.5 ms, confirm that the complexes emit from a cyclometalating-
ligand-centered excited state.
oxidize, that are transparent in the visible/near-UV range, and
that exhibit phosphorescence with very long radiative lifetimes.
INTRODUCTION
■
We, and others, have recently reported that cationic bis-
cyclometalated iridium(III) complexes with 2-phenylpyridines
and tert-butyl isocyanide, [(C∧N)2Ir(CNtBu)2]+, exhibit blue/
green phosphorescence from a 2-phenylpyridine-centered
excited state with high quantum yields (up to 76%), and long
excited-state lifetimes (up to 84 μs) at room temperature.1−6
Non-chromophore strong-field electron-withdrawing tert-butyl
isocyanide ligands7 destabilize the excited states, blue-shift the
phosphorescence maximum, and enhance the phosphorescence
efficiency of these complexes.1−6 Phosphorescence of the
mono-isocyanide iridium(III) complexes8 and of the isocyanide
complexes of copper(I),9 platinum(II),10 rhenium(I),11−15 and
ruthenium(II)16−21 has been investigated as well.
Pyridine, a UV chromophore and a strong π-acceptor/σ-
donor, introduces low-energy π−π* and charge-transfer excited
states in metal complexes with polypyridines and cyclo-
metalating arylpyridines.22−25 To increase the excited-state
energy of a complex, one can replace the pyridine with another
metal-binding heterocycle.22−32 Here, we report heteroleptic
cationic iridium(III) complexes with alkyl/aryl isocyanides and
cyclometalating N-arylazoles (1−7, Scheme 1). We tune the
redox and optical properties of Ir(III) complexes to the
extremes by adjusting the π-conjugation in the ligands and by
changing the metal-binding heterocycle. We report the first
cyclometalated iridium(III) complexes that are hard to reduce/
RESULTS AND DISCUSSION
■
Synthesis. We prepared the new ligand L by Cu2O-
catalyzed C−N coupling33 of 9,9-dihexyl-2-bromofluorene with
pyrazole (Scheme 2). The reaction of L with IrCl3·3H2O in 2-
ethoxyethanol/water gave the cyclometalated complex
[(L)2Ir(μ-Cl)]2 (Scheme 2).
Seven new iridium(III) isocyanide complexes (1−7, Scheme
1) were prepared by the reaction of [(C∧N)2Ir(μ-Cl)]2 (C∧N =
N-arylazole)31,32,34 with silver triflate (to remove the chloride
anion) and with an isocyanide CNR [R = tert-butyl (CNtBu),
2,6-dimethylphenyl (CNPh*)].1,4−6 Purification by column
chromatography on silica and by recrystallization gave 1−7 as
air- and moisture-stable white solids that are soluble in polar
organic solvents. 1−7 are the first iridium(III) isocyanide
complexes with cyclometalating N-arylazoles, and 2, 4, and 6
are the first bis-cyclometalated bis(aryl isocyanide) Ir(III)
complexes.1−6,8
1H and 19F NMR spectra of 1−7 (i) exhibit a single set of
signals for the C∧N and CNR ligands, (ii) confirm the 1:1 ratio
of C∧N to CNR, (iii) confirm the presence of the F groups and
Received: September 19, 2012
Published: January 9, 2013
© 2013 American Chemical Society
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Article
a
Structures of Ir(III) Isocyanide Complexes. The iridium-
(III) ion in 3 and 4 (Figures 1 and 2) is in a distorted-
Scheme 1. New Iridium(III) Isocyanide Complexes
Figure 1. Structure of 3 (50% probability ellipsoids; H atoms and
triflate anion omitted; ORTEP). Heteroatoms: N, blue; F, green; Ir,
black.
a
Reaction conditions: (a) under Ar, room temperature; (i) AgCF3SO3,
CH3OH/CH2Cl2; (ii) CNR, CH2Cl2.
Figure 2. Structure of 4 (50% probability ellipsoids; H atoms and
triflate anion omitted; ORTEP). Heteroatoms: N, blue; F, green; Ir,
black.
a
Scheme 2. Ligand L and Complex [(L)2Ir(μ-Cl)]2
octahedral [(C∧N)2Ir(C)2]+ coordination environment. The
two N(C∧N) atoms are in positions trans to each other. The
metal−ligand bond lengths increase in the order Ir−C(CNR) <
Ir−N(C∧N) < Ir−C(C∧N) (Table 1). The Ir−C bonds with
CNPh* (4) are shorter than are those with CNtBu (3) [the
reported Ir−CNtBu bond lengths in the analogous com-
plexes1,4−6 are 2.004(6)−2.062(6) Å]. The Ir−isocyanide
fragments, Ir−CN and CN−C, are not linear (Table 1).
The C∧N ligands are nearly planar with dihedral angles
between the phenyl and azole of 1.6−8.9° (Table 1).
a
Reaction conditions: (a) bromohexane, KOtBu, dry DMF, under
Weak face-to-face π−π stacking between the C∧N ligands in
the CNtBu complex 3 gives a dimer structure with an
interplanar C∧N···C∧N distance of 3.166 Å. Weak face-to-face
π−π stacking of the CNPh* complex 4 gives a chain structure:
it involves one of the CNPh* ligands (centroid···centroid
distance between the phenyls 3.650 Å) and one of the C∧N
ligands (interplanar C∧N···C∧N distance 3.311 Å). The shortest
Ir···Ir distance in 3 and 4 exceeds 8 Å.
argon, 60 °C; (b) pyrazole, Cs2CO3, Cu2O (catalyst), dry DMF, under
argon, 120 °C; (c) IrCl3·3H2O, 2-ethoxyethanol/water (3/1), under
argon, 120 °C.
−
of the CF3SO3 anion, and (iv) indicate that the complexes
have C2 symmetry. Mass spectra of 1−7 exhibit a peak of the
[(C∧N)2Ir(CNR)2]+ cation.
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a
Table 1. Structural Parameters of Iridium(III) Isocyanide Complexes
bond lengths (Å)
isocyanide
C∧N
bond angles (deg)
b
complex
Ir−C
Ir−C
Ir−N
C∧N
Ir−CN
CN−C
3
2.026(4)
2.043(3)
2.018(3)
2.025(3)
2.064(3)
2.057(3)
2.069(3)
2.073(3)
2.035(3)
2.031(3)
2.044(2)
2.034(2)
8.90
1.90
1.60
6.54
178.8(3)
173.7(3)
175.6(2)
174.7(3)
178.6(4)
173.6(4)
172.9(3)
178.0(3)
4
a
b
Each row corresponds to one ligand. The isocyanide ligand is in a position trans to the carbon atom of the C∧N ligand in the same row. Angle
between the aryl and azole rings.
Electrochemistry. We have measured redox potentials of
1−7 (against ferrocene couple) by cyclic voltammetry (CV) in
acetonitrile (ACN) and DMF (Figures 3 and 4 and Figures
Figure 4. Cyclic voltammograms of 5−7 in acetonitrile (glassy-carbon
electrode, 0.1 M NBu4PF6, 100 mV/s). The unit on the vertical axis is
20 μA. The peaks at −1.4 to −2.0 V are the return waves of irreversible
processes. CVs of 5−7 in DMF are shown in the Supporting
Information.
Figure 3. Cyclic voltammograms of 1−4 in acetonitrile (glassy-carbon
electrode, 0.1 M NBu4PF6, 100 mV/s). The unit on the vertical axis is
50 μA. The peaks at −0.4 to −2.0 V are the return waves of irreversible
processes. CVs of 1−4 in DMF are shown in the Supporting
Information.
a
Table 2. Redox Properties
c
d
Ered, V
Eox, V
ΔE, V
b
complex CNR
DMF
ACN
DMF
ACN
DMF
ACN
1
2
3
4
5
6
7
R
tBu
Ph*
tBu
Ph*
tBu
Ph*
tBu
tBu
−2.74
−2.50
−2.63
−2.37
−2.71
−2.51
−2.39
−2.38
−2.73
−2.47
−2.70
−2.37
−2.60
−2.45
−2.37
−2.38
1.30
1.34
1.56
4.03
3.81
4.26
S1−S4 in the Supporting Information). All redox processes
were irreversible (Table 2 and Tables S2 and S3 in the
Supporting Information). Complexes 1−7 exhibit a reduction
at −2.74 to −2.37 V, an oxidation at 0.99−1.56 V, and a redox
gap, ΔE = Eox − Ered, of 3.49−4.26 V (at CV scan rate 100 mV/
s; Table 2). Electron-withdrawing 2′,4′-fluorines25,28,31 increase
the redox potentials from 1 and 2 to 3 and 4 by ≤130 mV
(Ered) and ≤260 mV (Eox). Changing tert-butyl isocyanide (1, 3,
5) to the stronger π-acceptor 2,6-dimethylphenyl isocyanide35
(2, 4, 6) increases the redox potentials by ≤330 mV (Ered) and
≤50 mV (Eox). Replacing a phenyl (1, 2) with a stronger
electron-donor fluorenyl (5, 6) facilitates the oxidation by ≤310
mV. Replacing a pyrazole (1) with a stronger σ-donor/π-
acceptor indazole32 (7) facilitates both the reduction (by ≤360
mV) and the oxidation (by 160 mV).
We find that (i) the redox potentials of 1−7 are nearly
solvent-independent in DMF and ACN at a scan rate of 100
mV/s (Table 2), (ii) the redox processes remain irreversible
and the trends in redox parameters of 1, 3, 5, and 7 do not
change when the scan rate is increased from 100 mV/s to 1 V/s
in ACN (Table 2; Figures S2 and S3 and Table S2 in the
Supporting Information), and (iii) at scan rates 20−1000 mV/s
1.00
1.02
0.99
1.04
1.14
1.23
3.71
3.53
3.59
3.49
3.51
3.61
e
a
In acetonitrile (ACN) or DMF. All redox processes were irreversible.
Oxidation or reduction peak potentials are reported. Relative to Fc+/
Fc. Estimated errors: 50 mV. On glassy-carbon working electrode, in
b
the presence of 0.1 M (NBu4)PF6, at scan rate 100 mV/s. Substituent
in the isocyanide ligand. Ph* = 2,6-dimethylphenyl. The oxidation
c
process was outside of the electrochemical window for 1−4 and 7 in
d
e
DMF (>1.1 V) and for 4 in ACN (>1.6 V). ΔE = Eox − Ered. Data
from the literature. R = [(N,C2′-2-phenylpyridyl)2Ir(CNtBu)2]-
(CF3SO3).5
in ACN, the redox processes of 3 remain irreversible with the
peak potentials and gap of −2.66 to −2.78 V (Ered), 1.56−1.69
V (Eox), and 4.25−4.40 V (ΔE) (Table S3 and Figure S4 in the
Supporting Information).
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The redox potentials of 1−7 indicate that the reduction is
determined by the azole and isocyanide and the oxidation by
the Ir−aryl fragment. The irreversibility of redox processes,
which probably arises from a chemical reaction that follows the
electron transfer,6 prevented us from determining the formal
redox potentials; nevertheless, we consider that the peak
potentials and the redox gap correctly reproduce the trends in
the energies of the HOMO, LUMO, and HOMO−LUMO gap
of 1−7.5,6,36 The redox gap increases on fluorination from 1
and 2 to 3 and 4 but decreases when tert-butyl isocyanide (1, 3,
5) is replaced by 2,6-dimethylphenyl isocyanide (2, 4, 6) and
when an aromatic system of the N-arylazole ligand is extended
from phenyl or pyrazole (1, 2) to fluorenyl (5, 6) or indazole
(7) (Table 2).
Because pyrazole is a weaker π-acceptor/σ-donor22,23,25,28,31
than pyridine, the 1-phenylpyrazole complex 1 in ACN exhibits
more negative reduction (by −0.35 V) and more positive
oxidation (by 0.07 V) than the reported 2-phenylpyridine
analogue R does5 (Table 2). On the other hand, the reduction
potential and π-acceptor strength of 1-phenylindazole (7) are
similar to those of 2-phenylpyridine (R) (Table 2). The high
oxidation potentials of 1−7 arise from the positive charge of the
complexes, the strong electron-withdrawing isocyanide ligand,
and the weak σ-donor pyrazole.
To summarize, (i) complexes 1−7, especially 1−4, are hard
to reduce/oxidize and exhibit a large redox gap, (ii) 3 exhibits
the largest redox gap reported for a cyclometalated iridium(III)
complex, 4.26 V at 100 mV/s (all of the known Ir(III)
complexes with redox gaps >3.5 V exhibit irreversible redox
processes5,6,31,37), and (iii) the redox gap of 1−7 is reduced by
extending the π-conjugation in the ligands.
Absorption Spectroscopy. The infrared absorption
spectra of 1−7 in neat films exhibit two peaks separated by
20−26 cm−1 at 2214−2177 cm−1 (CNtBu complexes) or
2193−2155 cm−1 (CNPh* complexes) that are characteristic of
stretching vibrations of the isocyanide CN bond (Table 3
and Figures S6 and S7 in the Supporting Information).5,6 The
presence of two IR peaks confirms the cis geometry21 of the
isocyanides in 1−7.
Figure 5. Absorption spectra of 1−7 at (5.51−12.3) × 10−5 M in
dichloromethane. The unit on the vertical axis is 10 × 103 M−1 cm−1.
onset corresponds to the larger redox gap for the complexes
with the same isocyanide ligand. (ii) Fluorination of the
electron-rich phenyl ring of the C∧N ligand blue-shifts the
absorption from 1 and 2 to 3 and 4 (Figure 5). (iii) Replacing a
phenyl or pyrazole with a stronger electron-donor (fluorenyl)
or a stronger electron-acceptor (indazole), respectively, red-
shifts and enhances the absorption from 1−4 to 5−7 (we note
that fluorenyl and indazole chromophores in 5−7 have lower-
energy and higher-intensity π−π* transitions than pyrazole and
phenyl chromophores do in 1−4) (Figure 5). We conclude
from i−iii that the lowest energy electronic absorption of the
complexes 1−7 is determined by the (Ir−aryl)-to-azole charge-
transfer state (CT).5,6
The absorption of 1−7 at 250−300 nm increases by up to 3
× 104 M−1 cm−1 when tert-butyl isocyanide is replaced by the
stronger π-acceptor 2,6-dimethylphenyl isocyanide (Figure 5).
These new intense high-energy electronic transitions are
associated with the (Ir−aryl)-to-CNPh* charge-transfer
(CT*).8,13,17
Table 3. UV−Vis and IR Absorption Maxima
3 and 4 are the first cationic bis-cyclometalated iridium(III)
complexes that are transparent in the UV range to 320 nm
(Figure 5). The CT and π−π* absorption transitions of 3 and 4
have high energy because (i) pyrazole is a weak π-acceptor/σ-
donor with high-energy π−π* transitions,22,23,25,28,31 (ii) 2,4-
difluorophenyl is a weak electron donor, and (iii) tert-butyl and
2,6-dimethylphenyl isocyanides are non-chromophores in the
visible and near-UV spectral ranges17 and are strong electron-
withdrawing ligands.
a
b
IR, cm−1
λabs, nm (ε/103 M−1 cm−1
)
L
1
2
3
4
5
6
7
296 (24), 316 (23)
2200, 2177
2181, 2156
2214, 2194
2193, 2172
2199, 2177
2181, 2155
2206, 2185
277 (12), 299 (11)
278 (29, sh)
275 (13, sh)
255 (55, sh)
258 (31), 292 (26), 304 (31), 336 (45), 349 (40)
257 (60), 290 (37), 304 (31), 335 (47), 349 (42)
259 (49), 283 (19), 293 (20), 336 (14)
To summarize, the (Ir−aryl)-to-azole charge-transfer state
(CT) determines the absorption onset in 1−7; however, we
expect the CT state to be mixed with a cyclometalating-ligand-
centered (LC) state in 1−7 and with a CT* state in 2 and 4.
The absorption onset of 1−7 is red-shifted by extending the π-
conjugation in the N-arylazole (but not in the isocyanide).
Phosphorescence Spectroscopy. We have studied the
photophysical properties of the complexes 1−7 in dichloro-
methane (DCM) and acetonitrile (ACN) solutions at room
temperature (under argon) and at 77 K (Figure 6 and Table 4;
Figure S8 in the Supporting Information). The emission of 1−7
is completely quenched by oxygen at room temperature in
liquid solution.
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. Estimated errors: 2 nm for λabs
5 nm for λonset 5% for ε.
;
;
Complexes 1−7 are white solids that give colorless solutions
in dichloromethane. 1−7 exhibit electronic transitions at very
high energy for cyclometalated iridium(III) complexes (Figure
5). We find the following: (i) The wavelength of the absorption
onset is determined by the N-arylazole ligand and varies in the
order 7 (380 nm) > 5, 6 (370 nm) > 1, 2 (340 nm) > 3, 4 (320
nm) (Figure 5). The shorter wavelength of the absorption
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only by ≤4 nm from DCM to ACN. We find that 5−7 exhibit
higher Φ and longer τ times in dichloromethane than they do
in acetonitrile; however, τrad in both solvents are similar within
experimental error. We consider that acetonitrile (or the trace
impurities in it) quenches the extremely long-lived excited
states of 5−7 more than dichloromethane does.
At 77 K, the complexes exhibit blue (1−4, λ0−0 = 387−406
nm) or green (5−7, λ0−0 = 469−474 nm) phosphorescence
(Figure 6 and Table 4). The spectra have better resolved
vibronic structure at 77 K than they do at room temperature
(Figure 6), but λ0−0 blue-shifts only by ≤5 nm from room
temperature to 77 K. The luminescence decays of 1−7 at 77 K
are biexponential functions with components of 20−250 μs and
140−1300 μs (Figure S11, Supporting Information).
The structured and solvent-independent phosphorescence
spectra, together with the long radiative lifetimes, indicate that
1−7 emit from a cyclometalating-ligand-centered excited state
(LC) coupled to an (Ir−aryl)-to-azole charge-transfer state
(CT).5,6,38,39 Replacing CNtBu with CNPh* red-shifts and
broadens the emission spectrum from 1 and 3 to 2 and 4 (but
not from 5 to 6) because the LC/CT states in 2 and 4 (but not
in 6) are close in energy/coupled to the (Ir−aryl)-to-CNPh*
charge-transfer state (CT*).
Figure 6. Corrected and normalized luminescence spectra of 1−7 in
10−5 M argon-saturated dichloromethane solution at room temper-
ature (red) and at 77 K (blue).
Table 4. Photophysical Properties
We consider that, at room temperature, the LC/CT state of
1−4 is quenched through thermal population of the proximate
non-emissive metal-centered d−d state; hence, Φ(1−4) ≤ 0.1%
(the same non-radiative deactivation mechanism works for the
reported Ir(III) complexes with 1-phenylpyrazoles26,27,29). At
77 K, however, 1−4 are phosphorescent and have long excited-
state lifetimes because thermally activated quenching is too
slow at 77 K to compete with radiative decay.26,27,29
Replacing pyridine with pyrazole increases the redox gap and,
therefore, destabilizes the CT state and blue-shifts the
phosphorescence spectrum from R (λ0−0 = 455 nm; room
temperature, DCM)5 to 1 by 50 nm (2700 cm−1). In the same
way, fluorination of the C∧N ligand further blue-shifts the
phosphorescence spectrum from 1 and 2 to 3 and 4 by 13−17
nm (840−1080 cm−1; λ0−0, 77 K). 3 and 4 have the highest
energy phosphorescence (λ0−0 = 387−389 nm, 77 K) reported
for [(C∧N)2Ir(C)2]+ and [(C∧N)2Ir(C∧C)]+ com-
plexes.1−6,40,41 Although the quantum yields of 3 and 4 at
room temperature are very low, <0.1%, we expect that by
replacing a pyrazole with another azole30 one may get efficient
high-energy-emitting [(C∧N)2Ir(CNR)2]+ complexes.
At room temperature, 5−7 have >30-fold higher emission
quantum yields than 1−4 do because the LC/CT states (but
not the d−d states) are stabilized (in other words, the energy
gap between LC/CT and d−d states increases) when the π
conjugation in the N-arylazole ligand is extended from 1−4 to
5−7.
Phosphorescent metal complexes with long excited-state
lifetimes are used for singlet oxygen generation2,42 and for
oxygen sensing.4,9,43,44 Because iridium(III) promotes strong
spin−orbit coupling, the majority of phosphorescent Ir(III)
complexes have relatively short radiative lifetimes: 1−100
μs.38,39,45,46 The rare Ir(III) complexes that do exhibit long
radiative lifetime of hundreds to thousands of microseconds are
[(C∧N)2Ir(CNtBu)2]+,1−6 [(C∧N)2Ir(P∧P)]+ (P∧P = diphos-
phine),1,46 Ir(III)−corrole,47,48 Ir(III)−porphyrin,44,48 and
[Ir(1,10-phenanthroline)3]3+.49
a
b
c
d
e
f
complex medium
λ0−0, nm
λmax, nm
Φ, %
τ, μs
τrad, ms
1
DCM
77 K
77 K
77 K
77 K
DCM
ACN
77 K
DCM
ACN
77 K
DCM
ACN
77 K
405
400
428
425
426
410
424
512
510
474
512
509
473
505
502
500
∼0.1
2
3
4
5
406 (br)
387
389 (sh)
477
8
3
280
75
3.5
2.5
474
474
6
7
478
10
3
350
90
3.5
3.0
474
473
474
25
8
140
62
0.5
0.8
473
469
a
Dichloromethane (DCM) or acetonitrile (ACN) solution at room
temperature under argon (10−5 M). DCM glass at 77 K. The extreme
sensitivity of 5−7 to quenching by trace oxygen/impurities in
solutions at room temperature causes a large error of 25% for Φ
b
and τ. Highest energy vibronic luminescence peak (0−0 transition).
c
d
Maximum of the luminescence spectrum. λexc = 280−300 nm. Φ <
e
0.1% for 2−4 in DCM at room temperature. The luminescence decay
of 1−4 and 7 in DCM at 77 K is a biexponential function with
components of 20−40/140−380 μs (1−4), 200−250/1100−1300 μs
f
(5, 6), and 80/390 μs (7). Calculated radiative lifetime: τrad = τ/Φ.
At room temperature, (i) 1 exhibits blue phosphorescence
with 0−0 transition λ0−0 = 405 nm and the quantum yield Φ ≈
0.1%, (ii) 2−4 are non-emissive with Φ < 0.1%, and (iii) 5−7
exhibit green phosphorescence with λ0−0 = 473−478 nm, Φ =
3−25%, observed excited-state lifetime τ = 62−350 μs, and
calculated radiative lifetime τrad = τ/Φ = 0.5−3.5 ms (Figure 6
and Table 4; Figure S8 in the Supporting Information). The
excitation and absorption spectra of the complexes match
(Figure S9, Supporting Information). The monoexponential
luminescence decays of 5−7 confirm the presence of one
emissive center in solution at room temperature (Figure S10,
Supporting Information).
To our knowledge, 5 and 6 have some of the highest
radiative lifetimes of the excited state at room temperature
(2.5−3.5 ms) and the highest excited-state lifetimes at 77 K (up
The phosphorescence spectra of 5−7 at room temperature
are solvent-independent: for example, λ0−0 and λmax blue-shift
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Organometallics
Article
to 1.3 ms) reported for cyclometalated Ir(III) complexes.39,45
We consider that, in 5 and 6, a π-conjugated fluorenyl
chromophore stabilizes the LC state, while the weak electron
acceptor pyrazole destabilizes the CT state, thereby reducing
the LC−CT coupling and increasing both the LC character and
the radiative lifetime of the excited state [in iridium(III)
complexes, LC states have longer radiative lifetime than CT
states do38,39,45].
The radiative lifetime of the complex decreases from 5 and 6
(2.5−3.5 ms) to 7 (0.5−0.8 ms) because the indazole (7)
stabilizes the CT state and promotes the LC−CT coupling
more than the pyrazole does (5, 6) (recall that indazole is a
stronger electron acceptor than pyrazole, Table 2). Variation of
the isocyanide from 5 (CNtBu) to 6 (CNPh*) does not
significantly change the spectrum (λ0−0, λmax), Φ, τ, or τrad
(Table 4), thereby confirming that the emissive state of the
complex is N-arylazole-centered.
0.5% methanol in CH2Cl2 removed the impurities. Elution with 1.0−
1.5% methanol in CH2Cl2 recovered the product as a colorless eluate
(brown and blue impurities followed 2 and 4, respectively, while a
yellow impurity preceded 6; these impurities were easily separated).
Purification by chromatography gave the pure product, unless stated
otherwise. The complexes were often isolated as oils that solidified on
standing. 1−6 are non-emissive in the powder form. 7 exhibits weak
yellow phosphorescence in the powder form. Further details are
provided below.
Complex 1. [(C∧N)2Ir(μ-Cl)]2 (C∧N = 1-phenylpyrazole;31 100
mg, 0.097 mmol), AgCF3SO3 (55 mg, 0.214 mmol), and tert-butyl
isocyanide (0.5 mL, 365 mg, 4.4 mmol) gave a white solid: 114 mg
(0.144 mmol, 74%). Anal. Calcd for C29H32F3IrN6O3S (MW 793.88):
1
C, 43.87; H, 4.06; N, 10.59. Found: C, 44.16; H, 4.00; N, 10.29. H
NMR (400 MHz, CD2Cl2): δ 8.27 (d, J = 2.8 Hz, 2H), 7.92 (d, J = 2.8
Hz, 2H), 7.34 (dd, J = 8.0, 0.8 Hz, 2H), 7.08 (td, J = 8.0, 1.6 Hz, 2H),
6.92−6.82 (m, 4H), 6.19 (dd, J = 7.6, 1.2 Hz, 2H), 1.45 (s, 18H, tert-
butyl) ppm. 19F NMR (376 MHz, CD2Cl2): δ −78.92 (triflate) ppm.
ESI+ TOF MS: m/z 645.3 ({M − CF3SO3}+, 100%).
Complex 2. [(C∧N)2Ir(μ-Cl)]2 (C∧N = 1-phenylpyrazole;31 100
mg, 0.097 mmol) in CH2Cl2 (10 mL) AgCF3SO3 (58 mg, 0.226
mmol), and 2,6-dimethylphenyl isocyanide (195 mg, 1.49 mmol) gave
a white solid: 155 mg (0.174 mmol, 90%). Anal. Calcd for
C37H32F3IrN6O3S (MW 889.97): C, 49.93; H, 3.62; N, 9.44. Found:
C, 50.66; H, 3.65; N, 8.90. 1H NMR (400 MHz, CD2Cl2): δ 8.32 (d, J
= 3.2 Hz, 2H), 8.09 (d, J = 2.4 Hz, 2H), 7.41 (dd, J = 8.0, 0.8 Hz, 2H),
7.28 (t, J = 7.6 Hz, 2H), 7.19−7.11 (m, 6H), 6.95 (td, J = 7.6, 0.8 Hz,
2H), 6.87 (t, J = 2.4 Hz, 2H), 6.35 (dd, J = 7.6, 1.2 Hz, 2H), 2.18 (s,
12H, CH3) ppm. 19F NMR (376 MHz, CD2Cl2): δ −78.98 (3F,
triflate) ppm. ESI+ TOF MS: m/z 741.2 ({M − CF3SO3}+, 100%).
Complex 3. [(C∧N)2Ir(μ-Cl)]2 (C∧N = 1-(2′,4′-difluorophenyl)-
pyrazole;31 100 mg, 0.085 mmol), AgCF3SO3 (48 mg, 0.187 mmol),
and tert-butyl isocyanide (0.5 mL, 365 mg, 4.4 mmol) gave a white
solid: 119 mg (0.137 mmol, 81%). Anal. Calcd for C29H28F7IrN6O3S
(MW 865.84): C, 40.23; H, 3.26; N, 9.71. Found: C, 41.33; H, 3.45;
The phosphorescence spectra of 1 and 5, 6 resemble those of
the tris-cyclometalated analogues24,26,29 [Ir(N,C2′-1-phenyl-
pyrazolyl)3] and [Ir(N,C3′-1-(9′,9′-dimethyl-2′-fluorenyl)-
pyrazolyl)3], respectively; however, the radiative lifetimes of 5
and 6 (2.5−3.5 ms) are >25-fold higher than that of their
[Ir(C∧N)3] analogue (9724 or 59 μs29 at room temperature)
[we note that enhancement of excited-state lifetime by
isocyanide ligands was first reported for Ru(II) complexes18].
We consider that electron-withdrawing isocyanide ligands
strongly destabilize the (Ir−aryl)-to-azole CT state and
decouple it from the N-arylazole LC state, thereby increasing
the radiative lifetime from [Ir(C∧N)3] to [(C∧N)2Ir(CNR)2]+.
Conclusions. Iridium(III) isocyanide complexes with cyclo-
metalating N-arylazoles, [(C∧N)2Ir(CNR)2]+, exhibit extremely
wide redox and optical windows and very long excited-state
radiative lifetimes. Facile variation of the N-arylazole and
isocyanide ligands opens the way to redox-inert, transparent,
and high-energy phosphorescent organometallic iridium(III)
complexes.
1
N, 9.32. H NMR (400 MHz, CD2Cl2): δ 8.49 (d, J = 2.8 Hz, 2H),
7.93 (d, J = 2.4 Hz, 2H), 6.88 (t, J = 2.8 Hz, 2H), 6.74−6.65 (m, 2H),
5.68−5.61 (m, 2H), 1.49 (s, 18H, tert-butyl) ppm. 19F NMR (376
MHz, CD2Cl2): δ −78.89 (3F, triflate), −112.05 (d, JF−F = 6 Hz, 2F),
−123.95 (d, JF−F = 6 Hz, 2F) ppm. ESI+ TOF MS: m/z 717.2 ({M −
CF3SO3}+, 100%).
Complex 4. The reaction was performed with [(C∧N)2Ir(μ-Cl)]2
(C∧N = 1-(2′,4′-difluorophenyl)pyrazole;31 100 mg, 0.085 mmol),
AgCF3SO3 (48 mg, 0.187 mmol), and 2,6-dimethylphenyl isocyanide
(200 mg, 1.52 mmol). After chromatography, the product still
contained impurities; therefore, it was recrystallized. It was dissolved in
CH2Cl2 (3 mL) and poured into ether (30 mL) with stirring. The
product was filtered and washed with ether to give a white solid: 116
mg (0.121 mmol, 71%). Anal. Calcd for C37H28F7IrN6O3S (MW
961.93): C, 46.20; H, 2.93; N, 8.74. Found: C, 46.28; H, 2.67; N, 8.46.
1H NMR (400 MHz, CD2Cl2): δ 8.56 (d, J = 3.2 Hz, 2H), 8.14 (d, J =
2.4 Hz, 2H), 7.32 (t, J = 7.6 Hz, 2H), 7.19 (d, J = 7.6 Hz, 4H), 6.92 (t,
J = 2.8 Hz, 2H), 6.81−6.72 (m, 2H), 5.87−5.81 (m, 2H), 2.23 (s, 12H,
CH3) ppm. 19F NMR (376 MHz, CD2Cl2): δ −78.98 (3F, triflate),
−111.38 (d, JF−F = 6 Hz, 2F), −123.43 (d, JF−F = 6 Hz, 2F) ppm. ESI+
TOF MS: m/z 813.2 ({M − CF3SO3}+, 100%).
EXPERIMENTAL SECTION
■
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 1. 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! [(C∧N)2Ir-
(μ-Cl)]2 was dissolved in CH2Cl2 (20 mL) and methanol (5 mL) at
room temperature. A solution of AgCF3SO3 (excess, Aldrich) in
methanol (5 mL) was added dropwise. A precipitate of AgCl
immediately formed. The reaction mixture was stirred for 4 h. It
was filtered through a paper filter to remove AgCl and evaporated to
dryness (these operations were done in air). The resulting Ir(III) bis-
solvato complex was suspended in degassed CH2Cl2 (15 mL), and
isocyanide (excess, Aldrich) was added. The reaction mixture became a
solution, and its color changed from yellow to nearly colorless. It was
stirred at room temperature under argon for 96 h (for tert-butyl
isocyanide) or 48−72 h (for 2,6-dimethylphenyl isocyanide) to give a
solution. It was directly loaded on the chromatography column (silica,
12 g) to avoid rotavaporating foul-smelling isocyanides. Elution with
Complex 5. [(L)2Ir(μ-Cl)]2 (Supporting Information; 100 mg,
0.049 mmol), AgCF3SO3 (28 mg, 0.11 mmol), and tert-butyl
isocyanide (0.25 mL, 183 mg, 2.2 mmol) gave a white solid: 121
mg (0.093 mmol, 94%). Anal. Calcd for C67H88F3IrN6O3S (MW
1306.73): C, 61.58; H, 6.79; N, 6.43. Found: C, 61.64; H, 6.87; N,
1
6.17. H NMR (400 MHz, CD2Cl2): δ 8.38 (d, J = 2.8 Hz, 2H), 7.98
(d, J = 2.0 Hz, 2H), 7.45−7.38 (m, 2H), 7.34 (s, 2H), 7.33−7.26 (m,
2H), 7.27−7.21 (m, 4H), 6.97−6.92 (m, 2H), 6.60 (s, 2H), 2.02−1.92
(m, 4H), 1.93−1.83 (m, 4H), 1.37 (s, 18H, tert-butyl), 1.14−0.85 (m,
24H), 0.76 (t, J = 7.2 Hz, 6H), 0.64 (t, J = 6.8 Hz, 6H), 0.68−0.58 (m,
4H), 0.51−0.41 (m, 4H) ppm. 19F NMR (376 MHz, CD2Cl2): δ
−78.9 (3F, triflate) ppm. ESI+ TOF MS: m/z 1157.67 ({M −
CF3SO3}+, 100%).
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Organometallics
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Complex 6. [(L)2Ir(μ-Cl)]2 (Supporting Information; 100 mg,
0.049 mmol), AgCF3SO3 (30 mg, 0.117 mmol), and 2,6-
dimethylphenyl isocyanide (148 mg, 1.13 mmol) gave a white solid:
109 mg (0.078 mmol, 79%). Anal. Calcd for C75H88F3IrN6O3S (MW
1402.82): C, 64.21; H, 6.32; N, 5.99. Found: C, 64.47; H, 6.28; N,
(8) Dedeian, K.; Shi, J.; Forsythe, E.; Morton, D. C.; Zavalij, P. Y.
Inorg. Chem. 2007, 46, 1603.
(9) Smith, C. S.; Mann, K. R. J. Am. Chem. Soc. 2012, 134, 8786.
(10) Lai, S.-W.; Lam, H.-W.; Lu, W.; Cheung, K.-K.; Che, C.-M.
Organometallics 2002, 21, 226.
1
5.76. H NMR (400 MHz, CD2Cl2): δ 8.44 (d, J = 1.2 Hz, 2H), 8.17
(11) Sacksteder, L.; Lee, M.; Demas, J. N.; DeGraff, B. A. J. Am.
(d, J = 2.4 Hz, 2H), 7.45−7.39 (m, 4H), 7.34−7.21 (m, 8H), 7.10 (d, J
= 7.6 Hz, 4H), 6.97 (t, J = 2.4 Hz, 2H), 6.74 (s, 2H), 2.15 (s, 12H,
CH3), 2.04−1.94 (m, 4H), 1.94−1.84 (m, 4H), 1.15−0.85 (m, 24H),
0.76 (t, J = 7.2 Hz, 6H), 0.64 (t, J = 6.8 Hz, 6H), 0.69−0.59 (m, 4H),
0.57−0.45 (m, 4H) ppm. 19F NMR (376 MHz, CD2Cl2): δ −78.96
(3F, triflate) ppm. ESI+ TOF MS: m/z 1253.7 ({M − CF3SO3}+,
100%).
Chem. Soc. 1993, 115, 8230.
(12) 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.
(13) Villegas, J. M.; Stoyanov, S. R.; Reibenspies, J. H.; Rillema, D. P.
Organometallics 2005, 24, 395.
(14) Villegas, J. M.; Stoyanov, S. R.; Huang, W.; Rillema, D. P. Inorg.
Chem. 2005, 44, 2297.
(15) (a) Ng, C.-O.; Lo, L. T.-L.; Ng, S.-M.; Ko, C.-C.; Zhu, N. Inorg.
Chem. 2008, 47, 7447. (b) Ko, C.-C.; Siu, J. W.-K.; Cheung, A. W.-Y.;
Yiu, S.-M. Organometallics 2011, 30, 2701.
(16) Connor, J. A.; Meyer, T. J.; Sullivan, B. P. Inorg. Chem. 1979, 18,
1388.
Complex 7. [(C∧N)2Ir(μ-Cl)]2 (C∧N = 1-phenylindazole;32 90 mg,
0.073 mmol), AgCF3SO3 (42 mg, 0.163 mmol), and tert-butyl
isocyanide (0.35 mL, 255 mg, 3.1 mmol) gave a white solid: 112 mg
(0.125 mmol, 86%). Anal. Calcd for C37H36F3IrN6O3S (MW 894.00):
1
C, 49.71; H, 4.06; N, 9.40. Found: C, 50.13; H, 4.04; N, 9.08. H
NMR (400 MHz, CD2Cl2): δ 8.57 (s, 2H), 8.33 (d, J = 8.8 Hz, 2H),
8.10 (d, J = 8.0 Hz, 2H), 7.90 (d, J = 8.0 Hz, 2H), 7.81−7.74 (m, 2H),
7.56 (t, J = 7.6 Hz, 2H), 7.18−7.11 (m, 2H), 6.76 (td, J = 7.6, 0.8 Hz,
2H), 6.11 (dd, J = 7.6, 1.2 Hz, 2H), 1.45 (s, 18H, tert-butyl). 19F NMR
(376 MHz, CD2Cl2): δ −78.9 (3F, triflate). ESI+ TOF MS: m/z
745.26 ({M − CF3SO3}+, 100%).
(17) Larowe, J. E.; McMillin, D. R.; Stacy, N. E.; Tetrick, S. M.;
Walton, R. A. Inorg. Chem. 1987, 26, 966.
(18) Indelli, M. T.; Bignozzi, C. A.; Marconi, A.; Scandola, F. J. Am.
Chem. Soc. 1988, 110, 7381.
(19) Myrick, M. L.; De Armond, M. K. J. Phys. Chem. 1989, 93, 7099.
(20) Villegas, J. M.; Stoyanov, S. R.; Huang, W.; Lockyear, L. L.;
Reibenspies, J. H.; Rillema, D. P. Inorg. Chem. 2004, 43, 6383.
(21) 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.
(22) Jameson, D. L.; Blaho, J. K.; Kruger, K. T.; Goldsby, K. A. Inorg.
Chem. 1989, 28, 4312.
(23) Ayers, T.; Scott, S.; Goins, J.; Caylor, N.; Hathcock, D.; Slattery,
S. J.; Jameson, D. L. Inorg. Chim. Acta 2000, 307, 7.
(24) Sajoto, T.; Djurovich, P. I.; Tamayo, A.; Yousufuddin, M.; Bau,
R.; Thompson, M. E.; Holmes, R. J.; Forrest, S. R. Inorg. Chem. 2005,
44, 7992.
(25) Tamayo, A. B.; Garon, S.; Sajoto, T.; Djurovich, P. I.; Tsyba, I.
M.; Bau, R.; Thompson, M. E. Inorg. Chem. 2005, 44, 8723.
(26) Karatsu, T.; Ito, E.; Yagai, S.; Kitamura, A. Chem. Phys. Lett.
2006, 424, 353.
(27) (a) Treboux, G.; Mizukami, J.; Yabe, M.; Nakamura, S. Chem.
Lett. 2007, 36, 1344. (b) Yang, L.; Okuda, F.; Kobayashi, K.; Nozaki,
K.; Tanabe, Y.; Ishii, Y.; Haga, M.-a. Inorg. Chem. 2008, 47, 7154.
(28) He, L.; Duan, L.; Qiao, J.; Wang, R.; Wei, P.; Wang, L.; Qiu, Y.
Adv. Funct. Mater. 2008, 18, 2123.
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental techniques; synthesis of 9,9-dihexyl-2-bromo-
fluorene, ligand L, and complex [(L)2Ir(μ-Cl)]2; crystallo-
graphic data (Table S1); cyclic voltammograms (Tables S2 and
S3; Figures S1−S4); absorption spectra (Figures S5−S7);
emission spectra (Figure S8); excitation spectra (Figure S9);
luminescence decays (Figures S10 and S11); NMR spectra;
CIF of the crystal structures of 3 and 4, CCDC 909628 and
909629. This material is available free of charge via the Internet
at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
■
*Tel: +41 21 693 6124. Fax: +41 21 693 4111. E-mail: nail.
shavaleev@epfl.ch (N.M.S.); nicola.armaroli@cnr.it (N.A.);
mdkhaja.nazeeruddin@epfl.ch (M.K.N.).
(29) Sajoto, T.; Djurovich, P. I.; Tamayo, A. B.; Oxgaard, J.;
Goddard, W. A., III; Thompson, M. E. J. Am. Chem. Soc. 2009, 131,
9813.
Notes
The authors declare no competing financial interest.
(30) (a) Mydlak, M.; Bizzarri, C.; Hartmann, D.; Sarfert, W.; Schmid,
G.; De Cola, L. Adv. Funct. Mater. 2010, 20, 1812. (b) Costa, R. D.;
Ortí, E.; Bolink, H. J.; Graber, S.; Housecroft, C. E.; Constable, E. C. J.
Am. Chem. Soc. 2010, 132, 5978. (c) Sykes, D.; Tidmarsh, I. S.;
Barbieri, A.; Sazanovich, I. V.; Weinstein, J. A.; Ward, M. D. Inorg.
Chem. 2011, 50, 11323. (d) Ladouceur, S.; Fortin, D.; Zysman-
Colman, E. Inorg. Chem. 2011, 50, 11514.
ACKNOWLEDGMENTS
■
Financial support was given by the European Union (CELLO,
STRP 248043; https://www.cello-project.eu/) and the CNR
(MACOL, PM.P04.010).
REFERENCES
■
(31) Shavaleev, N. M.; Scopelliti, R.; Baranoff, E.; Gratzel, M.;
̈
(1) 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.
(2) Abdel-Shafi, A. A.; Bourdelande, J. L.; Ali, S. S. Dalton Trans.
2007, 2510.
(3) Wang, X.; Li, J.; Thompson, M. E.; Zink, J. I. J. Phys. Chem. A
2007, 111, 3256.
(4) Habibagahi, A.; Mebarki, Y.; Sultan, Y.; Yap, G. P. A.; Crutchley,
R. J. ACS Appl. Mater. Interfaces 2009, 1, 1785.
(5) Shavaleev, N. M.; Monti, F.; Costa, R.; Scopelliti, R.; Bolink, H.
Nazeeruddin, Md. K. Inorg. Chim. Acta 2012, 383, 316.
(32) Shavaleev, N. M.; Scopelliti, R.; Gratzel, M.; Nazeeruddin, Md.
̈
K. Inorg. Chim. Acta 2012, 388, 84.
(33) Correa, A.; Bolm, C. Adv. Synth. Catal. 2007, 349, 2673.
(34) (a) Nonoyama, M. J. Organomet. Chem. 1975, 86, 263.
(b) Sprouse, S.; King, K. A.; Spellane, P. J.; Watts, R. J. J. Am.
Chem. Soc. 1984, 106, 6647.
(35) Treichel, P. M.; Dirreen, G. E.; Mueh, H. J. J. Organomet. Chem.
1972, 44, 339.
(36) Cardona, C. M.; Li, W.; Kaifer, A. E.; Stockdale, D.; Bazan, G. C.
Adv. Mater. 2011, 23, 2367.
J.; Ortí, E.; Accorsi, G.; Armaroli, N.; Baranoff, E.; Gratzel, M.;
Nazeeruddin, Md. K. Inorg. Chem. 2012, 51, 2263.
̈
(37) (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) Song, Y.-H.; Chiu, Y.-C.; Chi, Y.; Cheng, Y.-M.; Lai, C.-
(6) Shavaleev, N. M.; Monti, F.; Scopelliti, R.; Armaroli, N.; Gratzel,
M.; Nazeeruddin, Md. K. Organometallics 2012, 31, 6288.
(7) Kuznetsov, M. L. Russ. Chem. Rev. 2002, 71, 265.
̈
466
dx.doi.org/10.1021/om300894m | Organometallics 2013, 32, 460−467

Organometallics
Article
H.; Chou, P.-T.; Wong, K.-T.; Tsai, M.-H.; Wu, C.-C. Chem. Eur. J.
2008, 14, 5423.
(38) Colombo, M. G.; Hauser, A.; Gudel, H. Inorg. Chem. 1993, 32,
̈
3088.
(39) Flamigni, L.; Barbieri, A.; Sabatini, C.; Ventura, B.; Barigelletti,
F. Top. Curr. Chem. 2007, 281, 143.
(40) Chin, C. S.; Eum, M.-S.; Kim, S. y.; Kim, C.; Kang, S. K. Eur. J.
Inorg. Chem. 2007, 372.
(41) Yang, C.-H.; Beltran, J.; Lemaur, V.; Cornil, J.; Hartmann, D.;
Sarfert, W.; Frohlich, R.; Bizzarri, C.; De Cola, L. Inorg. Chem. 2010,
̈
49, 9891.
(42) Djurovich, P. I.; Murphy, D.; Thompson, M. E.; Hernandez, B.;
Gao, R.; Hunt, P. L.; Selke, M. Dalton Trans. 2007, 3763.
(43) (a) Bacon, J. R.; Demas, J. N. Anal. Chem. 1987, 59, 2780.
(b) Demas, J. N.; DeGraff, B. A.; Coleman, P. B. Anal. Chem. 1999, 71,
793A. (c) Huo, C.; Zhang, H.; Zhang, H.; Zhang, H.; Yang, B.; Zhang,
P.; Wang, Y. Inorg. Chem. 2006, 45, 4735. (d) Borisov, S. M.; Nuss, G.;
Haas, W.; Saf, R.; Schmuck, M.; Klimant, I. J. Photochem. Photobiol. A:
Chem. 2009, 201, 128.
(44) (a) Koren, K.; Borisov, S. M.; Saf, R.; Klimant, I. Eur. J. Inorg.
Chem. 2011, 1531. (b) Koren, K.; Dmitriev, R. I.; Borisov, S. M.;
Papkovsky, D. B.; Klimant, I. ChemBioChem 2012, 13, 1184.
(45) (a) Dixon, I. M.; Collin, J.-P.; Sauvage, J.-P.; Flamigni, L.;
Encinas, S.; Barigelletti, F. Chem. Soc. Rev. 2000, 29, 385. (b) Williams,
J. A. G.; Wilkinson, A. J.; Whittle, V. L. Dalton Trans. 2008, 2081.
(c) You, Y.; Park, S. Y. Dalton Trans. 2009, 1267. (d) Ulbricht, C.;
Beyer, B.; Friebe, C.; Winter, A.; Schubert, U. S. Adv. Mater. 2009, 21,
4418. (e) Hu, T.; He, L.; Duan, L.; Qiu, Y. J. Mater. Chem. 2012, 22,
4206. (f) Costa, R. D.; Ortí, E.; Bolink, H. J.; Monti, F.; Accorsi, G.;
Armaroli, N. Angew. Chem., Int. Ed. 2012, 51, 8178.
(46) Lowry, M. S.; Hudson, W. R.; Pascal, R. A., Jr.; Bernhard, S. J.
Am. Chem. Soc. 2004, 126, 14129.
(47) Palmer, J. H.; Durrell, A. C.; Gross, Z.; Winkler, J. R.; Gray, H.
B. J. Am. Chem. Soc. 2010, 132, 9230.
(48) Palmer, J. H.; Brock-Nannestad, T.; Mahammed, A.; Durrell, A.
C.; VanderVelde, D.; Virgil, S.; Gross, Z.; Gray, H. B. Angew. Chem.,
Int. Ed. 2011, 50, 9433.
(49) Ayala, N. P.; Flynn, C. M., Jr.; Sacksteder, L.; Demas, J. N.;
DeGraff, B. A. J. Am. Chem. Soc. 1990, 112, 3837.
467
dx.doi.org/10.1021/om300894m | Organometallics 2013, 32, 460−467