Efficient enhancement of the visible-light absorption of cyclometalated Ir(III) complexes triplet photosensitizers with bodipy and applications in photooxidation and triplet-triplet annihilation upconversion

Article abstract of DOI:10.1021/ic302210b

We report molecular designing strategies to enhance the effective visible-light absorption of cyclometalated Ir(III) complexes. Cationic cyclometalated Ir(III) complexes were prepared in which boron-dipyrromethene (Bodipy) units were attached to the 2,2′-

Full text of DOI:10.1021/ic302210b

Article
pubs.acs.org/IC
Efficient Enhancement of the Visible-Light Absorption of
Cyclometalated Ir(III) Complexes Triplet Photosensitizers with
Bodipy and Applications in Photooxidation and Triplet−Triplet
Annihilation Upconversion
Jifu Sun, Fangfang Zhong, Xiuyu Yi, and Jianzhang Zhao*
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, E-208 West Campus, 2
Ling Gong Road, Dalian 116024, China
*
S Supporting Information
ABSTRACT: We report molecular designing strategies to
enhance the effective visible-light absorption of cyclometalated
Ir(III) complexes. Cationic cyclometalated Ir(III) complexes were
prepared in which boron−dipyrromethene (Bodipy) units were
attached to the 2,2′-bipyridine (bpy) ligand via −CC− bonds at
either the meso-phenyl (Ir-2) or 2 position of the π core of Bodipy
(
Ir-3). For the first time the effect of π conjugating (Ir-3) or
tethering (Ir-2) of a light-harvesting chromophore to the
coordination center on the photophysical properties was compared
in detail. Ir(ppy) (bpy) (Ir-1; ppy = 2-phenylpyridine) was used as
2
model complex, which gives the typical weak absorption in visible
−1
−1
range (ε < 4790 M cm in region > 400 nm). Ir-2 and Ir-3
showed much stronger absorption in the visible range (ε = 71 400 M cm−1 at 499 nm and 83 000 M−1 cm−1 at 527 nm,
respectively). Room-temperature phosphorescence was only observed for Ir-1 (λem = 590 nm) and Ir-3 (λem = 742 nm). Ir-3
gives RT phosphorescence of the Bodipy unit. On the basis of the 77 K emission spectra, nanosecond transient absorption
spectra, and spin density analysis, we proposed that Bodipy-localized long-lived triplet excited states were populated for Ir-2 (τT
−1
=
(
23.7 μs) and Ir-3 (87.2 μs). Ir-1 gives a much shorter triplet-state lifetime (0.35 μs). Complexes were used as singlet oxygen
1
1
O ) photosensitizers in photooxidation. The O quantum yield of Ir-3 (Φ = 0.97) is ca. 2-fold of Ir-2 (Φ = 0.52).
2
2
Δ
Δ
Complexes were also used as triplet photosensitizer for TTA upconversion; upconversion quantum yields of 1.2% and 2.8% were
observed for Ir-2 and Ir-3, respectively. Our results proved that the strong absorption of visible light of Ir-2 failed to enhance
production of a triplet excited state. These results are useful for designing transition metal complexes that show effective strong
visible-light absorption and long-lived triplet excited states, which can be used as ideal triplet photosensitizers in photocatalysis
and TTA upconversion.
INTRODUCTION
absorption of visible light and a long-lived triplet excited state
are highly desired.
■
4
2,43
Cyclometalated Ir(III) complexes have attracted much
attention owing to their applications in electroluminscence,
luminescent molecular probes,
ular arrays and photoinduced charge separation,
recently triplet−triplet annihilation (TTA) upconversion.
Normally cyclometalated Ir(III) complexes show weak
absorption of visible light and short triplet excited-state lifetimes
τ, a few microseconds).
plexes were used for electroluminescence, but they are not
1
−14
However, simply attaching a visible-light-absorbing organic
ligand to the coordination center could not guarantee effective
funneling of the excitation energy to the triplet excited
1
5−23
24−26
photocatalysis,
molec-
and more
2
7−30
16,43−47
3
1−33
state.
For example, 4,4-difluoro-4-bora-3a,4a-diaza-s-
indacene (boron−dipyrromethene, Bodipy) has been seminally
4
8,49
used to prepare Ru(II) and Ir(III) complexes,
but the
2
7,34−38
effective absorption of these complexes was not enhanced, that
(
Conventionally these com-
is, the excitation energy harvested by the ligand was not
4
8
effectively transferred to the triplet-state manifold.
A
suitable for application in the newly developed areas, such as
2
4,39,40
15,18,20,41
cyclometalated Ir(III) complex with Bodipy on the coordina-
tion ligand was reported, but application of the triplet excited
photocatalysis,
luminescent molecular probes,
33
and TTA upconversion, for which strong absorption of visible
light or long-lived triplet excited states are desired.
example, cyclometalated Ir(III) complexes were used for
49
4
2,43
state was not studied. The energy-transfer efficiency from the
For
singlet excited state of the ligand to the triplet excited state of
1
photocatalysis (H production and O sensitizing), but these
2
2
complexes are still limited to those with weak absorption of
visible light. Therefore, Ir(III) complexes with strong
Received: October 10, 2012
2
4
©
XXXX American Chemical Society
A
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Inorganic Chemistry
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a
Scheme 1. Synthesis Routes of Ir-1, Ir-2, and Ir-3
aThe complexes are cationic, and the counter anion PF6− was omitted for clarity. The molecular structure of the triplet acceptor perylene used in
TTA upconversion, the model triplet photosensitizers tetraphenylporphyrin (TPP) and methylene blue (MB) for photooxidation are also shown. (a)
2
,2′-Bipyridine, CH Cl /MeOH (2:1, v/v), Ar, reflux, 6 h. (b) Dry CH Cl , CF COOH, DDQ, BF ·OEt , NEt , argon, rt. (c) 5-Ethynyl-2,2′-
2
2
2
2
3
3
2
3
bipyridine, NEt , Pd(PPh ) Cl , PPh , CuI, argon, reflux, 8 h. (d) [Ir(ppy) ]Cl , CH Cl /MeOH (2:1, v/v), argon, reflux, 6 h. (e) Dry CH Cl ,
3
3
2
2
3
2
2
2
2
2
2
BF ·OEt , NEt , argon, rt. (f) NIS (1.0 equiv), rt. (g) 5-Ethynyl-2,2′-bipyridine, NEt , Pd(PPh ) Cl , PPh , CuI, argon, 60 °C, 12 h.
3
2
3
3
3
2
2
3
4
3,47
the complexes may be evaluated by application of the
complexes in triplet−triplet energy-transfer (TTET) process.
Recently, we prepared Ru(II) complexes with a coumarin
moiety and showed that the relative energy level of the ligand
and coordination center must be matched to ensure efficient
metalation concept,
i.e., the π core of the Bodipy
chromophore is directly attached to the Ir(III) coordination
center via a π-conjugation linker.
4
3,45,47
Both Ir-2 and Ir-3 show
strong absorption of visible light. Ir-3 shows the room-
temperature (RT) phosphorescence of Bodipy, but Ir-2 did not
show RT phosphorescence of the Bodipy unit. We found that
Ir-3 is more efficient than Ir-2 as triplet photosensitizer in
photooxidation and TTA upconversion. Our results may be
useful for designing new visible-light-absorbing cyclometalated
Ir(III) complexes and applications of these complexes in
photocatalysis, photovoltaics, and TTA upconversion.
5
0
energy transfer. However, it is clear that these molecular
design strategies need to be generalized with more exemplars.
Herein we demonstrate that the energy transfer from light-
absorbing ligand to the triplet excited-state manifold of the
Ir(III) complexes can be enhanced by attaching organic
chromophores to the coordination center via a π-conjugation
4
3,45,47
linker (CC triple bond).
With this method, the heavy
RESULTS AND DISCUSSION
atom effect of Ir(III) can be maximized and the excitation
energy can be efficiently funneled to the triplet excited states.
As a result, application of the Ir(III) complexes in photo-
catalysis or TTA upconversion will be enhanced.
■
Molecules Design and Synthesis. The principal molec-
ular design strategy of Ir(III) complexes Ir-2 and Ir-3 is to
compare the effect of the different connection profile of the
light-harvesting ligand to the coordination center.
Ir-2, Bodipy is connected at the meso phenyl group; thus, the
Ir(III) coordination center is isolated from Bodipy. For Ir-3,
however, the 2 position of the π core of the Bodipy
chromophore is connected to the coordination center via the
4
3,44,47,49
Following this line, we prepared two cyclometalated Ir(III)
complexes with Bodipy ligands (Ir-2 and Ir-3, Scheme 1). Ir-2
follows the conventional structural profile, i.e., the π core of the
Bodipy chromophore was not directly attached to the
For
49
4
9
coordination center. Ir-3, however, follows the direct
B
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Inorganic Chemistry
Article
4
7
CC bond. Thus, we expected that the heavy-atom effect in
Ir-3 is more significant than that in Ir-2. Bodipy was selected as
the light-absorbing ligand owing to its versatile derivatization
chemistry, strong absorption of visible light, and good
Previously a cyclometalated Ir(III) complex with structure
49
similar to Ir-2 was reported, but Bodipy-containing Ir(III)
complexes similar to the structural profile of Ir-3 were never
reported. A cyclometalated Ir(III) complex with dipyrrinato
ligands was reported with slightly smaller molar absorption
5
1−58
photostability.
coefficients (ε < 38 400 M− cm at 483 nm).
1
−1
44
Preparation of the Bodipy-containing ligands L2 and L3 were
carried out using Sonogashira coupling reactions. 5-Ethynyl-
Both of the ligands (L2 and L3) gave intense fluorescence in
the visible range (Figure 2a). The fluorescence quantum yields
2
,2′-bipyridine was used as the intermediate. Ir(III) complexes
59
were synthesized from the di-Ir(III) intermediate. All
complexes were obtained with satisfactory yields (for more
detail, see the Experimental Section). Ir-1 was prepared as the
model complex for photophysical studies.
(Φ ) of L2 and L3 were determined as 43.9% and 33.6%,
F
respectively (Table 1). Interestingly, L3 gives a more red-
shifted emission than L2. This is an indication that the π-
conjugation framework in L3 is larger than that in L2.
Ir-1 shows broad and structureless emission at 590 nm
Steady-State Electronic Spectroscopy (Absorption
62
and Emission). L2 shows strong absorption at 499 nm (ε =
(
Figure 2b). Ir-2 and Ir-3 give blue-shifted emission at 514
1
−1
8
6 400 M− cm ), which is similar to the Bodipy chromophore
and 553 nm, respectively. Emission bands of Ir-2 and Ir-3 are
drastically narrower than that of Ir-1. Weak emission at 742 nm
was observed for Ir-3. The emission wavelengths of Ir-2 and Ir-
(
see Figure S29, Supporting Information). For L3, however, the
absorption is red shifted by 28 nm and ε decreased to 58 500
−
1
−1
M
cm (Figure 1a). Absorption of L2 and L3 shows a
3
are close to emission of L2 and L3. Thus, the major emission
bands of Ir-2 and Ir-3 were assigned to emission of Bodipy
ligands. The minor emission band of Ir-3 at 742 nm is due to
4
7−49
the RT phosphorescence of the Bodipy unit.
phosphorescence of the Bodipy unit was not observed for Ir-
. Furthermore, upon excitation at 507 nm, where both
RT
2
complexes Ir-2 and Ir-3 show the same ε value, much weaker
fluorescence was observed for Ir-3 than that for Ir-2 (Figure
2
c).
The emission properties of the complexes were studied
under different atmospheres (Figure 3). For Ir-1, the broad,
structureless emission band can be quenched by 81.6% in
aerated solution compared to that in deaerated solution. In O2-
saturated solution, emission was quenched by 95.3%. This is
Figure 1. (a) UV−vis absorption spectra of ligands L1, L2, and L3.
(
b) UV−vis absorption spectra of complexes Ir-1, Ir-2, and Ir-3. c =
−5
1
.0 × 10 M in CH CN at 20 °C.
3
63−66
typical for phosphorescent complexes.
The luminescence
lifetime of Ir-1 was determined as 0.30 μs, which confirmed the
phosphorescence feature of the emission of Ir-1.
In contrast to Ir-1, emission of Ir-2 is not sensitive to O2
substantial difference in the range of 250−400 nm. Absorption
of L3 is red shifted compared to the unsubstituted Bodipy, but
L2 shows a similar absorption band in the visible region to
unsubstituted Bodipy (see Figure S29, Supporting Informa-
tion). Thus, we conclude that the Bodipy unit in L3 is in π
conjugation with bpy ligand but not in L2.
(
Figure 3b). The luminescence lifetime of Ir-2 was determined
−
1
as 0.9 ns; the Stokes shift is small (15 nm, 585 cm ), which
confirmed the fluorescence feature of the emission. As proof,
the emission lifetime of Ir-2 is much shorter than the free
ligand L2 (1.9 ns). Fluorescence of the ligand in Ir-2 was
Ir-2 shows the absorption profile in the visible range similar
to L2 (Figure 1b). For Ir-3, however, absorption in visible
−1
−1
range is enhanced (ε = 83 000 M cm at 527 nm) compared
to L3. Thus, the electronic interaction between Bodipy and the
quenched (Φ
F
= 1.8%), compared to the free ligand L2 (Φ =
F
43.9%).
4
5,46,60,61
Ir(III) coordination center is significant for Ir-3.
Ir-1
The O sensitivity of the emission bands confirms that the
2
shows absorption in the UV range, which is typical for
emission of Ir-3 at 553 nm is due to the fluorescence, but the
5
9,62−65
13
cyclometalated Ir(III) complexes.
To the best of our
emission at 742 nm is phosphorescence (Figure 3c).
knowledge, very few cyclometalated Ir(III) complexes show
such intense absorption in the visible range like Ir-3.
Previously a Bodipy-containing cyclometalated Ir(III) complex
was reported, but the phosphorescence of Bodipy can be
1
0,43
−
6
Figure 2. (a) Emission spectra of ligands L2 (λ = 500 nm) and L3 (λ = 510 nm), c = 1.0 × 10 M in CH CN at 20 °C. (b) Normalized emission
ex
ex
3
spectra of complexes Ir-1 (λ = 410 nm), Ir-2 (λ = 500 nm), and Ir-3 (λ = 510 nm); note the RT phosphorescence of Ir-3 (λ = 742 nm), c =
.0 × 10 M in CH CN at 20 °C. (c) Comparison of the emission intensity of complexes Ir-2 and Ir-3 under the same conditions (λ = 507 nm;
ex
ex
ex
em
−6
1
3
ex
the absorbance of both Ir-2 and Ir-3 at 507 nm is 0.06).
C
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Inorganic Chemistry
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Table 1. Photophysical Properties of the Ligands and Cyclometalated Ir(III) Complexes
e
triplet-state lifetime
luminescence lifetime
a
b
c
d
f
g
compounds
λabs/nm
ε
λem /nm
Φ /%
43.9
τ /μs/(N )
τT/ns/(air)
τL/(RT)
τL/(77 K)
T
2
L2
499
527
255
499
527
8.64
5.85
4.99
7.14
8.30
512
565
590
514
h
h
1.9 ns
h
L3
33.6
4.5
h
h
3.5 ns
h
Ir-1
Ir-2
Ir-3
0.35
23.7
87.2
57.8
264.6
303.3
0.30 μs
0.9 ns
4.8 μs
2.8 ns
1.8
i
553/742
0.3/0.03
2.6 ns/−
3.9 ns/4.5 ms
a
−5
b
4
−1
−1
Maxima UV−vis absorption wavelength in CH CN (1.0 × 10 M, 20 °C). Molar absorption coefficient at absorption maxima. ε = 10 M cm .
Maxima emission wavelength in CH CN (1.0 × 10 M, 20 °C). Luminescence quantum yields in CH CN (20 °C) with complex
3
c
−5
d
3
3
Ru(dmb) [PF ] (Φ = 7.3% in CH CN) and 2,6-diiodo-1,3,5,7-tetramethyl-8-phenyl-4,4-difluoroboradiazaindacene (Φ = 2.7% in CH CN) as
3
6
2
p
3
F
3
e
−5
f
−5
g
standard. Measured by transient absorption in CH CN (1.0 × 10 M, 20 °C). In CH CN (1.0 × 10 M, 20 °C). In EtOH/MeOH (4:1, v/v, 1.0
10 M). Not applicable. Too weak to be determined accurately.
3
3
−5
h
i
×
Figure 3. Emission spectra of the complexes in N -, air-, and O -saturated solution. (a) Ir-1 (λ = 410 nm, λ = 590 nm). (b) Ir-2 (λ = 500 nm,
2
2
ex
em
ex
−
5
λem = 514 nm). (c) Ir-3 (λex = 510 nm, λem = 553 and 742 nm). c = 1.0 × 10 M in CH CN at 20 °C.
3
49
observed only at 77 K. The photophysical properties of the
ligands and cyclometalated Ir(III) complexes are listed in Table
1.
Excitation spectra of the complexes were also studied
Supporting Information, Figure S30). For Ir-2, the MLCT
(
absorption band is less efficient than the Bodipy band to
produce the Bodipy ligand fluorescence. Therefore, we propose
1
that the energy transfer from the MLCT* state to the
1
Bodipy* state is nonefficient, possibly due to the lower energy
1
1
level of the relaxed MLCT* state than the Bodipy* state or
1
3
1
the fast MLCT*→ MLCT* process; therefore, MLCT* →
1
Bodipy* is nonefficient. It should be pointed out that it is
1
difficult to study the energy level of the relaxed MLCT* state
(
note it is not the excitation energy gap), which is
1
3
nonluminescent due to the fast MLCT* → MLCT* process.
For Ir-3, similar results were observed (Figure S30, Supporting
Information). The excitation spectrum with an emission
wavelength at 742 nm was also recorded. We found that the
Bodipy absorption band in the region of 450−600 nm is
efficient to produce the emission at 742 nm, which is similar to
the MLCT absorption band. Therefore, we propose that both
Figure 4. Nanosecond time-resolved transient difference absorption
spectra: (a) Ir-1 (λ = 355 nm); (b) decay trace of Ir-1 at 610 nm; (c)
ex
3
3
1
3
−5
the MLCT → Bodipy* and Bodipy* → Bodipy* processes
are efficient.
Ir-3 (λ = 532 nm); (d) decay trace of Ir-3 at 530 nm. c = 1.0 × 10
ex
M in deoxygenated CH CN at 20 °C.
3
Nanosecond Time-Resolved Transient Difference
Absorption Spectroscopy. In order to study the triplet
excited state of the complexes, the nanosecond time-resolved
transient difference absorption spectra were studied (Figure 4).
Upon pulsed laser excitation, transient absorption (TA) bands
at 378 and 763 nm were observed for Ir-1 (Figure 4a). The
bleaching band at 618 nm is due to the phosphorescence of Ir-
the triplet excited state of Ir-3 is localized on the Bodipy ligand,
not on the Ir(III) coordination center. The lifetime of Ir-3 was
determined as 87.2 μs, much longer than Ir-1 (0.35 μs).
The TA spectrum of Ir-2 is similar to that of Ir-3, with the
bleaching band in the slightly blue-shifted range (see Figure
S33, Supporting Information). The lifetime of the transient was
determined as 23.7 μs (Table 1), which is close to a similar
1
(Figure 2b). The lifetime was 0.35 μs (Figure 4b).
49
For Ir-3, the positive transient absorption in the range of
Bodipy-containing Ir(III) complex (25 μs).
6
00−750 nm is more significant than Ir-1 (Figure 4c). The
Emission Spectra at 77 K. The luminescence of the
complexes at 77 K was studied (Figure 5). For Ir-1, the
emission is broad and structureless at 77 K, which is similar to
bleaching band for Ir-3 is located at 526 nm, which is in good
agreement with the steady-state absorption (Figure 1b). Thus,
D
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Inorganic Chemistry
Article
3
49
2
can be recognized as a Bodipy-localized IL state. This
conclusion is in agreement with the time-resolved transient
difference absorption spectroscopy (Figure S33, Supporting
Information, and Figure 4) as well as quenching of the MLCT
emission of the coordination center in Ir-2 and Ir-3 (Figure 2
and Scheme 2) because Bodipy shows a T state with a much
1
Scheme 2. Qualitative Jablonski Diagram for the
Photophysical Process of the Ir(III) Complexes Exemplified
a
with Ir-3
Figure 5. Normalized emission spectra of the Ir(III) complexes at RT
(
20 °C) and 77 K in EtOH/MeOH mixed solvent (4:1, v/v): (a) Ir-1,
λex = 405 nm; (b) Ir-2, λex = 500 nm; (c) Ir-3, λex = 510 nm, spectra
were normalized at 742 nm; (d) Ir-3, λ = 510 nm, fluorescence of Ir-
ex
3
at 553 nm is normalized, indicating the greatly increased
−5
phosphorescence at 77 K. c = 1.0 × 10 M.
a
Solid lines represent excitation or radiative decay; dotted lines
3
that at RT (Figure 5a). However, the emission at 77 K is blue
shifted by 62 nm compared to that at RT. This large thermally
represent non-radiative processes. Note the MLCT phosphorescence
is quenched by the low-lying Bodipy* state. IC stands for internal
conversion, and ISC stands for intersystem crossing.
3
−
1
induced Stokes shift (ΔE = 2100 cm ) is an indication of the
S
3
32
MLCT feature of the emissive triplet excited state of Ir-1.
The luminescence of Ir-2 at 77 K is located at 511 nm, which
is very close to that at RT. The luminescence lifetime at 77 K is
.8 ns, compared to that at RT (0.9 ns). The lifetime suggests
lower energy level than the Ir(III) MLCT state. Similar spin
density was observed for Ir-3 (Figure 6). Thus, different from
2
Ir-1, the T excited states of both Ir-2 and Ir-3 can be identified
as a IL excited state. This conclusion is in full agreement with
the transient absorption spectroscopy.
The photophysical processes involved in the Ir(III)
complexes can be illustrated in Scheme 2. For Ir-1, the
1
3
that the emission is fluorescence not phosphorescence.
Furthermore, a minor emission band at 757 nm was observed
at 77 K. This emission band is most probably due to the
49
phosphorescence of the Bodipy unit.
Emission of Ir-3 at 77 K is drastically different from that at
RT (Figure 5c and 5d). The emission band at 553 nm becomes
much weaker than the emission band at 742 nm. The lifetime
of the emission band at 742 nm was determined as 4.5 ms at 77
K; it is an indication of the phosphorescence of the organic
1
MLCT* state is populated upon photoexcitation. With the
3
heavy-atom effect of the Ir(III) atom, the MLCT* excited
3
state is populated. The MLCT* state is emissive; thus, Ir-1
1
gives phosphorescence. For Ir-2, the Bodipy* state energy
1
III
level is lower than that of the MLCT* state (resides on the Ir
6
7,68
chromophore.
coordination center). However, based on the excitation
Spin Density Surfaces of the Complexes. The spin
1
1
spectrum, the MLCT → IL internal conversion is non-
density of the lowest-lying triplet state can be indicated by the
1
efficient. Thus, the energy transfer from the Bodipy* state to
3
2,43−47,50
localization of the spin density of the complexes.
1
3
the MLCT* state is frustrated; the population of the Bodipy*
The spin density of Ir-1 is localized on ppy and bpy as well as
the Ir(III) atom (Figure 6). This spin density profile is in
agreement with the MLCT/IL triplet excited state of
50
state is dependent on the ISC capability of the complexes.
1
The ISC efficiency for the transformation from the Bodipy*
3
state to the Bodipy* state can be indicated either by the
6
2
Ir(ppy) (bpy). For Ir-2, however, the spin density is mainly
2
residual fluorescence of the Bodipy unit or the property of the
localized on the Bodipy ligand; the Ir(III) center and the bpy
3
Bodipy*, such as the emissive or nonemissive feature.
ligands make little contribution. Thus, the T excited state of Ir-
1
Photooxidation of 1,5-Dihydroxynaphthalene with
1
the Ir(III) Complexes as Singlet Oxygen ( O ) Photo-
2
1
sensitizer. Next, we will use singlet oxygen ( O ) photo-
2
3
sensitizing to study the efficiency of producing the Bodipy*
triplet excited state in Ir-2 and Ir-3.
To evaluate the 1O -producing capability of the Ir(III)
complexes, 1,5-dihydroxynathalene (DHN) was used as the O
2
1
2
2
6,69,70
1
scavenger (Scheme 3).
DHN can be oxidized by O to
2
produce juglone, which is a versatile intermediate for
71
preparation of antitumor reagents. Previously, production of
naphthoquinone is based on catalytic oxidation of naphthalene,
which is not environmentally benign. Photooxidation of DHN
can be monitored by the decrease of the absorption of DHN at
301 nm. The velocity of the photooxidation is proportional to
Figure 6. Isosurfaces of the spin density of Ir-1, Ir-2, and Ir-3 at the
optimized T excited-state geometry (isovalue ± 0.0004) calculated at
1
1
the B3LYP/6-31G/LANL2DZ level with Gaussian 09W.
the capability of O2 production. Previously, conventional
E
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Inorganic Chemistry
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Scheme 3. Mechanism of the Photooxidation of DHN with a
1
26
Singlet Oxygen ( O ) Photosensitizer
2
Figure 8. Plots of chemical yields of juglone vs irradiation time for
Ir(III) complexes were used for 1O2 photosensitizing.26
However, those complexes show very weak absorption of
visible light, which is the disadvantage of conventional Ir(III)
complexes.
The Ir(III) complexes were used as triplet photosensitizers
for photooxidation of DHN (Figure 7). More significant
1
2
photooxidation of DHN using Ir (III) complexes, MB, and TPP as O
photosensitizers.
Table 2. Photophysical and Photooxidation of DHN-Related
Parameters of the Ir(III) Complexes, MB, and TPP,
Measured in CH Cl /CH OH (9:1, v/v) mixed solvent (20
2
2
3
°
C)
λabs
yield
i
a
b
c
d
e
f
nm
ε
τT μs
kobs
νi
ΦΔ
(%)
g
Ir-1
Ir-2
Ir-3
MB
TPP
256
504
534
656
416
50 700
75 590
95 380
131 030
0.35
23.7
7.8
21.5
85.5
48.1
81.1
15.6
43.0
0.92
0.52
0.97
0.57
0.65
37.4
71.8
91.4
77.4
90.9
h
h
87.2
83.3
82.5
171.0
96.2
284 360
162.2
a
b
Absorption maxima. Molar absorption coefficient at the absorption
−1
−1
c
maxima. ε= M cm . Triplet excited-state lifetimes; measured by
nanosecond time-resolved transient absorption, 20 °C. Pseudo-first-
order rate constant, ln(C /C ) = -kobst. In 10 min . Initial
d
−3
−1
e
t
0
−7
−1
consumption rate of DHN, v = k [DHN]. In 10 M min .
i
obs
f
1
g
Singlet oxygen ( O ) generation quantum yield. Literature value Φ
2
Δ
26 h
=
0.97. Measured in methanol using Rose Bengal (RB, Φ = 0.80 in
Δ
i
CH OH) as a reference. Chemical yield of juglone after photoreaction
3
for 40 min.
Figure 7. Photooxidation of DHN using Ir(III) complexes, MB, and
were also determined (Table 2). The Φ value of Ir-3 (Φ =
Δ
Δ
1
TPP as O photosensitizers. Change of UV−vis absorption spectra
2
9
7%) is almost 2-fold of Ir-2 (Φ = 52%, Table 2).
Δ
using Ir-1 (a), Ir-2 (b), and Ir-3 (c) as sensitizers. (d) Plots of ln(C /
t
Triplet−Triplet Annihilation Upconversion. The com-
C ) against irradiation time (t) for photooxidation. Irradiated with a 35
0
−
2
plexes described herein were used as triplet photosensitizers for
another triplet−triplet energy-transfer (TTET) process, i.e.,
TTA upconversion. TTA upconversion has attracted much
attention due to its advantage over other upconversion
W xenon lamp (20 mW cm at the photoreactor). c [photosensitizer]
2.0 × 10 M in CH Cl /CH OH (9:1, v/v) at 20 °C.
−5
=
2 2 3
3
3,72−80
methods,
such as upconversion with two-photon
1
81
82−85
photooxidation with Ir-2 and Ir-3 as O photosensitizer was
absorption dyes or rare earth materials.
TTA upconver-
2
observed than that with Ir-1. Photooxidation of DHN with
sion requires triplet photosensitizer for absorbing of the
excitation energy and triplet acceptor for the upconverted
emission. The energy is transferred from the photosensitizer to
the acceptor by TTET process; then the singlet excited state of
the acceptor will be produced and the fluorescence from the
acceptor can be observed. Previously, a cyclometalated Ir(III)
complex, with weak absorption in the visible range, was used as
1
different O photosensitizers can be quantitatively compared
2
by plotting ln(C /C ) against the irradiation time. Oxidation
t
0
rate constants can be derived from the slope of the curves
2
6
(
Figure 7d). On the basis of the results, Ir-2 and Ir-3 are
1
more efficient O photosensitizers than Ir-1 due to the weak
2
absorption of Ir-1 in the visible range. Therefore, production of
juglone with Ir-2 and Ir-3 is more efficient than that with Ir-1
as the triplet photosensitizer.
Interestingly, the Kobs value of Ir-3 is 4-fold of Ir-2. The large
Kobs value of Ir-3 may indicate that the ISC of Ir-3 is more
efficient than that of Ir-2. The performance of Ir-3 is much
better than a known triplet photosensitizer methylene blue
31
a triplet photosensitizer for TTA upconversion. Recently, we
reported coumarin-containing Ir(III) complexes as triplet
32
photosensitizers for TTA upconversion as well as some
86
organic triplet photosensitizers. To the best of our knowl-
edge, strong absorption of Bodipy in visible range has not been
used in Ir(III) complexes for TTA upconversion.
(
MB) (Figures 7 and 8 and Table 2).
The yields of the photooxidation with different photo-
Upon 532 nm laser excitation (Figure 9), the complexes give
emission similar to that observed in Figure 2. Upon addition of
perylene, blue emission in the 445−470 nm range was observed
with Ir-3 as the triplet photosensitizer. Excitation of the
photosensitizer or acceptor perylene alone at 532 nm did not
produce any blue emission band. Thus, TTA upconversion was
sensitizers were studied (Figure 8). Ir-3 is more efficient than
Ir-2. Moreover, the chemical yield of juglone with Ir-3 as the
triplet photosensitizer is higher than that with Ir-2. O2
1
quantum yields (Φ ) of the different triplet photosensitizers
Δ
F
dx.doi.org/10.1021/ic302210b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 9. Upconversion with Ir-1, Ir-2, Ir-3, and Ru(dmb) [PF ]
6 2
Figure 11. (a) Delayed fluorescence of perylene with Ir-3 as triplet
photosensitizer for TTA upconversion. Ir-3 was selectively excited at
532 nm, and decay of the emission of perylene was monitored at 445
nm. (b) Prompt fluorescence decay of perylene determined in a
different experiment (excited with a picosecond 405 nm laser, decay of
3
(
Ru-1) as triplet sensitizers and perylene (Py) as triplet acceptor,
−2
excited by a 532 nm laser (continuous wave, 70 mW cm ). (a)
Emission of the complexes alone with a 532 nm laser excitation. (b)
Upconversion emission of the mixtures of the sensitizers and perylene
upon selective excitation of sensitizers with a 532 nm laser. c
−5
the emission at 445 nm was monitored). c [Sensitizers] = 1.0 × 10
−5
−5
−5
[
sensitizers] = 1.0 × 10 M and c [perylene] = 5.0 × 10 M in
M and c [Perylene] = 5.0 × 10 M in deaerated CH CN at 20 °C.
3
deaerated CH CN at 20 °C.
3
the emission in the upconversion experiment is the delayed
fluorescence, which is characteristic for the TTA upconver-
confirmed. No upconversion was observed with Ir-2 or Ir-1 as
the triplet photosensitizer due to the unmatched excitation
75,86b,c
sions.
Thus, TTA upconversion with Ir-3 as the triplet
wavelength. The TTA upconversion quantum yield (Φ ) with
photosensitizer was unambiguously confirmed. Similarly
delayed fluorescence was observed with Ir-2 as the triplet
photosensitizer (see Figure S47, Supporting Information).
In order to study the TTET efficiency of TTA upconversion,
quenching of the triplet excited states of the photosensitizers by
triplet acceptor perylene was studied (Figure 12). The KSV
UC
Ir-3 as the triplet photosensitizer was determined as 2.8%.
Considering the strong absorption of Ir-3, the upconversion
capability is significant.
We found that TTA upconversion can be observed with
excitation of Ir-3 by ambient light (noncoherent), for example,
the excitation light from a spectrofluorometer (Figure 10). We
Figure 12. Stern−Volmer plots generated from triplet excited-state
Figure 10. Upconversion excited by a spectrofluorometer (507 nm,
−2
lifetime (τ ) quenching of Ir-1, Ir-2, and Ir-3 measured as a function
T
noncoherent, 4.5 mW cm ) with Ir-2 and Ir-3 as triplet sensitizers
and perylene as triplet acceptor. Ir-2 and Ir-3 give the same
absorbance at 507 nm (A = 0.44). (a) Emission spectra of
photosensitizers alone. (b) Upconversion emission spectra of mixtures
of the concentration of quencher (perylene). Triplet-state lifetimes
τ ) were measured by nanosecond time-resolved transient difference
(
T
−
5
absorption (λ = 532 nm) c [sensitizers] = 1.0 × 10 M in deaerated
ex
−5
CH CN at 20 °C.
3
of the sensitizers and acceptor. c [sensitizers] = 1.0 × 10 M and c
−5
[
perylene] = 5.0 × 10 M in deaerated CH CN at 20 °C.
3
value of Ir-3 is ca. 1000-fold of Ir-1. The quenching constant
for Ir-3 is 2-fold of Ir-2 (Table 3). The efficient TTET of Ir-3
selected 507 nm as the excitation wavelength at which both Ir-2
and Ir-3 show the same ε value. Thus, the TTA upconversion
of Ir-2 and Ir-3 can be compared directly by the upconverted
emission intensity. The upconverted emission intensity with Ir-
Table 3. Upconversion-Related Parameters of the Ir(III)
a
Complexes and Ru-1
3
as the triplet photosensitizer is almost 2-fold of Ir-2 (Figure
b
K /(10 M−1)e k /(10 M s−1
3
9
−1
f
g
sensitizers ΦUC/(%)
)
τDF /μs
sv
q
10b). This result indicated that the triplet excited state of Ir-3 is
c
Ir-1
Ir-2
Ir-3
Ru-1
0.3
1.2
2.8
0.6
2.8
1243.4
2051.5
3.9
8.0
52.5
23.5
5.3
128.8
21.3
19.4
83.4
more efficiently populated than Ir-2. Herein the T state
1
c
lifetime will not have a substantial difference on the
upconversion quantum yield because the lifetimes of both Ir-
d
c
2
and Ir-3 are much longer than the required lifetime for an
76a,b,77
efficient diffusion-controlled process.
a
−5
b
In CH CN, 1.0 × 10 M, 20 °C. Upconversion quantum yields;
3
In order to confirm the TTA upconversion, the luminescence
lifetimes of the blue emission in the TTA upconversion
experiments were measured (Figure 11). The luminescence
lifetime was determined as 19.4 μs with Ir-3 as the triplet
photosensitizer. In a different experiment, the lifetime of the
prompt fluorescence of perylene was determined as 4.0 ns. The
exceptionally long-lived lifetime of luminescence confirmed that
measured with 2-iodo-boron-dipyrromethene as the standard (Φ =
F
c
d
0
.036 in CH CN). Excited by a 473 nm laser. Excited by a 532 nm
laser. Stern−Volmer quenching constants (K ) of the quenching of
lifetimes of the triplet excited states of Ir(III) complexes by perylene.
3
e
sv
f
g
Bimolecular quenching constants (k ), K = k τ. Delayed
q
sv
q
fluorescence lifetimes observed in the TTA upconversion with
complexes as triplet photosensitizer and perylene as triplet acceptor.
G
dx.doi.org/10.1021/ic302210b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
1
may be responsible for the significant TTA upconversion than
the other triplet photosensitizers. The data of a benchmark
triplet photosensitizer for TTA upconversion, Ru(dmb) [PF ]
Bodipy* singlet excited state is produced. Note that Bodipy*
1
→ MLCT energy transfer is impossible due to the lower
energy level of the Bodipy* state than that of the MLCT
1
1
3
6 2
3
1
(
Ru-1), is also presented in Table 3 for comparison.
Upconversion is clearly visible with the unaided eye (Figure
state. Bodipy* is produced by the ISC from the Bodipy*
state. The heavy-atom effect is crucial for the process. The
triplet excited state of perylene was populated via the TTET
between the triplet photosensitizer (Ir(III) complexes) and
perylene. TTA of perylene as the triplet excited state will
produce the singlet excited state. The radiative decay from the
S1 state of perylene produced the delayed fluorescence, which
has been proved by measurement of the luminescence lifetime
1
3). For Ir-2 and Ir-3, the emission color changed drastically
(
4
for Ir-3, the lifetime of the delayed fluorescence is 19.4 μs vs
.0 ns for the prompt fluorescence).
CONCLUSION
■
We demonstrated the molecular designing method to enhance
the effective visible-light absorption of Ir(III) complexes.
Simply attaching an organic chromophore to the Ir(III)
complex does not necessarily guarantee effective visible-light
absorption, that is, the complex gives strong absorption of
visible light but the excitation energy may be not efficiently
transferred to the triplet excited state of the complex. In this
case the strong absorption of the complex is useless. We proved
that the π core of the light-harvesting organic chromophore
must be connected to the Ir(III) coordination center via a
conjugation linker, such as the −CC− bond. This strategy
was proved by preparation of two cationic cyclometalated
Figure 13. Photographs of the upconversions: (a) Ir(III) complexes
alone; (b) upconversion (mixed solution with perylene). CIE diagram
of (c) Ir(III) complexes alone and (d) in the presence of perylene
(
upconversion). Ir-1 and Ir-2 were excited by a 473 nm laser (5 mW),
−
5
and Ir-3 was excited by a 532 nm laser (5 mW). c = 1.0 × 10 M in
−
Ir(III) complexes (PF6 as the anions) with the Bodipy
deaerated CH CN at 20 °C.
3
chromophore. Although both of the complexes show intense
absorption of visible light, the complex (Ir-3) with direct
connection of the π core of the visible-light-harvesting
chromophore (Bodipy) to the coordination center shows
weaker ligand fluorescence than the complex with connections
at the meso phenyl of Bodipy (Ir-2). Furthermore, Ir-3 shows
RT phosphorescence of the Bodipy ligand at 742 nm, whereas
no RT phosphorescence was observed for Ir-2. The Ir(III)
complexes were used as triplet photosensitizers in two different
upon addition of triplet acceptor into the solution of the
complexes. The color changes were quantified with the CIE
coordinates (Figure 13c and 13d). For Ir-1, however, no
emission color change was observed.
The mechanism of the TTA upconversion can be illustrated
in Scheme 4. Upon excitation at the visible range (532 nm), the
Scheme 4. Qualitative Jablonski Diagram Illustrating the
triplet−triplet energy-transfer processes, i.e., photooxidation via
TTA Upconversion with Ir(III) Complexes (exemplified by
1
the singlet oxygen ( O ) photosensitizing and triplet−triplet
a
2
Ir-3) as Triplet Photosensitizer and Perylene as Acceptor
annihilation (TTA) upconversion; both require a triplet excited
1
state for initiation. Ir-3 shows more efficient O sensitizing
2
1
(
(
1
O quantum yield Φ = 97%) and TTA upconversion
2
Δ
quantum yield Φ = 2.8%) than Ir-2 (Φ = 52%, Φ
.2%). Therefore, the link of the π core of a visible-light-
=
UC
Δ
UC
harvesting chromophore to the Ir(III) coordination center is an
effective way to maximize the ISC effect, so that the excitation
energy harvested by the chromophore can be efficiently
funneled to the triplet excited state of the complexes. This
information is useful for design of visible-light-absorbing
transition metal complexes and application of these complexes
in photocatalysis, photovoltaics, and TTA upconversions, etc.
EXPERIMENTAL SECTION
Analytical Measurements. All chemicals are analytical pure and
■
a
The effect of the light-absorbing ability and triplet excited-state
lifetime of the Ir(III) sensitizer on the efficiency of TTA upconversion
is also shown. The wavelength of the laser used in the upconversion
used as received. Solvents were dried and distilled for synthesis. 5-
8
7
Ethynyl-2,2′-bipyridine, 2-iodo-1,3,5,7-tetramethyl-8-phenyl-4,4-di-
1
86a
experiments is 532 nm. E is energy. GS is ground state (S ). Bodipy*
fluoro-4-bora-3a-azonia-4a-aza-s-indacene,
and the cyclometalated
59
0
is intraligand singlet excited state (Bodipy localized). ISC is
Ir(III) chloro-bridge dimers [Ir(ppy) ]Cl2 were synthesized
according to literature methods; 1,3,5,7-tetramethyl-8-(4-bromophen-
yl)-4,4-difluoro-4-bora-3a-azonia-4a-aza-s-indacene was synthesized
according to a modified literature method
Information for molecular structural characterization data). L2 and
L3 were synthesized by a Sonogashira coupling reaction using 5-
ethynyl-2,2′-bipyridine and 1,3,5,7-tetramethyl-8-(4-bromophenyl)-
2
intersystem crossing. 3Bodipy* is intraligand triplet excited state.
3
TTET is triplet−triplet energy transfer. Perylene* is the triplet
1
86a
excited state of perylene. TTA is triplet−triplet annihilation. Per-
(see Supporting
ylene* is the singlet excited state of perylene. The typical power
−2
density of the laser used in the upconversion is 70 mW cm , too low
to observe simultaneous two-photon absorption.
H
dx.doi.org/10.1021/ic302210b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
4
,4-difluoro-4-bora-3a-azonia-4a-aza-s-indacene, 2-iodo-1,3,5,7-tetra-
119.94, 119.77, 91.51, 91.25, 15.03, 14.77, 13.45, 13.08. 19F (376 MHz,
11
methyl-8-phenyl-4,4-difluoro-4-bora-3a-azonia-4a-aza-s-indacene, re-
spectively (see Supporting Information). Complexes Ir-1, Ir-2, and
Ir-3 were synthesized according to a modified method.
CDCl ): δ −146.43, −146.50, −146.59, −146.68. B (128 MHz,
3
+
CDCl ): δ 1.09, 0.84, 0.59. TOF MS ESI (C H BF IrN ): calcd m/z
3
53 41
2
6
32
= 1003.3083, found m/z = 1003.3071. Anal. Calcd for
NMR spectra were recorded on a 400 MHz Varian Unity Inova
spectrophotometer. Mass spectra were recorded with Q-TOF Micro
and MALDI micro MX spectrometers. Elemental analysis was carried
out with VarioEL III Element analyzer (Elementar, Germany).
Fluorescence quantum yields were measured with 2,6-diiodo-1,3,5,7-
tetramethyl-8-phenyl-4,4-difluoroboradiazaindacene (2I-BDP) as
C H BF IrN P: C, 55.45; H, 3.60; N, 7.32. Found: C, 55.45; H,
3.59; N, 7.33.
Nanosecond Time-Resolved Transient Difference Absorp-
tion Spectroscopy. Nanosecond time-resolved transient difference
absorption spectra were recorded on a LP 920 laser flash photolysis
spectrometer (Edinburgh Instruments, Livingston, U.K.). Samples
53
41
8
6
86a
standard (ΦF = 2.7% in CH CN).
Phosphorescence quantum
were purged with N or argon for 30 min before measurement.
2
3
yields were measured with Ru(dmb) [PF ] (Φ = 7.3% in deaerated
Samples were excited with a 355 or 532 nm nanosecond pulsed laser,
and transient signals were recorded on a Tektronix TDS 3012B
oscilloscope.
3
6
2
P
8
6a
CH CN) or 2I-BDP as the references. The emission spectra at 77 K
3
were measured with a Oxford Optistat DN cryostat and FLS920
spectrofluorometer.
DFT Computational Methods. Geometry optimizations were
calculated using the B3LYP functional with the 6-31G(d)/LanL2DZ
Synthesis of Ir-1. [Ir(ppy) ]Cl (53.6 mg, 0.05 mmol) and 2,2′-
2
2
8
8
basis set. The spin density of the triplet excited state was calculated
with the energy minimized triplet geometries. Solvents were used in
calculations (CPCM model). All calculations were performed using
bipyridine (18.7 mg, 0.12 mmol) were dissolved in CH Cl /MeOH
2
2
(
12 mL, 2:1, v/v). Then the mixture was refluxed for 6 h under an
argon atmosphere. The mixture was cooled to RT; a 10-fold excess of
ammonium hexafluorophosphate was added. The suspension was
stirred for 15 min and then filtered to remove insoluble inorganic salts.
The solution was evaporated to dryness under reduced pressure to
obtain a yellow solid. The crude product was further purified with
8
9
the Gaussian 09W software (Gaussian, Inc.).
Photooxidation. A 35 W xenon lamp with a focusing reflector was
used for photooxidation. The light power was measured with a solar
power meter. The mixed solution of the complex (photosensitizer)
−2
and DHN was irradiated with 35 W xenon lamp (20 mW cm ). Light
column chromatography (silica gel, dichloromethane/methanol =
1
with a wavelength shorter than 385 nm was blocked by 0.72 M NaNO2
1
0:1, v/v); yellow solid was obtained (46.8 mg, yield 71.3%). H NMR
solution. Photooxidation of DHN was recorded on the UV−vis
(
400 MHz, CDCl /CD OD): δ 8.49 (d, 4H, J = 7.8 Hz), 8.18 (t, 1H, J
3 3
spectrophotometer at intervals of 1−5 min depending on the efficiency
of the sensitizer. DHN consumption was monitored by a decrease of
the absorption at 301 nm, and the concentration of DHN was
=
=
9.0 Hz), 7.94−7.87 (m, 6H), 7.78 (t, 1H, J = 7.8 Hz), 7.70 (d, 1H, J
7.3 Hz), 7.52 (d, 1H, J = 7.8 Hz), 7.42−7.36 (m, 6H), 7.07−7.00
(
m, 2H), 6.94 (t, 1H, J = 7.1 Hz), 6.31 (d, 1H, J = 7.6 Hz). TOF MS
−
1
+
4
calculated using its molar absorption coefficient (ε = 7664 M
ESI (C H IrN ): calcd m/z = 657.1630, found m/z = 657.1625.
32
24
−
1
26
cm ). Juglone production was monitored by an increase in the
absorption at 427 nm. The concentration of juglone was calculated
using its molar absorption coefficient (ε = 3811 M cm ), and the
Anal. Calcd for C H F IrN P: C, 47.94; H, 3.02; N, 6.99. Found: C,
32
24
6
4
4
7.85; H, 3.05; N, 6.94.
Synthesis of Ir-2. [Ir(ppy) ]Cl (53.6 mg, 0.05 mmol) and L2 (60.3
−1
−1
2
2
yield of juglone was obtained by dividing the concentration of juglone
mg, 0.12 mmol) were dissolved in CH Cl /MeOH (12 mL, 2:1, v/v).
2
2
2
6
with the initial concentration of DHN. Photostability experiments
Then the mixture was refluxed for 6 h under an argon atmosphere.
After completion of the reaction, the mixture was cooled to RT; a 10-
fold excess of ammonium hexafluorophosphate was added. The
suspension was stirred for 15 min and then filtered to remove
insoluble inorganic salts. The solution was evaporated to dryness
under reduced pressure to obtain a crude yellow solid. Crude product
was further purified with column chromatography (silica gel,
were carried out using the same method.
1
Singlet Oxygen ( O ) Quantum Yields (Φ ). Φ values of the
2
Δ
Δ
triplet photosensitizers were determined according to a modified
literature method with Rose Bengal (RB, Φ = 0.80 in methanol) as
the standard. 1,3-Diphenylisobenzofuran (DPBF) was used as the
9
0
Δ
9
1
1
1
O scavenger due to its fast reaction with O . The absorbance of
2
2
DPBF was adjusted around 1.0 at 410 nm in air-saturated methanol.
Then photosensitizer was added to the cuvette, and photosensitizer’s
absorbance was adjusted to around 0.2−0.3. Then we exposed the
cuvette to monochromatic light at the specific wavelength for 10 or 20
s depending on the efficiency of the dye sensitizer. The irradiation
wavelength for Ir-1, Ir-2, and Ir-3 are 322 nm, 510 nm, and 537 nm,
respectively. Absorbance was measured after each irradiation (six data
points were collected). The slope of the curves of absorbance maxima
of DPBF at 410 nm versus irradiation time for each photosensitizer
dichloromethane/methanol =15:1, v/v); a red solid was obtained
1
(
76.6 mg, 76.4%). H NMR (CDCl , 400 MHz): δ 9.89 (d, 1H, J = 6.7
3
Hz), 9.78 (d, 1H, J = 6.9 Hz), 8.41 (d, 1H, J = 7.0 Hz), 8.29 (t, 1H, J =
5
7
7
.8 Hz), 7.99−7.89 (m, 5H), 7.82−7.77 (m, 2H), 7.74−7.69 (m, 2H),
.61 (d, 2H, J = 7.8 Hz), 7.55−7.47 (m, 2H), 7.42 (t, 1H, J = 6.3 Hz),
.32 (d, 1H, J = 8.0 Hz), 7.09−6.91 (m, 6H), 6.33−6.27 (m, 2H), 5.99
s, 2H), 2.55 (s, 6H), 1.38 (s, 6H). 1 C NMR (100 MHz, CDCl ): δ
3
(
3
1
1
1
1
9
67.99, 167.87, 156.08, 155.60, 155.04, 151.77, 150.07, 148.57, 148.38,
43.53, 143.45, 142.96, 142.72, 140.38, 140.29, 138.35, 136.55, 132.76,
31.86, 131.69, 131.13, 131.02, 128.93, 128.59, 128.19, 127.67, 127.00,
25.11, 124.98, 124.44, 123.45, 122.87, 121.60, 121.43, 119.97, 119.89,
were calculated. Singlet oxygen quantum yields (Φ ) were calculated
Δ
according to the equation
19
6.31, 85.54, 14.69.1 F (376 MHz, CDCl ): δ −146.55, −146.63,
3
1
munk
F
std
−
146.72, −146.81. B (128 MHz, CDCl ): δ 1.22, 0.97, 0.71. TOF
3
ΦΔunk = ΦΔstd
+
6
MS ESI (C H BF IrN ): calcd m/z = 1003.3083, found m/z =
m F
std unk
(1)
53
41
2
1
003.3058. Anal. Calcd for C H BF IrN P: C, 55.45; H, 3.60; N,
53 41 8 6
7
.32. Found: C, 55.41; H, 3.53; N, 7.34.
Synthesis of Ir-3. [Ir(ppy) ]Cl (53.6 mg, 0.05 mmol) and L3 (55.3
where “unk” and “std” designate the “Ir(III) photosensitizers” and
“RB”, respectively, “m” is the slope of the difference in the change in
absorbance of DPBF (410 nm) with the irradiation time, and “F” is the
absorption correction factor, which is given by F = 1 − 10 (A is
absorption at the irradiation wavelength).
TTA Upconversion. A diode-pumped solid state laser was used for
upconversions. The laser power was measured with a phototube. The
mixed solution of the complex (triplet photosensitizer) and perylene
2
2
mg, 0.11 mmol) were dissolved in CH Cl /MeOH (12 mL, 2:1, v/v).
Then the mixture was refluxed for 6 h under argon. Thereafter the
synthesis procedure is similar to that of Ir-2; a red solid was obtained
2
2
−A
1
(
72.1 mg, 71.9%). H NMR (CDCl , 400 MHz): δ 9.77−9.68 (m,
3
2
7
7
2
H), 8.27−8.16 (m, 2H), 7.94−7.87 (m, 3H), 7.80−7.76 (m, 3H),
.71−7.65 (m, 2H), 7.54−7.48 (m, 5H), 7.39 (t, 1H, J = 6.1 Hz),
.06−6.88 (m, 5H), 6.32−6.29 (m, 2H), 6.09 (s, 1H), 4.92 (s, 3H),
.59 (d, 6H, J = 33.4 Hz), 1.41 (d, 6H, J = 16.3 Hz). 13C NMR (100
(triplet acceptor) was degassed for at least 15 min with N or argon
2
before measurement. Note, absorption of perylene at 532 nm is very
weak; thus, the triplet acceptor cannot be excited by a 532 nm laser
irradiation.
Upconversion quantum yields were determined with 2-iodo-1,3,5,7-
tetramethyl-8-phenyl-4,4-difluoro-4-bora-3a-azonia-4a-aza-s-indacene
MHz, CDCl ): δ 167.89, 159.76, 156.05, 155.73, 153.79, 151.52,
3
1
1
1
50.31, 150.23, 149.91, 148.56, 146.28, 143.51, 142.66, 142.56, 140.61,
40.33, 138.29, 138.24, 134.30, 133.31, 131.81, 130.93, 130.07, 129.56,
29.51, 127.79, 127.34, 126.80, 125.33, 124.95, 123.40, 123.12, 122.78,
I
dx.doi.org/10.1021/ic302210b | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
8
6a
(
Φ = 3.6%, in CH CN) as the standard. Upconversion quantum
F
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■
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ASSOCIATED CONTENT
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AUTHOR INFORMATION
(19) Murphy, L.; Congreve, A.; Palsson, L. O.; Williams, J. A. G.
̊
■
Chem. Commun. 2010, 46, 8743−8745.
Corresponding Author
(20) Xie, Z.; Ma, L.; DeKrafft, K. E.; Jin, A.; Lin, W. J. Am. Chem. Soc.
*E-mail: zhaojzh@dlut.edu.cn.
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The authors declare no competing financial interest.
(
2
(
ACKNOWLEDGMENTS
■
We thank the NSFC (20972024, 21073028, and 21273028),
the Royal Society (UK) and NSFC China-UK Cost-Share
Science Networks (21011130154), Science Foundation Ireland
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the Ministry of Education (NCET-08-0077 and
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(c) Takizawa, S.-y.; Perez-Bolívar, C.; Anzenbacher, P., Jr.; Murata, S.
financial support.
Eur. J. Inorg. Chem. 2012, 3975−3979. (d) Yuan, Y.-J.; Zhang, J.-Y.; Yu,
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dx.doi.org/10.1021/ic302210b | Inorg. Chem. XXXX, XXX, XXX−XXX

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